Advanced Materials for Micro- and Nano-Systems (AMMNS)

ZnO Nanorods Grown on p-GaN Using Hydrothermal Synthesis and Its Optoelectronic Devices Application

Mon, 01 Jan 2007 00:00:00 GMT

ZnO Nanorods Grown on p-GaN Using Hydrothermal Synthesis and Its Optoelectronic Devices Application Le, Hong Quang; Chua, Soo-Jin; Fitzgerald, Eugene A.; Loh, Kian Ping The ZnO nanorods with the length of 1-1.5 μm were deposited on p-GaN by hydrothermal synthesis at low temperature 100°C. The structural and optical properties of the as-grown ZnO rods were investigated by X-Ray diffraction (XRD) and photoluminescence (PL) spectra. After annealing treatment the as-grown films in air at 600°C, 30min, and the ZnO rods showed good crystallinity and optical properties with strong UV emission at 378 nm. In addition, a sharp UV emission peak at 369.45 nm with the FWHM 20 meV, which attributed to the bound exciton recombination, was also observed from the ZnO rods at 80K. Next, the e-beam evaporation method was used to deposit metal contact on n-ZnO and p-GaN. Here, we use Au and Ni/Au as metal contacts for n-ZnO and p-GaN, respectively. The current-voltage characteristics of the fabricated n-ZnO/p-GaN heterojunction revealed rectifying behavior with a leakage current of 10⁻⁸ A at -10V, a forward current 4x10⁻⁶ A at 10V bias. The heterojunction also showed a good photoresponse, with the change of the current – voltage characteristics under ultraviolet illumination. Under UV illumination, the forward turn on voltage changed to 7.5V. This result showed the ability to manipulate the electron transport in the ZnO based heterojunction devices.

Workfunction Tuning of n-Channel MOSFETs Using Interfacial Yttrium Layer in Fully Silicided Nickel Gate

Mon, 01 Jan 2007 00:00:00 GMT

Workfunction Tuning of n-Channel MOSFETs Using Interfacial Yttrium Layer in Fully Silicided Nickel Gate Yu, Hongpeng; Pey, Kin Leong; Choi, Wee Kiong; Chi, D.Z.; Fitzgerald, Eugene A.; Antoniadis, Dimitri A. Continual scaling of the CMOS technology requires thinner gate dielectric to maintain high performance. However, when moving into the sub-45 nm CMOS generation, the traditional poly-Si gate approach cannot effectively reduce the gate thickness further due to the poly-depletion effect. Fully silicided Ni metal gate (FUSI) has been proven to be a promising solution. Ni FUSI metal gate can significantly reduce gate-line sheet resistance, eliminate boron penetration to channels and has good process compatibility with high-k gate dielectric. But Ni FUSI has a mid-gap workfunction which is not suitable for high-performance CMOS applications where the band-edge workfunction is required. In this paper, we propose to tune the nickel (Ni) fully silicided metal gate (FUSI) workfunction via an yttrium/Si/Ni gate stack structure. The workfunction of such structure indicates that the Y interlayer can effectively tune the Ni FUSI workfunction from the mid gap to the conduction band edge of silicon by controlling the interlayer thickness. The gate stack workfunction starts to saturate to the pure yttrium value when the yttrium interlayer is >1.6 nm. This indicates the chemical potential of the material adjacent to gate electrode/gate insulator plays an important role in the determination of the workfunction.

Study of Stress Evolution of Germanium Nanocrystals Embedded in Silicon Oxide Matrix

Mon, 01 Jan 2007 00:00:00 GMT

Study of Stress Evolution of Germanium Nanocrystals Embedded in Silicon Oxide Matrix Chew, Han Guan; Choi, Wee Kiong; Chim, Wai Kin; Foo, Y.L.; Fitzgerald, Eugene A. Germanium (Ge) nanocrystals had been synthesized by annealing co-sputtered SiO₂-Ge in N₂ and/or forming gas (90% N₂ + 10% H₂) at temperatures ranging from 700 to 1000°C from 15 to 60 min. It was concluded that the annealing ambient, temperature and time have a significant influence on the formation and evolution of the nanocrystals. We also showed that a careful selective etching of the annealed samples in hydrofluoric solution enabled the embedded Ge nanocrystals to be liberated from the Si oxide matrix. From the Raman results of the as-grown and the liberated nanocrystals, we established that the nanocrystals generally experienced compressive stress in the oxide matrix and the evolution of these stress states was intimately linked to the distribution, density, size and quality of the Ge nanocrystals.

Ordering Control of Self-Assembled Colloidal Crystals

Mon, 01 Jan 2007 00:00:00 GMT

Ordering Control of Self-Assembled Colloidal Crystals Koh, Yaw Koon; Chiang, Yet-Ming; Wong, Chee Cheong Colloidal crystals are 3D nanostructures formed by self assembly of nanoparticles in suspension. The interaction forces between the colloid particles are expected to affect the ordering and the defect density in the resultant crystal. Based on this insight, the effect of ionic strength on the quality of the colloidal crystal is examined. It is found that at intermediate ionic strength, it is possible to get the best ordering of the colloidal crystal. The reason for this is explained based on previous work on the structural changes in an assembling colloidal crystal. A method for reducing the defect density in colloidal crystal will also be proposed.

High Temperature Deformation Behavior of Bulk Metallic Glass and Its Composites

Mon, 01 Jan 2007 00:00:00 GMT

High Temperature Deformation Behavior of Bulk Metallic Glass and Its Composites Fu, X.L.; Li, Yi; Schuh, C.A. The homogeneous deformation of Zr-based bulk metallic glass composites is studied near the glass transition temperature, at various levels of reinforcement volume fraction. Through examination of the constitutive response, it is seen that the presence of in-situ reinforcements increases the flow resistance of the glass dramatically. This strengthening effect is shown to arise from two separate contributions: load transfer from the amorphous matrix to the reinforcements, and changes to the glass composition and structure upon in-situ precipitation of reinforcements.

First-Principles Study of Point Defects in LaAlO₃

Mon, 01 Jan 2007 00:00:00 GMT

First-Principles Study of Point Defects in LaAlO₃ Zheng, J.X.; Ceder, Gerbrand; Chim, Wai Kin; Choi, Wee Kiong In this study, the native point defects including oxygen vacancy and interstitial, metal (La, Al) vacancy and interstitial, and metal antisite in perovskite LAO are studied. Defect formation energies are studied as a function of the external chemical potentials and Fermi level. The stable defects are identified under different external chemical potentials and Fermi levels. The effect of image charge corrections is also investigated. Finally, based on results in this study, optimal growth conditions can be proposed to achieve better defect engineering for LAO gate dielectrics.

Fabrication and Characterization of Nano-porous GaN Template for Strain Relaxed GaN Growth

Mon, 01 Jan 2007 00:00:00 GMT

Fabrication and Characterization of Nano-porous GaN Template for Strain Relaxed GaN Growth Hartono, Haryono; Soh, C.B.; Chua, Soo-Jin; Fitzgerald, Eugene A. A simple and cost-effective Si-doped porous GaN is fabricated by UV-enhanced electrochemical etching. An optimum current density of 20 mA/cm² applied for an hour in dilute NaOH solution produces a high density of uniform pores. Cross-section TEM reveals that etching takes place along the (0001) direction. A red shift of 0.7 cm⁻¹ in the E₂(high) phonon peak of GaN from micro-Raman indicates a relaxation of compressive stress in the porous GaN surface with respect to the underlying single crystalline epitaxial GaN. Subsequent growth of GaN layer on the porous template results in air gap formation, which is believed to serve as sinks for dislocations for reducing residual strain in the film. Reduction of FWHM of the XRD rocking curve as much as 0.033° and double intensity of the PL spectrum confirm the crystalline and optical quality improvement of the overgrown GaN layer as compared to as-grown. A red shift of ~0.4 cm⁻¹ towards the stress-free GaN also indicates a relaxation of compressive stress in the overgrown GaN layer.

Electrochemical Behavior and Li Diffusion Study of LiCoO₂ Thin Film Electrodes Prepared by PLD

Mon, 01 Jan 2007 00:00:00 GMT

Electrochemical Behavior and Li Diffusion Study of LiCoO₂ Thin Film Electrodes Prepared by PLD Xia, H.; Meng, Shirley Y.; Lu, Li; Ceder, Gerbrand Preferred c-axis oriented LiCoO₂ thin films were prepared on the SiO₂/Si (SOS) substrates by pulsed laser deposition (PLD). Thin film electrodes without carbon and binder are ideal samples to study the electrochemical properties of materials. We did galvanostatic charge/discharge measurements between 3 and 4.7 V on the Li/LiCoO₂ cell to study its electrochemical behavior. Potentiostatic intermittent titration technique (PITT) was used to measure the Li diffusivity in the LixCoO₂ film at different Li concentrations (0.15 < x < 0.75). The dependence of Li diffusivity on the c-lattice parameter and valence of cobalt ions is discussed.

High Temperature Deformation Behavior of in-situ Bulk Metallic Glass Matrix Composites

Sun, 01 Jan 2006 00:00:00 GMT

High Temperature Deformation Behavior of in-situ Bulk Metallic Glass Matrix Composites Fu, X.L.; Li, Yi; Schuh, C.A. Macroscopic ductility is promoted in bulk metallic glasses by both composite reinforcements (at low temperatures) and by the activation of viscous flow mechanisms (at high temperatures). It is of fundamental interest to understand deformation physics when both of these strategies are employed at the same time. Despite the quickly growing literature around the room-temperature mechanical properties of metallic glass matrix composites (MGMCs), the deformation behavior of MGMCs over a wide range of temperatures and strain rates has yet to be systematically investigated, especially at high temperatures close to Tg. Here the high temperature compressive behavior of Zr-based MGMCs with in-situ reinforcements is explored systematically over a series of strain rates. Additionally, the volume fraction of second-phase reinforcements was tailored to explore its effect on both inhomogeneous and homogeneous deformation modes.

Effect of Oxygen on Ni-Silicided FUSI Metal Gate

Sun, 01 Jan 2006 00:00:00 GMT

Effect of Oxygen on Ni-Silicided FUSI Metal Gate Yu, H.P.; Pey, Kin Leong; Choi, Wee Kiong; Chi, D.Z.; Fitzgerald, Eugene A.; Antoniadis, Dimitri A. Continual evolution of the CMOS technology requires thinner gate dielectric to maintain high performance. However, when moving into the sub-65 nm CMOS generation, the traditional poly-Si gate approach cannot effectively reduce the gate thickness further due to the poly-depletion effect. Fully silicided metal gate (FUSI) has been proven to be a promising solution. FUSI metal gate can significantly reduce gate-line sheet resistance, eliminate boron penetration to channels and has good process compatibility with high-k gate dielectric. In this paper, the effect of oxygen introduced by the process of conventional furnace annealing in FUSI metal gate is investigated. A 120 nm amorphous Si layer was sputtered on dielectric oxides of various thicknesses grown using a standard oxidation process. Raman spectra showed that the 120 nm thick pre-sputtered amorphous Si recrystallized after annealing in a conventional furnace at 900°C. Secondary ion mass spectrometry (SIMS) revealed that the annealed Si film contained traces of oxygen which were incorporated into the film during the furnace annealing process. It is suspected that the oxygen was originated from a few ppm of impurities present in the high-purity annealing gas (N2). When a 100 nm of Ni was deposited using a DC sputterer on such sample and was rapid thermal annealed (RTA) at 400°C to form a fully silicide film, the transmission electron micrograph showed the existence of unreacted oxygen-rich Si layer along the interface of the NiSi/SiO2, leading to areal non-uniformity in the workfunction. It is suggested that the presence of oxygen can effectively retard the Ni diffusion into the Si film during the silicidation process such that the FUSI process is delayed, and the equivalent oxide thickness (EOT) increased as shown by capacitance-voltage (C-V) measurements. The workfunction of Ni-silicided FUSI film determined by C-V measurement on MOS structures was found to increase compared to the as-deposited amorphous Si film (the control sample).

TEM Study on the Evolution of Ge Nanocrystals in Si Oxide Matrix as a Function of Ge Concentration and the Si Reduction Process

Sun, 01 Jan 2006 00:00:00 GMT

TEM Study on the Evolution of Ge Nanocrystals in Si Oxide Matrix as a Function of Ge Concentration and the Si Reduction Process Chew, Han Guan; Choi, Wee Kiong; Foo, Y.L.; Chim, Wai Kin; Fitzgerald, Eugene A.; Zheng, F.; Samanta, S.K.; Voon, Z.J.; Seow, K.C. Growth and evolution of germanium (Ge) nanocrystals embedded into a silicon oxide (SiO₂) system have been studied based on the Ge content of co-sputtered Ge-SiO₂ films using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy. It was found that when the proportion of Ge relative to Ge oxide is 20%, TEM showed that annealing the samples at 800°C for 60 min resulted in the formation of a denuded region between the silicon/silicon oxide (Si/SiO₂) interface and a band of Ge nanocrystals towards the surface of the film. By introducing a 20nm thick thermal oxide barrier on top of the silicon (Si) substrate on which the film is deposited, no denuded region in the bulk of this sample is observed. It is proposed that this barrier is effective in reducing both Ge diffusion into the Si substrate and Si diffusion from the substrate into the film. Si diffusing from the Si substrate reduces the Ge oxide into Ge which can subsequently diffuse into the Si substrate. However, the oxide barrier is able to confine the Ge within the oxide matrix so that the denuded region in the bulk of the film cannot form. However the reduction in diffusion should be more significant for Ge as its diffusion coefficient is lower than Si due to its larger size. It is suggested that the denuded region consists of amorphous Ge diffusing towards the Si/SiO₂ interface. When the Ge content is increased to slightly more than 70%, TEM showed that Ge nanocrysyals formed after annealing at 800°C for only 30 min for samples with and without the oxide barrier. There is no denuded region between the Ge nanocrystals band and the Si/SiO₂ interface for both samples but it was observed that coarsening effects were more prominent in the film deposited on top of the oxide barrier. The reduction effect of Si on Ge oxide should not play a significant role in these samples as the Ge content is high.

Native Point Defects in yttria as a High-Dielectric-Constant Gate Oxide Material: A First-Principles Study

Sun, 01 Jan 2006 00:00:00 GMT

Native Point Defects in yttria as a High-Dielectric-Constant Gate Oxide Material: A First-Principles Study Zheng, J.X.; Ceder, Gerbrand; Maxisch, T.; Chim, Wai Kin; Choi, Wee Kiong Yttria (Y₂O₃) has become a promising gate oxide material to replace silicon dioxide in metal-oxide-semiconductor (MOS) devices. The characterization of native point defect in Y₂O₃ is essential to understand the behavior of the material. We used the first-principles pseudopotential method to study the electronic structure, defect structure and formation energy of native point defects in Y₂O₃. Vacancies, interstitials and antisites in their relevant charge states are considered. The dominant defect types are identified under different chemical potentials and different Fermi levels. Oxygen vacancies are the dominant defect types under high yttrium chemical potential condition. Lower yttrium chemical potential leads to oxygen interstitials and ultimately yttrium vacancies when Y₂O₃ is used as a high dielectric constant gate oxide material in MOS devices.

Monitoring Defect Formation in Colloidal Self Assembly using Photonic Bandgap Variations

Sun, 01 Jan 2006 00:00:00 GMT

Monitoring Defect Formation in Colloidal Self Assembly using Photonic Bandgap Variations Koh, Yaw Koon; Wong, Chee Cheong Defect control in colloidal crystals is essential for these nanostructures to be effective as photonic bandgap (PBG) materials. We have used in-situ monitoring of the PBG of a colloidal crystal to study the structural changes during colloidal self assembly, with a focus on the formation of macroscopic defects such as cracks. These findings allow us to model the final stages of colloidal self assembly and explain the formation of growth defects in colloidal crystal. Our model suggests that cracks are intrinsic to self assembly growth methods. . However, by tuning the interaction potential between the colloids, it is possible to minimize the cracks in colloidal crystals.

Fabrication of Two-Dimensional Photonic Crystals in AlGaInP/GaInP Membranes by Inductively Coupled Plasma Etching

Sun, 01 Jan 2006 00:00:00 GMT

Fabrication of Two-Dimensional Photonic Crystals in AlGaInP/GaInP Membranes by Inductively Coupled Plasma Etching Chen, A.; Chua, Soo-Jin; Wang, B.; Fitzgerald, Eugene A. The fabrication process of two-dimensional photonic crystals in an AlGaInP/GaInP multi-quantum-well membrane structure is developed. The process includes high resolution electron-beam lithography, pattern transfer into SiO₂ etch mask by reactive ion etching, pattern transfer through AlGaInP/GaInP layer by inductively coupled plasma (ICP) etching and a selective undercut wet etch to create the freestanding membrane. The chlorine-based ICP etching conditions are optimized to achieve a vertical sidewall. The photonic crystal structures with periods of a=160-480nm are produced.

Fabrication and I-V Characterization of ZnO Nanorod Based Metal-Insulator-Semiconductor Junction

Sun, 01 Jan 2006 00:00:00 GMT

Fabrication and I-V Characterization of ZnO Nanorod Based Metal-Insulator-Semiconductor Junction Quang, Le Hong; Chua, Soo-Jin; Fitzgerald, Eugene A. We report on the characteristics of a ZnO based metal insulator semiconductor (MIS) diode comprised of a heterostructure of n-ZnO nanorods/n-GaN. The MIS structure consisted of unintentional - doped n type ZnO nanorods grown on n-GaN sample using hydrothermal synthesis at low temperature (100°). The ZnO nanorod layer was vertically grown from the GaN sample, having the diameter 100nm and length 2µm. Then, an insulator layer for electrical isolation was deposited on the top of ZnO nanorod layer by using spin coating method. A metal layer (gold) was finally deposited on the top. The I-V dependences show a rectifying diode like behavior with a leakage current of 2.10⁻⁵ A and a threshold voltage of about 3V. Depend on the thickness of the insulator, the I-V dependences of the n-ZnO/n-GaN heterostructure was varied from rectifying behavior to Ohmic and nearly linear.

Enhancement in Indium Incorporation for InGaN Grown on InN Intermediate Layer

Sun, 01 Jan 2006 00:00:00 GMT

Enhancement in Indium Incorporation for InGaN Grown on InN Intermediate Layer Hartono, Haryono; Chen, P.; Fitzgerald, Eugene A.; Chua, Soo-Jin InN has been grown on GaN with a thin intermediate layer of InGaN by metalorganic chemical vapor deposition (MOCVD) to further enhance indium incorporation in subsequent InGaN layer. Trimethylindium (TMI) and ammonia (NH₃) were used as the source for InN growth and transmission electron microscopy (TEM) confirmed the presence of pyramid-like structure of InN. A layer of InGaN subsequently grown on top of these InN pyramids shows a red-shift of ~20 nm relative to InGaN layer grown directly on GaN using the same growth condition. However, there is no significant pits reduction. An alternative method to enhance indium incorporation is to grow the InN by adding a small amount of trimethygallium (TMG) into the TMI and NH₃ flow. This method provides a seed layer for the InN growth and it gives a higher density of InN pyramids. X-ray diffraction (XRD) measurement of this sample shows a high indium incorporation to give InGaN with x~0.26 as compared to x~0.22 for sample grown without TMG flow in the InN layer.

Effects of Applied Loads, Effective Contact Area and Surface Roughness on the Dicing Yield of 3D Cu Bonded Interconnects

Sun, 01 Jan 2006 00:00:00 GMT

Effects of Applied Loads, Effective Contact Area and Surface Roughness on the Dicing Yield of 3D Cu Bonded Interconnects Leong, Hoi Liong; Gan, C.L.; Pey, Kin Leong; Thompson, Carl V.; Li, Hongyu Bonded copper interconnects were created using thermo-compression bonding and the dicing yield was used as an indication of the bond quality. SEM images indicated that the Cu was plastically deformed. Our experimental and modeling results indicate that the effective contact area is directly proportional to the applied load. Furthermore, for first time, results have been obtained that indicate that the dicing yield is proportional to the measured bond strength, and the bond strength is proportional to the effective contact area. It is also shown that films with rougher surfaces (and corresponding lower effective bonding areas) have lower bond strengths and dicing yields. A quantitative model for the relationship between measured surface roughness and the corresponding dicing yield has been developed. An appropriate surface-roughness data acquisition methodology has also been developed. The maximum possible applied load and the minimum possible surface roughness are required to obtain the maximum effective contact area, and hence to achieve optimum yields (both mechanically and electrically).

Characterization of LiNi₀.₅Mn₁.₅O₄ Thin Film Cathode Prepared by Pulsed Laser Deposition

Sun, 01 Jan 2006 00:00:00 GMT

Characterization of LiNi₀.₅Mn₁.₅O₄ Thin Film Cathode Prepared by Pulsed Laser Deposition Xia, Hui; Lu, Li; Ceder, Gerbrand LiNi₀.₅Mn₁.₅O₄ thin films have been grown by pulsed laser deposition (PLD) on stainless steel (SS) substrates. The crystallinity and structure of thin films were investigated by X-ray diffraction (XRD). Microstructure and surface morphology of the thin films were examined using a field-emission scanning electron microscope (FESEM). The electrochemical properties of the thin films were studied with cyclic voltammetry (CV) and galvanostatic charge-discharge in the potential range between 3.0 and 4.9 V. The electrochemical behavior of LiNi₀.₅Mn₁.₅O₄ thin films showed reversible capacity above 4.7 V and good cycle performance up to 50 cycles.

Amorphous Al-transition Metal Alloys as Anode Material for Lithium Ion Battery

Sun, 01 Jan 2006 00:00:00 GMT

Amorphous Al-transition Metal Alloys as Anode Material for Lithium Ion Battery Wang, C.Y.; Ceder, Gerbrand; Li, Yi Al based alloy powders (Al₈₅Ni₅Y₆Co₂Fe₂) are produced by spray atomization method. High energy ball milling is done to modify the surface topology and particle size for better electrochemical performance. X ray diffraction (XRD), differential scanning calorimeter (DSC), scanning electron microscope (SEM) and transmission electron microscope (TEM) were conducted to characterize the microstructure of the alloys after ball milling. It is found that 5 hours ball milling gives the minimum crystallization and structure change. Thin film sample is also deposited on stainless steel substrate by pulsed laser deposition (PLD) method for electrochemical test. The capacity and reversibility for different samples are compared and discussed. A capacity of 200mAh/g is obtained for the battery with thin film sample as anode and a capacity of 140mAh/g is obtained for that with electrode from powder sample. Both of the batteries give up to 94% capacity retention after 20 cycles.

The Influence of Adjacent Segment on the Reliability of Cu Dual Damascene Interconnects

Sat, 01 Jan 2005 00:00:00 GMT

The Influence of Adjacent Segment on the Reliability of Cu Dual Damascene Interconnects Chang, Choon Wai; Choi, Z.-S.; Thompson, Carl V.; Gan, C.L.; Pey, Kin Leong; Choi, Wee Kiong; Hwang, N. Three terminal â€˜dotted-I’ interconnect structures, with vias at both ends and an additional via in the middle, were tested under various test conditions. Mortalities (failures) were found in right segments with jL value as low as 1250 A/cm, and the mortality of a dotted-I segment is dependent on the direction and magnitude of the current in the adjacent segment. Some mortalities were also found in the right segments under a test condition where no failure was expected. Cu extrusion along the delaminated Cu/Si₃N₄ interface near the central via region was believed to cause the unexpected failures. From the time-to-failure (TTF), it is possible to quantify the Cu/Si₃N₄ interfacial strength and bonding energy. Hence, the demonstrated test methodology can be used to investigate the integrity of the Cu dual damascene processes. As conventionally determined critical jL values in two-terminal via-terminated lines cannot be directly applied to interconnects with branched segments, this also serves as a good methodology to identify the critical effective jL values for immortality.

Two-dimensional Photonic Crystals Fabricated by Nanoimprint Lithography

Sat, 01 Jan 2005 00:00:00 GMT

Two-dimensional Photonic Crystals Fabricated by Nanoimprint Lithography Chen, A.; Chua, Soo-Jin; Fonstad, Clifton G. Jr.; Wang, B.; Wilhelmi, O. We report on the process parameters of nanoimprint lithography (NIL) for the fabrication of two-dimensional (2-D) photonic crystals. The nickel mould with 2-D photonic crystal patterns covering the area up to 20mm² is produced by electron-beam lithography (EBL) and electroplating. Periodic pillars as high as 200nm to 250nm are produced on the mould with the diameters ranging from 180nm to 400nm. The mould is employed for nanoimprinting on the poly-methyl-methacrylate (PMMA) layer spin-coated on the silicon substrate. Periodic air holes are formed in PMMA above its glass-transition temperature and the patterns on the mould are well transferred. This nanometer-size structure provided by NIL is subjective to further pattern transfer.

Strained Silicon on Silicon by Wafer Bonding and Layer Transfer from Relaxed SiGe Buffer

Sat, 01 Jan 2005 00:00:00 GMT

Strained Silicon on Silicon by Wafer Bonding and Layer Transfer from Relaxed SiGe Buffer Isaacson, David M.; Taraschi, G.; Pitera, Arthur J.; Ariel, Nava; Fitzgerald, Eugene A.; Langdo, Thomas A. We report the creation of strained silicon on silicon (SSOS) substrate technology. The method uses a relaxed SiGe buffer as a template for inducing tensile strain in a Si layer, which is then bonded to another Si handle wafer. The original Si wafer and the relaxed SiGe buffer are subsequently removed, thereby transferring a strained-Si layer directly to Si substrate without intermediate SiGe or oxide layers. Complete removal of Ge from the structure was confirmed by cross-sectional transmission electron microscopy as well as secondary ion mass spectrometry. A plan-view transmission electron microscopy study of the strained-Si/Si interface reveals that the lattice-mismatch between the layers is accommodated by an orthogonal array of edge dislocations. This misfit dislocation array, which forms upon bonding, is geometrically necessary and has an average spacing of approximately 40nm, in excellent agreement with established dislocation theory. To our knowledge, this is the first study of a chemically homogeneous, yet lattice-mismatched, interface.

Preliminary Characterisation of Low-Temperature Bonded Copper Interconnects for 3-D Integrated Circuits

Sat, 01 Jan 2005 00:00:00 GMT

Preliminary Characterisation of Low-Temperature Bonded Copper Interconnects for 3-D Integrated Circuits Leong, Hoi Liong; Gan, C.L.; Pey, Kin Leong; Tsang, Chi-fo; Thompson, Carl V.; Hongyu, Li Three dimensional (3-D) integrated circuits can be fabricated by bonding previously processed device layers using metal-metal bonds that also serve as layer-to-layer interconnects. Bonded copper interconnects test structures were created by thermocompression bonding and the bond toughness was measured using the four-point test. The effects of bonding temperature, physical bonding and failure mechanisms were investigated. The surface effects on copper surface due to pre-bond clean (with glacial acetic acid) were also looked into. A maximum average bond toughness of approximately 35 J/m² was obtained bonding temperature 300 C.

Poly-Si₁â‚‹xGex Film Growth for Ni Germanosilicided Metal Gate

Sat, 01 Jan 2005 00:00:00 GMT

Poly-Si₁â‚‹xGex Film Growth for Ni Germanosilicided Metal Gate Yu, Hongpeng; Pey, Kin Leong; Choi, Wee Kiong; Fitzgerald, Eugene A.; Antoniadis, Dimitri A. Scaling down of the CMOS technology requires thinner gate dielectric to maintain high performance. However, due to the depletion of poly-Si gate, it is difficult to reduce the gate thickness further especially for sub-65 nm CMOS generation. Fully silicidation metal gate (FUSI) is one of the most promising solutions. Furthermore, FUSI metal gate reduces gate-line sheet resistance, prevents boron penetration to channels, and has good process compatibility with high-k gate dielectric. Poly-SiGe gate technology is another solution because of its enhancement of boron activation and compatibility with the conventional CMOS process. Combination of these two technologies for the formation of fully germanosilicided metal gate makes the approach very attractive. In this paper, the deposition of undoped Poly-Si₁â‚‹xGex (0 < x < 30% ) films onto SiO₂ in a low pressure chemical vapor deposition (LPCVD) system is described. Detailed growth conditions and the characterization of the grown films are presented.

Oblique Angle Deposition of Germanium Film on Silicon Substrate

Sat, 01 Jan 2005 00:00:00 GMT

Oblique Angle Deposition of Germanium Film on Silicon Substrate Chew, Han Guan; Choi, Wee Kiong; Chim, Wai Kin; Fitzgerald, Eugene A. The effect of flux angle, substrate temperature and deposition rate on obliquely deposited germanium (Ge) films has been investigated. By carrying out deposition with the vapor flux inclined at 87° to the substrate normal at substrate temperatures of 250°C or 300°C, it may be possible to obtain isolated Ge nanowires. The Ge nanowires are crystalline as shown by Raman Spectroscopy.

Nanocrystalline Ge Flash Memories: Electrical Characterization and Trap Engineering

Sat, 01 Jan 2005 00:00:00 GMT

Nanocrystalline Ge Flash Memories: Electrical Characterization and Trap Engineering Kan, Eric Win Hong; Koh, B.H.; Choi, Wee Kiong; Chim, Wai Kin; Antoniadis, Dimitri A.; Fitzgerald, Eugene A. Conventional floating gate non-volatile memories (NVMs) present critical issues for device scalability beyond the sub-90 nm node, such as gate length and tunnel oxide thickness reduction. Nanocrystalline germanium (nc-Ge) quantum dot flash memories are fully CMOS compatible technology based on discrete isolated charge storage nodules which have the potential of pushing further the scalability of conventional NVMs. Quantum dot memories offer lower operating voltages as compared to conventional floating-gate (FG) Flash memories due to thinner tunnel dielectrics which allow higher tunneling probabilities. The isolated charge nodules suppress charge loss through lateral paths, thereby achieving a superior charge retention time. Despite the considerable amount of efforts devoted to the study of nanocrystal Flash memories, the charge storage mechanism remains obscure. Interfacial defects of the nanocrystals seem to play a role in charge storage in recent studies, although storage in the nanocrystal conduction band by quantum confinement has been reported earlier. In this work, a single transistor memory structure with threshold voltage shift, Vth, exceeding ~1.5 V corresponding to interface charge trapping in nc-Ge, operating at 0.96 MV/cm, is presented. The trapping effect is eliminated when nc-Ge is synthesized in forming gas thus excluding the possibility of quantum confinement and Coulomb blockade effects. Through discharging kinetics, the model of deep level trap charge storage is confirmed. The trap energy level is dependent on the matrix which confines the nc-Ge.

High Optical Quality Nanoporous GaN Prepared by Photoelectrochemical Etching

Sat, 01 Jan 2005 00:00:00 GMT

High Optical Quality Nanoporous GaN Prepared by Photoelectrochemical Etching Vajpeyi, Agam P.; Chua, Soo-Jin; Tripathy, S.; Fitzgerald, Eugene A. Nanoporous GaN films are prepared by UV assisted electrochemical etching using HF solution as an electrolyte. To assess the optical quality and morphology of these nanoporous films, micro-photoluminescence (PL), micro-Raman scattering, scanning electron microscopy (SEM), and atomic force microscopy (AFM) techniques have been employed. SEM and AFM measurements revealed an average pore size of about 85-90 nm with a transverse dimension of 70-75 nm. As compared to the as-grown GaN film, the porous layer exhibits a substantial photoluminescence intensity enhancement with a partial relaxation of compressive stress. Such a stress relaxation is further confirmed by the red shifted E₂(TO) phonon peak in the Raman spectrum of porous GaN.

High Indium Concentration InGaN/GaN Grown on Sapphire Substrate by MOCVD

Sat, 01 Jan 2005 00:00:00 GMT

High Indium Concentration InGaN/GaN Grown on Sapphire Substrate by MOCVD Hartono, Haryono; Chua, Soo-Jin; Fitzgerald, Eugene A.; Song, T.L.; Chen, Peng The InGaN system provides the opportunity to fabricate light emitting devices over the whole visible and ultraviolet spectrum due to band-gap energies E[subscript g] varying between 3.42 eV for GaN and 1.89 eV for InN. However, high In content in InGaN layers will result in a significant degradation of the crystalline quality of the epitaxial layers. In addition, unlike other III-V compound semiconductors, the ratio of gallium to indium incorporated in InGaN is in general not a simple function of the metal atomic flux ratio, f[subscript Ga]/f[subscript In]. Instead, In incorporation is complicated by the tendency of gallium to incorporate preferentially and excess In to form metallic droplets on the growth surface. This phenomenon can definitely affect the In distribution in the InGaN system. Scanning electron microscopy, room temperature photoluminescence, and X-ray diffraction techniques have been used to characterize InGaN layer grown on InN and InGaN buffers. The growth was done on c-plane sapphire by MOCVD. Results showed that green emission was obtained which indicates a relatively high In incorporation.

High Density Single Crystalline GaN Nanodot Arrays Fabricated Using Template-Assisted Selective Growth

Sat, 01 Jan 2005 00:00:00 GMT

High Density Single Crystalline GaN Nanodot Arrays Fabricated Using Template-Assisted Selective Growth Wang, Yadong; Zang, Keyan; Chua, Soo-Jin; Fonstad, Clifton G. Jr. High density, uniform GaN nanodot arrays with controllable size have been synthesized by using template-assisted selective growth. The GaN nanodots with average diameter 40nm, 80nm and 120nm were selectively grown by metalorganic chemical vapor deposition (MOCVD) on a nano-patterned SiO2/GaN template. The nanoporous SiO2 on GaN surface was created by inductively coupled plasma etching (ICP) using anodic aluminum oxide (AAO) template as a mask. This selective regrowth results in highly crystalline GaN nanodots confirmed by high resolution transmission electron microscopy. The narrow size distribution and uniform spatial position of the nanoscale dots offer potential advantages over self-assembled dots grown by the Stranski–Krastanow mode.

Growth of ZnO Nanorods on GaN Using Aqueous Solution Method

Sat, 01 Jan 2005 00:00:00 GMT

Growth of ZnO Nanorods on GaN Using Aqueous Solution Method Quang, Hong Le; Chua, Soo-Jin; Loh, Kian Ping; Chen, Zhen; Thompson, Carl V.; Fitzgerald, Eugene A. Uniformly distributed ZnO nanorods with diameter 80-120 nm and 1-2µm long have been successfully grown at low temperatures on GaN by using the inexpensive aqueous solution method. The formation of the ZnO nanorods and the growth parameters are controlled by reactant concentration, temperature and pH. No catalyst is required. The XRD studies show that the ZnO nanorods are single crystals and that they grow along the c axis of the crystal plane. The room temperature photoluminescence measurements have shown ultraviolet peaks at 388nm with high intensity, which are comparable to those found in high quality ZnO films. The mechanism of the nanorod growth in the aqueous solution is proposed. The dependence of the ZnO nanorods on the growth parameters was also investigated. While changing the growth temperature from 60°C to 150°C, the morphology of the ZnO nanorods changed from sharp tip with high aspect ratio to flat tip with smaller aspect ratio. These kinds of structure are useful in laser and field emission application.

Growth and Characterization of LiCoO₂ Thin Films for Microbatteries

Sat, 01 Jan 2005 00:00:00 GMT

Growth and Characterization of LiCoO₂ Thin Films for Microbatteries Hui, Xia; Lu, Li; Ceder, Gerbrand LiCoO₂thin films have been grown by pulsed laser deposition on stainless steel and SiO₂/Si substrates. The film deposited at 600°C in an oxygen partial pressure of 100mTorr shows an excellent crystallinity, stoichiometry and no impurity phase present. Microstructure and surface morphology of thin films were examined using a scanning electron microscope. The electrochemical properties of the thin films were studied with cyclic voltammetry and galvanostatic charge-discharge techniques in the potential range 3.0-4.2 V. The initial discharge capacity of the LiCoO2 thin films deposited on the stainless steel and SiO₂/Si substrates reached 23 and 27 µAh/cm², respectively.

Effects of Platinum on NiPtSiGe/n-SiGe and NiPtSi/n-Si Schottky Contacts

Sat, 01 Jan 2005 00:00:00 GMT

Effects of Platinum on NiPtSiGe/n-SiGe and NiPtSi/n-Si Schottky Contacts Jin, Lijuan; Pey, Kin Leong; Choi, Wee Kiong; Fitzgerald, Eugene A.; Antoniadis, Dimitri A.; Chi, D.Z. Solid phase reaction of NiPt/Si and NiPt/SiGe is one of the key issues for silicide (germanosilicide) technology. Especially, the NiPtSiGe, in which four elements are involved, is a very complex system. As a result, a detailed study is necessary for the interfacial reaction between NiPt alloy film and SiGe substrate. Besides using traditional material characterization techniques, characterization of Schottky diode is a good measure to detect the interface imperfections or defects, which are not easy to be found on large area blanket samples. The I-V characteristics of 10nm Ni(Pt=0, 5, 10 at.%) germanosilicides/n-Si₀/₇Ge₀.₃ and silicides/n-Si contact annealed at 400 and 500°C were studied. For Schottky contact on n-Si, with the addition of Pt in the Ni(Pt) alloy, the Schottky barrier height (SBH) increases greatly. With the inclusion of a 10% Pt, SBH increases ~0.13 eV. However, for the Schottky contacts on SiGe, with the addition of 10% Pt, the increase of SBH is only ~0.04eV. This is explained by pinning of the Fermi level. The forward I-V characteristics of 10nm Ni(Pt=0, 5, 10 at.%)SiGe/SiGe contacts annealed at 400°C were investigated in the temperature range from 93 to 300K. At higher temperature (>253K) and larger bias at low temperature (<253K), the I-V curves can be well explained by a thermionic emission model. At lower temperature, excess currents at lower forward bias region occur, which can be explained by recombination/generation or patches due to inhomogenity of SBH with pinch-off model or a combination of the above mechanisms.

The Effect of Periodic Silane Burst on the Properties of GaN on Si (111) Substrates

Sat, 01 Jan 2005 00:00:00 GMT

The Effect of Periodic Silane Burst on the Properties of GaN on Si (111) Substrates Zang, Keyan; Chua, Soo-Jin; Thompson, Carl V. The periodic silane burst technique was employed during metalorganic chemical vapor deposition of epitaxial GaN on AlN buffer layers grown on Si (111). Periodic silicon delta doping during growth of both the AlN and GaN layers led to growth of GaN films with decreased tensile stresses and decreased threading dislocation densities, as well as films with improved quality as indicated by x-ray diffraction, micro-Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. The possible mechanism of the reduction of tensile stress and the dislocation density is discussed in the paper.

Defects in Self Assembled Colloidal Crystals

Sat, 01 Jan 2005 00:00:00 GMT

Defects in Self Assembled Colloidal Crystals Koh, Yaw Koon; Teh, L. K.; Wong, Chee Cheong Colloidal self assembly is an efficient method for making 3-D ordered nanostructures suitable for materials such as photonic crystals and macroscopic solids for catalysis and sensor applications. Colloidal crystals grown by convective methods exhibit defects on two different scales. Macro defects such as cracks and void bands originate from the dynamics of meniscus motion during colloidal crystal growth while micro defects like vacancies, dislocation and stacking faults are indigenous to the colloidal crystalline structure. This paper analyses the crystallography and energetics of the microscopic defects from the point of view of classical thermodynamics and discusses the strategy for the control of the macroscopic defects through optimization of the liquid-vapor interface.

Characterization of ZnO Nanorods Grown on GaN Using Aqueous Solution Method

Sat, 01 Jan 2005 00:00:00 GMT

Characterization of ZnO Nanorods Grown on GaN Using Aqueous Solution Method Quang, Hong Le; Chua, Soo-Jin; Loh, Kian Ping; Chen, Zhen; Thompson, Carl V.; Fitzgerald, Eugene A. Uniformly distributed ZnO nanorods with diameter 70-100 nm and 1-2μm long have been successfully grown at low temperatures on GaN by using the inexpensive aqueous solution method. The formation of the ZnO nanorods and the growth parameters are controlled by reactant concentration, temperature and pH. No catalyst is required. The XRD studies show that the ZnO nanorods are single crystals and that they grow along the c axis of the crystal plane. The room temperature photoluminescence measurements have shown ultraviolet peaks at 388nm with high intensity, which are comparable to those found in high quality ZnO films. The mechanism of the nanorod growth in the aqueous solution is proposed. The dependence of the ZnO nanorods on the growth parameters was also investigated. While changing the growth temperature from 60°C to 150°C, the morphology of the ZnO nanorods changed from sharp tip (needle shape) to flat tip (rod shape). These kinds of structure are useful in laser and field emission application.

Carbon Nanotube Growth Using Ni Catalyst in Different Layouts

Sat, 01 Jan 2005 00:00:00 GMT

Carbon Nanotube Growth Using Ni Catalyst in Different Layouts Nguyen, H. Q.; Krishnan, R.; Choi, K. W.; Thompson, Carl V.; Lim, F. Y. Vertically aligned carbon nanotubes have been grown using Ni as catalyst by plasma enhanced chemical vapor deposition system (PECVD) in various pre-patterned substrates. Ni was thermally evaporated on silicon substrates with anodized alumina mask prepared in different methods including 2 step anodization of porous alumina template and interference lithography assisted array of pores. The templates helped to define Ni nanodots inside the pores which in turn catalyzed the growth of carbon nanotubes inside the PECVD system at temperature of 700-750C using mixture of ammonia and acetylene gases. The resulting well-aligned multi-walled carbon nanotubes were further investigated using SEM, TEM and Raman spectroscopy. The size, shape and structure of the grown carbon nanotubes were also discussed.

Vibrational thermodynamics: coupling of chemical order and size effects

Tue, 01 Jan 2002 00:00:00 GMT

Vibrational thermodynamics: coupling of chemical order and size effects van de Walle, Axel; Morgan, Dane; Wu, Eric; Ceder, Gerbrand We study the effects of vibrations in the Pd₃ system using first-principles pseudopotential calculations. We find that upon disordering from the DO₂₂ phase, the decreases by 0.07kB. We explain our results in terms of atomic relaxations and size effects.

Synthesis of Germanium Nanocrystals and its Possible Application in Memory Devices

Tue, 01 Jan 2002 00:00:00 GMT

Synthesis of Germanium Nanocrystals and its Possible Application in Memory Devices Teo, L.W.; Heng, C.L.; Ho, V.; Tay, M.S.; Choi, Wee Kiong; Chim, Wai Kin; Antoniadis, Dimitri A.; Fitzgerald, Eugene A. A novel method of synthesizing and controlling the size of germanium nanocrystals was developed. A tri-layer structure comprising of a thin (~5nm) SiO₂ layer grown using rapid thermal oxidation (RTO), followed by a layer of Ge+SiO₂ of varying thickness (6 - 20 nm) deposited using the radio frequency (r.f.) co-sputtering technique and a SiO₂ cap layer (50nm) deposited using r.f. sputtering, was investigated. It was verified using TEM that germanium nanocrystals of sizes ranging from 6 – 20 nm were successfully fabricated after thermal annealing of the tri-layer structure under suitable conditions. The nanocrystals were found to be well confined by the RTO SiO₂ and the cap SiO₂ under specific annealing conditions. The electrical properties of the tri-layer structure have been characterized using MOS capacitor test devices. A significant hysteresis can be observed from the C-V measurements and this suggests the charge storage capability of the nanocrystals. The proposed technique has the potential for fabricating memory devices with controllable nanocrystals sizes.

Studies on Nano-Indentation of Polymeric Thin Films Using Finite Element Methods

Tue, 01 Jan 2002 00:00:00 GMT

Studies on Nano-Indentation of Polymeric Thin Films Using Finite Element Methods Shen, Xiaojun; Yi, Sung; Anand, Lallit; Zeng, Kaiyang In this paper, the numerical simulation for nano-indentation is performed to measure time-dependent behavior of polymeric films. The possibility to extract the relaxed shear modulus of the polymer is evaluated using a rigid ball indenter. The viscoelastic behavior of the polymer was represented by the standard model. The effects of Poisson’s ratio are also discussed.

Strained Ge channel p-type metal-oxide-semiconductor field-effect transistors grown on Siâ‚â‚‹xGex/Si virtual substrates

Tue, 01 Jan 2002 00:00:00 GMT

Strained Ge channel p-type metal-oxide-semiconductor field-effect transistors grown on Siâ‚â‚‹xGex/Si virtual substrates Lee, Minjoo L.; Leitz, Christopher W.; Cheng, Zhiyuan; Antoniadis, Dimitri A.; Fitzgerald, Eugene A. We have fabricated strained Ge channel p-type metal-oxide-semiconductor field-effect transistors (p-MOSFETs) on Siâ‚€.â‚ƒGeâ‚€.â‚‡ virtual substrates. The poor interface between silicon dioxide (SiOâ‚‚) and the Ge channel was eliminated by capping the strained Ge layer with a relaxed, epitaxial silicon surface layer grown at 400° C. Ge p-MOSFETs fabricated from this structure show a hole mobility enhancement of nearly 8 times that of co-processed bulk Si devices, and the Ge MOSFETs have a peak effective mobility of 1160 cmÂ²/V-s. These MOSFETs demonstrate the possibility of creating a surface channel enhancement mode MOSFET with buried channel-like transport characteristics.

Solid-shell element model of assumed through-thickness electric distribution for laminate composite piezoelectric structures

Tue, 01 Jan 2002 00:00:00 GMT

Solid-shell element model of assumed through-thickness electric distribution for laminate composite piezoelectric structures Yi, Sung; Yao, Lin-Quan The eight-node solid-shell finite element models have been developed for the analysis of laminated composite pate/shell structures with piezoelectric actuators and sensors. To resolve the locking problems of the solid-shell elements in laminated materials and improve accuracy, the assumed natural strain method and hybrid stress method are employed. The nonlinear electric potential distribution in piezoelectric layer is described by introducing internal electric potential. The developed finite element models, especially, electric potential node model, have the advantages of simpler modeling and can obtain same effect that exact solution described.

Si Industry at a Crossroads: New Materials or New Factories?

Tue, 01 Jan 2002 00:00:00 GMT

Si Industry at a Crossroads: New Materials or New Factories? Fitzgerald, Eugene A.; Leitz, Christopher W.; Lee, Minjoo L.; Antoniadis, Dimitri A.; Currie, Matthew T. Many trends in the silicon industry could be interpreted as the herald of the end of traditional Si scaling. If this premise holds, future performance and system-on-chip applications may not be reached with conventional Si technology extensions. We review progress towards our vision that a larger crystal structure on Si, namely relaxed SiGe epitaxial layers, can support many generations of higher performance Si CMOS and new system-on-chip functionality without the expense of significant new equipment and change to CMOS manufacturing ideology. We will review the impact of tensile strained Si layers grown on relaxed SiGe layers. Both NMOS and PMOS exhibit higher carrier mobilities due to the strained Si MOSFET channel. Heterostructure MOSFETs designed on relaxed SiGe can have multiple-generation performance increases, and therefore determine a new performance roadmap for Si CMOS technology, independent of MOSFET gate length. We also indicate that this materials platform naturally leads to incorporating new optical functionality into Si CMOS technology.

SiGe-On-Insulator (SGOI) Technology and MOSFET Fabrication

Tue, 01 Jan 2002 00:00:00 GMT

SiGe-On-Insulator (SGOI) Technology and MOSFET Fabrication Cheng, Zhiyuan; Fitzgerald, Eugene A.; Antoniadis, Dimitri A. In this work, we have developed two different fabrication processes for relaxed Si₁₋xGex-on-insulator (SGOI) substrates: (1) SGOI fabrication by etch-back approach, and (2) by "smart-cut" approach utilizing hydrogen implantation. Etch-back approach produces SGOI substrate with less defects in SiGe film, but the SiGe film uniformity is inferior. "Smart-cut" approach has better control on the SiGe film thickness and uniformity, and is applicable to wider Ge content range of the SiGe film. We have also fabricated strained-Si n-MOSFET’s on SGOI substrates, in which epitaxial regrowth was used to produce the surface strained Si layer on relaxed SGOI substrate, followed by large-area n-MOSFET’s fabrication on this structure. The measured electron mobility shows significant enhancement (1.7 times) over both the universal mobility and that of co-processed bulk-Si MOSFET’s. This SGOI process has a low thermal budget and thus is compatible with a wide range of Ge contents in Si₁₋xGex layer.

SiGeC Near Infrared Photodetectors

Tue, 01 Jan 2002 00:00:00 GMT

SiGeC Near Infrared Photodetectors Li, Baojun; Chua, Soo-Jin; Fitzgerald, Eugene A.; Leitz, Christopher W.; Miao, Lingyun A near infrared waveguide photodetector in Si-based ternary Si₁âˆ’xâˆ’yGexCy alloy was demonstrated for 0.85~1.06 µm wavelength fiber-optic interconnection system applications. Two sets of detectors with active absorption layer compositions of Si₀.₇₉Ge₀.₂C₀.₀₁ and Si₀.₇₀Ge₀.₂₈C₀.₀₂ were designed. The active absorption layer has a thickness of 120~450 nm. The external quantum efficiency can reach ~3% with a cut-off wavelength of around 1.2 µm.

Processing, Structure, Properties, and Reliability of Metals for Microsystems

Tue, 01 Jan 2002 00:00:00 GMT

Processing, Structure, Properties, and Reliability of Metals for Microsystems Thompson, Carl V. Research on the processing, structure, properties and reliability of metal films and metallic microdevice elements is reviewed. Recent research has demonstrated that inelastic deformation mechanisms of metallic films and microelements are a function of temperature, encapsulation, and dimension. Reduced dimension can lead to strengthening or softening, depending on the temperature and strain rate. These results will help in the analysis and prediction of the stress state of films and microelements as a function of their thermal history. Experimental characterization and modeling of stress evolution during film formation has also been undertaken. New microelectromechanical devices have been developed for in situ measurements of stress during processing, and experiments relating stress and structure evolution are underway for electrodeposition and reactive film formation as well as vapor deposition. Experiments relating current-induced stress evolution (electromigration) to the reliability of Cu based interconnects are also being carried out.

Process development of silicon-silicon carbide hybrid structures for micro-engines (January 2002)

Tue, 01 Jan 2002 00:00:00 GMT

Process development of silicon-silicon carbide hybrid structures for micro-engines (January 2002) Choi, D.; Shinavski, R.J.; Spearing, S. Mark MEMS-based gas turbine engines are currently under development at MIT for use as a button-sized portable power generator or micro-aircraft propulsion sources. Power densities expected for the micro-engines require very high rotor peripheral speeds of 300-600m/s and high combustion gas temperatures of 1300-1700K. These harsh requirements for the engine operation induce very high stress levels in the engine structure, and thus call for qualified refractory materials with high strength. Silicon carbide (SiC) has been chosen as the most promising material for use due to its high strength and chemical inertness at elevated temperatures. However, the state-of-the art microfabrication techniques for single-crystal SiC are not yet mature enough to achieve the required level of high precision of micro-engine components. To circumvent this limitation and to take advantage of the well-established precise silicon microfabrication technologies, silicon-silicon carbide hybrid turbine structures are being developed using chemical vapor deposition (CVD) of thick SiC (up to ~70µm) on silicon wafers and wafer bonding processes. Residual stress control of thick SiC layers is of critical importance to all the silicon-silicon carbide hybrid structure fabrication steps since a high level of residual stresses causes wafer cracking during the planarization, as well as excessive wafer bow, which is detrimental to the subsequent planarization and bonding processes. The origins of the residual stress in CVD SiC layers have been studied. SiC layers (as thick as 30µm) with low residual stresses (on the order of several tens of MPa) have been produced by controlling CVD process parameters such as temperature and gas ratio. Wafer-level SiC planarization has been accomplished by mechanical polishing using diamond grit and bonding processes are currently under development using CVD silicon dioxide as an interlayer material. This paper reports on the work that has been done so far under the MIT micro-engine project.

A Novel Testing Apparatus for Tribological Studies at the Small Scale

Tue, 01 Jan 2002 00:00:00 GMT

A Novel Testing Apparatus for Tribological Studies at the Small Scale Gearing, B.P.; Anand, Lallit A novel flexure-based biaxial compression/shear apparatus has been designed, built, and utilized to conduct tribological studies of interfaces relevant to MEMS. Aspects of our new apparatus are detailed and its capabilities are demonstrated by an investigation of two interfaces for MEMS applications. Tribological tests may be performed with normal and tangential forces in the µN to N range and relative sliding displacements in the nm to mm range. In this testing range, the new experimental apparatus represents an improvement over existing techniques for tribological studies at the small scale.

Methods for Calculating the Optical Band Structure of Photonic Composites

Tue, 01 Jan 2002 00:00:00 GMT

Methods for Calculating the Optical Band Structure of Photonic Composites Maldovan, Martin. Lately, there has been an increasing interest in studying the propagation of electromagnetic waves in periodic dielectric structures (photonic crystals). Like the electron propagation in semiconductors, these structures are represented by band diagrams in which gaps can be found where the electromagnetic propagation is forbidden. Much effort is dedicated to find structures that can prohibit the propagation of light in all directions. This effect could lead to light localization.

Metastable Intermediate in LixMnO₂ Layered to Spinel Phase Transition

Tue, 01 Jan 2002 00:00:00 GMT

Metastable Intermediate in LixMnO₂ Layered to Spinel Phase Transition Reed, John; Ceder, Gerbrand; Van Der Ven, A. Ab Initio calculations suggest that partially lithiated layered LixMnO₂ transforms to spinel in a two-stage process. In the first stage, a significant fraction of the Mn and Li ions rapidly occupy tetrahedral sites, forming a metastable intermediate. The second stage involves a more difficult coordinated rearrangement of Mn and Li ions to form spinel. This behavior is contrasted to LixCoO₂. The susceptibility of Mn for migration into the Li layer is found to be controlled by oxidation state which suggests various means of inhibiting the transformation. These strategies could prove useful in the creation of superior Mn based cathode materials.

Mechanical Characterization of the Heat Affected Zone of Gold Wirebonds Using Nanoindentation

Tue, 01 Jan 2002 00:00:00 GMT

Mechanical Characterization of the Heat Affected Zone of Gold Wirebonds Using Nanoindentation Shah, M.; Zeng, K.; Tay, A.A.O.; Suresh, Subra With increasing miniaturization in microelectronics the wirebonds used in IC packages are witnessing a thrust towards fine pitch wirebonding. To have a precise control over loop height of the wirebond for fine pitch wirebonding, it is imperative to do mechanical characterization of the wirebond. The present work studies the mechanical properties of gold wire and wirebond using nanoindentation. The wirebond specimen surface was planarized using mechanical polishing. The loop height of the gold wirebond is directly proportional to the length of the heat affected zone (HAZ) above the ball of gold wirebond. Metallographic preparation of gold wirebond cross section reveals the presence of undesirable coarse grain structure in HAZ due to recrystallization and grain growth in the gold wire adjacent to the ball. The recrystallization temperature of our gold wire was found using D.S.C. to be 340.66°C. The doping elements present in the gold wire used, were identified using TOF-SIMS. Nanoindentation of the gold wire was done at different maximum loads to observe the hardness variation with load. The nanoindentation of gold wirebond has confirmed a v-shaped hardness profile in the HAZ. The hardness minima for the particular gold wire used with a ball size ratio of 2.4 was observed at distance of 160-170 µm from the neck of the ball. The elastic modulus was found to vary randomly and to be independent of the microstructure in the wirebond. A yield stress profile based on empirical hardness-yield strength correlation has been predicted for the gold wirebond.

Magnetically-Assisted Statistical Assembly - a new heterogeneous integration technique

Tue, 01 Jan 2002 00:00:00 GMT

Magnetically-Assisted Statistical Assembly - a new heterogeneous integration technique Fonstad, Clifton G. Jr. This paper presents a new technique for the monolithic heterogeneous integration of compound semiconductor devices with silicon integrated circuits, and establishes the theoretical foundation for a key element of the process, tailored magnetic attraction and retention. It is shown how a patterned thin film of hard magnetic material can be used to engineer the attraction between the film and nanopills covered with a soft magnetic material. With a suitable choice of pattern, it is anticipated that it will be possible to achieve complete filling of recesses in the surface of fully-processed integrated circuit wafers, preparatory to subsequent processing to fabricate the nanopills into heterostructure devices integrated monolithically with the pre-existing electronics.

Length Effects on the Reliability of Dual-Damascene Cu Interconnects

Tue, 01 Jan 2002 00:00:00 GMT

Length Effects on the Reliability of Dual-Damascene Cu Interconnects Wei, F.; Hau-Riege, S.P.; Gan, C.L.; Thompson, Carl V.; Clement, J.J.; Tay, H.L.; Yu, B.; Radhakrishnan, M.K.; Pey, Kin Leong; Choi, Wee Kiong The effects of interconnect length on the reliability of dual-damascene Cu metallization have been investigated. As in Al-based interconnects, the lifetimes of Cu lines increase with decreasing length. However, unlike Al-based interconnects, no critical length exists, below which all Cu lines are â€˜immortal’. Furthermore, we found multi-modal failure statistics for long lines, suggesting multiple failure mechanisms. Some long Cu interconnect segments have very large lifetimes, whereas in Al segments, lifetimes decrease continuously with increasing line length. It is postulated that the large lifetimes observed in long Cu lines result from liner rupture at the bottom of the vias, which allows continuous flow of Cu between the two bond pads. As a consequence, the average lifetimes of short lines and long lines can be higher than those of lines with intermediate lengths.

Investigation of the Fundamental Reliability Unit for Cu Dual-Damascene Metallization

Tue, 01 Jan 2002 00:00:00 GMT

Investigation of the Fundamental Reliability Unit for Cu Dual-Damascene Metallization Gan, C.L.; Thompson, Carl V.; Pey, Kin Leong; Choi, Wee Kiong; Wei, F.; Hau-Riege, S.P.; Augur, R.; Tay, H.L.; Yu, B.; Radhakrishnan, M.K. An investigation has been carried out to determine the fundamental reliability unit of copper dual-damascene metallization. Electromigration experiments have been carried out on straight via-to-via interconnects in the lower metal (M1) and the upper metal (M2), and in a simple interconnect tree structure consisting of straight via-to-via line with an extra via in the middle of the line (a "dotted-I"). Multiple failure mechanisms have been observed during electromigration testing of via-to-via Cu interconnects. The failure times of the M2 test structures are significantly longer than that of identical M1 structures. It is proposed that this asymmetry is the result of a difference in the location of void formation and growth, which is believed to be related to the ease of electromigration-induced void nucleation and growth at the Cu/Si₃N₄ interface. However, voids were also detected in the vias instead of in the Cu lines for some cases of early failure of the test lines. These early failures are suspected to be related to the integrity and reliability of the Cu via. Different magnitudes and directions of electrical current were applied independently in two segments of the interconnect tree structure. As with Al-based interconnects, the reliability of a segment in this tree strongly depends on the stress conditions of the connected segment. Beyond this, there are important differences in the results obtained under similar test conditions for Al-based and Cu-based interconnect trees. These differences are thought to be associated with variations in the architectural schemes of the two metallizations. The absence of a conducting electromigration-resistant overlayer in Cu technology allows smaller voids to cause failure in Cu compared to Al. Moreover, the Si₃N₄ overlayer that serves as an interlevel diffusion barrier provides sites for easy nucleation of voids and also provides a high diffusivity path for electromigration. The results reported here suggest that while segments are not the fundamental reliability unit for circuit-level reliability assessments for Al or Cu, vias, rather than trees, might be the appropriate fundamental units for the assessment of Cu reliability.

Graded InGaN Buffers for Strain Relaxation in GaN/InGaN Epliayers Grown on Sapphire

Tue, 01 Jan 2002 00:00:00 GMT

Graded InGaN Buffers for Strain Relaxation in GaN/InGaN Epliayers Grown on Sapphire Song, T.L.; Chua, Soo-Jin; Fitzgerald, Eugene A. Graded InGaN buffers are employed to relax the strain arising from the lattice and thermal mismatches between GaN/InGaN epilayers grown on sapphire. The formation of V-pits in linearly graded InGaN/GaN bulk epilayers is illustrated. The V-pits were sampled using Atomic Force Microscopy and Scanning Electron Microscopy to examine their variation from the theoretical geometry shape. We discovered that the size of the V-pit opening in linearly graded InGaN, with and without GaN cap layer, has a Gaussian distribution. As such, we deduce that the V-pits are produced at different rates, as the growth of the InGaN layer progresses. In Stage I, the V-pits form at a slow rate at the beginning and then accelerate in Stage II when a critical thickness is reached before decelerating in Stage III after arriving at a mean size. It is possible to fill the V-pits by growing a GaN cap layer. It turns out that the filling of the V-pits is more effective at lower growth temperature of the GaN cap layer and the size of the V-pits opening, which is continued in to GaN cap layer, is not dependent on the GaN cap layer thickness. Furthermore, graded InGaN/GaN layers display better strain relaxation as compared to conventionally grown bulk GaN. By employing a specially design configuration, the V-pits can be eliminated from the InGaN epilayer.

Glass Forming Ability in Pr-(Cu, Ni)-Al Alloys

Tue, 01 Jan 2002 00:00:00 GMT

Glass Forming Ability in Pr-(Cu, Ni)-Al Alloys Zhang, Yong; Li, Yi Glass forming ability (GFA) in the Pr-rich Pr-(Cu, Ni)-Al alloys at or near the eutectic points was systematically studied. It was found that the GFA in the pseudo-ternary alloys of Pr-(Cu, Ni)-Al is higher than that of the ternary alloys of Pr-Cu-Al. Two eutectic compositions in Pr-(Cu, Ni)-Al alloys were found by DSC, namely, Pr₆₈(Cu₀.₅Ni₀.₅)₂₅Al₇ and Pr₅₂(Cu₀.₅Ni₀.₅)₂₅Al₂₃ (at %). The later one shows better GFA than the first one. However, the best GFA was obtained at an off-eutectic composition of Pr₅₄(Cu₀.₅Ni₀.₅)₃₀Al₁₆, which can be formed in fully amorphous rod with diameter of 1.5 mm by copper mould casting. The deviation of the best GFA composition from the eutectic point [Pr₆₈(Cu₀.₅Ni₀.₅)₂₅Al₇] was explained in terms of the asymmetric coupled eutectic zone and the higher glass transition temperature Tg on the hypereutectic side.

Frequency Dependence Modulus of Pd₄₀Ni₁₀Cu₃₀P₂₀ Amorphous Alloy around the Glass Transition by Dynamic Mechanical Analysis

Tue, 01 Jan 2002 00:00:00 GMT

Frequency Dependence Modulus of Pd₄₀Ni₁₀Cu₃₀P₂₀ Amorphous Alloy around the Glass Transition by Dynamic Mechanical Analysis Lee, M.L.; Li, Yi; Feng, Y.P.; Carter, W. Craig Dynamic Mechanical Analyzer (DMA) was used to study the frequency dependence of storage and loss modulus of amorphous Pd₄₀Ni₁₀Cu₃₀P₂₀ alloy over a broad frequency range around its glass transition temperature. The amorphous samples were subjected to two testing conditions: constant frequency with continuous heating and isothermal with frequency sweep. The storage modulus Eâ€² exhibited a sigmoidal change from about 90 GPa to a low value of about 0 GPa over the glass transition region. The loss modulus, Eâ€³, was characterized by an asymmetrical peak with a smaller slope at the low temperature side than at the high temperature side upon heating. These changes in moduli were associated with mechanical relaxation due to atomic motion. Similar results were also obtained under isothermal condition. The Kohrausch-Williams-Watts function was used to fit the data obtained under the isothermal condition. The peak frequencies obtained were then fitted to the VFT equation and the scaling law equation.

Research Summary: The Effect of Microstructure on the Macroscopic Response of Electroactive Systems

Tue, 01 Jan 2002 00:00:00 GMT

Research Summary: The Effect of Microstructure on the Macroscopic Response of Electroactive Systems García, R. Edwin; Carter, W. Craig; Langer, Stephen A.; Chiang, Yet-Ming A framework to model the effect of the microstructural features and crystallographic anisotropy on the macroscopic response of electractive ceramics is described. The model accounts for mechanical, electric and concentration fields, as well as couplings such as piezoelectricity and electromigration. The setup starts from single crystal properties and incorporates them into a numerical setup by applying on the finite element method. This was implemented by modifying the Object Oriented Finite Element Analysis for Materials Science software (OOF). The model is validated against analytic solutions. This framework is applied to describe a) the effect of crystallographic texture and grain microstructure in ceramic ferroelectrics and b) the transport processes of charged species for rechargeable Li-ion batteries.

A Constitutive Model for the Mechanical Behavior of Single Crystal Silicon at Elevated Temperature

Tue, 01 Jan 2002 00:00:00 GMT

A Constitutive Model for the Mechanical Behavior of Single Crystal Silicon at Elevated Temperature Moon, H.-S.; Anand, Lallit; Spearing, S. Mark Silicon in single crystal form has been the material of choice for the first demonstration of the MIT microengine project. However, because it has a relatively low melting temperature, silicon is not an ideal material for the intended operational environment of high temperature and stress. In addition, preliminary work indicates that single crystal silicon has a tendency to undergo localized deformation by slip band formation. Thus it is critical to obtain a better understanding of the mechanical behavior of this material at elevated temperatures in order to properly exploit its capabilities as a structural material. Creep tests in simple compression with n-type single crystal silicon, with low initial dislocation density, were conducted over a temperature range of 900 K to 1200 K and a stress range of 10 MPa to 120 MPa. The compression specimens were machined such that the multi-slip <100> or <111> orientations were coincident with the compression axis. The creep tests reveal that response can be delineated into two broad regimes: (a) in the first regime rapid dislocation multiplication is responsible for accelerating creep rates, and (b) in the second regime an increasing resistance to dislocation motion is responsible for the decelerating creep rates, as is typically observed for creep in metals. An isotropic elasto-viscoplastic constitutive model that accounts for these two mechanisms has been developed in support of the design of the high temperature turbine structure of the MIT microengine.

Computation and Simulation of the Effect of Microstructures on Material Properties

Tue, 01 Jan 2002 00:00:00 GMT

Computation and Simulation of the Effect of Microstructures on Material Properties Carter, W. Craig Methods for and computed results of including the physics and spatial attributes of microstructures are presented for a number of materials applications in devices. The research in our group includes applications of computation of macroscopic response of material microstructures, the development of methods for calculating microstructural evolution, and the morphological stability of structures. In this review, research highlights are presented for particular methods for computing the response in: 1) ferroelectric materials for actuator devices; 2) coarse-graining of atomistic data for simulations of microstructural evolution during processing; 3) periodic and non-periodic photonic composites; and 4) re-chargeable battery microstructures.

Charge Storage Effect in a Trilayer Structure Comprising Germanium Nanocrystals

Tue, 01 Jan 2002 00:00:00 GMT

Charge Storage Effect in a Trilayer Structure Comprising Germanium Nanocrystals Heng, C.L.; Choi, Wee Kiong; Chim, Wai Kin; Teo, L.W.; Ho, Vincent; Tjiu, W.W.; Antoniadis, Dimitri A. A metal-insulator-semiconductor (MIS) device with a trilayer insulator structure consisting of sputtered SiO₂ (~50nm)/evaporated pure germanium (Ge) layer (2.4nm)/rapid thermal oxide (~5nm) was fabricated on a p-type Si substrate. The MIS device was rapid thermal annealed at 1000°C. Capacitance-voltage (C-V) measurements showed that, after rapid thermal annealing at 1000°C for 300s in Ar, the trilayer device exhibited charge storage property. The charge storage effect was not observed in a device with a bilayer structure without the Ge middle layer. With increasing rapid thermal annealing time from 0 to 400s, the width of the C-V hysteresis of the trilayer device increased significantly from 1.5V to ~11V, indicating that the charge storage capability was enhanced with increasing annealing time. High-resolution transmission electron microscopy results confirmed that with increasing annealing time, the 2.4nm amorphous middle Ge layer crystallized gradually. More Ge nanocrystals were formed and the crystallinity of the Ge layer improved as the annealing time was increased. When the measurement temperature was increased from –50°C to 150°C, the width of the hysteresis of the MIS device reduced from ~10V to ~6V. This means that the charge storage capability of the trilayer structure decreases with increasing measurement temperature. This is due to the fact that the leakage current in the trilayer structure increases with increasing measurement temperature.

Atomistic Simulations of Metallic Cluster Coalescence

Tue, 01 Jan 2002 00:00:00 GMT

Atomistic Simulations of Metallic Cluster Coalescence Takahashi, A. R.; Thompson, Carl V.; Carter, W. Craig A new computational method is introduced to investigate the stresses developed in the island-coalescence stage of polycrystalline film formation during deposition. The method uses molecular dynamics to examine the behavior of clusters of atoms both in free space and on substrates. Continuum treatments used in previous models may not be applicable at small length scales or low dimensionality. In atomistic simulations, the effects of surface diffusion, bond straining and defect formation can be directly studied. TEM experiments will be used to evaluate the validity of the simulation model.

Anisotropic Superelasticity of Textured Ti-Ni Sheet

Tue, 01 Jan 2002 00:00:00 GMT

Anisotropic Superelasticity of Textured Ti-Ni Sheet Thamburaja, P.; Gao, S.; Yi, S.; Anand, Lallit A recently developed crystal-mechanics-based constitutive model for polycrystalline shape-memory alloys (Thamburaja and Anand [1]) is shown to quantitatively predict the in-plane anisotropy of superelastic sheet Ti-Ni to reasonable accord.

Amorphous Metallic Glass as New High Power and Energy Density Anodes For Lithium Ion Rechargeable Batteries

Tue, 01 Jan 2002 00:00:00 GMT

Amorphous Metallic Glass as New High Power and Energy Density Anodes For Lithium Ion Rechargeable Batteries Meng, Shirley Y.; Li, Yi; Arroyo, Elena M.; Ceder, Gerbrand We have investigated the use of aluminum based amorphous metallic glass as the anode in lithium ion rechargeable batteries. Amorphous metallic glasses have no long-range ordered microstructure; the atoms are less closely packed compared to the crystalline alloys of the same compositions; they usually have higher ionic conductivity than crystalline materials, which make rapid lithium diffusion possible. Many metallic systems have higher theoretical capacity for lithium than graphite/carbon; in addition irreversible capacity loss can be avoided in metallic systems. With careful processing, we are able to obtain nano-crystalline phases dispersed in the amorphous metallic glass matrix. These crystalline regions may form the active centers with which lithium reacts. The surrounding matrix can respond very well to the volume changes as these nano-size regions take up lithium. A comparison study of various kinds of anode materials for lithium rechargeable batteries is carried out.

PALM: Predicting Internet Network Distances Using Peer-to-Peer Measurements

Thu, 01 Jan 2004 00:00:00 GMT

PALM: Predicting Internet Network Distances Using Peer-to-Peer Measurements Lehman, Li-wei; Lerman, Steven Landmark-based architecture has been commonly adopted in the networking community as a mechanism to measure and characterize a host's location on the Internet. In most existing landmark based approaches, end hosts use the distance measurements to a common, fixed set of landmarks to derive an estimated location on the Internet. This paper investigates whether it is possible for participating peer nodes in an overlay network to collaboratively construct an accurate geometric model of its topology in a completely decentralized peer-to-peer fashion, without using a fixed set of landmarks. We call such a peer-to-peer approach in topology discovery and modeling using landmarks PALM (Peers As LandMarks). We evaluate the performance characteristics of such a decentralized coordinates-based approach under several factors, including dimensionality of the geometric space, peer distance distribution, and the number of peer-to-peer distance measurements used. We evaluate two PALM-based schemes: RAND-PALM and ISLAND. In RAND-PALM, a peer node randomly selects from existing peer nodes as its landmarks. In ISLAND (Intelligent Selection of Landmarks), each peer node selects its landmarks by exploiting the topological information derived based on existing peer nodes' coordinates values.

Strategies of Lithography for Trapping Nano-particles

Thu, 01 Jan 2004 00:00:00 GMT

Strategies of Lithography for Trapping Nano-particles Rajter, Rick Current research in materials science and engineering continues to drive it's attention to systems on the nanoscale. Thin films, nano-particles, quantum dots, nano-wires, etc are just a few of the areas that are becoming important in projects ranging from biomedical transport to nano-gears. Thus, understanding, producing, and creating these system is also becoming an important challenge for scientists and engineers to overcome. Physically manipulating objects on the atomic scale requires more than just "micro tweezers" to arrange them in a particular system. Another concern is that forces and interactions that could be ignored or approximated at larger scales no longer hold in this regime. It is the goal of this project to use computational models to simulate nano-particles interacting with customized, highly tailored surfaces in order to confine and pattern them to desired specifications. The interactions to be considered include electrostatic attraction and repulsion, hamaker forces, steric effects, dielectric effects of the medium, statistical variability, mechanical induced surface vibrations, etc. The goal is to be able to manufacture such systems for experimentation in order to compare results to the models. If the models do not hold, we hope to understand the origin of these discrepancies in order to create more robust models for this length scale. Lithography, CVD, and chemical etching will be the primary methods used to create these surfaces on glass substrates. TEM analysis will be compared to modeling through various MD program packages.

RM³ Processing for In-plane Optical Interconnects on Si-CMOS and the Impact of Topographic Features on Losses in Deposited Dielectric Waveguides

Thu, 01 Jan 2004 00:00:00 GMT

RM³ Processing for In-plane Optical Interconnects on Si-CMOS and the Impact of Topographic Features on Losses in Deposited Dielectric Waveguides Barkley, Edward; Fonstad, Clifton G. Jr. This paper describes recent progress in a continuing program to develop and apply RM³ (recess mounting with monolithic metallization) technologies for heterogeneous integration. Particular emphasis is placed on the applicability of RM³ integration to in-plane geometries for on-chip optical clock and signal distribution and on the suitability of commercially processed IC wafers for use as substrates for rectangular dielectric waveguides.

TiNi-based thin films for MEMS applications

Thu, 01 Jan 2004 00:00:00 GMT

TiNi-based thin films for MEMS applications Fu, Yongqing; Du, Hejun; Huang, Weimin; Zhang, Sam; Hu, Min In this paper, some critical issues and problems in the development of TiNi thin films were discussed, including preparation and characterization considerations, residual stress and adhesion, frequency improvement, fatigue and stability, as well as functionally graded or composite thin film design. Different types of MEMS applications were reviewed and the prospects for future advances in fabrication process and device development were discussed.

A theory of amorphous polymeric solids undergoing large deformations: application to micro-indentation of poly(methyl methacrylate)

Thu, 01 Jan 2004 00:00:00 GMT

A theory of amorphous polymeric solids undergoing large deformations: application to micro-indentation of poly(methyl methacrylate) Ames, N.M.; Anand, Lallit Although existing continuum models for the elasto-viscoplastic response of amorphous polymeric materials phenomenologically capture the large deformation response of these materials in a reasonably acceptable manner, they do not adequately account for the creep response of these materials at stress levels below those causing “macro-yield”, as well as the Bauschinger-type reverse yielding phenomena at strain levels less than ≈ 30% associated with the macro-yield transient. Anand [1] has recently generalized the model of Anand and Gurtin [2] to begin to capture these important aspects of the mechanical response of such materials. In this work, we summarize Anand’s constitutive model and apply it to the amorphous polymeric solid poly(methyl methacrylate) (PMMA), at ambient temperature and compressive stress states under which this material does not exhibit crazing. We describe our compression-tension and creep experiments on this material from which the material parameters in the model were determined. We have implemented the constitutive model in the finite-element computer program ABAQUS/Explicit [3], and using this finite-element program, we show numerical results for some representative problems in micro-indentation of PMMA, and compare them against corresponding results from physical experiments. The overall predictions of the details of the load, P, versus depth of indentaion, h, curves are very encouraging.

Synthesis, electrochemistry and First Principles Calculation studies of layered Li-Ni-Ti-O compounds

Thu, 01 Jan 2004 00:00:00 GMT

Synthesis, electrochemistry and First Principles Calculation studies of layered Li-Ni-Ti-O compounds Kang, Kisuk; Carlier, Dany; Reed, John; Arroyo, Elena M.; Meng, Shirley Y.; Ceder, Gerbrand New layered cathode materials, Li₀.₉Ni₀.₄₅Ti₀.₅₅O₂, were synthesized by means of ion-exchange from Na₀.₉Ni₀.₄₅Ti₀.₅₅O₂. The degree of cation disordering in the material depends critically on the synthesis conditions. Longer times and higher temperatures in the ion-exchange process induced more cation disordering. However, the partially disordered phase showed better capacity retention than the least disordered phase. First principles calculations indicated this could be attributed to the migration of Ti⁺⁴ into the Li layer during the electrochemical testing, which seems to depend sensitively on the Ni⁺² -Ti⁺⁴ configuration in the transition metal layer. The poor conductivity of this material could also be the reason for its low specific capacity according to the Density of States (DOS) obtained from first principles calculations indicating that only Ni participates in the electronic conductivity.

Structural analysis of metalorganic chemical vapor deposited AlN nucleation layers on Si (111)

Thu, 01 Jan 2004 00:00:00 GMT

Structural analysis of metalorganic chemical vapor deposited AlN nucleation layers on Si (111) Zang, Keyan; Wang, Lianshan; Chua, Soo-Jin; Thompson, Carl V. AlN nucleation layers are being investigated for growth of GaN on Si. The microstructures of high-temperature AlN nucleation layers grown by MOCVD on Si (111) substrates with trimethylaluminium pre-treatments have been studied using atomic force microscopy (AFM) and transmission electron microscopy (TEM). The AFM results show that with TMA pre-treatments, AlN grows in a pseudo-2-dimensional mode because the lateral growth rate of AlN is increased, and the wetting property of the AlN on silicon is improved. Also, no amorphous SiNx layer was observed at the interface with TMA pre-treatments and AlN films with good epitaxial crystalline quality were obtained. Transmission electron diffraction patterns revealed that the AlN and Si have the crystallographic orientation relationship AlN [0001]â•‘Si[111] and AlN[11 2 0] â•‘Si[110]. High resolution transmission electron microscopy indicates a 5:4 lattice matching relationship for AlN and Si along the Si [110] direction. Based on this observation, a lattice matching model is proposed.

Review of Direct Metal Bonding for Microelectronic Interconnections

Thu, 01 Jan 2004 00:00:00 GMT

Review of Direct Metal Bonding for Microelectronic Interconnections Zhang, G.G.; Wong, Chee Cheong Microelectronic interconnections require advanced joining techniques. Direct metal bonding methods, which include thercomsonic and thermocompression bonding, offer remarkable advantages over soldering and adhesives joining. These processes are reviewed in this paper. The progress made in this area is outlined. Some work concerned with the bonding modeling is also presented. This model is based on the joint interface mechanics resulting from compression. Both bump and substrate deformation are taken into account. The improved understanding of the relationship between the deformation and bonding formation may provide more accurate joint evaluation criterion.

Plastic Relaxation In Single InᵡGa₁â‚‹ᵡN/GaN Epilayers Grown On Sapphire

Thu, 01 Jan 2004 00:00:00 GMT

Plastic Relaxation In Single InᵡGa₁â‚‹ᵡN/GaN Epilayers Grown On Sapphire Song, T.L.; Chua, Soo-Jin; Fitzgerald, Eugene A.; Chen, Peng; Tripathy, S. Plastic relaxation was observed in InᵡGa₁â‚‹ᵡN/GaN epilayers grown on c-plane sapphire substrates. The relaxation obeys the universal hyperbolic relation between the strain and the reciprocal of the layer thickness. Plastic relaxation in this material system reveals that there is no discontinuous relaxation at critical thickness and once a layer starts to relieve, it follows the same strain-thickness dependence, unconstrained by the original misfit until the material system work hardens. From x-ray diffraction calibration, the in-plane and normal relaxation constants KP0 and KN0 for the InᵡGa₁â‚‹ᵡN/GaN grown on sapphire were found to be âˆ’0.98 ± 0.03 and +0.51 ± 0.03 nm, respectively.

Photonic Crystals: Numerical Predictions of Manufacturable Dielectric Composite Architectures

Thu, 01 Jan 2004 00:00:00 GMT

Photonic Crystals: Numerical Predictions of Manufacturable Dielectric Composite Architectures Carter, W. Craig.; Maldovan, Martin.; Maskaly, Karlene. Photonic properties depend on both dielectric contrast in a microscopic composite and the arrangement of the microstructural components. No theory exists for direct prediction of photonic properties, and so progress relies on numerical methods combined with insight into manufacturable composite architectures. We present a discussion of effective photonic crystal production techniques and several numerical methods to predict dispersion relations of hypothetical but fabricable structures.

Optically pumped InxGa₁â‚‹xN/InyGa₁â‚‹yN multiple quantum well vertical cavity surface emitting laser operating at room temperature.

Thu, 01 Jan 2004 00:00:00 GMT

Optically pumped InxGa₁â‚‹xN/InyGa₁â‚‹yN multiple quantum well vertical cavity surface emitting laser operating at room temperature. Chen, Zhen; Chua, Soo-Jin; Chen, Peng; Zhang, Ji Room temperature vertical cavity lasing at the wavelength of 433nm has been successfully realized in InxGa₁â‚‹xN/InyGa₁â‚‹yN multiple quantum well without Bragg mirrors under photo-excitation. At high excitation intensity, one of the modes of the Fabry-Perot cavity formed by the GaN/sapphire and the GaN/air interfaces, shows a strong superlinear increase in intensity with excitation intensity rise. The vertical cavity surface emitting laser (VCSELs) structure is grown by metal-organic chemical vapor phase deposition and the threshold is as low as 200kW/cm². The lasing in the sample probably results from the ultrahigh material gain due to the spontaneous formation of dense array of nanoscale InGaN quantum dots (QDs) having an exceptional high area density.

Nanocomposite Thin Films for both Mechanical and Functional Applications

Thu, 01 Jan 2004 00:00:00 GMT

Nanocomposite Thin Films for both Mechanical and Functional Applications Zhang, Sam; Fu, Yongqing; Du, Hejun; Liu, Yang; Chen, Tupei The design methodology and realization of nanocomposite films aiming for mechanical (superhardness, toughness) and functional (optical, microelectronic) properties were discussed in this paper. Superhard TiCrCN and nc-TiN/a-SiNx films and super-tough nc-TiC/a-C(Al) films were prepared through co-sputtering method by optimal design of microstructure. The nanocrystalline silicon (nc-Si) passivated with a matrix of thermally grown silicon dioxide were prepared using implantation of Si into SiO₂ film, and showed improved photoluminescence and optical properties. Also discussed is the nano-composite design of thin film resistor with optimized temperature coefficient of resistivity.

Mortality Dependence of Cu Dual Damascene Interconnects on Adjacent Segments

Thu, 01 Jan 2004 00:00:00 GMT

Mortality Dependence of Cu Dual Damascene Interconnects on Adjacent Segments Chang, Choon Wai; Gan, C.L.; Thompson, Carl V.; Pey, Kin Leong; Choi, Wee Kiong; Hwang, N. Electromigration experiments have been carried out on straight interconnects that have single vias at each end, and are divided into two segments by a via in the center ("dotted-I" structures). For dotted-i structures in the second metal layer (M2) and with 25µm-long segments length, failures occurred even when the product of the current density and segment length (jL) was as low as 1250A/cm, even though via terminated 25µm-long lines are "immortal" when (jL)cr < 1500 A/cm. Moreover, we found the mortalities of the dotted-I segments to be dependent on the current density and current direction in the adjacent segment. These result suggest that there is not a definite value of jL product that defines true immortality in individual segments that are part of an interconnect tree, and that the critical value of jL for Cu dual damascene segments is dependent on the magnitude and direction of current flow in adjacent segments. Therefore, (jL)cr values determined in two-terminal via-terminated lines cannot be directly applied to interconnects with branched segments, but rather the magnitude as well as the direction of the current flow in the adjoining segments must be taken into consideration in determining the immortality of interconnect segments.

Micro Raman Spectroscopy of Annealed Erbium Implanted GaN

Thu, 01 Jan 2004 00:00:00 GMT

Micro Raman Spectroscopy of Annealed Erbium Implanted GaN Vajpeyi, Agam P.; Chua, Soo-Jin; Fitzgerald, Eugene A.; Tripathy, S. Wurtzite GaN epilayers grown by metal organic chemical vapor deposition on sapphire substrates were subsequently ion implanted with Er to a dose of 5×10¹⁵ cm⁻². The implanted samples were annealed in nitrogen atmosphere at different temperatures to facilitate recovery from implantation related damage. In this paper we report the annealing behavior of Erbium implanted GaN by using micro Raman spectroscopy and optimized annealing condition. We have observed almost full damage recovery of the crystalline quality of Er implanted GaN after annealing at 1000°C for 2 minute. This observation is further confirmed by using AFM images.

Mechanical Properties of Bulk Metallic Glasses and Composites

Thu, 01 Jan 2004 00:00:00 GMT

Mechanical Properties of Bulk Metallic Glasses and Composites Lee, M.L.; Li, Yi; Zhong, Yi; Carter, W. Craig We have studied the mechanical properties of monolithic bulk metallic glasses and composite in the La based alloys. La₈₆₋yAl₁₄(Cu, Ni)y (y=24 to 32) alloy systems was used to cast the in-situ structure and subsequently tested under compression. We found that the ductility of the monolithic is actually poorer than that of the fully crystalline composite.

Investigation on Thin Film Lithium Microbatteries

Thu, 01 Jan 2004 00:00:00 GMT

Investigation on Thin Film Lithium Microbatteries Shi, Z.; Lü, L.; Ceder, Gerbrand Thin film lithium microbatteries were investigated in this project in which LiCoO₂ cathodes about 200 to 500 nm were fabricated by pulsed-laser deposition (PLD) at different processing parameters such as laser energy and fluence, substrate temperature, background gas pressure, and target-substrate distance. Structure, microstructure and composition of as-deposited LiCoO₂ films were determined by XRD, SEM and XPS. Optimal deposition parameters were identified. Relaxation of open-circuit voltage of as-prepared cells and charge-discharge cycling were conducted to characterize the electrochemical properties of microbatteries made of these LiCoO₂ films.

High hole and electron mobilities using Strained Si/Strained Ge heterostructures

Thu, 01 Jan 2004 00:00:00 GMT

High hole and electron mobilities using Strained Si/Strained Ge heterostructures Gupta, Saurabh; Lee, Minjoo L.; Leitz, Christopher W.; Fitzgerald, Eugene A. PMOS and NMOS mobility characteristics of the dual channel (strained Si/strained Ge) heterostructure have been reviewed. It is shown that the dual channel heterostructure can provide substantially enhanced mobilities for both electrons and holes. However, germanium interdiffusion from the germanium rich buried layer into the underlying buffer layer could potentially reduce the hole mobility enhancements.

Growth and Properties of (001)-oriented Pb(Zr₀.₅₂Ti₀.₄₈)O₃/LaNiO₃ Films on Si(001) Substrates with TiN Buffer Layers

Thu, 01 Jan 2004 00:00:00 GMT

Growth and Properties of (001)-oriented Pb(Zr₀.₅₂Ti₀.₄₈)O₃/LaNiO₃ Films on Si(001) Substrates with TiN Buffer Layers Zhu, Tie-Jun; Lu, Li; Thompson, Carl V. Pulsed laser deposition has been used to grow Pb(Zr₀.₅₂Ti₀.₄₈)O₃ (PZT)/LaNiO₃ (LNO) heterostructures with restricted crystallographic orientations on bare Si(001) and SiO₂-coated Si(001) substrates, using TiN buffer layers. The effect of background gas pressure on orientation of the thin films was investigated in detail. XRD analyses showed that under optimized conditions, (001)-oriented PZT/LNO/TiN heterostructures could be grown on either Si(001) or SiO₂/Si substrates. The (001)-textured PZT films had remnant polarizations as high as 23µC/cm², and also had a low coercive field. Up to 10¹⁰ switching cycles have been achieved in these PZT films.

Gold Thermocompression Wafer Bonding

Thu, 01 Jan 2004 00:00:00 GMT

Gold Thermocompression Wafer Bonding Spearing, S. Mark; Tsau, Christine H.; Schmidt, Martin A. Thermocompression bonding of gold is a promising technique for the fabrication and packaging microelectronic and MEMS devices. The use of a gold interlayer and moderate temperatures and pressures results in a hermetic, electrically conductive bond. This paper documents work conducted to model the effect of patterning in causing pressure non-uniformities across the wafer and its effect on the subsequent fracture response. A finite element model was created that revealed pattern-dependent local pressure variations of more than a factor of three. This variation is consistent with experimental observations of bond quality across individual wafers A cohesive zone model was used to investigate the resulting effect of non-uniform bond quality on the fracture behavior. A good, qualitative agreement was obtained with experimental observations of the load-displacement response of bonds in fracture tests.

GaN Nanopore Arrays: Fabrication and Characterization

Thu, 01 Jan 2004 00:00:00 GMT

GaN Nanopore Arrays: Fabrication and Characterization Wang, Yadong; Peng, Chen; Sander, Melissa; Chua, Soo-Jin; Fonstad, Clifton G. Jr. GaN nanopore arrays with pore diameters of approximately 75 nm were fabricated by inductively coupled plasma etching (ICP) using anodic aluminum oxide (AAO) films as etch masks. Nanoporous AAO films were formed on the GaN surface by evaporating an Al film onto a GaN epilayer and subsequently anodizing the aluminum. To minimize plasma-induced damage, the template was exposed to CF4-based plasma conditions. Scanning electron microscopy (SEM) analysis shows that the diameter and the periodicity of the nanopores in the GaN were directly transferred from the original anodic alumina template. The pore diameter in the AAO film can be easily controlled by tuning the anodization conditions. Atomic force microscopy (AFM), photoluminescence (PL) and micro-Raman techniques were employed to assess the quality of the etched GaN nanopore surface. Such a cost-effective method to produce nano-patterned GaN template would be useful for growth and fabrication of III-Nitrides based nanostructures and photonic band gap materials.

Fatal Void Size Comparisons in Via-Below and Via-Above Cu Dual-Damascene Interconnects

Thu, 01 Jan 2004 00:00:00 GMT

Fatal Void Size Comparisons in Via-Below and Via-Above Cu Dual-Damascene Interconnects Choi, Z.-S.; Gan, C.L.; Wei, F.; Thompson, Carl V.; Lee, J.H.; Marieb, T.; Maiz, J.; Pey, Kin Leong; Choi, Wee Kiong The median-times-to-failure (t₅₀’s) for straight dual-damascene via-terminated copper interconnect structures, tested under the same conditions, depend on whether the vias connect down to underlaying leads (metal 2, M2, or via-below structures) or connect up to overlaying leads (metal 1, M1, or via-above structures). Experimental results for a variety of line lengths, widths, and numbers of vias show higher t₅₀’s for M2 structures than for analogous M1 structures. It has been shown that despite this asymmetry in lifetimes, the electromigration drift velocity is the same for these two types of structures, suggesting that fatal void volumes are different in these two cases. A numerical simulation tool based on the Korhonen model has been developed and used to simulate the conditions for void growth and correlate fatal void sizes with lifetimes. These simulations suggest that the average fatal void size for M2 structures is more than twice the size of that of M1 structures. This result supports an earlier suggestion that preferential nucleation at the Cu/Si₃N₄ interface in both M1 and M2 structures leads to different fatal void sizes, because larger voids are required to span the line thickness in M2 structures while smaller voids at the base of vias can cause failures in M1 structures. However, it is also found that the fatal void sizes corresponding to the shortest-times-to-failure (STTF’s) are similar for M1 and M2, suggesting that the voids that lead to the shortest lifetimes occur at or in the vias in both cases, where a void need only span the via to cause failure. Correlation of lifetimes and critical void volumes provides a useful tool for distinguishing failure mechanisms.

Effect of Pt on agglomeration and Ge out-diffusion in Ni(Pt) germanosilicide

Thu, 01 Jan 2004 00:00:00 GMT

Effect of Pt on agglomeration and Ge out-diffusion in Ni(Pt) germanosilicide Jin, Lijuan; Pey, Kin Leong; Choi, Wee Kiong; Fitzgerald, Eugene A.; Antoniadis, Dimitri A.; Chi, D.Z. The effect of Ni and Ni(Pt) alloy with ~5 and 10 at. % Pt on the agglomeration and Ge out-diffusion in Nickel germanosilicide formed on Si₀.₇₅Ge₀.₂₅(100) has been studied. A remarkable improvement in the agglomeration behavior with increasing Pt atomic percentage is observed by sheet resistance measurements and scanning electron microscopy (SEM). In addition, x-ray diffraction (XRD) shows that only NiSiGe or Ni(Pt)SiGe phase exists from 400 to 800°C. However, Ge out-diffusion from the monogermanosilicide grains is obvious at 600°C and 700°C for Ni/SiGe and Ni(Pt)(Pt at.%~10%)/SiGe, respectively, evident by XRD and micro-Raman spectroscopy. The improved melting temperature of Ni(Pt)SiGe solution compared to that of NiSiGe is the likely reason of seeing better surface morphology and suppressing Ge out-diffusion of the germanosilicide grains observed.

Effect of Microstructure Changes on Mechanical Properties of La₆₆Al₁₄(Cu, Ni)₂₀ Amorphous and Crystalline Alloys

Thu, 01 Jan 2004 00:00:00 GMT

Effect of Microstructure Changes on Mechanical Properties of La₆₆Al₁₄(Cu, Ni)₂₀ Amorphous and Crystalline Alloys Zhang, Yong; Lee, Irene Mei Ling; Tan, Hao; Jing, Qin; Li, Yi The microstructure, and phase selections of La₆₆Al₁₄(Cu, Ni)₂₀ alloy were studied by Bridgman solidifications, and composite materials of dendrites in amorphous matrix or micro- and nano- sized eutectic matrix were formed with different cooling rates. The volume fraction of the dendrite phase reaches a maximum at the cooling rate of about 15 K/s, the secondary dendrite arm spacing λ₂ decreases from 4.3 µm to 0.6 µm with the increasing of cooling rate R, and obeys the equation of λ₂R⁰.⁵⁷=1.74µm(K/s)R⁰.⁵⁷. The compression strength, as well as the elastic strain limit of the dendrite/amorphous matrix composite are 600 MPa, and 2.3%, respectively. Improved ductility was observed for the dendrite amorphous matrix composites with more dendrite phase by slow cooling rate.

Dependence of nanocrystal formation and charge storage/retention performance of a tri-layer memory structure on germanium concentration and tunnel oxide thickness

Thu, 01 Jan 2004 00:00:00 GMT

Dependence of nanocrystal formation and charge storage/retention performance of a tri-layer memory structure on germanium concentration and tunnel oxide thickness Teo, L.W.; Ho, Van Tai; Tay, M.S.; Choi, Wee Kiong; Chim, Wai Kin; Antoniadis, Dimitri A.; Fitzgerald, Eugene A. The effect of germanium (Ge) concentration and the rapid thermal oxide (RTO) layer thickness on the nanocrystal formation and charge storage/retention capability of a trilayer metal-insulator-semiconductor device was studied. We found that the RTO and the capping oxide layers were not totally effective in confining the Ge nanocrystals in the middle layer when a pure Ge middle layer was used for the formation of nanocrystals. From the transmission electron microscopy and secondary ion mass spectroscopy results, a significant diffusion of Ge atoms through the RTO and into the silicon (Si) substrate was observed when the RTO layer thickness was reduced to 2.5 nm. This resulted in no (or very few) nanocrystals formed in the system. For devices with a Ge+SiO₂ co-sputtered middle layer (i.e., lower Ge concentration), a higher charge storage capability was obtained than with devices with a thinner RTO layer, and the charge retention time was found to be less than in devices with a thicker RTO layer.

Charge storage in nanocrystal systems: Role of defects?

Thu, 01 Jan 2004 00:00:00 GMT

Charge storage in nanocrystal systems: Role of defects? Kan, Eric Win Hong; Choi, Wee Kiong; Chim, Wai Kin; Antoniadis, Dimitri A.; Fitzgerald, Eugene A. Wet thermal oxidations of polycrystalline Si₀.₅₄Ge₀.₄₆ films at 600°C for 30 and 50 min were carried out. A stable mixed oxide was obtained for films that were oxidized for 50 min. For film oxidized for 30 min, however, a mixed oxide with Ge nanocrystallites embedded in the oxide matrix was obtained. A trilayer gate stack structure that consisted of tunnel oxide/oxidized polycrystalline Si₀.₅₄Ge₀.₄₆/rf sputtered SiO₂ layers was fabricated. We found that with a 30 min oxidized middle layer, annealing the structure in N₂ ambient results in the formation of germanium nanocrystals and the annealed structure exhibits memory effect. For a trilayer structure with middle layer oxidized for 50 min, annealing in N₂ showed no nanocrystal formation and also no memory effect. Annealing the structures with 30 or 50 min oxidized middle layer in forming gas ambient resulted in nanocrystals embedded in the oxide matrix but no memory effect. This suggests that the charge storage mechanism for the trilayer structure is closely related to the interfacial traps of the nanocrystals.

Ballistic Transport in Nanostructures, and its Application to Functionalized Nanotubes

Thu, 01 Jan 2004 00:00:00 GMT

Ballistic Transport in Nanostructures, and its Application to Functionalized Nanotubes Marzari, Nicola We developed and implemented a first-principles based theory of the Landauer ballistic conductance, to determine the transport properties of nanostructures and molecular-electronics devices. Our approach starts from a quantum-mechanical description of the electronic structure of the system under consideration, performed at the density-functional theory level and using finite-temperature molecular dynamics simulations to obtain an ensemble of the most likely microscopic configurations. The extended Bloch states are then converted into maximally-localized Wannier functions to allow us to construct the Green's function of the conductor, from which we obtain the density of states (confirming the reliability of our microscopic calculations) and the Landauer conductance. A first application is presented to the case of pristine and functionalized carbon nanotubes.

Ballistic Transport in Carbon Nanotubes from First-Principles Molecular Dynamics Simulations

Thu, 01 Jan 2004 00:00:00 GMT

Ballistic Transport in Carbon Nanotubes from First-Principles Molecular Dynamics Simulations Lee, Young-Su; Nardelli, Marco Buongiorno; Marzari, Nicola We determined the Landauer ballistic conductance of pristine nanotubes at finite temperature via a novel scheme that combines ab-initio molecular dynamics, maximally-localized Wannier functions, and a tight-binding formulation of electronic transport in nanostructures. Large-scale ab-initio molecular dynamics simulations are used to obtain efficiently accurate trajectories in phase space. The extended Bloch orbitals for states along these trajectories are converted into maximally-localized orbitals, providing an exact mapping of the ground-state electronic structure onto a short-ranged Hamiltonian. Green's functions, self-energies, and ballistic conductance can then be obtained for any given configuration, and averaged over the appropriate statistical ensemble.

Wafer-Level Thermocompression Bonds

Wed, 01 Jan 2003 00:00:00 GMT

Wafer-Level Thermocompression Bonds Tsau, Christine H.; Schmidt, Martin A.; Spearing, S. Mark Thermocompression bonding of gold is a promising technique for achieving low temperature, wafer-level bonding without the application of an electric field or complicated pre-bond cleaning procedure. The presence of a ductile layer influences the fracture behavior of the bonds. The fabrication process was described. In addition, the effect of plasticity was explored by varying the gold bonding thickness between 0.23 to 1.4 µm. Wafers were bonded at 300°C and two different pressures: 1.25 and 7 MPa. The bond toughness of the specimens were characterized using a four-point bend delamination technique. Cohesive failure was found to be the dominant fracture mode in the thicker films. Bonds made with thin gold films failed adhesively and at lower strain energy release rates.

TiNi shape memory alloy thin films for microactuator application

Wed, 01 Jan 2003 00:00:00 GMT

TiNi shape memory alloy thin films for microactuator application Fu, Yongqing; Du, Hejun TiNi films were prepared by co-sputtering TiNi target and a separate Ti target. Crystalline structure and phase transformation behaviors of TiNi films were investigated. Results showed that TiNi films had fine grain size of about 500 nm and fully martensitic structure at room temperature. X-ray photoelectron spectroscopy (XPS) results indicated that there is adherent and natural TiO₂ film, which is beneficial to its corrosion resistance and biocompatibillity. Results from differential scanning calorimeter (DSC), in-situ X-ray diffraction (XRD) and curvature measurement revealed clearly martensitic transformation upon heating and cooling. The TiNi films were further deposited on micromachined silicon cantilever and membrane structures in order to form micro-gripper or microvalve with large deformation due to shape-memory effect.

Simplified Model and Numerical Analysis of Multi-layered Piezoelectric Diaphragm

Wed, 01 Jan 2003 00:00:00 GMT

Simplified Model and Numerical Analysis of Multi-layered Piezoelectric Diaphragm Yao, Lin-Quan; Lu, Li The validity of the dynamic analysis based on simplified plate model was investigated using of FE-codes ANSYS in the present paper. The simplified clamped multi-layered plate model was first verified by comparison with the exact model. The simply supported plate model was confirmed to be not a suitable model due to its large error as comparing with exact model. Influence of dimensions of laminar diaphragm on nature frequencies was studied. Deflection and voltage response driven by mechanical and electric loads were described. The optimized thickness ratio of PZT layer to SiO₂ and Si layers was given in the paper to obtain the best deflection export of actuator in design.

Reliability of Multi-Terminal Copper Dual-Damascene Interconnect Trees

Wed, 01 Jan 2003 00:00:00 GMT

Reliability of Multi-Terminal Copper Dual-Damascene Interconnect Trees Gan, C.L.; Thompson, Carl V.; Pey, Kin Leong; Choi, Wee Kiong Electromigration tests on different Cu dual-damascene interconnect tree structures consisting of various numbers of straight via-to-via lines connected at the common middle terminal have been carried out. Like Al-based interconnects, the reliability of a segment in a Cu-based interconnect tree strongly depends on the stress conditions of connected segments. The analytic model based on a nodal analysis developed for Al trees gives a conservative estimate of the lifetime of Cu-based interconnect trees. However, there are important differences in the results obtained under similar test conditions for Al-based and Cu-based interconnect trees. These differences are attributed to the variations in the architectural schemes of the two metallization systems. The absence of a conducting electromigration-resistant overlayer in Cu technology and the low critical stress for void nucleation at the Cu/inter-level diffusion barrier (i.e. Si₃N₄) interface leads to different failure modes between Cu and Al interconnects. As a result, the most highly stressed segment in a Cu-based interconnect tree is not always the least reliable. Moreover, the possibility of liner rupture at stressed dual-damascene vias leads to significant differences in tree reliabilities in Cu compared to Al. While an interconnect tree can be treated as a fundamental unit whose reliability is independent of that of other units in Al-based interconnect architectures, interconnect trees can not be treated as fundamental units for circuit-level reliability analyses for Cu-based interconnects.

Progress in Developing and Extending RM³ Heterogeneous Integration Technologies

Wed, 01 Jan 2003 00:00:00 GMT

Progress in Developing and Extending RM³ Heterogeneous Integration Technologies Fonstad, Clifton G. Jr.; Atmaca, Eralp; Giziewicz, Wojciech; Perkins, James; Rumpler, Joseph This paper describes recent progress in a continuing program to develop and apply RM³ (recess mounting with monolithic metallization) technologies for heterogeneous integration. Particular emphasis is placed on the APB (aligned pillar bonding) and MASA (magnetically assisted statistical assembly) technologies. Next, ongoing research on applications of RM3 integration to produce optoelectronic integrated circuits (OEICs) for optical clock distribution, diffuse optical tomography, and smart pixel arrays are described. Finally, potential new applications of these technologies in intra- and interchip optical signal interconnects, in fluorescent dye detection and imaging for biomedical applications, and in III-V mini-IC integration on Si-CMOS for enhancing off-chip drive capabilities are outlined.

Orientation of MgO thin films on Si(001) prepared by pulsed laser deposition

Wed, 01 Jan 2003 00:00:00 GMT

Orientation of MgO thin films on Si(001) prepared by pulsed laser deposition Zhu, Tie-Jun; Lu, Li Pulsed laser deposition method was employed to grow MgO thin films with preferred orientation on bare Si(100) and SiO₂/Si(100) substrates. The orientation of MgO thin films was systematically investigated by varying deposition parameters. XRD analysis showed that the preferred orientation of MgO thin films would change from (111) to (100) when laser fluence decreased and oxygen pressure increased to certain extend. But it was difficult to fabricate completely (100)-oriented MgO films. Substrate temperature seemed to have little influence on the orientation of MgO thin films at high laser fluence. SEM images of the MgO thin films on Si(100) deposited at 400°C and the laser fluence of 5J/cm² in the oxygen ambient of 200mTorr demonstrated that there was no presence of interfacial reactions or cracks and the film surface was very smooth. Such film is suitable as buffer layers for the growth of high-quality ferroelectric and superconducting overlayers.

Observation of Joule Heating-Assisted Electromigration Failure Mechanisms for Dual Damascene Cu/SiO₂ Interconnects

Wed, 01 Jan 2003 00:00:00 GMT

Observation of Joule Heating-Assisted Electromigration Failure Mechanisms for Dual Damascene Cu/SiO₂ Interconnects Chang, Choon Wai; Gan, C.L.; Thompson, Carl V.; Pey, Kin Leong; Choi, Wee Kiong Failure mechanisms observed in electromigration (EM) stressed dual damascene Cu/SiO₂ interconnects trees were studied and simulated. Failure sites with â€˜melt patch’ or â€˜crater’ are common for test structures in the top metal layer, though the occurrence of such failure modes probably depends on the passivation layer thickness. Interconnects that were EM stressed for a short time and then stressed with increasing current to induce Joule heating in the line had similar failure sites to lines that were stressed to failure under standard EM conditions. This shows that some failure mechanisms during EM could be assisted by Joule heating effect.

MOSFET Channel Engineering using Strained Si, SiGe, and Ge Channels

Wed, 01 Jan 2003 00:00:00 GMT

MOSFET Channel Engineering using Strained Si, SiGe, and Ge Channels Fitzgerald, Eugene A.; Lee, Minjoo L.; Leitz, Christopher W.; Antoniadis, Dimitri A. Biaxial tensile strained Si grown on SiGe virtual substrates will be incorporated into future generations of CMOS technology due to the lack of performance increase with scaling. Compressively strained Ge-rich alloys with high hole mobilities can also be grown on relaxed SiGe. We review progress in strained Si and dual channel heterostructures, and also introduce high hole mobility digital alloy heterostructures. By optimizing growth conditions and understanding the physics of hole and electron transport in these devices, we have fabricated nearly symmetric mobility p- and n-MOSFETs on a common Si₀.₅Ge₀.₅ virtual substrate.

Investigation on Aluminum-Based Amorphous Metallic Glass as New Anode Material in Lithium Ion Batteries

Wed, 01 Jan 2003 00:00:00 GMT

Investigation on Aluminum-Based Amorphous Metallic Glass as New Anode Material in Lithium Ion Batteries Meng, Shirley Y.; Li, Yi; Ceder, Gerbrand Aluminum based amorphous metallic glass powders were produced and tested as the anode materials for the lithium ion rechargeable batteries. Ground Al₈₀Ni₁₀La₁₀ was found to have a low first cycle capacity of about 100 Ah/Kg. The considerable amount of intermetallic formed in the amorphous glass makes the aluminum inactive towards the lithium. The ball milled Al₈₈Ni₉Y₃ powders contain pure aluminum crystalline particles in the amorphous matrix and have first cycle capacity of about 500 Ah/Kg. Nevertheless, polarization was caused by oxidation introduced by the ball-milling process. The electrochemical performances of these amorphous metallic glasses need to be further investigated. Their full lithium insertion capacities cannot be confirmed until the compositions and particle size inside the metallic glass anodes, the conformation of the electrodes and the mechanical milling processes are optimized.

The interfacial reaction of Ni on (100) Si₁â‚‹xGex (x=0, 0.25) and (111) Ge

Wed, 01 Jan 2003 00:00:00 GMT

The interfacial reaction of Ni on (100) Si₁â‚‹xGex (x=0, 0.25) and (111) Ge Jin, Lijuan; Pey, Kin Leong; Choi, Wee Kiong; Fitzgerald, Eugene A.; Antoniadis, Dimitri A.; Pitera, Arthur J.; Lee, Minjoo L.; Chi, D.Z. The interfacial reaction of Ni with Si, Si₀.₇₅Ge₀.₂₅, and Ge at 400°C has been investigated. A uniform epitaxial NiSi film was obtained at 400°C for Ni-Silicidation on Si using rapid thermal annealing method. Similarly, uniform film of NiGe was formed at 400°C for Ni reaction with Ge. Whereas using in situ annealing at 400°C, Ni₃Ge₂ and NiGe were observed. For the interfacial reaction of Ni with relaxed Si₀.₇₅Ge₀.₂₅ films rapid thermal annealed at 400°C, a mixed layer consisting of Ni₃(Si₁â‚‹xGex)₂, Ni(Si₁â‚‹yGey), and Si₁â‚‹zGez (z>y>x) was formed; whereas only Ni₃(Si₁â‚‹xGex)₂ and Ni(Si₁â‚‹yGey>) were observed by in situ annealing.

Graded InGaN Buffers for Strain Relaxation in GaN/InGaN Epilayers Grown on sapphire

Wed, 01 Jan 2003 00:00:00 GMT

Graded InGaN Buffers for Strain Relaxation in GaN/InGaN Epilayers Grown on sapphire Chua, Soo-Jin; Fitzgerald, Eugene A.; Song, T.L. Graded InGaN buffers were employed to relax the strain arising from the lattice and thermal mismatch in GaN/InGaN epilayers grown on sapphire. An enhanced strain relaxation was observed in GaN grown on a stack of five InGaN layers, each 200 nm thick with the In content increased in each layer, and with an intermediate thin GaN layer, 10 nm thick inserted between the InGaN layers, as compared to the conventional two-step growth of GaN epilayer on sapphire. The function of the intermediate layer is to progressively relax the strain and to annihilate the dislocations that build up in the InGaN layer. If the InGaN layers were graded too rapidly, more dislocations will be generated. This increases the probability of the dislocations getting entangled and thereby impeding the motion of the dislocations to relax the strain in the InGaN layer. The optimum growth conditions of the intermediate layer play a major role in promoting the suppression and filling of the V-pits in the GaN cap layer, and were empirically found to be a thin 10 nm GaN grown at 750 0°C and annealed at 1000 0°C.

Formation of Nanocrystalline Germanium via Oxidation of Si₀.₅₄Ge₀.₄₆ for Memory Device Applications

Wed, 01 Jan 2003 00:00:00 GMT

Formation of Nanocrystalline Germanium via Oxidation of Si₀.₅₄Ge₀.₄₆ for Memory Device Applications Kan, Eric Win Hong; Leoy, C.C.; Choi, Wee Kiong; Chim, Wai Kin; Antoniadis, Dimitri A.; Fitzgerald, Eugene A. In this work, we studied the possibility of synthesizing nanocrystalline germanium (Ge) via dry and wet oxidation of both amorphous and polycrystalline Si₀.₅₄Ge₀.₄₆ films. In dry oxidation, Ge was rejected from the growing SiO₂ forming a Ge-rich polycrystalline layer. As for wet oxidation, Ge was incorporated into the oxide, forming a layer of mixed oxide, SixGe₁â‚‹xOy. Formation of nanocrystalline Ge was observed when the layer of SixGe₁â‚‹xOy was annealed in a N₂ ambient. We have fabricated a metal-insulator-semiconductor structure with nanocrystalline Ge embedded within the insulator layer to study its feasibility as a memory device.

Bulk Glass Formation in Eutectic of La-Cu-Ni-Al Metallic Alloys

Wed, 01 Jan 2003 00:00:00 GMT

Bulk Glass Formation in Eutectic of La-Cu-Ni-Al Metallic Alloys Zhang, Yong; Tan, Hao; Li, Yi A eutectic in La-rich La-Cu₀.₅Ni₀.₅-Al alloys was determined by studying the melting behaviors and the microstructure observations. The microstructures of the La-Cu-Ni-Al alloys prepared by Bridgman Solidification and copper mould casting were studied by using scanning electron microscope (SEM). The results show that La₆₆[Cu₀.₅Ni₀.₅]₂₀Al₁₄ alloy is very near to a pseudo-ternary eutectic. When the cooling rate is higher than 450 K/s, fully amorphous can be formed; when the cooling rate is within 15 K/s to 450 K/s, the alloy has a microstructure of dendrite plus amorphous, when the cooling rate is within 12 K/s to 1.5 K/s, the microstructures of the alloy are dendrite plus eutectic, and when the cooling rate is lower than 0.12 K/s, the morphology of the alloy is eutectic microstructure. The off eutectic alloy has better glass forming ability, the best glass forming alloy obtained at La₆₂[Cu₀.₅Ni₀.₅>]₂₄Al₁₄ along the composition line of La₈₆₋x[Cu₀.₅Ni₀.₅]xAl₁₄. It has a potential to form bulk metallic glassy rod samples with diameter larger than 12 mm.

Novel CMOS-Compatible Optical Platform

Wed, 01 Jan 2003 00:00:00 GMT

Novel CMOS-Compatible Optical Platform Pitera, Arthur J.; Groenert, M. E.; Yang, V. K.; Lee, Minjoo L.; Leitz, Christopher W.; Taraschi, G.; Cheng, Zhiyuan; Fitzgerald, Eugene A. A research synopsis is presented summarizing work with integration of Ge and III-V semiconductors and optical devices with Si. III-V GaAs/AlGaAs quantum well lasers and GaAs/AlGaAs optical circuit structures have been fabricated on Si using Ge/GeSi/Si virtual substrates. The lasers fabricated on bulk GaAs showed similar output characteristics as those on Si. The GaAs/AlGaAs lasers fabricated on Si emitted at 858nm and had room temperature cw lifetimes of ~4hours. Straight optical links integrating an LED emitter, waveguide and detector exhibited losses of approximately 144dB/cm. A process for fabrication of a novel CMOS-compatible platform that integrates III-V or Ge layers with Si is demonstrated. Thin Ge layers have been transferred from Ge/GeSi/Si virtual substrates to bulk Si utilizing wafer bonding and an epitaxial Si CMP layer to facilitate virtual substrate planarization. A unique CMP-less method for removal of Ge exfoliation damage induced by the SmartCutâ„¢ process is also presented.

Evolution of AlN buffer layers on Silicon and the effect on the property of the expitaxial GaN film

Wed, 01 Jan 2003 00:00:00 GMT

Evolution of AlN buffer layers on Silicon and the effect on the property of the expitaxial GaN film Zang, Keyan; Wang, Lianshan; Chua, Soo-Jin; Thompson, Carl V. The morphology evolution of high-temperature grown AlN nucleation layers on (111) silicon has been studied using atomic force microscopy (AFM). The structure and morphology of subsequently grown GaN film were characterized by optical microscopy, scanning electron microscopy, x-ray diffraction, and photoluminescence measurement. It was found that a thicker AlN buffer layer resulted in a higher crystalline quality of subsequently grown GaN films. The GaN with a thicker buffer layer has a narrower PL peak. Cracks were found in the GaN film which might be due to the formation of amorphous SiNx at the AlN and Si interface.

Charge Storage Mechanism and Size Control of Germanium Nanocrystals in a Tri-layer Insulator Structure of a MIS Memory Device

Wed, 01 Jan 2003 00:00:00 GMT

Charge Storage Mechanism and Size Control of Germanium Nanocrystals in a Tri-layer Insulator Structure of a MIS Memory Device Teo, L.W.; Ho, Van Tai; Tay, M.S.; Lei, Y.; Choi, Wee Kiong; Chim, Wai Kin; Antoniadis, Dimitri A.; Fitzgerald, Eugene A. A method of synthesizing and controlling the size of germanium nanocrystals is developed. A tri-layer metal-insulator-semiconductor (MIS) memory device structure comprising of a thin (~5nm) silicon dioxide (SiO₂) layer grown using rapid thermal oxidation (RTO), followed by a layer of Ge+SiO₂ of varying thickness (3 - 6 nm) deposited using a radio frequency (rf) co-sputtering technique, and a capping SiO₂ layer (50nm) deposited using rf sputtering is investigated. It was verified that the size of germanium (Ge) nanocrystals in the vertical z-direction in the trilayer memory device was controlled by varying the thickness of the middle (cosputtered Ge+SiO₂) layer. From analyses using transmission electron microscopy and capacitance-voltage measurements, we deduced that both electrons and holes are most likely stored within the nanocrystals in the middle layer of the trilayer structure rather than at the interfaces of the nanocrystals with the oxide matrix.

Solid State Thin Film Lithium Microbatteries

Wed, 01 Jan 2003 00:00:00 GMT

Solid State Thin Film Lithium Microbatteries Shi, Z.; Lü, L.; Ceder, Gerbrand Solid state thin film lithium microbatteries fabricated by pulsed-laser deposition (PLD) are suggested. During deposition the following process parameters must be considered, which are laser energy and fluence, laser pulse duration, laser pulse frequency, target composition, background gasses, substrate temperature, target-substrate distance and orientation. The effects of the variations of the process parameters can be obtained by measuring stoichiometry, thickness, phases and structure (grain size and texture), and stress of the deposited films. Electrochemical measurements will be conducted to test the microbattery properties through open-circuit voltage, charge-discharge cycling, cyclic voltammetry, and impedance analysis.

SiGe-On-Insulator (SGOI): Two Structures for CMOS Application

Wed, 01 Jan 2003 00:00:00 GMT

SiGe-On-Insulator (SGOI): Two Structures for CMOS Application Cheng, Zhiyuan; Jung, Jongwan; Lee, Minjoo L.; Nayfeh, Hasan; Pitera, Arthur J.; Hoyt, Judy L.; Fitzgerald, Eugene A.; Antoniadis, Dimitri A. Two SiGe-on-insulator (SGOI) structures for CMOS application are presented: surface-channel strained-Si on SGOI (SSOI) and dual-channel SGOI structures. Comparisons between two structures are made from both device performance and CMOS process point of view. We have demonstrated both structures on SGOI, and have fabricated n-MOSFET’s and p-MOSFET’s on those two structures respectively. Device characteristics are presented. The devices show enhancement on both electron and hole mobilities.

Research on Polycrystalline Films for Micro- and Nano-Systems

Wed, 01 Jan 2003 00:00:00 GMT

Research on Polycrystalline Films for Micro- and Nano-Systems Thompson, Carl V. Polycrystalline films are used in a wide array of micro- and nano-scale devices, for electronic, mechanical, magnetic, photonic and chemical functions. Increasingly, the properties, performance, and reliability of films in these systems depend on nano-scale structure. In collaborative research with a number of SMA Fellows, Associates, and students, our group is carrying out research focused on probing, modeling and controlling nano-scale structural evolution during both vapor-phase and solid-phase polycrystalline film formation. In particular, high-sensitivity in-situ and real-time stress measurements are being used to study atomic scale forces and to characterize structure formation and evolution at the nano-scale. In other collaborative research, the affects of controlled structure and multi-film architectures on properties, such as piezoelectric characteristics and electromigration-limited reliability, are being explored. Through these interrelated activities, basic principles of the science and engineering of nano-scale materials are emerging.

Research Summary: Object Oriented Finite Element Analysis for Materials Science*: A Tool for Viscoelastic Polymer Composite Deformation Analysis

Wed, 01 Jan 2003 00:00:00 GMT

Research Summary: Object Oriented Finite Element Analysis for Materials Science*: A Tool for Viscoelastic Polymer Composite Deformation Analysis Raghavan, Rajesh; Carter, W. Craig A public domain code "Object Oriented Finite element analysis for materials science" (OOF) has been extended to include tools for analysis of viscoelastic materials. Utility of these tools has been discussed along with possible applications in this publication. Added features in OOF include means to quantitatively analyze the spatiotemporal response of a composite polymeric material in dynamic as well as in static deformation conditions. These coupled with the existing features of OOF, in particular, the complete analysis of mechanical characteristics of materials provide a comprehensive tool for the studies of time dependent behavior of variety of materials including polymeric solid composites, polymer nanocomposites, polymer blends, block copolymers, and so on. The viscoelastic module draws its strength from the underlying OOF architecture to provide a macroscopic evaluation of mechanical properties using microstructural details. An application of this module for deformation analysis is the characterization of mechanical behavior a polymer nanocomposites. The deformation behaviour of polymer composite depends on the combined characteristic relaxation times of its constituents as well as its microstructural details. Results of analysis are expected to provide better insight into the role of microstructure as well as the role of interphase on the average mechanical

Metallic Cluster Coalescence: Molecular Dynamics Simulations of Boundary Formation

Wed, 01 Jan 2003 00:00:00 GMT

Metallic Cluster Coalescence: Molecular Dynamics Simulations of Boundary Formation Takahashi, A. R.; Thompson, Carl V.; Carter, W. Craig During the evaporative deposition of polycrystalline thin films, the development of a tensile stress at small film thicknesses is associated with island coalescence. Several continuum models exist to describe the magnitude of this tensile stress but the coalescence stress becomes significant at small enough thicknesses to draw the continuum models into question. For nanometer-sized islands, we perform atomistic simulations of island coalescence to determine if the atomistic methods and continuum models are mutually consistent. The additional detail provided by the atomistic simulations allows for study of the kinetics of island coalescence and the treatment of different crystallographic orientations. We find that the atomistic simulations are consistent with the continuum models. We also note that the atomistic simulations predict extremely fast coalescence times and include the possibility of island rotations during coalescence.

MEMS Materials and Processes: a research overview

Wed, 01 Jan 2003 00:00:00 GMT

MEMS Materials and Processes: a research overview Spearing, S. Mark An overview is provided of materials and processes research currently being conducted in support of MEMS device design at MIT. Underpinning research is being conducted in five areas: room temperature strength characterization, elevated temperature strength characterization, processing of Si/SiC hybrid structures, modeling of wafer bonding processes and development of high temperature fluid interconnections. Emphasis is placed on the key areas of materials science and engineering.

Mechanical properties of La-based bulk amorphous alloy and composites

Wed, 01 Jan 2003 00:00:00 GMT

Mechanical properties of La-based bulk amorphous alloy and composites Lee, Irene Mei Ling; Li, Yi; Carter, W. Craig Influence of different microstructure of La-based fully amorphous samples and its composites on the impact fracture energy were investigated and discussed. Results showed improvement in fracture energy of glassy metals with the presence intermetallic phases, but deteriorated in the presence of dendrite phases and high volume % of crystalline phases.

Laser Fabrication by Using Photonic Crystal

Wed, 01 Jan 2003 00:00:00 GMT

Laser Fabrication by Using Photonic Crystal Vajpeyi, Agam P.; Chua, Soo-Jin; Fitzgerald, Eugene A. This paper involves the calculation for composition of different layer used in laser structure and the simulation of cavity, formed by creating air columns in the InGaAsP medium, for square lattice. The aim of this project is to fabricate approximately zero threshold current lasers. This project involves FDTD simulation for optimizing dimension of the device, fabrication of laser structure and finally characterization of the device structure.

GaN Based Nanomaterials Fabrication with Anodic Aluminium Oxide by MOCVD

Wed, 01 Jan 2003 00:00:00 GMT

GaN Based Nanomaterials Fabrication with Anodic Aluminium Oxide by MOCVD Wang, Yadong; Sander, Melissa; Peng, Chen; Chua, Soo-Jin; Fonstad, Clifton G. Jr. A highly self-ordered hexagonal array of cylindrical pores has been fabricated by anodizing a thin film of Al on substrate and subsequent growth of GaN and InGaN in these nanoholes has been performed. This AAO template-based synthesis method provides a low cost process to fabricate GaN-based nanomaterials fabrication.

First Principles Modeling for Research and Design of New Materials

Wed, 01 Jan 2003 00:00:00 GMT

First Principles Modeling for Research and Design of New Materials Ceder, Gerbrand First principles computation can be used to investigate an design materials in ways that can not be achieved with experimental means. We show how computations can be used to rapidly capture the essential physics that determines the useful properties in different applications. Some applications for predicting crystal structure, thermodynamic and kinetic properties, and phase stability are discussed. This first principles tool set will be demonstrated with applications from rechargeable batteries and hydrogen storage materials.

Fabrication of Highly Ordered Nanoparticle Arrays Using Thin Porous Alumina Masks

Wed, 01 Jan 2003 00:00:00 GMT

Fabrication of Highly Ordered Nanoparticle Arrays Using Thin Porous Alumina Masks Lei, Y.; Teo, L.W.; Yeong, K.S.; See, Y.H.; Chim, Wai Kin; Choi, Wee Kiong; Thong, J.T.L. Highly ordered nanoparticle arrays have been successfully fabricated by our group recently using ultra-thin porous alumina membranes as masks in the evaporation process. The sizes of the nanoparticles can be adjusted from 5-10 nm to 200 nm while the spacing between adjacent particles can also be adjusted from several nanometers to about twice the size of a nanoparticle. The configuration of the nanoparticles can be adjusted by changing the height of the alumina masks and the evaporation direction. Due to the high pore regularity and good controllability of the particle size and spacing, this method is useful for the ordered growth of nanocrystals. Different kinds of nanoparticle arrays have been prepared on silicon wafer including semiconductors (e.g., germanium) and metals (e.g., nickel). The germanium nanoparticle arrays have potential applications in memory devices while the nickel catalyst nanoparticle arrays can be used for the growth of ordered carbon nanotubes.

Effect of Wafer Bow and Etch Patterns in Direct Wafer Bonding

Wed, 01 Jan 2003 00:00:00 GMT

Effect of Wafer Bow and Etch Patterns in Direct Wafer Bonding Spearing, S. Mark; Turner, K.T. Direct wafer bonding has been identified as an en-abling technology for microelectromechanical systems (MEMS). As the complexity of devices increase and the bonding of multiple patterned wafers is required, there is a need to understand the factors that lead to bonding failure. Bonding relies on short-ranged surface forces, thus flatness deviations of the wafers may prevent bonding. Bonding success is determined by whether or not the surface forces are sufficient to overcome the flatness deviations and deform the wafers to a common shape. A general bonding criterion based on this fact is developed by comparing the strain energy required to deform the wafers to the surface energy that is dissipated as the bond is formed. The bonding criterion is used to examine the case of bonding bowed wafers with etch patterns on the bonding surface. An analytical expression for the bonding criterion is developed using plate theory for the case of bowed wafers. Then, the criterion is implemented using finite element analysis, to demonstrate its use and to validate the analytical model. The results indicate that wafer thickness and curvature are important in determining bonding success and that the bonding criterion is independent of wafer diameter. Results also demonstrate that shallow etched patterns can make bonding more difficult while deep features, which penetrate through an appreciable thickness of the wafer, may facilitate bonding. Design implications of the model results are discussed in detail. Preliminary results from experiments designed to validate the model, agree with the trends seen in the model, but further work is required to achieve quantitative correlation.

A continuum theory of amorphous solids undergoing large deformations, with application to polymeric glasses

Wed, 01 Jan 2003 00:00:00 GMT

A continuum theory of amorphous solids undergoing large deformations, with application to polymeric glasses Anand, Lallit This paper summarizes a recently developed continuum theory for the elastic-viscoplastic deformation of amorphous solids such as polymeric and metallic glasses. Introducing an internal-state variable that represents the local free-volume associated with certain metastable states, we are able to capture the highly non-linear stress-strain behavior that precedes the yield-peak and gives rise to post-yield strain-softening. Our theory explicitly accounts for the dependence of the Helmholtz free energy on the plastic deformation in a thermodynamically consistent manner. This dependence leads directly to a backstress in the underlying flow rule, and allows us to model the rapid strain-hardening response after the initial yield-drop in monotonic deformations, as well as the Bauschinger-type reverse-yielding phenomena typically observed in amorphous polymeric solids upon unloading after large plastic deformations. We have implemented a special set of constitutive equations resulting from the general theory in a finite-element computer program. Using this finite-element program, we apply the specialized equations to model the large-deformation response of the amorphous polymeric solid polycarbonate, at ambient temperature and pressure. We show numerical results to some representative problems, and compare them against corresponding results from physical experiments.

Computation and Simulation of the Effect of Microstructures on Material Properties

Wed, 01 Jan 2003 00:00:00 GMT

Computation and Simulation of the Effect of Microstructures on Material Properties Carter, W. Craig Many material properties depend on specific details of microstructure and both optimal material performance and material reliability often correlate directly to microstructure. In nano- and micro-systems, the material's microstructure has a characteristic length scale that approaches that of the device in which it is used. Fundamental understanding and prediction of material behavior in nano- and micro-systems depend critically on methods for computing the effect of microstructure. Methods for including the physics and spatial attributes of microstructures are presented for a number of materials applications in devices. The research in our group includes applications of computation of macroscopic response of material microstructures, the development of methods for calculating microstructural evolution, and the morphological stability of structures. In this review, research highlights are presented for particular methods for computing the response in: 1) rechargeable lithium ion battery microstructures, 2) photonic composites with anisotropic particulate morphologies, 3) crack deflection in partially devitrified metallic glasses.

Characterization and Modeling of Stress Evolution During Nickel Silicides Formation

Wed, 01 Jan 2003 00:00:00 GMT

Characterization and Modeling of Stress Evolution During Nickel Silicides Formation Liew, K.P.; Li, Yi; Yeadon, Mark; Bernstein, R.; Thompson, Carl V. An curvature measurement technique was used to characterize the stress evolution during reaction of a Ni film and a silicon substrate to form nickel silicide. Stress changes were measured at each stage of the silicide growth. When the nickel films were subjected to long-time isothermal annealing, stresses that developed during silicide formation gradually relaxed. Fitting the experimental results with a kinetic model provides insight into the volumetric strain and relaxation behavior of the reacting film and the reaction product.

Ballistic Transport in Nanostructures from First-Principles Simulations

Wed, 01 Jan 2003 00:00:00 GMT

Ballistic Transport in Nanostructures from First-Principles Simulations Marzari, Nicola We developed and implemented a first-principles based theory of the Landauer ballistic conductance, to determine the transport properties of nanostructures and molecular-electronics devices. Our approach starts from a quantum-mechanical description of the electronic structure of the system under consideration, performed at the density-functional theory level and using finite-temperature molecular dynamics simulations to obtain an ensemble of the most likely microscopic configurations. The extended Bloch states are then converted into maximally-localized Wannier functions to allow us to construct the Green’s function of the conductor, from which we obtain the density of states (confirming the reliability of our microscopic calculations) and the Landauer conductance. A first application is presented to the case of carbon nanotubes.

Advanced Materials for Micro- and Nano-Systems (AMMNS)

ZnO Nanorods Grown on p-GaN Using Hydrothermal Synthesis and Its Optoelectronic Devices Application

Workfunction Tuning of n-Channel MOSFETs Using Interfacial Yttrium Layer in Fully Silicided Nickel Gate

Study of Stress Evolution of Germanium Nanocrystals Embedded in Silicon Oxide Matrix

Ordering Control of Self-Assembled Colloidal Crystals

High Temperature Deformation Behavior of Bulk Metallic Glass and Its Composites

First-Principles Study of Point Defects in LaAlO₃

Fabrication and Characterization of Nano-porous GaN Template for Strain Relaxed GaN Growth

Electrochemical Behavior and Li Diffusion Study of LiCoO₂ Thin Film Electrodes Prepared by PLD

High Temperature Deformation Behavior of in-situ Bulk Metallic Glass Matrix Composites

Effect of Oxygen on Ni-Silicided FUSI Metal Gate

TEM Study on the Evolution of Ge Nanocrystals in Si Oxide Matrix as a Function of Ge Concentration and the Si Reduction Process

Native Point Defects in yttria as a High-Dielectric-Constant Gate Oxide Material: A First-Principles Study

Monitoring Defect Formation in Colloidal Self Assembly using Photonic Bandgap Variations

Fabrication of Two-Dimensional Photonic Crystals in AlGaInP/GaInP Membranes by Inductively Coupled Plasma Etching

Fabrication and I-V Characterization of ZnO Nanorod Based Metal-Insulator-Semiconductor Junction

Enhancement in Indium Incorporation for InGaN Grown on InN Intermediate Layer

Effects of Applied Loads, Effective Contact Area and Surface Roughness on the Dicing Yield of 3D Cu Bonded Interconnects

Characterization of LiNi₀.₅Mn₁.₅O₄ Thin Film Cathode Prepared by Pulsed Laser Deposition

Amorphous Al-transition Metal Alloys as Anode Material for Lithium Ion Battery

The Influence of Adjacent Segment on the Reliability of Cu Dual Damascene Interconnects

Two-dimensional Photonic Crystals Fabricated by Nanoimprint Lithography

Strained Silicon on Silicon by Wafer Bonding and Layer Transfer from Relaxed SiGe Buffer

Preliminary Characterisation of Low-Temperature Bonded Copper Interconnects for 3-D Integrated Circuits

Poly-Si₁â‚‹xGex Film Growth for Ni Germanosilicided Metal Gate

Oblique Angle Deposition of Germanium Film on Silicon Substrate

Nanocrystalline Ge Flash Memories: Electrical Characterization and Trap Engineering

High Optical Quality Nanoporous GaN Prepared by Photoelectrochemical Etching

High Indium Concentration InGaN/GaN Grown on Sapphire Substrate by MOCVD

High Density Single Crystalline GaN Nanodot Arrays Fabricated Using Template-Assisted Selective Growth

Growth of ZnO Nanorods on GaN Using Aqueous Solution Method

Growth and Characterization of LiCoO₂ Thin Films for Microbatteries

Effects of Platinum on NiPtSiGe/n-SiGe and NiPtSi/n-Si Schottky Contacts

The Effect of Periodic Silane Burst on the Properties of GaN on Si (111) Substrates

Defects in Self Assembled Colloidal Crystals

Characterization of ZnO Nanorods Grown on GaN Using Aqueous Solution Method

Carbon Nanotube Growth Using Ni Catalyst in Different Layouts

Vibrational thermodynamics: coupling of chemical order and size effects

Synthesis of Germanium Nanocrystals and its Possible Application in Memory Devices

Studies on Nano-Indentation of Polymeric Thin Films Using Finite Element Methods

Strained Ge channel p-type metal-oxide-semiconductor field-effect transistors grown on Siâ‚â‚‹xGex/Si virtual substrates

Solid-shell element model of assumed through-thickness electric distribution for laminate composite piezoelectric structures

Si Industry at a Crossroads: New Materials or New Factories?

SiGe-On-Insulator (SGOI) Technology and MOSFET Fabrication

SiGeC Near Infrared Photodetectors

Processing, Structure, Properties, and Reliability of Metals for Microsystems

Process development of silicon-silicon carbide hybrid structures for micro-engines (January 2002)

A Novel Testing Apparatus for Tribological Studies at the Small Scale

Methods for Calculating the Optical Band Structure of Photonic Composites

Metastable Intermediate in LixMnO₂ Layered to Spinel Phase Transition

Mechanical Characterization of the Heat Affected Zone of Gold Wirebonds Using Nanoindentation

Magnetically-Assisted Statistical Assembly - a new heterogeneous integration technique

Length Effects on the Reliability of Dual-Damascene Cu Interconnects

Investigation of the Fundamental Reliability Unit for Cu Dual-Damascene Metallization

Graded InGaN Buffers for Strain Relaxation in GaN/InGaN Epliayers Grown on Sapphire

Glass Forming Ability in Pr-(Cu, Ni)-Al Alloys

Frequency Dependence Modulus of Pd₄₀Ni₁₀Cu₃₀P₂₀ Amorphous Alloy around the Glass Transition by Dynamic Mechanical Analysis

Research Summary: The Effect of Microstructure on the Macroscopic Response of Electroactive Systems

A Constitutive Model for the Mechanical Behavior of Single Crystal Silicon at Elevated Temperature

Computation and Simulation of the Effect of Microstructures on Material Properties

Charge Storage Effect in a Trilayer Structure Comprising Germanium Nanocrystals

Atomistic Simulations of Metallic Cluster Coalescence

Anisotropic Superelasticity of Textured Ti-Ni Sheet

Amorphous Metallic Glass as New High Power and Energy Density Anodes For Lithium Ion Rechargeable Batteries

PALM: Predicting Internet Network Distances Using Peer-to-Peer Measurements

Strategies of Lithography for Trapping Nano-particles

RM³ Processing for In-plane Optical Interconnects on Si-CMOS and the Impact of Topographic Features on Losses in Deposited Dielectric Waveguides

TiNi-based thin films for MEMS applications

A theory of amorphous polymeric solids undergoing large deformations: application to micro-indentation of poly(methyl methacrylate)

Synthesis, electrochemistry and First Principles Calculation studies of layered Li-Ni-Ti-O compounds

Structural analysis of metalorganic chemical vapor deposited AlN nucleation layers on Si (111)

Review of Direct Metal Bonding for Microelectronic Interconnections

Plastic Relaxation In Single InᵡGa₁â‚‹ᵡN/GaN Epilayers Grown On Sapphire

Photonic Crystals: Numerical Predictions of Manufacturable Dielectric Composite Architectures

Optically pumped InxGa₁â‚‹xN/InyGa₁â‚‹yN multiple quantum well vertical cavity surface emitting laser operating at room temperature.

Nanocomposite Thin Films for both Mechanical and Functional Applications

Mortality Dependence of Cu Dual Damascene Interconnects on Adjacent Segments

Micro Raman Spectroscopy of Annealed Erbium Implanted GaN

Mechanical Properties of Bulk Metallic Glasses and Composites

Investigation on Thin Film Lithium Microbatteries

Strained Ge channel p-type metal-oxide-semiconductor field-effect transistors grown on Siâ‚â‚‹xGex/Si virtual substrates