A study of micromachined displacement pumps for vacuum generation

Abstract

Micromachined vacuum pumps are one of the key components in miniature systems for chemical and biological analysis. Miniature sensors and analyzers are normally operated at the pressure range lower than a few millitorr. We are developing a micromachined vacuum pump that is comprised of a mechanical rough pump integrated with micromachined ion-pumps. The rough pump generates a low vacuum of tens of torr from atmospheric pressure for the ion-pumps to initialize. Field ionization and electron impact ionization pumps that connect to the rough pumps continue to pump from the low vacuum of tens of torr to high vacuum of millitorr or even microtorr. The focus of this thesis work is on the development of the micromachined rough pump. A micromachined displacement pump concept is adopted for the development of the chip scale vacuum rough pump. The micro displacement pump is designed with the aid of analytical and numerical modeling. The rough pump is fabricated by deep-reactive ion etching and other standard micromachining techniques. Systematic study into operation of this class of pumps allows us to now report on a pump that achieves 164 torr absolute pressure, which is to our knowledge the lowest measured pressure in a micromachined vacuum pump operated from atmospheric pressure. This performance improvement is significant in that it enables a base pressure of less than 35 torr for a two-stage design, which allows integration with the ion pump, thus leading to realization of miniature chemical and biological analyzers. More importantly, the understanding of the micromachined displacement pumps for vacuum generation has been greatly improved and a universal model has been developed, which is very powerful to describe and predict the micromachined displacement pump behavior for vacuum generation.