MEMS micropump for a Micro Gas Analyzer

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 164-177).This thesis presents a MEMS micro-vacuum pump designed for use in a portable gas analysis system. It is designed to be pneumatically-driven and as such does not have self-contained actuation (the focus of future work). This research was carried out through a series of modeling, design, fabrication, and experimental testing tasks. Non-linear stress modeling tools characterizing the structural deformations of the micropump pistons and tethers, and fluid-flow modeling tools characterizing the vacuum generation and pumping rates were developed. A systematic design procedure based on these tools enabled the design and prediction of different valve and pump layouts to satisfy the stress limitations, and flow and power consumption requirements set forth by the MIT Micro Gas Analyzer project. The micropumps were fabricated using MEMS fabrication techniques, comprised of silicon and pyrex micromachining and bonding. Fabrication challenges, in particular the deep-reactive ion etching (DRIE) of the drive pistons and membrane structures, were overcome, and a completely computer controlled pneumatic testing platform for the rapid characterization of valve and micropump performance at different actuation pressures and frequencies was developed. Valve leakage data for various valve designs was collected and compared with models, and a micropump capable of generating 258Torr of vacuum below atmosphere was demonstrated at 0.75Hz operation. The maximum frequency of operation for these devices was experimentally measured to be just above 2Hz, which was consistent with fluid flow models.(cont.) This thesis presents vacuum generating micropump performance that comparables well with the best published to date, and explores future micropump designs and modeling/testing approaches that could improve overall performance and bring us closer to meeting the specifications set forth by the MGA project. Finally, general guidelines for micropump design and fabrication for any application are also presented.by Vikas Sharma.Ph.D

Design, modeling, fabrication, and testing of a multistage micro gas compressor with piezoelectric unimorph diaphragm and passive microvalves for microcooling applications

This dissertation investigates the development of a multistage micro gas compressor utilizing multiple pump stages cascaded in series to increase the pressure rise with passive microvalves and piezoelectric unimorph diaphragms. This research was conducted through modeling, simulation, design, and fabrication of the microcompressor and its components. A single-stage and a two-stage microcompressor were developed to demonstrate and compare the performance and effectiveness of using a cascaded multistage design. Steady fluid flow through static microvalves structure was studied to gain insight on its gas flow dynamics and characteristics. Transient analysis combined with the structure\u27s interaction was investigated with an analytical model and FEM model. The static analysis and transient analysis enabled lumped model parameter extraction for modeling and simulations. The transient FEM solution of the microvalve fluid-structure interaction (FSI) allows for extraction of the damping ratio for the lumped model. The microvalves were fabricated with MEMS microfabrication methods and integrated into a machined microcompressor housing. Study from the simulation of the microvalve fluid-structure dynamics in Simulink showed the frequency of the microvalves, at which frequency the mierovalve is more prone to leakage. Simulation indicated that the reverse leakage from the sealing of the microvalve can have a significant impact on the pressure rise performance of the compressor. A model of the single- and the two-stage microcompressor were developed with Simulink to observe the dynamics and performance of the multistage microcompressor. The simulation shows the dead volume between the two chambers to decrease in the overall pressure rise of the multistage microcompressor. Operating scenarios with different frequency and in phase and out of phase actuation between stages were simulated to understand the dynamics and performance of the multistage design. The fabricated single- and two-stage microcompressor produced a maximum pressure rise of 10 kPa and 18 kPa, respectively, and a maximum flow rate of 32 sccm for both. To obtain these maximum pressure rises, the microcompressors were operated at high frequency at the resonance of the piezoelectric diaphragm. This dissertation investigated the feasibility and operation of a multistage gas microcompressor with passive microvalves, allowing the exploration of its miniaturization

A study of micromachined displacement pumps for vacuum generation

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 159-162).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.by Hui Zhou.Ph.D