Integrated micro devices for small scale gaseous flow study

Citation

Liu, Jianqiang (1995) Integrated micro devices for small scale gaseous flow study. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/sra1-0d58. https://resolver.caltech.edu/CaltechETD:etd-10162007-133943

Abstract

Microfluidics has been an active research field for several years. Numerous micro devices such as pumps, valves, flow sensors and integrated systems for chemical analysis and medical applications have been developed. However, experimental studies of fluid flow in those micro devices are rare to find. As a result, design and analysis of microfluidic devices are mostly based upon continuous flow theory which is subjected to serious suspection as dimensions of the device become smaller and smaller. Several experimental studies have actually shown their results can not be explained with continuous flow model. So far, almost all the experimental studies of microflow are limited to the two-point pressure (inlet and outlet) and flow rate measurements using either conventional capillaries or micromachined channels. In order to measure the microflow with more details, several integrated microflow systems are presented in the thesis. These systems include microchannels (with either uniform or non-uniform cross-sections) and pressure sensors (which are distributed along the channels). Using the integrated microflow systems, some preliminary gas flow experiments have been conducted. For the first time, the gaseous pressure distribution inside microchannels are measured experimentally. The pressure distribution inside a microchannel with uniform cross-sectional area is found to be nonlinear. The experimental results can be explained with an isothermal viscous flow model with slip-flow boundary conditions. Furthermore, it is found that a channel with non-uniform cross-sections can cause a non-trivial pressure change. During the developments of the integrated microflow systems, several related problems has been studied and solved, for example, a universal model has been found which can be used to simulate PSG or oxide sacrificial layer etching process in HF based solutions, a surface micromachined pressure sensor has been designed and modeled. Many technical difficulties such as, thin film stress, etching and sealing of the microchannels and chambers, process integration for microchannels and pressure sensors, etc., have been overcome. All the details related to the design and fabrication have been discussed in the thesis.

Thesis Files