Microfluidic MEMS

The advent of MEMS (micro-electro-mechanical systems) has enabled dramatic changes in diverse technological areas. In terms of control and distribution of liquids and gases (microfluidics), MEMS-based devices offer opportunities to achieve increased performance, and higher levels of functional integration, at lower cost, with decreased size and increased reliability. Microfluidic actuators include distribution microchannels and orifices, microvalves, micropumps, and microcompressors. Related microsensors are required to measure temperature, flow, pressure, viscosity, and density. This work focuses on the application of microfabricated valves based on the principles of thermopneumatic actuation. A brief comparison to other actuation techniques is made. The science and technology of silicon-based thermopneumatic microvalves is then detailed. The dynamics of the controlled fluid, and thermal and mechanical behavior of structures, necessary to understand the relationships between flow, pressure, and temperature are presented. The power required for actuation, the response speed, and the effect of shrinking size on these parameters are also derived. In terms of applications, previous research and product development efforts have demonstrated the application of thermopneumatic microvalves to problems of industrial gas and liquid control. Wide ranges of pressure, temperature, and flow rate have been achieved. Expansion valves for refrigeration control have also been produced. Most recently, the integration of microfluidic components using advanced packaging techniques has been used to create devices with higher levels of functionality. Specifically, high-precision pressure regulators, and pressure-based mass flow controllers, have been devised, based upon both normally-open and normally-closed microvalves. Also, low leak-rate shut-off valves, appropriate for use in vacuum system applications, have been developed successfully. At the highest level of integration, these modules have been themselves integrated into mesoscale gas sticks, and gas distribution panels, for use in distribution and control of electronics specialty gases.