High Temperature, High-Pressure Fluid Connections for Power Micro-Systems
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High Temperature, High-Pressure Fluid Connections for Power Micro-Systems
Todd S. Harrison, Adam P. London and S. Mark Spearing Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA 02139, [email protected]
ABSTRACT High power density micro-systems offer the potential to revolutionize technologies for portable electrical power generation, propulsion and flow control. Devices are being designed and fabricated which include micro-gas turbine engines, micro-rocket engines, micro-motorcompressors, micro-pumps and micro-hydraulic transducers. Common to all of this family of devices is the need to create packages that service the devices, and interface them with the macro-scale environment. Fluid interconnections are a particularly demanding packaging element for this class of devices. In order to achieve high power densities, these devices are required to operate at high pressures and, in some cases, high temperatures. This paper describes the design, analysis, fabrication and testing of high-pressure, high temperature fluid connections for the micro-engine and micro-rocket applications. A glass bonding technology has been developed to allow the creation of multiple fluidic connections consisting of Ni/Fe alloy tubes to silicon devices. Key strategies to achieve high strength connections are: to minimize the mismatch in coefficients of thermal expansion between the components, to eliminate voids from the glass and to promote adequate wetting of the glass to both the tubes and the silicon. Mechanical test results are presented which correlate the strength and statistical reliability of such bonds to the processing conditions, choice of glass and surface preparation prior to bonding. Successful examples of packaged micro-engine and micro-rocket devices are presented.
INTRODUCTION A range of micro-systems are currently under development which offer the potential for operation at high thermo-mechanical power densities. These include a micro-gas turbine engine, micro-rocket and a micro-turbo generator [1]. In addition there are efforts underway to create micro-systems to function as chemical reactors [2] and other high operating temperature MEMS. All of these devices are designed to operate at high temperatures and require the delivery of liquids, either for fuel, cooling or as the feedstock for a chemical reactor. In some cases the operating pressures of the device may also be high, ranging from atmospheric to over two orders of magnitude higher. These requirements are challenging for the packaging of these microsystems. For the most part existing micro-electromechanical systems (MEMS) have utilized packaging concepts and technologies drawn directly from those used for more conventional micro-electronics applications. Clearly the significantly higher pressures and temperatures associated with high-power density MEMS negate this as an option. The paper provides an overview of one strategy for introducing fluids at high temperatures and pressures to microfabricated devices, a more d
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