Silicon Carbide MEMS for Harsh Environments MEHRAN MEHREGANY, MEMBER, IEEE, CHRISTIAN A. ZORMAN, NARAYANAN RAJAN, AND CHIEN HUNG WU Invited Paper Silicon carbide (SiC) is a promising material for the development of high-temperature solid-state electronics and transducers, owing to its excellent electrical, mechanical, and chemical properties. This paper is a review of silicon carbide for microelectromechanical systems (SiC MEMS). Current efforts in developing SiC MEMS to extend the silicon-based MEMS technology to applications in harsh environments are discussed. A summary is presented of the material properties that make SiC an attractive material for use in such environments. Challenges faced in the development of processing techniques are also outlined. Last, a review of the current state of SiC MEMS devices and issues facing future progress are presented. Keywords— Harsh environments, high-temperature sensors, MEMS, SiC processing technology, silicon carbide. I. INTRODUCTION Many measurement and control applications that re- quire microsensor and microactuator technologies are in the presence of harsh environments. Harsh environments include locations of high temperatures, intense vibrations, erosive flows, and/or corrosive media. Application fields characterized by harsh environments include, for example, aerospace, micropropulsion, automotive, turbomachinery, oil well/logging equipment, industrial process control, nu- clear power, and communication. For example, optimized engine performance in aerospace and automotive systems requires a stable, high-temperature material for solid-state sensors and electronics. The comprehensive instrumentation needed to maximize the efficiency of gas turbine, rocket, and internal combustion engines must be able to reliably monitor operating parameters in and around combustion en- vironments. This need includes the measurement of steady- state and transient phenomena (e.g., temperature, pressure, Manuscript received February 6, 1998; revised February 23, 1998. This work was supported by the Defense Advanced Research Project Agency under Contract DABT63-95-C0070, the Army Research Office under Contract DAAH04-95-10097, and the National Aeronautics and Space Administration under Cooperative Agreement NCC3-252. The authors are with the Microfabrication Laboratory, Department of Electrical Engineering and Applied Physics, Case Western Reserve University, Cleveland, OH 44106 USA. Publisher Item Identifier S 0018-9219(98)05090-7. acceleration, and flow parameters), as well as monitoring of the by-products of the combustion process. Silicon (Si) is well suited for a broad range of sensor and actuator applications but is generally limited in electronic device performance to below 250 C and in mechanical device performance to below 600 C (due to a decline in its elastic modulus with increasing temperature). The bulky packaging required to keep Si-based microelectromechan- ical systems (MEMS) within operating limits (in practice, below 250 C) in high-temperature environments is both space and cost intensive, if not impractical, for many applications. Consequently, for high-temperature MEMS applications (e.g., above 350 C), there is a need for semi- conductors with good mechanical and thermal stability and a wide bandgap for stable electronic properties at elevated temperatures. Silicon carbide (SiC) has these properties, as well as additional attractive features. Compared to Si, SiC demonstrates higher chemical inertness and radiation resistance, which expands its potential to MEMS for space satellite systems. At the same time, single and polycrys- talline SiC can be grown on large area substrates and are compatible with batch-fabrication processes used in Si micromachining and integrated circuit (IC) industries. To a large extent, SiC device fabrication technology leverages off of the Si technology infrastructure. A principal focus area for SiC MEMS has been SiC sensor systems for gas turbine engines. To meet the effi- ciency, emissions, cost, and safety goals set by military and commercial customers, the next generation of gas turbine designs require instrumentation in or near the hot-gas flow path, which must operate above 350 C. Sensors are needed for turbine development testing and in-flight service in order to measure combustor liner temperature, rotor and stator metal temperatures, internal cooling temperatures, steady-state and transient cooling flow and temperature, pressure and rate of change of pressure, hot gas path leakage, and coolant leakage. Conversion of electronic control and sensor systems from Si to SiC-based devices will not only increase efficiency and safety through enabling instrumentation but also reduce the overall weight of an aircraft by eliminating the packaging, wiring and connectors 0018–9219/98$10.00  1998 IEEE 1594 PROCEEDINGS OF THE IEEE, VOL. 86, NO. 8, AUGUST 1998