Emerging materials for microelectromechanical systems at elevated temperatures
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Chris Keimel GE Global Research, Niskayuna, New York, USA
Kevin J. Hemkera) Mechanical Engineering Department, Johns Hopkins University, Baltimore, Maryland, USA (Received 15 April 2014; accepted 8 July 2014)
Extension of microelectromechanical systems (MEMS) into more extreme operating conditions will require a wider range of material properties than are currently available in conventional systems. Successful integration of new materials is dependent on concurrent development of compatible fabrication routes and scale appropriate evaluation techniques. This review focuses on emerging material classes that have potential to replace silicon-based MEMS in elevated temperature applications. Basic silicon mechanical properties and micromachining methods are reviewed to provide context for developing material systems such as silicon carbide, silicon carbonitrides, and several nickel-based alloys. Potential improvements in strength, thermal stability, and reliability are juxtaposed with fabrication, reproducibility, and economic feasibility issues that must also be addressed.
I. INTRODUCTION
Microelectromechanical systems (MEMS) have broadened the definition of functional microsystems through integration of mechanical and electronic components within a single structure. The unique capabilities of these systems in combination with the economic advantage of high volume/low unit cost production have expanded the application of MEMS1 to include devices such as sensors,2 actuators,3 micropower generators,4 chemical reactors,5 and biomedical devices.6 Continued diversification of this portfolio is widely anticipated, but predicated on concomitant development of appropriate materials, fabrication technologies, and modeling approaches. History has shown that MEMS-based devices are becoming more complex. Decades ago, the industry witnessed inkjet print heads, a silicon-based MEMS device with no moving parts containing a heating element and an orifice, transform document printing. In subsequent decades, silicon-based devices became more complex and included moving components that enabled the creation and commercialization of pressure sensors, accelerometers, and gyros. Through miniaturization, improved sensor design and controls, and volume fabrication MEMS-based sensors have made their way into a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.183 J. Mater. Res., Vol. 29, No. 15, Aug 14, 2014
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consumer-based products where the sensor is valued for its ability to monitor and control. An emerging opportunity for the miniaturization of sensors and MEMS exists from industrial process controls to the monitoring of residential and commercial spaces as described by the concept of the “Internet of Things”.7 Taking sensors into the often harsh environments (temperatures greater than 200 °C, power levels above 100 W) will require new approaches to MEMS devices and that often begins with identifying the materials to construct these sensors fro
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