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7

Single-Crystal Silicon

Carbide MEMS:

Fabrication,

Characterization, and

Reliability

7.1 Introduction ......................................................................7-1
7.2 Photoelectrochemical Fabrication of 6H-SiC ..................7-3
7.3 Characterization of 6H-SiC Gauge Factor ........................7-8
Temperature Effect on Gauge Factor • Temperature Effect on
Resistance
7.4 High Temperature Metallization......................................7-14
General Experimental and Characterization Procedure
• Characterization of Ti/TiN/Pt Metallization • Ti/TaSi /Pt
2
Scheme
7.5 Sensor Characteristics ......................................................7-23
7.6 Reliability Evaluation ........................................................7-27
Reliability by Package Design • Transducer Parametric Analysis
Robert S. Okojie • AST Protocol • Stability of Transducer Parameters
NASA Glenn Research Center • Long-Term Stability

7.1 Introduction

Pressure monitoring during deep-well drilling and in automobiles and jet engines requires pressure sen-
sors and electronics that can operate reliably at temperatures between 200°C and 600°C [Alexander’s Gas
and Oil Connections, 2003, Matus et al., 1991]. Conventional silicon semiconductor pressure transduc-
ers increasingly suffer instability and failure as the operation is extended toward higher-temperature
regimes. The failures include degradation of metal/semiconductor contacts and weakening of wire-bonds
caused by temperature-driven intermetallic diffusion [Khan et al., 1988]. Robust architecture based on
Silicon-On-Insulator (SOI) technology has extended device operation to near 400°C [Tyson and
Grzybowski, 1994]. However, at 500°C the onset of thermoplastic deformation of silicon becomes the
ultimate factor limiting silicon-based microelectromechanical systems (MEMS) [Huff et al., 1991].
Several commercially available silicon and piezoceramic pressure transducers employ complex and costly

7-1

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