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Fabrication and testing of bulk micromachined silicon carbide piezoresistive pressure sensors for high temperature applications

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3 Author(s)
Chien-Hung Wu ; Dept. of Electr. Eng. & Comput. Sci., Case Western Reserve Univ., Cleveland, OH, USA ; Zorman, C.A. ; Mehregany, M.

This paper explores the development of high-temperature pressure sensors based on polycrystalline and single-crystalline 3C-SiC piezoresistors and fabricated by bulk micromachining the underlying 100-mm diameter (100) silicon substrate. In one embodiment, phosphorus-doped APCVD polycrystalline 3C-SiC (poly-SiC) was used for the piezoresistors and sensor diaphragm, with LPCVD silicon nitride employed to electrically isolate the piezoresistor from the diaphragm. These piezoresistors fabricated from poly-SiC films deposited at different temperatures and doping levels were characterized, showing -2.1 as the best gauge factor and exhibited a sensitivities up to 20.9-mV/V*psi at room temperature. In a second embodiment, epitaxially-grown unintentionally nitrogen-doped single-crystalline 3C-SiC piezoresistors were fabricated on silicon diaphragms, with thermally grown silicon dioxide employed for the piezoresistor electrical isolation from the diaphragm. The associated 3C-SiC/SiO2/Si substrate was fabricated by bonding a (100) silicon wafer carrying the 3C-SiC onto a silicon wafer with thermal oxide covering its surface. The 3C-SiC handle wafer was then etched away in KOH. The diaphragm was fabricated by time etching the silicon substrate. The sensors were tested at temperatures up to 400°C and exhibited a sensitivity of 177.6-mV/V*psi at room temperature and 63.1-mV/V*psi at 400°C. The estimated longitudinal gauge factor of 3C-SiC piezoresistors along the [100] direction was estimated at about -18 at room temperature and -7 at 400°C.

Published in:

Sensors Journal, IEEE  (Volume:6 ,  Issue: 2 )