Capacitive pressure sensors and switches fabricated using strain compensated SiGeB

Abstract

The fabrication of capacitive pressure sensors and pressure switches using a 2.4 μm thick strain compensated heavily boron doped SiGeB diaphragm is presented. The process relies on the silicon fusion bonding of two silicon wafers to seal the pressure sensor cavity and construct the device. Both rectangular and circular type pressure sensors and pressure switches have successfully been fabricated using this process. Results are presented of a capacitive type sensor operating in the medical pressure regime (0–300 mmHg) with a sensitivity to pressure of 1.5 fF/mmHg or 305 ppm/mmHg, and of a pressure switch operating in the 3–8 bar pressure range and are thus suitable for a number of industrial and automotive applications. The current flowing through the switch when biased at 2 V jumps over six orders of magnitude when its two plates come in contact at a well defined pressure threshold.