Fused silica as substrate material for surface micromachined capacitive pressure sensors operable in touch-mode

This paper reports the fabrication and characterization of capacitive pressure sensors on fused silica substrates operable in normal- and touch-mode. It demonstrates the feasibility of surface micromachining of LPCVD layers on fused silica. This substrate offers advantages for capacitive transducers: elimination of parasitic capacitances, simplification of the sensor equivalent circuit and improvement of membrane stress control. Backend processing is enhanced: substrate contacts are unnecessary, large bond pads and conductive adhesives do not create parasitic capacitances. A set of fabricated sensors is presented and the measured characteristics agree well with the electrical and mechanical models. The designs feature: die sizes of 0.66 mm(2) and high touch-mode sensitivities up to 26 %/bar FS.