Trench-Isolated Bulk-Type Pressure Sensor on Silicon-on-Insulator for High-Temperature and High-Pressure Downhole Applications

Abstract

Presently reported is a dielectric-isolated bulk-type pressure sensor fabricated on silicon-on-insulator (SOI) that offers higher pressure capability than conventional diaphragm-type pressure sensors and wider temperature operating range than a recently reported junction-isolated bulk-type pressure sensor. The isolated piezoresistors are realized on the SOI device layer via trench etching and oxidation. Two types of trenches are formed: narrow ones that are completely filled with silicon dioxide and wide ones that are thermally oxidized on the sidewalls but partially filled. The pressure sensitivity is enhanced by relieving the transverse stress acting on selected piezoresistors isolated with the wide trenches.