Realization and Characterization of a Bulk-Type All-Silicon High Pressure Sensor

Distinct from conventional diaphragm-type pressure sensors, a silicon-based bulk-type high pressure sensor has been analyzed, realized, and characterized. External hydrostatic pressure acting on the sensor is converted to a biaxial compression inside an all-silicon encapsulated vacuum cavity. The stress anisotropy is analytically modeled and numerically simulated. The biaxial compression is measured using two pairs of piezoresistors oriented to optimally utilize the anisotropy of silicon piezoresistance. An improved pressure seal in the test-package allowed extended testing of the sensor up to a pressure of 200 MPa and a temperature of 175 °C. Reported also is a zero-offset of the sensor, largely attributed to the tensile stress induced by the insulating cover oxide after cooling from the high-temperature dopant activation anneal.