High pressure piezoresistive transducer

Abstract

A method of fabricating a high pressure piezoresistive pressure transducer having a substantially linear pressure versus stress output over its full range of operation. The method involves bonding a carrier wafer having a dielectric isolating layer on one surface and a supporting member on the opposite surface, to a pattern wafer containing at least two single crystalline longitudinal piezoresistive sensing elements of a second conductivity. Both the pattern wafer and sections of the carrier wafer are etched leaving the piezoresistive sensing elements bonded directly to the dielectric isolating layer, and a diaphragm member having a deflecting portion and a non-deflecting portion. The diaphragm member is constructed to have an aspect ratio which is of the order of magnitude of one. The piezoresistive sensing elements have a large transverse piezoresistive coefficient normal to the plane of the diaphragm and both a large longitudinal piezoresistive coefficient and a small transverse piezoresistive coefficient in the plane of the diaphragm. One of the at least two piezoresistive sensing elements is positioned above the non-deflection portion of the diaphragm in an area of minimal longitudinal stress and the other is positioned above the deflecting portion of the diaphragm in an area of high compressive stress. The positioning of the second sensor over the deflecting portion of the diaphragm is selected so that there will be equal and opposite resistance changes registered from the sensors. The method results in an improved transducer design when compared to prior art devices.