Piezoresistive n-type 4H-SiC pressure sensor with membrane formed by mechanical milling

A 4H-SiC pressure sensor with piezoresistive transducers, for harsh environment applications, e.g., high temperature (~650°C) and/or in corrosive chemicals is presented. The sensing membrane, 1 mm in diameter and 50 μm in thickness, was formed by milling (drilling) a bulk single crystal SiC wafer. Both transverse and longitudinal piezoresistors were formed on the membrane out of an n-type SiC epitaxial layer. Ohmic contacts were obtained with Ta/Ni/Pt metallization followed by annealing at 1000°C for 20 min. The sensor was assembled on a small board and characterized under hydrostatic pressures up to 60 bar at room temperature. The obtained pressure sensitivity was 268 μV/V/bar. The sensor chip was exposed in air at 600°C for 165 hours and changes in bridge resistance were measured.