Hydrostatic Calibration of the Piezoresistive Coefficients on 4H Silicon Carbide

Silicon carbide (SiC) has been shown to be a good alternative to silicon in the development of stress sensors for harsh environments due to its desirable material properties. The piezoresistive behavior of stress sensors is characterized by piezoresistive coefficients, which must be calibrated before use in stress measurement. Four-point bending calibration method can extract only two of the six piezoresistive coefficients which can be used for measurement of in-plane stress components. However, for out-of-plane normal stress measurement, a third piezoresistive coefficient π
_1
3
is required. This paper discusses the resistive sensor design used for measuring the out-of-plane normal stress component. A hydrostatic test method utilizes a high-capacity pressure vessel to apply a triaxial load to a single die. The changes of resistance of the sensors on the die are collected during the test procedure, and piezoresistive coefficient Π13 is extracted by combining results from the four-point bending and hydrostatic tests. Errors induced by the off-axis plane are discussed, and the off-axis angle of our sample is determined by electron backscattering diffraction analysis (EBSD).