Optimal design of SiC piezoresistive pressure sensor considering material anisotropy

Material properties of SiC determine the application potential of corresponding sensors in a high temperature and harsh environment. However, few reports are available to describe basic design principles of SiC sensors. In this paper, aiming at improving the sensitivity of the sensor, the structural design of a full-SiC piezoresistive pressure sensor is studied from the aspects of diaphragm structure, material, piezoresistor arrangement, and dimension. The differences between the isotropy theoretical calculation and the anisotropy simulation are analyzed. Furthermore, in order to conform to the anisotropic intrinsic properties of the SiC material, a fitting curve between the diaphragm stress and the corresponding design parameter a/h is obtained by using a quadratic function. Through comparison, a square diaphragm can obtain more stress than a circular diaphragm; however, it is not suitable for SiC pressure sensors due to the process difficulties in anisotropic etching. Both experiment and simulation results show that higher output sensitivity can be obtained when the four piezoresistors are distributed along the radial direction of the diaphragm. With the control variable method, we found that when the area of the edge piezoresistors is increased by 10 times, output sensitivity will decline by 23.66%. Instead, the size of the two piezoresistors at the center shows a minor impact. Therefore, the size of edge piezoresistors has a significant effect on output sensitivity, which is worth paying attention to and should be minimized. Sensor prototypes were fabricated with optimal design, and preliminary experimental results show that zero output is only slightly affected by temperature due to the good thermal stability of SiC materials.