Design of silicon-on-sapphire pressure sensor for high temperature and high pressure applications

In this paper, a design scheme of high pressure and high temperature piezoresistive pressure sensor is presented. In order to meet the design requirements, SOS(silicon on sapphire) technology and circular flat diaphragm structure are adopted. Through theoretical analysis, the geometric dimensions of the diaphragm and the position of the piezoresistors on the SOS wafer are optimized for high sensitivity and linearity. A circle flat diaphragm with a radius of 2.5mm and a thickness of 0.8mm is designed, which enables the sensor to operate in high pressure condition (such as 28 MPa). The design is verified by the FEM (finite element method), and the simulation results are consistent with the theoretical results. It is also proved that the design of circular diaphragm has higher sensitivity compared to the square and rectangular diaphragm. With the advantages of high temperature resistance, wide operation range, high sensitivity and good linearity, the design ought to be an ideal candidate for high temperature and high pressure sensing in real application.