Design and fabrication of a high temperature pressure sensor

Based on Silicon on Insulator (SOI) and Micro Electro Mechanical System (MEMS) technology, a single-crystal silicon piezoresistive strain gage was fabricated and constituted by silicon substrate, a thin SiO₂ layer by Separation by Implantation of Oxygen (SIMOX), an optimized boron ion implantation doping layer photolithographed to discrete piezoresistors, stress matching Si₃N₄ layer, and metallization scheme of Ti/Pt/Au as beam lead layer for connecting piezoresistors to be Wheatstone bridge configuration. A special buried SiO₂ layer with the thickness of 367 nm was fabricated by the SIMOX technology, which replaced p-n junction to isolate the piezoresistors from the bulk silicon substrate, so this kind of single-crystal silicon strain gage can be used in many harsh fields under high temperature up to 350°C. By the single-crystal silicon strain gage packaged on the metallic circular flat diaphragm, and along with other thermal treatments and compensating methods, a high temperature pressure sensor has been developed with the pressure range of 0-120 MPa under high temperature above 200°C. The testing results show that the sensor has good static performances under 200°C and fine dynamic characteristics to meet the requirements of the modern industry, such as petroleum and chemistry, mobile industry, military industry, wind tunnels, materials processing.