Research and evaluation of a high temperature pressure sensor chip

In order to solve the pressure measurement problem in the harsh environment, such as high temperature above 200degC, a special piezoresistive pressure sensor chip has been developed. Based on the MEMS (micro electro-mechanical system) and SIMOX (separation by implantation of oxygen) technology, the piezoresistive pressure sensor chip was constituted by silicon substrate, a thin buried silicon dioxide layer by SIMOX, an optimized boron ion implantation doping layer, photolithographically patterned on a Wheatstone bridge configuration, stress matching layer with silicon nitride, and beam lead layer (Ti-Pt-Au) for bonding the gold wires. A special buried silicon dioxide layer with the thickness 367 nm, which used to isolate the upper measuring circuit layer from the silicon substrate, was fabricated by the SIMOX technology with the oxygen ion dose of 1.4times10¹⁸/cm² and implantation energy of 200 keV, so the leak-current between the upper measuring circuit layer and the silicon substrate was avoided. Utilizing the developed sensor chip and high temperature packaging process, a pressure sensor was fabricated with the range of 0~25 MPa, the experimental results showed that this pressure sensor had good performances under the high temperature of 200degC, such as accuracy of 0.114%FS and natural frequency of about 694.4 kHz.