The Research On A Piezoresistive Silicon Carbide Pressure Sensor For High Temperature Applications

Pressure measurement under adverse circumstances like high-temperatureconditions has got more and more attention. Silicon carbide, the third generation wideband gap semiconductor material, owing to its excellent electrical, mechanical andchemical properties, is a promising material for the development of high-temperaturepressure sensors. There have been a lot of researches on optical, capacitive andpiezoresistive SiC pressure sensors abroad.Under this background, this paper focosed on developing a high temperature6H-SiC piezoresistive pressure sensor operating up to400℃. The main contentsinclude sensor chip design and key MEMS processes for6H-SiC. In this paper, thedevelopment and status of SiC pressure sensors around the world is reviewed. Basedon the principle of piezoresistive pressure sensor and the material properties of6H-SiC, the form and size of diaphragm and piezoresistance are dicussed. Theprocess flow, chip packages and the photomask layout are also designed according tothe sensor chip structure. By using ANSYS software, the thermal stress between thechip package substrate and SiC chip were calculated.This paper also investigates the key MEMS processes for6H-SiC, includingepitaxial, etching and ohmic contact. A series of experiments and tests are carried out.Chemical vapor deposition method is used for epitaxial growth. An n-type epitaxiallayer with1.8×10¹⁸cm^-3doping concentration is achieved. SiC bulk micromachininguses dry plasma etching process. By using RIE, about80μm SiC is etched with100nm/min etching rate, and the etching surface acheives good quality. Ohmiccontact is formed with Ti/TiN/Pt metal layers, and through Kelvin method thespecific contact resistance is tested to be8.42×10^-4 cm².