Design Of Polysilicon Nano-film Pressure Sensor

The semiconductor pressure sensors have a wide range of applications in a modern society.the use of new materials is an effective way that improve the sensor performance. The reseachs show that the piezoresistive characteristics of polysilicon nanofilm(PNSF) is more excellent than common poly-Si films.In order to apply the film in sensors effectively,in this dissertation,the design methods of existing semiconductor pressure sensors have been studied systematically,the piezoresistive properties of materials are realized fully,the design method of the PNSF pressure sensor is established,the chip of pressure sensor is fabricated using conventional semiconduct technics,test data show the design objectives achieved.PNSF is poly-Si film of more or less than 100nm in thickness,as doping concentration is approximately 3×10²⁰ cm^-3,PNSF has significant tunnel piezoresistive effect,show better piezoresistive characteristics than that of poly-Si films.The gauge factor(GF) can reach 34(20%higher than that of common poly-Si films);the gauge factor temperature coefficient(TCGF) can be less than 1×10^-3/℃(lower than half TCGF of common poly-Si films);the resistance temperature coefficient(TCR) can be less than 1×10^-4/℃(almost an order lower than that of common poly-Si films).It has an important application value for the development of high-sensitivity,low temperature drift,wide operating temperature range of low-cost pressure sensor.According to PNSF piezoresistive characterics and conditions of etch technologyes for the silicon cup,the elastic membrance structure is designed.Then dimensions of the membrance and distribution of strain resistors are optimized by finite-element analysis method.In order to achieve temperature compensation,a schottky diode is design as tempetature sensor on the pressure sensors,which don't increase the sensor process steps. With MEDICI software,Simulation results show that junction temperature coefficient of schottky diode is -6.70mV/℃.According to optimized design,the chips of pressure sensors in 1 MPa span are fabricated.Measured sensor sensitivity is 10mV/MPa·V;zero drift coefficient≤1×10^-3 FS/℃;sensitivity drift coefficient numerical value(pre-compensation circuit)≤|-1×10^-3|FS/℃;full-precision≤0.24%FS.The test data show that the chips possess simple process,excellent temperature and sensitivity characterics and reach high precision level.