Research On Piezoresistive Micropressure Sensor For Automobile Fuel Steam Pressure Detection

In order to control the emission of pollutants from automobile fuel steam,fuel evaporation control system has been widely used in the automotive field,which can monitor and treat the fuel steam on the line.Fuel vapor pressure sensor is the key part of the system,it needs to realize accurate detection of small range pressure under the harsh environment of oil pollution,vibration and wide temperature area.At present,piezoresistive micropressure sensors on the market are usually difficult to achieve high sensitivity and linearity at the same time,and because micropressure detection requires sensor chips to have higher sensitivity,which also leads to the micropressure sensor chips are more susceptible to packaging stress and temperature changes and other factors.Therefore,in view of the harsh use environment and demand of fuel vapor pressure sensor,this thesis designs a sensor chip that can detect the micro range pressure,and designs the package of fuel vapor pressure sensor based on the designed micro pressure chip.At the same time,the temperature compensation of silicon pressure sensor is studied,the research content is summarized as follows:(1)The micro-pressure sensor chip structure was optimized and the performance parameters of different chip structures were compared by finite element simulation.The effects of different film thickness and length on the stress and deflection of the pressure-sensitive chip with beam membrane island structure were analyzed,and the optimal structure sizes of the chip and the pressure-sensitive resistor were obtained.According to the optimal structure parameters of pressure sensitive chip,the wafer process is designed.The sensitivity of the pressure-sensitive chip is 20.21mV/kPa under 5kPa,and the nonlinearity is 0.34%FS.(2)According to the use environment and actual use requirements of fuel steam pressure sensor,the package design of micro-pressure chip was carried out,and the package method of the back pressure of the chip was proposed,and the compensation chip and peripheral circuit were integrated on a circuit board.The influence of key package parameters on the pressure-sensitive chip was studied by using finite element simulation software.It is found that different shell materials have an effect on the stress of the chip,the thicker circuit board can reduce the stress of the chip,the adhesive with large Young’s modulus has a great effect on the stress of the chip,and increasing the thickness of the adhesive will reduce the dynamic performance of the chip.According to the designed package structure,the fuel vapor pressure sensor test sample was made,and the data test and calibration compensation were completed,which met the vehicle standard.(3)The key factors causing the temperature drift of the silicon piezoresistive pressure sensor are analyzed,the mathematical model of the influence of these factors on the sensor output under the temperature change is deduced,and the output model is verified based on the original data collected from the sensor.At the same time,a compensation algorithm based on nonlinear fitting and Newton interpolation is proposed.After compensation,the maximum error in the whole temperature region of the sensor decreases from 15.27%FS to 0.2%FS.