Study On Temperature Effect Of MEMS Pirani Gauge

Nowadays,vacuum is needed in some fields of daily production and scientific experiments,so it is especially important to accurately measure the ambient pressure.Pirani vacuum gauge is a kind of common vacuum measuring device.Based on the principle that the heat dissipation rate of heating wire under low pressure is related to the ambient pressure,the real-time pressure can be obtained by measuring the resistance of electrified wire.Nowadays,with the development of Micro-Electro Mechanical System(MEMS),minituraized and highly integrated devices can be developed,and MEMS pirani gauges were realized for a variety of applications.Compared with traditional pirani gauges,MEMS pirani gauges have smaller size,lower power consumption,lower cost and can be integrated with IC.Therefore,it has attracted an increasing interests within recent years.The pirani gauge studied in this thesis is mainly composed of heating wire,micro-hot plate made of composite inorganic film and silicon-based support engraved on the back of micro-hot plate.The heating wire is made of platinum for its good stability and linearity;the micro-hot plate is a composite inorganic thin film layer with low stress,high stability and low thermal conductivity,which deposited with silicon dioxide and nitride-silicon;etching of the back of silicon substrate can be done by KOH wet etching or ICP dry etching.Devices with resistance layers of gold and platinum were fabricated respectively in clean room.The repeatability and stability of the devices is tested,and the stability is further improved by annealing.Through their comparison of reliability,platinum was finally selected as the heating resistance material,and the test results showed that the resistance change of platinum resistance was less than 0.1 ? after 4000 minutes of electrifying.The sensitivity of the pirani gauge in its linear range from 0.74 Pa to 32.66 Pa is 31.83 ?/lg(Pa),and the linearity is 5.7%.At the same time,the metal coil is integrated on the pirani chip for measuring ambient temperature.The pirani gauge reflects the pressure information by measuring the temperature of the micro-hot plate.When the ambient temperature changes,the temperature of the microhot plate will also changes,which will eventually affect the output of the device.In order to reduce the effect of ambient temperature,three different methods,namely expression solution,fixed proportion interpolation and resistance ratio method,are proposed in this thesis.By using these methods,the accuracy of ±15% reading value in its linear range can be achieved.In this thesis,the stability of pirani gauge is improved by annealing,the integration of thermometer and pirani gauge is completed,and the solution to reduce the temperature effect is given.Finally,the reliability of the device is further improved.