Research On MEMS Humidity Sensor Based On PI Film

With the rapid development of Internet of things and microelectronics technology,MEMS technology is closely combined with traditional sensor industry.MEMS sensor will be the inevitable trend of sensor,and China also attaches great importance to the strategic significance of MEMS sensors.As one of the common sensors in the market,humidity sensors are widely used in food storage,electronic manufacturing,industrial automation,agricultural planting,textile production,home monitoring,medical experiment and other occasions.There is also an urgent need for miniaturization and integration.Therefore,following the trend of the times,the research on high-performance MEMS humidity sensor is of great significance to respond to the needs of national strategy.The existing MEMS humidity sensors are still moving towards the direction with high sensitivity,low humidity hysteresis,fast response,small size,good linearity and high stability.Polyimide has the characteristics of good moisture absorption and high stability,and is often used as the humidity sensitive material of humidity sensor.Therefore,this thesis selects research on the MEMS humidity sensor based on polyimide and makes performance optimization.The specific scientific research work and results are as follows:1.Firstly,this thesis introduces different types of MEMS humidity sensors and humidity sensing mechanism,selects the preparation of interdigital capacitive humidity sensor.Then,the relationship between structural parameters and device performance is discussed and analyzed,and the humidity sensitive performance of the sensor is optimized from the interdigital structure.Meanwhile,the heating layer structure is designed to accelerate dehumidification and keep the device dry.At the same time,the materials and processes used in each structural layer are confirmed.Fluorinated polyimide is selected as the humidity sensitive material to reduce humidity hysteresis.2.The relationship between humidity sensor potential,capacitance,humidity sensing film thickness and capacitance is simulated and verified to confirm the structural feasibility of the device and the thickness size of humidity sensing film.After that,The layout design is completed according to the size,position,material and process of each structural layer of the sensor.Then the fabrication of humidity sensor is completed by MEMS process technology.Finally,the interdigital capacitance and sensitive film are analyzed by SEM,EDS,atr-ftird and other relevant characterization tools.3.After completing the device packaging and the construction of the test system,the performance parameters of MEMS humidity sensor are tested to obtain the performance law of humidity sensor.The sensor has excellent linearity in the relative humidity range of 10% to 70%,the sensitivity is 0.052 p F/%RH,the average sensitivity is 0.27 p F/%RH under high humidity,the humidity hysteresis is 2.52%,and the maximum temperature coefficient is 0.069% /℃.It has good repeatability and stability.Finally,the design of sensor application detection module is completed based on the test data.