MEMS capacitive humidity sensor with plate array structure using polyimide sensing layer

Abstract

The structure of MEMS Humidity Sensor is developed with silicon as substrate material. The proposed humidity sensor works on the principle of change in dielectric constant of the polyimide that occurs because of absorption/desorption of water vapor. It is observed that humidity sensor's output depends linearly on the relative humidity in the range of 20 to 90%. The sensitivity of the sensor shows that the range is 0.13 for 0.04fF per %RH to 1.36 for 4 fF per %RH. Modeling and simulation is carried out with parameters of different input values of pressures in accordance with minimum distances between micro plates array, the number of plates and the width of the plates for analysis. As the model is used to observe the water diffusivity in the polymer, polyimide layer is based on Fick's law and Henry's law. And hence could be extended for the parametric optimization of capacitive sensors in terms of stress, displacement and surface analysis. A Humidity sensor that works on capacitive principle is implemented in this paper. Sensor consists of array of plates onto the sensitive polyimide layer. The polyimide layer is sandwiched between the top electrode array and the bottom oxide layer.