Influence of Dimension and Temperature on Capacitive Humidity Sensor

The influence of dimension and temperature on a MEMS-based capacitive humidity sensor is researched in this paper. Looyenga’s equation and Dubinin’s semi-empirical data are used to describe the change of dielectric constant of sensing film when absorbing or desorbing water. For these equations and data, a picture of the relationship between dielectric constant and temperature, relative humidity is presented. In the basis of this theory, a simulation is finished, a curve showing good linearity and presenting the relationship between capacitance and relative humidity is obtained. A graph showing the influence of temperature on capacitance at different %RH is given, which considers the change of dielectric constant of Looyenga’s equation and Dubinin’s semi-empirical data only. the result shows that the capacitance decreases with the increasing of temperature. Influence of sensing layer thickness on sensitivity is presented. It shows that when the thickness of sensing layer is about 0.6 micron, the model of humidity sensor has the highest sensitivity.