Modeling and optimization of a fast response capacitive humidity sensor

This paper presents a model which predicts the temporal response of capacitive humidity sensors made of parallel electrodes and a polymer sensitive coating. This model is used for the simulation of the response of the sensor subjected to specific conditions. The model includes electrostatic and molecular diffusion calculation. As a validation, the model is confronted with finite-element simulation and experimental results. Experiments were carried out for divinyl siloxane benzocyclobutene (DVS-BCB) polymer films with different film thicknesses and upper electrode dimensions. As an application example, the model is used to simulate the response of several humidity sensor structures exposed to the conditions of a medical application related to breath analysis. The model may also be helpful to predict the effects of fabrication process uncertainties. Because the model used to describe water diffusion in DVS-BCB is based on Henry's law and Fick's law, it could be extended to the optimization of capacitive sensors for other vapors