3-DIMENSIONAL MODELING OF CAPACITIVE HUMIDITY SENSORS

We present the first three-dimensional modelling of integrated capacitive humidity sensors based on interdigitated microelectrodes coated with a moisture-absorbing dielectric layer. We obtain the electric potential and field distributions outside the electrodes by solving the Laplace equation, subject to appropriate boundary conditions, using the isoparametric finite-element method. The solution also determines the surface charge induced on the electrodes, from which the capacitance of the full structure is readily obtained. We obtain excellent agreement with the experimentally measured values of the capacitance. Apart from humidity sensors, our modelling results are relevant for capacitive microdielectrometry in general.