Improvement of the Micro-capacitive Humidity Sensor by the Package Optimization

To achieve good properties such as the hysteresis, repeatability, stability, linearity and response time in this work, the optimisation processes of the package are presented for a microcapacitive humidity sensor. On the basis of theoretical analysis, the optimisation will be conducted in two ways, including reducing the effect of parasitic capacitance in the microcapacitive humidity sensor measurement system and decreasing the adsorption of water molecules on the package surface. The reduction of the influence of parasitic capacitance was realised by reasonably designing the PCB and the isolation package. The decrease of water adsorption on the package surface was achieved by coating a layer of hydrophobic material. The experimental results proved that the package optimisation enables the humidity sensor with better performance; for instance the hysteresis error is more than six times lower, the repeatability error is more than ten times lower, and the temperature drift is about two times lower, and the linear fitting error is three times lower than the pre-optimised humidity sensor. Especially, the humidity response time in both adsorption and desorption is extremely improved.