Compliant and Low-cost Humidity Sensors using Nano-porous Polymer Membranes

This paper proposes non-fragile compliant humidity sensors that can be fabricated inexpensively on various types of nano-porous polymer membranes such as polycarbonate, cellulose acetate, and nylon membranes. The sensor contains a pair of interdigitated electrodes deposited on the nano-porous polymer membranes. The resistance and/or capacitance between these electrodes vary at different humidity levels with a very high sensitivity due to the water adsorption (capillary condensation) inside the nano-pores. The proposed sensors are low-cost in both material and fabrication. Due to its compliance, the sensors can be suitable for certain applications such as in-situ water leakage detection on roofs, where people can walk on top of them. Testing results demonstrated that the sensor changes resistance within large range of humidity values. For most sensors, the resistance changes from 0.1 GΩ to 2000 GΩ when the relative humidity changes from 39% to 100% at room temperature. It takes about 4-8 minutes for the resistance to reach steady state when the sensor was taken from 100% to 39% relative humidity at the room temperature.