Compliant and low-cost humidity nanosensors using nanoporous polymer membranes

This paper proposes non-fragile compliant humidity nanosensors that can be fabricated inexpensively on various types of nanoporous polymer membranes such as polycarbonate, cellulose acetate, and nylon membranes. The nanosensor contains a pair of interdigitated electrodes deposited on the nanoporous 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 nanopores. 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 relative humidity (RH) values (40–100% RH) with very high sensitivity. Design A and B sensors exhibit high sensitivities, 2.5 and 1.3 GΩ/% RH, respectively, to relative humidity changes but are not linear in response till 55% RH is reached (R2 ∼ 0.7391 for design A, R2 ∼ 0.8824 for design B). For the design C sensors, sensitivity is around 20 GΩ/% RH and the response is highly linear (R2 ∼ 0.96) for 40–100% relative humidity range. These results showed the feasibility of the proposed compliant and low-cost nanopore polymer membrane based humidity nanosensors which could be used for in situ water leakage and humidity level detection on three-dimensional and complex surfaces such as roofs and airplane bodies in the near future.