The humidity sensing properties of organic-inorganic (AMPS/SiO2) hybrid materials

In this study, the impedance-type humidity sensor was prepared by using a novel organic-inorganic composite material and the sensing performances were experimentally investigated. The 2-acrylamido-2-methyl-propane sulfonic acid (AMPS) was hybridized in sol-gel process with silica gel (SiO₂). This hybrid material was coated on the Al₂O₃ substrate with interdigitated electrodes by using the spin coating method to be used as a sensing material. The interpenetrating polymer network (IPN) structure of hybrid sensing film could increased the water-resistivity and decreased the response time (10s from 95% to 20% RH) for this device. The impedance varied more than three orders of magnitude in the range of 25∼95% RH under the 1 kHz and 25°C conditions. The temperature dependence is 0.23 to 0.37 RH°C^-1 under 15-55°C, respectively, and the hysteresis was below 1.5% RH. Furthermore, the surface properties, hybrid structure and sensing performances of this humidity sensor were investigated by using the SEM, ASAP and contact angle.