Effect of interdigital electrode gap on the performance of SnO2-modified MoS2 capacitive humidity sensor

To improve the sensitivity of humidity sensors, the interdigital electrode size should be paid more attention, apart from the development of high performance sensing materials. This paper investigated the interaction between testing electrode and the performance of capacitive humidity sensor. To our best knowledge, no other reported papers have investigated it before. We found that the gap size of interdigital electrode had crucial influence on the response of SnO2/MoS2 based capacitive humidity sensors due to the different surface electrical conduction mechanisms. For the sensor with small gap interdigital electrode structure, the capacitance decreases exponentially as relative humidity (RH) rises so that high sensitivity is obtained at low humidity range (0%-45% RH). While the gap is wide enough, the capacitance increases exponentially as RH grows to get ultrahigh sensitivity at high humidity range (45%-90% RH). The experimental results show that the sensor with 5 μm gap have the largest sensitivity (161 μF/% RH) at low humidity range while the best sensitivity of 3170 pF/% RH is obtained at high humidity range for the sensor with gap of 100 μm. The as-prepared SnO2/MoS2 hybrid sensing nanocomposite was synthesized through a two-step hydrothermal route and its morphology and structure were further characterized using field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). Moreover, the SnO2/MoS2 based capacitive humidity sensors have fast response, short recovery time, little hysteresis and good repeatability.