Resistive Humidity Sensor Based on Onion-Like Carbon-PVA Composite Sensing Film

Experimental behavior of a resistive relative humidity (RH) sensor including a Si substrate, a SiO2 layer, interdigitated transducer (IDT) electrodes, and, as a sensing layer, a nanocomposite comprising onion-like carbon (OLC) and polyvinyl alcohol (PVA) at 1/1 w/w ratio is reported and analyzed. Scanning Electron Microscopy (SEM) and RAMAN spectroscopy are employed to characterize the sensing layer. Measured curves show the resistance having a moderate, linear increase with RH for RH below 82% and a strong increase with RH for RH between 82% and 95%. To explain the measured dependence, two types of sensing mechanisms are identified and discussed. The hard-soft acid-base (HSAB) principle also supports this mechanism. It is also shown that the hysteresis of the proposed sensor characteristic is significantly improved after the first operating cycle.