An Investigation on Electrical and Hydrogen Sensing Characteristics of RF Sputtered ZnO Thin-Film With Palladium Schottky Contacts

Abstract

Fabrication and characterizations of a hydrogen sensor with palladium Schottky contacts, grown on radio frequency sputtered zinc oxide thin film is reported. Temperature dependence performance analysis of the proposed sensor was carried out at different hydrogen concentrations (50–1000 ppm) and temperatures (25°C–200°C) using current–voltage ( $I$ – $V$ ) measurements. Lateral shifts have been observed in the Schottky diode $I$ – $V$ characteristic when the device was exposed to hydrogen, and this could be attributed to the reduction of Schottky barrier height (SBH). The optimum performance of the sensor was obtained at 150 °C with maximum SBH variation of 144 meV at 1000 ppm hydrogen. Transient sensor performance at optimum temperature has also been analyzed and sensitivities ranging from 224% to 1125% with a minimum response time of 55 s and a recovery time of 26 s have been obtained. The response of sensor toward methane and nitrogen dioxide is also discussed. The basic $I$ – $V$ and capacitance–voltage characteristics of Pd/ZnO thin film are also reported, which confirmed its excellent rectifying properties. The basic microstructure studies of ZnO thin film were also investigated using X-ray diffraction, scanning electron microscope, atomic force microscopy, energy dispersive X-ray spectroscopy, and photoluminescence measurements. The proposed sensor has proven to be economical, due to its high sensitivity and easy to fabricate structure with a limited number of processing steps.