Room Temperature Hydrogen Sensing Investigation of Zinc Oxide Schottky Thin-Film Transistors: Dependence on Film Thickness

Radio frequency (RF) sputtered ZnO thin-film transistors (ZnO TFTs) with titanium/palladium (Ti/Pd) Schottky source and drain electrodes grown on SiO₂/n-Si substrate have been investigated with a compatible fabrication process for different channel thicknesses ranging from 50 to 200 nm as room temperature (RT) hydrogen sensors. Rapid and concentration-dependent (500-4500 ppm) sensor responses (in terms of drain current increase due to the lowering of the Schottky barrier height) with the maximum sensitivity of 72.7% have been achieved excluding the need of heating with relatively fast response/recovery times under RT. Apart from selectivity analysis of the sensors toward methane, acetone, and nitric oxide, structural, optical, mechanical, and electrical characteristics of the devices depending on film thickness are studied. The performance of the sensors in terms of repeatability, time-dependent stability, and under humid ambient conditions has been demonstrated. Hydrogen adsorption kinetics has also been investigated from a thermodynamic analysis.