Effect of film thickness on low temperature NO 2 detection of thermally oxidized WO 3 gas sensors

Abstract The escalating emission of NO 2 underscores the urgent need for effective gas sensors. Among metal oxides, tungsten oxide (WO 3 ) is a promising candidate for NO 2 detection. In this work, WO 3 thin films were fabricated via thermal oxidation of DC magnetron-sputtered tungsten, with tungsten thickness varied from 50–200 nm. Grazing incidence x-ray diffraction (GIXRD) analysis confirmed crystallization and crystallite size enhancement with increasing thickness. Field emission scanning electron microscopy (FESEM) images depicted grain-based film structures, with surface Porosity increasing with thickness. Raman spectroscopy confirmed the chemical composition of WO 3 , while x-ray photoelectron spectroscopy (XPS) showed higher surface oxygen for the 100 nm film. The study explored thickness-dependent NO 2 sensing at different operating temperatures. The study found that 100 nm film operated at 100 °C exhibited a high response of 1122% and 55% at room temperature, with lowest detection concentration of 100 ppb, which is highest compared to other thicknesses. Selectivity study found that the sensor is strongly selective towards NO 2 , along with promising repeatability.