Highly selective and sensitive O2 plasma treated sputtered thin film sensor for sub-ppm level NH3 detection at room temperature

In this work, a SnO2 gas sensor with high specific surface area and hydroxylation property has shown enhanced sensitivity and selectivity for ammonia (NH3) detection at room temperature (RT). SnO2 thin film layer composed of nanograins of size ~ 8–24 nm is synthesized by dual step method including RF sputtering technique, followed by oxygen (O2) plasma treatment, intended to fabricate a high performance ammonia sensor operating at room temperature. The crystalline nature and surface morphology of the deposited layer have been investigated by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). A photoluminescence (PL) study is used to analyze the presence of oxygen vacancies in O2 plasma treated and untreated samples. The sensor is found suitable for extreme low ammonia concentration detection viz. 200 ppb with 20.2% response, with appreciable response/recovery time at RT. The sensing response of the fabricated sensor is analyzed in concentration range 200 ppb–500 ppm along with measuring the relative response (RR) of the sensor towards triethanolamine (TEA), 2-propanol, ethanol, acetone and methanol, in order to confirm the highly selective nature of the sensor towards target analyte. The response of the pure SnO2 (untreated O2 plasma) sensor is also investigated from RT to 250 °C, to identify the minimum (Tmin) and critical (Tc) operating temperature of the untreated sensor. Efforts in the present study are emphasized to achieve the response of the sputtered SnO2 thin film sensor at RT by significantly modifying the surface morphology through oxygen plasma treatment for selective ammonia detection.