A SAW-based H2S sensor coated with SnO2 thin film

A surface acoustic wave (SAW)-based sensor coated with SnO₂ thin layer is investigated for H₂S sensing. The conventional semiconductor sensor usually works in higher temperature (>;150°C) by resistance effect and performs with low sensitivity (>;10ppm). Compared with conventional semiconductor sensor, the SAW-based sensor is affected not only by conductivity but also by mass loading. Both of effects enhance the sensitivity and result in similar change of SAW propagation velocity. Therefore it is possible to achieve higher sensitivity or to detect H₂S at room temperature by employing a SAW-based sensor. This paper firstly gives the relative theoretical analysis, and then the experimental settings. A relative larger K² and SH-wave substrate, 36°YX-LiTaO₃, is adopted for Love wave mode, and Single-Phase Uni-Directional Transducer (SPUDT) is used to reduce bidirectional loss. The SnO₂ thin film is deposited on substrate by sputtering process. The sensor is detected from room temperature to 120°C respectively. Lastly experimental results are given. When the devices work at about 146MHz, this sensor can detect 200ppm H₂S at room temperature, and achieve a better sensitivity, 10ppm H₂S, at 120 °C. The good recover ability and repeatability is also demonstrated. Although response velocity is slower, the optimization algorithm can predict the response procedure according to the repeatability response figure. The developed sensor is promising for gas sensing at room temperature and low concentration.