High temperature CO2 sensing and its cross-sensitivity towards H2 and CO gas using calcium doped ZnO thin film coated langasite SAW sensor

Abstract

Development of indigenous CO2 sensing element operating at high temperature (≥ 350 °C) is highly desirable. Use of langasite (LGS) based surface acoustic wave (SAW) gas sensors is extremely beneficial compared with other commercially available sensors as it can operate at a higher temperature (> 800 °C). In the present work, we have shown CO2 sensing and its cross-sensitivity performance using LGS based SAW sensor. Compared with LGS with other sensing electrodes, calcium doped ZnO thin film (Ca_ZnO) coated LGS substrate shows enhanced CO2 sensing performance. The interdigitated electrodes (IDT) made of Pt was plated and Ca_ZnO thin film was synthesized and deposited on the LGS substrate. Additionally, we have compared the chemo-resistive gas sensing characteristics of Ca_ZnO thin film with the Ca_ZnO coated SAW sensors. Furthermore, temperature effect on CO2 sensing was studied where optimum response (change in resonant frequency ˜2.469 KHz) was observed at 400 °C. Also, the gas adsorption effect which leads to the change of the resonant frequency of the sensors has been deliberated. Besides, we have discussed the predominant effect of sensor conductivity than mass loading which enhances the reduction of the resonant frequency for thin film coated SAW sensors has been deliberated. Additionally, we have demonstrated the cross-sensitivity of H2 and CO gas in CO2 sensing and their mixed gas sensing behavior operating at 400 °C.