Surface acoustic wave ammonia sensor based on SiO <sub>2</sub> –SnO <sub>2</sub> composite film operated at room temperature
Yuanjun Guo, G. D. Long, Yongliang Tang, Jinlong Wang, Qingbo Tang, Xiaotao Zu, J Y, Bo Du, Hamdi Torun, Yongqing Fu
Abstract
Abstract Sensitive thin film layers of SnO 2 , SiO 2 and SiO 2 –SnO 2 were deposited on a surface acoustic wave resonator using sol-gel method and spin coating techniques. Their ammonia-sensing performance operated at room temperature was characterized and their sensing mechanisms were comprehensively studied. When exposed to ammonia, the sensors made of SnO 2 and SiO 2 –SnO 2 films exhibit positive frequency shifts, whereas the SiO 2 film sensors exhibit a negative frequency shift. The positive frequency shift is related to the dehydration and condensation of hydroxyl groups, which makes the films stiffer and lighter. The negative frequency shift is mainly caused by the increase of mass loading due to the adsorption of ammonia. The gas sensor based on SiO 2 –SnO 2 film shows a positive frequency shift of 631 Hz when it is exposed to ammonia with a low concentration of 3 ppm, and it also shows good repeatability and stability, as well as a good selectivity to ammonia compared with gases of C 6 H 14 , C 2 H 5 OH, C 3 H 6 O, CO, H 2 , NO 2 , and CH 4 .