Design of thin-film configuration of SnO <sub>2</sub> –Ag <sub>2</sub> O composites for NO <sub>2</sub> gas-sensing applications
Yuan‐Chang Liang, Yu-Wei Hsu
Abstract
Abstract In this study, a two-layered thin-film structure consisting of a dispersed nanoscaled Ag 2 O phase and SnO 2 layer (SA) and a mono-composite film layer (CSA) consisting of a nanoscale Ag 2 O phase in the SnO 2 matrix are designed and fabricated for NO 2 gas sensor applications. Two-layered and mono-layered SnO 2 –Ag 2 O composite thin films were synthesized using two-step SnO 2 and Ag 2 O sputtering processes and Ag 2 O/SnO 2 co-sputtering approach, respectively. In NO 2 gas-sensing measurement results, both SA and CSA thin films that functionalized with an appropriate Ag 2 O content exhibit enhanced gas-sensing responses toward low-concentration NO 2 gas in comparison with that of pristine SnO 2 thin film. In particular, a gas sensor made from the mono-composite SnO 2 –Ag 2 O layer demonstrates apparently higher NO 2 gas-sensing performance than that of double-layered SnO 2 –Ag 2 O thin-film sensor. This is attributed to substantially numerous p–n junctions of Ag 2 O/SnO 2 formed in the top region of the SnO 2 matrix. The gas-sensing response of the optimal sample (CSA270) toward 10 ppm NO 2 gas is 5.91, and the response/recovery speeds in a single cycle dynamic response plot are 28 s/168 s toward 10 ppm NO 2 , respectively. Such a p–n thin-film configuration is beneficial to induce large electric resistance variation before and after the introduction of NO 2 target gas during gas-sensing tests. The experimental results herein demonstrate that the gas-sensing performance of p–n oxide composite thin films can be tuned via the appropriate design of composite thin-film configuration.