Effects of Porous Structure for Gas Sensor on Sensitivity Using Tin Oxide with Low Density

Abstract

Recently, gas sensor has been studied because of increasing accidents caused by harmful and explosive gas, which is hard to detect olfactory system. Tin oxide is one of the most promising candidates for gas sensing materials owing to its many advantages, such as various gas detecting capability, good stability and high sensitivity. In gas sensor, the kinds of sensing materials as well as detecting layer structures are important. The sensing materials with high surface areas show high sensing performance, so nanowire structure with mechanical contact between nanowires has been widely used. However, electric signal of nanowire along mechanical contacts is not stable and the external vibration and fast gas flow generates the inaccurate signal. In this research, the low density tin oxide film with stable interconnection between nanoparticles was prepared using the physical vapor deposition by controlling the processing pressure, temperature and power. Macrostructure and interconnected structure between tin oxide nanoparticles were observed using scanning electron microscope (SEM) and transmission electron microscope (TEM) and crystal structure was analyzed by X-ray diffraction (XRD). Platinum and titanium electrodes were fabricated by lift-off process on the silicon substrate with the silicon nitride film of 300 nm, and then tin oxide with low density was deposited on it using shadow mask. The characteristics of the gas sensor were examined using carbon mono-oxide (CO) and ethanol (C2H5OH) changing concentration of gas, operating temperature and post heat-treatment temperature. In conclusion, porous nanostructure of tin oxide was composed of a lot of interconnected nanoparticles of about 10 nm and showed stable resistance in dry air. And post heat-treatment enhanced the stability in spite of inreasing the particle size. It could be suggested that the oxide films with lower density showed the superior sensitivity and the shorter response time than the oxide films with higher density. Figure 1