High sensitivity ethanol gas sensor integrated with a solid-state heater and thermal isolation improvement structure for legal drink-drive limit detecting

The paper reports the successful fabrication of ethanol gas sensors with tin-dioxide (SnO₂) thin films integrated with a solid-state heater, which is realized with technologies of micro-electro-mechanical systems (MEMS), and are compatible with VLSI processes. The main sensing part with dimensions of 450×400 μm² in this developed device is composed of a sensing SnO₂ film, which is fabricated by electron-gun evaporation with proper annealing in ambient oxygen gas to yield fine particles and good structure. An integrated solid-state heater with a 4.5 μm-thick cantilever bridge (1000×500 μm²) structure is made of silicon carbide (SiC) material by MEMS technologies. The sensitivity for 1000 ppm ethanol gas reaches as high as 90 with 10 s and 2 min for the response and recovery time, respectively, at an operating temperature of 300°C. Those experimental results also exhibit a much superior performance to that of a popular commercial ethanol gas sensor TGS-822. Therefore, the developed sensor with high performance is a good candidate for some specific application in automobile to detect drink-drive limit and allows an array integration available with various films for controlling each element at separate resistance.