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 wi th tin-dioxide (SnO2) thin films integrated with a solid-state heater, which is realized with technologies of micro-electro-mechanical syste ms (MEMS), and are compatible with VLSI processes. The main sensing pa rt with dimensions of 450 x 400 mu m(2) in this developed device is co mposed of a sensing SnO2 film, which is fabricated by electron-gun eva poration with proper annealing in ambient oxygen gas to yield fine par ticles and good structure. An integrated solid-state heater with a 4.5 mu m-thick cantilever bridge (1000 x 500 mu m(2)) structure is made o f 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 fo r the response and recovery time, respectively, at an operating temper ature of 300 degrees C. Those experimental results also exhibit a much superior performance to that of a popular commercial ethanol gas sens or 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 vario us films for controlling each element at separate resistance. (C) 1998 Elsevier Science S.A. All rights reserved.