The fabrication of novel micro hot-wire sensor

Abstract

Many works to improve the stability and sensitivity of metal oxide based gas sensors have been carried out during last several decades. As one of stability problems, we can present one example that the resistance alters to some extent when the devices are exposed to the normal air, which becomes an obstacle to its practical use. In this paper, we proposed new type of micro gas sensor with single electrode for improving stability and sensitivity. Generally, metal oxide gas sensors have two electrodes for heating and sensing. But this new type sensor has only a single electrode by forming a sensing material onto heating electrode. This micro gas sensor shows low resistance(a few hundred /spl Omega/) for parallel values of Pt resistance and SnO/sub 2/ sensing resistance. Therefore, it is appeared that the deviation of total resistance in the normal air condition is very low and stability is improved. Pt as a heating and sensing electrode is sputtered on glass (pyrex 7740) substrate and SnO/sub 2/ sensing material is thermally evaporated on Pt electrode. SnO/sub 2/ is patterned by lift-off process and then thermally oxidized in O/sub 2/ condition for 1 hr., 600/spl deg/C. The size of fabricated sensor is 2/spl times/2 mm/sup 2/. As a result of CO gas sensing characteristics, this sensor shows 100 mV voltage output for 1,000 ppm and linearity for wide range(0/spl sim/20,000 ppm) of gas concentration. And the sensor shows a good recovery characteristic of 1% deviation compared to initial resistance. The deviation of sensor resistance is about 5% for 6 months and a little influence for humidity of 90 R.H.%.