Development of a microfabricated chlorine gas sensor

A Clark-type electrochemical(EC) chlorine gas sensor has been used for a le akage-gas detector. The EC sensor, which has a PTFE porous filter as a gas permeable membrane, shows excellent performance in terms of rapid response, sensitivity, reproducibility and long-term stability. However, the size of the conventional EC sensor is as large as several centimeters. We have fab ricated a micro Clark-type EC chlorine sensor using micromachining. Pyrex g lass used as a sensor body was processed using a dicing-saw. Pt/Ti thin mem branes adhered to the glass by means of ECR- sputtering are used as a worki ng electrode and a counter electrode. Porous silicon of 160 mum in thicknes s, which had systematic phi 30 mum micro-pores with a pitch of 100 mum, by means of the DeepRIE, was used as a gas-permeable membrane. It was stored i n the vapor of 1,1,1,3,3,3-hexamethyldisilazane to obtain a water-repellent surface for 24 hours, and adhered to the sensor body using a silicone adhe sive. The size of sensor body was 5 x 5 x 3 mm. A MBr (M: alkaline metal) s olution as an electrolyte was injected to the sensor body adhered on a TO-8 package. The linear calibration curve and correlation factor in the concen trating range from 0 to 0.5 ppmCl(2) was I = - 16.886C - 1.195 (nA) and 0.9 98, respectively. The lower detection limit was 0.1 ppm. The 50% response t ime and the 90% recovery time were within 10 s. and several minutes, respec tively. The reproducibility for 2 ppm was the deviation of the sensor signa ls within +/- 1 nA. This miniaturized EC chlorine sensor showed good perfor mances.