Sensing properties of copper oxide thin film upon exposure of methane gas in air

Abstract

Application of p-type semiconductor copper oxide thin films as methane gas sensors in air was investigated. A series of copper oxide thin film had been prepared. The thin films were fabricated by using direct current (DC) sputtering technique on corning glass substrates at different deposition time (30 to 180 min. at 30 min. interval) hence different thicknesses of thin films were produced. The target used for the copper oxide thin film growth was metallic copper (99.99% purity). The thin film thicknesses were measured by using surface profiler (Dektak 3). Aluminum comb-like inter digital electrodes were deposited onto each substrate by thermal evaporation technique. Gas sensing characteristics mainly the resistance, sensitivity, response time and recovery time of copper oxide thin films upon exposure of methane gas in air were studied using gas sensing characterization system (GSCS) by varying the operating temperature starting from 100ºc to 300ºc with an increment of 50ºc. The thicknesses of copper oxide thin films were in the range of 178 nm to 513 nm at a deposition rate of 2.20 nm/min. The films resistances were found to increase in the presence of methane gas, and decreased with the presence of synthetic air. The resistances of copper oxide thin films as a function of operating temperature at 100ºc to 300ºc were found to decrease with the increased of operating temperature. Sample s3 with film thickness 274 nm exhibited the highest sensitivity (3.29) for methane at operating temperature of 200ºc with corresponding response time of 108 s and recovery time > 600 s. Whereas, for double array series, a2 (30 + 90 minute) showed the best sensitivity (2.01) with corresponding response time 86 s and recovery time > 600 s at operating temperature of 150ºc. Accordingly, it can be concluded that single sample showed excellent sensitivity compared to double array series. Therefore, single sample was preferable as gas sensor for the detection of methane gas in air.