Gas sensing characteristics of copper phthalocyanine films: effects of film thickness and sensing temperature

Copper phthalocyanine (CuPc) was vacuum-deposited onto gold patterned glass substrate and used for low temperature operation of NO2 sensing. The effects of film thickness, as well as the sensing temperature, on the sensitivity and recovery characteristics of the CuPc film were investigated. The results show that both film thickness and sensing temperature have significant effect to the sensing characteristics. At room temperature operation, the recovery characteristic is satisfactory for the 50 nm film, and it becomes poor as increasing film thickness. Besides, the sensitivity shows little dependence on the film thickness. When the sensing temperature is elevated to 100degreesC, the recovery ratio of the thicker films can be improved satisfactorily, but the sensitivity of thinner films (50, 100 nm) decrease as a result. However, the sensitivity increases notably with increase of film thickness and approaches the maximum value, which is comparable or even superior to that at 25 degreesC, at about 200 nm. The present results indicate that the poor recovery characteristic found in the literature can be improved by reducing the film thickness and NO2 doping period. Besides, to get superior sensing properties, a small film thickness (50 nm) should be controlled for room temperature operation, but a higher thickness (200 nm) is required when the operation is elevated up to 100 degreesC. (C) 2003 Elsevier B.V. All rights reserved.