Electrical impedance analysis of ZnO thin films for ammonia gas sensors

R, Mariappan ; S, Dinagaran ; P, Srinivasan ; S, Vijayakumar

Abstract

The electrical impedance analysis of the ZnO films has been performed using complex impedance spectroscopy in the frequency range from 100 Hz to 1 MHz with temperature change from 70 to 175℃. Combined impedance and modulus plots have been used to analyse the sample behaviour as a function of frequency at different temperatures. Temperature dependence of ac conductivity indicates that the electrical conduction in the material is a thermally activated process. The frequency dependence of the ac conduction activation energy is found to obey a mathematical formula. It is concluded that the conductivity mechanism in the ZnO sensor is controlled by surface reaction. The operating temperature of the ZnO gas sensor is 175℃. The impedance spectrum also exhibited a decreased semicircle radius as the ammonia concentration is increased from 50 to 500 ppm. In addition, the impedance spectrum also exhibited a decreased semicircle radius with the exposure time increase from 0 to 20 min thereafter slightly increased. Impedance spectroscopy analysis has shown that the resistance variation due to grain boundaries significantly contributed to the gas sensor characteristics.

Keyword(s)

ZnO device; Impedance analysis; Ammonia sensor


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