Electrical and gas-sensitive properties of a resistive thin-film sensor based on tin dioxide
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ICS OF SEMICONDUCTOR DEVICES
Electrical and Gas-Sensitive Properties of a Resistive Thin-Film Sensor Based on Tin Dioxide O. V. Anisimova^, V. I. Gamanb, N. K. Maksimovaa, S. M. Mazalova, and E. V. Chernikova aKuznetsov
Siberian Physicotechnical Institute at the Tomsk State University, Tomsk, 634050 Russia ^e-mail: [email protected] bTomsk State University, Tomsk, 634050 Russia Submitted September 29, 2005; accepted for publication November 7, 2005
Abstract—A simple model of a resistive thin-film sensor is used to derive an analytic expression that describes the dependences of the response to the effect of reducing gas on temperature, partial gas pressure, the concentration of donor impurity in the SnO2 film, and the duration of the exposure to gas. An analysis of experimental data showed that the processes of adsorption and desorption of H2 molecules at T < 510 K are mainly controlled – by adsorption centers occupied by oxygen in the form of O 2 , while the centers with O– control these processes at T > 563 K. At T ≥ 510 K, the methane molecules interact with the centers occupied by O–. The desorptionactivation energies are determined in a wide temperature range using the data on the time dependences of the response. This energy equals 0.36 eV for hydrogen at T < 510 K. At T > 563 K for hydrogen and T > 510 K for methane, the desorption-activation energy is equal to 1.3 eV. The adsorption-activation energy is equal to 2.5 eV for methane. PACS numbers: 07.07.Df, 73.50.Dn, 68.43.Mn DOI: 10.1134/S1063782606060170
1. INTRODUCTION The potential of using thin-film resistive sensors based on tin dioxide (SnO2) is based on their high sensitivity to the effect of a number of reducing gases (hydrogen, methane, carbon oxide, and so on) and the fairly fast response. Possible mechanisms of the effect of reducing gases on the electrical conductivity of the sensors based on ceramic SnO2 and, partially, of those based on thin films obtained by RF sputtering were analyzed in [1, 2]. In order to obtain more detailed and complete information about these mechanisms, it is necessary to undertake further studies of the temperature, concentration, and time dependences of the sensor’s response. Previously, we performed such complex studies for thin-film sensors exposed to carbon monoxide in a wide range of both temperatures of the SnO2 film and gas concentrations [3–5]. There is a much smaller volume of data in the publications concerned with the interaction of sensors with hydrogen and methane. The mechanisms of the transient process of establishing the highest possible response of the sensor after the onset of exposure to a gas have been studied the least adequately. In this study, we use the simplest model of a thinfilm resistive sensor to derive the expression for the response to the exposure to a reducing gas. This expression was used to analyze the experimental dependences of the response on the partial pressure of the reducing gas (hydrogen and methane), the temperature of the
SnO2 film, and the time elapsed since the beginning
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