MODEL FOR THE OPERATION OF A THIN-FILM SNOX CONDUCTANCE-MODULATION CARBON-MONOXIDE SENSOR
MODEL FOR THE OPERATION OF A THIN-FILM SNOX CONDUCTANCE-MODULATION CARBON-MONOXIDE SENSOR
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DOI：
10.1149/1.2129098
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发表时间：
1979-01-01
影响因子：
3.9
通讯作者：
MARK, P
中科院分区：
文献类型：
--
作者：
WINDISCHMANN, H;MARK, P
The fabrication and operation of a thin-film SnOx conductance modulation CO sensor is described and a microscopic model for its operation is developed. The physical basis of the model comprises the oxidation of CO on the sensor surface by chemisorbed oxygen and the subsequent emission of an electron from the chemisorbed species into the conduction band of the sensor. The model accounts for the following experimental observations:(i) the dependence of the sensor conductance on the square root of the CO partial pressure;(ii) the requirement of oxygen as a constituent of the background gas; and (iii) the existence of a temperature window outside of which the sensor does not function. The model also touches on the selectivity of the sensor for CO in the 1-100 ppm range in a background gas containing oxidizing and reducing constituents.Semiconductor materials whose conductance G is modulated directly by interaction with an active gas have been studied for over 20 years since it was discovered in the 1950's that the reversible chemisorption of reactive gases at the surfaces of certain metals, oxides, and chalcogenides could be accompanied by reversible changes in conductance (1-10). Unlike metal thin films, whose conductance modulation by gas adsorption is small and is caused by changes in the mobility g owing to changes in surface scattering, the conductance changes in the semiconductor materials are large and are caused primarily by changes in the conduction band electron (or valence band hole) concentration brought on by charge exchange with the adsorbed species from the gas phase (10). The conduction band electron concentration n in the semiconductor sensors can vary more or less linearly with pressure P over a range of up to eight decades (9, 10), while variations in~ are generally less than a factor of two over the same pressure range (8, 11). It is this large and reversible variation in conductance with active gas pressure that has made semiconductor ma-
