A Model for the Operation of a Thin‐Film SnO_x Conductance‐Modulation Carbon Monoxide Sensor

The fabrication and operation of a thin‐film conductance modulation sensor is described and a microscopic model for its operation is developed. The physical basis of the model comprises the oxidation of 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 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 in the 1–100 ppm range in a background gas containing oxidizing and reducing constituents.