Chemical Sensors with Catalytic Metal Gates: Switching Behavior and Kinetic Phase Transitions

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Abstract
Rapid transitions in the response of platinum‐based chemical sensors occurring at given hydrogen‐oxygen concentration ratios are explained by kinetic phase transition or switching phenomena on the catalytic metal surface. Below the transition point the response of platinum‐insulator silicon carbide devices is small and above the transition it is large. It is found that the critical ratio depends on the operation temperature and the properties of the device. Three different cases are identified, namely, injection‐, diffusion‐, and reaction‐rate‐determine transition. At sufficiently large temperatures the transition is injection limited and occurs at the stoichiometric ratio of hydrogen and oxygen in the gas mixture. The implications of the experimental observations on the applications of chemical sensors with catalytic sensing layers are discussed.

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