PERFORMANCE AND DETECTION MECHANISM OF A NEW CLASS OF CATALYST (PD, PT, OR AG)-ADSORPTIVE OXIDE (SNOX OR ZNO)-INSULATOR-SEMICONDUCTOR GAS SENSORS

A new class of gas-sensitive capacitors utilizing a catalytic gate-adsorptive oxide-insulator-semiconduction (CAIS) structure has been developed. The incorporation of Pd, Pt, or Ag as the catalytic gate, and SnOx or ZnO as the gas-adsorptive oxide with the silicon MIS capacitor enhances the detection of O-2, CO, and H-2 at a relatively low temperature. Device performances in terms of sensitivity, response rate, response time, repeatability, and stability are presented. A detection model based on adsorption/reduction of chemisorbed oxygen ions at the catalytic metal-adsorptive oxide interface is proposed for the sensing mechanism. Fundamental analytical relations are established to explain the change in V-fb characteristics in terms of the gas reaction kinetics. Analysis of the experimental data using the proposed reaction kinetics has confirmed that the detection of O-2 is attributed to the dissociation and chemisorption of O-2 molecules at the catalyst-adsorptive oxide interface in the form of negatively charged oxygen ions. The detection of CO is mainly through the reaction of CO with the chemisorbed oxygen ions. The detection mechanism of H-2 is due to the hydrogen dipoles in addition to the reduction of chemisorbed oxygen at the interface.