Performance analysis of a new metal-insulator-semiconductor capacitor incorporated with Pt-SnOx catalytic layers for the detection of O2 and CO gases

The integration of the catalytic properties of platinum (Pt) and tin oxide (SnOx) in the Pt-SnOx-Si3N4-SiO2-Si metal-insulator-semiconductor (MIS) capacitor allows the detection of oxygen (O2) and carbon monoxide (CO) gases at a much lower operating temperature than that of the conventional solid-state gas detectors. The operation characteristics of the device for the detection of O2 and CO are described as a function of the gas pressure and temperature ranging from 27 to 100 °C. Repeatability of the device for CO detection in an open air ambient is also presented. A model based on adsorption/reaction of oxygen ions at the Pt-SnOx interface of the MIS capacitor is proposed for oxygen/carbon monoxide detection. The physical and chemical mechanisms responsible for the gas sensing behaviors are discussed. The detection mechanisms explain the device behaviors and account for the following experimental observations and reaction kinetic analysis of the experimental data: (1) the dependence of the reaction kinetics on the square root of the O2 partial pressure, (2) the requirement of oxygen as a constituent of the background gas for CO detection, (3) the inverse proportional relationship of the reaction kinetics to CO partial pressure, and (4) the need of Pt and SnOx as the catalytic layers in the MIS capacitor for gas detection.