Metal Oxide Gas Sensors Based on ZnO Thin Films: A Review of Synthesis, Mechanisms, and Sensing Parameters

Abstract

Efficient air quality monitoring necessitates sensors capable of detecting gaseous pollutants at extremely low concentrations, reaching parts per billion (ppb) and parts per trillion (ppt) levels. These sensors must demonstrate high sensitivity, selectivity, and rapid response/recovery times. Metal oxide semiconductor (MOS) sensors, particularly those employing Zinc Oxide (ZnO), hold significant promise due to their cost-effective manufacturing processes and versatility in detecting various target gases. MOS sensors function by adsorbing target gas molecules onto their surface, leading to electron capture from the conduction band and consequent changes in conductivity.This review synthesizes the latest experimental insights into Metal Oxide gas sensors, focusing prominently on Zinc Oxide (ZnO) thin films. Sensitivity enhancement strategies involve nanostructuring MOS materials to augment porosity and surface-to-volume ratio, while selectivity can be fine-tuned through chemical composition modifications. The paper critically assesses diverse techniques for nanostructuring MOS materials using chemiresistive elements and elucidates how these techniques contribute to tailoring the desired characteristics of gas sensors.