A Low Power Bridge-Type Gas Sensor With Enhanced Sensitivity to Ethanol by Sandwiched ZnO/Au/ZnO Film Sputtered in O₂ Atmosphere

Abstract

This paper proposes a ZnO-based gas sensor fabricated entirely by micro-electro-mechanical system (MEMS) process. The gas sensor is based on a narrow bridge-type micro-heater, which achieve ultra-low static power consumption. A physical vapor deposition (PVD) sputtering method was employed in depositing n-type ZnO-based sensing materials on this heater. Ethanol, a common VOC gas was selected as a choice of gas to be tested, and to enhance the performance of ethanol, a thin layer of metal additive Au is buried between two ZnO film layers in an atmosphere of O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> to form a “sandwiched” ZnO/Au/ZnO structure. The morphology and microstructure of the sensors are observed by SEM and AFM, its crystal structure is characterized by XRD, and its surface characteristic is analyzed by XPS. The results indicate that the “sandwiched” sensing layer shows higher response to ethanol compared with single-layer ZnO, and 15 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{R}_{\text{air}} /\text{R}_{\text{gas}}$ </tex-math></inline-formula> ) was achieved as the best sensitivity to 100 ppm ethanol with the sensor consuming a low power consumption of just 12.17 mW