Improving Surface Structures of Al-Doped Zinc Oxide Thin Films to Apply in CO Gas-Sensing Property by Designing Processes Through RF Magnetron Sputtering

Because of their favorable sensitivity in chemical environments, zinc oxide (ZnO) materials are widely used in gas sensing. This study performed deposition of aluminum-doped ZnO nanofilms through radiofrequency magnetron sputtering. Oxygen flux and power during sputtering were altered to adjust the films' surface morphology, produce a highly porous structure, and increase sensitivity to carbon monoxide. For sensitivity testing, the film was encapsulated in a gas sensor by sputtering copper electrodes and fixing wires to the copper electrodes with silver glue. Field-emission scanning electron microscopy and x-ray diffractometry were used to analyze the films' surface microstructure and crystallinity. Ultraviolet–visible spectrophotometry was used to measure the film surface's light absorbance and porousness. Sensitivity to carbon monoxide (CO) under lower temperatures was tested using our gas-sensing circuitry, which involves a Keithley 2400 source meter used to monitor changes in impedance in real time. The results demonstrate that an oxygen flux of 10 sccm and sputtering power of 175 W produced films with favorable surface morphology and increased the maximum CO response value. Thus, the surface structure of the films can be adjusted by optimizing sputtering parameters, which increases sensitivity to CO gas reactions. This study demonstrated the films' potential application in gas sensors.