Nano-crystalline Cu-doped ZnO thin film gas sensor for CO

A Cu-doped ZnO (CZO) film was prepared on a glass substrate by co-sputtering using ZnO and Cu targets. The CZO film possessed a columnar structure consisting of small crystals with an average grain size of around 5 nm. The CO-sensing properties of the CZO film were tested at operating temperatures of 150, 300, 350 and 400 °C. It was found that CZO-based sensor exhibited the highest sensitivity to CO at 350 °C. An obvious change in resistance of the CZO film was also observed when the sensor was exposed to 6 ppm CO at 150 °C. The sensing mechanism of the nano-structured CZO sensor is discussed.