Study of activation energy and humidity sensing application of nanostructured Cu-doped ZnO thin films

In this paper we have reported analysis on activation energy and humidity sensing studies of Cu-doped ZnO thin films. Thin Films of undoped and Cu-doped ZnO nanomaterials were prepared. Undoped and Cu-doped ZnO thin films annealed at 600 °C showed the best results with sensitivity of 20.63 MΩ/%RH and 39.14 MΩ/%RH respectively in the 15–95% RH range. Low value of activation energy indicated that this sensing element had low operating temperature and could be used at room temperature. Other parameters like response time, recovery time, hysteresis, and aging effects were also studied. The crystallite size for the sensing element of pure ZnO annealed at 600 °C calculated from Scherrer’s formula is in the 24–38 nm range. For the sensing element of 7% Cu doped ZnO the range of crystallite size is 25–41 nm. The average grain size as measured from SEM micrograph for 7% Cu doped ZnO and pure ZnO sensing elements were 36 and 42 nm, respectively.