Research On Sensor Response Characters Of SnO₂ Thin Films Prepared By Sol-Gel Method

Tin dioxide, a sort of n-type semiconductor material, is widely used to fabricate gas sensor devices. Domestic and foreign research progresses in SnO₂ thin films were reviewed in this paper. Sol-Gel dip-coating method was adopted because of its advantages, such as low cost and easy deposition of thin films.Firstly, pure SnO₂ thin films were fabricated. The relationship between the thickness and sensitivity was studied. In order to analyze the results, gas diffusion model was employed. After that, the relationship between resistance of thin films and gas concentration was discussed and the boundary barrier control model was used to explain the results. At last the boundary barrier control model and heterojunction model were coalesced to deduce the relationship between the donor concentration and sensor responses. The reason why Sb doping decreased the sensitivity was given after the deduction.Sol-gel dip coating technique was employed to prepare Cu-doped SnO₂ thin films, which were able to detect H2S gas at room temperature with high sensitivity and revealed fast response characteristics. The highest sensor response (the ratio of resistance in air versus in H2S) was 3648 under H2S concentration of 68.5 ppm at room temperature. Recoverability of the thin films appeared when the temperature raised to 50℃. The films were analyzed by means of XRD and the dried gel powder was studied by TG-DTA test. Influences of sintering temperature and doping level on the H2S response were discussed. The average grain size of the SnO₂ was about 25 nm.The method of preparing SnO₂ thin films which used to detect CO was investigated preliminarily. The sol-gel technique and solid reaction process were used to get PdO and In2O3 doped SnO₂ thin films. Spillover and Femi energy control models were employed to analyze the results.