Open Access Conference Proceedings

In this contribution, the deposition of tin oxide thin films and the resulting layer properties are investigated. An atmospheric pressure PECVD process using a non-thermal plasma jet was applied, creating the coatings on silicon and glass slides. For a highly reactive oxygen atmosphere, the plasma process was driven with air as working gas. The precursor substance tetra-n-butyltin was provided as an aerosol towards the active plasma zone and is further converted to form the ~100 nm thin layers. Structural, electrical and gas sensing properties were determined of the undoped SnOx layers, deposited at substrate temperatures between 20°C and 500°C.With increasing substrate temperature a decrease in film thickness and roughness of the films could be observed. In general, the films consists of a dense part near the substrate surface and a more porous structure on top. At 300 °C the lowest electrical resistivity with about 7.2 × 10-2 Ωcm occurs in 4-point probe measurements. Experiments for the gas sensing characteristics revealed an electrical response to different atmospheres (water vapour, aqueous ammonia solution) already at elevated measuring temperatures of 150°C. Ammonia concentrations until 25% were tested. The thin films are showing distinct properties in gas selectivity between the changing atmospheres, gas sensitivity during ammonia interaction as well as recurring reversibility after a surface recovery step with pressurized air. So, tin oxide coatings created by atmospheric pressure PECVD are showing already in its undoped state and without further layer post-treatments high application potential.

Keywords: Atmospheric pressure PECVD, plasma jet, tin oxide, transparent conductive oxide (TCO), gas sensor