Thin film transistors (TFTs) with a ZnO channel layer deposited by atmospheric pressure plasma jet (APPJ) were demonstrated. ZnO channel layers were fabricated with a non-vacuum and low-temperature process (100°C). The effects of different carrier gases (nitrogen gas and compressed dry air) and channel thickness on the characteristics of ZnO TFTs were investigated. Reactive oxygen species can effectively repair the oxygen vacancies result in a low leakage current. By reducing the channel thickness, the undesired source to drain current flow can be eliminated. By using CDA as a carrier gas and reducing the channel thickness, a subthreshold swing of 3.75 V/decade, a field-effect mobility of 3.49 cm2/Vs and a Ion/Ioff current ratio of 4.08×107 were obtained.