Low temperature processes and high quality gate insulator are very important for organic thin film transistors (OTFTs). We utilized atmospheric pressure plasma jet (APPJ) to deposit silicon oxide as gate insulator of OTFTs at low temperature. We found carrier gas's flow rate would influence the deposition mechanism which lead to influence surface roughness and film quality. Leakage current density of our proposed silicon oxide was about 2.53E-8 A/cm
at 0.5 MV/cm. Our proposed OTFTs shows a low subthreshold swing of only 700 mV/dec., a low threshold voltage of -0.8 V, a low operation voltage of -2 V. The low-voltage OTFTs would reduce the power consummation of flexible display.