ECR thermal oxide has been grown by use of ECR plasma and applied to low-temperature polycrystalline thin film transistors. Actually, the LPCVD on ECR thermal oxiJe structure was used as the gate insulating layer. The characterization of this two layer oxide showed the leakage current of $1.8\times10^{-8}A/cm^2$ and breakdown field of 8MV/cm. The fixed charge at the interface was $5.7\times10^{11}q/cm^2$ and the interface trap state density($D_{it}$) was $1.1\times10^{11}cm^{-2}eV^{-1}$. Poly-Si TFT's with the above gate oxide had the subthreshold slope of 1.21V/dec and the maximum on/off current ratio of them was $4.3\times10^6$. The surface mobilty was as good as 12.3$cm^2$/V S.
