High leakage current and threshold voltage shift(ΔVth) are demerits of a-Si:H TFT. These characteristics are influenced by gate insulator and active layer film quality, surface roughness, and process conditions. The purpose of this investigation is to improve off current(Ioff) and ΔVth characteristics. Nitrogen-rich deposition condition was applied to gate insulator, and hydrogen-rich deposition condition was applied to active layer to reduce electron trap site and improve film density. I(off) improved from 1.01 pA to 0.18 pA at 65 ℃, and ΔV(th) improved from -1.89 V to 1.22 V.