The effects of the volume ratio of ammonia to silane gas($R=NH_3/SiH_4$) in a-$SiN_x$:H gate insulator have been investigated. R was 4, 7.5,15,30 and 60. The field effect mobility and ON-currents decrease with R due to the interface defect states near the a - Si:H/a-$SiN_x$:H interface. The threshold voltage shift (under positive bias) is due to electron trapping in the localized states of a - $SiN_x$:H and the deep states near the a - Si:H/a-$SiN_x$:H interface. Temperature dependent current voltage (I-V) characteristics were measured from-185℃ to 124℃. Transport mechanism is explained by the extended state conduction and nearest-neighbor (n-n) hopping. Threshold voltage shift is discussed by charge trapping and flat band voltage shift in high and low temperature region.
