Source-drain contact impacts on electrical performances and low frequency noise of InZnO thin-film transistors down to 7 K

Source-drain contacts seriously affect low frequency noise (LFN) in amorphous IZO (a-IZO) thin-film transistors with bilayer ITO/Mo electrodes at cryogenic temperatures. In the range of 7-300 K, electrical and LFN performances of devices are measured, and the temperature dependence of channel resistances (R-ch) and contact resistances (R-sd) is also analyzed. The carrier transport transition both occurs in a-IZO channels at 80 K and in ITO/Mo electrodes at 100 K, which causes the variation in R-sd and R-ch. Below 80 K, the variable range hopping conduction dominates in the channels and contacts with R-sd/R-ch ratio > 1. The LFN measured results indicate that the noise is contact-dominated. At higher temperatures above 120 K, the band conduction dominates in the channel, with R-sd/R-ch ratio < 1, and the noise is channel-dominated. The main mechanism of noise transfers from the mobility fluctuation to the carrier number fluctuation. We consider that the contribution of contact noise to total LFN is determined by the R-sd/R-ch ratio. This work provides comments for the selection of electrode materials in devices applied to cryogenic integration circuits.