Localization effect of a current-path in amorphous In-Ga-Zn-O thin film transistors with a highly doped buried-layer

The highly-doped buried layer (carrier concentration of ∼ 1019 cm-3) in an amorphous indium-gallium-zinc oxide (a-IGZO) channel layer of thin film transistor (TFT) led to dramatic improvements in the performance and prolonged bias-stability without any high temperature treatment. These improvements are associated with the enhancement in density-of-states and carrier transport. The channel layer is composed of Ga-doped ZnO (GZO) and a-IGZO layers. Measurements performed on GZO-buried a-IGZO (GB-IGZO) TFTs indicate enhanced n-channel active layer characteristics, such as Vth, μFE, Ioff, Ion/off ratio and S.S, which were enhanced to 1.2 V, 10.04 cm2/V.s, ∼ 10-13A, ∼ 107 and 0.93 V/decade, respectively. From the result of simulation, a current path was well defined through the surface of oxide active layer especially in GB-IGZO TFT case because the highly-doped buried layer plays the critical role of supplying sufficient negative charge density to compensate the amount of positive charge induced by the increasing gate voltage. The mechanism underlying the high performance and good stability is found to be the localization effect of a current path due to a highly-doped buried layer, which also effectively screens the oxide bulk and/or back interface trap-induced bias temperature instability.