Effects of channel thickness variation on bias stress instability of InGaZnO thin-film transistors

Here, we report on the effects of channel (or active) layer thickness on the bias stress instability of InGaZnO (IGZO) thin-film transistors (TFTs). The investigation on variations of TFT characteristics under the electrical bias stress is very crucial for commercial applications. In this work, the initial electrical characteristics of the tested TFTs with different channel layer thicknesses (40, 50, and 60 nm) are performed. Various gate bias (V-GS) stresses (10, 20, and 30 V) are then applied to the tested TFTs. For all V-GS stresses with different channel layer thickness, the experimentally measured threshold voltage shift (Delta V-th) as a function of stress time is precisely modeled with stretched-exponential function. It is indicated that the Delta V-th is generated by carrier trapping but not defect creation. It is also observed that the Delta V-th shows incremental behavior as the channel layer thickness increases. Thus, it is verified that the increase of total trap states (N-T) and free carriers resulted in the increase of Delta V-th as the channel layer thickness increases. (C) 2011 Elsevier Ltd. All rights reserved.