Hot Carrier Effect in Self-Aligned In-Ga-Zn-O Thin-Film Transistors with Short Channel Length

Abstract

This study examines the impact of channel length (L) on the performance of amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors with self-aligned structures. The negative threshold voltage (V-TH) displacement for IGZO transistors with increasing drain voltage (V-DS) becomes severe with decreasing L from 10 to 2 mu m. The V-DS-dependent negative V-TH shift can be mitigated by increasing the oxygen flow rate (OFR) ratio during a-IGZO preparation from 40% to 80%, which suppresses the number of oxygen vacancy defects near the n+ drain of the a-IGZO region. In contrast, the hot carrier stress (HCS)-induced degradation in terms of the threshold voltage was accelerated for devices with increasing OFR ratio, presumably due to the creation of excessive oxygen-originated defects. The rationale for these observations is discussed with regard to the increasing local electric field near the drain junction, which was calculated by technology computer-aided design (TCAD) simulation. We concluded that an acceptable compromise between short channel effect and HCS-induced degradations can be achieved by choosing an intermediate OFR ratio of 64%.