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 ( ${V}_{\text{TH}}$ ) displacement for IGZO transistors with increasing drain voltage ( ${V}_{\text{DS}}$ ) becomes severe with decreasing ${L}$ from 10 to $2~ \mu \text{m}$ . The $V_{\text{DS}}$ -dependent negative $V_{\text{TH}}$ 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%.