Hot Carrier Effect in Self-Aligned In–Ga–Zn–O Thin-Film Transistors With Short Channel Length
Nuri On, Bo Kyoung Kim, Sueon Lee, Eun Hyun Kim, Jun Hyung Lim, Jae Kyeong Jeong
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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> ) displacement for IGZO transistors with increasing drain voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> ) becomes severe with decreasing L from 10 to 2 μm. The V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> -dependent negative V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> 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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> 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%.