High-Performance Indium-Based Oxide Transistors with Multiple Channels Through Nanolaminate Structure Fabricated by Plasma-Enhanced Atomic Layer Deposition
Min Hoe Cho, Cheol Hee Choi, Min Jae Kim, Jae Seok Hur, Taikyu Kim, Jae Kyeong Jeong
Abstract
An atomic-layer-deposited oxide nanolaminate (NL) structure with 3 dyads where a single dyad consists of a 2-nm-thick confinement layer (CL) (In 0.84 Ga 0.16 O or In 0.75 Zn 0.25 O), and a barrier layer (BL) (Ga 2 O 3 ) was designed to obtain superior electrical performance in thin-film transistors (TFTs). Within the oxide NL structure, multiple-channel formation was demonstrated by a pile-up of free charge carriers near CL/BL heterointerfaces in the form of the so-called quasi-two-dimensional electron gas (q2DEG), which leads to an outstanding carrier mobility (μ FE ) with band-like transport, steep gate swing ( SS ), and positive threshold voltage ( V TH ) behavior. Furthermore, reduced trap densities in oxide NL compared to those of conventional oxide single-layer TFTs ensures excellent stabilities. The optimized device with the In 0.75 Zn 0.25 O/Ga 2 O 3 NL TFT showed remarkable electrical performance: μ FE of 77.1 ± 0.67 cm 2 /(V s), V TH of 0.70 ± 0.25 V, SS of 100 ± 10 mV/dec, and I ON/OFF of 8.9 × 10 9 with a low operation voltage range of ≤2 V and excellent stabilities (Δ V TH of +0.27, −0.55, and +0.04 V for PBTS, NBIS, and CCS, respectively). Based on in-depth analyses, the enhanced electrical performance is attributed to the presence of q2DEG formed at carefully engineered CL/BL heterointerfaces. Technological computer-aided design (TCAD) simulation was performed theoretically to confirm the formation of multiple channels in an oxide NL structure where the formation of a q2DEG was verified in the vicinity of CL/BL heterointerfaces. These results clearly demonstrate that introducing a heterojunction or NL structure concept into this atomic layer deposition (ALD)-derived oxide semiconductor system is a very effective strategy to boost the carrier-transporting properties and improve the photobias stability in the resulting TFTs.