High-Performance Thin-Film Transistors with an Atomic-Layer-Deposited Indium Gallium Oxide Channel: A Cation Combinatorial Approach

Abstract

The effect of gallium (Ga) concentration on the structural evolution of atomic-layer-deposited indium gallium oxide (IGO) (In1–x Ga x O) films as high-mobility n-channel semiconducting layers was investigated. Different Ga concentrations in 10–13 nm thick In1–x Ga x O films allowed versatile phase structures to be amorphous, highly ordered, and randomly oriented crystalline by thermal annealing at either 400 or 700 °C for 1 h. Heavy Ga concentrations above 34 atom % caused a phase transformation from a polycrystalline bixbyite to an amorphous IGO film at 400 °C, while proper Ga concentration produced a highly ordered bixbyite crystal structure at 700 °C. The resulting highly ordered In0.66Ga0.34O film show unexpectedly high carrier mobility (μFE) values of 60.7 ± 1.0 cm2 V–1 s–1, a threshold voltage (V TH) of −0.80 ± 0.05 V, and an I ON/OFF ratio of 5.1 × 109 in field-effect transistors (FETs). In contrast, the FETs having polycrystalline In1–x Ga x O films with higher In fractions (x = 0.18 and 0.25) showed reasonable μFE values of 40.3 ± 1.6 and 31.5 ± 2.4 cm2 V–1 s–1, V TH of −0.64 ± 0.40 and −0.43 ± 0.06 V, and I ON/OFF ratios of 2.5 × 109 and 1.4 × 109, respectively. The resulting superior performance of the In0.66Ga0.34O-film-based FET was attributed to a morphology having fewer grain boundaries, with higher mass densification and lower oxygen vacancy defect density of the bixbyite crystallites. Also, the In0.66Ga0.34O transistor was found to show the most stable behavior against an external gate bias stress.

High-mobility hydrogenated polycrystalline In2O3 (In2O3:H) thin-film transistors

“…Recently, crystalline OSs have been proposed to enhance the carrier mobility because the disorder-induced subgap states can be suppressed via lattice ordering. Yang et al reported a μ FE value of 60.7 cm 2 V −1 s −1 for a TFT obtained using polycrystalline In–Ga–O annealed at 700 °C 31 . Although high annealing temperatures result in better electrical properties of the oxide active channel layer, such high temperatures are unsuitable for device application on glass or plastic substrates.…”

Recent progress and perspectives on atomic‐layer‐deposited semiconducting oxides for transistor applications

“…Although binary metal‐oxide channel systems offer simple composition and processing, securing the high mobility and controllability of V TH and excellent I ON/OFF ratio simultaneously can be difficult. To overcome this limit of binary oxides, multi‐component oxide materials such as ternary (indium gallium oxide [IGO], 55–57 indium zinc oxide [IZO], 58–60 and zinc tin oxide [ZTO] 61,62 ) and quaternary oxide (indium gallium zinc oxide [IGZO], 63–68 and indium zinc tin oxide [IZTO] 69,70 ) species have been examined as active‐material candidates for high‐performance TFTs. The design rationale should balance mobility enhancement and carrier suppression.…”

“…Ternary IGO is an interesting active system because of its high carrier mobility and controllable microstructure, depending on the ratio between indium and gallium. Yang et al 56 described a cation combinatorial approach to creating IGO thin films by varying the ALD super‐cycle. Discernible structures in amorphous, polycrystalline, and highly aligned crystalline phases were obtained by adjusting the gallium fraction during ALD growth of IGO films and subsequent post‐annealing at 700°C, as shown in Figure 6A.…”

“…(C) Representative transfer characteristic of In 0.66 Ga 0.34 O TFT annealed at 700°C. Reprinted with permission 56 . Copyright 2020, American Chemical Society.…”

Significance of Pairing In/Ga Precursor Structures on PEALD InGaOx Thin-Film Transistor

“…ALD IGO has the potential for both high mobility due to the In 5s orbital and high stability from suppression of oxygen deficiency. ,, In previous research on ALD IGO, Sheng et al reported the surface reaction mechanisms of IGO using different precursor–reactant dose sequences; TFT performance was optimized (9.45 cm 2 /(V s)) when a 3InO–GaO sequence was used. Yang et al investigated the ZnO/IGO heterojunction via ALD and achieved high mobility (63.2 cm 2 /(V s)) using ZnO/IGO TFTs …”