High-Performance Indium Gallium Tin Oxide Transistors with an Al₂O₃ Gate Insulator Deposited by Atomic Layer Deposition at a Low Temperature of 150 °C: Roles of Hydrogen and Excess Oxygen in the Al₂O₃ Dielectric Film

Abstract

In this work, high-performance amorphous In0.75Ga0.23Sn0.02O (a-IGTO) transistors with an atomic layer-deposited Al2O3 dielectric layer were fabricated at a maximum processing temperature of 150 °C. Hydrogen (H) and excess oxygen (Oi) in the Al2O3 film, which was controlled by adjusting the oxygen radical density (PO2: flow rate of O2/[Ar+O2]) in the radio-frequency (rf) plasma during ALD growth of Al2O3, significantly affected the performance and stability of the resulting IGTO transistors. The concentrations of H and Oi in Al2O3/IGTO stacks according to PO2 were characterized by secondary ion mass spectroscopy, X-ray photoelectron spectroscopy, hard X-ray photoemission spectroscopy, and thermal desorption spectroscopy. The high concentration of H at a low PO2 of 2.5% caused heavy electron doping in the underlying IGTO during thermal annealing at 150 °C, leading to a conductive behavior in the resulting transistor without modulation capability. In contrast, a high PO2 condition of 20% introduced O2 molecules (or Oi) into the Al2O3 film, which negatively impacted the carrier mobility and caused anomalous photo-bias instability in the IGTO transistor. Through in-depth understanding of how to manipulate H and Oi in Al2O3 by controlling the PO2, we fabricated high-performance IGTO transistors with a high field-effect mobility (μFE) of 58.8 cm2/Vs, subthreshold gate swing (SS) of 0.12 V/decade, threshold voltage (V TH) of 0.5 V, and I ON/OFF ratio of ∼109 even at the maximum processing temperature of 150 °C. Simultaneously, the optimized devices were resistant to exposure to external positive gate bias stress (PBS) and negative bias stress (NBS) for 3600 s, where the V TH shifts for exposure to PBS and NBS for this duration were 0.1 V and −0.15 V, respectively.

Near-Ideal Top-Gate Controllability of InGaZnO Thin-Film Transistors by Suppressing Interface Defects with an Ultrathin Atomic Layer Deposited Gate Insulator

“…The bias instabilities of AOS TFT are usually related to the charge trapping into GI or at the AOS/GI interface . In the fabricated AlO x -gated a-IGZO TFTs, some deep states of interface Vo defects may be ionized into shallow-state V O 2+ and release electrons under NBS, , as schematically illustrated in Figure c. The nature relaxation of V O 2+ back into neutral V O takes quite a long time, resulting in the negative Δ V th .…”

Structural, Optical, and Dielectric Properties of Ion-Conducting LiAlO2 Thin Films Produced by Reactive Magnetron Co-sputtering

“…According to previous reports, in the case of thicker dielectric layers, a high capacitance value can be achieved without significant leakage current . There are many metal oxides with high dielectric constants, such as Ta 2 O 5 , TiO 2 , Al 2 O 3 , HfO 2 , ZrO 2 , Y 2 O 3 , and SrTiO 3 , which are used in the electronic industry. In the case of metal oxides, the dielectric constant is inversely related to the band gap energy ( E g ).…”

Threshold-Voltage Extraction Methods for Atomically Deposited Disordered ZnO Thin-Film Transistors

“…However, oxide-semiconductor-based thin-film transistors (TFTs) suffer from severe threshold shifts during operation; therefore, compensation circuits are generally incorporated in their applications [5,6]. The threshold voltage (V th ) of TFTs is a gate voltage required to turn the devices on and is estimated using several methods, including a commonly used linear fitting method [7,8], a field-effect mobility derivation method [9], and a constant-current method [10]. However, the definition of the threshold voltage of TFTs is ambiguous.…”