Record-High-Performance Hydrogenated In-Ga-Zn-O Flexible Schottky Diodes

Unveiling transient current response in bilayer oxide-based physical reservoirs for time-series data analysis

Physical reservoirs employed to map time-series data and analyze extracted features have attracted interest owing to their low training cost and mitigated interconnection complexity. This study reports a physical reservoir based on a bilayer oxide-based dynamic memristor. The proposed device exhibits a nonlinear current response and short-term memory (STM), satisfying the requirements of reservoir computing (RC). These characteristics are validated using a compact model to account for resistive switching (RS) via the dynamic evolution of the internal state variable and the relocation of oxygen vacancies. Mathematically, the transient current response can be quantitatively described according to a simple set of equations to correlate the theoretical framework with experimental results. Furthermore, the device shows significant reliability and ability to distinguish 4-bit inputs and four diverse neural firing patterns. Therefore, this work shows the feasibility of implementing physical reservoirs in hardware and advances the understanding of the dynamic response.

Tailored Self-Assembled Monolayer using Chemical Coupling for Indium-Gallium-Zinc Oxide Thin-Film Transistors: Multifunctional Copper Diffusion Barrier

Controlling the contact properties of a copper (Cu) electrode is an important process for improving the performance of an amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistor (TFT) for high-speed applications, owing to the low resistance-capacitance product constant of Cu. One of the many challenges in Cu application to a-IGZO is inhibiting high diffusivity, which causes degradation in the performance of a-IGZO TFT by forming electron trap states. A self-assembled monolayer (SAM) can perfectly act as a Cu diffusion barrier (DB) and passivation layer that prevents moisture and oxygen, which can deteriorate the TFT on-off performance. However, traditional SAM materials have high contact resistance and low mechanical-adhesion properties. In this study, we demonstrate that tailoring the SAM using the chemical coupling method can enhance the electrical and mechanical properties of a-IGZO TFTs. The doping effects from the dipole moment of the tailored SAMs enhance the electrical properties of a-IGZO TFTs, resulting in a field-effect mobility of 13.87 cm²/V·s, an on-off ratio above 10⁷, and a low contact resistance of 612 Ω. Because of the high electrical performance of tailored SAMs, they function as a Cu DB and a passivation layer. Moreover, a selectively tailored functional group can improve the adhesion properties between Cu and a-IGZO. These multifunctionally tailored SAMs can be a promising candidate for a very thin Cu DB in future electronic technology.

Conduction Mechanism Analysis of Abrupt- and Gradual-Switching InGaZnO Memristors

In this work, two types of InGaZnO (IGZO) memristors were fabricated to confirm the conduction mechanism and degradation characteristics of memristors with different electrode materials. The IGZO memristor exhibits abrupt switching characteristics with the Pd electrode owing to the formation and destruction of conductive filaments but shows gradual switching characteristics with the p-type Si electrode according to the amount of generated oxygen vacancy. The electrical characteristics and conduction mechanisms of the device are analyzed using an energy band diagram and experimentally verified with random telegraph noise characteristics confirming the trap effects on the device conduction.

Influence of Grain Boundary Scattering on the Field-Effect Mobility of Solid-Phase Crystallized Hydrogenated Polycrystalline In2O3 (In2O3:H)

Hydrogenated polycrystalline In₂O₃ (In₂O₃:H) thin-film transistors (TFTs) fabricated via the low-temperature solid-phase crystallization (SPC) process with a field-effect mobility (μ_FE) exceeding 100 cm² V^-1 s^-1 are promising candidates for future electronics applications. In this study, we investigated the effects of the SPC temperature of Ar + O₂ + H₂-sputtered In₂O₃:H films on the electron transport properties of In₂O₃:H TFTs. The In₂O₃:H TFT with an SPC temperature of 300 °C exhibited the best performance, having the largest µ_FE of 139.2 cm² V^-1 s^-1. In contrast, the µ_FE was slightly degraded with increasing SPC temperature (400 °C and higher). Extended X-ray absorption fine structure analysis revealed that the medium-range ordering in the In₂O₃:H network was further improved by annealing up to 600 °C, while a large amount of H₂O was desorbed from the In₂O₃:H films at SPC temperatures above 400 °C, resulting in the creation of defects at grain boundaries. The threshold temperature of H₂O desorption corresponded well with the carrier transport properties; the µ_FE of the TFTs started to deteriorate at SPC temperatures of 400 °C and higher. Thus, it was suggested that the hydrogen remaining in the film after SPC plays an important role in the passivation of electron traps, especially for grain boundaries, resulting in an enhancement of the µ_FE of In₂O₃:H TFTs.

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

Oxide semiconductors have been extensively studied as active channel layers of thin-film transistors (TFTs) for electronic applications. However, the field-effect mobility (μFE) of oxide TFTs is not sufficiently high to compete with that of low-temperature-processed polycrystalline-Si TFTs (50–100 cm2V−1s−1). Here, we propose a simple process to obtain high-performance TFTs, namely hydrogenated polycrystalline In2O3 (In2O3:H) TFTs grown via the low-temperature solid-phase crystallization (SPC) process. In2O3:H TFTs fabricated at 300 °C exhibit superior switching properties with µFE = 139.2 cm2V−1s−1, a subthreshold swing of 0.19 Vdec−1, and a threshold voltage of 0.2 V. The hydrogen introduced during sputter deposition plays an important role in enlarging the grain size and decreasing the subgap defects in SPC-prepared In2O3:H. The proposed method does not require any additional expensive equipment and/or change in the conventional oxide TFT fabrication process. We believe these SPC-grown In2O3:H TFTs have a great potential for use in future transparent or flexible electronics applications.

Defect Passivation and Carrier Reduction Mechanisms in Hydrogen-Doped In-Ga-Zn-O (IGZO:H) Films upon Low-Temperature Annealing for Flexible Device Applications

Low-temperature activation of oxide semiconductor materials such as In-Ga-Zn-O (IGZO) is a key approach for their utilization in flexible devices. We previously reported that the activation temperature can be reduced to 150 °C by hydrogen-doped IGZO (IGZO:H), demonstrating a strong potential of this approach. In this paper, we investigated the mechanism for reducing the activation temperature of the IGZO:H films. In situ Hall measurements revealed that oxygen diffusion from annealing ambient into the conventional Ar/O2-sputtered IGZO film was observed at >240 °C. Moreover, the temperature at which the oxygen diffusion starts into the film significantly decreased to 100 °C for the IGZO:H film deposited at hydrogen gas flow ratio (R[H2]) of 8%. Hard X-ray photoelectron spectroscopy indicated that the near Fermi level (EF) defects in the IGZO:H film after the 150 °C annealing decreased in comparison to that in the conventional IGZO film after 300 °C annealing. The oxygen diffusion into the film during annealing plays an important role for reducing oxygen vacancies and subgap states especially for near EF. X-ray reflectometry analysis revealed that the film density of the IGZO:H decreased with an increase in R[H2] which would be the possible cause for facilitating the O diffusion at low temperature.

Nondegenerate Polycrystalline Hydrogen-Doped Indium Oxide (InOx:H) Thin Films Formed by Low-Temperature Solid-Phase Crystallization for Thin Film Transistors

We successfully demonstrated a transition from a metallic InO_x film into a nondegenerate semiconductor InO_x:H film. A hydrogen-doped amorphous InO_x:H (a-InO_x:H) film, which was deposited by sputtering in Ar, O₂, and H₂ gases, could be converted into a polycrystalline InO_x:H (poly-InO_x:H) film by low-temperature (250 °C) solid-phase crystallization (SPC). Hall mobility increased from 49.9 cm²V^-1s^-1 for an a-InO_x:H film to 77.2 cm²V^-1s^-1 for a poly-InO_x:H film. Furthermore, the carrier density of a poly-InO_x:H film could be reduced by SPC in air to as low as 2.4 × 10¹⁷ cm^-3, which was below the metal-insulator transition (MIT) threshold. The thin film transistor (TFT) with a metallic poly-InO_x channel did not show any switching properties. In contrast, that with a 50 nm thick nondegenerate poly-InO_x:H channel could be fully depleted by a gate electric field. For the InO_x:H TFTs with a channel carrier density close to the MIT point, maximum and average field effect mobility (μ_FE) values of 125.7 and 84.7 cm²V^-1s^-1 were obtained, respectively. We believe that a nondegenerate poly-InO_x:H film has great potential for boosting the μ_FE of oxide TFTs.