Graphene nanoribbons (GNRs) have recently emerged as promising candidates for channel materials in future nanoelectronic devices due to their exceptional electronic, thermal, and mechanical properties and chemical inertness. However, the adoption of GNRs in commercial technologies is currently hampered by materials science and integration challenges pertaining to synthesis and devices. In this Review, we present an overview of the current status of challenges, recent breakthroughs toward overcoming these challenges, and possible future directions for the field of GNR electronics. We motivate the need for exploration of scalable synthetic techniques that yield atomically precise, placed, registered, and oriented GNRs on CMOS-compatible substrates and stimulate ideas for contact and dielectric engineering to realize experimental performance close to theoretically predicted metrics. We also briefly discuss unconventional device architectures that could be experimentally investigated to harness the maximum potential of GNRs in future spintronic and quantum information technologies.

Materials Science Challenges to Graphene Nanoribbon Electronics.

Ultrahigh-resolution displays for augmented reality (AR) and virtual reality (VR) applications require a novel architecture and process. Atomic-layer deposition (ALD) enables the facile fabrication of indium-gallium zinc oxide (IGZO) thin-film transistors (TFTs) on a substrate with a nonplanar surface due to its excellent step coverage and accurate thickness control. Here, we report all-ALD-derived TFTs using IGZO and HfO2 as the channel layer and gate insulator, respectively. A bilayer IGZO channel structure consisting of a 10 nm base layer (In0.52Ga0.29Zn0.19O) with good stability and a 3 nm boost layer (In0.82Ga0.08Zn0.10O) with extremely high mobility was designed based on a cation combinatorial study of the ALD-derived IGZO system. Reducing the thickness of the HfO2 dielectric film by the ALD process offers high areal capacitance in field-effect transistors, which allows low-voltage drivability and enhanced carrier transport. The intrinsic inferior stability of the HfO2 gate insulator was effectively mitigated by the insertion of an ALD-derived 4 nm Al2O3 interfacial layer between HfO2 and the IGZO film. The optimized bilayer IGZO TFTs with HfO2-based gate insulators exhibited excellent performances with a high field-effect mobility of 74.0 ± 0.91 cm2/(V s), a low subthreshold swing of 0.13 ± 0.01 V/dec, a threshold voltage of 0.20 ± 0.24 V, and an ION/OFF of ∼3.2 × 108 in a low-operation-voltage (≤2 V) range. This promising result was due to the synergic effects of a bilayer IGZO channel and HfO2-based gate insulator with a high permittivity, which were mainly attributed to the effective carrier confinement in the boost layer with high mobility, low free carrier density of the base layer with a low VO concentration, and HfO2-induced high effective capacitance.

Achieving a Low-Voltage, High-Mobility IGZO Transistor through an ALD-Derived Bilayer Channel and a Hafnia-Based Gate Dielectric Stack.

This review aims to provide a technical roadmap and progress update for backplane thin film transistors (TFTs) used in organic light emitting diodes flat panel displays and next-generation flexible...

https://www.tandfonline.com/doi/pdf/10.1080/15980316.2020.1818641

Recent progress in the development of backplane thin film transistors for information displays

Metal oxide thin-film transistors have been continuously researched and mass-produced in the display industry. However, their phototransistors are still in their infancy. In particular, utilizing metal oxide semiconductors as phototransistors is difficult because of the limited light absorption wavelength range and persistent photocurrent (PPC) phenomenon. Numerous studies have attempted to improve the detectable light wavelength range and the PPC phenomenon. Here, recent studies on metal oxide phototransistors are reviewed, which have improved the range of light wavelengths and the PPC phenomenon by introducing an absorption layer of oxide or non-oxide hybrid structure. The materials of the absorption layer applied to absorb long-wavelength light are classified into oxides, chalcogenides, organic materials, perovskites, and nanodots. Finally, next-generation convergence studies combined with other research fields are introduced and future research directions are detailed.

A Review of Phototransistors Using Metal Oxide Semiconductors: Research Progress and Future Directions.

Low-temperature (≤400 °C), stackable oxide semiconductors are promising as an upper transistor ingredient for monolithic three-dimensional integration The atomic layer deposition (ALD) route provi

Atomic Layer Deposition Process-Enabled Carrier Mobility Boosting in Field-Effect Transistors through a Nanoscale ZnO/IGO Heterojunction

Amorphous InGaZnOx (a-IGZO) thin-film transistors (TFTs) are currently used in flat-panel displays due to their beneficial properties. However, the mobility of ∼10 cm2/(V s) for the a-IGZO TFTs used in commercial organic light-emitting diode TVs is not satisfactory for high-resolution display applications such as virtual and augmented reality applications. In general, the electrical properties of amorphous oxide semiconductors are strongly dependent on their chemical composition; the indium (In)-rich IGZO achieves a high mobility of 50 cm2/(V s). However, the In-rich IGZO TFTs possess another issue of negative threshold voltage owing to intrinsically high carrier density. Therefore, the development of an effective way of carrier density suppression in In-rich IGZO will be a key strategy to the realization of practical high-mobility a-IGZO TFTs. In this study, we report that In-rich IGZO TFTs with vertically stacked InOx, ZnOx, and GaOx atomic layers exhibit excellent performances such as saturation mobilities of ∼74 cm2/(V s), threshold voltage of -1.3 V, on/off ratio of 8.9 × 108, subthreshold swing of 0.26 V/decade, and hysteresis of 0.2 V, while keeping a reasonable carrier density of ∼1017 cm-3. We found that the vertical dimension control of IGZO active layers is critical to TFT performance parameters such as mobility and threshold voltage. This study illustrates the potential advantages of atomic layer deposition processes for fabricating ultrahigh-mobility oxide TFTs.

Kyoung Rok Kim

Papers

Amorphous IGZO TFT with High Mobility of ∼70 cm2/(V s) via Vertical Dimension Control Using PEALD