The development of polyimides (PIs) with a superheat resistance and a high thermal dimensional stability is required urgently for application in the rapidly growing area of flexible-display substra...

Synthesis of Superheat-Resistant Polyimides with High Tg and Low Coefficient of Thermal Expansion by Introduction of Strong Intermolecular Interaction

Towards colorless polyimide/silica hybrids for flexible substrates

Synthesis and characterization of optically transparent semi-aromatic polyimide films with low fluorine content

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.

In today's society, displays are indispensable for digital interaction and personal contact. Therefore, the development of displays is an urgent need for the next generation. Leading the commercialization trends is the development of industrial, high-resolution, portable, and multifunctional displays. Moreover, for small-size portable displays, the most critical factor affecting future applications is their flexibility. Among the various materials that can act as the channel layer, low-temperature polycrystalline silicon (LTPS) is a potential candidate for next-generation portable displays, which require high resolution and stable reliability, and which can achieve virtual reality applications. This article is a review of the development of the LTPS thin-film transistors (TFTs) on soft and flexible electronics, especially the effect of mechanical strain. This article starts by providing an overview of the difficulties in fabricating LTPS TFTs on flexible substrates. The physical mechanism corresponding to each degradation caused by mechanical stress is presented next. Finally, to support the development of the flexible technologies and realize their commercialization, methods to overcome these mechanical strain-induced degradations are reported in three different aspects by understanding the physical degradation model.

Flexible low-temperature polycrystalline silicon thin-film transistors

For conventional active-matrix organic light-emitting diode (AMOLED) flat panel displays, low temperature poly-silicon thin-film transistor (LTPS TFT) on rigid glass substrate process has already been well established. However, this technology cannot be applied directly on polyimide (PI) substrate for flexible display. This is because PI has the different coefficient of thermal expansion (CTE) from the glass, which will result in PI film peeling-off and/or warpage issues under conventional LTPS-TFT process technology. In this paper, a process flow of LTPS TFT on PI substrate for flexible display application was discussed. A flexible display demo system was successfully made by optimizing the LTPS TFT process.

LTPS TFT Process on Polyimide Substrate for Flexible AMOLED

In this paper, the failure mechanism of TFT devices on flexible substrate was investigated using bending test. The results show that the TFT fails due to the micro-cracks in M2 lines; the micro-cracks first generate at the brittle layers and then migrate to the M2 lines.

Xiaoyu Gao

Papers

LTPS TFT Process on Polyimide Substrate for Flexible AMOLED

Failure mechanism of TFT devices on flexible substrate by cyclic bending test