Polycrystalline InGaO Thin‐Film Transistors with Coplanar Structure Exhibiting Average Mobility of ≈78 cm² V^‐1 s^‐1 and Excellent Stability for Replacing Current Poly‐Si Thin‐Film Transistors for Organic Light‐Emitting Diode Displays

Abstract

large-area processability to achieve high carrier mobility with ultra-low off-currents, and very smooth surface, opening a wide window as an active semiconductor layer for the active-matrix (AM) transparent and flexible electronics. [1] Especially, indium oxide (In 2 O 3 ) based materials with the addition of zinc oxide (ZnO), gallium oxide (Ga 2 O 3 ), and tin oxide (SnO 2 ) are widely investigated for a TFT channel semiconductor for active-matrix organic light-emitting diode (AMOLED) technology. [2][3][4][5] Among them, amorphous InGaZnO (a-IGZO) becomes an industrial standard for display backplane technology. [4] But, the key issue of a-IGZO is its limited mobility because of its material disorder in the amorphous state. [4] In the hexagonal IGZO materials, crystallization of room-temperature (RT) deposited amorphous IGZO can be possible by high-temperature annealing over 700 °C. [6] On the other hand, by raising both the deposition temperature and oxygen partial pressure, a crystalline IGZO with a C axis aligned crystal orientation (CAAC-IGZO), can be obtained. It exhibits some unique properties in terms of performance such as ultra-low off-state current, close to ideal subthreshold swing (SS) because of the absence of minority carriers, which can differentiate them from the amorphous one. By having well defined CAAC crystal structure it is possible to achieve excellent TFT performance compared to the randomly orientated IGZO crystallites. The maximum reported mobility is 65.5 cm 2 V −1 s −1 for a sputtered coplanar CAAC-IGZO with a dual-gate structure. [7] Several TFT structures are investigated including back-channel etched (BCE), etch stopper inverted staggered, and self-aligned coplanar, however, the coplanar structure has the advantage of having the minimum overlap parasitic capacitance which is suitable for the large area, AMOLED displays.The requirement for a high drain current with high mobility TFT is increasing for large area, high-resolution displays. Crystalline oxide is being studied to overcome the mobility issue associated with the amorphous phase. Among them, crystalline In 2 O 3 is known as the wide bandgap (≈3.7 eV), highly Highly ordered polycrystalline indium gallium oxide (PC-IGO) film is obtained by the crystallization of room temperature sputtered amorphous IGO on a hot plate at 350 °C for 1 h and then annealed for 1 h in an N 2 O environment. A high-density PC-IGO of ≈7.15 g cm -3 with reduced oxygen vacancy (≈14.83%) and hydroxyl (OH) related defects (≈10.96%) has been obtained by N 2 O annealing. Self-aligned coplanar thin-film transistor (TFT) with the PC-IGO exhibits the average saturation mobility of 78.73 cm 2 V -1 s -1 , threshold voltage of -1.07 V, subthreshold swing of 0.147 V dec -1 , and the on/off current ratio of over 10 8 . The TFTs show excellent stability under bias-temperature stress with a negligible threshold voltage shift (ΔV TH ) of + 0.1 and -0.1 V for the positive and negative bias stresses, respectively. The TFTs exhibit very stable environmental stability when...

81‐4: High Performance Coplanar Polycrystalline InGaO TFTs on Polyimide Substrate for Foldable AMOLED Display

“…The most prominent peak was found at 2θ = 31.24° with a preferred orientation on (222), suggesting a highly aligned polycrystalline structure. Relatively weaker InOx polycrystalline peaks were found at 2θ = 22 o , 36.24 o , 52.04 o , 61.90 o with preferred orientations of ( 211), ( 400), (440), and (622), respectively (1,(6)(7)(8).…”

“…In the last few decades, oxide semiconductor-based thin film transistors (TFT) is of increasing attention because of their excellent performance over silicon-based TFTs in terms of low off-state current, low-temperature large area process, and relatively high mobility. An additional key requirement is to use a flexible substrate for active matrix organic light emitting diode (AMOLED) displays (1). There are some very popular material compositions including Zinc (Zn), Indium (In), Gallium(Ga), and Tin (Sn) as parent materials for high-performance oxide TFTs.…”

High Performance Amorphous In0.5Ga0.5O Thin‐Film Transistor Embedded with Nanocrystalline In2O3 Dots for Flexible Display Application

“…On the other hand, a negative shift in the binding energy for both Ga 2p (−0.38 eV) and In 3d (−0.25 eV) indicates the carrier increment by defects passivation upon N 2 O PFA. [ 51,54 ]…”

“…This transforms it into the amorphous phase, making it suitable for use in coplanar TFT applications. [ 51 ]…”

Plasma-Enhanced Atomic Layer Deposition Assisted Low-Temperature Synthetic Routes to Rationally Designed Metastable c-Axis Aligned Hexagonal In-Zn-O

“…From a material point of view, oxide semiconductors are required to have high mobility and reliability, and several materials have been explored including IGZO, − IGO, − ITZO, − and IZO. − Among them, IZO is well-known as a candidate material that has high mobility and appropriate carrier concentration because it is composed of In 2 O 3 and ZnO, each an n-type material. However, IZO thin films are generally reported as an amorphous phase because each In 2 O 3 and ZnO has a distinct ground-state crystal structure (cubic and wurtzite, respectively) formed by different metal ionic sizes and charges.…”