We have fabricated 6.5 in. flexible full-color top-emission active matrix organic light-emitting diode display on a polyimide (PI) substrate driven amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs). The a-IGZO TFTs exhibited field-effect mobility (μFE) of 15.1 cm2/V s, subthreshold slope of 0.25 V/dec, threshold voltage (VTH) of 0.9 V. The electrical characteristics of TFTs on PI substrate, including a bias-stress instability after 1 h long gate bias at 15 V, were indistinguishable from those on glass substrate and showed high degree of spatial uniformity. TFT samples on 10 μm thick PI substrate withstood bending down to R=3 mm under tension and compression without any performance degradation.

Nowadays, active-matrix organic light-emitting diode (AMOLED) technology has been intensively utilized in commercial large-size flat panel markets such as notebooks, personal computers, display monitors, and high-definition televisions. [1,2] This widespread use is due to the many attractive features that are offered by AMOLEDs, including wide viewing angles, high contrast ratios, low power consumption, and fast response times. Despite these advantages, one of the most critical issues for the technology is the inability to incorporate thin-film transistors (TFTs) in these large-sized applications (!7th generation glass size of 1.9 m  2.2 m (max)). The only mature technology compatible with producing large-sized panels (!7th generation) is based on amorphous Si (a-Si) TFTs, whose inferior long-term stability [3][4][5][6] under gate or/and drain bias stressed conditions hinders their utilization in AMOLED panels.Recently, ZnO-based TFTs have become attractive for use as driving devices in large-sized AMOLED applications, due to their better device performance and reliability; in addition, they offer large-size scalability features with good uniformity, and low product cost, comparable to their a-Si TFT counterparts. [7,8] Furthermore, the transparency of ZnO-based oxide semiconductor and their low-temperature process capability could open the opportunity to the next generation of applications, including ''see-through'' and/or ''flexible'' AMOLED displays, which cannot be realized via silicon-based TFT technologies due to their intrinsic limitations.There have been many reports of high-performance TFTs with oxide semiconductors, including ZnO, [8][9][10] InZnO, [11][12][13] ZnSnO, [14] and InGaZnO [15][16][17][18][19] as the channel materials. The field-effect mobilities (m FE ), sub-threshold gate swing (S), and I on/ off ratios of ZnO-based TFTs have been dramatically improved since Hosono and coworkers reported the usage of amorphous InGaZnO as a channel material using physical-vapor-deposition techniques.[7] Thus, the device performance of ZnO-based TFTs reported in the literature includes high mobility (>10 cm 2 V s À1 ), excellent sub-threshold gate-voltage swing (<0.4 V decade À1 ), and high I on/off ratios (>10 7 ), which are superior to those found in a-Si TFT applications. [7,8,15,16,18,19] However, the stability of ZnO-based TFT devices has remained the most important and critical issue still to be resolved to allow them to be used as driving devices in AMOLED displays. This is because any positive shift in the threshold voltage (V th ) of the driving transistor during the on-state bias stressed condition causes a rapid drop in the output drain current, leading to reduction in the luminance of the OLED device. The nonuniformity in the V th shift of the pixel driving transistors as a result of the different data voltages obviously causes the well-known problem of the image sticking in the resulting panel brightness. [20][21][22] Several studies on bias-induced instabilities in ZnO-based TFTs have reported...

Zinc‐based metal oxide semiconductors have attracted attention as an alternative to current silicon‐based semiconductors for applications in transparent and flexible electronics. Despite this, metal oxide transistors require significant improvements in performance and electrical reliability before they can be applied widely in optoelectronics. Amorphous indium–zinc–tin oxide (a‐IZTO) has been considered an alternative channel layer to a prototypical indium–gallium–zinc oxide (IGZO) with the aim of achieving a high mobility (>40 cm2 Vs−1) transistors. The effects of the gate bias and light stress on the resulting a‐IZTO field‐effect transistors are examined in detail. Hydrogen impurities in the a‐IZTO semiconductor are found to play a direct role in determining the photo‐bias stability of the resulting transistors. The Al2O3‐inserted IZTO thin‐film transistors (TFTs) are hydrogen‐poor, and consequently show better resistance to the external‐bias‐thermal stress and photo‐bias‐thermal stress than the hydrogen‐rich control IZTO TFTs. First‐principles calculations show that even in the amorphous phase, hydrogen impurities including interstitial H and substitutional H can be bistable centers with an electronic deep‐to‐shallow transition through large lattice relaxation. The negative threshold voltage shift of the a‐IZTO transistors under a negative‐bias‐thermal stress and negative‐bias‐illumination stress condition is attributed to the transition from the acceptor‐like deep interstitial Hi− (or substitutional H‐DX−) to the shallow Hi+ (or HO+) with a high (low) activation energy barrier. Conclusively, the delicate controllability of hydrogen is a key factor to achieve the high performance and stability of the metal oxide transistors.

Amorphous-oxide thin-film-transistor (TFT) arrays have been developed as TFT backplanes for large-sized active-matrix organic light-emitting-diode (AMOLED) displays. An amorphous-IGZO (indium gallium zinc oxide) bottom-gate TFT with an etch-stop layer (ESL) delivered excellent electrical performance with a field-effect mobility of 21 cm 2 /V-sec, an on/off ratio of >10 8 , and a subthreshold slope (SS) of 0.29 V/dec. Also, a new pixel circuit for AMOLED displays based on amorphous-oxide semiconductor TFTs is proposed. The circuit consists of four switching TFTs and one driving TFT. The circuit simulation results showed that the new pixel circuit has better performance than conventional threshold-voltage (V TH ) compensation pixel circuits, especially in the negative state. A full-color 19-in. AMOLED display with the new pixel circuit was fabricated, and the pixel circuit operation was verified in a 19-in. AMOLED display. The AMOLED display with a-IGZO TFT array is promising for large-sized TV because a-IGZO TFTs can provide a large-sized backplane with excellent uniformity and device reliability.

Amorphous oxide thin film transistor (TFT) arrays have been developed as TFT backplanes for large size active-matrix organic light emitting diode (AMOLED) displays. An amorphous IGZO (Indium Gallium Zinc Oxide) bottom gate TFT with an etch-stop layer (ESL) delivered excellent electrical performance with fieldeffect mobility of 21 cm 2 /V-s, an on/off ratio of >10 8 , and subthreshold slope (SS) of 0.29V/dec. A full color 19-inch AMOLED display has been developed using the amorphous IGZO TFT backplane.