Shiben Hu

High-Performance Doping-Free Hybrid White OLEDs Based on Blue Aggregation-Induced Emission Luminogens

Doping-free white organic light-emitting diodes (DF-WOLEDs) have aroused research interest because of their simple properties. However, to achieve doping-free hybrid WOLEDs (DFH-WOLEDs), avoiding aggregation-caused quenching is challenging. Herein, blue luminogens with aggregation-induced emission (AIE) characteristics, for the first time, have been demonstrated to develop DFH-WOLEDs. Unlike previous DFH-WOLEDs, both thin (<1 nm) and thick (>10 nm) AIE luminogen (AIEgen) can be used for devices, enhancing the flexibility. Two-color devices show (i) pure-white emission, (ii) high CRI (85), and (iii) high efficiency. Particularly, 19.0 lm W1- is the highest for pure-white DF-WOLEDs, while 35.0 lm W1- is the best for two-color hybrid WOLEDs with CRI ≥ 80. A three-color DFH-WOLED shows broad color-correlated temperature span (2301-11628 K), (i) the first sunlight-like OLED (2500-8000 K) operating at low voltages, (ii) the broadest span among sunlight-like OLED, and (iii) possesses comparable efficiency with the best doping counterpart. Another three-color DFH-WOLED exhibits CRI > 90 at ≥3000 cd m-2, (i) the first DF-WOLED with CRI ≥ 90 at high luminances, and (ii) the CRI (92.8) is not only the highest among AIE-based WOLEDs but also the highest among DF-WOLEDs. Such findings may unlock an alternative concept to develop DFH-WOLEDs.

Effect of Post Treatment For Cu-Cr Source/Drain Electrodes on a-IGZO TFTs

We report a high-performance amorphous Indium-Gallium-Zinc-Oxide (a-IGZO) thin-film transistor (TFT) with new copper-chromium (Cu-Cr) alloy source/drain electrodes. The TFT shows a high mobility of 39.4 cm2·V−1·s−1 a turn-on voltage of −0.8 V and a low subthreshold swing of 0.47 V/decade. Cu diffusion is suppressed because pre-annealing can protect a-IGZO from damage during the electrode sputtering and reduce the copper diffusion paths by making film denser. Due to the interaction of Cr with a-IGZO, the carrier concentration of a-IGZO, which is responsible for high mobility, rises.

High-performance back-channel-etched thin-film transistors with amorphous Si-incorporated SnO2 active layer

In this report, back-channel-etched (BCE) thin-film transistors (TFTs) were achieved by using Si-incorporated SnO2 (silicon tin oxide (STO)) film as active layer. It was found that the STO film was acid-resistant and in amorphous state. The BCE-TFT with STO active layer exhibited a mobility of 5.91 cm2/V s, a threshold voltage of 0.4 V, an on/off ratio of 107, and a steep subthreshold swing of 0.68 V/decade. Moreover, the device had a good stability under the positive/negative gate-bias stress.

Direct Inkjet Printing of Silver Source/Drain Electrodes on an Amorphous InGaZnO Layer for Thin-Film Transistors

Printing technologies for thin-film transistors (TFTs) have recently attracted much interest owing to their eco-friendliness, direct patterning, low cost, and roll-to-roll manufacturing processes. Lower production costs could result if electrodes fabricated by vacuum processes could be replaced by inkjet printing. However, poor interfacial contacts and/or serious diffusion between the active layer and the silver electrodes are still problematic for achieving amorphous indium–gallium–zinc–oxide (a-IGZO) TFTs with good electrical performance. In this paper, silver (Ag) source/drain electrodes were directly inkjet-printed on an amorphous a-IGZO layer to fabricate TFTs that exhibited a mobility of 0.29 cm2·V−1·s−1 and an on/off current ratio of over 105. To the best of our knowledge, this is a major improvement for bottom-gate top-contact a-IGZO TFTs with directly printed silver electrodes on a substrate with no pretreatment. This study presents a promising alternative method of fabricating electrodes of a-IGZO TFTs with desirable device performance.

All-sputtered, flexible, bottom-gate IGZO/Al2O3 bi-layer thin film transistors on PEN fabricated by a fully room temperature process

In this work, an innovative all-sputtered bottom-gate thin film transistor (TFT) using an amorphous InGaZnO (IGZO)/Al2O3 bi-layer channel was fabricated by fully room temperature processes on a flexible PEN substrate. A bi-layer channel consisting of 10 nm-thick IGZO and 3 nm-thick Al2O3 was clearly observed in high resolution TEM images. The chemical structure of IGZO was dependent on different sputtering modes (pulse-DC/DC/RF), which were investigated by XPS measurements. The ultrathin Al2O3 layer on IGZO showed a significant effect on enhancing the mobility, reducing the off-state current, and improving the gate-bias stability. As a result, the IGZO/Al2O3 bi-layer TFT eventually exhibited a saturation mobility of 18.5 cm2 V−1 s−1, an Ion/Ioff ratio of 107, an on-state voltage of 1.5 V and a subthreshold swing of 0.27 V decade−1, as well as good stability under NBS/PBS and bending strain. The fabrication of this TFT can be suitably transferred to large-size arrays or paper-like substrates, which is in line with the trend of display development.

All-Aluminum Thin Film Transistor Fabrication at Room Temperature

Bottom-gate all-aluminum thin film transistors with multi conductor/insulator nanometer heterojunction were investigated in this article. Alumina (Al2O3) insulating layer was deposited on the surface of aluminum doping zinc oxide (AZO) conductive layer, as one AZO/Al2O3 heterojunction unit. The measurements of transmittance electronic microscopy (TEM) and X-ray reflectivity (XRR) revealed the smooth interfaces between ~2.2-nm-thick Al2O3 layers and ~2.7-nm-thick AZO layers. The devices were entirely composited by aluminiferous materials, that is, their gate and source/drain electrodes were respectively fabricated by aluminum neodymium alloy (Al:Nd) and pure Al, with Al2O3/AZO multilayered channel and AlOx:Nd gate dielectric layer. As a result, the all-aluminum TFT with two Al2O3/AZO heterojunction units exhibited a mobility of 2.47 cm2/V·s and an Ion/Ioff ratio of 106. All processes were carried out at room temperature, which created new possibilities for green displays industry by allowing for the devices fabricated on plastic-like substrates or papers, mainly using no toxic/rare materials.

A novel nondestructive testing method for amorphous Si–Sn–O films

Traditional methods to evaluate the quality of amorphous silicon-substituted tin oxide (a-STO) semiconductor film are destructive and time-consuming. Here, a novel non-destructive, quick, and facile method named microwave photoconductivity decay (μ-PCD) is utilized to evaluate the quality of a-STO film for back channel etch (BCE) thin-film transistors (TFTs) by simply measuring the D value and peak reflectivity signal. Through the μ-PCD method, both optimum deposition procedure and optimal annealing temperature are attained to prepare a-STO film with superior quality. The a-STO TFTs are fabricated by the obtained optimum procedure that exhibits a mobility of 8.14 cm2 V−1 s−1, a I on/I off ratio of 6.07 × 109, a V on of -1.2 V, a steep subthreshold swing of 0.21 V/decade, a low trap density (D t) of 1.68 × 1012 eV−1 cm−2, and good stability under the positive/negative gate-bias stress. Moreover, the validity of the μ-PCD measurement for a-STO films is verified by x-ray photoelectron spectroscopy, Hall effect measurement, and the performance of STO TFTs measured by traditional methods. The non-destructive μ-PCD method sheds light on the fast optimization of the deposition procedure for amorphous oxide semiconductor films with excellent quality.

Mobility Enhancement in Amorphous In-Ga-Zn-O Thin-Film Transistor by Induced Metallic in Nanoparticles and Cu Electrodes

In this work, we fabricated a high-mobility amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) based on alumina oxide (Al2O3) passivation layer (PVL) and copper (Cu) source/drain electrodes (S/D). The mechanism of the high mobility for a-IGZO TFT was proposed and experimentally demonstrated. The conductivity of the channel layer was significantly improved due to the formation of metallic In nanoparticles on the back channel during Al2O3 PVL sputtering. In addition, Ar atmosphere annealing induced the Schottky contact formation between the Cu S/D and the channel layer caused by Cu diffusion. In conjunction with high conductivity channel and Schottky contact, the a-IGZO TFT based on Cu S/D and Al2O3 PVL exhibited remarkable mobility of 33.5–220.1 cm2/Vs when channel length varies from 60 to 560 μm. This work presents a feasible way to implement high mobility and Cu electrodes in a-IGZO TFT, simultaneously.

High Mobility Amorphous Indium-Gallium-Zinc-Oxide Thin-Film Transistor by Aluminum Oxide Passivation Layer

This letter demonstrates a high-mobility amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistor (TFT) with aluminum oxide (Al₂O₃) passivation layer by radio frequency (RF) magnetron sputtering and copper (Cu) source/drain electrodes. The fabricated a-IGZO TFT exhibited 20 times higher saturation mobility (142.0 cm²/Vs) than the reference device without Al₂O₃ passivation layer. The generation of metallic indium at the back-channel interface caused by the bombardment of the sputtered Al₂O₃ is the main principle for the remarkable enhancement of saturation mobility. Furthermore, the a-IGZO TFT maintains high mobility and air-ambient-stable characteristics up to four months in ambient conditions.

Highly conductive AZO thin films obtained by rationally optimizing substrate temperature and oxygen partial pressure

ABSTRACT In this work, an optimal procedure was proposed to prepare aluminum-doped zinc oxide (AZO) thin films with a sheet resistance of 17.03 Ω/sq by rationally optimizing oxygen partial pressure and substrate temperature. The results showed that increased temperature has an improving trend in the resistivity of AZO thin films while elevated oxygen partial pressure exhibited a deteriorating trend. With rising of substrate temperature in an oxygen-rich atmosphere, oxygen adsorption phenomenon gets stronger. Adsorbed oxygen atoms or molecules suppress the formation of oxygen vacancy and trap electrons, which is responsible for the increase of resistivity. Besides, atomic force microscope analysis indicated that surface roughness of AZO thin films decreases as increase of substrate temperature.