Rihui Yao

Enhancement of bias and illumination stability in thin-film transistors by doping InZnO with wide-band-gap Ta2O5

Thin-film transistor (TFT) with Ta2O5-doped InZnO (TIZO) channel layer was demonstrated. The TIZO-TFT exhibited smaller subthreshold swing and higher capability of carrier controlling when bearing nitrogen pre-annealing than the InZnO-TFT. Detailed studies showed that Ta had an effect of suppressing oxygen out-diffusing during thermal annealing, resulting in improving of the stability under positive gate bias stress. Furthermore, the TIZO-TFT displayed better stability under light illumination than InZnO-TFT, owing to its wider band gap and lower absorption after doped with wider-band-gap Ta2O5.

InGaZnO thin-film transistors with back channel modification by organic self-assembled monolayers

InGaZnO (IGZO) thin-film transistors (TFTs) with back channel modified by different kinds of self-assembled monolayers (SAMs) were fabricated. The mobility and electrical stability of the IGZO-TFTs were greatly improved after SAM-modification, owing to the good interface coupling and less water adsorption-desorption effect on the IGZO surface. Meanwhile, the octadecyltriethoxysilane (OTES) treated IGZO-TFT exhibited a higher mobility of 26.6 cm2 V−1 s−1 and better electrical stability compared to the octadecanethiol (ODT) treated one, which was attributed to the formation of a more compact and steady SAM on the IGZO surface after OTES treatment.

Influence of source and drain contacts on the properties of the indium-zinc oxide thin-film transistors based on anodic aluminum oxide gate dielectrics

Thin-film transistors (TFTs) based on indium-zinc oxide (IZO) active layer and anodic aluminum oxide (Al2O3) gate dielectric layer were fabricated. The influence of source and drain (S/D) contacts on TFT performance was investigated by comparing IZO–TFTs with different S/D electrodes. The TFT with Mo S/D electrodes had higher output current and lower threshold voltage, but had poorer subthreshold swing and lower effective electron mobility compared to that with ITO S/D electrodes. By using x-ray photoelectron spectroscopy (XPS) depth profile analyzing method, it was observed that Mo was diffusing seriously into IZO, resulting in the variation of the effective channel length, thereby causing serious short-channel effect, poor subshreshold swing, and bad uniformity of the TFTs with Mo S/D electrodes.

Gate bias stress stability under light irradiation for indium zinc oxide thin-film transistors based on anodic aluminium oxide gate dielectrics

Thin-film transistors (TFTs) using indium zinc oxide as the active layer and anodic aluminium oxide (Al2O3) as the gate dielectric layer were fabricated. The device showed an electron mobility of as high as 10.1?cm2?V?1?s?1, an on/off current ratio of as high as ~108, and a turn-on voltage (Von) of only ?0.5?V. Furthermore, this kind of TFTs was very stable under positive bias illumination stress. However, when the device experienced negative bias illumination stress, the threshold voltage shifted to the positive direction. It was found that the instability under negative bias illumination stress (NBIS) was due to the electrons from the Al gate trapping into the Al2O3 dielectric when exposed to the illuminated light. Using a stacked structure of Al2O3/SiO2 dielectrics, the device became more stable under NBIS.

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.

Direct patterning of silver electrodes with 2.4 μm channel length by piezoelectric inkjet printing

The control of channel length is of great significance in the fabrication of thin film transistors (TFTs) with high-speed operation. However, achieving short channel on untreated glass by traditional piezoelectric inkjet printing is problematic due to the impacting and rebounding behaviors of droplet impinging on solid surface. Here a novel method was proposed to obtain short channel length on untreated glass by taking advantage of the difference in the retraction velocities on both sides of an ink droplet. In addition, droplets contact mechanism was first introduced in our work to explain the formation of short channel in the printing process. Through printing droplets array with optimized drop space and adjusting appropriate printing parameters, a 2.4μm of channel length for TFT, to the best of our knowledge, which is the shortest channel on substrate without pre-patterning, was achieved using piezoelectric inkjet printing. This study sheds light on the fabrication of short channel TFT for large size and high-resolution displays using inkjet printing technology.

Room-Temperature Fabrication of High-Performance Amorphous In–Ga–Zn–O/Al2O3 Thin-Film Transistors on Ultrasmooth and Clear Nanopaper

Integrating biodegradable cellulose nanopaper into oxide thin-film transistors (TFTs) for next generation flexible and green flat panel displays has attracted great interest because it offers a viable solution to address the rapid increase of electronic waste that poses a growing ecological problem. However, a compromise between device performance and thermal annealing remains an obstacle for achieving high-performance nanopaper TFTs. In this study, a high-performance bottom-gate IGZO/Al2O3 TFT with a dual-layer channel structure was initially fabricated on a highly transparent, clear, and ultrasmooth nanopaper substrate via conventional physical vapor deposition approaches, without further thermal annealing processing. Purified nanofibrillated cellulose with a width of approximately 3.7 nm was used to prepare nanopaper with excellent optical properties (92% transparency, 0.85% transmission haze) and superior surface roughness (Rq is 1.8 nm over a 5 × 5 μm2 scanning area). More significantly, a bilayer channel structure (IGZO/Al2O3) was adopted to fabricate high performance TFT on this nanopaper substrate without thermal annealing and the device exhibits a saturation mobility of 15.8 cm2/(Vs), an Ion/Ioff ratio of 4.4 × 105, a threshold voltage (Vth) of -0.42 V, and a subthreshold swing (SS) of 0.66 V/dec. The room-temperature fabrication of high-performance IGZO/Al2O3 TFTs on such nanopaper substrate without thermal annealing treatment brings industry a step closer to realizing inexpensive, flexible, lightweight, and green paper displays.