Feilong Zhao

High Performance Ti-Doped ZnO TFTs With AZO/TZO Heterojunction S/D Contacts

In this paper, we successfully fabricated Ti-doped ZnO (TZO) thin film transistors (TFTs). Al-doped ZnO (AZO) film was adopted as source/drain (S/D) electrode, forming an AZO/TZO hetero-junction S/D contact. Meanwhile, TZO TFTs with ITO S/D electrode were also fabricated for comparison. Both AZO and ITO films were fabricated using radio frequency (RF) magnetron sputtering at room temperature (RT). Compared with ITO, device with AZO S/D electrodes exhibits higher I_on/I_off ratio of 1.9 ×10 ⁹, lower I off of 570 fA, and comparable saturation mobility (μsat) of 108.6 cm² ·V ^-1 ·S ^-1. Whats more, as channel length decreases, TFTs with AZO S/D electrodes still show good performances.

Flexible nickel-doped zinc oxide thin-film transistors fabricated on plastic substrates at low temperature

High-performance nickel (Ni)-doped zinc oxide thin-film transistors (NZO TFTs) have been successfully fabricated on transparent flexible plastic substrates at a low temperature. The effect of different oxygen partial pressures during channel deposition on the electrical properties of NZO TFTs was studied to improve the device performance. We found that the oxygen partial pressure during channel deposition has a significant influence on the performance of NZO TFTs. Finally, it was demonstrated that a NZO film with 100% Ar sputtering gas during channel deposition exhibited the best electrical properties, with a drain current on/off ratio of 108, a positive threshold voltage of 2.59 V, a subthreshold swing of 233 mV/decade, and a saturation mobility of 118.9 cm2V−1s−1. The results show that Ni-doped ZnO is a promising candidate for flexible fully transparent displays.

Semiconductor performance of rare earth gadolinium-doped aluminum–zinc oxide thin film

Abstract Rare earth element gadolinium-doped aluminum–zinc oxide (Gd–AZO) semiconductor thin film material was deposited on both silicon and glass substrate by radio frequency (RF) sputtering at room temperature. Electrical properties and microstructure of Gd–AZO thin film were mainly modulated by altering O2 partial pressure (OPP) during the RF sputtering process. Scanning electron microscope (SEM) and X-ray diffraction (XRD) test were carried out to uncover the microstructure variation trend with the sputtering OPP, and amorphous structure which is beneficial to large mass industry manufacture was also demonstrated by the XRD pattern. Transmittance in visible light spectrum implies the potential application for Gd–AZO to be used in transparent material field. Finally, bottom gate, top contact device structure thin film transistors (TFTs) with Gd–AZO thin film as the active channel layer were fabricated to verify the semiconductor availability of Gd–AZO thin film material. Besides, the Gd–AZO TFTs exhibit preferable transfer and output characteristics.

Studies on fully transparent Al?Sn?Zn?O thin-film transistors fabricated on glass at low temperature

High-performance fully transparent Al–Sn–Zn–O thin-film transistors (ATZO TFTs) with excellent electrical performance have been successfully fabricated by RF magnetron sputtering on glass at low temperatures. Two kinds of appropriate ATZO compositions are compared from several perspectives, including film material characteristics, device electrical performances, and fabrication process conditions. Finally, we achieve two excellent ATZO TFTs with competitive advantages. The ATZO TFT with larger amounts of dopants exhibits a superior field effect mobility μFE of 102.38 cm2 V−1 s−1, an ON/OFF current ratio (Ion/Ioff) of 1.18 × 107, and a threshold voltage VT of 1.35 V. The device with smaller amounts of dopants demonstrates better crystal quality and an excellent subthreshold swing SS of 155 mV/dec. Furthermore, it is less affected by oxygen partial pressure. The ATZO thin films display a high transmittance of over 80% in the visible light range.

Performance improvement of tin-doped zinc oxide thin-film transistor by novel channel modulation layer of indium tin oxide/tin zinc oxide

By applying a novel active modulation layer of indium tin oxide/tin zinc oxide (ITO/TZO), we have successfully fabricated high-performance bottom-gate-type dual-active-layer thin-film transistors (TFTs) on a glass substrate at a low temperature by a simple process. The as-fabricated dual-active-layer ITO/TZO TFTs exhibited excellent electrical properties compared with single-active-layer TZO TFTs. We found that the dual-layer ITO/TZO TFT with an optimized stack structure of ITO (5 nm)/TZO (45 nm) as the channel layer exhibits excellent properties, namely, a high saturation mobility of 204 cm2 V−1 s−1, a steep subthreshold slope of 219 mV/dec, a low threshold voltage of 0.8 V, and a high on–off current ratio of 4.3 × 107. A physical mechanism for the electrical improvement is also deduced. Owing to its advantages, namely, a low processing temperature, a high electrical performance, a simple process, and a low cost, this novel active modulation layer is highly promising for the manufacture of oxide semiconductor TFT and transparent displays.

High mobility transparent Al-Sn-Zn-O thin film transistors fabricated at low temperature

Fully-transparent inverted-staggered Aluminum and Tin co-doped ZnO (ATZO) thin film transistors (TFTs) have been fabricated by RF magnetron sputtering on glass substrate at low temperature. The characteristics of ATZO TFTs fabricated at various partial pressures of oxygen are studied. The ATZO TFTs demonstrate excellent performance, including a high field effect mobility of 145.33 cm2/Vs, a threshold voltage of 1.71 V, a subthreshold swing of 0.22 V/dec and an on-to-off current ratio of 7.5×107.

High-performance fully transparent Ti-Zn-O thin film transistors

Since the report [1] in 2004 on transparent and flexible thin film transistors (TFTs) using amorphous In-Ga-Zn-O (IGZO), an increasing number of companies [2] have taken part into developing this type of TFTs and have demonstrated various flat panel displays (FPDs), including e-papers, organic light-emitting diodes (OLEDs) and liquid crystal displays (LCDs). Undeniably, IGZO TFTs exhibit excellent performances in various aspects, such as high mobility, comparably good stability and mature fabrication process [3-4]. However, In element is a toxicant element, which is harmful to human body. Whats worse, the storage of both In and Ga element is very limited, leading to their high price. This is very detrimental to industrial production. So we need to develop some new materials.

Titanium doped Zinc-oxide based Thin Film Transistors: Optimization of the source/drain materials

This paper aims at improving the performances of Titanium-doped Zinc-oxide (TZO) Thin-Film-Transistors (TFTs) by optimizing the source/drain materials. We successfully fabricate TZO TFTs with different source/drain materials, such as Al, Mo, Cr, Mo/Al/Mo and Cr/Al/Cr. No intentional substrate-heating is performed during each deposition step and the highest process temperature is 80°C. The results show that TFTs adopting Cr/Al/Cr as source/drain exhibit improved electrical properties with a high saturation mobility (μ_sat) of 171.4 cm²V^-1S^-1, a low subthreshold swing (SS) of 0.25 V/decade, a high I_on/I_off ratio of 2×108 and a threshold voltage (V_th) of 3.0V.

High negative bias stability Gadolinium-doped Aluminum-Zinc-Oxide thin film transistors

Thin film transistors (TFTs) with Gadolinium-doped Aluminum-Zinc-Oxide (Gd-AZO) thin film as the active layer were fabricated on glass substrate at room temperature. Amorphous Gd-AZO crystal structure which is benefit for high performance devices was obtained. The variation trend of TFTs properties with O2 partial pressure was investigated. Excellent negative bias stress stability and transmittance Gd-AZO TFTs was realized, too. The ultimate TFT has excellent properties such as a saturation mobility of 238 cm2/V·s, an on-to-off current ratio of 6.08×108, a threshold of 1.92V, and a sub-threshold swing of 161 mV/decade.

Effects of radio frequency power on properties of titanium-doped zinc oxide based TFTs

In this paper, titanium-doped zinc oxide (TZO) films were prepared by radio frequency (RF) sputtering at different RF powers acting as the channel layers of thin film transistors (TFTs). Through the analysis of scanning electron microscope (SEM), X-Ray diffraction (XRD) and transfer characteristics, we studied the effects of RF power on properties of TZO films and TZO-based TFTs and obtained optimum device characteristics at the RF power of 100W. The TZO-based TFT fabricated at the optimum RF power exhibits a high saturation mobility (μ_sat) of 213 cm²V^-1S^-1, a low subthreshold swing (SS) of 143 mV/decade and a high I_on/I_off ratio of 7.4×10⁸.