Zhuofa Chen

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.

High-Performance Flexible Tin-Zinc-Oxide Thin-Film Transistors Fabricated on Plastic Substrates

Full transparent high-performance tin-zinc-oxide thin-film transistors (TZO TFTs) had been successfully fabricated on flexible plastic substrate by radio frequency (RF) sputtering. Excellent properties of TZO TFT with L_G = 10 μm gate length were realized, namely high saturation mobility (μ_s) of 175 cm²/V · s, high linear mobility (μl) of 127 cm²/V · s, a suitable threshold voltage (V_th) of 1.81 V, a steep subthreshold swing (SS) of 220 mV/decade, an ON/OFF current ratio (I_ON/IO_FF) of ~1 × 10⁸, and good transmittance of 91.9%, which compare favorably to those made on glass substrates. Mechanical stability of flexible TZO TFTs was investigated by bending tests. The flexible TZO TFTs exhibited good electrical performance, good uniformity, and good flexibility. Thereby, we demonstrated the feasibility of high-performance TZO TFTs for flexible display applications.

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.

Insights into resistive switching characteristics of TaO x -RRAM by Monte-Carlo simulation

An atomistic Monte-Carlo simulator is developed for TaO_x-based resistive switching random access memory (RRAM) including both the generation & recombination effect of oxygen vacancy defects with oxygen ions and the phase change effect between Ta₂O₅ and TaO₂. Using the developed simulation tool, the resistive switching characteristics of the bi-layered Ta₂O₅/TaO_x RRAM are investigated. The typical self-compliance behavior measured in the bi-layered Ta₂O₅/TaO_x RRAM is reproduced by considering the interaction between Ta₂O₅ and TaO_x, indicating that TaO_x layer plays a critical role to the self-compliance behavior.

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.

Flexible aluminum-doped zinc-oxide thin-film transistor fabricated on plastic substrates

We have studied processing and characteristics of flexible Aluminum-doped Zinc Oxide thin-film transistors (AZO TFTs) fabricated on plastic substrates using radio frequency (rf) magnetron sputtering. To improve the performance of flexible AZO TFT, we studied effects of device structures on characteristics of the aluminum-doped zinc oxide thin film transistors. The electrical properties of top-gate type and bottom-gate type AZO TFTs were investigated, respectively. The top-gate type AZO TFTs shows a threshold voltage of 1.4 V, a Ion/Ioff current ratio of 1.0×107, a field effect mobility of 28.2 cm2/ V•s, a subthreshold swing of 0.19 V/decade. And the bottom-gate type AZO TFTs shows a threshold voltage of 1.7 V, a Ion/Ioff ratio of 1.0×107, a field effect mobility of 209 cm2/ V•s, a subthreshold swing of 0.16 V/decade, and the off current of less than 10-11A at room temperature. Both TFTs show low threshold voltage, high Ion/Ioff ratio and high field effect mobility. By comparison, the bottom-gate type AZO TFTs shows better characteristics. The flexible AZO-TFT is a very promising low-cost optoelectronic device for the next generation of invisible and flexible electronics due to flexible, transparency, high mobility, and low-temperature processing.

Physical understanding and optimization of resistive switching characteristics in oxide-RRAM

In this paper, the physical mechanism and models of oxide-based resistive-switching random access memory (RRAM) and the optimization of the devices and arrays are addressed and reviewed. The review focuses on our research achievements on the unified physical mechanism, physical-based models including switching and reliability behaviors, and the optimization design issues of the oxide-based RRAM.

Fully-transparent Mo-doped ZnO TFTs fabricated in different oxygen partial pressure at low temperature

Fully-transparent Mo-doped ZnO (MZO) thin film transistors (TFTs) have been successfully fabricated on glass substrate by radio frequency Magnetron Sputtering at room temperature and its characteristics have been studied in different oxygen partial pressure. The results show that the MZO TFTs which were deposited at low oxygen partial pressure (10%) have excellent performance such as subthreshold swing of 388 mV/decade, the saturation mobility of 5.8 cm2/V·s, the threshold voltage of 3.97 V, the Ioff value of 5×10-12 A, and the on/off current ratio of 2.4×107. To identify properties of the film formed at oxygen partial pressure of 10%, X-ray diffraction, scan electron microscopy, and transmittance were used to investigate the microstructure of the films. All conclusions suggest that MZO TFTs will become a promising candidate for TFT-LCD.