Wen Yu

Fully transparent flexible tin-doped zinc oxide thin film transistors fabricated on plastic substrate

In this work, we have successfully fabricated bottom gate fully transparent tin-doped zinc oxide thin film transistors (TZO TFTs) fabricated on flexible plastic substrate at low temperature by RF magnetron sputtering. The effect of O2/Ar gas flow ratio during channel deposition on the electrical properties of TZO TFTs was investigated, and we found that the O2/Ar gas flow ratio have a great influence on the electrical properties. TZO TFTs on flexible substrate has very nice electrical characteristics with a low off-state current (Ioff) of 3 pA, a high on/off current ratio of 2 × 107, a high saturation mobility (μsat) of 66.7 cm2/V•s, a steep subthreshold slope (SS) of 333 mV/decade and a threshold voltage (Vth) of 1.2 V. Root-Mean-Square (RMS) roughness of TZO thin film is about 0.52 nm. The transmittance of TZO thin film is about 98%. These results highlight that the excellent device performance can be realized in TZO film and TZO TFT can be a promising candidate for flexible displays.

High-Performance Al–Sn–Zn–O Thin-Film Transistor With a Quasi-Double-Channel Structure

We successfully fabricated high-performance Al-Sn-Zn-O thin-film transistors (ATZO TFTs) with a quasidouble-channel (QDC) structure on glass by radio-frequency magnetron sputtering. The bilayer ATZO films are fabricated with different oxygen partial pressures during the sputtering process. The structure of the top ATZO layer is optimized to improve OFF-state performances. With this QDC structure, the ATZO TFT demonstrates excellent electrical performances, including a low OFF-state current of 840 fA, an ON/OFF current ratio of 1.08 × 109, a steep threshold swing of 0.16 V/decade, a superior saturation mobility of 108.28 cm2V-1s-1, and a threshold voltage of 2.09 V.

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.

Effects of various oxygen partial pressures on Ti-doped ZnO thin film transistors fabricated on flexible plastic substrate

By applying a novel active layer of titanium zinc oxide (TiZO), we have successfully fabricated fully transparent thin-film transistors (TFTs) with a bottom gate structure fabricated on a flexible plastic substrate at low temperatures. The effects of various oxygen partial pressures during channel deposition were studied to improve the device performance. We found that the oxygen partial pressure during channel deposition has a significant impact on the performance of TiZO TFTs, and that the TFT developed under 10% oxygen partial pressure exhibits superior performance with a low threshold voltage (V th) of 2.37 V, a high saturation mobility (μsat) of 125.4 cm2 V−1 s−1, a steep subthreshold swing (SS) of 195 mV/decade and a high I on/I off ratio of 3.05 × 108. These results suggest that TiZO thin films are promising for high-performance fully transparent flexible TFTs and displays.

High-performance calcium-doped zinc oxide thin-film transistors fabricated on glass at low temperature

High-performance calcium-doped zinc oxide thin-film transistors (Ca-ZnO TFTs) have been successfully fabricated on transparent glass at low temperature by RF magnetron sputtering. To study the effects of calcium doping on zinc oxide thin-film transistors, the characteristics of Ca-ZnO TFTs and ZnO TFTs are compared and analyzed in detail from different perspectives, including electrical performance, surface morphology, and crystal structure of the material. The results suggest that the incorporation of calcium element can decrease the root-mean-square roughness of the material, suppress growth of a columnar structure, and improve device performance. The TFTs with Ca-ZnO active layer exhibit excellent electrical properties with the saturation mobility (μsat) of 147.1 cm2 V−1 s−1, threshold voltage (V t) of 2.91 V, subthreshold slope (SS) of 0.271 V/dec, and I on/I off ratio of 2.34 × 108. In addition, we also study the uniformity of the devices. The experimental results show that the Ca-ZnO TFTs possess good uniformity, which is important for large-area application.

Investigation of c-axis-aligned crystalline gadolinium doped aluminum-zinc-oxide films sputtered at room-temperature

The c-axis-aligned crystalline (CAAC) rare earth gadolinium doped aluminum-zinc-oxide (Gd-AZO) thin films sputtered at room temperature are investigated in this work. It is found that the polycrystalline AZO is restructured into CAAC Gd-AZO through gadolinium doping. The X-ray diffraction spectrum and high-resolution transmission electron microscopy images indicate the (002) crystalline orientation of the local Gd-AZO grains. The film-formation mechanism of room-temperature sputtered CAAC Gd-AZO thin films is analyzed. Bottom gate oxide thin film transistors with a Gd-AZO active layer are fabricated by low temperature processes. The devices show preferable electrical properties, such as good I-V characteristics, high uniformity, and excellent bias stress stability.

Effects of channel structure consisting of ZnO/Al2O3 multilayers on thin-film transistors fabricated by atomic layer deposition

By applying a novel active layer comprising ZnO/Al2O3 multilayers, we have successfully fabricated fully transparent high-performance thin-film transistors (TFTs) with a bottom gate structure by atomic layer deposition (ALD) at low temperature. The effects of various ZnO/Al2O3 multilayers were studied to improve the morphological and electrical properties of the devices. We found that the ZnO/Al2O3 multilayers have a significant impact on the performance of the TFTs, and that the TFTs with the ZnO/15-cycle Al2O3/ZnO structure exhibit superior performance with a low threshold voltage (V TH) of 0.9 V, a high saturation mobility (μsat) of 145 cm2 V−1 s−1, a steep subthreshold swing (SS) of 162 mV/decade, and a high I on/I off ratio of 3.15 × 108. The enhanced electrical properties were explained by the improved crystalline nature of the channel layer and the passivation effect of the Al2O3 layer.

Characteristic research of zinc oxide based thin film transistor by ALD technology

Zinc oxide is a well-known wide band gap semiconductor material which can be applied to thin film transistors. Al-doped ZnO (AZO) has a better electrical conductivity than Zinc oxide at the same time with good photoelectric properties. In this paper, the method of atomic layer deposition (ALD) was used to prepare the ZnO and Al:ZnO (AZO) thin films as the active layers on silicon substrates at 100 °C. TEM and SEM were used to compare the characters of these films. While, transfer characteristic was an important basis for measuring the electrical characteristics of the devices with different active layers before and after annealing. The unannealed three-layers AZO-based thin film transistor (TFT) exhibits saturation mobility (µsat) of 5.97cm2V−1S−1, a lower subthreshold swing (SS) of 188mV/decade and a high Ion/Ioff ratio of 1.47 × 108.

Investigation on Power Effect of Gallium-Doped Zinc Oxide Thin Film Semiconductor Performance

Gallium-doped zinc oxide (GZO) thin films were fabricated by radio frequency (RF) magnetron sputtering on glass and silicon substrate at room temperature. The fabrication process, structure, optical properties, and electrical properties of the thin films with different powers (50 W, 70W, and 100 W) were studied to obtain more knowledge about the semiconductor performance. X-ray diffraction (XRD) analysis indicated that the GZO films were polycrystalline and preferred c axis orientation. The average transmittance decreased form 93% to 84% in the visible range, and all the optical band gap was about 3.05 eV when the power increased from 50W to 100W. Simultaneously, the GZO thin film transistors (TFTs) with excellent transfer characteristic prove that GZO thin film is a potential semiconductor material candidate which can be used for the active layer in thin film transistors fabrication.

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.