Yingying Cong

High-performance dual-layer channel indium gallium zinc oxide thin-film transistors fabricated in different oxygen contents at low temperature

In this work, fully transparent dual-layer channel amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs) are fabricated on glass substrates at low temperature. Dual-layer channel a-IGZO TFTs are studied by changing the partial pressure of oxygen while sputtering IGZO layers for comparison with single-layer channel TFTs which are fabricated with a constant oxygen content. All four types of dual-layer channel TFT sample demonstrate better performance, on-to-off ratios of ~108 and low subthreshold swing (SS) of less than 200 mV/decade, than the single-layer ones. TFTs with two layers, a low-oxygen layer and a high-oxygen layer formed using oxygen partial pressures of 0.01 and 0.05 Pa, respectively demonstrate relatively better performance with a mobility of more than 60 cm2 V−1 s−1. Among them, the TFTs with a channel layer thickness ratio of 3 : 1 show the best transfer characteristics with a high on-to-off current ratio (Ion/off) of 1.8 × 108 and a low SS of 135 mV/decade.

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 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 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.

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.

Fully transparent high performance thin film transistors with bilayer ITO/Al-Sn-Zn-O channel structures fabricated on glass substrate

In this work, fully transparent high performance double-channel indium-tin-oxide/Al–Sn–Zn–O thin-film transistors (ITO/ATZO TFTs) are successfully fabricated on glass by radio frequency (RF) magnetron sputtering. The ITO layer acts as the bottom channel layer to increase the channel carrier concentration. The top ATZO channel layer, which is deposited via high oxygen partial pressure in the sputtering process, is useful to control the minimum off-state current. After annealing, the ITO/ATZO TFT demonstrates outstanding electrical performances, including a high ON/OFF current ratio (Ion/Ioff) of 3.5 × 108, a steep threshold swing (SS) of 142.2 mV/decade, a superior saturation mobility (μsat) of 246.0 cm2/Vs, and a threshold voltage VT of 0.5 V. The operation mechanisms for double-channel structures are also clarified.

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.

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.