Junchen Dong

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.

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.

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-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.