Shui-Jinn Wang

Use of patterned laser liftoff process and electroplating nickel layer for the fabrication of vertical-structured GaN-based light-emitting diodes

The fabrication process and performance characteristics of a vertical-structured GaN-based light-emitting diode (VM-LED) employing nickel electroplating and patterned laser liftoff techniques are presented. As compared to regular LED, the forward voltage drop of the VM-LED at 20–80 mA is about 10%–21% lower, while the light output power (Lop) is more than twice in magnitude. Especially, the Lop exhibits no saturation or degradation at an injection current up to 520 mA which is about 4.3 times higher than that of the regular one. Substantial improvements in the VM-LEDs performances are mainly attributed to the use of metallic substrate which results in less current crowding, larger effective area, and higher thermal conductivity.

High-Performance InGaZnO Thin-Film Transistors Using HfLaO Gate Dielectric

In this letter, we report a low-voltage-driven amorphous indium-gallium-zinc oxide thin-film transistor with a high-kappa-value HfLaO gate dielectric. Good characteristics were achieved including a low <i>VT</i> of 0.22 V, small subthreshold swing of 76 mV/dec, high mobility of 25 cm²/ Vmiddots, and large <i>I</i> _on/<i>I</i> _off ratio of 5 times 10⁷. These good performances are obtained at an operation voltage as low as 2 V. These characteristics are attractive for high-switching-speed and low-power applications.

Low-Voltage-Driven Flexible InGaZnO Thin-Film Transistor With Small Subthreshold Swing

A flexible thin-film transistor (TFT) was made by integrating a high- HfLaO gate dielectric and an amorphous-InGaZnO (a-IGZO) active layer on a polyimide substrate. This flexible HfLaO/a-IGZO TFT exhibits a low threshold voltage of 0.1 V, a small subthreshold swing of 0.18 V/dec, a high maximum saturation mobility of 22.1 cm2/V s, and an acceptable on/off current ratio of 2 × 10-5. The low threshold voltage and small subthreshold swing allow the device to operate at 1.5 V for low-power applications, which should enable significant future progress in energy efficiency.

The influence of oxygen content in the sputtering gas on the self-synthesis of tungsten oxide nanowires on sputter-deposited tungsten films

The self-synthesis of tungsten oxide (W18O49) nanowires on sputter-deposited W films prepared under different O2/Ar flow rate ratios (OAFRRs) in the sputtering gas is reported. After thermally annealing at 700?850??C in N2 ambient for 15?min, dense and well crystalline W18O49 (010) nanowires or nanobelts were obtained depending on the oxygen content in the sputtering gas. Experimental results show that the annealing temperature required for the full growth of W18O49 nanowires reduced when the OAFRR in the sputtering gas was increased. It is found that the oxygen absorbed in the surface region is responsible for the growth of nanowires. As the OAFRR was increased to (8?sccm)/(24?sccm), which resulted in a saturated oxygen content of about 55 at.% inside the W film, large-scale nanobelts or nanosheets of W18O49 were grown. The possible growth mechanism which governs the evolution from nanowires to nanobelts as the OAFRR was changed is also discussed.

A Nonvolatile InGaZnO Charge-Trapping-Engineered Flash Memory With Good Retention Characteristics

We report an amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor nonvolatile memory (NVM). This NVM shows a large 1.2-V extrapolated ten-year memory window, along with low 10-V/-12-V program/erase voltage, fast 1-ms/100-¿s speed, and good endurance. This was achieved using a charge-trap-engineered structure and high- ¿ layers.

High Temperature Stable [Ir3Si-TaN]/HfLaON CMOS with Large Work-Function Difference

The authors report novel 1000degC-stable [Ir₃Si-TaN]/HfLaON CMOS for the first time, where the self-aligned and gate-first process are full compatible to current VLSI. Good Phi_m-eff of 5.08 and 4.24 eV, low V_t of -0.10 and 0.18 V, high mobility of 84 and 217 cm²/Vs at 1.6 nm EOT, and small 85degC BTI <20 mV (10 MV/cm for 1 hr) are measured

Preparation of p-SnO/n-ZnO Heterojunction Nanowire Arrays and Their Optoelectronic Characteristics under UV Illumination

In this work, the use of a ZnO-nanowire (NW)-based heterojunction array structure for application to UV sensors is proposed. Nano-heterojunction arrays (NHAs) were formed via the oblique-angle sputtering deposition of p-type tin monoxide onto vertically aligned ZnO-NWs grown by hydrothermal growth (HTG). The current density–voltage (J–V) curve in darkness shows that the prepared SnO/ZnO-NW NHAs have rectifying current–voltage characteristics. They also exhibit a superior response to UV (254 nm) light illumination. The optoelectronic properties of the SnO/ZnO-NW NHAs with different SnO thicknesses (50–1000 nm) under different UV light intensities (2–6 mW/cm2) were investigated and discussed. UV sensitivity (IUV/Idark) as high as 8.5 was obtained.

Thermal Stability of Sputtered Tungsten Carbide as Diffusion Barrier for Copper Metallization

This work investigated the thermal stability of tungsten carbide (WC x ) films deposited by a sputtering process with a WC target as diffusion barrier layer between Cu and Si. The as-deposited WC x film has a nanocrystalline structure and a low electrical resistivity of around 227 μΩ cm. Film characterization reveals that the WC x film was able to preserve the integrity of the Cu (2000 A)/WC x (500 A)/n-Si structure without formation of Cu 3 Si, up to a 600°C annealing for 30 min. In addition, diode leakage current measurements on the same contact structure, but with a p + n-Si substrate did not show deterioration of electrical characteristics up to a 550°C annealing. As the thickness of the WC x barrier was reduced to 150 A, the WC x film retained the integrity of diodes up to 500°C without increasing the diode leakage current, The failure of WC x film after high temperature annealing is attributed to the Cu diffusion into the Si substrate through grain boundaries or local defects of the WC x barrier layer, in which some local defects may arise from the formation of W 5 Si 3 .

Preparation of tungsten oxide nanowires from sputter-deposited WCx films using an annealing/oxidation process

The self-synthesis of tungsten oxide (W18O49) nanowires on sputter-deposited WCx films using a simple annealing/oxidization process was reported. It was found that thermal annealing of WCx films at 680°C for 30min in nitrogen followed by oxidation at 450°C for 30min in pure oxygen would yield dense and well-crystallized monoclinic W18O49 (010) nanowires with a typical length/diameter of about 0.15–0.2μm∕10–20nm. The formation of W18O49 nanowires is attributed to the nuclei of immature W2C nanowires experiencing a regrowth process, accompanied by carbon depletion and the oxidization of tungsten during the subsequent oxidization process.

Effect of Surface Treatment on the Performance of Vertical-Structure GaN-Based High-Power Light-Emitting Diodes with Electroplated Metallic Substrates

Large-area (0.6 ×0.6 and 1 ×1 mm2) highly-efficient GaN-based light-emitting diodes (LEDs) with a vertical-conducting structure (VM-LEDs), using a patterned laser lift-off technique and a Ni electroplating process as well as a surface treatment of the top n-GaN epilayer by plasma and chemical etching, were successfully fabricated and investigated. Compared to regular LEDs of the same size, both the forward voltage drop and the light output power (Lop) of the VM-LED were substantially improved. With inductively coupled plasma (ICP) etching followed by an additional KOH etching and an HF/HCl treatment on the n-GaN layer, an increase in Lop by 227% (195%) at 350 (800) mA has been achieved for the (1 ×1 mm2)-sized VM-LEDs.