Chin Pao Cheng

High Mobility Field-Effect Thin Film Transistor Using Room-Temperature High-kappa Gate Dielectrics

This paper reports an InGaZnO thin-film transistor (TFT) that involves using fully room-temperature gate dielectrics on a flexible substrate. The wide bandgap dielectrics of HfO₂ and Y₂O₃ exhibited favorable adhesion properties on a flexible substrate compared with conventional low-κ SiO₂ film. Based on the experimental results, the room-temperature IGZO/HfO2 TFTs demonstrated effective device integrity, and achieve a low drive voltage of V, a low threshold voltage of 0.46 ±006 V, a low sub-threshold swing of 110 ±6 mV/decade and an extremely high mobility of 60.2 ±32 cm ²/V·s. The excellent performance of this TFT indicated that it demonstrates considerable potential for active-matrix liquid crystal display applications requiring low power consumption and a high driving current.

Ultraviolet Lasing of Sol-Gel-Derived Zinc Oxide Polycrystalline Films

The effect of post-annealing on sol–gel-derived ZnO films has been investigated. For these films, structural investigations including analyses of surface morphology and microstructures were carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Also, optical properties were determined by photoluminescence analysis, ellipsometry and optical pumping measurement. The XRD results indicate that the (002) peak will predominate with increasing annealing temperature. SEM images show that grain size increased with annealing temperature. Moreover, photoluminescence spectra revealed the enhancement in UV emission intensity with annealing temperature, which was attributed to an improvement in crystal quality. Room-temperature ultraviolet random lasing action was observed in the ZnO films. The threshold intensity for the lasing was estimated to be ~70 kW/cm2. Furthermore, it was found that the formation of random laser action is affected by post-annealing, which is associated to the presence of a high-gain medium and efficient light scattering.

Structural stability of thermoelectric diffusion barriers: Experimental results and first principles calculations

This study demonstrates the feasibility of producing a tantalum nitride (TaN) thin film as a diffusion barrier and buffer layer for p-type bismuth telluride [(Bi,Sb)2Te3] thermoelectric devices. A network of TaN with nitrogen (N) incorporation is structurally more stable on (Bi,Sb)2Te3 than the conventional Ni diffusion barrier because of less inter-diffusion and a greater likelihood of stoichiometry in the TaN/(Bi,Sb)2Te3 interface. The atomic inter-diffusion between the barrier layers and (Bi,Sb)2Te3 was evaluated in terms of interface adhesion energy using nanoscratching, and proved with first-principles calculations.

Crystallized Ohmic Contact Effect in AlGaN/GaN High Electron Mobility Transistor

In this study, we investigate the grain size effect of high electron mobility transistor devices with ohmic contact metals of stacked Ti/Al/Ni/Au and Ti/Al/Mo/Au. In addition to a comparison of electrical characteristics, the ohmic contacts were also examined by a scratch test for the observation of adhesion behavior. The experimental results demonstrate that the metal grain size is strongly dependent on metal adhesion, which may lead to bonding issues. Moreover, the grain-induced lateral stress lowers the drive current and increases the off-state current owing to the degraded gate swing and transconductance of transistor switching characteristics.

Electrodeposition-Based Fabrication and Characteristics of Tungsten Trioxide Thin Film

In this study, tungsten trioxide WO3 thin films were electrodeposited on indium tin oxide ITO glass to form WO3-coated glass. The electrodeposition ED time tED and ED current IED were varied to control the film thickness and morphology. Furthermore, the crystallization of the thin films was controlled by annealing them at 250°C, 500°C, and 700°C. The results showed that the thickness of the WO3 thin films increased with tED and IED. The as-deposited thin films and those annealed at 250°C were amorphous, whereas the WO3 thin films annealed at 500 and 700°C were in the anorthic phase. Moreover, the amorphous WO3-coated glass exhibited high transmittance in visible light and low transmittance in near-infrared light, whereas the anorthic WO3-coated glass had high transmittance in near-infrared light. An empirical formula for determining the thickness of WO3 thin films was derived through multiple regressions of the ED process parameters.

Observation of Ultraviolet Lasing from Polycrystalline ZnO Films

In this article, we report the optical pumped lasing from the ZnO thin films prepared by chemical solution method. The observation of room-temperature ultraviolet lasing indicates the high-quality of ZnO films.