Nam Gyu Cho

Thin-walled NiO tubes functionalized with catalytic Pt for highly selective C2H5OH sensors using electrospun fibers as a sacrificial template

Hollow thin walled NiO tubes functionalized by catalytic Pt were synthesized via nanofiber templating and multilayered sputter-coating of Pt and NiO thin overlayers followed by heat-treatment at 600 °C. Sandwich Pt-NiO-Pt tube networks exhibited superior C(2)H(5)OH sensing response and remarkable selectivity against CO and H(2) gases.

Low voltage operating InGaZnO4 thin film transistors using high-k MgO–Ba0.6Sr0.4TiO3 composite gate dielectric on plastic substrate

The authors report on the dielectric and leakage current properties of room temperature grown MgO-Ba0.6Sr0.4TiO3 (MgO-BST) composite thin films to be utilized InGaZnO4 thin films transistors (TFTs) fabricated on a polyethylene terephthalate (PET) substrate. The InGaZnO4 TFTs with MgO-BST gate dielectrics exhibited low operation voltage of 4V, high on/off current ratio of 4.13×106, and high field effect mobility of 10.86cm2∕Vs. These results verify that a room temperature grown MgO-BST gate dielectric is a good candidate for producing high performance InGaZnO4 TFTs on plastic substrates.

High Stability InGaZnO4 Thin-Film Transistors Using Sputter-Deposited PMMA Gate Insulators and PMMA Passivation Layers

We report on the fabrication and characterization of sputter-deposited poly(methyl methacrylate) (PMMA) thin films used as gate insulators as well as passivation layers in high performance InGaZnO 4 thin-film transistors (TFTs). Sputter-deposited PMMA thin films exhibited a dielectric constant of 4.3 and low leakage current characteristics (< ∼ 2 × 10- 8 A/cm 2 at 0.3 MV/cm). The InGaZnO 4 TFTs utilizing PMMA gate insulators and PMMA passivation layers exhibited a high on/off current ratio of 4.08 × 10 6 and a high field-effect mobility of 36.1 cm 2 /V s. Threshold voltage and field-effect mobility remained constant after aging in air atmosphere for 5 months.

Highly Transparent InGaZnO4 Thin Film Transistors Using Indium-Doped ZnO Electrodes on Plastic Substrate

We investigated indium- (In)-doping effects on the structural and electrical properties of a ZnO film. It was found that structural properties degraded as In-doping content increased, whereas electrical properties improved. We fabricated fully transparent and flexible InGaZnO 4 thin film transistors (TFTs) using In-doped ZnO electrodes on polyethylene terephthalate (PET) substrate. The InGaZnO 4 /MgO-Ba 0.6 Sr 0.4 TiO 3 /3% In-doped ZnO/PET stacks exhibited a high transmittance of 80% in the visible range. The InGaZnO 4 TFT with a 3% In-doped ZnO electrode showed a high field effect mobility of 1.04 cm 2 /V s and a moderate on/off ratio of 7.48 X 10 5 .

InGaZnO4-Based Thin Film Transistors Using Room-Temperature Grown Mg2Hf5O12 Gate Insulator

This study reports the dielectric and leakage current properties of Mg 2 Hf 5 O 12 thin films deposited at room temperature by radio-frequency magnetron sputtering. Polycrystalline Mg 2 Hf 5 O 12 thin films showed a reasonably high dielectric constant (e r = 22) and greatly enhanced leakage current characteristics (<2 × 10 ―7 A/cm 2 ) compared to the leakage current (∼ 2 × 10- 5 A/cm 2 ) of HfO 2 thin films at 0.4 MV/cm. A bandedge spectroscopic analysis revealed lower conduction bandedge defect states and a greater p-type-like Fermi energy level of Mg 2 Hf 5 O 12 compared to the HfO 2 thin films. The suitability of Mg 2 Hf 5 O 12 films as gate insulators for low voltage operating InGaZnO 4 thin film transistors (TFTs) was investigated. All room-temperature processed InGaZnO 4 TFTs on plastic substrates exhibited a high field effect mobility of 27.32 cm 2 /Vs and a current on/off ratio of 4.01 × 10 6 . The threshold voltage and subthreshold swing were 2 V and 440 mV/dec, respectively. The fabrication and compositional manipulation method of the Mg 2 Hf 5 O 12 films described in this work is simple and versatile, providing fascinating opportunities for new high-k gate dielectrics.

STRUCTURAL AND ELECTRICAL PROPERTIES OF HIGH TEMPERATURE DEPOSITED EPITAXIAL ZNO THIN FILM FABRICATED BY RF MAGNETRON SPUTTERING

ABSTRACT We investigated the growth behaviors of ZnO epilayers on sapphire substrates fabricated using RF magnetron sputtering and RTA. The effects of deposition temperature and oxygen partial pressure in plasma on the structural and electrical properties were measured by XRD, AFM, SEM, and Hall effect measurement. It was found that ZnO thin films became denser and smoother with increasing deposition temperature and O2 content in the sputtering gas. ZnO thin film of oxygen and argon with a ratio of 5:5 had an electron concentration of 8.048 × 1018 cm−3, resistivity of 0.0141Ω · Cm, and mobility of 55.07 cm2/V· s.

STRUCTURAL AND ELECTRICAL PROPERTIES OF INDIUM DOPED ZNO THIN FILM ON 6H-SIC SUBSTRATE BY RF MAGNETRON SPUTTERING

ABSTRACT We investigated the indium doping and annealing effects of ZnO thin film on a 6H-SiC substrate using RF magnetron sputtering for deposition and RTA for annealing. The structural and electrical properties of ZnO and 1 at.% indium doped ZnO thin films were measured by X-ray diffraction, AFM, SEM, TEM, and Hall effect measurement. According to this study, the 1 at.% indium doped ZnO thin film deposited at 800°C and annealed at 850°C with an oxygen to argon ratio of 9:1 showed the electron concentration of 7.25 × 1018 cm−3, resistivity of 0.032 Ω·cm, and mobility of 26.90 cm2/V·s and, can be a good candidate for application to LEDs.