Jwayeon Kim

Microfabrication and characteristics of double-rectangular spiral type thin-film inductors with an upper NiFe magnetic core

Simple, double-rectangular spiral-type thin-film inductors with an upper Ni81Fe19 core for 5 MHz drive dc–dc converter application were investigated. Copper films 10-μm-thick covered by a 3-μm-thick NiFe film were used as the coils. The inductors fabricated in this study are 2.5×3.4–3.5×5.5 mm2. The inductors developed, with a small size of 2.97×3.1 mm2, exhibit L of 1.43 μH, quality factor of 15.8, and resistance of 2.88 Ω at 5 MHz, and show results comparable to those reported in recent literature for similar inductors sandwiched by more complex magnetic core materials. An analysis of the experimental data suggests an equivalent circuit of the fabricated inductors. From the equivalent circuit analysis, C was shown to have a negligibly small effect over the frequency ranges used. The calculated data obtained from the equivalent circuit and the well-known equation of Q described the high-frequency data of the L, Q, and impedance of the inductors developed well.

Photoluminescence enhancement of red-emitting GdVO4:Eu and YVO4:Eu phosphors by adding zinc

Abstract We synthesized the rare-earth activated R 0.94- x Eu 0.06 Zn x VO 4 (R: Gd and Y; 0≤ x ≤0.08) phosphors with a spherical morphology and a smooth surface by the ultrasonic spray pyrolysis. The annealed R 0.94- x Eu 0.06 Zn x VO 4 crystallized in the tetragonal zircon type structure, belonging to the space group of I 4 1 / amd . The incorporation of a small amount of Zn to R 0.94 Eu 0.06 VO 4 improved the emission characteristics. The emission intensities of the Gd 0.88 Eu 0.06 Zn 0.06 VO 4 and Y 0.9 Eu 0.06 Zn 0.04 VO 4 phosphors at 619 nm were 72% and 21% stronger than those of the Gd 0.94 Eu 0.06 VO 4 and Y 0.94 Eu 0.06 VO 4 phosphors, respectively. We demonstrated that the addition of Zn to R 0.94 Eu 0.06 VO 4 was quite effective for improving the photoluminescent properties.

Decomposition of DyF3 and its effect on magnetic performance of DyF3-doped Nd-Fe-B-type hot-deformed magnet

Decomposition of DyF3 and its effect on the magnetic performance of the hot-pressed compact and die-upset magnet of melt-spun Nd-Fe-B-type material were investigated. DyF3 was thermally decomposed above 660 °C, and this decomposition was linked closely to the coercivity enhancement. When the DyF3 doped flakes were hot-pressed above the decomposition temperature of DyF3, the diffusion of Dy into the flakes was promoted, and leading to profound coercivity enhancement. Coercivity of the hot-pressed magnet was further enhanced by post-hot-press annealing, and coercivity as high as 24.5 kOe was obtained after the optimum annealing. The DyF3 doped hot-deformed magnet exhibited enhanced magnetic performance (iHc = 17.5 kOe, Br = 12.8 kG, (BH)max = 37.6 MGOe) with respect to the un-doped magnet without sacrificing significant remanence. Coercivity was improved by 30%. In magnet in which the decomposition of DyF3 and Dy diffusion were fully accomplished, the region originally occupied by added DyF3 was completely ...

Misfit dislocation generated in InAs epilayer and InP substrate interfaces grown by metalorganic chemical-vapor deposition

Abstract The properties of InAs epilayer grown on (001) InP substrates (oriented 2° off (001) toward the [110] direction) using meta-organic chemical-vapor deposition (MOCVD) are reported. The epilayer of 17 nm thickness grown at 405 °C showed three kinds of misfit dislocation arrays. Their Burgers vectors in all cases were of the form a/2〈101〉 inclined 45° to the interface. Upon annealing 600, 140 and 220 nm InAs epilayers at 660 °C, most misfit dislocations became Lomer-type oriented exactly along the 〈110〉 direction. Average distance between misfit dislocations at early stage of growth was inversely proportional to the InAs thickness. This phenomena was interpreted to the relationship between the dislocation interaction energy and residual InAs epilayer strain energy.

Photoluminescence of GdVO4:Eu3+, Al 3+ Phosphors under VUV Excitation

The microstructure and photoluminescence properties of Gd0.94-xAlxEu0.06VO4 (0≤x≤0.04) phosphors with various Al3+ contents were investigated. The phosphors showed a nanocrystalline nature and a high-quality powder characteristic. The crystallite sizes of the phosphors were calculated to be 46-48 nm. The annealed Gd0.94-xAlxEu0.06VO4 phosphors crystallized in the tetragonal structure. In the emission spectra, several emission peaks were observed over the measured wavelength range (500-750 nm), which were caused by the difference in the transitions of Eu3+ ions, depending on the local symmetry (5D0 → 7Fj, j = 1, 2, 3, and 4). The strongest emission peak was located at 619 nm, providing a high-purity red emission. The doped Al3+ yielded significantly enhanced the emission intensity. The most intense high-purity red emission was obtained for Gd0.93Al0.01Eu0.06VO4.

Microstructure and electrical properties of porous (Ba, Sr)TiO3 ceramics

Abstract Porous and fine-grained (Ba,Sr)TiO 3 ceramics were fabricated by the addition of partially oxidized Ti or Ti powders into the (Ba,Sr)TiO 3 powders. The crystalline structure of the porous (Ba,Sr)TiO 3 ceramics was strongly dependent on the oxygen contents. The room-temperature crystalline structure of the vacuum-sintered (Ba,Sr)TiO 3 was cubic, while that of the vacuum-sintered and then paste-baking treated (Ba,Sr)TiO 3 was tetragonal. The paste-baking treated (Ba,Sr)TiO 3 , containing 5–7 vol.% partially oxidized Ti, showed the excellent positive temperature coefficient of resistivity (PTCR) characteristics.

Fabrication of Nano-Sized Tin Oxide Powder by Spray Pyrolysis Process

By using tin chloride solution as the raw material, a nano-sized tin oxide powder with average particle size below 50 nm is generated by spray pyrolysis reaction. This study also examines the influences of the reaction parameters such as reaction temperature and the concentration of raw material solution on the powder properties. As the reaction temperature increases from 800 to 850 ℃, the average particle size of the generated powder increases from 20 nm to 30 nm. As the reaction temperature reaches 900 ℃, the droplets are composed of nano-particles with average size of 30 nm, while the average size of individual particles increases remarkably up to 80˜100 nm. When the tin concentration reaches 75 g/L, the average particle size of the powder is below 20 nm. When the tin concentration reaches 150 g/L, the droplets are composed of nano particles with average size around 30 nm, whereas the average size of independent particles increases up to 80˜100 nm. When the concentration reaches 400 g/L, the droplets are composed of nano-particles with average size of 30 nm.

ELECTRICAL AND MICROSTRUCTURAL ANALYSES ON THE AU/NI/AU/GE/PD OHMIC CONTACT TO N-INGAAS AND N-GAAS

The Au/Ni/Au/Ge/Pd ohmic contact systems on n-InGaAs and n-GaAs were studied and compared. In the contact to n-InGaAs, relatively good ohmic behavior was found even without annealing due to lower barrier height, and a better ohmic contact was obtained by rapid thermal annealing up to 400°C. However, above 425°C it was deteriorated by intermixing and phase reaction of the ohmic metals and InGaAs substrate. The out-diffusion of In and As degraded the ohmic contact due to an increase in barrier height and charge compensation. As for the contact to n-GaAs, non-ohmic behavior was shown before annealing, but significant reduction of the specific contact resistance was made by annealing. In both contacts, non-spiking and planar interfaces were observed even when annealed at 425°C, and surface morphologies were nearly the same as the as-deposited contacts up to 400°C, which showed smooth and shiny surfaces.

The analysis of one-dimensional conductance quantization in V|amorphous-V2O5|V thin film devices

We report experiments to determine whether the room temperature one-dimensional conductance quantization (1DCQ) is present at the V|amorphous-V2O5 interphase in as-deposited V|amorphous-V2O5|V devices, or nucleated by a critical event at the threshold voltage VT where ballistic transport was initiated. The fit of the material parameters (barrier width, barrier height, dielectric constant) to the I–V data, the oxide thickness independence of resistance, and variations in the device capacitance with junction area and oxide thickness, suggest that the 1DCQ is associated with the formation of a low dimensional conducting filament through a ∼20 A-thick VOx interphase layer. The data show that VT is unusually low (∼8 kT/q where T=300 °K), nearly independent of device area and oxide thickness, and has only a small (∼kT/q) statistical variation from device to device. These data suggest that the interphase transition at the voltage VT is reversible, but, were inconclusive in determining whether the interphase tran...