"The optical properties of ZnO thin film have been studied using photolurninescence(PL) spectroscopy with the change of sample temperatures from 10 K to 290 K. The spectrum at 10 K showed the characteristic emission lines of ZnO which were as follows: free exciton(FX) at 3.369 eV, neutral donor-bound exciton(D^0X) at 3.360 eV, two electron satellite(TES) at 3.332 eV, D^0X-1LO at 3.289 eV, and donor-acceptor pair(DAP} transiton at 3.217 eV. From the spectral evolution with temperatures, two features could be identified as temperature went higher: (1) the bound excitons changed gradually into free excitons, (2) DAP turned into free electron-acceptor transition(e.A^0). The PL intensity of free exciton increased with the increase of temperatures, which was accompanied by the decrease of the intensity of bound excitions and bound excition-related transitons such as TES and D^0X-1LO. At 80 K DAP transition disappeared, while (e.A^0) transition started to appear at 30 K."

Carbon-nanotube field-effect transistors (CNFETs) have drawn wide attention as one of the potential substitutes for metal-oxide-semiconductor field-effect transistors (MOSFETs) in the sub-10-nm era. Output characteristics of coaxially gated CNFETs were simulated using FETToy simulator to reveal the dependence of drain current on the nanotube diameter and gate oxide thickness. Nanotube diameter and gate oxide thickness employed in the simulation were 1.5, 3, and 6 nm. Simulation results show that drain current becomes large as the diameter of nanotube increases or insulator thickness decreases, and nanotube diameter affects the drain current more than the insulator thickness. An equation relating drain saturation current with nanotube diameter and insulator thickness is also proposed.

In this paper the author proposes a method of implementing a numerical model for threshold voltage (V_th) shift in organic thin-film transistors (QTFTs) into SPICE tools. V_th shift is first numerically modeled by dividing the shift into sequentially ordered groups. The model is then used to derive a simulations model which takes into simulation parameters and calculation complexity. Finally, the numerical and simulation models are implemented in AIM-SPICE. The SPICE simulation results agree well with the V_th shift obtained from an OTFT fabricated without any optimization. The proposed method is also used to implement the stretched-exponential time dependent V_th shift in AIM-SPICE and the results show the proposed method is applicable to various types of V_th shifts.

The alumina substrates that Ni electrode was printed on and the multi-layered PTCR thermistors of which composition is (Ba_0.998Ce_0.002)TiO_3 + 0.001MnCO_3 + 0.05BN were fabricated by a thick film process, and the effect of re-oxidation temperature on their resistivities and resistance jumps were investigated, respectively. Ni electroded alumina substrate and the multi-layered PTC thermistor were sintered at l,150℃ for 2 h under PO_2= 10^-6 Pa and then re-oxidized at 600∼850℃ for 20 min. With increasing the re-oxidation temperature, the room temperature resistivity increased and the resistance jump (LogR_290/R_25) decreased, which seems to be related to the oxidation of Ni electrode. The small sized chip PTC thermistor such as 2012 and 3216 exhibits a nonlinear and rectifying behavior in I-V curve but the large sized chip PTC thermistor such as 4532 and 6532 shows a linear and ohmic behavior. Also, the small sized chip PTC thermistor such as 2012 and 3216 is more dependent on the re-oxidation temperature and easy to. be oxidized in comparison with the large sized chip PTC thermistor such as 4532 and 6532. So, the re-oxidation conditions of chip PTC thermistor may be determined by considering the chip size.

In this paper, the 0.95(Na_0.5K_0.5)_0.04[(Nb_0.8Ta_0,20)_0.994Co_0.015]O_3(abbreviated as NKNT) + 0.05KNbO_3 lead-free piezoelectric ceramics were synthesized by the conventional mixed oxide method route with normal sintering. And also, the effects of calcination temperature on the microstructure, dielectric properties, and piezoelectric properties were investigated. A polymorphic phase transition(PPT) between orthorhombic and tetragonal phases was observed in specimens calcined at 810℃∼850℃. The ceramics calcined at 830℃ showed excellent piezoelectric properties: d_33= 179 pC/N, k_p= 0.384, Q_m= 79.73). These results indicate that the ceramic is a promising candidate material for lead-free piezoelectric ceramics.

ZnO thin films were synthesized on Si substrates by MOCVD using diethyl zinc as a precursor. Effects of O_2/DEZ gas mixing ratio on the growth rate, surface morphology, preferred orientation, and electrical properties of the ZnO thin films were investigated with SEM, XRD, and Hall measurement. The surface reflectance variations of ZnO thin films were analyzed using laser-photometer apparatus. As the O_2/DEZ mixing ratio increased, growth rate and I_(002)/I_(101) in XRD of ZnO thin films decreased, and the crystal structure was changed from columnar to planar structure. All ZnO films deposited at various CVD conditions exhibited c-axis (002) plane preferred orientation. The electrical properties of ZnO thin films mainly depended on the carrier mobility.

In this study, coupled mode piezoelectric devices for AE sensor application with excellent displacement and piezoelectric characteristics were simulated using ATILA FEM program, and then fabricated. Displacements and electromechanical coupling factors of the piezoelectric devices were investigated. The simulation results showed that excellent displacement and electromechanical coupling factor were obtained when the ratio of diameter/thickness was 1.0. The piezoelectric device of ф/T= 1.0 exhibited the optimum values of fr= 406 kHz, displacement= 6.11 × 10^-8[m], k_eff= 0.648. The results show that the coupled vibration mode piezoelectric device is a promising candidate for the application of AE sensor piezoelectric device.

In this paper, semiconducting shield specimens for a DC cable is fabricated and characterized by measurement of volume resistance, tensile strength, and the coefficient of expansion to show the electrical and mechanical characteristics of the semiconducting shield. Due to the PTC phenomenon, the volume resistance at 25℃ increases rapidly in comparison to the volume resistance at 90℃. Since the compounding ratio of carbon black is low, the tensile strength and density become lower and the coefficient of expansion is increased. As the general specification of the tensile strength and density is 0.8 kgf/㎟ and 150%, respectively, the fabricated specimen in this paper has excellent mechanical characteristic.

This paper presents a study on the dispersion effect of the X-Ray diffraction, glass transition and DIMA properties of organic modifier clay/epoxy nanocomposites produced in a homogenizer. Several experiments were conducted including different types of dispersion condition with varying processing conditions such as homogenizer rotor speed and applied time of homogenizer. The effects of these variables on the dispersion properties of nanocomposites were then studied. In order to fully understand the experimental results, a X-ray diffraction, DSC and DMA were used to investigate the effect of above mentioned variables on microstructure and intercalation/exfoliation of organic modifier clay/epoxy nanocomposites. The results from this work could be used to determine the best processing condition to obtain appropriate levels of d-spacing, glasss transition temperature and storage modulus in organic modifier clay/epoxy nanocomposites.

When the accident occurred in power distribution system, it needs to control efficiently the fault current according to the fault angle and location. The flux-lock type superconducting fault current limiters (SFCL) can quickly limit when the short circuit accidents occurred and be made the resistance after the fault current. The flux-lock type SFCL has a single triggering element, detects and limits the fault current at the same time regardless of the size of the fault current. However, it has a disadvantage that broken the superconductor element. If the flux-lock type SFCL has separated structure of the triggering element and the limiting element, when large fault current occurs, it can reduce the burden of power and control fault current to adjust impedance. In this paper, this system is composed by triggering element and limiting element to analyze operation of limiting current. When the fault current occurs, we analyzed the limiting and operating current characteristics of the two triggering current level, and the compensation characteristics of bus-voltage sag according to the fault angle and location.

Lowering surface reflectance of silicon wafer by texturization is one of the most important processes to improve the efficiency of silicon solar cells. Generally, the texturing of crystalline silicon was carried out using alkaline solution. The average reflectance of this method was 11% at the wavelength between 400 and 1,000 nm. In this study. the wafers were first texturing by NaOH solution at 80℃ for 35 min. Then the wafers were texturing by SF_6 and O_2 plasma in RIE (Reactive Ion Etching). The average reflectance of two step texturing was reduced to below 5% at the wavelength between 400 and 1,000 nm.

A New Ag-pastes were developed for integrating the high efficiency mono-Si solar cell. The pastes were the mixture of 84 wt% Ag, 2 wt% glass frit, 11 wt% solvent of buthyl cabitol acetate, and 3 wt% additives. After fabricating the Ag-pastes by using a 3-roll mill, they were coated on a SiN_x/n+/p- stacks of a commercial mono-Si solar cell. And the post-thermal process was also optimized by varying the process conditions of peak temperature. The optimized solar cell efficiency on a 6-inch mono-Si wafer was 18.28%, which was the one of the world best performances. It meaned that the newly developed Aa-paste could be adopted to fabricate a commercial bulk Si solar cell.

In this paper, properties of pattern using LBG (Linde-Buzo-Gray) Algorithm was explored including the exactness of K-means algorithm and process time of EM (Expectation Maximization) algorithm in order to develop analysis algorithm of partial discharge pattern in a cable using acoustic data analysis system. Partial discharge was measured by generating inner fault due to lamination of XLPE which is used for cable insulation material. Discharge pattern was analysed by changing the number of swarm article to 2, 4, and 6 in order to interpret swarm structure and properties.

In this paper, thermal analysis of heatsink for 30 W class Chip-on-Board (COB) LED light source is performed by using SolidWorks Flow Simulation package. In order to increase the convection heat transfer, number of fin and shape of the heatsink is optimized. Furthermore, a copper spread is applied between the COB LED light source and the heatsink to mitigate the heat concentration on the heatsink. With the copper spread, the junction temperature between the COB LED light source and the heatsink is 5O.9℃, which is 5.4℃ lower than the heatsink without the copper spread. Due to the improvement of the junction temperature, the light output is improved by 5.8% when the LED light source is stabilized. The temperature difference between the simulation and measured result of the heatsink with the copper spread is within 2℃, which verifies the validity of the thermal design method using a simulation package.

The effect of co-sputtering condition on the structural properties of Mg_xZn_1-xO thin films grown by RF magnetron co-sputtering system was investigated for manufacturing UV LED. Mg_xZn_1-xO thin films were grown with ZnO and MgO target varying RF power. Structural properties were investigated by X-ray diffraction (XRD) and Energy dispersive spectroscopy (EDS). The Mg_xZn_1-xO thin films have sufficient crystallinity on the high ZnO power. The EDS analyzed showed that the Mg content in the Mg_xZn_1-xO films decreased from 3.99 to 24.27 at.% as the RF power of ZnO target increased. The Mg content in the Mg_xZn_1-xO films could be controlled by co-sputtering power.