Eui-Jung Yun

Effect of high-energy electron beam irradiation on the properties of ZnO thin films prepared by magnetron sputtering

In this work we demonstrate that high-energy electron beam irradiation (HEEBI) performed in air at room temperature affects remarkably the electrical, optical, and structural properties of undoped ZnO films prepared on SiO2 substrates by magnetron sputtering techniques. Hall and photoluminescence measurements revealed that the p-type conductivity was realized in HEEBI treated films with low dose of 1014 electrons/cm2 and converted to n-type conductivity with further increase in the amount of dose. X-ray photoelectron spectroscopy showed that indiffusion of Si from the substrate as well as N from the ambient into the films took place as a result of HEEBI treatment at high and low doses, respectively. X-ray diffraction analysis indicated that all as-grown films were found to have compressive stress, which was relieved to some extent by HEEBI treatment with high dose of 1016 electrons/cm2. It was also found that better crystallinity with a bigger grain size was observed in HEEBI treated ZnO films with a high...

Characterization of Al-As codoped p-type ZnO films by magnetron cosputtering deposition

We report the preparation of Al–As codoped p-type ZnO films by rf magnetron cosputtering deposition. The p-type conductivity of the films was revealed by Hall measurements, x-ray photoelectron spectroscopy (XPS), and photoluminescence measurements after being annealed in O2. It was observed by XPS that Al content increased with increasing AlAs target power from 80 to 160 W and reached a maximum value at an AlAs target power of 160 W. Hole concentration decreased with increasing Al content. With increasing AlAs target power greater than 160 W, the samples exhibit increases in As and O contents and decreases in Al and Zn contents, which contribute to the increase in hole concentration. A high hole concentration of 2.354×1020 cm−3, a low resistivity of 2.122×10−2 Ω cm, and a Hall mobility of 0.13 cm2/V s for the films with high As content of 16.59% were obtained. XPS has also been used to address the unresolved issues related to the p-type formation mechanism of As-doped ZnO, supporting that the acceptor is ...

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.

Multiresolution approach for texture segmentation using MRF models

Texture is an important characteristic of an image. Texture segmentation/classification have been widely utilized in remote sensing application such as scene classification and feature extraction since remotely sensed data include abundant texture characteristics. Markov Random Field (MRF) models have been successfully employed in texture modeling since they exploit contextual behavior. In this study, the method for characterization and segmentation of textured image in multiresolution MRF frame is proposed. The discrete wavelet transform (DWT) is utilized as a multiresolution technique to enable utilization of feature information at multiple scales and provide computational efficiency. Here, the sub-images of a textured image decomposed with the DWT are modeled with MRFs. Texture segmentation is successively carried out with MAP criterion from the coarse resolution to a finer resolution refining segmentation map. This method can be applied to change detection and feature extraction based on remotely sensed data.

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.

Electrical Characteristics of a-IGZO TFTs With Gate Insulator Prepared by RF Sputtering

This study examined the electrical properties of a-IGZO thin-film transistors (TFTs) with a gate insulator of SiO₂, in which a more TFT-industry-compatible sputtering technique was used for all processing steps. Instead of plasma enhanced chemical vapor deposition, a room-temperature sputtered SiO₂ gate insulator was used, which is more preferable for the simple and low cost process for oxide TFTs. The dielectric strength of the sputtered SiO₂ film with an oxygen ratio of 6.25% was 6.3 MV/cm, which is sufficient for a gate insulator. The a-IGZO TFTs with the sputtered SiO₂ gate insulators showed the optimal device parameters after post-annealing at 400°C for 1 hour in air: saturation field-effect mobility of 3.80 cm²/V·s, V_th of -2.84 V, on/off ratio of 1.43×10⁵, and S.S of 0.88 V/dec.

Stabilities of amorphous indium gallium zinc oxide thin films under light illumination with various wavelengths and intensities

We investigated the photo responses of an amorphous indium gallium zinc oxide (a-IGZO) thin film under light illumination with various wavelengths and intensities. By using the measured photo-conductivities of a-IGZO thin films, we extracted the photo excitation activation energy and dark relaxation activation energy through extended stretched exponential analysis. The stretched exponential analysis was found to describe well both the photoexcitation and the dark-relaxation characteristics. These analyses indicated that recombination takes place more slowly and through activation processes that are more deeply bound with the broader distribution of activation energies (Eac) than those corresponding to the photo-generation process. The longer wavelength of the incident light, the slower the dark-relaxation occurs because of the formation of higher Eac for the ionized oxygen vacancy (Vo2+) states. For the dark-relaxation process, we also observed that the stretching exponent increases and the distribution of energy levels became narrower for longer wavelengths. This suggests that the neutralization of Vo2+ to Vo is slower for longer wavelengths due to the higher energy barrier height (Eac) for the neutralization of Vo2+.

Influences of Gate Bias and Light Stresses on Device Characteristics of High-Energy Electron-Beam-Irradiated Indium Gallium Zinc Oxide Based Thin Film Transistors

Under white light illumination, amorphous indium–gallium–zinc oxide (a-IGZO)-based thin-film transistors (TFTs) showed a large negative shift of threshold voltage of more than -15 V depending on the process conditions. We investigated the influences of both gate bias and white light illumination on device properties of IGZO-based TFTs untreated and treated with high-energy electron beam irradiation (HEEBI). The TFTs were treated with HEEBI in air at room temperature (RT), electron beam energy of 0.8 MeV, and a dose of 1×1014 electrons/cm2. The HEEBI-treated TFTs showed an improved stability under negative bias illumination stress (NBIS) and positive bias illumination stress (PBIS) compared with non-HEEBI-treated TFTs, suggesting that the acceptor-like defects might be generated by HEEBI treatment near the valence band edge.

A Study on the Design and Fabrication of High Performance Large Current Mica Capacitor for Energy Storage Facility Applications

Abstract - In this study, large-current (75 - 400 A), high-voltage (500 - 1000 V rms ), reliable capacitors with capacitances (C) of 100 - 1000 nF were developed for energy storage facility applications. Mica was used as the dielectric of the capacitors. In order to form a parallel stack of a capacitor element, 50 ㎛ thick mica sheets with a size of 30mm×35mm were used with lead foils for the plate lead type of mica capacitors (HCM-L), while the same sizes of mica sheets coated by Ag paste were employed with lead foils for the parallel plate terminal type (HCM-C). The developed capacitors exhibited well behaviored device characteristics which meet the requirements of the capacitors. The developed capacitors also showed excellent characteristics for thermal shock test. The stability characteristics of developed capacitors for large current stress was superior to those measured for the capacitors prepared recently by CDE Tm .Key Words : Large-current, Mica capacitor, High-voltage, Energy storage*비 회 원 : 안양대 공대 디지털미디어학과 교수†교신저자, 정회원 : 호서대 공대 시스템제어공학과 교수E-mail : ejyun@hoseo.edu 접수일자 : 2011년 8월 4일 최종완료 : 2011년 9월 1일

Development of Core Technologies for Integrating Combustible Hydrogen Gas Sensor

Core technologies for integrating hydrogen gas sensor were investigated. In this study, the thermally isolated micro-hot-plate with areas of was fabricated by utilizing surface micromachining technique that provides better manufacturing yield than bulk micromachining counterpart. The optimum design of the sensor was peformed by analyzing the thermal profile of the structure obtained from a ANSYS simulator. The 400-nm-thick polysilicon films doped with phosphorus, the 300-nm-thick aluminum films, and the 200-nm-thick (or ZnO)films were used as the micro-heater material, the temperature sensor material, and the gas sensitive material, respectively. The experimental results show that the developed gas sensors can detect concentration as low as 1 ppm.