Young Sung Kim

Fabrication and magnetic properties of Al2O3/Co nanocomposites

Abstract Al 2 O 3 /Co nanocomposites were synthesized by dispersing submicron-sized cobalt particles into Al 2 O 3 matrix via vacuum hot-pressing technique. The size of cobalt particles increased with increasing cobalt content, and the growth as well as coalescence of cobalt particles occurred at 50xa0wt.% Co addition. The phases formed in the Al 2 O 3 /Co composites were f-Co(fcc), h-Co(hcp), α-Al 2 O 3 , and a small amount of C. Ferromagnetic properties with high mechanical properties were achieved simultaneously by incorporating submicron-sized cobalt particles into the Al 2 O 3 matrix.

Organic Light-Emitting Devices with In-Doped (4 at. %) ZnO Thin Films as the Anodic Electrode

We have investigated transparent conducting properties of using In-doped (4 at. %) zinc oxide (IZO) thin films deposited on glass substrate by pulsed DC magnetron sputtering at low processing substrate temperatures. As increase of the substrate temperature, IZO thin films with better c-axis orientations were grown in perpendicular to the substrate and work functions of IZO films slightly decrease. The optical properties showed high transmittance of higher than 85% in the UV–visible region and exhibited the absorption edge of about 350 nm. The electrical properties exhibited the low resistivity of 1.1 ×10-3 Ω cm and the high mobility of ~7.8 cm2 V-1 s-1. The organic light emitting diodes (OLEDs) with an IZO anode achieved a maximum luminance efficiency of 2.7 cd/A and external quantum efficiency of 0.47%, which are compared to the values of a control device fabricated on commercial ITO anode. These results indicate that IZO films hold promise for anodic electrodes in the OLEDs application.

Growth of TiO2 thin films on Si(100) and Si(111) substrates using single molecular precursor by high-vacuum MOCVD and comparison of growth behavior and structural properties

Abstract We have deposited titanium dioxide (TiO 2 ) thin films on Si(1xa00xa00) and Si(1xa01xa01) substrates in the temperature range of 500–750°C and in the pressure range of 3.0×10 −7 –5.0×10 −5 xa0Torr using a single molecular precursor such as titanium (IV) iso-propoxide (Ti[OCH(CH 3 ) 2 ] 4 , 97%) by high-vacuum metal-organic chemical vapor deposition method. Highly oriented, stoichiometric TiO 2 thin films with rutile phase were successfully deposited on both Si(1xa00xa00) and Si(1xa01xa01) substrates between 650°C and 750°C under a working pressure of 1.0×10 −5 xa0Torr. X-ray diffraction results clearly showed different growth behaviors between Si(1xa00xa00) and Si(1xa01xa01) substrates. The main film growth directions are [1xa01xa00] on Si(1xa00xa00) and [2xa00xa00] on Si(1xa01xa01), respectively. Scanning electron microscope and transmission electron microscope images showed a quite smooth surface with no cracks and sharp interface between film layers, suggesting good adhesion and uniformity in depth. In the case of TiO 2 films, grown under low temperature below 600°C and high pressure above 3.0×10 −5 xa0Torr, transmission electron diffraction pattern showed a mixed structure with spot and ring patterns, resulting in polycrystalline film formation. By increasing the growth temperature to 650°C and decreasing the pressure to 3.0×10 −7 xa0Torr, however, strong spot images with weak ring pattern were observed, indicating that the film crystallinity as well as growth direction was strongly affected by deposition temperature and pressure.

Organic Solar Cells with Hydrogenated In-Doped ZnO Replacing Sn-Doped In2O3 as Transparent Electrode

Hydrogenated In-doped ZnO (IZO:H) anodic films grown at different ratios (R) of hydrogen to argon were deposited at a low processing temperature of 100 °C on a glass substrate by pulsed DC magnetron sputtering for photovoltaic cells. Even at a low substrate temperature, the transparent electrode showed an average optical transmittance of 88% in the visible range and a reduced resistivity of less than 3.5×10-3 Ωcm. The organic photovoltaic cells with an IZO:H (R=0.08) electrode achieved a maximum power conversion efficiency (η) of 0.53%, which is as good as the values of the control device fabricated on a commercial ITO electrode (η=0.48%). This indicates that the efficiency of the organic photovoltaic cells is critically affected by the injection of hydrogen gas during the deposition of IZO:H. The high quality IZO:H film developed herein is promising as an alternative to conventional ITO film.

Transparent and Flexible Antenna for Wearable Glasses Applications

This paper aims to design, fabricate, and analyze transparent and flexible monopole antennas for an application in wearable glasses. A multilayer electrode film composed of 100-nm-thick indium-zinc-tin oxide (IZTO)/Ag/IZTO (IAI), a type of transparent conducting oxide electrodes, is selected as the conductors of antennas and ground planes of the wearable glasses. The average transparency of the proposed antennas is measured to be 81.1% in the visible wavelength, and the electrical conductivity of the proposed antennas is measured to be 2 000 000 S/m. The proposed antennas are fabricated with physical vapor deposition process in high vacuum. Moreover, nontransparent antennas made of a 40-nm-thick silver (Ag) thin film are designed and fabricated to compare their performances with the transparent IAI antennas. To reduce the electromagnetic field absorption of the human head, we introduced and analyzed three configurations (types A-C) of monopole antennas having different directions of radiation patterns. The fabricated IAI antennas show the average efficiency of 40% and 4-dBi peak gain at 2.4-2.5 GHz. Furthermore, they have a specific absorption rate lower than 1.6 W/kg, which complies with the Federal Communications Commission standard, when the input power is 15 dBm, which is Google Glasss.

Recovery of indium tin oxide (ITO) and glass plate from discarded TFT-LCD panels using an electrochemical method and acid treatment

The recovery of ITO and the glass substrate from discarded TFT-LCDs, without crushing the glass substrate, was done by using an electrochemical method and acid treatments. Anodic conditions did not show any redox reaction of the ITO except oxygen evolution. The oxygen evolution lifted the ITO layer off the glass substrate with the remaining colour filer and black matrix. Recovery of the ITO was 75%, but it showed an In–Sn ratio of 15.9:1. The recovered ITO was not suitable for reuse directly. It may be that it needed the addition of extra Sn. However, this work presented a new process for the resource circulation of the indium from discarded LCD panels. The free glass substrate was then recovered after removing the colour filter and black matrix by using an acid solution. The optical transmittance of the recovered glass substrate was about 90% in the visible region, and the average roughness was 0.96 nm.

Enhanced performance in polymer light emitting diodes using an indium–zinc–tin oxide transparent anode by the controlling of oxygen partial pressure at room temperature

The amount of indium in indium zinc tin oxide (IZTO) was reduced by over 20% by manufacturing an IZTO target containing ZnO for application as the transparent conducting oxide (TCO) anode of polymer light emitting diodes (PLEDs). The IZTO target was manufactured with the composition In2O3 (70 at%)–ZnO (15 at%)–SnO2 (15 at%), and IZTO films were formed at room temperature using a pulsed DC magnetron sputtering system at oxygen partial pressures of 0–4%. The optical and electrical properties of the IZTO films and the device performance of PLEDs with IZTO film were characterized. Amorphous IZTO films prepared at an oxygen partial pressure of 3% showed the best properties. The resistivity, mobility, transmittance, figure of merit and work function of the IZTO film were 5.6 × 10−4 Ω cm, 44.59 cm2 V s−1, 81% (visible region), 3.0 × 10−3 ohm−1, and 5.56 eV, respectively. The PLEDs with the IZTO film deposited under the optimum conditions showed the maximum brightness and the maximum luminance efficiency of 23u2006485 cd cm−2 and 2.29 cd A−1, respectively, which showed a 21% enhancement in device performance compared to PLEDs with commercial ITO film. In addition, the stability of the fabricated device was improved.

Transparent Microstrip Patch Antennas With Multilayer and Metal-Mesh Films

This letter presents transparent microstrip patch antennas made of two types of transparent conductive films, which are multilayer film (MLF; IZTO/Ag/IZTO) and metal-mesh film (MMF; Cu). The sheet resistance levels of the MLF and MMF are 2.52 and 0.18 Ω/□. The transparencies of the MLF and MMF are over 80% and 60% at a 550-nm wavelength, respectively. The design and dimensions of the antennas follow the conventional simple microstrip patch antenna. A transparent acryl substrate is used for the proposed transparent antennas. The conductive parts of the proposed antennas are also made of copper sheets (CS; case 1) for the performance comparison to two types of transparent antennas made of MLF (case 2) and MMF (case 3). The resonance frequency band of the antennas is 2.4–2.5 GHz for Wi-Fi service. The case-1, case-2, and case-3 antennas have peak gains of 4.75, −4.23, and 2.63 dB and have radiation efficiencies of 66.32%, 7.76%, and 42.69% at the center frequency of the Wi-Fi service band (2.45 GHz), respectively.

Mechanical Integrity of Flexible In–Zn–Sn–O Film for Flexible Transparent Electrode

The mechanical integrity of transparent In–Zn–Sn–O (IZTO) films is investigated using outer/inner bending, stretching, and twisting tests. Amorphous IZTO films are grown using a pulsed DC magnetron sputtering system with an IZTO target on a polyimide substrate at room temperature. Changes in the optical and electrical properties of IZTO films depend on the oxygen partial pressure applied during the film deposition process. In the case of 3% oxygen partial pressure, the IZTO films exhibit s resistivity of 8.3×10-4 Ω cm and an optical transmittance of 86%. The outer bending test shows that the critical bending radius decreases from 10 to 7.5 mm when the oxygen partial pressure is increased from 1 to 3%. The inner bending test reveals that the critical bending radius of all IZTO films is 3.5 mm regardless of oxygen partial pressure. The IZTO films also show excellent mechanical reliability in the bending fatigue tests of more than 10,000 cycles. In the uniaxial stretching tests, the electrical resistance of the IZTO film does not change until a strain of 2.4% is reached. The twisting tests demonstrate that the electrical resistance of IZTO films remains unchanged up to 25°. These results suggest that IZTO films have excellent mechanical durability and flexibility in comparison with already reported crystallized indium tin oxide (ITO) films.

Study on the Mechanical Properties and Thermal Conductive Properties of Cu/STS/Cu Clad Metal for LED/semiconductor Package Device Lead Frame

Abstract Lead frame which has a high thermal conductivity and high mechanical strength is one of core technology for ultra-thin electronics such as LED lead frames, memory devices of semiconductors, smart phone, PDA, tablet PC, notebook PC etc. In this paper, we fabricated a Cu/STS/Cu 3-layered clad metal for lead frame packaging materials and characterized the mechanical properties and thermal conductive properties of the clad metal lead frame material. The clad metal lead frame material has a comparable thermal conductivity to typical copper alloy lead frame materials and has a reinforced mechanical tensile strength by 1.6 times to typical pure copper lead frame materials. The thermal conductivity and mechanical tensile strength of the Cu/STS/Cu clad metal are 284.35 W/m·K and 52.78 kg/mm 2 , respectively. Key Words : Clad metal, Lead frame, LED, Semiconductor 1. 서 론 ‘발광다이오드’로 해석되는 LED(light emitting diode)는 빛을 방출하는 광소자이다. LED는 화합물반도체 특성을 이용해 전기 에너지를 빛 에너지로 전환시키는 반도체의 일종으로서 1962년 GaAsP를 사용하여 적색 가시광선 방출이 GE(general electric)의 Nick Holonyak Jr.에 의해 최초로 개발되었다. 이후 황색 LED, 1995년 일본 니치아사의 나카무라슈지에 의한 청색 LED의 개발에 이어 백색 LED가 개발되었다. LED는 기존의 광원대비 월등히 높은 광원효율과 저전력소모(백열등의 약 10%), 장수명(5만시간정도), 빠른 반응속도, 친 환경성(무수은) 등의 장점을 가지고 있다