Papers by Author: Moo Whan Shin

Abstract: In this paper we report on the effects of variables in thermal resistance measurement of high power GaN-based light-emitting diodes (LEDs). The investigated variables include ambient temperature, thermal interface material (TIMs) at different pressure. The combination of transient thermal measurement method and optical measurement was employed for the study. The measured thermal resistance of LED packages was found to increase with the ambient temperature. The temperature dependence of optical efficiency, forward voltage, and thermal properties of packaging materials are thought to be responsible for the increase of thermal resistance with the ambient temperature. The interface effect on the thermal resistance was studied by applying different external pressure on the interface with different TIMs. And the measured thermal resistances were found to reach stabilization at certain pressure level after initial decrease with the external applied pressure.

Abstract: This paper discusses about thermal performance of high power light emitted diode (HPLED) implemented with sintered metal wick type heat pipe(SWHP). The HPLED(2.5 W) samples were surface mounted device(SMD) package used in our experiments. The experiments were made for SWHP with diameters of 6.0 mm. The length of the SWHP is 150 mm. The working fluid in the heat pipes is pure water. The electrical-thermal transient technique was employed for the junction temperature measurement. It was found that the SWHP leads to decreased of thermal resistance by 35 % compared with a simple copper bar in oil bath (forced cooling condition). Employment of copper cap as a LED attachment was more advantageous over the phosphor bronze. After the increase of input power, the thermal resistance of HPLED package has decreased with the increase of effective thermal conductivity of SWHP.

Abstract: The spin transport in a lateral spin-injection device with an FeCo/Si/FeCo junction has been investigated. Magnetoresistance (MR) signals were found to appear at low magnetic fields in the range 4 – 300 K. This is attributable to the switching of the magnetization of the two ferromagnetic contacts in the device for certain magnetic fields over which the magnetization in one contact is aligned antiparallel to that in the other. Our results suggest that the spin-polarized electrons are injected from the first contact and, after propagating through the bulk Si, are collected by the second contact.

Abstract: One of obstacles hindering a realization of large area size twisted nematic liquid crystal display (TN-LCD) flat panel (for example, 1100 x 1250 mm) is a slow response time. The slow response time is due to the inverse proportionality of turn on time with the frame frequency and pixel number (number of gate lines) in the twisted nematic liquid crystal system. It is known that the slow response time in the active matrix system of LCD be solved by reducing the sheet resistance of color filter electrodes. In this paper, we report on the processing details of the deposition of transparent ITO films using a DC sputtering system. The thickness of ITO layer was set for high transmittance and good conductivity and the films were characterized with respect to the transmittance and sheet resistance. The deposited ITO films show a good uniformity across the whole area and the average thickness of the ITO is about 1350 Å under the DC power of 10.7 kW. The transmittance is increased from 72.5 to about 93 % as the oxygen content is increased to 2.5 sccm for the samples without annealing. It was found that the transmittance is significantly improved by the annealing process at 220 oC for 40 min. up to 94 %. The sheet resistance is decreased with the DC power and exhibits below 22
/ after the samples were annealed.