Hyo Soo Lee

Bio: Hyo Soo Lee is an academic researcher from KITECH. The author has contributed to research in topics: Ultimate tensile strength & Thermal management of high-power LEDs. The author has an hindex of 3, co-authored 23 publications receiving 59 citations.

Analysis on thermal resistance of LED module with various thermal vias

Abstract: Light Emitting Diode (LED) has been already familiar that is used as lighting sources of general electronic devices and various displays. LED has many advantages such as long life, low power consumption and high reliability. In the future, as alternative to fluorescent lighting, it is sure that LED in lighting products is expected to receive much attention. However, the components related with advanced LED packages or modules have been issued on the heat from LED chip. And the LED chip is still being developed to the high power devices which are generating more heat. In this study, we investigated the variation of thermal resistance in LED modules embedded with thermal via. Through the analysis of thermal resistance with various test vehicles, we could obtain the concrete relationship between thermal resistance and structure of thermal via.

Rotationally symmetric colorization of metal surfaces through omnidirectional femtosecond laser-induced periodic surface structures.

Abstract: Following femtosecond (fs) laser pulse irradiation, the formation of a new type of low-spatial-frequency laser-induced periodic surface structure (LSFL) patterns, namely, omnidirectional LSFLs (OD-LSFLs) with the periodic ordering of their orientations, are investigated on Ni in this Letter. Using a liquid crystal polymer patterned depolarizer, we periodically rotate the polarization of fs laser pulses across the laser spot and create OD-LSFLs by raster scanning fs laser pulses. We also show that the period of the OD-LSFL orientation rotation can be controlled with the defocused distance, and OD-LSFLs can significantly expand the viewing angle of the structural colors in the azimuthal direction without noticeable color degradations.

Microstructure and Hardness Property of Internally Oxided AgCdO Alloy

Abstract: Microstructure and hardness property of AgCd alloy internally oxided at 973K for 1 h - 24 h with O2 atmosphere of 3 atm was investigated. Band typed CdO phase was formed at grain boundaries, and particle typed CdO phase was formed at grain interior. In this alloy, it was found that oxygen adsorpted at surface diffuses to interior through grain boundaries, and it subsequently diffuses into grain interior during internal oxidation. No Ag exduation was found in this alloy. The thickness of oxidized layer increased with increasing holding time at given temperature. Hardness of the oxidation zone was 125 ± 5 Hv, which value is higher two times than that of the oxidation free zone. The higher hardness of oxided region than the oxidation free zone was attributed to the dispersion strengthening by CdO particles.

Thermal management of LEDs: Package to system

Abstract: Light emitting diodes, LEDs, historically have been used for indicators and produced low amounts of heat. The introduction of high brightness LEDs with white light and monochromatic colors have led to a movement towards general illumination. The increased electrical currents used to drive the LEDs have focused more attention on the thermal paths in the developments of LED power packaging. The luminous efficiency of LEDs is soon expected to reach over 80 lumens/W, this is approximately 6 times the efficiency of a conventional incandescent tungsten bulb. Thermal management for the solid-state lighting applications is a key design parameter for both package and system level. Package and system level thermal management is discussed in separate sections. Effect of chip packages on junction to board thermal resistance was compared for both SiC and Sapphire chips. The higher thermal conductivity of the SiC chip provided about 2 times better thermal performance than the latter, while the under-filled Sapphire chip package can only catch the SiC chip performance. Later, system level thermal management was studied based on established numerical models for a conceptual solid-state lighting system. A conceptual LED illumination system was chosen and CFD models were created to determine the availability and limitations of passive air-cooling.

Recent progress on graphene-based substrates for surface-enhanced Raman scattering applications.

Abstract: Since the intriguing and inspiring discovery of graphene-enhanced Raman scattering (GERS) in 2010, graphene and graphene-based substrates have attracted significant attention in both theoretical research and application exploration of surface-enhanced Raman scattering (SERS); this makes graphene-involved SERS a burgeoning area in many scientific branches. The introduction of graphene not only overcomes some intrinsic drawbacks of SERS, but also has a great synergistic effect with traditional noble metal nanoparticle enhancement substrates and thus greatly improves the sensing performance of SERS and largely expands its application area. To better learn about the recent progress in graphene-based SERS substrates and shed light on future research, an overview of graphene and graphene-based SERS substrates is presented herein. In this review, the role played by graphene in graphene-based SERS substrates is first summarized, and then, the classification and preparation methods of graphene-based substrates are presented, which are helpful for understanding the structure–property relationship. Furthermore, the SERS applications of graphene-based substrates in biomedical areas, including biomolecule detection, bio-imaging, cancer diagnosis and therapy and drug delivery, are highlighted. Other applications in hot-topic areas such as food safety and environmental monitoring are also briefly discussed. Finally, challenges and perspectives on the deficiencies, future development and achievements are presented.