Cheng-Chung Chiang

Improved thermal management of GaN/sapphire light-emitting diodes embedded in reflective heat spreaders

Using maskless lithography and electroforming techniques, we have demonstrated an enhanced performance of GaN/sapphire light-emitting diode (LED) embedded in a reflective copper heat spreader. The chip size and dominant wavelength of the blue emitter used in this research is 1×1 mm2 and 455 nm, respectively. The cup-shaped LED heat sink is electroformed on sapphire directly using the spin-coated photoresist coated with the Au/Cr/Ag mirror as a mold and dicing into the embedded LED with a Cu base dimension of 3×3 mm2, which effectively enhances the heat dissipation down to the metal frame and reaps the light flux generated from the side emission. With the aid of a reflective heat spreader, the encapsulated LED sample driven at 1 A yields the light output power of 700 mW and around 2.7-times increase in the wall-plug efficiency compared to that of the conventional GaN/sapphire LED. Infrared thermal images confirm the GaN/sapphire LED with more efficient heat extraction and better temperature uniformity. The...

Novel Device Design for High-Power InGaN/Sapphire LEDs Using Copper Heat Spreader With Reflector

Direct integration of InGaN/sapphire LED with a cup-shaped copper heat spreader was proposed for enhancing light extraction and heat dissipation by self-aligned photolithography and copper electroforming techniques. Based on optical simulation results, geometric design for a copper heat spreader is crucial to luminous property of an LED chip. An InGaN/sapphire LED embedded with the optimized cup-shaped copper heat spreader was demonstrated to exhibit superior light output power than a conventional LED by a factor of 2.68 times at an injection current of 1 A. Moreover, the power efficiency is remarkably increased from 4.2% to 15.7% at the same driven current. The improved device performance can be attributed to both of the enhanced light extraction of the laterally emitted light from an LED chip and efficient heat dissipation by the highly reflective and excellently thermal conductive copper heat spreader. These results suggest an efficient alternative simultaneously with two functions of thermal management and light extraction for high-power InGaN/sapphire LEDs application from chip to package design.

An ultrathin (∼100μm thick) flexible light plate fabricated using self-alignment and lift-off techniques

An ultrathin (∼100μm thick) flexible light plate was designed and fabricated on a parylene template using a combination of self-alignment and lift-off techniques. The solid-state InGaN light-emitting diodes (LEDs) (λp=465nm) was used as the light source to overcome the problem of conventional organic light-emitting devices which require perfect encapsulation against the permeation of water and oxygen. After the sidewalls of LEDs were passivated by the photodefinable polymer, the LED chip array can be further sandwiched by the indium-tin oxide (ITO) and Al electrodes to form a thin-film package with all the processing temperatures below 250°C. The ITO-coated transparent parylene template can be peeled off from the glass carrier after forming the ultrathin LED light plate. The flexible light plates present no damage even after they were flexed 1000 times around a 3-cm-diameter cylinder. The present self-alignment or mask-less process is a very promising approach to flexible backlight applications.

Thermal Management Design from Chip to Package for High Power InGaN/sapphire LEDs Applications

Thermal Management Design from Chip to Package for High Power InGaN/Sapphire LED Applications R. H. Horng,* C. C. Chiang, Y. L. Tsai, C. P. Lin, K. Kan, H. I. Lin, and D. S. Wuu Institute of Precision Engineering and Department of Materials Science and Engineering, National Chung Hsing University, Taichung 402, Taiwan Kinik Company, Yingge, Taipei 239, Taiwan Liung Feng Industrial Company, Limited, Tucheng City, Taipei 236, Taiwan