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 X 1 mm(2) 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 X 3 mm(2), 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. These results exhibit an alternative solution to thermal management of high power LED-on-sapphire samples besides the laser lift-off technique. (C) 2008 American Institute of Physics

Device performances were investigated for InGaN/sapphire light-emitting diodes ͑LEDs͒ with advanced heat dissipation design from chip to package. By directly contacting a copper heat spreader with sapphire, the maximum junction temperature of the LED chip was reduced from 62.9°C of a conventional LED to 48.3°C at an injection current of 350 mA. Further temperature reduction to 37.3°C could be achieved by packaging the copper-surrounded LED chip on the heat sink coated with a diamond-like layer which acts as the second heat spreader. The reduced junction temperature was attributed to good heat dissipation from both the copper and the diamond-like layer due to their low thermal resistance. The copper heat spreader not only extracts heat efficiently, but also enhances the light extraction of the LED, as the copper was designed with a proper geometry such as cup-shaped profile. The improved LED performance suggests that the proposed thermal management from chip to package is an efficient alternative for high power applications. High power GaN-based light-emitting diodes ͑LEDs͒ are essential for next-generation lighting applications. To achieve higher light output performance, it is necessary to drive a GaN-based LED to a high current density level. However, under such a high current injection, the LED typically exhibits the performance deterioration of power saturation.

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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

Abstract-For the use of green energy and ubiquitous computing, this study investigates miniature electric generators that are constructed with piezoelectric benders. Electric power is generated by vibratory deformation of piezoelectric benders. Three different designs of piezoelectric generators are created and compared in this study by using mechanics analysis. The result shows that the cantilever design yields more power than symmetric and airfoil designs. Experimental results show that generated voltage rises with not only attached point masses, but also the swing frequency of a swing arm, to which the proposed piezoelectric generator is attached. In addition, At 6.5 Hz swing frequency, the maximum power 0.3µW is generated.