Osram Opto Semiconductors has reported record results in the laboratory for green-emitting ThinGaN and red-emitting AlGaInP chips. The company expects the first LEDs based on these chips to go into series production by the middle of 2008.
The performance of green chips, fabricated using Osram's ThinGaN technology, has been increased due to a new epitaxial (material deposition) process and improved chip design.
Green-emitting (527 nm wavelength) chips measuring 1 mm2 achieved a luminous flux in the laboratory in excess of 180 lumens at 1 A (see graph 1). When driven at 350 mA, the chip produced 100 lm and consumesd 1.4 W (equivalent to 72 lm/W).
By contrast, the conventional generation of chips in the current green Platinum Dragon LED would need an operating current of 1 A to produce 100 lm.
When introduced next year, the chips will be used in Dragon and Ostar LEDs, and are aimed at LCD backlighting applications. With higher output levels, a smaller number of LEDs will be required to backlight large displays.
Red chip records
Under laboratory conditions, a red-emitting AlGaInP chip with a wavelength of 615 nm achieved more than 300 lm from an operating current of 2 A (see graph 2). With a power consumption of 6 W, the efficiency is 52 lm/W.
By comparison, the current red Platinum Dragon LED has an output of 96 lm from a consumption of 2.5 W, giving a luminous efficacy of 38 lm/W.
"We have achieved this enormous increase in brightness above all by designing the new chips to handle higher currents. This has resulted from optimizing the series resistance," said Ralph Wirth, development engineer at Osram Opto Semiconductors.
The improved InGAlP thin-film technology chips are designed primarily for projection applications, and will be used in Dragon and Ostar LEDs, particularly in Ostar Projection. Offering a much greater luminance (flux per unit area) than predecessors, the new devices produce more light to inject into external optical systems.