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29 October 2018

Nitride Semiconductors forms subsidiary Micro Nitride to make micro UV-LED chips for displays

© Semiconductor Today Magazine / Juno PublishiPicture: Disco’s DAL7440 KABRA laser saw.

Japan’s Nitride Semiconductors Co Ltd (which was spun off from Tokushima University in 2000 and claims to have developed the first highly efficient ultraviolet light-emitting diode), says that on 1 November it is establishing the subsidiary Micro Nitride Co Ltd to develop, manufacture and sell micro UV LED chips for display applications. With capital of ¥50m plus a capital reserve of ¥50m, total capitalization will be ¥100m.

In recent years, self-emissive displays typified by organic light-emitting diodes (OLEDs) have been adopted for smartphones and the like but, due to their short lifetime and durability against heat, the development of micro-LED displays is becoming active, says the firm.

Currently, there are two methods for realizing micro-LED displays: three-LED type using red, blue and green LEDs, and the blue-LED-excitation type, with blue LEDs exciting red and green phosphors.

Regarding the three-LED type, it is impossible to produce micro red chips because the material is fragile. Also, it is difficult to mount LED chips of different colors with different structures in high density. Their current and voltage reaction speeds are different, so control of each chip becomes complicated, says Nitride Semiconductors.

By comparison, the micro blue-LED-excitation method can integrate all mounted LED chips into blue μ-LEDs, so the difficulty of mounting decreases and the current and voltage can also be unified. However, the blue light is emission whereas the red light and green light are excitation, so there is a time lag in reaction speed. Also, there is another problem that the color reproducibility is low due to the low luminance of red and green as a result of the blue excitation.

The firm says that these problems can be solved by μUV-LEDs + RGB phosphor. It found that luminous efficiency is doubled when fabricating μUV-LED chips with a strained-layer superlattice (SLS) structure in both the n and p layers (for which a patent is pending).

The reason is that, since the distance for current diffusion is short, the light emission recombination increases and the internal quantum efficiency improves. Also, since the distance from the light-emitting layer to the outside becomes short, the external quantum efficiency improves.

Tags: UV LEDs

Visit: www.nitride.co.jp

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