News: LEDs
7 October 2021
Nitride Semiconductors granted micro-UV-LED related patents in Europe and USA
Japan’s Nitride Semiconductors Co Ltd (which was spun off from Tokushima University in 2000) says that patents regarding high-efficiency technology for micro UV(ultraviolet)-LEDs were granted to it in the UK, Germany and France on 8 September (European patent number 3644379) and in the USA on 5 October (US patent number: 11,139,342).
In collaboration with professor Shiro Sakai at Tokushima University, Nitride developed what it claims was the first high-efficiency UV-LED as early as 2000. It has since continued to manufacture and sell UV-LED products, and says that it has invested heavily in R&D to develop and enhance its UV-LED technology.
Regarding the latest patented technology, micro-LED displays are being actively developed by various companies (including Apple) as next-generation display technologies, superseding organic electro-luminescent (EL) displays (which have problems with durability). Since the light from conventional red, blue and green LEDs has different wavelengths, the compound semiconductor material differs depending on the color. Not only do the electrical characteristics differ but also the reaction speed and deterioration characteristics make it difficult to control the display. In addition, since the bandgap energy of the red LED is narrow, the electrical characteristics deteriorate due to micronization. Furthermore, since the material is brittle, it is difficult to reduce the size to 50μm or less, and each company is working on development.
The patented technology improves luminous efficiency in micro-LED chips with wavelengths of 385-400nm by reducing the chip size to 50μm or less, mainly by using a superlattice structure, and using a patterned sapphire substrate (PSS). Unlike LEDs of other colors whose luminous efficiency decreases due to micro-sizing, this patent suppresses the decrease in efficiency.
Micro-UV-LEDs can achieve full color by exciting red, blue and green phosphors. It is difficult and time-consuming to mount LED chips as small as wheat flour (20-30μm in size) on a TFT display board. By unifying the LED chips from three types (red, blue and green) to one type (UV-LED), not only mounting is easy but also current and voltage control is easy, says Nitride Semiconductors. Although it was said that the luminous efficiency of UV-LEDs is low, this high-efficiency technology can greatly improve the feasibility of micro-LED displays, reckons the firm.
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