New Microstructures on Substrate Boost LED Brightness

Mar 8, 2014
Tetsuo Nozawa, Nikkei Electronics
A comparison in LED brightness. The "ND (nanodot array)-PSS" is used for the right lamp.
A comparison in LED brightness. The "ND (nanodot array)-PSS" is used for the right lamp.
[Click to enlarge image]
A comparison in OLED brightness. A microstructure was formed on the surface of the right device's glass substrate. Oji Holdings calls it "plasmonic OLED."
A comparison in OLED brightness. A microstructure was formed on the surface of the right device's glass substrate. Oji Holdings calls it "plasmonic OLED."
[Click to enlarge image]
The microstructures formed on the surfaces of sapphire substrates
The microstructures formed on the surfaces of sapphire substrates
[Click to enlarge image]
Composite structures with several hundred nanometer and several micrometer pitches
Composite structures with several hundred nanometer and several micrometer pitches
[Click to enlarge image]

Oji Holdings Corp established a micromachining technology based on a high-precision coating technology for fine particles and succeeded in improving the brightnesses of LED and OLED by about 100%.

Oji Holdings plans to ship sapphire substrates whose surfaces are treated with the new micromachining technology for LEDs in 2016. The company exhibited LEDs and OLEDs manufactured using the technology at LED Next Stage 2014, a trade show that took place from March 4 to 7, 2014, in Tokyo.

Recently, many high-efficiency LEDs are made using sapphire substrates that have minute concave and convex or wave-like structures on their surfaces (PSS: patterned sapphire substrate). With a PSS, light coming from the gallium nitride (GaN) crystal on the substrate becomes more likely to be reflected, and the light extraction efficiency of LED improves, increasing luminous efficiency by 20-30% in many cases.

Common technologies to form a PSS include optical lithography and nanoimprinting, which are semiconductor manufacturing technologies.

Composite structure with several hundred nanometer and several micrometer pitches

The LED that Oji Holdings made this time also uses a PSS. However, the company employed the "ND (nanodot array)-PSS," which is made by using its own high-precision coating technology for fine particles instead of optical lithography or nanoimprinting.

Though Oji Holdings has not disclosed the details of the coating technology, it enables to realize an ND-PSS having concave and convex structures with a pitch as small as 200nm and an ND-PSS with a composite structure having both several hundred nanometer and several micrometer pitches.

According to the company, an LED (luminous wavelength: 385nm) made by using such an ND-PSS had a 2.4 times higher brightness and a 1.8 times higher total luminous flux (in the front direction). Its luminous efficiency was not disclosed.

Also, when Oji Holdings applied the new technology to the glass substrates of OLED devices, brightness in the front direction improved by about 100% with a red light-emitting device and by about 70% with a white light-emitting device. Furthermore, it realized a lower power consumption and a longer product life.

With this technology, the concave and convex structures formed by treating the surface of a glass substrate function as electrodes, extracting surface plasmons from the surface of the electrodes. This is the result of a joint research with Riken, the company said.

Oji Holdings plans to release 2- to 6-inch PSSes (mainly 4-inch PSS) in 2016. The company has not yet shipped any sapphire substrate for LEDs. So, it will be a new entry into the market.