Good news for those anxiously awaiting more affordable prices for Micro LED-based flat-panel televisions and other display devices using the advanced self-emissive technology.

A team consisting of engineers from South Korea-based Seoul Viosys and the Santa Barbara, Calif.-based Solid State Lighting & Energy Electronics Center (SSLEEC) claim to have successfully developed blue and green micro LEDs with 1 μm diameter and addressed issues related to red micro LEDs of less than 70 μm.

These red micro LEDs have been notoriously difficult to mass produce due to a resulting decrease in External Quantum Efficiency (EQE). External Quantum Efficiency is the ratio of the number of photons emitted by the LED divided by the number of injected electrical charge.

Unlike LED-LCD TVs or mini-LED TVs that use LEDs as backlights, Micro LED displays use millions of tiny individually addressable Red, Green and Blue LEDs as pixels that directly emit light. MicroLED is therefore a self-emissive technology like today’s OLED TVs, except MicroLEDs have no issues with burn-in risk while achieving much higher brightness levels. Micro LED panels or modules can also be fitted together to assemble a wide variety of screen sizes ranging up to filling full walls

For the past several years, manufacturers including Samsung, Sony and LG have shown MicroLED prototypes for early super home theaters and commercial MicroLED displays costing many thousands of dollars. But mass production of such displays in volume is still next to impossible.

In 2021, Samsung showed a $156,000 110-inch model Micro LED display along with announcing plans for models measuring as small as 88- and 99-inches.

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Sony’s spin on MicroLED is called Crystal LED, which thus far have been directed primarily at commercial applications and has included huge video walls. At the same time manufacturers of personal devices and mobile display products are looking to very small applications of the technology for use in smart glasses and virtual reality (VR) and augmented reality (AR) headsets.

Heretofore, reducing the size of the LEDs resulted in a decrease in the total amount of emitted light. Overcoming this would require driving them harder and/or increasing their efficiency, and driving them harder means adding more power which generates heat.

Shrinking the gap between the pixels, or the “pitch size,” is another huge challenge for Micro LED technology. Without reducing the pixel pitch size its difficult to reduce the size of the MicroLED display.

(a) Electroluminescence (EL) Wavelength Spectrum of Red Micro LED (b) Blue and green Micro LEDs with a diameter of 1 μm viewed under an electron microscope.
Source: Seoul Viosys

Therefore, making chipsets measuring under 14 microns, as the Seoul Semiconductor team claims, is especially important for making display devices for VR and AR gear, among many others.

The developing team, which was led by Nobel Prize-winning physics Professor Shuji Nakamura, of the University of California, Santa Barbara (UCSB), called overcoming the efficiency challenges of MicroLED manufacturing “a game-changer” in that it now enables the start of mass production processes.

Seoul Viosys, which is billed as “the leading global compound semiconductor device provider” and a subsidiary of Seoul Semiconductor, announced that the team is now able to maintain External Quantum Efficiency and production yield necessary for the mass production of MC04 and MC02 products to which 70μm red micro LED is applied. In addition, the company said it is preparing to release 30μm one-pixel Micro LED products in the second half of 2021 and 10μm one-pixel Micro LED products in 2022.

“Seoul Viosys supported the SSLEEC team for 20 years to develop micro LEDs with a diameter of 1μm and made it possible to produce ultra-small micro LED solutions and improve the brightness by increasing the External Quantum Efficiency of red Micro LEDs by 150%, which had been limited to apply because the smaller the size, the lower the light-emitting efficiency,” the announcement states. {Thesis Name: Optics Express 5787, Vol. 28, No. 4 (2020) / Appl. Phys. Lett. 116, 071102 (2020)}.

The announcement referenced data from Taiwan-based research firm TrendForce predicting the annual sales of Micro LED chips for TVs will increase to an annual average of 250% from 2021 to 2025. It expected that the size of the market, which was only worth $23 million in 2021, will increase 150 times in the next five years.

Seoul Viosys said it will begin a rapid commercialization of all display applications also including smartphones, ARs and VRs through the improved micro LED technology.

“According to our principle to supply new products first to the companies that respect intellectual property rights, we will first supply the new ultra-small size 10μm and 30μm one-pixel Micro LEDs to the customers who have purchased our products (MC04, MC02, Wicop MINI, etc.) and are using them,” Seoul Viosys said in the technology statement.

Seoul Viosys has posted to the Seoul Semiconductor YouTube Channel an online seminar recorded July 2 on Micro LED, here and here.

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By Greg Tarr

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