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Research and development of micro-LED display is progressing in the fild of the wearable devide like AR glass or VR glass and so on as a next-generation display that applies ultrafine micro LED chips of flour size.

There are three methods of micro-LED display, "3 LEDs" using red, blue, green LEDs, "Blue LED + RG phosphor" that RB phosphors are excited by blue LED and "UV LED + RGB phosphor" that RGB phosphors are excited by UV LED. Currently, "3 LEDs" method is the mainstream. In case of "3 LEDs", the mass transfer is difficult because the compound material is different depending on the wavelength of red, blue and green LEDs.The control of each chip is complicated because of varies in the drive current, voltage and reaction speed of each color chips. In addition, the electric characteristics of micro red LED deteriorate due to micronization and it is a problem that the material is brittle.

Mass transfer of "Blue LED + RG phosphor" is relatively easy and, the current and voltage can also be unified because all the LED chips to be mounted are the micro blue LED. But there is a time lag because blue emits self-emission of blue LED, red and green emits by the phosphor excitation. In addition, there is a problem that color rendering is poor because of low illuminance of red and green by blue excitation.

"UV LED + RGB phosphor" can solve mass transfer and control problems but low conversion efficiency of RGB phosphors have been a demerit. We found that the luminous efficiency of micro UV-LED chips could be improved by making the n layer and p layer of the semiconductor structure an SLS structure, and we have obtained a patent.


Comparison of micro-LED display methods

Method 3 LEDs Blue LED + RG phosphor UV LED + RGB phosphor
Spectrum
Advantages •High color rendering •Easy control
•Reasonable cost
•Easy mass transfer
•Easy control
•High color rendering
Demerit •Difficulty in mass transfer
•Difficult control
•High cost
•Difficult to manufacture high quality red LED
•Poor color rendering
•Control difficulty middle level
•Vary in brightness of blue LED
•Low conversion efficiency of phosphor excitation

Cell structure of micro LED desplay by "UV LED + RGB phosphor"

Images are provided by V-Technology Co., Ltd.

Movie of RGB phosphor excited by UV LED

Emission Area of UV LED Module:20×24mm²
Current density converted to
micro LED chips : about 1µA/mm²
Emission of RGB phosphor film by UV LED

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