For a more vivid and immersive reality display, high-density full-color pixels are necessary. Professors Young Joon Hong (Sejong University) and Jeehwan Kim (Massachusetts Institute of Technology), along with their research colleagues, recently reported the creation of ultra-high-density full-color micro-LED pixels through remote and van der Waals epitaxy. The work was published in Nature on February 1, 2023, EST. 

The remote and van der Waals epitaxy method involves fabricating releasable semiconductor devices on a two-dimensional (2d) nanomaterial-coated wafer. The researchers grew red, green, and blue (R, G, B) LEDs on 2d nanomaterial-coated substrate and then gently peeled them off in a wafer sacle without a damage. The released R, G, B LED membranes were vertically stacked like pancakes, and then the stacked R/G/B LEDs were patterned into vertical pixels through a well-developed, minute photolithography technique. The vertically stacked R/G/B was singulated to a pixel on 4×4 μm2, which corresponds to a resolution of higher than 5,000 ppi. Pure R, G, B and full-color emission were achieved by modulating the injection currents to the R, G, B LEDs. After the LED membranes were exfoliated, the remaining wafers were refurbished to grow more LEDs. 

Prof. Hong stated, "This is the highest density full-color micro-LED pixel ever reported. By stacking R, G, B LEDs vertically, the pixel size could be reduced by at least one third." He also mentioned, "Conventionally, micro-LEDs were assembled side by side for full-color pixels, and even a small misalignment in assembly results in defective pixels that do not emit light. Our pixel fabrication method is based on patterning rather than assembly, like cutting a pancake with a knife, so we don't have to worry about misalignment in pixel fabrication." Prof. Kim added, "This work could shift the paradigm of LED display fabrication from assembly to patterning, which significantly reduces fabrication costs while improving productivity to meet industry standards."

(a) Illustration of vertical stack R/G/B LED architecture (left) and cross-sectional electron microscopic image of the vertical stack micro-LEDs. (b) Photographs of R, G, B emission from vertical stack micro-LED arrays. The micro-LED size was reduced to less than 5 ㎛ for 5,100 ppi. (c) Full-color emission of single micro-LED pixel.  

[Reference] Shin J. et al., (2023) “Vertical full-colour micro-LEDs via 2D materials-based layer transfer” Nature vol. 614, pp. 81-87

[Main Authors] Jiho Shin (MIT), Hyunseok Kim (MIT), Suresh Sundaram (Georgia Tech-Europe), Junseok Jeong (Sejong University), Kyusang Lee (University of Virginia), Kwanghun Chung (MIT), Young Joon Hong* (Sejong University), Abdallah Ougazzaden (Georgia Tech-Europe), Jeehwan Kim* (MIT) 

* Contact email : Professors Young Joon Hong (yjhong@sejong.ac.kr) & Jeehwan Kim (jeehwan@mit.edu)