Close Menu
    Demo
    Academic Papers

    Fluidic self-assembly for MicroLED displays by controlled viscosity

    Doris MiniMicroLEDBy Updated:No Comments6 Mins Read33 Views
    Fluidic self-assembly for MicroLED displays by controlled viscosity
    Fluidic self-assembly for MicroLED displays by controlled viscosity

    Daewon Lee, Seongkyu Cho, Cheolheon Park, Kyung Ryoul Park, Jongcheon Lee, Jaewook Nam, Kwangguk Ahn, Changseo Park, Kiseong Jeon, Hwankuk Yuh, Wonseok Choi, Chung Hyun Lim, Taein Kwon, Young Hwan Min, Minho Joo, Yoon-Ho Choi, Jeong Soo Lee, Changsoon Kim & Sunghoon Kwon

    Published: 12 July 2023   Nature 619(7971):1-6

    DOI:10.1038/s41586-023-06167-5

    Abstract

    Displays in which arrays of microscopic ‘particles’, or chiplets, of inorganic light-emitting diodes (LEDs) constitute the pixels, termed MicroLED displays, have received considerable attention1,2 because they can potentially outperform commercially available displays based on organic LEDs3,4 in terms of power consumption, colour saturation, brightness and stability and without image burn-in issues1,2,5,6,7. To manufacture these displays, LED chiplets must be epitaxially grown on separate wafers for maximum device performance and then transferred onto the display substrate. Given that the number of LEDs needed for transfer is tremendous—for example, more than 24 million chiplets smaller than 100 μm are required for a 50-inch, ultra-high-definition display—a technique capable of assembling tens of millions of individual LEDs at low cost and high throughput is needed to commercialize MicroLED displays. Here we demonstrate a MicroLED lighting panel consisting of more than 19,000 disk-shaped GaN chiplets, 45 μm in diameter and 5 μm in thickness, assembled in 60 s by a simple agitation-based, surface-tension-driven fluidic self-assembly (FSA) technique with a yield of 99.88%. The creation of this level of large-scale, high-yield FSA of sub-100-μm chiplets was considered a significant challenge because of the low inertia of the chiplets. Our key finding in overcoming this difficulty is that the addition of a small amount of poloxamer to the assembly solution increases its viscosity which, in turn, increases liquid-to-chiplet momentum transfer. Our results represent significant progress towards the ultimate goal of low-cost, high-throughput manufacture of full-colour MicroLED displays by FSA.

    Fabrication of a MicroLED lighting panel by FSA a, Schematic of the dip-soldering process whereby solder bumps are selectively formed on Au patterns on the substrate; scale bars, 5 μm. b, Schematic of agitation process. c, Top, scanning electron microscope (SEM) image of a very large number of GaN LED chiplets; scale bar, 200 μm; bottom, schematic showing a region near the substrate during the agitation process. d, Enlarged view of a binding site showing the assembly process. e, SEM image of a single GaN LED chiplet assembled on the substrate; scale bar, 20 μm. f, SEM image showing an array of assembled chiplets (pitch dimensions, 360 × 120 μm²); scale bar, 45 μm. g, Image of an operational blue-emitting MicroLED lighting panel (detail shown in Fig. 3a); scale bar, 50 μm. e,f, Au layer on the substrate is unpatterned (that is, it covers the entire substrate).
    Fabrication of a MicroLED lighting panel by FSA a, Schematic of the dip-soldering process whereby solder bumps are selectively formed on Au patterns on the substrate; scale bars, 5 μm. b, Schematic of agitation process. c, Top, scanning electron microscope (SEM) image of a very large number of GaN LED chiplets; scale bar, 200 μm; bottom, schematic showing a region near the substrate during the agitation process. d, Enlarged view of a binding site showing the assembly process. e, SEM image of a single GaN LED chiplet assembled on the substrate; scale bar, 20 μm. f, SEM image showing an array of assembled chiplets (pitch dimensions, 360 × 120 μm²); scale bar, 45 μm. g, Image of an operational blue-emitting MicroLED lighting panel (detail shown in Fig. 3a); scale bar, 50 μm. e,f, Au layer on the substrate is unpatterned (that is, it covers the entire substrate).
    Difference in assembly mechanism between large and small chiplets and its effect on assembly yield a, Top, for large chiplets the inertial force (red arrow) allows the chiplets to collide with the substrate with sufficient momentum. Bottom, image of cubic Si chiplets of edge length 150 μm assembled with yield exceeding 89%; scale bar, 300 μm. b, Top, small chiplets, on the other hand, collide with the substrate with insufficient momentum (blue arrow) owing to decrease in inertia. As a result, assembly yield for small GaN chiplets (width, 30 μm; depth, 30 μm; height, 5 μm) is much smaller (below 5%; bottom) compared with the large chiplets in a; scale bar, 500 μm. c, Top, when a small amount of poloxamer is added to the assembly solution the viscosity of the solution increases which, in turn, increases liquid-to-chiplet momentum transfer (large blue arrow). Consequently, the chiplets used in b were assembled with significantly increased yield (exceeding 97%; bottom); scale bar, 500 μm.
    Difference in assembly mechanism between large and small chiplets and its effect on assembly yield a, Top, for large chiplets the inertial force (red arrow) allows the chiplets to collide with the substrate with sufficient momentum. Bottom, image of cubic Si chiplets of edge length 150 μm assembled with yield exceeding 89%; scale bar, 300 μm. b, Top, small chiplets, on the other hand, collide with the substrate with insufficient momentum (blue arrow) owing to decrease in inertia. As a result, assembly yield for small GaN chiplets (width, 30 μm; depth, 30 μm; height, 5 μm) is much smaller (below 5%; bottom) compared with the large chiplets in a; scale bar, 500 μm. c, Top, when a small amount of poloxamer is added to the assembly solution the viscosity of the solution increases which, in turn, increases liquid-to-chiplet momentum transfer (large blue arrow). Consequently, the chiplets used in b were assembled with significantly increased yield (exceeding 97%; bottom); scale bar, 500 μm.
    MicroLED lighting panel manufactured by a simple agitation-based FSA process a, Left, schematic of the blue-emitting MicroLED panel showing the arrangement of the bottom (orange) and top (yellow) electrodes. MicroLED chiplets, with diameter 45 μm and thickness 5 μm, were assembled to form an array with pitch dimensions 360 × 120 μm². Right, detailed side view of the assembled chiplet and a pixel detailing layer structure. b, Microscopy image of a single LED chiplet in operation; scale bar, 20 μm. c, Image of the 3 × 3 square-cm MicroLED panel; scale bar, 1.3 cm. d, Magnified view of the MicroLED panel shown in c; scale bar, 1 mm. e, Current-versus-voltage characteristic of the MicroLED panel. f, Electroluminescent spectrum of the MicroLED panel. g, Microscopy images of MicroLED under no bias (left) and under DC bias taken under illumination (middle) and in the dark (right); scale bars, 100 μm. MQW, multiple quantum well; PI, polyimide; a.u., arbitrary units.
    FR of agitation-based FSA processes versus chiplet mass a, For our poloxamer-added FSA process with GaN chiplets, three data points are plotted: lowest failure rate (FR, red circle), FR with highest number of binding spots (N) (inverted red triangle) and FR averaged over ten experiments (red square; Extended Data Table 1). Values of N are grouped into four categories, represented by large coloured circles centred at data points. Data points with FR = 10−∞ correspond to a yield of 100%, which was reported only with small N (≤820). Chiplet dimensions: a30×30×6 μm³; b45 μm (diameter), 5 μm (thickness); c40×20×5 μm³; dAll data points given in references are plotted; eThe minimum FR is plotted; fin the case of N = 10,000, maximum FR is plotted because no other information is given in the paper; in the case of N = 600 the average FR is plotted. b, Frequency (left) and cumulative frequency (right) histograms of alignment error (distance between centroid coordinates of chiplet and corresponding binding site). c, Scatter plot of alignment errors. Grey line and light yellow shading represent chiplet perimeter and Au pad, respectively.

    Disclaimer: The views and opinions expressed in this article are those of the original authors and do not necessarily reflect the official policy or position of MiniMicroLED Insights . While we strive to ensure the accuracy and reliability of the information provided, the content on this website may include translations, re-edited versions of second-hand information, or information derived from unverifiable sources. MiniMicroLED Insights makes no representations or warranties, express or implied, regarding the completeness, accuracy, or timeliness of such content. The information in this article is for informational purposes only and should not be construed as professional advice. Any reliance you place on such information is strictly at your own risk. To the fullest extent permitted by law, MiniMicroLED Insights disclaims all liability for any direct, indirect, incidental, consequential, or punitive damages arising out of your use of, or reliance on, the information contained in this article.

    Copyright Notice: This article may include translated and re-edited content derived from various online sources, including websites and social media platforms. While we strive to credit the original authors and sources to the best of our ability, we may not always be able to verify the original source of the content. All rights to the original content remain with the original author or source publication. Where applicable, this content is reproduced for educational and informational purposes under the fair use doctrine. If you believe any content on this site infringes upon your intellectual property rights, or if you are the copyright owner and believe we have not credited you correctly, please contact us at minimicroled.business@gmail.com. We will investigate and take corrective action, including removing or properly crediting the content if necessary.

    Content sourced and adapted by MiniMicroLED Insights (Doris).

    Share.
    Doris MiniMicroLED

    Related Posts

    Leave A Reply