Fluidic self-assembly for MicroLED displays by controlled viscosity.

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 issues1,2,5-7. 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.

Conductance stable and mechanically durable bi-layer EGaIn composite-coated stretchable fiber for 1D bioelectronics.

Deformable semi-solid liquid metal particles (LMP) have emerged as a promising substitute for rigid conductive fillers due to their excellent electrical properties and stable conductance under strain. However, achieving a compact and robust coating of LMP on fibers remains a persistent challenge, mainly due to the incompatibility of conventional coating techniques with LMP. Additionally, the limited durability and absence of initial electrical conductivity of LMP restrict their widespread application. In this study, we propose a solution process that robustly and compactly assembles mechanically durable and initially conductive LMP on fibers. Specifically, we present a shearing-based deposition of polymer-attached LMP followed by additional coating with CNT-attached LMP to create bi-layer LMP composite with exceptional durability, electrical conductivity, stretchability, and biocompatibility on various fibers. The versatility and reliability of this manufacturing strategy for 1D electronics are demonstrated through the development of sewn electrical circuits, smart clothes, stretchable biointerfaced fiber, and multifunctional fiber probes.

Numerical Simulations and In Situ Optical Microscopy Connecting Flow Pattern, Crystallization, and Thin-Film Properties for Organic Transistors with Superior Device-to-Device Uniformity.

Currently, due to the lack of precise control of flow behavior and the understanding of how it influences thin-film crystallization, strict tuning of thin-film properties during solution-based coating is difficult. In this work, a continuous-flow microfluidic-channel-based meniscus-guided coating (CoMiC) is introduced, which is a system that enables manipulation of flow patterns and analysis connecting flow pattern, crystallization, and thin-film properties. Continuous supply of a solution of an organic semiconductor with various flow patterns is generated using microfluidic channels. 3D numerical simulations and in situ microscopy allow the tracking of the flow pattern along its entire path (from within the microfluidic channel to near the liquid-solid boundary), and enable direct observation of thin-film crystallization process. In particular, the generation of chaotic flow results in unprecedented device-to-device uniformity, with coefficient of variation (CV) of 7.3% and average mobility of 2.04 cm2 V-1 s-1 in doped TIPS-pentacene. Furthermore, CV and average mobility of 9.6% and 11.4 cm2 V-1 s-1 are achieved, respectively, in a small molecule:polymer blend system. CoMiC can serve as a guideline for elucidating the relation between flow behavior, liquid-to-solid phase transition, and device performance, which has thus far been unknown.

Curving silver nanowires using liquid droplets for highly stretchable and durable percolation networks.

Silver (Ag) nanowires (NWs) are promising building blocks for the fabrication of stretchable electrodes, but they may undergo mechanical fracture at low tensile strains, which leads to degradation in electrical performance of Ag NW-based stretchable electrodes. Here we report on a simple route to create the percolation networks of Ag NW rings via a conventional spray coating process. We discovered that Ag NWs can be bent into curved shapes within micrometer-sized liquid droplets generated during the spraying process due to elasto-capillary interaction. This curving phenomenon allowed the deposition of Ag NW rings directly on a desired substrate without the need for any complicated process. The network of Ag NW rings effectively releases the applied tensile strains thanks to curved shapes of the constituent NWs, enabling the achievement of excellent electromechanical stability as well as high stretchability. Our approach not only provides a simple, low cost, and scalable route to the fabrication of high-performance Ag NW-based stretchable electrodes, but also opens a new and useful way of engineering the structure of NWs for various applications.