MicroLED Integration via Fluidic Self-Assembly: Chemistry Meets Design

Next-generation semiconductor technologies increasingly demand massively parallel assembly methods that can integrate discrete microscopic chiplets with high throughput, precision, and scalability ^1,2 . Fluidic self-assembly (FSA) ³ has emerged as a powerful candidate for parallel integration ⁴ , yet its application has remained limited to chiplets larger than several tens of micrometers. Here, we present the FSA of microscopic light-emitting diodes (microLEDs) onto molten solder-based receptor arrays, where the chiplets attach, self-align, and form electrical connections autonomously until all receptors are occupied. MicroLEDs with dimensions of 18 × 18 × 2 µm ³ are assembled with a 99.77% yield and at rates exceeding 12,000 chiplets per minute. These metrics push the FSA into the deep microscale by achieving dimensions five and twelve times smaller in area and volume, respectively, than previous records ⁵ . Three mutually necessary criteria define the operational window for high-yield assembly, each addressing a distinct challenge inherent to this scale. First, a mobile slurry of chiplets maximizes efficient chiplet-receptor interaction across the solder bumps. Second, precisely tuned acid concentration in the fluidic transfer medium enables reliable solder wetting and attachment. Third, a 20-fold suppression of oxidation is essential, as oxide growth kinetics increasingly outcompete solder wetting at the microscale. Device functionality is validated through a self-assembled microLED display with a transparent top electrode. Ultimately, these results demonstrate massively parallel assembly of truly microscopic chiplets at scales previously inaccessible, opening new pathways for emerging photonic and semiconductor integration technologies.