Innovative Approaches to Enhancing MicroLED Display Technology: Insights from TNO / Holst Centre

In recent years, there has been a significant surge in the adoption of micro-LED-based display technology by major industry players. However, the current assembly process faces fundamental bottlenecks. While state-of-the-art pick-and-place equipment can process over 60,000 units per hour (UPH), the technique is ill-suited when it comes to assembling micro-components with dimensions smaller than 100 μm. Furthermore, with the high number of microLEDs per display, there is a need to accelerate the assembly process. Take, for instance, the current high-end smartphone display, which would need about 10 million microLEDs – this would require a traditional pick-and-place machine a week to assemble. Additionally, defect management for dead pixel-free displays requiring accurate and fast placement of a single die is also currently a challenge. Due to these bottlenecks, manufacturers are actively exploring alternative cost-effective, accurate, and fast assembly solutions. Holst Centre has developed an innovative and proprietary release stack that enables the fast release of micro-LED-sized components with an adaptive pitch and high selectivity using a low-cost laser source. Our technology exhibits exceptional scalability and flexibility, facilitating the transfer of both mini- and microLEDs. In an R&D environment at Holst Centre, we achieved a remarkable microLED transfer precision with displacements of 1µm (1σ) and rotations of 1° (1σ), coupled with a yield surpassing 99.9% on a sample set with over ten thousand components. This advancement not only enables defect management but also offers compatibility with die-on-demand release from ultrahigh-density wafers, achieving edge-to-edge die spacing down to just a few micrometers. The transfer of microcomponents to our release stack relies on a lamination process utilizing a temporary carrier. There is a difficulty in procuring micro-LEDs due to their limited commercial availability during development, a problem that is further exacerbated by the absence of standardization in microLED sizes and buildup architecture. The microLEDs have a diverse range of architectures, form factors, and sizes, introducing additional complexity to the systematic testing of this technology. Therefore, we have developed a new process of monolithically fabricating ultrasmall dummy dies on our proprietary release stack which can be transferred via a laser. The use of this new process enables precise and accurate fabrication of dummy dies with varying sizes, aspect ratios, and adaptive pitches — matching form factors and dimensions of various microLEDs.