The rapid implementation of Mini and MicroLED lighting technologies has promoted innovation in every aspect of the SMT assembly process. Printing, placement, and reflow are all impacted when these assemblies are performed. The main challenge posed by this type of assembly is simply the scale of the components. The dimensions involved are below the visual threshold for most human beings. One of the biggest challenges for assembly in this sector involves the printing of solder paste. Tens, if not hundreds of thousands of ultra-miniature deposits must be made with micron precision in a single stroke of a squeegee. Furthermore, his needs to be accomplished at production speed and scale without room for error. In this presentation, we share our knowledge and solutions acquired as one of the largest solder suppliers in the world to the Mini and MicroLED market.

Emerging MicroLED technology offers compelling potential for near-eye devices. However, the MicroLED supply chain currently lacks readiness for mass production due to significant manufacturability and cost challenges. For near-eye device applications, this technology requires ultra-fine pixels (<10 micrometers) and highly miniaturized silicon transistors on the backplane. A heterogeneous integration approach adopted from a 3-D semiconductor system can address many MicroLED process technology, design, and cost challenges. This talk is concerned with two main strategies for drastic cost reduction: (1) lowering the cost of individual LEDs through the monolithic fabrication of GaN RGB diodes on a 300 mm silicon wafer, and (2) decreasing frontplane-to-backplane integration costs using wafer-to-wafer bonding, specifically bonding a 300 mm RGB wafer to a 300 mm silicon CMOS wafer. Our presentation will explore these strategies from the perspective of cost-effective and scalable semiconductor system integration, leveraging the mature 300 mm high-volume-manufacturing supply chain extensively used in the semiconductor industry for about 25 years, incorporating high-performance and low-power CMOS design for backplane devices, and utilizing recent advancements in 3-D heterogeneous integration with hybrid bonding.

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Balancing the quality and quantity of digital expressions presented to discerning customers.

MicroLED is seen to be a promising technology for future display. However, traditional display technologies are making progress and are currently challenging the intrinsic performances of MicroLED for traditional display. One competitive advantage of MicroLED consists in its exceptional high luminance efficiency requiring less active light emitting surface. This unique property paves the way for disruptive features such as transparent display and multifunctional display. In this presentation, we will review some key applications that could leverage multifunctional display. Some insight of MicroLED technology will be provided to the light of development performed at CEA-Leti.Then some proposal and comparison between new types of architecture combining efficient sensor and MicroLED arrangement tailored to multifunctional display will be drawn.

Laser technologies are essential for display fabrication today. Several laser processes and laser types are required for state-of-the-art display manufacturing. With the move from OLED to microLED displays some processes remain and several new manufacturing processes are required. The success of microLED displays is mainly driven by costs and availability of volume manufacturing equipment. Thus, microLEDs must become very small and need to be processed with highest throughput and yield. Lasers have proven their capability already in many applications but also in display fabrication. In this presentation, we will provide an overview of the microLED display process chain and highlight the individual laser processes.

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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.

Many aspects of today’s modern society are enabled by advances in semiconductor technologies. Most of those innovations have been driven by the incumbent corporates in the industry but some of them have come from ambitious startups globally. Despite the size of the market and the potential for key innovation, startups active in semiconductor technologies have often struggled to raise sufficient capital in the past decade, even in times when other sectors of the venture capital market have been very active. Since one to two years, though, we start to see a change in sentiment of venture capital investors towards semiconductor technology startups. This is driven by external market factors, such as the onset of artificial intelligence technology, driving global increase of data center traffic and compute performance, as well as geopolitical considerations and dependencies.imec.xpand is one of the world’s largest independent venture capital funds dedicated to early-stage semiconductor innovation. Since 2018 we have been investing in ambitious startups where the knowledge, expertise and infrastructure of imec, the world-renowned semiconductor and nanotechnology R&D center, can play a determining role in their growth. imec.xpand has an outspoken international mindset towards building disruptive global companies and strongly believes that sufficient funding from the start is key to future success. Our position gives us a unique view on the startup landscape in the sector, which we will share with the audience.

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µLED displays are still encountering obstacles in the consumer market, despite numerous samples demonstrated in different fields. The cost of µLED displays is currently a well- known obstacle, while the power consumption is another potential issue for µLED displays. The power loss caused by driving backplanes and pixel circuits is usually overlooked and potentially undermines the advantages of µLED display in certain applications, such as mobile displays. To accelerate the commercialization of µLED products, obstacles of cost and power loss need to be overcome. We delve into these two issues and present solutions based on our proprietary technology.

Since the development of the blue LED in the latter years of last century, LED technology has revolutionised the display industry. Now with demands for small high resolution displays used for AR/VR/XR applications and as a competitor to OLEDs for use in watches and mobile phones, a concerted effort is being made to transfer this technology to the much smaller microLEDs, with typical dimensions in the range of 1 to 10 microns. This transfer is far from straightforward as size effects begin to dominate. Our discussion herein has explored various etching methodologies for GaN and AlInGaP mesas, isolation, and pillar etching related to LED or microLED applications. The excellence of these etching processes holds paramount importance in shaping the ultimate performance of microLED devices. Our presentation will elucidate strategies for achieving well controlled profile angles, smooth surface, and sidewall with optimised processes. OIPT has an ongoing programme investigating correction of size effects, for the transition to the smallest devices &lt;5 microns, where the damage in sidewalls begins to dominate in a way that is not seen in typical larger devices.

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One of the intriguing yet largely unexplored technological approaches to fabricating microLED displays involves utilizing UV micro LEDs alongside colloidal quantum dots as light-converting materials. A main difference from traditional blue LEDs backlighting lies in the necessity of integrating hard-to-make and hard-to-get blue QDs in addition to red and green QDs. Despite this challenge, this approach offers several significant advantages, such as the lack of blue light leakage or better absorption efficiency of red and green QDs in the UV range as to name the most important ones. In this presentation, we will show the properties of our UV curable inks, which are based on heavy metal-free, blue light-emitting QDs known as PureBlue.dots, which can be used for UV light conversion to high quality 455 nm blue light which can be used in microLED displays. Furthermore, we will showcase our recent findings obtained from electroluminescent devices utilizing PureBlue.dots as the active material.

In the category of near-eye displays used in AR/XR devices, the Micro-LED technology pathway is widely regarded as the ultimate display solution due to its advantages such as high efficiency, brightness, and energy savings. However, at the current stage of development, achieving full colorization of Micro-LEDs is a challenge that the industry generally cannot overcome. Addressing the production bottleneck of Micro-LED micro- displays, we have developed a solution based on Nano-Porous Quantum Dot (NPQD®) technology, which enables direct integration of red, green, and blue colors at the wafer level on low-cost blue LED substrates. Through electro-chemical etching, nanometer-sized pores are etched into gallium nitride material, in which quantum dot materials are then injected. This structure serves as a natural container to help quantum dots perform color conversion, with highlights including high conversion efficiency and reliability. Simultaneously, the team has independently developed a complete set of technologies from epitaxy to module,making it possible to mass-produce new full-color Micro-LED display chips and micro-display modules that are high-efficiency, low-cost, small-sized, and highly reliable.

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The developments of high performance InGaN based RGB micro-light-emitting diodes (µLEDs) are discussed. Through novel epitaxial growth and processing, and transparent packaging we have achieved external quantum efficiencies as high as 58% EQE at blue wavelengths (450nm) and 21% for green (520nm) for microLEDs. The critical challenges of µLEDs, namely full-color scheme, decreasing pixel size and mass transfer technique, and their potential solutions are explored. Recently, we have demonstrated efficient microLEDs emitting in the blue to red at dimensions as small of 1 micron. Using metalorganic chemical vapor deposition (MOCVD) and strain relaxation methods we have also extending the wavelength range of the InGaN alloys as into the red with emission as long as 640nm. Red InGaN based red MicroLEDs with efficiencies of 6% has been fabricated, and they display superior temperature performance in comparison to AlGaInP based devices. Recently, we have employed tunnel junction technology to vertically stack blue and green MicroLEDs monolithically on the same wafer. Independent control of the BG colors with high efficiency is demonstrated with tunnel junctions. This work was supported by the Solid State Lighting and Energy Electronics Center(SSLEEC) at UC Santa Barbara.

The rapid advancement of Micro-LED technology has brought forth unprecedented opportunities, yet significant challenges remain in achieving scalable manufacturing processes. In this presentation, we delve into the critical issues of mass transfer efficiency and cost barriers that hinder widespread adoption. We propose a transformative approach of Continuous Roll-Transfer Printing to overcome these challenges, paving the way for the realization of high-performance Micro-LED displays on a commercial scale.

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