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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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MicroLED displays are poised to play a significant role in the future of the display market due to their advanced features, which may fill the gap of lack of luminance of incumbent technologies and market demand for energy efficient displays.This talk introduces designs, use cases, challenges and technical solutions for automotive products opportunities.

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.

Micro-LEDs are promising for next-generation displays such as AR/VR. InGaN material can generate emissions in red, green, and blue. In the same material system, the LED devices can be stacked continuously, making it possible to fabricate monolithic RGB micro-LEDs on the same wafer. The low efficiency of red LEDs is the bottleneck for RGB micro-LED development. In this presentation, we will discuss the growth technology for InGaN-based red LEDs and the realization of monolithic RGB micro-LEDs.

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Polychrome microLED displays of high brightness (one million nits), high resolution (>3000ppi) on CMOS backplanes are showing potential for millimeters size, near-eye display applications. As a step towards developing these millimeter size displays, Applied Materials has fabricated direct-view microLED displays on thin-film transistor (TFT)-based glass backplanes. These displays offer enhanced outdoor visibility and improved battery life for smartwatches and smartphones,owing to their high brightness and energy efficiency. Key components of the novel display include a backplane with 4-subpxiel R/G/B/W configuration, UV-A micro-LEDs, pixel isolation (PI) structure, ink-jetted Cd-free R/G/B quantum dots (QDs), and a UV blocker that absorbs residual UV-A, together with touch and other contrast-ratio enhancement elements. We have built several active-matrix (AM) smartwatch displays using commercial-scale process and equipment scalable to manufacturing. This presentation will provide details on our pilot-scale manufacturing of smartwatch display modules as well as details on development efforts of other near-eye and direct-view microLED display applications.

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.

Light-matter interactions at scales much smaller than the wavelength of the light opens new possibilities to control light. This field is called nano-photonics and enables improvements and new applications in micro-LEDs that are not possible with classical optics and current micro-structuring methods.Micro-LEDs have 3 challenges that can be “overcome” by making use of wafer-scale sub- 100nm patterns with single nm reproducibility. First, by making use of templated growth a full RGR LED system can be made on one substrate. For high resolution displays, the recombination process is not required anymore. Second, the light generated in the high refractive index semiconductor needs to be couple to air-modes. In macroscopic LEDs this is achieved by micro-patterns, light re-direction and recycling. This method is not possible to use in micro-LEDs as the micro-patterns are the size of the LED size. Photonic crystals can extract the light and also shape the extraction to either beam-like or bat-wing, compared to Lambertian in conventional LEDs. This creates directly more usable light by the enhanced out-coupling and directionality. Last, depending on the application, LED size and use of photonic crystals ,additional beam shaping might be required. The fast growing field and adoption of meta-lenses can help to keep the whole optical system efficient and compact. Metalenses function by precisely positioning nano-resonators that control the phase of the light and thereby can shape the wave-front and the (freeform) lens. These are robust, flat, thin (lens < 1micron) and therefore allow for easier integration. All the above mentioned applications of nano-photonics require feature sizes below 50nm with 1-5nm absolute size control to achieve the desired functions. The patterning method that can achieve this in a cost efficiency production method is based on nanoimprinting to form inorganic hard masks or functional devices. In the contribution the technology and nano-photonic applications will be discussed.

Methods to measure subpixel luminance & chromaticity for correction (Demura) & Quality Control for MicroLED displays. This inorganic emissive technology offers many benefits over other display technologies including high brightness, contrast, wide colour gamut, longevity, and high pixel density, improving visual performance in various ambient-light conditions from total darkness to full daylight and from multiple viewing angles. What are the challenges to efficiently control the quality of microLED displays and how to enable display correction?

In this presentation we will introduce our latest technology in micro-LED wafer inspection based on photoluminescence analysis. We are introducing our new imaging module mounted in our full wafer micro-LED inspection machine. This imaging module can simultaneously capture intensity and wavelength of light emitted from micro-LEDs by illuminating them with a stable light source. It allows a rapid acquisition of the photoluminescence over the whole wafer surface. By detecting the intensity and wavelength of the micro-LED emission the system makes quick pass/fail decisions to find abnormalities on the surface and semiconductor level.

The talk provides a brief overview of how laser-based processes revolutionize µLED production. It highlights the use of LIFT & line beam solutions to enhance yield and productivity. The talk also showcases a novel process chain involving LIFT and bonding on the backplane receiver, as the development and optimization of backplane materials alongside the laser process are crucial for successful bonding processes.

In the past decades the color gamut and resolution of displays was increased, as well as the energy efficiency. Under the current circumstances and with respect to their size microLEDs offer benefits for light weight smart glasses, transparent displays and automotive interior displays. Even the implementation in automotive rear lamps seems to be interesting for designers and engineers. An important material class are adhesives or so called functional polymers. Directional conductive adhesives can be coated over lager areas enabling the electrical and mechanical connection, while intrinsically preventing short circuits. Moreover functional polymers can be tailored in terms of color, transmission and viscosity to name only a few important parameters. It will be shown, that a reliable electrical and mechanical connection of miniLEDs with adhesives is possible after automated pick and place and thermal curing as an alternative to conventional solder materials.

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Inkjet printing of has become a manufacturing standard for obtaining high-end QD-enhanced OLED displays. To extend the viability of this approach towards microLED manufacturing, the conventional inkjet process is too limiting though in terms of droplet size and precision. Also, the low viscosity of inks is a major concern, since layer thickness of printed QD layers needs to be minimized, in order to reduce light-losses at the black matrix. All these problems can be coped with by using EHD printing instead of conventional piezo-based ejection, as the process not only delivery sub-micron resolution but is also compatible with much higher ink viscosities. So far, the limitation, like so often, is not quality but quantity though. Scrona offers multinozzle based EHD printheads that combine the benefits of the EHD process with MEMS-based throughput-scaling that conceptually mimics that of conventional piezo-based inkjet heads, thereby finally paving the way for the technology to mature into production environments.

There are three main types of mass transfer technology in Micro LED. 1) Pick & Place method, 2) Laser Galvano scanning, 3) Line laser scanning. Each method has its advantages and challenges, and I will give the current status of these methods.

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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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Our novel bottom-up concept based on InGaN/GaN uLEDs offers solutions to several challenges that the uLED development is facing right now, namely miniaturization of the die without efficiency droop, sufficient small pitch to reach FHD resolution, and focused light emission to reach sufficient incoupling efficiency into waveguide optics. By using selective area growth, the dies can be placed deterministically onto the lithographically patterned SiN-masked GaN templates and die sizes down to 300nm have been achieved. As no etching of the die itself is needed the efficiency of the InGaN quantum wells, which are the active emitters, stay intact. The geometic structure of the uLED, a hexagonal pyramid, facilitates the focused emission and a sub-lambertian emission was obtained.

LED manufacturing is a complex and technically challenging process. very few companies worldwide operate across all segments of the value chain. The areas of specialization and expertise existing in the industry break down the value chain for LED manufacturing into three large segments, i.e., substrate production, LED die fabrication and packaged LED assembly. As micro-LED takes a core importance due to immense energy-saving benefits there is a push to upscale to 8-inch LED epitaxy and consequently 8-inch substrate platform. This is to achieve surface-area multiplier, and accordingly, the yield multiplier benefits in the LED die fabrication process. Sapphire crystal-based substrate indicates specific advantages over other substrate materials regarding the balance of lattice match and cost competitiveness for LED epitaxy application. However, the Sapphire crystal growth in the substrate production is one of the most energy intensive processes in the entire LED production chain with an energy contribution of 160.46 kWh per 8-inch wafer with the conventional Kyropoulos growth process employed in Asia. This is equivalent to a CO2 emission of 96.27 kg per wafer. At FAMETEC GmbH in Austria, a highly energy-efficient technology named as McSap (Multi-Crystal-Sapphire) growth has been developed that brings down the energy contribution to 28.16 kWh per 8-inch wafer and the equivalent CO2 emission to 10.00 kg per wafer. This is equivalent to 89.61% decrease in CO2 emission in sapphire substrate wafers produced in Europe when compared to the emission produced from the prevalent technology in Asia. The dramatic reduction in environmental footprint is achieved by a leading-edge thermal design of McSap simultaneous growth of multiple sapphire crystals along the crystal axis in 8-inch cylindrical volumes eliminating the need for the wasteful coring and grinding steps typically required in traditional growth methods. Which led to the increase in the yield of usable, high-quality sapphire material.

This talk will explore the limitations in hexagonal GaN LED devices for longer wavelength microLEDS and the opportunity to develop the cubic form of GaN into the de facto solution for microLEDs, not only in the red wavelengths, but also for RGB solutions. Cubic GaN is the current state-of-the-art solution for this market and offers a manufacturing route that is not only similar to existing GaN LED epitaxial manufacture, using MOCVD, but also scalable to 300mm in the future.

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 <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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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.

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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.

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.

Many companies have announced their own products, prototypes and strategies for Micro LED display. OMDIA will cover the latest issues of micro LED display technology & market in this session. Especially, OMDIA will share our own market forecast of micro LED display by various technology and process.

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