​

Colloidal quantum dots (QDs) have been known to be the best candidates for emissive materials owing to their unique optical properties including high color purity and quantum efficiency. Cd-based QDs like CdSe, CdS, and CdTe have been extensively studied and their synthesis and application methods are very well developed, despite their potential harmful effects on health and the environment. Instead, InP QDs have been considered as the best alternative because of their band gaps corresponding to visible light as well as their relatively low toxicity. However, they could be easily oxidized to InPOx and have weak electronic tolerance to surface defects due to their relatively high covalent character. In this presentation, I will talk InP-based QDs showing almost unity photoluminescence quantum efficiency and long-term stability on high power blue irradiation. Based on this superior optical properties, the QDs could be applied for the color conversion pixels on blue OLED display.

Micro LED display has been considered as the next generation self-emitting display technology, because LED has been known as better luminance efficiency, durability & reliability than OLED. Lots of companies have been suggested about the key technologies of the manufacturing micro LED chips, intermediate process, manufacturing backplane, mass transferring, chip bonding & repair process. But, in this moment, there are only a few applications with micro LED display yet due to significant technical issues. In this speech, we will check the current status, technical issues & market forecast of micro LED display technology. Especially, we will review these agenda with analyzing the recent studies, prototypes & products from lots of companies. So, we can suggest that how the micro LED display should be developed and focused in the future.

Issues and experience of mini LED adapted into the display stepping to address micro LED display outlook.

​

​

​

The roadmaps for MicroLED sizes are clearly indicating that future manufacturing technologies needs to be prepared for sizes down to 5 µm. Some current technologies adapted from MiniLED production are capable to process today´s MicroLED´s of around 50 µm but running into yield and basic challenges for the next generations.
Lasers are a key enabling manufacturing technology. This is because lasers have an unrivalled ability to yield smaller and more precise features at high throughput, and to work without physically damaging or overheating delicate parts.
Our presented laser processing technologies are capable to process very small MicroLED´s either from the growth (EPI) wafer, called the Laser Lift-off (LLO) or the mass transfer from temporary carriers. This is a future-proof technology approach and help MicroLED display makers to invest once, adapt a technology for the next years, and transfer the processing technologies into mass production.
We will present our latest information and results about laser processing solutions for MicroLED displays – from very small to very large displays.

​

With the growing demand for ever-smaller devices, such as mini- and microLED displays with higher resolution rates, there is an unstoppable trend towards miniaturisation of components. High-speed, mass-production of these electronics is getting more and more difficult, because the handling and accurate placement of these tiny components is very challenging. Each component needs to be carefully selected, transferred and then accurately placed and assembled with interconnects – all at lightning speeds. As conventional industrial equipment fail to deposit ultrafine pattens of die attach material and handle such tiny components at required high rates, this calls for development of alternative high-throughput assembly technologies.

Holst Centre is continually pushing the boundaries of hybrid printed electronics technologies to open new frontiers and enable new promising applications. Leveraging on over a decade-long experience in development and maturing of Laser Induced Forward Transfer (LIFT) technology and bringing it to the next level, we have developed a new laser-assisted printing technology – Volume-Controlled Laser Printing (VCLP) – capable of high-throughput deposition of ultrafine interconnects, such as conductive adhesives and solder pastes, from structured carrier plated covered with a proprietary permanent release layer. At Holst Centre we believe that high-throughput deposition of ultrafine interconnect patterns using VCLP technology opens up new possibilities for various applications, particularly, flip chip integration of micro-LED displays.

To complement VCLP interconnect printing technology and complete high-throughput integration of microcomponents, at Holst Centre we have developed another laser-assisted technology targeted to selectively and accurately transfer microcomponents from carrier wafers populated with high-density arrays of microcomponents. The technology has no fundamental limits to scale down to transfer of sub-10 µm microcomponents with dicing street as narrow as 5 µm. We have already demonstrated that our innovative and proprietary release stack developed at Holst Centre enables high-throughput, fast and well-controlled transfer of microcomponents, as small as 40x40x10 µm3 with 20 µm dicing street.

GaN microled is the key display technology for the next generation AR/MR glasses and Metaverse. Microled arrays driven by CMOS circuits are needed for GaN microdisplays and large area displays.
Several technologies can be used to hybridize the two parts. We will review the challenges for their fabrication, show solution provided such as microtube technology and recent results with hybrid bonding.

​

​

We have developed a versatile, flexible and sustainable printing process to print micrometre semiconductor/optoelectronic devices into a surface to create functional surfaces such as displays at the yield and throughput required for such products. In addition, we have developed a self-aligned process that can enable the ultimate displays needed for augmented reality (super high brightness, ultra-high resolution, full colour, low power, and very compact).

The cartridge-based printing process is developed to offer a simple, scalable tool with faster throughput, higher yield, and high uniformity. This solution does not require picking microLED for every transfer and does not require a laser for releasing microLEDs into the display substrate. As a result, it benefits from simple tools that can be scaled to a large area and offer high throughput due to simple process steps.

​

Tight pitch integration of compound semiconductor with advanced node CMOS like in microLED displays requires a full wafer level monolithic approach in 300mm. At pitches below 5um, the CMOS bonding is at the center and cannot be considered as an afterthought of a great LED process. Here we show a 9150ppi µLED process-flow with backplane integration that is realized in a 300mm CMOS pilot line using standard volume manufacturing equipment with a similar integration scheme as is done for 3D-stacked backside illuminated imager (BSI). This includes the realization of wafer level optics for beam-shaping. The achieved brightness exceeds 1Mnits. We discuss the inter-dependency of pitch vs manufacturing yield including epi-defectivity and epi-uniformity.

Ultra-Precise Deposition (UPD) is an additive manufacturing technique for fabricating conductive and non-conductive features at a micrometer scale. The process does not require an electric field, the deposition can be made on any substrate (conductive and non-conductive, planar and 3D) and materials with viscosities up to 1 000 00 cP can be printed in full resolution range. The combination of unique features can be used for fabricating next-generation OLED, MicroLED, and QD-LED displays.
Due to precise pressure control and the system's design, UPD allows depositing material with femtoliter precision. Together with the possibility to deposit materials with viscosities up to 1 000 000 cP and high solid content the UPD technology can be used for depositing conductive microdots below 10 µm in diameter and a very high aspect ratio for flip-chip application (for example micro-LED assembly).
UPD technology can also be used for the deposition of color-conversion layers based on quantum dots. We demonstrated technology that allows direct deposition of Quantum Dots material, simplifying the whole process and reducing the overall manufacturing cost. Moreover, it increases resolution: microdots currently obtained on the market usually have about 50 μm, the minimum is 20 μm – while we demonstrated with UPD technology dots with a diameter of even less than 5 μm. Compared to other digital additive manufacturing techniques like inkjet and EHD, UPD technology allows the deposit of high uniformity and repeatability structures with the use of inks with a higher concentration of QDs. This, according to Beer’s law, directly affects light absorption by the QDs. The combination of unique capabilities of the UPD printing method provides the solution for efficient fabrication of QD color conversion for next-generation Micro-LED displays.

Morphotonics has set the standard in the replication of structures that range from 500 microns down to 50 nanometers on large areas of greater than 1-meter square. Our Roll-to-Plate (R2P) technology and
equipment not only enable manufacturing scalability (thus lowering unit costs) but also offer high replication fidelity down to picometer-scale. R2P technology is already being used to manufacture optical components inside commercial displays currently on the market. Additionally, R2P-based waveguide manufacturing is a strong candidate for addressing the high-volume manufacturing needs of emerging Augmented Reality (AR) glasses.
We have replicated many Micro Lens Array (MLA) optical structures for a variety of applications. Using aligned micro-optics, we can address the light collimation challenges that Mini- and MicroLEDs face to
achieve higher energy efficiency and lower power consumption. We are currently developing equipment that will significantly improve the overlay accuracy down to ±5 microns, allowing us to address the optical collimation needs of MicroLED displays.
Consequently, we are exploring several ways to address this emerging segment of the display market inthe near future.

​

MicroLED is still mostly in the process of transitioning from the lab to high-volume manufacturing. MiniLEDs, on the other hand, have already attracted more than $15 billion of investment for manufacturing infrastructure and are commonly used in high volume consumer products as well as in B2B, direct view LED displays.
MiniLEDs backlights can supercharge LCD panels, allowing them to compete against OLEDs in high-end, high-added value consumer markets. In industrial markets, narrow pixel pitch miniLED displays are growing at a 24% CAGR.
With OLED continuously improving, is the window of opportunity already closing for miniLED backlights? Will miniLED dominate in direct view LED displays and converge with microLEDs to break into the consumer market?
This presentation will discuss miniLED markets, applications, supply chain as well as technology trends based on device teardowns and performance measurements conducted by Yole Group.

As MicroLED displays move from prototype to production, there is a near-zero tolerance for dead pixels, which can be easily detected by the human eye. Meeting this requirement demands accurate transfer and placement of millions of micron-scale components, each of which carries the potential to kill yield through transfer damage or placement error. Conventional assembly techniques have been challenged by these requirements, resulting in a rush to develop new assembly techniques that maximize yield, facilitate defect repair, and support throughput several orders of magnitude greater than today’s best-in-class approaches. Laser-based LLO/LIFT is now a fait accompli for MicroLED panel assembly tools as evidenced by announcements from at least 5 major capital equipment companies. Critical to the LIFT process is the Transfer Material, which needs to both hold the MicroLEDs securely without drift prior to release, then when activated by the LIFT process, cleanly release and propel the MicroLEDs towards the substrate without damage and with no residue. This presentation will show how a photopolymer transfer material specifically engineered to support the LIFT process can achieve sub-micron placement accuracy while enabling additional optimizations in the entire subsystem, resulting in the lowest Cost of Ownership. For example, a lower activation energy supports the use of a lower-cost laser, and masks can be used to facilitate mass transfer without adding complexity to the positioning stages. These optimizations of the LLO system have a direct impact on yield, throughput, and cost.

Submicron-scale, high-efficiency, multicolor light sources monolithically integrated on a single chip are required by the display technologies of tomorrow. Today’s GaN-based blue LEDs are bright, stable, and efficient but are produced in only one color across an entire wafer. And achieving efficient green and red LEDs using GaN-based technology has proven stubbornly difficult. But recent InGaN nanowire structure studies have shown promise to solve such critical challenges. Nanostructured LEDs exhibit low dislocation densities and improved light extraction efficiency. Multicolored emission can be demonstrated from InGaN nanowire arrays integrated on a single chip. The emission cone and direction can be tailored by the one-dimensional columnar design of each nanostructure, essential to realizing ultrahigh definition displays. Critical to these emerging technology areas is the realization of full-color, tunable emitters on a single chip. This capability requires fine-tuning of alloy composition in different nanostructured regions with compositional variations made in a single process step.

Dr. Coe-Sullivan will describe how display technologies based on nano-LED pixel arrays integrated on a single chip have the potential to become the ultimate emissive light sources for televisions and electronic signage, microdisplays for augmented reality and virtual reality (AR/VR) applications, mobile phones, smart watches, and many other applications. He will explain how monolothic integration of single nanowire, multicolor LEDs on a single substrate can be achieved by incorporating multiple InGaN/GaN quantum discs in GaN nanowires of various diameters grown in selective area epitaxy in a single molecular-beam epitaxy (MBE) process step. Red, orange, green, and blue InGaN/GaN nanowire LEDs can be formed simultaneously on the same chip, with representative current-voltage curves and strong visible light emission. This process offers a new avenue for achieving multiprimary optoelectronic devices at the nanometer level on a single chip for many applications, including imaging, micro-LEDs, microdisplays, sensing, spectroscopy, communications, and UVC disinfection.

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 450nm 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 green at dimensions as small of 1 micron. Using 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 4% has been fabricated, and they display superior temperature performance in comparison to AlGaInP based devices.

​

MicroLED technology is poised to disrupt the display market by bringing a whole new value proposition to consumers products. Flexible, high brightness and excellent lifetime are but a few keywords to describe a new generation of displays spanning virtual reality to wearable applications. To date, challenges in scaling pick-and-place processes and in producing highly efficient red and green native microLEDs hamper microLED mass production. A quantum dot (QD) color conversion strategy to produce an RGB display from an array of blue microLEDs is an elegant way to simplify the manufacturing process and to overcome several technological challenges in the mass-transfer process, the display brightness and the driving electronics.
Quantum dots have earned their place as down-convertors for displays since the commercialization of Cd-based QDs in LCDs in the early 2010’s and the commercialization of QD-OLED almost a decade later. The benefits in terms of color quality and conversion efficiency are widely recognized as key selling points. A shift towards greener, Cd-free materials has been initiated by European RoHS directives that restrict the use of Cd in consumer appliances. This stimulated the development of InP- based QDs, which can nowadays be produced through economical synthesis routes and with excellent optical properties.
The successful application of RoHS-compliant QDs for microLED combines challenging requirements in terms of absorption, solid loading, conversion efficiency and photostability. Over the years, we have developed on-chip grade and RoHS-compliant QDs that can showcase the viability of InP-based QDs for microLED applications. We will discuss our progress on red and green QDs towards relevant film thicknesses and light intensities.