Quantum Dots: Material Innovations and Commercial Applications

Perovskite quantum dots are well known for their unmatched color purity but unfortunately also for their strong tendency to degrade under humidity, temperature and blue flux due to the fact that perovskite quantum dots are based on a halide salt compositions. Over the last 7 years we have intensively worked on our green perovskite quantum dots and achieved a near- unity quantum efficiency, an FWHM of 22nm and last but not least a sufficient stability against humidity, temperature and blue flux turning our perovsite QDs commercially viable now. In this presentation we give an overview about our technical perovskite solutions for miniLED backlight films (LCD displays) and also QD pixelated color converters (QD-PCC) for microLED displays.
A color conversion film with green and red color conversion materials is needed for mini-LED based LCD displays because the traditional approach of using phosphors on-chip does not work for such displays due to technical limitations. Thus we present different color conversion films with our green perovskite QDs and different red conversion materials and show the benefits these films will bring to LCD displays and the LCD industry in general.
MicroLED displays are getting more mature and are close to market-entry but one of the main challenges is manufacturing costs due to chip mass transfer and involved pixel repair processes of red, green and blue microLEDs. Therefore the microLED industry requests green and red QD color conversion materials to be able to only use blue LED chips in the manufacturing process. Perovskite QDs also excel in this type of application due their advantageous properties including highest absorbance, lowest FWHM and highest quantum efficiency. Here we present our development status for QD-PCC materials based on green perovskite QDs including optical properties and different pixel deposition processes.

MicroLEDs have a tremendous potential for future displays. However, there are several technical challenges to overcome prior to widespread deployment of MicroLEDs. One key hurdle is developing a process to release the dies from the sapphire growth wafer. Another is a process to transfer these to the display substrate with micron-level precision and reliability. Laser processing offers several opportunities for MicroLED display production, such as Laser Lift-Off (LLO) to separate the finished MicroLEDs from the sapphire growth wafer and Laser-Induced Forward Transfer (LIFT) to move the devices from a donor to the substrate.

In this presentation, laser-based system solutions for the different manufacturing steps for microLEDs, will be presented. Integrated process control and monitoring are used to assure stable and reliable operation to ensure high throughput and low yield losses.

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Even though µ-LED manufacturing has moved forward over recent years, it is still in early development stage, resulting high costs and poor yields. Thus, finding pathways to reduce manufacturing costs and improve overall yield is of major interest to the industry. An alternative path would be to replace the solder paste in solder paste printing by plating process. To solve this issue Atotech Group has developed a new auto-catalytic tin process that can overcome the thickness limitation of existing immersion tin process. Besides that, the process allows tin deposition not only limited to copper, but also different metal stacks.

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.

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.

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

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Recently, as the growth of the technology and market of printing based displays, demands and importance of high-resolution printing technology have been increased rapidly. Solution-based inkjet printing fabrication process has advantages of rapid and large area fabrication, low cost and easy tunability.
The electrohydrodynamic (EHD) jet printing method was suggested to one of the alternatives and advanced printing technique. The EHD jet printing uses a force balance of electrical force and fluid dynamics to control jetting phenomena. This could allow the smaller droplet generation than nozzle size and ejection of a wide range of ink viscosity. Due to these advantages, more precise and smaller patterning of different materials was possible such as silver or QD inks in micro scales. These high-resolution patterning also have the advantage of suppressing the coffee-ring effect from its extremely small droplet size.
In this talk, we present the successful contribution of EHD Inkjet technology for micro-LED display development. For example, we could fabricate the bond-pads for transferring chips and repair the electrodes of display panels. We also could make uniform small dots of QDs. Recently we opened multi-nozzle EHD inkjet printhead in a market and tried to apply for micro- LED display. This multi-nozzle EHD inkjet printhead could show high performance of high resolution printing and high production capability.

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Quantum Dots (QDs) have been considered as key materials of the next generation display with wavelength-tunable, high color purity and high quantum yield properties.
After the QD film technology commercialized successfully, various new QD technologies are being developed, including QD on-chip LED, QD light guide plate(LGP), QD OLED, QD mini-LED, QD micro-LED and electroluminescence (EL) QLED.
QD mini-LED and QD micro-LED are among the most attractive products in the near future. QD mini-LED can upgrade the performance of general LCD to be able to compete with popular OLED display with nice contrast ratio, wider color gamut and better reliability. Then, full color micro-LED display can be fabricated with combining color-converted red and green QD layers and blue LED chips. The challenge of mass transferring and the cost of driving circuits can be largely reduced. Also, the disadvantage of the lower EQE of micro-sized red chips can be significantly improved by red QDs.
HsinLight and NTHU QLabs are devoted into new QD technology development and dedicated to collaborate with display supply chain partners to new QD application introduction and proof-of-concept. We would like to share you with our latest results in our new patented non-Cd QDs materials, QD color-converted micro-LED, inkjet printing EL QLED and the flexible and transparent QLED display.

Stretchability is the ultimate target in flexible displays. There are three significant hurdles in the commercialization of stretchable displays. First, the stretching of display panels inevitably accompanies image distortion and non-uniform deformation. Second, the conventional display substrate suffers from low stretchability. Third, the stretchable rubber substrate [1] is incompatible with today’s display fabrication process due to its significant thermal expansion and low dimensional stability. This talk presents a stretchable meta-display [2] enabled by micro-LEDs to overcome the limitations of conventional stretchable displays. An auxetic metamaterial with a Poisson’s ratio of -1 and electric interconnections was developed as a substrate of the stretchable display for stretching without image distortion and with uniform deformation. A highly stretchable circuit board was realized using a polyimide substrate, a conventional display substrate for commercialized OLED flexible displays. The structural stretchability of kirigami overcomes the low material stretchability of polyimide and reaches a panel stretchability of 24.5%. In addition, roll transfer technology was used to interconnect the micro-LEDs with the circuit board reliably, and its scalability was demonstrated by realizing a three-inch stretchable display panel.

We examined to utilize the gravure offset printing method to print high-precision micro bumps.
Currently, the minimum diameter that can be printed with SAC (Sn, Ag, Cu) solder paste is 6 μm and the distance between the centers of the bumps is 30 μm.
For the reflow method, the formic acid reduction method is used for bumps with a diameter of 15 μm or more.
The film thickness can be increased by printing several times.
The smaller the bump diameter, the higher the aspect ratio.

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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.

In this presentation, we discuss the current state of the MicroLED display industry, highlighting the AR/VR, large-area tiled TVs and wearables market. We also discuss the potential of microLEDs and some performance highlights. Finally, we introduce the new MicroLED Industry Association.

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.

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.

Quantum Dot technology is playing an increasingly important role in emissive displays such as QD-OLEDs, QD-microLEDs, and emissive NanoLEDs. In this talk, we will discuss the latest developments in Quantum Dot Color Conversion (QDCC) for QD-OLED displays and QD-microLED displays.

Applying QDCC to blue microLEDs or OLEDs can lead to lower cost, brighter, high contrast displays with a wide color gamut. Nanosys has developed new, heavy metal-free QD materials with enhanced blue absorption, high quantum yield, and narrow, tunable emission. These attributes enable the fabrication of patternable QDCC films with high photon conversion efficiency and BT.2020 gamut coverage. These new QD materials have delivered greater flexibility to the design of printable inks and formulations. Fabrication can be done using inkjet printing or photolithography, depending on the feature size, mass production, and cost requirements of the display product.

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.

QD-enabled displays have become a mainstay of modern display technology, especially in the TV segment. QD-films are the most commonly utilized form factor used to convert blue LED light to red and green. However more recently QD-OLED has become a top-tier display using QDs to convert from blue OLED at the sub-pixel level, providing an amazing viewing experience. We take a peek inside TVs with QDs, from the basic QD-film approach, through the newest QD-OLED approach, with in-depth optical and spectral analysis and complete video tear-downs so you can see all the components that make up your QD-enabled TV.

MicroLED display is believed to be the ultimate display which fulfills all display feature requirements. There are already many MicroLED demonstrations in different applications, such as large-size TV, automotive transparent display, flexible display, wearable device, and picture generation unit of AR and HUD. MicroLED is already proved its high brightness, high contrast, wide color gamut, good reliability, flexible, and high transparency.

To realize such high performance MicroLED display, we have three major solutions for different applications. The first solution is PixeLED Display, which is to build MicroLED displays on TFT substrate. This is the best solution to produce transparent display, flexible display, and most of display applications. The second solution is PixeLED Matrix, which is MicroLED on modular PCB and could enable ultra large size fine pitch display. The third solution is µ-PixeLED micro-display for AR glasses with the chip size smaller than 5µm on silicon-based CMOS backplane.

MicroLED can be used in a variety of different application scenarios, and it provides the ultimate visual experience. Whether it is an existing display or an innovative application, MicroLED is the best choice.

PbS quantum dots (QDs), when deposited as a film, form a photosensitive semiconductor layer applicable in various sensors. For example, this material has recently appeared on the market as an active layer of SWIR (short-wave infrared) cameras. Another less explored application for QDs is direct conversion X-ray detection, which will be presented in the talk.

In direct conversion sensors, X-rays are captured and converted to electrical charges in a single step in a photosensitive semiconductor frontplane, yielding the best resolution images in the market. There is a single material used in large area X-ray detectors (for example, mammography application): amorphous selenium. However, this material is associated with certain flaws, such as low sensitivity at low dose, not being able to detect X-rays harder than approximately 30keV and complex manufacturing procedures. This, respectfully, increases the patient’s radiation dose during the imaging exam, limits the application to soft X-rays (mostly mammography) and is a costly solution for hospitals.

PbS QDs, when applied for direct conversion X-ray detectors, release the limitations of amorphous selenium. Due to high mass fraction of lead in the material, the QD frontplane is sensitive for higher X-ray energies expanding the application of large area direct conversion sensors beyond mammography to other (non)-medical applications. Good charge transport properties allow benefits of high sensitivity even at low radiation doses decreasing the dose for patients. High stability and scalable manufacturing methods driving cost reduction for vendors and, subsequently, for health care providers.

Photodetection in the short-wave infrared (SWIR) is preparing to transform from a niche market with high-cost products to mass market adoption of disruptive technologies. Quantum Dot (QD) absorbers have several unique advantages including spectral range, cost effective production, and potential for high resolution. To process QD absorber layers the current approach deposits up to 10 layers with ligand exchange performed on each layer, complicating processing, and increasing the probability for defect formation. An ideal approach would utilise a QD ink that enables the QD absorber layer to be deposited in a single step. Lead free quantum dot materials are an attractive prospect particularly for applications in the consumer market where environmental and health concerns are strongly associated with branding. A lack of lead free QD materials with absorption in the SWIR or quality matching those of the Pb counterparts has kept Pb QDs as the most widely used material to date. Quantum Science Ltd. presents progress in both areas.

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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.

Colloidal semiconductor nanoparticle technology, known as colloidal quantum dot (CQD) technology, very recently has been leveraged commercially for its ability to absorb a broad spectrum of wavelengths of light and convert that light into photocurrent. It took roughly 20 years of R&D to commercialize CQD image sensors, which are the first commercial products in the marketplace to use CQDs in electro-active devices in contrast to all of the other current products that use CQDs in photoluminescence mode. We are now entering into a new era of CQD-based products starting with photodetectors and very likely soon QD-LEDs and solar cells, and eventually lasers.

It has recently become clear that PbS CQD image sensors have a strong value-proposition in the infrared region of the spectrum versus InGaAs and SiGe image sensor technologies. The short-wave infrared (SWIR) region of the spectrum is between 1000nm and 2500nm and the PbS CQD system can be tuned, based on particle size, to absorb throughout this region with the added benefit of being able to also absorb the near infrared, visible, and UV regions of the spectrum at the same time. Pixel architecture versatility combined with low cost and broad spectral sensing capabilities create a great opportunity to use CQD image sensors for a diverse set of sensing needs in the industry now and into the future.

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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 has long been regarded as the “ultimate display technology“for its compact size, high efficiency, and good reliability. However, as the dimension of LED reduces, problems such as low red efficiency and high system cost start to emerge. Assembling an RGB micro-LED array with less than 5 µm sub-pixel size for AR/VR applications is also rather challenging. Saphlux team developed the first NPQD® color-converted micro-LEDs to address these issues.
NPQD® stands for “Nano-pores for Quantum Dots.” Leveraging our proprietary technologies, a nano-porous structure can be directly formed inside LEDs to serve as a natural vessel for in-situ QD integration. The effective light path can thus be extended to boost the overall efficiency due to the strong scattering effect. The reliability of quantum dots is also improved greatly because of the high thermal conductivity of gallium nitride materials.
Saphlux now supplies NPQD® R-1 micro-LED products in volume for fine-pitch display applications. We also developed NPQD® T-1 full-color Micro-LED array with a sub-pixel size of 2 µm and are now collaborating with customers for AR/VR micro-LED display developments.

Over the last decades inkjet printing has substantially improved, for example by adapting microfabrication technology in the production of the most recent inkjet printheads. However, the further enhancement of the inkjet printhead architecture is becoming physically limited and therefore increasingly expensive. The goal of making inkjet printheads higher resolved and use them as additive manufacturing tools in printed electronics and related fields has therefore been restricted. To make inkjet printing compatible with high-resolution 3D printing not incremental innovation in needed but actual disruption, a complete change of paradigm. Electrohydrodynamic printing, the basis of Scrona's NanoDrip printing, creates the force required to eject droplets directly inside the ink, at the nozzle exit where the force is actually needed. All problems related to creating a force inside the printhead itself and transmitting it to the nozzle exit inside a viscous medium are thereby eliminated. This leads to nothing less than the potential of increasing both the printing resolution and ink viscosity more than a hundredfold.

HMDs and AR glasses are expected to be the next generation communication devices to replace smartphones. There are many prototypes and early products using several display devices. Various display devices have been proposed, including LCD, micro OLED, Laser Beam Scan (LBS), LED LCOS, and Laser LCOS. LCD is one of the major display device for VR HMDs, however, it is very heavy and has a limitation to pixel density. Furthermore, although the laser-based display devices are compact and can achieve high brightness, the image quality of the display is not excellent because of speckle noise, one of the specific issue of laser-based display. Micro OLED and LED LCOS are at a high level of technological maturity and widely used to HMDs, but their brightness is not enough to the outdoor AR. Micro LED has been attracting a lot of attention as a display device to solve disadvantages in other display devices.
We have developed full color micro LED, "Silicon-Display", and demonstrated the first prototype with 1,053 ppi. Figure 1 shows the process-flow of Silicon Display, RGB full-color micro LEDs using color conversion. Blue micro LEDs are formed on a sapphire substrate and one LED array contains 352 x 198 micro LED dies of 24 um x 8 um in size. The cathode (N-type electrode) and anode (P-type electrode) are fabricated for each micro LED die to apply driving voltage independently to each die. LSI with the circuit driving the LEDs is fabricated on Si wafer. The Au bump electrodes are fabricated in accordance with the pitch of the LED dies. LED and LSI chips are divided into chips, and then LED chip is bonded to LSI chip with Au electrodes. After that, the sapphire substrate of the LED is removed by laser lift-off, resulting in a blue monochromatic micro LED display. QDs (Quantum Dots) are patterned on LED dies to generate red and green emission.
Figure 2 shows a schematic diagram of a pixel structure including RGB sub-pixels. To convert blue emission from LEDs to green and red, QDs are fabricated. Color filters are fabricated on the top surface of the QDs to improve color reproducibility. Light shielding walls (LSWs) are also fabricated to prevent optical cross talk.
We developed the 1,053 ppi prototype, however, there is a strong demand for higher resolution for the practical AR application. Therefore, we have been working on a 3,600 ppi prototype. Figure 3 shows the difference between 1,053 ppi and 3,600 ppi. The small size of micro LED dies makes brightness low due to small active emission area. To solve this problem, we designed and applied the common cathode structure. The area of micro LEDs contributing to light emission in one pixel was improved from 23% to 38%. As a result, brightness of 11 knits was achieved.
The current brightness is not sufficient for outdoor AR applications. We plan to improve the brightness furthermore by improving the QD performance and the LSW structure.

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.

The aspect ratio (width to thickness ratio) of the designed pixel pattern in the quantum dot color conversion (QDCC) layer is crucially important to the light extraction and the final performance of the microLED devices. Different level of resolution is required for different products ranged from low (as in public information display) to high (as in AR and VR), which results in different QDCC manufacture processes with different pixel configurations and material specifications. Based on simulation and practical experiments, only a high value of aspect ratio can ensure high light extraction for products of very high pixel resolution such as AR and VR, which requires QDs with higher blue light absorption coefficient to maintain a thin QDCC film thickness. For Iow–PPI process (≤ 200 PPI), IJP (inkjet printing) process is beneficial, while for high–PPI process (≥ 400 PPI), photolithography process is feasible. Both QD IJP ink for printing process and QD photoresist for photolithography process can provide products with color gamut higher than 90% BT2020, and their energy consumption can match the RGB-chip microLEDs.

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.

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.

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.

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.

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.