Mini- & Micro-LED Displays: Markets, Manufacturing Innovations, Applications, Promising Start-ups

Although OLED display market has grown on the small sized display area for the past decades, but it still has some limitation of higher resolution and larger size. From these reasons, Micro LED display is getting more interesting with its superior optical performance. But, the production process of micro LED display is still struggling in terms of its efficiency (through put, yield rate). In this session, Omdia will summarize the latest Technical Trend & Market Forecast of micro LED display focusing on the main issues of the industry.

Toray Engineering has developed series of technologies to manufacture micro-LED displays based on technologies cultivated through its manufacturing equipment of LCD displays and semiconductors. By combining these technologies, Toray Engineering offers proposal for total solution, and so far, has large delivery records of micro-LED-related manufacturing equipment worldwide. In this presentation, Toray Engineering’s approach to the manufacturing process that utilizes its visual inspection system that uses photoluminescence technology, laser repair equipment, mass transfer equipment, and laser mass transfer equipment shall be introduced. Toray Engineering’s approach focuses measures against these main challenges ahead for the Micro-LED Display Manufacturing:
1) Smaller micro-LED chips & Stable process
It is important which method we use to achieve stable process in Micro LED.
2) Efficient repair process
In case of watch production, 500k chips are used in per product. So if the defect rate is 1%, 5 thousand chips need repairs. In case of a TV, 25 million chips are used. So 250k (two fifty thousand) chips need repairs.
3) Minimizing of image discoloration
Micro-LED chips have variation in luminance and wavelength caused in their manufacturing process. If such variations are transferred to the display pixels, they result in uneven images or mura. There is a need to reduce such image mura.
 
Toray Engineering is ready to offer total solutions to overcome these challenges to help realize high volume production of micro-LED display in the near future.

In order to get higher-resolution LED module for public information displays,
the size of LED chips must be further reduced.

Lextar Electronics, a subsidiary of Ennostar, has initiated the development of
Micro LED since 2018. The idea is to combine the existing millimeter-level
packaging technology and the advantages of Micro LED chips in high
resolution, high contrast and low color difference to develop
i-Pixel ® solution that is different from other approaches. In this talk, the
development background, performance and merits of i-Pixel ® would be
introduced.

Lextar looks forward to expanding the application of i-Pixel ® technology from
large indoor/outdoor high-brightness public information displays to consumer
displays, such as automobiles, electric vehicles, and home electronics.

The advantages of µLED are known well and positioned as a next-generation Display. To be widely applied on consumer electronics, cost and performance are both crucial factors. It is direct that micron-scale µLED (lateral size < 10 µm) brings the cost advantage. Therefore we choose the vertical structure to realize 5µm LED chips. Our proprietary process makes it easy to fabricate but high performance at the meantime. In addition, the micron-scale µLEDs also bring the merit of uniform current spreading, Lambertian emission, and even more, it is eye-friendly.
In terms of mass transfer technology, we develop a fast and concise stamp transfer specifically for micron-scale µLEDs. It is operated at a low temperature of 200 ºC, and press-free. We are focusing on these technologies to establish an effective and productive pipeline toward the true µLED Display.

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Despite most microLED application are currently at prototype stage the race for miniaturization is already ongoing towards 10-micron edge length and even below. This necessitates new solutions for the transfer and connecting these microLED chips to the main substrate. A promising material class are functional polymers or adhesives. These materials can be tailored in certain ways to comply with the demands of the display manufacturers.

In this talk we will present the capabilities of adhesives for electrical connection under the assumption of a non-monolithic flip chip design. It will be shown that the adhesive can be applied in multiply ways, while printing seems to be a promising option, yet. The tests have been conducted under lab scale conditions with two different pick & place tools (automated and manual). Moreover, two different substrates have been investigated, one is a wafer the other is rigid PCB.

The presented test results will show that adhesives are a versatile material candidate to enable the further development of microLED displays.

Despite the promising features of GaN-based micro-LED displays, their application has been impeded due to complexities in incorporating transistor logic and crafting multi-color emissions. Our research presents a comprehensive single wafer approach, capitalizing on GaN for micro-LEDs, transistor integration, and adjustable InGaN color-tunability. We showcase superior GaN MOSFETs with impressive on-off ratios exceeding eight orders of magnitude and electron mobility surpassing 300 cm2/V*s. These are vertically integrated with micro-LEDs for enhanced functionality. By manipulating different crystal planes, we engineer color-tunable InGaN micro-LEDs, enabling emissions from 640 to 425 nm. Our methods involve MOCVD growth and conventional semiconductor tools for fabrication. This research illustrates the multitude of advantages offered by a fully-integrated GaN-based solution, paving the way for the future of micro-LED displays.

Electronic displays have changed the way our society lives and interacts with technology. From the first TVs and personal computing devices to current smartphones and smart wearables, every new generation of technology demands a better display than the last. We want brighter, longer lasting, more energy efficient, and higher resolution displays—all at a lower cost. For years, microLEDs have been a sought after technology for achieving superior displays, but have been impeded by cost and manufacturing challenges.

Q-Pixel's Tunable Polychromatic microLED (TP-LED) technology introduces full-color tunability across a single 4-micron pixel, replacing traditional single-color (RGB) LED subpixels to overcome major manufacturing obstacles of current microLED-based displays. Q-Pixel’s TP-LED core competence both simplifies microLED assembly as we know it and facilitates previously unattainable pixel densities. In 2023, using TP-LED technology, Q-Pixel successfully demonstrated the world's first full-color LED display with a record-breaking pixel density of 5000 pixels per inch (PPI). With disruptive advances of the TP-LED, we expect the display industry to undergo a major paradigm shift, with microLED displays displacing most OLED and miniLED based technologies in coming years.

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Micro-LED technology provides a route to high brightness, high contrast, low power consumption displays with a superior lifetime to OLED. Deposition and patterning of the LEDs is performed separately from the active-matrix backplane, unlike in OLED, therefore joining of the LEDs and TFTs must be achieved, sometimes with millions of devices to generate the final display. Mass-transfer techniques have therefore been the subject of intense R&D work in the past few years. In this paper we present a mass-transfer-free approach where an organic thin-film-transistor (OTFT) backplane can be deposited and patterned on top of the source wafer using low temperature processing. Such an approach can yield high resolution and high brightness displays with good uniformity and stability due to the OSC materials in the device. Effective planarization of the LED wafer is achieved using a specially designed UV cross-linkable organic polymer. This allows an OTFT device to be solution processed on top of the LED, achieving charge mobilities of 2 cm2/Vs at channel lengths of 3.7um with on/off ratios of >108. Displays with pixel spacings of 1mm, 300um and 100um were demonstrated in arrays of 16x16 and 48x48, with brightness of over 100K nits for the 254ppi version. Ultimate brightness of 200K nits was achieved with the larger pixel size and optimized designs show potential for >500K nits soon. This approach to processing monolithic micro-LED displays can be used with source wafers (for small sized displays), but also could be applied to LEDs on a transfer sheet (where LEDs have been removed from the sapphire onto an intermediate substrate, with the pitch adjusted for the final display format). Processing on the wafer is perhaps suited for very high ppi AR/VR displays at >1000ppi. In the second case, the usage of the micro-LED is much more efficient and hence this could permit a much wider range of displays to be made with good yield and performance. It does require a mass transfer from the source wafer to an intermediate substrate, but the yield of this transfer can be higher than for the final transfer from transfer sheet to backplane since the metal pads must be joined in a eutectic bond. In our scheme, the metallization is formed in the same way as a conventional via process (coating a metal on another metal) and therefore it is a much more established process with high yield

The display is the cornerstone of immersive and interactive augmented reality (AR) experiences. In this presentation, we will introduce Mojo Vision's revolutionary uLED full-color display technology for AR, featuring high-efficiency miniature uLEDs and proprietary high-performance, reliable Quantum Dots (QDs).

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In the mid-2000s, OLED panel makers entered the display space targeting the LCD monopoly. By 2022, OLEDs generated $42b of the $137b in display revenue and 50% of all the smartphone shipped. OLEDs targeted the high end of the TV, smartphone, monitor and automotive markets and is moving rapidly into tablets and notebooks. In the near eye segment, OLEDoS, which has been installed in Apple’s Vision Pro is rapidly replacing LCoS and LCDs as the go to technology.

15 years later, MicroLED technology seeks to enter the display market, but their base is much wider. When OLEDs entered the market, Samsung alone carried the banner, soon to be joined by LG Display. In 2023, just about every display maker has a MicroLED initiative and powerful new participates, such as Apple, Google, Meta and Microsoft have embraced the technology.

MicroLEDs currently operate in two spheres, very large TVs and very small micro displays. They are relegated to high prices and low efficiency, which limits access to the primary markets. Even the expected 2025 release of Apple’s MicroLED based watch is expected to cost at least 3x a comparable OLED display and have comparable luminance, but with enhanced lifetime. The bourgeoning technology is researching smaller LED die sizes, larger wafers, more productive mass transfer, new error detection and repair techniques, all to reduce costs.

But the OLED industry is not standing still; is close to solving the problem of low blue efficiency and are qualifying an emitter expected to be available in 2024; new manufacturing approaches that double the luminance and triple the lifetime will be used in 2025. Panel makers are experimenting with patterning lithographically to increase pixel density, add luminance and lifetime and reduce production costs by eliminating Fine Metal Masks (FMM). By the end of the decade, a whole new material technology called plasmons could increase the EQE up to 3X the present level, making OLEDs the most efficient display technology while increasing lifetime and luminance.

This talk will provide a roadmap and rationale for how MicroLEDs will compete with LCDs and OLEDs through the end of the decade, speculating on how the advances will affect the penetration and the rate of adoption.

Spearheaded by efforts from apple and others, MicroLED has generated a lot of excitement over the past decade. All leading display makers now have sizable microLED efforts. The supply chain is shaping up, with alliances and takeovers amongst large LED and display makers. As some leading players are starting to establish volume manufacturing capacities, the industry is entering a “make or break” era. The success (or failure) of those first large-scale manufacturing efforts will decide on the fate of the technology.

Time has brought up more clarity about the benefits and challenges of microLED. We will take a closer look at what could be realistic expectations for microLED in a variety of consumer applications. Which applications are achievable and under which conditions.

The explosion in interest in augmented reality (AR) and virtual reality (VR) applications amongst the big technology players in recent years has already triggered frantic development activity in the markets for the key enabling hardware, components, and materials. With the ability to deliver a cost-effective, head-mounted display that delivers a world-beating user experience central to success in AR/VR applications, it is unsurprising that the technologies that have the potential to unlock this have seen accelerated investment in recent years.

Several candidate technologies are being pursued including liquid crystal displays (LCD), organic light emitting diodes (OLED), miniLEDs and microLEDs. It seems clear that if it can be made to work at a full commercial level, the microLED approach offers the optimum combination of attributes for this application. Forecasts suggest that the opportunity for microLEDs driven by AR/VR applications could hit USD21Bn by 2027 with a CAGR of 81% (ResearchAndMarkets.com, Dec 29, 2021). But despite millions of dollars of investment in the past few years, the market remains in its infancy and microLED use is currently confined to a few high-end applications where the resolution of the display can be catered for using current LED technology.

It is obvious that despite significant progress, there are still outstanding issues with microLED display technology. Most worryingly, there are signs that the improvements in performance available from squeezing conventional devices are dwindling. With a breakthrough required, a radical approach may be called for and one which combines advantages over existing technology but can be simply dropped into existing manufacturing lines would be very compelling.

This talk reviews the merits of one potential solution based on producing LEDs using the cubic form of gallium nitride, rather than the usual hexagonal phase of the material. Anyone who manages to overcome the technology stumbling blocks in microLEDs stands to control the AR/VR displays market.

The miniaturization of LEDs has made them suitable for displays of different sizes. As a new display technology, Micro-LEDs have unique advantages in the field of micro-displays. They have high brightness, low power consumption, and high reliability, making them considered the only solution for AR/XR devices. Building upon the foundation of traditional LED manufacturing processes, the development of Micro-LED micro-displays began with sapphire and flip-chip solutions, which were suitable for low-resolution displays in the initial stage. However, they faced numerous bottlenecks that couldn't meet the requirements of AR/XR displays. Additionally, due to limitations in GaN material growth and integration processes, achieving single-chip color displays has been a challenge. Now, Raysolve will redefine monolithic integration technology to achieve wafer-level full-color Micro-LED micro-displays, making it the best micro-display technology for the future AR/XR industry.

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Microdisplays for AR/VR headsets are set to usher in a new era of human-machine interactions. These microdisplays are typically manufactured using hybrid integration via chip-to-chip bonding performed using packaging-based technologies. However, the technical barriers to achieving high-throughput and cost-effective mass-manufacturing using these methods has limited the adoption of microdisplays to date.

At nsc, we have taken a different approach to microdisplay manufacturing that involves wafer-scale integration of GaN LEDs and CMOS devices using a truly monolithic solution. By leveraging existing CMOS devices and established back-end-of-line processes along with nsc’s proprietary wafer scale layer transfer techniques, we create microdisplays in a highly scalable and manufacturable process. This enables groundbreaking chip-based display solutions on a commercial scale, which will pave the way for innovative product, system, and software designs.

This is made possible by two key factors: (1) maintaining compatibility with existing silicon fabrication processes and equipment, thus avoiding cost and yield issues associated with advanced packaging solutions; and (2) and capitalizing on the wealth of knowledge amassed by the semiconductor industry over the last 50+ years. This approach facilitates rapid scalability and the adoption of CMOS + GaN microLED chips ideally suited for AR/VR displays in a truly manufacturable and economically advantageous way.

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The role of InGaN microLEDs as the material and device choice for next-generation displays is becoming increasingly clear. Versatile displays of different sizes and use cases can be manufactured by QubeDot's SMILE platform technology.

SMILE is an acronym for “Structured Micro Illumination Light Engine” and covers our microLED display and array product range with different pixel counts and sizes, wavelengths and intensities. Several light engines with adequate control circuits and software are available and allow direct pattern creation for display and illumination use cases out of the box.

Highly efficient microLED pixels and their mass transfer are key elements of SMILE Technology. Following up on these key elements, the talk will focus on how SMILE Technology aims to be the enabler for real production versatility in the display industry.

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MicroLED display technology is in a period of rapid technological development and different architectures are being evaluated to fit a wide range of market applications from microdisplays to video walls. In particular, color converted architectures using quantum dots have been proposed to enable ease of manufacturing as compared to RGB displays assembled from direct emitting LEDs. InGaN and AlGaInP have been proposed for direct emitting red microLEDs, while quantum dot conversion of red by InP quantum dots has been proposed from both blue and UV InGaN LEDs.

We have modeled the efficiency tradeoffs of these architectures based on a meta-analysis of literature data in combination with experimental results as a function of pixel size. The expected resolution limitations for downconverted and direct architectures are also compared. In addition to efficiency, color gamut and resolution are also critical factors in choosing a microLED architecture. The color gamut of direct and color converted architectures are calculated from our meta-analysis of literature data, and advantages of different architectures are demonstrated.

Reducing the size of pixels is a key goal in microLED display technology development. Smaller pixel sizes allow for higher resolutions, improved image quality, and more compact displays. However, reducing the size of microLED pixels comes with a set of challenges and considerations.

As pixels become smaller, precise placement and alignment becomes crucial to maintain the integrity of the display. Achieving an accuracy better than 5 micrometers is a challenging endeavor due to several technical and practical limitations inherent in the processes and technologies involved. Conventional printing methods fail to consistently achieve such accuracy, because of variations and deviations in drop formation, size and ejection leading to uneven distribution of ink, affecting printing quality.

High Precision Capillary printing (HPCAP) is a disruptive printing technology based on capillary forces. HPCAP does not require external sources like pressure, electrical field or ultrasound, which simplifies the printing process and minimizes its variability. The technology incorporates real-time capillary monitoring, feedback mechanisms, and automated adjustments to the substrate topography, unlocking the capability to print tapered surfaces.

HPCAP involves the controlled deposition of materials, achieving high pixel densities with accurate alignment at extremely small sizes (sub-micron scale). It is a non-damaging process, as capillary forces typically exert gentle pressure on the substrate, which is advantageous when working with delicate or sensitive materials.

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μLED technology is thought to replace legacy technologies for existing display applications. Even more exciting is that brand new – previously impossible – Augmented Reality (AR) applications will enable new human experiences, empowered by μLED-technology.

With micron-sized pixels, unprecedented luminosity and higher efficiency, μLED-enabled micro-displays can be made small yet powerful enough to resolve the roadblock for broader Augmented Reality adoption. However fundamental challenges remain, especially when also taking manufacturability into consideration. The performance bottleneck persists and this talk will review how technology choices have performance implications, as well as present some approaches to addressing the bottleneck.”

MicroLED displays offer many key performance benefits such as brightness, contrast, power consumption and lifetime, however, cost and manufacturing maturity remain barriers to wide market acceptance. Improved yield through better process control provides a pathway to lower costs and manufacturing readiness. In this paper we discuss yield and end-to-end process control from epitaxy and microLED patterning, driver IC (optional), backplane, mass-transfer, and bonding.

For MicroLED technology to achieve a growth trajectory similar to OLED, it must address critical fabrication challenges and offer viable solutions for smartphone applications. Specifically, the industry requires a MicroLED transfer method that can be scaled to high-volume production while ensuring cost-competitive displays. This solution should achieve over 80% wafer utilization, exhibit reduced sensitivity to wafer non-uniformities, and enable the efficient transfer of MicroLEDs from a wafer with a pitch of smaller than 10 micrometers, all while maintaining high yield and throughput. VueReal's pioneering microSolid printing technology has emerged as the answer to these pressing demands.

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