François Templier | CEA: Can we achieve a sub-2-micron pixel pitch by eliminating alignment tolerances altogether?
00:09:44.600 - 00:12:31.300
Other snippets from this talk
Summary of the clip:
Can we achieve a sub-2-micron pixel pitch by eliminating alignment tolerances altogether?
Even with advanced wafer-to-wafer hybrid bonding, sub-micron scaling is fundamentally constrained by the alignment tolerances of wafer bonder tools. To completely bypass this physical alignment bottleneck, researchers are utilizing a monolithic "direct transfer" approach where raw, unpatterned GaN-on-silicon or GaN-on-sapphire layers are bonded directly onto the CMOS active matrix.
Once the blanket epitaxy layer is bonded and its native growth substrate is removed, the individual microLED pixels are patterned using high-precision CMOS photolithography tools. Because the pixel definition is done directly on top of the CMOS circuit itself, the alignment precision is governed by advanced semiconductor lithography scanners rather than wafer bonding equipment, allowing for virtually unlimited scaling.
This monolithic integration strategy has transitioned rapidly from early academic proofs of concept to commercial reality. Companies like Jade Bird Display (JBD) have leveraged this architecture to mass-produce highly compact, ultra-bright monolithic microdisplays with pixel pitches as small as 2 to 3 microns, delivering unprecedented optical efficiency for AR waveguides.
In this short video, you can learn:
* How bonding unpatterned GaN epi-wafers onto CMOS removes wafer-to-wafer alignment as a limiting factor.
* Why utilizing native semiconductor lithography to pattern LEDs on CMOS enables sub-2-micron pixel pitches.
* The commercial progress of monolithic microdisplays, featuring high-volume products with 2-micron pixel sizes.
📋 **Clip Abstract** The speaker introduces the monolithic direct transfer approach, where a continuous GaN layer is bonded to CMOS before undergoing pixel patterning. This method leverages high-precision semiconductor lithography to achieve sub-2-micron pitches, as demonstrated by early CEA-Leti prototypes and JBD's commercial displays.
#MonolithicIntegration, #GaNonCMOS, #DirectTransferBonding, #SubTwoMicronPitch, #MicroLEDMicrodisplays, #ARWaveguides
This is a highlight of the presentation:
More Highlights from the same talk.
00:03:37 - 00:06:08
Why are current quantum dot color conversion technologies hitting a hard physical wall at a 3-micron pixel pitch?
Why are current quantum dot color conversion technologies hitting a hard physical wall at a 3-micron pixel pitch?
While quantum dots (QDs) are a mature color conversion technology for LCDs, their application in ultra-compact augmented reality (AR) microdisplays is severely bottlenecked by their optical absorption properties. Because standard QDs feature non-absorbing outer shells, their blue light absorption coefficient is relatively moderate, necessitating color conversion layers that are 5 to 10 microns thick to achieve complete blue-to-green or blue-to-red conversion.
A thick conversion layer introduces severe geometric and optical challenges, particularly when trying to pattern individual pixels at the sub-micron scale required for high-resolution AR. Even state-of-the-art shell-less quantum dots developed by companies like Avantama only manage to reduce the required thickness to 3 microns.
This thickness remains completely incompatible with the sub-micron pixel pitches (typically 1 micron or less) required to realize true compact AR glasses. To unlock next-generation AR displays, the industry must transition to alternative inorganic color-converting materials with far superior absorption properties.
In this short video, you can learn:
* Why conventional core-shell quantum dots require extremely thick (5-10 μm) layers for full color conversion
* The performance limits of shell-less quantum dot alternatives which still stop at 3 μm
* Why sub-micron pixel pitches demand a fundamental shift away from quantum dots to new converter classes
📋 **Clip Abstract** This clip analyzes the physical limitations of quantum dot color converters, explaining why their low absorption coefficients require thick layers that prevent scaling to sub-micron pitches. Francois Templier discusses how even cutting-edge shell-less QDs fail the ultra-compact pixel pitch requirements of next-generation AR displays.
#QuantumDotColorConversion, #SubMicronPixelPitch, #ShellLessQuantumDots, #AbsorptionCoefficient, #MicroLEDMicrodisplays, #AugmentedRealityOptics
00:03:45.700 - 00:05:36.500
How can we break past the physical pitch barriers of indium solder bumps in microLED microdisplays?
How can we break past the physical pitch barriers of indium solder bumps in microLED microdisplays?
Traditional flip-chip packaging processes rely heavily on indium solder bumps, which face severe mechanical and thermal scaling limits below a 10-micron pitch. When designing high-density microdisplays for augmented reality, standard reflow processes introduce significant lateral alignment drift and bridging risks, forcing designers to seek alternative mechanical interconnect architectures.
CEA-Leti developed a unique room-temperature hybridization technology called "microtube" insertion to solve this scaling bottleneck. By fabricating hard, microscopic metal microtubes on the CMOS backplane and pairing them with soft pad contacts on the GaN LED wafer, electrical and mechanical connections are established simultaneously using pure mechanical pressure at room temperature.
This mechanical microtube approach successfully circumvents the thermal mismatch and pitch constraints of solder reflow. Prototypes developed with this technique have demonstrated pixel pitches down to 5 microns while unlocking extraordinary luminance values, reaching over 1 million nits for blue and 10 million nits for green microLED displays.
In this short video, you can learn:
* Why standard indium solder bumps fail to scale below 10-micron pitches for microdisplays.
* How the room-temperature mechanical insertion of microtubes into soft pads prevents alignment drift.
* The performance metrics of microtube-assembled displays, including achieving up to 10 million nits in green.
📋 **Clip Abstract** This video outlines CEA-Leti's proprietary room-temperature microtube insertion technology designed to overcome the physical scaling limits of traditional indium solder bumps. By utilizing mechanical pressure to press hard micro-tubes into soft contact pads, they demonstrate high-resolution, ultra-bright microLED hybridization down to a 5-micrometer pitch.
#MicrotubeHybridization, #RoomTemperatureInsertion, #FinePitchInterconnect, #GaNOnCMOS, #MicroLEDMicrodisplays, #HeterogeneousIntegration
00:06:26 - 00:08:29
Can inorganic halide perovskite thin films finally resolve the efficiency and pixel-density trade-offs that limit next-generation microdisplays?
In high-performance AR/MR displays, traditional color conversion materials struggle with absorption efficiency and pixel scaling. Inorganic halide perovskite thin films offer a compelling alternative to quantum dots, as their emission wavelengths are tuned via chemical composition rather than particle size. This yields exceptionally narrow emission spectra for superior color purity, combined with a high absorption coefficient of $10^5 \text{ cm}^{-1}$ that enables ultra-thin conversion layers.
Minimizing color conversion layer thickness is critical to mitigate optical crosstalk and achieve the sub-micron pixel pitches demanded by near-eye displays. The high absorption density of these fully inorganic perovskites allows shrinking pixel dimensions without sacrificing optical density or light-conversion efficiency. Furthermore, the fully inorganic matrix provides superior thermal and photochemical stability compared to organic counterparts, addressing a historical bottleneck in microdisplay longevity.
To deposit these sensitive films without degrading their optoelectronic properties, researchers leverage specialized pulsed laser deposition (PLD). This solvent-free, low-damage physical vapor deposition technique uses a UV laser to ablate a target, creating a stoichiometric plasma plume that condenses into a high-quality thin film. Because PLD operates under moderate vacuum and replicates the target's exact chemical composition, it represents a controllable, scalable pathway for integrating perovskites directly onto micro-LED backplanes.
In this short video, you can learn:
* How inorganic halide perovskites achieve precise color tuning through compositional engineering rather than quantum confinement.
* The role of high absorption coefficients in reducing color converter thickness to enable smaller, high-density pixels for AR/MR.
* The advantages of pulsed laser deposition (PLD) as a solvent-free, stoichiometric, and low-damage manufacturing method for perovskite thin films.
📋 **Clip Abstract**
The speaker introduces inorganic halide perovskite thin films as high-absorption, composition-tuned color converters designed to enable smaller pixels and better stability in AR/MR displays. He then explains how pulsed laser deposition (PLD) is utilized as a solvent-free, low-damage method to deposit these films with precise target stoichiometry.
🎤 Speaker: François Templier
🏢 Company: CEA-Leti
📅 Event: Printed Electronics Innovation Day 2024
📍 Location: TechBlick | Online Platform
🌐 Learn more at the next TechBlick event: https://www.techblick.com
#SlotDieCoating, #PerovskiteTandemSolar, #RollToRollProcessing, #FlexibleOptoelectronics, #PrintedElectronics, #BuildingIntegratedPhotovoltaics