MicroLED and QDs: Market Forecasts, Mass Transfer, QD-CMOS SWIR Imagers, Volume Controlled Laser Transfer

We highlight important advancements in MicroLED and/or QD displays in this article using technology slides. These advancements of the art will be presented at TechBlick’s 2-day global conference on “Mini- & Micro-LED Displays: Markets, Manufacturing Innovations, Applications, Promising Start-ups” taking place online in TechBlick’s ‘in-person virtual’ platform on 30 Nov - 1 Dec 2022.

The agenda includes the likes of Samsung, Sharp, AUO, Coherent, ASMPT, Komori, CEA, Micledi, 3D Micromac, Allows Semiconductors, and many more. The full agenda can be seen here www.TechBlick.com/microLEDs

What is the future market for microLEDs in terms of unit sales, application, chip type, and backplane?

The slides below share some key forecasts and analyses by Jerry Kang from Omdia - one of the leading analysts in the field - who will present live online at TechBlick's microLED and QD event on 30Nov-1Dec www.TechBlick.com/microLEDs

Slide 1 shows that the microLED market will experience substantial growth in the coming years. In 2021, the sales were expected to be just 0.12k units, reflecting the lack of technology maturity and the manufacturing high cost/low yield. In 2029, the figure is expected to reach 12.7M units per area. This is a transformational growth, and yet still represents just 0.3% of the total FPD market!

Slide 1 also shows the split of the market - in thousands of units - by application. The first to arrive were public displays owing to low technical barriers and much larger dies as well as ultra-low PPI. Premium TV have also arrived and will grow. Here, the superior performance of colour gamut, luminance, and contrast delivers value. Smartwatches will be a drive of unit sales, as here the small size and lower PPI translate to lower technical barriers.

Slide 2 shows the evolution of the market by backplane technology. MicroLED on Silicon (on CMOS) is suited to high PPI AR or HUD devices. LTPS backplane is ideal for small and medium-sized applications like smartwatches due to the high mobility of LTPS but LTPS does not scale to large areas due to the ultra-large non-uniformity of p-Si. Oxide TFTs can be scaled to Gen8 whilst PCBs will be used for ultra large displays such as signage.

Slide 2 also shows the forecast split by chip type. The on-wafer option means growing the uLED array directly on the epiwafer. Here, pixels can be very small but overall size is limited by wafer size (6-12inch). Flip chip means that microLEDs will have bottom electrodes so that they can be flip-chipa throughoutthe mounted onto the target substrate/backplane

Join us on 30Nov-1 Dec 2022 to learn more about the technology and market for microLED and Qunatum dots. You will hear from a fantastic lineup of speakers including Samsung, AUO, Sharp, ST Micro, Omdia, Yole, Coherent, Allos, etc. Check out the agenda here www.TechBlick.com/microLEDs

QD-Si Image Sensors- beating InGaAs and SiGe in the NIR and SWIR regions with 1.62-2.2um pixel pitch

It took roughly 20 years of R&D to commercialize colloidal quantum dots (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.

First, why quantum dots? The particle size of PbS QDs can be tuned to absorb thoughout the SWIR region spanning from 1000nm to 2500nm. This is shown in slide below, showing also that these QDs can also absorb in the NIR, visible, and UV regions at the same time.

Second, why quantum dots + silicon? Obviously, the most advanced imaging technology is based on silicon. However, silicon is not sensitive to NIR and SWIR. As such, InGaAs and SiGe sensors have taken hold of this market. However, they are often expensive and their heterogenous integration with silicon read-out circuity (ROIC) can add to complexity and limit pixel sizes/pitches although advances in Cu-Cu bonding may change this.

As shown in the slide below, The QDs can be spin coated atop a 300mm silicon wafer. Single PbS QDs are formed into thin QD films with a ligand matrix. Out of this, a QF (quantum film) photodiode if formed with top and bottom electrodes (which must be transparent to a broad light spectrum). These QD photodiodes are formed atop the BEOL of a top-side illuminated image sensor. Cu vias are then used to connect the QD layer to the image sensor.

In addition to bringing silicon image sensor technology to the NIR/SWIR spectrum, the QD technology can also enable 100% fill factor and help shrink a complex global shutter pixel (which otherwise would need a larger space for the photodiode)

In this study, to be presented at TechBlick's Quantum Dot and microLED conference on 30Nov-1Dec, Jonathan Steckel from ST will outline the state-of-the-art, showing how 1.62-2.2um pixel pitches have been demonstrated on 300mm wafers. The quantum efficiency (QE) is >60% (940-1400nm)

To learn more join Jonathan and many other world-class speakers on 30Nov-1Dec online in TechBlick's interactive and engagement platform visit here www.TechBlick.com/quantumdots

Mass Transfer of uLEDs: Overcoming dimensional/manufacturing variations with magnetic head/stamp tech

microLED display technology requires massive parallel transfer technology. This is a complex technology as it is and will grow even more complex as displays with smaller dies and high PPIs are considered. This has been one of the frontiers of development in the uLED industry.

Many parallel transfer approaches have been proposed. Most are based on a type of stamp which picks up the microLED dies from the growth substrate and transfers them onto the target substrates, placing them at the right spot.

A critical challenge is how to overcome inevitable height and dimensional variations of uLEDs using standard elastomer-based microLED technology, which, if not managed properly, can adversely impact that all-important figure-of-merit: yield!

LuxNour Technologies Inc. is proposing a novel approach based on electromagnetic stamps which can - as shown in slide 1- tolerate tens of σ in uLED variation! This increases yield and easeclose-up the pressure on exact control of the microLED dimensions during the growth. Join the specialist TechBlick conference on microLEDs on 30-Nov and 1-Dec to learn morewww.TechBlick.com/microLEDs

Makarem Hussein in slide one shows the structure of such an electromagnetic head, containing a bulk electromagnetic at the back, a non-magnetic dielectric element in between, and a pattern of high permeability materials (e.g., Ni) and openings. The high permeability areas shield the bulk magnetic, preventing its flux from protruding out. In contrast, the openings represent discontinuities in the shield, allowing the EM force to penetrate out. Slide 2 shows a close up of the structure as well as the resultant magnetic flux

In this approach, the microLEDs will also require a layer of metallization with a ferroelectric material. As shown in slide 2, when the magnetic field is on, the microLEDs - regardless of height variations - are picked up by EM force at the location of openings/discontinuities. When the field is off, the dies are released (or placed).

Slide 3 shows an example of a 100mx100mm stamp on a 150mm Si wafer. Here, the high-permeability material is nickel. This stamp can handle 15um microLED dies with a spacing of just 7.5um.

This is a very interesting technology with excellent potential. Of course, there is significant know-how and expertise and technology in EM stamp/head development (see patent: ). Furthermore, the microLED wafer manufacturers must adopt their metallization step to deposit a ferrous material.

Makarem Hussein will join speakers from Samsung, Sharp, AUO, ST, Coherent and many others to discuss the present and future of microLED technology on 30 NOV - 2 Dec - see agenda here www.TechBlick.com/microLEDs

MicroLEDs, printed electronics and laser printing?

Holst has developed and advanced the so-called LIFT technology to enable even the laser transfer or laser printing of micro components such as microLEDs with high 1-um precision.

In the first slide, you can see a comparison of the classical Laser Induced Forward Transfer (LIFT) vs the technique developed at Holst which is Volume-Controlled Laser Printing (VCLP).

In LIFT, the laser illumination causes a jetting of low to medium-viscosity inks onto the acceptor or target substrate. This is not a young technology and some consider it the digitization of screen printing. In the example here you can see 200um dots of conductive paste printed with the LIFT process.

The VCLP is different. Here, the laser releases fine droplets onto the target/acceptor substrate. Given the volume control, better resolution is accessible. The example herein shows 40um dots of highly viscous solder paste printed using VCLP technology. Note that here the high-throughput deposition of ultrafine interconnects, such as conductive adhesives and solder pastes, is from a structured carrier plate covered with a proprietary permanent release coating.

An important feature of the VCLP technique is the control of heat flux. Without this laser printing can result in the blurred or poor definition. To manage the heat flux, Holst has developed a proprietary “permanent” stack for clean, fine interconnect printing. In the second slide, you can see the positive impact of this layer in achieving well-defined high-resolution laser printing.

What is amazing is that not only inks and pastes (also adhesive and solders) can be printed, but also micro components such as microLED dies. In the schematic in slide 3, you can see the concepts. Here, the microLEDs are laser released across the print gap onto the acceptor/target substrate. The dies can be <10um with a <5um dicing street. This technique can reach >10M UPH (units per hour) with 1um assembly accuracy.

The final slide shows examples of mini as well as microLED transferred using this technique. The mini LEDs are 125x125x80 um3 and the microLEDs are 60x60x10 um3.

These are incredible results and point towards a new high throughput laser printing technique able to print fine lines of inks as well as highly viscous pastes, and mini and micro components.

To learn more join our microLED event online on 30NOV-1Dec where this technology will be presented www.TechBlick.com/microLEDs

It is now time to join the most important specialist event on microLEDs and Quantum Dots taking place online on 30 NOV - 1 DEC. The agenda is shown below and features the likes of Samsung, Sharp Omdia, Yole, Playnitride, Enjet, ASMPT, Coherent, Allos Semiconductor, and many more. It is truely a wonderful agenda. See more details here