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Diverse world of printing in displays: how printing impacts AMOLED, AMQLED, microLEDs, AR/VR, etc



In this article, I will show you how different types of printing are impacting, and will impact, various display technologies including AMOLED, AMQLED, microLEDs, electrochromic, and beyond.


Many of the innovations and trends highlighted below will be part of TechBlick’s unique upcoming LIVE(online) conference and tradeshow on Innovations in Displays and Lighting taking place on 14-16 July.


 

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At this conference, we bring together hand-picked speakers, each representing an important innovation trend in display material development, microLEDs, flexible displays, AR/VR, large-area lighting, printed displays, and beyond.


The speaker line-up includes Dolby, Volvo, Google, Microsoft, GE Research, IBM, Parc (Xerox), Lamar Advertising, Nanosys, VueReal, PlayNitride, Royole, Applied Materials, Universal Display Corp, Morphotonics, Avantama, Enjet, Optomec, Kent Display, DSCC, Yole, Fraunhofer IAP, Nanosys, Schott, Ten Flecs, Metamaterials, iBeam Materials Heilo, imec, C3Nano, Pixelligent, TNO/Holst, XTPL, Scrona, Inuru, OTI Lumionics, QustomDot, Quantum Solutions, etc. See full agenda here

The events are very interactive. Don’t take our word for it and read the testimonials here!

With a single Annual Pass, one can participate in this event and all LIVE (online) future events at TechBlick for 12 months. Furthermore, one can access TechBlick’s growing library of on-demand talks from its past events.



AMOLED: from TFE to printed RGB emitters


Inkjet printed has already been commercialized in OLED displays. It is used in the deposition of the organic layer in multi-layer thin-film encapsulation. Here, inkjet printed organics act as buffer layers separating PECVD-deposited inorganic layers. This is shown below. This is already an incumbent process.



Example of inkjet printed and UV cured organic buffer layers in multi-later thin film encapsulation. Image is from Kateeva 2017


The printing of the emissive RGB layers are more challenging. The technology has been in development for at least 20 years. Indeed, solution processed OLED materials have come a long way in their twenty years of developments. Today, both polymeric and small molecule solution-processed materials show performance level that is almost on a per with evaporated ones.


The three benchmarking charts- update as of Q1 2021- benchmark the performance levels for printed red, green, and blue vs evaporated versions. Here both small molecule and polymeric materials system from the leading suppliers are included. We can see that the performance gaps are now largely bridged, especially for red and green, paving the way for adoption without too much performance penalty. The lifetime, especially blue, perhaps need further refinement.



The charts compare printed OLED performance vs evaporated materials (as of Q1 2021). Note that for blue we did not include a reference evaporated material as it is difficult to compare because of exact color coordinates. Instead, we included the bottom right chart. This chart is from 2020 (Samsung) and compares evaporated vs printed blue whilst factoring in color coordinates. Here, TE and BE denote top and bottom emission, respectively. To hear more about all key innovation trends in displays and lighting join the TechBlick’s LIVE(online) event with an Annual Pass between 14-16 July.



The printing machinery and process know-how have also come a long way. The image below simply showcases some examples of inkjet printed OLED displays. There are improvements both in size and PPI. These trends will continue. Indeed, some manufacturing have been in mass production mode for 21.6”inch displays since 2018. There will be more to come.




Note that additive deposition is not limited just to inkjet printing and solution processed materials. UDC (Universal Display Corp) has an interesting approach of vapor jetting evaporated OLED materials, thus achieving additive manufacture whilst keeping the performance of evaporated materials.




This is a fully evaporated additive side-by-side RGB deposition with performance of evaporated material and a route to Gen10 scale up. This is from UDC. To hear more about all key innovation trends in displays and lighting join the TechBlick’s LIVE(online) event with an Annual Pass between 14-16 July. UDC will also present this technology together with their latest material developments.


QLED: from enhancement film to OLED-QLED to AMQLED


Quantum Dots (QDs) are a major success story. As color converters, they deliver value to LCD, OLED, and microLED displays. They widen the color gamut of LCD, enabling them to remain performance competitive against OLEDs. They can be used on blue OLEDs to achieve WCG large-area partially printed displays with excellent contrast. In microLEDs, they enable achieving RGB using small-sized blue LEDs. In addition, there is the use of QLEDs in truly emissive QD-based displays.


The main application remains LCDs today. Here, the current dominant mode of integration in displays remains the enhancement mode film. I mention this here because the QD-filled resins are R2R coated. An example is shown below.


R2R slot die coated QD resin enhancement films for expanding the color gamut of LCDs. To hear more about all key innovation trends in displays and lighting join the TechBlick’s LIVE(online) event with an Annual Pass between 14-16 July.




In the quantum dot and narrowband phosphor field, you can hear from the following companies: Nanosys, GE Research, Avantama, Heilo Materials, Fraunhofer IAP, Emberion, QustomDots, Quantom Solutions, etc


QDs can of course be used as color filters/color convertors both on LCDs and OLEDs. The integration with OLEDs is particularly interesting. One approach is to deposit a continuous blue layer stack (or multiple blue layer stacks to divide up the voltage and thus prolong lifetime). To get red and green, narrowband quantum dots (QDs) can then be inkjet printed on each pixel, acting as a color filter/color converter.


This approach is promising because it allows achieving fully emissive, printed, and large area displays with excellent color gamut and contrast. This approach is actively pursued by Samsung (seeking to find a way to bring OLED and emissive display to larger areas) and multiple other firms. There is significant multi-billion dollar investment in this approach.


This approach is also interesting because it provides excellent learnings on the way towards the future fully printed AMQLED. Emissive QLED materials are at a relatively early stage of development, but they promise to be the ultimate form of display: inkjet printed, large area, emissive, high EQE, high contract, thin, WCG, etc.


The technology development is of course not straightforward. The non-Cd containing QDs need to improve the EQE and lifetime, better blue compositions need to be formulated, the entire stack materials including transport layers need to be developed and optimized, suitable device architecture developed, and finally an active-matrix mass production process that goes beyond spin coating.


There is rapid progress here and it is not my purpose to detail all the developments. Just to show the complexity level, I showcase the example below from BOE, which is a 55-inch fully inkjet printed AMQLED (May 2021).




This is an IJP 55-inch AMQLED by BOE. The EQE and other performance data were reported only for spin coated QLED device and not IJP AMQLED. To hear more about all key innovation trends in displays and lighting join the TechBlick’s LIVE(online) event with an Annual Pass between 14-16 July.


In the quantum dot and narrowband phosphor field, you can hear from the following companies: Nanosys, GE Research, Avantama, Heilo Materials, Fraunhofer IAP, Emberion, QustomDots, Quantom Solutions, etc.

Precision and repair


Digital printing is evolving well beyond inkjet. Indeed, emerging approaches enhance the printing resolution to the sub-micron range and/or enable deposition on non-flat surfaces. These electrohydrodynamic (single or multi-head), aerosol, and/or micro-dispensing technologies can have many potential applications in the display industry.


The example below shows how micro-dispensing can be deployed to repair open defects on a complex non-flat AMOLED surface. Another example below shows how this process, or version with multiple EHD print heads, can deposit the attach materials for placement of ever smaller microLEDs.




Two examples of how precision digital printing can be used in OLED and microLED display. These examples are from XTPL using their microdispensing machine and their highly viscous silver nanoinks. To hear more about all key innovation trends in displays and lighting join the TechBlick’s LIVE(online) event with an Annual Pass between 14-16 July.


In the precision digital printing field you can hear from Optomec, Enjet, XTPL, Scrona, and more.

MicroLEDs: printed in every step of the process from wafer onwards


MicroLEDs remain a topic of intense interest in the industry. I want to showcase how printing and R2R can deliver value here.


One of the main challenge in microLED fabrication is a high-yield (>>99.99%) and high-throughput transfer process. Many approaches have been developed. Some interesting techniques involve some form of printing (stamp transfer, R2R, etc). Here, I only highlight two interesting approaches.


The first is from VueReal who is developing a cartridge-based approach. The process is shown below. Here, the donor substrate containing the microchips is brought into contact with the receiver substrate. The two substrates are then aligned before the transfer takes place. There is a need to apply some force mechanism to overcome the force keeping the micro chips attached to the donor substrates. It is not clear whether this is mechanical, heat adhesive (based on material added to receiving substrate), or a combination thereof.




Schematic outline of the process steps involved in VueReal’s cartridge-based printed microLED approach. To hear more about all key innovation trends in displays and lighting join the TechBlick’s LIVE(online) event with an Annual Pass between 14-16 July.


Regarding MicroLED innovation, you can hear from Intel, PlayNitride, VueReal, iBeam, Parc, Imec, Applied Materials, and others.


Another interesting, earlier stage, development is by Parc, a Xerox company. The idea is based upon xerographic printing. Here, micro chips such as micro GaN LEDs are suspended in a solution. They are then cast onto an active-matrix substrate controlling a 2D array of electrodes which generate electrostatic force to spatially move the individual chips under the gaze of a camera. The assembled microchips are then transferred using a roller onto the final target substrate.


The 2021 demonstrator is still small size (2.5 x 2.5 cm) on 50um LEDs with no yield data. The assembly process is achieved using a projector addressing a photoswitch array. The assembly process, from mass disordered deposition from liquid to final alignment, is shown below. Currently it is too slow, but an order of magnitude improvement can make it competitive.


The process has interesting development potential as it does not require any special microchip structure. The alignment and positioning is also software controlled, thus allowing arbitrary and complex shapes.




The microprinter process being developed at Parc based on the idea of xerographic printing. To hear more about all key innovation trends in displays and lighting join the TechBlick’s LIVE(online) event with an Annual Pass between 14-16 July.


Regarding MicroLED innovation, you can hear from Intel, PlayNitride, VueReal, iBeam, Parc, Imec, Applied Materials, and others

The transfer step has been receiving substantial attention in recent years. There are many other critical steps in microLED production too. I mention this because printing and conductive inks can play important roles in some of these steps too.


The example below, by Applied Materials, show various examples. Screen printing can be used to print conductive pastes to fill vias. It can be used to print fine-line electrodes between the front and backplanes. Furthermore, it can also print wrap-around electrodes, connecting the microLEDs with the driver IC. Finally, it can print various adhesives (solder, ECA, etc) for the placement and bonding of micro LEDs.



The above images are from Applied Materials. They show how advanced fine-line screen printing can play a role in microLED fabrication. Screen printing can, without requiring a vacuum-based PVD process and etching, print fine-line electrodes and interconnects, create wrap-around electronics, fill vias, and even place attach materials. To hear more about all key innovation trends in displays and lighting join the TechBlick’s LIVE(online) event with an Annual Pass between 14-16 July.

Regarding MicroLED innovation, you can hear from Intel, PlayNitride, VueReal, iBeam, Parc, Imec, Applied Materials, and others.

There are many incredible innovations in the microLED field. Another one that we wish to highlight is in creating a method to assemble large-area microLED displays from tape-on-reel approach.


This is shown below. Here, the microLEDs are first transferred into a larger panel and are then cut into smaller tiles. The tiles undergo an inspection step and the black filling material is added to enhance contrast. The titles are then added onto a reel, creating a tape-on-reel approach enabling the construction of large microLED displays using a SMT-like process! This is a very interesting innovation in the field by PlayNitride.



These images show the steps needed to create a reel-on-tape approach to large-area microLED displays. This innovation is by PlayNitride. To hear more about all key innovation trends in displays and lighting join the TechBlick’s LIVE(online) event with an Annual Pass between 14-16 July.



Waveguides for AR/VR displays


There are many other uses of printing or R2R/R2P in the display industry. Another use case is in R2P (roll-to-plate) nanoimprinting for creating in- and out-coupling features for AV/VR glasses.


Such in- or out-couplings can be made on 300mm wafers, but the throughput is low. With R2P nanoimprinting the throughput may be substantially extended.


An interesting approach is by Morphotonics. Here, they tile together their nanoimprint stamps to create a Gen 5 R2P nanoimprinting line able to achieve sub-micron features and 480 eyepieces per imprint cycle. The R2P nanoimprint process requires solvent-free resins with high refractive index. Here, for example, zirconia and titania based formulations by Pixelligent can result in resin with a refractive index of 1.857.




A tiling approach can result in Gen5 R2P nanoimprint tool with integrated UV curing to achieve nano or sub-microfeatures with replication fidelity. The images above are from Morphotonics .To hear more about all key innovation trends in displays and lighting join the TechBlick’s LIVE(online) event with an Annual Pass between 14-16 July.


Regarding nanoimprinting, you can hear from the leading innovators such as Meta, Morphotonics, and Pixelligent.

Nanoimprinting can have many uses cases in displays also beyond AR/VR. One example is in development of highly transparent and high conducting metal mesh transparent conductive films.


One example is from Meta (Metamaterials) Inc. They have a rolling lithography system. Here, the UV light is wrapped within a soft rolled-up mask. The rolling nanolithography is used to create sub-micron exposures on a photoresist coated metal substrate. The photoresist is then etched, creating extremely high-resolution metal mesh.




The schematic at bottom left shows the idea of a rolling UV nanolithography by Meta (Metamaterials) Inc. The images on top left shows ultra fine feature metal mesh. The benchmarking chart shows that this process can create ultra transparent and highly conductive films. Currently the web width is 300mm but could be scaled to 1-1.2m.



Fully printed R2R low-cost displays

Printing plays a role also in simple (i.e., segmented) low-cost high-volume displays with applications in smart packaging and beyond.


One example is in R2R printed electrochromic displays. A leading player here is Ynvisible. The image set on the left below shows snapshots of full R2R line (printer and converting). This level of automated R2R production is a real progress in the field.


The images on the right images show some application examples. There are numerous applications in smart packaging, IoT sensors, low-cost ubiquitous indicators, etc.


We have leveraged our 15 years of insights into the field of displays and lighting to handpick a fantastic line-up of speakers. At TechBlick’s next LIVE (online) event you will hear about all the key innovation trends from the most innovative companies.


With a single Annual Pass, one can participate in this event and all LIVE (online) future events at TechBlick for 12 months. Furthermore, one can access TechBlick’s growing library of on-demand talks from its past events.


The events are very interactive.

Don’t take our word for it and read the testimonials here!

The speaker line-up includes Dolby, Volvo, Google, Microsoft, GE Research, IBM, Parc (Xerox), Lamar Advertising, Nanosys, VueReal, PlayNitride, Royole, Applied Materials, Universal Display Corp, Morphotonics, Avantama, Enjet, Optomec, Kent Display, DSCC, Yole, Fraunhofer IAP, Nanosys, Schott, Ten Flecs, Metamaterials, iBeam Materials Heilo, imec, C3Nano, Pixelligent, TNO/Holst, XTPL, Scrona, Inuru, OTI Lumionics, QustomDot, Quantum Solutions, etc


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