Four Materials Stories from Display Week 2016
The show in San Francisco highlighted intriguing advances in the areas of electrophoretic displays, OLED materials and processing, quantum dots, and glass.
by Ken Werner
I could begin this article by saying for the hundredth time that the most significant display developments depend on advances in materials. But you already know that. As the narrator used to say at the beginning of an old TV show, “There are 8 million stories in the Naked City….” Four of the most interesting materials (and processing and device-architecture) stories that came out of Display Week 2016 in San Francisco deal with electro-phoretic displays, OLED materials and processing, quantum dots, and glass. We will start with electrophoretic displays:
E Ink’s Color Display Almost Steals the Show
E Ink’s Carta reflective electrophoretic display (EPD) is a near-perfect device for
reading black text on a white background. But there are applications, such as many types of signage, which demand vibrant
color. Until now, the only way to get “full” color from an EPD — at least the only way that E Ink has shown us — is by placing a matrix color filter in front of the monochrome display.
The problem with this approach for a reflective display is that the 40% of light
reflected from a good EPD is brought down to 10–15% by the filter. This results in a limited gamut of rather dark, muddy colors. E Ink showed the way forward a few years ago with a black, white, and red
display, which managed to control particles of three different colors using
differences in mobility and a cleverly designed controlling waveform.
At Display Week, E Ink introduced an impressive expansion of this approach, in
which particles of four different colors are included within each microcapsule,
given different mobilities through different sizing, and driven with a pulsed
controlling waveform that permits the creation of thousands of colors, said E Ink’s Giovanni Mancini (Fig. 1).
Fig. 1: E Ink’s new color technology uses particles of four different colors within each
microcapsule (left) that are controlled in such a way as to create thousands of colors for an unusually vibrant electrophoretic display (right).
The resulting display showed impressively bright and saturated colors and drew
crowds. When a new image was written, the display would flash several times. It took about 10 sec for a new image to build to its final colors. One possible application Mancini mentioned is a color E Ink sign powered by
photocells, as shown at the far right of Fig. 1 This is an important development that will significantly expand the range of applications EPDs can address.
In any other year, E Ink’s new electro-phoretic display, which creates full color without the cost and
light loss of a matrix color filter, would have had no competition as the most
exciting and significant electrophoretic story coming out of Display Week. But this year, E Ink had competition.
First, some background: Good, very-low-power monochrome reflective displays with
slow redraw times exist, and with the introduction of E Ink’s color display, a good low-power color reflective display with very slow redraw
times now exists. What we have not had is a reflective video-rate display, and for good reasons. The only reflective technology that has proved to have both broad application and business feasibility has been electro-phoretic (think E Ink), and
electrophoretic displays operate by moving charged particles slowly through a
significant fluid layer. The redraw time cannot be fast. (Well, it can be faster, but then the charged particles collide violently and
tear each other apart, with unfortunate results.)
A development-stage company called CLEARink, which has an extremely impressive
technical team, has turned the conventional electrophoretic model on its head. The CLEARink display has a thin optical plate with lenslets on the inner
surface. In the white state, incoming light experiences total internal reflection (TIR)
and returns to the viewer. Reflectivity is an impressive 60%.
Lurking behind the optical plate is an “ink” containing black particles that are moved toward or away from the plate. When the particles touch the plate (actually, when they get close enough to interfere with the evanescent light wave), the TIR is defeated and light at that point is absorbed.
That’s clever, but it’s still electrophoresis, with a particle being moved through a fluid. How can that produce video rate? Because, in CLEARink’s architecture, the particle only has to move through 0. 5 microns to interrupt the evanescent wave, and that a very small distance can be traversed rapidly (Fig. 2).
Fig. 2: CLEARink’s innovative electrophoretic architecture enables a much faster response time – even supporting video imagery.
The technology was announced several weeks prior to Display Week, but at the
conference the company showed technology demonstrations in a suite. To demonstrate the monochrome video-rate display, CLEARview engineers had
purchased a Kobo eReader and simply replaced the E Ink imaging film with its
own. With the application of a video signal, the display showed very clean, 30-fps
video with subjectively good contrast and that bright 60% reflectivity. CEO Frank Christiaens noted that the technology is compatible with pretty much any backplane and requires no precision alignment.
As impressive as the monochrome display is, Christiaens did not want my
colleague Bob Raikes and me to forget that color via matrix color filter (MCF)
is part of the company’s mid-term road-map, and his demos were effective. Using an MCF with an otherwise monochrome EPD has not been a satisfying approach
in the past because too much of the reflective light was absorbed. The difference here is that CLEARink starts out with 60% reflectivity rather
So, said Christiaens, CLEARink will soon be providing something that has never
before been available: a reflective, color, video-rate display. In either a color or monochrome version, CLEARink’s fast EPD will enable new applications that cannot be realized by existing display technologies.
OLED Materials and Processes Make Large Steps Forward
A good blue OLED phosphor must do three things well: It must have the proper color coordinates (that is, the right shade of blue) to
create a wide color gamut; it must be energy-efficient; and it must have a long
lifetime. Currently, OLED panel makers use phosphorescent OLED phosphors for red and
green, which do a good job of balancing all three requirements, and fluorescent
phosphor for blue, which provides good color coordinates, poor efficiency, and
just acceptable (or, depending on who you talk to, not-quite-acceptable)
lifetime for television.
Incidentally, “lifetime” does not mean time until death; it means time until the initial luminance drops to a particular percentage. For instance, T95 is the time it takes for display luminance to drop to 95% of its original value. At T50, the display has dropped to 50% of its original output. (When companies talk about lifetime, it is prudent to make sure which “lifetime” they are specifying.)
The chemistry of blue OLED phosphors has made it impossible until now to
optimize the three characteristics simultaneously. However, at Display Week we saw two companies – KyuLux and Cynora – that are exploring a quantum-mechanical mechanism called thermally activated delayed fluorescence (TADF), which is perhaps a way of combining for blue the
benefits of fluorescence (good color co-ordinates and better lifetime) with phosphorescence (efficiency).
As explained by Cynora’s Thomas Baumann, in TADF the singlet and triplet states are energetically very close to each other, which permits thermal energy to cause the triplet states to migrate to the singlet state. After a delay of a few picoseconds, fluorescent emission occurs from the singlet state with an internal quantum efficiency of 100%, since the (originally) triplet state and the singlet state are both captured. Color coordinates and efficiency are good, said Baumann, but material lifetime still needs work. Baumann anticipates customer qualification in 2017, and the first commercial panel incorporating the material in late 2018 or early 2019. But that assumes the lifetime issues are resolved in the next year. Baumann tried to sound optimistic about that, but this is the kind of material development issue that has not always yielded to optimism.
My colleague Bob Raikes reports that in the Business Conference, Junji Adachi, CTO of year-old Kyulux, described his company’s version of TADF, which Adachi called “hyperfluorescent” technology. The light output of normal TADF has a fairly wide spectrum, Adachi said, which limits color saturation. Kyulux claims to have solved this problem, hence the name “hyperfluorescence.” The technology is based on fluorescent materials that have a narrower spectrum, with 4 times the light output. Using evaporation, it is a simple matter to combine the TADF and host materials, Adachi said.
At an investor’s meeting, Kyulux CEO Christopher Savoie showed data indicating a lifetime (unspecified in this presentation) of 1600 hours at an initial output of 1000 cd for TADF green. The company will announce blue lifetimes in September, said Savoie, but he claimed the latest blue materials have 20% external quantum efficiency (EQE) and long life.
According to the company, its materials have long life, high brightness, and low
cost, and Kyulux wants to work with other companies that make materials. Kyulux believes its materials can help panel makers move back from Pentile
structures to RGB. (There was no comment about why this might be a good thing.) Kyulux is working with Kyushu University, which has a research cluster in
Fukuoka, Japan. Companies involved in the latest investment round include Samsung Display, LG
Display, Japan Display, and JOLED, said Savoie. This could be an impressive endorsement of the Kyulux approach or it might be an
example of placing stakes in the ground just in case.
Given that neither Kyulux nor Cynora has yet to demonstrate long life for blue,
it is unclear whether we should be optimistic that a commercially suitable TADF
blue will come to market before a phosphorescent blue does. Since UDC has been working on the phosphorescent-blue problem for years, and to
date has not suggested it is making significant progress, perhaps TADF can win
this horse race after all. Kyulux’s strong technical team of ex-Sony, Samsung, Sharp, and Fuji Film personnel is presumably trying hard.
Other than OLED front-plane materials, a huge challenge has been a
manufacturable pixel-switch backplane that can drive OLED pixels with economy,
stability, and long life. Samsung, and now others, solved that problem with low-temperature polysilicon
(LTPS) for small- and medium-sized displays. However, the LTPS process is difficult to scale to large sizes, in addition to
having issues of material waste and acceptable but less-than-ideal uniformity. LG uses an amorphous metal-oxide backplane, which has had yield and stability
problems when used with OLEDs. The ideal would be using single-crystal silicon for the backplane, if anybody
can figure out (1) how to do it technically and (2) how to do it economically.
Now, a Canadian team from the University of Waterloo, Christie Digital Systems,
and DifTek Lasers is reporting “single-crystal device mobility >300 cm²/V-sec in a scalable process suitable for electronic backplanes for large-area
OLED displays.” This report was made in a Display Week late-news poster paper entitled “Device Mobility >300 cm²/V-sec Using Planarized Single-Crystal-Silicon Spheres for Large-Area-Display
Backplanes,” by R. S. Tarighat and colleagues. The authors embedded single-crystal-silicon spheres in a ceramic substrate and
planarized the surface, and they suggest this approach can be used to make
large-area substrates with high mobility (Fig. 3).
Fig. 3: Single-crystal-silicon spheres are embedded in a ceramic substrate that is then
planarized at the surface in an approach that could be used to make large-area substrates with high mobility. Source: R. S. Tarighat et. al.
The authors developed a method for fabricating transistors on their backplane, and the performance results look very good indeed; just what you would expect
from single-crystal silicon. However, the backplane fabrication process requires grinding and etching. The authors performed these steps on a silicon-wafer-sized substrate because grinding and etching equipment for such sizes is readily available. However, it remains to be seen whether a panel maker could implement a grind and etch process on a Gen 8 or Gen 10 substrate uniformly. If that can be done, and the process can be scaled up economically, this could
be an important development.
A more comprehensive approach to the backplane and phosphor problems was put
forth by nVerpix in its Innovation-Zone booth, an approach that won the company
SID’s Best Prototype Award. nVerpix is developing what it calls CN-VOLET technology, a new architecture that
incorporates the OLED layers in the transistor stack, creating what can be viewed as a light-emitting transistor. (For more about nVerpix, see the I-Zone review article in this issue.)
Samsung Display introduced a display with the industry’s highest OLED pixel density yet: 806 pixels per inch (ppi) in a 5.5-in. panel
targeted at virtual-reality applications. Samsung claimed 306 nits and 97% color gamut (the gamut was not referenced) for
this 3840 × 2160-pixel panel.
The company also waded into the “unhealthy blue display light” discussion by demonstrating its “Bio Blue” display, which adds a light-blue phosphor to the existing RG(darkB) pixel structure. Samsung’s explanation was not entirely clear, but I assume the light blue is used as a
primary for those colors that can be made with a light blue, and that this blue light has an increased percentage of its spectral output outside of the biologically problematic range.
A company statement said, “Of the total blue spectrum, the proportion of blue light harmful to the human eye is 66% for LCDs and 32% for AMOLED displays.” Samsung added that AMOLED displays will be able to reduce this figure to 6% in the future. I suppose it is understandable that Samsung did not discuss the fact that LCD designers can select their blue LEDs and quantum dots such that their blue light, too, is largely outside the biologically sensitive range. Samsung also showed a 5.7-in. rollable OLED display. (Tianma showed a 5.5-in. flexible display.) Other than bend-once applications such as the Samsung Galaxy S7 Edge, I am still waiting for a convincing usage case for 5-in. rollable displays.
Finally, there was a lot of discussion of Samsung’s pre-SID announcement that it was discontinuing its plans for developing
commercial OLED TV. There were lots of rumors and lots of competing interpretations. For now, let’s just say it will be interesting to see what TV technology the company promotes in 2017. (For about TVs, see the review article by Steve Sechrist in this issue.)
Quantum Dots – Startling Progress on Major Issues
In addition to the major introduction (Hyperion quantum dots, discussed below) Nanosys planned to make at Display Week, it added
another when CEO Jason Hartlove apparently went “off the script” at the Business Conference and announced the development of quantum dots that are stable in air thanks to individual encapsulation.
Quantum dots are sensitive to oxygen and moisture, and commercially available quantum-dot products, such as QD Vision’s thin glass tube and Nanosys/3M’s QDEF film, have elements that protect the dots from air and moisture. To prove that the company’s air-stable QDs are indeed stable in air, Nanosys Corporate Communications Manager Jeff Yurek provided a lab-bench-style technical demo behind closed doors. With each dot snug and cozy in its individual encapsulation, significant new uses become possible: electrical, instead of just optical, excitation; ink-jet printing; and even gravure printing, according to Hartlove.
Think of making a color “filter” by ink-jetting patterns of red- and green-converting quantum dots on a film
that sits in front of a blue direct-addressed backlight. Instead of inefficiently blocking light with a conventional color filter, you
would be converting the blue light to red and green where you wanted it to make full-color pixels. Yurek suggested a possible efficiency improvement of 2–3 times.
Yurek said there is a “huge pull” from a customer who would like to go to market with an air-stable-based product in 2018, but Nanosys thinks 2019 is more likely.
Nanosys’s scheduled announcements and booth demonstrations were also exciting. The company’s Hyperion quantum-dot system matches the performance of cadmium-selenide quantum dots while being officially “cadmium free” under RoHS regulations, said Yurek. The Hyperion approach combines a completely cadmium-free red quantum dot with a green dot that contains very little cadmium. A QDEF sheet using the new formulation has a cadmium level less than the 100 parts-per-million limit set by the European RoHS Directive, so no exemption is required.
In a paper delivered at the SID symposium, Nanosys R&D VP Charlie Hotz said an Hyperion QDEF sheet provided over 90% of the BT.2020
color gamut, just as conventional cadmium-selenide (CdSe) quantum-dot sheets do. This was supported by a side-by-side demonstration in the Nanosys booth. So, if there are no unforeseen difficulties, panel makers and TV manufacturers (such as Samsung) will not have to choose between high-performing and more
efficient CdSe dots and the less effective but RoHS exemption-free indium-phosphide (InP) dots. Nanosys says QDEF manufacturing partners will be evaluating the new materials in Q3’ 16, with volume production of Hyperion QDEF expected in early 2017. Hartlove said there is no cost differential between Hyperion and CdSe dots, and that the manufacturing costs of Hyperion are actually lower.
The attentive reader may have noticed the use of the plural word partners in the preceding paragraph, and that was the subject of another Nanosys announcement. Nanosys has now added Hitachi Chemical as a partner for developing QDEF films for display applications, in addition to 3M. In a press release issued in May 2016, Hiroyuki Morishima, the GM of Hitachi Chemical’s R&D Headquarters, was quoted as saying “We plan to begin shipping product in mass-production volumes during the second half of 2016.” During a booth tour for institutional investors sponsored by Sanford C. Bernstein (Hong Kong) Limited, Hartlove said “[Total market size] should hit 200 million square meters over the next couple of years; this year we expect [QD market penetration] to be roughly 5% of that.”
Finally, Nanosys was promoting President Obama’s award of the National Medal of Science to company co-founder Paul Alivisatos for his work on quantum dots.
Given the transition from edge lighting to direct backlighting in TVs, it came as no surprise that QD Vision is working on a film-based approach with a
partner, but the company’s emphasis at Display Week was how cost-effective the company’s ColorIQ thin-tube quantum-dot optic can be in smaller displays. (For additional coverage of QD-enhanced TVs, again see Steve Sechrist’s TV report in this issue.)
In its booth, QD Vision was introducing the Philips 276E7 27-in. 1920 × 1080 monitor to the U.S. market. The monitor displays images
with 250-nits luminance and 99% of the Adobe RGB gamut. The Philips monitor brand, which is controlled by TPV, has been sold primarily in Europe and Asia, but TPV plans to make a marketing push in North America, too.
Also announced was a 27-in. monitor from TPV-owned AOC, which has specs similar to the Philips 27 in. It will be available in North America Q3 at a price that will probably be close to $300 (Fig. 4).
Fig. 4: AOC has introduced a quantum-dot-enhanced 27-in. monitor that should sell for approximately $300.
The LEDs, and the ColorIQ optic, are on the bottom edge in these monitors. QD Vision executives stressed that ColorIQ can be very cost-effective for
consumer monitors and smaller TVs.
Other ColorIQ monitors and small TVs being introduced in the booth were a 24-in. AOC monitor, a 24-in. Philips monitor, and 32-in. Philips and AOC monitors
currently available in China.
QD Vision execs said the company continues to work on QLED (a structure in which the quantum-dot material is electrically rather than optically excited and is therefore suitable for an emissive display that could compete directly with OLED). The company believes that QLED is the ultimate display, and it expects to be
making product in 2 years. The company continues to develop the demanding dot-on-chip, “if not for LCD then for lighting.” Quantum dots for mobile-phone displays will have to be dot-on-chip, an executive said, since there is no room for anything else.
QD Vision had a side-by-side comparison (using the outdated NTSC color gamut, but still providing a helpful comparison) of four TVs: QD Vision CdSe film (105%), InP film (91%), OLED (82%), and standard white-LED-lit LCD (72%). It is no longer a surprise to anyone that CdSe quantum dots outperform InP dots,
and the difference is easy to see. The very poor showing of the OLED TV was more surprising. In a recent Display Daily, OLED Association Managing Director Barry Young suggested that an older model OLED TV was being used for the comparison.
Roughly spherical dots are not the only form in which quantum particles come. The directional characteristics of quantum rods open new applications in color
filters and other products, said Bob Miller of Merck affiliate EMD. In an invited paper entitled “Quantum-Rod-Containing Film Development for Display Applications,” Merck Japan’s Masayoshi Suzuki discussed some of the details. Among them is that Q-Rods have a smaller overlap between the absorption and emission spectra than Q-Dots, which means there is less quenching of the output when the Q-structures become more concentrated. There is also a higher out-coupling efficiency because the distribution of emitted light is directed more toward the normal to the film plane.
As influential as quantum dots have already been, we saw dramatic technical developments at Display Week that herald further significant market growth. One somewhat surprising takeaway is that cost-effective quantum-dot consumer monitors are here, and with TPV supplying about half of the world’s monitors, we are likely to see a lot more of them.
Glass and Films: More Interesting than You May Think
Glass is essential to the display and lighting worlds, but it is hard to make it as exciting as, for example, a big bright TV. Still, makers of glass and associated materials were doing their best to stir the crowds.
Corning was showing LCD modules with its Iris Glass, which won a Display Component of the Year Award from SID. (AGC won the same award for its similar technology). Iris glass was designed to replace acrylic and other polymers as the light-guide plate (LGP) in edge-lit LCDs. Using glass instead of polymer provides greater dimensional stability and a thinner LGP without sacrificing performance, a Corning representative said. Although transmissivity was a problem, Corning says it has now been overcome. Iris Glass is being used in edge-lit TVs that are available today, and more seem to be under development in China and elsewhere.
Sets were being shown in Corning’s booth that measured only about 5 mm thick, and thicknesses less than 4 mm are possible, a Corning rep said. That is not too much more than the 2.57-mm thickness of LG’s top-of-the-line OLED TV. Not far from the Corning booth, BOE was showing a 65-in. 8K × 4K 10-bit-per-channel module using Iris glass and measuring only 3.8 mm thick.
Corning was also promoting both its Lotus and Eagle high-stability NXT glasses. There is significant interest in NXT glass for the coming generation of 8K LCDs,
Corning said, because display drivers get hot enough for the stability of normal glass to be an issue. But that issue is not limited to TV-sized displays. Since last August, Samsung Display has been using Lotus NXT for the LTPS OLED display in the Samsung Galaxy Note 5, which packs Quad-HD pixel content into a 5.7-in. display.
Particularly for automotive applications, Corning was showing anti-glare Gorilla Glass with different amounts of haze. Samples with 3%, 10%, and 20% haze were shown.
AGC was showing its award-winning XCV extremely transparent glass for LGPs. Asahi was demonstrating the improved inner transmittance of XCV compared to
conventional extra-clear glass, showing a significant difference, especially at
longer wavelengths. Asahi also compared the properties of XCV with those of poly(methyl
methacrylate), better known as PMMA, acrylic, or Lucite, which is a very common
material for LGPs. The thermal conductivity of XCV glass is five times that of PMMA, its water
absorption is 0.0% versus 0.3% for PMMA, and its thermal expansion coefficient
is 84 × 10 × K-1 compared to PMMA’s 700. AGC will supply XCV with a light-extracting dot pattern but did not say when it would be available to panel makers or what the maximum available size will be. (Corning has Iris Glass available up to Gen 10.)
AGC also showed its Glascene glass projection screen that retains its transparency during image projection. The company also showed its Infoverre smart glass windows that change from transparent to highly diffusive.
Merck/EMD was also demonstrating smart windows using the company’s guest-host liquid crystal, which it calls Licrivision. The window can turn from clear to diffuse and can also change from clear to a color with the appropriate guest material (Fig. 5).
Fig. 5: Merck demonstrated smart windows that could turn from clear (left) to diffuse (right), courtesy of the company’s liquid-crystal-material Licrivision.
The technology is well-developed, said Merck/EMD, and the company is now working with architectural glass makers on high-volume production. Interest from architects and builders is high, said EMD’s Bob Miller.
3M showed its Advanced Light Control Film (ALCF) family. The polycarbonate films contain internal optical louvers for controlling the direction of light. 3M sees the primary application as reducing windshield reflections in automotive displays. The film can be included in the LCD’s optical stack. A hardcoated version can be the top film over the front polarizer.
Luminit was showing its well-known light-control films. New are products based on computer-generated holograms. One customer is using the technology to create an automobile welcome application, which projects the brand’s logo on the ground to welcome the owner to his car. Luminit would not reveal its customer, but Lincoln is known to offer such a feature.
Global Lighting Technologies (GLT) has been a master of precision light guides and light-guide-based lamps for years. An unusual addition to GLT’s technological portfolio this year was an extremely thin and flexible light guide that can be sewn into clothing. In the photo in Fig. 6, a GLT rep wears a flat lamp based on the light guide behind the cut-out Los Angeles logo on the front of his baseball cap. (The lamp is not lit in this photo.)
Fig. 6: Logowear outfitted with GLT’s lightguide lamps has been a big seller for the company, according to its representatives.
Finally, a company called Redux was showing a glass panel with transducers that created a very sophisticated, adjustable, and localized haptic experience. Virtual controls – such as sliders, knobs, and pushbuttons – could be established anywhere on the panel, and they felt much like the mechanical controls they mimicked. Adjustments could be made for button resistance, button edge sensation, friction, and clicks in a rotary control, etc. The same transducers can make the panel, which can be a separate panel or the front glass of a display, act like a loudspeaker (or a stereo pair). If the audio part of the Redux technology sounds a lot like that of the defunct company NXT, it’s because Redux acquired NXT’s IP and hired some of its former employees. There was nothing wrong with NXT’s technology, said Redux Chief Commercial Officer John Kavanagh, just its product strategy. But Redux is adding its very sophisticated haptics to NXT’s audio-on-panel approach. These Display Week exhibitors have not been sitting on their glasses.
In materials and devices, this was an unusually exciting Display Week. It will be interesting to see what structures the companies build on the foundations laid in San Francisco this year. •
Ken Werner is Principal of Nutmeg Consultants, specializing in the display industry, manufacturing, technology, and applications, including mobile devices and television. He can be reached at email@example.com.