Category Archives: Flexible Displays

Bend them, stretch them, twist them, fold them: modern materials that are light, flexible and highly conductive have extraordinary technological potential, whether as artificial skin or electronic paper.

Making such concepts affordable enough for general use remains a challenge but a new way of working with copper nanowires and a PVA “nano glue” could be a game-changer.

Previous success in the field of ultra-lightweight “aerogel monoliths” has largely relied on the use of precious gold and silver nanowires.

By turning instead to copper, both abundant and cheap, researchers at Monash University and the Melbourne Centre for Nanofabrication have developed a way of making flexible conductors cost-effective enough for commercial application.

“Aerogel monoliths are like kitchen sponges but ours are made of ultra fine copper nanowires, using a fabrication process called freeze drying,” said lead researcher Associate Professor Wenlong Cheng, from Monash University’s Department of Chemical Engineering.

“The copper aerogel monoliths are conductive and could be further embedded into polymeric elastomers – extremely flexible, stretchable materials – to obtain conducting rubbers.”

Despite its conductivity, copper’s tendency to oxidation and the poor mechanical stability of copper nanowire aerogel monoliths mean its potential has been largely unexplored.

The researchers found that adding a trace amount of poly(vinyl alcohol) (PVA) to their aerogels substantially improved their mechanical strength and robustness without impairing their conductivity.

What’s more, once the PVA was included, the aerogels could be used to make electrically conductive rubber materials without the need for any prewiring. Reshaping was also easy.

“The conducting rubbers could be shaped in arbitrary 1D, 2D and 3D shapes simply by cutting, while maintaining the conductivities,” Associate Professor Cheng said.

The versatility extends to the degree of conductivity. “The conductivity can be tuned simply by adjusting the loading of copper nanowires,” he said. “A low loading of nano wires would be appropriate for a pressure sensor whereas a high loading is suitable for a stretchable conductor.”

Affordable versions of these materials open up the potential for use in a range of new-generation concepts: from prosthetic skin to electronic paper, for implantable medical devices, and for flexible displays and touch screens.

They can be used in rubber-like electronic devices that, unlike paper-like electronic devices, can stretch as well as bend. They can also be attached to topologically complex curved surfaces, serving as real skin-like sensing devices, Associate Professor Cheng said.

In their report, published recently in ACS Nano, the researchers noted that devices using their copper-based aerogels were not quite as sensitive as those using gold nanowires, but had many other advantages, most notably their low-cost materials, simpler and more affordable processing, and great versatility.

MarketResearchReports.Biz released a new market research report this week entitled “Metal Oxide TFT Backplanes For Displays 2014-2024: Technologies, Forecasts, Players.”

According to the new report, metal oxide display backplanes have already gone commercial. Sharp has invested in establishing a Gen8 IGZO plant at its Kameyama plant in Japan while LG has also selected IGZO backplanes for its large-sized white OLED technology. At the same time, Chinese companies such as BOE are fast playing catch up with both prototype and production capacity announcements.

IDTechEx estimates that 7 km sqr of metal oxide backplanes will be used in the OLED industry in 2024, enabling a 16 billion USD market at the display module level. The LCD display market will add an extra demand of at least 1 km sqr per year in 2024 for metal oxide backplanes.

The display industry continues to rapidly change and seek new markets. Long term trends are still prevalent and shape global activity. Examples include reducing power consumption, improving image resolution, and decreasing device thickness. At the same, the need to differentiate and capture new markets such as wearable electronics is first bringing in robust and then flexible and bendable displays. These trends will drastically affect the technology requirements at many levels including the backplane level. This will stretch several existing solutions beyond likely performance limits, thereby creating openings and opportunities for new entrants and the technology space for backplanes is complex. It consists of (a) mature technologies such as amorphous and polycrystalline silicon, (b) emerging technologies such as organic and metal oxides and (c) early state technologies such as graphene, carbon nanotubes, nanowires, etc. No single technology offers a one-size-fits-all solution and many technologies will co-exist in the market. Betting on the right technology will remain a decision-making nightmare.

It is within this emerging, complex yet changing space that metal oxide are emerging. They promise low leakage currents, high mobility, amorphousity, stability and wide bandgap. These attributes promise to enable, respectively, power consumption reduction, compatibility with current-driven OLEDs and/or 3D displays, image uniformity over large areas, long lifetime and transparency.

In the short term, this will help enable higher resolution and lower power consumption levels in displays including LCDs (particularly in medium- to large-sized displays); while in the medium- to long-term metal oxides will help enable uniform medium- to large-sized OLED displays.

The report specifically addresses the big picture – including OLED displays and lighting, to thin film photovoltaics to flexible sensors and much more. Importantly, it includes not only electronics which are printed, organic and/or flexible now, but it also covers those that will be. Realistic timescales, case studies, existing products and the emergence of new products are given, as are impediments and opportunities for the years to come.

Over 3,000 organizations are pursuing printed, organic, flexible electronics, including printing, electronics, materials and packaging companies. While some of these technologies are in use now – indeed there are three sectors which have created billion dollar markets – others are commercially embryonic.

FlexTech Alliance announced the conference theme, Call for Papers, and the industry chairs for the 14th Annual Flexible & Printed Electronics Conference & Exhibition — 2015FLEX — set for February 23 – 26, 2015 at the Monterey Conference Center, Monterey, California.   “Bringing Technology & Products to Markets” as a theme reflects the steadily growing integration of flexible and printed electronics components in a wide-array of products and processes. The theme will be used to focus on how flexible electronics are demonstrating the value of light weight, low power products to non-traditional electronics markets, and thereby by delivering on the true promise of making lives healthier, safer, simpler and smarter.

The Flex Conference relies on a strong group of industry members to ensure leading edge business and technical content. This year’s committee is led by key industry veterans Ross Bringans of PARC, a Xerox Company; Michael Idacavage of Esstech; Thomas Kolbusch of Coatema Corp.; and Robert Praino of Chasm Technologies. The chairs guide the committee in identifying thought leaders for invited and keynote presentations, and in searching the industry for breakthroughs and advancements that spur market growth and partnerships.

The conference Call for Papers and Posters outlines the categories noted by the committee to be of highest interest for event attendees. Researchers from industry and academia, as well as national institutes, are encouraged to submit an abstract by October 17, 2014 to be considered for presentation in one of 24 different technical sessions. This year’s topics include the emerging, exciting sector of nano-bio devices, as well as manufacturing technologies that underpin the popularity of wearable electronics.

A nanoparticle ink that can be used for printing electronics without high-temperature annealing presents a possible profitable approach for manufacturing flexible electronics.

Printing semiconductor devices are considered to provide low-cost high performance flexible electronics that outperform amorphous silicon thin film transistors currently limiting developments in display technology. However the nanoparticle inks developed so far have required annealing, which limits them to substrates that can withstand high temperatures, ruling out a lot of the flexible plastics that could otherwise be used. Researchers at the National Institute of Materials Science and Okayama University in Japan have now developed a nanoparticle ink that can be used with room-temperature printing procedures.

Developments in thin film transistors made from amorphous silicon have provided wider, thinner displays with higher resolution and lower energy consumption. However further progress in this field is now limited by the low response to applied electric fields, that is, the low field-effect mobility. Oxide semiconductors such as InGaZnO (IGZO) offer better performance characteristics but require complicated fabrication procedures.

Nanoparticle inks should allow simple low-cost manufacture but the nanoparticles usually used are surrounded in non-conductive ligands – molecules that are introduced during synthesis for stabilizing the particles. These ligands must be removed by annealing to make the ink conducting. Takeo Minari, Masayuki Kanehara and colleagues found a way around this difficulty by developing nanoparticles surrounded by planar aromatic molecules that allow charge transfer.

The gold nanoparticles had a resistivity of around 9 x 10-6 Ω cm – similar to pure gold. The researchers used the nanoparticle ink to print organic thin film transistors on a flexible polymer and a paper substrate at room temperature, producing devices with mobilities of 7.9 and 2.5 cm2 V-1 s-1 for polymer and paper respectively – figures comparable to IGZO devices.

As the researchers conclude in their report of the work, “This room temperature printing process is a promising method as a core technology for future semiconductor devices.”

By Jeff Dorsch

In wearable gadgets, flexible electronics may have met its dream application. And that’s no stretch of the imagination.

For example: The 711th Human Performance Wing of the U.S. Air Force is looking at sweat sensors that could be embedded in a printed electronic plaster and attached to the arms of pilots to monitor whether they need to drink more fluids or if taking amphetamines would be advised to maintain optimal alertness in flight.

IDTechEx has forecast that the worldwide market for flexible, printed, and organic electronics will increase from $16.04 billion last year to $76.79 billion in 2023. The overall market will continue to be dominated organic light-emitting diode displays this year and in 2015, the market research firm predicts. Conductive ink and photovoltaics represent large segments of the total market. “On the other hand, stretchable electronics, logic and memory, thin-film sensors are much smaller segments but with huge growth potential as they emerge from R&D,” IDTechEx states.

Printed and flexible sensors are a $6.3 billion market, according to IDTechEx, with much of that total representing biosensors – disposable blood-glucose test strips that diabetics use to check their blood-sugar levels.

Frost & Sullivan forecasts that the printed electronics market will enjoy a compound annual growth rate of 34 percent through 2021.

Semiconductor Equipment and Materials International has taken a large interest in flexible and printed electronics for several years, establishing the SEMI Plastic Electronics Special Interest Group. In cooperation with FlexTech Alliance, SEMI will present a SEMICON West workshop on Thursday, July 10, on “Flexible Hybrid Electronics for Wearable Applications – Challenges and Solutions,” commencing at 10 a.m. at the San Francisco Marriott Marquis Hotel.

SEMI also will stage the annual Plastic Electronics Conference and Exhibition on October 7-9 in Grenoble, France. The plastic electronics show will alternate between Grenoble and Dresden, Germany, in the years ahead.

Belgium-based imec has been working with thin-film materials in flexible electronics – not the generally inflexible silicon, but indium gallium zinc oxide (IGZO), according to Philip Pieters, imec’s business development director. It is a very thin, flexible, unbreakable material, and “almost invisible,” he says.

IGZO thin-film transistors were first developed more than a decade ago by the Tokyo Institute of Technology and the Japan Science and Technology Agency. The IGZO-TFT technology has been licensed to Samsung Electronics and Sharp Electronics.

“We could make microprocessors, AC/DC circuits, etc.,” with IGZO, Pieters says. “Our processes are compatible with large-format glass plates. It could be processed in a cost-effective way for large-scale manufacturing.” IGZO could prove to be cheaper than silicon-based electronics, he adds.

As a research and development organization, imec keeps its production of IGZO-based electronics on a small scale, but the process could be ported to large-scale plants “in the next year or so,” Pieters says.

Stretchable electronics that “could be put on skin” are one potential application in wearable devices, the imec executive adds.

Printed, flexible, and organic electronics are clearly a growing opportunity, one that is attracting an increasing number of manufacturers and suppliers.

IGZO

Ultrathin glass is well suited for use as interposers in semiconductor packaging applications.

BY JUILA GOLDSTEIN, Senior Associate Analyst, NanoMarkets, Glen Allen, VA

Flexible glass seemed like a natural fit for the display industry, combining the impermeability of glass with the flexibility of plastic. In 2012 it appeared as though flexible and ultrathin glass companies were going to benefit from the explosion of touchscreens in displays of all sizes, but the market made an abrupt turnaround. Now suppliers of ultrathin and flexible glass are looking for applications beyond displays to bring in revenue in the next few years, and one of the places they are looking is in semiconductor packaging.

For those who approach flexible glass from the point of view of a display, an application where the glass is hidden between layers of silicon and other materials may not seem to make a lot of sense. As far as NanoMarkets can tell, no one really thought about semiconductor packaging as a use for flexible glass until the display application began to fail. The flexible glass sector itself was firmly focused on displays until then and the semiconductor packaging sector had probably never considered flexible glass as an option.

Nonetheless, using ultrathin glass in semiconductor packaging may actually be a very good idea, even though its optical properties and flexibility may be irrelevant in this application.

The Role of glass in interposers

For many years the semiconductor packaging industry has been developing packages that are smaller, thinner, and lighter than what has come before. Ultrathin glass, 30 to 100 μm, may be able to further progress toward this goal.

The target application is 2.5D or 3D multi-chip or chip scale packages (CSP), where semiconductor chips are placed in close proximity or stacked on top of each other to provide a space-saving configuration. Such packages traditionally use a layer of thinned silicon as an interposer to connect chips to each other and to the underlying organic substrate. Silicon has the advantage of being a familiar material with a well-established infrastructure in the semiconductor packaging industry, but it does have some drawbacks, the major one being cost.

FIGURE 1. A 30 μm thick flexible glass interposer made by Schott Glass.

FIGURE 1. A 30 μm thick flexible glass interposer made by Schott Glass.

Glass may be preferable to silicon as an interposer because it is a less expensive material, it can be provided in thin sheets (silicon has to be ground and polished to the proper thickness) and it is thermally insulating. Silicon is a semicon- ductor, not an electrical insulator, which can cause problems with crosstalk between chips. FIGURE 1 shows a 30 μm thick flexible glass interposer made by Schott Glass.

Silicon conducts heat better than glass, making the semiconductor industry a bit suspicious of the ability of glass to conduct heat sufficiently to avoid hot spots in sensitive ICs. The answer is in the through-glass vias (TGV), channels drilled through the interposer that are filled with metal (usually copper) and form electrical connections between the chip and the organic substrate. Solid filled vias act like heat pipes to provide a path for heat conduction.

The potential cost advantages of glass can best be achieved using large sheets of glass, thus allowing facilities to process more units in parallel than is possible with silicon wafers. The largest possible cost savings of using flexible glass is realized if it can be integrated into a roll- to-roll production process. Several suppliers are producing flexible glass on rolls, but the semiconductor industry is not necessarily prepared to process it.

Re-evaluating the supply chain

While glass may be a compelling interposer material from the point of view of glass makers, lack of infra- structure in this application is a real problem. In order for glass to be useful as an interposer, someone needs to drill vias through the glass and metallize them, and it is not yet clear who that would be. Several industries could participate in the supply chain, but there are barriers in all cases:

  • Semiconductor packaging houses: The industry is not used to working with glass and is not inclined to do so. It is very resistant to change and may be especially averse to implementing R2R processing. Convincing semiconductor packaging facilities to process glass will clearly be an uphill battle.
  • Flat-panel display manufacturers: These companies have experience with glass but have not historically had anything to do with semiconductor packaging. It may be possible to build awareness in this sector, but the flat panel display industry prefers to sell large pieces of glass.
  • Printed circuit board manufacturers: The PCB industry currently makes organic interposers, geared toward applica- tions where fine pitch is not required. Glass suppliers might be able to work with the PCB industry, which is used to large panels, if they want to supply sheets of glass. It still may be difficult, however, to implement very thin glass using this approach. It also will probably be difficult to integrate TGV production into a PCB-like process flow.

Organizations that are promoting ultrathin glass interposers are attempting to address the infrastructure challenge:

  • Georgia Tech: The Packaging Resource Center at Georgia Tech has been working with industry partners on glass interposers since 2010 and has moved from initial trials with 180-μm thick glass down to the thinnest products that today’s glass suppliers are producing. The PRC is working with major glass suppliers such as Corning and Schott, who are interested in flexible glass interposers.

The PRC has been working on transferring the technology from prototype to low volume, and perhaps eventually high volume, commercial production. It has made some real progress in developing the technology and moving proto- typing from labs into industry, but admits that the greatest challenge in moving forward is lack of infrastructure to support the transition.

nMode solutions that is partially funded by Asahi Glass Company, is providing some missing segments in the supply chain. Triton has developed a production process to create through glass vias (TGVs) that is sufficient for today’s 2.5D applications and it is making interposers for MEMS, RF, and optics at its manufacturing facility in Carlsbad, CA. According to Triton, the major advantage it provides over silicon is the ability to produce solid filled, hermetic TGVs.

Existing commercial products use glass interposers from Triton, but this is much thicker glass, typically 0.3mm or greater. The glass is cut into wafers, matching the form factor of silicon but not requiring backgrinding. This provides the convenience of a process that fits easily into existing manufacturing lines but doesn’t take advantage of glass’ potential to provide thinner interposers at much lower cost than silicon. Triton can make large panels of 0.1-mm glass with TGVs, but customers do not know how to handle it and may not be inclined to learn.

NanoMarkets understands the potential advantage thin glass would have as an interposer, but is not especially optimistic about its future, especially in the near term. It seems very unlikely that flexible glass will be able to generate large revenues in this space, even if penetration rates get large. Each product uses a very small amount of glass compared to what would be needed for even a smart phone display.

The semiconductor packaging industry may be an even more difficult environment for introducing new processes than the display industry, and we know flexible glass has had challenges there. Still, we feel this sector is worth keeping an eye on to see if glass has an opportunity to succeed where silicon has not.

Yesterday, the Society for Information Display (SID) unveiled the winners of its prestigious 19th annual Display Industry Awards. These are the display industry’s most coveted awards, and the honorees will be recognized during a special luncheon tomorrow, Wed., June 4, as part of Display Week 2014, which is taking place this week at the San Diego Convention Center.

Research and innovation continue to be alive and well, and this past year was no exception given the caliber of nominated candidates. The six winners, two in each of three main categories, were chosen by a distinguished panel of experts who evaluated the nominees for their degree of technical innovation and commercial significance, in addition to their potential for positive social impact.

It is notable that three of this year’s winners are curved devices, and two of the winners are materials that support flexible devices, signaling that the “flat” in flat panel displays may be a thing of the past. Four of the six winners are also OLED-based, while the debut of the internet giant, Google, in this year’s award race reminds that LCDs are still here to stay. The winning products and a brief description of each are listed below. A more comprehensive description of the award winners is included in the Display Week 2014 Show Issue of Information Display magazine.

Display of the Year: Granted to a display with novel and outstanding features such as new physical or chemical effects, or a new addressing method

Gold Award Winner: Samsung Display’s 5.68-in. Curved (Flexible) AMOLED Display

The Samsung 5.68-in. FHD curved AMOLED display represents a major milestone for the entire display industry, as it’s the world’s first truly flexible full-fidelity display technology to be mass produced and adapted for use in a mass-market product. Now being produced on a plastic substrate, the new Samsung display panel enables smartphones such as the Samsung Galaxy Round to be curved, significantly improving a user’s grip. Smartphone users will be able to comfortably hold a larger-screen version of the panel with just one hand. The smartphone has a curvature of 400 mm, while human hands have a natural curvature of about 300-500 mm. Also, the display enables a more visually immersive mobile experience with a “landscape” view aspect ratio of 1.88:1, comparable to the Vista Vision technology (1.83:1) now used in most movie theaters. In addition, the curved screen is more readable thanks to a significant reduction in light reflectance. Samsung’s new curved display will later evolve into bendable and foldable displays that will further revolutionize the use of smartphones and other mobile-product form factors.

Silver Award Winner: LG Display’s 55-in. FHD Curved OLED TV Panel

LG’s 55-in. FHD curved OLED TV panel offers exceptionally vibrant imagery in a curved format that offers viewers a comfortably immersive environment. LG’s curved OLED TV was introduced last year, and uses the company’s WRGB OLED technology with an oxide TFT backplane, the company’s technical solution of choice for large-sized OLED panels. The panel is slim – only 4 mm thick with side bezel widths of 11 mm. At 19.2 pounds, the TV is also substantially lighter than competitive products. At the same time, it offers superior picture quality, achieving remarkably rich and natural colors. In addition to the vivid and enhanced picture-quality experience, the curved structure of the new OLED TV panel offers viewing comfort. The curvature mimics a human’s normal line of vision, which makes it more eye friendly and allows viewers to feel less fatigue even when watching the screen, while also allowing for a wider and brighter field of view.

Display Component of the Year: Granted for a novel component (sold as a separate part and incorporated into a display) that has significantly enhanced a display’s performance. A component may also include display-enhancing materials and/or parts fabricated with new processes

Gold Award: UDC’s Green Phosphorescent UniversalPHOLED Emitter Material

Universal Display Corporation’s (UDC’s) proprietary green phosphorescent OLED (PHOLED) emissive system can reduce an OLED display’s power consumption by approximately 25 percent, while providing excellent color in mobile displays. Adding green PHOLEDs to displays has increased OLED’s competitiveness with LCDs for mobile applications. This new material is expected to be a key driver in the commercialization of OLED TVs as well as OLED lighting. Through years of R&D work and achievements, UDC has produced UniversalPHOLED materials that provide record-breaking energy efficiencies, vibrant colors, long operating lifetimes and manufacturing versatility. The green PHOLED emitter builds on the successful commercialization of UDC’s red UniversalPHOLED emitter, first launched in commercial passive-matrix display products in 2003. PHOLED materials are expected to drive wider adoption of OLED technology and greater growth in the display and lighting markets because they significantly reduce power consumption and lower heat emission compared to prior fluorescent OLED materials.

Silver Award: Canatu Oy’s Carbon NanoBud (CNB) Film

Canatu Oy’s Carbon NanoBud (CNB) Film, made from carbon nanotubes and fullerenes, provides superior optical performance for flat, flexible, or formable touch screens, displays and touch-sensitive surfaces. This transparent conductive film is used in capacitive touch sensors for portable devices such as mobile phones, tablets, and digital cameras, and in automobiles that require excellent display readability in outdoor and bright indoor environments. CNB Films are also applied in capacitive touch sensors for flexible or formable devices such as smart watches, flexible and foldable mobile phones and tablets, and automobile center consoles.

Display Application of the Year: Granted for a novel and outstanding application of a display, where the display itself is not necessarily a new device

Gold Award: LG Display’s G Flex

LG Display’s G Flex smartphone incorporates a flexible OLED panel that is based on a plastic substrate instead of glass. By applying film-type encapsulation technology and attaching the protection film to the back of the panel, LG Display made the panel bendable and unbreakable. Compared to an OLED display panel based on glass, the flexible OLED panel is lightweight, thin and features design flexibility. This allows for a design that naturally fits the contour of a smartphone user’s face. What’s more, the panel is also the world’s lightest, weighing a mere 7.2 grams, even with a 6-in. screen, the largest among current smartphone OLED displays. In the future, LG plans to use this process applicable for the production of large-sized devices, including laptops, monitors and TVs, as well as eReaders and more.

Silver Award: Google Chromebook Pixel

Chromebooks are built for the way that people use computers and the web today. They make computing faster, simpler and more secure – for everyone. The LCD on the Chromebook Pixel is stunning, providing users with a rich, immersive experience. The 12.85-in. touch screen had, at launch, the highest pixel density of any laptop (239 ppi), and the 3:2 photographic format is specifically designed for using the web by reducing the need for scrolling. For users, text is crisp, colors are vivid, touch interactions are smooth – and each of the 4.3 million pixels seems to disappear into one spectacular picture. Google used amorphous silicon (a-Si) TFT technology for the pixel to reduce the cost of the glass panel. The transmissivity of its high-ppi a-Si TFT panel was lower than panels fabricated with oxide transistors or low-temperature polysilicon. To attain low-power consumption using a-Si, the company optimized the remaining components (including LEDs, optical films, and light pipe). The company’s goal is to continue to push the laptop experience forward, working with its entire ecosystem of partners to build the next generation of Chrome OS devices.

The 51st SID International Symposium, Seminar and Exhibition, or Display Week 2014, will take place June 1-6, 2014 at the San Diego Convention Center in San Diego, Calif. Display Week is an international gathering of scientists, engineers, manufacturers and users in the field of electronic information displays.

Samsung Display announced today that it won the Gold Display of the Year Award with the world’s first 5.68-inch curved super AMOLED display panel at the Society for Information Display’s (SID) Display Week 2014 being held in the San Diego Convention Center June 3-5.

Samsung Display's 5.68-inch flexible display wins Display of Year award at Display Week 2014. (Photo: Business Wire)

Samsung Display’s 5.68-inch flexible display wins Display of Year award at Display Week 2014. (Photo: Business Wire)

Donggun Park, president and CEO of Samsung Display said, “Samsung Display has received one of the highest honors in the display industry by winning the SID Gold Display of the Year Award.” He also said, “We will continue to try to provide the best differentiated solutions to our customers with the most innovative products.”

The SID Display of the Year Awards are the display industry’s most prestigious honor, bestowed annually since 1995 to recognize the best display products and applications introduced to the market during the previous calendar year. Each year, a Gold and a Silver Award winner are selected in each of three categories – Display of the Year, Display Application of the Year, and Display Component of the Year – by the Display Industry Awards Committee based on nominations from SID members and non-members alike.

Samsung Display’s 5.68-inch full HD curved super AMOLED display, selected for Samsung Electronics’ Galaxy Round smartphone which was commercialized last year, attracted much attention as the world’s first flexible display. With its concave design, the full HD curved super AMOLED display has received critical acclaim around the world, and set a new milestone in display technology history.

Displaymate, a display research laboratory, recently reviewed the full HD curved, super AMOLED display and referred to it as a very important and major innovation in smartphone display technology, including improving screen visibility by subtly bending away distracting light reflections. It reported its findings in the 2013 Curved and Flexible Smartphone Display Technology Shoot-Out report.

The 400R curvature of Samsung’s full HD curved, super AMOLED display is the key to a series of optical effects that have resulted in significantly reducing interference from reflected ambient light. It substantially improves screen readability, image contrast, color accuracy and overall picture quality, and can also increase the battery run time because the screen brightness and power consumption level can be lowered, due to reduced light interference from ambient reflections.

The Samsung curved Super AMOLED display is a flexible display that can be bended by evaporating organic light-emitting diodes on a polyimide substrate made of a very thin plastic material. It has a 0.28mm thickness, remarkable color reproduction and an unlimited contrast ratio. In addition, it can be regarded as the optimal display for next-generation mobile and wearable devices.

Samsung Display, with its current leading-edge flexible display technology and ambitious further flexible display development plans, intends to move aggressively to expand the flexible display market.

By Sara Ver-Bruggen, contributing editor

Flexible displays is a technological field that has been in R&D and pre-commercial development for several years, but what needs to happen to make volume production a reality, in areas including substrates, materials and production processes? Semiconductor Manufacturing & Design discussed the issues with Max McDaniel, Director and Chief Marketing Officer, Display Business Group, Applied Materials, Michael Ciesinski, MD of the Flextech Alliance, and Keri Goodwin, Principal Scientist from the Centre for Process Innovation (CPI), in the UK.

SemiMD: Taking a step back and looking at the timeline for flexible display R&D and achievements so far, where is the industry in terms of entering volume production – how close is the industry to resolving those outstanding challenges to volume production, such as cost-effective barrier technologies, for example?

McDaniel: Curved displays are here as evidenced by several curved smartphones and TVs showcased at the Consumer Electronics Show (CES) in January 2014. People are ready for flexible displays, but production volume will take some more time. As the smartphone market matures, brands are embattled in a ‘resolution arms race’. The key challenge for the brand makers is to come up with the next big thing that will differentiate their products and spur new demand from consumers. The display plays a key role in defining the device, and a new form factor – like flexible displays – can bring new opportunities to the market, but the technology is not ready for the mass market because of cost and technology challenges.

Ciesinski: FlexTech initiated its R&D program into flexible displays in 1998 with substantial project funding beginning in 2002 and continuing today. We’ve worked with companies and R&D organizations in the areas of substrates, encapsulation, barrier coating, roll-to-roll (R2R) manufacturing and other key areas. Generally, the supply chain for flexible electronics is adequate but not yet robust, which will occur once large volume production is achieved. In building flat panel displays (FPDs) that industry could build on IC manufacturing strengths and simply scale the equipment. For volume manufacturing on a flexible substrate, many new tools and processes have to be developed from scratch, such as metrology, as experts must build a system to account for a substrate that can shrink or expand depending on temperature, and move in multiple directions. As for barriers, several solutions are available and ready for production. The extreme requirements for OLED thin film barriers have been achieved in production and the main focus now is on cost reduction. The materials industry is quite competitive and ready for volume. In order to obtain better utilization of these materials in production new printing equipment is being developed.

Goodwin: There are still significant challenges to overcome in flexible display volume production. A cost-effective flexible barrier with a very low water transmission vapor rate (WVTR) is still to be developed, this will be required if OLED frontplanes are to be used. Typically these barriers are still multilayer structures with a mix of inorganic and organic coatings to minimize defect levels. While this can be achieved R2R, perhaps via a combination of sputter deposition and solution processing such as slot die, the cost will ultimately be set by the number of multiple coatings required.

An alternative method may be to use R2R atomic layer deposition (ALD), which should yield a significantly lower level of defects, thereby improving the barrier capability of a single layer and reducing, or removing, the need for multiple coatings. However, process scale up is required. CPI envisages that R2R ALD will play important roles in various aspects of flexible printable electronics, where highly conformal nanoscale thin films are required. CPI has been evaluating ALD technology for several years and recently signed an agreement with Beneq to deliver an ALD system to CPI for pilot scale production.

Layer-to-layer registration is another major challenge to overcome in volume production with flexible substrates typically distorting during processing. This issue can be overcome in several ways such as development of lower temperature processes or development of lamination materials to allow sheet-to-sheet (S2S) production without distortion.

And, in terms of commercialization for flexible (as opposed to curved) displays what time frame are we talking?

McDaniel: The approach for early adopters of flexible displays has been a production process that adheres the flexible substrate onto glass, running it through what’s mostly the normal rigid OLED processing, and then delaminating that flexible substrate from the rigid one at the end of processing. What remains is a flexible substrate that has all the transistor structures built onto it. However, this is still a complex process, and due to the cost and complexity involved in manufacturing on a high-volume scale, it is still a ways off from full mass production.

Goodwin: Overall, there are multiple approaches to volume production of flexible displays but all require scale up towards a commercialization solution, therefore it would be expected that the timeline for a product is still five years away. What is important in the short term is to demonstrate controlled processes that can yield products with good lifetime and performance, which then can be scaled up for commercialization.

Ciesinski: Displays in a conformable format have been produced and exhibited; a truly flexible and foldable display is much more than that and there are many approaches to achieving this result in the next few years.

Various flexible display R&D has focused on different substrates, different thin film transistor (TFT) materials and so on. Is there likely to be one approach that will make it to volume production?

Ciesinski: Multiple approaches are currently being considered by the market. For example, plastic substrate films from DuPont Teijin and other suppliers have a strong a presence. Corning’s introduction of flexible glass provides a competitive choice. As for the display technology, LCDs, OLEDs and electrophoretic displays have all been built in a flexible format. Materials will continue to improve and there will be multiple TFT materials for the next few years.

McDaniel: Materials have a key role to play in the R&D efforts for enabling flexible displays. OLED is promising as the rigid glass encapsulation required to protect the organic material from moisture and air can be replaced by thin film. You can make flexible LCD displays but maintaining the required cell gap between the color filter and backplane is very difficult to do. Both OLED and LCD require a TFT backplane. A major challenge for the industry is how to move away from rigid glass while not compromising the operation of the TFT when flexed, folded, or bent.

We have discussed the backplane and encapsulation; but for OLED to get to mass production (especially in large sizes); the industry also has to address challenges in EL evaporation such as lifetime of organic materials, low deposition efficiency, low yield from defects and scalability of evaporation technology which affect the cost of volume production but are not necessarily related to the issues around flexibility. All display technologies, including OLED displays, require very high levels of precision in film uniformity and particle control to maintain yield. There is the potential for OLED display production to become less expensive, and Applied Materials is leveraging its expertise in precision materials engineering to help solve these technology hurdles to reduce the cost and complexity.

Goodwin: It is likely that there will be multiple options for volume production. This will depend on final product requirements, such as limits of flexibility, level of resolution of display and cost of display. For example, metal oxide-based TFT displays already demonstrate high performance in terms of the TFT, and therefore can achieve high resolution displays, but ultimately will be very limited in the flexibility.

Organic electronics show excellent flexibility, but historically have tended to have a lower performance for OLED display backplanes and therefore may not achieve the same level of display resolution as metal oxide in the short term. More recently this gap in performance has been closed substantially making organic TFT backplanes a good candidate for a wide variety of display formats and resolutions. In addition OTFT backplanes may ultimately be a lower cost of production. Overall, it is likely that the different TFT technologies will independently develop the substrate types suitable for their processes, for example metal oxide on high temperature substrates and for organics the substrates are likely to be more flexible and suitable for lower temperature processes.

SemiMD: In terms of production equipment and tool advances, which technologies are most promising for enabling volume production of flexible displays?

Goodwin: Metal oxide is currently deposited via industrially used techniques/tools in the display industry, such as sputter deposition. This makes it a likely candidate for early adoption in the display industry, with moderate investment required to enable scale-up. However, solution-processing of organic based materials is likely to provide a lower cost of manufacture via the route of additive printing and R2R manufacture. CPI is working with a number of SMEs in building scale up capability across a range of printed and plastic electronics technology areas such as OLED, OTFT and barrier encapsulation, to help take forward new research ideas into technology prototypes and then into manufacturing demonstrators.

McDaniel: Flexible and other future bendable form factors in display will require precision engineered materials including thin film technologies that deliver performance with stringent uniformity and defect requirements at lower cost and less power. Advances in CVD and PVD systems for LTPS and metal oxide will play an important role in achieving high resolution but even these processes will require materials modification to support the full promise of flexible displays. One example of a required modification is indium tin oxide (ITO), a mainstay process step in TFT-LCD but as a material may prove to be too brittle in the production of more flexible displays.

Applied is also looking to help display makers mass produce larger scale, more efficient manufacturing processes and advanced materials as a means of gaining economies of scale at the factory.

Ciesinksi: FlexTech has funded and successfully completed projects for key steps in flex display manufacturing, such as lithography and deposition. Clearly various printing technologies and RTR additive manufacturing processes are capable of achieving major advances in flexible display production which will be seen over the next few years.

SemiMD: New display technologies that commercialise successfully have done so because they have enabled new products. The mass volume production of LCDs has helped to initiate smart phones, tablet devices, for example, while e-paper (E-Ink) display technology is largely responsible for e-reader devices such as the ubiquitous Kindle. So what potential new class of consumer/portable electronic device might flexible display technology enable? On the other hand, will the technology, in the nearer term, be more beneficial for enabling rugged/unbreakable display-based electronic devices?

McDaniel: There is a lot of potential. Think about what our phones looked like six or seven years ago. Now we’re seeing HD-quality screens on a device we can slip into our pockets. We could see flexible displays enabling devices that can be rolled up or folded into more compact shapes. Some studies have said that for a tablet, people prefer semi-rigid displays to something that is flopping around, to provide structure while they’re reading it. In the public environment flexible could bring the possibility of more immersive or interactive displays at airports or on billboards, or even on the sides of buildings. There are a lot of possibilities.

Goodwin: Rugged displays are likely to have military applications and so may attract funding support from this sector and therefore this may be a route to the first marketable products. However, the learning from the production of those rugged displays can likely be used within new mainstream product development. Many major display manufacturers are already trying to patent areas of interest such as smart watches and early products may focus on these smaller displays. Ultimately, if volume production is possible and large area displays can be produced then there is a vast range of products that can be envisaged from clothing applications, rollable/foldable phones, large scale advertising hoarding or even replacement of aircraft windows with lightweight displays.

Ciesinski: Technology adopters fall into several categories. For example, early adopters are those with the first cellular phone, the first tablet, etc. These users are willing to sacrifice elegance or product maturity for functionality. Other adopters waited until smart phones became fully functional before consolidating to a primary device from a combination of a PC, cell phone, and pager. Wearable electronics, as a class, represents a game-changing technology. A wearable device – even with limited functionality – is attractive, for example, to competitive athletes if it can help improve performance even modestly. Once wearable technology matures, it can explode into other markets to monitor the chronically ill, aged/infirm, or paediatric patients. Then, it jumps to the packaging or automotive or aerospace markets in the form of sensors.

Once flexible display technologies reach volume production, how fast might the technology establish itself – evolve from niche to mainstream?

Ciesinski: Successful technologies ramp quickly and displace incumbent technologies ruthlessly. Just consider the displacement of CRTs by FPDs or CCFL backlights by LED backlights. FlexTech believes that flexible electronics – of which flexible displays is a subset – will grow rapidly in multiple markets, led by disposable and wearable electronics. Our recent user survey indicated substantial purchases of flexible electronics by key end users within three years; adoption by large contract manufacturers is already taking place due to their customer demands.

Goodwin: This is likely to be dependent on the product uptake. For example the rise of tablets and smart phones drove the development of OLED frontplane and materials development. The same is likely to happen with flexible displays. Early products may have limited flexibility, for example the already available curved display products from LG and Samsung, but later products will need to show the truly flexible nature of these advanced displays. Once market pull is established a range of products are likely to be developed that will aid the flexible display to become a mainstream product. CPI can play a vital role in the move from niche to mainstream by providing the infrastructure and environment for companies to de-risk and scale up their innovative ideas from concept to market.

McDaniel: Five years ago, when display manufacturers wanted to start bending and curving the design, they faced a new set of struggles. Applied Materials had insights on where the market was heading and was already working on technologies to address the challenges. We have seen similar waves of technology with laptops and smartphones, and the acceleration of flexible or curved display devices or other form factors could take off in a similar manner. Display analyst firms are anticipating strong growth for the flexible and curved displays market over the next several years. For instance, Touch Display Research has forecast flexible and curved displays to achieve 16% of the global display revenue market by 2023 compared with 1% in 2013.

This article originally appeared on SemiMD, part of the Solid State Technology network

University of Illinois researchers have developed a way to heal gaps in wires too small for even the world’s tiniest soldering iron.

Led by electrical and computer engineering professor Joseph Lyding and graduate student Jae Won Do, the Illinois team published its results in the journal Nano Letters.

Carbon nanotubes are like tiny hollow wires of carbon just 1 atom thick – similar to graphene but cylindrical. Researchers have been exploring using them as transistors instead of traditional silicon, because carbon nanotubes are easier to transport onto alternate substrates, such as thin sheets of plastic, for low-cost flexible electronics or flat-panel displays.

Carbon nanotubes themselves are high-quality conductors, but creating single tubes suitable to serve as transistors is very difficult. Arrays of nanotubes are much easier to make, but the current has to hop through junctions from one nanotube to the next, slowing it down. In standard electrical wires, such junctions would be soldered, but how could the gaps be bridged on such a small scale?

“It occurred to me that these nanotube junctions will get hot when you pass current through them,” said Lyding, “kind of like faulty wiring in a home can create hot spots. In our case, we use these hot spots to trigger a local chemical reaction that deposits metal that nano-solders the junctions.”

Lyding’s group teamed with Eric Pop, an adjunct professor of electrical and computer engineering, and John Rogers, Swanlund professor in materials science and engineering, experts on carbon nanotube synthesis and transfer, as well as chemistry professor Greg Girolami. Girolami is an expert in a process that uses gases to deposit metals on a surface, called chemical vapor deposition (CVD).

The nano-soldering process is simple and self-regulating. A carbon nanotube array is placed in a chamber pumped full of the metal-containing gas molecules. When a current passes through the transistor, the junctions heat because of resistance as electrons flow from one nanotube to the next. The molecules react to the heat, depositing the metal at the hot spots and effectively “soldering” the junctions. Then the resistance drops, as well as the temperature, so the reaction stops. (See video for demonstration of the process.)

The nano-soldering takes only seconds and improves the device performance by an order of magnitude – almost to the level of devices made from single nanotubes, but much easier to manufacture on a large scale.

“It would be easy to insert the CVD process in existing process flows,” Lyding said. “CVD technology is commercially available off-the-shelf. People can fabricate these transistors with the ability to turn them on so that this process can be done. Then when it’s finished they can finish the wiring and connect them into the circuits. Ultimately it would be a low-cost procedure.”

Now, the group is working to refine the process.

“We think we can make it even better,” Lyding said. “This is the prelude, we hope, but it’s actually quite significant.”

The National Science Foundation and the Office of Naval Research supported this work.  Lyding and Rogers also are affiliated with the Beckman Institute for Advanced Science and Technology at the U. of I.