Category Archives: Flexible Displays

The display industry has developed towards in realizing large-screen and high quality image so far. But in the future, the development directions would go toward the reasonably priced flexible displays. Flexible displays are lighter, thinner, and unbreakable, compared to the existing glass substrate using displays. With such traits, flexible displays are expected to replace the existing market that the conventional displays could not enter due to the limits in application, and to enter new markets.

IHS Electronics & Media (E&M) recently published an Emerging Displays Report – Flexible Displays Technology – 2013, which contains the flexible display technology development trends and R&A conducted by related companies. It also provides the outlook for the flexible display market through 2023.

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According to the report, the flexible display market will grow to $1.3 billion in 2016, and then continuously make a rapid growth to $67.7 billion by 2023, accounting for about 20% of the total flat display market. Shipments of flexible displays will amount to 24 million units in 2016, and the figure is expected to expand to 1.8 billion by 2023, making up about 25% of the total flat display market.

The flexible display market will not only replace the existing display market, but also create markets for new kinds of display applications, driving the growth of the display market. The report forecasts that the substitute market will amount to $900 million in 2016 and hike to $32.8 billion by 2023, while the new market will total $400 million in 2016 to $34.9 billion by 2023.

Fujifilm and imec have developed a new photoresisttechnology for organic semiconductors that enables the realization of submicron patterns.

Due to their lightness, flexibility, and the possibility to manufacture them in large area, research and development on organic semiconductors has intensified in recent years. Organic semiconductors can be used in various applications such as organic solar cells, flexible displays, organic photodetectors and various other types of sensors. Current methods for patterning organic semiconductors include shadow masking and inkjet printing. However, these patterning methods are not suitable for high-resolution patterning on large-size substrates. Patterning based on photolithography6 would solve this issue. But photolithography is currently mainly adopted for patterning of silicon semiconductors. When applying it to organic semiconductors using standard photoresists, the photoresist dissolves the organic semiconductor material during processing.

Fujifilm and imec have developed a new photoresist technology that enables submicron patterning on large-size substrates without damaging the organic semiconductor materials. The new photoresist technology was developed by fusing the semiconductor processing technology of Fujifilm and imec, with Fujifilm’s synthetic-organic chemistry material design technology. Since existing i-line photolithography equipment can be used, and investment for new equipment is unnecessary, the new technology contributes to a cost-effective production of high-resolution organic semiconductor devices.

For technical verification, Fujifilm and imec developed organic photo detectors (OPD) and organic light-emitting diodes (OLED) using the new photolithography technology, and tested their performance. Organic semiconductor materials were patterned to produce OPD composed of fine light receiving elements down to 200μm×200μm size. Generally, patterning of organic semiconductor materials degrades the property of converting light into electricity (photoelectric conversion property), but the OPD developed in this case were patterned without degradation. With respect to the OLED arrays that were produced using the newly developed photolithography pattering method: 20μm pitch OLEDs emitting uniform light, were realized.

Fujifilm and imec officials say they plan to continue to contribute to industrialization of organic electronics by advancing research and development of semiconductor materials, processing technology and system integration.

fujifilm photoresist 1

Anyone who’s stuffed a smart phone in their back pocket would appreciate the convenience of electronic devices that could bend. Flexible electronics could spawn new products: clothing wired to cool or heat, reading tablets that could fold like newspaper, and so on.

The yellow electric charge races through a "speed-lane" in this stylized view of a polymer semiconductor, but pauses before leaping to the next fast path. Stanford engineers are studying why this occurs with an eye toward building flexible electronics.

The yellow electric charge races through a “speed-lane” in this stylized view of a polymer semiconductor, but pauses before leaping to the next fast path. Stanford engineers are studying why this occurs with an eye toward building flexible electronics.

Alas, electronic components such as chips, displays and wires are generally made from metals and inorganic semiconductors — materials with physical properties that make them fairly stiff and brittle.

In the quest for flexibility many researchers have been experimenting with semiconductors made from plastics or, more accurately polymers, which bend and stretch readily enough.

“But at the molecular level polymers look like a bowl of spaghetti,” says Stanford chemical engineering professor Andrew Spakowitz, adding: “Those non-uniform structures have important implications for the conductive properties of polymeric semiconductors.”

Spakowitz and two colleagues, Rodrigo Noriega, a postdoctoral researcher at UC Berkeley, and Alberto Salleo, a Stanford professor of Materials Science and Engineering, have created the first theoretical framework that includes this molecular-level structural inhomogeneity, seeking to understand, predict and improve the conductivity of semiconducting polymers.

Their theory, published Monday, Sep. 23, 2013 in the Proceedings of the National Academy of Sciences, deals with the observed tendency of polymeric semiconductors to conduct electricity at differing rates in different parts of the material – a variability that, as the Stanford paper explains, turns out to depend on whether the polymer strands are coiled up like a bowl of spaghetti or run relatively true, even if curved, like lanes on a highway.

In other words, the entangled structure that allows plastics and other polymers to bend also impedes their ability to conduct electricity, whereas the regular structure that makes silicon semiconductors such great electrical switches tends to make it a bad fit for our back pockets.

The Stanford paper in PNAS gives experimental researchers a model that allows them to understand the tradeoff between the flexibility and conductivity of polymeric semiconductors.

Grasping how they created their model requires a basic understanding of polymers. The word “polymer” is derived from the Greek for “many parts” which aptly describes their simple molecular structure, which consists of identical units, called monomers, that string together, end to end, like so many sausages. Humans have long used natural polymers such as silk and wool, while newer industrial processes have adapted this same technique to turn end-to-end chains of hydrocarbon molecules, ultimately derived from petroleum byproducts, into plastics.

But it was only in the late 1970s that a trio of scientists discovered that plastics which, until then were considered non-conductive materials suitable to wrap around wires for insulation could, under certain circumstances, be induced to conduct electricity.

The three scientists, Alan Heeger, Alan MacDiarmid and Hideki Shirakawa, shared the Nobel Prize in Chemistry in 2000 for their co-discovery of polymeric semiconductors. In recent years, with increasing urgency, researchers have been trying to harness the finicky electrical properties of plastics with an eye toward fashioning electronics that will bend without breaking.

In the process of experimenting with polymeric semiconductors, however, researchers discovered that these flexible materials exhibited “anomalous transport behavior” or, simply put, variability in the speed at which electrons flowed through the system.

One of the fundamental insights of the Stanford paper is that electron flow through polymers is affected by their spaghetti-like structure – a structure that is far less uniform than that of the various forms of silicon and other inorganic semiconductors whose electrical properties are much better understood.

“Prior theories of electrical flow in polymeric semiconductors are largely extrapolated from our understanding of metals and inorganic semiconductors like silicon,” Spakowitz said, adding that he and his collaborators began by taking a molecular-level view of the electron transport issue.

In essence, the variability of electron flow through polymeric semiconductors owes to the way the structure of these molecular chains creates fast paths and congestion points (refer to diagram). In a stylized sense imagine that a polymer chain runs relatively straight before coming to a hairpin turn to form a U-shape. An electric field moves electrons rapidly up to the hairpin, only to stall.

Meanwhile imagine a similar U-shape polymer separated from the first by a tiny gap. Eventually, the electrons will jump that gap to go from the first fast path to the opposing fast path. One way to think about this is a traffic analogy, in which the electrons must wait for a traffic light to cross from one street, though the gap, before proceeding down the next.

Most importantly, perhaps, in terms of putting this knowledge to use, the Stanford theory includes a simple algorithm that begins to suggest how to control the process for making polymers – and devices out of the resulting materials – with an eye toward improving their electronic properties.

“There are many, many types of monomers and many variables in the process,” Spakowitz said. The model presented by the Stanford team simplifies this problem greatly by reducing it to a small number of variables describing the structural and electronic properties of semiconducting polymers. This simplicity does not preclude its predictive value; in fact, it makes it possible to evaluate the main aspects describing the physics of charge transport in these systems.

“A simple theory that works is a good start,” said Spakowitz, who envisions much work ahead to bring bending smart phones and folding e-readers to reality.

Following Samsung’s introduction of the first flexible organic light-emitting diode (OLED) products this year, demand for these elastic displays is expected to grow by more than a factor of four next year, with sales reaching nearly $100 million in 2014.
 
Global market revenue for flexible OLEDs will rise to $94.8 million in 2014, up from $21.9 million in 2013, according to a new report entitled “In-depth analysis for Technical Trends of Flexible OLED” from IHS Inc., a global source of critical information and insight.

The projected growth next year will equate to a 334 percent expansion from this year, as presented in the figure below, paving the way for much larger sales in the future.

Click image to see full screen.

Click image to see full screen.

OLEDs represent a major segment of the larger flexible display market, which in the coming years will also include liquid-crystal display (LCD) and electronic paper (e-paper) technology.

“The buzz about flexible displays has been growing louder, ever since Samsung Display demonstrated its Youm line of bendable OLED products at the Consumer Electronics Show in January,” said Vinita Jakhanwal, director of mobile and emerging displays and technology at IHS. “Samsung is expected to begin shipping its first flexible OLED display—a 5-inch screen—in the second half of this year.”

Samsung’s initial product is likely to be a first-generation flexible display, employing a non-glass substrate that yields superior thinness and unbreakable ruggedness. However, such displays are flat and cannot be bent or rolled. Flexible displays are expected to eventually evolve into rollable and foldable OLED screens that are likely to be introduced after 2016.

Even so, it is too early for flexible OLED panels to fully replace conventional OLED screens. This is because the plastic substrate, thin-film encapsulation and other related technologies for flexible OLED remain immature for immediate application. Moreover, manufacturing processes are still being tested.

“A wide range of complementary technologies are under development to accelerate the advancement of flexible displays,” Jakhanwal said. “The success of the flexible OLED market will ultimately be determined by the maturity of the materials and manufacturing processes that will enable large-volume production at reasonable costs.”

Electronic devices with touchscreens are ubiquitous, and one key piece of technology makes them possible: transparent conductors. However, the cost and the physical limitations of the material these conductors are usually made of are hampering progress toward flexible touchscreen devices.

Fortunately, a research collaboration between the University of Pennsylvania and Duke University has shown a new a way to design transparent conductors using metal nanowires that could enable less expensive — and flexible — touchscreens.

The research was conducted by graduate student Rose Mutiso, undergraduate Michelle Sherrott and professor Karen Winey, all of the Department of Materials Science and Engineering in Penn’s School of Engineering and Applied Science. They collaborated with graduate student Aaron Rathmell, and professor Benjamin Wiley of Duke’s Department of Chemistry.

Their study was published in the journal ACS Nano.

The current industry-standard material for making transparent conductors is indium tin oxide, or ITO, which is deposited as two thin layers on either side of a separator film. Contact, in the form of a fingertip or a stylus, changes the electrical resistance between the two ITO layers enough so that the device can register where the user is touching. While this material performs well, its drawbacks have led industrial and academic researchers to look for alternatives.

“There are two problems with ITO; indium is relatively rare, so its cost and availability are erratic, and, more importantly for flexible devices, it’s brittle,” Winey said. “We’d like to make touchscreens that use a network of thin, flexible nanowires, but predicting and optimizing the properties of these nanoscale networks has been a challenge.”

Metal nanowires are increasingly inexpensive to make and deposit; they are suspended in a liquid and can easily be painted or sprayed onto a flexible or rigid substrate, rather than grown in vacuum as is the case for ITO. The challenge stems from the fact that this process forms a random network, rather than a uniform layer like ITO.

A uniform sheet’s overall quality in this context depends on only two parameters, both of which can be reliably derived from the bulk material’s properties: its transparency, which should be high, and its overall electrical resistance, which should be low. To determine the electrical properties for a network of nanowires, however, one needs to know the nanowires’ length and diameter, the area they cover and a property known as contact resistance, which is the amount of resistance that results from electrons traveling from one wire to another. The details of how these four independent parameters impact the electrical and optical properties of nanowire networks have been unclear.

“What this means is that people will synthesize nanowires, deposit them in a network, measure the network’s overall electrical resistance and optical properties and then claim victory when they get a good one,“ Winey said. “The problem is that they don’t know why the good ones are good, and, worse, they don’t necessarily know why the bad ones are bad.”

For example, low overall resistance could be the result of a particular synthesis method that produced a few unexpectedly long nanowires, or a processing method that reduced the contact resistance between nanowires. Without a way of isolating these factors, researchers can’t determine which combination of parameters will be most successful.

Winey’s group has previously worked on simulating nanowire networks in three-dimensional nanocomposites, particularly the number of nanowires it takes to ensure there is a connected path from one end of the system to the other. Duke’s Wiley took note of this work and contacted Winey, asking her if she would be interested in developing two-dimensional simulations that could be applied to data from silver nanowire networks his group had fabricated.

With Wiley’s group able to provide the nanowire length, diameter and area fraction of their networks, Winey’s team was able to use the simulation to work backward from the network’s overall electrical resistance to uncover the elusive contact resistance. Alternative methods for finding the contact resistance are laborious and incompatible with typical network processing methods.

“Once we have reliable and relevant contact resistances, we can start asking how we can improve the overall sheet resistance by changing the other variables,” Mutiso said. “In playing with this simulation, we can see how much better our networks get when we increase the length of the nanowires, for example.”

The Penn team’s simulation provides further evidence for each variable’s role in the overall network’s performance, helping the researchers home in on the right balance of traits for specific applications. Increasing the coverage area of nanowires, for example, always decreases the overall electrical resistance, but it also decreases optical transparency; as more and more nanowires are piled on the networks appear gray, rather than transparent.

“For specific applications and different types of nanowires, the optimal area fraction is going to be different,” Winey said. “This simulation shows us how many nanowires we need to apply to reach the Goldilocks zone where you get the best mix of transparency and resistance.”

Future collaborations between Winey’s team at Penn and the Wiley group at Duke will use this simulation to test the effect of different processing techniques on nanowires, pinpointing the effect various post-deposition processing methods has on contact resistance and ultimately on overall sheet resistance.

“We can now make rational comparisons between different wires, as well as different processing methods for different wires, to find the lowest contact resistance independent of nanowire length, diameter and area fraction,” Winey said. “Now that we know where all the levers are, we can start adjusting them one at a time.”

In the next generation of modeling studies, the Penn team will consider several additional parameters that factor into the performance of nanowire networks for transparent conductors, including nanowire orientation, to mimic nanowire networks produced by various continuous deposition methods, as well as the degree to which individual nanowires vary in length or diameter.

The research was supported by the National Science Foundation and Penn’s Materials Science Research and Engineering Center.

Michelle Sherrott is now a doctoral student in materials science at the California Institute of Technology.

After experiencing runaway growth in recent years, the OLED display market is gearing up to make another big leap. Flexible OLED technology is expected to bring about an unprecedented change in flat displays which have ruled the display market for the last 20 years since the emergence of a liquid crystal display. Flexible OLED technology has already been introduced in a series of exhibitions and conferences for the last few years, and it is expected to make an innovative change in the conventional display industry structure once commercialized.

Unlike the conventional rigid OLED screen, the flexible OLED panel refers to the OLED display with flexibility. It is a very attractive product concept in that flexible OLED technology enables consumer goods manufacturers to develop applications in a variety of shapes to maximize its usability. For panel makers, the technology can cut manufacturing costs and simplify manufacturing processes by minimizing the use of glass substrates.

More Flexible Displays news

In order to produce a flexible OLED display, alternative substrate materials and encapsulation process to a conventional glass substrate are required. Until before 2010, most prototypes had used a metal foil substrate. But the trend recently shifted to a flexible OLED panel using a plastic substrate because the metal foil substrate has a rough surface and lacks flexibility. A wide range of methods are also being studied to develop alternative encapsulation techniques encompassing the use of plastic film and thin-film deposition technologies.

Read more: Flexible substrate market to top $500 million in 2020

Still, technological approaches vary depending on panel makers. Performance of a flexible OLED display, productivity and costs change significantly depending on flexible materials and manufacturing techniques which could also determine the marketability of flexible OLED displays. Therefore, there is a big difference in the time frames under which each panel maker plans to enter the flexible OLED market.

At this point of time, the “Flexible OLED Competitiveness and Market Forecasts” report from Displaybank, now part of IHS Inc., analyzes strategies taken by each panel maker for a flexible OLED display to take root in the display panel market, as well as various relevant technological issues. It discusses the growth potential of flexible OLED panels in the existing display market at the current point in time. This report is expected to help panel makers set a plan on how to approach the flexible OLED market in terms of technologies and come up with appropriate strategies to make a successful foray into the conventional display market with flexible OLED technology.

Whereas the current display industry has developed its technology and products centered on scaling-up to large sizes and realizing high-resolution images, the future industry development direction is expected to focus on flexible displays. Compared to the conventional glass substrate, flexible displays are thinner, lighter, and less prone to break. With such properties, it is expected that flexible electronic devices will be able to replace the existing market as well as create new ones.

The flexible (thin glass, metal thin film, plastic) substrate is gaining importance as a key component that determines the processability, performance, reliability, and price of flexible displays. To this end, IHS Electronics & Media publishes a Flexible Display Substrate Technology report to analyze the technology development, industrial conditions, and R&D trends of flexible substrates.

According to the report, the flexible substrate market is forecast to grow to $506.7 million by 2020 from a $2.5 million in 2013. The OLED display, another market that can be created by applying the flexible substrate technology, is expected to make up 91 percent of the overall market.

ISORG and Plastic Logic have co-developed the first conformable organic image sensor on plastic, with the potential to revolutionize weight/power trade-offs and optical design parameters for any systems with a digital imaging element. First mechanical samples will be publicly unveiled at LOPE-C 2013 (ISORG / CEA booth B0-509) from June 12 to 13 in Munich, Germany.

The collaboration is based on the deposition of organic printed photodetectors (OPD), pioneered by ISORG, onto a plastic organic thin-film transistor (OTFT) backplane, developed by the technology leader, Plastic Logic, to create a flexible sensor with a 4×4 cm active area, 375um pitch (175um pixel size with 200um spacing) and 94 x 95 = 8 930 pixel resolution.

organic image sensor

The backplane design, production process and materials were optimized for the application by Plastic Logic to meet ISORG’s requirements. The result, a flexible, transmissive backplane, represents a significant breakthrough in the manufacture of new large area image sensors and demonstrates the potential use of Plastic Logic’s unique flexible transistor technology to also move beyond plastic displays. Combined with ISORG’s unique organic photodetector technology, it opens up the possibilities for a range of new applications, based around digital image sensing, including smart packaging and sensors for medical equipment and biomedical diagnostics, security and mobile commerce (user identification by fingerprint scanning), environmental, industrial, scanning surfaces and 3D interactive user interfaces for consumer electronics (printers, smartphones, tablets, etc.).

ISORG’s CEO, Jean-Yves Gomez stated: “We are extremely pleased to showcase our disruptive photodiode technology in a concrete application for imaging sensing. The ability to create conformal and large area image sensors, which are also thinner, lighter and more robust and portable than current equipment is of increasing importance, especially in the medical, industrial and security control sectors.”

Indro Mukerjee, CEO Plastic Logic said: “I am delighted that Plastic Logic can now demonstrate the far-reaching potential of the underlying technology. Our ability to create flexible, transmissive backplanes has led us not only to co-develop a flexible image sensor, but is also key to flexible OLED displays as well as unbreakable LCDs.”

Demand for flexible displays is set to undergo massive growth during the next seven years, with a broad variety of applications—ranging from smartphones to giant screens mounted on buildings—driving a nearly 250 times expansion in shipments from 2013 through 2020.

Global shipments of flexible displays are projected to soar to 792 million units in 2020, up from 3.2 million in 2013, according to a new IHS report entitled “Flexible Display Technology and Market Forecast.”  Market revenue will rise to $41.3 billion, up from just $100,000 during the same period.

“Flexible displays hold enormous potential, creating whole new classes of products and enabling exciting new applications that were impractical or impossible before,” said Vinita Jakhanwal, director for mobile and emerging displays and technology at IHS. “From smartphones with displays that curve around the sides, to smart watches with wraparound screens, to tablets and PCs with roll-out displays, to giant video advertisements on curved building walls, the potential uses for flexible displays will be limited only by the imagination of designers.”

Generation flex

IHS classifies flexible displays into four generations of technology. The first generation is the durable display panels that are now entering the market. These panels employ a flexible substrate to attain superior thinness and unbreakable ruggedness. However, these displays are flat and cannot be bent or rolled.

Second-generation flexible displays are bendable and conformable, and can be molded to curved surfaces, maximizing space on small form-factor products like smartphones.

The third generation consists of truly flexible and rollable displays that can be manipulated by end users. These displays will enable a new generation of devices that save space and blur the lines separating traditional product categories, such as smartphones and media tablets.

The fourth generation consists of disposable displays that cost so little that they can serve as a replacement for paper.

Starting small

With their thin, light and unbreakable nature, flexible displays initially are expected to be used in smaller-sized products, such as mobile phones and MP3 players. However, once large-size displays are available, flexible technology will be used in bigger screen-size platforms, such as laptops, monitors and televisions.

The largest application for flexible displays during the next several years will be personal electronic devices. This segment will be led by smartphones, with shipments climbing to 351 million units by 2020, up from less than 2 million this year.

Flexible stars at SID

Flexible displays were a major topic at the Society for Information Display (SID) Display Week event in Vancouver in May.

During an SID keynote address, Kinam Kim, president and CEO of Samsung Display Co., discussed his company’s flexible organic light-emitting diode (OLED) display technology. Kim said that the technology will be suitable for wearable electronics devices like Google Glass.

Also at SID, LG Display showed a 5-inch OLED panel constructed out of plastic that was both flexible and unbreakable.

Furthermore, Corning at SID showed its Willow Glass, which can be used as with both OLEDs and liquid-crystal displays (LCD) in mobile devices such as smart phones, tablets and notebook PCs. Because of its thinness, strength and flexibility, Willow Glass could enable future displays to be wrapped around a device or a structure.

IHS predicts OLEDs will be the leading flexible display technology during every year for the foreseeable future, accounting for 64 percent of shipments in 2020.

Transparent electrodes refer to oxide degenerate semiconductor electrodes that possess a high level of light transmittance (more than 85 percent) in the visible light spectrum, and low resistivity (less than 1×10-3 Ω-㎝) at the same time. Transparent electrodes are key materials in the IT industry, used in flat displays, photovoltaics, touch panels, and transparent transistors, which need light transmission and current injection/output simultaneously. Up until now, sputtered ITOs (SnO2-doped In2O3) have been widely used.

Recently with the remarkable development in flexible photoelectronic technologies, such as flexible displays, photovoltaics and electric devices, more attention is being put on flexible transparent electrode technology, which can be produced on a flexible substrate rather than the conventional glass substrate. ITO tends to be vulnerable to the substrate’s bending, and thus CNT-, graphene-, and silver-based transparent electrodes as well as polymer transparent electrodes are suggested to replace the ITO.

The usage of transparent electrodes vary: they are used as electrode materials for LCDs, OLEDs, PDPs and transparent displays, while they are used as touch sensors for resistive and capacitive touch panels. They are also used as electrodes for a-Si, CIGS, CdTe, and DSSC photovoltaics.

Displaybank published the “Transparent Electrode Technology Trends and Market Forecast 2013” report. It covers the technological developments related to transparent electrodes and business activities as well as its market forecast up to 2020.

The overall transparent electrode market is forecast to grow to $5.1 billion by 2020, from $1.9 billion in 2012. By market size, display and touch sensor markets are deemed to be the largest. In the display segment, the flexible display will expand to make up 11 percent in 2019, thereby making way for transparent electrodes to replace the ITO and oxide transparent electrodes. In 2020, the oxide transparent electrode is forecast to make up 8 percent of the total market, and silver-based materials or carbon nanotubes will most likely be the strong candidates.

In terms of production cost, the touch sensor market is the best for the transparent electrode to enter, particularly compared to the display market. But the next generation transparent electrode applied to touch sensors will not reach 10 percent of the total market until 2020. It is because the alternative to the ITO must have the same level of properties as the ITO at low production cost. Strategic collaboration with major brands will be inevitably required. Currently, there is no next generation electrode that can perform on a similar level as the ITO and that is able to be mass produced. But if the flexible display market opens up earlier than expected, next generation transparent electrodes will likely replace ITOs at a faster rate.