The challenges of commercializing flexible displays
05/01/2006
One of the most exciting areas in the flat panel display industry is the emergence of flexible displays. In recent years, liquid crystal displays (LCDs) have come to absolutely dominate the displays industry, but LCDs are glass-based solutions. Literally hundreds of companies are now working on various approaches to devise displays built on plastic, metal foils, or other substrates in an effort to dislodge the pre-eminence of LCDs. The market, manufacturing challenges, and infrastructure required to commercialize flexible displays are reviewed.
Mark Fihn, Veritas et Visus, Temple, Texas
In August 2005, Philips Polymer Vision unveiled a concept e-reading device called the Readius to demonstrate the viability of rollable displays in mobile applications. Although many companies had shown prototype displays, this was the first time that an actual product with a fully flexible display had been showcased. The announcement was a bit of a milestone in the fledgling flexible displays industry because it identified that with flexible electronics, large-area displays could be incorporated within small-area devices (Fig. 1).
While the rollable display concept shown by Polymer Vision unquestionably qualifies as a flexible display, other devices also fall into the category that are merely bendable, or conformable, so there is some debate about the definition of a “flexible display.” In fact, many applications do not really require the display to be flexible, but other advantages of the underlying technologies are quite desirable; for example, the displays can be thinner, lighter, and more durable than their glass-based counterparts. Another major driver for flexible displays is that manufacturing can conceivably shift to a roll-to-roll process, not unlike high-quality printing processes on paper. With roll-to-roll processing, the driver for flexible displays is not the display itself, but the manufacturing process.
Moving to flexible substrates
Moving from glass to a flexible substrate is not a simple matter. Although plastic substrates are the most likely choice, companies are experimenting with thin glass, stainless steel foil, fabrics, and even paper as potential substrates. The alternatives to glass and plastic suffer from the obvious deficiency of being opaque. For some technologies, which are reflective rather than emissive or transmissive, transparency is not necessary. Some emissive displays are able to emit from the top surface of the display and do not require a transparent backplane.
One of the biggest problems associated with plastic substrates is that they require relatively low processing temperatures, typically much lower than required by the underlying display electronics. Finding an appropriate balance between the characteristics of the plastic and the display manufacturing processes has been a challenge, which makes alternatives such as steel foil and flexible glass quite attractive.
Perhaps the biggest issue with using plastic as a substrate for flexible displays is that it does not provide an adequate barrier against water and oxygen permeation so the delicate electrical and chemical materials are quickly destroyed. As such, several companies (such as Vitex Systems, General Electric, and Symmorphix) are busily working to develop barrier layers. An advantage of steel foil substrates is their excellent barrier properties.
Unfortunately, adding layers is not a good thing when it comes to flexible displays. Each time a layer is added, the elastomeric and thermal properties of the different materials result in varying effects that, while trouble enough on a flat surface, cause all sorts of problems on flexible surfaces. One of the most difficult layers facing display manufacturers is the transparent conductive layer required by transmissive displays. The most popular transparent conductor is ITO (indium tin oxide), but unfortunately, ITO is rather brittle and cracks easily when flexed. Accordingly, many companies are now working feverishly to come up with alternatives to ITO that enable similar conductivity and transparency, while also meeting the challenges of flexibility.
Numerous display technologies are being evaluated for creating flexible displays. To date, the most promising seem to be electrophoretic technologies (which are being developed by several companies, including E Ink, Sipix Imaging, Bridgestone, Zikon, and others). While electrophoretic displays boast advantages of bistability (requiring power only to refresh an image), the technology may be limited to niche markets since it currently does not really support mass-market requirements for full-color motion video. Many companies, nevertheless, are hoping that electronic paper will help establish new markets for displays.
Flexible displays are also under development by various LCD technologists (amorphous silicon TFT, low-temperature poly-silicon TFT, cholesteric, and others); by OLED manufacturers (both polymer and small-molecule developers), and by several other unique display technologies. These include such novel devices as the FASwitch technology from Rolltronics (which was recently acquired by Seertech Corp.), UPD technology from UniPixel Display, electrowetting technology from LiquaVista, polymer cholesteric liquid crystal (PCLC) flake/fluid hosts under development at the U. of Rochester, and smectic memory displays under development by PolyDisplay, to mention but a few.
The market
Just how to go about dislodging glass-based LCDs from their pre-eminent position is a significant challenge. While some niche markets seem promising, flexible display manufacturers are hoping to find a killer application that will propel the business into large-scale production. While computing and entertainment devices are likely to continue to be supported by LCDs for the foreseeable future, many are hopeful that books, magazines, and newspapers may transition to flexible displays. Other prime candidates include signage (both point-of-purchase and large-scale billboards), labeling (for things like retail shelf edges), and smart card devices with integrated displays.
 Figure 2. Recent timeline predictions about the emergence of markets using flexible displays. (Source: iSuppli) |
Numerous market research companies have been working diligently to identify the potential of these markets (see Fig. 2). Kimberly Allen, an analyst at iSuppli, recently advised, “Although many theoretical possibilities exist, no ‘killer app’ is evident for flexible displays, and it is likely that people will devise surprising uses once the panels are on the market in greater volume. Display makers would do well to remain alert to the feedback on early products in order to design more effective second-generation products.”
Allen further suggests that “early penetration of simple applications like signage, shelf labels, and electronic display cards can provide a revenue stream to assist with development of larger and more advanced flexible displays for large-area signage, e-readers, e-newspapers, and, ultimately, active matrix applications.” She thinks that the first products in each category are likely to be rigid or formed displays on thicker plastic substrates. The development of genuine flexibility or rollability will evolve in time as the underlying components-chiefly the flexible backplane-become technically feasible.
Addressing manufacturing challenges
Identifying and resolving the challenges associated with enabling flexible electronics have moved to the forefront of electronics and materials development efforts around the world. In particular, various consortia and government-sponsored efforts are underway, particularly in the US and in Europe, to help hasten the development of the flexible displays industry. With virtually 100% of LCDs currently being manufactured in Asia, US and European interests seem intent on ensuring that emerging flexible displays serve to break up the Asian monopoly in the displays market. As such, numerous consortia have emerged, including:
- In the US, the Flexible Displays Center became operational at Arizona State University.
- In the US, the CAMM facility was inaugurated at Binghamton U.
- In the US, the USDC (US Display Consortium) funds several key technologies related to flexible displays.
- The UK Displays Network was established, with a focus on flexible displays via the FlexyNet.
- The Polymer Electronics Technology Center was established in northeast England.
- Various EU programs, including efforts at the Dutch Polymer Institute, FlexiDis, FLEXled, the VDMA, OMEC, the Fraunhofer Institute, and the Organic Electronics Association are working on flexible displays.
- The Flexible Substrate Standards Working Group is developing performance measures and guidelines.
Not to be outdone, Asian groups have united to work on establishing an infrastructure to support the emergence of flexible displays:
- The Taiwanese formed the Flexible Electronics Industry Alliance.
- Korea’s 21st Century Frontier R&D Program and KIST funded the development of flexible TFT LCDs.
- Japan’s Technology Research Association for Advanced Display Materials is focused on plastic substrates.
- Singapore’s Institute of Materials Research and Engineering is developing multilayer plastic substrates.
Such substantial national and international cooperation bodes well for the emerging flexible displays market.
Infrastructure for LCD production
In trying to find ways to compete with the dominant TFT LCD market, the biggest obstacle has to do with the huge infrastructure built up to support LCD production. With new fabs costing up to $3 billion (plus additional investments for various subcomponents), many argue that TFT LCD manufacturers have created a barrier to entry that is unassailable by alternative technologies.
Proponents of flexible displays, however, argue that if the large-scale TFT LCD fabs, which are based on batch processing of photo-lithographic and vapor deposition processes, can be replaced with low-cost printing technologies, then the TFT LCD’s infrastructure will not be a barrier to entry so much as a burden. Accordingly, many companies are working hard to develop printing technologies that will enable high-resolution patterning of electronic circuits on flexible substrates. Visionaries are even talking about the eventual possibility of printing entire computer systems in a roll-to-roll process.
While roll-to-roll processing of displays is still likely to be several years away, it seems quite possible that roll-to-roll processing of other electronic devices is coming more quickly. Flexible electronics may be applied to a wide range of applications, including photovoltaics, RFID tags, and longer-term options like solid-state lighting. Displays are only one application for flexible electronics and may not even be the largest. It is likely that other applications, such as solar cells, will help pave the way for the successful development of the roll-to-roll process for displays.
In the meantime, several companies are working to develop flexible displays in ways that utilize the existing TFT LCD infrastructure. Philips has developed a technique it calls the EPLaR process (electrophoretic laser release) while Seiko Epson has developed a process they call SUFTLA (surface-free technology by laser ablation). Both techniques involve patterning on plastic using a traditional glass substrate host, from which the plastic layers are separated after processing. These methods may very well enable the introduction of large-scale flexible displays rather quickly, without the need to develop the technologies and associated infrastructure related to roll-to-roll processing.
Conclusion
While there are still substantial technical and economic hurdles to the full realization of flexible displays, there is no doubt that we will increasingly see devices built on non-glass substrates. The advantages of shifting to flexible substrates, both from an application perspective and a manufacturing perspective are substantial.The promise of new devices and more efficient manufacturing will almost certainly result in entirely new applications that will serve to further refine the underlying technologies. The Readius device from Polymer Vision is a precursor to the sort of display electronics we will increasingly see in the years to come.
Mark Fihn was educated at St. Olaf College, Northfield, MN, the American Graduate School of International Management, Phoenix, AZ; St. Edward’s U., Austin, TX, and in the U. of Texas at Austin’s doctoral program in international business. He has close to 20 years experience in the display industry and is currently principal at Veritas et Visus, 3305 Chelsea Place, Temple, TX 76502; ph 254/791-0603;, e-mail [email protected].