Flexible Electronics
Plastics Playing Vital Role in Display Development
By Richard Stewart
Flexible electronics, key to the production of portable devices with displays that bend and fold thanks to the use of polymer materials, is a rapidly growing field driven by consumer demand for increasingly smaller, lighter, and higher-performing electronic products with larger displays. Flexible plastic displays and flex circuit technologies offer distinct advantages over rigid printed circuit boards and liquid crystal displays (LCDs) in digital cameras, cell phones, e-book readers, and other portable devices. Thin plastic films, substrates, coatings, and plastic-based inks play a vital role in the development of these products.
Key Enabling Technology
A key player in the field of plastic electronics is E Ink Corp, the leading developer and marketer of active matrix electronic displays using its proprietary Vizplex™ Imaging Film. Attached to the film are arrays of active switching elements that change color from black to white to represent text and images on a display (see sidebar). E Ink's electrophoretic “electronic paper” display technology is used by most eBook companies. Displays are bistable – able to retain the displayed contents without consuming power, only drawing power to change the display. These reflective displays can easily be read in a wide range of lighting environments.
E-paper technology is seen as a future challenger to LCDs for displays, according to a report from NanoMarkets, a research and analysis firm which focuses on thin film, organic, and printable electronics-related markets. E-paper's hallmark low power consumption and compatibility with high-volume manufacturing on plastic substrates make it very appealing for next-generation technology, says NanoMarkets.
“E-paper architecture and manufacturing have reached sufficient maturity to readily meet the needs of some very large markets in a number of different areas, including electronic signage, mobile communications, handheld computing, and disposable electronics,” reports NanoMarkets in “The Future of E-Paper: A Technology Assessment and Market Forecast” (June 2008). “E-paper can come close to matching the visual quality of actual paper, while offering some features that paper will never be able to match, especially the ability to update and organize information electronically,” the report adds.
Organic Demand to Grow
In a white paper entitled “Opportunities in Organic Electronic Materials” (March 2008), NanoMarkets states that while organic electronic materials, comprising conjugated polymers and low molecular weight organic solids, are in no position to replace silicon, they offer a competitive or superior mix of performance and economics in many applications. The analysts expect to see a dramatic increase by 2015 in the commercialization of displays, lighting, RFID tags, smart packaging, photovoltaics, textiles, medical products, and other devices that depend on organic electronics.
The paper relates that printing is fundamental to the technology's primary attraction – its ability to produce electronics at low cost on large-area, flexible substrates. “Printing equipment costs relatively little; the process has inexpensive or non-existent masking requirements; and throughputs are suitable for many applications,” says the paper, noting that ink-jet, screen, and flexo are the most important printing processes in use. The researchers expect the market for plastic substrates and electronic inks to see strong growth. Polymers are easily solubilized are relatively easy to make into inks for printable electronic applications.
NanoMarkets expects polymers to dominate the substrate market, observing that no other type of material is so suitable for flexible products and roll-to-roll production processes at such a low price. PET and other polymers that offer curing advantages predominate, although potential exists for the growth of PEN in this field because of its greater dimensional and thermal stability, the analysts observe.
Range of E Ink Devices
At the 2008 Society for Information Display ( SID ) Display Week/International Symposium and Exhibition last May in Los Angeles , E Ink demonstrated displays with fast screen response and flexibility, showcasing six electronic readers, plus products ranging from smartcards to watches and key fobs featuring Vizplex displays. The company recently announced availability of its next-generation segmented display cell (SDC) technology, which produces paper-thin, flexible displays of simple information suitable for smart cards, capacity indicators, electronic shelf labels, signage, and similar applications.
Requiring minimal battery power, SDC displays incorporate the same Vizplex technology as E Ink's matrix product family, but cater to a different set of applications and markets – those requiring alpha-numeric and icon-based information to make critical decisions. The new SDCs are 40% thinner and offer a wider operating temperature range and increased flexibility, says the company.
Prototyping Kits for segmented as well as active matrix technologies are available to engineers and designers for fast prototyping and application-specific projects using E Ink displays. Both types of kits include all the hardware and software needed to produce fully functional displays. The company also offers rapid product development service. From a customer-supplied CAD file, E Ink can supply production-ready samples within eight weeks after artwork approval. It can enter mass production within 12 weeks.
E Ink and Wacom, the leading manufacturer of digital pen tablets and computer interface technologies, have announced a partnership to integrate Wacom's digital pen input technology with E Ink's Vizplex electronic paper displays. The development will enable users to interact freely with electronic paper, digitally jotting notes in the column of an e-book or circling an entry in a newspaper article.
First in Rollable Displays
Polymer Vision, a Philips Electronics spin-off, was the first company to bring organic semiconductor-based flexible and rollable displays to production and the first to launch a related commercial product. The company uses conventional lithographic printing techniques to produce circuits. At SID 2008, the company exhibited the first prototype of its rollable display with full color along with a high-resolution (254 ppi) rollable monochrome display, which is said to be the highest resolution e-paper display ever shown at the industry show.
Polymer Vision displays are as thin as paper with the ability to be rolled up to a minimum roll radius of 6mm, about the diameter of a pen. The company also exhibited its Readius® e-reader/mobile phone with a 5-inch, fold-out and rollable display. The device, which uses E Ink technology, is expected to be introduced to the U.S. in early 2009.
In the UK , Plastic Logic, a Cambridge University spin-off, has been a leader in the production of active-matrix displays, creating a range of devices with E Ink imaging film, including a reader, which is expected to enter the market next year. In 2006, the company raised US $100 million to build a facility to manufacture plastic electronics on a commercial scale.
That same year, flexible displays from Plastic Logic were used by 60 product design students from around the world in a competition to demonstrate how flexible displays will change people's lives by 2010. Prize winning products included a rollable digital musical score reader to eliminate the need for musicians to turn paper pages, a design-changeable fashion belt, and a wearable and updateable medical patient tag and storage device to display patient information and medication details.
Lighting Applications
California-based Add-Vision, Inc. (AVI) is a pioneer in fully printed polymer organic light-emitting- display (P-OLED) technology for use in low-resolution displays and solid-state lighting applications. AVI has developed a proprietary light-emitting polymer ink, which is formulated with additives and transport materials that avoid the need for vacuum-deposited electrodes. Air-stable printable cathode materials are used, enabling low-temperature handling of barrier-coated PET/PEN flexible substrates.
AVI successfully demonstrated a P-OLED device that reportedly exceeded 1,000 hours of operating lifetime at peak luminance of 100 candelas per square meter (cd/m2), more than doubling the lifetime results of devices tested two years earlier and a key target for commercialization of the technology. The P-OLED devices were screen printed under ambient conditions onto thin flexible substrates.
The technology enables manufacturers to fabricate robust P-OLED displays on plastics in which every layer can be rapidly deposited at low cost using conventional printing equipment and methods under normal atmospheric conditions. The company is working on a number of projects incorporating P-OLEDs, including wearable displays for military applications, biosensors, merchandising cards, illuminated keypads, light-emissive switches, smart media products, and specialty signage.
Funding More Research
The U.S. Display Consortium ( USDC ), a public/private partnership chartered with developing flexible electronics and display technologies, recently announced a $280,000 cost-shared award to Arizona-based Sigma Technologies International. The funds will be used to develop and demonstrate new conductive, transparent polymer-based coatings for use in flexible displays, organic light-emitting-diodes (OLEDs), and other applications such as solar collectors and image sensors.
Sigma has demonstrated its ability to successfully produce these new coatings with an economical process that achieves a film thickness of as little as 2-3 nanometers. The project's goal is aimed at developing this alternative material for broader and more cost-effective commercial use.
USDC also recently announced the completion of a cooperative R&D program with GE Global Research which has the potential to accelerate commercialization of flexible OLED displays. GE has demonstrated an ultra high barrier thin-film encapsulation process on a wide variety of OLED structures through a batch-mode, plasma-enhanced chemical vapor deposition process. This method solves a critical need in the display industry for high-performance, hermetic packaging. It enables lightweight, flexible, rugged flat panel devices to be manufactured by a low-cost, high-throughput process such as roll-to-roll manufacturing, according to USDC .
Researchers at the UC Berkeley Laser Thermal Lab have developed low-cost, high-resolution techniques to produce electronic circuits on flexible polymer substrates using gold nanoparticles at low temperatures under ambient atmospheric pressure. The techniques include Inkjet deposition of a nanoparticle solution to the substrate and laser sintering with a focused laser beam for efficient melting. The techniques, demonstrated in fabrication of organic field effect transistors (OFETs), can be used to produce inexpensive, large-area flexible electronics on polymer substrates.
The Flexible Display Center at Arizona State University is in its fifth year of a 10-year partnership with the U.S. Army in the development of new display technology for use in equipment for soldiers. The Army wants to replace rigid, glass-based screens in existing equipment with shatter-proof, flexible displays that consume less power. The vision is for soldiers to wear bendable display devices and use rollup or folding displays to enhance their capability to communicate on the battlefield.
Polymer Memory Arrays
Norwegian company Thin Film Electronics has developed an all-organic memory technology that combines the properties of specially developed polymers and unique system architecture. Extremely thin layers of polymer are used to coat a substrate, which constitutes a layer in a stack. The layers are sandwiched between two sets of crossed electrodes, with each intersection representing a memory cell containing one bit of information.
The electrodes are printed directly onto the polymer layers. Voltage is applied between the top and bottom electrodes to activate the cell and modify the organic material. Being solution-based, the polymer memory arrays can easily be applied to large surfaces with conventional printing and coating techniques.
Branded Plastics Materials
Inherently conductive polymers are widely used in the electronics industry. H.C. Starck offers the CLEVIOS® product family, formerly called Baytron®, in a wide range of compounds and formulations for electronic applications. Developed by Bayer, these inherently conductive polymers, based on thiophenes, are used in the electronics and semiconductor industries in the fabrication of displays and printed circuit boards and as antistatic film coatings. Starck is developing thiophen-derived compounds that can be used as organic conductors and semiconductors in polymer electronics.
Conductive inks from Ciba won an award at IDTechEx Printed Electronics Europe 2008 in Dresden , Germany in April. Ciba XYMARA™ Electra conductive inks offer low drying temperatures and good line definition and resolution. They enable users to print at high speeds with excellent adhesion on a wide range of substrates, says Ciba. The IDTechEx conference was attended by 600 delegates from 28 countries.
Kapton® Polyimide Films from DuPont are widely used as a substrate material for flexible printed circuit applications. Kapton films have the ability to maintain their physical, electrical, and mechanical properties over a wide temperature range. The films are available in a broad range of thicknesses and are easily laminated, metallized, adhesive coated, and formed. DuPont Riston® FX Series™ dry film photoresists are well suited for the manufacture of printed circuit boards. The films enable high resolution, exact line edge definition, excellent conformation, and productivity in flex circuit fabrication, notes the company.
[SIDEBAR with E Ink with diagram]
E Ink Display Technology
E Ink's Vizplex™Imaging Film is the technology leader for high-resolution active matrix electronic paper displays. Millions of tiny microcapsules, each about the diameter of a human hair, are applied to a plastic substrate coated with transparent, conductive indium tin oxide (ITO) in a fast, efficient roll-to-roll process. The microcapsules contain positively charged white particles and negatively charged black particles of pigment suspended in a clear fluid. Controlled by electrodes, the white particles move to the top of the microcapsule when a negative field is applied, making the display appear white at that spot. An opposite electric field pulls the black particles to the bottom of the microcapsules, where they are hidden. Reversing this process makes the black particles appear at the top of the capsule, creating letters on an eBook page. The film is combined with a thin adhesive coating and a plastic release sheet for shipment to display manufacturers.
[SIDEBAR]
E-Paper on Newstands
To celebrate its 75 th anniversary, Esquire magazine plans to incorporate e-paper technology on the cover of its printed October issue. Words and images will scroll across the flexible display embedded in the groundbreaking cover. Plus, the inside cover will feature an e-paper advertisement for Ford's new Flex Crossover vehicle, displayed using the same Vizplex™ flexible display technology from E Ink Corp. Esquire expects to distribute 100,000 issues of the magazine with the electronic displays through newsstands and bookstores.
[SIDEBAR with Kindle photos]
Glimpse of Amazon Kindle
Amazon's Kindle eBook reader has enjoyed huge success since its launch last November, according to the company. Although the device houses a 6-inch rigid not a flexible display in its molded plastic case, it illuminates the vast potential for future applications of electronic paper technology. Lighter than a paperback at 10.3 ounces, the Kindle uses E Ink's Vizplex Imaging Film. The electrophoretic display (600-by-800-pixel, 167-pixels-per-inch) delivers crisp black text which can be read even in dim light or bright sunlight in a choice of six type sizes. Free wireless access, using Sprint's EVDO high-speed network, enables users to download from Amazon, a selection of over 140,000 books, magazines, and newspapers. A New York Times best seller can be delivered wirelessly to the device in less than one minute, at a cost of $9.95. Its internal memory holds over 200 books. Full battery recharging takes two hours. A QWERTY keyboard enables users to make annotations. The device also provides a built-in dictionary, access to an online encyclopedia, and the ability to accept emailed content. Cost of the Kindle is $359, including delivery, from Amazon.