by Elise Co and Nikita Pashenkov
The television screen and computer monitor are so ubiquitous in our daily lives that the notion of a “display” is almost inevitably linked to something rigid and rectangular. However, even as technology moves towards smaller and more portable devices, there is also a strong interest in the materiality of the things that we interact with on a daily basis.
Here we present an overview of emerging display technologies with particular emphasis on their application to flexible and deformable devices that can potentially obtain any shape or form. In each case, we see that the most important factor is how the technology is adapted to integrate with an existing flexible substrate, which can be, e.g., a solid sheet of plastic or woven fabric. In this sense, the field of flexible displays is as much a matter of process innovation and materials research as it is a question of electrical or computer engineering.
Sometimes hailed as a successor to current LCD technology, organic light-emitting diode (OLED) displays are based on organic polymer molecules that compose emissive and conductive layers of the display structure, which are composited together using a form of printing. The layers are deposited in rows and columns resulting in a matrix of pixels that emit light. Emissive OLED displays do not require backlighting and are viewable at oblique angles. They are also transparent; red, green and blue layers can be stacked such that a full-color (RGB) pixel is a fully color-mixed single pixel with depth, rather than a closely-spaced planar cluster of pixels as in traditional CRT or LCD displays.
OLEDs already appear in a mass market of smaller displays such as in car stereos, mp3 players, and cell phones. More innovative uses of the technology awaits the streamlining of manufacturing methods. For example, flexible display screens are being developed using plastic substrates, such as thin polyester films, or bendable metallic foils. Technology demonstrations by companies like Polymer Vision feature devices with such interfaces as rollable displays (see figure on page X). Taking the concept one step further we may imagine large, flexible display interfaces that can bend, flex and conform to many surfaces.
OLED technology is also a focus of interest as a path to energy-efficient solid-state lighting. Since organic polymer layers can be manufactured as large-area active elements, it is possible to combine area color, shape and flexibility to create novel interactive objects and interfaces. For instance, researchers at General Electric Global Research are already thinking about such applications as light-emissive curtains and wallpapers.
Electrophoretic displays (EPD), often associated with the brand name E-Ink, are specifically marketed as alternatives to traditional flexible paper. A type of particle display, “electronic ink” consists of thousands of microcapsules deposited onto a substrate. Each microcapsule contains positively charged white particles and negatively charged black particles suspended in a clear fluid. When a negative electric field is applied, the white particles move to the top of the microcapsule, causing that “pixel” to appear white, and vice versa (see Figure 1). The microcapsules are bi-stable, meaning that once configured black or white, no further energy is required to hold their state. As with OLED, flexibility is achieved through the use of flexible substrates (plastic) and conductors (metal foil or printed conductive traces).
Figure 1. Principle of operation of electrophoretic electronic paper displays.
Applications of E-Ink are in traditionally monochrome paper-based uses such signage and e-books, but also include examples of irregularly shaped and flexible displays. For example, the Seiko Watch Corporation has produced a limited run of unique watches based on a small, flexible E-Ink display. E-Ink has also prototyped various color displays and demonstrated multicolor EPDs using color filters .
In addition to newer technologies still being developed and refined, existing technologies can offer some of their benefits as a display or light-emitting material. Electroluminescent (EL) lighting is one technology currently used to produce thin, flexible lamps via a printing process. A layer of phosphor is sandwiched between two conductive layers, illuminating when an AC signal is applied across the layers. EL is widely used in backlighting applications for portable electronics and can be applied to large-surface-area applications. For instance, DuPont Microcircuit Materials is pursuing flexible EL lamps for advertising and signage, as well as for packaging concepts.
We have applied the materials and processes used in the manufacturing of commercial electroluminescent panels to hand-print custom-designed light panels on paper and fabric within a studio environment. Puddlejumper raincoat by Elise Co features EL panels silk-screened onto flexible fabric and activated via water droplet sensors printed with conductive inks. (see Figure 2)
Figure 2: Puddlejumper raincoat features electroluminescent panels silk-screened onto flexible fabric. The panels light up with rain drops falling on them
In addition to flat panels, EL lamps are also manufactured as wire elements and packaged in clear plastic tubing of varying diameters. In this form, the material is well-suited to creative manipulation as a fiber, combined with other materials or integrated directly into textiles with either a woven or knitted structure. Designers and artists have utilized EL wire to make light-emitting objects from lamps to fashion accessories and party clothes.
Optical fiber is another existing product that can be utilized creatively as a material for lighting and display. Specially treated ‘side-emitting’ fibers, with outer coatings that diffuse light along the length of the strand rather than reflecting it perfectly within the interior core, are produced in thicknesses up to 1/4″. Strands of such fiber can be combined together, woven into fabric, or embedded into other materials, then coupled with light sources at the fiber ends to create unique textile and flexible display surfaces. These same integration techniques are also applicable to standard (end-emitting) fibers, resulting in small points of light rather than glowing lines or strands.
Discrete light-emitting diode (LED) lights can also be used to create various active surface topologies. Although LEDs are not inherently flexible, their small manufacturable size and simple driving circuitry make them dispersable over a flexible substrate. Companies like ColorKinetics and Element Labs offer products that incorporate LEDs into collapsible bendable matrix configurations or flexible strands. Others embed matrices of LEDs in flexible substrate that can be curved, formed to a surface, or even used as a wearable material. Philips Research’s Lumalive technology demonstrations feature fabrics and clothes embedded with LED matrix displays constructed in this fashion.
Innovative display interfaces are not limited to light-emitting sources. Alternative active materials such as thermochromic inks, which change color with temperature, can be employed in the construction of novel display surfaces. Several artists and designers, including International Fashion Machines and XS Labs, have used these inks as overprints on top of textiles incorporating conductive spun threads. When a current is applied to the textile, resistive heating activates the printed ink and initiates a color change. By heating or cooling the metal filaments, the color of the textile-display is manipulated over time . As with the other examples given here, even the relatively limited behavior of this type of system can be parlayed into a sophisticated multi-channel output device via creativity of process and craft.
In some ways, the practical application of flexible displays to particular user scenarios seems strongest right now in the research, design, military and fashion technology communities. Flexibility or, perhaps as important, elasticity, is an inherently desirable property for anything worn on the body. The tactile properties of soft or malleable surfaces also make sense in myriad design and interactive environments. What is interesting about the general realm of non-rigid displays is that so many aspects of design and engineering converge to generate displays that are also materials. From these we can imagine displays that curve to fit any space or form; flex to accommodate motion; deform in response to physical interaction. Displays that are physically and conceptually flexible so as to permit the design of many novel and exciting user interface concepts.
1. Berzowska, J. and Bromley, M. Soft Computation through Conductive Textiles. 2007. In Proceedings of the International Foundation of Fashion Technology Institutes (IFFTI) Conference. 2007
2. Lieberman, D. Divergence of E-Paper Displays. EETimes. www.eetimes.com December 3, 2007
Elise Co (elise[at]aeolab[dot]com) is a media artist, programmer and a founder of Aeolab, a design and technology consulting firm in Los Angeles. She is a former Professor of New Media at the Hochschule für Gestaltung und Kunst in Basel, Switzerland, where she taught courses in interaction design and physical computing. Co holds a Master of Science degree in Media Arts and Sciences and a Bachelor of Science in architecture from MIT. At the MIT Media lab, Co explored the synthesis of fashion and technology. Her work has been shown internationally, including at the Museum of Modern Art NY, SIGGRAPH, IMRF Tokyo, Cooper Union, and the New York Art Directors Club.
Nikita Pashenkov (nik[at]aeolab[dot]com) was born in the former Soviet Union, lived in USA since 1991, and in Tokyo between 2003-2004. He earned a Bachelors Degree with Honors from Architecture School at Princeton University and Master of Science from Massachussetts Institute of Technology. At MIT, he was a member of Aesthetics & Computation Group led by John Maeda at the Media Laboratory. In 2005 Pashenkov co-founded Aeolab, a design and technology firm located in Los Angeles. His work investigates the intersection between design, programming and electronics technology and has been featured in exhibitions at MoMA (New York), Institute of Contemporary Art (London), Eyebeam Atelier (New York), and Ginza Gallery (Tokyo).Filed under | Comments Off