Changing colours beckon future world

A just held conference has revealed that techniques to inkjet print electronic, sub micron thick, organic light emitting displays, revealed in Eureka’s September 2002 cover story, are more than ideas in development. The first, small displays are already in mass production and large displays are being shown at overseas trade exhibitions. Future developments are likely to include flexible displays based on the same technology. With the impetus of commercial consumer markets and heavy development efforts in the US and Far East, now is the time to think of the real killer applications before other people do. Small functional displays may be the products being demonstrated, but with much lower computing speeds than silicon and competing with established display technologies that work pretty well, it is in totally new products, not possible to make today, that organic displays and other products are likely to predominate. Speaking at “Advances in Carbon Electronics” at the Institution of Electrical Engineers in London, Dr Hans Hofstraat, from Philips Research Laboratories in Eindhoven, revealed that his company has been commercially producing displays based on organic light emitting polymers for some time. The first product to use them is the Philishave Sensotec shaver, launched in July 2002. This has a red and orange passive matrix polymer 2 inch LED display. Philips displays are made by spin coating a solution of polyphenylenevinylene (PPV) copolymer on a passive matrix structure and are manufactured at Heerlen in The Netherlands. For those who wish to incorporate similar devices into their own products, the company sells a polyLED matrix display evaluation kit. The next stage on the company roadmap is a 100 x 200 pixel full colour display. The active emission layer in the displays is only 300nm thick and so is eminently suitable for manufacturing flexible displays. At the moment lifetime requirements necessitate the use of packaging approaches protecting the devices from oxygen and water, in the form of inflexible glass substrates, but a breakthrough allowing use of flexible plastics could occur at any time, if it has not done so somewhere already. Organic displays and organic electronics generally should not be seen as a replacement for silicon. Organic semiconductors can only be made p-type so far, which allows the fabrication of field effect transistors but offers only limited charge carrier mobilities. Hofstraat remarked that a 600MHz Pentium chip realised in polymer would run at around 60Hz Philips sees opportunities in what it terms, “Ambient intelligence” in the ‘connected house’ and the ‘portable office’. Such concepts will require a combination of displays, sensors and actuators, wireless connectivity, and an energy supply. Concepts include flat panels, ‘intelligent windows’, wearable electronics and single control terminals, unlike the mess of modules, cables, and infrared remote terminals common in the house or office of today. At the same time, the technologies should be low cost, adaptable to present day production technologies, environmentally friendly, conformable if not flexible and of low weight and bulk. Organic polymers fulfil all such goals pretty well. Industrial products under development by Philips include radio frequency identification tags. Intelligent tags require a memory that can be programmed with a unique code, allowing the reader to identify the tag and so the item on which it is placed. The company made its first functional organic transponder with an integration level of 326 transistors to provide a 15-bit digital code generator as long ago as 1998. The most advanced polymer IC at Philip produces a 64-bit code, with 48 programmable bits. It includes about 700 transistors and is laid with 2.5-micron wide tracks on a total area of 3.2 x 2mm. Just when those present at the meeting were feeling satisfied that Europe had maintained control of the commercial opportunities offered by polymer electronics, Professor Ghassan Jabbour happened to mention the advanced development of large organic, full colour displays, some of which have been shown and demonstrated, by Sony, Toshiba, Kodak and similar companies. He then went on to described how his team in Tucson, Arizona could not only inkjet print organic electronic materials, but could also screen print them onto textiles and gravure print them onto paper, employing similar printing technology to that used to produce Eureka. Although he had a non-working example of organic electronic materials printed onto newsprint, it is likely to be a few years yet before your favourite magazine is able to glow electronically and display animated diagrams. He thought that large area printed lighting was still 10 to 20 years away, but back lights would be on sale much sooner. Encapsulation is an essential part of the technology, to prevent the materials being oxidised in air. Interestingly, he reported being able to screen print 30 to 35nm droplets using 460 mesh screens. While this might sound impossible, it can apparently be achieved by carefully controlling the viscosity of the substances and making use of surface effects. With the imminent availability of low cost, thin and flexible displays and other ‘Smart’ products in the near future, designers should now be thinking of truly radical ways of using them. It becomes possible to consider clothes or car bodies whose colours or designs could be changed to suit the mood of the owner. It is also likely to be possible to use textile based electronics to drive changes in other properties, such as changing textiles from open pored and ventilating to warming and waterproof. Adaptive camouflage for soldiers that could imitate surroundings like a chameleon was seriously suggested in the corridors of the conference. Alternatively, uniforms could be switched to red with gold piping for parades and when soldiers wanted to be seen. Building windows could not only be made to darken in bright sunlight or opaque, but could be made to show displays. These might be a favourite television programme, or a more pleasant landscape view than is available by looking outside. Or facing outwards, windows could be made to show a message such as “Burglar”, “Help”, “Merry Christmas” or “Welcome.” Alternatively, they could gather electric power by day on the outside, and serve as lamps on the inside at night. Fitted to the outside of domestic appliances, they could indicate on the outside of a microwave cooker that the meal inside is cooked, or that a refrigerator is getting warm because the door has been left open or that a washing machine has completed its task. The representative of a leading pollution control company represented at the conference suggested smart materials that could assist in the simulation of clean up operations. It is also possible that walls of future houses, offices, and concert halls could just be used to display art, either static, or dynamically changing in response to the inputs of artists, amateur or professional. What could be done will only be limited by imagination. Dr Hans Hofstraat Professor Ghassan Jabbour Pointers · Small polymer two colour light emitting displays are already in large scale commercial production. Their active layer is only 300nm thick, cheap to make and may soon become flexible · Larger, full colour displays have been demonstrated but are still in development, with work underway to improve lifetimes · Organic FET transistor based devices work well, but are a million times slower than silicon · Organic electronics can be ink jet printed, but screen printing and gravure printing has also been shown to be feasible Eureka says Organic polymer based electronics, displays in particular, are coming along faster than anticipated. Now that the Japanese heavies seem to have become involved we can expect to see striking new commercial products in the near future