Printed electronics bends the rules for designing in displays

4 min read

Displays used to be rigid in every sense. Not just as a hard, flat, glass-covered surface, but also in terms of the options they presented the designer.

Now, there is a bit more flexibility as developments in organic electronics are opening up new possibilities for displays and interfaces. Plastic Logic is a company spun out of the University of Cambridge to develop plastic electronics technology. At the core of its technology is a polymer that can be built up in layers to produce an array of organic thin film transistors (OTFT). A crucial characteristic of this polymer is that it can be processed in liquid form in order to produce a flexible circuit. In turn, this gives an opportunity for the displays themselves to be genuinely flexible or conformable depending on the application. Lightweight, low power and flexible Plastic Logic uses this polymer to create a back plane (the 'control' layer) which can then be coupled with a front plane (the 'visual imaging' layer). The front plane uses the E Ink materials, which bring a number of attributes that mirror those of the polymer electronics and therefore allow them to be realised. Most significantly, they are lightweight, low power and flexible. E Ink, itself a spin off from MIT, has developed the electrophoretic ink based displays used on some e-readers and other mobile devices. Applications for the technology, according to Rachel Lichten, head of marketing communications at Plastic Logic, are limited only by the imagination of the designers. One recent concept was MorePhone, developed by researchers at Queens University in Canada. This smartphone can morph its shape to give users a silent, yet visual, cue of an incoming phone call, text message or email. The same researchers came up with the concept for PaperTab – a flexible tablet computer. More mainstream applications concern smartphones, e-readers and general displays. Lichten commented: "The important thing about the technology is that it's been fully industrialised – we have taken it from the lab to the factory and they are the only flexible displays available on the market." The factory was set up in Dresden in 2007 and had an initial capacity of around 2million displays. With many displays now of non standard size – many are smaller – the capacity in terms of units is larger. "The technology can be used in a wide range of products and that is the exciting thing," said Lichten. "It is an enabler for a variety of markets. However, the technology is new – it is the first time that real flexible displays have been on the market. We are working with our customers to develop product and design concepts to show until the products are launched because, for some, it is difficult to visualise what they can do with this display – what is its potential." Plastic Logic has YouTube channel, with 19 videos showing some concepts in action – a large e-reader being particularly impressive. But, beyond the possibilities offered by its flexibility, the technology can benefit existing applications, even standard rigid displays. One YouTube video shows a display being subjected to, and surviving, a 'stamp test' that would have destroyed its rigid equivalent. It is also very low power, particularly when coupled with the E Ink front plane and considerably lighter than a glass display. Putting these attributes together makes it worth considering for any mobile device. An extension is the concept, already being deployed using LCDs, of having a secondary display either embedded in the back of mobile phones and tablets, or as part of an accessory. This could be particularly useful for those doing a lot of reading and could use this display as a low power alternative to using the LCD. Equally, an important document, like a flight boarding pass for example, could be stored on the secondary display and not be lost if the battery ran out. This is because the electronic ink is bistable – power is only needed to change or update the picture. No power is needed to read the text or look at the picture. The ink itself does have a drawback that prevents it from being used as a primary display where high quality video is required, as Lichten explained: "Ink itself is a relatively slow media to change. We have produced video rates at 12frame/s and that is a world first – it's the first time that ink has been driven by an organic transistor. So we have the know-how to work with the front plane media to enable that. What you are looking at here is the possibility to have Flash applications, for example, with the display being used on an e-reader to illustrate some text passages in a newspaper or book by embedding small videos. It looks good, but it is not aimed at showing the next Hollywood blockbuster – there are limits. The limiting factor is the front plane, not the back plane, so we couple our backplane technology with other display media. We are working on projects to develop flexible OLED displays and to combine with liquid crystals to produce a flexible LCD." At the moment, Plastic Logic is using its technology to print transistor arrays – around 1.2m of them in a standard 10.7in display – with a resolution of 150dot/in. However, it is possible that, further down the line, the technology could be extended to, for example, printing passive components. Printing intelligent products And it does not need to stop there according to Lichten: "At the moment you can make 3d printed products, but they are dumb – for example, you can you print parts of a car. The potential to print the electronics means you can make them intelligent. Although it will probably be a long time coming, instead of printing a part of a car, you could print all of it. That is the way that 3d printing is going, but the ability to print the electronics can also make the final products work." In terms of using the technology in current projects Licheten claims there is nothing that designers need to be worried about: "There is nothing difficult. You are just working with a different medium and it might mean that rather than creating the same product with a different display in it, the next generation might be slightly flexible or slightly conformed. Maybe you curve the edge of your device so it fits nicely in your hand. If it was a watch you could have the whole of the wrist band being a display rather than a bit of glass that was connected with a couple of bits of leather – it really depends on what the final product is."