Printed electronics vie for the low end

Two years ago, the hot topic at the Printed Electronics conference in Dresden was plastic colour displays. Since then, though, Sony has beaten a hasty retreat, and commercial monochrome printed or plastic displays have taken longer to realise than expected. This year, the emphasis is on the considerably less sexy end of the business: smart labels and packaging - low-end stuff that barely needs any circuitry at all.

Even in displays, some companies are now looking at a way to cut the cost of making existing types of screen - such as liquid-crystal display (LCDs) - rather than trying to open up a market for organic LED screens, especially now that Sony has retired hurt. However, Peter Harrop - chairman of IDTechEx, the company that organises the conference - told delegates returning to Dresden in April 2010 that those companies will be back with updated versions at some stage.

Sharp is looking seriously at a way of using printing to replace lithography in the manufacture of its LCDs. According to Tolis Voutsas, director of the materials and devices applications lab at Sharp Laboratories of America, the company could knock 60 per cent out of the cost of making some LCDs simply by 'abolishing lithography', once printed transistors get to the necessary level of performance.

'Solution processing has progressed quite substantially. It is not the same as silicon, but it can provide more elegant solutions for many systems if only we can do it in manufacturing,' says Voutsas, asking: 'What if we could strategically replace a number of steps used today? We could go to hybrid manufacturing, reducing costs without changing performance.'

The Japanese company is looking at a variety of materials and techniques that could yield much cheaper production techniques. Inorganic oxides and organic chemicals are on the menu, as are different printing techniques ranging from traditional gravure through inkjet - currently used by Plastic Logic for its flexible displays - to the novel approach developed by the University of Illinois at Urbana-Champaign of electro-hydrodynamic printing.

'Like conventional semiconductor manufacturing, where you have mix-and-match lithography, the same will happen here,' says Voutsas. 'Some layers will put down by inkjet with others laid down by gravure or other techniques.'

At Printed Electronics, Samsung chose to talk about its own work on low-cost LCDs rather than shiny, attractive OLED displays. Its 5in prototype based on organic semiconductors shows a dingy-looking image, but the development was enough to demonstrate the viability of moving from silicon to plastic transistors in the circuits that sit underneath the liquid crystal in some kinds of display.

Sharp has worked with inorganic oxide specialist Inpria, founded by specialists in their chemistry at Oregon State University, to find out how they might work in displays. Voutsas says the materials are potentially interesting, not least because they are transparent. This would improve the transmission of the light that is needed behind an LCD through the display electronics. But work so far has yet to yield thin-film transistors (TFTs) with sufficiently low threshold voltages. 'This is why you don't see a product that uses amorphous oxides in TFTs. But we think this is one of the technologies that will emerge soon.'

For the moment, at least, Voutsas sees organic chemicals as being more advanced and with the potential to remake large parts of the display industry and open up new markets.

'Smart objects are where we expect to see the huge markets for printed electronics. We haven't scratched the surface of that yet,' says Voutsas.

Seeking new markets

Outside the electronics industry, the big corporations are taking note, even if they find working with such a young and understandably technology-focused industry problematic. A lot of the technologies are looking for an application, although one good sign is that companies are trying to reach out from their networks of customers and suppliers to see if someone is out there, anywhere, who can help.

Kimberly-Clark made 60 tonnes of its conductive paper as part of a feasibility study but came up blank in terms of products within its own portfolio that could make use of it. A reason for research scientist Tom Ales to turn up at the conference this week in Dresden was to see if someone could use a conductive paper loaded with carbon fibre in what they were doing.

The people at Kimberly-Clark had a good think about what they could do with the paper, and not necessarily the first things you think of when someone says 'conductive'. For example, one of the possible applications they looked at was in heating - possibly replacing those chemically activated heat pads with something that might combine paper and a small battery or fuel cell. Being up to 30 per cent carbon fibre - beyond that level, it gets very brittle because the fibres are, as Ales pointed out, 'like uncooked spaghetti' - the cPaper is conductive, but not all that conductive.

Combine the heating effect with an oil or detergent soaked into the paper fraction and there is potential for something that may clean things more easily than just using the materials on their own as a lot of these things work better at a higher temperature.

Elsewhere, Novalia's journey into the simple got off to an early start. Formed by Kate Stone after leaving Plastic Logic, it took a sales call to trigger a drastic change in approach. She wanted to sell a company making trading-card games on the idea of using printed transistors to make them more interactive. They asked her to return in a few months to show how it might look.

'That event totally changed my perspective. It was going to take a couple of years to do that. I couldn't do it,' she said.

The prototype she did come up with had no printed transistors in it whatsoever. 'I thought, if I am going to get anything to work I am going to have to use existing technology,' she said.

In later conversations with potential customers, she has found herself lowering their expectations of what printed electronics is currently capable of.

'One company said they wanted to print RFID tags on their packaging. They had heard about printed electronics, but I had to sit them down and explain we can't print RFID tags today,' said Stone. 'But I realised that if they had conductive inks they could create a grid of lines and put a code onto the packaging. The concept was invented by thinking about what machines they had on the floor.'

To support more advanced designs such as interactive books and greeting cards, Novalia has gone back to silicon - embedding a programmable custom chip into the product that carries some sensor inputs and speaker and LED outputs. It's not that different from the talking cards that have been on the market for some years. The main difference is in the way conventional conductive inks are used to send data to the controller.

Professor Karl Leo of the Fraunhofer Institute of Photonics and Microsystems in Dresden said at Future Horizons' 2010 International Electronics Forum: 'My personal opinion is that there are some applications where organic electronics are close to the market. But otherwise organic electronics for logic are still struggling because the killer application is missing. It was going to be the RFID tag but silicon is so cheap that plastic electronics struggle against it.'

Ultimately, some applications are likely to move towards printed transistors, but only when they deliver on the promise of being cheaper and manufacturable. Even then, there's a good chance little lumps of silicon will wind up inside many products, talking to the plastic bits.

For example, technologists at Nokia's research centre are working with Stephanie Lacour's group at the University of Cambridge with flexible plastic films that use stretchable gold interconnects to connect silicon chips mounted on rigid islands scattered across the surface of the film.

We may even see people going back and having a new look at the packaging for silicon to see if there are cheaper ways to do it so that products can be slung together in high-volume, low-tech assembly lines.