Cheap tricks for plastic circuits


Two years ago, the hot topic at Printed Electronics in Dresden was colour displays. But since then, Sony has beaten a hasty retreat and it’s taken longer to get to commercial monochrome printed or plastic displays than people had hoped in 2008. This year, the emphasis is on the definitely 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 - although Peter Harrop, chairman of IDTechEx, the company that organises the conference, reckons they will be back with updated versions at some stage.

Sharp is seriously looking 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.

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.

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 tons 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.

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.

Ultimately, some of this stuff is 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. 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.