Thin-film research could lead to flexible displays and cheaper motherboards

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Thin-film research could lead to flexible displays and cheaper motherboards

Cliff Saran
Dundee University breakthrough could slash production costs.

The University of Dundee has developed a cost-effective process for fixing atoms or molecules to a range of surfaces. The technique could have applications in electro-plating, circuit board production, liquid crystal displays, plasma display panels and gas sensors.

The university has been a pioneer of thin-film transistor (TFT) technology since the 1970s. It developed the amorphous silicon transistor that forms the basis of today's TFT display screens. Each transistor represents an individual pixel that can be switched on or off independently to create an image.

Displays are manufactured using a process known as photolithography, where the inside surface of the glass screen that makes the display is coated with a substance called indium trioxide. A light-sensitive coat, known as a resist, is then applied on top of the indium trioxide layer.

When ultra-violet light is shone through a template known as a mask onto the resist, the surface changes chemically, making it more soluble. Exposed areas of indium trioxide, where the resist has dissolved, can then be etched away, leaving a transparent wire matrix, which connects the transistors that represent the pixels on the display.

Jim Cairns, a professor at the University of Dundee, has been investigating how to improve this process. One method would be to use copper instead of indium trioxide for the wire matrix, but to be invisible to the naked eye the copper tracks would have to be 10 microns or less wide. The problem is that such thin copper tracks cannot be bonded to glass easily. This is why the process requires indium trioxide.

"A film of indium trioxide needs to be deposited on the glass surface using a vacuum system, which is quite an expensive process," explained Cairns. The process involves heating the indium trioxide in a vacuum until it vaporises and then allowing it to condense on the glass.

Cairns said a cheaper approach would be "spin coating". Here a drop of liquid spreads evenly across the glass substrate as it spins on a turntable. At the University of Dundee, Cairns' research team developed a technique, which allows copper, rather than indium trioxide to be bonded onto glass, without the expensive vacuum process.

"We have developed a technique for depositing a liquid film onto a range of substrates, such as glass and silicon," said Cairns.

Cairns' research has led to a process to deposit a liquid film just a few hundred nanometres deep on a glass surface. The film is light-sensitive and only sets when illuminated by ultra-violet light. Cairns said metal could be bonded to the film easily using standard electro-plating.

The process is based on a nano-engineered coating - effectively a thin, light-sensitive glue, that can be applied uniformly across the glass on the inside of a TFT display using a technique like spin coating. The glass is then irradiated with ultra-violet light shone through a mask, which defines the required wiring. The areas of the coating not exposed to the ultra-violet light are then washed off, leaving tracks of the coating.

Using electro-plating, the tracks can be coated with a metal such as copper to create the wires. Cairns said, "The process uses up to 80% less metal, since it is not necessary to coat the surface of the glass with metal, which lowers costs."

Furthermore, he said the copper tracks could be produced 10 microns wide - invisible to the naked eye - and yet remain bonded to the glass, so there would be no need to produce wires using indium trioxide.

The process is not only limited to glass. The coating could also be applied to a flexible plastic. "We have deposited metal onto a plastic file," said Cairns. This could eventually lead to the development of displays that could be rolled up.

Another application would be in printed circuit boards such as PC motherboards. Cairns said, "Motherboards would require far less copper." This would reduce production costs, and ultimately, the cost of devices.

Cairns said five years from now the technique could be used to lay optical tracks, which would allow engineers to build devices where optical fibre is linked directly into a chip.

Cairn's goal is to create a process that can be easily industrialised. "We need a technology that is amenable to mass -production and is robust." He believes the process his team has created could be the answer.

Dundee University has set up a spin-off company called Aktina, of which Cairns is chief technology officer, to develop products based on the technology. The company presented the technique at a conference last month organised by Connect Scotland, an organisation set up to help emerging technology businesses in Scotland.

www.aktina.co.uk/html/fiber.html

How does it work?
  • Nano-engineered coating is deposited on substrates such as glass, flexible plastic or silicon

  • Coating is light sensitive

  • Tracks are created by illuminating the coating with ultra-violet light through a mask

  • Areas not exposed to ultra-violet light can be washed off

  • Remaining film can be electro-plated to produce metal tracks.

Benefits
  • Removes the need for expensive production techniques such as vacuum coating

  • Process uses up to 80% less metal

  • Promises to simplify printed circuit board and TFT display manufacturing.
Connect Scotland

Connect Scotland is a non-profit-making organisation founded in 1996 to nurture the creation, development and growth of emerging technology companies. It provides a nationwide support infrastructure which brings together universities, venture capitalists, banks and technology experts, as well as corporates, local enterprise companies, lawyers and individuals with specific management or sector experience.

A spinout of the University of Edinburgh, Connect Scotland is supported by all 14 of Scotland's universities.

www.connectonthenet.com

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