A material that turns into an electrical conductor at the flash of a light has been developed by Japanese researchers. Circuits could be created on the material using a stencil, or by 鈥渨riting鈥� with a directed light beam.
The advance promises to reduce the cost of producing the large liquid crystal (LCD) displays used in laptop computers, and to lead to new forms of optical storage. Current LCD screens are manufactured by a costly production process called photolithography, involving a long series of layering and etching steps.
The compound, developed by Katsuro Hayashi and colleagues at the Japan Science and Technology Corporation in Kawasaki, is a transparent oxide insulator that permanently becomes a conductor after exposure to ultraviolet light.
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Peter Raynes, professor of opto-electronic engineering at Oxford University, says: 鈥淚t would be nice to have a coating that you could put on glass and then produce a pattern in a single step.鈥�
Hayashi says his present production techniques may make that possible. 鈥淥ur present technique makes it possible to omit most of the photolithography process in circuit formation,鈥� he told 快猫短视频.
Trapped ions
To create the novel material, Hayashi鈥檚 team took a transparent insulating oxide and trapped negatively charged hydrogen ions in its cage-like crystalline structure.
Subsequent radiation of the material with ultraviolet light caused the hydrogen ion to release its electron, transformed the oxide into a conductive state. This persisted after the UV was switched off because the hydrogen atoms combined into H2 molecules.
The new application to LCDs is possible because an LCD display is composed of two layers of transparent conductor sandwiching a film of liquid crystal. The two layers must be finely patterned to provide anodes and cathodes for each pixel on the screen.
鈥淭he ability to write transparent conducting lines purely by UV exposure would be very useful,鈥� says Seamus Burns at Plastic Logic, a Cambridge, UK, company developing printed electronics technology.
But Raynes warns that there may well be some technical hurdles that still need to be overcome. 鈥淎ccording to their figures, the resulting material is just too resistive for current LCDs,鈥� he told 快猫短视频.
Furthermore, he speculated that the material could be adversely affected by the UV radiation in sunlight. But Hayashi says this can be overcome easily by using a 鈥渃overing transparent film which is opaque to UV light after the pattern has been etched.鈥�
Write, re-write
Burns agrees with Hayashi that the compound could also be used in production of high-density optical storage media. 鈥淭he ability to write, and possibly re-write, conductive paths across a surface with UV light gives a kind of versatility that would be very useful, if it can be made to work,鈥� Burns says.
At present, the compound needs to be heated to above 320 掳C to return it to its resistive state. 鈥淚t would be nice if you could anneal and re-write the material in situ,鈥� says Raynes. 鈥淏ut at present that鈥檚 difficult as it requires heating to high temperatures.鈥�
Hayashi says there is already a precedent for this, noting that focussed laser light can enable the heating of a local area in magneto-optic discs.
Journal reference: Nature (vol 419, page 462)