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Boffins build bendy Flash array

Organic floating-gate transistors employed

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Japanese boffins have created a flexible sheet of Flash memory out of organic transistors.

The team, led by Takao Someya of the University of Japan's Applied Physics, and Electrical and Electronic Engineering departments, built the transistors using a dielectric material composed of a 2nm-thick polymer layer and a 4nm-thick sheet of aluminium oxide.

The layers insulate each transistor's 'floating' metal gate from the rest of the structure - a control gate above and the source and drain below. The metal gate can retain a charge, allowing to 'store' a binary memory value.

Someya told the journal Science that each transistor - there are 676 in the group's test array - can last for 1000 write cycles. Silicon Flash has a longevity of more than 100,000 write cycles, of course, but these are early days for Someya's process, and his transistor sheet is both flexible and considerably cheaper to mass-produce than silicon Flash.

While the organic transistors are not likely to replace Flash chips any time soon, they may find a role in devices that need to bend or be fitted to an irregular shape. Disposable memory products are another possibility.

Memory for a foldable e-newspaper, anyone?

To show one possible application and to test the transistors' storage longevity, Someya's team bonded the sheet to a pressure sensor forming a plastic device that's less than 700µm thick and can record pressure patterns. The patterns are retained completely for 20 minutes, but begin to degrade after that until, 24 hours or so later, they are gone.

Someya believes that these figures can be improved significantly, as can the memory cells' write-cycle lifetime. ®

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