Organic transistors hit silicon speed

A polymer that matches the electrical performance of amorphous silicon has been discovered by researchers in Britain and the US and could lead to a cheap way to make electronic paper.

Amorphous (ie non-crystalline) silicon is electronically sluggish compared with the more structured form used to make the transistors in a computer processor.

But it has the advantage of being relatively easily to deposit over large areas, and is commonly used to create the matrix of thin-film transistors (TFT) that drive most LCD displays.

Companies such as Plastic Logic in Cambridge have been developing organic (ie carbon based) materials , with silicon-like semiconductor properties, that promise less-expensive ways to do the same job.

The materials can be made up into inks so that transistors and entire circuits can be printed out by inkjet – or, for mass-production of larger surfaces, gravure press.

The new polymer, reported in the April Edition of Nature Materials, is said to have six times the electronic performance of any previously reported for these materials. It was developed at the Merck laboratories at Southampton, and by researchers at Stanford and other California establishments.

Iain McCulloch, project manager at Merck, says a primary motivation of the research was to reduce manufacturing costs, because the use of amorphous silicon required high temperatures and high-vacuum processes producing a lot of waste products.

But polymer semiconductors are also compatible with plastic substrates which could 'enable a new generation of flexible, lightweight and ultimately large area displays'.

They can also be used to print simple logic circuits so they may be seen first in disposable novelty electronic items, followed by small reflective PDA displays or e-paper, and posters.

'Further away are large, high resolution displays such as active-matrix LCD or OLED (organic light emitting diode), and possibly even item level RFID tags,' McCulloch told Nature. 

He added: 'The first demonstrator products are already here and the commercial possibilities are encouraging.'

One problem the new materials will not solve is that of notebook battery life. Polymer displays will draw as much power as those with a silicon matrix.