Information technologists have dreamt for decades of making an electronic display that is

as good as paper: cheap enough to be pasted on to wails and billboards, clear enough to be read in broad daylight, and thin and flexible enough to be bound as hundreds of flippable leaves to make a book. Over the past few years they have got close. In particular, they have worked out how to produce the display itself, by sandwiching tiny spheres that change colour in response to an electric charge inside thin sheets of flexible, transparent plastic. What they have not yet found is a way to mass-produce flexible electronic circuitry with which to create that charge. But a paper just published in the Proceedings of the National Academy of Sciences suggests that this, too, may be done soon.

The process described by John Rogers and his colleagues from Bell Laboratories, an arm of Lucent Technologies, in New Jersey, and E Ink Corporation, in Cambridge, Massachusetts, starts with E Ink's established half-way house towards true electronic paper. This is based on spheres containing black, liquid dye and particles of white, solid pigment. The pigment particles are negatively charged, so they can be pushed and pulled around by electrodes located above and below the sheet.

The electrodes, in turn, are controlled by transistors under the sheet. Each transistor manipulates a single picture element (pixel), making it black or white. The pattern of pixels, in turn, makes up the picture or text on the page. The problem lies in making the transistors and connections. Established ways of doing this, such as photolithography, use silicon as the semiconductor in the transistors. That is all right for applications suck as pesters. It is too fragile and too expensive, though, for genuine electronic paper—which is why cheap and flexible electronic components are needed.

For flexibility, Dr. Rogers and his colleagues chose pentacene as their semiconductor, and gold as their wiring. Pentacene is a polymer whose semiconducting properties were discovered only recently. Gold is the most malleable metal known, and one of the best electrical conductors. Although it is pricey, so little is needed that the cost per article is tiny.

To make their electronic paper the researchers started with a thin sheet of Mylar, a tough plastic, that was coated with indium-tin oxide (ITO), a transparent electrical conductor. To carve this conductor into a suitable electric circuit, they used an innovation called microcontact printing lithography. This trick involves printing the pattern of the circuit on to the ITO using a rubber stamp. The "ink" in the process is a solvent-resistant chemical that protects this part of the ITO while allowing the rest to be dissolved.

From the first paragraph of the passage, we can learn that an electronic display ______.

A．can be made as good as paper

B．is cheap enough to be pasted on to walls and billboards

C．will be as thin and flexible as paper

D．is difficult to be created in the form. of flexible electronic circuitry