Ink on paper has evolved over the millennia to become the easiest medium to read and the most efficient means for conveying information. And despite all the talk about paperless offices, computers have contributed mightily to today’s deluge of printed material instead of helping diminish it. But that hasn’t stopped researchers around the world from trying to replicate print on paper electronically.

While making flexible displays in monochrome has been difficult, adding colours and making them switch fast enough for full-motion video has been a tougher nut to crack. The trick to making such furlable displays has been to fabricate the electrode arrays for switching the display’s millions of picture elements (“pixels”) from either conducting plastics or extremely thin metal foil. Fortuitously, the recent improvement in plastic electronics for ink-jet printers has invigorated the whole of the e-paper business.

Like real paper, e-paper has to be both highly reflective and passive - ie, it should need no juice for backlighting or for maintaining the image. The best way to do that is to use a medium that’s bi-stable. Like a tossed coin, a bi-stable material can flip between two possible states - and then remain stable, and require no energy, in one or the other state until flipped again.

The first attempts to devise a bi-stable ink were made 30 years ago at Xerox’s legendary Palo Alto Research Centre in California. Called Gyricon, the technology was based on a transparent silicone sandwich with millions of tiny polyethylene spheres floating in oil between the upper and lower surfaces. Each of the tiny beads, less than a hair’s width in diameter, was black on one side and white on the other, with each hemisphere carrying an opposing electric charge. When an external charge was applied to an electrode array on the upper surface of the sandwich, the beads floating beneath them rotated promptly to reveal either their white or black sides - spelling out words and images, depending on the pattern of surface electrodes switched on or off.

Nowadays, a Xerox subsidiary called Gyricon LLC sells its SmartPaper - the polarised-bead form of e-paper - as reprogrammable displays for draping inside retail stores, hotels, conference centres and colleges. The flexible signs are connected wirelessly to computerised databases so they can be changed with the click of a mouse.

The bi-stable technology that has progressed the furthest, however, is a refinement perfected at the Massachusetts Institute of Technology (MIT) in the early 1990s. This uses tiny microcapsules filled with electrically-charged particles of white titanium dioxide suspended in an oily solution of black dye. The capsules themselves are trapped in a liquid polymer that’s sandwiched between two arrays of electrodes.

When a negative charge is applied to individual electrodes, the titanium-dioxide particles move to the top of the microspheres and make that part of the display appear white. As with the Gyricon, the pattern of electrodes switched on or off determines the image on the display.

E-Ink, the company spun off from MIT to commercialise the idea, supplies such displays to electronics firms around the world, including LG Philips, Samsung, Motorola and Prime View as well as Sony. The first e-book reader launched by Sony in 2004 used an E-Ink display with electronics supplied by Philips.

Sony’s latest announcement promises to bring e-paper even closer to everyday use. This time the device appears to be a home-grown development. Unlike the electrophoretic displays used in E-Ink’s products, which rely on charged particles being physically moved by an electric field, Sony’s new imaging device uses an organic electroluminescence display (OLED). Such displays emit light in response to an electric current or field being passing through them.

OLEDs generally use a glass substrate, or backing material. But Sony has found a way of forming the organic transistors for switching the pixels on and off on a flexible plastic substrate. The 2.5-inch prototype is little thicker than a sheet of actual paper and weighs about the same without its associated electronics.
Don’t expect such a clever innovation to be wasted on something as prosaic as a portable reader for e-books. Apple’s multimedia iPhone may be the gadget du jour, but Sony may trump it with an all-singing-and-dancing gizmo, built around a foldable display for downloading television, which can run for days without recharging. Now that’s something not to be sneezed at.

From The Economist, June 2007

 

 

1) How is odinary paper made? Do we still have a paper factory in Switzerland?

2) How many tons of paper is used for a day's issue of 'Tages Anzeiger'?

3) What could be the benefits of e-paper?

4) Name some typical applications where e-paper would make sense.