Electronic paper is catching up with the real thing

Paper chase
Jun 15th 2007
From Economist.com
Electronic paper is catching up with the real thing





AN INVENTOR meets a venture capitalist in a bar. He pulls out of his pocket something that looks like a grubby handkerchief, straightens it out on the bar top, and begins his pitch for $10m of venture money.

It’s a video display that can be furled, folded or rolled up into a ball, the inventor enthuses. He shows how it can be viewed from any angle, is easy to read in bright sunlight, has a contrast ratio better than a laptop’s liquid-crystal display (LCD), is light and portable, and can run for months without being recharged. It will change the way we view the world, swears the wide-eyed inventor. “Naw, it’s all been done better and cheaper before,” says the unimpressed VC, as he crumples the newspaper he was reading and tosses it into the bin.

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.

The one thing going for e-paper, which the dead-tree version can’t hope to match, is its programmability. Imagine a newspaper that could be updated as events developed during the day. Think of a book that could change its contents after you’d finished reading it. How about a laptop-sized screen that unfurled from your mobile phone so you could watch TV while strap-hanging to work? What if your tee-shirt could flash intimate messages to attractive passers-by?

Sony is the latest in a long line of gadget-makers to flaunt a paper-like electronic display. The flexible 2.5-inch display it demonstrated a couple of weeks ago was notable for two reasons: it offered full-motion video and was in living colour.

E Ink Corporation




In some ways, Sony is playing catch-up here. LG Philips, a joint venture between LG of South Korea and Philips of the Netherlands, has been showing off a 14-inch colour screen that’s flexible enough to wrap around a lamp post. Prime View International of Taiwan has something similar. So does Samsung of South Korea and both Seiko Epson and Fujitsu of Japan, as well as a handful of start-ups in Britain and America. But until recently, few of them were able to display colour video properly.

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.