DISPLAYS

You`ve been working your way through a technical history of the semiconductor industry and you want a change of pace. So you press a button on the spine of the book you`re reading and--presto--The Hunt for Red October appears in your hands. This scenario, or something like it, is envisioned by Joseph Jacobson of the Media Laboratory at the Massachusetts Institute of Technology (MIT; Cambridge, MA). He and his colleagues have developed an electrophoretic ink that lets them create rewriteable disp

Oct 1st, 1998

DISPLAYS

New ink promises paper-thin displays

Neil Savage

You`ve been working your way through a technical history of the semiconductor industry and you want a change of pace. So you press a button on the spine of the book you`re reading and--presto--The Hunt for Red October appears in your hands. This scenario, or something like it, is envisioned by Joseph Jacobson of the Media Laboratory at the Massachusetts Institute of Technology (MIT; Cambridge, MA). He and his colleagues have developed an electrophoretic ink that lets them create rewriteable displays on paper. Whole libraries consisting of a single volume printed in this ink could be available in the next few years, Jacobson says.1

The ink consists of white and black microparticles, 100 nm to 5 µm in size (see figure). White microparticles are rutile titanium dioxide. Black microparticles are made of a mixture of organic dyes. The two types are suspended in molten polyethylene, then dispersed in a mixture of tetrachloroethylene and an aliphatic hydrocarbon. This, in turn, is treated with urea and formaldehyde, creating optically clear microcapsules about 50 µm in diameter.

The researchers print a grid of electrodes onto the substrate, apply the electrophoretic ink, then add a transparent set of electrodes on top, attached to a standard display driver. The white microparticles have a negative charge, so applying charges to them can either bring them to the top of the microcapsule, obscuring the black dye, or push them to the bottom, leaving the black visible. A 12.1-in. display of electronic ink would draw about 12 mW for addressing. Because the particles are bistable, the display remains unchanged indefinitely, until a new charge is applied. Unlike a liquid-crystal display, the print can be read from a wide variety of angles and in bright light.

The researchers have not determined whether the display would eventually fade. "We have things up on the wall that we`ve written an image to that have been there for at least four or five months," Jacobson said.

Jacobson has achieved a resolution of about 1200 dots/in., which he said is comparable to a good laser printer. And he has made displays about 100 µm thick, "very close in size to a piece of Xerox paper." His samples have been flexible enough that they can be rolled to a radius of curvature of about 5 mm. Ink samples have been switched between black and white more than 10 million times without any loss of performance. "Basically any kind of printing technology can be used to print or coat these microcapsules onto a surface of paper or plastic," Jacobson said.

There are other types of particle displays, such as Gyricon, invented by Xerox Palo Alto Research Center 20 years ago but shelved, although researchers are once again working on it. Gyricon consists of half-black, half-white spheres, which rotate to the desired side when a charge is applied. It can be difficult, however, to make the spheres rotate completely, thus creating insufficient contrast, Jacobson notes.

"Cool company"

MIT holds patents on the technology, which it has licensed to a new company, E Ink Corp. (Cambridge, MA), of which Jacobson is a director. The company, with 21 employees, has received $15.8 million in venture capital from Motorola Inc. (Schaumburg, IL), the Hearst Corp. (New York, NY), Creavis GmbH (Marl, Germany), and several venture-capital companies. In June, Fortune named E Ink as one of its "cool companies" of 1998.

The company is working on scaling up the technique to marketable levels and plans to enter the market with rewritable signs that could be used by retailers. Right now, said E Ink president James Iuliano, if a department store such as J. C. Penney wanted to advertise a sale in each of its 400 stores across the country, it would have to have signs printed and delivered, then hope each store manager took care of having someone hang them. Iuliano envisions a system in which signs would be installed once, and a person at corporate headquarters could have them all changed simultaneously with the push of a button, using something like a pager system.

"We`d like to see these networked signs in the market and generating revenue in the back half of 1999," Iuliano said. A year or so later, he said, the technology could replace the liquid-crystal displays in hand-held devices, such as cell phones or Palm Pilots. Iuliano does not expect that the company will address the issue of adding color for another couple of years and that a refresh rate necessary for full animation is at least three to five years away. "Until we deliver those two, I don`t think we`re an immediate threat to, say, a display on a notebook computer," he said.

REFERENCE

1. B. Comiskey et al., Nature 394, 253 (16 July 1998).

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