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Electronic Imaging & Signal Processing

PAPER PRODUCTS

Electronic paper combines programmability, portability, and reusability.

From oemagazine December 2001
30 December 2001, SPIE Newsroom. DOI: 10.1117/2.5200112.0007

Paper as a display medium has some obvious strengths: It is flexible, it can be viewed in room light, and it is easy to read from any angle. Compare this to a laptop screen, for example: It is portable but rigid, it requires backlighting, it is difficult to read in brightly lit locations, it exhausts batteries, and it limits the user's viewing angle. Even so, the laptop screen is an advance from bulky CRTs. The main advantage of computer displays is that they can be electronically updated, compared to paper, which is a write-once medium.

At Gyricon, we are developing a new display medium that combines the advantages of paper with electronic addressability. Science-fiction writers have described a number of different visions for electronic paper, but the technical hurdles have prevented any version from becoming a commercial reality thus far. The technology has the potential to enable whole new classes of applications for electronic paper.

tiny bubbles

Our basic display structure consists of a thin layer of elastomeric material embedded with bichromal spheres (see figure). Each sphere sits inside its own cavity, which is filled with silicon oil, allowing the sphere to rotate. The spheres are fabricated such that one hemisphere appears white and one hemisphere appears another color (typically black), with each hemisphere having a different permanent charge. In a stable situation, the balls gravitate to one side of the cavity and adhere to the wall. When we apply an electric field across the sheet of elastomer, however, the ball unsticks from the side of the cavity so it can rotate to align with the field. After the ball has rotated, it settles again against the cavity wall and becomes stably attached until a reverse electric field is applied. If an image is converted into a planar voltage pattern applied to the surface of the sheet, then the electrical field induces rotation of the balls, and the image is transferred to the balls. Light reflected off the balls shows the image.

The Gyricon display material consists of electrostatically charged, two-color spheres about 30 to 90 µm in diameter, each encapsulated in its own cavity. When electrodes create an electrical potential across the material, the spheres align themselves with the field. In the absence of an applied field, the spheres tend to stick to the walls of their cavities in this same orientation.

The balls can be of different sizes, but they are normally between 30 and 90 µm in diameter, so that each piece of the image is made up of many balls, much like toner particles on a piece of printed paper. We manufacture the balls by allowing pigmented molten polyethylene to fall onto the surface of a spinning disk enclosed in a chamber. The fluid material flows to the edge of the disk where it spins off into space. By using black material on one side of the disk and white on the other, we cause the flows of the two materials to meet at the disk edge. After the material leaves the disk, surface tension pulls it into a sphere. These bichromal spheres harden in flight and are solid when they hit the walls of the chamber where they are collected.

To manufacture the displays, we blend the spheres with uncured elastomer and feed the mixture into a web-fed sheet coater, generating a sheet of material 250 to 500 µm thick. The cured sheet is soaked in silicon oil, which causes it to swell and release each ball within its own cavity.

The material has a wide viewing angle in reflected light (like paper), bistability (which enables very low power applications), and flexibility (see table). In addition, the manufacturing method allows us to fabricate large sheets at low cost.

programmable signs

The electrical field necessary to change the image can be introduced by a circuit board laminated to the paper, from an active matrix array, or from a printer that deposits charge on the surface of the material. Potential applications include indoor and outdoor signs, PDA displays, fold-out displays, and rewriteable and downloadable books and newspapers. Truly electronic books and newspapers may ensue when thin-film polymer transistors enable very inexpensive printable electronic arrays at high resolution.

As an example of the first application in the retail signage market, the material has been made into retail pricing and point-of-purchase signs. These signs take advantage of the bistable characteristic of the material to enable battery-operated performance. We expect the batteries will last for more than a year. The system that uses these signs includes an RF network to communicate with the signs and a set of software with a graphical user interface, which allows users to change prices and couple the prices displayed to prices stored in the point-of-sale database. This system enables stores to change prices in a timely manner, to ensure that the signs are always connected to the point-of-sale database, to allow the store capability for timely sales, and to respond to changes in inventory. A network of such signs, trademarked as Smartpaper, has already been installed at a Macy's department store in Bridgewater, NJ.

Our display material is manufacturable and has demonstrated its utility for large retail signs. Future applications include electronic printing on erasable material as well as an electronic replacement of printed materials through direct application of thin-film transistor arrays. oe


practical innovations

Robert Sprague is an innovator and entrepreneur at heart. In the 25 years that he's been with Xerox Palo Alto Research Center (PARC; Palo Alto, CA), Sprague has helped start three spinoff companies, has won numerous prestigious President's Awards from Xerox for his work in ink-jet printing, and holds more than 60 patents. Not all of these efforts are in the same field. In the mid-'80s, Sprague started Optimem, the first American optical disk-drive company. In the 1990s, he helped with the spinoff of display specialist dPIX (Palo Alto, CA), and he currently serves as the interim chief technology officer of Gyricon Media Inc. (Palo Alto, CA), which specializes in the development of electronic paper.

Sprague is an innovator off the job as well, which is evident in his affiliation with SPIE. Since joining in the early 1970s, Sprague has served on the SPIE board of directors and has held several leadership offices, including, in 1991, president of SPIE. As president, he had the opportunity to oversee the founding of several SPIE chapters in former Soviet Union countries. "The Soviet Union had just been dissolved," he says, "and a lot of countries behind the iron curtain were trying to make inroads to the West."

To help get them started, SPIE donated a set of SPIE proceedings to Moscow, St. Petersburg (then Leningrad), Poland, and the Czech Republic (then Czechoslovakia). Because Russian scientists couldn't take money out of the Soviet Union, no one could travel to attend SPIE meetings in the states, Sprague notes. "So we set up a system so they could." SPIE chapters held conferences in their country, collected information for the proceedings, and sent it to SPIE headquarters. SPIE published and distributed the proceedings worldwide. Money generated from the sale went into a U.S. bank account to help support chapter activities, including international travel. "Whenever engineers or scientists wanted to come to the United States, we would pay for their airline ticket and travel from this account," Sprague says. "We paid for hundreds of scientists to come to the United States in this manner."

While in Poland, Sprague met Malgorzata Kujawinska, SPIE's 2002 secretary. "I remember sitting at her kitchen table until four in the morning writing down all the action items we needed to get the Polish chapter started," he says. "It was quite an experience." Today the Poland chapter is one of SPIE's strongest international chapters. —Laurie Ann Toupin


Robert Sprague

Robert Sprague is vice president and CTO of Gyricon Media Inc., a spinout of the Xerox Palo Alto Research Center. Robert Sprague is an SPIE fellow and past president. He is currently chairman of the publications committee.