Ductile displays yield flexible photolithography

07/01/2003

By Mark A. DeSorbo

What sounds like an all too familiar paperboy problem is actually the concept behind E Ink. Corp.'s flexible electronic-ink display screen, a giant step toward changing the way the world receives information and even how substrates are fabricated.

From the confines of its ISO Class 4 and ISO Class 6 cleanrooms, E Ink has unveiled a super-thin substrate that is just 0.012 inch thick, which the young company says will also pave the way for wearable computer screens and smart identity cards.

Michael McCreary, vice president of research and development, says the display, the next generation of an existing E Ink technology, consists of two components. The front portion switches according to electronic signals and the back component is a circuit made of transistors that control each individual pixel that composes the display.

Each pixel needs a circuit, made of transistors, behind it to function. In order to make electronic paper the transistors have to be made on a very thin and flexible substrate.

"The first generation was a thin film transistor with a traditional glass backing, which is rigid," McCreary explains. "This display is made with a metal foil back pane, which is about three-tenths of a millimeter, five to 10 times thinner than a tradition liquid crystal display."

The other integral part of the display, he says, is the electronic ink, which is made up of millions of tiny microcapsules about the diameter of a human hair. Each microcapsule contains positively charged white particles and negatively charged black particles, which are suspended in a clear fluid.

When a negative electric field is applied, white particles move to the top of the microcapsule where they become visible. This makes the surface appear white at that spot. An opposite electric field pulls the black particles to the bottom of the microcapsules where they are hidden. By reversing this process, the black particles appear at the top of the capsule, making the surface appear dark at that spot.

That's why trips to newsstand and daily newspaper delivery will no longer be necessary because with e-paper the latest headlines can be refreshed wirelessly or through the Internet.

"It's the closest thing demonstrated today to electronic paper," Yu Chen, an electrical engineer at E Ink and a visiting scientist at Princeton University in New Jersey, told Reuters.

Chen, who reported the research in the science journal Nature, says the size can vary from a business card to a computer screen. The current device is too thick to be folded in half but Chen and his team are working on a thinner a version.

"When it is fully developed e-paper will look and perhaps feel like paper, but powered by wireless or Internet-based technology to display black and white and color text," McCreary adds.

E Ink, he says, has been talking with "potential partners" to ramp up production of is flexible electronic-ink displays.

"It would involve building a new facility, and converting a factory, modifying the equipment to handle a flexible substrate," McCreary says. "That opens up all kinds of design opportunities for the final product."

While the technology is "ready to go," commercialization of the first-generation, glass-back version is still in the infancy stage.

Last May, E Ink, along Dutch electronic giant Philips showcased a working prototype of electronic paper at the Society for Information Display Exposition and Symposium in Baltimore.

The prototypes were shown in a book-like, dual-screen case designed by Philips, with a display that features a resolution at 160 pixels per inch. Toppan Printing Co. Ltd. (Japan) laminated the ink portion of the device to the thin-film back pane.