Menlo Park, Calif.-based Kateeva Inc. unveiled Yeildjet, technology to manufacture OLED displays using ink-jet printing, at Printed Electronics 2013, Nov. 20-21 in San Jose, Calif.

Kateeva’s Yieldjet tool manufactures OLED displays using ink-jet printer techniques.
(Source: Kateeva)

Today, OLEDs are manufactured in a vacuum chamber using shadow masks to deposit the organic materials, which is wasteful of materials and adversely affects yields as stray particles are generated when masks are changed.

“Up to 90 percent of the deposited material is wasted,” says Madigan. “And even a one-micron-sized particle can destroy a pixel.”

Ink-jet printing, on the other hand, deposits material only where needed, thus being more economical of raw materials. Yieldjet also produces fewer stray particles, thus boosting yields by as much as 10 times, according to Kateeva, by producing fewer particles to begin with, and capturing any particles that are produced before they cause a problem.

Samsung concept smartwatch using a flexible OLED display.
(Source: Samsung)

The second major concern of OLED manufacturers is the lifetime of the displays, which are adversely affected by the oxygen and moisture in air. Traditionally, a vacuum chamber is used for deposition, thus isolating the materials from oxygen and moisture. Ink-jet printers, on the other hand, cannot print in a vacuum, leading other ink-jet printer makers to operate in air, thus exposing the delicate organic films to oxygen and moisture during manufacturing — adversely affecting the lifetime of OLEDs.

“Printing in air inherently lowers device quality,” says Madigan.

To solve that problem, Kateeva isolates its printer in a nitrogen environment during manufacturing, which it claims up to doubles the lifetime of OLED displays manufactured by its Yieldjet.

The third key problem Kateeva claims to have solved is print uniformity. Anybody who has used an ink-jet printer is familiar with the banding problem when jets get clogged — a problem what would be disastrous for yields when manufacturing OLED panels. However, Kateeva claims to have solved this problem by borrowing from the lessons learned on graphics ink-jet printing presses.

“We’ve adopted the algorithms used in the graphics arts industry to average out the non-uniformity they get from nozzles, and adapt them to OLED manufacturing,” says Madigan. “We also directly monitor all of the nozzles that are printing in our system so that we have accurate information about the volume of each drop coming out of each nozzle at all times. Then we layer on top of that algorithms that make us much more tolerant of variations.”

Yieldjet is a Gen-8-sized printer, handling OLED panels up to 2,500 by 2,200 millimeters (98 by 86 inches) with smaller models available for flexible displays. Kateeva claims to already have customers for its Yieldjet, and that displays manufactured using them will begin appearing in 2014.

— R. Colin Johnson, Advanced Technology Editor, EE Times

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