Cheaper LEDs

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Rogers says the method should be cheaper than conventional methods for printing inorganic LEDs because it requires less of the expensive semiconducting materials. Using the chemical etching and stamping techniques, it's possible to make each individual LED smaller. "The materials cost is a significant component of the final cost, so you have to use the minimum amount," says Rogers. LEDs made using conventional sawing techniques range are about a half a millimeter per side. But because they're bright, these LEDs can be much smaller and still provide the same display resolution. "To light a 100-micrometer pixel, you only need a 5-micrometer LED because to your eye, it looks the same," says Rogers.

The researchers have so far demonstrated the printing process for red LEDs made from gallium arsenide. Rogers says that the same approach can be used to make other colors of LEDs using different materials. "Conceptually it's the same process," he says. Rogers says he has also used the method to make blue LEDs using nitrides, though this work has not yet been published.

"These are conventional LEDs made by an unconventional process," says Colaneri. If Rogers and his coworkers can "demonstrate that this dramatically reduces the cost," he says, then "this is a potential competitor with OLEDs, though it's far from proven."

Rogers says the university is in talks with recently formed Canadian start-up Cool Edge to license the printing method and expects the first applications to be in lighting. Existing LED lightbulbs cost $30 to $100 for a single fixture, says Steven DenBaars, professor of materials science and co-director of the Solid-State Lighting Center at the University of California, Santa Barbara. "We've got to reduce the costs," he says.