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Tiny LEDs line up in largest array

08 Jan 2003

UK researchers make the world's largest grid of miniature LEDs.

Researchers at Strathclyde University's Institute of Photonics in the UK claim to have fabricated the largest array of gallium nitride microLEDs. The record-breaking array contains 12 288, 20µm diameter emitters arranged in a 128 x 96 array measuring 3.5 x 2.5 mm. The team says these devices will be useful in microdisplays and optical biochips for efficient DNA analysis.

As well as being some 25 times smaller than conventional LEDs, project leader Martin Dawson says that microLEDs also offer several benefits over their larger counterparts. "They are more efficient and have operating speeds of a few hundred picoseconds," he explains. "The array is also a multi-element device where you can control the emitters independently. Conventional LEDs are a single-element emitter technology."

The team process epitaxial multilayer wafers to make the emitters. "We use photolithography and a form of dry etching called inductively coupled plasma etching to pattern the wafer," Dawson told Optics.org. "A mask allows us to pattern more than one array on each wafer. We use laser micromachining to separate the arrays."

Dawson says that this approach results in high-power and efficient emitters. Current power levels are about 0.1 mW per element with an operating voltage of about 3.5 Volts.

To date the researchers have made arrays that emit blue light at 470 nm and are now exploring practical applications. The team has made a prototype alphanumeric monochrome microdisplay. According to Dawson, there is potential to extend this to full color operation by adding a polymer or phosphor material on top of selected elements to shift their emission wavelength.

The researchers are also using their technology to excite fluorescently-marked organic materials. "This is potentially a very compact and quick way to analyse multiple DNA samples," said Dawson. "Instead of scanning one laser source over the samples, you can use a 2D multi-element emitter source to read the information simultaneously."

Dawson and colleagues are now developing 370 nm (violet) and 540 nm (green) devices. They hope to commercialise their technology in 2-3 years.

Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.

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