The Tyndall National Institute in Cork is developing micro LEDs that operate from tiny amounts of power.

"A single pixel is only 15µm across," application specialist Dr Bill Henry told Electronics Weekly. "One of the important things is, we get awful lot of light extracted. We can generate visible light with nanowatts of power. In the dark you will see a little green light at 30nW."

The Institute was created in 2004 by the Irish government and University College Cork to bring together photonics, electronics and networking research in Ireland. It has 350 staff including 10 working towards PhDs. "We expect to expand to 500 over the next 18 months," said Henry.

For the micro LEDs, dubbed FLAME (future lighting applications for miniature emitters), Tyndall is working with the University of Cambridge which specialises in LED materials.

Etching a parabolic structure around a standard LED (green) reduces its emission angle from to the red curve "making it more suitable for many applications which require focused light," said Cork's Tyndal Institute.

The cork group is responsible for the high extraction efficiency. "We etch a parabolic reflector around the light emitting structure," said Henry (see diagram). "The emissive angle of a normal LED is [+/-]60°. We have it coming out at [+/-]25-30° and hope to improve it to [+/-]15° by optimising the shaping process."

Also compared with a standard LED, "we have an extraction efficiency about eight times higher - about 95mW/mm².

Up to 1,000 pixels per mm² can be fabricated claims Henry: "We have technology in the pipeline to address them individually."

The institute is looking at several applications. "It would be very handy for measuring flow in microfluidics," said Henry. "It works by scattering and usually uses lasers. We can produce light very efficiently from the same sort of aperture."

Light from a microLED coupled into a 125µm diameter plastic optical fibre

For flow sensing Tyndall will combine a GaN micro LED and receiver in the same package. "The receiver semiconductor does not need to be so small," said Henry.

Optical fibre coupling is another area of research: the small emissive size coupling well with fibre cores. "One we have aligned the fibre with the LED, the light will go into the fibre. We have a couple of different techniques to align," said Henry. "We are looking for a co-developer for this technology."

As well as the fibre coupling project, Henry also wants a development partner for a security and authenticity application - emissive labels for branded consumer items. "A couple of coin cells will run one of these LEDs for 80 years. In our next iteration, we will look to shape designs for logos. Imagine a flickering shining logo instead of a hologram."

Lastly, the team is investigating its LED for future handheld medical analysers.

See also: Electronics Weekly's roundup of content related to LEDs, with a special focus on both white LEDs and coloured LEDs:

LED technology - White LEDs

LED technology - Coloured LEDs

LED technology - LEDs general