To cut LED lighting costs, Bridgelux rides silicon

Company says it has demonstrated the production of LED light chips on silicon, an effort that could ultimately result in cheaper energy-efficient light fixtures.

To get the same economics of the computer semiconductor industry, the LED lighting world needs to start manufacturing on the same equipment, says Bridgelux CEO Bill Watkins.

The LED light source maker said today that it demonstrated the production of LED light chips on silicon, a transition that will cut production costs by 75 percent and ultimately result in cheaper, energy-efficient light fixtures. Bridgelux intends to start making LEDs, which will be fitted into bulbs made by other companies, with the process in two or three years.

An 8-inch gallium nitride on silicon wafer.
An 8-inch gallium nitride on silicon wafer. Bridgelux

Light fixtures with LEDs use semiconductors made by growing Gallium nitride (GaN) on a substrate of sapphire or silicon carbide. Using GaN on silicon, Bridgelux engineers have been able to get the same light quality and comparable efficiency to today's commercial products, the company said.

Silicon Valley-based Bridgelux is now making its LEDs on 2-inch and 4-inch wafers. But the silicon process technology will allow it to get higher yields by contracting with silicon chip makers, which will lower production costs.

"We can partner with a semiconductor company to take advantage of their fully depreciated fab and manufacture at 8-inch scale, which you probably can't do on sapphire, with very minor tweaking to existing machines," Watkins said. "That's why the semi companies are all over this space--they want to put this on silicon."

Bridgelux has been able to get about 135 lumens per watt, which is about what the efficiency of GaN was on sapphire two to three years ago. For a light bulb with the color temperature of a typical halogen, that translates to about 85 lumens per watt, said Jason Posselt, the vice president of marketing.

General lighting play
Researchers for years have tried to put GaN on silicon, but there are challenges in making the two materials work together, notably the differences in thermal expansion. One of the common problems is defects or cracks that occur on the chip.

Rather than a single breakthrough, Bridgelux engineers have made a few changes to the manufacturing process, Posselt said. There still are engineering challenges, but the company is confident it can make the transition to GaN on silicon.

The move to silicon, which other companies are pursuing, could significantly knock down the price of LEDs for general lighting, since the LED light sources are about half the cost of a consumer bulb, said Posselt.

Because they are efficient and controllable, LEDs are already being adopted by retail outlets and other commercial customers. In the past year, LED bulbs designed for home use have come out as well, but at significantly higher prices than traditional bulbs.

There are 40-watt and 60-watt equivalent LED bulbs sold at large retail outlets, such as Home Depot and Lowes, with prices in the range of $18 to about $40. Lighting manufacturers expect prices to go down steadily for the LED bulbs, some of which are rated to last 25 years and are far more efficient than incandescent bulbs. But in the near term, the purchase price will still be higher than existing technologies.

Moving to a cheaper manufacturing process, coupled with ongoing efficiency improvements of GaN, will help push LED lighting into general lighting based on purchase cost, Posselt said. Watkins, the former CEO of disk driver maker Seagate, said the manufacturing technology means LED companies can lower prices faster.

"The quantity and quality of light you can now get out of an LED source has really dramatically improved," Watkins said. "Now the issue is cost and how to get the cost lower."

 

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