Bridgelux hits 160 lm/W in lab

Bridgelux hits 160 lm/W in lab

9 Aug 2011
Using gallium nitride on 8-in silicon wafers, Bridgelux is achieving LED efficacy in the lab on par with LEDs produced on sapphire or silicon-carbide wafers.
Bridgelux announced that it has fabricated LEDs in the lab using gallium-nitride-on-silicon (GaN-on-Si) technology that delivers 160 lm/W (cool white) and 125 lm/W (warm white) efficacy.
The performance realized using 8-in wafers is similar to the best efficacy demonstrated in the lab by leading LED vendors using traditional sapphire or silicon carbide wafers, and Bridgelux believes the GaN-on-Si approach will ultimately yield a "75% inmrovement in cost" for LED components that will in turn reduce the cost of solid-state-lighting (SSL) lamps and luminaires.
The new LEDs deliver a cool-white CCT of 4350K and a warm white CCT of 2940K. The warm white devices have a CRI of 80. The company said that its 1.5-mm blue LEDs can deliver wall-plug efficiency as high as 59% at 350 mA – and says that exceeds any published values from other vendors. The company also claims waveform uniformity of sigma 6.8 nm with a median wavelength of 455 nm.

Getting from the lab to production
Of course the Bridgelux announcement is focused on lab prototypes and production is perhaps two years away. Still it shows progress. Back in March, the company announced the demonstration of 135 lm/W LEDs. Since, the company was able to both boost efficacy considerably and demonstrate that performance on 8-in substrates that are, in large part, a key to lower-cost components.
Bridgelux VP of global marketing Jason Posselt said, "It‘s important that we demonstrated this on an 8-in wafer." Posselt also believes that Bridgelux has largely closed the performance gap relative to sapphire-based LEDs. Bridgelux‘s silicon-based LEDs appeared to be 12 to 18 months behind state-of-the-art LEDs in terms of efficacy at the public launch of the company‘s GaN-on-Si program.
But Posselt acknowledged the challenge that remains in terms of commercializing the technology. The company is building wafers that yield as many as a thousand good die now and ultimately they need to produce 20,000 good die on an 8-in wafer.
Silicon cost advantages
The allure of silicon-based LEDs is purely cost and the savings come in two primary areas. First, the semiconductor industry has the proven ability to manufacture low-cost large silicon wafers. Silicon would both lower baseline wafer cost and pave a smoother transition to larger wafer sizes. Long Yang, vice president of chip technology at Bridgelux, noted that you can get the equivalent number of LEDs from 3 8-in silicon wafers that you get from 42 2-in sapphire wafers today.
The second set of savings come in the back-end of the manufacturing process where fully-depreciated, and fully-automated silicon fabs stand ready to fabricate LEDs. Posselt said "Typical LED fabs are very labor intensive, and not automated like silicon fabs." And those automated fabs are ready to handle 8-in wafers and the far greater number of die on those wafers.
Of course there are technical challenges that stand in the way of a silicon transition as well as