Rubicon Technology to ease LED manufacture by ramping patterned sapphire substrate production and more. Compound Semiconductor reports.

Patterned substrates: Rubicon is ramping up sapphire substrate patterning at its Malaysia plant.

While industry players debate whether silicon or sapphire is the best foundation for the GaN LED, US sapphire substrate manufacturer, Rubicon Technology, has sold $28.2 million of common stock to fund expansion.

Developing sapphire substrate fabrication for LEDs is high on the company's investment list, chief financial officer, Bill Weissman, tells Compound Semiconductor. And plans are underway to do this soon.

The company will first extend sapphire substrate patterning facilities. Etching a nano-pattern onto the sapphire wafer eases epitaxial growth and reduces the light reflected back into the LED from the polished surface, boosting light output.

But according to Weissman, LED chip manufacturers are becoming more and more interested in outsourcing this production step. "We're seeing a real trend here," he says. "So a lot of the money we are raising is going into the expansion of our LED patterning operation.

The company started supplying 4 and 6 inch patterned sapphire substrates last year - Weissman reckons only Rubicon offers 6 inch wafers - and will now triple capacity in its existing cleanroom at its fabrication facility in Penang, Malaysia. Then, if demand for patterned sapphire substrates continues, construction of additional polishing and patterning facilities to this plant could follow by the end of the year.

"We don't think chip manufacturers are going to shut down their internal patterning operations, but we do think they will stop investing and expanding those capabilities, and so will outsource more and more," he says.

At the same time, Rubicon is eyeing other LED opportunities, including aluminium nitride on sapphire templates. Here the company would deposit an AlN layer onto its patterned 4 and 6 inch sapphire substrates, onto which chip manufacturers could then directly grow GaN layers.

Kyma, for one, has demonstrated 10 inch diameter AlN on sapphire templates for LED growth and alongside the likes of Azzuro Semiconductors and Translucent, is also working on 300mm (12 inch) AlN on silicon templates.

"Templates could be a next potential step downstream for us," says Weissman. "The jury is still out on whether chip manufacturers are interested in this product - issues include contamination for example - but this is something we're looking at as an additional product within the LED market."

Silicon rivals

But while Rubicon executives grow their LED materials empire aren't they concerned about a potential industry transition from sapphire to silicon substrates?

Only late last year, business analyst IHS, forecast that come 2020, GaN-on-silicon LEDs will increase market share from today's 1 percent to 40 percent, mostly at the expense of GaN-on-sapphire devices. This forecast lies at the extreme end of the predictions for silicon success, but nonetheless indicates a rising interest in growing LED structures in depreciated CMOS facilities.

But Weissman says the company isn't worried and he doesn't expect GaN-on-sapphire LEDs to lose market share to silicon-based alternatives in the near future. Many organisations have been developing methods to circumvent the dramatically different GaN and silicon coefficients of thermal expansion, but he asserts: "No-one has really demonstrated a solution that works well in the production of high brightness LEDs."

"Toshiba recently bought Bridgelux but to my knowledge is not selling any meaningful volumes into the high brightness LED market," he adds. "I think in time we may see some of the LED market convert to silicon substrates but this is years away and will probably only be for a limited market."

In the meantime, Rubicon will continue to build its product base. Since its inception in 2001, the company has focused on developing a highly vertically integrated business for a range of markets. From processing of alumina to wafer polishing, and now patterning, Rubicon claims to have the most vertically integrated business model in the sapphire industry.

But its not all about LEDs. Right now, the company is developing large rectangular optical sapphire windows for defence and medical applications and exploring how to cut the costs of sapphire cover glass for smartphone camera lenses and other applications.

Still, LEDs remains its number one market. "MOCVD tool utilisation rates are now very high and LED manufacturers want to find ways to extend throughput without extending footprint; moving to larger substrates is a great way to do this," says Weissman.

"We believe strongly that LED manufacturers are going to move to 6 inch substrates soon," he adds. "We've always had a strong leadership in larger diameters and I think we're going to reap the benefits of this in the next few years."