Toshiba and US-based Bridgelux will reportedly start volume production of 8-inch Si-substrate GaN wafers for use to make LED chips in the first quarter of 2013, according to Taiwan-based makers. However, president Jacob Tam for TSMC Solid State Lighting (SSL), a wholly owned subsidiary of Taiwan Semiconductor Manufacturing Company (TSMC), indicated that it is difficult for 8-inch Si-substrate GaN wafers to replace sapphire wafers to become mainstream LED material because the former's manufacturing process is complicated and brightness of LED chips is lower.
LED chips made from 8-inch Si-substrate GaN wafers are claimed to be 50% lower in cost than LED chips made from sapphire wafers, posing competitive pressure on makers of LED chips using sapphire wafers, these Taiwan-based makers indicated.
While some China- and Taiwan-based LED makers have undertaken R&D of 8-inch Si-substrate GaN wafers, none have overcome technological barriers, Tam pointed out. It is worthwhile to keep an eye on results of R&D jointly done by Toshiba and Bridgelux, but the report that it has a much lower cost of 8-inch Si-substrate GaN wafers than that of sapphire wafers is questionable, Tam indicated.
Although TSMC SSL has adopted Si substrates, it uses a different manufacturing process, Tam said. The luminous efficiency of LED chips produced by TSMC SSL is competitive with that for international vendors such as Cree and Japan-based Nichia, Tam pointed out. TSMC SSL provides a total solution from LED epitaxial wafers, chips, packaging to optical engines, with volume production beginning in the third quarter of 2012 and output expected to be double in 2013, Tam noted.
In addition, chairman Lee Biing-jye for Taiwan-based LED maker Epistar indicated that yield rates for Si-substrate GaN wafers are still low and Epistar is developing production technology for breakthrough.
