Currently, more than 80 percent of light-emitting diodes (LEDs) for both electronics and energy-efficient LED or solid-state lighting are manufactured using sapphire substrates as the platform for the chip. According to analyst firm Canaccord Genuity, LEDs account for 40 percent of the bill of materials for LED light bulbs, thus being the most expensive component. In order to make LED lighting more affordable compared to compact fluorescents and other options, it is necessary to produce them with larger diameter sapphire wafers, well beyond the current 2 to 4-inch size.
A French market research firm, Yole Developpément, recently predicted that the proportion of LEDs made on 6-inch sapphire substrates will increase to 16 percent in 2012 and more than 55 percent in 2015. Initial evaluation of 8-inch wafers at the research and development level is already underway at several LED chipmakers.
By transitioning to larger wafers, companies are able to incorporate more LED chips along the outer perimeter due to reduced curvature, especially important for larger high-brightness LEDs dedicated to lighting applications. Interestingly enough, the surface area of a 6-inch wafer is nine times that of a 2-inch wafer; however, it offers enough real estate for over ten times as many chips.
Fabrication of LEDs on larger substrates also provides the benefit of more efficient film deposition during the manufacturing process. In specific, each coating step in a reactor can cover a larger substrate area used to produce more LED chips. A recent study by an industry leading equipment-maker for LEDs, Aixtron, reported that tool throughput increases by 52 percent if a platter in a MOCVD tool, used for growing single crystal thin-film layers, is filled with just seven 6-inch substrates versus 42 2-inch substrates, whether they are typical sapphire or the alternative of gallium nitride. Similar trends have been recognized and executed in the semiconductor industry, which commonly utilizes 12-inch silicon substrates for high-performance microchips. As a result, common equipment and workforce expertise concerning this larger wafer size in general already exists on the market, which can be dedicated to LEDs as well.
The bottleneck in the whole process is obtaining the same quality of sapphire at the larger wafer size, which is vital for enabling the transition. LED makers require substrates that are flat, uniformly polished, and have an essentially atomically-clean surface that is free of particulates. Moreover, LED chipmakers need sapphire substrates to be essentially stress- and crack-free, which can be difficult to achieve during growth, which occurs at temperatures up to 1200°C.
Nonetheless, the game is on for making energy-efficient LED lighting more affordable for consumers, and anticipated consolidation across the industry and the high overall barrier-to-entry will help facilitate this transition.
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