Phosphor trends for LED manufacturing
The phosphor market is largely a game of scale and relationships, as much of the intellectual property (IP) around phosphors was created in the 1970-80s (at least for select element combinations) and protection has by now expired, analysts from Barclays Capital. However, Intertech Pira Phosphor attendees saw some of the top LED makers pursuing phosphor development to improve LED efficiency and color quality.
Phosphor color mixing: Most of the LED industry uses a blue LED die topped with a yellow-phosphor-coated lens for white light emission. Leading LED makers presented new manufacturing approaches, adding a red phosphor to the yellow phosphor to increase the white light quality (the color rendering index [CRI] increases from 67 to 78).
Remote phosphors: Philips introduced a remote phosphor architecture several years ago, wherein the LED die are arranged in a bulb or module topped with a phosphor-coated ceramic plate. This avoids the heat generation, lowered efficiency, and precise match between the wavelength of the die and the composition of the phosphor of putting the phosphor inside the LED package. Remote-phosphor packaged LEDs withstand higher system-level temperatures and enable more flexibility at system-level design -- mixing and matching LED die and phosphor plates to achieve consistent light output and quality.
Remote phosphor plates use more phosphor than standard coated lenses. The presenters at the Intertech Pira Phosphor Summit are working on stacking the phosphors in a remote phosphor plate (i.e. a yellow followed by a red layer) rather than mixing them together.
Silicone encapsulants: The LED industry has traditionally used epoxy encapsulants to seal the LED, despite the materials' tendency to brown with heat exposure. Now, LED makers are switching to silicone encapsulants.
Rare earths: Rare earths compose LED phosphors: terbium, europium, and yttrium. Phosphor is expensive and is increasing in price due to rare earth supply constraints instituted in China, where 95% of rare earth production is concentrated. The industry expects shortages of these rare earths to last through at least 2015. Phosphors account for ~10-15% of rare earth volume end demand. Given expectations for supply tightness and growing demand for LED phosphors as unit shipment continue grow, phosphor prices are likely to continue to move higher. However, phosphors explicitly account for <5% of an LED chip's total cost, higher from a BOM perspective.
Barclays also finds that LED manufacturing and materials patents will soon run out, potentially draining value from material/chip/package suppliers and turning LEDs into commodities. Read that story at http://bit.ly/Hb9kuM ???M.C.
Solid State Technology, Volume 55, Issue 4, May 2012