LED makers tackle costs

Electrical engineers who attended school during the early 1970s may be able to recall their first exposure to light-emitting diodes (LEDs). It was often in a circuits lab where the instructor wired up a single LED on a breadboard — mere undergrads were generally not allowed anywhere near the novel and expensive components. Students huddled around the instructor were astounded to see a dim, red light coming from a tiny spot on the circuit board.

Thus were the humble beginnings of solid-state lighting, the vast majority of it comprised of LEDs. Today LEDs continue to get brighter, but the main trends in place for solid-state illumination include a quest for reduced manufacturing costs and initiatives to make over-enthusiastic LED lighting suppliers meet their own published specifications.

It isn’t just developed countries adopting LED illumination. China recently installed more than 10,000 street lights hosting about a million Cree high efficiency LEDs on a highway project in Shenzhen. And like the U.S. and Europe, China is phasing out incandescent bulbs. It is banning the sale of 100-W incandescents starting next October. Sixty watters will get the axe there two years later, 15-W bulbs two years after that.

The market research firm DisplaySearch says lighting installations like those on the Shenzhen highway help explain why the market for LEDs was $7.2 billion last year and is expected to hit $12.7 billion by 2014. China is the biggest market for LED street lighting, thanks to policies of the Chinese government toward infrastructure investment and energy efficiency.

Another market research company, IMS Research, believes LEDs will account for 40% of the total global lamp market by 2013, thanks to longer lifetimes and better energy efficiency. Efficiency is a key in that experts say nearly 20% of the world’s energy resources go toward illumination. The U.S. Dept. of Energy (DoE) estimates that use of solid-state lighting could save between 10.5 and 16.0 quads of energy over the next 20 years. (An energy quad is equal to the average annual per-capita energy consumption of 2.9 million people, or about 16 million barrels of oil.) And these figures do not include energy and cost savings obtained from less maintenance.

Cost conscious
Illumination-grade LEDs are still expensive but their cost is dropping every day. GE Lighting Solutions president Jaime Irick says LED costs have been dropping about 20% annually and thinks the trend will continue. But he figures it will be about 10 years before LED lighting will be able to compete on price with other energy efficient lighting technologies, such as compact fluorescents.

It costs more to fabricate LEDs than ICs occupying the same amount of real estate. One reason is that LED chips are made on smaller wafers and, thus, entail higher handling costs. Most high-volume ICs are cut from silicon wafers that are 300 mm in diameter. In contrast, high-brightness LEDs are made on sapphire wafers, not silicon, and the wafers themselves have diameters about half that at most, with many production processes still using 50-mm.-diameter wafers (about two inches). At least one supplier has demonstrated a 300-mm. sapphire substrate, but not as a production item.

LEDs also use a fabrication process unlike that of ordinary ICs. Metalorganic chemical-vapor deposition (MOCVD) is employed for producing thin films of compound semiconductors, as typically used in LEDs, through chemical reactions on the surface of the substrate. The reactions take place at temperatures above about 800°F at pressures up to about 100 kPa in the absence of oxygen.

LED wafer sizes are rising. The market research firm Yole Développement, Lyon, France says more than 65% of the MOCVD reactors shipped in the latter half of last year were set up for 100-mm.-diameter wafers or larger. The firm expects that for the first time in 2011, 50-mm. wafers will represent less than half of all LED substrates. The firm also thinks this could tighten the supply of sapphire wafers because larger wafers are thicker than their 50-mm. counterparts and tend to produce lower yields. (Volumetrically, a 150-mm. sapphire wafer is the equivalent of seventeen 50-mm. wafers.)