Solid-state lighting as an industry is actually fairly young, with commercial production of white light LEDs first starting less than 20 years ago. Sapphire and silicon carbide are great technologies. We’ve produced billions of LEDs on sapphire substrates. The price of a kilolumen, enough white-light LEDs to generate 1,000 lumens, cost $302 in 2000. By 2011, the price had dropped to $7. Efficacy, a measure of how many lumens (a measure of light) can be generated per watt, rose from 15 in 2000 to 160 last year. We’ve made billions of LEDs on traditional substrates.
Both sapphire and silicon carbide are somewhat exotic, expensive materials. The sapphire used for these wafers isn’t dug out of the ground in Thailand or Australia. It is synthetically grown in labs, but that doesn’t make it any less expensive. These wafers typically only measure two to four inches in diameter.
Enter GaN-on-Silicon. GaN-on-Silicon is a way of growing gallium nitride on good ol’ silicon wafers. By using the same exact material, we can reap the same exact rewards. We devised a breakthrough a few years ago that allows us to grow GaN-on-Silicon wafers. Toshiba has announced plans to make them too. Other manufacturers are eyeing similar concepts.
Let me run through some numbers. By switching from sapphire to silicon wafers, the wafer size jumps from two or four inches to eight inches. Each time you migrate in diameter, you dramatically expand the surface area of the wafer. Think Pi R squared. A two-inch wafer has 3.14 square inches of surface area. A four-inch wafer has a surface area of 12.56 square inches (2 x 2 x 3.14). But an eight-inch wafer has a surface area of over 50 square inches (A four-inch radius squared times Pi).
Osram says its silicon-based white LEDs produce 127 lumens for each watt of power, with a power efficiency of 58 percent, comparable to state-of-the-art commercial LEDs grown on sapphire. Peter Stauss, a project manager at Osram, says researchers are now testing and optimizing the devices, and expect to start selling them in the next two to three years.
Osram joins a few other companies in the race to bring cheaper gallium-nitride-on-silicon LEDs to market. China’s Lattice Power claims to have already started commercial production using the same technique. Last month, California startup Bridgelux announced that it has teamed up with Toshiba to make LEDs on silicon. Meanwhile, U.K.-based Plessey Semiconductors plans to produce gallium-nitride-on-silicon LEDs by the end of this year using technology acquired from Cambridge University spinoff CamGaN. Philips and Samsung are also said to be pursuing the silicon approach.
Osram has not said how much cheaper its new LEDs will be, but Bridgelux and Plessey both claim that the silicon approach could cut LED production costs by 75 percent or more. Bridgelux also predicts that its process could bring the cost of a 75-watt equivalent LED lightbulb, which now costs $40, down to under $5.
Compared to sapphire, it’s easier and cheaper to make large-diameter silicon wafers, which cuts cost. Another appealing reason to switch to silicon is to take advantage of existing machines that are used to fabricate silicon computer chips. Bridgelux has already demonstrated devices grown on 20-centimeter-wide silicon wafers.
The challenge with growing gallium-nitride on silicon is that the two materials expand and contract at different rates. LEDs are made at high temperatures, and when the materials are cooled, the light-emitting gallium-nitride layer cracks because of tension with the silicon underneath
Aledia progresses on microwire-based silicon LEDs, announces funding
27 Mar 2013
Startup makes LEDs on 8-in silicon substrates using microwire technology and has received a EUR 10 million investment to commercialize the technology.
Aledia has announced that it has successfully transferred its microwire gallium-nitride-on-silicon (GaN-on-Si) LED technology to 8-in (200-mm) silicon wafers and is now pushing forward to commercialize the technology. The company also said it received EUR 10 million ($13 million) in first-round financing during 2012, and is using those funds to pursue the microwire technology that it believes will be a disruptive force in the solid-state lighting (SSL) world.
Grenoble, France-based Aledia is using technology originally developed during a six-year period at the LETI-CEA research laboratory in Grenoble. Subsequently, Aledia secured the exclusive IP rights to the CEA research as it applies to the use of microwires in lighting.
Aledia believes it can ultimately reduce the cost of LED manufacturing by a factor of four. The microwire technology is used to build 3D structures that will allow a greater density of LED chips per wafer. And the use of 8-in silicon substrates means that the back end of the manufacturing process can utilize fully-depreciated CMOS IC foundries.
"Since our financing last year, we have scaled up our microwire manufacturing process and transferred it to 8-inch (200mm) silicon wafers,' said Giorgio Anania, Aledia co-founder, president and CEO. "We can now push forward to optimize the performance of these products and bring them to market."