MORE LIGHT, LESS COST
The high-brightness, packaged LED lighting market is forecasted to reach US$15 billion by 2016. However, significant cost-reduction breakthroughs are needed to allow continued market growth. This is especially crucial in segments such as indoor and residential lighting where, to enable market growth, manufacturers of LED retrofit light bulbs will be required to reduce their selling prices by more than 90 percent between 2010 and 2015.
Aledia is ready to meet these needs with our WireLED™ microwire technology, spun out of CEA-LETI, Europe's largest semiconductor and nanotechnology R&D institute based in Grenoble, France. We are the first company to grow high-density, coaxial gallium nitride (GaN) microwires directly onto large-diameter silicon wafers using processes that are fully compatible with today's CMOS semiconductor foundries. As a result, our next-generation LED chip is inherently low cost – as little as 25 percent of the cost of conventional LED chips – requires very little material to fabricate and is ideally suited for high-volume production using an efficient, fabless business model.
Conventional LEDs are planar, two-dimensional (2D) devices that emit light from a thin material layer at or near their flat surfaces. They typically are made by depositing multiple layers of various materials, each having different thermal expansion and crystal lattice constants, on small wafers with diameters between 2 inches and 6 inches. The vast majority of LEDs are made of GaN and indium gallium nitride (InGaN) material. Depositing high-quality layers of these materials requires the GaN to be grown on substrate wafers that are made of expensive materials such as sapphire, silicon carbide or gallium nitride, as these materials are closely matched to GaN in terms of thermal expansion coefficient and crystal lattice parameters. Building planar GaN LEDs on larger and less expensive wafers made of silicon – a material that is very different from GaN in terms of thermal expansion and crystal lattice constant – is being tried, but to date this approach has shown only moderate cost savings while often incurring high defect densities, lower performance and lower yields. These factors contribute to the high costs of today's LEDs.
In contrast, Aledia's WireLED product technology uses economical silicon wafers with diameters of 8 inches (200 mm) or larger. On each wafer, millions of vertical microwires or microrods of GaN are grown, each with a diameter of less than 1 micron. Each microwire is an LED, capable of emitting light from all sides.
Because Aledia's technology allows the use of larger substrates, the processing cost per individual chip is reduced. The substrate is significantly less expensive than those currently used for 2D LEDs. Very little material is used to form the microwires so the cost of materials is approximately two-thirds less than for planar LEDs. The processing time for the key epitaxy stage is shorter, which reduces the capital investment needed for expensive MOCVD production equipment and, for the rest of the process, only about half the processing steps are required compared to 2D LEDs. And the fact that the WireLED process is fully compatible with manufacturing in existing silicon CMOS semiconductor fabs means that there is access to high-volume, very low-cost manufacturing facilities on a foundry basis without the need for additional dedicated investment. Finally, Aledia's microwire LED chips can be packaged by existing LED chip-assembly lines around the world.
The GaN/InGaN material used in the large majority of today's LEDs only emit light efficiently in the blue part of the spectrum. To obtain white light, phosphor materials are deposited onto the chip. The phosphors absorb blue light and re-emit it in other colors, so that the final result is a chip that emits white light. However, the phosphors significantly reduce (by up to one-third) the efficiency of the LED chip, degrade over time, are expensive and often lead to a different color distribution depending on temperature. It is possible to obtain efficient red LEDs without using phosphors, but this requires using a completely different material structure (aluminum gallium indium phosphide or AlGaInP), which behaves differently from GaN over temperature, again leading to color shifts over temperature.
By contrast, WireLED chips can be designed to contain microwires that emit light over a broad range of different wavelengths, making it possible to produce green or red LEDs using the same material as in industry-standard blue GaN LEDs. This also means that, by incorporating different populations of microwires on the same chip, white-light-emitting microwire LEDs can be made without using phosphors, which are required in manufacturing today's LEDs. The spectrum can thus also be tailored to obtain different types of white light distribution.
Aledia's WireLED microwire technology is leading an LED revolution by providing significant cost savings and performance advantages.
2D (Planar) LEDs:
3D (Microwire) LEDs: