Nowadays, most of the LED technologies are based on the Sapphire substrates. However, the silicon substrate development has begun in earnest for several years. In addition to Cree』s silicon carbide substrate technology, Lattice Power, China chip maker located in Jiangxi, broke through the technology to implement the GaN based LED chip on a silicon substrate. And now the technology is also ready for mass production. The GaN based silicon substrate technology might be one of the most important milestones in semiconductor optoelectronic lightning industry. The technology has the intellectual property protection and has received more than 70 domestic and international patents. At present, sapphire, silicon carbide, and silicon have become three mainstream substrates in LED industry.
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| Lattice Power's silicon based thin film process |
When trying to overcome the research bottleneck of silicon substrate material, mismatch between Lattice constants and mismatch between thermal expansion coefficients might be the most important issues. The mismatch between Lattice constants forms defects on the surface, which leads to absorption of emitting electron hole pair and affect the light efficiency. Besides, the temperature will reach about 1,000 degree during the process, so the mismatch between thermal expansion coefficients will make cracks during the cooling of the material. In 2006, Nanchang University announced associated study which leads to the possible solutions to these two important issues.
In fact, Lattice Power has already had the ability to run mass production. In addition to the production line of 200mm x 200mm backlight device, high brightness lightning LED chip is already in the phase of pilot production. To high brightness products, one LED chip has 100~110lm optical output, which is about 95lm / W or so.
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| High-performance 500 μm and 1 mm chips made from GaN-on-silicon substrates |
In comparison of two technologies, about 95% of the world market use sapphire as a substrate. In recent years, numerous studies focused on the sapphire have made the efficiency of the LED into a single chip 160 ~ 170lm become possible, while the silicon substrate technology have better cost advantages. While MOCVD has a long process time each layer, benefits of using the silicon substrate mainly driven by the easy material supply, mature large-size wafer production technology and synergy of using semiconductor related process and equipment, and the maturity of silicon substrate technology. With silicon substrate technology, semiconductor manufacturers can have a better competition advantage when entering the LED market, such as TSMC. In the near future, silicon substrate technology will get more positive attention.
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