LED industry continues to resist GaN-on-Si solutions
“GaN-on-Si technology appeared naturally as an alternative to GaN-on-Sapphire, the main stream technology for LED applications. Today, despite potential cost benefits, the mass adoption of GaN-on-Si technology for LED applications remains unclear,” explained Dr Hong Lin, Technology & Market Analyst, Compound Semiconductors & Power Electronics at Yole Développement.
In a report entitled ‘GaN on Silicon Substrate Patent Investigation’ Yole and KnowMade details the technological challenges and known solutions facing the technology and conclude that although most major LED makers have a patenting activity related to GaN-on-Si technology, so far, few have made it the core of their strategy and technology roadmap.
Rather than being welcomed by the LED industry, Yole Développement and KnowMade is forecasting that GaN-on-Si is more likley to be widely adopted by power electronics and RF applications because of its lower cost and CMOS compatibility.
The growth of GaN-on-silicon substrate was first reported in the early – 1970s (T. L. Chu et al., J. Electrochemical Society, Vol. 118, page 1200), since the early 1990s more and more academics and industrials have been involved in developing this technology. GaN-on-Si technology is now poised to tackle a list of
technical challenges. The high lattice mismatch between GaN and Si results in a high defect density in epitaxial layers (dislocations). The high thermal expansion coefficient (TCE) mismatch between GaN and Si leads to a large tensile stress during cooling from the growth temperature to room temperature. The tensile stress causes film cracking and a concave bending of the wafer (warpage). These factors combine to make both dislocation density and crack/warpage reduction a challenging task.
”The patents addressing the challenges have been selected, and an in-depth analysis of patent holders and corresponding patented technologies is provided. This report does not include patents related to active layers or GaN-based devices,” explained Dr Nicolas Baron, CEO & Co-founder, KnowMade.
Fundamental patents describing a gallium-nitride-based compound semiconductor grown on a silicon substrate were filed before the 1990s with the most significant assigned to TDK and Fujitsu. In the early 1990s, Toyoda Gosei and the University of Nagoya filed the first concepts of a buffer layer for improving the crystallinity of GaN. Those fundamental patents have been followed by an ever increasing number of applications since 1995 as more companies competed in GaN-on-Si technology to meet the technological challenges, the market demand and to lower manufacturing costs.
Currently, the patented technologies reflect the significant improvements that have been made on key material issues such as dislocation density reduction and stress management for preventing cracks and warpage of the wafer.
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