The chip is the core component of LED. At present, there are many LED chip manufacturers in China and abroad, but there is no unified standard for chip classification. If it is classified by power, there are high power and small and medium power; if it is classified by color, it is mainly red, green, and blue; The shape classification is generally divided into two kinds of square slices and round slices; if it is classified according to voltage, it is divided into low voltage DC chips and high voltage DC chips. In terms of the comparison between Chinese and foreign chip technologies, foreign chip technologies are new, while China's chip output is not important.
Substrate material and wafer growth technology become key
At present, the key to the development of LED chip technology lies in substrate materials and wafer growth technology. In addition to traditional sapphire, silicon (Si), and silicon carbide (SiC) substrate materials, zinc oxide (ZnO) and gallium nitride (GaN) are also the focus of current LED chip research. At present, most of the market uses sapphire or silicon carbide substrates to epitaxially grow wide bandgap semiconductor gallium nitride. These two materials are very expensive and are monopolized by large foreign companies. The price of silicon substrates is higher than that of sapphire and carbonized Silicon substrates are much cheaper, and larger substrates can be made to increase the utilization rate of MOCVD, thereby improving the yield of transistors. Therefore, in order to break through international patent barriers, Chinese research institutes and LED companies started to study from silicon substrate materials.
But the problem is that the high-quality combination of silicon and gallium nitride is the technical difficulty of LED chips. The high density of defects and cracks caused by the huge mismatch between the lattice constant and thermal expansion coefficient of the two have long hindered the chip field. development of.
Undoubtedly, from the perspective of the substrate, the mainstream substrate is still sapphire and silicon carbide, but silicon has become the future development trend in the chip field. For China, where the price war is relatively serious, the silicon substrate has more cost and price advantages: the silicon substrate is a conductive substrate, which can not only reduce the die area, but also eliminate the dry etching step of the gallium nitride epitaxial layer In addition, the hardness of silicon is lower than that of sapphire and silicon carbide, which can also save some costs in processing.
At present, the LED industry is mostly dominated by 2-inch or 4-inch sapphire substrates. If silicon-based GaN technology can be used, at least 75% of the raw material cost can be saved. According to the estimation of Japan Sanken Electric Company, the manufacturing cost of using silicon substrates to make large-size blue gallium nitride LEDs will be 90% lower than that of sapphire substrates and silicon carbide substrates.
The difference between Chinese and foreign chip technology
First-class companies such as Osram, BRIDGELUX, and SAMCO INC have made breakthroughs in the research of large-scale silicon-based GaN-based LEDs. Philips, Samsung, LG, Toshiba, and other international The LED giant also set off a wave of research on GaN-based LEDs on silicon substrates. Among them, in 2011, Bridgelux developed a high-efficiency gallium nitride-based LED on an 8-inch silicon substrate, and achieved a luminous efficiency of 160lm / W comparable to the performance of top-level LED devices on sapphire and silicon carbide substrates. ; In 2012, Osram successfully produced a 6-inch GaN-based LED with silicon substrate.
In contrast, the breakthrough point of LED chip enterprise technology in China is mainly to increase production capacity and large-size sapphire crystal growth technology. In addition to the successful production of 2-inch silicon substrate gallium nitride-based high-power LED chips by Jingneng Optoelectronics in 2011, China Chip companies have made no major breakthroughs in the research of GaN-based LEDs on silicon substrates. At present, Chinese LED chip companies are still focusing on production capacity, sapphire substrate materials and wafer growth technologies. Most chip giants have also made breakthroughs in production capacity.
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