The chip is the core component of the LED. At present, there are many LED chip manufacturers at home and abroad, but there is no uniform standard for chip classification. If classified by power, there are high power and medium and small power. If classified by color, it is mainly red, green and blue; Classified by shape, generally divided into square pieces, wafers; if classified by voltage, it is divided into low-voltage DC chips and high-voltage DC chips. In terms of comparison of chip technologies at home and abroad, foreign chip technology is new, and domestic chip production is not heavy.
Substrate material and wafer growth technology are 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), silicon carbide (SiC) substrate materials, zinc oxide (ZnO) and gallium nitride (GaN) are also the focus of current LED chip research. At present, sapphire or silicon carbide substrates are mostly used in the market to epitaxially grow wide-bandgap semiconductor gallium nitride. These two materials are very expensive and are monopolized by large foreign companies, and the price of silicon substrates is higher than that of sapphire and carbonization. Silicon substrates are much cheaper, making larger substrates and increasing the utilization of MOCVD, thereby increasing die yield. Therefore, in order to break through international patent barriers, Chinese research institutions and LED companies began research on silicon substrate materials.
However, the problem is that the high-quality combination of silicon and gallium nitride is a technical difficulty of the LED chip. The technical problems of high defect density and crack caused by the large mismatch between the lattice constant and the 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 of 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 not only reduces the die area, but also eliminates the dry etching step of the gallium nitride epitaxial layer. In addition, silicon has a lower hardness than sapphire and silicon carbide, and it can also save some costs in processing.
At present, the LED industry is mostly based on 2 or 4 inch sapphire substrates. If silicon-based GaN technology can be used, at least 75% of raw material cost can be saved. According to estimates by Japan's Sanken Electric Co., the manufacturing cost of fabricating large-size blue GaN LEDs using silicon substrates is 90% lower than that of sapphire substrates and silicon carbide substrates.
Different chip technologies at home and abroad
In foreign countries, first-class companies such as OSRAM, American Puri, and Japan Sanken have made breakthroughs in the research of large-size silicon-based GaN-based LEDs. Philips, South Korea's Samsung, LG, Japan's Toshiba and other international LED giants have also set off a The research boom of GaN-based LEDs on silicon substrates. Among them, in 2011, Puri developed high-efficiency GaN-based LEDs on 8-inch silicon substrates, achieving luminous efficiency comparable to that of top-level LED devices on sapphire and silicon carbide substrates of 160 lm/W. In 2012, OSRAM successfully produced a 6-inch silicon-on-silicon gallium-based LED.
In contrast, in mainland China, the breakthrough point of LED chip enterprise technology is mainly to improve the production capacity and large-size sapphire crystal growth technology. In addition to the successful mass production of GaN-based high-power LED chips on 2-inch silicon substrate in 2011, Chinese chip companies have no major breakthrough in the research of GaN-based LEDs on silicon substrates. At present, LED chip companies in China are still focusing on production capacity, sapphire substrate materials and wafer growth technology, Sanan Optoelectronics, Dehao Runda, Tongfang Most of the mainland chip giants have also made breakthroughs in production capacity.
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