Micro LED: another important application opportunity of GaN based technology for crystalline silicon substrate

Because of its high resolution, high color saturation, nanosecond response time and low power consumption, Micro LED has become a new generation display technology for Apple, Sony, Facebook, Samsung, LG, OSRAM, Nichia and other international factories.

As the leader of the GaN based LED technology in the global silicon substrate, crystal energy has also recently turned its attention to Micro LED.

The choice of route for Micro LED chip must take into account the cost, yield and compatibility with transfer / bonding process. The larger the size of the epitaxial wafer, the lower the chip cost and the utilization ratio of the epitaxial area, and it is more easily compatible with the IC process to enhance the production efficiency and yield of Micro LED.

According to Fu Yi, vice president of crystal energy, at present, only silicon substrate GaN based LED achieves 8 inch mass production, and the excellent uniformity of wavelength dispersion less than 1nm in 8 inch epitaxial wafers is achieved in monolithic MOCVD cavity, which is very important for Micro LED. Commercial silicon wafers with a size of 12 inch and above have been fully matured. With the introduction of high uniformity MOCVD epitaxial large cavity, it is not essential for LED epitaxy to upgrade to larger circle size.

Fu Yi introduced that the GaN substrate LED on silicon substrate used chemical wet process to remove the substrate technology to obtain LED film chips. This wet stripping avoids the damage to the epitaxial layer of LED, and is very critical to ensure the light efficiency and yield of Micro LED driven by micro current.

As a comparison, the damage of laser ablation on sapphire substrate to GaN epitaxial layer is difficult to avoid, and it is predictably that when the sapphire substrate can be upgraded to a larger size, the challenge of laser peeling off substrate will become more and more challenging. In the process of thin film fabrication, although the LED of SiC and GaN substrate does not need to be stripped by laser, because of the high price of these two substrates (especially large size substrates), it will increase the market competition of Micro LED and OLED.

He pointed out that the structural design of the Micro LED thin film chip is divided into two types: flip chip (the same side double electrodes) and vertical (upper and lower electrodes). For the typical size Micro LED (chip length not more than 10 m), if the same side double electrode structure is used, the positive and negative pole connection can be accomplished by the primary bonding of the backplane. However, the short circuit of the positive and negative electrodes is prone to occur during the bonding process, and the accuracy of the bonding also has great challenges. Compared with the above, the vertical Micro LED of the upper and lower electrodes is more helpful to the bonding yield, but a layer of common cathode (or co solar) transparent electrode is needed.

In a word, whether the back-end process requires the same side double electrode structure or the upper and lower electrode structure, the LED thin film chip fabrication process of large silicon substrate can produce low cost and high yield Micro LED chips accordingly.

Fu Yi believes that low cost, large size and lossless silicon substrate LED technology will strongly promote the development and industrialization of Micro LED.

For the research camp of Micro LED, which is joined by the photoelectric energy, Yi Mei Guang CTO Dr Liu Guoxu commented: "the characteristics of GaN based technology on silicon substrate is the natural choice for making Micro LED chips. The crystal energy has accumulated more than ten years of technology and mass production experience on the silicon substrate GaN base LED field, if it can be transferred to Micro LED, Micro Micro application. It will take a big step forward. "

Perhaps as Liu Guoxu said, Micro LED will be another important application opportunity of crystal energy.

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