Micro LED: Another major application opportunity for GaN-based technology on Crystalline Optoelectronic silicon substrates

Due to its advantages of ultra-high resolution, high color saturation, nanosecond response time and low power consumption, Micro LED has become a new generation of display technology that Apple, Sony, Facebook, Samsung, LG, OSRAM, Nichia and other international manufacturers are vying to deploy.

As the global leader in GaN-based LED technology on silicon substrates, Crystalline has recently set its sights on Micro LEDs.

The choice of micro LED chip route must take into account cost, yield, and compatibility with the transfer/bonding process. The larger the epitaxial wafer size, the more likely it is to reduce the chip cost and improve the utilization rate of the epitaxial area, and it is easier to be compatible with the IC process to improve the production efficiency and yield of Micro LED.

Fu Yi, vice president of Jingneng Optoelectronics, said that at present, only GaN-based LEDs on silicon substrates have achieved 8-inch mass production, and excellent uniformity of wavelength dispersion less than 1nm in 8-inch epitaxial wafers has been achieved in a single MOCVD cavity, which is very important for Micro LED. Commercial silicon wafers of 12 inches and above have fully matured, and with the introduction of high-uniformity MOCVD epitaxial large cavities, there is no inherent difficulty in upgrading silicon substrate LED epitaxy to larger wafer sizes.

Fu Yi introduced that the silicon substrate GaN-based LED uses a chemical wet removal substrate process to obtain LED thin film chips, which avoids the damage to the LED epitaxial layer, which is very critical to ensure the luminous efficiency and yield of Micro LEDs driven by small currents.

As a comparison, the damage to the GaN epitaxial layer caused by laser peeling of sapphire substrates is unavoidable, and it is foreseeable that when sapphire substrates can be upgraded to larger sizes, laser peeling substrate yields will become more and more challenging. Although SiC and GaN substrate LEDs do not require laser stripping in the thin-film chip manufacturing process, the extremely high price of these two substrates (especially for large-size substrates) will increase the competition between Micro LED and OLED markets.

He pointed out that the current structural design of Micro LED thin-film chips is divided into flip (double electrodes on the same side) and vertical (upper and lower electrodes). For micro-LEDs of typical size (chip edge length of less than 10 μm), if the two-electrode structure on the same side is adopted, the positive and negative electrodes can be connected with the control backplane in a single bond, but the positive and negative electrodes are prone to short circuits during the bonding process, and the bonding accuracy is also very challenging. In contrast, thin-film vertical Micro LEDs with upper and lower electrodes are more conducive to bonding yield, but a layer of common cathode (or common anony) transparent electrodes needs to be added.

In short, regardless of whether the back-end process requires the same side dual electrode structure or the upper and lower electrode structure, the large-size silicon substrate LED thin film chip manufacturing process can correspondingly produce low-cost and high-yield Micro LED chips.

Fu Yi believes that the low-cost, large-size, non-destructive peelable silicon substrate thin film LED process will strongly promote the development and industrialization of Micro LED.

Dr. Liu Guoxu, CTO of Crystalron Optoelectronics, commented: "The characteristics of GaN-based technology on silicon substrates are a natural choice for manufacturing Micro LED chips, and Crystallight has accumulated more than ten years of technology and mass production experience in the field of GaN-based LEDs on silicon substrates. ”