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​Talking about LED Technology part 3


Chip bonding technology

Optoelectronic devices have certain performance requirements for the required materials, and usually require a large bandwidth difference and a large change in the refractive index of the material. Unfortunately, there is usually no natural material. Homogeneous epitaxial growth techniques generally cannot produce the required bandwidth difference and refractive index difference. Using conventional heteroepitaxial techniques, such as epitaxially growing GaAs and InP on a silicon wafer, are not only cost-intensive, but also interface-bound. Meta-error density is also very high, it is difficult to form high-quality optoelectronic integrated devices. Since the low-temperature bonding technology can greatly reduce the thermal mismatch between different materials and reduce stress and dislocation, high-quality devices can be formed. With the gradual understanding of the bonding mechanism and the maturation of the bonding process technology, it has become possible to bond the chips of many different materials to each other, and thus it is possible to form some special-purpose materials and devices. A new structure can be formed by forming a silicide layer on a silicon wafer and then bonding. Due to the high conductivity of the silicide, it can replace the buried layer in bipolar devices, reducing the RC constant.

 Laser Stripping Technology (LLO)

Laser lift-off technology (LLO) is the use of laser energy to decompose the GaN buffer layer at the GaN/sapphire interface to separate the LED epitaxial wafer from the sapphire substrate. The technical advantage is that the epitaxial wafer is transferred to a high thermal conductivity heat sink, which can improve the current spreading in large-size chips. The n-plane is the light-emitting surface: the light-emitting area is increased and the electrodes are light-blocked, which facilitates the preparation of the microstructure and reduces the etching, polishing, and dicing. What's more important is that the sapphire substrate can be reused.