Research On Local Laser Annealing Process Of Amorphous YIG Thin Films

With the development of silicon-based optoelectronic technology,silicon photonic chips have put forward urgent requirements for the heterogeneous integration technology of optoelectronic materials.Magneto-optical materials,such as yttrium iron garnet films doped with rare earth elements,have the characteristics of high Faraday rotation angle and low loss,and have been widely studied and applied in optical isolators.Although the material can be directly integrated on the device by wafer bonding and direct deposition,the material still requires a high annealing temperature(>500 ℃)to achieve thin film crystallization.The source silicon photonics chip will produce irreversible damage,so it is not compatible with the CMOS back-end process.Aiming at the incompatibility between YIG and Ce:YIG materials and CMOS backend technology,this thesis uses laser annealing to locally heat and crystallize the materials,and mainly studies the influence of laser annealing process on the structure and properties of YIG and Ce:YIG films,and also studies the influence of laser annealing process on the transmission loss of films on waveguides,and confirms the transmission loss of films on micro-ring devices.The main research contents and conclusions of this thesis are as follows:(1)By using COMSOL software and multi-physical field coupling finite element simulation method,a model of heating of amorphous YIG thin films during laser annealing is established,which can be used to understand the temperature distribution of thin films during laser annealing.(2)The crystallization of amorphous YIG/Ce:YIG thin films was realized by laser annealing.The effects of process parameters on the structure and properties of the films were studied by different laser annealing processes.Garnet-phase,fully crystallized and crack-free films can be obtained by high-speed scanning for many times,which provides a new method for the compatible integration of materials and CMOS back-end processes.(3)The optimized laser annealing process is used to locally anneal the thin film deposited on the waveguide.The results show that increasing the thickness and oxygen pressure of the thin film properly can help to reduce the optical transmission loss of the thin film on the waveguide.It is determined that the transmission loss of YIG thin film on the Si N waveguide at 1550 nm is about 89.7 dB/cm,and it is further determined that the transmission loss of YIG thin film on the Si N micro-ring device is about 81.56 dB/cm.