Studies Theoretically And Experimentally On Direct Bonding Of Laser Crystals

This work is supported by National Science Fund Council of China under the program (No. 60578022) of"Research of double-cladding waveguide lasers by using direct bonding technology."As an attractive technology emerging in the field of heterogeneous materials integration, direct bonding technique has overcome the limitations of heterogeneous epitaxy in lattice match and increased flexibility in device design. Currentlly, it has been widely applied in various fields such as microelectronics, optoelectronic devices and MEMS.The research object of this thesis is to bond the YAG crystal with Sapphire directly without any glue. There are two reasons of choosing these two kinds of crystals. One is that these materials are both nice heat conductors which could transfer the wasted heat to coolant fast. The other one is that there is a large refractive index difference between YAG and Sapphire which are suitable to be core and clad materials respectively to confine the waveguide modes within a small space. Additionally, the configuration of planar waveguide has benefit on reducing the heat-lens effects and scaling the output power of lasers.This thesis focus on theory and technique related to laser crystals direct bonding, and the main contents are as follows:1. Summarizing the origin, development and classification of semiconductor direct bonding technology, introducing emphatically development and state-of-the-art of direct bonding technology for laser crystals.2. Determining DMT theory as the most reasonable theory for direct bonding of laser crystals in three different theories by re-examing their applied conditions and accuracies of them. The calculations and analysis of the strength of bonding have been made by defining a parameterθwhich called surface adhesion parameter and is relative with the profile and properties of the surfaces to be bonded. That parameterθcould not only quantified the strength of bonding, but also demonstrate what are the key surface parameters which effect on the strength of bonding. That could guide us to modify the processing for enhancing the bonding energy.3. Direct bonding processing is an important part in direct bonding technology. This paper describes in detail the mechanism and processing of direct bonding. The conclusion is that polishing, cleaning and activation are difficulty in the whole processing. Several test methods for checking the effect on bonding materials which have been used in semiconductor heterogenous bonding field are summarized.4. Experiments about polishing, cleaning and activation have been done. And the pre-bonding between YAG and YAG have been tried. Some experiences are obtained for improving the further research.