Theoretical And Experimental Investigation On Sn-based Materials

Sn-based materials have been extensively used in the industrial fields of interconnect packaging and opti-electronic devices due to their excellent electrical, mechanical and optical properties. Recently, because of the miniaturization of portable devices and the development of spintronic and optic-electronic materials, the researches on Sn-based materials mainly focus on the reliability of Sn-based alloy interconnect, the mechanical and thermodynamic properties of Sn-based interfacial intermetallics and the magnetic and optical properties of Sn-based oxide compounds. Thus, to do systematic and depth investigations on the above physical properties of Sn-based materials is very important and valuable.In this thesis, the electromigration of Sn-based alloy, the mechanical and thermodynamic properties of Cu-Sn and Pt-Sn intermetallics and the magnetic and optical properties of doped SnO₂ were experimentally and theoretically (first-principles calculations and finite element method) investigated systematically.The researches on the electromigration of Sn-based alloy give conclusions below. Firstly, the irregular morphology of interfacial Cu-Sn intermetallic layer induced the formation of local current crowding region which could accelerate the growth of electromigration defects. Secondly, Zn continuously diffused to the anode and cathode interfaces driven by both the chemical potential gradient and the electromigration force. It resulted in that the Cu5Zn8 intermetallic compounds were squeezed out from the surfaces of the interfacial intermetallic layers. Lastly, it was found that the layer-like structure formed in SnBi alloy thin film during the electromigration progress, which was due to the different migration velocities of Sn and Bi atoms. And the fine microstructure of SnBi alloy was considered to enhance the electromigration of Bi atoms based on the results of experiments and first-principles calculations.The first-principle calculations were employed to investigate the mechanical and thermodynamic properties of Cu-Sn and Pt-Sn intermetallic compounds. It was found that the calculated bulk modulus decreased with the Sn content. And all investigated Sn-based intermetallic exhibited relatively high elastic anisotropy. The elastic anisotropy results from the directional distribution of covalent bonds between Cu and Sn atoms which was determined by the symmetry of crystal. Meanwhile, the calculated results indicated that the thermodynamic quantities of Sn-based intermetallics, such as heat capacity, decreased with the Pt content. And the above things implied that the physical properties of Sn-based intermetallics were influenced by the properties and content of pure metal compound of intermetallics.As for the Sn-based oxide compounds, we predicted the room temperature ferromagnetism in K doped SnO₂ from first-principle calculations. And the typical RKKY interaction played an important role in the magnetic order in this system. Then, the room temperature ferromagnetism was experimentally observed in the K doped SnO₂ powders prepared by the sol-gel method. And the non-uniform distribution of K impurities and interstitial K and H would reduce the magnetic moments. On the other hand, the calculated results indicated that W6+ could be easily introduced into SnO₂, which would enhance the conductivity and increase the optical gap. And the formation of O defects could enhance the conductivity and optical absorption in the visible region. Additionally, it was found that the directional distribution of atoms and bonds resulted in the optical anisotropy in this system.