Computer Simulation On Thermal Properties Of Silicon Crystal Thin Films

With the development of micro-electronic mechanical system (MEMS) and semiconductor technology, more and more people are studying the properties of semiconductor materials. Silicon crystal thin film is both a kind of MEMS component and a kind of semiconductor material, and it is widely used and has obvious advantages. Thermal conductivity property of it is a property that determines the heat dissipation capability of the material. And it is also a decisive component to ensure the normal operation of the semiconductor at a certain temperature.In this dissertation, we calculate the thermal conductivity of silicon crystal thin films, and we use the form of computer simulation and lattice dynamics method to analyse the relationship between the thermal conductivity and the size of silicon crystal thin films. Nowadays, the usual approach to study the thermal conductivity properties of MEMS components on atomic or molecular level is molecular dynamics(MD) simulation.However, molecular dynamics has produced a number of shortcomings which are difficult to overcome. Therefor, in this dissertation, we use the lattice dynamics analysis method.In this dissertation, we start from the bulk crystal, obtain the lattice dynamics matrix, the third order an-harmonic potentials energy by using the lattice dynamics method, and then we obtain the linewidth and the spectural line width of phonon which is derived based on Green’s sfunction. After that, we extend it to the crystal thin film, to obtain the lattice dynamics matrix, the third order an-harmonic potential energy and phonon Green’s function of silicon thin film. Finally, computer simulation of spectrum of phonon, the lattice vibration wave and the spectural line width of phonon are done.Based on the lattice dynamics theories of the crystal thin films, with the help of Hardy formula for energy flux and Green-Kubo formula, the thermal conductivity of the crystal film is derived. The formula shows it is related to the line-width of phonon and the spectural line width of phonon, which are related to the thickness of the crystal film. Therefor, the thermal conductivity of silicon crystal thin films is related to the thickness of it. The calculation result of silicon crystal thin films shows that the thermal conductivity is smaller when the silicon crystal thin film become thinner. Therefor, the results plays a great role in guiding the manufacture the correct design of silicon crystal film. Due to the result, the effect of crystal film thickness on heat conduction should be considered when people design MEMS to avoid problems caused by crystal film cooling equipment failure.