Molecular Dynamics Simulation Of Thermal Expansion Property Of Single-Crystal Si Film

Silicon single-crystal film is commonly used as substrates materials in MEMS devices,which is irreplaceable.It is widely applied to the manufacturing of various micro-actuators,micro sensors and other microelectronic devices due to its thermal expansion properties.It has great significance in the design and manufacture of these devices:on one hand,the mismatch of thermal expansion coefficient between silicon single-crystal film and other films will produce thermal stress,causing the microelectronic devices or the micro-mechanical structure invalid or to be damaged;on the other hand,the thermal expansion can become the power source of the micro-thermal actuators.Silicon single-crystal thin film is different from bulk material in the thermal expansion properties,based on the shortcomings of theoretical research and experimental measurements,the properties of the thermal expansion is studied by molecular dynamics method in this dissertation.In terms of the structural features of silicon single-crystal film,physical model of studying the thermal expansion properties was built,the S-W potential energy function which can reflect the thermal expansion properties of silicon single-crystal film was chose to describe the molecular interactions.What's more,the Verlet algorithm was used to calculate the kinetic equation integral solution.By correcting the molecular dynamics temperature with phonon density function and combining he theory of lattice thermal expansion,thermal expansion properties of the single-crystal silicon thin film was studied.On this basis,the silicon bulk material with a temperature range of 300K?800K and silicon single-crystal thin film with a thickness of 10 lattices(5.432nm)were simulated respectively.When carried out molecular dynamics simulations to the thermal expansion of the silicon bulk material with the S-W potential function,we got some results as follow:the coefficient of thermal expansion showed a nonlinear function that the trend of increase gradually weakened until reaching a constant value with increasing temperature,there was no negative thermal expansion happened in the whole range.While carrying out molecular dynamics simulations to the thermal expansion of the silicon single-crystal thin film with the S-W potential function,we found that is significantly different from other bulk materials in thermal expansion:In the low temperature(200K?400K),the number of dimerized atoms on the surface of the silicon single-crystal thin film significantly grows with the increase of temperature,resulting in the thermal expansion coefficient different from other bulk materials;At high temperatures(400K?800K),the number of dimerized atoms became stable with the increase of temperature,the influence of conventional thermal expansion properties gradually increased,as a result,the thermal expansion coefficient showed a nonlinear function that the trend of increasing gradually weakened until reaching a constant value with the increase of temperature,consequently,dimensional effect is obvious.