Molecular Dynamics Research On Normal Thermal Conductivity Of Nanoscale Films

As the rise and development of microelectronics, optoelectronics, MEMS and nanotechnology, thin film material became applied more and more widely. Thin films have already become important components of the micro devices. The stability and reliability of these devices are strongly dependent on the heat conduction in thin films. Study of thermal conductions and thermal parameters of thin films is of great significance for the development of various electronic devices. These studies can be divided into three types: experimental study, theoretical study and computer simulation study. For nano-films with thickness in 1¹00nm, thermal conductivity measure is extremely difficult. In this case, molecular dynamics simulation becomes an effective research method. Thin films made from SiO₂ are widely used in microelectronics industry for its excellent electrical insulation and process feasibility. This paper will adopt molecular dynamics simulation method to study the normal thermal conductivity of SiO₂ thin films.The micro-scale heat transfer, size effect of nano-films thermal conductivity are described, and research on nano-film thermal conductivity are summarized and generalized at first. Then, this paper introduces the basic principle and process of molecular dynamics simulation. The applicability of various simulation methods is discussed, in order to set up the reliable simulation scheme of nano-film thermal conductivity.Thermal conductivity of Lennard-Jones potential bulk solid Ar and its nano-films are calculated from molecular dynamics simulations. Green-Kubo approach equilibrium molecular dynamics and imposed-temperature gradient non-equilibrium molecular dynamics method are utilized to study the bulk and nano-film solid Ar, respectively. Simulation results of solid Ar in this paper show good agreement with the literatures. Non-equilibrium molecular dynamics simulations results of thermal conductivity of SiO₂ nano-film are obtained from crystal and amorphous models, respectively. The results show that: thermal conductivity of SiO₂ nano-film is smaller than its bulk materials, with a significant size effect; at the same temperature and thickness, thermal conductivity of cristobalite crystal SiO₂ nano-films is larger and show different thickness-dependence and temperature-dependence to amorphous ones. These provide an evidence of size effect from film thickness and grain morphology differences.