Study Of The Thermal Conductivity Of Submicron Thin Films

Submicron-thick films are widely used in the fields of information, microelectronics, photoelectron and aerospace. Heat conduction in these films will have a crucial impact on their performance and reliability. Thermal conductivities of these films markedly differ from their bulk counterparts due to size effects. Study on the heat conduction in submicron thin films is not only benefit to thermal design and thermal management, but also to improvement of the material fabrication and development of the theory of micro scale heat transfer.A transient thermal reflectance experimental setup, which is adapted to measure the thermal conductivity of submicron thin films, is built. The theory model of heat transfer is analyzed and the method of data processing is determined before experiment. In order to optimize the measurement system, several main factors influencing the quality of test are taken into account. After confirming the reliability of this setup with SiO2 thin films, the thermal conductivities of two dielectric films including alumina (Al2O3) and silicon nitride (Si3N4), two combined phase change memory films including Ta2O5-doped GST and N-doped Sb2Te3, and hard diamond-like carbon (DLC) films, are measured respectively. Thermal conductivities of Al2O3 thin films with thickness of 330-1000 nm don't show thickness dependency. The average value of them is about 3.3 Wm-1K-1. Thermal conductivities of Si3N4 films with thickness of 37-200 nm are in the range of 1.24-2.09 Wm-1K-1. They decrease with the decreasing film thickness. And this tendency is more obvious for films that are<100 nm thick. Effective thermal conductivities of DLC films with thickness of 100 nm are different due to the different microstructure inducing by deposition bias voltages in the fabrication process. Thermal conductivities of nanoscale Ta2O5-doped GST and N-doped Sb2Te3 films decrease with the increasing concentration of doping. The doping restrains the growth of the grain. The less grain size leads to the more intensely grain boundary scattering. The reduced thermal conductivity is benefit to the power consumption reduction of PCRAM.Using an ab-initio force field, COMPASS, the thermal conductivities of amorphous carbon and diamond films with the thickness of 2-6 nm are predicted under the temperature of 100-1000 K by utilizing non-equilibrium molecular dynamics simulations (NEMDS). The thermal conductivities of amorphous carbon films are 2.68-4.82 Wm-1K-1 and those of diamond films are 12.47-60.03 Wm-1K-1. The thermal conductivities of the crystalline and amorphous carbon films decrease with the decreasing film thickness. A notable size effect is presented in the range of the film thickness calculated. The thermal conductivities of the amorphous carbon films increase with the increasing temperature. When the temperature is above 400 K, the increasing tendency slows down. The thermal conductivities of the diamond films show different temperature dependence comparing with their bulk counterparts and are related with film thickness.Size effects of the thermal conductivities of thin films are explained theoretically. The boundary scattering, the microstructure of the films and the interface thermal resistance are the main factors to the reduced thermal conductivity of the films. The microstructure contributed by preparation process plays an important role on the heat conduction in the measured thin films. For the very thin films measured, size effects of the thermal conductivities are remarkable. The reason is that the interface thermal resistance may exert a significant influence on heat conduction besides the microstructure of the films. For the calculated films, we contribute the obvious size effects to the boundary scattering.Thermal conductivities of some important submicron thin films are studied by experiment and molecular dynamics simulation. The influences of thickness, preparation method, preparation conditions, annealing and doping to the thermal conductivities of thin films are investigated. The study will help to improve thermal management and design of microelectronic devices and develop the fabrication of thin film materials.