Molecular Dynamics Simulation And Experimental Study On Thermal Properties Of HfO₂ Thin Films

HfO₂ thin films have been widely used in the fields of microelectronics,optics and information technology.Due to various boundary effects and other factors,the thermal properties of the material are usually quite different from those of bulk materials.Therefore,the measurement of thermal characteristic parameters of submicron thin films has become an urgent problem to be solved.Carrying out relevant research is beneficial to improve the stability and reliability of the device,and it is of great significance for the theoretical development of micro-scale heat transfer.In this paper,the thermal conductivity of HfO₂ thin films with different phases was investigated by using the molecular dynamics method,cubic and amorphous HfO₂ thin films with temperature ranging from 200 to 600K and thickness ranging from 5.12 to 31.70nm was calculated.The simulation results show that the thermal conductivity of monoclinic HfO₂ is0.49-1.20W/mK,that of cubic HfO₂ is 1.31-1.96W/mK,and that of amorphous HfO₂ is0.17-0.24W/mK.In the simulated scale range,the thermal conductivity of HfO₂ films with different phases show obvious size effect,but show different temperature dependence,which is due to the relative different changes of heat capacity and phonon scattering intensity with the increase of temperature.The interfacial heat transfer characteristics between HfO₂ and SiO₂ under different conditions were studied by molecular dynamics method.The simulation results show that the interfacial thermal resistance between crystals is significantly greater than that between amorphous and amorphous.The calculation results of phonon density of states show that the phonon vibration mode matching between amorphous HfO₂ and amorphous SiO₂ is better,so the difference of phonon mismatch degree is the main reason for the difference of interface thermal resistance between amorphous HfO₂ and amorphous SiO₂.In addition,with the increase of temperature,the interfacial thermal resistance of different contact types will decrease to a certain extent,which is due to the excitation of more phonons to participate in thermal conduction at high temperatures.The thermal conductivity of crystalline and amorphous HfO₂ films with thickness of70-190nm were measured by transient thermal reflection method.The total thermal resistance of HfO₂ films increases linearly with the increase of film thickness in the range of test thickness,while the thermal conductivity of the films does not change with the increase of thickness.The thermal conductivity of amorphous and crystalline HfO₂ films is0.42±0.042W/mK and 1.32±0.132W/mK respectively.Because the thin films tested in this paper are thicker,there is no dependence of thermal conductivity on thickness.In this paper,the films before and after annealing were tested by AFM,XRD and XPS.The characterization shows that the increase of thermal conductivity of crystalline HfO₂ is caused by the increase of crystallization degree of the materials on the one hand,on the other hand,the decrease of oxygen vacancy defects and the increase of phonon mean free path during annealing,which leads to the increase of thermal conductivity.In this paper,the thermal properties of HfO₂ thin films are studied by combining molecular dynamics simulation with experimental measurements,which provides an important reference for thermal management and thermal planning of related devices.