Research On Temperature-dependent Thermal Conductivity And Heat Transmission Mechanism Of Phase-change Superlattices

Over the past few decades,as next-generation nonvolatile memory,phase change memory(PCM)has attracted wide attention across the globe.To this kind of memory whose operation is exclusively based on thermal energy,large needed programming current and thermal crosstalk between adjacent cells have become a bottleneck of PCM’s development.It is quite possible to resolve these difficulties owing to lower thermal conductivity of phase-change superlattices.However,the research of phase-change superlattices has just started and the thermal transmission has been studied only at room temperature;and the temperature characteristic of thermal conductivity still not been applied to PCM anywhere.It is necessary to investigate the thermal behavior of at various temperature environment.What is more,the temperature-dependent thermal conductivity would make for our understanding of basic mechanics of transport process in phase-change superlattices.Our study is mainly focused on the temperature-dependent thermal conductivity of phase-change GeTe/Bi2Te3 superlattices.An experimental setup based on 3ω method has been depicted,which could be used to measure the temperature dependent thermal conductivities of thin film.First of all,through analyzing the characteristics of the third harmonic voltages,the effect of temperature to the setup is eliminated.Secondly,the temperature dependence of the thermal conductivity for SiO2 film is measured and an accurate platform is verified;and the range of frequency is determined that the boundary resistance would not affect the data analysis.Last but not least,temperature-dependent thermal conductivities of phase-change GeTe/Bi2Te3 superlattices are measured by our experimental setup.The effects of annealing temperature and environment temperature on the thermal conductivities of GeTe/Bi2Te3 superlattices are study and the results show that the thermal conductivities of GeTe/Bi2Te3 superlattices have significant change when the state changes from amorphous to crystalline.It is quite helpful to suppress the thermal crosstalk,which should be a key consideration during the scaling down process of PCM.Temperature-dependent thermal conductivities of phase-change GeTe/Bi2Te3 superlattices in amorphous and crystalline states are measured in the temperature range of 40 to 300 K,which shows that thermal conductivity increases with increasing temperature.Two main reasons are suggested:(1)the interface scattering that is not sensitive to temperature dominate the phonon transport,which is then demonstrated by the periodic thickness dependence of the thermal conductivity of GeTe/Bi2Te3 superlattices;(2)the contribution of electron to the total thermal conductivity could not been neglected,even acts as a significant role,owing to the low lattice thermal conductivity and high dopant concentration of GeTe/Bi2Te3 superlattices.Our work herein makes for our understanding of basic mechanics of transport process in GeTe/Bi2Te3 superlattices.Finally,an interesting phenomenon,i.e.,V3ω does not linearly depend on lnω is observed and some reasonable analysis is mentioned.