Thermodynamic Modeling Of Te-Cu-Ge And Te-Cu-Ga Phase Change Memory Materials

PCM（Phase Change Memory）is considered as one of the most promising next-generation memory because of its advantages of fast read/write rate,low power consumption and high memory density.The performance of PCM depends on the physical properties of PCM materials.In order to screen the constituents of the phase-change storage materials and optimize the preparation process more efficiently,it is necessary to study the phase diagram thermodynamics of the phase-change storage materials system to obtain an accurate thermodynamic database.In this paper,the CALPHAD（CALculation of PHAse Diagrams）method is used to study the phase diagram of Te-based PCM materials combined with first-principles calculation and experimental data,including the binary system composed of Cu,Ga,Ge and Te and Te-Cu-Ga and Te-Cu-Ge ternary systems.The main research results are as follows:（1）Intermetallic compounds at Te contents from 33 to 36.5 at.%in Te-Cu system were considered in the present work.The liquid phase of Te-Cu and Te-Ga binary system were described using association model.The self-consistent thermodynamic parameters of Te-Cu and Te-Ga were obtained in combination with enthalpy of formation calculated by the first-principles calculation in this work.The comparison between the calculated results and the experimental data shows that the thermodynamic parameters can accurately describe the experimental results,including heat capacity,enthalpy of formation and enthalpy of mixing and activity and etc.（2）The calculation results of marginal binary system phase diagrams and experimental data of Te-Cu-Ga and Te-Cu-Ge ternary systems were critically evaluated.Thermodynamic parameters of Ge-Te and Cu-Ge systems were reoptimized.The thermodynamic databases of Te-Cu-Ga and Te-Cu-Ge ternary systems were constructed by combining the marginal binary system thermodynamic parameters and ternary system experimental data.The two-sublattice model（Cu,Ga）_0.5（Cu,Te）_0.5 and three-sublattice model（Cu,Va）_0.25（Cu,Ga）_0.25（Te）_0.5 were used to describe the Ga Te phase and ternary compound CuGaTe₂,respectively.The Cu₂Ge Te₃ phase was described as a stoichiometric compound.Self-consistent thermodynamic parameters of Te-Cu-Ga and Te-Cu-Ge ternary systems were obtained.The calculated results are compared with the experimental isothermal section and vertical section.The calculated results can accurately describe the solubility of Cu in Ga Te phase and the composition range of CuGaTe₂ at923K.The ternary thermodynamic parameters can accurately describe the phase relation information,liquidus and composition range of ternary phases.