Estimation of kinetic parameters for the phase change memory materials by DSC measurements

Abstract

The non-isothermal method for estimating the kinetic parameters of crystallization for the phase change memory (PCM) materials was discussed. This method was applied to the perspective PCM material of Ge2Sb2Te5 with different Bi contents (0, 0.5, 1, 3 mass%) for defining the kinetic triplet. Rutherford backscattering spectroscopy and X-ray diffraction were used to carry out elemental and phase analysis of the deposited films. Differential scanning calorimetry at eight different heating rates was used to investigate kinetics of thermally induced transformations in materials. Dependences of activation energies of crystallization (Ea) on the degree of conversion were estimated by model-free Ozawa–Flynn–Wall, Kissinger–Akahira–Sunose, Tang and Starink methods. The obtained values of Ea were quite close for all of these methods. The reaction models of the phase transitions were derived with using of the model-fitting Coats–Redfern method. In order to find pre-exponential factor A at progressive conversion values, we used values of Ea already estimated by the model-free isoconversional method. It was established that the crystallization processes in thin films investigated are most likely describes by the second and third-order reactions models. Obtained kinetic triplet allowed predicting transition and storage times of the PCM cells. It was found that thin films of Ge2Sb2Te5 + 0.5 mass% Bi composition can provide the switching time of the phase change memory cell less than 1 ns. At the same time, at room temperature this material has a maximum storage time among the studied compositions.