Ultrafast heating and resolution of recorded crystalline marks in phase-change media

Abstract

This work presents an analytical study of the thermally activated amorphous-to-crystalline phase-change process when the heating source has a delta function temporal profile. This simulates the case of ultrafast heating where crystallization in the amorphous phase-change medium occurs during cooling. The study produced closed-form expressions that predict the necessary peak temperature, and hence energy density, in the phase-change medium for successful crystallization during ultrafast annealing as functions of the kinetic and thermal parameters of the medium. Closed-form expressions were also derived that provide estimates of the final crystalline mark widths and tail lengths when phase change has ceased. The analysis indicated the need to reduce the activation energy of crystallization and the thermal diffusivity of the medium to reduce the initial peak temperature, produced by the heating source, to avoid melting, to increase the crystallization rate, to achieve sufficient levels of crystalline fractions during cooling, and to reduce the size of recorded crystalline marks. Perturbation analysis was carried out to study the effects of latent heat of crystallization during the fast kinetics phase. The result was reductions in the cooling rate of the phase-change material, thus requiring lower peak temperatures to achieve higher volumes of crystalline fraction. Nevertheless, the effects of heat release during crystallization were found to be modest for the class of current phase-change material used in data storage.