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

Abstract

In situ structure characterization of Pb(Yb1/2Nb1/2)O3-PbTiO3 crystals under high pressure-temperature Appl. Phys. Lett. 101, 062904 (2012) Martensitic transformation and magnetic domains in Mn50Ni40Sn10 studied by in-situ transmission electron microscopy J. Appl. Phys. 112, 033904 (2012) Structural and chemical properties of the nitrogen-rich energetic material triaminoguanidinium 1-methyl-5-nitriminotetrazolate under pressure J. Chem. Phys. 137, 054501 (2012) First-principles theoretical analysis of transition-metal doping of ZnSe quantum dots J. Appl. Phys. 112, 024301 (2012) High-pressure neutron study of the morphotropic lead-zirconate-titanate: Phase transitions in a two-phase system J. Appl. Phys. 112, 014104 (2012) Additional information on J. Appl. Phys. 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.

The effect of thermal anisotropies during crystallization in phase-change recording media

“…The above results indicate that such approximations have a wider validity than might have been expected. In particular they allow an isotropic kinetic analysis, 6 which brings in the dependence on parameters such as the annealing activation energy. Table I.…”

“…However, this analysis is based on the heat diffusion process alone and hence provides upper estimates for the spreading time and length scales in this problem. The detailed kinetics are included in another report 6 by examining the role of the initial peak temperature, and hence energy density in the medium, and considering the relative contributions to the crystallization rate made by the thermal diffusive flow and the phasechange reaction rate.…”

Mechanisms of fast crystallization in amorphous Ge2Sb2Te5 films

“…Privitera et al 4) use c ≈ 1.55 J (g −1 •K −1 ), 20) which is large by an order from others, ∼0.2 J (g −1 •K −1 ). 19,21,39) Also, Aziz et al 48) assert that the effect of heat released during crystallization is modest, the conclusion being derived under extremal conditions assuming deltafunction impulses. In contrast, Scoggin et al 40) take its role into numerical studies of a PRAM cell.…”

A transfer function approach to reaction rate analysis with applications to phase-change materials and devices

“…Exact analytical solutions to the non-linear rate equation in Eq. (1) are only available for simple temperature functions including constant (isothermal) temperatures, and linearly increasing 5,6 or decreasing 7 temperature changes. While the use of linear temperature functions is useful for the analysis of laboratorybased calorimetry experiments, as used extensively to study the reaction dynamics of phase-change materials and to extract relevant activation energies (for example Ref.…”