Phase Change Optical Recording Materials Research Articles

Characterization of Amorphous Phases of Ge2Sb2Te5 Phase-Change Optical Recording Material on Their Crystallization Behavior

The difference in crystallization behavior between the as-deposited amorphous state and the melt-quenched amorphous state of Ge2Sb2Te5 alloy has been studied using a dynamic tester. The melt-quenched amorphous alloy showed much shorter crystallization time than did the as-deposited one. We laser-annealed the as-deposited amorphous alloy under a certain condition so as to make it exhibit the same crystallization property as that of the melt-quenched one. The crystallization kinetics of this laser-annealed amorphous alloy and the as-deposited amorphous alloy has been explained by applying transmission electron microscopy (TEM) and continuously heating the specimens in a differential scanning calorimeter (DSC). From the TEM results, it has been shown that preexisting atomic clusters accelerate the crystallization speed of the amorphous alloy. The two states have been found to have different crystallization temperatures and activation energies.

Complex Refractive Indices of GeSbTe-Alloy Thin Films: Effect of Nitrogen Doping and Wavelength Dependence

The effects of nitrogen doping on the complex refractive indices of Ge2Sb2Te5 phase-change optical recording materials and their wavelength dependence were examined. With an increase in nitrogen concentration, the extinction coefficients decreased monotonically. The calculated reflectance spectra at normal incidence showed a good quantitative agreement with the measured values. The observed optical properties were correlated with the characteristic features of the microstructure, including grain size refinement, internal residual stresses, and changes in the bonding state.

相変化光記録材料の物性と要求特性

相変化光記録材料の物性と要求特性

相変化を利用した新規な４元系Ａｇ‐Ｉｎ‐Ｓｂ‐Ｔｅ光記録材料

Reversible phase change optical recording material with a new quarternary system of Ag-In-Sb-Te has been studied. The starting material for the Ag-In-Sb-Te system is a combination of AgInTe2 with the chalcopyrite structure and Sb. In this work, we report the basic properties of the Ag-In-Sb-Te films investigated by means of DSC, XRD, ED, and HR-TEM. We also discuss the phase change process of the Ag-In-Sb-Te system.

Discussion on the Mechanism of Reversible Phase Change Optical Recording

In stoichiometric GeTe-Sb2Te3 films, reversible phase change optical recording materials, Sb addition is used widely in order to improve the crystallization speed, the data retention time and the stability of cyclic operation, but its mechanism is not clear. V-VI compounds (GeTe, SnTe) are well known as compounds in which the ferroelectric structural phase transition occurs. The dielectric constant ε0 changes largely due to a change in the short-range order of weakly bound nearest neighbors in the crystal to more strongly bound nearest neighbors in the amorphous phase. Therefore, it is necessary to discuss the effect of Sb addition in the stoichiometric GeTe-Sb2Te3 composition upon the thermal stabilities, the dynamic properties of crystallization and the dielectric constant change Δε0 based on the amorphous-to-crystalline phase transition.

Kinetic studies of the crystallization of Te 92Pb 8 thin films

A method to obtain the crystallized volume fraction X and the time taken for crystallization t is proposed. The Avrami equation X = 1 − exp(− kt n ) is used to calculate the time exponent n and rate constant of crystallization k. The nucleation mechanism, nucleation rate and the growth rate of nuclei of Te 92Pb 8 are discussed in relation to different n and k values. It is found that the nucleation at the start of the transformation, plus continuing nucleation at grain boundaries or grain edges, determine the kinetics at lower temperatures. Both the nucleation and the growth rate of nuclei are low at 32° C. They increase slowly with temperature below 46° C. From 46° C, the nucleation rate increase rapidly. Its maximum may be in the temperature region between 65° C and 80° C. The maximum growth rate of nuclei is at a temperature higher than 80° C. A nonlinearity in the plots of lnln 1/(1 − X) vs ln t caused by the variation of n is also found and discussed. The amorphous state of Te 92Pb 8 is unstable. The possibility of using it as erasable phase change optical recording material is evaluated.

In–Se–Pb–Based High Speed Reversible Phase Change Optical Recording Films

A new high speed reversible phase change optical recording material In–Se–Pb–Cu film is reported. The roles of Pb and Cu elements on erasing speed and stability of In–Se–based films are discussed.