The relation of the local structure of the phase-change recording material and the interface layer has not been
clarified while we already reported that the interface layer affects the electronic state of recording material by
using the HX-PES method. It is necessary to understand more detailed physical phenomenon for crystallization
mechanism of recording layer in order to develop the high-speed and higher density rewritable optical
recording media. The influence of the interface layer to the local structure for atomic arrangement of a GeBiTe
phase-change material was investigated by using XAFS on the actual rewritable HD DVD media. The XAFS
signal and EXAFS oscillation from the actual media is obtained nondestructively. It has been shown that the
interface layer influence slightly the local atomic arrangement of the recording layer, while the electronic state
of recording layer is changed by the presence of the interface layer.
We have developed a single-side dual-layer rewritable HD DVD media having a larger capacity of 40 GB
(20 GB per layer) for the optical system with the NA of 0.65 and the wavelength of 405 nm, and achieved the
good recording characteristics. For both layers, the same track pitch of 0.34 μm as HD DVD-RAM was used.
We applied more accurate thermal analysis to the dual-layer rewritable media. It was expected that the effect
of the cross-erase was very small. By optimizing thermal balance of dual-layer media, the good recording
characteristics were obtained for both layers with enough tilt margins. The feasibility of the dual-layer
rewritable media of 40 GB user data capacity was shown for HD DVD system.
The influence of the interface layer to the chemical and electronic states of a phase-change recording material, GeBiTe (GBT) alloy, used in the high-speed rewritable HD DVD media was investigated for the first time using the hard x-ray photoelectron spectroscopy (HX-PES). The density of states (DOS) for the valence band of the amorphous state without an interface layer was smaller than that of the crystalline state. The band-edge energy of the amorphous state without an interface layer was lower by about 0.5 eV than that of the crystalline state. On the other hand, the DOS and the band-edge energy of the amorphous state of GBT with interface layers were almost same as that of the crystalline state, respectively. This result may lead to almost the same career density for electrical conduction for the crystal as the amorphous, which is totally unexpected thus very interesting because the atomic arrangements should differ from each other. We speculate that this effect is a factor for a high-speed crystallization.
Thermal conductivities and boundary thermal resistances of thin films having the thickness of the order of ten nanometers were measured by using the thermo-reflectance method at room temperature. A thermal simulation of HD DVD-ARW (the next-generation advanced rewritable DVD) media was carried out to clarify the effect of boundary thermal resistance at the interface of those films. The thermal conductivity of thin films greatly depends on film thickness. The result of the thermal simulation depends significantly on whether the boundary thermal resistance is considered or not. Thus it is important to consider the boundary thermal resistances and using thermal properties of thin films to perform more accurate calculation for the phase change recording media. The results of the thermal simulation also suggested that the boundary thermal resistances dominate the thermal diffusion and response of the medium.