Michikazu Horie

Microstructural changes in GeSbTe film during repetitious overwriting in phase‐change optical recording

Microstructural changes that occur in a GeSbTe film during repetitious overwriting in phase‐change optical recording were investigated. The GeSbTe active layer was melted by a focused laser diode (LD) beam during each overwriting process over amorphous mark formation. The repetitious solidification and liquefaction process in such a short time as 50–200 ns resulted in microstructural changes in the active layer: a segregation, sink, and void formations. The sink was formed in the low‐density active layer due to the shrinking of the volume during the resolidification process. Sink formation could be suppressed when a high‐density active layer, having more than 80% of the bulk density, was used. Such a high‐density GeSbTe film, however, resulted in a void formation of the size of 0.1 μm. The voids were thought to be nucleated by residual vacancies and Ar precipitation, since the active layer contained a high concentration of Ar impurities, due to the atomic peening effect. The subsequent void coalescence an...

High-speed rewritable DVD up to 20 m/s with nucleation-free eutectic phase-change material of Ge(Sb70Te30)+Sb

High speed overwriting capability of the nucleation-free and growth-dominant eutectic Ge(Sb70Te30)+Sb phase- change material, and its application to high speed overwritable DVD and CD, are discussed. The addition of Ge to Sb70Te30+Sb binary system could effectively suppress the nucleation in recrystallization process, while high Sb/Te ratio could realize a selective enhancement of crystalline growth-speed initiated from the boundary of an amorphous mark and its crystalline background. This resolved a trade-off in high speed erasure and archival stability of amorphous marks. Highly enhanced crystalline growth also caused serious recrystallization during amorphous mark formation, resulting in shrinkage of amorphous mark size (premature cooling issue). This premature cooling issue as well as premature heating issue, in multiple pulse strategy with such a short writing and cooling pulse as below 10 nsec at high clock frequency of > 100 MHz for over 4X speed rewritable DVD, were resolved with a 2T-period based multiple pulse strategy. Thus, feasibility of 2 - 4.8X CAV operatable rewritable DVD and 16X CD-RW was demonstrated.

Rewritable mutlilevel recording using blue laser and growth-dominant phase-change optical discs

MultiLevel recording for high-density, blue-laser systems has achieved approximately 5 X 10-5 BER before ECC using growth-dominant phase-change materials on a 0.6mm cover-layer, 405nm-wavelength, 0.65-NA system.

Simple birefringence measurement method for coated optical disks with a fixed incident angle ellipsometer

In a coated and laminated optical disk, only a reflectance method is available for oblique incidence retardation measurements to evaluate the birefringence in a polycarbonate substrate. I propose a simple measurement method that simultaneously measures both the lateral and vertical birefringence in a coated substrate. In this reflectance method, only two oblique incidence retardation values with a fixed incident angle are measured from the radial and the circumferential directions of the disk. Using the sum and the difference of these two retardation values, we can calculate both birefringences without any cumbersome curve-fitting procedure. This method can easily be introduced into the routine inspection for optical disk manufacturing.

Interface structure modified by plasma‐surface interaction and its effect on ablative hole opening process in a bilayer system of TeSeF film and a fluorocarbon subbing layer

The effect of a plasma‐surface interaction on the adhesion force of a thin metal film was investigated using a bilayer system consisting of a TeSeF film and a fluorocarbon subbing layer. The change in an ablative hole opening process with a focused laser beam in this bilayer system was also affected by the modification of the adhesion force due to the plasma‐surface interaction. An Ar plasma treatment of the fluorocarbon subbing layers prior to the TeSeF film deposition increased the adhesion force and the threshold energy for the ablative hole opening. Even without such intentional plasma treatment, the interface chemical structure depended on the plasma‐surface interaction during the TeSeF active layer deposition, where the active layer was deposited by the rf or dc reactive sputtering of TeSe in a SeF6/Ar gaseous mixture. The rf sputtered TeSeF film required larger threshold energy for hole opening than the dc sputtered one. The modified interface chemical structure by the plasma‐surface interaction wa...