Analysis of the Degradation Mechanism during Repeated Overwrite of Phase-Change Discs

概要

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Rewritable optical digital versatile discs (DVDs) were analyzed to identify alterations in layer composition after repeated overwrite cycles. Elemental depth profiling revealed the presence of S in the phase-change layer in areas with high jitter values. This we relate to a decomposition of the ZnS:SiO2 dielectric layer during repeated overwrite. The S concentration in the phase-change layer at the location of the repeatedly overwritten tracks is estimated to range between 0.1 and 1 at. %, depending on whether or not a caplayer is present between the ZnS:SiO2 layer and the phase-change layer. From electron microscope images we established that repeated overwrite cycles induce voids in the phase-change layer. By analyzing the repeatedly overwritten areas of various recording stacks we collected evidence that a caplayer may suppress void formation. Both S diffusion and void formation will limit the overwrite cyclability of optical discs, which explains the frequently reported beneficial effect of a caplayer on overwrite performance.
2007-03-15