Andrei Mijiritskii

Numerical simulation of mark formation in dual-stack phase-change recording

Dual-stack phase-change recording is an option to further increase the data capacity of rewritable optical disks. Such disks consist of two recording stacks that are both recorded and read from the same side of the disk. Consequently, the first recording stack needs therefore to be semitransparent to allow recording in the second recording stack. Thick nontransparent metal layers can therefore not be used in the first recording stack, which makes the first recording stack the most challenging stack from a thermal point of view. A numerical model based on crystal growth was developed to study formation and erasure of amorphous marks in phase-change stacks that are based on fast-growth doped SbTe phase-change materials. The validity of the model was demonstrated from transmission electron microscopy analyses of recorded marks that showed a good correspondence with the calculated mark shapes in a conventional single-stack recording stack. The model was subsequently applied to analyze formation and erasure of marks in slow-cooling phase-change stacks for digital versatile disk, (DVD) and digital video recording (DVR) recording conditions. The effect of the recording velocity, the erase power, and the crystal growth velocity on the erasability of amorphous marks was simulated. The calculated phenomena are in good agreement with the phenomena observed from DVD and DVR erasability measurements. Mark formation in slow-cooling recording stacks is characterized by severe recrystallization during writing. Two possible solutions are indicated in this article, aiming at reducing the heat accumulation and the resulting recrystallization during writing of amorphous marks. Additional semitransparent heat sinks improve the mark formation considerably but also require higher write powers. Another solution is the application of modified write strategies. Modeling and recorder results are discussed for both approaches.

Dual-Layer Blu-ray Disc Based on Fast-Growth Phase-Change Materials

A dual-layer disc is developed for blue-laser phase-change recording. The two recording stacks are based on fast-growth phase-change materials (FGMs). Both layers show good recording performance at a total disc capacity of 46.6 GB and with a slightly high jitter at 50 GB. The thicknesses of both the cover and spacer layers are controlled such that the deviations from the reference thicknesses of both recording layers are less than 2 µm. This eliminates the need for dynamical spherical aberration correction in the drive. The absolute difference in transmission between the written and unwritten states of the upper layer is only 2%. It is shown that this transmission difference causes no problem for readout and writing of the lower layer.

Development of Recording Stacks for a Rewritable Dual-Layer Optical Disc

In this paper results are presented on the development of recording layers for a rewritable dual-layer phase-change optical disc. The disc is based on the digital video recording (DVR) system utilising a blue laser and a high numerical-aperture objective lens. With such a disc the capacity of the DVR system could be increased to about 45 GB. Various stack designs, write strategies and recording characteristics of the media are discussed. For each recording layer a design with a fairly good performance is found.

System Aspects of Dual-Layer Phase-Change Recording with High Numerical Aperture Optics and Blue Laser.

In this publication, key technologies for blue laser recording and dual layer phase-change disks with a total capacity of 50 Gbytes are explained and system margins are evaluated. Key challenges are the phase-change recording layer design, a robust read and write system with low intrinsic noise and the optical pickup design including, e.g., high numerical aperture (NA) objective lens, spherical aberration compensation devices and beam shaping optics. Blue-laser dual-layer technology will be emerging as the next-generation optical data storage standard beyond compact discs (CDs) and digital versatile discs (DVDs).

Advances in thermal modeling of dual-layer DVR-blue fast-growth media

Dual-layer phase-change recording is an option to further increase the data-capacity of re-writeable optical discs. A numerical model based on crystal growth was used to study formation and erasure of amorphous marks in dual-layer stacks based on fast-growth doped eutectic SbTe phase-change materials. The effect of the linear velocity, erase power, and crystal growth velocity on the erasability of amorphous marks was simulated. The calculated effects are in good agreement with the phenomena observed from DVD and DVR measurements. Mark formation in slow-cooling dual-layer stacks is characterized by severe re-crystallization during writing. Two possible solutions are indicated in the paper aimed at reducing the heat accumulation in the recording stack, and thus re-crystallization, during writing of amorphous marks. Additional transparent heat sinks improve the mark formation considerably but also require higher write powers. Another solution is based on an appropriate write strategy. Recording results obtained with this such a write strategy are shown.

Rewritable dual-layer blu-ray disc media

The Blu-ray Disc (BD) optical recording system utilizes a blue laser (405 nm wavelength) in combination with a high-numerical-aperture (NA = 0.85) objective lens. This BD-format allows storing 23 - 27 GB on a single-layer and 46 - 54 GB on a dual-layer 12 cm disc at 36 Mbps user data rate. This paper reports on the design, manufacturing, and the recording performance of our dual-layer rewritable optical media. These media are based on the eutectic, fast-growth phase-change materials, which are promising candidates for high-speed applications. The performance of these materials in the case of dual-layer recording is discussed, with special attention for transmission balance for the semitransparent recording stack.

Dual-layer Blu-ray Disc based on fast-growth phase-change materials

Blu-ray Discs are recorded and read with a blue-violet 405 nm laser through a high numerical aperture 0.85 objective lens. The main application of Blu-ray Discs will be high definition television (HDTV) recording. Future demand for a major capacity increase within the Blu-ray Disc family is anticipated by development of multi-layer technology. However, the optical and thermal characteristics of the currently used phase-change materials restrict the number of layers to two. Such a dual-layer re-writable disc still allows for design choices, which affect system performance. First we describe the spacer technology we have used for making of our dual-layer disc. The two recording layers are based on stack designs with fast-growth materials.