Rewritable Triple-Layer Phase-Change Optical Disk Providing 100 Gbyte Capacity

Abstract

A rewritable phase-change optical disk providing a large capacity of 100 Gbyte on a 120 mm disk was first demonstrated using the multilayer Bluray Discä (BD-XL) format. The doubled capacity of this optical disk compared with that of a conventional dual-layer disk was achieved firstly by stacking triple recording layers and secondly by increasing the recording capacity per layer from 25 to 33.4 Gbyte at 33.6%. The high transmittances of 50% (middle layer) and 60% (front layer) were achieved by thinning a Ge-Sb-Te phase-change film to 7.5 and 6 nm and also by thinning a Ag-alloy film to 9 and 7 nm, respectively. An additional TiO 2 -based film formed on the Ag-alloy film was effective in improving the transmittance at 3%, compared with the structure using a conventional TiO 2 film. Furthermore, a transmittance-balanced structure was adopted for these layers in order to stabilize the recording-reading properties. To improve cyclability, ZrO 2 -Cr 2 O 3 -based interface films were provided on both sides of the phase-change film for the middle and front layers. The increase in recording capacity per layer was achieved by reducing the minimum mark length from 0.149 to 0.112 m. Since the optical changes degrade with the reductions in the mark lengths and thicknesses of the Ge-Sb-Te and Ag-alloy films, a phase-change material with a GeTe-rich composition on a GeTe-Sb 2 Te 3 pseudo-binary line was adopted for every layer to compensate it. It was confirmed that the sample disk successfully satisfies all the requirements of the BD-XL format.

Origin, secret, and application of the ideal phase‐change material GeSbTe

“…As a method to overcome the limitation, a lamination method of the recording layers has been developed. Figure 9 shows the layer stacks of the latest product: the triple-layer Blu-ray Disc [19]. To smoothly record on and read from the deep recording layer, the front side recording layers must be highly transparent.…”

A layered Ge2Sb2Te5phase change material

“…On contrary, the formation of amorphous phase needs higher temperature and short pulse duration, which the GST film has to be heated above melting temperature and rapidly quenched. Specifically, the length of pulse duration can be as short as 10 ns in amorphous phase and 50 ns in crystallization phase with laser pulses 9 .…”

Growth control of epitaxial GeTe–Sb2Te3 films using a line-of-sight quadrupole mass spectrometer

“…Distinctive features are large optical and electrical contrast between the amorphous and crystalline states, rapid and reversible switching between the two phases, high thermal stability, good scalability and low cost. On these grounds the commercialization of optical discs such as CDs, DVDs and Blu ray discs for data storage [2][3][4][5][6] was enabled. In addition, recently the electrical contrast is utilized to fabricate non-volatile phase change RAM: considered as a promising candidate for the replacement of conventional charge based storage technologies [7][8][9][10][11][12].…”