Multilayer phase-change optical storage medium
An optical storage medium has a substrate having a first surface and an opposite second surface, light being incident via the first surface in recording or reproduction and at least two composite layers formed on the second surface of the substrate, each composite layer having at least a recording film. At least one composite layer, except a composite layer farther or farthest from the first surface of the substrate, has at least a first protective film, an interface film, a semi-transparent recording film, a second protective film, a third protective film, and a semi-transparent reflective film formed in order when viewed from the substrate, the semi-transparent reflective film having a thickness below 10 nm, the first protective film, the interface film, the second protective film, and the third protective film having a relation σ2>σk>σ1≧σ3 in which σ1, σk, σ2, and σ3 denote thermal conductivity of the first protective film, the interface film, the second protective film, and the third protective film, respectively.
1 . An optical storage medium comprising:
a substrate having a first surface and an opposite second surface, light being incident via the first surface in recording or reproduction; and
at least two composite layers formed on the second surface of the substrate, each composite layer having at least a recording film,
wherein at least one composite layer, except a composite layer farther or farthest from the first surface of the substrate, has at least a first protective film, an interface film, a semi-transparent recording film, a second protective film, a third protective film, and a semi-transparent reflective film formed in order when viewed from the substrate, the semi-transparent reflective film having a thickness below 10 nm, the first protective film, the interface film, the second protective film, and the third protective film having a relation σ2>σk>σ1>σ3 in which σ1, σk, σ2, and σ3 denote thermal conductivity of the first protective film, the interface film, the second protective film, and the third protective film, respectively.
2 . The optical storage medium according to claim 1 , wherein the thermal conductivity σ1 of the first protective film is below 10 W/m/K, the thermal conductivity σk of the interface film is 10 W/m/K or higher but below 50 W/m/K, the thermal conductivity σ2 of the second protective film is 50 W/m/K or higher but below 180 W/m/K, and the thermal conductivity σ3 of the third protective film is below 10 W/m/K.
3 . The optical storage medium according to claim 1 , wherein the first and third protective films are made of a material including at least either ZnS or SiO 2 , the interface film is made of a material including GeN as a major component having a percentage of 50% or higher in the material, and the second protective film is made of a material including SiC as the major component.