| 摘要 |
PROBLEM TO BE SOLVED: To suppress flawing on a transparent cover layer to be irradiated with light and the failure thereof, to assure reliability, to enable the dealing with higher NA and to make a capacity higher. SOLUTION: The one main surface side of a recording layer is provided with the transparent cover layer having a Young's modulus of >=70 (GPa) and the recording and/or reproducing of information is executed by using an objective lens having NA of >=0.7. The thickness of the transparent cover layer is specified to <=150 (μm). The transparent cover layer is formed of a two- layered structure and the Young's modulus of the layer which is a front surface side is specified to >=150 (Gpa). The thickness of the layer is specified to 2 to 230 (nm). The front surface side of the transparent cover layer is formed of a material contg. at least one kind among C100-x Hx (1(atomic.%)<X <45(atomic.%)), Si3 N4 , MgF2 , Al2 O3 and SiO2 . The thickness (t) of the transparent cover layer of the region of an information signal part 11 is specified to t=3 to 177 (μm) and the irregular thickness Δt of the transparent cover layer is so determined that the relation Δt<=±5.26(λ/NA<4> ) (μm) holds between NA and a wavelength λ. |
