| 摘要 |
PURPOSE: To make it possible to correctly execute recording or/and reproducing by suppressing the occurrence of warpage by a temp. change of external environment. CONSTITUTION: A disk-shaped warpage preventive plate 9 consisting of a material having the coefficient of thermal expansion smaller than the coefft. of thermal expansion of the constituting material of a disk-shaped substrate 1 formed with a recording layer 2 consisting of at least one layer of function film on one main surface is disposed near the central part of the main surface on the side opposite to the recording layer 2 forming surface of the substrate 1. The function film is preferably a metallic film and/or dielectric film. Further, the substrate in a room temp. state has such a shape that the inner peripheral side on the main surface side of the side opposite to the recording layer forming surface of the substrate complies with the substrate shape so as to project and that the main surface of the side opposite to the recording layer forming surface of the substrate complies with the substrate shape so as to recess. The warpage angle of the main surface of the side opposite to the recording layer forming surface of the substrate is preferably larger on the inner peripheral side than the outer peripheral side. |
