| 摘要 |
PROBLEM TO BE SOLVED: To reduce the camber in an optical disk due to temp. change, to make it possible to precisely record/reproduce information in a use temp. environment and to remarkably improve the reliability by satisfying a thin film part shape and a physical characteristic of a pair of disk single bodies with a specified relation. SOLUTION: A pair of disk single bodies 1, 2 are stuck to each other opposing thin film parts 12 to each other. The thin film part 12 of protective films 21, 23, a recording film 22 and a reflection film 24 is formed on a disk substrate 11. At this time, respective coefficients are set so that the thin film part is satisfied with the relation. However, h1 is 200nm or below in the film thickness of a thin film with the smallest coefficient of linear expansion, h2 is 1.2mm or below in the disk substrate thickness, d is 15mm<=d<=120mm in the width in the radial direction of the disk of a film formation area of the thin film part, T is a temp. variable width and k is a proportional coefficient satisfying (γ1-γ2) (6E2/E1) when the Young's moduli and the coefficients of linear expansion of the thin film part and the disk substrate are denoted respectively E1, E2, γ1, γ2. In the condition, the camber in the optical disk due to the temp. change is reduced, and the information is recorded/reproduced precisely in the use temp. environment. |
