Sony Corporation

Mikio Yoshida

Masaki Takenouchi

Atsushi Takeuchi

Etsuro Ikeda

Shuichi Igarashi

An optical disc having a functional film, formed by a thin metal plate, and a protective film, formed on a transparent substrate, is disclosed. The protective film satisfies a condition d.gtoreq.2d.sub.0, where d is a maximum film thickness at an outer periphery of the protective film and d.sub.0 is a mean film thickness at a flat portion on a data area. A magneto-optical disc having a functional film which is a metal thin film having magneto-optical effects is also disclosed, wherein the protective film satisfies a condition that a difference L.sub.1 between a maximum film thickness d at the outer periphery of the protective film and a mean film thickness d.sub.0 at a flat portion of the data area is 40 .mu.m or less and the protective film has a curved surface having a radius of curvature R.sub.1 .gtoreq.12.48 mm at the outer periphery of the protective film. The present invention provides an optical disc having superior recording properties and a sufficient corrosion resistance even when the disc is provided with a highly corrosive thin metal film, such as a rare earth-transition metal amorphous thin film.

Optical disc having a protective layer which is thicker at its outer

An optical disc having, as a recording layer, a first Sb--Se based thin film, a Bi--Te based thin film and a second Sb--Se based thin film, deposited in this order on a disc substrate, and a thin Al film deposited on the recording layer, is disclosed. Each of the first Sb--Se thin film and the second Sb--Se thin film has a composition such that Se accounts for not less than 70 atm % of the composition. The film thicknesses of the first Sb--Se based thin film and the second Sb--Se based thin film are set to not larger than 30 nm and to 15 to 25 nm, respectively, with the reflectance of the recording layer with respect to the laser beam with a wavelength of 680 nm being 10 to 25%. Alternatively, the first Sb--Se based thin film is of Sb.sub.2 Se.sub.3, the Bi--Te based thin film is of Bi.sub.2 Te.sub.3 and the second Sb--Se based thin film is of Sb.sub.2 Se.sub.3, and the film thickness of the second Sb--Se based thin film is set to 15 to 25 nm, so that the reflectance of the recording layer with respect to the laser beam with a wavelength of 680 nm will be 10 to 25%.

Optical disc

A magneto-optic disc comprised of a substrate on which are formed a recording layer and a protective film and on which information is recorded by a magnetic head floating above the magneto-optic disc by a predetermined floating distance at least at the time of recording the information, wherein the height of the projections on the surface of the protective film of the magneto-optic disc is smaller than the floating distance of the magnetic head.

Growing community of inventors

Miyagi, Japan

Mikio Yoshida