JPH0714210A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To provide an optical information recording medium from which reproduced signals having very little inter-pit interference can be obtained and which can be applied to phase transition type disks also. CONSTITUTION:A magneto-optical type optical information recording medium has a multilayered dielectric film 2 the transmissivity of which depends upon the incident angle of light on a transparent substrate 1 in which grooves and phase pits are formed. The medium also has a protective film 3 and recording film 4 successively formed on the dielectric film 2 so that the interval between the films 3 and 2 can be kept constant by the protective film 3. In addition, a protective film 5 and reflecting film 6 are successively formed on the recording film 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium in which information is recorded in high density, and more specifically, a function for converting information recorded in high density into high quality and high resolution optical information. And an optical information recording medium having

[0002]

2. Description of the Related Art FIG. 5 shows a schematic sectional view of a magneto-optical disk as an example of a conventional optical information recording medium. In a conventional magneto-optical disk, a first protective layer 3 having an enhancing effect is formed on a transparent substrate 1 such as polycarbonate, and a magneto-optical recording layer 4, a second protective layer 5, and a reflective layer are formed on the first protective layer 3. The structure has the aluminum layer 6 which is Further, an example is known in which a magnetic super-resolution magnetic film using an exchange coupling film is applied to the magneto-optical recording film 4.

[0003]

SUMMARY OF THE INVENTION In the prior art,
The recording layer of the magneto-optical disk has a form in which recording and reproducing are always performed in a state in which the beam waist position narrowed down to the diffraction limit by the objective lens of the optical head used for recording and reproducing information on the recording layer is always matched. However, since the diameter of the beam waist is determined by the numerical aperture of the objective lens and the wavelength of light emitted by the laser, the resolution is naturally limited. Further, when utilizing the magnetic super-resolution, an initializing magnet, a reproducing bias magnet and the like were required. Furthermore, because the laser power during playback is higher than in the normal playback system,
There is a problem that the recorded magnetic domain is easily destroyed. Therefore, the problem to be solved by the present invention is
It is intended to improve the resolution limit determined by the wavelength of irradiation light and the numerical aperture of the objective lens to increase the recording capacity.

[0004]

In order to solve the above problems, the present inventor has found out to use a dielectric multi-layered layer whose transmittance greatly depends on the incident angle of irradiation light, and arrived at the present invention.

That is, in order to solve the above-mentioned problems, the present invention provides (1) a dielectric multilayer film whose transmittance depends on the incident angle of irradiation light on a substrate on which grooves and phase pits are formed. (2) A protective layer and a recording layer are sequentially provided on the dielectric multilayer film, and the distance between the recording layer and the dielectric multilayer film is kept constant by the protective layer. (3) The optical information recording medium according to (1) above, and (3) a magneto-optical recording medium according to (2) above, wherein a protective layer and a reflective layer are sequentially provided on the recording layer. An optical information recording medium as described above is provided.

Materials used for the dielectric multilayer film of which transmittance depends on the incident angle of irradiation light used in the present invention include, for example, SiN _x , SiO _x , ZnS, etc., and are shown in FIG. It satisfies the relationship between the incident angle of irradiation light and the transmittance, and is formed by the vacuum deposition method. Note that the relationship between the irradiation light and the transmittance shown in FIG. 2 is that the set wavelength is 780 nm ± 10 nm.
And the transmittance on the vertical axis is 100% at vertical incidence.
Is the relative transmittance. As is clear from FIG. 2, since the incident angle dependence of the transmittance behaves almost the same as the wavelength dependence of the transmittance, when the wavelength is fixed, the transmittance decreases as the incident angle increases. .

The substrate used in the present invention is, for example,
Examples thereof include a substrate in which a guide groove is directly formed in resin or glass such as polycarbonate, polymethylmethacrylate, and amorphous polyolefin, and a substrate in which a guide groove is formed on a flat plate of glass or resin by a photopolymer method.

The resin-made substrate has insufficient scratch resistance,
In order to overcome such a defect, it is desirable to provide a hard coat layer on the surface opposite to the recording layer using a transparent material having high hardness. As a means for hard coating, a method of applying and curing an organic polymer such as a UV-curable resin containing a polyfunctional urethane acrylate and a photopolymerization initiator by a spin coating method, a 2P method, or the like, silicon dioxide by a precipitation method, a sputtering method, or the like. And the like, a ceramic hard coat layer is not suitable for mass production due to poor productivity, and thus a hard coat layer using an ultraviolet curable resin is preferable.

Examples of the material forming the magneto-optical recording layer used in the present invention include TbFeCo, DyFeCo,
TbFe, GdTbFeCo, NdDyFeCo, Tb
Co and the like can be mentioned, and those obtained by adding other metals to these amorphous alloys for the purpose of improving oxidation resistance can also be used.

As the sputtering conditions for forming the magneto-optical recording layer, the sputtering gas pressure is changed. in this case,
Although the same target is used, the film formation rate varies depending on the sputtering gas pressure. Therefore, in order to control the film thickness, the film formation rate is obtained in advance and the sputtering time at each gas pressure is determined.

The material of the protective layer used in the present invention is
In general the optical constants and the transmittance is large, large SiN _X effect of protecting the recording layer, SiO _X, AlSiON, Al
_{SiN, AlN, AlTiN, Ta 2} O 5, ZnS , and the like.

The protective layer is formed by a physical vapor deposition method (PVD) such as sputtering or ion plating, or a chemical vapor deposition method (CVD) such as plasma CVD.

As the material of the reflective layer used in the present invention,
Examples thereof include Al and alloys of Al and other metals. Among them, an alloy in which Ti is added to Al which is considered to have a large effect of protecting the recording film is particularly preferable.

The reflective layer is formed by a physical vapor deposition method (PVD) such as sputtering or ion plating, a chemical vapor deposition method (CVD) such as plasma CVD, or the like.

The optical disk thus formed into a film may be used alone or may be used by laminating two disks.

[0016]

A reproducing system of an optical head used for recording / reproducing information on / from an optical information recording medium by using a dielectric multilayer film whose transmittance decreases as the incident angle of irradiation light increases, for an optical information recording medium. In the above, since the beam waist of the irradiation light transmitted through the dielectric multilayer film is sharper than the beam waist determined only by the numerical aperture of the objective lens and the wavelength of the irradiation light, the reproduction resolution of the recording pit is improved.

[0017]

The present invention will be described in detail below with reference to the drawings according to the embodiments of the present invention.

FIG. 1 is a schematic sectional view showing an example of the optical information recording medium of the present invention. The optical information recording medium shown in FIG. 1 has the characteristics shown in FIG. 2 on a transparent substrate 1 made of polycarbonate having grooves and phase pits.
The transmittance decreases as the incident angle of the irradiation light 7 increases, the dielectric multilayer film 2, the first protective layer 3 made of SiN, and Te.
Magneto-optical recording layer 4 made of FeCo, second layer made of SiN
The magneto-optical disk has a structure in which the protective layer 5 and the reflective layer 6 made of Al are laminated.

The dielectric multilayer film 2 satisfies the relationship between the incident angle of irradiation light and the transmittance shown in FIG. 2, is made of magnesium fluoride and silicon oxide, and is formed by the vacuum deposition method. .

The protective layer 3 is provided to keep the gap between the magneto-optical recording layer 4 and the dielectric multilayer 2 constant. The spacing is determined by the numerical aperture of the objective lens (not shown) of the optical head used for recording / reproducing information on / from the magneto-optical recording layer 4 and the plane wave of the beam waist position of the convergent light determined by the wavelength of the irradiation light 7 is spherical. Λ / π (f / a) (f /, where λ is the wavelength of the irradiation light 7, f is the focal length of the objective lens, and a is the radius of the objective lens. a)
It is represented by. In such a configuration, the focus control of the objective lens is performed so that the irradiation light 7 narrowed down to the diffraction limit by the objective lens reaches the dielectric multilayer film 2 in the region immediately before the transition from the spherical wave to the plane wave. There is. Further, the protective layer 3 has a function of enhancing the magneto-optical Kerr effect.

In FIG. 1, the beam profile of the irradiation light transmitted through the dielectric multilayer film 2 in the magneto-optical recording layer 4 simply shows the beam profile determined by the numerical aperture of the objective lens and the wavelength of the irradiation light 7. 3 to FIG. 4, and the beam waist becomes thin.

A part of the irradiation light 7 thus narrowed down is reflected by the magneto-optical recording layer 4. Further, the light flux which is not absorbed by the magneto-optical recording layer 4 and passes therethrough passes through the second protective layer 5, is reflected by the reflecting layer 6, and is irradiated with the irradiation light 7 reflected by the magneto-optical recording layer 4 again through the objective lens. After passing, it is guided to a magneto-optical signal detection optical system (not shown), and high-resolution signal detection is achieved.

[0023]

The luminous flux narrowed by the dielectric multilayer film 2 having the beam profile shown in FIG. 4 is applied to the magnetic domain recorded in the magneto-optical recording layer 4, so that reproduction with very little inter-pit interference is performed. The signal is obtained. In other words, the recording areal density can be dramatically improved, the size of the medium can be reduced, and the medium drive device can be reduced in size. Further, in the present invention, since the conventional medium driving device can be used as it is without any modification to the medium driving device, it is very advantageous in terms of compatibility. Furthermore, the present invention is very versatile because it is not directly related to the recording layer, and can be applied to a phase change disk. Therefore, the present invention can provide an optical information recording medium suitable for high density recording / reproducing.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of an optical information recording medium of the present invention.

FIG. 2 is a chart showing the incident angle dependence of the transmittance of irradiation light in the dielectric multilayer film used in the present invention.

FIG. 3 is a beam profile of a light flux narrowed down to a diffraction limit determined by a numerical aperture of an objective lens and a wavelength of irradiation light.

FIG. 4 is a beam profile of irradiation light on a recording layer of the optical information recording medium of the present invention.

FIG. 5 is a schematic cross-sectional view showing an example of a conventional optical information recording medium.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Dielectric multilayer film 3 First protective layer 4 Magneto-optical recording layer 5 Second protective layer 6 Reflective layer 7 Irradiation light

Claims (3)

[Claims] 1. An optical information recording medium, characterized in that a dielectric multilayer film whose transmittance depends on an incident angle of irradiation light is provided on a substrate on which grooves and phase pits are formed. 2. A protective layer and a recording layer are sequentially provided on the dielectric multilayer film, and the gap between the recording layer and the dielectric multilayer film is kept constant by the protective layer. Item 1. The optical information recording medium according to item 1. 3. An optical information recording medium according to claim 2, wherein a protective layer and a reflective layer are sequentially provided on the recording layer.