JPH0628724A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To provide the magneto-optical recording medium which has excellent reliability and sensitivity and is less changed in the laser output necessary for recording from the inner peripheral part to the outer peripheral part by changing the film thickness of a first dielectric layer and the Al compsn. of an Al alloy reflection layer in a diametral direction. CONSTITUTION:This magneto-optical recording medium is constituted by laminating the first dielectric protective layer 2, a magneto-optical recording layer 3, the second dielectric protective layer 4, the Al alloy reflection layer 5a and a UV curing resin layer 6 in this order on a transparent disk substrate 1. The ratio of the At compsn. of the Al alloy reflection layer 5a is lower the nearer the outer periphery of the diameter of the recording medium. In addition, the film thickness of the first dielectric protective layer 2a changes likewise in the same diametral direction and the outer peripheral side is thinner than the inner peripheral side. The first dielectric protective layer 2a acts a heat reservoir in the case where the heat of the magneto-optical recording layer 3 diffuses. The magneto-optical recording layer 3 is more easily deprived of heat as the film thickness of this layer is larger. In addition, the thermal efficiency by the irradiation with the laser on the peripheral side is made better than on the inner peripheral side. The thermal efficiency of the Al alloy reflection layer is improved as well by increasing the ratio of the Ti compsn. on the outer peripheral side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium for recording, reproducing and erasing information by using laser light.

[0002]

2. Description of the Related Art As a magneto-optical recording method, a so-called CAV method is widely used in which a magneto-optical disk is used while rotating at a constant rotational speed in order to simplify a magneto-optical recording apparatus. In order to record on a magneto-optical disk, it is necessary to heat the part to be recorded above a certain temperature.
In the V method, the linear velocity of the disk in the laser irradiation portion is higher on the outer peripheral side than on the inner peripheral side, and the thermal efficiency is reduced. Therefore, in order to make the temperature of the laser irradiation portion uniform over the entire surface of the disk, a stronger laser output is required toward the outer circumference.

However, when the magneto-optical disk is driven by the CAV method, it is necessary to increase the power margin of the semiconductor laser and increase the output control in order to increase the recording laser output stepwise from the inner circumference toward the outer circumference. It complicates the circuit, etc. and is a burden on the drive side.

In Japanese Patent Application Laid-Open No. 57-152555, T
The Curie point is continuously reduced from the inner circumference to the outer circumference by the magneto-optical recording layer in which the composition of bFe is continuously changed from the inner circumference to the outer circumference. By changing the Curie point, the contrast of recorded bits is made uniform.
However, controlling the composition of the recording layer on the inner and outer peripheries of the disk is complicated in terms of film-forming technology, and it is particularly difficult for the sputtering method, which is excellent in terms of throughput and yield.

In Japanese Patent Laid-Open No. 61-211852, in a magneto-optical recording medium having a supporting substrate, a protective layer, a magneto-optical recording layer and a reflecting layer, the thickness of the reflecting layer is changed in the radial direction. However, in this structure, since the reflective layer is in close contact with the magneto-optical recording layer, the thermal diffusivity is large, and the laser output required for recording is large compared with the case where the second dielectric protective layer is provided, and the power margin is increased. Is not preferable. Further, a large change in film thickness is required to set the thermal diffusivity gradient in the radial direction. This is one of the causes of lowering the reliability of the disc.

In Japanese Patent Laid-Open No. 3-69039, in a magneto-optical recording medium having a transparent disk-shaped substrate, a dielectric, a heat diffusion film, and a protective film, the thickness of the heat diffusion film is changed from the central portion to the outer peripheral portion of the substrate. It is continuously or stepwise thinned over time. This case is also not preferable for the same reason as in JP-A-61-211852.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magneto-optical recording medium which is excellent in reliability and sensitivity and has a small change in laser output required for recording from the inner circumference to the outer circumference.

[0008]

The above object of the present invention is to provide a first dielectric protective layer, a magneto-optical recording layer, a second dielectric protective layer, an Al alloy reflective layer and an ultraviolet curable resin on a transparent disk substrate. A first dielectric protective layer, an Al alloy reflective layer, a second dielectric protective layer among the layers of the magneto-optical recording medium in which the layers are laminated in this order,
This is achieved by continuously or stepwise changing the film thickness of the magneto-optical recording layer in the radial direction of the recording medium, or by further changing the Al composition of the Al alloy reflective layer in the radial direction.

That is, the Al composition of the Al alloy reflective layer changes in the radial direction, the proportion of the Al composition decreases toward the outer periphery of the diameter, and the film thickness of the first dielectric protective layer changes in the radial direction of the recording medium. In this case, the magneto-optical recording medium is characterized in that the film thickness on the outer peripheral side is thinner than that on the inner peripheral side.

Further, the film thickness of the first dielectric protective layer changes in the radial direction of the recording medium, in which case the film thickness on the outer peripheral side is thinner than that on the inner peripheral side and the film thickness of the Al alloy reflective layer is the recording medium. Of the magneto-optical recording medium in which the film thickness on the outer peripheral side is thinner than that on the inner peripheral side.

Furthermore, the film thickness of the first dielectric protective layer changes in the radial direction of the recording medium, the film thickness on the outer peripheral side is smaller than that on the inner peripheral side, and the film thickness of the second dielectric protective layer. Changes in the radial direction of the recording medium, and at that time, the film thickness on the outer peripheral side is thicker than that on the inner peripheral side.

Further, the film thickness of the first dielectric protective layer changes in the radial direction of the recording medium, the film thickness on the outer peripheral side is smaller than that on the inner peripheral side, and the film thickness of the magneto-optical recording layer is smaller than that of the recording medium. Of the magneto-optical recording medium in which the film thickness on the outer peripheral side is thinner than that on the inner peripheral side.

The present invention will be described below with reference to the drawings.
For convenience of comparison, the conventional magneto-optical recording medium will be described first.

FIG. 1 shows a conventional magneto-optical recording medium, in which a first dielectric protective layer 2, a magneto-optical recording layer 3, a second dielectric protective layer 4 and an Al alloy reflective layer 5 are provided on a transparent disk substrate 1. And the ultraviolet curable resin layer 6 are laminated in this order. When the magneto-optical disk is rotating at 1800 rpm, the radius is 24
Since the linear velocity in mm is 4.5 m / s and the linear velocity in a radius of 39.5 mm is 7.4 m / s, when the recording medium is heated with the same laser output, the energy received per unit area becomes closer to the outer circumference. Becomes smaller, and it is necessary to increase the laser output toward the outer peripheral side in order to heat the irradiation part to a uniform temperature over the entire surface of the disk. That is, in the CAV method,
It is necessary to increase the laser output required for recording on the outer circumference side than the inner circumference side. When the output of the recording laser is appropriate, an appropriate recording bit is formed in the magneto-optical recording layer, but when the laser output above the appropriate level is applied, the recording bit becomes too large and the CNR (Carrier to Noise Ratio) decreases. . The CNR is also reduced when the laser output is below the proper level.

In the conventional case of FIG. 1, a silicon nitride film as a first dielectric protection layer 2 is 900Å and a magneto-optical recording layer 3 is Dy15T on a polycarbonate substrate 1 having a diameter of 86 mm.
b7Fe70Co8 is 200 Å The second dielectric protection layer 4 is a silicon nitride film 300 Å, the Al alloy reflection film 5 is an aluminum / titanium alloy 500 Å, and the UV curable resin 1 μm is laminated. The sex is shown in FIG. Radius 24.1mm
And the non-uniformity of CNR at a radius of 39.5 mm is noticeable.

FIG. 2 shows an embodiment of the magneto-optical recording medium of the present invention. The first dielectric protective layer 2a is a silicon nitride film having a refractive index of 2.15, a radius of 24 mm, a length of 1000 Å, and a radius of 3.
The film was formed to have a thickness of 900 Å at 9.5 mm. Further, the Al composition of the Al alloy reflection layer 5a is changed continuously or stepwise so that the Al composition reaches 95% at the innermost circumference and 90% at the outermost circumference. Ti is used as an element added to Al.
The conditions for the other layers are the same as in FIG.

The first dielectric protective layer acts as a heat reservoir when the heat of the magneto-optical recording layer 3 heated by the laser diffuses, and the thicker the first dielectric protective layer is, the magneto-optical recording layer. It becomes easy to take away heat from. For this reason, the thermal efficiency of the laser irradiation on the outer peripheral side relative to the inner peripheral side is improved. Further, since the Al alloy having a higher proportion of Ti has a lower thermal conductivity, the heat is less likely to escape toward the outer peripheral side, and the thermal efficiency is improved.

FIG. 7 shows the dependence of the CNR of the magneto-optical disk having this structure on the recording laser output. Inner circumference (radius 24.
2 mm) and the outer circumference (39.5 mm) have improved CNR uniformity. Therefore, it is not necessary to change the laser output between the inner circumference and the outer circumference of the disk.

FIG. 3 is a diagram showing another embodiment of the magneto-optical recording medium of the present invention, in which the first dielectric protective layer 2a has a refractive index of 2.15.
The silicon nitride film of 1000 Å with a radius of 24 mm and a radius of 3
Further, the magneto-optical recording layer 3a is made of a TbDyFeCo alloy having a radius of 24 mm and a thickness of 200 mm so as to be 900 Å at 9.5 mm.
Å, a film having a radius of 39.5 mm and a thickness of 150 Å. The conditions for the other layers are the same as in FIG. The heat of the magneto-optical recording layer 3a heated by the laser is diffused and emitted to the Al reflection layer 5 through the second dielectric protection layer 4, and the heat of the magneto-optical recording layer 3a is also discharged to the first dielectric protection layer 2a.
Be spread to. The heat capacity of the magneto-optical recording layer 3a increases as the film thickness increases. Moreover, since the film thickness of the first dielectric protective layer on the outer peripheral side is thin, the thermal efficiency by laser irradiation on the outer peripheral side is improved rather than on the inner peripheral side.

FIG. 4 shows another embodiment of the magneto-optical recording medium of the present invention. The first dielectric protective layer 2a is a silicon nitride film having a refractive index of 2.15 and a radius of 24 mm of 1000.
Å, the second dielectric protector 4a is a silicon nitride film having a refractive index of 2.15 of 250 Å with a radius of 24 mm and 300 Å with a radius of 39.5 mm.
The film was formed so as to become Å. The conditions for the other layers are the same as in FIG. Since the second dielectric protection layer acts as a thermal resistance when the heat of the magneto-optical recording layer 3 heated by the laser diffuses to the Al alloy reflection layer 5, the thicker the second dielectric protection layer is, the more the magneto-optical property is increased. It becomes difficult for heat to escape from the recording layer. Further, since the thickness of the first dielectric protective layer on the outer peripheral side is thin, the thermal efficiency due to laser irradiation on the outer peripheral side is improved rather than on the inner peripheral side.

FIG. 5 shows still another embodiment of the magneto-optical recording medium of the present invention. The first dielectric protective layer 2a is a silicon nitride film having a refractive index of 2.15 and a radius of 24 mm of 1000.
Å, the metal reflective layer 5b is made of aluminum / titanium alloy with a radius of 24 m so that the radius becomes 39.5 mm and 900Å.
The film was formed so as to have a thickness of 600Å in m and a radius of 39.5 mm in 500Å. The conditions for the other layers are the same as in FIG. The heat of the magneto-optical recording layer 3 heated by the laser is transmitted through the second dielectric protection layer 4 to the Al alloy reflection layer 5
It is diffused and emitted to b. The Al alloy reflection layer is a good conductor of heat, and the larger the thickness of the thin film, the larger the heat capacity, and the more the heat of the magneto-optical recording layer escapes, the cheaper it becomes. Moreover, since the film thickness of the first dielectric protective layer on the outer peripheral side is thin, the thermal efficiency by laser irradiation on the outer peripheral side is improved rather than on the inner peripheral side.

[0022]

As described above, in each of the magneto-optical recording media according to the present invention, the thermal efficiency of the laser irradiation on the outer circumference side with respect to the inner circumference is improved, so that the laser output is uniform over the entire disk surface. CNR is obtained. Therefore, the output control circuit of the semiconductor laser can be simplified.

[Brief description of drawings]

FIG. 1 is a schematic view showing a cross section of a conventional magneto-optical recording medium.

[Fig. 2]

[Figure 3]

[Figure 4]

FIG. 5 is a schematic view showing a cross section of the magneto-optical recording medium of the present invention.

[Figure 6]

7 is a diagram showing the recording laser output dependence of CNR of a magneto-optical recording medium, FIG. 6 showing that of a conventional magneto-optical recording medium, and FIG. 7 showing that of a magneto-optical recording medium of the present invention.

[Explanation of symbols]

 1 transparent substrate 2, 2a first dielectric protective layer 3, 3a magneto-optical recording layer 4, 4a second dielectric protective layer 5, 5a, 5b Al alloy reflective film 6 ultraviolet curable resin layer

Claims (8)

[Claims] 1. A first dielectric protective layer on a transparent disk substrate,
In a magneto-optical recording medium in which a magneto-optical recording layer, a second dielectric protective layer, an Al alloy reflective layer and an ultraviolet curable resin are laminated in this order, the film thickness of the first dielectric protective layer changes in the radial direction of the recording medium. In addition, the magneto-optical recording medium is characterized in that the alloy composition of the Al alloy reflective layer changes in the radial direction of the recording medium, and the proportion of Al composition on the outer peripheral side is lower than that on the inner peripheral side. 2. The first dielectric protective layer has a refractive index of 2.00 to
2. The silicon nitride film of 2.30, wherein the film thickness of the first dielectric protective layer located from the outermost peripheral portion to the innermost peripheral portion of the group of substrates is in the range of 800 to 1000Å. Magneto-optical recording medium. 3. The film thickness on the outer peripheral side of the first dielectric protective layer is thinner than that on the inner peripheral side, and the film thickness of the magneto-optical recording layer changes in the radial direction of the recording medium. 3. The magneto-optical recording medium according to claim 2, wherein is thinner than the inner peripheral side. 4. The magneto-optical recording layer is made of a TbDyFeCo alloy, and the film thickness of the magneto-optical recording layer located from the outermost peripheral side to the innermost peripheral portion of the substrate group is set in the range of 150 to 300Å. Item 3. A magneto-optical recording medium. 5. The film thickness on the outer peripheral side of the first dielectric protective layer is thinner than that on the inner peripheral side, and the film thickness of the second dielectric protective layer changes in the radial direction of the recording medium. The magneto-optical recording medium according to claim 2, wherein the film thickness is thicker than the inner peripheral side. 6. The second dielectric protective layer has a refractive index of 2.00 to
6. The silicon nitride film of 2.30, wherein the film thickness of the second dielectric protection layer located from the outermost peripheral portion to the innermost peripheral portion of the substrate group is in the range of 250 to 350Å. Magneto-optical recording medium. 7. The film thickness on the outer peripheral side of the first dielectric protective layer is thinner than that on the inner peripheral side, and the film thickness of the Al alloy reflective layer changes in the radial direction of the recording medium, in which case the film thickness on the outer peripheral side. 3. The magneto-optical recording medium according to claim 2, wherein is thinner than the inner peripheral side. 8. The magneto-optical recording medium according to claim 7, wherein the film thickness of the Al alloy reflective layer located from the outermost peripheral portion to the innermost peripheral portion of the groove of the substrate is in the range of 400 to 650Å.