JP2001216685A - Recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording medium in which warpage of the medium caused by changes in the environmental temperature can be decreased. SOLUTION: The magneto-optical recording medium 100 has a laminated body 10 on one face of a substrate 1 and has a warpage preventing film 9 on the other face. At least, one of the structural material or the film thickness of the warpage preventing film 9 is decided in such a manner that the product of the Young's modulus and the film thickness of the warpage preventing film 9 is almost equal to the total sum of the products of the Young's modulus and the film thickness of the respective layers 2 to 8 which constitute the laminated body 10. Thus, the stress added to the medium is balanced on both sides of the substrate 1 by a bi-metal effect and the warpage of the disk caused by changes in the environmental temperature is significantly decreased. This method is extremely suitable for an optical recording medium which uses a thin substrate having low rigidity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical recording medium in which a recording layer or the like is laminated on a substrate, and more particularly, to an optical recording medium capable of reducing a change in radial tilt due to a change in environmental temperature. .

[0002]

2. Description of the Related Art Optical recording media are widely used as information recording media on which digital data such as moving image data and audio data can be recorded or reproduced. Optical recording media are read-only optical recording media such as CDs and CD-ROMs,
Write-once optical recording media such as CD-R, MO and DVD-R
It is roughly classified into a rewritable optical recording medium such as W. In recent years, along with higher image quality and higher sound quality of moving images and audio data,
The amount of data handled is increasing. For this reason, in the optical recording medium, a further increase in the capacity is demanded in order to sufficiently cope with the increase in the data amount.

In order to meet this demand, a method of forming a fine recording mark to improve the recording density and reading out the fine recording mark with a fine light spot has been studied. The light spot diameter is proportional to the wavelength of light and inversely proportional to the numerical aperture of the lens that collects the light. Therefore, in order to reduce the light spot diameter, it is only necessary to shorten the wavelength of the laser light used for recording and reproduction or to increase the numerical aperture (NA) of the objective lens. This enables high-density recording.

However, when the numerical aperture of the objective lens is increased, the coma aberration of the lens increases, so that the margin for the tilt (tilt) of the optical recording medium becomes extremely small.
Therefore, in an optical recording medium for recording and reproducing information by irradiating light from the substrate side, it is necessary to reduce the thickness of the substrate.
For example, in the case of a DVD, a substrate (0.6 m thick) having about half the thickness of a substrate (1.6 mm thick) used for a CD is used.
By using m), the NA of the objective lens is increased.

[0005]

However, it has been found that the use of a thin substrate for an optical recording medium causes the following problems.

In an optical recording medium, a laminated body composed of a recording layer for recording information, a reproducing layer for reproducing information, and the like is usually formed on a substrate. For example, in the case of a magneto-optical recording medium, a magnetic film, a dielectric film, a metal reflection film, and the like are laminated. The constituent materials of the film bodies laminated on these substrates have different coefficients of thermal expansion. Therefore, when the temperature of the environment in which the optical recording medium is used changes, the optical recording medium is warped due to the difference in the coefficient of thermal expansion between the substrate and the material laminated on the substrate. In particular, since the rigidity of the substrate is proportional to the cube of the plate thickness, when the plate thickness is reduced to 1/2, the rigidity is extremely reduced to 1/8. In an optical recording medium using such a substrate, there is a problem that a radial tilt (a tilt angle of a disk) greatly changes according to an ambient temperature to be used. Further, when the laminated structure of the optical recording medium becomes complicated due to the high density, there is a problem that the radial tilt changes significantly due to the environmental temperature change.

[0007] Japanese Patent No. 2662474 discloses a magneto-optical storage element in which the warpage of a substrate is prevented. In this publication, in order to prevent warping of the substrate due to moisture absorption of the substrate when the substrate having various coating films formed on the back surface in a vacuum is taken out to the atmosphere, the surface of the substrate is covered with the coating film. A dielectric film is formed as a covering film. However, this publication does not describe or suggest warpage based on the difference in the coefficient of thermal expansion of the material laminated on the substrate. In the configuration of the magneto-optical memory element described in this publication, The problem of radial tilt change based on change cannot be solved.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide an optical recording system capable of reducing a warpage of a disk caused by a change in temperature of an environment in which the disk is used. To provide a medium.

[0009]

According to a first aspect of the present invention, there is provided a recording medium having a laminated body composed of a plurality of films on one surface of a substrate. There is provided a recording medium including a warpage preventing film for preventing the recording medium from warping caused by a change in temperature.

[0010] The recording medium of the present invention comprises, on one surface of a substrate, a laminate comprising, for example, a recording layer or a reproducing layer for recording information, and a recording medium on the opposite surface of the substrate. And a warp prevention film for preventing warpage. The warpage prevention film is obtained by adding the product of the Young's modulus and the film thickness of the material constituting the warpage prevention film and the product of the Young's modulus and the film thickness of each layer laminated on one surface for each layer. It is preferable that the difference from the sum is sufficiently small. That is, assuming that the first to n-th film bodies are formed as a laminate on one surface of the substrate, the Young's modulus of each of the film bodies is E1, E2,.
, En, and the film thickness are represented by h1, h2,... Hn, and the Young's modulus and the film thickness of the warpage preventing film are represented by Ec and hc, respectively, and | (E1 × h1) + (E2 × h2) + ・ ・
・ + (En × hn) − (Ec × hc) | ≦ 3.0 × 10
Preferably, an anti-warp film is formed on the other surface of the substrate so as to satisfy the relationship of ⁷ (dyn / cm) (= 3.0 × 10 ⁴ N / m). More preferably 1.0 × 10
⁷ (dyn / cm) (= 1.0 × 10 ⁴ N / m) or less. Here, when the optical recording medium is a magneto-optical recording medium, for example, if the optical recording medium is a magneto-optical recording medium, the first to n-th film bodies constituting the laminated body include magneto-optical layers such as a magneto-optical recording layer, a reproducing layer, a reflective layer, and a dielectric layer. It corresponds to a known layer used in a recording medium. If the warpage prevention film is configured so as to satisfy the above conditions, the optical recording medium hardly warps even when the environmental temperature at which the optical recording medium is used changes. The change in the environmental temperature includes not only the ambient temperature in which the optical recording medium is used, but also the case where the temperature of the optical recording medium itself rises due to irradiation of the optical recording medium with recording or reproduction light.

Further, since the recording medium of the present invention has an anti-warpage film, even if the thickness of the substrate used for the optical recording medium is reduced to 0.7 mm or less, for example, It is possible to reduce the occurrence of warpage due to the difference in the coefficient of thermal expansion from the film laminated on the substrate. That is, by providing an anti-warpage film on the substrate surface opposite to the side on which the laminated body is formed, the stress applied to the recording medium generated by the bimetal effect is balanced, and the optical recording medium generated based on a change in environmental temperature. Warpage can be corrected.

When a laminated body including a recording layer and a reproducing layer is formed by sputtering or the like, the disk may be warped due to the film stress of each layer. However, the laminated body is formed with a warpage preventing film. By forming it on the substrate surface opposite to the side, the warpage of the disk caused by the film stress can be effectively reduced.

In the recording medium of the present invention, it is preferable that the warp prevention film is formed using silicon nitride, silicon oxide, silicon carbide, or a mixture thereof. Also,
The materials constituting the anti-warpage film are selected such that the refractive index is represented by nc and the refractive index of the substrate is represented by ns so that they satisfy the relationship of | nc−ns | ≦ 0.3. Is preferably performed. More preferably, it is 0.15 or less. Accordingly, when light is incident from the substrate side, it is possible to prevent the incident light from being reflected at the interface between the warpage prevention film and the substrate.

Further, it is preferable that the warp prevention film of the optical recording medium of the present invention is formed using a material having a high Young's modulus. As described above, the product of the Young's modulus and the film thickness of the anti-warpage film is equal to a desired value, that is, a value obtained by adding the product of the Young's modulus and the film thickness of each film body constituting the laminate. Since the material and thickness of the warp prevention film are selected so that the material has a high Young's modulus, the thickness of the warp prevention film can be reduced. Therefore, when the warpage prevention film is formed by using, for example, a sputtering method or the like, the film formation time can be shortened, and the optical recording medium is excellent in mass production. As a material having a high Young's modulus, for example, Si
N, SiC, SiO, diamond-like carbon,
Mixtures containing some of them can be used.

The substrate used for the recording medium of the present invention is preferably, for example, a resin substrate made of polycarbonate, amorphous polyolefin, polymethyl acrylate, or polystyrene, or a glass substrate. 0.8mm ~
0.3 mm is preferred.

According to a second aspect of the present invention, in a recording medium having a single film on one surface of a substrate, the recording medium is prevented from warping caused by a temperature change on the other surface of the substrate. A recording medium provided with a warp prevention film for performing the recording.

The recording medium of the present invention includes, for example, a single film such as a reflective layer on a substrate surface on which information is formed as a concavo-convex pattern, and a substrate on the opposite side to the surface on which the reflective layer is formed. An anti-warpage film is provided on the surface. As the difference between the product of the Young's modulus and the film thickness of the material constituting the warpage prevention film and the product of the Young's modulus and the film thickness of the material constituting the single film such as the reflective layer is reduced. The material and the thickness of the warpage prevention film are selected. By forming the warpage prevention film in this way,
It is possible to effectively prevent the recording medium from being warped due to a temperature change. Such a recording medium is suitable, for example, as a read-only optical recording medium that irradiates a medium with light and reproduces information by using a change in light intensity of reflected light from the medium.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the optical recording medium according to the present invention will be specifically described with reference to the drawings, but the present invention is not limited thereto.

[0019]

FIG. 1 schematically shows a sectional structure of a magneto-optical recording medium according to the present invention. The magneto-optical recording medium 100 has the laminated body 10 on one surface of the transparent substrate 1 and has the warpage prevention film 9 on the other surface. The laminate 10 includes a first dielectric layer 2,
It has a structure in which a reproduction layer 3, a reproduction auxiliary layer (mask layer) 4, a nonmagnetic layer 5, a recording layer 6, a second dielectric layer 7, and a heat radiation layer 8 are sequentially laminated.

In the structure shown in FIG.
Is a polycarbonate substrate produced by using an injection molding machine (not shown), and has irregularities on its surface corresponding to the preformat pattern. The refractive index of the transparent substrate 1 is 1.5
6, and the plate thickness was 0.6 mm. First dielectric layer 2
Is a layer for causing a reproduction light beam to cause multiple interference in the layer to substantially increase the detected Kerr rotation angle;
N. The reproduction layer 3 is a layer to which the magnetization information of the recording layer 6 is transferred, and is made of a rare earth-transition metal amorphous film GdFeCo which shows in-plane magnetization at room temperature. The reproduction auxiliary layer 4 is a layer that functions as a mask layer during information reproduction, and is a rare earth-transition metal amorphous film G that exhibits in-plane magnetization at room temperature.
It is composed of dFe. The nonmagnetic layer 5 is a layer for cutting the exchange coupling force between the reproducing layer 3 and the recording layer 6 to perform magnetostatic coupling, and is made of SiN. The recording layer 6 is a layer in which information is recorded as magnetization information, and is composed of a rare earth-transition metal amorphous film TbFeCo having perpendicular magnetization. The second dielectric layer 7 and the heat radiating layer 8 are both layers for controlling the heat distribution by the laser beam.
It consists of 1Ti. The warp prevention film 9 is a layer for preventing warpage of the magneto-optical recording medium due to a change in environmental temperature, and is made of SiN. These layers 2 to 9 were sequentially formed using a sputtering apparatus (not shown) as shown below.

First, layers 2 to 8 were formed on one surface of the substrate. In forming the first dielectric layer 2, SiN was used as a target material, and the film thickness was 60 nm. In the formation of the reproducing layer 3, a Gd simple substance target and a Fe ₈₀ Co ₂₀ alloy target were simultaneously sputtered. In the simultaneous sputtering, the compensation temperature and the Curie temperature of the reproduction layer after film formation are both 300 ° C. or more, and the critical temperature at which the easy magnetization direction transitions from the in-plane direction to the vertical direction is about 150 ° C. Film formation was performed while changing the ratio of the input power. The thickness of the reproducing layer 3 was 30 nm.

In forming the auxiliary reproduction layer 4, a single target of Gd and a single target of Fe are simultaneously sputtered, and the Curie temperature of the auxiliary reproduction layer 4 after the film formation is set to 150 ° C.
Films were formed while changing the ratio of the power supplied to each target. The thickness of the reproduction auxiliary layer 4 was 15 nm. Non-magnetic layer 5
In the film formation, SiN was used as a target material, and the film thickness was 5 nm. In the formation of the recording layer 6, a Tb simple substance target and an Fe ₉₀ Co ₁₀ alloy target are simultaneously sputtered, and each target is adjusted so that the compensation temperature of the recording layer after film formation is about 75 ° C. and the Curie temperature is 250 ° C. The film formation was performed while changing the input power ratio. The thickness of the recording layer 6 is 50 n
m.

In forming the second dielectric layer 7, SiN was used as a target material, and the film thickness was set to 20 nm. In forming the heat radiation layer 8, Al ₉₇ Ti ₃ was used as a target material, and the film thickness was set to 40 nm.

Next, the substrate was turned upside down, and an anti-warpage film was formed on the surface opposite to the side on which the layers 2 to 8 were laminated.
In forming the anti-warpage film, SiN was used as a target material, and the film thickness was 200 nm. Thus, a magneto-optical recording medium 100 having the laminated structure shown in FIG. 1 was manufactured. Table 1 below shows the Young's modulus, the film thickness of each of the layers 2 to 9 constituting the laminate 10 and the product thereof.

[0025]

[Table 1]

The obtained magneto-optical recording medium 100 is a magneto-optical recording medium capable of reproducing information according to a CAD type magnetic super-resolution reproducing method. This magneto-optical recording medium 100
For example, a magnetic field modulation recording method or an optical pulse magnetic field modulation recording method may be used to record information at high density. For example, in the magnetic field modulation recording method, a magnetic head (not shown) for applying a magnetic field to the magneto-optical recording medium 100 is placed on the side opposite to the substrate 1, that is, on the side (film) on which a film such as the recording layer 6 is formed. Surface side)
Need to be close to. Therefore, the single-plate structure shown in FIG. 1 is adopted as the medium structure as in the present embodiment. In addition, when recording information, it is necessary to make the magnetic head run stably on the film surface, so that the medium is required to be flat. As will be described later, the magneto-optical recording medium 100 according to the present embodiment allows the magnetic head to run stably on the film surface because there is almost no change in radial tilt. Thus, information can be reliably recorded from the film surface side. The optical recording medium of the present invention is particularly effective for a thin recording medium that satisfies (medium thickness) / (medium diameter) ≦ 5.0 × 10 ⁻³ .

Next, regarding the magneto-optical recording medium 100,
The change in radial tilt was measured using a tilt sensor while changing the environmental temperature. In the measurement of the radial tilt, the magneto-optical recording medium 100 was subjected to environmental conditions (25 ° C., 5 ° C.).
0% RH), environmental conditions (55 ° C., 30% RH), and environmental conditions (5 ° C., 50% RH) for two hours.
The radial tilt at a predetermined position of 0 was measured. At this time, it took one hour each to shift from the environmental condition to the environmental condition and to shift from the environmental condition to the environmental condition. The measurement results under these conditions are shown in the graph of FIG. In this graph, for the sake of comparison, the warpage prevention film was made of SiO ₂ and its film thickness was adjusted to 400 nm and 100 nm.
Types of magneto-optical recording media (Comparative Example 1 and Comparative Example 2 respectively)
Are also shown. As can be seen from this graph, the magneto-optical recording medium of the present invention has a small radial tilt change amount under any of the environmental conditions
The maximum was 0.22 °. Therefore, it is possible to record and reproduce information very well. On the other hand, the two types of magneto-optical recording media shown as comparisons showed a significant change in radial tilt under environmental conditions. In particular, the radial tilt of the magneto-optical recording medium of Comparative Example 2 changed significantly under environmental conditions.

Although the optical recording medium according to the present invention has been described with reference to the embodiments, the present invention is not limited to this. In the above embodiment, a magneto-optical recording medium of a type in which light is incident from the substrate side is used, but the present invention can also be applied to a type in which light is incident from the side opposite to the substrate, that is, from the film side. In this case, it is not necessary to consider the light reflection at the interface between the warp prevention film and the substrate when selecting the material constituting the warp prevention film.

In the above embodiment, a magneto-optical recording medium was manufactured as the optical recording medium according to the present invention. However, the present invention is not limited to this, and it is also possible to manufacture a phase-change optical recording medium or a write-once optical recording medium. is there.

Further, in order to protect each layer laminated on the substrate, as shown in FIG. 3, an ultraviolet curable resin is further applied on the heat radiation layer 8 and cured to form an ultraviolet curable resin layer 11. It is also possible. in this case,
The UV-curable resin layer 11 is also regarded as a part of the laminate 10, and the product of the Young's modulus and the film thickness of the UV-curable resin layer 11 is further added to the sum of the product of the Young's modulus and the film thickness of each of the layers 1 to 8. The added value and the product of the Young's modulus and the film thickness of the warp prevention film 9 may be adjusted so as to be substantially equal to each other. Here, the UV-curable resin layer 11 is further formed on the warp prevention film 9 or the substrate 1.
And the anti-warp film 9. As described above, by similarly providing the ultraviolet curable resin layer 11 'on the side where the warpage prevention film 9 is formed, control for preventing warpage is further facilitated. In the present invention, FIG.
As shown in (1), it is also possible to additionally form an arbitrary film 2 ′... N ′ in addition to the warpage prevention film 1 ′ on the side where the warpage prevention film 1 ′ is formed. In this case, the thickness and material of each layer can be appropriately selected so as to satisfy the following formula.

[0031]

(Equation 1)

In the formula, E _k and E _l indicate the Young's modulus of the fifth layer and the l-th layer, respectively, and h _k and h _l indicate the thickness of the k-th layer and the l-th layer, respectively.

In order to prevent light reflection at the interface between the warp prevention film and the substrate, the multiple interference effect of light can be used. FIG. 5 is a graph showing the relationship between the light reflectance at the interface between the warpage prevention film and the substrate and the thickness of the warpage prevention film by calculation. In this calculation, when a warp preventing film and an ultraviolet curable resin layer are formed on one surface of the substrate as shown in FIG. 6, when a laser beam is incident from the ultraviolet curable resin layer side, The light reflectance was determined. The wavelength λ of the laser beam was 640 nm, the refractive index of the ultraviolet-curable resin layer was 1.59, the film thickness was 10 μm, and the refractive index of air was 1.0. The refractive index of the substrate is 1.59, and the refractive index of the warpage prevention film is 1.9, 2..
Cases of 0, 2.1, and 2.2 were shown. As shown in FIG. 5, it can be seen that the reflectance R changes according to the thickness d of the warpage prevention film. Therefore, by appropriately selecting the thickness d of the warp prevention film, surface reflection at the interface between the warp prevention film and the substrate can be sufficiently reduced (10% or less).

[0034]

The optical recording medium of the present invention has an anti-warp film on the substrate surface opposite to the surface on which the laminate composed of the recording layer and the reproducing layer is formed. Is
Since the product of the Young's modulus and the film thickness is adjusted so as to be substantially equal to the sum of the products of the Young's modulus and the film thickness of each layer constituting the laminate, the product is generated based on the change in the environmental temperature. The amount of change in radial tilt can be significantly reduced. Further, since the recording medium of the present invention can correct the warpage of the optical recording medium caused based on the difference between the coefficient of thermal expansion of each layer constituting the laminate and the coefficient of thermal expansion of the substrate, by the warpage prevention film. This is extremely effective for a recording medium having a thin substrate for high density recording.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a magneto-optical recording medium according to the present invention.

FIG. 2 is a graph showing an amount of change in radial tilt with respect to a change in environmental temperature.

FIG. 3 is a diagram showing a state in which an ultraviolet-curable resin layer is formed on a reflection layer and a warpage prevention film of the magneto-optical recording medium shown in FIG.

FIG. 4 is a view showing a structure in which first to n-th layers are formed on one surface of a substrate;
FIG. 4 is a diagram schematically illustrating a cross-sectional structure of a recording medium having a warpage prevention film 1 ′ and second ′ to n′th layers formed on the other surface.

FIG. 5 is a graph showing the relationship between the light reflectance at the interface between the warpage prevention film and the substrate and the thickness of the warpage prevention film.

FIG. 6 is a diagram for explaining a calculation condition of light reflectance at an interface between the warpage prevention film and the substrate shown in FIG. 5, wherein the warpage prevention film and the ultraviolet curable resin layer are provided on one surface of the substrate. The state when laser light is incident from the UV-curable resin layer side when formed is shown.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 1st dielectric layer 3 Reproducing layer 4 Reproducing auxiliary layer 5 Nonmagnetic layer 6 Recording layer 7 2nd dielectric layer 8 Heat dissipation layer 9 Warp prevention film 10 Stack 100 Magneto-optical recording medium

Continuing on the front page (72) Inventor Katsusuke Shimazaki 1-88 Ushitora, Ibaraki City, Osaka Prefecture Inside Hitachi Maxell Co., Ltd. (72) Eiji Koyama 1-188 Ushitora 1-City, Ibaraki City, Osaka Hitachi Maxell F term in the company (reference) 5D029 HA07 KB14 LA13 LA14 LA16 LA17 LB02 LB07 LC06 LC11 NA19 5D075 EE03 FG10

Claims (11)

[Claims] 1. A recording medium comprising a laminated body composed of a plurality of film bodies on one surface of a substrate, wherein the other surface of the substrate is warped to prevent the recording medium from being warped due to a change in temperature. A recording medium characterized by comprising a prevention film. 2. The product of the Young's modulus and the film thickness of the warpage prevention film is the sum of the product of the Young's modulus and the film thickness of each film constituting the laminate for each film. The recording medium according to claim 1, wherein the recording medium is substantially equal to: 3. The laminated body is composed of n layers (n is an integer of 2 or more) of films, and the first to n-th films have Young's moduli of E1, E2,. , The film thicknesses of the first to n-th film bodies are represented by h1, h2,.
When the Young's modulus of the warpage prevention film is represented by Ec and the film thickness is represented by hc, they are | (E1 × h1) + (E2 × h2)
+ ... + (En × hn) − (Ec × hc) | ≦ 3.0
The recording medium according to claim 1, wherein a relationship of × 10 ⁷ (dyn / cm) is satisfied. 4. The recording medium is a magneto-optical recording medium,
The recording medium according to any one of claims 1 to 3, wherein the laminate includes a recording layer on which information is recorded, a reproduction layer on which information on the recording layer is transferred, and a dielectric layer. 5. The refractive index of the warpage prevention film is represented by nc,
When the refractive index of the substrate is expressed in ns, they are |
The recording medium according to claim 1, wherein a relationship of nc−ns | ≦ 0.3 is satisfied. 6. The thickness of the substrate is 0.3 mm to 0.8.
The recording medium according to any one of claims 1 to 5, wherein the distance is within the range of mm. 7. The recording medium according to claim 1, wherein information is recorded by using a magnetic field modulation method. 8. The method according to claim 1, wherein the temperature change of the radial tilt in a temperature range of 5 ° C. to 60 ° C. is in a range of −0.5 ° to + 0.5 °. The recording medium according to claim 1. 9. The method according to claim 1, wherein the warpage prevention film is formed using at least one selected from the group consisting of silicon nitride, silicon oxide, and silicon carbide, or a mixture thereof. The recording medium according to claim 1. 10. A recording medium provided with a single film on one surface of a substrate, wherein a warpage preventing film for preventing warpage of the recording medium caused by a temperature change is provided on the other surface of the substrate. Recording medium characterized by the above-mentioned. 11. The recording medium according to claim 10, wherein the recording medium is an optical recording medium from which information is reproduced by using a change in light reflectance, and the single film is a reflection layer. Recording medium.