JP3205921B2 - Magneto-optical recording medium - Google Patents

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,
In particular, it relates to a magneto-optical recording medium having an improved life.

[0002]

2. Description of the Related Art Magneto-optical disks use a laser beam for recording, reproducing and erasing information, so that they have a large storage capacity like conventional optical disks, and are rewritten because a magnetic material is used for the recording layer. Is possible. In addition, recording and reproduction can be performed in a non-contact manner, and since there is no influence from dust, the reliability is excellent. Further, since it was commercialized several years ago, the development to an optical file system and the like has been rapidly progressing, and active research is being conducted with the aim of improving performance.

When the substrate of the magneto-optical recording medium is glass, it is easily broken, is expensive, and it is not easy to form a pre-blue. Therefore, polycarbonate (PC), amorphous polyolefin (APO), etc. obtained by injection molding are used. Plastic substrates are generally used.

[0004] Materials for the magneto-optical recording layer (hereinafter abbreviated as recording layer) include, for example, TbFeCo and NdDyF.
Rare earth-transition metal (hereinafter abbreviated as RE-TM) amorphous alloys such as eCo and TbDyFeCo are currently most frequently used because they have no grain boundary noise and a perpendicular magnetization film can be easily obtained by using sputtering. ing.

[0005] However, particularly the rare earth (hereinafter abbreviated as RE) component of this RE-TM amorphous alloy is susceptible to oxidative corrosion, and the magnetic properties such as the coercive force and perpendicular magnetic anisotropy of the film deteriorate with time. There is a disadvantage of doing so. This oxidative corrosion is caused by oxygen remaining in the vacuum chamber when the recording layer is formed, oxygen or water adsorbed on the surface of the plastic substrate, oxygen contained in the target material in the vacuum chamber, oxygen or water in the atmosphere, etc. However, a particularly significant effect is the intrusion of oxygen and water from the substrate and the atmosphere. Therefore, a method of covering the recording layer from both sides with a dielectric film such as a SiN film has been adopted as means for preventing intrusion of oxygen or water.

On the other hand, under severe environmental conditions such as high temperature and high humidity or a rapid change in temperature and humidity, a magneto-optical recording medium using a plastic substrate is locally localized due to the difference in linear expansion coefficient between the substrate and each layer. There is a problem that cracks and peeling occur in the film, and the nucleus causes corrosion to progress throughout the film, thereby shortening the service life.

[0007] To solve this problem, for example, reverse sputtering is performed on the film formation surface of the plastic substrate to modify the substrate surface, thereby improving the adhesion between the substrate and each layer.
Means for preventing the occurrence of cracks and peeling have been proposed.

[0008] However, reverse sputtering has no effect if it is too weak, and if it is performed too strongly, the substrate temperature rises to deteriorate the mechanical properties (warpage and surface runout) of the substrate, or the unevenness of the substrate surface becomes large, resulting in reproduction. There is a problem that the noise level of the signal becomes high.

[0009]

Therefore, in order to prevent cracks and peeling, it is conceivable to provide an interference layer made of a material having strong adhesion to the plastic substrate between the plastic substrate and the recording layer. Further, it is necessary to use a dielectric material having a high refractive index (usually 1.8 or more) for this interference layer, and the apparent Kerr rotation angle (θk ) Is increased, thereby increasing the C (carrier) level, and decreasing the reflectivity, thereby lowering the N (noise) level.
/ N is to be improved.

Further, as described above, when a material which is susceptible to corrosion due to oxidation or the like, such as an RE-TM amorphous alloy, is used for the recording layer, the interference layer also has a role of preventing corrosion of the recording layer. There must be. It prevents water and oxygen from penetrating from the substrate, has high corrosion resistance of itself,
In addition, it is necessary that the reactivity with the recording layer is small.

As such a specific material, Si
Oxides such as O, SiO ₂ , Al ₂ O ₃ , and Ta ₂ O ₅ are mentioned. These oxides have strong adhesion to polycarbonate (PC) which is generally used as a plastic substrate, and have the above-described conditions as an interference layer.

However, when the interference layer is an oxide, the oxygen contained in the interference layer adversely affects the oxidizable RE (rare earth) or the like in the recording layer, so that it is liable to change with time and has a long life. There is a problem in the point.

An object of the present invention is to use an interference layer having a strong adhesion to a plastic substrate such as a PC and an excellent protective function of a recording layer, thereby preventing cracks and peeling even under severe environmental conditions. An object is to obtain a magneto-optical recording medium having a long life and high reliability.

[0014]

According to the present invention, there is provided a magneto-optical recording medium having at least an interference layer, a recording layer, and a protective layer sequentially provided on a plastic substrate. A magneto-optical recording medium comprising a thin film of an oxide containing 0.5 to 3 atomic% of Ar is provided.

Hereinafter, the configuration of the magneto-optical recording medium of the present invention will be described based on the configuration example of FIG. In FIG. 1, 1 is a plastic substrate with a pregroove, 2 is an interference layer, 3 is a recording layer, 4 is a protective layer, and 5 is a reflective layer.

As the plastic substrate 1, polycarbonate (PC), polymethyl methacrylate (PMM)
A) and a substrate made of a resin such as amorphous polyolefin (APO). These substrates are disk-shaped and have a thickness of about 0.6 to 1.2 mm.

In the present invention, an interference layer 2 is provided between the plastic substrate 1 and the recording layer 3. Interference layer 2
As described above, a transparent film having a high refractive index (1.8 or more) is used as described above, and the apparent Kerr rotation angle (θk) is increased by using multiple reflection of the reproduction light in this layer, whereby C ( Carrier level), and by lowering the reflectivity, the N (noise) level is lowered.
Improve. Further, the recording layer 3 must also serve as a protective layer for preventing corrosion. In addition, it is necessary to use a material having a strong adhesion to the plastic substrate 1. Disks were prepared using various oxides and the like for the interference layer 2 in Table 1 and subjected to a temperature / humidity cycle test (Z / AD test,
2 (see FIG. 2).

[0018]

[Table 1]

As shown in Table 1, a thin film of an oxide such as SiO or Ta ₂ O ₅ has a stronger adhesion to a polycarbonate substrate (PC) than other nitride thin films and the like. And peeling are not seen.

However, when the interference layer 2 is an oxide,
Oxygen contained in the interference layer 2 easily oxidizes the recording layer 3. Therefore, in the present invention, Ar is contained in these oxides forming the interference layer 2 and the content thereof is set to 0.5 to 3 atomic%, so that the recording layer 3 can be formed without impairing the adhesion to the plastic substrate 1. Interference layer 2 that does not adversely affect
Are obtained. Among them, Ta ₂ O ₅ containing Ar, in particular, an oxide represented by the following general formula (I) provides excellent characteristics.

Embedded image [Ta _X O _{100 — X} ] _Y Ar _{100 — Y} (I) (wherein the values of X and Y are 20 ≦ X ≦ 40, 97 ≦ Y
≤ 99.5. ) The Ar content in the interference layer 2 is:
It can be controlled by changing the film formation speed depending on each sputtering condition (see FIG. 3). The interference layer 2 may be a thin film having a two-layer structure, and the thickness varies depending on the refractive index, but is generally 500 to 1200 °, preferably 8 °.
It is 00-1200 °. When the interference layer 2 has a two-layer structure, the specific oxide thin film is formed on the plastic substrate 1.
On the side.

Next, as the recording layer 3, TbFeCo, N
RE-TM amorphous alloy thin films such as dDyFeCo and TbDyFeCo, BaFe ₁₂ O ₁₉ , CoFe ₂ O ₄ , (B
i, Y) ₃ Fe ₅ oxide thin film O _12, etc., MnBi, CoP
and polycrystalline alloy thin films such as t. Among them, the RE-TM amorphous alloy thin film is suitable for the recording layer 3 because it has no grain boundary noise and is easy to produce. Further, each of them has an easy axis of magnetization in a direction perpendicular to the film surface. The thickness of the alloy thin film is preferably from 200 to 1000 °, and the thickness of the oxide thin film is not particularly limited, since most of them have a large light-transmitting property with respect to recording / reproducing light.
Is preferred. Further, the recording layer 3 is not limited to a single-layer film, but may be a multilayer film.

Usually, a protective layer 4 is provided on the recording layer 3. Even if the protective layer 3 is not provided, the effect of the present invention is not impaired. This protective layer 4 prevents invasion of harmful substances such as moisture, oxygen or halogen elements into the recording layer 3 from the air (in the case of single-sided specification) or from the adhesive (in the case of double-sided specification). 3 is provided for the purpose of protecting the recording layer 3.
It is necessary that the reactivity with is small. Specific materials are the same as those shown in Table 1. However, among them, compounds composed of two or more atoms selected from Si, B, O, and N in terms of ease of production and thermal conductivity, and compounds containing at least Si and N (SiN, SiON, SiB
N SiBON). The thickness of the protective layer 4 has a great influence on the C / N and the recording sensitivity.
600 ° is preferred.

The reflective layer 5 may be provided directly on the recording layer 3 or via the protective layer 4. In order to increase the C / N and the sensitivity of the recording medium, it is preferable that the reflection layer 5 has a high reflectance with respect to the reproduction light and a low thermal conductivity. Also, of course, it must have corrosion resistance. Specific materials such as Si and T
An Al alloy containing at least one of i, Cr, Zr, Mo, Pd, Pt, and Ta, particularly an Al alloy represented by the following general formula (II) is preferable.

Embedded image Al _x Me _{100 — X} (II) (wherein Me is Ti, Ta, Cr, Zr, Si, Mo,
Represents Pd or Pt. The value of X is 95 ≦ X ≦ 1.
00. If the thickness of the reflective layer 5 is too small, the C / N ratio is reduced, and if the thickness is too large, the recording sensitivity deteriorates.
0 ° is appropriate.

Means for forming each layer on the substrate include physical vapor deposition methods such as sputtering and ion plating,
A chemical vapor deposition method such as plasma CVD is used.

[0025]

The present invention will be described more specifically with reference to the following examples.

Example 1 PC with a pregroove having a diameter of 86 mm and a thickness of 1.2 mm
After pre-baking the molded substrate in the air at 90 ° C. for 2 hours in advance, the substrate was set in a vacuum chamber of a sputtering apparatus and evacuated until the vacuum pressure became 5 × 10 ⁻⁷ Torr or less. Thereafter, a mixed gas of Ar and O ₂ was introduced into the vacuum chamber, the pressure was adjusted to 5 × 10 ⁻² Torr, and Ta ₂ O ₅ was formed by RF magnetron sputtering using metal Ta as a target.
An (Ar) film was formed to a thickness of 1100 ° to form an interference layer.
Next, a Tb ₂₁ Fe ₇₀ Co ₉ film was formed as a recording layer by 200 °,
250 ° Si ₃ N ₄ film as protective layer, Al as reflective layer
After forming a ₉₉ Ti ₁ film at 500 ° C., it was carried out from the vacuum chamber to the atmosphere to obtain the magneto-optical recording medium of the present invention. FIG. 4 shows the result of examining the composition distribution in the depth direction of this medium by RBS (Rutherford backscattering method).

Examples 2 to 5 The magneto-optical recording media of Examples 2 to 5 were obtained in the same manner as in Example 1 except that the material and thickness of the interference layer were as shown in Table 2.

Comparative Examples 1 to 4 Magneto-optical recording media of Comparative Examples 1 to 4 were obtained in the same manner as in Examples 1 to 4 except that the interference layer did not contain Ar.

A cover layer made of an acrylic UV-curable resin was applied on the reflective layers of the magneto-optical recording media of Examples 1 to 5 and Comparative Examples 1 to 4 by a spinner to a thickness of 5 to 10 μm. Then, each medium was placed in an environment of 80 ° C. and 85% RH for 2 hours.
After leaving for 000 hours, a life acceleration test was performed. Table 2 shows the bit error rates (BER) before and after the test.

[0030]

[Table 2]

As is evident from Table 2, the BER of the magneto-optical recording medium of the comparative example is increased by one digit or more compared to the initial state when left for 2000 hours in an environment of 80 ° C. and 85% RH. On the other hand, the embodiment according to the present invention has almost the BER
No increase is seen.

[0032]

As described above, according to the present invention, an interference layer composed of a thin film of an oxide containing a specific amount of Ar is interposed between a plastic substrate and a recording layer, whereby the plastic substrate and each layer can be separated. A magneto-optical recording medium having a long life and high reliability with improved adhesion, no cracking or peeling even under a severe environment, and no change over time such as oxidation of the recording layer can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a graph showing retention time-temperature and retention time-humidity in a temperature-humidity cycle test of an interference layer.

FIG. 3 is a graph showing a relationship between a film formation speed by sputtering and an Ar content in an interference layer.

FIG. 4 is a graph showing a composition distribution in a depth direction of the magneto-optical recording medium.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent substrate (plastic substrate) 2 Interference layer 3 Recording layer 4 Protective layer 5 Reflective layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 11/105 526 G11B 11/105 531

Claims (5)

(57) [Claims] 1. A magneto-optical recording medium in which at least an interference layer, a recording layer, and a protective layer are sequentially provided on a plastic substrate, wherein the interference layer comprises a thin film of an oxide containing 0.5 to 3 atomic% of Ar. A magneto-optical recording medium characterized by the above-mentioned. 2. The magneto-optical recording medium according to claim 1, wherein the interference layer is made of an oxide thin film represented by the following general formula (I). Embedded image [Ta _X O _{100 — X} ] _Y Ar _{100 — Y} (I) (wherein the values of X and Y are 20 ≦ X ≦ 40, 97 ≦ Y
≤ 99.5. ) 3. The method according to claim 1, wherein the interference layer is a thin film having a two-layer structure,
3. The magneto-optical recording medium according to claim 1, wherein a layer on the substrate side is made of the oxide thin film. 4. The magneto-optical recording medium according to claim 1, wherein said recording layer comprises a rare earth-transition metal amorphous alloy thin film. 5. The protective layer is a compound comprising at least two kinds of atoms selected from Si, B, O, and N, and is formed of a compound thin film containing at least Si and N. The magneto-optical recording medium according to any one of claims 1 to 4, wherein a reflection layer made of a thin film of an Al alloy represented by the following general formula (II) is provided. Embedded image Al _x Me _{100 — X} (II) (wherein Me is Ti, Ta, Cr, Zr, Si, Mo,
Represents Pd or Pt, and the value of X is 95 ≦ X ≦ 1
00)