JPH081709B2 - Magneto-optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Use> The present invention uses information from a laser or the like to record or reproduce information.
The present invention relates to a magneto-optical recording medium that erases data. More specifically, a magneto-optical recording in which a recording layer made of a metal thin film having an easy magnetization direction in a direction perpendicular to the film surface is formed on a transparent substrate, information is recorded by the photothermomagnetic effect, and is reproduced by the magnetooptical effect. Regarding the medium.

<Prior Art> Various researches and developments have been made on optical recording media as high-density and large-capacity information recording media. In particular, a magneto-optical recording medium capable of erasing information has a wide range of application fields, and various materials and systems have been announced, and their practical application is expected.

Examples of the above-mentioned magneto-optical recording material include, for example, JP-A-52-
FeTb described in JP 31703, FeTbGd described in JP-A-56-126907, FeTbCo described in JP-A-58-73746, FeCoD
y, many proposals such as FeNd described in JP-A-61-165846 have already been made. However, in order to put these magneto-optical recording media into which information can be erased into practical use, it is necessary to further improve the recording and reproducing characteristics.

On the other hand, a method of providing a metal reflective layer on the magneto-optical recording layer or on the magneto-optical recording layer via a dielectric layer has been proposed. This method is excellent in that a high C / N ratio can be obtained by using the Kerr effect and the Faraday effect together. Conventionally, as the metal reflection layer, one using Al (Japanese Patent Laid-Open No. 58-83346, Japanese Patent Laid-Open No. 59-132434), and one using Cu (Japanese Patent Laid-Open No. 59-59434).
-8150), using an Al alloy (Japanese Patent Laid-Open No. 62-13
7743, JP 64-4938), those using stainless steel (JP 59-171054), those using Te (JP 62-52744), amorphous metal Those using a membrane (Japanese Patent Laid-Open No. 61-57053) have been proposed. However, when high reflectivity Al, Cu, etc. is used, the recording sensitivity is greatly reduced due to its high thermal conductivity, while when stainless steel and Te, which have relatively low thermal conductivity, are used, the recording sensitivity is Although it is improved, it has a drawback that a sufficient C / N ratio cannot be obtained because the reflectance is low.

<Object of the Invention> The present invention has been made in view of the above circumstances, and an object thereof is to provide a magneto-optical recording medium having high sensitivity and a high C / N ratio.

<Structure and Action of Invention> As a result of intensive studies to overcome the above-mentioned drawbacks, the present inventors formed a metal reflective layer with a specific substance,
It has been found that a magneto-optical recording medium having a high recording sensitivity and a high C / N ratio and excellent stability over time can be obtained.

That is, the present invention provides a magneto-optical recording medium having a metal reflective layer, wherein the metal reflective layer contains Ag in an amount of 0.5 to 30 at% (atomic%), and at least one of Ta and Ti is 0.5 to 0.5.
A magneto-optical recording medium characterized by comprising an Ag alloy containing about 15 at%.

The present invention described above has been made as follows. That is, the present inventors have focused on the Ag film of high reflectance for the purpose of improving C / N, Ag is a poor corrosion resistance material,
Ag film alone is not practical. Therefore, as a result of studying addition of other metals as an improvement, the AgCu alloy film formed by adding 0.5 to 30 at% Cu formed on the slide glass has a high reflectance, and the standard accelerated deterioration test condition of the magneto-optical recording medium is used. It has been found that the reflectance does not decrease even when left for 72 hours or more in an atmosphere of 80 ° C and 85% relative humidity, and it has durability. In addition,
Even if the Cu content was less than 0.5 at% or more than 30 at%, the reflectance decreased to 90% or less of the initial value within 24 hours.
As described above, the AgCu alloy film has a high reflectance (eg, Ag ₈₅ Cu ₁₅ (subscript is at% composition) alloy film has a reflectance of 98% at a wavelength of 830 nm) and durability is not bad, but this AgCu film is It was further found that the magneto-optical recording medium having a high thermal conductivity and using it as a reflective film has a lower recording sensitivity.

The present inventors further focused on the improvement of this point by adding the third element, and as a result of earnest research, as a result of adding 0.5 to 15 at% of at least one of Ta or Ti to the AgCu film, the recording sensitivity and corrosion resistance are significantly improved. As a result, they have come to the present invention.

If the content of Ta or Ti is less than this range, there is no effect of improving the recording sensitivity, and conversely, if it is more than this range, the reflection decreases and the C / N deteriorates. Furthermore, the content of Ta and Ti has a large effect of improving the sensitivity, and the effect of improving the C / N is not hindered.
-10at% is more preferable. Incidentally, in order to further improve the stability over time, a small amount of another element such as Cr, Nb or Re may be added.

The thickness of this metal reflective layer is preferably 100 to 1000Å, 200
~ 700Å is more preferable. If it is too thick, the sensitivity decreases, and if it is too thin, the reflectance decreases and the C / N becomes poor.

In the present invention, a metal film having a low thermal conductivity such as Ti or a dielectric film may be additionally provided in contact with the side of the metal reflection layer opposite to the magneto-optical recording layer side. Especially when the metal reflective layer of the present invention is as thin as 400 Å or less to suppress heat conduction, T
Providing an i-layer metal film prevents a decrease in reflectance and improves corrosion resistance, and more preferable results are obtained. Similarly, the dielectric film may be provided as a protective layer when the magneto-optical recording medium is expected to be used in an extremely harsh environment.

The method for forming the metal reflective layer may be a known vacuum vapor deposition method, sputtering method, ion beam sputtering method, CVD method, or the like, but the adhesiveness with the underlying layer, the controllability of the alloy composition, the composition distribution, etc. Therefore, the sputtering method is preferable. The deposition rate of the film, the sputtering gas pressure, etc. are appropriately selected in consideration of productivity and film stress.

The magneto-optical recording layer of the present invention may be any as long as it can record by the photo-thermomagnetic effect, and it is well known that a magnetic metal thin film having a direction of easy magnetization in a direction perpendicular to the film surface and having a large magneto-optical effect, for example, A typical example is an amorphous alloy of a rare earth element-transition metal element such as FeTb alloy, FeTbCo alloy, FeTbGd alloy and NdDvFeCo alloy. The film thickness of the magneto-optical recording layer is 150 to 1000Å, preferably 200 to 500Å.

The structure of the magneto-optical recording medium of the present invention is not particularly limited except that the metal reflection layer is formed on the side opposite to the light incident surface of the magneto-optical recording layer. Even if the metal reflection layer is provided directly on the magneto-optical recording layer, the sensitivity, C / N
It may be provided via a transparent dielectric layer for the purpose of improvement. However, the metal reflective film made of an Ag alloy containing at least one of Ta or Ti and Cu of the present invention is directly provided in contact with the magneto-optical recording layer, and is practically sufficient in its recording sensitivity and C / N. This structure is preferable from the viewpoints of productivity and medium cost because it exhibits performance and the transparent dielectric layer is not necessary.

Even when a transparent dielectric layer is provided between the magneto-optical recording layer and the metal reflective layer, this transparent dielectric layer needs to be as thin as 600Å or less to obtain optimum performance.
The present invention is effective because its heat insulating effect is reduced. In general, the thicker the transparent dielectric layer is, the higher its heat insulating effect is, and Ta or Ti of the metal reflective film of the present invention is increased.
The content of may be small.

In the magneto-optical recording medium of the present invention, a transparent dielectric layer may be provided between the substrate and the magneto-optical recording layer for the purpose of improving C / N, reducing the reflectance of the medium, and preventing moisture permeation.

Both the transparent dielectric layer on the substrate side of the magneto-optical recording layer and the metal reflection layer side used in the above-mentioned structure, it is necessary to exhibit the effects of optical interference effect, Kerr effect enhancement, etc. depending on the purpose, and high refraction of a certain level or more. It is preferable to have a rate. In addition, it is necessary that the laser light used is transparent, and as a transparent dielectric layer, a metal oxide, as is known,
Nitrides, sulfides, carbides, fluorides or composites thereof can be applied. Specifically, silicon oxide, indium oxide, tantalum oxide, aluminum oxide, silicon nitride,
Needless to say, examples thereof include, but are not limited to, aluminum nitride, titanium nitride, zinc sulfide, magnesium fluoride, aluminum fluoride, silicon carbide, and composites thereof. Further, organic materials such as parylene, polyimide, and paraffin can be applied, and the film thickness of these transparent dielectric layers cannot be uniquely determined because the optimum value changes depending on the medium structure and refractive index, but it is usually about 400 to 1500 Å, especially Five
A value of 00 to 1000Å is preferably used. These transparent electric conductor layers are formed by a conventional method. For example, the above-mentioned inorganic material is produced by a known vacuum deposition method, sputtering method, ion beam sputtering method, CVD method, or the like.

Further, as the substrate, glass, acrylic resin, polycarbonate resin, epoxy resin, 4-methylpentene resin and modified products thereof are preferably used, but mechanical strength, price, weather resistance, heat resistance, moisture permeability Polycarbonate resin is preferable from the viewpoint.

Examples of the present invention will be described below, but the present invention is not limited to the following examples.

<Examples and Comparative Examples> A high frequency magnetron sputtering device (available from Anelva Corp.) capable of installing 3 targets on a disk substrate made of polycarbonate resin (PC) having a disk of diameter 130 mm, thickness 1.2 mm and grooves of 1.6 μm pitch. It was placed in a vacuum chamber (SPF-430H type) and evacuated to 4 × 10 ⁻⁷ Torr.

Next, a mixed gas of Ar and N ₂ (Ar: N ₂ = 70: 30 vol%) was introduced into the vacuum chamber, and the flow rate of the Ar / N ₂ mixed gas was adjusted so that the pressure was 10 m Torr. As the target, a disk made of a sintered body of 100 mm in diameter and 5 mm in thickness of Al ₅₀ Si ₅₀ (hereinafter, the subscripts indicate the composition (atomic%)) was used, and high frequency sputtering was performed at a discharge power of 500 W and a discharge frequency of 13.56 MHz. AlSiN as a transparent dielectric while rotating (rotating) the PC substrate
A film of 800 Å was deposited.

Subsequently, using a Tb ₂₁ Fe ₇₁ Co ₈ alloy target as the magneto-optical recording layer, high frequency sputtering was performed under the conditions of Ar gas pressure of 2 m Torr and discharge power of 150 W to deposit a TbFeCo alloy film of about 300 Å.

Further subsequently, using an Ag ₈₅ Cu ₁₅ alloy target, a 5 mm square × 1 mm t Ta tip was appropriately arranged on the target, and high frequency sputtering was performed under the conditions of Ar gas pressure of 2 m Torr and discharge power of 100 W. A 400 Å metal reflective layer was deposited with each composition to obtain a magneto-optical disk having a laminated structure of PC substrate / AlSiN / TbFeCo / metal reflective layer. Ta of each AgCuTa alloy film of the metal reflection layer
The amount was adjusted to each composition by changing the number of Ta chips on the AgCu alloy target.

During the formation of each of these layers, the PC substrate was rotated at 20 rpm.

The obtained magneto-optical disk was evaluated for C / N and optimum recording laser power under the following conditions using a magneto-optical recording / reproducing apparatus (OMS-1000 type manufactured by Nakamichi Co., Ltd.). The optimum recording condition was set when the semiconductor laser power during writing was changed and the secondary high frequency of the reproduced signal was minimized.

[Recording conditions] Disk rotation speed: 1800 rpm, recording track position: radius
30 mm position, recording frequency: 3.7 MHz, applied magnetic field during recording: 500
Oersted [Playback conditions] Disc rotation speed: 1800 rpm, Read laser power: 1.2
Table 1 shows the measurement results of mW optimum recording laser power and C / N.
Shown in

In addition, Comparative Example 1 in Table 1 is the same as Example 1 except for the metal reflection layer.
4 is a magneto-optical disk made of Ag ₈₅ Cu ₁₅ alloy containing no metal and having a metal reflection layer formed by removing the Ta chips of Examples 1-4.

In addition, as Comparative Example 2, the configuration other than the metal reflective layer is the same as that of Examples 1 to 4, and an Al target provided with a Ta chip is used as the metal reflective layer, and the metal reflective layer of Examples 1 to 4 is used. By high frequency sputtering in the same way,
A magneto-optical disk in which an Al ₉₂ Ta ₈ alloy film was formed in a 400 Å laminated structure was prepared and evaluated in the same manner.

Also, the optimum recording laser power of 10 mW in Comparative Example 1 in Table-1
The above shows that recording was not possible even with the maximum laser output of 10 mW used.

Further, an ultraviolet curable phenol novolac epoxy acrylate resin was applied by a spin coater on the metal reflective layers of the disks of Example 2 and Comparative Example 2 and then cured by ultraviolet irradiation to provide an organic protective layer of about 20 μm.
These samples were tested at a temperature of 80 ° C and a humidity of 85% for 1000
When the time acceleration test was conducted, no change was observed in Example 2, but in Comparative Example 2, ten or more pinholes were generated.

Further, in the same manner as in Examples 1 to 4, a magneto-optical disk having exactly the same configuration except that a Ti chip was placed on an AgCu target instead of Ta and the metal reflection layer was the AgCuTi alloy shown in Table 2 was used. Samples were prepared and evaluated in the same way. The results are shown in Table-2.

As described above, as shown in the examples, Cu of the present invention, Ta or Ti
With a metal reflective film made of an Ag alloy containing at least one of the above, it is possible to obtain a magneto-optical recording medium having excellent C / N, sensitivity, and high durability. In particular, when the content of Ta, Ti is 2 at% or more, the decrease of the optimum recording laser power, that is, the improvement of the recording sensitivity is remarkable, and the C / N is also known, such as AlT.
It is far superior to a magneto-optical disk that uses an alloy film as a reflective film. In terms of such effects, the content of Ta and Ti is 2 to 10 at
% Is particularly preferred.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadanori Nakatani 4-3-2 Asahigaoka, Hino-shi, Tokyo Inside Teijin Ltd. Tokyo Research Center (72) Inventor Kiyoshi Chiba 4-32-3 Asahigaoka, Hino-shi, Tokyo Teijin Limited Tokyo Research Center (56) References JP 59-8150 (JP, A)

Claims (3)

[Claims] 1. A magneto-optical recording medium having a metal reflective layer, wherein the metal reflective layer contains Ag in an amount of 0.5 to 30 at%.
Furthermore, a magneto-optical recording medium comprising an Ag alloy containing at least 0.5 to 15 at% of Ta or Ti. 2. The magneto-optical recording medium according to claim 1, wherein the metal reflective layer is provided in contact with the magneto-optical recording layer. 3. The total content of Ta or Ti is 2 to 10 at%.
The magneto-optical recording medium according to claim 1 or 2.