JP2938233B2 - 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 for recording / reproducing information by means of a magneto-optical effect using a light beam such as a laser, and more particularly to a metal reflection layer behind a magneto-optical recording layer. The present invention relates to a provided magneto-optical recording medium.

[0002]

2. Description of the Related Art Various researches and developments have been made on optical recording media as high-density, large-capacity information recording media. In particular, magneto-optical recording media capable of rewriting information have a wide range of application fields,
Various materials and systems have been announced and are attracting attention.

The basic structure is such that a magneto-optical recording layer made of a rare earth-transition metal amorphous alloy magnetic film having an easy axis of magnetization in a direction perpendicular to the film surface is provided on a transparent substrate.

[0004] The magneto-optical recording layer of the amorphous alloy magnetic film alone has poor durability and a small Kerr rotation angle, so that a satisfactory C / N (carrier signal / noise) cannot be obtained during reproduction. Has problems. Therefore, various proposals have been already made to improve those characteristics.

For example, a four-layer structure in which a substrate / a first metal nitride transparent dielectric layer / a recording layer / a second metal nitride transparent dielectric layer / a metal reflection layer is laminated in this order has a Kerr effect and a Faraday effect. High C / N due to combined use and enhancement effect by dielectric
Value is obtained, and the use of metal nitride as the dielectric is excellent in durability. Although the recording sensitivity is reduced by providing the metal reflection layer as compared with the case without the metal reflection layer, as a method of obtaining appropriate recording sensitivity, adjusting the film thickness of the metal reflection layer or adding an additive to the metal reflection layer For example, a method of reducing the heat conduction of the metal reflection layer has been proposed.

[0006]

However, according to the study of the present inventors, when the heat conduction of the metal reflective layer is reduced in the four-layer structure, the recording sensitivity is improved, but the escape of heat from the recording layer is deteriorated. It turns out that various problems arise. For example, when information is recorded, adjacent bits thermally affect each other, and a phenomenon occurs in which the deviation from the position where the bit is to be written increases. This positional shift can be detected as a peak shift of the reproduced signal. If the bit shift is large, the peak shift increases, causing a problem that errors during reproduction increase. further,
At the time of erasing information, a high-power laser beam is irradiated, so that the recording layer may be deteriorated by heating in a configuration in which heat escapes poorly. In fact, according to the study by the inventors, when continuously irradiating a high-power laser beam, the C / N may decrease. That is, there is a problem in long-term stability to laser light.

The present invention solves the above-mentioned problems,
Making use of the characteristics of the transparent dielectric layer and metal reflective layer described above,
The purpose of the present invention is to obtain a magneto-optical recording medium having good recording sensitivity and excellent long-term stability to laser light.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a magneto-optical recording medium in which a magneto-optical recording layer and a metal reflective layer are sequentially laminated on a substrate is provided. Between the layer and the metal reflection layer, a transparent heat insulating material containing at least one of Al-OH, Si-OH, which is a nitride, oxide, or nitride oxide composed of at least one of Al and Si. Layers are provided, plus gold
Transparent dielectric layer made of oxynitride separates from magneto-optical recording layer
Between the thermal layer and / or between the magneto-optical recording layer and the substrate
The metal reflection layer is provided, and a value of thermal conductivity × film thickness is 1.3 μW / K or more.

[0009]

Operation One of the causes of the shift of the bit position during recording, in other words, the peak shift, is considered to be thermal interference between adjacent bits. That is, when the magneto-optical recording layer is heated to a temperature higher than the temperature required for writing, it is considered that the heat affects adjacent bits. Further, it is considered that the cause of the decrease in C / N when continuously irradiated with high-power laser light is that the magneto-optical recording layer is heated to a temperature higher than the temperature required for erasing.

[0010] Therefore, in order to prevent such a problem, it is necessary to provide a structure for improving the escape of heat. However, simply increasing the thermal conductivity of the metal reflective layer or increasing the film thickness will not
Recording sensitivity decreases. Therefore, in consideration of the recording sensitivity, in order to obtain a medium having a small peak shift and excellent long-term stability against a high-power laser beam, the temperature tends to rise up to a certain temperature (recording temperature). ,
Above that, a configuration is required in which the temperature is unlikely to rise and an unnecessarily high temperature is prevented.

As a result of intensive studies on the realization of such a configuration, a transparent heat-insulating layer having sufficient heat-insulating properties is provided on the front surface of the metal reflection layer, while preventing the magneto-optical recording layer from overheating, so that the recording sensitivity is not reduced. In order to achieve this, it has been found that a combination configuration using a metal reflective layer with good heat dissipation can be used.

And a nitride, oxide or oxynitride of at least one of Al and Si,
A transparent heat-insulating layer containing at least one of OH and Si-OH is provided between the metal reflective layer and the magneto-optical recording layer, and a metal having a value of thermal conductivity × thickness of 1.3 μW / K or more. By adopting a configuration in which the thermal conductivity is improved by using a reflective layer, magneto-optics having a high C / N, good recording sensitivity, a small peak shift of a reproduction signal, and excellent long-term stability to a high-power laser. It was confirmed that a recording medium was obtained.

In the above configuration, the thermal conductivity of the transparent heat-insulating layer is extremely low, so that the temperature of the magneto-optical recording layer tends to increase due to its heat-insulating effect. Moreover, high sensitivity can be maintained even if the thermal conductivity of the metal reflection layer is considerably improved. On the other hand, excessive heat is released by the metal reflection layer, so that excessive heating is prevented. The above is considered to be the reason why the present invention achieves high C / N, high sensitivity, low peak shift, and long-term stability against high-power laser light.

When the magneto-optical recording layer is in direct contact with the transparent heat-insulating layer, especially the oxide layer, the magneto-optical recording layer may be oxidized (for example, by the influence of pre-sputtering) depending on the manufacturing method. It is more desirable to provide a transparent dielectric layer made of a metal nitride between the magneto-optical recording layer and the transparent heat-insulating layer in order to prevent the above. As such a nitride transparent dielectric layer, known SiN, AlN, and their metal composite nitrides are preferable. However, the present invention is not limited to this as long as the metal nitride has good transparency. Further, the thicker the film, the better the protection is. However, considering the enhancement of the Faraday effect, it is 5-30.
nm is preferred. And the above nitride transparent dielectric layer,
It is formed by an ordinary method. Examples of the method include a known vacuum evaporation method, a sputtering method, an ion beam sputtering method, and a CVD method.

The transparent heat-insulating layer in the present invention is a nitride, oxide or nitride oxide composed of at least one of Al and Si, and contains at least one of Al-OH and Si-OH. Here, Al and Si may be each alone or a mixture of both. Oxides, nitrides, and nitrides are appropriately selected depending on transparency, weather resistance, and ease of film formation.

A major feature of the present invention is that the transparent heat-insulating layer contains -OH groups. It is considered that when the metal-OH group bond is generated, the bond is broken inside the three-dimensional structure, and there is no heat transfer due to lattice vibration, so that the thermal conductivity is reduced. If the content of -OH groups is too large, the mechanical strength of the film and the moisture permeability of water and the like are reduced, so that a problem occurs in the weather resistance. So -OH
The content of the group is 0.5 to 30 atom%, preferably 1 to 15 atom%.
An atom% range is preferred.

There are several methods for forming these transparent heat-insulating layers. Using a metal element, an oxide, or a nitride target, N ₂ , O ₂ , and H are used in addition to Ar gas.
_The reactive sputtering method of mixing ₂ is preferably used.

The thickness of the transparent heat insulating layer increases as the thickness increases, but the thickness is preferably 5 to 50 nm in consideration of the enhancement of the Faraday effect by this layer.

The metal reflection layer in the present invention has an important role of dissipating heat, and the better the thermal conductivity of the metal reflection layer, the greater the effect of the present invention. The thermal conductivity of the metal reflective layer improves as the thermal conductivity increases and the film thickness increases. According to the study of the present inventors, the thermal conductivity of a metal thin film in a magneto-optical recording medium substantially corresponds to a value of thermal conductivity × film thickness, and it is possible to compare the thermal conductivity with the value. all right.
When the thermal conductivity is defined by this method, it is necessary for the metal reflective layer that achieves the object of the present invention to have a value of thermal conductivity × thickness of 1.3 μW / K or more, more preferably 2.0 μW / K or more is required.

The thermal conductivity mentioned here is a value determined in the following manner. As shown in FIG.
Was prepared on a glass substrate 1. However, the width a of the metal thin film 2 was 10 mm, and the thickness d was 100 nm. Next, four Au electrodes 3 to 6 were formed on the metal thin film 2 by vapor deposition at equal intervals as shown in FIG. The distance b between the Au electrodes 3 to 6 was 4 mm. In the above sample, the electric resistance R of the metal thin film 2
Was measured by a four-terminal method, and the electrical conductivity σ and the thermal conductivity λ were determined by the following equations. Where L is the Lorentz number (Lorenz
number), T is the measurement temperature, L = 24.5 nWΩ
/ K ² , T = 300K. σ = b / (adR) λ = LTTσ

The electric conductivity of the Al film is 1.6 × 10 ⁷ Ω ^-1 ·
m ^-1 , the thermal conductivity was 1.2 × 10 ² W · m ⁻¹ · K ⁻¹ , and the electrical conductivity of the Al _92.7 Au _4.8 Ti _2.5 alloy film was 1.8 ×
10 ⁶ Ω ^-1 · m ^-1 , thermal conductivity 1.3 × 10 W · m ^-1 ·
K ^-1 (subscripts indicate atom%).

For the above-mentioned reasons, the material of the metal reflection layer is preferably a metal having good heat conductivity, and Ag, Au, Al, Cu or an alloy mainly containing these is suitably used. These metals also have an advantage that a high C / N can be obtained because of high light reflectance. Among them, AgAu alloys and AlAu alloys are excellent from the viewpoints of reflectivity, thermal conductivity, and durability, and a reflective layer further added with Ti is more preferable in this respect. The thickness of the metal reflective layer is determined by controlling heat dissipation to an appropriate range. When the thermal conductivity of the metal is low, a thick film is required, and when it is high, the metal may be thin. However, in terms of manufacturing efficiency and cost, the film thickness is 5
It is preferably from 500 to 500 nm. These metal reflective layers are formed by a known vacuum evaporation method or sputtering method.

The magneto-optical recording layer of the present invention can be recorded / reproduced / erased by the photo-thermomagnetic effect, more specifically, has an easy magnetization direction perpendicular to the film surface and forms an arbitrary reversed magnetic domain. Any magnetic metal thin film capable of recording, reproducing, and erasing information based on the photothermal magnetic effect can be used.For example, TbFe, TbFeCo, GdTbFe, GdFeCo, NdDyFeCo, NdDyTbFe
Amorphous alloy films of rare earth elements such as Co, NdFe, PrFe and CeFe and transition metal elements, their two-layer films utilizing exchange coupling,
An artificial lattice multilayer film of Co / Pt, Co / Pd, or the like can be used.

As a material of the substrate, a polycarbonate resin, an acrylic resin, an epoxy resin, a 4-methyl-pentene resin, a polymer resin such as a copolymer thereof, an amorphous polyolefin, a glass, or the like can be used. Among them, polycarbonate resin is preferable in terms of mechanical strength, weather resistance, heat resistance, and moisture permeability.

Although the basic configuration of the present invention has been described above, the configuration of the magneto-optical recording medium of the present invention is not limited to the above. In particular, a configuration having a second transparent dielectric layer for enhancing the Kerr effect between a known substrate and a magneto-optical recording layer is preferable. Such a transparent dielectric layer is preferably made of silicon nitride or aluminum / silicon nitride because of its good durability under high temperature and high humidity. The thickness of the dielectric layer between the magneto-optical recording layer and the metal reflective layer is also related to the thickness of the dielectric layer between the magneto-optical recording layer and the metal reflective layer. The thickness of the dielectric layer is about 3 to 60 nm, and the thickness of the second transparent dielectric layer between the substrate and the magneto-optical recording layer is 30 to 1
It is preferably about 60 nm.

Further, usually, an organic light and heat curable organic light-curing type is provided on the metal reflection layer via the inorganic protective layer made of the above-mentioned dielectric or the like for the purpose of mechanical protection and further improvement of durability. In general, an organic protective layer made of a resin or a thermoplastic resin is provided.

The magneto-optical recording medium having the above-described structure may be used as a single-sided recording medium by adding necessary protection such as a protective flat plate and a protective film, or may be used as a single-sided recording medium. It is used as a double-sided recording medium bonded by the above.

As described above, according to the present invention, by combining the transparent heat-insulating layer and the metal reflective layer having good heat conductivity, both the peak shift related to the bit error rate and the contradictory characteristics of the recording sensitivity are improved, and a high C / C ratio is obtained. N realizes a magneto-optical recording medium having excellent long-term stability against laser light.

Hereinafter, examples of the present invention will be described in comparison with comparative examples. A magneto-optical disk was prepared as described below, and its optimum recording laser power, C / N, and peak shift were evaluated.

Further, the long-term stability to laser light is as follows:
The C / N was measured after continuously irradiating the laser beam at a low rotation speed of the disk, and evaluated by the rotation speed of the disk irradiated with the laser beam until 2 dBC / N was reduced from the initial value.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS On a substrate, a first nitride transparent dielectric layer, a magneto-optical recording layer, a second nitride transparent dielectric layer, a transparent heat insulating layer, and a metal reflection layer are sequentially laminated, and further, an organic protective layer is formed. A magneto-optical disk having a stacked configuration was manufactured as follows.

A disc substrate (PC substrate) made of a polycarbonate resin having a group of 1.6 mm pitch with a disk having a diameter of 130 mm and a thickness of 1.2 mm is arranged in a vacuum chamber of a magnetron sputtering apparatus capable of setting three targets. Evacuation was performed until 0.4 μTorr.

Next, a mixed gas of Ar and N ₂ (Ar: N ₂ = 7)
0:30 vol%) into the vacuum chamber at a pressure of 10 mTorr.
It was adjusted to become. 100 diameter as target
Using a disk made of a sintered body of Al ₃₀ Si ₇₀ mm and a thickness of 5 mm, high-frequency sputtering is performed at a discharge power of 500 W and a discharge frequency of 13.56 MHz, and the PC substrate is rotated (rotated).
While doing so, an AlSiN film having a thickness of 112.5 nm was deposited as a first nitride transparent dielectric layer.

The composition of the formed AlSiN film was analyzed using an Auger electron spectrometer (PHI, SAM610).
Al ₁₉ Si ₃₉ N ₄₂ .

Subsequently, a diameter of 100 mm and a thickness of 4.5 mm
Ar gas pressure of 4 using Tb ₁₉ Fe _72.5 Co _8.5 alloy target
DC sputtering was performed under the conditions of mTorr and a discharge power of 150 W, and a 22.5 nm-thick Tb _20.5 Fe _70.9 Co _8.6 amorphous alloy film was deposited as a magneto-optical recording layer.

Subsequently, a second nitride transparent dielectric layer was formed under the same conditions as those of the first nitride transparent dielectric layer.
A 5 nm-thick SiN film was deposited.

Next, using the same target made of Al ₃₀ Si ₇₀ , Ar, N ₂ , O ₂ , H ₂ (Ar: N ₂ : O ₂ : H ₂ =
70: 15: 5: 10), high frequency sputtering was performed in a 10 mmTorr atmosphere of a mixed gas, and Al was used as a transparent heat insulating layer.
A 30 nm thick SiONH film was deposited.

Further, Al having a diameter of 100 mm and a thickness of 5 mm
Ar gas pressure 1. Using _92.5 Au _4.5 Ti _3.0 alloy target.
DC sputtering was performed at 5 mTorr and a discharge power of 125 W, and an Al _92.7 Au _4.8 Ti _2.5 alloy film having a thickness of 120 nm was deposited as a metal reflection layer.

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

Subsequently, an ultraviolet-curable phenol novolak epoxy acrylate resin was applied on the metal reflective layer with a spin coater, and then an organic protective layer having a thickness of about 10 μm was cured by irradiation with ultraviolet light.

[0041]

[Comparative Example 1] As the transparent heat insulating layer,
Instead of the NH film, an AlSiN film was deposited to a thickness of 30 nm under the same conditions as the nitride transparent dielectric layer of the example, and the thickness of the Al _92.7 Au _4.8 Ti _2.5 alloy film of the example was used as a metal reflective layer. A magneto-optical disk was manufactured in the same manner as in the example except that the thickness was 60 nm.

[0042]

Comparative Example 2 Al _92.7 Au of Comparative Example 1 was used as a metal reflecting layer.
_A magneto-optical disk was manufactured in the same manner as in Comparative Example 1, except that the thickness of the _4.8 Ti _2.5 alloy film was changed to 120 nm.

Next, the magneto-optical disks obtained in Examples and Comparative Examples 1 and 2 were optimized for C / N under the following conditions using a magneto-optical recording and reproducing apparatus (DDU-1000, manufactured by Pulstec Industrial). The recording laser power was evaluated. The semiconductor laser power at the time of writing was changed, and the time when the second harmonic of the reproduction signal became minimum was determined as the optimum recording laser power.

[Recording conditions] Disk rotation speed = 180
0 rpm, recording track position = radius 30 mm position, recording frequency = 3.7 MHz, applied magnetic field during recording = 250 Oe, recording pulse width = 90 nsec.

[Reproduction conditions] Disk rotation speed = 180
0 rpm, reading laser power = 1.5 mW.

Further, the peak shift was measured. The peak shift referred to here is the time T2 between the pulses of the signal to be recorded when the signal shown in FIG.
The absolute value of the difference from the average value <T2 '> of the time T2' between the peaks of the actually reproduced signal was used. Therefore, peak shift = | T2-<T2 '> |. For recording and reproduction, the magneto-optical reproducing device was used. The recording and reproduction conditions are described below. The time T2 'between the peaks of the reproduced signal is determined by a frequency and interval analyzer (FREQUENCY AND INTE) manufactured by Hewlett Packard.
RVAL ANALYZER).

[Recording conditions] Disk rotation speed = 180
0 rpm, recording track position = radius 30 mm position, recording laser power = 6 mW, applied magnetic field during recording = 250 Oe, recording pulse width = 90 nsec.

[Reproduction conditions] Disk rotation speed = 180
0 rpm, reading laser power = 1.5 mW.

Further, the long-term stability to laser light was measured. The criterion is a radius 30m of the rotated disk.
The C / N is measured after rotating the disk by an appropriate number of rotations while continuously irradiating a specific track at the m position with the laser,
The number of rotations at which the C / N from the initial value was reduced by 2 dB was determined, and it was considered that the larger the number of rotations, the more stable. The rotation speed of the disk during continuous laser irradiation was 300 rpm in order to accelerate the temperature rise of the magneto-optical recording layer, and the laser power for continuous irradiation was 6 mW. The C / N measurement method and the recording / reproducing conditions are as described above.

The measurement results of the optimum recording laser power, C / N, peak shift, and the number of laser irradiations at which the C / N is reduced by 2 dB are as follows.

In the embodiment, the optimum recording laser power = 4.
5 mW, C / N maximum value = 48.7 dB, peak shift =
9.2 ns, the number of laser irradiations with C / N 2 dB reduction = 3.
8 × 10 ³ times.

In Comparative Example 1, the optimum recording laser power =
4.5 mW, C / N maximum value = 48.4 dB, peak shift = 12.8 nsec, number of laser irradiations with C / N 2 dB reduction =
2.0 × 10 times.

In Comparative Example 2, the optimum recording laser power =
5.7 mW, C / N maximum value = 48.3 dB, peak shift = 10.8 nsec, number of times of laser irradiation with C / N 2 dB decrease =
6.5 × 10 ² times.

In the example using the AlSiONH film, all the characteristics were good, but in Comparative Example 1, the peak shift value and the stability to the laser beam were poor. Increasing the thickness of the metal reflective layer slightly improves peak shift and stability against laser light, but increases the optimum recording power and lowers the recording sensitivity.

Further, the magneto-optical disk of the embodiment was set at 80 ° C. /
After leaving for 2,000 hours at 85% relative humidity, no deterioration in characteristics was observed.

[0056]

As described in detail above, the present invention makes use of the characteristics of the transparent dielectric layer and the metal reflective layer to achieve high C / N, good recording sensitivity, and excellent long-term stability to laser light. A magnetic recording medium can be obtained.

[Brief description of the drawings]

FIG. 1 is a layout diagram of the thermal conductivity measurement.

FIG. 2 is an explanatory diagram of a peak shift.

[Explanation of symbols]

 1 Glass substrate 2 Metal thin film (sample) 3-6 Au electrode

Claims (1)

(57) [Claims] In a magneto-optical recording medium in which a magneto-optical recording layer and a metal reflective layer are sequentially laminated on a substrate, at least one of Al and Si is provided between the magneto-optical recording layer and the metal reflective layer. nitrides comprising an oxide or a nitride oxide, Al-OH, and the transparent heat insulating layer is provided that contains at least one of Si-OH, from further metal nitride
Transparent dielectric layer between the magneto-optical recording layer and the transparent heat insulating layer.
And / or provided between the magneto-optical recording layer and the substrate.
And the metal reflective layer has a value of thermal conductivity × thickness of 1.3.
A magneto-optical recording medium characterized by being at least μW / K.