JPH10208322A - Magneto-optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen the change in recording and reproducing characteristics, by successively laminating a metallic reflection film, a first dielectric film, a magneto-optical recording film, and a second dielectric film on a substrate, and specifying the film thicknesses of the respective films to specific ranges. SOLUTION: The metallic reflection film 12, the first dielectric film 13, the magneto-optical recording film 14 and the second dielectric film 15 are formed in this order on the substrate 11. The film thicknesses of the respective films are specified to the ranges of 400nm<=d1 , 800nm<=d2 <=1200nm, 10nm<=d3 <=300nm, 65nm<=d4 <=800nm if the film thickness of the metallic reflection film 12 is defined as d1 , the film thickness of the first dielectric film 13 as d2 , the film thickness of the magneto-optical recording film 14 as d3 and the film thickness of the second dielectric film 15 as d4 . The metallic reflection film 12 consists essentially of aluminum; the first and second dielectric films 13, 15 comprise silicon and nitrogen and the magneto-optical recording film comprises rare earth metals and transition metals. As a result, the magneto-optical recording medium executes stable recording and reproducing operation with high reliability.

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 reproducing information by optical means and recording information by using light and magnetism, and more particularly, performs recording and reproduction by irradiating light from the recording film surface side. The present invention relates to a magneto-optical recording medium.

[0002]

2. Description of the Related Art In magneto-optical recording, a magneto-optical recording film is generally provided on an optically transparent substrate, and recording and reproduction are performed by irradiating a laser beam from the substrate side. Of capacity is commercialized. In magneto-optical recording, a laser beam is converged by an objective lens, a minute beam spot is converged on a magneto-optical recording film, and recording and reproduction of minute marks are performed. This objective has a 0.4 to 0.6
In general, a laser beam having a numerical aperture of about (hereinafter referred to as NA) is used. However, since the convergence size of the laser beam is inversely proportional to the NA, a smaller mark is formed to improve the recording density. Is effective to increase NA.

As a method of obtaining a larger NA, there is a method of installing a lens made of glass having a high refractive index between an objective lens and a magneto-optical recording medium. The lens installed between this objective lens and the magneto-optical recording medium is Solid Immersi
This is called on lens (hereinafter, referred to as SIL). If the refractive index of the SIL is increased, the NA can be increased, and the laser light can be converged to a smaller value. In order to further enhance the convergence ability, the SIL is effectively a hemisphere or a shape obtained by cutting a sphere in a plane. For such a shape, the focus is S
Formed immediately after IL.

In a conventional magneto-optical recording medium, a laser beam is focused on a magneto-optical recording film through an optically transparent substrate having a thickness of usually 1.2 mm. In a system using SIL, a focal point is formed in the substrate. As a result, the laser beam cannot be converged on the surface of the recording film. As a solution to this problem, a method is conceivable in which laser light is incident not from the substrate but from the recording film surface side. If a laser beam is incident from the recording film surface side, it is possible to focus on the magneto-optical recording film even at the above-mentioned minute focal length. But,
In this case, a device for stably maintaining a small gap of about 100 nm is required so that the lens and the recording film do not come into contact with each other to destroy the recorded information.

As a method for maintaining such a minute gap, it is possible to use a flying head technique which is put to practical use in a hard disk recording apparatus. That is, as shown in FIG. 3, for example, the SIL 42 is formed on the slider 41 of the flying head, and the SIL 42 is floated while maintaining a small gap on the recording medium by an air bearing effect generated by the rotation of the recording medium 1. Focus can be focused on the recording film. The flying height of the slider on the recording medium changes due to a difference in moving speed between the inner circumference and the outer circumference of the recording medium rotating at a constant rotational speed, external impact, undulation of the recording medium disk shape, and the like. An air layer (air gap 49) exists between the SIL and the recording medium.
Is different from the refractive index of the surface of the recording medium, the interference state changes due to a small change in the thickness of the air gap (hereinafter, referred to as the air gap length). When the interference state changes, there are problems that the amount of light returning from the recording medium surface changes, the Kerr rotation angle changes, the reproduction characteristics change, and the required recording power changes.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an SI
It is possible to suppress a change in the optical interference state due to a change in the flying height of the flying head provided with L, and to ensure a stable recording / reproducing state.

[0007]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, by setting the thickness of each thin film layer constituting the recording medium to a predetermined value,
The inventors have found that it is possible to suppress a change in the optical interference state due to a change in the flying height of the flying head in which the IL is installed, and it is possible to secure a stable recording / reproducing state, and thus completed the present invention.

That is, in the magneto-optical recording medium of the present invention, a metal reflective film, a first dielectric film, a magneto-optical recording film and a second dielectric film are laminated in this order on a substrate. The film thickness is in the following range.

40 nm ≦ d ₁ 80 nm ≦ d ₂ ≦ 120 nm 20 nm ≦ d ₃ ≦ 30 nm 65 nm ≦ d ₄ ≦ 80 nm where d ₁ is the thickness of the metal reflection film, d ₂ is the thickness of the first dielectric film, d ₃ is the thickness of the magneto-optical recording film, d ₄ is the thickness of the second dielectric film.

[0010] In the magneto-optical recording medium of the present invention, the metal reflection film is mainly composed of aluminum.
The first dielectric film is composed of silicon and nitrogen, the magneto-optical recording film is composed of a rare earth metal and a transition metal, and the second dielectric film is composed of silicon and nitrogen. More preferably, it is.

Hereinafter, the present invention will be described in more detail.

A conventional magneto-optical recording medium has a first dielectric film 22, a magneto-optical recording film 23, a second dielectric film 22 on an optically transparent substrate 21 as shown in a partial sectional view of FIG. The body film 24 and the reflection film 25 are laminated in this order. Here, the first dielectric film and the second dielectric film are formed of a material having a refractive index of about 1.8 to 2.4 and having no optical absorption in order to have an optical interference function. , Si
N, TiO, SiN: H, SiAlON or the like is used. In this structure, recording / reproduction from the recording film surface side is impossible. However, in order to perform recording / reproduction from the recording film surface side, a structure opposite to the above structure, that is, for example, FIG. As shown in FIG. 2, a reflective film 12, a first dielectric film 13, a magneto-optical recording film 14, and a second dielectric film 15 are laminated in this order on a substrate 11 (not necessarily optically transparent). What is necessary is just to make it the structure which did. In this case, for example, light that has passed through an SIL having a refractive index of 1.8 has a refractive index of 1.0.
Through the air gap, and the refractive index is from 1.8 to 2.
The light is incident on about four second dielectric films. Here, since the air gap length is as thin as about 100 nm, optical interference occurs. Therefore, due to factors such as a change in the moving speed of the recording medium and the flying angle of the slider of the flying head, when the flying height of the slider changes, the air gap length changes and the interference state changes. As a result, the interference state changes. Problems occur in the recording / reproducing characteristics such as a change in the amount of light reflected from the recording medium and a change in required recording power.

The magneto-optical recording medium of the present invention has a metal reflection film 12, a first dielectric film 13, a magneto-optical recording film 14, a second dielectric film It has a configuration in which the body films 15 are laminated in this order, and the thickness of each of these thin films is set to a predetermined range as described above. When the thickness d ₁ of the metal reflective film 12 is less than 40 nm, laser light is transmitted and total reflection is not performed, so that good optical characteristics cannot be obtained.
For the case of more than nm is sufficiently reflected, since no optical change is more thickness, 40 nm ≦ d ₁
The first dielectric film 13, the magneto-optical recording film 1
4. The optimum ranges of the film thicknesses d ₂ , d ₃ , and d ₄ of the second dielectric film 15 are experimentally determined as described later.

Although not shown in FIG. 1, guide grooves and pits carrying address information and the like can be formed on the substrate 11 as necessary.

Light for recording / reproduction is applied to the second dielectric film 1
5, the substrate used is not necessarily required to be optically transparent, and a resin such as polycarbonate, amorphous polyolefin, epoxy, acrylic, or vinyl chloride is used. Alternatively, glass or a metal such as aluminum or titanium can be used.

As the metal reflection film 12, aluminum,
Metal film of titanium, chromium, silver, gold, etc. or 2
An alloy film made of at least one of these metals can be used, but an alloy film containing aluminum as a main component is preferably used.

It is preferable to use a dielectric film having a refractive index of about 1.8 to 2.4 for the first dielectric film 13 and the second dielectric film 15 in order to sufficiently obtain the Kerr effect increasing function. It is more preferable to use a dielectric film having a refractive index of 1.9 to 2.2. As such a dielectric film, S
iN, AlN, AlSiN, TaO, TiO, NbO,
A thin film of ZrO, SiC, SiN: H or the like can be used.

The magneto-optical recording film 14 is made of TbFeCo, Dy
Rare earth transition metal alloys such as FeCo, TbDyFeCo, and TbDyFeCo, and perpendicular magnetization films such as a PtCo multilayer film can be used. Further, a plurality of these magneto-optical recording films can be stacked, and further, an additive can be added for improving corrosion resistance and controlling magnetic properties.

In addition, a resin is coated on a non-film-forming surface of the substrate (the surface on which the above-mentioned recording film or the like is not formed) to prevent electrification or to adjust a warp angle, and a glass plate is bonded. Of course, it is also possible to perform a treatment such as bonding a metal plate. After forming each of the above films, it is of course possible to coat a lubricant or the like by a spin coating method or a dipping method. Further, it is of course possible to use two magneto-optical recording media according to the present invention as a medium capable of recording and reproducing on both front and back surfaces by bonding the non-film forming surfaces of the substrates.

[0020]

EXAMPLE A polycarbonate made of 130 mm in diameter, having a pitch of 0.55 μm and a groove depth of 110 nm.
An Al alloy film containing a small amount of Cr as a reflective film is formed on a substrate having a guide groove by DC magnetron sputtering.
SiN is used as the first dielectric film by RF reactive magnetron sputtering, and TbDyFeCoTi is used as the magneto-optical recording film.
Magnetic films of various thicknesses were produced by continuously forming a magnetic film by DC magnetron sputtering and SiN as a second dielectric film by RF reactive magnetron sputtering (Examples 1 to 7). And Comparative Examples). Table 1 shows the thickness of each film of each of the produced magneto-optical disks.

[0021]

[Table 1]

In order to determine the refractive index of the dielectric film, 100 nm of SiN is formed on a silicon wafer and a wavelength of 68 nm.
The refractive index was determined with a 0 nm ellipsometer. As a result, the refractive index of the SiN film was 2.03.

A wavelength 680 having a flying head in which a SIL having a refractive index of 1.8 as shown in FIG. 3 is embedded in a slider.
The reflectivity and CN ratio (ratio between carrier level and noise level) of the magneto-optical disk were measured using an optical system of nm. FIG. 3 is a conceptual diagram showing a recording / reproducing optical system having an SIL used for measurement. A laser beam 48 is reflected by a mirror 47, passes through an objective lens 44 held by an actuator 46, and passes through an SIL 42. It is configured to focus on the recording film of the magneto-optical recording medium 1.

In the measurement of the reflectivity, Al was added to flat glass without grooves at first without mounting the SIL.
The amount of light returning to the detector of the pickup from the disk (Al disk) formed in nm was measured, and the reflectance of this Al disk was set to 90%.

The reflectivity of the magneto-optical disk is calculated by obtaining the amount of light reflected from the magneto-optical disk and returning to the detector of the pickup in a state where the SIL is mounted, and comparing it with the previously obtained amount of reflected light from the Al disk. did.

The CN ratio is as follows: a radius of 30 mm, a recording magnetic field strength of 200 Oe, and a mark length of 0.2 μm with the SIL mounted.
m.

At the position of a radius of 30 mm, the number of revolutions is changed, and the air gap length is changed by changing the flying height of the flying head on which the SIL is mounted. Was used to determine the reflectance and the CN ratio. The air gap length in the measurement is 90 nm,
The thickness was set to 100 nm and 110 nm.

FIG. 4 shows the measurement results of the reflectivity of the magneto-optical disks of the comparative example and Examples 1 to 7, and FIG. 5 shows the measurement results of the CN ratio.
Shown in

In the magneto-optical disk of the comparative example, good values were obtained for both the reflectance and the CN ratio when the air gap length was 100 nm. However, the reflectance greatly changes due to the change in the air gap length, and the air gap length 110n
For m, it is about 27%. The reflectivity of a magneto-optical disk is specified in the range of about 12% to 25% by ISO standards or the like in order to guarantee the operation of the drive.
The reflectance of 27% is a reflectance outside this standard. CN
The ratio is as good as about 47 dB when the air gap length is 100 nm, but the air gap length is 90 nm or 110 n.
m, the result was less than 45 dB. As described above, in the comparative example, when the air gap length changes, the reflectivity and the CN ratio greatly change, which is problematic.

On the other hand, in the magneto-optical disks of Examples 1 to 7, the change in the reflectance is only about 3% when the air gap length is in the range of 90 nm to 110 nm, and there is no problem with the value. . The CN ratio is 45 dB or more when the air gap length is in the range of 90 nm to 110 nm. Thus, in the example, it is clear that a stable and highly reliable recording / reproducing operation can be obtained even when the air gap length changes, and the characteristics thereof are excellent.

In the recording / reproducing operation, a change in the reflectivity causes a change in the recording laser power, resulting in a change in the sensitivity of the magneto-optical disk, and an automatic gain for operating the reproduction system to keep the signal intensity constant. A more powerful function is required for the control, which leads to an increase in the cost of the recording / reproducing apparatus. Therefore, it is necessary to suppress the change in the reflectance as low as possible, and it can be seen that the present invention is effective. It is desirable that the CN ratio be as high as possible. Generally, it is considered that there is no problem in the reproduction characteristics if it is 45 dB or more, but in the comparative example, the value may be less than 45 dB due to a change in the air gap length. ing. Therefore, the effect of the present invention is apparent also in terms of the CN ratio. If the CN ratio is kept high, it is possible to keep the recording / reproducing error small, and a stable and highly reliable recording / reproducing operation becomes possible.

[0032]

According to the magneto-optical recording medium of the present invention, the SIL is placed on the slider of the flying head having a small air gap.
In the recording / reproducing system in which is formed, it is possible to reduce the change in the recording / reproducing characteristics due to the fluctuation of the air gap length, and it is possible to keep the recording / reproducing error small. Not only can this be achieved, but it can also contribute to reducing the cost of the recording / reproducing device.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing an example of the structure of a magneto-optical recording medium that performs recording and reproduction by irradiating light from a recording film side.

FIG. 2 is a partial sectional view showing the structure of a conventional magneto-optical recording medium.

FIG. 3 is a conceptual diagram showing a recording / reproducing optical system having an SIL used for measurement in Examples and Comparative Examples.

FIG. 4 is a diagram showing the air gap length dependence of the reflectivity of the magneto-optical disks of Comparative Example and Examples 1 to 7.

FIG. 5 is a diagram showing the air gap length dependence of the CN ratio of the magneto-optical disks of the comparative example and Examples 1 to 7.

[Explanation of symbols]

 1: Magneto-optical recording medium 11, 21: Substrate 12, 25: Metal reflective film 13, 22: First dielectric film 14, 23: Magneto-optical recording film 15, 24: Second dielectric film 41: Slider 42: SIL 43: Holder of a slider having a spring function 44: Objective lens 45: Optical pickup housing 46: Objective lens actuator 47: Mirror 48: Laser light 49: Air gap

Claims (2)

[Claims] A metal reflective film, a first dielectric film,
A magneto-optical recording medium, wherein a magneto-optical recording film and a second dielectric film are laminated in this order, and the thickness of each film is in the following range. 40 nm ≦ d ₁ 80 nm ≦ d ₂ ≦ 120 nm 20 nm ≦ d ₃ ≦ 30 nm 65 nm ≦ d ₄ ≦ 80 nm where d ₁ is the thickness of the metal reflection film, d ₂ is the thickness of the first dielectric film, and d ₃ is the thickness of the first dielectric film. the film thickness of the magneto-optical recording film, d ₄ is the thickness of the second dielectric film. 2. A metal reflection film comprising aluminum as a main component, a first dielectric film comprising silicon and nitrogen, and a magneto-optical recording film comprising a rare earth metal and a transition metal. 2. The magneto-optical recording medium according to claim 1, wherein the second dielectric film is composed of silicon and nitrogen.