JPH038148A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain the magneto-optical recording medium having excellent recording and reproducing characteristics and high reliability by making the refractive index of the 1st dielectric film laminated on a substrate smaller than the refractive index of the 2nd dielectric film laminated thereon via a thin magnetic film intervened therebetween. CONSTITUTION:The recording medium is formed by laminating the 1st dielectric film 2, the thin magnetic film 3, the 2nd dielectric film 4, and a metallic reflecting film 5 on the transparent substrate 1. The refractive index of the film 2 is made smaller than the refractive index of the film 4. the films 4, 5 reflect the light transmitted through the film 3 and increase the Kerr rotating angle and the Faraday rotating angle in the film 3 by an interference effect. The film 2 increases the quantity of the reflected light by a multiple interference effect. Since the refractive index of the film 2 is smaller than the refractive index of the film 4, the reflectivity decreased by the film 4 is compensated by the film 2 and, therefore, the Kerr rotating angle is increased without decreasing the quantity of the reflected light. The recording medium having the excellent recording and reproducing performance and the high reliability is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical recording medium in which information is recorded, reproduced, erased, etc. by irradiation with light such as a laser.

[Conventional technology]

Magneto-optical recording has recently attracted attention as an optical disc on which information can be written, and rare earth transition metal alloy films are used as the recording medium.

However, since the Kerr rotation angle of a rare earth transition metal alloy film is as small as 0.3 to 0.4 degrees, research is being carried out on methods of increasing the Kerr rotation angle using the interference effect of light.

FIGS. 4 and 5 are partial cross-sectional views of a magneto-optical recording medium using the method of increasing the Kerr rotation angle by N6.

In FIG. 5, light incident from the transparent substrate 1 side is reflected at the interface between the dielectric film 11 and the magnetic thin film 3, causing Kerr rotation. This light is reflected at the interface between the MTM body 1 11 and the substrate 1, and is reflected again by the magnetic thin film 11 3, causing Kerr rotation. In this way, by repeating multiple reflections within the dielectric film 2, the Kerr rotation angle increases. However, since the magnetic thin film absorbs a portion of the light without reflecting it, the absorption rate also increases as the Kerr rotation angle increases, resulting in a decrease in the reflectance.

In addition, in the case of lateral propagation in FIG. 4, the same multiple reflections as described above in the first dielectric film 2 are combined with the Faraday rotation effect of the light passing through the magnetic thin film 3, and the 2 dielectric film 4
Due to the addition of rotation of the plane of polarization due to 1f reflection, the Kerr rotation angle further increases, but the reflectance decreases.

In both cases, the Kerr rotation angle increases and the reflectance decreases at the same time, but the performance number, which is a quantity proportional to the S/N (signal-to-noise ratio) of the medium, can be increased by 7 orders of magnitude. can. Here, when R is the reflectance and θ2 is the Kerr rotation angle, the figure of merit F is given by R-(ih(α=-orl).

As a conventional example of the above-mentioned method, there is
17236 and JP-A-59-152552 JP-A-57-1
69996, JP-A No. 60-63747, and the like.

In JP-A-57-159995 and JP-A-60-63747, the refractive index of the first dielectric film 2 shown in FIG.
It is proposed to make the refractive index relatively higher than that of the dielectric film 4. That is, −1st 1 dielectric + 1Sk 2
The reflection film 5 is increased by increasing the Kerr rotation angle due to the interference effect in the multiple pieces inside and lowering the refractive index of the second dielectric film 4.
and the second dielectric film 4, the refractive index is O.
The aim is to make the reflectance as close as possible and to increase the reflectance.

However, 4 using the interference effect in the first dielectric film 2
1. It is true that the Kerr rotation angle can be increased, but at the same time, the reflectance decreases significantly, and the readout figure of merit de = R
・θ0 cannot be made too large, and since the film thickness of the first dielectric film 2 is fixed under the condition of a very thick Kerr rotation angle, the film thickness can be increased. This prevents corrosion such as oxidation of the magnetic thin film 3. The protective effect cannot be increased. Furthermore, since the 111 refractive index of the first dielectric film 2 is large, there is a problem that the film 1v of the first dielectric film 2, which is a condition for maximum Kerr rotation angle, becomes 74.

[Problem to be solved by the invention] As described above, in order to further increase the performance index using the methods shown in Figs. Since it is also used for dregs, a certain amount of light 1t is required.

Further, from the viewpoint of corrosion resistance, it is desirable that the film thickness of the dielectric +1!5 L be as small as possible, but in the conventional example, the film thickness was limited by the figure of merit.

SUMMARY OF THE INVENTION An object of the present invention is to provide a magneto-optical recording medium that increases the Kerr rotation angle without lowering the reflectance and provides good recording and reproducing characteristics.

Another object of the present invention is to provide a magneto-optical recording medium that can significantly improve corrosion resistance while maintaining good recording and reproducing characteristics.

Means for Solving Problem C] The above object is achieved by making the refractive index of the dielectric film 1 lower than the refractive index of the dielectric film 2. This can be achieved by setting 80 to 120% of the distance J where the Kerr rotation angle is maximum, and setting the film thickness of the attracting body film 1 to 120 to 250% of the film H where the reflectance is the minimum.

[Effect]

The second dielectric film 4 and the metal film 5 reflect the light that has passed through the magnetic thin film 3, and the Kerr rotation angle and the magnetic '
It has the effect of increasing the Faraday rotation angle in t"r II"a U. The first 11\ electric film 2 moves to increase the amount of reflected light due to the effect of multi-11j interference.

Due to these effects, the first dielectric film 2 compensates for the reflectance reduced by the second dielectric film 4, so the Kerr rotation angle can be increased without reducing the amount of reflected light. At this time, the first dielectric film 2 becomes thicker than before, but this tends to increase the effect of preventing the magnetic thin film 3 from oxidation. This makes it possible to obtain a magneto-optical recording medium with improved recording and reproducing performance and reliability.

If we convert H, the value is the product of the thickness of the second dielectric film 4 and the refractive index plus the product of the thickness of the magnetic thin film 3 and its refractive index,
That is, since the sum of the optical lengths of the second dielectric film 4 and the magnetic thin film 3 is approximately one-fourth of the wavelength of the irradiated light, these two layers act as a kind of anti-reflection film, and , the effective number of times light travels back and forth in the magnetic film due to multiple reflections increases.
The effect of Faraday rotation becomes larger, and the Kerr rotation angle on j' increases.

Furthermore, since the product of the film J) and the refractive index of the "th" dielectric film 2, that is, the optical length, is approximately one half of the wavelength of the irradiated light, the first vIm body film 2 is Acting as a reflective film, the interference increases the reflected light scene. Therefore, according to the configuration of the present invention, the second dielectric film 4 can increase the Kerr rotation angle, and the first dielectric film 2 can increase the amount of reflected light.

In the present invention, the thickness of the second dielectric film 4 has a large effect on the Kerr rotation angle 7, as shown in FIG. 80 of the film thickness 15 of the second dielectric film 4 where the Kerr rotation angle 7 is maximum
% to 120%, the Kerr 1rJJ rotation angle 7 is sufficiently large as shown in FIG. 2, and the effect of the present invention appears. Considering only the Kerr rotation angle 7, the film thickness of the second dielectric film 4 may be smaller than 80% of the film thickness 15 at which the Kerr rotation angle becomes maximum, but from the viewpoint of the corrosion resistance of the medium. The film thickness is limited to 80%.

As shown in FIG. 3, when the thickness of the first dielectric film 2 has a minimum reflectance 8, the Kerr rotation angle 7 does not reach its maximum, and the peak of the Kerr rotation angle 7 shifts to the thicker side. There is. Therefore, the figure of merit F has a large value when the film thickness of the first dielectric film 2 is 120% to 220% of the film thickness at which the reflectance 8 is the minimum, and has a large value when the film thickness is 220% or more. Decrease. Therefore, the thickness of the first dielectric film 2 is preferably 120% to 220% of the film thickness that provides the minimum reflectance.

Moreover, the second dielectric film 4 and! When the sum of the optical thicknesses of the magnetic thin film 3 becomes about 174 of the wavelength of the light used, the interface between the first 7Ipt tube film 2 and the magnetic thin film 3.

Since the interference of light between the metal reflective films 5 is maximized, the Kerr rotation angle is maximized. This optical film; V is 1 of the wavelength of light.
/2, the Kerr rotation angle is zero.

At least, in order to provide the effects of the present invention, the optical film thickness needs to be 1/8 or more and 378 times or less of the wavelength.

Regarding the first dielectric film 2, the minimum reflectance is given when the optical film thickness is about 174 wavelengths of light, and the maximum reflectance is given when the optical film thickness is about 1/2 of the wavelength of light. give. Therefore, as an effect of the present invention, in order to obtain a high reflectance, the film thickness of the first dielectric film 2 must be set to 3/8 or more or more than 9/9 of the wavelength of light.
It is better to set it to 8 or less.

〔Example〕

Examples of the present invention will be shown below.

Example 1 In FIG. 1, a polycarbonate substrate 1 manufactured by injection molding has 7-shaped tracking guide grooves formed at a pitch of 1.6 μm.

The polycarbonate substrate 1 was first held in a vacuum at 80° C. for 3 hours to dehydrate the water contained in the substrate. After this, the refractive index n3 of this polycarbonate substrate 1 is 1.5.
It is.

Next, the polycarbonate substrate 1 is loaded into a high-frequency magnetron sputtering device, and after the vacuum chamber is evacuated to below 8X10'-' Torr, a mixed gas of Ar gas and N2 gas is introduced to target the SiN sintered body. as I
A SiN film of 1000A was formed on the polycarbonate substrate 1 as the first dielectric film 2 by sputtering at a gas pressure of It is desirable that the flexural index n I l of the 1000-layer thick SiN screen thus formed is 2.0.

Next, after a similar vacuum evacuation, Ar gas was introduced and TbFe
An alloy target consisting of Co is 5
Sputtered at a gas pressure of rr, and T with an Ad refractive index n5 of 3.0.
Only 200 people formed the bFcCo magnetic thin film 3.

Next, after similar vacuum evacuation, Ar gas was introduced and Si
Sputtering is performed using a sintered body of N as a target at a gas pressure of lXl0"" Torr, and a second *electrical film 4 is formed of Si.
A N film was formed by 300 people. The refractive index n'X of this 5iNIN is 2.2. After this, after performing the same evacuation again, Ar gas was introduced, and an AQ-Ti alloy target was sputtered at a gas pressure of 3 x 10-'' Torr to form a gold alloy film 5 with a refractive index of n, is 2.0 AQ
A -Ti alloy film was formed to a thickness of 500 mm.

The polycarbonate substrate 1 with the film formed thereon is taken out of the vacuum chamber, and a magnetic field of 20 kOe is applied in a direction perpendicular to the film surface to perform initial magnetization. After that, similarly l1i
It is closely bonded to another polycarbonate substrate l having a J formed thereon with an adhesive 13 so that the metal film side is in contact with the other polycarbonate substrate l to form the structure shown in FIG.

The magneto-optical recording medium produced in this way has n s < nr
<nX<nr is satisfied, and Example B in Table 1
As shown in the figure, the reflectance was 24%, the Kerr rotation angle was 0.75 degrees, and the figure of merit R・θ was 0.18 degrees, which is approximately 1% compared to the conventional model.
．． I saw a 4x improvement.

In the present invention, as shown in FIG.
The film thickness is set so that the Kerr rotation angle is maximized.

At this film thickness, the interference effect due to multiple reflections of light in the second dielectric film becomes maximum, and the Kerr rotation angle of the reflected light becomes maximum.

Further, as shown in FIG. 3, the thickness of the first dielectric film 2 is set close to the thickness at which the reflected light becomes maximum.

With such a configuration, it is possible to increase the Kerr rotation angle without reducing the reflectance. However, if the thickness of the first dielectric film 2 is set to maximize the Kerr rotation angle and the H-nove of the second dielectric film 1 is set to maximize the reflectance, the above No such effect was observed. As shown in FIG. 3, even if the thickness of the first dielectric film 2 is changed, the figure of merit R・θ, which is the product of the Kerr rotation angle and the reflectance, hardly changes, but the second This is because when the thickness of the dielectric film 4 is changed, the figure of merit changes greatly. Physically, the second dielectric film 4
The interference effect is caused by the Kerr rotation of the reflection by the magnetic thin film,
This is due to the combination of two effects, the Faraday effect of light transmitted through a magnetic thin film, and therefore there are film thicknesses where both effects strengthen each other, and film thicknesses where they weaken each other.

Example 2 In FIG. 7, a chemically strengthened glass substrate 1 having a U-shaped tracking guide groove and a refractive index ns of 1.5 was loaded into a high frequency magnetron sputtering device, and a 8 x 10-
'After exhausting the vacuum chamber to below Torr, Ar gas and 0
A mixed gas of two gases is introduced, and sputtering is performed using a sintered body of Zr0z as a target at a gas pressure of I X L O-''Torr to form a Zr0z film 2 as a first dielectric 1t!I!2.
900 people M'J'fl. Ko (1) Z r Ox
The refractive index nr of film 2 was 262.

Next, after a similar vacuum evacuation, Ar gas was introduced and the FeC
An alloy target consisting of 5 X I O"-8To
TbF with a refractive index nr of 3.0 sputtered at a gas pressure of rr
Only 200 eCo&I thin films 3 were formed.6 Then, after vacuum evacuation in the same manner again, using a ZnS sintered target, sputtering was performed at an Ar pressure of 2 x 10-''Torr to laminate 2508 Znsv to form the second dielectric. It is assumed to be a body membrane 4. The refractive index n- of this membrane is 2.4.

After that, the same vacuum evacuation was performed again, Ar gas was introduced, and the AQ target was sputtered at a gas pressure of 3 X I O'Torr, and gold 1. Let LlclIψ5. A
The film thickness of Q++ is 300 people, and the HD refractive index is 2.0.

The disk on which the film was formed in this way was taken out of the vacuum chamber, and
After initial magnetization is performed by applying a magnetic field of 20 KOe perpendicular to the film surface, an ultraviolet curable resin (UV resin) is spin-coated as the protective coat 14, and is cured by exposure to ultraviolet light for 1 minute in a vacuum. The protective coat 14 serves to protect the recording film from damage caused by sliding of the slider of the floating magnetic head.

It also has the effect of increasing the monolithicity of the recording film.

In this way, the static characteristics of the magneto-optical recording medium manufactured are shown as Example C in Table 1.
It is also possible to produce media with the static properties of Examples A and B of the table. When the recording and reproducing characteristics of the magneto-optical recording medium having the characteristics of Example C were evaluated by using a floating magnetic head and applying a modulated magnetic field, a C/N ratio of 60 dB was obtained.

FIG. 8 shows the recording and reproducing characteristics when using the magneto-optical recording medium according to the present invention. As the figure of merit increases, in the example of the present invention, the C/N ratio is significantly improved compared to the conventional example, and the recording sensitivity is also improved.

Note that the configuration of the magneto-optical recording medium of the present invention is not limited to the above-described embodiment, and the following configurations are also possible. That is, (1) as the first dielectric film 2 and the second dielectric film 4,
Oxides such as SiO, Taxoa, T' a N .

A nitride such as SiN or a sulfide such as CdS is used.

(2) A Q + Cu + A g as the metal film 5
g Au rTi, Ni, Cr stainless steel, etc., or alloys thereof are used.

(3) For the substrate 1, acrylic, ultraviolet curing resin, polyolefin, etc. are used.

(4) T b - Fe, G d as the magnetic thin film 3
-"1' b -F a , B y -F e -
Amorphous alloys of rare earths and transition metals such as Go, or these, and Ti.

An amorphous alloy containing at least one element added to improve corrosion resistance such as Ta, Cr, V, and Nb is used.

Furthermore, when performing magneto-optical recording using the magneto-optical recording medium of the present invention, recording may be performed by changing the intensity of the laser beam, or recording may be performed by changing the magnetic field intensity while keeping the laser beam intensity constant. You can go 4N.

〔Effect of the invention〕

As explained in detail above, according to the present invention, the film thickness of the first dielectric film 2 laminated on the substrate 1 is set to 120% to 220% of the film thickness at which the reflectance becomes the minimum, and Since the thickness of the second dielectric film 4 laminated with the magnetic thin film 3 in between is set to 80% to 120% of the film thickness at which the Kerr rotation angle is maximum, the first M electric film 2 Since the refractive index of the second dielectric film is lower than that of the second dielectric film, the Kerr rotation angle can be increased without decreasing the reflectance.

[Brief explanation of the drawing]

1, 6 and 7 are cross-sectional views showing the structure of a magneto-optical recording medium according to an embodiment of the present invention, and FIGS. 4 and 5 are cross-sectional views showing the structure of a conventional magneto-optical recording medium. , Figures 2 and 3
The figure is a relationship curve diagram showing the relationship between the film thickness of the first and second dielectric films, the Kerr rotation angle, and the reflectance. Figure 8 is the relationship curve between recording laser power and S/N showing the effect of the present invention. It is a diagram. DESCRIPTION OF SYMBOLS 1... Substrate, 2... First dielectric film, 3... Magnetic film, 4... Second I/I electric film, 5... Metal film, 6...
・Light beam, 7... Kerr rotation angle, 8... Reflectance, 1
DESCRIPTION OF SYMBOLS 1... Dielectric film, 12... Protective film, 13... Adhesive, 14... Protective coat. Diagram Kaya Dai? No. 3 Kasumi No. 3] Illustration

Claims (1)

[Scope of Claims] 1. In a magneto-optical recording medium in which a first dielectric film, a magnetic thin film, a second dielectric film, and a metal reflective film are laminated in this order on a transparent substrate, the first dielectric film A magneto-optical recording medium characterized in that the refractive index of the film is smaller than or equal to the refractive index of the second dielectric film. 2. In the magneto-optical recording medium according to claim 1, the thickness of the first dielectric film is 80% to 120% of the thickness at which the Kerr rotation angle of light incident from the transparent substrate side is maximum. ,
A magneto-optical recording medium characterized in that the thickness of the second dielectric film is 120% to 220% of the film thickness that minimizes the reflectance of light incident from the transparent substrate side. 3. In the magneto-optical recording medium according to claims 1 and 2, the refractive index of the transparent substrate, the first dielectric film, the magnetic thin film, the second dielectric film, and the metal film are set to n in order.
A magneto-optical recording medium characterized in that, where s, n^I, nr, n^II, and n_m, ns<n^I <n^II<nr and n_m<n^II. 4. In the magneto-optical recording medium according to claims 1 and 3, the optical thickness of the first dielectric film is 3/8 or more and 5/8 or less of the wavelength of the irradiated light, and Said second
A magneto-optical recording medium characterized in that the sum of the optical thicknesses of the dielectric film and the magnetic thin film is 1/8 or more and 3/8 or less of the wavelength of the irradiated light.