JP2001344842A - Magneto-optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve jitter characteristics and signal quality in an overwritable magneto-optical recording medium. SOLUTION: In the magneto-optical recording medium 1 in which a first dielectrics layer 3, a magneto-optical recording layer 4, a second dielectrics layer 5, a reflecting layer 7 and a protective layer 8 are succeedingly formed on a light transparent substrate 2, the double refractivity in the intra-plane direction is defined as -40 [nm] to 25 [nm], and the vertical double refractivity is specified within the range of 200 [nm] to 300 [nm].

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a magneto-optical recording medium.

[0002]

2. Description of the Related Art In recent years, in the field of information recording medium development, researches on optical recording systems have been conducted in various places.
This optical recording system uses a laser beam to record and reproduce information. As an optical recording medium using this system, a read-only digital audio disk (so-called compact disk) and an optical video disk ( So-called laser disks) are widely used.

On the other hand, a user repeatedly records information,
As a writable optical recording medium capable of performing erasing and erasing, a magneto-optical recording medium is being developed and commercialized. As such a magneto-optical recording medium, a mini disk (MD) is widely used.

In such a magneto-optical recording medium, a magnetic thin film having an easy axis of magnetization in a direction perpendicular to the surface of the light transmitting substrate and having a large magneto-optical effect is formed on a light transmitting substrate made of, for example, polycarbonate. A dielectric layer and a metal reflective layer are laminated on the magneto-optical recording layer, and the magneto-optical recording layer, the dielectric layer, and the metal reflective layer It constitutes a recording layer. On this recording layer, a protective layer made of, for example, an ultraviolet curable resin is laminated.

[0005] A magneto-optical recording medium such as a mini disk (MD) can easily record music and the like as a consumer recording device, and thus can be used in various situations, such as home use or use in a car. The way is possible.
As described above, when the range of usage is widened, a variety of reproducing apparatuses, that is, drives for reproducing signals from this magneto-optical recording medium are also widespread, and their optical performances are also various.

[0006]

However, in a wide variety of types of reproducing devices (drives), the optical characteristics of the optical pickup differ depending on their specific performances. However, in other reproduction apparatuses, the jitter value (time-axis fluctuation value) increases, the error rate may deteriorate, and a stable signal characteristic may not be obtained.

In view of such a problem, the characteristics of the groove formed in the light-transmitting substrate are improved so that the laser light can accurately trace the magneto-optical recording layer constituting the magneto-optical recording medium. By adjusting the thickness of the dielectric layer having a higher refractive index than the refractive index of the light-transmitting substrate, the apparent Kerr rotation angle can be enhanced by obtaining the effects of multiple reflection and interference. In other words, the signal characteristics have been improved by the so-called enhanced effect.

However, in the above,
It has been difficult to obtain practically sufficient signal characteristics according to various kinds of reproducing apparatuses. Accordingly, the present inventors have conducted intensive studies, and as a result, improved the jitter characteristics of the magneto-optical recording medium, improved the signal quality, and obtained an excellent magnetic field modulation that can obtain excellent signal characteristics according to various types of reproducing devices. A writable magneto-optical recording medium is provided.

[0009]

According to the present invention, a first dielectric layer, a magneto-optical recording layer, a second dielectric layer, a reflective layer, and a protective layer are sequentially formed on a light transmitting substrate. The birefringence in the in-plane direction is in the range of -40 [nm] to 25 [nm], and the birefringence in the vertical direction is 200 [nm] to 300 [nm]. [N
m].

According to the present invention, the birefringence in the in-plane direction and the birefringence in the vertical direction of the light-transmitting substrate are specified within the predetermined numerical ranges as described above, thereby improving the jitter characteristics. Thus, a magneto-optical recording medium with improved signal quality and capable of accurately tracing the magneto-optical recording layer according to various signal reproducing devices can be obtained.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the magneto-optical recording medium of the present invention, a first dielectric layer, a magneto-optical recording layer, a second dielectric layer, a reflective layer, and a protective layer are formed on a light-transmitting substrate. It is assumed that the magneto-optical recording medium is formed sequentially, the birefringence in the in-plane direction is in the range of -40 [nm] to 25 [nm], and the birefringence in the vertical direction is 200 [nm]. ~ 300 [n
m].

Hereinafter, the magneto-optical recording medium of the present invention will be described by way of an example, but the magneto-optical recording medium of the present invention is not limited to the following examples.

FIG. 1 is a schematic sectional view showing an example of the magneto-optical recording medium 1 according to the present invention. In the magneto-optical recording medium 1 of the present invention, a first dielectric layer 3, a magneto-optical recording layer 4, and a second dielectric layer 5 are sequentially laminated on a light-transmitting substrate 2 made of a thermoplastic resin. A recording layer 6 is formed, and a reflective layer 7 and a protective layer 8 are formed on the recording layer 6.

When recording or reproducing information on or from the magneto-optical recording medium 1 shown in FIG. 1, a laser beam having a predetermined wavelength, for example, a laser beam L having a wavelength of 780 nm is transmitted from the light transmitting substrate 2 side. Is performed by condensing and irradiating with the objective lens 11.

The light transmitting substrate 2 is provided with a laser beam L having the above wavelength.
On the other hand, it can be formed by a material having transparency, for example, by injection molding using polycarbonate, acrylic resin, amorphous polyolefin, or styrene resin. Glass as well as resin can be used as the material of the light-transmitting substrate. On the surface of the light-transmitting substrate 2, predetermined fine irregularities forming pits or grooves may be formed. Light transmitting substrate 2
When a groove is formed on the surface of the optical recording medium 1, the laser light L can be moved to an arbitrary position on the magneto-optical recording medium 1 by using the groove as a guide groove.
This becomes an information signal, and the recorded information can be read by irradiating the laser beam. The predetermined fine irregularities can be formed by injection molding or a photopolymerization method (2P method).

First dielectric layer 3 and second dielectric layer 5
Is formed for the purpose of improving C / N characteristics and preventing corrosion of the magneto-optical recording layer 4. That is, since the light transmissive substrate 2 and the protective layer 8 often contain components that corrode metals, such as chlorine ions, the first dielectric layer 3 and the second dielectric layer 5 Is formed so as to sandwich the magneto-optical recording layer 4 in the middle, it is possible to avoid being directly affected by components that corrode the metal, and to improve the characteristics of the magneto-optical recording medium. The first dielectric layer 3 is usually formed to a thickness of about 30 to 100 [nm], and the second dielectric layer 5 is usually formed to a thickness of 5 to 100 [nm].
[Nm] thickness.

The first dielectric layer 3 and the second dielectric layer 5 are different from each other with respect to the applied wavelength of the recording / reproducing laser beam.
It is necessary to be formed of a material having low absorption capacity. For example, a ZnS—SiO ₂ mixture, Al, Si, Ta,
Layers composed of nitrides, oxides, carbides, fluorides, nitrides, nitrocarbides, oxycarbides, SiAlON, etc. of metals and metalloids such as Ti, Zr, Mg, B, Zn, Pd, La, and Ge , And a material containing these as main components can be used.

The reflection layer 7 is made of, for example, Al, Ag, Au,
Cu, Ni, Cr, Ti. Pd, Co, Si, Ta,
It can be formed of a simple metal such as W, Mo, Ge or the like, or an alloy containing these as a main component. For example, Al
-Ti, Al-Cr, Al-Co, Al-Mg-Si,
Ag-Pd-Cu, Ag-Pd-Ti-, Si-B and the like can be applied. In particular, an Al-based or Ag-based material has a high reflectance to laser light even in a short wavelength region, and is therefore suitable as a material for forming the reflective layer 7. The reflection layer 7 may have a single-layer structure.
A multilayer structure having more than two layers can also be used.

The protective layer 8 is formed on the reflective layer 7 by lamination, and can be formed of an ultraviolet curable resin. The protective layer 8 can have a thickness of about 5 to 20 [μm].

The magneto-optical recording layer 4 constituting the magneto-optical recording medium 1 of the present invention is formed of a material capable of performing a magnetic field reversal with a low applied magnetic field. For example, amorphous Tb-
Fe-Co alloy film or. Amorphous Gd-Dy-Fe-
A Co alloy film or the like can be used.

When information is recorded on the magneto-optical recording medium 1 shown in FIG. 1, the laser beam L condensed by the objective lens 11 is continuously irradiated to cure the recording layer 6 of the magneto-optical recording medium. While heating to a temperature equal to or higher than Tc, the magnetic field applied by the magnetic head 20 is modulated at high speed in synchronization with desired information, and the direction of the magnetic field in a predetermined portion of the magneto-optical recording layer 4 is changed to write information. I do.

When reproducing information from the magneto-optical recording medium 1 shown in FIG. 1, a laser beam having a predetermined wavelength, for example, a laser beam having a wavelength of 780 nm, is applied from the light transmitting substrate 2 side. The light is condensed by the objective lens 11 and irradiated. When playing back information,
The laser power is set so that the portion of the recording layer 6 is not heated so that the magnetization reversal does not occur.

Next, regarding the magneto-optical recording medium of the present invention,
Hereinafter, specific examples and comparative examples will be described, but the present invention is not limited to the examples described below.

Example 1 A magneto-optical recording medium having the structure shown in FIG. 1 was manufactured as follows. Light transmitting substrate 2
The outer diameter is 64 [m
m] and a disk-shaped substrate having a thickness of 1.2 [mm] is manufactured. Subsequently, in an Ar atmosphere, a silicon nitride film was formed on the light-transmitting substrate 2 by sputtering using Si as a target to form a first dielectric layer 3. Next, A
amorphous Gd-D by sputtering in an atmosphere of
A magneto-optical recording film 4 made of a y-Fe-Co alloy was formed. Subsequently, in an Ar atmosphere, a silicon nitride film is formed by sputtering using Si as a target to form a second silicon nitride film.
Was formed. On the second dielectric layer 5, Al
A reflective layer 7 was formed by forming a metal layer by sputtering using a Ti alloy as a target. Next, a protective layer 8 is formed by spin-coating an ultraviolet-curable resin on the reflective layer 7 to form the target magneto-optical recording medium 1.
Was prepared. The birefringence in the in-plane direction of the light transmitting substrate 2 of the magneto-optical recording medium 1 manufactured as described above is -10 [n
m], and the vertical birefringence was 220 [nm].

The birefringence in the in-plane direction and the birefringence in the vertical direction of the light transmissive substrate 2 are determined, for example, by Dr. Schen
It can be measured using a birefringence measuring instrument such as PROmetenus MT-136 manufactured by K.

Example 2 The birefringence in the in-plane direction of the light transmitting substrate 2 of the magneto-optical recording medium 1 was 25 [nm], and the birefringence in the vertical direction was 200 [nm]. In addition, the first dielectric layer 3, the magneto-optical recording layer 4, the second dielectric layer 5, the reflective layer 7, and the protective layer 8 are formed in the same manner as in [Example 1]. Regarding each film forming order [Example 1]
A magneto-optical recording medium was produced in the same manner as in the above.

Example 3 The birefringence in the in-plane direction of the light transmitting substrate 2 of the magneto-optical recording medium 1 was -7 [nm], and the birefringence in the vertical direction was 300 [nm]. In addition, the first dielectric layer 3, the magneto-optical recording layer 4, the second dielectric layer 5, the reflective layer 7, and the protective layer 8 are formed in the same manner as in [Example 1]. Regarding each film forming order [Example 1]
A magneto-optical recording medium was produced in the same manner as in the above.

Example 4 The birefringence in the in-plane direction of the light transmitting substrate 2 of the magneto-optical recording medium 1 was -40 [nm], and the birefringence in the vertical direction was 250 [nm]. In addition, the first dielectric layer 3, the magneto-optical recording layer 4, the second dielectric layer 5, the reflection layer 7
The protective layer 8 was formed in the same manner as in [Example 1], and a magneto-optical recording medium was manufactured in the same order as in [Example 1].

Next, a comparative example for comparison with the magneto-optical recording medium of the present invention will be described.

Comparative Example 1 The birefringence in the in-plane direction of the light transmitting substrate 2 of the magneto-optical recording medium 1 was 5 [nm], and the birefringence in the vertical direction was 190 [nm]. In addition, the first dielectric layer 3, the magneto-optical recording layer 4, the second dielectric layer 5, the reflective layer 7, and the protective layer 8 are formed in the same manner as in [Example 1]. A magneto-optical recording medium was prepared in the same manner as in [Example 1] for each film formation order.

Comparative Example 2 The birefringence in the in-plane direction of the light transmitting substrate 2 of the magneto-optical recording medium 1 was -50 [nm], and the birefringence in the vertical direction was 310 [nm]. In addition, the first dielectric layer 3, the magneto-optical recording layer 4, the second dielectric layer 5, the reflection layer 7
The protective layer 8 was formed in the same manner as in [Example 1], and a magneto-optical recording medium was manufactured in the same order as in [Example 1].

Comparative Example 3 The birefringence in the in-plane direction of the light transmitting substrate 2 of the magneto-optical recording medium 1 was -12 nm, and the birefringence in the vertical direction was 400 nm. In addition, the first dielectric layer 3, the magneto-optical recording layer 4, the second dielectric layer 5, the reflection layer 7
The protective layer 8 was formed in the same manner as in [Example 1], and a magneto-optical recording medium was manufactured in the same order as in [Example 1].

Comparative Example 4 The birefringence in the in-plane direction of the light transmitting substrate 2 of the magneto-optical recording medium 1 was set to 28 [nm], and the birefringence in the vertical direction was set to 400 [nm]. In addition, the first dielectric layer 3, the magneto-optical recording layer 4, the second dielectric layer 5, the reflective layer 7, and the protective layer 8 are formed in the same manner as in [Example 1]. Regarding each film forming order [Example 1]
A magneto-optical recording medium was produced in the same manner as in the above.

Example 1 produced as described above
The jitter values of the samples of the magneto-optical recording media of [Example 4] and [Comparative Examples 1] to [Comparative Example 4] were measured. The jitter value is obtained by measuring the signal extracted from the optical disk error rate evaluator using a jitter meter (KENWOOD).
(DB-8260). In this case, the jitter value is a 3T jitter value corresponding to a laser beam having a short wavelength. As for the jitter level, if a value of 20 [ns] or less was obtained, it was evaluated that practically sufficient characteristics were obtained.

Further, the optical characteristics of each sample of the magneto-optical recording medium of [Example 1] to [Example 4] and [Comparative Example 1] to [Comparative Example 4] manufactured as described above were obtained. Types of playback devices (first to third drives) differing from each other
Was used to read a signal, which was evaluated. In selecting each drive, a blank drive having a standard defocus tolerance is used as the first drive, and a drive having a narrower defocus tolerance on the Near side than the first drive, that is, a drive having a lower tolerance on the Near side. Is a second drive, and a drive whose defocus tolerance is narrower on the Far side than the first drive, that is, a drive with a lower margin on the Far side, is a third drive.

Here, the near side is when the optical pickup is brought close to the magneto-optical recording medium, the far side is when the optical pickup is moved away from the magneto-optical recording medium, and the near side and the far side are By measuring the error rate level on the side, the defocus tolerance is specified.

In the evaluation of the read signal, those having a low error rate and having a practically sufficient C / N were evaluated as ○, and those having too many errors and having a practically insufficient C / N were evaluated. Indicated as x.

The measurement conditions are as follows. Laser wavelength: 780 [nm] A. : 0.45 Recording laser power: 4.55 [mW] Reproduction laser power: 0.6 [mW] Bias magnetic field: 100 [Oe]

The birefringence [nm] in the in-plane direction and the birefringence in the vertical direction of each magneto-optical recording medium of [Example 1] to [Example 4] and [Comparative Example 1] to [Comparative Example 4]. Refraction [nm], jitter value [ns], and the first
The following Table 1 shows the evaluation results of the read signals of the respective magneto-optical recording media when the drives No. 1 to No. 3 are applied.

[0040]

[Table 1]

As shown in Table 1, the birefringence in the in-plane direction is in the range of -40 [nm] to 25 [nm], and the birefringence in the vertical direction is 200 [nm] to 300 [nm]. In each of the magneto-optical recording media 1 of [Example 1] to [Example 4], the jitter value was 20 [n].
s] or less, and the jitter characteristics are improved, which is a practically sufficient value. Further, in the magneto-optical recording medium 1 of [Example 1] to [Example 4],
By specifying the birefringence in the in-plane direction and the birefringence in the vertical direction of the light transmissive substrate 2 within the above ranges, any one of three types of reproducing devices (first to third drives) having different optical characteristics can be used. In the case where the signal was read by using the above method, accurate tracing of the magneto-optical recording layer could be performed according to each drive, the error rate was low, and a practically sufficient C / N was obtained.

[Comparative Example 1] shows that the birefringence in the vertical direction is 2
In this example, the jitter value is higher than 20 [ns], and the jitter value is higher than 20 [ns].
In the case of using the drive of (1), the error rate increased, and a good reproduction signal could not be obtained in practical use.

[Comparative Example 2] shows that the in-plane birefringence was-
This is an example of a case where -50 [nm] is less than 40 [nm] and the birefringence in the vertical direction is 310 [nm] which is larger than 300 [nm]. In this magneto-optical recording medium,
The jitter value was higher than 20 [ns], and when the first drive was applied, the error rate was increased, and a practically good reproduced signal could not be obtained.

In Comparative Example 3, the birefringence in the vertical direction was 30
This is an example in the case of 400 [nm] larger than 0 [nm]. However, in this magneto-optical recording medium, the jitter value becomes higher than 20 [ns], and the second drive, Also, when the third drive was applied, the error rate increased, and a practically good reproduction signal could not be obtained.

[Comparative Example 4] shows that the birefringence in the in-plane direction was 2
This is an example in which 28 [nm] is larger than 5 [nm] and the birefringence in the vertical direction is 330 [nm] larger than 300 [nm]. In this magneto-optical recording medium, the jitter value is 20 [ns], and when the first drive was applied, the error rate increased, and a practically good reproduced signal could not be obtained.

As described above, according to the present invention, the birefringence in the in-plane direction and the birefringence in the vertical direction of the light-transmitting substrate 2 constituting the magneto-optical recording medium 1 are specified within a predetermined range. In addition, the jitter characteristics can be improved, and accurate tracing of the magneto-optical recording layer can be performed in accordance with various types of signal reproducing devices, thereby improving the signal quality.

According to the magneto-optical recording medium of the present invention, the jitter characteristic can be improved, so that the margin of the error rate can be improved, the influence of disturbance can be reduced, and the signal obtained by irradiating the laser can be improved. The quality could be improved and stable signal characteristics could be obtained.

[0048]

According to the present invention, the birefringence in the in-plane direction and the birefringence in the vertical direction of the light transmitting substrate constituting the magneto-optical recording medium are specified within a predetermined range, thereby improving the jitter characteristic. As a result, a magneto-optical recording medium having improved signal quality and capable of accurately tracing the magneto-optical recording layer in accordance with various types of signal reproducing devices was obtained.

In the magneto-optical recording medium of the present invention, since the jitter characteristics can be improved, the margin of the error rate is also improved, the influence of disturbance is reduced, and the quality of the signal obtained by irradiating the laser is improved. And stable signal characteristics could be obtained.

[Brief description of the drawings]

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

[Explanation of symbols]

REFERENCE SIGNS LIST 1 magneto-optical recording medium, 2 light-transmitting substrate, 3 first dielectric layer, 4 magneto-optical recording layer, 5 second recording layer, 6 recording layer, 7 reflective layer, 8 protective layer, 11 objective lens, 2
0 Magnetic head

Claims (1)

[Claims] 1. A magneto-optical recording medium in which a first dielectric layer, a magneto-optical recording layer, a second dielectric layer, a reflective layer, and a protective layer are sequentially formed on a light-transmitting substrate. The birefringence in the in-plane direction is -40 [nm] to 25 [nm], and the birefringence in the vertical direction is 200 [nm] to 300 [nm].
A magneto-optical recording medium, characterized in that: