JPH0512751A - Optical recording medium - Google Patents

Abstract

PURPOSE:To record and reproduce two bits (quad recording) at the same time at the same position of one medium and, therefore, increase the density of recording information by composing the optical recording medium of a magnetooptical recording film and a phase shifting film and recording and reproducing the information of the magnetooptical recording film and the information of the phase shifting film at the same position of the medium separately. CONSTITUTION:The optical recording medium 1 has at least the optical recording film 3, where the information is recorded and reproduced according to the direction of magnetism, and the phase shifting film 4, where the information is recorded and reproduced according to variation in optical constant due to phase variation between a crystal state and a noncrystalline state, on a substrate 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is capable of recording / reproducing 2-bit (4-level recording) information at the same position on one medium at the same time, and thus increasing the density of recorded information. Recording medium

[0002]

BACKGROUND OF THE INVENTION A magneto-optical recording medium or a phase-change type optical recording medium has been actively researched and developed in recent years as a large capacity memory capable of rewriting recorded information, and is practically used.

In a magneto-optical recording medium, the medium is irradiated with a laser beam to raise the temperature of the irradiated portion to reverse the magnetization in the weak magnetization direction of the external magnetic field to record information and reverse the magnetic field direction. The information is erased by irradiating the laser beam again. Further, the change of the Kerr rotation angle in which the plane of polarization of the reflected light from the medium slightly rotates depending on the direction of magnetization is detected to reproduce the information.

On the other hand, the phase change type optical recording medium utilizes the fact that the atomic arrangement reversibly changes in a special substance having a regular crystalline state and a disordered amorphous state.
Information is recorded by irradiating a strong light pulse for a short period of time to rapidly heat and quench the recording material to a temperature higher than the melting point and fix the amorphous material while the atomic arrangement is disturbed to make it amorphous. Information is erased by gradually heating and cooling above the crystallization temperature to return the atomic arrangement to the crystalline state. Information reproduction is detected as a change in the amount of reflected light by utilizing the difference in reflectance between the crystalline state and the amorphous state.

By the way, in such an optical recording medium as well, there is a demand for higher information density, and various developments are being made. However, at present, as described above, the magneto-optical recording medium adopts a recording / reproducing method suitable only for magneto-optical, and the phase change type optical recording medium adopts a recording / reproducing method suitable only for phase change. Each is recorded and reproduced by a completely different method, and recording / reproducing for recording only a 1-bit signal at one position on the optical recording medium.
Only the playback method was adopted. Therefore, there has been a problem that the density of the optical recording medium cannot be increased in spite of the desire to increase the density.

Further, as one of the methods for increasing the density,
Currently, there are multiple recording methods, such as PHB and holography, but it is difficult to put them into practical use, and it cannot be said that they are practical methods.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and it is possible to record / reproduce 2-bit (four-value recording) information at the same position on one medium at the same time. As a result, it is an object of the present invention to provide an optical recording medium capable of increasing the density of recorded information.

[0008]

SUMMARY OF THE INVENTION To achieve this object, an optical recording medium according to the present invention comprises a magneto-optical recording film on a substrate for recording / reproducing information based on the direction of magnetization, a crystalline state and an amorphous state. And a phase change film in which information is recorded / reproduced based on a change in optical constant due to a phase change with the state.

As described above, in the present invention, the optical recording medium is
It is composed of a magneto-optical recording film and a phase change film, and is constructed so that the information of the magneto-optical recording film and the information of the phase change film can be separately recorded / reproduced at the same position on one medium. ing. Therefore, two bits (four-valued recording) can be recorded / reproduced at the same position on one medium at the same time.
It is possible to increase the density of recorded information.

[0010]

DETAILED DESCRIPTION OF THE INVENTION An optical recording medium according to an embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, an optical recording medium 1 according to the present embodiment has a magneto-optical recording film 3 on and from which information is recorded / reproduced on a substrate 2 based on the direction of magnetization and a crystalline state. And a phase change film 4 for recording / reproducing information based on a change in optical constant due to a phase change with a crystalline state.

Further, the information of the magneto-optical recording film 3 and the information of the phase change film 4 are separately recorded and reproduced at the same position on one medium. Information is recorded on the magneto-optical recording film 3 by irradiating the medium 1 with a laser beam to raise the temperature of the irradiated portion and reversing the magnetization in the weak magnetization direction of the external magnetic field. The reproduction of the information from is performed not only based on the Kerr rotation angle (θ _k ) but also based on the Kerr ellipticity (η). Recording of information on the phase change film 4 is performed by irradiating a strong light pulse for a short time to rapidly heat and quench the recording material to a temperature higher than the melting point to fix the material while the atomic arrangement is disturbed and to make it amorphous. The reproduction of information from the change film 4 is performed not only by detecting the reflectance (R) based on the phase change but also by using the Kerr ellipticity (η). Details of these will be described later, and first, the medium 1 will be described.

Magneto-Optical Recording Film The magneto- optical recording film 3 of the type based on Kerr ellipticity or Kerr rotation angle is (i) at least one selected from the 3d transition genus, and (iii) at least selected from rare earths. 1 element, or (i) at least one element selected from 3d transition metals, (ii) a corrosion resistant metal, and (iii) at least one element selected from rare earths. Preferably.

(I) 3d transition metals include Fe and C
O, Ti, V, Cr, Mn, Ni, Cu, Zn or the like is used, and Fe or Co or both of them is preferable.

The 3d transition metal is present in the magneto-optical recording film 3 in an amount of 20 to 90 atom%, preferably 30 to 85 atom%, and more preferably 35 to 80 atom%. (Ii) The corrosion resistance metal can be included in the magneto-optical recording film 3 to enhance the oxidation resistance of the magneto-optical recording film 3. Examples of such corrosion resistant metals include Pt and P
Although d, Ti, Zr, Ta, Nb, etc. are used, Pt, Pd, and Ti are preferable, and Pt or P is particularly preferable.
d or both are preferable.

This corrosion resistant metal is contained in the magneto-optical recording film 3 at 30 atomic% or less, preferably 5 to 25 atomic%, more preferably 10 to 25 atomic%, and further preferably 10 to 20 atomic%.
It is present in the amount of atomic%.

The rare earth elements include the following elements. Gd, Tb, Dy, Ho, Er, Tm,
Yb, Lu, La, Ce, Pr, Nd, Pm, Sm, E
u Of these, Gd, Tb, Dy, Ho, Nd, Sm, Pr
Is preferably used.

At least one selected from the above group
The rare earth element of the seed is 5 to 50 atomic% in the magneto-optical recording film 3,
Preferably 8-45 atom%, more preferably 10-40
It is present in the amount of atomic%.

In the present invention, the magneto-optical recording film 3 preferably has a composition as described below. (I) 3d transition element In the magneto-optical recording film 3 according to the present invention, (i) 3d transition element preferably contains Fe or Co or both, and Fe and / or Co is 40 atomic%.
It is desirable to be present in an amount of 80 atomic% or more and 80 atomic% or less, preferably 40 atomic% or more and less than 75 atomic%, and more preferably 50 atomic% or more and 70 atomic% or less.

Further, Fe and / or Co is Co /
The (Fe + Co) ratio [atomic ratio] is 0 or more and 0.3 or less, preferably 0 or more and 0.2 or less, and more preferably 0.01 or more and 0.1 or less.
It is desirable that the magneto-optical recording film 3 be present in an amount of 2 or less.

The amount of Fe and / or Co is 40 atomic%
When the content is in the range of 80 atomic% or less, the magneto-optical recording film 3 having excellent oxidation resistance and having an easy axis of magnetization in the direction perpendicular to the film surface can be obtained.

When Co is added to the magneto-optical recording film 3, (a) the Curie point of the magneto-optical recording film 3 rises,
Further, (b) the phenomenon that the Kerr rotation angle (θk) becomes large is recognized, and as a result, the recording sensitivity of the magneto-optical recording film 3 can be adjusted by the addition amount of Co, and the addition of Co causes the reproduction. The carrier level of the signal can be increased. In the magneto-optical recording film 3 according to the present invention, the Co / (Fe + Co) ratio [atomic ratio] is 0 or more and 0.3 or less, preferably 0 or more and 0.2 or less in terms of noise level and C / N ratio.
More preferably, it is desired to be 0.01 or more and 0.2 or less.

The magneto-optical recording film 3 used in the present invention as described above.
Causes film deterioration even after repeated recording and erasing.
There is no slippage. For example, Pt in atomic% according to the invention_Ten
Tb ₂₆Fe₆₁Co₃Magneto-optical recording film 3 having the following composition
Is C even after recording and erasing 100,000 times.
No decrease in / N ratio is observed.

(Ii) Corrosion-Resistant Metal The magneto-optical recording film 3 used in the present invention preferably contains Pt or Pd or both as (ii) a corrosion-resistant metal, and Pt and / or Pd is 5 to 30 atomic% in the magneto-optical recording film 3, preferably more than 10 atomic% and 30 atomic% or less, more preferably more than 10 atomic% and less than 20 atomic%, particularly preferably 11 atomic% or more. 1
It is desirable to be present in an amount of 9 atomic% or less.

Pt and / or P in the magneto-optical recording film 3
When the amount of d is 5 atomic% or more, particularly more than 10 atomic%, the magneto-optical recording film 3 has excellent oxidation resistance, does not cause pitting corrosion even after long-term use, and deteriorates C / N ratio. It has the advantage of not doing it.

For example, the magneto-optical recording film 3 according to the present invention having a composition represented by Pt ₁₃ Tb ₂₈ Fe ₅₀ Co ₉ (atomic%) or Pd ₁₂ Tb ₂₈ Fe ₅₃ Co ₇ (atomic%) has a relative humidity of 85%. The C / N ratio does not change at all even when kept for 1000 hours in an environment of 80 ° C.

On the other hand, T containing no Pt or Pd
The magneto-optical recording film 3 having a composition represented by b ₂₅ Fe ₆₈ Co ₇ (atomic%) has a relative humidity of 85% and an ambient temperature of 80 ° C.
If it is held for 000 hours, the C / N ratio is greatly reduced.

Further, by adding Pt and / or Pd in the magneto-optical recording film 3 in an amount within the above range,
When recording or reading information on the magneto-optical recording film 3, a sufficiently high C / N ratio can be obtained with a small bias magnetic field. If a sufficiently high C / N ratio can be obtained with a small bias magnetic field, the magnet for generating the bias magnetic field can be made small and the heat generated by the magnet can be suppressed. The drive device can be simplified. Moreover, since a sufficiently large C / N ratio can be obtained with a small bias magnetic field,
It is easy to design a magnet for overwritable magnetic field modulation recording.

(Iii) Rare Earth Element (RE) In the magneto-optical recording film 3 according to the present invention, the rare earth element (R) is used.
E) is contained, and as the rare earth element, Nd,
Sm, Pr, Ce, Eu, Gd, Tb, Dy or Ho
Is used.

Among these, Nd, Pr, Gd, T
b and Dy are preferably used, and Tb is particularly preferable. Two or more rare earth elements may be used in combination, and in this case, T
It is preferable that b is contained in an amount of 50 atomic% or more of the rare earth element.

This rare earth element is RE / (R) from the viewpoint of obtaining a magneto-optical property having an easy axis of magnetization in a direction perpendicular to the film surface.
E + Fe + Co) ratio [atomic ratio] is expressed as x, 0.15 ≦ x ≦ 0.45, preferably 0.20 ≦ x ≦ 0.4
It is desirable that the magneto-optical recording film 3 be present in an amount such that

In the present invention, a small amount of various elements may be added to the magneto-optical recording film 3 to improve the Curie temperature, the compensation temperature, the coercive force Hc, the Kerr rotation angle θk, or reduce the cost. These elements can be used in a ratio of, for example, less than 10 atom% with respect to the total number of atoms constituting the recording film.

Examples of other elements that can be used in combination include the following elements. (I) 3d transition element other than Fe and Co Specifically, Sc, Ti, V, Cr, Mn, Ni, C
u and Zn are used.

Of these, Ti, Ni, Cu, Zn and the like are preferably used. (II) 4d transition element other than Pd Specifically, Y, Zr, Nb, Mo, Tc, Ru, R
h, Ag and Cd are used.

Of these, Zr and Nb are preferably used. (III) 5d transition element other than Pt Specifically, Hf, Ta, W, Re, Os, Ir, A
u and Hg are used.

Of these, Ta is preferably used. (IV) Group IIIB element Specifically, B, Al, Ga, In and Tl are used.

Of these, B, Al and Ga are preferably used. (V) Group IVB element Specifically, C, Si, Ge, Sn, and Pb are used.

Of these, Si, Ge, Sn and Pb are preferably used. (VI) Group VB element Specifically, N, P, As, Sb and Bi are used.

Of these, Sb is preferably used. (VII) VIB Group Element Specifically, S, Se, Te and Po are used.

Of these, Te is preferably used. The magneto-optical recording film 3 having the composition as described above has an easy axis of magnetization perpendicular to the film surface, and most of them are perpendicular magnetic and magneto-optically recordable amorphous thin films showing a square loop with good Kerr hysteresis. That is confirmed by wide-angle X-ray diffraction.

In the present specification, the expression of a square loop having a good Kerr hysteresis is the Kerr rotation angle (θk ₁ ) which is the Kerr rotation angle in the maximum external magnetic field and the Kerr rotation angle when the external magnetic field is zero. Car rotation angle (θk
₂ ) and the ratio θk ₂ / θk ₁ is 0.8 or more.

The magneto-optical recording film 3 has a thickness of 100-60.
0Å, preferably 100-400Å, more preferably 2
It is about 00 to 350Å. Particularly, as the magneto-optical recording film 3 suitable for the case of Kerr ellipticity, TbFe, TbCo,
TbFeCo, GdFe, GdCo, GdFeCo, G
dTbFe, GdTbCo, GdTbFeCo, NdF
e, NdCo, NdTbFe, NdTbCo, NdTb
FeCo, DyFe, DyCo, DyTbFe, DyT
A magneto-optical recording film made of bCo, DyTbFeCo, CoPt, CoPd is preferable.

Phase Change Film Any phase change film may be used as long as its optical constant changes in accordance with a change in state, such as TeO, TeGeO, TeGe.
Su, TeGeOSu, Te-Ge, TeGeSe, T
eGeSb, TeGeSeSb, InSe, InSeT
lCo, SbTe, SnTeSe, GaSeTe, Ga
A recording film such as SeTeGe, BiTe, SbSe can be used.

Next, a recording / reproducing method for the optical recording medium 1 including the magneto-optical recording film 3 and the phase change film 4 will be described. In this embodiment, a recording / reproducing system based on the following three patterns can be adopted.

The pattern is reproduced on the magneto-optical recording film 3 based on the Kerr rotation angle (θ _k ), whereas the pattern is reproduced on the phase change film 4 based on the Kerr ellipticity (η). θ _k ), while the phase change film 4 reproduces based on the reflectance (R). The magneto-optical recording film 3 reproduces based on the Kerr ellipticity (η), while the phase change film 4 reproduces. Pattern to be reproduced based on reflectance (R) Pattern of Kerr rotation angle (? _K ) -Kerr ellipticity (?) First, the pattern will be described.

In the signal detection method for an optical recording medium, as shown in FIG. 2, linearly polarized laser light emitted from a laser 11 which is, for example, a semiconductor laser is incident on a non-polarizing beam splitter 12 and a part thereof is input. After being reflected, it passes through the non-polarizing beam splitter 12 and is condensed on the optical recording medium 1 by a focusing lens (not shown). The half mirror 13 splits the reflected light reflected by the medium 1 into first and second separated lights.

In the pattern of 1, the first separated light is
While being guided to the detection optical system 20, a reproduction signal based on the Kerr ellipticity is obtained, while the second separated light is guided to the second detection optical system 30, the reproduction signal based on the Kerr rotation angle is obtained.

That is, in the first detection optical system 20,
The first separated light is transmitted from the half mirror 13 to the quarter wavelength plate (λ
/ 4 plate) 23. The quarter wave plate 23 has an azimuth θ of 40 ° + 90 ° × n ₁ ≦ θ ≦ 50 ° + 90 °
× n ₁ and they are arranged in approximately 45 ° + 90 ° × n ₁ azimuth, and the phase delay amount δ is λ / 4−0.05λ ≦
It is set to δ ≦ λ / 4 + 0.05λ. The first separated light is changed from linearly polarized light to circularly polarized light by passing through such a quarter wave plate 23.

The light converted into the circularly polarized light is then guided to the polarization beam splitter 24. The polarization beam splitter 24 has an azimuth θ of −5 ° ≦ θ ≦ 5 °, and is arranged in an approximately 0 ° azimuth. The light converted into circularly polarized light by the polarization beam splitter 24 arranged in this way is divided into a P component and an S component.

The P component and the S component are detected by the photoelectric detectors 25a and 25b, respectively, and the P component signal and the S component signal are differentially amplified by the differential amplifier 26, resulting in the Kerr ellipticity. A reproduced signal based on the detected signal is detected.

On the other hand, in the second detection optical system 30, the second separated light is guided from the half mirror 13 to the polarization beam splitter 34. This polarization beam splitter 34
Are arranged at an azimuth of approximately 45 °. The second separated light is divided into a P component and an S component by the polarization beam splitter 34 arranged in this way.

The P component and the S component are detected by the photoelectric detectors 35a and 35b, respectively, and the P component signal and the S component signal are differentially amplified by the differential amplifier 36. As a result, the Kerr rotation angle is changed. A reproduced signal based on the detected signal is detected.

As described above, the optical recording medium is a medium in which the Kerr ellipticity and the Kerr rotation angle can be changed separately, and the reproduction signal based on the Kerr ellipticity and the Kerr rotation can be obtained from the same position of one optical recording medium. Two signals, a corner-based playback signal, can be obtained simultaneously.

The magnetization direction of the magneto-optical recording film changes vertically, while the optical constants of the phase change recording film change to N ₁ and N ₂ depending on whether it is crystalline or amorphous. The magnetic Kerr effect of an optical recording medium can be classified as follows depending on the combination of the magnetization direction and the optical constant.

Utilizing the interference structure, η _k2 ≠ η _k1 , θ _k1 ≈
If the medium is designed so as to be θ _k2 , the direction of θ _k is different depending on the upper and lower sides of the magnetization, and further, it corresponds to the optical constant.
The magnitude of η _k is different. Therefore, it is possible to detect the upper and lower sides of the magnetization and the difference in the optical constants separately.

[0056]

[Table 1]

The recording of information in this case is performed by irradiating a strong light pulse for a short time to rapidly heat and quench the recording material to a temperature above the melting point to immobilize it while the atomic arrangement is disturbed and amorphize it. The principle by which the reproduction signal based on the Kerr ellipticity η can be obtained by the configuration of the first detection optical system 20 is as follows.

Linearly polarized light is made incident on the optical recording medium, and the azimuth of the polarization direction at this time is 0 °. The reflected light including the reproduction information reflected by the optical recording medium 1 is approximately

[0059]

[Equation 1]

It is expressed as The quarter-wave plate 23 arranged in an orientation of about 45 ° (η ₁ = 0)

[0061]

[Equation 2]

It is expressed as The polarization beam splitter 24 arranged in the 0 ° (η ₃ = 0) direction has a P component and an S component, respectively.

[0063]

[Equation 3]

It is expressed as Therefore, the reflected light reflected by the optical recording medium 1 passes through the ¼ wavelength plate 23, and the electric field vectors E ₁ and E ₂ of the P component and the S component which are separated by the polarization beam splitter 23 are

[0065]

[Equation 4]

It is represented as Therefore, the intensity I of the P component
₁ , the intensity I _{2 of the} S component is

[0067]

[Equation 5]

It is expressed as In this embodiment, since differential detection is performed, the differential signal S is expressed as S = I ₂ −I ₁ = 2η. Since this S formula is expressed only by η which is the Kerr ellipticity, it has been proved that the first detection optical system 20 shown in FIG.

Kerr ellipticity (η) -reflectance (R) pattern
In the signal detection method of the optical disc recording medium, as shown in FIG. 3, for example, linearly polarized laser light emitted from a laser 11 which is a semiconductor laser is converted into a non-polarization beam splitter 12.
Is incident on the optical recording medium 1 and is partially reflected on the optical recording medium 1 after passing through the non-polarizing beam splitter 12. The reflected light reflected by the medium 1 includes information based on the Kerr ellipticity (η) at the magneto-optical recording film 3 and information based on the reflectance (R) at the phase change film 4. ..

This reflected light is guided to the quarter-wave plate (λ / 4 plate) 23 through the non-polarizing beam splitter 12. This quarter wave plate 23 has an azimuth θ of 40 ° + 9.
0 ° × n ₁ ≦ θ ≦ 50 ° + 90 ° × n ₁ , almost 4
They are arranged in the 5 ° + 90 ° × n ₁ azimuth and the phase delay amount δ is λ / 4−0.05λ ≦ δ ≦ λ / 4 + 0.05.
It is set to λ. The reflected light is changed from linearly polarized light to circularly polarized light by passing through such a quarter-wave plate 23.

The light converted into the circularly polarized light is then guided to the polarization beam splitter 24. The polarization beam splitter 24 has an azimuth θ of + 90 ° × n ₂ −5.
° ≦ θ ≦ + 90 ° × n ₂ + 5 °, which is almost 90 ° × n
It is arranged in _two directions. The light converted into circularly polarized light by the polarization beam splitter 24 arranged in this way is divided into a P component and an S component. These P component and S component are detected by the photoelectric detectors 25a and 25b, respectively.

The P component signal and the S component signal are differentially amplified by the differential amplifier 26, and as a result, a reproduction signal based on the Kerr ellipticity (η) is detected. On the other hand, the P component signal and the S component signal are also supplied to the amplifier 27, whereby a reproduction signal based on the change (R) in the reflectance of the reflected light on the medium is detected.

In this pattern, the magneto-optical recording film 3
Is designed based on the Kerr ellipticity (η) by designing the film so that the Kerr ellipticity (η) changes greatly with the change of magnetization (↑ ↓), while the Kerr rotation angle (θ _k ) decreases. A reproduction signal can be obtained. The recording of information in this case is the medium 1
Irradiate with a laser beam to raise the temperature of the irradiated part,
The magnetization is reversed in the weak magnetization direction of the external magnetic field.

On the other hand, the phase change film 4 has optical constants N ₁ and N ₂
The film can be designed so that the reflectance (R) can be changed by changing the value, and a reproduction signal based on this can be obtained. Recording of information in this case is performed by irradiating a strong light pulse for a short time to rapidly heat and quench the recording material to a temperature equal to or higher than the melting point and fix the recording material while the atomic arrangement is disturbed to make it amorphous.

Kerr rotation angle (θ _k ) -reflectance (R)
In the signal detection method for a turn optical recording medium, as shown in FIG. 4, for example, linearly polarized laser light emitted from a laser 11 which is a semiconductor laser is converted into a non-polarized beam splitter 12.
After passing, the light is condensed and reflected on the optical recording medium 1 by a focusing lens (not shown). The reflected light reflected by the medium 1 includes information based on the Kerr rotation angle (θ _k ) on the magneto-optical recording film 3 and information based on the reflectance (R) on the phase change film 4. There is.

This reflected light is reflected by the unpolarized beam splitter 1
It is guided to the polarization beam splitter 24 via 2. The polarization beam splitter 24 has an azimuth θ of +40.
° + 90 ° × n ₃ ≦ θ ≦ 50 ° + 90 ° × n ₃ ,
It is arranged in an orientation of about 45 ° + 90 ° × n ₃ . With the polarization beam splitter 24 arranged in this way,
The reflected light is divided into a P component and an S component. These P component and S component are detected by the photoelectric detectors 25a and 25b, respectively.

The P component signal and the S component signal are differentially amplified by the differential amplifier 26, and as a result, a reproduction signal based on the Kerr rotation angle (θ _k ) is detected. On the other hand, the P component signal and the S component signal are also supplied to the amplifier 27, whereby a reproduction signal based on the change (R) in the reflectance of the reflected light on the medium is detected.

In this pattern, the magneto-optical recording film 3
Is designed based on the Kerr rotation angle (θ _k ) by designing the film so that the Kerr rotation angle (θ _k ) changes greatly with the change of magnetization (↑ ↓), while the Kerr ellipticity (R) decreases. The reproduced signal can be obtained. The recording of information in this case is the same as the pattern.

On the other hand, the phase change film 4 has optical constants N ₁ and N ₂
The film can be designed so that the reflectance (R) can be changed by changing the value, and a reproduction signal based on this can be obtained. The recording of information in this case is the same as the pattern.

[0080]

As described above, in the present invention, the optical recording medium comprises the magneto-optical recording film and the phase change film, and the information of the magneto-optical recording film and the information of the phase change film are provided. Are configured so that they can be separately recorded and reproduced at the same position on one medium. Therefore, two bits (four-valued recording) can be recorded / reproduced at the same position on one medium at the same time.
As a result, the density of recorded information can be increased.

[Brief description of drawings]

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

FIG. 2 is a schematic diagram of a pattern used in a detection optical system applied to the optical recording medium according to the present invention.

FIG. 3 is a schematic diagram of a pattern used in a detection optical system applied to the optical recording medium according to the present invention.

FIG. 4 is a schematic diagram of a pattern used in a detection optical system applied to the optical recording medium according to the present invention.

[Explanation of symbols]

 1 optical recording medium 2 substrate 3 magneto-optical recording film 4 phase change film

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[Procedure amendment]

[Submission date] October 1, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

Title: Optical recording medium

[Claims]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is capable of recording / reproducing 2-bit (4-level recording) information at the same position on one medium at the same time, and thus increasing the density of recorded information. Recording medium

[0002]

BACKGROUND OF THE INVENTION A magneto-optical recording medium or a phase-change type optical recording medium has been actively researched and developed in recent years as a large capacity memory capable of rewriting recorded information, and is practically used.

In a magneto-optical recording medium, the medium is irradiated with a laser beam to raise the temperature of the irradiated portion, the magnetization is reversed in the direction of the external magnetic field to record information, while the direction of the magnetic field is reversed and the laser beam is emitted again. Irradiate the beam to erase information. Further, the change of the Kerr rotation angle in which the plane of polarization of the reflected light from the medium slightly rotates depending on the direction of magnetization is detected to reproduce the information.

On the other hand, the phase change type optical recording medium utilizes the fact that the atomic arrangement reversibly changes in a special substance having a regular crystalline state and a disordered amorphous state.
Information is recorded by irradiating a strong light pulse for a short period of time to rapidly heat and quench the recording material to a temperature higher than the melting point and fix the amorphous material while the atomic arrangement is disturbed to make it amorphous. Information is erased by gradually heating and cooling above the crystallization temperature to return the atomic arrangement to the crystalline state. Information reproduction is detected as a change in the amount of reflected light by utilizing the difference in reflectance between the crystalline state and the amorphous state.

By the way, in such an optical recording medium as well, there is a demand for higher information density, and various developments are being made. However, at present, as described above, the magneto-optical recording medium adopts a recording / reproducing method suitable only for magneto-optical, and the phase change type optical recording medium adopts a recording / reproducing method suitable only for phase change. Each is recorded and reproduced by a completely different method, and recording / reproducing for recording only a 1-bit signal at one position on the optical recording medium.
Only the playback method was adopted. Therefore, there has been a problem that the density of the optical recording medium cannot be increased in spite of the desire to increase the density.

Further, as one of the methods for increasing the density,
Currently, there are multiple recording methods, such as PHB and holography, but it is difficult to put them into practical use, and it cannot be said that they are practical methods.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and it is possible to record / reproduce 2-bit (4-value recording) information at the same position on one medium at the same time. As a result, it is an object of the present invention to provide an optical recording medium capable of increasing the density of recorded information.

[0008]

SUMMARY OF THE INVENTION To achieve this object, an optical recording medium according to the present invention comprises a magneto-optical recording film on a substrate for recording / reproducing information based on the direction of magnetization, a crystalline state and an amorphous state. And a phase change film in which information is recorded / reproduced based on a change in optical constant due to a phase change with the state.

As described above, in the present invention, the optical recording medium is
It is composed of a magneto-optical recording film and a phase change film, and is constructed so that the information of the magneto-optical recording film and the information of the phase change film can be separately recorded and reproduced at the same position of one medium. ing. Therefore, two bits (four-valued recording) can be recorded / reproduced at the same position on one medium at the same time.
It is possible to increase the recording information density.

[0010]

DETAILED DESCRIPTION OF THE INVENTION An optical recording medium according to an embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, an optical recording medium 1 according to the present embodiment has a magneto-optical recording film 3 on and from which information is recorded / reproduced on a substrate 2 based on the direction of magnetization and a crystalline state. And a phase change film 4 for recording / reproducing information based on a change in optical constant due to a phase change with a crystalline state.

Further, the information of the magneto-optical recording film 3 and the information of the phase change film 4 are separately recorded and reproduced at the same position on one medium. Information is recorded on the magneto-optical recording film 3 by irradiating the medium 1 with a laser beam to raise the temperature of the irradiated portion and reversing the magnetization in the direction of the external magnetic field. The reproduction of information is performed not only based on the Kerr rotation angle (θ _k ) but also based on the Kerr ellipticity (η). Information is recorded on the phase-change film 4 by irradiating a strong light pulse for a short time to rapidly heat and quench the recording material to a temperature higher than the melting point to immobilize the recording material while the atomic arrangement is disturbed to make it amorphous. The reproduction of information from the change film 4 is performed not only by detecting the reflectance (R) based on the phase change but also by using the Kerr ellipticity (η). Details of these will be described later, and first, the medium 1 will be described.

Magneto-Optical Recording Film The magneto-optical recording film 3 used in the present invention has a special feature.
Is not limited, but, for example, at least one selected from (A) (i) 3d transition metals
Element and at least one selected from (iii) rare earths
An alloy consisting of an element of (B) (i) at least one selected from 3d transition metals
Elements, (ii) corrosion-resistant metals, and (iii) rare earths
Alloy consisting of at least one element selected from (C) (i) at least one selected from 3d transition metals
Examples of the alloy include the alloy of (1 ) and (ii) a corrosion-resistant metal, (D) Pt / Co composition modulation film, or (E) Pd / Co composition modulation film.

Examples of the 3d transition metal include Fe and C
o, Ti, V, Cr, Mn, Ni, Zn, etc. are used.
It In the alloy films of (A) and (B) above, 3d
The content of transition metal is 20 to 90 atomic%, preferably 3
It is desirable that the content of (C) is 0 to 85 atom%.
In the gold film, the content of 3d transition metal is 10 to 60 original
It is desirable to be child%.

As the rare earth element, for example, Gd,
Tb, Dy, Ho, Er, Tm, Nd, Sm, Pr, etc.
Used. Odors in the alloy films of (A) and (B) above
The content of the rare earth element is 5 to 50 atomic%, preferably
Is preferably 8 to 45 atomic%.

Examples of corrosion-resistant metals include Pt and P
d, Ti, Zr, Ta, Nd, etc. are used. the above
In the alloy film of (B), the content of corrosion resistant metal is 3
0 atomic% or less, preferably 5 to 25 atomic%
desirable. In addition, in the alloy film of (C) above, corrosion resistance
The content of the functional metal is preferably 90 to 40 atomic%.
Yes.

In particular, a magneto-optical recording suitable for the case of Kerr ellipticity
As the recording film, TbFe, TbFeCo, GdFe, G
dFeCo, GdTbFe, GdTbFeCo, NdT
bFe, NbTbFeCo, CoPt, CoPt, Co
Pd, DyTbFe, DyTbFeCo, TbCo, G
It consists of dCo, GdTbCo, DyTbCo, NdFe
A magneto-optical recording film is preferable.

The thickness of this magneto-optical recording film is preferably 50.
~ 600 angstroms, more preferably 50-40
0 angstrom, more preferably 50-350 on
It is about Gstrom.

Phase Change Film The phase change film may be any one whose optical constant changes in accordance with a change in state, such as TeO, TeGeO, TeGe.
S n, TeGeOS n, TeGe, TeGeSe, Te
GeSb, TeGeSeSb, InSe, InSeTl
Co, SbTe, SnTeSe, GaSeTe, GaS
A recording film of eTeGe, BiTe, SbSe, or the like can be used.

Next, a recording / reproducing method for the optical recording medium 1 including the magneto-optical recording film 3 and the phase change film 4 will be described. In this embodiment, a recording / reproducing system based on the following three patterns can be adopted.

In the magneto-optical recording film 3, reproduction is performed based on the Kerr rotation angle (θ _k ), whereas in the phase change film 4, reproduction is performed based on the Kerr ellipticity (η). θ _k ), while the phase change film 4 reproduces based on the reflectance (R). The magneto-optical recording film 3 reproduces based on the Kerr ellipticity (η), while the phase change film 4 reproduces. Pattern to be reproduced based on reflectance (R) Pattern of Kerr rotation angle (? _K ) -Kerr ellipticity (?) First, the pattern will be described.

In the signal detection method for an optical recording medium, as shown in FIG. 2, for example, linearly polarized laser light emitted from a laser 11 which is a semiconductor laser is incident on a beam splitter 12 and a part thereof is reflected. After passing through the beam splitter 12, it is focused on the optical recording medium 1 by a focusing lens (not shown). The reflected light reflected by the medium 1 is reflected by the half mirror 13 into the first and second light beams.
Disperse into separated light.

In the pattern of,
While being guided to the detection optical system 20, a reproduction signal based on the Kerr ellipticity is obtained, while the second separated light is guided to the second detection optical system 30, the reproduction signal based on the Kerr rotation angle is obtained.

That is, in the first detection optical system 20,
The first separated light is transmitted from the half mirror 13 to the quarter wavelength plate (λ
/ 4 plate) 23. The quarter wave plate 23 has an azimuth θ of 40 ° + 90 ° × n ₁ ≦ θ ≦ 50 ° + 90 °
× a n _1, is arranged substantially 45 ° + 90 ° × n ₁ orientation, is the phase delay δ, λ / 4-0.05λ ≦
It is set to δ ≦ λ / 4 + 0.05λ. The first separated light is changed from linearly polarized light to circularly polarized light by passing through such a quarter wave plate 23.

The light converted into the circularly polarized light is then guided to the polarization beam splitter 24. The polarization beam splitter 24 has an azimuth θ of −5 ° ≦ θ ≦ 5 °, and is arranged in an approximately 0 ° azimuth. The light converted into circularly polarized light by the polarization beam splitter 24 arranged in this way is divided into a P component and an S component.

The P component and the S component are detected by the photoelectric detectors 25a and 25b, respectively, and the P component signal and the S component signal are differentially amplified by the differential amplifier 26. As a result, the Kerr ellipticity is reduced. A reproduced signal based on the detected signal is detected. Furthermore
Between the λ / 4 plate 23 and the polarization beam splitter 24
By inserting a λ / 2 plate into it and determining the azimuth angle appropriately.
The P component and S component generated in optical elements and magneto-optical recording media
The phase difference with the minute can be canceled and the S / N ratio of the reproduced signal can be adjusted.
It is also possible to improve further.

On the other hand, in the second detection optical system 30, the second separated light is guided from the half mirror 13 to the polarization beam splitter 34. This polarization beam splitter 34
Are arranged at an azimuth of approximately 45 °. The second separated light is divided into a P component and an S component by the polarization beam splitter 34 arranged in this way.

The P component and the S component are detected by the photoelectric detectors 35a and 35b, respectively, and the P component signal and the S component signal are differentially amplified by the differential amplifier 36. As a result, the Kerr rotation angle is changed. A reproduced signal based on the detected signal is detected. Also
Half mirror and polarized beam splitter with azimuth angle of almost 45 °
Insert a λ / 2 plate with an azimuth angle of about π / 8 between
It is also possible.

As described above, the optical recording medium is a medium in which the Kerr ellipticity and the Kerr rotation angle can be changed separately, and the reproduction signal based on the Kerr ellipticity and the Kerr rotation can be obtained from the same position of one optical recording medium. Two signals, a corner-based playback signal, can be obtained simultaneously.

The magnetization direction of the magneto-optical recording film changes vertically, while the optical constants of the phase change recording film change to N ₁ and N ₂ depending on whether it is crystalline or amorphous. The magnetic Kerr effect of an optical recording medium can be classified as follows depending on the combination of the magnetization direction and the optical constant.

Utilizing the interference structure, η _k2 ≠ η _k1 , θ _k1 ≈
If the medium is designed so as to be θ _k2 , the direction of θ _k is different depending on the upper and lower sides of the magnetization, and further, it corresponds to the optical constant.
The magnitude of η _k is different. Therefore, it is possible to detect the upper and lower sides of the magnetization and the difference in the optical constants separately.

[0032]

[Table 1]

Information recording in this case is performed by irradiating a strong light pulse for a short period of time to rapidly heat and quench the recording material to a temperature higher than the melting point and fix the recording material with the atomic arrangement disturbed to make it amorphous.

Kerr ellipticity (η _k ) and Kerr rotation angle
(Θ _k ) is the substrate, magneto-optical recording film, phase change film and
And optical constants of the enhanced film (refractive index n and extinction coefficient k)
And calculated from the media configuration, etc. Therefore,
By selecting and setting these parameters appropriately
Therefore, the design of the medium such that η _k2 ≠ η _k1 , θ _k1 ≈ θ _k2
It is possible.

Consider, for example, the following optical recording medium.
It

[0036]

[Table 2]

The disk structure is the substrate / SiN film (100
0Å) / magneto-optical recording film (65Å) / SiN film (280
Å) / Laser light used as a phase change film (1000 Å)
Is 830 nm, θ _k and η _k are
Desired.

[0038]

[Table 3]

Note that, due to the configuration of the first detection optical system 20,
The principle by which a reproduction signal based on the Kerr ellipticity η can be obtained is as follows.

Direction of polarization of linearly polarized light incident on an optical recording medium
The direction is defined as an azimuth of 0 °. Of the electric field vector of the incident light
Jones vector

[0041]

[Equation 1]

Then, the reproduction information reflected by the optical recording medium is
The Jones vector of the reflected light including the information is approximately

[0043]

[Equation 2 ]

It is expressed as follows. Jones matrix of quarter-wave plate 23 arranged at an angle of approximately 45 ° (η ₁ = 0)
Su

[0045]

[Equation 3 ]

It is represented by Jones matrix of the polarization beam splitter 24 arranged in the 0 ° (η ₃ = 0) direction
Box is, P component, for each S component,

[0047]

[Equation 4]

Is represented by Therefore, the reflected light reflected by the optical recording medium 1 passes through the ¼ wavelength plate 23, and the electric field vectors E ₁ and E ₂ of the P component and the S component which are separated by the polarization beam splitter 23 are

[0049]

[Equation 5]

It is expressed as follows. Therefore, the intensity I of the P component
₁ , the intensity I _{2 of the} S component is

[0051]

[Equation 6]

It is expressed as In this embodiment, since differential detection is performed, the differential signal S is expressed as S = I ₂ −I ₁ = 2η _k . This differential signal S has a Kerr ellipticity η _k
It is proved that the reproduction signal is obtained by utilizing the Kerr ellipticity by the first detection optical system 20 shown in FIG.

Kerr ellipticity (η) -reflectance (R) pattern
In the signal detection method of the optical disc recording medium, as shown in FIG. 3, for example, linearly polarized laser light emitted from a laser 11 which is a semiconductor laser is incident on a beam splitter 12 and a part thereof is reflected. After passing through the beam splitter 12, the light is condensed on the optical recording medium 1 by a focusing lens (not shown) and reflected. The reflected light reflected by the medium 1 includes information based on the Kerr ellipticity (η) at the magneto-optical recording film 3 and information based on the reflectance (R) at the phase change film 4. ..

This reflected light is guided to the quarter-wave plate (λ / 4 plate) 23 via the beam splitter 12. The quarter wave plate 23 has an azimuth θ of 40 ° + 90 ° × n.
₁ ≤ θ ≤ 50 ° + 90 ° x n ₁ , almost 45 ° + 9
They are arranged in the 0 ° × n ₁ azimuth and the phase delay amount δ
Is set to λ / 4−0.05λ ≦ δ ≦ λ / 4 + 0.05λ. The reflected light is generated by such a quarter wavelength plate 23.
Is changed from linearly polarized light to circularly polarized light.

The light converted into the circularly polarized light is then guided to the polarization beam splitter 24. The polarization beam splitter 24 has an azimuth θ of + 90 ° × n ₂ −5.
° ≦ θ ≦ + 90 ° × n ₂ + 5 °, which is almost 90 ° × n
It is arranged in _two directions. The light converted into circularly polarized light by the polarization beam splitter 24 arranged in this way is divided into a P component and an S component. These P component and S component are detected by the photoelectric detectors 25a and 25b, respectively.

The P component signal and the S component signal are differentially amplified by the differential amplifier 26, and as a result, a reproduction signal based on the Kerr ellipticity (η) is detected. On the other hand, the P component signal and the S component signal are also supplied to the amplifier 27, whereby a reproduction signal based on the change (R) in the reflectance of the reflected light on the medium is detected.

In this pattern, the magneto-optical recording film 3
Is designed based on the Kerr ellipticity (η) by designing the film so that the Kerr ellipticity (η) changes greatly with the change of magnetization (↑ ↓), while the Kerr rotation angle (θ _k ) decreases. A reproduction signal can be obtained. The recording of information in this case is the medium 1
Irradiate with a laser beam to raise the temperature of the irradiated part,
The magnetization is reversed in the direction of the external magnetic field.

On the other hand, the phase change film 4 has optical constants N ₁ and N ₂
The film can be designed so that the reflectance (R) can be changed by changing the value, and a reproduction signal based on this can be obtained. Recording of information in this case is performed by irradiating a strong light pulse for a short time to rapidly heat and quench the recording material to a temperature equal to or higher than the melting point and fix the recording material while the atomic arrangement is disturbed to make it amorphous.

Kerr rotation angle (θ _k ) -reflectance (R)
In the signal detection method for the turn optical recording medium, as shown in FIG. 4, for example, linearly polarized laser light emitted from a laser 11 which is a semiconductor laser passes through a beam splitter 12 and is optically recorded by a focusing lens (not shown). It is condensed on the medium 1 and reflected. The reflected light reflected by the medium 1 includes information based on the Kerr rotation angle (θ _k ) on the magneto-optical recording film 3 and information based on the reflectance (R) on the phase change film 4. There is.

This reflected light is guided to the polarization beam splitter 24 via the beam splitter 12. The polarization beam splitter 24 has an azimuth θ of + 40 ° + 9.
0 ° × n ₃ ≦ θ ≦ 50 ° + 90 ° × n ₃ , almost 4
It is arranged in the direction of 5 ° + 90 ° × n ₃ . By the polarization beam splitter 24 arranged in this way, the reflected light is divided into a P component and an S component. These P component and S component are detected by the photoelectric detectors 25a and 25b, respectively.

The P component signal and the S component signal are differentially amplified by the differential amplifier 26, and as a result, a reproduction signal based on the Kerr rotation angle (θ _k ) is detected. On the other hand, the P component signal and the S component signal are also supplied to the amplifier 27, whereby a reproduction signal based on the change (R) in the reflectance of the reflected light on the medium is detected.

In this pattern, the magneto-optical recording film 3
Is designed based on the Kerr rotation angle (θ _k ) by designing the film so that the Kerr rotation angle (θ _k ) changes greatly with the change of magnetization (↑ ↓), while the Kerr ellipticity (R) decreases. The reproduced signal can be obtained. The recording of information in this case is the same as the pattern.

On the other hand, the phase change film 4 has optical constants N ₁ and N ₂
The film can be designed so that the reflectance (R) can be changed by changing the value, and a reproduction signal based on this can be obtained. The recording of information in this case is the same as the pattern.

[0064]

As described above, in the present invention, the optical recording medium comprises the magneto-optical recording film and the phase change film, and the information of the magneto-optical recording film and the information of the phase change film are provided. Are configured so that they can be separately recorded and reproduced at the same position on one medium. Therefore, two bits (four-valued recording) can be recorded / reproduced at the same position on one medium at the same time.
As a result, the density of recorded information can be increased.

[Brief description of drawings]

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

FIG. 2 is a schematic diagram of a pattern used in a detection optical system applied to the optical recording medium according to the present invention.

FIG. 3 is a schematic diagram of a pattern used in a detection optical system applied to the optical recording medium according to the present invention.

FIG. 4 is a schematic diagram of a pattern used in a detection optical system applied to the optical recording medium according to the present invention.

[Explanation of symbols] 1 optical recording medium 2 substrate 3 magneto-optical recording film 4 phase change film ─────────────────────────────── ───────────────────────

[Procedure amendment]

[Submission date] October 5, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0019

[Correction method] Change

[Correction content]

Phase Change Film The phase change film may be any one whose optical constant changes in accordance with a change in state, such as TeO, TeGeO, TeGe.
Sn, TeGeOSn, TeGe, TeGeSe, Te
GeSb, TeGeSeSb, InSe, InSeTl
Co, SbTe, SnTeSe, GaSeTe, GaS
A recording film of eTeGe, BiTe, SbSe, or the like can be used. The thickness of this phase change film is preferably 50-
2000 angstrom, more preferably 50 to 10
It is 00 angstrom.

Claims (1)

Claim: What is claimed is: 1. A magneto-optical recording film in which information is recorded / reproduced based on the direction of magnetization on a substrate, and a change in optical constant due to a phase change between a crystalline state and an amorphous state. An optical recording medium comprising at least a phase change film for recording / reproducing information based on the above.