JPH0589521A - Optical recording medium - Google Patents

Abstract

PURPOSE:To obtain the optical recording medium which is large in Kerr effect enhancement, exhibits excellent C/N, prevents the degradation in a push-pull signal for tracking, obviates an increase in crosstalks in spite of narrowing a track pitch and has high productivity. CONSTITUTION:A 1st dielectric layer 14, a guide layer 16, a 2nd dielectric layer 18, and a recording layer 20 are laminated on a transparent substrate 12. This medium has a guide film for tracking, an interference layer and the recording layer and a part of the guide layer is removed. The refractive indices of the 1st and 2nd dielectric layers 14, 18 are higher than the refractive index of the substrate 12. The phase change generated in the light passing back and forth therein is made into about pi or the value obtd. by adding integer times of about 2pi thereto. The phase difference between the reflected light from the part where the guide layer 16 is removed and the reflected light form the part where the guide layer 16 is not removed is simultaneously prevented from attaining about pi or the value obtd. by adding integer times of about 2pi thereto.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium used in an optical disk memory for recording / reproducing information with a laser beam.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 7, an optical recording medium 70 is made of SiAlO on a transparent substrate 72 such as polycarbonate provided with a tracking guide groove 71 by injection molding.
Interference layer 74 of N, AlN, etc., GdTbFe, TbFeC
A magneto-optical recording layer 76 such as o, a protective layer 78 such as SiAlON and AlN, and a reflective layer 80 such as Al are sequentially laminated.
In such a magneto-optical recording medium 70, information is recorded by irradiating the magneto-optical recording layer 76 with a laser beam, heating it to a Curie temperature or a compensation temperature or higher, and at the same time applying a magnetic field from the outside to reverse the magnetization. It is carried out by The reproduction is performed by utilizing the Kerr effect that the rotation of the polarization plane of the reflected light is reversed depending on the direction of magnetization when the magneto-optical recording layer 76 is irradiated with the linearly polarized laser light. Further, in order to increase the apparent rotation angle and improve C / N by Kerr effect enhancement, multiple layers in the interference layer 74 and the protective layer 78 sandwiched between the substrate 72, the magneto-optical recording layer 76 and the reflective layer 80. The interference effect of reflection is used.

[0003]

However, in the conventional magneto-optical disk, the interference layer 74, the magneto-optical recording layer 76,
In order to increase the car enhancement due to the interference effect in the protective layer 78 and the reflective layer 80, the film thickness of the interference layer 74 is set to about λ / 4n ₂ when the refractive index of the interference layer 74 is set to n _2, and the magneto-optical recording is performed. Since the film thickness of the layer 76 is also set to have a minimum reflectance, the reflectance in the groove 71 required for tracking is also extremely small. As a result, the tracking servo becomes unstable, and a stable reproduction output cannot be obtained. Further, when the track pitch is narrowed, there is a problem that crosstalk increases and molding defects due to the narrowing of the groove 71 increase, which lowers the production efficiency.

The present invention has been made to solve the above-mentioned problems, and its purpose is to provide a first dielectric layer, a guide layer, and a second dielectric layer on a transparent substrate. Layer and a recording layer are laminated, a part of the guide layer is removed, and the refractive index of the dielectric layer is made higher than that of the substrate, so that Kerr effect enhancement is large and excellent C / N is exhibited. In addition to providing a high-quality optical recording medium that prevents the reduction of push-pull signals required for tracking and has stable tracking characteristics, crosstalk does not increase even if the track pitch is narrowed, and productivity is improved. It is to provide a high optical recording medium.

[0005]

In order to achieve this object, in an optical recording medium of the present invention, a first dielectric layer, a guide layer and a second dielectric layer laminated on a transparent substrate. And a recording layer, and a part of the guide layer is continuously or discontinuously removed along a spiral shape, a concentric shape, a linear shape, or the like.
The sum of the width of the removed portion and the width of the portions not removed on both sides thereof is equal to or wider than the laser spot diameter on the recording layer. The refractive index of the first and second dielectric layers is higher than that of the substrate, and the phase change generated in the light traveling back and forth through the first and second dielectric layers is approximately π.
Alternatively, the film thicknesses of the first and second dielectric layers are determined so as to have a value obtained by adding an integer multiple of approximately 2π. Furthermore, the phase difference between the reflected light from the part where the guide layer is removed and the reflected light from the part where the guide layer is not removed is not approximately π or a value obtained by adding an integer multiple of approximately π, Desirably, the film thickness of each layer is determined to be a value of about π / 2 or a value obtained by adding an integer multiple of about π.

Further, the phase change generated in the light traveling back and forth through the first and second dielectric layers is approximately π or a value obtained by adding an integer multiple of approximately 2π to the refractive index of the second dielectric layer. n ₂ and the wavelength of light in vacuum is λ and m is an integer, the film thickness of the second dielectric layer is approximately [(λ / (4n ₂ ) ± λ / (12n ₂ )] + mλ / The film thicknesses of the first and second dielectric layers may be determined so as to be 4.

Furthermore, the difference between the phase change generated in the light traveling back and forth only in the first dielectric layer and the phase change generated in the light traveling back and forth in the first and second dielectric layers is approximately π / 2 or approximately that. It is a value obtained by adding an integer multiple of π, and the phase change generated in the light traveling back and forth through the first and second dielectric layers is approximately π or a value obtained by adding an integer multiple of approximately 2π The film thicknesses of the first and second dielectric layers may be set.

[0008]

In the optical recording medium having the above structure, the first and second dielectric layers, the recording layer and the guide layer can be produced by well-known thin film forming means and photolithography, and injection molding can be performed. Since it is not necessary to use it, it can be easily manufactured even if the track pitch is narrowed.
Even if the track pitch is narrowed, the width of the removed portion of the guide layer, that is, the width of the recording area and the width of the portions not removed on both sides thereof is equal to the laser spot diameter on the recording layer. Since it is wider than that, the irradiated laser light does not reach the adjacent recording area, and the crosstalk does not increase.

Since the first and second dielectric layers have a higher refractive index than the substrate, the reproduction light is reproduced in the first and second dielectric layers between the substrate and the recording layer in the removed portion of the guide layer. Multiple reflections of. Here, the film thicknesses of the first and second dielectric layers of the optical recording medium of the present invention are the same as those of the first and second dielectric layers.
Since the amount of phase change that occurs in the reproduction light that travels back and forth through the dielectric layer is π, the Kerr effect enhancement due to multiple reflection increases and C / N improves. Further, in the structure of the present invention, the push-pull signal for tracking is the reflected light from the removed portion of the guide layer,
The phase difference of the reflected light from the part of the guide layer where the guide layer is not removed becomes maximum when the phase difference is approximately π / 2. At this time, the reflectance of the portion of the guide layer that has not been removed does not decrease as much as the reflectance of the recording area, so that the tracking signal can be prevented from decreasing and stable tracking servo can be performed.

When the guide layer is relatively thick, the phase change caused by the light reflected by the guide layer and reciprocating only through the first dielectric layer and the phase change caused by the recording layer are reflected by the first and second dielectric layers. The film thicknesses of the first and second dielectric layers are set so that the difference in the phase change caused by the light traveling back and forth through the layers becomes approximately π / 2 or a value obtained by adding an integer multiple of approximately π. Good. Furthermore, by making the refractive indices of the first and second dielectric layers equal, unnecessary reflection at the boundary between the first and second dielectric layers does not occur, so that C / N and tracking characteristics are improved.

Further, the phase change generated in the light traveling back and forth through the first and second dielectric layers becomes about π or a value obtained by adding an integer multiple of about 2π, and the refractive index of the second dielectric layer is changed. n ₂ and the wavelength of light in vacuum is λ and m is an integer, the film thickness of the second dielectric layer is approximately [(λ / (4n ₂ ) ± λ / (12n ₂ )] + mλ / By setting the film thicknesses of the first and second dielectric layers so as to be 4, the push-pull signal becomes slightly smaller,
Since the preformatted signal strength from the portion where the guide layer is discontinuously removed with a predetermined signal pattern becomes large, it can also be used as a preformatted disc.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of an essential part of an optical recording medium 10 according to an embodiment of the present invention.
A first dielectric layer 14, a guide layer 16, a second dielectric layer 18, a recording layer 20, a protective layer 2 are formed on a transparent substrate 12 such as glass.
It is configured by sequentially stacking two.

The guide layer 16 is made of a metal such as Al or Ta, and is continuously or discontinuously formed in a spiral shape, a concentric circle shape, or a linear shape as shown in FIG. It has been removed. The portion continuously removed by a certain length is used for recording information and becomes a recording area 30. Further, the discontinuously removed portion constitutes the pit 32 as it is. Therefore, a signal such as a sector mark can be recorded in advance by the pit 32, and pre-formatting can be performed.

The first and second dielectric layers 14, 18 are
Higher refractive index than the substrate 12, eg SiO, SiAl
It is composed of ON, TiO ₂ , ZnS, ZnO, SiN, AlN and the like. At this time, the first and second dielectric layers 14, 1
By configuring 8 with the same material, unnecessary reflection does not occur at the boundary between the first and second dielectric layers 14 and 18 in the recording region 30 that is the removed portion of the guide layer 16.

For the recording layer 20, for example, a magneto-optical material which is an amorphous alloy containing a rare earth and a transition metal as main components, that is, TbFeCo (terbium iron cobalt alloy) is used. The protective layer 22 is for protecting the recording layer 20 from chemical changes and is made of SiAlON, AlN, or the like.

The light incident from the substrate 12 is mainly the guide layer 1.
6 and the recording layer 20. Therefore, tracking can be performed by the well-known push-pull method using the diffraction effect generated by the guide layer 16 and the recording layer 20.

Further, as shown in FIG. 3, since a part of the incident light 40 is blocked by the guide layer 16, the width of the pit or magnetic domain recorded in the recording layer 20 is the recording area 30 where the guide layer 16 is removed. Limited to the width of. Therefore, the recording area 30
Width w, track pitch P, recording layer 2 of irradiation light 40
Assuming that the spot diameter on 0 is d, the total width W of the recording region 30 and the portions of the guide layer 16 on both sides thereof which have not been removed is W = P + (P−w) = 2P−w (1) .. Therefore, if W is larger than the spot diameter d,
Since the irradiation light 40 does not reach the adjacent recording area, the crosstalk does not increase. That is, by setting d = 2P-w (2), the track pitch can be made smaller than the spot diameter without increasing crosstalk, and the density can be increased by narrowing the track pitch.

The optical recording medium of the present invention is produced by a well-known thin film forming means and photolithography. That is, the transparent dielectric layer 14 such as SiAlON is formed on the substrate 12 by a predetermined thickness, for example, by sputtering. A metal film of Al, Ta or the like is formed thereon by means such as vacuum deposition or sputtering, and a photoresist is applied thereon by a spin coating method or the like. next,
The photoresist is continuously or discontinuously removed in a spiral shape or a concentric shape by a laser exposure method or the like. In the case of removing it discontinuously, the laser may be modulated with a signal such as a sector mark at the time of exposure and the photoresist may be irradiated.
Further, the portion of the metal film from which the photoresist has been removed is etched by etching using an acid or alkali solution or by plasma etching. After that, the guide layer 16 is formed by removing the resist with an organic solvent or the like. Further, the second dielectric layer 18, the recording layer 20, and the protective layer 22 are laminated thereon by a well-known thin film forming means such as sputtering, whereby the optical recording medium 10 is produced.

As described above, the optical recording medium 10 of the present invention is
Since the guide groove is not required in the substrate, defective molding of the groove portion due to injection molding does not occur, and an optical recording medium having a narrow track pitch can be easily manufactured.

When the recording layer 20 is irradiated with the laser light through the substrate 12 of the optical recording medium 10, the Kerr rotation angle of the reflected light changes in relation to the local magnetization direction in the recording layer 20 due to the magneto-optical effect. The information is read based on the Kerr rotation angle of the reflected light. Also,
When writing information, the recording layer 20 is locally heated to the Curie point or the compensation temperature by irradiation with laser light,
Information corresponding to the magnetization direction is recorded by controlling the direction of the external magnetic field in a desired direction during cooling of this local portion.

In the optical recording medium 10 having the above structure,
The first and second dielectric layers 14 and 18 are translucent materials having a high refractive index, and multiple reflection occurs between the substrate 12 and the recording layer 20 in the recording area 30. Here, the amount of phase change generated in the light traveling back and forth through the first and second dielectric layers 14 and 18 is A, the film thicknesses of the first and second dielectric layers are d ₁ and d ₂ , respectively, and the refractive index is Assuming n ₁ and n ₂ respectively, (3)
The formula holds.

A = 2 (2π / λ) (n ₁ d ₁ + n ₂ d ₂ ) (3) Further, the same material is used for the first and second dielectric layers 14 and 18, and the refractive index thereof is n _I Then equation (3) becomes (4)
It is expressed as an expression.

A = 2n _I (2π / λ) (d ₁ + d ₂ ) (4) Here, as is well known, when A = π + 2mπ (m is an integer) (5), the Kerr effect in the recording layer is obtained. The enhancement is maximized and the apparent car rotation angle is increased, so the C / N is improved. At this time, from equations (4) and (5), d ₁ + d ₂ = λ / (4n _I ) + mλ / (2n _I ) (6) That is, the first and second dielectric layers 14, 1
The sum of the film thicknesses of 8 is the first and second dielectric layers 1 of the reproduction light.
In the optical recording medium of the present invention, which is set to about 1/4 of the wavelength in 4, 18 or an integer multiple of half wavelength, the Kerr effect enhancement in the recording layer 20 increases and C / N is improved.

In the structure of the present invention, the push-pull signal for tracking is reflected by the guide layer 16 and is reflected by the recording layer 20 as well as the phase change that occurs in the light that travels back and forth only in the first dielectric layer 14. First and second
When the difference in the phase change generated in the light that travels back and forth through the dielectric layers 14 and 18 is about π / 2 or a value obtained by adding an integer multiple of about π, it becomes maximum, and becomes zero when π + mπ.
Letting B be the amount of phase change that occurs in light that travels back and forth only in the first dielectric layer 14, B is expressed by B = 2n _I (π / λ) d ₁ (7), and the phase difference is AB Becomes Here, when the equation (5) that maximizes the Kerr effect enhancement is satisfied, and AB = π / 2 + lπ (l is an integer) (8) that maximizes the push-pull signal, the first and second conditions are satisfied. Dielectric layers 14, 18
Film thicknesses d ₁ and d ₂ of d ₁ = λ / (8n _I ) + l λ / (4n _I ) (9) d ₂ = λ / (8n _I ) + (2m−l) λ / (4n _I ) (10 ) Becomes. At this time, the reflectance in the recording area 30 is almost minimum, but the reflectance of the portion of the guide layer 16 which is not removed is not the minimum, and the push-pull signal is reduced as compared with the conventional grooved disc. Can be prevented.

When the push-pull signal becomes zero and recording / reproducing cannot be performed on the optical recording medium, that is, AB = π + lπ (11), d ₂ = λ / (4n _I irrespective of d _1. ) + Lλ / (4n _I ) (12). Therefore, in the optical recording medium of the present invention, a push-pull signal is obtained and recording / reproduction is possible unless the thickness of the second dielectric layer 18 satisfies the condition (12). Then, by appropriately selecting the film thickness of the first dielectric layer, the C / N can be improved by the Kerr effect enhancement.

For example, when reproducing the pit 32 formed by discontinuously removing a part of the guide layer 16, the film thickness of the second dielectric layer when the reproduction signal becomes maximum is (12 However, since the push-pull signal necessary for tracking cannot be obtained, the film thickness is shifted from the equation (12), and d ₂ = [(λ / (4n _I ) + λ / (12n _I )] + lλ / ( 4n _I ) (13) or d ₂ = [(λ / (4n _I ) −λ / (12n _I )] + lλ / (4n _I ) (13 ′) so that the thickness of the second dielectric layer is May be defined.
At this time, when the film thickness of the first dielectric layer 14 is determined so as to satisfy the equation (5) so that the Kerr effect enhancement becomes maximum, d ₁ = (2m−1) λ / (4n _I ) −λ / become (12n _I) (14) or _{d 1 = (2m-l)} λ / (4n I) + λ / (12n I) (14 '). In this case, since the push-pull signal and the signal from the pit are obtained with sufficient strength, it is possible to satisfactorily record / reproduce on / from the pregroove disc.

While one embodiment of the present invention has been described in detail above with reference to FIGS. 1 and 3, the present invention can be implemented in other modes.

That is, the film thicknesses of the recording layer 20 and the guide layer 16 are not particularly limited. For example, as shown in FIG. 4, the recording layer 20 is thinned, and Al and A are formed on the protective layer 22.
You may provide the reflective layer 24 which consists of u, Cu, etc. That is,
Light incident from the substrate 12 side passes through the magnetic thin film,
It is reflected by the reflective layer and again passes through the magnetic thin film. As a result, not only the Kerr effect but also the Faraday effect is added, so that even greater Kerr effect enhancement occurs. Also in this case, the reflectance of the guide layer 16 is prevented from lowering, and stable tracking characteristics can be obtained. When the guide layer 16 is thin, the irregularities generated in the recording layer 20 are also small, and the effect of suppressing deterioration from the stepped portion of the recording layer 20 is large. At this time, part of the light incident from the side of the substrate 12 is guided by the guide layer 16
Through the second dielectric layer 18 and is reflected by the recording layer 20. At this time, interference due to multiple reflection also occurs between the recording layer 20 and the guide layer 16, and the phase change generated in the light emitted to the substrate 12 side becomes complicated.

As described above, when the guide layer 16 and the recording layer 20 are thin, there is a phase change between the reflected light from the removed portion of the guide layer 16 and the reflected light from the unremoved portion of the guide layer 16. Although complicated, if the difference is approximately π / 2 or a value obtained by adding an integer multiple of approximately π, an optimum push-pull signal can be obtained. Note that the phase difference may deviate from this value as long as tracking is possible, and the film thickness of each layer is adjusted so that it does not become a value obtained by adding approximately π which is a phase difference at which the push-pull signal becomes zero and an integer multiple thereof. It only needs to be set.

The material of each layer is not particularly limited, and an acrylic resin, a polycarbonate resin, an amorphous polyolefin resin or the like may be used as the substrate material instead of glass.

Further, the recording layer 20 is not only a magneto-optical material, but also a perforated type such as Te, Bi, GeSbTe, TeO.
A phase change material such as _x , an organic material such as a pigment, or the like can be used. Even when a material other than the magneto-optical material is used, the phase change that occurs in the light traveling back and forth through the first and second dielectric layers 14 and 18 is approximately π or a value obtained by adding an integer multiple of approximately 2π. If the film thickness is determined, the recording sensitivity will be improved.

The removal pattern of the guide layer is not particularly limited, and the guide layer may be continuously removed in a spiral shape or a concentric shape. At this time, the preformatted signal may be recorded in the recording layer.

Further, the first and second dielectric layers 14, 1
The materials of 8 are not particularly limited, and they do not have to be the same, and may be composed of different materials. For example, as shown in FIG. 5, SiAlON or the like is used for the first dielectric layer 14, and
The dielectric layer 50 is made of TiO ₂ , PLZT or the like prepared by spin coating and heat treatment, and the recording layer 2
0 may be made substantially flat. Further, as shown in FIG. 6, Ti prepared by spin coating as the second dielectric layer 14 is used.
A flattening layer 50 such as O ₂ or PLZT and a dielectric film 52 made of SiAlON or the like formed thereon by sputtering or the like.
May be provided. That is, each of the first and second dielectric layers 14 and 18 does not have to be made of a single material, and may be made of a multilayer film using a plurality of materials.

Further, the tracking method is not limited to the push-pull method, and the three-beam method can be similarly favorably performed.

[0036]

As is apparent from the above description, in the optical recording medium of the present invention, a part of the irradiation light is blocked by the guide layer and does not reach the adjacent recording area. Does not increase crosstalk, and since injection molding is not used for manufacturing, productivity is increased. In addition, the first and second dielectric layers are formed of a translucent material having a higher refractive index than the substrate, and C / N is improved by increasing the apparent Kerr rotation angle of the recording layer due to Kerr effect enhancement. At the same time, the push-pull signal required for tracking can be prevented from lowering and stable tracking characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of essential parts of an optical recording medium that is an embodiment of the present invention.

FIG. 2 is a plan view of an essential part of the optical recording medium, which is an embodiment of the present invention, viewed from the substrate side.

FIG. 3 is a cross-sectional view of essential parts of an optical recording medium that is an embodiment of the present invention.

FIG. 4 is a cross-sectional view of essential parts of an optical recording medium that is another embodiment of the present invention.

FIG. 5 is a cross-sectional view of essential parts of an optical recording medium that is another embodiment of the present invention.

FIG. 6 is a cross-sectional view of an essential part of an optical recording medium that is another embodiment of the present invention.

FIG. 7 is a cross-sectional view of essential parts showing an example of a conventional magneto-optical recording medium.

[Explanation of symbols]

 10 Optical Recording Medium 12 Glass Substrate 14 First Dielectric Layer 16 Guide Layer 18 Second Dielectric Layer 20 Recording Layer 30 Recording Area (Removed Area of Guide Layer) 32 Pits (Removed Area of Guide Layer)

Claims (9)

[Claims] 1. A transparent substrate, a first dielectric layer laminated on the substrate, a guide layer, a second dielectric layer, and a recording layer, and a part of the guide layer. An optical recording medium characterized in that 2. The optical recording medium according to claim 1, wherein the guide layer is continuously or discontinuously removed along a spiral shape, a concentric shape, a linear shape or the like, and the width of the removed portion and its width. An optical recording medium, wherein the sum of the widths of the unremoved portions on both sides is equal to or wider than the laser spot diameter on the recording layer. 3. The optical recording medium according to claim 1, wherein the refractive index of one or both of the first and second dielectric layers is higher than that of the substrate. 4. The optical recording medium according to claim 1, wherein the first and second dielectric layers have the same refractive index. 5. The optical recording medium according to claim 1, wherein the phase change generated in the light traveling back and forth through the first and second dielectric layers is about π or a value obtained by adding an integer multiple of about 2π. In the optical recording medium, the film thicknesses of the first and second dielectric layers are defined. 6. The optical recording medium according to claim 1, wherein the phase difference between the reflected light from the part where the guide layer is removed and the reflected light from the part where the guide layer is not removed is approximately π or An optical recording medium characterized by not being a value obtained by adding an integer multiple of approximately π to it. 7. The optical recording medium according to claim 1, wherein a phase difference between reflected light from the removed portion of the guide layer and reflected light from the unremoved portion of the guide layer is approximately π /. An optical recording medium having a value of 2 or an integer multiple of approximately π. 8. The optical recording medium according to claim 1, wherein when the refractive index of the second dielectric layer is n ₂ and the wavelength of light in vacuum is λ and m are integers, The thicknesses of the first and second dielectric layers such that the thickness of the second dielectric layer is approximately [(λ / (4n ₂ ) ± λ / (12n ₂ )] + mλ / (4n ₂ ). An optical recording medium characterized in that 9. The optical recording medium according to claim 1, wherein a phase change produced in light traveling back and forth only through the first dielectric layer and a phase variation produced in light traveling back and forth through the first and second dielectric layers. The difference in change is about π / 2 or a value obtained by adding an integer multiple of about π to it, and the phase change generated in the light traveling back and forth through the first and second dielectric layers is about π or an integer of about 2π. An optical recording medium, wherein the film thicknesses of the first and second dielectric layers are determined so as to have a value obtained by doubling.