JPH04362523A - Optical recording medium - Google Patents

Abstract

PURPOSE:To provide an optical recording medium where crosstalk is small and density can be made high by providing a recording area and a non-recording area and recording data only in the recording area. CONSTITUTION:The non-recording area 18 consisting of a metallic film is formed in a concentric form and a spiral form. An area sandwiched by the non- recording areas 18 in a recording layer 19 becomes a recording area 22. Since data cannot be recorded in the non-recording areas 18 and an adjacent recording area is not irradiated with a laser beam 24 at the time of reproduction, a track pitch can be made smaller than the spot diameter of the laser beam 24 without increasing crosstalk, and density can be made high. A wobbling pit 14 is formed in such a way that the center of it almost matches with the center of the non- recording area 18 and straight lines connecting the centers of the mutually adjacent wobbling pits 14 and the center of the optical recording medium are prevented from being matched. Stable tracking can be executed by a sample servo system.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a method of recording information by light.
The present invention relates to an optical recording medium that performs reproduction or erasing, and more particularly to an optical recording medium that allows high-density recording.

0002

2. Description of the Related Art Conventionally, in addition to optical recording media in which tracking guide grooves are formed on a substrate and tracking is performed by a push-pull method, there are also types in which tracking is performed by a sample servo method. As shown in FIG. 10, the main part of the sample servo type optical recording medium 100 is a pair of wobbling pits 104 and 105 provided on both sides of the center 102 of the track through which the laser spot 101 passes.
It consists of a servo area 106 having
This servo area 106 and data area 109 constitute one sector 110.

[0003] The wobbling pits 104 and 105 consist of recesses 113 formed in a substrate 112, as shown in the cross-sectional view of FIG. 11, on which a recording layer 115 and a protective layer 117 are laminated. Laser light 118 is irradiated from the substrate side. In the servo area 106, in addition to the wobbling pits 104 and 105, pits for providing addresses and clocks (not shown) are also formed.

[0004] When the laser spot 101 is irradiated onto the wobbling pits 104 and 105, the amount of reflected light is reduced by diffraction and a signal is detected. When the laser spot 101 passes through the center 102 of the track, the intensities of the signals 120 and 121 generated by the wobbling pits 104 and 105 become equal, as shown in FIG. 12(a). Laser spot 1
01 is shifted to the left from the center 102 of the track, the signal 120 from the wobbling pit 104 becomes larger than the signal 121 from the wobbling pit 105, as shown in FIG. 4(b).

On the other hand, when the laser spot 101 is shifted to the right from the center 102 of the track, the signal 121 from the wobbling pit 105 becomes larger than the signal 120 from the wobbling pit 104, as shown in FIG. 2(c). Therefore, by comparing the magnitudes of signals 120 and 121, the laser spot 101 and the track center 10
2 can be detected, and a tracking error signal can be obtained. Control is performed in the servo area 106 so that the difference between the signals 120 and 121 becomes 0, and this state is maintained in the data area 109. Tracking is performed by repeating this operation for each sector 110.

The substrate 112 is made of acrylic resin, polycarbonate resin, or glass, and the protective layer 117 is made of SiO2, A
Oxides and nitrides such as IN are used. In addition, recording layer 1
As the material 15, a drilling material such as Te, a phase change material such as GeTeSb, or a magneto-optical material such as TbFeCo is used.

A laser beam 118 focused by an objective lens (not shown) or the like is irradiated onto the recording layer 115 through the substrate 112 to cause deformation, phase change, magnetization reversal, etc. of the recording layer 115 in the irradiated portion 101, The recording bit 10 has a different reflectance or Kerr rotation angle from the non-irradiated area.
Recording is performed by forming 8. Information is reproduced by detecting changes in the reflectance and Kerr rotation angle of the recorded bits 108.

[0008]

However, since the recording layer 115 generally has high thermal conductivity, the temperature around the laser irradiation area also rises due to thermal conduction, and the recorded bits 108 spread. As a result, when playing a certain track 102,
Since part of the bits recorded on the adjacent track is also irradiated with laser light, there are problems in that signals that should not be reproduced are mixed in, causing crosstalk and increasing noise. In particular, when the track pitch was reduced to increase density, crosstalk increased significantly.

The present invention has been made to solve the above-mentioned problems, and its purpose is to provide a recording area and a non-recording area, and to record only in the recording area, thereby reducing crosstalk. The object of the present invention is to provide an optical recording medium that has a small size and can achieve high density.

0010

[Means for Solving the Problems] In order to achieve this object, the optical recording medium of the present invention includes a transparent substrate, a protective layer formed on the substrate, and a concentric circle, spiral or A recordable area formed continuously or discontinuously along a straight line, etc., a non-recordable area formed between adjacent recording areas where recording is not possible, and between the substrate and the protective layer. It is preferable that the recording area and the non-recording area have a surface on the substrate side substantially on the same plane.

At this time, the reflectance of the recording area and the non-recording area are approximately equal, and the center of the wobbling pit substantially coincides with the center of the non-recording area when viewed from the substrate side, and the center of the wobbling pits adjacent to each other is substantially equal to the center of the non-recording area. It is preferable that the straight lines connecting the optical recording medium and the center of the optical recording medium are formed so that they do not coincide with each other. Further, in order to form the recording area in a concentric circle, a spiral, a straight line, etc., and to form the non-recording area between adjacent recording areas, the non-recording area is formed on the substrate in a concentric, spiral, linear, etc. The recording area may be formed by forming it in a straight line or the like and providing a recording layer thereon.

0012

[Operation] In the optical recording medium of the present invention having the above configuration,
Since tracking is performed by a sample servo method using wobbling pits provided between the substrate and the protective layer, stable tracking can be performed even if the track pitch is made small. At this time, the surfaces of the recording area and the non-recording area on the substrate side are substantially on the same plane, and by making their reflectances approximately equal, there is no influence of the boundary between the recording area and the non-recording area. A stable tracking error signal can be obtained.

[0013] Also, the center of the wobbling pit is substantially aligned with the center of the non-recording area when viewed from the substrate side, and the straight lines connecting the centers of the adjacent wobbling pits 14 and the center of the optical recording medium are not aligned. By forming this, the track pitch can be reduced. Even if the track pitch is made smaller and the width of the recording area becomes smaller than the diameter of the laser spot, as long as the laser spot does not deviate from the recording area and the non-recording areas formed on both sides of it, recording will continue in the adjacent recording area. Since no regeneration takes place, crosstalk does not increase.

[0014]

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

As shown in FIG. 1, an optical recording medium 10 to which the present invention is preferably applied includes a transparent substrate 12, wobbling pits 14 formed thereon, and a protective layer that provides a phase difference necessary for tracking. 16, a metal film 18 that serves as a non-recording area, a recording layer 19 on which information is recorded, and a protective layer 20 that protects the recording layer 19. The transparent substrate 12 is made of resin such as acrylic or polycarbonate, or glass. The wobbling pits 14 and the metal film 18 are made of metal such as Ta, Cr, Al, etc., and the recording layer 19
In the case of magneto-optical recording media, for example, rare earth transition metal amorphous alloys such as TbFeCo, TbFe, and GdT are used.
A superlattice thin film made by laminating multiple layers of extremely thin films such as bFe or Pt and Co is used.

Further, the protective layers 16 and 20 are made of glass, Si, etc.
Transparent oxides, nitrides, etc. such as O2 and AlN are used. The protective layers 16 and 20 serve to protect the recording layer 19 from oxidation and the like. The thickness of the protective layer 16 is approximately λ/8n (λ: wavelength of light, n: protective layer 1
6), but is not particularly limited to this thickness.

The wobbling pit 14 is located on the optical recording medium 1.
As shown in FIG. 2, which is viewed from the substrate 12 side, the center of the wobbling pit 14 substantially coincides with the center of the non-recording area 18 made of a metal film, and the wobbling pits 14 adjacent to each other are
The straight lines connecting the center of the optical recording medium 10 and the center of the optical recording medium 10 do not coincide with each other.

The non-recording area 18 is formed in a concentric or spiral shape, and the area of the recording layer 19 sandwiched between the non-recording area 18 becomes the recording area 22 . Therefore, the recording areas 22 also have a concentric or spiral shape, and a non-recording area 18 exists between adjacent recording areas 22. The laser spot 24 is irradiated along the recording area 22. The area where the wobbling pits 14 are formed becomes the servo area 26, and the other area becomes the data area 28 where information is recorded. The servo area 26 and data area 28 are combined to form one sector 29.

The method for manufacturing the optical recording medium of this example will be explained using FIG. 3.

First, as shown in FIG. 3A, a metal thin film 30 such as Ta, which will become the wobbling pits 14, is formed on the substrate 12 by a well-known thin film forming method such as sputtering or vacuum evaporation. A negative photoresist 32 is applied onto the metal thin film 30 using a spin coating method or the like. Next, while rotating the substrate 12 and simultaneously moving it in one direction, the position where the wobbling pit 14 is to be formed is irradiated with a laser beam 34 such as an Ar laser for exposure. At this time, exposure is performed in a spiral shape if the light is moved continuously in one direction, and in a concentric circle if the light is moved discontinuously every rotation.

After exposure, development is performed to leave the photoresist 32 in the area irradiated with the laser beam 34, as shown in FIG. 3(b). Here, the portion of the metal thin film 30 on which the photoresist 32 is not attached is removed by a well-known etching method such as plasma etching or chemical etching using acid or alkali, and then the photoresist 32 is removed using a solvent or the like. When removed, wobbling pits 14 are formed as shown in FIG. 3(c).

As shown in the figure (d), for example, a liquid metal alkoxide such as Si is supplied and applied by a spin coating method, and this is heated and solidified to protect SiO2, etc. Layer 16 is formed. This results in
The gap between the wobbling pits 14 is filled and the protective layer 16
The surface opposite to the substrate 12 is a wobbling pit 14.
It is almost flat regardless of the unevenness of the surface. Furthermore, a metal film 36 of Ta or the like is formed by a well-known thin film forming method such as sputtering or vacuum evaporation.

A positive type photoresist 38 is coated on the metal thin film 36 using a spin coating method or the like, and at the same time as the substrate 12 is rotated, Ar is applied while tracking control is performed using a sample servo method using the wobbling pit 14. Exposure is performed by irradiating a laser beam 34 such as a laser.

After exposure, the photoresist 38 is developed by melting the portion irradiated with the laser beam 34, leaving only the portion that will become a non-recording area, as shown in FIG. 3(e). Here, the portion of the metal film 36 on which the photoresist 38 is not attached is removed by a well-known etching method such as plasma etching or chemical etching using acid or alkali, and then the photoresist 38 is removed using a solvent or the like. When removed, the metal film 18 remains as a non-recording area, as shown in FIG. 2(f).

Finally, the recording layer 19 and the protective layer 20 are formed using well-known thin film forming means such as sputtering method (g).
).

To record information, the recording layer 19 in the recording area 22 with a width wR is heated by irradiating the laser beam 24 with a constant output from the substrate 12 side, and at the same time, a magnetic field is applied to magnetize the recording layer 19 in a constant direction. After alignment, the direction of the applied magnetic field is reversed, the recording layer 19 is heated by being irradiated with laser light 24 modulated by information, and the magnetization of the recording layer 19 is reversed, thereby forming a bit.

Note that the metal film 18 is also heated by the laser beam 24, but since the metal film 18 and the recording layer 19 are laminated, the temperature rise is small, and at the same time no recording is performed in the non-recording area 18. , heat is not transmitted to the recording layer 19 of the adjacent recording area 22, and the spread of bits is also suppressed. Here, the sum wP+ of the track pitch wP and the width wN of the non-recording area
By making wN approximately equal to the spot diameter d of the irradiated laser beam 24, the laser beam 24 will not be irradiated onto the adjacent recording area during playback, so the track pitch wP can be adjusted to the spot diameter of the laser beam 24 without increasing crosstalk. The diameter can be made smaller than the diameter d, allowing higher density.

Tracking is performed using the sample servo method as shown in Figure 4.
This is done as described in .

When the laser spot 24 is irradiated onto the wobbling pit 14, the amount of reflected light is reduced due to diffraction and a signal is detected. Here, the laser spot 24 is shown in FIG.
), when passing through the center of the recording area 22, the changes in the amount of reflected light caused by diffraction by the wobbling pits 40, 42 are equal. Therefore, signals 120 and 121 of equal strength as shown in FIG. 12(a) are obtained.

As shown in FIG. 4(b), when the laser spot 24 is shifted to the left from the center of the recording area 22, as shown in FIG.
As shown in FIG. 2(b), the signal 120 from the wobbling pit 40 becomes larger than the signal 121 from the wobbling pit 42.

On the other hand, as shown in FIG. 4(c), when the laser spot 24 is shifted to the right from the center of the recording area 22, the signal 121 from the wobbling pit 42 is wobbling as shown in FIG. 12(c). Signal 1 from pit 40
It becomes larger than 20. Therefore, signals 120 and 12
By comparing the size of laser spot 24
and the center of the recording area 22 can be detected,
A tracking error signal can be obtained. That is, control is performed in the servo area 26 so that the difference in magnitude between the signals 120 and 121 becomes 0, and this state is maintained in the data area 28. Tracking is performed by repeating this operation for each sector 29.

Note that by making the reflectance of the metal film 18 and the recording layer 19, that is, the non-recording area 18 and the recording area 22 almost equal, it is possible to prevent roughness of the boundary between the non-recording area 18 and the recording area 22. It is possible to suppress the generation of noise.

Although one embodiment of the present invention has been described above in detail with reference to FIGS. 1 to 4, the present invention can be implemented in other forms. For example, the material of the recording layer 19 is not limited to a magneto-optical recording material, but may include an organic dye, a hole-making material such as Te, etc.
A phase change material such as GeTeSb may also be used. Further, a reflective layer made of metal such as Al may be provided on the protective layer 20. Substrate 12, wobbling pit 14, metal film 18
, the materials and film thicknesses of the protective layers 16 and 20 and the reflective layer are not particularly limited. The thickness of the recording layer 19 is also not particularly limited. The non-recording area does not need to be formed of the metal film 18, and may be formed of a material that absorbs light, such as a dye. Further, the protective layer 20 is not necessarily required and may not be provided. Furthermore, the reflectances of the metal film 18 and the recording layer 19 do not necessarily have to be equal.

Further, as shown in FIG. 5, in addition to the wobbling pits 14, pits 50 for providing addresses and clocks may be formed along the recording area 22 in the servo area 26. In this case, the pits 50 for providing addresses and clocks may be formed by forming a metal film between the substrate 12 and the protective layer 16 in the same manner as the wobbling pits 14, or may be formed by recording them on the recording layer 19 in advance. Good too.

Further, the size of the wobbling pit 14 is not particularly limited, and in the above-mentioned embodiment, the size of the wobbling pit 14 is
Although the width is larger than the width of the non-recording area 18, it may be the same width as the non-recording area 18, as shown in FIG. 6(a), for example. Alternatively, the width may be smaller than the width of the non-recording area 18, as shown in FIG. 2(b). Further, the centers of the wobbling pit 14 and the non-recording area 18 do not necessarily have to coincide. Furthermore, the track pitch and the width of the recording area 22 do not need to be constant in the same optical recording medium, and may vary. That is, the recording area width and track pitch may be made smaller toward the outer circumference of the optical recording medium.

Furthermore, the wobbling pits 14 do not need to be located in the non-recording area, and if the track pitch is relatively large as shown in FIG. You can. Furthermore, a protective layer 7 is also provided between the substrate 12 and the wobbling pit 14.
0 may be provided.

Furthermore, the surface of the protective layer 16 opposite to the substrate 12 does not need to be substantially flat, and may have a surface shape that reflects the shape of the wobbling pits 14, as shown in FIG.

Further, as shown in FIG. 8, a recording area 61 is formed by forming a recording film 60 in a spiral shape, a concentric shape, etc., a metal film 62 is formed thereon, and a non-recording area 6 is formed.
3 may be formed.

Furthermore, the recording area and the non-recording area do not need to be continuous; for example, as shown in FIG. 9(a),
The recording area 80 may be formed only in the area where the data area 28 or the wobbling pit 14 is not present, and the entire area other than the area where the servo area 26 or the wobbling pit 14 is present may be the non-recording area 81. At this time, the recording area 80
are formed discontinuously along concentric circles, spirals, or straight lines. Furthermore, as shown in FIG. 2B, the non-recording area 81 may be formed only in the data area 28 or the portion where the wobbling pit 14 is not present.

Further, the shape of the optical recording medium does not have to be circular, and when applied to an optical card or the like, the shape of the non-recording area or the recording area may be linear. Further, the recording area does not need to be formed continuously; for example, a portion where a sector code or the like is previously formed may be omitted, or may be discontinuously concentric, spiral, or linear.

[0041]

[Effect of the invention] As is clear from the above explanation,
According to the optical recording medium of the present invention, by providing a recording area and a non-recording area and recording only in the recording area, an increase in crosstalk due to a narrow track pitch can be suppressed, and the sample servo can be stabilized. Since it is possible to obtain accurate tracking, higher density is possible.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the structure of an optical recording medium of the present invention.

FIG. 2 is a top view showing the structure of the optical recording medium of the present invention.

FIG. 3 is an explanatory diagram showing a method for manufacturing an optical recording medium of the present invention.

FIGS. 4A, 4B, and 4C are top views showing the tracking operation in the optical recording medium of the present invention.

FIG. 5 is a top view showing another embodiment of the optical recording medium of the present invention.

FIGS. 6A, 6B, and 6C are top views showing other embodiments of the optical recording medium of the present invention.

FIG. 7 is a sectional view showing another embodiment of the optical recording medium of the present invention.

FIG. 8 is a sectional view showing another embodiment of the optical recording medium of the present invention.

FIGS. 9(a) and 9(b) are top views showing other embodiments of the optical recording medium of the present invention.

FIG. 10 is a top view showing the configuration of a conventional optical recording medium.

FIG. 11 is a cross-sectional view showing the structure of a conventional optical recording medium.

FIGS. 12A, 12B, and 12C are explanatory diagrams showing tracking error signals in sample servo.

[Explanation of symbols]

12 Board 14 Wobbling pit 16 Protective layer 18 Non-recording area 19 Recording layer 22 Recording area

Claims (5)

[Claims] Claim 1: A transparent substrate, a protective layer formed on the substrate, and a record capable of continuous or discontinuous recording formed on the protective layer along concentric circles, spirals, straight lines, etc. 1. An optical recording medium comprising: a recording area; a non-recording area where recording is not possible formed between the adjacent recording areas; and a wobbling pit provided between the substrate and the protective layer. 2. The optical recording medium according to claim 1, wherein surfaces of the recording area and the non-recording area on the substrate side are substantially on the same plane. 3. The optical recording medium according to claim 1, wherein the recording area and the non-recording area have substantially the same reflectance. 4. In the optical recording medium according to claim 1, the center of the wobbling pit substantially coincides with the center of the non-recording area when viewed from the substrate side, and the center of the wobbling pits adjacent to each other and the center of the optical recording medium are different from each other. An optical recording medium characterized in that the straight lines connecting the center do not match. 5. The optical recording medium according to claim 1, wherein the non-recording area on the substrate has a concentric shape, a spiral shape,
An optical recording medium characterized in that it is formed in a straight line or the like, and a recording area is formed by providing a recording layer thereon.