JP2000268409A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical recording medium which allows the sure detection of a tracking error signal by a push-pull method. SOLUTION: A first laminate 10 constituting the optical recording medium has a light absorption layer 2, a reflection layer 3 and a protective layer 4 on a substrate 1. The angle Ga of inclination of the side walls in the position of the half-value width of a recessed part G of the reflection layer 3 corresponding to the groove Tg of the substrate 1 is regulated to 15 to 80 deg.. As a result, reflection layer 3 reflects the shape of the groove Tg of the substrate 1 and the tracking error signal may be obtained with sufficiently signal intensity from the recessed part G of the reflection layer 3. Further, the distance d1 from the base surface of the groove Tg to the reflection layer 3 right thereabove is specified to 75 to 200 nm. As a result, the large signal modulation degree may be obtd. even at the time of recording.

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 for detecting a tracking signal by a push-pull method. More specifically, the present invention relates to an optical recording medium for detecting a tracking signal during reproduction while maintaining a sufficient signal modulation during recording. The present invention relates to an optical recording medium capable of performing the following.

[0002]

2. Description of the Related Art An optical recording medium is known as a medium used for an external memory such as a computer. The optical recording medium can handle a large amount of data such as a moving image and a sound, and is therefore frequently used as a recording medium in the multimedia age. Optical recording media are classified into read-only optical recording media on which information cannot be written, write-once optical recording media on which information can be written only once, and rewritable optical recording media on which information can be rewritten any number of times. .

One type of write-once optical recording medium has a diameter of 12 mm.
A CD-R having a recording capacity of 640 MB in a disk shape of 0 mm is known. For a recording film of a write-once optical recording medium such as a CD-R, for example, an organic dye such as cyanine or phthalocyanine is used. In order to write information on an optical recording medium using an organic dye for a recording film, a laser beam is condensed and irradiated on a minute region of the recording film. As a result, light energy is converted into heat energy, and the properties of the recording film change to form pits. In order to reproduce the recorded information, the pit is irradiated with a laser beam having an output lower than that of the laser beam used for writing the information. Since there is a difference in contrast between the portion where the pit is formed and the portion where the pit is not formed, the difference is read as a change in the electric signal (signal modulation degree).

[0004] The servo in the optical recording medium is, for example, a CD.
As seen from -R, a servo system using a pre-groove is widely used, and a push-pull method is generally adopted as a tracking servo method. In the push-pull method, a tracking error is obtained by extracting light reflected and diffracted by a groove on a disk as an output difference between two light receiving sections on a two-segment photodetector symmetrically arranged with respect to the center in the track width direction. To detect.

[0005]

In recent years, DVD-Rs have been developed as write-once optical recording media realizing a large capacity. This is due to the increased number of users and general-purpose devices that are trying to utilize enormous data such as high-resolution images and high-quality audio frequently used in high-definition and multimedia. This is because a large-capacity recording medium has become indispensable. DVD-Rs have a storage capacity about six times that of CD-Rs, and can be played back on DVD players. In a DVD-R, the track pitch is set to about half of that of a conventional CD-R (0.7
μm to 0.8 μm) to increase the recording density in the track width direction.

However, in an optical recording medium having a narrow track pitch such as a DVD-R, if a tracking error signal is detected by the push-pull method as described above, the obtained signal intensity is small, and the tracking servo can be accurately performed. It was difficult to do. If the tracking servo cannot be performed accurately, the information mark cannot be accurately recorded and reproduced.

The present invention has been made to solve the above-mentioned problems of the prior art, and an object thereof is to provide an optical recording medium capable of reliably detecting a tracking error signal by using a push-pull method. Is to do. An object of the present invention is to provide an optical recording medium capable of obtaining a sufficient signal modulation degree during recording.

[0008]

According to the present invention, a recording layer and a reflective layer are provided on a grooved substrate in this order,
In an optical recording medium in which a tracking signal is detected by the push-pull method, the distance d1 from the groove bottom surface of the substrate to the reflection layer located immediately above the groove is 75 nm ≦ d1.
≦ 200 nm, and the inclination angle Ga in the half width of the depression of the reflection layer corresponding to the groove of the substrate is 15 ° ≦
An optical recording medium characterized by satisfying Ga ≦ 80 ° is provided.

According to the study of the present inventors, it has been found that the tracking error signal detected from the optical disk in the push-pull method largely depends not only on the groove shape of the substrate but also on the shape of the reflection film. It was found that the tracking error signal detected as flat was small. In particular, in a write-once optical recording medium in which an organic dye is used for the recording layer, the light absorption layer is applied to the grooved substrate by spin coating or the like. The surface of the reflective layer laminated on the surface also becomes flat. For this reason, when the laser beam crosses between the land and the groove, the difference in the amount of reflected light detected from each of the land and the groove becomes small, and accordingly, the tracking error signal also becomes small. In the case of a medium having a further narrower track pitch, such as a DVD, the surface of the light absorption layer becomes flatter than before, and the tracking error signal tends to be smaller. For this reason, it is considered that tracking servo could not be performed accurately in the push-pull method.

Therefore, in the optical recording medium of the present invention, as shown in FIG. 2, the inclination angle Ga of the side wall at the half width of the concave portion G of the reflective layer 3 corresponding to the groove Tg of the substrate is 1.
Since the shape of the reflective layer 3 is adjusted so as to be within the range of 5 ° to 80 °, the reflective layer 3 reflects the shape of the groove of the substrate, and therefore, the tracking signal detected from the reflective layer is a sufficient signal. Can be obtained with strength. As a result, tracking servo can be performed reliably. The half-value width of the concave portion of the reflective layer in the present invention is a concept meaning the width of the concave portion of the reflective layer at a position where the depth of the concave portion of the reflective layer corresponding to the substrate is half. In order to adjust the inclination angle Ga of the side wall of the concave portion G of the reflective layer 3, for example, the thickness, concentration, and viscosity of a dye as a recording film interposed between the reflective layer and the substrate are appropriately adjusted, What is necessary is just to adjust the inclination angle of the groove side wall.

Further, in the present invention, the distance d1 from the bottom surface of the groove Tg of the substrate in FIG. 2 to the reflective layer 3 located immediately above it, that is, the thickness of the recording layer 2 near the center of the groove portion is set to 75 nm to 200 nm. Therefore, a large signal modulation degree can be obtained. d1 is 200n
If it is larger than m, the signal modulation degree will increase,
It is difficult to control pits during recording. For example, recording pits may spread in the track width direction during recording. Such recording pits are not preferable because they may cause crosstalk during reading. On the other hand, if the thickness is smaller than 75 nm, the amount of the dye constituting the recording film is reduced, so that a sufficient signal modulation cannot be obtained.

In the present invention, as shown in FIG. 3, when the inclination angles at the side walls Gs1 and Gs2 of the concave portion G of the reflection layer 3 are Gsa1 and Gsa2, respectively, | Gsa1
-Gsa2 | ≦ 20 ° is preferably satisfied. ｜ G
If sa1−Gsa2 |> 20 °, the reflected light intensity distribution detected by the two-segment detector becomes unbalanced, and
The output difference from the split detector does not become 0, and it is recognized that the optical axis of the recording light or the reproduction light is not at the center of the track, so that accurate tracking may not be performed.

In the present invention, the light absorbing layer can be formed directly on the substrate or through an arbitrary layer, and is formed by using a known organic dye used for a recording film of a write-once optical recording medium. Can be. For example, it can be constituted by using an organic dye or a dye composition containing a cyanine dye or an azo dye. Further, another material such as an inorganic composition formed by a sputtering method or an evaporation method may be used.

The reflective layer of the optical recording medium of the present invention comprises 9
It preferably shows a reflectance of 0% or more, and Au, Ag,
It is preferable to use a material containing at least one metal selected from the group consisting of Al and Cu. Further, the thickness of the reflective layer is preferably 50 nm to 200 nm. If the film thickness is less than 50 nm, the reflectance is lowered and a sufficient reproduced signal cannot be obtained. When the film thickness is 200
If the thickness is larger than nm, the mechanical properties of the substrate may be deteriorated.

The substrate of the optical recording medium of the present invention has a wavelength of 600
It is preferable to use a resin, glass, or the like which has a substantial transmittance for recording light and reproducing light of nm to 700 nm, preferably 650 nm. Such a substrate is, for example, polycarbonate, polymethyl methacrylate,
It is obtained by injection molding a transparent resin material such as polymethylpentene or epoxy, or by forming a replica layer of a photocurable resin on one side of a transparent ceramic plate such as glass (so-called 2P method). It is processed into a disk shape having a preformat pattern and having a center hole at the center. Grooves formed in the substrate may be spiral or concentric, for example,
The track pitch can be 0.7 μm to 0.9 μm, and the half width of the groove can be 0.25 μm to 0.45 μm. Recording and reproduction can be performed by using such grooves as recording tracks.

In the present invention, as shown in FIG. 2, the depth at both ends of the groove bottom surface of the substrate is set to ds, respectively.
1, ds2, | ds1-ds2 | ≦ 20n
m is preferably satisfied. | Ds1-ds2 |> 2
When a substrate having a thickness of 0 nm is used, the thickness of the light absorption layer and the reflection layer formed on the substrate fluctuates on both sides of the center of the groove in the track width direction, and the film is accurately and stably formed by the push-pull method. Therefore, it becomes difficult to obtain a tracking error signal.

Further, the optical recording medium of the present invention can be a laminated optical recording medium. The laminated optical recording medium can be manufactured by, for example, bonding another substrate directly or via an arbitrary layer to the reflective layer using an adhesive or the like. Alternatively, a laminate having a substrate and a light absorbing layer and a reflective layer formed thereon is formed by one.
A set may be prepared, and the laminates may be manufactured by bonding them together via an adhesive such that the light absorption layer and the reflection layer are inside and the substrate is outside. As the adhesive, a hot melt adhesive, an ultraviolet curing adhesive, an epoxy adhesive, a silicone adhesive, or the like can be used.

On the reflective layer of the optical recording medium of the present invention, a UV protective layer made of various resins can be provided as a protective layer. Further, an arbitrary layer such as an intermediate layer may be provided between the substrate and the light absorbing layer or between the light absorbing layer and the reflecting layer.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the optical recording medium according to the present invention will be specifically described, but the present invention is not limited to the following embodiments.

[0020]

FIG. 1 is a sectional view showing an optical recording medium according to the present invention. The optical recording medium 100 includes a first stacked body 10, a second stacked body 20, and an adhesive layer 5. The first laminated body 10 and the second laminated body 20 have the same laminated structure. FIG. 2 shows the first
1 shows a cross-sectional view of a laminate 10. The first laminate 10 has a structure in which a light absorbing layer 2, a reflective layer 3, and a protective layer 4 are sequentially laminated on a transparent substrate 1. First laminate 1 having such a structure
0 was produced as shown below.

First, a stamper on which a concavo-convex pattern corresponding to a pregroove was formed was loaded into a mold of an injection molding machine, and a molten polycarbonate resin was injected and filled into the mold to produce a transparent substrate 1. The manufactured transparent substrate 1 had a diameter of 120 nm and a thickness of 0.6 mm. The transparent substrate 1 has a groove with a track pitch of 0.8 μm on its surface, and the side wall Tg of the groove Tg in FIG.
The inclination angle of s is 79 °, the depths ds1 and ds2 of both ends of the groove are both 169 nm, and the half value width Gw of the groove is 3
It was 65 nm.

Next, a light absorbing layer 2 was formed on the obtained transparent substrate 1 as follows. First, 1 part by weight of a trimethine cyanine dye (1,3,3,1 ′, 3 ′, 3′-hexamethyl-2,2 ′-(4,5-benzo) indocarbocyanine perchlorate) and an aminium compound 0.1 parts by weight of IRG002 manufactured by Nippon Kayaku Co., Ltd. was dissolved in 100 parts by weight of tetrafluoropropanol, and filtered using a membrane filter having a pore size of 0.25 μm to prepare a dye solution. This solution was applied onto the groove forming surface of the transparent substrate 1 by spin coating, and annealed in an oven at 80 ° C. for 60 minutes to form the light absorbing layer 2.

Next, the transparent substrate 1 on which the light absorbing layer 2 is formed
Was loaded into a sputtering apparatus (not shown). By sputtering using silver as a target material, a reflective layer 3 made of silver was formed to a thickness of 100 nm on the light absorption layer 2. The transparent substrate 1 on which the reflective layer 3 is formed is taken out of the sputtering apparatus, and an ultraviolet curable resin is applied on the reflective layer 3 by spin coating to a film thickness of 5 μm, and then the ultraviolet curable resin is irradiated to cure the ultraviolet curable resin, thereby protecting the protective layer 4. Was formed. Thus, the first laminated body 10 having the laminated structure shown in FIG. 2 was manufactured. In the manufactured first laminate, the distance S1 from the center position of the groove bottom surface to the reflective layer surface is 103 nm, and the distance d2 between the substrate and the reflective layer between the grooves (land portion L) is 82 nm. Scanning Ele
ctron Microscope: scanning electron microscope). Further, the inclination angle Ga at the half-value width of the concave portion of the reflection layer is
Was calculated by drawing a tangent line at the half-value width position in the SEM photograph, and it was 31 °.

Next, in the same manner as in the first laminate 10, the second
A laminate 20 is prepared, and the first laminate 10 and the second laminate 20
Were bonded so that the respective protective layers faced each other with an ultraviolet curable adhesive therebetween. Thus, a laminated optical recording medium 100 having the laminated structure shown in FIG. 1 was manufactured.

The obtained optical recording medium was loaded on an optical disk evaluation device (not shown) manufactured by Pulstec Industrial equipped with a red semiconductor laser head having a wavelength of 640 nm, and servo signals were evaluated. In the evaluation of the servo signal, the linear velocity was 3.8 m / s, and the laser power during recording was 11 mW.
I went in. For the evaluation of the servo signal, a standardized push-pull signal can be used. The standardized push-pull signal PPb is obtained by dividing the output difference between the two light receiving units on the split photodetector into the PPD and the split photodetector output. If the sum of is taken as SS, then PPb = PPD / SS. Standardized push-pull signal PPb
Is suitable as a reference when comparing servo signals between different types of disks having different recording films. Therefore, in this embodiment and a comparative example described later, the servo signals were evaluated using this PPb. The optical disk manufactured in this example had a PPb of 0.35 and was 58% recorded.
Signal modulation degree was obtained, and good characteristics were shown in the servo signal and the recording characteristics.

[0026]

COMPARATIVE EXAMPLE 1 The inclination angle of the groove side wall Tgs in FIG. 2 was 52 °, and the depths ds1 and ds2 at both ends of the groove.
A laminated optical recording medium was produced in the same manner as in Example 1 except that a polycarbonate substrate having a groove having a thickness of 165 nm and a groove half-value width Gw of 357 nm was used. The distance d2 between the land L of the substrate and the reflective layer 4 is 81 nm, the distance d1 from the center of the substrate groove Tg to the reflective layer immediately above it is 107 nm, and the maximum inclination angle Ga of the reflective layer at the substrate groove Tg is 9 ° SEM
Confirmed by This optical recording medium was loaded into the evaluation device used in the above embodiment, and servo signals were evaluated in the same manner as in the embodiment. In the optical recording medium manufactured in Comparative Example 1, a large signal modulation degree of 62% was obtained during recording.
Pb was 0.14, and it was difficult to perform stable tracking.

[0027]

COMPARATIVE EXAMPLE 2 The inclination angle of the groove side wall Tgs in FIG. 2 was 49 °, and the depths ds1 and ds2 at both ends of the groove.
A bonded optical recording medium was produced in the same manner as in Example 1, except that a polycarbonate substrate having both 171 nm and a groove half width of 364 nm was used. The distance d2 between the substrate land portion L and the reflection layer 4 is 53 nm, and the substrate groove portion T
The distance d1 from the center of g to the immediately above reflective layer is 68n
m, the maximum inclination angle Ga of the reflection layer at the substrate groove portion Tg
Was 13 ° by SEM. This optical recording medium was loaded into the evaluation apparatus used in the above embodiment, and servo signals were evaluated in the same manner as in the embodiment. The optical recording medium manufactured in Comparative Example 2 had a PPb of 0.42, and could perform tracking stably. However, only a small signal modulation degree of 45% was obtained during recording.

[0028]

According to the optical recording medium of the present invention, the shape of the reflection layer is adjusted so that the inclination angle of the depression of the reflection layer corresponding to the groove of the substrate is in the range of 15 ° to 80 °. When the tracking servo is performed by the push-pull method, a tracking error signal can be obtained accurately and reliably, and at the same time, the distance from the groove bottom of the substrate to the reflection layer is 75 n.
Since m ≦ d1 ≦ 200 nm, a sufficient signal modulation degree can be obtained even during recording. The optical recording medium of the present invention is extremely suitable for a write-once optical recording medium having a narrow track pitch such as a DVD-R.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a bonded optical recording medium according to the present invention.

FIG. 2 is a partially enlarged sectional view of a first laminate of the optical recording medium shown in FIG.

FIG. 3 is a schematic diagram for explaining an inclination angle of both side walls of a concave portion of a reflective layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Light absorption layer 3 Reflective layer 4 Protective layer 5 Adhesive layer 10 1st laminated body 20 2nd laminated body 100 Optical recording medium G Depression part of reflection layer Tg Substrate groove part Tp Track pitch Gw Half width of substrate groove part

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yuichi Sakurai 1-1-88 Ushitora, Ibaraki City, Osaka Prefecture Inside Hitachi Maxell Co., Ltd. (72) Inventor Takuya Hayashi 1-188 Ushitora, Ibaraki City, Osaka Prefecture F term in Hitachi Maxell, Ltd. (reference) 5D029 MA13 MA14 WA01 WB11 WB14 WB17 WB21 WC01 WD12

Claims (8)

[Claims] 1. An optical recording medium in which a light absorbing layer and a reflective layer are provided in this order on a substrate having a groove, and a tracking signal is detected by a push-pull method. The distance d1 to the layer satisfies 75 nm ≦ d1 ≦ 200 nm, and the inclination angle Ga in the half width of the depression of the reflection layer corresponding to the groove of the substrate satisfies 15 ° ≦ Ga ≦ 80 °. Optical recording medium. 2. A track pitch t of a groove of the substrate.
2. The optical recording medium according to claim 1, wherein p satisfies 0.7 μm ≦ tp ≦ 0.9 μm, and the half width Gw of the groove satisfies 0.25 μm ≦ Gw ≦ 0.45 μm. 3. When the depths at both ends of the bottom surface of the groove of the substrate are ds1 and ds2, respectively, | ds
2. The optical recording medium according to claim 1, wherein 1-ds2 | ≦ 20 nm is satisfied. 4. The inclination angles Gsa1 and Gsa2 of both side walls in the half width of the depression of the reflection layer are | Gsa1-Gsa2.
The optical recording medium according to claim 1, wherein | ≦ 20 ° is satisfied. 5. The material constituting the reflection layer is Au, A
The optical recording medium according to any one of claims 1 to 4, comprising at least one metal selected from the group consisting of g, Al, and Cu. 6. The reflective layer has a thickness of 50 nm to 200 nm.
The optical recording medium according to any one of claims 1 to 5, wherein the optical recording medium is in a range of nm. 7. The optical recording medium according to claim 1, further comprising another substrate on the reflection layer. 8. A first laminate having the substrate and the light absorbing layer and the reflective layer laminated thereon, and a second laminate having the same laminate structure as the first laminate,
The optical recording medium according to any one of claims 1 to 6, wherein the optical recording medium has a structure in which the first stacked body and the second stacked body are bonded to each other such that the substrates are on the outside.