JPH03203825A - Asymmetric double-face optical disk its production, and optical disk device using this optical disk - Google Patents

Abstract

PURPOSE:To reduce the whole thickness of a double-face optical disk by using one substrate, a thin cover layer and a buffer layer. CONSTITUTION:The transparent substrate used consists of a transparent material having physical supporting strength, specified thickness, the first and second surfaces facing to each other apart from a distant of this thickness. The disk consists of this transparent substrate 1, a fist recording layer 2 formed on th second surface of the transparent substrate 1, a buffer layer 3 formed on the first recording layer 2, and further a second recording layer 4 provided on the buffer layer 3. A transparent cover layer 5 consisting of a transparent material and having the thickness half of or less than the specified thickness of the transparent substrate 1 is deposited on the second recording layer 4. By this method, thickness of the double-face optical disk can be reduced, which realizes a small-sized device since the disk can be stored in a limited narrow space.

Description

[Detailed Description of the Invention] [Summary] Regarding an optical disc suitable for miniaturization, a manufacturing method thereof, and an optical disc device using the optical disc, an object of the present invention is to provide an optical disc having a double-sided structure that can be stored even in a limited narrow space. a transparent substrate having a predetermined thickness and first and second surfaces facing each other with this thickness in between; and a second surface of the transparent substrate. a first recording layer formed thereon;
a buffer layer formed on the recording layer of
a second recording layer disposed on the transparent substrate; and a transparent cover layer made of a transparent material, disposed on the second recording layer and having a thickness not more than half the predetermined thickness of the transparent substrate. It is configured to have the following.

[Industrial Field of Application] The present invention relates to an optical disc, and more particularly to an optical disc suitable for miniaturization, a manufacturing method thereof, and an optical disc device using the optical disc.

[Prior Art] FIGS. 2(A) and 2(B) show optical discs according to the prior art.

FIG. 2(A) shows a double-sided optical disc in which a recording layer 12 is formed on a transparent substrate 11, and a similarly transparent substrate 1
A recording layer 15 is formed on top of the image recording layer 12.
．． 15 are butted against each other and bonded by an adhesive layer 17. As a result, a plane-symmetric configuration is created.

FIG. 2(B) shows a transparent substrate 1 showing a single-sided optical disc.
A recording layer 12 is formed on the recording layer 1, and a cover layer 19 is formed on the recording layer 12 to protect the recording layer 12.

When writing and reading information on these optical disks, a laser beam is focused with a lens and the substrate 11.
through which a light spot is focused onto the recording layer 12.15. In order to achieve high-density recording, the spot diameter should be small. For example, in order to obtain a beam spot diameter of about 0.8 μm, the numerical aperture of the lens should be approximately 0°5 to 0.55. If the substrate thickness is about 1-1.2 nn, the lens aperture should be 4-51 nn.
It will be about the size of 1. The entire head including such lenses has a height or thickness of about 1.0 to 1.5 cm.

When using the double-sided optical disk shown in FIG. 2 (A>), there are two methods: a method in which the head is provided only on one side and the optical disk is turned over, and a method in which the heads are placed on both sides of the optical disk.

In the case of writing on a magneto-optical disk, data is recorded by applying a magnetic field from the outside at the same time as laser irradiation to generate magnetization in a direction corresponding to the data.

It is desirable that an optical disk having such a structure be used in a replaceable form, like a floppy disk. Under these circumstances, optical disks are being made smaller.

Currently, for optical discs with a diameter of 5 inches, as shown in Fig. 2 (A
Standardization of double-sided optical discs as shown in > is underway. However, for optical discs with a diameter of 3.5 inches or less, miniaturization is prioritized, and the standard for optical disc containers is limited to a thickness of approximately 2u. The thickness of the substrate of an optical disk is about 1 to 1.5 mm, and if two substrates are bonded together, the thickness will be 2 to 3 mm, which means that it will not fit in a container. For smaller diameter optical discs, a double-sided structure cannot be used.

1. Problems to be Solved by the Invention] As explained above, the thickness of the substrate cannot be ignored for miniaturization of optical discs. If the configuration is similar to the conventional one, only a single-sided structure can be used as an optical disk to be stored in a narrow storage space.

An object of the present invention is to provide an optical disc having a double-sided structure that can be stored even in a limited narrow space.

Another object of the invention is to provide a method for manufacturing such an optical disc.

Still another object of the present invention is to provide an optical disc device using such an optical disc.

[Means to solve the problem] FIGS. 1(A) to 1(D) are diagrams explaining the principle of the present invention.

In FIG. 1 (A>), a first recording layer 2 is formed on a transparent substrate 1, a buffer layer 3 is disposed on it, a second recording layer 4 is disposed on it, and a second recording layer 2 is disposed on it. A transparent cover layer 5 covers the recording layer 4 .

The transparent cover layer 5 has a thickness that is less than half the thickness of the transparent substrate 1.

FIGS. 1(B) and 1(C) show a method for manufacturing an optical disc as shown in FIG. 1(A>).

In FIG. 1(B), first, a first layer is placed on a transparent substrate 1.
The first recording layer 2 is formed on the cover layer 5, and the second recording layer 4 is formed on the cover layer 5. Adhesion is achieved using a buffer layer 3 having an adhesive effect.

In FIG. 1(C), a first recording layer 2 is formed on a transparent substrate 1, a buff T layer 3 is formed on it, and a second recording layer 4 is further formed on it. . Second recording layer 4
A protective cover layer 5 is formed on top of the .

In FIG. 1(C), the second and third steps may be integrated to prepare the buffer layer 3 on which the second recording layer 4 is placed and form it on the first recording layer 2. .

For example, as in FIG. 1(B), a second
A recording layer 4 is formed, and this sheet-like member is adhered to the first recording layer 2.

FIG. 1(D) shows an optical disc device using the optical disc shown in FIG. 1(A), which includes a substrate 1, a first recording layer 2,
The optical disc 10 having the buffer layer 3, the second recording layer 4, and the cover layer 5 is rotated as shown by the arrow. A large diameter laser beam is emitted from a first head including a lens 6 having a large diameter, passes through the substrate 1, and focuses a light spot on the first recording layer 2. A laser beam with a small diameter is emitted from the second head 9 including a lens 7 with a small diameter, passes through the cover layer 5, and focuses a light spot on the second recording layer 4. The cover layer 5 has a significantly smaller thickness compared to the substrate 1.

[Function] Instead of using two substrates, a single substrate 1, thin cover layer 5 and buffer layer 3 are used as shown in FIG. The thickness can be reduced.

According to the manufacturing method shown in FIG. 1(B), the optical disc shown in FIG. 1(A) is manufactured by forming a recording layer on the substrate 1 and the cover layer 5 in the same manner, and then bonding them together. can do.

The cover layer 5 may have a thickness sufficient to maintain accuracy during the manufacturing process.

In the manufacturing method shown in FIG. 1(C), one substrate 1
Since a laminated structure is sequentially created on the substrate, the thickness of each layer on the substrate can be made sufficiently uniform.In addition, in the process of creating the second recording layer 4, If they are already created on the same substrate, the accuracy of centering etc. can be improved.

When using an optical disc as shown in FIG. 1(A), writing and reading are performed on the first recording layer 2 using light that has passed through the substrate 1, but light to the second recording layer 4 does not pass through the substrate. Since the cover layer 5 is extremely thin compared to the substrate 1, a lens with a small aperture can be used.

[Embodiment] FIG. 3 shows a cross-sectional view of an optical disk according to an embodiment of the present invention. A substrate 21 made of transparent polycarbonate has a thickness of about 1.5 mm.
It is 2 ml. Terbium (T) is placed on one side of this substrate 21.
b) The first recording layer 22 is formed of a magneto-optical recording layer of /iron (Fe) and /7 balt (Co) (composition ratio 21 near 1:8).

On the other hand, bits representing information to be recorded are formed on one side of a sheet 25 made of transparent plastic such as PMMA,
A reflective film such as an aluminum film is formed thereon to form the second recording layer 24.

In this way, the substrate 21 on which the recording layer is not formed and the sheet 25 are placed so that the recording layers are butted against each other, and the adhesive layer 23 is placed between them and bonded together.

Here, the sheet 25 has a thickness of about 200 μm to withstand, for example, a reflective film forming process, and the adhesive layer 23 has a thickness of about 2.30 μm.

Further, the first and second recording layers 22,24 have a thickness of 1 μm or less. In other words, the total thickness of the optical disc is
It is defined by the thickness of the substrate 21 and the sheet 25,
1.2+0.2=about 1.41m. According to the conventional symmetrical laminated structure, the thickness is approximately 1.2X2=2.4
11, the nonlinear structure described above can reduce the thickness by about 1.

In the case of this embodiment, the first recording layer 22 is a magneto-optical recording layer, and can perform writing and reading. The second recording layer is an aluminum layer formed on the pits by vapor deposition, sputtering, etc., and is read-only.

Since the sheet 25 is extremely thin compared to the substrate 21, even if the same clearance is set between the sheet and the lens, the second
The objective lens can be placed closer to the recording layer 24, and the aperture of the objective lens can be reduced. However, when dust or the like adheres to the surface of an optical disk, if the diameter of the light beam is large, it is less susceptible to the influence of dust, but if the diameter of the light beam itself is made small, the influence of dust becomes easier. In the case of writing, if the intensity of the light beam decreases, writing itself may become impossible, whereas in the case of reproduction, the intensity of the light beam decreases due to the presence of dust, etc. However, the optical intensity of the signal only decreases, and it is often not difficult to read out the information.

FIG. 4 shows an optical disk according to another embodiment of the present invention. Forming a first recording layer 22 of a magneto-optical recording material on a substrate 21 of polycarbonate or the like is the same as in the embodiment of FIG. It is. A second recording layer 24 is formed on the sheet 25, and contrary to the case shown in FIG. do.

In this case, since the second recording layer 24 is exposed on the surface, the surface is covered with a cover layer 26 to protect the second recording layer 24. The sheet 25 needs to have a certain thickness to prevent deformation etc. when forming the second recording layer. In contrast, since the cover layer 26 only needs to protect the second recording layer 24, it can be made thinner than the sheet 25. For this reason, in the structure of FIG. 3, the thickness of the cover layer 26 corresponding to the cover layer composed of the sheet 25 is reduced,
A second recording layer is provided nearer to the second recording layer than in the embodiment of FIG.
This makes it possible to arrange several optical heads.

In the structure shown in FIG. 4, the adhesive layer 23 and the sheet 25
It is also possible to use a structure in which these are integrated. That is,
After forming the first recording layer 22 on the substrate 21, a layer of, for example, photocurable plastic is applied thereon. After forming pits to record information in this plastic layer,
The plastic is cured by irradiation with light, a light reflective film such as an aluminum film is formed thereon, and finally a cover layer 26 is formed.

If the layers are formed sequentially on one surface of the substrate 21 in this way, the configuration is simpler, and the second recording layer 24 can be created while being aligned with the first recording layer 22. You can also do it. Further, since the sheet 25 is substantially unnecessary, it is also possible to further reduce the thickness of the entire optical disc.

Above, we have described an asymmetric double-sided optical disk that has a write/read recording layer consisting of one magneto-optical recording layer, one aluminum reflective layer, etc., and a read-only recording layer. For example, it is possible to use a magneto-optical recording layer, or both layers can be read-only layers.

In these cases, the structure is also of non-compatible type.

FIGS. 5A and 5B are diagrams for explaining the influence that the thickness of the substrate has on the size of the head.

FIG. 5(A) shows the case where the recording layer is irradiated with a light beam that has passed through the substrate.
2 is formed, and the laser beam 33 is transmitted through the substrate 21.
Let us consider that the light is focused and irradiated by the lens 31.

In order to obtain a small light spot on the first recording layer 22,
The angle θ requires a certain value.

Assuming that the thickness of the substrate 21 is d, while the light beam passes through the substrate 21, the light beam expands according to the number of holes therebetween.4 This expanding light beam is further passed through the lens 31 through the gap between the substrate and the lens. Receive it at

Therefore, the lens 31 is separated from the recording layer 22 by a distance d+f1M, and its aperture becomes large.

FIG. 5(B) shows readout when the second recording layer 24 is formed on the surface of the substrate 21, the cover layer is omitted, and a numerical aperture equivalent to that of FIG. 5(A) is required. Even so, the predetermined clearance 9 between the second recording layer 24 and the lens 32 is sufficient. Therefore, recording layer 2
The laser beam focused on 4 is about the same as lens 32! and has a smaller diameter. Therefore, a lens with a small diameter can be used as the lens 32.

An optical system that handles a laser beam with a large diameter requires large optical components such as a lens with a large diameter, making the entire head large. The larger the head, the greater the weight.
Moving at high speeds becomes a nuisance. An optical head that handles a laser beam with a small diameter can be constructed by using small optical parts such as a lens 32 with a small diameter, and the overall size of the head can be reduced and its weight can be reduced. Therefore, it is possible to speed up the read operation itself.

FIG. 6 shows an optical disk device according to another embodiment of the present invention. The optical disk 30 has a magneto-optical recording film on a substrate 21, and an aluminum reflective film with pit-shaped recorded information formed near the upper surface thereof. It has a read-only recording layer. In order to read/write to and read from these recording layers, a large-diameter lens 3 is installed below the optical disc 30.
A first head 38 having an optical disc 3 is disposed, and a first head 38 having a
A second head 39 having a small diameter lens 32 is placed above the lens 0 . These first and second heads 38, 39 are connected to a read/write circuit 41 and a read circuit 42, respectively.

For example, assume that 10 grams of the system is recorded on the read-only recording layer and data is recorded on the magneto-optical recording layer. With such a configuration, a large amount of data can be handled on one optical disc. Further, since the weight of the second head 39 can be reduced, it is possible to operate it at high speed, and it is possible to improve the reading speed of the system.

Although the present invention has been described above with reference to the embodiments, it will be obvious to those skilled in the art that the present invention is not limited to these, and that, for example, various modifications, improvements, combinations, etc. can be made.

[Effects of the Invention] As explained above, according to the present invention, it is possible to downsize a double-sided optical disc.

A manufacturing method for manufacturing such a double-sided optical disc is provided.

An optical disc device using such an optical disc is provided.

[Brief explanation of drawings]

1(A) to 1(D) are diagrams explaining the principle of the present invention, and FIG. 1(A) is a sectional view showing the structure of an optical disc, and FIG.
B) and (C) are cross-sectional views for explaining the manufacturing method, the first
Figure (D) is a schematic diagram for explaining the optical disc device, Figures 2 (A) and (B) are diagrams showing the conventional technology, and Figure 2 (A) is a cross section showing the structure of a double-sided optical disc. 2(B) is a cross-sectional view showing the structure of a single-sided optical disk, FIG. 3 is a cross-sectional view showing the structure of an optical disk according to an embodiment of the present invention, and FIG. 4 is a cross-sectional view showing the structure of an optical disk according to another embodiment of the present invention. 5(A) and 5(B) are sectional views for explaining the influence of substrate thickness on the head. FIG. 6 is an optical disc device according to another embodiment of the present invention. FIG. 2 is a schematic block diagram for explanation. In the figure: 11.14 12.15 7 9 1 2 3 4 Substrate First recording layer Buffer layer Second recording layer Cover layer Lens with large aperture Lens with small aperture First head Second head Substrate Recording Layer Adhesive layer Cover layer Substrate First recording layer Adhesive layer Second recording layer 5 6 0 1 2 3 4 8 9 1 2 Sheet cover layer Optical disk Large diameter lens Small diameter lens Large diameter laser beam Small diameter Laser beam 1st head 2nd head Read/write circuit Readout circuit (A) Structure of optical disk FIG. 1 (Part 1) (A) Double-sided optical disk (B) Single-sided optical disk Optical disk according to the embodiment FIG. 3 Others Optical disk according to the embodiment Figure 4 OGo 01- to σ attack

Claims (1)

[Scope of Claims] (1) A transparent substrate (1) made of a transparent material, having physical support, having a predetermined thickness, and having first and second opposing surfaces; The first recording layer formed on the second surface of the transparent substrate (
2); a buffer layer (3) formed on the first recording layer; a second recording layer (4) disposed on the buffer layer; An optical disc comprising a transparent cover layer (5) disposed on the recording layer and having a thickness less than half the predetermined thickness of the transparent substrate. (2) A method for manufacturing an optical disc according to claim 1, comprising: forming the first recording layer (2) on the transparent substrate (1); and forming the first recording layer (2) on the transparent cover layer (5). a step of forming the second recording layer (4), a first recording layer (2) on the transparent substrate (1) and a second recording layer (4) on the cover layer (5); The buffer layer (3)
A method for manufacturing an optical disc, comprising: a step of bonding the disc together via a . (3) A method for manufacturing an optical disc according to claim 1, comprising: forming the first recording layer (2) on the transparent substrate (1); a step of forming the buffer layer (3) on which the second recording layer (4) is placed; a step of forming the second recording layer (4); and a step of forming the second recording layer (4). (4) forming the cover layer (5) thereon; and a method for manufacturing an optical disc. (4) The step of forming a buffer layer (3) on which the second recording layer (4) is placed is a step of forming the buffer layer (3) on the first recording layer (2). 4. The method of manufacturing an optical disc according to claim 3, comprising the steps of: and forming the second recording layer (4) thereon. (5) An optical disc device for using the optical disc according to claim 1, comprising: an accommodation space for accommodating the optical disc; and a side facing the first surface of the transparent substrate (1) of the optical disc to be accommodated. a first head (8) arranged on the side facing the transparent cover layer (5) of the optical disc to be accommodated, the first head (8) including a lens (6) having a relatively large aperture; and a second head (9) including a lens (7) having a small aperture.