JPH11195244A - Optical recording medium and recording/reproducing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording medium capable of effectively removing organic dirt stuck to the surface of a substrate and preventing the increase of jitter, and high in reliability. SOLUTION: A protective layer 8 and a titanium oxide layer 9 having light absorption edge in a 400 to 850 nm wavelength region are successively laminated on the surface of the laser light beam incident side of a transparent substrate 2. Then, an optical recording medium 1 is formed by joining layers in which an under dielectric layer 3, a recording layer 4, an upper dielectric layer 5, a reflection layer 6 and a lacquer layer 7 are laminated on the opposite side of the laser light beam incident side of the substrate 2 in this order while the layers 7 are opposed to each other through an adhesive layer 10.

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 recording and / or reproducing information by using a laser beam, and a method for recording / reproducing the same. The present invention relates to an optical recording medium capable of efficiently removing organic stains therein, such as a fingerprint, and a recording / reproducing method of the optical recording medium.

[0002]

2. Description of the Related Art In recent years, research on optical recording media has been actively conducted. This optical recording medium can perform recording / reproduction in a non-contact manner, so that it is more resistant to dust, dust, fingerprints, and the like than a magnetic recording medium. It has a number of advantages, such as being compatible with read-only, write-once, and rewritable memory types, and can be applied to a wide range of applications as a method for realizing inexpensive large-capacity files. At present, the demand for optical recording media having higher density has increased,
Various methods are being studied to achieve this.

As an effective means for increasing the density of an optical recording medium, a short-wavelength laser beam is used to make the spot diameter of a laser beam used for recording and reproduction smaller, and a numerical aperture (NA: Numerical) is used. Apertur
There is a method of recording and reproducing minute pits at a high density by using a large objective lens e). For example, CDs (Compact Disks) that are currently spreading are 780n
m near the laser wavelength, DV is expected to spread in the future
D (Digital Video Disk) is 650
It is anticipated that a laser wavelength near nm will be used, and a laser wavelength near 410 nm will be used for an optical recording medium expected to be put to practical use in the future.

[0004] By the way, the substrate used for the optical recording medium is a resin or glass such as polycarbonate, 2P (photopolymer), polymethyl methacrylate, etc., which is transparent to the irradiated laser beam and easy to copy. Is used. Particularly, polycarbonate having excellent thermal and mechanical properties is widely used. However, resin is easily charged because it is an insulator. When the optical recording medium is charged, minute dust and dirt adhere to the laser light incident side of the optical recording medium due to static electricity and hinder recording / reproducing of information. As described above, a high-density optical recording medium that performs recording / reproduction with a minute spot, which is currently under study,
The influence of dust, dirt, fingerprints, scratches, etc. on the recording / reproducing of information may be greater than ever.

At present, for the purpose of preventing charging of an optical recording medium, it has been proposed to provide an antistatic film or a transparent conductive film on the surface of the optical recording medium on the laser light incident side. Furthermore,
Organic dirt such as dust and fingerprints chemically attached to the substrate surface
A method of wiping with a cloth or the like has also been proposed. However, the method of providing an antistatic film or a transparent conductive film has a problem that the effect on organic stains such as fingerprints is not always sufficient. Further, in the case of a method of wiping with a cloth or the like, since the polycarbonate substrate or the like has a low surface hardness, the substrate is easily damaged, and there is a possibility that information recording / reproduction may be hindered.
There was an issue that was not always enough.

In such a situation, Japanese Patent Application Laid-Open No. 9-180253 discloses a method for removing organic stains (fingerprints and the like) mainly composed of human fats and oils on a substrate constituting an optical recording medium. Thickness 0.01 ~
There has been proposed an optical recording medium in which a thin film of silicon oxide having a thickness of 3.0 μm is provided and a titanium oxide thin film having a thickness of 0.05 to 10 μm is provided outside the silicon oxide thin film.

In this method, the surface of an optical recording medium is cleaned by utilizing the photocatalytic function of titanium oxide to oxidize and decompose fats and oils, which are the main components of a fingerprint, by exposing it to sunlight or the like. The photocatalytic reaction of titanium oxide or the like has been spotlighted as an artificial photosynthesis-type process that can directly convert light energy into chemical energy, and research aimed at practical use has been recently active. In particular, titanium oxide is expected as a photocatalyst closest to practical use in a wide range because of its high activity, stability and non-toxicity.

[0008]

However, titanium oxide has no absorption in the visible light region, and can utilize only ultraviolet rays contained in sunlight at 3 to 5%. For this reason, as described in the official gazette, the conventional optical recording medium described above has a problem in that it has to be exposed to sunlight for more than ten minutes to clean organic dirt, which is inefficient.

The present invention has been made in view of the above-mentioned circumstances, and it is a reliable technique that can efficiently remove dust, dirt, fingerprints, scratches, and the like, especially organic stains, from the surface of a substrate and can prevent an increase in jitter. It is an object to provide an optical recording medium having high performance. It is another object of the present invention to provide a recording / reproducing method for an optical recording medium which uses this optical recording medium to remove organic stain simultaneously with recording / reproduction.

[0010]

Therefore, according to the first aspect of the present invention, in an optical recording medium for recording and / or reproducing information by using a laser beam, a laser beam on a substrate constituting the optical recording medium is used. 400 nm to 850 on the incident side surface
A titanium oxide layer having a light absorption edge in a wavelength region of nm is formed.

In this structure, the titanium oxide layer has a thickness of 350 n.
Since it has sufficient absorption in the visible light wavelength region of m or more, it is possible to remove organic dirt attached to the optical recording medium by visible light contained in half or more of sunlight. As a result, the time for exposure to light such as sunlight can be extremely reduced, the effect of removing organic dirt can be improved, and an increase in jitter can be prevented. still,
The light absorption edge of the titanium oxide layer can be controlled by, for example, a dye photosensitization method (B.O'Regan, Nature, 357, 73).
7 (1991) and ion implantation (Takeuchi et al., Catalyst, 36,
157 (1994) or the like.

It is preferable that the wavelength of the laser light is shorter than the wavelength of the light absorption edge of the titanium oxide layer. According to such a configuration, by irradiating a laser beam used for recording / reproduction, it is possible to remove organic stains, and to perform recording and / or reproduction.
Alternatively, organic dirt can be removed simultaneously with regeneration.

According to a third aspect of the present invention, when a protective layer made of an inorganic substance substantially transparent to the laser beam is provided between the substrate and the titanium oxide layer, the substrate can be made of resin or the like. In the case of the organic substance, the substrate can be protected from the photocatalytic reaction of titanium oxide. Further, when the substrate is glass, it is possible to prevent the function of titanium oxide from lowering due to the diffusion of Na in the glass.

According to the fourth aspect of the present invention, the optical recording medium according to the second or third aspect is irradiated with a laser beam so that the titanium oxide layer exhibits a photocatalytic function simultaneously with recording and / or reproduction. And a recording / reproducing method for an optical recording medium.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the optical recording medium according to the present invention will be described. FIG. 1 is a cross-sectional view illustrating a configuration example of the optical recording medium according to the present embodiment. FIG. 1 shows an example of a phase change type optical recording medium using a phase change type recording material for a recording layer in this embodiment. A lower dielectric layer 3, a recording layer 4, an upper dielectric layer 5, a reflective layer 6, and a lacquer layer 7 are formed in this order on the opposite side of the transparent substrate 2 from the laser beam incident side. On the light incident side,
A protective layer 8 and a titanium oxide layer 9 having a light absorption edge in a wavelength region of 400 nm to 850 nm are laminated in this order. The two optical recording media thus formed were joined via an adhesive layer 10 with the lacquer layer 7 side facing each other to form an optical recording medium 1 for double-sided recording.

The titanium oxide layer 9 is generally formed by a sputtering method, a vacuum evaporation method, a plasma CVD method, a photo CVD method, an electron beam evaporation method, a sol-gel method, a spray pyrolysis method,
It is formed by a dip coating method or the like. Although an impurity is added to the titanium oxide layer, the method of addition is not particularly limited. For example, it can be added simultaneously during the formation of the thin film, or the dye photosensitization method or the ion implantation method described above is used. You can also. The most efficient dye used in the dye photosensitization method is a ruthenium complex [Ru
(4,4'-dicarboxyl-2,2'-bipyridine)
₂ (NCS) ₂ ], and the ion to be implanted by the ion implantation method is preferably a metal ion, and more preferably a transition metal ion such as a Cr ion or a V ion. The thickness of the titanium oxide layer 9 is preferably 1000 nm or less,
nm or less is more preferable. This is because the photocatalytic reaction occurs near the surface of the titanium oxide layer, and the effect does not change even if the thickness is 1000 nm or more.

Titanium oxide, which is a semiconductor, strongly absorbs light having a wavelength equal to or shorter than its light absorption edge and is used for a photocatalytic reaction.
Since the light absorption edge of pure titanium oxide to which impurities are not added is at about 380 nm, pure titanium oxide can use only a small wavelength of light of 380 nm or less in visible light (350 nm to 750 nm) for the photocatalytic reaction. In the present invention, an impurity is added to titanium oxide to shift the light absorption edge to a longer wavelength side so that the titanium oxide exists at 400 nm to 850 nm. As a result, light in a wider wavelength range of sunlight can be used for a photocatalytic reaction,
The contamination on the optical recording medium surface can be more efficiently removed. Note that a significant effect cannot be expected unless the position of the light absorption edge to which the impurity is added and moved is on the longer wavelength side than 400 nm. Further, the light absorption edge is set to 850 by adding impurities.
Shifting to a longer wavelength side than nm is difficult in principle. When the wavelength of the laser light used for recording and / or reproduction is shorter than the light absorption edge of the titanium oxide layer, the titanium oxide layer also absorbs the laser light and uses it for the photocatalytic reaction. Can be. That is, the laser beam performs recording and / or reproduction of a signal and, at the same time, removes contamination on the surface of the optical recording medium.

As a method for adding impurities, an ion implantation method is a preferable method for the following reasons. Ion implantation is performed by a method in which metal ions are accelerated at a high energy of several hundred keV and implanted into a titanium oxide thin film.
More specifically, the ion implantation is performed. Ion implantation is an indispensable technology in LSI manufacturing, and has the following features that cannot be obtained by other methods.

(1) The impurity concentration and distribution in the depth direction are:
It can be accurately controlled by the ion acceleration voltage, current, and implantation time. (2) The purity of the impurity to be doped is extremely high. (3) Creation of a metastable substance can be expected because arbitrary impurities can be injected in a short time.

(4) A doping pattern according to the mask pattern is possible. The ions to be implanted by the ion implantation method are preferably metal ions as described above, and more preferably Cr ions or V ions. The light absorption region can be arbitrarily changed to some extent depending on the concentration of the metal ions to be implanted. The implantation amount of metal ions is 0.01 × 10 ^{16 to} 100 × 10 ¹⁶ / cm ²
Is preferably 0.1 × 10 ¹⁶ to 30 × 10 ¹⁶ / cm ²
Is more preferred. Moreover, several tens of n
When the ion implantation is performed so as to be localized at a depth of m, the efficiency of the photocatalytic reaction increases. When the substrate is glass, the titanium oxide layer can be heat-treated as necessary.

The protective layer 8 is formed for the purpose of protecting the transparent substrate 2 from the photocatalytic reaction of the titanium oxide layer 9 when the transparent substrate 2 is an organic substance such as a resin, and when the transparent substrate 2 is glass. It is formed for the purpose of preventing the function of titanium oxide from lowering due to the diffusion of Na in the glass. The protective layer 8 is preferably made of an inorganic material that is substantially transparent to the light beam used, and specific examples include, for example, SiO, SiO ₂ , ZnO,
_{A1 2 0 3, SnO 2,} In 2 0 3, MgO, ZrO 2
Metal oxides such as Si ₃ N ₄ , AIN, BN, TiN,
Nitrides such as ZrN, sulfides such as ZnS, In ₂ S ₃ and TaS ₄ , SiC, TaC, WC, TiC, ZrC, B ₄
Carbides such as C and diamond-like carbon.
These materials can be used alone or as a mixture of two or more materials. Further, it may contain impurities as needed. The protective layer 8 can be formed by a sputtering method, a vacuum evaporation method, a plasma CVD method, a photo CVD method, or an electron beam evaporation method. The thickness of the protective layer 8 is 5
It is preferably about 1000 nm, more preferably 10 nm to 100 nm. When the thickness is less than 5 nm, the transparent substrate 2 is directly affected by the photocatalytic reaction of the titanium oxide layer 9, and the effect of the protective layer does not change even when the thickness is more than 1000 nm.

Next, components other than the titanium oxide layer 9 and the protective layer 8 will be described. The transparent substrate 2 is preferably made of a material that is transparent to the light beam to be used, for example, a resin or glass, and is particularly preferably a resin because it is easy to handle and inexpensive. Specifically, for example, polycarbonate, 2P, polymethyl methacrylate, or the like is used as the resin. The shape and dimensions of the substrate are not particularly limited, but are usually disk-shaped, and the thickness is usually about 0.5 to 3 mm, and the diameter is 40 to 360 m.
m. A predetermined pattern such as a groove is provided on the surface of the transparent substrate 2 as needed for tracking, addressing, and the like.

The lower dielectric layer 3 and the upper dielectric layer 5 are provided as a heat radiation layer for multiple interference of incident light and heat accumulated in the recording layer 4 during recording. The material is the same as that of the protective layer 8. , Oxides, nitrides, sulfides, carbides, etc. alone or in a mixture. The thickness of the lower dielectric layer 3 is 50 to 300.
nm, and the thickness of the upper dielectric layer 5 is 10-25.
It is about 0 nm.

The recording layer 4 is preferably made of an Au-In-Sb-Te alloy, an Ag-In-Sb-Te alloy, a Ge-Sb-Te alloy or the like, but is not limited thereto. The thickness of the recording layer 4 is about 10 to 200 nm. The reflection layer 6 is provided as a layer for reflecting incident light and as a heat radiation layer, and may be made of a highly reflective metal such as Al, Au, Ag, Pt, Cu, or a simple substance or an alloy containing at least one of these. The thickness of the reflection layer 6 is about 30 to 300 nm.

The lacquer layer 7 is provided for improving abrasion resistance and corrosion resistance, and is preferably composed of various organic substances. It is preferable to be composed of an organic material cured by radiation such as an electron beam and ultraviolet rays. The thickness of the lacquer layer 7 is usually about 0.1 to 100 μm, and may be formed by a usual method such as spin coating, gravure coating, or spray coating.

The adhesive layer 10 is desirably composed of various organic substances. The adhesive layer 10 is formed by curing a thermoplastic substance, an adhesive substance, a radiation-curable compound or a composition thereof by radiation such as an electron beam or ultraviolet rays. It is preferable that the organic material is made of an organic material. The thickness of the adhesive layer 10 is 0.1 to 100 μm
It may be formed by an optimum method selected according to the material constituting the adhesive layer 10, for example, spin coating, gravure coating, spray coating, roll coating, or the like.

According to the optical recording medium having such a configuration, 400
Since the titanium oxide layer 9 having a light absorption edge in the wavelength region of 850 nm to 850 nm is provided, the photocatalytic function of titanium oxide is exhibited by visible light contained in half or more of sunlight, and the optical recording medium 1
Organic dirt (fingerprints and the like) adhered to the surface can be efficiently oxidized and decomposed. For this reason, the exposure time to sunlight is shorter than that of the conventional one. In addition, when the wavelength of the laser beam used for recording and / or reproduction is shorter than the wavelength of the light absorption edge of the titanium oxide layer, the titanium oxide layer 9 can be used even during recording or reproduction by irradiation with the laser beam. Organic dirt on the surface of the optical recording medium 1 can be removed. Therefore, when recording or reproducing information, organic dirt can be decomposed and removed at the same time, which is extremely efficient. Thus, it is possible to prevent an increase in jitter due to dust, dirt, fingerprints, scratches and the like, especially fingerprints (organic stains), and to obtain the optical recording medium 1 with high reliability. Further, by providing the protective layer 8, it is possible to prevent the transparent substrate 2 from being adversely affected by the photocatalytic reaction of the titanium oxide layer 9, thereby further improving the reliability of the optical recording medium 1.

In this embodiment, the phase change type optical recording medium has been described as an example. However, the present invention is not limited to this, and various types such as a read-only type, a write-once type, and a rewritable type are available. Can be applied to the optical recording medium. [Examples and Comparative Examples] Next, the present invention will be described in more detail with reference to specific examples of the present invention. However, these examples do not limit the present invention in any way.

(Example 1) Diameter 120 mm, thickness 0.6
2 polycarbonate with mm land / groove
Oxidation as a protective layer 8 on the laser beam incident side of the
Silicon to 100 nm thickness, titanium oxide thin film to 100 nm
Thickness, and then 200k
12 × 10 Cr ions using an eV ion implanter¹⁶
Pieces / cm^TwoInjected and has light absorption edge at light wavelength 500nm
A titanium oxide layer 9 was formed. Further, the laser light of the substrate 2
On the side opposite to the incidence side, Z
nS-SiO_Two(SiO_Two: 20 mol%) to 140 n
m-thick Au—In—Sb—Te alloy as the recording layer 4
25 nm thick, ZnS-SiO as the upper dielectric layer 5 _Two
(SiO_Two: 20 mol%) to a thickness of 22 nm and a reflective layer 6
To a thickness of 100 nm and a lacquer layer 7 of 10
μm layer in order.
The car layer 7 side is opposed to and joined via the adhesive layer 10,
An optical recording medium 1 having the configuration shown in FIG. 1 was formed. Adhesive layer 1
0 had a thickness of 30 to 50 μm. Land of substrate 2 /
The groove has a track pitch of 0.74 μm and a depth of 70 n.
m.

After the production of the optical recording medium 1, the recording layer 4 was amorphous. For this reason, the recording layer 4 was sufficiently crystallized by a high-output semiconductor laser beam having a wavelength of 810 nm to be in an initialized state. The recording on the optical recording medium 1 thus obtained has a wavelength of 6
By irradiating a 35 nm semiconductor laser beam from the titanium oxide layer 9 side through an objective lens with NA = 0.6 and narrowing down to a spot diameter of about 1 μm on the surface of the recording layer 4,
A random signal of an 8/16 modulation system signal was recorded at a linear velocity of 3.5 m / s. The recording power was 13 mW. The reproduction of the optical recording medium 1 is performed by using a semiconductor laser having a wavelength of 635 nm and a wavelength of 4 nm.
A 20 nm SHG laser was used, and a laser beam was irradiated from the titanium oxide layer 9 side at a linear velocity of 3.5 m / s.
The reproducing power is 1 mW at 635 nm and 1.3 at 420 nm.
mW. Jitter measured the jitter of the random signal using a time interval analyzer.

First, recording was performed on the optical recording medium 1 with a 635 nm semiconductor laser, and reproduction was performed with a 635 nm semiconductor laser. At that time, the jitter of the optical recording medium 1 was 8%. Next, a finger was brought into contact with the laser beam incident side of the optical recording medium 1 on which the recording was made, that is, on the titanium oxide layer 9 with bare hands to adhere a fingerprint and further adhere dust. The fingerprint and dust were combined to make an organic stain. Thereafter, the optical recording medium 1 was reproduced with a 635 nm semiconductor laser, and the jitter was measured. The jitter was 15% on average.

Next, the stained side of the optical recording medium 1 to which the organic stain has adhered is exposed outdoors to sunlight for 5 minutes.
When the data was reproduced with a semiconductor laser of nm and the jitter was measured, the jitter was 8%. This allows
It was found that the organic catalyst can be efficiently removed by the photocatalytic reaction of the titanium oxide layer 9 having a light absorption edge at 500 nm, and an increase in jitter can be prevented.

(Comparative Example 1) An optical recording medium 1 was prepared in the same manner as in Example 1 except that pure titanium oxide into which Cr ions were not implanted was used for the titanium oxide layer. At this time, the light absorption edge of the pure titanium oxide was about 380 nm.
In the same manner as in Example 1, recording was performed on the optical recording medium 1 with a 635 nm semiconductor laser, and reproduction was performed with a 635 nm semiconductor laser, and jitter was measured.
%Met. Further, the jitter of the optical recording medium 1 after the organic stain was attached was 15% on average.

On the other hand, when the optical recording medium 1 to which the organic stain was attached was exposed to sunlight outdoors in the same manner as in Example 1, and the jitter was measured, the jitter remained at 15%, and no improvement was observed. Was. (Example 2) It was produced in the same manner as in Example 1. The optical recording medium 1 to which organic stains were adhered was reproduced with a 420 nm SHG laser, and the jitter was measured. The jitter was 10% on average. That is, by irradiating the 420 nm SHG laser to the optical recording medium 1 to which the organic dirt has adhered,
Jitter was reduced by 5%.

At present, this cannot be performed due to the performance limit of the 420 nm SHG laser. However, if recording is performed on the optical recording medium 1 to which organic dirt is adhered by the 420 nm SHG laser, a stronger power can be applied, and the jitter can be improved. Is expected to be even more promising. As described above, if recording and / or reproduction is performed on the optical recording medium 1 having the titanium oxide layer 9 having a light absorption edge at 500 nm with a laser beam having a shorter wavelength than the light absorption edge, the photocatalytic reaction of the titanium oxide layer 9 can be improved. It was found that organic stains could be removed at the same time. Therefore, according to the optical recording medium 1 of the present embodiment,
Organic dirt can be removed at the same time as recording / reproducing to prevent an increase in jitter.

(Comparative Example 2) A battery was prepared in the same manner as in Comparative Example 1. Optical recording medium 1 to which organic dirt has adhered is 420 nm SH
When reproduction was performed with a G laser and the jitter was measured, the jitter remained at an average of 15%, and no improvement was observed. This is because the wavelength of the 420 nm SHG laser used for reproduction was longer than the wavelength (380 nm) at the light absorption edge of the titanium oxide layer (containing no impurities).

[0037]

As described above, according to the first aspect of the present invention, the surface of the substrate constituting the optical recording medium, on the laser incident side, is doped with an impurity to a wavelength of 400 nm to 850 nm.
Since a titanium oxide layer with a light absorption edge in the wavelength region of nm is formed, organic dirt can be removed by using visible light contained in more than half of sunlight, so that the There is a great effect that the attached organic dirt can be more efficiently removed. Therefore, an increase in jitter can be prevented, and the reliability of the optical recording medium can be improved.

According to the second aspect of the present invention, the organic dirt adhering to the substrate surface can be removed by the laser beam used for recording / reproducing. Therefore, by irradiating a laser beam during recording and / or reproduction of the optical recording medium, organic dirt can be removed simultaneously with recording / reproduction, and the substrate surface can be cleaned very efficiently. Can be

According to the third aspect of the invention, in addition to the effects of the first and second aspects, the substrate can be protected from the photocatalytic reaction of the titanium oxide layer, and the reliability of the optical recording medium can be further improved. Can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of an optical recording medium of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical recording medium 2 Transparent substrate 3 Lower dielectric layer 4 Recording layer 5 Upper dielectric layer 6 Reflective layer 7 Lacquer layer 8 Protective layer 9 Titanium oxide layer 10 Adhesive layer

Claims (4)

[Claims] 1. An optical recording medium for recording and / or reproducing information by using a laser beam, comprising:
An optical recording medium comprising a titanium oxide layer having a light absorption edge in a wavelength region of 400 nm to 850 nm. 2. The optical recording medium according to claim 1, wherein a wavelength of said laser beam is shorter than a wavelength at a light absorption edge of said titanium oxide layer. 3. The optical recording medium according to claim 1, wherein a protective layer made of an inorganic substance substantially transparent to the laser beam is provided between the substrate and the titanium oxide layer. 4. An optical recording medium according to claim 2, wherein the optical recording medium is irradiated with a laser beam so that the photocatalytic function of the titanium oxide layer is simultaneously exhibited during recording and / or reproduction. An optical recording medium recording / reproducing method.