JP2003338080A - Write-once optical recording media - Google Patents

Abstract

(57) [Problem] An organic material capable of coping with a blue laser wavelength region, capable of using a shallow groove substrate having good transferability, and having little change in recording characteristics and reflectivity with respect to a change in recording / reproducing wavelength. Provision of write-once optical recording media using materials. SOLUTION: (1) A photocatalyst layer made of a material exhibiting photocatalytic activity is provided on a substrate, and a main absorption band at the time of non-recording exists on a longer wavelength side with respect to a recording / reproducing wavelength. A write-once optical recording medium having a structure in which an organic material layer having no light absorbing function is laminated adjacently in this order or in reverse order. (2) At least a photocatalytic layer made of a material exhibiting photocatalytic activity on the substrate and a main absorption band at the time of non-recording exist on the longer wavelength side with respect to the recording / reproducing wavelength, and absorb light at the recording / reproducing wavelength. An organic material layer having no function is laminated adjacently in this order or reverse order, and further has a structure in which a light-transmitting cover layer is laminated thereon, and recording / reproduction is performed from the cover layer side Write-once optical recording medium.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a write-once type (WOR
M: Write Once Read Many) optical recording medium, and more particularly to a write-once type optical recording medium capable of high density recording even in a blue laser wavelength region of about 350 to 500 nm.

[0002]

2. Description of the Related Art Development of a blue laser capable of recording at an extremely high density is rapidly progressing, and a write-once type optical recording medium corresponding to it is being developed. In the conventional write-once type optical recording medium, a recording pit is formed by irradiating a recording layer made of an organic material with a laser beam to cause a change in the refractive index mainly due to the decomposition and alteration of the organic material. The optical constants and decomposition behavior of the organic material used are important factors for forming good recording pits. Therefore,
As the organic material used for the recording layer, it is necessary to select a material having appropriate optical properties and decomposition behavior with respect to the blue laser wavelength. That is, in order to increase the reflectance at the time of non-recording and to cause the organic material to be decomposed by laser irradiation to cause a large change in the refractive index (which results in a large modulation degree), the recording / reproducing wavelength has a large absorption band. It is selected to be located at the bottom of the long wavelength side.

This is because the skirt on the long wavelength side of the large absorption band of the organic material is a wavelength region where an appropriate absorption coefficient and a large refractive index are obtained. However,
No organic material has yet been found that has a conventional optical property with respect to a blue laser wavelength. This is because in order to obtain an organic material having an absorption band near the blue laser wavelength,
This is because it is necessary to make the molecular skeleton smaller or the conjugated system shorter, which causes a decrease in absorption coefficient, that is, a decrease in refractive index. That is, there are many organic materials having an absorption band near the wavelength of the blue laser, and it is possible to control the absorption coefficient, but since it does not have a large refractive index, it becomes impossible to obtain a large modulation degree.

As an organic material compatible with a blue laser, for example, Japanese Patent Laid-Open Nos. 2001-181524 and 2001-1 are available.
58865, JP 2000-343824 A, JP 2
000-343825, JP-A-2000-335110.
There is a description in each publication. However, these publications only measure the spectra of the solution and the thin film even in the examples, and there is no description regarding recording and reproduction. Japanese Patent Laid-Open No. 11-22
1964, JP-A-11-334206, JP-A-200
In each of JP-A No. 0-43423, although the recording is described in the example, the recording wavelength is 488 nm, there is no description about the recording condition and the recording density, and there is only a description that a good recording pit can be formed. Is. Japanese Patent Laid-Open No. 11-58
In the Japanese Patent Publication No. 955, although there is a record of the example,
The recording wavelength is 430 nm, and there is no description about recording conditions or recording density, but only a description that a good modulation degree is obtained.

Japanese Patent Laid-Open Nos. 2001-39034 and 200
0-149320, JP-A-2000-113504,
JP-A-2000-108513, JP-A-2000-222
772, JP-A-2000-218940, JP-A-200
0-222771, JP-A-2000-158818,
JP-A-2000-280621, JP-A-2000-280
In each publication of No. 620, the recording wavelength is 430 nm, N
There is a recording example with A0.65, but the shortest pit is 0.4μ.
It is a low recording density condition of m (recording density equivalent to DVD). In Japanese Patent Laid-Open No. 2001-146074, the recording / reproducing wavelength is 405 to 408 nm, but there is no specific description regarding the recording density, which is a low recording density condition of recording 14T-EFM signals.

Further, the following techniques have been disclosed regarding the layer structure and recording method different from those of the conventional CD and DVD type optical recording media. Japanese Unexamined Patent Publication No. 7-304258 discloses a technique of recording by changing the extinction coefficient (absorption coefficient in the present invention) of a saturable absorbing dye with a layer structure of substrate / saturable absorbing dye containing layer / reflection layer. It is disclosed. Japanese Patent Application Laid-Open No. 8-83439 discloses a technique in which recording is performed by discoloring or deforming a metal vapor deposition layer by heat generated by the light absorption layer, which has a layer structure of substrate / metal vapor deposition layer / light absorption layer / protective sheet. Is disclosed. JP-A-8-1
Japanese Patent No. 38245 discloses a technique of performing recording by changing the depth of the groove portion by changing the film thickness of the recording layer in a layer structure of a substrate / dielectric layer / recording layer including a light absorber / reflection layer. ing.

Japanese Unexamined Patent Publication (Kokai) No. 8-297838 discloses a layer structure of a substrate / a recording layer including a light absorber / a metal reflective layer.
A technique for recording by changing the film thickness of the recording layer by 10 to 30% is disclosed. JP-A-9-198714
Japanese Patent Laid-Open Publication No. 2003-242242 discloses a technique of recording by increasing the groove width of the substrate by 20 to 40% with respect to an unrecorded portion in a layer structure of substrate / recording layer containing organic dye / metal reflective layer / protective layer. It is disclosed. In Japanese Patent No. 2506374,
There is disclosed a technique in which recording is performed by forming a bubble by deforming a metal thin film with a layer structure of substrate / intermediate layer / metal thin film. Japanese Patent No. 2591939 discloses a substrate /
Disclosed is a technique of performing recording by deforming the recording auxiliary layer into a concave shape and deforming the light reflecting layer into a concave shape along with the deformation of the recording auxiliary layer with a layer structure of a light absorbing layer / a recording auxiliary layer / a light reflecting layer. Has been done.

Japanese Patent No. 2591940 discloses a substrate /
The layer structure of light absorption layer / porous recording auxiliary layer / light reflection layer or substrate / porous recording auxiliary layer / light absorption layer / light reflection layer transforms the recording auxiliary layer into a concave shape and also assists recording. A technique is disclosed in which recording is performed by deforming the light reflecting layer into a concave shape along with the deformation of the layer. Patent No. 259194
Japanese Patent Laid-Open Publication No. 1-1990 discloses a substrate / porous light absorbing layer / light reflecting layer having a layered structure in which the light absorbing layer is deformed into a concave shape and the light reflecting layer is deformed into a concave shape along with the deformation of the light absorbing layer. A technique for recording is disclosed in. Patent No. 298292
No. 5 discloses a layer structure of a substrate / a recording layer containing an organic dye / a recording auxiliary layer, in which the recording auxiliary layer and the organic dye are compatible with each other,
A technique for recording by shifting the absorption spectrum of the organic dye to the short wavelength side is disclosed.

Japanese Patent Laid-Open No. 9-265660 discloses that a composite functional layer having a function of a reflection layer and a recording layer and a protective layer are sequentially formed on a substrate, and the substrate and the composite functional layer form bumps. A technique for recording is disclosed in. The composite function layer is defined as a metal such as nickel, chromium, or titanium, or an alloy thereof. JP-A-10
JP-A-134415 discloses a layer structure in which a metal thin film layer, a deformable buffer layer, a reflective layer, and a protective layer are sequentially formed on a substrate. A technique for recording by reducing the film thickness is disclosed. The metal thin film layer is defined as a metal such as nickel, chromium, or titanium, or an alloy thereof. Further, it is described that a resin that is easily deformed and has an appropriate fluidity is used as the buffer layer, and that a dye may be added to accelerate the deformation.

Japanese Unexamined Patent Publication (Kokai) No. 11-306591 discloses a layer structure in which a metal thin film layer, a buffer layer, and a reflective layer are sequentially laminated on a substrate to deform the substrate and the metal thin film layer, and at the same time, the buffer layer in the deformed portion. A technique for recording by changing a film thickness and an optical constant is disclosed. In addition, it is described that the metal thin film layer is preferably a metal such as nickel, chromium, or titanium, or an alloy thereof. The buffer layer is made of a mixture of a dye and an organic polymer, and a dye having a large absorption band near the recording / reproducing wavelength is used. Japanese Patent Laid-Open No. 10-12
Japanese Patent No. 4926 discloses a layer structure in which a metal recording layer, a buffer layer, and a reflective layer are sequentially laminated on a substrate, and the substrate and the metal recording layer are deformed, and at the same time, the buffer layer film thickness and the optical constant at the deformed portion are described. A technique of recording by changing the information is disclosed. In addition, it is described that a metal such as nickel, chromium, or titanium, or an alloy thereof is preferable for the metal recording layer. The buffer layer is made of a mixture of a dye and a resin, and a dye having a large absorption band near the recording / reproducing wavelength is used.

As described above, the above-mentioned various prior arts are not aimed at the realization of the write-once type optical recording medium in the blue laser wavelength region, and are not the layer structure and recording method effective in the blue laser wavelength region. . Particularly, in the vicinity of 405 nm which is the center of the oscillation wavelength of the blue semiconductor laser which is currently put into practical use, most organic materials have optical constants similar to those required for the recording layer of the conventional write-once type optical recording medium. It doesn't exist. In addition, there is no example in which the recording condition is clarified in the vicinity of 405 nm and the recording density is higher than that of the DVD. Furthermore, many of the examples in the above-mentioned conventional art are experiments with a conventional disk configuration (see FIG. 1), and although a configuration different from the conventional disk configuration has been proposed, the dye used therein is The same optical characteristics and functions as in the past are required, and there is no effective proposal for the layer structure, recording principle, and recording method that can easily realize the write-once type optical recording medium made of an organic material in the blue laser wavelength region.

Further, in the write-once type optical recording medium using a conventional organic material, from the viewpoint of securing the degree of modulation and the reflectance, a large refractive index and a relatively small absorption coefficient (0.
Only organic materials having a thickness of about 05 to 0.07) can be used. That is, since the organic material does not have sufficient absorption ability for recording light, it is impossible to reduce the film thickness of the organic material. Therefore, it is necessary to use a substrate having a deep groove. (Since the organic material is usually formed by a spin coating method, the organic material was buried in a deep groove to form a thick film). Therefore, it becomes very difficult to form a substrate having a deep groove, which has been a factor of deteriorating the quality of the write-once type optical recording medium. Further, in a write-once type optical recording medium using a conventional organic material, the main absorption band of the organic material exists near the recording / reproducing wavelength, so that the wavelength dependence of the optical constant of the organic material increases (the optical constant depends on the wavelength. The problem is that the recording characteristics such as recording sensitivity, modulation degree, jitter, and error rate, and the reflectivity change greatly with respect to changes in the recording / reproducing wavelength due to individual differences in lasers and changes in environmental temperature. was there.

[0013]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems of the prior art and to realize a write-once type optical recording medium having the following characteristics. (A) A write-once type optical recording medium having an organic material layer and capable of high density recording, which can easily perform recording / reproduction even in a blue laser wavelength region (about 350 to 500 nm), particularly in a wavelength region near 405 nm. (B) A write-once type optical recording medium having an organic material layer that allows easy recording and reproduction even on a shallow groove substrate having good transferability. (C) A write-once type optical recording medium in which the recording characteristics such as recording sensitivity, modulation degree, jitter, and error rate, and the change in reflectance and the like are small with respect to changes in the recording / reproducing wavelength.

[0014]

[Means for Solving the Problems] The above problems are solved in the following 1) to
This is solved by the invention 9) (hereinafter, referred to as the present inventions 1 to 9). 1) At least a photocatalyst layer made of a material exhibiting photocatalytic activity on the substrate, and a main absorption band at the time of unrecording exists on the long wavelength side with respect to the recording / reproducing wavelength, and absorbs light with the recording / reproducing wavelength. A write-once type optical recording medium, which has a structure in which an organic material layer having no function is adjacently laminated in this order or in the reverse order. 2) At least a photocatalyst layer made of a material exhibiting photocatalytic activity and a main absorption band at the time of non-recording exist on the long wavelength side with respect to the recording / reproducing wavelength on the substrate, and have an absorbing function for the light of the recording / reproducing wavelength. A write-once type optical recording medium having a structure in which an organic material layer not having a layer is laminated adjacently in this order or in the reverse order, and a reflective layer is further laminated thereon. 3) At least a photocatalyst layer made of a material exhibiting photocatalytic activity and a main absorption band at the time of unrecording are present on the long wavelength side of the recording / reproducing wavelength on the substrate, and have an absorption function for light of the recording / reproducing wavelength. And an organic material layer not having a layer are laminated adjacent to each other in this order or in the reverse order, and a light-transmitting cover layer is further laminated thereon, and recording / reproducing is performed from the cover layer side. A write-once type optical recording medium characterized by: 4) At least the reflective layer on the substrate, the photocatalytic layer made of a material exhibiting photocatalytic activity, and the main absorption band at the time of non-recording are on the long wavelength side with respect to the recording / reproducing wavelength. An organic material layer that does not have a function of absorbing light of a wavelength is laminated in this order or in reverse order adjacently, and further has a structure in which a light-transmissive cover layer is laminated thereon. A write-once type optical recording medium characterized in that recording and reproduction are performed from the side. 5) As an organic material constituting the organic material layer, an organic material which is decomposed by the oxidation action of the photocatalyst layer and has an increased absorption coefficient at a recording / reproducing wavelength is used 1) to
The write-once type optical recording medium according to any one of 4). 6) The write-once type optical recording medium according to 5), characterized in that an organic material having an increased absorption coefficient at a recording / reproducing wavelength of 350 to 500 nm is used. 7) The write-once type optical recording medium according to 5) or 6), wherein the organic material is a dye. 8) The write-once type optical recording medium according to any one of 1) to 7), wherein the photocatalyst layer is made of a material containing an oxide semiconductor or a II-VI group semiconductor as a main component. 9) The write-once type optical recording medium according to 8), wherein the oxide semiconductor is TiO ₂ .

Hereinafter, the present invention will be described in detail. In the present invention, the basic principle of recording is to decompose the organic material in the organic material layer by the oxidation action of the photocatalyst layer and increase the absorption on the short wavelength side of the main absorption band of the organic material. The write-once type optical recording medium of the present invention is conventionally a light absorbing / converting layer (meaning a layer that absorbs light and converts it into other energy. It can be said that it conventionally absorbs light and converts it into heat), Moreover, it is characterized in that the light absorption / conversion function and the recording function of the organic material layer, which functioned as the recording layer due to the change in the refractive index (the real part of the complex refractive index) caused by the decomposition / alteration, are separated. That is, the light absorption / conversion function is removed from the organic material layer, and the photocatalyst layer as the light absorption / conversion layer is provided adjacent to the organic material layer.

In the conventional write-once type optical recording medium, the absorption coefficient at the recording / reproducing wavelength is lowered by decomposition and alteration of the organic material, and the large change in the refractive index is used to generate the modulation factor (see FIG. 10). The arrow below the horizontal axis indicates the recording / reproducing wavelength). On the other hand, in the write-once type optical recording medium of the present invention, by the oxidative decomposition of the organic material by the photocatalyst,
The molecules and molecular groups that compose the organic material are absorbed (increasing the absorption coefficient on the shorter wavelength side than the large absorption band), and the absorption wavelength band of this molecule or molecular group and the recording / reproducing wavelength are By setting so as to overlap, the absorption coefficient at the recording / reproducing wavelength is increased to generate the modulation degree (see FIG. 1).
1). As a result, the organic material layer has no restriction on the refractive index at all, and does not need to have a light absorbing ability with respect to the recording / reproducing wavelength.

The only requirement for the organic material is that it can be reliably decomposed by an oxidizing action and that its decomposition characteristics (decomposition speed, decomposition amount, etc.) are excellent. Therefore, even if recording / reproduction is performed in the blue region, the material of the organic material layer has a large absorption band in the red laser wavelength region and does not have a large absorption band in the blue laser wavelength region, but has excellent decomposition characteristics. Organic materials such as CD-R and DV
A dye for D-R can be used. Also, conventionally,
For wavelength control, it was necessary to use a complicated substituent or a dye having high synthetic difficulty as a recording layer, but such a complicated wavelength control is not necessary in the organic material layer of the present invention, so that the cost is low. It is possible to select cheap organic materials.

Explaining the above recording principle in a little more detail, the organic material used in the present invention is an organic material in which a small molecule or a molecular group is bound, or a complex or association is formed to form a large conjugated system. Therefore, each molecule or group has a large main absorption band on the longer wavelength side than the intrinsic absorption wavelength of the molecule or group (corresponding to the absorption spectra A and B in FIG. 12). Has an absorption spectrum in which the unique absorption band disappears or is attenuated (corresponding to absorption spectrum C in FIG. 13). When λ1 as shown in FIG. 13 is selected as the recording / reproducing wavelength for such an organic material, a large molecule was formed by decomposition of the organic material from the state where absorption at λ1 was small when unrecorded. The intrinsic absorption of molecules and groups increases (see Figure 12), and λ
The absorption at 1 also increases, and the recording portion can be formed by the change of the absorption coefficient. Therefore, a molecule in which only a small molecule or a molecular group is bound and the conjugated system does not form a spread is in the state as shown in FIG. 13, that is, the intrinsic absorption of the molecule or the molecular group. Since the band disappears or decays and a state in which a new large sharp absorption band is formed is not realized, the change in the absorption coefficient before and after recording does not become large, and the recording pit cannot be formed.

Further, in the conventional write-once type optical recording medium, since the organic material layer has both the function of the recording layer and the function of the light absorption / conversion layer, the refractive index n is relatively large and relatively small with respect to the recording / reproducing wavelength. Having an absorption coefficient k is an essential condition for the organic material, and therefore, a relatively thick film thickness is required to reach the temperature at which the organic material is decomposed (also a phase change type write-once type optical recording medium). In contrast, the groove depth of the substrate was very deep). However, in the recording medium of the present invention,
Since the light absorption function and the recording function are separated, the film thickness of the organic material layer can be made thinner than before. In addition, since the organic material layer can be made thinner, it is possible to use a substrate with excellent groove transferability (formability) and a shallow groove depth, which significantly improves the signal quality of the write-once type optical recording medium. In addition to being improved, the substrate can be easily (and cheaply) manufactured (molded) as compared with the conventional one.

Further, the photocatalyst (light absorption) layer of the present invention comprises
Because a material with a normal refractive index can be used, and for the organic material layer, an organic material such as a dye having a large absorption band on the wavelength side sufficiently longer than the recording / reproducing wavelength is used. In the vicinity of the band, the refractive index shows anomalous dispersion and the property that the refractive index varies greatly depending on the wavelength, but in the wavelength region sufficiently distant from the large absorption band, the refractive index shows normal dispersion and the refractive index varies with wavelength. The recording characteristics such as recording sensitivity, modulation degree, jitter, and error rate, and the reflectivity change significantly in response to variations in the recording / reproducing wavelength due to individual differences among lasers and changes in environmental temperature. It is possible to largely solve the conventional problem of doing. In the expression "organic material layer having no absorption function for light having a recording / reproducing wavelength" used in the present invention, "does not have absorption function" means that the organic material layer alone has an optical absorption function. This means that the temperature does not reach such a point that the material itself is decomposed (that is, it means that the material does not substantially perform the absorption function required as the light absorption layer). Therefore, specifically, when the absorption coefficient of the organic material is small,
This refers to the case where the film thickness is thin.

Since the present invention utilizes the recording principle of increasing the absorption on the shorter wavelength side of the main absorption band of the organic material as described above, there is no limitation on the range of the recording / reproducing wavelength. It can be applied to a write-once type optical recording medium corresponding to a wide range of recording / reproducing wavelengths including a red region to a blue region and a region having a shorter wavelength than the blue region. And
To create a medium compatible with a wide range of recording / reproducing wavelengths by selecting an organic material containing molecules or molecular groups having appropriate absorption bands according to the laser wavelength used for recording / reproducing of the target medium. You can However, for the following reasons (1) to (3), it is preferable that the recording / reproducing wavelength range to which the present invention is applied be 500 nm or less (currently, it is 350 in view of the wavelength of usable laser light).
Is about 500 nm). (1) In the wavelength region exceeding 500 nm, the molecular skeleton becomes large, so that there are many materials having excellent decomposition characteristics. (2) The absorption wavelength of the molecule or molecular group generated by the decomposition of the dye should be approximately 500 nm or less. (3) The wavelength at which TiO ₂ or the like used for the photocatalyst layer is sensitive to light and exerts a catalytic function is generally 400 nm or less, and even if an additive is added to make it sensitive to visible light as well. It is considered that a sufficient effect can be obtained at 500 nm or less.

In the present invention, the recording is carried out by utilizing the decomposition of the organic material by the photocatalyst layer to increase the absorption coefficient at the recording / reproducing wavelength of the organic material layer. ) Can also be used for recording auxiliary. However, in this case, it is preferable that the recording due to the deformation of the substrate or the like be the same as the recording polarity (which indicates whether the reproduction signal is lowered or increased by the recording) due to the increase of the absorption coefficient due to the decomposition of the organic material. . The recording polarity due to the deformation of the substrate or the like can be controlled by the groove shape of the substrate, the deformation amount, or the like.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION
A detailed description will be given with reference to the attached drawings. As a substrate material
Has excellent thermal and mechanical properties, and from the substrate side
When recording / reproducing (through the substrate)
There is no special limitation as long as it has excellent properties. Concrete
Examples include polycarbonate, polymethacrylic acid methyl ester.
Polymer, amorphous polyolefin, cellulose acetate,
Polyethylene terephthalate, etc.
Carbonates and amorphous polyolefins are preferred. Board
The thickness depends on the application and is not particularly limited. Photocatalyst layer
As the material of CdS, CdSe, ZnS, ZnS
e, PbS, In_TwoS_Three, Cu_TwoS, MoS_Two, W
S_Two, Sb_TwoS_Three, Bi_TwoS_Three, ZnCdS _Two, WSe
_Two, HgSe, PdSe, CdTe and other II-VI group semiconductors
Body; TiO_Two, ZnO, CdO, WO_Three, Fe_TwoO_Three,
SnO_Two, SrTiO_Three, ZrO_Two, In_TwoO_Three, Ag
_TwoO, MnO_Two, Cu_TwoO, V_TwoO₅Such as oxide semiconductor
Body: Fe, Co, Ni, Cu, Ru, Rh, Pd, A
Transition metals such as g and Pt; porphyrins, phthalocyanines
Metal complexes such as silicon; SiC, GaAs, GaP, Si
(N), Ge (n), etc. are preferred.
Yes. Here, the main component is 50% by weight or more of the entire material.
Means to occupy. The thickness range of the photocatalyst layer is 5 to 20.
0 nm is preferred.

A dye is preferable as a material used for the organic material layer. As the dye, polymethine-based, naphthalocyanine-based, phthalocyanine-based, squarylium-based, croconium-based, pyrylium-based, naphthoquinone-based, anthraquinone (indanthrene) -based, xanthene-based, triphenylmethane-based, azulene-based, tetrahydrocholine-based,
Examples include phenanthrene-based dyes, triphenothiazine-based dyes, and metal complex compounds. For example, the following cyanine dye [Chemical formula 1], which is known to have the decomposition behavior that the methine chain connecting the left and right heterocycles is most easily decomposed and cleaved by oxidation, but the left and right heterocycles remain is suitable for the present invention. It is an example of a dye. Further, the left and right heterocycles of the dye of [Chemical Formula 1] are preferably molecules or molecular groups each having an absorption peak at 350 to 500 nm. As a result, the increase in the absorption coefficient at the time of decomposition becomes large in the blue laser wavelength region, and the signal detection in this region becomes easy. In addition, X, Y, and Z ⁻ in [Chemical Formula 1] represent various substituents or anions contained in a known cyanine dye.

[0025]

[Chemical 1]

The dye layer is formed by vapor deposition, sputtering,
It can be carried out by a usual means such as CVD or solvent coating. When the coating method is used, the dye or the like is dissolved in an organic solvent, spraying, roller coating,
It can be performed by a conventional coating method such as dipping or spin coating. Examples of the organic solvent used include alcohols such as methanol, ethanol and isopropanol; ketones such as acetone, methyl ethyl ketone and cyclohexanone; amides such as N, N-dimethylacetamide and N, N-dimethylformamide; sulfoxides such as dimethyl sulfoxide. Ethers: ethers such as tetrahydrofuran, dioxane, diethyl ether, ethylene glycol monomethyl ether;
Esters such as methyl acetate and ethyl acetate; Aliphatic halogenated carbons such as chloroform, methylene chloride, dichloroethane, carbon tetrachloride and trichloroethane; Aromatic compounds such as benzene, xylene, monochlorobenzene and dichlorobenzene; Methoxyethanol Cellosolves such as ethoxyethanol; hydrocarbons such as hexane, pentane, cyclohexane, and methylcyclohexane. The thickness of the dye layer is 100Å to 10 μm,
It is preferably 100 to 2000Å.

The cover layer is necessary when using a lens having a high NA in order to increase the density. For example, when the NA is increased, it is necessary to reduce the thickness of the portion through which the reproduction light is transmitted. This is because, with the increase in the NA, the angle (so-called tilt) at which the disc surface deviates from the vertical with respect to the optical axis of the optical pickup. Angle, which is proportional to the square of the product of the reciprocal of the wavelength of the light source and the numerical aperture of the objective lens), and the tilt angle is affected by the aberration of the substrate thickness. This is because it is easy. Therefore, in general, the thickness of the substrate is reduced so that the influence of the aberration on the tilt angle is minimized. Therefore, for example, unevenness is formed on a substrate to form a recording layer, a reflective layer is provided thereon, and a light-transmitting cover layer that transmits recording / reproducing light is further provided thereon to reproduce from the cover layer side. A write-once type optical recording medium having a structure capable of reproducing information in a recording layer by irradiating light, or a reflective layer provided on a substrate, a recording layer formed on the reflective layer, and further recording / reproducing on the recording layer. A write-once type optical recording medium having a structure in which a cover layer having a light-transmitting property is provided and information in the recording layer can be reproduced by irradiating reproduction light from the cover layer side has been proposed. . By doing so, it is possible to cope with a higher NA of the objective lens by making the cover layer thinner. That is, by providing a thin cover layer and recording / reproducing from this cover layer side, a higher recording density can be achieved. Incidentally, such a cover layer is generally formed of a polycarbonate sheet or an ultraviolet curable resin.

The principle of recording information on the write-once type optical recording medium according to the present invention will be described below. When a laser having a wavelength of 500 nm or less (light having energy higher than the bandgap energy of the photocatalyst layer) is used as a light source and the optical recording medium is irradiated with power of about 5 to 15 mW, electrons (e ⁻ ) Is excited in the conduction band, holes (h ⁺ ) are formed in the valence band, and the excited state occurs. Taking TiO ₂ as an example, the following reaction proceeds, for example. TiO ₂ + hν → TiO ₂ ^* + e ⁻ + h ⁺ (1) O ₂ + e ⁻ → O ₂ ⁻ (2) H ₂ O + h ⁺ → · OH + H ⁺ … (3) This “O ₂ ⁻ ” or “· OH” Radicals have a strong oxidizing power and oxidize and decompose organic materials. By this decomposition, the organic material is divided into individual molecules or molecular groups that constitute the organic material, and the strength of the absorption band of these individual molecules or molecular groups is increased. At the recording pit formed by laser irradiation, the intensity of the absorption band of each individual molecule or molecular group increases, which causes a large difference in reflectance from the unrecorded area. It becomes possible to detect.

The functions of the components shown in FIGS. 2 to 9 will be described below. FIG. 2 shows an example of a layer structure for realizing a write-once type optical recording medium compatible with a blue laser wavelength, which has a structure in which a photocatalyst layer and an organic material layer are sequentially provided on a substrate. FIG. 3 shows another example, which has a structure in which an organic material layer and a photocatalyst layer are sequentially provided on a substrate. FIG. 4 shows still another example, which has a structure in which a photocatalyst layer, an organic material layer, and a reflective layer are sequentially provided on a substrate. FIG. 5 shows still another example, which has a structure in which an organic material layer, a photocatalyst layer, and a reflective layer are sequentially provided on a substrate. In these structures, normal recording / reproducing is performed from the substrate side. That is, recording is performed by causing the photocatalyst layer to react by the laser light irradiation from the substrate side, inducing the decomposition of the organic material by the oxidation action, and increasing the absorption coefficient at the recording / reproducing wavelength.

FIG. 6 shows still another example of the layer structure for realizing the write-once type optical recording medium corresponding to the blue laser wavelength.
It has a structure in which a photocatalyst layer, an organic material layer, and a cover layer are sequentially provided on a substrate. FIG. 7 shows still another example, which has a structure in which an organic material layer, a photocatalyst layer, and a cover layer are sequentially provided on a substrate. FIG. 8 shows still another example, which has a structure in which a reflective layer, an organic material layer, a photocatalyst layer, and a cover layer are sequentially provided on a substrate. FIG. 9 shows still another example, which has a structure in which a reflective layer, a photocatalyst layer, an organic material layer, and a cover layer are sequentially provided on a substrate. In these structures, normal recording / reproduction is performed from the cover side. That is, recording is performed by reacting the photocatalyst layer by laser light irradiation from the cover layer side, inducing decomposition of the organic material by an oxidizing action, and increasing the absorption coefficient at the recording / reproducing wavelength.

[0031]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

Example 1 A TiO ₂ (photocatalyst layer) having a film thickness of 50 nm was provided on a polycarbonate substrate having a guide groove having a groove depth of 50 nm by a sputtering method, and a dye represented by the following [Chemical formula 2] was formed thereon. An organic material layer having a film thickness of about 60 nm is formed by spin coating, and Ag having a film thickness of 150 nm is further formed thereon.
A write-once optical recording medium was prepared by providing a (reflection layer). The complex refractive index of [Chemical Formula 2] at the laser wavelength of 405 nm is 1.407-i0.076, which is significantly inferior to the complex refractive index required for the organic material used for the write-once type optical recording medium ( For example, the complex refractive index of the dye used for DVD-R in the vicinity of the recording / reproducing wavelength is 2.5-
i is about 0.10.)

An optical disk evaluation device DDU-1000 manufactured by Pulstec Industrial Co., Ltd. is used for the write-once type optical recording medium.
Recording was performed under the following conditions using (wavelength: 405 nm, NA: 0.65), and as a result, a signal with a modulation of 45% was obtained. Also, peel off the reflective layer of the write-once type optical recording medium,
The dye in the recorded portion and the unrecorded portion was dissolved in ethanol and the respective spectra were measured. As a result, as shown in FIG. 14, a clear increase in absorption (absorption coefficient) was recognized in the recorded portion (since recording was performed only in the groove portion,
A large amount of unrecorded part components are present in the spectrum of the recorded part), and the recording principle in the write-once type optical recording medium of the present invention could be confirmed. <Recording conditions> Recording linear density: 1T = 0.0917 (μm) Recording linear velocity: 6.0 (m / sec) Recording strategy: Basic strategy T _top −T _mp = 1.40−0.75 (T) Recording power: 10.5 (mW) Recording pattern: 8-16 modulation signal

[0034]

[Chemical 2]

Comparative Example 1 (Example in which the conventional layer structure is applied in the blue region) On a polycarbonate substrate having a guide groove with a groove depth of 150 nm, a film thickness of about 1 including a dye represented by the following [Chemical Formula 3] is obtained.
A 20 nm organic material layer was formed by a spin coating method, and an Ag reflective layer having a film thickness of 150 nm was further provided thereon to prepare a write-once type optical recording medium. The laser wavelength 405
The complex refractive index of [Chemical Formula 3] in nm is 2.285-i.
0.069, which has a complex refractive index relatively close to the complex refractive index required for the organic material used for the write-once type optical recording medium (for example, in the vicinity of the recording / reproducing wavelength of the dye used in DVD-R). The complex refractive index is about 2.5-i0.10). An optical disk evaluation device DDU-1000 manufactured by Pulstec Industrial Co., Ltd. for the above-mentioned write-once type optical recording medium.
As a result of recording under the following conditions using (wavelength: 405 nm, NA: 0.65), a relatively large modulation factor was obtained in the long mark, but a sufficient signal was not obtained in the short mark. The signal was noisy regardless of the mark length.

Further, the substrate was the same as in Example 1 except that the groove depth was 5
Change to a polycarbonate substrate with a 0 nm guide groove,
In addition, a film thickness of about 6 consisting of the dye represented by the following [Chemical Formula 3]
A 0 nm organic material layer is formed by spin coating,
Further, an Ag reflective layer having a film thickness of 150 nm was further provided thereon to prepare a write-once type optical recording medium, and the same recording as the above was performed, but no recording was possible. <Recording conditions> Recording linear density: 1T = 0.0917 (μm) Recording linear velocity: 6.0 (m / sec) Recording strategy: Basic strategy T _top −T _mp = 1.40−0.75 (T) Recording power: 12.0 (mW) Recording pattern: 8-16 modulation signal

[0037]

[Chemical 3]

From Example 1 and Comparative Example 1 described above, the layer structure and recording principle of the write-once type optical recording medium of the present invention is very effective for realizing the write-once type optical recording medium using an organic material compatible with a blue laser wavelength. It was confirmed that In addition, in the write-once type optical recording medium using the conventional organic material, it is necessary to generate heat in the organic material layer, so that the organic material layer cannot be thinned,
Although a deep groove (for example, 150 to 180 nm) was required, it was confirmed that the recording principle of the present invention enables thinning of the organic material, and that a substrate having a very shallow guide groove of 50 nm can be used.

Example 2 A complex refractive index (refractive index n and absorption coefficient k) of a dye represented by the following [Chemical Formula 4] which can be used for a conventional DVD-R,
A dye (NK4) manufactured by Hayashibara Biochemical Laboratory Co., Ltd., which can be used in the present invention and can also be used in a conventional DVD-R.
382) and the complex refractive index of TiO ₂ (refractive index n and absorption coefficient k) and the complex refractive index of TiO ₂ (refractive index n and absorption coefficient k). FIG. 15 shows the complex refractive index of the dye represented by [Chemical Formula 4], and FIG. 16 shows the complex refractive index of the dye (NK4382).
FIG. 17 shows the complex refractive index of TiO ₂ . From the results shown in FIG. 15, when the conventional recording method in which the recording / reproducing wavelength is positioned on the long wavelength side of the main absorption band of the organic material is applied to the conventional recording material, the refractive index is changed with respect to the fluctuation of the recording / reproducing wavelength. It was confirmed that the rate n and the absorption coefficient k varied greatly.
On the other hand, as can be seen from the results shown in FIG.
Since the recording method is such that the recording / reproducing wavelength is located on the sufficiently short wavelength side from the main absorption band of the organic material, the refractive index n and the absorption coefficient k are changed with respect to the variation of the recording / reproducing wavelength.
It was confirmed that there was almost no change. Further, TiO ₂ used as the photocatalyst layer is
It was confirmed that the refractive index n and the absorption coefficient k did not change significantly. As described above, with the layer structure of the write-once type optical recording medium of the present invention, recording characteristics such as recording sensitivity, modulation degree, jitter, and error rate, and changes in reflectance and the like are small with respect to changes in the recording / reproducing wavelength. It was confirmed that a write-once type optical recording medium could be realized.

[0040]

[Chemical 4]

[0041]

According to the present invention, it is possible to use a shallow groove substrate which is compatible with a blue laser wavelength region of about 350 to 500 nm and has good transferability, and it is possible to use the recording sensitivity and the degree of modulation with respect to the fluctuation of the recording / reproducing wavelength. It is possible to easily and inexpensively provide a write-once type optical recording medium using an organic material, which has little change in recording characteristics such as jitter and error rate and reflectance. Further, according to the present inventions 1 and 2, a write-once type optical recording medium capable of achieving high density by recording / reproducing from the substrate side is provided, and according to the present inventions 3 to 4, by recording / reproducing from the cover layer side. It is possible to provide a write-once type optical recording medium capable of achieving high density.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a layer structure of a conventional write-once type optical recording medium.

FIG. 2 is a diagram for explaining an example of the layer structure of the write-once type optical recording medium of the present invention.

FIG. 3 is a diagram for explaining another example of the layer structure of the write-once type optical recording medium of the present invention.

FIG. 4 is a diagram for explaining still another example of the layer structure of the write-once type optical recording medium of the present invention.

FIG. 5 is a diagram for explaining still another example of the layer structure of the write-once type optical recording medium of the present invention.

FIG. 6 is a diagram for explaining still another example of the layer structure of the write-once type optical recording medium of the present invention.

FIG. 7 is a diagram for explaining still another example of the layer structure of the write-once type optical recording medium of the present invention.

FIG. 8 is a diagram for explaining still another example of the layer structure of the write-once type optical recording medium of the present invention.

FIG. 9 is a diagram for explaining still another example of the layer structure of the write-once type optical recording medium of the present invention.

FIG. 10 is a diagram for explaining the recording principle of a conventional write-once type optical recording medium.

FIG. 11 is a diagram for explaining the recording principle of the write-once type optical recording medium of the present invention.

FIG. 12 is a diagram for explaining characteristics of an organic material used in the write-once type optical recording medium of the present invention.

FIG. 13 is a diagram for explaining characteristics of an organic material used in the write-once type optical recording medium of the present invention.

FIG. 14 is a diagram showing a spectrum change of a dye used in Example 1 before and after recording.

FIG. 15 is a diagram showing a complex refractive index of a dye represented by [Chemical Formula 4] in a recording / reproducing wavelength region.

FIG. 16 is a diagram showing a complex refractive index of a dye (NK4382) in a recording / reproducing wavelength region.

FIG. 17 is a diagram showing a complex refractive index of TiO ₂ used in the present invention.

[Explanation of symbols]

1 substrate 2 Photocatalyst layer 3 Organic material layer 4 Reflective layer 5 cover layers

Claims (9)

[Claims] 1. A photocatalyst layer made of a material exhibiting photocatalytic activity on a substrate, and a main absorption band at the time of non-recording exists on the long wavelength side with respect to the recording / reproducing wavelength, and the light of the recording / reproducing wavelength is present. On the other hand, a write-once type optical recording medium having a structure in which an organic material layer having no absorption function is adjacently stacked in this order or in the reverse order. 2. A photocatalyst layer made of a material exhibiting photocatalytic activity and a main absorption band at the time of unrecording are present on the long wavelength side with respect to the recording / reproducing wavelength on the substrate, and with respect to light of the recording / reproducing wavelength. A write-once type optical recording medium having a structure in which an organic material layer having no absorption function is laminated adjacently in this order or in the reverse order, and a reflective layer is further laminated thereon. 3. A photocatalyst layer made of a material exhibiting photocatalytic activity and a main absorption band at the time of non-recording are present on a long wavelength side with respect to a recording / reproducing wavelength on a substrate, and with respect to light having a recording / reproducing wavelength. And an organic material layer having no absorption function are laminated adjacent to each other in this order or in the reverse order, and a light-transmitting cover layer is further laminated thereon, and recording and reproduction can be performed from the cover layer side. A write-once type optical recording medium characterized by being performed. 4. A photocatalytic layer having at least a reflective layer on a substrate, the photocatalytic layer made of a material exhibiting photocatalytic activity, and a main absorption band at the time of non-recording are present on the long wavelength side with respect to the recording / reproducing wavelength. , An organic material layer having no absorption function for light of a recording / reproducing wavelength is laminated adjacent to this order or reverse order, and further has a structure in which a light-transmitting cover layer is laminated thereon,
A write-once type optical recording medium, wherein recording / reproducing is performed from the cover layer side. 5. The organic material constituting the organic material layer,
The write-once type optical recording medium according to any one of claims 1 to 4, wherein an organic material which is decomposed by an oxidizing action of the photocatalyst layer and has an increased absorption coefficient at a recording / reproducing wavelength is used. 6. The write-once type optical recording medium according to claim 5, wherein an organic material having an increased absorption coefficient at a recording / reproducing wavelength of 350 to 500 nm is used. 7. The write-once type optical recording medium according to claim 5, wherein the organic material is a dye. 8. The write-once type optical recording medium according to claim 1, wherein the photocatalyst layer is made of a material containing an oxide semiconductor or a II-VI group semiconductor as a main component. 9. The write-once type optical recording medium according to claim 8, wherein the oxide semiconductor is TiO ₂ .