JP2007280588A - Recordable two-layer configuration optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recordable two-layer configuration optical recording medium of high reflectivity and high sensitivity, having an easy and simplified layer configuration, capable of realizing high refractive index and a small absorption coefficient to recording-reproducing wavelength in high density recording. <P>SOLUTION: The medium has, from a laser beam incidence side, at least a first information layer, an intermediate layer and a second information layer in this sequence. In the first information layer, sequentially from a laser beam irradiation side, a thin film (an Re layer) containing Bi as main component, a dielectrics layer, a reflective layer and a thermal diffusion layer are formed by lamination. In the second information layer, sequentially from the laser beam irradiation side, a thin film (an Re layer) containing Bi as main component, a dielectrics layer, and a reflective layer are formed by lamination. The thermal diffusion layer contains an oxide having electrical conductivity of specific resistance of 1×10<SP>-1</SP>Ωcm or lower. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a write once read many (WORM) optical recording medium capable of high-density recording even in a blue laser light wavelength region, and particularly includes at least a first information layer, an intermediate layer, and a second information layer. The present invention relates to a write-once two-layer optical recording medium.

As an optical recording medium that can be recorded by irradiation with a laser beam, there are write-once type optical recording media such as CD-R and DVD-R. These optical recording media are reproduction compatible with CD-ROMs or DVD-ROMs, and are used as small-scale distribution media and storage media. However, CD-R and DVD-R are currently mainly used media using organic dyes, and mass production is performed at low cost. When the write-once type optical recording medium is realized with an inorganic recording layer, as the number of layers increases, the cost increases and there is no merit as a product. Therefore, write-once type optical recording media with as few layers as possible have been proposed. The write-once type optical recording media include a punching type, a phase change type, and an alloying type. From the viewpoint of cost, a punching recording method is promising, but there is a problem that C / N becomes low in punching recording. It was. This was due to the molten film remaining in the pits as polka dots in the pits where the holes were drilled or swelled in the periphery. Further, since the hole recording method has a single layer structure, the recording film that has been used normally cannot cope with the high reflectivity of the ROM and has become a non-standard product.
There are compounds of Te and Au or Ag as punching recording materials (Patent Documents 1 and 2, etc.), but the boiling point of these materials is 1000 ° C. or higher, and the optical recording medium has very low sensitivity.
Compared to the phase change type in which the temperature only needs to be raised to the melting point, the punching recording method requires a large amount of heat to raise the temperature to the boiling point or higher for recording. Therefore, a large laser power is required as compared with the phase change type, and the power of the semiconductor laser becomes insufficient for high linear velocity recording. Therefore, a recording film with higher sensitivity is required.

Patent Document 3 discloses an invention in which a corrosion-resistant metal layer is formed on a first layer that liberates volatile components at a temperature of 400 ° C. or lower and attempts to increase recording sensitivity. Increasing the rate is not aimed at and cannot be ROM compatible. Corrosion-resistant metals are Au, Ag, etc., but these have extremely high thermal conductivity, and the heated energy escapes by diffusion, resulting in low effectiveness and inappropriate for high linear velocity recording. It was.
Further, as an alloying method, in Patent Document 4, a layer made of any element of Ge, Si, Sn and a layer made of any element of Au, Ag, Al, Cu are irradiated with laser light, Although a method of recording by alloying these two layers has been proposed, it becomes low to high recording and cannot be ROM compatible.
Further, as an invention for forming a phase change type recording layer with an alloy of In and Te, there is Patent Document 5, and by setting In: Te = 2: 1 to 1: 1 or 2: 3 to 2: 5, An object of the present invention is to provide a phase change type optical recording medium. However, the present invention requires an initialization process because the state during film formation is amorphous and the reflectance is low. Therefore, the process increased and the cost was increased.

Patent Document 6 discloses a first layer (phase change alloy thin film) made of Ag—Zn and a second layer (low melting point thin film) mainly composed of one kind selected from Te, Se, and S. An invention is disclosed in which recording is performed by diffusing two layers, but the first layer is made 300 to 700 mm thick and the second layer is made 500 to 1500 mm thick in order to increase reflectivity. It was disadvantageous to tact and cost. In addition, although the reflectance is greatly increased by increasing the film thickness, in our investigation, since the reflectance is too high and the absorptance is too small, heat absorption hardly occurs on the recording film, and the sensitivity is very high. It turned out to be bad. For this reason, it cannot be used for a medium such as a DVD that requires a high linear velocity. Moreover, Ag, Te, Se, etc. are very reactive, and the reaction of the two layers occurred and the reflectance was lowered only by irradiating the reading laser beam or simply leaving the medium.
Further, in Patent Document 7, the first layer is a thin film mainly composed of In, and the second layer is a thin film containing 5B and 6B group elements of the periodic table, accompanied by a change in reflectance due to reaction or alloying between the two layers. Although a medium is disclosed, this medium was also very unstable because of the high reactivity of In and Te as in the invention of Patent Document 6.
The various problems described above have been a major obstacle to the spread of write-once optical recording media having a recording layer made of an inorganic material with a small number of layers.

In addition, the inventors previously filed Japanese Patent Application No. 2004-363010 as a prior application relating to a write-once type optical recording medium using a laser beam in a blue region. The contents are briefly described as follows.
That is, in the write-once type optical recording medium of the prior application, an organic layer that has conventionally functioned as a heat generation layer by a light absorption function and a recording layer by a change in refractive index (real part of the complex refractive index) due to decomposition and alteration. It is characterized in that a recording layer (Re layer) mainly made of bismuth oxide, which is an inorganic layer, is provided instead of the material thin film. In the prior application, it was described that the medium layer configuration was important, and great utility was found by optimizing it. The inventors of the present invention applied a recording layer mainly made of bismuth oxide to a write-once optical recording medium compatible with a blue laser, and confirmed that excellent recording / reproducing characteristics can be obtained.

Recently, from the viewpoint of increasing the recording capacity of a rewritable write-once optical recording medium, a single-sided two-layer configuration has been proposed (see, for example, Patent Documents 8 to 9 and Non-Patent Document 1).
The write-once optical recording medium having a Re layer developed by the present inventors has a recording principle mainly composed of Bi crystallization. In order to obtain a medium with high sensitivity and appropriate reflectance, Media design is very important.
However, since Bi in the Re layer of the prior application has a high crystallization speed, it is necessary to quickly release heat to the adjacent reflective layer or the like in order not to spread the mark in the lateral direction. That is, it is a material that needs to have a rapid cooling structure, and there is a problem that it is difficult to form a minute mark in a thin structure of a reflective layer such as a recording layer single-sided two-layer type.

Using a nitride or carbide that has a relatively high thermal conductivity and a low light absorption rate, a layer (thermal diffusion layer) that assists the thermal diffusion function that the reflective layer was responsible for is provided on the reflective layer to provide a rapid cooling structure. A method of approaching the above is proposed for a single-layer phase change information recording medium (Patent Document 10), a two-layer phase change information recording medium (Patent Document 11), and the like. This method is considered to be an effective method for solving the above-mentioned drawbacks that occur when the reflective layer constituting the first information layer is thinned.
However, these materials such as nitrides and carbides tend to cause cracks in the formed thermal diffusion layer due to large stress, and as a result, sufficient overwrite characteristics cannot be obtained for an optical disc provided with the thermal diffusion layer. There is a problem. In addition, the carbide material has particularly large absorption on the short wavelength side, and in the next generation system such as the Blu-ray Disk system using a blue-violet laser, the light transmittance of the first information layer cannot be increased. The problem that occurs.

JP-A-60-179952 JP-A-60-179953 JP 57-157790 A JP-A-4-226784 JP-A-1-162247 Japanese Patent No. 2948899 JP-A-11-34501 JP 2003-200633 A JP 2003-203383 A JP-A-8-50739 JP 2000-222777 A International Symposium on Optical Memory 2003 (ISOM 2003) Proceedings p. 74

  In view of the conventional problems as described above, the present invention has a simple and simple layer structure, and can realize a large refractive index and a small absorption coefficient with respect to a recording / reproducing wavelength in high-density recording, and has high reflectivity and high sensitivity. It is an object of the present invention to provide a write once type two-layer optical recording medium.

The above problems are solved by the following inventions 1) to 15) (hereinafter referred to as the present inventions 1 to 15).
1) At least a first information layer, an intermediate layer, and a second information layer in this order from the laser light incident side. The first information layer is a thin film containing at least Bi as a main component in this order from the laser light irradiation side. (Re layer), a dielectric layer, a reflective layer, and a thermal diffusion layer are laminated, and the second information layer is a thin film (Re layer) containing at least Bi as a main component in order from the laser light irradiation side, Write-once two-layer light comprising a dielectric layer and a reflective layer, wherein the thermal diffusion layer contains an oxide having an electrical conductivity of 1 × 10 ⁻¹ Ωcm or less. recoding media.
2) The write-once two-layer structure according to 1), wherein the oxide having electrical conductivity is either IZO (In ₂ O ₃ —ZnO) or ITO (In ₂ O ₃ —SnO ₂ ). Optical recording medium.
3) The thickness of the reflective layer of the first information layer T1 and the thickness of the thermal diffusion layer T2 are in the range of T2 / T1 = 2-8. Configuration optical recording medium.
4) The write-once two-layer optical recording medium according to any one of 1) to 3), wherein the thermal diffusion layer has a thickness of 30 to 90 nm.
5) The thickness t1 of the dielectric layer of the first information layer and the thickness t2 of the dielectric layer of the second information layer are in the range of t2 / t1 = 0.7 to 1.5. 4) The write-once two-layer structure optical recording medium according to any one of 4) to 4).
6) The thickness t1 of the dielectric layer of the first information layer and the thickness t2 of the dielectric layer of the second information layer are in the range of t2 / t1 = 4.5 to 6.0. 4) The write-once two-layer structure optical recording medium according to any one of 4) to 4).
7) The thickness of the Re layer of the first information layer is 5 to 25 nm, the thickness of the dielectric layer is 10 to 30 nm, the thickness of the Re layer of the second information layer is 5 to 25 nm, and the film of the dielectric layer The write-once two-layer optical recording medium according to any one of 1) to 4), wherein the thickness is 10 to 30 nm.
8) The thickness of the Re layer of the first information layer is 5 to 25 nm, the thickness of the dielectric layer is 10 to 30 nm, the thickness of the Re layer of the second information layer is 5 to 25 nm, and the film of the dielectric layer The write-once two-layer optical recording medium according to any one of 1) to 4), wherein the thickness is 90 to 120 nm.
9) Before the Re layer of the first information layer, a layer containing a compound containing a typical element as a main component (a compound layer containing a typical element) is formed in a layered manner. The write-once two-layer optical recording medium according to any one of the above.
10) The write-once two-layer optical recording medium according to 9), wherein the thickness of the compound layer containing a typical element is 70 nm or less.
11) The write-once two-layer structure optical recording medium according to any one of 1) to 10), wherein the Re layer is mainly composed of Bi oxide.
12) The Re layer is made of Al, Cr, Mn, Sc, In, Ru, Rh, Co, Fe, Cu, Ni, Zn, Li, Si, Ge, Zr, Ti, Hf, Sn, Pb, Mo, V, The write-once two-layer optical recording medium according to any one of 1) to 11), which contains one or more elements M selected from B and Nb.
13) The write-once two-layer optical recording medium according to any one of 1) to 12), wherein the dielectric layer contains ZnS and SiO ₂ as main components.
14) The write-once two-layer optical recording medium according to 13), wherein the blending ratio of ZnS and SiO ₂ is in the range of 70:30 to 90:10 (mol%).
15) The recordable die 2 according to any one of 1) to 14), wherein the typical element of the compound layer containing the typical element is one or more elements selected from Zn, In, Al, and Sn. Layered optical recording medium.

Hereinafter, the present invention will be described in detail.
The write-once two-layer structure optical recording medium of the present invention has, as a basic layer structure, a thin film (Re layer) containing at least Bi as a main component, a dielectric layer, and a reflective layer in this order from the laser light irradiation side. They are stacked.
Here, the thin film (Re layer) containing Bi as a main component means that Bi is an essential component in the composition of the Re layer and that Bi occupies 30 atomic% or more of the entire constituent elements excluding oxygen. Means. For example, when the Re layer is made of Bi, Fe, and O (oxygen), it means that Bi occupies 30 atomic% or more of the total amount of Bi and Fe.

The Re layer is a layer responsible for the main light absorption function in the optical recording medium of the present invention.
The Re layer is made of a material exhibiting normal dispersion, and is not a material having a large absorption band in a certain wavelength range like an organic material, so that the wavelength dependency of the complex refractive index is small. For this reason, recording characteristics such as recording sensitivity, modulation degree, jitter, error rate, reflectance, etc. greatly change with respect to fluctuations in recording / reproducing wavelength due to individual differences in laser light or changes in environmental temperature. This problem can be solved significantly.
In a known write-once type optical recording medium, the organic material thin film has both a recording layer and a light absorption layer, and therefore has a large refractive index n and a relatively small absorption coefficient k with respect to the recording / reproducing wavelength. Therefore, in order to reach the temperature at which the organic material is decomposed, it has been necessary to form a relatively thick film. Further, for the phase change type optical recording medium, it is necessary to make the groove depth of the substrate very deep.

As a result of intensive studies by the present inventors, it has been found that jitter and PRSNR are improved by employing a layer structure as in the present invention 1 and using a specific compound for the thermal diffusion layer.
PRSNR is an abbreviation of “Partial Response Signal to Noise Ratio”, and is an index that can simultaneously represent the S / N of the reproduction signal and the actual reproduction waveform and theoretical PR waveform line formation, and is a bit error rate of the disk. It is one of the necessary indicators for estimating A target signal is created by specially processing the amplitude information obtained from the reproduced waveform, and the difference from the actual reproduced signal is normalized as PRSNR. The larger the value of PRSNR, the better the signal characteristics. In general, a value of 15 or more is required to keep the error rate within a practical range.

In the present invention, since the medium using the Re layer is a recording layer single-sided two-layer type, the thickness of the reflective layer of the first information layer must be thin enough to transmit light. On the other hand, as described above, since Bi has a high crystallization speed, it is necessary to quickly release heat to an adjacent reflection layer or the like so as not to spread the mark in the lateral direction. That is, it is a material that needs to have a rapid cooling structure, and there is a problem that it is difficult to form a minute mark with a thin reflective layer structure.
Therefore, as in the first aspect of the present invention, by providing a thermal diffusion layer using a material containing an oxide having an electrical conductivity with a specific resistance of 1 × 10 ⁻¹ Ωcm or less, rapid cooling is achieved even in a thin reflective layer structure. The structure can be secured, and a minute mark can be formed, so that the PRSNR can be greatly improved.
It is also desirable that the absorptivity at the wavelength of the laser beam used is small so that the second information layer can be recorded and reproduced. In the wavelength of the laser beam used for recording / reproducing information, the extinction coefficient is preferably 0.5 or less, and more preferably 0.3 or less. If the extinction coefficient is larger than 0.5, the absorption rate in the first information layer increases, and recording / reproduction of the second information layer becomes difficult.
Examples of oxides that satisfy these characteristics and exhibit electrical conductivity include In ₂ O ₃ , SnO ₂ , ZnO, CdO, TiO, CdIn ₂ O ₄ , Cd ₂ SnO ₂ , and Zn ₂ SnO. However, among them, ITO (In ₂ O ₃ —SnO ₂ ) and IZO (In ₂ O ₃ —ZnO) have high thermal conductivity and are preferable as the thermal diffusion layer material (Invention 2).
These oxides may be used alone or in combination.

  The write-once two-layer optical recording medium needs to have an ability to transmit an appropriate amount of light that can be recorded and reproduced in the second information layer while maintaining the characteristics that can be recorded in the first information layer. The balance between the thickness and the thickness of the thermal diffusion layer is very important, and the inventors of the present invention set the ratio of the thickness T1 of the reflective layer of the first information layer and the thickness T2 of the thermal diffusion layer to T2 / T1 = It was found that the recording / reproduction characteristics of the first information layer and the second information layer were balanced by setting the ratio in the range of 2 to 8, and good signal characteristics and sensitivity could be realized in both information layers (Invention 3). When the value of T2 / T1 is smaller than 2, the reflectivity of the first information layer is increased too much, so that the amount of light reaching the second information layer is reduced, and the sensitivity of the second information layer and the PRSNR value are deteriorated. On the other hand, if T2 / T1 is greater than 8, the transmittance of the first information layer becomes too high, and the sensitivity and PRSNR of the first information layer are deteriorated.

In addition, by setting the film thickness of the thermal diffusion layer to 30 to 90 nm, it is possible to secure a rapid cooling structure even in a thin structure of the reflective layer, and it is possible to form a minute mark, resulting in a large PRSNR. Improvement is possible (Invention 4).
The rapid cooling structure is important due to the properties of Bi as described above. However, if the thickness of the thermal diffusion layer is thinner than 30 nm, it is difficult to form a minute mark with the thin structure of the reflective layer, and the signal characteristics deteriorate rapidly. . On the other hand, if the thickness is larger than 90 nm, a phenomenon in which heat is diffused excessively occurs and the sensitivity of the first information layer is deteriorated.

Further, as in the present invention 5, the thickness t1 of the dielectric layer of the first information layer and the thickness t2 of the dielectric layer of the second information layer are in the range of t2 / t1 = 0.7 to 1.5. If it is made to exist or it is made to exist in the range of t2 / t1 = 4.5-6.0 like this invention 6, the transmittance | permeability of a 1st information layer and the reflectance of a 2nd information layer Is optimal, and good recording characteristics (PRSNR, reflectance, sensitivity) can be obtained in both information layers.
If it is less than 0.7, the sensitivity of the second information layer is very poor because the reflectance of the first information layer is high and the transmittance is low. In the range of more than 1.5 and less than 4.5, the reflectivity of the second information layer is significantly increased, the sensitivity of the second information layer is significantly deteriorated, and the PRSNR is also deteriorated. If the value exceeds 6.0, the dielectric layer of the second information layer becomes too thick, causing deformation of the substrate or groove due to heat during film formation, and also causing the sensitivity of the second information layer to increase and the sensitivity to deteriorate significantly. It also becomes.
That is, according to the present invention 5 to 6, by optimizing the film thickness ratio of the dielectric layer of the first information layer and the second information layer, in both information layers, high PRSNR, high reflectance, and high sensitivity. Characteristics can be realized with a relatively simple layer structure.

Further, if the thickness of each layer is selected as in the present invention 7 or the present invention 8, the balance between the transmittance of the first information layer and the reflectance of the second information layer is optimal, and good recording is achieved in both information layers. Characteristics (PRSNR, reflectance, sensitivity) are obtained.
When each film thickness of the first information layer is out of the limited range, the transmittance of the first information layer is lowered, the sensitivity of the second information layer is remarkably deteriorated, and the PRSNR is also deteriorated. When each film thickness of the second information layer is out of the limited range, the reflectance of the second information layer is significantly increased, and the sensitivity and PRSNR of the second information layer are deteriorated.
That is, according to the present invention 7-8, by optimizing the thickness of each layer of the first information layer and the second information layer, the characteristics of high PRSNR, high reflectance, and high sensitivity are compared in both information layers. Can be realized with a simple layer structure.

Further, as in the present invention 9, a layer containing a compound containing a typical element as a main component (a compound layer containing a typical element) is laminated in front of the Re layer (as viewed from the laser light incident side) of the first information layer. It is preferable to form. Usually, since the substrate contains moisture and oxygen and easily permeates, when the recording layer is in contact with the substrate, it is oxidized to deteriorate the characteristics. However, if a compound layer containing a typical element is provided, the permeating oxygen and The effect of blocking moisture and improving storage characteristics is obtained. However, even if there is no compound layer containing a typical element, the recording characteristics hardly change, and there is no problem in the reliability of the optical recording medium in the normal specification.
Examples of the compound used for the compound layer containing a typical element include aluminum oxide (Al ₂ O ₃ or the like), ZnSSiO ₂ , indium tin oxide (ITO), or the like.
The main component means that it accounts for 30 mol% or more of the entire material, but usually only the above compounds are used.
The film thickness of the compound layer containing a typical element is preferably 70 nm or less as in the present invention 10. If the film thickness exceeds 70 nm, the film formation takes time and the tact time is increased, and the substrate and the groove are deformed by the heat of film formation, and the recording characteristics are remarkably deteriorated. In addition, if the film thickness is too thin, it is impossible to completely prevent the transmission of oxygen and moisture.

In the eleventh aspect of the present invention, a layer mainly composed of Bi oxide is used as the Re layer. Here, the main component means that the amount of Bi in the Re layer is used so as to satisfy the above-described conditions.
By using Bi oxide as the material for the Re layer, an extremely good PRSNR can be obtained and the reflectance can be improved.
Such a layer can be formed by using a Bi oxide or Bi alloy oxide as a target for forming the Re layer, or by sputtering Bi or Bi alloy in a mixed atmosphere of argon and oxygen. Film can be formed.

In the present invention 12, the Re layer is made of Al, Cr, Mn, Sc, In, Ru, Rh, Co, Fe, Cu, Ni, Zn, Li, Si, Ge, Zr, Ti, Hf, Sn, Pb, Mo. 1 or more elements M selected from V, B, and Nb. The addition amount of the element M is selected in the range of about 30 to 40% by weight with the best characteristics.
By including the element M, good recording can be performed with respect to light having a blue wavelength. Obtaining the degree of modulation by making the crystal structure of the unrecorded state different from the crystal structure of the recording mark has been conventionally performed in phase change recording or the like. In the present invention, two or more kinds of oxides are obtained. By forming the recording mark in a state where crystals are mixed, the difference in refractive index between the recorded mark and the unrecorded portion becomes larger, and a large modulation degree can be obtained. Furthermore, the presence of not only each oxide crystal but also a single element crystal can provide a greater effect. In addition, the growth of crystals can be suppressed by mixing crystals of different elements or crystal structures. That is, a recording mark made of two or more different elements and / or crystals having a crystal structure can be prevented from growing and spreading, and a small recording mark can be formed.

The material of the dielectric layer is determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion, and the like. In general, oxides, sulfides, nitrides, carbides, and fluorides such as Ca, Mg, and Li that are highly transparent and have a high melting point can be used.
As a preferred material, a composite dielectric containing 50 to 90 mol% of at least one selected from ZnS, ZnO, TaS ₂ and rare earth sulfides and a heat-resistant compound having a melting point or decomposition point of 1000 ° C. or higher. Is mentioned.
Examples of the heat-resistant compound having a melting point or decomposition point of 1000 ° C. or higher include Mg, Ca, Sr, Y, La, Ce, Ho, Er, Yb, Ti, Zr, Hf, V, Nb, Ta, Zn, Al, Oxides such as Si, Ge, and Pb, nitrides, or carbides, and fluorides such as Ca, Mg, and Li can be used. Among these, a material containing ZnS and SiO ₂ as main components is preferable (Invention 13). Here, the main component means that it accounts for 50 mol% or more of the entire material, but usually only ZnS and SiO ₂ are used. Furthermore, the blending ratio of ZnS and SiO ₂ is preferably in the range of 70:30 to 90:10 (mol%) (Invention 14). Within this range, a better PRSNR can be obtained and the reflectance can be improved. If it is out of the above range, the optical characteristics n and k values are shifted in the thicknesses and combinations of the constituent layers of the optical recording medium, making it difficult to obtain good characteristics in both information layers.
Note that the oxides, sulfides, nitrides, carbides, and fluorides do not necessarily have a stoichiometric composition, and the compositions can be controlled or mixed for controlling the refractive index and the like. It is.

Further, as in the present invention 15, the typical element of the compound layer containing a typical element is preferably one or more elements selected from Zn, In, Al, and Sn. By providing the compound layer containing these typical elements between the Re layer and the substrate, the stability in the environmental resistance test characteristics is greatly improved. Moreover, even if a compound layer containing this typical element is used, it is one of the features that it does not have an adverse effect such as a decrease in reflectance.
Examples of the compound containing the typical element include ZnS, ZnSSiO ₂ , InO ₂ , SnO ₂ , Al ₂ O ₃ , and AlN.

The intermediate layer preferably has low light absorption at the wavelength of light irradiated for recording / reproduction. As a material, a resin is suitable in terms of moldability and cost, and an ultraviolet curable resin, a slow-acting resin, and a thermoreversible resin. Resins can be used. In addition, a double-sided tape for bonding optical disks (for example, Nitto Denko's adhesive sheet DA-8321) can be used.
The intermediate layer is one in which the pickup can discriminate between the first information layer and the second information layer and can be optically separated during recording and reproduction, and the thickness is preferably 10 to 70 μm.
The optical recording medium of the present invention may be formed by combining various conventionally known layers in addition to the layers defined in the claims.

The material of the substrate is not particularly limited as long as it has excellent thermal and mechanical properties and also has excellent light transmission properties when recording / reproducing is performed from the substrate side (through the substrate). It is not a thing.
Examples of the material include polycarbonate, polymethyl methacrylate, amorphous polyolefin, cellulose acetate, polyethylene terephthalate, and the like, and polycarbonate and amorphous polyolefin are preferable.
The film thickness of a board | substrate can be suitably set with a use, and is not specifically limited.

The material of the reflective layer is preferably a material having a sufficiently high reflectance at the wavelength of the reproduction light.
For example, metals such as Au, Al, Ag, Cu, Ti, Cr, Ni, Pt, Ta, and Pd can be used alone or as an alloy. In particular, Au, Al, and Ag have high reflectivity and are suitable as a material for the reflective layer.
Further, the above metal may be the main component and other elements may be included. Examples of other elements include Mg, Se, Hf, V, Nb, Ru, W, Mn, Re, Fe, Co, Rh, Ir, Mention may be made of metals and metalloids such as Zn, Cd, Ga, In, Si, Ge, Te, Pb, Po, Sn, Bi. Among them, those containing Ag as a main component are particularly suitable because they are inexpensive and easy to obtain a high reflectance.
Further, it is also possible to form a multilayer film by alternately stacking a low refractive index thin film and a high refractive index thin film using a material other than metal, and use it as a reflective layer.
Examples of the method for forming the reflective layer include sputtering, ion plating, chemical vapor deposition, and vacuum vapor deposition.
The thickness of the reflective layer is preferably 10 to 25 nm for the first information layer and 50 to 200 nm for the second information layer.

When Ag or the like is used for the reflective layer, if the ZnSSiO ₂ layers are stacked adjacent to each other, S in the ZnSSiO ₂ is gradually mixed with Ag, which may cause deterioration in characteristics, a phenomenon of reflectance, and the like. Therefore, a layer called an anti-sulfurization layer may be further provided between the reflective layer and the ZnSSiO ₂ layer as appropriate. Examples of the material include oxides such as SiO, ZnO, SnO ₃ , Al ₂ O ₃ , TiO ₃ and In ₂ O ₃ , nitrides such as Si ₃ N ₄ , AlN and TiN, and carbides such as SiC. . A commonly used material is SiC, which is a suitable material and can be used in the present invention as needed.

In addition, a known inorganic or organic overcoat layer, undercoat layer or adhesive layer is provided on the substrate or under the reflective layer in order to improve reflectivity, improve recording characteristics, or improve adhesion. May be.
A protective layer may be appropriately provided on the reflective layer or between other constituent layers. As the material of the protective layer, any conventionally known material can be applied as long as it has a function of protecting from an external force.
Examples of the organic material include a thermoplastic resin, a thermosetting resin, an electron beam curable resin, and an ultraviolet curable resin. Examples of the inorganic _{materials, SiO 2, Si 3 N 4} , MgF 2, SnO 2 and the like.
As a method for forming the protective layer, a coating method such as a spin coating method or a casting method, a sputtering method, a chemical vapor deposition method, or the like is used as in the recording layer, and a spin coating method is particularly preferable.
The protective layer made of a thermoplastic resin or a thermosetting resin can be formed by applying and drying a coating solution in which the resin is dissolved in an appropriate solvent.
The protective layer made of an ultraviolet curable resin can be formed by applying a coating solution in which the resin is dissolved as it is or in an appropriate solvent, and irradiating it with ultraviolet light to cure. As the ultraviolet curable resin, for example, acrylate resins such as urethane acrylate, epoxy acrylate, and polyester acrylate can be applied.
These materials may be used alone or in combination, and may be used as a multilayer film as well as a single layer.
The thickness of the protective layer is generally in the range of 0.1 to 100 μm, but 3 to 30 μm is particularly preferable.

Further, the optical recording medium of the present invention is not limited to the configuration in which recording and reproduction are performed by irradiating light from the substrate side, and a recording layer is provided by irradiating light from the cover layer side provided with a cover layer. You may make it reproduce | regenerate.
The cover layer is necessary when using a lens with 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 due to the angle at which the disk surface deviates from the optical axis of the optical pickup as the NA increases (so-called tilt angle, 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). This is because the allowable amount of generated aberration is reduced, and this tilt angle is easily affected by the aberration due to the thickness of the substrate. Therefore, the thickness of the substrate is reduced to minimize the influence of aberration on the tilt angle.

Therefore, for example, a recording layer is formed by forming irregularities on a substrate, a reflective layer is provided on the recording layer, and a light-transmitting cover layer, which is a thin film that transmits light, is provided on the recording layer. An optical recording medium that reproduces information on the recording layer by irradiating light, or a reflective layer provided on the substrate, a recording layer provided thereon, and a cover layer having optical transparency thereon. An optical recording medium that reproduces information on a recording layer by irradiating the reproducing light from the cover layer side has been proposed. In this case, care must be taken because the order of the layer configuration is from the cover layer on which the laser beam is incident.
In this way, the NA of the objective lens can be increased by reducing the thickness of the cover layer. That is, it is possible to further increase the recording density by providing a thin cover layer and recording / reproducing from the cover layer side.
Such a cover layer is generally formed of a polycarbonate sheet or an ultraviolet curable resin. Further, the cover layer referred to in the present invention may include a layer for adhering the cover layer.
The laser beam used in the optical recording medium of the present invention is preferably as the wavelength is short for high-density recording, but a laser beam with a wavelength of 350 to 530 nm is particularly preferable, and a representative example thereof is a laser beam with a center wavelength of 405 nm. It is done.

  According to the present invention, the recording characteristics of the first information layer can be improved by using the thermal diffusion layer of the present invention in a write-once two-layer optical recording medium having a Re layer as a recording layer. As a result, a high-reflectivity, high-sensitivity write-once two-layer optical recording medium is provided that has a simple and simple layer structure, can realize a large refractive index and a small absorption coefficient with respect to the recording / reproducing wavelength in high-density recording. it can.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited by these Examples.

Example 1
<Production of write-once type two-layer optical recording medium>
A first substrate and a second substrate made of polycarbonate resin having a radius of 120 mm and a thickness of 0.58 mm having a guide groove with a track pitch of 0.43 μm and a groove depth of 21 nm on the surface were prepared.
Next, using a single wafer sputtering apparatus manufactured by Balzers, a compound layer containing a typical element having a thickness of 20 nm made of Al ₂ O ₃ and a Re layer having a thickness of 20 nm made of Bi ₂ O ₃ are formed on the first substrate. By sequentially forming a 20 nm thick dielectric layer made of ZnS.SiO ₂ (80:20 mol%), a 15 nm thick reflective layer made of Ag, and a 50 nm thick thermal diffusion layer made of IZO, A first information layer was produced.
Similarly, on the second substrate, a 100 nm thick reflective layer made of Ag, a 20 nm thick dielectric layer made of ZnS.SiO ₂ (80:20 mol%), and a 20 nm thick film made of Bi ₂ O _3. The second information layer was fabricated by sequentially forming the Re layer.
Next, a coating solution containing an ultraviolet curable resin (Nippon Kayaku Co., Ltd. DVD003) is applied by spin coating on the film surface of the first information layer, and after the ultraviolet curable resin is applied on the second substrate in the same manner, Bonding was performed under a reduced pressure atmosphere. Thereafter, ultraviolet light was irradiated from the first substrate side to cure the ultraviolet curable resin to form an intermediate layer having a thickness of 30 μm.
As described above, a write-once two-layer optical recording medium in which the first substrate, the first information layer, the intermediate layer, the second information layer, and the second substrate were laminated in this order was produced. (See Figure 6)
In this example, SiO ₂ was mixed with IZO to change the electrical conductivity, and the specific resistance was measured. Then, a write-once two-layer optical recording medium having the above-described layer configuration using these materials as a thermal diffusion layer was prepared, and the PRSNR was measured to obtain the relationship between the specific resistance of the thermal diffusion layer and the PRSNR. . PRSNR uses ODU-1000 manufactured by Pulstech as an evaluation machine, writes a random pattern by rotating the substrate at a laser wavelength of 405 nm, NA of 0.6, clock frequency of 64.8 MHz and a linear velocity of 6.61 m / s. evaluated.
The results are shown in FIG. 1. As can be seen from this figure, when the specific resistance exceeds 1 × 10 ⁻¹ Ωcm, that is, when the electrical conductivity is deteriorated, the signal characteristics of the first information layer are rapidly deteriorated. This is presumably because the thin reflective layer is used as described above, and heat is not sufficiently diffused to make it difficult to form minute pits. In these evaluations, a value less than PRSNR15 was set as a nonstandard value (15 or more for the HD DVD-R standard).
Further, even when ITO was used instead of IZO, the same result as in this example was obtained.

(Example 2)
Write-once two layers in the same manner as in Example 1 except that the ratio T2 / T1 was varied by changing the thickness T1 of the Ag reflective layer of the first information layer and the thickness T2 of the thermal diffusion layer IZO. A constituent optical recording medium was prepared and PRSNR was measured. Specifically, the thickness of the Ag reflective layer of the first information layer was changed to 10 nm, 15 nm, and 20 nm, and T2 / T1 was obtained by shaking T2 for each.
The results are shown in FIG. 2. As can be seen from FIG. 2, when T2 / T1 is smaller than 2, the PRSNR of the second information layer deteriorates rapidly, and when T2 / T1 is larger than 8, the first information layer PRSNR deteriorated rapidly.

(Example 3)
A write-once two-layer optical recording medium was manufactured in the same manner as in Example 1 except that the thickness of the thermal diffusion layer was changed, and PRSNR was measured.
The results are shown in FIG. 3. As can be seen from this figure, the PRSNR of the first information layer rapidly deteriorates when the thickness of the thermal diffusion layer becomes thinner than 30 nm, and the PRSNR of the second information layer becomes thicker than 90 nm. Worsened.

Example 4
A write-once two-layer optical recording medium is manufactured in the same manner as in Example 1 except that the thickness t1 of the first information layer and the thickness t2 of the second information layer are varied. PRSNR and sensitivity were measured. The results are shown in FIGS. Sensitivity is measured using the ODU-1000 manufactured by Pulstec as an evaluation machine, the erasing power is fixed at 3 mW, the recording power is varied, and the recording power showing the best PRSNR value is shown as the optimum power on the vertical axis in FIG. Indicated. In these evaluations, the case where the PRSNR was less than 15 and the sensitivity Pw (mW) exceeded 13 mW was regarded as out of specification.
As can be seen from FIGS. 4 and 5, in the range of t2 / t1 = 0.7 to 1.5 or 4.5 to 6.0, good PRSNR is obtained in both the first information layer and the second information layer. Sensitivity was shown. However, outside these ranges, the sensitivity of the second information layer in particular deteriorated and the PRSNR value also deteriorated. This is mainly due to the fact that the reflectivity becomes too high and deviates from the optimum value that can be recorded from the relationship between n and k of ZnSSiO ₂ and its film thickness.

(Example 5)
The thickness of the compound layer containing the typical element of the first information layer is 0 to 70 nm, the thickness of the Re layer is 5 to 25 nm, the thickness of the dielectric layer is 10 to 30 nm, and the Re layer of the second information layer A write-once two-layer optical recording medium was manufactured in the same manner as in Example 1 except that the film thickness was 5 to 25 nm and the film thickness of the dielectric layer was 10 to 30 nm or 90 to 120 nm.
These media showed a value of PRSNR 20-30 satisfying the HD DVD-R standard 15 or higher, and the reflectivity also showed a good value of 5-7% satisfying the HD DVD-R standard 4.5% or higher. In addition, good characteristics were exhibited such that the sensitivity could be written at 9 to 11 mW.
If the reflectance increases, the sensitivity deteriorates, and it is necessary to introduce a larger power during recording. However, if recording is performed with a large power, the adjacent mark or the adjacent track is greatly affected. It is considered that PRSNR deteriorates due to this.

(Example 6)
Bi ₂ O ₃ of the Re layer includes Al, Cr, Mn, Sc, In, Ru, Rh, Co, Fe, Cu, Ni, Zn, Li, Si, Ge, Zr, Ti, Hf, Sn, Pb, and Mo. A write-once two-layered optical recording medium is prepared in the same manner as in Example 1 except that one or more elements M selected from V, B, and Nb are contained. evaluated.
As a result, it was found that PRSNR and sensitivity could be further improved by adding these elements.

(Example 7)
Write-once two-layer configuration in the same manner as in Example 1 except that the ratio of ZnS and SiO ₂ in the ZnSSiO ₂ layers of the first information layer and the second information layer was changed in the range of 70:30 to 90:10. An optical recording medium was produced.
In these composition ranges, a good PRSNR satisfying the HD DVD-R standard 15 or higher can be obtained, and both the first information layer and the second information layer satisfy the HD DVD-R standard 4.5% or higher. Appropriate reflectance was shown and good sensitivity was shown.
If the composition ratio is out of the range, the optical characteristics n and k values are shifted in the thicknesses and combinations of the constituent layers of the optical recording medium, and good characteristics cannot be obtained in both information layers. It was confirmed that.

(Examples 8 to 10)
The material of the compound layer containing the typical element of the first information layer was changed to Example 8; ZnS.SiO ₂ (80:20 mol%), Example 9; InO ₂ , Example 10; SnO ₂ , and the film thickness was changed. A write-once two-layer optical recording medium was manufactured in the same manner as in Example 1 except that the thickness was 60 nm.
With respect to these write-once type two-layer optical recording media, the PRSNR was measured in the same manner as in Example 1. As a result, good PRSNR satisfying the HD DVD-R standard 15 or higher was obtained in any of Examples 8-10. I was able to. Further, both the first information layer and the second information layer showed an appropriate reflectance satisfying the HD DVD-R standard of 4.5% or more, and showed a good sensitivity.
However, even if a compound layer containing the above-described typical element is used, if the film thickness exceeds 70 nm, the optical characteristics n and k values are shifted in the respective film thicknesses of the constituent layers of the optical recording medium and the combinations thereof. It was confirmed that good characteristics could not be obtained in both information layers.

(Example 11)
Bi ₂ O ₃ film, Al, Cr, Mn, Sc, In, Ru, Rh, Co, Fe, Cu, Ni, Zn, Li, Si, Ge, Zr, Ti, Hf, Sn, Pb, Mo, V A write-once two-layer structure optical recording medium was prepared in the same manner as in Example 1 except that one or more elements M selected from B, N, and Nb were contained, and evaluated in the same manner as in Example 1. did.
The results are shown in Table 1, and it can be seen that PRSNR and sensitivity can be further improved by adding the various elements described above.

The figure which shows the relationship between the specific resistance of a thermal-diffusion layer, and PRSNR. The figure which shows the relationship between T2 / T1 and PRSNR. The figure which shows the relationship between the film thickness of a thermal-diffusion layer, and PRSNR. The figure which shows the relationship between t2 / t1 and PRSNR. The figure which shows the relationship between t2 / t1 and a sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS FIG.

Claims (15)

At least a first information layer, an intermediate layer, and a second information layer are provided in this order from the laser light incident side, and the first information layer is a thin film containing at least Bi as a main component in this order from the laser light irradiation side ( Re layer), a dielectric layer, a reflective layer, and a heat diffusion layer are laminated, and the second information layer is a thin film (Re layer) containing at least Bi as a main component in order from the laser light irradiation side, a dielectric layer A write-once two-layer optical recording medium, wherein a reflective layer is laminated, and the thermal diffusion layer contains an oxide having an electric conductivity of a specific resistance of 1 × 10 ⁻¹ Ωcm or less. The write-once two-layer structure light according to claim 1, wherein the electrically conductive oxide is either IZO (In ₂ O ₃ -ZnO) or ITO (In ₂ O ₃ -SnO ₂ ). recoding media.   The write-once two-layer structure light according to claim 1 or 2, wherein the thickness T1 of the reflective layer of the first information layer and the thickness T2 of the thermal diffusion layer are in the range of T2 / T1 = 2-8. recoding media.   The write-once two-layer optical recording medium according to any one of claims 1 to 3, wherein the thermal diffusion layer has a thickness of 30 to 90 nm.   The thickness t1 of the dielectric layer of the first information layer and the thickness t2 of the dielectric layer of the second information layer are in the range of t2 / t1 = 0.7 to 1.5. The write-once two-layer structure optical recording medium according to any one of?   2. The thickness t1 of the dielectric layer of the first information layer and the thickness t2 of the dielectric layer of the second information layer are in the range of t2 / t1 = 4.5 to 6.0. The write-once two-layer structure optical recording medium according to any one of?   The thickness of the Re layer of the first information layer is 5 to 25 nm, the thickness of the dielectric layer is 10 to 30 nm, the thickness of the Re layer of the second information layer is 5 to 25 nm, and the thickness of the dielectric layer is The write-once two-layer optical recording medium according to any one of claims 1 to 4, wherein the optical recording medium has a thickness of 10 to 30 nm.   The thickness of the Re layer of the first information layer is 5 to 25 nm, the thickness of the dielectric layer is 10 to 30 nm, the thickness of the Re layer of the second information layer is 5 to 25 nm, and the thickness of the dielectric layer is The write-once two-layer optical recording medium according to any one of claims 1 to 4, wherein the optical recording medium has a thickness of 90 to 120 nm.   9. The layer according to claim 1, wherein a layer containing a compound containing a typical element as a main component (a compound layer containing a typical element) is formed before the Re layer of the first information layer. The write-once two-layer optical recording medium described in 1.   The write-once two-layer optical recording medium according to claim 9, wherein the thickness of the compound layer containing a typical element is 70 nm or less.   The write-once two-layer optical recording medium according to claim 1, wherein the Re layer is mainly composed of Bi oxide.   Re layer is Al, Cr, Mn, Sc, In, Ru, Rh, Co, Fe, Cu, Ni, Zn, Li, Si, Ge, Zr, Ti, Hf, Sn, Pb, Mo, V, B and The write-once two-layer structure optical recording medium according to any one of claims 1 to 11, comprising at least one element M selected from Nb. The write-once two-layer optical recording medium according to claim 1, wherein the dielectric layer contains ZnS and SiO ₂ as main components. The mixing ratio of ZnS and SiO ₂ is 70: 30 to 90: 10 (mol%) write-once two-layer optical recording medium according to claim 13, wherein a is in the range of.   The write-once two-layer structure according to any one of claims 1 to 14, wherein the typical element of the compound layer containing the typical element is one or more elements selected from Zn, In, Al, and Sn. Optical recording medium.