JP2006248177A - Write-once optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a write-once type optical recording medium which exhibits good recording / reproduction characteristics in a blue laser wavelength region (500 nm or less), particularly in a wavelength region near 405 nm, is capable of high density recording and has high storage stability.
(1) On a substrate, at least a Bi oxide and M (M is at least one element selected from Mg, Al, Zn, Li, Si, Hf, Sn, Y, and B) A write-once type optical recording medium comprising a recording layer mainly composed of an oxide of), wherein the oxygen content of the oxide is less than the stoichiometric composition.
(2) On the substrate, there is provided a recording layer containing at least Bi oxide and any one of Fe, Co, V, and W as main components, and the oxygen content of the oxide is in a stoichiometric composition. Write-once type optical recording medium characterized by being less than the above.
[Selection figure] None

Description

  The present invention relates to a write once read many (WORM) optical recording medium, and more particularly to a write once optical recording medium excellent in stability capable of high density recording in a blue laser wavelength region. The present invention can also be applied in the wavelength region near 660 nm used for conventional DVDs.

The development of blue lasers capable of ultra-high-density recording on recordable optical recording media capable of recording / reproducing below the blue laser wavelength is progressing rapidly. Yes.
In a conventional write-once optical recording medium, a recording layer made of an organic material is irradiated with laser light to cause a refractive index change mainly due to decomposition and alteration of the organic material, thereby forming recording pits. The optical constants and decomposition behavior of the organic material obtained are important factors for forming good recording pits.
Therefore, it is necessary to select an organic material used for the recording layer of the write-once type optical recording medium compatible with blue laser, which has an appropriate optical property and decomposition behavior with respect to the blue laser wavelength. In other words, the recording / reproducing wavelength has a large absorption band in order to increase the reflectivity when unrecorded, and to cause a large change in refractive index due to decomposition of the organic material by laser irradiation (this provides a large degree of modulation). It is selected so as 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 having an appropriate absorption coefficient and a large refractive index.

However, no material has been found that has a conventional optical property with respect to the blue laser wavelength. This is because it is necessary to reduce the molecular skeleton or shorten the conjugated system in order to make the absorption band of the organic material near the blue laser wavelength, but this leads to a decrease in absorption coefficient, that is, a decrease in refractive index. Because. That is, there are many organic materials having an absorption band in the vicinity of the blue laser wavelength, and the absorption coefficient can be controlled, but since it does not have a large refractive index, a large degree of modulation cannot be obtained. In addition, since organic dyes are inferior in light resistance to inorganic materials, there is a problem in storage stability in a bright place.
Therefore, it has been studied to use an inorganic material for the recording layer. Although a material using a phase change material similar to that of a rewritable optical recording medium has been proposed (Patent Document 1), a write-once optical recording medium is required to be stored for a long period of time, so that the phase change material has insufficient storage characteristics It is. In addition, a method of laminating a plurality of inorganic materials and recording using the reaction as in Patent Document 2 has also been proposed, but a method using a reaction of a plurality of layers is a long-term because the reaction proceeds with time. Not suitable for storage.

As a write-once type optical recording medium capable of high-density recording even at a wavelength less than or equal to the blue laser wavelength, the present inventors have disclosed in prior applications (Japanese Patent Application Nos. 2004-66210, 2004-64452, JP-A-2003-48375, etc.) It proposes the usefulness of a recording layer mainly composed of a metalloid oxide, especially bismuth oxide.
As a write-once type optical recording medium using a metal or metalloid oxide as a recording layer, Patent Document 3 and the like to which Te, O and other elements are added are disclosed for blue-violet laser light. In addition, Patent Document 4 discloses that an incomplete oxide of a transition metal is used, and the invention includes an element containing an element other than the transition metal. There is no description. The definition of transition metal is unclear because it may or may not contain Zn, Y, etc., and there is no detailed description other than W and Mo.

There is also an old technology that uses a material with less oxygen than the stoichiometric composition in the red and infrared wavelength regions. For example, at least one selected from TeOx (0 <x <2) (Patent Document 5), TeOx, GeOx, SnOx, BiOx, SbOx, and TlOx and at least one of S and Se are used. Including (Patent Document 6), Te and Sb are contained in low oxide GeOx, or Te and Ge are contained in SbOx (Patent Document 7), Ni low oxide represented by NiOx was used. And an information recording method (Patent Document 9) that forms an image by irradiating a low oxide of In with a laser beam.
Further, Patent Document 10 discloses an invention in which an element selected from Sn, In, Bi, Zn, Al, Cu, Ge, and Sb is added to TeOx with respect to a low oxide in a red wavelength region. The text also describes BiOx, which is effective when Te, Sb, and Ge are added. This invention is an invention utilizing the so-called blackening phenomenon in which the light transmittance is changed by light irradiation. Therefore, what is recorded by blackening is an invention of a film having reversibility that returns to the original transmittance again by light irradiation. However, there is no description regarding the effect of BiOx in the blue region. Further, there is no detailed description other than the system including TeOx.

JP 09-286174 A JP 2004-79020 A JP 2002-133712 A JP 2003-237242 A JP 50-46317 A Japanese Patent No. 1444471 Japanese Patent No. 1849839 Japanese Patent No. 2656296 Japanese Patent Laid-Open No. 51-21780 Japanese Patent Publication No. 7-25209

  An object of the present invention is to provide a write-once optical recording medium that exhibits good recording / reproduction characteristics in a blue laser wavelength region (500 nm or less), particularly in a wavelength region near 405 nm, is capable of high-density recording, and has high storage stability.

The above problems are solved by the following inventions 1) to 6) (hereinafter referred to as the present inventions 1 to 6).
1) On the substrate, at least an oxide of Bi and an oxide of M (M is at least one element selected from Mg, Al, Zn, Li, Si, Hf, Sn, Y, and B). A write-once type optical recording medium comprising a recording layer as a main component, wherein the oxygen content of the oxide is less than the stoichiometric composition.
2) The recordable optical recording medium according to 1), wherein the recording layer contains any one of Fe, Co, V, and W.
3) A recording layer comprising at least a Bi oxide and any one of Fe, Co, V, and W as main components is provided on a substrate, and the oxygen content of the oxide is higher than the stoichiometric composition. Write-once type optical recording medium, characterized by
4) The write-once optical recording medium according to any one of 1) to 3), wherein at least the recording layer, the protective layer, and the reflective layer are sequentially laminated on a substrate.
5) The write-once type optical recording medium according to any one of 1) to 3), wherein at least a reflective layer, a protective layer, the recording layer, and a cover layer are sequentially laminated on a substrate.
6) The write-once type optical recording medium according to any one of 1) to 5), wherein the recording layer is sandwiched between inhibition layers that prevent oxygen and moisture from entering and leaving the recording layer.

Hereinafter, the present invention will be described in detail.
In the present invention 1, oxidation of Bi oxide and M (M is at least one element selected from Mg, Al, Zn, Li, Si, Hf, Sn, Y, and B) is formed on the recording layer. A material mainly composed of a material is used, and the oxygen content of the Bi oxide and the M oxide is made lower than the stoichiometric composition. The oxide of Bi and the oxide of M may be included in any state of a mixture, a composite oxide, and other forms. Here, the main component means that the content (mol%) of the oxide of Bi, the oxide of M, and the oxide containing both Bi and M is the highest in the recording layer.
The Bi oxide absorbs light in the blue wavelength region well, so that good recording is easy. In addition, in the combination of the oxide of Bi and the oxide of another element, if the oxygen content is less than the stoichiometric composition, crystals of Bi or other additive elements are likely to precipitate, which is sufficient even in the blue wavelength region. The degree of modulation is obtained. However, with only Bi oxides or oxides of other elements, the deposited crystals become too large, and it becomes difficult to record small marks. Therefore, if other elements are added to the Bi oxide to suppress the precipitation of crystals, the formation of small marks becomes good and the density can be increased easily. Further, the addition of other elements stabilizes the recording mark and improves storage stability.

In oxides, the ratio of the combination of element and oxygen is determined, which is called the stoichiometric composition. For example, Bi is a form in which a Bi ₂ O ₃ state in which the Bi atom is 2 and the oxygen atom is 3 can be taken as a normal compound. The ratio of Bi to oxygen is the stoichiometric composition. The stoichiometric composition varies depending on the element that combines with oxygen. For example, MgO, Al ₂ O ₃ , ZnO, Li ₂ O, SiO ₂ , HfO ₂ , SnO ₂ , Y ₂ O ₃ , B ₂ O ₃ , Fe ₂ O ₃ , Co ₂ O ₃ , V ₂ O ₅ , VO ₂ , oxides such as V ₂ O ₃ , WO ₃ etc. are formed. The oxygen content is lower than the stoichiometric composition in the case of Bi ₂ O ₃ where 0 <x <1.5 where the Bi oxide is BiOx.
Recording sensitivity is improved by making the oxygen content smaller than the stoichiometric composition. As a result, since the intensity of the recording light can be reduced, a smaller mark can be recorded with good controllability.

Taking a recording layer mainly composed of Bi oxide and Zn oxide as an example, when Bi: Zn is included at a ratio of 2: 1, the stoichiometric composition is Bi ₂ O ₃ and ZnO. Therefore, if a film having a composition ratio of Bi: Zn: O = 2: 1: 4 is formed, the stoichiometric composition is obtained. On the other hand, when O is less than 4, it means less than the stoichiometric composition.
Further, taking a recording layer mainly composed of Bi oxide and B oxide as an example, when Bi: B is included at a ratio of 2: 1, Bi ₂ O ₃ and B ₂ O ₃ are included. Since the film has a stoichiometric composition, if a film having a composition ratio of Bi: B: O = 2: 1: 4.5 is formed, the stoichiometric composition is obtained. There is also a compound called BiBO _{3, in} which case the stoichiometric composition is Bi: B: O = 1: 1: 3.
That the oxygen content is less than the stoichiometric composition means that there are atoms that are not oxidized and exist as metals. Since metal absorbs light more easily than oxide, sensitivity is improved. When a Bi oxide and an oxide of at least one element selected from Mg, Al, Zn, Li, Si, Hf, Sn, Y, and B are used in combination, a small mark can be formed. Thus, a write-once optical recording medium capable of high-density recording can be realized. In particular, Bi has a large absorption of blue wavelength light and exhibits good characteristics.

The present invention 2 is one in which any of Fe, Co, V, and W is added to the combination of oxides defined in the present invention 1, thereby enabling high-density recording. For example Bi, Si, Fe, if made of _{O, Bi 2 O 3, SiO} 2, Fe 2 O 3 is given as the stoichiometric composition. Assuming that Bi: Si: Fe = 3: 1: 4, the stoichiometric composition is obtained when O is 10.5.
Further, when V or W is added, the sensitivity is improved and good recording can be performed.

In the third aspect of the present invention, the recording layer uses a material mainly composed of an oxide of Bi and any one of Fe, Co, V, and W, and oxygen of the oxide of Bi and the oxide of another element. The content is less than the stoichiometric composition. The oxide of Bi and the oxide of other elements may be included in any state of a mixture, a composite oxide, and other forms. Here, the main component means that the content (mol%) including an oxide containing any of Bi, Fe, Co, V, and W is the highest.
Similar to the present invention 1, since there is less oxygen than in the stoichiometric composition, Bi metal is present in the recording layer, and when recording is performed, Bi crystals and the like are present in the recording mark, Small marks can be realized and high density recording can be performed.
Both Bi and Fe can easily absorb light having a blue wavelength, and can be recorded satisfactorily. Further, there are compounds of Bi, Fe, and oxygen such as BiFeO ₃ , and Bi: Fe: O = 1: 1: 3 is the stoichiometric composition in this case. Bi oxide alone makes the Bi crystal too large and the recording characteristics are difficult to improve, but combining Bi and Fe suppresses the growth of Bi or Bi oxide or Fe oxide crystals. Recording characteristics are improved.
In the case of V, there are compounds such as BiVO ₄ , and Bi: V: O = 1: 1: 4 is the stoichiometric composition in this case.
In the case of Co, it is considered that Bi ₂ O ₃ and Co ₃ O ₄ are mixed.
In the case of W, there are also compounds of Bi, W and O such as a mixture of Bi ₂ O ₃ and WO ₃ , Bi ₂ WO ₆ , Bi ₁₄ W ₂ O ₂₇ .

Invention 4 has a configuration in which the recording layer according to any one of Inventions 1 to 3, a protective layer, and a reflective layer are sequentially laminated. An organic protective layer made of an ultraviolet curable resin may be further provided on the reflective layer.
By optimizing the thickness of each layer and increasing the reflectance, good recording can be achieved. Further, the protective layer prevents mixing of the recording layer and the reflective layer and also controls the thermal conductivity. The reflective layer has a function of reflecting light and a function of dissipating heat to realize good recording.
The substrate material is not particularly limited as long as it has excellent thermal and mechanical properties and has excellent light transmission characteristics when recording / reproduction is performed from the substrate side (through the substrate).
Specific examples include polycarbonate, polymethyl methacrylate, amorphous polyolefin, cellulose acetate, polyethylene terephthalate and the like, and polycarbonate and amorphous polyolefin are preferred.
The thickness of the substrate varies depending on the application and is not particularly limited.

As a material of the reflective layer, a material having a sufficiently high reflectance at the wavelength of the reproduction light, for example, a metal such as Au, Al, Ag, Cu, Ti, Cr, Ni, Pt, Ta, Pd, alone or in an alloy is used. Can be used. Among them, 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 preferable because they are inexpensive and easy to achieve a high reflectance. An Ag alloy containing a small amount of In, Bi or the like is particularly preferable because of its high reflectance, high corrosion resistance, and high stability. 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.
A preferable film thickness of the reflective layer is 50 to 300 nm.

As the protective layer, a material that does not cause decomposition, sublimation, cavitation or the like due to the heat of the recording layer is usually preferable. For example, Al ₂ O ₃ , MgO, CeO, ZrO ₂ , Nb ₂ O ₅ , SiO ₂ , ZnO, Simple oxides such as TiO ₂ ; SiO ₂ , 2MgO · SiO ₂ , MgO · SiO ₂ , CaO · SiO, ZrO · SiO, 3AlO · 2SiO, 2MgO · 2AlO · 5SiO ₂ , Li ₂ O · Al ₂ Silicate oxides such as O ₃ .4SiO ₂ ; Al ₂ TiO ₅ , MgAl ₂ O ₄ , Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ , BaTiO ₃ , LiNbO ₃ , PZT [Pb (Zr, Ti ) _{O 3],} PLZT [(Pb, La) (Zr, Ti) O 3 ], oxides of multiple oxide such as ferrite; _{or, Si 3 N 4, Si 6} -Z _{l Z O Z N 8-Z} , AlN, BN, non-oxide of the nitride such as _{TiN; SiC, B 4 C,} TiC, non-oxide carbide system such as _{WC; LaB 6, TiB 2,} ZrB 2 Boride-based non-oxides such as MgF, fluorides such as MgF, sulfide-based non-oxides such as CdS and MoS ₂ ; silicide-based non-oxides such as MoSi ₂ ; amorphous carbon, graphite, diamond, etc. Carbon-based non-oxides can be used. Mixtures of these, for example composite oxides, can also be used. Further, an organic material can be used as the protective layer.

For example, it is preferable to use SiO ₂ or ZnS · SiO ₂ as a main component (main component) from the viewpoint of transparency to recording / reproducing light and productivity. A composite oxide of Nb ₂ O ₅ , CeO, and SiO _2, a composite oxide mainly composed of ZnO, and the like are also preferable. In order to obtain a sufficient heat insulating effect, it is also preferable to use ZrO ₂ as a main component (main component). Further, an oxide composed of ZnS, ZrO ₂ , Y ₂ O ₃ , SiO ₂ , or composed of ZrO ₂ , TiO ₂ , SiO ₂ , and X, where X is Y ₂ O ₃ , CeO, Al ₂ O ₃ , MgO, An oxide that is at least one selected from CaO, Nb ₂ O ₅ , ZnO, and rare earth oxides is also preferable.
Usually, the protective layer is preferably transparent to the recording / reproducing wavelength in order to increase the reflectance, but in order to adjust the recording sensitivity, a light absorption function to the recording / reproducing wavelength can be given to some extent. is there.

Invention 5 has a configuration in which at least a reflective layer, a protective layer, the recording layer according to any one of Inventions 1 to 3 and a cover layer are sequentially laminated on a substrate. As a result, a write-once optical recording medium capable of high-density recording by entering light not from the substrate side but from the cover layer side is obtained. As the substrate, the reflective layer, and the protective layer, those described above can be used. 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.
By reducing the thickness of the cover layer, the NA of the objective lens can be increased. 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 present invention 6 has a configuration in which the recording layer according to any one of the present inventions 1 to 3 is sandwiched between inhibition layers that prevent oxygen and moisture from entering and leaving the recording layer.
A substrate such as polycarbonate easily allows oxygen or moisture to pass through. If the substrate and the recording layer are in contact with each other, the recording layer may be damaged by moisture or oxygen that has entered through the substrate. Therefore, in order to inhibit oxygen, moisture, etc. from entering the recording layer, providing an inhibition layer on both sides of the recording layer is effective in improving stability.
The material of the inhibition layer is not particularly limited as long as it is difficult for oxygen and moisture to pass therethrough and satisfies the conditions. For example, oxides such as Al ₂ O ₃ , MgO, CeO, ZrO ₂ , Nb ₂ O ₅ , SiO ₂ , ZnO, TiO ₂ , composites thereof, or nitrides such as SiN, AlN, BN, and TiN, SiC , Carbides such as B ₄ C, TiC, and WC, fluorides such as MgF, carbon-based materials such as amorphous carbon, and diamond can be used. Mixtures of these, for example composite oxides, can also be used. Furthermore, it is also possible to use an organic substance that hardly allows oxygen or moisture to pass through, such as an ultraviolet curable resin used for a cover layer or the like as a protective layer. From the viewpoint of transparency with respect to recording / reproducing light and productivity, a material mainly composed of SiO ₂ or ZnS · SiO ₂ is preferable. A composite oxide of TiOC, Nb ₂ O ₅ —SiO ₂ , Nb ₂ O ₅ —CeO—SiO _2, a composite oxide mainly composed of ZnO, or the like is also preferable.
The inhibition layer is usually preferably transparent with respect to the recording / reproducing wavelength in order to increase the reflectance. However, in order to adjust the recording sensitivity, a light absorption function with respect to the recording / reproducing wavelength can be given to some extent. is there. Further, depending on the material, the protective layer can also serve as the inhibition layer.

  According to the present invention, it is possible to provide a write-once type optical recording medium that exhibits good recording / reproduction characteristics in a blue laser wavelength region (500 nm or less), particularly a wavelength region near 405 nm, is capable of high density recording, and has high storage stability.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited by these Examples.

Example 1
On a polycarbonate substrate having guide grooves (groove depth 21 nm, track pitch 0.46 μm, groove width 0.3 μm), a BiBO layer (recording layer) having a thickness of 5 nm and ZnS—SiO ₂ (80 : A protective layer having a thickness of 14 nm was sequentially laminated.
The recording layer was formed using a Bi ₂ BOx target having a diameter of 76.2 mm at an RF power of 100 W and an Ar gas flow rate of 40 sccm. The target of Bi ₂ BOx is obtained by mixing and firing Bi ₂ O ₃ and B ₂ O ₃ at a ratio of 2: 1. Since the oxygen content after firing was not quantified, it was described as Ox.
When this recording layer was quantitatively analyzed by the RBS (Rutherford Backscattering Spectrometry) method, the ratio was approximately Bi: B: O = 4: 2: 6. Since the stoichiometric composition of the 2: 1 mixture of Bi ₂ O ₃ and B ₂ O ₃ is Bi: B: O = 4: 2: 9, the oxygen content of the recording layer is higher than the stoichiometric composition. It will be less.
Subsequently, an Ag reflective layer having a film thickness of 100 nm is formed by sputtering, and an organic protective layer having a film thickness of about 5 μm made of an ultraviolet curable resin (San Nopco Co., Ltd .: NopcoCure 134) is formed by spin coating. Got.
Binary recording was performed on the above optical recording medium under the following conditions using an optical disc evaluation apparatus DDU-1000 (wavelength: 405 nm, NA: 0.65) manufactured by Pulstec Industrial Co., Ltd.
・ Modulation method: 1-7 modulation
Recording linear density: shortest mark length 2T = 0.204 (μm)
Recording linear velocity: 6.61 (m / s)
・ Waveform equalization: Limit equalizer As a result, with a recording power of 10.8mW, a jitter of 6.3% and a modulation factor of 50% can be obtained in the continuous recording unit, realizing good binary recording characteristics. It was.
Further, even when the recording power exceeds the optimum recording power, the reproduction signal level (RF Level) of the recording mark portion does not change greatly, and has a high modulation degree and a wide recording power margin. The medium could be realized.

Example 2
On a polycarbonate substrate having guide grooves (groove depth 21 nm, track pitch 0.46 μm, groove width 0.3 μm), a BiSiFeO film (recording layer) having a thickness of 10 nm and ZnS—SiO ₂ (80 A protective layer having a film thickness of 65 nm was sequentially formed to obtain a write-once type optical recording medium.
The recording layer was formed using a Bi ₃ SiFe ₄ Ox target having a diameter of 152.4 mm at an RF power of 400 W and an Ar gas flow rate of 40 sccm.
When this recording layer was quantitatively analyzed by the RBS method, it was about Bi: Si: Fe: O = 4: 1: 1: 5. When Bi ₂ O ₃ , SiO ₂ and Fe ₂ O ₃ are mixed at 4: 1: 1, the stoichiometric composition of the mixture is Bi: Si: Fe: O = 4: 1: 1: 9.5. Therefore, the oxygen content of the recording layer is less than the stoichiometric composition.
Using the same optical disk evaluation apparatus as in Example 1, binary recording was performed on the optical recording medium under the following conditions.
・ Modulation method: 1-7 modulation
Recording linear density: shortest mark length 2T = 0.204 (μm)
Recording linear velocity: 6.00 (m / s)
・ Waveform equalization: Limit equalizer As a result, with continuous recording part, values of 7.4% jitter and 55% modulation can be obtained at recording power of 9.3mW, and good binary recording characteristics can be realized. It was.

Example 3
On a polycarbonate substrate having a guide groove (groove depth 50 nm, track pitch 0.46 μm, groove width 0.22 μm), a BiZnO film (recording layer) having a film thickness of 15 nm is provided by sputtering, and write-once optical recording A medium was obtained.
The recording layer was formed using two targets of Bi ₂ O ₃ and Zn with a diameter of 76.2 mm at an RF power of 100 W and an Ar gas flow rate of 40 sccm.
When this recording layer was quantitatively analyzed by the RBS method, Bi: Zn: O = 4: 3: 6. When Bi ₂ O ₃ and ZnO are mixed at a ratio of 4: 3, the stoichiometric composition of the mixture is Bi: Zn: O = 4: 3: 9. Therefore, the oxygen content of the recording layer is more than the stoichiometric composition. Will be less.
Using the same optical disk evaluation apparatus as in Example 1, binary recording was performed on the optical recording medium under the following conditions.
・ Modulation method: 1-7 modulation
Recording linear density: shortest mark length (2T) = 0.231 (μm)
Recording linear velocity: 6.0 (m / s)
・ Waveform equalization: Normal equalizer As a result, with a recording power of 5.5 mW, a jitter value of 8.8% and a modulation factor of 60% or more can be obtained in a continuous recording unit, realizing good binary recording characteristics. did it.

Example 4
On a polycarbonate substrate having a guide groove (groove depth 21 nm, track pitch 0.46 μm, groove width 0.3 μm), a BiFeO film (recording layer) having a thickness of 5 nm and ZnS—SiO ₂ (80 : A protective layer having a film thickness of 98 nm is sequentially formed to obtain a write-once type optical recording medium.
The recording layer was formed using a Bi ₁₀ Fe ₅ Ox target having a diameter of 76.2 mm at an RF power of 100 W and an Ar gas flow rate of 40 sccm.
When this recording layer was quantitatively analyzed by the RBS method, it was almost Bi: Fe: O = 3: 1: 5. Since the stoichiometric composition of the mixture of Bi ₂ O ₃ and Fe ₂ O ₃ is Bi: Fe: O = 3: 1: 6, the oxygen content of the recording layer is less than the stoichiometric composition value. Become.
As a result of performing binary recording on the optical recording medium using the same optical disk evaluation apparatus as in Example 1 under the same conditions as in Example 2, the recording power was 5.7 mW and the jitter was 4. The values of 6% and modulation degree 63% were obtained, and good binary recording characteristics could be realized.

Example 5
Write-once light in the same manner as in Example 1 except that a recording layer was formed using a Bi ₂ WOx target prepared by mixing and sintering Bi ₂ O ₃ and WO ₃ at a ratio of 2: 1. A recording medium was obtained.
When this recording layer was quantitatively analyzed by the RBS method, it was almost Bi: W: O = 4: 1: 5. Since the stoichiometric composition of the 2: 1 mixture of Bi ₂ O ₃ and WO ₃ is Bi: W: O = 4: 1: 9, the oxygen content of the recording layer is less than the stoichiometric composition value. It will be.
As a result of recording on the optical recording medium in the same manner as in Example 1, in the continuous recording portion, values of 10.7% jitter and 51% modulation were obtained at a recording power of 10.2 mW. Binary recording characteristics could be realized.

上記光記録媒体に対し、実施例１と同じ光ディスク評価装置を用いて、以下の条件で、二値記録を行った。
・変調方式 ： １−７変調
・記録線密度： 最短マーク長（２Ｔ）＝０．２０４（μｍ）
・記録線速度： ６．０（ｍ／ｓ）
・波形等化 ： ノーマルイコライザ
その結果、連続記録部において、記録パワー６．９ｍＷでジッタ１０．２％という値が得られ、良好な二値記録特性を実現することができた。
また、記録パワーが最適記録パワーを超えた場合でも、記録マーク部の再生信号レベル（ＲＦ Ｌｅｖｅｌ）が大きく変化することがなく、高い変調度を有し、広い記録パワーマージンを有する追記型光記録媒体を実現することができた。 Example 6
A polycarbonate substrate having guide grooves (groove depth 50 nm, track pitch 0.46 μm, groove width 0.22 μm) is made of ZnS—SiO ₂ (80:20 mol%) with a film thickness of 65 nm by sputtering. A protective layer and a 15 nm thick BiFeO film (recording layer) were sequentially laminated.
The recording layer was formed using a Bi ₃ Fe ₅ Ox target having a diameter of 154.2 mm at an RF power of 400 W and an Ar gas flow rate of 40 sccm.
When this recording layer was quantitatively analyzed by the RBS method, it was almost Bi: Fe: O = 4: 5: 12. Since the stoichiometric composition of the mixture of Bi ₂ O ₃ and Fe ₂ O ₃ is Bi: Fe: O = 4: 5: 13.5, the oxygen content of the recording layer is smaller than the stoichiometric composition value. It will be.
Next, on the recording layer, an organic material layer (average film thickness of about 30 nm) composed of a dye represented by the following [Chemical Formula 1] is formed by spin coating, and further Ag reflection having a film thickness of 150 nm is formed thereon by sputtering. A write-once type optical recording medium was obtained by providing an organic protective layer having a film thickness of about 5 μm consisting of a layer, an ultraviolet curable resin (manufactured by San Nopco: NopcoCure 134).
The dye of [Chemical Formula 1] is a material used for conventional DVD-R and DVD + R, and is a material that hardly absorbs in the blue laser region.

Using the same optical disk evaluation apparatus as in Example 1, binary recording was performed on the optical recording medium under the following conditions.
・ Modulation method: 1-7 modulation
Recording linear density: shortest mark length (2T) = 0.204 (μm)
Recording linear velocity: 6.0 (m / s)
-Waveform equalization: Normal equalizer As a result, a value of 10.2% jitter was obtained at a recording power of 6.9 mW in a continuous recording portion, and good binary recording characteristics could be realized.
Further, even when the recording power exceeds the optimum recording power, the reproduction signal level (RF Level) of the recording mark portion does not change greatly, and has a high modulation degree and a wide recording power margin. The medium could be realized.

Example 7
On a polycarbonate substrate having guide grooves (groove depth 20 nm, track pitch 0.32 μm, groove width 0.155 μm), a 100 nm-thick Ag reflection layer, 16 nm-thickness ZnS—SiO ₂ (by sputtering) is used. 85:15 mol%) and a BiFeO layer (recording layer) having a thickness of 7 nm were sequentially laminated. This recording layer is the same film as in Example 4.
Next, a 0.1 mm thick cover layer (manufactured by Teijin: Pure Ace) made of an ultraviolet curable resin was adhered to obtain a write-once type optical recording medium.
Using the same optical disk evaluation apparatus as in Example 1, binary recording was performed on the optical recording medium under the following conditions.
・ Modulation method: 1-7 modulation
Recording linear density: shortest mark length (2T) = 0.149 (μm)
Recording linear velocity: 4.9 (m / s)
-Waveform equalization: Limit equalizer As a result, a jitter value of 8.0% was obtained at a recording power of 7.3 mW, and good binary recording characteristics could be realized.
Further, even when the recording power exceeds the optimum recording power, the reproduction signal level (RF Level) of the recording mark portion does not change greatly, and has a high modulation degree and a wide recording power margin. The medium could be realized.

Example 8
The same substrate and BiFeO film as in Example 4 were used, and on this substrate, a 2 nm-thickness inhibition layer made of ZrN, a 5 nm-thickness BiFeO film (recording layer), ZnS—SiO ₂ (80 : A 20 nm thick protective layer with a thickness of 14 nm and an Ag reflective layer with a thickness of 80 nm are sequentially formed, and further a film thickness of an ultraviolet curable resin (manufactured by San Nopco Co., Ltd .: NopcoCure 134) by spin coating. A write-once type optical recording medium was obtained by providing an organic protective layer of about 5 μm. The protective layer also serves as an inhibition layer.
As a result of recording on this optical recording medium in the same manner as in Example 1, with a recording power of 10.1 mW, a jitter of 7.2% and a modulation factor of 0.56 were obtained, and good binary recording characteristics were obtained. Was able to be realized.
Further, even when the recording power exceeds the optimum recording power, the reproduction signal level (RF Level) of the recording mark portion does not change greatly, and has a high modulation degree and a wide recording power margin. The medium could be realized.

Claims (6)

  The main component is at least an oxide of Bi and M (M is at least one element selected from Mg, Al, Zn, Li, Si, Hf, Sn, Y, and B) on the substrate. A write-once optical recording medium, characterized in that the oxygen content of the oxide is less than the stoichiometric composition.   2. The write-once type optical recording medium according to claim 1, wherein the recording layer contains any one of Fe, Co, V, and W.   Provided on the substrate is a recording layer containing at least a Bi oxide and one of Fe, Co, V, and W as main components, and the oxygen content of the oxide is less than the stoichiometric composition. A write-once optical recording medium characterized by the above.   The write-once type optical recording medium according to claim 1, wherein at least the recording layer, the protective layer, and the reflective layer are sequentially laminated on a substrate.   The write-once type optical recording medium according to claim 1, wherein at least a reflective layer, a protective layer, the recording layer, and a cover layer are sequentially laminated on the substrate. The write-once type optical recording medium according to claim 1, wherein the recording layer has a configuration sandwiched between inhibition layers that prevent oxygen and moisture from entering and leaving the recording layer.