JP2007059039A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve high speed recording to a semi-transparent information layer without excessively increasing the power of a laser, deteriorating the thermal stability of an amorphous mark, and causing peeling of a film in an optical recording medium having two or more information layers. <P>SOLUTION: The optical recording medium 10 has a substrate 12, a first information layer 14 which is provided in the beam incident side of the substrate 12, and a second information layer 16 which serves as the semi-transparent information layer and is provided more in the beam incident side from the first information layer. The second information layer 16 is configured to include: a recording film 18 formed of a phase-change material which is rewritable by means of an optical system of λ/NA≤650 nm, NA being the numerical aperture of an objective lens, λ being a wavelength of a laser beam; and an interface layer 20 which is provided adjacent to the beam incident side of the recording film 18. The interface layer 20 is formed of ZnS, SiO<SB>2</SB>, and Cr<SB>2</SB>O<SB>3</SB>, and the recording film 18 contains Sb as a main component and Ge as a minor component. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical recording medium called a next generation DVD (digital versatile disk).

  A next-generation DVD has been proposed that uses an optical system with a laser wavelength λ of 405 nm (blue) and a numerical aperture NA = 0.85 of the objective lens. It has two information layers on one side and a rewriting speed. Has been commercialized as a rewritable optical recording medium with a 1 × speed (linear velocity of about 5.0 m / s). In addition to this, there is a next-generation DVD of a standard with a laser wavelength λ = 405 nm and a numerical aperture NA = 0.65.

  In such a next-generation DVD, further increase in storage capacity and higher speed recording are required.

  In the optical recording medium having two layers or more information layers on one side as described above, the information layers other than the information layer farthest from the light incident surface of the laser beam are directed to the information layers farthest from the light incident surface. Is translucent to enable recording and reproduction.

  In this case, it is necessary to reduce the thickness of the phase change recording film included in the information layer. However, as the film thickness is reduced, the crystallization speed and the erasure rate decrease, and the recording mark (amorphous) is erased. (Crystallization) becomes difficult and the rewriting speed is reduced.

  The reduction in the erasure rate becomes more remarkable as the time for the laser beam spot size to pass through a certain point on the phase change recording film becomes shorter. That is, the higher the linear velocity, the lower the erasure rate. Therefore, the higher the density and capacity of the optical recording medium, the more difficult it is to improve the rewriting speed.

As a means for improving the crystallization speed of the phase change recording film as described above, for example, as described in Patent Document 1, a phase change recording film made of a compound phase change material such as Ge ₄ Sb ₂ Te _{7 is} used. It is disclosed that Cr ₂ O ₃ is used as the interface layer, and the effect of improving the number of rewrites by preventing the diffusion of ZnS into the recording film and improving the crystallization speed can be obtained.

However, when a compound phase change material such as GeSbTe or GeBiTe is used for the recording film of the semi-transmissive information layer in the multilayer optical recording medium and a Cr ₂ O ₃ interface layer is added, a high-speed recording is studied, and the laser wavelength is 405 nm. In an optical system with NA = 0.85 (or 0.65), amorphous crystallization could not be achieved at a linear velocity of 20 m / s (4 × speed). Therefore, in the field of next-generation DVD, it has been difficult to cope with high-speed recording at a quadruple speed or higher by using a compound material such as GeSbTe or GeBiTe as the phase change recording film in the semi-transmissive information layer.

  In contrast, when an SbTe eutectic material containing Sb as a main component is used as the phase change recording film, the crystallization rate can be controlled by the Sb content, and the melting point is higher than that of the compound material. Since the temperature is 600 ° C. or lower, the power of the laser beam for forming the amorphous mark can be reduced.

  However, when this SbTe eutectic material is used as a recording film, if the Sb content is increased in order to cope with high-speed recording, the crystallization / activation energy decreases and the thermal stability of the amorphous mark This causes the problem of damage.

In contrast, the inventor formed a recording film of a phase change material in the semi-transmissive information layer with Sb and Ge as main components and Mg as an additive component, and a laser beam was applied to the recording film. It has been found that by forming the interface layer adjacent to the light incident side from Cr ₂ O ₃ , high-speed recording can be performed without excessive laser power and without impairing the thermal stability of the amorphous mark. And filed in Japanese Patent Application No. 2005-095880.

  However, this optical recording medium has a problem that if it is stored under high temperature and high humidity, the interface layer may be peeled off and recording may become impossible.

JP 2003-228881 A

  The present invention has been made in view of the above problems, and can perform high-speed recording without increasing the laser power for forming an amorphous mark and without impairing the thermal stability of the amorphous mark, It is an object of the present invention to provide an optical recording medium in which the interface layer does not peel even when stored under high temperature and high humidity.

As a result of diligent research, the present inventor has found that when the interface layer is formed of ZnS, SiO ₂ and Cr ₂ O ₃ instead of Cr ₂ O ₃ as described above, the interface layer can be stored even at high temperature and high humidity. The present inventors have found that high speed recording can be performed without causing peeling.

  That is, the above-described problems are solved by the following embodiments.

(1) A substrate, a first information layer provided on the light incident side of the laser beam in the substrate, and at least one semi-transmissive information layer provided further on the light incident side than the first information layer The semi-transmissive information layer includes a recording film and an interface layer provided adjacent to the light incident side of the recording film, and the recording film includes an objective lens. An optical recording medium formed of a phase change material rewritable by an optical system of λ / NA ≦ 650 nm where NA is the numerical aperture and λ is the wavelength of the laser beam, and the recording film contains Sb as a main component An optical recording medium characterized in that it contains at least Ge as a subcomponent, and the interface layer is made of ZnS, SiO ₂ and Cr ₂ O ₃ .

(2) The optical recording medium according to (1), wherein the content of Cr ₂ O ₃ in the interface layer is 15 mol% or more and 90 mol% or less.

  (3) The optical recording medium according to (1) or (2), wherein the recording film has Sb of 77.2 at% or more and 88 at% or less and Ge of 9.9 at% or more and 21 at% or less. .

  (4) The optical recording medium according to (1), (2), or (3), wherein the recording film contains 1 at% or more and 3.9 at% or less with Mg as an additive component.

  (5) The optical recording medium according to any one of (1) to (4), wherein the interface layer has a thickness of 0.4 nm to 9 nm.

  (6) The optical recording medium according to any one of (1) to (4), wherein the thickness of the interface layer is not less than 0.5 nm and not more than 8 nm.

(7) The composition of the interface layer is {(ZnS) _0.8 (SiO ₂ ) _0.2 } _(100-X) (Cr ₂ O ₃ ) _X , and 39 ≦ X ≦ 86. The optical recording medium according to any one of (1) to (6).

In the optical recording medium of the present invention, the recording film is formed of an SbGe eutectic material, and an interface layer made of ZnS, SiO ₂ , Cr ₂ O ₃ is formed on the laser beam incident side. However, the interface layer promotes the generation of crystal nuclei from the recording film interface, the crystal nuclei are rapidly grown from the generated crystal nuclei, the crystallization time is shortened, without increasing the laser power, and High-speed recording is possible without impairing the thermal stability of the amorphous mark. Further, the interface layer did not peel off even after storage at high temperature and high humidity.

An optical recording medium according to the best mode includes a substrate, a first information layer provided on the light incident side of the laser beam on the substrate, and a half provided on the light incident side further than the first information layer. A translucent information layer, and the semi-transparent information layer includes a recording film and an interface layer provided adjacent to the light incident side of the recording film, and the recording film includes: A phase-change material rewritable by an optical system of λ / NA ≦ 650 nm when Sb is a main component and at least Ge is a subcomponent, the numerical aperture of the objective lens is NA, and the wavelength of the laser beam is λ. The interface layer is made of ZnS, SiO ₂ and Cr ₂ O ₃ .

  As a configuration example of the transflective information layer, a first dielectric layer, a reflective layer, a second dielectric layer, a recording film (layer), an interface layer, a third dielectric layer, and a heat dissipation layer are sequentially stacked on a substrate. The thing which was done is mentioned.

The first dielectric layer is provided for protecting the reflective layer and adjusting the light transmittance, and the material is not particularly limited. Ti, Zr, Hf, Ta, Si, Al, Mg, Y, Ce, Zn An oxide, nitride, sulfide, carbide, fluoride, or a composite thereof containing at least one metal selected from In, Cr, Nb, or the like is used. In the best mode, it is formed of a material containing zirconium oxide as a main component. The main component here means that the molar ratio to the whole is 60% or more. The film thickness D ₁ of the first dielectric layer is preferably ₁ nm ≦ D ₁ ≦ 60 nm. If the thickness is less than 1 nm, the protection of the reflective layer is insufficient, and if it is thicker than 60 nm, the light transmittance is outside the preferred range.

  The reflective layer is provided for heat dissipation and optical interference effect, and an Ag alloy is preferably used as the material, and the film thickness Tr is 0 <Tr <30 nm for a semi-transmissive structure. More preferably, 0 <Tr <20 nm. The preferred film thickness Trec of the recording film (layer) is 2 nm ≦ Trec ≦ 12 nm, preferably 2.5 nm ≦ Trec ≦ 8 nm.

  Accordingly, the light transmittance at the recording wavelength of the entire transflective information layer is set to be 30% or more and 80% or less. If the light transmittance of the semi-transmissive information layer is less than 30%, it becomes difficult to record on the information layer farthest from the light incident surface of the laser beam, and if it exceeds 80%, it becomes difficult to record on the semi-transmissive information layer. Because. This is a general condition required for a translucent information layer.

  The recording film (layer) is composed of at least Sb and Ge. Further, at least one additive component selected from Mg, Al, Si, Mn, Zn, Ga, Sn, Bi, In, and the like may be included.

  A preferable atomic weight ratio of Sb is 77.2 ≦ Sb ≦ 88, and more preferably 81 ≦ Sb ≦ 88. If Sb is less than 77.2 at%, the crystallization speed decreases, and it becomes difficult to erase the mark. In addition, the thermal stability of the mark is impaired. A preferred atomic weight ratio of Ge is 10 ≦ Ge <22, and more preferably 10 ≦ Ge ≦ 21. If Ge is less than 10 at%, the thermal stability of the mark is impaired. On the other hand, if it exceeds 21 at%, the crystallization speed decreases and it becomes difficult to erase. A preferable atomic weight ratio of at least one additive component selected from Mg and the like is 1 ≦ Mg ≦ 3.9. If Mg is less than 1 at%, a noise reduction effect cannot be obtained. On the other hand, if it is more than 3.9 at%, the crystallization speed is lowered and erasure becomes difficult.

The second dielectric layer controls the protection of the recording layer and the reflective layer and controls heat dissipation from the recording layer to the reflective layer. The material is not particularly limited, and is an oxide or nitride containing at least one metal selected from Ti, Zr, Hf, Ta, Si, Al, Mg, Y, Ce, Zn, In, Cr, Nb, and the like. Sulphides, sulfides, carbides, fluorides, or composites thereof. In the embodiment of the present invention, it is formed of a material containing zirconium oxide as a main component. The main component means that the molar ratio in the whole is 60% or more. The film thickness D ₂ is preferably ₂ nm ≦ D ₂ ≦ 20 nm. If the thickness is less than 2 nm, the protection of the recording layer and the reflective layer is insufficient. If the thickness is greater than 20 nm, the heat from the recording layer cannot quickly escape to the reflective layer, and the cooling rate decreases to accurately form an amorphous mark. Difficult to do.

The interface layer controls the crystallization rate. By using ZnS, SiO ₂ , Cr ₂ O ₃ as the interface layer, and particularly using Cr ₂ O ₃ , the crystallization speed can be improved. The film thickness Ti of the interface layer is 0.5 nm ≦ Ti ≦ 8 nm. Thickness maximum line speed rewritable is less than 0.5nm interface layer can not be obtained, also it is thicker and rewritable maximum linear velocity than 8nm improved, the semi-transparent information layer by light absorption by Cr ₂ O ₃ Will reduce the light transmittance.

The third dielectric layer adjusts optical characteristics and controls heat dissipation from the recording layer to the heat dissipation layer. The material is not particularly limited, and is an oxide or nitride containing at least one metal selected from Ti, Zr, Hf, Ta, Si, Al, Mg, Y, Ce, Zn, In, Cr, Nb, and the like. Sulphides, sulfides, carbides, fluorides, or composites thereof. Preferably, it is formed by a mixture of ZnS and SiO ₂ . A preferred molar ratio of ZnS to SiO ₂ is 50:50 to 95: 5. Outside this range, the refractive index of the mixture of ZnS and SiO ₂ changes, making it difficult to adjust the optical characteristics. The thickness D ₃ of the third dielectric layer is preferably 5 nm ≦ D ₃ ≦ 50 nm. If the thickness is less than 5 nm, it is difficult to protect the recording layer and adjust the optical characteristics. If the thickness is more than 50 nm, the heat dissipation from the recording layer to the heat dissipation layer decreases.

The heat dissipation layer is for controlling the heat dissipation from the recording layer and enhancing the cooling effect of the recording layer to facilitate the accurate formation of the amorphous mark. The material is not particularly limited, but a material having higher thermal conductivity than the material of the third dielectric layer is preferable, and AlN, SiN, BN, Al ₂ O ₃ , TiO _{2 and the} like are preferable. In the best embodiment, it is formed by AlN. A preferable film thickness Theat of the heat dissipation layer is 15 ≦ Theat <150 nm, and more preferably 20 ≦ Theat <120 nm. When the film thickness of the heat dissipation layer is less than 15 nm, the heat dissipation effect from the recording layer is reduced, and when it is 150 nm or more, the time required for film formation becomes long and the productivity is lowered.

  The first, second and third dielectric layers may be composed of a single layer or a plurality of dielectric layers of two or more layers.

  Hereinafter, an optical recording medium 10 according to the first embodiment of the present invention will be described in detail with reference to FIG.

  The optical recording medium 10 includes a substrate 12, a first information layer 14 provided on the light incident side (upper side in FIG. 1) of the substrate 12, and light further than the first information layer 14. A second information layer 16 which is a transflective information layer provided on the incident side, and the second information layer 16 is adjacent to the recording film 18 and the light incident side of the recording film 18. The interface layer 20 is provided.

  A spacer layer 22 is provided between the first information layer 14 and the second information layer 16, and a light transmission layer 24 is provided on the light incident side of the second information layer 16. .

The second information layer 16 is composed of, for example, a first dielectric layer 26 made of a ZrO ₂ film having a thickness of 5 nm and an AgPdCu (98: 1: 1 at%) film having a thickness of 10 nm, for example, from the spacer layer 22 side. The reflective layer 28, the second dielectric layer 30 made of a ZrO ₂ film having a thickness of 5 nm, the recording film 18 having a thickness of 6 nm, and the ZnS, SiO ₂ , Cr ₂ O ₃ film having a thickness of 5 nm, for example. Sputtering of the interface layer 20, a third dielectric layer 32 made of, for example, a ZnS: SiO ₂ (80:20 mol%) film having a thickness of 15 nm, and a heat dissipation layer 34 made of, for example, an AlN film having a thickness of 50 nm. It is formed and constituted.

  The substrate 12 is made of polycarbonate having a thickness of 1.1 mm, the spacer layer 22 has a thickness of 25 μm, and the light transmission layer 24 has a thickness of 75 μm by spin coating using an ultraviolet curable resin. Is formed. The light transmission layer 24 is formed after the second information layer is crystallized on the entire surface by an initializer.

  In Example 1, the recording film 18 is made of SbGe (87.0: 13.0 at%).

  The optical recording medium 10 according to Example 1 is an evaluator having an optical system with NA = 0.85 by a laser beam having a wavelength of 405 nm. The linear velocity is 19.68 m / s (quad speed), and the clock frequency is 264 MHz. The recording erasure characteristics were evaluated under the condition of the recording signal (1,7) RLL modulation signal. Reproduction was performed at a linear velocity of 4.92 m / s. Moreover, film | membrane peeling confirmed the sample after 80 degreeC85% RH50 50-hour storage with the optical microscope.

  Table 1 shows the evaluation of film peeling, erasing characteristics, and jitter of samples 1 to 10 in which the composition of the interface layer is changed in the optical recording medium having the above conditions. Here, if the erasure rate when erasing the 8T signal once at DC at 4 × speed is 25 dB or more, ○ is less than 25 dB, and × 4 × jitter is the jitter value at the 10th recording of the mixed signal is less than 9%. ○, if it is 9% or more and less than 12%, x if it is 12% or more, x if a release film is generated, and ○ if it is not generated.

Also shows the relationship between the content and the 4-speed erasing ratio of Cr ₂ O ₃ in Table 1 in FIG. When the erasing rate was 25 dB, Cr ₂ O ₃ was 15 mol%.

  FIG. 3 shows the change in DC erasure rate when the linear velocity during erasure of Samples 1, 4, 6, 7, and 10 is changed. From FIG. 3, it can be seen that samples 4, 6, 7, and 10 have an erasure rate of 25 dB or more at a quadruple speed (linear velocity 19.68 m / s).

  FIG. 4 shows the jitter characteristics of Samples 4, 6, 7, and 10 in 4 × speed recording. FIG. 4 shows that good recording characteristics with a jitter value of 9% or less are obtained in a region where the recording power is in a certain range.

Next, in the optical recording medium, the interfacial layer thickness was changed, and the quadruple speed erasure rate, quadruple speed jitter, and modulation degree were measured, and the results are shown in Table 2. The composition of ZnS: SiO ₂ : Cr ₂ O ₃ is 26: 7: 67 (mol%).

  The criteria for determining the quadruple speed erasure rate and quadruple speed jitter are the same as in Table 1. As for the degree of modulation, ◯ is given when it is 35% or more, Δ is given when it is 30% or more and less than 35%, and x is given when it is less than 30%. Here, the degree of modulation is measured by measuring the reflectance of the crystal part (unrecorded part) and the amorphous part (recording part) after recording a signal of a random pattern, and (reflectance of crystal part−reflectance of amorphous part) / The reflectance of the crystal part × 100 was defined as the modulation degree.

From the above, the composition of the interface layer is {(ZnS) _0.8 (SiO ₂ ) _0.2 } _(100-X).
(Cr ₂ O ₃ ) _X , 39 ≦ X ≦ 86, and a film thickness of 0.5 nm or more and 8 nm or less enables high speed recording without impairing the quadruple speed erasure rate and quadruple speed jitter characteristics. In addition, it can be seen that the film peeling of the interface layer does not occur.

  In Example 2, an optical recording medium (samples 11 to 21) similar to that in Example 1 in which the composition of the SbGeMg recording film was changed was prepared. The erasure rate when erasing once with an erasing power of 4 mW was measured. Further, from the relationship between the erasing linear velocity and the erasing rate, the linear velocity at which an erasing rate of 25 dB, which is an erasable standard, was obtained. This erasable maximum linear velocity is the maximum rewritable linear velocity, and the higher the numerical value, the higher the recording speed.

  The measurement results are shown in Table 3. As can be seen from Table 3, sample 11 was erasable even at a linear velocity of 40 m / s, but the signal reproduction mark after recording mark formation partially crystallized, causing reproduction degradation. This is considered to be a result of a decrease in the thermal stability of amorphous because the crystallization rate is too high.

  In sample 21, the mark could not be erased. This is considered to be a result of a marked decrease in the crystallization rate. From the above results, the preferable composition ranges of Sb and Ge are 77.2 at% to 88 at% and Ge is 9.9 at% to 21 at%.

  Further, according to another experiment of the present inventor, if Mg is less than 1 at%, the noise reduction effect cannot be obtained, and if it exceeds 3.9 at%, the crystallization speed is lowered. Therefore, the composition of Mg is 1 at% or more 3 .9at% or less.

  The above example relates to a DVD with a standard with a laser wavelength λ of 405 nm and a numerical aperture NA of the objective lens of 0.85. The above characteristics are DVDs with a standard with λ = 405 nm and NA = 0.65. The same was true for. Further, the above embodiment is for an optical recording medium having two information layers, but the present invention is not limited to this, and can be applied to an optical recording medium having three or more information layers. Is.

Sectional drawing which shows typically the optical recording medium based on Example 1 of this invention FIG. 5 is a diagram showing the relationship between the Cr ₂ O ₃ content in the interface layer of the optical recording medium of Example 1 and quadruple speed erasure The diagram which shows the relationship between the recording linear velocity and the erasure | elimination rate in the sample of the optical recording medium of the same structure except the optical recording medium which concerns on the Example 1 having a different composition of an interface layer Diagram showing jitter characteristics in quadruple speed recording in a plurality of samples having similar interface layer compositions

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Optical recording medium 12 ... Board | substrate 14 ... 1st information layer 16 ... 2nd information layer (semi-transmissive information layer)
18 ... Recording film 20 ... Interface layer 22 ... Spacer layer 24 ... Light transmission layer

Claims (7)

A substrate, a first information layer provided on the light incident side of the laser beam in the substrate, and at least one semi-transmissive information layer provided on the light incident side further than the first information layer, The semi-transmissive information layer includes a recording film and an interface layer provided adjacent to the light incident side of the recording film, and the recording film has a numerical aperture of the objective lens. NA, an optical recording medium formed of a phase change material rewritable by an optical system of λ / NA ≦ 650 nm when the wavelength of the laser beam is λ,
The optical recording medium, wherein the recording film contains Sb as a main component and contains at least Ge as a subcomponent, and the interface layer is made of ZnS, SiO ₂ and Cr ₂ O ₃ . In claim 1,
An optical recording medium, wherein the content of Cr ₂ O ₃ in the interface layer is 15 mol% or more and 90 mol% or less. In claim 1 or 2,
The optical recording medium, wherein the recording film has Sb of 77.2 at% or more and 88 at% or less, and Ge of 9.9 at% or more and 21 at% or less. In any one of Claims 1 thru | or 3,
The optical recording medium is characterized in that the recording film contains 1 at% or more and 3.9 at% or less with Mg as an additive component. In any one of Claims 1 thru | or 4,
An optical recording medium, wherein the interface layer has a thickness of 0.4 nm to 9 nm. In any one of Claims 1 thru | or 4,
An optical recording medium, wherein the interface layer has a thickness of 0.5 nm or more and 8 nm or less. In any one of Claims 1 thru | or 6.
The composition of the interface layer is
_{{(ZnS) 0.8 (SiO 2} ) 0.2} (100-X) (Cr 2 O 3) a _X, 3
9. An optical recording medium, wherein 9 ≦ X ≦ 86.

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