JP2008221647A - Phase change type optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phase change type optical recording medium which has a good recording sensitivity, an excellent high-speed recording characteristic and a good adhesion and is of low cost. <P>SOLUTION: The phase change type optical recording medium has at least a lower protective layer, a phase change type recording layer, the upper protective layer and a reflecting layer sequentially from the incident side of recording-reproducing light. The phase change type recording layer consists of an alloy constituted mainly of In and Sb, and when the respective contents of In and Sb in the alloy are denoted by α and β (atom%), α and β satisfy the condition of 0.73≤β/(α+β)≤0.90. The upper protective layer is a single layer and is constituted mainly of Nb<SB>2</SB>O<SB>5</SB>. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical recording medium (phase change optical recording medium) having a rewritable phase change optical recording layer. Examples thereof include CD-RW, DVD-RW (Digital Versatile Disc Rewriteable), DVD + RW, DVD-RAM, BD-RE, HD DVD-Rewriteable, and the like.

In recent years, there has been a demand for an optical recording medium capable of high-capacity and high-speed recording for storing high-definition image / moving image data. CD-RW, DVD + RW, DVD-RW, DVD-RAM, etc. are widely used as phase-change optical recording media that can be repeatedly recorded, and even higher-capacity Blu-ray discs and HD DVDs have been commercialized for higher speed. Standardization is in progress toward multi-layering. To increase the capacity, it is possible to record a small mark by shortening the wavelength of the semiconductor laser to be recorded / reproduced and further increasing the lens NA (Numerical Aperture) to narrow the laser. The Blu-ray disc uses a pickup with a wavelength of 405 nm and NA of 0.85 to realize a large-capacity optical recording medium of 25 GB for one layer and 50 GB for two layers on a disc having a diameter of 12 cm. The HD DVD uses a pickup with a wavelength of 405 nm and NA 0.65, and the capacity is 15 GB for one layer and 30 GB for two layers, which is slightly smaller than the Blu-ray disc, but it is the same NA 0.65 as DVD, so the current DVD Can be manufactured with a structure close to that, and there is an advantage that the cost can be suppressed.
In the case of a phase-change optical recording medium capable of repeated recording, the smaller the mark, the greater the thermal interference between the marks. Therefore, the structure of the optical recording medium will be optimized to obtain optimum thermal characteristics. There is a need. In this case, what is particularly important is the thermal conductivity of the reflective layer and the second protective layer. For the second protective layer, ZnS—SiO ₂ has been widely used for reasons such as good chemical stability and good adhesion to the recording layer and low residual stress. The present inventors have also studied various dielectrics other than ZnS—SiO ₂ , but a desired thermal conductivity is obtained, the adhesiveness with the recording layer is good, and the residual stress is similar to that of ZnS—SiO _2. I couldn't find a small material.

On the other hand, in order to store and reproduce a large amount of data in a short time, it must be possible to record and erase at high speed. In order to perform high-speed recording, a rapidly cooled disk is required, and the effect of accelerating crystallization at the interface between the phase-change recording layer having a high crystallization speed and the recording layer is important. In the case of a drive using a semiconductor laser with a wavelength of 405 nm, such as a Blu-ray disc or HD DVD, high power cannot be produced due to restrictions of the semiconductor laser. Therefore, an optical recording medium with good recording sensitivity capable of recording with as low power as possible is desired. Particularly in high-speed recording, since the rotational speed is high, it is difficult to apply sufficient heat to the recording layer, and high recording power is required. In a multilayer optical recording medium having two or more recording layers, the recording layer far from the light incident surface is irradiated with laser light through the recording layer close to the light incident surface, and the intensity is weakened. The layer is desired to have good recording sensitivity.
As phase change materials, many materials such as Sb—Te, In—Se, Ga—Te, and Ge—Te, which are chalcogenide materials, have been studied, and in particular, CD-RW and DVD + RW quadruple speed. For disks, the AgInSbTe system, which is a material mainly composed of Sb and Te and added with several kinds of elements, has been put into practical use.
For example, Patent Document 1 discloses a recording layer mainly composed of a GeSbTe-based alloy and second and fourth dielectric layers composed mainly of a composite oxide of Nb ₂ O ₅ and ZrO ₂ and / or ZnO ( An optical recording medium having an upper protective layer) is disclosed. However, the present invention focuses on light transmission and prevention of sulfuration of the reflective layer, and does not describe high-speed recording or improvement of recording sensitivity. A recording layer mainly composed of an SbTe-based alloy such as GeSbTe increases the crystallization speed by increasing the amount of Sb, but at the same time, the crystallization temperature decreases drastically and the archival characteristics become very poor. However, it is difficult to put to practical use a medium that is more than 4 × speed recording, and that is more than 2 × speed recording of Blu-ray Disc and HD DVD.

Therefore, Ga—Sb, Ge—Sb, In—Sb, and the like have been proposed as materials that can be changed to SbTe.
Patent Document 2 discloses a recording layer mainly composed of (Sb1-xGex) 1-yIny (where 0.1 ≦ x ≦ 0.25, 0.05 ≦ y ≦ 0.4). However, the present invention is at a time when the recording mark length is large and the recording linear velocity is slow, and the conventional protective layer of ZnS—SiO ₂ is used for the upper protective layer.
Patent Document 3 discloses a recording layer of MγInαSbβ (0.73 ≦ β / (α + β) ≦ 0.90) M = Ge, Te, O, S, Se, Al, Ag, Mn, Cu, Au, and N. However, conventional ZnS—SiO ₂ is used for the second dielectric.
Patent Document 4 discloses a recording layer of (Sb100-xInx) 100-yZny (10 atomic% ≦ x ≦ 27 atomic%, 1 atomic% ≦ y ≦ 10 atomic%), but the upper protective layer is ZnS. -SiO ₂ or a transparent conductive film-based material is used, and no mention is made regarding recording sensitivity, adhesion to the recording layer, and the like.

JP 2005-302264 A JP 2002-347341 A JP 2006-44215 A

  An object of the present invention is to solve the problems in the prior art and to provide a low-cost phase-change optical recording medium having good recording sensitivity, high-speed recording characteristics, and good adhesion.

The above problems are solved by the following inventions 1) to 8).
1) In order from the recording / reproducing light incident side, at least a lower protective layer, a phase change recording layer, an upper protective layer, and a reflective layer are provided, and the phase change recording layer is made of an alloy containing In and Sb as main components. The contents of In and Sb in the alloy are α and β (atomic%), α and β satisfy the following conditions, the upper protective layer is a single layer, and Nb ₂ O ₅ is the main component. A phase change optical recording medium characterized by the above.
0.73 ≦ β / (α + β) ≦ 0.90
2) The phase change optical recording medium according to 1), wherein the upper protective layer contains ZrO ₂ and / or ZnO in addition to Nb ₂ O ₅ .
3) The phase change optical recording medium according to 1) or 2), wherein the thickness of the upper protective layer is 4 to 20 nm.
4) A plurality of information layers having a phase change recording layer are formed between the cover layer on the near side as viewed from the incident side of the recording / reproducing light and the inner substrate via the intermediate layer, and the incident side of the recording / reproducing light , Each information layer other than the innermost side includes five layers of a lower protective layer, a phase change recording layer, an upper protective layer, a translucent reflective layer, and a heat diffusion layer, and the innermost information layer In a phase change optical recording medium having a structure including a lower protective layer, a phase change recording layer, an upper protective layer, and a reflective layer, the innermost phase change recording layer is composed mainly of In and Sb. The contents of In and Sb in the alloy are α and β (atomic%), α and β satisfy the following conditions, and the uppermost upper protective layer is a single layer and Nb _2. A phase change optical recording medium comprising ₂ O ₅ as a main component.
0.73 ≦ β / (α + β) ≦ 0.90
5) The phase change optical recording medium according to 4), wherein the uppermost upper protective layer contains ZrO ₂ and / or ZnO in addition to Nb ₂ O ₅ .
6) The phase change optical recording medium according to 4) or 5), wherein the thickness of the innermost protective layer on the innermost side is 4 to 20 nm.
7) The phase change optical recording medium according to any one of 1) to 6), wherein the alloy mainly composed of In and Sb is represented by the following composition formula:
InαSbβGeγZnδTeε (α, β, γ, δ, ε are atomic%)
0.73 ≦ β / (α + β) ≦ 0.90
α + β ≧ 65
γ + δ + ε ≦ 30
0 ≦ γ ≦ 15
0 ≦ δ ≦ 15
0 ≦ ε ≦ 15
8) The phase change optical recording medium according to any one of 1) to 7), wherein the reflective layer is made of Ag or an Ag alloy.

Hereinafter, the present invention will be described in detail.
The optical recording medium of the present invention has a cover layer, a lower protective layer, a phase change recording layer, an upper protective layer, a reflective layer, and a substrate in order from the incident side of the recording / reproducing light, for example, as shown in FIG. Furthermore, it has another layer as needed.
(Upper protective layer)
In the present invention, the upper protective layer is a single layer and made of a material mainly composed of Nb ₂ O ₅ . Here, the main component means to occupy 50 mol% or more of the entire material.
For CD-RW with low recording linear density and DVD + RW for low-speed recording, chemical stability is good, adhesion to the recording layer is excellent, and ZnS-SiO ₂ having low thermal conductivity is optimal for the upper protective layer. Yes, it has been used frequently. However, when it comes to high-speed recording DVD + RW, high-density Blu-ray discs, and HD DVDs, heat control becomes very important for recording small marks at high speed with good control, and ZnS-SiO ₂ with low thermal conductivity is sufficient. It turned out that it was not possible to bring out the characteristic. When a recording layer having a high crystallization speed is used for high-speed recording, recrystallization from the periphery of the amorphous mark tends to occur, the mark becomes thin, and the modulation degree tends to be small. In order to make this recrystallization region as small as possible, it is better to shorten the time during which recrystallization is held at a temperature at which recrystallization occurs. Therefore, the upper protective layer should be made of a material with high thermal conductivity to have a rapid cooling structure. Is preferred. As a material having high thermal conductivity, a material containing In ₂ O ₃ , ZnO, SnO known as a transparent conductive film as a main component or a mixture thereof, or TiO ₂ , Al ₂ O ₃ , ZrO ₂ as a main component Although some of these materials have good recording characteristics, there is a problem that the thermal conductivity is too high and a high recording power is required for recording. I understand.

In the case of a drive using a semiconductor laser with a wavelength of 405 nm, such as a Blu-ray disc or HD DVD, high power cannot be produced due to restrictions of the semiconductor laser. Therefore, an optical recording medium with good recording sensitivity capable of recording with as low power as possible is desired. In particular, in high-speed recording, since the rotational speed is high, it is difficult to apply sufficient heat to the recording layer, and high recording power is required.
The optical recording medium of the present invention is particularly effective in the case of a Blu-ray disc or HD DVD using a 405 nm semiconductor laser. Blu-ray discs are more effective than 4x recording, and HD DVDs are more effective than 3x recording.
Further, in a multilayer optical recording medium having two or more recording layers, the laser beam is irradiated to the recording layer far from the light incident surface through the recording layer close to the light incident surface, so the intensity of the laser light is weakened. It is desired that the recording layer far from the light incident surface has good recording sensitivity. Therefore, applying the present invention to the recording layer and the upper protective layer far from the light incident surface of the multilayer optical recording medium has a great effect.

Further, when the upper protective layer is in contact with the recording layer, the upper protective layer also plays a role of assisting the crystallization of the recording layer. Therefore, in order to obtain good recording characteristics, the combination of the recording layer material and the upper protective layer is also important. Therefore, as a result of studying combinations of various materials with an upper protective layer using an alloy containing InSb, which is advantageous for high linear velocity recording, as a recording layer, a material containing Nb ₂ O ₅ as a main component is InSb. It also has the effect of promoting crystallization of the alloy, and makes it easy to erase amorphous marks when repeatedly recording at high speeds, but the marks do not become too thin and sufficient modulation is obtained, so high speed recording characteristics are good, and An optical recording medium having a low recording power and good recording sensitivity, since heat conductivity is lower than that of a material mainly composed of In ₂ O ₃ , ZnO, and SnO, which is known as a transparent conductive film, so that heat does not escape too much. It was found that

ZnO and / or ZrO ₂ may be added to Nb ₂ O ₅ . Increasing the amount added slightly reduces the recording sensitivity, but improves the adhesion to the recording layer and provides an optical recording medium with excellent storage reliability. At the time of commercialization, it is preferable to use a configuration in which both storage reliability and recording sensitivity are compatible in consideration of the adhesion between the recording layer and the upper protective layer. When Nb ₂ O ₅ is 50 mol% or more, the characteristics of this oxide can be sufficiently exhibited, the adhesion is improved, and both storage reliability and recording sensitivity can be achieved. The addition of ZrO ₂ improves the adhesion, but ZnO may be added to further improve the adhesion.
When Ag is used for the reflective layer, diffusion of Ag can be prevented even in the case of Nb ₂ O ₅ alone or in the case of a complex oxide to which ZnO, ZrO ₂ or the like is added. In addition, since the layer between the reflective layer and the recording layer can be formed as a single layer, an optical recording medium having a small number of layers can be obtained, which is advantageous for cost reduction. In addition, a material mainly composed of Nb ₂ O ₅ has an advantage of low absorption and high transmittance.
The film thickness of the upper protective layer is preferably 4 to 20 nm. If the thickness is less than 4 nm, the recording layer hardly absorbs heat and the jitter is deteriorated. If the thickness exceeds 20 nm, the recording layer is heated too much to be amorphous and the jitter is deteriorated. In order to obtain particularly good jitter in high-speed recording, the thickness is preferably 4 to 10 nm.

(Recording layer)
The high-speed recording characteristics of phase-change optical recording media that can be repeatedly recorded include the ease of amorphization and crystallization speed of the recording layer material, as well as the interface state with the layer in contact with the recording layer and the thermal characteristics of the upper protective layer. Therefore, the combination of the recording layer composition with an InSb alloy of 60 atomic% or more and the upper protective layer was examined. Although it is one method to improve the high-speed recording characteristics by providing an interface layer between the recording layer and the dielectric layer, the number of layers is increased and the cost is increased, and a thin film thickness is provided uniformly. The upper protective layer preferably has both functions because of difficulties.
A material containing an InSb alloy as a main component has a low melting point and a high crystallization speed, and is suitable for high-speed recording. However, if there is too much In, crystal stability will deteriorate, and if there is too much Sb, amorphous stability will deteriorate. There's a problem. Therefore, considering the balance between the two, the contents of In and Sb in the alloy are α and β (atomic%) so that α and β satisfy the following conditions.
0.73 ≦ β / (α + β) ≦ 0.90
If it is less than 0.73, the crystallization speed becomes slow, so that the recording mark cannot be completely erased, and 4X recording becomes difficult. On the other hand, if it exceeds 0.9, the crystallization speed becomes too fast and it becomes difficult to form amorphous marks, so that 4X recording becomes difficult.

Furthermore, it is preferable to add an element such as Ge, Zn, Te, Se, B, Al, Ga, Sn, or Cu to the InSb alloy to improve the characteristics.
Particularly preferred is InαSbβGeγZnδTeη (α, β, γ, δ, η is atomic%, 10 ≦ α ≦ 25, 60 ≦ β ≦ 80, 0 ≦ γ ≦ 15, 0 ≦ δ ≦ 15, 0 ≦ η ≦ 5). It is. Ge has an effect of improving the stability of reproduction light. However, if the addition amount is too large, the crystallization speed is lowered and the high-speed recording characteristics are deteriorated. Zn has an effect of improving the archival characteristics, but if it is added too much like Ge, the crystallization speed is lowered and the high-speed recording characteristics are deteriorated. Te has an effect of improving the stability of the crystal, but if the addition amount is too large, the stability of the reproduction light is deteriorated, so that it is preferably 5 atomic% or less.
The film thickness of the recording layer is suitably 6 to 18 nm, and if it is thinner than 6 nm, the light absorption ability is lowered and the function as the recording layer may be lost. On the other hand, if it is thicker than 18 nm, the recording sensitivity becomes worse.
The recording layer is preferably formed by sputtering. As an example of a method for producing a sputtering target, a charged amount is previously weighed and heated and melted in a glass ampoule, and then taken out and pulverized by a pulverizer, and the obtained powder is heated and sintered to form a disk shape. Can get the target.

(Reflective layer)
As the reflective layer, Ag having a high thermal conductivity or Ag alloy such as Ag-Bi, Ag-In, Ag-Pd, Ag-Pd-Cu, and Ag-Cu is suitable. When a recording layer having a high crystallization speed is used, recrystallization from the periphery of the amorphous mark tends to occur, the mark becomes thin, and the modulation degree tends to be small. In order to make this recrystallization region as small as possible, it is better to shorten the time for which recrystallization is held at a temperature at which recrystallization occurs. Therefore, a rapid cooling structure using Ag or an Ag alloy having high thermal conductivity for the reflective layer It is preferable to do this. Also, in high speed recording, the thicker the film thickness, the greater the degree of modulation. Therefore, a thicker film is preferable. However, if the film thickness is too large, film peeling tends to occur. Therefore, the thickness of the reflective layer is preferably 100 to 300 nm.
When Ag or an Ag alloy is used for the reflective layer, if a material containing S is used for the upper protective layer, S contained in the upper protective layer reacts with Ag contained in the reflective layer, and Ag ₂ S , The storage reliability deteriorates. However, if a thin film mainly containing Nb ₂ O ₅ not containing S is used for the upper protective layer as in the present invention, the upper protective layer can also serve as an anti-sulfurization layer, and the reflective layer and the recording layer Therefore, a low-cost optical recording medium with a small number of layers and reduced material costs can be obtained.

(Lower protective layer)
The lower protective layer has effects such as preventing deterioration and deterioration of the recording layer, increasing the adhesive strength of the recording layer, and improving recording characteristics. Examples of the material include metal oxides such as SiO, SiO ₂ , ZnO, SnO ₂ , Al ₂ O ₃ , TiO ₂ , In ₂ O ₃ , MgO, and ZrO ₂ , Si ₃ N ₄ , AlN, TiN, BN, Examples thereof include nitrides such as ZrN, sulfides such as ZnS, In ₂ S ₃ and TaS ₄ , carbides such as SiC, TaC, B ₄ C, WC, TiC and ZrC, diamond-like carbon, and mixtures thereof. Among them, the mixture of ZnS and SiO ₂ is excellent in heat resistance, low thermal conductivity, and chemical stability, has small film residual stress, and does not easily deteriorate characteristics such as recording sensitivity and erasure ratio even by repeated recording. From the viewpoint of excellent adhesion to the recording layer.
Further, a single layer of the above materials or a mixture thereof or a multilayer structure of two or more layers may be used.
Since the reflectance of the optical recording medium is greatly changed by changing the film thickness of the lower protective layer, adjusting the film thickness of the lower protective layer so that the reflectance of the optical recording medium is decreased, Recording sensitivity can also be increased. However, if it falls outside the range of reflectivity determined by each standard such as Blu-ray Disc and HD DVD, it becomes difficult for the drive to read the signal of the optical recording medium, so the thickness of the lower protective layer is subject to reflectivity It is preferable to adjust so as to be within the standard value. For example, when ZnS—SiO ₂ (20 mol%) is used for the lower protective layer, the thickness is preferably 40 to 80 nm for DVD + RW, 20 to 50 nm for Blu-ray Disc, and 30 to 60 nm for HD DVD.

(substrate)
As the substrate material, glass, ceramics, resin, and the like are usually used, but a resin substrate is preferable in terms of moldability and cost.
Examples of the resin include polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicone resin, fluorine resin, ABS resin, and urethane resin. Polycarbonate resin and acrylic resin are preferable from the viewpoint of properties, optical characteristics, and cost.

(Cover layer)
When using a high NA objective lens such as a Blu-ray disc, the cover layer is required to have a thickness of 0.3 mm or less, preferably 0.06 to 0.2 mm. Is preferred. The cover layer may be formed by applying an adhesive made of an ultraviolet curable resin by a spin coating method and bonding a polycarbonate film thereon.
When the NA is about 0.6 to 0.65, such as DVD + RW and HD DVD, a cover substrate with a thickness of 0.6 mm is used, an ultraviolet curable resin is applied on the protective layer, and the cover substrate is placed on the cover substrate. May be cured to form a cover layer.

  According to the present invention, it is possible to provide a low-cost phase change type optical recording medium having good recording sensitivity, good high-speed recording characteristics, and good adhesion.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated further more concretely, this invention is not limited by these Examples. The film formation by the sputtering method was performed using a single wafer sputtering apparatus (manufactured by UNAXIS) in an Ar gas atmosphere under conditions of an input power of 1 to 5 kW and an Ar gas pressure of 2 × 10 ⁻³ Torr.

(Example 1)
-Fabrication of phase change optical recording media-
On a polycarbonate substrate having a guide groove having a diameter of 12 cm, a thickness of 1.1 mm, a groove depth of 22 nm, a groove width of 0.165 μm, and a track pitch of 0.32 μm, a reflection layer, an upper protective layer, a recording layer, A lower protective layer was formed in order.
The reflective layer was made of Ag-Bi (0.5 wt%) as a target and had a thickness of 140 nm.
The upper protective layer was Nb ₂ O ₅ as a target and had a thickness of 8 nm.
The recording layer used InSb as a target and had a thickness of 11 nm. The ratio of In and Sb was changed between 0.7 ≦ β / (α + β) ≦ 0.94.
The lower protective layer was made of ZnS—SiO ₂ (20 mol%) as a target and had a thickness of 33 nm.
Further, an adhesive made of an ultraviolet curable resin (DVD003 manufactured by Nippon Kayaku Co., Ltd.) is applied on the lower protective layer so as to have a thickness of 25 μm by a spin coat method, and a polycarbonate film (75 μm thick) ( A cover layer having a thickness of 0.1 mm was formed.
Thus, the phase change optical recording medium of Example 1 was produced.

-Initial crystallization-
An initialization device (POP120-SSS manufactured by Hitachi Computer Co., Ltd.) having a laser head with a focusing function is used to rotate the recording medium at a constant linear velocity of 14 m / s, and a wavelength of 810 nm. Initial crystallization was performed by irradiating a laser beam having a width of about 1 μm, a length of 96 μm, and a power of 1400 mW in a radial direction while moving the laser beam at 50 μm / r.
-Evaluation-
Recording and reproduction of the phase-change optical recording medium after the initial crystallization was performed using a Blu-ray disc evaluation apparatus (ODU-1000 manufactured by Pulstec Industrial Co., Ltd.) having a pickup head with a wavelength of 405 nm and a numerical aperture NA of 0.85, and jitter ( (σ / Tw) was evaluated. Jitter is a value obtained by using a limit equalizer while reproducing at 1 × speed (4.92 m / s), and repeating a random pattern with a shortest mark length of 0.149 μm by the 17PP modulation method at 4 × speed of Blu-ray Disc 10 This is the value when recorded once. As the recording strategy, a 2T period strategy was used in which the pulse period for forming the amorphous mark was 2T, the recording power (Pw) was fixed at 7.5 mW, the recording strategy was optimized, and the jitter was evaluated.
The results are shown in FIG. FIG. 2 (a) is a graph of the data shown in FIG. 2 (b).
As can be seen from the figure, in the range of 0.73 ≦ β / (α + β) ≦ 0.9, the jitter is a sufficiently practical level of 7% or less, and 0.77 ≦ β / (α + β) ≦ 0. In the range of 85, a further excellent value of jitter of 6.5% or less was obtained.

(Examples 2-6, Comparative Examples 1-2)
Each phase change was carried out in the same procedure as in Example 1 except that the composition of the target of the upper protective layer and the recording layer was changed to those shown in the columns of Examples 2 to 6 and Comparative Examples 1 and 2 in Table 1. Type optical recording media were prepared and subjected to initial crystallization. However, in Example 2, the target of the upper protective layer was not changed.
For each phase-change optical recording medium after the initial crystallization, recording / reproduction was performed in the same manner as in Example 1 except that the recording power (Pw) was changed, and the recording power dependency of jitter was evaluated. The recording power at which the lowest jitter (bottom jitter) is obtained when the recording power is changed is the optimum recording power. The lower the optimum recording power, the better the recording sensitivity.
The evaluation results of Examples 2 to 4 and Comparative Examples 1 and 2 are shown in FIG. 3, and the evaluation results of Examples 5 to 6 are shown in FIG.
As can be seen, Comparative Example 1 using ZnO—Al ₂ O ₃ for the upper protective layer had an optimum recording power of 9 mW and a bottom jitter of 8.2%.
In Comparative Example 2 in which Ge ₁₅ Sb ₇₀ Sn ₁₅ (atomic%) was used for the recording layer, the optimum recording power was 9 mW and the bottom jitter was 8.4%.
On the other hand, in Example 2 in which In ₁₇ Sb ₇₆ Zn ₇ (atomic%) was used for the recording layer and Nb ₂ O ₅ was used for the upper protective layer, the optimum recording power was as low as 7 mW and the bottom jitter was as small as 6.2%. It was.
In Examples 3 and 4, a composite oxide in which 20 mol% of Nb ₂ O ₅ and ZrO ₂ or ZnO were mixed was used for the upper protective layer, but the optimum recording power was as low as 7.5 mW, and the bottom jitter was They were 6.2% and 6.3%, respectively.
In Examples 5 and 6, Nb ₂ O ₅ composite oxide in which the ratio of ZrO ₂ and ZnO in the upper protective layer was increased and mixed by 50 mol% was used, but the optimum recording power was as low as 7.5 mW and the bottom jitter was also low. And 6.2% and 6.3%, respectively.

-Storage reliability evaluation-
Random patterns were recorded on the phase change optical recording media of Examples 2 to 4 at 4 times the speed of a Blu-ray Disc, and then stored for 300 hours under conditions of 80 ° C. and 85% RH, and archival characteristics were evaluated. Also, as a peel test, cut two straight lines with a cutter in the cover layer, apply a commercially available adhesive tape (3M mending tape) to it, and press it with your finger once. On the other hand, the test which peels to a perpendicular direction was done.
As a result, although the jitter did not change in the optical recording medium of Example 2, pinholes were observed in some places. In the peel test, part of the film was isolated and the adhesion was poor.
In the optical recording media of Examples 3 and 4, almost no pinholes were observed and the archival characteristics were good. In the peel test, it was found that the film was difficult to peel off and the adhesion was good.
In particular, the optical recording medium of Example 4 had the best archival characteristics even when stored under conditions of 80 ° C. and 85% RH for 500 hours, and was the most preferred configuration. In addition, even after storage for 500 hours, the film was hardly peeled off in the peel test, and the adhesion was good.

(Comparative Example 3)
A phase change optical recording medium was produced and initially crystallized in the same manner as in Example 2 except that the upper protective layer was changed to ZnS—SiO ₂ (20 mol%).
The phase change optical recording medium was evaluated in the same manner as in Example 2. As a result, the initial recording was good with a jitter of 7%. However, when repeated recording was performed 10 times, the jitter was worse than 12%, and the recording strategy was reduced. Even after adjustment, it was not less than 12%.

(Comparative Example 4)
Between the recording layer and the upper protective layer ZnS-SiO _{2, [ZrO} 2 (3 _mol% Y 2 _{O 3)]} - except having a surface layer consisting of 20 mol% TiO _2, in the same manner as in Example 2 Thus, a phase change optical recording medium having a layer structure shown in Table 2 was prepared and initially crystallized.
This phase change optical recording medium was evaluated in the same manner as in Example 2. As a result, the initial recording was good with a jitter of 6.5%, but when repeated recording was repeated 10 times, the jitter became worse with 11% or more. Even after adjusting the strategy, it did not fall below 11%.

(Example 7)
The recording layer was changed to In ₁₇ Sb ₇₇ Ge ₃ Zn ₃ (atomic%), the upper protective layer was changed to Nb ₂ O ₅ —ZrO ₂ (20 mol%), and the thickness of the upper protective layer was changed between 3 to 21 nm. Except for these points, an optical recording medium was prepared and crystallized in the same manner as in Example 2.
With respect to this phase change type optical recording medium, jitter was evaluated in the same manner as in Example 2 when recording was repeated 10 times at a 4 × speed of the Blu-ray Disc. The recording power was fixed at 7.5 mW.
The results are shown in FIG. 5, and the jitter in the range of 3 to 21 nm is 8. %, The jitter is as good as 7.0% or less in the range of 4 to 20 nm, and especially in the range of 4 to 10 nm, the jitter is even better as 6.5% or less. .

(Examples 8 to 13)
Except for the point that the layer configuration was changed as shown in Table 3, the optical recording media of Examples 8 to 13 were prepared and initially crystallized in the same manner as Example 2.
For these phase change optical recording media, the jitter was evaluated in the same manner as in Example 2 when recording was repeated 10 times at a 4 × speed of the Blu-ray Disc.
The optimum recording power and jitter at that time are shown in Table 3. In each of Examples 8 to 13, the optimum recording power was 8 mW or less, and the jitter was 7% or less.

(Example 14)
A phase-change optical recording medium was prepared in the same procedure as in Example 1 except that the recording layer target was changed to one represented by the composition formula InαSbβGeγZnδTeε (α, β, γ, δ, and ε are atomic%). After fabrication and initial crystallization, jitter was evaluated in the same manner as in Example 1.
However, β / α + β was fixed at 0.80.
The results are shown in FIG. 6 to FIG. 9. As can be seen from FIG. 6, as for α + β, jitter is 8.0 or less when 65 atomic% or more, and jitter is 7.0 or less when 70 atomic% or more. there were.
As can be seen from FIG. 7, the jitter was 8.0 or less when it was 15 atomic% or less, and the jitter was 7.1 or less when it was 10 atomic% or less.
As can be seen from FIG. 8, when δ is 15 atomic% or less, the jitter is 8.0 or less, and when it is 5 atomic% or less, the jitter is 7.0 or less.
As can be seen from FIG. 9, when ε is 15 atomic% or less, the jitter is 8.0 or less, and when it is 10 atomic% or less, the jitter is 7.0 or less.

(Example 15)
On a polycarbonate substrate, reflective layer Ag-Bi (0.5 wt%), an upper protective layer _{Nb 2 O} 5 -ZrO 2 (20 mol%), the first recording layer InSbGeTe, lower protective layer _ZnS-SiO 2 (20 mol %), Resin intermediate layer (UV curable resin, Mitsubishi Materials Corporation SD318), fifth dielectric layer IZO, heat dissipation layer Ag, fourth dielectric layer ZnO—Al ₂ O ₃ (2 wt%), second recording layer AgInSbTe, a third dielectric layer ZnS-SiO ₂ , and a cover layer were formed in this order to produce a two-layer phase change optical recording medium having the layer structure shown in FIG. The thickness of each layer is as follows, the resin intermediate layer is formed by a spin coat method, and the cover layer is made of an ultraviolet curable resin adhesive (DVD003 manufactured by Nippon Kayaku Co., Ltd.) to a thickness of 25 μm by the spin coat method. Then, a 75 μm-thick polycarbonate film (manufactured by Teijin Ltd.) was laminated thereon to form. The other layers were formed while controlling the thickness by a sputtering method.
Reflective layer: 100 nm, upper protective layer: 8 nm, first recording layer: 11 nm, lower protective layer: 35 nm, resin intermediate layer: 35 μm, fifth dielectric layer: 30 nm, heat dissipation layer: 8 nm, fourth dielectric layer: 6 nm Second recording layer: 6 nm, Third dielectric layer: 30 nm
After first crystallizing the first recording layer and the second recording layer of the above two-layer phase change optical recording medium in the same manner as in Example 1, the first recording layer is subjected to Blu-ray Disc 2 in the same manner as in Example 1. A random pattern was repeatedly recorded 10 times in double speed recording, the recording power and the recording strategy were optimized, and the recording power dependence of jitter was evaluated.
As a result, the bottom jitter was 8%, and the optimum recording power at that time could be recorded with a relatively low power of 10 mW.

(Comparative Example 5)
A phase change optical recording medium was prepared in the same procedure as in Example 1 except that the composition of the target of the recording layer was changed to Ge _3.5 Sb ₇₂ Te _24.5 (atomic%). Went. This medium corresponds to the medium according to the cited reference 1 described above.
This phase change optical recording medium was recorded and reproduced at a speed four times that of a Blu-ray disc in the same manner as in Example 1 to evaluate jitter. As a result, the initial recording was good with a jitter of 7%. However, it was found that the jitter was poor with 13% or more after 10 times of repetitive recording, and even if the recording strategy was adjusted, it was not 13% or less. It was.

The figure which shows the layer structural example of the phase change type optical recording medium of this invention. The figure which shows the evaluation result of Example 1. FIG. (A) Graph, (b) Original data. The figure which shows the evaluation result of Examples 2-4 and Comparative Examples 1-2. The figure which shows the evaluation result of Examples 5-6. The figure which shows the evaluation result of Example 7. FIG. The figure which shows the evaluation result regarding (alpha) + (beta) of Example 14. FIG. The figure which shows the evaluation result regarding (gamma) of Example 14. FIG. The figure which shows the evaluation result regarding (delta) of Example 14. FIG. The figure which shows the evaluation result regarding (epsilon) of Example 14. FIG. The figure which shows the layer structural example of the two-layer phase change type optical recording medium of this invention.

Claims (8)

In order from the incident side of the recording / reproducing light, it has at least a lower protective layer, a phase change recording layer, an upper protective layer, and a reflective layer, and the phase change recording layer is made of an alloy containing In and Sb as main components, The contents of In and Sb in the alloy are α and β (atomic%), α and β satisfy the following conditions, the upper protective layer is a single layer, and Nb ₂ O ₅ is the main component. A phase change optical recording medium.
0.73 ≦ β / (α + β) ≦ 0.90 The phase change optical recording medium according to claim 1, wherein the upper protective layer contains ZrO ₂ and / or ZnO in addition to Nb ₂ O ₅ .   3. The phase change optical recording medium according to claim 1, wherein the upper protective layer has a thickness of 4 to 20 nm. A plurality of information layers having a phase change recording layer are formed through an intermediate layer between the cover layer on the front side when viewed from the incident side of the recording / reproducing light and the substrate on the far side, and viewed from the incident side of the recording / reproducing light. In addition, each information layer other than the innermost side includes five layers of a lower protective layer, a phase change recording layer, an upper protective layer, a translucent reflective layer, and a heat diffusion layer, and the innermost information layer includes In the phase change optical recording medium having a structure including the lower protective layer, the phase change recording layer, the upper protective layer, and the reflective layer, the innermost phase change recording layer is an alloy containing In and Sb as main components. The contents of In and Sb in the alloy are α and β (atomic%), α and β satisfy the following conditions, the innermost upper protective layer is a single layer, and Nb ₂ O A phase change optical recording medium comprising ₅ as a main component.
0.73 ≦ β / (α + β) ≦ 0.90 _5. The phase change optical recording medium according to claim 4, wherein the innermost upper protective layer contains ZrO ₂ and / or ZnO in addition to Nb ₂ O ₅ .   6. The phase change optical recording medium according to claim 4, wherein the innermost protective layer has a thickness of 4 to 20 nm. The phase change optical recording medium according to any one of claims 1 to 6, wherein the alloy mainly composed of In and Sb is represented by the following composition formula.
InαSbβGeγZnδTeε (α, β, γ, δ, ε are atomic%)
0.73 ≦ β / (α + β) ≦ 0.90
α + β ≧ 65
γ + δ + ε ≦ 30
0 ≦ γ ≦ 15
0 ≦ δ ≦ 15
0 ≦ ε ≦ 15   The phase change optical recording medium according to claim 1, wherein the reflective layer is made of Ag or an Ag alloy.

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