JP2005119194A - Phase change-type optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phase change-type optical recording medium which is as much of a high packing density and large capacity as DVD-ROM; can be not only easily initialized in an initialization process but also can secure a sufficient degree of modulation to deal with the overwrite of information in a wide range of 3.5 to 35 m/s and at a high recording linear speed; and shows outstanding recording sensitivity, overwrite characteristics and shelf stability. <P>SOLUTION: This phase change-type optical recording medium has a recording layer composed of at least a phase change-type recording material formed on a substrate; gives rise to a reversible phase change in the recording layer by emitting an electromagnetic wave; and thereby, can at least record/reproduce information. In this recording medium, it is characteristic that the phase change-type recording material is expressed by the composition formula: InαSbβHγGeδXε(in the formula, X is Se and/or Te; α, β, γ, δ, ε are each an atomic%, α+β+γ+δ+ε=100, 8≤α≤35, 50≤β≤85, 2≤γ≤10, 1≤δ≤5, 2≤ε≤15). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is a phase change type applied to high-speed and large-capacity high-density recording that can record and reproduce at least information by causing an optical constant change in a recording layer by irradiating electromagnetic waves. The present invention relates to an optical recording medium.

Conventionally, as an example of an optical recording medium capable of recording, reproducing, erasing and overwriting (rewriting) information by irradiation with a light beam such as an electromagnetic wave, particularly a laser beam, a crystal-amorphous phase or a crystal-crystalline phase 2. Description of the Related Art Phase change optical recording media such as phase change optical discs that utilize the phase transition of are known. This phase change type optical recording medium can be overwritten by a single beam, and since the optical system of the drive side device is simple, it is used as a recording medium for computers and video / audio.
As a recording material for such a phase change type optical recording medium, Ge—Te, Ge—Te—Se, In—Sb, Ga—Sb, Ge—Sb—Te, Ag—In— have been used so far. Phase change type recording materials such as Sb—Te are used.
In particular, the Ag—In—Sb—Te phase change type recording material has the characteristics that the recording sensitivity is high and the outline of the recording mark in an amorphous state is clear. in use.
Ag-In-Sb-Te phase change recording materials are disclosed in Patent Documents 1 to 3, for example. Ag-Sb-Te phase change recording materials that are similar systems are disclosed in Patent Documents 4 to 5.

However, the recording material is used for a recording medium having a relatively low recording density such as CD-RW (Compact Disk-Rewritable), for example, a DVD (Digital Versatile Disk) -RAM or a DVD-RW (Digital Versatile). In the case of application to disk-rewriteable), overwriting is possible at a recording linear velocity of about 3.5 m / s (1 × speed), but when it is 7.0 m / s (2 × speed) or more, There arises a problem that the overwrite characteristic is deteriorated.
The cause of this characteristic deterioration is that it is difficult to overwrite at a high recording linear velocity because the crystallization speed of the phase change recording material is low.
In order to prevent this characteristic deterioration, the crystallization speed of the phase change recording material can be increased by increasing the composition amount of Sb, which is the composition of the phase change recording material. In this case, the crystallization temperature decreases due to an increase in the composition amount of the Sb amount, and the storage characteristics of the recording mark are further deteriorated.
Patent Document 6 discloses the use of an Ag—In—Ge—Sb—Te phase change recording material as a method for preventing the deterioration of the storage characteristics. However, the phase change optical recording medium having this recording material can be overwritten when the recording linear velocity is in the range of 3.0 to 20 m / s, but in the case of a higher recording linear velocity, that is, more than 20 m / s. It cannot be overwritten at high speeds.

On the other hand, Non-Patent Document 1 reports a Ga—Sb phase change recording material as a material for increasing the recording linear velocity.
This Ga-Sb phase change recording material has been reported to have a very high crystallization speed, but since the crystallization temperature is as high as 350 ° C., an initialization process for bringing the recording material into an unrecorded state. There is a problem that initial crystallization is difficult. In addition, since the Ga—Sb phase change recording material has a relatively high melting point of 630 ° C. even with a eutectic composition, it has a problem in recording sensitivity at a high linear velocity.
Further, Ga—Sb-based phase change recording materials include, for example, Mo, W, Ta, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Al, Tl, Si, Ge, Sn, Pb, As. Patent Documents 7 to 8 disclose attempts to improve characteristics by adding metal elements such as Bi, S, Se, and Te as components. However, an optical recording medium using such a phase change recording material does not satisfy sufficient overwrite characteristics and storage characteristics at the same time while ensuring a sufficient degree of modulation when overwriting at a high recording linear velocity. Absent. In-Sb recording materials are disclosed in Patent Documents 9 and 10, but this system does not simultaneously satisfy the overwrite characteristics and storage reliability under high linear velocity recording.
As described above, various phase change recording materials have been reported, but none of them can satisfy all the characteristics required for an overwritable phase change optical recording medium. Therefore, it is a high-density and large-capacity recording medium such as a DVD-ROM, and can cope with the case where the recording linear velocity is further increased (up to 35 m / s), and can secure a sufficient modulation and overwrite. Development of an overwritable phase change optical recording medium that simultaneously satisfies characteristics, recording sensitivity, and storage characteristics is an issue.

In an optical recording medium using a phase transition between a crystal and an amorphous phase, when the diameter of the laser beam used for recording, reproducing, erasing and overwriting of information is 1 μmφ, the laser beam has a high recording linear velocity (35 m The time for crossing a point on the disk (Disk) rotating at / s) is about 29 nsec (nanoseconds). Therefore, at a high recording linear velocity (35 m / s), it is necessary to overwrite the phase change recording material of the optical recording medium within 29 nsec, that is, to rewrite the old recording mark to the new recording mark.
In a DVD or the like which is a high-density and large-capacity recording medium, the laser wavelength of the optical system used is 650 nm, which is shorter than the conventional 780 nm, so that the beam diameter is smaller than 1 μmφ, and the laser beam has a high recording linear velocity (35 m The time to cross one point on the rotating disk at / s) is shorter than 29 nsec. For example, if the beam diameter is 0.7 μmφ, the time to cross one point on the disk is about 20 nsec, and it is necessary to overwrite in such a short time, and this requires a very fast crystallization speed. .
Even in the phase change type recording materials of the above-mentioned prior art, such as Ag—In—Sb—Te, Ga—Sb, and Ge—Sb—Te, overwriting is possible within this time. There has been a problem in initial crystallization and the like, and a recording material that can satisfy all these characteristics at a high recording linear velocity (35 m / s) has not been known.

Japanese Patent Laid-Open No. 3-231889 Japanese Patent Laid-Open No. 4-191089 JP-A-4-23279 JP-A-4-267192 JP-A-5-345478 JP 2000-322740 A U.S. Pat. No. 4,818,666 US Pat. No. 5,072,423 JP-A-60-177446 Japanese Patent Laid-Open No. 61-134944 “Phase-change optical data storage in GaSb”, Applied Optics, Vol. 26, no. 22115, November, 1987

  The present invention is a high-density and large-capacity optical recording medium similar to a DVD-ROM, and is not only easy to initialize in the initialization process, but also has a wide and high range from 3.5 m / s to 35 m / s. An object of the present invention is to provide a phase change type optical recording medium that can secure a sufficient degree of modulation that can cope with overwriting of information at a recording linear velocity and is excellent in recording sensitivity, overwriting characteristics, and storage characteristics.

The above problems are solved by the following inventions 1) to 2) (hereinafter referred to as the present invention 1 and 2).
1) Phase change light capable of providing a recording layer made of at least a phase change recording material on a substrate, irradiating the recording layer with electromagnetic waves to cause a reversible phase change, and recording and reproducing at least information A phase change optical recording medium, wherein the phase change recording material is represented by the following composition formula.
InαSbβHγGeδXε
(Wherein X is Se and / or Te, α, β, γ, δ, ε is atomic%)
8 ≦ α ≦ 35
50 ≦ β ≦ 85
2 ≦ γ ≦ 10
1 ≦ δ ≦ 5
2 ≦ ε ≦ 15
α + β + γ + δ + ε = 100
2) The phase change optical recording medium according to 1), wherein the phase change recording material is represented by the following composition formula.
InαSbβHγGeδXεYκ
(Wherein X is Se and / or Te, Y is at least one element selected from Sn, Bi, and I, and α, β, γ, δ, ε, and κ are atomic%)
8 ≦ α ≦ 35
50 ≦ β ≦ 85
2 ≦ γ ≦ 10
1 ≦ δ ≦ 5
2 ≦ ε ≦ 15
2 ≦ κ ≦ 10
α + β + γ + δ + ε + κ = 100

Hereinafter, the present invention will be described in detail.
As a result of intensive studies focusing on the recording material in order to solve the above-mentioned problems, the present inventors have solved the above-mentioned problems when using the phase-change recording material represented by the composition formula of the present invention 1. When a phase change recording material represented by the composition formula of the present invention 2 to which at least one element selected from Sn, Bi, and I is added is used, a high-speed line is found. It has been found that it is possible to improve the speed and further stabilize the overwrite characteristics at a linear speed of 25 m / s or more, and based on these findings, the present invention has been completed.
That is, by using In and Sb as constituent elements as a phase change recording material, the problems of high-speed crystallization and initial crystallization are solved, and by adding H (hydrogen) and Ge, the recording sensitivity is improved. The signal characteristics including the modulation factor and the overwrite characteristics are greatly improved, and the problem of storage reliability is solved by adding Se and / or Te.
Furthermore, by adding at least one element selected from Sn, Bi, and I, a further increase in the linear velocity can be realized, so that there is a margin in the overwrite characteristics at a linear velocity of 25 m / s or more. I was able to.

Although it is known that GaSb has a very high crystallization speed, initialization crystallization is extremely difficult because the crystallization temperature is as high as about 350 ° C. Therefore, two problems of high-speed crystallization and initial crystallization were solved by using In of the same family instead of Ga and using In and Sb. The reason for the high-speed crystallization of InSb is not clear, but it is thought that, as in GaSb, the distance between adjacent atoms in the crystalline phase and the amorphous phase is approximately the same. On the other hand, since the crystallization temperature of InSb is about 180 ° C., the initial crystallization can be easily performed as compared with GaSb.
By adding H (hydrogen) to InSb, it is possible to improve recording characteristics and signal characteristics including modulation. The reason is that by adding H, H compensates the dangling bonds of InSb, so that light scattering due to defects caused by dangling bonds is reduced, and light absorption efficiency is improved. Further, compensation of dangling hands by H reduces the average coordination number of InSb and stabilizes the amorphous phase, thereby improving signal characteristics such as jitter. However, the reason for the improvement of the modulation factor is unknown.
In addition, the addition of Ge improves the overwrite characteristics. This is presumably because Ge is an element having a large binding energy and improves the stability of the structure of the amorphous phase and the crystalline phase.
Further, when Se and / or Te is added to the recording material composed of In, Sb, H, and Ge, the storage reliability is greatly improved. This is because InSb is considered to be an n-type semiconductor, and when InSb is oxidized, it is considered that it retains the n-type. Therefore, Se and Te serving as donors to InSb prevent InSb from being oxidized. This is considered to improve storage reliability.
Further, the addition of Sn, Bi, and I further improves the crystallization speed, because Sn and Bi are highly metallic and I acts as a terminator.

In the composition formula of the phase change recording material of the first aspect of the present invention, if α is in the range of 8 to 35 atomic% and β is in the range of 50 to 85 atomic%, the crystallization speed is improved and the overwrite is performed at a high linear velocity. Therefore, initial crystallization is easy. If γ is in the range of 2 to 10 atomic%, the recording sensitivity and the signal characteristics including the degree of modulation can be improved. If γ is in the range of 1 to 5 atomic%, the repetition is caused by overwriting. The characteristics can be improved. If ε is in the range of 2 to 15 atomic%, the storage reliability can be improved.
Further, in the composition formula of the phase change recording material of the second invention, α to ε are the same as those in the first invention. The speed can be increased and the overwrite characteristic at a linear speed of 25 m / s or more can be further stabilized.
The recording layer of the present invention is formed by various vapor deposition methods (vacuum deposition method, sputtering method, photo CVD method, ion plating method, etc.). The film thickness is usually 50 to 1000 mm, preferably 100 to 350 mm, more preferably 150 to 250 mm. In this range, the function as a recording layer is excellent because the light absorption capability of laser light or the like is sufficient, and the interference effect of the recording medium is also excellent because the transmitted laser light is sufficient.

In the phase change type optical recording medium of the present invention, a heat-resistant protective layer, a reflective layer, a protective layer, etc. can be provided on the substrate in addition to the recording layer as the constituent layer, and it is configured according to the purpose and required characteristics. The form of the layer is chosen. An example of the layer structure of the phase change optical recording medium of the present invention will be described with reference to the drawings.
The phase change optical recording medium of the present invention can be configured as shown in FIGS. That is, the first heat-resistant protective layer 2, the recording layer 3, the second heat-resistant protective layer 4, and the reflective layer 5 are sequentially provided on the substrate 1 (FIG. 1), or on the reflective layer 5 having the structure shown in FIG. In addition, a configuration in which a protective layer 6 is further provided (FIG. 2) can be employed. The heat-resistant protective layer is not necessarily provided on both sides of the recording layer 3, but when the substrate 1 is made of a material having low heat resistance such as polycarbonate resin, the substrate 1 and the recording layer 3 as shown in FIGS. The first heat-resistant protective layer 2 may be provided between the recording layer 3 and the reflective layer 5 (the second heat-resistant protective layer 4 in FIGS. 1 and 2) may be omitted. Note that these configurations are examples for explaining the embodiment, and other configurations may be used, but the configuration mode of FIG. 2 is generally preferable.

Next, each constituent layer other than the recording layer will be described.
The material used for the substrate 1 generally includes glass, ceramics, resin, etc., but a resin substrate is desirable in terms of moldability and cost.
Representative examples of the resin include polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, polyethylene resin, polypropylene resin, silicone resin, fluorine resin, ABS resin, urethane resin, etc., but in terms of processability, optical properties, etc. To polycarbonate resin.
The substrate 1 may have any shape such as a disk shape, a card shape, and a sheet shape, but is preferably a desk shape from the viewpoint of operability.
The thickness of the substrate is usually 0.75 mm of the DVD substrate.

Materials used for the heat-resistant protective layer (first heat-resistant protective layer 2 or second heat-resistant protective layer 4) include metal oxides such as SiO ₂ , ZnO, and ZrO ₂ ; nitrides such as AlN, Si ₃ N ₄ , and TiN Etc .; sulfides such as ZnS, CaS, Al ₂ S _{3 and the} like can be mentioned, but a mixture of ZnS and SiO ₂ is preferable from the viewpoint of refractive index.
Various vapor deposition methods are used for forming the heat-resistant protective layer as in the case of the recording layer. In particular, it is preferable to form a dielectric layer by forming a film by sputtering using (ZnS) · (SiO ₂ ).
Since this dielectric layer has a function as a heat-resistant protective layer and a function as a light interference layer, it is necessary to form a layer so that these functions are exhibited to the maximum. Is 200 to 3000cm, preferably 350 to 800cm. When the thickness is less than 200 mm, the function as a heat-resistant protective layer is lost.

Examples of the material used for the reflective layer 5 include metals such as Ag, Au, and Cu having high thermal conductivity and high reflectivity that can cope with overwriting under high linear velocity, and alloys thereof. Specific examples include Ag alloys such as Ag—Pd—Cu, Ag—In, and Ag—Cu—Ni, among which Ag—Pd—Cu is preferable.
The film can be formed by various vapor deposition methods, for example, a sputtering method, as in the case of the recording layer.
The film thickness is 500 to 2000 mm, preferably 700 to 1500 mm, and more preferably 800 to 1200 mm. In this range, the optical reflectance and thermal conductivity are equivalent to those of the bulk alloy, so that the function of the reflective layer is sufficiently obtained.
The material used for the protective layer 6 is not particularly limited as long as it is a material having excellent workability and capable of forming a uniform thin film and satisfying the function for a recording medium. A resin material such as an epoxy resin or an acrylic resin that can form a thin film by a method such as the above is preferable.
Electromagnetic waves (visible light, ultraviolet rays, infrared rays, electron beams, etc.) are used for recording, reproduction, erasing and rewriting of the phase change optical recording medium of the present invention. A light beam such as laser light is preferred.

  By using the phase change type recording material of the present invention 1 or 2 for the recording layer, the recording sensitivity is as large as the DVD-ROM, and the recording linear velocity is wide from 3.5 m / s to 35 m / s. It is possible to provide an excellent phase change type optical recording medium having good and sufficient modulation characteristics, good overwrite and its repetition characteristics, and high storage reliability.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in more detail, this invention is not limited at all by these Examples.

Example 1
A first heat-resistant protective layer 2, a recording layer 3, a second heat-resistant protective layer 4, and a reflective layer 5 are sputtered on a polycarbonate substrate 1 having a track pitch of 0.7 μm, a groove depth of 400 mm, a thickness of 0.6 mm, and a diameter of 120 mm. Then, a protective layer 6 made of acrylic resin and having a thickness of about 5 nm is provided on the reflective layer 5 by a spin coating method, and a phase change optical recording medium for evaluation having the same layer configuration as that shown in FIG. .
The first heat-resistant protective layer 2 has (ZnS) ₇₀ (SiO ₂ ) ₃₀ with a thickness of 800 mm, and the recording layer 3 has In ₂₄ Sb ₆₈ H ₃ Ge ₂ Se ₃ with a thickness of 160 mm. The heat-resistant protective layer 4 is controlled by sputtering so that (ZnS) ₇₀ (SiO ₂ ) ₃₀ has a thickness of 300 mm and the reflective layer 5 is Ag ₉₅ Pd ₃ Cu ₂ with a thickness of 900 mm. Were laminated.
The material composition and film thickness of each constituent layer are as shown in Table 1.

Examples 2-8
In Example 1, instead of In ₂₄ Sb ₆₈ H ₃ Ge ₂ Se ₃ used as the recording layer 3, the following materials were used in exactly the same manner as in Example 1 except that the following materials were used. A phase change optical recording medium for evaluation was produced.
Example 2: In ₂₄ Sb ₆₈ H ₃ Ge ₂ Te ₃
Example 3: In ₂₂ Sb ₆₇ H ₃ Ge ₂ Se ₃ Sn ₃
Example 4: In ₂₂ Sb ₆₇ H ₃ Ge ₂ Te ₃ Sn ₃
Example 5: In ₂₂ Sb ₆₇ H ₃ Ge ₂ Se ₃ Bi ₃
Example 6: In ₂₂ Sb ₆₇ H ₃ Ge ₂ Te ₃ Bi ₃
Example 7: In ₂₂ Sb ₆₇ H ₃ Ge ₂ Se ₃ I ₃
Example 8: In ₂₂ Sb ₆₇ H ₃ Ge ₂ Te ₃ I ₃
Table 1 summarizes the material compositions and film thicknesses of the constituent layers of Examples 2 to 8.

Comparative Examples 1-6
A phase change optical recording medium of a comparative example was produced in the same manner as in Example 1 except that the recording layer material was changed to that shown in Table 2. The material composition and film thickness of each constituent layer in the comparative example are as shown in Table 2.

Since the recording layers of the phase change optical recording media for evaluation obtained in Examples 1 to 8 and Comparative Examples 1 to 6 are in an amorphous state, it is necessary to initially crystallize the recording media for evaluation. There is. Therefore, initial crystallization was performed according to the following initialization method.
For the initial crystallization, a semiconductor laser initialization apparatus (beam diameter: 1 μm × 75 μm, manufactured by Hitachi Computer) with a 2000 mW output was used, and the laser wavelength was 810 nm, the initial crystallization linear velocity was 12 m / s, and the moving speed of the light source was The phase change optical recording medium for evaluation was irradiated for 60 seconds at 20 μm per rotation.
After initialization, the overwrite characteristics, modulation degree, and storage reliability of each phase change optical recording medium for evaluation were measured and evaluated.
In the evaluation, the recording linear velocity and the recording power (on the recording medium) were set to 3.5 m / s (10 mW), 15 m / s (16 mW), 25 m / s (26 mW), and 35 m / s (36 mW), respectively. Further, the recording laser wavelength is set to 650 nm, overwriting is repeated with a random pattern of EFM (Eight Fourteen Modulation, 8-14 modulation), and the evaluation of the reproduction signal characteristics is performed by evaluating the jitter value of the 3T signal and the modulation degree of the 14T signal. I went there. The storage reliability was evaluated based on the jitter value of the 3T signal and the modulation factor of the 14T signal at the 1000th overwriting after holding the recording medium overwritten 1000 times at a temperature of 80 ° C. and 85% humidity for 300 hours. .
The evaluation results of Examples 1 to 8 and Comparative Examples 1 to 6 are summarized in Tables 3 to 4.

As shown in Table 3, each of Examples 1 to 8 using the phase change recording material of the present invention has a sufficient degree of modulation, excellent recording sensitivity and overwrite characteristics, and initial crystallization. Can also be done easily.
On the other hand, as shown in Table 4, in the comparative example which is the prior art, a recording medium using the composition of In ₅₀ Sb ₅₀ (Comparative Example 1) and the eutectic composition of In ₃₂ Sb ₆₈ (Comparative Example 2). However, overwriting at a high linear velocity is possible, but it can be seen that the degree of modulation, recording sensitivity, storage reliability, and overwriting characteristics are inferior to those of the optical recording medium of the embodiment.
In Comparative Example 3 in which Ag is added to the In—Sb phase change recording material, the recording sensitivity and the modulation degree are improved, but the storage reliability and the overwrite characteristics are not improved so much.
In Comparative Example 4 in which Se was added to the In—Sb phase change recording material, the storage reliability was improved, but the recording sensitivity and the modulation degree were inferior to those of the examples in the overwrite characteristics.
Further, Comparative Example 5 in which Ge is added to the In—Sb phase change recording material has good overwrite characteristics and storage reliability, but cannot be said to have good recording sensitivity, modulation degree, and overwrite characteristics.
In Comparative Example 6 using the Ag—In—Sb—Te phase change recording material, overwriting at high linear speeds (25 m / s and 35 m / s) was impossible.

It is sectional drawing which shows the layer structural example for describing embodiment of the phase change type optical recording medium of this invention. It is sectional drawing which shows the other layer structural example for describing embodiment of the phase change type optical recording medium of this invention. It is sectional drawing which shows the further another layer structural example for describing embodiment of the phase change type optical recording medium of this invention. It is sectional drawing which shows the further another layer structural example for describing embodiment of the phase change type optical recording medium of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 First heat-resistant protective layer 3 Recording layer 4 Second heat-resistant protective layer 5 Reflective layer 6 Protective layer

Claims (2)

A phase change type optical recording medium in which a recording layer made of at least a phase change type recording material is provided on a substrate, and an electromagnetic wave is irradiated to the recording layer to cause a reversible phase change, and at least information can be recorded and reproduced. And a phase change recording material, wherein the phase change recording material is represented by the following composition formula:
InαSbβHγGeδXε
(Wherein X is Se and / or Te, α, β, γ, δ, ε is atomic%)
8 ≦ α ≦ 35
50 ≦ β ≦ 85
2 ≦ γ ≦ 10
1 ≦ δ ≦ 5
2 ≦ ε ≦ 15
α + β + γ + δ + ε = 100 2. The phase change type optical recording medium according to claim 1, wherein the phase change type recording material is represented by the following composition formula.
InαSbβHγGeδXεYκ
(Wherein X is Se and / or Te, Y is at least one element selected from Sn, Bi, and I, and α, β, γ, δ, ε, and κ are atomic%)
8 ≦ α ≦ 35
50 ≦ β ≦ 85
2 ≦ γ ≦ 10
1 ≦ δ ≦ 5
2 ≦ ε ≦ 15
2 ≦ κ ≦ 10
α + β + γ + δ + ε + κ = 100

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