JP2003291534A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phase transition type optical information recording medium which has the capacity equal to that of a DVD-ROM, can secure a sufficient modulation degree even in such a wide range of recording linear velocity as 3.5 m/s to 35 m/s, excellent overwrite repetition characteristics and high preservation reliability. <P>SOLUTION: In the phase transition type optical information recording medium which comprises a first heat resistant protective layer, a recording layer, a second heat resistant protective layer and a reflective layer in this order or in the reverse order, wherein the recording layer is caused to develop a phase change reversibly under the irradiation by an electromagnetic wave to execute the recording and reproduction of information using the optical change, the optical recording medium is constituted of Ga, Sb, Sn and Co (1). When the composition formula of the recording material is expressed by GaαSbβSnγCoδ (wherein, α, β, γ, δ are each an atom.%, α+β+γ+δ=100), the relation among α, β, γ, δ in the optical recording medium expressed in (1) satisfies formulas; 3≤α≤52; 42≤β≤92; 3≤γ≤25; 0.1≤δ≤2 (2). <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase change type optical recording medium capable of recording / reproducing information and rewriting it by causing an optical change in a recording material by irradiating an electromagnetic wave. is there.

[0002]

2. Description of the Related Art Recording and reproduction of information by irradiation of a light beam,
As one of the erasable and rewritable optical recording media,
There is known a so-called phase change type optical disk which utilizes a phase transition between a crystalline-amorphous phase or a crystalline-crystalline phase.
This optical disc can be overwritten by a single beam, and is used as a recording medium for computers and AV because the optical system on the drive side is simple. As the recording material, Ge-Te, Ge-Te-Se,
In-Sb, Ga-Sb, Ge-Sb-Te, Ag-I
n-Sb-Te or the like is used. Above all, Ag-In
-Sb-Te is characterized by high sensitivity and a clear outline of an amorphous portion of a recording mark, and is used as a material for recording a mark edge (JP-A-3-231889).
Japanese Patent Laid-Open No. 4-1910989, Japanese Laid-Open Patent Publication No. 4-2
32779, JP-A-4-267192, JP-A-5-345478, etc.).

However, these recording materials are CD-RW.
(Compact Disk-Rewritable)
Used in a recording medium having a relatively low recording density such as a DVD (Digital Versati).
le Disk) When used for RAM, DVD-RW, etc.,
Overwriting is possible at a recording linear velocity of about 3.5 m / s (1 × speed), but there is a problem that the overwrite characteristic deteriorates at a recording linear velocity of 2 × or more. This is because the crystallization speed of the above recording material is slow and it becomes difficult to overwrite at a high linear velocity. Although the crystallization rate can be increased by increasing the amount of Sb, the increase in Sb lowers the crystallization temperature and deteriorates the storage characteristics. As a measure for solving this problem, Japanese Patent Laid-Open No. 2000-322740.
Japanese Patent Laid-Open Publication No. Hei 11-242242 discloses a method using an Ag-In-Ge-Sb-Te-based recording material. This method is applicable in the recording linear velocity range of 3.0 to 20 m / s, but cannot cope with a higher linear velocity, for example, 20 m / s or more.

On the other hand, GaSb has been proposed as a high-speed crystallization material ("phase-change Opti").
cal data storage in GaSb "
Applied optics / vol. 26, No2
2115 November 1987). It is reported that this alloy system has an extremely high crystallization rate, but initial crystallization is difficult because the crystallization temperature is extremely high at 350 ° C. Furthermore, Mo, W, Ta, Ni, Pd, P on GaSb
t, Cu, Ag, Au, Zn, Cd, Al, Tl, S
U.S. Pat. No. 4,8,8 is an attempt to improve the characteristics by adding i, Ge, Sn, Pb, As, Bi, S, Se, Te and the like.
No. 18,666 and No. 5,072,423, the overwrite characteristics, the modulation degree, and the storage reliability in high-speed recording are not satisfied at the same time.
As described above, various phase change recording materials have been reported.
None of them can satisfy all the characteristics required for a rewritable phase change type optical recording medium. In particular,
It has the same high-density recording capacity as DVD-ROM, and can cope with the case where the recording linear velocity is further increased (up to 35 m / s), and simultaneously satisfies the overwrite characteristic, the modulation degree, and the storage reliability. It wasn't something.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and its object is DV.
The D-ROM has a large capacity, the recording linear velocity is in a wide range of 3.5 m / s to 35 m / s, and a sufficient degree of modulation is ensured even in a high linear velocity, and the overwrite characteristics of the overwrite are good and the storage reliability is high. To provide a phase change type optical recording medium having high efficiency.

[0006]

In order to solve the above-mentioned problems, the inventors of the present invention have conducted intensive studies focusing on recording materials, and as a result, as the recording material, an alloy composed of Ga, Sb, Sn, and Co is used. It has been found that the above problems can be solved when used, and further improvement of storage reliability can be realized by adding one element selected from Ag, Cu, In, Ge, C and B to this alloy. The present invention has been completed based on the findings. That is, the above-mentioned subject is the following 1)-
It can be solved by the invention of 4). 1) At least a first heat-resistant protective layer, a recording layer, a second heat-resistant protective layer, and a reflective layer are provided on the substrate in this order or in reverse order, and the recording layer undergoes a reversible phase change upon irradiation with electromagnetic waves, and its optical In a phase change type optical recording medium in which information is recorded, reproduced, erased and rewritten by utilizing such changes, the recording material is Ga, Sb, Sn, Co. 2) When the composition formula of the recording material is GaαSbβSnγCoδ (where α, β, γ, δ are atomic%, α + β + γ +
The optical recording medium according to 1), wherein δ = 100), α, β, γ, and δ satisfy the following conditions. 3 ≦ α ≦ 52 42 ≦ β ≦ 92 3 ≦ γ ≦ 25 0.1 ≦ δ ≦ 2 3) One element selected from Ag, Cu, In, Ge, C and B is added to the recording material. The optical recording medium as described in 1) or 2) above. 4) The optical recording medium according to 3), wherein M is in the range of 0.1 to 10, where M (atomic%) is the amount of the element added to the recording material.

The present invention will be described in detail below. As a means for solving the above problems, the present invention has developed a novel recording material composed of Ga, Sb, Sn and Co. First, in an optical recording medium that utilizes a phase transition between an amorphous phase and a crystalline phase, in order to be able to overwrite even at a high linear velocity of 35 m / s, the laser beam diameter is 1 μmφ.
It can be calculated that the crystallization time must be about 29 ns (nanosecond). Further, in high density recording such as DVD, the wavelength of the laser used is 650 nm, which is shorter than the conventional 780 nm, so the beam diameter is 1
When the linear velocity is 35 m / s, the laser beam traverses a point on the rotating desk at a linear velocity of 35 m / s, which is shorter than 29 ns. For example, when the beam diameter is 0.7 μmφ, the time is about 20 ns, and overwriting (erasing (crystallizing) old marks and writing new marks) must be performed within this time. That is, it is necessary to crystallize in 20 ns. Prior art Ag-In-Sb-
Even in the Te system, GaSb system, and Ge-Sb-Te system, it is possible to perform high-speed crystallization within this time, but there are problems of storage reliability and initial crystallization, and 35 m / s
There was no recording material that could satisfy all the characteristics at the linear velocity.

In the present invention, attention is paid to the high-speed crystallization performance of GaSb, and these two elements are used as constituent elements for high-speed crystallization, and Sn is added to lower the crystallization temperature.
In addition to solving the difficulty of initial crystallization due to the high crystallization temperature, which is a defect of b, at the same time, it has succeeded in achieving a further high speed crystallization as compared with GaSb and obtaining a sufficient modulation degree.
Moreover, by adding Co, the storage reliability and overwrite characteristics are improved. The reason why the recording material composed of Ga and Sb crystallizes at high speed is currently being analyzed. One idea is that the distance between the nearest neighbor atoms of GaSb is 2.65Å when the amorphous phase is In this case, since it is extremely close to 2.64Å, it is speculated that the phase transition from the amorphous phase to the crystalline phase may be easily performed. In addition, Sn has a weak covalent bond, and therefore acts to weaken the covalent bond with GaSb forming a covalent bond, lowering the crystallization temperature and facilitating the rearrangement of atoms to accelerate the crystallization speed. I can do things. Further, by adding Sn, the change in the structure of the amorphous phase and the crystal phase becomes larger than that in GaSb, so that the change in the optical constant between the two phases due to the phase transition becomes large and a sufficient modulation degree is obtained. Can be realized. The reason why the addition of Co improves the storage reliability and the overwrite characteristic is not known so far, but it is thought that the addition of Co may cause passivation to prevent the progress of oxidation.

The composition of the recording material is represented by Gaα
SbβSnγCoδ (where α, β, γ and δ are atomic%,
It is preferable that α + β + γ + δ = 100) satisfy the following conditions. 3 ≤ α ≤ 52 42 ≤ β ≤ 92 3 ≤ γ ≤ 25 0.1 ≤ δ ≤ 2 Here, when α and β are less than 3 atom% and 42 atom%, respectively, the crystallization speed is lowered, and 35 m / Overwriting becomes difficult under the linear velocity of s, and when α and β are greater than 52 atom% and 92 atom%, respectively, the number of overwrite repetitions decreases. Further, when γ is less than 3, the crystallization temperature is not lowered and the initial crystallization becomes difficult, and at the same time, it becomes difficult to secure a sufficient degree of modulation, and when γ is more than 25, the storage reliability decreases. Further, when δ is less than 0.1, storage reliability and overwrite performance are deteriorated, and when it is more than 2, recording sensitivity is deteriorated.

Further, in the present invention, Ga, Sb, Sn, C
The recording material consisting of o, Ag, Cu, In, Ge, C,
By adding one element selected from B, the storage characteristics can be further improved. The reason is G
In the case of e, C, and B, since the coexisting bond strength is strong, it is considered that they bond with the dangling bonds of the base material and prevent oxidation. Ag,
Although it is unknown about Cu and In, it is considered that Cu and In are similarly bonded to the dangling bonds of the base material to prevent oxidation. The preferable addition amount of these elements is in the range of 0.1 to 10 atom%, and if the amount is less than 0.1 atom%, the effect is small and 1
If it is more than 0 atom%, the crystallization speed will be slow and will be 35 m / s.
It becomes difficult to overwrite under the linear velocity.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a structural example of an optical recording medium of the present invention will be described with reference to the drawings. FIG. 1 shows an example of the configuration of the optical recording medium of the present invention, in which a substrate 1 is provided with a first heat resistant protective layer 2, a recording layer 3, a second heat resistant protective layer 4, and a reflective heat dissipation layer 5. The heat-resistant protective layers are not necessarily provided on both sides of the recording layer, but when the substrate 1 is made of a material having low heat resistance such as a polycarbonate resin, it is desirable to provide the first heat-resistant protective layer. Further, although not shown, an environmental protection layer may be provided if necessary. The material of the substrate 1 is usually glass, ceramics or resin, and a resin substrate is preferable in terms of moldability and cost. Typical examples of the resin include polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicone resin, fluororesin, ABS resin, urethane resin, and the like. Polycarbonate resin is preferable from the viewpoints of workability and optical characteristics. The substrate may have any shape such as a disk shape, a card shape, and a sheet shape.

The heat-resistant protective layer, that is, the dielectric layer is made of (ZnS).
A film is formed by a sputtering method using (SiO ₂ ). Since this dielectric layer has a function as a heat-resistant protective layer and a function as an optical interference layer, it is necessary to make the most of these functions.
200-3000Å, preferably 350-2000Å
And If it is less than 200Å, the function as a heat-resistant protective layer is lost, and if it exceeds 3000Å, interfacial peeling tends to occur, which is not preferable. The recording layer of the present invention is usually formed by a sputtering method, and the film thickness is 100 to 1000Å, preferably 200 to 350.
It is Å. When the thickness is less than 100 Å, the light absorption ability is lowered and the function as a recording layer is lost, and when the thickness is more than 1000 Å, the transmitted light is reduced, and the interference effect cannot be expected. An Ag alloy is used for the reflective layer of the present invention, and its film can be formed by a sputtering method. The reflective layer also has a function as a heat dissipation layer. The film thickness is 500 to 2000Å, preferably 700 to 1500Å.

[0013]

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

Examples 1 to 10, Comparative Examples 1 to 5 Track pitch 0.7 μm, groove depth 400 Å, thickness 0.
On a polycarbonate substrate with a diameter of 6 mm and a diameter of 120 mmφ, a first heat-resistant protective layer (thickness 650Å) and a recording layer (thickness 1
50 Å), a second heat-resistant protective layer (thickness 250 Å), a reflective layer (thickness 1000 Å) are sequentially formed by a sputtering method, and an environmental protection layer is further provided on the reflective layer by a spin coating method to form an optical recording medium. It was made. For the recording layer, the materials shown in the following [Table 1] were used, and for the first and second heat-resistant protective layers,
ZnS.SiO ₂ (20:80 mol%) was used, and Ag ₉₆ Cu ₂ Ni ₂ was used for the reflective layer. Then, after the obtained optical recording medium was initially crystallized, the recording linear velocity and recording power were 3.5 m / s (10 mW) and 15 m / s (16 m).
W), 25 m / s (26 mW), 35 m / s (36 m
W). The wavelength of the recording laser at this time is 650.
The reproduction signal characteristics are evaluated by the jitter value of the 3T signal and the modulation factor of the 14T signal, and the storage characteristic is 1
Optical recording medium overwritten 000 times at 80 ℃, 85
Overwrite 1 after holding at a temperature of 300% for 300 hours
The 3T signal jitter value at the second time and the modulation factor of the 14T signal were evaluated. The results are shown in [Table 2] and [Table 3] below.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

As is apparent from [Table 2] and [Table 3] above, the optical recording medium constituted by using the recording material of the present invention is 3.5 m / s, 15 m / s, 25 m / s, 35 m. /
a wide range of linear velocity of s, which was difficult especially in the prior art 2
It can be seen that overwriting is possible even at a linear velocity exceeding 5 m / s, the reproduced signal has a good jitter value and a good modulation factor, and the storage reliability and repetitive overwrite characteristics are excellent. On the other hand, a Ga ₅₀ Sb ₅₀ compound or a eutectic composition Ga ₁₂ S as a recording material, which is a conventional technique, is used.
When the optical recording medium using a b ₈₈ (Comparative Examples 1 and 2) is susceptible overwriting at high linear velocity is different from the optical recording medium using the recording material of the present invention, Jitter value, modulation factor, storage reliability, overwrite overwrite characteristics are poor, initial crystallization is difficult, and eutectic composition Ga
_In the case of Comparative Example 3 in which Sn is added to ₁₂ Sb ₈₈ as an additional element, the modulation factor and the initial crystal are improved, but the repetitive property due to overwriting and the storage reliability are deteriorated. Further, in the case of Comparative Example 4 in which Ge is added as an additional element to Ga ₁₂ Sb ₈₈ having a eutectic composition, the storage reliability is good, but the modulation degree is low, and the repetitive overwrite characteristic is worse than that of Comparative Example 3. Moreover, Ag-In-Sb of Comparative Example 5 was used.
-In case of Te recording material, linear velocity is 25 m / s, 35 m / s
Overwriting in is impossible.

[0019]

According to the present invention, with the same capacity as a DVD-ROM, it is possible to secure a sufficient degree of modulation in a wide range of a recording linear velocity of 3.5 m / s to 35 m / s, and an overwrite repetitive characteristic. It is possible to provide a good phase change type optical recording medium having excellent storage reliability, and it is extremely important to contribute to the field of optical information recording.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration example of an optical recording medium of the present invention.

[Explanation of symbols]

1 substrate 2 First heat-resistant protective layer 3 recording layers 4 Second heat-resistant protective layer 5 Reflective layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroko Tashiro             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh (72) Inventor Mizutani Mirai             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh (72) Inventor Michiaki Shinozuka             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh (72) Inventor Hiroyuki Iwasa             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh F term (reference) 2H111 EA05 EA23 FA01 FA12 FA14                       FB05 FB06 FB09 FB17 FB21                       FB23 FB29 FB30                 5D029 JA01

Claims (4)

[Claims] 1. A substrate having at least a first heat-resistant protective layer, a recording layer, a second heat-resistant protective layer, and a reflective layer in this order or in reverse order, which causes a reversible phase change in the recording layer upon irradiation with electromagnetic waves, A phase change type optical recording medium in which information is recorded, reproduced, erased, and rewritten by utilizing the optical change, wherein the recording material is Ga, Sb, Sn, Co. 2. The composition formula of the recording material is GaαSbβSnγ
When Coδ (where α, β, γ, δ are atomic%, α +
The optical recording medium according to claim 1, wherein β + γ + δ = 100), α, β, γ, and δ satisfy the following conditions. 3 ≦ α ≦ 52 42 ≦ β ≦ 92 3 ≦ γ ≦ 25 0.1 ≦ δ ≦ 2 3. A recording material containing Ag, Cu, In, Ge,
The optical recording medium according to claim 1 or 2, wherein one element selected from C and B is added. 4. The addition amount of the element added to the recording material is M
4. The optical recording medium according to claim 3, wherein M is (atomic%) in the range of 0.1 to 10.