JP2877704B2 - Optical information recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel optical information recording medium, and more particularly to an optical information recording medium capable of obtaining a high-quality reproduced signal with little deterioration of a jitter value in repeated overwrite recording. is there.

[0002]

2. Description of the Related Art In recent years, optical information recording media have been actively researched and developed as means for recording, reproducing, and erasing an enormous amount of information. In particular, a so-called phase-change optical disc that performs recording and erasing of information by utilizing the fact that the optical recording layer reversibly changes phase between two states, crystalline and amorphous, changes the power of laser light. Has the advantage that new information can be simultaneously recorded while erasing old information (hereinafter referred to as overwriting).
Promising.

As a recording material for the overwriteable phase change type optical disk, an In-Se alloy having a low melting point and high laser beam absorption efficiency (Appl. Phys.
Lett. 50, 667 pages, 1987) and I
n-Sb-Te (Appl. Phys. Lett.
0, page 16, 1987), and a chalcogen alloy such as a Ge-Te-Sb alloy (JP-A-62-53886) is mainly used.

On the other hand, when recording / erasing is actually performed using these chalcogen alloys, deformation of the substrate due to heat during recording / erasing is prevented, oxidation of the optical recording layer, mass transfer along the guide groove, or In order to prevent deformation, usually, at least one of metal or metalloid oxides, carbides, fluorides, sulfides, and nitrides at least one selected from the group consisting of oxides, carbides, fluorides, sulfides, and nitrides directly under and / or immediately above the optical recording layer. A recording layer made of a chalcogen alloy, a protective layer provided immediately below and / or immediately above the recording layer, and a reflective layer (for example, a cooling layer provided on the opposite side of the recording layer from the substrate side) Al
An alloy having a three-layer or four-layer structure made of an alloy on a transparent substrate has become the mainstream of phase-change optical disks because of its favorable recording and erasing characteristics.

[0005]

However, in such a three-layer or four-layer phase change optical disk, when performing overwriting with a single beam, recording on a crystalline portion, and recording on an amorphous portion. The difference between the thermal conductivity of the crystalline part and the amorphous part, and the difference in the temperature rise process of each part due to the effect of latent heat, as a result, each part by the irradiated laser Will reach different maximum temperatures. This causes a problem that the size and shape of the recording pits, that is, the recording state is different, adversely affects the erasing characteristics, and a problem that information cannot be reproduced correctly at the time of high density using pit edge recording or the like. There was a point.

Japanese Patent Laid-Open Publication No. 1-149238 discloses a proposal for improving the erasing rate and reducing the jitter value (shift in the time axis direction) during overwriting. It is disclosed that the absorbance is equal to or higher than that of the optical recording medium, and JP-A-3-113844 discloses that the difference in the optical absorption in the optical recording layer is reduced to 10% or less. These techniques are effective in improving the initial jitter characteristics, but since the protective layer, which is the upper layer of the recording layer, has a thick film structure, it reduces the repetition durability required for practical use and repeats. There is a disadvantage that the jitter value is deteriorated due to this.

Further, Japanese Patent Application Laid-Open No. 2-196688 discloses that a light absorbing auxiliary layer such as Hf, Zr, Nb, Ti, Ta, etc. is provided.
In the No. 0 public information, Ti, Ni, W, Mo, V, N
It is disclosed that a light-absorbing layer of b, Cr, Fe or the like and a heat radiation layer are formed thereon. Furthermore, Japanese Patent Application No. 5-1717
No. 13 discloses that the relationship between the refractive index n of the reflective layer and the extinction coefficient k is k ≦ 0.76n + 1.8.

However, even when any of the light absorbing layers disclosed in these publications is used, the layer structure or the material constituting the layer structure does not satisfy practically sufficient jitter characteristics. However, the deterioration of the jitter value due to this has not been sufficiently solved. SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel optical information recording medium capable of reducing jitter and achieving good repetition characteristics when overwriting is performed with a single beam.

[0009]

The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems. As a result, the recording layer has a light absorption rate of Ac in a crystalline state and a light absorption rate in an amorphous state. Aa
And the thickness d of the protective layer formed between the recording layer and the reflective layer
When (nm) is satisfied, satisfying the following expressions (a) and (b) Ac / Aa ≧ 1.1 (a) d ≦ 50 (b) is a condition for solving the above problem. The present inventors have found and completed the present invention based on the findings.

[0010]

That is, claim 1 of the present invention relates to an optical information recording medium for recording information by changing optical characteristics,
A recording layer, a dielectric layer, and a reflective layer are sequentially formed on a transparent substrate, the thickness d (nm) of the dielectric layer satisfies d ≦ 50, and the reflective layer is represented by the following general formula. An optical information recording medium comprising a material. AxB (100-x) where 50 ≦ x ≦ 95 where A is at least one selected from the group consisting of Ge and Si, and B is selected from the group consisting of Al, Au, Ag, Ti and V At least one type.

According to a second aspect of the present invention, in an optical information recording medium for recording information by changing optical characteristics, a recording layer, a dielectric layer and a reflective layer are sequentially formed on a transparent substrate, and the film of the dielectric layer is formed. An optical information recording medium characterized in that the thickness d (nm) satisfies d ≦ 50 and the reflective layer is made of a material represented by the following general formula. AxB (100-x) where 20 ≦ x ≦ 80 where A is at least one member selected from the group consisting of Mo and W, and B is at least one member selected from the group consisting of V, Nb and Ti. is there.

In the optical information recording medium of the present invention, a recording layer, a dielectric layer, and a reflection layer can be sequentially formed on a transparent substrate. Preferably, a dielectric layer is formed between the recording layer and the substrate. It can have a four-layer structure. Further, it is possible to form a fifth layer for adjusting thermal properties on the reflective layer. In this case, as the fifth layer, Au, A
and highly reflective materials such as alloys based on them.

When the extinction coefficient k at the complex refractive index n '= n + ik of the reflective layer of the optical information recording medium having such a layer structure is larger than 1.0n-0.8 (n is the refractive index), the reflective layer Has a higher light reflectance, lowers the absorption efficiency with respect to the transmitted light from the recording layer in the amorphous state, and the ratio of Ac to Aa is less than 1.1, thereby obtaining a good result with respect to the repetition durability. Can not.

[0015] When k is 1 or less, the amount of light transmitted from the optical information recording medium thus produced increases, and thus problems such as a decrease in recording sensitivity and an increase in noise may occur. In this case, it is desirable to form a layer structure that blocks transmitted light by forming a metal with high light reflectivity, for example, Au, Al, or an alloy based thereon, on the reflective layer in the present invention.

Further, if the thickness of the dielectric layer formed between the recording layer and the reflective layer is more than 50 nm, the rate of cooling the recording layer heated by the laser is reduced, so that the repetitive durability is deteriorated. Easy to cause. Further, by using the reflective layer particularly for a Ge—Te—Sb phase change type optical recording medium, better repetition durability can be realized.

A novel material that can satisfy the optical constant with good repetition durability is represented by the following equation. AxB (100-x) (3) A is at least one selected from Ge and Si;
B is at least one selected from Al, Au, Ag, Ti, and V. Here, when x is less than 50, no great effect is obtained in the improvement of the repetition durability, and when x is more than 95, the value is preferably 50 or more and 95 or less in order to lower the optical contrast. In addition, since many of these material systems belong to the eutectic system according to the phase diagram, the optical constants and thermophysical properties can be controlled by the composition ratio, and therefore, the selection of the material according to various optical recording conditions is possible. It can be done easily.

Further, a novel material which can satisfy the optical constant having good repetition durability is represented by the following formula. AxB (100-x) (4) A is at least one selected from Mo and W;
Is at least one selected from V, Nb, and Ti. Here, when x is less than 20, there is no significant effect on improvement of the repetition durability, and when x is more than 80, the recording sensitivity is lowered.
Many of these material systems belong to the solid solution phase diagram,
Control of the optical constants and thermophysical properties by the composition ratio can be relatively easily performed, so that the material can be selected according to various optical recording conditions.

[0019]

According to the present invention, the light transmitted from the recording layer in the amorphous state is absorbed by the reflective layer or the novel layer according to the present invention. As a result, the light absorptance of the recording layer in the amorphous state is reduced, and the ratio of Ac to Aa is set to 1 in a structure in which the thickness of the dielectric layer formed between the recording layer and the reflective layer is 50 nm or less. It can be controlled to one or more, and good repetition durability can be obtained.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. In the examples, a phase change type recording material will be described as an example, but the present invention is not limited to this. Further, as a method for evaluating the characteristics of the optical information recording medium in the following examples, the disk was rotated at 3600 rpm and the measurement was performed at a position with a radius of 39 mm. Pit edge recording was performed using a laser wavelength of 680 nm as an optical system and a 1-7 modulation signal. Jitter measurement is 2T
w signal (recording frequency: 12.3 MHz) is recorded, and 7T
The jitter when the w signal (recording frequency: 3.5 MHz) was overwritten was analyzed by a jitter analyzer and evaluated by the standard deviation σ. Further, in order to evaluate the durability, σ at the time of initial overwriting and σ after 10,000 times were respectively measured.

FIG. 1 shows a configuration example of the optical information recording medium of the present invention. Reference numeral 1 denotes a transparent resin material on a disk having a center hole and having a diameter of 3.5 inches and a thickness of 0.6 mm.
This is a substrate provided with grooves having a pitch of 0 μm. On this transparent substrate 1, for example, a protective layer (dielectric) 2, an optical recording layer 3, a protective layer (dielectric) 4, and a reflective layer 5 are sequentially laminated by a sputtering method. Ge-Te as the optical recording layer
-An Sb-based alloy was used. As the dielectric, ZnS-
An SiO ₂ mixture was used.

FIG. 2 shows the results of optical calculations when the thickness of each layer, the refractive index n of the reflective layer, and the extinction coefficient k are changed in this configuration. In this calculation, the modulation degree (modulation degree = (Rc−Ra) /
(Rc + Ra) * 100, where Rc is a reflectance in a crystalline state, and Ra is a reflectance in an amorphous state, and the conditions were set to 70% or more. Table 1 shows the optical constants and the thickness ranges of the respective layers used in this calculation. As shown in FIG. 2, when the optical constant of the reflective layer is k ≦ 1.0n−0.8, Ac / A
It can be seen that a ≧ 1.1 is satisfied.

[0023]

[Embodiment 1] Next, as shown in FIG. 1, ZnS-SiO ₂ (SiO ₂ : 2
A protective layer 2 having a thickness of 70 nm was formed from a target consisting of (0 mol%) by RF sputtering. Then G
An optical recording layer 3 having a thickness of 15 nm made of an e-Te-Sb-based alloy, a protective layer 4 having a thickness of 15 nm made of ZnS-SiO ₂ (SiO ₂ : 20 mol%), and a GeAl (G
e: 90 mol%) was formed by sputtering successively at 150 nm. After that, U
An optical information recording medium was formed by forming a V-cured resin layer 6 by spin coating.

At this time, the optical constants of the reflective layer material, the initial jitter value, the jitter value after 10,000 repetitions, and the optical constants of the reflective layer single layer are shown in Example 1 of Table 2.

[0025]

Embodiments 2 to 8 Each of the reflection layers was made of SiAu (Si: 8).
0 mol%), GeAg (Ge: 65 mol%), Si
Ti (Si: 78 mol%), SiV (Si: 73 mo)
1%), WV (W: 50 mol%), MoNb (Mo:
An optical information recording medium was manufactured in the same manner as in Example 1 except that MoTi (Mo: 50 mol%) and MoTi (Mo: 50 mol%) were used and had the same film thickness structure. The results are shown in Example 3 of Table 2.

[0026]

Ninth Embodiment As shown in FIG. 3, in the same manner as in the first embodiment, a protective layer 12 having a thickness of 70 nm, an optical recording layer 13 having a thickness of 15 nm, and a protective layer 1 having a thickness of 15 nm are formed on a transparent substrate 11.
4. 150 nm thick reflective layer 15 (GeAl: Ge95
mol%), and an Al layer having a thickness of 100 nm was formed as a heat radiation layer 16 on the reflective layer 15. Thereafter, a UV curable resin layer 17 was formed by a spin coating method in the same manner as in Example 1 to produce an optical information recording medium. The results are shown in Example 2 of Table 2.

[0027]

Embodiment 10 An optical recording medium having the structure shown in FIG. 3 was formed on a transparent substrate 11 in the same manner as in Embodiment 9 by forming a protective layer 12 having a thickness of 70 nm, an optical recording layer 13 having a thickness of 15 nm, and a film thickness of 15 nm.
Protective layer 14 and a 150 nm-thick reflective layer 15 (WV: W
Then, an AlTi alloy layer having a thickness of 100 nm was formed as a heat radiation layer 16 on the reflective layer 15. Thereafter, a UV curable resin layer 17 was formed by a spin coating method in the same manner as in Example 1 to produce an optical information recording medium. The results are shown in Example 10 of Table 2.

[0028]

Comparative Examples 1-2 Hf and GeAl (G
e: 90 mol%), except that a protective layer 2 having a thickness of 70 nm, an optical recording layer 3 having a thickness of 15 nm, a protective layer 4 having a thickness of 160 nm, and a reflective layer 5 having a thickness of 150 nm were formed as the thickness structure of each layer. Produced an optical information recording medium in the same manner as in Example 1. The results are shown in Comparative Examples 1 and 2 of Table 2.

[0029]

Comparative Examples 3 to 9 Cr and GeAl (G
e: 40 mol%), Ge, W, SiAu (Si: 45
mol%), Si, WV (W: 10 mol%)
Optical information recording was performed in the same manner as in Example 1, except that the first protective layer thickness was 70 nm, the recording layer thickness was 15 nm, the second protective layer thickness was 15 nm, and the reflective layer thickness was 150 nm. Created media. The results are shown in Comparative Examples 3 to 9 in Table 2.

From Table 2, it can be seen that Examples 1 to 10 have good repetition durability with respect to jitter. Next, σ representing the range of jitter necessary for practical use
/Tw<11.3% (σ: standard deviation, Tw: window width) and the performance of the optical information recording medium obtained by the present invention are shown in FIG.
Shown in FIG. 4 shows that the optical information recording medium according to the present invention has achieved practically sufficient performance. That is, by using the material according to the present invention, it is possible to reduce the initial jitter in overwrite recording using a single beam and to obtain an optical information recording medium having excellent jitter repetition durability.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

As described above, according to the present invention,
An optical information recording medium that can reduce initial jitter in overwrite recording using a single beam and has excellent jitter repetition durability can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a layer structure of an optical information recording medium according to an embodiment of the present invention.

FIG. 2 shows the ratio (Ac) between the optical constant of a reflective layer and the light absorptivity in a crystalline state and an amorphous state of a recording layer.
/ Aa).

FIG. 3 is a sectional view showing a layer structure of an embodiment of the optical information recording medium of the present invention.

FIG. 4: σ / Tw <1 required to satisfy practical performance
FIG. 3 is a diagram showing 1.3% and a jitter characteristic region of the optical information recording medium according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 11 Transparent substrate 2, 12 Protective layer (dielectric) 3, 13 Optical recording layer 4, 14 Protective layer (dielectric) 5, 15 Reflective layer 5, 6, 17 UV curing resin layer 16 Heat dissipation layer

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-1-149238 (JP, A) JP-A-5-282704 (JP, A) JP-A-3-113844 (JP, A) JP-A-2- 54443 (JP, A) JP-A-2-289934 (JP, A) JP-A-3-178031 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 7/24 538

Claims (2)

(57) [Claims] In an optical information recording medium for recording information by changing optical characteristics, a recording layer, a dielectric layer, and a reflective layer are sequentially formed on a transparent substrate, and a film thickness d (n
m) satisfies d ≦ 50, and the reflective layer is made of a material represented by the following general formula. AxB (100-x) where 50 ≦ x ≦ 95 where A is at least one selected from the group consisting of Ge and Si, and B is selected from the group consisting of Al, Au, Ag, Ti and V At least one type. 2. In an optical information recording medium for recording information by changing optical characteristics, a recording layer, a dielectric layer and a reflective layer are sequentially formed on a transparent substrate, and the thickness d (n) of the dielectric layer
m) satisfies d ≦ 50, and the reflective layer is made of a material represented by the following general formula. AxB (100-x) where 20 ≦ x ≦ 80 where A is at least one member selected from the group consisting of Mo and W, and B is at least one member selected from the group consisting of V, Nb and Ti. is there.