JP2002301869A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording medium suitable for high linear speed recording not less than 17.2 m/s or five times of the reproduction linear speed 3.44 m/s of DVD-ROM. SOLUTION: Not less than 90% of atomic percentage of the recording layer 3 of the optical recording medium, provided with at least a recording layer 3 on a substrate 1 to record, reproduce and erase an information utilizing the phase change of the recording layer 3, is constituted of a compound shown by a formula; Dyα SbβTeγ . (in the formula; α, β, γ show the atomic percentage and 0.01<=α<=0.10, 0.60<=β<=0.95 and α+β+γ=1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an optical recording medium.

[0002]

2. Description of the Related Art An optical recording medium capable of recording / reproducing and erasing information by irradiating a semiconductor laser beam has a magneto-optical recording system in which magnetization is reversed by using heat to record and erase information, There is a phase change recording method that can record and erase using a reversible phase change. The latter is capable of single-beam overwriting and is characterized by being simpler than the optical system on the drive side, and has been applied as a computer-related or audio-visual recording medium. Ge-Sb-Te and Ag-In-Sb-Te are practically used as the recording material. In particular, Ag-In-Sb-Te is a material having high sensitivity and a clear outline of an amorphous portion, and suitable for high-density recording. JP-A-11-070738 discloses an optimum composition ratio and an optimum layer configuration of an AgInSbTe quaternary material having a high overwriting frequency and excellent storage reliability. Also, Cr or
By adding Zr, the storage characteristics are further improved.

The use of phase change recording media for high density image recording is expected to expand in the future. For that purpose, it is necessary to realize high-speed overwriting, and a recording layer material having a high crystallization speed is required. It is becoming. The crystallization speed of the AgInSbTe quaternary material can be improved by increasing the mixing ratio of In or Sb. However, when the compounding ratio of In is increased, the deterioration due to overwriting tends to proceed. In addition, when the compounding ratio of Sb is increased, a disadvantage that storage reliability is reduced is caused. Furthermore,
As the crystallization speed of the recording material increases, there is a problem in that the recording layer is inevitably made amorphous and the formation of recording marks becomes difficult.

[0004]

According to the present invention, a DVD-ROM
It is an object of the present invention to provide an optical recording medium suitable for high linear velocity recording up to 17.2 m / s or more, which is five times as high as the reproduction linear velocity of 3.44 m / s.

[0005]

According to the first aspect of the present invention, there is provided an optical recording medium for providing at least a recording layer on a substrate and recording, reproducing and erasing information by utilizing a phase change of the recording layer. An optical recording medium, characterized in that the atomic ratio of the recording layer is 90% or more of a compound represented by the following formula. Dy _α Sb _β Te _γ (where α, β, and γ represent atomic ratios, and 0.01 ≦ α ≦
0.10 and 0.60 ≦ β ≦ 0.95, and α + β
+ Γ = 1) The invention according to claim 2 is the optical recording medium according to claim 1, wherein the recording layer further contains Ag. Claim 3
The invention of (1) is the optical recording medium according to claim 1, wherein the recording layer further contains Ge. The invention according to claim 4 is the optical recording medium according to claim 1, wherein the recording layer further contains Ag and Ge. The optical recording medium according to any one of claims 1 to 4, wherein the recording layer is formed by a sputtering method using an alloy target having a predetermined composition. It is. According to a sixth aspect of the present invention, in the optical recording medium, at least a lower dielectric layer, a recording layer, an upper dielectric layer, and a reflective layer are provided in this order on a substrate, and the reflective layer contains at least 90% Ag. The optical recording medium according to any one of claims 1 to 4, wherein the optical recording medium is a metal containing at least 1%. According to a seventh aspect of the present invention, the upper dielectric layer has at least a two-layer structure, and one of the layers has a width of 1 nm or more from the interface with the reflective layer toward the inside of the upper dielectric layer and has a sulfuric acid concentration of 1 nm or more. 7. The optical recording medium according to claim 6, wherein the optical recording medium is a layer containing no substance. The invention of claim 8 is
8. The optical recording medium according to claim 7, wherein the sulfide-free layer is made of a carbonized material or a material obtained by mixing an oxide or a nitride with a carbonized material. The invention according to claim 9 is the optical recording medium according to claim 8, wherein the carbonized material is SiC. According to a tenth aspect of the present invention, there is provided the optical recording medium according to any one of the first to ninth aspects, wherein an initially crystallized recording layer is used. In the invention according to claim 11, the initial crystallization is performed by a melting initialization method using a laser beam, or
The optical recording medium according to claim 10, wherein the optical recording medium has been formed by solid-phase initialization.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have proposed that a recording layer be made of DySbTe having a specific composition range and, if necessary, be made of a quaternary or quinary composition to which Ag or Ge or both Ag and Ge are added. It was found that an optical recording medium suitable for high linear velocity recording and excellent in overwrite characteristics and storage characteristics could be formed. AgInSbTe is a phase change recording material having excellent repetitive recording characteristics. However, SbTe, which is a base material of AgInSbTe, has a poor stability of an amorphous phase and has a problem in high-temperature storage reliability of about 70 ° C. Therefore, usually, one or more third elements such as Ag and In for increasing the crystallization temperature and stabilizing the amorphous phase are added and used. Ag and In not only improve storage stability, but Ag facilitates initialization and improve recording density, while In improves recording linear velocity and improve recording density. There is also. However, if the added amount is too large, it adversely affects overwrite characteristics and the like. In the present invention, by replacing a part or all of In with Dy, even if the amount of Dy is smaller than In, the contribution to the improvement of the recording linear velocity is large, so that the recording linear velocity can be improved without adversely affecting the overwrite characteristics. I found it. Also,
At this time, it was found that by adding Ag and Ge, a disk having high recording density and high linear velocity recording, excellent storage reliability, excellent overwrite characteristics, and easy initialization can be formed. However, Ag and Ge added to Dy-Sb-Te
It must be less than 10% in total. If it is larger than this, the recording sensitivity and the overwrite characteristics will be reduced. Dy is also set to 10% or less with respect to Sb-Te.
This is because if it is larger than this, the overwrite characteristics are also deteriorated. Sb is more than 60% of Dy-Te, 9
5% or less. Conventionally, it has been considered that when the Sb content exceeds 80%, the storage reliability is reduced and the overwrite characteristics are deteriorated.
Addition was possible up to the range.

Although the optical recording medium of the present invention has the above-mentioned recording layer, the layer structure of the optical recording medium, for example, a disk is, as shown in FIG. ,
It comprises a recording layer 3, an upper dielectric layer 4, a reflective layer 5, and an organic protective layer 6. When a recording material having a high crystallization speed is used for the purpose of realizing high-speed overwriting, as the crystallization speed of the recording material increases, it becomes inevitably difficult to amorphize the recording layer, and recording marks are formed. There is a problem that it becomes difficult. Therefore, thermal design by layer configuration is very important. That is, it is important to optimize the thermal conductivity and the film thickness of each layer in order to increase the cooling rate during the resolidification of the recording layer. Therefore, the reflection layer is desirably made of a material having high thermal conductivity in order to promote heat radiation as much as possible. For example, Al, A
A reflective layer made of u, Ag, or a metal containing 90% or more thereof is exemplified. In the present invention, the reflective layer is made of Ag or Ag.
It was found that an optical recording medium more suitable for high linear velocity recording can be formed by using an alloy containing 90% or more of

As the upper dielectric layer and the lower dielectric layer, for example, ZnS / SiO ₂ (a mixture of ZnS and SiO ₂ ) is used.
When the reflective layer is made of Ag or an alloy containing 90% or more of Ag, it is necessary to prevent a sulfurization reaction with sulfur contained in the protective layer. In the present invention, the upper protective layer has at least a two-layer structure, one of which has a width of 1 nm or more from the interface with the reflective layer toward the inside of the upper dielectric layer and does not contain sulfide. By being a layer, the sulfidation reaction could be prevented. That is, the sulfurization reaction could be prevented by providing a barrier layer made of carbonized material or a mixture of carbonized material and oxide or nitride between ZnS / SiO ₂ and the reflective layer. By using a carbonized material as a base material, durability and ease of film formation were obtained. S as a carbide
iC and the like are preferred.

[0009]

The present invention will be described below with reference to examples. diameter
A 12 cm, 0.6 mm thick, grooved polycarbonate disc substrate having a track pitch of 0.74 μm was dehydrated at a high temperature, and then a lower dielectric layer, a recording layer, an upper dielectric layer, and a reflective layer were sequentially formed by a sputtering method. Zn for lower dielectric layer
The thickness was 70 nm using an S.SiO ₂ target. The recording layer was sputtered with an alloy target having a predetermined composition ratio at an argon gas pressure of 3 × 10 ⁻³ torr and an RF power of 300 mW to have a film thickness of 20 nm. The composition of the recording layer is shown in Examples. The upper dielectric layer is made of ZnS
_The thickness was set to 20 nm using _two targets. As the reflective layer, an Al / Ti alloy target was used and the thickness was 120 nm. Further, an organic protective layer made of an acrylic UV curable resin was applied on the reflective heat dissipation layer to a thickness of 5 to 10 μm by a spinner, and cured by UV. In addition to this surface, 12c in diameter
A polycarbonate disk having a thickness of 0.6 mm and a thickness of 0.6 mm was bonded together with an adhesive sheet, and the recording layer was initially crystallized by irradiating a large-diameter LD beam to obtain an optical recording medium. For recording and reproduction, a pickup having a wavelength of 656 nm and NA of 0.65 was used. Recording was performed using a pulse modulation method, and recording data was recorded using an EFM + modulation method at an optimum recording linear velocity and an optimum recording power according to each recording layer. The recording strategy was also optimized and used so as to minimize the jitter. All reproduction is power 0.7mW, linear velocity 3.5
The measurement was performed at m / s, and the data to clock jitter and the reflectance were measured.

[Example 1] Recording characteristics of a disk having a recording layer composition of Dy ₆ Sb ₇₈ Te ₁₆ were evaluated. Recording density 0.267μm /
In the bit, the jitter σ / Tw could not be reduced to 10% or less even if the linear velocity and the recording strategy were adjusted. Therefore, when the recording density was set to 0.300 μm / bit, the recording linear velocity became 1
Good recording was possible up to 7.5 m / s, and the jitter σ / Tw after the first recording and after 1000 repetitive recordings were both less than 10%. Further, even after performing a storage test for 1000 hours under an environment of 70 ° C. and 85% RH, no deterioration of the initial recording portion was observed. However, the jitter in the portion where the recording was repeated 1000 times was increased to about 12%.

Example 2 The recording characteristics of a disk having a recording layer composition of Ag ₁ Dy ₅ Sb ₇₈ Te ₁₆ were evaluated. Recording density 0.267μm
In / bit, good recording was possible up to a recording linear velocity of 17.5 m / s, and the value of jitter σ / Tw after initial recording and after repeated recording 1000 times was less than 10%. Further, even after performing a storage test for 1000 hours under an environment of 70 ° C. and 85% RH, no deterioration of the initial recording portion was observed.
However, the jitter in the portion where the recording was repeated 1000 times was increased to about 12%.

Comparative Example 1 The recording characteristics of a disk having a recording layer composition of Ag ₁ In ₅ Sb ₇₈ Te ₁₆ were evaluated. Recording density 0.267μm
The linear velocity at which good recording was possible at 1 / bit was 12 m / s. Therefore, in order to enable recording up to 17.5 m / s as in Example 1, the composition of the recording layer was changed to Ag ₁ In ₁₅ Sb ₆₈ Te ₁₆ , Ag ₁ In ₅ Sb ₈₁ Te _13.
Was evaluated. In the former case, the jitter of the first recording was less than 10%, but after 1000 times, it increased to 12%. In the latter case, the jitters after the initial recording and after 1000 repetitive recordings were both less than 10%, but when stored for 1000 hours in an environment of 70 ° C. and 85% RH, the jitter increased to 12% even in the initial recording section. .

Example 3 The recording characteristics of a disk having a recording layer composition of Ge ₃ Dy ₅ Sb ₇₈ Te ₁₄ were evaluated. Good recording is possible up to a recording linear velocity of 17.5 m / s at a recording density of 0.267 μm / bit as in Example 2, and the jitter σ / Tw after the initial recording and after 1000 repetitive recordings are both less than 10%. Was obtained. Further, when this disk was subjected to a storage test for 1000 hours in an environment of 70 ° C. and 85% RH, the initial recording,
Also, no deterioration was observed in all of the repeated recordings 1000 times. However, at the time of initial crystallization, unless the scanning linear velocity of the large-diameter LD beam is reduced by 0.5 m / s as compared with Example 2,
The reflectivity was not uniform.

Example 4 The recording layer composition was Ag ₁ In ₁ Ge ₃ Dy ₅ Sb ₇₇
The recording characteristics of the disk with Te ₁₃ were evaluated. As in Example 2, the recording linear velocity was 17.5 m / bit at a recording density of 0.267 μm / bit.
s, and the jitter σ / Tw after the initial recording and after 1000 repetitive recordings were both less than 10%. In addition, this disc is
When a storage test was performed for 1000 hours in a% RH environment, no deterioration was observed in both the initial recording and the repeated recording 1000 times. When the disk was initially crystallized, the scanning linear velocity of the large-diameter LD beam was lower than that in the first embodiment.
By making the delay 0.2 m / s, a uniform reflectance was obtained.

Fifth Embodiment In the fourth embodiment, the structures of the upper dielectric layer and the reflection layer are changed as follows. That is,
The upper dielectric layer is ZnS.SiO ₂ (16 nm thick) and SiC (4 nm thick)
And the reflective layer side was made of SiC. An Ag target was used as the reflective heat dissipation layer, and the thickness was 120 nm.
The recording characteristics of this disc were evaluated. As in Example 4, the value of jitter σ / Tw of less than 10% was obtained after the initial recording and after 1000 repetitive recordings.
In Example 5, a smaller value of / Tw was obtained. Also,
The modulation degree in the first recording was 68% in Example 4, whereas it was 73% in Example 5. In each case, it was found that better characteristics were obtained than in Example 4. Further, when this disk was subjected to a storage test for 1000 hours in an environment of 70 ° C. and 85% RH, no corrosion due to sulfuration of Ag was observed in both the initial recording and the repeated recording 1,000 times.

Comparative Example 2 In Example 5, the upper dielectric layer was a single layer of ZnS.SiO ₂ (film thickness: 20 nm). This disk was subjected to a storage test for 1000 hours in an environment of 70 ° C. and 85% RH, and the reflectance of the disk was measured. As a result, dropout (reduction in reflectance) due to sulfuration corrosion of Ag was remarkable.

Comparative Example 3 In Example 5, the upper dielectric layer was made of _two layers of ZnS.SiO ₂ (16 nm thick) and ZnO (4 nm thick), and the reflective layer side was made of ZnO. Keep this disc at 70 ℃ 85
When the storage test was performed for 1000 hours in a% RH environment and the reflectance of the disk was measured, no corrosion due to Ag sulfidation was observed in the initial recording, but dropout due to Ag sulfidation corrosion was observed 1000 times repeatedly. (Decrease in reflectance)
Was remarkable.

Comparative Example 4 The same recording layer composition as in Example 1 was used, but the initial crystallization was performed by lamp annealing.
Although the reflectivity was uniform, it was not possible to perform recording worthy of evaluation even by adjusting the recording strategy or power.
Therefore, only the recording layer is formed on the glass substrate by sputtering,
The crystal structure of the thin film crystallized by the LD beam and the lamp annealing was examined by the powder X-ray diffraction method. The film crystallized by the LD beam had a diffraction spectrum that was thought to be due to a crystalline phase close to a single NaCl structure, whereas
The film crystallized by lamp annealing is not a single crystal phase, but hexagonal or Sb ₂ Te ₃
It is considered that the appearance of trigonal crystals presumed to be accompanied by the precipitation of γ was observed, so that it was impossible to record.

[Comparative Example 5] When forming a recording layer, a Sb, Dy, Ag, Ge chip was mounted on an Sb-Te alloy target having a predetermined composition, and sputtering was performed. However, it was difficult to obtain a recording layer having a desired composition, and a recording phase having the same composition could not be stably formed.

[0020]

According to the first aspect of the present invention, there is provided an optical recording medium in which at least a recording layer is provided on a substrate and information is recorded, reproduced and erased by utilizing a phase change of the recording layer. 90% or more of the optical recording medium is characterized by comprising a compound represented by the following formula,
An optical recording medium capable of high linear velocity recording and having excellent overwrite characteristics can be provided. Dy _α Sb _β Te _γ (where α, β, and γ represent atomic ratios, and 0.01 ≦ α ≦
0.10 and 0.60 ≦ β ≦ 0.95, and α + β
In the invention according to claim 2, the recording layer further contains Ag, so that the optical recording medium according to claim 1 can improve the recording density. The invention of claim 3 is the optical recording medium according to claim 1, wherein the recording layer further contains Ge, so that the storage reliability can be improved. The invention according to claim 4 is the optical recording medium according to claim 1, wherein the recording layer further contains Ag and Ge, so that the recording density, storage reliability, overwrite characteristics, and initial crystallization time It is possible to provide an excellent optical recording medium which is well-balanced in shortening the optical recording medium. The optical recording medium according to any one of claims 1 to 4, wherein the recording layer is formed by a sputtering method using an alloy target having a predetermined composition. Therefore, it is possible to stably provide an optical recording medium having excellent recording characteristics and reliability. According to a sixth aspect of the present invention, in the optical recording medium, at least a lower dielectric layer, a recording layer, an upper dielectric layer, and a reflective layer are provided in this order on a substrate, and the reflective layer contains at least 90% Ag. % Of the metal, so that the optical recording medium according to any one of claims 1 to 4 can provide an optical recording medium more suitable for high linear velocity recording. According to a seventh aspect of the present invention, the upper dielectric layer has at least a two-layer structure, and one of the layers has a width of 1 nm or more from the interface with the reflective layer toward the inside of the upper dielectric layer and has a sulfuric acid concentration of 1 nm or more. 7. The optical recording medium according to claim 6, wherein the optical recording medium is a layer that does not contain a substance, and since a sulfurization reaction of Ag can be prevented, an optical recording medium more suitable for high linear velocity recording can be obtained in a highly reliable state. Can be provided by The invention of claim 8 is
The optical recording medium according to claim 7, wherein the sulfide-free layer is made of a carbonized material or a material obtained by mixing an oxide or a nitride with a carbonized material.
Since the sulfurization reaction of Ag can be prevented, an optical recording medium more suitable for high linear velocity recording can be provided in a highly reliable state. According to a ninth aspect of the present invention, since the carbonized material is SiC, the sulfurating reaction of Ag can be prevented, so that the optical recording medium is more suitable for high linear velocity recording. Can be provided with high reliability. According to a tenth aspect of the present invention, since the optical recording medium according to any one of the first to ninth aspects, the recording layer is formed by initial crystallization. In addition, it is possible to provide an optical recording medium having excellent repetitive recording properties in a state where an amorphous mark can be recorded. In the invention according to claim 11, the initial crystallization is performed by a melting initialization method using a laser beam, or
11. The optical recording medium according to claim 10, wherein the optical recording medium is formed by solid-phase initialization. Can be provided in condition.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of an optical recording medium according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Lower dielectric layer 3 Recording layer 4 Upper dielectric layer 5 Reflective layer 6 Organic protective layer

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G11B 7/24 534 G11B 7/24 535G 535 535H 538D 538 B41M 5/26 X (72) Inventor Hajime Yojihara Ota-ku, Tokyo 1-3-6 Nakamagome Ricoh Co., Ltd. (72) Inventor Masato Hariya 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Yoshiyuki Kageyama 1-chome Nakamagome, Ota-ku, Tokyo No. 3-6 Ricoh F-term (Reference) 2H111 EA03 EA12 EA32 EA48 FA01 FA12 FA21 FB05 FB09 FB12 FB16 FB17 FB24 FB30 GA03 5D029 HA05 HA06 HA01 JA01 JB18 LA12 LB04 LB07 LB11 LC21 MA13

Claims (11)

[Claims] At least a recording layer is provided on a substrate, and recording, reproducing, and reproducing information by utilizing a phase change of the recording layer.
An optical recording medium for erasing, wherein an atomic ratio of the recording layer of 90% or more comprises a compound represented by the following formula. Dy _α Sb _β Te _γ (where α, β, and γ represent atomic ratios, and 0.01 ≦ α ≦
0.10 and 0.60 ≦ β ≦ 0.95, and α + β
+ Γ = 1) 2. The optical recording medium according to claim 1, wherein the recording layer further contains Ag. 3. The optical recording medium according to claim 1, wherein the recording layer further contains Ge. 4. The optical recording medium according to claim 1, wherein the recording layer further contains Ag and Ge. 5. The optical recording medium according to claim 1, wherein the recording layer is formed by a sputtering method using an alloy target having a predetermined composition. 6. An optical recording medium wherein at least a lower dielectric layer, a recording layer, an upper dielectric layer, and a reflective layer are provided on a substrate in this order, and the reflective layer contains at least 90% of Ag. The optical recording medium according to any one of claims 1 to 4, wherein the optical recording medium is a metal. 7. An upper dielectric layer having at least a two-layer structure, one of which has a width of 1 nm or more from an interface with a reflective layer toward the inside of the upper dielectric layer and has a sulfide structure. The optical recording medium according to claim 6, wherein the optical recording medium is a layer that does not contain any. 8. The optical recording medium according to claim 7, wherein the sulfide-free layer is made of a carbonized material or a material obtained by mixing an oxide or a nitride with a carbonized material. 9. The optical recording medium according to claim 8, wherein the carbonized material is SiC. 10. The optical recording medium according to claim 1, wherein an initial crystallized recording layer is used as the recording layer. 11. The optical recording medium according to claim 10, wherein the initial crystallization is performed by a melting initialization method using a laser beam or a solid phase initialization.