JP2002288875A - Optical information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve high-speed recording by adjusting the recording layer material of a medium and the film thickness of each layer constituting the medium, and setting the activation energy at the interface between amorphous and crystal in an optimum range. The present invention provides an optical information recording medium having good signal characteristics after overwriting and having sufficient storage reliability. SOLUTION: A transparent substrate has at least one recording layer containing at least a phase change material as a main component and a reflective layer, and a recording mark length modulation method is used as a modulation method of information recorded on the recording layer. An optical information recording for optically recording, reproducing, and erasing information, wherein an amorphous area in the recording layer becomes an area where a recording mark is formed, and the amorphous area is crystallized to become a crystallized area so that the recording mark is erased. An optical information recording medium, wherein the crystallization of the amorphous region, which is the recording mark, proceeds by moving the interface between the amorphous region and the crystallized region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CD-RW, a DV
The present invention relates to a rewritable optical information recording medium technology represented by a phase change optical disk such as a D-RAM, a DVD-RW, a DVD + RW, and a PD.

[0002]

2. Description of the Related Art CD-RW, PD, DVD-RAM, D
2. Description of the Related Art Rewritable optical disks represented by VD-RW and DVD + RW have been adopted as information recording media for computer devices and home electric appliances. The greatest feature of such a rewritable optical information recording medium is that direct overwriting can be performed without performing an erasing process.

However, since it does not include the erasure process,
The signal characteristics after overwriting greatly depend on the state before recording, and the improvement of the characteristics after the first direct overwrite is an issue. In addition, since the recording method is based on a thermal process, there is a problem that the film is deteriorated in a large number of times of recording and the signal is deteriorated.

[0004] These tendencies become more remarkable in high-speed recording. However, if a recording layer material that can cope with high-speed recording is selected, the storage reliability is significantly reduced. As described above, there has been no rewritable optical information recording medium capable of coping with high-speed recording by direct overwriting and having high storage reliability.

[0005] For example, in the technique proposed in Japanese Patent Application Laid-Open No. Hei 8-224961, an optical recording method in which a dielectric layer is provided on an AgSbTe ₂ -based recording layer and the activation energy of the recording layer is 3.0 eV or more. Although it is a medium, its storage life is improved, but it cannot support high-speed recording.

Similarly, the technology described in Japanese Patent Application Laid-Open No. 08-263871 is an optical recording medium in which the activation energy of an AgInSbTe-based recording layer is 1.1 eV or more and the composition of the recording layer is regulated. Although the storage life can be improved, it cannot support high-speed recording.

In the technique proposed in Japanese Patent Application Laid-Open No. 09-248965, it is stated that the characteristics at the time of overwriting can be improved by using an optical recording medium in which the activation energy of the recording layer is 3.5 eV or less. Anxiety remains in terms of reliability.

Further, Japanese Patent Application Laid-Open No. 11-129620 discloses that the composition, crystallization temperature,
An optical information recording medium in which activation energy is specified has been proposed. According to this technique, the quality of a recording signal can be improved, and high reliability can be obtained by setting the activation energy to 1.5 eV or more. But actually,
In some cases, signal characteristics after overwriting during high-speed recording are not good, and there has been a problem that reliable storage reliability cannot be obtained. Thus, there has been a demand for an optical information recording medium having good signal characteristics after overwriting during high-speed recording and having sufficient storage reliability.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to adjust the recording layer material of a medium and the thickness of each layer constituting the medium, and the like.
By setting the activation energy at the interface between the amorphous and the crystal in the optimum range, it is possible to provide an optical information recording medium having good signal characteristics after overwriting during high-speed recording and sufficient storage reliability. It is.

[0010]

In order to solve the above-mentioned problems, an optical information recording medium of the present invention has at least one layer of a phase change material as a main component on a transparent substrate. A recording layer having a layer and a reflective layer, and using a recording mark length modulation system as a modulation system of information to be recorded on the recording layer, an amorphous region in the recording layer becomes a region where a recording mark is formed, and the amorphous region is crystallized and crystallized. A recording mark is erased by becoming a recording area, and optically recording, reproducing, and erasing information in an optical information recording medium, the crystallization of the amorphous area as the recording mark is caused by the amorphous area and the crystallization area. This is an optical information recording medium that travels by moving the interface.

Further, the optical information recording medium of the present invention is characterized by claim 1
3. The optical information recording medium according to claim 1, wherein the area of the amorphous area as the recording mark is S.
When the, by the movement of the interface between the amorphous region and the crystalline region, the temperature dependency absolute temperature T of the area -dS / dt of the amorphous region which decreases per unit time, with the Boltzmann constant k _B follows Arrhenius And the activation energy Ea of the interface movement is 2.
2. The optical information recording medium according to claim 1, wherein the optical information recording medium is smaller than 4 eV.

[0012]

[Number 3] _{-dS / dt α exp (-E a} / k B T) ...... (I)

Further, the optical information recording medium of the present invention is characterized in claim 1
Alternatively, in the optical information recording medium according to claim 2, when the area of the amorphous area serving as the recording mark is S, the unit moves due to the movement of the interface between the amorphous area and the crystallized area. temperature dependence absolute temperature T of the area -dS / dt decreasing per time can be approximated by the formula for a Arrhenius (II) with a Boltzmann constant k _B, the activation energy Ea of the movement of the interface 1. 0
It is an optical information recording medium larger than eV.

[0014]

[Number 4] _{-dS / dt α exp (-E a} / k B T) ...... (II)

Further, the optical information recording medium of the present invention has the following features.
In the optical information recording medium according to any one of claims 3 to 3, the recording layer is made of Ag, I,
When n, Sb, and Te are contained and their composition ratios are represented as α, β, γ, and δ using atomic percent, 0.1
≦ α ≦ 7.0, 2.0 ≦ β ≦ 10.0, 64.0 ≦ γ ≦
92.0, 5.0 ≦ δ ≦ 26.0, α + β + γ + δ ≧ 9
7 is an optical information recording medium that satisfies all the relationships of 7.

Further, the optical information recording medium of the present invention has a first aspect.
In the optical information recording medium according to any one of claims 3 to 5, the recording layer is made of Ge, In,
When Sb and Te are contained and their composition ratios are expressed as ε, β, γ, and δ using atomic percent, 0.1 ≦ ε ≦ 7.
0, 2.0 ≦ β ≦ 10.0, 64.0 ≦ γ ≦ 92.0,
The optical information recording medium satisfies all the relationships of 5.0 ≦ δ ≦ 26.0 and ε + β + γ + δ ≧ 97.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The optical information recording medium of the present invention is a phase-change type optical information recording medium and has at least one
It has a recording layer composed of more than two layers of phase change material. As an example of the layer configuration, the one shown in FIG. 1 is a typical example. It is obtained by sequentially forming a lower protective layer 2, a recording layer 3, an upper protective layer 4, and a reflective heat dissipation layer 5 on a transparent substrate 1.
Further, as shown in FIG. 1, an overcoat layer 6 may be formed on the reflective heat radiation layer 5 and a hard coat layer 7 may be formed on the lower surface of the substrate 1.

The main purpose of the substrate 1 is to support a medium, and when an electromagnetic wave used for recording and reading enters from the substrate surface, the substrate 1 needs to be transparent in the wavelength region of the incident electromagnetic wave. Examples of the transparent substrate material of the substrate 1 include glass, ceramics, and resin, and it is preferable to use a resin from the viewpoint of transparency and ease of molding. Examples of the resin include polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, and acrylonitrile resin. Styrene copolymer resin, polyethylene resin, polypropylene resin, silicone resin, fluorine resin, ABS resin, urethane resin, and the like, but polycarbonate resin or acrylic resin, which is excellent in moldability, optical properties, and cost, are preferable. .

It is preferable that a guide groove 1a is formed on the transparent substrate 1 as shown in FIG. 1 in order to enable position control (tracking) of the recording optical pickup in a state where information is not recorded. The shape of the guide groove, such as the width, interval, and depth, is optimized according to the characteristics of the recording / reproducing optical pickup and the information recording density of the medium. The guide groove 1a may have address information. Examples of the address information include a method of recording frequency-modulated information in a meandering guide groove and a method of forming and recording prepits.

The lower protective layer 2 and the upper protective layer 4 have thermal characteristics,
A dielectric is used because of its optical characteristics. As the dielectric, SiO
_{2, SiO, ZnO, SnO 2} , TiO 2, In 2 O 3, M
oxides such as gO and ZrO ₂ , Si ₃ N ₄ , AlN, Ti
Nitride such as N, BN, ZrN, ZnS, In ₂ S ₃ , Ta
Sulfides such as _{S 4, SiC, TaC, B} 4 C, WC, Ti
There are carbides such as C and ZrC or diamond-like carbon, and a dielectric alone or a mixture of two or more thereof is used.

The protective layers 2 and 4 are formed by a vacuum film forming method. Examples of the film forming method include a vacuum deposition method, a sputtering method, an ion plating method, and a CVD method. It is preferable to use a sputtering method because of high performance and low cost.

The materials and thicknesses of the lower protective layer 2 and the upper protective layer 4 can be set arbitrarily and independently, and optimal values are set from optical characteristics and thermal characteristics. The film thickness is 10 nm to 5000 nm
It is about. For the recording layer 3, a phase change material is used. As a phase change material suitable for an optical information recording medium, an alloy-based material is preferably used, and GeTe, GeTeSe, Ge
TeS, GeSeSb, GeSeSb, GeAsSe,
InTe, SeTe, SeAs, Ge-Te- (Sn,
Au, Pd), GeTeSeSb, GeTeSb, Ag
An InSbTe alloy system can be exemplified, and the composition ratio of each alloy system is optimized from optical and thermal characteristics.

As the optical characteristics, those having significantly different optical characteristic values at the reproduction wavelength in the crystallized region (stable phase (crystallized state)) and the amorphous region (metastable phase (amorphized state)) This is preferable because a high CN ratio can be obtained during information reproduction. The thermal characteristics are optimized so that an amorphous state and a crystallized state can be easily realized in a recording light intensity region and a recording linear velocity region, and a high overwrite characteristic can be realized by such optimization. Note that the amorphous region in the present invention refers to a region in which amorphous is at least a main component and has an optical characteristic value substantially equal to that of a completely amorphous region. An area may be included. In addition, an arbitrary element may be mixed as an impurity into the alloy system containing the above element as a main component, and B, N, C, O, Si, P, S, S
e, Al, Ti, Zr, V, Mn, Fe, Co, Ni,
Examples include Cr, Cu, Zn, Sn, Pd, Pt, and Au. These impurities are generally added to finely adjust the above optical and thermal characteristics.

Among these alloy-based phase change materials, in particular, A
When a gInSbTe-based material is used, a stable phase (crystallized phase) and a metastable phase (amorphous phase) formed by recording are used.
This is suitable for a recording method using the mark length modulation method because the boundary between them is clear. By adding a small amount of N as an impurity, a wide recording linear velocity margin can be obtained.

The recording layer is laminated by a vacuum film forming method. Examples of the vacuum film forming method include a vacuum deposition method, a sputtering method, an ion plating method, and a CVD method. The sputtering method is used from the viewpoint of productivity and low cost. It is desirable to do.

The reflective heat radiation layer 5 has a function of reflecting recording / reproducing light and radiating heat generated during recording. Metals and alloys are used as the material of such a reflective heat dissipation layer, for example, Ag, Au, Al, or Ti,
An alloy obtained by mixing at least one of Si, Cr, Ta, Cu, Pd, C, etc. may be mentioned. However, in consideration of thermal characteristics, optical characteristics and productivity, an alloy containing Ag or Ag as a main component or Ag is used. It is preferably used. The composition of these alloys and the thickness of the reflective layer can be set arbitrarily, and it is desirable to optimize them from the thermal characteristics and optical characteristics.

The overcoat layer 6 uses a resin material mainly composed of a photocurable resin, an electron beam curable resin, or the like. As these resins, it is desirable to use a resin material containing a photocurable resin as a main component from the viewpoint of film-forming properties and simplicity of curing. As the photocurable resin, an ultraviolet curable resin is generally used. Examples of the film forming method include a dipping method and a spin coating method, and a spin coating method is preferable in consideration of uniformity of film thickness after film formation, productivity, and the like.

Since the hard coat layer 7 has a function of protecting the recording / reproducing light incident surface of the medium, it is preferable to form the hard coat layer to secure the recording / reproducing reliability of the medium. As the hard coat material, the same material as the overcoat layer material can be used, but since a defect on the hard coat greatly affects the recording / reproducing reliability of the medium, it is necessary to use a material having good coatability and uniformity. Preferably, a solvent for dilution, a leveling agent and the like may be mixed. Further, an antistatic agent or the like may be mixed in order to prevent dust and the like from adhering to the surface of the hard coat layer.

The formed recording layer material is usually in a metastable state (amorphous state). In order to increase the reflectance of the medium and obtain a high CN ratio, it is necessary to initialize the recording layer to a stable state (crystallized state). The initialization method is a method of irradiating and scanning a focused laser, and irradiating the entire medium with strong energy (flash)
An example of such a method is described in JP-A-9-073.
As described in Japanese Patent Application Laid-Open No. 666 or Japanese Patent Application Laid-Open No. 10-312582, a scan initialization method using an apparatus using a high-power semiconductor laser is appropriate from the viewpoint of productivity and medium characteristics.

Further, one or more resin layers may be further laminated on the overcoat layer in order to protect the laminated layers and enhance the appearance. These layers are generally formed by film-forming and curing a photo-curing resin or an electron beam-curing resin by screen printing, and mixing an inorganic filler to ensure strength, or Coloring materials such as dyes and pigments may be mixed to maintain the color.

Further, the overcoated surfaces of the medium may be bonded to each other to form a double-sided medium. At least a plate including a transparent substrate may be bonded to secure the single-sided recording and the thickness of the double-sided recording medium.

In recording on the optical information recording medium of the present invention, the recording layer is condensed and irradiated with a laser using an optical pickup so that the recording layer is in a stable state (crystallized state) and a metastable state (amorphous state). State) by reversibly changing the state. The realization of the stable state and the metastable state can be performed only by the intensity modulation of the laser to be irradiated. A multi-pulse method is preferable as a recording method. Examples of the recording method are JP-A-9-219021 and It is preferable to use the method described in JP-A-138947, because high recording signal characteristics and overwrite characteristics can be obtained.

The information modulation method includes a mark edge method and a mark position method, but the mark length modulation method is preferable because the information density can be increased. The mark thus recorded corresponds to a metastable state (amorphous state) region (amorphous region) existing in a crystal in a stable state. The transition from the metastable state to the stable state may be realized by melting and slowly cooling, or may be realized by moving the interface between the amorphous region and the crystallized region at a temperature lower than the melting point (eutectic point). . In the optical information recording medium of the present invention, it is necessary that crystallization occurs by movement of the interface between the amorphous region and the crystallized region.

When crystallization is performed by moving the interface between the amorphous region and the crystallized region in this manner, it is not necessary to raise the temperature of the recording layer to a temperature higher than the melting point for crystallization. it can. Therefore, thermal damage to the recording layer can be reduced, and an optical information recording medium having a high reflectance and a high degree of modulation and a low jitter can be obtained even after a number of overwrites.

Further, the optical information recording medium of the present invention can improve the characteristics at the time of the first overwrite, particularly the jitter, by setting the activation energy of the interface movement defined below in the optimum range.

Here, since the recording layer is a thin film, the movement of the interface between the amorphous region and the crystallized region is two-dimensional. The area of the recording mark projected from the perpendicular direction of the thin film is represented by S
Then, the recording marks correspond to a metastable state (amorphous state) in a stable state (a crystalline state), and their interface moves and crystallization proceeds over time. Therefore, the mark area S decreases with time.

The movement of the interface is caused by the progress of crystallization near the interface, and is microscopically greatly related to the diffusion phenomenon and rearrangement of atoms, and therefore greatly depends on the temperature in the recording layer. Come.

As for the mechanism of the movement of the interface between the amorphous region and the crystallized region, there are many studies on the order-disorder phase transition of the alloy, and it is generally known that the transition can be approximated by a diffusion phenomenon. In such a diffusion phenomenon, the diffusion coefficient D is expressed by the following equation (III) using the absolute temperature T, the Boltzmann constant k _B , and the activation energy E _a, and can be expressed by the Arrhenius equation.

[0039]

D５exp (−E _a / k _B T) (III)

Here, as a result of analyzing the crystallization mechanism, the rate at which the area of the recording mark decreases—dS / dt
It has been found that (t: time) depends on the temperature similarly to the diffusion coefficient and can be approximated by Arrhenius equation (I) (see FIG. 4).

[0041]

[6] _{-dS / dt α exp (-E a} / k B T) ...... (I)

Further, the activation energy E _a of this interface
It depends on the overwriting characteristics of the medium. In this case, by suppressing the activation energy E _a low, it is possible to easily realize the crystallization described above. Therefore, a recording mark in an amorphous state can be crystallized with a low erasing power (laser power applied at the time of erasing a mark), and characteristics in the first overwriting, particularly, jitter can be improved.

Usually, the deterioration of the jitter in the first overwrite is caused by the difference between the reflectance level of the portion where the recording mark is erased and the reflectance level of the portion where the land (crystal state) is erased. However, by keeping the activation energy low, this difference can be reduced, and jitter can be reduced. Here, in order to suppress the jitter after the first overwriting, the activation energy E
it is preferable to _a to to satisfy E _a <2.4 eV.

On the other hand, when the activation energy E _a is too low, crystallization occurs even at room temperature, decreases significantly the life of the media. Therefore, the activation energy E _a is E _a>
It is preferable to satisfy 1.0 eV. This activation energy can be brought close to a desired value mainly by optimizing the composition and thickness of the recording layer. Further, fine adjustment can be made by the above-mentioned additional element added to the recording layer.

A method for obtaining the above activation energy will be described below. As a method of measuring the mark area S, T
Although there are methods using a microscopic method using EM, SEM, etc. and a normal reproducing method using an optical pickup, the former method is difficult to prepare a sample, and at the same time, it is a destructive measurement.
The latter method using an optical pickup is more preferable.
As a method using an optical pickup, an amorphous mark equal to or smaller than the beam area of the pickup is created, and the amplitude of the reflectance is measured. in this case,
The amplitude of the change in reflectivity is proportional to the area of the mark.

Further, in the case of measurement using an optical pickup, since the measurement is performed by averaging the area variation of a large number of marks existing on the medium, a highly reliable measurement result with little variation can be obtained. CD-R as an example of measurement
In the case of W, a pattern consisting of only a 3T mark and a 3T land is recorded and reproduced, and the variation in the area can be calculated by measuring the amplitude or modulation of the 3T signal.
From the activation energy. That is, when the 3T modulation degree is m3, the relationship of the formula (IV) is established. Where t is time.

[0047]

[Equation 7] -dm3 / dt α -dS / dt α exp (-E a / k B T) ...... (IV)

It can be understood that the activation energy can be calculated by changing the temperature T and the time t according to the equation (IV) and measuring the 3T modulation factor. As a specific method, the medium may be annealed in a high-temperature environment, and the change in the degree of modulation with respect to time may be measured.

[0049]

Embodiments of the present invention will be described below. However,
The following examples are examples of embodiments of the present invention, and do not limit the scope of the claims. A lower protective layer, a recording layer, an upper protective layer, a reflective heat dissipation layer, and an overcoat layer are sequentially laminated on a transparent substrate for a CD-RW made of polycarbonate to which a continuous groove has been transferred, and the CD-RW whose cross section is modeled in FIG. It was created.

As the lower protective layer and the upper protective layer, Z
Dielectrics containing nS and SiO ₂ as main components were formed by vacuum sputtering, but since these were insulators, they were formed by high frequency sputtering. At this time, the thickness of the lower protective layer was 90 nm, and the thickness of the upper protective layer was 35 nm.

As the recording layer, two kinds of material systems were used. One is an AgInSbTe-based alloy material, and the other is one obtained by adding Ge to this material system. These C
The composition ratio (atomic percent) of the material of the recording layer of D-RW is as follows when each composition ratio of Ag, In, Sb, Te and Ge is α, β, γ, δ, ε using atomic percent. Satisfying the range (where α =
When 0.0, ε ≧ 0.1, when ε = 0.0, α ≧
0.1) AgInSbTe of various compounding ratios,
AgGeInSbTe and GeInSbTe were obtained. 0.0 ≦ α ≦ 7.0 2.0 ≦ β ≦ 10.0 64.0 ≦ γ ≦ 92.0 5.0 ≦ δ ≦ 26.0 0.0 ≦ ε ≦ 7.0 α + β + γ + δ + ε ≧ 97 (atoms percent)

The recording layer was formed by a vacuum sputtering method, and a mixed gas of Ar gas and N ₂ gas was used as a sputtering gas. At this time, the amount of nitrogen added as an impurity in the recording layer was controlled by adjusting the mixing ratio of Ar gas and N ₂ gas. Further, samples having different activation energies were produced by adjusting the thickness of the recording layer in the range of 14 to 20 nm.

The reflective heat dissipation layer was made of a mixture of Al and a small amount of Ti, and was formed by vacuum sputtering. The thickness of the reflective heat dissipation layer was 150 nm. This was initialized by a commercially available CD-RW initialization device to obtain CD-RW disks having different activation energies. The prepared sample is Orange Book Part III vol. CD-RW media satisfying the initial characteristics of No. 2. By conducting a high temperature and high humidity environment test on these samples,
The time change of the mark area S was measured to determine the activation energy.

As described above, since the change in the area is proportional to the change in the modulation factor (see the equation (II)),
Calculate the change in area. CD-RW for each condition sample
The 3T mark and the pattern corresponding to the 3T land were recorded, and the 3T modulation was used as the initial evaluation for measurement. Recording and measurement is C
A spindle tester DDU1000 for D-RW was used. Optical pickup: λ (wavelength): 780 nm, NA
(Numerical Aperture): Use of 0.50 was used.

Using this spindle tester device, according to the recording method (recording strategy) described in the Orange Book,
A pattern composed of 3T marks and 3T lands was recorded at 12.0 m / s corresponding to 10 times the speed of a CD. Recording was performed at an inner peripheral portion having a radius of 25 mm to minimize the influence of the amount of warpage of the disk substrate after the environmental test. After recording, the signal was reproduced by the same device, and the modulation m3 was measured. The degree of modulation at this time is m3 _0.

An environmental test was performed on these samples after the initial evaluation. The environment is the three conditions shown in Table 1
C). A sample was prepared for each condition, and the same initial evaluation was performed.

[0057]

[Table 1]

After the completion of these environmental tests, the samples were measured again to determine m3. M3 after the test was smaller than the initial value, and it was confirmed that crystallization had progressed. The value of m3 after test and m3 _1. The activation energy is obtained from the following calculation according to the equation (V). In addition,
Let the test time be t ₀ .

[0059]

−dm3 / dt = (m30−m3 ₁ ) / t ₀ (V)

From equation (V), -d after each environment of A, B and C
m3 / dt performed Arrhenius plots for, can be obtained E _a from the slope. Arrhenius plots for determining the E _a shown in FIG.

From FIG. 2, it was confirmed that the reduction rate of m3 obeys Arrhenius equation. Therefore, it was confirmed that the crystallization proceeded by the movement of the interface, and the activation energy thereof conformed to the formula (I). In the sample of FIG. 2, E _a
= Is 2.41eV, the E _a of samples obtained 0.
The range was 6 to 3.0 eV.

The recording characteristics and the overwrite characteristics of these samples (samples under the same conditions that were not subjected to the environmental test) were evaluated. Recording was performed in the same manner using the spindle tester described above. However, EFM was used as a recording signal, and a signal that could be reproduced by a normal CD-RW drive was recorded. The record is one overwrite and
The measurement was performed 1000 times, and the 3T jitter was measured using the same apparatus.

[0063] FIG. 3 shows a first overwriting after the relationship between the jitter and the activation energy E _a. From the point that the activation energy is higher than 2.4 eV, it can be understood that the jitter is rapidly deteriorated.

[0064] Further, for a sample of E _a <1.0 eV, shelf life at 70 ° C. is less than 500 hours, it was found that storage reliability is severely degraded. In consideration of the above, the appropriate activation energy range is from 1.0 eV to
It can be understood that it is 2.4 eV.

[0065]

According to the optical information recording medium of the present invention, since the crystallization of the amorphous region where the recording mark is formed easily proceeds by moving the interface between the amorphous region and the crystallized region, the erasure of the recording mark is performed. Power required for the recording can be kept low. As a result, good recording signal characteristics can be maintained even after a number of overwrites.

In the optical information recording medium according to the second aspect, since the activation energy of the movement of the interface is suppressed to a low level, the erasability of the recording mark is good, and the first overwrite characteristic, particularly the jitter, is reduced. Can be reduced.

In the optical information recording medium according to the third aspect, the activation energy is optimized.
The storage life of the data at room temperature can be sufficiently ensured. Furthermore, in the optical information recording medium according to the fourth aspect, since the composition of the recording layer is optimized, a desired activation energy can be easily realized.

In the optical information recording medium according to the fifth aspect, the composition of the recording layer is optimized, so that a desired activation energy can be easily realized, and since Ge is added, the data is Can have a sufficient storage life.

[Brief description of the drawings]

FIG. 1 is a model diagram showing a cross section of an example of an optical information recording medium of the present invention.

2 is a Arrhenius plot for determining the activation energy E _a.

FIG. 3 is a diagram illustrating _a relationship between jitter and activation energy Ea after a first overwrite.

FIG. 4 shows the speed of decreasing the area of a recording mark—dS / dt.
FIG. 3 is a diagram showing that is dependent on temperature similarly to the diffusion coefficient and can be approximated by Arrhenius equation (I).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 1a Guide groove 2 Lower protective layer 3 Recording layer 4 Upper protective layer 5 Reflection / radiation layer 6 Overcoat layer 7 Hard coat layer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Katsuyuki Yamada, Inventor 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (Reference) 2H111 EA04 EA23 EA37 EA40 FA12 FB05 FB09 FB12 FB17 FB21 FB30 5D029 JA01 JC18 JC20

Claims (5)

[Claims] 1. A transparent substrate having at least one recording layer containing at least a phase change material as a main component and a reflective layer, wherein a recording mark length modulation system is used as a modulation system of information recorded on the recording layer. Optical information for optically recording, reproducing, and erasing information, wherein the amorphous region in the recording layer becomes a region where a recording mark is formed, and the amorphous region is crystallized to become a crystallized region so that the recording mark is erased. 2. An optical information recording medium according to claim 1, wherein the crystallization of the amorphous area as the recording mark progresses by moving an interface between the amorphous area and the crystallized area. 2. When the area of the amorphous region as the recording mark is S, the temperature dependence of the area of the amorphous region, which decreases per unit time, −dS / dt, due to the movement of the interface between the amorphous region and the crystallized region. The property can be approximated by the following Arrhenius equation (I) using the absolute temperature T and the Boltzmann constant k _B, and the activation energy Ea of the movement of the interface is smaller than 2.4 eV.
An optical information recording medium according to claim 1. [Number 1] _{-dS / dt α exp (-E a} / k B T) ...... (I) 3. When the area of the amorphous region as the recording mark is S, the temperature dependence of the area −dS / dt, which decreases per unit time due to the movement of the interface between the amorphous region and the crystallized region, is absolute. It can be approximated by the following Arrhenius equation (II) using the temperature T and the Boltzmann constant k _B, and the activation energy Ea of the interface movement is 1.0 e
3. The method according to claim 1, wherein the value is larger than V.
An optical information recording medium according to claim 1. [Number 2] _{-dS / dt α exp (-E a} / k B T) ...... (II) 4. The recording layer contains Ag, In, Sb, and Te, and the composition ratio of each of the recording layers is α,
When represented as β, γ, δ, 0.1 ≦ α ≦ 7.0, 2.0 ≦ β ≦ 10.0, 64.0 ≦ γ ≦ 92.0, 5.0 ≦ δ ≦ 26.0 4. The optical information recording medium according to claim 1, wherein all of the following relationships are satisfied: α + β + γ + δ ≧ 97. 5. The recording layer contains Ge, In, Sb, and Te, and the composition ratio of ε, β, and
When represented as γ and δ, 0.1 ≦ ε ≦ 7.0, 2.0 ≦ β ≦ 10.0, 64.0 ≦ γ ≦ 92.0, 5.0 ≦ δ ≦ 26.0, ε + β + γ + δ The optical information recording medium according to any one of claims 1 to 3, wherein all of the relationships of &gt; 97 are satisfied.