JP2000222776A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a write-once optical recording medium in which information is recorded and reproduced by the phase transition of a recording material by irradiation with laser light and in which the change rate of reflectance due to the phase transition from an amorphous phase to a crystal phase is increased to increase the CN ratio of the reproduced signals and to obtain excellent storage property for a long time of the information. SOLUTION: A first dielectric layer 12 of a ZnS-SiO2 layer, a recording layer 14 of a AgInSbTe layer with addition of N, a second dielectric layer 16 of an AlN layer, and a reflection layer 18 of an Al-Ti layer are formed on a transparent substrate 10 made of a polycarbonate substrate in this order. The product of the refractive index (n) and the layer thickness(d) of the second dielectric layer 16 satisfies (nd)>130 nm so that the reflectance Ra of the amorphous phase region and the reflectance Rc in the crystal phase region in the recording layer 14 always have the relation of Ra>Rc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium,
In particular, the present invention relates to an optical recording medium for recording and reproducing information by a phase change of a recording material due to laser beam irradiation.

[0002]

2. Description of the Related Art With the recent increase in the capacity of information, optical disks as high-density, large-capacity memories have been receiving attention. This optical disc includes a read-only type that can only read recorded information, a write-once type that can be written only once and cannot be erased, and a rewritable type that can perform both recording and erasing and can be rewritten. .

[0003] Among them, a write-once optical disk, which is most suitable as a file memory for permanent storage, includes a hole-drilling type in which a hole is formed in the recording layer due to heat generation of the recording layer due to absorption of laser light, and a laser beam to the two recording layers. There are a diffusion alloy type in which the reflectance is changed by thermal diffusion by irradiation, and a phase change type in which a recording material is changed from an amorphous phase to a crystalline phase by laser light irradiation to form a crystalline recording mark.

For example, for a write-once type and diffusion alloy type optical disk, a transparent first substrate is provided with an amorphous first recording layer in a film-forming state and a crystalline second recording layer in a film-forming state. A method has been proposed in which the first and second recording layers are melt-diffusion alloyed by laser light irradiation to form a crystalline recording mark (see Japanese Patent Application Laid-Open No. 7-93806). However, in the method according to the above proposal, C
There is a problem that the N ratio is small and a sufficient reproduced signal cannot be obtained.

Further, for example, a write-once type and phase change type optical disk uses a recording layer in a non-destructive manner, and the protective cover does not need to be made of an air sandwich using glass or the like. Because of the advantage of requiring a structure, it has been reported that a recording material such as a TeOx layer, which is a uniform mixture of Te and TeO2, is used as a recording material (Recording and Storage Technology Handbook (Maruzen 1992). August 25))).

When this conventional TeOx layer is used as a recording material, the TeOx recording layer in an amorphous state at the time of film formation is a state in which Te particles of about several nm are uniformly dispersed in an amorphous TeO2 matrix. When this is irradiated with laser light, it is heated and melted, and in the cooling process, Te fine particles grow into crystal grains and crystallization proceeds. At some point, a phase change from the amorphous phase to the crystalline phase occurs. With the phase change from the amorphous phase to the crystalline phase of the TeOx recording layer, the optical constant, for example, the reflectance also changes. Therefore, utilizing this phase change, a crystalline recording mark is formed, and a change in reflectivity is detected by, for example, weak laser light to read information.

However, when the above-mentioned conventional TeOx layer is used as a recording material, it takes a long time until the crystallization is completed during the phase change from the amorphous phase to the crystalline phase of the TeOx recording layer. However, there is a drawback that it takes several minutes for the reproduction signal to stabilize.

In order to improve such disadvantages, TeOx
It has been proposed to add a noble metal such as Au or Pt to the recording layer (see Kunio Kimura et al., "New write-once optical memory based on Te-TeO2", Optical Memory Symposium 1985, pp. 33-38). According to this proposal, by adding a noble metal such as Au or Pt to the TeOx recording layer, the above-mentioned disadvantages are improved, and crystallization proceeds at high speed, so that the response speed is improved. Also,
Since the dislocation temperature at which the optical constant changes increases, the thermal stability also improves.

[0009]

However, the above conventional T
In the method of adding a noble metal such as Au or Pt to the eOx recording layer, the response speed and the thermal stability are improved, but the crystal anisotropy is reduced by the formation of the AuTe compound or the like. And the optical anisotropy also becomes smaller, so that the rate of change of the optical constant when the phase of the TeOx recording layer changes from the amorphous phase to the crystalline phase becomes smaller, and the CN ratio of the reproduced signal deteriorates. There has been a problem that it is difficult to simultaneously satisfy the information recording sensitivity and the long-term storage property.

The present invention has been made in view of the above-mentioned problems, and is directed to a write-once type optical recording medium for recording and reproducing information by a phase change of a recording material caused by laser light irradiation. It is an object of the present invention to provide an optical recording medium in which the rate of change of the reflectance due to the phase change to a large value, the CN ratio of the reproduced signal is high, and the information is excellent in the long-term preservability of information. Further, the reflectivity in the amorphous phase is made larger than the reflectivity in the crystalline phase, so-called H
It is an object of the present invention to provide an optical recording medium that realizes crystallization recording using a high-to-low (high-to-low) disk and facilitates control of a servo system.

[0011]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have conducted intensive experiments, and as a result, a first dielectric layer, a recording layer, a second dielectric layer,
And the relative magnitude of the reflectance Ra of the amorphous phase region and the reflectance Rc of the crystalline phase region in the recording layer with the change in the thickness of the second dielectric layer in the optical recording medium having the laminated structure of the reflection layer and the reflection layer. When the thickness of the second dielectric layer becomes larger than a certain value, the reflectance Ra of the amorphous phase region in the recording layer becomes larger than that of the crystalline phase region irrespective of the thickness of the first dielectric layer. Has been found to be greater than the rate Rc.

However, if the thickness of the second dielectric layer is increased, the heat generated when recording is performed by irradiating the recording layer with a laser beam becomes difficult to be dissipated to the reflective layer, and information is recorded, particularly at high density. There was a problem with recording. Therefore, in order to facilitate heat radiation from the recording layer to the reflective layer even if the thickness of the second dielectric layer is increased, the material of the second dielectric layer must have a high thermal conductivity. Becomes As a result of studying various materials by the present inventors, it has been found that a nitride dielectric material is suitable as an optically transparent material having a high thermal conductivity.

Therefore, the above object is achieved by the following optical recording medium according to the present invention. That is, the optical recording medium according to claim 1 has a first dielectric layer, a recording layer,
An optical recording medium in which a second dielectric layer and a reflective layer are sequentially stacked, and crystallization recording of information is performed by a phase change from an amorphous phase to a crystalline phase due to laser light irradiation of the recording layer, wherein the second dielectric layer When the layer is made of a nitride dielectric material and the thickness of the second dielectric layer is d and the refractive index is n, nd> 130 nm is satisfied.

As described above, in the optical recording medium according to the first aspect, since the thickness of the second dielectric layer is sufficiently large to satisfy nd> 130 nm, the reflectance of the amorphous phase region in the recording layer is improved. Ra> Rc is established between Ra and the reflectance Rc of the crystalline phase region, and the reflectance Ra of the amorphous phase region becomes larger than the reflectance Rc of the crystalline phase region.
Crystallization recording by a to Low disk is realized, and control of the servo system is easily performed as in the related art. In addition, since the difference (Ra-Rc) between the reflectance Ra of the amorphous phase region and the reflectance Rc of the crystalline phase region in the recording layer also increases, the CN ratio of the reproduced signal increases.

Further, at this time, the second dielectric layer is made of a nitride dielectric material having a high thermal conductivity, so that the second dielectric layer has a high thermal conductivity.
Even when the thickness of the dielectric layer is sufficiently large, the heat generated when recording is performed by irradiating the recording layer with laser light is easily radiated to the reflective layer, and the recording layer is rapidly cooled. Therefore, recording of high-density information is performed without any trouble.

In the optical recording medium according to the first aspect, the nitride dielectric material forming the second dielectric layer may be:
AlN, GaN, Si3 N4 or BN are preferred.

According to a third aspect of the present invention, in the optical recording medium according to the first or second aspect, the amorphous phase of the recording layer is an amorphous phase in an as-deposited state after film formation. And Here, the “as-deposition state” refers to a state immediately after forming a film by, for example, a sputtering method without particularly performing other processing.

As described above, in the optical recording medium according to the third aspect, since the amorphous phase of the recording layer is an amorphous phase in an as-deposited state after film formation, a process for particularly converting the recording layer to the amorphous phase is performed. Since it is not necessary to perform the process, the creation is facilitated and the process is simplified.

The optical recording medium according to claim 4 is the optical recording medium according to any one of claims 1 to 4, wherein the recording layer is made of a material containing Ag, In, Sb, or Te as a main component. It is characterized by the following.

As described above, in the optical recording medium according to the fourth aspect, since the recording layer is made of a material containing Ag, In, Sb, or Te as a main component, the recording layer can be converted from an amorphous phase caused by laser beam irradiation. Since the change in the optical constant due to the phase change to the crystal phase is large, the CN ratio of the reproduced signal is sufficiently high.

An optical recording medium according to a fifth aspect is the optical recording medium according to the fourth aspect, wherein N (nitrogen) is added to the recording layer. As described above, in the optical recording medium according to the fifth aspect, since N (nitrogen) is added to the recording layer, the crystallization transition temperature when recording information is recorded by irradiating the recording layer with laser light. As a result, the thermal stability of the optical recording medium on which the information is recorded is ensured, and the long-term storage of the information is improved.

In the optical recording medium according to any one of claims 1 to 5, the first dielectric layer is made of ZnS and SiO2.
And the reflection layer is preferably an Al-Ti layer which is an alloy of Al and Ti.

[0023]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the present invention will be described. FIG. 1 is a sectional view showing a write-once and phase-change optical recording medium according to an embodiment of the present invention.

As shown in FIG. 1, an optical recording medium according to this embodiment has a first dielectric layer 12 on a transparent substrate 10.
The recording layer 14, the second dielectric layer 16, and the reflective layer 18 are sequentially laminated by a sputtering method. Further, on the reflective layer 18, a UV curable resin film 20 for protection is spin-coated.

Here, as the transparent substrate 10, a plastic substrate such as acrylic or polycarbonate (PC) is used.
Alternatively, a glass substrate is used. The first dielectric layer 12 is made of ZnS, which is a mixture of ZnS and SiO2.
An S-SiO2 layer is used. However, the material of the first dielectric layer 12 is not limited to the ZnS-SiO2 layer, and a dielectric layer made of another dielectric material may be used.

As the recording layer 14, Ag, In,
A material containing Sb or Te as a main component is used.
However, the material of the recording layer 14 is not limited to these, and another material, for example, a chalcogenide-based material such as InSbTe may be used.

The second dielectric layer 16 is made of a nitride dielectric material having a very high thermal conductivity, specifically, AlN,
GaN, Si3 N4, or BN has been used. Since the second dielectric layer 16 is made of a nitride dielectric material having an extremely high thermal conductivity, when cooling the heated recording layer 14 by irradiating a laser beam, the recording layer 14 The heat is radiated through the adjacent second dielectric layer 16 having an extremely high thermal conductivity, and the cooling rate of the recording layer 14 is increased.

The reflective layer 18 has a thermal conductivity to further radiate the heat conducted from the recording layer 14 through the second dielectric layer 16 having a very high thermal conductivity. Very high material, specifically Al, Al
-A metal material such as a Ti alloy, Au, Ag, or Cu is used.

Next, on the premise of the optical recording medium shown in FIG. 1, some experiments performed to clarify an embodiment satisfying the best conditions will be described. (First Experiment) FIG. 2 shows the reflectance Ra of the amorphous phase region, the reflectance Rc of the crystalline phase region, and the modulation M of the recording layer of the write-once and phase-change optical recording medium according to the first experiment. 4 is a graph showing the relationship between the thickness of a first dielectric layer and the thickness of the first dielectric layer.

The write-once and phase-change type optical recording medium according to the first experiment is, as shown in FIG.
In a structure in which a first dielectric layer 12, a recording layer 14, a second dielectric layer 16, a reflective layer 18, and an ultraviolet curable resin film 20 are sequentially stacked on a substrate 0, a polycarbonate substrate is used as the transparent substrate 10. , Zn as the first dielectric layer 12
AgInS is used as the recording layer 14 using an S-SiO2 layer.
A bTe layer is used, and a wavelength of 635 is used as the second dielectric layer 16.
An AlN layer having a refractive index n of 2.1 with respect to incident light of nm was used, and an Al—Ti layer was used as the reflective layer 18.

The recording layer 14 has a thickness of 15 nm,
The thickness of the dielectric layer 16 is 100 nm, the thickness of the reflection layer 18 is 120 nm, and the thickness of the first dielectric layer 12 is 0 nm.
To 240 nm.

In this case, the reflectance Ra of the amorphous phase region in the unrecorded state of the recording layer 14 and the crystallized recording mark in the recorded state, that is, the reflectance Rc of the crystalline phase region, are generally well known. When the calculation was performed using the matrix method, the graph shown in FIG. 2 was obtained.
Here, the laser wavelength λ was calculated at λ = 635 nm. The modulation M is defined by M = (Ra−Rc) / Ra × 100, and the calculation result is as shown in the graph of FIG.

As is clear from the graph of FIG. 2, regardless of the change in the thickness of the first dielectric layer 12, the recording layer 14 is in the recording state with the reflectance Ra of the unrecorded amorphous phase region. Ra> Rc always holds between the reflectance Rc of the crystalline phase region and the reflectance Ra of the amorphous phase region in the unrecorded state is always higher than the reflectance Rc of the crystalline phase region in the recorded state. ing. Modulation M
Is also a value of M = 40 to 60%.

(Second Experiment) FIG. 3 shows the reflectance Ra of the amorphous phase region and the reflectance R of the crystalline phase region of the recording layer in the write-once and phase-change optical recording medium according to the second experiment.
9 is a graph showing the relationship between c, modulation M, and the thickness of a first dielectric layer.

The write-once and phase-change type optical recording medium according to the second experiment basically has the same structure as the optical recording medium according to the first experiment. 1
Since the same material is used for the dielectric layer 12, the recording layer 14, the second dielectric layer 16, the reflective layer 18, and the ultraviolet curable resin film 20, the description thereof is omitted.

However, the thickness of the recording layer 14 is 15 nm,
The thickness of the dielectric layer 16 is 80 nm, and the thickness of the reflection layer 18 is 1
20 nm, and the thickness of the first dielectric layer 12 is changed from 0 nm to 240 nm. That is, the difference is that the thickness of the second dielectric layer 16 is reduced from 100 nm in the first experiment to 80 nm.

In this case, the reflectance Ra of the amorphous phase region in the unrecorded state of the recording layer 14, the reflectance Rc of the crystalline phase region in the recorded state, and the modulation M
Was calculated in the same manner as in the case of the first experiment, and was as shown in the graph of FIG.

As is apparent from the graph of FIG. 3, regardless of the change in the thickness of the first dielectric layer 12, the recording layer 14 is in the recording state with the reflectance Ra of the unrecorded amorphous phase region. As in the case of the first experiment, Ra> Rc always holds between the reflectance Rc of the crystal phase region and the reflectance Ra of the amorphous phase region in the unrecorded state in the recorded state. It is always higher than the reflectance Rc of the phase region. Modulation M
Also, M = 50 to 90%, which is an even larger value than in the case of the first experiment.

(Third Experiment) FIG. 4 shows the reflectivity Ra of the amorphous phase region and the reflectivity R of the crystalline phase region of the recording layer in the write-once and phase-change optical recording medium according to the third experiment.
9 is a graph showing the relationship between c, modulation M, and the thickness of a first dielectric layer.

The write-once and phase-change type optical recording medium according to the third experiment has basically the same structure as the optical recording medium according to the first experiment. 1
Since the same material is used for the dielectric layer 12, the recording layer 14, the second dielectric layer 16, the reflective layer 18, and the ultraviolet curable resin film 20, the description thereof is omitted.

However, the thickness of the recording layer 14 is 15 nm,
The thickness of the dielectric layer 16 is 60 nm, and the thickness of the reflection layer 18 is 1
20 nm, and the thickness of the first dielectric layer 12 is changed from 0 nm to 240 nm. That is, the difference is that the layer thickness of the second dielectric layer 16 is reduced from 100 nm in the first experiment to 60 nm.

In this case, the reflectance Ra of the amorphous phase region in the unrecorded state of the recording layer 14, the reflectance Rc of the crystalline phase region in the recorded state, and the modulation M
Was calculated in the same manner as in the case of the first experiment, and was as shown in the graph of FIG.

As is apparent from the graph of FIG. 4, when the thickness of the first dielectric layer 12 is about 0 to 70 nm or about 140 to 220 nm, the amorphous layer region in the unrecorded state of the recording layer 14 is formed. While Ra> Rc is satisfied between the reflectivity Ra and the reflectivity Rc of the crystalline phase region in the recording state, the thickness of the first dielectric layer 12 is about 70.
In the range of nm to 140 nm, Ra <Rc holds, and the magnitude relationship is reversed. That is, according to the change in the layer thickness of the first dielectric layer 12, the reflectance Ra of the amorphous phase region in the unrecorded state becomes larger or smaller than the reflectance Rc of the crystalline phase region in the recorded state. I do.

(Fourth Experiment) The write-once and phase-change type optical recording medium according to the fourth experiment has basically the same structure as the optical recording medium according to the first experiment. Since the same material is used for the transparent substrate 10, the first dielectric layer 12, the recording layer 14, the second dielectric layer 16, the reflective layer 18, and the ultraviolet curable resin film 20, the description is omitted. I do.

However, the thickness of the recording layer 14 is 15 nm,
The thickness of the dielectric layer 16 is 20 nm, and the thickness of the reflective layer 18 is 1
20 nm, and the thickness of the first dielectric layer 12 is changed from 0 nm to 240 nm. That is, the difference is that the layer thickness of the second dielectric layer 16 is reduced from 100 nm in the first experiment to 20 nm.

In this case, the reflectance Ra of the amorphous phase region in the unrecorded state of the recording layer 14, the reflectance Rc of the crystalline phase region in the recorded state, and the modulation M
Is calculated in the same manner as in the first experiment, although not shown, the reflectance Ra of the amorphous phase region in the unrecorded state of the recording layer 14 and the reflectance Rc of the crystalline phase region in the recorded state are not shown. And Ra <Rc always holds. That is, regardless of the change in the thickness of the first dielectric layer 12, the reflectance Ra of the amorphous phase region in the unrecorded state is always smaller than the reflectance Rc of the crystalline phase region in the recorded state.

As described above, according to the first to fourth experiments,
When the layer thickness of the second dielectric layer 16 is 100 nm or 80 nm, the reflectance of the amorphous phase region in the unrecorded state of the recording layer 14 regardless of the change in the layer thickness of the first dielectric layer 12. Ra and the reflectance Rc of the crystalline phase region in the recording state
And Ra> Rc always holds, and the reflectance Ra in the amorphous phase region is always higher than the reflectance Rc in the crystalline phase region.

The thickness of the second dielectric layer 16 is 60 nm.
In this case, the reflectivity Ra of the amorphous phase region becomes larger or smaller than the reflectivity Rc of the crystalline phase region in accordance with the change in the layer thickness of the first dielectric layer 12.

Further, the thickness of the second dielectric layer 16 is 20 nm.
In this case, Ra <Rc always holds between the reflectivity Ra of the amorphous phase region and the reflectivity Rc of the crystalline phase region, and regardless of the change in the layer thickness of the first dielectric layer 12, The reflectivity Ra of the phase region is always smaller than the reflectivity Rc of the crystalline phase region.

That is, as the thickness of the second dielectric layer 16 increases, Ra <Rc tends to always hold between the reflectance Ra in the amorphous phase region and the reflectance Rc in the crystalline phase region. There is.

As a result of examining this tendency in more detail, the refractive index of the second dielectric layer 16 was set to n, and the thickness of the second dielectric layer 16 was set to d.
When the product nd of these n and d satisfies nd> 130 nm, the relationship Ra <Rc between the reflectance Ra in the amorphous phase region and the reflectance Rc in the crystalline phase region is always expressed as (unit: nm). It turned out to hold.

(Fifth Experiment) The write-once and phase-change optical recording medium according to the fifth experiment has basically the same structure as the optical recording medium according to the first experiment. The same applies to the layer thickness of each layer forming the laminated structure, and therefore, the description thereof is omitted.

The transparent substrate 10, the first dielectric layer 12,
The material of each layer of the recording layer 14, the second dielectric layer 16, the reflective layer 18, and the ultraviolet curable resin film 20 is basically the same as that of the optical recording medium according to the first experiment. , A ZnS—SiO 2 layer as the first dielectric layer 12, and an AgI layer as the recording layer 14.
An nSbTe layer is used, and AlN is used as the second dielectric layer 16.
Layer, and an Al—Ti layer is used as the reflection layer 18, but the AgInSbT used as the recording layer 14 is used.
The difference is that N (nitrogen) is added to the e layer.

The addition of N to the recording layer 14 is performed by flowing an appropriate amount of N 2 (nitrogen) gas when the recording layer 14 made of an AgInSbTe layer is formed on the first dielectric layer 12 by sputtering. . Here, specifically, Ag
At the time of sputtering the InSbTe layer, N was supplied at a flow rate of 3 sccm.
By flowing 2 gases, N was added to the recording layer 14 composed of the AgInSbTe layer.

In this case, the crystallization transition temperature Tc at the time of recording information by irradiating the recording layer 14 with laser light.
Is measured, the recording layer 14 composed of the AgInSbTe layer is measured.
The crystallization transition temperature Tc in the case of the optical recording medium according to the first experiment in which N was not added was Tc = about 200 ° C., whereas N 2 at a flow rate of 3 sccm was formed when the AgInSbTe layer was formed by sputtering. AgInSb with flowing gas
The crystallization transition temperature Tc of the optical recording medium according to the fifth experiment in which N was added to the recording layer 14 composed of a Te layer was increased to about Tc = 270 ° C.

As described above, according to the fifth experiment, AgIn
When N was added to the recording layer 14 composed of the SbTe layer, the crystallization transition temperature Tc increased. In a write-once and phase-change optical recording medium, the thermal degradation when information is stored for a long time depends on the crystallization transition temperature Tc. Therefore, the higher the crystallization transition temperature Tc, the higher the optical recording. It becomes thermally stable as a medium. Therefore, by adding N to the recording layer 14 made of the AgInSbTe layer, it is possible to secure the thermal stability in the long-term storage of information.

[0057]

EXAMPLES On the basis of the first to fifth experiments, an optical disk as an optical recording medium according to an example having the following best conditions was manufactured. That is, on a transparent substrate 10 made of a polycarbonate substrate provided with lands and grooves,
A first dielectric layer 12 made of a ZnS-SiO2 layer having a thickness of 60 nm is formed by a sputtering method. Then, this first
A 16 nm thick A layer is formed on the dielectric layer 12 by sputtering.
A gInSbTe layer is formed, and at that time, a flow rate of 0.1 gSbTe is used.
The recording layer 14 in which N is added to the AgInSbTe layer is formed by flowing 5 sccm N2 gas.

Subsequently, a second dielectric layer 16 made of an AlN layer having a thickness of 100 nm is formed on the recording layer 14 by a sputtering method. Subsequently, on this second dielectric layer 16,
The reflection layer 18 made of an Al-Ti layer having a thickness of 150 nm is formed by a sputtering method. Thereafter, an ultraviolet curable resin film 20 is spin-coated on the reflective layer 18 to protect the surface. Thus, an optical disk was manufactured.

Then, the optical disk thus produced was rotated at a linear velocity of 3.5 m / sec, and a signal of 20 MHz was recorded on the track. At this time, the laser wavelength λ was set to 635 nm, the numerical aperture NA of the objective lens was set to NA = 0.6, and the recording power P was set to P = 8 mW.

From the reproduced signal of this optical disk, a value of Ra = 28% can be obtained as the reflectance Ra of the amorphous phase region in the unrecorded state of the recording layer 14, and the crystalline phase region in the recorded state can be obtained. As a reflectance Rc, a value of Rc = 9% could be obtained, and as a modulation M, a value of M = 68% could be obtained.

[0061]

As described in detail above, according to the optical recording medium of the present invention, the following effects can be obtained. That is, according to the optical recording medium of the first aspect, the first dielectric layer, the recording layer, the second dielectric layer, and the reflective layer are sequentially laminated on the transparent substrate, and the recording layer is irradiated with laser light. An optical recording medium for performing crystallization recording of information by a phase change from an amorphous phase to a crystalline phase, wherein the thickness d of the second dielectric layer having a refractive index n is sufficiently large such that nd> 130 nm is satisfied. Thereby, Ra> Rc is established between the reflectance Ra of the amorphous phase region and the reflectance Rc of the crystalline phase region in the recording layer, and the reflectance Ra of the amorphous phase region is larger than the reflectance Rc of the crystalline phase region. High to
Crystallization recording using a Low disk can be realized, and servo system control can be performed easily as in the conventional case. In addition, the difference (Ra−) between the reflectance Ra of the amorphous phase region and the reflectance Rc of the crystalline phase region in the recording layer.
Rc) also increases, so that it is possible to increase the CN ratio of the reproduction signal, and it is possible to improve the recording / reproduction characteristics.

Further, at this time, the second dielectric layer is made of a nitride dielectric material having a high thermal conductivity, so that the second dielectric layer has a high thermal conductivity.
Even if the thickness of the dielectric layer is sufficiently large, the heat generated when recording and irradiating the recording layer with laser light is easily dissipated to the reflective layer, and the recording layer is rapidly cooled. High-density information can be recorded without any trouble.

According to the optical recording medium of the third aspect, since the amorphous phase of the recording layer is an amorphous phase in an as-deposited state after the film is formed, a process for converting the recording layer into an amorphous phase is performed. Since it is not necessary to perform the process, its creation is facilitated and the process can be simplified.

According to the optical recording medium of the fourth aspect, the recording layer is made of a material containing Ag, In, Sb, or Te as a main component. Since the change in the optical constant due to the phase change to the crystal phase increases, the CN ratio of the reproduction signal can be made sufficiently high, and the recording / reproduction characteristics can be improved.

According to the optical recording medium of the fifth aspect, since N is added to the recording layer, the crystallization transition temperature at the time of recording information by irradiating the recording layer with laser light is reduced. As a result, the thermal stability of the optical recording medium on which information is recorded can be ensured, and the long-term storability of information can be improved.

[Brief description of the drawings]

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

FIG. 2 shows a reflectance R of an amorphous phase region of a recording layer in a write-once and phase-change optical recording medium according to a first experiment.
a, the reflectance Rc of the crystal phase region, and the modulation M
4 is a graph showing the relationship between the thickness of a first dielectric layer and the thickness of the first dielectric layer.

FIG. 3 shows a reflectance R of an amorphous phase region of a recording layer in a write-once and phase-change optical recording medium according to a second experiment.
a, the reflectance Rc of the crystal phase region, and the modulation M
4 is a graph showing the relationship between the thickness of a first dielectric layer and the thickness of the first dielectric layer.

FIG. 4 shows a reflectance R of an amorphous phase region of a recording layer in a write-once and phase-change optical recording medium according to a third experiment.
a, the reflectance Rc of the crystal phase region, and the modulation M
4 is a graph showing the relationship between the thickness of a first dielectric layer and the thickness of the first dielectric layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Transparent substrate 12 1st dielectric layer 14 Recording layer 16 2nd dielectric layer 18 Reflection layer 20 UV curable resin film

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 7/24 538 G11B 7/24 538E

Claims (6)

[Claims] 1. A first dielectric layer, a recording layer,
An optical recording medium in which a second dielectric layer and a reflective layer are sequentially stacked, and crystallization recording of information is performed by a phase change from an amorphous phase to a crystalline phase due to laser light irradiation of the recording layer, An optical recording medium, wherein the dielectric layer is made of a nitride dielectric material, and when the thickness of the second dielectric layer is d and the refractive index is n, nd> 130 nm is satisfied. 2. The optical recording medium according to claim 1, wherein the nitride dielectric material forming the second dielectric layer is AlN,
An optical recording medium characterized by being GaN, Si3 N4 or BN. 3. The optical recording medium according to claim 1, wherein the amorphous phase of the recording layer is an as-deposited amorphous phase after film formation. 4. The optical recording medium according to claim 1, wherein the recording layer is made of a material containing Ag, In, Sb, or Te as a main component. . 5. The optical recording medium according to claim 4, wherein nitrogen is added to the recording layer. 6. The optical recording medium according to claim 1, wherein said first dielectric layer comprises a ZnS--SiO2 layer, and said reflection layer comprises an Al--Ti layer. Optical recording medium.