JP2000030298A - Information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an information recording medium, capable of steadily executing focusing and tracking at reproducing and expanding a power margin of laser beam usable for recording and erasing. SOLUTION: This information recording medium 1 is equipped with a light- transmissive substrate 2, a semitransparent interference film 3 formed on the principal surface of one side of the substrate 2, a recording film 5 formed on the semitransparent interference film 3 and generating a change in an optical characteristic due to reversible phase transition through irradiation of a light beam, a semitransparent reflection layer 7 formed on the recording film 5, a first light-transmissive protective film 4 provided between the semitransparent interference film 3 and the recording film 5 and having a higher melting point than the recording film 5, and a second light-transmissive protective film 6 provided between the recording film 5 and the semitransparent reflection layer 7 and having a melting point higher than that of the recording film 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording medium having a recording film whose optical characteristics change when irradiated with predetermined light.

[0002]

2. Description of the Related Art In recent years, optical disks have attracted attention as large-capacity memories. Among them, the phase-change optical disk has attracted particular attention because it can freely record and erase information.

FIG. 7 shows a cross-sectional view of a conventional phase change optical disk. In FIG. 7, the phase-change optical disk 51 has a structure in which a first protective film 53, a recording film 54, a second protective film 55, and a reflective layer 56 are sequentially laminated on a substrate 52.

In general, in the above-mentioned phase change optical disk 51, a substrate 52 is made of glass or plastic material, and first and second protective films 53 and 55 are made of ZnS, Si.
It consists of O ₂ , Al ₂ O ₃ and mixtures thereof. The recording film 54 is formed by depositing a chalcogenide such as GeSbTe on a substrate by a vacuum evaporation method, a sputtering method, or the like. The reflection layer 56 is made of Al or A
1 is made of an alloy containing Ti, Mo, Zr, Cr and the like.

The recording and erasing of information on the phase-change type optical disk 51 is performed, for example, by the following method.
First, light is applied to the entire surface of the optical disk 51 immediately after fabrication. As a result, the recording film 54 is heated to a state of high crystallinity, that is, a state in which atoms are arranged relatively regularly (hereinafter, referred to as a crystalline state). Next, the recording film 54 in the crystalline state is irradiated with high-intensity pulsed light to melt and rapidly cool the recording film 54. Thereby, the pulsed light irradiating portion of the recording film 54 is in a state where the crystallinity is reduced, that is, a state where the atomic arrangement is disordered (hereinafter, referred to as an amorphous state), and information is written.

Here, since the crystalline state and the amorphous state have different atomic arrangement structures, their optical properties (transmittance, reflectivity, etc.) are different. By detecting from the intensity, the recorded information can be reproduced. The erasure of the recorded information is performed by changing the recording portion of the recording film 54 from an amorphous state to a crystalline state. This can be achieved by irradiating the recording section with a low intensity pulse light to heat the recording section to a temperature higher than the crystallization temperature and lower than the melting point.

The above-described recording / erasing method uses the optical disk 5
1 is a case immediately after production, but the following overwrite recording can be performed on the optical disk 51 on which information has already been recorded.

FIG. 8 is a graph showing the power of laser light required for overwrite recording. In the figure, the horizontal axis represents time, and the vertical axis represents the power of laser light. As shown in FIG. 8, overwrite recording is performed by superimposing a recording signal on an erase signal. That is, by controlling the power of the laser beam between the erasing power (bias power) and the recording power, new recording can be performed while erasing the recorded information.

Conventionally, recording on the optical disk 51 has been performed only on one of the groove portion and the land portion. However, in recent years, the optical disc 51
In addition, as shown in FIGS. 9A and 9B, a land / groove recording method in which recording is performed on both a land portion and a groove portion has been proposed.

FIGS. 9A and 9B schematically show a land / groove recording method. FIG. 9A is a perspective view showing the optical disk 51, and FIG.
FIG. On the optical disk 51 shown in FIGS. 9A and 9B, a land portion 61 and a groove portion 62 are formed. Further, recording marks 63 are formed on the land portions 61 and the groove portions 62.

For recording on both the land portion 61 and the groove portion 62, for example, N. Miyagawa et al.
As disclosed in JJ Appl. Phys. Vol. 32 (1993) pp. 5324-5328, the depth of the groove portion 62 with respect to the land portion 61 is set to about λ / 6 (λ is the wavelength of the laser beam used for recording).
This makes it possible to prevent crosstalk from adjacent tracks.

The optical disk 51 described above includes a type in which the reflectance is lower during recording than in the unrecorded state, and a type in which the reflectance is higher during recording than during the unrecorded state. Hereinafter, each type will be described.

As described above, according to the optical disk 51, the recorded information is reproduced by measuring the intensity of the reflected light. The optical interference between the reflected light from each interface greatly affects the reflected light intensity. Therefore,
Depending on the optical constant of the material used for each layer, the film thickness that can maximize the change in reflected light intensity (change in reflectance) differs.

FIG. 10 is a graph showing an example of the relationship between the thickness of the protective film and the reflectance. The graph shown in FIG. 10 shows an example of data obtained when the recording film 54 is made of GeSbTe, Al is used for the reflective layer 56, and ZnS / SiO ₂ mixture is used for the protective films 53 and 55.

In the figure, the horizontal axis indicates the thickness of the protective film 55, and the vertical axis indicates the reflectance and the amount of change in the reflectance. Data obtained when the recording film 54 is in an amorphous state is indicated by a curve 57, data obtained when the recording film 54 is in a crystalline state is indicated by a curve 58, and a difference between these data is indicated by a curve 59. Is shown.

As is apparent from FIG. 10, the thickness of the protective film 55 is set to about 10 to 20 nm or 140 to 1 nm.
When the thickness is about 50 nm, the amount of change in reflectance can be maximized. Further, the thickness of the protective film 55 is set to 10 to 20.
When it is set to about nm, the reflectance change amount is positive.
That is, in this case, by recording the information, the reflectance is lower than that when no information is recorded. On the other hand, when the thickness of the protective film 55 is about 140 to 150 nm, the change in reflectance is negative. That is, in this case, by recording the information, the reflectance increases as compared with the case where the information is not recorded. By controlling the thickness of the protective film 55 in this way, it is considered that different types of optical disks 51 can be realized.

However, when the protective film 55 is formed thick, the heat dissipation is reduced. In this case, the recording film 54
Cannot be quenched, resulting in a decrease in recording characteristics (T.
OHTAet al. JJAP.VOL 128 (1989) SUPPLEMENT28-3, pp123-
128). Therefore, in an optical disc in which the recording film 54 is made of a recording material such as GeSbTe, the protective film 55 is usually formed to a thickness of about 10 to 20 nm.
That is, conventionally, the optical disk 51 is formed in a type in which the reflectance is lower during recording than when not recording.

However, when the optical disk 51 is of a type whose reflectivity is lower during recording than when it is not recorded,
When recording digital data on the optical disk 51, the following problems occur. Hereinafter, the case where the mark position recording method and the mark length recording method are adopted as the recording method will be described.

FIGS. 11A and 11B schematically show a mark position recording method and a mark length recording method, respectively.
FIG. 11A is a diagram schematically showing a mark length recording method. As shown in this figure, in the mark length recording method, information “0” and “1” correspond to recording marks 61 and 62 having different lengths, respectively.

If this mark length recording method is applied to the optical disk 51 of a type in which the reflectivity during recording is lower than that during non-recording, the light absorptance of the recording part becomes larger than that of the unrecorded part. . Therefore, even if a laser beam of the same power is irradiated, it is not possible to obtain a temperature which is as high as that of a recorded portion in an unrecorded portion. Further, latent heat is required to melt the unrecorded portion of the recording film 54.

Therefore, when the overwrite recording is performed on the optical disk 51, the recording marks formed in the unrecorded area are smaller than the recording marks formed in the recording area. Here, the mark length recording method is a recording method using the length of a recording mark. Therefore, in the mark length recording method, the size of the recording mark formed by overwrite recording is not constant, so that there is a problem that the recording accuracy is reduced.

FIG. 11B schematically shows a mark position recording method. As shown in this figure, in the mark position recording method, the recording marks 60 formed on the recording film 54 are formed in the same shape, and the information “0” is determined based on the distance between the center positions between the adjacent recording marks 60. "And" 1 "are distinguished.

When the mark position recording method is adopted for an optical disk 51 of a type in which the reflectivity is lower at the time of recording than at the time of non-recording, the following problems occur. When the optical disc 51 is of a type in which the reflectivity during recording is lower than that during non-recording, the average reflectivity during reproduction is such that the area ratio of the recorded portion (amorphous portion) to the unrecorded portion (crystalline portion) is smaller. It decreases as the size increases. In a general optical disk drive, in order to perform focusing and tracking sufficiently stably, the average reflectance at the time of reproduction needs to be at least about 10% or more.

When recording digital data on the optical disk 51 by the mark length recording method, the area of the recording portion of the optical disk 51 is larger than the area of the unrecorded portion. On the other hand, when the recording is performed by the mark position recording method, the area of the recording portion of the optical disk 51 is not large as compared with the area of the unrecorded portion. For example, in the mark length recording method, when the width of the recording mark is 0.78 μm and the recording density is the same, the area ratio of the recording portion to the unrecorded portion is 44%.
On the other hand, in the mark position recording method, when the diameter of the recording mark is 0.78 μm and the recording density is a certain value,
The area ratio of the recorded portion to the unrecorded portion is 26%.

As described above, according to the mark position recording method,
The average reflectance at the time of reproduction is higher than that of the mark length recording method. Therefore, in the conventional mark position recording method, a sufficient average reflectance was obtained even during reproduction, and focusing and tracking could be stably performed.

However, in recent years, higher recording density has been demanded. To increase the recording density in the mark position recording method, it is necessary to narrow the interval between recording marks. In this case, since the area ratio of the recording portion to the unrecorded portion increases, the average reflectance may be reduced to, for example, about 60% of the related art. Here, assuming that the thickness of the protective film 55 is the thickness shown in FIG. 9A, the average reflectance during reproduction is 10% or less.

In order to increase the average reflectance at the time of reproduction, the protective film 55 may be formed thicker. However, if the thickness of the protective film 55 is increased, the amount of change in reflectance cannot be maximized.

As described above, when the mark position recording method is used for the optical disk 51 of which the reflectivity is lower at the time of recording than at the time of non-recording, the recording density is increased and the reproducing It has been difficult to stably perform focusing and tracking and to obtain a sufficient amount of change in reflectance.

As a method for solving the above-mentioned problem, it has been proposed to interpose a semi-transparent metal layer (semi-transparent interference film) or a high refractive index layer between the substrate 52 and the protective film 53 of the optical disk 51. I have. According to this method, since the semi-transparent metal layer and the high refractive index layer affect the optical interference condition, the protective film 55 can be formed thin and the reflectance at the time of recording can be increased as compared with the time of non-recording. That is, even when the recording density is increased, focusing and tracking can be stably performed during reproduction.

However, in the conventional optical disk 51 in which a translucent metal layer or a high refractive index layer is interposed between the substrate 52 and the protective film 53, the ratio of the light absorptivity between the recorded portion and the unrecorded portion, When the difference in reflectivity between the portion and the unrecorded portion was optimized, the allowable range of the power of the laser beam used for recording / erasing was extremely small. That is, in the conventional optical disk 51, when the recording density is increased, focusing and tracking during reproduction are performed stably.
Also, it has been difficult to increase the power margin of the laser beam used for recording / erasing.

[0031]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and enables stable focusing and tracking at the time of reproduction.
It is an object of the present invention to provide an information recording medium capable of expanding a power margin of a laser beam usable for erasing.

[0032]

In order to solve the above-mentioned problems, the present invention provides a light-transmitting substrate, a translucent interference film formed on one main surface of the substrate, and a translucent interference film formed on the translucent interference film. A recording film that changes its optical characteristics by reversibly changing its phase by irradiating a light beam, a translucent reflective layer formed on the recording film, the translucent interference film and the recording film And a light-transmissive first protective film having a melting point higher than the recording film, and a melting point higher than the recording film provided between the recording film and the translucent reflective layer. An information recording medium provided with a light-transmitting second protective film having the following.

Preferred embodiments of the information recording medium are described below. The reflectance observed by irradiating the recording film with a light beam from the substrate side is such that the recording film is in a more unstable phase than when the recording film is in a more stable phase. Higher in the case.

The translucent reflective layer is made of Au, Cu, A
g and a material substantially selected from the group consisting of alloys containing these as a main component. -The recording film is substantially made of a GeSbTe-based alloy.

At least one of the first and second protective films is made of a ZnS.SiO ₂ mixture, SiO ₂ , TiO
₂ and a material selected from the group consisting of Al ₂ O ₃ .

The translucent interference film is made of Au, Ag, C
u, Si, Ge, and a material selected from the group consisting of alloys containing these as main components. -The recording film is substantially made of a GeSbTe-based alloy;
The first and second protective films are made of ZnS.SiO ₂ respectively.
The translucent interference film and the translucent reflective layer are each substantially made of a material selected from the group consisting of Au, Cu, Ag, and an alloy containing these as a main component.

The thickness of the recording film is 35 nm or less. -The thickness of the translucent interference film is 80 nm or less. The thickness d ₁ of the first protective film satisfies the relationship shown in the following inequality (1) or (2), and the thickness d ₂ of the first protective film satisfies the following inequality (3) or (4): Satisfy the relationship shown.

The thickness of the translucent reflection layer is 30 nm or less. -The recording film is substantially made of a GeSbTe-based alloy;
The first and second protective films are made of ZnS.SiO ₂ respectively.
The translucent interference film and the translucent reflective layer are each substantially made of a material selected from the group consisting of Au, Cu, Ag and an alloy containing these as a main component, and The thickness of the interference film is 80 nm or less, the thickness d ₁ of the first protective film satisfies the relationship represented by the following inequality (1) or (2), and the thickness of the recording film is 3
5 nm or less, the thickness d ₂ of the first protective film satisfies the relationship represented by the following inequality (3) or (4), and the thickness of the translucent reflective layer is 30 nm or less.

A land and a groove are formed on one main surface of the substrate. -The depth D of the groove portion with respect to the land portion satisfies the following inequality (5) or (6).

The phase change is a change between a crystalline state and an amorphous state. The phase change is a change between a crystalline state and an amorphous state, and the light beam is applied to a portion of the recording film in a crystalline state and a portion of the recording film in an amorphous state. The phase difference at the wavelength of ± 45 ° or less.

0.2 · λ / n ≦ d ₁ ≦ 0.4 · λ / n (1) 0.7 · λ / n ≦ d ₁ ≦ 0.9 · λ / n (2) 0.05 _{· λ / n ≦ d 2 ≦} 0.36 · λ / n ... (3) 0.54 · λ / n ≦ d 2 ≦ 0.86 · λ / n ... (4) 0.14 · λ / n ≦ D ≦ 0.2 · λ / n (5) 0.3 · λ / n ≦ D ≦ 0.4 · λ / n (5) In the above inequalities (1) to (6), λ is the light It shows the wavelength of the beam, and n shows the refractive index of the first and second protective films.

[0042]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 shows a sectional view of an information recording medium according to an embodiment of the present invention. In FIG.
The information recording medium (optical disk) 1 has a structure in which a translucent interference film 3, a first protective film 4, a recording film 5, a second protective film 6, and a translucent reflective layer 7 are sequentially laminated on a substrate 2. have.

In the optical disc 1, the substrate 2 is made of a light-transmitting material such as a plastic material such as polymethyl methacrylate resin or polycarbonate resin, glass, or the like.

The recording film 5 needs to be made of a material that undergoes a reversible phase change between an amorphous state and a crystalline state by light irradiation. This recording film 5 is usually formed to a thickness of 35 nm or less. Examples of the material forming the recording film 5 include chalcogenides such as GeSbTe-based alloys.

The first and second protective films 4 and 6 correspond to the recording film 5
It is provided to prevent the recording film 5 from evaporating when irradiating the recording film 5 with laser light or the like. That is, by providing the first and second protective films 4 and 6, perforation of the recording film 5 can be prevented, and the heat resistance of the recording film 5 can be protected.

The material used for the first and second protective films 4 and 6 is, for example, a ZnS.SiO ₂ mixture, Si
Light transmitting dielectrics such as O ₂ , TiO ₂ , and Al ₂ O ₃ can be mentioned. In the optical disc 1, the protective films 4 and 6 are designed so as to optically enhance the reproduced signal by a synergistic effect with the translucent interference film 3 and the translucent reflective layer 7.

The translucent interference film 4 affects the optical interference conditions of the optical disk 1 and makes it possible to increase the reflectivity during recording as compared with the unrecorded state even when the protective film 6 is formed thin. . Therefore, according to the optical disc 1, focusing and tracking can be stably performed during reproduction even when the recording density is increased.

The translucent interference film 3 is made of Au, Ag, Cu, S
i, Ge and alloys containing these as main components. The translucent interference film 3 needs to be thin enough to allow the laser light irradiated from the substrate 2 side to reach the recording film 5. Further, the translucent interference film 3 needs a certain thickness in order to cause light interference between the translucent interference film 3 and the translucent reflection layer 7 to enhance the reproduction signal. Therefore, the translucent interference film 3 is usually formed to a thickness of about 1 to 30 nm.

In the optical disk 1, the translucent reflection layer 7 is formed so as to transmit a part of the laser beam irradiated from the substrate 2 side and reflect the rest. Here, in order for the translucent reflective layer 7 to transmit a part of the laser beam, it is defined that the light transmittance of the translucent reflective layer 7 needs to be 10% or more.

In the conventional optical disk, a reflection layer was provided instead of the translucent reflection layer 7. The reflection layer in the conventional optical disk reflects or absorbs all of the laser light emitted from the substrate 2 side. Therefore, in order to obtain a desired interference condition in the conventional optical disk, there is no other choice but to control a layer structure interposed between the substrate and the reflective layer.

On the other hand, according to the optical disk 1,
The interference condition can be controlled by the reflectance or light transmittance of the translucent reflective layer 7 or the like. The reflectance or light transmittance of the translucent reflective layer 7 can be easily controlled by the material used for the translucent reflective layer 7 or its thickness.

The present inventor has examined the relationship between the thickness of the translucent reflective layer 7 and the like and the optical characteristics of the optical disc 1, and has found the following relationship. That is, the ratio of the light absorptivity between the recorded portion and the unrecorded portion of the recording film 54 hardly depends on the film thickness of the translucent reflective layer 7. It changes according to.

Therefore, for example, by optimizing the layer structure other than the translucent reflective layer 7 formed on the substrate 2, the ratio of the light absorptivity between the recorded portion and the unrecorded portion of the recording film 54 can be set to a desired value. By optimizing the thickness of the translucent reflective layer 7, a desired recording sensitivity or the like can be obtained. That is, the power margin of the laser beam usable for recording / erasing can be increased without substantially affecting the ratio of the light absorptivity between the recorded portion and the unrecorded portion.

In the optical disc 1, it is preferable that the material used for the translucent reflective layer 7 has a refractive index n of complex refractive index n-ik and an extinction coefficient k satisfying the following inequality. n ≦ 0.5 k ≧ 2 When such a material is used, it is possible to form the translucent reflective layer 7 with a uniform thickness and control the light transmittance of the translucent reflective layer 7 to a desired value. It becomes possible. Examples of the material whose refractive index n and extinction coefficient k satisfy the above inequality include Au,
Metals such as Cu and Ag or alloys containing these as main components can be given. In addition, when the above-mentioned material is used, the above-mentioned effect becomes remarkable by setting the thickness of the translucent reflective layer 7 to 30 nm or less.

The optical disc 1 may be of a type that records information on lands and grooves. In this case, the depth of the groove with respect to the land is 0.14λ.
/ N to 0.20λ / n or 0.30λ / n to 0.40
It is preferably λ / n. When the depth of the groove portion relative to the land portion is within the above range, the amount of signal leakage (crosstalk) from an adjacent track can be reduced. Here, n is the refractive index of the protective films 4 and 6, and λ
Is the wavelength of the laser light used for recording / erasing.

When the optical disk 1 is of the above type, the phase difference of the reflected light between the recorded portion and the unrecorded portion is ± 45 °.
It is preferable to control the layer configuration so as to be as follows. By setting the phase difference within the above range, it is possible to make the signal amplitudes of the land portion and the groove portion uniform.

[0057]

Embodiments of the present invention will be described below. (Example 1) The relationship between the optical characteristics of the optical disk 1 shown in FIG. 1 and the thickness of each layer was examined by the following method.

FIG. 2 is a graph showing the relationship between the thickness of the protective film of the optical disc according to the embodiment of the present invention and the amount of change in reflectance. In the figure, the abscissa represents a value obtained by multiplying the thickness of the first protective film 4 by n / λ, and the ordinate represents the thickness of the second protective film 6 by n / λ.
, And the numerical value attached to the contour line indicates the amount of change in reflectance at the time of recording with respect to the time of non-recording. In addition,
n is the refractive index of the protective films 4 and 6, and λ is the wavelength (660 nm) of the laser beam used for recording / erasing.

The data shown in FIG. 2 shows that the translucent interference film 3 is a 10 nm thick Au film and the recording film 5 is 10 nm thick.
m GeSbTe film, and the thickness of the translucent reflective layer 7 is 30 n.
This was obtained when the Au film was m in thickness.

As is apparent from FIG. 2, the first protective film 4
Has a film thickness of 0.2 · λ / n to 0.4 · λ / n and 0.7 · λ / n.
λ / n to 0.9 · λ / n, and the thickness of the second protective film 6 is 0.05 · λ / n to
0.36 · λ / n and 0.54 · λ / n to 0.86 · λ
/ N is within one of the ranges, a large change in reflectance can be obtained. Thus, the protective film 4
The reason why the reflectance change amount changes in accordance with the film thickness of No. 6 is that laser light incident from the substrate 2 side causes multiple reflection at the interface between the layers.

Next, the ratio of the light absorptance of the unrecorded portion to the light absorptance of the recorded portion was examined under the same conditions as described with reference to FIG. The result is shown in FIG. FIG. 3 is a graph showing the relationship between the thickness of the protective film of the optical disc according to the embodiment of the present invention and the ratio of the light absorptivity of the unrecorded portion to the recorded portion.
In the figure, the abscissa indicates a value obtained by multiplying the thickness of the first protective film 4 by n / λ, and the ordinate indicates a value obtained by multiplying the thickness of the second protective film 6 by n / λ. The numeral attached to indicates the ratio of the light absorptivity of the unrecorded portion to the recorded portion.

As is apparent from FIG. 3, when the thicknesses of the protective films 4 and 6 are within the range where a large amount of change in reflectance is obtained in FIG. The ratio of the light absorptivity of the (crystalline part) can be made larger than 1. As described above, a larger amount of heat is required to melt a crystalline part than an amorphous part. Therefore, when the ratio of the light absorptivity of the crystalline portion to the amorphous portion is set to be larger than 1, the temperatures can be increased at substantially the same rate. That is, it is possible to reduce the size variation of the recording mark between the recorded portion and the unrecorded portion.

Next, regarding the optical disc 1 shown in FIG.
The influence of the film thickness of the translucent interference film 3 and the film thickness of the translucent reflective layer 7 on the light absorptance of the unrecorded portion relative to the recorded portion of the recording film 5 was examined. Further, the influence of the thickness of the translucent interference film 3 and the thickness of the translucent reflective layer 7 on the light absorptance of the unrecorded portion of the recording film 5 was examined. Here, the recording film 5 has a thickness of 10
nm GeSbTe film, and the thickness of the first protective film 4 is n
The value obtained by multiplying the thickness of the second protective film 6 by n / λ was set to 0.1, and the value obtained by multiplying / λ was set to 0.3. 4 and 5 show the results.

FIG. 4 is a graph showing the relationship between the thickness of the translucent interference film and the translucent reflective layer of the optical disc according to the embodiment of the present invention, and the ratio of the light absorptivity of the unrecorded portion to the recorded portion. In the figure, the abscissa indicates the thickness of the translucent interference film 3, the ordinate indicates the thickness of the translucent reflective layer 7, and the numerical value attached to the curve is
The ratio of the light absorptivity of the unrecorded portion to the recorded portion is shown.

FIG. 5 is a graph showing the relationship between the thickness of the translucent interference film and the translucent reflective layer of the optical disc according to the embodiment of the present invention and the light absorption of the unrecorded portion. In the figure, the abscissa indicates the thickness of the translucent interference film 3, the ordinate indicates the thickness of the translucent reflective layer 7, and the numerical value attached to the curve indicates the light absorptivity of the unrecorded portion.

As is apparent from FIG. 4, the ratio of the light absorptivity of the unrecorded portion to the recorded portion changes according to the thickness of the translucent interference film 3. Little dependence. On the other hand, as is apparent from FIG. 5, by changing the film thickness of the translucent reflective layer 7 between 5 and 30 nm, the light absorption of the recording portion is changed between 0.65 and 0.9. Can be.

As described above, by setting the film thickness of the translucent reflective layer 7 in accordance with the linear velocity of recording, the recording pulse time and the power thereof, the ratio of the light absorptivity between the recorded part and the unrecorded part is obtained. It was confirmed that the optimum recording sensitivity could be obtained with little effect on the recording quality.

(Embodiment 2) FIG.
The optical disk 1 shown in FIG. 1 was manufactured below, and the relationship between the thickness of the translucent reflective layer 7 and the recording / erasing characteristics was examined.

First, a translucent interference film 3 made of Au and having a thickness of 10 nm was formed on a polycarbonate disk disk 2 having a diameter of 90 mm and a thickness of 0.6 mm having a spiral groove formed on the surface thereof. Next, on the translucent interference film 3, ZnS
A protective film 4 made of a mixture of SiO ₂ and SiO ₂ was formed to a thickness of 93 nm. Note that the thickness 93 nm of the protective film 4 is set to 0.1.
3 · λ / n (where λ is the wavelength of the laser beam and n is the refractive index of the protective film 4).

Next, a recording film 5 made of GeSbTe was formed on the protective film 4 to a thickness of 30 nm. The atomic ratio of Ge, Sb, and Te in the recording film 5 was 2: 2: 5. A protective film 6 made of a mixture of ZnS and SiO ₂ is formed on the recording film 5 to a thickness of 31 nm (0.1 · λ / n), and a translucent reflective layer 7 made of Au is formed on the protective film 6. It was formed to a thickness of 100 nm. Note that a vacuum sputtering method was used for the film formation on the substrate 2.

Further, the same disc made of polycarbonate as that of the substrate 2 was adhered to the translucent reflection layer 7 by using an ultraviolet curable resin, whereby the optical disc 1 was obtained. The optical disk 1 manufactured as described above was used as a sample (1).
And

Next, an optical disc 1 was manufactured in the same manner as described for the sample (1) except that the translucent reflection layer 7 was formed to a thickness of 10 nm. The optical disk 1 manufactured as described above is referred to as a sample (2).

The recording / erasing characteristics of the samples (1) and (2) produced by the above-described method were examined by using the apparatus shown in FIG. FIG. 6 is a diagram schematically showing an optical disk drive device used in the embodiment of the present invention.

As shown in FIG. 6, the optical disk 1 is held on a rotating shaft of a spindle motor 32. Optical disk 1
Is rotated at a predetermined rotation speed by controlling the rotation speed of the spindle motor 32.

The signal input from the input device 36 is digitized by the modulation circuit 35 into a signal of “1” or “0”. The digital signal from the modulation circuit 35 is sent to the laser driver 37, and controls ON / OFF of the laser light emitted from the optical head 33. This allows
Data is written on the disk 1.

A reproduction signal obtained by irradiating the disk 1 with laser light of a predetermined power is
The signal is amplified by a preamplifier 38 connected to the third amplifier 3. The amplified reproduced signal is then digitized from an analog signal to a digital signal in a binarization circuit 39. The digitized reproduction signal is further demodulated in the demodulation circuit 40 and output to the output device 41 as an analog signal.

In FIG. 6, the control system 43 controls the intensity of laser light emitted from the optical head 33 via a laser driver 37, and controls the linear motor 34 via a linear motor drive control system 46, for example. It is used to drive the optical head 33 to a desired position by driving. The control system 43 includes a focus drive control system 44.
By driving the objective lens actuator provided in the optical head 33 via the optical disk drive and the track drive control system 45, the optical head 33 is used to control the position of the objective lens so as to follow the surface deflection of the disk 1 and the eccentricity of the track. Can be

Before measuring the recording / erasing characteristics of the samples (1) and (2) using the optical disk drive device 30 configured as described above, the samples (1) and (2) are measured.
Was crystallized using an argon laser.

Next, by using the optical disk drive 30 shown in FIG.
The information was recorded on Samples (1) and (2) while controlling at rpm. In this recording, the recording signal is a single signal,
The recording was performed so that the recording mark length became 0.6 μm.

The above samples (1) and (2) are of the type in which the reflectivity increases during recording as compared with the unrecorded state.
Focusing and tracking could be performed stably both before and after recording. The reflectance of the unrecorded portion is 11%, and the reflectance of the recorded portion is 35%.
Met.

Next, for the samples (1) and (2), the relationship between the signal-to-noise ratio (CNR value) and the power of the laser beam used for recording was examined. In this recording, the recording signal was a single signal, and the power of the laser beam was 12 mW.
Was performed such that a recording mark having a length of 0.6 μm was formed.

The above samples (1) and (2) were irradiated with a 12 mW laser beam so that the recording mark length became 0.6 μm, and recording was performed. And the relationship with the erasure rate of the record was examined.
Note that the erasure rate is a value obtained by subtracting the CNR value immediately after recording from the CNR value after erasing the recording. The results are shown in Tables 1 and 2 below.

[0083]

[Table 1]

[0084]

[Table 2]

As is clear from Table 1, in Sample (1), the CNR value changed according to the power of the laser beam. On the other hand, in the sample (2), when the power of the laser beam was set to 12 mW or more, the change in the CNR value reached saturation. That is, it can be said that the laser light power has less influence on the recording characteristics in the sample (2) than in the sample (1).

As is clear from Table 2, a higher erasing rate was obtained in sample (2) than in sample (1). Further, in the sample (2), the power range of the laser beam enabling erasing is expanded as compared with the sample (1).

As described above, according to the optical disk of the embodiment of the present invention, by appropriately setting the thickness of the translucent reflective layer 7, the power margin of the laser beam usable for recording / erasing can be expanded. It becomes possible.

(Comparative Example) Instead of the translucent reflection layer 7, A
An optical disc was manufactured in the same manner as described for the sample (1) in Example 2 except that the reflective layer made of l was formed to a thickness of 100 nm. The optical disk manufactured as described above is used as a comparative sample (2).

Further, instead of the translucent reflection layer 7, Al
An optical disk was manufactured in the same manner as described for the sample (1) in Example 2 except that the reflective layer made of was formed to a thickness of 10 nm. The optical disk manufactured as described above is used as a comparative sample (2).

Incidentally, none of the reflection layers of the comparative samples (1) and (2) have light transmittance. When trying to form a translucent reflective layer using Al, the film thickness must be controlled to be extremely thin. However, it is practically impossible to form such an extremely thin translucent reflective layer to a uniform thickness using Al.

Next, after the recording films of the comparative samples (1) and (2) were crystallized by using an argon laser, respectively, the optical disc drive device 30 shown in FIG.
Information was recorded by controlling the number of revolutions of the spindle motor 32 to 1800 rpm. The recording was performed such that the recording signal was a single signal and the recording mark length was 0.6 μm.

Since the comparative samples (1) and (2) are of a type in which the reflectance increases during recording compared to the non-recording state, focusing and tracking are performed stably both before and after recording. I was able to. The reflectance of the unrecorded portion was 10%, and the reflectance of the recorded portion was 32%.

Next, the comparative samples (1) and (2)
For, the relationship between the signal-to-noise ratio (CNR value) and the power of the laser beam used for recording was examined. In this recording, the recording signal was a single signal, and the power of the laser beam was 1 unit.
The operation was performed so that a recording mark having a length of 0.6 μm was formed when the power was 2 mW.

The comparative samples (1) and (2)
Then, recording was performed by irradiating a laser beam of 12 mW so that the recording mark length became 0.6 μm, and the relationship between the power of the laser beam used for erasing the recording and the erasing rate of the recording was examined. Note that the erasure rate is a value obtained by subtracting the CNR value immediately after recording from the CNR value after erasing the recording. The results are shown in Tables 3 and 4 below.

[0095]

[Table 3]

[0096]

[Table 4]

As is clear from Table 3, the CNR values of both the comparative samples (1) and (2) changed according to the power of the laser beam, and did not reach saturation. That is, in the comparative samples (1) and (2), it can be said that the laser light power has a large effect on the recording characteristics.

Further, as is apparent from Table 4, in the comparative samples (1) and (2), it was not possible to obtain an erasing rate as large as that of the sample (2) in Example 2. Further, in the comparative samples (1) and (2), the power range of the laser beam enabling erasing was narrower than the sample (2) of the second embodiment.

Further, as is clear from Tables 3 and 4, almost the same data was obtained from the comparative samples (1) and (2). From the above, the comparative sample (1),
According to (2), even if the film thickness of the reflective layer is changed, it is clear that it is difficult to increase the power margin of the laser beam usable for recording / erasing.

[0100]

As described above, the information recording medium of the present invention has a translucent interference film. Since the translucent interference film affects the optical interference conditions of the information recording medium, the protective film can be formed thin and the reflectance at the time of recording can be higher than at the time of non-recording. That is, even when the recording density is increased, focusing and tracking can be stably performed during reproduction. Further, the information recording medium of the present invention is provided with a translucent reflective layer instead of the reflective layer.
When a translucent reflective layer is used, recording / erasing can be performed without affecting the ratio of the light absorptivity between the recorded portion and the unrecorded portion of the recording film by controlling the reflectance and transmittance. It is possible to expand the power margin of the laser beam that can be used for the laser beam.

That is, according to the present invention, there is provided an information recording medium capable of stably performing focusing and tracking during reproduction and expanding a power margin of laser light usable for recording / erasing. Is done.

[Brief description of the drawings]

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

FIG. 2 is a graph showing the relationship between the thickness of the protective film of the optical disc and the amount of change in reflectance according to the embodiment of the present invention.

FIG. 3 is a graph showing a relationship between a thickness of a protective film of an optical disc according to an embodiment of the present invention and a ratio of a light absorptivity of an unrecorded portion to a recorded portion.

FIG. 4 is a graph showing the relationship between the thickness of the translucent interference film and the translucent reflective layer of the optical disc according to the embodiment of the present invention, and the ratio of the light absorptivity of the unrecorded portion to the recorded portion.

FIG. 5 is a graph showing the relationship between the thickness of the translucent interference film and the translucent reflective layer of the optical disc according to the embodiment of the present invention, and the light absorptivity of the unrecorded portion.

FIG. 6 is a diagram schematically showing an optical disk drive used in the embodiment of the present invention.

FIG. 7 is a cross-sectional view showing a conventional phase change optical disk.

FIG. 8 is a graph showing the power of laser light required for overwrite recording.

FIG. 9 is a diagram schematically showing a land / groove recording method.

FIG. 10 is a graph showing an example of the relationship between the thickness of a protective film and the reflectance.

FIG. 11 is a diagram schematically showing a mark length recording method.

[Explanation of symbols]

 1, 51 optical disk 2, 52 substrate 3 translucent interference film 4, 6, 53, 55 protective film 5, 54 recording film 7 translucent reflective layer 30 optical disk drive 32 spindle motor 33 optical Head 34 Linear motor 35 Modulation circuit 36 Input device 37 Laser driver 38 Preamplifier 39 Binarization circuit 40 Demodulation circuit 41 Output device 43 Control system 44 Focus drive control system 45 Track drive control system 46 ... Linear motor drive control system 56 ... Reflection layer 57-59 ... Curve 60-63 ... Recording mark 61 ... Land part 62 ... Groove part

Claims (5)

[Claims] 1. A light-transmissive substrate, a translucent interference film formed on one main surface of the substrate, and a reversibly formed by irradiating a light beam on the translucent interference film. A recording film that undergoes a phase change to change the optical characteristics, a translucent reflective layer formed on the recording film, provided between the translucent interference film and the recording film, and A light-transmissive first protective film having a high melting point; and a light-transmissive second protective film provided between the recording film and the translucent reflective layer and having a higher melting point than the recording film. An information recording medium comprising: 2. The reflectivity observed by irradiating a light beam from the substrate side to the recording film indicates that the recording film is more unstable than when the recording film is in a stable phase. 2. The information recording medium according to claim 1, wherein the information recording medium is higher when in phase. 3. The translucent reflective layer is made of Au, Cu, A
3. The information recording medium according to claim 1, wherein the information recording medium is substantially made of a material selected from the group consisting of g and an alloy containing these as a main component. 4. The recording film according to claim 1, wherein the recording film is substantially made of a GeSbTe-based alloy.
The information recording medium described in the section. 5. At least one of the first and second protective films is made of a ZnS.SiO ₂ mixture, SiO ₂ , TiO
_2, and any one of materials selected from the group consisting of Al ₂ O ₃ of claims 1 to 4, characterized in that a substantially 1
The information recording medium described in the section.