JPH06155921A - Optical recording medium - Google Patents

Abstract

PURPOSE:To provide an optical recording medium capable of reducing the thermal effect of a second dielectric layer generated heretofore without damaging high reflectivity, capable of obtaining a high modulation degree and enabling good overwrite recording. CONSTITUTION:An optical recording medium is constituted of a substrate 10, the first dielectric layer 11 formed on the substrate 10, the second dielectric layer 12 formed on the first dielectric layer 11 and having a refractive index different from that of the first dielectric layer 11, the third dielectric layer 13 formed on the second dielectric layer 12 having heat conductivity or specific heat smaller than that of the second dielectric layer 12, the recording layer 7 formed on the third dielectric layer 13 and containing a phase change type recording material, the fourth dielectric layer 14 formed on the recording film 7 and the reflecting film 15 formed on the fourth dielectric layer 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a writable optical recording medium, particularly an optical recording medium having a dielectric layer, a recording film containing a phase change type optical recording material, and a light reflecting layer on a substrate. Recording / erasing characteristics and recording sensitivity improvement.

[0002]

2. Description of the Related Art Conventionally, as an optical recording medium capable of recording and erasing information, GeSbTe is used as an optical recording material, and recording or erasing is performed by a phase change induced in a recording film by irradiation of a light beam. A phase change type recording medium is well known as an example.

As an example of a recording method using this medium, for example, the entire recording film is heated to be crystallized in advance, and the irradiation surface is made amorphous by irradiating laser light having a narrow pulse width. Done by Information is erased, for example, by heating the entire recording film to crystallize the recording film.

On the other hand, unlike such a medium, a so-called ROM (read onl) in which data is already recorded in advance.
y memory) type medium also exists and has been widely put to practical use in the fields of voice recording and information processing. However, this does not have a writable recording film as described above. That is, the pre-pits corresponding to the data to be reproduced are already formed by press molding on the plastic substrate, the reflective layer made of metal such as Au, Ag, Cu, Al is formed on the plastic substrate, and the protective layer is further formed thereon. Layers have been formed. A typical medium of this ROM type is a so-called C
It is a compact disc called D. The specifications of the recording and reading signals of the CD have been standardized, and in accordance with this standard, a CD reproducing device is widely used as a compact disc player (CD player).

The writable or erasable optical recording medium is similar to a CD in that a laser beam is used, and is similar to a CD in that the medium has a disk shape. Therefore, a writable medium that complies with the standard of the CD specification and can be used as it is for a CD player is being actively developed.

[0006] As an example, a medium using a phase change type optical recording material can obtain a reflectance conforming to the CD standard, is compatible with a CD player, and is writable. A recording medium is proposed in JP-A-1-273240. This is a ZnS
A first dielectric (protective) film such as SiO _2, a second dielectric (protective) film such as SiO ₂ , a recording film of SbTeGe, a third dielectric (protective) film such as SiO ₂ , and an organic protective film. The medium structure is formed sequentially.

[0007]

However, although such a conventional proposed medium structure can provide a disk having a high reflectance, the low refractive index material used as the second dielectric (protective) film is limited. , Mainly used SiO ₂
However, since both the thermal conductivity and the specific heat are large, the recording film is adversely affected by heat during recording, and the degree of modulation, recording / erasing characteristics and sensitivity are deteriorated.

That is, as shown in FIG. 6 (a),
Originally, the portion where the laser beam was irradiated to the unrecorded portion (crystalline) was a beautiful substantially elliptical phase change recording portion (amorphous) 71.
However, as shown in FIG. 6 (b), since the second dielectric (protective) film having large thermal conductivity and large specific heat is present, the amorphous phase recorded once undergoes phase change. There is an inconvenience that a part of the quality portion (particularly, a long pit (for example, 11T)) returns to crystalline due to the heat retained in the second dielectric (protection) film. As a result, a high degree of modulation cannot be obtained.

The present invention was conceived in view of the above circumstances, and an object thereof is to solve the above-mentioned inconvenience and to prevent the heat of the second dielectric film from being deteriorated without impairing the high reflectance and high modulation degree. An object of the present invention is to provide an optical recording medium which can reduce the influence on the optical disc and can perform good overwrite recording.

[0010]

In order to solve the above problems, the present invention provides a substrate, a first dielectric layer formed on the substrate, and a first dielectric layer formed on the first dielectric layer. A second dielectric layer having a refractive index different from that of the first dielectric layer and a thermal conductivity of the second dielectric layer formed on the second dielectric layer. Alternatively, a third dielectric layer having a thermal conductivity or a specific heat smaller than the specific heat, a recording film formed on the third dielectric layer and containing a phase change type recording material, and a recording film of the recording film. A fourth dielectric layer formed above,
And a reflective film formed on the fourth dielectric layer.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred example of the optical recording medium of the present invention will be described below with reference to FIG. FIG. 1 is a schematic diagram in which the medium is shown as a cross section and the portion is enlarged so that the medium configuration can be clearly understood.

As shown in this figure, the optical recording medium 1 of the present invention includes a substrate 10, a first dielectric layer 11 formed on the substrate 10, and a first dielectric layer 11. A second dielectric layer 12 formed on the second dielectric layer 12 and having a refractive index different from that of the first dielectric layer, and the second dielectric layer 12 formed on the second dielectric layer 12. A third dielectric layer 13 having a thermal conductivity or specific heat smaller than that of the dielectric layer 12 and a phase change type recording material formed on the third dielectric layer 13 are provided. The recording film 7 contains, the fourth dielectric layer 14 formed on the recording film 7, and the reflective film 15 formed on the fourth dielectric layer 14. Further, the organic protective film 1 is usually formed on the reflective film 15.
6 is formed.

The substrate 10 usually has a disk shape,
A pregroove for tracking is usually formed in a concentric or spiral shape on a flat surface on one side of the substrate 10. The substrate 10 having such a pre-groove is
From the viewpoint of improving productivity, it is preferable to use a so-called integrally formed injection-molded resin substrate.
For example, it is formed from a transparent material such as a polycarbonate resin (PC) or a polymethylmethacrylate resin (PMMA). Further, the substrate is not limited to the integrally formed injection-molded resin substrate, and may be a substrate formed by a so-called 2P (photo-polymer) method. The thickness of the substrate 10 is 1.0 to
It is about 1.5 mm.

A first dielectric layer 11 is formed on such a substrate 10, and a second dielectric layer 12 is formed thereon. Specific materials for the dielectric layers 11 and 12 include highly transparent materials such as Mg, Ca and S.
r, Y, La, Ce, Pr, Nd, Pm, Sm, Eu,
Gd, Tb, Dy, Ho, Er, Tm, Yb, La, T
i, Zr, Hf, Y, Nb, Ta, Zn, Al, Si,
Ge, Sn, Pb and other oxides, nitrides, sulfides, L
Fluorides such as i, Na, Mg, and Ca, or a mixture thereof can be used. However, the second dielectric layer 12
Is added to the condition that the material has a refractive index lower than that of the first dielectric layer 11, and a specific material is selected so as to meet this condition.

More specific preferable materials for the second dielectric layer 12 include SiO ₂ (1.48), MgF ₂ (1.38) and Nd _3.
AlF ₆ (1.35), ThF ₄ (1.46), CeF ₂ (1.63), A
1 ₂ O ₃ (1.63) and the like. The numerical value in parentheses indicates the refractive index.

As a more specific preferable material for the first dielectric layer 11, ZnS (2.30), ZnS-SiO ₂ (20 mol%)
(2.11), TiO ₂ (2.20), Ta ₂ O ₅ (2.08) and the like.

The thickness d ₁ of the first dielectric layer 11 is d ₁ = (λ / when the wavelength of recording light or reproducing light is λ and the refractive index of the first dielectric layer is n _1. 4n ₁ ) (2m + 1)
It is preferable to set so that Where m is 0
Represents a positive integer including.

Further, the thickness d _{2 of} the second dielectric layer 12 is
Is d ₂ = (λ / 4n ₂ ) (2 m, where λ is the wavelength of the recording light or reproducing light and n ₂ is the refractive index of the first dielectric layer.
It is preferable to set it so that it becomes +1). Here, the above m represents a positive integer including 0.

A third dielectric layer 13 is formed on the second dielectric layer 12 as described above. Third dielectric layer 13
Is formed of a material having a thermal conductivity or a specific heat smaller than that of the second dielectric layer 12. This is to prevent heat retention of the second dielectric layer 12 which has been a problem in the related art, promote heat diffusion to the reflective film side, and maintain a good recording state. As the material of the third dielectric layer 13, ZnS, ZnO, ZnSe alone, ZnS, Z
nO, ZnSe, Mg, Ca, Sr, Y, Ce, T
i, Zr, V, Nb, Tb, Cr, Mo, W, Al, I
10 to 6 oxides such as n, Si, Ge, Sn, Pb, and Sb, nitrides, and fluorides such as Li, Nb, Mg, and Cd are used.
Examples include a mixture of 0 mol%. The more specific material of the third dielectric layer 13 is selected in consideration of the material of the second dielectric layer 12. For example, the second dielectric layer 12
When the material of SiO ₂ is SiO ₂ , the third dielectric layer 1
The material of 3 is ZnS, ZnS.SiO ₂ (10 to 30 mol%)
Is preferred.

The thickness d _{3 of} the third dielectric layer 13 as described above.
Is d ₃ = (λ / 2n ₃ ) (2 m, where λ is the wavelength of the recording light or reproducing light and n ₃ is the refractive index of the first dielectric layer.
It is preferable to set it so that it becomes +1). Here, the above m represents a positive integer including 0.

A recording film 7 containing a phase change type recording material is formed on the third dielectric layer 13. Specific materials for the recording film 7 include GeTeSb and G
eTePd, GeTeCo, GeTeSn, GeTeB
i, GeTeSe, InSbTe, and the like. The film thickness of the recording film 7 is about 100 to 300Å.

A fourth dielectric layer 14 is formed on the recording film 7. The material of the fourth dielectric layer 14 is
The material may be appropriately selected from the materials used for the first to third dielectric layers and used. The thickness d ₄ of the fourth dielectric layer 14 is preferably about 100 to 300Å.

On such a fourth dielectric layer 14,
Reflective layer 15 for increasing light reflectance and promoting heat diffusion
Is provided. The reflective layer 15 is made of a metal such as Au, Al, Ag, and Cu, and is formed by vacuum vapor deposition, sputtering, ion plating, or the like. The thickness of such a light reflection layer 14 is set to about 0.02 to 0.2 μm.

Incidentally, the first to fourth dielectric layers 1
1, 12, 13, 14 and the recording film 7 are also the reflection layer 1
Similar to 5, the film is formed by vacuum evaporation, sputtering, ion plating or the like.

A protective layer 16 is usually provided on the reflective layer 15 to protect the recording film 7, the dielectric layers 11, 12, 13, 14 and the reflective layer 15. The protective layer 16 is generally formed by spin-coating an ultraviolet curable resin and then applying the resin.
It is formed by irradiating ultraviolet rays to cure the coating film. Other,
Epoxy resin, acrylic resin, silicone resin, urethane resin or the like is used as the material of the protective layer 16. The thickness of such a protective layer 16 is usually about 0.1 to 100 μm.

The recording film of the medium of the present invention is generally irradiated with recording light in a pulsed form under rotation. At this time, a part of the recording film undergoes a phase change to form a recording pit. The reproduction of the pit information formed in this way is performed by detecting the difference in the reflected light of the read light also while the medium is rotating.

The present invention will be further described below by showing concrete examples.
Will be described in detail.Preparation of sample 1 of the present invention 12 cm diameter and 1.2 mm thick polycarbonate (P
C) ZnS / SiO on the substrate 11₂(20mol%)
Sputtering the first dielectric layer 11 (refractive index: 2.11)
A ring method was used to form a layer having a thickness of 920 angstroms.
On top of this, SiO₂The second dielectric layer 12 (refraction
Rate: 1.48, Thermal conductivity: 2.26 × 10^-2Cal / cm.s.
k, specific heat: 1.80 × 10^-1 cal / g.k) spatterin
Layer to a thickness of 1300 angstroms. This
On top of ZnS / SiO₂(20mol%) third invitation
Electrical layer 13 (refractive index: 2.11, thermal conductivity: 1.57 x
10 ^-3Cal / cm.s.k, specific heat: 1.34 × 10^-1 cal / g.k)
Is sputtered to a thickness of 1850 angstroms
Was set up. On top of this, Ge (29) Sb (23) Te (48) atm%
The recording film consisting of a 200 angstrom thick spa
Layered by the tattering method. ZnS / SiO₂
The fourth dielectric layer 14 (20 mol%) is turned on for 150
The layer was formed by sputtering to a thickness of Gstrom. This
A reflective layer 15 made of Al on top of
A film having a thickness of the storm was formed by a sputtering method. Accuse
After that, a UV-curable acrylate resin is used on the reflective layer 15.
The protective film 16 composed of 10 μm thick is formed, and
Created a pull.

When this sample is manufactured, at the same time, the thickness of the recording film, the film thickness of the first dielectric layer, the film thickness of the second dielectric layer, and the film of the third dielectric layer of the sample described above are used. The effect of reflectance on the change in thickness was investigated respectively. The results are shown in FIGS.

From the results shown in FIG. 2, it can be seen that the recording film thickness at which the reflectance is 60% or more in the crystalline state and the difference from the amorphous state is maximum is around 200 Å. From the results shown in FIGS. 3 and 4,
A suitable film thickness of the first dielectric layer and the second dielectric layer is
It can be seen that the film thickness is an odd multiple of λ / 4n1 and λ / 4n2, respectively. From the results shown in FIG. 5, it can be seen that the preferable film thickness of the third dielectric layer is an odd multiple of .lambda. / 2n3.

Then, a comparative sample was prepared in the following manner. Preparation of Comparative Sample The third dielectric layer 13 was removed from the configuration of the sample of the present invention. Other than that, in the same manner as the sample of the present invention,
A comparative sample was prepared.

After the initial crystallization was performed on these two samples, the linear velocity was 1.4 m / s and the recording power was 30 m.
An EFM signal was recorded at W and an erasing power of 12 mW, and then the recorded signal was reproduced.

As a result, in the comparative sample, the tip of the recording portion of the long pit was thinned due to recrystallization, and the reproduction signal level of the recorded amorphous portion could not be obtained. On the other hand, in the sample of the present invention, a good eye pattern was obtained without causing such inconvenience, and repetitive recording by overwriting was also possible.

[0033]

The effect of the present invention is clear from the above experimental results. That is, the optical recording medium of the present invention comprises a substrate,
A first dielectric layer formed on the substrate, and a second dielectric layer formed on the first dielectric layer and having a refractive index different from that of the first dielectric layer. A body layer, a third dielectric layer formed on the second dielectric layer and having a thermal conductivity or a specific heat smaller than the thermal conductivity or the specific heat of the second dielectric layer; A recording film formed on the third dielectric layer and containing a phase change type recording material, a fourth dielectric layer formed on the recording film, and a fourth dielectric layer on the fourth dielectric layer. It is possible to reduce the thermal effect of the second dielectric layer that has been conventionally generated without impairing the high reflectance and to obtain a high degree of modulation and a good overwrite. It has the effect of being able to record.

[Brief description of drawings]

FIG. 1 is a partial enlarged cross-sectional view for explaining a schematic configuration of an optical recording medium of the present invention.

FIG. 2 is a graph showing the relationship between the recording film thickness and the reflectance of the optical recording medium of the present invention, where the solid line shows the amorphous state and the dotted line shows the crystalline state.

FIG. 3 is a graph showing the relationship between the film thickness and the reflectance of the first dielectric layer of the optical recording medium of the present invention, where the solid line shows the amorphous state and the dotted line shows the crystalline state.

FIG. 4 is a graph showing the relationship between the film thickness and the reflectance of the second dielectric layer of the optical recording medium of the present invention, where the solid line shows the amorphous state and the dotted line shows the crystalline state.

FIG. 5 is a graph showing the relationship between the film thickness and the reflectance of the third dielectric layer of the optical recording medium of the present invention, where the solid line shows the amorphous state and the dotted line shows the crystalline state.

FIG. 6A is a diagram schematically showing the state of recording pits and the state of reproduction waveforms when recording is performed by irradiating a light beam having a predetermined recording waveform using the optical recording medium of the present invention,
(B) shows the state of recording pits when recording is performed by irradiating a light beam having a predetermined recording waveform using a conventional optical recording medium,
In particular, it is a diagram schematically showing a state in which a recrystallized region is generated and a state of a reproduced waveform thereof.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical recording medium 7 ... Recording film 10 ... Light transmissive substrate 11 ... First dielectric layer 12 ... Second dielectric layer 13 ... Third dielectric layer 14 ... Fourth dielectric layer 15 ... Reflection Layer 16 ... Protective film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichi Yokozeki 6-1-1, Fujimi, Tsurugashima City, Saitama Pioneer Research Institute

Claims (2)

[Claims] 1. A substrate, a first dielectric layer formed on the substrate, and a refractive index different from the refractive index of the first dielectric layer formed on the first dielectric layer. A second dielectric layer having a refractive index, and a third dielectric layer formed on the second dielectric layer and having a thermal conductivity or specific heat smaller than that of the second dielectric layer. A dielectric layer, a recording film formed on the third dielectric layer and containing a phase change type recording material, a fourth dielectric layer formed on the recording film, An optical recording medium, comprising: a reflective film formed on a fourth dielectric layer. 2. The film thickness d ₃ of the third dielectric layer is d ₃ = (λ where λ is the wavelength of recording light or reproducing light and n ₃ is the refractive index of the third dielectric layer. The optical recording medium according to claim 1, wherein the optical recording medium is / 2n ₃ ) (2m + 1). Here, the above m represents a positive integer including 0.