JPH06124480A - Optical disk - Google Patents

Abstract

PURPOSE:To enhance the sensitivity, the repetition durability and the C/N (S/N) ratio of an ultrahigh-resolution playback-type optical disk. CONSTITUTION:At least a first dielectric layer 4, a phase-change material layer 3 and a second dielectric layer 5 are laminated on a transparent substrate 2 in which optically readable phase pits 1 have been formed according to an information signal. The phase change material layer 3 is changed partly into a liquid phase inside the scanning spot of a beam of readout light when the beam of readout light is shone. In an optical disk formed in this manner, a dielectric whose thermal conductivity has a value of 0.006 to 0.25J/cmKs is used for the dielectric layers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk for reproducing information by irradiating a laser beam, and more particularly to an optical disk suitable for high density recording.

[0002]

2. Description of the Related Art For optical discs such as digital audio discs (so-called compact discs) and video discs, an aluminum reflection film is formed on a transparent substrate on which phase pits are formed in advance according to an information signal, and an aluminum reflection film is formed thereon. It is configured by forming a protective film and the like. In such an optical disc, the signal is read (reproduced) by irradiating the disc surface with the reading light and detecting a large decrease in the amount of reflected light due to the diffraction of the light at the phase pit forming portion.

By the way, in the above-mentioned optical disk, the resolution of signal reproduction is almost determined by the wavelength λ of the light source of the reproduction optical system and the numerical aperture NA of the objective lens, and the spatial frequency 2NA / λ is the reproduction limit.

Therefore, in order to realize high density in such an optical disc, it is necessary to shorten the wavelength λ of the light source (for example, semiconductor laser) of the reproducing optical system or increase the numerical aperture NA of the objective lens. Will be needed.

[0005]

However, the wavelength λ of the light source is
There is a limit to the improvement of the numerical aperture NA of the objective lens and the objective lens, and it is difficult to dramatically increase the recording density by this. Therefore, the present applicant has proposed an optical disc that can obtain a resolution higher than the above-mentioned limits by the wavelength λ and the numerical aperture NA by utilizing the reflectance change due to the partial phase change in the scanning spot of the reading light. (Japanese Patent Application No. 2-94452, Japanese Patent Application No. 3-24951)
No. 1 application).

The inventions relating to these applications relate to an optical disc or a reproducing system thereof for performing super-resolution reproduction by changing the reflectance by a partial phase change in the laser spot of the reading light. However, in the inventions related to these applications, when the phase change material layer is used,
No consideration was given to reproduction sensitivity and deterioration caused by melting accompanying reproduction, that is, repeated durability.

It is an object of the present invention to improve the repetition durability as described above in such an optical disc and to obtain a high carrier / noise ratio (C / N).

[0008]

According to the present invention, an optically readable recording pit, in this case, a phase pit 1 is formed according to an information signal, as shown in FIG. At least a first dielectric layer 4 is formed on the transparent substrate 2 thus formed, and a phase change material layer 3 capable of changing the reflectance after melting is formed on the first dielectric layer 4. The second dielectric layer 5 is formed on the layer 3, and when the reading light is irradiated, the phase change material layer 3 is partially liquefied in the scanning spot of the reading light and the reflectance is increased. At least a first optical disc adapted to change
And the second dielectric layers 4 and 5 have a thermal conductivity of 0.006J.
/ CmKs to 0.25 J / cmKs is used as the dielectric material.

Further, the present invention provides the above-mentioned phase change material layer 3 with
The composition ratio of Ge and Te is 3: 1 to 3: 9, and S
The composition ratio of b and Te is 12: 3 to 12:28,
The composition ratio of Ge, Te and Sb, Te is set to an arbitrary value.

Furthermore, the present invention has a structure in which a nitride, an oxide, a sulfide of a metal and a semiconductor element, or a mixture thereof is used for the above-mentioned first and second dielectric layers.

Further, according to the present invention, the reflection film 6 is provided on the second dielectric layer 5 as shown in FIG. 2 which is a schematic cross-sectional view of the essential part of the above-mentioned structure, and the reflection film 6 is formed. On membrane 6,
A metal having good thermal conductivity and reflectance is used.

[0012]

The optical disk according to the present invention utilizes the temperature distribution in the scanning spot of the read light in reading or reproducing the recording by the recording pits, and partially uses the phase change material in the high temperature region generated in the spot. A liquid phase state is generated in the layer so that, for example, the reflectance here is remarkably increased so that, for example, the phase pits in the liquid phase state portion can be read out by, for example, diffraction.

That is, it is possible to form a region in which a recording pit optically appears in the read light spot and read only one recording pit in this spot, for example, and to perform super-resolution reproduction not restricted by λ / 2NA. Can be done. In particular, for example, if the reflectance in the low temperature portion is remarkably reduced and the reflectance in the high temperature portion is increased, the film thickness may be limited and sufficient reproduction may not be possible with the semiconductor laser.

In the present invention, in particular, the first and second dielectric layers provided above and below the phase change material layer have a thermal conductivity of 0.
By using a material of 006 to 0.25 J / cmKs, it is possible to obtain an optimum layer structure for reproduction,
It was possible to improve the sensitivity, obtain a sufficient reproduction output, and improve the durability.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1 showing the basic structure of the present invention, at least a first dielectric layer 4 is formed on a transparent substrate 2 on which recording pits, in this case, phase pits 1 are formed.
To form a phase change material layer 3 on the first dielectric layer 4 that can return to an initial state after melting, and further form a second dielectric layer 5 on the phase change material layer 3. Form.

When the reading light, for example, a laser beam is applied to the phase change material layer 3, the reading light of the phase change material layer 4 partially enters a liquid phase state and the reflectance increases. At the same time, the reflectance after the reading is returned to the initial state.

In the example shown in FIG. 1, phase pit 1
In this case, the phase change material layer 3 is formed on the transparent substrate 2 having the first dielectric layer 4 and the second dielectric layer 5 is further formed thereon. The phase pit 1 is shown in FIG.
A phase change material layer 3 is formed on a transparent substrate 2 having a first dielectric layer 4, a second dielectric layer 5 is further formed on the phase change material layer 3, and a reflective film 6 is further formed on the second dielectric layer 5. A third dielectric layer 7 is formed on this, and a protective film (not shown) is further formed on the third dielectric layer 7 if there is any, and the first and second dielectric layers 4 and 5 provide optical characteristics such as It is also possible to adopt a configuration in which the reflectance and the like are set. In this case, the third
The dielectric layer 7 can improve the mechanical strength of the laminated film and improve the repeated read durability.

The optical disc according to the present invention utilizes the temperature distribution of the reading light in the scanning spot upon reproduction thereof, so that the phase change material layer 3 is partially in a liquid phase state in a high temperature region generated in the spot. Is generated to cause the reflectance here to increase remarkably, for example, the phase pits in this liquid phase state portion can be reproduced with super-resolution by reading by diffraction, for example.

That is, the case where the optical disk according to the present invention is irradiated with a laser spot will be described with reference to FIG.
In FIG. 3, the horizontal axis represents the position of the spot in the scanning direction. Looking at the state where the optical disk is irradiated with the laser light spot L by laser irradiation, in this case, the light intensity is shown by the broken line A in FIG. The distribution is shown. On the other hand, the temperature distribution corresponding to the temperature distribution in the phase change material layer 3 corresponds to the scanning speed of the laser spot L, as indicated by the solid line B in FIG. The distribution is delayed, and the reflectance also shows the same distribution.

Here, as described above, the laser spot L
However, if the optical disc is scanned in the direction indicated by arrow C in FIG. 3, the temperature of the optical disc gradually rises from the leading end side in the traveling direction of the laser spot L, and then the temperature of the melting point MP of the phase change material layer 3 or higher. Becomes At this stage, the phase-change material layer 3 changes from the initial crystalline state to the molten state, and the transition to this molten state increases the reflectance. That is, in the laser light spot L, there are a region Px having a high reflectance, that is, a region Px in which the phase pit 1 can be read, and a region Pz having a low reflectance, which are shaded in the drawing.

Therefore, in this case, even if, for example, two phase pits 1a and 1b exist in the same spot L as shown in the figure, only one phase pit 1a existing in the region Px having a high reflectance is shown. The reading can be performed, and the other phase pits 1b are not read because they are in the region Pz where the reflectance is extremely low. Even if a plurality of phase pits 1a and 1b are present in the same spot L as described above, since the reading can be performed only with respect to a single phase pit 1a, the numerical aperture NA of the lens system and the wavelength λ of the read light. Super resolution reproduction is possible without being limited to.

At this time, the reflectance is specified by the optical constant and the film thickness of the constituent material of each layer. Therefore, the sensitivity can be adjusted by using dielectrics having the same optical constant but different thermal conductivity. Here, in the super-resolution reproduction in the present invention, since the phase change material layer flows due to the melting, repeated reproduction becomes difficult. Therefore, it does not mean that sensitivity is good, but it is necessary to strike a balance between sensitivity and repeated durability.

In the present embodiment, optical disks are constructed by using the same material having a thermal conductivity in a predetermined range as each dielectric material, and by making the film thicknesses different from each other, that is, dielectric materials having different heat capacities. Was constructed and its reproduction characteristics were measured. This will be described below.

Example 1 In this example, a glass 2P substrate was used as the transparent substrate 2 when the configuration described in FIG. 2 was adopted. The 2P referred to here is a photopolymer method. In this example, the track pitch P = 1.6μ
m, pit depth about 120 nm, pit width W = 0.3,
It was formed under the setting conditions of 0.4, 0.5, 0.8, 1.2 and 2.0 μm.

Then, the transparent substrate 2 having the pits 1
90nm thick with thermal conductivity of 0.25J / cm
A first dielectric layer 4 made of AlN, which is Ks, was deposited, and a phase change material layer 3 made of Ge ₂ Sb ₂ Te ₅ ternary alloy with a thickness of 17 nm was deposited on the first dielectric layer 4. Further, a second dielectric layer 5 made of AlN and having a thickness of 66 nm was deposited thereon. Further, an Al reflection film 6 is formed on top of this.
Deposition to a thickness of 80 nm, and then a thickness of 9
A third dielectric layer 7 of 0 nm AlN was deposited.

With respect to the optical disc thus formed, the linear velocity is set to 3.6 m / s and the reproducing power is set to 1
Regeneration was performed at 0 mW. C of each pit width at this time
The relationship between / N and the pit length is shown in FIG. The number of repetitions required to deteriorate the C / N by performing the reproduction is 1
It was 00000 times. The deterioration referred to here is the original C
/ N means a decrease of 1 dB or more.

Example 2 In this example, the first, second and third dielectric layers 4,
Si having thermal conductivity of 0.03 J / cmKs in 5 and 7
The same structure as in Example 1 was used except that ₃ N ₄ was used.

With respect to the optical disc thus formed, the linear velocity is set to 3.6 m / s and the reproduction power is set to 1
The relationship between the C / N and the pit length at 0 mW is shown in FIG. The number of repetitions required for the regeneration to deteriorate the C / N was 10,000 times.

Example 3 In this example, ZnS and Si ₂ having a thermal conductivity of 0.006 J / cmKs are applied to the first, second and third dielectric layers.
The structure was the same as in Example 1 except that a mixture of O ₃ in an atomic ratio of 8: 2 was used.

For the optical disc thus formed, the linear velocity is set to 3.6 m / s and the reproduction power is set to 1
FIG. 5 shows the relationship between the C / N and the pit length when reproduction was performed at 0 mW. The number of repetitions required for the regeneration to deteriorate the C / N was 1000 times.

On the other hand, in the above-mentioned structure, the optical disk was formed by omitting the second dielectric layer.
This is shown as a comparative example below. Comparative Example In the above structure, the Al reflective film 6 having a thermal conductivity of 2.144 J / cmKs is formed directly on the phase change material layer 3, and the other parts have the same material structure as the above example. An optical disc was constructed. With respect to this optical disk, the C / N of a pit length of 0.3 μm was 20 dB when the linear velocity was set to 1.0 m / s and the reproduction power was set to 10 mW, which was not suitable for practical use.

From these results, the above-mentioned first to third embodiments
And as can be seen from the comparative example, at least the material of the second dielectric layer 5 on the layer change material layer 3 has a thermal conductivity of 0.0
According to the optical disk of the present invention, which uses the material of which the amount is set to 06 J / cmKs to 0.25 J / cmKs, the sensitivity is improved and the C which is about 30 to 40 dB or more is sufficient for practical use.
It is understood that / N can be obtained and the durability of repeated reproduction can be sufficiently enhanced.

As the material of the above-mentioned transparent substrate 2, acrylic resin, polyolefin resin, glass or the like can be used.

Further, as the phase change material layer 3, Ge,
The composition ratio of Te is 3: 1 to 3: 9, and the composition ratio of Sb and Te is 12: 3 to 12:28.
The composition ratio of Sb and Te can be applied to the optical disc of the present invention as long as it takes an arbitrary value. Especially 2:
Those with values of 2: 5, 1: 2: 4, 1: 4: 7 are high C
/ N (S / N) can be obtained.

The first and second dielectric layers 4 and 5 include nitrides, oxides and sulfides of metals such as Al and Si and semiconductor elements, and these compounds are used in the semiconductor laser wavelength region. It has no absorption and has a thermal conductivity of 0.
Any value in the range of 006 J / cmKs to 0.25 J / cmKs may be used.

Further, as the reflective film 6, any metal such as Al or Au having a good reflectance and thermal conductivity can be used.

Further, in each of the above embodiments, the phase pit 1 is formed on the transparent substrate 2, but the present invention can be applied to the case of forming other optically readable recording pits. Needless to say, various modifications and changes are possible.

[0038]

As described above, according to the present invention, the difference in the reflectance is caused by the difference in the temperature distribution in the read light spot so that the read can be performed only with respect to a specific phase pit in the light spot. Super-resolution reproduction can be performed, and particularly in the present invention, at least the second dielectric layer has a thermal conductivity of 0.006 J / cm.
By using a dielectric having a value of Ks to 0.25 J / cmKs, reproduction with high C / N (S / N) can be performed, and the durability of repeated reading can be significantly improved.

[Brief description of drawings]

FIG. 1 is an enlarged schematic cross-sectional view of a main part of an example of an optical disc.

FIG. 2 is a schematic enlarged cross-sectional view of a main part of another example of an optical disc.

FIG. 3 is a diagram showing a relationship between a light intensity distribution of a laser spot and a temperature distribution of an optical disc.

FIG. 4 is a diagram showing a relationship between a pit length and C / N in one embodiment of the present invention.

FIG. 5 is a pit length and C / N in another embodiment of the present invention.
It is a figure which shows the relationship of.

FIG. 6 is a pit length and C / N in another embodiment of the present invention.
It is a figure which shows the relationship of.

[Explanation of symbols]

 1 Phase Pit 2 Transparent Substrate 3 Phase Change Material Layer 4 First Dielectric Layer 5 Second Dielectric Layer 6 Reflective Film 7 Third Dielectric Layer

Claims (4)

[Claims] 1. At least a first dielectric layer is formed on a transparent substrate on which optically readable recording pits are formed according to an information signal, and a phase change material is formed on the first dielectric layer. A layer is formed, and a second dielectric layer is formed on the phase change material layer, and when the read light is irradiated, the phase change material layer is partially formed in the scanning spot of the read light. An optical disk which is made to be in a liquid phase and whose reflectance is changed, wherein at least the first and second dielectric layers have a thermal conductivity of 0.006 J / cmKs to 0.25 J / cmKs. An optical disc comprising a material. 2. In the phase change material layer, the composition ratio of Ge and Te is 3: 1 to 3: 9 and the composition ratio of Sb and Te is 12: 3 to 12:28. And Sb,
2. The optical disk according to claim 1, wherein a material having an arbitrary Te composition ratio is used. 3. The first and second dielectric layers according to claim 1, wherein a nitride, an oxide, a sulfide of a metal and a semiconductor element, or a mixture thereof is used. The described optical disc. 4. The at least reflective film is formed on the second dielectric layer, and the reflective film is made of a metal having good thermal conductivity and reflectance. 1. The optical disc according to 1.