JPH06183152A - Optical disk - Google Patents

Abstract

PURPOSE:To perform ultrahigh resolving power reproduction good in C/N (S/N) by using a Bi-Te alloy in the phase change material layer of an optical disk of an ultrahigh resolving power reproduction system to increase the change quantity of reflectivity as the partial liquid phase state due to temp. distribution. CONSTITUTION:In an optical disk wherein a phase change material layer 4 is formed on a transparent substrate 2 having phase pits 1 optically readable corresponding to a data signal formed therein and partially becomes a liquid phase within the scanning spot of reading light at the time of the irradiation with reading light to change in its reflectivity, a Bi-Te alloy is used in the phase change material layer 4.

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 disk, a signal is read out or reproduced by irradiating the disk surface with a reading light and detecting a large decrease in the amount of reflected light due to the diffraction of the light in the phase pit forming portion. There is.

By the way, in the optical disc as described above, 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 of the reproducing optical system, for example, the semiconductor laser, or increase the numerical aperture NA of the objective lens. Becomes

[0006]

However, the improvement of the wavelength λ of the light source and the numerical aperture NA of the objective lens is naturally limited, and it is difficult to dramatically increase the recording density. 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 ( JP-A-3-292632, Japanese Patent Application No. 3-249511
No.).

The inventions relating to these applications relate to an optical disk 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.

In the present invention, as described above, the super-resolution reproducing system utilizing the reflectance change due to the partial phase change in the reproducing laser beam spot is adopted, and the material and composition of the phase change material layer causing the reflectance change By optimizing, the difference in reflectance between the target read-out phase pit and other parts is made more noticeable and stable and high C / N (carrier / noise ratio) is ensured.
Alternatively, an optical disk capable of performing super-resolution reproduction with a high S / N (sound / noise ratio) is provided.

[0009]

According to the present invention, as shown in FIG. 1 which is a schematic enlarged sectional view of a main part thereof, a transparent substrate having a phase pit 1 which is optically readable according to an information signal is formed. An optical disc having a phase-change material layer 4 formed on the optical disc 2, and when the read-out light is irradiated, the phase-change material layer 4 is partially liquefied in a scanning spot of the read-out light to change the reflectance. In, the phase change material layer 4 is made of a BiTe alloy.

Further, according to the present invention, in the optical disk having the above-mentioned structure, the composition ratio of Bi and Te is 1: 1 to 1: 3.
Select and configure within the range.

[0011]

In the optical disk according to the present invention, the reflectance may change after melting on the transparent substrate 2 on which the phase pits 1 are formed.
The phase change material layer 4 made of a Te alloy is formed, and when the reading light is irradiated, the phase change material layer 4 is partially liquefied in a scanning spot of the reading light, particularly in a high temperature portion, and the reflectance is increased. Changes, and the reflectance is returned to the initial state in a state where the temperature decreases after reading and the recording density is improved, and the difference in reflectance between the target read phase pit and other parts is further improved. It is possible to make it remarkable, and it is possible to more stably and reliably perform super-resolution reproduction with high C / N or high S / N.

That is, in reproducing the recording by the phase pit 1, the temperature distribution in the scanning spot of the reading light is utilized, that is, in the high temperature region generated in the spot, the phase change material layer 4 is partially in the liquid phase state. Can be generated, and the reflectance here can be remarkably increased, for example, so that the phase pits in the liquid phase state portion can be read out by, for example, diffraction.

That is, it is possible to partially form a region where the phase spot optically appears in the read light spot and read only one phase pit, for example, of the plurality of phase pits existing in this spot. You can
Super-resolution reproduction that is not limited to λ / 2NA can be performed.

And, in particular, by appropriately selecting the composition of the BiTe alloy as the material, C / N or S /
N can be improved more stably and reliably. That is Bi
By selecting the material composition ratio of and Te in the range of 1: 1 to 1: 3, the C / N or S / N can be remarkably improved.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1 showing an example of the basic structure of the present invention, a phase change material layer 4 capable of returning to an initial state after melting on a transparent substrate 2 on which phase pits 1 are formed. To form.

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

In the example shown in FIG. 1, the phase change material layer 4 is formed directly on the transparent substrate 2. For example, FIG. On the transparent substrate 2 having the phase pits 1 as shown in FIG.
A phase change material layer 4 is formed via the dielectric layer 3 of the above, a second dielectric layer 5 is further formed thereon, a reflection film 6 is formed thereon, and a third dielectric layer is formed thereon. A layer 7 is formed, and a protective film (not shown) is further formed on the layer 7 if any, and optical characteristics such as reflectance are set by the first and second dielectric layers 3 and 5. It can be configured. Further, the third dielectric layer 7 improves the mechanical strength of the laminated film and improves the repeated read durability.

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 was 1.6 μm, the pit depth was about 120 nm, and the pit length was 0.3 μm (repetition period 0.6 μm).

Then, a first dielectric layer 3 made of ZnS-SiO ₂ having a thickness of 136 nm is deposited on one main surface of the transparent substrate 2 having the pits 1, and a thickness of 34 nm is formed thereon.
The phase change material layer 4 made of Bi ₂ Te ₃ alloy was deposited. On top of this, a ZnS-SiO layer having a thickness of 116 nm is formed.
_{A second} dielectric layer 5 of 2 was deposited. Further, an AlTi reflection film 6 is formed thereon to a thickness of 200 nm, and a ZnS-SiO ₂ film having a thickness of 150 nm is further formed thereon.
The third dielectric layer 7 was deposited and formed.

With respect to the optical disk thus formed, the reproducing power is set to 10 mW and the linear velocity is 3.7 m /
The value of C / N when gradually increasing from s is shown in FIG. When that reproduction was performed and the signal part was reproduced,
The C / N of the signal was 45 dB.

Example 2 In this example as well, the transparent substrate 2 made of the same material as in Example 1 is formed in the case of adopting the structure described in FIG. It was constructed by forming pit 1.

Then, a first dielectric layer 3 made of ZnS-SiO ₂ having a thickness of 146 nm is deposited on one main surface of the transparent substrate 2 having the pits 1, and a thickness of 17 nm is formed thereon.
The phase change material layer 4 made of Bi ₂ Te ₃ alloy was deposited. On top of this, ZnS-SiO with a thickness of 140 nm
_{A second} dielectric layer 5 of 2 was deposited. Further, an AlTi reflection film 6 is formed thereon to a thickness of 200 nm, and a ZnS-SiO ₂ film having a thickness of 150 nm is further formed thereon.
The third dielectric layer 7 was deposited and formed.

For the optical disc thus formed, the reproducing power is set to 10 mW and the linear velocity is 3.7 m /
The value of C / N when gradually increasing from s is shown in FIG. When the signal portion after the reproduction was reproduced, the C / N of the signal was 40 dB.

Comparative Example 1 In this example, the same structure as in Example 1 was used except that the phase change material layer 4 was made of Bi ₂ Te alloy. A reproduction power of 1 is applied to an optical disc formed in this way.
Although it was set to 0 mW and the linear velocity was gradually increased from 3.7 m / s, the signal could not be reproduced.

Comparative Example 2 In this example, the structure was the same as that of the above-described Example 1 except that BiTe ₄ alloy was used for the phase change material layer 4. A reproduction power of 1 is applied to an optical disc formed in this way.
Although it was set to 0 mW and the linear velocity was gradually increased from 3.7 m / s, the signal could not be reproduced.

As can be seen from these results, when the phase change material layer 4 has a composition ratio of Bi and Te of 2: 1 and 1: 4, a reproduction output cannot be sufficiently obtained and it is not practically used. Therefore, in the present invention, the composition ratio is selected to be 1: 1 to 1: 3. In particular, in this example, high C / N could be obtained by selecting the composition ratio as 2: 3. Therefore, it is desirable to select the composition ratio of Bi and Te to be approximately 2: 3.

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

As the dielectric layers 3 and 5, Al,
Examples thereof include nitrides, oxides, and sulfides of metals such as Si and semiconductor elements, and any compound that does not absorb in the semiconductor laser wavelength region may be used.

Further, the reflection film 6 may be made of any metal having good reflectance and thermal conductivity, such as Al, Au and T.
i, Ag, Cu, etc. may be used, and a small amount of additive may be added to these elements.

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 4 is partially in the liquid phase state in the high temperature region generated in the spot. Is generated, and the reflectance here is remarkably increased, for example, the phase pits in this liquid phase state portion can be read with super-resolution by reading by, for example, diffraction.

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. 5, 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 wavy line A in the figure. The distribution is shown. Corresponding to this, the temperature distribution generated in the phase change material layer 4 corresponds to the scanning speed of the laser spot L, and corresponds to the temperature distribution of the solid line B in the figure slightly delayed with respect to the scanning direction of the spot L indicated by the arrow C. The reflectance distribution corresponding to this is obtained.

Here, as described above, the laser spot L
However, if the optical disc is scanned in the direction indicated by arrow C in the figure, the temperature of the optical disc gradually rises from the tip side in the traveling direction of the laser spot L, and then the melting point M of the phase change material layer 4 is reached.
The temperature is P or higher. At this stage, the phase change material layer 4 changes from the initial crystalline state to the molten state, and the transition to this molten state increases the reflectance. That is, the laser beam spot L
In the figure, there are a region Px having a high reflectance, that is, a region Px in which the reading of the phase pit 1 is possible, and a region Pz having a low reflectance, which are shaded in the figure.

Therefore, in this case, even if, for example, two phase pits 1 exist in the same spot L as shown in the figure, only one phase pit 1 existing in the region Px having a high reflectance is read out. For other phase pits, this is in the region Pz where the reflectance is extremely low, and the readout is not performed.
Even if a plurality of phase pits 1 are present in the same spot L as described above, the readout can be performed only for a single phase pit 1, so that the numerical aperture N of the lens system is
A. Super-resolution reproduction is possible without being limited by the wavelength λ of the read light.

On the other hand, in the case of adopting the conventional optical recording method only by changing the reflectance due to the phase change, it is preferable to use a BiTe eutectic alloy as the phase change material layer, for example, Japanese Patent Laid-Open No. 62-200.
It is reported in Japanese Patent Publication No. 544. However, in this case, information is recorded / reproduced by amorphizing the recording pit portion, and the purpose is to obtain a stable amorphous state for a long period of time. For example, the composition ratio of Bi and Te is 15:85. (≈1: 5.7)
It is considered as a degree.

When super-resolution reproduction is performed by directly applying this configuration to the present invention, it is expected from Comparative Example 2 described above that a good reproduction output cannot be obtained.

On the other hand, in the present invention, the BiTe alloy is useful in order to improve the reproduction characteristics in the case of performing super-resolution reproduction as described above, and the composition ratio thereof is particularly 1: 1 to 1. By setting the ratio to be in the range of 3 :, it is possible to more stably and surely improve the reproduction characteristics.

In the above embodiment, the transparent substrate 2
Although the phase pit 1 is formed on the upper side, the present invention can be applied to other optical readable recording pits. Needless to say, various modifications and changes can be made to the material configuration.

[0039]

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. Thus, an optical disc with a high recording density can be obtained which can be reproduced at a high resolution and can be reproduced with a high C / N (S / N) by using a BiTe alloy as a phase change material.

Further, by setting the composition ratio of Bi and Te to 1: 1 to 1: 3, and particularly to a composition of about 2: 3, super-resolution reproduction can be stably and reliably achieved with high C / N or high S / N. It can be performed.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a main part showing a basic configuration of the present invention.

FIG. 2 is a schematic cross-sectional view of an essential part showing the configuration of an embodiment of the present invention.

FIG. 3 is a drawing showing the linear velocity and C / used to explain the first embodiment of the present invention.
It is a figure which shows the relationship of N.

FIG. 4 is a graph showing a linear velocity and C / used for explaining a second embodiment of the present invention.
It is a figure which shows the relationship of N.

FIG. 5 is a diagram showing a relationship between a light spot and a temperature distribution of an optical disc.

[Explanation of symbols]

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

Front page continued (72) Inventor Masumi Ono 6-735 Kitashinagawa, Shinagawa-ku, Tokyo Sony Corporation

Claims (2)

[Claims] 1. A phase-change material layer is formed on a transparent substrate on which optically readable phase pits are formed according to an information signal, and the phase-change material layer is formed when read light is irradiated. In the optical disc in which the reflectance is changed by partially liquefying in the scanning spot of the reading light, a BiTe alloy is used for the phase change material layer. 2. The optical disk according to claim 1, wherein the composition ratio of Bi and Te is selected in the range of 1: 1 to 1: 3.