JPH08306073A - Optical disk - Google Patents

Abstract

PURPOSE: To form a recording layer and an optical shutter layer with the same components and to produce a high density type optical disk without considerably altering a producing process. CONSTITUTION: A recording layer 4 and an optical shutter layer 6 are formed with a phase change material consisting essentially of Fe, Sb and Te and causing a phase change between crystal and amorphous phases under irradiation with light. The ratio of Ge:Sb:Te in the recording layer 4 is regulated to (0.5-1.5):(2.5-4):(3-4.5) and that in the optical shutter layer 6 is regulated to (1.5-3):(1.5-2.5):(4.5-7.5).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk capable of optically recording and reproducing information, and more particularly to an optical disk capable of high density recording and reproducing.

[0002]

2. Description of the Related Art In recent years, increasing the capacity of optical disks has been studied and various proposals have been made. In high density recording of an optical information medium, it is possible to form a recording mark smaller than the light spot diameter by controlling the laser light power during recording. However, in reality, the recording limit depends on the resolution of the medium, the threshold for the light intensity of the medium, and the response speed.

On the other hand, in reproduction, the spot when the laser beam is focused by a lens has a limit value that does not limit it to a certain value or less, and the high density depends on how the playback laser spot can be made small. ing. Repetition wavelength (recording wavelength) of the recording mark at the reproduction limit is λ / 2N
Given by A. Where λ is the wavelength of light and NA is the numerical aperture of the lens. It can be seen that in order to identify and reproduce a mark having a shorter recording wavelength, reproduction with light having a short wavelength λ or a lens with a large NA may be used. However, it is technically difficult to shorten the wavelength of a semiconductor laser used for reproduction, and it is not easy to incorporate a lens having a large NA into a reproduction device for an optical disc.

In addition to these methods, a method of effectively reducing the spot diameter of the reproducing laser beam is "solid state physics".
vol.26 393 (1991). Utilizing the low temperature area and high temperature area in the spot generated during laser irradiation,
Only the high temperature part or low temperature part can be read out. As a result, the effect of substantially reducing the light spot area can be obtained. However, this technique is premised on a rewritable optical disc of a magneto-optical system, and has a problem that it cannot be applied to an optical disc made of other recording material or a read-only optical disc.

On the other hand, in recent years, a nonlinear optical material whose optical characteristics such as light transmittance, reflectance, and refractive index change according to temperature and light intensity is provided on an optical disc in a layered manner, and temperature distribution and light intensity distribution are set in an irradiation spot. By making use of the fact that the difference can be made, a part of the irradiation spot is masked, and research is being conducted to reproduce a minute pit that is less than the reproduction limit determined by the light source wavelength and the lens NA. As the non-linear optical material, an organic dye material whose light transmittance or refractive index reversibly changes according to temperature change or light intensity is used, or a metal-nonmetal of a substance exhibiting a metal-nonmetal transition according to temperature change. There is a method using the difference in refractive index between the two.

[0006]

However, the optical shutter layer using the above organic dye material has a problem that deterioration due to heat during irradiation of light repeatedly causes deterioration of the characteristics and the CN ratio. Further, in the optical shutter layer using the substance exhibiting the metal-nonmetal transition, a VO ₂ film is used as the substance exhibiting the metal-nonmetal transition, but it is difficult to form this VO ₂ film and the substrate. Since heating is required, there is a problem that the substrate selection width is very narrow. Further, the material used for the optical shutter layer is usually composed of a material different from the material used for the recording layer, and the manufacturing process requires a device and a process different from those of the recording layer, and they are continuously used in the same system. Some could not be manufactured and required significant changes to the manufacturing process.

Therefore, the present invention has been made by paying attention to the above points, and it is possible to manufacture the recording layer and the optical shutter layer by using the same component and to manufacture them without significantly changing the manufacturing process. It is an object to provide a high density optical disc.

[0008]

Means for Solving the Problems The present invention provides, as a means for achieving the above-mentioned object, "a main component containing three elements of Ge, Sb, and Te that undergo a phase change between a crystalline phase and an amorphous phase by light irradiation. Has a recording layer made of the phase change material on a light-transmissive substrate, and records a recording mark according to information by utilizing the difference in optical characteristics between the crystalline phase and the amorphous phase of the phase change material. In such an optical disc, the composition ratio of the three elements of Ge, Sb, and Te is made different from that of the recording layer, and when the reproducing laser light for reading the information is irradiated, the optical spot is partially melted. An optical disc having an optical shutter layer configured as described above and reducing the effective spot diameter of the reproduction laser light by the optical shutter layer.

In order to form the recording layer for recording information and the optical shutter layer for reducing the effective spot diameter of the laser light spot from the same material, the present inventor has made the recording layer and the optical shutter layer. It was considered to be composed of a phase change material containing as a main component three elements of Ge, Sb, and Te, which undergo a phase change between a crystalline phase and an amorphous phase by light irradiation. This G
The phase change material consisting of the three elements e, Sb, and Te is used as a rewritable recording layer in recent years, and the crystallization rate can be controlled by changing the composition ratio. Therefore, depending on its composition, it is possible to bring a portion in the laser beam spot having a temperature equal to or higher than a predetermined temperature into a molten state. According to this structure, the refractive index can be locally changed within the spot, and it can be used as an optical shutter layer for super-resolution reproduction. The composition ratio of the three elements of the recording layer is different from that of the optical shutter layer so that the crystallization speed is slower than that of the optical shutter layer. If the recording layer is configured in this way, the recorded information is not erased when the reproducing laser beam is irradiated, and super-resolution reproduction by the optical shutter layer becomes possible.
In addition, recording marks can be recorded on the recording layer by being configured so as to remain in a crystalline state without being in a molten state when irradiated with a recording laser beam.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a sectional view showing the structure of an embodiment of the optical disc of the present invention. The optical disc 1 shown in FIG.
On the light transmissive substrate 2, the first dielectric layer 3, the recording layer 4,
The second dielectric layer 5, the optical shutter layer 6, the reflective layer 7, and the UV curable resin protective film 8 are laminated in this order.

The light transmissive substrate 2 is made of polycarbonate, polyolefin, polymethacrylate ester resin,
A light-transmitting resin such as an epoxy resin, glass, or the like that is used as a conventional optical disk substrate can be used. A guide groove 2A for tracking is formed on the light transmissive substrate 2 in a concentric or spiral shape. The method of forming the guide groove 2A is not particularly limited, and it is formed by a known method.

The first dielectric layer 3 and the second dielectric layer 5 are the thermal damage to the light transmissive substrate 2 or the recording layer 4.
It is provided in order to reduce deformation, evaporation, and thermal deterioration. These dielectric layers 3 and 5 are made of a material having a high refractive index and a low thermal conductivity, and are made of a sulfide or an oxide, or a transparent dielectric obtained by adding a nitride to the sulfide or the oxide. ing. Examples of the sulfides forming the dielectric layers 3 and 5 include ZnS, and examples of the oxides include SiO ₂ , GeO ₂ , BiO ₃ , and WO.
₃ , ZrO ₂ , and AlO ₃ , and examples of the above-mentioned nitride include AlN, Si ₃ N ₄ , TiN, BN, and TaN.
Can be given.

The first dielectric layer 3 is the recording layer 4
It also has a role of causing optical interference in order to read the recording mark recorded on the first recording layer, and the film thickness of the first dielectric layer 3 is determined by the wavelength of the laser beam for reproduction. The second dielectric layer 5 includes the recording layer 4 to the optical shutter layer 6,
It also has a role of adjusting the amount of heat radiation to the reflective layer 7. That is, when the amount of heat radiated to the optical shutter layer 6 and the reflective layer 7 is too large, it is necessary to use a high-power laser light source, and when the laser light is irradiated, a high temperature portion spreads on the recording layer 4. Therefore, it becomes impossible to record a minute recording mark. On the contrary, when the amount of heat radiation is too small, the recording layer 4 is easily deteriorated by heat. Therefore, the second dielectric layer 5 is set in consideration of the heat radiation amount of the recording layer 4. The first dielectric layer 3 and the second dielectric layer 5 may be made of the same dielectric or different dielectrics.

The recording layer 4 and the optical shutter layer 6 are also provided.
Is composed of a compound of at least three elements of Ge (germanium), Sb (antimony), and Te (tellurium), and causes a phase change between an amorphous phase and a crystalline phase by light irradiation. Information is recorded on the recording layer 4 by utilizing the difference in optical characteristics due to the phase change. Further, the optical shutter layer 6 is configured such that a high temperature portion in the reproducing laser light spot is in a molten state and the refractive index locally changes in the spot. Since the optical shutter layer 6 in the molten state has a light transmittance different from that of the unmelted portion, the spot diameter of the reproducing laser light can be substantially reduced.

The recording layer 4 and the optical shutter layer 6 are
As described above, they are made of the same material but have different composition ratios. Since the crystallization speed can be controlled by changing the composition of Ge, Sb, and Te, it is necessary to configure the composition ratio as an optimum for the recording layer or the optical shutter layer. That is, the optical shutter layer 6 is configured to be melted only for a time immediately after being exposed to light, and to return to the original amorphous state immediately after the irradiation of light is stopped. Further, the recording layer 4 has an optical shutter layer 6 when irradiated with a reproducing laser beam.
So that the phase state does not change even when it becomes a melted state, and when irradiated with a recording laser light whose irradiation light intensity is stronger than the reproducing laser light, it does not become a melted state and remains in a crystalline state. Configure.

As an example, Ge ₂ Sb ₂ Te ₅ has a high rate of heating from an amorphous state to a crystalline state, and if heated further from this crystalline state, it easily reaches a molten state. Since the melted portion has a refractive index different from that of the surrounding non-melted portion, it exhibits properties suitable for the optical shutter layer 6.
When this Ge ₂ Sb ₂ Te ₅ is used as the optical shutter layer 6 and Ge ₁ Sb ₃ Te ₄ whose crystal acceleration is slower than this is used as the recording layer 4, the irradiation light intensity of the laser light is adjusted to adjust the inside of the irradiation spot. Ge ₂ Sb ₂ Te ₅ is in a melted state in the high temperature portion, but Ge ₁ Sb ₃ Te ₄ can be kept in a crystalline state, whereby a recording mark can be recorded. Further, when the reproducing laser light whose irradiation light intensity is weaker than the recording laser light is irradiated so that the phase state of the recording layer 4 does not change during reproduction, only the optical shutter layer 6 has a high temperature in the spot. Then, it becomes a molten state and super-resolution reproduction can be performed.

As described above, the composition ratio of the optical shutter layer 6 must be set so that the crystallization speed is higher than that of the recording layer 4.
In the experiment of the present inventor, when the composition ratios of Ge, Sb, and Te are a, b, and c, respectively, the optical shutter layer 6 is 1.5
≦ a ≦ 3, 1.5 ≦ b ≦ 2.5, 4.5 ≦ c ≦ 7.5, and the recording layer 4 has 0.5 ≦ a ≦ 1.5, 2.5 ≦
It has been found that the above-described super-resolution reproduction and recording can be performed within the range of b ≦ 4 and 3 ≦ c ≦ 4.5.

The reflective layer 7 is the same as the metal reflective layer generally used in optical discs, and is composed of a metal having a high light reflectance such as gold or aluminum, or a thin film of an alloy thereof. The protective layer 8 is provided for the purpose of weather resistance and protection of the signal surface, and is made of a UV curable resin (ultraviolet curable resin).

Next, an example of a method of manufacturing the optical disc 1 will be described. The substrate 2 and the target are arranged to face each other in the vacuum chamber, and the inside of the vacuum chamber is evacuated to 4 × 10 ⁻⁴ Pa or less by a vacuum pump in advance.
Ar gas and O ₂ gas are introduced to obtain a predetermined vacuum degree, and Ta
The metal is sputtered to form the first dielectric layer 3 made of TaOx. When the first dielectric layer 3 reaches a predetermined film thickness, the discharge is stopped and Ar gas and O ₂ gas are stopped. Next, after evacuating the vacuum chamber to 4 × 10 ⁻⁴ Pa or less, Ar is introduced, and a target made of Ge, Sb, and Te is sputtered to form the recording layer 4. After that, the target is changed and the second dielectric layer 5 is formed in the same manner as the first dielectric layer 3. After forming the second dielectric layer 5, the optical shutter layer 6 is formed using Ge, Sb, and Te as targets. After forming the optical shutter layer 6, the target is changed and the reflective layer 7 is formed by sputtering to a predetermined thickness. Finally, an ultraviolet curable resin is spin-coated on the reflective layer 7 to form a protective film 8.

As described above, the optical disc 1 is excellent in durability and weather resistance because the optical shutter layer 6 uses the phase change material consisting of Ge, Sb, and Te, which is less likely to be thermally deteriorated. Further, the first dielectric layer 3 to the formation of the reflective layer 7 can be continuously manufactured by changing the target in the same system, and the film forming process of the optical shutter layer 6 is performed by the conventional phase change type optical disk. Since only one step is added to the manufacturing process, a large change in the manufacturing method is unnecessary.

Next, a concrete experimental example will be shown. The atmosphere in the vacuum chamber was evacuated to 3 × 10 ⁻⁴ Pa and then oxygen was introduced to adjust the pressure to 6.0 × 10 ⁻² Pa. Continuously introducing argon to 3.0 × 10 ⁻¹ Pa, current 1.2A, voltage 3
Sputtering of Ta was performed at 90V. 20n film thickness
When it reached m, the discharge was stopped and the first dielectric layer was formed.
After that, the system was evacuated to 4 × 10 ⁻⁴ Pa and then argon was introduced to make 2 × 10 ⁻¹ Pa, and GeSbTe was sputtered at a current of 0.07 A and a voltage of 350 V to form a recording layer having a thickness of 20 nm. did. After that, Ta sputtering is performed again under the same conditions, and a second film with a film thickness of 100 nm is formed.
Of the dielectric layer was formed. After that, G for the optical shutter layer
Sputtering of eSbTe was performed to form an optical shutter layer having a film thickness of 40 nm. Then, aluminum was formed as a reflective film by sputtering to a thickness of 70 nm. In addition,
The GeSbTe target is Ge ₁ S for the recording layer.
b ₃ Te ₄ , Ge ₂ Sb ₂ Te ₅ for the optical shutter layer
Was used.

When the reflectance change due to the temperature of the optical shutter layer of the optical disc constructed as described above was measured at a wavelength of 690 nm, the reflectance change was confirmed at around 180 ° C., and when the film thickness was 10 nm, 25% before melting, It was found that a thin film with a molten state of 5% and a large optical change rate was obtained.

[0023]

As described above, according to the optical disc of the present invention, since the phase change material used for the optical shutter layer has the same composition as the material used for the recording layer, a small change is made to the manufacturing process of the conventional phase change type optical disc. It is possible to manufacture a high-density type optical disc by itself. Further, since the phase change material containing the three elements of Ge, Sb, and Te as the main components is less deteriorated by heat, the number of times of rewriting can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the configuration of an embodiment of an optical disc of the present invention.

[Explanation of symbols]

 1 Optical Disc 2 Light Transmissive Substrate 3 First Dielectric Layer 4 Recording Layer 5 Second Dielectric Layer 6 Optical Shutter Layer 7 Reflective Layer

Claims (2)

[Claims] 1. A recording layer made of a phase-change material containing, as a main component, three elements of Ge, Sb, and Te, which change phase between a crystalline phase and an amorphous phase by light irradiation, is provided on a light-transmissive substrate,
In an optical disc in which a recording mark corresponding to information is recorded by utilizing a difference in optical characteristics between a crystalline phase and an amorphous phase of the phase change material, the composition ratio of the three elements Ge, Sb, and Te The optical shutter layer configured to be partially melted in the light spot when the reproducing laser beam for reading the information is made different from the recording layer. An optical disk characterized in that the effective spot diameter of the laser light for use in the laser is reduced. 2. The optical disc according to claim 1, wherein when the composition ratio of the three elements Ge, Sb, and Te of the recording layer and the optical shutter layer is represented by a, b, and c, the recording layer is 0. 5 ≦ a ≦ 1.5, 2.5 ≦ b ≦ 4, 3 ≦ c ≦ 4.
5 and the optical shutter layer has a thickness of 1.5.
An optical disc, which is configured to be in the range of ≤a≤3, 1.5≤b≤2.5, and 4.5≤c≤7.5.