JP2005092927A - Multilayer optical disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer optical disk where each information recording layer is stably initialized. <P>SOLUTION: In the multilayer optical disk, on a reflection layer 2 provided on the surface of a substrate 1 having a groove part 1a, information recording layers 3 with phase transition material as recording material and an intermediate layer are formed in this order so that the information recording layers may not be less than two layers. On the information recording layer of the top layer, the intermediate layer is not provided. A laser beam L is made incident on a surface opposite to the surface of the substrate. Between the intermediate layer and the information recording layer positioned adjacent to the intermediate layer at a surface side on which the laser beam is made incident, a wavelength selection reflection layer 5 obtained by laminating a plurality of dielectric thin films having different refractive indexes for reflecting 10 % or more initialization laser beams having a wavelength longer than that of recording laser beams is interposed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a multilayer optical disc having a plurality of information recording layers using a phase change material as a recording material.

  An optical disc is known as a recording medium that can record a large amount of information and has a short access time. With the development of today's information society, higher density recording is desired. For example, Blu-ray Disc-Rewriteable (hereinafter “BD”) for blue laser light using phase change recording proposed in 2002 is desired. In other words, the wavelength of the recording / reproducing laser light conventionally used in DVD-RW / RAM is shortened from 650 nm to 405 nm, and the numerical aperture (NA) of the objective lens is 0.6. In addition to an increase in NA to 0.85, a method for newly forming two information recording layers has been added.

In an optical disk typified by BD that performs phase change recording, a phase change recording film or the like is formed by laminating a film using a sputtering apparatus in the manufacturing process, but the phase change recording film is usually in an amorphous state. When recording information, an initialization process for crystallizing the information is required (for example, Patent Document 1).
Here, when two or more information recording layers are laminated, a method of usually initializing a phase change recording film formed first and subsequently initializing a phase change recording film formed later Was taken.
The initialization apparatus uses a focusing system similar to the optical disk recording / reproducing apparatus. However, in order to increase the efficiency of the laser beam used for initialization, a laser beam having a wavelength of about 800 nm can easily obtain a power of 1 W or more. Is used.
JP 2001-250265 A

  By the way, in the conventional optical disc described above, the wavelength of the laser beam for initialization is recorded / reproduced with a laser beam having a wavelength near 400 nm, even though the wavelength of the laser beam for initialization is near 800 nm. It is designed so that the transmittance and reflectance of laser light in the vicinity of 400 nm are optimized. For this reason, the reflectance in the initialization wavelength band of the semi-transparent second information recording layer (information recording layer located on the laser beam incident side) may be insufficient, and the focus may be lost during initialization. There was a problem that it could not be stabilized.

Further, when a large number of information recording layers are stacked, the reflectance of each information recording layer is lowered, and there is a problem that the focus becomes more unstable in the conventional initialization apparatus.
The present invention has been devised to pay attention to the above problems and to effectively solve them. An object of the present invention is to provide a multilayer optical disc in which initialization of each information recording layer can be performed stably by interposing a wavelength selective reflection layer between the intermediate layer and the information recording layer. .

  According to the present invention, an information recording layer using a phase change material as a recording material and an intermediate layer are arranged in this order on the reflective layer provided on the surface of the substrate having a groove portion, so that the information recording layer is at least two layers or more. In the multilayer optical disc that is formed in such a manner that an intermediate layer is not provided for the uppermost information recording layer, and a laser beam is incident from a surface opposite to the surface of the substrate. At least 10% of initialization laser light having a wavelength longer than that of the recording laser light is present between the intermediate layer and the information recording layer positioned adjacent to the surface on which the laser light is incident on the intermediate layer. In order to reflect the above, a multilayer optical disc characterized by comprising a wavelength selective reflection layer formed by laminating a plurality of dielectric thin films having different refractive indexes.

  According to the multilayer optical disk of the present invention, the wavelength selective reflection layer is provided between the intermediate layer and the information recording layer located on the laser beam incident side with respect to the intermediate layer, and the initialization laser beam is protected. Since the reflectance is increased, each information recording layer can be stably initialized.

Hereinafter, an embodiment of a multilayer optical disc according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a partially enlarged sectional view showing a first embodiment of the multilayer optical disc of the present invention, and FIG. 2 is a partially enlarged sectional view showing a second embodiment of the multilayer optical disc of the present invention.
As shown in the drawing, a multilayer optical disc D1 according to the present invention has a substrate 1 on which a groove-like groove portion 1a for tracking is formed. A reflective layer 2 made of, for example, a metal film is formed on the entire surface of the substrate 1 on which the groove portion 1a is formed.

  Then, the first information recording layer 3, the first intermediate layer 4, the first wavelength selective reflection layer 5, the second information recording layer 6, and the recording / reproducing laser beam L are transmitted through the reflective layer 2 of the substrate 1. It consists of a transparent cover layer 7 and is formed by sequentially laminating in this order. The laser beam L is irradiated and incident from the transparent cover layer 7 side. The first information recording layer 3 includes a first lower protective film 3a, a first phase change recording film 3b, and a first upper protective film 3c from the substrate 1 side. The second information recording layer 6 includes a second lower protective film 6a, a second phase change recording film 6b, and a second upper protective film 6c. Further, a heat sink layer 8 having a high thermal conductivity may be provided between the first intermediate layer 4 and the second information recording layer 6 as in the second embodiment shown in FIG.

The substrate 1 is preferably formed by injection molding or injection compression molding using a polycarbonate resin, an acrylic resin, a polyphenylene ether resin, a polybutylene terephthalate resin, a polyolefin resin, or the like, which is advantageous in terms of cost. In particular, it is desirable to use polycarbonate resin, which has a proven record in optical disks. Further, the substrate 1 may be provided with a groove portion 1a formed of an ultraviolet curable resin on a glass plate.
The reflection layer 2 can be formed of a metal reflection film made of, for example, Ag or an Al alloy. The first information recording layer 3 has ZnS—SiO ₂ , SiN, AlN, AlO on and under the first phase change recording film 3 b containing Sb such as Ge—Sb—Te, Ag—In—Sb—Te, for example. The first lower protective film 3a and the first upper protective film 3c made of a dielectric material such as

The initialization of the first information recording layer 3 may be performed at this stage before the first intermediate layer 4 is formed or after the first intermediate layer 4 is formed.
The first intermediate layer 4 is formed of an ultraviolet curable resin that preferably transmits 80% or more of the wavelength λ1 of the recording / reproducing laser beam of the first information recording layer 3. Specifically, this resin is applied by spin coating, and a groove portion 1b serving as a guide groove of the second information recording layer 6 is formed by a 2P method with a stamper such as transparent or translucent quartz. After forming the first intermediate layer 4 by irradiating with ultraviolet rays, the stamper is peeled off.

Here, in the case of a conventional multilayer optical disc having two or more information recording layers, the second information recording layer 6 is formed next. In the present invention, the first wavelength is formed before the second information recording layer 6 is formed. The selective reflection layer 5 is formed. The wavelength selective reflection layer 5 is formed by laminating a plurality of dielectric thin films having different refractive indexes. Specifically, the wavelength selective reflection layer 5 includes a thin film 5a made of a first dielectric having an extinction coefficient smaller than 0.1 and a relatively high refractive index n, and an extinction coefficient smaller than 0.1. In addition, it can be obtained by laminating a thin film 5b made of a second dielectric having a refractive index n smaller than the first dielectric with a predetermined thickness. As a specific representative example, TiO, ZnS—SiO ₂ , SiN, SiO, AlN, MgF, etc. are used, and the refractive index of the wavelength λx to increase the reflectance is nx, and the film thickness is λx / (4 × nx). It can be realized by repeatedly forming two or more layers as a whole by obtaining the relationship. That is, the dielectric thin film may be formed by stacking three or more layers. In the illustrated example, the case of two layers is described as a representative.
Here, regarding the film thickness (λx / (4 × nx)), the first and second information recording layers 3 and 6 can be distinguished in the S-curve characteristic at the time of focusing as shown in FIG. Therefore, the error range of each film thickness is within ± 20%, preferably within ± 10%.

The second information recording layer 6 includes a second lower protective film 6a made of a dielectric material such as ZnS—SiO ₂ , SiN, AlN, AlO, or Sb such as Ge—Sb—Te, Ag—In—Sb—Te, or the like. the second phase change recording film _{6b, ZnS-SiO 2, SiN} , AlN, consists second upper protective layer 6c made of a dielectric material such as AlO, laser for recording and reproduction for the recording and reproduction of the first information recording layer 3 Since it is necessary to transmit the light wavelength λ1 by 40% or more, the thickness of the second phase change recording film 6b having an extinction coefficient of 1 or more is desirably 10 nm or less.
Further, for the purpose of diffusing heat at the time of recording, a metal heat sink layer 8 (see FIG. 2) made of an Ag or Al alloy is formed with a thickness within a range that ensures a transmittance of 40% or more, that is, 10 nm or less. You may do it.

  The initialization of the second information recording layer 6 may be performed at this stage before the transparent cover layer 7 is formed or after the transparent cover layer 7 is formed. The transparent cover layer 7 may be formed by applying an ultraviolet curable resin by spin coating, attaching a transparent polycarbonate sheet having a predetermined thickness thereon, and then irradiating and curing with ultraviolet light. You may form by apply | coating an ultraviolet curable resin by predetermined thickness and irradiating an ultraviolet light and making it harden | cure.

  A dielectric having a different refractive index between the first intermediate layer 4 and the second information recording layer 6 that is translucent and transmits, for example, 40% or more of the recording / reproducing laser beam (wavelength λ1) of the first information recording layer 3 By forming the first wavelength selective reflection layer 5 formed by laminating the films, the wavelength used for information recording / reproduction is low reflection and high transmittance for laser light having a wavelength of, for example, around 400 nm, and the wavelength used for initialization. However, for example, the reflectivity can be increased for laser light in the vicinity of 800 nm, and thus tracking and the like can be performed stably, so that the information recording layers 3 and 6 can be initialized stably. it can. In this case, even if there are three or more information recording layers, the initialization of each information recording layer can be stabilized by providing the wavelength selective reflection layer as described above between the intermediate layer and the information recording layer. Can be done automatically.

  Next, an example of the multilayer optical disc as described above was actually produced and evaluated, and the evaluation result will be described. A comparative example will also be described.

<Example 1: Two-layer information recording layer structure>
The thin films 3a, 3b, and 3c of the reflective layer 2 and the first information recording layer 3 are formed by sputtering on a 1.1 mm thick polycarbonate substrate 1 having a pitch of 0.32 μm and a depth of 23 nm. Filmed. Here, the first lower protective film 3a and the first upper protective film 3c are each made of ZnS—SiO ₂ , the reflective layer 2 is made of an Ag-based alloy, the first phase change recording film 3b is made of GeSbTe, and has a wavelength of 400 nm. The film thickness of each layer was determined so that the reflectivity at 10 was about 20% after initialization. Specifically, the reflective layer 2 is 150 nm, the first lower protective film 3a is 10 nm, the first phase change recording film 3b is 15 nm, and the first upper protective film 3c is 40 nm.

Before forming the first intermediate layer 4, the first information recording layer 3 was initialized with LK201 (trade name) manufactured by Shiba-Soku using a laser beam having a wavelength of 810 nm. The laser power at this time is 400 mW, and the linear velocity is 4 m / sec.
Thereafter, in order to form the first intermediate layer 4, an ultraviolet curable resin (EX8210 (trade name) manufactured by Dainippon Ink Co., Ltd.) is applied by spin coating, and the track guide groove of the second information recording layer 6 is formed. The quartz stamper on which the groove portion was formed was pressed at a predetermined pressure so as to be uniform with a thickness of 20 μm, and cured by irradiating ultraviolet light from the quartz stamper side. Thereby, the first intermediate layer 4 was formed.

Subsequently, the first wavelength selective reflection layer 5 and the second information recording layer 6 were sequentially formed by a sputtering apparatus. The first wavelength selective reflection layer 5 includes a ZnS-SiO ₂ film having a wavelength λi = 810 nm of a laser beam used for initialization, a refractive index n1 of 2.1, and an extinction coefficient k1 of 0.0005. A SiN film having a refractive index n2 of 1.6 and an extinction coefficient k2 of 0.0005 is used, and the film thickness of the ZnS-SiO ₂ film is λi / (4 × n1) = 96 nm, SiN. Similarly, the film thickness was 126 nm (λi / (4 × n2)), and the first wavelength selective reflection layer 5 was formed in a three-layer structure in the order of ZnS—SiO ₂ film, SiN film, and ZnS—SiO ₂ film.

Next, a metal heat sink layer 8 is formed of an Ag-based alloy with a thickness of 7 nm. Next, as the second information recording layer 6, a second lower protective film 6a is formed of ZnS—SiO _{2 with a} thickness of 12 nm. The two-phase change recording film 6b was formed of GeSbTe with a thickness of 5 nm, and the second upper protective film 6c was formed of ZnS—SiO _{2 with a} thickness of 50 nm.
Finally, an ultraviolet curable resin (Dai Nippon Ink Co., Ltd. EX8210 (trade name)) was applied by spin coating to a thickness of 80 μm and cured with ultraviolet light to form a transparent cover layer 7.
In this state, POP-120SE (trade name) manufactured by Hitachi Computer was used to initialize the second information recording film 6 (laser wavelength: 810 nm). It was confirmed that the initialization of the second information recording film 6 was focused and could be performed without any problem.

  The multilayer optical disk of Example 1 was applied to the first information recording layer 3 and the second information recording layer 6 by using a disk evaluation machine LM330A (trade name) manufactured by Shibasoku using a laser beam for recording and reproduction (wavelength: 405 nm). As a result of recording 1-7 modulation signals at a speed of 5.28 m / s, a jitter of 10% or less was obtained, respectively, and good results were obtained.

<Comparative Example 1>
When the first wavelength selective reflection layer 5 is manufactured by using only a ZnS-SiO ₂ film (film thickness: 90 nm) in the same process as in the first embodiment, the focus becomes unstable when the second information recording layer 6 is initialized. Initialization was not satisfactory. This point will be described with reference to FIG. FIG. 4 is a graph showing the relationship of the transmittance with respect to the wavelength of the laser light of Example 1 and Comparative Example 1. 4A shows a graph of Comparative Example 1, and FIG. 4B shows a graph of Example 1. FIG. As shown in the figure, in the vicinity of the wavelength of 810 nm of the laser beam for initialization, in the case of the comparative example 1 shown in FIG. 4A, the reflectance is about 6%, which is very low, whereas in FIG. In the case of Example 1 shown, the reflectance increased to about 14 to 15%, and it was confirmed that good results were obtained.

<Example 2: Three-layer information recording layer structure>
The same processes as in Example 1 were performed until the formation of the second information recording layer 6. Then, POP-120SE (trade name) manufactured by Hitachi Computer was used for the produced second information recording layer 6 to initialize the second information recording layer 6 at a laser power of 600 mW and a linear velocity of 4 m / s (laser). Light wavelength: 810 nm).
Thereafter, in order to form a second intermediate layer (not shown), an ultraviolet curable resin (EX8210 (trade name) manufactured by Dainippon Ink Co., Ltd.) is applied by spin coating, and a third information recording layer (not shown) is formed. The quartz stamper on which the groove portion, which is a track guide groove, was formed, was pressed with a predetermined pressure so as to be uniform with a thickness of 20 μm, and cured by irradiating with ultraviolet light from the quartz stamper side. As a result, a second intermediate layer (not shown) was formed.

Next, a second wavelength selective reflection layer (not shown) was formed. This second wavelength selective reflection layer includes a ZnS—SiO ₂ film having a wavelength λi = 810 nm of a laser beam used for initialization, a refractive index n1 of 2.1, an extinction coefficient k1 of 0.0005, and a laser used for initialization. A SiN film having a light wavelength of 810 nm and a refractive index n2 of 1.6 and an extinction coefficient k2 of 0.0005 is used. The film thickness of the ZnS—SiO ₂ film is λi / (4 × n1) = 96 nm. Similarly, the thickness was 126 nm, and a ZnS—SiO ₂ film, a SiN film, and a ZnS—SiO ₂ film were formed in this order in a three-layer structure.

Next, a metal heat sink layer was formed of an Ag-based alloy with a thickness of 7 nm, and then a third information recording layer (not shown) was formed. In the third information recording layer, the third lower protective film is a ZnS-SiO ₂ film with a thickness of 12 nm, the third phase change recording film is a GeSbTe film with a thickness of 5 nm, and the third upper protective film is a ZnS-SiO ₂ film. Each film was formed to a thickness of 50 nm. Finally, an ultraviolet curable resin (Dai Nippon Ink Co., Ltd. EX8210 (trade name)) was applied by spin coating so as to have a thickness of 60 μm, and cured with ultraviolet light to form the transparent cover layer 7. Thus, a multilayer optical disc having three information recording layers was produced.

Next, POP-120SE (trade name) manufactured by Hitachi Computer was used for the multilayer optical disk of the second embodiment, and the third information recording layer was initialized at a laser power of 600 mW and a linear velocity of 4 m / s (laser). Light wavelength: 810 nm).
The third information recording layer (not shown) was applied to the multi-layer optical disk of Example 2 with a disk evaluation machine LM330A (trade name) manufactured by Shibaoku Co., Ltd. using a recording / reproducing laser beam wavelength of 405 nm. As a result of recording 1-7 modulation signals at / s, jitter of 12% or less was obtained. It was also confirmed that the first information recording layer 3 and the second information recording layer 6 were able to obtain good results of 35 dB or more in C / N at 4 MHz.

Thus, it is shown that the structure of the multilayer optical disc of the present invention can be realized with any number of layers regardless of the number of layers.
In addition, the material of each said layer or each thin film is only an example, and of course is not limited to this.

It is a partial expanded sectional view which shows 1st Example of the multilayer optical disk of this invention. It is a partial expanded sectional view which shows 2nd Example of the multilayer optical disk of this invention. It is a graph which shows an example of the S-shaped curve characteristic at the time of a focus. It is a graph which shows the relationship of the transmittance | permeability with respect to the wavelength of the laser beam of Example 1 and Comparative Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 1a ... Groove part, 2 ... Reflection layer, 3 ... 1st information recording layer, 4 ... 1st intermediate | middle layer, 5 ... 1st wavelength selective reflection layer, 6 ... 2nd information recording layer, 7 ... Transparent cover Layer 8 heat sink layer D1 multilayer optical disk L laser light

Claims (1)

An information recording layer using a phase change material as a recording material and an intermediate layer are formed in this order on the reflective layer provided on the surface of the substrate having a groove portion so that the information recording layer is at least two layers or more. In the multilayer optical disc constructed so that the intermediate layer is not provided for the uppermost information recording layer and the laser beam is incident from the surface opposite to the surface of the substrate,
At least 10 initialization laser light having a wavelength longer than that of the recording laser light is provided between the intermediate layer and the information recording layer positioned adjacent to the surface on which the laser light is incident on the intermediate layer. A multilayer optical disk comprising a wavelength selective reflection layer formed by laminating a plurality of dielectric thin films having different refractive indexes so as to reflect at least%.

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