JP2005129176A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a write-once type optical recording medium of a diffusion system which has a simpler structure and is inexpensive. <P>SOLUTION: The write once type optical recording medium of the diffusion system performing recording and reproduction of information by irradiation with a light beam is provided with a first layer containing a transition metal element and a second layer provided in contact with a light beam incident side of the first layer and containing an element 2B. The element 2B of the second layer is diffused into the first layer by irradiation with the light beam and optical characteristics of the first layer are changed to record information. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical recording medium in which information is recorded and reproduced by irradiation with a light beam, and more particularly to a write-once type optical recording medium in which information can be recorded only once.

  Until now, magnetic tape has been the mainstream video recording medium for home use, but in recent years, the spread of the optical recording medium to home video recording medium has been rapidly increasing. By using an optical recording medium instead of a magnetic tape as a video recording medium, a very convenient new function such as follow-up playback becomes possible. However, optical recording media are more expensive than magnetic tape. Therefore, further cost reduction is necessary to further spread the optical recording medium as a video recording medium.

  Optical recording media are classified into several types according to their use and recording method. The write-once type optical recording medium that can record information only once is a write-once type optical recording medium that records information by changing the reflectivity by deforming the recording layer or the substrate by irradiation of the light beam. Perforation type optical recording medium for recording information by forming holes in the recording layer by irradiation, and recording information by changing the optical characteristics of the dye in the recording layer by irradiating with a light beam using a dye material for the recording layer Examples include a dye recording medium. In addition, the rewritable optical recording medium includes a phase change recording medium that uses a phase change material for the recording layer and discriminates information recording / non-recording in a crystalline state or an amorphous state of the phase change material, In addition, there is a magneto-optical recording medium that uses a magnetic material to discriminate information recording / non-recording according to a difference in magnetization direction.

  At present, optical recording media most used as home video recording media are phase change recording media such as DVD-RAM and DVD-RW and dye recording media such as DVD-R. Compared to phase change recording media, dye recording media are inexpensive and advantageous in terms of cost. However, the dye recording medium has a characteristic defect such that the recording signal is easily deteriorated with respect to the reproduction light.

  Recently, as a write-once type optical recording medium other than a dye recording medium, a recording layer is constituted by two layers made of an inorganic material (metal material), and the recording layer is constituted by irradiating the recording layer with a light beam. A so-called diffusion system (also referred to as a reaction system) write-once type optical recording medium has been proposed in which information is recorded by changing the optical characteristics (reflectance) of the recording layer by mixing constituent elements between the layers ( For example, see Non-Patent Document 1 and Non-Patent Document 2.) In the diffusive write-once optical recording medium described in Non-Patent Documents 1 and 2, a reflective layer, a protective layer, a Cu alloy layer, a Si layer, a protective layer, and a cover layer are sequentially laminated on a substrate. A recording layer is formed by the alloy layer and the Si layer. In this diffusive write-once type optical recording medium, information is recorded by irradiating blue-violet laser light from the cover layer side, mixing Si and Cu by the thermal energy of the laser light, and changing the reflectance of the recording layer. .

  The diffusion-type write-once optical recording medium proposed in Non-Patent Documents 1 and 2 substantially eliminates problems such as degradation of the recording signal with respect to the reproduction light, as compared with the dye-type write-once optical recording medium. However, when compared in terms of cost, the cost is lower than that of a phase-change-type rewritable optical recording medium, but the cost is higher than that of a dye-based write-once optical recording medium.

Hiroshi Kubo and 18 others, “Thorough dissection of next-generation optical disc technology (2nd)”, Nikkei Electronics, May 12, 2003, p. 123 Hiroyasu Inoue and five others, “Inorganic Write-Once Disc for High Speed Recording”, Phase Change Optical Information Storage 2002 (2002), 2002 Year, p. 38-42

  The present invention has been made to solve the above-described problems of the prior art, and an object thereof is to provide a diffusion-type write once optical recording medium having a simpler structure and a lower price.

  According to the present invention, there is provided an optical recording medium for recording and reproducing information by irradiation with a light beam, which is provided in contact with a first layer containing a transition metal element and the light beam incident side of the first layer. And an optical recording medium characterized in that information is recorded by changing the optical characteristics of the first layer by irradiation of the light beam.

  In the optical recording medium of the present invention, the transition metal element contained in the first layer is preferably a Group 1B element, and in particular, the Group 1B element contained in the first layer is preferably Cu. .

  In the optical recording medium of the present invention, the Group 2B element contained in the second layer is preferably Zn. The second layer is preferably a dielectric layer containing Zn.

  The optical recording medium of the present invention is a diffusive write-once type optical recording medium, wherein the recording layer includes a first layer containing a transition metal element, and a 2B group element provided in contact with the light beam incident side of the first layer. And a second layer including The present inventors have intensively studied to achieve the above object. As a result, the first layer containing the transition metal element and the group 2B of the periodic table provided in contact with the light beam incident side of the first layer are included. By irradiating and heating an optical recording medium having a recording layer composed of at least two layers including a second layer containing an element, the 2B group element of the second layer is diffused into the first layer. Then, it was found that the optical characteristics (for example, reflectance) of the first layer change, and it was found that information can be recorded by utilizing the change of the optical characteristics.

  The transition metal element contained in the first layer is preferably a group 1B element of the periodic table of elements, Ti, Mn, Fe, Co, Ni, or the like. In particular, considering corrosion resistance and storage stability, Group 1B elements are preferred. Among the group 1B elements, Cu is preferable, and it is possible to further reduce the price by using Cu.

  As the Group 2B element contained in the second layer, Zn is preferable in view of safety to the environment. As the second layer containing Zn, ZnS, ZnO, or the like is preferable.

In addition, a dielectric layer containing Zn such as ZnS—SiO ₂ , ZnS—SnO ₂ , ZnO—SiO ₂ or the like used as a protective layer for protecting the recording layer in a conventional optical recording medium is used in the optical recording medium of the present invention. It may be used as the second layer. Even when a dielectric layer containing Zn such as ZnS—SiO ₂ is used for the second layer, Zn is mainly the first element among the elements constituting the dielectric layer by light beam irradiation during recording. The optical characteristics of the first layer are changed by diffusing to the first layer. In addition, since a dielectric layer containing Zn such as ZnS—SiO ₂ can be used not only as a recording layer but also as a protective layer, it is not necessary to newly provide a protective layer. Therefore, since the number of stacked optical recording media can be reduced, the media structure can be simplified and further cost reduction can be achieved.

  The optical recording medium of the present invention further includes a third layer containing a group 2B element, and the third layer is provided in contact with the side opposite to the light beam incident side of the first layer. Preferably it is. In the optical recording medium of the present invention, the Group 2B element contained in the third layer is preferably Zn. The third layer is preferably a dielectric layer containing Zn.

  The optical recording medium of the present invention may further include a third layer containing a Group 2B element, and the third layer may be provided in contact with the opposite side of the first layer from the light beam incident side. That is, a sandwich structure in which the first layer is sandwiched between the second and third layers may be used. The third layer can be formed of the same material as the second layer. When the recording layer having such a structure is irradiated with a light beam and heated, the 2B group elements of the second and third layers diffuse into the first layer from the surfaces on both sides of the first layer. Therefore, even if the film thickness of the first layer is increased to some extent, the 2B group element of the second and third layers diffuses throughout the film thickness direction of the first layer. As a result, even if the thickness of the first layer is increased to some extent, the difference in optical characteristics between the recorded area and the unrecorded area becomes clear, and information can be recorded and reproduced with higher accuracy.

In the write-once type optical recording medium of the diffusion system of the present invention, the recording layer includes a first layer containing a transition metal element and a second layer containing a Group 2B element provided in contact with the light beam irradiation side of the first layer. It consists of the layers. Therefore, particularly when a Cu layer is used as the first layer and a dielectric layer containing Zn such as ZnS—SiO ₂ is used as the second layer, the film configuration of the optical recording medium can be simplified. can do. As a result, it is possible to provide a diffusion type write-once optical recording medium at a lower price.

  Examples of the optical recording medium of the present invention will be described below, but the present invention is not limited thereto.

[Optical recording medium and recording principle]
FIG. 1 shows a schematic cross-sectional view of a diffusive write-once optical recording medium produced in the example. The optical recording medium 10 manufactured in this example has a structure in which a reflective layer 2, a recording layer 3, and a cover layer 4 are sequentially laminated on a substrate 1, as shown in FIG. As shown in FIG. 1, the recording layer 3 includes a third recording layer 3a (third layer), a first recording layer 3b (first layer), and a second recording layer 3c (second layer) on the reflective layer 2. The layer is laminated in the order of That is, in this example, the recording layer 3 having a sandwich structure in which the first recording layer 3b is sandwiched between the second recording layer 3c and the third recording layer 3a is formed.

  A method for manufacturing the optical recording medium manufactured in this example will be described. First, a Blu-ray Disk standard BD-R substrate made of polycarbonate having a diameter of 120 mm and a track pitch of 0.32 μm was used as the substrate 1. On the surface of the substrate 1, a tracking pregroove having a groove depth of 25 nm is formed in a spiral shape so that the grooves and lands are continuously connected alternately.

Next, an Ag alloy having a thickness of 100 nm was formed on the substrate 1 as the reflective layer 2 by sputtering. Next, (ZnS) ₈₀ (SiO ₂ ) ₂₀ [mol%] was formed as a third recording layer 3a on the reflective layer 2 by sputtering so as to have a thickness of 35 nm.

  Next, Cu was formed to a thickness of 8 nm as the first recording layer 3b on the third recording layer 3a by sputtering. As the first recording layer 3b, in addition to Cu, a Cu alloy such as Cu-MO, Cu-Ti, or Cu-Al, or a 1B group element of Ag or Au may be used. The film thickness of the first recording layer 3b is preferably about 2 to 12 nm. When the film thickness of the first recording layer 3b is thinner than 2 nm, the reflectance becomes too high and the output signal becomes small. On the other hand, when the thickness of the first recording layer 3b is greater than 12 nm, the reflectance becomes too low and the output signal also becomes small.

Next, (ZnS) ₈₀ (SiO ₂ ) ₂₀ [mol%] was formed as a second recording layer 3c with a thickness of 30 nm on the first recording layer 3c by sputtering. In addition to the (ZnS) ₈₀ (SiO ₂ ) ₂₀ , a dielectric layer such as ZnS, ZnO, ZnS—SnO ₂ , ZnO—SiO ₂ or the like can be used as the second recording layer 3c and the third recording layer 3a.

  Finally, 100 μm of an ultraviolet curable resin was formed as the cover layer 4 on the second recording layer 3c. With the above manufacturing method, the diffusive write once optical recording medium 10 shown in FIG. 1 was obtained.

  The principle of information recording in the optical recording medium produced in this example is as follows. At the time of information recording, as shown in FIG. 1, when a predetermined area of the optical recording medium 10 is irradiated with a light beam from the cover layer 4 side, the second recording layer 3c and the third recording layer in the predetermined area heated by the irradiation of the light beam. Of the constituent elements in the layer 3a, mainly Zn enters and diffuses into the first recording layer 3b from the surfaces on both sides of the first recording layer 3b. As a result, the reflectance of the region of the first recording layer 3b where Zn is diffused is higher than the region where Zn is not diffused. That is, in the first recording layer 3b, the reflectance of the portion where the information is recorded by the light beam irradiation is higher than the reflectance of the portion where the light is not irradiated. Information is recorded and reproduced using this change in reflectance.

In the optical recording medium manufactured in this example, since the second recording layer 3c and the third recording layer 3a are formed of (ZnS) ₈₀ (SiO ₂ ) ₂₀ (dielectric layer), the second recording layer 3c The third recording layer 3a can also be used as a protective layer for the first recording layer 3b. That is, in the optical recording medium manufactured in this example, the second recording layer 3c and the third recording layer 3a serve as both the recording layer and the protective layer. Therefore, in the optical recording medium 10 manufactured in this example, it is not necessary to newly provide a protective layer for protecting the recording layer 3, so that the number of laminated magneto-optical recording media can be reduced. As a result, in the optical recording medium manufactured in this example, the film configuration can be made simpler and the cost can be further reduced.

[Recording and playback characteristics]
In this example, an information recording apparatus (including a semiconductor laser (wavelength 405 nm, numerical aperture 0.85), a waveform generator for generating a recording pulse, a laser driver, a waveform equivalent circuit, and a binarization circuit) (Not shown) was used to record information on the optical recording medium produced in this example. In the information recording apparatus used in this example, it is possible to record a recording mark having a shortest mark of 0.16 μm by the mark edge recording method by 1-7PP modulation.

  In this example, using the information recording apparatus, laser light was irradiated from the cover layer side of the optical recording medium, and 3T and 8T continuous mark / space patterns were recorded on the optical recording medium at a linear velocity of 5.28 m / s. . However, T is a clock cycle (= 15.15 ns). The recording frequency is 11 MHz for the 3T pattern and 4.125 MHz for the 8T pattern. In this example, information is recorded only on the groove portion (the convex portion of the substrate when viewed from the light beam side). In addition, information was recorded by changing the recording power from 2 mW to 10 mW.

  Next, the reproduction characteristics were evaluated by irradiating the optical recording medium on which information was recorded as described above with irradiation light, detecting the reflected light from the optical recording medium. The results are shown in FIG. FIG. 2 is a diagram showing the recording power dependence of the signal-to-noise ratio (C / N) in 3T and 8T recording marks recorded on the optical recording medium manufactured in this example. In FIG. 2, the horizontal axis represents the laser beam recording power (Write Power [mW]), and the vertical axis represents the signal-to-noise ratio (C / N [dB]).

  As is apparent from FIG. 2, a C / N of about 40 dB was obtained at a recording power of 10 mW for both 3T and 8T recording marks. Further, as apparent from FIG. 2, it was found that C / N increases as the recording power increases. Therefore, when the recording power is further increased from 10 mW, it is expected that the C / N is further improved.

In the above embodiment, the recording layer 3 having a sandwich structure in which both sides of the first recording layer 3b (Cu) are sandwiched between the second recording layer 3c and the third recording layer 3a ((ZnS) ₈₀ (SiO ₂ ) ₂₀ ) is formed. However, the present invention is not limited to this. The recording layer 3 may be composed of the first recording layer 3b and the second recording layer 3c provided in contact with the light beam incident side of the first recording layer 3b.

In the above embodiment, (ZnS) ₈₀ (SiO ₂ ) ₂₀ is used as the second recording layer 3c and the third recording layer 3a, and the second recording layer 3c and the third recording layer 3a are used as the recording layer / protective layer. However, the present invention is not limited to this. A protective layer may be newly provided separately from the second recording layer 3c and the third recording layer 3a.

  In the above embodiment, the example in which the information is recorded only on the groove portion (the convex portion of the substrate when viewed from the light beam side) has been described, but the present invention is not limited to this. The same effect can be obtained by recording on land (a concave portion of the substrate as viewed from the light beam side) or recording on both land and groove (land / groove recording).

  In the above embodiment, information is recorded using the 1-7PP modulation method, but the present invention is not limited to this. Other modulation schemes such as 8-16 modulation scheme, RLL (2, 7), NRZI, etc. may be used.

  In the above embodiment, a semiconductor laser having a wavelength of 405 nm is used, but the present invention is not limited to this. Even when a laser beam having a longer wavelength, for example, a laser beam having a wavelength near 655 nm, 780 nm, or 830 nm, was used, the same result as in the above example was obtained. In this embodiment, an objective lens having a numerical aperture of 0.85 is used. However, the present invention is not limited to this, and an objective lens having a numerical aperture of 0.45 to 0.7 may be used. Furthermore, the effective numerical aperture may be set to 1 or more in combination with SIL (Solid Immersion Lens), and information may be recorded using evanescent light by SIL.

According to the diffusion write-once optical recording medium of the present invention, the first layer containing the transition metal element and the second layer containing the group 2B element provided in contact with the light beam irradiation side of the first layer In particular, when a Cu layer is used as the first layer and a dielectric layer containing Zn such as ZnS—SiO ₂ is used as the second layer, Since it can serve as both a recording layer and a protective layer, the film configuration of the optical recording medium can be further simplified. As a result, it is possible to provide a diffusion type write-once type optical recording medium at a lower price.

FIG. 1 is a schematic cross-sectional view of a diffusive write-once type optical recording medium manufactured in an example. FIG. 2 is a diagram showing the recording power dependence of the signal-to-noise ratio (C / N) of the diffusion write-once type optical recording medium produced in the example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Reflection layer 3 Recording layer 3a Third recording layer 3b First recording layer 3c Second recording layer 4 Protective layer 10 Optical recording medium

Claims (8)

An optical recording medium for recording and reproducing information by irradiation with a light beam,
A first layer comprising a transition metal element;
A second layer containing a group 2B element provided in contact with the light beam incident side of the first layer,
An optical recording medium, wherein information is recorded by changing the optical characteristics of the first layer by irradiation of the light beam. The optical recording medium according to claim 1, wherein the transition metal element contained in the first layer is a Group 1B element. The optical recording medium according to claim 2, wherein the Group 1B element contained in the first layer is Cu. The optical recording medium according to claim 1, wherein the 2B group element contained in the second layer is Zn. The optical recording medium according to claim 1, wherein the second layer is a dielectric layer containing Zn. Furthermore, it is provided with the 3rd layer containing 2B group element, The 3rd layer is provided in contact with the opposite side to this light beam incident side of the 1st layer, The 1st feature characterized by the above-mentioned. The optical recording medium according to claim 5. The optical recording medium according to claim 6, wherein the 2B group element contained in the third layer is Zn. 8. The optical recording medium according to claim 6, wherein the third layer is a dielectric layer containing Zn.

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