JP2006179123A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make an information recording density high by realizing super resolution reproduction in an optical recording medium wherein the recording and reproduction of an information signal are performed by emitting laser beams and the recorded information signal can be rewritten. <P>SOLUTION: In the optical recording medium, at least a first dielectric layer 1, a phase change recording layer 2 wherein recording of the information signal is performed by phase change between a crystal phase and an amorphous phase, a second dielectric layer 3, a signal reinforcing layer 4 provided on at least either side of the second dielectric layer 3 and containing metal fine particles and a reflection layer 5 are laminated from a laser beam 21 irradiation side. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a rewritable optical recording medium that records and reproduces an information signal by irradiating a laser beam.

  2. Description of the Related Art Conventionally, an optical recording medium that records or reproduces an information signal by irradiating a laser beam has attracted attention as a player who plays a central role in a recording medium in an advanced information society. For example, “CD” (Compact Disc: trade name) on which music information and computer programs are recorded, and “DVD” (Digital Versatile Disc: trade name) on which image information is recorded are known.

  In these optical recording media, further increase in information recording density is required. The information recording density is limited by the resolution limit of the optical system represented by λ / 4NA, where λ is the wavelength of the laser beam to be irradiated and NA is the function of the objective lens for irradiating this laser beam. Therefore, in order to improve the information recording density, it is necessary to shorten the wavelength λ of the laser beam and increase the objective aperture NA of the objective lens. For example, in “CD”, the wavelength λ of the laser beam is 780 nm and the objective aperture NA of the objective lens is 0.45. However, at present, the wavelength λ of the laser beam is 405 nm, and the objective aperture NA of the objective lens is set to 0. A “blu-ray disc” system has been proposed in which the information recording density is increased as 85.

  However, there is a strong demand for higher information recording density, and realization of an optical recording medium with higher density and larger capacity is desired. For that purpose, it is necessary to further shorten the wavelength λ of the laser beam or to increase the objective aperture NA of the objective lens, but these developments are approaching the limit. Therefore, in order to further increase the information recording density, it is considered necessary to develop a new technology that breaks the resolution limit.

  Here, various so-called super-resolution reproduction methods have been proposed as reproduction methods for breaking the resolution limit. For example, Patent Document 1 uses the fact that the cross-sectional intensity distribution of a laser beam applied to an optical recording medium is a Gaussian distribution, so that the optical characteristics of the surface portion of the optical recording medium are limited only to a portion having a high light intensity. Describes a method of providing a mask layer in which the change is. In this method, the beam diameter of the laser beam can be effectively reduced, so that the reproduction resolution can be improved. However, even if the beam diameter is effectively reduced to increase the resolution, the signal intensity itself obtained from a minute recording mark remains small, and it is difficult to obtain a practically sufficient signal intensity.

On the other hand, Non-Patent Document 1 proposes a system called a “Super-RENS” method as a method for breaking the diffraction limit without using a mask layer. Several structures have been proposed for this “Super-RENS” method, but at present, as described in Non-Patent Document 2, metal oxides such as PtO _X are formed in the vicinity of the phase change recording layer. High characteristics are obtained by using a structure in which layers are arranged.

The reproduction principle of this “Super-RENS” method is still unclear, but it has been confirmed that the metal oxide layer is deformed and metal fine particles are deposited by the laser beam irradiation. It is thought that it acts on the reproduction signal of minute recording marks below the limit. According to this “Super-RENS” method, a high-intensity reproduction signal can be read from a minute recording mark below the diffraction limit.
Japanese Patent Laid-Open No. 11-180043 Jpn.J.Appl.Phy.Vol.39, pp.980-981 (2000) Appl.Phys.Lett (81) 4697 (2002)

  By the way, in the “Super-RENS” type optical recording medium, as described above, deformation of the metal oxide layer and precipitation of metal fine particles occur when the laser beam is irradiated. This phenomenon is irreversible and cannot be restored once deformation or precipitation has occurred. Therefore, when this “Super-RENS” method is applied to an optical recording medium, only a so-called “write-once medium” capable of writing an information signal only once can be formed.

  However, there is a high demand for higher information recording density in “rewritable media” where information signals can be rewritten any number of times, and there is a demand for the realization of super-resolution reproduction on such “rewritable media”. Yes.

  Accordingly, the present invention has been proposed in view of the above-described circumstances, and an optical recording medium capable of recording and reproducing an information signal by irradiating a laser beam and rewriting the recorded information signal. The purpose is to enable super-resolution reproduction and achieve a high information recording density.

  In order to solve the above-described problems, an optical recording medium according to the present invention is an optical recording medium capable of recording and reproducing an information signal by irradiating a laser beam and rewriting the recorded information signal. , From the side irradiated with the laser beam, at least a first dielectric layer, a phase change recording layer for recording information signals by crystal and amorphous phase changes, a second dielectric layer, and A signal enhancement layer containing metal fine particles provided on at least one side of the second dielectric layer and a reflective layer are laminated to each other.

  In this optical recording medium, the signal enhancement layer containing metal fine particles is provided behind the phase change recording layer and on the front side of the reflective layer, as viewed from the laser beam irradiation side, Super-resolution playback is possible.

  In the optical recording medium according to the present invention, the signal enhancement layer containing metal fine particles is provided behind the phase change recording layer and in front of the reflective layer as seen from the laser beam irradiation side. As a result, super-resolution reproduction is possible, and the information recording density is increased.

  That is, the present invention enables super-resolution reproduction on an optical recording medium in which information signals are recorded and reproduced by irradiating a laser beam, and the recorded information signals can be rewritten. High density can be achieved.

  Hereinafter, the best embodiment of the optical recording medium of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a configuration of an optical recording medium according to the present invention.

  As shown in FIG. 1, an optical recording medium according to an embodiment of the present invention has a disk-shaped transparent substrate 11, and a first dielectric layer 1, a phase change recording layer 2, The second dielectric layer 3, the signal enhancement layer 4, the metal reflection layer 5, and the resin protective layer 6 are sequentially laminated. The optical recording medium is irradiated with a laser beam 21 for recording and reproducing information signals from the transparent substrate 11 side. The signal enhancement layer 4 may be formed between the phase change recording layer 2 and the second dielectric layer 3.

  The order in which these layers are stacked is in a system in which a recording / reproducing laser beam 21 is incident from the transparent substrate 11 side, such as “CD” and “DVD”. On the other hand, the optical recording medium according to the present invention can also be configured as an optical recording medium that is irradiated with the laser beam 21 from the opposite side of the transparent substrate 11 like “blu-ray Disc”. In this case, the resin protective layer 6, the metal reflective layer 5, the signal enhancement layer 4, the second dielectric layer 3, the phase change recording layer 2 and the first dielectric layer 1 are sequentially formed on the surface of the transparent substrate 11. The laser beam 21 for recording and reproducing information signals is irradiated from the opposite side of the transparent substrate 11. Alternatively, the resin protective layer 6, the metal reflective layer 5, the second dielectric layer 3, the signal enhancement layer 4, the phase change recording layer 2, and the first dielectric layer 1 are sequentially laminated on the surface of the transparent substrate 11. The laser beam 21 for recording and reproducing information signals is irradiated from the opposite side of the transparent substrate 11.

  The thickness of the transparent substrate 11 is about 0.2 mm to 3 mm, preferably about 0.3 mm to 2 mm. As a material for forming the transparent substrate 11, synthetic resin or ceramic can be used. This synthetic resin includes various thermoplastic resins such as polycarbonate, polymethyl methacrylate, polystyrene, polycarbonate / polystyrene copolymer, polyvinyl chloride, alicyclic polyolefin, polymethylpentene, and various radiation curable resins (ultraviolet rays). A curable resin and a visible light curable resin are preferable. Further, as the ceramic, soda lime glass, soda aluminosilicate glass, borosilicate glass, quartz glass and the like are suitable.

In addition, ZnS—SiO ₂ , SiO ₂ , Al ₂ O ₃ or the like is suitable as a material forming the first and second dielectric layers 1 and ₃ .

  The phase change recording layer 2 is a layer that can record information signals by crystal and amorphous phase changes. As the phase change material forming the phase change recording layer 2, a known phase change recording material such as GeSbTe, AgInSbTe, or CuAlTeSb can be used. In order to improve various characteristics such as environmental characteristics, additives such as titanium (Ti) and indium (In) may be added to these materials.

  As the material forming the metal reflection layer 5, a known high reflectivity material can be used. For example, aluminum (Al), gold (Au), silver (Ag), copper (Cu), titanium (Ti), chromium (Cr), nickel (Ni), tantalum (Ta), molybdenum (Mo), iron (Fe), zinc (Zn), gallium (Ga), arsenic (As), palladium (Pd), or other metals, or these (Including oxides, nitrides, carbides, sulfides and fluorides) are preferred. In particular, aluminum, silver, and gold are suitable.

The signal enhancement layer 4 is a thin film layer containing metal fine particles, and a dielectric such as SiO ₂ or Al ₂ O ₃ is coated with silver (Ag), gold (Au), copper (Cu), platinum (Pt), or the like. A layer in which metal fine particles are dispersed or an oxide thin film layer of these metals may be used.

  When a metal oxide thin film layer is used as the signal enhancement layer 4, no metal fine particles are present in the film immediately after film formation. And after laminating | stacking each layer, a metal fine particle is produced | generated in a film | membrane by thermally decomposing the oxide in a film | membrane by irradiating a laser beam, and the signal enhancement layer 4 is completed.

  The layer thickness of each of the above-mentioned layers can be appropriately set as appropriate according to the selected material.

  In this optical recording medium, the presence of the signal enhancement layer 4 provides the following effects. That is, when the information signal is read from the phase change recording layer 2 by irradiating the phase change recording layer 2 with the laser beam 21, the enhancement effect of the near-field light by the metal fine particles in the signal enhancement layer 4 is obtained. Near-field light is light that is generated on the surface of an object by light irradiation and does not normally propagate far away. However, if the near-field light can be observed by various methods, a minute recording mark can be reproduced without depending on the resolution of the optical system. That is, as a reproduction principle of this optical recording medium, the near-field light generated in the vicinity of the recording mark is scattered by the metal fine particles in the signal enhancement layer 4 and converted to propagating light so that it can be observed. It is considered that strong reproduction light is generated by resonating with surface plasmons generated by metal fine particles.

  Therefore, in this optical recording medium, super-resolution reproduction is possible and information recording density is increased. An irreversible reaction is not included in the process of recording and reproducing information signals on this optical recording medium. Therefore, this optical recording medium can be rewritten any number of times, and is configured as a “rewritable” optical recording medium.

  Specific examples will be described below.

[Example 1]
A transparent substrate 11 having a diameter of 120 mm on which lands / grooves having a track pitch of 0.74 μm and a groove depth of 30 nm were formed by injection molding using polycarbonate as a material. On this transparent substrate 11, a first dielectric layer 1 is a ZnS-SiO ₂ layer having a thickness of 64 nm, a phase change recording layer 2 is an AgInSbTe layer having a thickness of 15 nm, and a second dielectric layer 3 is a layer. A ZnS—SiO ₂ layer having a thickness of 14 nm, an Ag + SiO ₂ layer having a thickness of 10 nm as the signal enhancement layer 4, and an AgPdCu alloy layer having a thickness of 100 nm as the metal reflection layer 5 were formed by sputtering.

The signal enhancement layer 4 was formed by placing an Ag chip on a SiO ₂ target. The first dielectric layer 1, the phase change recording layer 2, the second dielectric layer 3, the signal enhancement layer 4, and the metal reflection layer 5 were formed in the same sputtering apparatus. Thereafter, the protective layer 6 was formed by spin coating using an acrylic ultraviolet curable resin.

[Example 2]
The signal enhancement layer 4 in Example 1 was replaced with a platinum oxide layer having a layer thickness of 15 nm, and other layers were formed in the same manner as in Example 1 to produce an optical recording medium.

  The platinum oxide layer was formed by sputtering using a platinum target in an atmosphere in which oxygen was added to argon (Ar). At this time, the flow rate of argon was 15 sccm, and the flow rate of oxygen was 6 sccm.

  In a phase change type optical recording medium, in general, before recording / reproduction, an amorphous phase change recording layer is crystallized immediately after the layering, so that an operation called initialization is performed in which a heat treatment is performed by irradiating a laser beam. Is called. This initialization is performed in the same manner for the optical recording medium of Example 1 and the optical recording medium of a comparative example described later. However, in the optical recording medium of Example 2, a metal oxide layer (oxidation layer) is formed by heat treatment by this initialization. The metal oxide in the platinum layer) is thermally decomposed to produce metal fine particles.

[Comparative Example]
FIG. 2 is a cross-sectional view showing a configuration of an optical recording medium in a comparative example.

  In this comparative example, as shown in FIG. 2, the signal enhancement layer 4 is not provided, the thickness of the metal reflective layer 5 made of an AgPdCu alloy layer is set to 200 nm, and the rest is the same as in the optical recording medium in Example 1. Configured. The configuration of Comparative Example 1 is the same as that of a conventional phase change optical recording medium.

[Contrast between each example and comparative example]
Table 1 below shows the jitter value of the reproduction signal in the optical recording media of the examples and comparative examples. The jitter value is one of numerical values indicating the recording / reproducing characteristics of the optical recording medium, and the lower the value, the better. In the optical system used here, the wavelength λ of the laser beam was 635 nm, and the objective NA of the objective lens of the optical pickup was 0.6. The recording power was optimized for each optical recording medium, and the reproduction power was fixed at 0.7 mW. The recording capacity shown in [Table 1] is a value per one disk having a diameter of 120 mm, which is changed by changing the linear velocity.

  As shown in [Table 1], in the recording capacity corresponding to “DVD”, the jitter value is a low value of around 7% in each of the examples and the comparative examples. By increasing the capacity and recording at a high density, the jitter value gradually deteriorates. However, in each of the examples, the upward trend of the jitter value is moderate, and the jitter value is lower than 15% at which the system fails even at the time of high density recording equivalent to 6 GB. This indicates that the optical recording medium according to the present invention is effective for high-density recording. It was also confirmed that in the optical recording medium of each example, the recording signal could be performed in the same way as a normal phase change optical recording medium, and that the information signal could be erased and rewritten.

It is sectional drawing which shows the structure of the optical recording medium based on this invention. It is sectional drawing which shows the structure of the optical recording medium in a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st dielectric material layer 2 Phase change recording layer 3 2nd dielectric material layer 4 Signal enhancement layer 5 Metal reflective layer 6 Resin protective layer 11 Transparent substrate 21 Laser beam

Claims (1)

An optical recording medium that records and reproduces an information signal by irradiating a laser beam, and can rewrite the recorded information signal,
From the side irradiated with the laser beam, at least a first dielectric layer, a phase change recording layer for recording information signals by crystal and amorphous phase changes, a second dielectric layer, and An optical recording medium comprising: a signal enhancement layer containing metal fine particles provided on at least one side of a second dielectric layer; and a reflection layer.

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