JP2004220758A - Optical information recording medium and information recording / reproducing method for optical information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a write-once optical information recording medium capable of a high transfer rate and an information recording / reproducing method for the optical information recording medium.
SOLUTION: On a substrate 11 made of polycarbonate, a reflection layer 12, a first dielectric layer 13, a recording layer 14 made of a phase change material, an erasure prevention layer 15, a second dielectric layer 16, and a transparent made of an ultraviolet curable resin. The optical information recording medium is formed by stacking the various cover layers 17. By providing the erasure prevention layer 15 made of cobalt (IV) cobalt (II) (Co ₃ O ₄ ) with a thickness of 1 to 5 nm in contact with the recording layer 14, irradiation of laser light with a wavelength of 500 nm or less is performed. The recording layer 14 that undergoes a phase change from a crystalline phase to an amorphous phase upon receiving is suppressed from changing from an amorphous phase to a crystalline phase again, making it difficult to rewrite information recorded on the recording layer 14.
[Selection diagram] Fig. 1

Description

  The present invention relates to an optical information recording medium and an information recording / reproducing method of the optical information recording medium, and more particularly, to an optical information recording medium which can be used as a write-once medium capable of a high transfer rate, and information recording of the optical information recording medium. Reproduction method.

  In recent years, information such as audio, still images, and moving images as well as computer information has been digitized, and the amount of information handled has become extremely large. There is a need for recording media. In response to this demand, optical information recording media such as DVD-R, DVD-RAM, and DVD-RW have been commercialized. Furthermore, as the processing speed of the CPU is further improved, and peripheral devices and software are being developed and developed, an environment for freely handling enormous image information and audio signals is being prepared. As for the performance, with the increase in capacity, the need for higher speed is increasing more and more.

  Here, an optical information recording medium (optical disk) that records and reproduces information by irradiating laser light is a write-once medium that can be recorded only once and cannot be rewritten, and a rewritable medium that can be repeatedly recorded. It is known that there is. Above all, the write-once medium is not suitable for recording public documents or the like in which information falsification poses a problem because the recording information cannot be rewritten.

  As write-once media, those using an organic dye as a recording material and those using a phase change type are widely used. When the organic dye is used as a recording material, for example, a photosensitive organic dye such as a benzophenone dye, a phthalocyanine dye, a naphthalocyanine dye, or a cyanine dye is used. Among the write-once type media, phase change type media change the phase by irradiating a Te-Ox film or a Te-Ox-Pd film with a laser beam, and detect a change in reflectance accompanying the phase change. Thus, reproduction is performed (see Patent Document 1).

JP-A-61-168151

  From the viewpoint of such high speed required for the optical information recording medium, the following problems exist in the conventional write-once medium. For example, when an organic dye is used as a recording material, recording sensitivity tends to be insufficient when performing high-speed recording by increasing the linear velocity of a medium, and it is difficult to achieve a high transfer rate. There is also a problem that it is difficult to design an organic dye for short-wavelength recording / reproducing light.

  In the case of a write-once type phase change recording film using a Te-Ox film or a Te-Ox-Pd film, the amorphous recording layer is irradiated with a laser beam so that the recording layer has a temperature higher than the crystallization temperature and lower than the melting point. In this phase change process, it takes a long time to complete crystallization, and a high transfer rate is realized. Is difficult.

  On the other hand, among the rewritable media, those using a phase change type material include, for example, Te-Ge, As-Te-Ge, In-Sb-Te, Ga-Sb-Te and the like. An amorphous recording mark is formed by irradiating the formed crystalline recording layer with a laser beam of a high power level to be melted and rapidly cooling from a molten state. As described above, since the recording mark is formed by changing the phase of the crystalline recording layer to amorphous, recording is performed, and the mark formation time is relatively shorter and higher than that of the write-once phase change recording film. Transfer rates may be easier to achieve. Furthermore, since this crystalline recording layer instantaneously absorbs laser light and reaches its melting point, it has higher sensitivity than a write-once medium of a method involving decomposition of an organic dye at the time of recording, and has a recording power of a recording line. It has the advantage that it does not depend much on speed.

Against this background, we have been studying the possibility of using the (crystalline / amorphous) phase change material used in such a rewritable medium as a write-once medium. for example, (1.1 mm substrate / Ag alloy reflective film / ZnS-SiO ₂ protective film / GeSbTe based recording film / ZnS-SiO ₂ protective film /0.1mm cover layer) film surface incident type of rewritable media having a structure of Focused on the phenomenon that direct overwriting is difficult when information is recorded and reproduced using blue laser light having a wavelength of 405 nm. The reason that such a phenomenon occurs is that the beam spot diameter of the blue laser light is smaller than that of the red laser light, and that the heat absorption of the amorphous recording mark is larger than that of the crystalline laser, And the like. For this reason, when the blue laser light is applied to the amorphous recording mark, the time required to crystallize the amorphous mark is shorter than in the case of the red laser light. It is conceivable that the crystallization cannot be performed completely, or the length of the recording mark is not the same between the case where the information is overwritten on the amorphous recording mark and the case where the information is overwritten on the crystalline space.

  However, such a (crystalline to amorphous) phase-change recording material has a problem that it is difficult to use it as a write-once medium for the following reasons. That is, after forming an amorphous recording mark on a crystalline GeSbTe-based recording film by using a laser beam, an operation of irradiating the amorphous recording mark with laser light of a low power level two or three times is performed again. Then, the amorphous recording mark crystallizes, and as a result, the recorded information is completely erased, and new information can be overwritten. Therefore, even when information is recorded and reproduced using blue laser light having a wavelength of 405 nm, it cannot be used as a write-once medium as it is.

  However, even if the rewritable GeSbTe-based recording film is used, an Sb film is provided in contact with the GeSbTe-based recording film, and the GeSbTe-based recording film and the Sb film are mixed by a laser beam irradiated for recording information. At the same linear velocity as at the time of recording, it is possible to make it difficult to rewrite recorded information. However, in this case, the recorded information is rewritten at a linear velocity different from that at the time of recording.

  Thus, the present invention has been made to solve the technical problem of developing a write-once medium using a phase-change type crystalline recording layer used for a rewritable medium. An object of the present invention is to provide a write-once optical information recording medium capable of a high transfer rate and an information recording / reproducing method for the optical information recording medium.

  In order to achieve such an object, the optical information recording medium to which the present invention is applied is characterized in that an erasure preventing layer for suppressing the recording layer from changing from an amorphous phase to a crystalline phase is replaced with a crystalline recording layer. Provided in contact. That is, the optical information recording medium to which the present invention is applied is a substrate, a recording layer provided on the substrate, on which information is recorded by undergoing light irradiation and undergoing a phase change from a crystalline phase to an amorphous phase, An erasure prevention layer provided in contact with the recording layer and for suppressing a phase change from an amorphous phase formed by changing the phase of the recording layer to a crystalline phase. The erasure preventing layer suppresses the reversible phase change of the recording layer from the amorphous phase to the crystalline phase again.

  The erasure prevention layer in the optical information recording medium to which the present invention is applied is characterized by containing an element or a compound which changes physically or chemically at a temperature of 600 ° C. or higher. If such an element or compound is characterized by being oxygen or an oxide, a phase change of the recording layer from an amorphous phase to a crystalline phase is effectively suppressed. Further, the compound is preferably a metal oxide. Specifically, the erasure prevention layer is characterized by being a layer containing at least a cobalt element or a cobalt compound, and preferably has a thickness of 1 nm or more and 5 nm or less. Further, the optical information recording medium to which the present invention is applied is characterized in that the recording layer records and reproduces information by irradiating a laser beam from the substrate side or the side opposite to the substrate.

  The optical information recording medium to which the present invention is applied is formed from a crystalline phase-change recording material, and is provided in contact with the recording layer for recording information by irradiating light having a wavelength of 500 nm or less. And an erasure preventing layer for preventing overwriting of information on the recording layer by light irradiation. The erasure prevention layer may be characterized by containing an element or compound that combines with the phase change material to generate a substance that suppresses overwriting of information on the recording layer. Specifically, the erasure prevention layer is characterized by containing at least cobalt (IV) oxide and cobalt (II). Further, the recording layer is characterized in that the amorphous phase does not change to a crystalline phase when continuous light is irradiated to the amorphous phase formed by changing the phase of the phase change recording material.

  On the other hand, an optical information recording medium to which the present invention is applied includes a substrate and a crystalline recording layer, and a layer containing at least a cobalt element or a cobalt compound is formed on one or both sides of the recording layer. It can be characterized. This recording layer is characterized in that, when it undergoes a phase change from a crystalline phase to an amorphous phase upon irradiation with light having a wavelength of 500 nm or less, a cobalt element or a cobalt compound physically or chemically changes. is there. Further, the recording layer is characterized in that it has a layer containing a cobalt element or a cobalt compound whose crystal structure changes around 900 ° C.

  Further, the present invention provides a recording layer made of a crystalline phase-change recording material formed on a substrate, and a recording layer for preventing an amorphous recording mark formed on the recording layer from being erased. Irradiating the recording layer with laser light having a wavelength of 500 nm or less from the substrate side or the opposite side to the optical information recording medium provided with the erasure preventing layer provided in contact with the optical information recording medium to record or reproduce information; It can be understood as an information recording / reproducing method for an optical information recording medium characterized by the following.

  Incidentally, in the optical information recording medium to which the present invention is applied, the recording layer formed on the substrate, in addition to the case where it is directly formed on the substrate surface, if necessary, between the substrate and the recording layer, For example, the case where the layer is formed via another layer such as a reflective layer, a dielectric layer, and a protective layer is also included.

  Thus, according to the present invention, an optical information recording medium that is effective as a write-once recording medium using a phase-change recording material can be obtained.

Hereinafter, an optical information recording medium to which the present embodiment is applied and a recording / reproducing method for the optical information recording medium will be described in detail with reference to the drawings.
(1st Embodiment)
FIG. 1 is a diagram for explaining the structure of the first embodiment of the optical information recording medium to which the present embodiment is applied. The single-plate type film-surface-incidence type optical disk shown here has a transparent substrate 11, a reflective layer 12, a first dielectric layer 13, and a recording layer made of a phase change material which are sequentially formed on the substrate 11. 14, each layer of an erasure prevention layer 15 and a second dielectric layer 16 provided in contact with the side of the recording layer 14 on which the laser light is incident, and a layer of the second dielectric layer 16 are laminated. A transparent cover layer 17 is formed. The laser light is incident on the recording layer 14 from the cover layer 17 side via the second dielectric layer 16 and the erasure prevention layer 15 to record and reproduce information. For recording and reproducing information, for example, a laser beam having a wavelength of 500 nm or less is used.

  The substrate 11 is formed by, for example, forming a groove having a width of 0.16 μm and a depth of 24 nm at a pitch of 0.32 μm on a surface of a polycarbonate resin plate having a diameter of 120 mm and a thickness of 1.1 mm, and performing injection molding. Disc recognition information, address information, and the like are recorded on the substrate 11 in advance by wobbling grooves. These pieces of information can also be formed by pre-pits. Either a groove or a space between grooves is used as a track for recording information.

  The material of the substrate 11 is not particularly limited, but is usually, for example, an acrylic resin, a methacrylic resin, a polycarbonate resin, a polyolefin resin (especially an amorphous polyolefin), or a polyester resin conventionally used as a substrate material. , A resin made of resin such as polystyrene resin or epoxy resin, a resin made of glass, and a glass provided with a resin layer made of a radiation-curable resin such as a photo-curable resin are all used as the material of the substrate 11. can do. In addition, injection molded polycarbonate is preferable in terms of high productivity, cost, moisture absorption resistance, and the like.

  The reflection layer 12 has a thickness of 50 to 200 nm made of a metal or an alloy. Specifically, for example, metals of Au, Al, Ag, Cu, Ti, Cr, Ni, Pt, Ta, Cr and Pd can be used alone or as an alloy. Further, besides containing these as main components, for example, Mg, Se, Hf, V, Nb, Ru, W, Mn, Re, Fe, Co, Rh, Ir, Cu, Zn, Cd, Ga, In, Si , Ge, Te, Pb, Po, Sn, Bi, and other metals and metalloids.

The first dielectric layer 13 has a thickness of 15 to 35 nm, and the second dielectric layer 16 has a thickness of 50 to 150 nm, and is provided on both sides of the recording layer 14. The material for forming the first dielectric layer 13 and the second dielectric layer 16 is not particularly limited. For example, a mixture of ZnS and SiO ₂ ; SiO ₂ , Al ₂ O ₃ , Cr ₂ O ₃ , SnO ₂ , and Ta Oxides such as ₂ O ₅ ; nitrides such as SiN, GeN, TaN, and AlN.

  The recording layer 14 is a phase change type crystal recording layer made of a phase change type recording material and having a thickness of 6 to 20 nm. The recording layer 14 made of a phase-change recording material is excellent in that deformation is unlikely to occur. The phase-change type crystal recording layer reads and writes data according to a phase change of a substance called crystal / amorphous. Specific examples of the phase-change recording material include, for example, Sb-Te, Ge-Te, Ge-Sb-Te, In-Sb-Te, Ag-In-Sb-Te, and MA-Ge-. Sb-Te system (MA is Au, Cu, Pd, Ta, W, Ir, Sc, Y, Ti, Zr, V, Nb, Cr, Mo, Mn, Fe, Ru, Co, Rh, Ni, Ag, Tl , S, Se and Pt), Sn-Sb-Te system, In-Se-Tl system, In-Se-Tl-MB system (MB is Au, Cu, Pd, Ta, W, Ir , Sc, Y, Ti, Zr, V, Nb, Cr, Mo, Mn, Fe, Ru, Co, Rh, Ni, Ag, Tl, S, Se and Pt), Sn-Sb- Examples include Se-based materials.

  In the present embodiment, the recording layer 14 is formed using such a phase-change recording material, and the recording layer 14 has, for example, a wavelength of 500 nm or less from the transparent cover layer 17 provided on the side opposite to the substrate 11. Recording and reproduction of information are performed by making a laser beam incident. The melting point of the phase-change recording material constituting the recording layer 14 is at least 300 ° C. or higher, preferably 300 ° C. to 800 ° C., and more preferably 600 ° C. to 700 ° C.

  The erasure prevention layer 15 in the film-surface-incidence type optical disc of this embodiment is physically or chemically stable at least at a temperature of about 200 ° C., and at a temperature of 600 ° C. or more, preferably 800 ° C. or more. , A thin layer containing elements or compounds that change physically or chemically. In the present embodiment, the erasure prevention layer 15 is provided in contact with the recording layer 14 made of the phase-change recording material on the side where the laser beam is incident. Here, the physical or chemical change at a temperature of 600 ° C. or higher includes, for example, decomposition, melting, phase transition, phase change, change in crystal structure, and the like. In the film surface incidence type optical disk to which the present embodiment is applied, the temperature when the recording layer 14 made of the phase change type recording material is initialized by irradiating a laser beam is about 200 ° C. The temperature at which information is recorded by irradiating the recording layer 14 with a blue laser beam to record information by a phase change of crystal / non-crystal of the phase change type recording material is considered to be about 600 ° C. or more. Therefore, in the present embodiment, the erasure prevention layer 15 maintains a stable state at the temperature at which the recording layer 14 is initialized, and irradiates the recording layer 14 with a blue laser beam to form the phase change type recording material. Is considered to change physically or chemically at the temperature at which information is recorded by the phase change of crystalline / non-crystalline.

Elements or compounds contained in the erasure prevention layer 15 include oxygen or oxide. Further, the compound contained in the erasure prevention layer 15 is a metal which is physically or chemically stable at a temperature of about 200 ° C. and which physically or chemically changes at a temperature of 600 ° C. or more. Oxides. Examples of such metal oxides, for _{example, Sb 2 O 5, Sb 2} O 4, BaO 2, Bi 2 O 5, Co 2 O 3, Co 3 O 4, MnO 2, PtO, Ag 2 O, TeO 3 And the like. Among them, a metal oxide containing a cobalt element as a metal is preferable, and particularly, cobalt (IV) cobalt (II) (Co ₃ O ₄ ) is preferable. Cobalt (IV) Cobalt (II) has a property of maintaining a stable state at a temperature of about 200 ° C. and decomposing in a temperature range of 800 to 1000 ° C. Cobalt (IV) Cobalt (II) is known to change to cobalt (II) oxide (CoO) at a temperature near 900 ° C. (Constitution of Binary Alloys Second Edition: McGRAW-HILL BOOK COMPANY, 1985) , 487-P.488). Further, the crystal structure changes from the spinel type of cobalt (IV) cobalt (II) oxide to the NaCl type of cobalt (II) oxide. As described above, it is preferable that the erasure prevention layer 15 in the film surface incidence type optical disc of the present embodiment is formed as a thin layer containing at least a Co (cobalt) element or a cobalt compound.
Further, nitrogen or a nitrogen compound can be used as an element or a compound contained in the erasure prevention layer 15. Specific examples of such a nitrogen compound include, for example, Cu ₃ N, Mg ₃ N _{2 and the} like.

  The thickness of the erasure prevention layer 15 is formed in the range of 1 to 5 nm. If the thickness of the erasure preventing layer 15 is too small, overwriting becomes possible, and if the thickness of the erasing preventing layer 15 is too large, light absorption increases and the recording sensitivity decreases.

  In the film surface incidence type optical disc of the present embodiment, the erasure prevention layer 15 is provided in contact with the recording layer 14 on the side where the laser beam is incident, so that the information recorded on the recording layer 14 is erased by the continuous light. Irradiates the crystallizing operation of the amorphous recording mark, the amorphous recording mark does not return to the crystalline state. Therefore, the recorded information is not erased, and new information cannot be overwritten. As a result, the recording layer 14 made of the (crystalline / amorphous) phase change type recording material becomes a write-once medium. Can be used as

  The cover layer 17 is formed with a thickness of 30 to 100 μm. As the material of the cover layer 17, an ultraviolet curable resin obtained by curing a prepolymer component and a monomer component using a photopolymerization initiator such as benzophenone or benzoin ether can be used. Examples of the prepolymer component include polyester acrylate, polyurethane acrylate, epoxy acrylate, and polyether acrylate. Examples of the monomer component include dicyclopentanyl diacrylate, ethylene oxide (EO) -modified bisphenol A acrylate, trimethylpropane triacrylate, and EO-modified trimethylolpropane triacrylate dipentaerythritol hexaacrylate.

Each layer laminated on the substrate 11 in the present embodiment is formed, for example, by the following method. That is, the substrate 11 has a plurality of sputtering chambers, is set in a load lock chamber in a sputtering apparatus having excellent uniformity and reproducibility of the film thickness, and then, after moving the substrate 11 to the first sputtering chamber, Using Ag ₉₈ Ru ₁ Au ₁ (atomic%) as a target, the Ag ₉₈ Ru ₁ Au ₁ reflective layer 12 having a thickness of 50 nm is formed in an argon gas. Next, after moving the substrate 11 to the second sputtering chamber, a mixture of ZnS and SiO ₂ was used as a target, and a 20 nm-thick (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) first mixture was used in an argon gas. The dielectric layer 13 is formed. Next, after moving the substrate 11 to the third sputtering chamber, using a Ge ₃₃ Sb ₁₃ Te ₅₄ (atomic%) sintered target, recording of Ge ₃₃ Sb ₁₃ Te ₅₄ with a thickness of 15 nm in an argon gas. The layer 14 is formed. Next, after moving the substrate 11 to the fourth sputtering chamber, a Co ₃ O ₄ erasure preventing layer 15 having a thickness of 3 nm is formed in an argon gas using a Co ₃ O ₄ sintered target. Next, the substrate 11 is moved to a fifth sputtering chamber, and a (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) second dielectric layer 16 having a thickness of 55 nm is formed in the same manner as the formation of the first dielectric layer 13. Form. Finally, the substrate 11 on which the respective layers are laminated is taken out of the sputtering apparatus, and the uppermost layer (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) is formed on the second dielectric layer 16 with a thickness of 0. A cover layer 17 of 1 mm is formed.

  The initialization of the recording layer 14 of the film surface incidence type optical disc in the present embodiment is performed by, for example, irradiating a laser beam having an elliptical beam having a wavelength of 810 nm, a beam major axis of 96 μm, and a minor axis of 1 μm. In the groove recording / reproduction, the initialized optical disk is rotated at a linear velocity of 5.28 m / sec, and a semiconductor laser beam having a wavelength of 405 nm, for example, having a numerical aperture of 0.85 The light is condensed by the objective lens described above, and tracking is performed by a push-pull method while performing tracking control. For recording, a waveform obtained by modulating the laser power between 4.5 mW and 0.3 mW is used, and a multi-pulse recording waveform for dividing a recording pulse into a plurality of pulses is used.

  A single pattern is recorded in the groove portion on the film-incidence type optical disc in the present embodiment, the reproduction power is 0.3 mW, the resolution bandwidth is 30 kHz, the video bandwidth is 10 Hz, and the C / N ratio is measured by a spectrum analyzer. As a result, when recording was performed on an unrecorded track at a recording frequency of 4.1 MHz, a C / N ratio of 58.5 dB was obtained. When recording was performed on an unrecorded track at a recording frequency of 11.0 MHz, a C / N ratio of 54.5 dB was obtained. The amorphous recording mark length when recorded at a recording frequency of 4.1 MHz is about 0.64 μm, and the amorphous recording mark length when recorded at a recording frequency of 11.0 MHz is about 0.24 μm. .

  In the recording layer 14 of the film-illuminated optical disk according to the present embodiment, the erasing prevention layer 15 is provided in contact with the recording layer 14 on the side of the recording layer 14 where the laser beam is incident. Even if the operation is performed, the amorphous recording mark does not return to the crystalline state. Specifically, a track on which a signal was recorded at a recording frequency of 4.1 MHz was irradiated with continuous light at a laser power of 1.5 mW 30 times, and thereafter, an operation of overwriting a single pattern at a recording frequency of 11.0 MHz was performed. Even if this is performed, only a C / N ratio of 51.0 dB is obtained, and the C / N ratio is reduced by 3.5 dB as compared with a case where a single pattern is recorded in an unrecorded portion at a recording frequency of 11.0 MHz. . This result indicates that the recording layer 14 cannot be overwritten, that is, the film-incidence type optical disc in the present embodiment is a write-once medium using a phase-change recording material used in a rewritable medium. Is effective.

  In the film-incidence type optical disc of the present embodiment, the erasure preventing layer 15 is provided in contact with the recording layer 14 so that the amorphous recording mark can be maintained even when the amorphous recording mark is crystallized by continuous light irradiation. The reason why the result that the recording layer 14 cannot be overwritten without returning to the crystalline state is not clear, but can be considered as follows, for example. That is, when the recording layer 14 is irradiated with a blue laser beam to melt the crystalline recording layer made of the phase-change recording material to record an amorphous recording mark, the temperature at the center of the molten portion is about 1000 ° C. It can be estimated that the substance generated by the bonding of the metal in the molten portion and the oxygen atom of cobalt (IV) cobalt (II) constituting the erasure prevention layer 15 suppresses the crystallization of the amorphous recording mark. It is thought that.

From another point of view, cobalt (IV) cobalt (II) oxide changes into cobalt (II) oxide at a temperature near 900 ° C., whereby the crystal structure is changed to cobalt (IV) cobalt (II) oxide. Is considered to be caused by the change from the spinel type to the NaCl type of cobalt (II) oxide. That is, cobalt (IV) cobalt (II) is a mixed valence oxide in which divalent Co ²⁺ ions and trivalent Co ³⁺ ions are present in one unit cell, and therefore has a crystal structure that is not. It is stable and easily generates defects on the crystal plane. On the other hand, in cobalt (II) oxide, Co ²⁺ forms a regular hexahedron with oxygen atoms, and has a stable crystal structure, so that defects are less likely to occur in the crystal plane. It is generally known that a crystal nucleus is generated very easily when a defect is present on a crystal plane. Thus, when the recording layer 14 is melted during information recording, the erasure prevention layer 15 changes from cobalt (IV) cobalt (II) oxide to cobalt (II) oxide, and the amorphous recording mark of the recording layer 14 is changed. It can be considered that a state occurs in which a crystal nucleus is hardly generated at the boundary surface between the layer and the erasure preventing layer 15, which makes it difficult to crystallize a portion that has once become amorphous.

It should be noted that the Ge ₃₃ Sb ₁₃ Te ₅₄ recording layer 14 formed from the phase change recording material of the film incidence type optical disc in the present embodiment cannot be directly overwritten using a laser beam having a wavelength of 405 nm. That is, even if an overwrite operation is performed on a track on which the recording frequency is recorded at 4.1 MHz and the recording frequency is 11.0 MHz, the C pattern is compared with the case where the single pattern is recorded on the unrecorded portion at the recording frequency of 11.0 MHz. The result is that the / N ratio is reduced by 4.5 dB and overwriting cannot be performed with laser light having a wavelength of 405 nm.

  In addition, when the initialization process using the laser beam having a wavelength of 810 nm is not performed on the film surface incidence type optical disc of the present embodiment, for example, an attempt was made to record and reproduce a semiconductor laser beam having a wavelength of 405 nm using an objective lens having a numerical aperture of 0.85. In such a case, tracking control is difficult. For example, when land / groove recording is performed with the recording frequency set to 4.1 MHz while performing tracking control, the signal amplitude for recording and reproduction is reduced to 1/10 or less as compared with the case where initialization processing is performed. Further, in the present embodiment, the case of the groove (groove) recording of the substrate 11 has been described. However, the same effect can be obtained also when the information is recorded in both the land (land) recording and the land / groove. .

(Second embodiment)
FIG. 2 is a diagram for explaining the structure of the second embodiment of the optical information recording medium to which the present embodiment is applied. In the single-plate type film-surface incident type optical disk shown here, the erasure prevention layer 15 is provided in contact with the recording layer 14 on the side opposite to the side on which the laser beam is incident. As shown in FIG. 2, an Ag ₉₈ Ru ₁ Au ₁ reflective layer 12 having a thickness of 50 nm, a (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) first dielectric layer 13 having a thickness of 18 nm are provided on a substrate 11. 3 nm thick Co ₃ O ₄ erasure prevention layer 15, 15 nm thick Ge ₃₃ Sb ₁₃ Te ₅₄ (at%) recording layer 14, 60 nm thick (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) second The dielectric layer 16 and the cover layer 17 are sequentially laminated. Each layer is formed by the same method as in the first embodiment.

  The recording layer 14 of the film-surface-incidence type optical disc according to the present embodiment is similar to the first embodiment by providing the erasure prevention layer 15 in contact with the recording layer 14 on the side opposite to the side on which the laser beam is incident. In addition, even if a crystallization operation of an amorphous recording mark is performed by continuous light irradiation, a result is obtained in which the recording layer 14 cannot be overwritten. That is, when a track in which a signal was recorded at a recording frequency of 4.1 MHz on an unrecorded track was irradiated with continuous light 30 times at a laser power of 1.5 mW, the recording frequency was changed to 11.0 MHz and a single pattern was overwritten. Is performed, the C / N ratio is reduced by 2.5 dB as compared with the case where recording is performed on an unrecorded track.

  Further, as in the case of the first embodiment, the recording layer 14 cannot be directly overwritten using laser light having a wavelength of 405 nm. That is, when recording is performed at a recording frequency of 4.1 MHz, a C / N ratio of 58.0 dB can be obtained. However, even if an overwrite operation is performed at a recording frequency of 11.0 MHz, compared to the case where recording is performed on an unrecorded track. As a result, the C / N ratio is reduced by 3.5 dB.

(Third embodiment)
FIG. 3 is a cross-sectional view for explaining the structure of the third embodiment of the optical information recording medium to which the present embodiment is applied. The single-plate type film-surface-illuminated optical disk shown here has two erasure prevention layers provided on both sides of the recording layer 14. As shown in FIG. 3, a reflective layer 12 having a thickness of 50 nm made of Ag ₉₈ Ru ₁ Au ₁ (atomic%) and a thickness made of (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) are formed on a substrate 11. A first dielectric layer 13 of 18 nm, a first erasure prevention layer 15 a of Co ₂ O _{4 having} a thickness of 2 nm, a recording layer 14 of Ge ₃₃ Sb ₁₃ Te ₅₄ (atomic%) having a thickness of 15 nm, _A 2 nm thick second erasure prevention layer 15b made of ₃ O _{4, a} 60 nm thick second dielectric layer 16 made of (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%), and a cover layer 17; Are sequentially laminated.

  The recording layer 14 of the film-illuminated optical disk according to the present embodiment has a first erasure prevention layer 15a and a second erasure prevention layer 15b provided on both sides of the recording layer 14, respectively. As in the case, even if the crystallization operation of the amorphous recording mark is performed by continuous light irradiation, a result is obtained in which the recording layer 14 cannot be overwritten. That is, when a track in which a signal was recorded at a recording frequency of 4.1 MHz on an unrecorded track was irradiated with continuous light 30 times at a laser power of 1.5 mW, the recording frequency was changed to 11.0 MHz and a single pattern was overwritten. Is performed, the C / N ratio is reduced by 3.5 dB as compared with the case where recording is performed on an unrecorded track.

  Further, as in the case of the first embodiment, the recording layer 14 cannot be directly overwritten using laser light having a wavelength of 405 nm. That is, when recording is performed at a recording frequency of 4.1 MHz, a C / N ratio of 57.5 dB can be obtained. However, even if an overwrite operation is performed at a recording frequency of 11.0 MHz, compared to the case where recording is performed on an unrecorded track. As a result, the C / N ratio is reduced by 4.0 dB.

FIG. 4 is a diagram for explaining the structure of a conventional optical information recording medium. Here, a single-plate film-surface-incidence type optical disk without an erasure preventing layer is shown. As shown in FIG. 4, a 50 nm thick Ag ₉₈ Ru ₁ Au ₁ (atomic%) reflective layer 12 and a 20 nm thick (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) first A dielectric layer 13, a Ge ₃₃ Sb ₁₃ Te ₅₄ (atomic%) recording layer 14 having a thickness of 15 nm, a (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) second dielectric layer 16 having a thickness of 60 nm, The cover layer 17 is sequentially laminated.

In such a film-surface incident type optical disc as such a conventional optical information recording medium, a track on which a signal is recorded at an unrecorded track at a recording frequency of 4.1 MHz is irradiated with continuous light three times at a laser power of 1.5 mW three times. When the recording frequency is set to 11.0 MHz and a single pattern is overwritten, the same C / N ratio of 55.0 dB is obtained as in the case where recording is performed on the unrecorded track at the recording frequency of 11.0 MHz. This result indicates that when the Co ₃ O ₄ erasure preventing layer is not formed in contact with the Ge ₃₃ Sb ₁₃ Te ₅₄ recording layer 14, the crystallization of the amorphous recording mark proceeds by irradiating the continuous light a plurality of times, This indicates that the medium cannot be used as a write-once medium because overwriting is possible.

  However, such a conventional surface-illuminated optical disc, which is an optical information recording medium, cannot be directly overwritten when a laser beam having a wavelength of 405 nm is used. That is, when recording is performed at a recording frequency of 4.1 MHz, a C / N ratio of 59.0 dB is obtained. Here, the recording frequency is set to 4.1 MHz, and the recording frequency is set to 11.0 MHz. Even if the recording is performed, the C / N ratio is reduced by 1.0 dB as compared with the case where the recording frequency is recorded on an unrecorded track at 11.0 MHz.

(Fourth embodiment)
FIG. 5 is a sectional view for explaining the structure of the fourth embodiment of the optical information recording medium to which the present embodiment is applied. In the laminated type substrate-incident optical disk shown here, the erasure preventing layer 15 is provided in contact with the recording layer 14 on the side where the laser beam is incident. As shown in FIG. 5, a substrate 18, a (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) second dielectric layer 16 having a thickness of ₄₀ nm and a Co ₃ O ₄ having a thickness of 2 nm are formed on the substrate 18. An erasure prevention layer 15, a Ge ₃₃ Sb ₁₃ Te ₅₄ (atomic%) recording layer 14 having a thickness of 20 nm, a (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) first dielectric layer 13 having a thickness of 20 nm, An Al ₉₉ Ti ₁ (wt%) reflection layer 19 having a thickness of 100 nm is sequentially laminated, and a polycarbonate resin plate 18 ′ having a thickness of 0.6 mm is bonded thereon via an ultraviolet-curable resin adhesive layer 20. The recording layer 14 is irradiated with the laser light from the substrate 18 side.

  The substrate 18 has grooves of 0.34 μm in width and 30 nm in depth formed at a pitch of 0.68 μm on the surface of a polycarbonate resin plate having a diameter of 120 mm and a thickness of 0.6 mm by injection molding. Disc recognition information, address information, and the like are recorded on the substrate 18 in advance by wobbling grooves. These pieces of information can also be formed by pre-pits. On this substrate 18, a second dielectric layer 16, an erasure prevention layer 15, a recording layer 14, a first dielectric layer 13, and a reflective layer 19 were sequentially formed. Then, an ultraviolet curable resin adhesive layer 20 was formed on the uppermost layer by spin coating, and bonded to a polycarbonate resin plate 18 'having a diameter of 120 mm and a thickness of 0.6 mm, on which no thin film was formed. The conditions and method for initializing the recording layer 14 of the substrate-incident optical disk manufactured as described above are the same as those described in the first embodiment.

  The recording layer 14 of the laminated substrate-incident type optical disc of the present embodiment is similar to that of the first embodiment by providing the erasure prevention layer 15 in contact with the recording layer 14 on the side where the laser beam is incident. In addition, even if a crystallization operation of an amorphous recording mark is performed by continuous light irradiation, a result is obtained in which the recording layer 14 cannot be overwritten. That is, when a track in which a signal was recorded at a recording frequency of 4.1 MHz on an unrecorded track was irradiated with continuous light 30 times at a laser power of 1.5 mW, the recording frequency was changed to 11.0 MHz and a single pattern was overwritten. Is performed, the C / N ratio is reduced by 3.0 dB as compared with the case where recording is performed on an unrecorded track.

  Further, the recording layer 14 of the laminated substrate-incident optical disk cannot be directly overwritten by using a laser beam having a wavelength of 405 nm. That is, when recording is performed at a recording frequency of 4.1 MHz, a C / N ratio of 54.5 dB is obtained. However, even if an overwriting operation is performed at a recording frequency of 11.0 MHz, compared with the case where recording is performed on an unrecorded track. As a result, the C / N ratio decreases by 5.0 dB.

(Fifth embodiment)
The fifth embodiment of the optical information recording medium to which the present embodiment is applied is a laminated type substrate incident type optical disk, wherein the erasure prevention layer is in contact with the recording layer on the side opposite to the side where laser light is incident. It has a structure provided. Since it has a structure substantially similar to that of the fourth embodiment, the drawing is omitted. The laminated substrate-injected optical disk of this embodiment has a (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) second dielectric layer having a thickness of 40 nm and a Ge ₃₃ Sb ₁₃ Te having a thickness of 20 nm on a substrate. ₅₄ recording layer, 2 nm thick Co ₃ O ₄ erasure preventing layer, 20 nm thick (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) first dielectric layer, 100 nm thick Al ₉₉ Ti ₁ (wt%) A) A reflective layer is sequentially formed, and a polycarbonate resin plate having a diameter of 120 mm and a thickness of 0.6 mm, on which a thin film is not formed, is laminated via an ultraviolet curable resin adhesive layer. The recording layer is irradiated with laser light from the substrate side.

  The recording layer of the laminated substrate-incident optical disk of the present embodiment has an erasure prevention layer provided in contact with the recording layer on the side opposite to the side where the laser beam is incident, so that the amorphous recording mark is formed by continuous light irradiation. When the crystallization operation is performed, the amorphous portion does not return to the crystalline state, and a result that the recording layer cannot be overwritten is obtained. That is, when a track in which a signal was recorded at a recording frequency of 4.1 MHz on an unrecorded track was irradiated with continuous light 30 times at a laser power of 1.5 mW, the recording frequency was changed to 11.0 MHz and a single pattern was overwritten. Is performed, the C / N ratio is reduced by 2.0 dB as compared with the case where recording is performed on an unrecorded track.

  Further, the recording layer cannot be directly overwritten using laser light having a wavelength of 405 nm. That is, when recording is performed at a recording frequency of 4.1 MHz, a C / N ratio of 54.0 dB is obtained. However, even if an overwriting operation is performed at a recording frequency of 11.0 MHz, the C / N ratio is higher than when recording is performed on an unrecorded track. As a result, the C / N ratio is reduced by 2.5 dB.

(Sixth embodiment)
A sixth embodiment of the optical information recording medium to which the present embodiment is applied is a laminated substrate incident type optical disk, in which two erasure preventing layers are in contact with both sides of one recording layer, respectively. It has the structure provided. Since it has substantially the same structure as the third embodiment described above, the drawing is omitted. The laminated substrate-injected optical disk of this embodiment has a (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) second dielectric layer having a thickness of ₄₀ nm and a Co ₃ O _{4 having} a thickness of 2 nm on a substrate. 1 Erase prevention layer, Ge ₃₃ Sb ₁₃ Te ₅₄ recording layer with a thickness of 20 nm, Co ₃ O ₄ second erasure prevention layer with a thickness of 2 nm, (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) with a thickness of 20 nm 1. A dielectric layer and a 100 nm thick Al ₉₉ Ti ₁ (wt%) reflective layer are sequentially formed and bonded to a polycarbonate resin plate having a diameter of 120 mm and a thickness of 0.6 mm where no thin film is formed. You.

  The recording layer of the laminated substrate incident type optical disc of the present embodiment has an erasure prevention layer provided on both sides of the recording layer, so that the amorphous recording mark can be crystallized by continuous light irradiation. As a result, a result is obtained in which the recording layer cannot be overwritten. That is, when a track in which a signal was recorded at a recording frequency of 4.1 MHz on an unrecorded track was irradiated with continuous light 30 times at a laser power of 1.5 mW, the recording frequency was changed to 11.0 MHz and a single pattern was overwritten. Is performed, the C / N ratio is reduced by 3.0 dB as compared with the case where recording is performed on an unrecorded track.

  Further, the recording layer cannot be directly overwritten using laser light having a wavelength of 405 nm. That is, when recording is performed at a recording frequency of 4.1 MHz, a C / N ratio of 53.0 dB can be obtained. However, even if an overwrite operation is performed at a recording frequency of 11.0 MHz, compared to the case where recording is performed on an unrecorded track. As a result, the C / N ratio is reduced by 3.5 dB.

Note that a conventional laminated substrate-injected optical disk without an erasure preventing layer is, for example, a 40 nm-thick (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) second dielectric layer on a substrate; the thickness 20nm _Ge 33 _Sb 13 _{Te 54} recording _layer, (ZnS) 80 _{(SiO 2) 20} and the first dielectric layer having a thickness of 20nm consisting (mol%), a thickness of 100 nm _Al 99 _Ti 1 (wt %) A reflective layer is sequentially formed, and this is laminated with a polycarbonate resin plate having a diameter of 120 mm and a thickness of 0.6 mm on which a thin film is not formed.

  When a laser beam having a wavelength of 405 nm is used, direct overwriting cannot be performed also on the recording layer of such a conventional optical information recording medium, ie, a laminated substrate-incident optical disk. Then, the crystallization of the amorphous recording mark progresses and overwriting becomes possible, so that it cannot be used as a write-once medium.

FIG. 2 is a diagram for describing a structure of an optical information recording medium according to a first embodiment to which the present embodiment is applied. It is a figure for explaining the structure of the 2nd embodiment of the optical information recording medium to which this embodiment is applied. It is a figure for explaining the structure of the 3rd embodiment of the optical information recording medium to which this embodiment is applied. FIG. 9 is a cross-sectional view illustrating a structure of a conventional optical information recording medium. It is a figure for explaining the structure of the 4th embodiment of the optical information recording medium to which this embodiment is applied.

Explanation of reference numerals

11, 18: substrate, 12: reflection layer, 13: first dielectric layer, 14: recording layer, 15: erasure prevention layer, 15a: first erasure prevention layer, 15b: second erasure prevention layer, 16: second Dielectric layer, 17: cover layer, 18 ': polycarbonate resin plate, 19: reflective layer, 20: ultraviolet curable resin adhesive layer

Claims (15)

Board and
A recording layer provided on the substrate, on which information is recorded by undergoing light irradiation and undergoing a phase change from a crystalline phase to an amorphous phase,
An erasure prevention layer provided in contact with the recording layer and suppressing a phase change from an amorphous phase formed to the recording layer to a crystalline phase,
An optical information recording medium comprising:   2. The optical information recording medium according to claim 1, wherein the erasure prevention layer contains an element or a compound that changes physically or chemically at a temperature of 600 ° C. or higher.   3. The optical information recording medium according to claim 2, wherein said element or compound is oxygen or oxide.   3. The optical information recording medium according to claim 2, wherein the compound is a metal oxide.   2. The optical information recording medium according to claim 1, wherein the erasure prevention layer is a layer containing at least a cobalt element or a cobalt compound.   2. The optical information recording medium according to claim 1, wherein the erasure prevention layer has a thickness of 1 nm or more and 5 nm or less.   2. The optical information recording medium according to claim 1, wherein the recording layer records and reproduces information by irradiating a laser beam from the substrate side or a side opposite to the substrate. A recording layer formed from a crystalline phase-change recording material and recording information by irradiating light having a wavelength of 500 nm or less;
An erasure prevention layer provided in contact with the recording layer and preventing overwriting of information on the recording layer by the irradiation of the light,
An optical information recording medium comprising:   9. The optical information recording medium according to claim 8, wherein the erasure prevention layer contains at least cobalt (IV) oxide and cobalt (II).   The recording layer is characterized in that, when continuous light is applied to an amorphous phase formed by changing the phase of the phase-change recording material, the amorphous phase does not change to a crystalline phase. 8. The optical information recording medium according to item 8. Board and
A crystalline recording layer,
An optical information recording medium, wherein a layer containing at least a cobalt element or a cobalt compound is formed on one or both sides of the recording layer.   The optical information recording medium according to claim 11, wherein the recording layer is made of a phase change type recording material.   When the recording layer undergoes light irradiation at a wavelength of 500 nm or less and undergoes a phase change from a crystalline phase to an amorphous phase, the cobalt element or the cobalt compound physically or chemically changes. Item 12. The optical information recording medium according to Item 11.   The optical information recording medium according to claim 11, wherein the recording layer includes a layer containing a cobalt element or a cobalt compound whose crystal structure changes around 900 ° C. A recording layer made of a crystalline phase change recording material formed on a substrate,
An optical information recording medium comprising an erasure prevention layer provided in contact with the recording layer to prevent the amorphous recording mark formed on the recording layer from being erased,
An information recording / reproducing method for an optical information recording medium, comprising irradiating a laser beam having a wavelength of 500 nm or less to the recording layer from the substrate side or the side opposite to the substrate to record or reproduce information.

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