JP3830938B2 - Optical information recording medium and information recording / reproducing method of optical information recording medium - Google Patents

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 specifically, an optical information recording medium that can be used as a write-once medium capable of a high transfer rate and information recording of the optical information recording medium. It relates to a playback method.

  In recent years, not only computer information but also information such as voice, still images, and moving images has been digitized, and the amount of information handled has become extremely large. Accordingly, information that can record and reproduce large amounts of data at high density and at high speed can be obtained. There is a need for a recording medium. 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 the development and development of peripheral devices and software are progressing, an environment for freely handling enormous amounts of image information and audio signals is now being prepared, which is required for optical information recording media. As performance increases, the need for higher speed is increasing more and more.

  Here, an optical information recording medium (optical disk) that records and reproduces information by laser light irradiation 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. In particular, write-once media are not suitable for rewriting recorded information, and are therefore suitable for recording official documents and the like in which falsification of information is a problem.

  As write-once media, those using organic dyes as recording materials and those of phase change type are widely used. A material using an organic dye as a recording material uses a photosensitive organic dye such as a benzophenone dye, a phthalocyanine dye, a naphthalocyanine dye, or a cyanine dye. Further, among the write-once media, the phase change type media changes the phase by irradiating a Te-Ox film, Te-Ox-Pd film or the like with laser light, and detects a change in reflectance accompanying this 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 conventional write-once medium has the following problems. For example, when an organic dye is used as the recording material, the recording sensitivity tends to be insufficient when performing high-speed recording by increasing the linear velocity of the medium, and it is difficult to realize a high transfer rate. There is also a problem that it is difficult to design an organic dye for recording / reproducing light having a short wavelength.

  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, and the recording layer is heated to a crystallization temperature or higher and lower than the melting point. The crystal grains are grown by raising the temperature up to the temperature of 1 to form crystal recording marks, but in the process of this phase change, it takes a long time to complete crystallization, realizing a high transfer rate Is difficult.

  On the other hand, among the rewritable media, those using a phase change material are, for example, Te—Ge, As—Te—Ge, In—Sb—Te, Ga—Sb—Te, and the like. An amorphous recording mark is formed by irradiating and melting a high power level laser beam on the crystalline recording layer to be formed, and rapidly cooling from the molten state. As described above, since the recording mark forming method records the crystalline recording layer by changing the phase to amorphous, the mark formation time is relatively short compared to the write-once phase change recording film, There is a possibility that the transfer rate is easy to realize. Furthermore, since this crystalline recording layer instantaneously absorbs the laser beam and reaches the melting point, it has higher sensitivity than a write-once medium that involves decomposition of the organic dye during recording, and the recording power is the recording line. It has the advantage of not relying heavily on speed.

Against this background, we were studying the possibility of using the (crystalline / amorphous) phase change material used in such a rewritable medium as a write-once medium, For example, a film surface incident type rewritable medium having a configuration of (1.1 mm substrate / Ag alloy reflective film / ZnS—SiO ₂ protective film / GeSbTe-based recording film / ZnS—SiO ₂ protective film / 0.1 mm cover layer) Focused on the phenomenon that direct overwriting is difficult when recording and reproducing information using a blue laser beam having a wavelength of 405 nm. The reason why 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 rate of the amorphous recording mark is larger than the heat absorption rate of the crystalline material, Etc. For this reason, when the amorphous recording mark is irradiated with the blue laser light, the time required to crystallize the amorphous mark is shorter than that of the red laser light. It may be impossible to crystallize completely, or the lengths of the recording marks may not be the same when the information is overwritten on the amorphous recording mark and when the information is overwritten on the crystalline space.

  However, such a (crystalline → amorphous) phase change recording material has a problem that it is difficult to use as a write-once medium for the following reasons. That is, after an amorphous recording mark is formed on a crystalline GeSbTe-based recording film using a laser beam, an operation of irradiating the amorphous recording mark with a low power level laser beam 2 to 3 times is performed again. As a result, the amorphous recording mark crystallizes, and as a result, the recorded information is completely erased, and overwriting of new information becomes possible. For this reason, even when information is recorded / reproduced using a blue laser beam having a wavelength of 405 nm, it cannot be used as a write-once medium.

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

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

In order to achieve such an object, an optical information recording medium to which the present invention is applied has an erasure preventing layer for suppressing a phase change from an amorphous phase to a crystalline phase in the crystalline recording layer. They are in contact. That is, an optical information recording medium to which the present invention is applied includes a substrate, a recording layer provided on the substrate, on which information is recorded by phase change from a crystalline phase to an amorphous phase upon receiving light irradiation, An erasure that is provided in contact with the recording layer, suppresses a phase change from an amorphous phase formed by changing the phase of the recording layer to a crystalline phase , and contains a metal oxide containing a cobalt element as a main component. And a prevention layer. This erasure preventing layer suppresses the reversible phase change of the recording layer from the amorphous phase to the crystalline phase again.

The metal oxide containing cobalt element contained in the erasure prevention layer in the optical information recording medium to which the present invention is applied is characterized in that it changes physically or chemically at a temperature of 600 ° C. or higher. Such a metal oxide containing a cobalt element effectively suppresses the phase change of the recording layer from the amorphous phase to the crystalline phase. Specifically, the erasure prevention layer is a layer containing at least cobalt tetroxide (Co ₃ O ₄ ), and the erasure prevention layer preferably has a thickness of 1 nm to 5 nm. . Furthermore, 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.

An optical information recording medium to which the present invention is applied is formed of a crystalline phase change recording material, and is provided in contact with a recording layer for recording information by irradiating light with a wavelength of 500 nm or less. And an erasure preventing layer containing cobalt trioxide (Co ₃ O ₄ ) as a main component , which prevents overwriting of information on the recording layer by light irradiation. . This erasure prevention layer contains an element or compound that forms a substance that combines with the phase change material and suppresses overwriting of information to the recording layer . Furthermore, the recording layer is characterized in that when the amorphous phase formed by changing the phase of the phase change recording material is irradiated with continuous light, the amorphous phase does not change into a crystalline phase.

Furthermore, the present invention provides a recording layer made of a crystalline phase change recording material formed on a substrate, and an amorphous recording mark formed on the recording layer in order to prevent the recording layer from being erased. A laser beam having a wavelength of 500 nm or less is applied to an optical information recording medium provided in contact with the optical information recording medium provided with an erasure prevention layer containing cobalt tetroxide (Co ₃ O ₄ ) as a main component from the substrate side or the side opposite to the substrate. It can be grasped as an information recording / reproducing method of an optical information recording medium characterized in that information is recorded or reproduced by irradiating the recording layer.

  In the optical information recording medium to which the present invention is applied, the recording layer formed on the substrate is formed directly on the surface of the substrate, and if necessary, between the substrate and the recording layer, For example, the case where it forms via other layers, such as a reflection layer, a dielectric material layer, and a protective layer, is also included.

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

Hereinafter, an optical information recording medium to which this embodiment is applied and a recording / reproducing method of the optical information recording medium will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 is a diagram for explaining the structure of a first embodiment of an optical information recording medium to which the present embodiment is applied. The single-plate type film surface incidence type optical disk shown here includes 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 of an erasure prevention layer 15 provided in contact with the laser beam incident side of the recording layer 14 and a second dielectric layer 16 are laminated, and further, an ultraviolet curable resin is formed on the second dielectric layer 16 A transparent cover layer 17 is formed. Laser light is incident on the recording layer 14 from the cover layer 17 side via the second dielectric layer 16 and the erasure preventing layer 15 to record and reproduce information. For information recording / reproduction, for example, laser light having a wavelength of 500 nm or less is used.

  For example, the substrate 11 is formed by injection molding on a surface of a polycarbonate resin plate having a diameter of 120 mm and a thickness of 1.1 mm, with grooves having a width of 0.16 μm and a depth of 24 nm formed at a pitch of 0.32 μm. On this substrate 11, disk recognition information, address information, and the like are recorded in advance by groove wobble. Such information can also be formed by pre-pits. Note that either a groove or a space between grooves is used as an information recording track.

  Although it does not specifically limit as a material of the board | substrate 11, Usually, conventionally used as a board | substrate material, for example, acrylic resin, methacrylic resin, polycarbonate resin, polyolefin resin (especially amorphous polyolefin), polyester resin Any of those made of resin such as polystyrene resin and epoxy resin, glass, and a resin layer made of a radiation curable resin such as a photocurable resin on the glass are used as the material of the substrate 11. can do. In view of high productivity, cost, moisture absorption resistance, etc., injection molded polycarbonate is preferable.

  The reflective layer 12 is made of metal or alloy and has a thickness of 50 to 200 nm. 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. In addition to 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, 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 , Ta Examples thereof include oxides such as ₂ O ₅ ; nitrides such as SiN, GeN, TaN, and AlN.

  The recording layer 14 is composed of a phase change recording material and is a phase change crystal recording layer having a thickness of 6 to 20 nm. The recording layer 14 made of a phase change recording material is excellent in that it hardly deforms. The phase change type crystal recording layer reads and writes data by the phase change of the crystalline / non-crystalline substance. 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 series (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, In—Se—Tl, In—Se—Tl—MB (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 thereof include Se-based materials.

  In the present embodiment, the recording layer 14 is formed using such a phase change recording material, and the wavelength of, for example, 500 nm or less is applied from the transparent cover layer 17 side provided on the recording layer 14 on the side opposite to the substrate 11. Information is recorded / reproduced by entering laser light. 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., more preferably 600 ° C. to 700 ° C.

  The erasure preventing layer 15 in the film surface incident type optical disc of the present embodiment is physically or chemically stable at least at a temperature of about 200 ° C., and at a temperature of 600 ° C. or higher, preferably 800 ° C. or higher. , A thin layer containing an element or compound that changes physically or chemically. In the present embodiment, the erasure prevention layer 15 is provided in contact with the laser beam incident side of the recording layer 14 made of a phase change recording material. Here, the physical or chemical change at a temperature of 600 ° C. or higher includes, for example, decomposition, melting, phase transition, phase change, crystal structure change, and the like. In the film surface incident type optical disc to which the present embodiment is applied, the temperature at which the recording layer 14 made of the phase change recording material is initialized by being irradiated with laser light is about 200 ° C. In addition, it is considered that the temperature at which information is recorded by irradiating the recording layer 14 with blue laser light and recording information by the phase change of crystal / amorphous of the phase change recording material is 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 the recording layer 14 is irradiated with blue laser light to thereby change the phase change recording material. It is considered that the temperature changes when the information is recorded due to the phase change of crystal / non-crystal.

The compound contained as a main component in the erasure prevention layer 15 is a metal that is physically or chemically stable at a temperature of about 200 ° C. and changes physically or chemically at a temperature of 600 ° C. or higher. It is an oxide. Examples of such metal oxides include metal oxides containing a cobalt element as a metal , such as Co ₂ O ₃ and Co ₃ O ₄ . Among these, cobalt tetroxide (Co ₃ O ₄ ) is particularly preferable. Tricobalt tetraoxide (Co ₃ O ₄ ) maintains a stable state at a temperature of about 200 ° C. and exhibits a property of decomposing in a temperature range of 800 to 1000 ° C. It is known that cobalt tetraoxide (Co ₃ O ₄ ) changes to cobalt oxide (II) (CoO) at a temperature around 900 ° C. (Constitution of Binary Alloys Second Edition: McGRAW-HILL BOOK COMPANY, 1985, P.487-P.488). Further, the crystal structure changes from the spinel type of tribasic cobalt oxide (Co ₃ O ₄ ) to the NaCl type of cobalt (II) oxide (CoO) .
Thus, it is preferable that the erasure prevention layer 15 in the film surface incident type optical disk of the present embodiment is formed as a thin layer containing at least cobalt tetroxide (Co ₃ O ₄ ) as a main component .
Further, as another element or compound contained in the erasure prevention layer 15, nitrogen or a nitrogen compound can be used. Specific examples of such nitrogen compounds include 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 nm to 5 nm. If the thickness of the erasure prevention layer 15 is excessively small, overwriting becomes possible, and if the thickness of the erasure prevention layer 15 is excessively large, light absorption increases and recording sensitivity decreases.

  In the film surface incident type optical disk of the present embodiment, the erasure prevention layer 15 is provided in contact with the laser beam incident side of the recording layer 14, thereby erasing information recorded on the recording layer 14. Even if the amorphous recording mark is crystallized by irradiating with, the amorphous recording mark does not return to crystalline. Therefore, the recorded information is not erased, and overwriting of new information cannot be performed. As a result, the recording layer 14 made of a (crystalline / amorphous) phase change recording material has a write-once medium. Can be used as

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

Each layer laminated | stacked on the board | substrate 11 in this embodiment is formed with the following method, for example. That is, the substrate 11 has a plurality of sputtering chambers and is installed in a load lock chamber in a sputtering apparatus having excellent film thickness uniformity and reproducibility. Next, after moving the substrate 11 to the first sputtering chamber, Ag ₉₈ Ru ₁ Au ₁ (atomic%) is used as a target, and 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 (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) first having a thickness of 20 nm in argon gas. The dielectric layer 13 is formed. Next, after moving this substrate 11 to the third sputtering chamber, recording of Ge ₃₃ Sb ₁₃ Te ₅₄ having a thickness of 15 nm in argon gas using a Ge ₃₃ Sb ₁₃ Te ₅₄ (atomic%) sintered body target. Layer 14 is formed. Next, the substrate 11 is moved to the fourth sputtering chamber, and then 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 body target. Next, the substrate 11 is moved to the fifth sputtering chamber, and the (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 each layer is laminated is taken out from the sputtering apparatus, and the thickness of the upper layer (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) is set to 0. A 1 mm cover layer 17 is formed.

  Initialization of the recording layer 14 of the film surface incidence type optical disc in the present embodiment is performed, for example, by 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 groove recording / reproduction, the initialized optical disk is rotated so as to have a linear velocity of 5.28 m / sec, and, for example, semiconductor laser light having a wavelength of 405 nm is applied through the cover layer 17 to a numerical aperture of 0.85. The light is condensed by the objective lens and tracking control is performed by the push-pull method. 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 that divides the recording pulse into a plurality is used.

  In the present embodiment, a single pattern is recorded in the groove portion on the film surface incident type optical disc, 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 with a spectrum analyzer. As a result, when the recording frequency was recorded on an unrecorded track at 4.1 MHz, a C / N ratio of 58.5 dB was obtained. Further, 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. Note that the amorphous recording mark length when recording at a recording frequency of 4.1 MHz is about 0.64 μm, and the amorphous recording mark length when recording at a recording frequency of 11.0 MHz is about 0.24 μm. .

  In the recording layer 14 of the film surface incidence type optical disc in the present embodiment, the erasure preventing layer 15 is provided in contact with the laser beam incident side of the recording layer 14 so that the amorphous recording mark is crystallized by continuous light irradiation. Even if the operation is performed, the amorphous recording mark does not return to crystalline. Specifically, a track on which a signal is recorded with a recording frequency of 4.1 MHz is irradiated with continuous light 30 times with a laser power of 1.5 mW, and then a single pattern is overwritten with a recording frequency of 11.0 MHz. Even if the recording 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 at 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 surface incidence type optical disc in this embodiment is a write-once medium using a phase change recording material used in a rewritable medium. As effective.

In the film surface incident type optical disc of the present embodiment, by providing the erasure preventing layer 15 in contact with the recording layer 14, the amorphous recording mark can be formed even if the amorphous recording mark is crystallized by continuous light irradiation. The reason why the recording layer 14 was not overwritten without returning to crystalline is not clear, but can be considered as follows, for example. That is, when the amorphous recording mark is recorded by irradiating the recording layer 14 with blue laser light to melt the crystalline recording layer made of the phase change recording material, the temperature at the center of the melted portion is about 1000 ° C. It can be estimated that the material produced by the bonding of the molten portion metal and the oxygen atom of cobalt trioxide (Co ₃ O ₄ ) constituting the erasure prevention layer 15 causes the crystallization of the amorphous recording mark. It is thought to suppress.

From another point of view, cobalt tetraoxide (Co ₃ O ₄ ) changes to cobalt oxide (II) (CoO) at a temperature in the vicinity of 900 ° C., so that the crystal structure is changed to cobalt trioxide ( The cause is considered to be the change from the spinel type of Co ₃ O ₄ ) to the NaCl type of cobalt oxide (II) (CoO) . That is, tribasic cobalt oxide (Co ₃ O ₄ ) is a mixed valence oxide in which a divalent Co ²⁺ ion and a trivalent Co ³⁺ ion are present in one unit cell. It is unstable and defects are likely to occur on the crystal plane. On the other hand, in cobalt oxide (II) (CoO) , since Co ²⁺ forms a regular hexahedron with an oxygen atom and has a stable crystal structure, defects are hardly generated on the crystal plane. In general, it is known that crystal nuclei are generated very easily when there are defects on the crystal plane. From this, when the recording layer 14 is melted during information recording, the erasure preventing layer 15 changes from cobalt trioxide (Co ₃ O ₄ ) to cobalt (II) oxide (CoO) , and the non-recording layer 14 is not coated. It can be considered that crystal nuclei are hardly generated at the boundary surface between the crystalline recording mark and the erasure preventing layer 15, and this makes it difficult to crystallize the portion once amorphous.

Note that the Ge ₃₃ Sb ₁₃ Te ₅₄ recording layer 14 formed from the phase-change recording material of the film surface 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 when an overwriting operation is performed with a recording frequency of 11.0 MHz on a track recorded with a recording frequency of 4.1 MHz, C is compared to a case where a single pattern is recorded on an unrecorded portion with a recording frequency of 11.0 MHz. The / N ratio is reduced by 4.5 dB, and a result in which overwriting cannot be performed with a laser beam having a wavelength of 405 nm is obtained.

  In addition, when the film surface incidence type optical disc of this embodiment is not subjected to the initialization process with the laser beam with the wavelength of 810 nm, for example, recording / reproduction of the semiconductor laser beam with the wavelength of 405 nm using the objective lens with the numerical aperture of 0.85 was attempted. In this case, tracking control is difficult. For example, when land / groove recording is performed at a recording frequency of 4.1 MHz while performing tracking control, the recording / reproducing signal amplitude is reduced to 1/10 or less as compared with the case where initialization processing is performed. In the present embodiment, the groove (groove) recording of the substrate 11 has been described. However, the same effect can be obtained when information is recorded on both the groove (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 side opposite to the side on which the laser light of the recording layer 14 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, Co ₃ O ₄ erasure prevention layer 15 with a thickness of ₃ nm, Ge ₃₃ Sb ₁₃ Te ₅₄ (atomic%) recording layer 14 with a thickness of 15 nm, (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) with a thickness of 60 nm A dielectric layer 16 and a 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 in this embodiment is the same as in the first embodiment by providing the erasure prevention layer 15 in contact with the side opposite to the laser beam incident side of the recording layer 14. In addition, even if the amorphous recording mark is crystallized by continuous light irradiation, the recording layer 14 cannot be overwritten. That is, when a track with a recording frequency of 4.1 MHz on an unrecorded track is irradiated with continuous light 30 times at a laser power of 1.5 mW, the single pattern is overwritten with a recording frequency of 11.0 MHz. Even if the recording is performed, the C / N ratio is reduced by 2.5 dB compared to the case of recording on an unrecorded track.

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

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

  The recording layer 14 of the film surface incidence type optical disc in the present embodiment is provided with the first erasure prevention layer 15a and the second erasure prevention layer 15b in contact with both sides of the recording layer 14, respectively. Similarly to the case, even if the amorphous recording mark is crystallized by continuous light irradiation, the recording layer 14 cannot be overwritten. That is, when a track with a recording frequency of 4.1 MHz on an unrecorded track is irradiated with continuous light 30 times at a laser power of 1.5 mW, the single pattern is overwritten with a recording frequency of 11.0 MHz. Even if the recording is performed, the C / N ratio is reduced by 3.5 dB as compared with the case of recording on an unrecorded track.

  Further, as in the case of the first embodiment, the recording layer 14 cannot be directly overwritten using a laser beam having a wavelength of 405 nm. That is, when recording 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, it is compared with the case of recording on an unrecorded track. As a result, the C / N ratio decreases by 4.0 dB.

FIG. 4 is a diagram for explaining the structure of a conventional optical information recording medium. Here, a single plate type film surface incidence type optical disc without an erasure prevention layer is shown. As shown in FIG. 4, an Ag ₉₈ Ru ₁ Au ₁ (atomic%) reflective layer 12 having a thickness of ₅₀ nm and (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) first having a thickness of 20 nm are formed on a substrate 11. 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; A cover layer 17 is sequentially laminated.

Such a film surface incidence type optical disc, which is a conventional optical information recording medium, irradiates a continuous recording light three times at a laser power of 1.5 mW onto a track on which a signal is recorded with a recording frequency of 4.1 MHz on an unrecorded track. When a single pattern is overwritten with a recording frequency of 11.0 MHz, the same C / N ratio of 55.0 dB as when recording on an unrecorded track at a recording frequency of 11.0 MHz is obtained. As a result, 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 if the continuous light is irradiated a plurality of times. This indicates that it cannot be used as a write-once medium because overwriting is possible.

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

(Fourth embodiment)
FIG. 5 is a cross-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 bonded type substrate incident type optical disk shown here, the erasure prevention layer 15 is provided in contact with the side of the recording layer 14 on which the laser beam is incident. As shown in FIG. 5, a substrate 18, (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) second dielectric layer 16 having a thickness of ₄₀ nm, and Co ₃ O ₄ having a thickness of 2 nm are formed on the substrate 18. An erase 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%) reflective layer 19 having a thickness of 100 nm is sequentially laminated, and a 0.6 mm polycarbonate resin plate 18 ′ is bonded thereon via an ultraviolet curable resin adhesive layer 20. Incidentally, the laser beam is applied to the recording layer 14 from the substrate 18 side.

  The substrate 18 is formed by injection molding with grooves having a width of 0.34 μm and a depth of 30 nm formed on the surface of a polycarbonate resin plate having a diameter of 120 mm and a thickness of 0.6 mm at a pitch of 0.68 μm. Disc recognition information, address information, and the like are recorded in advance on the substrate 18 by groove wobbles. Such information can also be formed by pre-pits. On the substrate 18, the second dielectric layer 16, the erasure preventing layer 15, the recording layer 14, the first dielectric layer 13, and the reflective layer 19 were sequentially formed. Then, an ultraviolet curable resin adhesive layer 20 was formed on the uppermost layer by spin coating, and was 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. Note that the conditions and method for initializing the recording layer 14 of the substrate-incident optical disk manufactured in this way are the same as those described in the first embodiment.

  The recording layer 14 of the bonded substrate incident type optical disc in the present embodiment is the same as in the first embodiment by providing the erasure preventing layer 15 in contact with the laser light incident side of the recording layer 14. In addition, even if the amorphous recording mark is crystallized by continuous light irradiation, the recording layer 14 cannot be overwritten. That is, when a track with a recording frequency of 4.1 MHz on an unrecorded track is irradiated with continuous light 30 times at a laser power of 1.5 mW, the single pattern is overwritten with a recording frequency of 11.0 MHz. Even if the recording is performed, the C / N ratio is reduced by 3.0 dB compared to the case of recording on an unrecorded track.

  Further, the recording layer 14 of the bonded substrate incident type optical disc cannot be directly overwritten using a laser beam having a wavelength of 405 nm. That is, when recording at a recording frequency of 4.1 MHz, a C / N ratio of 54.5 dB can be obtained. However, even if an overwrite operation is performed at a recording frequency of 11.0 MHz, it is compared with the case of recording 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 bonded substrate incident type optical disc, in which the erasure prevention layer is in contact with the side opposite to the side on which the laser light is incident. The structure is provided. Since it has substantially the same structure as the fourth embodiment described above, the drawing is omitted. The bonded type substrate incident type optical disc in 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 the 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 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 bonded through an ultraviolet curable resin adhesive layer. Note that the laser beam is applied to the recording layer from the substrate side.

  The recording layer of the bonded substrate incident type optical disc in the present embodiment is provided with an erasure prevention layer in contact with the side opposite to the laser beam incident side of the recording layer, so that the amorphous recording mark is irradiated by continuous light irradiation. Even if the crystallization operation is performed, the amorphous portion does not return to the crystalline state, and the recording layer cannot be overwritten. That is, when a track with a recording frequency of 4.1 MHz on an unrecorded track is irradiated with continuous light 30 times at a laser power of 1.5 mW, the single pattern is overwritten with a recording frequency of 11.0 MHz. Even if the recording is performed, the C / N ratio is reduced by 2.0 dB compared to the case of recording on an unrecorded track.

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

(Sixth embodiment)
The sixth embodiment of the optical information recording medium to which the present embodiment is applied is a bonded substrate incident type optical disc, in which two erasure prevention 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 bonded type substrate incident type optical disk in the present embodiment has a (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) second dielectric layer having a thickness of ₄₀ nm and a Co ₃ O ₄ thickness of 2 nm on the substrate. 1 erasure 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 One 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, on which a thin film is not formed. The

  The recording layer of the bonded substrate incident type optical disc in the present embodiment is provided with an erasure preventing layer in contact with both sides of the recording layer, so that the amorphous recording mark can be crystallized by continuous light irradiation. As a result, the recording layer cannot be overwritten. That is, when a track with a recording frequency of 4.1 MHz on an unrecorded track is irradiated with continuous light 30 times at a laser power of 1.5 mW, the single pattern is overwritten with a recording frequency of 11.0 MHz. Even if the recording is performed, the C / N ratio is reduced by 3.0 dB compared to the case of recording on an unrecorded track.

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

The conventional substrate-incidence type optical disk without the erasure prevention layer is, for example, a (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) second dielectric layer having a thickness of 40 nm on the substrate, A Ge ₃₃ Sb ₁₃ Te ₅₄ recording layer having a thickness of 20 nm, a first dielectric layer having a thickness of 20 nm made of (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%), and Al ₉₉ Ti ₁ (wt) having a thickness of 100 nm. %) A reflective layer is sequentially formed, and this is bonded to 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.

  Such a conventional optical information recording medium, which is a bonded type substrate-incident optical disc, cannot be directly overwritten when laser light having a wavelength of 405 nm is used, but it is irradiated with continuous light multiple times. Then, the crystallization of the amorphous recording mark proceeds and overwriting becomes possible, so that it cannot be used as a write-once medium.

It is a figure for demonstrating the structure of 1st Embodiment of the optical information recording medium with which this Embodiment is applied. It is a figure for demonstrating the structure of 2nd Embodiment of the optical information recording medium with which this Embodiment is applied. It is a figure for demonstrating the structure of 3rd Embodiment of the optical information recording medium with which this Embodiment is applied. It is sectional drawing for demonstrating the structure of the conventional optical information recording medium. It is a figure for demonstrating the structure of 4th Embodiment of the optical information recording medium with which this Embodiment is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11, 18 ... Board | substrate, 12 ... Reflective layer, 13 ... 1st dielectric material layer, 14 ... Recording layer, 15 ... Erase prevention layer, 15a ... 1st erase prevention layer, 15b ... 2nd erase prevention layer, 16 ... 2nd Dielectric layer, 17 ... cover layer, 18 '... polycarbonate resin plate, 19 ... reflection layer, 20 ... UV curable resin adhesive layer

Claims (8)

A substrate,
A recording layer provided on the substrate, on which information is recorded by a phase change from a crystalline phase to an amorphous phase upon receiving light irradiation;
It is provided in contact with the recording layer, suppresses a phase change from an amorphous phase formed by changing the phase of the recording layer to a crystalline phase , and contains a metal oxide containing a cobalt element as a main component. Including an anti-erasure layer,
An optical information recording medium comprising: 2. The optical information recording medium according to claim 1, wherein the metal oxide containing the cobalt element contains an element or a compound that changes physically or chemically at a temperature of 600 ° C. or higher. The optical information recording medium according to claim 1, wherein the erasure preventing layer contains at least cobalt tetroxide (Co ₃ O ₄ ) .   The optical information recording medium according to claim 1, wherein the erasure prevention layer has a thickness of 1 nm to 5 nm.   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 of a crystalline phase change recording material and recording information by irradiating light with a wavelength of 500 nm or less;
An erasure preventing layer provided in contact with the recording layer, preventing overwriting of information to the recording layer by irradiation of the light, and containing cobalt trioxide (Co ₃ O ₄ ) as a main component ;
An optical information recording medium comprising:   2. The recording layer according to claim 1, wherein when the amorphous phase formed by changing the phase of the phase change recording material is irradiated with continuous light, the amorphous phase does not change into a crystalline phase. 6. The optical information recording medium according to 6. A recording layer made of a crystalline phase change recording material formed on a substrate;
An erasure preventing layer provided in contact with the recording layer to prevent the amorphous recording mark formed on the recording layer from being erased, and containing cobalt trioxide (Co ₃ O ₄ ) as a main component ; In an optical information recording medium equipped with
An information recording / reproducing method for an optical information recording medium, wherein information is recorded or reproduced by irradiating the recording layer with a laser beam having a wavelength of 500 nm or less from the substrate side or the side opposite to the substrate.

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