JP4542922B2 - Optical information recording medium and manufacturing method thereof - Google Patents

Description

The present invention relates to thin film formed on a substrate, by irradiating a high energy beam such as a laser, it relates an optical information recording medium and its manufacturing how capable of recording and reproducing an information signal .

  A thin film of chalcogen material or the like formed on the substrate is irradiated with a laser beam and locally heated, and an amorphous phase and a crystalline phase having different optical constants (refractive index n, extinction coefficient k) depending on the irradiation conditions It is possible to change the phase between This is already widely known, and research and development and commercialization of so-called phase change type optical information recording media using this phenomenon have been actively conducted.

  In a phase change optical information recording medium, the laser output is modulated according to the information signal between at least two power levels of the recording level and the erasing level, and the existing signal is erased by irradiating the information track. However, it is possible to record a new signal at the same time.

  In such an optical information recording medium, in addition to the recording layer, a protective layer made of a dielectric material having excellent heat resistance, on the side of the recording layer close to the substrate (lower side) and on the side opposite to the substrate (upper side) Is generally provided. The protective layer has functions such as preventing evaporation of the recording layer and thermal deformation of the substrate during repeated recording, and enhancing the optical absorption rate and optical change of the recording layer by an optical interference effect. It is also common to provide a reflective layer made of a metal / alloy material or the like. The reflective layer has functions such as making efficient use of incident light and improving the cooling rate to make it easily amorphous.

  Furthermore, it has been proposed to provide an interface layer between the recording layer and the dielectric layer. The interface layer promotes crystallization of the recording layer and improves erasing characteristics, prevents interdiffusion of atoms and molecules between the recording layer and the dielectric protective layer, and improves durability in repeated recording Furthermore, it is desirable to have environmental reliability that does not cause peeling or corrosion between the recording layer and the recording layer.

  It has also been proposed to provide a material layer between the upper dielectric layer and the reflective layer. The material layer increases the erasure rate by adjusting the ratio of the light absorption rate between the case where the recording layer is crystalline and the case where the recording layer is amorphous, and prevents the mark shape from being distorted at the time of overwriting. It has functions such as increasing the difference in reflectance between when the layer is crystalline and when it is amorphous, increasing the C / N ratio, and has a high refractive index and absorbs light appropriately. Is desirable (see, for example, Patent Document 1).

  As a basic means for increasing the amount of information that can be stored per optical information recording medium, by shortening the wavelength of the laser beam or increasing the numerical aperture of the objective lens that collects the laser beam. There is a method of reducing the spot diameter of laser light and improving the recording surface density. In recent years, as represented by a recordable DVD, an optical system having a wavelength of 660 nm and a numerical aperture of about 0.6 is used. Furthermore, it has been studied to apply a blue laser diode having a wavelength of about 400 nm, which is approaching the stage of practical use, and to further increase the numerical aperture to about 0.85. When the numerical aperture is increased in this manner, the allowable width with respect to the tilt of the optical disk is reduced. Therefore, the thickness of the transparent substrate on the laser light incident side is reduced from 0.6 mm to 0.1 mm of the recordable DVD. Proposed.

  Furthermore, in order to increase the amount of information that can be handled per medium, a multilayer structure medium in which a plurality of layers for recording / reproducing information has been proposed. In such a multilayer recording medium, the information layer closer to the laser light source absorbs light, and therefore the information layer far from the laser light source is recorded and reproduced with attenuated laser light. However, there is a problem that the reflectivity and amplitude are reduced during reproduction. Therefore, in a multilayer recording medium, the information layer closer to the laser light source has a higher transmittance, and the information layer far from the laser light source has a higher reflectance, difference in reflectance and sensitivity, with a limited laser power. It is necessary to obtain sufficient recording / reproduction characteristics.

In the optical information recording medium, it is important to increase the recording density as described above, and it is also important to increase the recording speed in order to handle a large amount of data in a short time. In order to cope with high-speed recording, it is necessary to increase the crystallization speed of the recording layer. A typical recording material, Ge—Sb—Te, particularly a composition near GeTe—Sb ₂ Te ₃ has a high crystallization rate.
JP 2000-215516 A

  As described above, the recording speed of a newly developed recording / reproducing apparatus tends to be higher, and a medium corresponding to this is required. At the same time, in order to ensure compatibility with existing drives that can only record at low speed, it is necessary to be able to record at low speed on the same medium. Further, it is preferable from the viewpoint of reducing the load on the motor to keep the rotation speed of the medium constant regardless of the radial position of the medium. In this case, since recording is performed at different linear velocities at the outer peripheral portion and the inner peripheral portion of the medium, it is also necessary to be able to record the medium in the range of high speed to low speed, that is, a linear speed of a certain level or higher.

  In order for the medium to support high-speed recording, it is necessary to use a recording layer having a high crystallization speed as described above. On the other hand, when this recording layer is used for recording at low speed, the crystallization speed is too high. That is, there is a problem that the signal amplitude is lowered because the amorphous is hardly formed and the mark is difficult to be enlarged.

The present invention aims to provide a recording medium that excellent recording and reproducing characteristics can be obtained and its manufacturing how in a wide range of linear velocity.

The optical information recording medium of the present invention is an optical information recording medium having at least a recording layer on a transparent substrate, and the recording layer includes at least a first phase change film and a first layer in order from the side close to the transparent substrate. Each of the first phase change film and the second phase change film includes 10 atomic% to 50 atomic% of Ge and 45 atomic% to 60 atomic% of Te, The difference between the Bi content ratio of the one phase change film and the Bi content ratio of the second phase change film is 4 atomic% or more.
Thereby, it becomes possible to deal with a wide linear velocity range, and a recording medium having good recording / reproducing characteristics can be obtained.

Furthermore, another optical information recording medium of the present invention is an optical information recording medium having at least a recording layer on a transparent substrate, and is formed on the transparent substrate in order from the side close to the transparent substrate. 1 information layer, separation layer, second information layer, at least one of the first information layer and the second information layer has at least a recording layer, and the recording layer is close to the transparent substrate In order from the side, at least a first phase change film and a second phase change film are included, and each of the first phase change film and the second phase change film includes 10 atomic% or more and 50 atomic% or less of Ge and 45 atomic%. The difference between the Bi content ratio of the first phase change film and the Bi content ratio of the second phase change film is 4 atom% or more.

The optical information recording medium of the present invention preferably has at least a recording layer and a reflective layer in this order from the side closer to the transparent substrate.

Further, it is preferable to have an upper dielectric layer between the recording layer and the reflective layer.
It is preferable to further have an upper interface layer between the recording layer and the upper dielectric layer.
The upper interface layer is preferably made of a material containing an oxide of at least one element selected from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ga, and Si. Thereby, a layer excellent in moisture resistance and erasure rate can be obtained.

Moreover, it is preferable to further have a light absorption layer between the upper dielectric layer and the reflective layer.
The light absorption layer is preferably made of a material containing at least one element selected from Si and Ge. Thereby, sufficient C / N ratio is obtained.
The optical information recording medium of the present invention preferably further has a lower dielectric layer between the recording layer and the transparent substrate.

Further, it is preferable to further have a lower interface layer between the lower dielectric layer and the recording layer.
The lower interface layer is preferably made of a material containing at least one oxide selected from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ga, and Si. Thereby, a layer excellent in moisture resistance and erasure rate can be obtained.

The method for producing an optical information recording medium of the present invention is a method for producing an optical information recording medium having at least a recording layer on a transparent substrate, wherein the recording layer is at least in order from the side closer to the transparent substrate. It consists of a first phase change film and a second phase change film, and each of the first phase change film and the second phase change film is 10 atomic% to 50 atomic% Ge and 45 atomic% to 60 atomic%. And a step of forming a film so that a difference between the Bi content of the first phase change film and the Bi content of the second phase change film is 4 atomic% or more.

The method for producing an optical information recording medium of the present invention is a method for producing an optical information recording medium having at least a recording layer on a transparent substrate, and at least the first information in order from the side closer to the transparent substrate. A layer, a separation layer, and a second information layer, and at least one of the first information layer and the second information layer has at least a recording layer, and the recording layer is from a side close to the transparent substrate. In order, the phase change film includes at least a first phase change film and a second phase change film, and each of the first phase change film and the second phase change film includes 10 atomic% to 50 atomic% Ge and 45 atomic% to 60%. Including a step of forming a film so that a difference between the Bi content ratio of the first phase change film and the Bi content ratio of the second phase change film is 4 atom% or more, including Te of atomic% or less. To do.

  The recording method and the recording apparatus of the present invention include a recording / reproducing method for reproducing information before or after recording of information, or a recording / reproducing apparatus having a reproducing mechanism together with an information recording mechanism.

Above As described, according to the present invention, it is possible to provide good recording recording medium reproducing characteristics can be obtained and its manufacturing how in a high density and a wide range of linear velocity.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 to 4 are partial cross-sectional views of a configuration example of the optical information recording medium of the present invention.
As shown in FIG. 1, the optical information recording medium of the present invention comprises a transparent dielectric substrate 1, a lower dielectric layer 2, a first phase change film 3-1, and a second phase change film 3-2, for example. The recording layer 3, the upper dielectric layer 4, the reflective layer 5, and the protective substrate 6 are provided in this order. With respect to this optical information recording medium, the laser beam 7 is condensed by the objective lens 8 from the transparent substrate 1 side, and the recording layer 3 is irradiated to perform recording and reproduction.

As shown in FIG. 2, the light absorbing layer 9 is disposed between the upper dielectric layer 4 and the reflective layer 5, the lower interface layer 10 is disposed between the lower dielectric layer 2 and the recording layer 3, and the recording layer 3 The upper interface layer 11 may be appropriately provided between the upper dielectric layer 4 and the uppermost dielectric layer 12 may be appropriately provided between the reflective layer 5 and the protective substrate 6.
As shown in FIGS. 3 and 4, the optical information recording medium of the present invention has a first information layer 14 and a second information layer 15 between a transparent substrate 1 and a protective substrate 6 with a separation layer 13 interposed therebetween. In addition, up to the nth information layer 16 (where n is an integer of 3 or more) may be provided. At that time, one of the information layers needs to be the same as the multilayer thin film structure shown in FIG. Laser light 7 is condensed with an objective lens 8 from the transparent substrate 1 side to each information layer of the optical information recording medium and irradiated to perform recording / reproduction.

  The material of the transparent substrate 1 is preferably substantially transparent at the wavelength of the laser beam 7, and is a polycarbonate resin, polymethyl methacrylate resin, polyolefin resin, norbornene resin, ultraviolet curable resin, glass, or a combination thereof as appropriate. A thing etc. can be used. Moreover, although the thickness of the transparent substrate 1 is not specifically limited, the thing of about 0.01-1.5 mm can be used.

Examples of materials for the lower dielectric layer 2 and the upper dielectric layer 4 include Y, Ce, Ti, Zr, Nb, Ta, Co, Zn, Al, Si, Ge, Sn, Pb, Sb, Bi, and Te. Oxides such as Ti, Zr, Nb, Ta, Cr, Mo, W, B, Al, Ga, In, Si, Ge, Sn, Pb, and other nitrides, Ti, Zr, Nb, Ta, Cr, Mo , Carbides such as W and Si, sulfides such as Zn and Cd, selenides or tellurides, fluorides such as rare earth such as Mg, Ca and La, simple substances such as C, Si and Ge, or a mixture thereof be able to. Among them, a material that is substantially transparent and has low thermal conductivity, for example, a mixture of ZnS and SiO ₂ is preferable. The lower dielectric layer 2 and the upper dielectric layer 4 may be made of different materials and compositions as needed, or may be made of the same material and composition. Here, the film thickness of the upper dielectric layer 4 is preferably 2 nm or more and 80 nm or less, and more preferably 5 nm or more and 50 nm or less. If the thickness of the upper dielectric layer 4 is too thin, the distance between the recording layer 3 and the reflective layer 5 becomes too close and the cooling effect of the reflective layer 5 becomes strong, and thermal diffusion from the recording layer 3 increases and the recording sensitivity increases. And the recording layer 3 becomes difficult to crystallize. On the other hand, if the upper dielectric layer 4 is too thick, the distance between the recording layer 3 and the reflective layer 5 is too large, and the cooling effect of the reflective layer 5 is weakened. This is because 3 becomes difficult to become amorphous. The thickness of the lower dielectric layer 2 is not particularly limited, but is preferably 10 nm or more and 200 nm or less.

  As materials for the lower interface layer 10 and the upper interface layer 11, among the materials listed above as the materials for the lower dielectric layer 2 and the upper dielectric layer 4, there are some materials that play the role. For example, nitrides based on Ge, Si, etc., oxides such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ga and Si, or composite oxides thereof can be used. In particular, oxides such as Ti, Zr, Hf, V, Nb and Ta to which oxides such as Cr, Mo, W and Ga are added are superior in terms of moisture resistance, and oxidation of Si and the like. The thing which added the thing can make an erasure | elimination rate higher. The film thickness of the lower interface layer 10 and the upper interface layer 11 is not particularly limited, but if it is too thin, the effect as an interface layer cannot be exhibited, and if it is too thick, it leads to a decrease in recording sensitivity. It is preferable that The lower interface layer 10 and the upper interface layer 11 exhibit the above-described effects even if only one of them is provided, but it is more preferable to provide both, and when both are provided, different materials / compositions may be used as necessary. Alternatively, the same material / composition may be used.

  The materials of the first phase change film 3-1 and the second phase change film 3-2 constituting the recording layer 3 are required to contain 10 atomic% to 50 atomic% Ge and 45 atomic% to 60 atomic% Te. In addition, only one of them contains Bi, or both contain Bi, and both contain Bi and use different material compositions. Further, the Ge content may be 20 atomic% or more and 50 atomic% or less. By using such a recording layer, the C / N ratio and the erasure rate can be kept high in a wide linear velocity range. In addition to Ge, Te, and Bi, Sb, Sn, In, Ga, Zn are used for the purpose of adjusting the crystallization rate, thermal conductivity, optical constants, etc., or improving the durability of repetition, heat resistance, or environmental reliability. One or more elements selected from metals, semi-metals or semiconductor elements such as Cu, Ag, Au, and Cr, or non-metallic elements such as O, N, F, C, S, and B, as necessary. The total amount of the first phase change film 3-1 or the whole second phase change film 3-2 may be 20 atomic% or less, preferably 10 atomic% or less, particularly preferably 5 atomic% or less.

  If the total film thickness of the recording layer 3 is 2 nm or more and 20 nm or less, a sufficient C / N ratio can be obtained. When the recording layer 3 is less than 2 nm in total, sufficient reflectivity and change in reflectance cannot be obtained, so the C / N ratio is low. On the other hand, when the recording layer 3 exceeds 20 nm, thermal diffusion in the thin film plane of the recording layer 3 is not achieved. Since it is large, the C / N ratio is lowered in high-density recording. Furthermore, the total film thickness of the recording layer 3 is more preferably 4 nm or more and 14 nm or less. The ratio of the first phase change film 3-1 and the second phase change film 3-2 to the total film thickness of the recording layer 3 is 5% to 95%, more preferably 10% to 90%. Hereinafter, the desired effect can be obtained if it is more preferably 20% or more and 80% or less.

  As the light absorption layer 9, the ratio of the light absorptance between the case where the recording layer 3 is crystalline and the case where it is amorphous is adjusted so that the mark shape is not distorted at the time of overwriting. In order to increase the erasure rate of the recording layer 3 and to increase the difference in reflectance between when the recording layer 3 is crystalline and when it is amorphous, the C / N ratio is increased. A material having a refractive index n of 3 or more and 6 or less, an extinction coefficient k of 1 or more and 4 or less, more preferably n of 3 or more and 5 or less, and k of 1.5 or more and 3 or less. Use it. Specifically, Ge alloys and Si alloys that are amorphous such as Ge—Cr, Ge—Mo, Si—Cr, Si—Mo, Si—W, or Ti, Zr, Nb, Ta, Cr, Mo, W, W It is preferable to use crystalline metals, semi-metals and semiconductor materials such as SnTe and PbTe. In particular, a Si-based material is more preferable because it has a higher melting point than Ge and has good heat resistance and a high thermal conductivity, resulting in a large C / N ratio. Further, in order to prevent mixing, corrosion, and the like due to the reaction between the upper dielectric layer 4 and the reflective layer 5 instead of the light absorbing layer 9, the lower dielectric layer 2 and the upper dielectric layer are added as additional interface layers. As the material of the layer 4, a material close to transparency may be used from the materials listed above.

  As the material of the reflective layer 5, for example, Au, Ag, Cu, Al, Ni, Cr, or an alloy material based on these is used. In particular, Ag alloy has high thermal conductivity and reflectivity, and Al alloy is also preferable from the viewpoint of cost. The reflective layer 5 may be used in combination of a plurality of layers.

As the material of the uppermost dielectric layer 12, an appropriate material is used from the materials listed above as the materials of the lower dielectric layer 2 and the upper dielectric layer 4. In particular, when the reflective layer 5 is thin and translucent, for example, 20 nm or less, it is preferable to use TiO ₂ , Bi ₂ O ₃ or the like having a high refractive index n because the reflectance change or the contrast of the reflectance can be increased.

  The multilayer thin film can be examined for the material and composition of each layer by a method such as Auger electron spectroscopy, X-ray photoelectron spectroscopy, or secondary ion mass spectrometry. In the embodiment of the present application, it was confirmed that the target material composition of each layer and the composition of the actually formed thin film were substantially equivalent. However, depending on the film forming apparatus, film forming conditions, target manufacturing method, and the like, the target material composition may differ from the actually formed thin film composition. In such a case, it is preferable to obtain a correction coefficient for correcting the composition deviation in advance from an empirical rule and to determine the target material composition so that a thin film having a desired composition can be obtained.

  As the material of the protective substrate 6, the same materials as those described as the material of the transparent substrate 1 can be used. However, the material may be different from that of the transparent substrate 1, and may not necessarily be transparent at the wavelength of the laser light 7. Good. Moreover, the thickness of the protective substrate 6 is not particularly limited, but a thickness of about 0.01 to 3.0 mm can be used.

  As the separation layer 13, an ultraviolet curable resin or the like can be used. The thickness of the separation layer 13 is set so that at least the numerical aperture NA of the objective lens 8 and the laser beam are reduced so that crosstalk from the other when the first information layer 14 or the second information layer 15 is reproduced is reduced. It is desirable that the thickness be equal to or greater than the depth of focus determined by the wavelength λ of 7, and it is also necessary that the thickness be within a range where all the information layers can be condensed. For example, the thickness of the separation layer 13 is preferably 10 μm or more and 100 μm or less when λ = 660 nm and NA = 0.6, or 5 μm or more and 50 μm or less when λ = 405 nm and NA = 0.85. However, if an optical system capable of reducing crosstalk between layers is developed, the thickness of the separation layer 13 may be made thinner than the above.

The first information layer 14 desirably has a transmittance of 30% or more, but can be not only a rewritable type but also a write-once type or a read-only type information layer.
The two optical information recording media are bonded to each other with their protective substrates 6 facing each other to form a double-sided structure, thereby further doubling the amount of information that can be stored per medium. it can.

Each of the above thin films can be formed by vapor phase thin film deposition methods such as vacuum deposition, sputtering, ion plating, CVD (Chemical Vapor Deposition), and MBE (Molecular Beam Epitaxy).
The thin film layer and the separation layer 13 may be formed or bonded to the protective substrate 6 after being sequentially formed on the transparent substrate 1, or conversely, the transparent substrate 1 may be formed or formed after being sequentially formed on the protective substrate 6. You may stick together. In particular, the latter is suitable when the transparent substrate 1 is as thin as 0.4 mm or less. In that case, the concave / convex patterns such as grooves and address signals, which are grooves for guiding the laser beam, are formed on the surfaces of the protective substrate 6 and the separation layer 13, that is, transferred from those in which a desired concave / convex pattern such as a stamper is formed in advance. Need to be done. At that time, the 2P method (photo-polymerization method) can also be used when it is difficult to produce by the commonly used injection method because the film thickness is particularly thin like the separation layer 13.

Since the recording layer 3 of the optical recording medium is generally in an amorphous state as it is formed, the recording layer 3 becomes a completed disk by applying an initialization process to a crystalline state by annealing with laser light or the like. Playback can be performed.
FIG. 5 shows a schematic diagram of an example of the minimum necessary configuration of a recording / reproducing apparatus that performs recording / reproducing of an optical information recording medium as an example of the recording apparatus of the present invention. The laser beam 7 emitted from the laser diode 17 is focused on an optical information recording medium (disk) 20 rotated by a motor 19 through a half mirror 18 and an objective lens 8. Information reproduction is performed by causing reflected light from the optical information recording medium 20 to enter the photodetector 21 and detecting a signal. The controller 22 is configured to control the laser diode 17 and the motor 19 in order to record and reproduce information on the optical information recording medium 20 of the present invention. The control unit 22 preferably includes a microcomputer incorporating a control program for controlling the laser diode 17 and the motor 19. The control unit 22 may include a conventional input interface circuit, an output interface circuit, or a storage unit such as a ROM (Read Only Memory) or a RAM (Random Access Memory).

  When recording an information signal, the intensity of the laser beam 7 is modulated between a plurality of power levels. As the laser light intensity modulating means for modulating the laser intensity, current modulating means for modulating the driving current of the semiconductor laser may be used, and means such as an electro-optic modulator and an acousto-optic modulator may be used. A single rectangular pulse with a peak power P1 may be used for the portion where the recording mark is to be formed. However, in the case where a long mark is particularly formed, in order to eliminate excessive heat and make the mark width uniform, FIG. As shown, a recording pulse train composed of a plurality of pulse trains modulated between the peak power P1 and the bottom power P3 (where P1> P3) is used. Further, a cooling section with cooling power P4 may be provided after the last pulse. For a portion where no mark is formed, the bias power P2 (where P1> P2) is kept constant.

  By recording the laser power modulation pulse waveform for forming the recording mark by dividing the time integral of the emission power by the maximum emission power, the higher the linear velocity, the better the recording / reproduction in a wider linear velocity range. The characteristics can be kept. To increase the value obtained by dividing the time integral of the light emission power by the maximum light emission power, specifically, for example, in the pulse waveform shown in FIG. 6, the width of a part or all of each pulse of the peak power P1 is widened. Alternatively, it can be realized by increasing the power level P3, and is particularly effective in improving the erasure rate at a high linear velocity.

  Here, each pattern such as the length of the mark to be recorded and the length of the space before and after the mark causes irregularities in the mark edge position, which may cause an increase in jitter. In the recording method of the optical information recording medium of the present invention, in order to prevent this and improve jitter, the position or length of each pulse of the pulse train is adjusted as necessary so that the edge position is aligned for each pattern. Can also be compensated.

  In the present invention, two or more modes are applied at the time of recording information, the medium is rotated at two or more linear velocities different according to the two or more modes, and two or more different according to the two or more linear velocities. If the laser power modulation pulse waveform is used, and the two or more laser power modulation pulse waveforms are set so that the value obtained by dividing the time integral of the light emission power by the maximum light emission power increases as the linear velocity increases. Good.

Hereinafter, the present invention will be described more specifically. However, the present invention is not limited to the examples.
A substrate made of polycarbonate resin having a diameter of 12 cm, a thickness of 0.6 mm, a groove pitch of 1.23 μm, and a groove depth of about 55 nm was prepared as a transparent substrate. A lower dielectric layer made of (ZnS) ₈₀ (SiO ₂ ) ₂₀ and having a thickness of 130 nm, (ZrO ₂ ) ₂₅ (SiO ₂ ) ₂₅ (Cr ₂ O ₃ ), is formed on the surface of the transparent substrate on which the grooves are formed. A lower interface layer of ₅₀ nm thickness, a 4 nm thick first phase change film and a 4 nm thick second phase change film of various material compositions are laminated in this order from the side close to the transparent substrate. Recording layer with a total thickness of 8 nm, upper interface layer with a thickness of 5 nm made of (ZrO ₂ ) ₂₅ (SiO ₂ ) ₂₅ (Cr ₂ O ₃ ) _50, and a thickness of 35 nm made of (ZnS) ₈₀ (SiO ₂ ) ₂₀ Each layer of an upper dielectric layer, a light absorption layer made of CrSi _{2 with a} thickness of 30 nm, and a reflection layer made of Ag ₉₈ Pd ₁ Cu _{1 with a} thickness of 80 nm was sequentially laminated by sputtering.

  As the first phase change film and the second phase change film of the recording layer, as shown in (Table 1), a material composed of some or all of Ge, Sb, Bi, and Te, each having a different composition ratio Was used.

In the formation of each layer, the recording layer was formed while flowing an Ar—N ₂ mixed gas (N ₂ partial pressure of about 3%), and the other layers with only Ar flowing as a sputtering gas.
A protective substrate made of polycarbonate was bonded onto the multilayer thin film surface thus formed via an ultraviolet curable resin, and cured by irradiation with ultraviolet light. The entire recording layer was initialized by annealing with a laser beam from the transparent substrate side of the disk.

  These disks are rotated under two conditions of a linear velocity of 8.2 m / s (reference clock T = 17.1 ns) and a linear velocity of 20.5 m / s (reference clock T = 6.9 ns), and the wavelength is 660 nm · NA 0.6. Measurement was performed using the optical system. At any linear velocity, 3T signal and 11T signal were alternately recorded 11 times on the groove and land, and this track was reproduced with the 3T signal recorded, and its C / N ratio was measured with a spectrum analyzer. Further, the erasure rate when the 11T signal was recorded once, that is, the attenuation ratio of the 3T signal amplitude was measured with a spectrum analyzer.

  The laser modulation waveform for recording a signal is a single rectangular pulse having a width of 1.5T (power level P1) for a 3T signal at any linear velocity, and a head having a width of 1.5T for an 11T signal. The pulse train (power level P1) is composed of a pulse followed by 8 sub-pulses with a width of 0.5T, and the width between each pulse (power level P3) is also 0.5T. In the portion where no mark is recorded, continuous light of power level P2 is used. P3 = P2 when the linear velocity was 8.2 m / s, and P3 = P2 + 1 mW when the linear velocity was 20.5 m / s. As for how to determine each power level, the recording power level P1 is 1.5 times the lower limit of the power at which the C / N ratio exceeds 45 dB, the power level P2 is the median value of the power range where the erasure rate exceeds 20 dB, and the reproduction power level. P5 was 1.0 mW.

Table 1 shows the results of measuring the C / N ratio and erasure rate of each disk under the above conditions. The C / N ratio and the erasure rate did not differ greatly between the groove and the land for each disk, but (Table 1) shows the lower value.
The disks 0a, 0b and 0c use recording layers whose compositions are not different between the first phase change film and the second phase change film, and are comparative examples for the disk of the embodiment of the present invention. The disk 0a has a high C / N ratio and an erasing rate in recording at a low speed, but the erasing rate is low because the crystallization speed is insufficient at a high speed. On the contrary, the disk 0b has a high C / N ratio and an erasure rate at a high speed, but at a low speed, the crystallization speed becomes excessive and the C / N ratio is low. The disk 0c has a slightly excessive crystallization speed in recording at a low speed, so that a sufficient C / N ratio cannot be obtained. On the contrary, the crystallization speed is insufficient in a recording at a high speed. The rate is insufficient. Thus, although the crystallization speed can be adjusted by the Bi content ratio, it can be seen that there is a limit to the linear velocity range that can be handled.

  On the other hand, in other disks which are embodiments of the present invention, a sufficient C / N ratio is obtained even at a low speed, the erasure rate at a high speed is high, and good recording characteristics are exhibited from a low speed to a high speed. . Among them, the discs 2x and 2y show better recording characteristics than the discs 1x and 1y, and the difference in the Bi content ratio between the first phase change film and the second phase change film is larger. This indicates that a wider linear velocity range can be accommodated. In addition, the first phase change film and the second phase change film can correspond to a wide linear velocity range regardless of which Bi content is large, but the disk 1y is more than the disk 1x, and the disk 2x is more than the disk 1x. The disk 2y has a higher C / N ratio but a lower erasure rate. The first phase change film is crystallized and the second phase change film has a relative influence on amorphization. It can be seen that it is big. Further, the larger the Bi content ratio and the smaller the Ge content ratio of the disk 3x and further the disk 4x with respect to the disk 2x, the C / N ratio tends to be slightly lower, although the ratio is sufficient. This is because the optical contrast between crystal and amorphous is lowered, and the linear velocity range that can be handled in terms of thermophysical properties is not narrowed, but from the optical side, the Bi content ratio is Too large is not practically preferable. On the other hand, the disk 5z has the same Bi content of the first phase change film as that of the disk 4x, so that the C / N ratio decreases. However, the Ge content of the second phase change film is the same as that of the disk 2x. Since the C / N ratio is increased, the C / N ratio is increased. As a result, both the C / N ratio and the erasure rate are achieved at low speed and high speed. Therefore, the present invention can be implemented if the difference in Bi content between the first phase change film and the second phase change film is 2 atomic% or more, but the difference is 4 atomic% or more, and further 8 atoms. % Or more is preferable.

In this embodiment, the film thicknesses of the first phase change film and the second phase change film are fixed to be the same. However, when the ratio of the film thickness is changed without changing the total film thickness, the balance between the two is changed. The crystallization speed changes due to the change, but a balance can be achieved by changing and adjusting the Bi amount accordingly.
From the above results, it was found that good recording / reproduction characteristics can be obtained in a wide linear velocity range by using the phase change films having different Bi content ratios as a recording layer.

  The optical information recording medium of the present invention is useful as a medium for storing data that can be digitized, such as video, music, and information.

Sectional drawing of the example of 1 structure of the optical information recording medium of this invention Sectional drawing of the example of 1 structure of the optical information recording medium of this invention Sectional drawing of the example of 1 structure of the optical information recording medium of this invention Sectional drawing of the example of 1 structure of the optical information recording medium of this invention Schematic of an example of a recording / reproducing apparatus for an optical information recording medium of the present invention Schematic of an example of a recording pulse waveform used for recording and reproduction of the optical information recording medium of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Lower dielectric layer 3 Recording layer 3-1 1st phase change film 3-2 2nd phase change film 4 Upper dielectric layer 5 Reflective layer 6 Protective substrate 7 Laser beam 8 Objective lens 9 Light absorption layer 10 Lower interface layer 11 Upper interface layer 12 Uppermost dielectric layer 13 Separation layer 14 First information layer 15 Second information layer 16 nth information layer 17 Laser diode 18 Half mirror 19 Motor 20 Optical information recording medium 21 Photo detector 22 Control Part

Claims (13)

An optical information recording medium having at least a recording layer on a transparent substrate,
The recording layer is composed of at least a first phase change film and a second phase change film in order from the side closer to the transparent substrate,
Each of the first phase change film and the second phase change film includes 10 atomic% to 50 atomic% Ge and 45 atomic% to 60 atomic% Te,
The difference between the Bi content of the first phase change film and the Bi content of the second phase change film is 4 atomic% or more ,
Optical information recording medium. An optical information recording medium having at least a recording layer on a transparent substrate,
On the transparent substrate, in order from the side close to the transparent substrate, at least a first information layer, a separation layer, a second information layer,
At least one of the first information layer and the second information layer has at least a recording layer,
The recording layer is composed of at least a first phase change film and a second phase change film in order from the side closer to the transparent substrate,
Each of the first phase change film and the second phase change film includes 10 atomic% to 50 atomic% Ge and 45 atomic% to 60 atomic% Te,
The difference between the Bi content of the first phase change film and the Bi content of the second phase change film is 4 atomic% or more ,
Optical information recording medium. In order from the side close to the transparent substrate, and having at least the recording layer and the reflective layer, the optical information recording medium according to claim 1 or 2. The optical information recording medium according to claim 3 , further comprising an upper dielectric layer between the recording layer and the reflective layer. The optical information recording medium according to claim 4 , further comprising an upper interface layer between the recording layer and the upper dielectric layer. The upper interface layer is made of a material containing an oxide of at least one element selected from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ga, and Si. Item 6. The optical information recording medium according to Item 5 . Wherein between the upper dielectric layer and the reflective layer, further characterized by having a light-absorbing layer, the optical information recording medium according to any one of claims 4-6. The optical information recording medium according to claim 7 , wherein the light absorption layer is made of a material containing at least one element selected from Si and Ge. Further comprising a lower dielectric layer between the recording layer and the transparent substrate,
The optical information recording medium according to any one of claims 1-8. The optical information recording medium according to claim 9 , further comprising a lower interface layer between the lower dielectric layer and the recording layer. The lower interface layer is made of a material containing an oxide of at least one element selected from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ga and Si. The optical information recording medium according to claim 10 . A method for producing an optical information recording medium having at least a recording layer on a transparent substrate,
The recording layer is composed of at least a first phase change film and a second phase change film in order from the side closer to the transparent substrate,
Each of the first phase change film and the second phase change film includes 10 atomic% to 50 atomic% Ge and 45 atomic% to 60 atomic% Te,
An optical information recording medium comprising a step of forming a film so that a difference between a Bi content ratio of the first phase change film and a Bi content ratio of the second phase change film is 4 atomic% or more . Production method. A method for producing an optical information recording medium having at least a recording layer on a transparent substrate,
In order from the side closer to the transparent substrate, at least a first information layer, a separation layer, a second information layer,
At least one of the first information layer and the second information layer has at least a recording layer,
The recording layer is composed of at least a first phase change film and a second phase change film in order from the side closer to the transparent substrate,
Each of the first phase change film and the second phase change film includes 10 atomic% to 50 atomic% Ge and 45 atomic% to 60 atomic% Te,
An optical information recording medium comprising a step of forming a film so that a difference between a Bi content ratio of the first phase change film and a Bi content ratio of the second phase change film is 4 atomic% or more . Production method.

Images