JP2006066071A - Information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayered information recording medium wherein contrast when recording/reproduction is performed by using a blue laser is improved and which has satisfactory reproducing characteristics. <P>SOLUTION: The information recording medium has a substrate 1, information surfaces of N layers of recording films 3 and 9 wherein information is recorded by change of atomic arrangement generated by irradiation with light (N is an integer of 2 or more) and (N-1) pieces of spacer layers 7. Transmittance of each information surface is so set as to have a relation of information surface 1>information surface 2 ... information surface N-1>information surface N when the information surfaces are counted from a light incident side information surface and the thickness of the substrate is specified to be 0.578 to 0.592 mm and/or the thickness of the spacer layers are specified to be 13 to 27 μm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an information recording medium used for an optical disc.

 There are various known principles for recording information on a thin film (recording film) by irradiating laser light. Among them, atoms such as phase changes (also called phase transitions) and photodarkening of film materials are caused by laser light irradiation. Those using an array change are hardly accompanied by deformation of the thin film, so that a double-sided disk structure information recording medium or a multilayer structure information recording medium having a plurality of information surfaces can be obtained by directly bonding two disk members together. Has advantages.

 In an ordinary optical disk, a light source generally called a red laser having a wavelength of around 660 nm is used. These information recording media have a structure in which a lower protective layer, a GeSbTe-based recording film, a ZnS-SiO2 upper protective layer, and a reflective layer having a high reflectance such as Al are sequentially laminated on a substrate. There are several methods for increasing the recording capacity, and a method using a light source having a wavelength shorter than the wavelength near 660 nm, a method using a multilayer structure, and the like have been proposed. ODS / ISOM '99 Proceedings, page 110 (Reference 1) shows a two-layer information recording medium for wavelengths near 400 nm. This medium has a first information surface having no reflection layer on the light incident side and a second information surface having an Al alloy reflection layer on the side far from the light. However, this data does not show improvement in the point that the contrast generated when recording / reproducing is performed only by the calculation result. A similar two-layer information recording medium for a wavelength of around 400 nm is disclosed in PCOS '99 Lecture Proceedings, page 22 (Reference 2), but this medium also has a reflective layer on the light incident side. It has the information side.

  Japanese Patent Laid-Open No. 10-293942 describes that a plurality of phase change recording media comprising a transparent lower protective film, a phase change recording film, a transparent upper protective film, a transparent reflective film, or a transparent interference film are provided. Yes.

  Note that a short-wavelength laser near a wavelength of 400 nm is generally called a blue, blue-green, blue-violet, or green laser in contrast to a long-wavelength red laser. Call.

In this specification, “phase change” and “phase change” include not only the phase change between crystal and amorphous, but also melting (change to liquid phase) and recrystallization, and phase change between crystal state and crystal state. The term “atomic arrangement change” is used. Mark edge recording refers to a recording method in which the edge portion of a recording mark corresponds to a signal “1”, and between the marks and within the mark corresponds to a signal “0”. In this specification, an optical disk refers to a disk (disc) on which information that can be reproduced by light irradiation is written and / or an apparatus that reproduces information by light irradiation.
ODS / ISOM'99 Proceedings, page 110 PCOS '99 Lecture Proceedings 22 Japanese Patent Laid-Open No. 10-293942

  Any of the conventional multilayer information recording media has a problem of low contrast when used as a high-density rewritable phase change type multilayer information recording medium using a blue laser.

  Japanese Patent Laid-Open No. 10-293942 has no idea about the transmittance of the transparent reflective layer.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a multilayer information recording medium that improves contrast when recording / reproducing is performed with a blue laser and has good reproduction characteristics.

  In order to solve the above-mentioned problems, the present invention firstly includes an information recording medium, a substrate, and an information surface of an N-layer recording film on which information is recorded by an atomic arrangement change caused by light irradiation (N is 2 N−1 spacer layers, and when the information surface is counted from the information surface on the light incident side, the transmittance of the information surface is information surface 1> information surface 2... Information surface N -1> information plane N, and the thickness of the substrate is 0.578 mm or more and 0.592 mm or less.

  Second, an information recording medium includes a substrate, an information surface of an N-layer recording film on which information is recorded by an atomic arrangement change caused by light irradiation (N is an integer of 2 or more), and N-1 spacers. When the information plane is counted from the information plane on the light incident side, the transmittance of the information plane is in the relationship of information plane 1> information plane 2 ... information plane N-1> information plane N, In addition, the spacer layer has a thickness of 13 μm or more and 27 μm or less.

  Third, an information recording medium includes a substrate, an information surface of an N-layer recording film on which information is recorded by an atomic arrangement change caused by light irradiation (N is an integer of 2 or more), and N−1 spacers. When the information plane is counted from the information plane on the light incident side, the transmittance of the information plane is in the relationship of information plane 1> information plane 2 ... information plane N-1> information plane N, And the thickness of the said board | substrate was 0.578 mm or more and 0.592 mm or less, and it was set as the structure that the thickness of the said spacer layer was 13 micrometers or more and 27 micrometers or less.

  Fourth, the information recording medium is an information recording medium that is recorded / reproduced by an optical system with NA of 0.65, and includes a substrate and an N-layer recording film on which information is recorded by an atomic arrangement change caused by light irradiation (N is an integer greater than or equal to 2) and N-1 spacer layers, and when the information surface is counted from the information surface on the light incident side, the transmittance of the information surface is information surface 1> Information surface 2... Information surface N-1> Information surface N, and the thickness of the substrate is 0.578 mm or more and 0.592 mm or less.

  Fifth, the information recording medium is an information recording medium that is recorded / reproduced by an optical system with NA of 0.65, and includes a substrate and an N-layer recording film on which information is recorded by an atomic arrangement change caused by light irradiation (N is an integer greater than or equal to 2) and N-1 spacer layers, and when the information surface is counted from the information surface on the light incident side, the transmittance of the information surface is information surface 1> Information surface 2... Information surface N-1> Information surface N, and the spacer layer has a thickness of 13 μm to 27 μm.

  Sixth, the information recording medium is an information recording medium that is recorded / reproduced by an optical system with NA of 0.65, and includes a substrate and an N-layer recording film on which information is recorded by an atomic arrangement change caused by light irradiation (N is an integer greater than or equal to 2) and N-1 spacer layers, and when the information surface is counted from the information surface on the light incident side, the transmittance of the information surface is information surface 1> Information surface 2... Information surface N-1> Information surface N, the thickness of the substrate is 0.578 mm or more and 0.592 mm or less, and the thickness of the spacer layer is 13 μm or more and 27 μm or less. Made the configuration.

  Seventh, in the information recording medium having any one of the first to sixth configurations, the recording film has a thickness of 4 nm to 25 nm.

  According to the present invention, an information recording medium having good recording / reproducing characteristics can be obtained.

  Hereinafter, the present invention will be described in detail by way of examples.

(Configuration and production method of information recording medium of the present invention)
FIG. 1 is a schematic diagram showing a cross-sectional structure of a disc-shaped information recording medium according to a first embodiment of the present invention. This medium was manufactured as follows. First, on a polycarbonate substrate 1 having a diameter of 12 cm and a thickness of 0.6 mm and having a tracking groove on the surface, a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about 30 nm and an Al ₄₀ O ₅₇ film having a thickness of about 4 nm. N ₃ film and the film thickness of about 1nm of _Cr 40 _O 57 _{N 3} film was laminated comprising L0 lower protective layer 2, a film thickness of about 6nm of _Ge 5 _Sb 2 _Te 8 L0 recording film 3, the film thickness of about 1nm Cr ₂ O ₃ film and the film thickness of about 4 nm _Al 2 _{O 3} film and the film thickness of about _{125nm (ZnS) 80 (SiO 2} ) formed by laminating a ₂₀ film L0 upper protective layer 4, the thickness of about 35 nm _(Al 2 O ₃ ) The L0 transparent reflecting layer 5 made of a film and the L0 uppermost protective layer 6 made of a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about 50 nm were sequentially formed. A transparent reflective layer is obtained by using the optical interference generated by the multilayer lamination of the layers 4, 5, and 6 as described above. The laminated film was formed by a magnetron sputtering apparatus. A first disk member was thus obtained.

On the other hand, a second disk member having a configuration different from that of the first disk member was obtained by the same sputtering method. The second disk member has a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about 80 nm on the L1 reflective layer 11 made of an Ag ₉₈ Pd ₁ Cu ₁ film having a thickness of about 80 nm on the polycarbonate protective substrate 12. L1 upper protective layer 10 formed by stacking about 5 nm thick Cr ₂ O ₃ , about 18 nm thick Ge ₅ Sb ₂ Te ₈ L1 recording film 9, about 5 nm thick Cr ₄₀ O ₅₇ N ₃ film and film The L1 lower protective layer 8 formed by laminating (ZnS) ₈₀ (SiO ₂ ) ₂₀ films having a thickness of about 80 nm is sequentially formed.

  Thereafter, the first disk member and the second disk member are bonded to the L0 uppermost protective layer 6 and the L1 lower protective layer 8 via the spacer layer 7, respectively, and the two-layer information recording medium (disk) shown in FIG. A) was obtained.

  For each information surface, L0 is a constituent film on the light incident side (from the L0 lower protective layer 2 to the L0 uppermost protective layer 6), and L1 is a constituent film far from the light (from the L1 lower protective layer 8 to the L1 reflective layer 11). It was.

(Construction and manufacturing method of conventional information recording medium)
In order to clarify the effect of the transparent reflective layer, a disc-shaped information recording medium having no transparent reflective layer was produced. FIG. 2 is a schematic diagram showing the cross-sectional structure of this medium.

This medium was manufactured as follows. First, on a polycarbonate substrate 1 having a diameter of 12 cm and a thickness of 0.585 mm and having a tracking groove on the surface, a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about 30 nm and an Al ₄₀ O ₅₇ film having a thickness of about 4 nm. L0 lower protective layer 2 made of N ₃ film and Cr ₄₀ O ₅₇ N ₃ film having a thickness of about 1 nm, L0 recording film 3 made of Ge ₅ Sb ₂ Te _{8 having} a thickness of about 6 nm, Cr ₂ O having a thickness of about 1 nm _The L0 upper protective layer 4 composed of _three films, an Al ₂ O ₃ film with a thickness of about 4 nm, and a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film with a thickness of about 125 nm was sequentially formed. The laminated film was formed by a magnetron sputtering apparatus. A first disk member was thus obtained.

On the other hand, a second disk member having a configuration different from that of the first disk member was obtained by the same sputtering method. The second disk member has a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about 80 nm on the L1 reflective layer 11 made of an Ag ₉₈ Pd ₁ Cu ₁ film having a thickness of about 80 nm on the polycarbonate protective substrate 12. L1 upper protective layer 10 made of Cr ₂ O _{3 with} a film thickness of about 5 nm, L1 recording film 9 made of Ge ₅ Sb ₂ Te _{8 with} a film thickness of about 18 nm, Cr ₄₀ O ₅₇ N ₃ film with a film thickness of about 5 nm The L1 lower protective layer 8 made of (ZnS) ₈₀ (SiO ₂ ) ₂₀ film of about 80 nm is sequentially formed.

  Thereafter, the first disk member and the second disk member are bonded to each other via the spacer layer 7 and the L0 upper protective layer 4 and the L1 lower protective layer 8 are bonded to each other, and the information recording medium (disc B) shown in FIG. Obtained.

(Initial crystallization)
Initial crystallization was performed on the L0 recording films 3 of the disc A and the disc B manufactured as described above as follows. Although only the L0 recording film 3 and the L1 recording film 9 will be described below, the same applies to recording films of other multilayer media.

  The medium (disk A, disk B) is rotated so that the linear velocity at the point on the recording track is 5 m / s, and the laser power of the semiconductor laser having a wavelength of about 810 nm is set to 300 mW to focus on the recording film of L1. The laser power was set to 700 mW, and the recording film 9 was irradiated in the shape of an ellipse that was long in the radial direction of the medium through the substrate 1, the L0 film, and the spacer layer. The movement of the spot was shifted by 1/24 of the spot length in the radial direction of the medium per one rotation of the medium. Thus, initial crystallization was performed. This initial crystallization may be performed once, but when it was repeated three times, the noise increase due to the initial crystallization could be reduced a little. This initial crystallization is advantageous in that it can be performed at high speed.

  Next, the laser power of a semiconductor laser having a wavelength of about 810 nm is set to 300 mW, the focus position of the laser is changed to focus on the L0 recording film, and then the laser power is set to 700 mW to pass through the substrate 1 to the recording film 3 in the radial direction of the medium. Irradiation was in the form of a long oval spot. The movement of the spot was shifted by 1/24 of the spot length in the radial direction of the medium per one rotation of the medium. Thus, initial crystallization was performed. This initial crystallization may be performed once, but when it was repeated three times, the noise increase due to the initial crystallization could be reduced a little. This initial crystallization is advantageous in that it can be performed at high speed.

  The initialization sequence may be performed from the L1 recording film or the L0 recording film, or may be performed randomly in a multilayer information recording medium having three or more layers.

(Record / Erase / Play)
The recording / erasing / reproduction specific evaluation was performed on the medium manufactured as described above and subjected to initial crystallization as follows. Hereinafter, only the recording film 9 of L1 will be described, but the same applies to the recording film 3 of L0, and the same applies to the recording films on the respective information surfaces in a multilayer information recording medium having three or more layers. .

  While performing tracking and automatic focusing on the recording area of the recording film 9 where the initial crystallization has been completed, the power of the recording laser beam is changed between the intermediate power level Pe (3 mW) and the high power level Ph (7 mW). Recorded information. The linear velocity of the recording track is 9 m / s, the semiconductor laser wavelength is 405 nm, and the numerical aperture (NA) of the lens is 0.65. The amorphous or near portion formed in the recording area by the recording laser beam is a recording point. The reflectivity of this medium is higher in the crystalline state, and the reflectivity of the recorded region in the amorphous state is lower.

  The power ratio between the high level and the intermediate level of the recording laser beam is preferably in the range of 1: 0.3 to 1: 0.7. In addition, other power levels may be set for a short time. As shown in FIG. 3, during the formation of one recording mark, the power is repeatedly reduced to the bottom power level Pb lower than the intermediate power level Pe by half the window width (Tw / 2), and the cooling power level Pc is set to the recording pulse. When recording / reproduction was performed with an apparatus having means for generating a waveform at the end of the waveform, the jitter value and error rate of the reproduced signal waveform were reduced. The cooling power level Pc is lower than the intermediate power level Pe and higher than or equal to the bottom power level Pb. This waveform is characterized in that the first pulse width Tp varies depending on the combination of the recording mark and the length of the space provided immediately before the mark, and the cooling pulse width Tc (the time width to decrease to the Pc level at the end of the recording pulse). It has characteristics determined by the combination of the recording mark and the subsequent space length of the mark. The shorter the space length immediately before the mark and the longer the mark, the shorter the Tp, the longer the space length immediately before the mark, and the shorter the mark, the longer the Tp. However, depending on the structure of the medium, when the Tp of the recording waveform for recording of the 6 Tw mark is particularly long, the effect of reducing the jitter is large. Further, the longer the subsequent space length and the longer the mark, the shorter the Tc, and the shorter the subsequent space length and the shorter the mark, the longer the Tc.

  FIG. 3 shows only recording waveforms of 3Tw, 4Tw, 6Tw, and 11Tw, but 5Tw is a series of high power level pulse trains of 6Tw recording waveform, and a power level Ph of Tw / 2 and Tw / The bottom power level Pb of 2 is reduced by one each. In addition, in the recording waveform for 7 Tw to 10 Tw, a pair of Tw / 2 high power level Ph and Tw / 2 bottom power level Pb are added one by one immediately before the last high power level pulse of the 6 Tw recording waveform. It is a thing. Accordingly, 11 Tw is obtained by adding 5 sets.

  Here, the shortest recording mark length corresponding to 3 Tw was set to 0.26 μm. After passing the portion to be recorded, the laser beam power is lowered to the low power level Pr (1 mW) of the reproducing (reading) laser beam.

In such a recording method, if new information is recorded by overwriting without erasing a portion where information is already recorded, the information is rewritten to new information. In other words, overwriting with a single substantially circular light spot is possible.

  However, the recorded information is made uniform by irradiating the continuous power of the power-modulated recording laser beam with an intermediate power level (3 mW) or a power close thereto at one or more rotations of the first disk at the time of rewriting. Erasing and then information between the bottom power level (0.5 mW) and the high power level (7 mW) or between the intermediate power level (3 mW) and the high power level (7 mW) in the next rotation. You may make it record by irradiating the laser beam power-modulated according to the signal. In this way, if the information is erased and then recorded, the remaining information that has been written before is reduced. Therefore, rewriting when the linear velocity is doubled becomes easy.

(Effect of transparent reflective layer)
Comparison was made for L0 of the information recording medium (disc A) shown in FIG. 1 having the transparent reflective layer described in the present example and the conventional information recording medium (disc B) shown in FIG. 2 having no transparent reflective layer. When comparing the C / N (carrier-to-noise ratio) of the shortest recording signal (3 Tw) at the time of the first recording, the C / N was 50 dB in the disk A, but the C / N was small in the B and was 46 dB. . The reason why the C / N was increased in the disk A is that the interference between the recording film and the transparent reflection layer can be used by providing the transparent reflection layer, and the signal amplitude has increased.

(Optical characteristics of transparent reflective layer)
The optical property dependency of the transparent reflective layer 5 was measured. A plurality of media with varying optical properties were created. C / N at the time of recording a repetitive signal of the shortest recording mark 3Tw and 3T space was measured. The results are shown in Table 1. When the composition of the transparent reflective layer changes, the extinction coefficient of the transparent reflective layer changes, and the amount of absorption in the reflective layer increases. Therefore, the difference in reflectance when the transmittance is constant is reduced, and C / N (dB) Decreased. It was. This shows that the extinction coefficient of the transparent reflective layer is preferably small. In order to secure C / N at a practical level, 48 dB or more is required, and therefore, the extinction coefficient of the transparent reflective layer is preferably 0.5 or less. In consideration of degradation due to environmental temperature fluctuations of the laser, since C / N is required to be 49 dB or more, the extinction coefficient of the transparent reflective layer is more preferably 0.3 or less. The reflectance of the transparent reflective layer is desirably 5% or more and 50% or less.

Next, the refractive index dependency of the transparent reflective layer 5 was measured. This is shown in Table 2. When the refractive index n of the transparent reflective layer changes, the amount of light interference between the upper protective layer and the transparent reflective layer changes, and therefore the difference in reflectance when the transmittance is constant is changed. Here, the reflectance difference means a difference in reflectance between the crystalline state and the amorphous state of the recording film, that is, the unrecorded state and the recorded state, in the medium.

  Accordingly, the refractive index of the transparent reflective layer needs to be 4% or more in order to ensure a practical level of the difference in reflectance, so that the refractive index of the transparent reflective layer is preferably 2.2 or less or 2.5 or more. . Further, in consideration of degradation due to environmental temperature fluctuations of the laser, a difference in reflectance of 5% or more is necessary, and therefore, the refractive index of the transparent reflective layer is more preferably 2.0 or less or 2.6 or more. .

  Furthermore, it can be seen that a larger difference from the refractive index (2.35) of the upper protective layer is preferable. The difference between the refractive index of the upper protective layer and the refractive index of the transparent reflective layer is preferably 0.15 or more. In consideration of deterioration due to environmental temperature fluctuations of the laser, the difference between the refractive index of the upper protective layer and the refractive index of the transparent reflective layer is more preferably 0.25 or more.

  It is preferable that the thickness of the transparent reflective layer, the thickness of the upper protective layer, and the thickness of the uppermost protective layer are determined so as to obtain a large difference in reflectance because C / N becomes large. The thickness of the upper protective layer is preferably 80 to 160 nm, and more preferably 100 to 140 nm. The total thickness of the transparent reflective layer and the uppermost protective layer is preferably 50 to 130 nm, and more preferably 70 to 110 nm.

  In order to use interference, the minimum thickness of the transparent reflective layer is preferably 5 nm or more, and more preferably 10 nm or more.

Transparent reflective layer materials are SiO ₂ , SiO, TiO ₂ , Al ₂ O ₃ , Y ₂ O ₃ , CeO ₂ , La ₂ O ₃ , In ₂ O ₃ , GeO, GeO ₂ , PbO, SnO, SnO ₂ , BeO. , Bi ₂ O ₃ , TeO ₂ , WO ₂ , WO ₃ , Sc ₂ O ₃ , Ta ₂ O ₅ , ZrO ₂ , Cu ₂ O, MgO and other oxides, TaN, AlN, BN, CrN, Si ₃ N ₄ , GeN, and nitrides such as Al—Si—N based materials (for example, AlSiN ₂ ) are preferable. These elemental ratio in the compound, for example the ratio of the metal element and oxygen element and sulfur element in the oxide or _{sulfide, Al 2 O 3, Y 2} O 3, La 2 O 3 is _{2: 3, SiO 2, ZrO} 2 , GeO ₂ is preferably 1: 2, Ta ₂ O ₅ is 2: 5, and ZnS is 1: 1 or close to the ratio, but the same effect can be obtained even if the ratio is out of the ratio. However, when deviating from the above integer ratio, for example, Al—O has a ratio of Al to O of Al ₂ O ₃ to Al amount of ± 10 atomic% or less, and Si—O has a ratio of Si to O of SiO ₂ to Si. The deviation of the amount of metal elements, such as ± 10 atomic% or less, is preferably 10 atomic% or less. When the deviation was 10 atomic% or more, the optical characteristics were changed, so that the degree of modulation decreased by 10% or more.

  In addition, materials having the above optical characteristics can also be used. It has been found that when the impurity element in the transparent reflective layer material exceeds 5 atomic%, the increase in jitter at the time of overwriting 10,000 times or more becomes 5% or more. Therefore, it is preferable that the impurity element in the transparent reflective layer material is 5 atomic% or less of the transparent reflective layer component because deterioration of the rewriting characteristics can be reduced. More preferably, it is 2 atomic% or less.

(Lower protective layer)
In this embodiment, the L1 lower protective layer 8 has a two-layer structure of (ZnS) ₈₀ (SiO ₂ ) ₂₀ and Cr ₄₀ O ₅₇ N ₃ layers. The L0 lower protective layer 2 has a three-layer structure in which a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film, an Al ₄₀ O ₅₇ N ₃ film having a thickness of about 4 nm, and a Cr ₄₀ O ₅₇ N ₃ film having a thickness of about 1 nm are stacked. It is said. As a material replacing the (ZnS) ₈₀ (SiO ₂ ) ₂₀ of the lower protective layers 2 and 8 having a two-layer structure, a material in which the mixing ratio of ZnS and SiO ₂ is changed is preferable. Also, ZnS, Si—N-based material, Si—O—N-based material, SiO ₂ , SiO, TiO ₂ , Al ₂ O ₃ , Y ₂ O ₃ , CeO ₂ , La ₂ O ₃ , In ₂ O ₃ , GeO _{, GeO 2, PbO, SnO,} SnO 2, BeO, Bi 2 O 3, TeO 2, WO 2, WO 3, Sc 2 O 3, Ta 2 O 5, ZrO 2, Cu 2 O, oxides such as MgO, _{TaN, AlN, BN, Si 3} N 4, GeN, Al-Si-N material (e.g., AlSiN ₂₎ nitride such _{as, ZnS, Sb 2 S 3,} CdS, in 2 S 3, Ga 2 S 3, GeS , SnS ₂ , PbS, Bi ₂ S ₃ , sulfides, SnSe ₂ , Sb ₂ Se ₃ , CdSe, ZnSe, In ₂ Se ₃ , Ga ₂ Se ₃ , GeSe, GeSe ₂ , SnSe, PbSe, Bi _Using selenides such as ₂ Se ₃ , fluorides such as CeF ₃ , MgF ₂ , and CaF ₂ , Si, Ge, TiB ₂ , B ₄ C, B, C, or those having a composition close to the above materials Also good. Further, a layer of a mixed material such as ZnS—SiO ₂ or ZnS—Al ₂ O ₃ or a multilayer thereof may be used. Among them, ZnS has a high sputter rate, and if ZnS occupies 60 mol% or more, the film formation time can be shortened. Therefore, in the case of a mixture containing 60 mol% or more, the point that the sputtering rate of ZnS is large and oxides and nitrides These are combined with good chemical stability. Other sulfides and selenides obtained characteristics similar to ZnS.

These elemental ratio in the compound, for example the ratio of the metal element and oxygen element and sulfur element in the oxide or _{sulfide, Al 2 O 3, Y 2} O 3, La 2 O 3 is _{2: 3, SiO 2, ZrO} 2 , GeO ₂ is preferably 1: 2, Ta ₂ O ₅ is 2: 5, and ZnS is 1: 1 or close to the ratio, but the same effect can be obtained even if the ratio is out of the ratio. However, when deviating from the above integer ratio, for example, Al—O has a ratio of Al to O of Al ₂ O ₃ to Al amount of ± 10 atomic% or less, and Si—O has a ratio of Si to O of SiO ₂ to Si. The deviation of the amount of metal elements, such as ± 10 atomic% or less, is preferably 10 atomic% or less. When the deviation was 10 atomic% or more, the optical characteristics were changed, so that the degree of modulation decreased by 10% or more.

  The material is preferably 90% or more of the total number of atoms of the lower protective layer. When impurities other than the above materials were 10 atomic% or more, the rewriting characteristics were deteriorated such that the number of possible rewritings was ½ or less.

  The extinction coefficient k of the lower protective layer used in this example is preferably 0 or close to 0. Furthermore, if the extinction coefficient k is k ≦ 0.01 at a film thickness of 80% or more of the lower protective layer material, it is preferable that the decrease in contrast can be suppressed to 2% or less.

If the lower protective layer is made of two or more layers and the lower protective layer material on the recording film side is Cr ₂ O ₃ or Cr ₄₀ O ₅₇ N ₃ , the diffusion of Zn and S to the recording film can be suppressed at the time of rewriting many times, and the rewriting characteristics are improved. It was found to be good. As a material replacing Cr ₂ O ₃ of the lower protective layer material on the recording film side, a mixture of Cr ₂ O ₃ and SiO ₂ , Ta ₂ O ₅ , Al ₂ O ₃ , ZrO ₂ —Y ₂ O ₃ is preferable. . Next, CoO or GeO ₂ , NiO, and a mixture of these and Cr ₂ O ₃ are preferable. These oxides have a small extinction coefficient k and very low absorption in the lower interface layer. Therefore, there is an advantage that the modulation degree can be kept large.

In addition, if a part of Cr ₂ O ₃ or Cr ₄₀ O ₅₇ N ₃ is changed to Al ₂ O ₃ or Al ₄₀ O ₅₇ N ₃ , the absorption other than the recording film is reduced and the transmittance can be increased. C / N is great and this is good. Similar characteristics were obtained even when SiO ₂ or Si ₃₃ O ₆₃ N ₄ was used instead of Al ₂ O ₃ or Al ₄₀ O ₅₇ N ₃ , or those having different ratios of nitrogen and oxygen.

Further, AlN, BN, CrN, Cr2N , GeN, HfN, Si 3 N 4, Al-Si-N material (e.g., AlSiN _2), Si-N-based material, Si-O-N-based material, TaN, TiN, Nitrides such as ZrN have a longer shelf life and are more resistant to changes in ambient temperature, which is more preferable. Adhesive strength is improved even with a recording film composition containing nitrogen or a material having a composition close thereto.

_{Other, BeO, Bi 2 O 3,} CeO 2, Cu 2 O, CuO, CdO, Dy 2 O 3, FeO, Fe 2 O 3, Fe 3 O 4, GeO, GeO 2, HfO 2, In 2 O 3, La ₂ O ₃ , MgO, MnO, MoO ₂ , MoO ₃ , NbO, NbO ₂ , PbO, PdO, SnO, SnO ₂ , Sc ₂ O ₃ , SrO, ThO ₂ , TiO ₂ , Ti ₂ O ₃ , TiO, TeO ₂ , VO, V ₂ O ₃ , VO ₂ , WO ₂ , WO ₃ and other oxides, C, Cr ₃ C ₂ , Cr ₂₃ C ₆ , Cr ₇ C ₃ , Fe ₃ C, Mo ₂ C, WC, W A carbide such as ₂ C, HfC, TaC, CaC ₂ , a composition close to the above material, or a mixed material thereof may be used.

  When an oxide or nitride layer is provided on the recording film side of the lower protective layer, diffusion of Zn, S, etc. into the recording film can be prevented, and increase in disappearance can be suppressed. Further, in order not to lower the recording sensitivity, it is preferably 25 nm or less, and more preferably 10 nm or less. A uniform film can be formed at about 2 nm or more, and 5 nm or more is even better. Accordingly, it is preferable that the thickness of the lower protective layer on the recording film side is 2 to 25 nm because the recording / reproducing characteristics are improved. In the case of less than C, the C / N decreased due to recrystallization. Further, when the thickness of the lower protective layer was less than 10 nm, the protective effect of the recording film was lost, so the number of rewritable times decreased by one digit or more. What is described as the lower protective layer means the L0 lower protective layer, the L1 lower protective layer, and the lower protective layer of the multilayer information recording medium.

(Recording film)
In this embodiment, the recording film 3 and the recording film 9 are made of Ge ₅ Sb ₂ Te ₈ . The refractive index at the reproduction wavelength of the recording film is 2.0 in the crystalline state and 2.6 in the amorphous state, which is smaller in the crystalline state.

As materials for the recording films 3 and 9 instead of Ge ₅ Sb ₂ Te ₈ , Ag ₃ Ge ₃₀ Sb ₁₄ Te ₅₃ , Cr ₃ Ge ₃₂ Sb ₁₃ Te ₅₂ , Ag-Ge-Sb-Te system, Cr-Ge-, etc. Sb—Te materials having different composition ratios are preferable because the degree of modulation increases. If the amount of Ag or Cr in the recording film 3 and / or recording film 9 is large, the change in reflectance at a short wavelength increases, but the crystallization speed decreases. Therefore, the amount of Ag or Cr added is preferably 2 atomic% or more and 10 atomic% or less. However, overwriting is possible even with a Ge—Sb—Te-based material to which no Ag is added. As an element added to the recording films 3 and 9 instead of Ag, any of Cr, W, Mo, Pt, Co, Ni, Pd, Si, Au, Cu, V, Mn, Fe, Ti, and Bi Even when replaced with at least one of the above, it was found that the overwrite characteristics were good. All of these recording film 3 and 9 materials have a refractive index at the reproduction wavelength that is smaller in the crystalline state than in the amorphous state.

In this example, the thickness of the recording film 9 was changed, and the jitter (σ / Tw) after 10 times of rewriting and 100,000 times of rewriting was measured. With respect to the film thickness (nm) of the recording film 9, the value of the worse edge edge or rear edge jitter (%) after 10 rewrites, and the front edge jitter value (%) after 10,000 rewrites. showed that.

  From this, it was found that when the film thickness of the recording film 9 is reduced, the jitter after 10 times of rewriting increases due to the flow and segregation of the recording film, and when it is increased, the jitter after 10,000 times of rewriting increases. Accordingly, the film thickness of the recording film 9 is 4 nm or more and 25 nm or less, and the jitter can be 20% or less, and if it is 5 nm or more and 20 nm or less, the jitter can be 15% or less, which is more preferable.

  Regarding the film thickness of the recording film 3 and the recording film thickness on the 1-N-1 information surface (layer), the recording film thickness on the information surface is information surface 1 ≦ information surface 2 ≦. ≦ Information plane N is preferable because recording / reproduction can be performed on each information plane. Further, it is preferable that the total film thickness of the first to N-1th information surface recording films from the light incident side substrate is 10 nm or less because the C / N of the Nth information surface can be increased to 48 dB or more. The total film thickness of 8 nm or less is more preferable because the C / N of the Nth information surface can be as large as 49 dB or more.

(Upper protective layer)
In this example, the upper protective layer 10 was formed of ZnS—SiO ₂ and Cr ₄₀ O ₆₀ . The L0 upper protective layer 4 has a three-layer structure in which a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film, an Al ₄₀ O ₆₀ film with a thickness of about 4 nm, and a Cr ₄₀ O ₆₀ film with a thickness of about 1 nm are stacked.

As the material of the upper protective layer in place of ZnS—SiO ₂ , Si—N materials, Si—O—N materials, ZnS, SiO ₂ , SiO, TiO ₂ , Al ₂ O ₃ , Y ₂ O ₃ , CeO _{2 are used.} , La ₂ O ₃ , In ₂ O ₃ , GeO, GeO ₂ , PbO, SnO, SnO ₂ , BeO, Bi ₂ O ₃ , TeO ₂ , WO ₂ , WO ₃ , Sc ₂ O ₃ , Ta ₂ O ₅ , ZrO ₂ , oxides such as Cu ₂ O, MgO, nitrides such as TaN, AlN, BN, Si ₃ N ₄ , GeN, and Al—Si—N-based materials (eg, AlSiN ₂ ), ZnS, Sb ₂ S ₃ , CdS _{, in 2 S 3, Ga 2} S 3, GeS, SnS 2, PbS, sulfides such as _{Bi 2 S 3, SnSe 2,} Sb 2 Se 3, CdSe, ZnSe, in 2 Se 3, Ga 2 Se 3, G _Se, GeSe 2, SnSe, PbSe, selenides, such as _{Bi 2 Se 3, CeF 3,} MgF 2, fluorides such as CaF _2, or _{Si, Ge, TiB 2, B} 4 C, B, C or above, A composition close to the material may be used. Further, a layer of a mixed material such as ZnS—SiO ₂ or ZnS—Al ₂ O ₃ or a multilayer thereof may be used. The extinction coefficient is preferably 0 or close to 0.

These elemental ratio in the compound, for example the ratio of the metal element and oxygen element and sulfur element in oxide or _{sulfide, Al 2 O 3, Y 2} O 3, La 2 O 3 is _{2: 3, SiO 2, ZrO} 2 , GeO ₂ is preferably 1: 2, Ta ₂ O ₅ is 2: 5, and ZnS is 1: 1 or close to the ratio, but the same effect can be obtained even if the ratio is out of the ratio. In the case of deviation from the above integer ratio, for example, Al—O has a ratio of Al to O of Al ₂ O ₃ to Al amount of ± 10 atomic% or less, and Si—O has a ratio of Si to O of SiO ₂ to Si amount. The deviation of the amount of metal elements such as ± 10 atomic% or less is preferably 10 atomic% or less. When the deviation was 10 atomic% or more, the optical characteristics were changed, so that the degree of modulation decreased by 10% or more.

  The material is preferably 90% or more of the total number of atoms in the upper protective layer. When impurities other than the above materials were 10 atomic% or more, the rewriting characteristics were deteriorated such that the number of possible rewritings was ½ or less.

It can be seen that if the upper protective layer is made of two or more layers and the upper protective layer material on the recording film side is Cr ₂ O ₃ , the diffusion of Zn and S to the recording film can be suppressed at the time of rewriting many times, and the rewriting characteristics are improved. It was.

Furthermore, it was found that it is preferable to change a part of the material to Al ₂ O ₃ or SiO ₂ because the contrast can be increased.

  The term “upper protective layer” means the L0 upper protective layer, the L1 upper protective layer, and the upper protective layer of the multilayer information recording medium.

(Reflective layer)
In this example, an Ag ₉₈ Pd ₁ Cu ₁ film was used for the reflective layer 11. As the material of the other reflective layer, a material mainly composed of an Ag alloy such as Ag—Pt, Ag—Au or the like is preferable. Ag can also be used. When the content of elements other than Ag in the Ag alloy is in the range of 0.5 atomic% to 4 atomic%, the characteristics and bit error rate at the time of rewriting many times are improved, and 1 atomic% to 2 atomic%. It was found that the range was better.

In addition, a Zn ₉₈ Pd ₂ film, a Zn ₉₈ Pt ₂ film, a Zn ₉₈ Cu ₂ film, a Zn ₉₈ Ni ₂ film, a Zn—Pd film, a Zn—Pt film, a Zn—Cu film, and a Zn—Ni film are made of an Ag-based material. There is an advantage that the cost is lower than that. Zn can also be used. When the content of elements other than Zn in the Zn alloy is in the range of 0.5 atomic% to 4 atomic%, the characteristics and bit error rate at the time of rewriting many times are improved, and 1 atomic% to 2 atomic%. It was found that the range was better.

  Then, Au, Al, Cu, Ni, Fe, Co, Cr, Ti, Pd, Pt, W, Ta, Mo, Sb, Bi, Dy, Cd, Mn, Mg, V element simple substance, or Au alloy, Other than these alloys, such as an Ag alloy, a Cu alloy, a Pd alloy, a Pt alloy, or the like, or a layer made of these alloys may be used. As described above, the reflective layer is made of a metal element, a metalloid element, an alloy thereof, or a mixture thereof.

  Among these, those having a high reflectance such as Ag, Al, Al alloy, Ag alloy, etc. have a high contrast ratio and good rewriting characteristics. The adhesive strength of the alloy is greater than that of the simple substance. In this case, if the content of elements other than Al, Ag, etc. as the main component is in the range of 0.5 atomic% or more and 5 atomic% or less, as in the case of the Ag alloy, the contrast ratio is large and the adhesive force can be increased. there were. It became better in the range of 1 atomic% to 2 atomic%. When the reflectance near a wavelength of 400 nm is compared, Ag or Ag alloy is about 95% and Al and Al alloy are about 92%, which is larger in the Ag system, but the material cost is also high. As materials next to these, Zn and Zn alloys were about 89%, and Pt and Pt alloys were about 65%, showing high reflectivity at short wavelengths and high contrast.

  The material is preferably 95% or more of the total number of atoms in the reflective layer. When impurities other than the above materials were 5 atomic% or more, the rewriting characteristics were deteriorated such that the number of rewritable times was ½ or less.

  When the thickness of the reflective layer is less than 20 nm, the strength is weak, the thermal diffusion is small, and the recording film flows easily, so that the jitter after 10,000 rewrites is greater than 15%. It can be reduced to 15% at 30 nm. Further, when the thickness of the reflective layer was greater than 200 nm, the time for producing each reflective layer was increased, and the formation time was doubled by dividing the process into two or more steps or providing two or more vacuum chambers for sputtering. Further, when the thickness of the reflective layer was 5 nm or less, the film was formed in an island shape, and noise increased. Accordingly, the thickness of the reflective layer is preferably 5 nm or more and 200 nm or less from the viewpoint of noise, jitter, and formation time.

(substrate)
In this embodiment, the polycarbonate substrate 1 having a tracking groove directly on the surface is used. Instead, a polyolefin, epoxy, acrylic resin, chemically tempered glass having an ultraviolet curable resin layer formed on the surface, or the like is used. Also good. Quartz or CaF may be used instead of tempered glass.

  A substrate having a tracking groove is a groove having a depth greater than or equal to λ / 12n ′ (n ′ is the refractive index of the substrate material) when the recording / reproducing wavelength is λ on all or part of the substrate surface. It is a substrate with The groove may be formed continuously in one round or may be divided in the middle. It has been found that when the groove depth is about λ / 6n ′, the crosstalk becomes small. Further, it has been found that when the groove depth is deeper than about λ / 3n ′, the yield at the time of forming the substrate is deteriorated, but the cross erase becomes small, which is preferable.

  Further, the groove width may vary depending on the location. A substrate with a sample servo format without any groove, another tracking method, a substrate with another format, or the like may be used. A substrate having a format capable of recording / reproducing in both the groove portion and the land portion may be used, or a substrate having a format in which recording is performed on one of them may be used. If the track pitch is small, signal leakage from the adjacent track is detected and becomes noise. Therefore, the track pitch is preferably at least 1/2 of the spot diameter (region where the light intensity is 1 / e 2). .

  The disk size is not limited to a diameter of 12 cm, but may be other sizes such as 13 cm, 8 cm, 3.5 inches, 2.5 inches, and the like. The disc thickness is not limited to 0.6 mm, but may be other thicknesses such as 1.2 mm, 0.8 mm, 0.4 mm, and 0.1 mm.

  In this embodiment, the spacer layers are used for bonding, but a disk member having a different configuration or a protective substrate may be used instead of the second disk member. The disk member or the protective substrate used for bonding may be formed from the protective substrate side as shown in FIG. 5 and finally the light incident side substrate 1 may be formed or bonded. Alternatively, the two disks produced in this way may be bonded to form a double-sided disk. When the transmittance in the ultraviolet wavelength region is large, the bonding can also be performed with an ultraviolet curable resin. Bonding may be performed by other methods. In addition, when an ultraviolet curable resin is applied to the uppermost layer of the first and second disk members to a thickness of about 10 μm before the first and second disk members are bonded together, It can be reduced more.

(Film thickness and material of each layer)
The recording / reproduction characteristics and the like of the thickness and material of each layer can be improved only by taking a single preferred range, but the effect is further enhanced by combining the preferred ranges.

(Configuration and production method of information recording medium)
An information recording medium having the cross-sectional structure shown in the schematic diagram of FIG. This medium was manufactured as follows. First, on a polycarbonate substrate 1 having a diameter of 12 cm and a thickness of 0.6 mm and having a tracking groove on the surface, a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about 30 nm and an Al ₄₀ O ₅₇ film having a thickness of about 4 nm. L0 lower protective layer 2 made of N ₃ film and Cr ₄₀ O ₅₇ N ₃ film having a thickness of about 1 nm, L0 recording film 3 made of Ge ₅ Sb ₂ Te _{8 having} a thickness of about 6 nm, Cr ₂ O having a thickness of about 1 nm _{From the} L0 upper protective layer 4 composed of _three films, an Al ₂ O ₃ film with a film thickness of about 4 nm and a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film with a film thickness of about 125 nm, from an (Al ₂ O ₃ ) film with a film thickness of about 35 nm The L0 transparent reflective layer 5 and the L0 uppermost protective layer 6 made of (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about 50 nm were sequentially formed. The laminated film was formed by a magnetron sputtering apparatus. A first disk member was thus obtained.

On the other hand, a second disk member having a configuration different from that of the first disk member was obtained by the same sputtering method. The second disk member has a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about 120 nm on the L1 reflective layer 11 made of an Ag ₉₈ Pd ₁ Cu ₁ film having a thickness of about 80 nm on the polycarbonate protective substrate 12. L1 upper protective layer 10 made of Cr ₂ O _{3 with} a thickness of about 5 nm, L1 recording film 9 made of Ge ₅ Sb ₂ Te _{8 with} a thickness of about 10 nm, Cr ₄₀ O ₅₇ N ₃ film with a thickness of about 5 nm and a thickness The L1 lower protective layer 8 made of (ZnS) ₈₀ (SiO ₂ ) ₂₀ film of about 95 nm is sequentially formed.

  Thereafter, the first disk member and the second disk member are bonded to the L0 uppermost protective layer 6 and the L1 lower protective layer 8 via the spacer layer 7, respectively, and the two-layer information recording medium (disk) shown in FIG. A) was obtained.

  For each information surface, L0 is a constituent film on the light incident side (from the L0 lower protective layer 2 to the L0 uppermost protective layer 6), and L1 is a constituent film far from the light (from the L1 lower protective layer 8 to the L1 reflective layer 11). It was.

  As a result, the reflectivity of the L1 disk was lower in the crystal state than in the amorphous state. Further, when the film thickness of the lower protective layer, the recording film, and the upper protective layer is changed, the absorption ratio of the recording film Ac / Aa (Ac is absorption in the recording film in the crystalline state, and Aa is absorption in the recording film in the amorphous state). Compared with L1 of the multilayer information recording medium described in Example 1, it was found that L1 of this example can reduce the jitter at the time of overwriting by 5% or more.

  A preferable range of the L1 lower protective layer 8 film thickness is 70 nm to 140 nm, and a more preferable range is 80 nm to 130 nm. A preferable range of the L1 upper protective layer 10 film thickness is 95 nm to 155 nm, and a more preferable range is 105 nm to 145 nm. The preferred range of the L1 recording film 9 film thickness is as described in Example 1.

(Configuration and production method of information recording medium of the present invention)
FIG. 4 is a schematic diagram showing a cross-sectional structure of the multilayer disc-shaped information recording medium of the present invention. Two or more layers of media were produced in this way. A three-layer medium is shown as an example.

First, on a polycarbonate protective substrate 30 having a diameter of 12 cm and a thickness of 0.6 mm and having a tracking groove on the surface, a film thickness of about 80 nm is formed on an L2 reflective layer 29 made of an Ag ₉₈ Pd ₁ Cu ₁ film having a film thickness of about 80 nm. (ZnS) ₈₀ (SiO ₂ ) ₂₀ film, an L2 upper protective layer 28 made of Cr ₂ O ₃ with a film thickness of about 5 nm, an L2 recording film 27 made of Ge ₅ Sb ₂ Te _{8 with} a film thickness of about 18 nm, and a film thickness of about The L2 lower protective layer 26 composed of a 5 nm Cr ₄₀ O ₅₇ N ₃ film and an approximately 80 nm thick (ZnS) ₈₀ (SiO ₂ ) ₂₀ film is sequentially formed.

Thereafter, an L1-L2 spacer layer 25 having a tracking groove on the surface was formed by a photopolymerization method (2P method) in which the tracking groove was transferred from a stamper using an ultraviolet curable resin. On top of this, L1 was formed. On the L1-L2 spacer layer 25, the L1 uppermost protective layer 24 made of a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about 50 nm, and the L1 transparent made of an (Al ₂ O ₃ ) film having a thickness of about 35 nm. Reflective layer 23, L1 upper protective layer 22 made of (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about 120 nm, Al ₂ O ₃ film having a thickness of about 4 nm, and Cr ₂ O ₃ film having a thickness of about 1 nm, film An L1 recording film 21 made of Ge ₅ Sb ₂ Te _{8 having} a thickness of about 5 nm, a Cr ₄₀ O ₅₇ N ₃ film having a thickness of about 1 nm, an Al ₄₀ O ₅₇ N ₃ film having a thickness of about 4 nm, and a (ZnS) film having a thickness of about 125 nm. ) L1 lower protective layer 20 made of ₈₀ (SiO ₂ ) ₂₀ film was sequentially formed.

  Next, an L0-L1 spacer layer 19 was formed by the same 2P method as before.

On the L0-L1 spacer layer 19, the L0 uppermost protective layer 18 made of (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a film thickness of about 50 nm, and the L0 transparent reflection made of (Al ₂ O ₃ ) film having a film thickness of about 35 nm. Layer 17, L0 upper protective layer 16 composed of (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about 120 nm, Al ₂ O ₃ film having a thickness of about 4 nm, and Cr ₂ O ₃ film having a thickness of about 1 nm, film thickness An L0 recording film 3 made of Ge ₅ Sb ₂ Te ₈ having a thickness of about 4 nm, a Cr ₄₀ O ₅₇ N ₃ film having a thickness of about 1 nm, an Al ₄₀ O ₅₇ N ₃ film having a thickness of about 4 nm, and a (ZnS) film having a thickness of about 125 nm. _{80 (SiO 2) 20} composed of a film L0 lower protective layer 15, the film thickness of about _{25nm (ZnS) 80 (SiO 2} ) were sequentially formed L0 uppermost protective layer 14 made of ₂₀ film. Finally, the substrate 13 was attached. The laminated film was formed by a magnetron sputtering apparatus. A multilayer disk member was thus obtained. Initialization and recording / reproducing methods are the same as those in the first embodiment. In this way, recording / reproduction can be performed with three or more layers on one side.

(Configuration and production method of information recording medium)
A multilayer information recording medium was produced in which only the thickness of the substrate 1 of the information recording medium of Example 1 was changed in the range of 0.575 to 0.596 mm. (Disc E1-E8)
(Substrate thickness dependency)
A recording signal of 3 Tw was recorded on each layer of the information recording media (discs E1 to E8) of this example, and the S / N ratio (signal to noise ratio) was measured. The results are shown in Table 4.

  As described above, when the substrate thickness is too thick, the focus is shifted, so the S / N of L1 is lowered, and when the plate thickness is too thin, the focus is shifted and the S / N of L0 is lowered. Therefore, it was found that the substrate thickness of the multilayer information recording medium is preferably 0.578 mm or more and 0.592 or less because a signal can be reproduced without error when recording / reproducing with an optical system of NA 0.65. Furthermore, since it can reproduce | regenerate at the level applicable also to the fluctuation | variation of environmental temperature, the board | substrate thickness is 0.58 mm or more and 0.59 mm or less more preferable. Moreover, since the laser wavelength is shorter than 660 nm, the plate thickness tolerance is small. Accordingly, the difference between the maximum thickness and the minimum thickness is preferably 0.014 mm or less, and more preferably 0.01 mm or less.

  Matters not described in the present embodiment are the same as those in the first to third embodiments and the fifth embodiment.

(Configuration and production method of information recording medium)
A multilayer information recording medium in which the thickness of the spacer layer 7 of the information recording medium of Example 1 was changed in the range of 10 to 31 μm was produced. (Disc F1-F8)
(Substrate thickness dependency)
A recording signal of 3 Tw was recorded on each layer of the information recording media (discs F1 to F8) of this example, and the S / N ratio (signal to noise ratio) was measured. The results are shown in Table 5.

  As described above, when the spacer layer thickness is too thick, the focus is shifted, so that the S / N ratio of L1 is lowered. When the spacer layer thickness is too thin, the focus is shifted and the S / N ratio of L0 is lowered. Therefore, it was found that the spacer layer thickness of the multilayer information recording medium is preferably 13 μm or more and 27 μm or less because a signal can be reproduced without error when recording / reproducing with an optical system of NA 0.65. Furthermore, the spacer layer thickness is more preferably 15 μm or more and 25 μm or less because it can be regenerated at a level applicable to fluctuations in environmental temperature. Also, since the laser wavelength is shorter than 660 nm, the allowable spacer layer thickness is small. Therefore, the difference between the maximum thickness and the minimum thickness is preferably 14 μm or less, and more preferably 10 μm or less.

  Matters not described in the present embodiment are the same as those in the first to fourth embodiments.

(Configuration and production method of information recording medium)
A multilayer information recording medium in which the thickness of the substrate 1 of the information recording medium of Example 1 was changed to 0.094 mm and the thickness of the spacer layer 7 was changed to 9 μm was produced. In this method of manufacturing the medium, as described in Example 3, the L1 film was stacked from the protective substrate side, the spacer layer was then formed by the 2P method, and then the L0 film was stacked to form the substrate 1. The substrate 1 may be formed by any one of spin coating and 2P methods, a combination thereof, or another method. The plate thickness is preferably in the range of Example 7. When the plate thickness is shifted, the S / N is deteriorated, but recording / reproducing is possible.

  About the matter which is not described in a present Example, it is the same as that of Examples 1-3, 7-8.

(Configuration and production method of information recording medium)
A multilayer information recording medium was produced in which only the thickness of the substrate 1 of the information recording medium of Example 1 was changed in the range of 0.091 to 0.097 mm. (Disks H1-H8)
(Substrate thickness dependency)
A recording signal of 3 Tw was recorded on each layer of the information recording medium (discs H1 to H8) of this example, and the S / N ratio (signal to noise ratio) was measured. The results are shown in Table 6.

  As described above, when the substrate thickness is too thick, the focus is shifted, so the S / N of L1 is lowered, and when the plate thickness is too thin, the focus is shifted and the S / N of L0 is lowered. Therefore, it was found that the substrate thickness of the multilayer information recording medium is preferably 0.091 mm or more and 0.097 mm or less because a signal can be reproduced without error when recording / reproducing with an optical system of NA 0.85. Furthermore, since it can reproduce | regenerate at the level applicable also to the fluctuation | variation of environmental temperature, 0.092 mm or more and 0.096 mm or less are more preferable. Moreover, since the laser wavelength is shorter than 660 nm, the plate thickness tolerance is small. Therefore, the difference between the maximum thickness and the minimum thickness is preferably 0.006 mm or less, and more preferably 0.004 mm or less.

  Matters not described in the present embodiment are the same as those in the first to third embodiments and the sixth and eighth embodiments.

(Configuration and production method of information recording medium)
A multilayer information recording medium in which the thickness of the spacer layer 7 of the information recording medium of Example 6 was changed in the range of 7 to 13 μm was produced. (Disks J1-J8)
(Substrate plate thickness dependency) A recording signal of 3 Tw was recorded on each layer of the information recording medium (discs J1 to J8) of this example, and the S / N ratio (signal to noise ratio) was measured. The results are shown in Table 7.

  As described above, when the spacer layer thickness is too thick, the focus is shifted, so that the S / N ratio of L1 is lowered. When the spacer layer thickness is too thin, the focus is shifted and the S / N ratio of L0 is lowered. Therefore, it was found that the spacer layer thickness of the multilayer information recording medium is preferably 7 μm or more and 13 μm or less because signals can be reproduced without error when recording / reproducing with an optical system of NA 0.85. Furthermore, the spacer layer thickness is more preferably 8 μm or more and 12 μm or less because it can be reproduced at a level applicable to fluctuations in environmental temperature. Also, since the laser wavelength is shorter than 660 nm, the allowable spacer layer thickness is small. Therefore, the difference between the maximum thickness and the minimum thickness is preferably 6 μm or less, and more preferably 4 μm or less.

  About the matter which is not described in a present Example, it is the same as that of Examples 1-3 and 6-7.

The cross-sectional schematic diagram of an example of the information recording medium by this invention. The cross-sectional schematic diagram of the information recording medium of conventional structure. The figure which shows the recording waveform used for the recording and reproducing characteristic evaluation of the information recording medium of this invention. The cross-sectional schematic diagram which shows the other example of the information recording medium by this invention. The cross-sectional schematic diagram which shows the other example of the information recording medium by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1 'board | substrate 2,2' lower protective layer 3,3 'recording film 4,4' upper protective layer 5,5 'cooling control layer 6,6' reflective layer 7 bonding resin 8,8 'contrast expansion layer 14 Substrate T Wind width (Tw)
Pc Cooling pulse power level Pe Intermediate power level Ph High power level Pp Preheat power level P1 Power level 0 Tc Cooling pulse width Tp First pulse width

Claims (7)

  A light incident side having a substrate, an information surface of an N-layer recording film on which information is recorded by an atomic arrangement change caused by light irradiation (N is an integer of 2 or more), and N-1 spacer layers When the information surface is counted from the information surface, the transmittance of the information surface is in the relationship of information surface 1> information surface 2 ... information surface N-1> information surface N, and the thickness of the substrate is 0. An information recording medium characterized by being 578 mm or more and 0.592 mm or less.   A light incident side having a substrate, an information surface of an N-layer recording film on which information is recorded by an atomic arrangement change caused by light irradiation (N is an integer of 2 or more), and N-1 spacer layers When the information surface is counted from the information surface, the transmittance of the information surface is in the relationship of information surface 1> information surface 2... Information surface N-1> information surface N, and the thickness of the spacer layer is 13 μm. An information recording medium having a thickness of 27 μm or less.   A light incident side having a substrate, an information surface of an N-layer recording film on which information is recorded by an atomic arrangement change caused by light irradiation (N is an integer of 2 or more), and N-1 spacer layers When the information surface is counted from the information surface, the transmittance of the information surface is in the relationship of information surface 1> information surface 2 ... information surface N-1> information surface N, and the thickness of the substrate is 0. An information recording medium characterized in that it is 578 mm or more and 0.592 mm or less, and the spacer layer has a thickness of 13 μm or more and 27 μm or less.   An information recording medium that is recorded / reproduced by an optical system with NA of 0.65, and includes an information surface of a substrate and an N-layer recording film on which information is recorded by an atomic arrangement change caused by light irradiation (N is 2 or more) N−1 spacer layers, and when the information surface is counted from the information surface on the light incident side, the transmittance of the information surface is information surface 1> information surface 2... Information surface N− 1> An information recording medium having an information plane N relationship, and the thickness of the substrate being 0.578 mm or more and 0.592 mm or less.   An information recording medium that is recorded / reproduced by an optical system with NA of 0.65, and includes an information surface of a substrate and an N-layer recording film on which information is recorded by an atomic arrangement change caused by light irradiation (N is 2 or more) N−1 spacer layers, and when the information surface is counted from the information surface on the light incident side, the transmittance of the information surface is information surface 1> information surface 2... Information surface N− 1> An information recording medium which has an information plane N relationship, and the spacer layer has a thickness of 13 μm to 27 μm.   An information recording medium that is recorded / reproduced by an optical system with NA of 0.65, and includes an information surface of a substrate and an N-layer recording film on which information is recorded by an atomic arrangement change caused by light irradiation (N is 2 or more) N−1 spacer layers, and when the information surface is counted from the information surface on the light incident side, the transmittance of the information surface is information surface 1> information surface 2... Information surface N− 1> An information recording medium having an information plane N relationship, wherein the substrate has a thickness of 0.578 mm to 0.592 mm, and the spacer layer has a thickness of 13 μm to 27 μm.   7. The information recording medium according to claim 1, wherein the recording film has a thickness of 4 nm to 25 nm.

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