JP4080515B2 - Optical recording method for two-layer phase change information recording medium - Google Patents

Description

  The present invention relates to an optical information recording medium that performs optical information recording / reproduction, and more particularly to an optical recording method for a two-layer phase change information recording medium.

  Optical discs such as CD-R and CD-RW have a recording layer provided on a plastic circular substrate such as polycarbonate, and a reflective layer is formed thereon by vapor deposition or sputtering of a metal such as aluminum, gold or silver. Then, laser light is incident from the substrate surface side to record and reproduce signals. In recent years, since the amount of information handled by computers and the like has increased, the signal recording capacity of optical disks such as DVD-RAM, DVD-RW, and DVD + RW has increased and the density of signal information has increased. The recording capacity of a CD is about 650 MB and the DVD is about 4.7 GB, but further higher recording density is required in the future.

  As a prior art of the present invention, in order to realize such a high recording density medium, it has been proposed to shorten the laser wavelength used to the blue light region. Further, by increasing the numerical aperture of an objective lens used for a pickup for recording / reproducing, the spot size of laser light irradiated on the optical recording medium can be reduced, and high recording density can be achieved. However, there is a limit to the method of increasing the recording density by reducing the spot size by shortening the wavelength of the laser or increasing the numerical aperture of the objective lens. A technology for increasing the capacity by providing two information recording layers on one side. However, Japanese Patent No. 2702905 is disclosed.

  However, the two-layer phase change optical disc has many problems and has not yet been put into practical use. For example, if the recording layer positioned in front of the laser beam irradiation side does not sufficiently transmit the laser beam, the recording layer positioned on the back side cannot be recorded or reproduced. Therefore, in order to sufficiently transmit the laser light, it is necessary to eliminate or make the reflection layer of Ag or Al of the first information recording layer very thin.

  In general, in phase change type optical recording, an amorphous mark is formed by melting a recording layer by laser light irradiation and quenching, but the first information recording layer without a reflective layer is amorphous because of low thermal diffusion. It becomes difficult to form a quality mark.

  On the other hand, when recording and reproducing the second information recording layer on the back side as viewed from the laser beam incident side, the laser beam is absorbed to some extent by the first information recording layer before returning to the pickup. 2 The information recording layer must be highly absorbing and highly reflective. For that purpose, a reflective layer having a sufficient thickness must be provided.

  Therefore, the first information recording layer and the second information recording layer are thermally completely different from each other, and the first information recording layer is hard to be rapidly cooled compared to the second information recording layer, that is, amorphous. The phenomenon that it is difficult to improve occurs. In order to solve this problem, the crystallization speed of each recording layer material is changed so that the first recording layer is also easily amorphized, and the recording / reproduction characteristics of both layers are improved. Recording with different recording methods is required. A recording material having a slower crystallization rate can be amorphized even if the cooling rate of the recording layer is slower than that of a faster material, that is, it is not rapidly cooled. That is, by using a material with a low crystallization speed for the first recording layer that is difficult to cool rapidly, both the first and second recording layers can be recorded and reproduced satisfactorily under the same recording conditions (recording linear velocity).

  The present invention solves the above-mentioned problems in a phase change optical recording medium having a two-layer structure, and recording on a two-layer phase change information recording medium having excellent recording and reproducing characteristics in both the first information recording layer and the second information recording layer. It aims to provide a method.

In order to solve the above-described problem, in claim 1 , a two-layer phase change in which a light transmission layer, a first information recording layer, a transparent layer, and a second information recording layer are laminated in this order from the light incident side. In a recording method for recording and erasing information by causing a phase change in the recording layer of the two-layer phase change information recording medium by irradiating a light beam onto the type information recording medium, the recording of the first information recording layer The ratio of the recording power Pw1 to the erasing power Pe1, and Pw1 / Pe1 is 2.5 ≦ Pw1 / Pe1 ≦ 3.2, and the ratio of the recording power Pw2 to the erasing power Pe2 in the recording of the second information recording layer is Pw2. The main feature is that / Pe2 is an optical recording method for a two-layer phase change information recording medium in which 1.7 ≦ Pw2 / Pe2 ≦ 2.7 .

  As an effect of the present invention, in a phase change optical recording medium having a two-layer structure, a recording method for a two-layer phase change information recording medium having excellent recording and reproducing characteristics for both the first information recording layer and the second information recording layer is provided. Can do.

  Hereinafter, embodiments of the present invention will be described in detail. FIG. 1 is a schematic cross-sectional view of a two-layer change type information recording medium according to an embodiment of the present invention. The first information recording layer 1, the transparent layer 4, the second information recording layer 2, and the protective substrate 5 are sequentially stacked on the light transmission layer 3. The first information recording layer 1 includes a first lower protective layer 11, a first recording layer 12, a first upper protective layer 13, a first reflective layer 14, and a first heat dissipation layer 15, and the second information recording layer 2 includes It consists of a second lower protective layer 21, a second recording layer 22, a second upper protective layer 23, and a second reflective layer 24.

  The material of the light transmission layer 3 and the transparent layer 4 is usually glass, ceramics or resin, and a resin substrate is preferable in terms of moldability and cost. Examples of the resin include polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicone resin, fluorine resin, ABS resin, urethane resin, etc. Acrylic resins such as polycarbonate resin and polymethyl methacrylate (PMMA), which are excellent in terms of moldability, optical characteristics, and cost, are preferable.

The light transmissive layer 3 or the transparent layer 4 is provided with an uneven pattern such as a guide groove, and is formed by injection molding or a photopolymer method. The transparent layer 4 has a thickness that enables the pickup to distinguish between the first information recording layer and the second information recording layer and perform optical separation when recording and reproduction are performed, and is preferably 30 to 50 μm. If the thickness is larger than 50 μm, spherical aberration occurs when recording / reproducing the second information recording layer, and recording / reproducing becomes difficult.

As the material of the serial Rokuso 12, 22, Sb-Te eutectic alloy is used. The Ag-In-Sb-Te quaternary alloy used in CD-RW is also mainly composed of an Sb-Te eutectic alloy, and has a very good recording (amorphization) sensitivity / speed and erasure ratio. Therefore, it is suitable as a material for the recording layer. Further, the crystallization speed is high, and it is suitable for high linear velocity recording and high density recording. In addition to Ag and In for the purpose of further improving performance and reliability, these recording layer materials include Au, Al, B, Bi, C, Ca, Cu, Cr, Co, Cd, Ce, Cs, and Dy. Fe, Ge, Gd, Hf, K, La, Li, Mn, Ni, Nb, N, Nd, Na, O, Os, Pd, Pr, Pb, Ru, Rh, Rb, S, Sb, Si, Sm , Sc, Se, Ti, Tb, Ta, V, W, Y, Zn, Zr, and other elements and impurities can be added. It is known that the crystallization speed of the Sb—Te eutectic alloy changes depending on the ratio of Sb—Te. That is, the larger the Sb-Te ratio, the faster the crystallization rate.

  The crystallization speed of the recording material is usually measured by measuring the transition linear velocity and estimating the crystallization speed from the measured value. The transition linear velocity means a linear velocity at which the reflectivity starts to decrease after DC erasing while increasing the linear velocity, that is, a linear velocity at which amorphization has started. Naturally, the higher the crystallization speed, the higher the linear speed at which amorphization starts. Therefore, it is possible to relatively evaluate whether the crystallization speed is fast or slow depending on the transition linear speed.

By appropriately selecting the Sb-Te ratio of the first recording layer material constituting the first information recording layer and the Sb-Te ratio of the second recording layer material constituting the second information recording layer, respectively, A two-layer phase change information recording medium having excellent recording / reproducing characteristics was obtained for both the one information recording layer and the second information recording layer. That is, if Sb / Te atomic ratio Sb-Te = X constituting the first recording layer material and Sb / Te atomic ratio Sb-Te = Y constituting the second recording layer material, X ≦ Y. Thus, the two layers were found to have high C / N and an excellent erase ratio. The Sb-Te ratio is preferably 2 ≦ Sb−Te ≦ 4.6 for both the first recording layer and the second recording layer. If it is less than 2, the crystallization speed is too slow, high linear velocity recording becomes impossible, and the erasure ratio also deteriorates. If it is larger than 4.6, the C / N value becomes insufficient in the first information recording layer, and the storage characteristics also deteriorate. It is preferable to adjust Sb-Te within the above range so that the difference in transition linear velocity between the first recording layer and the second recording layer is 2 m / s or more.

The first recording layer material may be a material mainly composed of GeTe—Sb ₂ Te ₃ pseudo binary alloy. The GeTe-Sb ₂ Te ₃ pseudo binary alloy recording layer is known to increase the difference in optical constant between crystal and amorphous when GeTe is increased, like the first information recording layer, Even when the amount of reflection is small, there is an advantage that the difference in reflectance between crystal and amorphous can be increased. However, there are demerits that the erasing power margin is narrow and the recording characteristics are not excellent unless an interface layer is provided adjacent to the recording layer.

Sb-Te eutectic alloy, utilizing the GeTe-Sb ₂ Te ₃ pseudo binary alloy, respectively advantages and the first recording layer GeTe-Sb ₂ Te ₃ pseudo binary alloy, the second recording layer Sb By using a recording material mainly composed of a -Te eutectic alloy, a two-layer phase change information recording medium having excellent recording and reproducing characteristics was obtained for both layers. This is also one form of the present invention. The recording layer of the present invention can be formed by various vapor phase growth methods such as vacuum deposition, sputtering, plasma CVD, photo CVD, ion plating, and electron beam evaporation. Among these, the sputtering method is excellent in mass productivity and film quality.

  As the reflective layers 14 and 24, metal materials such as Al, Au, Ag, Cu, and Ta, or alloys thereof can be used. Further, Cr, Ti, Si, Pd or the like is used as an additive element. Such a reflective layer can be formed by various vapor deposition methods such as vacuum deposition, sputtering, plasma CVD, photo CVD, ion plating, and electron beam deposition. Among these, the sputtering method is excellent in mass productivity and film quality. The second reflective layer 24 is 50 to 200 nm, preferably 80 to 150 nm. When the thickness is less than 50 nm, the reflectance decreases, and when the thickness is greater than 200 nm, the sensitivity is lowered.

  In order to prevent a decrease in the light transmittance of the first information recording layer, it is preferable not to provide the first reflective layer 14, but by providing the first reflective layer 14, the heat of the first recording layer 12 is increased during recording. 1 Diffused to the first reflective layer 14 via the upper protective layer 13, the cooling rate becomes faster, the formation of amorphous marks becomes easier, and the jitter value also becomes lower. Further, according to the optical simulation, the difference between the reflectance of the crystal part and the reflectance of the amorphous part can be increased, and a large reproduction signal amplitude can be obtained. However, in consideration of the laser light transmitted to the second information recording layer, the thickness of the reflective film 14 is preferably 10 nm or less. If it is thicker than 10 nm, the transmittance decreases and it becomes difficult to record and reproduce the second information recording layer.

Of the reflected light amorphous state and the reflected light in the crystalline state of the first recording layer, a higher reflectance R _1High, lower the When R _1Low, with R _1High / R _1Low ≧ 1.5 In addition, the light transmittance in the crystalline state and the amorphous state is preferably 40% or more. When R _1High / R _1Low is out of the above range, the reproduction signal amplitude obtained from the first information recording layer is insufficient. Further, if the light transmittance is less than 40%, recording / reproduction of the second information recording layer becomes difficult.

Of the reflected light amorphous state and the reflected light in the crystalline state of the second recording layer, a higher reflectance R _2High, lower the When R _2Low, with R _2High / R _2Low ≧ 1.5 In addition, it is preferable that the light absorptance in the crystalline state and the amorphous state is 50% or more. When R _2High / R _2Low is outside the above range, the reproduction signal amplitude obtained from the second information recording layer is insufficient. If the light absorption rate is less than 50%, the recording sensitivity of the second information recording layer is insufficient.

Protective layer 11,13,21,23 prevents deterioration alteration of the recording layer 12 and 22 to increase the bonding strength of the recording layers 12 and 22, and as it has the effect of such increase recording characteristics, SiO, SiO _2, Metal oxides such as ZnO, SnO ₂ , Al ₂ O ₃ , TiO ₂ , In ₂ O ₃ , MgO, ZrO ₂ , nitrides such as Si ₃ N ₄ , AlN, TiN, BN, ZrN, ZnS, In ₂ S ₃ , sulfides such as TaS ₄ , carbides such as SiC, TaC, B ₄ C, WC, TiC, ZrC, diamond-like carbon, or a mixture thereof. These materials can be used alone as a protective layer, but may also be a mixture of each other. Moreover, you may contain an impurity as needed. The melting point of the protective layer needs to be higher than that of the recording layer. Such a protective layer can be formed by various vapor phase growth methods such as vacuum deposition, sputtering, plasma CVD, photo CVD, ion plating, and electron beam deposition. Among these, the sputtering method is excellent in mass productivity and film quality.

  The thickness of the first lower protective layer 11 and the second lower protective layer 21 is preferably 20 to 200 nm. When the thickness is 20 nm or less, the function as a protective film is not achieved. If it is thicker than 200 nm, a problem arises in mass productivity. In these ranges, the film thickness is designed so as to obtain an optimum reflectance. The film thicknesses of the first upper protective layer 13 and the second upper protective layer 23 are preferably 3 to 40 nm. If it is thinner than 3 nm, the recording sensitivity is lowered. If it is thicker than 40 nm, the heat dissipation effect cannot be obtained.

As the heat dissipation layer 15, AlN, Si ₃ N ₄ , SiC, Al ₂ O ₃ , BN, indium oxide / tin oxide composite oxide (ITO), tin oxide / antimony oxide composite oxide (ATO), diamond-like carbon ( DLC) and the like having a relatively high thermal conductivity. These may be used alone or a mixture thereof may be used. As long as the thermal conductivity does not decrease, impurities may be included as necessary. The film thickness of the heat dissipation layer 15 is preferably 20 to 200 nm. If it is thinner than 20 nm, the heat dissipation effect cannot be obtained. If it is thicker than 200 nm, a problem arises in mass productivity.

Next , the recording method of the two- layer phase change information recording medium will be described in detail. The recording method of the two-layer phase change information recording medium of the present invention is a recording method for forming a recording mark by a constant linear velocity (CLV) method, and the linear velocity when recording on the first information recording layer is 2 It is characterized by being faster than the linear velocity when recording on the information recording layer. By doing so, it has been found that both the first information recording layer and the second information recording layer have low jitter and an excellent erasure ratio. There is a close relationship between the linear velocity during recording and the cooling rate. As described above, the cooling rate of the first information recording layer with the thin reflective layer 14 is slower than that of the second information recording layer. Therefore, by increasing the linear velocity of the first information recording layer, it is easy to cool and an amorphous mark can be easily formed. By using such a recording method, it is possible to provide an optical disc having excellent recording characteristics in both layers without greatly changing the material configuration of the first recording layer and the second recording layer.

Further, the ratio Pw ₁ / Pe ₁ of the recording power Pw ₁ and the erasing power Pe ₁ in the recording of the first information recording layer, the ratio of the recording power Pw ₂ and the erasing power Pe ₂ in the recording of the second information recording layer Pw ₂ / It has been found that by making it larger than Pe ₂ , both the first information recording layer and the second information recording layer have low jitter and an excellent erase ratio.

  EXAMPLES The present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

Reference example 1
A first lower protective layer 150 nm made of ZnS · SiO ₂ and Ag—In—Sb—Te on a polycarbonate substrate having a diameter of 12 cm, a thickness of 0.6 mm, and a surface of the groove having a tracking groove with a pitch of 0.4 μm on the surface. A first recording layer 6 nm, a first upper protective layer 10 nm made of ZnS · SiO _{2, a} first reflective layer 10 nm made of AlTi, and a heat dissipation layer 200 nm made of AlN were formed in this order to form a first information recording layer. The film forming method is a sputtering method in an Ar gas atmosphere. The transmittance of the first recording layer thus formed was measured. On this first information recording layer, a transparent layer having irregularities of tracking guides by continuous grooves with a pitch of 0.4 μm was formed by 2P photopolymerization. The thickness of the transparent layer is 40 μm. Further thereon, a second lower protective layer 40nm made of _{ZnS · SiO 2, Ag-In} -Sb-Te second recording layer 12nm made of, the second upper protective layer 15nm made of ZnS · SiO _2, first made of AlTi Two reflective layers were formed in the order of 150 nm to form a second information recording layer. The film forming method is a sputtering method in an Ar gas atmosphere.

  On top of that, an overcoat layer was provided using a spin coater to prepare a two-layer phase change optical disc. For the first recording layer material and the second recording layer material, several types of the above-mentioned two-layer phase change type optical discs were produced by changing the Sb-Te ratio while the amounts of Ag and In were constant. Next, the initialization process of the recording layer of each optical disk was performed by an initialization apparatus having a large-diameter semiconductor laser.

  For each of the produced optical disks, the C / N and erasure ratio of the 3T mark were measured under the conditions of laser wavelength 407 nm NA (numerical aperture) = 0.65 linear velocity 6.5 m / s linear density 0.19 μm / bit. FIG. 4 shows a graph in which Sb-Te of the first recording layer and the second recording layer of each medium is plotted on the horizontal axis, and CN and erase ratio are plotted on the vertical axis. As can be seen from the figure, the optimum value of the Sb-Te ratio in the first recording layer and the second recording layer is smaller in the first recording layer. In addition, FIG. 5 shows the relationship between the Sb—Te ratio of the phase change optical disk using Ag—In—Sb—Te and the transition linear velocity. 4 and 5, the Sb-Te ratio of the first recording layer is smaller than the Sb-Te ratio of the second recording layer, that is, the crystallization speed of the first recording layer material is higher than the crystallization speed of the second recording layer. By slowing down, a two-layer phase change optical disk having a high C / N ratio and an excellent erasure ratio can be obtained.

Reference example 2
On a polycarbonate substrate having a diameter of 12 cm, a thickness of 0.6 mm, and a groove with tracking guides formed by continuous grooves with a pitch of 0.4 μm on the surface, a first lower protective layer 150 nm made of ZnS · SiO ₂ , an interface layer 3 nm made of GeN, Ge The first recording layer 6 nm made of ₂ Sb ₂ Te _{5, the} interface layer 3 nm made of GeN, the first upper protective layer 10 nm made of ZnS · SiO _2, the first reflective layer 10 nm made of AlTi, and the heat dissipation layer 200 nm made of AlN in this order. A film was formed to form a first information recording layer. The film forming method is a sputtering method in an Ar gas atmosphere. The transmittance of the first recording layer thus formed was measured. On this first information recording layer, a transparent layer having tracking guide concavities and convexities formed by continuous grooves having a pitch of 0.4 μm was formed by the 2P method. The thickness of the transparent layer is 40 μm.

Further thereon, consisting of ZnS · SiO ₂ and a second lower protective layer 40nm, Ag ₁ In ₇ Sb ₆₅ second recording layer 12nm made of Te _27, a second upper protective layer 15nm made of ZnS · SiO _2, AlTi The second reflective layer was formed in the order of 150 nm to form a second information recording layer.

  The film forming method is a sputtering method in an Ar gas atmosphere. On top of that, an overcoat layer was provided using a spin coater to prepare a two-layer phase change optical disc. Next, the initialization process of the recording layer of the optical disk was performed by an initialization apparatus having a large-diameter semiconductor laser.

The C / N and erasure ratio of the 3T mark were measured on this optical disc under the same conditions as in Reference Example 1 . In addition, optical characteristics of the first information recording layer and the second information recording layer are shown. The reflectance, light transmittance, and light absorptance shown below are values when the intensity of light incident on each information recording layer is 100%.
First information recording layer C / N: 52 dB
Erase ratio: 35 dB
Crystal part reflectance: 11.6%
Light transmittance: 56.4%
Light absorption rate: 32.0%
Amorphous part reflectance: 4.7%
Light transmittance: 50.8%
Light absorption rate: 44.5%
Second information recording layer C / N: 56 dB
Erase ratio: 48 dB
Crystal part reflectance: 40.2%
Light absorption rate: 59.8%
Amorphous part reflectance: 19.8%
Light absorption rate: 80.2%

Separately from this sample disk, single-layer optical disks using Ge ₂ Sb ₂ Te ₅ and Ag ₁ In ₇ Sb ₆₅ Te ₂₇ as recording materials were prepared. (Substrate / ZnS · SiO _2: 50nm / recording _{material: 15nm / ZnS · SiO 2:} 15nm / Ag: 120nm) using the optical disc where, to erase the irradiation power of 7 mW, was measured transition linear velocity, Ge ₂ Sb ₂ Te ₅ was 1.5 m / s, and Ag ₁ In ₇ Sb ₆₅ Te ₂₇ was 8 m / s.

  From the above results, since this optical disk has a high light transmittance in the first information recording layer, it was possible to make light of sufficient intensity incident on the second information recording layer. In addition, since both the first information recording layer and the second information recording layer have a large difference in reflectance between crystal and amorphous, it is possible to obtain a sufficient signal amplitude, a large C / N, and an excellent erasure ratio. Therefore, good recording / reproduction characteristics could be obtained.

Also, from Reference Examples 1 and 2 and other prototype experiments, in order to obtain a sufficient signal amplitude from the second information recording layer, the crystal: amorphous reflectance ratio R _1High / R _1Low ≧ 1 of the first recording layer .5 and second recording layer crystal: amorphous reflectance ratio R _{2 High} / R _{2 Low} ≧ 1.5, and light transmission in the crystalline and amorphous states of the first recording layer It was confirmed that the light absorption rate in the crystalline state and the amorphous state of the second recording layer was preferably 50% or more when the rate was 40% or more.

Example 1
A first lower protective layer 150 nm made of ZnS · SiO ₂ and Ag ₁ In ₇ Sb ₆₅ Te ₂₇ on a polycarbonate substrate having a diameter of 12 cm, a thickness of 0.6 mm, and a surface of a groove having a tracking guide with a pitch of 0.4 μm on the surface. A first recording layer 6 nm, a first upper protective layer 10 nm made of ZnS · SiO _{2, a} first reflective layer 10 nm made of AlTi, and a heat dissipation layer 200 nm made of AlN were formed in this order to form a first information recording layer. . The film forming method is a sputtering method in an Ar gas atmosphere. The transmittance of the first recording layer thus formed was measured. On this first information recording layer, a transparent layer having tracking guide concavities and convexities formed by continuous grooves having a pitch of 0.4 μm was formed by the 2P method. The thickness of the transparent layer is 40 μm.

Further thereon, consisting of ZnS · SiO ₂ and a second lower protective layer 40nm, Ag ₁ In ₇ Sb ₆₅ second recording layer 12nm made of Te _27, a second upper protective layer 15nm made of ZnS · SiO _2, AlTi The second reflective layer was formed in the order of 150 nm to form a second information recording layer. The film forming method is a sputtering method in an Ar gas atmosphere. On top of that, an overcoat layer was provided using a spin coater to prepare a two-layer phase change optical disc. Next, the initialization process of the recording layer of each optical disk was performed by an initialization apparatus having a large-diameter semiconductor laser.

FIG. 7 shows the result of recording by changing the ratio of the write power Pw and the erase power Pe of the first information recording layer and the second information recording layer, and measuring the C / N and the erasure ratio. As is apparent from the figure, the ratio of the recording power Pw1 to the erasing power Pe1 in the recording of the first information recording layer, Pw1 / Pe1, is 2.5 ≦ Pw1 / Pe1 ≦ 3.2, and the second information recording layer When the ratio of the recording power Pw2 and the erasing power Pe2 in the recording of Pw2 / Pe2 is 1.7 ≦ Pw2 / Pe2 ≦ 2.7, the erasing ratio is the same for both the first information recording layer and the second information recording layer. It was found that the recording / reproducing characteristics were excellent at 40 dB or more.

Reference example 3
FIG. 6 shows the result of measuring the C / N and the erasure ratio by performing recording on the first recording layer and the second recording layer of the two-layer optical disk of Example 1 by changing the recording linear velocity by the CLV method. As is apparent from the figure, the recording linear velocity at which the high C / N and the erasure ratio are maximized is faster in the first information recording layer than in the second information recording layer. Therefore, in the recording method in which the recording mark is formed by the constant linear velocity (CLV) method, the linear velocity when recording on the first information recording layer is higher than the linear velocity when recording on the second information recording layer. It was found that if the speed was increased, both the first information recording layer and the second information recording layer were excellent in recording / reproducing characteristics.

  As an application example of the present invention, in a phase change type optical recording medium having a two-layer structure, both the first information recording layer and the second information recording layer are suitable for a recording method of a two-layer phase change information recording medium excellent in recording / reproducing characteristics. Can be used.

1 is a schematic cross-sectional view of a two-layer phase change information recording medium according to an embodiment of the present invention. It is a schematic sectional drawing of the two-layer phase change type information recording medium concerning other embodiment of this invention. It is a schematic sectional drawing of the two-layer phase change type information recording medium concerning further another embodiment of this invention. It is explanatory drawing which shows the relationship between Sb-Te ratio of a 1st and 2nd information recording layer, CN ratio, and an erase ratio. It is explanatory drawing which shows the relationship between Sb-Te ratio of a recording material, and a transition linear velocity. It is explanatory drawing which shows the relationship between the recording linear velocity of a 1st and 2nd information recording layer, CN ratio, and an erasure ratio. It is explanatory drawing which shows the relationship of CN ratio with respect to the ratio of the recording power P and the erasing power of a 1st information recording layer and a 2nd information recording layer, and an erasing ratio.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st information recording layer 2 2nd information recording layer 3 Light transmission layer 4 Transparent layer 5 Protective substrate 11 1st lower protective layer 12 1st recording layer 13 1st upper protective layer 14 1st reflection layer 15 Heat dissipation layer 16 Interface layer 17 Interface layer 21 Second lower protective layer 22 Second recording layer 23 Second upper protective layer 24 Second reflective layer

Claims (1)

By irradiating a light beam onto a two-layer phase change information recording medium in which a light transmission layer, a first information recording layer, a transparent layer, and a second information recording layer are laminated in this order from the light incident side , In the recording method for recording and erasing information by causing a phase change in the recording layer of the two-layer phase change type information recording medium, the ratio of the recording power Pw1 to the erasing power Pe1 in the recording of the first information recording layer, Pw1 / Pe1 Is 2.5 ≦ Pw1 / Pe1 ≦ 3.2, and the ratio of the recording power Pw2 to the erasing power Pe2 in the recording of the second information recording layer, Pw2 / Pe2, is 1.7 ≦ Pw2 / Pe2 ≦ 2. 7. An optical recording method for a two-layer phase change information recording medium,