JP3987557B2 - Information recording medium - Google Patents

Description

  The present invention relates to an information recording medium for optically or electrically recording, erasing, rewriting and reproducing information, a manufacturing method thereof, and a recording / reproducing method thereof.

  There is a phase change information recording medium as an information recording medium for recording, erasing, rewriting, and reproducing information using a laser beam. For recording, erasing, and rewriting information on the phase change information recording medium, a phenomenon in which the recording layer reversibly changes between a crystalline phase and an amorphous phase is used. In general, when information is recorded, information is recorded with an irradiated portion in an amorphous phase by irradiating a laser beam to melt and quench the recording layer. On the other hand, when erasing information, the previous information is erased by irradiating a laser beam having a lower power than that at the time of recording to raise the temperature of the recording layer and gradually cooling the irradiated portion as a crystal phase. Therefore, in the phase change information recording medium, new information is recorded while erasing the recorded information by irradiating the recording layer with a laser beam whose power is modulated between a high power level and a low power level. Or it is possible to rewrite (for example, refer nonpatent literature 1).

  In recent years, various techniques have been studied as techniques for increasing the capacity of information recording media. For example, the spot diameter of the laser beam can be made smaller by using a short wavelength blue-violet laser, or by using a lens with a large numerical aperture NA by reducing the thickness of the substrate on which the laser beam is incident. Therefore, a technique for performing high-density recording is being studied. In addition, a technique for recording and reproducing two information layers using a laser beam incident from one side using an information recording medium having two information layers has been studied (see Patent Document 1). In this technique, the recording density can be almost doubled by using two information layers.

  In an information recording medium that records and reproduces two information layers from one side (hereinafter sometimes referred to as a two-layer information recording medium), a laser that has passed through an information layer on the incident side of a laser beam (hereinafter referred to as a first information layer) Recording and reproduction of an information layer (hereinafter referred to as a second information layer) opposite to the laser beam incident side is performed using the beam. Accordingly, the transmittance of the first information layer is preferably 40% or more. On the other hand, the second information layer is desired to have high recording sensitivity (recording marks can be formed even with a low-power laser beam) in terms of recording characteristics, and high reflectivity in terms of reproduction characteristics.

  In order to increase the transmittance of the laser beam to the first information layer to 40% or more, it is necessary to reduce the thickness of the first recording layer to about 6 nm. However, when the recording layer is thinned, the crystal nuclei formed are reduced when the recording layer is crystallized, and the distance that atoms can move is shortened. For this reason, even in the recording layer made of the same material, the crystallization speed tends to be relatively lowered in the thin recording layer. Therefore, the thinner the recording layer, the harder the crystal phase is formed, and the erasure rate decreases.

Conventionally, as a recording layer material (phase change material), a GeSbTe-based material having a high crystallization speed, excellent rewrite performance, and high reliability has been used. Using this material, optical discs for computer data recording and video recording have been commercialized. Among GeSbTe-based materials, the quasi-binary composition on the GeTe-Sb ₂ Te ₃ line has the fastest crystallization rate. The inventors conducted a recording / reproducing experiment using a red laser having a wavelength of 660 nm. As a result, in recording at a high linear velocity of 9 m / s, a good erasure rate of 30 dB was obtained even when the thickness of the recording layer made of GeTe—Sb ₂ Te ₃ was reduced to 6 nm. With this technology, the feasibility of a two-layer information recording medium using a red laser has been found.

In addition, an information recording medium in which a recording layer made of a phase change material is phase-changed by applying a current has been conventionally studied. In this information recording medium, the recording layer is sandwiched between two electrodes. In this information recording medium, when a current is gradually passed through the recording layer in an amorphous phase, the recording layer changes into a crystalline phase at a certain threshold current, and the electric resistance rapidly decreases. To do. Further, by applying a large current pulse with a short pulse width to the recording layer in the crystalline phase state, the recording layer can be melted and rapidly cooled to return to the high resistance amorphous phase. Since the difference in electrical resistance can be easily detected by ordinary electrical means, a rewritable information recording medium can be obtained by using such a recording layer.
Yoshito Tsunoda et al., "Basics and Applications of Optical Disk Storage", edited by IEICE, 1995, Chapter 2 JP-A-12-36130

  In order to increase the capacity of the information recording medium, it is desired to put to practical use a two-layer information recording medium that performs recording and reproduction using a short wavelength blue-violet laser. By using a short-wavelength laser beam or an objective lens having a large numerical aperture, the spot diameter of the laser beam can be reduced, and higher-density recording becomes possible. In order to perform recording using a laser beam with a short wavelength, an information recording medium capable of forming a small recording mark in a good shape is necessary. When a blue-violet laser is used, the time for which the recording layer is irradiated with the laser beam becomes relatively short. Therefore, in order to form a small recording mark, it is necessary to form the recording layer with a material having a high crystallization speed. Become. Further, in order to obtain a sufficient signal amplitude even with a small recording mark, it is desirable to form the recording layer using a material having a large change in optical characteristics between the crystalline phase and the amorphous phase.

In the experiments by the inventors, when a conventional two-layer information recording medium using a red laser is applied as it is as an information recording medium for a blue-violet laser, recording marks formed in the first information layer and the second information layer are recorded. As a result, a sufficient signal amplitude could not be obtained. Further, regarding the first information layer, when the thickness of the recording layer was set to about 6 nm in order to ensure sufficient transmittance, the erasure rate was an insufficient value of less than 15 dB. In order to obtain a large signal amplitude, it has been found through experiments by the inventors that the ratio of GeTe should be increased in the pseudo-binary composition on the GeTe-Sb ₂ Te ₃ line. However, since the melting point of the material tends to increase as the proportion of GeTe increases, the laser power (recording power) for forming the amorphous phase increases as the proportion of GeTe increases. The output of currently available blue-violet lasers is smaller than that of red lasers. For this reason, when a composition containing a large amount of GeTe is applied to the second information layer for recording / reproducing with the laser beam transmitted through the first information layer, a signal amplitude that is saturated due to insufficient recording power is obtained. I could not.

  As described above, in the two-layer information recording medium using the blue-violet laser, it was found that securing the erasure rate of the first information layer and increasing the recording sensitivity of the second information layer are important issues. .

  For practical use of a two-layer information recording medium using a blue-violet laser, a first information layer having a high transmittance and a good recording / erasing performance, and a good recording / erasing performance having a high reflectance and recording sensitivity A second information layer is required. Therefore, for practical use, it is necessary to consider the materials of the first and second recording layers and the configurations of the first and second information layers.

  In addition, as a material for the recording layer that causes a phase change by applying a current, a material mainly composed of Te has been put into practical use. However, the time required for crystallization of the conventional material is as long as μs. In addition, an electrical phase change information recording medium having good recording / erasing performance and having two recording layers has not yet been put into practical use.

  It is an object of the present invention to provide an information recording medium having two recording layers and good recording / erasing performance, a manufacturing method thereof, and a recording / reproducing method thereof.

  In order to achieve the above object, an information recording medium of the present invention is an information recording medium comprising a first information layer and a second information layer, wherein the first information layer is irradiated with a laser beam. Or a first recording layer that causes a reversible phase change between a crystalline phase and an amorphous phase by Joule heat generated by application of current, and the second information layer is formed by irradiation with the laser beam. Or a second recording layer that causes a reversible phase change between a crystalline phase and an amorphous phase by Joule heat generated by the application of the current, and the first recording layer is made of a first material. The second recording layer is made of a second material, and the first material and the second material are different. According to the information recording medium of the present invention, good recording / reproducing characteristics can be obtained in each information layer.

  According to the information recording medium and the manufacturing method thereof of the present invention, an information recording medium having two recording layers and excellent recording / erasing performance can be obtained.

  Also, according to the recording / reproducing method of the present invention, high-density recording is possible.

  In the information recording medium of the present invention, the first material includes Ge, Sb, and Te, and the second material is at least one selected from Ag, In, Ge, Sn, Se, Bi, Au, and Mn. It may be composed of two elements M1, Sb, and Te. According to this configuration, with respect to a recording medium for recording information using a laser beam (hereinafter sometimes referred to as an optical information recording medium), the first information layer having a high transmittance and erasing rate, the reflectance and the recording An information recording medium comprising a second information layer with high sensitivity is obtained. In particular, this optical information recording medium is suitable for high-density recording using a blue-violet laser. In addition, regarding a recording medium for recording information using an electric current (hereinafter sometimes referred to as an electrical information recording medium), the first recording layer, the second recording layer, or both are selectively used as a crystalline phase. The phase can be easily changed between the amorphous phase.

In the information recording medium of the present invention, the first material is a composition formula Ge _a Sb _b Te _{3 + a.}
(However, 0 <a ≦ 10, 1.5 ≦ b ≦ 4)
It may be represented by According to this configuration, good recording / reproducing characteristics can be obtained even when the first recording layer is extremely thin.

In the information recording medium of the present invention, the first material, composition formula _{(Ge- Sn) a Sb b Te} 3 + a
(However , 0 <a ≦ 10, 1.5 ≦ b ≦ 4)
It may be represented by According to this configuration, Sn substituted with Ge having a Ge—Sb—Te ternary composition improves the crystallization ability, and a sufficient erasure rate can be obtained even when the first recording layer is extremely thin.

In the information recording medium of the present invention, the first material has a composition formula (Ge _a Sb _b Te _{3 + a} ) _100-c M3 _c
(However, M3 is at least one element selected from Cr and Sn , and 0 <a ≦ 10, 1.5 ≦ b ≦ 4, 0 <c ≦ 20)
It may be represented by According to this configuration, the element M3 added to the Ge—Sb—Te ternary composition increases the melting point and the crystallization temperature of the recording layer, thereby improving the thermal stability of the recording layer.

In the information recording medium of the present invention, the second material is a composition formula (Sb _x Te _100-x ) _100-y M1 _y.
(However, 50 ≦ x ≦ 95, 0 <y ≦ 20)
It may be represented by According to this configuration, since the melting point of the second recording layer is low and the refractive index difference between the crystalline phase and the amorphous phase is large, the recording sensitivity is high and the reflectance difference between the crystalline phase and the amorphous phase is high. A large second information layer is obtained.

  In the information recording medium of the present invention, the first and second recording layers are layers that cause a reversible phase change upon irradiation with the laser beam, and the first information layer is the second information layer. The melting point of the second material may be lower than the melting point of the first material. According to this configuration, a second information layer with high recording sensitivity can be obtained.

  In the information recording medium of the present invention, the first and second recording layers are layers that cause a reversible phase change upon irradiation with the laser beam, and the first information layer is the second information layer. It may be arranged closer to the incident side of the laser beam. According to this configuration, an optical information recording medium can be obtained.

  In the optical information recording medium, the thickness of the first recording layer may be 9 nm or less. According to this configuration, it is easy to increase the transmittance of the first information layer so that the amount of laser light necessary for recording / reproduction of the second information layer reaches the second information layer.

  In the optical information recording medium, the thickness of the second recording layer may be in the range of 6 nm to 15 nm. According to this configuration, the recording sensitivity of the second recording layer can be particularly increased. By setting the thickness to 6 nm or more, the amount of light absorption in the recording layer can be increased. By setting the thickness to 15 nm or less, it is possible to reduce the volume of the portion to be melted when forming the recording mark, so that it is possible to prevent a decrease in recording sensitivity.

In the optical information recording medium, the transmittance Tc (%) of the first information layer when the first recording layer is in a crystalline phase, and the case where the first recording layer is in an amorphous phase The transmittance Ta (%) of the first information layer of the laser beam having a wavelength of 390 nm or more and 430 nm or less,
40 ≦ (Tc + Ta) / 2
May be satisfied. According to this configuration, particularly good recording / erasing characteristics can be obtained for the second information layer.

  The optical information recording medium further includes an optical separation layer disposed between the first information layer and the second information layer, and the first information layer includes the first substrate and the first information layer. A second lower protective layer, a second upper protective layer, and a second reflective layer. The lower protective layer, the first upper protective layer, and the first reflective layer are further included. And a second substrate, the first substrate, the first lower protective layer, the first recording layer, the first upper protective layer, the first reflective layer, and the optical The separation layer, the second lower protective layer, the second recording layer, the second upper protective layer, the second reflective layer, and the second substrate are separated from the incident side of the laser beam. They may be arranged in order. According to this configuration, the reflectivity, recording sensitivity, erasing sensitivity, and transmittance (particularly the first information layer) of the first and second information layers are optimized in accordance with the recording / erasing / reproducing conditions. Can be In addition, the first information layer and the second information layer can be optically separated by the optical separation layer.

  The optical information recording medium may further include a transparent layer disposed between the first substrate and the first lower protective layer.

  The optical information recording medium is at least selected from the interface between the first lower protective layer and the first recording layer, and the interface between the first upper protective layer and the first recording layer. You may further provide the interface layer arrange | positioned at one interface. The optical information recording medium is selected from the interface between the second lower protective layer and the second recording layer, and the interface between the second upper protective layer and the second recording layer. It may further comprise an interface layer disposed on at least one interface. The optical information recording medium is selected from an interface between the first upper protective layer and the first reflective layer, and an interface between the second upper protective layer and the second reflective layer. You may further provide the interface layer arrange | positioned at an at least 1 interface. According to these structures including the interface layer, atomic diffusion between adjacent layers can be prevented, and an information recording medium having particularly high characteristics and reliability can be obtained.

  The optical information recording medium may further include a transmittance adjusting layer for adjusting the transmittance of the first information layer between the first reflective layer and the optical separation layer. According to this configuration, the transmittance of the first information layer can be particularly increased.

  The optical information recording medium may further include an interface layer disposed between the first reflective layer and the transmittance adjusting layer. According to this configuration, atomic diffusion between the first reflective layer and the transmittance adjusting layer can be prevented, and an information recording medium with particularly high reliability can be obtained.

  In the optical information recording medium, the thickness of the first substrate may be in the range of 10 μm to 800 μm. According to this configuration, by changing the numerical aperture (NA) of the objective lens, the length, width, and interval of the recording mark are optimized in accordance with the groove shape of the first substrate and the recording / erasing / reproducing conditions. Can be For example, when the thickness of the first substrate is 100 μm, good recording / erasing performance was obtained at NA = 0.85. When the thickness of the first substrate was 600 μm, good recording / erasing performance was obtained with NA = 0.6.

  In the optical information recording medium, the thickness of the second substrate may be in the range of 400 μm to 1300 μm. According to this configuration, by changing the NA of the objective lens, the length, width, and interval of the recording mark can be optimized according to the groove shape of the second substrate and the recording / erasing / reproducing conditions. When the thickness of the first substrate is about 100 μm, the thickness of the second substrate is about 1100 μm, and when the thickness of the first substrate is about 600 μm, the thickness of the second substrate is about 600 μm. Thus, it is preferable to select the thicknesses of the first and second substrates so that the thickness of the information recording medium is about 1200 μm.

  The information recording medium of the present invention further includes first and second electrodes, wherein the first and second recording layers are layers that cause a reversible phase change by the application of the current. The first recording layer, the second recording layer, and the second electrode may be laminated in this order on the electrodes. According to this configuration, an electrical information recording medium can be obtained.

  The electrical information recording medium may further include an intermediate electrode disposed between the first recording layer and the second recording layer. According to this configuration, since atomic diffusion between the first recording layer and the second recording layer can be prevented, it is possible to improve the repetition characteristics and the reliability. Further, according to this configuration, a current can be applied to only one of the first recording layer and the second recording layer.

The manufacturing method of the present invention is a method of manufacturing an information recording medium comprising a first information layer and a second information layer,
(A) forming the first information layer;
(B) forming the second information layer,
The first information layer includes a first recording layer that causes a reversible phase change between a crystalline phase and an amorphous phase by Joule heat generated by irradiation of a laser beam or by application of a current,
The second information layer includes a second recording layer that causes a reversible phase change between a crystalline phase and an amorphous phase by Joule heat generated by irradiation of the laser beam or by application of the current. ,
The step (a) includes a step of forming the first recording layer using a base material containing Ge, Sb, and Te,
In the step (b), the second recording layer is formed using a base material containing at least one element M1, Sb and Te selected from Ag, In, Ge, Sn, Se, Bi, Au and Mn. A step of forming. According to this manufacturing method, the information recording medium of the present invention can be easily manufactured.

  In the manufacturing method of the present invention, the first and second recording layers may be formed by a sputtering method using a sputtering gas containing argon gas or krypton gas. The sputtering gas may further include at least one gas selected from nitrogen gas and oxygen gas. According to this configuration, an information layer having excellent repeated recording performance can be manufactured.

  In the manufacturing method of the present invention, the thickness of the first recording layer is 9 nm or less, and in the step (a), the first recording layer is formed at a film formation rate in the range of 0.1 nm / second to 3 nm / second. The recording layer may be formed. According to this configuration, an optical information recording medium including the first recording layer with little variation in thickness can be manufactured with high productivity.

  In the manufacturing method of the present invention, the thickness of the second recording layer is in the range of 6 nm to 15 nm, and in the step (b), the film formation rate is in the range of 0.3 nm / second to 10 nm / second. The second recording layer may be formed. According to this configuration, an optical information recording medium including the second information layer with high recording sensitivity can be manufactured with high productivity.

In the production method of the present invention, the step (b) is performed before the step (a), and after the step (b) and before the step (a),
(C) further comprising a step of forming an optical separation layer on the second information layer;
In the step (a), the first information layer may be formed on the optical separation layer.

  Further, the first method of the present invention for recording / reproducing information recording medium is that the information recording medium is the information recording medium of the present invention, and the first information layer of the information recording medium is Information is recorded / reproduced by a laser beam incident from the first information layer side, and information is recorded / reproduced by the laser beam transmitted through the first information layer with respect to the second information layer of the information recording medium. The wavelength of the laser beam is not less than 390 nm and not more than 430 nm. According to the first recording / reproducing method, it is possible to perform recording / reproduction with high density and reliability with respect to the first and second information layers of the optical information recording medium.

  In the first recording / reproducing method of the present invention, the linear velocity of the information recording medium when information is recorded / reproduced may be 3 m / sec or more and 30 m / sec or less.

  In the first recording / reproducing method of the present invention, the laser beam may be a laser beam condensed by an objective lens, and the numerical aperture NA of the objective lens may be 0.5 or more and 1.1 or less. According to this configuration, the length, width, and interval of the recording mark can be optimized according to the thickness of the first and second substrates, the shape of the groove, and the recording / reproducing conditions.

  In addition, in a second method of the present invention for recording / reproducing an information recording medium, the information recording medium is the information recording medium of the present invention, and the first and second recording layers of the information recording medium are A layer that undergoes a reversible phase change between a crystalline phase and an amorphous phase by Joule heat generated by application of a current, wherein the first or second recording layer changes from an amorphous phase to a crystalline phase; The amplitude Ic and the pulse width tc of the current pulse applied to the first or second recording layer, and the first recording layer when the first recording layer is changed from a crystalline phase to an amorphous phase. The amplitude Ia1 and pulse width ta1 of the current pulse applied to the layer, and the amplitude Ia2 and pulse of the current pulse applied to the second recording layer when changing the second recording layer from the crystalline phase to the amorphous phase The width ta2 is Ic <Ia2 <Ia1 Engagement, and characterized by satisfying the relation ta1 ≦ tc or ta2 ≦ tc. According to the second recording / reproducing method, in the electrical information recording medium, the first recording layer, the second recording layer, or both are selectively changed into a crystalline phase or an amorphous phase. Can do. In addition, since the electrical information recording medium of this invention produces the change of the electrical resistance by a phase change, it can also be used as a component of the programmable circuit which can be changed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiment is an example, and the present invention is not limited to the following embodiment. In the following embodiments, the same portions may be denoted by the same reference numerals and redundant description may be omitted.

(Embodiment 1)
In the first embodiment, an example of the information recording medium of the present invention will be described. A partial cross-sectional view of the information recording medium 22 of Embodiment 1 is shown in FIG. In the information recording medium 22, recording / reproduction is performed by irradiation with the laser beam 23.

  With reference to FIG. 1, the information recording medium 22 includes an optical separation layer 21, and a first information layer 11 and a second information layer 20 disposed so as to sandwich the optical separation layer 21. The first information layer 11 is disposed closer to the incident side of the laser beam 23 than the second information layer 20.

  The first information layer 11 includes a first substrate 1, a first lower protective layer 2, a first lower interface layer 3, a first recording layer 4, which are arranged in order from the incident side of the laser beam 23. A first upper interface layer 5, a first upper protective layer 6, a first interface layer 7, a first reflective layer 8, a first uppermost interface layer 9, and a transmittance adjusting layer 10 are provided.

  The second information layer 20 includes a second lower protective layer 12, a second lower interface layer 13, a second recording layer 14, and a second upper interface layer arranged in order from the incident side of the laser beam 23. 15, a second upper protective layer 16, a second interface layer 17, a second reflective layer 18, and a second substrate 19. In the names of the interface layer and the protective layer, the lower side means the incident side of the laser beam 23 from the recording layer, and the upper side is the opposite side of the recording layer from the incident side of the laser beam 23. It means that.

  The laser beam 23 is incident from the first substrate 1 side. The second information layer 20 is recorded and reproduced by the laser beam 23 that has passed through the first information layer 11 and the optical separation layer 21.

  The first substrate 1 and the second substrate 19 are transparent and disk-shaped substrates. The first substrate 1 and the second substrate 19 can be formed using, for example, a resin such as polycarbonate, amorphous polyolefin, or PMMA, or glass. The first substrate 1 may be formed by applying a resin on the first lower protective layer 2 and then curing the resin.

  Guide grooves for guiding a laser beam may be formed on the inner surfaces (on the optical separation layer 21 side) of the first substrate 1 and the second substrate 19 as necessary. The outer surface of these substrates is preferably smooth. These substrates preferably have a small optical birefringence in a short wavelength region. As a material for these substrates, polycarbonate is particularly useful because of its excellent transferability and mass productivity and low cost. The thickness of the 1st board | substrate 1 exists in the range of 10 micrometers-800 micrometers (preferably 50 micrometers-150 micrometers or 550 micrometers-650 micrometers), for example. The thickness of the second substrate 19 is, for example, in the range of 400 μm to 1300 μm (preferably 550 μm to 650 μm or 1050 μm to 1150 μm).

  An example of an information recording medium in which a groove for guiding a laser beam is formed on both the first substrate 1 and the second substrate 19 is shown in FIG. In the information recording medium 22a of FIG. 2, the first information layer 11a includes the first substrate 1a, and the second information layer 20a includes the second substrate 19a. Grooves (grooves) 1b are formed in the first substrate 1a and the second substrate 19a. In the information recording medium 22a, information may be recorded in a portion of the groove 1b which is a groove surface on the incident side of the laser beam 23, or a portion between the grooves 1b (a groove far from the incident side of the laser beam 23). Or may be referred to as a land 1c). Information may be recorded on both the groove 1b and the land 1c.

The first lower protective layer 2, the first upper protective layer 6, the second lower protective layer 12, and the second upper protective layer 16 are all made of a dielectric. These protective layers have the function of adjusting the optical distance to increase the light absorption efficiency of the recording layer and the function of increasing the change in the amount of reflected light before and after recording to increase the signal amplitude. For these protective layers, for example, oxides such as SiO _x (x is 0.5 to 2.5), Al ₂ O ₃ , TiO ₂ , Ta ₂ O ₅ , ZrO ₂ , ZnO, or Te—O are used. Can be used. Further, a nitride such as Si—N, Al—N, Ti—N, Ta—N, Zr—N, or Ge—N can be used. Further, a sulfide such as ZnS or a carbide such as SiC can also be used. A mixture of the above materials can also be used. Among these, ZnS—SiO ₂ which is a mixture of ZnS and SiO ₂ is particularly excellent as a material for the protective layer. ZnS—SiO ₂ is an amorphous material, has a high refractive index, a high deposition rate, and good mechanical properties and moisture resistance.

  The thickness of the first lower protective layer 2 and the first upper protective layer 6 is such that the amount of reflected light varies between when the first recording layer 4 is in a crystalline phase and when it is in an amorphous phase. It can be determined strictly so that the transmittance of the first information layer 11 is large and the light absorption efficiency of the first recording layer 4 is large. Specifically, these thicknesses can be determined using calculations based on, for example, a matrix method.

  Similarly, the thicknesses of the second lower protective layer 12 and the second upper protective layer 16 are also different in the amount of reflected light when the second recording layer 14 is in the crystalline phase and when it is in the amorphous phase. It can be determined strictly so that the change is large and the light absorption efficiency of the second recording layer 14 is increased. The first lower protective layer 2, the first upper protective layer 6, the second lower protective layer 12, and the second upper protective layer 16 may be formed of different materials and compositions, or the same material -You may form with a composition.

  The transmittance adjusting layer 10 has a function of adjusting the transmittance of the first information layer 11. The transmittance adjusting layer 10 allows the transmittance Tc (%) of the first information layer 11 when the first recording layer 4 is in a crystalline phase and the case where the first recording layer 4 is in an amorphous phase. Both the transmittance Ta (%) of the first information layer 11 can be increased. Specifically, in the information recording medium 22 including the transmittance adjusting layer 10, the transmittance of the first information layer 11 is increased by about 2% to 6% as compared with the case where the transmittance adjusting layer 10 is not provided. The transmittance adjusting layer 10 can be formed of the material described for the protective layer. In the information recording medium 22, it is preferable that 40 ≦ (Tc + Ta) / 2 (more preferably 45 ≦ (Tc + Ta) / 2) (the same applies to the information recording medium 26 of the second embodiment).

  The first lower interface layer 3, the first upper interface layer 5, the second lower interface layer 13, and the second upper interface layer 15 are respectively the first lower protective layer 2 and the first recording layer. Layer 4, between the first upper protective layer 6 and the first recording layer 4, between the second lower protective layer 12 and the second recording layer 14, and second upper protective layer The substance is prevented from moving between 16 and the second recording layer 14. These interfacial layers in particular prevent mass transfer caused by repeated recording. These interface layers can be formed of nitrides such as Si—N, Al—N, Ti—N, Ta—N, Zr—N, and Ge—N, nitride oxides including these, or carbides such as SiC. . Among these, Ge—N is particularly preferable. Ge-N is easy to form by reactive sputtering and has excellent mechanical properties and moisture resistance. If the interface layer is thick, the reflectivity and absorptance of the information layer will change greatly, affecting the recording / erasing performance. Therefore, the thickness of the interface layer is preferably in the range of 1 nm to 10 nm, and more preferably in the range of 2 nm to 5 nm.

  The first interface layer 7, the first uppermost interface layer 9, and the second interface layer 17 are respectively disposed between the first upper protective layer 6 and the first reflective layer 8, and between the transmittance adjusting layer 10 and the second interface layer 17. The material is prevented from moving between the first reflective layer 8 and between the second upper protective layer 16 and the second reflective layer 18. These interfacial layers prevent mass transfer caused by recording, particularly in high temperature and high humidity environments. These interface layers can be formed of the materials described for the first lower interface layer 3, the first upper interface layer 5, the second lower interface layer 13, and the second upper interface layer 15. The thickness of these interface layers is preferably in the range of 1 nm to 10 nm, and more preferably in the range of 2 nm to 5 nm.

The first recording layer 4 is made of a material that causes a reversible phase change between a crystalline phase and an amorphous phase when irradiated with a laser beam. The first recording layer 4 can be formed of a material containing, for example, Ge, Sb, and Te. Specifically, the first recording layer 4 can be formed of a material represented by the composition formula Ge _a Sb _b Te _{3 + a} . In the case of a = 0, this material has a very stable crystal phase and lacks the stability of the amorphous phase. On the other hand, when 10 <a, the signal amplitude increases, but the melting point increases and the crystallization speed decreases. Therefore, a preferably satisfies the relationship 0 <a ≦ 10, and more preferably satisfies the relationship 1 ≦ a ≦ 9. In addition, this material has a very stable crystal phase and lacks the stability of the amorphous phase when b <1.5. On the other hand, when 4 <b, the signal amplitude increases, but the crystallization speed decreases. Therefore, b preferably satisfies the relationship of 1.5 ≦ b ≦ 4, and more preferably satisfies the relationship of 1.5 ≦ b ≦ 3.

Further, the first recording layer 4 may be formed of a material represented by the composition formula (Ge- Sn) _a Sb _b Te _{3 + a} . This composition formula means that Ge and element Sn are contained in total of 100 · a / (3 + 2a + b) atomic%. The composition of this material is a composition in which a part of Ge in the material represented by the composition formula Ge _a Sb _b Te _{3 + a} is replaced with the element Sn . When this material is used, since the element Sn substituted with Ge improves the crystallization ability, a sufficient erasure rate can be obtained even when the first recording layer 4 is very thin. Element Sn is not toxic. Also when using this material, it is preferable that 0 <a ≦ 10 (more preferably 1 ≦ a ≦ 9) and 1.5 ≦ b ≦ 4 (more preferably 1.5 ≦ b ≦ 3). .

The first recording layer 4 is formed of a material represented by a composition formula (Ge _a Sb _b Te _{3 + a} ) _100-c M3 _c (where M3 is at least one element selected from Cr and Sn ). May be. The composition of this material is a composition obtained by adding the element M3 to the material represented by the composition formula Ge _a Sb _b Te _{3 + a} . In this case, since the added element M3 increases the melting point and the crystallization temperature of the recording layer, the thermal stability of the recording layer can be improved, and as a result, the recording / reproducing performance of the first information layer 11 can be improved. This material preferably has 0 <c ≦ 20, more preferably 2 ≦ c ≦ 10, since the crystallization rate is insufficient when 20 <c. Further, it is preferable that 0 <a ≦ 10 (more preferably 1 ≦ a ≦ 9) and 1.5 ≦ b ≦ 4 (more preferably 1.5 ≦ b ≦ 3).

  The second recording layer 14 is made of a material that causes a reversible phase change between a crystalline phase and an amorphous phase when irradiated with a laser beam. The second recording layer 14 is formed of a material different from the material of the first recording layer 4. The second recording layer 14 is preferably made of a material having a lower melting point than the material of the first recording layer 4.

The second recording layer 14 can be formed of a material composed of at least one element M1, Sb, and Te selected from Ag, In, Ge, Sn, Se, Bi, Au, and Mn. Specifically, it can be formed of a material represented by a composition formula (Sb _x Te _100-x ) _100-y M1 _y . This material is obtained by adding the element M1 to the Sb—Te alloy near the Sb ₇₀ Te ₃₀ eutectic composition. When x and y satisfy 50 ≦ x ≦ 95 and 0 <y ≦ 20, respectively, this material has a low melting point and a high refractive index. Therefore, by forming the second recording layer 14 using a material having a composition in this range, the second information layer 20 having high recording sensitivity and high reflectance can be obtained.

  In the case of 65 ≦ x, the crystallization speed is particularly fast, and a particularly good erasure rate can be obtained. In addition, in the case of x ≦ 85, it is possible to suppress the appearance of a plurality of phases, and thus it is possible to suppress deterioration of characteristics due to repeated recording. Therefore, it is more preferable that 65 ≦ x ≦ 85. In order to obtain good recording / reproducing performance, it is preferable to add the element M1 for adjusting the crystallization speed. y is more preferably 1 ≦ y ≦ 10. In the case of y ≦ 10, it is possible to suppress the appearance of a plurality of phases, and thus it is possible to suppress deterioration of characteristics due to repeated recording.

Here, the refractive index, extinction coefficient, and melting point of (Ge _0.74 Sn _0.26 ) ₈ Sb ₂ Te ₁₁ and (Sb _0.7 Te _0.3 ) ₉₅ Ge ₅ , (Sb _0.7 Te _0.3 ) ₉₀ Ag ₅ In ₅ were examined. The results are shown in Table 1. The refractive index and extinction coefficient were obtained by measuring with a spectroscope a sample in which a 10 nm thick layer made of the above material was formed on a quartz substrate. The melting point was measured by a differential scanning calorimeter (DSC method).

In Table 1, n _c is the refractive index when a layer of the sample is in the crystalline phase. n _a is the refractive index when a layer of the sample is amorphous phase. [Delta] n is represented by Δn = n _c -n _a, indicating a change in the refractive index between the case if the layer the layer is in the crystalline phase is an amorphous phase. k _c represents the extinction coefficient when the sample layer is in the crystalline phase. k _a indicates the extinction coefficient when the sample layer is in an amorphous phase. .DELTA.k is, .DELTA.k = is represented by k _c -k _a, shows the change in the extinction coefficient between when the case and the layer the layer is in the crystalline phase is an amorphous phase.

As shown in Table 1, the extinction coefficient of (Ge _0.74 Sn _0.26 ) ₈ Sb ₂ Te ₁₁ is (Sb _0.7 Te _0.3 ) ₉₅ regardless of whether the sample layer is crystalline or amorphous. Ge ₅ and than _{(Sb 0.7 Te 0.3) 90 Ag} 5 in the extinction coefficient of _5, was about 0.3 smaller. Further, (Sb _0.7 Te _0.3 ) ₉₅ Ge ₅ and (Sb _0.7 Te _0.3 ) ₉₀ Ag ₅ In ₅ are compositions in which the element M1 is added to the Sb—Te alloy near the Sb ₇₀ Te ₃₀ eutectic composition. Compared with (Ge _0.74 Sn _0.26 ) ₈ Sb ₂ Te _{11 in} which Ge having an Sb—Te ternary composition was substituted with Sn, the melting point was lower by about 50 ° C., and the refractive index change Δn had a larger absolute value.

From the above results, it is preferable to use a Ge—Sb—Te ternary composition or a composition based on the Ge—Sb—Te ternary composition that can increase the transmittance because the extinction coefficient is small. Further, as the material of the second recording layer 14, a (Sb-Te) -M1 composition in which the recording sensitivity can be increased because the melting point is low and the reflectance change can be increased because the refractive index change Δn is large is used. preferable. As a specific combination of the first recording layer 4 / second recording layer 14, for example, Ge ₆ Sb ₂ Te ₉ / (Sb _0.7 Te _0.3 ) ₉₅ Ge ₅ , Ge ₈ Sb ₂ Te ₁₁ / (Sb _{0.7 Te 0.3) 95 Ge 5, Ge} 8 Sb 2 Te 11 / (Sb 0.7 Te 0.3) and the like ₉₀ Ag ₅ In _5.

  The thickness of the first recording layer 4 increases the transmittance of the first information layer 11 so that the amount of laser light necessary for recording / reproducing of the second information layer 20 reaches the second information layer 20. Therefore, it is preferably 9 nm or less, and more preferably in the range of 5 nm to 7 nm.

  The thickness of the second recording layer 14 is preferably in the range of 6 nm to 15 nm in order to increase the recording sensitivity of the second information layer 20. When the second recording layer 14 is thick, the thermal effect on the adjacent region due to the diffusion of heat in the in-plane direction, and when the second recording layer 14 is thin, the reflectance of the second information layer 20 is decreased. In consideration of the above, the thickness of the second recording layer 14 is more preferably in the range of 8 nm to 12 nm.

  The first reflective layer 8 and the second reflective layer 18 have an optical function of increasing the amount of light absorbed by the first recording layer 4 or the second recording layer 14. These reflective layers also have a thermal function of quickly diffusing heat generated in the first recording layer 4 or the second recording layer 14 and making the recording layer amorphous. Furthermore, these reflective layers also have a function of protecting the multilayer film from the environment in which it is used.

  For the material of the first reflective layer 8 and the second reflective layer 18, a single metal having a high thermal conductivity such as Al, Au, Ag, Cu can be used. In addition, an alloy containing one or more of these metal elements as a main component and one or more other elements added for the purpose of improving moisture resistance or adjusting thermal conductivity can also be used. Specifically, an alloy such as Al—Cr, Al—Ti, Au—Pd, Au—Cr, Ag—Pd, Ag—Pd—Cu, Ag—Pd—Ti, Ag—Ru—Au, or Cu—Si is used. Can be used. These alloys are all excellent materials that have excellent corrosion resistance and satisfy rapid cooling conditions. In particular, an Ag alloy is preferable as a material for the first reflective layer 8 because of its high thermal conductivity and high light transmittance.

  In order to make the transmittances Tc and Ta of the first information layer 11 as high as possible, the thickness of the first reflective layer 8 is preferably in the range of 5 nm to 15 nm, and in the range of 8 nm to 12 nm. Is more preferable. When the first reflective layer 8 is thinner than 5 nm, its thermal diffusion function is insufficient, and the reflectance of the first information layer 11 is lowered. Further, when the first reflective layer 8 is thicker than 15 nm, the transmittance of the first information layer 11 is insufficient. On the other hand, the second information layer 20 does not require high transmittance. Therefore, the thickness of the second reflective layer 18 is preferably in the range of 30 nm to 150 nm, and more preferably in the range of 70 nm to 90 nm. When the second reflective layer 18 is thinner than 30 nm, its thermal diffusion function is insufficient, and the second recording layer 14 is difficult to become amorphous. On the other hand, when the second reflective layer 18 is thicker than 150 nm, the thermal diffusion function becomes too large and the recording sensitivity of the second information layer 20 is lowered.

The optical separation layer 21 is provided to distinguish between the focus position of the first information layer 11 and the focus position of the second information layer 20. As the material of the optical separation layer 21, a photocurable resin or a delayed action resin can be used. The material of the optical separation layer 21 preferably has small light absorption at the wavelength of the laser beam 23 used for recording and reproduction. The thickness of the optical separation layer 21 needs to be not less than the depth of focus ΔZ determined by the numerical aperture NA of the objective lens and the wavelength λ of the laser beam 23. Assuming that the reference of the intensity of the focal point is 80% of the case of no aberration, ΔZ can be approximated by ΔZ = λ / {2 (NA) ² }. When λ = 400 nm and NA = 0.6, ΔZ = 0.556 μm, and within ± 0.6 μm is within the depth of focus. Therefore, in this case, the thickness of the optical separation layer 21 needs to be 1.2 μm or more. The distance between the 1st information layer 11 and the 2nd information layer 20 needs to exist in the range which can condense the laser beam 23 using an objective lens. Therefore, the sum of the thickness of the optical separation layer 21 and the thickness of the first substrate 1 is preferably within the tolerance of the substrate thickness that the objective lens can tolerate. For this reason, the thickness of the optical separation layer 21 is preferably in the range of 1.2 μm to 50 μm.

  The information recording medium 22 of the first embodiment can be manufactured by the method described in the third embodiment.

(Embodiment 2)
In Embodiment 2, another example of the information recording medium of the present invention will be described. A partial cross-sectional view of the information recording medium 26 of Embodiment 2 is shown in FIG. In the information recording medium 26, recording / reproduction is performed by irradiation with the laser beam 23.

  With reference to FIG. 3, the information recording medium 26 includes an optical separation layer 21, and a first information layer 25 and a second information layer 20 disposed so as to sandwich the optical separation layer 21.

  The first information layer 25 includes a first substrate 1, a transparent layer 24, a first lower protective layer 2, a first lower interface layer 3, and a first layer arranged in order from the incident side of the laser beam 23. A recording layer 4, a first upper interface layer 5, a first upper protective layer 6, a first interface layer 7, a first reflective layer 8, a first uppermost interface layer 9, and a transmittance adjusting layer 10 are provided. .

  The second information layer 20 includes a second lower protective layer 12, a second lower interface layer 13, a second recording layer 14, and a second upper interface layer arranged in order from the incident side of the laser beam 23. 15, a second upper protective layer 16, a second interface layer 17, a second reflective layer 18, and a second substrate 19.

  As will be described in Embodiment 4 below, when the information recording medium 26 is manufactured, first, the second reflective layer 18 to the second lower protective layer 12 and the optical separation layer are formed on the second substrate 19. 21. The layers are laminated in the order of the transmittance adjusting layer 10 to the first lower protective layer 2. Then, the information recording medium 26 can be formed by bonding the first lower protective layer 2 and the first substrate 1 using the transparent layer 24. Alternatively, the first substrate 1 may be formed by applying and curing a resin without forming the transparent layer 24.

  As a material for the optical separation layer 21 and the transparent layer 24, a photo-curing resin or a slow-acting resin can be used. This material preferably has small light absorption at the wavelength of the laser beam 23 used for recording and reproduction. The thicknesses of the optical separation layer 21 and the transparent layer 24 are preferably in the range of 1.2 μm to 50 μm, respectively, for the reason described in the first embodiment.

  A guide groove for guiding the laser beam 23 may be formed on the surface of the optical separation layer 21 on the first information layer 25 side. Similar to the information recording medium 22 of Embodiment 1, the laser beam 23 is incident from the first substrate 1 side. In the second information layer 20, recording / reproduction is performed by the laser beam 23 transmitted through the first information layer 25 and the optical separation layer 21.

  Note that the first substrate 1, the first lower protective layer 2, the first lower interface layer 3, the first recording layer 4, the first upper interface layer 5, the first upper protective layer 6, the first 1 interface layer 7, first reflective layer 8, first uppermost interface layer 9, transmittance adjustment layer 10, second lower protective layer 12, second lower interface layer 13, second recording layer 14, the second upper interface layer 15, the second upper protective layer 16, the second interface layer 17, the second reflective layer 18, and the second substrate 19 are the same as those described in the first embodiment. Can be used. Further, the shape and function thereof are the same as those described in the first embodiment.

(Embodiment 3)
In Embodiment 3, a method for manufacturing the information recording medium 22 of the present invention will be described.

  The manufacturing method of Embodiment 3 includes a step of forming the first information layer 11 (step (a)). Specifically, first, a first substrate 1 (having a thickness of, for example, 0.1 mm) having a guide groove for guiding the laser beam 23 is prepared. Next, the first substrate 1 is placed in a film forming apparatus, and the first lower protective layer 2 is formed on the first substrate 1. At this time, when the guide groove is formed on the first substrate 1, the first lower protective layer 2 is formed on the side where the guide groove is formed. The first lower protective layer 2 can be formed by reactive sputtering of a base material made of a metal constituting the first lower protective layer 2 in a mixed gas atmosphere of Ar gas and reactive gas. The first lower protective layer 2 can also be formed by sputtering a base material made of a compound in an Ar gas atmosphere or a mixed gas atmosphere of Ar gas and a reactive gas.

  Subsequently, a first lower interface layer 3 is formed on the first lower protective layer 2. The first lower interface layer 3 can be formed by reactive sputtering of a base material made of a metal constituting the first lower interface layer 3 in a mixed gas atmosphere of Ar gas and reactive gas. The first lower interface layer 3 can also be formed by sputtering a base material made of a compound in an Ar gas atmosphere or a mixed gas atmosphere of Ar gas and a reactive gas.

Subsequently, the first recording layer 4 is formed on the first lower interface layer 3. The first recording layer 4 has a base material made of a Ge—Sb—Te— Sn alloy, or a base material made of a Ge—Sb—Te—M3 alloy, depending on its composition. The material can be formed by sputtering using a single power source. That is, the first recording layer 4 can be formed using a base material containing Ge, Sb, and Te.

The sputtering atmosphere gas (sputtering gas) includes Ar gas, Kr gas, a mixed gas of Ar gas and a reactive gas (at least one gas selected from oxygen gas and nitrogen gas), or a mixture of Kr gas and reactive gas. Gas can be used. The first recording layer 4 can also be formed by simultaneously sputtering each base material of Ge, Sb, Te, Sn , or M3 using a plurality of power supplies. In addition, the first recording layer 4 is formed by simultaneously using a plurality of power sources with a binary base material or a ternary base material in which any element of Ge, Sb, Te, Sn , or M3 is combined. It can also be formed by sputtering. Even in these cases, sputtering is performed in an Ar gas atmosphere, a Kr gas atmosphere, a mixed gas atmosphere of Ar gas and a reactive gas, or a mixed gas atmosphere of Kr gas and a reactive gas.

  The film formation rate of the first recording layer 4 is preferably in the range of 0.1 nm / second to 3 nm / second. As described in Embodiment 1, the thickness of the formed first recording layer 4 is preferably 9 nm or less (more preferably 7 nm or less). The film formation rate can be controlled by turning on the power. If the film formation rate is lowered too much, the film formation time becomes longer, and the gas in the atmosphere is mixed in the recording layer more than necessary. If the film formation rate is increased too much, the film formation time can be shortened, but it becomes difficult to accurately control the thickness of the recording layer. Therefore, the film formation rate of the first recording layer 4 is preferably in the range of 0.1 nm / second to 3 nm / second.

  Subsequently, a first upper interface layer 5 is formed on the first recording layer 4. The first upper interface layer 5 can be formed by the same method as the first lower interface layer 3 (the same applies to the following interface layers). The composition of the base material used when forming these interface layers is selected according to the composition of the interface layer and the sputtering gas (the same applies to the steps of forming other layers). That is, the interface layer may be formed using a base material having the same composition, or the interface layer may be formed using a base material having a different composition (in the process of forming another layer). Is the same).

  Subsequently, a first upper protective layer 6 is formed on the first upper interface layer 5. The first upper protective layer 6 can be formed by the same method as the first lower protective layer 2 (the same applies to the following protective layers).

  Subsequently, a first interface layer 7 and a first reflective layer 8 are sequentially formed on the first upper protective layer 6. The first reflective layer 8 can be formed by sputtering a base material made of a metal or an alloy constituting the first reflective layer 8 in an Ar gas atmosphere.

  Subsequently, the first uppermost interface layer 9 and the transmittance adjusting layer 10 are sequentially formed on the first reflective layer 8. The transmittance adjusting layer 10 can be formed by the same method as the first lower protective layer 2.

  In this way, the first information layer 11 is formed. If necessary, an initialization step for crystallizing the entire surface of the first recording layer 4 may be performed after forming the transmittance adjusting layer 10. The crystallization of the first recording layer 4 can be performed by irradiating a laser beam.

  Before or after the step (a) or in parallel, the second information layer 20 is formed (step (b)). Specifically, first, a second substrate 19 (having a thickness of 1.1 mm, for example) is prepared. Then, the second substrate 19 is placed in the film formation apparatus, and the second reflective layer 18 is formed on the second substrate 19. At this time, when the guide groove is formed in the second substrate 19, the second reflective layer 18 is formed on the side where the guide groove is formed. The second reflective layer 18 can be formed by sputtering a base material made of a metal or an alloy constituting the second reflective layer 18 in an Ar gas atmosphere.

  Subsequently, the second interface layer 17, the second upper protective layer 16, and the second upper interface layer 15 are formed in this order on the second reflective layer 18.

  Subsequently, the second recording layer 14 is formed on the second upper interface layer 15. The second recording layer 14 can be formed by sputtering a base material made of an Sb—Te—M1 alloy using one power source. That is, the second recording layer 14 can be formed using a base material containing Sb, Te, and the element M1. The sputtering atmosphere gas (sputtering gas) includes Ar gas, Kr gas, a mixed gas of Ar gas and a reactive gas (at least one gas selected from oxygen gas and nitrogen gas), or a mixture of Kr gas and reactive gas. Gas can be used. The second recording layer 14 can also be formed by simultaneously sputtering each base material of Sb, Te and M1 using a plurality of power supplies. The second recording layer 14 can also be formed by simultaneously sputtering a binary base material combining any element of Sb, Te, and M1 using a plurality of power supplies. Even in these cases, sputtering is performed in an Ar gas atmosphere, a Kr gas atmosphere, a mixed gas atmosphere of Ar gas and a reactive gas, or a mixed gas atmosphere of Kr gas and a reactive gas.

  The film forming rate of the second recording layer 14 is preferably in the range of 0.3 nm / second to 10 nm / second. As described in the first embodiment, the thickness of the second recording layer 14 is preferably in the range of 6 nm to 15 nm. The film formation rate of the second recording layer 14 can be controlled by the power-on power. If the film formation rate is lowered too much, the film formation time becomes longer and gas in the atmosphere is mixed into the recording layer more than necessary. If the film formation rate is increased too much, the film formation time can be shortened, but it becomes difficult to accurately control the layer thickness. Therefore, the film formation rate of the second recording layer 14 is preferably in the range of 0.3 nm / second to 10 nm / second.

  Subsequently, the second lower interface layer 13 and the second lower protective layer 12 are formed in this order on the second recording layer 14.

  In this way, the second information layer 20 can be formed. Note that, after forming the second lower protective layer 12, an initialization step of crystallizing the entire surface of the second recording layer 14 may be performed as necessary. Crystallization of the second recording layer 14 can be performed by irradiating a laser beam.

  Finally, the first information layer 11 and the second information layer 20 are bonded together via the optical separation layer 21. Specifically, first, an ultraviolet curable resin as a material of the optical separation layer 21 is spin-coated on the transmittance adjusting layer 10 or the second lower protective layer 12, and then the first information layer 11 and the first information layer 11 are formed. The two information layers 20 are brought into close contact with each other. Thereafter, the optical recording layer 22 is obtained by curing the optical separation layer 21 by irradiating ultraviolet rays from the first information layer 11 side. Note that when a slow-acting resin is used as the material of the optical separation layer 21, irradiation with ultraviolet rays is not necessary.

(Embodiment 4)
In the fourth embodiment, a method for manufacturing the information recording medium 26 will be described.

  In the manufacturing method of Embodiment 4, first, the second information layer 20 is formed (step (b)). Specifically, first, a second substrate 19 (having a thickness of, for example, 1.1 mm) is prepared and placed in a film forming apparatus.

  Subsequently, the second reflective layer 18 is formed on the second substrate 19. At this time, when the guide groove is formed on the second substrate 19, the second reflective layer 19 is formed on the side where the guide groove is formed. Then, on the second reflective layer 18, the second interface layer 17, the second upper protective layer 16, the second upper interface layer 15, the second recording layer 14, the second lower interface layer 13, And the 2nd lower side protective layer 12 is formed in order. Each of these layers can be formed by the method described in Embodiment 3.

  In this way, the second information layer 20 can be formed. Note that, after forming the second lower protective layer 12, an initialization process for crystallizing the entire surface of the second recording layer 14 may be performed as necessary.

  Subsequently, the optical separation layer 21 is formed on the second lower protective layer 12 of the second information layer 20 (step (c)). The optical separation layer 21 can be formed by spin-coating a photocurable resin or a slow-acting resin on the second lower protective layer 12 and then curing the resin. In the case where the optical separation layer 21 includes a guide groove on the laser beam incident side surface, the substrate (mold) on which the groove is formed is brought into close contact with the resin before curing, and then the resin is cured, The guide groove can be formed by peeling off the substrate (mold).

  Subsequently, the first information layer 25 is formed on the optical separation layer 21 (step (a)). Specifically, first, on the optical separation layer 21, the transmittance adjusting layer 10, the first uppermost interface layer 9, the first reflective layer 8, the first interface layer 7, the first upper protective layer 6, The first upper interface layer 5, the first recording layer 4, the first lower interface layer 3, and the first lower protective layer 2 are formed in this order. Each of these layers can be formed by the method described in Embodiment 3. After the first lower protective layer 2 is formed, an initialization process for crystallizing the entire surface of the first recording layer 4 may be performed as necessary.

  Finally, the first lower protective layer 2 and the first substrate 1 are bonded together by the transparent layer 24. Specifically, first, an ultraviolet curable resin, which is a material of the transparent layer 24, is spin-coated on the first substrate 1 or the first lower protective layer 2, and then the first substrate 1 and the first substrate 1 are coated. The lower protective layer 2 is adhered. Then, the 1st information layer 25 arrange | positioned on the optical separation layer 21 can be formed by irradiating an ultraviolet-ray from the 1st information layer 25 side and hardening resin. In addition, when the transparent layer 24 consists of a slow-acting resin, irradiation of an ultraviolet-ray is unnecessary. In this way, the information recording medium 26 can be manufactured.

(Embodiment 5)
In the fifth embodiment, the recording / reproducing method of the information recording medium of the present invention described in the first and second embodiments will be described.

  FIG. 4 schematically shows a partial configuration of the recording / reproducing apparatus 50 used in the recording / reproducing method of the present invention. Referring to FIG. 4, the recording / reproducing apparatus 50 focuses the spindle motor 27 for rotating the information recording medium 51, the optical head 30 including the semiconductor laser 29, and the laser beam 23 emitted from the semiconductor laser 29. Objective lens 28. The information recording medium 51 is the information recording medium described in the first or second embodiment, and includes the first recording layer 4 and the second recording layer 14. The objective lens 28 condenses the laser beam 23 on the first recording layer 4 or the second recording layer 14.

  The numerical aperture NA of the objective lens 28 is preferably 0.5 or more and 1.1 or less (more preferably, 0.6 or more and 1.0 or less). The wavelength of the laser beam 23 is preferably 350 nm to 500 nm (more preferably 390 nm to 430 nm). The linear velocity of the information recording medium when recording information is preferably 3 m / sec or more and 30 m / sec or less (more preferably 4 m / sec or more and 15 m / sec or less).

  Information recording is performed by modulating the power of the laser beam 23 into a high power peak power (Pp (mW)) and a low power bias power (Pb (mW)). By irradiating the laser beam 23 with the peak power, an amorphous phase is formed, and the amorphous phase becomes a recording mark. Between the recording marks, a laser beam 23 with a bias power is irradiated to form a crystal phase.

  When recording is performed on the first information layer 11 or 25, information is recorded on the first recording layer 4 with the focus of the laser beam 23 being aligned with the first recording layer 4. Reproduction is performed using the laser beam 23 reflected from the first recording layer 4. When recording is performed on the second information layer 20, the laser beam 23 is focused on the second recording layer 14 and transmitted through the first information layer 11 or 25 and the optical separation layer 21. 23, information is recorded. The reproduction is performed by using a laser beam 23 reflected by the second recording layer 14 and transmitted through the optical separation layer 21 and the first information layer 11 or 25.

  In addition, when any of the first substrate 1, the optical separation layer 21, and the second substrate 19 of the information recording medium to be recorded / reproduced includes a groove 1b, information is recorded in the groove 1b. Alternatively, it may be recorded on the land 1c. Information may be recorded on both the groove 1b and the land 1c. Both the first information layer 11 or 25 and the second information layer 20 may record information in the same part (groove, land, or groove and land), or record information in different parts. May be.

(Embodiment 6)
In Embodiment 6, another example of the information recording medium of the present invention will be described. A partial cross-sectional view of the information recording medium 41 of Embodiment 6 is shown in FIG. In the information recording medium 41, information is recorded by applying electrical energy, specifically, by applying a current pulse.

  Referring to FIG. 5, an information recording medium 41 includes a substrate 31, a first electrode 32, a first recording layer 33, an intermediate electrode 34, and a second recording layer that are sequentially stacked on the substrate 31. 35 and a second electrode 36. The first recording layer 33 constitutes a first information layer. The second recording layer 35 constitutes a second information layer.

As the substrate 31, a resin substrate made of a resin made of polycarbonate or the like, a glass substrate, a ceramic substrate made of ceramic made of Al ₂ O ₃ or the like, an Si substrate, or a metal substrate made of various metals (for example, copper) is used. Can do. Note that the substrate 31 may be used as the first electrode 32 when the substrate 31 has conductivity. Hereinafter, a case where an insulating substrate is used as the substrate 31 will be described.

  The information recording medium 41 can be manufactured by sequentially laminating the first electrode 32, the first recording layer 33, the intermediate electrode 34, the second recording layer 35, and the second electrode 36 on the substrate 31. The composition and formation method of the first recording layer 33 are the same as the composition and formation method of the first recording layer 4 described in the first and third embodiments. The composition and formation method of the second recording layer 35 are the same as the composition and formation method of the second recording layer 14 described in the first and third embodiments. The first recording layer 33 and the second recording layer 35 cause a reversible phase change between the crystalline phase and the amorphous phase by Joule heat generated by application of current.

  As materials for the first electrode 32, the intermediate electrode 34, and the second electrode 36, single metals such as Al, Au, Ag, Cu, Pt, Ti, and W can be used. Alternatively, an alloy material containing one or more of these metal elements as a main component and one or more other elements added for improving moisture resistance or adjusting thermal conductivity can also be used. . The first electrode 32, the intermediate electrode 34, and the second electrode 36 can be formed by sputtering a base material made of a metal or an alloy constituting these electrodes in an Ar gas atmosphere.

  Hereinafter, a recording / reproducing method using the information recording medium 41 will be described. A pulse power source 37 is connected between the first electrode 32 and the second electrode 36 and between the intermediate electrode 34 and the second electrode 36 via a switch 39. A resistance measuring device 38 is connected between the first electrode 32 and the second electrode 36 via a switch 40.

  In the information recording medium 41, information is recorded by changing the phase of the first recording layer 33 and the second recording layer 35 between an amorphous phase and a crystalline phase, respectively. Information is reproduced by utilizing the fact that the resistance of the recording layer in the amorphous phase is higher than the resistance of the recording layer in the crystalline phase. Specifically, information is reproduced by measuring the resistance values of the first recording layer 33 and the second recording layer 35.

  When the first recording layer 33 in the amorphous phase (high resistance state) is changed to the crystal phase (low resistance state), the switch 39 is closed to the terminal 39a side (the switch 40 is open), A current pulse is applied between the electrode 32 and the second electrode 36. At this time, since the material of the first recording layer 33 has a lower crystallization temperature and a longer crystallization time than the material of the second recording layer 35, the amplitude and pulse width of the applied current pulse are adjusted. Only the first recording layer 33 can be phase-changed.

  When the second recording layer 35 in the amorphous phase is changed to the crystalline phase, the switch 39 is closed to the terminal 39b side (the switch 40 is opened), and the intermediate electrode 34 and the second electrode 36 are connected. A current pulse is applied between them. When the recording layer is returned from the crystalline phase to the amorphous phase again, a current pulse having a relatively higher amplitude (current value) than that during crystallization is applied in a shorter time.

  Specifically, when the first recording layer 33 (or the second recording layer 35) is changed from an amorphous phase to a crystalline phase, a current pulse having an amplitude Ic and a pulse width tc is applied to the first recording layer 33 (or the second recording layer 35). Applied to the recording layer 33 (or the second recording layer 35). Further, when the first recording layer 33 is changed from the crystalline phase to the amorphous phase, a current pulse having an amplitude Ia1 and a pulse width ta1 is applied to the first recording layer 33. Further, when the second recording layer 35 is changed from the crystalline phase to the amorphous phase, a current pulse having an amplitude Ia2 and a pulse width ta2 is applied to the second recording layer 35. Here, it is preferable that these amplitudes and pulse widths satisfy the relationship of Ic <Ia2 <Ia1 and the relationship of ta1 ≦ tc or ta2 ≦ tc.

  The resistance values of the first recording layer 33 and the second recording layer 35 are measured by the resistance measuring device 38 with the switch 40 closed (the switch 39 opened). By measuring the resistance values of the first recording layer 33 and the second recording layer 35, the recorded information can be read out.

  A large capacity rewritable memory can be obtained by arranging a large number of information recording media 41 in a matrix. An example of the configuration of such an information recording medium is schematically shown in FIG.

  Referring to FIG. 6, information recording medium 42 includes a plurality of word lines 43 arranged in stripes, a plurality of bit lines 44 arranged in stripes, and a plurality of memories. Cell 45. The word line 43 and the bit line 44 are electric wirings for applying a current pulse and measuring resistance. The word line 43 and the bit line 44 are arranged so as to be orthogonal to each other. The memory cell 45 is disposed so as to be sandwiched between the word line 43 and the bit line 44 at the intersection (indicated by hatching in FIG. 6) between the word line 43 and the bit line 44. An information recording medium 41 in which the intermediate electrode 34 is omitted can be used for the memory cell 45.

  In the information recording medium 42, information can be recorded by changing the voltage between the word line 43 and the bit line 44 and applying a current pulse to the memory cell.

  The recording / reproducing method when the intermediate electrode 34 is omitted will be described below. When changing the first recording layer 33 to the crystalline phase, a current pulse having an amplitude of Ic1 and a pulse width of tc1 is applied. When changing the second recording layer 35 to the crystalline phase, a current pulse having an amplitude of Ic2 and a pulse width of tc2 is applied. When the first recording layer 33 is changed to an amorphous phase, a current pulse having an amplitude Ia1 and a pulse width ta1 is applied. When the second recording layer 35 is changed to an amorphous phase, a current pulse having an amplitude Ia2 and a pulse width ta2 is applied.

  The temperature Tx1 at which the material of the first recording layer 33 changes from the amorphous phase to the crystalline phase is lower than the temperature Tx2 at which the material of the second recording layer 35 changes from the amorphous phase to the crystalline phase (Tx1 < Tx2). The time tx1 required for the material of the first recording layer 33 to change from the amorphous phase to the crystalline phase is the time tx1 required when the recording material of the second recording layer 35 changes from the amorphous phase to the crystalline phase. It is longer than the required time tx2 (tx2 <tx1). Therefore, each recording layer can be selectively crystallized by making the amplitude Ic1, the pulse width tc1, the amplitude Ic2 and the pulse width tc2 satisfy Ic1 <Ic2 and tc1> tc2. Also, by applying a current pulse having an amplitude of Ic2 and a pulse width of tc1 to the first recording layer 33 and the second recording layer 35, both the recording layers can be crystallized simultaneously.

  Further, the melting point of the material of the first recording layer 33 is higher than the melting point of the material of the second recording layer 35. Therefore, by shortening ta2 and satisfying Ia1> Ia2, only the second recording layer 35 can be made amorphous. On the other hand, when the pulse width ta1 is short, when a current pulse having an amplitude of Ia1 and a pulse width of ta1 is applied, the two recording layers are both in an amorphous phase. In this case, only the first recording layer 33 can be made into an amorphous phase by crystallizing only the second recording layer 35.

  A method for determining the state of each recording layer will be described below. Resistance value Ra1 when the first recording layer 33 is in an amorphous phase, resistance value Rc1 when the first recording layer 33 is in a crystalline phase, and when the second recording layer 35 is in an amorphous phase And the resistance value Rc2 when the second recording layer 35 is in the crystalline phase. The sum of the resistance values of the two recording layers is Ra1 + Ra2, Ra1 + Rc2, Rc1 + Ra2, or Rc1 + Rc2, depending on the state of the two recording layers. Here, by making Ra1 and Ra2 different values and making Rc1 and Rc2 values much smaller than those values, the state of each recording layer can be easily determined from the resistance value. Thus, four different states of the recording layer, that is, binary information can be detected by a single measurement of the resistance value.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1
In Example 1, the transmittance of the first information layer 11 of the information recording medium 22 of FIG. 1 was measured, and the effect of the transmittance adjusting layer 10 was examined.

  First, a sample for measuring transmittance was prepared. Specifically, the first information layer 11 was prepared, and the sample was prepared by bonding the first information layer 11 and the second substrate 19 with the optical separation layer 21 interposed therebetween.

On the other hand, as a comparative example, a sample without the transmittance adjusting layer 10 was also prepared, and the transmittance was measured. The sample of this comparative example was manufactured as follows. First, a polycarbonate substrate (diameter 120 mm, thickness 0.6 mm) was prepared as the first substrate 1. On the polycarbonate substrate, a ZnS—SiO ₂ layer (SiO ₂ : 20 mol%) as the first lower protective layer 2, a GeN layer (thickness: 5 nm) as the first lower interface layer 3, the first (Ge _0.74 Sn _0.26 ) ₈ Sb ₂ Te ₁₁ layer (thickness: 6 nm) as the recording layer 4, GeN layer (thickness: 5 nm) as the first upper interface layer 5, and ZnS as the first upper protective layer 6. A sputtering method in which a SiO ₂ layer (SiO ₂ : 20 mol%), a GeN layer (thickness: 5 nm) as the first interface layer 7, and an Ag alloy layer (thickness: 10 nm) as the first reflective layer 8 are sequentially sputtered Laminated. Thus, the sample of the comparative example was manufactured.

When a sample including the transmittance adjusting layer 10 is formed, a GeN layer (thickness: 3 nm) is further formed as the first uppermost interface layer 9 on the first reflective layer 8, and the transmittance adjusting layer 10 is formed. A ZnS—SiO ₂ layer (thickness: about 30 nm, SiO ₂ : 20 mol%) was sequentially laminated by a sputtering method. Then, the second substrate 19 was spin-coated with an ultraviolet curable resin that is a material of the optical separation layer 21. And the 1st information layer 11 was stuck on resin, and ultraviolet rays were irradiated and the resin was hardened. A transmittance measurement sample was manufactured as described above.

  Here, the thickness of the first lower protective layer 2 and the first upper protective layer 6 is determined by a matrix method (see, for example, Hiroshi Kubota, “Wave Optics”, Iwanami Shoten, 1971, Chapter 3) It was strictly determined by calculation based on. Specifically, these thicknesses are such that the change in the amount of reflected light at a wavelength of 405 nm is larger between the case where the first recording layer 4 is in the crystalline phase and the case where it is in the amorphous phase, and the first information layer 11 is larger, and the light absorption efficiency of the first recording layer 4 is determined to be larger. Further, the thickness of the transmittance adjusting layer 10 determines the difference in the amount of reflected light between the case where the first recording layer 4 is in the crystalline phase and the case where it is in the amorphous phase, and the light absorption efficiency of the first recording layer 4. It was determined strictly so that the transmittance of the first information layer 11 was increased without being lowered.

  With respect to the sample thus obtained, first, the transmittance Ta (%) when the first recording layer 4 was in an amorphous phase was measured. Thereafter, an initialization process for crystallizing the first recording layer 4 was performed, and the transmittance Tc (%) when the first recording layer 4 was in a crystalline phase was measured. A spectroscope was used for measurement, and the transmittance value at a wavelength of 405 nm was examined. After the measurement, a value of (Tc + Ta) / 2 was calculated.

  Table 2 shows the measurement results of transmittance. Here, in the first information layers 11 of Samples 2-1 and 2-3 in Table 2, the reflectance when the recording layer is a crystalline phase is the reflectance when the recording layer is an amorphous phase. Higher than. Samples 2-1 and 2-3 have substantially the same reflectivity when the recording layer is in a crystalline phase. In the first information layer 11 of Samples 2-2 and 2-4, the reflectance when the recording layer is in an amorphous phase is higher than the reflectance when the recording layer is in a crystalline phase. Samples 2-2 and 2-4 have substantially the same reflectance when the recording layer is in an amorphous phase.

  As shown in Table 2, in the first information layer 11 of samples 2-3 and 2-4 provided with the transmittance adjusting layer 10, the first of samples 2-1 and 2-2 having no transmittance adjusting layer 10 is provided. Compared with the information layer 11, the value of (Tc + Ta) / 2 was improved by about 2% to 6% without lowering the reflectance. Therefore, the first information layer 11 preferably includes the transmittance adjustment layer 10.

  As a result of measuring the transmittance of the first information layer 25 of the information recording medium 26 of FIG. 2 by the same method, it was confirmed that the transmittance adjusting layer 10 had the same effect.

(Example 2)
In Example 2, the relationship between the characteristics of the first information layer 11 and the thickness of the first recording layer 4 was examined. Specifically, the first information layer 11 is produced by changing the thickness of the first recording layer 4, and the first information layer 11 and the second substrate 19 are bonded via the optical separation layer 21. Combined samples were made. With respect to the formed sample, the erasure rate of the first information layer 11, the amplitude to noise ratio (CNR), and the transmittance were measured.

A sample manufacturing method will be described below. First, a polycarbonate substrate (diameter 120 mm, thickness 0.6 mm) was prepared as the first substrate 1. On the polycarbonate substrate, a ZnS—SiO ₂ layer (thickness: about 40 nm, SiO ₂ : 20 mol%) as the first lower protective layer 2 and a GeN layer (thickness) as the first lower interface layer 3 are formed. : 5 nm), (Ge _0.74 Sn _0.26 ) ₈ Sb ₂ Te ₁₁ layer (thickness: 4 nm to 10 nm) as the first recording layer 4, GeN layer (thickness: 5 nm) as the first upper interface layer 5, ZnS—SiO ₂ layer (thickness: about 5 nm, SiO ₂ : 20 mol%) as the upper protective layer 1, GeN layer (thickness: 5 nm) as the first interface layer 7, and Ag as the first reflective layer 8 An alloy layer (thickness: 10 nm), a GeN layer (thickness: 5 nm) as the first uppermost interface layer 9, and a ZnS-SiO ₂ layer (thickness: about 30 nm, SiO ₂ : 20 mol) as the transmittance adjustment layer 10 %) Are sequentially deposited by sputtering. It was. Thereafter, an initialization process for crystallizing the entire surface of the first recording layer 4 was performed. In this way, the first information layer 11 was formed.

  Next, an ultraviolet curable resin that is a material of the optical separation layer 21 was spin-coated on the second substrate 19. And the 1st information layer 11 was stuck on this resin, and resin was hardened by irradiating with ultraviolet rays. As described above, a plurality of samples having different thicknesses of the first recording layer 4 were produced.

  About the produced sample, the transmittance | permeability of the 1st information layer 11 was measured by the method similar to Example 1. FIG. Further, the erasure rate and CNR of the first information layer 11 were measured for the manufactured sample using the apparatus shown in FIG. At this time, the wavelength of the laser beam 23 was 405 nm, the NA of the objective lens 28 was 0.65, the linear velocity of the sample during measurement was 8.6 m / s, and the shortest mark length was 0.294 μm. Information was recorded in the groove.

  CNR was measured with a spectrum analyzer after recording (8-16) modulated 3T signal 10 times. The erasing performance was evaluated by recording the 3T signal 10 times, measuring the amplitude, overwriting the 11T signal once, measuring the amplitude of the 3T signal again, and calculating the attenuation rate of the 3T signal. . Hereinafter, the attenuation rate of the 3T signal is referred to as an erasure rate.

  Table 3 shows the measurement results of the erasure rate and CNR of the first information layer 11 and the calculation result of (Tc + Ta) / 2.

  In Table 3, A to D indicate values of (Tc + Ta) / 2, CNR, and erasure rate. Specifically, for the value of (Tc + Ta) / 2, D <30%, 30% ≦ C <40%, 40% ≦ B <50%, 50% ≦ A. Regarding CNR, 40 (dB) ≦ C <50 (dB) and 50 (dB) ≦ B. The erasure rate is 20 (dB) ≦ C <30 (dB) and 30 (dB) ≦ B. The first information layer 11 preferably has a value of (Tc + Ta) / 2 of 30% or more, and more preferably 40% or more. Moreover, it is preferable that CNR is 40 dB or more, and it is more preferable that it is 50 dB or more. Further, the erasure rate is preferably 20 dB or more, and more preferably 30 dB or more.

  As shown in Table 3, in Sample 3-1, the thickness of the first recording layer 4 was 4 nm, the transmittance was sufficient, but the CNR and the erasure rate were insufficient. In Sample 3-4 (thickness of the first recording layer 4: 10 nm), the CNR and the erasure rate were high, but the transmittance was less than 30%. In Sample 3-2 (the thickness of the first recording layer 4: 6 nm) and Sample 3-3 (the thickness of the first recording layer 4: 9 nm), the transmittance is 35% to 45% and the CNR is Good results of 50 dB and an erasure rate of 30 dB were obtained. From the above results, the film thickness of the first recording layer 4 is preferably 9 nm or less.

  Note that the same results were obtained for the first information layer 25 of the information recording medium 26 of FIG. 2 as a result of measuring the erasure rate, CNR, and transmittance by the same method.

(Example 3)
In Example 3, the relationship between the characteristics of the first information layer 11 and the material of the first recording layer 4 was examined. Specifically, the first information layer 11 is produced by changing the composition of the first recording layer 4, and the first information layer 11 and the second substrate 19 are bonded together via the optical separation layer 21. A sample was prepared. For the formed sample, the CNR, erasure rate, and transmittance of the first information layer 11 were measured.

Below, the manufacturing method of a sample is demonstrated. First, a polycarbonate substrate (diameter: 120 mm, thickness 0.6 mm) was prepared as the first substrate 1. On the polycarbonate substrate, a ZnS—SiO ₂ layer (thickness: about 40 nm, SiO ₂ : 20 mol%) as the first lower protective layer 2 and a GeN layer (thickness) as the first lower interface layer 3 are formed. : 5 nm), the first recording layer 4 (thickness: 6 nm), the GeN layer (thickness: 5 nm) as the first upper interface layer 5, and the ZnS-SiO ₂ layer (thickness) as the first upper protective layer 6 : About 5 nm, SiO ₂ : 20 mol%), GeN layer (thickness: 5 nm) as the first interface layer 7, Ag alloy layer (thickness: 10 nm) as the first reflective layer 8, first uppermost interface layer A GeN layer (thickness: 5 nm) as 9 and a ZnS—SiO ₂ layer (thickness: about 30 nm, SiO ₂ : 20 mol%) as the transmittance adjusting layer 10 were sequentially laminated by sputtering. Here, (Ge _0.74 Sn _0.26 ) ₈ Sb ₂ Te ₁₁ , (Sb _0.7 Te _0.3 ) ₉₅ Ge ₅ , or (Sb _0.7 Te _0.3 ) ₉₀ Ag ₅ In ₅ is used as the material of the first recording layer 4. It was. After forming the transmittance adjusting layer 10, an initialization process for crystallizing the entire surface of the first recording layer 4 was performed. In this way, three types of first information layers 11 having different compositions of the first recording layer 4 were produced.

  Next, an uncured ultraviolet curable resin, which is a material of the optical separation layer 21, was spin-coated on the second substrate 19. And the 1st information layer 11 was stuck on this resin, and resin was hardened by irradiating with ultraviolet rays. As described above, a plurality of samples having different compositions of the first recording layer 4 were produced.

  About the produced sample, the transmittance | permeability of the 1st information layer 11 was measured by the method similar to Example 1. FIG. For these samples, the CNR and erasure rate of the first information layer 11 were measured in the same manner as in Example 2.

  Table 4 shows the CNR and erasure rate of the first information layer 11 and the calculation result of (Tc + Ta) / 2.

  In Table 4, B to D show values of (Tc + Ta) / 2, CNR, and erasure rate. Specifically, for the value of (Tc + Ta) / 2, 30% ≦ C <40% and 40% ≦ B <50%. Regarding CNR, D <40 (dB) and 50 (dB) ≦ B. The erasure rate is 20 (dB) ≦ C <30 (dB) and 30 (dB) ≦ B.

As shown in Table 4, Samples 4-2 and 4-3 had insufficient transmittance, CNR, and erasure rate. On the other hand, in Sample 4-1, good results were obtained with a transmittance of 45%, a CNR of 50 dB, and an erasure rate of 30 dB. From the above results, a material represented by the composition formula (Ge _0.74 Sn _0.26 ) ₈ Sb ₂ Te ₁₁ is preferable as the material of the first recording layer 4 in the above sample.

  Note that the same results were obtained for the first information layer 25 of the information recording medium 26 of FIG. 2 as a result of measuring the erasure rate, CNR, and transmittance by the same method.

(Example 4)
In Example 4, the relationship between the characteristics of the second information layer 20 and the material of the second recording layer 14 was examined. Specifically, the second information layer 20 is formed by changing the material of the second recording layer 14, and the first substrate 1 and the second information layer 20 are bonded together via the optical separation layer 21. A sample was prepared. With respect to the formed sample, the recording sensitivity, CNR, and reflectance of the second information layer 20 were measured.

Below, the manufacturing method of a sample is demonstrated. First, a polycarbonate substrate (diameter 120 mm, thickness 0.6 mm) was prepared as the second substrate 19. Then, on the polycarbonate substrate, an Al alloy layer (thickness: 80 nm) as the second reflective layer 18 and a ZnS-SiO ₂ layer (thickness: about 10 nm, SiO ₂ : 20 mol%) as the second upper protective layer 16. ), A GeN layer (thickness: 5 nm) as the second upper interface layer 15, a second recording layer 14 (thickness: 10 nm), a GeN layer (thickness: 5 nm) as the second lower interface layer 13, Then, a ZnS—SiO ₂ layer (thickness: about 60 nm) was sequentially laminated as the second lower protective layer 12 by a sputtering method. Here, (Ge _0.74 Sn _0.26 ) ₈ Sb ₂ Te ₁₁ , (Sb _0.7 Te _0.3 ) ₉₅ Ge ₅ , or (Sb _0.7 Te _0.3 ) ₉₀ Ag ₅ In ₅ was used as the second recording layer 14.

  The thicknesses of the second lower protective layer 12 and the second upper protective layer 16 are calculated based on the matrix method, and the reflected light amount when the second recording layer 14 is in the crystalline phase at the wavelength of 405 nm is the second amount. The amount of reflected light is greater when the recording layer 14 is in the amorphous phase, the change in reflected light amount is greater when the second recording layer 14 is in the crystalline phase and in the amorphous phase, and the second The recording layer 14 was determined strictly so as to increase the light absorption efficiency.

  Next, an initialization process for crystallizing the entire surface of the second recording layer 14 was performed. Next, an ultraviolet curable resin that is a material of the optical separation layer 21 was spin-coated on the first substrate 1. And the 2nd information layer 20 was stuck on this resin, and ultraviolet rays were irradiated and the resin was hardened. As described above, a plurality of samples having different compositions of the second recording layer 14 were formed.

  About the formed sample, the reflectance in the mirror surface part of a board | substrate was measured. For these samples, the recording sensitivity and CNR of the second information layer 20 were measured using the apparatus shown in FIG. At this time, the wavelength of the laser beam 23 was 405 nm, the NA of the objective lens 28 was 0.65, the linear velocity of the sample during measurement was 8.6 m / s, and the shortest mark length was 0.294 μm. Information was recorded in the groove. Here, the recording sensitivity is a value defined by a peak power Pp (mW) that is 1.3 times the peak power Pp (mW) that gives an amplitude that is 3 dBm lower than the saturation value of the amplitude (dBm) (the following). The same applies to the examples). A smaller value of recording sensitivity indicates that recording is possible with a lower laser power. The average value (Tc + Ta) / 2 of the transmittance of the first information layer 11 is about 40%, and the maximum power of the semiconductor laser 29 incident on the first substrate 1 is about 12 mW. The laser power reaching the information layer 20 is about 5 mW. For this reason, the recording sensitivity of the second information layer 20 is preferably 5 mW or less.

  Table 5 shows the measurement results of the recording sensitivity, CNR, and reflectance when the second recording layer 14 is in the crystalline phase.

  In Table 5, B to D indicate values of recording sensitivity, CNR, and reflectance. Specifically, the recording sensitivity is 5 (mW) <D and B ≦ 5 mW. Regarding CNR, 50 (dB) ≦ B. The reflectances are 10% ≦ C <20% and 20% ≦ B <30%. In the second information layer 20, the CNR is preferably 40 dB or more, and more preferably 50 dB or more. Moreover, it is preferable that a reflectance is 10% or more, and it is more preferable that a reflectance is 20% or more.

As shown in Table 5, it was found that in Sample 5-1, the CNR was not saturated at a recording laser power of 5 mW or less, the recording sensitivity was not sufficient, and the reflectance was insufficient. Samples 5-2 and 5-3 using (Sb _0.7 Te _0.3 ) ₉₅ Ge ₅ or (Sb _0.7 Te _0.3 ) ₉₀ Ag ₅ In ₅ which are low melting point materials have a recording sensitivity of 5 mW or less and a high CNR. It was found that both can be achieved.

  Note that the recording sensitivity of the second information layer 20 of the information recording medium 26 shown in FIG. 3 was measured by the same method, and the same result was obtained.

(Example 5)
In Example 5, based on the results of Examples 3 and 4, the information recording medium 22 of FIG. 1 was manufactured. And about the manufactured information recording medium 22, the transmittance | permeability, CNR, and erasure rate of the 1st information layer 11, and the recording sensitivity, reflectance, and CNR of the 2nd information layer 20 were measured.

In Example 5, the composition of the first recording layer 4 and the second recording layer 14 was (Ge _0.74 Sn _0.26 ) ₈ Sb ₂ Te ₁₁ or (Sb _0.7 Te _0.3 ) ₉₅ Ge ₅ . The thickness of the first recording layer 4 was 6 nm, and the thickness of the second recording layer 14 was 10 nm.

  The first information layer 11 was subjected to an initialization process after forming each layer. The transmittance of the first information layer 11 was measured before and after the initialization process. The second information layer 20 was also subjected to an initialization process after film formation. Thereafter, an uncured ultraviolet curable resin, which is a material of the optical separation layer 21, is spin-coated on the second lower protective layer 12, and the first information layer 11 and the second information layer 20 are brought into close contact with each other. It was. And ultraviolet rays were irradiated and the resin was hardened. In this way, a sample (information recording medium 22) including the first information layer 11 and the second information layer 20 was manufactured. The configuration and manufacturing conditions other than the recording layer and the optical separation layer are the same as those in Examples 3 and 4.

  For the sample thus obtained, the CNR and erasure rate of the first information layer 11 were measured. Further, the recording sensitivity, reflectance, and CNR of the second information layer 20 were measured. These measurements were performed in the same manner as described in the above examples. Table 6 shows the measurement results.

  In Table 6, B to D show the results of each measurement. The values of (Tc + Ta) / 2 are 30% ≦ C <40% and 40% ≦ B <50%. Regarding CNR, D <40 (dB), 40 (dB) ≦ C <50 (dB), and 50 (dB) ≦ B. The erasure rate is 20 (dB) ≦ C <30 (dB) and 30 (dB) ≦ B. The recording sensitivity is 12 (mW) <D and B ≦ 12 (mW). The reflectance in Table 6 is the reflectance of the second information layer 20 when the second recording layer 14 is in a crystalline phase, and 10% ≦ C <20% and 20% ≦ B <30%.

In the sample 6-1, the compositions of the first recording layer 4 and the second recording layer 14 are both (Ge _0.74 Sn _0.26 ) ₈ Sb ₂ Te ₁₁ . In Sample 6-2, the composition of the first recording layer 4 is (Ge _0.74 Sn _0.26 ) ₈ Sb ₂ Te ₁₁ , and the composition of the second recording layer 14 is (Sb _0.7 Te _0.3 ) ₉₅ Ge ₅ . In Sample 6-3, the compositions of the first recording layer 4 and the second recording layer 14 are both (Sb _0.7 Te _0.3 ) ₉₅ Ge ₅ .

  As shown in Table 6, in the sample 6-1, similarly to the result of Example 4, the recording sensitivity and the reflectance of the second information layer 20 were not sufficient. Further, in the sample 6-3, similarly to the result of the third example, the transmittance, the CNR, and the erasure rate are insufficient, and the transmittance of the first information layer 11 is not sufficient. The recording sensitivity, reflectance, and CNR of 20 decreased. On the other hand, in Sample 6-2, both the first information layer 11 and the second information layer 20 had a good result that the CNR was 50 dB or more and the erasure rate was 30 dB or more.

  The case where information is recorded in the groove has been described above. Furthermore, when the same measurement was performed for the case where information was recorded on the land and the case where information was recorded on both the land and the groove, similar results were obtained.

(Example 6)
In Example 6, the information recording medium 26 of FIG. 3 was manufactured by the manufacturing method of Embodiment 4. Then, for the manufactured information recording medium 26, the CNR and erasure rate of the first information layer 25 and the erasure rate and CNR of the second information layer 20 were measured.

Below, the manufacturing method of a sample is demonstrated. First, a polycarbonate substrate (diameter 120 mm, thickness 1.1 mm) was prepared as the second substrate 19. Then, on the polycarbonate substrate, an Al alloy layer (thickness: 80 nm) as the second reflective layer 18 and a ZnS-SiO ₂ layer (thickness: about 10 nm, SiO ₂ : 20 mol%) as the second upper protective layer 16. ), GeN layer (thickness: 5 nm) as the second upper interface layer 15, (Sb _0.7 Te _0.3 ) ₉₅ Ge ₅ layer (thickness: 10 nm) as the second recording layer 14, second lower interface layer A GeN layer (thickness: 5 nm) as 13 and a ZnS—SiO ₂ layer (thickness: about 60 nm, SiO ₂ : 20 mol%) as the second lower protective layer 12 were sequentially laminated by sputtering. Thereafter, an initialization process for crystallizing the entire surface of the second recording layer 14 was performed.

  Subsequently, an ultraviolet curable resin was spin-coated on the second lower protective layer 12, and a substrate on which guide grooves were formed was placed thereon, and after the resin was cured, the substrate was peeled off. By this step, the optical separation layer 21 in which the guide groove for guiding the laser beam 23 was formed on the first information layer 25 side was formed.

Thereafter, a ZnS—SiO ₂ layer (thickness: about 30 nm, SiO ₂ : 20 mol%) as the transmittance adjusting layer 10 and a GeN layer (thickness: 3 nm) as the first uppermost interface layer 9 on the optical separation layer 21. ), An Ag alloy layer (thickness: 10 nm) as the first reflective layer 8, a GeN layer (thickness: 5 nm) as the first interface layer 7, and a ZnS—SiO ₂ layer (thickness) as the first upper protective layer 6. Length: about 5 nm, SiO ₂ : 20 mol%), GeN layer (thickness: 5 nm) as the first upper interface layer 5, and (Ge _0.74 Sn _0.26 ) ₈ Sb ₂ Te ₁₁ layer (thickness) as the first recording layer 4 6 nm), a GeN layer (thickness: 5 nm) as the first lower interface layer 3, and a ZnS-SiO ₂ layer (thickness: about 40 nm, SiO ₂ : 20 mol) as the first lower protective layer 2. %) Were sequentially laminated by a sputtering method. Thereafter, an initialization process for crystallizing the entire surface of the first recording layer 4 was performed.

  Next, a polycarbonate substrate (diameter 120 mm, thickness 0.1 mm) was prepared as the first substrate 1. Then, an ultraviolet curable resin that is a material of the transparent layer 24 was spin-coated on the first substrate 1. Then, the 1st lower side protective layer 2 was stuck on the resin, and ultraviolet rays were irradiated and the resin was hardened. A sample (information recording medium 26) was manufactured as described above.

  About the manufactured sample, CNR and the erasure rate of the 1st information layer 25 and the 2nd information layer 20 were measured using the apparatus of FIG. At this time, the wavelength of the laser beam 23 was 405 nm, the NA of the objective lens 28 was 0.85, the linear velocity of the information recording medium 26 at the time of measurement was 5.0 m / s, and the shortest mark length was 0.206 μm. Information was recorded in the groove. As a result, both the first information layer 25 and the second information layer 20 had good results with a CNR of 50 dB or more and an erasure rate of 30 dB or more.

(Example 7)
In the case where Sn, Se, Bi, Au, or Mn was added to the material of the second recording layer 14 instead of Ag, In, and Ge as M1, the same measurement as in Examples 4, 5, and 6 was performed. . As a result, the same effects as in Examples 4, 5 and 6 were obtained.

(Example 8)
In Example 8, the information recording medium 41 of FIG. 5 was manufactured, and the phase change of the recording layer due to the application of electric energy (current pulse) was confirmed.

First, as the substrate 31, a Si substrate whose surface was nitrided was prepared. On the Si substrate, an Au layer (area: 1.0 mm × 1.0 mm, thickness: 0.1 μm) is used as the first electrode 32, and (Ge _0.74 Sn _0.26 ) ₈ Sb is used as the first recording layer 33. ₂ Te ₁₁ layer (area: 0.6 mm × 0.6 mm, thickness: 0.5 μm), Au layer (area: 0.6 mm × 0.6 mm, thickness 0.1 μm) as the intermediate electrode 34, second layer The recording layer 35 is a (Sb _0.7 Te _0.3 ) ₉₅ Ge ₅ layer (area: 0.2 mm × 0.2 mm, thickness: 0.5 μm), and the second electrode 36 is an Au layer (area: 0.2 mm × 0.2 mm, thickness: 0.1 μm) were sequentially laminated by a sputtering method.

  Thereafter, lead wires made of Au were bonded to the first electrode 32, the intermediate electrode 34, and the second electrode 36. A pulse power source 37 was connected between the first electrode 32 and the second electrode 36 and between the intermediate electrode 34 and the second electrode 36 via a switch 39. The change in the resistance value due to the phase change of the first recording layer 33 and the second recording layer 35 is caused by a resistance measuring device 38 connected between the first electrode 32 and the second electrode 36 via the switch 40. Detected.

  When both the first recording layer 33 and the second recording layer 35 are in a high resistance state (amorphous phase), the amplitude between the first electrode 32 and the second electrode 36 is 50 mA and the pulse width is 100 ns. When a current pulse was applied, both recording layers changed to a low resistance state (crystalline phase). Next, when a current pulse having an amplitude of 150 mA and a pulse width of 50 ns is applied between the first electrode 32 and the second electrode 36, only the second recording layer 35 changes from the low resistance state to the high resistance state. did. When both the first recording layer 33 and the second recording layer 35 are in the low resistance state, a current pulse having an amplitude of 200 mA and a pulse width of 50 ns is applied between the first electrode 32 and the second electrode 36. As a result, the two recording layers both changed from the low resistance state to the high resistance state. Furthermore, when both the first recording layer 33 and the second recording layer 35 are in a high resistance state, a current pulse having an amplitude of 50 mA and a pulse width of 100 ns is applied between the intermediate electrode 34 and the second electrode 36. Only the second recording layer 35 changed from the high resistance state to the low resistance state.

  As described above, in the information recording medium 41 in FIG. 5, each of the first recording layer 33 and the second recording layer 35 is electrically reversibly changed between a crystalline phase and an amorphous phase. I was able to. As a result, there are four states, that is, the first recording layer 33 and the second recording layer 35 are both in a high resistance state, the first recording layer 33 is in a low resistance state, and the second recording layer 35 is in a high resistance state. The first recording layer 33 has a high resistance and the second recording layer 35 has a low resistance, and both the first recording layer 33 and the second recording layer 35 have a low resistance.

  Although the embodiments of the present invention have been described above by way of examples, the present invention is not limited to the above-described embodiments, and can be applied to other embodiments based on the technical idea of the present invention.

It is a partial cross section figure which shows an example about the information recording medium of this invention. It is a partial cross section figure which shows another example about the information recording medium of this invention. It is a partial cross section figure which shows another example about the information recording medium of this invention. It is a figure which shows typically a part of structure about the recording / reproducing apparatus used for the recording / reproducing method of this invention. It is a figure which shows typically a structure about another example of the information recording medium of this invention, and an example of the recording / reproducing apparatus. It is a figure which shows typically a part of structure about another example of the information recording medium of this invention.

Explanation of symbols

1, 1a First substrate 1b Groove
1c land 2 first lower protective layer 3 first lower interface layer 4,33 first recording layer 5 first upper interface layer 6 first upper protective layer 7 first interface layer 8 first Reflective layer 9 First uppermost interface layer 10 Transmittance adjusting layer 11, 11a, 25 First information layer 12 Second lower protective layer 13 Second lower interface layer 14, 35 Second recording layer 15 First 2 upper interface layer 16 second upper protective layer 17 second interface layer 18 second reflective layer 19, 19a second substrate 20, 20a second information layer 21 optical separation layers 22, 22a, 26, 41 , 42 Information recording medium 23 Laser beam 24 Transparent layer 27 Spindle motor 28 Objective lens 29 Semiconductor laser 30 Optical head 31 Substrate 32 First electrode 34 Intermediate electrode 36 Second electrode 37 Pulse power supply 38 Resistance measuring device 39, 40 Switch 43 Lead wires 44 bit lines 45 memory cells

Claims (20)

An information recording medium comprising a first information layer and a second information layer,
The first information layer includes a first recording layer that causes a reversible phase change between a crystalline phase and an amorphous phase by Joule heat generated by irradiation of a laser beam or by application of a current,
The second information layer includes a second recording layer that causes a reversible phase change between a crystalline phase and an amorphous phase by Joule heat generated by irradiation of the laser beam or by application of the current. ,
The first recording layer is made of a first material;
The second recording layer is made of a second material;
The transmittance in the first information layer when the first recording layer is in a crystalline phase is Tc (%),
When the transmittance in the first information layer when the first recording layer is in an amorphous phase is Ta (%),
40 ≦ (Tc + Ta) / 2
The filling,
The second material has a composition formula (Sb _x Te _100-x ) _100-y M1 _y
(However, 50 ≦ x ≦ 95, 0 <y ≦ 20, M1 is at least one element selected from Ag, In, Ge, Sn, Se, Bi, Au and Mn)
An information recording medium represented by   The information recording medium according to claim 1, wherein the first material includes Ge, Sb, and Te. The first material has a composition formula Ge _a Sb _b Te _{3 + a}
(However, 0 <a ≦ 10, 1.5 ≦ b ≦ 4)
The information recording medium according to claim 2, represented by: The first material has a composition formula (Ge- Sn) _a Sb _b Te _{3 + a}
(However , 0 <a ≦ 10, 1.5 ≦ b ≦ 4)
The information recording medium according to claim 2, represented by: The first material has a composition formula (Ge _a Sb _b Te _{3 + a} ) _100-c M3 _c
(However, M3 is at least one element selected from Cr and Sn , and 0 <a ≦ 10, 1.5 ≦ b ≦ 4, 0 <c ≦ 20)
The information recording medium according to claim 2, represented by: The first and second recording layers are layers that cause a reversible phase change by irradiation with the laser beam,
The information recording medium according to claim 1, wherein the first information layer is disposed closer to the laser beam incident side than the second information layer.   The information recording medium according to claim 6, wherein the thickness of the first recording layer is 9 nm or less.   The information recording medium according to claim 6 or 7, wherein a thickness of the second recording layer is in a range of 6 nm to 15 nm.   The information recording medium according to claim 1, wherein a wavelength of the laser beam is not less than 390 nm and not more than 430 nm. An optical separation layer disposed between the first information layer and the second information layer;
The first information layer further includes a first substrate, a first lower protective layer, a first upper protective layer, and a first reflective layer;
The second information layer further includes a second lower protective layer, a second upper protective layer, a second reflective layer, and a second substrate;
The first substrate, the first lower protective layer, the first recording layer, the first upper protective layer, the first reflective layer, the optical separation layer, and the second lower protective layer The second recording layer, the second upper protective layer, the second reflective layer, and the second substrate are arranged in this order from the incident side of the laser beam. 10. The information recording medium according to any one of 9 above.   The information recording medium according to claim 10, further comprising a transparent layer disposed between the first substrate and the first lower protective layer.   An interface disposed at at least one interface selected from the interface between the first lower protective layer and the first recording layer and the interface between the first upper protective layer and the first recording layer. The information recording medium according to claim 10, further comprising a layer.   An interface disposed at at least one interface selected from the interface between the second lower protective layer and the second recording layer and the interface between the second upper protective layer and the second recording layer The information recording medium according to claim 10, further comprising a layer.   An interface layer disposed at at least one interface selected from the interface between the first upper protective layer and the first reflective layer and the interface between the second upper protective layer and the second reflective layer The information recording medium according to claim 10, further comprising:   The information recording medium according to claim 10, further comprising a transmittance adjusting layer for adjusting a transmittance of the first information layer between the first reflective layer and the optical separation layer.   The information recording medium according to claim 15, further comprising an interface layer disposed between the first reflective layer and the transmittance adjusting layer.   The information recording medium according to claim 10, wherein a thickness of the first substrate is in a range of 10 μm to 800 μm.   The information recording medium according to claim 10, wherein a thickness of the second substrate is in a range of 400 μm to 1300 μm. A first electrode and a second electrode;
The first and second recording layers are layers that undergo a reversible phase change upon application of the current;
6. The device according to claim 1, wherein the first recording layer, the second recording layer, and the second electrode are stacked in this order on the first electrode. 7. Information recording medium.   The information recording medium according to claim 19, further comprising an intermediate electrode disposed between the first recording layer and the second recording layer.

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