Kojima, Rie (Kadoma, JP)
Yamada, Noboru (Hirakata, JP)
Sakaguchi, Takeshi (Ibaraki, JP)
Plaque It!
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| 5221588 | Method for recording and erasing information | June, 1993 | Morimoto et al. | 430/19 |
| 5591501 | Optical recording medium having a plurality of discrete phase change data recording points | January, 1997 | Ovshinsky et al. | |
| 6268034 | Optical information recording medium and method for producing the same, method for recording and reproducing information thereon and recording/reproducing apparatus | July, 2001 | Kitaura et al. | 428/64.1 |
| 6416837 | Information recording medium, a method for manufacturing the same and a method for recording/reproducing information thereon | July, 2002 | Kojima et al. | 428/64.1 |
| 6432502 | Optical recording medium and method of manufacturing the same | August, 2002 | Kitaura et al. | 428/64.1 |
| 6456584 | Optical information recording medium comprising a first layer having a phase that is reversibly changeable and a second information layer having a phase that is reversibly changeable | September, 2002 | Nagata et al. | |
| 6670013 | Optical recording medium and use of such optical recording medium | December, 2003 | Zhou | 428/64.1 |
| 6670014 | Information recording medium and method for producing the same, and method for recording/reproducing information thereon | December, 2003 | Nishihara et al. | 428/64.1 |
| 6699637 | Process for producing optical information recording medium and optical information recording medium produced by the process | March, 2004 | Ogawa et al. | 430/270.13 |
| 6723411 | Information recording medium and method for manufacturing an information recording medium | April, 2004 | Hirotsune et al. | 428/64.1 |
| 20020160306 | Optical information recording medium and method | October, 2002 | Hanaoka et al. | 430/270.13 |
| EP0825595 | March, 1997 | OPTICAL DATA RECORDING MEDIUM, METHOD OF PRODUCING THE SAME AND METHOD OF REPRODUCING/ERASING RECORD | ||
| EP1039448 | September, 2000 | |||
| JP10275360 | October, 1998 | OPTICAL INFORMATION RECORDING MEDIUM AND ITS PRODUCTION | ||
| JP200036130 | February, 2000 | |||
| JP2001273673 | October, 2001 | OPTICAL RECORDING MEDIUM AND METHOD FOR PRODUCING THE SAME | ||
| JP20022116 | January, 2002 | |||
| JP2002123977 | April, 2002 | WRITE ONCE READ MANY OPTICAL RECORDING MEDIUM | ||
| JP2002225436 | August, 2002 | OPTICAL INFORMATION RECORDING MEDIUM AND ITS MANUFACTURING METHOD | ||
| JP2003288737 | October, 2003 | OPTICAL DATA RECORDING MEDIUM | ||
| WO/1997/034298 | September, 1997 | OPTICAL DATA RECORDING MEDIUM, METHOD OF PRODUCING THE SAME AND METHOD OF REPRODUCING/ERASING RECORD | ||
| WO/2001/082297 | November, 2001 | OPTICAL RECORDING MEDIUM AND USE OF SUCH OPTICAL RECORDING MEDIUM |
Morigaki et al. Basics of Amorphous Semiconductor, Chapter 8. Kikuchi et al. (Ed.) (1982) with partial English translation.
Yamada et al. “Phase-change optical disk having a nitride interface layer”. Japanese Journal of Applied Physics, vol. 37, pp. 2104-2110 (1998).
Kubota. Wave Optics, Chapter 3. (1971) with partial English translation.
1. An information recording medium including a substrate and an information layer arranged on the substrate, the information layer comprising: a recording layer that is changed in phase reversibly between a crystalline phase and an amorphous phase by at least one of optical means and electrical means; and at least one crystalline nucleation layer that contains at least one element selected from Bi and Te and at least one element (M1) selected from Sc, Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Yb, and Lu, and is provided in contact with the recording layer, wherein the recording layer contains at least one element (M2) selected from Sb and Bi, Ge, and Te, and where the element M2, Ge, and Te are represented by a composition formula Gea(M2)bTe3+a, 2≦a≦50 and 2≦b≦4 are satisfied.
2. An information recording medium including a substrate and an information layer arranged on the substrate, the information layer comprising: a recording layer that is changed in phase reversibly between a crystalline phase and an amorphous phase by at least one of optical means and electrical means; and at least one crystalline nucleation layer that contains at least one element selected from Bi and Te and at least one element (M1) selected from Sc, Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Yb, and Lu, and is provided in contact with the recording layer, wherein the recording layer contains Sb, Te, and at least one element (M5) selected from Ag, In, Ge, Sn, Se, Si, Au, and Mn, and where Sb, Te, and the element M5 are represented by a composition formula (SbdTe100−d)100−c(M5)c, 50≦d≦95 and 0<e≦20 are satisfied.
3. The information recording medium according to claim 1, wherein the crystalline nucleation layer contains at least one selected from Bi(M1) and Te(M1).
4. The information recording medium according to claim 1, wherein the crystalline nucleation layer contains at least one selected from BiTe(M1)2, Bi2Te(M1), and BiTe2(M1).
5. The information recording medium according to claim 1, wherein the crystalline nucleation layer contains at least one element selected from N and O.
6. The information recording medium according to claim 1, wherein in the composition formula Gea(M2)bTe3+a, at least one element (M3) selected from, Sn and Pb is substituted for at least a part of Ge.
7. The information recording medium according to claim 1, wherein in the recording layer, the element M2 is Sb, and Bi is substituted for at least a part of Sb.
8. The information recording medium according to claim 6, wherein in the recording layer, a content ratio of Sn atoms is more than 0 atom % and less than 20 atom %.
9. The information recording medium according to claim 7, wherein in the recording layer, a content ratio of Bi atoms is more than 0 atom % and less than 10 atom %.
10. The information recording medium according to claim 1, wherein the recording layer further contains at least one element (M4) selected from Si, Ti, V, Cr, Mn, Fe, Ce, Ni, Cu, Se, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Ta, W, Os, Ir, Pt, and Au, and where the elements M2 and M4, Ge, and Te are represented by a composition formula (Gea(M2)bTe3+a)100−c(M4)c, 2≦a≦50, 2≦b≦4, and 0<c≦20 are satisfied.
11. The information recording medium according to claim 1, wherein the crystalline nucleation layer has a thickness not less than 0.2 nm and not more than 3 nm.
12. The information recording medium according to claim 1, wherein the recording layer has a thickness not less than 3 nm and not more than 14 nm.
13. The information recording medium according to claim 1, the medium having a multi-layer structure in which a first to an N-th information layers (N represents a natural number not smaller than 2) are laminated, wherein at least one of the first to N-th information layers is the information layer.
14. The information recording medium according to claim 1, wherein the recording layer is changed in phase reversibly between a crystalline phase and art amorphous phase by irradiation of a laser beam, and the information layer further comprises a dielectric layer provided on both sides of a laminated body formed of the recording layer and the crystalline nucleation layer, and a reflective layer arranged on a side opposite to an incident side of the laser beam with respect to the laminated body.
15. The information recording medium according to claim 14, wherein the information layer further comprises a light absorption correction layer arranged between the laminated body and the reflective layer.
16. The information recording medium according to claim 1, wherein the recording layer is changed in phase reversibly between a crystalline phase and an amorphous phase by irradiation of a laser beam, the information layer comprises at least a first dielectric layer, a second dielectric layer, the recording layer, a third dielectric layer, and a reflective layer in this order from an incident side of the laser beam, and the crystalline nucleation layer is formed at least one of between the second dielectric layer and the recording layer and between the third dielectric layer and the recording layer.
17. The information recording medium according to claim 16, wherein the information layer further comprises a fourth dielectric layer provided between the third dielectric layer and the reflective layer.
18. The information recording medium according to claim 16, wherein the information layer further comprises an interface layer that is provided between the third dielectric layer and the reflective layer and has a thermal conductivity lower than that of the reflective layer.
19. The information recording medium according to claim 16, the medium having a multi-layer structure in which a first to an N-th information layers (N represents a natural number not smaller than 2) on which information is recorded by irradiation of a laser beam are laminated in this order from an incident side of the laser beam, wherein at least the first information layer is the information layer.
20. The information recording medium according to claim 19, wherein the information layer further includes a transmittance adjusting layer and the transmittance adjusting layer contains at least one selected from TiO2, ZrO2, ZnO, Nb2O5, Ta2O5, SiO2, Al2O3, Bi2O3, Cr2O3, Sr—O, Ti—N, Zr—N, Nb—N, Ta—N, Si—N, Ge—N, Cr—N, Al—N, Ge—Si—N, Ge—Cr—N, and ZnS.
21. The information recording medium according to claim 17, wherein the fourth dielectric layer contains (ZnS)80(SiO2)20.
22. The information recording medium according to claim 16, wherein the third dielectric layer is formed of an oxide-fluoride-based material containing at least one selected from HfO2 and ZrO2, SiO2, Cr2O3, and a fluoride.
23. The information recording medium according to claim 22, wherein the fluoride contains at least one selected from CeF3, ErF3, GdF3, LaF3, TbF3, DyF3, NdF3, YF3, and YbF3.
24. The information recording medium according to claim 22, wherein where the oxide-fluoride-based material is represented by a composition formula (HfO2)A1(SiO2)B1(Cr2O3)C1(fluoride)100−A1−B1−C1 or (ZrO2)A1(SiO2)B1(Cr2O3)C1(fluoride)100−A1−B1−C1, A1, B1, C1, and A1+B1+C1 satisfy: 10≦A1≦50; 10≦B1≦50; 10≦C1≦50; and 50≦A1+B1+C1≦90, respectively.
25. The information recording medium according to claim 16, wherein at least one of the second dielectric layer and the third dielectric layer is formed of an oxide-based material containing at least one selected from HfO2 and ZrO2, SiO2, and Cr2O3.
26. The information recording medium according to claim 25, wherein where the oxide-based material is represented by a composition formula (HfO2)A2(SiO2)B2(Cr2O3)100−A2−B2 or (ZrO2)A2(SiO2)B2(Cr2O3)100−A2−B2, A2, B2, and A2+B2 satisfy: 10≦A2≦50; 10≦B2≦50; and 20≦A2+B2≦80, respectively.
27. A method for manufacturing an information recording medium that is provided with at least one information layer on a substrate, wherein a step of forming the information layer comprises: a step of forming a recording layer that is changed in phase reversibly between a crystalline phase and an amorphous phase by at least one of optical means and electrical means and contains at least one element (M2) selected from Sb and Bi, Ge, and Te, wherein where the element M2, Ge, and Te are represented by a composition formula Gea(M2)bTe3+a, 2≦a≦50 and 2≦b≦4 are satisfied; and a step of forming a crystalline nucleation layer by performing sputtering using a sputtering target containing at least one element selected from Bi and Te and at least one element (M1) selected from Sc, Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Yb, and Lu, and the step of forming the recording layer and the step of forming the crystalline nucleation layer are performed sequentially.
28. The method for manufacturing an information recording medium according to claim 27, wherein the sputtering target contains at least one selected from Bi(M1) and Te(M1).
29. The method for manufacturing an information recording medium according to claim 27, wherein the sputtering target contains at least one selected from BiTe(M1)2, Bi2Te(M1), and BiTe2(M1).
30. The method for manufacturing an information recording medium according to claim 27, wherein in the step of forming the crystalline nucleation layer, at least one selected from Ar gas, Kr gas, a mixture of Ar gas and a reactive gas, and a mixture of Kr gas and a reactive gas is used in performing sputtering, the reactive gas being at least one selected from N2 gas and O2 gas.
TECHNICAL FIELD
The present invention relates to an information recording medium on which information recording, erasing, rewriting, and reproduction are performed optically or electrically, and a method for manufacturing the same.
BACKGROUND ART
Phase-change type optical information recording media have been known as information recording media on which information recording, erasing, rewriting, and reproduction are performed optically by using laser beams. Information recording, erasing, and rewriting are performed on a phase-change type optical information recording medium by utilizing a phenomenon in which a recording layer included in the medium is changed in phase reversibly between a crystalline phase and an amorphous phase. Generally, when recording information, a recording layer is allowed to melt by irradiation of a laser beam at a high power (recording power) and cooled rapidly, so that an irradiated portion is changed in phase to an amorphous phase, thereby allowing the information to be recorded. On the other hand, when erasing the information, the recording layer is raised in temperature by irradiation of a laser beam at a lower power (erasing power) than the power used for recording and cooled gradually, so that a laser beam irradiated portion is changed in phase to a crystalline phase, thereby allowing the recorded information to be erased. Thus, in a phase-change type optical information recording medium, a laser beam that is modulated in power level between a high power level and a low power level is irradiated to a recording layer, thereby making it possible to record new information while erasing information that has been recorded, i.e., to rewrite information (see, for example, “Basics and Applications of Optical Disk Storage” by Yoshito TSUNODA et al., The Institute of Electronics, Information and Communication Engineers, 1995, Chapter 2).
Further, phase-change type electrical information recording media also have been known on which information recording is performed by changing the state of a phase change material in a recording layer by, instead of irradiation of a laser beam, Joule heat generated by application of a current. In such a phase-change type electrical information recording medium, a phase change material in a recording layer is changed in state between a crystalline phase (low resistance) and an amorphous phase (high resistance) by Joule heat generated by application of a current, and a difference in electrical resistance between the crystalline phase and the amorphous phase is detected and read as information. When a current is applied to a recording layer of an amorphous phase sandwiched between electrodes gradually, the recording layer is changed in phase to a crystalline phase at a certain threshold current, so that the electrical resistance decreases rapidly. Further, by applying a large current pulse having a short time pulse width to the recording layer of a crystalline phase, the recording layer is allowed to melt and is cooled rapidly, thereby regaining the recording layer of an amorphous phase of high resistance. Thus, such recording media can be used as rewritable information recording media. The difference in electrical resistance between a crystalline phase and an amorphous phase can be detected easily by usual electrical means, and thus by using a recording layer that is changed in phase reversibly between a crystalline phase and an amorphous phase, a rewritable information recording medium can be obtained (see, for example, “Basics of Amorphous Semiconductor” by Makoto KIKUCHI, Ohmsha, Ltd., 1982, Chapter 8).
Examples of phase-change type optical information recording media include a 4.7 GB/DVD-RAM that has been commercialized by the inventors. The 4.7 GB/DVD-RAM, which is shown in FIG. 21 as an information recording medium 1000, has an information layer 1010 of an eight-layer structure in which, seen from an incident side of a laser beam 10, a first dielectric layer 1002, a second dielectric layer 1003, a crystalline nucleation layer 1004, a recording layer 1005, a third dielectric layer 1006, a fourth dielectric layer 1007, a light absorption correction layer 1008, and a reflective layer 1009 are laminated in this order. The information layer 1010 is laminated to a dummy substrate 1012 with an adhesive layer 1011.
The first dielectric layer 1002 and the fourth dielectric layer 1007 have an optical function and a thermal function. For the optical function, an optical distance is adjusted so that the light absorption efficiency with respect to the recording layer 1005 is increased, and thus a change in reflectance between a crystalline phase and an amorphous phase is increased, thereby allowing the signal amplitude to be increased. For the thermal function, the substrate 1001, the dummy substrate 1012, and the like that have low resistance to heat are insulated from the recording layer 1005 that is heated to a high temperature in recording. A mixture of 80 mol % ZnS and 20 mol % SiO2 (hereinafter, which may be referred to as “(ZnS)80(SiO2)20 (mol %)”), which is used generally for the first dielectric layer 1002 and the fourth dielectric layer 1007, is an excellent dielectric material that is transparent, has a high refractive index, a low thermal conductivity and a good thermal insulation property, and is excellent in mechanical properties and moisture resistance.
As a material of the crystalline nucleation layer 1004, Sn—Te or Pb—Te is used, which is a material that accelerates crystallization of the recording layer 1005 when it is provided in contact with the recording layer 1005. By using such a material, the crystallization ability of the recording layer is allowed to be increased without decreasing the signal amplitude of the information recording medium 1000 and with archival characteristics secured, and not only an initial recording/rewriting capability but also excellent archival characteristics (capability of reproducing recorded information that has been stored for a long term) and archival overwrite characteristics (capability of recording/rewriting information that has been stored for a long term) are realized (see, for example, JP 2001-273673 A).
As a material of the recording layer 1005, a pseudobinary phase change material represented by a point on a line of GeTe—Sb2Te3 is used, thereby realizing an excellent repeated rewriting capability.
The second dielectric layer 1003 and the third dielectric layer 1006 have a function of preventing mass transfer from being caused between the first dielectric layer 1002 and the recording layer 1005 and between the fourth dielectric layer 1007 and the recording layer 1005. The mass transfer is a phenomenon caused when (ZnS)80(SiO2)20 (mol %) is used for each of the first dielectric layer 1002 and the fourth dielectric layer 1007. In this phenomenon, when recording/rewriting is performed repeatedly by irradiation of laser beams to the recording layer 1005, S is diffused in the recording layer 1005. When S is diffused in the recording layer 1005, the repeated rewriting capability is deteriorated (see, for example, N. Yamada et al., Japanese Journal of Applied Physics, Vol. 37 (1998), pp. 2104-2110). In order to prevent the deterioration in repeated rewriting capability, a nitride containing Ge should be used for the second dielectric layer 1003 and the third dielectric layer 1006 (see, for example, WO 97-34298 and JP 10 (1998)-275360).
The above-mentioned technology has allowed an excellent rewriting capability and high reliability to be achieved and led to the commercialization of the 4.7 GB/DVD-RAM.
Furthermore, various forms of technologies for increasing the capacity of information recording media further have been studied. For example, for optical information recording media, a technology is studied for achieving high-density recording using a laser beam with a reduced spot diameter, which can be obtained by the use of a blue-violet laser beam having a wavelength shorter than that of a conventionally used red laser beam, or the use of a substrate that is thinner on an incident side of a laser beam in combination with the use of an objective lens having a high numerical aperture (NA). Furthermore, studies also have been made on a technology in which a recording capacity is doubled by using an optical information recording medium including two information layers and with respect to these two information layers, recording/reproduction is performed using a laser beam incident from a side of one side of the optical information recording medium (see, for example, JP 2000-36130 A).
In order to perform recording using a laser beam with a reduced spot diameter to increase the capacity of information recording media, it is necessary to use an optical information recording medium that allows even a recording mark reduced in size to be formed into an excellent shape. When recording is performed using a laser beam with a reduced spot diameter, the laser beam is irradiated to a recording layer for a relatively shorter time. Thus, to form a recording mark reduced in size, it is necessary to use a material that realizes a high crystallization speed for the recording layer, or to provide a film having a high effect of accelerating crystallization in contact with the recording layer.
In the optical information recording medium including two information layers (hereinafter, which may be referred to as a “two-layer optical information recording medium) that allows information recording/reproduction to be performed with respect to the two information layers by irradiation of a laser beam from a side of one side, the laser beam that has been transmitted through an information layer (hereinafter, referred to as a “first information layer”) arranged at a position closer to an incident surface of the laser beam is used to perform recording/reproduction with respect to an information layer (hereinafter, referred to as a “second information layer”) arranged at a position farther from the laser beam incidence surface. To this end, it is required that a much thinner film be used as a recording layer in the first information layer so that a higher light transmittance can be obtained. However, when the recording layer becomes thinner, crystalline nuclei formed when the recording layer is crystallized are reduced, and further a distance in which atoms are allowed to move becomes shorter. For theses reasons, a thinner recording film hinders the formation of a crystalline phase more (which means the crystallization speed is decreased).
Further, when an information transfer rate is increased by decreasing a time for information recording on an information recording medium, a time for crystallization is reduced. Thus, to realize information recording media adaptable to a high transfer rate, it also is required that the recording layer have a higher crystallization ability. Further, when information recording is performed at a high transfer rate, the recording layer that has been raised in temperature is cooled at a speed higher than that achieved when recording is performed at a lower transfer rate, and thus microcrystalline nuclei are less likely to be formed in an amorphous phase after recording. In other words, a more stable amorphous phase is likely to be obtained. An amorphous phase tends to be changed to a still more stable energy state after long-term storage. Therefore, when information recording is performed at a high transfer rate, it becomes more difficult to allow the recording layer to be crystallized, resulting in a deterioration in archival overwrite characteristics.
According to the test performed by the inventors, it has been revealed that by the use of a recording layer having a composition in which Sn is substituted for a part of Ge in a pseudobinary composition represented by a point on or near the line of GeTe—Sb2Te3, the crystallization speed of a recording layer can be increased. However, in this case, as the amount of Sn as a substituent is increased, the change in optical property between a crystalline phase and an amorphous phase becomes small, thereby decreasing the signal amplitude. Further, when the amount of Sn is increased, a recorded amorphous phase is crystallized gradually, and thus the archival characteristics are deteriorated in the case where recording is performed at a particularly low transfer rate.
As described above, as the capacity of information recording media increases, it becomes difficult to realize in a single information recording medium both the archival overwrite characteristics at a high transfer rate and the archival characteristics at a low transfer rate.
To allow the crystallization ability of the recording layer to be increased without decreasing the signal amplitude and with the archival characteristics secured, as described above, a crystalline nucleation layer made of Sn—Te or the like that accelerates crystallization of the recording layer should be provided in contact with the recording layer. According to the test performed by the inventors, it has been revealed that the crystallization ability of the recording layer can be increased by the use of Bi—Te for the crystalline nucleation layer. However, Sn—Te and Bi—Te have a low melting point, and thus a phenomenon is caused in which when the recording layer is raised in temperature in recording, Sn—Te or Bi—Te melts and, after repeated rewriting operations, is mixed into the recording layer gradually. As a result, the repeated rewriting capability is deteriorated.
As described above, in conventional information recording media, it is difficult to realize both an excellent information erasing rate (a phase change to a crystalline phase) as well as excellent archival overwrite characteristics at a high transfer rate and excellent archival characteristics at a low transfer rate, and at the same time, an excellent repeated rewriting capability.
DISCLOSURE OF INVENTION
An information recording medium of the present invention includes a substrate and an information layer arranged on the substrate. The information layer includes: a recording layer that is changed in phase reversibly between a crystalline phase and an amorphous phase by at least one of optical means and electrical means; and at least one crystalline nucleation layer that contains at least one element selected from Bi and Te and at least one element (M1) selected from Sc, Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Yb, and Lu, and is provided in contact with the recording layer.
A method for manufacturing an information recording medium of the present invention is a method for manufacturing an information recording medium that is provided with at least one information layer on a substrate. A step of forming the information layer includes: a step of forming a recording layer that is changed in phase reversibly between a crystalline phase and an amorphous phase by at least one of optical means and electrical means; and a step of forming a crystalline nucleation layer by performing sputtering using a sputtering target containing at least one element selected from Bi and Te and at least one element (M1) selected from Sc, Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Yb, and Lu. The step of forming the recording layer and the step of forming the crystalline nucleation layer are performed sequentially.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a cross-sectional view showing an exemplary configuration of an information recording medium according to Embodiment 1 of the present invention.
FIG. 2 is a cross-sectional view showing another exemplary configuration of an information recording medium according to Embodiment 1 of the present invention.
FIG. 3 is a cross-sectional view showing still another exemplary configuration of an information recording medium according to Embodiment 1 of the present invention.
FIG. 4 is a cross-sectional view showing an exemplary configuration of an information recording medium according to Embodiment 2 of the present invention.
FIG. 5 is a cross-sectional view showing another exemplary configuration of an information recording medium according to Embodiment 2 of the present invention.
FIG. 6 is a cross-sectional view showing still another exemplary configuration of an information recording medium according to Embodiment 2 of the present invention.
FIG. 7 is a cross-sectional view showing an exemplary configuration of an information recording medium according to Embodiment 3 of the present invention.
FIG. 8 is a cross-sectional view showing another exemplary configuration of an information recording medium according to Embodiment 3 of the present invention.
FIG. 9. is a cross-sectional view showing still another exemplary configuration of an information recording medium according to Embodiment 3 of the present invention.
FIG. 10. is a cross-sectional view showing an exemplary configuration of an information recording medium according to Embodiment 4 of the present invention.
FIG. 11 is a cross-sectional view showing another exemplary configuration of an information recording medium according to Embodiment 4 of the present invention.
FIG. 12. is a cross-sectional view showing still another exemplary configuration of an information recording medium according to Embodiment 4 of the present invention.
FIG. 13 is an explanatory view schematically showing a partial configuration of a recording/reproducing apparatus for performing information recording/reproduction on an information recording medium of the present invention.
FIG. 14 is a cross-sectional view showing an exemplary configuration of an information recording medium according to Embodiment 6 of the present invention.
FIG. 15 is a cross-sectional view showing another exemplary configuration of an information recording medium according to Embodiment 6 of the present invention.
FIG. 16 is a cross-sectional view showing still another exemplary configuration of an information recording medium according to Embodiment 6 of the present invention.
FIG. 17 is a cross-sectional view showing yet another exemplary configuration of an information recording medium according to Embodiment 6 of the present invention.
FIG. 18 is an explanatory view showing a partial cross section of an information recording medium and a schematic configuration of an electrical information recording/reproducing apparatus for performing information recording/reproduction on the information recording medium according to Embodiment 7 of the present invention.
FIG. 19 is an explanatory view schematically showing a partial configuration of a large-capacity electrical information recording medium according to Embodiment 7 of the present invention.
FIG. 20 is an explanatory view schematically showing a partial configuration of the electrical information recording medium and a recording/reproduction system therefor according to Embodiment 7 of the present invention.
FIG. 21 is a cross-sectional view showing an exemplary configuration of a conventional information recording medium.
BEST MODE FOR CARRYING OUT THE INVENTION
An information recording medium of the present invention has a configuration in which a crystalline nucleation layer provided in contact with a recording layer contains at least one element selected from Bi and Te and at least one element (M1) selected from Sc, Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Yb, and Lu. Therefore, an excellent information erasing rate (a phase change to a crystalline phase) at a high transfer rate can be realized, and excellent archival overwrite characteristics also can be realized since the crystalline nucleation layer has a high melting point and excellent thermal stability. In addition, excellent archival characteristics at a low transfer rate can be obtained, and an excellent repeated rewriting capability also can be achieved at the same time.
In the information recording medium of the present invention, the crystalline nucleation layer may contain at least one selected from Bi(M1) and Te(M1). Therefore, it is possible to obtain an information recording medium 1 in which the crystalline nucleation layer has a high melting point and excellent thermal stability, and which has an excellent capability of rewriting information that has been stored for a long term.
In the information recording medium of the present invention, the crystalline nucleation layer may contain at least one selected from BiTe(M1)2, Bi2Te(M1), and BiTe2(M1). Therefore, it is possible to obtain an information recording medium 1 in which the crystalline nucleation layer has a high melting point and excellent thermal stability, and which has an excellent capability of rewriting information that has been stored for a long term.
In the information recording medium of the present invention, the crystalline nucleation layer may contain at least one element selected from N and O. Therefore, thermal stability of the crystalline nucleation layer is enhanced. Further, in particular, when N is added to the crystalline nucleation layer, crystal grains tend to be more uniform and smaller in size. Thus, recording noise generated in a low-frequency region in recording can be reduced.
In the information recording medium of the present invention, the recording layer may be formed of a material that contains at least one element (M2) selected from Sb and Bi, Ge, and Te. Where the element M2, Ge, and Te are represented by a composition formula Gea(M2)bTe3+a, 2≦a≦50, and 2≦b≦4 are satisfied. Therefore, even when a thin layer having a thickness of about not more than 14 nm is used as the recording layer, an excellent recording/reproduction capability can be obtained. Further, when the element M2 contains Bi, the crystallization ability is increased, and an excellent rewriting capability can be obtained even at a high transfer rate.
In the information recording medium of the present invention, the recording layer may be formed of a material represented by a composition formula (Ge-(M3))a(M2)bTe3+a in which at least one element (M3) selected from Sn and Pb is substituted for a part of Ge in Gea(M2)bTe3+a. Therefore, Sn or Pb substituted for Ge in a tertiary composition of Ge-M2-Te improves the crystallization ability. Thus, even when an extremely thin layer having a thickness of about not more than 7 nm is used as the recording layer, a sufficient rewriting capability can be obtained.
In the information recording medium of the present invention, the recording layer may be formed of a material in which the element M2 is Sb and Bi is substituted for at least a part of Sb, i.e., a material represented by a composition formula Gea(Sb—Bi)bTe3+a. In such a case, preferably, a content ratio of Sn atoms is more than O atom % and less than 20 atom %, and a content ratio of Bi atoms is more than 0 atom % and less than 10 atom %.
In the information recording medium of the present invention, the recording layer may be formed of a material that contains at least one element (M2) selected from Sb and Bi, at least one element (M4) selected from Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Ta, W, Os, Ir, Pt, and Au, Ge, and Te. Where the elements M2 and M4, Ge, and Te are represented by a composition formula (Gea(M2)bTe3+a)100-c(M4)c, 2≦a≦50, 2≦b≦4, and 0≦c≦20 are satisfied. Therefore, the element M4 added to the tertiary composition of Ge—M2-Te increases a melting point and a crystallization temperature of the recording layer, and thus the thermal stability of the recording layer can be improved.
In the information recording medium of the present invention, the recording film may be formed of a material that contains Sb, Te, and at least one element (M5) selected from Ag, In, Ge, Sn, Se, Bi, Au, and Mn. Where Sb, Te, and the element M5 are represented by a composition formula (SbdTe100-d)100-e(M5)e , 50≦d≦95, and 0<e≦20 are satisfied. Therefore, the recording layer has a low melting point, and thus even with energy that is relatively low, an excellent recording property can be obtained.
In the information recording medium of the present invention, preferably, the crystalline nucleation layer has a thickness not less than 0.2 nm and not more than 3 nm. In particular, in the case of an information recording medium on which recording/reproduction is performed using a so-called blue-violet laser, more preferably, the crystalline nucleation layer has a thickness not less than 0.3 nm. This is because it is possible to obtain an information recording medium that has an excellent erasing capability and capability of rewriting information that has been stored for a long term even at a high transfer rate.
In the information recording medium of the present invention, preferably, the recording layer has a thickness not less than 3 nm and not more than 14 nm. In particular, in the case of an information recording medium on which recording/reproduction is performed using a so-called red laser, more preferably, the recording layer has a thickness of 6 nm to 12 nm. Therefore, an information recording medium that has an excellent erasing capability and a large signal amplitude can be obtained.
In the case where the information recording medium of the present invention has a multi-layer structure in which a first to an N-th information layers (N represents a natural number not smaller than 2) are laminated, at least one of the first to N-th information layers may have the configuration of the present information layer. Therefore, in addition to an excellent information erasing rate (a phase change to a crystalline phase) and excellent archival overwrite characteristics at a high transfer rate, as well as excellent archival characteristics at a low transfer rate and an excellent repeated rewriting capability, large capacity also can be achieved.
In the information recording medium of the present invention, the recording layer is changed in phase reversibly between a crystalline phase and an amorphous phase by irradiation of a laser beam, and the information layer further may include a dielectric layer provided on both sides of a laminated body formed of the recording layer and the crystalline nucleation layer, and a reflective layer arranged on a side opposite to an incident side of the laser beam with respect to the laminated body. Further, the information layer further may include a light absorption correction layer arranged between the laminated body and the reflective layer.
In the information recording medium of the present invention, the recording layer is changed in phase reversibly between a crystalline phase and an amorphous phase by irradiation of a laser beam, and the information layer may include at least a first dielectric layer, a second dielectric layer, the crystalline nucleation layer, the recording layer, a third dielectric layer, and a reflective layer in this order from an incident side of the laser beam. Further, the information layer may include at least a first dielectric layer, a second dielectric layer, the recording layer, the crystalline nucleation layer, a third dielectric layer, and a reflective layer in this order from an incident side of the laser beam. Further, the information layer may include at least a first dielectric layer, a second dielectric layer, the crystalline nucleation layer, the recording layer, the crystalline nucleation layer, a third dielectric layer, and a reflective layer in this order from an incident side of the laser beam. Further, the information layer further may include a fourth dielectric layer provided between the third dielectric layer and the reflective layer. At this time, the fourth dielectric layer may contain (Zns)80(SiO2)20. Further, the information layer further may include an interface layer that is provided between the third dielectric layer and the reflective layer and has a thermal conductivity lower than that of the reflective layer.
In the case where the information recording medium of the present invention has a multi-layer structure in which a first to an N-th information layers (N represents a natural number not smaller than 2) on which information is recorded by irradiation of a laser beam are laminated in this order from an incident side of the laser beam, preferably, at least the first information layer is the present information layer, the recording layer included in the first information layer is changed in phase reversibly between a crystalline phase and an amorphous phase by irradiation of the laser beam, and the first information layer includes at least a first dielectric layer, a second dielectric layer, the crystalline nucleation layer, the recording layer, a third dielectric layer, a reflective layer, and a transmittance adjusting layer in this order from the incident side of the laser beam. Therefore, the transmittance of the first information layer can be increased, and thus an excellent recording property also can be obtained in the second to N-th information layers.
In the case where the information recording medium of the present invention has a multi-layer structure in which a first to an N-th information layers (N represents a natural number not smaller than 2) on which information is recorded by irradiation of a laser beam are laminated in this order from an incident side of the laser beam, the information recording medium may be configured such that at least the first information layer is the present information layer, the recording layer included in the first information layer is changed in phase reversibly between a crystalline phase and an amorphous phase by irradiation of the laser beam, and the first information layer includes at least a first dielectric layer, a second dielectric layer, the recording layer, the crystalline nucleation layer, a third dielectric layer, a reflective layer, and a transmittance adjusting layer in this order from the incident side of the laser beam. Therefore, the transmittance of the first information layer can be increased, and thus an excellent recording property also can be obtained in the second to N-th information layers. Further, an information recording medium having an excellent erasing capability and rewriting capability can be realized.
In the case where the information recording medium of the present invention has a multi-layer structure in which a first to an N-th information layers (N represents a natural number not smaller than 2) on which information is recorded by irradiation of a laser beam are laminated in this order from an incident side of the laser beam, the information recording medium may be configured such that at least the first information layer is the present information layer, the recording layer included in the first information layer is changed in phase reversibly between a crystalline phase and an amorphous phase by irradiation of the laser beam, and the first information layer includes at least a first dielectric layer, a second dielectric layer, the crystalline nucleation layer, the recording layer, the crystalline nucleation layer, a third dielectric layer, a reflective layer, and a transmittance adjusting layer in this order from the incident side of the laser beam. Therefore, the transmittance of the first information layer can be increased, and thus an excellent recording property also can be obtained in the second to N-th information layers. Further, an information recording medium having an excellent erasing capability and rewriting capability can be realized.
In the case where the information recording medium of the present invention includes a transmittance adjusting layer in the information layer, preferably, the transmittance adjusting layer contains at least one selected from TiO2, ZrO2, ZnO, Nb2O5, Ta2O5, SiO2, Al2O3, Bi2O3, Cr2O3, Sr—O, Ti—N, Zr—N, Nb—N, Ta—N, Si—N, Ge—N, Cr—N, Al—N, Ge—Si—N, Ge—Cr—N, and ZnS. Therefore, the transmittance of the information layer can be increased.
In the case where the information recording medium of the present invention includes a third dielectric layer in the information layer, the third dielectric layer may be formed of an oxide-fluoride-based material containing at least one selected from HfO2 and ZrO2, SiO2, Cr2O3, and a fluoride. As the fluoride, at least one selected from CeF3, ErF3, GdF3, LaF3, TbF3, DyF3, NdF3, YF3, and YbF3 can be used.
Where the oxide-fluoride-based material is represented by a composition formula (HfO2)A1(SiO2)B1 (Cr2O3)C1(fluoride)100 -A1-B1-C1 or (ZrO2)A1(SiO2)B1 (Cr2O3)C1(fluoride)100 -A1-B1-C1, A1, B1, C1, and A1+B1+C1 preferably satisfy: 10≦A1≦50; 10≦B1≦50; 10≦C1≦50; and 50≦A1+B1+C1≦90, respectively.
In the case where the information recording medium of the present invention includes a second dielectric layer and a third dielectric layer in the information layer, at least one of the second dielectric layer and the third dielectric layer may be formed of an oxide-based material containing at least one selected from HfO2 and ZrO2, SiO2, and Cr2O3.
Where the oxide-based material is represented by a composition formula (HfO2)A2(SiO2)B2 (Cr2O3)100-A2-B2 or (ZrO2)A2(SiO2)B2 (Cr2O3)100-A2-B2, A2, B2, and A2+B2 preferably satisfy: 10≦A2≦50; 10≦B2≦50; and 20≦A2+B2≦80, respectively.
Next, the description is directed to a method for manufacturing the information recording medium of the present invention.
According to a method for manufacturing an information recording medium of the present invention, a crystalline nucleation layer that contains at least one element selected from Bi and Te and at least one element (M1) selected from Sc, Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Yb, and Lu can be formed in contact with a recording layer. Therefore, it is possible to provide an information recording medium that has an excellent information erasing rate (a phase change to a crystalline phase) and excellent archival overwrite characteristics at a high transfer rate, as well as excellent archival characteristics at a low transfer rate, and further an excellent repeated rewriting capability.
In the method for manufacturing an information recording medium of the present invention, a sputtering target used in a step of forming a crystalline nucleation layer may contain at least one selected from Bi(M1) and Te(M1).
In the method for manufacturing an information recording medium of the present invention, the sputtering target used in the step of forming the crystalline nucleation layer may contain at least one selected from BiTe(M1)2, Bi2Te(M1), and BiTe2(M1).
In the method for manufacturing an information recording medium of the present invention, in the step of forming the crystalline nucleation layer, at least one selected from Ar gas, Kr gas, a mixture of Ar gas and a reactive gas, and a mixture of Kr gas and a reactive gas may be used in performing sputtering, the reactive gas being at least one selected from N2 gas and O2 gas.
Hereinafter, embodiments of the present invention will be described with reference to the drawings. Each of the following embodiments is to be regarded as an example, and the present invention is not limited thereto. Further, in the following embodiments, the same components are denoted with the same reference numerals, and repeated descriptions thereof may be omitted.
Embodiment 1
The description is directed to one embodiment of an information recording medium of the present invention. An information recording medium of this embodiment is a medium suitable for use in information recording/reproduction using a so-called blue-violet laser having a wavelength of 390 to 420 nm. FIG. 1 is a partial cross-sectional view of an information recording medium 1 of this embodiment. The information recording medium 1 is an optical information recording medium that allows information recording/reproduction by irradiation of a laser beam 10.
In the information recording medium 1, one information layer 12 is provided on a substrate 11, and a transparent layer 13 further is provided on the information layer 12. The information layer 12 includes a first dielectric layer 101, a second dielectric layer 102, a crystalline nucleation layer 103, a recording layer 104, a third dielectric layer 105, a fourth dielectric layer 106, an interface layer 107, and a reflective layer 108 that are laminated in order from an incident side of the laser beam 10.
Preferably, a material of the transparent layer 13 is a resin such as a photocurable resin (particularly, an ultraviolet curable resin) and a delayed-action-type thermosetting resin, a dielectric material, or the like, and has a low light absorptance with respect to the laser beam 10 to be used. Further, preferably, the material optically has a low birefringence at a wavelength in a short wavelength region. Further, a transparent disk-shaped layer made of a resin such as polycarbonate, amorphous polyolefin, and PMMA (polymethyl methacrylate), glass, or the like, for example, may be used as the transparent layer 13. In such a case, the transparent layer 13 is allowed to be laminated to the first dielectric layer 101 with, for example, a resin such as a photocurable resin (particularly, an ultraviolet curable resin) and a delayed-action-type thermosetting resin.
When focusing the laser beam 10, a beam spot thus obtained has a diameter determined by a wavelength λ of the laser beam 10 (a shorter wavelength λ allows the beam spot to be reduced in diameter more). Thus, preferably, in high-density recording, the laser beam 10 particularly has a wavelength λ of not more than 450 nm. However, when the wavelength λ has a value less than 350 nm, light absorption by the transparent layer 13 or the like is increased. On this account, more preferably, the laser beam 10 has a wavelength λ in a range of 350 nm to 450 nm.
The substrate 11 is, for example, a transparent disk-shaped substrate, and can be made of, for example, a resin such as polycarbonate, amorphous polyolefin, and PMMA, glass, or the like.
When necessary, guide grooves for guiding the laser beam 10 may be formed on a surface of the substrate 11 on a side of the information layer 12 (side of the reflective layer 108). Preferably, a surface of the substrate 11 on a side opposite to the side of the reflective layer 108 is made smooth. As a material of the substrate 11, polycarbonate is particularly useful since it exhibits an excellent transfer property and suitability for mass production, and achieves a cost reduction. Preferably, the substrate 11 has a thickness in a range of 500 μm to 1200 μm so as to have sufficient strength and allow the information recording medium 1 to have a thickness of about 1200 μm. When the transparent layer 13 has a thickness of about 600 μm (where NA=0.6, this thickness allows excellent recording/reproduction to be performed), preferably, the substrate 11 has a thickness in a range of 550 μm to 650 μm. Further, when the transparent layer 13 has a thickness of about 100 μm (where NA=0.85, this thickness allows excellent recording/reproduction to be performed), preferably, the substrate 11 has a thickness in a range of 1050 μm to 1150 μm.
The first dielectric layer 101 is formed of a dielectric. The first dielectric layer 101 has a function of preventing oxidation, corrosion, deformation, and the like of the recording layer 104, a function of increasing the light absorption efficiency of the recording layer 104 by adjusting an optical distance, and a function of increasing the signal amplitude by increasing a change in an amount of reflected light between before and after recording. The first dielectric layer 101 can be made of, for example, an oxide such as TiO2, ZrO2, ZnO, Nb2O5, Ta2O5, SiO2, Al2O3, Bi2O3, and Cr2O3. Further, a nitride such as C—N, Ti—N, Zr—N, Nb—N, Ta—N, Si—N, Ge—N, Cr—N, Al—N, Ge—Si—N, and Ge—Cr—N also can be used. Further, a sulfide such as ZnS, a carbide such as SiC, and a fluoride such as LaF3 also can be used. Further, a mixture of the above-mentioned materials also can be used. For example, a mixture of ZnS and SiO2, i.e., ZnS—SiO2 is a particularly excellent material to be used for the first dielectric layer 101, since ZnS—SiO2 is an amorphous material that has a high refractive index and a high film-forming speed, and is excellent in mechanical properties and moisture resistance.
By calculation based on a matrix method (see, for example, “Wave Optics” by Hiroshi Kubota, published by Iwanami Shoten, 1971, Chapter 3), the film thickness of the first dielectric layer 101 can be determined exactly so as to satisfy the condition that a change in an amount of reflected light between when the recording layer 104 is in a crystalline phase and when the recording layer 104 is in an amorphous phase can be increased and light absorption in the recording layer 104 can be increased.
The second dielectric layer 102 has a function of preventing mass transfer from being caused between the first dielectric layer 101 and the crystalline nucleation layer 103 and between the first dielectric layer 101 and the recording layer 104 by repeated recording. As described later, the crystalline nucleation layer 103 is formed so as to be extremely thin, having a thickness of 0.3 nm to 3 nm, and thus is likely to have an island shape. In view of this, the second dielectric layer 102 may be partially in contact with the recording layer 104. Therefore, preferably, the second dielectric layer 102 is formed of a material that has a low light absorptance as well as such a high melting point as not to allow the second dielectric layer 102 to melt in recording and exhibits excellent adhesion to the crystalline nucleation layer 103 and the recording layer 104. In order to prevent a part of the second dielectric layer 102 from melting so as to be mixed into the crystalline nucleation layer 103 and the recording layer 104 upon irradiation of a high-power laser beam 10, the material of the second dielectric layer 102 is required to have this property of having such a high melting point as not to allow the second dielectric layer 102 to melt in recording. This is because when the material of the second dielectric layer 102 is mixed, the compositions of the crystalline nucleation layer 103 and the recording layer 104 are changed, thereby substantially deteriorating the rewriting capability. Further, in order to secure reliability, the material of the second dielectric layer 102 is required to have this property of exhibiting excellent adhesion to the crystalline nucleation layer 103 and the recording layer 104.
The second dielectric layer 102 can be made of a material in the same system as that of the material of the first dielectric layer 101. Preferably, above all, a material containing Cr, Zr, and O is used, and further, a mixture of Cr2O3 and ZrO2 is used, in which Cr2O3 is formed from Cr and O and ZrO2 is formed from Zr and O. Cr2O3 is a material exhibiting excellent adhesion to the recording layer 104. Further, ZrO2 is a transparent material having a melting point as high as 2700° C. and a thermal conductivity that is low compared with other oxides, thereby contributing to an improvement in repeated rewriting capability. The second dielectric layer 102 is formed of a material as the mixture of these two types of oxides, thereby realizing an optical information recording medium 15 having an excellent repeated rewriting capability as well as high reliability, in which the second dielectric layer 102 is partially in contact with the recording layer 104. Preferably, in order to secure adhesion to the recording layer 104, in Cr2O3—ZrO2, Cr2O3 is contained in an amount of not less than 10 mol %. Further, preferably, in order to maintain a low level of light absorption in the second dielectric layer 102, Cr2O3 is contained in an amount of not more than 60 mol % (when Cr2O3 is contained in an increased amount, light absorption tends to increase). Thus, more preferably, in Cr2O3—ZrO2, Cr2O3 is contained in an amount of not less than 20 mol % and not more than 50 mol %.
The second dielectric layer 102 also may be made of a material further containing Si in addition to Cr, Zr, and O. Preferably, above all, a mixture of SiO2, Cr2O3, and ZrO2 is used, in which Cr2O3 is formed from Cr and O, ZrO2 is formed from Zr and O, and SiO2 is formed from Si and O. This is because when SiO2 is contained, the effect of accelerating crystallization of the recording layer 104 is enhanced, thereby allowing an optical information recording medium 1 having an excellent rewriting capability to be realized. Preferably, in SiO2—Cr2O3—ZrO2, SiO2 is contained in an amount of not less than 5 mol %, and preferably, in order to secure adhesion to the recording layer 104, SiO2 is contained in an amount of not more than 40 mol %. More preferably, in SiO2—Cr2O3—ZrO2, SiO2 is contained in an amount of not less than 10 mol % and not more than 35 mol %. Further, preferably, in order to secure an excellent recording/rewriting capability, SiO2 and Cr2O3 are contained in a total amount of not more than 95 mol %.
In order to prevent a change in an amount of reflected light between before and after recording on the information recording medium 1 from being decreased by light absorption in the second dielectric layer 102, the second dielectric layer 102 has a thickness, desirably, in a range of 1 nm to 10 nm, and more preferably, in a range of 2 nm to 7 nm.
The third dielectric layer 105 has a function of increasing the light absorption efficiency of the recording layer 104 by adjusting an optical distance and a function of increasing the signal amplitude by increasing a change in an amount of reflected light between before and after recording. The third dielectric layer 105 can be made of a material in the same system as that of the material of the first dielectric layer 101. Preferably, as in the case of the second dielectric layer 102, a material containing Cr, Zr, and O is used. Preferably, above all, a mixture of Cr2O3 and ZrO2 is used, in which Cr2O3 is formed from Cr and O and ZrO2 is formed from Zr and O. The third dielectric layer 105 tends to show poorer adhesion to the recording layer 104 than the second dielectric layer 102. Therefore, preferably, in Cr2O3—ZrO2, Cr2O3 is contained in an amount of not less than 20 mol % and not more than 80 mol %, which is larger than an amount of Cr2O3 contained in the second dielectric layer 102, and more preferably, in an amount of not less than 30 mol % and not more than 70 mol %.
As the second dielectric layer 102, the third dielectric layer 105 may be made of a material further containing Si in addition to Cr, Zr, and O. Preferably, above all, a mixture of SiO2, Cr2O3, and ZrO2 is used, in which Cr2O3 is formed from Cr and O, ZrO2 is formed from Zr and O, and SiO2 is formed from Si and O. In order to secure adhesion to the recording layer 104, in SiO2—Cr2O3—ZrO2, SiO2 is contained, preferably, in an amount of not more than 35 mol %, which is smaller than an amount of SiO2 contained in the second dielectric layer 102, and more preferably, in an amount of not less than 5 mol % and not more than 30 mol %. Further, preferably, in order to secure an excellent recording/rewriting capability, SiO2 and Cr2O3 are contained in a total amount of not more than 95 mol %.
The third dielectric layer 105 has a thickness, preferably, in a range of 2 nm to 75 nm, and more preferably, in a range of 2 nm to 40 nm. The third dielectric layer 105 is formed so as to have a thickness in this range, and thus heat generated in the recording layer 104 can be diffused effectively to the side of the reflective layer 108.
The fourth dielectric layer 106 is arranged on a surface of the third dielectric layer 105 on a side opposite to the incident side of the laser beam. In this case, the fourth dielectric layer 106 can be made of a material in the same system as that of the material of the first dielectric layer 101. The mixture of ZnS and SiO2, i.e., ZnS—SiO2 also can be used as an excellent material for the fourth dielectric layer 106. In this embodiment, the fourth dielectric layer 106 is provided. However, a configuration without the fourth dielectric layer 106 also is possible.
The fourth dielectric layer 106 has a thickness, preferably, in a range of 2 nm to 75 nm, and more preferably, in a range of 2 nm to 40 nm. The fourth dielectric layer 106 is formed so as to have a thickness in this range, and thus heat generated in the recording layer 104 can be diffused effectively to the side of the reflective layer 108.
The crystalline nucleation layer 103 of the present invention is a layer for generating crystalline nuclei, thereby allowing the crystallization ability of the recording layer 104 to be increased. The crystalline nucleation layer 103 can be formed of a material containing at least one element selected from Bi and Te, and M1 (M1 is at least one element selected from Sc, Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Yb, and Lu). Herein, preferably, the crystalline nucleation layer 103 contains at least one of Bi(M1) in which Bi and M1 are mixed at a ratio of approximately 50:50 and Te(M1) in which Te and M1 are mixed at a ratio of approximately 50:50. This is because Bi(M1) has a melting point at least as high as 1500° C., and Te(M1) has a melting point at least as high as 1300° C. Particularly, a binary phase diagram shows that BiGd, BiTh, BiDy, and BiY have a melting point at least as high as 2000° C. Therefore, the use of such a material realizes an information recording medium 1 having an excellent capability of rewriting information that has been stored for a long term, in which the crystalline nucleation layer 103 has a high melting point and excellent thermal stability. Further, Bi(M1) and Te(M1) have a rock-salt-type crystal structure. Therefore, in the case where the recording layer 104 is made of, for example, a GeTe—Sb2Te3 compound group or the like having a rock-salt-type structure, the crystalline nucleation layer 103 has the same crystal structure as that of the recording layer 104. Thus, crystalline nuclei are generated easily at an interface between the crystalline nucleation layer 103 and the recording layer 104, thereby allowing crystal growth in the recording layer 104 to be accelerated. As a result, an information recording medium 1 having excellent archival overwrite characteristics can be obtained.
Further, the crystalline nucleation layer 103 may contain at least one selected from BiTe(M1)2, Bi2Te(M1), and BiTe2(M1). The use of such a material realizes an information recording medium 1 having excellent archival overwrite characteristics, in which the crystalline nucleation layer 103 has a high melting point and excellent thermal stability and crystalline nuclei are generated easily at the interface between the crystalline nucleation layer 103 and the recording layer 104, thereby allowing crystal growth in the recording layer 104 to be accelerated.
The crystalline nucleation layer 103 has a thickness, preferably, in a range of 0.3 nm to 3 nm, and more preferably, in a range of 0.5 nm to 2 nm, so as to have an excellent erasing capability (crystallization ability) and capability of rewriting information that has been stored for a long term even at a high transfer rate. Further, even when the crystalline nucleation layer 103 has an island shape or a thin-film shape, the above-mentioned effects of the crystalline nucleation layer 103 can be obtained.
The recording layer 104 is formed of a material that allows a reversible phase change between a crystalline phase and an amorphous phase to be caused by irradiation of the laser beam 10. The recording layer 104 can be formed of a material containing, for example, three elements of Ge, M2, and Te (M2 is at least one element selected from Sb and Bi). Specifically, the recording layer 104 can be formed of a material represented by a formula Gea(M2)bTe3+a. Herein, desirably, a relationship 2≦a≦50 is satisfied, and more preferably, a relationship 4≦a≦23 is satisfied, in which the stability in an amorphous phase and a large signal amplitude are achieved and an increase in melting point and a decrease in crystallization speed are suppressed. Further, preferably, a relationship 2≦b≦4 is satisfied, and more preferably, a relationship 2≦b≦3 is satisfied, in which the stability in an amorphous phase and a large signal amplitude are achieved and a decrease in crystallization speed is suppressed.
Further, the recording layer 104 may be formed of a material represented by a composition formula (Ge-(M3))a(M2)bTe3+a (M3 is at least one element selected from Sn and Pd). When such a material is used, the element M3 substituted for Ge increases the crystallization ability, and thus a sufficient erasing rate can be attained even when the recording layer 104 has a thin film thickness. As the element M3, Sn is used more preferably since Sn possesses no toxicity. When using this material, preferably, 2≦a≦50 (more preferably, 4≦a≦23) and 2≦b≦4 (more preferably, 2≦b≦3) also are satisfied.
Furthermore, the recording layer 104 also may be formed of a material represented by a composition formula (Gea(M2)bTe3+a)100-c(M4)c (M4 is at least one element selected from Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Ta, W, Os, Ir, Pt, and Au). In such a case, the added element M4 increases the melting point and crystallization temperature of the recording layer 104, and thus the thermal stability of the recording layer 104 is enhanced. In such a material, preferably, 0<c≦20 is satisfied, and more preferably, 2≦c≦10 is satisfied. Furthermore, preferably, 2≦a≦50 (more preferably, 4≦a≦23) and 2≦b≦4 (more preferably, 2≦b≦3) are satisfied.
Furthermore, the recording layer 104 also may be formed of a material represented by a composition formula (SbdTe100-d)100-e(M5)e (M5 is at least one element selected from Ag, In, Ge, Sn, Se, Bi, Au, and Mn). When d and e satisfy 50≦d≦95 and 0≦e≦20, respectively, it is possible to increase a difference in reflectance of the information recording medium 1 between when the recording layer 104 is in a crystalline phase and when the recording layer 104 is in an amorphous phase, and thus an excellent recording/reproduction property can be obtained. When 65≦d is satisfied, the crystallization speed can be increased particularly, thereby allowing the erasing rate to be improved particularly. Furthermore, when d≦85 is satisfied, it becomes easy to cause a phase change to an amorphous phase. Thus, more preferably, 65≦d≦85 is satisfied. Furthermore, in order to obtain an excellent recording/reproduction capability, preferably, the element M5 used for adjusting the crystallization speed is added. More preferably, e satisfies 1≦e≦10. When e≦10 is satisfied, the emergence of a plurality of phases can be suppressed, and thus a deterioration in properties due to repeated recording can be suppressed.
Preferably, in order to increase the recording sensitivity of the information recording medium 1, the recording layer 104 has a thickness in a range of 6 nm to 14 nm. Even when this range is satisfied, in the case where a thick layer is used as the recording layer 104, heat diffusion in an in-plane direction causes neighboring regions to be affected thermally to a greater degree. Further, in the case where a thin layer is used as the recording layer 104, the reflectance of the information recording medium 1 is decreased. On this account, more preferably, the recording layer 104 has a thickness in a range of 8 nm to 12 nm.
The reflective layer 108 has an optical function of increasing an amount of light to be absorbed by the recording layer 104. Further, the reflective layer 108 also has a thermal function of allowing heat generated in the recording layer 104 to be diffused smoothly, thereby allowing the recording layer 104 to be changed in phase to an amorphous phase easily. Furthermore, the reflective layer 108 also has a function of protecting a multi-layer film from an environment of use.
As a material of the reflective layer 108, a single metal having a high thermal conductivity such as Ag, Au, Cu, and Al can be used. Further, an alloy such as Al—Cr, Al—Ti, Au—Pd, Au—Cr, Ag—Pd, Ag—Pd—Cu, Ag—Pd—Ti, Ag—Ru—Au, Ag—Cu—Ni, Ag—Zn—Al, and Cu—Si also can be used. Particularly, an Ag alloy has a high thermal conductivity, and thus is used preferably as a material of the reflective layer 108. Preferably, the reflective layer 108 has a thickness of not less than 30 nm, which is a thickness that allows a sufficient heat diffusing function to be obtained. Even when this range is satisfied, in the case where the reflective layer 108 has a thickness larger than 200 nm, the heat diffusing function is enhanced excessively, thereby decreasing the recording sensitivity of the information recording medium 1. On this account, more preferably, the reflective layer 108 has a thickness in a range of 30 nm to 200 nm.
The interface layer 107 is provided at an interface of the reflective layer 108 on the incident side of the laser beam. In this case, the interface layer 107 can be made of a material having a thermal conductivity lower than that of the material described with regard to the reflective layer 108. Preferably, when an Ag alloy is used for the reflective layer 108, Al or an Al alloy is used for the interface layer 107. Also, the interface layer 107 can be made of a material containing an element such as Cr, Ni, Si, and C, or an oxide such as TiO2, ZrO2, ZnO, Nb2O5, Ta2O5, SiO2, Al2O3, Bi2O3, and Cr2O3. Further, a nitride such as C—N, Ti—N, Zr—N, Nb—N, Ta—N, Si—N, Ge—N, Cr—N, Al—N, Ge—Si—N, and Ge—Cr—N also can be used. Further, a sulfide such as ZnS, a carbide such as SiC, or a fluoride such as LaF3 also can be used. Further, a mixture of the above-mentioned materials also can be used. Preferably, the interface layer 107 has a film thickness in a range of 3 nm to 100 nm (more preferably, in a range of 10 nm to 50 nm).
The crystalline nucleation layer may be arranged between the recording layer 104 and the third dielectric layer 105. In such a case, as an information recording medium 14 as shown in FIG. 2, the information layer 12 and the transparent layer 13 are provided on the substrate 11. The information layer 12 is formed of the first dielectric layer 101, the second dielectric layer 102, the recording layer 104, a crystalline nucleation layer 109, the third dielectric layer 105, the fourth dielectric layer 106, the interface layer 107, and the reflective layer 10 that are laminated in order from the incident side of the laser beam. Further, the crystalline nucleation layers may be arranged between the recording layer 104 and the second dielectric layer 102 and between the recording layer 104 and the third dielectric layer 105, respectively. In such a case, as an information recording medium 15 as shown in FIG. 3, the information layer 12 and the transparent layer 13 are provided on the substrate 11. The information layer 12 is formed of the first dielectric layer 101, the second dielectric layer 102, the crystalline nucleation layer 103, the recording layer 104, the crystalline nucleation layer 109, the third dielectric layer 105, the fourth dielectric layer 106, the interface layer 107, and the reflective layer 108 that are laminated in order from the incident side of the laser beam. The crystalline nucleation layer 109 can be made of a material in the same system as that of the material of the crystalline nucleation layer 103, and also has the same configuration and function as those of the crystalline nucleation layer 103.
Next, the description is directed to a method for manufacturing each of the information recording media 1, 14, and 15 as shown in FIGS. 1, 2, and 3, respectively.
Initially, the substrate 11 (having a thickness of, for example, 1100 μm) is prepared and placed in a film forming device.
Then, the reflective layer 108 is formed on the substrate 11. When guide grooves for guiding the laser beam 10 are formed on the substrate 11, the reflective layer 108 is formed on a surface on which these guide grooves are formed. The reflective layer 108 can be formed by performing sputtering with respect to a sputtering target formed of a metal or an alloy constituting the reflective layer 108 in Ar gas atmosphere or an atmosphere of a mixture of Ar gas and a reactive gas (at least one gas selected from oxygen gas and nitrogen gas).
Then, the interface layer 107 is formed on the reflective layer 108 as required. The interface layer 107 can be formed by performing sputtering with respect to a sputtering target formed of elements constituting the interface layer 107 in Ar gas atmosphere or an atmosphere of a mixture of Ar gas and a reactive gas.
Then, the fourth dielectric layer 106 is formed on the interface layer 107 (in a configuration without the interface layer 107, on the reflective layer 108) as required. The fourth dielectric layer 106 can be formed by performing sputtering with respect to a sputtering target formed of a compound constituting the fourth dielectric layer 106 in Ar gas atmosphere or an atmosphere of a mixture of Ar gas and a reactive gas. Further, the fourth dielectric layer 106 also can be formed by performing reactive sputtering with respect to a sputtering target formed of a metal containing elements constituting the fourth dielectric layer 106 in an atmosphere of a mixture of Ar gas and a reactive gas.
Then, the third dielectric layer 105 is formed on the fourth dielectric layer 106 (in a configuration without the fourth dielectric layer 106, on the interface layer 107 or the reflective layer 108). The third dielectric layer 105 can be formed in the same manner as the fourth dielectric layer 106.
Then, the crystalline nucleation layer 109 is formed on the third dielectric layer 105 as required (in the case of manufacturing the information recording medium 14 or 15 as shown in FIG. 2 or 3, respectively). The crystalline nucleation layer 109 can be formed by performing sputtering, using one power source, with respect to a sputtering target containing at least one element selected from Bi and Te, and M1, a sputtering target containing at least one selected from Bi(M1) and Te(M1), or a sputtering target containing at least one selected from BiTe(M1)2, Bi2Te(M1), and BiTe2(M1) according to the composition of the crystalline nucleation layer 109.
As a gas used in an atmosphere for sputtering in forming the crystalline nucleation layer 109, Ar gas, Kr gas, a mixture of Ar gas and a reactive gas, or a mixture of Kr gas and a reactive gas, for example, can be used. Further, the crystalline nucleation layer 109 also can be formed by simultaneously performing sputtering, using a plurality of power sources, with respect to respective sputtering targets of Bi, Te, and M1. Further, the crystalline nucleation layer 109 also can be formed by simultaneously performing sputtering, using a plurality of power sources, with respect to a binary sputtering target, a ternary sputtering target, or the like in which any of Bi , Te, and M1 are combined. In each of these cases where such sputtering targets are used, the crystalline nucleation layer 109 also can be formed by performing sputtering in an atmosphere of Ar gas, Kr gas, a mixture of Ar gas and a reactive gas, or a mixture of Kr gas and a reactive gas.
Then, the recording layer 104 is formed on the crystalline nucleation layer 109 (in a configuration without the crystalline nucleation layer 109, on the third dielectric layer 105). The recording layer 104 can be formed by performing sputtering, using one power source, with respect to a sputtering target formed of a Ge-M2-Te alloy, a sputtering target formed of a Ge-M2-Te-M3 alloy, a sputtering target formed of a Ge-M2-Te-M4 alloy, or a sputtering target formed of an Sb—Te-M5 alloy according to the composition of the recording layer 104.
As a gas used in an atmosphere for sputtering in forming the recording layer 104, Ar gas, Kr gas, a mixture of Ar gas and a reactive gas, or a mixture of Kr gas and a reactive gas can be used. Further, the recording layer 104 also can be formed by simultaneously performing sputtering, using a plurality of power sources, with respect to sputtering targets containing a required element selected from Ge, M2, Te, M3, M4, and M5. Further, the recording layer 104 also can be formed by simultaneously performing sputtering, using a plurality of power sources, with respect to binary sputtering targets, ternary sputtering targets, or the like in which required elements selected from Ge, M2, Te, M3, M4, and M5 are combined. In each of these cases where such sputtering targets are used, the recording layer 104 also can be formed by performeing sputtering in an atmosphere of Ar gas, Kr gas, a mixture of Ar gas and a reactive gas, or a mixture of Kr gas and a reactive gas.
Then, the crystalline nucleation layer 103 is formed on the recording layer 104 as required (in the case of manufacturing the information recording medium 1 or 15 as shown in FIG. 1 or 3, respectively).
Then, the second dielectric layer 102 is formed on the crystalline nucleation layer 103 (in a configuration without the crystalline nucleation layer 103, on the recording layer 104). The second dielectric layer 102 can be formed by performing sputtering with respect to a sputtering target formed of a compound constituting the second dielectric layer 102 in Ar gas atmosphere or an atmosphere of a mixture of Ar gas and a reactive gas. Further, the second dielectric layer 102 also can be formed by performing reactive sputtering with respect to a sputtering target formed of a metal constituting the second dielectric layer 103 in an atmosphere of a mixture of Ar gas and a reactive gas.
Then, the first dielectric layer 101 is formed on the second dielectric layer 102. The first dielectric layer 101 can be formed by performing sputtering with respect to a sputtering target formed of a compound constituting the first dielectric layer 101 in Ar gas atmosphere or an atmosphere of a mixture of Ar gas and a reactive gas. Further, the first dielectric layer 101 also can be formed by performing reactive sputtering with respect to a sputtering target containing elements constituting the first dielectric layer 101 in an atmosphere of a mixture of Ar gas and a reactive gas.
Finally, the transparent layer 13 is formed on the first dielectric layer 101. The transparent layer 13 can be formed in the following manner. That is, a photocurable resin (particularly, an ultraviolet curable resin) or a delayed action type thermosetting resin is applied on the first dielectric layer 101, and then an entire laminate thus obtained is rotated so that the resin is spread uniformly (spin-coated), after which the resin is allowed to cure. Further, for the transparent layer 13, a transparent disk-shaped substrate made of a resin such as polycarbonate, amorphous polyolefin, and PMMA, or glass also may be used. In the case of using such a substrate, the transparent layer 13 can be formed by performing spin coating in which a resin such as a photocurable resin (particularly, an ultraviolet curable resin) and a delayed action type thermosetting resin is applied on the first dielectric layer 101 and then the substrate is bonded onto the first dielectric layer 101, after which the resin is allowed to cure. Further, it also is possible to bond a substrate, on which an adhesive resin is applied uniformly in advance, to the first dielectric layer 101.
After forming the first dielectric layer 101, or after forming the transparent layer 13, an initializing process in which an entire surface of the recording layer 104 is crystallized may be performed as required. The recording layer 104 can be crystallized by irradiation of laser beams.
Each of the information recording media 1, 14, and 15 according to this embodiment can be manufactured in the above-mentioned manner.
In this embodiment, a sputtering method was used as a method for forming each film. However, there is no limitation on the method to be used, and it also is possible to use a vacuum deposition method, an ion plating method, a CVD (Chemical Vapor Deposition) method, MBE (Molecular Beam Epitaxy), or the like.
Embodiment 2
The description is directed to another embodiment of the information recording medium of the present invention. An information recording medium of this embodiment is a medium suitable for use in information recording/reproduction using a so-called blue-violet laser having a wavelength of 390 to 420 nm. FIG. 4 shows a partial cross-sectional configuration of an information recording medium 2 of this embodiment. The information recording medium 2 is an optical information recording medium with a multi-layer structure that includes a plurality of information layers and allows information recording/reproduction to be performed with respect to each of the information layers by irradiation of a laser beam 10 from one side.
In the information recording medium 2, N(N represents a natural number satisfying N≧2) layers of first to N-th information layers 221 to 22N are laminated on a substrate 21, and a transparent layer 23 further is provided on the information layers. In this specification, the first information layer and the N-th information layer when counted from an incident side of the laser beam 10 are referred to as the first information layer 221 and the N-th information layer 22N, respectively. Each adjacent pair of the information layers are laminated through an optical separation layer 24. In the information recording medium 2, each of the first to (N−1)-th information layers 221 to 22N−1 is provided with a light transmission property. This is because it is necessary to allow the laser beam 10 to reach the N-th information layer 22N.
The substrate 21 and the transparent layer 23 can be made of the same materials as those of the substrate 11 and the transparent layer 13 described with regard to Embodiment 1, respectively. Further, these substrate and layer also have the same configurations and functions as those of the substrate 11 and the transparent layer 13 described with regard to Embodiment 1, respectively.
Preferably, the optical separation layer 24 is made of a resin such as a photocurable resin (particularly, an ultraviolet curable resin) and a delayed action type thermosetting resin, or a dielectric, and has a low light absorptance with respect to the laser beam 10 to be used. Further, preferably, the optical separation layer 24 optically has a low birefringence at a wavelength in a short wavelength region.
The optical separation layer 24 provided between each pair of the information layers is used to separate respective focusing positions of the first information layer 221, the second information layer 222, and . . . to the N-th information layer 22N from one another. It is required that the optical separation layer 24 have a thickness of not less than a focal depth ΔZ determined by a numerical aperture (NA) of an objective lens and a wavelength λ of the laser beam 10. Assuming that a reference light intensity of a focal point corresponds to 80% of that obtained when there is no aberration, the focal depth ΔZ can be approximated by a formula ΔZ=λ/{2(NA)2}. Where λ=400 nm and NA=0.6, ΔZ=0.556 μm and thus ±0.6 μm defines a range of the focal depth. Thus, in this case, it is required that the optical separation layer 24 have a thickness of not less than 1.2 μm. Further, desirably, a distance between each pair of the information layers is set so as to be in a range that allows the laser beam 10 to be focused using an objective lens. Thus, preferably, the optical separation layer 24 has a thickness that falls within a range of tolerances defined by an objective lens (for example, not more than 50 μm).
In the optical separation layer 24, guide grooves for guiding the laser beam 10 may be formed as required on a surface on the incident side of the laser beam 10.
In such a case, by irradiation of the laser beam 10 from one side alone, recording/reproduction can be performed with respect to a K-th information layer 22K (K represents a natural number satisfying 1<K≦N) using the laser beam 10 that has been transmitted through the first information layer 221 to a (K−1)-th information layer 22K−1.
Hereinafter, a configuration of the first information layer 221 will be described in detail.
The first information layer 221 includes a first dielectric layer 201, a second dielectric layer 202, a crystalline nucleation layer 203, a recording layer 204, a third dielectric layer 205, a reflective layer 206, and a transmittance adjusting layer 207 that are arranged in order from the incident side of the laser beam 10.
The first dielectric layer 201 can be made of the same material as that of the first dielectric layer 101 described with regard to Embodiment 1. Further, this layer also has the same function as that of the first dielectric layer 101 in Embodiment 1.
By calculation based on the matrix method, the film thickness of the first dielectric layer 201 can be determined so as to satisfy the condition that a change in an amount of reflected light between when the recording layer 204 is in a crystalline phase and when the recording layer 204 is in an amorphous phase can be increased and light absorption in the recording layer 204 can be increased.
The second dielectric layer 202 can be made of the same material as that of the second dielectric layer 102 described with regard to Embodiment 1. Further, this layer also has the same function and configuration as those of the second dielectric layer 102 in Embodiment 1.
The third dielectric layer 205 can be made of the same material as that of the third dielectric layer 105 described with regard to Embodiment 1. Further, this layer also has the same function and configuration as those of the third dielectric layer 105 in Embodiment 1.
The crystalline nucleation layer 203 can be made of the same material as that of the crystalline nucleation layer 103 in Embodiment 1. Further, this layer also has the same function as that of the crystalline nucleation layer 103 in Embodiment 1.
The crystalline nucleation layer 203 has a thickness preferably in a range of 0.3 nm to 1.5 nm, and more preferably in a range of 0.5 nm to 1 nm, so as to have an excellent erasing capability and capability of rewriting information that has been stored for a long term even at a high transfer rate, and to obtain the highest possible transmittance of the first information layer 221.
The recording layer 204 can be made of the same material as that of the recording layer 104 described with regard to Embodiment 1. Preferably, the recording layer 204 has a thickness as thin as possible for the following reason. That is, in order to allow laser beams in an amount required in recording/reproduction to reach an information layer (an information layer arranged farther from the incident side of the laser beam 10 than the first information layer 221) with respect to which information recording/reproduction is to be performed using a laser beam that has been transmitted through the first information layer 221, it is required that the first information layer 221 have a higher transmittance. For example, when the recording layer 204 is made of any of a material represented by a composition formula Gea(M2)bTe3+a, a material represented by a composition formula ((Ge-(M3))aSbbTe3+a) in which (M3) is substituted for a part of Ge in Gea(M2)bTe3+a, and a material represented by a composition formula (Gea(M2)bTe3+a)100-c(M4)c, the recording layer 204 has a thickness preferably in a range of 4 nm to 9 nm, and more preferably in a range of 5 nm to 8 nm. Further, when the recording layer 204 is formed of a material represented by a composition formula (SbdTe100-d)100-e(M5)e , the recording layer 204 has a thickness preferably in a range of 3 nm to 8 nm, and more preferably in a range of 4 nm to 6 nm.
The reflective layer 206 can be made of the same material as that of the reflective layer 108 described with regard to Embodiment 1. Further, this layer also has the same function as that of the reflective layer 108 in Embodiment 1. In order to obtain the highest possible transmittance of the first information layer 221, the reflective layer 206 has a thickness preferably in a range of 3 nm to 15 nm, and more preferably in a range of 8 nm to 12 nm. The reflective layer 206 has a thickness in this range, and thus a sufficient heat diffusing function for the reflective layer 206 can be obtained, and a sufficient reflectance in the first information layer 221 can be secured. Further, a sufficient transmittance of the first information layer 221 also can be attained.
The transmittance adjusting layer 207 is formed of a dielectric and has a function of adjusting the transmittance of the first information layer 221. By this transmittance adjusting layer 207, both a transmittance Tc (%) in the first information layer 221 obtained when the recording layer 204 is in a crystalline phase and a transmittance Ta (%) in the first information layer 221 obtained when the recording layer 204 is in an amorphous phase can be increased. Specifically, the first information layer 221 including the transmittance adjusting layer 207 has values of the transmittances Tc and Ta increased by about 2% to 10% compared with the first information layer 221 without the transmittance adjusting layer 207. Further, the transmittance adjusting layer 207 also has a function of allowing heat generated in the recording layer 204 to be diffused effectively.
In order to obtain a further enhanced action of increasing the transmittances Tc and Ta of the first information layer 221, the transmittance adjusting layer 207 has a refractive index n and an extinction coefficient k that preferably satisfy 2.0≦n and k≦0.1, and more preferably satisfy 2.0≦n≦3.0 and k≦0.05, respectively.
The transmittance adjusting layer 207 has a film thickness d1 preferably in a range represented by ( 1/32) λ/n≦d1≦( 3/16) λ/n or ( 17/32) λ/n≦d1≦( 11/16) λ/n, and more preferably in a range represented by ( 1/16) λ/n≦d1≦( 5/32) λ/n or ( 9/16) λ/n≦d1≦( 21/32) λ/n. For example, where the wavelength λ of the laser beam 10 and the refractive index n of the transmittance adjusting layer 207 satisfy 350 nm ≦λ≦450 nm and 2.0≦n≦3.0, respectively, the film thickness d1 is preferably in a range represented by 3 nm≦d1≦40 nm or 60 nm≦d1≦130 nm, and more preferably in a range represented by 7 nm≦d1≦30 nm or 65 nm≦d1≦120 nm. The film thickness d1 has a value selected from values in this range, and thus both the transmittances Tc and Ta of the first information layer 221 can be increased.
The transmittance adjusting layer 207 can be made of, for example, an oxide such as TiO2, ZrO2, ZnO, Nb2O5, Ta2O5, SiO2, Al2O3, Bi2O3, Cr2O3, and Sr—O. Further, a nitride such as Ti—N, Zr—N, Nb—N, Ta—N, Si—N, Ge—N, Cr—N, Al—N, Ge—Si—N, and Ge—Cr—N also can be used. Further, a sulfide such as ZnS also can be used. Further, a mixture of the above-mentioned materials also can be used. Preferably, above all, particularly, TiO2 or a material containing TiO2 is used. Such materials have a high refractive index (n=2.5 to 2.8) and a low extinction coefficient (k=0.0 to 0.05), and thus the action of increasing the transmittance of the first information layer 221 can be enhanced.
In order to allow laser beams in an amount required for recording/reproduction to reach the second to N-th information layers 222 to 22N, the transmittances Tc and Ta of the first information layer 221 preferably satisfy 40<Tc and 40<Ta, and more preferably satisfy 46<Tc and 46<Ta, respectively. The transmittances Tc and Ta of the first information layer 221 preferably satisfy −5≦(Tc−Ta)≦5, and more preferably satisfy −3≦(Tc−Ta)≦3. If the transmittances Tc and Ta satisfy these conditions, when information recording/reproduction is performed with respect to the second to n-th information layers 222 to 22n, less influence is caused by a change in transmittance depending on a state of the recording layer 204 in the first information layer 221, thereby allowing an excellent recording/reproduction property to be obtained.
Preferably, a reflectance Rcl of the first information layer 221 when the recording layer 204 is in a crystalline phase and a reflectance Ral of the first information layer 221 when the recording layer 204 is in an amorphous phase satisfy Ral<Rcl. This allows the reflectance to be higher in an initial state where information has not been recorded yet than in the state where the information has been recorded, thereby allowing a stable recording/reproducing operation to be performed. Further, in order to obtain an excellent recording/reproduction property by increasing a difference in reflectance (Rcl−Ral), Rcl and Ral preferably satisfy 0.1≦Ral≦5 and 4≦Rcl≦15, and more preferably satisfy 0.1≦Ral≦3 and 4≦Rcl≦10.
In the first information layer 221, the crystalline nucleation layer may be arranged between the recording layer 204 and the third dielectric layer 205. In such a case, as an information recording medium 25 as shown in FIG. 5, the first to N-th information layers 221 to 22N and the transparent layer 23 are provided on the substrate 21. The first information layer 221 is formed of the first dielectric layer 201, the second dielectric layer 202, the recording layer 204, a crystalline nucleation layer 208, the third dielectric layer 205, the reflective layer 206, and the transmittance adjusting layer 207 that are laminated in order from the incident side of the laser beam. Further, in the first information layer 221, the crystalline nucleation layers may be arranged between the recording layer 204 and the second dielectric layer 202 and between the recording layer 204 and the third dielectric layer 205, respectively. In such a case, as an information recording medium 26 as shown in FIG. 6, the first to N-th information layers 221 to 22N and the transparent layer 23 are provided on the substrate 21. The first information layer 221 is formed of the first dielectric layer 201, the second dielectric layer 202, the crystalline nucleation layer 203, the recording layer 204, the crystalline nucleation layer 208, the third dielectric layer 205, the reflective layer 206, and the transmittance adjusting layer 207 that are laminated in order from the incident side of the laser beam. The crystalline nucleation layer 208 can be made of a material in the same system as that of the material of the crystalline nucleation layer 203, and also has the same configuration and function as those of the crystalline nucleation layer 203.
The information layers other than the first information layer 221 that are included in each of the optical information recording media 2, 25, and 26 according to this embodiment may have the same film structure as that of the first information layer 221, and further, may have another structure. Further, at least one of a plurality of the information layers may have the same film structure as that of the first information layer 221 described with regard to this embodiment, and the other information layers may have a different structure. In such a case, preferably, the first information layer 221 arranged at a position closest to a surface on the incident side of the laser beam has the film structure described with regard to this embodiment. Further, any one of the information layers other than the first information layer 221 may be configured as a ROM (Read Only Memory) type information layer or as a WO (Write Once) type information layer that allows writing to be performed only once.
Next, the description is directed to a method for manufacturing each of the information recording media 2, 25, and 26 according to this embodiment.
Initially, on the substrate 21 (having a thickness of, for example, 1100 μm), (N−1) layers of the N-th to second information layers 22N to 222 are laminated in order through the optical separation layers 24. Each of the information layers is formed of a single-layer film or a multi-layer film, and the films can be formed by sequentially performing sputtering with respect to sputtering targets used as materials, respectively, in a film forming device. Further, the optical separation layer 24 can be formed in the following manner. That is, a photocurable resin (particularly, an ultraviolet curable resin) or a delayed action type thermosetting resin is applied on the information layer, and the resin is allowed to be spread uniformly by performing spin coating, after which the resin is allowed to cure. When guide grooves for the laser beam 10 are formed on the optical separation layer 24, a transfer substrate (mold) with a surface on which grooves having a predetermined shape are formed is bonded to the resin before being cured. Then, the substrate 21 and the transfer substrate are rotated so that spin coating is performed, and after that, the resin is allowed to cure. Subsequently, the transfer substrate is peeled off from the cured resin, thereby allowing the optical separation layer 24 with a surface on which predetermined guide grooves are formed to be formed.
As described above, (N−1) layers of the information layers are laminated in order on the substrate 21 through the optical separation layers 24, and the optical separation layer 24 further is formed on the information layers.
Then, the first information layer 221 is formed on the optical separation layer 24 formed on the (N−1) layers of the information layers. To be specific, initially, the substrate 21 on which the (N−1) layers of the information layers and the optical separation layers 24 are formed is placed in the film forming device, where the transmittance adjusting layer 207 is formed on the optical separation layer 24. The transmittance adjusting layer 207 can be formed by performing sputtering with respect to a sputtering target formed of a compound constituting the transmittance adjusting layer 207 in Ar gas atmosphere or an atmosphere of a mixture of Ar gas and a reactive gas. Further, the transmittance adjusting layer 207 also can be formed by performing reactive sputtering in an atmosphere of a mixture of Ar gas and a reactive gas using a metal formed of elements constituting the transmittance adjusting layer 207 as a sputtering target.
Then, the reflective layer 206 is formed on the transmittance adjusting layer 207. The reflective layer 206 can be formed in the same manner as in the case of forming the reflective layer 108 described with regard to Embodiment 1.
Then, the third dielectric layer 205 is formed on the reflective layer 206. The third dielectric layer 205 can be formed in the same manner as in the case of forming the third dielectric layer 105 described with regard to Embodiment 1.
Then, the crystalline nucleation layer 208 is formed on the third dielectric layer 205 as required (in the case of manufacturing the information recording medium 25 or 26 as shown in FIG. 5 or 6, respectively). The crystalline nucleation layer 208 can be formed in the same manner as in the case of forming the crystalline nucleation layer 109 described with regard to Embodiment 1. In the case where the crystalline nucleation layer 208 is not formed on the third dielectric layer 205 (in the case of the information recording medium 2 as shown in FIG. 4), the crystalline nucleation layer 203 is formed on the recording layer 204 described later.
Then, the recording layer 204 is formed on the crystalline nucleation layer 208 (in a configuration without the crystalline nucleation layer 209, on the third dielectric layer 205). The recording layer 204 can be formed in the same manner as in the case of forming the recording layer 104 described with regard to Embodiment 1.
Then, the crystalline nucleation layer 203 is formed on the recording layer 204 as required (in the case of manufacturing the information recording medium 2 or 26 as shown in FIG. 4 or 6, respectively).
Then, the second dielectric layer 202 is formed on the crystalline nucleation layer 203 (when the crystalline nucleation layer 203 is not provided, on the recording layer 204). The second dielectric layer 202 can be formed in the same manner as in the case of forming the second dielectric layer 102 described with r