Optical information recording medium

Abstract: An optical information recording medium includes a substrate with guide grooves thereon, a recording layer provided on the substrate, including a recording material of which phase is reversibly changeable from a stable state to a semistable state and vice versa, a heat-resistant dielectric protective layer provided on the recording layer, including a protective material which includes Zn, Si, S and O, and a light reflection and heat dissipation layer provided on the heat-resistant dielectric protective layer.

Description: The present invention relates to an optical information recording medium, more particularly to a phase-change type optical information recording medium. There is conventionally known a phase-change type optical information recording medium which utilizes phase changes between a crystalline phase and an amorphous phase or between one crystalline phase and another crystalline phase as one of the optical recording media which are capable of recording, reproducing and erasing information, for instance, by the application of a laser beam thereto. This kind of phase-change type optical information recording medium is capable of overwriting information by the application of a single laser beam thereto. Such a phase-change type optical information recording medium is generally composed of a substrate made of polycarbonate, a first protective layer provided on the substrate, a recording layer provided on the first protective layer, a second protective layer provided on the recording layer, and a light reflection and heat dissipation layer; see, for instance, EP-A-564260, EP-A-574025 reflecting the preamble of claim 1, EP-A-630007, EP-A-639830, EP-A-717404, US-A-5453346, US-A-5470628 and Japanese Journal of Applied Physics, Vol. 32, No. 5A, part 1, 1.05.1993, pages 1980-1982. Representative examples of recording materials for use in the above-mentioned recording layer are the so-called chalcogen-based alloys, such as Ge-Te, Ge-Se-Sb and Ge-Te-Sn as disclosed in US-A-3,530,441, and Ge-Te-Se-Sb and Ge-Te-Sb, with the composition ratios of such elements being specifically selected for improvement of the recording/erasing repetition performance thereof as proposed in JP-A-62-73438 and 63-228433. Furthermore, as the materials for the above-mentioned protective layers, there are conventionally known oxides such as SiO 2 and Al 2 O 3 , and nitrides such as BN, Si 3 N 4 and AlN. However, protective layers composed of such an oxide or nitride are known to have the shortcoming that the protective layers are thermally damaged by the heat applied thereto during the cycles of heating with the application of a laser beam and cooling, resulting in the reduction of the reliability of the performance of the optical information recording medium comprising such a protective layer. In order to eliminate the above-mentioned shortcoming, mixed materials, such as a material composed of ZnS and SiO 2 , are proposed as disclosed in JP-A-63-259855 and JP-B-4-74785. It is reported that by using such a material in the protective layer, the above-mentioned recording/erasing repetition performance can be significantly improved for high line speed recording media, but the recording/erasing repetition performance cannot be sufficiently improved for low line speed recording media such as compact disks. It is therefore a first object of the present invention to provide a phase-change type optical information recording medium with high heat resistance. A second object of the present invention is to provide a phase-change type optical information recording medium which has excellent recording, reproduction and erasing repetition performance (hereinafter referred to as repetition use performance), and high recording sensitivity. A third object of the present invention is to provide a phase-change type optical information recording medium which has excellent repetition use performance, in particular, from low line speed operation through high line-speed operation. These objects of the present invention can be achieved by an optical information recording medium as claimed in claim 1 which comprises (a) a substrate with guide grooves thereon, (b) a recording layer provided on the substrate, comprising a recording material of which phase is reversibly changeable from a stable state to a semistable state and vice versa, (c) a heat-resistant dielectric protective layer provided on the recording layer, comprising a protective material which comprises Zn, Si, S and O, and (d) a light reflection and heat dissipation layer which is provided on the heat-resistant dielectric protective layer. The optical information recording medium is characterized in that the protective material for the heat-resistant dielectric protective layer comprises ZnS, ZnO and SiO 2 . The desired heat resistance can be obtained by use of the above-mentioned heat-resistant dielectric protective layer. When the substrate is not sufficiently heat resistant for use in practice, an additional heat-resistant dielectric protective layer which may be the same as the above-mentioned heat-resistant dielectric protective layer may be provided between the substrate and the recording layer. Furthermore, in the above protective material, it is preferable that the composition ratio of ZnS, ZnO and SiO 2 be such that the composition ratio thereof be represented by formula (I) in order to obtain excellent repetition use performance, in particular, from low line speed operation through high line speed operation: (ZnS) α (ZnO) β (SiO 2 ) γ provided that 30≤ α ≤90, 5≤ β ≤50, and 5≤ γ ≤30, and α + β + γ = 100 mole%. Furthermore, for achieving the above-mentioned object, it is also preferable that the protective material have a thermal conductivity in a range of 1.2 W/m•k to 24.0 W/m•k. For obtaining a phase-change type optical information recording medium having excellent repetition use performance and high recording sensitivity, it is preferable that the recording material for the recording layer comprise Ag, In, Sb and Te. Furthermore, it is preferable that the recording material for the recording layer further comprise at least one element selected from the group consisting of N and Cl. Furthermore, it is preferable that the recording material for the recording layer comprise Ag, S, one of Sb or As, and at least one element selected from the group consisting of Zn, Si, Ge and Sn. For achieving the above-mentioned objects, it is also preferable that the recording material for the recording layer comprise Ag and S, and one element selected from the group consisting of Sb and As and be present in the form of Ag 3 SbS 3 or Ag 3 AsS 3 in a crystalline state in the stable state, and in an amorphous state in the semistable state. In the above, it is preferable that the recording material be in an amorphous state in the semistable state, and initialization and erasing be performed in the crystalline state. In the above, it is also preferable that the recording layer comprise Ag 3 SbS 3 or Ag 3 AsS 3 in the stable state, with at least one element selected from the group consisting of Zn, Si, Ge and Sn being added thereto. Furthermore, in the above, it is preferable that the recording layer comprise a compound of formula (II) or a compound of formula (III): (Ag 3 SbS 3 ) x M 100-x wherein M represents an element selected from the group consisting of Zn, Ge, Si and Sn, and 92 ≤ X ≤ 99, X indicating mole%; and (Ag 3 AsS 2 ) x M 100-x wherein M represents an element selected from the group consisting of Zn, Ge, Si and Sn, and 92 s X ≤ 99, X indicating mole%. A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: Fig. 1 is a schematic cross-sectional view of an example of an optical information recording medium of the present invention. In the phase-change type optical recording medium, the recording layer is fused by the application of a laser beam thereto and cooled for solidification for recording, reproduction and erasing. This fusing and cooling cycle is repeated, so that the material in the recording layer is caused to flow during the repetition of the fusing and cooling cycle. As a result, it may occur that the heat-resistant layer is peeled off the recording layer or cracks are formed in the heat-resistant layer by thermal shocks during the repetition of the fusing and cooling cycle, resulting in considerable deterioration of the phase-change type optical information recording medium (hereinafter referred to as the optical information recording medium). In particular, the heat-resistant protective layer for the optical information recording medium is required to control the quantity of heat generated and accumulated in the recording layer by the application of laser beam thereto, and therefore plays a significantly important role for forming excellent recording marks with minimum jitters and for achieving high operation reliability in the course of repeated use of the optical information recording medium. The heat-resistant protective layer capable of playing the above-mentioned role is required to have the following properties: (1) having high resistance against thermal shocks. (2) capable of controlling the thermal conductivity of the heat-resistant protective layer as desired. (3) having an appropriate refractive index for having the recording layer absorb laser beams effectively. (4) chemically stable. The optical information recording medium of the present invention is of a phase-change type and capable of recording information therein and erasing recorded information therefrom and being initialized before use, and comprises a substrate with guide grooves thereon; a recording layer provided on the substrate, comprising a recording material of which phase is reversibly changeable from a stable state to a semistable state and vice versa; a heat-resistant dielectric protective layer provided on the recording layer, comprising a protective material which comprises Zn, Si, S and O; and a light reflection and heat dissipation layer provided on the heat-resistant dielectric protective layer. As mentioned previously, in the above, when the substrate is not sufficiently heat resistant, an additional heat-resistant dielectric protective layer comprising the same protective material as mentioned above may be interposed between the substrate and the recording layer. In the present invention, the above-mentioned protective material for use in the heat-resistant dielectric layer is a mixture of ZnS, ZnO and SiO 2 . SiO 2 is known as a heat-resistant material which is highly resistant to thermal shocks. However, when SiO 2 is used alone in the above-mentioned heat-resistant protective layer, since the thermal coefficient of expansion of SiO 2 is much smaller than that of the recording layer, so that the heat-resistant protective layer made of SiO 2 tends to peel off the recording layer while in use. In order to solve this problem, it is proposed to use a mixture of SiO 2 and ZnS as disclosed in Japanese Laid-Open Patent Application 63-259855 and Japanese Patent Publication 7-111786. It is reported that the mixture of SiO 2 and ZnS exhibits excellent properties in terms of the thermal coefficient of expansion. However, the thermal conductivity of the mixture of SiO 2 and ZnS is as small as 1 w/m·k, which is considered to be much smaller than the thermal conductivities of other materials for use in the heat-resistant protective layer. When a heat-resistant protective layer having such a small thermal conductivity is used in an optical information recording medium for compact disks for use at a low line speed, heat dissipation is not sufficient for repeated use due to the small thermal conductivity and therefore the repeated operation characteristics and mark jitter characteristics tend to deteriorate while in repeated use. In the present invention, ZnO is added to the mixture of SiO 2 and ZnS in order to increase the thermal conductivity. Furthermore, the refractive index of the mixture of SiO 2 and ZnS is 2.1, while the refractive index the mixture of SiO 2 , ZnS and ZnO is 1.9. Thus, by the addition of ZnO, the refractive index of the heat-resistant protective layer can be decreased, so that the light enclosing effect of the recording layer which is interposed between the substrate and the heat-resistant protective layer or between a pair of the heat-resistant protective layers is increased. As a result, the laser beam applied to the recording layer is more efficiently and effectively used, so that the recording sensitivity of the recording layer can be increased. In order to fabricate a phase-change type optical information recording medium which can be employed with high operation reliability and excellent repetition use performance in a low line speed range through a high line speed range, the inventors of the present invention have experimentally confirmed that it is preferable to set the thermal conductivity of the heat-resistant protective layer or that of the protective material used in the heat-resistant protective layer in the range of 1.2 w/m•k to 24.0 w/m•k. In the present invention, the above-mentioned thermal conductivity can be attained when the composition ratio of ZnS, ZnO and SiO 2 in the heat-resistant dielectric protective layer is set as represented by formula (I): (ZnS) α (ZnO) β (SiO 2 ) γ wherein 30≤ α ≤90, 5≤ β ≤50, and 5≤ γ ≤30, and α + β + γ = 100 mole%. By adjusting the composition ratio of ZnS, ZnO and SiO 2 in the heat-resistant dielectric protective layer and accordingly by adjusting the thermal conductivity of the heat-resistant protective layer, the repetition use performance of rewritable CD-RW and DVD-RAM compact disks can be significantly improved. This can be attained by the addition of ZnO to the mixture of SiO 2 and ZnS as mentioned above. In the present invention, it is preferable that the recording material comprising Ag, In, Sb and Te be employed, more preferably with the addition thereto of at least one element selected from the group consisting of N and Cl. The addition of a nitrogen atom improves the repetition use performance of the recording material, while the addition of a chlorine atom increases the light absorption performance of the recording material and therefore improves the recording sensitivity of the recording material. By use of the above recording material in the recording layer in combination with the above-mentioned the heat-resistant protective layer, the recording sensitivity and repetition use performance of the optical information recording medium can be significantly improved. Ag-In-Sb-Tb recording materials are proposed as recording materials having high recording sensitivity and high erasing performance in overwriting as disclosed in Japanese Laid-Open Patent Applications 2-37466, 2-171325 and 4-141485. However, when the recording layer composed of the above-mentioned Ag-In-Sb-Tb recording material is used in combination with the conventional ZnS•SiO 2 protective layer, the repetition use performance of the recording layer is not sufficient for use in compact disks used in a low line speed range. For achieving the above-mentioned advantages of the present invention over the conventional optical information recording media, the recording material for use in the optical information recording medium of the present invention comprise Ag, S, one of Sb or As, and at least one element selected from the group consisting of Zn, Si, Ge and Sn. The above-mentioned recording material may be present in the form of Ag 3 SbS 3 or Ag 3 AsS 3 in a crystalline state in the stable state and in an amorphous state in the semistable state. Furthermore, in the present invention, recording can be performed in the amorphous state, and initialization and erasing can be performed in the crystalline state. Furthermore, the recording layer may comprise Ag 3 SbS 3 or Ag 3 AsS 3 in the stable state, with at least one element selected from the group consisting of Zn, Si, Ge and Sn being added thereto. In the above, Zn serves as a donor and Si, Ge and Sn serve as an acceptor. Furthermore, the recording layer may comprise a compound of formula (II) or a compound of formula (III): (Ag 3 SbS 3 ) x M 100-x wherein M represents at least one element selected from the group consisting of Zn, Ge, Si and Sn, and 92 ≤ X ≤ 99, X indicating mole%; and (Ag 3 AsS 3 ) x M 100-x wherein M represents at least one element selected from the group consisting of Zn, Ge, Si and Sn, and 92 ≤ X ≤ 99, X indicating mole%. With reference to Fig. 1, the structure of an example of the optical information recording medium of the present invention will now be explained. In Fig. 1, on a substrate 1, there are successively overlaid a first heat-resistant protective layer 2, a recording layer 3, a second heat-resistant protective layer 4 and a light reflection and heat dissipation layer 5. As mentioned previously, it is not always necessary to provide a pair of the first and second heat-resistant protective layers between which the recording layer is to be interposed. However, when the substrate 1 is not heat resistant, for example, when the substrate 1 is made of polycarbonate, it is preferable to provide the first heat-resistant protective layer 2 as illustrated in Fig. 1. Examples of the materials for the substrate 1 are glass, ceramics and resins. In view of moldability and cost, a substrate made of a resin is preferable for use in the present invention. Representative examples of resins for the substrate 1 are polycarbonate resin, acrylic resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicone resin, fluorine plastics, ABS resin and urethane resin. Of these resins, polycarbonate resin is most preferable in view of the workability and optical characteristics thereof. The substrate 1 may be in the shape of a disk, a card or a sheet. The heat-resistant protective layers 2 and 4 for use in the present invention are dielectric layers and serve not only as heat-resistant protective layer, but also as optical interference layer. In order to have the protective layer serve as a suitable heat-resistant protective layer for use in the present invention, without causing the problem of peeling off the substrate or the recording layer, it is preferable that the heat-resistant protective layer have a thickness in the range of 20 to 300 nm (200Å to 3000Å), more preferably in the range of 35 to 200 nm (350Å to 2000Å). The heat-resistant protective layer for use in the present invention can be formed by sputtering, using a ZnS•ZnO•SiO 2 target. The recording layer for use in the present invention can also be formed by sputtering. It is preferable that the recording layer have a thickness in the range of 10 to 100 nm (100Å to 1000Å), more preferably in the range of 20 to 35 nm (200Å to 350Å), in order to maintain appropriate light absorption performance and interference effect without reducing light transmittance thereof. The light reflection and heat dissipation layer can be made of, for example, an aluminum alloy. The light reflection and heat dissipation layer can also be formed by sputtering. It is preferable that the light reflection and heat dissipation layer have a thickness in the range of 50 to 200 nm (500Å to 2000Å), more preferably in the range of 70 to 150 nm (700Å to 1500Å). Other features of this invention will become apparent in the course of the following description of exemplary embodiments, which are given for illustration of the invention and are not intended to be limiting thereof. Examples 1 to 13 On a disk-shaped polycarbonate substrate with a diameter of 120 mm and a thickness of 1.2 mm, with guide grooves with a pitch of 1.6 µm and a depth of about 60 nm (600 Å) being formed thereon, there were successively overlaid a first heat-resistant protective layer, a recording layer, a second heat-resistant protective layer, and a light reflection and heat dissipation layer by rf sputtering method. The composition and thickness of each of the first heat-resistant protective layer, the recording layer, the second heat-resistant protective layer, and the light reflection and heat dissipation layer are shown in TABLE 1. Thus, phase-change type optical recording media No 1 to No. 13 of the present invention were respectively fabricated in Examples 1 to 13. In each of these phase-change type optical recording media, the first heat-resistant protective layer and the second heat-resistant protective layer have the same composition as shown in TABLE 1. Comparative Example 1 The procedure of fabrication of the phase-changeable optical recording medium No. 1 in Example 1 was repeated except that the first and second heat-resistant protective layers employed in Example 1 were respectively replaced by a first heat-resistant protective layer with the composition as shown in TABLE 1, and a second heat-resistant protective layer with the composition as shown in TABLE 1, whereby a comparative phase-change type optical recording medium No. 1 was fabricated. Comparative Example 2 The procedure of fabrication of the phase-changeable optical recording medium No. 10 in Example 10 was repeated except that the first and second heat-resistant protective layers employed in Example 10 were respectively replaced by a first heat-resistant protective layer with the composition as shown in TABLE 1, and a second heat-resistant protective layer with the composition as shown in TABLE 1, whereby a comparative phase-change type optical recording medium No. 2 was fabricated. In each of the above comparative phase-change type optical recording media, the first heat-resistant protective layer and the second heat-resistant protective layer have the same composition as shown in TABLE 1. Test samples with a thickness of 1 µm were prepared from the heat-resistant protective layers employed in Examples 1 to 13 and Comparative Example 1 and 2. Using these test samples, the thermal conductivity (w/m•k) of each of the heat-resistant protective layers employed in Examples 1 to 13 and Comparative Example 1 and 2 was measured by an optical alternate-current (A.C.) method. Also using the same test samples, the thermal conductivity of each of the heat-resistant protective layers employed in Examples 1 to 13 and Comparative Example 1 and 2 was measured, using Ellipso Meter. The results are shown in TABLE 2. The thus obtained optical information recording media No. 1 to No. 9 of the present invention and comparative optical information recording medium No. 1 were evaluated by the following evaluation method A: [Evaluation Method A] Each of the above-mentioned optical information recording media was initialized and then subjected to overwriting with an EFM random pattern at a line speed of 1.4 m/s repeatedly. Thereafter, each optical information recording medium was evaluated with respect to the recording power dependence of 3T signals by reproduction of the overwritten EFM random pattern. The line speed at the reproduction was 2.8 m/s. The results are shown in TABLES 3 to 12. with respect to the comparative optical information recording medium No. 1 in Comparative Example 1, the number of repeatable overwriting times thereof was 1000 as shown in TABLE 12. In sharp contrast, with respect to the optical information recording media No. 1 to No. 9 of the present invention in Examples 1 to 9, the number of repeatable overwriting times was more than 3000. It is considered that this is because the thermal conductivity of each of heat-resistant protective layers employed in the optical information recording media No. 1 to No. 9 of the present invention in Examples 1 to 9 is greater than that of each heat-resistant protective layer employed in the comparative optical information recording medium No. 1 in Comparative Example 1, so that the recording layers in the optical information recording media No. 1 to No. 9 were thermally less damaged than the recording layer in the comparative optical information recording medium No. 1 in Comparative Example 1. In particular, when the content ratio of ZnO is 5 mol% or more, the above-mentioned effect becomes conspicuous. In Example 2, the content ratio of ZnO is greater than that in Example 1, so that the thermal conductivity of each heat-resistant protective layer in Example 2 is increased in comparison with the thermal conductivity of each heat-resistant protective layer in Example 1, so that 5,000 to 10,000 times overwriting was possible in the optical information recording medium No. 2 in Example 2. In Example 3, the ZnO content ratio in each heat-resistant protective layer is 20 mole%, so that the thermal conductivity of each heat-resistant protective layer in Example 3 is increased to 11.9 W/m•k. As a result, the heat dissipation effect of each heat-resistant protective layer in Example 3 is greater than that of each heat-resistant protective layer in Example 2, but the recording sensitivity at relatively low recording powers is slightly lowered. However, the number of repeatable overwriting times is increased up to 15,000. In Example 4, the ZnO content ratio in each heat-resistant protective layer is 30 mole%, so that the thermal conductivity of each heat-resistant protective layer in Example 4 is increased to 14.8 W/m•k. As a result, the heat dissipation effect of each heat-resistant protective layer in Example 4 is increased, so that the recording sensitivity at relatively low recording powers is slightly lowered. However, the number of repeatable overwriting times is increased up to 20,000. In Example 5, the ZnO content ratio in each heat-resistant protective layer is 50 mole%, so that the. thermal conductivity of each heat-resistant protective layer in Example 5 is increased to 23.8 W/m•k. Accordingly the heat dissipation effect of the heat-resistant protective layer in Example 5 is increased, so that the recording sensitivity at relatively low recording powers is slightly lowered. However, the number of repeatable overwriting times is increased up to 30,000 or more. When the ZnO content ratio exceeds 50 mole%, 'the thermal conductivity of the heat-resistant protective layer is further increased and therefore the recording sensitivity at relatively low recording powers is further lowered. Therefore, the ZnO content ratio of more than 50 mole% is not always useful in practice. In Example 6, the ZnO content ratio in each heat-resistant protective layer is 20 mole%, so that the thermal conductivity of the heat-resistant protective layer in Example is smaller than that of the heat-resistant protective layer in Example 5. However, the number of repeatable overwriting times is 20,000 or more. In Example 7, the optical information recording medium No. 7 thereof was fabricated in the same manner as in Example 3 except that the recording layer in Example 3 was replaced by a recording layer which was modified so as to include a nitrogen atom in the recording layer in Example 3. The number of repeatable overwriting times of the optical information recording medium No. 3 in Example 3 was 15,000, while the number of repeatable overwriting times of the optical information recording medium No. 7 in Example 7 was 30,000. This indicates that the addition of nitrogen to the recording layer improves the number of repeatable overwriting times of the optical information recording medium No. 7. In Example 8, the optical information recording medium No. 8 thereof was fabricated in the same manner as in Example 3 except that the recording layer in Example 3 was replaced by a recording layer which was modified so as to include a chlorine atom in the recording layer in Example 3. The number of repeatable overwriting times of the optical information recording medium No. 3 in Example 3 was 15,000, and the number of repeatable overwriting times of the optical information recording medium No. 8 in Example 8 was also 15,000. However, TABLE 10 indicates that the recording sensitivity of the optical information recording medium No. 8 in Example 8 is higher than that of the optical information recording medium No. 3 in Example 3. This indicates that the addition of chlorine to the recording layer improves the recording sensitivity without having any adverse effect on the number of repeatable overwriting times of the optical information recording medium No. 8. The previously obtained optical information recording media No. 10 to No. 13 of the present invention and comparative optical information recording medium No. 2 were evaluated by the following evaluation method B: (Evaluation Method B] Each of the above-mentioned optical information recording media was initialized. Recording was performed at a line speed of 1.2 m/s and a recording frequency (f1) of 0.4 MHZ, and then overwriting was performed with a recording frequency (f2) of 0.72 MHZ, using a recording laser with a wavelength of 780 nm. The C/N (dβ), the erasing ratio (dβ), the reflectivity of an erased portion, the reflectivity of a recorded portion, the contrast, and the number of repeatable overwriting times were measured. The results are shown in TABLE 13. The results shown in TABLE 13 indicate that the use of the heat-resistant protective layer composed of (ZnS) 70 (ZnO) 10 (SiO 2 ) 20 for both the first and second heat-resistant protective layers improves the recording sensitivity and the number of repeatable overwriting times. In particular, in Example 13, the recording layer includes not only Ag 3 SbS 3 , but also both Zn and Sn. In this recording layer, Zn serves as a donor and Sn serves as an acceptor, so that two energy levels are formed, which enhances the light absorption. Thus, the use of such recording layer significantly improves not only the recording sensitivity, but also the number of repeatable overwriting times. Example 1 Composition Thickness nm (Å) First Heat-resistant Protective Layer (ZnS) 90 (ZnO) 5 (SiO 2 ) 5 (mol%) 150 (1500) Recording Layer Ag 6 In 10 Sb 47 Te 38 (atm%) 20 (200) Second Heat-resistant Protective Layer (ZnS) 90 (ZnO) 5 (SiO 2 ) 5 (mol%) 25 (250) Light Reflection and Heat Dissipation Layer Al alloy 100 (1000) Example 2 Composition Thickness nm (Å) First Heat-resistant Protective Layer (ZnS) 80 (ZnO) 10 (SiO 2 ) 10 (mol%) 150 (1500) Recording Layer Ag 5 In 10 Sb 47 Te 38 (atm%) 20 (200) Second Heat-resistant Protective Layer (ZnS) 70 (ZnO) 10 (SiO 2 ) 20 (mol%) 25 (250) Light Reflection and Heat Dissipation Layer Al alloy 100 (1000) Example 3 Composition Thickness nm (Å) First Heat-resistant Protective Layer (mol%) (ZnS) 70 (ZnO) 20 (SiO 2 ) 10 180 (1800) Recording Layer Ag 5 In 10 Sb 47 Te 38 (atm%) 20 (200) Second Heat-resistant Protective Layer (ZnS) 70 (ZnO) 20 (SiO 2 ) 10 (mol%) 27.5 (275) Light Reflection and Heat Dissipation Layer Al alloy 100 (1000) Example 4 Composition Thickness nm (Å) First Heat-resistant Protective Layer (ZnS) 50 (ZnO) 30 (SiO 2 ) 20 (mol%) 200 (2000) Recording Layer Ag 5 In 10 Sb 47 Te 38 (atm%) 20 (200) Second Heat-resistant Protective Layer (ZnS) 50 (ZnO) 30 (SiO 2 ) 20 (mol%) 32.5 (325) Light Reflection and Heat Dissipation Layer Al alloy 80 (800) Example 5 Composition Thickness nm (Å) First Heat-resistant Protective Layer (ZnS) 30 (ZnO) 50 (SiO 2 ) 20 (mol%) 200 (2000) Recording Layer Ag 5 In 10 Sb 47 Te 38 (atm%) 20 (200) Second Heat-resistant Protective Layer (ZnS) 30 (ZnO) 50 (SiO 2 ) 20 (mol%) 35 (350) Light Reflection and Heat Dissipation Layer Al alloy 80 (800) Example 6 Composition Thickness nm (Å) First Heat-resistant Protective Layer (ZnS) 50 (ZnO) 20 (SiO 2 ) 30 (mol%) 180 (1800) Recording Layer Ag 5 In 10 Sb 47 Te 38 (atm%) 20 (200) Second Heat-resistant Protective Layer (ZnS) 50 (ZnO) 20 (SiO 2 ) 30 (mol%) 25 (250) Light Reflection and Heat Dissipation Layer Al alloy 100 (1000) Example 7 Composition Thickness nm (Å) First Heat-resistant Protective Layer (ZnS) 70 (ZnO) 20 (SiO 2 ) 10 (mol%) 180 (1800) Recording Layer Ag 5 In 10 Sb 46 Te 37 N 2 (atm%) 20 (200) Second Heat-resistant Protective Layer (ZnS) 70 (ZnO) 20 (SiO 2 ) 10 (mol%) 27.5 (275) Light Reflection and Heat Dissipation Layer Al alloy 100 (1000) Example 8 Composition Thickness nm (Å) First Heat-resistant Protective Layer (ZnS) 70 (ZnO) 20 (SiO 2 ) 10 (mol%) 180 (1800) Recording Layer Ag 5 In 10 Sb 46.9 Te 38 Cl 0.1 (atm%) 20 (200) Second Heat-resistant Protective Layer (ZnS) 70 (ZnO) 20 (SiO 2 ) 10 (mol%) 27.5 (275) Light Reflection and Heat Dissipation Layer Al alloy 100 (1000) Example 9 Composition Thickness nm (Å) First Heat-resistant Protective Layer (ZnS) 70 (ZnO) 20 (SiO 2 ) 10 (mol%) 180 (1800) Recording Layer Ag 5 In 10 Sb 45.9 Te 37 N 2 Cl 0.1 (atm%) 20 (200) Second Heat-resistant Protective Layer (ZnS) 70 (ZnO) 20 (SiO 2 ) 10 (mol%) 27.5 (275) Light Reflection and Heat Dissipation Layer Al alloy 100 (1000) Example 10 Composition Thickness nm (Å) First Heat-resistant Protective Layer (ZnS) 70 (ZnO) 10 (SiO 2 ) 20 (mol%) 180 (1800) Recording Layer (Ag 3 SbS 3 ) 95 Zn 5 (atm%) 28 (280) Second Heat-resistant Protective Layer (ZnS) 70 (ZnO) 10 (SiO 2 ) 20 (mol%) 31 (310) Light Reflection and Heat Dissipation Layer Al alloy 80 (800) Example 11 Composition Thickness nm (Å) First Heat-resistant Protective Layer (ZnS) 70 (ZnO) 10 (SiO 2 ) 20 (mol%) 180 (1800) Recording Layer (Ag 3 SbS 3 ) 95 Zn 5 (atm%) 30 (300) Second Heat-resistant Protective Layer (ZnS) 70 (ZnO) 10 (SiO 2 ) 20 (mol%) 30 (300) Light Reflection and Heat Dissipation Layer Al-Mg-Si 80 (800) Example 12 Composition Thickness nm (Å) First Heat-resistant Protective Layer (ZnS) 70 (ZnO) 10 (SiO 2 ) 20 (mol%) 180 (1800) Recording Layer (AgAsS) 90 Ge 10 (atm%) 30 (300) Second Heat-resistant Protective Layer (ZnS) 70 (ZnO) 10 (SiO 2 ) 20 (mol%) 30 (300) Light Reflection and Heat Dissipation Layer Al-Mg-Si 80 (800) Example 13 Composition Thickness nm (Å) First Heat-resistant Protective Layer (ZnS) 70 (ZnO) 10 (SiO 2 ) 20 (mol%) 180 (1800) Recording Layer (Ag 3 SbS 3 ) 94 Zn 3 Sn 3 (atm%) 30 (300) Second Heat-resistant Protective Layer (ZnS) 70 (ZnO) 10 (SiO 2 ) 20 (mol%) 28 (280) Light Reflection and Heat Dissipation Layer Al-Mg-Si 80 (800) Comparative Example 1 Composition Thickness nm (Å) First Heat-resistant Protective Layer (ZnS) 80 (SiO 2 ) 20 (mol%) 180 (1800) Recording Layer Ag 5 In 10 Sb 47 Te 38 (atm%) 20 (200) Second Heat-resistant Protective Layer (ZnS) 80 (SiO 2 ) 20 (mol%) 25 (250) Light Reflection and Heat Dissipation Layer Al alloy 100 (1000) Comparative Example 2 Composition Thickness nm (Å) First Heat-resistant Protective Layer (ZnS) 80 (SiO 2 ) 20 (mol%) 180 (1800) Recording Layer (Ag 3 SbS 3 ) 95 Zn 5 (atm%) 30 (300) Second Heat-resistant Protective Layer (ZnS) 80 (SiO 2 ) 20 (mol%) 30 (300) Light Reflection and Heat Dissipation Layer Al alloy 80 (800) First and Second Heat-resistant Protective Layers Composition (mol%) Thermal Conductivity (w/m•k) Refractive Index Ex. 1 (ZnS) 90 (ZnO) 5 (SiO 2 ) 5 1.20 2.02 Ex. 2 (ZnS 2 ) 80 (ZnO) 10 (SiO 2 ) 10 6.2 1.85 Ex. 3 (ZnS) 70 (ZnO) 20 (SiO 2 ) 10 11.9 1.97 Ex. 4 (ZnS) 50 (ZnO) 30 (SiO 2 ) 20 18.4 1.82 Ex. 5 (ZnS) 30 (ZnO) 80 (SiO 2 ) 20 23.8 1.81 Ex. 6 (ZnS) 50 (ZnO) 20 (SiO 2 ) 30 13.3 1.77 Ex. 7 (ZnS) 70 (ZnO) 20 (SiO 2 ) 10 11.9 1.97 Ex. 8 (ZnS) 70 (ZnO) 20 (SiO 2 ) 10 11.9 1.97 Ex. 9 (ZnS) 70 (ZnO) 20 (SiO 2 ) 10 11.9 1.97 Ex. 10 (ZnS) 70 (ZnO) 10 (SiO 2 ) 20 12.0 1.98 Ex. 11 (ZnS) 70 (ZnO) 10 (SiO 2 ) 20 12.0 1.98 Ex. 12 (ZnS) 70 (ZnO) 10 (SiO 2 ) 20 12.0 1.98 Ex. 13 (ZnS) 70 (ZnO) 10 (SiO 2 ) 20 12.0 1.98 Comp. Ex. 1 (ZnS) 80 (SiO 2 ) 20 0.91 2.18 Comp. Ex. 2 (ZnS) 80 (SiO 2 ) 20 0.91 2.18 Characteristics Example 10 Recording Power (Pw/Pe)(mW) 19/10 20/10 21/10 22/10 c/N(dβ) 48 48 49 50 Erasing ratio (dβ) 24 25 26 27 Reflectivity of erased portion (%) 70 70 69 68 Reflectivity of recorded portion (%) 28 27 26 24 Contrast 0.6 0.61 0.62 0.65 Repeatable number of overwriting times 60 60 58 57 Characteristics Example 11 Recording Power (Pw/Pe)(mW) 21/10 22/10 23/10 24/10 C/N(dβ) 48 48 49 50 Erasing ratio (dβ) 24 25 26 27 Reflectivity of erased portion (%) 70 70 69 68 Reflectivity of recorded portion (%) 28 28 27 26 Contrast 0.6 0.6 0.61 0.62 Repeatable number of overwriting times 80 78 77 75 Characteristics Example 12 Recording Power (Pw/Pe)(mw) 20/10 21/10 22/10 23/10 C/N(dβ) 47 48 48 49 Erasing ratio (dβ) 23 25 25 26 Reflectivity of erased portion (%) 71 70 70 69 Reflectivity of recorded portion (%) 31 30 30 29 Contrast 0.56 0.57 0.57 0.58 Repeatable number of overwriting times 80 80 79 78 Characteristics Example 13 Recording Power (Pw/Pe)(mW) 17/10 18/10 19/10 20/10 C/N(dβ) 48 49 50 51 Erasing ratio (dβ) 25 25 26 26 Reflectivity of erased portion (%) 69 68 68 67 Reflectivity of recorded portion (%) 30 29 28 27 Contrast 0.57 0.57 0.57 0.60 Repeatable number of overwriting times 95 93 93 92 Characteristics Comparative Example 2 Recording Power (Pw/Pe)(mW) 25/10 26/10 27/10 28/10 C/N(dβ) 45 46 46 47 Erasing ratio (dβ) 22 22 23 24 Reflectivity of erased portion (%) 68 68 69 68 Reflectivity of recorded portion (%) 29 28 28 27 Contrast 0.57 0.59 0.59 0.60 Repeatable number of overwriting times 20 20 19 19

Claims: An optical information recording medium capable of recording information therein and erasing recorded information therefrom, and being initialized, comprising: a substrate with guide grooves thereon; a recording layer provided on said substrate, comprising a recording material of which phase is reversibly changeable from a stable state to a semistable state and vice versa; a heat-resistant dielectric protective layer provided on said recording layer; and a light reflection and heat dissipation layer provided on said heat-resistant dielectric protective layer, . characterized in that said protective material in said heat-resistant dielectric protective layer comprises ZnS, ZnO and SiO 2 . The optical information recording medium as claimed in claim 1, wherein the composition ratio of ZnS, ZnO and SiO 2 in said heat-resistant dielectric protective layer is represented by formula (I): (ZnS) α (ZnO) β (SiO 2 ) γ wherein 30 ≤ α ≤ 90, 5 ≤ β ≤ 50, and 5 ≤ γ ≤ 30, and α + β + γ = 100 mole%. The optical information recording medium as claimed in claim 1 or 2, wherein said protective material has a thermal conductivity in a range of 1.2 W/m•k to 24.0 W/m•k. The optical recording medium as claimed in any one of claims 1-3, wherein said recording material comprises Ag, In, Sb and Te. The optical information recording medium as claimed in claim 4, wherein said recording material further comprises at least one element selected from N and Cl. The optical information recording medium as claimed in any one of claims 1-5, wherein said recording material in said recording layer comprises Ag, S, one of Sb or As, and at least one element selected from Zn, Si, Ge and Sn. The optical information recording medium as claimed in any one of claims 1-5, wherein said recording material comprises Ag and S, and one element selected from Sb and As and is present in the form of Ag 3 SbS 3 , or Ag 3 AsS 3 , in a crystalline state in said stable state and in an amorphous state in said semistable state. The optical information recording medium as claimed in claim 7, wherein recording is performed in said amorphous state, and initialisation and erasing are performed in said crystalline state. The optical information recording medium as claimed in claim 6, wherein said recording layer comprises Ag 3 SbS 3 or Ag 3 AsS 3 in said stable state, with at least one element selected from Zn, Si, Ge and Sn being added thereto. The optical information recording medium as claimed in claim 6, wherein said recording layer comprises a compound of formula (II) or a compound of formula (III): (Ag 3 SbS 3 ) x M 100-x wherein M represents at least one element selected from Zn, Ge, Si and Sn, and 92 ≤ x ≤ 99, x indicating mole%; and (Ag 3 AsS 3 ) x M 100-x wherein M represents at least one element selected from Zn, Ge, Si and Sn, and 92 ≤ x ≤ 99, x indicating mole%. The optical information recording medium as claimed in any one of claims 1-10, further comprising an additional heat-resistant dielectric protective layer comprising a protective material which comprises Zn, Si, S and O, which is interposed between said substrate and said recording layer.

Inventors: HARIGAYA MAKOTO, IWASAKI HIROKO, KAGEYAMA YOSHIYUKI, SHINOTSUKA MICHIAKI, HARIGAYA, MAKOTO, IWASAKI, HIROKO, KAGEYAMA, YOSHIYUKI, SHINOTSUKA, MICHIAKI
Applicants: RICOH KK, RICOH COMPANY, LTD
Application year: 1997
Main classification: G11B7
IPC codes: G11B7, B41M5