JP4352342B2 - Optical information recording medium - Google Patents

Description

  The present invention relates to an optical information recording medium, and more particularly to an optical information recording medium including a reflective layer or a semi-transmissive layer containing Ag.

  An optical information recording medium (optical disk) is a recording medium on which recording / reproduction is performed using laser light, and since there is no need to bring a head into contact with the optical disk, recording / reproduction can be performed at high speed. In addition, by miniaturizing the focal point of laser light, a large amount of information can be recorded and reproduced, and is used in various fields as a large-capacity memory.

  There are two types of optical discs: a read-only type that can only be played, a write-once type that can be played back and recorded once, and a rewritable type that can be played back and repeated. Further, the rewritable optical disk includes a phase change optical disk using a phase change of a recording film and a magneto-optical disk using a change in the magnetization direction of a perpendicular magnetization film. Among these, phase change optical discs are the mainstream of rewritable optical discs because they can record information without using an external magnetic field like magneto-optical discs, and are easy to overwrite information. It's getting on.

  By the way, an optical disk is required to have a larger storage capacity. In order to realize a large capacity, it is preferable to use a laser beam having a short wavelength. Therefore, research on optical disks using laser light having a large energy wavelength of around 405 nm has been conducted.

A phase change optical disk generally includes a dielectric layer, a recording layer, a dielectric layer, and a reflective layer sequentially on a transparent substrate, and records and reproduces the recording layer by making laser light incident from the transparent substrate side. . In general, a material containing Ag as a main component is used for the reflective layer. Ag is less expensive than other noble metal elements, but has a sufficiently high reflectivity for a wavelength of around 405 nm and can increase the signal amplitude. In addition, it has high thermal conductivity and is suitable for high-speed recording. In general, ZnS—SiO ₂ is used for the dielectric layer. ZnS—SiO ₂ has a high refractive index, has a high film formation rate, and is suitable for mass productivity.

By the way, in the phase change optical disk, the semi-transmissive layer and the reflective layer mainly composed of Ag are easily sulfided, and sulfur (S) is diffused from the ZnS-SiO ₂ dielectric layer due to the temperature rise at the time of laser light irradiation. There was a problem that the layer and the semi-transmissive layer were sulfided. If the reflective layer or the semi-transmissive layer is sulfided, the optical disk may be deteriorated due to deterioration of properties such as reflection and heat conduction.

To solve the above problem, a method of arranging a barrier layer for the purpose of preventing sulfurization of the reflective layer or the semi-transmissive layer between the reflective layer or semi-transmissive layer containing Ag and the ZnS-SiO ₂ dielectric layer is considered. It is done. An optical disc in which a barrier layer is disposed between a reflective layer or a semi-transmissive layer and a dielectric layer is described in Patent Document 1, for example.
JP 2002-144736 (paragraphs 0056 and 0057)

According to Patent Document 1, by disposing a barrier layer such as SiC, SiN, or GeN between a reflective layer or a semi-transmissive layer and a ZnS-SiO ₂ dielectric layer, mass transfer between these layers is performed. Can be suppressed. However, when the barrier layer is provided, the manufacturing process becomes complicated so that a new problem arises that the cost of manufacturing the optical disk increases.

  In view of the above, the present invention is an optical information recording medium including a reflective layer or a semi-transmissive layer containing Ag, and an optical that can suppress sulfidation of the reflective layer or the semi-transmissive layer without providing a barrier layer. It is an object to provide an information recording medium.

In order to achieve the above object, an optical information recording medium of the present invention is an optical information recording medium for recording and reproducing information by changing the optical characteristics of a recording layer by laser light irradiation.
At least one element selected from the group B consisting of oxides of aluminum, tantalum, silicon, cerium, and hafnium, the main component being an oxide of at least one element selected from group A consisting of niobium and zinc A dielectric layer comprising an oxide of
The dielectric layer is characterized in that the composition ratio of an oxide of an element selected from Group B is 10 mol% or more and 45 mol% or less.

According to the present invention, since the dielectric layer does not contain sulfur, it is possible to prevent sulfurization of a reflective layer or a semi-transmissive layer containing silver (Ag). In addition, since the dielectric layer has a refractive index higher than that of ZnS—SiO _{2, the} degree of freedom in optical design can be increased. Also, because it has a growth rate substantially equal to that of ZnS-SiO _2, it can be maintained high production efficiency.

  In the present invention, a reflective layer containing silver is provided, the reflective layer is disposed on a side farther than the recording layer as viewed from the laser light incident side, and the dielectric layer includes the recording layer and the reflective layer. And may be disposed adjacent to the reflective layer. Alternatively, a translucent layer containing silver is provided, and the transflective layer is disposed on a side farther from the recording layer when viewed from the laser beam incident side, and the dielectric layer includes the recording layer and the transflective layer. And adjacent to the semi-transmissive layer.

  In a preferred embodiment of the present invention, information is recorded / reproduced using laser light having a wavelength of 380 to 430 nm. By using laser light having a short wavelength, the capacity of the optical information recording medium can be increased.

  Hereinafter, the present invention will be described in more detail based on embodiments of the present invention with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing a layer structure of an optical disc according to the first embodiment of the present invention. The optical disc 100 is a rewritable phase change optical disc, for example, a DVD (Digital Versatile Disc). In the optical disc 100, a first dielectric layer 12, a first interface layer 13, a recording layer 14, a second interface layer 15, a second dielectric layer 16, and a reflective layer 17 are sequentially stacked on a transparent substrate 11. ing.

For the recording layer 14, a known recording material such as GeSbTe or AgInSbTe having a thickness of 13 nm is used. For the reflective layer 17, an alloy containing Ag as a main component is used from the viewpoint of achieving both high thermal conductivity and high light transmittance. In order to improve weather resistance, elements such as Pd, Cu, Ge, In, and Nd may be appropriately added to the reflective layer 17. The first dielectric layer 12 is made of ZnS—SiO ₂ having a composition formula of (ZnS) _x (SiO ₂ ) _1-x and in a range of 0.5 ≦ x ≦ 0.9. Thereby, for example, a high refractive index of about 2.3 and a high growth rate can be obtained. The interface layers 13 and 15 are disposed for the purpose of improving the crystallization speed and the number of repeated recording and reproducing operations, and use GeN, SiC, SiN, or the like.

The second dielectric layer 16 has, as a main component, an oxide of at least one element selected from the group A consisting of niobium and zinc, instead of ZnS-SiO ₂ that has been conventionally employed, and aluminum, tantalum, A material containing an oxide of at least one element selected from the group B consisting of silicon, cerium, and hafnium is used. In the second dielectric layer 16, the composition ratio of the oxide of the element selected from the group B is set to 10 mol% or more and 45 mol% or less.

The second dielectric layer 16 has a refractive index of 2.4 to 2.5 and a higher refractive index than ZnS—SiO ₂ . Further, it has a growth rate as high as that of ZnS—SiO ₂ . In the present embodiment, no barrier layer is provided between the second dielectric layer 16 and the reflective layer 17 in order to prevent the reflective layer 17 from being sulfided.

According to the optical disc 100 of the present embodiment, since the second dielectric layer 16 does not contain sulfur, sulfurization of the reflective layer 17 can be prevented. Further, since the second dielectric layer 16 has a higher refractive index than ZnS—SiO _{2, the} degree of freedom in optical design can be increased. Furthermore, because it has a growth rate substantially equal to that of ZnS-SiO _2, it can be maintained high production efficiency.

The high refractive index of the anti-sulfuration or the second dielectric layer 16 of the reflective layer 17, the second dielectric layer 16 as compared with the conventional optical disk using ZnS-SiO _2, greatly improve the repetitive recording Views Can do. If the composition ratio of the oxide of the element selected from group B in the second dielectric layer 16 is set to a value less than 10 mol% or greater than 45 mol%, a sufficient number of repeated recording / reproducing operations cannot be obtained.

  FIG. 2 is a cross-sectional view schematically showing a layer structure of an optical disc (type A optical disc) according to a second embodiment of the present invention. In the optical disc 101, the first dielectric layer 12, the first interface layer 13, the recording layer 14, the second interface layer 15, the second dielectric layer 16, the semi-transmissive layer 31, and the third dielectric layer are formed on the transparent substrate 11. 18 and a fourth dielectric layer 19 are sequentially stacked. These are called the first information layer 50. An optical separation layer 41 is formed on the first information layer 50, and a second information layer 51 is disposed on the optical separation layer 41.

  In the second information layer 51, the reflective layer 22, the fifth dielectric layer 23, the third interface layer 24, the recording layer 25, the fourth interface layer 26, and the sixth dielectric layer 27 are formed on the transparent substrate 21. They are sequentially stacked. In the optical disc 101, a laser beam used for recording / reproducing information is incident from the first information layer 50 side. When manufacturing the optical disc 101, the first information layer 50 and the second information layer 51 described above are formed on separate transparent substrates, and then bonded to each other via an optical separation layer 41 made of an ultraviolet curable resin. Match.

  For the recording layer 14, for example, a general recording material such as GeSbTe or AgInSbTe having a thickness of 7 nm is used. For the semi-transmissive layer 31, an alloy containing Ag as a main component is used from the viewpoint of achieving both high thermal conductivity and high light transmittance. The semi-transmissive layer 31 is formed to a thickness of, for example, 10 nm, and the light transmittance of the first information layer 50 is about 40% to 50% depending on the combination of the third dielectric layer 18 and the fourth dielectric layer 19. Can be set. At present, there is no known metal transflective film other than an Ag alloy thin film that exhibits translucency in the wavelength region of about 405 nm, and the Ag alloy thin film is indispensable as a transflective layer of an optical disc having multiple information layers. One of the materials. Elements such as Pd, Cu, Ge, In, and Nd may be appropriately added to the semi-transmissive layer 31 in order to improve weather resistance.

The first dielectric layer 12 is made of ZnS—SiO ₂ having a composition formula of (ZnS) _x (SiO ₂ ) _1-x and in a range of 0.5 ≦ x ≦ 0.9. Thereby, a high refractive index and a high film formation speed can be obtained. The interface layers 13 and 15 are disposed for the purpose of improving the crystallization speed and the number of repeated recording and reproducing operations, and use GeN, SiC, SiN, or the like.

As in the first embodiment, the second dielectric layer 16 is made of an oxide of at least one element selected from the group A consisting of niobium and zinc, instead of ZnS—SiO ₂ which has been conventionally employed. A material containing an oxide of at least one element selected from the group B consisting of aluminum, tantalum, silicon, cerium, and hafnium as a main component is used. In the second dielectric layer 16, the composition ratio of the oxide of the element selected from the group B is set to 10 mol% or more and 45 mol% or less. In the present embodiment, no barrier layer is provided between the second dielectric layer 16 and the reflective layer 17 in order to prevent the reflective layer 17 from being sulfided.

  The third dielectric layer 18 and the fourth dielectric layer 19 are disposed for the purpose of improving the light transmittance of the first information layer 50. The third dielectric layer 18 is a dielectric layer made of an oxide of at least one element selected from the group consisting of silicon, aluminum, and hafnium, and the fourth dielectric layer 19 is a sulfide. A dielectric layer made of an oxide of zinc and silicon is used. Instead of this, the same material as that of the second dielectric layer 16, or an oxide of Ti or Nb or a mixture of these oxides may be used for the fourth dielectric layer 19.

Further, as a combination of the third dielectric layer 18 and the fourth dielectric layer 19, low refractive index n ₁ of the third dielectric layer 18 than the refractive index n ₂ of the fourth dielectric layer 19, and they A material having a refractive index difference n ₂ −n ₁ of 0.4 or more is used. Thereby, the light transmittance of the first information layer 50 can be sufficiently increased.

  By the way, in the conventional optical disk, in order to prevent diffusion of sulfur contained in the fourth dielectric layer 19 to the semi-transmissive layer 31, the third dielectric layer 18 is used as a barrier layer, and a material such as GeN, SiC, SiN or the like. It consisted of However, when SiC, SiN, GeN, AlN, TiN, or TaN is used for the third dielectric layer 18, there is a difference in refractive index between the fourth dielectric layer 19 and the third dielectric layer 18. Therefore, even if various design changes are made, it is difficult to obtain the first information layer 50 having high light transmittance.

In contrast, the present inventor has found that sulfur diffusion hardly occurs in the third dielectric layer 18 disposed on the side opposite to the recording layer 14 when viewed from the semi-transmissive layer 31. Therefore, in the present embodiment, the third dielectric layer 18 and the fourth dielectric layer are used by using a dielectric layer made of an oxide of at least one element selected from the group consisting of silicon, aluminum, and hafnium. The light transmittance of the first information layer 50 can be effectively improved by increasing the refractive index difference n ₂ −n ₁ with the body layer 19.

According to the optical disc 101 of the present embodiment, in the first information layer 50, as in the first embodiment, the second dielectric layer 16 does not contain sulfur, and therefore the reflective layer 17 can be prevented from being sulfided. As a result, the number of repeated recording / reproducing operations can be greatly improved as compared with a conventional optical disk using ZnS—SiO ₂ for the second dielectric layer 16. Since the second dielectric layer 16 has a higher refractive index than ZnS—SiO _{2, the} degree of freedom in optical design can be increased. Also, because it has a growth rate substantially equal to that of ZnS-SiO _2, it can be maintained high production efficiency.

Further, by using a dielectric layer made of an oxide of at least one element selected from the group consisting of silicon, aluminum, and hafnium instead of the conventional barrier layer, the third dielectric layer 18 is used. The refractive index difference n ₂ −n ₁ between the third dielectric layer 18 and the fourth dielectric layer 19 can be increased, and the light transmittance of the first information layer 50 can be effectively increased. As a result, good recording / reproduction with respect to the second information layer 51 can be performed.

  FIG. 3 is a cross-sectional view schematically showing a layer structure of an optical disc (type B optical disc) according to a modification of the second embodiment. In the optical disk 102, a transparent sheet 32 made of an ultraviolet curable resin is provided in place of the transparent substrate 11 in the optical disk 101 of FIG. In the optical disc 102, laser light used for recording / reproducing information is incident from the first information layer 50 side as in the type A optical disc 101.

  In manufacturing the optical disc 102, first, as the second information layer 51, on the transparent substrate 21, the reflective layer 22, the fifth dielectric layer 23, the third interface layer 24, the recording layer 25, the fourth interface layer 26, After the sixth dielectric layer 27 is sequentially laminated, an optical separation layer 41 made of an ultraviolet curable resin is formed on the sixth dielectric layer 27. Next, guide grooves (not shown) made of lands and grooves are formed on the optical separation layer 41.

  Subsequently, as the first information layer 50 on the optical separation layer 41, the fourth dielectric layer 19, the third dielectric layer 18, the semi-transmissive layer 31, the second dielectric layer 16, the second interface layer 15, the recording After sequentially laminating the layer 14, the first interface layer 13, and the first dielectric layer 12, a thin transparent sheet 32 made of an ultraviolet curable resin and having a thickness of about 100 μm is formed on the first dielectric layer 12. Form.

  According to the optical disc 102 of this modification, although the manufacturing method is different from that of the optical disc 101 shown in FIG. 2, the layer structure seen from the laser light incident side is the same. Therefore, the same effect as the optical disc 101 of the above embodiment can be obtained.

  FIG. 4 is a cross-sectional view schematically showing the layer structure of an optical disc according to the third embodiment of the present invention. In the optical disk 103, the first dielectric layer 12, the first interface layer 13, the recording layer 14, the second interface layer 15, the second dielectric layer 16, the transflective layer 31, and the fourth dielectric are formed on the transparent substrate 11. The body layers 19 are sequentially stacked. These are called the first information layer 50. In the present embodiment, the third dielectric layer 18 in the optical disc 101 of the second embodiment shown in FIG. 2 is not disposed, and the fourth dielectric layer 19 is disposed directly on the semi-transmissive layer 31. ing. An optical separation layer 41 is formed on the first information layer 50, and a second information layer 51 is disposed on the optical separation layer 41.

  The second information layer 51 has the same configuration as the second information layer 51 in the optical disc 101 of the second embodiment shown in FIG. In manufacturing the optical disc 103, the first information layer 50 and the second information layer 51 described above are formed on different transparent substrates, and then bonded to each other via an optical separation layer 41 made of an ultraviolet curable resin. Match.

  For the recording layer 14, a general recording material such as GeSbInTe having a film thickness of 6 nm is used. For the semi-transmissive layer 31, an alloy containing Ag as a main component is used from the viewpoint of achieving both high thermal conductivity and high light transmittance. The semi-transmissive layer 31 is formed with a thickness of 8 nm, for example. Elements such as Pd, Cu, Ge, In, and Nd may be appropriately added to the semi-transmissive layer 31 in order to improve weather resistance.

The first dielectric layer 12 is made of ZnS—SiO ₂ having a composition formula of (ZnS) _x (SiO ₂ ) _1-x and in a range of 0.5 ≦ x ≦ 0.9. Thereby, a high refractive index and a high film formation speed can be obtained. The interface layers 13 and 15 are disposed for the purpose of improving the crystallization speed and the number of repeated recording and reproducing operations, and use GeN, SiC, SiN, or the like.

As in the second embodiment, the second dielectric layer 16 is made of an oxide of at least one element selected from the group A consisting of niobium and zinc, instead of ZnS—SiO ₂ which has been conventionally employed. A material containing an oxide of at least one element selected from the group B consisting of aluminum, tantalum, silicon, cerium, and hafnium as a main component is used. In the second dielectric layer 16, the composition ratio of the oxide of the element selected from the group B is set to 10 mol% or more and 45 mol% or less.

  The fourth dielectric layer 19 is disposed for the purpose of improving the light transmittance of the first information layer 50. In the present embodiment, the fourth dielectric layer 19 has a higher refractive index than the fourth dielectric layer 19 in the second embodiment for the purpose of sufficiently enhancing the optical interference effect with the semi-transmissive layer 31. A material having For example, it is desirable to use the same material as the second dielectric layer 16 or an oxide of Ti or Nb or a mixture of these oxides.

In the present embodiment, although the third dielectric layer 18 in the second embodiment is not provided, the thickness of the recording layer 14 and the semi-transmissive layer 31 is reduced as compared with the second embodiment, and the fourth dielectric is used. By increasing the refractive index of the body layer 19, the light transmittance of the first information layer 50 can be set to about 40% to 50%. The light transmittance value is either the value of the recording layer 14 in the crystalline state (T _c ) or the value of the amorphous state (T _a ).

  By the way, in the optical disk 101 of the second embodiment shown in FIG. 2, depending on the composition of the recording layer 14, the thickness of the recording layer 14 and the semi-transmissive layer 31 may be further reduced. In this case, since the light transmittance in the recording layer 14 and the semi-transmissive layer 31 is increased, the third dielectric layer 18 shown in FIG. 2 is omitted, and the space between the semi-transmissive layer 31 and the fourth dielectric layer 19 is omitted. The light transmittance of the first information layer 50 can be sufficiently increased only by increasing the optical interference effect. In this case, the manufacturing cost can be reduced because the number of layers is reduced.

  Therefore, in the present embodiment, the thickness of the recording layer 14 and the semi-transmissive layer 31 is reduced as compared with the second embodiment, and the fourth dielectric layer 19 having a higher refractive index is directly formed on the semi-transmissive layer 31. By disposing, the light transmittance of the first information layer 50 can be sufficiently increased and the manufacturing cost can be reduced.

[Example 1]
An optical disc was manufactured based on the first embodiment to obtain an optical disc of Example 1. In the optical disk of Example 1, the transparent substrate 11 was a polycarbonate substrate. The first dielectric layer 12 is ZnS—SiO ₂ with a thickness of 50 nm, the recording layer 14 is GeSbTe with a thickness of 12 nm, the first interface layer 13 and the second interface layer 15 are GeN, and the reflective layer 17 is Each formed a film of AgPdCu. With respect to the second dielectric layer 16, optical disks including the second dielectric layer 16 having various film compositions were manufactured by forming films with various film compositions.

As a comparative example, an optical disk in which the second dielectric layer 16 was made of ZnS—SiO _{2 in} the optical disk of Example 1 was manufactured, and the optical disk of Comparative Example 1 was obtained. In addition, an optical disk in which the reflective layer 17 was directly formed on the transparent substrate 11 and a ZnS-SiO ₂ dielectric layer was directly formed on the reflective layer 17 was manufactured, and an optical disk of Comparative Example 2 was obtained.

  After the optical disks of Example 1 and Comparative Examples 1 and 2 were manufactured, the optical disks were initialized for the optical disks of Example 1 and Comparative Example 1, and the film composition of the second dielectric layer 16 and the reflective layer 17 after the environmental test were obtained. The relationship between the presence or absence of sulfuration, the number of repetitive recording / reproducing operations, and the minimum laser light power (recording power) necessary for recording was investigated. Further, the optical disk of Comparative Example 2 was examined for the presence or absence of sulfuration of the reflective layer 17 after the environmental test.

  The conditions for the environmental test were left to stand for 500 hours in an environment where the temperature was 85 ° C. and the humidity was 90%. Since the area where corrosion due to sulfuration has occurred has a color different from that of the normal area, it can be discriminated visually or under a microscope. The number of repetitive recording / reproducing operations was determined by repeatedly overwriting a recording mark having a linear velocity of 6.6 m / sec and a length of 1 μm and reducing C / N by 3 dB. The wavelength of the laser beam was in the range of 380 to 430 nm.

Tables 1 to 3 below show the film composition of the second dielectric layer 16 when two kinds of elements are selected from the group B, and Table 4 shows the film composition of the second dielectric layer 16 when two kinds of elements are selected from the group A. The relationship between presence / absence, number of repeated recording / reproduction (OW), and recording power is shown. Table 1 shows the results when the second dielectric layer 16 is composed of Nb ₂ O ₅ , Al ₂ O ₃ , and Ta ₂ O ₅ . In the table, X, Y, and Z indicate the molar contents of Nb ₂ O ₅ , Al ₂ O ₃ , and Ta ₂ O ₅ , respectively. For the optical disk of Comparative Example 2, only the result of the presence or absence of sulfuration is shown.

Table 2 shows the results when the second dielectric layer 16 is composed of Nb ₂ O ₅ , Al ₂ O ₃ , and SiO ₂ . In the table, X, Y, and Z indicate the molar contents of Nb ₂ O ₅ , Al ₂ O ₃ , and SiO ₂ , respectively.

Table 3 shows the results when the second dielectric layer 16 is composed of Nb ₂ O ₅ , Ta ₂ O ₅ , and SiO ₂ . In the table, X, Y, and Z indicate the molar contents of Nb ₂ O ₅ , Ta ₂ O ₅ , and SiO ₂ , respectively.

Table 4 shows the results when the second dielectric layer 16 is composed of Nb ₂ O ₅ , ZnO, and SiO ₂ . In the table, X, Y, and Z indicate the molar contents of Nb ₂ O ₅ , ZnO, and SiO ₂ , respectively.

  In Tables 1 to 3, paying attention to the number of repetitive recording / reproducing operations, the second dielectric layer 16 is mainly composed of an oxide of niobium selected from the A group, and an oxide of an element appropriately selected from the B group. In addition, when the ratio of the oxide of the element selected from the group B is set to 10 to 45 mol%, it was found that the number of repeated recording / reproducing operations is 1000 times or more, which is greatly improved. This confirmed that a good optical design was made.

  On the other hand, it was found that when the ratio of the oxide of the element selected from the group B was set to a value less than 10 mol% or greater than 45 mol%, a sufficient number of repeated recording / reproducing operations could not be obtained. The former is because the recording power is increased by increasing the thermal conductivity of the second dielectric layer 16, and the latter is the second dielectric layer 16 by the relatively low refractive index of the second dielectric layer 16. This is considered to be because it is necessary to increase the thickness of the body layer 16 and the heat generated in the recording layer 14 is not easily transmitted to the reflective layer 17 having high thermal conductivity.

  From Table 4, it can be seen that the second dielectric layer 16 is mainly composed of an oxide of niobium selected from the group A and an oxide of zinc, and includes an oxide of silicon selected from the group B. Results similar to ~ 3 were obtained.

In Tables 5 and 6 below, when one type of element is selected from each of Group A and Group B, the film composition of second dielectric layer 16, the presence or absence of sulfuration, the number of repeated recording / reproduction (OW), and recording Shows the relationship with power. Table 5 shows the results when the second dielectric layer 16 is composed of Nb ₂ O ₅ and Al ₂ O ₃ . In the table, X and Y indicate the molar contents of Nb ₂ O ₅ and Al ₂ O ₃ , respectively.

Table 6 shows the results when the second dielectric layer 16 is composed of Nb ₂ O ₅ and Ta ₂ O ₅ . In the table, X and Y indicate the molar contents of Nb ₂ O ₅ and Ta ₂ O ₅ , respectively.

  From Tables 5 and 6, when one kind of element is selected from each of Group A and Group B, the ratio of the oxide of the element selected from Group B is 10 to 45 mol%, as in Tables 1 to 4. It was found that the number of repetitive recording / reproducing operations was 1000 times or more, and the number of repeated recording / reproducing operations was greatly improved.

  In addition to Tables 1 to 6, the second dielectric layer 16 has an oxide of one kind of element selected from the group A, and an oxide of one kind of element selected from the group B other than aluminum and tantalum. It was confirmed that the same effect can be obtained even when a protective film material containing is used. Furthermore, it is an oxide other than the oxides shown in Tables 1 to 6 and mainly contains an oxide of at least one element selected from the group A consisting of niobium and zinc, and includes aluminum, tantalum, silicon, and cerium. The same results were obtained for the dielectric layer containing an oxide of at least one element selected from the group B consisting of hafnium.

When focusing on the presence or absence of sulfuration in Tables 1 to 6, corrosion caused by sulfurization was observed when ZnS-SiO ₂ containing sulfur was used for the second dielectric layer 16, but the second dielectric layer 16 When no sulfur was contained, no corrosion due to sulfuration was observed.

By the way, in the optical disk of Comparative Example 2, although the ZnS-SiO ₂ dielectric layer was adjacent to the reflective layer 17, corrosion due to sulfurization was not observed. As a result, when the ZnS—SiO ₂ dielectric layer is disposed between the recording layer 14 and the reflective layer 17, the reflective layer 17 is easily sulfided, whereas the reflective layer 17 sees it. Thus, it was found that when the recording layer 14 was disposed on the side opposite to the recording layer 14, the reflective layer 17 was not easily sulfidized. This is presumably because the potential difference generated between the recording layer 14 and the reflective layer 17 affects the diffusion of sulfur.

[Example 2]
Based on the second embodiment, after the first information layer 50 was manufactured, it was bonded to a dummy substrate to obtain an optical disk of Example 2. In the optical disk of Example 2, the transparent substrate 11 was a polycarbonate substrate. The first dielectric layer 12 is made of ZnS—SiO ₂ with a thickness of 50 nm, the recording layer 14 is made of GeSbTe with a thickness of 7 nm, and the first interface layer 13 and the second interface layer 15 are made of GeN. AgPdCu was formed to a thickness of 3 nm and a thickness of 10 nm on the semi-transmissive layer 31.

The second dielectric layer 16 is a film having a thickness of 15 nm including 60 mol% of Nb ₂ O ₅ , 15 mol% of Al ₂ O ₃ and 25 mol% of Ta ₂ O ₅ among the films formed in Example 1. On the fourth dielectric layer 19, ZnS—SiO ₂ was deposited to a thickness of 110 nm. As for the third dielectric layer 18, an optical disk including the third dielectric layer 18 made of various materials was manufactured by forming a film using various materials.

The optical disk of Example 2 was manufactured, and the refractive index difference n ₂ −n ₁ between the third dielectric layer 18 and the fourth dielectric layer 19, the light transmittance of the first information layer 50, and the number of candidates that can be designed And the relationship with the presence or absence of sulfidation after the environmental test was investigated. Regarding the light transmittance of the first information layer 50, for convenience of design, the sum T of the light transmittance Ta when the recording layer 14 is in the amorphous state and the light transmittance Tc when the recording layer 14 is in the crystalline state was examined. Regarding the number of candidates that can be designed, parameters such as the film thickness of each layer are changed so that the reflectance when the recording layer 14 is in the crystalline state is 4% or more and the reflectance when the recording layer 14 is in the amorphous state is 2% or less. The number that can be designed under the condition was investigated. The wavelength of the laser beam was in the range of 380 to 430 nm. The conditions for the environmental test were the same as in Example 1. Table 7 shows the results.

[Example 3]
As the optical disk of Example 3, in the optical disk of Example 2, the second dielectric layer 16 contains only 70 mol% of Nb ₂ O ₅ and 30 mol% of Al ₂ O ₃ among the films formed in Example 1. An optical disk having a film thickness of 15 nm was manufactured, and the same items as in Table 7 were examined. Table 8 shows the results.

  Focusing on the difference in refractive index, light transmittance, and number of candidates in Tables 7 and 8, the larger the difference in refractive index, the higher the light transmittance and the larger the number of candidates. That is, it has been found that the larger the refractive index difference, the more stable recording / reproduction with respect to the second information layer 51 and the larger the design margin can be obtained.

Further, the refractive index difference was 0.4 or more, and particularly high light transmittance and a large number of candidates were obtained. The difference in refractive index is 0.4 or more because the third dielectric layer 18 has Al ₂ O ₃ , Al ₂ O ₃ —HfO ₂ , HfO ₂ , Al ₂ O ₃ —SiO ₂ , HfO ₂ —SiO _2. And SiO ₂ was used. On the contrary, when ZnS—SiO ₂ was used for the third dielectric layer 18, a particularly low light transmittance was obtained. In general, 85% or more is required as a measure of the light transmittance T (Ta + Tc) of the first information layer 50. The higher this value, the better.

In Tables 7 and 8, focusing on the presence or absence of sulfide, third dielectric layer 18 including the case made of ZnS-SiO _2, corrosion by sulfurization in any of the optical disk was observed. This is considered to be due to the factors described in the first embodiment. However, although it is not necessary to provide the third dielectric layer 18 functioning as a barrier layer, the refractive index is lower than that of the fourth dielectric layer 19 from the viewpoint of increasing the light transmittance of the first information layer 50. In addition, it is preferable to dispose the third dielectric layer 18 having a refractive index difference n ₂ −n ₁ of 0.4 or more.

  It should be noted that the second dielectric layer 16 is not limited to the above-described dielectric layer, and the same effect can be obtained regardless of the dielectric layer in the second embodiment. In the fourth dielectric layer 19, instead of the above-described dielectric layer made of zinc sulfide and silicon oxide, the second dielectric layer 16 in the second embodiment, or an oxide of Ti or Nb, or The same effect can be obtained by forming a film of a mixture of these oxides.

[Example 4]
Based on the third embodiment, after the first information layer 50 was manufactured, it was bonded to a dummy substrate to obtain an optical disk of Example 4. In the optical disk of Example 4, the transparent substrate 11 was a polycarbonate substrate. The first dielectric layer 12 is made of ZnS—SiO ₂ with a thickness of 50 nm, the recording layer 14 is made of GeSbTe with a thickness of 6 nm, and the first interface layer 13 and the second interface layer 15 are made of GeN. AgPdCu was deposited in a thickness of 3 nm and a thickness of 8 nm in the semi-transmissive layer 31.

The second dielectric layer 16 and the fourth dielectric layer 19 were formed with the same protective film material and with various film compositions as in Example 1. Thus, the optical disc of Example 4 including the second dielectric layer 16 and the fourth dielectric layer 19 having various film compositions was manufactured, and the film compositions of the second dielectric layer 16 and the fourth dielectric layer 19 were: The relationship between the light transmittance of the first information layer 50, the number of repeated OWs, and the recording power was examined. Table 9 shows the results when the second dielectric layer 16 and the fourth dielectric layer 19 are composed of Nb ₂ O ₅ , Al ₂ O ₃ , and Ta ₂ O ₅ .

Table 10 shows the results when the second dielectric layer 16 and the fourth dielectric layer 19 are composed of Nb ₂ O ₅ and Al ₂ O ₃ .

Table 11 shows the results when the second dielectric layer 16 and the fourth dielectric layer 19 are composed of Nb ₂ O ₅ and Ta ₂ O ₅ .

  From Tables 9-11, it turns out that the light transmittance of the 1st information layer 50 becomes high, so that content of the oxide of the element selected from B group becomes small. This is because the refractive index of the dielectric layer increases as the content of the oxide of the element selected from Group B decreases. Incidentally, the content of the oxide of the element selected from the group B is preferably in the range of 10 to 45 mol% as described in Example 1 from the balance between the number of repeated OWs and the recording power.

As a modification of the fourth embodiment, in the optical disk of the fourth embodiment, a ZnS—SiO ₂ layer is used for the second dielectric layer 16 as in the conventional case, and between the second dielectric layer 16 and the semi-transmissive layer 31. An optical disc with a barrier layer such as GeCrN or SiN interposed was manufactured. Similar to Example 3, the fourth dielectric layer 19 was made of Nb ₂ O ₅ , Al ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O _5, Al ₂ O _3, etc. It was confirmed that the same effect as 3 was obtained.

  Although the present invention has been described based on the preferred embodiments, the optical information recording medium of the present invention is not limited to the configuration of the above embodiment, and various modifications can be made from the configuration of the above embodiment. In addition, optical information recording media that have been modified are also included in the scope of the present invention.

1 is a cross-sectional view schematically showing a layer structure of an optical disc according to a first embodiment of the present invention. It is sectional drawing which shows typically the layer structure of the optical disk which concerns on 2nd Embodiment of this invention. It is sectional drawing which shows typically the layer structure of the optical disk which concerns on the modification of 2nd Embodiment. It is sectional drawing which shows typically the layer structure of the optical disk which concerns on 3rd Embodiment of this invention.

Explanation of symbols

11: transparent substrate 12: first dielectric layer 13: first interface layer 14: recording layer 15: second interface layer 16: second dielectric layer 17: reflective layer 18: third dielectric layer 19: fourth dielectric Body layer 21: Transparent substrate 22: Reflective layer 23: Fifth dielectric layer 24: Third interface layer 25: Recording layer 26: Fourth interface layer 27: Sixth dielectric layer 31: Transflective layer 32: Transparent sheet 41 : Optical separation layer 50: first information layer 51: second information layer 100, 101, 102, 103: optical disc

Claims (3)

An optical information recording medium for recording and reproducing information by changing the optical characteristics of the recording layer by laser light irradiation ,
A reflective layer containing silver and disposed on a side farther than the recording layer as viewed from the laser beam incident side;
In an optical information recording medium having a dielectric layer disposed between the recording layer and the reflective layer and adjacent to the reflective layer,
It said dielectric layer is an oxide of at least one element selected from the group A consisting of niobium and zinc as main components, and, aluminum,及 beauty, of at least one selected from the group B consisting of hafnium see containing the oxides of the elements, the composition ratio of the oxide of an element selected from the group B, the optical information recording medium which is characterized in that not more than 45 mol% with 10 mol% or more. An optical information recording medium for recording and reproducing information by changing optical characteristics of a recording layer by laser light irradiation,
Silver only contains a semi-transmissive layer disposed on the side farther than the recording layer when viewed from the incident side of the laser beam,
In an optical information recording medium having a dielectric layer disposed between the recording layer and the semi-transmissive layer and adjacent to the semi-transmissive layer ,
The dielectric layer is mainly composed of an oxide of at least one element selected from group A consisting of niobium and zinc, and at least one element selected from group B consisting of aluminum and hafnium. An optical information recording medium , wherein the composition ratio of the oxide of the element selected from Group B is 10 mol% or more and 45 mol% or less . The optical information recording medium according to claim 1 or 2 , wherein information is recorded / reproduced using a laser beam having a wavelength of 380 to 430 nm.

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