JP2507592B2 - Optical recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical recording medium for recording / reproducing / erasing information by using light from a laser or the like. More specifically, it relates to an optical recording medium having a metal film as a protective layer and / or a reflective layer.

[Prior Art] Various studies have been conducted on optical recording media as high-density, large-capacity information recording media. In particular, information rewritable magneto-optical recording media have a wide range of application fields and various materials and systems have been announced, and their practical application is expected.

As the above-mentioned magneto-optical recording material, for example, JP-A-52-31
TbFe described in JP 703, TbF described in JP-A-58-73746
There are already many proposals such as eCo and DyFeCo. However, in order to put these magneto-optical recording media into practical use, it is said that further improvement in recording / reproducing characteristics and durability is required.

As a solution to this, in order to improve the recording / playback characteristics,
A method of providing a transparent dielectric layer between the transparent substrate and the recording layer,
And / or a method of providing a reflective layer on the back surface of the recording layer has been studied. These are due to the enhancement effect
It is intended to enhance the apparent magneto-optical effect and improve the CN ratio. Various studies are currently being conducted on the reflective layer, but in order to increase the reproduction CN ratio, a performance index √R ·
It is necessary to increase θk (R: reflectance, θk: Kerr rotation angle), and for that purpose, it is said that it is preferable to use Al, Cu, Ag, Au or the like having high reflectance as the reflective film. However, since these materials have high thermal conductivity, there is a drawback in that the heat is diffused greatly when the bit is recorded by heating with a laser beam, the bit shape is disturbed, and the CN ratio is lowered.

In addition, if this metal reflective layer also serves as a protective layer for preventing corrosion of the recording layer, the structure will be simple, but the above-mentioned Al, Cu, Ag, Au, etc. will There is a problem of generation of holes, and when an organic protective layer is further provided to further improve durability, the recording layer and / or the metal layer itself is deteriorated by chlorine and acid remaining in the resin. However, it has been found that further improvement of such a metal layer is necessary.

[Object of the Invention] The present invention has been made in view of the above circumstances, and is the recording / reproducing characteristics and durability of an optical recording medium provided with a metal film as the protective layer and / or the reflective layer, particularly, the magneto-optical recording medium. The purpose is to further improve. In particular,
By improving the moisture resistance and acid resistance of the metal film to improve the durability of the entire medium, and improving the metal film to have a practically sufficient reflectance and low thermal conductivity, the recording bit shape can be improved. It is intended to improve the recording / reproducing characteristics by stabilizing and stabilizing the amount of reflected light of the reproduced signal.

[Structure / Operation of the Invention] The above-mentioned object is achieved by the present invention described below.

That is, the present invention provides an optical recording medium having a metal film as a protective layer and / or a reflective layer, wherein the metal film is Al, Cu, Ag, A
at least one metal element M selected from the group consisting of u
It is an optical recording medium characterized by comprising an alloy of Re and Re.

The present invention described above has been made as follows. That is, various investigations were performed by focusing on the addition of other elements to solve the drawbacks of the metal film of Al, Cu, Ag, and Au with good reflection performance described above, and by adding Re, reflection consisting of only Al, Cu, Ag, Au Sensitivity at the time of bit recording, and
It was made by finding that the CN ratio is improved and the durability of the medium is also greatly improved. The improvement is that the addition of Re reduces the thermal conductivity of the metal film and suppresses the diffusion of heat during bit recording, thus stabilizing the bit shape and improving the moisture resistance of the film itself. It is thought that this is due to the improved acid resistance.

From the above points, the metal film of the present invention, Al, C with good reflection performance
It is composed of an alloy M _100-x Re _x (x is atomic%) of at least one metal element M selected from the group consisting of u, Ag and Au and Re. The Re content x in this alloy film is 1 at (atom)% or more from the viewpoint of suppressing thermal diffusion during recording and enhancing durability of the film itself and the entire medium. From the viewpoint of improving the durability of the protective layer, the larger Re is, the more preferable. However, from the practical viewpoint of cost and the like, the protective layer is preferably 95 at% or less.
Further, if the content of Re is too large, the reflectance decreases, so that when used as a reflective layer, it is preferably 80 at% or less. Furthermore, considering that Re is expensive, the Re content x is 50 at in both cases.
% Or less is particularly preferable.

Further, from the characteristics of the metal film of the present invention, by providing the metal film between the transparent substrate such as a magneto-optical recording medium and the recording layer, particularly when a plastic substrate is used, the substrate to the recording layer is changed. The diffusion of moisture, oxygen, chlorine, etc. can be suppressed, and the oxidation resistance and moisture permeability can be improved. In particular, by providing the transparent dielectric layer and the recording layer, the moisture from the dielectric layer to the recording layer can be improved. The diffusion of oxygen, chlorine, etc. is suppressed, and the durability of the entire medium can be improved.

The thickness of this metal film needs to be 50 Å or less from the viewpoint of recording / reproducing from the substrate side, and particularly 20 Å or less from the viewpoint of increasing the CN ratio of the medium. On the other hand, when the metal film is used as the reflective layer, the film thickness of 500 Å or more is sufficient.

By the way, in the metal film made of the above-mentioned alloy M _100-x Re _x ,
Furthermore, by adding at least one additive element N selected from the group consisting of Cr, Ti, Ta, and Zr, it is possible to further improve the protective performance of the metal film, specifically, acid resistance and moisture permeability. The durability of the medium can be further improved. Its composition is the elemental composition of this alloy film expressed by the general formula (M _100-x Re _x ) _100-y N _y (x,
When y is expressed in atomic%), the content x of the metal element M is as described above. Further, the range of the content y of the additional element N can be improved by increasing the addition amount, but it is necessary to set it so that the reflectance of the alloy film itself is not excessively lowered, and preferably 50 at % Or less, more preferably 30
It is at% or less.

As a method for producing the metal film in the present invention, known vacuum vapor deposition method, physical vapor deposition (PVD) such as sputtering method, etc.
Although it is formed by a thin film forming method such as a sputtering method, it is preferable to form a film with high adhesiveness at the interface in order to prevent peeling and cracking that occur in the high temperature and high humidity environment resistance test. For this purpose, the sputtering method is used. Is preferred.

As the recording layer of the optical recording medium of the present invention, all known pit systems of compact discs, magneto-optical recording systems, phase change recording systems and the like can be applied, but among them, it is effectively applied to the magneto-optical recording system having the above-mentioned problems. it can. The recording layer of such a magneto-optical recording system may be any layer capable of recording / reproducing by the magneto-optical effect, and it has a direction of easy magnetization in a direction perpendicular to a known film surface, and a magneto-optical layer is formed by forming an arbitrary inversion domain. A magnetic metal thin film capable of recording / reproducing information based on the effect, for example, a known TbFeCo alloy, GdTbFe alloy, NdDyFeCo alloy, NdFe alloy, PrFe alloy, CeFe alloy or the like can be applied. These can be produced by a known vacuum vapor deposition method, sputtering method or the like.

As the transparent substrate of the optical recording medium of the present invention, a polycarbonate resin, an acrylic resin, an epoxy resin, a 4-methyl-pentene resin, or the like, or a synthetic resin substrate or a glass substrate made of a copolymer thereof can be applied. A polycarbonate resin substrate is preferable in terms of heat resistance, heat resistance, moisture permeability, and cost.

In the optical recording medium of the present invention, the transparent dielectric layer provided between the recording layer and the substrate and / or the transparent dielectric layer provided on the opposite side of the recording layer from the substrate in order to obtain an enhancing effect due to interference is recorded from the outside. In order to prevent oxygen, moisture, chlorine, etc. from entering the layer, a material with few cracks and pinholes is preferred. AIN, MgF ₂ , ZnS, CeF ₃ AlF ₃ 3NaF, SiN ₄ , SiO, SiO ₂ , Ti
_{O 2, ZrO 3, InO 3} , SnO 2, AlO 3, TaO 5, nitrides such as BiO _3, fluorides, oxides, can be applied, such as sulfides, or complexes thereof. These can be produced by a known vacuum vapor deposition method, sputtering method, or the like.

 The effects of the present invention described above are as follows.

In an optical recording medium having a metal film as a protective layer and / or a reflective layer on a transparent substrate, a known metal such as Al, Cu, Ag, Au or an alloy thereof is used as a metal layer as described above. When a disk is constructed, since these materials have high thermal conductivity, when the bit is recorded by heating with a laser beam, the heat is largely diffused from the heated portion to the metal layer, and the recording bit shape is disturbed. , CN ratio will also decrease. On the other hand, according to the present invention, an optical recording medium using an alloy film of at least one kind of metal element selected from the group of Al, Cu, Ag, and Au and Re metal has a recording bit shape as described later in Examples. There is no disturbance and the CN ratio can be improved. It is considered that this is because the thermal conductivity of the alloy film was small, so that the thermal diffusion from the heated portion by the laser light was small and the bit shape was stabilized.

Further, the optical recording medium using the Re alloy film, Al, Cu,
As compared with the case where a metal film made of a metal such as Ag or Au or an alloy thereof is used, the durability in the accelerated deterioration test under a high temperature and high humidity atmosphere is significantly improved as in the examples described later. This is considered to be because the addition of the Re metal improved the acid resistance and moisture permeability of the film itself. This effect is particularly effective for long-term stability under normal environment. This point can be confirmed by the fact that no pinholes due to oxidation of the magneto-optical recording layer were found in the disk using the Re alloy film of the present invention in Examples described later.

Further, by providing the Re alloy film of the present invention between the substrate and the optical recording layer, factors causing deterioration such as oxygen, chlorine, and moisture from the substrate and / or the transparent dielectric layer are recorded in the recording layer. It is possible to prevent intrusion.

Furthermore, by adding one or more elements selected from the group consisting of Cr, Ti, Ta, and Zr to the aforementioned Re alloy film of the present invention,
The durability of the medium can be further improved.

As described above, the present invention is an optical recording medium having a metal film as a protective layer and / or a reflective layer, wherein the metal layer is Al, C
It is an alloy film of Re with at least one metal element selected from the group consisting of u, Ag, and Au, and this alloy film is further selected from the group of Cr, Ti, Ta, and Zr. It is an alloy film containing the above metals added, and has realized an optical recording medium with high recording sensitivity, high CN ratio, and excellent environmental resistance, which makes a great contribution to industry. is there.

Examples in which the present invention is applied to a magneto-optical recording medium will be described below. The present invention is not limited to this embodiment.

Examples 1 to 8 The magneto-optical recording medium having the structure shown in FIG. 1 was prepared and evaluated as follows.

A polycarbonate resin (PC) disk substrate 1 having a diameter of 130 mm and a thickness of 1.2 mm and having a group of 1.6 μm pitch is used as a vacuum for a 3-target high-frequency magnetron sputtering device (SPF-430H type manufactured by Anerva Co., Ltd.). Fix in the bed and evacuate to below 4 × 10 ^-7 Torr. In the film formation, the substrate 1 was rotated at 15 rpm around the substrate center point.

Next, an Ar / N ₂ mixed gas (N ₂ content: 30 Vol%) was introduced into the vacuum chamber, and the flow rate of the Ar / N ₂ mixed gas was adjusted so that the pressure was 5 mTorr. The target is 100mm in diameter and thickness
A disc made of a sintered body of 5 mm and having an Al ₅₀ Si ₅₀ ratio (subscripts indicate composition (atomic%)) was used. Discharge power was 100 W and discharge frequency was 1
High frequency sputtering was performed under a discharge condition of 3.56 MHz to deposit about 800 Å AlSiN as the dielectric layer 2.

Then, as the front surface protective layer 3, the target was placed on the Al disk and was made of Re, Cr, Ti, T corresponding to the metal film of each sample in Table 1.
Each chip of a and Zr (5x5x1mmt) was changed to the one arranged appropriately, Ar gas (5N) was introduced into the vacuum chamber, and the metal film of the front surface protective layer 3 was about 15Å under the same discharge conditions as above. Deposited. The number of chips was adjusted so that the film composition was the value shown in the column of the metal film composition of each sample of Examples 1 to 8 in Table 1.

Next, as the magneto-optical recording layer 4, the target was Tb ₂₃ Fe ₆₉
A disk of CO ₈ alloy (subscripts indicate composition (atomic%)) was used, and a TbFeCo alloy film of about 400 Å was deposited under the same sputtering conditions as the front protective layer 3 described above.

Next, as the reflective layer 5 which also serves as a protective layer, the target is placed on the target of the front protective layer 3, that is, the disk of Al, and the chips of Re, Cr, Ti, Ta, and Zr are arranged corresponding to the metal film of Table 1. Then, the same metal film as that of the front surface protective layer 3 was deposited under the same sputtering condition as that of the front surface protective layer 3 by about 500Å.

PC / A whose laminated structure is shown in Fig. 1 by the above procedure
Each sample of the magneto-optical recording disk was prepared in which the front protective layer 3 and the reflective layer 5 were made of the metal film shown in Table 1 in the order of lSiN / front protective layer / TbFeCo / reflection layer.

CN ratio (carrier to noise ratio) of each sample,
For the measurement of recording sensitivity, a magneto-optical recording / reproducing device (Nakamichi OMS-1000TypeIII) was used, the disc was rotated at 1800 rpm, a 2.0 MHz signal was recorded by a semiconductor laser, and then reproduced by a 0.8 mW semiconductor laser beam. went. Record
The applied magnetic field during erasing is 500 Oersted. The optimum laser power during recording was set to a value that maximizes the difference between the first harmonic and the second harmonic of the reproduced signal, and the recording sensitivity of each sample was compared with this value. The measurement results are shown in Examples 1 to 8 in Table 1.

When the surface of each sample was visually observed, no pinhole was observed. Next, each of these samples was subjected to an accelerated deterioration test, specifically, 500 at 80 ° C and 85% RH under high temperature and high humidity.
Left for hours. After the test, the CN ratio and recording sensitivity were measured. The results are shown in Examples 1 to 8 in Table 1.

No pinholes were found on the surface of each sample after the accelerated deterioration test.

[Examples 9 to 16] The front protective layer 3 was prepared in the same manner as in Examples 1 to 8.
And a magneto-optical disk composed of PC / AlSiN / front protective layer / TbFeCo / reflective layer shown in FIG. 1 having exactly the same configuration except that the reflective layer 5 is a metal film having the composition shown in Examples 9 to 16 of Table 1. Each sample was prepared and evaluated.

The front protective layer 3 and the reflective layer 5 were also prepared by placing the target on a disk of Ag and using Re, Cr, and Corresponding to each composition of Examples 9 to 16 in Table 1.
Each metal film was deposited under exactly the same conditions and the same thickness as in Examples 1 to 8 except that one in which Ti, Ta, and Zr chips were arranged was used. The accelerated deterioration test of each of the obtained samples, the CN ratio before and after the accelerated deterioration test, and the recording sensitivity were measured in the same manner as in Examples 1 to 8. The results are shown in Examples 9 to 16 in Table 1. Further, when the surface of each sample was observed, Example 1
Similar to ~ 8, no pinhole was observed before and after the accelerated deterioration test.

[Comparative Examples 1 and 2] The front surface protective layer 3 was prepared in the same manner as in Examples 1 to 8.
And a magneto-optical disk composed of PC / AlSiN / front protective layer / TbFeCo / reflection layer shown in FIG. 1 having exactly the same configuration except that the reflection layer 5 is a metal film having the composition shown in Comparative Examples 1 and 2 of Table 1. Each sample was prepared and evaluated.

The front protective layer 3 and the reflective layer 5 are also used as targets for Al, A
Each metal film was deposited under the same conditions and the same thickness as in Examples 1 to 8 except that each disk target of g was used.

The CN ratio and the recording sensitivity of each sample are shown in Examples 1 to 8.
It measured on the same conditions as. The results are shown in Comparative Examples 1 and 2 in Table 1.

When the surface of each sample was observed, no defects such as pinholes were found. When each of the following samples was subjected to the same accelerated deterioration test as in Examples 1 to 8, corrosion occurred on the front surface of the sample, and the CN ratio and recording sensitivity could not be measured.

[Examples 17 to 24] The front protective layer 3 was prepared in the same manner as in Examples 1 to 8.
And a magneto-optical disk composed of PC / AlSiN / front surface protective layer / TbFeCo / reflection layer shown in FIG. 1 having exactly the same configuration except that the reflection layer 5 is a metal film having the composition shown in Examples 17 to 24 of Table 2. Each sample was prepared and evaluated.

The front protective layer 3 and the reflective layer 5 were also prepared by placing a target on a Cu disk on the basis of Re, Cr, corresponding to each composition of Examples 17 to 24 in Table 2.
Each metal film was deposited under exactly the same conditions and the same thickness as in Examples 1 to 8 except that one in which Ti, Ta, and Zr chips were arranged was used. The accelerated deterioration test of each of the obtained samples, the CN ratio before and after the accelerated deterioration test, and the recording sensitivity were measured in the same manner as in Examples 1 to 8. The results are shown in Examples 17 to 24 in Table 2. Further, when the surface of each sample was observed, Example 1
Similar to ~ 8, no pinhole was observed before and after the accelerated deterioration test.

[Examples 25 to 32] The front protective layer 3 was prepared in the same manner as in Examples 1 to 8.
Of the magneto-optical disk composed of PC / AlSiN / front protective layer / TbFeCo / reflection layer shown in FIG. 1 having exactly the same configuration except that the reflection layer 5 is a metal film having the composition shown in Comparative Examples 25 to 32 of Table 2. Each sample was prepared and evaluated.

The front protective layer 3 and the reflective layer 5 were also used as targets for each disk of Au, Re, Cr, corresponding to each composition of Examples 25 to 32 in Table 2.
Each metal film was deposited under exactly the same conditions and the same thickness as in Examples 1 to 8 except that one in which Ti, Ta, and Zr chips were arranged was used. The accelerated deterioration test of each of the obtained samples, the CN ratio before and after the accelerated deterioration test, and the recording sensitivity were measured in the same manner as in Examples 1 to 8. The results are shown in Examples 25 to 32 in Table 2. Further, when the surface of each sample was observed, Example 1
Similar to ~ 8, no pinhole was observed before and after the accelerated deterioration test.

[Comparative Examples 3 and 4] The front protective layer 3 was prepared in the same manner as in Examples 1 to 8.
And a magneto-optical disk comprising PC / AlSiN / front protective layer / TbFeCo / reflection layer shown in FIG. 1 having the same structure except that the reflection layer 5 is a metal film having the composition shown in Comparative Examples 3 and 4 of Table 2. Each sample was prepared and evaluated.

In addition, the front surface protective layer 3 and the reflective layer 5 are also made of Cu, A as a target.
Each metal film was deposited under exactly the same conditions and thicknesses as in Examples 1 to 8 except that each disk target of u was used.

The CN ratio and the recording sensitivity of each sample are shown in Examples 1 to 8.
It measured on the same conditions as. The results are shown in Comparative Examples 3 and 4 in Table 2.

When the surface of each sample was observed, no defects such as pinholes were found. Next, when each sample was subjected to the same accelerated deterioration test as in Examples 1 to 8, corrosion was generated over the front surface of the sample, and the CN ratio and recording sensitivity could not be measured.

From the above results, the optical recording medium having a protective layer and / or a reflective layer of a metal film made of an alloy film of a metal element selected from the group consisting of Al, Cu, Ag, and Au of the present invention and metal Re is Re It was found that the CN ratio, recording sensitivity, and durability of the medium can be improved as compared with a metal film not containing. In addition to Re, Cr, Ti, T
It was found that the durability can be further improved by adding one or more elements selected from the group of a and Zr.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a laminated structure of the magneto-optical disk of the embodiment. 1: Substrate, 2: Dielectric layer, 3: Front protective layer, 4: Magneto-optical recording layer, 5: Reflective layer

Claims (6)

(57) [Claims] 1. An optical recording medium having a metal film as a protective layer and / or a reflective layer, wherein the metal film comprises at least one metal element selected from the group consisting of Al, Cu, Ag and Au and Re. An optical recording medium comprising an alloy film. 2. The optical recording medium according to claim 1, wherein the metal film is a protective layer, and the Re content is in the range of 1 to 95 at%. 3. The optical recording medium according to claim 1, wherein the metal film is a reflective layer, and the Re content is in the range of 1 to 80 at%. 4. The alloy according to claim 1, wherein the metal film is an alloy in which at least one additive element selected from the group of Cr, Ti, Ta and Zr is added to the alloy. Any optical recording medium. 5. The optical recording medium according to claim 4, wherein the content of the additional element is 50 at% or less. 6. The optical recording layer is a magneto-optical recording layer.
Item 5. The optical recording medium according to any one of items 5.