JPH0831220B2 - Optical recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical recording medium.

[Conventional technology]

A conventional optical recording medium is a method of recording information by causing magnetization reversal by irradiating a focused laser beam focused on a magnetic recording layer, or irradiating a laser beam on a recording layer,
By changing the crystal structure of the recording layer (crystal to amorphous or vice versa, or hexagonal to cubic or vice versa), that is, by recording information by phase transformation, or by irradiating the recording layer with laser light. Make a hole. Alternatively, there is a method of recording information by changing the shape of a recording portion such as forming a bubble.

Particularly, as shown in FIG. 3, the conventional magneto-optical recording medium has a magneto-optical recording layer 32 of TbFe, GdTbFe, GdTbFeCo, TbFeCo, etc. on a plastic substrate (PMMA, PC, epoxy resin, etc.) 31 having guide grooves. Is formed, and a dielectric film 33 such as SiO ₂ is further formed thereon as a protective film. In addition to the plastic substrate, there is one using glass, which has a structure as shown in FIG. 41 is a glass substrate, 42
Is an ultraviolet curable resin layer provided to form a guide groove on the glass substrate. 43 and 44 are magneto-optical recording layers and dielectric films similar to those in FIG. However, the plastic board,
The UV curable resin layer has high hygroscopicity and gas permeability, and even if there is a protective film such as SiO ₂ on the film side, the magneto-optical recording layer is very easy to oxidize, so it is oxidized from the substrate side, resulting in deterioration of magnetic characteristics.
Problems such as film baldness were significant. Therefore, a structure in which a dielectric film is formed on the substrate side and the magneto-optical recording layer is sandwiched is the fifth.
In the figure, 51 is the same plastic substrate 2 as in FIG. 3 is the same glass substrate with UV curable resin as in FIG. 4, and a dielectric film such as SiO ₂ is deposited as 52 on the substrate. Five
3, 54 are magneto-optical recording layers and dielectric layers such as SiO ₂ similar to those in FIGS. 3 and 4.

Furthermore, a structure in which a reflective film is provided in the structure shown in FIG. 5 can be seen. The structure is shown in FIG. 6, and this reflective film is not for improving the weather resistance but for enhancing the magneto-optical effect. Reference numeral 61 is aluminum, copper or the like as the reflection film. However, although this weatherproof structure has improved weather resistance as compared with the structure shown in FIGS. 3 and 4, it is still insufficient in practical use. This is Si
This is because the dielectric film such as O ₂ itself is an oxide and free oxygen oxidizes the magneto-optical recording layer. Therefore, a non-oxidizing dielectric that does not emit free oxygen may be used. However, for plastic substrates (PMMA, PC, epoxy resin, etc.) or glass substrates with UV curable resin, SiO ₂ , TiO ₂ , Al ₂ O _3, etc. If only non-oxide dielectric film such as silicon nitride, aluminum nitride, zinc sulfide, etc. adheres only to the physical dielectric film, does cracking occur during film formation or cracking during weathering test? Either way, it could not be put to practical use. Therefore, in order to improve the weather resistance for practical use, the magneto-optical recording layer itself has weather resistance (Journal of the Japan Society for Applied Magnetics, Vo18, No.2, 1984, P105, 8th Annual Meeting of the Japan Society for Applied Magnetics). (P. pp. 125, etc.), or using a metal such as Al, Ti, etc. for the protective film to provide weather resistance (8th Annual Meeting of the Japan Society for Applied Magnetics, P. 148). Even with these improvements, it is impossible to prevent oxidation from the side of the substrate, and therefore it has been attempted to use only glass for the substrate itself, and the guide groove itself is also made of glass (No. 7).
Proceedings of the Annual Meeting of the Japan Society for Applied Magnetics P155, P8) However, although this has sufficient weather resistance and can be practically used, it is not mass-produced to form the guide groove in the glass, and the cost is very high, and it is not a method that can be put to practical use.

[Problems and objects to be solved by the invention]

Therefore, the present invention is to solve the above-mentioned problems, and an object thereof is to provide a non-oxide dielectric on a plastic substrate (PMMA, PC, epoxy resin, etc.) or a glass substrate with an ultraviolet curable resin. It is an object of the present invention to provide an optical recording medium which is inexpensive and has excellent weather resistance by adhering the film without cracking.

[Means for solving problems]

The optical recording medium of the present invention is an optical recording medium in which at least a dielectric film, a magneto-optical recording film, and a reflective film are laminated on a disk-shaped substrate, and the dielectric film is aluminum nitride,
It is characterized in that it is a composite film with at least one selected from the group consisting of titanium nitride, zirconium nitride, hafnium nitride and zinc sulfide.

[Action]

Conventionally, if a non-oxide dielectric film is formed on a transparent disk substrate (particularly a plastic substrate), cracks will occur during the film formation, or cracks will occur during the weather resistance test. I couldn't do it. However, if the film thickness is thin, cracks do not occur during film formation, and when cracks occur, the direction of cracks may be circumferential or radial depending on the components of the dielectric film. It has been found.

Therefore, according to the above configuration of the present invention, a composite dielectric film is provided in which at least two components of a dielectric component in the case where the direction is the circumferential direction and at least two components in the case where the direction is the radial direction are mixed are provided. As a result, an optical recording medium having excellent weather resistance without cracking can be obtained.

[Proposed Example 1] FIG. 1 is a structural diagram of a magneto-optical recording medium in which the dielectric films of the present invention are laminated in three layers. 1 is a PMMA substrate with a groove, a groove pitch is 1.6 μm, a groove width is 0.8 μm, It has a groove depth of 700Å. The dielectric film formed on the groove side of this PMMA substrate is 2.
3 and 4 according to the present invention. 2 is an aluminum nitride film 250Å, 3 is a silicon nitride film 500Å, 4 is an aluminum nitride film 250Å. Further, a magneto-optical recording layer GdTbFe film 300Å is formed as 5 thereon, and 6 is an amorphous silicon film 1
The polarization plane of the laser light that has passed through the magneto-optical recording layer 5 is enhanced at 50 Å. Then, an aluminum film 7 having a thickness of 300 Å was formed as a reflection film.

The magneto-optical recording medium having the structure according to the present invention and the conventional structure, that is, the dielectric of 2.3.4 in FIG. 1 is SiO ₂ 1000.
Fig. 7 shows the results of accelerated tests in a constant temperature bath at 60 ° C and 90% RH, prepared by replacing with Å and further by replacing with 1000Å of silicon nitride. The vertical axis is the product of the square root of the reflectance and the force-rotation angle and is generally called the figure of merit, which is almost proportional to the C / N of the medium, and the higher the better. The horizontal axis is the time when the acceleration test was performed. 80 is the magneto-optical recording medium of the present invention, 81 is a dielectric using only silicon nitride, 82 is a dielectric using only aluminum nitride, and 83 is a dielectric using only SiO _2. . As can be seen from this figure, the magneto-optical recording medium according to the present invention does not deteriorate in performance at all and can be used practically. Meanwhile dielectric is oxidized to SiO ₂ Hazugu, impractical. And even in the 81/82 medium using nitride as the dielectric, there is considerable deterioration in performance and there is a problem in practical use.Furthermore, as mentioned above, nitride is difficult to adhere to the plastic substrate and cracks occur. In this weather resistance experiment, cracking starts to occur after about 10 hours, and the performance index is not so bad as that of SiO _2, but cracking occurs immediately, which is not practical. On the other hand, as a matter of course, the medium 80 of the present invention does not cause cracking even after 1000 hours.

Here, the reason why the silicon nitride and aluminum nitride of the medium of 81 and 82 are set to 1000 Å thickness is the same as the total thickness of the dielectric layer of the medium 80 of the present invention, in addition to the silicon nitride and aluminum nitride plastic substrates ( The film thickness is 20 for glass substrates with PMMA, PC, epoxy resin, etc.) and UV curable resin.
This is because if it exceeds 00Å, a crack will occur at that point.

Other than this experiment, 81,82 media with silicon nitride and aluminum nitride film thickness of 1500Å and 2000Å are also at 60 ° C.
In an accelerated test in a constant temperature and humidity chamber of 0% RH, a crack was generated immediately as in Fig. 7, which was not practical.

8 (a), (b) and (c) schematically show the states of the media 80 ', 81' and 82 'after the acceleration test shown in FIG.
80 ', 81', 82 'correspond to 80, 81, 82, respectively. 80 'is a medium in which a laminated film of aluminum nitride and silicon nitride is used for the dielectric according to the present invention, and no crack is generated (a). Reference numeral 81 'is a medium in which only silicon nitride is used as a dielectric, and cracks are generated in the circumferential direction (b). Reference numeral 82 'is a medium in which only aluminum nitride is used for the dielectric, and cracks are generated in the radial direction (c). The substrate used in this experiment had a diameter of 12 cm and was cut to 1/4. In addition, a weather resistance test (60 ° C 90% RH) shows Bit Erro
The effect of investigating how the r Rate increases is shown in FIG. 9. 80 ″, 81 ″, 82 ″, 83 ″ is a structure corresponding to 80, 81, 82, 83, and 80 ″ is according to the present invention. In the medium having the structure shown in FIG. 1,
81 ″ is the one using silicon nitride as the dielectric, 82 ″ is the one using aluminum nitride as the dielectric, and 83 ″ is the one using Si as the dielectric.
It uses O ₂ . The vertical axis represents the Bit Error Rate and the horizontal axis represents the weather resistance test elapsed time. As is clear from this figure, the BER does not increase in the medium 80 ″ according to the present invention, but the BER increases sharply in the medium having other structures.
The medium shown in 3 ″ is severely deteriorated, and the part indicated by the broken line shows that the BER which cannot be measured is increased. The medium of the present invention based on the results of this accelerated test has a reliability of 10 years or more. Can be guaranteed.

[Proposed Example 2] Next, various dielectric films were formed on a PMMA substrate in an amount of 1000 liters, and a weathering test was performed. The results are shown in Table 1.

Therefore, a dielectric that causes cracks in the radial direction and a dielectric that causes cracks in the circumferential direction were laminated on PMMA by 500Å each, and it was investigated whether or not the cracks would occur in an acceleration test at 60 ° C, 90% RH, 1000 hours. The results are shown in Table 2.

From the above results, it was found that a dielectric without cracking can be formed by laminating a dielectric with cracking in the radial direction and a dielectric with cracking in the circumferential direction. The magneto-optical recording medium using the laminated dielectric film shown in Table 2 showed no deterioration in the performance index and BER in the accelerated test.
It was able to guarantee reliability for over 0 years. Further, as a matter of course, there is no problem even if the number of layers is three or four, and in the second embodiment, a dielectric film whose cracks are generated in the radial direction is formed first. There is no problem even if the dielectric film is cracked in the circumferential direction. In addition to the PMMA substrate, the present invention is also effective for PC substrates, epoxy resin substrates, and glass substrates with an ultraviolet curable resin.

〔Example〕

Next, FIG. 2 is a cross-sectional view of a magneto-optical recording medium in which a composite dielectric film is provided between the magneto-optical recording layer and the transparent substrate in the present invention. 8 is a PC board with a groove having a groove pitch of 1.6 μm, a groove width of 0.8 μm, and a groove depth of 700 Å. It is 9 that 1000 liters of composite dielectric film is formed on the groove side of this PC substrate, which is a composite of aluminum nitride and zinc sulfide. A magneto-optical recording layer GdTbFeCo film 300Å was formed thereon as 10, an amorphous silicon 150Å was formed as 11 and an aluminum film 300Å was formed as 12 as a reflective film. As a result of conducting an accelerated test at 60 ° C and 90% RH on this medium, no crack was generated even after 1000 hours, and neither the figure of merit nor the BER was changed, as with the medium using a multilayer dielectric film.

Therefore, even if a composite dielectric film is used, the reliability of the medium will be improved.
I knew that I could guarantee for 10 years. Furthermore, 1000 liters of other composite dielectric films were formed on the PC substrate, and the presence or absence of cracks was investigated after 1000 hours of the accelerated test.

 The results are shown in Table 3.

From the results, it was found that a dielectric without cracks can be formed by combining a dielectric with cracks in the radial direction and a dielectric with cracks in the circumferential direction. These composite dielectric films may be formed by simultaneous sputtering, co-evaporation, or sputtering using composite dielectrics as targets or reactive sputtering. Further, as the substrate, other than the PC substrate, a PMMA substrate or an epoxy resin substrate may be used, and a glass substrate with an ultraviolet curable resin may be used without any problem. The magneto-optical recording medium using the composite dielectric film shown in Table 3 has no deterioration in the performance index and the BER in the accelerated test, and can guarantee the reliability for 10 years or more.

In the example using the composite dielectric film according to the present invention, GdTbFeCo was used for the magneto-optical recording layer, but TbFe, TbFeCo, GdFe, G
Even if a heavy rare earth transition metal type magneto-optical recording layer such as dCo, TbCo or TbDyFeCo is used, the present invention is not damaged at all, and light rare earth metals such as Sm and Nd may be added. .
Although the magneto-optical recording medium is described in this embodiment, the crystal structure of the recording layer is changed (crystal to amorphous, or vice versa, or hexagonal to cubic, or vice versa), that is, phase transformation occurs. Then, a hole is formed in the rewritable optical recording medium or recording layer using the reflectance difference as a signal. The present invention is also effective for a write-once type optical recording medium by forming bubbles or causing phase transformation.

〔The invention's effect〕

INDUSTRIAL APPLICABILITY The optical recording medium of the present invention has an effect that it is possible to form a dielectric material which does not cause cracks and provide a highly reliable optical recording medium.

[Brief description of drawings]

FIG. 1 is a sectional view of a magneto-optical recording medium using a multilayer dielectric film. FIG. 2 is a sectional view of a magneto-optical recording medium using a composite dielectric film. FIG. 3 is a sectional view of a conventional magneto-optical recording medium. FIG. 4 is a sectional view of a conventional magneto-optical recording medium using a glass substrate. FIG. 5 is a sectional view of a conventional magneto-optical recording medium in which the magneto-optical recording layer is sandwiched with a dielectric film. FIG. 6 is a sectional view of a conventional magneto-optical recording medium provided with a reflective film. FIG. 7 is an acceleration test diagram in a constant temperature and humidity chamber at 60 ° C. and 90% RH. FIG. 8 (a) is a schematic diagram of a medium after an acceleration test using a laminated film of aluminum nitride and silicon nitride as a dielectric, and FIG. 8 (b) is a diagram after the acceleration test using silicon nitride as a dielectric. Schematic diagram of medium, and FIG. 8 (c)
FIG. 3 is a schematic diagram of a medium after an acceleration test using aluminum nitride as a dielectric. FIG. 9 is a time-dependent change diagram of BER by a weather resistance test at 60 ° C. and 90% RH. 1 ... Grooved PMMA substrate 2 ... Aluminum nitride film 250Å 3 …… Silicon nitride film 500Å 4 …… Aluminum nitride film 250Å 5 …… Magneto-optical recording layer GaTbFe film 300Å 6 …… Amorphous silicon film 150Å 7 …… Reflective film Aluminum film 300Å 8 …… PC substrate with groove 9 …… Composite dielectric film of aluminum nitride and zinc sulfide 1000
Å 10 …… Magneto-optical recording layer GdTbFeCo film 300 Å 11 …… Amorphous silicon 150 Å 12 …… Reflective film Aluminum film 300 Å 31 …… Plastic substrate with guide groove (PMMA, PC, epoxy resin, etc.) 32 …… Magneto-optical recording Layer 33 …… Dielectric film such as SiO ₂ 41 …… Glass substrate 42 …… UV curable resin layer 43 …… Magneto-optical recording layer 44 …… Dielectric layer 51 …… Plastic substrate or glass substrate with UV curable resin 52 …… Dielectric film 53 such as SiO ₂ ...... Magneto-optical recording layer 54 ...... Dielectric layer such as SiO ₂ 61 ...... Reflective film Aluminum, copper, etc. 80 ...... Magneto-optical recording medium of the present invention 81 ...... Only aluminum nitride as dielectric Using only aluminum nitride as the dielectric material 83 Using only SiO _{2 as the} dielectric material 80 Corresponding to 80 '... 81 Corresponding to 81' ... 81 82 '... 82 Compatible with 80 ″ …… 80 Compatible with 81 ″ …… 81 Compatible with 82 ″ …… 82 Compatible with 83 ″ …… 83

Continuation of front page (56) Reference JP 61-80640 (JP, A) JP 61-92459 (JP, A) JP 61-92456 (JP, A) JP 61-22458 (JP , A)

Claims (1)

[Claims] 1. An optical recording medium in which at least a dielectric film, a magneto-optical recording film, and a reflective film are laminated on a disk-shaped substrate, wherein the dielectric film is aluminum nitride, titanium nitride, or zirconium nitride. An optical recording medium, which is a composite film with at least one selected from the group consisting of hafnium nitride, and zinc sulfide.