JPH04134653A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To increase a recording speed so as to allow high-degree recording and to improve a writing speed and to increase a performance index so as to improve productivity by constituting a dielectric film of any SiC, SiN, BN, and SiCN contg. hydrogen. CONSTITUTION:A recording film b, the dielectric film c and a reflection film 3 are successively superposed on a substrate a. This film c is constituted of any among the SiC, SiN an BN contg. the hydrogen, by which the film c having the small thermal conductivity is formed. Then, the recording sensitivity of the medium is increased and the use of a semiconductor laser of low output and short wavelength which is heretofore not usable is made usable and, therefore, the recording at a higher density is possible. The writing speed is increased in the high-speed rotation of a disk and further this medium is made of a three- layered structural body, the reflectivity is increased while a large Kerr rotating angle is maintained. The magneto-optical recording medium having the high performance index is formed in this way and since the man-hours for film formation is smaller as compared with the four-layered structural body and, therefore, the productivity is improved.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a magneto-optical recording medium, particularly a dielectric film made of hydrogen-containing Sin, SiN, BN, or SiCN with low thermal conductivity. It has good sensitivity and can reduce the laser output during recording. This allows the use of low-power, short-wavelength semiconductor lasers that are currently not applicable for magneto-optical recording, and enables high-density recording. The present invention relates to a magneto-optical recording medium in which recording is possible even when the disk rotational speed is increased in order to improve recording sensitivity, and information writing speed can also be improved.

(Prior art) In recent years, with the development of the information society, rewritable magneto-optical memories or spouts have been gaining popularity, and magnetic films for these magneto-optical memories are made of rare earth elements such as TbFeCo and transmuted metal elements. Since the Kerr rotation angle that can be obtained with this force-shaping device using a thin film is not very large at about 0.3 degrees, the C during playback is
For the purpose of increasing /N, a device with an apparent Kerr rotation angle of approximately 0.8 degrees is used by utilizing the enhancement effect caused by multiple reflections of dielectric films and reflective films (Japanese Patent Application Laid-Open No. 1983-1999). Publication No. 12428, Special Publication No. 62-27458
(see Figures 1 to 4 of the publication).

Among these, the one currently widely used has a four-layer structure as shown in Figure 4, and this one has a first dielectric film with a refractive index of about 2.0. year,
Although the Kerr rotation angle is attempted to be increased by multiple reflections between the substrate and the recording film, this method has the disadvantage that the effect of increasing the C/N value is not sufficient because the reflectance decreases. be.

Furthermore, since it is desirable for this first dielectric film to be a material that is transparent, has a high refractive index, and has low permeation of oxygen and moisture, SiN films are currently used, or This S is adjusted so that the refractive index is as large as possible in order to cause multiple reflections and obtain a sufficient enhancement effect.
If the amount of nitrogen in the iN film is controlled, the absorption coefficient of the film increases and the reflectance of the medium decreases, which is disadvantageous.Currently, SiN is used due to its light refractive index, transmittance, and properties as a protective film. The material has not appeared.

(Problem to be Solved by the Invention) Therefore, in this magneto-optical recording medium, the dielectric film that was between the substrate and the recording film is provided between the recording film and the reflective film, as shown in FIG. It has also been proposed to produce an enhancement effect by causing multiple reflections of It is possible to create a medium with a large Kerr rotation angle if the film structure is designed so that the values of The disadvantage is that sufficient characteristics cannot be obtained in terms of recording sensitivity.

(Means for Solving the Problems) The present invention relates to a magneto-optical recording medium that can solve the above problems, and is made by sequentially stacking a recording film, a dielectric film, and a reflective film on a substrate. In magneto-optical recording media, the dielectric film is made of hydrogen-containing SiC, SiN, or B.
It is characterized by being made of either N or SiCN.

That is, the present inventors have made various studies to develop a magneto-optical recording medium that does not have the above-mentioned disadvantages of conventionally known magneto-optical recording media. If a recording film, a dielectric film, and a reflective film are sequentially stacked on top, and if this dielectric film is made of hydrogen-containing SiC, SiN, or BN, the dielectric film has a low thermal conductivity. It is possible to increase the recording sensitivity of the medium, and it also allows the use of low-power, short-wavelength semiconductor lasers that could not previously be used, allowing for higher-density recording. It is possible to improve the writing speed by rotating the disk at high speed, and because it has a three-layer structure, it is possible to increase the reflectance while maintaining a large Kerr rotation angle, so it has a high figure of merit. The present invention was completed by discovering that it is possible to create a magneto-optical recording medium, and that productivity can be improved because the number of steps required for film formation is smaller than that of a four-layer structure.

This will be explained in further detail below.

(Function) The present invention relates to a magneto-optical recording medium that has good recording sensitivity and is capable of high-density recording.

The magneto-optical recording medium of the present invention has a substrate a as shown in FIG.
It is said to have a structure in which a recording film C, a power generation material film, and a reflective film d are stacked on top of each other in this order, but this substrate, recording film, and reflective film themselves are all made of known materials. good.

Therefore, this substrate a may be a transparent plate made of glass, quartz glass, polycarbonate resin, polyolefin resin, polymethyl methacrylate resin, etc., on which a tracking guide group is formed, and this has a thickness of 0.
．． The thickness may be 5 to 2 mm. Further, the recording film formed on this substrate is made of a rare earth metal-transition metal element, for example, TbF is made of a rare earth metal such as Tb, [ly, Gd, Nd, etc., and a transition metal element such as Fe, Co, Ni, etc.
e, TbFeCo, GdTbFe, GdDyFeCo
The thickness should be thin enough to allow light to pass through the film in order to obtain a sufficient Faraday effect, but if it is thinned at the 8i edge, it will be vertical. 5 to 40 nm because it will not be possible to obtain a magnetized film and it will not be possible to create a film with good reproducibility.
It suffices to use m. The reflective film used here may be made of i, Au, Ag, Cu, or an alloy containing one of these elements, and the thickness may be set to a level that does not allow light to pass through. If it is too large, heat will escape through the reflective film and the recording sensitivity will decrease, so it may be about 10 to 1100 nm. Incidentally, the formation of the above-mentioned 8th film and the reflective film may be performed by ordinary high frequency or direct current magnetron sputtering method using an inert gas as an atmosphere, and a bias current may be applied during film formation.

On the other hand, since the dielectric film used here has low thermal conductivity, hydrogen-containing SiC, SiN,
It needs to be made of either BN or SiCN, and it needs to cause multiple reflections of light like the first dielectric film in the conventional example (Fig. 4). Since it is not necessary to obtain sufficient reflectance at the interface between the substrate and the dielectric film, the difference in refractive index between the substrate and the dielectric may be small. Also, this SiC, SiN, BN
, When SiCN contains hydrogen, its thermal conductivity decreases, but mixing a large amount of hydrogen also lowers the refractive index, so in conventional four-layer structures, the amount of hydrogen is limited. (Patent application No. 1-279472-2494
However, since the dielectric film of the present invention can be used in a wide range of refractive indexes from 1.3 to 2.5, there is no need to particularly limit the amount of hydrogen. Note that this dielectric film was formed using St, 5iC2SiN, BN in an atmosphere containing argon gas, nitrogen gas, and hydrogen gas.
sputtering using argon gas as a target, or in a mixed gas of argon gas, hydrogen gas, methane, and ethylene.
This can be done by sputtering using C, SiN, or BN as a target. Although the optimal value for the enhancement effect changes depending on the refractive index, the thickness of this film is 10 to 10% because it has a sufficiently low thermal conductivity. 50
It may be in the range of 0r++n, and this provides the advantage that a magneto-optical recording medium with excellent recording sensitivity can be easily obtained.

(Example) Next, examples of the present invention and comparative examples will be given.

Example 1, Comparative Example 1 A glass plate with a diameter of 20 m + nx 60 mm and a thickness of 1 inch was used as a substrate, and a glass plate with a thickness of 25 mm was used as shown in Fig. 5.
The magneto-optical recording medium of the present invention was prepared by sequentially stacking a recording film made of TbFeCo with a thickness of 50 nm, a dielectric film made of SiN containing hydrogen with a thickness of 50 nm, and a reflective film made of λ foil with a thickness of 60 nm. For this reason, as shown in FIG. 4, a first dielectric film made of SiN with a thickness of 1100 nm, a recording film made of TbFeCo with a thickness of 25 r+m, and a second dielectric film made of SiN with a thickness of 50 nm are placed on this glass plate. A magneto-optical recording medium as a comparative example was fabricated by overlapping a dielectric film of 1.0 and a reflective film of Al1 with a thickness of 50 nm.

The film thicknesses of these were controlled so that their reflectances were almost the same, but when we measured their reflectances and their Kerr rotation angles, we obtained the results shown in Table 1. It was confirmed that the inventive product showed almost the same reflectance as the comparative example, but the Kerr rotation angle was large.

Table 1 Example 2, Comparative Example 2 A slide glass with a diameter of 20 mm x 60 mm and a thickness of 1 mm was used as a substrate, and as shown in FIG.
A dielectric film made of hydrogen-containing ON whose refractive index was varied from 1.6 to 2.2 by changing the amount of hydrogen and nitrogen as shown in Figure 6 at ~20 Or+m, and a thickness of about 60 nm.
The magneto-optical recording medium of the present invention is prepared by sequentially depositing a reflective film consisting of one foil, and for comparison, as shown in FIG. nm
The first dielectric film is made of SiN with a thickness of 25 nm.
Recording film made of FeCo, with a thickness of 5 mm and a refractive index of 2.
A second dielectric film made of SiN with a thickness of 0 and a thickness of 6
A magneto-optical recording medium was prepared as a comparative example by sequentially depositing reflective films made of 0 nm A4 foil, and the Kerr rotation angles of these were examined. About the film thickness and refractive index value of dielectric material'fS
The results shown in Figure 7 were obtained, and it was confirmed that in this case, the Kerr rotation angle could be maximized by selecting the film thickness according to the refractive index. As for the film structure, the results shown in the Za diagram were obtained, so in this case, if the refractive index of the dielectric is 2.0 or less, the Kerr rotation angle enhancement effect is sufficient even if the film thickness is optimized. It turns out that's not the case.

Example 3, Comparative Example 3 A polycarbonate resin plate on which a tracking guide group with a diameter of 130 mm and a thickness of 1.2 mm was formed was used as a substrate, and as shown in FIG.
recording film made of TbFeCo, SiC:H, SiN:HlBN with the refractive index (n) and thickness shown in Table 2.
:H, SiCN:)l and a reflective film made of Aft foil with a thickness of 60 nm were sequentially deposited to produce the magneto-optical recording medium of the present invention, and a comparative example was also prepared for comparison. A four-layer film structure having a dielectric film made of SiN, which does not contain hydrogen, used in Example 1 was prepared. Note that the dielectric film in the magneto-optical recording medium of the present invention is Si, SiC, SiN,
Using BN as a target, the gas flow rate ratio during SiC:H film formation was ^r:H2=1:1, and SiN:H, BN:t(
The gas flow ratio during film formation was Ar:N2:Hz-2:2:1, and SiCN:l (the gas flow ratio during film formation was ^r:Nz:
CH3-1:1:1 and sputtered at a gas pressure of 3 x 10-3 torr, and the film thickness was set so that the Kerr rotation angle was about 1 degree based on the refractive index value.

Next, for the four types of optical discs obtained in this way, the wavelength of the recording and reproducing light: 830 nm, the rotation speed
・1.800rpm, frequency
3.7MHz, measurement position: 6 from the center
Under the measurement condition of 0 mm, the optimal recording power during recording (defined as the recording power when the second harmonic is the minimum)
When the C/N value at that time was measured, the results as listed in Table 2 were obtained, and the hydrogen-containing SiC,S
It was confirmed that the optimum recording power was smaller and the C/N value was larger for the dielectric films made of iN, BN, and SiCNIIi than those made of hydrogen-free SiN dielectric films. .

Table 1 (Effects of the Invention) The present invention relates to a magneto-optical recording medium with a novel structure, which is a magneto-optical recording medium in which a recording film, a dielectric film, and a reflective film are sequentially stacked on a substrate as described above. In the medium, the dielectric film is made of hydrogen-containing SiC, SiN, BN,
It is characterized by being made of SiCN,
According to this, the dielectric film has a low thermal conductivity, so the recording speed of the medium can be increased, and low-power, short-wavelength semiconductor lasers that could not be used in the past can be used, allowing for more advanced recording. It is also possible to improve the writing speed by rotating the disk at high speed.Furthermore, because it has a three-layer film structure, it is possible to increase the reflectance while maintaining a large Kerr rotational force, so it has a high figure of merit. This has the advantage of being able to create a magneto-optical recording medium, and it also has the advantage of improving productivity since it requires fewer deposition steps than conventional four-layer structures.

[Brief explanation of the drawing]

1 to 4 are block diagrams of conventionally known magneto-optical recording media,
FIG. 5 shows a configuration diagram of the magneto-optical recording medium of the present invention, and FIG. 6 shows the gas flow rate ratio of H2/Ar+H during production of hydrogen-containing BN in Example 2 of the present invention. FIG. 7 is a correlation diagram between the dielectric film thickness, refractive index, and Kerr rotation angle of the three-layer film structure in Example 2 of the present invention, and FIG. 8 is a correlation diagram with the refractive index in Comparative Example 2. 2 is a diagram showing the correlation between the film thickness of the dielectric film, the refractive index, and the Kerr rotation angle of the four-layer film structure. Figure 6 111111) Nail 1 ■ Hz/(Ar+H2) 17 Figure 8 Yellow, /j (mm) [Figure 8 Film Thickness (mm)

Claims (1)

[Claims] 1. In a magneto-optical recording medium in which a recording film, a dielectric film, and a reflective film are sequentially stacked on a substrate, the dielectric film is made of any one of hydrogen-containing SiC, SiN, BN, and SiCN. A magneto-optical recording medium comprising: 2. The magneto-optical recording medium according to claim 1, wherein the substrate is made of glass, polycarbonate resin or polyolefin resin. 3. The magneto-optical recording medium according to claim 1, wherein the recording film is composed of an alloy of a rare earth element and a transition metal and an additive. 4. The magneto-optical recording medium according to claim 1, wherein the recording film is composed of TbFeCo, a TbFeCo alloy, and additives. 5. The reflective film is Al, Au, Ag, Cu or one of these.
2. The magneto-optical recording medium according to claim 1, which is made of an alloy containing at least one element. 6. The magneto-optical recording medium according to claim 1, wherein the recording film, dielectric film, and reflective film are formed by a sputtering method.