JPH04162233A - Magneto optical recording medium - Google Patents

Abstract

PURPOSE:To improve recording sensitivity and durability by forming a first dielectric film, a recording film, a second dielectric film and a reflecting film sequentially on a substrate and by specifying the refractive index of the first dielectric film and a difference between the refractive indexes of the first dielectric film and the substrate respectively. CONSTITUTION:A first dielectric film, a recording film, a second dielectric film and a reflecting film are formed sequentially on a substrate so as to construct a four-layer structure, and the refractive index of the first dielectric film is made to be 1.4 through 1.8, while a difference between the refractive indexes of the first dielectric film and the substrate is made to be 0.35 or below. As the result, the reflectivity of light on an interface between the first dielectric film and the substrate is about zero and an enhance effect is dependent on multiple reflection on the second dielectric film laid between the recording film and the reflecting film. The reflective index thereof can be selected arbitrarily, and the optimum film thickness of the dielectric film becomes large when the film of which the refractive index is 1.8 or below is used. Consequently, a heat insulation effect between the recording film and the reflecting film becomes large and further the optimum film thickness of the recording film can be made small. According to this constitution, recording sensitivity and durability can be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magneto-optical recording medium, in particular, a method of sequentially forming a first dielectric film, a recording film, a second dielectric film, and a reflective film on a substrate. By configuring the magneto-optical recording medium with a four-layer structure so that the light reflectance at the interface between the first dielectric film and the substrate is approximately zero, the recording sensitivity is increased and the durability is improved. This invention relates to an improved magneto-optical recording medium.

[Prior art] In recent years, with the advancement of the information society, there has been a demand for high-density, large-capacity recording media. Among them, magneto-optical recording has been developed because of its large capacity and rewritable information. Media is attracting attention, and research is being conducted in various fields to further improve it.

In the magneto-optical recording media currently in practical use, the recording film is made of an alloy of rare earth metals and transition metals such as TbFeCo; Since the angle is as small as about 0.3 degrees, in order to increase the C/N during playback, the apparent Kerr rotation angle is reduced to about 0.8 by using the enhancement effect caused by multiple reflections of the dielectric film and reflective film. (Japanese Patent Publication No. 57-1'2428, No. 1)
(See Japanese Patent Publication No. 62-27458, Figures 2 to 4).

[HN3 to be solved by the invention However, as shown in FIG. 3, this magneto-optical recording medium has a three-layer structure in which a dielectric film, a recording film, and a reflective film are sequentially formed on a substrate. A three-layer structure in which a recording film, a dielectric film, and a reflective film are successively formed on a substrate as shown in FIG. 4 is known. As shown in Figure 6, the incident light is multiple-reflected on the dielectric film, but the one that is currently widely used is the first one on the substrate a as shown in Figure 5. dielectric film b, recording film c, N2 dielectric @d, reflection 1
This consists of a four-layer structure in which the first dielectric film has a refractive index of about 2°0, and
As shown in Fig. 7, the Kerr rotation angle is increased by multiple reflections between the substrate and the recording film, and in order to obtain the maximum figure of merit (F■1.), If the film thickness of each layer is optimized, there is a drawback that the recording sensitivity deteriorates because it is necessary to increase the film thickness of the recording film to about 20 nm under the condition that the refractive index of the dielectric is 2°0.

Furthermore, in the recording medium with the three-layer structure shown in FIG. Since the membranes are in direct contact, there is the disadvantage that moisture diffusion from the substrate to the membrane causes deterioration of the 8FM.

[Means for Solving the Problems] The present invention relates to a magneto-optical recording medium that solves these disadvantages, and includes a first dielectric film, a recording film,
In a magneto-optical recording medium having a four-layer structure in which a second dielectric film and a reflective film are sequentially formed, the first dielectric film has a refractive index of 1.4 or more and 1.8 or less, and The dielectric film is characterized in that the difference in refractive index between the dielectric film and the substrate is 0.35 or less.

That is, as a result of various studies aimed at developing a magneto-optical recording medium with good recording sensitivity and superior durability compared to conventional products, the present inventors found that a first dielectric film, a recording film, In a conventionally known magneto-optical recording medium comprising a four-layer structure in which a second dielectric film and a reflective film are sequentially formed, the first dielectric film has a refractive index of 1.4 or more and 1.8 or less, If the difference in refractive index between the first dielectric film and the substrate is set to 0.35 or less, the reflectance of light at the interface between the first dielectric film and the substrate will be approximately zero, so optical In terms of the three-layer structure shown in Figure 4, the enhancement effect is due to multiple reflections in the second dielectric film between the recording film and the reflective film. By fixing it at 20% and optimizing the film thickness of each layer, the recording sensitivity of the medium can be improved by making the recording film thinner than when a material with a high refractive index is used for the first dielectric film. We discovered that this first dielectric film acts as a protective film and can improve its durability.We conducted research on the composition of winter clothing used in this process, and published this book. Completed the invention.

This will be explained in further detail below.

[Function] The present invention relates to a highly durable magneto-optical recording medium with improved recording sensitivity.

The structure of the magneto-optical recording medium of the present invention is a known four-layer structure in which a first dielectric film, a recording film, a second dielectric film, and a reflective film are sequentially formed on a substrate. .

Therefore, in this device, a transparent resin such as glass, polycarbonate resin, or polyolefin resin on which a tracking guide group is formed is used as a substrate, and a first dielectric film, a recording film, a second dielectric film, It is said that a reflective film is formed. This first dielectric film is St,
SiC, which is formed by sputtering using B as a target in an atmosphere of hydrocarbon gas, nitrogen gas, etc.
SiN.

It may be made of BN, 5iCN, 5iBN, 5LCBN, etc., with a thickness of 10 to 5'OOn m, but this material should be transparent, impermeable to oxygen and moisture, and have low thermal conductivity. Since it is desirable that hydrogen gas be introduced into the atmosphere during sputtering, SiC, SiN, BN, 5iCN,
It is preferable to use hydrogen-containing materials such as 5iBN and 5iCBN. The recording film formed on the first dielectric film is made of rare earth metal-transition metal elements, for example, rare earth metals such as Tb, toy, Gd, and Nd, and transition metals such as Fe, Go, and Ni. Tb consisting of the element
Fe, TbFeCo, GdTb-Fe, GdDy
It may be made of an amorphous metal film such as FeCo, but a nonmagnetic metal film such as Pt or Pd and Fe or C may be used.
It can also be applied to other recording films, such as perpendicularly magnetized films with a stacked structure of magnetic metal films such as In order to obtain the effect, it is necessary to make the film thin enough to allow light to pass through it, but if the refractive index of the first dielectric film is set as described above, this may be 8 to 18 nm. The reflective film used here may be made of AfL, Au, ^g, Cu, or an alloy containing one of these elements, and its thickness may be set to a level that does not allow light to pass through. If it is too thick, heat will escape through the reflective film and the recording sensitivity will decrease.
The thickness may be approximately 1100n.

In the magneto-optical recording medium of the present invention, the first dielectric film in this four-layer structure has a refractive index of 1.4 or more and 1.8 or less, and the refractive index between the first dielectric film and the substrate is 1.4 or more and 1.8 or less. The difference is 0.35
According to this, the reflectance of light at the interface between the first dielectric film and the substrate becomes approximately zero, but in order to increase the recording sensitivity of this recording medium, As mentioned above, the refractive index is about the same as that of the substrate, minimizing the reflection of light at the interface between the substrate and dielectric film, increasing the reflectance of the medium, and preventing the intrusion of oxygen and moisture from the substrate, thereby improving corrosion resistance. Since it is necessary to increase the thermal conductivity and to decrease the thermal conductivity, this is a hydrogen-containing SiN, SiC, 8N, 5ill:N.

5iBN, 5iCBN, etc.

Furthermore, in the magneto-optical recording medium of the present invention, the light reflectance between the first dielectric film and the substrate is approximately zero as described above, but this enhancement effect is caused by the enhancement effect as shown in FIG. This depends on multiple reflections in the second dielectric film between the recording film and the reflective film, so the reflectance of this second IT film at the interface between the recording film and the reflective film is big,
Any material that has a high light transmittance at the wavelength of light used for recording and reproduction may be used, such as SiN, which is commonly used.

SiC, BN, 5iCN, 5iBN, 5iCBN
For example, the refractive index is 1.6.
When the thickness is about 45 to 50 nm, the thermal insulation between the recording film and the reflective film is good, and the recording sensitivity of this recording medium is improved, and the thickness of this recording film is also sufficient. In order to obtain a significant enhancement effect, the wavelength can be set to 8 to 18 nm, and the recording sensitivity is also improved from this point of view.

In addition, in the magneto-optical recording medium obtained in this way, the reflectance of light at the interface between the first dielectric film and the substrate is approximately zero, and this first dielectric film acts as an II film. Therefore, this structure also has the advantage of superior durability compared to the three-layer structure shown in Figure N4.

[Example] Next, examples of the present invention will be given.

Example 1 A polycarbonate resin plate of 20 mm + x 60 mm and 1 inch in thickness is used as a substrate, and on this a first dielectric film with a thickness of 20 nm, a recording film with a thickness of 15 nm, and a second dielectric film with a thickness of 50 nm are formed. A magneto-optical recording medium was manufactured by forming a film and a reflective film with a thickness of 50 nm by sputtering in that order.
10. Using 5fN:H as dielectric film, SiC
:) Those using I, those using 5iCN:H, BN
:Those using H, 5iBN:Those using H, 5i
CBN: 6f using H! A total of seven types were made, including one without the first dielectric film and one without the first dielectric film for comparison.

When forming the SiN+)I film, Si was used as the target and the gas flow rate ratio was Ar:Nz:Hz-3:3:1. gas pressure 5x
1O-3 torr, when forming a SiC:H film, St was used as a target and the gas flow rate ratio was Ar:C)I4-1:
1. Gas pressure 5 x 10-” torr, BN:)I
When forming the film, BN was used as the target, and the gas flow rate ratio was ^'': H2 = 2 = 1, gas pressure 5x IQ-s torr.
, When forming a film of 5iCN+H, Si was used as the target, and the gas flow rate ratio was ^r: CH4N2-1:1:4, gas pressure was 5X10-'torr, When forming a film of 5iBN:)l, Si and 8 were used as targets, and the gas The flow rate ratio is ^r
:N2:H2-3:3:1, gas pressure 5 x 1O-3t
orr, 5i When forming a film of CBN:H, Sl and 8 were used as targets, and the gas flow rate ratio was Ar:Na:C)14-
Sputtering was performed at a ratio of 1:1:4 and a gas pressure of sx of 10-3 torr.

Furthermore, TbFeCo was used as the recording film, SfN was used as the second dielectric film, and l was used as the reflective film.

Next, we placed these in an environment with a temperature of 80°C and a humidity of 85%, and conducted an accelerated test for 1,000 hours to examine the changes in coercive force during this time, and the results were as shown in the IT table. However, it was confirmed that the six types of magneto-optical recording media having these first dielectric films had excellent durability.

Example 2 A magneto-optical recording medium was fabricated using a polycarbonate resin plate as a substrate, on which a first dielectric film, a recording film, a second dielectric film, and a reflective film were sequentially formed by sputtering. 5iCN:H was used as the first and second dielectric films, TbFeCo was used as the recording film, and Sodium was used as the reflective film.
I used WS A1. St is used as a target for forming the dielectric film, and Ar, N,, C, etc. are used as the atmospheric gas.
A mixed gas of H4 was used.

Regarding this dielectric film, the refractive index n was changed from 1.6 to 2.4 by changing the gas flow rate ratio in this gas atmosphere, and the reflectance was 20% when the film thickness of the first dielectric was changed. , and other film thicknesses were optimized to maximize the apparent Kerr rotation angle. Also, the figure of merit at this time was F11
The optimum values for the thickness of the recording film and the second dielectric film were calculated and agreed with the experiments. Figure 2 shows the calculation results for the refractive index of 1.4 and the experimental results for the refractive index of 1.6 to 2.4.

Note that 1) in the $2 diagram is the figure of merit Fi1. when the film thickness (X) of the first dielectric film is changed. The maximum value of 2) in Figure 2
, 3) indicates the film thickness of the second dielectric film, the recording film, at which the figure of merit (2) is maximum, where n is the refractive index of the dielectric film, and y is TbFe (:.

The film thickness Z indicates the film thickness of the second dielectric film, and according to this, when the refractive index of the dielectric film is 2.0 or more, the film thickness of the first dielectric film However, if this refractive index is 1.8 or less, a high figure of merit ik can be stably obtained regardless of the thickness of the first dielectric film, and the reflectance is 20%. From 3), the smaller the refractive index is, the thinner the recording film can be, and from 2) the thickness of the second dielectric film is thicker. I know what will happen.

Example 3 A polycarbonate resin disk with a refractive index of 1.58, on which a tracking guide group is formed, with a diameter of 130 mm and a thickness of 1.2 mm is used as a substrate, and a first dielectric material is applied to this. A magneto-optical recording medium was manufactured in which a film, a recording film, a second dielectric film, and a reflective film were formed in this order.The second dielectric film was made of 5iCN:H and had a refractive index of 2.0.
I made a 2fl version of 1.6. In addition, the recording film is made of TbFe.
Co was used, and AJ2 was used for the reflective film. The thickness of each film was 20 nm for the first dielectric film and 50 nm for the reflective film, and the optimal film thicknesses for the recording film and the second dielectric film were selected according to Example 2. When the refractive index of the dielectric is 1.6, the second dielectric film is 48 nm and the recording film is 12 nm, and when it is 2.0, the second dielectric film is 35r+m and the recording film is 14 nm.

Next, when we measured the recording power and C/N value of these, we obtained the results shown in Table 2.
It was confirmed that by decreasing the refractive index of the dielectric film, the 8WA described above can be made thinner and the second dielectric film can be made thicker, so that although the optimum recording power becomes smaller, the C7N value becomes almost the same.

'tS2 Table [Effects of the Invention] The present invention relates to a magneto-optical recording medium with increased recording sensitivity and excellent durability, and as described above, this includes a first dielectric film, a recording film, In a magneto-optical recording medium having a four-layer structure in which a second dielectric film and a reflective film are sequentially formed, the first dielectric film has a refractive index of 1.4 or more and 1.8 or less, and The refractive index of the first dielectric film and the substrate is 0.35 or less, and according to this, the reflectance of light at the interface between the first dielectric film and the substrate is Since it is approximately zero, the enhancement effect depends on multiple reflections in the second dielectric film between the recording film and the reflective film, but this refractive index can be freely selected.
When a dielectric film of 1.8 or less is used, the optimum film thickness of the dielectric film increases, so the insulation effect between the recording film and the reflective film increases, and the optimum film thickness of the recording film can also be made smaller. This recording medium has the advantage that its recording sensitivity can be improved, and it also has the advantage that its durability is improved because the first dielectric film acts as an F1 film.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing multiple reflections of light in the magneto-optical recording medium of the present invention, and 1) in Figure 2 shows the correlation between the film thickness of the first dielectric material with various refractive indexes (n) and the figure of merit ik. Figure, 2 of Figure 2
) is the correlation diagram between the film thickness of the first dielectric film and the film thickness of the second dielectric film when the figure of merit is optimized, and 3) in Figure 2 is the correlation diagram of the film thickness of the first dielectric film when the figure of merit is optimized. 3 to 5 are block diagrams of conventionally known magneto-optical recording media, and FIG. 6 is a diagram showing the relationship between the thickness of one dielectric film and the thickness of a recording film. FIG. 7 is an explanatory diagram showing multiple reflections of light on the recording medium. FIG. 7 is an explanatory diagram showing multiple reflections of light on the magneto-optical recording medium shown in FIG. Fig. 1 Fig. 3 Fig. 5 Fig. 4 Fig. 6 Fig. 2 (+) 1 plan 1/l dielectric material thickness (nml) Figure 2 (3) □M→Beak 1 kyuunero (nm) Figure 7

Claims (1)

[Claims] 1. In a magneto-optical recording medium with a four-layer structure in which a first dielectric film, a recording film, a second dielectric film, and a reflective film are sequentially formed on a substrate, the first dielectric film is The refractive index of the film is 1.4 or more, 1.8
A magneto-optical recording medium, wherein the difference in refractive index between the first dielectric film and the substrate is 0.35 or less. 2. The magneto-optical recording medium according to claim 1, wherein the second dielectric film has a refractive index of 1.4 or more and 1.8 or less. 3. The magneto-optical recording medium according to claim 1, wherein the recording film has a thickness of 8 nm or more and 18 nm or less. 4. At least one of the first and second dielectric films contains hydrogen, such as SiN, SiC, BN, SiCN,
2. The magneto-optical recording medium according to claim 1, which is made of either SiBN or SiCBN.