JPH09320107A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simultaneously realize the increase in density by formation of recording layers to multiple layers and the increase in density by super- resolution reproduction. SOLUTION: The films of a ground surface layer 2, the recording layer 3 for magnetic recording and reproducing and a protective layer 4 are formed on a substrate 1 with guide grooves. A resin layer 5 with the guide grooves is formed on the protective layer 4. The films of a ground surface layer 6, the recording layer 7 for super-resolution reproduction and a protective layer 8 are formed on this resin layer 5. A masking layer exists in the recording layers for super-resolution reproduction. Since this layer has small transmittance and, therefore, the quantity of the reproducing light is decreased by the masking layer. The recording layer 7 distant from the substrate 1 side on which a laser beam is made incident is formed as the recording layer for super-resolution reproduction, by which the degradation in the transmittance by this layer is prevented from affecting the other recording layers. The formation of the recording layers in the multiple layers and the increase of the density by the super- resolution reproduction are simultaneously embodied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium having a plurality of recording layers capable of storing independent information.

[0002]

2. Description of the Related Art Optical recording media capable of accumulating high-density data and capable of high-speed information processing have attracted attention as computer memories. For optical recording media having a diameter of 5.25 inches or 3.5 inches, a magneto-optical type and a phase change type capable of rewriting information have been standardized by the ISO standard, and are expected to be further widely spread in the future. There is. In this optical recording medium, a guide for guiding a laser spot from a pickup of a recording / reproducing apparatus along information, that is, a tracking guide is formed in the form of a concave or convex groove from the inner circumference to the outer circumference of the medium. It is formed into a shape. This groove is called a guide groove. The guide groove will be described in detail. As defined by the ISO standard, a concave portion, ie, a distant portion when viewed from the pickup is called a land, and a convex portion, ie, a close portion is called a groove. .

In order to further increase the data density of such an optical recording medium, it is said that the light source wavelength of the optical head is shortened to reduce the reproduction light spot, thereby enabling reproduction of information recorded at high density. Although the method has been tried, there is a problem that the wavelength of the semiconductor laser used for the light source of the optical head is limited, and that the laser having a short wavelength has insufficient shape and output of the laser light.

[0004] Therefore, even if the wavelength of the light source and the size of the reproducing light spot are the same as they are now, magnetically super-resolution (Magnetically Induced) that can read out information recorded at high density.
A technique called Super-Resolution (hereinafter referred to as MSR) has been proposed. This uses the temperature distribution of the medium in the light spot generated by the combination of the temperature rise of the medium due to the reproduction light and the rotational movement of the medium to detect a part of the signal of the medium entering the light spot as a reproduction signal. This is to prevent the mask from being performed. As a result, the area of the effective aperture from which a signal can be read is smaller than the light spot, and higher-density information can be reproduced.

The RAD system, which is an example of such an MSR magneto-optical disk, will be briefly described with reference to FIG. FIG.
(A) is a plan view of a RAD type MSR magneto-optical disk,
FIG. 3B is a sectional view taken along the line AA of FIG. The RAD type MSR magneto-optical disk 21 has a recording layer 22.
And a reproduction layer 23 formed on the magnetic layer. Signal reproduction is performed from the reproduction layer side. Then, before reproducing, initialization is performed to align the magnetization direction of the reproducing layer 23 in a fixed direction as shown in FIG.

As shown in FIG. 3A, a reproduction light spot 24 is formed.
Is moved relative to the disk 21, the front area of the disk 21 that has entered the light spot 24 is in the low temperature area 2
5, there is a temperature difference in which the rear side becomes the high temperature region 26.
In the low temperature region 25 in the spot, the magnetization of the reproducing layer 23 shows the direction of the initial state regardless of the presence or absence of the recording mark 27, and serves as a mask that does not contribute to signal reproduction. On the other hand, in the high temperature region 26, the magnetization direction of the reproducing layer 23 is reversed to the magnetization direction of the recording layer 22 by the exchange coupling force (in FIG. 3B, the magnetization direction at the position B is reversed), and signal detection is performed. It functions as an opening that plays a role. Thus, only the recording marks in this area 26 can be read.

On the other hand, as another technique for increasing the data density of the optical recording medium, it is conceivable to make the recording layer multi-layered. If the above-mentioned MSR is applied to this recording layer, further increase in capacity can be expected. However, in the recording film for MSR reproduction, there is a reproducing layer 23 which functions as a masking layer for narrowing the effective opening area from the light spot, and this reproducing layer 23 cannot see through the state of the recording layer 22 therebelow. Since the performance is required, the transmittance is small. Therefore, when an MSR reproducing film having a masking layer is used for an optical recording medium having multiple recording layers, the amount of reproducing beam light obtained by reflection from the recording layer is reduced by the masking layer, and information is reproduced. However, it becomes impossible to secure a sufficient amount of reproduction beam.

[0008]

As described above, in the conventional optical recording medium, the recording layer is multi-layered, and M is added to this recording layer.
When an SR reproducing film is used, the amount of reproducing beam light is reduced by the masking layer, so that information cannot be reproduced, and the recording layer has a higher density and M
There is a problem that it is not possible to achieve high density by SR reproduction at the same time. The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical recording medium capable of simultaneously realizing high density by multilayer recording layers and high density by super-resolution reproduction. And

[0009]

The optical recording medium of the present invention comprises:
A transparent substrate with guide grooves has a plurality of recording layers capable of storing separate information, and the recording layer farthest from the substrate is a recording layer for super-resolution reproduction.
In this way, by making the recording layer farthest from the substrate with the guide groove on which the laser beam enters into the recording layer for super-resolution reproduction, the decrease in transmittance due to the masking layer in this recording layer affects other recording layers. Therefore, it is possible to read information from each recording layer.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION

1. Embodiment 1. FIG. 1 is a sectional view of an optical disc showing a first embodiment of the present invention. First, a method of manufacturing this optical disc will be described. First, a stamper having a guide groove pattern and a glass substrate are prepared. Then, the land 10 and the groove 1 are formed by a 2P method in which an ultraviolet curable resin is injected between the stamper and the substrate to cure the resin with ultraviolet rays.
A resin having a diameter of 1 is formed on a glass substrate.
A transparent substrate 1 with a mm guide groove is prepared.

Subsequently, by sputtering, an underlayer 2 made of SiN having a thickness of 60 nm, a recording layer 3 made of TbFeCo having a thickness of 30 nm, and a protective layer 4 made of SiN having a thickness of 50 nm are formed on the substrate 1 having the guide groove. The film is sequentially formed.
The first recording layer 3 is a recording film for ordinary magneto-optical recording / reproducing that is not MSR, and information can be recorded / reproduced by a known magneto-optical recording / reproducing method.

Next, a UV-curable resin having a thickness of 30 μm is coated on the protective layer 4, and a stamper is put on the resin (or a resin is coated on the stamper, and the above-prepared one is turned upside down). The protective layer 4 may be covered), and the transparent resin layer 5 with guide grooves having the lands 12 and the grooves 13 is formed by the 2P method in which the resin is cured by ultraviolet rays. The step (groove depth) between the land 10 and the groove 11 and between the land 12 and the groove 13 is, for example, 100.
It is about nm.

Then, an underlayer 6 of SiN having a thickness of 50 nm is formed on the resin layer 5 with the guide groove by sputtering. Then, a 30 nm thick Gd ₂₄ Fe ₆₀ Co ₁₆ layer (reproducing layer 2 in FIG. 3) is formed on the underlayer 6.
3), a recording layer 7 in which a Gd ₂₈ Fe ₆₇ Co ₅ layer (intermediate layer) having a thickness of 15 nm and a Tb ₂₀ Fe ₆₆ Co ₁₄ layer (recording layer 22 of FIG. 3) having a thickness of 40 nm are sequentially laminated is formed by sputtering. To do. Furthermore, a thickness of 5 is formed on the recording layer 7.
A protective layer 8 made of 0 nm SiN is formed.

The intermediate layer in the recording layer 7 which is not described in FIG. 3 controls the domain wall energy to reduce the magnitude of the reproducing magnetic field and the initializing magnetic field. Finally, a hard coat (not shown) such as an ultraviolet curable resin is formed on the protective layer 8 to complete the production of the optical disc. In order to produce a double-sided optical disc, the hard coats of the two optical discs produced as described above may be bonded together with an adhesive.

In the optical disk thus manufactured, the second recording layer 7 for reproducing MSR is provided on the side far from the substrate 1 with the guide groove.
Are arranged, and the reason for this will be described next. The laser beam for recording or reproduction enters from the lower side of FIG. 1, that is, from the substrate 1 side with the guide groove. Therefore, the first recording layer 3 is in the optical path of the laser beam for reproducing the second recording layer 7, and the absorption of the recording layer 3 reduces the amount of light reaching the recording layer 7. Similarly, a part of the reproduction light reflected by the recording layer 7 is also absorbed by the recording layer 3, so that the amount of reproduction light used for reading information is reduced. When the recording density is improved by increasing the number of layers, a decrease in the amount of light due to the recording layer in the optical path cannot be avoided.

Here, the reproduction light amount applied to the optical disk is P0, the reflectance of the first recording layer 3 is R1, the reflectance of the second recording layer 7 is R2, and the transmittance of the first recording layer 3 is Assuming that T1 is the absorption coefficient of the substrate 1, the resin layer 5, the underlayers 2, 6 and the protective layer 4 is so small as to be negligible, the reproduction light amount Pr1 by the reflection from the first recording layer 3 and the second recording layer 7
The reproduction light amount Pr2 due to reflection from can be expressed by the following equation. Pr1 = P0 × R1 ··· (1 ) Pr2 = P0 × T1 2 × R2 ··· (2)

As described above, the second recording layer 7 for reproducing MSR has a reproducing layer functioning as a masking layer on the laser beam incident side. Therefore, when the recording layer for MSR reproduction is arranged on the side of the substrate 1 and the recording layer which is not the MSR is arranged on the side far from the substrate 1, the transmittance is lowered due to the masking layer and the information is read from the recording layer which is not the MSR. Can't On the other hand, in the present embodiment, since the recording layer 7 for MSR reproduction is arranged on the side far from the substrate 1, the decrease in transmittance due to the masking layer does not affect other recording layers, and such a problem occurs. Does not occur.

However, as can be seen from the equation (2), the reproducing light amount Pr2 from the second recording layer 7 is influenced by the transmittance T1 of the first recording layer 3. That is, in order to secure a sufficient amount of reproducing light from the recording layer 7, it is desirable to increase the transmittance of the recording layer 3. This can be adjusted by thinning the first recording layer 3, and in the present embodiment, it can be adjusted to 3.
It is set to 0 nm. Note that the thicknesses of the underlayers 2 and 6 and the protective layer 4 also need to be taken into consideration, but the preferable thickness varies depending on the wavelength of the reproducing light, for example, 50 to 7 when the wavelength is 680 nm.
There is no problem if it is about 0 nm.

Further, in the optical disc of the present embodiment, when recording / reproducing information on the second recording layer 7, the focus servo is provided with an offset and the recording / reproducing can be performed by applying the servo to the recording layer 7. Becomes In order to prevent the servo signals of the first recording layer 3 or the second recording layer 7 from being confused, it is necessary to keep the distance ds between the recording layer 3 and the recording layer 7 at a sufficient value.

For example, if the reproduction light has a wavelength of 680 nm, it is possible to avoid confusion of the servo signal by keeping the distance ds of about 20 μm or more. The maximum value of the distance ds is limited by the movable range of the actuator and the tilt of the substrate, and is approximately 500 μm to 1 mm.
it is conceivable that.

Next, as a recording / reproducing test for the optical disk of the present embodiment, first, a recording / reproducing test for the first recording layer 3 was conducted. Here, the optical disc is 240
While rotating at 0 rpm, 300 at a position with a radius of 45 mm
A mark (information) with a length of 0.7 μm at a recording laser power of 5.0 mW by applying an Oe (oersted) magnetic field.
Was recorded. Then, when the C / N of the reproduction signal from the recording layer 3 was measured with a reproduction laser power of 1.5 mW,
A value of 49 dB was obtained.

Next, a recording / reproducing test was performed on the second recording layer 7 by adjusting the offset of the focus servo. Here, 5.6 is applied while applying a magnetic field of 300 Oe.
A mark of 0.43 μm was recorded with a recording power of mW.
Since the recording layer 7 is a recording film for MSR reproduction, an initialization magnet for initializing the reproduction layer immediately after reproduction is required.
By applying the initializing magnetic field of, the reproducing layer in which the magnetization direction is reversed is initialized.

Then, the C / N of the reproduced signal from the recording layer 7 was measured with a reproducing laser power of 1.5 mW, but no signal was obtained. While gradually increasing the playback power, C
When the / N was measured, the highest C / N was obtained at 3.0 mW. The C / N at this time was 41.0 dB.

For comparison, an MSR reproducing optical disk was prepared in which only the underlayer 6, the recording layer 7 and the protective layer 8 were formed on a substrate having guide grooves, and a length of 0.43 μm was obtained under the same conditions as above. 2.5mW when the mark is recorded and played back
C / N value of 45.5dB with the highest reproducing laser power
was gotten. The difference between the C / N value of 45.5 dB of this comparative example and the C / N value of 41 dB of the optical disc of the present embodiment substantially coincides with the decrease of C / N due to the absorption of light from the first recording layer 3. In this way, good C / N is achieved when a short mark is recorded.
From that, it was confirmed that the recording layer 7 was reproduced by MSR.

2 of the embodiment. FIG. 2 is a sectional view of an optical disc showing another embodiment of the present invention, and the same components as those in FIG. 1 are designated by the same reference numerals. Also in the present embodiment, the substrate 1 with the guide groove, the base layer 2, the recording layer 3,
The formation of the protective layer 4 is similar to that of the first embodiment.

Next, a substrate 5a with a guide groove is prepared in the same manner as the substrate 1 with a guide groove. Then, by sputtering, the underlayer 6a made of SiN and the recording layer 7 for MSR reproduction similar to the recording layer 7 are formed on the guide grooved substrate 5a.
The protective layer 8a made of a and SiN is sequentially formed.

Finally, the substrate 1 on which the protective layer 4 has been formed and the substrate 5a on which the protective layer 8a has been formed are bonded together by the air sandwich method. In the air sandwich method, the inner circumference and the outer circumference of the protective layer 4 and the protective layer 8a are bonded with a width of several millimeters. Therefore, as shown in FIG. 2, a space between the protective layer 4 and the protective layer 8a other than the inner circumference and the outer circumference is hollow by the thickness of the adhesive. In this way, it is possible to manufacture an optical disc that achieves the same effects as in the first embodiment.

If the reproducing light amounts Pr1 and Pr2 are greatly different from each other, it becomes difficult to reproduce the first and second recording layers by the same reproducing circuit in the drive device for reproducing the optical disk. It is desirable that the difference between This can be adjusted by controlling the reflectances R1 and R2 described above, respectively. The reflectances R1 and R2 can be adjusted, for example, by changing the film forming conditions of the underlayer, the composition of the material, and the film thickness.

In the first and second embodiments, the film for MSR reproduction of the RAD system is used as the second recording layer 7, but the medium for the MSR reproduction is not limited to the RAD system but FA.
D (Front Aperture Detection) method and CAD (Center
Aperture Detection) method has been invented. Since the same masking layer exists in the recording film according to these methods, these may be used as the recording layer 7. Further, in the first and second embodiments, the recording layer 3 which is not MSR is used as a recording film for magneto-optical recording / reproduction, but a recording film of other system such as phase change or perforated recording may be used.

Although the number of recording layers is two, it may be three or more. In this case, the recording layer farthest from the substrate 1 is a recording layer for MSR reproduction, and the other layers are recording layers other than MSR. do it. Further, in the first and second embodiments, the film for MSR reproduction is used as the recording layer for super-resolution reproduction, but there is also a method of using an optical mask in addition to the magnetic material for super-resolution, Such a film may be used. This utilizes, for example, a phenomenon in which a colored pigment material becomes transparent when absorbing light of a specific wavelength, only the transparent portion functions as an opening region, and the other portion functions as a mask.

[0031]

According to the present invention, the recording layer farthest from the substrate having the guide groove on which the laser beam is incident is used as the recording layer for super-resolution reproduction, and thus the transmittance is reduced by the masking layer in this recording layer. Does not affect other recording layers, so that information can be correctly read from each recording layer, and it is possible to realize high density by multi-layer recording layers and high density by super-resolution reproduction at the same time. . Further, since recording / reproducing can be performed independently for each recording layer, not only recording density but also transfer rate increase can be expected by simultaneously recording / reproducing each recording layer using a plurality of heads.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an optical disc showing a first embodiment of the present invention.

FIG. 2 is a sectional view of an optical disc showing another embodiment of the present invention.

3A and 3B are a plan view and a sectional view of a rear aperture detection type magneto-optical disk, which is an example of a magnetic super-resolution medium.

[Explanation of symbols]

1, 5a ... Substrate with guide groove, 2, 6, 6a ... Underlayer,
3, 7, 7a ... Recording layer, 4, 8, 8a ... Protective layer, 5 ... Resin layer with guide groove, 6 ... Underlayer, 10, 12, 12a ... Land, 11, 13, 13a ... Groove.

Claims (1)

[Claims] 1. A transparent substrate having a guide groove has a plurality of recording layers capable of storing separate information, and the information stored in each recording layer is independent by a laser beam emitted from the substrate side. An optical recording medium that is reproducible by means of the above, wherein the recording layer farthest from the substrate is a recording layer for super-resolution reproduction.