JPH09245378A - Optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce signal cross talk and cross erase. SOLUTION: A substrate 2 with a guide groove having a land 5 and a groove 6 is awaited. A substrate 3, a recording layer 4 and a protective layer are formed on the substrate 2. At this time, the substrate 2 is manufactured so as to make the depth d of the groove 6 of the substrate 2 100nm or above, and to be satisfied with the relation of d=λ/(an)+mλ/(bn). In the relation, λis a wavelength of reproducing light, and n is the refractive index of the substrate 2, and m=1, 2, 3..., 5.2<=a<=6.8, 1.9<=b<=2.1, or m=0, 1, 2, 3..., 2.8<=a<=3.3, b=2. By making the depth d 100nm or above, the cross erase is reduced, and by making d=λ/(an)+mλ/(bn), the cross talk is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc having both a land and a groove as recording / reproducing tracks.

[0002]

2. Description of the Related Art An optical disk capable of storing high-density data and capable of processing information at high speed has attracted attention as a computer memory. 2. Description of the Related Art For optical disks 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 become more widely used in the future. On this optical disk, a guide for guiding a laser spot from a pickup of the recording / reproducing apparatus along information, that is, a guide for tracking is formed in a spiral shape from the inner circumference to the outer circumference of the medium in the form of a concave or convex groove. Is formed. This groove is called a guide groove. The guide groove will be described in detail. As defined in the ISO standard, a portion that becomes concave when viewed from the pickup, that is, a portion that becomes distant, is called a land, and a portion that becomes convex, that is, a portion that becomes close is called a groove. . The distance from the center of the land to the center of the adjacent land is called the track pitch.

[0003] In an optical disk currently on the market, if the width at the top of the groove on the substrate surface is Wtop and the width at the bottom of the groove on the substrate surface is Wbottom, the groove width W is W = (Wtop + Wbotto).
m) / 2. Further, the height from the bottom of the groove to the top of the groove on the substrate surface, that is, the step is called the groove depth. In order to further increase the data density of such an optical disc, a method has been attempted in which the light source wavelength of the optical head is shortened to reduce the reproducing light spot, thereby enabling information recorded at a high density to be reproduced. However, the wavelength of the semiconductor laser used as the light source of the optical head is limited, and the short-wavelength laser has a problem that the shape and output of the laser light are insufficient.

[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. FAD, which is an example of such MSR using FIG.
The (Front Aperture Detection) method will be briefly described.
FIG. 4A is a plan view of a FAD type MSR disk, and FIG. 4B is a sectional view taken along the line I-I of FIG. 4A.

The optical disk 31 of the FAD system is
It has three magnetic layers: a recording layer 32 made of TbFeCo, a cutting layer 33 made of TbFe, and a reproducing layer 34 made of GdFeCo, and signal reproduction is performed from the reproducing layer side. In the initial state, as shown in FIG. 4B, the magnetization direction of each layer is the recording layer 32 on which information (recording mark 38) is recorded.
The direction of magnetization is aligned. This is because the exchange coupling force acts on the films that are in contact with each other. During reproduction, an external magnetic field Hr is applied. When the reproducing light spot 35 moves relative to the medium 31 as shown in FIG. 4A, the front region of the medium 31 entering the light spot 35 becomes a low temperature region 36, and the rear region becomes a high temperature region 37. There is a temperature difference.

When the temperature of the high-temperature region 37 reaches a temperature at which the magnetization of the cutting layer 33 disappears (Curie temperature), the magnetization of the reproducing layer 34 and the recording layer 32 via the cutting layer 33 intervene.
And the magnetization of the reproducing layer 34 is reversed to the direction of the external magnetic field Hr (in FIG. 4B, the direction of magnetization at the position A is reversed). That is, the high temperature region 37
In this case, the magnetization of the reproducing layer 34 shows a constant state irrespective of the presence or absence of the recording mark 38, and serves as a mask that does not contribute to signal reproduction. On the other hand, only the low temperature area 36 which holds the recording state serves as an effective opening portion of the light spot which carries out signal detection, whereby the recording mark 38a in this area 36 is formed.
Only can read.

As described above, in the FAD method, the conditions for forming the mask are determined by the Curie temperature of the cutting layer 33. That is, it is possible to manufacture the MSR disk relatively easily by controlling the composition of the cutting layer.
In addition to the FAD method as described above, the MSR disk has a RAD in which only the high temperature region serves as an opening and the rest serves as a mask.
(Rear Aperture Detection) method and CAD (Center A
perture detection) method has been proposed. In the RAD-type and CAD-type MSR discs, the high temperature region of the temperature distribution generated by the irradiation of the reproducing laser serves as an opening and the low temperature region serves as a mask, so that a small opening is formed. On the other hand, in the FAD-type MSR disc, the crescent-shaped low-temperature region 36 in the reproduction spot 35 serves as an opening, and thus such an opening can prevent signal leakage from an adjacent track. Can not.

On the other hand, a land / groove recording method has been proposed as another method for reducing the track pitch of an optical disk. This is a method in which data is conventionally recorded on one of the land or groove but is recorded on both the land and the groove, and the track pitch is pseudo halved to double the data capacity. However, if both the land and the groove are used as recording tracks, there is a problem in that signal crosstalk between adjacent lands and the groove becomes large, resulting in erroneous reading of information.

In addition to the above signal crosstalk, there is a problem of thermal crosstalk. Since the magneto-optical disk and the phase change optical disk are thermal recordings in which the temperature of the disk is raised by a laser beam, the thermal diffusion to the adjacent track becomes larger as the distance between the adjacent tracks becomes smaller. Therefore, when writing or erasing data on a track, there is a problem that the data on the adjacent track is also erased (hereinafter referred to as cross erase).
In particular, in land / groove recording, since both lands and grooves are used as recording tracks, they are easily affected by cross-erase.

[0010]

As described above, the MSR disk of the FAD system has a problem that the signal crosstalk cannot be reduced. In addition, when performing land-groove recording on a conventional optical disk, there is a problem that signal crosstalk between adjacent lands and grooves becomes large, and there is a problem that cross erase easily occurs. The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical disk for land / groove recording capable of reducing signal crosstalk and cross erase.

[0011]

According to the present invention, as described in claim 1, the depth d of the groove formed in the substrate with the guide groove is 100 nm or more, and the wavelength of the reproduction light is λ. The refractive index of n is n, and m = 1, 2, 3, ..., 5.2
When ≦ a ≦ 6.8 and 1.9 ≦ b ≦ 2.1, d = λ
This satisfies the relationship of / (an) + mλ / (bn). Further, as described in claim 2, the depth d of the groove formed in the substrate with the guide groove is 100 nm or more, the wavelength of the reproduction light is λ, the refractive index of the substrate is n, and m = 0,
When 2.8 ≦ a ≦ 3.3 and b = 2, the relationship of d = λ / (an) + mλ / (bn) is satisfied.

As described above, the groove depth d is 100 nm.
By the above, cross erase can be reduced, and by setting d = λ / (an) + mλ / (bn), adjacent tracks (for example, when the reproduction target track is a land, adjacent grooves, In this case, the signal crosstalk from the adjacent land) can be reduced.

[0013]

1 (a) is an external view of an optical disc showing a first embodiment of the present invention, and FIG. 1 (b) is an AA.
FIG. 2 is an enlarged view of a part B of the optical disc of FIG. Reference numeral 1 is an optical disk, 2 is a transparent substrate with a guide groove having a concave land 5 and a convex groove 6 when viewed from the optical pickup side (lower side in FIG. 1) not shown, and 3 is made of SiN formed on the substrate 2. The underlying layers 4 and 4 are recording layers formed on the underlying layer 3. In addition,
In FIG. 1B, the protective layer formed on the recording layer 4 is omitted.

Next, a method of manufacturing such an optical disk 1 will be described. In the present embodiment, an example of an FAD type MSR magneto-optical disk will be described. First, a master (stamper) of the optical disc 1 and a glass substrate are prepared. Then, a resin having lands 5 and grooves 6 is formed on a glass substrate 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, and a guide groove with a diameter of 3.5 inches is provided. The transparent substrate 2 is produced. The width of each of the land 5 and the groove 6 is 0.6 μm. Alternatively, a similar plastic substrate with a guide groove 2 may be produced by injection molding using a stamper.

Then, Si is formed on the substrate 2 with the guide groove.
The underlayer 3 made of N is formed by sputtering. Then, a GdFeCo layer (reproducing layer 34 in FIG. 4), a TbFe layer (cutting layer 33), and TbF are formed on the underlayer 3.
The recording layer 4 on which the eCo layer (recording layer 32) is sequentially formed is formed by sputtering. Furthermore, this recording layer 4
The production of the optical disc is completed by forming a protective layer (not shown) made of SiN on the above.

A plurality of optical discs were manufactured by changing the groove depth of the guide grooved substrate 2, that is, the depth d of the groove 6 by the above manufacturing method. Then, these optical disks were sequentially set in a recording / reproducing apparatus, and marks (information) were recorded on the lands or grooves of each disk, and the cross erase was measured. The measurement was performed with the reproduction light having a wavelength λ of 6
An optical pickup having 80 nm, a numerical aperture (NA) of the objective lens of 0.55, and a wavefront aberration of 0.025λ (rms value) was used, and the substrate rotation speed was 2400 rpm. The incident linear polarization direction is parallel to the groove (referred to as E-polarization).

FIG. 2 shows the result of the cross erase measurement.
The cross erase is a second track (first track) that is adjacent to a land or groove (this is the first track).
When the recording or erasing is performed on the groove when the track is a land and when the groove is a groove), the boundary portion of the mark recorded on the first track is erased by thermal interference from the second track. is there.

The cross erase margin of FIG. 2 is the recording power P1 when the mark is recorded on the first track (power of the laser beam irradiated at the time of recording) P1 and the recording power P1 when the second track is recorded or erased. The ratio P2 / P1 with the power P2 at which the mark recorded on the first track is erased and the carrier level on the first track is lowered is shown. The increase in the cross erase margin means that the cross erase margin is larger than the power P2 of the laser light with which the second track is irradiated.
It means that there is more room in the track and that cross erase is less likely to occur.

Therefore, as is clear from FIG. 2, in order to reduce cross erase (thermal crosstalk),
The depth d of the groove 6 may be increased. That is, the heat transfer distance to the adjacent track may be increased by increasing the step due to the groove 6. It is desirable to secure a cross erase margin of 20% or more (margin value is 1.2) with respect to the recording power P1. Therefore, the depth d of the groove 6 needs to be 100 nm or more.

As described above, in the conventional land-groove recording optical disk, the shallow groove depth (40 to 90 nm) is changed to a deep groove of 100 nm or more, whereby cross erase can be reduced.

Next, FIG. 3 shows the calculation results of the carrier level of the reproduced signal and the signal crosstalk. In FIG. 3, C
Indicates carrier level, and CT indicates crosstalk. Here, the carrier level is a relative value when the signal written on the mirror surface is used as a reference. Crosstalk is the difference between the carrier level of the short mark and the carrier level of the long mark when the short mark is recorded on one track where the long marks are recorded on both adjacent tracks.

As is apparent from FIG. 3, the carrier level fluctuation when the groove depth is changed is less than 10 dB, while the crosstalk level is different by about 40 dB. From this, it can be seen that the signal crosstalk can be reduced by limiting the groove depth. The depth d of the groove 6 that minimizes the signal crosstalk is 10
At 0 nm or more, there are three points of 150, 310, and 370 nm.

Therefore, optical discs in which the depth d of the groove 6 is set to 150, 310, and 370 nm are manufactured by the above-described manufacturing method, and the C / N (Carrier to Noise ratio) and crosstalk of reproduction signals of these optical discs are manufactured. Table 1 shows the result of measurement.

[0024]

[Table 1]

The C / N is such that a mark having a length of 0.4 μm is recorded at a position having a radius of 35 mm by using the recording / reproducing apparatus described above
It is a value when reproducing with a reproducing power of 3.0 mW while applying a magnetic field of 500 Oe (external magnetic field Hr of FIG. 4).
Further, the crosstalk is 1.6 in the second track on both sides of the first track on which a mark having a length of 0.4 μm is recorded.
This is the difference between the carrier level of 0.4 μm when a mark of μm is recorded and the first track is reproduced and the carrier level of 1.6 μm leaked from the second track. As a comparative example, the depth d of the groove 6 is 200 and 350 nm.
Table 2 shows the results of manufacturing the optical disk of No. 1 and measuring C / N and crosstalk in the same manner.

[0026]

[Table 2]

Thus, it can be seen that the actual measurement results of Tables 1 and 2 and the calculation results of FIG. 3 match. According to FIG.
In order to reduce the signal crosstalk to about -25 dB or less, the groove depth d is 137 to 162 nm, 282 to 3
It is desirable to set in the range of 26 nm and 364 to 389 nm. However, in FIG. 3, the wavelength λ of the reproduction light is 680n.
m, the characteristics when the refractive index n of the substrate 2 with the guide groove is 1.5, and if these are changed, the groove depth at which the crosstalk is minimized also changes.

Further, in FIG. 3, 80 nm (this peak is shallower than 100 nm, which is not the subject of the present invention), 3
Two types of peaks appear: a peak with a shallow groove depth of 10 nm (this is the first peak) and a peak with a deep groove depth of 150 nm, 370 nm (this is the second peak). And in FIG. 3, 400
Although only the calculation results up to nm are shown, the same two types of peaks are repeated for 400 nm or more.

From the above, the depth d of the groove 6 should be 100 nm or more and should satisfy the following equation. d = λ / (a × n) + m × λ / (b × n) (1) However, m, a, and b have the values regarding the first peak m =
1, 2, 3, ..., 5.2 ≦ a ≦ 6.8, 1.9 ≦ b
≦ 2.1, the value for the second peak is m = 0,
1, 2, 3 ... 2.8 ≦ a ≦ 3.3 and b = 2.

In this embodiment, the MS of the FAD method is used.
Although the case of the R magneto-optical disk has been described, since the present invention does not depend on the film formed on the substrate 2 with the guide groove, the same effect can be obtained even when applied to other types of MSR magneto-optical disks. . Further, the same effect can be obtained even when applied to a normal magneto-optical disk that is not an MSR, and the same effect can be obtained when applied to a phase change optical disk.

[0031]

According to the present invention, the groove depth d is set to 1
When the thickness is 00 nm or more, the cross erase can be reduced, and when d = λ / (an) + mλ / (bn), the signal crosstalk from the adjacent track can be reduced. As a result, a land-groove recording optical disc with a small cross erase and a small signal crosstalk can be realized, and high-density recording can be achieved by narrowing the track. Further, by applying the present invention to an MSR disc, it is possible to realize an MSR disc for land-groove recording with small cross erase and signal crosstalk, and it is possible to perform higher density recording by narrowing the track and shortening the mark. . In particular, if the present invention is applied to the FAD system, signal crosstalk, which is a problem thereof, can be reduced, so that the MSR disk can be realized by the FAD system that is easy to manufacture.

[Brief description of drawings]

1A and 1B are an external view of an optical disc according to a first embodiment of the present invention and an enlarged view of a portion of the optical disc as viewed obliquely from above.

FIG. 2 is a diagram showing measurement results of cross erase.

FIG. 3 is a diagram showing calculation results of a carrier level of a reproduced signal and signal crosstalk.

FIG. 4 is a plan view and a cross-sectional view of an FAD-type optical disc that is an example of an MSR optical disc.

[Explanation of symbols]

1 ... Optical disc, 2 ... Substrate with guide groove, 3 ... Underlayer, 4
... recording layer, 5 ... land, 6 ... groove.

Claims (2)

[Claims] 1. An optical disc having both a land and a groove formed on a substrate with a guide groove as recording / reproducing tracks, wherein the depth d of the groove formed on the substrate is 100 nm.
With the wavelength of the reproduction light being λ and the refractive index of the substrate being n, m = 1, 2, 3, ..., 5.2 ≦ a ≦ 6.8,
When 1.9 ≦ b ≦ 2.1, d = λ / (an) + m
An optical disk characterized by satisfying the relationship of λ / (bn). 2. An optical disc using both a land and a groove formed on a substrate with a guide groove as recording / reproducing tracks, wherein the depth d of the groove formed on the substrate is 100 nm.
As described above, the wavelength of the reproduction light is λ, the refractive index of the substrate is n, and m = 0, 1, 2, 3, ... 2.8 ≦ a ≦ 3.
3 and b = 2, d = λ / (an) + mλ / (b
An optical disk characterized by satisfying the relationship of n).