JPH08147779A - Information recording medium and reproducing method thereof - Google Patents

Abstract

(57) [Summary] [Structure] Information is recorded by the unevenness formed on the recording surface of the transparent substrate, which is in-plane magnetization at room temperature, and is perpendicular to the in-plane magnetization when heated above a predetermined temperature. An information recording medium provided with a reproducing layer that transitions to magnetization and, if necessary, further provided with an initialization layer made of a perpendicularly magnetized film whose magnetization directions are previously aligned in the same direction. To reproduce information, the recording surface is irradiated with laser light to raise the temperature of the reproducing layer to a temperature at which a part thereof is vertically magnetized, and the intensity change of a predetermined polarization component of the reflected light is detected. [Effect] A super-resolution read-only medium can be manufactured using a substrate manufactured by the same method as the conventional pit formation, and both linear density and track density can be improved.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a compact disc (C
D) and the like, an information recording medium for recording a signal by unevenness on a substrate and reproducing the recorded signal by irradiating a laser beam, and an information recording medium particularly suitable for high density recording, Regarding the reproducing method.

[0002]

2. Description of the Related Art An information recording medium on which information is recorded as unevenness formed on a substrate is typified by a CD and a CD-ROM, and has been remarkably popularized as a distribution medium for music and software for personal computers.

This information recording medium is usually constructed by laminating an aluminum reflective film and a protective coat on a transparent substrate. The information to be reproduced is recorded as pits composed of irregularities on the substrate, and these pits are formed by being transferred from the stamper when the substrate is molded. This information recording medium is usually reproduced by detecting changes in the intensity and phase of the reflected light of the irradiation laser light due to the pits on the substrate. The size and interval of the pits are determined by the size and interval of the pits of the stamper, so it is possible to make them quite small, but their reading is limited by the wavelength of the laser during reproduction, the aperture ratio of the lens, and the like.

An attempt to improve the recording density beyond the recording density determined by such a restriction on reproduction has been made, for example, in Japanese Patent Laid-Open No. Hei 4
No. 167237. This is because the phase change type thin film is sandwiched between the substrate and the reflection film and part of the phase change type thin film is changed from a crystalline state to a molten state by heating by irradiation of laser light at the time of reproduction, so that the reflectance is increased. By utilizing the decrease, the inter-symbol interference at the time of reproduction is reduced by the super-resolution using the melted portion as a mask, and the signal having the period less than the diffraction limit of light can be reproduced.

Further, in JP-A-1-179244, a magnetic film having a magneto-optical characteristic is formed on a pit formation surface of an information recording medium on which a signal is recorded by unevenness on a transparent substrate.
A method of reproducing a recorded signal by detecting a change in the car rotation angle has been proposed. This method utilizes the fact that the magnetic domains in the pit disappear due to the temperature rise during playback,
The super-resolution using this as a mask reduces the intersymbol interference at the time of reproduction and makes it possible to reproduce a signal having a period equal to or shorter than the diffraction limit of light.

The super-resolution described above is based on FAD (Front Aperture Dete) in which the temperature rising portion serves as a mask.
action). On the other hand, the RAD where the low temperature part becomes the mask and the high temperature part becomes the aperture (opening)
There is also (Rear Aperture Detection) super-resolution. An information recording medium using RAD super-resolution is formed by forming a magneto-optical perpendicular magnetization film on a substrate of an information recording medium on which a signal is recorded by a difference in surface roughness on a transparent substrate, and by using the difference in surface roughness. A method of reproducing by detecting the change of the Kerr rotation angle while reversing the magnetization of only a portion without a bit by utilizing the difference in coercive force of the magnetized film and the temperature rise at the time of reproduction is disclosed in, for example, JP-A-5-266523. Proposed in the gazette. In this method, it is necessary to initialize the magnetization direction of the magneto-optical perpendicular magnetization film in one direction in advance by an initialization magnet or the like, and it is necessary to apply an external magnetic field for reproduction.

Japanese Laid-Open Patent Publication No. 5-81717 discloses a rewritable magneto-optical recording medium using RAD super-resolution which does not require an initializing magnet. This magneto-optical recording medium is provided with a recording layer for magneto-optically recording information, and a reading layer that exhibits in-plane magnetization at room temperature, but shifts to perpendicular magnetization at a predetermined temperature or higher, and is heated by irradiation with laser light. By transferring a part of the read layer to perpendicular magnetization and transferring the magnetization of the recording layer to this part, it is possible to reproduce a signal having a period less than the diffraction limit of light.

[0008]

In the FAD super resolution, the linear density is improved, but the track density cannot be expected to be improved. To improve the track density of the information recording medium, RA
D super resolution is required. As an information recording medium using RAD super-resolution, a method of utilizing surface roughness requires an initializing magnet, which complicates a drive device. Further, as a method of roughening the surface, a step such as etching is required for manufacturing a stamper. There was a problem such as the need to newly introduce it.

The problem to be solved by the present invention is that the production is relatively easy and a large number of replicas can be produced at low cost.
An object of the present invention is to provide an information recording medium capable of high density recording using RAD super-resolution whose driving method is simple.

[0010]

DISCLOSURE OF THE INVENTION The inventors of the present invention have proposed an information recording medium in which a signal is recorded by unevenness on a transparent substrate,
A magneto-optical perpendicularly magnetized film is formed on the recording surface, which is the surface of the transparent substrate on which irregularities for carrying information are formed, and the magnetization of this perpendicularly magnetized film is aligned in one direction, and an irradiation laser for reproduction is used. By making the reflected light of the light mainly a predetermined polarization component, the area including the pit portion and the pit portion are completely included due to the interference effect due to the phase difference of the reflected light from the pit portion and the non-pit portion. We found that it is possible to detect the difference in the intensity of the reflected light from the non-existing region by measuring the specified polarization component, and further, the above-mentioned magneto-optical perpendicular magnetization film was in-plane magnetized at room temperature and at a specified temperature. If it shows the property that it becomes perpendicular magnetization, it is possible to detect the intensity change of the reflected light only from the area where it becomes perpendicular magnetization by measuring the predetermined polarization component, which can improve the resolution. This The found, leading to obtaining the present invention.

That is, the information recording medium of the present invention is an information recording medium in which information is recorded by unevenness on a transparent substrate, and at room temperature the recording surface, which is the surface of the transparent substrate on which the information-bearing unevenness is formed. An information recording medium having an in-plane magnetization and having a reproducing layer which changes from in-plane magnetization to perpendicular magnetization when heated above a predetermined temperature. In addition,
The transition from in-plane magnetization to perpendicular magnetization and the transition from perpendicular magnetization to in-plane magnetization of the reproducing layer are both reversible, and when the temperature of the reproducing layer again falls below a predetermined temperature, the reproducing layer is again formed. It becomes in-plane magnetization.

FIG. 1 shows a sectional view of an example of the information recording medium of the present invention. A dielectric layer 2 made of silicon nitride or the like on a transparent substrate 1 made of polycarbonate or the like on which information is recorded with unevenness on the recording surface, which is in-plane magnetized at room temperature and in-plane when heated above a predetermined temperature. A reproducing layer 3 that transitions from magnetization to perpendicular magnetization,
A dielectric layer 4 made of silicon nitride or the like and a reflective layer 5 made of aluminum or the like are laminated. In this example, the case of having two upper and lower dielectric layers and a reflective layer is shown, but these dielectric layer and reflective layer may be omitted. In the present invention, the recording surface refers to the surface of the upper and lower substrate surfaces of the transparent substrate on the side where irregularities for carrying information are formed.

In the reproducing method of the information recording medium of the present invention, a magnetic field larger than the coercive force in the perpendicular direction of the reproducing layer at the time when the reproducing layer changes from in-plane magnetization to perpendicular magnetization is perpendicular to the recording surface. In this direction, the recording surface of the information recording medium is irradiated with laser light to raise the temperature to a temperature at which the irradiated portion of the reproducing layer partially becomes perpendicularly magnetized, and the intensity of a predetermined polarization component of the reflected light is increased. By detecting the change, a reproducing method of reproducing the recorded information can be used.

The reproducing layer is heated while a magnetic field larger than the coercive force in the perpendicular direction of the reproducing layer at the time when the reproducing layer changes from in-plane magnetization to perpendicular magnetization is applied in the direction perpendicular to the recording surface. When the linearly polarized laser light is applied to the region that has become perpendicularly magnetized, the magnetization direction of the region that has become perpendicularly magnetized is aligned in one direction by the applied external magnetic field. Due to the Kerr effect, the polarization plane of the reflected light from that region rotates by the Kerr rotation angle with respect to the reference plane. On the other hand, with respect to the reflected light from the region where the reproducing layer is not perpendicularly magnetized due to insufficient heating, that region does not exhibit the Kerr effect, and therefore the polarization plane of the reflected light does not change with respect to the reference plane. Therefore, by using an analyzer or the like, by extracting the polarization component rotated by the Kerr rotation angle with respect to the reference plane from the reflected light, information about only the region in which the reproducing layer is perpendicularly magnetized by heating is extracted. be able to. That is, it is possible to perform RAD super-resolution reproduction by using a region where the reproducing layer is not perpendicularly magnetized as a mask and using a region where the reproducing layer is perpendicularly magnetized by heating as an aperture.

Generally, the intensity of the irradiation laser light is higher at the center of the beam spot (irradiation area on the recording surface), so that the irradiation laser light is perpendicularly magnetized so that the reproducing layer in the area smaller than the beam spot becomes perpendicularly magnetized. The power of can be adjusted. When information is continuously reproduced by relatively moving the information recording medium of the present invention and a detector for reproducing the information, in the direction orthogonal to the relative movement direction in the recording surface, The region where the reproducing layer is perpendicularly magnetized is always included in the beam spot. Regarding the direction of relative motion, the region where the reproduction layer is perpendicularly magnetized extends backward, and therefore, this region is not always included in the beam spot. However, in the area outside the beam spot in the area where the reproducing layer is perpendicularly magnetized, since it is outside the beam spot, there is no reflected light from that area, and in the end an aperture smaller than the beam spot is always obtained. be able to. That is, it is possible to extract information only in a region smaller than the beam spot of the irradiation laser light.

The information recording medium of the present invention is generally used as a disc-shaped disc medium by rotating it around an axis which is perpendicular to the disc surface and passes through the center of the disc. It is also conceivable to use the card-shaped medium or the tape-shaped medium with linear relative movement.

The reflected light of the irradiation laser light on the recording surface has a phase difference corresponding to the unevenness of the recording surface by an amount corresponding to the step. The height difference between the concave or convex pit portion and the non-pit portion formed on the recording surface is closer to λ / 4n, where λ is the wavelength of the irradiation laser light and n is the refractive index of the transparent substrate. Since the reflected light from and the reflected light from the part which is not a pit interfere with each other and the intensity decreases,
The intensity of the reflected light from the region including both the pit portion and the non-pit portion is smaller than that of the reflected light from the region that does not include the pit portion or the region that does not include the non-pit portion. When the "reflective light generation area" is defined as "the area where the reflected light whose intensity change is to be detected is the reflected light from that area", this decrease in intensity is included in the reflected light generation area. Since it is proportional to the area ratio between the pit portion and the non-pit portion, the presence or absence of pits on the recording surface can be detected by appropriately setting the size of the above aperture and detecting the intensity change of the reflected light. You can

That is, the width of the aperture is made larger than the width of the recording pit, and in the portion where the pit exists,
The area where the reflected light is generated may include both the pit portion and the non-pit portion, and the presence of the pit may be detected from the resulting decrease in the intensity of the reflected light. Equally, at the end of the pit in the relative movement direction, the area where the reflected light is generated includes both the pit portion and the non-pit portion, and as a result, the intensity of the reflected light is reduced to prevent the existence of the pit. You may make it detect. It is also possible to detect the end portion itself of the pit in the relative movement direction by the same method. The width of the aperture and the width of the recording pit represent respective lengths in the direction orthogonal to the relative movement direction on the recording surface.

The difference in height between the concave or convex pit portion and the non-pit portion formed on the recording surface is (2k-1) where k is a natural number in order to most effectively generate the interference effect.
· Most preferably λ / 4n, but (4k-3)
The range of λ / 8n to (4k−1) · λ / 8n is sufficient, and the range of λ / 8n to 3λ / 8n is practically sufficient.

In reproducing information from the information recording medium of the present invention, laser light for reproduction is applied from the side of the transparent substrate facing the recording surface.

The above-mentioned principle of pit detection and super-resolution will be described below with reference to the drawings. The reason why there is a difference between the magneto-optical signals (described later) in the pit portion and the non-pit portion is shown in FIG. When the irradiating laser beam is irradiating the pit portion, the diameter of the beam spot 30 of the laser beam is wider than the width of the pit.
The light reflected from the pit interferes with the light reflected from the periphery 32 of the pit and having a different phase, and the intensity of the reflected light is weakened as compared with the portion without the pit (33 indicates an objective lens). In other words, the intensity of reflected light is 3 depending on the presence or absence of pits.
4 is modulated. Modulation of the reflected light intensity is a reproducing principle of a conventional read-only medium such as a CD. Here, if the incident light is polarized, the reproduction layer is a perpendicularly magnetized film, and the direction of magnetization is aligned in advance, the plane of polarization of the reflected light is different from that of the material of the reproduction layer with respect to the plane of polarization of the incident light. It is rotated by a predetermined Kerr rotation angle determined by the structure of the dielectric thin film. This is detected by a detector through a dichroic analyzer 35 having a principal axis on the polarization plane of this reflected light, or by a polarization beam splitter, the reflected light is separated into mutually perpendicular polarization planes and differential detection is performed. The output 36 obtained by the method of detecting a magneto-optical disk (this is referred to as a "magneto-optical signal") detects light of a component corresponding to a predetermined Kerr rotation angle. The magneto-optical signal 36 is proportional to (reflectance) × (Kerr rotation angle) and the magnetization directions of the reproducing layer are aligned, so the Kerr rotation angle is constant and the intensity of this light is the same as that of the reflection described above. It is modulated by the change in rate.

Next, the super-resolution of pit reproduction by the reproduction layer of the present invention will be described. As shown in FIG. 3B, when the pits are arranged at a narrow interval near the diffraction limit determined by an optical system including a laser beam used for information reproduction and a lens, it is only due to a change in reflectance from the pits. The reproduction output is almost zero. However, since the magneto-optical signal from the reproducing layer 37 is obtained only from the region 39 (aperture) in which the direction of magnetization in the reproducing layer is vertical due to the heating by the irradiation laser beam 38, it has a reproducible size. It becomes an output. This method is a type of RAD because the aperture is located slightly behind the beam spot, and the width of the aperture is narrower than the beam spot, so that signal leakage (crosstalk) into the adjacent track is also reduced.

In order for the reproducing method of the information recording medium of the present invention to function, it is necessary that the magnetization direction of the region where the reproducing layer is perpendicularly magnetized is oriented in a predetermined direction. In fact
When an external magnetic field is not applied when the reproducing layer changes to perpendicular magnetization, the magnetization directions of the vertically magnetized regions are mixed up and down, so that a reproduction signal is hardly detected.

In order to orient the magnetization of the region where the reproducing layer is perpendicularly magnetized in a predetermined direction, it is necessary to apply an external magnetic field in a direction perpendicular to the recording surface. When the reproducing layer is heated to transfer from in-plane magnetization to perpendicular magnetization with an external magnetic field applied, when the strength of the applied external magnetic field changes to perpendicular magnetization, the film surface of the reproducing layer If it is larger than the coercive force in the direction perpendicular to, the temperature of the reproducing layer will rise further,
Even when the coercive force of the reproducing layer becomes large, the purpose of aligning the magnetization directions of the reproducing layer can be achieved. Since the coercive force in the direction perpendicular to the film surface of the reproducing layer at the time of transition to perpendicular magnetization is generally small, about 100 Oe is often sufficient as the strength of the applied external magnetic field. Further, the region to which the external magnetic field is applied may include at least the region where the reproducing layer has perpendicular magnetization.

The above-mentioned application of the external magnetic field necessary for reproduction is
An initialization layer made of a perpendicular magnetization film is laminated on the reproduction layer,
This can be omitted by preliminarily initializing the magnetization of the initializing layer in one direction at the time of manufacturing. That is, when the reproducing layer is heated and transferred to the perpendicular magnetization, the magnetization of the initialization layer is transferred to the reproducing layer by exchange coupling, so that the magnetization direction of the region of the reproducing layer which becomes the perpendicular magnetization is changed to a predetermined direction. Can be aligned.

FIG. 7 shows a sectional view of an example of the information recording medium provided with the initialization layer of the present invention. A dielectric layer 2 made of silicon nitride or the like on a transparent substrate 1 made of polycarbonate or the like having information recorded on the recording surface with irregularities, which has in-plane magnetization at room temperature,
A reproducing layer 3 which changes from in-plane magnetization to perpendicular magnetization when heated to a predetermined temperature or more, an initialization layer 6 made of a perpendicular magnetization film, and a dielectric layer 4 made of silicon nitride or the like are laminated. In this example, the case of having two upper and lower dielectric layers is shown, but these dielectric layers can be omitted.

As a reproducing method of the information recording medium having the above-mentioned initialization layer, the recording surface of this information recording medium is irradiated with laser light so that the irradiation portion of the reproducing layer is partially vertical, as described above. It is possible to use a reproducing method of reproducing recorded information by raising the temperature to a temperature at which it becomes magnetized and detecting a change in intensity of a predetermined polarization component of reflected light. In this case, as described above, it is not necessary to apply an external magnetic field for aligning the direction of magnetization in the region where the reproducing layer is perpendicularly magnetized in a predetermined direction.

As described above, the reproducing method of the information recording medium of the present invention is to extract a predetermined polarization component of the reflected light of the irradiated laser light and detect the intensity change thereof.
Only the detection of this signal can be performed by using the optical system and the signal processing system for reproducing the usual magneto-optical recording medium as they are. That is, as described above, the magneto-optical signal obtained by the ordinary detection method of the magneto-optical recording medium usually has a polarization angle (curve) corresponding to the magnetization direction of the recording film.
It is modulated by the rotation angle), but in the case of the present invention,
This change in the magneto-optical signal represents a change in the degree of interference of the reflected light from the pit portion and the non-pit portion. Therefore, the presence or absence of the pit can be detected by the magneto-optical signal.

In the information recording medium having the initializing layer of the present invention, a perpendicular magnetic film capable of magneto-optical recording is used for the initializing layer, and this is used as the recording layer in the rewritable portion.
The information recording medium of the present invention can be applied to a partial ROM having both a read-only section and a rewritable section.

That is, the recording surface of the transparent substrate has a read-only portion and a rewritable portion, and both the read-only portion and the rewritable portion have in-plane magnetization at room temperature and are heated to a predetermined temperature or higher. And a recording layer capable of magneto-optical recording and a reproducing layer for transitioning from in-plane magnetization to perpendicular magnetization, the reproduction-only portion having information recorded by unevenness of the recording surface, and the recording layer of the reproduction-only portion. The information recording medium is characterized in that the direction of magnetization is initialized in advance so as to be aligned in one direction.

FIG. 10 shows a cross-sectional view of an example of the information recording medium provided with the above-mentioned reproduction-only section and rewritable section of the present invention. A transparent substrate 1 made of a polycarbonate or the like in which necessary information is recorded on a part of the recording surface as a read-only portion by means of unevenness.
A dielectric layer 2 made of silicon nitride or the like, a reproducing layer 3 which has in-plane magnetization at room temperature and changes from in-plane magnetization to perpendicular magnetization when heated above a predetermined temperature, and a recording layer 7 capable of magneto-optical recording. , And a dielectric layer 4 made of silicon nitride or the like is laminated. In this example, the case of having two upper and lower dielectric layers is shown, but these dielectric layers can be omitted.

If only the reproduction-only portion of the recording surface of the transparent substrate is formed with irregularities to record necessary information and the other portion of the recording surface is made smooth so as to enable magneto-optical recording, the film forming process Even if the same film is formed over the entire recording surface, it can be used as a rewritable portion by magneto-optical recording except for the portion where information is recorded by the unevenness formed on the recording surface. Even in this rewritable portion, by the same method as the reproducing method of the information recording medium having the initializing layer of the present invention, irradiation is performed by the RAD super-resolution in which the region in which the reproducing layer is perpendicularly magnetized has the aperture as described above. It is possible to reproduce a signal having a period less than the diffraction limit determined by the laser light and the reproduction optical system.
Further, by devising the method of irradiating the laser light, it is possible to write in the rewritable portion by RAD super-resolution. That is, in the above-described information recording medium including the read-only section and the rewritable section of the present invention, it is possible to make the recording densities of the read-only section and the rewritable section equal to each other.
Further, in the read-only portion of the above-described information recording medium of the present invention, the recording layer functions as the above-mentioned initialization layer, so that the magnetization directions of the recording layers of this read-only portion are aligned in the same direction in advance. Therefore, the reproduction of information in the reproduction-only section does not require the application of an external magnetic field. Also,
As described above, in the reproduction of the information in the reproduction-only section of the information recording medium of the present invention, the signal detection itself should be performed using the optical system and the signal processing system used for reproducing the ordinary magneto-optical recording medium. Therefore, in the information recording medium provided with the read-only section and the rewritable section of the present invention, the reproduction of the information of the read-only section and the reproduction of the information of the rewritable section are performed by the same optical system and signal processing system. Can be done at. That is, in the information recording medium including the read-only section and the rewritable section of the present invention, the reproduction of the information of the read-only section and the recording and the reproduction of the information of the rewritable section are almost the same optical system and signal. It is also possible to use a processing system. The information recorded in the reproduction-only section includes various computer programs and various data, audio information such as music, image information such as still images and moving images, and sector marks of the information recording medium. Physical format information, servo information for tracking, information used for identifying and testing the medium, and the like.

The reproducing layer used in the information recording medium of the present invention is a material that is in-plane magnetized at room temperature and becomes perpendicularly magnetized as the temperature rises, as long as it has an appropriate curve rotation angle. Although not particularly limited, rare earth-rich GdFeCo, GdNdFeCo, GdD having a Curie temperature of 300 ° C. or higher
yFeCo, GdTbFeCo and the like are preferable. GdF
In the case of eCo, the Co / FeCo ratio is 0.2 or more, 0.6
The following is preferable and the compensation temperature is 150 to 350 ° C. The transition temperature from the in-plane magnetization to the perpendicular magnetization of the reproducing layer is preferably 100 to 300 ° C, and more preferably 120 to 200 ° C in consideration of the capability of the laser used. . The thickness of the reproducing layer is preferably 15 nm or more and 150 nm or less when there is no initialization layer. When the thickness of the reproducing layer is 60 nm or less, it is desirable that the reflective film is laminated on the reproducing layer. When the initialization layer is provided, the thickness of the reproduction layer is preferably 30 nm or more and 150 nm or less. The reason why the reproducing layer is required to be 30 nm or more is that the magnetization loop of the reproducing layer shifts due to the exchange coupling from the initializing layer and the curl rotation occurs even without a magnetic field.

The initializing layer is not particularly limited as long as it is a material having a large perpendicular magnetic anisotropy and a coercive force such as TbFeCo and DyFeCo. Preferably there is. If the coercive force at room temperature is not less than 20 kOe, it will be difficult to initialize with an electromagnet at room temperature. The thickness of the initialization layer is
It is preferably 10 nm or more and 100 nm or less.

In the case of an information recording medium having a read-only portion and a rewritable portion, the reproducing layer is preferably made of the same material and film thickness as those in the case where the initialization layer is provided. The recording layer is made of almost the same material as the initialization layer, but the Curie temperature is preferably 200 ° C. or higher and 300 ° C. or lower, and the film thickness is 15 nm or higher and 80 nm or lower in view of the relationship between recording retention and recording sensitivity during reproduction. preferable.

In the information recording medium of the present invention, a dielectric layer made of silicon nitride or the like is provided between the substrate and the reproduction layer, and a dielectric made of silicon nitride or the like is also provided on the reproduction layer or the initialization layer or the recording layer. By providing layers
The rotation angle is increased, and the reproduction layer or the initialization layer or the recording layer is prevented from being oxidized. Further, a protective coat made of resin or the like may be provided to protect these films. Further, when there is no initialization layer, a medium having a reflective type structure of substrate / dielectric layer / reproducing layer / dielectric layer / reflection layer can be used. With this structure, the car rotation angle can be considerably increased. Further, by interposing an intermediate layer having a lower Curie temperature than the initialization layer or recording layer between the reproduction layer and the initialization layer or recording layer to further reduce the aperture, it is possible to improve the resolution. is there. Further, in order to reduce the thickness of the reproducing layer, it is possible to interpose a second intermediate layer between the reproducing layer and the initialization layer or the recording layer, which has a function of weakening exchange coupling between the two. . These are particularly effective in the information recording medium provided with the read-only section and the rewritable section of the present invention.

[0037]

【Example】

Example 1, Comparative Example An RAD super-resolution information recording medium as shown in FIG. 1 was manufactured. Dielectric layer 2 (film thickness: 100 nm) made of silicon nitride by sputtering on transparent substrate 1 made of polycarbonate having a track pitch (26 in FIG. 2) of 1.1 μm, G
A reproducing layer 3 (thickness: 23 nm, made of d ₂₈ Fe ₃₆ Co ₃₆ ,
In-plane magnetic film at room temperature, perpendicular magnetic film at 150 ° C. or higher, compensation temperature: 250 ° C., Curie temperature: 350 ° C. or higher), dielectric layer 4 made of silicon nitride (film thickness: 30 nm), reflective layer 5 made of aluminum (Film thickness: 45 nm) was formed in order. As shown in FIG. 2, the transparent substrate 1 made of polycarbonate has pits 21 having a depth (22) of 0.13 μm formed on the lands 27 between the V-grooves 28. . The pit width 25 is about 0.5 μm and the pit length 23
0.3 to 1.0 μm, pit pitch 24 to pit length 2
3 times twice. In this embodiment, in order to measure the crosstalk, pits are formed every three tracks with a constant pit length 23 for one track.

As a comparative example, a medium in which the reproducing layer 3 was always Tb ₂₀ Fe ₆₈ Co ₁₂ which is a perpendicular magnetization film was also manufactured.

These media were recorded at a wavelength of 780 nm, NA0.
Linear velocity of 8 while irradiating laser with 55 magneto-optical head
Reproduced at m / s. A magneto-optical signal was used for reproduction.

In the medium of Example 1, when the pit length was 0.5 μm and the reproducing power was 2.5 mW, the reproducing magnetic field was changed to C.
/ N changed as shown in FIG. Reproducing magnetic field 100-300
C / N became maximum at Oe. When the output was less than 50 Oe, almost no output was obtained, and when it exceeded 300 Oe, the C / N gradually decreased. Since the coercive force of Gd ₂₈ Fe ₃₆ Co ₃₆ at 150 ° C. is about 80 Oe, it was found that a magnetic field higher than that is required for reproduction. In addition, the reproducing magnetic field is set to 150
When the reproducing power was changed as Oe, the C / N gradually increased as shown in FIG. 5 and was saturated at 2 mW or more.

A reproducing power of 2.5 mW was applied to the medium of Example 1.
With the reproducing magnetic field of 150 Oe, the medium of the comparative example was reproduced with a reproducing power of 1.5 mW and a reproducing magnetic field of 0 Oe (optimal reproducing condition of the medium of the comparative example). Figure 6 shows the C / N against the pit length
Shows the change in The shorter the pit length, the C / N6 of Example 1
The difference in C / N63 between 1 and the medium of the comparative example was large. Further, the C / N 62 of the SUM signal (output proportional to the amount of reflected light) of the medium of Example 1 is 6 when the pit length is long.
It was larger than 1 but reversed when the pit length became shorter, confirming the effectiveness of super-resolution due to photomagnetism.

When the crosstalk between adjacent tracks is examined when the pit length is 1.0 μm, the magneto-optical signal is -50 dB in the case of Example 1 and -24d in the case of Comparative Example.
B, in the case of the SUM signal of the medium of Example 1, it was -26 dB. It was confirmed that the magneto-optical signal in Example 1 was overwhelmingly low, and there was a margin to further lower the track pitch.

Example 2 On the same substrate as in Example 1, a RAD super-resolution reproducing medium as shown in FIG. 7 was manufactured. A dielectric layer 2 made of silicon nitride (film thickness: 80 nm) and a reproduction layer 3 made of Gd ₂₈ Fe ₃₆ Co ₃₆ (film thickness: 80 nm, an in-plane magnetized film at room temperature) on a transparent substrate 1 made of polycarbonate by a sputtering method. 15
Perpendicular magnetization film at 0 ° C or higher, compensation temperature: 250 ° C, Curie temperature: 350 ° C or higher), initialization layer 6 made of Tb ₁₉ Fe ₆₆ Co ₁₅ (film thickness: 40 nm, coercive force at room temperature: 8 kO)
e, Curie temperature 330 ° C.), and a dielectric layer 4 (film thickness: 80 nm) made of silicon nitride were sequentially formed. After film formation,
Initialization was performed with an electromagnet having a magnetic field of 20 kOe.

This medium was measured at a wavelength of 780 nm and NA of 0.55.
Linear velocity of 8m /
replayed in s. A magneto-optical signal was used for reproduction.

The reproduction power is 2.5 when the pit length is 0.5 μm.
When the reproducing magnetic field was changed at mW, the C / N changed as shown in FIG. The C / N became maximum when there was no reproducing magnetic field.

With a reproducing power of 2.5 mW and no reproducing magnetic field,
FIG. 9 shows the change in C / N with respect to the pit length during reproduction. As the pit length is shorter, C / which is almost the same as in Example 1
N was obtained up to a short pit length. The initialization layer enables reproduction without a reproducing magnetic field.

Example 3 An information recording medium having a medium structure shown in FIG. 10 and having a read-only portion of RAD super-resolution and a rewritable portion was manufactured. Dielectric layer 2 (film thickness: 80 nm) made of silicon nitride by sputtering on transparent substrate 1 made of polycarbonate, Gd
Reproducing layer 3 made of ₂₈ Fe ₃₆ Co ₃₆ (film thickness: 80 nm, in-plane magnetized film at room temperature, perpendicular magnetized film at 150 ° C. or higher, compensation temperature: 250 ° C., Curie temperature: 350 ° C. or higher), Tb ₁₉
A recording layer 7 made of Fe ₇₀ Co ₁₁ (film thickness: 30 nm, coercive force at room temperature: 8 kOe, Curie temperature 270 ° C.), and a dielectric layer 4 made of silicon nitride (film thickness: 80 nm) were sequentially formed. After the film formation, the recording layer was initialized with an electromagnet having a magnetic field of 20 kOe. Substrate has a track pitch of 1.0 μm
(V groove group), pits of random pattern having a depth of 0.13 μm and a shortest pit length of 0.5 μm were formed on the land of the reproduction-only portion. A random pattern having a shortest mark length of 0.5 μm was written in the rewritable portion with a magneto-optical head having a wavelength of 780 nm and an NA of 0.55. While irradiating laser light with the same head as above, linear velocity 10
When reproduction was performed with a magneto-optical signal at m / s, reproduction power of −2.8 mW, and no reproduction magnetic field, good reproduction signals were obtained in both the reproduction-only section and the rewritable section. Also, the reproduction of the prepits in the rewritable part could be favorably performed by the same method.

In the above embodiment, the pits were formed on the lands of the V-groove groove, but in addition to this, when tracking is performed by the sample servo, the data area may have no groove. However, even in this case, high-density recording / reproduction according to the present invention can be performed without any change. Further, according to the present invention, the servo signal of the sample servo due to the pendant mark can be satisfactorily obtained even at a narrow track pitch.

[0049]

According to the present invention, a super-resolution read-only medium can be manufactured with a substrate manufactured by the same method as the conventional pit formation, and both the linear density and the track density can be improved. Further, in the information recording medium having the initialization layer of the present invention, it is not necessary to apply an external magnetic field for reproduction,
The drive device can be simple.

Considering the case of distributing a large number of duplicates having the same information recorded therein, such as a CD-ROM, in a super-resolution rewritable medium using magneto-optical recording,
Since each piece of information must be recorded individually, the productivity is low and the cost is very high, while the information recording medium of the present invention is high-density recording using super-resolution. Since information can be recorded in a very short time by transferring from the stamper when the substrate is manufactured, the productivity is very high, and a large number of duplicates can be manufactured at low cost.

Further, since the information recording medium having the initialization layer of the present invention can be reproduced by the same method as the super-resolution rewritable medium using magneto-optical recording, it is a drive for this rewritable medium. It is also possible to make them compatible so that they can be played.

Further, by using a recording layer capable of magneto-optical recording as the initialization layer of the information recording medium having the initialization layer of the present invention, the read-only portion and the rewritable portion are different. By forming the same film on both parts without forming the films separately, both the read-only part and the rewritable part can be manufactured at the same time.
It is possible to provide a partial ROM in which the film forming process is very easy and which is a high-density recording medium using super-resolution and has a uniform recording density in the read-only section and the rewritable section. Moreover, in this partial ROM, it is possible to perform the reproduction of the information of the reproduction-only section and the reproduction of the information of the rewritable section by the same reproduction mechanism.

[0053]

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of the structure of an information recording medium of the present invention.

FIG. 2 is a diagram showing an example of a structure of a substrate of the information recording medium of the present invention.

FIG. 3 is a diagram illustrating an interference effect due to a phase difference of reflected light from pits in the information recording medium of the present invention and a principle of super-resolution of the present invention.

FIG. 4 is a diagram showing the reproducing magnetic field dependency of C / N at a pit length of 0.5 μm of the information recording medium of the present invention (Example 1).

FIG. 5 is a diagram showing the reproduction power dependency of C / N at a pit length of 0.5 μm of the information recording medium of the present invention (Example 1).

FIG. 6 is a diagram showing changes in C / N with respect to pit lengths of an information recording medium of the present invention (Example 1) and a comparative example.

FIG. 7 is a cross-sectional view showing another example of the structure of the information recording medium of the present invention.

FIG. 8 is a diagram showing the reproducing magnetic field dependence of C / N at a pit length of 0.5 μm of the information recording medium of the present invention (Example 2).

FIG. 9 is a diagram showing changes in C / N with respect to the pit length of the information recording medium (Example 2) of the present invention.

FIG. 10 is a cross-sectional view showing another example of the structure of the information recording medium of the present invention.

[Explanation of symbols]

 1: transparent substrate 2: dielectric layer 3: reproducing layer 4: dielectric layer 5: reflective layer 6: initialization layer 7: recording layer

Claims (5)

[Claims] 1. In an information recording medium in which information is recorded by unevenness on a transparent substrate, a recording surface, which is a surface of the transparent substrate on which unevenness for carrying information is formed, has in-plane magnetization at room temperature and has a predetermined temperature. An information recording medium having a reproducing layer which changes from in-plane magnetization to perpendicular magnetization when heated above. 2. The reproducing method for an information recording medium according to claim 1, wherein a magnetic field larger than a perpendicular coercive force of the reproducing layer at the time when the reproducing layer makes a transition from in-plane magnetization to perpendicular magnetization is perpendicular to the recording surface. In this direction, the recording surface of the information recording medium is irradiated with laser light to raise the temperature to a temperature at which the irradiated portion of the reproducing layer partially becomes perpendicularly magnetized, and the intensity of a predetermined polarization component of the reflected light is increased. A reproducing method of an information recording medium, characterized by detecting a change. 3. In an information recording medium in which information is recorded by unevenness on a transparent substrate, a recording surface, which is a surface of the transparent substrate on which unevenness for carrying information is formed, has in-plane magnetization at room temperature and has a predetermined temperature. It has a reproducing layer that changes from in-plane magnetization to perpendicular magnetization when heated above, and an initialization layer composed of a perpendicular magnetization film, and the magnetization direction of this initialization layer is aligned in one direction in advance. An information recording medium, which is initialized to. 4. The information recording medium reproducing method according to claim 3, wherein the recording surface of the information recording medium is irradiated with a laser beam to raise the temperature of the irradiated portion of the reproducing layer to a temperature at which it is partially perpendicularly magnetized. Then, the method for reproducing the information recording medium is characterized in that the intensity change of a predetermined polarization component of the reflected light is detected. 5. The recording surface of the transparent substrate has a read-only portion and a rewritable portion, and both the read-only portion and the rewritable portion have in-plane magnetization at room temperature and are heated to a predetermined temperature or higher. And a recording layer capable of magneto-optical recording and a reproducing layer for transitioning from in-plane magnetization to perpendicular magnetization, the reproduction-only portion having information recorded by unevenness of the recording surface, and the recording layer of the reproduction-only portion. An information recording medium in which the direction of magnetization of is initialized in advance so as to be aligned in one direction.