JPH1097735A - Optical information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect both tracks from being damaged even if highdensity recording is performed for both tracks by setting a level difference between high and low place information tracks to half of a light wavelength in a transparent substrate. SOLUTION: A plurality of recessed grooves 12 are formed in the surface of a transparent substrate 11, and the surface of the substrate 11 is set as a high place information track 13 while its bottom surface is set as a low place information track 14. A level difference between the tracks 13 and 14 is defined as (almost) half of the wavelength λ of a recording/reproducing optical beam in the substrate 11. Accordingly, when a level difference between the tracks is relatively large, heat diffusion to an adjacent track is small and, even if high-density recording is performed in both of the tracks 13 and 14, no damage occurs in information for both. During reproducing, the reflected light phase of the track 13 is the same, little difference is produced between reproducing signals from the tracks 13 and 14 even without setting a difference in reflected light phases between the crystal and non-crystal conditions of mutually changed recording layers on the substrate 11 to zero, and the reproducing signals are prevented from being made unstable by preventing interference between reflected lights.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium such as an optical card for a large-capacity file and an optical card for recording or reproducing information by using a light beam such as a laser beam, and in particular, provided on a medium substrate. The present invention relates to a high-density optical information recording medium capable of recording information on each of a bottom surface (low position) of a concave portion and a substrate surface (high position) between the concave portions.

[0002]

2. Description of the Related Art An optical information recording medium such as an optical disk has very excellent characteristics as a storage device for a large amount of information, like a hard disk. In particular, an optical disc is most suitable as a medium for distributing and transporting multimedia information data such as image data requiring an extremely large capacity, since information can be recorded / reproduced by a light beam and only the information storage section can be carried. . In order to record a large amount of information on such an optical information recording medium, the information recording density must be further improved. The information density of an optical information recording medium is
It is determined by the pitch of information tracks and the information density in the track direction, that is, the linear density of information. To improve the information density of an optical information recording medium, it is necessary to narrow the track pitch and increase the linear density.

In a conventional optical information recording medium, a guide groove of a minute concave portion having a width of 0.8 μm and a pitch of 1.6 μm is formed in a spiral shape on the surface of a disk-shaped transparent substrate, and this substrate is formed on the surface of the substrate by sputtering or the like. GeSbTe or AgInSb
Phase change recording materials such as Te, TbFeCoTi and TbF
A thin film of a magneto-optical recording material such as eCoTa is formed.
In many cases, the thin film layer of the recording material is sandwiched between protective film layers such as a transparent dielectric, and a reflective film layer is provided thereon. In many cases, a protective film layer is further provided thereon. In recent years, there has been proposed a medium in which the transparent substrate side of such a medium is placed outside and two sheets are bonded to increase the amount of recorded information. The transparent substrate with the guide grooves is exposed to a laser beam by photo-resist to cause a photoreaction, and then developed to form a concave part. Large amounts are copied by such methods.

In this conventional optical information recording medium, information is recorded / reproduced by passing a light beam through a transparent substrate at a low place (concave section) or a high place (convex section) in the vicinity of an uneven guide groove. It is performed by irradiating one of the surfaces. The guide groove is used for the light beam to accurately follow the position of the information track. A displacement signal (track error signal) between the light beam and the guide groove is detected by a push-pull method. That is, the far field pattern of the reflected light from the optical information recording medium is detected by a two-segment photodetector having two light receiving areas, and the difference between the photocurrents detected in the two light receiving areas is determined on the optical information recording medium. Position deviation between the guide groove and the light beam is detected. The depth of the information tracking guide groove is set to a value of λ / 8 (where λ is the wavelength of the light beam in the transparent substrate) at which the tracking error signal is the largest (for example, see Japanese Unexamined Patent Application Publication No. 8044
No. 3). Here, if the pitch of the guide grooves is narrowed to increase the density, it becomes difficult to manufacture the substrate.

In order to solve the problem associated with the increase in recording density due to the narrow guide groove pitch, both the bottom surface of the guide groove, which is a low place, and the substrate surface between the guide grooves, which is a high place, are provided. An information track system is disclosed in U.S. Pat.
No. 502 is proposed. In this method, even though the guide groove pitch is the same as the conventional one, information is recorded on each of the information tracks at the low place and the high place, so that it is possible to obtain a recording density almost twice as large as the conventional one.

[0006]

However, the inventor of the present invention has described a method of recording information on such information tracks at a high place and a low place and reproducing the information on a phase change optical disk or a magneto-optical disk. When high-density recording / reproduction experiments were performed using this method, recording information on a low-altitude information track affected the phase state and magnetic state of an adjacent high-altitude information track. The problem of damage occurred. Similarly, when information is recorded on a high-altitude information track, there is a problem that information on an adjacent low-altitude information track is damaged. For this reason, there is a problem that it is actually difficult to realize high-density recording / reproduction with high quality.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical information recording medium capable of preventing the recording information of adjacent low-altitude information tracks and high-altitude information tracks from being damaged and increasing the recording density. .

[0008]

SUMMARY OF THE INVENTION According to the present invention, a recording layer is formed on each of a bottom surface of a groove provided in a transparent substrate and a surface of the transparent substrate between the grooves, and these recording layers are formed at a low position. In an optical information recording medium configured as a track and a height information track, and recording or reproducing information by irradiating each information track with a light beam through the transparent substrate, the difference between the height of the height and the height of the height is less. Set to λ / 2 or a value in the vicinity of λ / 2. Here, the recording layer is a phase change recording layer made of a phase change material or a magneto-optical recording layer made of a magneto-optical material.

Further, in the present invention, it is preferable to provide a pre-pit for controlling a track of information recorded by a light beam. It is preferable that the track control prepits are arranged in a staggered manner, or that the depth of the prepits is approximately λ / 4.

[0010]

Next, embodiments of the present invention will be described with reference to the drawings. 1 and 2 are views for explaining an optical information recording medium according to an embodiment of the present invention. FIG. 1 is a schematic sectional perspective view of a transparent substrate 11, and FIG. FIG. 3 is a cross-sectional view when applied to a recording medium. In FIG. 1, a plurality of concave grooves 12 are formed as guide grooves on the surface of a transparent substrate 11, and the surface of the transparent substrate 11 between the guide grooves 12 serves as a high-altitude information track 13.
Two information tracks are provided alternately, with the bottom surface of the guide groove as the low-place information track 14. The guide groove 12 is formed in a spiral shape in the case of an optical disk, and is formed in a linear shape in the case of an optical card. Here, the height difference between the high-altitude information track 13 and the low-altitude information track 14 on the transparent substrate 11 is set to λ / 2 or a value near λ / 2. Here, λ is the wavelength of the recording / reproducing light beam in the transparent substrate 11. For example, wavelength 6 in air
Assuming a recording / reproducing laser of 40 nm, the width of the high-altitude information track 13 is 0.56 μm, the width of the low-altitude information track 14 is 0.56 μm, and the height difference is 202 nm.
A transparent substrate made of polycarbonate is used. That is, the difference between the heights of the information tracks is approximately λ / 2.

Then, as shown in FIG.
On the interference layer 2 consisting of a mixture of ZnS and SiO ₂
1 is 160 nm, phase change recording layer 2 made of GeSbTe
2 is 10 nm, the interference layer 23 made of a mixture of ZnS and SiO ₂ is 30 nm, and the reflection layer 24 made of AlTi is 6 nm.
0 nm, the protective layer 2 consisting of a mixture of ZnS and SiO ₂
5 is laminated to a thickness of 60 nm, and an organic protective layer 26 is formed thereon to form an optical recording medium. Further, in this embodiment, the optical recording medium thus formed is bonded to two optical recording media with a UV curable resin 27 with the protective layer side back to back so that the transparent substrate 11 is on the outside. Together, they constitute an optical information recording medium.

When information is recorded using this optical information recording medium, the optical information recording medium is moved at a predetermined speed along the length direction of the information tracks 13 and 14,
While controlling the track so that the light beam incident through the transparent substrate 11 is positioned on the information track, the intensity of the light beam is modulated between the amorphization levels depending on the information to be recorded. For example, when recording is performed so that a recording mark is in an amorphous state, a mark in an amorphous state is formed by irradiating a light beam with an amount of light enough to melt the phase change recording layer, and a mark other than the recording mark is formed. During the period, a light beam of an amount of light that does not melt is applied for crystallization. Therefore, during a period other than the recording mark, the state before irradiation is in a crystalline state regardless of whether the state is amorphous or crystalline. Therefore, overwriting (overwriting) is performed even in a place where information is already recorded. It will be. In addition, information recorded on the optical information recording medium is reproduced by utilizing the fact that the reflectance and the phase difference are different between the amorphous state and the crystalline state. For example, a light beam having a weak constant intensity is irradiated, reflected light from an optical information recording medium is received by a photodetector, and information is reproduced by a change in reflected light amount.

As described above, in the optical information recording medium of this embodiment, the height difference between the high information track 13 and the low information track 14 is set to 情報 of the wavelength λ. Even if information is recorded on both the location information track 13 and the low location information track 14 at a high density, the information is hardly damaged. It is considered that the reason for this is that, by increasing the difference between the heights of the two information tracks, the thermal diffusion during recording to the adjacent information track was reduced. At the time of reproduction, the phase of the reflected light from the high-altitude information track 13 and the phase of the reflected light from the low-altitude information track 14 are the same. Therefore, even if the difference between the phase of the reflected light when the phase change recording layer 22 is in the crystalline state and the phase of the reflected light when the phase change recording layer 22 is in the amorphous state is not set to zero, the high-altitude information track can be obtained. There is no significant difference between the reproduction signal from the low-frequency information track 14 and the reproduction signal from the low-level information track 14, and the reproduction signal is not destabilized due to interference between the reflected light signals.

Here, an optical head having a numerical aperture of 0.6 using a semiconductor laser having a wavelength of 640 nm in the air is used, and 9.7 M at a linear velocity of 6.6 m / sec.
Hz signal was recorded and reproduced. After the information was recorded on the high-altitude information track, the information was recorded on the immediately adjacent low-altitude information track, and then the information on the first high-altitude information track was reproduced. As a result, the information was not damaged. As a similar experiment, the information was recorded on the low-altitude information track, and then the information was recorded on the immediately adjacent high-altitude information track, and then the information on the first low-altitude information track was reproduced without any information damage. .

As a comparative example, the height difference between the high information track and the low information track is λ / 8 (the height difference is 50n).
The optical information recording medium of m) was manufactured, and the same recording and reproduction as in the above embodiment were performed and the evaluation was performed. It was confirmed that the film was damaged by changing to a crystalline state. In addition, as another comparative example, when an optical information recording medium having no difference in height was manufactured and the same evaluation was performed, it was confirmed that the damage to the adjacent track was even greater. That is, in the optical information recording media of these comparative examples, since the difference in height between the high information track and the low information track is small, adjacent information tracks are affected by heat and the crystal state is damaged. Will occur. In addition, the phase of the reflected light from the high-altitude information track and the phase of the reflected light from the low-altitude information track are different by 90 degrees, and the phase of the reflected light when the phase change recording layer is in a crystalline state is different from the phase of the reflected light. When the change recording layer is in an amorphous state, the phase of the reflected light also differs due to a slight difference in the laminated film configuration. Therefore, the reproduction signal behaves in a complicated manner due to the synergistic action thereof, and it is difficult to obtain a stable reproduction signal. It will be.

As described above, the optical information recording medium according to the above-described embodiment has the advantages that the influence on adjacent information tracks can be prevented and a stable reproduction signal can be obtained. Certain push-pull methods cannot be used. Therefore, pre-pits for track control are provided. FIG. 3 is a schematic plan view for explaining a desirable arrangement of track control prepits in the embodiment. Reference numeral 113 denotes a high-altitude information track, and 114 denotes a low-altitude information track. In the figure, a solid line indicates a boundary between the tracks, and a broken line indicates the center of each track. Each information track is divided into a servo area 101, an address area 102, and an information recording area 103. The servo area 101 is an area to which servo of an information track is applied, the address area 102 is an area for giving address information of an information track, and the information recording area 103 is an area for actually recording user information. Servo area 101
In the address area 102, a pre-pit 104, which is a concave portion provided in advance on the substrate, is formed. The address area 102 may not be present. That is, 102 and 1
03 may be repeated as a set. In some cases, a set of 101, 102, and 103 may be provided during the repetition. These 101, 102 and 103
In the case of a disc-shaped medium, it is preferable to provide one set or two equal sets in one circumference for moving image information and the like.

The pre-pits 104 in the servo area 101 are
As shown in FIG.
, The center of which is a symmetry axis, and are arranged in a staggered manner on both sides thereof, so that good track control can be performed. It should be noted that the track control is not limited to the method of providing the staggered pre-pits, and other methods may be used. For example, as shown in FIG. 4, a step 10 having a height of about λ / 8
5 may be provided.

The depth of the pre-pit 104 is as follows:
In the case of λ / 4, the signal becomes the largest, which is desirable. As a method for manufacturing such a substrate, a λ / 4 photoresist as a photoresist for laser beam exposure for manufacturing a stamper is used.
Can be used. Alternatively, as a simple manufacturing method, a single-layer photoresist having a film thickness of λ / 2 is applied, and it can be completely developed as a laser beam exposure amount to a low-altitude information track portion (the exposed photoresist is removed). There is a method in which the exposure amount is set to a small exposure amount so that intermediate development can be performed by setting the exposure amount to an exposure amount (which can be dissolved to the bottom with a developer).

In each of the above embodiments, the present invention is applied to a phase-change type optical recording medium. However, even when the present invention is applied to a magneto-optical recording medium, adjacent high-altitude information tracks and low-altitude tracks can be used. It is possible to obtain an optical information recording medium which prevents mutual influence between the information track and the information track, does not damage each record information, and stabilizes a reproduction signal.

[0020]

As described above, according to the optical information recording medium of the present invention, the difference between the heights of the high information track and the low information track is defined as λ / 2 of the wavelength λ of light in the transparent substrate. Therefore, according to this, an optical information recording medium is obtained in which even if information is recorded on both the high information track and the low information track at a high density, the respective information is not damaged.
Further, by providing the pre-pits for track control, it is possible to obtain an optical information recording medium capable of track control by the conventionally used push-pull method.

[Brief description of the drawings]

FIG. 1 is a perspective view of a part of a transparent substrate according to an embodiment of the present invention.

FIG. 2 is a sectional view of an optical recording medium according to an embodiment of the present invention.

FIG. 3 is a plan view of a part of an information track.

FIG. 4 is a cross-sectional view of a part of a transparent substrate according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Transparent substrate 12 Guide groove 13 High information track 14 Low information track 21 Interference layer 22 Phase change recording layer 23 Interference layer 24 Reflection layer 25, 26 Protective layer 27 UV curing resin 101 Servo area 102 Address area 103 Information recording area 104 Prepit 113 High-altitude information track 114 Low-altitude information track

Claims (7)

[Claims] 1. A bottom surface (low place) of a concave groove provided in a transparent substrate.
And forming a recording layer on each of the transparent substrate surfaces (high places) between the concave grooves, and configuring these recording layers as low-level information tracks and high-level information tracks, and passing each information track through the transparent substrate. In an optical information recording medium for recording or reproducing information by irradiating a light beam,
The optical information recording method according to claim 1, wherein the height difference between the high place and the low place is λ / 2 or a value near λ / 2 (where λ is the wavelength of the light beam in the transparent substrate). Medium. 2. The optical information recording medium according to claim 1, wherein the recording layer is a phase change recording layer made of a phase change material or a magneto-optical recording layer made of a magneto-optical material. 3. The transparent substrate according to claim 2, wherein low places and high places are alternately arranged on the surface of the transparent substrate, and an interference layer, a recording layer, an interference layer, a reflection layer, and a protective layer are sequentially formed on the surface. Optical information recording medium. 4. The optical information recording medium according to claim 3, wherein the two optical information recording media are integrated with the protective layer side back to back. 5. The optical information recording medium according to claim 1, further comprising a pre-pit for controlling a track of information recorded by a light beam. 6. The optical information recording medium according to claim 5, wherein the track control pre-pits are arranged in a staggered manner. 7. The optical information recording medium according to claim 2, wherein the depth of the prepit is substantially λ / 4.