JPH06203411A - Optical information recording medium and recording / reproducing method - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an optical disc for recording and reproducing information at high speed and high density, and in particular, to obtain stable tracking characteristics with small crosstalk even when signals are recorded on both the groove and the land. With the goal. An optical information recording medium comprising a substrate and a recording film on which a signal is recorded by laser light irradiation,
The surface of the substrate on which the recording film is provided has a groove for signal recording and a laser having a pair of projections and depressions at a position in the extension direction of the groove and slightly deviated from the position on the center line of the groove on both sides. Sample pits for spot guidance are alternately provided, the width of the groove and the distance between the grooves are substantially the same, and the depth D of the groove is λ / (7n) ≦ D <5λ / (14n) λ: reproduction The wavelength of light, n: The refractive index of the substrate is satisfied.

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 for recording and reproducing information at high speed and high density by using light, heat and the like.
In particular, it relates to an optical disc.

[0002]

2. Description of the Related Art When a laser beam is focused by a lens system, a light spot whose diameter is on the order of the wavelength of the light can be formed. Therefore, it is possible to create a light spot with a high energy density per unit area even from a light source with a small output. Therefore, it is possible to change a minute area of the substance, and it is also possible to read out the change of the minute area. An optical information recording medium uses this for recording / reproducing information. Less than,
Described as "optical recording medium" or simply "medium".

One of the optical recording media is the so-called phase change recording, in which the state of the recording film material is changed by the irradiation of laser light to change the optical constant, and the change in the reflectance accompanying it is detected to record / reproduce a signal. There is a medium. The phase change recording medium can record a signal without deforming the recording film,
Further, since it is possible to rewrite a signal by reversibly changing the state of the recording film material, research has been actively conducted in recent years.

As a phase change recording material, a chalcogen alloy is well known, for example, GeSbTe type, InSbTe type, GeSn type.
Te-based, InSe-based, SbTe-based, etc. are available. These materials are brought into an amorphous state by being melted and cooled by laser irradiation with relatively strong power, and the amorphous region reaches a crystallization temperature or higher by a laser irradiation with relatively weak power to be in a crystalline state. Since the optical constants are different between the amorphous state and the crystalline state, the recorded signal can be reproduced as a change in the amount of reflected light due to laser irradiation.

On the other hand, development aiming at high-density recording is also in progress, for example, not only on a guide groove for signal recording of an optical disk, but also on a signal between the guide groove (hereinafter, groove) and the guide groove (hereinafter, land). A method of recording to increase the recording density has been proposed (Japanese Patent Publication No. 63-57859). Further, in this case, if the groove shape such as the groove depth and the groove width is limited, a cross from an adjacent track (because the signal is recorded on both the groove and the land, both are recording tracks. It has been reported that the talk can be made very small.
Lecture number 18a-T-3. Further, it is detailed in Japanese Patent Application No. 4-79483. ).

Further, as a tracking method for the groove provided on the optical disk, there are mainly a three-beam method and a push-pull method.

In the push-pull method, a detector for detecting the reflected light of the laser light from the optical disk is divided into two parallel to the track direction, the difference signal of the outputs from the two divided detectors is taken, and this is controlled. Signal. When the spot is at the center of the track, the amount of reflected light is symmetric with respect to the track, so the difference signal is 0. Control is performed so that the spot follows the track.

In the three-beam method, the laser beam is divided into three beams, and the laser beams are focused in a line on the disk. At this time, the spot row is tilted slightly with respect to the track, for example, the main spot in the center is the center of the track, the sub-spot in the front is just to the right of the main spot, and the sub-spots in the rear are set to the main spot. Place it to the left rear of the spot and slightly above the track. Then, recording / reproduction of a signal is performed at the main spot, and tracking is performed by detecting the amount of reflected light from each of the preceding and following sub-spots and controlling the difference so that the difference becomes 0. It makes it possible.

[0009]

In the method of recording on both the groove and the land, the distance between the recording tracks is about half that of the method of recording only on the groove or only on the land. Spans adjacent tracks. Therefore, the reflected light is affected by the signal recording state of the adjacent track. For example, if a signal is recorded only on one of the adjacent lands when there is a laser spot on the groove, asymmetry occurs in the intensity distribution of the reflected light in the direction perpendicular to the track. In the push-pull method, an offset occurs in the tracking error signal due to this asymmetry, and also in the three-beam method, the offset occurs in the tracking error signal because the amount of reflected light at the front and rear tracking sub-spots is different. There is a problem that the tracking control becomes unstable, or the crosstalk becomes large because recording / reproducing is performed while being offset to one adjacent track.

[0010]

An optical information recording medium having at least a recording film on which a signal is recorded by laser light irradiation is provided on a substrate, wherein a surface of the substrate on which the recording film is provided is for signal recording. Irregular grooves, and alternately provided with sample pits for laser spot guide consisting of a pair of irregularities at positions slightly offset from the position on the center line of the groove in the extension direction of the groove, and The width of the groove and the distance between the grooves are substantially the same, and further, the depth D of the groove satisfies λ / (8n) ≦ D <5λ / (14n) λ: wavelength of reproducing light, n: refractive index of substrate To

In recording / reproducing and erasing a signal in such a medium, the reflected light or transmitted light from the pair of sample pits is detected on the groove, and tracking is controlled based on the light amount difference between them. In between, the polarity of the tracking signal is reversed and the reflected light or transmitted light from a pair of sample pits located on both sides of the extension line between the grooves is detected, and tracking is performed based on the difference in their light amounts. Do it with control.

[0012]

With the above structure, even if signals are recorded on both the land and the groove, the crosstalk from the adjacent track is small because the groove depth is limited, and the tracking is performed by the reflected light from the sample pit. Alternatively, since the transmitted light is used, the laser spot can be stably positioned at the track center regardless of the presence or absence of a signal on the adjacent track.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The optical information recording medium and the recording / reproducing method of the present invention will be described in detail below with reference to the drawings.

Various proposals have been made for increasing the density of optical discs, one of which is a method of recording a signal on both the groove and the land. Furthermore, in this case, crosstalk from adjacent tracks can be made extremely small by limiting the groove shape such as groove depth and groove width. Japanese Patent Application 4-
In No. 79483, in order to reduce the crosstalk amount to -20 dB or less, the groove depth D satisfies λ / (7n) ≤ D ≤ 5λ / (14n) λ: wavelength of reproducing light, and n: refractive index of substrate It should be set as follows, and further approximately λ / (5n)
Alternatively, it is shown that the crosstalk is minimized by setting approximately 3λ / (10n).

Therefore, recording / reproducing is performed by producing a phase change medium which causes a reversible state change between an amorphous phase and a crystalline phase on the substrate by varying the groove depth while keeping the land and the groove width substantially the same. As a result of repeated studies on the characteristics, the following facts were clarified.

1. The groove depth D is λ / (8n) ≦ D ≦
If it is set to satisfy 5λ / (14n), the crosstalk will be -20 dB or less. Especially λ / (7n) ≦ D ≦ 1
At 3λ / (40n), the crosstalk becomes -25 dB or less. Furthermore, approximately λ / (5n) or approximately 3λ / (10n)
At the crosstalk is minimal.

2, provided that the groove depth D is 9λ / (40
In the range of n) <D <11λ / (40n), the crosstalk becomes small, but the reproduction signal amplitude from the recording track itself also becomes small.

3. Further, when a signal is recorded on only one of the tracks adjacent to the track where the laser spot is located, for example, when the laser spot is located on the groove, the signal is only applied to one of the adjacent lands. If is recorded, tracking becomes unstable and a track jump may occur.

4. Similarly, when a signal is recorded on only one of the tracks adjacent to the track on which the laser spot is located, for example, only on one of the adjacent lands when the laser spot is located on the groove. Large crosstalk may occur when the signal is recorded.

The groove width and land width of the optical disk used in this study are both about 0.8 μm, the substrate is polycarbonate, the refractive index is 1.58, and the reflectance in the crystalline state is about 30%.
(When the wavelength is 780 nm), the reflectance of the amorphous state in the recording mark is about 5%, the recording mark length is about 0.8 μm, the laser wavelength of the evaluation device is 780 nm, and the numerical aperture NA of the objective lens is 0.50. is there. The amount of crosstalk is defined as the ratio of the reproduction signal amplitude when a signal is recorded on a track and the reproduction amplitude of the crosstalk signal from the track where an adjacent signal is recorded.

The above examination was carried out by the three-beam method, but the tracking method also appeared in the push-pull method for the phenomena 3 and 4. That is, it was found that the crosstalk reduction effect due to the limitation of the groove depth becomes small in some cases. As described in the above problem, the cause is considered to be that tracking offset occurs because the amount of reflected light from the left and right tracks of the track where the recording / reproducing spot is located is different.

Therefore, the present inventors propose a method of recording a signal on both the land and the groove, in which a signal recording area and a tracking control area are separated. There is a sample servo method as a method of separating the recording area and the tracking area of the signal. This is a method in which sample pits slightly displaced from the center line of the recording track to both sides are arranged at regular intervals on the track, and tracking is performed based on a reproduction signal from the sample pit. That is, by introducing the sample servo method to the method of recording signals on both the land and the groove of the optical disc whose groove depth is limited, stable tracking control can always be obtained, and recording / reproduction with a small crosstalk can always be performed. I found out that

FIG. 1 shows an example of the groove shape and sample pit shape of the optical disk used in the present invention. Reference numeral 1 is a groove, which is provided in a concave shape on the surface of the substrate. Although 2 is a land, in the present invention, since a signal is recorded in the land in the same manner as in the groove, the widths of the groove and the land are made substantially equal. Here, in order to reduce the crosstalk, the depth D of the groove may be in the range of λ / (8n) ≦ D ≦ 5λ / (14n) λ: the wavelength of the reproduction light, and n: the refractive index of the substrate, Especially λ / (7n) ≦ D ≦ 13
It is preferably in the range of λ / (40n). Further, if it is approximately λ / (5n) or approximately 3λ / (10n), the crosstalk will be minimal.

Reference numeral 3 is a sample pit for performing tracking control. The sample pits form a pair slightly offset from the center of the track (for example, S1A in the figure).
And S1B), for example, when the laser spot 4 moves from left to right in the figure, tracking can be performed on the groove G3 by controlling the amount of reflected light from the sample pit S3A and the amount of reflected light from S3B to be constant. . Since the sample pits and the grooves are arranged at regular intervals in the track direction on the optical disk, it is possible to record and reproduce the signals on the grooves while performing tracking based on the reproduced signals from the sample pits. Tracking control on the groove is performed by sampling and holding the control signal from the above-mentioned sample pit. That is, since the tracking control is performed only by the sample pits, stable control is always possible without being affected by the recording state on the groove or the recording state of the adjacent groove.

In order to perform tracking on the land, the polarity of the tracking control signal may be inverted.
As a result, for example, the amount of light reflected from the sample pits S4A and S3B can be controlled to be equal to each other, and the light is tracked on the land L3.

Reference numeral 5 is a clock pit, which is a pit provided to obtain a timing signal necessary for signal recording / reproduction. Clock pits are provided on the extension lines of both the groove and the land. However, the clock pit may be provided only on the groove, and when the laser spot is on the land, the clock pit on the adjacent groove may be reproduced by crosstalk to obtain the timing signal.

Similarly, the focus control is preferably performed outside the groove area, for example, in the mirror surface area before or after the sample pit.

FIG. 2 shows a sectional view of a recording area of an example of the optical disk used in the present invention. Here, a phase change recording medium capable of reversibly changing its state between an amorphous phase and a crystalline phase by laser irradiation, that is, rewritable will be described. Reference numeral 6 denotes a substrate, on which the groove having the above-mentioned depth D is provided. As the material of the substrate, transparent glass, quartz, polycarbonate, polymethylmethacrylate, etc. are generally used. A dielectric film 7, a recording film 8, a dielectric film 9 and a reflective film 10 are laminated in this order on the substrate. Further, a protective cover 11 may be provided to protect the thin film layer if necessary. As the recording film 8, a material generally known as a phase change material can be used. That is, it is an alloy such as Te, Se, Sb, In, Ge that causes a state change between an amorphous and a crystal, or between a crystal and a different crystal, such as GeSbT
Alloys of e, InSbTe, GaSb, InGaSb, GeSnTe, AgSbTe, etc.
The dielectric films 7 and 9 are preferably transparent and thermally stable substances, for example, semimetal oxides, nitrides, chalcogenides, fluorides, carbides and the like, and mixtures thereof,
Specifically, SiO2, SiO, Al2O3, GeO2, In2O3, TeO2, TiO2, MoO
3, WO3, ZrO2, Si3N4, AlN, BN, TiN, ZnS, CdS, CdSe, ZnSe, ZnT
It is e, AgF, PbF2, MnF2, NiF2, SiC alone or a mixture thereof. The reflection film 10 is composed of a metal film, and as a material thereof, for example, a simple substance such as Au, Al, Ti, Ni, Cu, Cr or the like or an alloy thereof can be used.

Although the structure having a reflective film is shown in FIG. 2, a structure without a reflective film, that is, a structure in which a dielectric film, a recording film and a dielectric film are laminated in this order on a substrate may be used. Further, as the recording film, an organic material or the like can be used in addition to the phase change material.

Although a rewritable optical disk has been described with reference to FIG. 2, the present invention can be applied to a so-called write-once optical disk that can be recorded only once.

Next, by using an optical disk having a groove and a sample pit as shown in FIG. 1 and a recording film structure as shown in FIG. A specific example in which the magnitude of talk is measured will be described.

Example 1 The substrate material was polycarbonate (refractive index n = 1.58), and the groove width and the land width were both about 0.8 μm. The groove depth D was set to about 100 nm, which is about λ / when the laser wavelength is 780 nm.
(5n). The dielectric films 7 and 9 in FIG.
A mixture of S and SiO2 (20mol%) is used, and the film thickness of the dielectric 7 is 130n.
m, and the film thickness of the dielectric 9 was 20 nm. The recording film 8 is a GeSbTe ternary system which is a phase change recording material capable of reversibly changing its state between an amorphous phase and a crystalline phase by laser irradiation.
The reflective film 10 was made of Al and had a thickness of 150 nm. All thin films were formed by the sputtering method. Since the recording film 8 is in an amorphous state immediately after the optical disc is manufactured, the tracks are preliminarily crystallized to the initial state. In this optical disc, recording is performed by forming an amorphous recording mark on a crystalline track. Since the crystalline state has a higher reflectance than the amorphous state, the recording signal can be detected as a reflectance change.

Then, this optical disk is rotated at a linear velocity of 10 m / s, a 780 nm semiconductor laser beam is focused on a recording film by a lens having a numerical aperture of 0.5, and signal recording / reproduction is performed while performing tracking control by a sample servo system. I did.

Signal recording was carried out as follows. First, 100 continuous tracks are selected (that is, 50 grooves and 50 lands). Next, select an arbitrary groove from among them and record a 5 MHz signal. Next, the polarity of tracking is reversed, and tracking is performed on a land, an arbitrary land is selected, and a 4 MHz signal is recorded. Further, the tracking polarity is reversed and tracking is performed on the groove, and one arbitrary groove is selected from the unrecorded grooves and a 5 MHz signal is recorded. By repeating this, signals are sequentially recorded in the groove and the land. 10
For 0 tracks all, 5MHz for groove, and for land
A 4 MHz signal was recorded. That is, according to this recording method, the recording of the signal in various states when the signal is not recorded on the track adjacent to the recording track, when the signal is recorded on both of them, or when the signal is recorded on only one of the grooves, is recorded in the groove. It is realized in both record and land record.

Crosstalk from the adjacent tracks was measured on all the tracks in which the signals were recorded in this way. That is, in the groove,
The crosstalk of the signal of 4MHz and the crosstalk of the signal of 5MHz from the adjacent groove were measured in the land. As a result, crosstalk is -30 dB on all tracks
It was below, and it was confirmed that it was suppressed to a very small value.

As described above, according to the present invention, it has been proved that stable tracking and crosstalk characteristics can be obtained regardless of the state of the adjacent track of the recording track.

Here, in order to further clarify the effectiveness of the present invention, an optical disk having a thin film similar to that shown in FIG.
An example of recording and reproducing signals while performing tracking control by the beam method will be described.

(Example 2) The groove shape of the optical disk was a continuous groove. Therefore, there is no sample pit as shown in FIG. The groove width, the land width, and the groove depth D were the same as in Example 1 above. Further, the materials and film thicknesses of the recording film, the dielectric film, and the reflective film are the same as those in the first embodiment.

This optical disk is also crystallized on the track in advance and then rotated at a linear velocity of 10 m / s, and a semiconductor laser beam of 780 nm is focused on the recording film by a lens having a numerical aperture of 0.5, and tracking control is performed by a push-pull method. While recording and reproducing signals.

The signal recording method and the crosstalk measuring method are the same as in the first embodiment. As a result, the crosstalk varies greatly depending on the track, for example, a good value of -30 dB or less may be obtained, but on the contrary, a large value of about -15 dB may also appear. Such a large crosstalk causes tracking offset when a signal is recorded on one of the tracks adjacent to the recording track, and the signal is recorded in a state where the laser spot is not located at the center of the track. It is thought to be a tame.

As a result of conducting the same examination for the case where the same optical disk is used to perform tracking control by the three-beam method, a large variation in crosstalk was observed as in the case of the push-pull method.

That is, from the first and second embodiments, in the conventional method of recording signals on both the land and the groove on the optical disk having the continuous groove, if the push-pull method and the three-beam method are used for tracking control, it may be necessary. Although tracking offset may occur, which may be a practical problem, the optical information recording medium and the recording / reproducing method according to the present invention provide stable tracking and crosstalk regardless of the state of adjacent tracks. It was found that the characteristics could be obtained.

Further, in order to accurately control the position of the laser spot on the optical disk and record / reproduce a signal on a predetermined track, it is necessary to accurately reproduce the address information provided on the track. When signals are recorded on both the land and the groove by the sample servo method, address pit rows having address information may be arranged on the extension lines of the land and the groove.

When the address pit row is provided only on the extension line of the groove and the laser spot is tracked on the groove, the address information is obtained from the address pit row on the track and the address pit is on the land. In this case, the address information may be obtained by crosstalk from the address pit row on the adjacent groove. A large change in the amount of reflected light can be obtained from the uneven pits provided on the substrate like the address pit row, so that the crosstalk becomes large and the address information can be reproduced as the crosstalk.

At this time, if the address pit rows are provided at the adjacent positions on the extension lines of all the grooves, the address information of the two adjacent grooves is simultaneously reproduced as crosstalk when the laser spot is on the land. Therefore, a means for separating this is required.

Therefore, as shown in FIG. 3, the address pit row provided on the odd-numbered groove and the address pit row provided on the even-numbered groove are provided at positions not adjacent to each other. In this way, when the laser spot is located on the land, the address information from two adjacent grooves can be detected as separate crosstalk signals, so the address of the land can be determined from the two address information. It can be uniquely specified. For example, in FIG. 3, when the laser spot 19 is located on the land L5, first the information of the 14 address pit rows A provided on the groove G5 is read by crosstalk, and then the information is provided on the groove G6. The information in the address pit row B is read by crosstalk. In other words, the laser spot 1 from these two address information
It can be recognized that 9 is located on the land L5 between the grooves G5 and G6.

In FIG. 3, sample pits and clock pits are provided in front of the respective address pit rows A and B and the signal recording area as in the case of FIG. Omitted.

[0048]

As described above in detail, according to the optical information recording medium and the recording / reproducing method of the present invention, the groove depth is limited even if a signal is recorded on both the land and the groove. Crosstalk from adjacent tracks is small,
Moreover, since the tracking is performed by using the reflected light or the transmitted light from the sample pit, the laser spot can be stably positioned at the track center regardless of the presence or absence of the signal on the adjacent track. That is, since the signal can be recorded on both the land and the groove, the recording density is high,
Further, it is possible to provide an optical information recording medium and a recording / reproducing method having small crosstalk and more stable tracking characteristics.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining a recording medium according to the present invention.

FIG. 2 is a sectional view for explaining a recording medium according to the present invention.

FIG. 3 is a schematic diagram for explaining a method of recording address information on a recording medium according to the present invention.

[Explanation of symbols]

 1, 13, 17 Groove 2, 12, 18 Land 3 Sample pit 4 Laser spot 5 Clock pit 6 Substrate 7, 9 Dielectric film 8 Recording film 10 Reflective film 11 Protective cover 14, 15 Address pit row 16 Signal recording area

Front page continued (72) Inventor Nobuo Akabira 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Noboru Yamada, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (10)

[Claims] 1. An optical information recording medium having at least a recording film on which a signal is recorded by laser light irradiation provided on a substrate, wherein a surface of the substrate on which the recording film is provided has an uneven shape for signal recording. The groove and the sample pit for guiding the laser spot, which is composed of a pair of concave and convex portions, are alternately provided at positions displaced from the position on the center line of the groove on both sides in the extension direction of the groove, and the width of the groove and The distance between grooves is substantially the same, and further, the depth D of the grooves satisfies λ / (8n) ≦ D ≦ 5λ / (14n) λ: wavelength of reproducing light, n: refractive index of substrate Optical information recording medium. 2. The depth D of the groove is λ / (7n) ≦ D ≦ 1
The optical information recording medium according to claim 1, which satisfies 3λ / (40n). 3. The optical information recording medium according to claim 2, wherein the depth D of the groove is approximately λ / (5n). 4. The optical information recording medium according to claim 2, wherein the depth D of the groove is approximately 3λ / (10n). 5. The recording film is made of a medium that changes the amount of reflected light when irradiated with a laser beam.
The optical information recording medium described. 6. The optical information recording medium according to claim 5, wherein the recording film is made of a phase change medium which reversibly changes its state between an amorphous phase and a crystalline phase when irradiated with a laser beam. 7. An address pit row provided on the extension of the groove as address pit rows, and an address pit row provided on the odd-numbered groove and an address pit row provided on the even-numbered groove. The optical information recording medium according to claim 1, wherein the optical information recording media are provided at positions that are not adjacent to each other. 8. A method for recording / reproducing optical information on / from an optical information recording medium, wherein at least a recording film, the amount of reflected light of which is changed by laser light irradiation, is provided on a substrate. , A signal recording concave-convex groove and a laser spot guide sample pit composed of a pair of concave-convex patterns are alternately arranged at a position in the extension direction of the groove, which is slightly displaced from the position on the center line of the groove to both sides. When provided, the tracking to the groove detects the reflected light or the transmitted light from the pair of sample pits and controls based on the light amount difference between them, and the tracking between the grooves uses the tracking signal. While reversing the polarity, detecting the reflected light or transmitted light from a pair of sample pits located on both sides of the extension line between the grooves and controlling them based on the difference in their light amounts. An optical information recording method characterized by recording and reproducing a signal. 9. The groove width and the groove distance are substantially the same, and the groove depth D is λ / (8n) ≦ D ≦ 5λ / (14n) λ: the wavelength of the reproducing light, n: the substrate The optical information recording medium according to claim 8, wherein the refractive index is satisfied. 10. When the address information is provided as an address pit string on the extension line of the groove, when the laser spot is between the grooves, the information from the address pit string is detected as crosstalk. The optical information recording method according to claim 8.