JPH11144326A - Phase change type optical information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of a weaving and to stably conduct a tracking having less crosstalks even though a track pitch is made narrower in order to realize a high density recording in the groove recording system which records information in only guide grooves. SOLUTION: Even though the track pitch is made narrower, the increase of the jitters caused by cross talk is suppressed to be less than 20%, which practically presents no problem, by setting push-pull fluctuations of the push-pull signals to more than 70%. Thus, by making the push-pull fluctuations to be more than 70%, the meandering against the guide grooves is prevented and a tracking having less crosstalks is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in the field of optical memory-related equipment and the like, and causes a phase change in a recording layer material by condensing and irradiating a laser beam on an optical information recording medium. Record or reproduce information, and
The present invention relates to a rewritable (overwriteable) phase change optical information recording medium.

[0002]

2. Description of the Related Art As one of optical memory media capable of recording, reproducing and erasing information by irradiating an electromagnetic wave, particularly a laser beam, a so-called phase-change type light utilizing a transition between a crystalline phase and an amorphous phase. Information recording media are well known. According to the phase change type optical information recording medium, overwriting with a single beam, which is particularly difficult with a magneto-optical disk memory, is possible, and the optical system on the drive side is simpler. R & D is active.

A typical example of such a phase-change optical information recording medium is a so-called chalcogen-based alloy material as disclosed in US Pat. No. 3,530,441. According to Japanese Patent Application Laid-Open No. Sho 62-73438, Ge-T
A composition such as e-Se-Sb is specified.

In recent years, so-called DVDs have been attracting much attention as next-generation disks having a high information recording density. In particular, a DVD-RAM capable of recording, reproducing, and erasing a DVD-ROM that can only be reproduced and a DVD-R that can be recorded and reproduced have attracted attention. in this case,
Higher density can be achieved by making the track pitch narrower. However, when the track pitch is made narrower, signals from adjacent tracks leak, the noise of the reproduced signal increases, and errors frequently occur. Several proposals have been made as countermeasures against such crosstalk.

[0005] For example, according to Japanese Patent Application Laid-Open No. 6-338064, L & G for recording on both lands and grooves is disclosed.
And the track groove depth and groove width are respectively λ / 5n to λ /
7n, 0.34R to 1.0R (R = beam diameter (1 / e
² )), crosstalk is reduced by optimization.

According to Japanese Patent Application Laid-Open No. H8-321078, in the L & G method, the groove depth, the land and the groove width are regulated so as to be optimum, so that high density and high O are achieved.
/ W.

[0007]

However, in a phase-change optical information recording medium of a groove recording system (groove G system) in which recording is performed only in guide grooves, a cross-talk limit is imposed when the track is narrowed. Yes, it is not fully studied like the L & G method.

[0008] For example, a report that crosstalk can be prevented by forming a deep groove ('96 Phase Change Recording Research Group Proceedings p7
7-80 "Development to DVD-RAM of Deep Groove system"), but in reality, it is an optical disk without even a tracking servo, which is not practical.

According to Japanese Patent Application Laid-Open No. 8-279187, it is described that cross talk can be reduced by reducing birefringence even when the track pitch is narrowed, and that the recording pitch is 1 μm or less. Have been. However, the publication also presupposes the L & G method, and the data of the L & G method cannot be directly reflected on the groove recording method because the focus position is different between the land and the groove. .

Therefore, according to the present invention, in a groove recording method for recording only in a guide groove, even if the track pitch is narrowed in order to increase the recording density, it is possible to prevent meandering and to stably perform tracking with less crosstalk. It is an object to provide a phase change type optical information recording medium.

Still another object of the present invention is to provide a phase change type optical information recording medium capable of further stabilizing the characteristics in that case.

[0012]

According to the first aspect of the present invention,
A transparent substrate and at least one or more recording layers and at least one
It has a multilayer structure including at least one dielectric layer and at least one reflective layer, and records / records information only in the guide groove.
In the erasable phase-change optical information recording medium, the push-pull fluctuation defined by the minimum / maximum of the push-pull signal is 70% or more. Therefore, even if the track pitch is made narrower, by making the push-pull fluctuation of the push-pull signal 70% or more, it is possible to prevent the guide groove from meandering and perform tracking with less crosstalk.

According to a second aspect of the present invention, in the phase-change type optical information recording medium according to the first aspect, the track pitch of the guide groove is equal to the beam diameter of the laser beam applied to the recording layer.
/ E ² is 70% or more. Accordingly, recording can be performed with recording marks having a pitch of about the beam diameter, and tracking with less crosstalk can be performed by preventing meandering of the guide grooves.

According to a third aspect of the present invention, in the phase-change optical information recording medium according to the first aspect, the thickness of the transparent substrate is:
It is 0.3 mm or more and 0.7 mm or less. Therefore, when the recording density is high, the NA of the objective lens in the optical pickup increases, so that it is necessary to reduce the thickness of the substrate.
By using a transparent substrate having a thickness of 3 mm or more and 0.7 mm or less, tracking with less crosstalk can be performed.

According to a fourth aspect of the present invention, in the phase change type optical information recording medium of the first aspect, a ratio of a groove width of the guide groove to a track pitch is 0.5 or more and 0.75 or less. Therefore, when the ratio between the groove width and the track pitch is 0.5 or more, the jitter as the recording / erasing characteristic is good, and when the ratio between the groove width and the track pitch is 0.75 or less, the push-pull variation is reduced by 70%. Since the above is sure, tracking with less crosstalk can be performed.

According to a fifth aspect of the present invention, in the phase-change optical information recording medium according to the first aspect, the main component material of the recording layer contains at least one of Ag, In, Sb, and Te. Therefore, it is possible to prevent the guide groove from meandering, to perform tracking with less crosstalk, and to improve recording / erasing characteristics.

According to a sixth aspect of the present invention, in the phase-change optical information recording medium according to the first aspect, the track groove depth of the transparent substrate is set such that the wavelength of the laser beam applied to the recording layer is λ, Assuming that the refractive index of the substrate is n, λ / 9n to λ /
5n. Accordingly, tracking with little crosstalk can be performed by preventing the guide groove from meandering, and the recording / erasing characteristics are good, and the push-pull signal and the track cross signal are also stabilized.

According to a seventh aspect of the present invention, in the phase change type optical information recording medium according to the first aspect, the recording layer has a thickness of 10%.
nm to 30 nm. It is possible to prevent the guide groove from meandering, to perform tracking with less crosstalk, and to improve recording / erasing characteristics.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings. First, as shown in FIG. 2, a phase change type optical information recording medium 1 used in the present embodiment has a lower protective layer (dielectric layer) 3, a recording layer 4, an upper protective layer 5, It has a multilayer structure in which a heat radiation layer (reflection layer) 6 and a UV protection layer 7 are sequentially laminated. Here, the transparent substrate 2 is formed of a polycarbonate resin. The shape of the transparent substrate 2 (therefore, the shape of the phase-change optical information recording medium 1) is, for example, a disk shape, but may be a card shape or a sheet shape. Upper and lower protective layers 3,
5 is made of, for example, ZnS, SiO ₂ , SiN _x, or the like. The recording layer 4 changes its optical constant when irradiated with an electromagnetic wave such as a laser beam. Preferably, the recording layer 4 is a phase-change material, and more preferably,
A material containing Ag, In, Sb and Te is preferable. Therefore,
The recording layer 4 is made of, for example, AgInSbTe or GeSb
It is formed of Te or the like. The heat radiation layer 6 is made of, for example, A
1 or Al alloy, Au, Ag, or the like. Although the heat radiation layer 6 is not always necessary, it is preferable to provide the heat radiation layer 6 in order to reduce the heat load on the disk (transparent substrate 2) by dissipating excessive heat by the heat radiation layer 6. UV
The protective layer 7 is formed of a UV curable resin.

The phase change type optical information recording medium 1 which can be used in the present embodiment is not limited to such a structure and a material. Is preferable since it becomes better.

It should be noted that even in such a phase change type optical information recording medium 1, an optical disk which is currently practically used and commercially available and can be recorded only once and cannot be rewritten (so-called write-once compact disk = WO) As in the case of (CD), recording and erasing in a CD format (for example, EFM modulation code of CD-ROM format code data) is possible, and a guide groove (track) for tracking is previously provided on the medium. It is spirally formed as a pregroove. Here, land is formed between the grooves, but in the present embodiment, a guide groove recording method for recording / erasing information only in the guide groove is assumed.

In this embodiment, such a phase-change type optical information recording medium 1 is designed to prevent the guide groove from meandering and perform tracking with less crosstalk even when the track pitch is narrowed. The specifications are set as follows.

First, the push-pull fluctuation defined by the minimum / maximum of the push-pull signal is set to be 70% or more. FIG. 1A shows the relationship between the push-pull variation ((min / max) [%]) of the push-pull signal and the jitter increase rate [%] due to crosstalk. Here, the push-pull fluctuation is, as shown in FIG. 1B, the minimum value min and the maximum value m of the error signal in the push-bull signal.
ax. According to the characteristics shown in FIG. 1A, it can be seen that by setting the push-pull fluctuation to 70% or more, it is possible to prevent an increase in jitter due to crosstalk even in the guide groove recording method and reduce the jitter. Incidentally, since the initial jitter ((σ / Tw) [%]) is about 7 to 11%, if the jitter increase rate is about 20% or less,
Since the jitter does not substantially exceed 14%, the error can be suppressed (the jitter and the error rate have a correlation,
Errors increase sharply from about 14-15% jitter),
High-density recording becomes possible.

Second, the track pitch is determined by the beam diameter (1/1).
The guide groove is formed so as to be 70% or more of e ² ). FIG. 3 shows a relationship between a track pitch and a jitter increase rate due to crosstalk. As the push-pull fluctuation,
An example of about 50% and about 70% are shown. When the track pitch is formed a guiding groove such that more than 70% of the beam diameter (1 / e ^2), it is possible to form a recording mark of about pitch beam diameter (1 / e ^2). Therefore, according to the characteristics shown in FIG. 3, the track pitch is equal to the beam diameter (1 / e).
^If the push-pull fluctuation is 70% or more in ² ) or more, the beam does not become large and cannot be read to the recording mark on the adjacent track, so that phase change optical information recording with little crosstalk and stable tracking is performed. It becomes medium 1.

Third, the thickness of the transparent substrate 2 is set to 0.3 mm or more and 0.7 mm or less. At high density recording, the NA of the objective lens in the optical pickup increases, so it is necessary to reduce the thickness of the transparent substrate 2.
By making the push-pull fluctuation 70% or more using the transparent substrate 2 having a thickness of 0.7 mm or more and 0.7 mm or less, the phase change type optical information recording medium 1 with less crosstalk and stable tracking can be obtained.

Fourth, the ratio between the groove width of the guide groove and the track pitch is set to be 0.5 or more and 0.75 or less. FIG. 4 shows the relationship between the ratio [%] between the groove width of the guide groove and the track pitch and the jitter ((σ / Tw) [%]). Therefore, according to the characteristics shown in FIG. 4, by setting the ratio [%] between the groove width of the guide groove and the track pitch to 50% or more, the jitter which is the recording / erasing characteristic is good (the jitter is 13% or less). If the ratio between the groove width and the track pitch is 0.75 or less, it is easy to make the push-pull variation 70% or more, so that the phase change type optical information recording medium with less crosstalk and stable tracking. It becomes 1.

Fifth, as described above, the main component material of the recording layer 4 contains at least one of Ag, In, Sb, and Te, and is typically made of AgInSbTe. Since the recording and erasing characteristics are good and the push-pull variation is 70% or more under such conditions, the phase change optical information recording medium 1 with less crosstalk and stable tracking is obtained.

Sixth, the guide groove depth of the transparent substrate 2 is λ / 9.
n to λ / 5n (where λ is the wavelength of the laser beam to be irradiated,
n is set to be the refractive index of the transparent substrate 2). FIG. 5 shows the relationship between the groove depth and the jitter ((σ / Tw) [%]) when the wavelength λ of the laser beam is 635 nm. Therefore, according to the characteristics shown in FIG.
If 9n to λ / 5n (53 nm to 85 nm), the jitter which is the recording / erasing characteristic is good (the jitter is 14% or less), and the push-pull signal and the track cross signal are also stabilized. Since the push-pull variation is set to 70% or more below, the phase-change optical information recording medium 1 with less crosstalk and stable tracking is obtained.

Seventh, the recording layer 4 has a thickness of 10 nm to 30 nm.
nm. FIG. 6 shows the relationship between the thickness of the recording layer 4 and the jitter ((σ / Tw) [%]). Therefore, according to the characteristics shown in FIG.
If it is set to 0 nm, the recording / erasing characteristic jitter is good (jitter is 14% or less).
Since the push-pull fluctuation is set to 70% or more, the phase change optical information recording medium 1 with less crosstalk and stable tracking can be obtained.

Here, as a more specific configuration example of the phase-change optical information recording medium 1, a transparent substrate 2 has a refractive index n = 1.
A lower protective layer 3 of ZnS—SiO ₂ is formed on the transparent substrate 2 with a thickness of 170 nm using a polycarbonate resin having a thickness of 0.6 mm and a thickness of 170 nm, and a recording layer 4 of Ag2In10Sb28Te60 is formed on the lower protective layer 3. It is formed to a thickness of 15 nm, and ZnS-Si
The upper protective layer 5 made of O ₂ has a thickness of 20 nm and a refractive index of 2.1.
And an Al-Ti (1 wt.
%), A heat radiation layer 6 made of an Al alloy having a thickness of 100 nm was formed, and a UV protection film 7 made of a UV curable resin was formed on the uppermost layer.

In such a configuration of the phase change type optical information recording medium 1, the jitter caused by crosstalk when each of the first to sixth conditions is changed so as to correspond to the samples 1 to 6. Table 1 shows the increase rate [%]. Incidentally, the phase-change optical information recording medium 1 used for these samples 1 to 6 is a disc having a diameter of 120 nm.
For samples 1 to 6, the depth of the guide groove is 60 n.
m. In contrast, Comparative Sample 1
An example in which the push-pull variation is set to about 50% will be described. On the other hand, the optical information recording / reproducing device used for the measurement evaluation is a normal CD-system recordable / erasable drive device, and is roughly composed of an optical pickup, a signal processing system, and a pickup control system. The pickup control system includes a tracking servo system for performing tracking control by a push-pull method. The wavelength of the laser beam used in this drive device is 635 nm, the numerical aperture of the objective lens is NA = 0.6, and the beam is Diameter (1 / e ² ) = 0.93 μm
It is. Further, the power of the laser light to be applied was a multi-pulse emission waveform having a peak power of 12 mW, a bottom power of 5 mW, and a read power of 1 mW in the case of a 3T write pulse as shown in FIG. In Table 1, the storage capacity is a reference value when a DVD-ROM is referred to.

[0032]

[Table 1]

Therefore, according to Samples 1 to 6, it can be understood that the storage capacity can be increased, that is, the density can be increased under the condition that the crosstalk is small.

[0034]

According to the first aspect of the present invention, in a phase-change optical information recording medium in which information can be recorded / erased only in the guide groove, the push-pull signal can be pushed even if the track pitch is narrowed. By setting the pull fluctuation to 70% or more, it is possible to prevent the guide groove from meandering and perform tracking with less crosstalk.

According to the second aspect of the present invention, since the push-pull fluctuation of the push-pull signal is set to 70% or more and the track pitch of the guide groove is set to 70% or more of the beam diameter 1 / e ² , the beam diameter is reduced. The recording can be performed with recording marks having a pitch of about, and meandering with respect to the guide groove can be prevented, and tracking with less crosstalk can be performed.

According to the third aspect of the invention, since the push-pull variation of the push-pull signal is set to 70% or more and the thickness of the transparent substrate is set to 0.3 mm or more and 0.7 mm or less, high density recording is achieved. Accordingly, even if the NA of the objective lens in the optical pickup increases, tracking with less crosstalk can be performed.

According to the fourth aspect of the invention, the push-pull signal has a push-pull variation of 70% or more, and the ratio of the guide groove width to the track pitch is 0.5 to 0.7.
Since the number is set to 5 or less, tracking with less crosstalk can be performed.

According to the fifth aspect of the present invention, the push-pull variation of the push-pull signal is set to 70% or more, and at least Ag, In, Sb,
Since any component of Te is included, meandering of the guide groove can be prevented, tracking with less crosstalk can be performed, and recording / erasing characteristics can be improved.

According to the sixth aspect of the present invention, the push-pull signal has a push-pull variation of 70% or more and the track groove depth of the transparent substrate is λ / 9n to λ / 5n. Not only can tracking be performed with less crosstalk by preventing meandering, the recording / erasing characteristics are good, and the push-pull signal and the track cross signal can be stabilized.

According to the seventh aspect of the present invention, since the push-pull variation of the push-pull signal is set to 70% or more and the thickness of the recording layer is set to 10 nm to 30 nm, meandering with respect to the guide groove is prevented. Tracking with less talk can be performed, and the recording / erasing characteristics can be improved.

[Brief description of the drawings]

FIGS. 1A and 1B show an embodiment of the present invention, in which FIG. 1A is a characteristic diagram of push-pull fluctuation-jitter increase rate, and FIG.

FIG. 2 is a sectional structural view showing a layer configuration of a phase change optical information recording medium.

FIG. 3 is a diagram showing a track pitch / beam diameter-jitter increase rate characteristic.

FIG. 4 is a graph showing a groove width / track pitch-jitter characteristic.

FIG. 5 is a graph showing a groove depth-jitter characteristic.

FIG. 6 is a diagram showing a recording layer thickness-jitter characteristic.

FIG. 7 is a time chart showing a pulse-type waveform for explaining peak power and the like at the time of measurement.

[Explanation of symbols]

 2 Transparent substrate 3 Dielectric layer 4 Recording layer 6 Reflective layer

Claims (7)

[Claims] 1. A multi-layer structure including a transparent substrate, at least one or more recording layers, at least one or more dielectric layers, and at least one or more reflective layers, and records information only in guide grooves. A phase-change optical information recording medium capable of erasing, wherein the push-pull fluctuation defined by the minimum / maximum of the push-pull signal is 70% or more. 2. The phase-change optical information according to claim 1, wherein the track pitch of the guide groove is at least 70% of the beam diameter 1 / e ² of the laser beam applied to the recording layer. recoding media. 3. The method according to claim 1, wherein the thickness of the transparent substrate is 0.3 mm or more.
2. The phase-change optical information recording medium according to claim 1, wherein the length is 7 mm or less. 4. The phase-change optical information recording medium according to claim 1, wherein a ratio of a groove width of the guide groove to a track pitch is 0.5 or more and 0.75 or less. 5. The recording layer comprising at least A as a main component material.
2. The phase-change optical information recording medium according to claim 1, further comprising any one of g, In, Sb, and Te. 6. The track groove depth of the transparent substrate is λ / 9n to λ / 5n, where λ is the wavelength of the laser beam applied to the recording layer and n is the refractive index of the transparent substrate. The phase-change optical information recording medium according to claim 1, wherein: 7. The phase-change optical information recording medium according to claim 1, wherein the recording layer has a thickness of 10 nm to 30 nm.