JP2007257809A - Optical recording medium and optical recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording method which performs high-speed recording and also performs recording on the same optical recording medium at a higher recording speed while keeping downward compatibility which achieves recording by a conventional drive for low-speed recording. <P>SOLUTION: When information is optically recorded by a mark-length recording method in which an amorphous mark and a crystalline space are recorded only to a groove on a substrate having a guide groove and the time lengths of the mark and space are represented by nT (wherein, T represents a basic clock cycle, and n represents a natural number), the spaces is formed by erasure pulse which radiates at least power Pe, and all the marks of more than 4T in length is formed by using multipulse which alternately radiates the heating pulse of power Pw and the cooling pulse of power Pb (wherein, Pw>Pb). In addition, an equation 0.15≤Pe/Pw≤0.4 is satisfied and an equation 0.4≤τw/(τw+τb)≤0.8 is also satisfied in the optical recording method (wherein, τw represents the sum of the lengths of heating pulses, and τb represents the sum of the lengths of cooling pulses). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a high-density optical recording medium having a phase change recording layer such as DVD + RW, DVD-RW, BD-RE, and HD DVD RW, and an optical recording method for the optical recording medium.

In recent years, there has been a remarkable increase in capacity of electronic information, but in storage devices that handle large amounts of data, the larger the capacity, the longer it takes to record, so an optical recording medium capable of recording at higher speed is required. ing. In particular, a disk-shaped optical recording medium is increasing in speed because it can increase the recording and reproducing speed by increasing the rotational speed. Among such optical discs, those that can be recorded only by intensity modulation of light irradiated during recording can reduce the cost of optical recording media and recording devices because of the simplicity of the recording mechanism. The optical recording medium of the recording method only for recording can be ensured high compatibility with the optical reproduction dedicated device, and is therefore widely used.
The conventional groove recording type recording mark is formed, for example, as described in Japanese Patent Application Laid-Open No. H10-228688, for example. In order to satisfy “rate−minimum reflectance) / maximum reflectance”, it is formed so as to protrude from the groove width. In this example, the recording linear velocity is about 2.4 times the standard velocity of DVD (2.4x = about 8.4 m / sec), and the scanning speed of the beam is slow at such a low recording velocity. Even if the width is larger than the groove, crystallization proceeds due to the residual heat from the beam after passing, and a sufficient erasure ratio is obtained.

CD-RW, DVD + RW, DVD-RW, etc. have been put to practical use so far as optical recording media that record only in the groove, using a rewritable phase change material for the recording layer. Optical recording media capable of recording at higher speeds have been developed. Recently, an optical disk system capable of recording with a blue LD, such as a Blu-ray disk capable of recording a larger capacity, has been put into practical use, and this will also increase in speed in the future. It is expected to be. Among such rewritable DVDs, DVD + RW, which is increasing in speed, has a standard up to 8 × speed (about 28 m / s), and development of a higher-speed optical recording medium is awaited.
Up to now, high-speed recording of phase-change optical recording media has been performed by using a material having a high crystallization speed for the recording layer or by increasing the crystallization speed in combination with a protective layer. However, it has become clear that the following various problems occur when the crystallization speed of an optical recording medium is increased in correspondence with a high recording speed exceeding 8 × speed of DVD.

The first problem is that a large crystal grows in the amorphous mark during the recording process, and when this mark is reproduced, the mark is apparently shorter than a predetermined length, resulting in an error. . As shown in FIGS. 1A to 1C, when recording is performed on an optical recording medium having a high crystallization speed, an abnormal crystal growth portion is generated in the mark depending on the recording conditions, and the reproduced signal is distorted to increase errors. I know that. Here, FIG. 1A is a schematic diagram for explaining an abnormal recrystallization region, wherein A and C are normal marks, and B is a mark having an abnormal recrystallization region. 1B shows a reproduction signal of marks A to C, and FIG. 1C shows a signal after binarization of marks A to C. This error tends to increase as the recordable speed increases. As a countermeasure, it is conceivable to develop a recording method that solves the problem on the low speed side without increasing the crystallization speed of the recording layer and improves the recording characteristics on the high speed side.
However, if recording is performed at a high speed by slowing down the crystallization speed, the crystal growth rate during recording mark formation is suppressed, and the width of the recording mark, which is an amorphous layer, becomes large, resulting in the problems described above. This is easily inferred from the principle of phase change recording, and it has been considered difficult to achieve both high-speed recording and a wide recording speed range.
Further, as an attempt to obtain sufficient recording characteristics at a wide range of recording speeds by changing the time constant of the recording strategy, there is an example as described in Patent Document 2, for example. This is due to the means for increasing the width. Further, the method disclosed in Patent Document 3 has a problem that overwriting becomes difficult at high speed, and the recording linear velocity range is not sufficient.

  The second point is a so-called cross-write problem in which a recorded amorphous mark is partially crystallized by recording on an adjacent track. Since an optical recording medium having a high crystallization speed is likely to be recrystallized, it is necessary to make a large melting region so that a sufficiently large amorphous mark can be recorded even if recrystallization is performed. In relation to this, since it is necessary to increase the power of the LD, there is a problem that a part of the recorded amorphous mark is crystallized by heating up to an adjacent track.

  The third problem is that low-speed recording cannot be performed under the same conditions as those of conventional optical recording media for low-speed recording, that is, backward compatibility becomes difficult. For example, in the case of DVD, there is a problem that even if high-speed recording exceeding 8 × speed can be realized, if the conventional 8 × speed recording drive cannot perform recording, user convenience is impaired.

  Therefore, it is possible to perform high-speed recording while avoiding the problems of increased errors due to abnormal recrystallization and increased jitter due to cross-write, and backward compatibility that enables recording with the same low-speed recording drive at low speeds on the same optical recording medium. However, an optical disc system capable of recording at a higher speed is still not available, and the prompt provision of the optical disc system is desired.

Japanese Patent Laid-Open No. 2002-237096 JP 2003-16643 A Japanese Patent No. 3572068

  An object of the present invention is to solve various problems in the prior art and achieve the following objects. In other words, the present invention can perform high-speed recording that avoids the problems of increased errors due to abnormal recrystallization and increased jitter due to cross-write, and can be recorded on the same optical recording medium at low speed with a conventional low-speed recording drive. It is an object of the present invention to provide an optical recording medium and an optical recording method capable of realizing an optical disc system capable of high-speed recording while having low backward compatibility.

Means for solving the problems are as follows. That is,
<1> Light is applied to a substrate having a guide groove and an optical recording medium having at least a phase change recording layer on the substrate, and corresponds to either a convex portion or a concave portion of the guide groove as viewed from the incident direction of the light. In an optical recording method for recording an amorphous mark and a crystal space in the phase change recording layer,
When recording information by a mark length recording method in which the time length of the mark and the space is represented by nT (where T represents a basic clock period and n represents a natural number),
The space is formed by an erasing pulse that irradiates at least power Pe,
Formation of all the marks having a length of 4T or more is performed by a multi-pulse that alternately irradiates a heating pulse of power Pw and a cooling pulse of power Pb (where Pw> Pb),
When Pe and Pw satisfy the following formula, 0.15 ≦ Pe / Pw ≦ 0.4, the sum of the lengths of the heating pulses is τw, and the sum of the lengths of the cooling pulses is τb An optical recording method satisfying the following formula: 0.4 ≦ τw / (τw + τb) ≦ 0.8.
<2> A substrate having a guide groove and an optical recording medium having at least a phase change recording layer on the substrate are irradiated with light to correspond to either a convex portion or a concave portion of the guide groove as viewed from the incident direction of the light. In an optical recording method for recording an amorphous mark and a crystal space in the phase change recording layer,
When recording information by a mark length recording method in which the time length of the mark and the space is represented by nT (where T represents a basic clock period and n represents a natural number),
The space is formed by an erasing pulse that irradiates at least power Pe,
The formation of the mark is performed by a heating pulse that irradiates at least power Pw (where Pw> Pe), and Pe and Pw satisfy the following expression: 0.15 ≦ Pe / Pw ≦ 0.5. An optical recording method is characterized.
<3> When recording and reproduction are performed with a laser beam having a wavelength of 640 to 660 nm, recording is performed at 10 times or more of the reference linear velocity, and when recording and reproduction is performed with a laser beam having a wavelength of 400 to 410 nm, the reference linear velocity is used. The optical recording method according to any one of <1> to <2>, wherein recording is performed at a quadruple speed or higher.
<4> The recording medium according to any one of <1> to <3>, wherein recording is performed such that an average value of minimum distances between marks on adjacent tracks in a radial direction is larger than ½ of a track pitch. This is an optical recording method.
<5> The optical recording method according to any one of <1> to <4>, wherein recording is performed so that a modulation degree M of the longest mark satisfies the following expression: 0.35 ≦ M ≦ 0.60.
<6> An optical recording medium, wherein information relating to the optical recording method according to any one of <1> to <5> is previously recorded on a substrate.

  According to the present invention, conventional problems can be solved, high-speed recording can be performed while avoiding problems such as an increase in errors due to abnormal recrystallization and an increase in jitter due to cross-write. It is possible to provide an optical recording medium and an optical recording method capable of realizing an optical disc system capable of recording at a higher speed while having backward compatibility capable of recording even with a low-speed recording drive.

(Optical recording medium and optical recording method)
The optical recording method of the present invention irradiates light onto a substrate having a guide groove and an optical recording medium having at least a phase change recording layer on the substrate, and the convex and concave portions of the guide groove as viewed from the incident direction of the light. In the phase change recording layer corresponding to any one of the above, an amorphous mark and a crystal space are recorded, and the time length of the mark and the space is nT (where T is a basic clock period, n When recording information using the mark length recording method represented by
In the first embodiment, the space is formed by an erasing pulse that irradiates at least power Pe,
Formation of all the marks having a length of 4T or more is performed by a multi-pulse that alternately irradiates a heating pulse of power Pw and a cooling pulse of power Pb (where Pw> Pb),
When Pe and Pw satisfy the following formula, 0.15 ≦ Pe / Pw ≦ 0.4, the sum of the lengths of the heating pulses is τw, and the sum of the lengths of the cooling pulses is τb The following equation is satisfied: 0.4 ≦ τw / (τw + τb) ≦ 0.8.
In the second embodiment, the space is formed by an erasing pulse that irradiates at least power Pe,
The mark is formed by a heating pulse that irradiates at least power Pw (where Pw> Pe), and Pe and Pw satisfy the following expression: 0.15 ≦ Pe / Pw ≦ 0.5.
In the optical recording medium of the present invention, information relating to the optical recording method of the present invention is recorded in advance on a substrate.
Hereinafter, the details of the optical recording medium of the present invention will be clarified through the description of the optical recording method of the present invention.

  First, in order to form an optical recording medium capable of repetitive recording at high speed, a method of using a phase change material having a high crystallization speed for the recording layer or increasing the crystallization speed in combination with a protective layer is usually used. Is used. This is because if the crystallization speed is high, the amorphous mark can be erased at a high speed, so that high-speed repetitive recording becomes possible. However, if the crystallization speed is increased in accordance with high-speed recording, the above-described various problems occur, so that the crystallization speed cannot be increased so much. In addition, if recording is performed at a high speed on an optical recording medium having an insufficient crystallization speed, the amorphous mark remains unerased when overwritten, resulting in a reproduction error.

  The materials practically used as the recording layer of the phase change type optical recording medium are roughly classified into those having Te as a main component and those having Sb as a main component, and are optical disc systems that record only in a groove. DVD + RW and DVD-RW use a recording layer containing Sb as a main component. This is because when a recording layer containing Sb as a main component is used, good recording characteristics can be obtained with a relatively simple layer structure, and compatibility with an optical reproduction apparatus is high. In the crystallization process from the amorphous state, nucleation is dominant in a material containing Te as a main component, whereas a material containing Sb as a main component is an amorphous region or a molten region and a crystalline region. The crystal growth from the boundary is dominant. As described above, in the recording layer containing Sb as a main component, if the size of the amorphous mark is large, the time required for all to crystallize becomes long, and if it is small, the crystallization is completed in a short time. Therefore, even if the crystallization speed is not high enough to cause various adverse effects, if a specific optical recording method is used and recording is performed so that the width of the amorphous mark is small, good repeated recording characteristics can be obtained at high speed. It is done.

  Here, in the case of DVD, the groove means a portion where the guide groove is convex when viewed from the light incident direction, and the concave portion is called a land. In the case of an optical disk system using a blue LD, in addition to this, the concave portion may be referred to as a groove, and the convex portion may be referred to as a land. In any case, in the present invention, the groove recording means recording on the recording layer corresponding to only one of the convex portion and the concave portion of the guide groove.

-Relationship between crystallization speed and recording linear velocity-
As a substitute characteristic of the crystallization rate, a value called a transition linear velocity can be used. Here, the measurement of the transition linear velocity can be performed using DDU-1000, ODU-1000, etc. manufactured by Pulstec Industrial Co., Ltd., which are normal recording and reproducing characteristics evaluation machines. The transition linear velocity can be obtained by measuring the reflectance after rotating the optical recording medium at a constant linear velocity and irradiating the laser beam to the extent that the recording layer can be melted for one round. When the same measurement is performed with the power of the continuous light to be irradiated being constant and changing the rotational linear velocity, the reflectance is high when the linear velocity is slow, but the reflectance starts to decrease when the linear velocity is exceeded. The linear velocity when the reflectance starts to decrease is referred to as a transition linear velocity. This is shown in FIG. Here, a straight line is drawn between a portion where the reflectivity is substantially constant with respect to the linear velocity and a portion where the reflectivity decreases with respect to the linear velocity, and the intersection of these is determined as the transition linear velocity. When the linear velocity is lower than the transition linear velocity, the recording layer is in a recrystallized state after being melted.When the linear velocity is higher than the transition linear velocity, all of the recording layer cannot be recrystallized and remains partially amorphous. Show. The transition linear velocity is determined not only by the crystallization speed of the recording layer, but also by the power of continuous light to be irradiated and the thickness of each layer forming the optical recording medium, that is, the optical condition and the thermal condition.

Recording on an optical recording medium so that the transition linear velocity is 21 to 30 m / s when continuous light with a disk surface power of 15 ± 1 mW is irradiated using a pickup head having a wavelength of 650 ± 10 nm and NA of 0.65 ± 0.01. When the layer composition and layer structure are determined, the DVD is suitable for 8 × speed recording (about 28 m / s).
However, using the same optical recording method as that used up to 8 × speed on the same optical recording medium, DVD 10 × speed (about 35 m / s) and DVD 12 × speed (about 42 m / s) are faster linear speeds. When recording is performed, the crystallization speed is slower than the recording linear velocity, so that the amorphous mark remains unerased, and good repeated recording characteristics cannot be obtained. For this reason, it has been considered that an optical recording medium having a transition linear velocity exceeding 30 m / s is necessary to perform repetitive recording at a DVD speed of 10 times or higher. However, as described above, problems such as the occurrence of abnormal recrystallized grains and cross light become remarkable, and good recording characteristics cannot be obtained simply by using an optical recording medium having a high transition linear velocity. Therefore, when recording is performed so that the width of the amorphous mark is reduced by using a specific recording method with respect to the same optical recording medium for DVD 8 × speed as the transition linear velocity is 21 to 30 m / s, 10 × speed is obtained. Even with the above, good recording characteristics can be obtained, and since the transition linear velocity is the same as that of an optical recording medium for DVD 8 × recording, backward compatibility is possible up to DVD 8 × using a conventional recording drive. It was found to have sex. However, good characteristics cannot be obtained by overwriting the portion recorded at a low speed so that the width of the mark becomes large with a recording that narrows the width of the mark. Care must be taken, such as recording small, or limiting the recordable linear velocity range by the radial position and recording only within the recording linear velocity range.
Therefore, in the optical recording method of the present invention, when recording and reproduction is performed with a laser beam having a wavelength of 640 to 660 nm, it is preferable to perform recording at a speed 10 times or more, particularly 10 to 16 times the reference linear speed. Here, the reference linear velocity (single speed) is about 3.5 m / s.

In addition, a Blu-ray disc, which is an optical disc system capable of higher-density recording using an LD with a wavelength of 405 ± 5 nm, and HD DVD RW are also recorded only in the groove. The reference linear velocity (1 × speed) is 4.92 m / s in the case of Blu-ray Disc, and 6.61 m / s in the case of HD DVD RW. Or it is being developed. It is effective to apply the same optical recording method to these also when recording at a high speed. When the transition linear velocity is measured under the condition of the surface power of 5 to 6 mW, it is in the range of 15 to 19 m / s. When an optical recording method in which the mark width is reduced at 4 × speed for a certain optical recording medium, good recording characteristics from 1 × to 4 × speed were obtained.
Therefore, in the optical recording method of the present invention, when recording and reproduction are performed with a laser beam having a wavelength of 400 to 410 nm, it is preferable to perform recording at a speed of 4 times or more, particularly 4 to 8 times the reference linear speed.

-Mark width and modulation depth-
The width of the amorphous mark can be estimated by examining the modulation degree M of the longest mark. When the signal recording method is EFM + modulation, the reflectance of the longest signal 14T space is I14H, and the reflectance of the 14T mark is I14L, which is a value represented by (I14H−I14L) / I14H. When the modulation degree M is large, the mark width is large. When the modulation degree M is small, the mark width can be regarded as small.
A larger value of the modulation factor M is preferred from the viewpoint of reproduction compatibility with ROM, etc. In the case of DVD + RW, the optical recording medium capable of recording up to 4 × speed is 0.60. The optical recording medium capable of recording at 8 × speed is defined as 0.55 or more.
In the present invention, the modulation degree M is preferably 0.35 to 0.60. If the modulation degree M is less than 0.35, good recording and reproduction cannot be performed from the initial recording, and jitter and errors may easily increase. Since it tends to occur, even if the initial recording is good, the jitter and error during repeated recording may increase.

  Here, when the optical recording medium recorded on the optical recording medium capable of 8 × speed recording with a modulation degree M of 0.63 is observed with a transmission electron microscope (TEM), as shown in FIG. 3, DVD + RW or DVD It can be seen that the amorphous mark of the optical recording medium for recording only in the groove such as -RW is wider than the width of the groove. Usually, since the land width and the groove width are about 1: 1, if the track pitch is Ltp, the distance between marks in the radial direction of adjacent tracks is Lrm, and the average value of Lrm is A (Lrm), A (Lrm) <1 / 2Ltp. If overwriting is performed at a speed 10 times faster than DVD (about 35 m / s), a wide range of marks cannot be crystallized, resulting in unerased residue and increased jitter and errors. However, as shown in FIG. 4, by recording so that A (Lrm) ≧ 1 / 2Ltp, DVD can be recorded at a high speed of 10 times speed (about 35 m / s) to 12 times speed (about 42 m / s). Even if overwriting is performed, since the width is narrow, it is possible to crystallize all of them, and good repeated recording can be performed. However, the degree of modulation in the case of FIG. 4 was as small as about 0.50. In addition to the example of FIG. 4, although the mark width is not confirmed by a transmission electron microscope (TEM), if the modulation degree M of the longest mark is recorded to be in the range of 0.35 to 0.60, the recording speed is high. It was found that good repeated recording characteristics can be obtained.

In this way, when the modulation degree of the recording mark is small, there is a risk of increasing the error rate. However, since the reading of the reproduction apparatus is performed by electrically converting the optical modulation degree of the mark by a detector such as a photodiode, the electrical dynamic range of the modulation degree is important. If the reflectivity is low, the absolute value of the electric signal is low even if the modulation degree is large, and there is a concern that the error rate may increase due to the inability to obtain a dynamic range. On the other hand, even when the modulation factor is small, if the reflectance of the entire optical recording medium is large, the dynamic range of the electrical signal corresponding to the modulation factor can be increased by increasing the absolute value of the signal. . In the case of a DVD system, the minimum reflectance is 18% in the two-layer ROM, DVD + RW, and DVD-RW standards, so the dynamic range after conversion to an electrical signal is the product of the modulation factor and the reflectance. If it is set to be constant, the same width is secured.
Therefore, in the DVD system, the same dynamic range can be obtained as long as 0.18 × 0.60 = 0.108 or more, and an increase in error rate can be suppressed.

  In the present invention, the reflectance is 27% or more when the degree of modulation is 0.40 to 0.55 in order to obtain sufficient characteristics in the range from 10 × to 16 × with a mark smaller than the groove width. I just need it. Even if the optical recording medium has a low reflectance, this relationship does not necessarily have to be satisfied if there is no problem in reproduction. However, if the reflectance is too high, it may not be possible to determine whether the optical reproducing apparatus is an optical recording medium or a reproduction-only optical recording medium due to the nature of the DVD system. In a rewritable DVD medium, it is preferable that the reflectance is 30% or less. In the case of an optical disc system using a blue LD, even a lower reflectance can be dealt with. In the case of a Blu-ray disc, 0.05 or more for a single layer and 0.016 or more for two layers. Just fill it.

Next, an optical recording method for recording so as not to increase the mark width will be described.
In the case of an optical disk using a phase change material for the recording layer, recording is performed by making the recording layer material into a rapidly cooled state and a gradually cooled state by intensity modulation of the irradiated light beam. After melting, the recording layer material becomes amorphous when rapidly cooled, and becomes crystalline when gradually cooled. Since amorphous and crystals have different optical properties, information can be recorded and reproduced. That is, the phase change type optical recording medium changes the disk reflectivity by irradiating the recording layer thin film on the substrate with laser light to heat the recording layer and changing the recording layer structure between crystal and amorphous. Information is repeatedly recorded. Usually, information is recorded by forming a crystal having a high reflectivity in an unrecorded state, and forming a space made of an amorphous mark having a low reflectivity and a crystal having a high reflectivity.
Recording is often performed by irradiating an optical recording medium with recording light that is pulse-divided and intensity-modulated to three or more values.

  FIG. 5A shows an example of a recording signal pattern (recording strategy) for repeatedly recording data consisting of marks and spaces. An amorphous mark is formed by a multi-pulse that alternately irradiates a heating pulse of power Pw and a cooling pulse of power Pb (where Pw> Pb), and a space made of a crystal is erased of the intermediate level power Pe. It is formed by irradiating a pulse. When the heating pulse and the cooling pulse are alternately applied, the recording layer is repeatedly melted and rapidly cooled to form an amorphous mark. When the erasing pulse is irradiated, the recording layer is gradually cooled after melting, or annealed in a solid state and crystallized to form a space. FIG. 5A shows an example of a 1T period strategy in which the period of a pulse for forming an amorphous mark is 1T (where T represents a basic clock period). When recording on a fast optical recording medium at a low speed, a 2T cycle strategy is used in which the pulse cycle is 2T.

FIG. 6 shows an example of a 2T cycle strategy. This is described in Japanese Patent No. 3572068, and intensity modulation of writing light is performed by alternately irradiating a heating pulse with irradiation power Pw and a cooling pulse with irradiation power Pb (where Pw> Pb) m times. This is an example of an optical recording method in which n = 2m when n = even and n = 2m + 1 when n = odd. It is described that by using such a recording strategy, the degree of modulation can be increased in a recording speed range up to 10 × DVD compared with a recording strategy of 1T period as used for 4 × DVD + RW, for example. .
In the case of a conventional groove recording type phase change disk, the method uses an optical recording medium with a higher crystallization speed. Therefore, recrystallization during recording is prevented, and an amorphous mark of a predetermined size is obtained. In order to form the above, it has been considered advantageous to use such a 2T cycle strategy, to increase the power of the heating pulse as much as possible, to shorten the irradiation time, and to increase the cooling time. However, when recording at a speed higher than 10 times the speed of DVD, even if the 1T cycle strategy used at the time of recording at about 4 times the speed of DVD + RW is used or the 2T cycle strategy is used, the cooling time is too long. It has become clear that it is effective to use a non-cooling strategy, and even a block type strategy without a cooling pulse. This is because these strategies enable recording without increasing the mark width.

-1T strategy
A description will be given by using an example of a recording strategy having a 1T period shown in FIG. 5A. Such a recording strategy is used for a phase change optical recording medium such as a DVD + RW of a relatively low speed up to 4 × speed, and has a pulse modulation system in which a pulse is added every 1T. In quadruple speed recording, the basic period Tw is about 9.5 ns, and when viewed as a duty ratio of about 0.5, which is a normal pulse duty, a heating pulse that melts the recording layer material, that is, a Pw level pulse, The time constant of the Pb level of the cooling pulse for cooling this to form an amorphous phase as a recording mark is 4.25 ns. In this case, the actual rise and fall characteristics of the laser light are as follows: Even if 5 to 2 ns is considered, sufficient cooling time is secured.
However, when a recording strategy of 1T period is used for, for example, a 12 × DVD + RW, the time constant of the heating pulse and the cooling pulse is only about 1.6 ns when the duty ratio is 0.5. It is confirmed from observation of the pulse waveform that the pulse has not reached the set value. FIG. 5B shows the state of pulse emission at this time. Judging from FIG. 5B, when a recording strategy of 1T period is used for recording at a DVD speed of 10 times or higher, the Pw level does not rise sufficiently, so that a sufficient melting range cannot be formed as compared with recording at low speed. . In addition, since the cooling pulse cannot be lowered sufficiently, recrystallization is likely to proceed as compared with the case where the crystal growth of the melted part is slow or the recording strategy of 2T period is used. As a result, the amorphous phase region can be reduced, and in order to obtain a good erasure ratio (to enable overwriting) on the high speed side, which is the object of the present invention, modulation is performed while suppressing the spread of the recording mark. An optical recording method capable of reducing the degree can be realized.

However, at this time, τw / (τw + τb, where τw is the total irradiation time of the heating pulse Pw for each mark length of all marks of 4T or longer and τb is the total irradiation time of the cooling pulse Pb. ) Is 0.4 or more. If the value of τw / (τw + τb) is smaller than 0.4, the phenomenon that the level of Pw does not rise sufficiently is remarkable, and a sufficient melting region cannot be secured even if the set power is increased. Further, even if the value of τw / (τw + τb) is too large, good jitter tends not to be obtained, and it is 0.8 or less, and preferably 0.7 or less. Rather than setting the value of τw / (τw + τb) to be larger than 0.8, it is better to record using a block type strategy that is not a multi-pulse but a long pulse of only Pw, as will be described later. This can be said from the experimental results, and the reason is unknown.
Note that the value of τw / (τw + τb) is not necessarily in the range of 0.4 to 0.8 for marks shorter than 4T, that is, 3T for DVD and 2T and 3T for Blu-ray or HD DVD.
The space is formed by irradiation with Pe, and the value of Pe / Pw at this time is 0.15 to 0.4. If Pe / Pw is less than 0.15, it may be difficult to obtain sufficient power to erase the recorded amorphous mark. If it exceeds 0.4, the reason is not clear. Jitter may worsen from recording.

-T strategy
In the case of a 2T cycle strategy, the total irradiation time of the heating pulse Pw for each mark length of a mark having a length of 4T or more is τw, the total irradiation time of the cooling pulse Pb is τb, and τw / (τw + τb) FIG. 7A and FIG. 7B show the relationship between the example of the recording strategy, the recrystallization region, and the amorphous mark when the value is changed. FIG. 7A shows a case where the value of τw / (τw + τb) is small, and FIG. 7B shows a case where the value of τw / (τw + τb) is large. When the peak power is adjusted so that the melting regions are substantially the same, the larger the heating pulse ratio τw / (τw + τb), the smaller the mark width because recrystallization proceeds. Therefore, in order to record a mark with a small width at a high speed, it is preferable that the cooling pulse is not so long. The value of τw / (τw + τb) is preferably larger than 0.4. In the case of the same linear velocity, the length of τw can be doubled even if the 2T cycle strategy is the same 0.4 in the 1T cycle strategy and the 2T cycle strategy, so that Pw rises to a sufficient level. It can be smaller than 0.4 in the sense of securing the melting region. If it does so, the time of a cooling pulse will become long, recrystallization will not progress, but the width | variety of a mark cannot be made small. Also, the value of τw / (τw + τb) tends to fail to obtain good jitter even if it is too large, and is preferably set to 0.8 or less. Rather than setting the value of τw / (τw + τb) to be larger than 0.8, it is better to record using a block type strategy that is not a multi-pulse but a long pulse of only Pw, as will be described later. This can be said from the experimental results, and the reason is unknown.
Note that the value of τw / (τw + τb) is not necessarily in the range of 0.4 to 0.8 for marks shorter than 4T, that is, 3T for DVD and 2T and 3T for Blu-ray and HD DVD.
The space is formed by irradiation with Pe, and the value of Pe / Pw at this time is 0.15 to 0.4. If Pe / Pw is less than 0.15, it may be difficult to obtain sufficient power for erasing the recorded amorphous mark, and if it is more than 0.4, the reason is not clear. Jitter may worsen from recording.

-Block strategy-
As shown in FIG. 8, a long pulse of only Pw may be irradiated instead of the multi-pulse. Conventionally, such continuous light is not preferable because a teardrop-shaped mark is formed as shown in FIG. 9A. This is because such a teardrop-shaped mark results in a reproduction error, or an unerased portion is generated in the wide end portion at the time of repeated recording. One of the causes of the teardrop-shaped mark is that the temperature increases as it goes backward due to the heat storage effect, and the melted area spreads in teardrop shape. Another cause is that recrystallization proceeds due to continuous heating.
However, it has been found that the heat storage effect is reduced at a high speed of 8 times or higher than that of a DVD, and further, if the optical recording medium has a rapid cooling structure, it is further reduced. Therefore, in the case of an optical recording medium in which the crystallization speed is conventionally considered to be too slow at a recording linear velocity of 8 times or higher than that of a DVD, the recrystallization speed is also slow. As a result, a mark having a good shape can be obtained.

Further, as shown in FIG. 10 to FIG. 13, a power Ph higher than Pw is applied for a short time at the head, back, or middle of a block-shaped pulse composed of Pw, or an erasing pulse is started from a pulse on a block composed of Pw. The characteristic may be improved by using a recording strategy such as temporarily providing a Pb level cooling pulse before moving to Pe. 10 to 12, Ph is added to 3T for a short time, but since 3T is short, all may be a single Ph level pulse as shown in FIG.
The space is formed by irradiation with Pe, and the value of Pe / Pw at this time is 0.15 to 0.5. If Pe / Pw is less than 0.15, it may be difficult to obtain sufficient power for erasing the recorded amorphous mark. If it is more than 0.5, the reason is not clear. Jitter may worsen from recording.

<Preformatting to optical recording media>
In the example of the parameters related to the recording strategy, ie, the 2T period strategy of FIG. 6, the values of Td1 / T, Toff, Td2, Td3, dT3, Tmp, T3, and Toff3 are specific to the optical recording medium. It is preferable to pre-format the recording medium in advance. Even in the 2T cycle strategy, it is preferable to pre-format the parameters according to the recording strategy even when the parameter determination method is different from that in FIG. 6, or in the case of the 1T cycle strategy or the block type strategy. The optical recording apparatus reads these parameters preformatted on the optical recording medium to be recorded before the operation, so that an optimum recording parameter (recording strategy) can be set at an arbitrary scanning speed v. Also, if the recording power information is preformatted, it becomes easier to set more optimal recording conditions.
Any method can be used for preformatting, and examples thereof include a prepit method, a wobble encoding method, and a formatting method.
The pre-pit method is a method for pre-formatting information on recording conditions using ROM pits in an arbitrary area on an optical recording medium. Since ROM pits are formed when the substrate is formed, it is excellent in mass productivity and uses ROM pits, which is advantageous in terms of reproduction reliability and information amount. However, the technology for forming ROM pits (ie, hybrid technology) has many problems, and preformat technology using RW prepits is considered difficult.
In the format method, information is recorded using an optical recording apparatus using a method similar to normal recording. However, this method is difficult in terms of mass productivity because it is necessary to format each medium after manufacturing the optical recording medium. Furthermore, since the preformat information can be rewritten, it is not suitable as a method for recording information unique to the optical recording medium.
The wobble encoding method is a method actually used in CD-RW and DVD + RW. This technique uses a technique for encoding address information of an optical recording medium into wobbling of a groove (guide groove on the optical recording medium). As an encoding method, frequency modulation may be used like ATIP (Absolute Time In Pregroove) of CD-RW, or phase modulation may be used like ADIP (Address In Pregroove) of DVD + RW. Since the wobble encoding method is created on the substrate together with the address information when forming the optical recording medium substrate, it is excellent in productivity, and at the same time, it is not necessary to form special ROM pits like the pre-pit method. Also has the advantage of being easy to do. In the case of CD-RW, these parameters are preformatted as ATIP Extra Informations, and in the case of DVD + RW, they are preformatted as Physical Information.

(Optical recording medium)
An example of the configuration of an optical recording medium used in the optical recording method of the present invention is shown in FIGS. FIG. 14 shows examples of DVD + RW, DVD-RW, and HD DVD RW. FIG. 15 shows an example of a Blu-ray disc.
In FIG. 14, at least a first protective layer 2, a recording layer 3, a second protective layer 4, and a reflective layer 5 are laminated in this order on the transparent substrate 1 having guide grooves as viewed from the light incident side. . In the case of DVD and HD DVD, an organic protective film 6 is formed on the reflective layer 5 by spin coating, and although not shown, a plate of the same size and usually the same material as the substrate is bonded.
In FIG. 15, the transparent cover layer 7, the first protective layer 2, the recording layer 3, the second protective layer 4, the reflective layer 5, and the transparent substrate 1 having a guide groove are stacked in this order as viewed from the light incident side. ing.
Note that the optical recording medium shown in FIGS. 14 and 15 is an example of a single recording layer type, but an optical recording medium having two recording layers via a transparent intermediate layer can also be used. In this case, the layer on the near side as viewed from the light incident side needs to be translucent in order to perform recording / reproduction of the back layer.

-Board-
Examples of the material for the substrate include glass, ceramics, and resin. Among these, the resin is preferable from the viewpoints of moldability and cost.
Examples of the resin include polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicone resin, fluorine resin, ABS resin, and urethane resin. Among these, polycarbonate resins and acrylic resins that are excellent in terms of moldability, optical characteristics, and cost are particularly preferable.

The substrate is formed so as to have a size, thickness, and groove shape suitable for the standard to be complied with.
Recording and reproduction are performed by controlling the laser beam to be irradiated to the center of the groove by the servo mechanism of the pickup. For this control, diffracted light generated in the direction perpendicular to the beam scanning direction by the guide groove is used. Is monitored, and positioning is performed at the center of the groove so as to cancel the left and right signal levels in the scanning direction. The signal intensity of the diffracted light used for this control is determined by the relationship between the beam diameter, the groove width, and the groove depth, and is generally converted into a signal intensity called a push-pull signal. This signal intensity increases as the groove width increases, but has a limit because the track pitch between recording marks is determined.
For example, in a DVD recording system having a track pitch of 0.74 μm, it is said that a value between 0.2 and 0.6 is preferable in an unrecorded state, such as DVD + RW, DVD + R, DVD-RW, DVD-R, etc. Similar values are defined in each standard. The groove width corresponding to this value is preferably 0.17 to 0.30 μm in the width of the bottom of the groove in the DVD + RW or DVD-RW rewritable recording medium related to the present invention. Although described in the publication, when used for a high-speed optical recording medium, 0.20 to 0.30 μm is preferable.
Even in a recording / reproducing system using a blue LD, the groove width is determined in the same proportional relation in relation to the beam diameter. In either case, the groove width is about half the track pitch or slightly smaller than that. Is set.
This guide groove is usually a meandering groove (wobble) in order for the recording device to sample the frequency during recording, and the phase of the wobble is reversed or the frequency is changed in a predetermined area. The address and information necessary for recording can be input.
In the optical recording method of the present invention, information such as strategy information and recording power necessary for recording is input to the innermost peripheral part (lead-in area) of the disc, and the recording apparatus reads this information, so that an optimum recording strategy and power are obtained. By recording under conditions, recording suitable for the recording speed is performed.

-First protective layer-
The material for the first protective layer is not particularly limited and can be appropriately selected from known materials according to the purpose. Examples thereof include Si, Zn, Sn, In, Mg, Al, Ti, and Zr. Each oxide; Each nitride such as Si, Ge, Al, Ti, B, and Zr; Each sulfide such as Zn and Ta; Each carbide such as Si, Ta, B, W, Ti, and Zr; Diamond-like carbon; Or the mixture of these is mentioned. Among these, a mixture of ZnS and SiO ₂ having a molar ratio in the vicinity of 7: 3 to 8: 2 is preferable. In particular, the first is located between the recording layer and the substrate accompanied by thermal damage due to thermal expansion change and high temperature to room temperature change. As the protective layer, (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) in which the optical constant, the thermal expansion coefficient, and the elastic modulus are optimized is preferable. In addition, different materials may be stacked and used.
Since the thickness of the first protective layer greatly affects the reflectivity, modulation degree and recording sensitivity, the recording sensitivity is preferably increased when the disc reflectivity is a minimum value relative to the thickness of the lower protective layer. . In order to obtain good signal characteristics at the recording / reproducing wavelength of DVD, when (ZnS) ₈₀ (SiO ₂ ) ₂₀ (mol%) is used for the first protective layer, the thickness is preferably 40 to 80 nm, and Blu-ray Disc. Then, 20 to 50 nm is preferable, and 30 to 60 nm is preferable for HD DVD. If the thickness of the first protective layer is thinner than these ranges, thermal damage to the substrate may increase and the groove shape may change, and if it is thick, the disk reflectivity increases and the sensitivity may decrease. is there.

-Phase change recording layer-
The recording layer material is composed of Sb—In, Sb—Ga, Sb—Te, Sb—Sn—Ge, or the like containing Sb as a main component and an element that promotes amorphization. The materials used were used. Here, the main component means 50 atomic% or more. Further, for the purpose of improving various properties, other elements are further added to these matrix phases.

The Sb—In system is preferably used in the following composition range.
(Sb _1-x In _x ) _{1- y My}
However, 0.15 ≦ x ≦ 0.27 and 0.0 ≦ y ≦ 0.2, and M represents one or more elements other than Sb and In.
Good repetitive recording characteristics can be obtained with only the Sb—In binary system, the crystallization temperature is as high as around 170 ° C., and the amorphous storage stability is also excellent. It is better to add element M to this for the purpose of further improving the storage stability, improving the repeated recording durability, and improving the ease of initialization. As the element M, for example, at least one element selected from Al, Si, Ti, V, Cr, Mn, Cu, Zn, Ge, Ga, Se, Te, Zr, Mo, Ag, and a rare earth element is added. May be. Further, since the addition of these elements often leads to a decrease in the crystallization speed, Sn or Bi may be further added for the purpose of improving the crystallization speed. In order not to impair the repetitive recording characteristics, the total amount of M added is preferably 20 atomic% or less.

The Sb—Ga system is preferably used in the following composition range.
(Sb _1-x Ga _x ) _{1- y My}
However, 0.05 ≦ x ≦ 0.2 and 0.0 ≦ y ≦ 0.3, and M represents one or more elements other than Ga and Sb.
Even with the Sb—Ga binary system alone, good repeated recording characteristics can be obtained, the crystallization temperature is as high as about 180 ° C., and the material is also excellent in amorphous storage stability. However, if the ratio of Sb is increased in order to increase the crystallization speed, there is a problem that the reflectance after initialization is not uniform, so that the uneven reflectance of initialization is improved for high-speed recording. It is better to add the element M. Examples of the element M include Al, Si, Ti, V, Cr, Mn, Cu, Zn, Se, Zr, Mo, Ag, In, Sn, Bi, and rare earth elements. In addition, by adding such an element M, the stability of the crystal phase is lost this time, the reflectance decreases after storage at room temperature or high temperature, and recording becomes impossible under the same conditions as before storage. Further, Ge, Te, or the like may be added. In order not to impair the repetitive recording characteristics, the total amount of M added is preferably 30 atomic% or less.

The Sb—Te system is preferable because it has good repetitive recording characteristics when used in the following composition range.
(Sb _1-x Te _x ) _{1- y My}
However, 0.2 <= x <= 0.4 and 0.03 <= y <= 0.2, and M represents one or more elements other than Sb and Te.
Even when only the Sb-Te binary system is used, good repetitive recording characteristics can be obtained. However, since the crystallization temperature of the binary system is as low as about 120 ° C., there is a problem that the recording mark is crystallized by high-temperature storage. It is essential to add an element M that raises the crystallization temperature and enhances the stability of the amorphous state. Examples of the element M that increases the stability of the amorphous material include Al, Si, Ti, V, Cr, Mn, Cu, Zn, Ga, Ge, Se, Zr, Mo, Ag, In, and rare earth elements. Is mentioned. In general, when these elements are added, the crystallization speed tends to decrease. Therefore, Sn, Bi, or the like may be further added for the purpose of improving the crystallization speed. The addition amount is not effective unless the total amount is 3 atomic% or more, and is preferably 20 atomic% or less so as not to impair repeated recording characteristics.

The Sb—Sn—Ge system is preferable because it has good repetitive recording characteristics when used in the following composition range.
_{(Sb 1-x-y Sn} x Ge y) 1-z M z
However, 0.1 ≦ x ≦ 0.25, 0.03 ≦ y ≦ 0.30, 0.00 ≦ z ≦ 0.15, and M represents one or more elements other than Sb, Sn, and Ge. To express.
Good recording characteristics can be obtained only with the Sb—Sn—Ge ternary system, but jitter is reduced when one or more elements are further added. Examples of effective elements include Al, Si, Ti, V, Cr, Mn, Cu, Zn, Ga, Ge, Se, Te, Zr, Mo, Ag, In, and rare earth elements. However, if the addition amount is too large, the jitter deteriorates conversely, so that at most 15 at.% Or less is preferable.

  The thickness of the recording layer is preferably 6 nm or more. If the thickness is thinner than this, the crystallization speed and the degree of modulation may be extremely reduced, and good recording may be difficult. In addition, the upper limit of the thickness is preferably 30 nm or less, more preferably 22 nm or less in the inner layer of the one-layer type or the two-layer type. In the two-layer type front layer, 10 nm or less is preferable, and 8 nm or less is more preferable. If it is thicker than this, the recording sensitivity will deteriorate and the repeated recording durability will deteriorate, and in the case of the two-layer type front layer, it will be difficult to secure transmitted light, and it will be difficult to record and reproduce the back layer. turn into.

-Second protective layer-
As the material of the second protective layer, the same material as the first protective layer can be used according to the purpose, for example, each oxidation of Si, Zn, Sn, In, Mg, Al, Ti, Zr, etc. Nitrides such as Si, Ge, Al, Ti, B, Zr; sulfides such as Zn and Ta; carbides such as Si, Ta, B, W, Ti, Zr; diamond-like carbon; or these Of the mixture. Although the second protective layer also affects the reflectance and the degree of modulation, it is important to use a layer having the greatest influence on the recording sensitivity and having an appropriate thermal conductivity. A mixture of ZnS and SiO ₂ having a molar ratio in the vicinity of 7: 3 to 8: 2 has a low thermal conductivity and a low heat dissipation rate to the reflective layer, so that the recording sensitivity is good. In the case of high-speed recording, a material having a high thermal conductivity may be selected. As such a material having a high thermal conductivity, a material mainly composed of In ₂ O ₃ , ZnO, SnO known as a transparent conductive film or a mixture thereof, or TiO ₂ , Al ₂ O ₃ , ZrO ₂ is used. A main component or a mixture thereof can be used. Furthermore, different materials may be used in a stacked manner.
The thickness of the second protective layer is preferably 4 to 50 nm, and more preferably 6 to 20 nm. If the thickness is less than 4 nm, the light absorptance of the recording layer is lowered, and heat generated in the recording layer is easily diffused to the reflective layer. When it is thick, cracks are likely to occur.

-Reflective layer-
As a material of the reflective layer, for example, a metal such as Al, Au, Ag, Cu, or an alloy containing them as a main component is preferable. Examples of additive elements for alloying include Bi, In, Cr, Ti, Si, Cu, Ag, Pd, and Ta.
The reflection layer reflects the light during recording and reproduction to increase the light use efficiency and also serves as a heat dissipation layer that releases heat generated during recording. In the case of a single-layer optical recording medium, or in the case of recording on the recording layer on the back side as viewed from the light incident side of the two-layer optical recording medium, the reflective layer is used from the viewpoint of securing the light use efficiency and the cooling rate. The thickness is preferably 70 nm or more. However, the light utilization efficiency and the cooling rate are saturated at a certain thickness or more, and if it is too thick, the substrate may be warped or peeled off due to film stress. Is preferred.
The reflection layer on the near side as viewed from the light incident side of the two-layer optical recording medium cannot be made too thick because it needs to transmit light, and is preferably 5 to 15 nm. However, since heat dissipation characteristics are poor in this case, good recording may not be possible. Therefore, a heat dissipation layer described below is used.

−Heat dissipation layer−
The heat-dissipating layer is provided between the reflective layer and the intermediate layer in order to ensure heat dissipation and adjust the reflectivity when recording on the front layer as viewed from the light incident side of the two-layer optical recording medium. It is preferable that the transmittance is high and the thermal conductivity is high, and those containing In ₂ O ₃ , ZnO, SnO as a main component or a mixture thereof known as a transparent conductive film, or a mixture thereof, TiO ₂ , Al ₂ O ₃ , ZrO Those having ₂ as a main component or a mixture thereof can be used. Depending on the composition of the recording layer, the heat dissipation may not be required so much. In that case, a mixture of ZnS and SiO ₂ often used as a protective film may be used.
The thickness of the heat dissipation layer is preferably 10 to 150 nm, and more preferably 20 to 80 nm. If the thickness is less than 10 nm, the function as a heat dissipation layer or an optical adjustment layer may be insufficient. If the thickness exceeds 150 nm, the substrate may be warped or peeled off due to film stress. It is.

-Anti-sulfurization layer-
When Ag or an Ag alloy is used as the reflective layer and a film containing S such as a mixture of ZnS and SiO ₂ is used as the second protective layer, generation of defects due to sulfurization of the reflective layer during storage is prevented. Therefore, an antisulfurization layer is provided between the second protective layer and the reflective layer.
Examples of the sulfidation prevention layer include Si, SiC, TiC, TiO ₂ , and a mixture of TiC and TiO ₂ . If the thickness of the sulfidation prevention layer is not 1 nm or more, a uniform film cannot be formed, and the sulfidation prevention function is impaired. The thickness of the antisulfurization layer is preferably 2 nm or more. The upper limit of the thickness is determined while considering the balance of optical characteristics and thermal characteristics of the optical recording medium. Usually, the balance is better when it is 10 nm or less, and good repeated recording characteristics are often obtained.

-Intermediate layer-
The intermediate layer is a layer for separating the two layers of the optical recording medium, and is formed of a transparent resin layer having a thickness of 50 μm for DVD and HD DVD and 25 μm for Blu-ray Disc.

-Cover layer-
In the case of a Blu-ray disc, it is a layer through which light is incident and transmitted. In the case of a single optical recording medium, it is formed of a transparent resin layer having a thickness of 100 μm. In the case of a two-layer optical recording medium, it is a transparent layer having a thickness of 75 μm. It is formed with a resin layer.

Each layer as described above is sequentially formed on a substrate by sputtering, and after forming or bonding an organic protective film or forming a cover layer, it is used as an optical recording medium through an initialization process.
The initialization is performed by irradiating a scanning laser beam of about 1 to 2 W shaped to about 1 × (several 10 to several 100) μm to crystallize an amorphous recording layer immediately after film formation. It is a process.

  Examples of the present invention will be described below, but the present invention is not limited to these examples. In the following examples, the value of jitter σ / Tw is used as an index for obtaining good recording characteristics. The standard value of DVD + RW is 9% or less, and the standard value of Blu-ray Disc is 6.5% or less. When this standard is satisfied or a value close to this is obtained, it is considered that good recording characteristics have been obtained.

(Examples 1-9 and Comparative Examples 1-6)
After a grooved polycarbonate resin disk substrate having a diameter of 12 cm, a thickness of 0.6 mm, and a track pitch of 0.74 μm is dehydrated at a high temperature, a first protective layer, a recording layer, a second protective layer, a sulfide are formed thereon by a sputtering method. A prevention layer and a reflective layer were sequentially formed to produce a phase change optical recording medium.
A first protective layer having a thickness of 65 nm was formed on a substrate using a ZnS-SiO ₂ target having a molar ratio of 8: 2 on a substrate by a sputtering apparatus (DVD Sprinter manufactured by Unaxis), and the results are shown in Table 1 above. Using an alloy target having a composition (composition ratio is an atomic ratio), a recording layer having a thickness of 16 nm is formed under sputtering conditions of an argon gas pressure of 3 × 10 ⁻³ torr and an RF power of 300 mW, and a first protective layer is formed thereon. In the same manner, a second protective layer having a thickness of 10 nm, an anti-sulfurization layer made of TiC and TiO ₂ having a mass ratio of 7: 3, and an Ag reflection layer having a thickness of 200 nm were stacked using a ZnS—SiO ₂ target. Next, an acrylic ultraviolet curable resin (Dainippon Ink and Chemicals, SD318) was applied on the reflective layer so as to have a thickness of 5 to 10 μm by a spin coating method, and UV-cured to form an organic protective layer. Next, a polycarbonate resin bonding substrate having a diameter of 12 cm and a thickness of 0.6 mm, which is the same as the substrate, is bonded onto the organic protective layer, and the phase change types of Examples 1 to 9 and Comparative Examples 1 to 6 are used. An optical recording medium was produced.
Next, each optical recording medium was initially crystallized with a large diameter LD.

Each optical recording medium obtained was recorded using the EFM + modulation method at a recording speed of 18 m / s (about 5.15 times speed) and 10 times speed (about 35 m / s). Recording and reproduction were performed using a DVD evaluation apparatus (DDU-1000, manufactured by Pulstec Industrial Co., Ltd.) having a pickup head having a wavelength of 659 nm and a lens NA of 0.65 in accordance with the recording / reproducing method of the DVD system.
For 18 m / s recording, 3T recording strategies of 1T, 2T, and block were used for 2T periodic strategy and 10x recording.
The 2T cycle strategy was performed by applying the recording strategy shown in FIG. Specifically, the pulse widths Tmp and T3 are 0.55T and 0.725T on the low speed side and 0.625T and 0.8125T on the high speed side (where T represents the basic clock period), and the jitter value is the lowest. The pulse delay amounts dT3, Td1, Td2, Td3 and the off-pulse widths Toff3, Toff were optimized and determined for each optical recording medium. The value of τw / (τw + τb) when forming a mark of 4T or more was set to 0.35 or less. Regarding the recording power, Pb was fixed at 0.1 mW, and Pw and Pe were determined so that the jitter was minimized in each optical recording medium.

  As shown in FIG. 5A, the 1T strategy was applied only to the high speed side using a pulse number of (n-1) when each mark length was n. As the set value, the head heating pulse width is set to 0.7T, and all other pulse widths are set to the same 0.5T width, and the final off-pulse is optimized for each optical recording medium so that the jitter is minimized. Used. As a result, the values of τw / (τw + τb) were all 0.5 to 0.8. Regarding the recording power, Pb was fixed at 0.1 mW, and Pw and Pe were determined so that the jitter was minimized in each optical recording medium.

The block type strategy is as shown in FIG. The pattern used for the 3T mark is a simple pulse, and the pattern used for the 4T to 14T mark is concave. The pulse width of the 3T mark is 2T, and in the pattern for recording a mark of 4T or more, Ttop and Tlp are 1.2T and 0.8T, respectively, and the total width is [(3T pulse Length) + (n−3)]. For the power setting, Pe is set to 5 mW, and the jitter value is minimized after the Pw condition is determined so that the width of the recording mark (evaluated by the modulation factor) is saturated or equal to or greater than 0.9 of the saturation value. Thus, Ph was optimized, and Pe was further optimized. Although an off pulse having a power level Pb indicated by a dotted line in FIG. 8 may be used, it is not used in this test.
Reproduction is performed at a speed of 3.5 m / s and a reproduction power of 0.7 mW, and a standard deviation σ of fluctuation at each mark edge portion is normalized by a reference window width Tw and a modulation value [(record mark The maximum reflectance of the recording portion-the minimum reflectance of the recording mark portion) / the maximum reflectance of the recording mark portion) and the reflectance of the erasing portion were evaluated. The results are shown in Table 1.

From the results in Table 1, except for Example 7, in the case of 18 m / s recording, the value of τw / (τw + τb) when forming a mark of 4T or more of the 2T period strategy is 0.35 or less. The jitters were all good at 8% or less. In Example 7, abnormal recrystallization occurred frequently and jitter was not lowered. In the case of 10-times speed recording, when a 1T period strategy having a value of τw / (τw + τb) of 0.5 to 0.8 and a block strategy are used, the modulation factor is smaller than 0.60, and jitter is also reduced. It could be 10% or less. In the case of Example 7 as well, when recording at high speed, it becomes difficult to create conditions for occurrence of abnormal recrystallization, so the jitter can be reduced to 10%.
On the other hand, as shown in Comparative Examples 1 to 6, when recording is performed using a 2T cycle strategy in which the value of τw / (τw + τb) is 0.35 or less, the modulation degree becomes larger than 0.60. The jitter could not be adjusted to 10% or less.

(Example 10)
For the phase change optical recording media manufactured in Examples 1 to 4, recording on the high speed side is performed at a recording speed of 12 times (about 42 m / second) using a 1T period strategy as shown in FIG. The width of was monitored. The 1T cycle strategy pattern and playback conditions were set in the same manner as in Example 1.
As a result, when the recording power was 30 mW or more, the modulation degree exceeded 0.45, and the width of the recording mark was about 0.75 with a groove width of 0.28 μm. At this time, the reflectance was 0.25, and R × M exceeded 0.11. Jitter was 10%.
As the recording power increased from this point, the jitter was 9.3%, the reflectance was 0.25, and R × M was 0.14 at 36 mW. At this time, the width of the recording mark was about 0.9 of the groove width.
When the power was further increased, the mark width was almost the same as or slightly smaller than the groove width when the recording power was 39 mW, and the mark did not spread even if the power was increased further. The modulation factor at this time was 0.59, and the jitter was 9.8%.

(Example 11)
In Example 1, the phase change was performed in the same manner as in Example 1 except that the thicknesses of the recording layer and the first protective layer were adjusted so that the reflectance was 18%, 22%, 24%, and 30%. Type optical recording medium was prepared, the above-mentioned 2T periodic strategy was used, the recording speed was set to 6 times, the recording power was changed, the modulation degree was adjusted, and the error rate during reproduction was evaluated. The results are shown in FIG.
From the results of FIG. 16, the modulation degree decreases as the recording power is lowered. A vertical dotted line in FIG. 16 indicates a modulation degree (0.6.0.5, about 0) where R × M = 0.11 when the reflectance is about 18%, 22%, 24%, and 30%. .46.about 0.37).
Further, it can be seen from the result of FIG. 16 that the error rate increases abruptly when R × M is around 0.11. Under the condition where the modulation factor is small, the error rate starts to increase from the modulation factor larger than the modulation factor of 0.11, but in the modulation factor of R × M = 0.11. An error rate lower than the correction capability level of the DVD indicated by the solid line A is obtained.
Therefore, it is considered that a recording system that can withstand normal use can be realized if the reflectance is high even when the modulation degree M is small.

(Examples 12 to 18 and Comparative Examples 7 to 13)
On a polycarbonate disk substrate with a guide groove having a diameter of 12 cm, a thickness of 0.6 mm, and a track pitch of 0.74 μm, ZnS and SiO having a molar ratio of 8: 2 as a first protective layer by a sputtering device (DVD Sprinter, manufactured by Unaxis). _A layer composed of _{2 is} deposited to a thickness of 60 nm, and the power is controlled so that the recording layer has a predetermined composition using a multi-source of In ₂₀ Sb ₈₀ , Ge, Zn, and Te as shown in Table 2. The film was formed to a thickness of 14 nm by co-sputtering. Further, a layer made of ZnS and SiO ₂ having a molar ratio of 8: 2 as the second protective layer has a thickness of 6 nm, and a layer made of TiC and TiO ₂ having a mass ratio of 7: 3 as the anti-sulfurization layer has a thickness of 4 nm and as the reflective layer. Ag was sequentially formed to a thickness of 200 nm by sputtering, and an organic protective film (Dainippon Ink Chemical Co., Ltd., SD318) was overcoated by a spin coating method, and then a polycarbonate disk having a thickness of 0.6 mm was bonded. As described above, the phase change optical recording media of Examples 12 to 18 and Comparative Examples 7 to 13 were produced.
Next, each obtained optical recording medium was initially crystallized by a large-diameter LD.

For each of the obtained optical recording media, the transition linear velocity and recording characteristics were evaluated using a DVD evaluation apparatus (DDU-1000, manufactured by Pulstec Industrial Co., Ltd.) having a pickup head with a wavelength of 660 nm and NA = 0.65. did. The results are shown in Table 2. Each optical recording medium has a different transition linear velocity depending on the type and amount of the additive element in the recording layer. The transition linear velocity is a value measured with a board power of 15 mW. Recording was repeated 10 times on the same track at a linear speed of 8 × (approximately 28 m / s), 10 × (approximately 35 m / s), and 12 × (approximately 42 m / s) DVDs, with a random pattern of 3T to 14T using an EFM + modulation system. went.
In Table 2, when the jitter σ / Tw at this time can be reduced to 10% or less, the result is indicated by ◯, and when the jitter σ / Tw cannot be decreased by 10% or less, it is indicated by x.
All 8 × speed recording is performed under the condition that the modulation degree M is larger than 0.60, and at 10 × speed and 12 × speed, the condition is such that the modulation degree M is larger than 0.60 and less than 0.60. When it was recorded in, it was divided and evaluated.
In the recording under the condition that M> 0.60 at 8 to 12 times speed, the 2T cycle strategy is used, the width of the multi-pulse heating pulse is 0.6T, the width of the cooling pulse is 1.4T, The final pulse position and width, and power were optimized and recorded. The value of τw / (τw + τb) when forming a mark of 4T or more was 0.35 or less.
For recording such that M ≦ 0.60 at 10 × speed and 12 × speed, a 1T cycle strategy is used, the width of the multi-pulse heating pulse is 0.55T, the width of the cooling pulse is 0.45T, and the first and last pulses The position, width, and power of each were optimized and recorded. The value of τw / (τw + τb) when forming a mark of 4T or more was 0.5 to 0.8. In all the recording conditions, the optimized power Pe / Pw value was in the range of 0.23 to 0.33.

From the results shown in Table 2, when the value of the reflectance R of each optical recording medium and the recording with a modulation factor M of 0.60 or less at 10-times speed or 12-times speed, recording with a jitter of 10% or less was achieved. The product of the reflectance with M is shown as R × M. The degree of modulation M was 0.4 or more.
In either case, when recording was repeated at a linear velocity 5 to 18 m / s faster than the transition linear velocity, good recording could not be performed under the condition of M> 0.60, but M ≦ 0.60. Good repetitive recording characteristics could be obtained by recording under the following conditions. In particular, Example 14, Example 15 and Example 16 are capable of repeated recording at 8 × speed under the same conditions as those for recording on an 8 × speed optical recording medium, and even at high speeds such as 10 × speed and 12 × speed. Good repetitive recording characteristics are obtained by performing recording under the condition of M ≦ 0.60.
Further, it was investigated whether or not the recording method was optimized by using the optical recording medium used in Example 15 so that the modulation degree M was smaller than 0.4, and good recording characteristics were obtained. As for the recording characteristics after 10 repeated recordings, the jitter was 12.8% when the modulation degree was 0.38.
On the other hand, in Comparative Examples 7 to 13, when M> 0.60 of 8 × speed, 10 × speed, and 12 × speed is 0.35 or less, the jitter σ / Tw exceeds 10%.

(Example 19)
Using the optical recording medium of Example 15, recording was performed at 12 × speed by changing the widths of the 1T period and 2T period heating pulses. FIG. 17 shows the relationship between τw / (τw + τb) and jitter σ / Tw after 10 repeated recordings, where τw is the sum of the lengths of the heating pulses and τb is the sum of the lengths of the cooling pulses. By adjusting the power, all modulation degrees are made smaller than 0.60, and the length and position of the leading pulse and the final pulse are optimized so that the jitter is low. By setting τw / (τw + τb) to 0.4 to 0.8, the jitter could be reduced to about 10% or less in both the 1T period and the 2T period.

(Example 20)
Using the optical recording medium of Example 15, 12-times speed recording was performed with a long pulse. The pulse waveform uses a pattern as shown in FIG. 11, and Ph added to the front and rear ends are both Pw + 5 mW, the length is 0.5 T, the cooling pulse is 0.2 mW, and the length is 0.5 T. Pw pulse length, position and power were optimized. When Pw = 19 mW and Pe = 8.6 mW, the best recording characteristics were obtained. At this time, the jitter after 10 repeated recordings was 9.2%, and the modulation factor was 0.48.

(Example 21)
Using the optical recording media of Examples 12 to 18, the optimum Pe / Pw range was examined at 8 × speed, 10 × speed, and 12 × speed. Two types of strategies were used: 8 × speed, 10 × speed, 2T cycle strategy, and 12 × speed, 2T cycle strategy, and the block strategy shown in FIG.
FIG. 18 shows the jitter value when the lowest value is obtained after 10 repeated recordings. When Pe / Pw was less than 0.15, jitter increased rapidly at any recording linear velocity, and good repeated recording could not be performed. When the initial recording is examined, the jitter is often good, and since Pe is small, the amorphous mark remains unerased at the time of repeated recording, and it is considered that the jitter is deteriorated. In addition, the jitter rapidly increased when the value was larger than 0.40 in the case of the 2T cycle strategy and larger than 0.50 in the case of the block strategy. These had poor jitter even at the first recording.

(Example 22)
In Example 12-18, except for changing the composition of the recording layer to _Ga 7 _Sb 67 _Sn 20 Ge ₆ was prepared the same optical recording medium as in Example 12-18.
Recording was performed on the obtained optical recording medium at 12 times speed using a 1T periodic strategy. At this time, the values of Pw = 32 mW, Pe = 8 mW, and τw / (τw + τb) were 0.5 or more. The reflectivity is 0.305, the transition linear velocity is 30 m / s, and at 8 × speed, good recording characteristics with a modulation degree of 0.6 or more and a jitter of 9% or less are obtained after 10 repeated recordings. The best recording characteristics after 10 repeated recordings obtained by optimizing the recording conditions at 12 × speed were a jitter of 9.5% and a modulation factor of 0.54.

(Example 23)
In Examples 12-18, the same optical recording media as in Examples 12-18 were prepared, except that the composition of the recording layer was changed to Te ₁₉ Sb ₇₄ Ge ₅ In ₂ .
Recording was performed on the obtained optical recording medium at a speed of 8 times using a 1T period strategy. The reflectance was 0.21, and the transition linear velocity was 14 m / s. The best recording characteristics after 10 repeated recordings obtained by optimizing the recording conditions at 8 × speed (about 28 m / s) are Pw = 28 mW, Pe = 7 mW, and the value of τw / (τw + τb) is 0.5. When ˜0.8, the jitter was 9.9% and the modulation degree was 0.45.

(Example 24 and Comparative Examples 14-15)
On a polycarbonate disk substrate with a guide groove having a diameter of 12 cm, a thickness of 1.1 mm, and a track pitch of 0.32 μm, Ag-0.5% by mass Bi as a reflective layer is 140 nm in thickness using a sputtering apparatus (DVD Sprinter manufactured by Unaxis). The power is controlled so that the second protective layer 4 has a predetermined composition using a multi-source of ZnO-3 mass% Al ₂ O ₃ with a thickness of 8 nm and the recording layer 3 with In ₂₀ Sb ₈₀ , Ge, Zn, Te. However, it was formed to a thickness of 11 nm by co-sputtering. Further, a layer made of ZnS and SiO ₂ having a molar ratio of 8: 2 was formed as a first protective layer 2 to a thickness of 33 nm, and an adhesive made of an ultraviolet curable resin was applied by a spin coat method, and a thickness of 0.75 μm was applied. A polycarbonate film (manufactured by Teijin Ltd.) was bonded to form a cover layer. Thus, a phase change type optical recording medium was produced.
Next, the obtained optical recording medium was initially crystallized with a large diameter LD.

About each obtained optical recording medium, the transition linear velocity and the recording characteristic were evaluated using the Blu-ray Disc evaluation apparatus (Pulstec Industrial Co., Ltd. product, ODU-1000) which has a pick-up head of wavelength 405nm and NA = 0.85. . The transition linear velocity measured with 5 mW continuous light was 17 m / s.
Recording was performed at a density corresponding to a recording capacity of 25 GB with a 17PP modulation method, a reference linear velocity (single speed) of 4.92 m / s, a minimum mark length of 0.149 μm, using a 2T cycle strategy. A random pattern of 2T to 8T was repeatedly recorded 10 times on three consecutive tracks, and the middle track was reproduced at 1 × speed, and the degree of modulation and jitter after limit echoization were evaluated.
Table 3 shows the recording conditions. Pb was all 0.1 mW. The value of τw / (τw + τb) is a condition for recording 4T to 8T marks. In the case of the example, 2T and 3T marks are recorded without providing cooling before moving to Pe with a single pulse of Pw, and in the case of Comparative Example 15, it is a single pulse of Pw but shifts to Pe. Before, a cooling pulse for once dropping the power to Pb was provided. 19 and 20 show the relationship between jitter and modulation factor.

From the results of Table 3 and FIGS. 19 and 20, good recording can be achieved at 4 × speed (19.68 m / s) in Example 24, whereas in the optical recording method of Comparative Example 14, the jitter is small. In addition, the degree of modulation has increased. However, when recording was performed at double speed (9.84 m / s) as in Comparative Example 15, good recording was possible even if the value of τw / (τw + τb) was the same as in Comparative Example 14. In Comparative Example 14 and Comparative Example 15, the value of τw / (τw + τb) is 0.42 only in the recording condition of 5T out of 4T to 8T, and the value of τw / (τw + τb) in all other recording conditions. Was less than 0.4.

(Example 25 and Comparative Example 16)
The recording layer is 11 nm thick using an alloy target of Ge ₁₃ Sb _67.5 Sn ₁₅ Mn _4.5 , and the second protective layer is a target of (ZrO ₂ -3 mol% Y ₂ O ₃ ) -20 mol% TiO _2. The optical recording medium was prepared in the same manner as in Example 23 except that the thickness was 8 nm, and the evaluation was performed in the same manner. Table 4 shows the recording conditions (2T strategy) at 4 × speed, the jitter and the modulation degree after 10 repeated recordings.

From the results of Table 4, when the value of τw / (τw + τb) is small as in Comparative Example 16, the jitter increases slightly by 1% compared to Example 25 where the value of τw / (τw + τb) is large. I understand that. In Comparative Example 16, the value of τw / (τw + τb) is 0.42 only in the recording condition of 5T out of 4T to 8T, and the value of τw / (τw + τb) is 0.4 in all other recording conditions. It was smaller.

  The optical recording medium and the optical recording method of the present invention are suitably used for, for example, an optical recording medium capable of high-density recording having a phase change recording layer such as DVD + RW, DVD-RW, BD-RE, and HD DVD RW.

FIG. 1A is a schematic diagram for explaining a state in which abnormal crystal growth occurs in a recording mark to cause a distortion in a reproduction signal and increase an error. FIG. 1B is a diagram showing reproduction signals of marks A to C. FIG. 1C is a diagram illustrating a signal after binarization of the marks A to C. FIG. 2 is a diagram for explaining the transition linear velocity. FIG. 3 is a TEM photograph of an optical recording medium recorded on an optical recording medium capable of 8 × speed recording so that the modulation degree M is 0.63. FIG. 4 is a TEM photograph of an optical recording medium recorded so as to have a relationship of A (Lrm) ≧ 1 / 2Ltp. FIG. 5A is a diagram illustrating an example of a 1T cycle strategy for repeatedly recording data including marks and spaces. FIG. 5B is a diagram illustrating a state of pulse emission in FIG. 5A. FIG. 6 is a diagram illustrating an example of a 2T period recording strategy. In FIG. 7A, in the case of the 2T period strategy, the total irradiation time of the heating pulse Pw for each mark length of 4T or more marks is τw, the total irradiation time of the cooling pulse Pb is τb, and τw / (τw + τb) FIG. 9 is a diagram showing a relationship between an example of a recording strategy, a recrystallized region, and an amorphous mark when the value of τ is changed and a value of τw / (τw + τb) is small. FIG. 7B is a diagram illustrating a case where the value of τw / (τw + τb) is large. FIG. 8 is a diagram illustrating an example of a block type recording strategy. FIG. 9A is a schematic diagram showing a relationship between a recrystallization region and an amorphous mark when recording is performed with the recording strategy of FIG. 8, and a state where a teardrop-shaped mark is formed. FIG. 9B is a schematic diagram showing a relationship between the recrystallized region and the amorphous mark when recording is performed with the recording strategy of FIG. 8, and a state where a mark having a good shape is obtained even with a long pulse. . FIG. 10 is a diagram showing an example of the block type recording strategy of the present invention. FIG. 11 is a diagram showing another example of the block type recording strategy of the present invention. FIG. 12 is a diagram showing still another example of the block type recording strategy of the present invention. FIG. 13 is a diagram showing still another example of the block type recording strategy of the present invention. FIG. 14 shows an example of the optical recording medium of the present invention, and is a schematic diagram showing examples of DVD + RW, DVD-RW, and HD DVD RW. FIG. 15 is a schematic diagram showing an example of an optical recording medium of the present invention and an example of a Blu-ray disc. FIG. 16 is a diagram showing a result of evaluating an error rate during reproduction by using a 2T cycle strategy, changing the recording power to 6 times the recording speed, and adjusting the modulation degree. FIG. 17 shows the relationship between τw / (τw + τb) and jitter σ / Tw after 10 repetitions of recording when the sum of the lengths of the heating pulses in Example 19 is τw and the sum of the lengths of the cooling pulses is τb. FIG. FIG. 18 is a diagram showing the jitter value when the lowest value is obtained after 10 times of repeated recording in Example 21. In FIG. FIG. 19 is a diagram illustrating the relationship between the jitter and the degree of modulation in Example 24 and Comparative Examples 14-15. FIG. 20 is a diagram illustrating the relationship between the jitter and the degree of modulation in Example 24 and Comparative Examples 14-15.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 1st protective layer 3 Recording layer 4 2nd protective layer 5 Reflective layer 6 Organic protective film 7 Cover layer Tw Basic window width dT3 Leading pulse delay amount of pattern for recording 3T mark T3 Pattern for recording 3T mark Pulse width Toff3 Off-pulse width of pattern for recording 3T mark Toff Off-pulse width of pattern for recording mark other than 3T mark Tmp Peak pulse width of pattern for recording marks other than 3T mark Td1 Recording odd-numbered T mark Td2 Pulse delay amount of multi-pulse part of pattern for recording odd T mark Td3 Last pulse delay amount of pattern for recording odd T mark T Basic window width Pp Peak power Pe Erase power Pb Bias pad -Ttop First pulse width Tlp Last pulse width A Normal mark B Mark with abnormal crystallization area C Normal mark t Time width of the signal after binarization (in this case, an alternating pattern of 3T mark and 3T space was recorded (In this case, in the abnormal mark portion, the time width of this signal is measured shorter than the time width of the 3T mark, and it is schematically shown that an error occurs.)

Claims (6)

A phase change corresponding to one of a convex portion and a concave portion of the guide groove as seen from the incident direction of light by irradiating light onto an optical recording medium having a substrate having a guide groove and at least a phase change recording layer on the substrate. In an optical recording method for recording a mark made of amorphous and a space made of crystal in a recording layer,
When recording information by a mark length recording method in which the time length of the mark and the space is represented by nT (where T represents a basic clock period and n represents a natural number),
The space is formed by an erasing pulse that irradiates at least power Pe,
Formation of all the marks having a length of 4T or more is performed by a multi-pulse that alternately irradiates a heating pulse of power Pw and a cooling pulse of power Pb (where Pw> Pb),
When Pe and Pw satisfy the following formula, 0.15 ≦ Pe / Pw ≦ 0.4, the sum of the lengths of the heating pulses is τw, and the sum of the lengths of the cooling pulses is τb An optical recording method satisfying the following formula: 0.4 ≦ τw / (τw + τb) ≦ 0.8. A phase change corresponding to one of a convex portion and a concave portion of the guide groove as seen from the incident direction of light by irradiating light onto an optical recording medium having a substrate having a guide groove and at least a phase change recording layer on the substrate. In an optical recording method for recording a mark made of amorphous and a space made of crystal in a recording layer,
When recording information by a mark length recording method in which the time length of the mark and the space is represented by nT (where T represents a basic clock period and n represents a natural number),
The space is formed by an erasing pulse that irradiates at least power Pe,
The formation of the mark is performed by a heating pulse that irradiates at least power Pw (where Pw> Pe), and Pe and Pw satisfy the following expression: 0.15 ≦ Pe / Pw ≦ 0.5. An optical recording method.   When recording and reproduction are performed with a laser beam having a wavelength of 640 to 660 nm, recording is performed at a speed 10 times or more of the reference linear velocity, and when recording and reproduction is performed with a laser beam having a wavelength of 400 to 410 nm, it is four times the reference linear velocity. The optical recording method according to claim 1, wherein recording is performed as described above.   4. The optical recording method according to claim 1, wherein recording is performed so that an average value of minimum values of distances between marks on adjacent tracks in the radial direction is larger than ½ of a track pitch.   5. The optical recording method according to claim 1, wherein recording is performed such that the modulation degree M of the longest mark satisfies the following expression: 0.35 ≦ M ≦ 0.60. 6. An optical recording medium, wherein information relating to the optical recording method according to claim 1 is recorded in advance on a substrate.