JP2004030923A - Optical recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording method capable of performing a mark length modulation recording with a high density wherein overwrite can be performed at a high speed and a jitter of mark edge is small. <P>SOLUTION: The optical recording method of recording information on an optical information recording medium having a phase change type recording layer wherein a crystalline part is brought into an unrecording or deleted state and an amorphous part is brought into a recording state by using a recording mark with a plurality of mark lengths nT (wherein T is a clock period and n is an integer of 2 or over) whose shortest mark length is 0.5μm or below, is characterized in that a temporal lengthα<SB>i</SB>T (1≤i≤m) to emit a laser light beam with a recording power Pw enough to melt the recording layer in the case of forming the recording marks is selected to be (Σα<SB>i</SB>)<0.5n. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an optical recording medium and an optical recording method for high-density recording having a phase-change type recording layer, such as a rewritable DVD, and more particularly to a linear velocity dependency and a recording power dependency during one-beam overwriting. The present invention relates to an optical recording medium and an optical recording method with improved stability of recording marks over time.

Generally, in a compact disk (CD) or a DVD, recording of a binary signal and detection of a tracking signal are performed by utilizing a change in reflectance caused by interference of reflected light from the bottom of a concave pit and a mirror surface.
In recent years, phase-change rewritable compact discs (CD-RW, CD-rewritable) have been widely used as media compatible with CDs. As for DVDs, various phase-change rewritable DVDs have been proposed.

These phase-change type rewritable CDs and DVDs detect a recording information signal by utilizing a change in a reflectance and a change in a phase difference caused by a difference in a refractive index between an amorphous state and a crystalline state. An ordinary phase change medium has a structure in which a lower protective layer, a phase change recording layer, an upper protective layer, and a reflective layer are provided on a substrate, and a reflectance difference and a phase difference are obtained using multiple interference of these layers. It can be controlled to make it compatible with CDs and DVDs.
In a CD-RW, compatibility between a CD and a recording signal and a groove signal can be ensured within a range where the reflectance is reduced to 15 to 25%, and reproduction is performed by a CD drive to which an amplification system for covering a low reflectance is added. Is possible.

It should be noted that the erasing and re-recording processes of the phase-change recording medium can be performed only by the intensity modulation of one focused light beam. And overwrite recording in which erasure and erasure are performed simultaneously.
For recording information using a phase change, a crystal, an amorphous state, or a mixed state thereof can be used, and a plurality of crystal phases can be used. In general, a recording medium is made to be in a crystalline state in an unrecorded / erased state, and to form an amorphous mark for recording. As a material of the recording layer, a chalcogen element, that is, a chalcogenide alloy containing S, Se, and Te is often used.

For example, the main component GeSbTe system mainly composed of GeTe-Sb ₂ Te ₃ pseudo-binary alloy, InSbTe system mainly composed of InTe-Sb ₂ Te ₃ pseudo-binary alloy, the Sb _0.7 Te _0.3 eutectic system AgInSbTe-based alloys, GeSnTe-based alloys, and the like.
Among, GeTe-Sb ₂ Te ₃ pseudo binary alloy system obtained by adding excess Sb in, in particular, Ge ₁ Sb ₂ Te _4, or Ge ₂ Sb ₂ Te ₅ intermetallic compound neighborhood composition such as mainly practical Have been.

These compositions are characterized by crystallization without phase separation, which is peculiar to intermetallic compounds, and have a high crystal growth rate, so that initialization is easy and the recrystallization rate during erasure is high. For this reason, a quasi-binary alloy system or a composition near an intermetallic compound has attracted attention as a recording layer exhibiting practical overwrite characteristics (Non-Patent Document 1 or Non-Patent Document 2).

However, in these compositions, metastable tetragonal crystal grains grow. These crystal grains have clear crystal grain boundaries and irregular sizes, and have a problem that optical anisotropy is remarkable depending on their orientation, so that optical white noise is easily generated.
Since such crystal grains having different particle diameters and optical characteristics are likely to grow around the amorphous mark, the jitter of the mark is likely to increase, or the optical characteristics are different from those of the surrounding crystals. It was easy to be detected as remaining.
For this reason, there has been a problem that good reproduction characteristics cannot be obtained in recording at a high linear velocity or high-density mark length modulation recording. Specifically, in the rewritable DVD standard, the shortest mark length is 0.6 μm, but it has been found that as the shortest mark length is further reduced, the jitter rapidly increases.

Incidentally, there is a so-called absorption rate correction as a measure for improving the jitter. In the conventional four-layer structure, the light energy absorbed by the recording layer is generally smaller than the light energy Ac absorbed in the crystalline state with high reflectance (Ac). <Aa). Therefore, at the time of overwriting, there is a problem that the shape or the like of a new recording mark changes depending on whether the original state is a crystalline state or an amorphous state, and jitter increases.
This makes the absorption efficiency of the light energy in the crystalline state and the amorphous state almost the same, stabilizes the mark shape regardless of the original state, and thereby reduces the jitter. Further, since the crystal needs extra heat for the latent heat at the time of melting, it is preferable that the crystal state absorbs more light energy (Ac> Aa).

関係 In order to achieve this relationship, there is a method in which at least one light-absorbing layer is added to form a structure of five or more layers, and a part of light absorption in an amorphous state is removed by this absorbing layer. For example, an absorption layer such as Au or Si is inserted between the lower protective layer and the substrate or on the upper protective layer (Non-Patent Documents 3 and 4).

However, such a layer configuration has problems in the heat resistance and adhesion of the absorbing layer, and when overwritten repeatedly, deterioration such as microscopic deformation and peeling is remarkable. In addition, the stability over time deteriorates because peeling or the like easily occurs.
That is, to achieve a high density while maintaining a conventional four-layer structure, it has been difficult in the GeTe-Sb ₂ Te ₃ pseudo binary alloy recording layer.
In addition, the GeTe-Sb ₂ Te ₃ pseudo binary alloy recording layer has a wavelength dependence such that the real part becomes smaller and the imaginary part becomes larger as the birefringence becomes shorter. In this case, it is difficult to achieve the condition of Ac> Aa.

Therefore, in recent years, a quaternary AgInSbTe alloy has been used as a recording layer material. The AgInSbTe quaternary alloy is characterized in that a high erasure ratio as high as 40 dB can be obtained. With a conventional four-layer structure, high linear velocity and high-density mark length modulation recording can be performed without correcting the absorptance. .
However, being able to perform high-speed recording usually means that the crystallization speed is high and erasure is easy, so that amorphous marks are also easily crystallized, and the recorded marks often have poor temporal stability.
Jpn. J. Appl. Phys. , Vol. 69 (1991), p2849 SPIE, Vol. 2514 (1995), pp 294-301. Jpn. J. Appl. Phys. , Vol. 37 (1998), pp 3339-3342. Jpn. J. Appl. Phys. , Vol. 37 (1998), pp 2516-2520

In recent years, the amount of information has increased, and in order to shorten the recording time and increase the speed of information transfer, recently, a medium capable of recording and reproducing at higher speed has been demanded. For example, the standard speed (1x speed) of a CD is 1.2 to 1.4 m / s, but a CD-RW capable of recording at 4x speed has been commercialized, and recording at 8x speed and 10x speed is possible. A compact CD-RW is required.
On the other hand, various types of rewritable DVDs such as DVD-RAM, DVD + RW, and DVD-RW have been proposed or commercialized. However, a 4.7 GB rewritable DVD having the same capacity as a read-only DVD has not yet been put to practical use.
In other words, there is a need for a medium that can record short marks at high speed and that has good mark stability.

However, conventionally, high-speed recording and mark stability are considered to be contradictory properties, and it has been considered difficult to satisfy both at the same time.
The present inventors have repeatedly studied the principles of crystallization and amorphization, and have found an epoch-making medium that satisfies all of these characteristics at the same time.
That is, the present invention provides an optical recording medium on which short marks can be satisfactorily recorded at high speed and which has good mark stability, and an optical recording method suitable for the medium.

The first gist of the present invention resides in the following optical recording method.

（ただし、ｍはパルス分割数でｍ＝ｎ−ｋ、ｋは０≦ｋ≦２なる整数とする。また、Σ_i
（α_i＋β_i）＋η₁＋η₂＝ｎとし、η₁はη₁≧０なる実数、η₂はη₂≧０なる実数、０≦η₁＋η₂≦２．０とする。α₁＝０．１〜１．５、α_i＝０．１〜０．８（２≦ｉ≦ｍ）、β_i＝０．３〜１．０（１≦ｉ≦ｍ−１）、β_m＝０〜１．５とする。α_i（２≦ｉ≦ｍ）
及びβ_i（２≦ｉ≦ｍ−１）はｉによらず一定とし、かつα₁≧α_iである。α_i＋β_i-1＝
１．０（３≦ｉ≦ｍ）として、α_i（２≦ｉ≦ｍ）の記録パルスをクロック周期に同期さ
せる。さらに、β₁及びβ_mをβ_iと異なる値をとりうるようにし、（Σα_i）＜０．５ｎとする。）となるように分割し、
　α_iＴ（１≦ｉ≦ｍ）の時間内においては、記録層を溶融させるにたるＰｗ≧Ｐｅなる
記録パワーＰｗの前記レーザー光ビームを照射し、
　β_iＴ（１≦ｉ≦ｍ）の時間内においては、０＜Ｐｂ≦０．２Ｐｅ（ただし、β_mＴにおいては、０＜Ｐｂ≦Ｐｅとなりうる）なるバイアスパワーＰｂの前記レーザー光ビームを
照射する
ことを特徴とする光記録方法に存する。 That is, for an optical information recording medium having a phase-change recording layer in which a crystal part is in an unrecorded or erased state and an amorphous part is in a recorded state, a plurality of marks having a minimum mark length of 0.5 μm or less are provided. A recording method for recording information using a long recording mark,
As the optical information recording medium, the amorphous portion due to competition between the amorphization of the melted region of the phase change recording layer and the recrystallization from the boundary of the solid phase crystal portion around the melted region. Using an optical information recording medium on which is formed
An optical system that irradiates a laser light beam having a wavelength of 350 to 680 nm to the phase-change recording layer through an objective lens having a numerical aperture NA of 0.55 or more and 0.9 or less,
Between the recording marks, the laser light beam of erasing power Pe capable of crystallizing the amorphous is irradiated,
Regarding the recording mark,
When the time length of one recording mark is nT (T is a clock cycle, n is an integer of 2 or more), the time length nT of the recording mark is

(Where, m is a pulse division number m = n-k, k is set to 0 ≦ k ≦ 2 becomes an integer. Further, sigma _i
(Α _i + β _i ) + η ₁ + η ₂ = n, η ₁ is a real number satisfying η ₁ ≧ 0, η ₂ is a real number satisfying η ₂ ≧ 0, and 0 ≦ η ₁ + η ₂ ≦ 2.0. α ₁ = 0.1 to 1.5, α _i = 0.1 to 0.8 (2 ≦ i ≦ m), β _i = 0.3 to 1.0 (1 ≦ i ≦ m−1), β _m = 0 to 1.5. α _i (2 ≦ i ≦ m)
And β _i (2 ≦ i ≦ m−1) are constant regardless of i, and α ₁ ≧ α _i . α _i + β _i-1 =
Assuming that 1.0 (3 ≦ i ≦ m), the recording pulse of α _i (2 ≦ i ≦ m) is synchronized with the clock cycle. Further, β ₁ and β _m can be different from β _i, and (Σα _i ) <0.5n. )
During the time of α _i T (1 ≦ i ≦ m), the laser light beam having a recording power Pw satisfying Pw ≧ Pe for melting the recording layer is applied;
Within the time of β _i T (1 ≦ i ≦ m), the laser light beam having a bias power Pb of 0 <Pb ≦ 0.2 Pe (however, in β _m T, 0 <Pb ≦ Pe) can be used. The optical recording method is characterized by irradiating.

ADVANTAGE OF THE INVENTION According to this invention, overwrite can be performed at high speed, the jitter of a mark edge is small, high-density mark length modulation recording can be performed, and the formed mark has very good stability over time. An information recording medium is obtained.
In addition, by selecting an appropriate recording layer composition and layer configuration, a phase-change optical recording medium having excellent reproduction compatibility with a read-only medium and high repeated overwrite durability can be obtained.
More specifically, it has playback compatibility with a so-called DVD disk, and can perform one-beam overwriting in a wide linear velocity range including a standard playback speed of 3.5 m / s to a double speed of 7 m / s. It is possible to provide an optical information recording medium and an optical recording method which can be used for a rewritable DVD disc and show no deterioration even if overwritten ten thousand times.
Further, since the medium of the present invention has a wide linear velocity margin, even when recording is performed by rotating the medium at a constant angular velocity such as the CAV method or the ZCAV method, the problem of the recording characteristic difference due to the linear velocity difference between the inner and outer circumferences of the medium is eliminated. I can overcome it. If the CAV method is adopted, there is no need to change the disk rotation speed for each radial position, and the access time can be reduced.

The present inventors have found that in a phase change medium in which the crystalline state of a recording layer is an unrecorded / erased state and the amorphous state is a recorded state, erasing is performed at a boundary between an amorphous portion or a fused portion and a peripheral crystalline portion. It has been found that a medium such as that performed by recrystallization that substantially proceeds by high-speed, high-density and stable recording can be performed by crystal growth from. That is, high-speed overwriting can be performed, high-density mark length modulation recording with small mark edge jitter can be performed, and the formed marks have very good temporal stability.

Generally, erasing of an amorphous mark occurs by heating a recording layer to a temperature higher than a crystallization temperature and lower than a melting point to bring it into an amorphous solid state or a molten state, and then recrystallizing when cooling.
According to the study of the present inventors, erasing of an amorphous mark, that is, recrystallization is performed by (1) generation of a crystal nucleus in an amorphous region, (2) an amorphous portion or a fused portion, The process proceeds by the two processes of crystal growth starting from the boundary with the part. By making the former crystal nucleation hardly occur, and substantially utilizing only the latter crystal growth process, It was found that such an effect was obtained.

Normally, crystallization proceeds at a temperature higher than the crystallization temperature and lower than the melting point, but crystal nucleation proceeds at a relatively low temperature and crystal growth proceeds at a high temperature within that temperature range. This is not to say that erasure cannot be performed without generation of crystal nuclei, and erasure is possible if crystal growth proceeds at a high speed using a boundary point with a peripheral crystal region surrounding an amorphous portion or a molten portion as a nucleus.
In particular, a finer mark or a shorter mark is more likely to be instantaneously crystallized to the center of the mark only by crystal growth from such a peripheral crystal part, and thus can be completely erased in an extremely short time. Therefore, the effect is remarkable only in a high-density recording medium using a minute mark whose shortest mark length is 0.5 μm or less, erasing can be performed in the order of 100 nanoseconds or less, and overwriting can be performed at high speed.
In general, the shorter the mark length, the shorter the length of the mark, the higher the recording density. However, from the viewpoint of the stability of the mark, the shortest mark length is preferably 10 nm or more.

Also, the narrower the width of the mark is, the more easily the crystal is instantaneously crystallized to the center of the mark only by crystal growth from the peripheral crystal part, which is preferable. Therefore, it is preferable that the track pitch of the information recording track is, for example, 0.8 μm or less so that the mark does not spread horizontally. Usually, the mark width is about half the track pitch. In general, the narrower the track pitch, the higher the recording density can be. However, from the viewpoint of the stability of the mark, the track pitch is preferably 0.1 μm or more. The track may be a groove only, or may be both a groove and a land.

The medium of the present invention is also excellent in the stability over time of the amorphous mark.
In other words, the crystal growth from the peripheral crystal part proceeds only in a relatively high temperature range close to the melting point and hardly progresses at a low temperature even in the range from the crystallization temperature to the vicinity of the melting point. It is hardly crystallized and has excellent stability over time. The crystallization temperature is usually in the range of 100 ° C. to 200 ° C., but up to this temperature, thermal stability can be maintained.

In particular, in a normal use range below 100 ° C., the recorded amorphous mark is extremely stable, and the amplitude of the recorded signal hardly deteriorates. Conversely, it can be concluded that such aging stability hardly involves crystal nucleation.
Further, the medium of the present invention has an advantage that a smooth mark edge with extremely small fluctuation can be formed in mark length recording.
In general, when recording an amorphous mark, the recording layer is once melted and re-solidified to be amorphous, but since the temperature at the edge of the mark is lower than that at the center, conventionally, at the edge of the mark, Recrystallization due to crystal nucleus growth is likely to occur, and coarse grains mixed with amorphous are generated, causing mark edge fluctuation.

In the medium of the present invention, at the time of erasing, the crystal growth from the boundary between the amorphous portion or the fused portion and the crystal portion is dominant and the speed is high. When re-solidified to become amorphous, only crystal growth from the peripheral crystal part occurs, and crystallization due to crystal nucleus growth hardly occurs, and the mark edge does not easily fluctuate.
That is, the crystal growth from the peripheral crystal part progresses only in a relatively high temperature range close to the melting point and hardly progresses at a low temperature even in the range from the crystallization temperature to the vicinity of the melting point. The boundary shape of the amorphous mark is determined only by the cooling rate at which the temperature decreases and passes the melting point.

Then, almost no coarse grains mixed with amorphous due to crystal nucleus growth occurring at the time of re-solidification, which is a problem in the past, are formed around the amorphous marks. This has been found to be extremely effective in suppressing noise due to mark edge fluctuation.
Furthermore, since the mark edge shape is stable without changing over time, not only the initial jitter is small, but also the jitter is hardly deteriorated with time.

The crystallization principle of the present invention will be described in more detail.
In the present medium, the boundary between the amorphous mark and the peripheral crystal portion becomes a nucleus for crystal growth, and almost no crystal nucleus is generated inside the amorphous mark. Therefore, the crystal grows only from the mark boundary.
On the other hand, in the conventional GeTe-Sb ₂ Te ₃ -based recording layer, crystal nuclei are randomly generated in the amorphous mark, and the nuclei grow and crystallize.
The difference between the two crystallization processes can be confirmed with a transmission electron microscope. When erasing light of relatively low power is applied to both recording layers after the formation of the amorphous mark in a DC manner, the GeTe-Sb2Te3-based recording layer crystallizes from the center of the amorphous mark where the temperature increases. While progress is observed, in the recording layer of the present invention, it is observed that crystals grow from the periphery of the amorphous mark. In particular, crystal growth from the front end and the rear end of the amorphous mark is remarkable.

A recording layer composition that is erased by such a principle is often found in an alloy system in which an excess of Sb and other elements up to about 20 atomic% are added to the composition near the eutectic point of Sb _0.7 Te _0.3 . That is, M _y (Sb _x Te _1-x ) _1-y 0.6 ≦ x ≦ 0.9, 0 <y ≦ 0.2, and M is Ga, Zn, Ge, Sn, Si, Cu, Au, Al , Pd, Pt, Pb, Cr, Co, O, S, Se, T
a) a thin film containing an alloy as a main component.
In the alloy containing excess Sb in Sb _0.7 Te _0.3 , the crystal growth from the crystal around the amorphous mark is remarkably larger than that of the GeTe-Sb ₂ Te ₃ pseudo binary alloy system. It has the feature that overwriting is possible. Excess Sb does not promote random crystal nucleation and crystal nucleus growth in the amorphous mark, but greatly increases the crystal growth rate from the peripheral crystal part.
However, in the case of the SbTe binary alloy, since crystal nuclei are generated to a considerable extent, the stability over time of the amorphous mark is extremely poor, and it is necessary to add an appropriate element.

According to the study of the present inventors, the addition of Ge is extremely effective in suppressing the generation of crystal nuclei.
Whether or not the recrystallization of the amorphous mark is substantially governed only by the recrystallization from the peripheral crystal part can be indirectly known from the evaluation of the temporal stability.
As a specific evaluation method, there is a method of measuring a modulation degree of a reproduced signal when an accelerated environmental test under high temperature and high humidity is performed.

That is, when a signal is recorded with a plurality of mark lengths having a minimum mark length of 0.5 μm or less, the modulation degree of a signal reproduced immediately after recording is M ₀ ,
Assuming that the modulation degree of the reproduced signal after the lapse of 1000 hours under the condition of 80 ° C. and 80% RH after recording is M ₁ ,

It is.
The mark length modulation method is not limited, and EFM modulation, EFM plus modulation, (1, 7) RLL-NRZI (run length limited-non return to zero inverted) modulation, or the like can be used. A random signal is recorded with a minimum mark length of 0.5 μm or less. In this evaluation, it is preferable that the shortest mark length is about 0.2 μm or more. Note that it is not necessary to satisfy the above expression under all evaluation conditions, and it is sufficient if the above expression is satisfied under one evaluation condition.

As an example, a random signal of the EFM plus modulation method is recorded with a plurality of mark lengths having a minimum mark length of 0.4 μm.
The modulation degree is obtained by standardizing the signal amplitude of the longest mark of the modulation method by the top signal strength. FIG. 6 shows a waveform of a DC reproduction signal (a reproduction signal including a DC component) when a random signal modulated by EFM plus is recorded and reproduced. The degree of modulation is defined as a ratio I ₁₄ / I _top between the signal intensity I _{top at} the top of the 14T mark and the signal amplitude I ₁₄ .
If the degree of modulation does not change, it can be determined that the amorphous mark size is sufficiently stable. If the degree of modulation of the random signal recorded before the acceleration test maintains 90% or more of the initial value after the acceleration test, it can be estimated that crystal nucleation is not substantially accompanied.

In the recording layer of the present invention, since crystal growth from the peripheral crystal part is likely to occur in a high temperature region immediately below the melting point, even when the recording layer is melted and re-solidified for forming an amorphous mark, crystal growth from the peripheral crystal part is performed. Can occur. Therefore, if the cooling rate after melting is slow and does not reach the critical cooling rate required for solidification as amorphous, the entire molten region is recrystallized almost instantaneously.

This can be confirmed by the following experiment.
On a 0.6 mm thick polycarbonate substrate provided with a groove for guiding recording / reproducing light, (ZnS
) ₈₀ (SiO ₂ ) ₂₀ first protective layer with a thickness of 68 nm, Ge _0.05 Sb _0.71 Te _0.24 recording layer with a thickness of 18 nm, (ZnS) ₈₀ (SiO ₂ ) ₂₀ second protective layer with a thickness of 20 nm, Al _0.995 Ta _0.005
A reflective layer was provided with a thickness of 250 nm in this order, and an ultraviolet curable resin protective layer was further provided with a thickness of 4 μm. These two sheets were laminated with a hot-melt adhesive with the side having the recording layer facing inward to obtain an optical recording medium. The composition of this recording layer was set to Sb / Te ≒ 3 so that overwriting was possible at a linear velocity of about 7 m / s or more. The medium was initialized by elliptical laser light having a major axis of about 100 μm and a minor axis of about 1.5 μm, which was scanned and melted and recrystallized in the minor axis direction.

The medium was irradiated with focused light having a wavelength of 637 nm and NA = 0.63 at a linear velocity of 7 m / s according to the guide groove. After irradiating a recording light with a recording power Pw of 10 mW in a DC manner, the power was rapidly dropped to 1 mW. That is, the recording light was substantially blocked. The beam diameter is about 0.9 μm, which corresponds to a region where the energy intensity of a Gaussian beam is 1 / e ² or more of the peak intensity.

FIG. 2 shows the change in reflectance before and after the recording light is blocked. As shown in the lower part of FIG. 2, the recording light was shut off as time passed. The recording light is irradiated continuously, that is, in a DC manner on the left side of the lower part of FIG. 2, and is blocked on the right side. When the same area was scanned with reproduction light having a reproduction power of 1.0 mW, a reproduction waveform as shown in the upper part of FIG. 2 was obtained. This corresponds to a change in reflectance.

(4) The reflectance decreases near the moment when the recording light is momentarily cut off, and the reflectance before and after that is almost the same. By TEM observation, it was confirmed that the reflectance-reduced portion was amorphous, and before and after it was crystalline. That is, as long as the recording light is continuously irradiated, the melted portion is recrystallized, and only the melted region near the portion where the recording light is blocked becomes amorphous.

This is because when the recording light is continuously irradiated, the cooling rate of the recording layer is suppressed by the residual heat from the subsequent portion, and the critical cooling rate required for forming an amorphous phase cannot be obtained. This is because once the light is blocked, the residual heat from the subsequent portion can be blocked, and the cooling rate can be increased.
When the recording power Pw was 7 mW or more, an amorphous mark was formed by blocking recording light.

As a result of the study, the medium of the present invention is substantially recrystallized by continuously irradiating recording light having a recording power Pw sufficient to melt the recording layer at a constant linear velocity, and melts the recording layer at a constant linear velocity. It was found that an amorphous mark was formed by irradiating a recording light with a power of almost 0 following a recording light with a sufficient recording power Pw. That the power is substantially 0 does not need to be exactly 0, but means that the bias power Pb satisfies 0 ≦ Pb ≦ 0.2Pw, more preferably the bias power Pb satisfies 0 ≦ Pb ≦ 0.1Pw.

In the present invention, recrystallization during resolidification of the molten portion occurs almost exclusively by crystal growth from the surrounding solid phase crystal portion. Therefore, since the recrystallized portion is not formed at the center of the amorphous mark, a smooth and continuous mark edge is formed.
Heretofore, it has been considered that such a material which is recrystallized remarkably is not suitable for a recording layer for recording a mark length. This is because if the recording light is irradiated for a long time to form a long mark, most of the melted region is crystallized.

However, according to the study of the present inventors, in high-density recording with a shortest mark length of less than 0.5 μm, the melting region becomes amorphous and the recrystallization from the boundary of the surrounding solid-phase crystal portion causes a problem. Good jitter can be obtained by actively using the competition process.
For this reason, it has been found that a pulse division method in which a recording power Pw application section and its cutoff section, that is, a bias power Pb application section are combined, is extremely effective for forming a mark having a length of nT as described later.

When recording is performed by the pulse division method, as shown in FIG. 1, an amorphous mark of an arrow-shaped (or crescent-shaped) amorphous portion is formed continuously.
The shape of the starting end of the mark is determined only by the shape of the starting end of the leading arrow feather-shaped amorphous portion, and the shape of the rear end of the mark is determined only by the shape of the trailing end of the trailing arrow-shaped amorphous portion.
Normally, the starting shape of the amorphous portion is smooth, so that the mark starting shape is also smooth. This is because the cooling rate is kept sufficiently high due to the escape of heat forward, so that the cooling rate substantially reflects the shape of the tip of the melting region and is therefore governed by the rise time of the recording pulse. The rising of the recording pulse, that is, the Pw application section may be 2 to 3 nanoseconds or less.

On the other hand, the shape of the rear end of the amorphous portion is determined by the cooling rate determined by the fall time of the recording pulse and the size of the recrystallized region that advances from the periphery, particularly the crystal portion at the rear end. In order to sufficiently increase the cooling rate, the fall of the Pw application section is desirably 2 to 3 nanoseconds or less. The size of the recrystallization region can be accurately controlled by the off-pulse, that is, the length of the Pb application section.
Further, by applying the above-described super-quenching structure as a layer configuration, the cooling rate of the recording layer is made as steep as possible, and the spatial distribution of the cooling rate is made sharp near the rear end of the mark, so that the position of the mark end is changed. It is also important that there is no fluctuation.

Now, the present inventors have a short mark can be recorded at high speed, and a result of intensive studies for superior optical recording medium temporal stability of recording marks, the specific composition in which the addition of Ge to the vicinity of Sb _0.7 Te _0.3 eutectic composition Was found to be particularly excellent, and by appropriately selecting the layer configuration, an optical recording medium excellent in other characteristics was obtained.
That is, the present inventors focused on an unconventional ternary alloy obtained by adding excess Sb and Ge to Sb _0.7 Te _0.3 and examined the suitability for high-density mark length modulation recording. As a result, in the GeSbTe ternary phase diagram shown in FIG. 3, a medium surrounded by four straight lines A, B, C, and D using a recording layer composition having a very limited Ge—Sb—Te ratio is In high-density mark length modulation recording, it has been found that repetitive overwrite durability and temporal stability are particularly excellent.

That is, in the GeSbTe ternary phase diagram,
A straight line A connecting (Sb _0.7 Te _0.3 ) and Ge,
A straight line B connecting (Ge _0.03 Sb _0.68 Te _0.29 ) and (Sb _0.95 Ge _0.05 ),
A straight line C connecting (Sb _0.9 Ge _0.1 ) and (Te _0.9 Ge _0.1 ) and a straight line D connecting (Sb _0.8 Te _0.2 ) and Ge
The recording layer is a thin film mainly composed of a GeSbTe alloy having a composition of a region surrounded by the four straight lines (but not including the boundaries). By using a layer configuration described later for this recording layer, a medium very suitable for high-density mark length modulation recording with a shortest mark length of 0.5 μm or less can be obtained. In addition, it is possible to obtain the same recording density as DVD and excellent reproduction compatibility with DVD.

In addition, it is possible to secure a wide margin for obtaining good jitter with respect to repetitive overwrite durability and fluctuations in recording power and erasing power.
Within this composition range, the larger the amount of Sb from y = 0.7 in the Sb _y Te _1-y alloy, increasing excess amount of Sb, it is possible to overwrite at a crystallization rate is high a high linear velocity.

More specifically, in EFM plus modulation recording (mark length modulation recording of 8-16 modulation), even if the length of the shortest mark 3T mark is reduced to about 0.4 μm or 0.35 μm, good jitter is obtained. Is obtained. Further, a sufficient servo signal can be obtained, and tracking servo can be applied with an existing read-only DVD drive. Further, overwriting is possible at any linear velocity of a linear velocity of 1 to 10 m / s.

As a result, a rewritable DVD having the same capacity as the read-only DVD and substantially compatible with reproduction can be obtained.
If the excess Sb amount is controlled, the above-mentioned high quality and high density overwriting can be performed at a high linear velocity of 8 m / s or more. Also, by changing the recording pulse division method (pulse strategy) according to the linear velocity as described later, good overwriting can be performed in a wide linear velocity range including at least 3 to 8 m / s.

This composition will be described in detail below.
In a composition near the eutectic point of Sb _0.7 Te _0.3 where the amount of Ge added is 10 atomic% or less, the crystallization rate tends to increase as the Sb / Te ratio increases. This is because Sb in excess of Sb _0.7 Te _0.3 precipitates as Sb clusters and acts as crystal nuclei during the recrystallization process. If there is no excess Sb than Sb _0.7 Te _{0.3, the} erasing performance is insufficient and overwriting is substantially impossible. There is also a problem that initialization is difficult and productivity is very poor because nucleation hardly occurs during initialization (straight line A).

On the other hand, when the amount of Sb is increased in the Sb _0.7 Te _0.3 eutectic binary alloy, the crystallization temperature is lowered in exchange for a higher crystallization speed, and the aging stability of the amorphous mark is impaired. . Further, it is not suitable for recording at a low linear velocity of about 3 m / s, and the formed amorphous mark disappears by short-time irradiation of reproduction light (about 1 mW of laser power). Therefore, Sb should not be included in excess of the straight line D connecting (Sb _0.8 Te _0.2 ) and Ge.

Further, in the range of the excess Sb amount defined by the straight lines A and D, if the binary SbTe is used, the crystallization temperature is low and the crystal nuclei of the excess Sb are present, so that the amorphous mark becomes unstable. Since the excess Sb amount is too large, Ge is added. Ge nucleation is almost completely suppressed by the four-coordinate bond of Ge. As a result, the crystallization temperature rises and the stability over time increases. A straight line B connecting (Ge _0.03 Sb _0.68 Te _0.29 ) and (Sb _0.95 Ge _0.05 ) defines this condition. More preferably, Ge is included more than the straight line B ′ connecting (Ge _0.03 Sb _0.68 Te _0.29 ) and (Sb _0.9 Ge _0.1 ).

と Furthermore, when the Ge content is 10 atomic% or more, the jitter at the time of recording the mark length deteriorates, and the Ge compound having a high melting point, particularly GeTe, easily segregates due to repeated overwriting. Further, it is not preferable because crystallization of the amorphous film immediately after film formation becomes extremely difficult (straight line C). In order to reduce jitter, Ge is more preferably set to 7.5 atomic% or less.

Note that overwriting at a linear velocity of 3m / s or more, the recording layer _{Ge x (Sb y Te 1-} y
It is preferable to use a thin film containing a _1-x alloy as a main component (0.04 ≦ x <0.10, 0.72 ≦ y <0.8). That is, the recording at a linear velocity 3m / s or more, to increase the amount of Sb, Sb _y
It is preferable that y ≧ 0.72 in the Te _1-y alloy. However, the stability of the amorphous mark is slightly deteriorated by increasing the amount of Sb. Therefore, it is preferable to increase x ≧ 0.04 and Ge to make up for this.
Furthermore, to overwriting at a linear velocity of 7m / s or more, the recording layer _{Ge x (Sb y Te 1-} y) 1-x alloy film on the basis of (0.045 ≦ x ≦ 0.075, 0.74 ≦ y <0.8). That is, the recording at a linear velocity of 7m / s or more, and further increase the amount of Sb, preferably with y ≧ 0.74 in Sb _y Te _1-y alloy. At this time, the Ge amount is set to x ≧ 0.045 in order to increase the stability of the amorphous mark. On the other hand, at high linear velocities, the jitter is likely to deteriorate, so the Ge amount is set to x ≦ 0.075 to compensate for this.

Heretofore, reports have been made on the GeSbTe ternary composition or the recording layer composition containing the additional element with the ternary composition as a base (Japanese Patent Application Laid-Open Nos. 61-258787, 62-53886, and 62-86). -152786, JP-A-1-63195, 1-211249, 1-277338).
However, all of the compositions described therein are compositions that are Sb poorer than the straight line A connecting (Sb _0.7 Te _0.3 ) and Ge, and are different from the composition range of the present invention.
Rather, they are mainly composed of a Sb ₂ Te ₃ metal compound composition. In the GeTe-Sb ₂ Te ₃ pseudo binary alloy system, contrary to the present invention, excessive Sb has an effect of slowing down the crystallization speed, so that overwriting is performed at a high linear velocity of 5 m / s or more. , the straight line of GeTe-Sb ₂ Te _3, especially Ge ₂ Sb ₂ Te ₅ composition, it is rather detrimental to incorporate excess Sb.
JP-A-1-100745 (composition range α in FIG. 4A) and JP-A-1-303643 are examples of compositions in which a third element containing Ge is selectively added near Sb _0.7 Te _0.3 containing excess Sb. Japanese Unexamined Patent Publication (Kokai) (FIG. 4A, composition range β).

However, JP-A-1-100745 are very wide and 0.10 ≦ x ≦ 0.80 in Sb _1-x Te _x is the matrix composition, uses only Sb excess space than Sb _0.7 Te _0.3 Accordingly, the idea of the present application that the overwrite durability and the stability over time are excellent in high-density recording is not seen.
Japanese Patent Application Laid-Open No. 1-303643 does not mention the adverse effect that the stability over time of an amorphous mark is impaired if Sb is excessively contained beyond the straight line D in high-density recording as in the present application. In addition, none of the publications mentions the harmful effects of excessive inclusion of Ge beyond the straight line C.

As shown in FIG. 4 (b), the composition partially overlapping the recording layer composition of the present invention is disclosed in JP-A-1-115885 (composition range γ) and JP-A-1-251342 (composition range). δ), JP-A-3-71887 (composition range ε) and JP-A-4-28587 (composition range η).
Japanese Patent Application Laid-Open No. 1-111585 discloses that Au and Pd are added with a composition range of γ as a matrix, but for the purpose of low-density recording, the composition is substantially distinguished from the composition of the present invention by a straight line A and a straight line B. I have. The composition of this publication is suitable for low-density recording corresponding to a mark length of about 1.1 μm (linear velocity of 4 m / s, frequency of 1.75 MHz, square wave of 50% duty) and DC erasing. It is considered that a suitable composition is different from the composition of the present invention intended for high-density recording including short marks.

The composition range δ in JP-A-1-251342 is an extremely Ge-rich GeSbTe system mainly composed of a eutectic of Sb _0.7 Te _0.3 added with about 10 atomic% or more of Ge, and is linear with the composition of the present invention. C is substantially distinguished. In a composition in which Ge is more than 10 atomic% in the composition range δ, the crystallization speed is low as described above, and particularly, the initialization operation for crystallizing the recording layer after film formation is difficult, so that the productivity is low. However, there is a serious problem that it is not practical for practical use. In this publication, Au and Pd serving as crystal nuclei are separately added in order to overcome the problem of the crystallization rate. However, in a region where Ge is smaller than the straight line C as in the present invention, such a necessary amount is not required. There is no.
Further, in this publication, it is described that if the amount of Ge is less than 10 atomic%, a sufficient change in the amount of light cannot be obtained between the recorded portion and the non-recorded portion. By devising a layer configuration including the light emitting element, a very large change in the amount of reflected light having a modulation factor of 60% or more is obtained.
The composition range ε in JP-A-3-71887 is intended for low-density recording, and is substantially distinguished from the composition of the present invention by a straight line C. In particular, the concept of the present application that the use of the composition range of the present invention is excellent in repeated overwrite durability and stability over time in high-density recording is not seen.
The composition range η in JP-A-4-28587 includes extremely Sb-rich and Ge-rich compositions, and is substantially distinguished from the composition of the present invention by a straight line D.
As described above, none of the above publications discloses the technical problem relating to high-density mark length modulation recording in which the shortest mark length is 0.5 μm or less, which is the object of the present invention. There is no disclosure of the selection of the optimum composition and the improvement of the layer structure and the recording method.

Next, the layer configuration of the optical information recording medium of the present invention will be described. The medium of the present invention is characterized in that the recording layer having the above-described composition is combined with the following layer configuration to perform high-density mark length modulation recording with a minimum mark length of 0.5 μm or less, at least 3 m / s to 8 m / s. A medium capable of overwriting over a wide linear velocity range, preferably covering 1 m / s to 10 m / s, can be realized. Then, reproduction compatibility with a so-called DVD can be maintained.
The phase change recording layer has at least one of the upper and lower layers covered with a protective layer.

Further, as shown in FIG. 5 (a), it has a structure of substrate 1 / first protective layer 2 / recording layer 3 / second protective layer 4 / reflective layer 5, on which ultraviolet or thermosetting resin is used. It is covered (protective coat layer 6). The order of the respective layers as shown in FIG. 5A is suitable when the recording layer is irradiated with a focused light beam for recording and reproduction via the transparent substrate.
Alternatively, a configuration in which the order of the above-described layers is reversed and the layers are stacked in the order of the substrate 1 / the reflective layer 5 / the second protective layer 4 / the recording layer 3 / the first protective layer 2 as shown in FIG. . This layer configuration is suitable when a focused light beam is incident from the first protective layer side. Such a configuration is useful when the objective numerical aperture NA is 0.7 or more and it is necessary to reduce the distance between the recording layer and the objective lens.

With the configuration shown in FIG. 5A, a transparent resin such as polycarbonate, acrylic, or polyolefin, or transparent glass can be used for the substrate.
Among them, polycarbonate resins are the most preferred because they have the track record of being most widely used in CDs and are inexpensive.
In the configuration shown in FIG. 5B, resin or glass can be used similarly, but the substrate itself does not need to be transparent. Rather, it is preferable to use glass or an aluminum alloy to enhance flatness and rigidity. is there.
The substrate is provided with a groove having a pitch of 0.8 μm or less for guiding recording / reproducing light, but this groove is not necessarily required to be a geometrically trapezoidal groove. A groove may be formed optically by forming something like a waveguide.

In the layer configuration shown in FIG. 5A, a first protective layer 2 is provided on the substrate surface and a second protective layer 4 is provided on the recording layer 3 in order to prevent deformation due to high temperature during recording. The second protective layer 4 also has a function of preventing mutual diffusion between the recording layer 3 and the reflective layer 5, and effectively releasing heat to the reflective layer 5 while suppressing deformation of the recording layer.
In FIG. 5B as well, when viewed from the focused light beam incident side, the second protective layer 4 has a function of preventing mutual diffusion between the recording layer 3 and the reflective layer 5, heat radiation, and preventing deformation of the recording layer. The first protective layer in FIG. 5B has functions of preventing deformation of the recording layer, preventing direct contact between the recording layer and air (prevention of oxidation contamination, etc.), and preventing damage due to direct contact with the optical pickup.

A protective layer may be further provided between the reflective layer and the substrate. For example, heat damage to the resin substrate can be prevented.
In the configuration shown in FIG. 5 (b), a harder dielectric or amorphous carbon protective film or an ultraviolet or thermosetting resin layer is further provided outside the first protective layer 2. Is desirable. Alternatively, a transparent thin plate having a thickness of about 0.05 to 0.6 mm may be attached, and a focused light beam may enter through the thin plate.

Further, a medium such as a DVD has a structure in which the medium shown in FIG. On the other hand, in the medium shown in FIG. 5B, the recording layers are bonded with the recording layer surface outside. Further, in the medium shown in FIG. 5B, tracking grooves may be formed on both surfaces of one substrate by injection molding, and a multilayer film may be formed on both surfaces by sputtering.
The recording layer 3, the protective layers 2, 4, and the reflective layer 5 are formed by a sputtering method or the like.
It is desirable to form a film using an in-line apparatus in which a target for a recording layer, a target for a protective layer, and if necessary, a target for a reflective layer material are installed in the same vacuum chamber, from the viewpoint of preventing oxidation and contamination between layers.

The material of the protective layers 2 and 4 is determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion, and the like. Generally, metal, semiconductor oxides, sulfides, nitrides, carbides, and fluorides such as Ca, Mg, and Li having high melting point and high melting point can be used.
These oxides, sulfides, nitrides, carbides, and fluorides do not always need to have a stoichiometric composition, and it is effective to control the composition for controlling the refractive index and the like, or to use a mixture thereof. is there.

The composition ratio and the mixing ratio of the protective layers 2 and 4 may be changed in the thickness direction. Further, the protective layers 2 and 4 may each be composed of a plurality of films. Each film can have different materials, composition ratios, and mixing ratios depending on the required characteristics.
In consideration of the repetitive recording characteristics, it is desirable that the film density of these protective layers be 80% or more of the bulk state from the viewpoint of mechanical strength. When a mixture dielectric thin film is used, the following theoretical density is used as the bulk density.

The recording layer 3 of the medium of the present invention is a phase change type recording layer, and its thickness is generally preferably in the range of 5 nm to 100 nm.
If the thickness of the recording layer 3 is less than 5 nm, it is difficult to obtain a sufficient contrast, and the crystallization speed tends to be slow, so that erasing in a short time tends to be difficult.
On the other hand, if it exceeds 100 nm, it is still difficult to obtain optical contrast, and cracks are likely to occur.
Further, for high-density recording in which it is necessary to obtain a contrast sufficient for compatibility with a read-only disk such as a DVD and the shortest mark length is 0.5 μm or less, the thickness is preferably 5 nm or more and 25 nm or less. If it is less than 5 nm, the reflectivity is too low, and the influence of a non-uniform composition and a sparse film in the initial stage of film growth tends to appear, which is not preferable.

On the other hand, if the thickness is more than 25 nm, the heat capacity becomes large, the recording sensitivity becomes poor, and the crystal growth becomes three-dimensional, so that the edge of the amorphous mark is disturbed and the jitter tends to be high. Further, the volume change due to the phase change of the recording layer becomes remarkable, and the repeated overwrite durability deteriorates, which is not preferable. From the viewpoint of the mark edge jitter and the repetitive overwrite durability, it is more preferable that the thickness be 20 nm or less.
Further, the density of the recording layer is desirably 80% or more, more preferably 90% or more of the bulk density. The bulk density here can be measured by, of course, preparing an alloy lump. In the above equation (1), the molar concentration of each component is replaced with the atomic% of each element, and the bulk density is replaced with each element. An approximate value can be obtained by substituting the molecular weight of

In the sputter deposition method, the density of the recording layer is applied to the recording layer by lowering the pressure of a sputtering gas (a rare gas such as Ar) at the time of film formation, or disposing a substrate close to the front of the target. It is necessary to increase the amount of high energy Ar to be obtained. High-energy Ar means that Ar ions applied to the target for sputtering are partially rebounded and reach the substrate side, or Ar ions in the plasma are accelerated by the sheath voltage on the entire surface of the substrate and reach the substrate. Is one of
Such an irradiation effect of a high-energy rare gas is called an atomic peening effect. In sputtering using Ar gas, which is generally used, Ar is mixed into a sputtered film due to an atomic peening effect. The atomic peening effect can be estimated from the amount of Ar in the film. That is, if the amount of Ar is small, it means that the high-energy Ar irradiation effect is small, and a film having a low density is easily formed. On the other hand, when the amount of Ar is large, high-energy Ar irradiation is intense and the density is increased, but Ar taken in the film becomes a void during repeated overwriting and precipitates, thereby deteriorating the durability of repetition. An appropriate amount of Ar in the recording layer film is 0.1 atomic% or more and 1.5 atomic% or less. Further, it is preferable to use high-frequency sputtering rather than DC sputtering because the amount of Ar in the film is reduced and a high-density film can be obtained.

In the present invention, the recording layer is composed of a thin film mainly composed of the GeSbTe alloy having the above-described composition. That is, the ratio of the amounts of the respective elements Ge, Sb, and Te in the recording layer may be within the above-described composition range, and if necessary, other elements may be added to the recording layer up to a total of about 10 atomic%. Good.
The optical constant of the recording layer can be finely adjusted by further adding at least one element selected from O, N, and S to the recording layer in an amount of from 0.1 atomic% to 5 atomic%. However, adding more than 5 atomic% is not preferable because it lowers the crystallization speed and deteriorates the erasing performance.

Further, in order to increase the stability over time without lowering the crystallization speed during overwriting, it is preferable to add at least one of V, Nb, Ta, Cr, Co, Pt and Zr at 8 atomic% or less. . More preferably, it is added in an amount of from 0.1 atomic% to 5 atomic%. It is desirable that the total addition amount of these additional elements and Ge with respect to SbTe is 15 atomic% or less in total. Excessive inclusion will induce phase separation other than Sb. In particular, when the Ge content is 3 atomic% or more and 5 atomic% or less, the addition effect is large.
In order to improve the aging stability and finely adjust the refractive index, it is preferable to add at least one of Si, Sn, and Pb to 5 atomic% or less. The total content of these additional elements and Ge is preferably 15 atomic% or less. These elements have the same four-coordinate network as Ge.

Addition of Al, Ga, and In at 8 atomic% or less has the effect of increasing the crystallization temperature and at the same time reducing jitter and improving the recording sensitivity. It is preferred that Further, the content together with Ge is desirably 15 atomic% or less, preferably 13% or less.
Addition of 8 atomic% or less of Ag is also effective in improving the recording sensitivity, and the effect is particularly remarkable when used when the Ge atomic weight exceeds 5 atomic%. However, the addition of more than 8 atomic% is not preferable because it increases the jitter or impairs the stability of the amorphous mark, and the addition of more than 15 atomic% with Ge is not preferable because segregation easily occurs. The most preferable Ag content is 5 atomic% or less.

Now, the state of the recording layer 3 of the recording medium of the present invention after film formation is usually amorphous. Therefore, after the film formation, it is necessary to crystallize the entire recording layer to be in an initialized state (unrecorded state).
As an initialization method, an alloy containing excess Sb in Sb _0.7 Te _0.3 can be initialized by annealing in a solid phase. However, in a composition containing Ge, the recording layer is once melted and re-solidified. Initialization by melt recrystallization for crystallization by slow cooling is desirable.
This recording layer has almost no crystal growth nuclei immediately after film formation, and it is difficult to crystallize in the solid phase.However, according to melt recrystallization, a small number of crystal nuclei are formed and then melted. It seems that recrystallization proceeds at high speed mainly due to crystal growth.

Further, in the recording layer of the present invention, the crystal formed by melting and recrystallization has a different reflectance from the crystal formed by annealing in a solid phase. Then, during actual overwrite recording, the erased portion becomes a crystal formed by melt recrystallization, and therefore, it is preferable that the initialization is also performed by melt recrystallization.
At this time, melting of the recording layer is local and limited to a short time of about 1 millisecond or less. If the melting region is wide or the melting time or the cooling time is too long, each layer is destroyed by heat or the surface of the plastic substrate is deformed.
In order to provide such a thermal history, high-power semiconductor laser light having a wavelength of about 600 to 1000 nm is focused on a long axis of 100 to 300 μm and a short axis of 1 to 3 μm and irradiated, and the short axis direction is set as a scanning axis. It is desirable to scan at a linear velocity of 10 to 10 m / s. Even with the same focused light, if it is close to a circle, the melting region is too wide and re-amorphization is likely to occur, and the multilayer structure and the substrate are greatly damaged, which is not preferable.
The fact that the initialization was performed by melt recrystallization can be confirmed as follows. That is, the medium after the initialization is irradiated with recording light having a recording power Pw focused on a spot diameter smaller than about 1.5 μm and having a recording power Pw for melting the recording layer, at a constant linear velocity in a DC manner. If there is a guide groove, the tracking servo and the focus servo are applied to the track formed between the grooves or between the grooves.

Thereafter, if the reflectivity in the erased state obtained by irradiating the same track with erasing light of erasing power Pe (≦ Pw) in DC is almost the same as the reflectivity in the unrecorded initial state, the initial The conversion state can be confirmed as a crystalline state upon melting.
The reason for this is that the recording layer is once melted by the irradiation of the recording light, and is completely recrystallized by the irradiation of the erasing light. This is because it is in the state of being transformed.
It is to be noted that the reflectance of the initialized state R _ini and the reflectance of the molten re-crystallized state R _cry are substantially the same as defined by (R _ini −R _cry ) / {(R _ini + R _cry ) / 2}. Means that the difference between the two reflectances is 20% or less. Normally, only by solid-phase crystallization such as annealing, the reflectance difference is larger than 20%.

Next, layers other than the recording layer will be described.
The layer configuration of the present invention belongs to a type of a layer configuration called a quenching structure. The quenching structure employs a layer configuration that promotes heat radiation and increases the cooling rate during resolidification of the recording layer, thereby avoiding the problem of recrystallization when forming an amorphous mark and achieving high crystallization by high-speed crystallization. Achieve an erasing ratio. Therefore, the thickness of the second protective layer is 5 nm or more and 30 nm or less. If the thickness is less than 5 nm, the recording layer is easily broken by deformation or the like when the recording layer is melted, and the power required for recording becomes unnecessarily large because the heat radiation effect is too large.

The thickness of the second protective layer of the present invention greatly affects the durability in repeated overwriting, and is particularly important in suppressing deterioration of jitter. If the film thickness is greater than 30 nm, the temperature difference between the recording side of the second protective layer and the reflective layer side during recording increases, and the protective layer itself is asymmetrically deformed due to the difference in thermal expansion on both sides of the protective layer. Easier to do. This repetition is not preferable because it causes microscopic plastic deformation to accumulate inside the protective layer and causes an increase in noise.
By using the recording layer of the present invention, low jitter can be realized in high-density recording with a shortest mark length of 0.5 μm or less. However, according to the study of the present inventors, a short-wavelength laser In the case of using a diode (for example, a wavelength of 700 nm or less), further attention must be paid to the layer structure of the quenching structure. In particular, in studying one-beam overwrite characteristics using a small focused light beam having a wavelength of 500 nm or less and a numerical aperture NA of 0.55 or more, flattening the temperature distribution in the mark width direction requires a high erasing ratio and erasing. It turned out to be important for widening the power margin.

This tendency is the same in an optical system for DVD using an optical system with a wavelength of 630 to 680 nm and NA of about 0.6. In high density mark length modulation recording using such an optical system, a material having low thermal conductivity is particularly used as the second protective layer. Preferably, the thickness is 10 nm or more and 25 nm or less.
In any case, the erasing ratio and the erasing power margin can be improved by forming the reflective layer 5 provided thereon on a material having a particularly high thermal conductivity.
According to the study, in order to exhibit the good erasing characteristics of the recording layer of the present invention in a wide erasing power range, not only the temperature distribution and the time change in the film thickness direction but also the film surface direction (recording beam scanning direction) are required. It is preferable to use a layer configuration that can make the temperature distribution (in the vertical direction) as flat as possible.

By appropriately designing the layer configuration of the medium, the present inventors flatten the temperature distribution in the cross-track direction in the medium, so that the medium can be recrystallized without melting and re-amorphization. The erasure rate and the erasing power margin were widened, and an attempt was made to increase the erasing width.
On the other hand, it was found that by promoting heat radiation from the recording layer to the reflection layer having extremely high thermal conductivity through the very thin second protective layer having a low thermal conductivity, the temperature distribution in the recording layer became flat. . Even if the thermal conductivity of the second protective layer is increased, the heat radiation effect is promoted. However, if the heat radiation is promoted too much, the irradiation power required for recording is increased, that is, the recording sensitivity is significantly reduced.

In the present invention, it is preferable to use a thin second protective layer having low thermal conductivity.
By using the thin second protective layer having a low thermal conductivity, the heat conduction from the recording layer to the reflective layer is given a time delay from several nsec to several tens of nsec at the start of recording power irradiation, Since the heat radiation to the recording medium can be promoted, the heat radiation does not unnecessarily lower the recording sensitivity.
The conventionally known protective layer material mainly composed of SiO ₂ , Ta ₂ O ₅ , Al ₂ O ₃ , AlN, SiN, etc. has too high a thermal conductivity of itself, and the second layer of the medium of the present invention It is not preferable as the protective layer 4. As described above, the thermal conductivity of the metal oxide or nitride is higher by one digit or more than that of the following protective layer used in the protective layer of the present invention, even in the same thin film state.

On the other hand, heat dissipation in the reflective layer can be achieved even if the thickness of the reflective layer is increased. The effect of improving the temperature distribution in the plane direction cannot be obtained. In addition, the heat capacity of the reflective layer itself increases, so that it takes time to cool the reflective layer and, consequently, the recording layer, thereby hindering the formation of amorphous marks. Most preferably, a reflective layer having high thermal conductivity is provided thinly to selectively promote heat radiation in the lateral direction.
The quenching structure conventionally used focuses only on one-dimensional heat dissipation in the film thickness direction, and is intended only to quickly release heat from the recording layer to the reflective layer. Sufficient attention was not paid to planarization.

In addition, the so-called “ultra-quenching structure in consideration of the heat conduction delay effect in the second protective layer” of the present invention, when applied to the recording layer according to the present invention, is more effective than the conventional GeTe—Sb ₂ Te ₃ recording layer. More effective. This is because, in the recording layer of the present invention, the crystal growth at the time of resolidification in the vicinity of Tm is rate-determining of recrystallization. In order to increase the instantaneous cooling rate near Tm to the utmost limit and to make the formation of the amorphous marks and their edges reliable and clear, an ultra-quenched structure is effective, and the temperature distribution in the film surface direction is effective. This is because, by the flattening, the high-speed erasing can be originally performed at around Tm, but the erasing by recrystallization can be surely secured to a higher erasing power.

In the present invention, it is desirable that the material of the second protective layer has low thermal conductivity, but the standard is 1 × 10 ⁻³ pJ / (μm · K · nsec). However, it is difficult to directly measure the thermal conductivity of such a low-thermal-conductivity material in a thin film state, and a guide can be obtained from a thermal simulation and an actual recording sensitivity measurement result.
The second protective layer material having a low thermal conductivity that provides a preferable result includes at least one kind of ZnS, ZnO, TaS ₂ or a rare earth sulfide of 50 mol% or more and 90 mol% or less, and has a melting point or a decomposition point of 1000 ° C. or more. And a composite dielectric containing the above heat-resistant compound.

More specifically, a composite dielectric containing rare earth sulfides such as La, Ce, Nd, and Y in an amount of 60 mol% or more and 90 mol% or less is desirable.
Alternatively, the range of the composition of ZnS, ZnO or rare earth sulfide is desirably 70 to 90 mol%.
As the heat-resistant compound material having a melting point or a decomposition point of 1000 ° C. or more to be mixed with these, Mg, Ca, Sr, Y, La, Ce, Ho, Er, Yb, Ti, Zr, Hf, V, Nb, Oxides such as Ta, Zn, Al, Si, Ge, and Pb, nitrides, carbides, and fluorides such as Ca, Mg, and Li can be used.
Particularly, as a material to be mixed with ZnO, a sulfide of a rare earth such as Y, La, Ce, Nd or a mixture of a sulfide and an oxide is preferable.
If the thickness of the second protective layer is larger than 30 nm, a sufficient flattening effect of the temperature distribution in the mark width direction cannot be obtained. Preferably, the thickness is 25 nm or less. If it is less than 5 nm, the effect of delaying heat conduction in the second protective layer portion is insufficient, and the recording sensitivity is significantly reduced, which is not preferable.
The thickness of the second protective layer 4 is preferably 15 nm to 25 nm when the wavelength of the recording laser beam is 600 to 700 nm, preferably 5 to 20 nm, and more preferably 5 to 15 nm when the wavelength is 350 to 600 nm.

The present invention is characterized in that the heat radiation effect in the lateral direction is promoted by using a thin reflective layer 5 having a very high thermal conductivity and 300 nm or less.
In general, the thermal conductivity of a thin film is significantly different from the thermal conductivity in a bulk state, and is generally small. In particular, in the case of a thin film having a thickness of less than 40 nm, the thermal conductivity may be reduced by one digit or more due to the effect of the island structure at the initial stage of growth, which is not preferable. Further, the crystallinity and the amount of impurities vary depending on the film forming conditions, and this causes a difference in thermal conductivity even if the composition is the same.

In order to define a high thermal conductivity reflective layer showing good characteristics in the present invention, the thermal conductivity of the reflective layer can be directly measured, but the quality of the thermal conductivity is estimated using electric resistance. be able to. This is because, in a material such as a metal film in which electrons mainly perform heat or electric conduction, there is a good proportional relationship between the thermal conductivity and the electric conductivity.
The electric resistance of a thin film is represented by a resistivity value standardized by its film thickness or the area of a measurement region. The volume resistivity and the sheet resistivity can be measured by an ordinary four-probe method, and are defined by JIS K7194. According to this method, data that is much simpler and has better reproducibility than actually measuring the thermal conductivity itself of the thin film can be obtained.
In the present invention, the reflective layer preferably has a volume resistivity of 20 nΩ · m or more and 150 nΩ · m or less, more preferably 20 nΩ · m or more and 100 nΩ · m or less. Materials having a volume resistivity of less than 20 nΩ · m are substantially difficult to obtain in a thin film state. Even when the volume resistivity is greater than 150 nΩ · m, the sheet resistivity can be reduced by forming a thick film having a thickness of more than 300 nm, for example. Even if only the sheet material was reduced in resistivity material, a sufficient heat radiation effect could not be obtained. It is considered that a thick film increases the heat capacity per unit area. Further, such a thick film is not preferable from the viewpoint of manufacturing cost because it takes a long time to form the film and increases the material cost. Further, the microscopic flatness of the film surface is deteriorated.
Preferably, a low volume resistivity material is used so that a sheet resistivity of 0.2 to 0.9 Ω / □ is obtained at a thickness of 300 nm or less. 0.5Ω / □ is most preferred.

Materials suitable for the present invention are as follows.
For example, it is an Al-Mg-Si alloy containing 0.3 wt% to 0.8 wt% of Si and 0.3 wt% to 1.2 wt% of Mg.
In addition, an Al alloy containing 0.2 to 2 atomic% of Ta, Ti, Co, Cr, Si, Sc, Hf, Pd, Pt, Mg, Zr, Mo, or Mn in Al has an additive element concentration of The volume resistivity increases in proportion, the hillock resistance is improved, and it can be used in consideration of durability, volume resistivity, film formation speed, and the like.
Regarding the Al alloy, if the amount of added impurities is less than 0.2 atomic%, the hillock resistance is often insufficient, depending on the film formation conditions. On the other hand, if it is more than 2 atomic%, it is difficult to obtain the above low resistivity.
When more importance is placed on the stability over time, Ta is preferred as an additive component. In particular, for the upper protective layer 4 containing ZnS as a main component, an AlTa alloy having Ta of 0.5 at% or more and 0.8 at% or less balances all of corrosion resistance, adhesion, and high thermal conductivity. It is desirable as a satisfactory reflection layer. In addition, in the case of Ta, the addition of only 0.5 atomic% provides a favorable effect in production that the film formation rate during sputtering is increased by 30 to 40% compared to pure Al or Al-Mg-Si alloy.
When the above-mentioned Al alloy is used as the reflection layer, a preferable film thickness is 150 nm or more and 300 nm or less. If it is less than 150 nm, the heat radiation effect is insufficient even with pure Al. When the thickness exceeds 300 nm, heat escapes in the vertical direction from the horizontal direction and does not contribute to improving the heat distribution in the horizontal direction, the heat capacity of the reflective layer itself is large, and the cooling rate of the recording layer is rather slowed down. In addition, the microscopic flatness of the film surface is deteriorated.

Furthermore, 0.2 atomic% of Ti, V, Ta, Nb, W, Co, Cr, Si, Ge, Sn, Sc, Hf, Pd, Rh, Au, Pt, Mg, Zr, Mo, or Mn is added to Ag. An Ag alloy containing at least 5 atomic% is also desirable. When more importance is placed on the stability over time, Ti and Mg are preferable as the additional components.
When the above Ag alloy is used as the reflection layer, the preferable thickness is 40 nm or more and 150 nm or less. If it is less than 40 nm, the heat radiation effect is insufficient even with pure Ag. If it exceeds 150 nm, heat escapes in the vertical direction from the horizontal direction, does not contribute to the improvement of the heat distribution in the horizontal direction, and an unnecessary thick film reduces productivity. In addition, the microscopic flatness of the film surface is deteriorated.

The present inventors have confirmed that, as described above, the volume resistivity of the additive element to Al and the additive element to Ag increase in proportion to the concentration of the additive element.
By the way, it is considered that the addition of impurities generally reduces the crystal grain size, increases electron scattering at grain boundaries, and lowers thermal conductivity. Adjusting the amount of added impurities is necessary for obtaining a high thermal conductivity inherent in the material by increasing the crystal grain size.
The reflective layer is usually formed by a sputtering method or a vacuum evaporation method. The total impurity amount including the amount of moisture and oxygen mixed at the time of film formation is 2 atomic%, as well as the amount of impurities in the target and the evaporation material itself. It is necessary to: For this reason, the ultimate vacuum degree of the process chamber is desirably set to 1 × 10 ⁻³ Pa or less.
If the film is formed at a degree of ultimate vacuum lower than 10 ⁻⁴ Pa, it is desirable to set the film formation rate to 1 nm / sec or more, preferably 10 nm / sec or more, to prevent impurities from being taken in.

Alternatively, when the intentional additive element is included in an amount of more than 1 atomic%, it is desirable to set the film formation rate to 10 nm / sec or more to prevent the addition of additional impurities as much as possible.
Film formation conditions may affect the crystal grain size regardless of the amount of impurities. For example, in an alloy film in which about 2 atomic% of Ta is mixed into Al, an amorphous phase is mixed between crystal grains, and the ratio of the crystalline phase to the amorphous phase depends on film forming conditions. For example, as the sputtering is performed at a lower pressure, the proportion of the crystal part increases, the volume resistivity decreases, and the thermal conductivity increases.
The impurity composition or crystallinity in the film also depends on the manufacturing method of the alloy target used for sputtering and the sputtering gas (Ar, Ne, Xe, etc.).
As described above, the volume resistivity in the thin film state is not determined only by the metal material and the composition.
In order to obtain a high thermal conductivity, it is desirable to reduce the amount of impurities as described above. On the other hand, pure metals such as Al and Ag tend to be inferior in corrosion resistance and hillock resistance. The optimum composition is determined in consideration of this.

It is also effective to form the reflective layer into multiple layers in order to obtain higher heat conduction and higher reliability. At this time, at least one layer substantially has a heat dissipation effect as the low volume resistivity material having a thickness of 50% or more of the total reflection layer thickness, and the other layers have corrosion resistance, adhesion to a protective layer, and resistance to heat. It is configured to contribute to the improvement of the hillock property.
More specifically, Ag, which has the highest thermal conductivity and the lowest volume resistivity among metals, has a poor compatibility with the S-containing protective layer, and tends to deteriorate slightly when repeatedly overwritten.
In addition, there is a tendency that corrosion occurs easily in an accelerated test environment of high temperature and high humidity.
Therefore, it is also effective to use Ag and an Ag alloy as the low volume resistivity material and to provide an alloy layer containing Al as a main component as an interface layer between 1 nm and 100 nm between the upper protective layer and the upper protective layer. When the thickness is 5 nm or more, the layer is easily formed uniformly without forming an island structure.
As the Al alloy, for example, an Al alloy containing 0.2 atomic% or more and 2 atomic% or less of Ta, Ti, Co, Cr, Si, Sc, Hf, Pd, Pt, Mg, Zr, Mo, or Mn. Is mentioned.
If the thickness of the interface layer is less than 1 nm, the protective effect is insufficient, and if it exceeds 100 nm, the heat radiation effect is sacrificed.
The use of the interface layer is particularly effective when the reflective layer is made of Ag or an Ag alloy. This is because Ag is relatively susceptible to corrosion due to sulfuration due to contact with a protective layer containing sulfide, which is preferred in the present invention.

Further, when the Ag alloy reflective layer and the Al alloy interface layer are used, since Ag and Al are a combination that is relatively easily diffused, it is more preferable to provide an interfacial oxide layer by oxidizing the Al surface to a thickness of more than 1 nm. If the thickness of the interfacial oxide layer exceeds 5 nm, especially 10 nm, it becomes a thermal resistance, which impairs the original purpose, ie, the function of the reflection layer having extremely high heat dissipation, which is not preferable.
The multilayer structure of the reflective layer is also effective for obtaining a desired sheet resistivity with a desired film thickness by combining a high volume resistivity material and a low volume resistivity material.
Adjusting the volume resistivity by alloying can simplify the sputtering process by using an alloy target, but also causes an increase in the target manufacturing cost and thus the raw material ratio of the medium. Therefore, it is also effective to obtain a desired volume resistivity by forming a multilayer of a thin film of pure Al or pure Ag and a thin film of the additive element itself.
If the number of layers is up to about three, although the initial apparatus cost is increased, the cost of each medium can be reduced.
The reflective layer is a multilayer reflective layer composed of a plurality of metal films, the total film thickness is 40 nm or more and 300 nm or less, and a metal thin film layer having a volume resistivity of 20 nΩ · m or more and 150 nΩ · m or less of 50% or more of the thickness of the multilayer reflective layer. (It may be a multilayer).
The thicknesses of the recording layer and the protective layer are not limited by the above-mentioned thermal characteristics, mechanical strength, and reliability. The amplitude of the signal, that is, the contrast between the recorded state and the unrecorded state is selected so as to increase.

For example, if the medium of the present invention is applied to a rewritable DVD to ensure compatibility with a read-only DVD, the degree of modulation must be high. In addition, it is necessary that a tracking servo method called DPD (Differential Phase Detection) method, which is usually used in a read-only player, can be applied as it is.
FIG. 6 shows a waveform of a DC reproduction signal (a reproduction signal including a DC component) when a random signal modulated by EFM plus is recorded and reproduced. The degree of modulation is defined as a ratio I ₁₄ / I _top between the signal intensity I _{top at} the top of the 14T mark and the signal amplitude I ₁₄ .
I _top actually corresponds to the reflectance in the groove of the unrecorded portion (crystal state). I ₁₄ has a problem of intensity difference and phase difference of reflected light from the crystal part and the amorphous part of the phase change medium.
The difference in reflected light intensity is basically determined by the difference in reflectance between the crystalline state and the amorphous state. When the modulation degree after the recording is approximately 0.5 or more, low jitter can be realized, and the tracking servo by the DPD method also operates well.

FIG. 7 shows a calculation example of the reflectance difference in a typical four-layer configuration. On a polycarbonate substrate, a (ZnS) ₈₀ (SiO ₂ ) ₂₀ protective layer, a Ge _0.05 Sb _0.69 Te _0.26 recording layer, a (ZnS)
An ₈₀ (SiO ₂ ) ₂₀ protective layer and an Al _0.995 Ta _0.005 reflective layer were provided.
The refractive index of each layer uses an actually measured value. The complex refractive index of each material at a wavelength of 650 nm is 2.12-0.0i for the upper and lower protective layers, 1.7-5.3i for the reflective layer, 1.56 for the substrate, and the recording layer is in an amorphous state (composed of 3.5-2.6i (measured immediately after the film) and 2.3-4.1i in the crystal state after initialization.
The thicknesses of the recording layer, the second protective layer, and the reflective layer were constant at 18 nm, 20 nm, and 200 nm, respectively.
As far as the first protective layer thickness dependency is concerned, the change in amplitude is usually small and strongly depends on the denominator I _top , that is, the reflectivity of the crystalline state. Therefore, it is desirable that the crystal state reflectance be as low as possible.

In the calculation example of FIG. 7, the first protective layer is formed of (ZnS) ₈₀ (SiO ₂ ) ₂₀ having a refractive index n = 2.12.
It was a membrane. In this case, the first minimum value d ₁ is a thickness 50 to 70 nm, the second minimum value d ₂ is a film thickness 200 to 220 nm. Thereafter, it changes periodically.
The thickness of the first protective layer at which the reflectance in the crystalline state is minimal is substantially determined only by the refractive index of the protective layer in a recording layer having a high reflectance. The minimum point film thickness at another refractive index n can be almost determined by adding 2.1 / n to d ₁ and d ₂ , but the dielectric used as the protective layer usually has n = about 1.8 to 2.3. And d ₁ is about 60 to 80 nm.
If the refractive index n of the first protective layer is smaller than 1.8, the reflectance at the minimum point increases, and the degree of modulation is remarkably reduced to less than 0.5, which is not preferable. Conversely, if the ratio is 2.3 or more, the reflectance at the minimum point becomes too low to achieve 20%, and it becomes difficult to perform focusing and tracking servo.

In the composition range of the recording layer according to the present invention, optical characteristics almost similar to those in FIG. 7 are exhibited.
From the viewpoint of productivity, it is desirable that the thickness of the first protective layer be kept to 150 nm or less. This is because, at present, the deposition rate of the dielectric protective layer by the sputtering method is at most 15 nm / sec, and it takes more than 10 seconds for the deposition to increase the cost. Further, the allowable value of the film thickness variation becomes severe, which is not preferable in production. That is, as seen from FIG. 7, the reflectance shifts Δd from the desired film thickness d _0, in the first minimum value d ₁ near fluctuates by the same in the second minimum value d ₂ vicinity.

On the other hand, the uniformity limit of the film thickness distribution in manufacturing is usually ± 2 to 3% with respect to d ₀ . Therefore, the smaller the _value of d ₀ , the smaller the variation width Δd of the film thickness, which is advantageous because the variation in the reflectivity within the disk surface or between disks can be suppressed.
Therefore, in an inexpensive stationary facing type sputtering apparatus that does not have a substrate rotation mechanism, it is desirable to adopt a film thickness near the _first minimum value d1.
On the other hand, since a thick protective layer has a large effect of suppressing the deformation of the substrate surface during repeated overwriting, if the improvement of the repeated overwriting durability is regarded as important, a film thickness near the _second minimum value d ₂ is adopted. It is desirable to do.
In a medium in which recording or reproduction is performed by irradiating recording / reproducing light through the substrate, the first protective layer must be thickened to some extent to protect the substrate from heat generated during recording. At the time of recording, the temperature of the recording layer is about 100 nanoseconds, but is 500 to 600 ° C. or higher. For this purpose, the film thickness is preferably set to 50 nm or more. If it is less than 50 nm, microscopic deformation is accumulated on the substrate when recording is repeated, and it is likely to cause noise and defects. This is particularly important when the substrate is made of a thermoplastic such as polycarbonate.

Next, an optical recording method that is preferable for use with the present medium will be described.
A preferred first recording method is to record the mark-length modulated information on a plurality of recording mark lengths on the above-described recording medium.
Between the recording marks, a recording light having an erasing power Pe capable of crystallizing the amorphous is irradiated,
When the time length of one recording mark is nT (T is a reference clock cycle, n is an integer of 2 or more),
The time length nT of the recording mark is

(However, m is the pulse division number, m = nk, and k is an integer satisfying 0 ≦ k ≦ 2.)
Also, Σ _i (α _i + β _i ) + η ₁ + η ₂ = n, η ₁ is a real number satisfying η ₁ ≧ 0, η ₂ is a real number satisfying η ₂ ≧ 0, and 0 ≦ η ₁ + η ₂ ≦ 2.0 .
α _i (1 ≦ i ≦ m) is a real number satisfying α _i > 0, β _i (1 ≦ i ≦ m) is a real number satisfying β _i > 0, and Σα _i <0.5n.
α ₁ = 0.1 to 1.5, β ₁ = 0.3 to 1.0, β _m = 0 to 1.5, and α _i = 0.1 to 0.8 (2 ≦ i ≦ m) I do.
It should be noted that in the case of 3 ≦ i ≦ m, α _i + β _i-1 = 0.5 to 1.5 and is constant regardless of i. )
Divided in the order of
irradiating the recording light barrel Pw ≧ Pe becomes recording power Pw to melt the recording layer is in the alpha _i T (1 ≦ i ≦ m) of time, beta _i T in the (1 ≦ i ≦ m) of the time Is 0 <Pb ≦
The recording light is applied with a bias power Pb of 0.2 Pe (however, at β _m T, 0 <Pb ≦ Pe).

By using this recording method in combination with the above-mentioned medium, the cooling rate at the time of resolidification of the recording layer is accurately controlled, and at least 3 m / s to 8 m / s, and further, 1 m / s to 15 m depending on the setting of recording conditions. / S over a wide linear velocity range, enables high-density mark length modulation recording with a minimum mark length of 0.5 μm or less, achieves overwrite 1000 or more repetitions, and has low jitter of less than 10% of the reference clock cycle T. realizable.
First, in order to realize high-density mark length modulation recording as described above, a wavelength of 350 to 680 is required.
A laser light beam of nm is condensed on the recording layer through an objective lens having a numerical aperture NA of 0.55 or more and 0.9 or less to obtain a minute focused light beam spot.

More preferably, NA is set to 0.55 or more and 0.65 or less. If the NA exceeds 0.65, the influence of the aberration due to the inclination of the optical axis becomes large, so that the distance between the objective lens and the recording surface needs to be extremely short. Therefore, when a focused light beam is incident through a substrate such as a DVD having a thickness of about 0.6 mm, the upper limit of NA is about 0.65.
Then, as shown in FIG. 8, by modulating the recording light power to at least three values, the power margin and the linear velocity margin during recording can be widened.
In FIG. 8, the start position of the _first recording pulse α ₁ T and the end position of the last off pulse β _m T do not necessarily need to match the start position and the end position of the original recording signal. Within the range of 0 ≦ η ₁ + η ₂ ≦ 2.0, η ₁ T may be placed at the beginning and η ₂ T may be placed at the end. Fine adjustment of the length of η ₁ T or η ₂ T according to the lengths of the marks before and after the mark and the length between the marks is also effective for accurately forming the marks.

Alternatively, by varying depending only beta _m to mark length nT, in some cases capable of forming a good mark. The last β _m may be set to 0. For example, 3T to 1 in EFM modulation
11T mark among the marks 1T, or 14T mark among the marks 3T~14T in EFM plus modulation, the heat tends to accumulate longer mark the like, to the longer the cooling time by increasing the final beta _m Is good.
Conversely, in the case of a short mark such as a 3T mark, it is preferable to shorten β _m . The adjustment range is 0
. It is about 5. In the case of high-density recording that exceeds the linear recording density of a so-called DVD, sufficient recording signal quality can be obtained without such fine adjustment.

The mark shape can also be controlled by changing the magnitude of the bias power Pb. FIG. 9 shows an example of a temporal change in the temperature of one point on the recording layer when two recording pulses are irradiated. This is a temperature change at a position where the recording pulse P1 is irradiated when the recording pulse P1, the off pulse, and the recording pulse P2 are continuously irradiated while the beam is relatively moved with respect to the medium. (A) is the case where Pb = Pe, and (b) is the case where Pb ≒ 0.
In FIG. 9B, since the bias power Pb in the off-pulse section is almost 0, TL ′ drops to a point sufficiently lower than the melting point, and the cooling rate in the middle is high. Therefore, the amorphous mark is melted during irradiation of the recording pulse P1, and is formed by rapid cooling during the subsequent off-pulse.
On the other hand, in FIG. 9A, the erasing power Pe is irradiated even in the off-pulse section, so that the cooling rate after the irradiation of the first recording pulse P1 is slow, and the minimum temperature TL reached by the temperature drop in the off-pulse section is the melting point Tm. It stays in the vicinity, and is further heated to the vicinity of the melting point Tm by the subsequent recording pulse P2, so that an amorphous mark is not easily formed.

Taking a steep temperature profile as shown in FIG. 9B with respect to the medium of the present invention is important for suppressing crystallization in a high temperature range and obtaining a good amorphous mark. is there. This is because the recording layer of the medium of the present invention shows a large crystallization rate only in the high temperature range just below the melting point, so that the profile of (b) in which the recording layer temperature hardly stays in the high temperature range prevents recrystallization. This is because it is considered possible.
Alternatively, the generation of crystal nuclei in a relatively low temperature range close to the crystallization temperature Tc is not dominant in each erasing process, and Sb clusters that can be crystal nuclei formed during the above-described initialization exist stably. It is considered that only the crystal growth in the region is dominant.
Therefore, by controlling the cooling rate and TL ', recrystallization is almost completely suppressed, and an amorphous mark having a clear contour almost coincident with the molten region can be obtained, and the jitter at the mark edge can be reduced.

On the other hand, in the GeTe-Sb ₂ Te ₃ pseudo binary alloy, FIG. 9 (a), (b) is not so different in the amorphous mark formation process at any temperature profile. This is because this material shows recrystallization although its speed is slightly slow even in a wide temperature range, particularly in a low temperature range near the crystallization temperature Tc. Alternatively, in this material, since crystal nucleation in a temperature range relatively close to Tc and crystal growth in a temperature range close to Tm are rate-determining, recrystallization at a relatively low speed over a wide temperature range as a whole is considered. Is likely to occur.
Even with GeTe-Sb ₂ Te ₃ , coarse grains may be suppressed by using an off-pulse with Pb <Pe. However, if Pb / Pe ≦ 0.2, crystallization near Tc is excessively suppressed. Erasing performance decreases.
However, in the recording layer material according to the present invention, crystallization at a relatively low temperature close to Tc is considered to hardly progress, so that it is preferable to set Pb / Pe ≦ 0.2. Alternatively, more specifically, it is more preferable to use Pb that is as low as possible as long as the tracking servo is stable and 0Pb ≦ 1.5 (mW), and to actively use the off pulse so as to cool as quickly as possible. Is preferable because the edge can be clearly formed.

In the pulse division method of FIG. 8, in particular, only the leading recording pulse α ₁ T is made longer than the succeeding pulse α _i T, and only the leading and trailing off-pulse widths β ₁ T and β _m T are changed to other pulses. Setting it separately from the off-pulse is most effective for balancing the characteristics of the long mark and the short mark.
Since the state-of-the-art pulse α ₁ T has no residual heat effect, it takes a little longer to raise the temperature. Alternatively, it is also effective to set the recording power of the most advanced pulse higher than that of the subsequent pulse.

Further, synchronizing pulse switching with the clock cycle T simplifies pulse control. FIG. 10 shows a pulse division method suitable for mark length modulation recording and a simple pulse control circuit. (B) shows a case where m = n−1 and (c) shows a case where m = n−2 as a pulse division method for recording mark length modulation data. In (b) and (c), T is omitted to simplify the drawing. In each case, α _i (2 ≦ i ≦ m) and β _i (2 ≦ i ≦ m−1) are constant regardless of i, and α ₁ ≧ α _i , α _i + β _i−1 = 1.0 (3 ≦ i ≦ m), α _i (2 ≦ i ≦ m)
Is synchronized with the clock pulse.
It is also effective to make Pb the same as the reproduction light power Pr in order to simplify the circuit. Making only the _first pulse α ₁ T longer than the subsequent pulse is necessary to improve the balance between the recording of the short mark and the recording of the long mark in a so-called eye pattern. Alternatively, only the first pulse may have higher power than the subsequent pulse.
Such a pulse can be achieved by determining three types of gate generation circuits as shown in FIG. 11 and the priorities among them.

FIG. 11 is a diagram illustrating an example of a pulse generation method according to the recording method of the present invention. (A) is a clock signal, (b) is a data signal, and are gate signals (c) Gate1, (d) Gate2, and (e) Gate3 generated from three types of gate generation circuits in the recording pulse generation circuit. By determining the priority of these three types of gate signals, the pulse division method of the present invention can be achieved.
Gate ₁ shows only the recording pulse generation section α ₁ T, and Gate 2 shows the subsequent pulse α _i
The timing for generating a predetermined number of T (2 ≦ i ≦ m) is determined. Here, the pulse width α _i is 2
A constant value alpha _c in ≦ i ≦ m. Gate 3 generates an off-pulse generation section β _i T. Pb is generated while Gate 3 is on (high level), and Pe is generated while Gate 3 is off (low level).
By determining only the independent alpha ₁ leading edge timing and pulse width may be a different value beta ₁ and beta _i.
It is preferable that the rising edges of Gate3 and Gate1 be synchronized. Gate1 and Gate2 generate Pw, respectively, but when Gate1 and Gate2 are on, priority is given to Gate3.
If the delay time T ₁ and α ₁ of Gate ₁ and the delay time (T ₁ + T ₂ ) and α _c of Gate ₂ are specified, the strategy of FIG. 10 can be specified.

Here, if T ₁ is 1T or more, a pulse in the case of m = n−1 in FIG.
If the number of subsequent pulses is reduced by one as less than 1T, a pulse in the case of m = n−2 in FIG. 10C is obtained. At this time, by making α ₁ T and β _m−2 T longer than in the case of m = n−1, the mark length to be formed is set to nT.
As a further application example of the present invention, it is desirable to use the following recording method in order to obtain a signal density equal to or higher than that of a read-only DVD and at least the same signal quality as a read-only DVD at the time of reproduction.

That is, an optical recording method for recording and reproducing data by condensing light having a wavelength of 350 to 680 nm on a recording layer through an objective lens having a numerical aperture NA of 0.55 to 0.9, where m = n− 1 or m = n−2, 0 ≦ Pb ≦ 1.5 (mW), and Pe / Pw is 0.3 or more and 0.6 or less. And
α ₁ = 0.3 to 1.5,
α ₁ ≧ α _i = 0.2 to 0.8 (2 ≦ i ≦ m),
α _i + β _i-1 = 1.0 (3 ≦ i ≦ m),
It is preferable that β _m = 0 to 1.5.

The reason why the ratio of Pe / Pw is kept constant is to increase the erasing power and widen the erasable range when the power is high and the recording mark is large when the power fluctuation occurs. If Pe / Pw is less than 0.3, Pe is always low and erasure tends to be insufficient. Conversely, if it is larger than 0.6, the excess of Pe tends to cause re-amorphization at the center of the beam, making it difficult to erase by complete recrystallization. In addition, the amount of energy applied to the recording layer becomes too large, and the recording layer is likely to be deteriorated by repeated overwriting.

In the recording layer having the composition according to the present invention, good jitter can be obtained in a range where α _i is particularly small. Therefore, Δα _i <0.5n, and (、 α _i ) / n decreases as k decreases. desirable. That is, it is preferable that (Σα _i ) <0.4n when k = 0 or k = 1 and (Σα _i ) <0.5n when k = 2.
Preferably, in order to apply such a recording pulse division method to overwriting at a linear velocity 3m / s or more, in the present invention the recording layer _{Ge x (Sb y Te 1-} y) 1-x, in particular y For overwriting at a linear velocity of 7 m / s or more, y is set to 0.74 or more. That is, the Sb / Te ratio is set to be 2.57 or more, more preferably 2.85 or more Sb-rich.

In the present invention, one of the preferable features is that even if the recording layer composition is Sb-rich, the amorphous mark has high stability and good storage stability.
JP-A-8-22644 describes an AgInSbTe recording layer in which Ag and In are added to a composition near Sb _0.7 Te _0.3 in a total amount of about 10 atomic%. However, when the Sb / Te ratio of the AgInSbTe recording layer is 2.57 or more, the amorphous mark becomes extremely unstable, and there is a problem in storage stability.
Hereinafter, a comparative description will be given using experimental examples. In performing the mark length recording of the EFM plus modulation, a mark having a length of nT is recorded using an optical system with a wavelength of 630 to 680 nm and NA = 0.6 in a linear velocity range of 2 m / s to 5 m / s. Consider a case where a recording pulse is divided into n-1 and recorded.
Ag _0.05 Ge _0.05 Sb _0.67 Te _0.23 (Sb / Te ≒ 2.91) was used as an example of the recording layer of the present invention, and Ag _0.05 In _0.05 Sb _0.63 Te _0.27 (Sb / Te 0.052) was used as an example of the AgInSbTe recording layer. .33) is used.

Since the recording layer of the composition of the present invention and the AgInSbTe recording layer have almost the same optical constants, the same layer configuration can be used to obtain the same reflectance and the same degree of modulation. Applicable.
The thickness of the first protective layer is 100 nm, the recording layer is 20 nm, the second protective layer is 20 nm, and the reflective layer is 200 nm. In all cases, β _i = about 0.5 (1 ≦ i ≦ n−1), Pw = 10 14 (m
W), Pe / Pw = 0.5, Pb ≒ 0.
At this time, in the conventional Ag _0.05 In _0.05 Sb _0.63 Te _0.27 recording layer, α ₁ = 0.8 to 1.0.
2, α _i = 0.4 to 0.6 (2 ≦ i ≦ n−1) is preferable. In particular, α ₁ = 1.0, α _i (2 ≦
When i ≦ n−1) = 0.5 and β _m = 0.5, Σα _i is 0.5n regardless of n.

On the other hand, in the Ag _0.05 Ge _0.05 Sb _0.67 Te _0.23 recording layer of the present invention, α ₁ = 0.3 to 0.5
, Α _i = 0.2 to 0.4 (2 ≦ i ≦ n−1) is a preferable range. More specifically, α ₁ = 0.6 and α _i (2 ≦ i ≦ n−1) = 0.35. In this case, when n = 3, Σα _i ≒ 0.32n, and when n = 4 or more, Σα _i
≒ 0.33n to 0.34n.
This means that in the medium of the present invention, the average irradiation power applied during recording can be reduced, and the substantial recording pulse irradiation time can be reduced to Δα _i <0.4n.

As a result, the following effects can be obtained.
(1) Deterioration of recording signal quality due to high power recording can be reduced. The problem of the high power recording is that the light energy applied to the recording layer becomes too large and the recording layer is confined. For this reason, the cooling rate becomes slow, and recrystallization of the amorphous mark occurs, and deterioration during repeated overwriting becomes remarkable.
By providing a low-power off-pulse section, the average input power is suppressed, and heat is released in the plane direction by a reflective layer with high thermal conductivity. , Adverse effects due to heat accumulation can be suppressed, and a good long mark can be formed.
(2) Thermal damage of each layer during repeated overwriting can be reduced, and repeated durability can be improved. By reducing the thermal damage each time, for example, deformation of a plastic substrate that is vulnerable to heat can be suppressed. In addition, the range over which damage is caused can be limited to a narrower range at the center of the laser beam profile.
In particular, the effect of reducing the substantial recording energy irradiation ratio (Σα _i ) / n is greater for a long mark where n = 4 or more, in which heat is easily stored. Therefore, 5m / s which is easily damaged by heat
Even at the following low linear velocities, the adverse effect on the medium can be reduced.

According to the present invention, the durability of repeated overwriting can be improved in this way, and the number of overwriting times larger by one digit or more than that of the related art can be achieved.
Furthermore, the recording layer, a _{Ge x (Sb y Te 1-} y) 1-x alloy thin film mainly (0.045 ≦ x ≦ 0.075,0.74 ≦ y <0.8), the line By making the recording pulse division method variable according to the speed, overwriting can be performed in a wide range of linear speeds including 3 m / s to 8 m / s.
That is, in the pulse division method of FIG. 8, k of m = nk is fixed, and as the linear velocity at the time of overwriting is lower, either Pb / Pe or α _i is monotonously decreased.
Note that changing the clock cycle in accordance with the linear velocity in order to keep the recording linear density constant, and changing Pw and Pe so as to keep them optimal at their respective linear velocities may be performed as necessary. .

The present invention further provides a method of recording a so-called EFM plus modulation signal having a shortest mark length of 0.35 to 0.45 μm at both 1 × and 2 × the standard reproduction linear velocity of a DVD. The standard reproduction linear velocity of the DVD is 3.49 m / s.
That is, light having a wavelength of 600 to 680 nm passes through an objective lens having a numerical aperture NA of 0.55 to 0.65, is condensed on a recording layer via a substrate, and has a minimum mark length of 0.35 to 0.45 μm. An optical recording method for recording and reproducing data as a range of
n is an integer of 1 to 14,
m = n−1,
Pb is constant irrespective of the linear velocity in the range of 0 ≦ Pb ≦ 1.5 (mW),
Pe / Pw can be changed in accordance with the linear velocity in the range of 0.4 to 0.6. (I) In the range of the recording linear velocity of 3 to 4 m / s, the reference clock cycle is To,
α ₁ = 0.3 to 0.8,
α ₁ ≧ α _i = 0.2 to 0.4 and is constant regardless of i (2 ≦ i ≦ m),
α ₂ + β ₁ ≧ 1.0,
α _i + β _i-1 = 1.0 (3 ≦ i ≦ m),
β _m = 0.3 to 1.5,
alpha _i T Within (1 ≦ i ≦ m) of the time by irradiating the recording light of recording power Pw _1, in the range of (ii) recording linear velocity 6-8 m / s, the reference clock period and the To / 2 ,
α ′ ₁ = 0.3 to 0.8,
α ′ ₁ ≧ α ′ _i = 0.3 to 0.5 and is constant regardless of i (2 ≦ i ≦ m),
α ′ _i + β ′ _i−1 = 1.0 (3 ≦ i ≦ m),
β ′ _m = 0 to 1.0,
When it is assumed that the recording light of the recording power Pw ₂ is irradiated within the time of α _i T (1 ≦ i ≦ m),
α ′ _i > α _i (2 ≦ i ≦ m), and
This is an optical recording method in which 0.8 ≦ Pw ₁ / Pw ₂ ≦ 1.2. According to experiments by the present inventors, particularly good jitter was obtained with this setting as long as the pulse division method shown in FIG. 10 was used.

Here, if α ₂ + β ₁ = 1.0, the independent parameters related to the pulse width are α ₁ ,
α _i and β _m , which are preferable because the recording signal source can be further simplified.
It is not necessary to take all integers from 1 to 14 as n, and from 3 to 11 and 14 in EFM plus modulation. A (1,7) RLL-NRZI (Run Length Limited-Non Return To Zero Inverted) code or the like can also be used.
Note that, in order to keep the recording density constant, the clock cycle at the time of 1 × speed recording is generally set to be twice that at the time of 2 × speed recording.
According to the present invention, not only the above-described method (constant linear velocity, CLV method) for recording over the entire recording area while maintaining a constant linear velocity, but also recording over the entire recording area at a constant rotational angular velocity. It is also effective for the method (constant angular velocity, CAV method). Alternatively, the present invention is also effective for a ZCLV (Zone CLV) method in which the radial direction is divided into a plurality of zones and overwriting is performed in the same zone by the CLV method.
The diameter of the optical disk varies as 86 mm, 90 mm (single CD size), 120 mm (CD size) or 130 mm, and the recording area ranges from a radius of 20 to 25 mm to a maximum of 65 mm. At this time, the difference between the linear velocities of the inner and outer circumferences is nearly three times at the maximum.

In general, in high-density mark length recording, the linear velocity range in which the phase change medium exhibits a good overwrite characteristic is about 1.5 times the linear velocity ratio. If the linear velocity is high, the amorphous layer is easily formed because the cooling rate of the recording layer is high, but the time for maintaining the crystallization temperature or higher is short, and erasing is difficult. On the other hand, when the linear velocity is reduced, erasing is easy, but the cooling rate of the recording layer is reduced, so that the recording layer is easily recrystallized and a good amorphous mark is not easily formed.
In order to solve this problem, it is possible to adjust the thickness of the reflective layer on the inner and outer circumferences so that the degree of heat dissipation by the reflective layer on the inner circumference is increased. Alternatively, by changing the composition of the recording layer,
It has also been proposed to increase the crystallization rate at the outer periphery or to lower the critical cooling rate required for amorphous formation at the inner periphery. However, it is not easy to create a disk having such a distribution.

On the other hand, according to the combination of the medium and the optical recording method of the present invention, if the linear velocity at the outermost periphery of the disk, that is, the maximum linear velocity is approximately 10 m / s or less, good recording can be performed even in the CAV method or the ZCLV method. It is possible.
In order to apply the present invention to a medium in which the linear velocity changes according to the radius as described above, the recording area is divided into a plurality of zones according to the radius, and the data reference clock frequency and the pulse division method are switched for each zone. It is desirable to use it.

That is, a method of recording information with a plurality of mark lengths by rotating an optical information recording medium having a predetermined recording area at a constant angular velocity, wherein the linear velocity at the innermost circumference of the recording area is 2 to 4 m / s. The medium is rotated so that the linear velocity at the outermost periphery of the recording area is 6 to 10 m / s. The recording area is composed of a plurality of zones separated by a radius, and the recording is performed according to the average linear velocity in each zone. The reference clock period T is changed so that the density becomes substantially constant.
At this time, the pulse division number m is constant regardless of the zone, and the Pb / Pe ratio and / or α _i (i is at least one of 1 ≦ i ≦ m) is monotonously changed from the outer zone to the inner zone. Decrease. As a result, it is possible to prevent incomplete formation of the amorphous mark due to insufficient cooling rate in the inner peripheral portion at a low linear velocity. Note that monotonically decreasing α _i (i is at least one of 1 ≦ i ≦ m) means, for example, that only α ₂ among α ₁ , α ₂ ,..., Α _m is decreased. Point.
More specifically, it is desirable to use a pulse division method according to the linear velocity based on the pulse division method shown in FIG. 10 since the variable pulse division method circuit can be simplified. At this time, dividing the recording area into p zones in the radial direction and changing the clock cycle and the pulse division method for each zone is easier than changing the clock area and the pulse division method continuously according to the radial position. .

In the present invention, the recording area is divided into p zones by radius, the innermost side is the first zone, the outermost side is the pth zone, and the qth zone (where q is an integer of 1 ≦ q ≦ p). the angular velocity omega _q in), the average linear velocity <v _{q> ave,} the maximum linear velocity <v _{q> max,} the minimum linear velocity <v _{q> min,} the reference clock period T _q, temporal length of the shortest mark Let n _min T _q be
<V _p > _ave / <v ₁ > _ave is in the range of 1.2 to 3, and <v _q > _max / <v _q > _min is preferably 1.5 or less. In the same zone, the same clock cycle and the same pulse division method are used. However, the linear velocity range that can be covered by the same pulse division method is generally limited to 1.5 times.

In the same zone, ω _q , T _q , α _i , β _i , Pe, Pb, and Pw are constant, and the physical length n _min T _q <v _q > _ave of the shortest mark is 0.5 μm. _Tq < _vq > _ave
Is substantially constant for all q satisfying 1 ≦ q ≦ p, and
m = n-1 or m = n-2,
α ₁ = 0.3 to 1.5,
α ₁ ≧ α _i = 0.2 to 0.8 (2 ≦ i ≦ m),
α _i + β _i-1 = 1.0 (3 ≦ i ≦ m),
0 ≦ Pb ≦ 1.5 (mW),
0.4 ≦ Pe / Pw ≦ 0.6.
Here, when m = n−1, α ₁ = 0.3 to 1.5, α _i = 0.2 to 0.5, and when m = n−2, α ₁ = 0.5 to 1 0.5 and α _i = 0.4 to 0.8.

It is important that the pulse division method is changed according to the following rules. Pb, Pw, Pe / Pw ratio, α _i , β ₁ , β _m are variable for each zone, and at least α _i (i is at least 1 ≦ i ≦ m) Monotonically).
The change of α _i for each zone is preferably in increments of 0.1T or in increments of 0.01T.
Here, by adding a high frequency base clock generation circuit having a period of about 1/100 with respect to the reference clock period T _p in the outermost peripheral zone, T _q and the divided pulse length in all the zones can be set to the base clock. It can be generated as a multiple.
Since the reference clock frequency at 1 × speed of DVD is about 26 MHz, a base clock frequency of about 2.6 GHz at the maximum, usually a base clock frequency of about 260 MHz at least one digit is sufficient.

Furthermore, when the maximum value of Pw in the recording area Pw _max, the minimum value and Pw _min, and _{Pw max / Pw min ≦ 1.2,} Pe = Pw = 0.4~0.6,0 ≦ Pb ≦ It can be 1.5 (mW). According to this, the setting range of the three types of power can be limited, so that the power generation circuit can be simplified.
In the present invention, it is also possible to cope with all linear velocities by changing only the pulse division method while keeping Pw, Pe / Pw ratio, and Pb constant. Also, β _m may be constant regardless of the zone, and only α ₁ and α _m may be used as zone-dependent parameters. This is extremely useful in simplifying the recording pulse control circuit of the drive.

In the present invention, at the time of recording, from the radial position information of the optical head, recording may be performed by virtually setting a zone on the recording medium, or according to the address information and zone information described in advance on the disk. A zone structure may be physically provided thereon. Regardless of whether it is virtual or physical, a recording pulse division method according to the linear velocity determined by the zone may be selected.
Next, another example in which the optical recording method of the present invention is applied to the ZCAV system will be described.
The recording area is divided into p zones according to the radius, the innermost side is the first zone, the outermost side is the pth zone, and the angular velocity in the qth zone (where q is an integer of 1 ≦ q ≦ p) is determined. ω _q ,
The average linear velocity is <v _q > _ave , the maximum linear velocity is <v _q > _max , the minimum linear velocity is <v _q > _min , the reference clock cycle is T _q , and the time length of the shortest mark is n _min T _q . I do.
In the ZCAV system, it is necessary to reduce the reference clock _Tq of the recording data as the zone shifts to the outer peripheral zone so that the recording linear density is almost constant.
That is, such that T _q <v _q > _ave is substantially constant for all q _satisfying 1 ≦ q ≦ p,
_Tq is changed according to the zone. Here, “substantially constant” includes an error of about ± 1%.
Also, in order to keep the maximum linear velocity and the minimum linear velocity in the same zone within a certain range,

Determine the width of the zone so that That is, (< _vq > _max- < _vq > _min ) is set to be less than 10% of (< _vq > _max + < _vq > _min ), and the width of the q-th zone is set to the average radius < _rq.
> A radius position of less than ± 10% of _ave is allowed.
More preferably, (< _vq > _max- < _vq > _min ) is less than 5% of (< _vq > _max + < _vq > _min ).
The width of the zone may be equally divided for each radius of the recording area, but may not be equally divided as long as this condition is satisfied. Although it depends on the recording area width, a recording area having a width of 30 to 40 mm is divided into about 10 or more pieces.

According to the study of the present inventors, the jitter value was at a practical level even if the shortest mark length was about 0.4 μm, if the expression (2) was satisfied.
The above two conditions are conditions for keeping the recording linear density constant, and for keeping the physical length of the mark or the channel bit length constant. Note that the channel bit length is a length per channel bit along a track.
In order to more reliably obtain reproduction compatibility with DVD, when the reference reproduction speed v is about 3.5 m / s and the reference clock cycle T is about 38.2 nsec, the variation of the channel bit length vT is approximately ± Preferably, it is less than 1%.
In order to satisfy this condition in the ZCAV medium, the following equation (3) is used.

Must be satisfied. That is, (<v _q > _max− <v _q > _min ) is (<v _q > _max + <v _q
> _Min ), and the width of the q-th zone is allowed up to a radius position of less than ± 1% of the average radius < _rq > _ave . Therefore, the recording area is divided into 200 or more zones. And,

And _Tq < _vq > _ave is set to be substantially constant for all q _satisfying 1 ≦ q ≦ p. Here, “substantially constant” includes an error of about ± 1%.
As a result, pseudo-density recording independent of the radius can be performed in spite of the ZCAV method, so that the CLV method can be reproduced and the compatibility with the CLV method DVD player is improved.
If necessary, the zone width may be smaller.

Now, an optical recording method for obtaining a recording density equivalent to that of a DVD under the above conditions will be described.
When light having a wavelength of 600 to 680 nm passes through an objective lens having a numerical aperture NA of 0.55 to 0.65 and is condensed on a recording layer via a substrate to perform data recording and reproduction,
The innermost circumference of the recording area is in a radius of 20 to 25 mm, the outermost circumference is in a range of 55 to 60 mm, the average linear velocity of the innermost zone is 3 to 4 m / s,
The angular velocity in the q-th zone (where q is an integer of 1 ≦ q ≦ p) is ω _q , and the average linear velocity is <
_vq > _ave , the maximum linear velocity is < _vq > _max , the minimum linear velocity is < _vq > _min , and the reference clock cycle is _Tq.
, And the time length of the shortest mark is n _min T _q ,
n is an integer of 1 to 14,
m = n−1,
ω _q , Pb and Pe / Pw are constant regardless of the zone,
T _q <v _q > _ave is substantially constant for all q _satisfying 1 ≦ q ≦ p, and

And (i) In the first zone,
α ^{₁ 1} = 0.3~0.8,
A ^{_{α 1 1 ≧ α 1 i =}} 0.2~0.4 constant irrespective of i (2 ≦ i ≦ m) ,
α ¹ ₂ + β ¹ ₁ ≧ 1.0,
α ¹ _i + β ¹ _i−1 = 1.0 (3 ≦ i ≦ m), and (ii) in the p-th zone,
α ^p ₁ = 0.3 to 0.8,
A ^{_{α p 1 ≧ α p i =}} 0.3~0.5 constant irrespective of i (2 ≦ i ≦ m) ,
When α ^p _i + β ^p _i−1 = 1.0 (2 ≦ i ≦ m), (iii) α ¹ _i ≦ α ^q _i ≦ α ^p _i (2 ≦ i ≦ m) in other zones and then, alpha ^q ₁ performs recording as a value between alpha ¹ ₁ and alpha ^p _1.

When the innermost circumference of the recording area is in the range of a radius of 20 to 25 mm and the outermost circumference is in a range of a radius of 55 to 60 mm, the radius width of the recording area is about 30 to 40 mm. Then, the disk is rotated at a constant angular velocity so that <v ₁ > _ave = 3 to 4 m / s in the first zone on the innermost circumference.
The first zone, for the first p zone performs recording by the condition for the other zones (2 ≦ q ≦ p-1 becomes the q ^{_{zones) α 1 i ≦ α q i}} ≦ α p i (2 ≦ i ≦ m) and then, alpha ^q ₁ is a value between the alpha ¹ ₁ and alpha ^p _1. In this case, it is desirable to set the value of α ^q ₁ in increments of 0.1T or 0.01T.
^{_{Preferably, α 1 1 ≧ α q 1}} ≧ α p 1 , however, the ^{_{α 1 1> α p 1)}} .

Further, Pb, Pe / Pw, β ₁ , and β _m are constant irrespective of the zone. If only α ₁ and α _i are changed depending on the zone, a wide linear velocity covering all linear velocities of 3 to 8 m / s is obtained. Good overwrite characteristics can be obtained within the range.
Preferably, these Pe / Pw, Pb, Pw, β m, (α 1 1, α p 1), (α 1 c, α p c)
By previously writing the numerical value of the above on the substrate by a pre-pit row or groove deformation, the drive may be able to select the optimum pulse division method and power for each recording medium and for each zone. These are normally recorded at a position adjacent to the innermost or outermost end of the recording area. If the bias power Pb is set to be the same as the reproduction power Pr, the bias power Pb may not need to be described. The groove deformation specifically means groove wobbling.

Alternatively, an optical information recording medium in which address information is previously recorded on a substrate by pre-pit row or groove deformation, along with the address information, an appropriate α _{1 at the} address.
And information on α _i .
Thereby, the pulse division method information can be read together with the address information at the time of access, and the pulse division method can be switched, and the pulse division method suitable for the zone to which the recording medium and the address belong can be changed without special correction. Can be selected.

The above-described method of performing recording over the entire circumference of the disk while changing the recording pulse division method for each zone can be applied to the ZCLV method (Zoned CLV). A specific example will be described below.
The recording area is divided into a plurality of zones in the radial direction, and recording is performed at a constant linear velocity in each zone.
The ratio v _out / v _in the recording linear velocity v _out in the recording linear velocity v _in and the outermost zone in the innermost zone is 1.2 to 2,
α _i = 0.3 to 0.6 (2 ≦ i ≦ m) and β _m = 0 to 1.5,
M, α _i + β _i-1 (3 ≦ i ≦ m), α ₁ T, Pe / Pw, and Pb are fixed irrespective of the linear velocity, and α _i (2 ≦ i ≦ m) and performing recording by changing the / or beta _m.
In the ZCLV method, the recording area is divided into a plurality of zones in the radial direction in the same manner as the ZCAV method. However, in the same zone, recording is performed while rotating the disk at a constant linear velocity in the CLV mode.

For this reason, when the recording method of the present invention is applied to the ZCLV method, when the linear velocities of the innermost zone and the outermost zone are V _in and V _out , respectively, the difference between V _in and V _out is reduced. By setting V _out / V _in to 1.2 to 2, the load on the medium that depends on the linear velocity is reduced.
The medium of the present invention can record over a wide range of linear velocities of 3 to 8 m / s by only slightly changing the recording pulse division method. Therefore, the ZCLV method of dividing into a relatively small number of zones can be applied.
At this time, in order to like recording density regardless of the zone, the reference clock period T _q of the recording data at a linear velocity V _q and each zone in each zone, irrespective of T _q <v _{q> ave} to q Almost constant.

Then, in each zone, an optimized recording pulse division method is used. That is, α _i = 0.3 to 0.5 (2 ≦ i ≦ m) and β _m = 0 to 1.5, and m, α _i +
Recording is performed by keeping β _i-1 (3 ≦ i ≦ m), α ₁ T, Pe / Pw, and Pb constant and changing α _i and / or β _m according to the linear velocity.
In the CLV system, ZCAV system, or ZCLV system described above, the example in which the recording pulse division method is made variable in accordance with the linear velocity at the time of overwriting is mainly performed by setting β _m constant irrespective of the linear velocity and using a pulse generation circuit. However, conversely, the pulse generation circuit can be simplified by positively changing β _m .

In other words, when recording information with a plurality of recording mark lengths having a minimum mark length of 0.5 μm or less, with the crystal part being in an unrecorded / erased state and the amorphous part being in a recorded state,
Between the recording marks, a recording light having an erasing power Pe capable of crystallizing the amorphous is irradiated,
When the time length of one recording mark is nT (T is a reference clock cycle, n is an integer of 2 or more),
The time length nT of the recording mark is

(However, m is the pulse division number, m = nk, and k is an integer satisfying 0 ≦ k ≦ 2.)
Also, Σ _i (α _i + β _i ) + η ₁ + η ₂ = n, η ₁ is a real number satisfying η ₁ ≧ 0, η ₂ is a real number satisfying η ₂ ≧ 0, and 0 ≦ η ₁ + η ₂ ≦ 2.0 .
α _i (1 ≦ i ≦ m) is a real number satisfying α _i > 0, and β _i (1 ≦ i ≦ m) is a real number satisfying β _i > 0.
Let α ₁ = 0.1 to 1.5, β ₁ = 0.5 to 1.0, β _m = 0 to 1.5, and for 2 ≦ i ≦ m, α _i is 0.1 to 0.8 And is constant irrespective of i.
Note that α _i + β _i-1 is in the range of 0.5 to 1.5 for _i satisfying 3 ≦ i ≦ m, and is constant regardless of i. )
Divided in the order of
During the time of α _i T (1 ≦ i ≦ m), the recording layer is irradiated with a recording light having a recording power Pw of Pw> Pe to melt the recording layer, and within the time of β _i T (1 ≦ i ≦ m). Is 0 <Pb ≦
Irradiating a recording light with a bias power Pb of 0.2 Pe (however, at β _m T, 0 <Pb ≦ Pe),
Let m, α _i + β _i-1 (3 ≦ i ≦ m), α ₁ T, and α _i T (2 ≦ i ≦ m) be constant regardless of the linear velocity, and β _m becomes monotonic as the linear velocity decreases. This is an optical recording method that is changed so as to increase.

First, in order to keep the recording density constant, the above-described ZCAV method or ZCLV method is applied, and the reference clock cycle T is changed in inverse proportion to the linear velocity.
At least 3 ≦ i ≦ m, preferably the α _i + β _i-1 in the 2 ≦ i ≦ m, by constant irrespective of the linear velocity and i, can simplify the pulse generating circuit, and, alpha _i Can be monotonously decreased as the linear velocity decreases, and the cooling rate of the recording layer can be increased. Normally, α _i + β _i-1 = 1.0.
In order to realize such a pulse division method, in the explanatory diagram of the timing of gate generation in FIG. 11, the width α ₁ T is synchronized with the reference clock cycle T (a certain delay may be added). Gat that determines the final off-pulse length β _m T while generating one fixed-length pulse (Gate 1) and a plurality of subsequent fixed-length pulses (Gate 2) having a width α _i T (α _c T)
Only e3 may be changed according to the linear velocity.

Here, when the maximum recording power at each recording linear velocity is Pw _max and the minimum recording power is Pw _min ,
Pw _max / Pw _min ≦ 1.2,
Pe / Pw = 0.4-0.6,
It is preferable that 0 ≦ Pb ≦ 1.5 (mW).
Further, as described above, at least when the linear velocity at the time of overwriting is 5 m / s or less, in order to prevent thermal damage at the time of repeated overwriting, at m = n-1, Δα _i
<0.4n, and when m = n−2, it is preferable that ０．５α _i <0.5n.

Furthermore, the beta _m at the maximum line speed during overwriting beta ^H _m, the beta _m at the lowest linear velocity as beta ^L _m, between the beta _m in linear velocity during the overwriting beta ^L _m and beta ^H _m As a value, a recording method in which Pb and Pe / Pw ratio are constant regardless of the recording linear velocity can be applied.
In this case, at least Pe / Pw _{ratio, Pb, Pw, α 1 T} , α i T, the value of ^{_{(β L m, β H m}} ), on the substrate in advance medium, have been recorded by the pre-pit train or groove deformation If this is the case, the optimum pulse division method can be automatically selected, which is preferable.

Furthermore, if the maximum linear velocity is about twice the minimum linear velocity, an optical recording method in which β _m is constant irrespective of the recording linear velocity while maintaining sufficiently practical signal quality is also possible. is there.
There is a CLV-type read-only DVD drive in which rotation is controlled by generating a data clock and a rotation synchronization signal based on a reference clock cycle obtained by reproducing a mark.

As described above, the medium on which the mark is recorded by the ZCAV system is directly reproduced by the reproduction-only DVD drive of the present system so that the shortest mark length or the channel bit length is substantially constant regardless of the recording radius. It is possible.
That is, it is possible to perform rotation synchronization control by a PLL (Phase Lock Loop) method so that the reference clock cycle T _q ′ of data generated from the recorded mark substantially matches the reference data clock Tr of the drive. Therefore, even if there is some fluctuation in the linear velocity or fluctuation in the channel bit length, the reproduction circuit can decode the fluctuation as it is.

In particular, the EFM plus modulation data recorded so that the shortest mark length is almost constant at 0.4 μm in all zones achieves CLV rotation synchronization by PLL control from the rotation synchronization signal generated from the recorded mark. Is done. At the same time, a reference data clock Tr having a frequency in the range of 25 to 27 MHz is generated. Based on this clock, the data can be reproduced as a CLV recording medium without being aware of the transition between zones.
Of course, if the rotation synchronization is achieved so that the reference data clock becomes Tr / 2, reproduction at double speed becomes possible. As a circuit for generating a rotation synchronizing signal by such a PLL method, a known method for a DVD player or a DVD-ROM drive can be used as it is.

By the way, the medium of the present invention can ensure reproduction compatibility with DVD in all signal characteristics other than the reflectance. For this purpose, recording in the groove is desirable, and it is preferable that the push-pull signal of the groove is small. This is because if the push-pull signal of the groove is large, the tracking servo signal in the DPD method used at the time of reproduction becomes small. Therefore, it is necessary to make the groove depth shallower than λ / (8n) at which the push-pull signal becomes maximum. Here, λ is the wavelength of the reproduction light in air, and n is the refractive index of the substrate. However, at the time of recording, a push-pull signal is usually used for tracking servo.

Regarding the reproduction signal characteristics, it is preferable that the modulation factor Mod is 0.5 or more in order to obtain a high CN ratio. Here, Mod is (the amplitude of the envelope of the DC reproduction signal) / (the upper end value of the envelope of the DC reproduction signal).
Preferred groove depths are d = λ / (20n) to λ / (10n). If it is too shallow than λ / (20n), the push-pull signal during recording will be too small to apply tracking servo, and if deeper than λ / (10n), the tracking servo during reproduction will not be stable. For example, when the recording / reproducing wavelength is about 630 to 670 nm and the numerical aperture NA of the objective lens is 0.6 to 0.65, the groove depth is desirably in the range of 25 to 40 nm.

Further, in order to secure the same capacity as that of a DVD, the pitch of the grooves is set to 0.6 to 0.8 μm. When the groove pitch is set to 0.74 μm, compatibility with DVD is easily obtained.
The groove width is desirably 0.25 to 0.5 μm. If it is smaller than 0.25 μm, the push-pull signal becomes too small. If it is larger than 0.5 μm, the width between the grooves becomes narrow, so that the resin does not easily enter during the injection molding of the substrate, and it becomes difficult to transfer the groove shape to the substrate accurately.
In the medium of the present invention, the reflectance decreases after recording. In order to lower the reflectivity in the groove in such a medium, that is, RGa <RLa, where RGa is the average reflectivity in the groove after recording and RLa is the average reflectivity between the grooves after recording. It is desirable that the groove width be smaller than the inter-groove width.

For example, if the groove pitch is set to 0.74 μm for compatibility with DVD, it is preferable that the groove width is narrower than 0.37 μm, which is half the groove pitch.
On the other hand, when the average reflectivity in the groove before recording is RGb and the average reflectivity between the grooves before recording is RLb, if RGb> RLb is satisfied as long as RGa <RLa is satisfied, the groove is By setting the width to 0.4 to 0.5 μm, the width of the amorphous mark recorded in the groove may be widened, and the modulation degree may be increased or the jitter may be reduced.
Now, these grooves may be periodically deformed in order to access a specific unrecorded track and to obtain a synchronization signal for rotating the substrate at a constant linear velocity. Generally, a wobble meandering in the cross-track direction is often formed. That is, if the groove meanders at a constant frequency fwo, a signal for rotation synchronization can be extracted by the PLL method by detecting the frequency.
It is desirable that the amplitude of the groove meandering be 40 to 80 nm (peak-to-peak value). If it is less than 40 nm, the amplitude is too small to deteriorate the SN ratio. If it exceeds 80 nm, the upper and lower ends of the envelope of the recording signal shown in FIG. 6 contain many low-frequency components derived from the wobble signal, and the distortion of the reproduced signal is large. turn into.
When the frequency of the wobble is close to the band of the recording data, the amplitude is desirably 80 nm or less.

Furthermore, as a carrier wave a meandering frequency f _wo, according to the specific address information, by forming a frequency-modulated or phase-modulated meandering can obtain the address information by reproducing it.
By forming the grooves meander meandering frequency f _wo is constant, the reference period T _w or multiple or submultiple thereof wobbling groove signals generated from the f _wo, it is also possible to generate a reference clock signal T for data.
Normally, the wobble cycle is set to a frequency sufficiently lower or higher than the frequency component of the data to prevent mixing with the data signal component and to be easily separated by a band-pass filter or the like. In particular, making f _wo about one or two digits lower than the data reference clock cycle has been put to practical use in recordable CDs and the like.
In the medium used for the CLV method, after the PLL rotation synchronization is achieved, f _wo is multiplied by about one or two digits to generate a data reference clock. In general, the data reference clock generated by such a method is accompanied by a fluctuation of the same order as the data reference clock (frequency) due to the influence of the rotation synchronization fluctuation (about 0.1 to 1% of f _wo ). Cheap. This degrades the window margin for data detection.

Therefore, it is also effective to insert a pre-pit or a special wobble having a large amplitude for every constant data length in order to correct the fluctuation of the data reference clock, separately from the groove meandering signal. On the other hand, if f _wo is the data reference clock frequency (1 / T) or a range from 1/100 to 100 times the rotation of the data reference clock, the data reference clock is generated as it is based on the extracted wobble signal after the rotation synchronization is achieved. Even so, sufficient accuracy can be secured. That is,

And
In the previously described ZCAV method, the reference clock period T _q is preferably allowed to occur as a multiple or submultiple of the reference period Tw _q of the groove wobbling of each zone. In other words, by forming the groove meandering at a constant angular velocity while changing the frequency f _wo for each zone, the reference clock generated as f _wo or its multiple frequency is generated as the data reference clock _Tq. Can be.
At this time, if the wobble of the groove is set to a relatively high frequency satisfying the expression (5), it becomes easy to generate the data reference clock for each zone. Then, the reference clock T _q for each zone
, And a variable pulse division method can be generated in synchronization with this signal, and the positional accuracy and fluctuation of each divided pulse can be reduced, which is preferable.
As an example of ZCAV type zone division, it is conceivable that one circumference of a groove is one zone. At this time, the groove has a wobble having a constant period regardless of the zone,
Assuming that the groove pitch is TP and the meandering period is _Two , approximately

When to satisfy the relationship: a constant wobble period Tw ₀ is formed over the entire recording area, each comprising on the outer periphery by the track round, so that a number of wobbles increases.
Then, Tw ₀ is an integral multiple of the reference clock period T, that is, Tw ₀ = m
The fact that T (m is a natural number) is desirable because the reference clock generation circuit can be simply simplified to a fraction of an integer when the reference clock is generated from Tw ₀ , so that the reference clock generation circuit can be simplified. In this case, m does not need to be approximately a natural number, and a deviation of about ± 5% is acceptable.

That is, for TP = 0.74 μm, v ₀ = 3.5 m / s and T = 38.23 ns
If c and n = 1, then m ≒ 34.7, and if the wobble period Tw ₀ = 35T approximately, the number of wobbles included in each round increases by one.
In this case, although the wobble is introduced in the CLV method, the phase of the wobble of the adjacent track is always the same, so that the fluctuation of the reproduction amplitude of the wobble signal due to interference (beat) is small. is there.

Although the application examples of the present invention have been described above, the present invention is effective for improving the linear velocity dependency and the recording power dependency in mark length recording of a general phase change medium, and is limited to a rewritable DVD. is not.
For example, even when performing mark length modulation recording with a shortest mark length of 0.3 μm or less using a blue laser beam having a wavelength of 350 to 500 nm and an optical system with an NA of 0.6 or more, the medium and the recording method of the present invention can be used. It is valid. The shortest mark length is preferably about 10 nm or more in consideration of the stability of the mark.
In this case, it is necessary to pay attention to flatten the temperature distribution in the cross-track direction, and it is effective to make the thickness of the second protective layer as extremely small as 5 to 15 nm.
When laser light having a wavelength of 350 to 450 nm is used, the thickness is more preferably 10 nm or less.

Further, the medium of the present invention may be applied to so-called land & groove recording in which recording is performed using both grooves as tracks. Although it is difficult to satisfy the same recording characteristics with the land and the groove, the track pitch is easily reduced while the groove width is wide, which is suitable for high-density recording. By setting both the groove width GW and the groove width LW to 0.2 to 0.4 μm, a stable tracking servo performance can be obtained even though the density is high. If the GW / LW ratio is 0.8 or more and 1.2 or less, the signal quality of both the groove and the space between the grooves can be kept equal. In order to reduce the crosstalk, it is desirable that the groove depth d be λ / (7n) to λ / (5n) or λ / (3.5n) to λ / (2.5n).

Examples are shown below, but the present invention is not limited to the following examples as long as the gist is not exceeded.
In the following examples, the substrate was made by injection molding. The substrate was an injection-molded polycarbonate resin substrate having a thickness of 0.6 mm. Unless otherwise specified, a substrate in which grooves having a groove pitch of 0.74 μm, a width of 0.34 μm, and a depth of 30 nm were formed on a spiral was used.
Unless otherwise specified, the groove had a wobble of a frequency of 140 kHz at a linear velocity of 3.5 m / s, and the amplitude of the wobble was about 60 nm (peak-to-peak value).

The groove shape was measured using an optical diffraction method similar to a U-groove. The groove shape may be measured with a scanning electron microscope or a scanning probe microscope. In this case, the groove width at a position half the groove depth is used.
Unless otherwise specified, after forming a four-layer structure as shown in FIG. 5A on the substrate, a protective layer made of an ultraviolet curable resin is provided thereon by spin coating, and another one of the same layer structure is formed. And a 0.6 mm thick substrate. In the following examples and comparative examples, the first protective layer in FIG. 5A is referred to as a lower protective layer, and the second protective layer is referred to as an upper protective layer.

The recording layer immediately after film formation is amorphous and has a linear velocity of 3.0 to 6.0 m / s by a laser light beam having a wavelength of 810 to 830 nm focused on a major axis of about 90 μm and a minor axis of about 1.3 μm. Among them, an appropriate linear velocity was selected, and light having an initializing power of 500 to 700 mW was irradiated to melt the entire surface and recrystallized to obtain an initial (unrecorded) state.
The composition of each layer was confirmed by a combination of X-ray fluorescence analysis, atomic absorption analysis, and X-ray excited photoelectron spectroscopy.
The film densities of the recording layer and the protective layer were determined from the change in weight when the film was formed as thick as several hundred nm on the substrate. The film thickness was used by calibrating the fluorescent X-ray intensity with the film thickness measured with a stylus meter.
The sheet resistivity of the reflective layer was measured with a four-probe resistance meter (Loresta FP, trade name, manufactured by Mitsubishi Yuka (currently Dia Instruments)).
The resistance was measured on a reflective layer formed on a glass or polycarbonate resin substrate serving as an insulator, or on the reflective layer serving as the uppermost layer after forming the four-layer structure (before the UV-curable resin protective coat) shown in FIG. .
Since the upper protective layer is a dielectric thin film and an insulator, even a four-layer configuration does not affect the measurement of the sheet resistivity of the reflective layer. In addition, the measurement was performed with the disk substrate having a diameter of 120 mm, which can be regarded as a substantially infinite area.
Based on the obtained resistance value R, the area resistivity ρs and the volume resistivity ρv were calculated by the following equations.

Here, t is a film thickness, and F is a correction coefficient determined by the shape of the thin film region to be measured, and takes a value of 4.3 to 4.5. Here, it is set to 4.4.
Unless otherwise specified, DDU1000 evaluator manufactured by Pulstec was used for evaluation of recording and reproduction. The wavelength of the optical head is 637 nm, and the numerical aperture NA of the objective lens is 0.6 or 0.63. The beam diameters are about 0.90 μm and about 0.87 μm, respectively. Note that the beam diameter corresponds to a region where the energy intensity of the Gaussian beam is 1 / e2 or more of the peak intensity.

The recording was performed by the pulse division method shown in FIG. 10, where m = n−1 and α _i + β _i−1 = 1.0 (2 ≦ i ≦ m) unless otherwise specified. Pb was constant at 1.0 mW which is the same as the reproducing power at all linear velocities. Pe / Pw was constant at 0.5 unless otherwise specified. Pb was kept constant between 0.8 and 1.0 mW, and Pw was changed to measure the degree of modulation and jitter.
The signal to be recorded was a random signal subjected to 8-16 modulation (EFM plus modulation) used in DVD. The shortest mark length was 0.4 μm unless otherwise specified. Unless otherwise specified, the measurement was performed with only a single track recorded, so that the influence of crosstalk was not included.
Recording was performed at various linear speeds such as 1 × speed and 2 × speed, with the standard linear speed of 3.5 m / s of DVD being 1 × speed.

Reproduction was always performed at a linear velocity of 3.5 m / s, and jitter was measured after binarizing the reproduction signal after passing through the equalizer. Note that the jitter indicates edge-to clock jitter, and the measured value is expressed as a percentage of the reference clock cycle T. The characteristics of the equalizer conformed to the read-only DVD standard. Reference clock cycle T = 38.2 nsec. (26.16 MHz), it is preferable to obtain a jitter of approximately less than 10% (more preferably, less than 8%) and a modulation factor of 50% or more, preferably 60% or more. Further, it is desirable that the increase in jitter after repeated overwriting is small, and that it can be maintained at less than 13% with respect to T even after at least 100 times, preferably after 1000 times.
In addition, from the standpoint of ensuring compatibility with a read-only DVD, it is important to measure with a reproduction light at 650 to 660 nm. It has been confirmed that the same jitter as in the 637 nm optical system used in the present invention can be obtained in the 660 nm optical system by adjusting the reproduction optical system.

(Example 1 and Comparative Example 1)
As a recording layer, in order to compare the InGeSbTe system according to the present invention with a conventionally known InAgSbTe quaternary system, a medium having almost exactly the same recording layer composition and layer configuration except for the composition of Ag and Ge was prepared as shown in Table 1. Prepared as follows.
Except for replacing Ag and Ge in both recording layers, the composition is within a range that can be regarded as sufficiently equivalent within a range of the measurement error. The reason why the thickness of the lower protective layer is different is that the reflectivity Rtop of the medium is adjusted to be the same. Such a correction is necessary because the refractive index of the recording layer is slightly different.However, in order to make the same light absorption efficiency to the recording layer and the same thermal damage effect by the reproduction light, a comparison was made. Is the necessary correction. Since the thickness of the recording layer and the thickness of the upper protective layer are the same, the heat radiation effect and the thermal damage can be regarded as equivalent.
The substrate is a 0.6 mm thick polycarbonate resin, groove pitch 0.74 μm, groove width 0.34 μm, groove depth 27 nm, wobble frequency 140 kHz (linear velocity 3.5 m / s), wobble amplitude 60 nm (peak-to-peak). Value), and recording was performed in the groove.

When recording was performed by EFM plus modulation on these two types of media at a recording linear velocity of 3.5 m / s and T = 38.2 nanoseconds, good overwrite recording characteristics were exhibited. The overwrite recording conditions were not the conditions under which the characteristics of the respective discs were always the best, but were performed under the common conditions that both characteristics were almost the same as shown in Table 1.
That is, in the pulse division method shown in FIG. 10A, m = n-1, α _i + β _i-1 = 1.0 (2 ≦ i ≦ m), α _i = α _c = constant (2 ≦ i ≦ m), α ₁ = 0.5, α _c = 0.3, β _m = 0.5, Pw = 13.5 mW, Pe = 6.5 mW, and Pb = 0.8 mW.
The signal thus recorded was repeatedly irradiated with reproduction light, and the reproduction light stability was examined. After irradiating a predetermined number of times with a predetermined reproduction light power Pr, the reproduction light power was sufficiently reduced to 0.5 mW to measure jitter and the like. FIG. 12 shows the results.
The medium of Example 1 did not show any deterioration due to the reproduction light up to 106 times at a reproduction light power of 1 mW. When the power is increased by 0.1 mW, deterioration is gradually accelerated.

On the other hand, in the medium of Comparative Example 1, the jitter suddenly increases during the first 100 to 1000 times and then gradually deteriorates in all the reproduction lights having the reproduction light power of 1 mW or more. Although the jitter value is high as a whole, the initial jitter deterioration is fatal.
In Comparative Example 1, the degree of modulation was also reduced by the reproduction light, and was reduced by about 10% after about 100 irradiations and settled down. It is considered that the decrease in the degree of modulation progresses unevenly because the jitter suddenly increases in the initial stage.
When the recorded media of Example 1 and Comparative Example 1 were left in an environment of 80 ° C./80% RH and subjected to an acceleration test, the characteristics of the disk of Example 1 changed almost completely after 250 hours. On the other hand, the recording signal of the disk of Comparative Example 1 was almost completely erased. It can be seen that the amorphous mark is extremely unstable in the recording layer material having the composition of Comparative Example 1.

As described above, the disk of Example 1 is excellent in stability against reproduction light and stability over time, as well as initial overwrite recording characteristics. This indicates that the addition of an appropriate amount of Ge is very effective in an alloy system containing excess Sb in Sb _0.7 Te _0.3 .
The acceleration test was performed on the medium of Example 1 in an environment of 80 ° C./80% RH. An acceleration test was performed up to 2000 hours. The deterioration of the jitter of the signal recorded before the acceleration test was only about 1%.
The modulation degree was 64% at the beginning, but hardly changed to 61% even after the 2000-hour acceleration test. The reflectance was almost unchanged at all. The deterioration of jitter when new recording was performed on an unrecorded portion after 2000 hours was about 3%, but this is a level that does not hinder practical use at all.
In the medium of Example 1, the dependency of jitter on the recording pulse division method was examined in detail for the cases where m = n−1 and m = n−2.

FIG. 13 is a contour diagram showing α ₁ and α _c dependence of jitter when recording at (a) m = n−1 and (b) m = n−2 at a linear velocity of 3.5 m / s, respectively. is there.
FIG. 14 is a contour line showing α ₁ and α _c dependence of jitter when (a) m = n−1 and (b) m = n−2 at a linear velocity of 7.0 m / s, respectively. FIG. Pw, Pe, Pb and beta _m used in the measurement of each Figure are shown above each Figure.
At a linear velocity of 3.5 m / s, α ₁ = 0.
It can be seen that the lowest jitter (approximately 7% or less) is obtained in the vicinity of 7 to 0.8 and α _c = 0.35 to 0.40.
At a linear velocity of 7.0 m / s, α ₁ = 0.0.0 in both cases of m = n−1 and m = n−2.
It can be seen that the lowest jitter is obtained around 5, and around α _c = 0.40. For α ₁ and α _c in the vicinity where the minimum jitter is obtained, the condition of Σα _i <0.5n is satisfied in each case.
In this embodiment, a lower jitter value is obtained by setting m = n−2 at both the linear velocity of 3.5 m / s and 7.0 m / s. as compared with the case of n-1, low jitter is obtained even for large alpha _1.

Furthermore, the linear velocity dependency of jitter was evaluated for the medium of Example 1 by using an evaluator with NA = 0.63 and changing the recording pulse division method as shown in Table-2. Note that the reference clock cycle T is inversely proportional to the linear velocity. In the pulse dividing method, m = n-1, α _i + β _i-1 = 1.0 (2 ≦ i ≦ m), and α _i = α _c = constant (2 ≦ i ≦ m). Pw, Pb, and Pe were constant regardless of the linear velocity. Here, in the pulse division method of Table 2, at all linear velocities, Δα _i <0.
5n are satisfied.
Good overwrite characteristics were obtained from 1 × to 2.5 × the standard linear speed of DVD. The present medium shows good overwrite characteristics over the entire recording area even in the CAV system by dividing the recording area into 3 to 4 zones and slightly changing the recording pulse strategy for each zone.

Similar results were obtained when recording and reproduction were performed using an evaluator having a wavelength of 660 nm and NA = 0.65.

(Example 2)
On the substrate, a lower protective layer (ZnS) ₈₀ (SiO ₂ ) ₂₀ and a recording layer Ge _0.05 Sb _0.73 Te _0.22
, Upper protective layer (ZnS) ₈₀ (SiO ₂ ) ₂₀ , reflective layer Al _0.995 Ta _0.005
Was provided by changing the thickness of each layer in various ways. Table 3 shows the thickness of each layer. All thin films were formed by sputtering without releasing the vacuum.
The film formation of the reflective layer was performed at an ultimate vacuum of 2 × 10 ⁻⁴ Pa or less, an Ar pressure of 0.54 Pa, and a film formation rate of 1.3 nm / sec.
The volume resistivity was 55 nΩ · m, and the sheet resistivity was 0.28 Ω / □.
Impurities such as oxygen and nitrogen are less than the detection sensitivity in X-ray excitation photoelectron spectroscopy, and can be considered to be less than about 1 atomic% in total. (ZnS) ₈₀ (SiO ₂ ) _{20 The} protective layer has a film density of 3.50 g.
/ Cm ³ , 94% of the theoretical bulk density of 3.72 g / cm ³ . The recording layer density was 90% of the bulk density. The thermal conductivity of the protective layer estimated from the thermal simulation was 3.5 × 10 ⁻⁴ pJ / (μm · K · nsec).

Recording (overwriting) was performed on the medium thus prepared at 1 × speed and 2 × speed by optimizing the pulse division method shown in FIG. 10A for each layer configuration of each medium. After that, the jitter was measured after the first, ten, and 1000 overwrites. For measurement, an optical system having a wavelength of 637 nm and NA = 0.63 was used for both recording and reproduction.
Table 3 summarizes the optimum pulse division method, jitter, Rtop, and modulation factor of each medium at 1 × speed.

In each case, mark length modulation recording with a minimum mark length of 0.4 μm was performed at 1 × speed, and a large initial modulation degree was obtained.
When the thickness of the upper protective layer was 20 nm, both the initial jitter and the jitter after overwriting 1000 times were less than 10%. When the thickness of the upper protective layer was 30 nm, the initial jitter was good, but the increase in jitter due to repeated overwriting was slightly large, and the jitter became 10 to 12% after overwriting 1000 times. When the thickness of the upper protective layer is 40 nm, the initial jitter is 13% or more, and the initial jitter is rapidly deteriorated by repeated overwriting to 20% or more.
Further, in Example 2 (h2) in which the thickness of the recording layer was increased to 30 nm, the initial recording jitter was 13% or more, and the deterioration of the jitter due to repeated overwriting was remarkable.
In Example 2 (i2) in which the lower protective layer had a thickness of 45 nm, repeated overwrite durability was poor.
Further, better jitter was obtained when the thickness of the reflective layer was 250 nm than when it was 200 nm. That is, in such a high-density mark length recording, it is understood that the "ultra-quenching structure" is preferable.

Next, the recording power Pw dependency of the jitter of the medium of Example 2 (g1) was evaluated. The pulse division method was as follows: m = n−1 in FIG. 10, Pw = 14 mW, Pe / Pw = 0.5, β _m = 0.5, and recording was performed at 1 × speed and 2 × speed. After that, the dependency of jitter on α ₁ and α _c = α _i (2 ≦ i ≦ m) was evaluated.
At 2 × speed, α ₁ = 0.5, α _c = 0.4, β _m = β _n−1 = 0.5, Pw = 14 mW, and at 1 × speed, α ₁ = 0.7 and α _c = 0.3. , Β _m = β _n-1 = 0.5 and Pw = 14 mW. At this time, at 2 × speed, Σα _i = 0.3n (n = 3), 0.33n (n = 4), 0.34n (
n = 5) and 0.38n or less (n = 6 to 14). At 1 × speed, Σα _i = 0.33n
(N = 3), 0.33n (n = 4), 0.32n (n = 5), and less than 0.32n (n = 6 to 14).
FIG. 15 shows the result. The dependence of the jitter on the recording power Pw after the first and ten overwrites and the dependence of the reflectance Rtop and the modulation Mod on the recording power Pw after the tenth overwrite are shown. (A) shows the case of double speed recording, and (b) shows the case of single speed recording. Note that Rtop corresponds to Itop in FIG. In the drawing, DOW (Direct Overwrite) indicates overwriting.
Next, the overwrite durability was evaluated. FIG. 16 shows the result. The values of the jitter, the reflectance and the degree of modulation were shown up to 1000 times after overwriting. (A) shows the case of double speed recording, and (b) shows the case of single speed recording. In each case, the jitter gradually increased up to about 10 times, but stabilized after 10 times, and the jitter, the degree of modulation, and the reflectance hardly deteriorated up to 1000 times.

Further, this medium was overwritten with Pw = 14 mW by the same pulse division method as the above-mentioned double speed (linear speed: 7 m / s) except that the linear clock was 9 m / s and the reference clock cycle was 14.9 nsec. . A sufficient value of the erase ratio of 30 dB or more was obtained. Also, the jitter was as good as less than 11%.
The medium of Example 2 (g1) was constant at Pw = 14 mW, Pb = 1 mW, Pe / Pw = 0.5, β _m = 0.5 and α _{1 in} the linear velocity range of 3 to 8 m / s. And by changing only α _c , good jitter was obtained. That is, when the linear velocity is 3 to 5 m / s, α ₁ = 0
. 7, α ₁ = 0.65, α _c = 0.4 for α _c = 0.35, linear velocity 5-7 m / s, α ₁ = 0.55, α for linear velocity 7-8 m / s _By changing at least three steps such as _c = 0.45, good jitter of less than about 9% was obtained. It is considered that better jitter can be obtained at each linear velocity by changing α ₁ and α _c in finer increments of 1 m / s.
When Pw = 11 to 14 mW, the best jitter was obtained when Pe / Pw was 0.4 to 0.5. Further, when Pb exceeded 1.5 mW, the jitter deteriorated rapidly. Here, when Pb dependence was examined with Pe / Pw = 0.5, almost the best jitter was obtained when Pb was less than 1.0 mW. That is, Pb / Pe is preferably less than 0.2.

Next, Example 2 (g1) in which the thickness of the upper protective layer is 20 nm is compared with Example 2 (d2) in which the thickness of the upper protective layer is 40 nm. For both media, the recording mark length dependency was measured at 1 × speed as follows.
Using an optical system with NA = 0.6, the mark length dependency of jitter was evaluated when the length of the 3T mark, which is the shortest mark in EFM plus modulation, was reduced from 0.5 μm. The recording linear velocity was constant at 3.5 m / s, the pulse division method was constant as described above, and the mark length was changed by changing the reference clock cycle. However, when the shortest mark length is 0.46 μm or more, the reproduction speed is set to 5 m / s because the CLV control becomes difficult at the reproduction speed of 3.5 m / s due to restrictions on the apparatus. The shortest mark length of 0.4 μm corresponds to the read-only DVD standard.
FIG. 17 shows the result. (A) is the medium of Example 2 (g1), and (b) is the medium of Example 2 (d2).

It can be seen that the medium of Example 2 (g1) can be used with a jitter of less than 13% up to the shortest mark length of about 0.38 μm.
When an optical system with NA = 0.63 was used, it was possible to reduce the jitter by about 2%. Also, by optimizing the equalizer at the time of reproduction, it was possible to reduce the jitter by about 2%. In addition, if an optical system with NA = 0.65 is used, it is considered that sufficiently good jitter can be obtained even at 0.35 μm.
In the medium of Example 2 (d2), jitter having almost no problem was obtained at a mark length of 0.45 μm or more, but the jitter increased sharply at a mark length of less than 0.45 μm, and 13% at a mark length of 0.40 μm. As a result, it became unusable.
Next, in order to evaluate a so-called tilt margin, after recording an EFM-plus-modulated random pattern signal over a plurality of tracks on the medium of Example 2 (g1), the substrate is intentionally moved with respect to the optical axis of the reproduction laser beam. By tilting, the change in jitter during reproduction was measured. The optical system for recording / reproducing is NA = 0.6, and the recording linear velocity is 1 × or 2 ×, both of which are reproductions after overwriting 10 times. FIG. 18 shows the measurement results. The tilt margin was ± 0.7 to 0.8 degrees in the radial direction and ± 0.5 to 0.6 degrees in the circumferential direction, which was a level that would cause no problem in a normal drive.

<Accelerated test>
EFM plus modulated random patterns were recorded on some tracks of the medium of Example 2 (g1) with Pw = 13 mW using the above-mentioned optimal pulse division method, and jitter was measured. After that, the medium was subjected to an acceleration test under high temperature and high humidity of 80 ° C./80% RH. When the jitter of this track was measured again after 500 hours and 1000 hours of the acceleration test, it was found that the jitter only deteriorated by about 1% after 1000 hours.
Further, after 1000 hours of the acceleration test, a random pattern was recorded on another track under the same conditions as above and the jitter was measured. As a result, about 2% deterioration was observed. .
Further, recording was similarly performed at 1 × speed and 2 × speed, and the degree of modulation before and after a 1000-hour acceleration test under high temperature and high humidity of 80 ° C./80% RH was evaluated. At 1 × speed, the initial modulation was 61%, and the modulation after the acceleration test was 58%. At 2 × speed, the initial modulation was 60% and the modulation after the acceleration test was 58%.
<Stability against reproduction light>
The medium of Example 2 (g1) was irradiated with reproduction light at a power of 1.2 mW, but did not deteriorate at all in about 10 minutes. Next, when the power was set to 1.0 mW and the reproduction light was repeatedly irradiated up to 1,000,000 times, the increase in jitter was less than 2%.

(Example 3)
A medium was prepared in the same layer configuration as in Example 2 except that the composition of the recording layer was Ge _0.05 Sb _0.71 Te _0.24 . Table 4 shows the thickness of each layer and the evaluation results. An optical system with NA = 0.63 was used for the measurement.
As in Table 3, α ₁ , α _c , β _n-1 are optimized in each layer configuration, and Pw, Pe
Also, the jitter was evaluated by setting the jitter to be the lowest.
In each case, mark length modulation recording with a minimum mark length of 0.4 μm was performed at 1 × speed, and a large initial modulation degree was obtained.
In Example 3 (a), similar to Example 2 (a1), good characteristics were obtained when the recording linear velocity was 1 × and 2 ×, but when the recording linear velocity was 9 m / s, it was 1-2 times higher than in Example 2 (a1). % Jitter was higher.
In Examples 3 (a) to 3 (f) in which the thickness of the upper protective layer was 30 nm, the jitter was less than 10%, and was less than 13% even after 100 times of overwriting. In Examples 3 (g) to (i) in which the thickness of the upper protective layer was as thick as 40 nm, the jitter could only be obtained with a value larger than 13%.

(Example 4)
The layer structure is such that the lower protective layer (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 215 nm thick, and the recording layer Ge _0.05
Sb _0.69 Te _0.26 was 18 nm, the upper protective layer (ZnS) ₈₀ (SiO ₂ ) ₂₀ was 18 nm, and the reflective layer Al _0.995 Ta _0.005 was 200 nm. The composition of the present recording layer is such that good characteristics can be obtained by recording at a linear velocity of 3 to 5 m / s, and is for so-called 1 × speed. However, since the amount of excess Sb is slightly smaller than that of Examples 2 and 3, the stability over time is excellent, and it is preferable to emphasize the storage stability of recorded information and deterioration due to repeated reproduction, that is, reproduction light durability. .
The following was evaluated using an optical system with NA = 0.6. The optimal pulse division method was determined as follows. At a recording linear velocity of 3.5 m / s, Pw = 13 mW, Pe / Pw = 0.5, and α ₁ and α _c are changed while β _m = 0.5 in FIG. I chose the pulse division method. FIG. 19 shows the dependency of jitter on α ₁ and α _c after 10 overwrites as a contour map of jitter. Almost the best jitter was obtained by setting α ₁ = 0.4 to 0.8 and α _c = 0.3 to 0.35, and based on this, α ₁ = 0.6 and α _c = 0.35 was selected. At this time, Σα _i = 0.32n (n = 3), 0.33n (n = 4), 0.3
n (n = 5) and less than 0.35n (n = 6 to 14).
The degree of modulation was 65%, a value comparable to that of a read-only DVD. Rtop is about 23%, but if it is 15% or more in practice, it is considered that reproduction can be performed with an existing read-only drive.
Therefore, when image data was recorded on the recording medium of the present invention at Pw = 12.5 mW and a linear velocity of 3.5 m / s, and reproduction was attempted on a commercially available reproduction-only DVD player, the focus servo, tracking servo signal, and jitter were reduced. Characteristics equivalent to those of a normal read-only DVD were obtained.

<Repeat overwrite durability>
FIG. 20 shows the dependence of the jitter, Rtop, and modulation on the number of repeated overwrites at Pw = 12.5 mW. Even after overwriting 1000 times or more, it shows sufficiently stable characteristics.

<Accelerated test>
EFM plus modulated random patterns were recorded on some tracks of this medium with Pw = 13 mW using the above-described optimal pulse division method, and jitter was measured. After that, the medium was subjected to an acceleration test under high temperature and high humidity of 80 ° C./80% RH. When the jitter of this track was measured again after 500 hours and 1000 hours of the acceleration test, it was found that the jitter only deteriorated by less than 0.5% after 1000 hours. The degree of modulation was 65% at the beginning and 63% after the accelerated test.
After 1000 hours of the acceleration test, a random pattern was recorded on another track under the same conditions as above, and the jitter was measured. As a result, about 1% deterioration was observed. .

<Stability against reproduction light>
The medium was irradiated with reproduction light at a power increased to 1.3 mW, but did not deteriorate at all in about 10 minutes. Next, with the power set to 1.0 mW, the reproduction light was repeatedly irradiated up to 1,000,000 times, but the increase in jitter was less than 1%.

(Example 5)
The recording layer in the layer structure of Example 2 (a1) was Ge _0.05 Sb _0.75 Te _0.20. The evaluation was performed using an optical system with NA = 0.6.
The best jitter was obtained when α ₁ = 0.4, α _c = 0.3, β _m = 0.5, Pw = 14 mW, and Pe / Pw = 0.5. The initial modulation was also sufficiently large. The jitter after 10 times of overwriting was barely less than 10%, and after 1000 times, less than 13% was maintained.

<Accelerated test>
EFM plus modulated random patterns were recorded on some tracks of this medium with Pw = 14 mW using the above optimal pulse division method, and jitter was measured. After that, the medium was subjected to an acceleration test under high temperature and high humidity of 80 ° C./80% RH. After 500 hours of the acceleration test, the jitter of this track was measured again, and it was only about 2% worse.
Also, after 500 hours of the accelerated test, a random pattern was recorded on another track under the same conditions as above and the jitter was measured. As a result, a deterioration of about 3% was observed. .

<Stability against reproduction light>
The medium was irradiated with reproduction light at a power increased to 1.0 mW, but did not deteriorate at all for about 10 minutes. Next, the power was set to 1.0 mW, and the reproduction light was repeatedly irradiated up to 1,000,000 times.

(Example 6)
In the layer structure of Example 4, the recording layer was changed to _{Ag 0.05 Ge 0.05 Sb 0.67 Te 0.23} . The evaluation was performed using an optical system having an NA of 0.6.
At a linear velocity of 3.5 m / s, the dependency of the jitter on the pulse division method (α ₁ and α _c ) was measured at Pw = 13 mW, Pe / Pw = 0.5, m = n−1, and β _m = 0.5. As a result, FIG.
The contour map shown in a) was obtained. α ₁ = 0.6 and α _c = 0.35 were almost optimal. In this case, Σα _i = 0.32n (n = 3), 0.33n (n = 4), 0.33n (n = 5
), Less than 0.35n (n = 6 to 14).

FIG. 21B shows the power dependence of the jitter after the first, ten, and 1000 overwrites, and FIG. 21C shows the power dependence of the Rtop and the modulation factor after the ten overwrites. Good jitter was maintained in a wide range of recording power up to after overwriting 1000 times, and Rtop of 18% and modulation degree of 60% or more could be achieved.
FIG. 22 shows changes in jitter, Rtop, and modulation factor after Pw = 13 mW after overwriting 10,000 times. There was no deterioration except for the initial increase of the jitter of about 1%.
FIG. 23 shows the result of measuring the shortest mark length dependency of jitter in the same manner as in Example 1. At the shortest mark length of 0.38 μm, the jitter was extremely good at less than 10%.
In addition, when the pulse division method with m = n−2 was evaluated for this medium, FIG. 21 was obtained when α ₁ = 1.0, α _c = 0.5, and β _m = 0.5. Similar characteristics were obtained.
n = 3 in Σα _i = 0.48n, n = 4 in _{Σα i = 0.48n, Σα i =} 0.46n with n ≧ 5
０．４0.47 n.

(Comparative Example 2)
In the layer configuration of the sixth embodiment, the recording layer was made of Ag _0.05 In _0.05 Sb _0.63 Te _0.27 .
When the linear velocity was 3.5 m / s, Pw = 13 mW, Pe / Pw = 0.5, and β _m = 0.5, and the dependency of the jitter on the pulse division method was evaluated. The contour map shown in FIG. was gotten. α1 = 1.0 and α _c = 0.5 were optimal, and in this case, Δα _i was constant at 0.5n regardless of n.
FIGS. 24B and 24C show the recording power dependency and the repetitive overwrite characteristics up to 1000 times. The jitter and power margin of the first recording were better than in Example 5, but deteriorated due to repeated overwriting, and became worse rather after 1000 times.
When the reproducing light power was further increased to 1 mW, the jitter deteriorated in about 5 minutes, and increased to more than 10%. This difference cannot be explained by a recording sensitivity difference of 0.5 to 1 mW. The main cause of the reproduction light deterioration is that the temperature rises to about 50 to 100 ° C., and it can be seen that the Ge addition of the present invention is effective for improving the thermal stability of the amorphous mark.

(Comparative Example 3)
The layer structure was (ZnS) ₈₀ (SiO ₂ ) _{20, the} lower protective layer was 90 nm thick, the Ge ₂ Sb ₂ Te ₅ recording layer was 21 nm, the (ZnS) ₈₀ (SiO ₂ ) ₂₀ upper protective layer was 23 nm, Al _0.995 Ta. _{The 0.005} reflective layer was 200 nm.
At the time of recording, fine adjustment was performed based on the pulse division method shown in FIG. 10A so as to obtain the best jitter at each mark length and linear velocity.
For this medium, as shown in FIG. 25, α ₁ = α _c = α ₀ = 0.3 to 0.4, and the best jitter is obtained by the strategy of β _m = 1.0. Was done. Also, Pw = 13m
W, Pe / Pw = 0.4 (Pe = 5 mW) and Pb = 2.0 mW are the optimum recording powers, and Pb / Pe = 0.4, which is higher than the optimum recording power. This is because it is necessary to maintain the TL in FIG. 9 somewhat higher in the layer.
Although the jitter was poor even when Pb was less than 1 mW, the jitter also deteriorated when Pb was 3 mW or more.
Based on this pulse division method, furthermore, a precise pulse width adjustment of about 0.02 with respect to α ₀ was performed according to the mark length, and the mark length dependency was measured as in Example 2. The results are shown in FIG. In addition, the linear velocity dependency during overwriting was measured. The results are shown in FIG.
Regarding the linear velocity dependency, the reference clock cycle was changed according to the linear velocity so that the shortest mark length was 0.4 μm, and reproduction was always performed at 3.5 m / s. Regarding the linear velocity dependency, the jitter after overwriting 10 times and the jitter when overwriting recording is performed once after DC erasure are shown.
As shown in FIG. 26A, the jitter was 10% at the shortest mark length of 0.4 μm, and when the length was shorter, the jitter rapidly deteriorated.
In addition, as shown in FIG. 26B, the jitter deteriorates at a recording linear velocity of 5 m / s or more. However, in the recording after DC erasure, the jitter is reduced by 2 to 3% or more. From this, it is considered that a non-uniform temperature rise due to a difference in absorptivity between the so-called crystalline state and the amorphous state causes defective erasing or distortion of the shape of the amorphous mark, thereby deteriorating jitter.

Although the jitter after overwriting at a linear velocity of 7 m / s was 20% or more, the recording after DC erasure was about 15%. Therefore, it is considered that the reason why the jitter at the time of the high linear velocity becomes high is that an appropriate pulse division method has not been selected.
Originally, the recording layer has a high jitter due to coarse grains. However, at a linear velocity of 5 m / s or more, the erasure of the previous mark becomes insufficient at the time of overwriting, and the jitter with the recording after the DC erasure is reduced. The difference clearly shows the effect.
The difference in jitter between when overwriting the medium of Example 2 (g1) at 7 m / s and when recording after DC erasure was less than 0.5%.
For GeTe-Sb ₂ Te ₃ pseudo binary alloy recording layer recording media using such as Ge ₂ Sb ₂ Te _5, the four-layer structure comprising protective layer / recording layer / protective layer / reflective layer, 5 to 6 m At high linear velocities of at least / s, there is no problem in recording after DC erasure as described above, but jitter deteriorates during overwriting. For this reason, in order to reduce jitter, it is necessary to take measures such as adding a light absorbing layer and correcting the absorptance.

(Comparative Example 4)
In Example 2 (g1), the recording layer was Ge _0.15 Sb _0.64 Te _0.21 . Initial crystallization is very difficult. Initializing was performed several times with an initializing beam, and the jitter was measured by overwriting. % Or less was not obtained. In addition, when overwriting was repeated, the jitter increased by several percent from 10 to 100 times.

(Comparative Example 5)
In the layer configuration of Example 2 (g1), the recording layer was Ge _0.05 Sb _0.80 Te _0.15 . At 7 m / s, α ₁ = 0.4, α _c = 0.3, β _m = 0.5, Pw = 14 mW, Pe / Pw =
The best jitter was obtained at 0.5, but the jitter was barely less than 11% after 10 overwrites, and was 13% or more after 1000 writes.

<Accelerated test>
EFM plus modulated random patterns were recorded on some tracks of this medium with Pw = 14 mW using the above optimal pulse division method, and jitter was measured. After that, the medium was subjected to an acceleration test under high temperature and high humidity of 80 ° C./80% RH. After 500 hours of the accelerated test, the jitter of this track was measured again.
Also, 500 hours after the acceleration test, a random pattern was recorded on another track under the same conditions as above, and the jitter was measured.

<Stability against reproduction light>
When the medium was irradiated with reproduction light at a power of 1.0 mW, the jitter increased by 3% after 10 minutes and was very unstable. In addition, the degree of modulation decreased and the marks tended to disappear.

(Example 7)
From the medium of Example 2 (a1) at 1 × speed (linear velocity 3.5 m / s, reference clock cycle T = 38.2 nsec) to 2.25 × speed (7.9 m / s, T = 17 nsec) α ₁ T = τ ₁ = 19 nsec and α _c T = τ _c = 11 nsec, which were constant at all linear velocities, and only T was inversely proportional to the linear velocity to record an EFM plus signal. Further, to determine the _{α i + β i-1 =} 1.0 constant at beta _i. Incidentally, only the final off pulse section beta _m, was changed so that the linear velocity becomes slower longer.
In such a pulse dividing method, in the explanatory diagram of the gate generation timing in FIG. 11, τ ₁ = 19 in synchronization with the reference clock cycle T (a certain delay may be added).
One fixed-length pulse of nsec (Gate 1) and a fixed-length pulse of τ _c = 11 nsec are represented by n−
Only two (Gate2) signals need to be generated, and only Gate3, which determines the final off-pulse length, needs to be changed according to the linear velocity. This is preferable because the pulse generation circuit can be simplified. Further, in this embodiment, since the recording power is constant at Pw = 13.5 mW, Pe = 5 mW, and Pb = 0.5 mW, the pulse generation circuit can be extremely simplified. Here, when the linear velocity is 5 m / s or less, Δα _i <0.47 n is satisfied, so that the thermal damage is sufficiently suppressed.
Table 5 summarizes the values of jitter when β _m was changed at each linear velocity.
In the table, “v” indicates a reference speed of 3.5 m / s. The wavelength of the pickup is 637 nm and NA = 0.63. The jitter value itself is slightly worse than when the pulse division method is made more flexible as in the second embodiment, but a value of less than about 10% is obtained from 1 × to 2.25 × speed. Have been.
Here, assuming that β ^H _m = 0.3 at 2 × speed and β ^L _m = 0.6 at 1 × speed (point enclosed by a square), β _m is changed in inverse proportion to the linear speed to obtain 1 × speed. It can be seen from the graph that a jitter of less than 10% can be obtained at each linear speed of 2 ×. Further, in the present embodiment, although the margin of β _m is small, even if β _m = 0.2 is constant, a jitter of less than 10% can be obtained from 1 × speed to 2.25 × speed. In this way, a pulse generation circuit that can be varied according to the linear velocity can be simplified.
Also, if Pb, Pe / Pw, Pw, τ ₀ , τ _c , (β ^L _m , β ^H _m ) are previously described on the recording medium by means of a concave / convex pit or a modulated groove meandering signal, optimal recording conditions Can be automatically determined according to the linear velocity at the time of overwriting.

(Example 8)
The layer structure is such that the lower protective layer (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 215 nm thick and the recording layer Ge _0.05
Sb _0.69 Te _0.26 was set to 19 nm, the upper protective layer (ZnS) ₈₀ (SiO ₂ ) ₂₀ was set to 20 nm, and the reflective layer Al _0.995 Ta _0.005 was set to 200 nm.
At a linear velocity of 3.5 m / s, the pulse division method is α ₁ = 0.5, α _c = 0.35, β _m = 0.5,
Pw = 11 mW, Pe = 6.0 mW, and Pb = 0.5 mW, and recording was performed by changing the reference clock period T and changing the shortest mark length (3T mark length) from 0.4 μm to 0.25 μm. T = 38.2 nsec when the mark length of the 3T mark is 0.4 μm, and T = 19.1 nsec when the mark length of the 3T mark is 0.2 μm. The recording laser wavelength is 637 nm and NA = 0.63.
Since this focused laser beam has a Gaussian distribution, it is possible to record at a higher density than the optical resolution by using only the high temperature portion at the center.
The recorded portion was reproduced with a blue laser beam having a wavelength of 432 nm, NA = 0.6 and power of 0.5 mW. This laser light is generated by a nonlinear optical effect from a laser light having a wavelength of about 860 nm. With this layer configuration, a large modulation degree of 50% or more was obtained even at 432 nm.
Further, FIG. 28 shows, as the shortest mark length dependency, the jitter when reproducing with the optical system of 637 nm and NA = 0.63 used for recording and the jitter when reproducing with the optical system of 432 nm and NA = 0.6. Indicated. In the measurement, the set value of the equalizer is optimized as much as possible at each measurement point. It can be seen that in this recording medium, a good jitter of less than 13% was obtained even with the shortest mark length of 0.3 μm in blue laser light reproduction.

(Comparative Example 6)
In the layer configuration of Example 2 (a ₁ ), the recording layer was Ge _0.05 Sb _0.64 Te _0.31 .
Recording evaluation was performed with an optical system having a wavelength of 637 nm and NA = 0.63. At a linear velocity of 3.5 m / s, m = n-1, α ₁ = 0.4, α _c = 0.4, β _m = 0.4, Pb = 0.5 mW, Pe
= 4.5 mW, and overwrite recording was performed up to the tenth time while changing only Pw. FIG. 27A shows the recording power dependency of the jitter at this time. In the figure, 1 write indicates initial recording on an unrecorded disk, 1 DOW indicates first overwriting, and 10 DOW indicates tenth overwriting.
Next, assuming that Pw was constant at 8.5 mW, overwriting recording was performed up to ten times by changing only Pe. FIG. 27B shows the dependence of the jitter on the erasing power.
In each case, good jitter was obtained in the first recording (1 write), but the jitter was sharply deteriorated by overwriting even once. It is considered that the composition of the recording layer in this comparative example is a composition richer than that of the straight line A in FIG. Can be

(Example 9 and Comparative Example 7)
In the layer configuration of Example 2 (a1), the composition of the recording layer was changed as shown in Table-6. The Ge amount was changed by co-sputtering a Ge _0.05 Sb _0.73 Te _0.22 target and Ge.
Using an optical system having a wavelength of 637 nm and NA = 0.63, m = n−1, Pb = 0.5 mW, β _m = 0.5, and changing α ₁ , α _c , Pw, and Pe over 10 times. We searched for the condition that minimizes the jitter after writing.
Table 6 shows the minimum jitter obtained for each recording layer composition. As the amount of Ge added increased, the jitter increased. When Ge was 10 atomic% or more, the jitter at double speed was as high as 14%.
When the medium was subjected to an acceleration test under the conditions of 80 ° C. and 80% RH, Examples 9 (b) and (c) were slightly better than Example 9 (a). That is, when the signal recorded before the acceleration test was read out 2000 hours after the acceleration test, in any of the examples 9 (a) to (c), the jitter was only deteriorated by about 1%. .
In addition, the initial modulation degrees of Examples 9 (a) to (c) were 61 to 63%, and the modulation degrees of 58 to 59% were obtained even after the acceleration test for 2000 hours. The reflectance was almost unchanged at all. In particular, in Examples 9 (b) and (c), the increase was within 0.5%.

Next, Ta was added by co-sputtering a Ge _0.05 Sb _0.73 Te _0.22 target and Ta. As a result, the best jitter was obtained when adding 1 to 2 atomic% of Ta to GeSbTe.

(Example 10 and Comparative Example 8)
In the layer configuration of Example 2 (g1), the recording layer was GeSbTe to which In was added. In is obtained by co-sputtering InSbTe to a GeSbTe target. The composition of each recording layer was Ge _0.05 Sb _0.74 Te _0.21 in Example 10 (a), In _0.023 Ge _0.048 Sb _0.719 Te _0.21 in Example 10 (b), and In _0.053 Ge _0.044 Sb _0.688 Te in Example 10 (c).
_0.215, Comparative Example 8 is _{In 0.118 Ge 0.041 Sb 0.617 Te 0.224} .
The results of evaluating the power dependency of the jitter of each medium are shown in FIGS. 29 (a), (b), (c) and (d). The upper graph shows the case where the recording linear velocity is 3.5 m / s, and the lower graph shows the case where the recording linear velocity is 7.0 m / s.
The optical systems used were all 637 nm, NA =. 63. When the linear velocity is 3.5 m / s, α ₁ = 0.6, α _c = 0.35, β _m = 0.5, and when 7.0 m / s, α ₁ = 0.4 and α _c = 0.4 and β _m = 0.5. Pb was fixed at 0.5 mW. Pe was fixed at two values, and only Pw was changed to measure the Pw dependency of the jitter. The addition of an In amount of about 2 to 5 atomic% significantly improved the Pw margin. However, when the content exceeds 10 atomic%, the jitter worsened as compared with the case where no addition was made.
In Examples 10 (a) to 10 (c), the jitter after 1000 overwrites was less than 10 atomic% in both linear velocities, but in Comparative Example 8, both linear velocities were higher than 13%. .

<Accelerated test>
The medium of Example 10 (b) was subjected to an acceleration test in an environment of 80 ° C./80% RH. An acceleration test was performed up to 2000 hours. The deterioration of the jitter of the signal recorded before the acceleration test was only about 1%.
The initial degree of modulation was 61%, and a 57% degree of modulation was obtained even after the acceleration test for 2000 hours. The reflectance was almost unchanged at all.
The deterioration of jitter when new recording was performed on an unrecorded portion after 2000 hours was about 3%, but this is a level that does not hinder practical use at all.

(Example 11)
In the layer configuration of Example 2 (g1), a disk having a recording layer of In _0.03 Ge 0.05 Sb _0.71 Te _0.21 was formed on a polycarbonate resin substrate having the groove shape shown in Table-7. In each case, the groove pitch is 0.74 μm.

The wobble modulation method was binary phase modulation in which the carrier wave period Tw was 32 times the reference data clock period T = 38.2 nanoseconds. Here, as shown in FIG. 30, the phase modulation wobble shifts the phase of the wobble wave by π in accordance with 0 or 1 of the digital data signal.
That is, the frequency _{f c = 1 / T w =} 1 / (32T) of the unmodulated carrier wave (cosine wave or sine wave), from 0 to the digital data for address 1 or one of the switching of 0, just phase π Just shift. Switching period T _d of the digital data 0 and 1 at low frequencies than T _w, since T _d is in a integral submultiple of T _w, be shifted phase [pi, wobble waveform varies continuously ing.
The preferable point of this modulation method is that, unlike frequency (FM) modulation used for ATIP (Absolute Time in Pregroove), since the meandering frequency is constant and the period is modulated at a high frequency of 32T, the wobble clock is used. To establish the rotation synchronization of the disk and generate a data clock directly in synchronization with the wobble clock.
In order to change the phase by modulating the digital data in this way, for example, a ring modulator as shown in FIG. 31 is used. Digital data is applied with positive and negative voltages ± V corresponding to 0 and 1. When a stamper master is prepared, a laser beam for photoresist exposure is exposed while meandering in the radial direction in accordance with a wobble waveform binary-modulated between voltages of ± Vw. At this time, by applying the output wave of the ring modulator to the EO modulator, the exposure beam can meander.

Hereinafter, it will be described in some detail. Figures, unmodulated carrier wave input terminal period cos (2πf _c t)
Comprising signal V _w · cos if (2πf _c t) is input, V _w · co the output of the input transformer
two of the carrier wave signal of s (2πf _c t) and _{-V w · cos (2πf c t} ) appears. If the digital data input is positive (+ V), and conducts D _1, D ₁ ', the carrier _{V w · cos (2πf c t} ) as it is passed through the D ₁ modulation appears at the output terminal. After the carrier of _{-V w · cos (2πf c t} ) is passed through the D ₁ ', it is inverted by the output transformer _{V w · cos (2πf c t} ) , and the added output of the D ₁ passes intertwined with V _w · obtain the output of cos (2πf _c t).
If the digital data input is negative (−V), that is, if D ₂ and D ₂ ′ become conductive, V _w
Since the signal of cos (2πf _c t) is led to the lower side of the output transformer via a diode D _2, modulation at the output terminal becomes -V _w cos (2πf _c t) which is inverted.

On the other hand, _{-V w · cos (2πf c t} ) and a carrier at the output of the input side transformer applied to the common mode input of the output transformer via a diode D ₂ ', as is polarity (-V _w · cos (2 [pi] f _c t) remains) appears at the modulated wave output terminal. Accordingly, the carrier wave passing through the path of the diode D2 and D2 'are combined becomes _{-V w · cos (2πf c t} ), modulation appears at the output terminal.
In the case of a ring modulator, V _w · c is applied to the output terminal depending on whether the digital data input is positive or negative.
will output the os (2πf _c t) or _{-V w · cos (2πf c t} ).
The wobble waveform modulated in this manner is input to the EO modulator, and the exposure beam can meander.
In this embodiment, the wobble amplitudes are all 60 nm (peak-to-peak value).
In the case of a medium in which recording is performed only in the groove, the preferable range of the groove depth is λ / (20n) = 20. 5 nm, and the upper limit is λ / (10n) = 40.8 nm.
For evaluation of this medium, an optical system having a wavelength of 637 nm and NA = 0.63 was used.

As in the second embodiment, a recording pulse dividing method in which m = n-1, α _i + β _i-1 = 1.0 (2 ≦ i ≦ m), and α _i = α _c = constant (2 ≦ i ≦ m) At a linear velocity of 3.5 m / s, α _i = 0.
5, α _c = 0.3, β _m = 0.5, Pw = 13 mW, Pe = 6 mW, and at a linear velocity of 7 m / s, α ₁ = 0.4, α _c = 0.35, β _m = 0.5, Pw = 14 mW, Pe = 7 mW.
First, recording was performed at a linear velocity of 3.5 m / s in the groove, and Rtop and the modulation were measured. The jitter of the recording signal was measured at 3.5 m / s and 7 m / s. The results are shown in Table-8.

First, Example 11 (k) had a very shallow groove with a depth of 18 nm, but could hardly detect a push-pull signal and could not apply tracking servo. Also, it is very difficult to form such a shallow groove evenly in terms of stamper preparation, and in practice, very large unevenness was observed in the tracking servo signal.
FIGS. 32A and 32B show the dependence of the modulation degree and Rtop on the groove shape. In Examples 11 (h) to (j), the grooves having a depth of 42 nm are provided, but the reflectivity is significantly reduced as compared with the case of a depth of 27 nm, which is not preferable because it is reduced by 5% or more. The degree of modulation decreased particularly when the groove was narrow. When the width was 0.23 μm, the degree of modulation was remarkable even at a depth of 35 nm.
In this embodiment, the layer configuration is the same. However, if the depth is 42 nm, if a layer configuration having a high reflectance is used in order to compensate for a reduction in the reflectance, the reduction in the degree of modulation becomes more remarkable. That is, a groove having a depth of 42 nm is not suitable for recording in the groove.
If the groove depth is 40 nm or more, the wobble signal significantly leaks into the recording data signal when the groove width is less than 0.3 μm. As compared with the case where the groove width is 0.3 μm or more, the jitter deteriorates by 1 to 2% or more at the linear velocity of 3.5 m / s, and deteriorates by 2 to 3% at the linear velocity of 7 m / s.

(Example 12)
The layer structure is such that the lower protective layer (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 65 nm thick, and the recording layer Ge _0.05 S
The thickness of b _0.73 Te _0.22 was 16 nm, the thickness of the upper protective layer (ZnS) ₈₀ (SiO ₂ ) ₂₀ was 20 nm, the thickness of the first reflection layer Al _0.995 Ta _0.005 was 40 nm, and the thickness of the second reflection layer Ag was 70 nm.
From the lower protective layer to the first reflective layer, the first reflective layer is formed by a sputtering method without releasing the vacuum. After the first reflective layer is formed, the film is released to the atmosphere and left for a few minutes. A film was formed.
After forming the second reflective layer, an ultraviolet curable resin was laminated as an overcoat layer by 4 μm by spin coating. Two of the resulting disks were bonded together such that the overcoat layers faced each other.
The first reflective layer was formed at an ultimate vacuum of 4 × 10 ⁻⁴ Pa or less and an Ar pressure of 0.55 Pa. The volume resistivity was 55 nΩ · m. Impurities such as oxygen and nitrogen were less than the detection sensitivity in X-ray excitation photoelectron spectroscopy, and were considered to be less than about 1 atomic% in total.
The second reflective layer was formed at an ultimate vacuum of 4 × 10 ⁻⁴ Pa or less and an Ar pressure of 0.35 Pa. The volume resistivity was 32 nΩ · m. Impurities such as oxygen and nitrogen were less than the detection sensitivity in X-ray excitation photoelectron spectroscopy, and were considered to be less than about 1 atomic% in total.
Using an optical system with a wavelength of 637 nm and NA of 0.60, a linear velocity of 3.5 m / s and α ₁ = 0.4
, Α _c = 0.35 and β _m = 0.5, the jitter was measured after overwriting 10 times, and the minimum was obtained when Pw = 11 mW, Pe = 6.0 mW, and Pb = 0.5 mW. A jitter of 6.5% was obtained.
The medium was left under high temperature and high humidity of 80 ° C. and 80% RH for 500 hours, and the same recording was performed. No deterioration was observed.

(Example 13)
A stamper having a spiral groove having a wobble having a groove pitch of 0.74 μm, a groove width of 0.3 μm, and a groove depth of 40 nm was formed. Based on this, a polycarbonate resin having a diameter of 120 mm and a thickness of 0.6 mm was prepared. The substrate was formed by injection molding.
As shown in Table-9, 36 mm from a radius of 22.5 mm to 58.5 mm was used as a recording area, and the recording area was divided into 255 bands (zones). Each band contains 191 tracks.
Since the band width is set so that the end of each band is exactly at the 191st track, each band width is not exactly 36/255. For this reason, the outermost end of the recording area is 58.54 mm.
The channel bit length is 0.133 μm, and a reference clock of 26.16 MHz (T = 38.23 nsec) is obtained at a linear velocity of 3.49 m / s. The wobble period was set to be 9 times the channel bit length at the center radius of each band. Its physical period is 1.2 μm.
First, the total number of channel bits and the total number of wobbles at the center radius of each band are calculated so that the number of channel bits or the number of wobbles included in one round in the same band is constant.

As shown in Table 9, the number of channel bits or the number of wobbles is constant with an accuracy of ± 1% at the beginning and end of the band. That is, recording with a constant linear density can be performed in the ZCAV system, which is not different from that in the CLV system, and the specification of the read-only DVD is sufficiently satisfied.
Based on the above assumptions, when the disk is rotated so that a linear velocity of 3.49 m / s is obtained at the center radius of each band, the wobble cycle is exactly nine times the reference clock cycle of DVD data T = 38.23 nsec. It becomes.
This medium is rotated so that the linear velocity becomes 3.49 m / s at the band center radius of the innermost peripheral band shown in Table 9, and used as a ZCAV system medium. The period of the carrier wave is reproduced from the wobble of each band in the CAV rotation and times 1/9, to generate data reference clock T _q in each band, to record data that has been EFM plus modulated based on the clock .
At the time of reproduction, if the rotation synchronization is achieved so that the data reference clock frequency generated from the recorded data becomes 26.16 MHz as described below, the variation of the channel bit length in each zone is less than ± 1%. Thus, the reproduction in the CLV mode can be performed substantially without any trouble.

That is, the reference clock 26.16 MHz (T = 38.23 nsec) is generated by a crystal oscillator, the phase is compared with a data reference clock generated from recorded data, and the phases are synchronized. The rotation speed is finely adjusted by a normal PLL (Phase Locked Loop) control method.
Such rotation control by PLL control is currently performed in DVD-ROM reproduction, and is useful in that the method can be applied as it is.

(Example 14)
In the layer configuration of Example 2 (a1), the reflection layer was made of Al _0.975 Ta _0.025 . The volume resistivity was 220 nΩ · m. A plurality of samples were prepared by changing the film thickness from 200 nm to 400 nm, and the jitter was measured using the optimum pulse division method in FIG. The best jitter of 12% was obtained at a film thickness of around 300 nm. Even if the reflection layer was made thicker or thinner, only worse jitter was obtained.

(Example 15)
In the layer structure of Example 11 (a), the thickness of the upper protective layer was set to 23 nm.
In-groove recording was performed on this medium. Using an optical system having a wavelength of 405 nm and NA = 0.65, a substantially circular beam having a spot diameter of about 0.5 μm (diameter at 1 / e ² intensity of a Gaussian beam) is generated, and a beam having a thickness of 0.6 mm is passed through a substrate having a thickness of 0.6 mm. Recording and playback.
At a linear velocity of 4.86 m / s, an EFM-plus-modulated signal with the shortest mark (3T mark) length of 0.25 μm was recorded.
By the same recording pulse division method as in the second embodiment, m = n-1, α ₁ = 0.5, α _c = 0.38, β _m = 0.67, Pw = 9.5 mW, Pb = 0. 10 at 5 mW, Pe = 4.0 mW
When overwriting was performed twice, the jitter was 10%.
It was found that higher quality recording was possible in the recording / reproducing with the blue laser than in the case of Example 7. Further, even with a medium designed for the current red laser, recording and reproduction can be performed with the blue laser as it is to increase the density.

(Example 16)
In the layer structure of Example 2 (a1), the recording layer was prepared medium was _{Ga 0.05 Ge 0.05 Sb 0.68 Te 0.22} . Initialization was performed in the same manner as in Example 2 (a1). For the measurement, an optical system having a wavelength of 637 nm and NA = 0.63 was used.
An EFM plus modulation signal with the shortest mark 3T having a length of 0.4 μm was performed at a linear velocity of 3.5 m / s. With the same recording pulse strategy as in the second embodiment, m = n-1, α _i + β _i-1 = 1.0 (2 ≦ i ≦ m), α _i = α _c = constant (2 ≦ i ≦ m), α ₁ = 0.5, α _c = 0.3, β _m = 0.5, Pw = 13.5 mW, Pe = 6.0 mW, Pb = 0.5 mW, and the overwrite characteristics were evaluated. The jitter was 6.9%, 6.7%, 7.0%, and 7.3% in the initial recording (non-overwrite), 10 overwrites, 100 overwrites, and 1000 overwrites, respectively. Was.
Similarly, at a linear velocity of 7.0 m / s, α ₁ = 0.4, α _c = 0.35, β _m = 0.5, Pw = 14.0 mW, Pe = 7.0 mW, and Pb = 0. The overwrite characteristics were evaluated at 0.5 mW. The jitter was 7.4%, 7.7%, 8.0%, and 8.5%, respectively, in the initial recording (non-overwriting), 10 times overwriting, 100 times overwriting, and 1000 times overwriting, respectively. Was.
The modulation degree was 55 to 60% in each case.
When this medium was left in an accelerated test environment of 80 ° C./80% RH for 1000 hours, recording was performed before the test. The deterioration of the jitter of the signal recorded before the acceleration test was less than 1%. In addition, a value of 52 to 57% was obtained for the degree of modulation.

(Example 17)
As in Example 2, a wobble groove having a pitch of 0.74 μm was formed in a polycarbonate resin substrate having a thickness of 0.6 mm, and as shown in FIG. The layers were formed in order.
The reflective layer Al _0.995 Ta _0.005 has a thickness of 165 nm, the second protective layer (ZnS) ₈₀ SiO ₂ ) ₂₀ has a thickness of 20 nm, the recording layer In _0.03 Ge _0.05 Sb _0.70 Te _0.22 has a thickness of 16 nm, and the first protective layer (ZnS). ₈₀ (SiO ₂ ) ₂₀ was formed to a thickness of 68 nm by a sputtering method.
Thereafter, a glass plate having a thickness of 0.6 mm was brought into close contact with the first protective layer. The initialization was performed by irradiating a laser beam of about 500 mW at a linear velocity of 5 m / s through a glass substrate.
The recording layer was irradiated with laser light through this glass substrate using an optical system having a wavelength of 637 nm and NA = 0.6 to perform recording and reproduction. Recording was performed on the far side of the irregularities when viewed from the laser incident side. This corresponds to the inside of the groove in the second embodiment.
An EFM plus modulation signal with the shortest mark 3T having a length of 0.4 μm was performed at a linear velocity of 3.5 m / s. With the same recording pulse strategy as in the second embodiment, m = n-1, α _i + β _i-1 = 1.0 (2 ≦ i ≦ m), α _i = α _c = constant (2 ≦ i ≦ m), α ₁ = 0.9, α _c = 0.35,
With β _m = 0.5, Pw = 12.0 mW, Pe = 6.0 mW, and Pb = 0.5 mW, the overwrite characteristics were evaluated. After 10 overwrites, the jitter was 10.5% and the modulation was 61%.
Further, at a linear velocity of 7.0 m / s, similarly, α ₁ = 0.55, α _c = 0.40, β _m = 0.5
Pw = 13.0 mW, Pe = 5.5 mW, Pb = 0.5 mW, and the overwrite characteristics were evaluated. After overwriting 10 times, the jitter was 11.2% and the modulation was 61%.

ADVANTAGE OF THE INVENTION According to this invention, overwrite can be performed at high speed, the jitter of a mark edge is small, high-density mark length modulation recording can be performed, and the formed mark has very good stability over time. An information recording medium is obtained.
In addition, by selecting an appropriate recording layer composition and layer configuration, a phase-change optical recording medium having excellent reproduction compatibility with a read-only medium and high repeated overwrite durability can be obtained.
More specifically, it has playback compatibility with a so-called DVD disk, and can perform one-beam overwriting in a wide linear velocity range including a standard playback speed of 3.5 m / s to a double speed of 7 m / s. It is possible to provide an optical information recording medium and an optical recording method which can be used for a rewritable DVD disc and show no deterioration even if overwritten ten thousand times.
Further, since the medium of the present invention has a wide linear velocity margin, even when recording is performed by rotating the medium at a constant angular velocity such as the CAV method or the ZCAV method, the problem of the recording characteristic difference due to the linear velocity difference between the inner and outer circumferences of the medium is eliminated. I can overcome it. If the CAV method is adopted, there is no need to change the disk rotation speed for each radial position, and the access time can be reduced.

The figure which shows the example of an amorphous mark shape. FIG. 4 is a diagram illustrating a change in reflectance when recording is performed on a medium according to an example of the invention. FIG. 3 is a GeSbTe ternary phase diagram showing the composition range of the recording layer of the medium of the present invention. GeSbTe ternary phase diagram showing the range of the conventional GeSbTe composition. FIG. 1 is a schematic diagram illustrating an example of a layer configuration of a medium of the present invention. FIG. 4 is a signal waveform diagram for illustrating a relationship among a signal strength, a signal amplitude, and a modulation factor. 9 is a graph for explaining the dependency of the reflectance on the thickness of the first protective layer. FIG. 3 is a diagram showing an example of a pulse division method in a power ternary modulation recording system. FIG. 3 is a schematic diagram for explaining a time change of a temperature of a recording layer. FIG. 3 is a diagram illustrating an example of a pulse division method of a power ternary modulation recording method suitable for mark length modulation recording. FIG. 11 is a conceptual diagram illustrating timings of three types of gate generation circuits for realizing the pulse division method in FIG. 10. 7 is a graph showing the dependence of the jitter on the reproduction light power in Example 1 and Comparative Example 1. 5 is a graph showing the dependency of the jitter on the recording pulse division method in the first embodiment. 5 is a graph showing the dependency of the jitter on the recording pulse division method in the first embodiment. 9 is a graph showing the recording power dependence of jitter, reflectance, and modulation in Example 2. 11 is a graph showing the dependency of the number of repetitive overwrites on the jitter, reflectance, and degree of modulation in Example 2. 11 is a graph showing mark length dependence of jitter in Example 2 (g1) and Example 2 (d2). 10 is a graph showing the dependency of the jitter on the tilt angle of the substrate in Example 2. 14 is a graph showing α1 and αc dependence of jitter after ten overwrites in Example 4. 14 is a graph showing the dependence of jitter, Rtop, and modulation factor on the number of repeated overwrites in Example 4. 13A is a graph showing the dependency of jitter on a pulse division method, the dependency of jitter on write power, and the dependency of Rtop and modulation after ten overwrites on write power in Example 6. FIG. 14 is a graph showing the dependence of jitter, Rtop, and modulation on the number of repeated overwrites in Example 6. 13 is a graph showing the mark length dependence of jitter in Example 6. 7A is a graph showing the dependency of jitter on the pulse division method, the dependency of jitter on the write power, and the dependency of Rtop and modulation after 10 overwrites on the write power in Comparative Example 2. FIG. 9 is a diagram showing a pulse division method of a recording method used in Comparative Example 3. 13 is a graph showing the mark length dependency and the linear velocity dependency of jitter in Comparative Example 3. 13 is a graph showing the dependency of jitter on Pw and Pe in Comparative Example 6. 18 is a graph showing the shortest mark length dependency of jitter in Example 8. 13 is a graph showing Pw dependency of jitter in Example 10 and Comparative Example 8. FIG. 4 is a diagram for explaining a relationship between a digital data signal and a wobble waveform. FIG. 4 is a diagram illustrating a mechanism for modulating a wobble waveform by a digital data signal. 21 is a graph showing the groove width dependence of the modulation degree and Rtop in Example 11.

Claims (15)

For an optical information recording medium having a phase-change recording layer in which the crystal part is in an unrecorded or erased state and the amorphous part is in a recorded state, the shortest mark length is 0.5 μm or less. A recording method for recording information by a recording mark,
As the optical information recording medium, the amorphous portion due to competition between the amorphization of the melted region of the phase change recording layer and the recrystallization from the boundary of the solid phase crystal portion around the melted region. Using an optical information recording medium on which is formed
An optical system that irradiates a laser light beam having a wavelength of 350 to 680 nm to the phase-change recording layer through an objective lens having a numerical aperture NA of 0.55 or more and 0.9 or less,
Between the recording marks, the laser light beam of erasing power Pe capable of crystallizing the amorphous is irradiated,
Regarding the recording mark,
When the time length of one recording mark is nT (T is a clock cycle, n is an integer of 2 or more), the time length nT of the recording mark is

(Where, m is a pulse division number m = n-k, k is set to 0 ≦ k ≦ 2 becomes an integer. Further, sigma _i
(Α _i + β _i ) + η ₁ + η ₂ = n, η ₁ is a real number satisfying η ₁ ≧ 0, η ₂ is a real number satisfying η ₂ ≧ 0, and 0 ≦ η ₁ + η ₂ ≦ 2.0. α ₁ = 0.1 to 1.5, α _i = 0.1 to 0.8 (2 ≦ i ≦ m), β _i = 0.3 to 1.0 (1 ≦ i ≦ m−1), β _m = 0 to 1.5. α _i (2 ≦ i ≦ m)
And β _i (2 ≦ i ≦ m−1) are constant regardless of i, and α ₁ ≧ α _i . α _i + β _i-1 =
Assuming that 1.0 (3 ≦ i ≦ m), the recording pulse of α _i (2 ≦ i ≦ m) is synchronized with the clock cycle. Further, β ₁ and β _m can be different from β _i, and (Σα _i ) <0.5n. )
During the time of α _i T (1 ≦ i ≦ m), the laser light beam having a recording power Pw satisfying Pw ≧ Pe for melting the recording layer is applied;
Within the time of β _i T (1 ≦ i ≦ m), the laser light beam having a bias power Pb of 0 <Pb ≦ 0.2 Pe (however, in β _m T, 0 <Pb ≦ Pe) can be used. An optical recording method comprising irradiating. 2. The optical recording method according to claim 1, wherein (Σα _i ) <0.4n when k = 0 or k = 1. The optical recording method according to claim 1 which is changed according to beta _m to mark length nT. 4. The optical recording method according to claim 3, wherein _βm is shortened for a short mark. Α _i + β _i-1 = 1.0 (3 ≦ i ≦ m) regardless of the recording linear velocity, and Pb, Pw, Pe / Pw ratios, α _i , β ₁ , and β _m are variable according to the recording linear velocity. 5. The method according to claim 1, wherein at least α _i (i is at least one of 1 ≦ i ≦ m) monotonically decreases as the recording linear velocity decreases. Optical recording method. The optical recording method according to claim 5, as the recording linear velocity is low beta _m is varied to increase monotonically. When the maximum recording power Pw _max at each recording linear velocity, the minimum recording power and _{Pw min, Pw max / Pw min} ≦ 1.2, Pe / Pw = 0.4~0.6,0 ≦ Pb ≦ 1 6. The optical recording method according to claim 5, wherein the power is 0.5 mW. The beta _m at the maximum recording linear velocity beta ^H _m, when the beta _m at the minimum recording linear velocity was set to beta ^L _m, a beta _m in linear velocity during the overwriting a value between beta ^L _m and beta ^H _m , P regardless of the recording linear velocity
8. The optical recording method according to claim 5, wherein b and the Pe / Pw ratio are constant. 8. The optical recording method according to claim 5, wherein β _m is constant irrespective of the recording linear velocity. A method of recording information with a plurality of mark lengths by rotating an optical information recording medium having a predetermined recording area at a constant angular velocity,
A recording method in which the recording area is composed of a plurality of zones separated by a radius, and a reference clock cycle T is changed so that a recording density is substantially constant according to an average linear velocity in each zone,
The recording area is divided into p zones by radius, the innermost side is the first zone, the outermost side is the pth zone, and the angular velocity in the qth zone (where q is an integer of 1 ≦ q ≦ p). the omega _q, the average linear velocity <v _{q> ave,} the maximum linear velocity <v _{q> max,} the minimum linear velocity <v _{q> min,} the reference clock period T _q, the time length of the shortest mark n _{Assuming min} T _q ,
<V _p > _ave / <v ₁ > _ave is in the range of 1.2 to 3, <v _q > _max / <v _q > _min is 1.5 or less,
(I) In the same zone, ω _q , T _q , α _i , β _i , Pe, Pb, and Pw are constant, and the physical length n _min T _q <v _q > _ave of the shortest mark is 0. 5 μm or less, and T _q <v _q > _ave is 1
Is substantially constant for all q satisfying ≦ q ≦ p, and
m = n-1 or m = n-2,
α ₁ = 0.3 to 1.5,
α ₁ ≧ α _i = 0.2 to 0.8 (2 ≦ i ≦ m),
α _i + β _i-1 = 1.0 (3 ≦ i ≦ m),
0 ≦ Pb ≦ 1.5 (mW),
0.4 ≦ Pe / Pw ≦ 0.6,
(Ii) m is constant regardless of the zone, and Pb, Pw, Pe / Pw, α _i (
1 ≦ i ≦ m), β ₁ , β _m are variable and monotonically decrease at least α _i (i is at least one of 2 ≦ i ≦ m) from the outer zone toward the inner zone. 7. The optical recording method according to 5 or 6. When the maximum value of Pw in the recording area is Pw _max and the minimum value is Pw _min , Pw _max / Pw
The optical recording method according to claim 10, wherein w _min ≤ 1.2. An optical recording method in which light having a wavelength of 600 to 680 nm passes through an objective lens having a numerical aperture NA of 0.55 to 0.65, is focused on a recording layer via a substrate, and records and reproduces data.
In the q-th zone (where q is an integer of 1 ≦ q ≦ p), the angular velocity is ω _q , the average linear velocity is <v _q > _ave , the maximum linear velocity is <v _q > _max , and the minimum linear velocity is <v _q >. _min , the reference clock cycle is T _q , and the time length of the shortest mark is n _min T _q ,
n is an integer of 1 to 14,
m = n−1,
ω _q is constant regardless of the zone,
T _q <v _q > _ave is substantially constant for all q _satisfying 1 ≦ q ≦ p, and

The filling,
(I) In the first zone,
α ^{₁ 1} = 0.3~0.8,
A ^{_{α 1 1 ≧ α 1 i =}} 0.2~0.4 constant irrespective of i (2 ≦ i ≦ m) ,
α ¹ ₂ + β ¹ ₁ ≧ 1.0,
α ¹ _i + β ¹ _i-1 = 1.0 (3 ≦ i ≦ m),
(Ii) In the p-th zone,
α ^p ₁ = 0.3 to 0.8,
A ^{_{α p 1 ≧ α p i =}} 0.3~0.5 constant irrespective of i (2 ≦ i ≦ m) ,
α ^p _i + β ^p _i-1 = 1.0 (2 ≦ i ≦ m),
In (iii) another zone, and ^{_{α 1 i ≦ α q i ≦}} α p i (2 ≦ i ≦ m), claim alpha ^q ₁ is a value between the alpha ¹ ₁ and alpha ^p ₁ 10 Or the optical recording method according to item 11. ^{_{α 1 1 ≧ α q 1 ≧}} α p 1 ( provided ^{_{that, α 1 1> α p 1}} ) The optical recording method according to any one of claims 10 to 12. 14. The optical recording method according to claim 12, wherein Pb, Pe / Pw, β ₁ , and β _m are constant regardless of the zone, and only α ₁ and α _i (2 ≦ i ≦ m) are changed according to the zone. A method of recording information by a plurality of mark lengths by rotating an optical information recording medium having a predetermined recording area,
The recording area is divided into a plurality of zones in the radial direction, and recording is performed at a constant linear velocity in each zone.
The optical recording method according to claim 5 or 6 ratio v _out / v _in the recording linear velocity v _out at the recording linear velocity v _in the outermost zone in the innermost zone is 1.2-2.

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