JP2001273638A - Method for recording phase transition type recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recording a rewritable phase transition type recording medium by which amorphous marks can be easily formed and erased in a rewritable phase transition type recording medium even when the reflection layer is thin or absent and the range of usable crystallization rate is not decreased. SOLUTION: The method includes a preceding step of low power pulse irradiation to irradiate a medium with bias power Pb for a first specified time yT prior to the top pulse as the section of initial irradiation of recording power Pw, and a succeeding step of low power pulse irradiation to irradiate the medium with bias power Pb for a second specified time xT just after the top pulse, with (x) and (y) satisfying the relation of 0.95<=x+0.7*y<=2.5. The irradiation period of succeeding pulses as the section of irradiation of high power energy beams after the above steps is controlled to >=0.5 T and <=1.5 T.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase change type medium having a large transmittance and a large transmittance, such as an optical disk capable of high density recording using a rewritable phase change type medium. And a recording method for a phase-change recording medium, which is suitable.

[0002]

2. Description of the Related Art In recent years, with an increase in the amount of information, a recording medium capable of recording and reproducing high-density and high-capacity data at a high speed has been demanded. An optical disk has just responded to such a demand. Expected. There are two types of optical disks: a write-once type, which allows recording only once, and a rewritable type, which allows recording and erasing many times. As types of the rewritable optical disk, a magneto-optical recording medium utilizing a magneto-optical effect and a phase change medium utilizing a change in reflectivity accompanying a reversible change in crystalline state (also referred to as a phase change medium) are available. No.

[0003] This phase change type medium has the advantage that recording and erasing can be performed only by modulating the power (output) of laser light without requiring an external magnetic field, and the recording and reproducing apparatus can be downsized. Furthermore, when a phase-change type medium is used, the recording density can be increased by using a short-wavelength light source without changing the material of the recording layer and the like from a medium that can record and erase at a wavelength of about 800 nm which is currently mainstream. Is possible.

As a material of a recording layer using this phase change medium, a chalcogen-based alloy thin film is often used. For example, GeSbTe, InSbTe, GeS
nTe-based and AgInSbTe-based alloys are exemplified. At present, a recording method for a rewritable phase-change recording medium that is put to practical use is performed by setting a recording layer to a crystalline state and forming amorphous bits in an unrecorded / erased state. Here, the amorphous bit is formed by heating the recording layer to a temperature higher than the melting point and rapidly cooling the recording layer.

[0005] In order to prevent the evaporation and deformation caused by the heat treatment of the recording layer, the upper and lower portions of the recording layer are usually sandwiched between heat-resistant and chemically stable dielectric protective layers. Generated as In general, a metal reflective layer is provided on the upper part of the sandwich structure, and the four-layer structure promotes thermal diffusion and stably forms an amorphous mark.

The metal reflective layer has a function of releasing heat generated when the recording layer is irradiated with a recording laser light beam (hereinafter sometimes referred to as a light beam). That is, when using an amorphous phase-change medium, the recording layer is locally melted by a light beam, and the recording layer is rapidly cooled to form an amorphous mark. . Therefore, if the heat radiation is insufficient, the amorphous mark is not formed well, and a metal reflection layer is required.

In order to stably form an amorphous mark, a pulse division method of dividing a laser pulse for forming a mark is generally performed. A method of irradiating a pulse train according to the mark length is often used. At this time, in order to make the temperature distribution in the mark uniform, the width of the first pulse (first pulse) is sometimes made longer than the width of the second and subsequent pulses.

In this pulse division method, a recording power Pw having a relatively high power value and a bias power Pb having a relatively low power value are alternately irradiated on a phase change type recording medium to thereby obtain a length nT. Of forming an amorphous mark. Here, n is a natural number of 4 or more. That is, the output pattern (pulse pattern) of the light beam is such that a pulse (recording pulse) output at a high power and a pulse (off pulse) output at a low power are divided into a plurality of parts, and these high and low powers alternate. Is repeated. Regarding the pulse width in the conventional pulse division method, for any pulse, the pulse width output with high power,
The pulse width output at low power is 0.5
It is about T.

The pulse patterns for forming the above-mentioned amorphous marks are disclosed in the following known documents 1 to 3. Known Document 1 ("The Feasibility of High Data Ra
te 4.7GB Media with Ag-In-Sb-Te Phase Change Mater
ial "," 1998 Symposium on Phase Change Recording, Symposium, "describes a technique related to pulse patterns.

[0010] Also, a known document 2 ("Rewritable Dual-Lay
er Phase-Change Optical Disk ", Jpn.J.Appl.Phys.Vo
l.38 (1999) pp. 1679-1686), there is described a technology relating to an optical disk using a rewritable phase-change medium having a multilayer structure. Have been. Further, the known document 3
(JP-A-3-185628 [U.S. Pat.
9, 373] describes a technique for recording a signal on an optical information recording member centered on an optical disc for recording and reproducing optical information at high speed and at a high density using a laser beam or the like, and a technique relating to a recording apparatus. A satisfactory value of the repetition period τ in the middle pulse train is described.

On the other hand, erasing (crystallization) is performed by heating the recording layer to a temperature higher than the crystallization temperature of the recording layer and lower than the melting point. In this case, the dielectric protective layer functions as a heat storage layer, and keeps the recording layer at a high temperature sufficient for solid-phase crystallization. Further, in a phase change medium capable of so-called one-beam overwriting, it is known that the above-described erasing and re-recording processes can be performed only by intensity modulation of one focused light beam (see Jpn. J. Appl. Phys. 26 (1987), suppl. 26-4, pp. 61-6
6). Further, by using a phase change type medium capable of one-beam overwriting, the layer structure of the recording medium and the circuit configuration of the recording drive device are simplified.
For this reason, a system using a phase-change medium capable of one-beam overwriting has been attracting attention as being capable of performing inexpensive, high-density, and large-capacity recording.

In recent years, multi-layered recording media have been studied in order to further increase the recording density. That is, this is an attempt to increase the recording density by stacking and fabricating two or more layers of recording medium portions separated by a distance greater than the depth of focus of the optical system used. In this case, a recording medium portion other than the farthest recording medium portion when viewed from the incident direction of the laser beam needs to have a high transmittance of 30% or more to transmit the laser beam.

Therefore, in order to transmit laser light, the above-mentioned metal reflection layer is basically not used, or even if a metal reflection layer is used, it is necessary to make it thin enough to obtain sufficient light transmission. Is required.

[0014]

However, when the metal reflection layer is not provided or when the metal reflection layer is thin, the above-mentioned heat dissipation effect becomes insufficient. However, there is a problem that recrystallization is likely to occur and it is difficult to form a beautiful amorphous mark.

There is a method of preventing the recrystallization by changing the composition of the recording layer to lower the crystallization speed and the like. However, this time, since the crystallization speed is low, after the amorphous mark is formed, the crystallization of the amorphous mark in a portion irradiated with the erasing power (hereinafter referred to as an erasing power irradiated portion) is not performed. There is a problem in that the amorphous mark cannot be erased sufficiently.

That is, when recording is performed on a phase-change type medium having no or thin metal reflective layer, it is difficult to prevent recrystallization of the recording mark while maintaining a sufficient erasing rate of the erasing power irradiating section. As a result, there is a problem that the range of the crystallization speed that can be used as a rewritable recording medium is narrowed. The present invention has been made in view of such problems, and in a rewritable phase-change recording medium, formation and erasing of an amorphous mark can be easily performed even if the reflective layer is thin or not. It is another object of the present invention to provide a recording method for a phase change recording medium that can be performed without narrowing the range of usable crystallization speed.

[0017]

SUMMARY OF THE INVENTION Accordingly, the gist of the present invention is to provide a phase change recording medium having a phase change recording layer with at least a high power energy beam having a relatively high power value and a relatively low power beam. A low power energy beam having a power value and a low power energy beam are alternately irradiated on the recording medium, and a length nT (T is a reference clock cycle, n
Is a recording method of a phase change type recording medium for forming an amorphous mark having a natural number of 4 or more, which is provided immediately before a head pulse which is a section for irradiating the high power energy beam first. A low-power pulse irradiation step prior to irradiating a power energy beam for a first set time yT (y is a number greater than or equal to 0); and a second set time xT (x: (A number larger than 0) irradiation step, and a low-power pulse irradiation step at a later stage, wherein 0.95 ≦ x + 0.
There is a relationship of 7 * y ≦ 2.5, and the irradiation period of each subsequent pulse which is a section for irradiating the subsequent high power energy beam is 0.5T or more and 1.5T or less.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. The present inventors have found that, in a phase change recording medium having a configuration in which the heat radiation effect is small, recrystallization of a mark during recording tends to proceed from the front end of the mark toward the rear end of the mark. I found The present inventors have found that recrystallization of the mark can be prevented by devising a method of rapidly cooling the front end of the mark, that is, the part where the mark starts to be formed.

According to the present invention, when performing recording using the pulse division method, in a series of pulse patterns for forming an amorphous mark, a long pulse is formed adjacent to a recording pulse forming a front end of the mark. Since an off pulse is applied, the front end of the mark can be particularly rapidly cooled, and recrystallization can be prevented. That is, in a series of pulse patterns, re-crystallization can be prevented by changing only the recording pulse and the off pulse forming the front end of the mark from the conventional method. According to the present invention, since other pulse patterns can use pulse division using the conventional technique, there are few technical changes and the circuit design becomes easy.

The present invention can be applied to, for example, an optical disk having a phase change type recording layer. Generally, a groove is formed in a spiral or concentric shape on an optical disk, and recording and reproduction are performed using a land portion inside the groove or a land portion between the grooves as a recording track. For example, in a CD-RW or DVD-RW, which is a kind of phase change optical disk, an amorphous mark is formed in a crystalline recording layer using the inside of a groove as a recording track.

These optical discs usually have a protective layer / phase-change recording layer / protective layer / reflective layer on a substrate. Alternatively, in a medium having two or more recording layers for increasing the capacity, a protective layer / phase change recording layer / protective layer / resin layer / protective layer / phase change type recording layer / protective layer / Reflection layer in some cases. Alternatively, two such optical disks may be bonded together. In any case, recording and reproduction are performed by inputting an energy beam from the substrate side. In some cases, recording / reproducing is performed by reversing the layer configuration on the substrate and applying an energy beam from the side opposite to the substrate.

The present invention relates to a medium having no reflective layer via a reflective layer or a protective layer adjacent to a recording layer, or a medium having a reflective layer or a protective layer adjacent to the recording layer having a thickness of 3 mm.
The effect is remarkable in a medium having a very thin reflection layer of 0 nm or less. In other words, when the conventional medium having a reflective layer having a normal thickness is easily recrystallized, the effect of preventing recrystallization by rapidly cooling the front end of the mark is relatively small.

Although there are several recrystallization processes, typical ones are considered as follows. In the process of forming an amorphous mark, the formed amorphous region is recrystallized from the edge between the amorphous region and the surrounding crystal region. According to the study of the present inventor, in the case of a medium having a small heat radiation effect, recrystallization is likely to occur from the vicinity of the center of the mark front end, particularly in the mark width direction (direction orthogonal to the track direction), From there it is presumed to proceed towards the rear end of the mark. On the other hand, in the case of a medium having a large heat radiation effect, it is presumed that recrystallization tends to proceed from the end in the width direction of the mark toward the center.

Since the present invention rapidly cools the front end of the mark and suppresses recrystallization, when applied to a medium having a small heat radiation effect, the progress of recrystallization from the front end of the mark to the rear end can be suppressed. High effect. Therefore, when the medium does not have a reflective layer adjacent to the recording layer or a reflective layer via a protective layer, or a very thin reflective layer having a thickness of 30 nm or less via the reflective layer or the protective layer adjacent to the recording layer. The effect is remarkable in the medium which has.

For example, when the phase-change recording medium is a medium having two or more phase-change recording layers with another layer interposed therebetween, as described above, it is far from the recording / reproducing energy beam. Since the energy beam needs to reach the other phase-change type recording layer, a thick reflective layer cannot be provided in the optical path up to that time. Therefore, the phase-change recording layer closer to the beam does not have a reflective layer adjacent to the recording layer or a reflective layer via a protective layer, or has a very thin reflective layer having a thickness of 30 nm or less. Is limited to The present invention is highly effective when used for recording on the phase change recording layer of such a medium which is closer to the recording / reproducing energy beam. In the present invention, it is necessary to rapidly cool this portion in order to prevent recrystallization of the front end of the mark. First, a pulse pattern will be described with reference to FIGS.

FIG. 1 is a laser pulse waveform diagram showing an example of a pulse pattern used in the recording method of the present invention. The horizontal axis represents time, and the vertical axis represents laser power. Pw is the recording power, Pe is the erasing power, Pb is the bias power,
Pr is the reproduction power. Basically, the recording power Pw and the bias power Pb are used for forming a mark, and the erasing power Pe is used for erasing. The reproduction power Pr is used for reproducing the recorded information. In the following description, a pulse output at a high power (recording power Pw) may be referred to as a recording pulse, and a section irradiated with the recording pulse may be referred to as a recording pulse section or a recording power irradiation section. This corresponds to a high-power laser irradiation part.

A pulse output at a low power (bias power Pb) may be referred to as an off-pulse, and a section irradiated with the off-pulse may be referred to as an off-pulse section or a bias power irradiation section. This corresponds to a low power laser irradiation part. FIG. 1 shows an example in which a mark having a length of 10T (T represents a reference clock cycle) is formed. The pulse pattern shown in FIG. 1 is divided into, for example, nine recording pulses denoted by reference numerals 1 to 9. In general, the length n
When forming a T mark, the number m of recording pulses is n,
n-1 or n-2. In the case of FIG. 1, m = n
It is -1.

The power values of these nine recording pulses 1 to 9 are equal to the recording power Pw, respectively.
The power value of each off pulse before and after each recording pulse is equal to the bias power Pb. In addition, the recording pulse,
The irradiation power value in a section other than the irradiation of the off pulse is equal to the erasing power Pe. Usually, the recording power Pw is preferably 20 mW or less, more preferably 14 mW or less. In general, a phase-change optical recording medium is more preferable as the medium can be recorded with a lower laser power. This is because the output of the laser used can be small. However, the recording power Pw
Is preferably 8 mW or more. The fact that recording can be performed with a very low power means that the recording is likely to be deteriorated during reproduction.

The value of the erasing power Pe may be selected so as to sufficiently crystallize an old amorphous mark to be erased during overwriting (overwriting). Usually, it is about 30% to 70% of the recording power Pw. Reproduction power Pr
Is the power of the beam emitted when reproducing the recorded information, and a low value is selected so as not to erase the recorded information. Usually, it is 0.5 to 1.0 mW.

The bias power Pb is selected so that the recording layer heated by the recording power Pw is rapidly cooled to form an amorphous mark. In order to increase the cooling rate of the recording layer, the smaller the bias power Pb is, the better. In terms of the ratio between the bias power Pb and the erasing power Pe, Pb / Pe ≦ 0.5 is usually satisfied.
Pb / Pe ≦ 0.3. In consideration of tracking performance and the like, the bias power Pb is preferably close to or the same as the value of the reproduction power Pr.

According to the recording method of the present invention, a high power energy beam having at least a relatively high power value and a low power energy beam having a relatively low power value are provided on a phase change recording medium having a phase change recording layer. Are alternately irradiated on the recording medium, and the phase-change recording layer has a length n
This is a recording method for a phase change type recording medium for forming an amorphous mark of T (T is a reference clock period, n is a natural number of 4 or more), and is a section in which the high power energy beam is first irradiated. The low power energy beam is provided immediately before a pulse and is set to a first set time yT (y is a number equal to or greater than 0).
A low-power pulse irradiation step prior to irradiation and a low-power pulse irradiation step provided immediately after the leading pulse and irradiating the low-power energy beam for a second set time xT (x is a number greater than 0). , The x and the y
And 0.95 ≦ x + 0.7 * y ≦ 2.5.

That is, in the present recording method, the width of the off-pulse section before and after the first pulse (recording pulse 1) shown in FIG. 1 is made longer than in the case of using the conventional pulse division method. . In the pulse pattern of FIG.
In order to rapidly cool the front end of the mark, a low power off pulse having a width xT is provided between the first pulse (recording pulse 1) and the second pulse (recording pulse 2) of the mark forming divided pulse. Here, x represents a number larger than 0.

According to the study by the present inventors, if at least the conditions such as the laser power are within the normal range, when the time width of the low-power laser irradiation section (off pulse) xT is significantly longer than the conventional one, It became clear that the front end of the mark was easily cooled rapidly, and excellent recording characteristics were obtained. Hereinafter, the off pulse having the width xT after the recording pulse 1 may be referred to as an xT pulse.

It is also effective to provide an off-pulse of width yT immediately before the head pulse. Here, y represents a number of 0 or more. Hereinafter, the off pulse having the width yT before the recording pulse 1 may be referred to as a yT pulse. x and 0.7 * y
Is too small, the effect of rapid cooling of the front end of the mark cannot be obtained. Therefore, it is set to 0.95 or more. Preferably 1.
3 or more. If the sum of x and 0.7 * y is too large, the old amorphous mark will not be erased, or the amorphous portion due to the first pulse and the amorphous portion after the recording pulse will be optically separated. Could be done. Therefore 2.5
The following is assumed. Preferably it is 2.0 or less.

The value of y may be small or zero. When y is 0, the head pulse, which is the section for first irradiating the recording power Pw, is irradiated for a predetermined time (head pulse irradiation step), and is provided immediately after the head pulse irradiation step, and the bias power Pb is set to the first pulse irradiation step. Irradiation for 2 set times xT (post-stage low power pulse irradiation step)
This x may be in a relationship of 0.95 ≦ x ≦ 2.5. That is, there is an effect even if the xT pulse is simply lengthened without providing the yT pulse.

However, in order to obtain the same cooling effect without providing yT, it is necessary to lengthen the xT pulse, so that the recording pulse 1 appears earlier and the length of the mark formed as a whole is longer. Could be Therefore, it is preferable and effective to combine both the xT pulse and the yT pulse. If the value of x is too small,
Since it is difficult to suppress the recrystallization of the front end of the mark, it is usually 0.1 or more, preferably 0.3 or more. However, if the value of x is too large, the old amorphous mark may not be erased, or the amorphous portion due to the first pulse may be optically separated from the amorphous portion after the recording pulse. Therefore, it is usually set to 2.0 or less.

If the value of y is too large, the crystallization of old marks may be insufficient during overwriting, so that the value of y is usually set to 2.0 or less. The present invention is preferably used when a mark is formed in a pulse pattern having two or more recording pulses. A short mark such as a 3T mark (n = 3 in an nT mark) may be formed in a pulse pattern having only one recording pulse. When there is only one recording pulse, only the bias power Pb or the erasing power Pe is irradiated after the recording pulse 1, so that the recording pulse is relatively easily cooled. On the other hand, when the recording pulse is 2
In this case, even if there is an off-pulse after the recording pulse 1, the recording pulse 2 having the next higher power is irradiated, so that it is difficult to be rapidly cooled. Therefore, the effect of lengthening the xT pulse and the yT pulse as in the present invention is great. Therefore, this application is 4
It is preferably applied to the formation of a mark having a length of T mark (n = 4 in nT mark) or more. Next, the pulse widths of the recording pulses 1 to 9 shown in FIG. 1 will be described with reference to FIG.

FIG. 2 is an explanatory diagram of a pulse width in an example of a pulse pattern used in the recording method of the present invention. The number of recording pulses shown in FIG. 2 is m (m is a natural number) in total, and an example where m = 6 is shown. Further, each of the recording pulses 1 to 6 has a pulse width α ₁ T
Have to? ₆ T, also, following each recording pulse, there is the off-pulse having a pulse width of β ₁ T~β ₆ T respectively.
The total time width of the m recording pulses and the m off pulses is approximately equivalent to the mark length nT. Therefore, the following equation (3) holds.

[0039] ^{_{Σ m i = 1 (α i}} + β i) ≒ n (3) i is a natural number, also, alpha _i is a coefficient that determines the i-th recording pulse width, beta _i is the i-th off-pulse This is a coefficient that determines the width. ^{_{Σ m i = 1 (α i}} + β i) is, i represents the sum of (α _i + β _i) from 1 to m. Here, Σ ^m _{i = 1}
(Α _i + β _i ) need not be exactly equal to n;
It is about -2 to n + 2.

Here, if the pulse width α ₁ T of the leading pulse (recording pulse 1) shown in FIG. 2 is too long, reheating cannot be suppressed even if the off-pulses before and after the heating are too long, so that marks are not formed. Recrystallization is easy. Therefore, it is preferably 1.5T or less, more preferably 1.0T or less, and still more preferably 0.8T or less. However, if it is too short, the temperature rise of the recording layer becomes insufficient.
T or more, more preferably 0.3T or more.

The pulse width α ₁ T is set to the second set time x
When shorter than T, the quenching effect at the front end of the mark becomes larger, which is preferable. Furthermore, the pulse width α _i T (i is a natural number satisfying i ≧ 2) of the second and subsequent recording pulses is also preferably 0.8 T or less, since recrystallization is difficult to suppress if it is too long. The following is more preferred. However, if it is too short, the temperature of the recording layer rises insufficiently, so it is preferably at least 0.2T, more preferably at least 0.3T.

The last β _m (eg, β ₆ ) is usually 0
T to 1.5T, and by changing this width,
The length of the amorphous mark can be controlled. This is because if it is too long, the crystallization of old marks during overwriting may be insufficient. In the present invention, the irradiation cycle of each of the subsequent pulses (after the recording pulse 2), which is the section for irradiating the high power energy beam following the first pulse (the recording pulse 1), is set to a value close to 1T. Specifically, it is not less than 0.5T and not more than 1.5T. here,
The cycle is the time width from the rise of a recording pulse to the rise of the next recording pulse.

That is, α _i + β _i (i is i = 2−m−
(A natural number of 1) is set to a value close to 1. In particular,
0.5 or more and 1.5 or less. α _i + β _i (i is i = 2
When the value of (自然 m-1 natural number) is significantly different from 1, the following problem occurs. In order to form an amorphous mark, it is necessary to increase β _i to some extent and to increase the cooling rate. But if α _i + β _i is much smaller than 1, then
Since β _i cannot be made sufficiently large, the cooling rate is reduced, and the mark is easily recrystallized. Conversely, if β _i is increased, α _i
And the temperature of the recording layer is hard to rise sufficiently.

On the other hand, an example in which the value of α _i + β _i (i is a natural number from i = 2 to m−1) is much larger than 1 is disclosed in Japanese Patent Application Laid-Open No. Hei 9-134525 (US Pat. No. 5,732,06).
No. 2). However, for example, α
Fixing _i + beta _i values of two or more of values, since the one increasing the mark length (off-pulse associated therewith a) recording pulses will be increased sentence 2T, this recording method is nT
Two types of marks having a difference of 1T, such as a mark and an (n + 1) T mark, cannot be recorded and separated.

Therefore, for example, a recording pulse (and its accompanying off-pulse) for which the value of α _i + β _i becomes 1 is given by nT
Add somewhere on the mark pulse pattern (n + 1)
By using the T mark pulse pattern, the difference between the nT mark length and the (n + 1) T mark length is set to 1T. That is, α
_{The value of i} + β _i (i is a natural number from i = 2 to m−1) is not uniform, and different values such as 1 and 2 are mixed.

However, since the values of α _i and β _i greatly affect the temperature distribution and the temperature change process in the recording layer, the temperature distribution and the temperature change process differ greatly in the portions where the values of α _i and β _i are different. This makes it difficult to control the mark shape including the mark length. Since the size of the recrystallized area after melting, which is related to the cooling rate and the like, as well as the ultimate temperature, considerably affects the temperature distribution of the recording layer, the mark shape changes in a complicated manner due to the temperature distribution of the recording layer. .

Under certain recording conditions, α _{i is set} so that the difference between the nT mark length and the (n + 1) T mark length is 1T.
It may be possible to determine the values of and β _i . However, this is a value that can be applied only to a very narrow recording condition, and there is a high possibility that a difference in mark length is greatly deviated from 1T even if recording conditions such as recording power are slightly changed. For example, such a problem occurs when the recording power is changed or the light intensity distribution in the laser beam spot is changed by changing the recording device.

This is because, when the value of α _i + β _i is different, the way of changing the temperature distribution and the like of the recording layer with respect to the change of the recording condition is different. For example, when the value of α _i + β _i is 1 and 2,
Since the way of changing the mark shape differs with the change of the recording condition, if these are mixed, it becomes difficult to control the mark shape. On the other hand, as in the present invention, α _i + β _i (i
When the value of (= natural number of 2 to m-1) is close to 1, by adding one pulse to the pulse train at the center of the mark forming pulse, the mark is reduced to 1 without significantly changing the temperature distribution.
Such a problem is unlikely to occur because it can be lengthened by T. This is because, since the value of α _i + β _i (i is a natural number of 2 to m−1) is constant, a change in the temperature distribution due to a change in the recording power or the like is the same at any mark length.

According to the present invention, recrystallization during recording is suppressed by rapid cooling of only the front end of the mark, so that it is not necessary to further change the irradiation cycle of each of the second and subsequent recording pulses. Therefore, the irradiation cycle of each of the subsequent pulses (after the recording pulse 2), which is the section for irradiating the high power energy beam following the first pulse (the recording pulse 1), is set to a value close to 1T.

However, especially when the mark is short,
Since the addition of the pulse slightly changes the temperature distribution at the front and rear ends of the mark, α _i + β _i (i = 2−m−
In some cases, it is better to slightly deviate the value of (a natural number of 1) from 1. Therefore, the irradiation cycle of each pulse of the high power energy beam is set to 0.5 T or more, preferably 0.8 T or more.
T or more. Further, it is set to 1.5T or less, preferably 1.2T or less.

Note that the rearmost α _m + β _m may be larger than 1.5. This is because, for example, the length of the amorphous mark can be controlled by changing the pulse width β _m T of the last off pulse. In this way, even when recording is performed on a thin medium that does not have a reflective layer adjacent to the phase-change recording layer or a reflective layer via a protective layer or that performs recording on a thin medium, a sufficient erasing rate is maintained while erasing power is applied. , Prevents re-crystallization of the mark during recording,
Also, without narrowing the range of usable crystallization rates,
Can record. In addition, since the influence of recrystallization is more significant in mark length modulation recording, the effect of the present invention is more significant in mark length modulation recording. next,
A configuration of a phase change recording medium suitable for applying the present invention will be described. First, the material used for the recording layer will be described.

The effect of the present invention is particularly remarkable when a material which easily recrystallizes is applied to a medium using a recording layer. Examples of such a material that is easily recrystallized include a material having a composition containing Sb in excess of the SbTe eutectic point composition. Specific examples of such a recording layer include:
(Sb _1-a Te _1-a ) _b M _1-b (0.6 <a <0.9, 0.
7 <b <1, M is Ge, Ag, In, Ga, Zn, S
n, Si, Cu, Au, Pd, Pt, Pb, Cr, C
o, O, S, Se, V, Nb, and Ta).

A recording layer having a composition containing Sb in excess of the SbTe eutectic point composition is more reproducible than a recording layer having a so-called Ge ₂ Sb ₂ Te ₅ composition which is usually used as a recording layer of a phase change type recording medium. It has a tendency to crystallize. The phenomenon that the amorphous mark is easily recrystallized is not necessarily clear why the recording layer of this composition is remarkable, but in the present recording layer, no crystal nucleus is generated in the amorphous mark,
While recrystallization proceeds from the edge with the surrounding crystal region,
One reason may be that the mechanism of recrystallization is different, since crystal nuclei are generated in the recording layer having the Ge ₂ Sb ₂ Te ₅ composition.

In a recording layer having such a composition, in a medium having a small heat radiation effect, recrystallization occurs from the front end of the mark, especially near the center in the mark width direction (direction perpendicular to the track direction). It is presumed that it proceeds from there toward the rear end of the mark. Since the present invention rapidly cools the mark front end and suppresses recrystallization, when applied to a medium having a small heat radiation effect, the progress of recrystallization from the mark front end to the rear end can be suppressed, and the effect is particularly high. . Therefore, the effect is remarkable when the medium does not have a reflective layer adjacent to the recording layer or a reflective layer via a protective layer or has a very thin reflective layer having a thickness of 30 nm or less.

For example, when the phase-change recording medium is a medium having two or more phase-change recording layers with another layer interposed therebetween, as described above, it is far from the recording / reproducing energy beam. Since the energy beam needs to reach the other phase-change type recording layer, a thick reflective layer cannot be provided in the optical path up to that time. Therefore, the phase-change recording layer closer to the beam does not have a reflective layer adjacent to the recording layer or a reflective layer via a protective layer, or has a very thin reflective layer having a thickness of 30 nm or less. Is limited to The present invention is highly effective when used for recording on the phase change recording layer of such a medium which is closer to the recording / reproducing energy beam.

Next, the layer structure of the phase change recording medium of the present invention will be described with reference to FIG. FIG. 3 is a schematic view of an example of the layer structure of the phase change recording medium. The phase change recording medium 10 shown in FIG. 3 includes a reflective layer 10a, a recording medium unit 1, a resin layer 10e, a recording medium unit 2, and a substrate 10i. The incident direction of the light beam is a direction from the lower side to the upper side in FIG.

Here, the reflection layer 10a has a function of reflecting a light beam and diffusing heat from the recording layer 10c flowing through the protection layer 10b. And the recording medium unit 1
It comprises protection layers 10b and 10d and a recording layer 10c. The protective layers 10b and 10d control the amount of absorption of the light beam in the recording layer 10c to adjust the reflectance, and control the heat radiation from the recording layer 10c to suppress the thermal deformation of the recording layer 10c. It is.

Further, the recording layer 10c is made of a phase-change material, and the crystalline state changes reversibly, so that its optical characteristics change. The resin layer 10e has a spacer function for adjusting the position of the recording layer 10c to the focal length of the light beam. Similarly, the recording medium unit 2 includes the protective layers 10f, 1
0h and a recording layer 10g. These protective layers 10f, 10h and 10g have the same functions as the above-described protective layers 10b, 10d and 10c, respectively. Therefore, further description is omitted.

The substrate 10i has a concave portion formed on the surface thereof. As the substrate material, a resin such as polycarbonate, polyacrylate, and polyolefin, or glass can be used. In this embodiment, since the light beam is incident through the substrate, the substrate 10i needs to be transparent. The same material as the substrate 10i can be used for the resin layer 10e.

The material and the like of the reflective layer 10a will be described. The material of the reflective layer preferably has a high reflectance and a high thermal conductivity. Examples of the material of the reflective layer having high reflectivity and thermal conductivity include metals mainly composed of Ag, Au, Al, Cu, and the like. Among them, Ag having the largest reflectance and the highest thermal conductivity is Ag. Since Au, Cu, and Al absorb light more easily than Ag at short wavelengths, it is particularly preferable to use Ag when using a short wavelength laser of 650 nm or less. Further, Ag is preferable because it is relatively inexpensive as a sputtering target, has stable discharge, has a high film-forming speed, and is stable in air.

Ag, Al, Au, Cu and the like are not preferable in this respect because impurities and thermal conductivity and reflectivity decrease when mixed with impurities. However, stability and film surface flatness may be improved. Cr, Mo, Mg, Zr of about atomic% or less,
V, Ag, In, Ga, Zn, Sn, Si, Cu, A
u, Al, Pd, Pt, Pb, Ta, Ni, Co, O,
It may contain impurity elements such as Se, Nb, Ti, and N.
The thickness of the reflective layer is usually preferably 50 to 200 nm. If it is too thin, sufficient reflectance and heat radiation effect cannot be obtained. If it is too thick, it is not preferable in terms of film stress, manufacturing time and cost.

In this embodiment, no reflective layer is provided between the protective layer 10f and the resin layer 10e. Recording layer 10
Since a light beam needs to reach c, a thick reflective layer cannot be provided in the optical path up to that time. However, a very thin reflective layer having a thickness of 30 nm or less may be provided. More preferably, it is 20 nm or less.

In the above-described layer structure, the recording method of the present invention is particularly effective for recording on the recording medium 2. This is because the recording medium unit 2 requires only a very thin reflective layer without a reflective layer because it requires a high transmittance, and therefore has a small heat radiation effect. Next, regarding the protective layers 10b, 10d, 10f, and 10h,
The material and the like will be described. These protective layers 10b, 10
The materials d, 10f, and 10h are determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion, and the like. In general, metals having high transparency and a high melting point, oxides, sulfides, nitrides of semiconductors, Ca, M
g, a fluoride such as Li can be used. Note that these oxides, sulfides, nitrides, and fluorides do not always need to have a stoichiometric composition, and it is effective to change the composition for controlling the refractive index and the like or to use a mixture thereof. is there.

In consideration of the repetitive recording characteristics, the material of the protective layers 10b, 10d, 10f, and 10h is preferably a dielectric mixture. More specifically, a mixture of ZnS or a rare-earth sulfide and a heat-resistant compound such as an oxide, a nitride, or a carbide is used. For example, a mixture of ZnS and SiO ₂ is often used for a protective layer of a phase change optical disk. The film density of these protective layers 10b, 10d, 10f, and 10h is preferably 80% or more of the bulk state from the viewpoint of mechanical strength.

Further, regarding the thickness, if the thickness of the dielectric layer (protective layer) is less than 10 nm, the effect of preventing deformation of the substrate 10i and the recording layers (recording layers 10c and 10g) is insufficient, and the protective layer 10b , 10d, 10f, and 10h. In addition, this thickness is 500 n
m, when the dielectric layer is placed on the substrate 10i,
Since the warpage is proportional to the thickness of the film, cracks are likely to occur. Particularly, the lower protective layers 10d and 10h
Need to suppress substrate deformation due to heat, respectively, and preferably have a thickness of 70 nm or more. This is because, when the thickness is less than 70 nm, microscopic substrate deformation is accumulated during repeated overwriting, and the reproduction light is scattered, resulting in a significant increase in noise.

Further, the protective layers 10b, 10d, 10f,
The upper limit of the thickness of 10 h is set at 20
The upper limit is substantially 0 nm, but the thickness is 200 nm.
If it is larger than this, the groove shape seen on the recording layer surface changes, which is not preferable. That is, when the depth of the groove is
It is not preferable because the surface becomes shallower than the intended shape and the groove width becomes smaller than the intended shape again on the surface of the substrate 10i. More preferably 150n
m or less.

The thickness of the recording layers 10c and 10g is preferably in the range of 3 nm to 20 nm. More preferably, it is 5 to 10 nm. This is because the recording layers 10c, 1
If the thickness of 0 g is thin, it is difficult to obtain a sufficient contrast between the reflectance in the crystalline state and the reflectance in the non-crystalline state, and it is difficult to perform initial crystallization. On the other hand, if it is too thick, the amount of transmitted light tends to be small. The recording layer 1
0c, 10g and protective layers 10b, 10d, 10f, 10
The thickness of h is good for the absorption efficiency of the laser light in consideration of the interference effect in addition to the above-mentioned limitations in terms of mechanical strength and reliability, and the amplitude of the recording signal, that is, the recorded state and the unrecorded state. The one that increases the contrast of the state is selected.

The protective layers 10b, 10d, 10f, 10h,
The recording layers 10c and 10g and the reflection layer 10a are generally formed by using a sputtering method. Furthermore, the target for the recording layer, the target for the protective layer, and the target for the reflective layer material, if necessary, can be formed on a sputtering apparatus (in-line apparatus) installed in the same vacuum chamber. It is desirable in preventing contamination. It is also excellent in productivity.

The present invention is not limited to the above-described embodiment and its modifications, and can be variously modified and implemented without departing from the gist of the present invention. The energy beam used for recording is not limited to laser light, and other devices can be used.

[0070]

EXAMPLES ZnS-SiO ₂ lower protective layer 0.6mm thick polycarbonate substrate having a guide groove (thickness 100n
m), Ge ₈ Sb ₆₅ Te ₂₇ recording layer (thickness 7 nm), Zn
An S-SiO ₂ upper protective layer (thickness: 160 nm) was formed by a sputtering method, and a protective coat made of an ultraviolet curable resin was further formed on the upper protective layer. Here, the depth of the guide groove of the substrate is 33 nm, the width of the guide groove is 348 nm, and the groove pitch is 0.74 μm.

This optical disk was set at a laser wavelength of 635 n.
m, an output power of 3 at a linear velocity of 1.8 m / s using an optical disk evaluation device having an optical system with a numerical aperture NA of 0.6.
Initial crystallization was performed by irradiating mW DC (direct current) light. Thereafter, the following measurements were performed. Also, all signals were recorded in the guide grooves.

First, the erasing rate indicating the rate of returning from amorphous to crystalline was measured. The conditions at this time are shown below.
The mark length is about 10T and the length between the marks is about 1
A single pattern signal of 0T has a linear velocity of 3.8 m / s and a reference clock period T of 38.2 ns (1 / 26.16 MH).
z), recording power Pw = 11 mW, erasing power Pe = 1
Recording was performed in the guide groove at each output of mW and bias power Pb = reproduction power Pr = 1 mW. Here, using the pulse pattern shown in FIG. 1, α _i (i ≧ 1) = 0.3, β _i
(I ≧ 2) = 0.7, x = 0.7, y = 0.

The inventor irradiates the signal thus recorded with DC light having a predetermined erasing power Pe at a linear velocity of 3.8 m / s, and measured the erasing rate. And the result was as shown in FIG. FIG. 4 is a diagram showing the transition of the erasing rate with respect to the erasing power Pe. As shown in FIG. 4, an erasing rate of about 25 dB was obtained at an erasing power Pe = 3.5 mW. The C / N ratio of the signal before erasing is 52
dB.

Next, recording was performed on the disk, and the disk was reproduced and the jitter was measured. Under basically the same recording conditions as in the above recording, the erasing power Pe is set to 3.5 mW at which the best erasing rate is obtained, the recording power Pw is set to 11 mW, and the pulse pattern shown in FIG. _i (i ≧
1) = 0.3, β _i (i ≧ 2) = 0.7, y = 0,
A similar single pattern was recorded with varying values of x. The signal thus recorded was reproduced at a linear velocity of 3.8 m / s at a reproduction power Pr = 0.8 mW, and the jitter was measured. The result was as shown in FIG.

FIG. 5 is a diagram showing the relationship between x and jitter in the low-power pulse irradiating section at the subsequent stage. It can be seen that when the value of x is small, the jitter is large, while when the value of x is large, the jitter is small. Here, from the reproduction waveform when x was small, it was observed that the front end of the mark was crystallized. Subsequently, the same measurement was performed while changing the value of y with x = 0.7. FIG. 6 shows the result.

FIG. 6 is a diagram showing the relationship between y and jitter in the former low-power pulse irradiation section. As the value of y increases, the jitter also decreases. That is, it is understood that both x and y are effective for reducing the jitter.
FIG. 7 is a diagram showing the relationship between x + 0.7 * y and jitter. As shown in FIG. 7, from the experiment, (x + 0.7
* Y) and the jitter correspond well, and (x + 0.7 *
y) When ≧ 0.95, the jitter is 10 ns or less,
When (x + 0.7 * y) ≧ 1.3, the jitter was 6.5 ns or less. The transmittance was about 55% when the recording layer was in an amorphous state and about 47% when it was in a crystalline state.

The transmittance was determined as follows.
A laser having a wavelength of 635 nm is passed through a polycarbonate substrate having a thickness of 0.6 mm and Al _99.5 Ta having a thickness of 200 nm is passed through.
_The amount of reflected light I ₁ when the _0.5 film was reproduced was measured, and a 200 nm-thick Al _99.5 was passed through the optical disk of this embodiment.
The reflected light amount I ₂ when the Ta _0.5 film was reproduced was measured. The transmittance was determined by the formula of (I ₂ / I ₁ ) ^1/2 * 100 (%).

There were some characteristics distributions in the disk which were considered to be caused by the fact that the substrate was thin and easy to warp, that there was transmitted light and the protective coat was not uniform. As described above, it can be seen that by setting x and y to specific ranges, formation and erasing of an amorphous mark can be easily performed without a reflective layer.

[0079]

Accordingly, as described in detail above, according to the recording method of the present invention, even if a phase change medium does not have a metal reflective layer, recrystallization of a recording mark peculiar to a thin phase change medium is achieved. In addition, since the conventional pulse can be used except for the front end of the divided pulse, there is an advantage that there are few technical changes and the circuit design can be simplified.

Even when a mark length is recorded on a phase change type recording medium having no or thin metal reflective layer, recrystallization of the mark at the time of recording can be prevented while maintaining a sufficient erasing rate of the erasing power irradiation section. There is an advantage that the range of possible crystallization rates can be prevented from being narrowed.

[Brief description of the drawings]

FIG. 1 is a laser pulse waveform diagram showing an example of a pulse pattern used in the recording method of the present invention.

FIG. 2 is an explanatory diagram of a pulse width in an example of a pulse pattern used in the recording method of the present invention.

FIG. 3 is a schematic diagram of a layer structure of a phase change recording medium.

FIG. 4 is a diagram showing a transition of an erasing rate with respect to erasing power in an example.

FIG. 5 is a graph showing x of a post-stage low-power pulse irradiation unit in an embodiment.
FIG. 6 is a diagram illustrating a relationship between the jitter and the jitter.

FIG. 6 shows y of a pre-stage low-power pulse irradiation unit in an embodiment.
FIG. 6 is a diagram illustrating a relationship between the jitter and the jitter.

FIG. 7 is a diagram illustrating a relationship between x + 0.7 * y and jitter in the example.

[Explanation of symbols]

 1, 2 recording medium section 10 phase change type recording medium 10a reflective layer 10b, 10d, 10f, 10h protective layer 10c, 10g recording layer 10e resin layer 10i substrate

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2H111 EA04 EA12 EA23 EA31 FA01 FA02 FA12 FA14 FB04 FB05 FB06 FB07 FB09 FB12 FB15 FB16 FB17 FB19 FB21 FB22 FB23 FB25 FB27 FB30 5D029 JA01 JB05 MA02 BB03

Claims (9)

[Claims] 1. A phase change type recording medium having a phase change type recording layer is provided with at least two types of a high power energy beam having a relatively high power value and a low power energy beam having a relatively low power value. A phase-change type recording medium recording method in which the recording medium is alternately irradiated to form an amorphous mark having a length of nT (T is a reference clock cycle, n is a natural number of 4 or more) on the phase-change type recording layer. A low-power pulse irradiation, which is provided immediately before the first pulse, which is a section for irradiating the high-power energy beam first, and irradiates the low-power energy beam for a first set time yT (y is a number equal to or greater than 0); And a subsequent low-power pulse irradiation step provided immediately after the first pulse and irradiating the low-power energy beam with the low-power energy beam for a second set time xT (x is a number greater than 0). There is a relationship of the following equation (1) between x and y (* represents multiplication): 0.95 ≦ x + 0.7 * y ≦ 2.5 (1) The method of recording a phase-change recording medium, characterized in that the irradiation cycle of each of the subsequent pulses that is a section for irradiating the power energy beam is 0.5 T or more and 1.5 T or less. 2. The method of claim 1, wherein y is a number greater than zero.
The recording method of the phase-change recording medium according to the above. 3. The recording method for a phase-change recording medium according to claim 1, wherein 1.3 ≦ x + 0.7 * y ≦ 2.0. 4. The phase change recording layer according to claim 1, wherein the phase change type recording layer has a composition containing Sb in excess of the SbTe eutectic point composition.
Or the recording method of the phase change recording medium according to 2. 5. The method according to claim 1, wherein the phase-change recording layer has the following general formula (2):
5. The recording method for a phase change recording medium according to claim 4, wherein a component represented by the following formula is used as a main component. (Sb _1-a Te _1-a ) _b M _1-b (2) (where a is a real number in the range of 0.6 <a <0.9, and b is a range of 0.7 <b <1. Where M is G
e, Ag, In, Ga, Zn, Sn, Si, Cu, A
u, Pd, Pt, Pb, Cr, Co, O, S, Se,
Represents at least one element selected from V, Nb, and Ta) 6. The time for irradiating the first pulse is the second pulse.
The recording method for a phase change recording medium according to claim 1, wherein the recording time is shorter than the set time xT. 7. The medium according to claim 1, wherein the phase-change recording medium has no reflective layer adjacent to the phase-change recording layer or a reflective layer via a protective layer. Recording method of a phase change type recording medium. 8. The phase-change recording medium having a thickness of 30 n via a reflective layer or a protective layer adjacent to the phase-change recording layer.
The recording method for a phase-change recording medium according to claim 1, wherein the recording medium is a medium having a reflective layer of m or less. 9. The phase change type recording medium is a medium having two or more phase change type recording layers with another layer interposed therebetween, and the phase change type recording layer closer to the energy beam. 9. The recording method for a phase-change recording medium according to claim 1, wherein the recording method is a recording method.