JP2003016643A - Optical recording method and optical information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording method which expands the linear velocity margin of a phase transition type optical recording medium. SOLUTION: Clock periods are changed according to the linear velocity V and the parameters of pulse division in recording laser pulses are changed in order to deal with the different linear velocities on the phase transition recording medium. In forming the marks of a length nT, periods αi T (1<=i<=) when recording power Pw is impressed and periods βi T when bias power Pb is impressed are alternately disposed, by which the laser power is divided to m-pieces of the pulses. In this division, the combinations of αi T and βi T are varied in correspondence to the linear velocity V. This method is adequately usable for a CD-E, etc., for which the mark length modulation recording largely varying in the linear velocities is adopted. The recording layer of the specific composition is disclosed as the recording layer suitable for this method.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an optical recording method and an optical information recording medium. More specifically, regarding a phase-change type optical recording medium capable of recording, erasing and reproducing information by irradiation with laser light, etc., a recording method capable of expanding a recordable linear velocity in a wide range and a recording medium used for the same Regarding

[0002]

2. Description of the Related Art In recent years, an optical disk using a laser has been actively developed as a recording medium that meets the demands for increasing the amount of information and increasing the recording and reproducing density and speed. Recordable optical disks include a write-once type that allows recording only once and a rewritable type that allows recording / erasing as many times as desired. Examples of the rewritable optical disk include a magneto-optical recording medium that utilizes the magneto-optical effect and a phase change medium that utilizes a reversible change in crystal state. The phase change medium does not require external magnetism, and recording / erasing is possible only by power modulation of laser light. Further, there is an advantage that one-beam overwriting is possible in which erasing and re-recording are simultaneously performed with a single beam. In the one-beam overwritable phase change recording method, it is general that a recording mark is formed by amorphizing a microscopic portion of the recording film of μm order, and erasing is performed by crystallizing the recording mark. . As a recording layer material used in such a phase change recording method, a chalcogen-based alloy thin film is often used. For example, Ge-Te-based, Ge-Te-Sb-based, In-Sb-based.
-Te series, Ge-Sn-Te series alloy thin films and the like can be mentioned.

Generally, in a rewritable phase change recording medium,
In order to realize two different states (crystallization and amorphization), two different levels of laser light power are used. This method will be described by taking as an example the case where an amorphous mark is formed from a crystallized initial state and the amorphous mark is erased by recrystallizing the amorphous mark. The crystallization is performed by heating the recording layer portion to a temperature sufficiently higher than the crystallization temperature of the recording layer and lower than the melting point. In this case, the recording layer is sandwiched by dielectric layers or an elliptical beam long in the beam moving direction is used so that the cooling rate becomes slow enough to cause sufficient crystallization. On the other hand, the amorphization is performed by heating the recording layer to a temperature higher than the melting point and quenching it. When one-beam overwriting is performed in a normal phase change medium, a recording pulse is modulated between a recording laser power and an erasing laser power lower than the recording laser power, and the previously recorded amorphous material is used. Record while erasing the mark. In this case, the dielectric layer also has a function as a heat dissipation layer for obtaining a sufficient cooling rate (supercooling rate) in the recording layer. Furthermore, in order to prevent deformation of the recording layer due to melting and volume change in the heating / cooling process, thermal damage to the plastic substrate, or deterioration of the recording layer due to moisture as described above, The dielectric layer plays an important role. Generally, the material of the dielectric layer is optically transparent to laser light, has a high melting point / softening point / decomposition temperature, is easy to form a film, and has suitable thermal conductivity. It is selected from the viewpoint of.

[0004]

DISCLOSURE OF THE INVENTION In the above phase change medium,
Since the thermal characteristics at the time of recording and erasing are greatly affected by the scanning speed of the laser beam, that is, the linear velocity, in order to improve the recording and erasing characteristics at the time of making the phase change medium, the target recording device It is necessary to optimize the recording layer composition or layer structure of the medium according to the disk linear velocity at the time of recording / erasing. Amorphous marks are formed by cooling the recording layer once melted with recording power at a speed equal to or higher than the critical cooling rate (Mitsubishi Kasei
R & D Review vol.4 No2 p68-81). This cooling rate depends on the linear velocity when the same layer structure is used. That is,
The cooling rate is high at high linear velocity, and is slow at low linear velocity. In order to confirm this, ZnS: was formed on a polycarbonate substrate, which is the layer structure used in the examples of the present invention.
100 nm of SiO ₂ mixed film and 25 n of GeSbTe recording layer
m, ZnS: SiO ₂ mixed film 20 nm, Al alloy film 10
A heat distribution simulation using a general difference method was performed on the disks sequentially formed with 0 nm. In this case, after the calculated recording power (level) Pw and the base power (level) Pb are irradiated and the recording layer is heated to the maximum attainable temperature 1350 ° C., the melting point (600 ° C. ) The critical cooling rate near
The examination was performed at a position 0.1 μm ahead of the pulse irradiation start position. The result shows that when the linear velocity is 10 m / s or more, it is several K / nse.
c or more and 4 m / s, 2.2 K / nsec, 1.4 m / s
s was 0.9 K / nsec.

On the other hand, in order to erase the amorphous mark, it is necessary to keep the recording layer at a temperature above its crystallization temperature and below its melting point for a certain period of time. On the contrary, this heat retention time is short at high linear velocity,
It tends to be long at low linear velocities. Therefore, in a recording apparatus with a relatively high linear velocity, when the light beam is irradiated, the heat distribution of the recording layer in the irradiated portion becomes relatively steep in terms of time and space, and the unerased portion during erasing Is concerned.
In order to cope with such a recording device, a compound having a relatively rapid crystallization composition is used for the recording layer so that crystallization, that is, mark erasing can be performed in a relatively short time, or a layer structure in which heat does not easily escape as a whole. Or On the contrary, in a recording apparatus having a relatively low linear velocity, the cooling rate becomes slow as described above, and thus recrystallization during recording is a concern. Therefore,
In order to deal with a recording device having a relatively small linear velocity, a compound having a relatively slow crystallization composition in the recording layer is used as a method of preventing recrystallization during formation of the recording mark in order to obtain a target mark length. Or using a layered structure that allows heat to escape easily.

Specifically, for a medium for high linear velocity, the heat insulating layer between the recording layer and the reflective layer is made thick to make it difficult for heat to escape, or the material is, for example, a GeSbTe alloy. When it is used, a device such as a composition on the GeTe—Sb ₂ Te ₃ line that is easily crystallized is used. on the other hand,
For low linear velocities, the thermal insulation layer should be thin so that heat can escape easily, or Sb should be added in a larger amount than when used for high linear velocities to prevent crystallization during resolidification. Is devised.

By adopting the recording layer composition as described above or optimizing the layer structure,
It is possible to record, erase and reproduce information with good characteristics. However, in a medium optimized for a recording device having a relatively high linear velocity, the crystallization speed is increased, so that in a region where the linear velocity is low, it is difficult to form an amorphous bit due to recrystallization, and therefore it is used. Can not. On the other hand, when the medium is adjusted to a low linear velocity, the composition / layer structure is such that an amorphous bit is easily formed, so that it is difficult to erase at a high linear velocity. After all, the linear velocity margin could not be widened only by optimizing the recording medium.

In recent years, the linear velocity of the medium at the time of recording and erasing has been increasing in order to shorten the time spent for recording and erasing, but on the other hand, there is a demand to record information in real time. . For example, this is the case of recording video, music, etc. In this case, it is essential to record in real time. Further, in this case, there is also a demand for high-speed recording for editing the information after recording in real time. Furthermore, the same recording medium can be recorded on a relatively low linear velocity (for example, 1.2 m / s
If it can be used for both applications at 1.4 m / s and its 4-6 times speed) and applications at high linear velocities such as current magneto-optical disks (about 10 m / s or more),
It is particularly preferable as a recording medium for multimedia. However, in order to meet such requirements, if the recording is performed at a linear velocity that is significantly smaller than the original linear velocity in which the layer structure and recording layer composition of the recording medium are optimized, the target mark length can be recorded. In some cases, information could not be recorded. In a phase change recording medium, an amorphous mark is generally formed by irradiating a minute portion of the recording layer with a laser, melting the minute portion, and then rapidly cooling the amorphous portion. It is considered that when is relatively small, recrystallization occurs after recording and melting, and it becomes difficult to form a sufficient amorphous mark, as described above. When the reproduced waveform of the recrystallized recording mark after melting is observed, it becomes as shown in FIG. 1. Referring also to FIG. 2 showing the state of the amorphous film portion, recrystallization is large in the first half portion of the recording mark,
It can be seen that the latter half of the mark is relatively well formed of amorphous. This means that the continuous irradiation with the laser beam corresponding to the recording power causes the heat generated by the laser irradiation to the area corresponding to the latter half of the mark to be transferred to the area corresponding to the first half of the melted mark. It can be explained that the first half is recrystallized without being rapidly cooled. In this case, in the latter half of the mark, since the laser beam corresponding to the recording power is not irradiated immediately after that, there is no extra heat conduction and the melted portion becomes a good amorphous state. In consideration of the above, if the recording pulse is divided by once reducing the power after the start of the irradiation of the recording power, the temporal temperature change of the recording layer is rapidly cooled, and the deterioration of the mark due to the recrystallization during the recording may occur. It can be inferred that it will be possible to suppress it.

As examples of recording methods in consideration of the above, Japanese Patent Application Laid-Open No. 2-165420, Japanese Patent Application Laid-Open No. 4-212735,
JP-A-5-62193, JP-A-5-325258,
JP-A-1-116927, JJAP. Vol.30 No.
4 (1991) p677-681, etc. In addition, in the case of using off-pulse, the 40th Spring Meeting of Applied Physics Association 29
aB-4, JP-A-7-37251, JP-A-6-4867
JP-A-1-253828, JP-A-1-15023
No. 0, JP-A-1-315030, JP-A-4-3138.
16, JP-A-2-199628, JP-A-63-11.
Each publication of No. 3938 is cited. However, in these methods, since the pulse division method is constant, it is effective when recording at a certain range of linear velocities, but good recording may not be possible under conditions where the linear velocities differ greatly. Many, as long as a constant pulse division method is used,
There is a limit to the range of linear velocities that can be supported by one specific medium.

[0010]

The present inventors propose here a method of pulse division according to the linear velocity in order to solve the above problems. The inventors of the present invention have devised that heat can be quickly released from the recording layer as the velocity becomes lower, and the amorphous layer is easily made amorphous, and the pulse division method can be specified in accordance with the linear velocity. That is, the gist of the present invention is not the recording pulse division method itself, but the method of changing the pulse division method according to the linear velocity. According to the present invention, it is possible to widen the use margin of the linear velocity of a specific disc.

The recording method of the present invention uses a laser beam of irradiation light.
Power in accordance with the clock cycle T, the recording power Pw, the erasing power
Power Pe and bias power Pb (however, Pb / Pe
≦ 0.25. ) Between the optical information
The recording medium has a plurality of non-identifiable
Mark length modulation recording by forming or erasing crystalline marks
The optical recording method that records and erases data by
NT (where n is an integer greater than or equal to 2 and
The minimum and maximum values are n_min, N_maxAnd ) Has
When forming an amorphous mark,
The recording power Pw having the intensity of₁T, α
₂T, ..., α_mT and apply bias power Pb
Β for the period₁T, β₂T, ..., β_mAs T,
The power application period is₁T, β₁T, α₂T, β₂
T, ..., α_mT, β_mT (however, k is 0 or more)
, J is a real number from 0 to 2, and m = n−k, n
_min−k ≧ 1, α₁+ Β₁＋ ・ ・ ・ ＋ α_m+ Β_m= N-j
To do. ), The recording power Pw is applied for m periods.
Irradiation is performed by dividing the pulse into
The linear velocity V when irradiating on the recording medium is the maximum linear velocity V_h
And minimum linear velocity V_LAs V_L≦ V ≦ V_h(V_h≧ 2
V_L) Is variable, and the black value changes according to the change in linear velocity V.
The clock cycle T is variable, i is an integer of 1 ≦ i ≦ m,
The application period width of each divided recording power Pw is α_i
T, the application period width of each bias power is β_iT, linear velocity
Degree V is V_L, V₁, V₂, V_hΑ when_iΑ respectively_iL,
α_i1, Α_i2, Α_ihAnd the linear velocity V_hΒ in_iΒ_ihWhen
, For all i above, α_i+ Β_iIs the linear velocity
Constant regardless of V_L<V₁<V ₂<V_hThen α_iL≤ α
_i1≤ α_i2≤ α_ih, And α_iL<Α_ihAnd further, α_ih= Β
_ihAnd the linear velocity V is V_L≦ V <V_hIn the range of 2 ≦
At i satisfying i ≦ m, 0.05 (α_i+ Β_i) <Α_i
<0.5 (α_i+ Β_i) And is characterized.

In the preferred optical recording method of the present invention, i is 1≤
If Pr is the reproducing light power in the range of i ≦ m,
The bias power Pb _{i at} β _i T is Pb _i = Pr ± 0.
It is 5 mW. It is also possible that β _i has a constant value for _{i in} the range of 1 ≦ i <m−1, and β _m is different from the constant value and can be 0. This is a preferred embodiment of the method. Furthermore, in the optical recording method of the present invention, the optical information recording medium is Pw, P so that one is selected from a plurality of pulse division methods according to the linear velocity V used.
A medium in which a combination of variable ones of e, Pb, m, j, k, α _i and β _i is recorded as pulse division information is preferable.

The optical information recording medium of the present invention is the optical information recording medium used in the optical recording method of the present invention, and one of a plurality of pulse division methods is selected according to the linear velocity V used. So that Pw, Pe, Pb, m, j,
It is characterized in that a combination of k, α _i and β _i which are variable is recorded as pulse division information. In this case, the disk drive selects the clock frequency corresponding to the linear velocity to be selected and, based on this information recorded on the medium, selects one of the plurality of pulse division methods corresponding to the linear velocity. select. In a preferable example of the optical information recording medium of the present invention, the pulse division information is recorded as concave and convex pit information. Further, it is preferable that the pulse division information is recorded by frequency modulation of the meandering groove.

The phase-change recording medium of the present invention which can adopt the above-mentioned pulse division method has a recording layer of {(GeTe) _y (Sb ₂ Te
₃ ) _1-y } _1-x Sb _x (where x is a number in the range of 0 ≦ x <0.1 and y is a number in the range of 0.2 <y <0.9) and {M _y (Te _1-x
Sb _x ) _1-y (y is in the range of 0 ≦ y <0.3 and x is 0.5
<X <0.9, where M is In, Ga, Zn, G
e, Sn, Si, Pb, Co, Cr, Cu, Ag, Au, Pd, P
t, S, Se, and O), and the recording layer has a thickness of 15-30.
nm, and the film thickness of the upper dielectric protection layer is preferably 10-30 nm.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As a recording method in which the linear velocity is almost constant, a general CLV (Constant Linear Velocit) is used.
y), ZCLV (Zoned where the linear velocity is constant for each zone)
CLV) etc. (supervised by Morio Onoue. Optical disc technology. Radio Technology Co., Ltd.). In the ZCLV format, the linear velocity slightly changes in the zone, but the linear velocity is kept almost constant as a whole. Today, it is a well-known technique to make the linear velocity of a CD variable between 1 × speed (1.2 m / s to 1.4 m / s).

For example, let T _h be a clock cycle adopted at a certain maximum linear velocity V _h . If you specify n, nT _h
The mark length to be recorded is determined by. In order to record marks of the same length at a low linear velocity V, the clock period T should be calculated (V _h / V) × T _h, and nT pulses should give marks of the same length. Such adjustment of the clock cycle T according to the linear velocity has already been generally performed. However, in reality, the length of the mark is increased by thermal diffusion,
Alternatively, the desired mark length cannot always be obtained because the mark length is shortened by recrystallization. This is especially likely to occur when the minimum linear velocity _VL is a low linear velocity of 4 to less than 6 m / s. Therefore, the recording pulse is divided and the width of each divided pulse is shortened to adjust the temperature distribution in the recording layer. A recording method in which the mark length is modulated is shown in FIG. A modulation method using such mark length modulation is 1-7
There are modulation, EFM modulation, and the like. In these mark length recordings, the starting end position and the trailing end position of the recording mark correspond to the recording data, which is particularly important.

In the present invention, parameters m = n−k, n−j = which determine the pulse division method in accordance with the linear velocity.
(Α ₁ + β ₁ + ... + α _m + β _m ), _nmin- k ≧ 1
Under the condition, at least one of α _i T and Pb is made variable according to the following law, and the applicable linear velocity of the same medium is widened. That is, in the present invention, when the linear velocity is small and the cooling rate is slow, the recording power Pw
Pulse width α _i T for turning on is shortened, time β _i T for turning off is lengthened, or laser light power (bias power) Pb _i applied during period β _i T for which recording power Pw is off. Is reduced as the linear velocity decreases, thereby suppressing the accumulation of heat in one mark, increasing the cooling rate, and preventing recrystallization. Alternatively, in addition to these, one of the recording pulses divided to record one mark is irradiated between the divided recording pulses in order to suppress reheating by a subsequent recording pulse. By controlling the light energy, the cooling rate of the region melted to form the amorphous mark is controlled. If more formulated in a range of linear velocity for recording information on a phase-change optical recording medium _{(V L ~V h), V} L <V 1 <V 2 <V h become linear velocity V _1, V _{In the case of 2} , α _iL ≦ α _i1 ≦ α _i2 ≦ α _ih (1) holds for all i satisfying 1 ≦ i ≦ m. Where α _iL , α _i1 , α _i2 , α
_ih is the divided individual pulse width at times V _L , V ₁ , V ₂ , and V _h , respectively.

Instead of the above or in addition to the above, the ratio Pb _i / Pe between the bias power Pb _i and the erase power Pe in the β _i T period is θ _i, and θ _iL , θ _i1 , θ _i2 And θ _{i h} are also θ when V _L , V ₁ , V ₂ and V _h , respectively.
_{When i} is set, θ _iL ≦ θ _i1 ≦ θ _i2 ≦ θ _ih (2) can be _satisfied .

In any of the above cases, at least in V _L , α _iL <α _ih (3) or θ _iL <θ _ih (4) holds for at least one i. However, as a matter of course, the recording power Pw and the erasing power Pe
Takes different values depending on the individual linear velocity.

In particular, Pe is selected as the power that can erase the amorphous mark when it is irradiated only once by direct current. More specifically, f _max = 1 / (2n
_max T) or f _min = 1 / (2n _min T) When a mark recorded at a single frequency (duty ratio 50%) is directly irradiated with Pe, the carrier level of the erased signal Pe is selected so that the attenuation is about 20 dB or more.
_{Alternatively, f max = 1 / (2n} max T) comprising a single frequency is on mark recorded with (a duty ratio of 50%), f _min
= 1 / (n _min T) single frequency (duty ratio 50
%) Overwriting (at this time, the recording pulse may or may not be divided, but is modulated by the binary value of Pw and Pe) and the carrier level of f _min and the erased f _max. Pe is selected so that the difference in carrier level of is about 20 dB or more. Incidentally, Pw is chosen to C / N ratio of a recording signal of f _max and f _{m in} (Carrier to Noise ratio) of about 45dB or more.

It is known that Pw, Pe and the clock period T are changed according to the linear velocity at the time of recording. However, the present inventors first proposed to change the pulse division method according to the linear velocity and according to a certain law as in the present invention. The parameters describing these pulse division methods may be continuously changed according to the linear velocity, or may be changed stepwise for each constant linear velocity range.

In the above-mentioned optical recording method, the bias power Pb _i in the β _i T period in which the recording power is turned off takes an arbitrary value equal to or lower than the power Pe required for erasing in the case of performing ordinary three-value modulation recording ( In addition, the value of Pb _i may change during β _i T and may take several levels. In this case, the heat distribution can be finely controlled, the shape of the amorphous mark can be adjusted, and the jitter of the recording signal can be improved. Further, since the material is cooled more rapidly, the recrystallized region can be made smaller and the recording sensitivity may be improved in some cases. Where P
When b _i becomes 0, the servo signal cannot be obtained and tracking servo is not applied, which is not preferable. Also, P
When b _i exceeds Pe, the recording layer is melted, and erasing becomes impossible, which is not preferable. After all, Pb _i is 0
It is preferably larger and not more than Pe.

At a high linear velocity where V is 10 m / s, P
It is desirable to use a medium capable of overwriting with b as Pb = Pe (constant). This is because at a high linear velocity, the clock cycle is short and the Pb switching circuit requires high-speed response. However, when used at low linear velocity, the clock period is long,
Since the requirement for the responsiveness of the pulse control circuit is relaxed, it is sometimes necessary to use a combination of several kinds of Pb instead of one kind of value in order to shape the shape of the amorphous mark, although the circuit becomes complicated. preferable. In the pattern for the 4T mark illustrated in FIG. 5B, the case where 0 <Pb <Pe is first set and then Pb = Pe is changed during the period of β _i T is described. Moreover, in the pattern illustrated in FIG. 5A, an example in which Pb = Pe is first taken and then Pb <Pe is changed is given. Thus, in β _i T, Pb _i has a plurality of values Pb _iJ (where β _i = Σ _J β _iJ , and Pb _iJ is β
If capable of forming a bias power values) to take in further dividing interval beta _iJ T within _i, instead of the _{θ i, θ i = Σ j} (Pb ij β ij T) / (Pe · β i T) Is defined so that the expressions (2) and (4) are satisfied.

In the above-mentioned optical recording method, since the laser power immediately before the mark is the erasing power and the temperature does not easily rise at the tip of the mark, it is preferable to make the pulse width of the first divided pulse longer than the pulse following it. There is.
This example is shown in FIG. Further, the rising edge of each divided recording pulse does not necessarily have to be synchronized with the clock cycle, but it is desirable to be synchronized in order to simplify the pulse control circuit. However, even in that case, only the rising edge of the first pulse or the last pulse for one mark length is at most T from the clock cycle T.
The offset is effective in correcting thermal interference between different marks. Further, in order to suppress thermal interference with the preceding mark, it is effective to provide an off pulse section immediately before the leading pulse of the succeeding mark (before the elapse of 2T time at the maximum), though it becomes complicated. This example is shown in FIG.

The recording power Pw is constant irrespective of the pulse length nT at each linear velocity, and is constant between the divided individual pulses in one mark. It is desirable in simplifying. However, the recording power of the subsequent pulse is gradually changed from the recording power of the first pulse in one mark,
In particular, lowering the recording power of the subsequent pulse is sometimes effective. Depending on the case, further, the laser power for the pulse length nT necessary for recording the nT mark,
That is, when a pulse train of (α ₁ + β ₁ + ... + α _m + β _m ) = n is applied, the heating time becomes too long,
Sometimes it is possible to write a mark that is longer than the required length.
In that case, (α ₁ + β ₁ + ... + α _m + β _m ) =
As n-j (j is a real number in the range of 0 <j ≦ 2), the pulse division number m = n-k may be changed accordingly. In FIG. 7, as an example, a pattern in which β _i (1 ≦ i ≦ m−1) is constant and only β _m has a different value is illustrated. In this case, by adjusting β _m , n−j can be changed to obtain a desired mark length nT.

As described above, there are at least two kinds of parameters of the pulse division method which should be changed according to the linear velocity. Among these parameters, the pulse division number m = n−k,
(1)-(4) at the linear velocities V ₁ and V _{2 where} V _L <V ₁ <V ₂ <V _h , where the pulse length n−j and α _i + β _i are constant regardless of the linear velocity. It is desirable to make all of the equations valid in order to simplify the pulse control circuit. Even more preferably, at the maximum linear velocity V _h used, α _1h = 0.5, 1.0, or 1.5, and β _1h = α _ih = 0.5 (2 ≦ i ≦ m), and , Α _i + β _i = 1.0 (2 ≦ i ≦ m) at all linear velocities. In this way, the rising edge of each recording pulse is synchronized with the reference clock, apart from the constant delay. Therefore, the design of the pulse control circuit becomes easier.
Here, in the linear velocity V in the range of linear velocity V _L ≦ V <V _h , the lower the linear velocity, the shorter the pulse width may be to prevent recrystallization. However, if the pulse width is made too short, the recording sensitivity is deteriorated, which is not preferable. Therefore, in practice, it is preferable to set the lower limit of 0.05 <α _i .

The present invention is intended for mark length modulation recording, but is not limited to the mark edge detection method. That is,
Jpn.J.Appl.Phys., Vol.31 (1992), 584-589pp, a simple DC level slicing, or peak detection by double differentiation may be used. Further, as disclosed in the same document, a method of separately detecting the mark end at the mark front end and the mark end is also effective.

The optical recording medium to which the present invention can be applied is a so-called phase change type recording medium in which the crystalline state is an unrecorded state and an amorphous recording mark is formed.
FIG. 8 shows an example of the structure of this type of phase change medium. Of course, the present invention is not limited to this layer structure. In FIG. 8, a lower protective layer 2, a phase-change recording layer 3, an upper protective layer 4, a reflective layer 5 made of metal or semiconductor, and a protective layer 6 made of ultraviolet or thermosetting resin are provided on a substrate 1.
Are sequentially formed. Each layer indicated by reference numeral 2-5 is
Usually, it is a thin film formed by a sputtering method. Focused light for recording and reproduction is generally transmitted through the transparent substrate 1 and applied to the recording layer 3. The recording layer 3 is locally heated and melted by the irradiation of the recording power Pw, and by turning off the focused light irradiation light,
It becomes amorphous when rapidly cooled and solidified. The amorphous mark is heated by the irradiation of Pe to a temperature below the melting point and above the crystallization temperature, recrystallized, and erased. As a recording layer material which can be overwritten by such a principle, GeSbTe alloys (among others, a pseudo binary alloy of GeTe and Sb ₂ Te ₃ ) as described above, Ag in the vicinity of the Sb ₇₀ Te ₃₀ eutectic composition, Examples thereof include Cu, Au, Ge, Pd, Pt and the like. In these alloys, the crystallization rate and the amorphous forming ability or the crystallization temperature are controlled by controlling the amount of Sb, and the alloy is optimized according to the linear velocity to be used. For example, when going Sb added to the GeTe-Sb ₂ Te ₃ pseudo binary alloy, an amorphous forming ability is increased, since the crystallization speed is reduced, the low linear velocity direction. Further, by controlling the thicknesses of the recording layer 2 and the protective layer 4, and the thermal conductivity of the protective layers 2 and 4 and the reflective layer 5, it is possible to control the supercooling rate of the melted region formed at the time of recording to obtain the linear velocity. It is possible to control to adapt to. For example, increase the thermal conductivity of the protective layer, or increase the thickness of the recording layer and the upper protective layer to 15-3.
When the thickness is set to 0 nm, if thermal diffusion from the recording layer to the reflective layer is promoted, amorphous formation is promoted, and the direction is low linear velocity.

As a concrete application example of the present invention, recording is possible.
A compact disc (CD-E) that can be used is mentioned. C
In D-E, V_L= 1.2 to 1.4 m / s, which is 1 time
It would be desirable if we could record and reproduce at all speeds and 2, 4, and 6x speeds.
Good The usage of CD-E is publicly announced.
Not, but now on the market, Wright
Once type recordable CD (CD-R, CD-Recrordabl
In e), it is possible to record at a wide linear velocity of 1-6 times speed.
It is said to be desirable. In this case, the preferred pulse division
As a method, first, as a mark length modulation method, m = n,
Adopt EFM modulation of n-1 or n-2,
V_L2V_L4V_LOr 6V_LTake a finite number of
Let's get it. Linear velocity 2V_LAbove α_1h= 1.5
Or 1.0, β_1h= Α_ih= 0.5 (2 ≦ i ≦ m),
And at all linear velocities, α _i+ Β_i-1= 1.0 (2
≦ i ≦ m). Furthermore, linear velocity 2V_LThen Pb_i=
Pr ± 0.5 mW (1 ≦ i ≦ m, Pr is the reproduction light power),
Linear velocity V_h= 4V_LOr 6V_LAt Pb_i= Pe ± 0.
5mW (1 ≦ i ≦ m), linear velocity V_LAt 0.05
<Α_i<0.5 (2 ≦ i ≦ m) and α_1L≤ α_1hWill be
The recording pulse division method is changed according to the linear velocity.
However, β_m≠ 0.5 (may be 0). Sanawa
The off pulse period at the end of each mark is off within the mark.
The time period can be different from the pulse period. do this
By doing so, various drive devices that record at various linear velocities
However, one type of medium can be used.

As a CD-E recording medium suitable for the above optical recording method, more specifically, at least a lower dielectric protective layer, {(GeTe) _y (Sb ₂ Te ₃ ) _1-y } _1- , is formed on a substrate. _x Sb
_x (0 ≦ x <0.1, 0.2 <y <0.9) a recording layer, an upper dielectric protection layer, and a metal reflection layer are sequentially provided, and the recording layer has a film thickness of 15 to 30 nm. Protective layer thickness is 10-
A phase change medium having a thickness of 30 nm can be used. Alternatively, this recording layer may be formed as M _y (Te _1-x Sb _x ) _1-y (0 ≦ y <0.3,
0.5 <x <0.9, M = In, Ga, Zn, Ge, Sn,
Si, Co, Cr, Cu, Ag, Au, Pd, Pt, S, Se,
At least one of O) may be substituted. Japanese Patent Laid-Open No. Hei 4
JP-A-212735 and JP-A-5-62193 are prior applications for a method relating to a phase-change recording medium using a GeSbTe recording layer rewritable especially at a CD linear velocity, and recording by dividing a recording pulse by a long mark. The method is shown. However, there is no suggestion of the pulse division method at the double speed 2V _{L, and} there is no mention of the problem of linear velocity dependence that occurs when recording at the speeds of 2, 4, and 6 times. Further, there is no disclosure about a method of overcoming the linear velocity dependence by changing the recording pulse division method according to a certain law. JP-A-7-372
Publication No. 51, and conference presentations by the inventors (Intern
ational symposium on Optical Memory, 1995, Knana
Sawa, Japan, No. P-33) exemplifies a CD-E medium using an AgInSbTe recording layer and a recording method thereof. However, again, there is no disclosure about the linear velocity dependence problem and its solution.

In the above example, the minimum linear velocity V _L is 1.2.
For mark length modulation recording in the range of up to 1.4 m / S, m is selected as m = n, n-1 or n-2, and the linear velocity V
There _{V = V L, 2V L,} 4V L, or chosen shall take also a finite number of values of 6V _L, in the each linear velocity V, i is 2
In the range of ≦ i ≦ m, α _i + β _i = 1.0, and i
In the range of 1 ≦ i ≦ m, Pb _i = Pr ± 0.5 mW,
When the linear velocity V decreases, α _i can be monotonically decreased for all i. In this case, β _m ≠ 0 is preferable from the viewpoint of tracking servo.

Another effective use of the present invention is to eliminate the linear velocity dependence caused by the difference in linear velocity between the inner and outer circumferences of the phase change type disk rotating at a constant angular velocity (CAV). . That is, in a medium having a large radius such that the inner and outer radii of the recording area are double or more, the linear velocity difference is double or more on the inner and outer circumferences.
It is difficult to change the recording layer composition and the layer structure on the inner and outer circumferences in order to overcome the linear velocity dependence, because it requires special measures during manufacturing. Therefore, by changing the recording pulse division method according to the present invention according to the linear velocities of the inner and outer circumferences, it is possible to record information on the entire surface of the disk without any inconvenience even on a medium which is uniform in the radial direction. The change of the recording pulse division method depending on the radial position is, for example, a normal ZCAV.
In the case of the (Zoned CAV) type medium, it may be performed in conjunction with the switching of the reference clock cycle at the radial position.

In order to use the optical recording method of the present invention more easily and effectively, information on pulse division is recorded beforehand on the disk to be used, for example, pit information of irregularities. The pulse division information is, for example, the parameter (Pw,
It is preferable that the combination of variable ones of Pe, Pb, m, j, k, α _i , β _i ) is changed according to the linear velocity to be used. This description is V _L ≤
For linear velocities V in the range of V ≦ V _h , the division method is described only for the linear velocities at V _L and V _h, and V in between.
For, it is possible to interpolate and use the parameters for V _L and V _h . Further, in the above CD-E, the information regarding the pulse division may be recorded in advance on the substrate by frequency modulation of the meandering groove in the lead-in area. The disk drive reads the pulse division method written on the disk in advance, and automatically implements a pulse division scheme in which recording is performed at a specified pulse division method and linear velocity. By adopting such a disk drive device, although the linear velocity dependence is different from each other,
Even when a plurality of phase change media having the same recording information format coexist in the market, the compatibility can be maintained. That is, according to the present invention, when recording is performed on a specific phase change medium by a disk drive device that adopts only a specific fixed pulse division method, recrystallization occurs and a normal mark is not recorded. Can solve the problem.

As described above, according to the present invention, by changing the pulse division method according to the linear velocity, even if recording is performed under the condition that the linear velocity is greatly different, for example, in the linear velocity range of V _h ≧ 2V _L , It becomes possible to create a good temperature distribution on the disc, suppress recrystallization at low linear velocity, unerased residue at high linear velocity, etc.
It can be used in a wide range of linear velocities that were previously impossible.

Examples of embodiments (examples) of the present invention will be shown below, but the present invention is not limited to the following examples. In the following examples and comparative examples, recording (1 beam overwriting) was performed using an optical disk drive tester manufactured by Pulstec Co., Ltd. equipped with a laser diode of 680 nm and an optical lens of NA = 0.60. The reproducing light power Pr was 1.0 mW and was constant regardless of the linear velocity. Also,
The clock cycle T is assumed to be inversely proportional to the linear velocity, and 1.4
When recording at m / s, T = 143 nsec (7 MHz),
It was selected so that T = 20.0 nsec at 10 m / s.

[Example 1, Comparative Examples 1 and 2] As Example 1, (ZnS) ₈₀ (Si
O ₂ ) ₂₀ [mol%] layer 100 nm, Ge _22.2 Sb _22.2 Te
_55.6 [at%] layer is 25 nm, (ZnS) ₈₀ (SiO ₂ ) ₂₀
A disk was prepared by sequentially stacking a [mol%] layer with a thickness of 20 nm and an Al alloy layer with a thickness of 100 nm by a magnetron sputtering method, and further providing an ultraviolet curable resin thereon to a thickness of 4 μm. First, 3T / 9T / 7T / 9T / 11
The evaluation was performed using a repeating pattern including a T / 9T pattern (the underlined portion corresponds to the mark and the non-underlined portion corresponds to the mark). After overwriting several times under appropriate conditions, the mark length was detected by slicing at the center level of the peak crest value of the 11T / 9T signal amplitude in the reproduced signal. A time interval analyzer (TIA, manufactured by Hewlett-Packard, E1725A) and a simple method (Jp
nJApp l. Phys., Vol. 31 (1992), 584-589 pp etc. was used.

At a linear velocity of 10 m / s, a pattern as shown in FIG. 9A, that is, m = n-j, j = 0 (P
Since e = Pb, the same holds true for j = 0.2), α ₁ = 1.
5, the pulse division method with β ₁ = 0.5 and α _i = β _i = 0.5 (i ≧ 2) was used (for example, Proc.Int.Symp.on Opt
ical Memory, 1991, 291-296 pp). Pw = 12.0m
W and Pe = 4.0 mW overwrite, and
A good reproduced waveform like the oscillograph shown in (a) was obtained. Similarly, when the clock period was adjusted according to the linear velocity and appropriate Pw and Pe were selected to attempt overwriting in the range of up to 20 m / s, good recording waveforms were all obtained. Further, good mark length jitter of less than 10% of T was obtained at mark lengths of 3T, 7T and 11T.

As Comparative Example 1, an attempt was made to overwrite at 1.4 m / s by adjusting only the clock cycle T without changing the pulse division pattern at the linear velocity with the same configuration. In this case, 7 for any combination of Pw and Pe
Recording of T and 11T marks was impossible. Figure 10
An example (relatively better example) of the waveform is shown in (b).
It is considered that when the mark length was long, the first half of the mark was recrystallized due to the residual heat during the recording of the second half of the mark, and the amorphous mark could not be recorded. Further, as Comparative Example 2, in order to optimize for 1.4 m / s, the composition of the recording layer was made to be Sb rich, Ge ₂₃ Sb ₂₈ Te _49, and the amorphous marks were sufficiently formed. Although formed, the crystallization speed was slow, so that the erasing ratio of the amorphous mark was insufficient at 10 m / s, which was not suitable for overwriting.

Therefore, the most difficult case is 10-
High linear velocity medium used at 20 m / s, even at 1.4 m / s
In order to perform good recording, according to the gist of the present invention,
We tried to optimize the pulse division method. [Example 2] Optimized for a linear velocity of 10-20 m / s
Repeat the above with a disc at a linear velocity of 1.4 m / s.
An attempt was made to overwrite with a mark length pattern. m =
n, j = 0.2, Pe = 4 mW, and Pb is Pb = Pb_i=
It is kept constant at 0.2 mW and for forming the nT mark.
The width Tp of the n divided recording pulses is Tp = α _iConstant with T
Then, the recording power Pw is made variable. This pulse pattern
Is shown in FIG. When Tp ≧ 50 nsec,
It does not become amorphous, but the detection of mark edge by TIA
I couldn't. 11A and 11B respectively show T
Mark length and mark length jitter when p is further shortened
Pt dependence of each nT mark (3T, 7T, 11T)
About. Tp = less than 30 nsec (that is, 0.2
(Less than 1T), Pw = 14 to 17 mW
A proper mark length corresponding to the recording mark nT, and 0.
A good jitter of less than 1T was selected. Note that Tp = 1
In 2 nsec (0.084T), Pw> 16 as Pw
mW or more is required, and the above tester lacks sensitivity.
It was

[0040] In this example, beta _i, except beta _n is all equal, it is adjusted only beta _n such that j = 0.2. Example 3 Tp = 20 nsec (α _i = 0.14),
Under the conditions of m = n, j = 0.2, Pe = 4.0 mW, Pb
And Pw were made variable. 12A and 12B show the dependence of the mark length and the mark length jitter on Pw and Pb, respectively, as in FIGS. 11A and 11B. If Pb is smaller than about 1 mW, then Pw = 14 to 17 mW, which is almost 0.
A good jitter of 1T or less was obtained. Note that 0 <Pb
<Pr does not affect the tracking servo or the like. Even if Pb = 0.2 mW and Pb is made lower than Pr, the tracking servo cannot be lost within this time.

From Examples 2 and 3, 1.4 m / s to 20 m
It has been found that when used in a wide range of linear velocities such as / s, particularly when the linear velocity is low, a combination of reducing α _i and reducing Pb gives good results. Example 4 Tp = 20 nsec (α _i = 0.14)
T), Pb = 0.2 mW, Pe = 4 mW, m = n
Alternatively, the dependence of the mark length and mark length jitter on Pw and j when m = n−1 is shown in FIG. 13 (when m = n) and FIG. 14 (when m = n−1), respectively. The mark length strongly depends on n−j = Σ (α _i + β _i ). m = n,
And m = n−1, j = 0.2 to 0.
It can be seen that the optimum point exists in the range of 7. m = n-1
In the case of, it is preferable that m is constant and only n−j and α _i are changed according to the linear velocity in the range of 1.4 m / s to 20 m / s. This is because it is preferable for the pulse control circuit from the viewpoint of the circuit configuration that it can be kept constant as compared with the case where m changes according to the linear velocity. Also, n =
Good results have been obtained with repetitive patterns containing mark lengths of 3, 7 and 11, so that patterns containing all mark lengths from n = 3 to 11 are adopted, for example in a compact disc (CD). This means that the EFM modulation method used allows overwriting in a wide range of linear velocities. However, 3T, which is the shortest mark length at T = 143 nsec, corresponds to 0.6 μm, which is higher in density than the current CD. However, even if this is 0.8 to 0.9 μm, which is the same as the current CD, if a slight optimization of the pulse width and the like is performed, overwriting can be performed in a wide range of linear velocities as well. On the other hand, the shortest mark length becomes smaller,
For example, the same applies to mark length modulation recording on a digital video disc. Rather, the shorter mark length
Since recrystallization is less likely to occur, the problem regarding linear velocity dependence is reduced. Even in such a high-density recording medium,
The pulse division method of the present invention is applicable.

[Embodiment 5] 10 m / s and 1.4 m / s
At an intermediate linear velocity between and, the phase change medium is overwritten with the repeating pattern, and as an example,
Recording was performed at 2.8 m / s. As a result, Tp
= 15-20 nanoseconds, j = 0.2, m = n, Pe = 4m
In the pulse division pattern with W and Pb = 0.2 mW, when Pw = about 15 mW or more, an appropriate mark length and 0.
A good jitter of 1T or less was obtained. Therefore, for the medium of this embodiment, at least the CD linear velocity of 1-
The same pattern can be applied at double speed. on the other hand,
At 5.6 m / s, which is about 4 times the CD linear velocity, m
= N-1, j = 0.0, Pb = Pe, Tp = 20nsec
When Pw = 16 mW and Pe = 4 mW,
A good jitter of 1T or less was obtained.

[Embodiment 6] The present invention can be applied to the case where the pulse length modulation method is different between the high linear velocity and the low linear velocity. In the sixth embodiment, in the range of 10-20 m / s,
Used in computer peripherals and optical recording media, n =
(1, 7) RLL (run- consisting of mark length from 2 to 8)
Attempts were made to overwrite by using EFM modulation at 1.4 m / s using a length-limited) code.
In this case, if the clock cycle T is constant, the mark edge detection circuit becomes easier. However, it does not necessarily have to be an exact match. The physical shortest mark length is the lower limit of the linear density determined by the physical characteristics of the medium, so it is better to keep it constant. Therefore, it is effective to change the clock cycle so that both the shortest mark 2T in the (1 and 7) modulation and the 3T mark in the EFM modulation are 0.6 μm. The linear velocity of 10 m is shown in each of FIGS.
The eye patterns at / s (EFM modulation), 5.6 m / s (EFM modulation), and 1.4 m / s (1-7 modulation) are shown. As shown in the figure, a good waveform was obtained at each linear velocity, and the mark length jitter was less than 0.1 T even at the shortest mark.

[Embodiment 7] As a recording medium, an alloy thin film of AgInSbTe was used for the recording layer, and a layer structure similar to that of Example 1 was prepared. For recording, the wavelength is 78
A 0 nm semiconductor laser and an optical lens with NA = 0.55 were used. At the CD double linear velocity of 4.8 m / s, the pulse division method shown in FIG.
When recording was performed with a pattern of w = 12 mW, Pe = 6 mW, Pb = Pr = 0.8 mW, a good eye pattern was obtained. That is, the jitter of each mark was less than 10% of the clock cycle. When this medium was recorded at the CD1 speed by doubling the clock cycle using the same pulse division method, recrystallization was remarkable and a good eye pattern could not be selected. However, α _i is 0.33 (2 ≦ i ≦ m, α ₁ is not changed at 1.0), Pw = 11 mw, Pe = 5 mW,
When Pb = Pr = 0.8 mW, a good eye pattern was obtained.

[0045]

By using the recording system of the present invention,
Without changing the material of the medium, the linear velocity margin of the medium,
In particular, the margin on the low linear velocity side can be widened, and overwrite recording can be performed in a wide linear velocity range. Also,
Although the recording data format is compatible, it is possible to support various drives with different linear velocities at the time of recording with the same medium, and there is no need to optimize for each linear velocity. It can be resolved.

[Brief description of drawings]

FIG. 1 is a graph showing the reflection characteristics of a conventional amorphous mark.

FIG. 2 is a schematic plan view showing the structure of the amorphous mark of FIG.

FIG. 3 is a waveform diagram illustrating a pulse pattern in a mark length modulation method for recording an nT mark.

FIG. 4 is a waveform diagram illustrating a pulse pattern in mark length modulation adopted in the present invention.

5A and 5B are waveform diagrams illustrating pulse patterns for recording a 4T mark, respectively.

6A and 6B are waveform diagrams illustrating pulse patterns when the pulse application period is changed, respectively.

FIG. 7 is a waveform diagram illustrating a pulse pattern adopted in the embodiment of the present invention.

FIG. 8 is a sectional view showing the layer structure of a recording medium adopted in the present invention.

9A and 9B are waveform diagrams of pulse patterns used in the embodiments of the present invention.

10A and 10B are oscillograph photographs showing reproduced waveforms of Example 1 and Comparative Example 1, respectively.

11A and 11B are graphs showing the recording power dependence of the mark length and the jitter in Example 2, respectively.

12A and 12B are graphs similar to FIGS. 11A and 11B in Example 3, respectively.

13A and 13B are graphs similar to FIGS. 11A and 11B in Example 4, respectively.

FIGS. 14A and 14B are diagrams similar to FIG. 13 when m = n and m = n−1 in the fourth embodiment, respectively.

15A to 15C are respectively EFM modulation or
An oscillograph photograph showing the reconstructed eye pattern for 1-7 modulation.

FIG. 16 is a waveform chart showing a pattern of a recording waveform in Example 7.

[Explanation of symbols]

1 substrate 2 Lower protective layer 3 recording layers 4 Upper protective layer 5 Reflective layer 6 protective layer

Continued front page    (72) Inventor Natsuko Nobukuni             1000 Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa             Mitsubishi Chemical Corporation Yokohama Research Institute (72) Inventor Totsuka Horie             1000 Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa             Mitsubishi Chemical Corporation Yokohama Research Institute F term (reference) 5D090 AA01 BB05 CC01 KK05

Claims (7)

[Claims] 1. The laser power of irradiation light is a clock cycle
According to T, the recording power Pw, the erasing power Pe, and the
As power Pb (however, Pb / Pe ≦ 0.25
It ) Between the optical information recording medium
Shapes of Amorphous Marks of Different Lengths that are Biologically Distinct
Data is recorded or erased, and data is recorded by the mark length modulation recording method.
In the optical recording method of recording and erasing, Length nT (where n is an integer greater than or equal to 2 and a possible value of n)
The minimum and maximum values of n_min, N_maxAnd ) Have
In forming the amorphous mark, Period of applying recording power Pw having a constant intensity in each period
Between α₁T, α₂T, ..., α_mT and bias power
The period for applying the power Pb is β₁T, β₂T, ..., β_mT
As the laser power application period₁T, β
₁T, α₂T, β₂T, ..., α_mT, β_mLet T
However, k is an integer of 0 or more, j is a real number from 0 to 2, and
m = n−k, n_min−k ≧ 1, α₁+ Β₁＋ ・ ・ ・ ＋ α_m+
β_m= N-j. ) By applying the recording power Pw
The irradiation period is divided into m pulses for irradiation.
hand, The linear velocity V when irradiating the recording medium with the irradiation light is the maximum line
Speed V_hAnd minimum linear velocity V_LAs V_L≦ V ≦ V_h(V_h
≧ 2V_L) Variable, The clock cycle T is made variable according to the change of the linear velocity V, i is an integer of 1 ≦ i ≦ m, and the divided individual records are
The application period width of the recording power Pw is α_iT, individual bias power
Application period width β_iT, linear velocity V is V_L, V₁, V₂, V
_hΑ when_iΑ respectively_iL, Α_i1, Α_i2, Α_ihAnd then the line
Speed V_hΒ in_iΒ_ihWhen For all i above, α_i+ Β_iIs independent of linear velocity
Constant, V_L<V₁<V ₂<V_hThen α_iL≤ α_i1≤ α_i2≤
α_ih, And α_iL<Α_ihage, Furthermore, α_ih= Β_ihAnd the linear velocity V is V_L≦ V <V_hof
In the range, when i satisfies 2 ≦ i ≦ m, 0.05 (α
_i+ Β_i) <Α_i<0.5 (α_i+ Β_i) With
Optical recording method. 2. The bias power Pb _{i at} β _i T is Pb _i = Pr ± 0.5 mW, where Pr is the reproduction light power in the range of i ≦ 1 ≦ i ≦ m. Item 2. The optical recording method according to Item 1. 3. β _i for i in the range of 1 ≦ i <m−1
Is a constant value, and β _m is different from the constant value,
The optical recording method according to claim 1, wherein the optical recording method can be 0. 4. Pw, Pe, Pb, m, j, k, α _i and β so that the optical information recording medium selects one of a plurality of pulse division methods according to the linear velocity V used. _4. The optical recording method according to claim 1, wherein the optical recording method is a medium in which a combination of variable ones of _i is recorded as pulse division information. 5. An optical information recording medium used in the optical recording method according to any one of claims 1 to 3, wherein one is selected from a plurality of pulse division methods according to a linear velocity V used. As described above, the optical information recording medium is characterized in that a combination of variable ones among Pw, Pe, Pb, m, j, k, α _i and β _i is recorded as pulse division information. 6. The optical information recording medium according to claim 5, wherein the pulse division information is recorded as uneven pit information. 7. The optical information recording medium according to claim 5, wherein the pulse division information is recorded by frequency modulation of the meandering groove.