JP2006018982A - Recording method and recording apparatus for phase change information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably form a minute amorphous mark on a phase change information recording medium, particularly a multilayer type phase change information recording medium, and to perform multi-valued recording of three or more values satisfactorily. Providing method and recording device thereof.
Recording power (Pw) light is applied to an information layer having a phase change recording layer in which information is recorded by causing a phase change between a crystalline state and an amorphous state by incidence of light. In the method of recording information by forming several types of amorphous marks with different areas by irradiation with repetition of light and cooling power (Pb) light, and forming crystal spaces by irradiation with erasing power (Pe) light (however, Pw>Pe> Pb), when forming at least one kind of amorphous mark, cooling adjustment power (Pm) light having a power level of Pw>Pm> Pb between the recording power light and the cooling power light For recording information on a phase change information recording medium.
[Selection] Figure 10

Description

  The present invention allows a laser beam to be incident on a rewritable phase change information recording medium, particularly a multilayer phase change information recording medium in which information layers are multilayered, to form a multi-value recording mark having three or more values in a recording cell. The present invention relates to a multilevel recording method and a recording apparatus for the same.

A phase change type optical disc (phase change type information recording medium) such as a CD-RW is generally provided with a recording layer made of a phase change type material on a plastic substrate, on which a light absorption rate of the recording layer is improved. In addition, a structure in which a reflective layer having a thermal diffusion effect is formed is a basic structure, and laser light is incident from the substrate surface side to record and reproduce information.
Phase change materials change between a crystalline state and an amorphous state by heating with laser light irradiation and subsequent cooling, become amorphous when rapidly cooled after rapid heating, and crystallize when cooled slowly. A phase change type information recording medium is one in which an optical change between crystal and amorphous is applied to information recording and reproduction. That is, the phase change type information recording medium changes the disk reflectivity by changing the recording layer material between crystal and amorphous by irradiating the phase change recording layer on the substrate with laser light and heating it. Is recorded / reproduced. Usually, information recording is performed by setting a non-recorded state as a high-reflectance crystal phase and forming a space made of a low-reflectance amorphous mark and a high-reflectance crystal part.
In order to prevent oxidation, transpiration or deformation of the recording layer caused by heating due to light irradiation, usually a lower protective layer (also referred to as a lower dielectric layer) is provided between the substrate and the recording layer, and between the recording layer and the reflective layer. An upper protective layer (also referred to as an upper dielectric layer) is provided. Furthermore, these protective layers have a function of adjusting the optical characteristics of the recording medium by adjusting the thickness thereof, and the lower protective layer softens the substrate by heat during recording on the recording layer. It also has a function to prevent this.

Next, the recording principle of the phase change information recording medium will be described in a little more detail.
Since the phase change information recording medium uses a complicated mechanism of “rapid cooling” and “slow cooling”, mark formation is performed by irradiating the recording laser that is pulse-divided and intensity-modulated into three values. . As a waveform light emission pattern (recording strategy) for repeatedly recording data consisting of marks and spaces, there is one used in DVD + RW as shown in FIG. The amorphous mark is formed by pulse irradiation by alternately repeating the recording power (Pw) light and the cooling power (Pb) light, and the space made of the crystal continuously emits these intermediate level erasing power (Pe) light. It is formed by irradiating. That is, it is possible to perform direct overwriting by erasing old data with one beam spot and simultaneously recording new data.
When a pulse train composed of recording power light and cooling power light is irradiated, the recording layer repeats melting and quenching to form amorphous marks. When the erasing power light is irradiated, the recording layer is melted and then slowly cooled or annealed in a solid state to crystallize to form a space. A pulse train composed of recording power light and cooling power light is usually divided into a head pulse, an intermediate pulse, and a last pulse, and the shortest 3T mark (T: basic clock period) is recorded only by the head pulse and the last pulse, and a 4T mark. An intermediate pulse is also used when forming the above marks. The intermediate pulse is also called a multi-pulse, and is provided in a 1T cycle, and the number of pulses is increased by one every time the mark length becomes 1T longer. That is, the number of pulse trains is (n-1) with respect to the length nT.

In recent years, the amount of information handled by computers and the like has increased, the capacity of hard disks has increased, and the recording capacity of CD and DVD optical recording media has become insufficient. The current recording capacity of CDs is about 650 MB, and DVDs are about 4.7 GB. However, technical development for further higher recording density and larger capacity will be required in the future.
As a method for increasing the recording density of such a phase change information recording medium, for example, the laser wavelength used is shortened to the blue light region, or the numerical aperture NA of an objective lens used for a pickup for recording / reproducing is set. It has been proposed to increase the size of the laser beam so that the spot size of the laser beam applied to the optical recording medium is reduced.
Separately from this, a multi-value recording method has been attracting attention as a technique that enables high-density and high-speed recording media. For example, in Non-Patent Document 1, the occupation ratio of the amorphous recording mark with respect to the peripheral crystal portion is noted. A method for recording multilevel information and achieving a recording capacity of 20 GB or more has been proposed.

Hereinafter, this multi-value recording technique will be described.
FIG. 2 shows the relationship between the mark occupation ratio and the Rf signal. The recording mark is virtually located at the center of each cell divided in the track direction. The same relationship applies to phase pits in which recording marks are recorded as rewritable phase change materials or asperities on the substrate. In the case of a phase pit in which the recording mark is recorded as an uneven shape of the substrate, the optical groove depth of the phase pit is λ / 4 (λ is the wavelength of the recording / reproducing laser) so that the signal gain of the Rf signal is maximized. Need to be. The Rf signal value is given as a value when the recording / reproducing focused beam is located at the center of the cell, and changes depending on the occupation ratio of the recording mark in one cell. In general, the Rf signal value is maximum when no recording mark exists, and is minimum when the occupation ratio of the recording mark is the highest.
For example, when multi-value recording is performed with the number of recording mark patterns (number of multi-value levels) = 6 by such an area modulation method, the Rf signal value from each recording mark pattern shows a distribution as shown in FIG. The Rf signal value is represented by a numerical value normalized with the width (dynamic range DR) of the maximum value and the minimum value being 1. Recording / reproduction is performed using an optical system with λ = 650 nm and NA = 0.65 (condensed beam diameter = about 0.8 μm), and the circumferential length of the cell (hereinafter referred to as cell length) is about 0. .6 μm. Such a multi-valued recording mark can be formed by laser modulation using a recording strategy as shown in FIG. 4 with the powers of Pw, Pe, and Pb and their start times as parameters.

  In the multi-value recording method as described above, when the recording linear density is increased (= the cell length in the track direction is shortened), the cell length gradually becomes shorter with respect to the focused beam diameter. When the cell to be reproduced is reproduced, the focused beam protrudes to the cells before and after the target cell. For this reason, even if the mark occupancy of the target cell is the same, the Rf signal value reproduced from the target cell is affected by the combination of the mark occupancy of the preceding and subsequent cells. That is, intersymbol interference with the preceding and following marks occurs. Due to this influence, as shown in FIG. 3, the Rf signal value in each pattern has a distribution with a deviation. In order to determine without error which recording mark pattern is the target cell, the interval between the Rf signal values reproduced from each recording mark needs to be more than the deviation. In the case of FIG. 3, the intervals and deviations of the Rf signal values of the recording marks are almost the same, which is a limit for determining the recording mark pattern.

As a technique for overcoming this limitation, a multi-value determination technique DDPR using three consecutive data cells has been proposed (Non-Patent Document 1). This technique learns a multi-value signal distribution composed of a combination pattern of three consecutive data cells (8 ³ = 512 patterns at the time of 8-value recording), creates a pattern table thereof, and a reproduction signal result of unknown data After predicting three consecutive mark patterns from the above, the step of referring to the pattern table for multi-value determination of unknown signals to be reproduced is included. This makes it possible to reduce the error rate of multilevel signal determination even in the conventional cell density or SDR value that causes intersymbol interference during reproduction. Here, the SDR value is the ratio between the average value of the standard deviation σ _i of each multi-value signal when the number of multi-value gradations is n and the dynamic range DR of the multi-value Rf signal, that is, Σσ _i / ( n × DR), which is signal quality corresponding to jitter in binary recording. In general, if the number n of multi-value gradations is constant, the SDR value becomes smaller as the standard deviation σ _i of the multi-value signal is smaller and the dynamic range DR is larger, so that the separability of the multi-value signal is improved and the error rate is improved. Becomes lower. On the contrary, when the multi-value gradation number n is increased, the SDR value is increased and the error rate is increased.
When such a multi-level determination technique is used, for example, even when the multi-level gradation number is increased to 8 and the distributions of the respective Rf signal values overlap, the error rate 10E-5 (10 ^{− 5} ) Multi-valued determination of 8 values can be made on the stand.

As a method for improving the recording capacity by improving the recording medium itself, two layers having a structure in which at least two information layers including a recording layer and a reflective layer are stacked on one side of a substrate and these information layers are bonded with an ultraviolet curable resin or the like. Phase change information recording media have been proposed in, for example, Patent Documents 1 to 5 and the like.
The separation layer (referred to as an intermediate layer in the present invention), which is an adhesion portion between the information layers, has a function of optically separating the two information layers, and the information layer on the back side has as much recording / reproducing laser light as possible. Therefore, it is made of a material that does not absorb laser light as much as possible.
The two-layer phase change information recording medium has been announced at academic societies as disclosed in Non-Patent Document 2, for example, but still has many problems.
For example, if the laser beam is not sufficiently transmitted through the information layer (first information layer) on the near side when viewed from the laser beam irradiation side, information is recorded on the recording layer of the information layer (second information layer) on the back side. Since recording and reproduction cannot be performed, it is conceivable that the reflective layer constituting the first information layer is eliminated or made extremely thin, or the recording layer constituting the first information layer is made extremely thin.
Recording with a phase change information recording medium is performed by irradiating a laser beam to the phase change material of the recording layer and quenching it to change the crystal to amorphous to form a mark. If it is very thin, such as about 10 nm, the thermal diffusion effect is reduced and it becomes difficult to form an amorphous mark.

Regarding the recording strategy of the first information layer, there are the following proposed examples.
First, in Patent Document 8, for a mark of 4T or more, a time for holding at a low power level about the cooling power is provided before the first pulse of the pulse train forming the mark. Specifically, when the period of irradiation with the high power of the leading pulse and the period of holding at the low power level are yT and xT, respectively, the relationship of 0.95 ≦ xT + 0.7 × yT ≦ 2.5 is satisfied, Furthermore, the period of the subsequent pulse is set to be 0.5T or more and 1.5T or less. Further, in Patent Document 9, the cooling time of the recording layer of the first information layer is made sharp by controlling the power holding time and power level of Pw and Pb of the pulse train forming the mark, and the amorphous mark is stably formed. It has been proposed to do. Moreover, in patent document 10, the head pulse and / or the last pulse are set to a level lower than the multi-pulse.
However, Patent Document 8 is a recording method for forming a comparatively long mark of 4T mark or more, and does not suggest any problem related to formation of a minute mark such as multi-value recording. Further, Patent Document 10 is effective for forming a relatively long mark provided with two or more pulse trains of Pw and Pe, but when forming a minute mark such as multi-value recording, it is usually shown in FIG. Thus, since there is only one pulse train, this technique is not suitable for multilevel recording.
Further, as shown in Patent Document 9, a method for forming a mark by shortening the Pw level pulse width or increasing the Pb level pulse width to make the recording layer cool down rapidly is binary. Although effective in recording, when the cell length is 0.25 μm and eight values are recorded with the strategy shown in FIG. 4, the mark shape is modulated into eight values only by adjusting the levels of Pw and Pe and the holding time. It was difficult. In particular, when the retention time of Pe is increased, recrystallization is suppressed and it is easy to form an amorphous mark. However, if the retention time is too long, a large amorphous mark is formed, which protrudes from the cell. It has been found that intersymbol interference increases.

The inventors used an optical disk evaluation apparatus DDU-1000 (manufactured by Pulstec Industrial Co., Ltd.) having a laser wavelength of 405 nm and NA = 0.65 for the first information layer of the two-layer phase change optical information recording medium. Multi-value recording with a basic cell = 0.24 μm, a linear velocity of 6.0 m / s, and a multi-value level number = 8 was performed. The recording strategy is set as shown in FIG. 8 for multi-value data mi (i = 0, 1,..., 7). This is a conventional recording strategy, and is set so that reflectance modulation is performed by changing the pulse width of Pb according to multi-value data.
FIG. 9 shows a reproduction signal waveform when recording is performed with Pw = 14 mW, Pe = 6 mW, and Pb = 0.1 mW using this recording strategy. The recorded data pattern is a repetition of four consecutive level 0s and one non-zero level. When the recording strategy as shown in FIG. 8 is used for the conventional single-layer phase-change optical information recording medium, as shown in FIG. 3, according to the multilevel levels 0, 1, 2, 3,. Although the reflected light intensity gradually decreased and good multilevel modulation could be performed, when a conventional recording strategy was used for a multilayer optical information recording medium, modulation could not be performed well in multiple stages as shown in FIG. . In addition to the recording strategy shown in FIG. 8, the Pw level and the Pw pulse width were changed, and similar results were obtained.

Japanese Patent No. 2702905 JP 2000-215516 A JP 2000-222777 A JP 2001-243655 A JP 2000-322770 A JP 2002-144736 JP 2002-367222 A JP 2001-273638 A JP 2003-178448 A Japanese Patent Laid-Open No. 2003-257025 International Symposium on Optical Memory 2001 Technical Digest P27 ODS2001 Technical Digest P22

  The present invention was devised in view of the above problems of the prior art, and can stably form a minute amorphous mark in a phase change information recording medium, particularly a multilayer type phase change information recording medium. It is an object of the present invention to provide a recording method and a recording apparatus that can satisfactorily perform multi-value recording of three or more values.

As a result of intensive studies in order to solve the above-mentioned problems, the present inventors have found the following solution means. That is, the above-mentioned problems are solved by the following inventions 1) to 14) (hereinafter referred to as the present inventions 1 to 14).
1) Recording power (Pw) light and cooling for an information layer having a phase change recording layer in which information is recorded by causing a phase change between a crystalline state and an amorphous state by the incidence of light. In a method of recording information by forming several types of amorphous marks with different areas by irradiation with power (Pb) light and forming crystal spaces by irradiation with erasing power (Pe) light (where Pw>Pe> Pb) When at least one kind of amorphous mark is formed, cooling adjustment power (Pm) light having a power level of Pw>Pm> Pb is irradiated between the recording power light and the cooling power light. And recording information on the phase change information recording medium.
2) The recording method according to 1), wherein multi-value data of three or more values is recorded as information by modulating the area of the amorphous mark in the recording cell.
3) The recording method according to 1) or 2), wherein Pe = Pm.
4) The recording method according to any one of 1) to 3), wherein the area of the amorphous mark is controlled by changing the irradiation time of the cooling adjustment power light.
5) The recording method according to any one of 1) to 4), wherein when the amorphous mark is formed, the irradiation time of the cooling adjustment power light is set longer for an amorphous mark having a smaller area. .
6) The phase change recording layer is mainly composed of a Sb—Te eutectic material, Ag, In, Ge, Se, Sn, Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Ga , Bi, Si, Dy, Pd, Pt, Au, S, B, C, and P. The recording method according to any one of 1) to 5), wherein the recording method includes:
7) Use a phase change information recording medium having a structure in which at least a lower protective layer, a phase change recording layer, an upper protective layer, a reflective layer, and a heat diffusion layer are stacked in this order or in reverse order on a substrate. The recording method according to any one of 1) to 6).
8) At least a first substrate, a first information layer, an intermediate layer, a second information layer, and a second substrate, wherein the first information layer is at least a first lower protective layer, a first recording layer, and a first upper protective layer. A phase change type information recording medium comprising a first reflective layer and a first thermal diffusion layer, wherein the second information layer comprises at least a second lower protective layer, a second recording layer, a second upper protective layer, and a second reflective layer 7) The recording method described in 7) above.
9) The recording method according to 7) or 8), wherein the heat diffusion layer uses a phase change information recording medium made of ITO (indium oxide + tin oxide) or IZO (indium oxide + zinc oxide).
10) The recording method according to any one of 7) to 9), wherein a phase change information recording medium having a thermal diffusion layer thickness of 10 to 200 nm is used.
11) Any one of 7) to 10), wherein the reflective layer uses a phase change information recording medium made of a material mainly composed of at least one of Au, Ag, Cu, W, Al, and Ta. The recording method described in 1.
12) The recording method according to any one of 8) to 11), wherein a phase change information recording medium having a thickness of the first reflective layer of 3 to 20 nm is used.
13) Using a multilayer phase change type information recording medium in which two or more information layers having a phase change type recording layer are provided via an intermediate layer, a phase change type arranged on the farthest side as viewed from the laser beam incident side The recording method according to any one of 1) to 12), wherein recording is performed on at least one phase change recording layer other than the recording layer.
14) A recording apparatus having a function of recording on a phase change information recording medium by the recording method according to any one of 1) to 13).

Hereinafter, the present invention will be described in detail with reference to the drawings.
In a phase change optical information recording medium applied to the recording method of the present invention, a lower protective layer, a recording layer, an upper protective layer, and a reflective layer are usually laminated on a substrate in this order or reverse order. In addition, there may be two or more recording layers in order to increase the capacity.
FIG. 6 is a schematic cross-sectional view showing an example of a phase change information recording medium having two recording layers. On the first substrate 3, a first information layer 1, an intermediate layer 4, a second information layer 2, It has a structure in which the second substrate 5 is sequentially laminated.
The first information layer 1 includes a first lower protective layer 11, a first recording layer 12, a first upper protective layer 13, a first reflective layer 14, and a first thermal diffusion layer 15, and the second information layer 2 includes 2 comprises a lower protective layer 21, a second recording layer 22, a second upper protective layer 23, and a second reflective layer 24. A barrier layer (not shown) may be provided between the first upper protective layer 13 and the first reflective layer 14 and / or between the second upper protective layer 23 and the second reflective layer 24. The first information layer and the second information layer of the optical information recording medium applied to the present invention are not limited to the above layer configuration.
FIG. 7 is a schematic sectional view showing another example of the phase change information recording medium having two recording layers, in which a transparent layer 6 is provided between the first substrate 3 and the first lower protective layer 11. Is. Such a transparent layer is provided when a thin sheet is used for the first substrate and the manufacturing method is different from that of the recording medium of FIG.

The first substrate needs to be made of a material that can sufficiently transmit the recording / reproducing light, but a material conventionally known in the technical field may be used.
As the material, glass, ceramics, resin and the like are usually used, and the resin is particularly preferable in terms of moldability and cost. Examples of the resin include polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicone resin, fluorine resin, ABS resin, and urethane resin. Acrylic resins such as polycarbonate resin and polymethyl methacrylate (PMMA), which are excellent in terms of moldability, optical characteristics, and cost, are preferable.
On the surface on which the information layer of the first substrate is formed, a concave / convex pattern, usually called a groove portion or a land portion, which is a spiral or concentric groove for tracking laser light, is formed as necessary. This is usually molded by an injection molding method or a photopolymer method.
Further, the thickness of the first substrate is preferably about 10 to 600 μm. More preferably, it is the range of 70-120 micrometers or 550-600 micrometers.
As the material of the second substrate, the same material as that of the first substrate can be used. However, a material opaque to the recording / reproducing light may be used, and the material and groove shape may be different from those of the first substrate. good.
The thickness of the second substrate is not particularly limited, but it is preferable to select the thickness of the second substrate so that the total thickness with the first substrate is 1.2 mm.
Similar to the first substrate, the second substrate may be formed with an uneven pattern such as a groove or a guide groove formed by injection molding or a photopolymer method.

The intermediate layer and the transparent layer preferably have smaller light absorption at the wavelength of the recording / reproducing light, and the material is preferably a resin in terms of moldability and cost, and is an ultraviolet curable resin, a slow-acting resin, a thermoplastic resin. Etc. can be used. Moreover, a double-sided adhesive tape for bonding optical disks (for example, an adhesive sheet DA-8320 manufactured by Nitto Denko Corporation) can be used.
Similar to the first substrate, an uneven pattern such as a groove or a guide groove formed by injection molding or a photopolymer method may be formed on the intermediate layer.
The intermediate layer is a layer that enables the pickup to discriminate between the first information layer and the second information layer and perform optical separation when recording / reproducing, and the thickness is preferably 10 to 70 μm. If the thickness is less than 10 μm, interlayer crosstalk occurs. If the thickness is more than 70 μm, spherical aberration occurs when recording / reproducing the second recording layer, and recording / reproduction tends to be difficult.
Although the thickness of the transparent layer is not particularly limited, the optical information recording medium having the optimum thickness of the first substrate of the optical information recording medium manufactured by the manufacturing method not provided with the transparent layer as shown in FIG. 6 and the optical information recording method different in the manufacturing method as shown in FIG. It is necessary to adjust the thicknesses of the first substrate and the transparent layer so that the total thickness of the first substrate and the transparent layer of the medium is approximately the same. For example, if NA = 0.85 and the first substrate of the optical information medium of FIG. 6 has a thickness of 75 μm and good recording and erasing performance is obtained, the first optical information medium of FIG. If the thickness of the substrate is 50 μm, the thickness of the transparent layer is preferably 25 μm.

The material of the first recording layer and the second recording layer is not particularly limited as long as it is a material that changes phase between crystal and amorphous by heating and cooling by light irradiation, and has been conventionally known in the technical field. The ones that apply are applied. For example, a thin film mainly containing a chalcogen alloy such as Ge—Te, Ge—Te—Sb, Ge—Sn—Te, and an Sb—Te eutectic material can be given. Here, the main component means that it accounts for 90 atomic% or more of the entire thin film material.
In view of recording (amorphization) sensitivity / speed and erasure ratio, it is preferable to use an Sb—Te eutectic material. Ag, In, Ge, Se, Sn, Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Ga, Bi, Si, Dy, Pd, for the purpose of further improving performance and reliability. Other elements and impurities such as Pt, Au, S, B, C, and P can be added.
Further, the Ge—Te compound material is preferable in that the transmittance is higher than that of the Sb—Te eutectic material and the crystal-amorphous contrast is large. However, since the crystallization speed is relatively slow, it is preferable to promote the crystallization by providing an interface layer adjacent to the recording layer. Ge-Te compound materials are also used for the purpose of further improving performance and reliability, such as Ag, In, Sb, Se, Sn, Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Ga, Bi. , Si, Dy, Pd, Pt, Au, S, B, C, P, and other elements and impurities can be added.

These recording layers can be formed by various vapor deposition methods such as vacuum deposition, sputtering, plasma CVD, photo CVD, ion plating, electron beam deposition, etc. Excellent film quality.
The thickness of the first recording layer is not particularly limited, but is preferably 3 to 10 nm. More preferably, it is the range of 3-8 nm. If it is less than 3 nm, it tends to be difficult to form a uniform film, and if it exceeds 10 nm, the transmittance tends to decrease.
The thickness of the second recording layer is not particularly limited, but is preferably 3 to 20 nm. More preferably, it is the range of 3-15 nm. If it is less than 3 nm, it tends to be difficult to form a uniform film, and if it exceeds 20 nm, the recording sensitivity tends to decrease, such being undesirable.

The first reflective layer and the second reflective layer have functions such as making efficient use of incident light, improving the cooling rate, and making it easy to become amorphous. For this reason, a metal having high thermal conductivity is usually used. For example, Au, Ag, Cu, W, Al, Ta, or an alloy thereof can be used. Alternatively, a material containing at least one of these elements as a main component and at least one element selected from Cr, Ti, Si, Pd, Ta, Nd, Zn and the like may be used. Here, the main component means that it accounts for 90 atomic% or more, preferably 95 atomic% or more of the entire reflective layer material.
In particular, the Ag-based material has a low refractive index even in the blue wavelength region, n is 0.5 or less, and light absorption can be suppressed to a low level. It is preferable as a material used for the reflective layer.
Such a reflective layer can be formed by various vapor phase growth methods such as vacuum deposition, sputtering, plasma CVD, photo CVD, ion plating, and electron beam deposition. Among these, the sputtering method is excellent in mass productivity and film quality.
Since the first information layer requires high transmittance, it is preferable to use Ag having a low refractive index and high thermal conductivity or an alloy thereof as the material of the first reflective layer. The thickness of the first reflective layer is preferably about 3 to 20 nm. More preferably, it is the range of 5-10 nm. If the thickness is less than 3 nm, it becomes difficult to form a dense film having a uniform thickness. If it is thicker than 20 nm, the transmittance is reduced, and recording / reproduction of the second information layer becomes difficult.
Further, the thickness of the second reflective layer constituting the second information layer is preferably 50 to 200 nm, more preferably 80 to 150 nm. If it is less than 50 nm, the repetitive recording characteristics are deteriorated, and if it is more than 200 nm, the sensitivity tends to be lowered.

The functions and materials of the first lower protective layer, the second lower protective layer, the first upper protective layer, and the second upper protective layer are the same as those of the single-layer phase change information recording medium. (2) Functions known to prevent deterioration and deterioration of the recording layer, increase adhesive strength, and increase recording characteristics, and conventionally known materials can be applied. Specific examples of materials include oxides such as SiO, SiO ₂ , ZnO, SnO ₂ , Al ₂ O ₃ , TiO ₂ , In ₂ O ₃ , MgO, and ZrO ₂ ; Si ₃ N ₄ , AlN, TiN, ZrN, and the like A nitride of ZnS, In ₂ S ₃ , TaS ₄ or the like; a carbide such as SiC, TaC, B ₄ C, WC, TiC, or ZrC; a diamond-like carbon; or a mixture thereof.
These materials can be used alone as a protective layer, but may also be a mixture of each other. Moreover, you may contain an impurity as needed. The melting point of the protective layer needs to be higher than that of the recording layer. Most preferred is a mixture of ZnS and SiO ₂ .
Such a protective layer can be formed by various vapor phase growth methods such as vacuum deposition, sputtering, plasma CVD, photo CVD, ion plating, and electron beam deposition. Among these, the sputtering method is excellent in mass productivity and film quality.
The thickness of the first lower protective layer and the second lower protective layer is preferably 30 to 200 nm. If the thickness is less than 30 nm, the first substrate or the intermediate layer may be deformed by heat at the time of recording, and if it is thicker than 200 nm, there is a tendency to cause a problem in mass productivity. Therefore, the film thickness is designed so as to obtain an optimum reflectance within the above range.
In addition, the thickness of the first upper protective layer and the second upper protective layer is preferably 3 to 40 nm. More preferably, it is the range of 6-20 nm. When the thickness is less than 3 nm, the recording sensitivity is lowered, and when it is thicker than 40 nm, the heat dissipation effect tends to be not obtained.

A barrier layer may be provided between the upper protective layer and the reflective layer. As described above, as the reflective layer, Ag alloy, as the protective layer, a mixture of ZnS and SiO ₂ is most preferred, if the two layers adjacent sulfur in the protective layer corrodes the Ag reflective layer There is a possibility that storage reliability may be reduced. In order to eliminate this problem, it is preferable to provide a barrier layer when an Ag-based material is used for the reflective layer. The barrier layer needs to contain no sulfur, have a higher melting point than the recording layer, and desirably has a low absorption rate at the laser wavelength. Specific examples include oxides such as SiO, ZnO, SnO ₂ , Al ₂ O ₃ , TiO ₂ , In ₂ O ₃ , MgO, and ZrO ₂ ; nitrides such as Si ₃ N ₄ , AlN, TiN, and ZrN; SiC , TaC, B ₄ C, WC, TiC, ZrC and other carbides; or a mixture thereof. Of these, SiC is preferable.
The barrier layer can be formed by various vapor deposition methods such as vacuum deposition, sputtering, plasma CVD, photo CVD, ion plating, and electron beam deposition. Among these, the sputtering method is excellent in mass productivity and film quality.
The thickness of the barrier layer is preferably 2 to 10 nm. More preferably, it is the range of 2-5 nm. When the thickness is less than 2 nm, the effect of preventing Ag corrosion cannot be obtained, and the storage reliability is lowered. If it is thicker than 10 nm, the heat dissipation effect cannot be obtained, or the transmittance tends to decrease.

As the first thermal diffusion layer, it is desired that the thermal conductivity is large in order to rapidly cool the recording layer irradiated with the laser. Further, it is desired that the absorption rate at the recording / reproducing laser wavelength is small so that the information layer on the back side can be recorded / reproduced. The extinction coefficient is preferably 0.5 or less, more preferably 0.3 or less, at the wavelength of the laser beam used for recording / reproducing information. If it is greater than 0.5, the absorptance in the first information layer increases, and recording / reproduction of the second information layer becomes difficult. The refractive index is preferably 1.6 or more at the wavelength of the laser beam used for recording / reproducing information. If it is smaller than this, it becomes difficult to increase the transmittance of the first information layer.
From the above, it is preferable that at least one of nitride, oxide, sulfide, nitride oxide, carbide and fluoride is included. For example, AlN, Al ₂ O ₃ , SiC, SiN, TiO ₂ , SnO ₂ , In ₂ O ₃ , ZnO, ITO (indium oxide-tin oxide), IZO (indium oxide-zinc oxide), ATO (tin oxide-oxide) Antimony), DLC (diamond like carbon), BN and the like. Among them, a material mainly containing In ₂ O ₃ is preferable, and ITO or IZO is more preferable.
The first thermal diffusion layer can be formed by various vapor deposition methods such as vacuum deposition, sputtering, plasma CVD, photo CVD, ion plating, and electron beam deposition. Among these, the sputtering method is excellent in mass productivity and film quality.
The thickness of the first thermal diffusion layer is preferably 10 to 200 nm. More preferably, it is the range of 20-100 nm. If it is thinner than 10 nm, the heat dissipation effect cannot be obtained. If it is thicker than 200 nm, the stress increases, and not only the repeated recording characteristics deteriorate, but also a problem arises in mass productivity.
Note that there is no problem even if a thermal diffusion layer is provided between the first lower protective layer and the first substrate to further improve the thermal diffusion effect.

Further, the first information layer preferably has a light transmittance of 40 to 70% at a recording / reproducing laser beam wavelength of 350 to 700 nm, more preferably 40 to 60%.
In the two-layer phase change information recording medium on which recording is performed after initialization, the area where the recording layer is in the amorphous state is smaller than the area where the recording layer is in the crystalline state, so the light transmittance in the amorphous state is light transmission in the crystalline state. It may be smaller than the rate.

Next, a recording method for recording data on the first information layer, particularly a recording strategy thereof will be described. A conventionally known recording strategy may be used for the second information layer.
Examples of pulse patterns used in the recording method of the present invention are shown in FIGS.
In the present invention, the minute recording mark is formed by light having a recording power Pw, an erasing power Pe, a cooling power Pb (where Pw>Pe> Pb), and a cooling adjustment power Pm having a level of Pw>Pm> Pb. The cooling adjustment power is provided between the recording power pulse and the cooling power pulse. When a plurality of recording power pulses and cooling power pulses are repeated, it is preferable that a cooling adjustment power pulse is provided at least at one position between the recording power pulse and the cooling power pulse. However, it is preferable that the number of recording power pulses and cooling power pulses for one mark be small in order to simplify the recording strategy.
The power levels of Pw, Pe, and Pb may be appropriately determined according to the structure of the optical information recording medium and the optical system of the recording apparatus. For example, Pw is preferably a value such that the recording layer reaches or exceeds the melting point, and Pb is preferably such that the recording layer heated by Pw is rapidly cooled to form an amorphous mark. The value of Pe is preferably such that the recording layer reaches or exceeds the crystallization temperature during overwriting and the amorphous mark is crystallized. For example, in a system having a wavelength λ = 405 nm and NA = 0.65, 7 mW ≦ Pw ≦ 20 mW, 0 mW <Pb ≦ 1 mW, and 1 mW ≦ Pe ≦ 10 mW are preferable ranges.
The cooling adjustment power level Pm is preferably lower than Pw and higher than Pb, and more preferably Pe = Pm in order to simplify the recording strategy.

  The recording method of the present invention is preferably applied to the first information layer (front side) of the two-layer phase change information recording medium. When three or more recording layers are provided, the recording method of the present invention can be used for recording layers other than the information layer provided on the innermost side when viewed from the laser irradiation side. Since the information layer placed on the near side like the first information layer has no reflection layer or has a very thin reflection layer, the heat of the laser beam during recording is difficult to diffuse in the thickness direction. . Further, since the thickness of the recording layer is 3 to 10 nm, which is thinner than the conventional one, the crystal growth rate is slow. In such a configuration, recrystallization at the time of recording mark formation is considered to depend greatly on the recording strategy. FIG. 12 schematically shows a conventional recording strategy for forming an amorphous mark of multivalued data 2, the recording strategy of the present invention, and the formed amorphous mark. In the conventional recording strategy on the left side of the drawing, since the crystal growth rate of the recording layer is slow, an amorphous mark longer than the ideal length is formed. In the conventional recording strategy in the middle of the figure, the pulse width of the cooling power is narrowed to reduce the rapid cooling effect, but recrystallization is accelerated at a stretch, and an amorphous mark shorter than the ideal length is formed. End up. On the other hand, in the recording strategy of the present invention in which the cooling adjustment power is inserted between the recording power and the cooling power on the right side of the drawing, it is possible to form a minute mark while suppressing the maximum crystallization.

When adjusting the area of the amorphous mark in the data cell in multi-value recording, it is preferable to adjust the mark size by changing the irradiation time (pulse width) of the cooling adjustment power. It is preferable that the mark with a larger area has a shorter cooling adjustment power irradiation time, and the mark with a smaller area has a longer cooling adjustment power irradiation time. For example, when performing 8-level multi-value recording, the recording strategy using the cooling adjustment power Pm of the present invention can be applied to level 1 (m1) and level 2 (m2). At this time, the pulse width of Pb of m1 is preferably set longer than the pulse width of Pb of m2. At this time, the power levels and pulse widths of Pw and Pb may be changed between marks.
The pulse width of Pw may be the same for each level, but the pulse width may be narrower as the level is lower (smaller amorphous mark). In general, the area of the amorphous mark can be controlled by the pulse width of Pb, and it is preferable to increase the pulse width of Pb as the level becomes large (large amorphous mark).
The present invention is effective for multilevel recording, but is also effective for high-density binary recording in which the size of an amorphous mark is smaller than the beam diameter of recording light. However, when the pulse pattern of the present invention is applied to binary recording, it is preferably applied to a mark (particularly the shortest mark) smaller than the beam diameter of the recording light, which is sufficient for the beam diameter of the recording light. When an amorphous mark having a size is formed, it is not necessarily applied.

Next, a configuration example of a recording apparatus for realizing the recording method based on the above-described recording strategy will be described with reference to FIG. FIG. 13 shows an example of a recording apparatus for performing binary recording using the EFM modulation method.
First, a rotation control mechanism 13 including a spindle motor 12 that rotationally drives the optical information recording medium 1 is provided for the optical information recording medium 1, and a laser beam is focused on the optical information recording medium 1. An optical head 14 including an objective lens to be irradiated and a light source such as a semiconductor laser is provided so as to be able to seek in the disk radial direction. A servo mechanism 15 is connected to the objective lens driving device and the output system of the optical head 14. In addition, a reproduction signal detection unit 16 involved in a reproduction operation such as calculating a modulation degree from a reproduction signal detected by a light receiving element or the like in the optical head 14 is provided. A wobble detection unit 18 including a programmable BPF 17 is connected to the servo mechanism 15 and the reproduction signal detection means 16. Connected to the wobble detection unit 18 is an address demodulation circuit 19 that demodulates an address from the detected wobble signal. A recording clock generator 21 including a PLL synthesizer circuit 20 is connected to the address demodulating circuit 19. A drive controller 22 is connected to the PLL synthesizer circuit 20.

A rotation mechanism 13, a servo mechanism 15, a reproduction signal detection means 16, a wobble detection unit 18, and an address demodulation circuit 19 are also connected to the drive controller 22 connected to the system controller 23. In addition, a recording power calculation unit 24 is provided, and an EFM encoder 25 and an LD control unit 26 are connected to the system controller 23. The LD control means 26 includes a recording pulse train generation unit 27 that generates a pulse train control signal defined by the recording strategy. On the output side of the LD control means 26, a light source drive for driving the semiconductor laser in the optical head 14 by switching the respective drive current sources 29 of the recording power Pw, the erasing power Pe, the cooling power Pb, and the cooling adjustment power Pm. The LD driving means 30 which is a driver circuit as means is connected.
In such a configuration, in order to record on the optical information recording medium 1, the rotation control mechanism controls the rotational speed of the spindle motor 12 under the control of the drive controller 22 so that the recording linear velocity corresponds to the target recording velocity. 13, the address is demodulated from the wobble signal separated and detected by the programmable BPF 17 from the push-pull signal obtained from the optical head 14, and the recording channel clock is generated by the PLL synthesizer circuit 20 and output to the recording pulse train generator 27. To do.
Next, in order to generate a recording pulse for the semiconductor laser, a recording channel clock and an EFM data as recording information are input to the recording pulse train generator 27 from the recording clock generator 21 and the EFM encoder 25, respectively. 27, a pulse train control signal as shown in FIG. 10 is generated. Then, the LD driving means 30 switches the driving current sources 19 of the light emission powers Pw, Pb, Pe, and Pm according to the respective pulses.

  According to the present invention, a minute amorphous mark can be stably formed on a phase change information recording medium, particularly a multilayer type phase change information recording medium, and multi-level recording of three or more values can be performed well. It is possible to provide a recording method and a recording apparatus that can perform the recording.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not limited at all by these Examples. Note that a description of the second information layer is omitted because a known recording strategy may be used.

Example 1
A first lower protective layer (thickness) made of (ZnS) _70. (SiO ₂ ) ₃₀ on a first substrate made of a polycarbonate resin having a diameter of 12 cm and a thickness of 0.6 mm and having irregularities for tracking guides by continuous grooves on the surface. 120 nm), a first recording layer (thickness 6 nm) made of Sb ₇₀ Te ₂₂ Ge _{8, a} first upper protective layer (thickness 15 nm) made of (ZnS) _70. (SiO ₂ ) ₃₀ , (TiC) _70. A first barrier layer (3 nm) made of (TiO ₂ ) _{30, a} first reflective layer (thickness 10 nm) made of Ag, and a first thermal diffusion layer made of IZO [(In ₂ O ₃ ) ₉₀ · (ZnO) ₁₀ ] Using a Balzers single wafer sputtering apparatus in the order of (thickness 40 nm), the first information layer was formed by sputtering in an Ar gas atmosphere.
Next, a second reflecting layer (thickness 120 nm) made of Ag ₉₈ Pd ₁ Cu _{1, a} second barrier layer (3 nm) made of SiC, and (ZnS) _70. A second upper protective layer (thickness 20 nm) made of SiO ₂ ) _{30, a} second recording layer (thickness 14 nm) made of composition formula Sb ₇₃ Te ₂₂ Ge _5, and a second recording layer made of (ZnS) _70. (SiO ₂ ) ₃₀ . Two lower protective layers (thickness 130 nm) were formed in this order by sputtering in an Ar gas atmosphere to form a second information layer.
Next, the first information layer and the second information layer were irradiated with laser light with a large diameter LD from the first substrate side and the second information layer film surface side, respectively, and an initialization process was performed.
Next, an ultraviolet curable resin is applied on the film surface of the first information layer, bonded to the second information layer surface side of the second substrate and spin-coated, and then irradiated with ultraviolet rays from the first substrate side. Was cured as an intermediate layer to prepare a two-layer phase change type information recording medium having two information layers. The thickness of the intermediate layer was 35 μm.
Multilevel recording was performed on the first information layer of the two-layer phase change information recording medium at a recording linear velocity of 6.0 m / sec using an optical head having a wavelength of 407 nm and a numerical aperture of 0.65. The cell length was 0.24 μm. Also, the recording strategy for each multi-level at this time is set as shown in FIG. The pulse holding period of the recording power pulse is referred to as Ttop, the cooling power period provided after the recording power pulse is referred to as Tcl, and the period of irradiation of Pm provided between the recording power pulse and the cooling power pulse is referred to as Tm. The set values for each power were Pw = 14 mW, Pb = 0.1 mW, and Pe = Pm = 6 mW. In the recording strategy of m1, Ttop = 4.44nsec, Tm = 2.22nsec, and Tcl = 4.44nsec are set. In the recording strategy of m2 to m7, Ttop = 5.56nsec, Tcl = 4.44nsec to 21.21. Optimized for 67 nsec.
In the evaluation of the recording characteristics, the SDR was obtained by using the multi-value determination technique DDPR, and in the optimum power, the case of SDR ≦ 3.2% was evaluated as “◯”, the 3% range was exceeded, and the 4% or more was evaluated as “X”. The results are shown in the table.

表１から分るように、どの記録媒体も光透過率は４０％以上で、ＳＤＲが両層共に良好な値となり、光記録媒体として優れている。
また、その他の試作実験からも、第１情報層の記録層膜厚が３〜１０ｎｍ、反射層が３〜２０ｎｍ、熱拡散層が１０〜２００ｎｍ、第２情報層の記録層膜厚が３〜２０ｎｍの範囲であると、第１情報層、第２情報層共に良好に記録再生ができた。しかし、第１情報層の記録層膜厚、反射層膜厚がそれぞれ１０ｎｍ、２０ｎｍより厚いと初期化後の光透過率を４０％以上にすることが出来ないために、第２情報層に良好に記録することができなかった。また、熱拡散層が２００ｎｍより厚いと、２層光ディスクを作成するのに少なくとも６０秒かかり、量産には困難であることが分った。 Examples 2-10, Comparative Examples 1-2
A two-layer phase change information recording medium was prepared in the same manner as in Example 1 except that the film thicknesses of the first thermal diffusion layer, the first reflective layer, the first recording layer, and the second recording layer were changed. (Each film thickness is as described in Table 1)
Multi-value recording was performed on the recording media of Examples 2 to 10 under the same conditions as in Example 1 to evaluate the recording characteristics. The results are summarized in Table 1.

As can be seen from Table 1, each recording medium has an optical transmittance of 40% or more, and the SDR is a good value in both layers, which is excellent as an optical recording medium.
Also, from other prototype experiments, the recording layer thickness of the first information layer is 3 to 10 nm, the reflective layer is 3 to 20 nm, the thermal diffusion layer is 10 to 200 nm, and the recording layer thickness of the second information layer is 3 to 3 nm. When the thickness was in the range of 20 nm, both the first information layer and the second information layer could be recorded and reproduced satisfactorily. However, if the recording layer thickness of the first information layer and the thickness of the reflective layer are larger than 10 nm and 20 nm, respectively, the light transmittance after initialization cannot be made 40% or more. Could not be recorded. Further, it has been found that if the thermal diffusion layer is thicker than 200 nm, it takes at least 60 seconds to produce a two-layer optical disc, which is difficult for mass production.

Comparative Example 3
Multi-level recording was performed on the first information layer of the same two-layer phase change information recording medium as in Example 1 at a recording linear velocity of 6.0 m / sec using an optical head having a wavelength of 407 nm and a numerical aperture of 0.65. . The cell length was 0.24 μm. Also, the recording strategy for each multi-level at this time is set as shown in FIG. Ttop was set to 5.56 nsec for all multilevel levels, and Tcl was optimized between 4.44 nsec and 21.67 nsec. When the SDR was measured, it was in the 4% range, and the SDR could not be lowered as compared with Example 1.

The figure which shows the recording strategy used by DVD + RW etc. FIG. The figure which shows the relationship between a mark occupation rate and a Rf signal. The figure which shows distribution of the Rf signal value from each recording mark pattern at the time of performing multi-value recording by the number of recording mark patterns (number of multi-value levels) = 6 by an area modulation system. The figure which shows the recording strategy for forming a multi-value recording mark. The figure which shows the example which the multi-value gradation number is 8, and the distribution of each Rf signal value overlaps. 1 is a schematic cross-sectional view showing an example of a phase change information recording medium having two recording layers. FIG. 6 is a schematic cross-sectional view showing another example of a phase change information recording medium having two recording layers. The figure which shows the conventional recording strategy set to change the pulse width of Pb according to multi-value data, and to take reflectance modulation. FIG. 9 is a diagram showing a reproduced signal waveform when recording is performed using the recording strategy of FIG. 8. The figure which shows an example of the pulse pattern used for the recording method of this invention. FIG. 6 is a diagram showing another example of a pulse pattern used in the recording method of the present invention. The figure which shows an example of the pulse pattern used for the recording method of this invention, and the pulse pattern used for the conventional recording method. The figure which shows an example of the optical information recording device for performing the binary recording using an EFM modulation system. FIG. 3 is a diagram illustrating a strategy used in the first embodiment. (A) is the case of m1, and (b) is the case of m2 to m7.

Explanation of symbols

T Basic clock period Pw Recording power Pe Erase power Pb Cooling power Pm Cooling adjustment power m1 to m7 Numbers indicating multilevel data Ttop Top pulse pulse holding period Tcl Cooling period provided after the last pulse Tm Recording power pulse and cooling power pulse Period of Pm irradiation provided between

Claims (14)

  Recording power (Pw) light and cooling power (with respect to an information layer having a phase change recording layer in which information is recorded by causing a phase change between a crystalline state and an amorphous state by the incidence of light) Pb) In a method of recording information by forming several kinds of amorphous marks with different areas by irradiation with light and forming crystal spaces by irradiation with erasing power (Pe) light (where Pw> Pe> Pb) When forming at least one kind of amorphous mark, cooling adjustment power (Pm) light having a power level of Pw> Pm> Pb is irradiated between the recording power light and the cooling power light. A recording method for a phase change type information recording medium, wherein information is recorded.   2. A recording method according to claim 1, wherein multi-value data of three or more values is recorded as information by modulating the area of the amorphous mark in the recording cell.   3. The recording method according to claim 1, wherein Pe = Pm.   4. The recording method according to claim 1, wherein the area of the amorphous mark is controlled by changing the irradiation time of the cooling adjustment power light.   5. The recording method according to claim 1, wherein when the amorphous mark is formed, the irradiation time of the cooling adjustment power light is set longer for an amorphous mark having a smaller area.   The phase change type recording layer is composed mainly of an Sb—Te eutectic material, Ag, In, Ge, Se, Sn, Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Ga, Bi. The recording method according to claim 1, comprising at least one of Si, Dy, Pd, Pt, Au, S, B, C, and P.   A phase change information recording medium having a structure in which an information layer comprising at least a lower protective layer, a phase change recording layer, an upper protective layer, a reflective layer, and a heat diffusion layer is laminated in this order or in reverse order on a substrate is used. The recording method according to claim 1.   At least a first substrate, a first information layer, an intermediate layer, a second information layer, and a second substrate, wherein the first information layer includes at least a first lower protective layer, a first recording layer, a first upper protective layer, a first A phase change type information recording medium comprising one reflective layer and a first thermal diffusion layer, and the second information layer comprising at least a second lower protective layer, a second recording layer, a second upper protective layer, and a second reflective layer is used. The recording method according to claim 7.   9. The recording method according to claim 7, wherein the heat diffusion layer uses a phase change information recording medium made of ITO (indium oxide + tin oxide) or IZO (indium oxide + zinc oxide).   The recording method according to claim 7, wherein a phase change information recording medium having a thermal diffusion layer thickness of 10 to 200 nm is used.   The phase change type information recording medium made of a material whose main component is at least one of Au, Ag, Cu, W, Al, and Ta is used for the reflective layer. Recording method.   The recording method according to claim 8, wherein a phase change information recording medium having a thickness of the first reflective layer of 3 to 20 nm is used.   Phase change type recording layer disposed on the innermost side when viewed from the laser beam incident side, using a multilayer phase change type information recording medium in which two or more information layers having a phase change type recording layer are provided via an intermediate layer The recording method according to claim 1, wherein recording is performed on at least one phase change recording layer other than the above. A recording apparatus having a function of recording on a phase change information recording medium by the recording method according to claim 1.

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