JP2006289940A - Phase change-type optical information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical information recording medium which enables a sufficient contrast to be available in a blue wavelength range, and a high amorphous stability under high temperature environments and successful preservation reliability. <P>SOLUTION: This phase change-type optical information recording medium uses a reversible phase transition phenomenon between a crystalline phase and and an amorphous phase by laser light irradiation with 405±15 nm wavelength. In addition, the medium has at least a phase change recording layer, formed on a substrate and a lower dielectric material layer positioned under the phase change recording layer, and an upper dielectric material layer and a reflective layer positioned above the phase change recording layer. Besides, the recording layer is composed mainly of GeαSbβ(5<α<25, 75<β<95), and contains an additional element for cubic crystallization which totals 10 to 40 atomic% to the main component, and the crystalline structure of the recording layer is the cubic crystal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a phase change type optical information recording medium, and more particularly to a phase change type multilevel recording medium having a recording / reproducing signal level of a recording pit higher than binary, and is applied to a large capacity data storage and a digital video disk.

(Recording material and binary recording)
A so-called phase change type optical information recording medium using a reversible phase change between a crystalline state and an amorphous state is known as an optical information recording medium currently in practical use. As the recording material, a GeTe—Sb ₂ Te ₃ pseudo binary composition, a Ge—Sb—Te ternary alloy material represented by a compound composition such as Ge ₂ Sb ₂ Te ₅ , and Sb ₇₀ Te _{30 are used.} There are SbTe eutectic materials typified by Ag-In-Sb-Te, which are mainly composed of eutectic compositions. The former GeSbTe material is widely used as a DVD-RAM, and the latter AgInSbTe eutectic material is widely used as a CD-RW, DVD-RW, and DVD + RW. Each of these phase change optical recording media has a structure in which a lower protective layer, a recording layer, an upper protective layer, a reflective layer, and the like are laminated on a plastic substrate having spiral or concentric grooves. The reflectance is controlled by using the optical constant change in the crystal and amorphous and the multiple interference of the laminated structure, and binary information is recorded / reproduced.

(High-speed and high-density flow)
On the other hand, with the progress of digitalization and the spread of broadband in recent years, the amount of information handled has increased, and a new recording system capable of recording and reproducing data at high density and high speed has been demanded. Against this backdrop, by shortening the recording / reproducing wavelength and increasing the numerical aperture (NA), the diameter of the focused beam is reduced, the size of the recorded marks is reduced, and the density and speed are increased. Technological development aimed at is actively conducted. For example, the current recordable DVD has a recording / reproducing wavelength λ = 650-660 nm, a numerical aperture NA = 0.65, and a recording capacity of 4.7 GB, but the recording / reproducing wavelength is shortened to λ = 400-420 nm. An optical recording system with a numerical aperture NA = 0.85 and a recording capacity of 20 GB or more has been proposed (Patent Document 1).

(Problems with NA of 0.85)
Such a high-speed and large-capacity optical recording / reproducing apparatus is capable of recording / reproducing a DVD-ROM or a recordable DVD and a CD-ROM, CD-R, CD-RW, etc. That is, it is desired that backward compatibility can be achieved. However, the above-mentioned system makes it difficult to ensure recording / playback compatibility with CDs and DVDs using the same pickup due to high NA, and a dedicated cartridge is used to prevent the recording medium surface from dirt such as fingerprints. Necessary, and the physical shape of the medium is difficult to be compatible.

(Conventional technology of multi-value recording)
On the other hand, a multi-value recording method has attracted attention as a technique for realizing higher density and higher speed while keeping the numerical aperture NA at about 0.65 of the conventional recordable DVD system. We have proposed a method for recording multi-value information by the difference in the occupation ratio of the amorphous recording mark with respect to the peripheral crystal part and achieving a recording capacity of 20 GB or more (Non-patent Document 1).
Since this system has a wide working distance as in the prior art, a bare disk that does not require a special case can be used like a CD-RW or a recordable DVD. In addition, since the NA of the optical system is the same as that of a conventional DVD, there is an advantage that the three generations including the CD and the DVD can be easily interchanged with one optical system.

(Storage task of multi-level records)
What is important in terms of signal quality in the multi-level recording method is that there is no change in mark shape or crystal state even when the medium is placed in a high temperature environment. In the multi-value recording method in which multi-gradation is recorded in multiple steps with the difference in reflectance, the allowable value for the change in reflectance under a high temperature environment becomes stricter than that in the conventional binary recording. In this respect, a recording material having a SbTe eutectic composition as a base cannot be said to have sufficient storage reliability. In particular, the SbTe eutectic material inevitably increases the Sb ratio for increasing the recording speed, but this is in the direction of deteriorating the stability of the amorphous, that is, the storage reliability of the mark. Compatibility of storage characteristics is a trade-off relationship. There is Patent Document 2 as another conventional example of a multi-value recording medium, but such a storage problem is not recognized at all, and there is no technical disclosure or suggestion for solving this problem. .

(Problems of GeSb-based materials)
As a recording material not containing a chalcogen element as a main component, there is a system mainly containing a GeSb eutectic system (Patent Document 3). It is known that the GeSb eutectic material has higher amorphous phase stability than the SbTe eutectic material. This is because the crystallization temperature of the SbTe eutectic composition is at most 120 ° C., whereas that of the GeSb eutectic composition is as high as 255 ° C. However, all of the GeSb eutectic materials disclosed in Patent Document 3 have a problem that the contrast (reflectance in the crystalline state and the amorphous state) is small in the violet wavelength region of 405 nm, and the separability of the multilevel signal is deteriorated. there were. In other words, since the multi-level recording method is a method of recording the reflected signal in multiple stages, increasing the difference in reflectance between each level and improving the discrimination of each signal reduces the error during demodulation. However, it is desirable that the contrast of the GeSb eutectic material is smaller than that of the SbTe eutectic material, and good multi-value recording characteristics have not been obtained.

Japanese Patent Laid-Open No. 10-326435 JP 2001-84591 A JP 2002-344719 A (Data Detection using Pattern Recognition, International Symposium on Optical Memory 2001, Technical Digest 2001, Pd-27)

  An object of the present invention is to provide an optical information recording medium that solves the above-described problems, provides a sufficient contrast in the blue wavelength region, has high amorphous stability in a high temperature environment, and has good storage reliability. It is to be.

The said subject is solved by the following (1)-(8) of this invention.
(1) “A phase change type optical information recording medium using a reversible phase transition between crystal and amorphous by irradiation with laser light having a wavelength of 405 ± 15 nm, comprising at least a phase change recording layer on the substrate, and the phase change recording A lower dielectric layer positioned below the layer, an upper dielectric layer positioned above the phase change recording layer, and a reflective layer, and the recording layer is GeαSbβ (5 <α <25, 75 <β <95 ) As a main component, and the total amount of the main component exceeds 10 atomic% and contains 40 atomic% or less of an additive element for crystallization, and the crystal structure of the recording layer belongs to the cubic system An optical information recording medium characterized by that. "
(2) “The optical information recording medium according to (1), wherein the additive element is made of at least one element selected from Zn, Ga, Sn, In, and Bi.”
(3) “The recording layer contains 10 <Sn ≦ 30 atomic% of Sn as the additive element, and the ratio of (Sb + Sn) in the recording layer is 70 ≦ (Sb + Sn) <85 atomic%. The optical information recording medium according to (1) or (2), characterized in that it is characterized.
(4) “A region where a recording mark is formed is divided into equal areas in the beam scanning direction (hereinafter, this temporally identified virtual region is referred to as a cell), and one recording mark is formed for the cell. The optical information recording medium according to any one of (1) to (3), wherein the optical information recording medium is formed and multi-value recorded as information of a ratio occupied by the recording mark with respect to the cell.
(5) “Optical information recording medium for recording / reproducing using an optical system having an objective lens numerical aperture NA of NA = 0.65 ± 0.3, and a substrate having a thickness of 0.6 ± 0.05 mm Groove groove is provided on the film forming surface side, the groove groove has a wobble with a constant period and phase modulation, the groove groove shape has a track pitch = 0.43 to 0.50 μm, and a groove width = 0. The optical information recording medium according to (4), wherein the optical information recording medium is 20 to 0.30 μm. ”
(6) The optical information recording medium according to (4) or (5), wherein the cell length is 0.20 to 0.30 μm.
(7) The optical information recording medium according to any one of (1) to (6), wherein the reflective layer is made of Ag or an Ag alloy and has a thickness of 140 nm or more and 300 nm or less. . "
(8) “The reflective film is made of Ag or an Ag alloy, and at least a reflective layer, a lower dielectric layer, a phase change recording layer, an upper dielectric layer, an adhesive layer, a cover substrate, or a reflective layer on a substrate, anti-sulfurization The optical information recording medium according to any one of (1) to (6) above, comprising a layer, a lower dielectric layer, a phase change recording layer, an upper dielectric layer, an adhesive layer, and a cover substrate in this order. "

  In an area-modulation type phase-change type multi-value recording medium, an optical recording medium that provides sufficient contrast even in the case of a blue laser having a recording / reproducing wavelength of about 405 nm and that has both a practically low SDR and good storage characteristics is provided. did it.

(Description of multi-value technology)
The multi-value recording used in the present invention will be described below.
FIG. 1 shows the relationship between the mark occupancy and the Rf signal.
The recording mark is located at the approximate center of each cell. The same relationship applies to phase pits in which the recording marks are recorded as rewritable phase change materials or asperities on the substrate. When the recording mark is a phase pit recorded as an uneven shape on 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. ). 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 the area modulation method, the Rf signal values from the respective recording mark patterns show 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 the recording strategy as shown in FIG. 3 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 than the focused beam diameter, When the target cell is reproduced, the focused beam protrudes to the target cell 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 occurs with the front and rear marks. Due to this influence, as shown in FIG. 2, the Rf signal value in each pattern has a distribution with a deviation. In order to determine without error which recording mark pattern the target cell has, the interval between the Rf signal values reproduced from each recording mark needs to be more than the deviation. In the case of FIG. 2, the intervals and deviations of the Rf signal values of the recording marks are almost equal, which is a limit for determining the recording mark pattern.

As a technique for overcoming this limitation, a multi-value determination technique (DDPR technique) using three consecutive data cells has been proposed. In this technique, a step of learning a multi-value signal distribution composed of a combination pattern of three consecutive data cells (8 ³ = 512 patterns at the time of 8-level recording) and creating a pattern table thereof, and a reproduction signal result of unknown data After the three continuous mark patterns are predicted, the unknown signal to be reproduced is determined in multiple values with reference to the pattern table. 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 of the average value of the standard deviation σi of each multilevel signal when the number of multilevel gradations is n to the dynamic range DR of the multilevel Rf signal = Σσi / (n × DR The signal quality is equivalent to the 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 σi of the multi-value signal is smaller and the dynamic range DR is larger, and the separability of the multi-value signal 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. Using such a multi-value determination technique, for example, even when the number of multi-value gradations is increased to 8 and the distributions of the Rf signal values overlap each other, the error rate is 10E-5 with 8 units. Multi-valued determination of values is possible.

(About claims 1 and 2)
In the configuration of the optical information recording medium of the present invention, the recording layer contains GeαSbβ (5 <α <25, 75 <β <95) as a main component, and the total amount exceeds 10 atomic% with respect to the main component. And 40 atomic% or less of additive elements, and the crystal layer has a cubic crystal.
As a result of intensive studies by the present inventors, GeαSbβ (5 <α <25, 75 <β <95) in the vicinity of the eutectic composition has a rhombohedral structure (hexagonal system) similar to Sb, and is blue. Although sufficient contrast cannot be obtained at the wavelength, an additive element composed of Zn, Ga, Sn, In, and Bi in a total amount exceeding 10 atomic% and having a total amount exceeding 10 atomic% (hereinafter referred to as cubic stability) It was found that the crystal system becomes cubic and the contrast becomes higher than that of the conventional SbTe eutectic system at the blue wavelength. The cubic stabilizing element is composed of at least one element selected from Zn, Ga, Sn, In, and Bi. When the total amount of the cubic stabilizing element is 10 atomic% or less, cubic crystals do not appear, so it is desirable to exceed 10 atomic%. Moreover, it is desirable that it is 40 atomic% or less so as not to impair the recording characteristics and storage characteristics.

When the crystal phase becomes a cubic crystal, the mechanism by which the contrast is increased has not yet been elucidated, but it has been found that there is a large difference in optical constants between the two. For example, the optical constants of Ge ₂₃ Sb ₇₇ and Ge ₂₃ Sb ₅₂ Sn ₂₅ are as shown in Table 1.
Comparing the refractive index difference Δn and the extinction coefficient difference Δk between the crystal and the amorphous substance that affect the contrast, the crystal phase contains Sn of the cubic stabilizing element (also referred to as “cubicizing additive element” in the present invention), and the crystalline phase is It can be seen that the refractive index difference of Ge ₂₃ Sb ₅₂ Sn ₂₅ belonging to the cubic system is larger. From this, for example, when the recording layer is cubic, the packing density of atoms is increased, or a specific crystal plane is oriented in the light incident surface, that is, the in-plane direction of the disk, so that the refractive index of the crystal phase is small. Therefore, it is considered that the reflectance of the crystal phase is increased and a larger contrast can be obtained.

  The crystal structure is identified by peeling the initialized (crystallized) optical information recording medium from the upper protective layer, setting the X-ray incident angle to 0.2 to 0.5 °, and performing in-plane X-ray diffraction of the recording layer. It can be confirmed by taking. The hexagonal system is indexed to a rhombohedral structure that inherits the crystal structure of Sb. That is, when the wavelength of the X-ray is λ = 1.54 mm (Cu Kα ray), 2θ = 23.7 ° indexed to the plane indices (003), (012), (104) and (110), Diffraction peaks appear around 28.7 °, 40.1 ° and 42.0 °. On the other hand, in the case of the cubic system, the diffraction peaks near 2θ = 24 ° and 40 ° seen in the hexagonal system disappear, and (200) and (220) are indexed near 2θ = 29 ° and 42 °. Diffraction peaks appear prominently. From these, hexagonal crystals and cubic crystals can be distinguished.

  As the additive element, the recording layer is selected from Ag, Au, Cu, Cr, Zr, B, Te, Mn, Al, Si, Pb, Mg, N, P, La, Ce, Cd, Tb, Dy, and the like. Additional elements can be included. A suitable content of the additive element is 15 atomic% or less, more preferably 10 atomic% or less, and still more preferably 8 atomic%.

  A desirable film thickness of the recording layer is 5 to 20 nm. If the thickness is less than 5 nm, the recording layer is too thin to obtain a sufficient reflectance. On the other hand, if it is thicker than 20 nm, the heat capacity is increased and the recording sensitivity is degraded. Further, the edge of the amorphous mark is disturbed and the SDR becomes high.

(Claim 3)
In the configuration of the optical information recording medium of the present invention, it is desirable that the cubic stabilizing element contains Sn, and the content thereof is 10 <Sn ≦ 30 atomic%. In this system, Sn has a function of lowering the crystallization temperature of the recording layer and facilitating initialization. However, if the Sn content exceeds 30 atomic%, the crystallization temperature of the recording layer becomes too low, which is not preferable in terms of storage characteristics. In addition, in order to perform good mark formation with a blue laser diode with an output of several tens of mW, which is currently available at mass production level, the ratio of (Sb + Sn) in the recording layer is 70 ≦ (Sb + Sn) <85 atomic%. It is desirable that When the amount of (Sb + Sn) is 70 atomic% or less, the crystallization speed is slow, and for example, good SDR cannot be obtained in multi-value recording. In practice, the transfer rate is lowered. On the other hand, if the amount of (Sb + Sn) exceeds 85 atomic%, the crystallization speed is too high and it becomes difficult to form amorphous marks, and similarly good SDR cannot be obtained.

(Claims 5 and 6)
In the configuration of the optical information recording medium of the present invention, a 0.6 mm thick substrate having groove grooves with a track pitch = 0.43 to 0.50 μm and a groove width = 0.20 to 0.30 μm on the film forming surface side. Is preferable in terms of multilevel recording. Here, the groove width of the groove represents the dimension of the deepest portion of the groove bottom surface. The substrate thickness of 0.6 mm is preferably 0.6 ± 0.05 mm, more preferably 0.6 ± 0.02 mm, and most preferably 0.6 ± 0.01 mm. According to this preferable example, the track pitch is 0.43 to 0.50 μm, the groove width is 0.20 to 0.30 μm, and the substrate thickness is 0.6 mm. Using the system and a laser with a wavelength of 405 ± 15 nm, good multilevel recording / reproduction is possible.

  When a laser with a wavelength of 405 nm and an optical system with NA = 0.65 are used, the track pitch is preferably 0.50 μm or less corresponding to the convergent diameter of the laser beam. If the track pitch is wider than this, for example, in order to obtain a storage capacity of 20 or more GB necessary for 2-hour recording of digital high-definition broadcasting, the cell density of multi-level recording must be increased, and intersymbol interference occurs. As a result, the quality of the reproduced signal cannot be obtained. On the contrary, when the track pitch is less than 0.43 μm, cross erase and cross talk between adjacent tracks become prominent, and the signal quality is similarly lowered. Further, when the push-pull method is used for tracking, the signal amplitude of the push-pull signal becomes small at a groove depth of 18 to 30 nm suitable for groove recording, so that stable tracking servo becomes difficult. For this reason, the track pitch is preferably 0.43 to 0.50 μm.

On the other hand, the groove width of the groove is preferably 0.30 μm or less. If the groove width is wider than this within the track pitch range, the groove-shaped land portion becomes too narrow, the push-pull signal amplitude becomes small, and it becomes difficult to obtain a wobble signal with sufficient amplitude. End up. Further, since the shape of the narrow land portion is uniformly formed, it is very difficult to mold the substrate and manufacture the stamper master. On the other hand, if the groove width is less than 0.20 μm, the recording mark easily protrudes from the land portion, so that the signal quality is deteriorated by the cross erase. In addition, in the groove groove depth of 18 to 30 nm, the reflectivity and the dynamic range become higher as the groove width becomes wider. Therefore, in order to sufficiently reduce the SDR, the groove width should be 0.25 to 0.30 μm. More desirable.
Due to the groove shape as described above, the optical recording medium according to the present invention can be recorded and reproduced at a wavelength of 405 ± 15 nm using the same optical system of NA = 0.65 as that of the recordable DVD. It becomes easy to take compatibility with.

(About media configuration)
A configuration example of the phase change optical information recording medium according to the present invention is shown in FIG.
As shown in the figure, on the transparent substrate (1), the lower protective layer (2), the phase change recording layer (3), the upper protective layer (4), and the reflective layer (5) are laminated in this order, and the organic protective layer (6 ), A cover substrate (7) having the same thickness is bonded.

  As the material of the substrate (1), a transparent resin such as polycarbonate, acrylic or polyolefin can be used. Of these, polycarbonate resins are most preferable because they have a track record in CDs and DVDs, are inexpensive, and exhibit high transmittance even in the vicinity of a wavelength of 400 nm. Grooves are formed in the substrate, and the depth is about 18 to 30 nm.

For the material of the lower protective layer (2) and the upper protective layer (4), a high-melting point material having high transparency such as metal, semiconductor oxide, sulfide, nitride, and carbide can be used. _{Specifically, SiOx, ZnO, SnO 2,} Al 2 O 3, TiO 2, In 2 O 3, MgO, ZrO 2, Ta 2 O metal oxide such as _{5, Si 3 N 4, AlN} , TiN, BN , nitrides such as ZrN, ZnS, a sulfide such as _{TaS 4, SiC, TaC, B} 4 C, WC, TiC, include carbides such as ZrC, it can be used as alone or mixture. The optimum material for the protective layer is determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion and the like. Among these, a mixed film with SiO ₂ containing 60 to 90 mol% of ZnS is preferable because it does not cause repeated recording, crystallization of the film itself in a high temperature environment, chemical change, and film deformation.

  The thickness of the lower protective layer (2) is preferably 30 to 200 nm. The lower protective layer (2) may be two layers or multiple layers. If the number of times of recording exceeds 10,000 in the case of repeated recording, the elements constituting the protective layer diffuse into the recording layer between the recording layer (3) and the lower protective layer (2). A layer made of highly specific carbide or nitride may be provided. Further, when the lower protective layer (2) is thin, if the recording power is high, the substrate is deformed by heat. Therefore, a film having high thermal conductivity may be provided on the substrate (1) side.

The upper protective layer (4) is preferably made of the same ZnS · SiO ₂ film as the lower protective layer (2). The film thickness of the upper protective layer (4) is preferably 8 to 20 nm. If the film thickness is thinner than 8 nm, the mechanical strength is lowered, which is not preferable in terms of repeated recording characteristics. Further, most of the laser energy is transferred to the reflective layer (5), and the mark width becomes small, so that the dynamic range DR cannot be obtained. In addition, the sensitivity is low and the medium becomes impractical without a power margin. On the other hand, if the film thickness is greater than 20 nm, the heat dissipation effect is reduced and a rapid cooling structure cannot be obtained. Conversely, cross erase between adjacent tracks and thermal interference between front and rear marks increase.

Similarly to the lower protective layer (2), the upper protective layer (4) may have two layers or multiple layers. In particular, when Ag or an Ag alloy is used for the reflective layer (5), a part of the ZnS · SiO ₂ upper protective layer (4) on the reflective layer (5) side is replaced with a dielectric material not containing sulfur, and the barrier layer Is desirable. As the barrier layer, metal oxides such as ZnO, SnO ₂ , Al ₂ O ₃ , TiO ₂ , In ₂ O ₃ , MgO, ZrO ₂ , Ta ₂ O ₅ , Si ₃ N ₄ , AlN, TiN, BN, ZrN Nitride such as SiC, TaC, B ₄ C, WC, TiC, ZrC and the like, and mixtures thereof are used. The film thickness of the barrier layer is about 2 to 6 nm.

(About claim 7)
In the configuration of the optical information recording medium of the present invention, the reflective layer (5) is most preferably composed mainly of Ag having a high thermal conductivity. As elements added to Ag, Au, Pd, Pt, Ru, Cu, Zn, Nd, Ce, In, Bi, other transition metal elements, rare earth elements, and the like are suitable. By adding these impurities, aggregation and crystal grain growth can be suppressed under the high temperature environment of the Ag film. However, the total content is desirably 2 atomic% or less, more desirably 1 atomic% or less, and most desirably 0.5 atomic% or less so as not to impair the good thermal conductivity of Ag.

  The thickness of the reflective film (5) is preferably 140 to 300 nm. If the film thickness is less than 140 nm, heat dissipation is insufficient, and the mark edges vary to cause an increase in SDR. The optimum film thickness of the reflective film can be selected in the range of 140 to 300 nm depending on the combination with the thermal conductivity of the material constituting the upper protective layer. For example, when the barrier layer contains a large amount of an oxide system having a relatively low thermal conductivity, 200 to 300 nm is preferable because the SDR is lowered. Even if the thickness of the reflective film is greater than 300 nm, the recording characteristics and sensitivity are not changed, and conversely, the mechanical characteristics of the medium are deteriorated by heating during film formation.

(About claim 8)
In the configuration of the optical information recording medium of the present invention, a configuration in which the order of each film is reversed from the configuration shown in FIG. 5 is preferable.
That is, an Ag or Ag alloy reflective layer, an antisulfuration layer, a lower protective layer, a recording layer, and an upper protective layer are laminated in this order on a substrate provided with a groove for writing a recording mark. According to this configuration, it is possible to improve the characteristics by using an inexpensive substrate as the substrate supporting the film and using a substrate having a small birefringence on the light incident surface side. In multi-value recording, the characteristics are likely to deteriorate due to high birefringence in the direction perpendicular to the incident surface and in the oblique direction. From the viewpoint of birefringence, a glass substrate is ideal on the light incident surface side, but it is expensive and difficult to handle. Therefore, it is preferable to use a plastic substrate having a photoelastic constant as small as possible. Further, when the numerical aperture of the objective lens of the optical pickup is higher than 0.65 and about 0.85, the thickness of the substrate on the light incident side needs to be thinner than 0.6 mm which is the case of NA 0.65. In this case, a substrate thicker than 0.6 mm is used as a substrate for laminating each layer constituting the medium. In the case of NA 0.85, each layer is formed using a substrate with a 1.1 mm thick groove, and then a very thin substrate of 0.1 mm thickness is bonded.

Examples of the phase change optical information recording medium according to the present invention and comparative examples will be described below.
The embodiments described below are preferred embodiments of the present invention, and thus various technically preferable limitations are given. However, the scope of the present invention is particularly limited in the following description. As long as there is no description which limits, it is not restricted to these aspects.

Examples 1-6, Comparative Examples 1-6
A polycarbonate substrate with a groove depth of 21 mm, a groove width of 0.28 μm, a track pitch of 0.46 μm, a groove groove containing a wobble with a period of 900 kHz and an amplitude of 15 nm (product name ST3000, Teijin Bayer Polytech) Made of ZnS: SiO ₂ = 70: 30 (mol%), a lower protective layer 44 nm consisting of ZnS: SiO ₂ = 70: 30 (mol%), a phase change recording layer 14 nm consisting of the material composition shown in Table 2, ZnS: SiO ₂ = 80: 20 (mol) %), An anti- _sulfur barrier layer made of SiC 3 nm, and a reflective layer 200 nm made of Ag _99.5 Bi _0.5 were sequentially laminated by sputtering.
On top of this, 7 μm of UV curable resin (Dainippon Ink SD318) is applied to form an organic protective layer, and a 0.6 mm thick cover substrate is bonded using UV curable resin (Nippon Kayaku DVD003). Five structures were produced, and optical information recording media of Examples 1 to 6 and Comparative Examples 1 to 6 were obtained.

Next, the recording layer of these media was initialized (crystallized). Initialization is performed by using an initialization apparatus using a large-diameter LD having a wavelength of 780 nm and a beam diameter of 200 μm × 1 μm (radial direction × track direction) while rotating the recording medium at a linear velocity of 3.0 m / s. The measurement was performed while feeding a large-diameter LD in the radial direction at 36 μm / rotation.
Next, the multi-valued recording characteristics of the medium were evaluated using a recording / reproducing apparatus equipped with an LD (laser diode) having a wavelength of 405 nm and a pickup head composed of an objective lens having an NA of 0.65. As the multi-value recording method, the recording linear velocity was 6.0 m / s, the basic cell length was 0.24 μm (recording frequency 25 MHz), and 8-value multi-value recording was performed. That is, the unrecorded portion having the highest reflectance is set to M0, and the mark is changed to seven levels of M1 to M7 to obtain eight values. The recording mark was recorded by generating the light emission waveform shown in FIG. That is, the maximum recording power (Pw) was 12 mW, the erasing power (Pe) was 62% of the recording power, and the bottom power (Pb) was 0.1 mW. In addition, since the recording power irradiation time Tmp was constant and the mark was recorded symmetrically at the center of the cell, the start time for irradiation of the recording power was shifted by Tms from the reference clock. The length of the mark was adjusted by the bottom power (Pb) irradiation time Tcl. The smaller the mark, the longer Tms and the shorter Tcl. Table 3 shows these conditions. The reproduction power was 0.5 mW.

  In order to examine the dynamic range DR of the optical information recording media of Examples 1 to 6 and Comparative Examples 1 to 6, multilevel signals of each level are repeatedly recorded in the order of M0 to M7 in 15 cells, and M0 and M7 are recorded. The reflectance difference was measured as DR.

Since Examples 1 to 6 all contain a cubic stabilizing element composed of Zn, Ga, Sn, In, and Bi in a total amount of more than 10 atomic% and 40 atomic% or less, the crystalline layer is cubic (Table A high DR of 190 to 200 mV was obtained.
On the other hand, in Comparative Examples 1 to 6, since the cubic stabilizing elements in the recording layer were all 10 atomic% or less, the crystal system remained hexagonal (hex in the table), and 105 to 120 mV. Only low DR was obtained.
The crystal structure is identified by peeling the initialized optical information recording medium from the upper protective layer, setting the X-ray wavelength to λ = 1.54 mm, and the incident angle from 0.2 to 0.5 °. In-plane X-ray diffraction was taken and judged from indexing of diffraction peaks.

Examples 7-14, Comparative Examples 7-16
Optical information recording media of Examples 7 to 14 and Comparative Examples 7 to 11 were obtained in the same manner except that the composition of the recording layer material was changed to Table 4. After initialization, random recording of the M0 to M7 signals was performed using the write strategy shown in FIG. 6 and Table 3, and fluctuations in the reflected signal at each level, that is, the aforementioned SDR was measured. In the SDR measurement, first, data of 80 sec (the number of 1221 cells per 1 sec) is acquired at a sampling frequency of 1 GHz. At the time of random data recording, a synchronization signal composed of continuous data of 5 bits each of M0 and M7 is recorded at the head of 1 sector. The reproduced signal is subjected to AGC processing using a synchronizing signal after removing a large reflected signal fluctuation of several kHz or less existing around one track through a filter according to the flow shown in FIG. This AGC processing is to process a signal having a certain level of amplitude by eliminating the amplitude fluctuation difference of the random signal recorded thereafter with reference to the amplitude of the M0 and M7 continuous signals. After that, a signal having a small amplitude is amplified through the waveform equivalent circuit (EQ), particularly the M1 and M2 marks. This signal was taken in, the standard deviation of the reflected potential at each level was determined, and the SDR value was determined.

  Table 4 shows the crystal structure of the recording layer identified from the X-ray diffraction, the DR and SDR values obtained from the amplitude of the synchronization signal, and the storage test results. Judgment of the storage test result is determined by leaving the randomly recorded medium in a high temperature and high humidity environment of 80 ° C. and 85% RH for 200 hours, then reproducing the mark recorded before the test, and increasing the SDR by 0.2% or less. The case of ◯ was marked with ○, and the case of exceeding 0.2% was marked with ×. From the results in Table 4, the following can be understood.

In each of Examples 7 to 14, since the cubic stabilizing element Sn is included in 10 <Sn ≦ 30 atomic%, the crystal layer belongs to the cubic system and exhibits a high DR of 190 to 200 mV. Further, since the ratio of (Sb + Sn) in the recording layer is 70 ≦ (Sb + Sn) <85 atomic%, a blue laser diode with 10 mW output available at mass production level is used, and the SDR is 2.8% or less. Good recording was possible. In addition, since the recording layer has a GeSb eutectic system as a main component, the SDR increase after storage was all 0.2% or less and excellent in reliability.
On the other hand, in the media of Comparative Examples 7 to 9, since the recording layer is mainly composed of the conventional SbTe eutectic system, the DR is as low as 150 to 160 mV, and the initial SDR exceeds 2.8%. It was a medium with no equipment margin. Further, the SDR increase after storage exceeded 0.2%, and the medium was low in reliability.
In the media of Comparative Examples 10 to 12, since the amount of the cubic stabilizing element is 10 atomic% or less, the crystal layer belongs to the hexagonal system, the DR is low, and the SDR is high. For this reason, no preservation test has been conducted.
In the media of Comparative Examples 13 to 16, since the amount of (Sb + Sn) exceeds 85 atomic%, the crystallization speed is too high, and a blue laser diode with 10 mW output cannot provide a sufficient cooling rate. The amorphous mark becomes thin in the radial direction, and the DR becomes small and a good SDR cannot be obtained.

It is a figure which shows the relationship between the occupation rate of the mark pattern in the unit cell area | region in the case of multi-value recording, and Rf signal. It is a figure which shows the relationship between the recording mark pattern using an area modulation system, and Rf signal. It is a figure which shows the example of a recording strategy for the pattern mark by multi-value recording. It is another figure which shows the relationship of the Rf signal by the difference in the recording mark pattern of this invention. It is a figure which shows the structural example of the phase change type | mold optical information recording medium of this invention. It is a figure which shows an example of the recording strategy in this invention. It is another figure which shows an example of the processing method of the reproduction signal of the mark pattern by the recording strategy of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Lower protective layer 3 Phase change recording layer 4 Upper protective layer 5 Metal reflective layer 6 Organic protective layer 7 Cover substrate

Claims (8)

A phase change optical information recording medium using a reversible phase transition phenomenon between a crystal and an amorphous state by irradiation with a laser beam having a wavelength of 405 ± 15 nm, comprising at least a phase change recording layer on a substrate and a lower side of the phase change recording layer A lower dielectric layer located on the upper side, an upper dielectric layer located above the phase change recording layer, and a reflective layer, and the recording layer is mainly composed of GeαSbβ (5 <α <25, 75 <β <95). And a total amount exceeding 10 atomic% and not more than 40 atomic% of an additive element for crystallization, and the crystal structure of the recording layer belongs to a cubic system. Optical information recording medium. The optical information recording medium according to claim 1, wherein the additive element comprises at least one element selected from Zn, Ga, Sn, In, and Bi. The recording layer includes Sn as an additive element of 10 <Sn ≦ 30 atomic%, and a ratio of (Sb + Sn) in the recording layer is 70 ≦ (Sb + Sn) <85 atomic%. Item 3. The optical information recording medium according to Item 1 or 2. A region for forming a recording mark is divided into equal areas in the beam scanning direction (hereinafter, this temporally identified virtual region is referred to as a cell), and one recording mark is formed for the cell. 4. The optical information recording medium according to claim 1, wherein multi-value recording is performed as information of a ratio occupied by the recording mark with respect to the cell. An optical information recording medium that performs recording and reproduction using an optical system having a numerical aperture NA of an objective lens of NA = 0.65 ± 0.3, and is a film formation surface of a substrate having a thickness of 0.6 ± 0.05 mm Groove groove is provided on the side, the groove groove has a wobble with a constant period and phase modulation, and the groove groove shape has a track pitch = 0.43 to 0.50 μm, a groove width = 0.20-0. The optical information recording medium according to claim 4, wherein the optical information recording medium is 30 μm. The optical information recording medium according to claim 4, wherein the cell length is 0.20 to 0.30 μm. The optical information recording medium according to claim 1, wherein the reflective layer is made of Ag or an Ag alloy and has a thickness of 140 nm or more and 300 nm or less. The reflective film is made of Ag or an Ag alloy, and includes at least a reflective layer, a lower dielectric layer, a phase change recording layer, an upper dielectric layer, an adhesive layer, a cover substrate, or a reflective layer, an antisulfuration layer, and a lower dielectric layer on the substrate. 7. The optical information recording medium according to claim 1, further comprising a body layer, a phase change recording layer, an upper dielectric layer, an adhesive layer, and a cover substrate in this order.

Images