JP2004206851A - Optical information recording medium and its recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical information recording medium (particularly, a CD-RW) which can perform high-speed direct overwrite, and to provide its recording method. <P>SOLUTION: In the optical information recording medium, at least a recording layer and a reflecting layer are stuck on a transparent substrate. The optical information recording medium records, erases and/or rewrites information by forming/erasing a recording mark on/from the recording layer by irradiating condensed light and performing scanning with the light. The recording layer contains an alloy or an intermetallic compound using Ga, Ge, Sb, and Te as main components and represented by the following formula, Ga<SB>x</SB>Ge<SB>y</SB>(Sb<SB>z</SB>Te<SB>1-z</SB>)<SB>1-x-y</SB>, where, x, y, z represent an atomic ratio, and a positive real number, less than 1; 0.02≤x≤0.06; 0.01≤y≤0.06; 0.80≤z≤0.86; x≥y; x+y≤0.1. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a phase change type optical information recording medium, in particular, a CD-RW and a recording method thereof.
[0002]
[Prior art]
In a compact disk (CD) or a DVD, information is reproduced by a change in the intensity of reflected light of light applied to a medium. In the case of a read-only optical disk, the above-described change in intensity is realized by forming irregularities on the substrate to generate a phase difference of reflected light and cause interference.
On the other hand, in the case of a recording type medium, the above-described change in the intensity of the reflected light is realized by forming regions having different optical characteristics in a minute region of a recording layer formed on a substrate of the medium. Specific materials for the recording layer include organic dye recording layers of CD Recordable (CD-R) and DVD + R (DVD Recordable), and phase change recording layers of CD Rewriteable (CD-RW) and DVD + RW (DVD ReWritable). .
In each case, by irradiating the condensed light to the vicinity of the recording layer, a state change is caused in a minute area, and a phase difference or an intensity difference is generated due to a difference in optical characteristics of the area to record information. Will be.
[0003]
When the above-described phase change material is used for the recording layer, a reversible phase change between crystal and amorphous is used for recording, so that a recording mark can be formed and erasing is also possible. . Therefore, a rewritable optical information recording medium can be realized. In addition, since the crystal-amorphous phase transition can control the phase by the heat history of rapid cooling and slow cooling of the material, recording and erasing can be performed by modulating the intensity of irradiation light, and therefore, there is an advantage that a recording apparatus can be manufactured at low cost. There is. Further, the recorded medium has been widely used because it can be reproduced by a reproduction-only device.
In recent years, with the demand for larger capacity of electronic information and higher speed of information processing, demands for larger capacity and higher speed of optical discs have been increasing. In order to meet these demands, increasing the density of the recording medium is the most effective means. Methods for realizing high-density media include a change in the optical system used for recording and reproduction (higher NA, shorter wavelength), a change in the modulation method, and the like. Can be However, high-density DVDs cannot be played back by existing CD playback devices. Such playback incompatibility is a major problem as a distribution medium. When compatibility is important, speeding up is the biggest issue.
[0004]
In a rewritable optical information recording medium using a phase change material, it is said that it is very difficult to increase the speed in comparison with a write-once (write-once: one-time recording is possible) medium using a dye. I have. In order to form a recording mark at a high speed, it is sufficient to irradiate a high recording power as in the case of the dye, but this would make it impossible to erase the recording mark. That is, at a high scanning speed, it becomes impossible to create the condition of “slow cooling” necessary to realize a crystal phase in an erased state.
Therefore, at present, the speed of a phase-change rewritable optical disk is slower than that of an optical disk using a dye. For example, at present, there is a relationship of 40 × speed (scanning speed 48 m / s, channel bit rate 1.6 Gbps) for CD-R and 10 × speed (scanning speed 12 m / s, channel bit rate 41 Mbps) for CD-RW.
[0005]
The following are known as patent documents known before the present application.
Patent Document 1 discloses that ((Sb_xTe_1-x)_yGe_1-y)_zM_1-z(Provided that 0.7 ≦ x ≦ 0.9, 0.8 ≦ y <1, 0.88 ≦ z <1, M is In and / or Ga). However, in addition to the wide range of the numerical limitation, the examples are only for the case of M = In, and no data for confirming the effect when M = Ga are shown at all. There is no description about the necessity of Ga and the large difference between Ga and In. Furthermore, there is no mention of the object of the present invention, namely, to secure storage reliability and to improve the direct overwrite characteristics at a scanning speed of 20 m / s or higher.
Patent Document 2 discloses a high-speed overwriteable optical information recording medium having a recording layer containing GeSbTe as a main component and adding an arbitrary metal element selected from many, As Example 16, Ga_0.06Ge_0.06Sb_0.68Te_0.22The high speed mentioned here is at most 10 m / s in view of the description of claim 31 and the like, and the overwriting at a scanning speed of 20 m / s or more as in the present invention is performed. No mention is made of the improvement of the properties, and the alloy composition of Example 16 is also outside the numerical limitation range of the present invention. Further, the effectiveness of Ga mentioned in the present invention is neither described nor suggested.
[0006]
Patent Literatures 3 and 4 disclose optical information recording media having a recording layer containing SbTe as a main component and adding an arbitrary element selected from a large number. However, GaGeSbTe alloy is specifically described. There is no target description at all. Further, neither the direct overwrite characteristic at a scanning speed of 20 m / s or more, which is the object of the present invention, nor the validity of Ga indicated in the present invention is described or suggested.
Patent Document 5 discloses an optical information recording medium having a recording layer containing GaGeSbTe as a main component. However, since the optical information recording medium is mainly made of a GeTe alloy (or an intermetallic compound), the Sb-Te eutectic alloy of the present invention is used. The composition range and characteristics are significantly different from those of a material system in which a trace amount of a metal element is added.
[0007]
[Patent Document 1]
JP 2000-313170 A
[Patent Document 2]
JP 2001-56958 A
[Patent Document 3]
JP 2001-236690 A
[Patent Document 4]
Japanese Patent No. 3255051 (JP-A-10-172179)
[Patent Document 5]
Japanese Patent No. 2629749 (JP-A-1-138634)
[0008]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide an optical information recording medium which is currently widely used, particularly a CD-RW, which can be directly overwritten at high speed and a recording method thereof.
[0009]
[Means for Solving the Problems]
The above object is achieved by the following inventions 1) to 13) (hereinafter, referred to as inventions 1 to 13).
1) At least a recording layer and a reflection layer are laminated on a substrate, and information is recorded, erased, and / or formed by irradiating and scanning condensed light to form and erase recording marks on the recording layer. In the optical information recording medium to be rewritten, the recording layer contains an alloy or an intermetallic compound containing Ga, Ge, Sb, and Te as main components and a composition ratio of these elements represented by the following formula. Optical information recording medium.
Ga_xGe_y(Sb_zTe_1-z)_1-xy
Here, x, y, and z are positive real numbers less than 1 representing an atomic ratio and satisfy the following requirements.
0.02 ≦ x ≦ 0.06
0.01 ≦ y ≦ 0.06
0.80 ≦ z ≦ 0.86
x ≧ y
x + y ≦ 0.1
2) The optical information recording medium according to 1), wherein the content of an alloy or an intermetallic compound containing Ga, Ge, Sb, and Te as a main component in the recording layer is 90 atomic% or more.
3) The light according to 1) or 2), wherein the alloy or intermetallic compound mainly containing Ga, Ge, Sb, and Te contains Mn in an atomic ratio in the range of 0.01 to 0.04. Information recording medium.
4) The recording layer is Ar and N₂Formed by a vacuum film formation method in an atmosphere containing_Ar, N₂Partial pressure of P_N, The maximum crystallization speed of the medium₀And P_N/ P_ArThe maximum crystallization speed of the medium when <0.001 is represented by v_LAnd if
1.1 ≦ v₀/ V_L≦ 1.3
The optical information recording medium according to any one of 1) to 3), which satisfies the following condition:
5) P_N/ P_ArThe optical information recording medium according to 4), wherein the ratio of Ge content y of the recording layer satisfies the following condition.
1 ≦ (P_N/ P_Ar) /Y≦1.5
6) The recording speed according to any one of 1) to 5), wherein the scanning speed for recording, erasing, and / or rewriting is preformatted, and the scanning speed is 9.6 to 33.6 m / s. Optical information recording medium.
7) The optical information recording medium according to any one of 1) to 6), wherein the reflective layer is made of Ag or an alloy containing 95 mol% or more of Ag.
8) A layer having an oxide as a main component adjacent to the recording layer on the substrate side and / or the reflection layer side as viewed from the recording layer, and having a thickness in the range of 1 to 5 nm. 7. The optical information recording medium according to any one of items 1) to 7).
9) Initialization (operation of turning the recording layer of the information recording area of the medium into a crystallized state before using the medium) by irradiating and scanning with a high-power laser at a scanning speed of 1 to 2.5 m / s. The optical information recording medium according to any one of 1) to 8), wherein the recording is performed.
10) A sputtering target for producing an optical information recording medium, characterized by containing an alloy or an intermetallic compound containing Ga, Ge, Sb, and Te as main components and a composition ratio of these elements represented by the following formula.
Ga_xGe_y(Sb_zTe_1-z)_1-xy
Here, x, y, and z are positive real numbers less than 1 representing an atomic ratio and satisfy the following requirements.
0.02 ≦ x ≦ 0.06
0.01 ≦ y ≦ 0.06
0.80 ≦ z ≦ 0.86
x ≧ y
x + y ≦ 0.1
11) The sputtering target according to 10), wherein the content of an alloy or an intermetallic compound containing Ga, Ge, Sb, and Te as a main component is 90 atomic% or more.
12) The sputtering according to 10) or 11), wherein the alloy or intermetallic compound mainly containing Ga, Ge, Sb, and Te contains Mn in an atomic ratio in the range of 0.01 to 0.03. target.
13) Initialization (operation of crystallizing the recording layer of the information recording area of the medium before using the medium) by irradiating and scanning a high-power laser at a scanning speed of 1 to 2.5 m / s. The method for initializing an optical information recording medium according to any one of 1) to 9), wherein the method is performed.
14) The recording mark is formed by alternately irradiating and scanning a pulse with an irradiation intensity P of P = Pw and a pulse of P = Pb, and the recording mark length is nTw (n is a natural number) with respect to the basic clock cycle Tw. When the number of pulses of P = Pw is m (m is a natural number equal to or less than n), the relationship of n = 2m (when n is an even number) or n = 2m + 1 (when n is an odd number) is obtained. The optical information recording medium according to any one of 1) to 9), wherein the mark is erased by irradiating and scanning light with a constant intensity of P = Pe, and Pw> Pe> Pb. Recording method.
15) The recording method according to 14), wherein n = m + 1 when the scanning speed is 22.4 m / s or less and Tw is 14.4 ns or more.
[0010]
Hereinafter, the present invention will be described in detail.
FIG. 1 shows a cross-sectional view (schematic diagram) of an example of the optical information recording medium of the present invention. The optical information recording medium of the present invention has at least a recording layer (3) and a reflective layer (5) on a substrate (1). Since light used for recording, erasing, and reproduction is incident from the substrate side below the figure, the substrate (1) has high transmittance and high intensity in the wavelength region of light used for recording, rewriting, and reproduction. Are preferred. Examples of such a substrate material include glass, ceramics, and resin, but it is preferable to use a resin-made substrate in consideration of strength, cost, and productivity, and further, in consideration of strength and low birefringence. Then, an acrylic resin or a polycarbonate resin is particularly preferable.
A light guide groove (groove) used for recording and reproduction may be provided on the substrate. The shape of the guide groove, that is, the groove depth and groove width are optimized by the wavelength of light used for recording / reproducing, the numerical aperture (NA) of an objective lens used for condensing, aberrations, and the like. For example, in a CD-RW using an optical system having a wavelength of 780 nm and an NA of 0.50, the groove width is preferably 500 to 650 nm, and the groove depth is preferably 30 to 50 nm, and more preferably 580 to 610 nm, and the groove depth is 32 to 50 nm. 44 nm. The groove may meander, and the preformatted address information may be encoded in the meandering (wobbling). Examples of the preformat of the address include CD-R / RW ATIP (Absolute Time in Pregroove) for frequency-modulating wobbling and DVD + RW / R ADIP (Address in Pregroove) for applying phase modulation to wobbling.
[0011]
As the recording layer (3), an alloy or an intermetallic compound containing GaGeSbTe as a main component is used. The proportion of the alloy or intermetallic compound in the recording layer is preferably at least 90 atomic%, more preferably at least 96 atomic%. If an impurity or an additive is added more than that, it becomes difficult to obtain a sufficient recrystallization speed, which causes deterioration of erasability at a high scanning speed. Further, the alloy or intermetallic compound has a composition of Ga, Ge, Sb, Te.
Ga_xGe_y(Sb_zTe_1-z)_1-xy
(Where x, y, and z are positive real numbers less than 1 representing the atomic ratio), x, y, and z need to satisfy the following requirements.
0.02 ≦ x ≦ 0.06
0.01 ≦ y ≦ 0.06
0.80 ≦ z ≦ 0.86
x ≧ y
x + y ≦ 0.1
[0012]
The recording layer material of the present invention is SbTe which is a eutectic mixture composition of SbTe._0.7Te_0.3Is the basic material. In this material system, the basic characteristics of the medium can be controlled by adjusting the value of z, which is the ratio of Sb to Te. By increasing z, the recrystallization speed is improved, and crystallization is facilitated even in a high scanning speed region, so that the amorphous mark can be erased at high speed, and direct overwriting (that is, erasing operation is not included) Overwriting) becomes possible. In order to enable direct overwriting at 28.8 to 33.6 m / s, which is equivalent to 24 × speed of a compact disc, z needs to be in the above range, and more preferably 0.815 or more. . On the other hand, when z is increased, the overwrite characteristics at high speed are improved, but the stability of the amorphous mark is significantly reduced. Since this phenomenon is remarkable even when an additional element described later is added, in order to secure a storage life of 1000 hours or more at 70 ° C., the above-mentioned upper limit of z must not be exceeded. (This finding clearly differs from the conventional CD-RW, that is, z-0.7 to 0.75 is optimal in a CD-RW corresponding to 10-times speed.)
[0013]
Further, by adding an additional element to SbTe, the stability of the amorphous mark can be improved. Examples of practical application of the SbTe eutectic mixture by adding an additional element include GeInSbTe alloy to which Ge and In are added, AgInSbTe alloy to which Ag and In are added, and AgGeInSbTe alloy to which Ag, Ge, and In are added. . However, in these recording layer material systems, when the composition ratio z is set higher and the crystallization rate is improved, there is a problem that the storage reliability is significantly reduced. That is, good characteristics are exhibited in a region where the scanning speed at the time of recording is 14 m / s or less, but it is very difficult to cope with a higher scanning speed.
[0014]
Further, in the case of AgInSbTe, GeInSbTe, and AgGeInSbTe, it is possible to achieve both crystallization speed and storage reliability by increasing the amount of In added. However, when the amount of In increases, the crystallization temperature decreases. And there is a problem that initialization with a high-power laser becomes very difficult. In the case of a recording material having such a high crystallization temperature, the fluctuation of the reflectance of the medium becomes large, and a noise component of a reproduced signal is loaded, which leads to an increase in jitter and an increase in error, thereby reducing the reliability of the medium. It becomes a factor to lower.
As a means for solving these problems, it is effective to replace In with Ga of the same group. Thereby, the crystallization speed can be increased and the rise in the crystallization temperature can be suppressed. Then, recording at 28.8 m / s (or 33.6 m / s when the reference linear velocity is 1.4 m / s), which is equivalent to 24 × speed of a compact disk, becomes possible, and the crystallization temperature is reduced to 200 ° C. or less. It can be suppressed, and initialization can be facilitated.
[0015]
From the above, it can be seen that the GaSbTe recording layer is effective for achieving both high-speed recording and ease of initialization. However, there remains a problem that the stability of the recording mark is low. That is, when the recorded amorphous mark is left in an environment of 70 ° C., a phenomenon occurs in which the mark crystallizes and disappears within 1000 hours.
As a means for solving this problem, there is addition of Ge. By adding Ge, it is possible to increase the temperature dependence of crystallization, and it is possible to increase the crystallization rate at a high temperature of 200 ° C. or higher and to reduce the crystallization rate near 70 ° C. It becomes. This makes it possible to achieve both excellent erasability at high speed (that is, overwrite characteristics) and stability of recorded marks.
The composition ratios x and y of Ga and Ge need to be in the above-mentioned ranges. Further, it is necessary that x + y ≦ 0.1. If Ge and Ga are excessively added, the light absorption of the recording layer increases, and as a result, the reflectivity of the medium is significantly reduced. As a result, the absolute amplitude of the reproduced signal is insufficient, and the reliability of the medium is reduced.
[0016]
By adding a trace element to the GaGeSbTe recording layer, the direct overwrite characteristics at high speed recording can be improved. The additive element is preferably less than 10 atomic% with respect to GaGeSbTe, more preferably 4 atomic% or less. By adding a small amount of Ag, Dy, Mg, Mn, Se, or Sn as an additive element, the crystallization speed of the recording layer can be finely adjusted. In particular, Mn can increase the crystallization speed and lower the crystallization temperature in the same manner as the effect of Ga described above, so that the direct overwrite characteristics at high speed can be improved, and at the same time, the initialization (recording layer formation) can be performed. (Operation of performing crystallization after film formation) can be facilitated. The added amount of Mn is preferably 1 to 4 atomic% (at an atomic ratio of 0.01 to 0.04), and more preferably 1 to 3 atomic%.
[0017]
The film thickness of the recording layer is set to an optimum value based on thermal characteristics related to recording sensitivity and overwrite characteristics and optical characteristics such as modulation and reflectance. An appropriate thickness range is from 10 to 25 nm, and more preferably from 12 to 18 nm. By setting this range, good overwrite characteristics can be realized in high-speed recording of 20 m / s or more.
Although any method can be used for forming the recording layer, a vacuum film forming method (gas phase method) is preferable from the viewpoint of mixing impurities and forming a film on a resin substrate. As the vacuum film formation method, there are a sputtering method, a vapor deposition method, a CVD (Chemical Vaporized Deposition) method, an ion plating method, and the like. The sputtering method is preferable in consideration of productivity.
In the case of using a sputtering method, since a difference between the element composition of the target and the element composition of the formed thin film is small, a thin film having a desired composition can be easily obtained by setting a target material to a desired composition. The target may be prepared by mixing and solid-solving pure substances of constituent elements at a desired composition ratio, or may be prepared by sintering fine particles of an alloy or a pure substance. In the case of sintering, the higher the density of the target, the higher the sputtering rate (the film thickness formed per unit time), which is preferable, and is preferably 90% or more.
[0018]
Furthermore, the optical information recording medium of the present invention can be used in an atmosphere containing nitrogen N (usually N₂Is preferably used. As a film forming method, a vacuum film forming method such as a vacuum evaporation method, an ion plating method, a CVD method, and a sputtering method is generally known. In the present invention, Ar and N are used.₂It is best to use a sputtering method using a mixed gas of Further, N₂By forming the recording layer in an atmosphere, it becomes possible to make the recording layer material more suitable for high-speed recording. That is, the crystallization upper limit speed can be increased.
Here, the definition of the crystallization upper limit speed referred to in the present invention will be described.
The reflectance after initialization of the medium (the details of initialization will be described later) is R₀And the irradiation power P₀The reflectance after irradiating this light at the scanning speed v is R. In addition, it is preferable to use the same optical system as that used for information recording on the medium for irradiating / scanning the medium and to measure the reflectance R, and the irradiation power P is in the range of 10 to 30 mW. Is preferred.
R ≧ R₀If, the recording layer is in a crystallized state, but R <R₀In the case of (1), the recording layer has an irradiated / scanned portion in an amorphous state or a state including an amorphous state. That is, it is considered that the average reflectance R decreases because an amorphous state having a low reflectance is formed in the recording layer. When the scanning speed v is increased, the recording layer approaches a quenched state, and thus tends to be in an amorphous state. Scanning speed v and normalized reflectance R / R of the medium₀Is as shown in FIG. That is, when v shown on the horizontal axis is small, the recording layer is gradually cooled and crystallized, and when v is large, the recording layer is in a rapidly cooled state and becomes amorphous, so that R / R₀Becomes lower. In the present invention, R / R₀The scanning speed v at which = 1₀Is defined as the upper limit of crystallization speed.
[0019]
This v₀Is high, it means that crystallization is possible even at a higher scanning speed. That is, the recording mark can be erased at high speed, and direct overwrite (DOW) at high speed can be performed. Therefore, as compared to FIG. 9A, DOW at higher speed is possible in FIG. 9B, and DOW is possible only at lower speed in FIG. 9C.
This v₀Is considered to be closely related to the crystallization speed of the recording layer, and thus can be adjusted by changing the composition of the constituent elements of the recording layer as described above. It is also possible to adjust according to the atmosphere at the time of forming the recording layer. In particular, the N₂It is easy to adjust by the partial pressure.
Partial pressure ratio P_N/ P_ArAnd v₀Is shown in FIG. As shown in FIG. 10, when the partial pressure ratio is increased, v₀Rises discontinuously. V in the region A where the partial pressure ratio is high in FIG.₀V_L, V in the region of C where the partial pressure ratio is high₀V_HThen v_L<V_HHolds. In the area of A, v₀Is low and the DOW characteristic at high speed cannot be ensured.₀And high speed. The area B is an unstable area in which A and C are mixed.
[0020]
What is characteristic here is that the state changes to "discontinuous". That is, N₂The state of the recording layer is clearly different due to film formation in an atmosphere containing.
In the optical information recording medium of the present invention, the crystallization upper limit velocity v₀Is N in the atmosphere when the recording layer is formed.₂To the extent that the partial pressure can be regarded as substantially zero with respect to the Ar partial pressure, that is, P_N/ P_ArCrystallization upper limit speed v when <0.001_LFor 1.1 ≦ v₀/ V_LIt is preferable that the relation of ≦ 1.3 is satisfied. v₀/ V_LIs smaller than 1.1, the effect of increasing the crystallization upper limit speed is small, and the characteristics in high-speed recording are slightly deteriorated. On the other hand, when the ratio exceeds 1.3, the stability of the recording mark (amorphous mark) at a low temperature of the medium, that is, at around room temperature (20 to 60 ° C.) is remarkably reduced, and from the viewpoint of the storage reliability of the recorded information. Not preferred.
Also, P_N/ P_ArVaries depending on the Ge composition ratio of the recording layer. For a recording layer material having a high Ge composition ratio, a higher P_N/ P_ArNeed to be set. Therefore, it is preferable to set the range to satisfy the following condition in accordance with the Ge composition y described above.
1 ≦ (P_N/ P_Ar) /Y≦1.5
[0021]
N₂The effect of the formation of the recording layer in the containing atmosphere on the upper limit of the crystallization rate has not been clarified, but it is considered that this may affect the structure of the recording layer after the formation.
The reason is that N is detected when the recording layer immediately after film formation is subjected to SIMS analysis (Secondary Ion Mass Spectroscopy analysis = secondary ion mass spectrometry), but N is detected in the recording layer after annealing or initialization. Is not detected and N₂N taken into the recording layer in the film formation process in the containing atmosphere is diffused by annealing or initializing the medium at 100 ° C. or lower (crystallization operation of the entire recording layer using a high-power laser described later). It is because it is seen to be gone.
Therefore, since recording on the medium is performed after initialization, it is not necessary that N is contained in the recording layer in the final form of the medium.
[0022]
In the optical information recording medium of the present invention, it is necessary to provide a reflective layer above the recording layer, that is, on the side opposite to the substrate. The reflection layer has a function of reflecting recording light and reproduction light incident from the substrate side. Therefore, it is preferable to use a material having a high reflectivity, and as the material having a high reflectivity, Au, Ag, Cu, Al, or an alloy or an intermetallic compound containing these metals as main components is preferable. Examples of additional elements that can be added to these materials include metals such as Au, Ag, Cu, Al, Pt, Pd, Ta, Ti, Co, Mn, Mo, Mg, Cr, Si, Sc, and Hf. No.
The reflective layer has an optical function of reflecting recording / reproducing light, and also has a role of releasing heat applied to the vicinity of the recording layer during recording / erasing. In order to cope with high-speed recording, it is necessary to use a recording layer material having a high crystallization rate as described above. Therefore, it is preferable that the medium itself has a rapid cooling structure. That is, by using a material having a high thermal conductivity as the material of the reflection layer, it is possible to form a mark of a sufficient size even with a recording layer material having a high recrystallization rate. Ag or an Ag alloy is used as a material having a high thermal conductivity. When an Ag alloy is used, the Ag content is preferably 95 mol% or more, and more preferably 99 mol% or more. As an additive element in the case of forming an alloy, the above-mentioned metals can be used. However, it should be noted that a large amount of the additive significantly lowers the thermal conductivity. When Ag alone is used, it is preferable that the purity is 99.99 mol% or more.
The reflective layer is preferably formed by a vacuum film forming method as in the case of the recording layer, and the film thickness is determined from the thermal characteristics and optical characteristics as in the case of the recording layer. If the reflective layer is too thin, recording and reproduction light will be transmitted, and a sufficient reflectance cannot be obtained. On the other hand, if the reflective layer is too thick, the heat capacity of the medium will increase and the recording sensitivity will decrease. The optimum value of the film thickness determined from the thermal characteristics and the optical characteristics is in the range of 800 to 3000 nm, and more preferably in the range of 1000 to 2200 nm.
[0023]
It is preferable to form protective layers above and below the recording layer. As shown in FIG. 1, a protective layer below the recording layer, that is, on the substrate side is defined as a lower protective layer (2), and a protective layer above the recording layer, that is, on the reflective layer side is defined as an upper protective layer (4).
The lower protective layer is necessary for protecting the resin substrate from heat generated in the recording layer and the vicinity of the recording layer during recording, erasing, and rewriting (overwriting). At the same time, by adjusting the optical constant (refractive index) and the film thickness, there is also a function of enhancing the contrast by the amorphous marks recorded on the recording layer.
As a material for the lower protective layer, a material having a high refractive index and a high melting point (1000 ° C. or higher) is preferable, and a dielectric is generally used. As the dielectric, compounds such as metal oxides, nitrides, sulfides, and halides and inorganic substances such as Si and Ge can be used. Further, these substances may be pure substances or mixtures.
[0024]
Examples of the above compounds include oxides such as Mg, Ca, Sr, Y, La, Ce, Ho, Er, Ti, Zr, Hf, V, Nb, Ta, Zn, Al, Si, Ge, and Pb, and sulfides. And carbides, and examples of halides include fluorides of Mg, Ca, and Li.
In particular, SiO is added to ZnS.₂Is widely used. The lower protective layer preferably has a thickness of 40 to 200 nm. If the thickness is smaller than 40 nm, thermal damage to the resin substrate increases. Is unfavorable because mechanical damage (cracks and the like) occurs due to the heat history. Further, it is preferable to set the value near the film thickness at which the reflected light at the reproduction wavelength becomes minimum. Therefore, the optimum thickness of the lower protective layer is in the range of 50 to 90 nm.
[0025]
The lower protective layer may be a single layer or a multilayer. When the same material is formed into multiple layers and formed by a plurality of film forming apparatuses, the manufacturing time of the medium can be shortened, and there is an effect of reducing the manufacturing cost of the medium. Further, by providing a layer that promotes crystallization of the recording layer in a layer adjacent to the recording layer, it is possible to secure a margin for initializing the medium. As a layer that promotes crystallization, Bi, GaN, or the like is generally used, but in the present invention, it is preferable to provide an oxide layer. Examples of oxides include Al₂O₃, SiO₂, TiO₂, ZrO₂, Y₂O₃, ZnO and the like. These oxides are considered to have an effect of promoting crystallization because the lattice constant of the crystal is relatively close to that of the SbTe-based material. An appropriate thickness of the oxide layer is 1 to 5 nm. If the thickness is less than 1 nm, a uniform film is not formed, and the uniformity of the optical disk is impaired. In addition, the above-mentioned oxide layer often has a sputtering rate of 1/5 or less as compared with a general protective layer material such as ZnS. Therefore, it is preferable to set the film thickness to the minimum thickness at which the effect of promoting crystallization is obtained.
When the lower protective layer is formed as a multilayer, the thickness of the entire protective layer is preferably within the above range, and the ratio can be set from optical characteristics, thermal characteristics, productivity, and the like.
[0026]
The upper protective layer has a function as an interface layer for preventing diffusion of the recording layer material into the reflection layer material or diffusion of the reflection layer material into the recording layer material, and a function of controlling thermal characteristics. As the upper protective layer material, it is possible to use the same material as the lower protective layer material described above, but it is preferable to use a material having a low thermal conductivity. When a material having a high thermal conductivity is used, the thermal efficiency is reduced, so that the volume of the recording layer material that reaches a temperature equal to or higher than the melting point when irradiated with a focused beam is reduced. Therefore, at the same time as the sensitivity of the medium is remarkably reduced, the recording mark becomes small, so that a sufficient reproduction signal amplitude cannot be secured.
[0027]
The thickness of the upper protective layer is preferably in the range of 5 to 50 nm, more preferably 10 to 23 nm. It is also possible to make the upper protective layer multilayer.
In particular, when a sulfide or a halide is used for the upper protective layer material and Ag or an alloy containing Ag as a main component is used for the reflective layer, corrosion of the reflective layer is likely to occur, and the storage reliability of the medium is reduced. Lower it. In such a case, it is preferable that the upper protective layer be multi-layered and a material having low Ag corrosion be laminated on the layer adjacent to the reflective layer. Materials for such a layer include Si, SiO₂, SiC, GeN, GaN, and the like. The thickness of such a layer is preferably from 2 to 10 nm, and preferably from 2 to 5 nm in order to maintain the reflectance of the medium. If the thickness is less than 2 nm, it does not play a role of preventing corrosion, so that it is not preferable.
Further, similarly to the lower protective layer, a material that promotes crystallization of the recording layer material may be provided at the interface with the recording layer.
[0028]
An overcoat layer (6) as shown in FIG. 1 may be provided to protect the multilayer film laminated on the medium substrate from physical and chemical damage. A resin material is generally used for the overcoat layer, and it is preferable to apply and cure an ultraviolet curable resin, an electron beam curable resin, a thermosetting resin, or the like. Among the resin materials, an ultraviolet curable resin is preferable because damage to a medium during film formation can be reduced. For film formation, a dipping method, a spin coating method, or the like is used, and it is preferable to use a spin coating method from the viewpoint of uniformity of the film thickness. When Ag or a material containing Ag as a main component is used for the reflective layer material, it is preferable to use a material that does not corrode Ag.
In order to further protect the optical disc from physical damage and chemical damage, a multilayer film may be formed on the overcoat layer.
[0029]
When the recording layer of the medium created as described above is in an amorphous state, initialization for crystallizing the recording area of the medium is required. As the initialization method, any method can be used, and examples thereof include a method of irradiating and scanning a high-power laser to crystallize the recording layer, and a flash method of irradiating the entire surface of the medium with light.
The method using a high-power laser is preferable because the irradiation energy of the laser can be converged to the vicinity of the recording layer using an objective lens. Furthermore, by using a high-power laser, it is possible to increase the irradiation beam diameter near the recording layer and to increase the scanning speed. The output of the high-power laser is preferably 500 mW or more in power consumption, more preferably 900 mW or more. The beam shape is preferably long in the direction perpendicular to the scanning direction because the area initialized by one scan is large. The size of the beam is preferably 0.5 to 2.0 μm in the scanning direction, and preferably 50 to 300 μm in the direction perpendicular to the scanning direction. The scanning speed of the beam differs depending on the beam width and the laser output. The higher the energy amount per unit area of the beam (that is, the smaller the beam diameter and the higher the output), the higher the scanning speed. The scanning speed is preferably in the range of 1.0 to 12.0 m / s. When a laser having an output of 900 mW is used, the scanning speed is optimally 1.0 to 2.5 m / s.
In addition, the recording layer is formed by N₂When the crystallization speed is increased in an atmosphere containing, the appropriate scanning speed is in the range of 5.0 to 7.0 m / s.
[0030]
Recording, erasing, reproducing, and rewriting of information on the optical information recording medium of the present invention is performed by irradiating condensed light to the vicinity of the medium recording layer and scanning. Laser light is used for recording and reproduction. The wavelength of the laser can be selected according to the recording density and the like. Examples include 780 nm CDs, 650 or 660 nm DVDs. The objective lens used for light collection is also determined by the wavelength and the recording density, and includes an NA of 0.50 for CD-R / RW, an NA of 0.55 for DD (double density) CD-RW, and an NA of 0.65 for DVD + R / RW. .
The information recorded on the optical information recording medium of the present invention records information modulated by a mark-to-mark length and mark length modulation system in which PWM (Pulse Width Modulation) is applied to an optical disc. Examples of this modulation method include 8-14 modulation (EFM) used for compact discs and EFM + which is a type of 8-16 modulation used for DVDs.
[0031]
The recording on the medium is performed by irradiating the modulated light. As an example using intensity modulation, a method disclosed in JP-A-9-219021 or a method described in Orange Book Part III can be used. In this method, the irradiation power is modulated by three values. An example of this technique is shown in FIG. FIG. 2A schematically shows an amorphous mark to be recorded. Since the figure shows an example of EFM (Eight to Fourteen Modulation), the mark length is 3 Tw, 4 Tw,. . . 11 Tw. Assuming that the mark length is nTw (n = 3, 4,... 11), the irradiation pattern used for recording (hereinafter referred to as a recording strategy) is as shown in FIG. As shown in the figure, the pulse is modulated into three values of Pw> Pe> Pb and the number of pulses of P = Pw becomes n-1.
The parameters of this recording method are represented by Ttop, dTtop, Tmp, and dTera.
[0032]
In this recording method, the response time of the laser may not catch up with the pulse width in high-speed recording in which the basic clock cycle at the time of writing becomes short. At 24 times the speed of a CD, the basic clock cycle is 9.6 ns, and the clock frequency is 104 MHz. In this case, in order to apply sufficient energy to the medium, it is necessary that the rise and fall times of laser emission be 1 ns or less.
As a technique for performing high-speed recording with a laser having a long rise and fall time, there is a technique for reducing the number of pulses as disclosed in US Pat. No. 5,732,062. That is, when m pulses are used to form an nTw mark, the relationship of n = 2m holds when n is an even number, and the relationship of n = 2m + 1 holds when n is an odd number. By using this recording strategy, it is possible to perform recording at 24 × speed even with a laser having a rise and fall time of 2 ns.
An example of this strategy is shown in FIG. FIG. 3 shows the case of the EFM similarly to FIG.
[0033]
Recording on the optical information recording medium of the present invention is performed at a scanning speed in the range of 9.6 to 33.6 m / s, and the basic clock cycle during recording is in the range of 9.6 to 29.0 ns. It is desirable that the information about the scanning speed at the time of recording be preformatted on an optical information recording medium. That is, it is desirable that information on the above-described recordable scanning speed range is added before the information is recorded on the medium.
Any preformatting method can be used. For example, a method of performing preformatting on the substrate itself, such as a method of providing embossed pits on the substrate or a method of inserting information into wobbling of grooves, and a method of recording There is a method of recording on a part of a medium using an apparatus. Of these, the method of preformatting the information on the substrate itself is preferable because it is advantageous in the production process of the medium. There is a problem in stamper processing for forming a substrate. Therefore, a method of preformatting the groove wobbling is most preferable.
[0034]
As such an example, there is a method of preformatting information on a scanning speed and an appropriate recording state instead of address information using a method similar to the above-described ATIP or ADIP. Examples of preformatting of the scanning speed information in the ATIP include HTS (Highest Testing Speed, highest test speed) and LTS (Lowest Testing Speed, lowest test speed) in CD-R and CD-RW. Examples of use include the Maximum Recording Velocity (maximum recording speed) and Reference Recording Velocity (reference recording speed) of DVD + R. The printing apparatus can set an appropriate printing scan speed by reading the information on the printable scan speed from the print medium.
The information on the scanning speed may be described in a format uniquely determined. In the case of CD-R and CD-RW preformatted in the above ATIP, a multiple of the reference scanning speed is preformatted, but the reference scanning speed of the CD is 1.2 to 1.4 m / s. , The scanning speed can be specified from the preformat information. For example, when the multiple of the preformatted scanning speed is “24 times”, the scanning speed is 28.8 to 33.6 m / s.
Further, in the speed area, there must be an area which can be recorded by both the recording strategy of m = n-1 and the recording strategy of n = 2m (or n = 2m-1). It is preferable that the recording range of the recording strategy of m = n-1 (that is, n = m + 1) is limited to the low-speed recording side, and is equal to or less than 16 times the speed of CD, that is, the scanning speed is 22.4 m / s or less, More preferably, the period Tw is 14.4 ns or more.
[0035]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.
[0036]
Example 1
An optical disk was prepared by sequentially laminating a lower protective layer, a recording layer, an upper protective layer, a reflective layer, and an overcoat layer on a polycarbonate transparent substrate to which a continuous spiral groove was transferred.
The substrate used was a CD-RW substrate having an outer diameter of 120 mm and a thickness of 1.2 mm. The substrate is formed by injection molding, and a spiral continuous groove is transferred using a stamper. When the shape of the groove transferred to the substrate was measured by AFM (atomic force microscope), the groove width was 620 nm and the groove depth was 40 nm. The groove was wobbling, and the meandering was such that the average frequency was 22.05 kHz when scanning at a linear velocity of 1.2 m / s. In wobbling, address information is preformatted using frequency modulation, and the modulation method and address information are commonly known as Orange Book Part III Volume 2 Version 1.1 (Recordable Compact DiscSystems Part III), which is an international standard for CD-RW. volume 2 version 1.1).
The birefringence of the substrate was adjusted to be 40 nm or less at a recording / reproducing wavelength of 780 nm in order to ensure the reliability of recording and reproduction of the medium. Birefringence was optimized by adjusting the resin injection speed and mold temperature during injection molding.
Further, before forming each layer described below, annealing was performed at 60 ° C. for 12 hours to sufficiently remove moisture adsorbed or taken into the substrate.
ZnS and SiO on the above transparent substrate₂Was provided on the lower protective layer. ZnS and SiO₂Was 80:20 in molar ratio. For the film formation, an RF magnetron sputtering method, which is a kind of vacuum film formation method, was used. Ar, which is a general inert gas, was used as a sputtering gas, the output of a high-voltage power supply for sputtering was 4 kW, and the inflow of Ar gas was 15 sccm. The thickness of the lower protective layer was 75 nm.
On the lower protective layer, a recording layer made of a material represented by the following composition formula was formed.
Ga_xGe_y(Sb_zTe_1-z)_1-xy
In the formula, x, y, and z are atomic ratios, and the values are as follows.
x = 0.038
y = 0.030
z = 0.815
The film was formed by a DC magnetron sputtering method using a GaGeSbTe alloy target. Ar was used as a sputtering gas, the flow rate thereof was set to 20 sccm, and the sputtering power was set to 400 W. The thickness of the recording layer was set to 16 nm.
An upper protective layer was further formed on the recording layer. The same material as the lower protective layer material was used for the upper protective layer material. Similarly, RF magnetron sputtering using Ar gas was used for film formation. However, the sputtering power was set to 1.5 kW. The thickness was 18 nm.
A 4 nm-thick Si film was formed on the upper protective layer in order to prevent Ag sulfidation. Si having a purity of 99.99% was used. The DC magnetron sputtering method was used for the film formation similarly to the recording layer. The sputtering power during film formation was set to 0.5 kW.
An Ag reflection layer was formed on the Si layer. The film was formed by a DC magnetron sputtering method using a target having a purity of 99.99% or more. The flow rate of Ar into the sputtering chamber was set to 20 sccm, and the sputtering power was set to 3 kW. The thickness of the reflective layer was 140 nm.
The thickness of each of the five thin films is a value optically measured using a spectroscopic ellipsometer. In addition, since the film was formed using a single-wafer sputtering apparatus, it was set so that it was not exposed to the air during the film formation from the lower protective layer to the reflective layer, and chemical reactions such as oxidation of the recording layer and gas adsorption were performed. Prevented.
An overcoat layer was formed on the reflective layer using a commercially available coating material for optical disks (UV curable resin SD318 manufactured by Dainippon Ink). The film was applied by a spin coating method and irradiated with a UV lamp to be cured. The film thickness of the overcoat layer was 8 μm at the inner circumference of the optical disc and 14 μm at the outer circumference of the optical disc.
[0037]
Since the recording layer of the completed optical disk was in a quenched state after sputtering and was entirely in an amorphous state, it was initialized by irradiating and scanning with a high-power laser. The high output laser used had an output of 900 mW. The beam shape of the laser is adjusted by adjusting the objective lens so that the laser beam is converged near the recording layer of the optical disc and becomes an ellipse. The ellipse was made shorter in the scanning direction (that is, the circumferential direction of the disk). That is, the adjustment was performed so that the short axis of the ellipse coincided with the scanning direction. Beam size is 1 / e of peak intensity²(Where e is the base of the natural logarithm), the edge of the beam was 1 μm on the short axis and 90 μm on the long axis. The entire surface of the optical disk was initialized by spirally scanning this beam at a scanning speed of 2 m / s. At this time, the spiral pitch (the amount of displacement in the radial direction per rotation) was set to 45 μm, and the laser beam was set to scan twice.
The optical disc that has been initialized is an unrecorded CD-RW that satisfies the mechanical characteristics and unrecorded signal characteristics described in Orange Book Part III.
Recording and overwriting were actually performed on the completed optical disk, and the recording signal characteristics were evaluated. For evaluation of signal characteristics, an optical disk evaluation device DDU1000 manufactured by Pulstec Industrial Co., Ltd. was used. The specifications of the optical pickup are NA 0.50, λ = 789 nm, and maximum emission power 35 mW. The rotation speed of the optical disk is 6000 rpm at the maximum, and an evaluation equivalent to 30 times the speed of a compact disk can be performed.
The recording strategy shown in FIG. 4 was used. That is, when the number of pulses is represented by m and the mark to be recorded is represented by the basic clock cycle nT, the light emission cycle of the pulse is made nT / m. Each strategy parameter was set as follows. Note that T in the drawing has the same meaning as Tw.
Tmp = 1.0T
Tmp '= 1.6T
Td1 = 0.5T
Td2 = 0T
δ = 0.125T
Scanning speed = 28.8 m / s (corresponding to 24 times speed of CD)
Basic clock cycle T = 9.64 ns
The recording powers Pw, Pe, Pb were set as follows.
Pw = 33mW
Pe = 11mW
Pb = 0.5mW
The information to be recorded was a pattern conforming to the rules of EFM. The recording was performed once to 1,000 times of direct overwriting.
With the same apparatus, the scanning speed was set to 1.2 m / s (corresponding to 1 × speed of CD), and the recording signal was evaluated. The evaluation items are 11T modulation degree, 3T mark jitter, and 3T space jitter. The CD-RW standard defines the following.
11T modulation degree: 0.55 to 0.70
Jitter: 35 ns or less
FIG. 5 shows the measurement results of the prepared optical disc. As can be seen from the figure, good results satisfying the standard were obtained over the repetitive recording times of 1 to 1000 times.
[0038]
Using the same optical disk as the optical disk evaluated above, recording was performed in exactly the same manner as described above except that the parameters of the recording strategy and the recording powers Pw, Pe, and Pb were changed as follows. Was evaluated.
Tmp = 0.5T
Tmp '= 0.8T
Td1 = 0.5T
Td2 = 0T
δ = 0.125T
Scanning speed: 9.6 m / s (corresponding to 8 times speed of CD)
Basic clock cycle T: 28.9 ns
Pw = 30mW
Pe = 10mW
Pb = 0.5mW
FIG. 6 shows the measurement results. As can be seen from the figure, good results satisfying the standard were obtained over the number of repetitions of 1 to 1,000.
Further, after the same optical disk as above was left under an environment of 80 ° C. and 85% RH for 300 hours, the 3T jitter of the recorded portion was measured. As a result, it was 35 ns or less, and it was confirmed that sufficient storage reliability was secured.
As is clear from the above results, a CD-RW disk which can be directly overwritten at 8 to 24 times the speed of a CD and has sufficient storage reliability was obtained.
[0039]
Comparative Example 1
An optical disk was prepared in the same manner as in Example 1 except that the composition of the recording layer material was changed as follows, and the optical disk was initialized in the same manner as in Example 1.
x = 0.029
y = 0.039
z = 0.820
However, in this optical disk, noise was generated on the reproduced signal in an unrecorded state, and recording and evaluation were performed in the same manner as in Example 1 when the scanning speed was 28.8 m / s. As a result, the jitter exceeded 35 ns and was out of the standard. It is probable that because the amount of Ge exceeds the amount of Ga added (x <y), the crystallization temperature was high and a uniform crystal phase could not be formed.
[0040]
Comparative Example 2
An optical disc was prepared in the same manner as in Example 1, except that the composition of the recording layer material was changed as follows.
x = 0.016
y = 0.049
z = 0.793
The initialization was also performed in the same manner as in Example 1 except that the scanning speed was set to 4.0 m / s.
Recording was performed on this optical disc in the same manner as in Example 1 except that the parameters of the recording strategy and the recording powers Pw, Pe, and Pb were changed as follows, and the signal characteristics were evaluated.
Tmp = 1.0T
Tmp '= 1.6T
Td1 = 0.5T
Td2 = 0T
δ = 0.125T
Scanning speed = 28.8 m / s (corresponding to 24 times speed of CD)
Basic clock cycle T = 9.64 ns
Pw = 30mW
Pe = 10mW
Pb = 0.5mW
As a result, the first recording showed a good result of 3T space jitter of 20 ns and 3T mark jitter of 19 ns. However, in the second recording (overwriting), both the space jitter and the mark jitter were about 42 ns. Therefore, it was confirmed that overwriting was not possible at 24 × speed of CD.
[0041]
Example 2
An optical disk was prepared in the same manner as in Example 1, except that the composition of the recording layer material was changed as in the following composition formula.
[Ga_xGe_y(Sb_zTe_1-z)_1-xy]_1-wMn_w
When represented by
x = 0.038
y = 0.030
z = 0.815
w = 0.02
The initialization was also performed in the same manner as in Example 1 except that the scanning speed was set to 2.5 m / s.
FIG. 7 shows the results of recording and evaluation of this optical disc in the same manner as in Example 1, with a scanning speed of 28.8 m / s, and FIG. 8 with a scanning speed of 9.6 m / s. However, as can be seen from the figure, good results were obtained in all cases, and by adding Mn to the recording layer, good characteristics could be secured at a higher scanning speed.
[0042]
Example 3
Between the lower protective layer and the recording layer, ZrO₂(77 mol%), TiO₂(20 mol%), Y₂O₃An optical disk was prepared in the same manner as in Example 1, except that an oxide layer of (3 mol%) was provided. The film was formed by the RF magnetron sputtering method which is the same method as the lower protective layer.
This optical disk was initialized in the same manner as in Example 1 except that the scanning speed was set to 2.5 m / s, and the noise on the reproduced signal in the unrecorded state was examined. It was equivalent. When recording and evaluation were performed in the same manner as in the case of Example 1 where the scanning speed was 28.8 m / s, the first recording jitter was 23 ns, which was a good result.
Accordingly, it was confirmed that the scanning speed for initialization can be increased by providing the oxide layer adjacent to the recording layer.
[0043]
Comparative Example 3
An optical disc was prepared in the same manner as in Example 1, except that the composition of the recording layer material was changed as follows.
x = 0.072
y = 0.029
z = 0.790
(X + y = 0.11)
This optical disk was initialized in the same manner as in Example 1 except that the scanning speed was set to 2.0 m / s.
The obtained disk had a low reflectance and was 0.14 in an unrecorded state, and could not satisfy the standard of 0.15 or more and 0.25 or less.
Further, recording and evaluation were performed in the same manner as in the case where the scanning speed of Example 1 was 28.8 m / s, and the jitter in the second recording exceeded 50 ns, and the characteristics could not be secured. .
This is presumably because x + y exceeded 0.1, the absorption coefficient of the recording layer was increased, and the reflectivity was lowered. As a result, good overwrite jitter could not be secured.
[0044]
Comparative Example 4
An optical disk was prepared in the same manner as in Example 1 except that the composition of the recording layer material was changed as follows, and the optical disk was initialized in the same manner as in Example 1.
x = 0.048
y = 0.031
z = 0.863
When recording and evaluation were performed on this optical disc in the same manner as in the case where the scanning speed of Example 1 was 28.8 m / s, the 11T modulation degree was 0.42, and a sufficient reproduction signal amplitude was obtained. Could not be done.
[0045]
Example 4
An optical disk was prepared in the same manner as in Example 1, except that the initialization conditions were set as follows.
Initialization power: 900mW
Scanning speed: 3.0m / s
Movement amount in the radial direction per rotation: 20 μm
Recording and evaluation were performed on this optical disc in the same manner as in the case where the scanning speed of Example 1 was 28.8 m / s. As a result, the jitter after 30 times of overwriting was as good as 30 ns. On the other hand, since noise due to the fine structure of the crystal occurred in the reproduced signal in the unrecorded state, the jitter in the first recording was 32 ns, which was a higher value as compared with Examples 1 to 3.
[0046]
Comparative Example 5
An optical disk was prepared in the same manner as in Example 1. However, InGeSbTe represented by the following composition formula was used as the recording layer material (Ga was replaced with In).
In_xGe_y(Sb_zTe_1-z)_1-xy
In the formula, x, y, and z are atomic ratios, and the values are as follows.
x = 0.035
y = 0.02
z = 0.802
Recording was performed once on the prepared disc by the method described in Example 1, and the disc was left for 300 hours in an environment of a temperature of 80 ° C. and a relative humidity of 85%. As a result, the jitter after the test was significantly reduced to 42 ns compared to the jitter of 23 ns before the environmental test.
When the same disk was recorded twice (that is, once overwritten) at a scanning speed of 28.8 m / s by the method described in Example 1, the jitter was 45 ns, which was a result that greatly exceeded the standard. It became.
From the above results, it has been clarified that when Ga is replaced with In, storage reliability and overwrite characteristics cannot be achieved.
[0047]
Example 6
An optical disk was prepared using the same method as in Example 1, except that the conditions for forming the recording layer and the conditions for initializing were changed as follows.
For the formation of the recording layer, Ar was used as a sputtering gas, the flow rate was set to 20 sccm, and the sputtering power was set to 400 W. Further, nitrogen gas having a purity of 99.99% was introduced into the sputtering chamber. The nitrogen gas flow rate was controlled using a mass flow (by adjusting the flow rate, N taken in the recording layer can be adjusted). The flow rate is adjusted within the range of 0 to 1.0 sccm, and the partial pressure P of Ar in the chamber is adjusted._ArAnd N₂Partial pressure P_NIs measured by a mass spectrum analyzer to obtain P_N/ P_ArWas quantified.
Initialization was performed under the following conditions.
Initialization power: 900mW
Scanning speed: 5.0m / s
Movement amount per rotation: 20 μm
The disc created as described above satisfies the Orange Book standard in an unrecorded state as in the first embodiment. The completed disk was analyzed by SIMS, but no element N was detected in the recording layer.
Next, the crystallization upper limit speed of the completed disk was measured. An optical disk evaluation device DDU1000 manufactured by Pulstec Industrial Co., Ltd. was used for the measurement. The specifications of the optical pickup were 0.50 NA, λ = 789 nm, the power at the time of measurement was 0.7 mW, and the irradiation power P was 20 mW.
Partial pressure ratio P_N/ P_ArFIG. 11 shows the result of measurement of the upper limit of the crystallization speed when Ge = 3%. It can be seen that the upper limit of the crystallization speed greatly increases at a partial pressure ratio of 0.035 or more.
Further, a single pattern of 10T-10T was recorded at a speed equivalent to 24 times the speed of a CD (scan speed: 28.8 m / s, clock frequency: 103.7 MHz). As the recording method, the same method as in Example 1 was used. The recorded pattern was reproduced at 1 × speed of CD (scanning speed 1.2 m / s), and the CN ratio was measured with a spectrum analyzer.
FIG._O/ V_LAnd the measurement results of the CN ratio are shown as the case of Ge = 3%. As can be seen, V_O/ V_LIs 1.1 or more, the CN ratio has a high value exceeding 55 dB.
Further, an erasing ratio was measured as a characteristic for determining the easiness of direct overwriting. The erasure ratio here is "S0 / S" measured as follows. That is, a single pattern of 10T-10T is recorded on the medium in the same manner as the measurement of the CN ratio described above, and the CN ratio is measured, and the measured value is set to S0. Next, the recorded portion is irradiated and scanned only once at P = 10 mW to perform a recording mark erasing operation, and then the CN ratio of the recorded portion is measured. The higher the S, the more unmarked marks remain. That is, the higher the value of S0 / S, the higher the erasability of the recording mark, and the medium is suitable for direct overwriting.
FIG. 13 shows the relationship between PN / PAr and the erase ratio.
From FIG. 13, it is found that at Ge 3%, V_O/ V_LIt can be seen that the erase ratio is high in the region of PN / PAr ≧ 0.035 where
Comparing these results with Comparative Example 2, it can be seen that a high CN and erase ratio can be obtained despite the high scanning speed of 5 m / s for initialization.
[0048]
Example 7
An optical disk was prepared in the same manner as in Example 6, except that the composition of the recording layer was changed as follows, and the maximum crystallization speed was measured in the same manner as in Example 1.
The results are shown in the case of Ge 2% in FIG. 11, and it was confirmed that the crystallization upper limit speed greatly increased when the partial pressure ratio was 0.02 or more.
x = 0.038
y = 0.020
z = 0.815
[0049]
Example 8
An optical disk was prepared in the same manner as in Example 6 except that the composition of the recording layer was changed as follows, and the maximum crystallization speed, CN ratio, and erasing ratio were measured in the same manner as in Example 6.
The results are shown in the case of Ge 1% in FIGS. 11 to 13, and it was found that a high erase ratio and CN can be obtained at a partial pressure ratio of 0.015 or more.
x = 0.038
y = 0.010
z = 0.815
[0050]
Example 9
Among the disks prepared in Example 6, the medium having a good erasing ratio and a partial pressure ratio of 0.045 was evaluated for recording at 24 × speed in the same manner as in Example 1, and the measured jitter value was as follows. As a result, good characteristics satisfying the jitter standard value of 35 ns up to DOW 1000 times were obtained. That is, by adding nitrogen, initialization at a higher scanning speed was made possible, and good characteristics were secured while shortening the initialization process time.
Initial record: 24.3 ns
DOW once: 28.4 ns
DOW1000 times: 32.5 ns
[0051]
【The invention's effect】
According to the first and second aspects of the present invention, good direct overwrite characteristics in a range of 9.6 to 33.6 m / s corresponding to 8 to 24 times speed recording of a CD-RW can be realized, and storage of recorded information. Life can be ensured.
According to the third aspect of the invention, the crystallization temperature of the recording layer material can be lowered, and crystallization with a high-power laser is facilitated. Obtainable.
According to the inventions 4 and 5, since the upper limit of the crystallization speed is increased, the initialization and the crystallization can be performed at a higher speed, and the initialization process time can be shortened while maintaining good recording quality.
According to the sixth aspect, recording, erasing, and / or rewriting can be performed at an appropriate scanning speed.
According to the seventh aspect, the recording layer can be easily cooled rapidly when information is recorded and / or rewritten by improving the thermal conductivity of the reflection layer, and the medium has a high scanning speed of 20 m / s or more. Even when high energy is not applied, an amorphous state can be formed, so that good recording sensitivity can be ensured even at high speed recording.
According to the eighth aspect, by forming an oxide film near the recording layer, crystallization of the recording layer can be promoted, and an effect equivalent to the third aspect can be obtained.
According to the ninth and thirteenth aspects of the invention, since the scanning speed of the high-power laser in the initialization process of the optical information recording medium is optimized, sufficient energy can be applied to the recording layer material, and the recording layer material can be used. A uniform state with less optical anisotropy can be obtained, and the reproduced signal can be reduced in noise.
According to the inventions 10 to 12, a sputtering target for forming a recording layer of the optical information recording medium of the invention can be provided.
According to the inventions 14 and 15, it is possible to provide an appropriate recording method for the optical information recording medium of the invention.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view (schematic diagram) of an example of an optical information recording medium of the present invention.
FIG. 2 is a diagram showing an example of a method of irradiating intensity-modulated light.
(A) A schematic representation of an amorphous mark to be recorded
(B) Irradiation pattern used for recording (recording strategy)
FIG. 3 is a diagram showing an example of a strategy for reducing the number of pulses.
FIG. 4 is a diagram showing a recording strategy used for evaluating a recording signal characteristic of the optical disc of Example 1.
FIG. 5 is a view showing measurement results of the optical disc of Example 1 at a scanning speed of 28.8 m / s.
FIG. 6 is a view showing measurement results of the optical disc of Example 1 at a scanning speed of 9.6 m / s.
FIG. 7 is a view showing measurement results of the optical disc of Example 2 at a scanning speed of 28.8 m / s.
FIG. 8 is a diagram showing measurement results of the optical disc of Example 2 at a scanning speed of 9.6 m / s.
FIG. 9 shows scanning speed v and normalized reflectance R / R of a medium.₀FIG.
FIG. 10: partial pressure ratio P_N/ P_ArAnd v₀FIG.
FIG. 11 shows a partial pressure ratio P_N/ P_ArThe figure which shows the measurement result of the crystallization upper limit speed when changing.
FIG. 12_O/ V_LAnd FIG. 11 is a diagram showing measurement results of the CN ratio.
FIG. 13: partial pressure ratio P_N/ P_ArFIG. 9 is a diagram showing measurement results of an erasing ratio when the value is changed.
[Explanation of symbols]
Tw Basic clock period
3Tw ~ 11Tw Mark length
Pw Recording power
Pe erase power
Pb bias power
Ttop First pulse width
dTtop First pulse start time
Tmp Width of peak power pulse of multi-pulse part
dTera erase start time
T Basic clock period
Tmp 'The width of the peak pulse when n = 3
Td1 Time from rising of data to rising of first peak pulse
Time from the position where Td2P = Pe to the fall of data
Td2 'Td2 when n = 3
Extended time of last pulse when δT n is odd (relative to Tmp)
R₀  Reflectance after media initialization
Irradiation power P to R medium₀Of light after irradiating with light at scanning speed v
v₀  Maximum crystallization speed
(A) Example of change in normalized reflectance
(B) Example of change in normalized reflectance
(C) Example of change in normalized reflectance
Av₀Area where DOW characteristics cannot be secured at high speed due to low
B A and C are mixed and unstable area
C v₀High and high-speed areas
v_L  P_N/ P_ArMaximum crystallization rate when <0.001
v_H

Claims (15)

At least a recording layer and a reflective layer are stacked on a substrate, and recording and erasing and / or rewriting of information is performed by forming and erasing a recording mark on the recording layer by irradiating and scanning the collected light. The optical information recording medium to be performed is characterized in that the recording layer contains an alloy or an intermetallic compound containing Ga, Ge, Sb, and Te as main components and a composition ratio of these elements represented by the following formula. Optical information recording medium.
_{Ga x Ge y (Sb z Te} 1-z) 1-x-y
Here, x, y, and z are positive real numbers less than 1 representing an atomic ratio and satisfy the following requirements.
0.02 ≦ x ≦ 0.06
0.01 ≦ y ≦ 0.06
0.80 ≦ z ≦ 0.86
x ≧ y
x + y ≦ 0.1 2. The optical information recording medium according to claim 1, wherein the content of the alloy or intermetallic compound containing Ga, Ge, Sb, Te as a main component in the recording layer is 90 atomic% or more. 3. The optical information recording according to claim 1, wherein the alloy or intermetallic compound containing Ga, Ge, Sb, and Te as a main component contains Mn in an atomic ratio of 0.01 to 0.04. Medium. The recording layer is formed by a vacuum film forming method in an atmosphere containing Ar and N _2, and the partial pressure of _{Ar is set} to P _Ar , the partial pressure of N ₂ is set to P _N , the crystallization upper limit speed of the medium is set to v _0, and P _{N is set.} / _P Ar <0.001 the crystallization limit velocity of the medium at the time of the case of the _{v L,}
1.1 ≦ v ₀ / v _L ≦ 1.3
The optical information recording medium according to any one of claims 1 to 3, wherein the following condition is satisfied. 5. The optical information recording medium according to claim 4, wherein the ratio of _PN / P _Ar to the Ge content y of the recording layer satisfies the following condition.
1 ≦ (P _N / P _Ar ) /y≦1.5 The optical information according to any one of claims 1 to 5, wherein a scanning speed of recording, erasing and / or rewriting is preformatted, and the scanning speed is 9.6 to 33.6 m / s. recoding media. 7. The optical information recording medium according to claim 1, wherein the reflection layer is made of Ag or an alloy containing 95 mol% or more of Ag. 2. A layer having an oxide as a main component adjacent to the recording layer on the substrate side and / or the reflection layer side as viewed from the recording layer, and having a thickness in a range of 1 to 5 nm. 8. The optical information recording medium according to any one of items 7 to 7. Initialization (operation of bringing the recording layer of the information recording area of the medium into a crystallized state before using the medium) is performed by irradiating and scanning the high-power laser at a scanning speed of 1 to 2.5 m / s. The optical information recording medium according to any one of claims 1 to 8, wherein: A sputtering target for producing an optical information recording medium, comprising an alloy or an intermetallic compound containing Ga, Ge, Sb, and Te as main components and a composition ratio of these elements represented by the following formula.
_{Ga x Ge y (Sb z Te} 1-z) 1-x-y
Here, x, y, and z are positive real numbers less than 1 representing an atomic ratio and satisfy the following requirements.
0.02 ≦ x ≦ 0.06
0.01 ≦ y ≦ 0.06
0.80 ≦ z ≦ 0.86
x ≧ y
x + y ≦ 0.1 The sputtering target according to claim 10, wherein the content of an alloy or an intermetallic compound containing Ga, Ge, Sb, and Te as a main component is 90 atomic% or more. The sputtering target according to claim 10 or 11, wherein the alloy or intermetallic compound containing Ga, Ge, Sb, and Te as a main component contains Mn in an atomic ratio in a range of 0.01 to 0.03. Initialization (operation of crystallizing the recording layer of the information recording area of the medium before using the medium) by irradiating and scanning with a high-power laser at a scanning speed of 1 to 2.5 m / s. The method for initializing an optical information recording medium according to claim 1, wherein: The recording mark is formed by alternately irradiating and scanning a pulse with an irradiation intensity P of P = Pw and a pulse of P = Pb, and the recording mark length is nTw (n is a natural number) with respect to the basic clock cycle Tw. Then, assuming that the number of pulses of P = Pw is m (m is a natural number equal to or less than n), the relationship of n = 2m (when n is an even number) or n = 2m + 1 (when n is an odd number) is obtained. 10. The optical information recording medium according to claim 1, wherein erasing is performed by irradiating and scanning light with a constant intensity of P = Pe, and Pw> Pe> Pb. Method. 15. The recording method according to claim 14, wherein n = m + 1 when the scanning speed is 22.4 m / s or less and Tw is 14.4 ns or more.

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