JP3654172B2 - Optical information recording medium and recording method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical information recording medium such as a high-density optical disc. In particular, an optical information recording medium having a phase-change recording layer that can be expected to improve cross erase characteristics, which is a problem when the recording track interval in the disk surface is narrowed and the recording density is increased, and durability against reproduction light The present invention relates to an optical information recording medium excellent in performance and a recording method.
[0002]
[Prior art]
A general phase change optical disk uses a phase change between a crystalline state and an amorphous state, and forms an amorphous state mark with the crystalline state as an erased state. Phase change type optical discs have been put into practical use as portable high-density recording media, and attempts are being made to further increase the density.
[0003]
One method of increasing the density is to narrow the recording track interval in the disk surface. However, at present, the recording track interval cannot be reduced to near the optically determined limit. The reason is that, when light is irradiated and heated to perform recording on a certain track, the temperature of the adjacent track also rises somewhat, and a part of the amorphous mark is crystallized and erased. This phenomenon is called a cross erase phenomenon.
[0004]
One of the reasons why cross erasure is likely to occur is that the operating temperature when the phase of the crystal is changed to amorphous and the operating temperature when the phase of the amorphous is changed to the crystal are greatly different. That is, in the former, it is indispensable to heat the recording layer to a temperature higher than the melting point, whereas in the latter, a phase change starts to occur if heated to a glass transition temperature lower than the melting point. Usually, the melting point is around 600 ° C. and the glass transition temperature is around 200 ° C.
[0005]
The temperature rise in the track adjacent to the recording track is naturally smaller than the temperature rise in the recording track, but when the recording track is set to a temperature higher than the melting point, the temperature of a part of the adjacent track may become higher than the glass transition temperature. Therefore, it is considered that cross erase occurs.
In some cases, the crystallization of the recording mark by the reproducing light may be a problem. The cause of this is also the difference between the phase change operating temperature during amorphization and the phase change operating temperature during crystallization, as in the case of the cross erase. Even with the reproduction light, the temperature of the recording layer rises to some extent, and the amorphous mark crystallizes.
[0006]
This phenomenon is particularly significant in an optical information recording medium that performs recording at a short wavelength. Since it is generally difficult to obtain a high output with a laser having a short wavelength, a disk configuration is often employed in which heat can not be easily escaped so that recording can be performed with low output power, that is, recording power can be reduced. At this time, the temperature easily rises due to the reproduction light, and the amorphous mark is easily crystallized.
[0007]
On the other hand, a phase change type optical disk is also known that uses a phase change between a stable crystal phase and a metastable crystal phase.
For example, Japanese Patent Laid-Open No. 63-225933 discloses an alloy recording layer mainly composed of Sb and Au, and a π phase of a metastable phase is obtained by rapid cooling after melting, and a stable phase is obtained by heat annealing the metastable phase. It is described that Japanese Patent Application Laid-Open No. 63-155438 describes an alloy in which a π phase of a metastable phase can be obtained by rapid cooling after melting, and an equilibrium phase can be obtained by slow cooling, such as an InSb—Sb eutectic alloy. It has been.
[0008]
However, these systems cannot be expected to fundamentally improve the cross erase characteristic and reproduction light deterioration characteristic.
In other words, a phase other than the stable phase can be obtained by rapid cooling after melting, while a stable phase can be obtained by annealing or slow cooling after melting, whereas in the former it is essential to heat the recording layer above the melting point. In the latter case, a phase change starts to occur when heated to a phase transition temperature lower than the melting point. This is the same process as the phase change between the crystalline phase and the amorphous phase described above, and it is the same in the sense that there is a difference in the phase change operating temperature, so the fundamental improvement of the cross erase characteristic and reproduction light deterioration characteristic Can't hope. This system has not been put into practical use due to problems such as slow phase change.
[0009]
Further, in Japanese Patent Laid-Open No. 63-161545, a microcluster and a defect become seeds of crystal nuclei, and are formed of a material that can take two crystal forms that can be crystallized without melting. A recording layer is described, for example, InSb alloy or Ge. In Japanese Patent Laid-Open No. 63-161546, it is formed of a material that can take two different crystal forms formed through two different crystallization processes formed through a non-equilibrium crystallization process without melting. Recorded recording layers are described, for example, InSb alloys.
[0010]
However, in both cases, the crystal is reversibly changed due to the difference in the output power of the irradiating laser. In other words, if the heating temperature is high, one phase change occurs, and if the heating temperature is low, the other phase change occurs. This is the same in the sense that there is a difference in the phase change operating temperature. A fundamental improvement in properties cannot be expected. This system has not been put into practical use due to problems such as slow phase change.
[0011]
[Problems to be solved by the invention]
The present invention has been made to solve the above problems, and its object is to provide an optical information recording medium such as an optical disk having excellent cross erase characteristics and excellent durability against reproduction light, and a recording method suitable therefor. There is in getting.
[0012]
[Means for Solving the Problems]
The present inventor has achieved excellent cross erase characteristics and reproduction by eliminating a substantial difference between the operating temperature in the phase change from the stable phase to the metastable phase and the operating temperature in the phase change from the metastable phase to the stable phase. It has been found that an optical information recording medium having excellent durability against light can be obtained, and the present invention has been completed.
[0013]
That is, the gist of the present invention is an optical information recording medium having a phase change recording layer that generates a phase change between a stable phase and a metastable phase by light irradiation, and the recording layer is formed by light irradiation. After heating, a stable phase is formed when cooled relatively rapidly, and a metastable phase is formed when cooled relatively slowly.
Another gist of the present invention is: the above A recording method for an optical information recording medium, wherein a stable phase is obtained by alternately irradiating a high power light and a low power light from a light irradiation unit to the medium while moving the light irradiation unit relative to the medium. The recording method is characterized by forming.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The optical information recording medium of the present invention is an optical information recording medium having a phase change recording layer that causes a phase change between a stable phase and a metastable phase by light irradiation. After heating by light irradiation, a relatively rapid cooling forms a stable phase, and a relatively slow cooling forms a metastable phase.
[0015]
Conventionally, when there is a metastable phase and a stable phase, the stable phase is stable, and therefore, it is said that it can be obtained by low temperature heating or slow cooling from a high temperature. In order to obtain a metastable phase, it has been essential to rapidly cool after heating at a high temperature so as not to become a stable phase.
On the contrary, the medium of the present application has a property that a metastable phase is obtained when the medium is heated to a predetermined temperature or higher and then slowly cooled. The predetermined temperature is a high temperature necessary for the phase change to the metastable phase, and is usually at least the glass transition temperature.
And when it is heated to the same degree and then rapidly cooled, a stable phase is obtained.
[0016]
Therefore, according to such an optical information recording medium, there is no substantial difference between the operating temperature in the phase change from the stable phase to the metastable phase and the operating temperature in the phase change from the metastable phase to the stable phase. As a result, an optical information recording medium having excellent cross erase characteristics and excellent durability against reproduction light can be obtained.
A phase change type recording layer having such properties is found, for example, in a specific composition of the Au—Ge—Sb system.
[0017]
This will be described in more detail below.
The fact that a stable phase is produced by rapid cooling and a metastable phase is produced by slow cooling is completely opposite to the normal phenomenon. Such a medium actually exists, and at this time, the fact that the difference in the phase change operating temperature is substantially eliminated will be described in the examples described later. First, what kind of action causes such a reverse phenomenon in the Au—Ge—Sb system will be considered.
[0018]
It is known that phase change recording between crystal and amorphous is possible in the Ge—Sb system (Appl. Phys. Lett. 60 (25), 1992, etc.). The Ge content is 40 at. In the range of less than or equal to%, the lower the Ge content, the higher the crystallization speed.
On the other hand, it is known that there are two types of crystal phases in the Au—Sb system and their reflectances are different.
[0019]
The inventor analyzed the recording phenomenon by changing the composition in the Au—Ge—Sb system, and considered as follows. For example, the phenomenon when adding Au to the Ge—Sb system is as follows. When the amount of added Au is small, a Ge-Sb crystal-amorphous phase change occurs. However, when the amount of added Au increases, a new crystalline phase having a reflectance close to amorphous becomes the most stable and this becomes a stable phase. . At this time, the original crystal phase becomes a metastable phase (the structure seems to change continuously with the addition of Au).
[0020]
Therefore, at this time, the Au—Ge—Sb system can take three types of amorphous phase, metastable crystal phase, and stable crystal phase at room temperature. When the amount of added Au is relatively small, the phase change rate from the amorphous phase to the stable phase and the phase change rate from the metastable phase to the stable phase are small in all temperature ranges. Therefore, a phase change occurs between the amorphous phase and the metastable crystalline phase. That is, as in the Ge—Sb system, the amorphous phase is obtained by rapid cooling after melting, and the metastable phase is obtained by slow cooling. At this time, almost no change to a stable phase is observed with a single light beam irradiation.
[0021]
On the contrary, when the amount of added Au increases, the phase change rate from the amorphous phase to the stable phase and the phase change rate from the metastable phase to the stable phase increase, and the stable phase is always observed at room temperature. In a limited composition range in the middle, the phase change rate from the amorphous phase to the stable phase is large, and the phase change rate between the metastable phase and the stable phase is small. At this time, the amorphous phase formed by rapid cooling after melting immediately becomes a stable phase, and the metastable phase formed by slow cooling remains as a metastable phase. As a result, a phase change between the stable phase and the metastable phase occurs, and after melting, a stable phase is generated by rapid cooling and a metastable phase is generated by slow cooling.
[0022]
In this case, a remarkable phenomenon occurs regarding the operating temperature of the phase change. That is, in both the phase change from the stable phase to the metastable phase and the phase change from the metastable phase to the stable phase, the phase change cannot occur in a short time unless it undergoes a melting process. This is because the phase change rate in the solid phase between the metastable phase and the stable phase is small. That is, in order to perform recording and erasing in a short time, both must be heated at a high temperature, and the operating temperature is high. Accordingly, the difference in the phase change operating temperature that causes the cross erase and reproduction light deterioration is substantially eliminated, and these characteristics are improved.
[0023]
The above consideration can explain the behavior of the recording phenomenon of the Au—Ge—Sb system without contradiction, and is a novel phase change process that has not existed before. It is considered that a similar phenomenon can occur in a recording layer other than the Au-Ge-Sb system if the composition is selected in a recording layer that can take an amorphous phase, a metastable phase, and a stable phase.
As the recording layer having such properties, a system mainly containing at least Au, Ge, and Sb as described above can be used. The Ge content is mainly related to the ability to form an amorphous material (as described above, the amorphous phase immediately changes into a stable phase). As is well known, when the recording linear velocity is high, the temperature history is rapidly cooled and amorphous is easily formed, but the amorphous forming ability can be adjusted by adjusting the Ge amount according to the recording linear velocity. For example, it is considered that it is better to reduce the amount of Ge because the higher the recording linear velocity, the easier it becomes amorphous. Any element other than Ge can be used as long as it can control the amorphous forming ability.
[0024]
The Au content is mainly related to the phase change rate from the amorphous phase to the stable phase and the phase change rate from the metastable phase to the stable phase. The phase change rate from the amorphous phase to the stable phase is preferably high, and the phase change rate from the metastable phase to the stable phase is preferably low. If the amount of Au is too small, the phase change rate from the amorphous phase to the stable phase decreases. On the other hand, if the amount of Au is excessive, the phase change rate from the metastable phase to the stable phase increases. Therefore, it is necessary to select an appropriate amount of Au. .
[0025]
Overall, the recording layer composition is, for example, (Ge _x Sb _1-x ) _y Au _1-y (However, an alloy having 0 ≦ x ≦ 0.4 and 0.5 ≦ y ≦ 0.9) as a main component is considered to be a preferable range. However, since the composition of each element affects all the phase change rates, and the temperature history varies depending on the recording conditions such as the linear velocity and wavelength of recording / erasing, and the layer structure, it is appropriate from the above composition range. It is good to use it by selecting the composition.
[0026]
The In—Sb system is also known to have a metastable crystal phase and a stable crystal phase, and a recording layer suitable for the present invention may be obtained even if Au is replaced with In. Further, other elements may be added to the recording layer.
The present inventor can reduce the phase change rate from the metastable phase to the stable phase while keeping the phase change rate from the amorphous phase to the stable phase by adding Te to the recording layer of the present invention. I also found something. From the above, the recording layer composition is, for example, ((Ge _x Sb _1-x ) _y Au _1-y ) _z Te _1-z In this case, 0 ≦ x ≦ 0.4, 0.5 ≦ y ≦ 0.9, and 0.8 ≦ z ≦ 1 are preferable ranges.
[0027]
In the present invention, the stable phase and the metastable phase are relatively defined, and the stable phase only needs to be more stable than the metastable phase. For example, when two phases are heated, a phase that does not change unless the temperature is higher is defined as a stable phase.
Moreover, rapid cooling and slow cooling are also relative, and the case where the cooling temperature is faster is called rapid cooling, and the case where the cooling temperature is slower is called slow cooling.
[0028]
The optical information recording medium having the phase change recording layer of the present invention is an excellent and stable medium with little cross erase and deterioration of reproduction light. This medium is of course suitable as a rewritable medium, but it is also suitable as a pseudo write-once medium (write-once medium) because it has little reproduction light deterioration and high long-term storage stability.
In the present invention, it is considered that forming a stable phase mark on the recording layer in the metastable phase state is preferable because the deterioration of the mark is small and the long-term storage stability is high. Further, when the metastable phase is a crystalline phase having a relatively high reflectance, and the stable phase is a crystalline phase having a relatively low reflectance, a low reflectance mark is formed on the recording layer having a high reflectance. Therefore, it is preferable because it is easy to make the reproduction mechanism common with the reproduction-only medium on which information is recorded in the concavo-convex rows, and it is easy to obtain compatibility.
[0029]
The recording layer thickness is preferably in the range of 5 nm to 100 nm. If the thickness of the recording layer is less than 5 nm, it is difficult to obtain sufficient contrast, and recording erasure in a short time tends to be difficult. On the other hand, if the thickness exceeds 100 nm, it is difficult to obtain an optical contrast, and cracks are liable to occur. On the other hand, if it is thicker than 30 nm, the heat capacity increases and the recording sensitivity tends to deteriorate.
[0030]
Next, other parts in the structure of the phase change optical disk will be described. Phase change optical disks often have a dielectric protective layer, a recording layer, a dielectric protective layer, and a reflective layer on a substrate in this order or in the reverse order.
As the substrate, a resin such as polycarbonate, acrylic, polyolefin, or glass can be used. When recording / reproducing light is incident from the substrate side, the substrate needs to be transparent to the recording / reproducing light.
[0031]
In many cases, the upper and lower sides of the recording layer are covered with protective layers. The material for the protective layer is determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion, and the like. In general, oxides, sulfides, nitrides, and fluorides such as Ca, Mg, and Li, which are highly transparent and have a high melting point, can be used. These oxides, sulfides, nitrides, and fluorides do not necessarily have a stoichiometric composition, and it is also effective to use a composition or a mixture for controlling the refractive index and the like. More specifically, a mixture of ZnS or a rare earth sulfide and a heat-resistant compound such as an oxide, nitride, or carbide can be used. For example, a mixture of ZnS and SiO2 is often used for a protective layer of a phase change optical disk. The film density of these protective layers is desirably 80% or more of the bulk state from the viewpoint of mechanical strength.
[0032]
The protective layer is usually provided with a thickness of 5 nm to 500 nm. If the thickness of the protective layer is less than 5 nm, the effect of preventing deformation of the recording film is insufficient, and there is a tendency not to serve as a protective layer. In order to protect the substrate, 20 nm or more is preferable. If it exceeds 500 nm, the internal stress of the dielectric itself constituting the protective layer and the difference in elastic properties with the film in contact with the film become prominent, and cracks are likely to occur.
[0033]
In mass-produced products, the thickness of the protective layer is substantially limited to about 200 nm in order to shorten the film formation time. More preferably, it is 150 nm or less. The protective layer provided between the recording layer and the reflective layer is preferably 5 nm or more in order to suppress deformation of the recording layer. However, if it is thicker than 60 nm, microscopic plastic deformation tends to accumulate inside the protective layer during repeated overwriting, which is not preferable because it scatters reproduction light and increases noise.
[0034]
The reflective layer material preferably has a high reflectivity and thermal conductivity. Examples of the reflective layer material having a high reflectance and thermal conductivity include metals containing Ag, Au, Al, Cu and the like as main components. Among these, Ag has the highest reflectance and thermal conductivity. In particular, Au, Cu, and Al are more likely to absorb light than Ag at short wavelengths, and therefore Ag is particularly preferable when a short wavelength laser of 650 nm or less is used. Further, Ag is preferable because it is relatively inexpensive as a sputtering target, has a stable discharge, has a high deposition rate, and is stable in the air.
[0035]
Ag, Al, Au, Cu, etc., when mixed with impurities, the thermal conductivity and reflectivity are lowered, but stability and film surface flatness may be improved. % Of Cr, Mo, Mg, Zr, V, Ag, In, Ga, Zn, Sn, Si, Cu, Au, Al, Pd, Pt, Pb, Ta, Ni, Co, O, Se, V, Impurity elements such as Nb, Ti, O, and N may be included. The thickness of the reflective layer is usually 50 to 200 nm. In order to obtain sufficient reflectivity and heat dissipation effect, 50 nm or more is preferable. If the thickness is more than 200 nm, the film stress increases, the production time becomes longer, and the cost becomes higher.
[0036]
Note that the thickness of the recording layer and the protective layer is not limited from the mechanical strength and reliability viewpoints, but also takes into account the interference effect associated with the multi-layer structure. That is, it is selected so that the contrast between the recorded state and the unrecorded state is increased.
The recording layer, the protective layer, the reflective layer, and the like are formed by a sputtering method or the like. In order to prevent oxidation and contamination between layers, it is desirable to form a film with an in-line apparatus in which each sputtering target is installed in the same vacuum chamber. It is also excellent in terms of productivity.
[0037]
You may protect by providing the protective coating layer which consists of ultraviolet curable resin etc. on these layers. Further, in order to increase the recording capacity, two or more recording layers may be provided on the substrate, or the above layers may be formed on the substrate and then bonded with an adhesive.
Next, the recording method of the present invention will be described.
[0038]
A recording method of the present invention is a recording method of an optical information recording medium having a phase change recording layer that causes a phase change between a stable phase and a metastable phase by light irradiation, and the light irradiation portion It is characterized in that a stable phase is formed by alternately irradiating the medium with high power light and low power light from the light irradiating unit while moving relative to the medium.
The light emitted from the light source is usually irradiated to the medium through the objective lens through various optical systems. The relative movement of the light irradiation unit with respect to the medium means, for example, that the recording track of the medium is irradiated with light from the lens while rotating the disk-shaped medium with the objective lens substantially fixed. When the recording track is formed in a spiral shape, the objective lens is gradually changed in the disc radial direction.
[0039]
Since the high power light and the low power light are alternately irradiated when forming the stable phase, the region heated by the high power light can be relatively rapidly cooled, and the stable phase can be formed. Note that the power of the low power light is preferably ½ or less, more preferably ¼ or less of the high power light. Usually, it is convenient that the power of the low power light is the same as that applied during reproduction. When it is desired to increase the cooling rate, the power of the low power light may be set to zero. That is, it is not necessary to irradiate light.
[0040]
At this time, it is preferable to continuously irradiate light having a power of 0.6 to 1.5 times that of the high power light when the metastable phase is formed. That is, by continuously irradiating light with high power equivalent to that of high-power light that is irradiated during the formation of the stable phase, the heated region is heated to the same level as that during the formation of the stable phase, and the heated region is relatively slowly cooled. And a metastable phase can be formed. Therefore, by combining these, both the stable phase and the metastable phase can be formed, and overwrite recording can be performed.
[0041]
More preferably, when the metastable phase is formed, light having a power 0.8 to 1.2 times that of the high power light is continuously irradiated. Particularly preferably, when the metastable phase is formed, light having substantially the same power as the high power light is continuously irradiated. The irradiation power control in the recording apparatus can be made only binary, which is preferable because the circuit design is simplified.
A specific example of alternately irradiating high power light and low power light when forming a stable phase is shown below. When forming a mark (stable phase) having a length nT (T is a reference clock period and n is a natural number), the time nT is pulse-divided into n−k pieces as follows:
[0042]
[Expression 1]
α ₁ T, β ₁ T, α ₂ T, β ₂ T, ..., α _m - ₁ T, β _m - ₁ T, α _m T, β _m T
(However, α ₁ + Β ₁ + Α ₂ + Β ₂ + ... α _m - ₁ + Β _m-1 + Α _m + Β _m T = n−j (0 ≦ j ≦ 2), m = n−k (k = 0, 1, 2), and n _min −k ≧ 1) In the above formula, α _i High power light is irradiated for a time T (1 ≦ i ≦ m), and β _i During time T (1 ≦ i ≦ m), recording is performed by irradiating with low power light. In a region between the marks (metastable phase), light having a power 0.6 to 1.5 times that of the high power light is irradiated. As a result, overwrite recording can be performed.
[0043]
【Example】
Example
On a disk-shaped polycarbonate substrate having a diameter of 12 mm and a thickness of 1.2 mm having guide grooves having a groove width of 0.5 μm, a groove depth of 40 nm, and a groove pitch of 1.6 μm, ZnS—SiO ₂ Layer (100 nm), Au ₃₀ Ge ₁₇ Sb ₅₃ Recording layer (= (Ge _{twenty four} Sb ₇₆ ) ₇₀ Au ₃₀ ) (18nm), ZnS-SiO ₂ A dielectric layer (40 nm) and an Al alloy reflective layer (200 nm) were produced by sputtering. The recording layer is Ge ₃₀ Sb ₇₀ The target and Au target were obtained by sputtering at the same time.
[0044]
After initial crystallization of the disk, recording and erasing were performed in the guide groove using a disk evaluation apparatus having a pickup with a laser wavelength of 780 nm and NA of 0.5, and the disk characteristics were evaluated as follows.
First, an EFM random signal was recorded at a linear velocity of 2.4 m / s using the pulse division recording method shown in FIG. That is, when forming a mark (stable phase) having a length nT (T is a reference clock period, n is a natural number of 3 to 11), the time nT is pulse-divided into n-1 as follows,
[0045]
[Expression 2]
α ₁ T, β ₁ T, α ₂ T, β ₂ T, ..., α _n - ₂ T, β _n - ₂ T, α _n-1 T, β _n-1 T (where α ₁ + Β ₁ + Α ₂ + Β ₂ + ... α _n - ₂ + Β _n - ₂ + Α _n-1 + Β _n-1 T = n−j, 0 ≦ j ≦ 2, n is an integer from 3 to 11, and T is a reference clock period)
In the above formula, α _i The recording power Pw is irradiated for a time T (1 ≦ i ≦ n−1), and β _i During the time T (1 ≦ i ≦ n−1), recording was performed by irradiating light of bias power Pb (= reproduction power Pr). In the region between the marks (metastable phase), the light having the erasing power Pe was irradiated.
[0046]
Here, the reference clock cycle T = 115.7 ns, the recording power Pw = 10 mW, the erasing power Pe = 10 mW, the bias power Pb = reproduction power Pr = 0.8 mW, α ₁ = 1, α ₂ ~ _n - ₁ = 0.5, β ₁ ~ _n - ₂ = 0.5, β _n - ₁ = 1 and j = 0.
When the jitter of the recorded portion was measured after recording, it was 10 ns, which was a practically no problem value. The mark portion reflectance was about 29%, and the mark-to-mark portion reflectance was about 17%.
[0047]
Next, in order to evaluate the ease of cross-erasing, the reflectance (Rtop) between the mark portions when DC light (continuous light) is irradiated once at a linear velocity of 2.4 m / s to this recording portion and 11T The reflectance (Rbottom) of the mark part was measured. The power of DC light was varied between 2-8 mW. The results are shown in FIG. When the power of the DC light is 5.5 mW or less, the reflectance (Rbottom) of the 11T mark portion is almost 17% and there is almost no change, and when the power is about 6 mW or more, the reflectance suddenly increases and erasure has started. .
[0048]
Subsequently, in order to evaluate the recording sensitivity, the EFM random signal was recorded by changing the recording power Pw. Recording was performed according to the pulse division recording method of FIG. 1 under the same conditions as above except that the erase power Pe was always the same as Pw. Pw was varied between 5 and 10 mW, and the inter-mark part reflectance (Rtop) and 11T mark part reflectance (Rbottom) at each Pw were measured. The results are shown in FIG. It can be seen that when the Pw is 6 to 6.5 mW or more, the reflectance (Rbottom) of the 11T mark portion starts to decrease, and the mark starts to be formed.
[0049]
From the above, it was found that the power at which recording starts and the power at which erasing starts are both about 6 mW, which are about the same. This strongly suggests that the phase change between the two states needs to go through the molten state regardless of the direction of the phase change. That is, there is substantially no difference in phase change operating temperature depending on the direction of phase change.
Further, when the recording portion was repeatedly irradiated with DC light having a power of 5 mW, which is considered not to melt, the mark portion reflectance (Rbottom) did not change, but the mark-to-mark reflectance (Rtop). Decreased from 29% to about 24%. This suggests that the state of the mark portion gradually changes to the state of the mark portion, which indicates that the state of the mark portion is more stable than the state of the mark portion. That is, the mark part is a stable phase and the part between marks is a metastable phase. Further, from this fact, it is considered that this medium has little deterioration in reproduction light.
[0050]
The medium was capable of overwriting the EFM random signal at a linear velocity of 2.4 m / s and in accordance with the pulse division recording method of FIG.
In addition, 10 at. In the case of adding about% Te, the phase change rate in the solid phase from the metastable phase to the stable phase was further slowed down. That is, the stability of the metastable phase increased.
[0051]
Comparative Example 1
Except for the recording layer, a disk was produced in the same manner as in the example. For the recording layer, the power ratio of co-sputtering is changed to reduce the amount of Au, and the composition is Au ₂₀ Ge ₁₉ Sb ₆₁ (= (Ge _{twenty four} Sb ₇₆ ) ₈₀ Au ₂₀ ).
After initial crystallization of the disc, recording was performed in the guide groove in the same manner as in the example using a disc evaluation apparatus having a laser wavelength of 780 nm and a pickup with NA of 0.5. The mark portion reflectance was about 26%, and the mark-to-mark portion reflectance was about 12%.
[0052]
Next, in order to evaluate the ease of cross-erasing, the reflectance (Rtop) between the mark portions when DC light (continuous light) is irradiated once at a linear velocity of 2.4 m / s to this recording portion and 11T The reflectance (Rbottom) of the mark part was measured. FIG. 4 shows the measurement results obtained by changing the power of the DC light at 2 mW or more. It can be seen that when the power of the DC light is 3 mW or more, the reflectance (Rbottom) of the 11T mark portion suddenly increases, and erasing has started.
[0053]
On the other hand, when the recording sensitivity was evaluated in the same manner as in Example 1, no recording mark was formed at a recording power of 6.5 mW or less.
That is, in this layer configuration and recording conditions, the phase change from the mark portion to the mark portion occurs at a power of 6.5 mW or more, and the change from the mark portion to the mark portion occurs at a power of 3 mW or more. When DC light of 3 to 6.5 mW is irradiated, the mark portion is considered to change into a more stable phase in the solid phase without melting. Therefore, the recording mark is not stable.
[0054]
In addition, since a decrease in the inter-mark part reflectance (Rtop) due to the multiple irradiation of DC light with a power of 5 mW is observed, the state of the inter-mark part is a metastable phase and is different from the mark part and the inter-mark part. There appears to be a stable phase with low reflectivity.
Comparative Example 2
Except for the recording layer, a disk was produced in the same manner as in the example. For the recording layer, the amount of Au is increased by changing the power ratio of simultaneous sputtering, and the composition is Au ₃₉ Ge ₁₅ Sb ₄₆ (= (Ge _{twenty five} Sb ₇₅ ) ₆₁ Au ₃₉ ).
[0055]
This disk had a reflectivity of 11% immediately after film formation (As-depo), and no change in reflectivity due to laser irradiation at various powers was observed. This is probably because phases other than the stable phase (metastable phase, amorphous phase) are unstable and a stable phase is always observed.
[0056]
【The invention's effect】
As described above, according to the present invention, there is no substantial difference between the operating temperature in the phase change from the stable phase to the metastable phase and the operating temperature in the phase change from the metastable phase to the stable phase. An optical information recording medium having cross erase characteristics and excellent durability against reproduction light and a recording method suitable for the medium can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a recording pulse dividing method used in the present invention.
FIG. 2 is a graph showing the stability of a recording mark with respect to DC light in an example.
FIG. 3 is a graph showing the recording power dependence of the mark portion and inter-mark portion reflectivities in Examples.
4 is a graph showing the stability of a recording mark with respect to DC light in Comparative Example 1. FIG.

Claims (7)

An optical information recording medium having a phase change recording layer that generates a phase change between a stable phase and a metastable phase by light irradiation, wherein the recording layer is relatively rapidly cooled after being heated by light irradiation. Then, a stable phase is formed, and a metastable phase is formed by relatively slow cooling.   The optical information recording medium according to claim 1, wherein the recording layer is melted by light irradiation and then relatively rapidly cooled to form a stable phase.   The optical information recording medium according to claim 1, wherein the metastable phase is formed by relatively slowly cooling the recording layer after being melted by light irradiation.   4. The optical information recording medium according to claim 1, wherein the medium is a medium for recording by forming a stable phase mark on a metastable phase recording layer.   The optical information recording medium according to claim 1, wherein the stable phase is a crystalline phase having a relatively low reflectance, and the metastable phase is a crystalline phase having a relatively high reflectance. 6. The method for recording an optical information recording medium according to claim 1 , wherein a high power light is applied from the light irradiation unit to the medium while the light irradiation unit is moved relative to the medium. And a low power light are alternately irradiated to form a stable phase.   The recording method according to claim 6, wherein the metastable phase is formed by continuously irradiating light having a power 0.6 to 1.5 times that of the high power light.

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