JP2003054135A - Optical recording medium and optical recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a write-once type optical recording medium excellent in long-term preservation reliability and regeneration durability, capable of selecting a recording/regeneration wavelength from a wide wavelength region and enabling high speed/high density recording, and a proper recording method at the time of adaptation of the write-once type optical recording medium to a multilayered optical recording medium. SOLUTION: The optical recording medium has a laminated recording layer containing a first sub-recording layer and a second sub-recording layer at least one by one. Both of the main component metal of the a first sub-recording layer and the main component metal of the second sub-recording layer have a melting point higher than 500 deg.C and, when both main component metals are mixed, they can form an alloy having a melting point higher than that of each of the main component metals. The main component metals contained in the respective sub-recording layers are diffused to be mixed by the irradiation with laser beam and a recording mark, of which the reflectivity is changed irreversibly, is formed by this mixing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium having a write-once recording layer and a method for recording on this optical recording medium.

[0002]

2. Description of the Related Art Recently, an optical recording medium capable of high-density and high-speed recording has been attracting attention.

At present, a write-once type optical recording medium in which an organic dye is applied is widely used as a recording layer. However, the organic dye has no problem in low-speed recording, but has insufficient recording sensitivity for high-speed recording. Further, when the laser wavelength is shortened in order to increase the recording density, there are problems that the usable organic dyes are limited at each wavelength and that it is difficult to synthesize the dyes at wavelengths below blue. .

As a write-once type optical recording medium using an inorganic material, there has been proposed a method of recording information by changing the reflectance by punching recording or recording using diffusion in a laminated film.

The medium on which perforation recording is performed is usually Te.
And a recording film made of a low melting point metal (or alloy) such as Bi. At the time of perforation recording, the recording film is locally melted by irradiating the recording film with a laser beam. The molten low melting point metal rises due to surface tension, while the region surrounded by the rise is depressed. This recessed area is used as a recording mark. Such a perforated recording medium needs to have a so-called air sandwich structure in order to prevent the movement of the molten metal. Therefore, the manufacturing cost becomes high, and it is practically impossible to secure reproduction compatibility with a reproduction-only medium such as a CD (Compact Disc) or a DVD (Digital Versatile Disk), and the practicality is low.

On the other hand, the recording medium utilizing the reflectance change due to the diffusion / mixing of the laminated metal films does not need to have a complicated structure such as the air sandwich structure used in the punching type, and the cost can be reduced. It is attracting attention as a medium.

For example, in Japanese Examined Patent Publication No. 4-838, a first metal film (Au, Ag) which shows a solid-phase reaction with a low melting point metal (In, Sn), and the low melting point metal as main components. Second
The recording method in which the first metal film and the second metal film are reacted in the solid phase by irradiating the recording material in which the metal film is laminated with a laser beam is described. The publication describes that when In is used as the low melting point metal, the solid-phase reaction rapidly proceeds at 125 ° C., and when Sn is used, the solid-state reaction proceeds at about 180 ° C. There is. Since the reaction proceeds at a relatively low temperature in this way, it is difficult to secure sufficient storage reliability with this recording material. Further, Au and Ag used in combination with the low melting point metal have remarkably higher melting points than the reaction temperature. Therefore, the solid-phase reaction in such a combination slows down the diffusion rate and is not suitable for high-speed recording.

In Japanese Utility Model Publication No. 6-32372, Ge, Te, Bi, Tl, and Ti, which have a small optical extinction coefficient, the first recording layer containing them as a main component, and an optical extinction larger than this. Te, Bi, Sn, Au, S with extinction coefficient
An optical disk comprising b, Ag, Al, In and a second recording layer of an alloy containing them as a main component is described. In this optical disc, both of the recording layers are mutually diffused by irradiation with light to be changed into a single layer. In the embodiment of the publication, the first
The thin film (recording layer) is made of Ge and the second thin film (recording layer) is made of Al.

Japanese Patent Laid-Open No. 2000-187884 discloses that
In a write-once type optical recording medium, the recording layer is composed of two layers, a first recording layer provided on the substrate side of the recording medium and a second recording layer provided thereon, and the first recording is performed by laser beam irradiation. An optical recording medium is described in which recording is performed by utilizing a phenomenon in which the concentration of the element forming the layer and the concentration of the element forming the second recording layer are reversed. The element forming the first recording layer is at least one of Sb, Ge, Bi, Te, Se and Si, and the element forming the second recording layer is I
It is at least one of n, Al, and Ga. In the example of the publication, the first recording layer is made of Ge or its alloy, and the second recording layer is made of Al or its alloy. The publication describes that the mutual diffusion rapidly progresses due to the laser beam irradiation, so that the concentration is reversed. However, it is unlikely that sufficient storage reliability can be obtained unless the element distribution is biased at the laser beam irradiation site (recording mark) and the mixed state is stable.

Japanese Patent Publication No. 29135/1992 discloses a first layer having a high transmittance for a laser beam, and a low melting point metal which absorbs the laser beam and easily forms an alloy with the first layer. An information recording medium which has a second layer as a main component and in which the first layer and the second layer are alloyed by laser beam irradiation is described. The first layer is composed of chalcogenide glass, and the second layer is Te, Bi,
It is composed of a low melting point metal such as Sb or In. In the example of the publication, the first layer is made of Sb ₂ Se ₃ and the second layer is made of Bi ₂ Te ₃ .

Japanese Unexamined Patent Publication No. 2-235789 discloses A
a layer (reflection layer) having a high reflectance composed of an element selected from u, Al, Ag, Pt, Pd, Ni, Cr and Co and an alloy containing these elements, and chalcogenide (Te, Se, S). An optical information recording member having a layer (absorption layer or recording layer) having a low reflectance composed of (1). In the publication, in addition to chalcogenide, Ge, Sn, In, S are added to the absorption layer or the recording layer.
It is described that b, Pb, Cu, Ni, Pd, Co, Si, oxides, nitrides and carbides may coexist.
The publication describes that the reflective layer constituent element forms a chalcogenide during recording. In the example of the publication, a combination of a reflective layer made of Au and a recording layer made of Te or a mixture of Te and TeO ₂ , a combination of a reflective layer made of Al and a recording layer made of Te, NiCr
A combination of a reflective layer made of and a recording layer made of Te,
A combination of a reflective layer made of Au and a recording layer made of an Sb layer and a Te layer is used. In the invention described in the publication, the melting point of the chalcogenide produced by the reaction between the reflective layer and the recording layer is lower than the melting point of the reflective layer (eg Au).
Has a melting point of 1083 ° C. and AuTe _{2 has} a melting point of 464 ° C.)
Therefore, the thermal stability of the recording mark does not become sufficiently high.

In addition to this, Japanese Patent Application Laid-Open No. 5-12711 discloses a first recording film composed of an element having a high reflectance and a low melting point element, and an alloy of the low melting point element in the first recording film. An optical disc is described with a second recording film containing an element that causes In Example 2 of the publication, Al-B is used.
The i (atomic ratio 1: 1) layer and the Sb-Se (atomic ratio 1: 1) layer are stacked. The function of this optical disc at the time of recording is that Bi in the Al-Bi layer diffuses to the Sb-Se layer side, Al is deposited, and the reflectance is improved at that portion.

None of the media shown in the above proposals has been put to practical use. It is considered that each of the above-mentioned media has room for improvement in storage reliability, reproduction durability, and high-speed recording.

[0014]

The present invention is excellent in long-term storage reliability and reproduction durability, and it is possible to select a recording / reproducing wavelength from a wide wavelength range, and high-speed, high-density recording is possible. It is an object of the present invention to provide a write-once type optical recording medium that can be used. Another object of the present invention is to provide an appropriate recording method when such a write-once type optical recording medium is applied to a multilayer optical recording medium.

[0015]

The above objects are achieved by the present invention described in (1) to (11) below. (1) A first sub-recording layer containing one kind of metal as a main component,
A second sub-recording layer containing at least one second sub-recording layer containing a metal other than the one kind of metal as a main component, the main component metal of the first sub-recording layer and the second sub-recording layer. The melting point of each of the main component metals of the layers is 500 ° C. or higher,
When the main component metal of the first sub-recording layer and the main component metal of the second sub-recording layer are mixed with each other, an alloy having a melting point higher than the melting point of each of them can be formed. By irradiating a recording laser beam, the main component metals contained in each sub-recording layer are diffused and mixed, and by this mixing, a recording mark whose reflectance is irreversibly changed is formed. . (2) The optical recording medium according to (1), wherein both the first sub-recording layer and the second sub-recording layer are crystalline. (3) The above (1) or (2), wherein the main component of the first sub-recording layer is Al and the main component of the second sub-recording layer is Sb.
Optical recording medium. (4) In the laminated recording layer, the atomic ratio Sb / Al is 1
The optical recording medium of (3) above, which is / 3 to 3. (5) The thermal stability of the reflectance of the recording mark is higher than the thermal stability of the reflectance of the area excluding the recording mark.
The optical recording medium according to any one of (4). (6) The optical recording medium according to any one of (1) to (5), wherein at least one sub-recording layer is melted by irradiation with a recording laser beam. (7) The optical recording medium according to any one of (1) to (6), wherein an inorganic protective layer made of an inorganic material is present on both sides of the laminated recording layer. (8) A medium having a recording layer in which at least two recording layers are laminated and recording / reproducing is performed by a laser beam irradiated through another recording layer, and at least one recording layer is the laminated recording layer. The above (1)
The optical recording medium according to any one of (7). (9) The optical recording medium according to the above (8), wherein at least one of the recording layers that transmits a laser beam used for recording / reproducing of another recording layer is the laminated recording layer. (10) The method of recording on the optical recording medium according to (8) or (9), wherein when recording a signal having a specific mark length, the recording pulse strategies are the same in all recording layers, and each recording is performed. An optical recording method that optimally controls the power of the recording laser beam for each layer. (11) The method of recording on the optical recording medium according to (8) or (9), wherein when recording a signal having a specific mark length, the power of the recording laser beam is the same in all recording layers, and , An optical recording method for optimally controlling the irradiation time of a recording laser beam for each recording layer.

The above-mentioned Japanese Patent Laid-Open No. 2000-187884 discloses the option of combining the first recording layer made of Sb and the second recording layer made of Al.
However, only the options are disclosed in the publication, and the effect is not confirmed by actually producing the medium with this combination. Described as an example in the publication is a first element made of Ge or its alloy.
Recording layer and a second recording layer made of Al or an alloy thereof, and as shown as a comparative example in this specification, this combination does not realize the effect of the present invention. Further, the publication describes that mutual diffusion rapidly progresses by laser beam irradiation, so that concentration reversal occurs, but as shown in Examples in the present specification, in the medium of the present invention, First sub-recording layer constituent element and second
It is mixed almost uniformly with the constituent elements of the sub-recording layer, and the concentration does not reverse.

By the way, Japanese Patent Application Laid-Open No. 5-159352 describes a medium in which the above-mentioned perforation recording is performed. The medium described in the publication has a multilayer recording film,
When the thin films that make up the recording film melt and mix with each other,
An alloy or intermetallic compound having a higher melting temperature than the material forming each thin film is produced. In the recording method described in the publication, after the recording layer is locally melted by irradiation with a recording energy beam to perform perforation recording, an energy beam for storage processing having a power level lower than that of the recording energy beam is applied to the recording film. Irradiate the entire area of. By the irradiation of the energy beam for storage processing, the entire area of the recording film is changed to a high melting point alloy or intermetallic compound, so that the long-term storage stability of the recorded information is improved.

In the medium described in JP-A-5-159352, when the thin films forming the recording film are melted and mixed with each other, an alloy or an intermetallic compound having a higher melting temperature than the material forming each thin film is produced. In that respect, it is similar to the medium of the present invention. However, the medium described in the publication is a perforation recording medium, and the perforation recording medium is high in cost as described above and is not practical. Further, in the example of the publication,
(1) Te (melting point m _P = 450 ° C.) film and Sn (m _P = 23)
(2) Te film and Bi (m _P = 2)
71 ° C. film, (3) Te film and Zn (m _P
(= 419 ° C.) is used in combination with a membrane. When the melting point of each thin film is low, the solidification reaction causes diffusion in the recording film during storage in a high temperature environment to generate a refractory metal, which makes recording impossible.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The optical recording medium of the present invention has a laminated recording layer including at least one first sub-recording layer and at least one second sub-recording layer. The first sub-recording layer and the second sub-recording layer are mainly composed of different kinds of metals. When this recording layer is irradiated with a recording laser beam, the main component metals contained in the respective sub-recording layers diffuse and mix in the irradiation area. The reaction product generated by this mixing changes the reflectance of the irradiated area,
This can be used as a recording mark. Since the reflectance change is irreversible, the medium of the present invention can be used as a write-once type optical recording medium.

The following is a preferred embodiment of the present invention, Al
A sub-recording layer containing S as a main component (hereinafter referred to as Al main component layer), and S
A medium having a laminated recording layer including at least one sub recording layer containing b as a main component (hereinafter referred to as Sb main component layer) will be mainly described.

In the recording mark, the main component metals are in a mixed state and exist as an intermetallic compound, or a mixture in which at least main component metals are bound to each other even if no intermetallic compound is produced. Is considered to exist. For example, in the case of a laminated recording layer including an Al main component layer and an Sb main component layer, it is considered that AlSb which is an intermetallic compound is generated. However, an intermetallic compound such as AlSb does not need to be crystal-grown, and has a crystallinity (microcrystalline state) that cannot be detected by electron diffraction.
However, the effects of the present invention are realized.

The present invention is characterized in that the thermal stability of the reaction product in the recording mark is higher than the thermal stability in the state where the sub-recording layers are laminated before recording. Specifically, in the laminated recording layer on which the recording mark is already formed,
When a recording laser beam of a power level capable of forming a recording mark is irradiated, the above-mentioned mixing occurs in the laminated recording layers to change the reflectance, while the already formed recording mark is irradiated by the recording laser beam. This means that the reflectance does not change. The melting point of Al is 660 ° C. and the melting point of Sb is 631 ° C. Both are sufficiently thermally stable alone, and can be melted by laser beam irradiation. In addition, a stable intermetallic compound AlSb (melting point: 106, which has a melting point sufficiently higher than that of each element by the reaction of Sb and Al, and whose crystal structure does not change at low temperature and high temperature.
0 ° C.) can be produced. As described above, in the present invention, it is necessary that an alloy (preferably an intermetallic compound) having a melting point higher than that of each main component metal can be formed when the main component metals contained in each sub-recording layer are mixed. There is.

Therefore, the medium of the present invention is stable even when the recording mark made of the reaction product is hard to change even if it is stored in a high temperature environment after recording. When reading the formed recording mark, a reproducing laser beam is emitted. Although the power of the reproducing laser beam is relatively low, the temperature of the laminated recording layer rises by several tens of degrees Celsius in the irradiation area. In the case of a recording mark having low thermal stability, the recording mark is changed by reproduction, particularly by repeated reproduction, but in the medium of the present invention, the recording mark does not easily change by reproduction, and the reproduction durability is excellent. Further, in the medium of the present invention, since the thermal stability of the recording marks is high, the phenomenon of erasing the recording marks of the adjacent tracks (cross erase) does not substantially occur during recording. Therefore, the recording track pitch can be narrowed, which is effective for high-density recording.

On the other hand, even when the two metal layers having different compositions are instantly heated by a laser beam and diffused, when the products produced by the diffusion are in a non-equilibrium state, for example, When the product has a eutectic mixture or a metastable structure, it changes to an equilibrium state by heating or long-term storage at room temperature (eg phase separation).
Occurs. Therefore, the recording mark composed of the product in the non-equilibrium state has significantly lower thermal stability than the recording mark of the present invention, and the reproduction durability and storage reliability are deteriorated.

The sub-recording layer may contain only the above-mentioned main component metal, but may contain other elements. The content of the main component metal in each sub-recording layer is preferably 80
It is at least atomic% and more preferably at least 90 atomic%. When the content of the main component metal in the sub recording layer is too small,
It becomes difficult to form a recording mark with high heat stability.

In the present invention, the Sb main component layer and the Al main component layer are preferably formed as crystalline layers. When the Sb main component layer and the Al main component layer are formed as crystalline layers, the reflectance is higher than that when formed as an amorphous layer, so that the reflectance of the region excluding the recording marks can be increased. As a result, the reproduction output can be increased.

The sub-recording layer is preferably formed by a vapor phase growth method such as a sputtering method or a vapor deposition method, and particularly preferably formed by a sputtering method. When the Sb main component layer is formed by the sputtering method, if the Sb content is large, it is formed as a crystalline layer. On the other hand, if the element that inhibits crystallization of Sb is added to some extent, the Sb main component layer is likely to be formed as an amorphous layer. Whether the Sb main component layer is crystalline or amorphous depends on the type of element other than Sb contained in the Sb main component layer and the content thereof. S
In order to form the b main component layer as a crystalline layer, the Sb content is preferably 80 atom% or more, more preferably 90 atom% or more, further preferably 95 atom% or more, and most preferably 100 atom%. It is desirable to set it as%. Note that the Al main component layer can be formed as a crystalline layer by using the sputtering method.

However, even if the composition can be formed as a crystalline layer, if the sub-recording layer is as thin as several nanometers or less as in the case of applying to a multilayer optical recording medium described later, the Sb main Both the component layer and the Al component layer may have a microcrystalline structure.

The elements added to the Al main component layer include
At least one metal element that improves corrosion resistance, such as Cr, Ti, or Ni, is preferable. On the other hand, as elements added to the Sb main component layer, 13 (IIIb), 14 (IVb), 1
At least one element belonging to each group of 5 (Vb) and 16 (VIb) is preferable. However, as described above, it is most preferable that the Sb main component layer is composed of only Sb.

In the laminated recording layer, the Al main component layer and S
Although it is preferably in contact with the main component layer b, an intervening layer containing other element as a main component may be present between these layers. Examples of the other element include at least one of the elements used as an additional element in the Al main component layer or the Sb main component layer. The intervening layer may be composed of a compound having a melting point in the range of 500 to 1000 ° C. The thickness of the intervening layer is preferably 5
nm or less, more preferably 3 nm or less. If the intervening layer is too thick, mixing of Al and Sb may be hindered.

The melting point of the main component metal is 500 ° C. or higher in any sub recording layer. If the sub-recording layer containing a main component metal having a low melting point is present, diffusion due to a solid-phase reaction will progress during reproduction and storage in a high temperature environment, resulting in poor reproduction durability and storage reliability.

The laminated recording layer can change the reflectance by causing diffusion by a solid-phase reaction even at a temperature lower than the melting point of each sub-recording layer constituting the laminated recording layer. For example, A
In the combination of the l main component layer and the Sb main component layer, 400
It is possible to cause a sufficient solid-phase reaction at a temperature of not less than ° C and less than the melting point. However, in order to record at high speed, it is preferable to use diffusion due to a liquid phase reaction with a high diffusion rate, and therefore it is preferable that at least one of the sub-recording layers melts when irradiated with a recording laser beam, More preferably, all the sub recording layers are melted. In this case, in order to increase the recording sensitivity, it is desirable that the melting point of the main component metal is 1000 ° C. or lower in at least one of the sub recording layers, preferably in all the sub recording layers. Since Al and Sb have similar melting points as described above, it is easy to melt both layers at the same time.

When the reaction at the time of recording proceeds at a temperature lower than the melting point of each main component metal, that is, when it is diffused by a solid-phase reaction, it is preferable that the melting points of the main component metals of the respective sub-recording layers are close to each other. Specifically, the melting point of the main component metal of each sub-recording layer is in a temperature range of 200 ° C. or less, particularly 100
It is preferably within the temperature range of ℃ or less. If the melting points of the main component metals are close to each other, all the sub-recording layers can be activated, so that diffusion proceeds at a relatively high speed. As described above, Al and Sb have sufficiently close melting points.

The thickness of the laminated recording layer, that is, the total thickness of all the sub-recording layers is preferably 3 to 50 nm, particularly 3 to 30 nm. If the laminated recording layers are too thin, it becomes difficult to secure a sufficient reflectance difference before and after recording. On the other hand, if the laminated recording layer is too thick, the heat capacity of the laminated recording layer becomes large, resulting in poor recording sensitivity.

The thickness of each sub-recording layer is 1 to 30 nm, especially 2
It is preferably ˜30 nm. If the sub recording layer is too thin, it becomes difficult to secure a sufficient reflectance difference before and after recording. On the other hand, if the sub recording layer is too thick, the total thickness of the laminated recording layer becomes too large, so that the heat capacity of the laminated recording layer becomes large and the recording sensitivity becomes low. The thickness of each sub-recording layer may be appropriately determined so that a recording mark having high thermal stability and a large reflectance difference is formed. For example, when the Al main component layer and the Sb main component layer are combined, it is considered that an intermetallic compound in which Al and Sb are bonded at a ratio of 1: 1 is generated. Therefore, the ratio of Al and Sb (atom in the laminated recording layer It is preferable to set the thickness of each sub-recording layer so that the ratio does not deviate significantly from 1: 1.

In the laminated recording layer consisting of the Al main component layer and the Sb main component layer, the atomic ratio Sb / Al is preferably 1/3 to 3, particularly 2/5 to 5/2. If this atomic ratio is too small or too large, it is difficult to sufficiently form a mixture that lowers the reflectance, and the reflectance difference before and after recording is not sufficiently large. As a result, a sufficiently high CNR (carr
ier to noise ratio) cannot be obtained. Therefore, Sb
It is preferable to set the ratio between the thickness of the Al main component layer and the thickness of the Sb main component layer so that / Al falls within the above range.

In the laminated recording layer including the Al main component layer and the Sb main component layer, the layer on the front side as viewed from the laser beam incident side may be the Al main component layer or the Sb main component layer. . In the present invention, since there is no problem in recording and reproduction in any of these cases, the degree of freedom in design is high. When the layer on the front side is made of an Al main component layer, high reflectance can be easily obtained in the unrecorded portion. On the other hand, if the layer on the front side is the Sb main component layer, it becomes easy to increase the recording sensitivity.

Since the laminated recording layer in the present invention changes the optical characteristics before and after recording in a wide wavelength range from blue to red, the wavelength of the recording / reproducing laser beam can be selected from a wide wavelength range.

The laminated recording layer in the present invention is thermally stable, but is not sufficiently stable against water vapor and other gases. Therefore, the medium of the present invention preferably has a structure in which the laminated recording layer is sandwiched between a pair of inorganic protective layers. The inorganic protective layer is made of an inorganic material. As the inorganic material, oxides, sulfides, nitrides, fluorides, carbides,
Various dielectrics such as mixtures thereof are preferred. It is also possible to increase the reflectance difference before and after recording by providing an inorganic protective layer made of a dielectric material and utilizing the optical interference effect. The constituent material and thickness of the inorganic protective layer may be appropriately determined according to the optical design and thermal design of the medium.

Further, in the medium of the present invention, it is preferable that the reflective layer is provided deeper than the laminated recording layers when viewed from the recording laser beam incident side. By using the return light from the reflective layer, the difference in reflectance before and after recording can be increased, and the recording sensitivity can be increased. The reflective layer may be formed of a metal (including a semimetal) film, a dielectric multilayer film, or the like. The constituent material and thickness of the reflective layer may be appropriately determined according to the optical design and thermal design of the medium.

Further, in order to protect the medium from external elements such as dust and abrasion, at least one surface of the medium of the present invention is
A top coat layer or a hard coat layer made of a resin or an inorganic material having a high hardness may be provided.

In the type (Low to High type) in which the reflectance increases due to the formation of the recording mark, the reflectance before the recording is low.
Focusing servo signal is small. Further, since the reflectance of the pre-pit is even lower, it is difficult to reproduce the signal held by the pre-pit. Therefore, it is preferable that the medium of the present invention is of a type (High to Low type) in which the reflectance decreases due to the formation of recording marks. In the present invention, when the laminated recording layer is composed of the Al main component layer and the Sb main component layer, it is easy to set the reflectance of the recording mark lower than the reflectance of the unrecorded area. However, when the present invention is applied to a transmission type medium or a medium that does not require high reflection, a Low to High type may be used. Even when the Al main component layer and the Sb main component layer are combined, a low-to-high type can be obtained by utilizing the optical interference effect of the dielectric layer.

Next, the case where the present invention is applied to a multilayer optical recording medium will be described.

The multi-layer optical recording medium has a structure in which a plurality of recording layers are laminated via a transparent intermediate layer having transparency for a recording / reproducing laser beam, and a laser beam irradiated through other recording layers. The medium has a recording layer on which recording / reproduction is performed. When the present invention is applied to this multilayer optical recording medium, at least one of the recording layers is the laminated recording layer. The other recording layer may be, for example, a phase-change recording layer or a read-only recording layer including a reflective layer having prepits, and is not particularly limited.

Conventionally, a multilayer optical recording medium in which a plurality of phase change recording layers are laminated has been proposed. In the phase change recording layer,
Amorphous recording marks are formed by melting the crystalline recording layer by laser beam irradiation and rapidly cooling it. In order to rapidly cool the recording layer, it is general to provide a heat dissipation layer made of metal in the vicinity of the recording layer, and it is necessary to thicken the heat dissipation layer in order to increase the cooling rate. However, if the heat dissipation layer is thickened, the light transmittance of the heat dissipation layer becomes low, which is not suitable for a multilayer optical recording medium. Further, in a multilayer optical recording medium having a phase change recording layer, in order to reduce jitter in all recording layers, it is necessary to optimally control the recording pulse strategy at the time of recording for each recording layer, and Since it is necessary to optimize the thermal design for each recording layer, it is complicated. The recording pulse strategy means a power control pattern of a recording laser beam. Generally, when recording on a phase change type optical recording medium,
Instead of continuously irradiating the recording laser beam corresponding to the length of the recording mark, for example, Japanese Patent Laid-Open No. 9-7176.
As described in Japanese Patent Publication, for controlling the shape of the recording mark, irradiation is performed as a pulse train composed of a plurality of pulses,
Moreover, the width of each pulse in the pulse train is often strictly controlled. A specific configuration of pulse division in this case is generally called a recording pulse strategy.

On the other hand, in the laminated recording layer used in the present invention, a recording mark can be formed only by instantly melting a plurality of metal layers, and it is not necessary to consider the cooling rate. Therefore, it is not necessary to provide the heat dissipation layer. Also,
Wide recording power margin. In addition, high-speed recording is possible. Further, it is not necessary to strictly control the recording pulse strategy. In addition, the degree of freedom regarding thermal design is high. Therefore, the laminated recording layer is suitable for a multilayer optical recording medium,
Particularly, it is most suitable for a recording layer through which a laser beam used for recording / reproducing of another recording layer is transmitted. Therefore, it is preferable to use at least one of the recording layers as the laminated recording layer.

In the multi-layer optical recording medium, the recording layer may be thinned toward the surface closer to the laser beam incident side to increase the light transmittance. In that case, the heat capacity and the light absorptance differ for each recording layer, and therefore the recording sensitivity also differs. When each recording layer is a phase-change recording layer, it is necessary to strictly control the recording pulse strategy for each recording layer to compensate for the difference in recording sensitivity between the layers.

On the other hand, in the recording layer composed of the above-mentioned laminated recording layers, since the control of the recording pulse strategy is substantially unnecessary, the difference in recording sensitivity can be compensated by controlling only the total energy of the recording laser beam. Therefore, when recording a signal with a specific mark length, a simple control method is used in which the recording pulse strategy is the same in all recording layers and the power of the recording laser beam is optimally controlled for each recording layer. it can. Further, for example, when the phase change recording layer is present in the plurality of recording layers,
The recording pulse strategy is fixed to the one corresponding to the phase-change recording layer, and when recording on the laminated recording layer, the recording pulse strategy is controlled by controlling the power of the recording laser beam, whereby the phase-change recording layer and the laminated recording layer are recorded. Good recording can be achieved in any of the layers.

Further, in order to control the total amount of energy of the recording laser beam, the duty ratio of the pulse-divided recording laser beam may be controlled. That is, when recording a signal of a specific mark length, a method is used in which the power of the recording laser beam is the same in all recording layers and the recording laser beam irradiation time is optimally controlled for each recording layer. May be.

The power of the recording laser beam between adjacent recording marks is not particularly limited. Normal,
In a write-once medium such as a DVD-R, the power of a recording laser beam between recording marks is lowered to a level where tracking is possible (similar to the reproduction power).
On the other hand, in a rewritable medium such as a DVD-RW capable of overwriting, the power of the recording laser beam between adjacent recording marks is equivalent to the erasing power and higher than the reproducing power. Any of these power control patterns may be used for the laminated recording layer.

In the multi-layer optical recording medium, it is preferable that the recording layers have substantially the same reflectance before recording in order to make the intensity of the servo signal and the signal due to the prepits uniform in each recording layer. Specifically, selecting the recording layer of any two layers, one of reflectance and R _M, the other reflectance when the R _N, in _{2/3 ≦ R M / R} N ≦ 3/2 Preferably there is. The transmittance of the laminated recording layer can be easily adjusted by controlling the thickness, and the multiple reflection condition can be easily controlled by providing a dielectric layer and / or a reflective layer in addition to the laminated recording layer. Therefore, in the multilayer optical recording medium to which the present invention is applied, it is easy to make the reflectance uniform so that R _M / R _N is in the above range.

In the multi-layer optical recording medium, the laminated recording layer through which the laser beam used for recording / reproducing of other recording layers is transmitted preferably has a thickness of 3 to 15 nm, more preferably 3 to 15 nm.
It is 10 nm. If it is too thin, it becomes difficult to secure a sufficient reflectance difference before and after recording. On the other hand, if it is too thick, the light transmittance will decrease, so
It adversely affects reproduction.

By the way, the light reflectance of the recording layer is R _B before recording and R _A after recording, the light absorptance of the recording layer is A _B before recording, and A _A after recording, and the light transmission of the recording layer is shown. T _B the rate before recording, when T _a after recording, the formula _{I R B + a B + T} B = R a + a a + T a = 1 is satisfied. In the multi-layer optical recording medium, it is preferable that the recording layer, through which the laser beam used for recording / reproducing of the other recording layer is transmitted, has substantially the same transmittance before and after recording (T _B ≈T _A ). If the transmittance differs before and after recording, the intensity of the transmitted light differs depending on the recording state of the recording layer, and this transmitted light affects the recording sensitivity and reflectance of the recording layer on which recording / reproduction is performed. Is. Further, as described above, the optical recording medium High to Low type (R _B> R
_A ) is preferable, and this is the same also in the multilayer optical recording medium.

The laminated recording layer having an Al main component layer and an Sb main component layer has substantially the same transmittance before and after recording (T _B ≈) in the design of the High to Low type (R _B > R _A ).
Since it can be easily changed to T _A ), it is suitable for a multilayer optical recording medium.

By the way, T_B≈T_AAnd R_B> R_AWhere is
Formulas I to A above_B<A_ABecomes That is, the recording mark
The absorption rate of black is higher than that of the unrecorded area. did
Therefore, the temperature of the recording mark is
It becomes higher than the temperature of the unrecorded area. Therefore, the recording mark
If the recording layer has low thermal stability, it should be noted during laser beam irradiation.
The temperature of the recording mark becomes high, and as a result,
Emissivity may change and reliability problems may occur. this
On the other hand, the laminated recording layer used in the present invention is as described above.
High thermal stability of recording mark reflectance. Therefore, the laminated
In the recording layer, T _B≈T_AAnd R_B> R_ABecause A_B<
A_AHowever, there is no problem in reliability.

When T _B ≈T _A in the multilayer optical recording medium, specifically, T _B / T _A should be within the range of 5/6 ≦ T _B / T _A ≦ 6/5. If T _B / T _A is too small or too large, the recording sensitivity and reflectance of other recording layers are greatly affected. Note that T _B and T _A can be controlled by the optical interference effect. Specifically, an inorganic protective layer (dielectric layer) may be provided before and after the laminated recording layer to control its optical characteristics and thickness.

On the other hand, the laminated recording layer which is used for recording / reproduction of the other recording layer and which does not transmit the laser beam, that is, the laminated recording layer farthest from the laser beam incident surface does not need to have high light transmittance. However, this laminated recording layer
Since the intensity of the laser beam reaching it is the lowest among all the recording layers, it is necessary to have high recording sensitivity. Therefore,
In order to reduce the heat capacity, this laminated recording layer has a thickness of 25
It is preferably not more than nm. Further, since the reflected light from this laminated recording layer is attenuated by the other recording layers, it is preferable that this laminated recording layer has a high reflectance. Therefore, it is preferable to provide the above-mentioned reflective layer on the rear side of this laminated recording layer when viewed from the laser beam incident surface side.
Further, when the reflective layer is provided, the amount of the recording laser beam returning to the laminated recording layer increases, so that the recording sensitivity can be apparently improved.

[0058]

EXAMPLES Example 1 Sample No. 101 An optical recording disk sample having the structure shown in FIG. 1 was produced by the following procedure.

A groove (depth: 40 nm) was simultaneously formed by injection molding on the substrate 2, with a diameter of 120 mm and a thickness of 0.6 mm.
Of polycarbonate was used. On this substrate 2, the recording track pitch in the groove recording system is 0.74.
μm. On this substrate 2, the first dielectric layer 31, the laminated recording layer 4, the second
The dielectric layer 32 and the top coat layer 6 were formed in this order.

The first dielectric layer 31 has a thickness of 80 nm and has a composition of ZnS-SiO ₂ (ZnS: 80 mol%, SiO ₂ :
20 mol%).

The laminated recording layer 4 has a two-layer structure, and from the first dielectric layer 31 side, the sub-recording layer 41: Sb layer having a thickness of 10 nm, the sub-recording layer 42: Al ₉₈ Cr ₂ (atomic ratio of 10 nm) )
Layers, and. In this laminated recording layer, the atomic ratio Sb / Al
Is 0.54. The atomic ratio is a value calculated from the density and the thickness of the sub recording layer.

The second dielectric layer 32 has a thickness of 50 nm and Z
nS / SiO ₂ target (ZnS: 80 mol%, Si
O ₂ : 20 mol%) was used and the film was formed by sputtering in an Ar atmosphere.

The top coat layer 6 was formed by applying an ultraviolet curable resin by spin coating and then curing it by irradiating it with ultraviolet rays. The thickness of the top coat layer 6 after curing was 5 μm.

Sample No. 102 Except for the laminated recording layer 4, it was prepared in the same manner as Sample No. 101. The laminated recording layer 4 has a two-layer structure, and from the first dielectric layer 31 side, a sub recording layer 41: an Al ₉₈ Cr ₂ (atomic ratio) layer having a thickness of 7 nm, a sub recording layer 42: an Sb layer having a thickness of 13 nm, And In this laminated recording layer, the atomic ratio Sb / Al
Is 1.01.

Comparative sample No. 103 was prepared in the same manner as Sample No. 101 except for the laminated recording layer 4. The laminated recording layer 4 has a two-layer structure, and from the first dielectric layer 31 side, a sub recording layer 41: a Te layer having a thickness of 10 nm, a sub recording layer 42: an Al ₉₈ Cr _{2 having a} thickness of 10 nm (atomic ratio)
Layers, and.

Comparative sample No. 104 was prepared in the same manner as Sample No. 101 except for the laminated recording layer 4. The laminated recording layer 4 has a two-layer structure, and from the first dielectric layer 31 side, the sub recording layer 41: a Ge layer having a thickness of 10 nm, the sub recording layer 42: Al ₉₈ Cr _{2 having a} thickness of 10 nm (atomic ratio)
Layers, and.

Evaluation For each of the above samples, an optical disk evaluation device was used.
The characteristics were evaluated by making a laser beam incident through the substrate 2.

Measurement conditions Laser wavelength: 634nm, Aperture ratio NA: 0.6, Linear velocity: 14m / s, Reproduction power: 0.9mW

By irradiating the laser beam, a single signal composed of a mark and a space each having a length of 1.87 μm is recorded, and a record mark row composed of a recorded portion corresponding to the mark and an unrecorded portion corresponding to the space is formed. Formed. Next, CNR (carrier to noise rat) of this recording mark sequence
io) was measured. In addition, each sample is 80 ℃, 80% R
A storage test was conducted in which the sample was stored in a H constant temperature and humidity chamber for 50 hours, and then the CNR was measured. Initial CNR and CNR after saving
Are shown in Table 1.

[0070]

[Table 1]

In Table 1, samples No. 101 and No. 1
No. 02 has no CNR deteriorated by the storage test. Further, even when the storage time was extended to 200 hours and the same measurement was performed, the CNR did not deteriorate. From these results, it can be seen that the samples of the present invention have good storage reliability.
On the other hand, in the comparative sample, the CNR deteriorates due to the storage test. Further, when the reflected light amount of the recorded portion and the unrecorded portion of each sample was measured before and after the storage test, no change was observed in the reflected light amount in the sample of the present invention,
In the comparative sample, the amount of reflected light at the recording portion changed. From this result, it can be seen that in the comparative sample, the CNR deteriorated because the state of the recording portion changed.

After forming the recording mark train on each sample, CNR was measured, and then the recording mark train was irradiated with a DC laser beam with an output of 3 mW for 1 minute while rotating the sample. CNR was measured.
Also in this case, CNR for sample No. 101 and No. 102
No deterioration was observed. From this result, it is understood that the sample of the present invention has good reproduction durability. On the other hand, the CNR of the comparative samples No. 103 and No. 104 deteriorated.

At this time, in the comparative sample No. 103, changes in the reflected light amount were observed both in the recorded portion and the unrecorded portion, so it can be seen that diffusion / mixing occurred in the unrecorded portion and the state of the recorded portion changed. . On the other hand, in the comparative sample No. 104, only the reflected light amount of the recording portion was changed. That is, it can be seen that the state of the recording portion changed in both comparative samples. In Comparative Sample No. 103, one sub-recording layer is made of Te, and Te has a melting point of 450 ° C.
Therefore, it is considered that diffusion / mixing proceeded even in the unrecorded area.

From the above, it can be seen that the recording portion is thermally stable only when the Sb main component layer and the Al main component layer are used as the sub recording layer. On the other hand, an Al main component layer and T
When combined with a layer containing e or Ge as a main component,
It can be seen that the recording part is not thermally stable. This is A
It is considered that a stable bond is not formed between 1 and Te and between Al and Ge. Al and Ge are a combination that can form a eutectic mixture (eutectic point 424 ° C.). Further, Al and Te are metastable metal compounds of Al ₂
Since it is a combination capable of forming Te ₃ , it is considered that storage at high temperature or long-term storage at room temperature causes phase separation or structural change.

Although Sample Nos. 101 and 102 and Comparative Sample No. 103 were High to Low type,
Comparative sample No. 104 was a Low to High type.

In order to analyze the state of the recording portion, a slide glass is used as a substrate 2, and a first dielectric layer 31, a laminated recording layer 4 and a second dielectric layer 32 are formed on the glass substrate 2 in the same manner as in Sample No. 101. To form a sample for analysis. The first dielectric layer 31 and the second dielectric layer 32 each have a thickness of 20 nm.
In the laminated recording layer 4, the thickness of the Sb layer is 100 nm,
The thickness of the Al ₉₈ Cr ₂ layer was 100 nm.

This analysis sample was heat-treated at 500 ° C. for 5 minutes, and analyzed by thin film X-ray diffraction before and after this heat treatment. As a result, before the heat treatment, the peak of Sb and A
Although the peak of 1 was observed, the peak showing the (111) plane of AlSb, which did not exist before the heat treatment, was the main peak after the heat treatment. From this result, in the laminated recording layer 4 in which the Sb main component layer and the Al main component layer are laminated,
It can be seen that heating causes diffusion to form AlSb, which is a stable intermetallic compound.

It is to be noted that the heat-treated sample is subjected to 50 times again.
After heat treatment at 0 ° C. for 5 minutes, no change was observed in the X-ray diffraction pattern. From this result, it is understood that the state in which Sb and Al are mixed is more thermally stable than the state in which the Sb main component layer and the Al main component layer are stacked.

Example 2 The effect of the dielectric layer and the reflective layer was investigated.

Sample No. 201 A sample having a structure in which the second dielectric layer 32 and the reflective layer 5 were omitted from the structure shown in FIG. 2 was produced by the following procedure.

As the substrate 2, the same one as the sample No. 101 was used.

The first dielectric layer 31 has a thickness of 60 nm and has a composition of ZnS-SiO ₂ (ZnS: 80 mol%, SiO ₂ :
20 mol%).

The laminated recording layer 4 has a two-layer structure. From the first dielectric layer 31 side, the sub-recording layer 41 is a 7 nm thick Al ₉₈ Cr ₂ (atomic ratio) layer, and the sub-recording layer 42 is a 13 nm thick layer. Sb layer.

The top coat layer 6 was sample No. 101.
Was formed in the same manner as.

Sample No. 202 Laminated recording layer 4 and top coat layer 6 of sample No. 201
The second dielectric layer 32 is provided between the first and second electrodes. Second
The dielectric layer 32 has a thickness of 50 nm and has a composition of ZnS-Si.
O ₂ (ZnS: 80 mol%, SiO ₂ : 20 mol%) was used.

Sample No. 203 In the structure of Sample No. 202, the reflective layer 5 was provided between the second dielectric layer 32 and the top coat layer 6. Reflective layer 5
Had a thickness of 50 nm and had a composition of Al ₉₈ Cr ₂ (atomic ratio).

Evaluation Recording mark arrays were formed on these samples in the same manner as in Example 1 except that the marks and spaces were both 0.4 μm. Then, a storage test was conducted in the same manner as in Example 1 except that the storage time was set to 200 hours, and the storage reliability was evaluated. Table 2 shows the initial CNR and the CNR after storage.

[0088]

[Table 2]

In Table 2, the CNR of Sample No. 201 in which the laminated recording layer 4 was not protected by the second dielectric layer 32 was deteriorated by the storage test. From this result, it is understood that the structure in which the laminated recording layer is sandwiched by the dielectric layers suppresses the deterioration of the laminated recording layer under high humidity conditions.

Recording mark trains were formed on the samples No. 202 and No. 203 in the same manner as in Example 1, and the relationship between the reflected light amount and the recording power of the recorded portion and the unrecorded portion was examined. The results are shown in Fig. 3.

As shown in FIG. 3, when the reflective layer is provided, the return light is utilized to increase the reflectance difference (reproduction signal output) between the recording section and the final recording section. Further, it is understood that when the reflective layer is provided, a large reflectance difference can be obtained even when the recording power is low.

With respect to sample No. 203 having the above-described recording mark row, the reflective layer 5 and the top coat layer 6 were peeled off with a tape, and then the substrate 2 was washed with chloroform.
Was dissolved and removed. For the laminated recording layer 4 in this state,
Observation with a transmission electron microscope and electron diffraction were performed. As a result, in the unrecorded portion, the diffraction pattern showing the Sb crystal phase and the diffraction pattern showing the Al crystal phase (Al (11
1) surface peak) was observed. On the other hand, these diffraction patterns were not observed in the recorded area. from this result,
It can be seen that a mixture of Al and Sb was generated by the laser beam irradiation in the recording area. In the recording unit, Sb
A trace of melting of Al and Al was seen. From this result, it can be seen that the laminated recording layer was melted over the entire thickness direction at the laser beam irradiation site, and melt diffusion occurred.

When each sample on which the recording mark row was formed was irradiated with a DC laser beam having an output of 7 mW once, the reflected light amount at the recorded portion did not change, but the reflected light amount at the unrecorded portion decreased. From this, it is understood that the mixture of the recording portion is more thermally stable than the laminated state before recording.

Further, when the sample No. 203 having the above-mentioned recording mark row was reproduced by an optical disk evaluation apparatus with a laser wavelength of 432 nm, the reflectance of the unrecorded portion was 32% and the degree of modulation was 65%. On the other hand, at the laser wavelength of 634 nm, the reflectance of the unrecorded portion was 19% and the degree of modulation was 70%. From this result, it is understood that the medium of the present invention can select the wavelength of the recording / reproducing laser beam from a wide wavelength range.

Example 3 An optical recording disk sample having the structure shown in FIG. 4 was prepared by the following procedure.

Diameter 120 mm made of polycarbonate,
The reflecting layer 5, the second dielectric layer 32, the laminated recording layer 4, and the first dielectric layer 31 were sequentially formed on the supporting substrate 20 having a thickness of 0.6 mm by a sputtering method in an Ar atmosphere.

The reflective layer 5 has a thickness of 50 nm and has a composition of Ag.
₉₈ Pd ₁ Cu ₁ (atomic ratio).

The second dielectric layer 32 has a thickness of 50 nm and has a composition of ZnS.SiO ₂ (ZnS: 80 mol%, SiO ₂ :
20 mol%).

The laminated recording layer 4 has a two-layer structure, and from the first dielectric layer 31 side, the sub recording layer 41: Al ₉₈ Cr _{2 with a} thickness of 14 nm (atomic ratio)
Sub recording layer 42: Sb layer having a thickness of 14 nm. In this laminated recording layer, the atomic ratio Sb / Al
Is 0.54.

The first dielectric layer 31 has a thickness of 70 nm and has a composition of ZnS—SiO ₂ (ZnS: 80 mol%, SiO ₂ :
20 mol%).

From the first dielectric layer 31 side of this sample,
The laminated recording layer 4 was irradiated with a laser beam having a wavelength of 810 nm and a beam spot diameter of 100 μm to form a uniform recording area (the same state as a recording mark) over a width of 20 mm. Next, elemental analysis was performed on the recorded area and the unrecorded area by Auger electron spectroscopy while etching from the first dielectric layer 31 side. The distribution of Sb and Al in the thickness direction of the laminated recording layer obtained by this analysis is shown in FIG.
And FIG. 6 respectively. 5 and 6 are graphs showing the relationship between etching time and element concentration (counts per unit time) in Auger electron spectroscopy. FIG. 5 is an element distribution in a recorded area, and FIG. 6 is an element in an unrecorded area. Distribution.

From the comparison between FIGS. 5 and 6, it can be seen that Sb and Al were mixed almost uniformly by the laser beam irradiation. By the way, Japanese Patent Laid-Open No. 2000-187884 described above utilizes a phenomenon in which the concentration of the first recording layer constituent element and the concentration of the second recording layer constituent element are reversed by laser beam irradiation. . On the other hand, in the present invention, unlike the invention described in the above publication, as shown in FIG. 5, a stable mixed state is obtained without biasing the element distribution in the laser beam irradiation site, so that sufficient storage reliability can be obtained.

Example 4 A multilayer optical recording disk sample having the structure shown in FIG. 7 was prepared by the following procedure. This sample was prepared on the supporting substrate 20.
It has a reflective layer 5, a first data layer DL-1, a transparent intermediate layer TL, a second data layer DL-2 and a substrate 2, and a laser beam is incident through the substrate 2. Each data layer includes the first dielectric layer 31 and the sub-recording layer 4 when viewed from the laser beam incident side.
1, 42, and the second dielectric layer 32 are provided in this order.

As the supporting substrate 20, a polycarbonate having a diameter (120 mm) and a thickness (1.1 mm) of which grooves (40 nm in depth) were simultaneously molded by injection molding was used. This support base 2
0, the recording track pitch in the land / groove recording method is 0.3 μm. The data layer D is formed on the supporting substrate 20 by sputtering in an Ar atmosphere.
Each layer up to L-2 was formed.

The reflective layer 5 has a thickness of 50 nm and has a composition of Ag.
₉₈ Pd ₁ Cu ₁ (atomic ratio).

In the first data layer DL-1, the first dielectric layer 31 has a thickness of 75 nm and the second dielectric layer 32 has a thickness of 90 nm.
And the composition is ZnS—SiO ₂ (ZnS: 80).
Mol%, SiO ₂ : 20 mol%). The sub recording layer 41 was an Al ₉₈ Cr ₂ (atomic ratio) layer having a thickness of 4 nm, and the sub recording layer 42 was an Sb layer having a thickness of 6 nm. In this laminated recording layer, the atomic ratio Sb / Al
Is 0.82.

The transparent intermediate layer TL was formed by applying an ultraviolet curable resin by spin coating and then curing it by ultraviolet irradiation while pressing it with a stamper having a groove pattern. The groove pattern was the same as the groove pattern on the support base 20. Transparent intermediate layer T after curing
The thickness of L was 20 μm.

In the second data layer DL-2, the first dielectric layer 31 has a thickness of 45 nm and the second dielectric layer 32 has a thickness of 65 nm.
And the composition is ZnS—SiO ₂ (ZnS: 80).
Mol%, SiO ₂ : 20 mol%). The sub-recording layer 41 was an Al ₉₈ Cr ₂ (atomic ratio) layer having a thickness of 3 nm, and the sub-recording layer 42 was an Sb layer having a thickness of 5 nm. In this laminated recording layer, the atomic ratio Sb / Al
Is 0.91.

Next, an ultraviolet curable resin was applied onto the second data layer DL-2 by spin coating and cured by irradiation with ultraviolet rays to form the base 2. The thickness of the substrate 2 after curing was 90 μm.

Evaluation With respect to this sample, a reflectance signal and a jitter were measured by recording a random signal in the groove of each data layer under the following conditions using an optical disk evaluation device.

Measurement conditions Laser wavelength: 405nm, Aperture ratio NA: 0.85, Recording signal: 1-7 modulation (bit length 0.13 μm), Recording linear velocity: 11.4m / s, Reproduction linear velocity: 6.5m / s, Recording power: values shown in Table 3, Reproduction power: 0.5mW

The recording pulse strategy was a binary pulse train in which the number of nT signal pulses was n-1, the width of the leading pulse was 0.6T, and the widths of the other pulses were 0.5T. That is, the 2T signal has a pulse number of 1, the 8T signal has a pulse number of 7, and the power between pulses is the reproduction power.

Table 3 shows the measurement results. The jitter shown in Table 3 is clock jitter. This clock jitter is the "signal fluctuation (σ)" measured by measuring the reproduced signal with a time interval analyzer (Yokogawa Electric Co., Ltd.).
Was calculated, and was calculated by σ / Tw (%) with the detection window width as Tw. If the clock jitter is 10% or less, it can be said that there is no problem in signal quality.

[0114]

[Table 3]

As shown in Table 3, the reflectance before recording (unrecorded portion) is almost equal in both data layers, and both are sufficiently high at 10% or more. Therefore, the output of the servo signal such as the tracking error signal was sufficiently high in both data layers. Further, both data layers are of the High to Low type, the reflectance is reduced to about 4% in the recording portion, and the reproduction signal output is sufficiently high at the modulation degree of about 60%. Further, when recording on both data layers, the recording pulse strategy is the same, and by controlling only the recording power, the jitter is 10% or less in any of the data layers, and good signal quality is obtained. .

A random signal having a width of several millimeters was recorded on the second data layer DL-2, and the transmittances before and after recording were compared. As a result, the transmittance T _B before recording was 49% and the transmittance T _A after recording was 50%. That is, this second
In the data layer DL-2, the transmittance hardly changes due to recording. In addition, before recording a random signal on the second data layer DL-2, recording and reproduction were performed on the first data layer DL-1, and the jitter was measured. Furthermore, the second
Even after recording a random signal in the data layer DL-2 of
Jitter was measured for the first data layer DL-1. At this time, the recording portion of the second data layer DL-2 is made transparent,
The laser beam was applied to the first data layer DL-1.
The relationship between the recording power and the jitter obtained by these measurements is shown in FIG. From FIG. 8, the second data layer DL-2
It can be seen that the recording sensitivity and the jitter of the first data layer are the same before and after the recording. Also, the first
The reflectivity of the data layer DL-1 and the envelope of the signal were also hardly affected by the recording on the second data layer DL-2. From these results, it is clear that stable recording / reproducing characteristics can be obtained in the multilayer optical recording medium when the transmittance of the recording layer hardly changes by recording.

At the time of recording on the first data layer DL-1, the width of the leading pulse is changed to 0.3T and the widths of other pulses are changed to 0.25T, and the recording power is set to the second value. When the value was changed to 7.0 mW, which was the same as when recording on the data layer, the jitter was 9.8%, and also good signal quality was obtained. From this result, it is understood that when recording on a plurality of data layers, the jitter can be sufficiently reduced by controlling only the recording laser beam irradiation time with the recording power fixed.

The data transfer rate in this embodiment is
It corresponds to 70 Mbps during recording and 40 Mbps during playback. In addition, the recording capacity reaches 45 GB for the entire two data layers. The data transfer rate and the recording capacity are remarkably large as compared with the currently practically used optical discs. Moreover, the data transfer rate at the time of recording is determined by the performance limit of the laser drive unit of the optical disc evaluation apparatus, and is not the limit in the sample of the present invention. That is, the sample of the present invention has the potential to realize a higher data transfer rate.

Recording was possible even with a sample in which the light transmittance of the data layer was improved by 10% or more. From this result, it is clear that the present invention can be applied to a multilayer optical recording medium having three or more recording layers.

After recording a random signal on the first data layer DL-1, reproduction was performed by irradiating a laser beam of 1.5 mW at a linear velocity of 6.5 m / s, and the reflectance of the unrecorded portion was measured. Was slightly reduced. This decrease in reflectance is considered to be a result of element diffusion occurring between the sub-recording layers due to the solid-phase reaction. However, no change in reflectance was observed in the recorded area. In this embodiment, since the laser beam of short wavelength (wavelength λ = 405 nm) is emitted by the objective lens of high NA (0.85), the laser beam spot diameter proportional to λ / NA is quite small. Therefore, output 1.5
Even with a mW laser beam, the energy per unit area in the beam spot is considerably high.

[0121]

According to the present invention, the write-once type optical recording medium has high storage reliability and reproduction durability, a recording / reproducing wavelength can be selected from a wide wavelength range, and high speed and high density recording is possible. A recording medium is realized.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a configuration example of an optical recording medium to which the present invention is applied.

FIG. 2 is a partial cross-sectional view showing a configuration example of an optical recording medium to which the present invention is applied.

FIG. 3 is a graph showing the relationship between recording power and the amount of reflected light from a medium.

FIG. 4 is a partial cross-sectional view showing a configuration example of an optical recording medium to which the present invention is applied.

FIG. 5 is a graph showing the results of Auger electron spectroscopy analysis in the recording area of the laminated recording layer.

FIG. 6 is a graph showing a result of Auger electron spectroscopy analysis in an unrecorded area of a laminated recording layer.

FIG. 7 is a partial cross-sectional view showing a configuration example of a multilayer optical recording medium to which the present invention is applied.

8 is a graph showing the relationship between recording power and jitter when recording / reproducing is performed on the first data layer DL-1 in the medium having the structure shown in FIG. 7.

[Explanation of symbols]

2 base 20 Support substrate 31 First Dielectric Layer 32 second dielectric layer 4 Layered recording layer 41, 42 sub recording layer 5 Reflective layer 6 Top coat layer DL-1, DL-2 data layer TL transparent intermediate layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Isamu Kuribayashi             1-13-1, Nihonbashi, Chuo-ku, Tokyo             -In DC Inc. F term (reference) 2H111 EA03 EA12 EA21 EA32 EA33                       EA40 EA41 EA43 FA02 FA14                       FA24 FB09 FB21 FB30                 5D029 JA01 JB03 JB17 JC17                 5D090 AA01 BB03 BB12 CC01 DD01                       EE02 KK03                 5D119 AA23 BA01 BB02 HA47 HA60

Claims (11)

[Claims] 1. A laminate including at least one layer of a first sub-recording layer containing one metal as a main component and a second sub-recording layer containing a metal other than the one metal as a main component. It has a recording layer, and the melting point of each of the main component metal of the first sub-recording layer and the main component metal of the second sub-recording layer is 500 ° C. or higher. The main component metal of the second sub-recording layer is such that when mixed, an alloy having a melting point higher than the melting point of each can be formed. By irradiating the laminated recording layer with a recording laser beam, The optical recording medium in which the main component metals contained in the sub recording layer are diffused and mixed, and by this mixing, a recording mark whose reflectance is irreversibly changed is formed. 2. The optical recording medium according to claim 1, wherein both the first sub recording layer and the second sub recording layer are crystalline. 3. The main component of the first sub-recording layer is Al,
3. The main component of the second sub recording layer is Sb.
Optical recording medium. 4. The atomic ratio Sb / A in the laminated recording layer.
The optical recording medium according to claim 3, wherein l is 1/3 to 3. 5. The optical recording medium according to claim 1, wherein the thermal stability of the reflectance of the recording mark is higher than the thermal stability of the reflectance of the area excluding the recording mark. 6. The optical recording medium according to claim 1, wherein at least one sub recording layer is melted by irradiation with a recording laser beam. 7. The optical recording medium according to claim 1, wherein an inorganic protective layer made of an inorganic material is present on both sides of the laminated recording layer. 8. A medium having a recording layer in which at least two recording layers are laminated and recording / reproducing is performed by a laser beam irradiated through another recording layer, and at least one recording layer is the laminated layer. It is a recording layer.
7. The optical recording medium of any one of 7. 9. The optical recording medium according to claim 8, wherein at least one of the recording layers through which a laser beam used for recording / reproducing of another recording layer is transmitted is the laminated recording layer. 10. The method for recording on the optical recording medium according to claim 8 or 9, wherein when recording a signal of a specific mark length, the recording pulse strategies are the same in all recording layers, and each recording layer An optical recording method that optimally controls the power of the recording laser beam for each. 11. A method for recording on an optical recording medium according to claim 8 or 9, wherein when recording a signal of a specific mark length, the recording laser beam power is made the same in all recording layers,
Also, an optical recording method for optimally controlling the irradiation time of the recording laser beam for each recording layer.