JP2012174298A - Super resolution reproduction optical recording medium and super resolution reproduction method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a super resolution reproduction optical recording medium which can expect the improvement of manufacturing efficiency due to low cost involved in a reduction in the number of use materials and a reduction in the number of manufacturing processes and is excellent in recording capacity by making a layer for performing recording and a layer for performing reproduction one layer while achieving super resolution reproduction, and the super resolution reproduction method thereof.SOLUTION: In the super resolution reproduction optical recording medium of the present invention, recording laser is irradiated to form a recording mark, reproduction laser is irradiated to be able to read the recording mark, and a recording mark of mark length shorter than the resolution limit of an optical system composed of the reproduction lasers represented by λ/4NA is included when the wavelength of the reproduction laser is regarded as λ, and the numerical aperture of an objective lens is regarded as NA. The super resolution reproduction optical recording medium has at least a substrate, and a recording and reproduction layer for forming the recording mark and reading the recording mark with one layer. The recording and reproduction layer has light transmissivity and a plurality of recording and reproduction layers are arranged on the substrate.

Description

  The present invention relates to a super-resolution reproduction optical recording medium having optical transparency and capable of performing recording and super-resolution reproduction in the same layer and a super-resolution reproduction method thereof.

  In an optical recording medium such as a digital video disc or a Blu-ray disc, the length of a recording mark and an unrecorded space adjacent to the recording mark are basically the same in a reproducing optical system having a laser light wavelength λ and a numerical aperture NA of an objective lens. Regarding the recording mark row, the length of the reproducible recording mark is not less than the resolution limit (λ / 4NA).

In such an optical recording medium, as a method of reproducing a recording mark having a length less than or equal to the resolution limit, a functional layer having a function of reducing a laser beam spot is added to the optical recording medium, and the NA in the medium is substantially reduced. Technology to improve the quality is being studied. For example, Ge ₂ Sb ₂ Te ₅ is used as the functional layer, and the change in refractive index accompanying the liquid phase of the same material is used, so that the carrier-to-noise ratio (CNR), which is an index of reproduction performance, is used. ) Can be realized (see, for example, Patent Document 1). Further, even when a functional layer material having a different composition containing Sb or Te is used, super-resolution reproduction with a high CNR can be similarly performed.

  In order to construct an optical recording medium for recordable super-resolution reproduction, usually, a protection for separating the recording layer (for example, write-once recording layer) and the two layers separately from the functional layer A total of three layers (sometimes referred to as dielectric layers) are required. This means that more layers need to be stacked compared to the case where the optical recording medium that does not perform super-resolution reproduction is only one recording layer. On the other hand, from the viewpoint of increasing the recording capacity, it has been studied to provide a plurality of laminated structures such as a recording layer and a protective layer in the same recording medium. However, the functional layer material containing Sb or Te has a relatively high extinction coefficient k of about 3 to 4 for a laser beam having a wavelength λ of 405 nm or 650 nm, and the laser is applied from the incident side layer to the deeper layer. Since it is difficult to guide light, there is a problem that the number of stacked structures including the functional layer cannot be increased so much.

It is known that oxides and nitrides such as Sb, Te, Ge, and Si have higher light transmittance than those simple substances. Further, when the composition x of oxygen or nitrogen is lower than that of oxide or nitride having a chemical equivalent that exists stably (for example, in the case of GeO _x being Ge oxide, x is less than 2), heating is performed. It is known that a state in which light transmittance is lowered can be generated by generating, granulating, and crystallizing Sb, Te, Ge, Si, and the like (see Non-Patent Documents 1 to 5). Examples of the oxide and nitride herein include SbO _x (x <1.5), TeO _x (x <2), GeO _x (x <2), SiO _x (x <2), and SbN _x ( x <1), TeN _x (x <1.33), GeN _x (x <1.33), and SiN _x (x <1.33).

  By the way, an optical recording medium in which recording and super-resolution reproduction are performed in the same layer by using a noble metal oxide has been proposed (see Patent Document 2). However, in order to actually perform super-resolution reproduction using this optical recording medium, it is necessary to separately provide a light absorption layer containing Sb or Te, resulting in a problem that the number of stacked layers cannot be reduced.

In addition, an optical recording medium in which recording and super-resolution reproduction are performed in the same layer using Ge ₂ Sb ₂ Te ₅ has been reported (see Non-Patent Document 6). Ge ₂ Sb ₂ Te ₅ is also known as a rewritable recording material that can be recorded by forming an amorphous phase and erasing by crystallization thereof. However, since the temperature required for crystallization is about 200 ° C. and the temperature required for liquid phase for super-resolution reproduction is about 600 ° C., there is a problem that recording cannot be maintained at the time of super-resolution reproduction. . In addition, this material has a problem that it is difficult to ensure high light transmittance.

  Furthermore, an optical recording medium in which recording and super-resolution reproduction are performed in the same layer using Ge—Sb—Te (composition ratio unknown) has been reported (see Non-Patent Document 7). In this report, after recording by forming an amorphous phase on Ge—Sb—Te, the crystal phase of an unrecorded portion is removed by etching, and the portion is filled with a transparent dielectric material. However, there is a problem that etching and filling cannot be performed in the optical disc player. That is, the optical recording medium according to this report is considered to be a read-only optical recording medium rather than a recording type.

  Further, by enabling super-resolution reproduction by the methods described in these conventional techniques, the recording capacity of the optical recording medium can be increased to a certain extent, but these methods alone are required in the market. There is a problem that a sufficient recording capacity cannot be secured.

JP-A-5-258345 Japanese Patent No. 4582755

Applied Physics Letters, 89 (2006), p. 011902. Chinese Physics Letters, 24 (2007), p. 1287. Journal of Applied Physics, 54 (1983) p. 5376-5380. Applied Physics Letters 96 (2010), p. 263514. Japan Journal of Applied Physics 46 (2007), p. 612-620. Technical Digest of International Symposium on Optical Memory 2000, p. 224-225. Japan Journal of Applied Physics, 45 (2006), p. 2593-2597.

  An object of the present invention is to solve the above problems in the prior art and achieve the following objects. In other words, while realizing super-resolution reproduction, the recording layer and the reproduction layer are combined into one layer, thereby reducing the cost associated with a decrease in the number of materials used and manufacturing efficiency by reducing the number of manufacturing processes. It is an object of the present invention to provide a super-resolution reproduction optical recording medium and a super-resolution reproduction method that can be expected to improve the recording capacity.

Means for solving the problems are as follows. That is,
<1> A recording mark is formed by irradiating a recording laser, and the recording mark can be read by irradiating a reproducing laser, the wavelength of the reproducing laser is λ, and the numerical aperture of the objective lens is NA A super-resolution reproducing optical recording medium including a recording mark having a mark length shorter than the resolution limit of the optical system composed of the reproducing laser represented by λ / 4NA, and comprising at least a substrate and the recording mark A recording / reproducing layer for forming and reading out the recording mark in one layer, wherein the recording / reproducing layer is light-transmitting, and a plurality of layers are arranged on the substrate. Image reproducing optical recording medium.
<2> The super-resolution reproduction optical recording according to <1>, wherein the recording mark is formed by a thermal reaction product generated by irradiating a recording laser to a layer forming material of an unrecorded recording / reproducing layer Medium.
<3> The super-resolution reproduction according to <2>, wherein the layer forming material is a heat-reactive compound including any element of Ge, Si, Sb, and Te and any element of O and N Optical recording medium.
<4> The thermally reactive compound contains at least one of GeO _x , GeN _x , SiO _x , SiN _x , SbO _x , SbN _x , TeO _x , TeN _x and these two element compounds. The super-resolution reproduction optical recording medium according to <3>. However, said x shows a value smaller than the chemical equivalent when the said 2 element compound exists stably.
<5> Any one of <1> to <4>, wherein an extinction coefficient of the recording / reproducing layer is 0.01 to 2.0 at a wavelength of any one of a recording laser and a reproducing laser to be used. The super-resolution reproduction optical recording medium described.
<6> The structure according to any one of <1> to <5>, wherein the recording / reproducing layer has a stacked structure in which the protective layer is sandwiched between two protective layers, and a plurality of the stacked structures are arranged via a spacer layer. Super-resolution playback optical recording medium.
<7> The super-resolution reproduction optical recording medium according to <6>, wherein at least three laminated structures are arranged.
<8> The super-resolution reproduction method for the super-resolution reproduction optical recording medium according to any one of <1> to <5>, wherein the recording / reproduction layer is irradiated with a recording laser to generate a product. A super-resolution reproduction method characterized by performing super-resolution reproduction.

  According to the present invention, the above-mentioned problems in the prior art can be solved, and the number of materials used can be reduced by making the recording layer and the reproducing layer into one layer while realizing super-resolution reproduction. To provide a super-resolution reproduction optical recording medium and a super-resolution reproduction method that can be expected to improve the production efficiency by reducing the cost associated with the decrease in the number of production processes and the number of production processes. Can do.

FIG. 1 is a cross-sectional view illustrating the structure of a super-resolution reproduction optical recording medium 10 according to a test example. FIG. 2 is a graph showing the relationship between the mark length of the recording mark and the CNR in the super-resolution reproduction optical recording medium 10. FIG. 3 is a graph showing the relationship between the reproduction laser beam power and the CNR for a recording mark having a mark length of 150 nm in the super-resolution reproduction optical recording medium 10. FIG. 4 is a cross-sectional view illustrating the structure of a super-resolution reproduction optical recording medium 110 according to an embodiment of the present invention. FIG. 5 is a cross-sectional view illustrating the structure of a super-resolution reproduction optical recording medium 210 according to another embodiment of the present invention. FIG. 6 is a graph showing the relationship between the reproduction laser beam power and the CNR for the super-resolution reproduction optical recording medium 210.

(Super-resolution reproduction optical recording medium and its super-resolution reproduction method)
In the super-resolution reproduction optical recording medium of the present invention, a recording mark is formed by irradiating a recording laser, the recording mark can be read by irradiating the reproducing laser, and the wavelength of the reproducing laser is λ, When the numerical aperture of the objective lens is NA, it includes a recording mark with a mark length shorter than the resolution limit of the optical system composed of the reproduction laser represented by λ / 4NA, and the structure is at least the substrate and the recording And a reproducing layer, and other members are arranged as necessary.

<Recording and playback layer>
The recording / reproducing layer performs the formation of the recording mark and the reading of the recording mark in one layer. Further, the recording / reproducing layer has optical transparency, and a plurality of recording / reproducing layers are arranged on the substrate.

  The method for forming a recording mark in the recording / reproducing layer is not particularly limited as long as a recording mark capable of super-resolution reproduction can be formed, and can be appropriately selected according to the purpose. Preferably, the recording mark is formed by a thermal reaction product generated by irradiating a recording laser on the layer forming material of the recording / reproducing layer.

There is no restriction | limiting in particular as said layer formation material, According to the objective, it can select suitably, For example, any element of Ge, Si, Sb, Te, Bi, Sn, Zn, Co, Mo, W and A compound containing any one element of O, O and N is mentioned, and among them, a thermally reactive compound containing any element of Ge, Si, Sb and Te and any element of O and N is mentioned. preferable. When a layer is formed of such a layer forming material, a recording / reproducing layer having excellent light transmittance is easily obtained.
The heat-reactive compound refers to a compound in which a part of the structure is separated, generated, granulated, and crystallized when heat is applied.

The heat-reactive compound is not particularly limited and may be appropriately selected depending on the intended purpose. GeO _x , GeN _x , SiO _x , SiN _x , SbO _x , SbN _x , TeO _x , TeN _x and these It is preferable that it is a compound containing at least any one of the multielement compound containing these 2 element compounds. In addition, the said multi-element compound refers to the compound in general containing elements other than the said 2 element.
These heat-reactive compounds have high light transmittance and can be balanced with light absorption necessary for recording by changing the composition ratio x. In the super-resolution reproduction optical recording medium, from the viewpoint of multilayering the recording layer, the recording / reproduction layer needs to have light transmittance, but in order to form a recording mark having excellent reproduction characteristics, It is preferable that a thermal reaction product is efficiently generated by receiving light absorption from the recording laser, and a balance between the light transmittance and the light absorption is required.

For example, the GeO _x generates a Ge microcrystal through a thermal reaction of GeO _x → Ge + GeO ₂ by irradiation of the recording laser to form a recording mark, and a Ge generated part (recording part); Recording is made possible by utilizing the difference in reflectance from the portion where no is generated, and super-resolution reproduction is made possible by Ge generated in the recording portion. If _x of the GeO _x sample before the thermal reaction is made smaller than 2 (GeO ₂ ), the light absorption tends to increase, and Ge microcrystals based on the thermal reaction are easily obtained. Therefore, by adjusting the composition ratio x, recording and super-resolution reproduction can be performed while maintaining a balance between light transmittance and light absorption.

The layer forming material is not limited to the oxide material. For example, a material in which Sb and Sb ₂ O ₃ or Te and TeO ₂ are mixed in advance, such as SbO _x or TeO _x , is used. You can also choose. As a result of irradiation of the recording laser, the light absorption rate of the recording part obtained by crystallization and graining of Sb and Te is higher than that of the unrecorded part. It becomes possible to perform super-resolution reproduction.

In the heat-reactive compound, the x is particularly preferably a material having a value smaller than the chemical equivalent when the two-element compound is stably present.
Specifically, as an upper limit value of _x in GeO _x , SiO _x , and TeO _x , x <2 is preferable, and as an upper limit value of _x in SbO _x , x <1.5 is preferable, and SiN _x , GeN _x As an upper limit value of _x in TeN _x , x <1.33 is preferable, and as an upper limit value of _x in SbN _x , x <1 is preferable.
On the other hand, if x is too small, Ge, Si, Te, and Sb constituting the two-element compound are not substantially different from the simple substance, and sufficient light transmittance cannot be obtained. The following values are preferable.
That is, the lower limit value of _x in GeO _x , SiO _x , and TeO _x is preferably x> 0.2, and the lower limit value of _x in SbO _x is preferably x> 0.27, and SiN _x , GeN _x and The lower limit value of _x in TeN _x is preferably x> 0.33, and the lower limit value of _x in SbN _x is preferably x> 0.1.
At this time, the reason why super-resolution reproduction can be performed using such a material containing at least one of Ge, Si, Sb, and Te is not clear enough, but in addition to the refractive index change accompanying high temperature or liquid phase, This is presumably because the nonlinear optical effect accompanying the size reduction appears.

  In the optical design of an optical recording medium using the recording / reproducing layer, in order to record with laser light, the light absorptivity cannot be made too low, and the laminated structure including the recording / reproducing layer is increased. In order to increase the recording capacity, it is required to sufficiently increase the light transmittance per stack. In order to effectively utilize the amount of light and increase the number of stacked structures, the reflectivity per stacked structure is preferably low enough to cause no problem for the optical disc evaluation machine. Designing low reflectivity during normal playback (non-super-resolution playback) increases the intensity of reflected light from the super-resolution spot generated in a part of the laser beam spot during super-resolution playback. This is preferable because this leads to a reflectance design guideline for increasing the number of laminated structures. Therefore, for example, by controlling the composition ratio x of the heat-reactive compound constituting the recording / reproducing layer and its film thickness, the light absorption rate is mainly adjusted, and the transparent protective layer sandwiched before and after that It is preferable to adjust the reflectance by controlling the film thickness.

The extinction coefficient of the recording / reproducing layer is not particularly limited and may be appropriately selected depending on the intended purpose. It is 0.01 to 2 at the light wavelength of either the recording laser or the reproducing laser to be used. 0.0 is preferred.
When the extinction coefficient is less than 0.01, a film thickness required to secure about 10% of the light absorption rate of the recording / reproducing layer is required to be several hundred nm, and the extinction coefficient exceeds 2.0. In addition, the film thickness necessary for securing the reflectance of about 1% of the optical recording medium having three or more recording / reproducing layers is about 10 nm or less.

<Board>
The substrate is arranged to support each constituent layer of the recording medium including the recording / reproducing layer.
There is no restriction | limiting in particular as said board | substrate, According to the objective, it can select suitably, For example, the board | substrate which consists of a well-known glass material and a plastic material can be mentioned. Further, when used in an optical system that does not perform recording and reproduction by laser light through the substrate, the substrate may be optically opaque to the laser light.

  The shape of the substrate is not particularly limited and can be appropriately selected depending on the purpose from a flat plate or a grooved one, but it gives a role of a guide when laser light is scanned on the substrate. From the viewpoint, a grooved shape (uneven shape) is preferable. This groove can also be formed in each layer disposed on the substrate.

<Other members>
There is no restriction | limiting in particular as said other member, According to the objective, it can select suitably, For example, a protective layer, a reflection layer, a spacer layer etc. are mentioned.

-Protective layer-
The protective layer has a role of protecting the recording / reproducing layer, and is disposed so as to sandwich the recording / reproducing layer from the front and back sides of the recording / reproducing layer. The super-resolution reproduction optical recording medium is not particularly limited, but preferably has a plurality of laminated structures in which the recording / reproducing layer is sandwiched between the two protective layers.
The material for forming the protective layer is not particularly limited as long as it plays the above role, and can be appropriately selected according to the purpose. For example, Si ₃ N ₄ , SiO ₂ , SiC, TiO ₂ , ZnS, ZrO ₂ , Ta ₂ O ₅ and a mixture of two or more of these may be mentioned, among which ZnS—SiO ₂ is preferred.
Relates the ZnS-SiO _2, mixture ratio of ZnS and SiO _2: Examples of (ZnS SiO _2), is not particularly limited, 90mol%: 10mol% ~60mol% : 40mol% are preferred.

-Spacer layer-
The spacer layer has a role of optically separating the plurality of recording / reproducing layers arranged on the super-resolution reproducing / recording medium, and is arranged between the adjacent recording / reproducing layers. Further, when the recording / reproducing layer has a plurality of laminated structures sandwiched between the two protective layers, the recording / reproducing layer is disposed between the adjacent laminated structures.
The material for forming the spacer layer is not particularly limited as long as each recording / reproducing layer can be optically separated, and can be appropriately selected according to the purpose. For example, a transparent resin material, a transparent film, etc. Can be mentioned.

-Reflective layer-
The reflective layer has a role of adjusting the reflectance and controlling the temperature of the laminated structure including the recording / reproducing layer. When the protective layer is provided, the protective layer is provided on one surface side of the laminated structure. In the case where the recording / reproducing layer is not present, the recording / reproducing layer is disposed on one side of the recording / reproducing layer on the side farther from the incident light.
The reflective layer may be disposed on the grooved substrate for the purpose of guiding laser light.
There is no restriction | limiting in particular as a forming material of the said reflection layer, According to the objective, it can select suitably, For example, metals, such as Ag, Al, Au, and an alloy containing these are mentioned.

Example 1
As shown in FIG. 1, the land width and the groove width is 340 nm, the depth of the groove grooves on grooved polycarbonate substrate 1 of 39 _nm, the _{(ZnS) 85 (SiO 2)} 15 (ZnS-SiO 2 ZnS: SiO 2 Is formed with a thickness of 86 nm, and a recording / reproducing layer 3 made of germanium oxide (GeO _x ) with a thickness of 47 nm is formed on the first protective layer 2a. Then, a second protective layer 2b made of (ZnS) ₈₅ (SiO ₂ ) ₁₅ was formed with a thickness of 40 nm on the recording / reproducing layer 3 to produce a super-resolution reproducing optical recording medium 10 according to a test example. In FIG. 1, a stacked structure including the first protective layer 2 a, the recording / reproducing layer 3, and the second protective layer 2 b is referred to as a stacked structure 5.

Here, the (ZnS) ₈₅ (SiO ₂ ) ₁₅ layer related to the first and second protective layers 2a and 2b is obtained by sputtering a target made of (ZnS) ₈₅ (SiO ₂ ) ₁₅ in an argon atmosphere. Formed.

The GeO _x layer related to the recording / reproducing layer 3 was formed by reactive sputtering using germanium (Ge) as a target in a gas atmosphere having a flow rate ratio of argon gas to oxygen gas of 78:22.
As for the optical constant of the obtained GeO _x layer, the refractive index n was 1.98 and the extinction coefficient k was 0.07 with respect to light having a wavelength of 405 nm.
The refractive index n and the extinction coefficient k are measured using a spectroscopic ellipsometer (manufactured by JA Woollam Co., Ltd., VASE) for a single film of GeO _{x formed} on a silicon wafer.

Further, the light transmittance in the laminated structure 5 of the super-resolution reproduction optical recording medium 10 according to the test example was estimated to be about 84% from the following optical calculation, and high light transmittance was obtained.
The optical calculation was performed using the Fresnel equation.

For example, the following reference reports a result of systematic examination of the relationship between the composition ratio x of GeO _x and the complex refractive index in the range of 0.27 ≦ x ≦ 2.0. According to this, as the composition ratio x increases, both the refractive index n and the extinction coefficient k decrease. At x = 2.0, the refractive index n = about 1.6 and the extinction coefficient k = about 0 at a wavelength of about 400 nm. 0.03 is shown.
Thus, optical constants (refractive index n, extinction coefficient k) of the GeO _x layer according to the measurement from the composition ratio x in the GeO _x is inferred to be the x <2.0.
Reference: Applied Optics, 33 (1994), p. 1203-1208.

  The measurement of the characteristics of the super-resolution reproduction optical recording medium 10 according to the test example is performed by measuring an optical disc composed of an optical system in which the wavelength (λ) of the laser beam is 405 nm and the numerical aperture (NA) of the objective lens is 0.65. The evaluation was performed using an evaluation apparatus (DDU-1000, manufactured by Pulse Tech Industrial Co., Ltd.). In the measurement, laser light was incident from the grooved substrate 1 side.

On the super-resolution reproduction optical recording medium 10 according to the super-resolution reproduction test example, marks of various lengths were recorded at a linear velocity of 2.2 m / s with a laser light power of 5 mW to 8 mW.
When the recorded optical recording medium 10 is reproduced with a laser beam power of 1.0 mW, as shown in FIG. 2, a CNR characteristic of about 36 dB is obtained for a recording mark having a recording mark length of 200 nm. A CNR characteristic of 40 dB or more was obtained for a recording mark having a length of 300 nm to 800 nm, and a high CNR characteristic could be confirmed.
However, the resolution limit in the optical disk evaluation apparatus is about 155 nm (= λ / 4NA). Therefore, as shown in FIG. 2, the CNR of the recording mark having a recording mark length of 150 nm was as low as about 8 dB.
Therefore, when the reproducing laser light power for the 150 nm recording mark is increased from 1.0 mW, the CNR characteristic can be improved as shown in FIG. When the reproduction laser beam power was 3.5 mW, the CNR was about 36 dB, and good super-resolution reproduction was possible.

<Calculation example>
In order to confirm the characteristics of the super-resolution reproducing optical recording medium according to the embodiment of the present invention in which a plurality of recording / reproducing layers are arranged, the reflectance characteristics are calculated assuming the super-resolution reproducing optical recording medium shown in FIG. went.
That is, a first protective layer 102a (forming material: (ZnS) ₈₅ (SiO ₂ ) ₁₅ ) having a thickness of 86 nm, a recording / reproducing layer 103 (forming material: GeO _x ) having a thickness of 47 nm, and a thickness of 40 nm. A three-layer structure 105a, 105b, 105c in which the second protective layer 102b (forming material: (ZnS) ₈₅ (SiO ₂ ) ₁₅ ) is laminated is a resin spacer layer 104 (refractive index n = 1). .55), and a third laminated structure 105c is supported by a grooved polycarbonate substrate 101 (refractive index n = 1.63). The light reflectance with respect to the structures 105a, 105b, and 105c was calculated. Note that here, the wavelength of light to be used was set to 405 nm, and the laser light L was incident from the laminated structure 105a side.
Here, the reflectance was calculated according to the following procedure. First, the reflectance and light transmittance in units of each laminated structure were calculated using the Fresnel equation. For the laminated structure 105a on the outermost surface when viewed from the laser light incident side, the calculation result is directly used as the reflectance as the optical recording medium. As for the laminated structure 105b in the back as viewed from the laser light incident side, the light transmittance of the laminated structure 105a in between is multiplied by the reflectance of the laminated structure unit by the number of times the light passes (twice). Thus, the reflectance as an optical recording medium was calculated. With respect to the laminated structure 105c farthest from the laser light incident side, the light transmittance of the laminated structures 105a and 105b between them is the reflectance of the laminated structure unit by the number of times the light passes (twice). Was multiplied to calculate the reflectance as an optical recording medium.
The reflectances of the layers closer to the laser beam incident side, that is, the laminated structure 105a, the laminated structure 105b, and the laminated structure 105c are about 3.0%, about 2.3%, and about 1.3%, respectively, in this order. It has been estimated that the super-resolution reproduction recording medium 110 can be multilayered with at least three recording / reproduction layers.

(Example 2)
As shown in FIG. 5, a reflective film 206 made of Ag ₉₈ Pd ₁ Cu ₁ was formed to 10 nm on a grooved polycarbonate substrate 201 having the same standard as that of a commercially available DVD, and a spacer layer 204a made of a resin material was formed to about 260 μm. On the spacer layer 204a, the first protective layer 202b made of (ZnS) ₈₅ (SiO ₂ ) ₁₅ has a thickness of 40 nm, the recording / reproducing layer 203 made of GeO _x has a thickness of 47 nm, and (ZnS) ₈₅ (SiO ₂ ) A second protective layer 202a made of ₁₅ was laminated in this order with a thickness of 86 nm to produce a laminated structure 205c.
On the stacked structure 205c, a spacer layer 204b having a thickness of approximately 14 μm, a stacked structure 205b having a structure similar to the stacked structure 205c, a spacer layer 204c having a thickness of approximately 14 μm, and a stacked structure 205a having a structure similar to the stacked structure 205c. Then, a spacer layer 204d having a thickness of about 41 μm was formed in this order, and the super-resolution reproduction optical recording medium 210 in Example 2 having three recording / reproduction layers 203 was produced.

Each spacer layer was formed by applying an ultraviolet curable resin, spin-coating, and curing the resin with an ultraviolet lamp.
The reflective film 206 was formed by sputtering a target made of Ag ₉₈ Pd ₁ Cu ₁ in an argon atmosphere.
The recording / reproducing layers and the protective layers were formed by the same method as in Example 1.

  The measurement of the characteristics of the super-resolution reproduction optical recording medium 210 in Example 2 is performed by measuring an optical disc evaluation device (pulse) having an optical system in which the wavelength of the laser beam is 405 nm and the numerical aperture (NA) of the objective lens is 0.85. This was carried out using ODU-1000) manufactured by Tech Kogyo Co., Ltd. For scanning the substrate groove in this apparatus, another laser beam having a wavelength of 650 nm provided coaxially with the 405 nm laser beam was used. In the measurement, both laser beams were incident from the opposite side of the substrate.

On the super-resolution reproduction optical recording medium 210 in Example 2, a mark having a length of 115 nm was recorded with a laser light power of 22 mW at a linear velocity of 2.46 m / s on the laminated structure 205c closest to the substrate side. The resolution limit in the optical disk evaluation apparatus is about 119 nm. Therefore, when reproduction was performed with a laser light power of 1.0 mW, the CNR was as low as about 6 dB as shown in FIG.
Therefore, when the reproduction laser beam power for the 115 nm recording mark is increased from 1.0 mW, the CNR characteristic can be improved as shown in FIG. When the reproduction laser beam power was 3.0 mW, the CNR was about 28 dB, and good super-resolution reproduction was possible.

1, 101, 201 substrate with groove (substrate)
2a, 102a, 202b 1st protective layer 2b, 102b, 202a 2nd protective layer 3, 103, 203 Recording / reproducing layer 5, 105a, 105b, 105c, 205a, 205b, 205c Laminated structure 206 Reflective film 10, 110, 210 Super-resolution reproduction optical recording medium 104, 204a, 204b, 204c, 204d Spacer layer L Laser light

Claims (8)

When the recording mark is formed by irradiating the recording laser, the recording mark can be read by irradiating the reproducing laser, the wavelength of the reproducing laser is λ, and the numerical aperture of the objective lens is NA. A super-resolution reproduction optical recording medium including a recording mark having a mark length shorter than the resolution limit of the optical system composed of the reproduction laser represented by / 4NA,
At least a substrate, and a recording and reproducing layer that performs formation of the recording mark and reading of the recording mark in one layer,
A super-resolution reproducing optical recording medium, wherein the recording / reproducing layer has optical transparency and a plurality of recording / reproducing layers are arranged on the substrate.   The super-resolution reproduction optical recording medium according to claim 1, wherein the recording mark is formed by a thermal reaction product generated by irradiating a recording laser to a layer forming material of an unrecorded recording / reproducing layer.   3. The super-resolution reproduction optical recording medium according to claim 2, wherein the layer forming material is a thermally reactive compound containing any one element of Ge, Si, Sb, and Te and any one element of O and N. The heat-reactive compound contains at least one of GeO _x , GeN _x , SiO _x , SiN _x , SbO _x , SbN _x , TeO _x , TeN _x and a multi-element compound including these two element compounds. The super-resolution reproduction optical recording medium described in 1.
However, said x shows a value smaller than the chemical equivalent when the said 2 element compound exists stably.   The super-resolution reproduction according to any one of claims 1 to 4, wherein the extinction coefficient of the recording / reproducing layer is 0.01 to 2.0 at a wavelength of any one of a recording laser and a reproducing laser to be used. Optical recording medium.   6. The super-resolution reproduction optical recording according to claim 1, wherein the recording / reproducing layer has a laminated structure in which two protective layers are sandwiched, and a plurality of the laminated structures are arranged via a spacer layer. Medium.   The super-resolution reproduction optical recording medium according to claim 6, wherein at least three laminated structures are arranged.   6. A super-resolution reproduction method for a super-resolution reproduction optical recording medium according to claim 1, wherein super-resolution reproduction is performed by a product generated by irradiating a recording / reproducing layer with a recording laser. And a super-resolution reproduction method.