JP2007095246A - High density optical recording medium and recording and reproducing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the constitution of an optical recording medium having no window of light transmittance and capable of recording and reproducing a fine recording mark having a size equal to or smaller than a light resolution limit, to provide the optical recording medium capable of forming the recording mark for obtaining a reproduction signal having high contrast, and to provide a recording and reproducing method for performing multi-valued recording and reproduction of information in a region having a size equal to or smaller than the light resolution limit. <P>SOLUTION: The optical recording medium having a first deformation material absorbing light, producing heat and deformed and a second deformation material transmitting light, receiving heat produced by the first deformation material and deformed according to the shape of the first deformation material on a supporting substrate is characterized in that the form of the recording mark after information is recorded is a shape protruding to a light source side to concentrate light and the size of the recording mark is equal to or smaller than the light resolution limit. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a configuration of an optical recording medium that records and reproduces high-density information below the optical resolution limit, and also relates to a technology for recording and reproducing high-density information below the optical resolution limit. In addition, the present invention relates to a technique for increasing the capacity of recorded information by multiple recording. Here, the resolution limit indicates a period represented by λ / 2NA, where λ is the wavelength of light and NA is the numerical aperture of the objective lens.

  As shown in FIG. 12, Patent Document 1 records / reproduces a recording mark row including a recording mark smaller than the resolution limit or a recording mark having a dimension that is equal to or larger than the resolution limit but close to the resolution limit. In order to obtain a high reproduction output at all the recording marks included and realize high reproduction durability, the optical recording medium having the noble metal oxide layer (24) is decomposed by the decomposition of the noble metal oxide. A technique for forming a recording mark row by deforming a noble metal oxide layer (24) is disclosed. Here, (231), (232), and (233) are dielectric layers, and (25) is a light absorption layer. Precious metal fine particles are irreversibly deposited in the noble metal oxide layer on which the record mark row is formed, and the recorded noble metal fine particles are irradiated with a reproduction laser beam to read out the record mark row, and use deformation of the thin film material. The recording mark below the resolution limit can be read out. However, the optical recording medium described in Patent Document 1 has a light absorption layer formed by thermal deformation of the noble metal oxide layer. By being pushed up and thinned, and the light transmittance locally changes, the light absorption layer functions as a window for generating near-field light, and reads recorded information smaller than the light resolution limit. In order to improve the recording density, it is necessary to read out a smaller recording mark, and it is necessary to make the light transmittance window smaller. As a result, a large part of the beam spot diameter is shielded, and the signal intensity is lowered and cannot be detected.

  In Patent Document 2, as a technique for increasing the recording density by utilizing a molten state of a thin film material, the optical recording medium is increased by a method other than shortening the wavelength of reproducing light or increasing the numerical aperture of the optical system of the reproducing apparatus. In order to enable recording and reproduction of density information, and to prevent deterioration of characteristics with respect to repeated reproduction, as shown in FIG. 13, it has a mask layer (332) formed of a low crystalline semiconductor alloy, and a recording light beam The thickness of the mask layer (332) is irreversibly decreased by irradiation, and a reproduction window (330) in which the light transmittance is increased by changing the multiple reflection condition is formed, and the recording mark is recorded on the recording layer (34). Although it is not necessary to change the mask layer at the time of reproduction, a technique for improving durability against repeated reproduction is disclosed, but the optical recording medium described in Patent Document 2 is also the same A window of light transmittance is formed by reducing the film thickness of the low crystalline semiconductor alloy, and a recording mark with a size less than the resolution limit of light is read, and the signal intensity decreases significantly as the recording density increases. End up.

  Further, Patent Document 3 uses a temperature distribution created by a light spot at the time of reading and emphasizes the contribution of the signal from the vicinity of the center of the light spot, thereby suppressing overlap of signals obtained from adjacent marks at the time of reading, In order to provide a high-density optical recording medium having a molten mask layer having a higher recording density than conventional ones, as shown in FIG. 14, a recording layer (43) having a variable optical constant that absorbs and alters light, and The upper transparent dielectric layer (44) and the lower transparent dielectric layer (42) sandwiching the recording layer (43), and the reflective layer (47), and the upper transparent dielectric layer (44) or the lower transparent dielectric layer By forming the molten layer (45) close to the (42) side and having a melting point lower than that of the recording layer (43), the reflectance change of the melted portion depending on the intensity distribution of the focused beam can be achieved. Use when reading Although a technique for apparently reducing the spot size of light irradiated to a recording mark has been disclosed, the optical recording medium described in Patent Document 3 also forms a light transmittance window by a molten layer having a low melting point. However, since a recording mark having a size smaller than the resolution limit of light is read out, the signal intensity is lowered for the same reason, and the signal cannot be detected.

  Furthermore, in Patent Document 4, as a technique for performing multi-value recording / reproduction using the difference in height of recording marks, a thin film of a polymer compound containing an azobenzene structure is irradiated with light to form an uneven pattern on the surface. In order to provide a method for increasing the information density when performing information recording, a circular laser beam linearly polarized on an azobenzene polymer thin film or an ellipse having bright and dark islands (or as shown in FIG. 15) When a (rectangular) laser is irradiated, a surface relief pattern characterized by alternately arranging k concave portions and (k + 1) convex portions on a straight line is obtained, and the anisotropy of this pattern is used. Thus, a technology capable of realizing a new information recording / reproducing method is disclosed. However, the optical recording medium described in Patent Document 4 has anisotropy of organic molecules. By utilizing the relationship between the deformation pattern and the deflection direction of the light that records the information and the depth information of the recording pattern, multi-level recording / reproduction of information has been realized. As long as the contrast is detected and the wave characteristics of light are used, it is impossible to detect recording marks below the resolution limit of light, and the recording density is limited by the wavelength of light. End up. Further, since it is necessary to control the polarization direction, a reproduction optical system having a form different from that of the conventional optical disk is required, and compatibility with the optical disk apparatus is impaired.

JP 2004-87073 A Japanese Patent No. 3602589 JP-A-5-73961 JP 2004-127484 A

Accordingly, an object of the present invention is to provide a configuration of an optical recording medium capable of recording / reproducing a minute recording mark having a light resolution limit or less in view of the above-described prior art, in a form having no light transmittance window. An object of the present invention is to provide a configuration of an optical recording medium capable of recording / reproducing.
Another object of the present invention is to provide an optical recording medium capable of forming a recording mark for obtaining a reproduction signal having a high contrast.
Also provided is a reproducing method for detecting a recording mark on an optical recording medium with a resolution below the resolution limit of light, and provides a reproducing method having a high contrast and a high light utilization efficiency. There is.
Another object of the present invention is to provide a recording / reproducing method for multi-value recording and reproducing multi-value information in an area below the light resolution limit, thereby realizing a large capacity of recorded information.

The above-described problem is (1) “a first deformable material that absorbs light and generates heat and deforms on a support substrate; and the first deformable material that transmits light and receives heat generated by the first deformable material. It has a second deformable material that deforms according to the shape, and the form of the recording mark after recording information is a shape that protrudes toward the light source side and concentrates light, and the size of the recording mark is below the resolution limit of light An optical recording medium characterized by being ",
(2) "The optical recording medium according to (1) above, wherein the height or shape of the recording mark changes depending on the intensity and irradiation time of the laser beam irradiated during recording",
(3) In the item (1) or (2), the intensity of the reflected light by the laser beam irradiated during reproduction varies depending on the height or shape of the recording mark. Optical recording media ",
(4) The above-mentioned items (1) to (3) are characterized in that the form of the recording mark after recording information is such that the first deformable material in each recording mark is isolated between adjacent recording marks. This is achieved by the “optical recording medium according to any one of items (3)”.
Further, the above-mentioned problem is (5) of the present invention that “the recording mark shape projecting to the light source side by the first deformable material and the second deformable material has the above-mentioned recording mark. Concentrating on the internal first deformable material, causing a change in the thermal optical constant of the first deformable material, and detecting a change in the reproduction signal intensity to reproduce a recording mark below the optical resolution limit. A method of reproducing an optical recording medium using the optical recording medium according to any one of (1) to (4),
(6) “By having a recording mark shape protruding to the light source side by the first deformable material and the second deformable material, the energy of the laser beam irradiated during reproduction is concentrated on the first deformable material inside the record mark. Item (1) above, wherein a recording mark below the light resolution limit is reproduced by causing a thermal volume change or deformation of the first deformable material and detecting a change in reproduction signal intensity. Thru | or the reproducing | regenerating method of the optical recording medium using the optical recording medium in any one of (4) terms, "
(7) “When recording information, the intensity or irradiation time of the laser beam to be irradiated is set to at least two or more stages, so that the first deformable material and the second deformable material have at least two or more heights. In forming a recording mark deformed to have a shape or reproducing information, the energy of the laser beam irradiated during reproduction is concentrated on the first deformable material inside the record mark, and the heat of the first deformable material The information can be recorded in multiple values and reproduced in multiple values by detecting a reproduction signal of two or more stages by a reproduction method that causes a change in optical constant and / or thermal volume change or deformation. This is achieved by the “recording / reproducing method of an optical recording medium using the optical recording medium according to any one of items (1) to (4)”.

That is, in the optical recording medium described in (1) above, a recording mark protruding toward the light source is formed to a size that is smaller than the light resolution limit by utilizing the fact that the deformation characteristics of the first deformable material and the second deformable material are different. When reproducing information, light is concentrated inside the recording mark due to the protruding shape of the recording mark, scattered according to the state of the recording mark, and the intensity of the reproduction signal changes. Information can be recorded and reproduced in a form that does not have a transmittance window.
Further, in the optical recording medium described in (2) above, the recording mark height is increased by utilizing the fact that the deformation characteristics of the first deformable material and the second deformable material are different and the magnitude of deformation differs depending on the temperature. By controlling the shape, it is possible to obtain a reproduction signal having high contrast.
Further, in the optical recording medium described in (3) above, it is possible to obtain a reproduction signal having high contrast by utilizing the fact that the intensity of the reproduction signal varies greatly depending on the height or shape of the recording mark. It has become.
Also, in the optical recording medium described in (4) above, the recording marks formed on the recording medium are formed so that the state of the first deformable material is isolated by each recording mark, thereby reproducing with high contrast. A signal can be obtained.
Further, in the reproducing method of the optical recording medium described in (5) above, the recording mark shape protruding toward the light source is formed on the optical recording medium, thereby concentrating the energy of the laser beam irradiated at the time of reproduction in a local region, By efficiently causing a change in the thermal optical characteristics of the first deformable material, it is possible to obtain a change in the reproduction signal with a resolution below the resolution limit of light.
Further, in the reproducing method of the optical recording medium described in the above (6), the recording mark shape protruding toward the light source side is formed on the optical recording medium, thereby concentrating the energy of the laser beam irradiated at the time of reproduction in a local region, By efficiently causing a thermal volume change or deformation of the first deformable material, it is possible to obtain a change in the reproduction signal with a resolution below the resolution limit of light.
Furthermore, in the recording / reproducing method of the optical recording medium described in (7) above, when recording information, it is used that the height or shape of the recording mark changes depending on the intensity and irradiation time of the laser beam to be irradiated. In this way, recording marks are formed in multiple stages, and information can be reproduced in multiple levels by reading differences in playback signal intensity due to differences in the height of the recording marks in multiple stages. It has become.

As will be apparent from the following detailed and specific description, in the optical recording medium of the present invention, recording marks below the resolution limit of light due to deformation are formed by utilizing the characteristics of two different deformable materials. In addition, an optical recording medium capable of increasing the recording information density and capacity can be provided.
Further, the shape of the recording mark can be modulated by the intensity and irradiation time of the laser beam irradiated during recording, and an optical recording medium having a high contrast for the reproduction signal can be provided. Further, it is possible to provide an optical recording medium capable of forming recording marks in multiple stages and recording multi-value information.
Further, since the contrast of the reproduction signal can be freely changed depending on the shape of the recording mark, an optical recording medium having high light utilization efficiency can be provided.
Further, in the optical recording medium of the present invention, by forming the shape of the recording mark in a closed shell structure, the energy of the laser beam during reproduction can be efficiently concentrated on the recording mark, and the light having high light utilization efficiency. A recording medium can be provided.
In the reproducing method of the optical recording medium of the present invention, the reflection intensity of the laser beam irradiated at the time of reproduction can be changed by causing a change in thermal optical characteristics and a volume change in the material inside the recording mark. . As a result, it is possible to read a recording mark having a size that is less than the resolution limit of light. Further, since the recording mark has a structure projecting toward the light source side of the optical recording medium, the energy of light can be concentrated on the recording mark, and a reproduction signal can be obtained with high light utilization efficiency.
Also, in the recording / reproducing method of the optical recording medium of the present invention, the multi-level recording of information is performed by modulating the intensity and irradiation time of the laser beam irradiated during recording in multiple stages, and the signal intensity detected during reproduction is measured at multiple levels. Thus, it is possible to detect the large amount of recorded information.

The present invention is described in detail below.
(Optical recording medium)
The optical recording medium of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view illustrating the medium configuration in an unrecorded state in the optical recording medium of the present embodiment. As shown in FIG. 1A, the optical recording medium of the present embodiment includes a first deformable material that absorbs light and generates deformation and heat generation on a support substrate, and a second deformation that deforms by receiving heat generated by the first material. It has the structure which laminated | stacked the material in order. More preferably, as shown in FIG. 1B, the first deformable material is sandwiched between the second deformable materials.
As the first deformable material in FIGS. 1A to 1B, a material that absorbs light and generates heat at the wavelength of light for recording information is used. In addition, a material that melts and deforms by generating heat is used. As a material having such characteristics, a low melting point metal material such as Bi, In, Sn, or Sb can be used. Alternatively, an intermetallic compound material containing a low melting point metal such as BiTe, BiIn, GaSb, InP, InTe, or SbSn can be used. A binary material having a composition ratio of Sb and Te in the range of 1.5 to 4 can be used. Further, a ternary material such as GeSbTe or a quaternary material such as AgInSbTe, which has a composition ratio of Sb and Te in a range of 1.5 to 4 and contains an element other than Sb and Te, can be used. Such SbTe compounds are known as phase change materials having a crystal structure and an amorphous structure. When the composition ratio of Sb and Te is in the range of 1.5 to 4, the crystal system is called a δ phase. belong to. When the temperature is raised, the SbTe-based compound having the δ phase composition is in a molten state without causing phase separation or phase transition. When phase separation or phase transition occurs, a plurality of signal levels are generated, which causes a reduction in signal quality. Therefore, the above-mentioned material that changes only in a simple solid state and a molten state is preferable for the optical recording medium of the present embodiment. The thickness of the thin film made of the first deformable material may be about the magnitude of the deformation amount, and is preferably between 10 nm and 30 nm.

As the second deformable material in FIGS. 1A to 1B, a material having a high light transmittance at the wavelength of light for recording information is used. In addition, a soft material is used in a heated state, which has a higher melting point than the first deformable material and deforms in accordance with the deformed shape of the first deformable material through the heat generation of the first deformable material. The melting point of the first deformable material described above is 100 to 700 ° C., and the second deformable material does not melt so long as the material has a melting point of 700 ° C. or higher, and preferably a material having a melting point of 1000 ° C. or higher. A material having low thermal conductivity is preferable so that a smaller recording mark can be written in the local region. As a material having such characteristics, Si compound materials such as SiO ₂ , SiON, and SiN can be used. Also, sulfide materials such as ZnS, CaS, BaS can be used. _Further, it is possible to use a fluorine compound materials such as CaF 2, BaF _2. In addition, resin materials such as polycarbonate, acrylic, polyolefin, epoxy, and vinyl ester can be used. Also, a composite oxide material containing ZnS and SiOx can be used. The thickness of the thin film composed of the second deformable material is such that the energy of the irradiated light reaches the first deformable material sufficiently, and the reflectance of the light by this optical recording medium is within the measurement sensitivity of the detector. It needs to be set, and needs to be set somewhat thick so as not to be affected by deterioration. Specifically, although depending on the optical characteristics of the material used, the film thickness of the first deformable material, the thin film configuration shown in FIGS. 1A and 1B, the light reflectance is about 20%. It suffices to have a film thickness of 40 nm to 100 nm. As a film forming method for the first deformable material and the second deformable material, a sputtering method can be used.

  In FIG. 1B, the second deformable material layer is disposed above and below the first deformable material layer. This is a structure for preventing the heat from being diffused by the first deformable material and increasing the heat utilization efficiency. is there. Also, it has a role of adjusting the reflectance by the optical recording medium. In addition, there is an effect of controlling the shape of the recording mark by suppressing the diffusion of heat to the support substrate and the deformation of the support substrate.

  The support substrate in FIGS. 1 (a) to 1 (b) may be a substrate material generally used for optical recording media, and a resin substrate such as polycarbonate, acrylic, polyolefin, epoxy, vinyl ester, or pet is used. Can do. Further, glass, quartz, or the like can be used. In addition, a substrate used for semiconductor manufacturing such as silicon or SOI (silicon on insulator) can be used. Also, hard disk substrates such as Al and opaque glass substrates can be used.

Example 1
Example 1 relates to an optical recording medium and a recording / reproducing method according to claims 1, 2, and 3.
Next, the principle of information recording in the optical recording medium of Example 1 will be described with reference to FIG. FIG. 2 is a cross-sectional view showing a state of the optical recording medium after information is recorded. Information recording is performed by condensing and irradiating laser light from the film surface of the optical recording medium. The light intensity distribution on the surface of the optical recording medium has a higher intensity at the center of the beam spot, and generally has a Gaussian distribution shape. Due to this light intensity distribution, the first deformable material near the center of the beam spot absorbs light and is deformed (raised) by generating heat. By adjusting the intensity of irradiation light or the irradiation time so that the area having a temperature sufficient to cause deformation is smaller than the beam spot diameter, a recording mark smaller than the resolution limit of light can be obtained. Can be formed. In response to the heat generation effect of the first deformable material, deformation of the second deformable material also occurs, which is formed to follow the shape of the first deformable material. That is, as shown in FIG. 2, the thickness of the first deformable material layer is thick in the vicinity of the center of the recording mark and thin in the portion around the recording mark, and has a shape protruding toward the light source side of the optical recording medium. Since the second deformable material deforms in accordance with the shape of the first deformable material, the film thickness does not change greatly before and after recording. The recording mark formed in this way has an effect of concentrating light inside the recording mark, and a high contrast reproduction signal can be obtained.

Next, the relationship between the power of the laser beam irradiated during recording and the recording mark shape will be described with reference to FIG. FIG. 3 shows the result of AFM observation of the recorded shape when the laser beam is irradiated. FIG. 3 is a concavo-convex image of the substrate as viewed from above. As shown in FIG. 2, the second deformable material (ZnS—SiO ₂ layer) / first deformable material (AgInSbTe layer) / second deformable material (ZnS—SiO _2). Layer). In the figure, in addition to this structure, the land / groove structure of the substrate can be seen. The produced optical recording medium has a film thickness of 50 nm, 20 nm, and 46 nm in the order of ZnS—SiO ₂ , AgInSbTe, and ZnS—SiO ₂ on the polycarbonate substrate from the substrate side, and is formed by sputtering. I did it. The composition ratio of the sputtering target is Sb / Te = 2.2 and ZnS / SiO ₂ = 4. As a recording condition, a GaN semiconductor laser having a laser wavelength of 405 nm was used, and irradiation with continuous light was performed using an objective lens having a numerical aperture NA = 0.85. The recording linear velocity was 4.5 m / s, and the laser power was modulated at three levels of P1 = 1.6 mW, P2 = 1.8 mW, and P3 = 2.0 mW. FIG. 3A shows an AFM image when the laser power is set to P3, and stripe-like deformation is observed due to irradiation with continuous light. FIG. 3B is a diagram in which a plurality of areas of the AFM image shown in FIG. 3A are measured, and a plurality of stripe pattern heights are plotted with respect to the irradiated laser power. It was confirmed that the height of the recording pattern was changed in a range of about 55 nm to 70 nm almost in proportion to the irradiation laser power.

Next, the result of numerical simulation is shown on the relationship between the power of the laser beam irradiated during reproduction and the reflected light intensity obtained as a signal. The change in the reflected light intensity depending on the height of the recording mark was confirmed by performing a numerical simulation to solve the Maxwell equation describing the motion of the electromagnetic field by the finite time domain difference method (FDTD method). FIG. 4 shows a part of the simulation model used for the calculation. The FDTD method is a technique for numerically solving the Maxwell equation (differential equation) describing the behavior of an electromagnetic field in space-time. An electromagnetic field distribution in the original space is obtained, and the discretization of the space is performed by dividing the space into minute cubes (cells), which is an effective means for electromagnetic field analysis of a complex structure. As a result, for example, in Example 4 to be described later, FIGS. 3A and 3B show that the height of the recording mark due to deformation changes with a width of about 10 to 15 nm by changing the intensity of the recording light. FIG. 5 shows that the reflected light intensity when reading marks with different heights varies by about 10% depending on the height difference of 0 to several tens of nm. When the mark height changes at two levels, three values of 0, 1, and 2 can be recorded on one mark.
4A shows the case of a flat optical recording medium without a recording mark (recording mark height 0 nm), and FIG. 4B reflects the light intensity distribution in the beam spot of the laser light irradiated during recording. In this case, the recording mark has a Gaussian distribution shape (recording mark height 20 nm). The laser beam to be irradiated was assumed to have a wavelength of 405 nm and a Gaussian beam having a beam diameter of 400 nm was condensed on the film surface. The optical recording medium is composed of ZnS—SiO ₂ (50 nm), AgInSbTe (20 nm), ZnS—SiO ₂ (46 nm) in this order from the support substrate side, and the optical constants (refractive index n, extinction coefficient) of these materials. k) was set such that ZnS—SiO ₂ was n = 2.33, k = 0.00, and AgInSbTe was n = 1.73, k = 2.91. Here, AgInSbTe corresponds to the first deformable material, and ZnS—SiO ₂ corresponds to the second deformable material. In the simulation model of the optical recording medium after recording shown in FIG. 4B, the pitch of the recording mark is 200 nm, the full width at half maximum is set to 50 nm, and the recording mark height is set to 30 nm with respect to the deformed portion of AgInSbTe. The shape of ZnS—SiO _{2 on} the surface of the optical recording medium was configured to follow the shape of AgInSbTe with a film thickness of 20 nm. The support substrate was polycarbonate (n = 1.58, k = 0), and the influence of reflected light from the back side of the support substrate was ignored by adopting the absorption boundary condition at the calculation region boundary. Further, the deformation of the support substrate and the second deformable material layer adjacent to the support substrate was ignored.
“Adopting the absorption condition at the boundary of the calculation region” means that when the FDTD method is used, the calculation including the entire film thickness of the optical recording medium cannot be performed due to the limitation of the memory of the computer. In addition, the polycarbonate substrate is in contact with the lower boundary of the calculation area. This means that all electromagnetic waves traveling from this part to the outside of the calculation area are absorbed. This means that the influence of the reflected light from the lower end surface of the substrate that should originally exist outside the calculation area is ignored.
However, the FDTD method is particularly suitable for an optical recording medium because it is easier to model a complex shape such as a convex shape than the finite element method.

  FIG. 5 shows the results obtained by this simulation. The average intensity at the end face of the calculation area on the light source side of the optical recording medium is defined as the reflection intensity, and the reflection intensity from the unrecorded reflection intensity shown in FIG. The rate of change in which the difference is normalized by the reflection intensity in an unrecorded state is plotted. The “average intensity at the end face of the calculation region” is obtained by taking a time average of the square (instantaneous intensity) of the electric field at the upper end of FIG. 4A over one period of the light wave. With respect to this average intensity (reflection intensity), two cases of an unrecorded state in FIG. 4A and a recorded state in FIG. 4B are calculated, and ((reflection intensity in recording state) − (reflection intensity in unrecorded state) ) / (Reflection intensity in an unrecorded state) is defined as the rate of change (reflectance). The reflection intensity defined here corresponds to the case where light is condensed by an objective lens having a numerical aperture NA of about 0.6 in terms of the distance from the calculation area of the simulation and the film surface of the optical recording medium. . The recording mark on the horizontal axis is the height of AgInSbTe at the center of the recording mark, and the reflection intensity was calculated in the range of 0 nm to 30 nm. From FIG. 5, it was found that in the present optical recording medium, the reflection intensity slightly increased when the height of the recording mark was from 0 nm to about 13 nm, and was greatly attenuated at a height higher than that. When the height of the recording mark is 30 nm, the change in the reflection intensity reaches about 14%. The reason why the reflection intensity is attenuated is that when the recording mark has a protruding shape, the laser beam irradiated during reproduction is scattered by the recording mark, and the light intensity detected in the aperture of the objective lens is reduced. . From this result, it can be seen that the reflection intensity can be modulated within a range of about 14% depending on the height of the recording mark.

From the above results, by using the optical recording medium of the present embodiment, it is possible to form a recording mark below the resolution limit of light, the recording mark by adjusting the intensity and irradiation time of the irradiated laser light, It was confirmed that the height or shape could be modulated. It was also confirmed that the difference in the height of the recording mark greatly changed the light reflectance in the optical recording medium of the present embodiment. Therefore, by using the optical recording medium of the present embodiment, information can be recorded at a high density below the light resolution limit, and a reproduced signal can be detected with high contrast. Further, even in the region within the beam diameter (the region having the intensity of (I / e ² ) of the central intensity (I) and including about 86.5% of the total light amount), the inner region and the outer peripheral region reflect light. Due to the difference in direction, various advantageous recording / reproducing methods as will be described later will be possible.

(Example 2)
Example 2 relates to a method for reproducing an optical recording medium according to claim 5.
A method for reproducing an optical recording medium of the present invention will be described with reference to FIGS. The optical recording medium used in the reproducing method of the present embodiment is as described with reference to FIG. 2 in Example 1. The first deformable material layer that absorbs light on the optical recording medium substrate and generates heat with deformation, A second deformable material layer that is thermally deformed in accordance with the deformation of the first deformable material layer, and the first and second deformable materials are deformed by irradiating a laser beam, on the light source side of the optical recording medium. A protruding recording mark is formed. In this embodiment, since the recording mark has a shape protruding to the light source side, the optical energy of the reproduction light can be concentrated in a local area centered on the recording mark, and the optical characteristics of the first deformable material can be improved. Information is reproduced with high light utilization efficiency.

  The reproduction principle of the optical recording medium of the present embodiment will be described with reference to FIG. FIG. 6A is a top view of the present optical recording medium and a diagram showing the time evolution of the reproduction signal level, and is a conceptual diagram showing a state in which a region without a recording mark is irradiated with laser light. Since the beam spot caused by the laser beam moves in the track direction as the disk rotates, the center of the beam spot is shifted from the region that absorbs light and generates heat. The hatched area in FIG. 6 represents an area where the first deformable material generates heat and changes its state. When there is no recording mark, the light reflected from the beam spot is constant at any position on the optical recording medium, and the reproduction signal level is a constant value. On the other hand, FIG. 6B is a top view of the optical recording medium in the case of having a recording mark and a diagram showing the time evolution of the reproduction signal level. In the top view of FIG. 6B, when the beam spot represented by the solid line is directly above the protruding recording mark, the thermal state of the first deformable material in the recording mark in the region through which the beam spot has passed changes. However, the recording mark on the tip side of the beam spot is in a state before heating. Due to the difference in this state, the irradiated light is scattered reflecting the state of both recording marks, so that the reproduction signal level is lowered. Further, in the top view of FIG. 6B, when the beam spot represented by the dotted line is at the center position of the two recording marks (when the intensity center of the reproduction light beam is at the intermediate position of the two recording marks). Compared with the case where it is directly above, the ratio of the area where the state of the recording mark has changed is reduced in the beam spot, and it is less susceptible to scattering by the area where the state has changed, so the reproduction signal level is high. Become. Thus, by obtaining the contrast of the reproduction signal, a recording mark below the light resolution limit can be detected with a resolution of one size of the recording mark, and information can be reproduced.

Next, it was confirmed by performing a numerical simulation based on the FDTD method used in Example 1 that the optical energy of the reproduction light can be concentrated in the local region by the recording mark of the present optical recording medium. FIG. 7 shows a numerical simulation result of the light intensity distribution in the cross section of the optical recording medium. The simulation model is as described with reference to FIG. 4, and the configuration of the optical recording medium, the light source wavelength to be used, and the beam shape are the same. FIG. 7A shows the light intensity distribution in the case of a flat thin film having no recording mark, and FIG. 7B shows the light intensity distribution of a field having a recording mark having a Gaussian distribution shape. As shown in FIG. 7A, when there is no recording mark, the light irradiated onto the film surface has a spatial distribution that is spread approximately isotropically on the surface ZnS—SiO ₂ layer. On the other hand, when the recording mark is formed as shown in FIG. 7B, the light intensity is concentrated on the central portion of the recording mark. It can also be seen that light intensity is concentrated at the boundary between the ZnS-SiO ₂ layer and the AgInSbTe layer, and AgInSbTe has a high light absorption rate, so that heat is generated and a state change of the first deformable material is induced.

The reproduction light is irradiated with ZnS—SiO ₂ or a laser power that does not deform the second deformable material as described in the first embodiment. At this time, the first deformation described in the AgInSbTe or the first embodiment is performed. The material undergoes a change in thermal optical properties. The change in thermal optical characteristics is a change in refractive index and extinction coefficient caused by melting, precipitation of metal elements, crystal-amorphous layer transition, electronic state transition, and the like. As a result, scattered light from the recording mark below the light resolution limit is selectively generated, and a large change appears in the reflected light intensity depending on the presence or absence of the recording mark, so that the signal intensity can be detected with high contrast.

(Example 3)
Example 3 relates to a method for reproducing an optical recording medium according to claim 6.
A method for reproducing an optical recording medium of the present invention will be described with reference to FIGS. The optical recording medium used in the reproducing method of the present embodiment is as described with reference to FIG. 2 in Example 1. The first deformable material layer that absorbs light on the optical recording medium substrate and generates heat with deformation, A second deformable material layer that is thermally deformed in accordance with the deformation of the first deformable material layer, and the first and second deformable materials are deformed by irradiating a laser beam, on the light source side of the optical recording medium. A protruding recording mark is formed. In the present embodiment, since the recording mark has a convex shape on the light source side, the light energy of the reproduction light can be concentrated in a local region centered on the recording mark, and the thermal energy of the first deformable material can be reduced. By reversibly causing volume change or deformation, information can be reproduced with high light utilization efficiency. Here, the thermal volume change or deformation includes thermal expansion of the first deformable material, deformation associated with a change in electronic state, deformation due to a thermochemical reaction, or the like.

  The principle that the light energy of the reproduction light is concentrated in the local region is the same as the result of the numerical simulation of the second embodiment. In this example, it was confirmed by numerical simulation based on the FDTD method that the reflectance of light greatly changes due to volume change or deformation. FIG. 8 is a diagram for explaining a simulation model, which has a shape in which the height or volume of the AgInSbTe layer of a recording mark that is locally heated by irradiation with reproduction light and passes through a beam spot is increased. Hereinafter, this volume change and height change are referred to as volume change. Since the region through which the beam passes has undergone a thermal volume change, modeling was performed such that the volume change was received over several recording marks located in the direction opposite to the arrow indicating the track direction. The height of the recording mark was set to 20 nm before the volume change and 30 nm after the volume change. FIG. 9 shows the center position of the adjacent recording mark with a volume change (0 nm) with the center position of the beam spot as the reference (0 nm) when the reproduction light is irradiated in such a situation. It is the figure which showed the change rate of reflected light intensity at the time of moving to 200 nm. Comparing the case where the beam spot is directly above the recording mark subjected to the thermal volume change and the case where the beam spot is immediately above the adjacent recording mark where no volume change has occurred, the reflection intensity is about 8%. The change was confirmed.

  From the above results, when the recording mark according to the present invention exists due to the irradiation of the reproduction light, a local volume change occurs in the first deformable material layer, and the change in the light reflectance causes a change in the light. Recording marks below the resolution limit can be selectively reproduced. In this simulation, the change in the optical characteristics of the first deformable material described in Example 2 is not taken into account, but a material that causes the effect of the volume change and the change in the optical characteristics at the same time is selected. As a result, a higher signal contrast can be obtained.

Example 4
Example 4 relates to a method for recording and reproducing an optical recording medium according to claim 7.
The recording / reproducing method of the optical recording medium of the present invention will be described with reference to FIGS. The optical recording medium used in the recording / reproducing method of the present embodiment is as described with reference to FIG. 2 in Example 1. The first deformable material layer that absorbs light and generates heat along with deformation on the optical recording medium substrate; A second deformable material layer that is thermally deformed in accordance with the deformation of the first deformable material layer, and the first and second deformable materials are deformed by irradiating a laser beam, and the light source side of the optical recording medium A recording mark projecting on the surface is formed. In the recording / reproducing method of the present embodiment, information multi-level recording and multi-level reproduction can be realized by forming recording marks having different heights or shapes at two or more levels.

  In the recording of information, as shown in FIG. 3B, recording marks having different heights can be formed by changing the power of the laser beam irradiated during recording to two or more levels. The level of multi-level information needs to be able to read the intensity difference sufficiently in the reproduction signal, and the change in the intensity of the reproduction signal due to the difference in height in one recording mark is 15 in the configuration of the optical recording medium of the present embodiment. Since a difference of about 5% can be detected, information of 2 to 4 levels can be recorded in multiple values. By selecting a material or a multilayer structure that can take a greater change in signal intensity due to a difference in height, the level of multi-value can be further increased.

  As shown in FIG. 5, information is reproduced by using a change in reflection intensity depending on the height of the recording mark. Further, as described in the second and third embodiments, information can be selectively obtained for one recording mark by utilizing the change in thermal optical characteristics and the change in thermal volume of the first deformable material. it can. For example, in the case of the configuration of the optical recording medium used in the numerical simulation of FIG. 5, when the information is recorded at three levels including the recording mark height of 22 nm and 26 nm and the state of no recording, the case of no recording On the other hand, a change in reflection intensity of 5% and 10% can be read as information.

  As described above, multilevel recording / reproduction of information is possible by using the optical recording medium according to any one of claims 1 to 4 and optimally selecting the power of the laser beam irradiated during recording to at least two levels or more. The capacity of recorded information can be increased.

(Example 5)
Example 5 relates to the optical recording medium according to claim 4.
The optical recording medium of the present invention will be described with reference to FIGS. The configuration of the optical recording medium of the present embodiment in the unrecorded state is the same as that described in the first embodiment, and the first deformable material layer that absorbs light and generates heat with deformation on the optical recording medium substrate; The second deformable material layer is thermally deformed following the deformation of the deformable material layer. On the other hand, in the configuration of the optical recording medium after recording, the recording mark is formed so that the first deformable material is isolated in each recording mark. The recording mark having such a shape can concentrate light energy strongly on the first deformable material of the recording mark, and the change in the thermal optical characteristics of the first deformable material described in the second embodiment, In the reproduction method using the thermal volume change of the first deformable material described in 3, information can be reproduced with high light utilization efficiency.

  FIG. 10 shows a cross-sectional view after information recording in the optical recording medium of the present embodiment. In the recording mark shape of Example 1 shown in FIG. 2, the first deformable material is continuously present in the adjacent recording marks. However, in this embodiment, the first deformable material in each recording mark is isolated. And has a closed shell structure covered with the second deformable material. Such a recording mark focuses laser light on an unrecorded optical recording medium having a multilayer film structure in which a second deformable material is arranged above and below the first deformable material as shown in FIG. As a result, the peripheral portion of the first deformable material in the recording mark moves to the central portion and is formed. For this purpose, it is necessary to select a soft material capable of large deformation as the second deformable material. When the reproducing light is condensed and irradiated on the optical recording medium having the recording mark shape formed as described above, the light energy can be more efficiently concentrated in the recording mark. Moreover, since it is covered with the second deformable material, diffusion of heat to the surroundings is suppressed, and recording / reproduction with high light utilization efficiency becomes possible.

In order to confirm that the energy of the reproduction light is efficiently concentrated on the recording marks in the optical recording medium of the present embodiment, a numerical simulation based on the FDTD method was performed. The simulation model is the same as that used in the optical recording medium of Example 1, and has a structure in which ZnS—SiO ₂ (50 nm), AgInSbTe (20 nm), and ZnS—SiO ₂ (46 nm) are stacked in this order on a polycarbonate substrate. Using. The height of the recording mark was set to 30 nm at the center of the recording mark of AgInSbTe as the first deformable material. However, the AgInSbTe portion is isolated between adjacent recording marks. A light intensity distribution when the reproducing laser beam is irradiated onto the optical recording medium having such a recording mark structure as shown in FIG. 11 was obtained. The light intensity is concentrated on the boundary surface between the ZnS-SiO ₂ layer and the AgInSbTe layer on the surface, and compared with the case where the first deformable material between the recording marks in FIG. Was strongly distributed. Therefore, absorption of light in the AgInSbTe layer occurs efficiently, and heat generation induces changes in the thermal optical characteristics described in Example 2 and thermal volume changes described in Example 3 with low energy. be able to.
As described above, the recording mark has a closed shell structure in which the first deformable material is covered with the second deformable material, thereby concentrating light energy and isolating the heat generating portion. Heat diffusion can be suppressed, information can be reproduced with lower laser power, and an optical recording medium having high light utilization efficiency can be realized.

It is sectional drawing of the optical recording medium of the unrecorded state to which this invention is applied. (A) Two-layer structure (b) Three-layer structure. It is sectional drawing of the optical recording medium after the information recording to which this invention is applied. (A) It is an AFM observation image explaining the state of a recording pattern. (B) It is a figure explaining the shape of the height of the recording pattern with respect to recording laser power. It is a figure explaining the model of numerical simulation. (A) Unrecorded model. (B) Model after recording. It is a numerical simulation result explaining the change rate of the reflection intensity with respect to the height of a recording mark. It is a figure explaining the reproducing | regenerating method of the optical recording medium to which this invention is applied. It is a numerical simulation result explaining the light intensity distribution in the cross section of the optical recording medium to which the present invention is applied. (A) Unrecorded state. (B) State after recording. It is a figure explaining the model of numerical simulation. It is a simulation result explaining the change of the reflection intensity accompanying the volume change of a recording mark. It is sectional drawing of the optical recording medium after the information recording to which this invention is applied. It is a numerical simulation result explaining the light intensity distribution in the cross section of the optical recording medium to which the present invention is applied. It is a figure explaining patent document 1. It is a figure explaining patent document 2. FIG. It is a figure explaining patent document 3. FIG. It is a figure explaining patent document 4.

Explanation of symbols

22 Substrate 24 Noble metal oxide layer 25 Light absorption layer 231 Dielectric layer 232 Dielectric layer 233 Dielectric layer 32 Substrate 34 Recording layer 35 Dielectric layer 36 Reflective layer 37 Protection layer 330 Playback window 331 Lower dielectric layer 332 Mask layer 333 Upper dielectric layer 340 Recording mark 41 Substrate 42 Underlying transparent dielectric layer 43 Recording layer 44 Upper transparent dielectric layer 45 Molten layer 46 Protective layer (ZnS + SiO ₂ )
47 Reflective layer 48 Epoxy resin sealing layer

Claims (7)

A first deformable material that absorbs light and generates heat and deforms on a support substrate, and a second deformable material that transmits light and receives heat generated by the first deformable material and deforms in accordance with the shape of the first deformable material. An optical recording medium having a recording mark after recording information and having a shape that protrudes toward the light source and concentrates light, and the size of the recording mark is equal to or less than a resolution limit of light. 2. The optical recording medium according to claim 1, wherein the height or shape of the recording mark changes depending on the intensity and irradiation time of the laser beam irradiated during recording. The optical recording medium according to claim 1 or 2, wherein the intensity of reflected light by the laser beam irradiated during reproduction varies depending on the height or shape of the recording mark. The form of a recording mark after recording information is a state in which the first deformation material in each recording mark is isolated between adjacent recording marks. Optical recording medium. By having a recording mark shape protruding to the light source side by the first deformable material and the second deformable material, the energy of the laser beam irradiated during reproduction is concentrated on the first deformable material inside the record mark, and the first deformable material 5. The recording mark below the resolution limit of light is reproduced by causing a change in the thermal optical constant of the material and detecting a change in reproduction signal intensity. Of reproducing an optical recording medium using the optical recording medium of No. 1. By having a recording mark shape protruding to the light source side by the first deformable material and the second deformable material, the energy of the laser beam irradiated during reproduction is concentrated on the first deformable material inside the record mark, and the first deformable material 5. The recording mark below the light resolution limit is reproduced by causing a thermal volume change or deformation of the material and detecting a change in reproduction signal intensity. Of reproducing an optical recording medium using the optical recording medium of No. 1. When recording information, the first deformable material and the second deformable material have at least two stages of height or shape by setting the intensity or irradiation time of the laser beam to be irradiated to at least two stages or more. When the information is reproduced by forming the deformed recording mark, the energy of the laser beam irradiated during reproduction is concentrated on the first deformable material inside the record mark, and the thermal optical constant of the first deformable material 5. Information can be recorded in multiple values and reproduced in multiple values by detecting a reproduction signal of two or more stages by a reproduction method that causes a change in volume and / or thermal volume change or deformation. A recording / reproducing method of an optical recording medium using any one of the optical recording media.

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