JP2006294249A - Optical information medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical information medium which realizes high-resolution reproduction exceeding the limit of diffraction and makes reproduction power less dependent on the linear velocity. <P>SOLUTION: The optical information medium is provided with a layer 10 which is composed of specific materials and has a specific thickness corresponding to each of the specific materials. As the specific materials, a simple substance including at least one element selected from the group consisting of Nb, Mo, W, Mn, Pt, C, Si, Ge, Ti, Zr, V, Cr, Fe, Co, Ni, Pd, Sb, Ta, Al, In, Cu, Sn, Te, Zn and Bi, an alloy thereof or a compound thereof is used. A simple substance or its compound is preferably used. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical information medium having a high recording density and a reproducing method thereof.

  Optical information media include read-only optical discs such as compact discs, rewritable optical recording discs such as magneto-optical recording discs and phase change optical recording discs, and write-once optical recording discs using organic dyes as recording materials. .

  An optical information medium can generally have an information density higher than that of a magnetic recording medium, but in recent years, it has been required to further increase the information density in order to process enormous information such as images. In order to increase the information density per unit area, there are a method of narrowing the track pitch and a method of increasing the linear density by reducing the interval between recording marks and phase pits. However, if the track density or the linear density is too high with respect to the beam spot of the reproduction light, the C / N (carrier to noise ratio) becomes low, and eventually signal reproduction becomes impossible. The resolution at the time of signal reproduction is determined by the beam spot diameter. Specifically, when the wavelength of the reproduction light is λ and the numerical aperture of the optical system of the reproduction apparatus is NA, generally the spatial frequency 2NA / λ is the reproduction limit. . Therefore, it is effective to shorten the wavelength of the reproduction light and increase the NA in order to improve the C / N and the resolution at the time of reproduction, and many technical studies have been made. It is necessary to solve specific problems.

  Under these circumstances, various methods for exceeding the reproduction limit determined by light diffraction, that is, so-called super-resolution reproduction methods have been proposed.

  The most common super-resolution reproduction method is a method in which a so-called mask layer is provided on a recording layer. In this method, utilizing the fact that the intensity distribution of the laser beam spot is a Gaussian distribution, an optical aperture smaller than the beam spot is formed in the mask layer, thereby narrowing the beam spot smaller than the diffraction limit. This method is roughly divided into a heat mode method and a photon mode method depending on the difference in the mechanism of optical opening formation.

  In the heat mode method, the optical characteristics change in a region where the temperature becomes a certain value or more in the beam spot irradiation part of the mask layer. The heat mode method is used, for example, in an optical disc described in Patent Document 1. This optical disc has a material layer whose reflectivity varies with temperature on a transparent substrate on which recording pits that can be optically read in accordance with an information signal are formed. That is, this material layer functions as a mask layer. The element specifically mentioned as the material constituting the material layer in the publication is a lanthanoid, and Tb is used in the examples. In the optical disc described in the publication, when the reading light is irradiated, the reflectance of the material layer changes depending on the temperature distribution in the scanning spot of the reading light, and after reading, the reflectance is in an initial state when the temperature is lowered. Returning to the above, the material layer does not melt at the time of reproduction. As a heat mode method, for example, as described in Patent Document 2, an amorphous-crystal transition material is used for a mask layer, and a high temperature region in a beam spot is crystallized to improve reflectance. A medium for performing super-resolution reproduction is also known. However, this medium is not practical because it is necessary to return the mask layer to amorphous again after reproduction.

  In the heat mode method, since the size of the optical aperture is uniquely determined by the temperature distribution of the mask layer, it is necessary to strictly control the power of the reproduction light in consideration of various conditions such as the linear velocity of the medium. For this reason, the control system becomes complicated, and the medium driving device becomes expensive. In the heat mode method, the mask layer is likely to be deteriorated by repeated heating, so that the reproduction characteristics are likely to be deteriorated by repeated reproduction.

On the other hand, in the photon mode method, the optical characteristics change in a region where the photon amount is a certain value or more in the beam spot irradiation part of the mask layer. The photon mode method is used in, for example, the information recording medium described in Patent Document 3, the optical recording medium described in Patent Document 4, and the optical information recording medium described in Patent Document 5. Patent Document 3 discloses a mask layer in which phthalocyanine or a derivative thereof is dispersed in a resin or an inorganic dielectric, and a mask layer made of chalcogenide. Further, in Patent Document 4, a super-resolution reproduction film containing a semiconductor material having a forbidden band in which light absorption characteristics are changed by electron excitation to the energy level of excitons by irradiation of the reproduction light is used as a mask layer. As a specific example of the mask layer, a material in which CdSe fine particles are dispersed in a SiO ₂ base material is cited. Moreover, in the said patent document 5, the glass layer from which the intensity distribution of the irradiated light and the intensity distribution of the transmitted light changes nonlinearly is used as a mask layer.

  In the photon mode type super-resolution reproduction medium, unlike the heat mode type super-resolution reproduction medium, deterioration due to repeated reproduction is relatively difficult to occur.

  The region where the optical characteristics change in the photon mode method is determined by the number of incident photons. The number of incident photons depends on the linear velocity of the medium with respect to the beam spot. Even in the photon mode method, the size of the optical aperture depends on the power of the reproduction light. If an excessive power is applied, the optical aperture becomes excessive, and super-resolution reproduction becomes impossible. Therefore, also in the photon mode method, it is necessary to strictly control the power of the reproduction light according to the linear velocity and according to the dimensions of the pit and recording mark to be read. The photon mode method also has a problem that the mask layer constituent material must be selected according to the wavelength of the reproduction light, that is, it is difficult to adapt to multi-wavelength reproduction.

JP-A-5-205314 Japanese Patent No. 2844824 JP-A-8-96412 Japanese Patent Laid-Open No. 11-86342 Japanese Patent Laid-Open No. 10-340482

  An object of the present invention is to provide an optical information medium capable of reproducing at a high resolution exceeding the diffraction limit and having a low dependence of reproducing power on the linear velocity.

  Such an object is achieved by the present inventions (1) to (8) below.

(1) An optical information medium having an information recording surface that has irregularities, can form recording marks, or has irregularities and can form recording marks,
It has a functional layer that has the function of improving the spatial resolution,
This functional layer includes Nb, Mo, W, Mn, Pt, C, Si, Ge, Ti, Zr, V, Cr, Fe, Co, Ni, Pd, Sb, Ta, Al, In, Cu, Sn, Te And a functional layer having a specific thickness corresponding to the composition thereof, wherein the functional layer is composed of a simple substance or an alloy containing at least one element selected from the group consisting of Zn and Bi, or a compound thereof. Optical information medium to be used.

(2) It has a base provided with pits for holding information, and has a functional layer on the pit forming surface of this base. 4NA · P _L (P _L is the minimum length of the pit, NA is the reproduction optical It is possible to reproduce information held by the pit when irradiated with reproduction light having a longer wavelength than the numerical aperture of the system. When the wavelength of the reproduction light is λ and the refractive index of the substrate is n, the pit Depth d is in the whole medium,
λ / 10n ≦ d <λ / 6n
And
Further, the functional layer includes Nb, Mo, W, Mn, Pt, C, Si, Ge, Ti, Zr, V, Cr, Fe, Co, Ni, Pd, Sb, Ta, Al, In, Cu, Sn And a functional layer having a specific thickness corresponding to the composition of the element or alloy containing at least one element selected from the group consisting of Te, Zn and Bi, or a compound thereof. Characteristic optical information medium.

(3) An optical information medium comprising an information recording surface that has irregularities, can form a recording mark, or has the irregularities and can form a recording mark,
It has a functional layer that has the function of improving the spatial resolution,
This functional layer is composed of any one of the following elements, and has the following thickness corresponding to the element.
Nb: 2 to 100 nm
Mo: 2 to 70 nm
W: 2 to 70 nm
Mn: 2 to 100 nm
Pt: 2 to 40 nm
C: 2 to 100 nm
Si: 2 to 100 nm
Ge: 2 to 100 nm
Ti: 2 to 100 nm
Zr: 2 to 100 nm
V: 2 to 100 nm
Cr: 2 to 30 nm
Fe: 2 to 80 nm
Co: 2 to 70 nm
Ni: 2 to 70 nm
Pd: 2 to 40 nm
Sb: 2 to 100 nm
Ta: 2 to 100 nm
Al: 2 to 20 nm
In: 2 to 100 nm
Cu: 2 to 10 nm
Sn: 2 to 40 nm
Te: 2 to 70 nm
Zn: 40 to 90 nm
Bi: 45-70 nm

(4) An optical information medium having an information recording surface that has irregularities, can form a recording mark, or has the irregularities and can form a recording mark,
It has a functional layer that has the function of improving the spatial resolution,
This functional layer is configured by adding at least one element selected from the group consisting of nitrogen, oxygen, fluorine, sulfur and carbon to any of the following elements, and includes the following elements contained in this functional layer: An optical information medium characterized by having the following thickness corresponding to:
Nb: 2 to 100 nm
Mo: 2 to 70 nm
W: 2 to 70 nm
Mn: 2 to 100 nm
Pt: 2 to 40 nm
C: 2 to 100 nm
Si: 2 to 100 nm
Ge: 2 to 100 nm
Ti: 2 to 100 nm
Zr: 2 to 100 nm
V: 2 to 100 nm
Cr: 2 to 30 nm
Fe: 2 to 80 nm
Co: 2 to 70 nm
Ni: 2 to 70 nm
Pd: 2 to 40 nm
Sb: 2 to 100 nm
Ta: 2 to 100 nm
Al: 2 to 20 nm
In: 2 to 100 nm
Cu: 2 to 10 nm
Sn: 2 to 40 nm
Te: 2 to 70 nm
Zn: 40 to 90 nm
Bi: 45-70 nm

(5) It has a base provided with pits for holding information, and has a functional layer on the pit forming surface of this base. 4NA · P _L (P _L is the minimum length of the pit, NA is reproduction optical It is possible to reproduce information held by the pit when irradiated with reproduction light having a longer wavelength than the numerical aperture of the system. When the wavelength of the reproduction light is λ and the refractive index of the substrate is n, the pit Depth d is in the whole medium,
λ / 10n ≦ d <λ / 6n
And
Furthermore, the functional layer is composed of any one of the following elements, and has the following thickness corresponding to the element.
Nb: 2 to 100 nm
Mo: 2 to 70 nm
W: 2 to 70 nm
Mn: 2 to 100 nm
Pt: 2 to 40 nm
C: 2 to 100 nm
Si: 2 to 100 nm
Ge: 2 to 100 nm
Ti: 2 to 100 nm
Zr: 2 to 100 nm
V: 2 to 100 nm
Cr: 2 to 30 nm
Fe: 2 to 80 nm
Co: 2 to 70 nm
Ni: 2 to 70 nm
Pd: 2 to 40 nm
Sb: 2 to 100 nm
Ta: 2 to 100 nm
Al: 2 to 20 nm
In: 2 to 100 nm
Cu: 2 to 10 nm
Sn: 2 to 40 nm
Te: 2 to 70 nm
Zn: 40 to 90 nm
Bi: 45-70 nm

(6) It has a base provided with pits for holding information, and has a functional layer on the pit forming surface of this base. 4NA · P _L (P _L is the minimum length of the pit, NA is reproduction optical) It is possible to reproduce information held by the pit when irradiated with reproduction light having a longer wavelength than the numerical aperture of the system. When the wavelength of the reproduction light is λ and the refractive index of the substrate is n, the pit Depth d is in the whole medium,
λ / 10n ≦ d <λ / 6n
And
Furthermore, the functional layer is configured by adding at least one element selected from the group consisting of nitrogen, oxygen, fluorine, sulfur, and carbon to any of the following elements, and included in the functional layer: An optical information medium having the following thickness corresponding to the element:
Nb: 2 to 100 nm
Mo: 2 to 70 nm
W: 2 to 70 nm
Mn: 2 to 100 nm
Pt: 2 to 40 nm
C: 2 to 100 nm
Si: 2 to 100 nm
Ge: 2 to 100 nm
Ti: 2 to 100 nm
Zr: 2 to 100 nm
V: 2 to 100 nm
Cr: 2 to 30 nm
Fe: 2 to 80 nm
Co: 2 to 70 nm
Ni: 2 to 70 nm
Pd: 2 to 40 nm
Sb: 2 to 100 nm
Ta: 2 to 100 nm
Al: 2 to 20 nm
In: 2 to 100 nm
Cu: 2 to 10 nm
Sn: 2 to 40 nm
Te: 2 to 70 nm
Zn: 40 to 90 nm
Bi: 45-70 nm

  (7) A light having a protective layer made of a material having a higher thermal conductivity than air on the functional layer of the optical information medium according to any one of (1) to (6). Information medium.

  (8) The optical information medium according to (7), wherein the protective layer is made of a resin.

  In the optical information medium according to the present invention, as described above, since the functional layer is composed of a predetermined element and has a predetermined thickness according to the element, high-resolution reproduction exceeding the diffraction limit is possible. Yes, and the linear velocity dependence of reproduction power is low.

  When compounded by adding at least one element selected from the group consisting of nitrogen, oxygen, fluorine, sulfur and carbon to the functional layer, expansion of the reproduction power range, improvement of maximum C / N, super-resolution reproduction Effects such as expansion of the range of possible functional layer thicknesses and suppression of C / N deterioration due to repeated reproduction are also obtained.

  Further, when a protective layer made of a material having a higher thermal conductivity than air is provided on a predetermined functional layer, reproduction with high power is possible, and high C / N can be obtained.

  The optical information medium of the present invention has an information recording surface. In this specification, the information recording surface means a region having irregularities composed of pits and / or grooves, a recording mark can be formed, or a region having the irregularities and capable of forming a recording mark. That is, the present invention can be applied to both a read-only medium and an optical recording medium (recordable medium or rewritable medium). In the read-only medium, pits provided on the substrate surface constitute the information recording surface, and in the optical recording medium, the recording layer constitutes the information recording surface. The recording layer may be any of a phase change type, a layer mainly composed of an organic dye, and a layer mainly composed of other organic materials or inorganic materials. The recording mark may be any one having a different optical constant such as a reflectance relative to the surroundings, a concave shape, or a convex shape.

  The inventors of the present invention have provided a layer formed of a specific material and having a specific thickness corresponding to each of the specific materials on the optical information medium, thereby super-resolution of a mechanism completely different from the conventional one. I found it possible to play it. In the present invention, as the specific material, Nb, Mo, W, Mn, Pt, C, Si, Ge, Ti, Zr, V, Cr, Fe, Co, Ni, Pd, Sb, Ta, Al, In, A simple substance or an alloy containing at least one element selected from the group consisting of Cu, Sn, Te, Zn and Bi, or a compound thereof is used, and preferably a simple substance or a compound thereof is used. In the present invention, the layer that enables super-resolution reproduction is referred to as a functional layer. By providing this functional layer, it becomes possible to detect pits, grooves, and recording marks having dimensions below the resolution limit determined by light diffraction.

  Details of the present invention will be described below.

[Application to the media structure shown in FIG. 1]
A configuration example of the optical information medium is shown in FIG. An optical information medium 1 shown in FIG. 1 is a read-only medium, and has a pit 21 on the surface of a light-transmitting substrate 2 and a layer 10 in close contact with the pit formation surface. The reproduction light is incident from the lower side in the figure. The layer 10 acts as the functional layer when it has a specific composition and a specific thickness.

(When the layer 10 is composed of a simple substance or an alloy)
An optical disk sample having the structure shown in FIG. 1 was produced by the following procedure. The substrate 2 was a disk-shaped polycarbonate (refractive index n = 1.58) having a diameter of 120 mm and a thickness of 0.6 mm, on which phase pits were simultaneously formed by injection molding. The base body 2 is of a banded type in which a plurality of annular pit formation regions having spiral tracks are provided concentrically and the pit length is constant in each pit formation region. That is, phase pits having different lengths are formed on a single substrate. The pit length (pit length) in each pit formation area is the value shown in FIG. 5, and the space between adjacent pits is the same length as the pit. The layer 10 was composed of a Si layer having a thickness of 15 nm or an Al alloy (Al-1.7 atomic% Cr) layer having a thickness of 100 nm. The layer 10 was formed by a sputtering method.

For these samples, C / N was measured using an optical disk evaluation apparatus (laser wavelength: 635 nm, numerical aperture: 0.60), linear velocity was 11 m / s, and reproduction power was 3 mW. The cut-off spatial frequency 2NA / λ in this optical disk evaluation apparatus is
2NA / λ = 1.89 × 10 ³ (line pair / mm)
Therefore, a pit row having the same length between the pit and the space between adjacent pits can be read if the spatial frequency is 1.89 × 10 ³ (line pair / mm) or less. In this case, the pit length (= space length) P _L corresponding to the readable spatial frequency is
P _L ≧ λ / 4NA = 265 (nm)
It becomes. Therefore, if C / N is obtained in a pit string having a pit length of less than 265 nm, it can be said that super-resolution reproduction is possible.

  FIG. 5 shows the relationship between the pit length and C / N in each sample. In FIG. 5, in the sample having the Si layer having a thickness of 15 nm, C / N of 40 dB or more is obtained at a pit length of 200 to 250 nm. On the other hand, in a sample having an Al alloy layer with a thickness of 100 nm, C / N is 0 dB at a pit length of 250 nm or less, and no signal is obtained. When the pit length is 300 nm, which is in the readable spatial frequency range, the C / N of the sample having the Al alloy layer is almost the same as that of the sample having the Si layer. From this result, it is understood that super-resolution reproduction can be achieved by providing a Si layer having a thickness of 15 nm.

  In this specification, “reproduction is possible” means that a C / N of 20 dB or more can be obtained. However, practically, it is necessary to obtain C / N of preferably about 30 dB or more, more preferably about 40 dB or more.

  Next, the layer 10 is made of Nb, Mo, W, Mn, Pt, C, Si, Ge, Ti, Zr, V, Cr, Fe, Co, Ni, Pd, Sb, Ta, Al, In, Cu, Sn, An optical disk sample was manufactured by using any one of Te, Zn, Bi, Au, and Ag and changing the thickness within a range of 5 to 100 nm. C / N was measured by changing the reproduction power in the range of 1 to 7 mW for the pit rows having a pit length of 250 nm of these samples. The above optical disk evaluation apparatus was used for C / N measurement, and the linear velocity during measurement was 11 m / s. Tables 1 to 4 show the relationship between the thickness of the layer 10 and C / N. In Tables 1 to 4, the highest C / N obtained when the reproducing power is changed between 1 to 7 mW at each thickness of the layer 10 is displayed for each constituent material of the layer 10. Table 1 shows that the maximum C / N is 40 dB or more, Table 2 shows that the maximum C / N is 30 dB or more and less than 40 dB, and Table 3 shows that the maximum C / N is 20 dB or more and less than 30 dB. Table 4 shows the cases where the maximum C / N is less than 20 dB, classified in each case.

  From Tables 1 to 4, it can be seen that the thickness of the layer 10 needs to be optimized in accordance with the constituent elements in order to enable super-resolution reproduction. For example, as shown in Table 2, super-resolution reproduction is possible when the layer 10 is an Al layer and the thickness is 15 nm, but when the thickness of the Al layer reaches 100 nm, that is, It can be seen that when the reflection layer is about the same as that of a normal ROM disk such as a CD-ROM or DVD-ROM, super-resolution reproduction cannot be performed as in the case of a normal ROM disk.

  FIG. 6 to FIG. 9 show the relationship between the reproduction power Pr and C / N for the samples with the maximum C / N obtained. The samples shown in FIGS. 6 to 9 correspond to Tables 1 to 4, respectively. C / N was measured for a pit train having a pit length of 250 nm. The optical disk evaluation apparatus was used for measurement, and the linear velocity during measurement was 11 m / s. 6 to 9, it can be seen that in most samples, the C / N tends to increase as the reproduction power increases. Although these figures do not show the reproduction output, the reproduction output showed the same behavior as C / N. In FIGS. 6 to 9, the data with no high Pr side does not have a reproduced signal due to deterioration of the layer 10 at that Pr, or the data is due to saturation of the reflected light detection system of the evaluation device. It was not obtained.

FIGS. 10 to 13 show the relationship between the reproduction power Pr and the amount of reflected light for the samples with the maximum C / N obtained. The samples shown in FIGS. 10 to 13 correspond to Tables 1 to 4, respectively. FIG. 13 also shows the results of a disk having a phase change material layer as a mask layer in order to show the change in the amount of reflected light of a conventional super-resolution medium using a mask layer. This disk, on the substrate, first dielectric layer with a thickness of 80nm made of ZnS-SiO _2, mask layer having a thickness of 20nm formed of Ge ₂ Sb ₂ Te ₅ (phase change material layer), ZnS-SiO ₂ A second dielectric layer made of 23 nm and a reflective layer made of Al having a thickness of 100 nm are laminated in this order, and the mask layer is in a state immediately after being formed by sputtering (amorphous state). . The amount of reflected light was measured for a pit row having a pit length of 250 nm. This reflected light amount is the average reflected light amount of the entire pit row. That is, the average reflected light amount of the recording track composed of pits and spaces between adjacent pits. The optical disk evaluation apparatus was used for measurement, and the linear velocity during measurement was 11 m / s. In FIGS. 10 to 13, the amount of reflected light increases substantially in proportion to the increase in the reproduction power Pr except for the comparative sample having the mask layer. This means that the reflectance is substantially unaffected by the reproduction power. That is, it means that the complex refractive index (n + ik) does not change as the reproduction power changes. In contrast, a conventional super-resolution medium having a mask layer requires a reproduction power (amount of heat or light) of a certain value or more to form an optical aperture, and the reflectance changes abruptly with the certain value as a boundary. To do. As a result, as seen in the comparative sample of FIG. 13, an inflection point exists at the constant value in the graph showing the relationship between the reproduction power and the amount of reflected light. In the Pr-reflected light amount line of the comparative sample shown in FIG. 13, the inflection point that appears at the position of Pr = 2 mW is due to the crystallization of the mask layer, and the inflection point that appears at the position of Pr = 6 mW. The point is due to the melting of the mask layer.

  As described above, in the sample of the present invention capable of super-resolution reproduction, the reflectance is the reproduction power as in the case of the sample incapable of super-resolution reproduction (for example, the sample having the Au layer or the Ag layer shown in FIG. 13). Not affected. From this result, the super-resolution reproduction mechanism in the present invention uses a change in reflectance due to a temperature change or a light amount change, unlike a conventional super-resolution medium that forms an optical aperture by a heat mode method or a photon mode method. It turns out that it is not a thing.

  However, as will be described later, a phase change material layer can also be used as a functional layer in the present invention. The phase change material layer that can be used as a functional layer in the present invention can be super-resolution reproduced when irradiated with reproduction light that does not change its complex refractive index, whether amorphous or crystalline. is there.

  The following experiment was further conducted on the relationship between temperature change and reflectance change. In this experiment, a 15 nm thick W layer or a 100 nm thick W layer was formed on a substrate (a slide glass having a thickness of 1.2 mm) by sputtering to produce a measurement sample, and the reflectance of the W layer was measured. The temperature dependence of was measured with a heating microscope. In this measurement, the heating rate was 30 ° C./min, and the reflectance was measured at a wavelength of 635 nm. In FIG. 14, the temperature dependence of the reflectance in 100-400 degreeC is shown. As shown in FIG. 14, in any case, substantially no change in reflectance is observed when heating up to 400 ° C. This result agrees well with the results shown in FIGS.

  FIG. 15 shows the C when the reproduction power Pr is changed in the range of 1 to 5 mW and the linear velocity LV is changed in the range of 3 to 11 m / s for the sample in which the layer 10 is composed of the W layer having a thickness of 15 nm. / N. C / N was measured for a pit row having a pit length of 250 nm, and the optical disk evaluation apparatus was used for the measurement. FIG. 15 shows that the linear velocity dependence of C / N is not substantially recognized. That is, in this linear velocity range, it can be seen that the performance related to super-resolution reproduction is not substantially affected by the linear velocity. Therefore, in this linear velocity region, it is not necessary to control the reproduction power even when the linear velocity is changed. The fact that the linear velocity can be freely selected in such a wide range is that the conventional super-resolution medium cannot be realized by either the heat mode method or the photon mode method. FIG. 15 shows only the results for a sample having a W layer having a thickness of 15 nm. In all of the above samples capable of super-resolution reproduction, C / N in such a wide linear velocity region is shown. The linear velocity dependence of was not substantially observed.

  For each of the above samples, when the reproduction light wavelength was 780 nm and the C / N was measured for a pit row having a pit length of 250 nm and a pit row having a pit length of 300 nm, it was confirmed that super-resolution reproduction was possible.

  Further, for a sample in which the layer 10 is an alloy of W and Mo and the thickness of the layer 10 is 15 nm, the optical disk evaluation apparatus is used, the linear velocity is 11 m / s, and the pit length C is 250 nm. / N was measured. The results are shown in FIG. FIG. 16 shows that super-resolution reproduction is possible even when an alloy is used.

Further, the above optical disk evaluation was performed on a sample in which the layer 10 was made of an amorphous Tb _19.5 Fe _70.5 Co ₇ Cr ₃ (atomic ratio) alloy formed by sputtering and the thickness of the layer 10 was 15 nm. Using the apparatus, the C / N of a pit row having a pit length of 250 nm was measured at a linear velocity of 11 m / s. The layer made of the alloy having this composition can be used as a magneto-optical recording layer, but in this sample, it is used as a reflective layer in a reproduction-only sample. FIG. 35 shows the relationship between the reproduction power Pr and the amount of reflected light in this sample. FIG. 36 shows the relationship between the reproduction power Pr and C / N. From FIG. 35, it can be seen that also in this sample, the amount of reflected light changes linearly depending on the reproduction power. FIG. 36 also shows that super-resolution reproduction is possible in this sample, and that the layer 10 made of a magneto-optical recording material functions as a functional layer in the present invention.

  For a sample in which the layer 10 is composed of a W layer having a thickness of 15 nm, a smooth polycarbonate plate having a thickness of 0.6 mm is adhered on the layer 10 with an adhesive sheet, and reproduction light is incident through the polycarbonate plate. Played. The polycarbonate plate is bonded to correct astigmatism of the objective lens of the reproducing optical system. As a result, the C / N of the pit train having a pit length of 250 nm was 13.8 dB at a reproduction power of 2 mW, 21.8 dB at 3 mW, and 27.8 dB at 4 mW, and super-resolution reproduction was possible. From this result, it is understood that super-resolution reproduction is possible even when a transparent resin layer (adhesive layer) is formed on the layer 10 and reproduction is performed therethrough.

(When layer 10 is composed of a compound)
In the optical information medium of the present invention, super-resolution reproduction is possible even when the layer 10 is made of various compounds such as nitrides, oxides, fluorides, sulfides, and carbides, and effects unique to such cases are possible. Is obtained. Note that the compound in this case is not limited to a compound having a stoichiometric composition, but also includes a compound in which nitrogen, oxygen, or the like is mixed with a metal or a semimetal at a ratio less than the stoichiometric composition. That is, according to the present invention, the layer 10 includes the metal or metalloid that can be super-resolved and reproduced by a simple substance or an alloy, and is further selected from other elements, preferably nitrogen, oxygen, fluorine, sulfur, and carbon. Including the case of containing at least one element. By constituting the layer 10 from such a compound, the reproduction power margin can be expanded, and the C / N can be improved. In addition, C / N deterioration due to repeated reproduction can be suppressed. Hereinafter, an experiment in the case where the layer 10 is composed of a compound will be described.

In the sample used in this experiment, the layer 10 was formed by sputtering in an Ar atmosphere or reactive sputtering in an Ar + reactive gas atmosphere. Si, Ta or Al was used for the sputtering target, and N ₂ or O ₂ was used for the reactive gas. For each sample having a different reactive gas flow rate when the layer 10 was formed, C / N was measured in a pit row having a pit length of 250 nm while changing the reproduction power in the range of 1 to 7 mW. The above optical disk evaluation apparatus was used for C / N measurement, and the linear velocity during measurement was 11 m / s. FIGS. 17, 18 and 19 show the relationship between the reproduction power Pr and C / N of samples using Si, Ta and Al as targets, respectively. The thickness of the layer 10 is 15 nm when an Si target and a Ta target are used, and 30 nm when an Al target is used. The reactive gas flow ratios (N ₂ ratio, O ₂ ratio) shown in each figure are the reactive gas flow rates relative to the sum of the reactive gas flow rate and the Ar flow rate.

As shown in FIG. 17, when the N ₂ flow ratio is zero, that is, when the layer 10 is made of Si, Pr = 3 mW, C / N is maximized and decreases at 4 mW, and when 5 mW, the layer 10 C / N could not be obtained due to deterioration of. Further, as shown in FIG. 18, when the layer 10 is made of Ta, reproduction is possible only when Pr = 1 mW, and if the reproduction power exceeding that is applied, the layer 10 deteriorates and reproduction is impossible. became. On the other hand, when the flow rate ratio of the reactive gas is increased, as shown in FIGS. 17 and 18, the C / N is lowered on the low Pr side, but a higher regeneration power can be used. N improved. When the flow rate ratio of the reactive gas was further increased, the maximum C / N decreased, and finally super-resolution reproduction became impossible.

As shown in FIG. 19, when the layer 10 is made of Al, super-resolution reproduction is impossible due to saturation of the reflected light detection system of the evaluation apparatus at a reproduction power of 3 mW or more, but the N ₂ flow rate ratio is increased. When it was made to be reproducible, extremely high C / N was obtained. When the N ₂ flow rate ratio was further increased, super-resolution reproduction was finally impossible.

Super-resolution reproduction was also possible for a sample in which the layer 10 was formed from a Ge-N layer having a thickness of 15 nm formed by sputtering a Ge target in an Ar + N ₂ atmosphere. Using the above optical disk evaluation apparatus, the linear velocity was 11 m / s, and the C / N in the pit row of this sample with a pit length of 250 nm was measured. As a result, the reproduction power was 7 mW and the result was 42.6 dB. Super-resolution reproduction was also possible for a sample having a layer 10 having a thickness of 15 nm formed by sputtering in an Ar atmosphere using a SiC target. Using the above optical disk evaluation apparatus, the linear velocity was set to 11 m / s, and the C / N in the pit row of this sample having a pit length of 250 nm was measured. At that time, it was 27.9 dB. In any of these cases, C / N improvement was observed as the reproduction power increased.

  20, FIG. 21 and FIG. 22 show the relationship between the reproduction power Pr and the amount of reflected light of the samples shown in FIG. 17, FIG. 18, and FIG. 19, respectively. In these figures, similarly to FIGS. 10 to 13 described above, the amount of reflected light increases almost in proportion to the increase in the reproduction power Pr. This means that the reflectance is substantially unaffected by the reproduction power. Therefore, even if the layer 10 is compounded, it is considered that the mechanism of super-resolution reproduction does not change.

FIG. 23 shows the relationship between the thickness of the layer 10 and C / N when an Al target is used and the N ₂ flow ratio is 0 or 0.08. C / N shown in the figure is the maximum C / N when the reproduction power is changed in the range of 1 to 7 mW. It can be seen from FIG. 23 that nitriding the layer 10 improves the maximum C / N and significantly extends the range of the layer 10 thickness capable of super-resolution reproduction.

Next, a sample using Si as a target, in which N ₂ was not introduced and in which N ₂ was introduced, was repeatedly reproduced to examine C / N degradation. The thickness of the layer 10 in these samples was 15 nm. The reproduction power was set to 3 mW for the sample into which N ₂ was not introduced, and 6 mW or 7 mW for the introduced sample. The results are shown in FIG.

In FIG. 24, in the sample in which N ₂ was not introduced, the C / N decreased by over 10 dB after 100,000 reproductions. On the other hand, in the sample into which N ₂ is introduced, there is almost no C / N reduction even after 100,000 cycles of regeneration. Moreover, when the reproduction power is 7 mW, the initial C / N is higher than that of the sample in which N ₂ is not introduced. From this result, it can be seen that compounding the layer 10 significantly improves the stability of repeated reproduction.

  Based on the results of the above experiments, the operational effects when the layer 10 is made of a compound will be described below.

  In the above experiment, when nitrogen, oxygen, fluorine, sulfur, carbon, etc. are introduced into the metal thin film or metalloid thin film, the thin film increases in transparency as the amount of introduction increases, that is, loses metallic luster. The transparency increased considerably as the amount introduced increased to near the stoichiometric composition. In any of FIGS. 17 to 19, the super-resolution reproduction is possible when the transparency of the layer 10 is relatively low. When the transparency of the layer 10 is relatively high, the super-resolution reproduction is impossible. It became. And when the transparency of the layer 10 improved by compounding, C / N in low Pr fell. This result suggests that the heat mode is involved in the super-resolution reproduction in the present invention. That is, it is considered that the C / N at low Pr was lowered due to the improvement in transparency of the layer 10 because the ultimate temperature was lowered due to the decrease in the light absorption rate of the layer 10. However, in the medium of the present invention, since the reflectance is not substantially affected by the reproduction power, the super-resolution reproduction in the present invention is different from the conventional heat-mode super-resolution reproduction medium in the optical aperture. It is thought that it is not due to the formation of.

  Also, from the results shown in FIG. 17 to FIG. 19, by adding an appropriate amount of nitrogen or oxygen to the layer 10 to form a compound, the usable reproduction power range is widened and the maximum C / N is improved. I know you get. The expansion of the reproduction power range and the improvement of the maximum C / N are considered to be related to the improvement of the chemical stability and transparency of the layer 10 by compounding. Further, from the results shown in FIG. 23, it can be seen that the range of the thickness of the layer 10 capable of super-resolution reproduction is significantly expanded by compounding the layer 10. This is considered to be related to the increase in transparency of the layer 10 by compounding. Further, from the results shown in FIG. 24, it can be seen that the compounding of the layer 10 significantly suppresses C / N deterioration due to repeated reproduction. This C / N deterioration suppression is considered to be due to the improvement of the chemical stability of the layer 10.

  First, the improvement in chemical stability by compounding and the action and effect thereof will be described. Metals or semimetals other than noble metals such as Au are generally produced in the form of compounds such as oxides and sulfides in nature. This indicates that the metal or metalloid is more stable as a compound than as a simple substance under normal circumstances. That is, the chemical stability of the metal or metalloid is greatly improved by compounding. On the other hand, the deterioration of the layer 10 due to high power regeneration and repeated regeneration is considered to be due to a chemical change (oxidation or the like) accompanying the temperature rise of the layer 10. Since the layer 10 is in contact with air, it is likely to be deteriorated by heating during irradiation with reproduction power. However, if the layer 10 is composed of a compound, the chemical change of the layer 10 is suppressed, so that reproduction with higher power is possible. Thus, the maximum C / N is improved, and it is considered that C / N deterioration due to repeated reproduction is suppressed. Therefore, the compounding of the layer 10 is extremely effective when a material that causes deterioration with a relatively low reproduction power is used.

  Next, the increase in transparency due to compounding and the operational effects thereof will be described. As described above, since the transparency of the layer 10 is increased by compounding, the light reflectance is decreased. When the light reflectance of the layer 10 decreases, the reflected light detection system is less likely to be saturated. As a result, it is considered that the usable reproduction power is increased and the maximum C / N is improved. Moreover, since the transparency per unit thickness of the layer 10 is improved by compounding, if the compound is compounded, the reflected light detection system is hardly saturated even if the layer 10 is made thicker. Therefore, as shown in FIG. 23, it is considered that the range of the layer 10 thickness capable of super-resolution reproduction has been remarkably expanded. Therefore, the compounding of the layer 10 is extremely effective when a material that causes saturation of the reflected light detection system with a relatively low reproduction power is used.

  On the other hand, when the introduction amount of nitrogen or oxygen is increased, the super-resolution reproduction becomes impossible because the transparency of the layer 10 becomes too high, that is, the absorption coefficient of the layer 10 approaches zero, and the reproduction light is reduced. This is probably because the function of the layer 10 could not be expressed. Therefore, when the layer 10 is compounded, it is necessary to appropriately set the degree of compounding so that sufficiently high C / N can be obtained according to the type of metal or metalloid to be compounded. Specifically, it is preferable to suppress the introduction amount of nitrogen, oxygen, or the like to less than the stoichiometric composition. In the above experiment, super-resolution reproduction was possible even when SiC having a stoichiometric composition was used for the layer 10, but higher C / N can be obtained by reducing the C content.

  In the above experiment, in order to compound the layer 10, a reactive sputtering method using a reactive gas such as nitrogen or oxygen or a sputtering method using a compound target was used. Can be used.

[Application to the media structure shown in FIG. 2]
Next, a medium sample having the structure shown in FIG. 2 was produced. In this sample, a resin protective layer 6 (top coat) generally provided in a normal optical information medium is provided on the medium layer 10 shown in FIG. The protective layer 6 was formed by applying an ultraviolet curable resin by spin coating and then curing by ultraviolet irradiation. The thickness of the protective layer after curing was 10 μm. The layer 10 of this sample was composed of a 15 nm thick Si layer. The layer 10 was formed by a sputtering method. A reference sample was also prepared in the same manner except that no protective layer was provided. C / N was measured for the pit row of each sample having a pit length of 250 nm using the optical disk evaluation apparatus while changing the reproduction power at a linear velocity of 11 m / s. FIG. 25 shows the relationship between the reproduction power of each sample and C / N.

  In FIG. 25, the sample without the protective layer generally has a higher C / N. This is considered to be because the temperature reached by the layer 10 at the time of reproduction light irradiation was lowered as a result of the protective layer acting as a heat dissipation layer, suggesting that the heat mode is involved in super-resolution reproduction in the present invention. .

  In the sample without the protective layer in FIG. 25, the C / N increase reaches its peak when the reproduction power is increased, and then the reproduction signal cannot be obtained due to the deterioration of the layer 10 at the reproduction power of 5 mW after the C / N decreases slightly. Yes. On the other hand, in the sample provided with the protective layer, the C / N gradually increases monotonously until the reproduction power reaches 7 mW. From this result, it can be said that the protective layer functioning as a heat dissipation layer has a function of extending the reproduction power range.

  Next, the constituent elements of the layer 10 and the thickness of the layer 10 are shown in Table 5. Other than that, samples are prepared in the same manner as both samples whose results are shown in FIG. The effect was investigated. Table 5 shows the maximum C / N for each thickness of the layer 10 and the reproduction power when it is obtained.

  In Table 5, when attention is paid to the case where the layer 10 is made of Ta, when the protective layer is not provided, deterioration occurs at a reproduction power of 2 mW when the thickness is 10 nm. Therefore, the maximum C / N is 23. Although it was 2 dB, when a protective layer was provided, a signal was obtained up to a reproduction power of 6 mW, and the C / N at that time was extremely high at 35.8 dB. For other samples as well, it can be seen that a higher reproduction power can be used by providing a protective layer, and in particular, when the protective layer is not provided, the layer 10 deteriorates at a relatively low reproduction power, resulting in a high C / N. In the sample that was not obtained, the C / N ratio was remarkably improved by providing a high reproducing power by providing the protective layer. In addition, it can be seen from Table 5 that the range of the thickness of the layer 10 capable of super-resolution reproduction is significantly expanded by providing the protective layer.

  From the above experimental results, the effect of providing the protective layer is clear. Since the protective layer has a higher thermal conductivity than air, the cooling of the layer 10 is accelerated by providing the protective layer. Further, the layer 10 is shielded from the air by the protective layer 6. As a result, the provision of the protective layer 6 makes it difficult for heat to accumulate in the layer 10 and makes it difficult for chemical changes to occur in the layer 10, so that the layer 10 does not deteriorate even when higher power reproduction light is used. On the other hand, as is clear from the above experimental results, the optical information medium of the present invention generally increases the reproduction output as the reproduction power increases, and this increase in output is until the layer 10 deteriorates due to heating during reproduction. Or it continues until just before that. Therefore, when a protective layer 6 is not provided, a sample with deterioration of the layer 10 at a relatively low reproduction power can be provided with a protective layer, so that reproduction at a high power is possible. As a result, a high C / N can be obtained. it is conceivable that.

  Next, the sample with and without the protective layer was repeatedly reproduced to examine C / N degradation. As the layer 10 of these samples, a Ge layer having a thickness of 10 nm was used. The reproduction power was 2 mW for the sample without the protective layer and 3 mW or 4 mW for the provided sample. The results are shown in FIG.

  In FIG. 26, the initial C / N of the sample without the protective layer is 41.3 dB, but is reduced by about 10 dB after 16,000 reproductions. On the other hand, in the sample provided with the protective layer, the initial C / N at a reproduction power of 3 mW is slightly low at 38.3 dB, but the C / N does not decrease at all after 100,000 times of reproduction. / N becomes higher at 42.7 dB, and C / N after 100,000 playbacks is 39.7 dB, and the deterioration is extremely small. From this result, it is understood that the stability of repeated reproduction is remarkably improved by providing the protective layer. This improvement in stability is thought to be due to the improvement in the cooling rate of the layer 10 and the fact that the layer 10 was shielded from the air.

  In the above experiments, a protective layer made of resin was used, but if it has a higher thermal conductivity than air, even protective layers made of various inorganic compounds such as oxides, nitrides, sulfides, carbides, Obviously, similar effects can be obtained.

[Thickness of layer 10]
From the results of each experiment described above, the preferred thickness of the layer 10 when composed of a single metal or metalloid is, for each constituent element,
Nb: 100 nm or less,
Mo: 70 nm or less, particularly 45 nm or less,
W: 70 nm or less, particularly 40 nm or less,
Mn: 100 nm or less, particularly 70 nm or less,
Pt: 40 nm or less, particularly 30 nm or less,
C: 100 nm or less,
Si: 100 nm or less,
Ge: 100 nm or less,
Ti: 100 nm or less,
Zr: 100 nm or less, particularly 25 to 100 nm,
V: 100 nm or less,
Cr: 30 nm or less, particularly less than 15 nm,
Fe: 80 nm or less, particularly 50 nm or less,
Co: 70 nm or less, particularly 45 nm or less,
Ni: 70 nm or less, particularly 50 nm or less,
Pd: 40 nm or less, particularly 30 nm or less,
Sb: 100 nm or less, particularly 60 nm or less,
Ta: 100 nm or less, particularly 60 nm or less,
Al: 20 nm or less, particularly less than 15 nm,
In: 100 nm or less, particularly less than 10 nm,
Cu: 10 nm or less,
Sn: 40 nm or less,
Te: 70 nm or less,
Zn: 40-90 nm,
Bi: 45-70 nm
It can be seen that it is. Although a sufficiently high C / N is obtained even at a thickness of 100 nm, there is no need to set the upper limit of the thickness to 100 nm in terms of characteristics, but in order to prevent a decrease in productivity, the thickness is usually increased. The thickness is preferably 100 nm or less. Moreover, even when comprised from any element, it is preferable that the thickness of the layer 10 is 2 nm or more. If the layer 10 is too thin, the reflectance will be low and tracking servo will not be easily applied, and sufficient C / N will be difficult to obtain.

  In addition, when the layer 10 is compounded, the preferable thickness range of the layer 10 is expanded as is apparent from the experimental results.

  Next, the case where a functional layer is comprised from an alloy is demonstrated. In addition, the functional element in the following description means the element which can comprise a functional layer by itself.

  When the functional layer is composed of a simple solid solution type binary alloy like the W-Mo alloy described above, and both elements are functional elements, the alloy layer is a functional layer as shown in FIG. Work as.

  In the simple solid solution type alloy layer, it is desirable that at least one, preferably all of the constituent elements are functional elements. The molar ratio of the functional element to the entire constituent elements is preferably 50% or more.

  In the amorphous alloy layer such as the magneto-optical recording material layer described above, it is desirable that at least one, preferably all of the constituent elements are functional elements as in the case of the simple solid solution type alloy layer. The molar ratio of the functional element to the entire constituent elements is preferably 50% or more.

  An Ag—In—Sb—Te phase change material, which will be described later, is a phase-separated alloy in which an Sb phase and other phases are separated when crystallized. In such a phase-separated alloy, It is desirable that at least one, preferably all of them can constitute a functional layer independently. For example, the Sb phase in the crystallized Ag—In—Sb—Te alloy acts as a functional layer alone.

  Similar to the single layer, the alloy layer has a thickness limit in order to function as a functional layer. For example, in the case of a simple solid solution type alloy layer, as shown in FIG. 16, it is considered that the thickness of the alloy layer may be set to a thickness at which a single layer of each functional element functions as a functional layer.

However, the specific composition and thickness of the alloy layer are preferably determined by actually verifying whether the alloy layer functions as a functional layer at each composition and thickness. For example, an intermetallic compound such as the above-described phase change material made of Ge ₂ Sb ₂ Te ₅ generally exhibits a behavior that cannot be inferred from each of its constituent elements.

[Application to the medium structure shown in FIGS. 3A and 3B]
Next, an experiment in the case where the present invention is applied to a medium having a structure shown in FIGS. 3A and 3B will be described. An optical information medium 1 shown in FIG. 3A is a read-only optical information medium, and has a pit 21 on the surface of a light-transmitting substrate 2 and a layer 10 on the pit formation surface side. A first dielectric layer 31 is provided between the substrate 2 and the layer 10, and a second dielectric layer 32 is provided on the layer 10. That is, the medium shown in FIG. 3A is obtained by sandwiching the upper and lower sides of the medium layer 10 shown in FIG. 1 between dielectric layers. Further, the medium shown in FIG. 3B has a structure in which the metal layer 5 is provided on the second dielectric layer 32 of the medium shown in FIG.

An optical disk sample having the configuration shown in FIG. 3A was manufactured by the following procedure. The substrate 2 is the same as the substrate used in the experiment. The layer 10 was composed of an Sb layer having a thickness of 15 nm. The layer 10 was formed by a sputtering method. The first dielectric layer 31 was composed of a silicon nitride layer having a thickness of 150 nm. The second dielectric layer 32 was composed of a silicon nitride layer having a thickness of 20 nm. These silicon nitride layers were formed by sputtering in an Ar atmosphere using Si ₃ N ₄ as a target.

  Further, the metal layer 5 was formed on the second dielectric layer 32 of the sample having the configuration shown in FIG. 3A, so that the sample having the configuration shown in FIG. The metal layer 5 was composed of an Al layer having a thickness of 100 nm. This Al layer was formed by sputtering using Al as a target.

  C / N was measured for the pit row of each sample having a pit length of 250 nm using the optical disk evaluation apparatus while changing the reproduction power and the linear velocity.

  FIG. 27A shows the relationship between the reproduction power of the sample without the metal layer 5 and C / N, and FIG. 27B shows the relationship between the reproduction power of the sample provided with the metal layer 5 and C / N. Indicates. The data shown in these figures is for a linear velocity of 11 m / s. From FIGS. 27A and 27B, it can be seen that super-resolution reproduction is possible even with the configuration shown in FIGS. 3A and 3B, respectively.

  In FIGS. 27A and 27B, as with most samples shown in FIGS. 6 to 9, C / N increases monotonously with an increase in reproduction power. Although these figures do not show the reproduction output, the reproduction output also increased monotonously with the increase in reproduction power.

  FIG. 28 shows the relationship between the reproduction power and C / N for a pit string having a pit length of 300 nm of the sample without the metal layer 5. From FIG. 28, it can be seen that when the pit length is longer than the reproduction limit determined by diffraction, C / N does not depend on the reproduction power as in the case of a normal medium.

  Next, the effects of the presence or absence of the metal layer 5 on the reproduction power Pr and C / N will be considered by comparing FIG. 27A and FIG.

  When the reproduction power is 1 to 2 mW, the sample without the metal layer 5 has a higher C / N. This is probably because the metal layer 5 worked as a heat dissipation layer in the same manner as the protective layer described above, and as a result, the temperature reached by the layer 10 during reproduction light irradiation was lowered, and the heat mode was used for super-resolution reproduction in the present invention. Suggest involvement.

  Further, in the sample without the metal layer 5, when the reproduction power is further increased, the C / N increase reaches its peak, and when the reproduction power is 5 mW, the reproduction signal cannot be obtained due to the deterioration of the layer 10. On the other hand, in the sample provided with the metal layer 5, the C / N increases monotonously until the reproduction power reaches 5 mW, and finally the C / N is higher than that in the sample without the metal layer 5. From this result, when the layer 10 constituting material is appropriately selected and the C / N is monotonously increased as the reproduction power is increased, the metal layer 5 functioning as a heat dissipation layer and an air blocking layer is provided to reproduce the layer 10. It turns out that the upper limit of power becomes high and as a result, higher C / N can be realized.

  FIG. 29A shows the relationship between the linear velocity of the sample without the metal layer 5 and C / N, and FIG. 29B shows the linear velocity of the sample with the metal layer 5 and C / N. The relationship with N is shown. The reproduction power Pr is shown in the figure. From these figures, even when the structure shown in FIG. 3A or FIG. 3B is used, the linear velocity dependence of C / N is substantially recognized within the linear velocity range in which super-resolution reproduction is possible. I understand that there is no. Further, in the sample in which the metal layer 5 was not provided, the layer 10 deteriorated when the reproduction power was 4 mW and the linear velocity was 8 m / s or less, and when the reproduction power was 5 mW. In the sample provided with the layer 5, as shown in FIG. 29 (B), high C / N was obtained at all linear velocities of 3 to 11 m / s even with a reproduction power of 5 mW. That is, the metal layer 5 that functions as a heat dissipation layer and an air blocking layer has an effect of widening the linear velocity margin.

In the structure shown in FIG. 3B, the layer 10 is made of an Ag _5.6 In _3.8 Sb _63.2 Te _25.2 Ge _2.2 (atomic ratio) alloy layer having a thickness of 20 nm, and the first dielectric layer 31 is made of ZnS ( 80 mol%) — SiO ₂ (20 mol%) layer, and the second dielectric layer 32 is composed of a 20 nm thick ZnS (80 mol%) — SiO ₂ (20 mol%) layer. Was prepared from a 100 nm thick Al-1.7 mol% Cr layer. Each of these layers was formed by sputtering. In this sample, the as-deposited layer 10 was in an amorphous state. A layer made of an alloy having this composition can be used as a phase change recording layer, but the layer 10 is not used as a recording layer in this sample.

  FIG. 37 shows the relationship between the reproduction power Pr and the amount of reflected light in the sample immediately after formation. From this figure, it can be seen that until Pr = 2 mW, the amount of reflected light increases linearly with an increase in Pr, crystallization occurs between 2 mW and 2.5 mW, and the amount of reflected light changes abruptly. With respect to this sample, the C / N of a pit row having a pit length of 250 nm was measured using the above optical disk evaluation apparatus and a linear velocity of 11 m / s. FIG. 38 shows C / N in the range of Pr ≦ 2 mW where the amount of reflected light changes linearly with respect to Pr. From FIG. 38, it can be seen that super-resolution reproduction is possible in the range of Pr ≦ 2 mW in this sample. The dielectric layer in this sample has high transparency, and the dielectric layer having high transparency does not contribute to super-resolution reproduction as described above. Also, an Al-1.7 mol% Cr layer having a thickness of 100 nm does not contribute to super-resolution reproduction. Therefore, the results shown in FIG. 38 indicate that the phase change material layer in the amorphous state functions as a functional layer in the present invention.

  Next, after the layer 10 of this sample was initialized (ie, crystallized) by a bulk eraser, the amount of reflected light and C / N were measured in the same manner as described above. The results are shown in FIGS. 37 and 38, respectively. From this result, it is understood that even in a read-only medium having the crystallized phase change material layer as the layer 10, the amount of reflected light changes linearly with respect to the reproduction power Pr, and super-resolution reproduction is possible within this range. .

  In the case where a phase change material layer is provided as a functional layer on a read-only medium, not only the medium structure shown in FIG. 3B but also any one of the structures shown in FIGS. 1, 2, and 3A, for example. Alternatively, other structures may be used. The medium structure to be used may be appropriately determined according to various conditions such as the reproduction wavelength.

[Application to medium structure shown in FIGS. 4A and 4B]
Next, an experiment in the case where the present invention is applied to a medium having a structure shown in FIGS. 4A and 4B will be described.

  The optical information medium shown in FIG. 4A is an optical recording medium. The optical information medium has a groove 22 on the surface of the light-transmitting substrate 2, and the first dielectric layer 31, the layer 10, the first dielectric layer 31 are formed on the groove forming surface side. The two dielectric layers 32, the recording layer 4, and the third dielectric layer 33 are provided in this order. The light incident through the substrate 2 is transmitted through the layer 10 to reach the recording layer 4, is reflected by the recording layer 4, and then is transmitted through the layer 10 and the substrate 2 again to be emitted.

An optical disk sample having the structure shown in FIG. 4A was produced by the following procedure. Each dielectric layer was formed by sputtering in an Ar atmosphere using Si ₃ N ₄ as a target. The thickness of the first dielectric layer 31 was 170 nm, the thickness of the second dielectric layer 32 was 20 nm, and the thickness of the third dielectric layer 33 was 20 nm. The layer 10 was made of Ge or W and had a thickness of 15 nm or 100 nm. The recording layer 4 was a phase change type, and was formed by sputtering in an Ar atmosphere using an Ag—In—Sb—Te—Ge alloy as a target. The composition of the recording layer (atomic ratio) in the composition formula _{(Ag a In b Sb c Te} d) 1-e Ge e, a = 0.07, b = 0.05, c = 0.59, d = 0 29, e = 0.05. The thickness of the recording layer 4 was 20 nm.

  The optical information medium shown in FIG. 4B is an optical recording medium, and has a groove 22 on the surface of the light-transmitting substrate 2, and the first dielectric layer 31, the recording layer 4, It has the 2nd dielectric material layer 32, the layer 10, and the 3rd dielectric material layer 33 in this order. The light incident through the substrate 2 is transmitted through the recording layer 4 to reach the layer 10, is reflected by the layer 10, and then is transmitted through the recording layer 4 and the substrate 2 again and emitted. The optical disk sample having the structure shown in FIG. 4A was manufactured in the same manner as the sample having the structure shown in FIG. 4B except that the positional relationship between the layer 10 and the recording layer 4 was reversed.

  These samples were mounted on the optical disk evaluation apparatus, and a single signal was recorded at a linear velocity of 2 m / s. The frequency of this single signal was determined so that the recording mark length was 200 nm. In this experiment, the phase change recording layer was used without being initialized (crystallized).

  Next, C / N of these samples was measured at a linear velocity of 11 m / s using the optical disk evaluation apparatus. As a result, the results shown in Table 6 below were obtained.

  From Table 6, it can be seen that super-resolution reproduction according to the present invention is also possible on an optical recording medium. The reason why the C / N is generally lower than that of the above-described reproduction-only sample is that the medium structure, specifically, the thickness of each dielectric layer is not optimized. Even those having a C / N of less than 20 dB can obtain a C / N of 20 dB or more by optimizing the medium structure. It is considered that the sample using a W layer having a thickness of 100 nm as the layer 10 did not obtain C / N because the reproduction light hardly transmitted through the layer 10.

  In addition, when the recording layer after recording was observed with a transmission electron microscope, in the sample having the Ge layer as the layer 10 and having the structure shown in FIG. 4A, the recording layer was perforated to become a recording mark. It was. On the other hand, in other samples, crystalline recording marks were formed in the amorphous recording layer.

  4A and 4B illustrate a configuration in which the recording layer is irradiated with reproduction light through the functional layer, or the functional layer is irradiated with reproduction light through the recording layer. However, if the functional layer is made of a material capable of forming a recording mark by irradiation of recording power, the functional layer can also serve as the recording layer.

[Application to medium structure shown in FIG. 4C]
Next, an experiment in the case where the present invention is applied to a medium having the structure shown in FIG.

  The optical information medium shown in FIG. 4C is an optical recording medium. The optical information medium has a groove 22 on the surface of the light-transmitting substrate 2, and the first dielectric layer 31, the layer 10, the first dielectric layer 31 are formed on the groove forming surface side. Two dielectric layers 32 and a metal layer 5 are provided in this order. The recording / reproducing light enters through the substrate 2. The structure shown in FIG. 4C is obtained by changing the pit 21 to the groove 22 in the read-only medium shown in FIG.

In the same manner as the reproduction-only sample having the phase change material layer made of the Ag _5.6 In _3.8 Sb _63.2 Te _25.2 Ge _2.2 alloy as the layer 10 and having the structure shown in FIG. An optical recording disk sample having the structure shown in FIG. The composition and thickness of the layer 10, the first dielectric layer 31, and the second dielectric layer 32 were the same as those of the reproduction-only sample.

  After the layer 10 of this optical recording disk sample was initialized (crystallized) with a bulk eraser, the optical disk evaluation apparatus was used to apply a single layer 10 to the layer 10 under the conditions of a linear velocity of 6 m / s, a recording power of 13 mW, and an erasing power of 5 mW. The signal was recorded. The frequency of this single signal was determined so that the length of the amorphous recording mark formed on the layer 10 was 200 nm. Next, C / N of this sample was measured at a linear velocity of 6 m / s using the optical disk evaluation apparatus. FIG. 39 shows the relationship between the reproduction power Pr and C / N. Note that the amorphous recording mark is not erased in the reproducing power range shown in FIG.

  It can be seen from FIG. 39 that super-resolution reproduction is possible even with this sample. As described above, since the first dielectric layer 31, the second dielectric layer 32, and the metal layer 5 do not contribute to super-resolution reproduction, the layer 10 in this sample functions as a recording layer and at the same time in the present invention. It can be seen that it works as a functional layer.

  Thus, if the functional layer is made of a material capable of forming a recording mark by irradiation of recording power, the functional layer can also serve as the recording layer.

  As will be described later, since it is considered that the reproduction power has a great influence on the super-resolution reproduction in the present invention, as shown in FIG. 4C, in the configuration in which the layer 10 serves as both the functional layer and the recording layer. The crystallization temperature of the layer 10 is increased, the quenching structure is such that the second dielectric layer 32 is thinned, or the second dielectric layer 32 and / or the metal layer 5 is made of a material having high thermal conductivity. Therefore, it is desirable to be able to use high-power reproduction light. However, even in this case, it is preferable to design the medium so that the recording characteristics are not significantly impaired.

[Operation of super-resolution reproduction]
From the experimental results shown above, it can be seen that the super-resolution reproduction realized by the present invention is completely different from the conventional super-resolution reproduction.

  First, in the conventional super-resolution reproduction, as described above, in both the heat mode method and the photon mode method, the mask layer is irradiated with the laser beam, and the energy distribution in the laser beam spot is used to make the beam spot more than the beam spot. Improve the transmittance or reflectance of small areas. Therefore, for example, as shown in FIG. 9 of Japanese Patent Laid-Open No. 11-86342, the C / N increases as the reproduction power increases, and when the light transmittance of the mask layer reaches a constant, the C / N ratio increases. The rise reaches a peak, and when the reproduction power is further increased, the optical aperture (transmittance increase region) becomes too large, and the C / N rapidly decreases. In the conventional super-resolution reproduction medium, the C / N behavior with respect to the reproduction power change is the same even in the type using the increase in reflectance.

  Further, in the conventional super-resolution reproduction, since a certain amount of heat or photon amount is required to form an optical aperture in the mask layer, there is a threshold value in the reproduction power that enables super-resolution reproduction, In addition, the reflectance of the medium changes abruptly with this threshold as a boundary.

  In conventional super-resolution reproduction, when reproducing while changing the linear velocity with a constant reproduction power, as the linear velocity increases, the temperature near the center of the beam spot decreases and the number of incident photons decreases. Become. Therefore, in the conventional super-resolution reproduction, C / N greatly changes with a change in linear velocity regardless of the heat mode method or the photon mode method.

  On the other hand, in the super-resolution reproduction in the present invention, as shown in FIGS. 6 to 9 and FIGS. 17 to 19, the increase in C / N accompanying the increase in the reproduction power Pr, the subsequent peak, and the slight decrease thereafter As can be seen, the C / N does not drop sharply except when the reproduction signal cannot be obtained due to the deterioration of the layer 10. Further, as derived from FIGS. 10 to 13 and FIGS. 20 to 22, the reflectance is not affected by the reproduction power. In super-resolution reproduction according to the present invention, as shown in FIG. 15, FIG. 29 (A) and FIG. 29 (B), the linear velocity dependence of C / N is substantially recognized in a wide linear velocity region. Absent. From these results, it is considered that the functional layer in the present invention enables super-resolution reproduction by a mechanism completely different from the mask layer in the conventional super-resolution medium. That is, in the present invention, it is considered that the layer 10 itself improves the spatial resolution, for example, instead of forming a minute region having changed transmittance or reflectance in the layer 10 due to reproduction light irradiation.

  It is considered that the heat mode is involved in the super-resolution reproduction in the present invention as described above. In order to confirm this, the relationship between the temperature reached by the layer 10 during reproduction light irradiation and C / N was examined. The ultimate temperature of the layer 10 is the reproduction power, the refractive index and absorption coefficient of the constituent material of the layer 10 at the reproducing light wavelength (635 nm), the thermal conductivity, the constant pressure specific heat and density of the constituent material of the layer 10, the thickness of the layer 10, the laser beam. The spot diameter and linear velocity (11 m / s) of the medium were calculated as parameters. 30 to 32 are graphs showing the relationship between the ultimate temperature of the layer 10 and C / N for each thickness of the layer 10.

  In any of these graphs, there is a correlation between the ultimate temperature of the layer 10 and C / N, and this correlation is particularly clear in FIG. That is, regardless of the constituent elements of the layer 10, it is recognized that the higher the temperature reached by the layer 10, the higher the C / N. However, the temperature at which C / N rises varies depending on the constituent elements. This result strongly suggests that the heat mode is involved in the super-resolution reproduction in the present invention.

  Assuming that C / N is substantially determined by the temperature reached by the layer 10, super-resolution reproduction can be performed with lower-power reproduction light by using reproduction light with a shorter wavelength. The spot diameter of the laser beam can be reduced as the laser wavelength is shorter, and as a result, the power density can be increased. Therefore, if a laser beam with a short wavelength is used, the temperature in the beam spot can be raised to a predetermined temperature with lower power. Therefore, as long as the reproduction wavelength is shorter, a lower reproduction power can be used unless the absorption coefficient is particularly low at a short wavelength. In order to confirm this, the ultimate temperature of the layer 10 was determined when the wavelength of the reproduction light was 410 nm, the reproduction power was 3 mW, and the linear velocity of the medium was 11 m / s. Then, the ultimate temperature at this time was compared with the ultimate temperature of the layer 10 when the reproduction light wavelength was 635 nm, the reproduction power was 3 mW, and the linear velocity of the medium was 11 m / s. As a result, it was confirmed that the ultimate temperature increased in all the constituent materials by shortening the wavelength of the reproduction light. For example, the ultimate temperature when the layer 10 is made of Cu was 66 ° C. at a wavelength of 635 nm, but was 488 ° C. at a wavelength of 410 nm.

  As described above, it is considered that the temperature of the functional layer plays an important role in the super-resolution reproduction in the present invention. In order to confirm this, the following experiment was further conducted.

  Among the samples prepared in the above experiment, the C / N of a pit row having a pit length of 250 nm was measured at room temperature (RT) for a sample having the layer 10 made of a Si layer having a thickness of 15 nm. Subsequently, this sample was stored in a constant temperature bath at 60 ° C. for 2 days, then C / N was measured, then stored in a freezer for 10 minutes, then C / N was measured, and subsequently, a constant temperature bath at 60 ° C. After storing for 5 minutes, C / N was measured. These C / N measurement results are shown in FIG. In FIG. 33, when C / N is compared when the reproduction power is the same, it can be clearly seen that C / N is improved by high temperature storage and C / N is decreased by low temperature storage. From this result, it is clear that the temperature of the functional layer is involved in the super-resolution reproduction in the present invention.

[Playback method]
In the medium of the present invention, as described above, the functional layer temperature during reproduction correlates with C / N. Therefore, in the present invention, super-resolution reproduction can be performed by raising the temperature of the functional layer to a predetermined value or higher according to the functional layer constituent material. In the present invention, only the reproduction light (laser beam) irradiation may be used to raise the temperature of the functional layer to a predetermined temperature or higher. In addition to this, a temperature rise of the environmental temperature may be used. In addition, if the temperature of the functional layer can be set to a predetermined value or more only by controlling the environmental temperature, super-resolution reproduction can be performed with a reproduction power that does not substantially raise the temperature of the functional layer. If the ambient temperature is raised, the reproduction power can be kept low, which is effective when the reflectance of the layer 10 is too high and saturation occurs in the reflected light detection system. In addition, when using a temperature increase of the environmental temperature, it is only necessary to irradiate the reproduction power with the temperature raised to a certain temperature in advance and raise the temperature to a predetermined temperature. it can. Therefore, it is effective when the functional layer is made of a material that easily deteriorates due to a rapid temperature rise.

  In order to raise the environmental temperature, various heating means may be provided in the driving device, and the entire medium or the vicinity of the reproduction target area may be partially heated. As the heating means, for example, a planar heating element may be provided at a position facing the medium in the driving device, or a resistance heating coil that moves in conjunction with the movement of the optical pickup may be provided in the vicinity of the optical pickup.

  In the medium of the present invention, there is an upper limit on the usable reproduction power depending on the constituent material of the layer 10 and the medium structure. Therefore, it is preferable to record the optimum reproduction power corresponding to these conditions in advance on the medium of the present invention, read the optimum reproduction power before reproduction, and perform reproduction with this optimum power. Further, if necessary, trial reproduction may be performed to determine the optimum reproduction power.

[Pit depth]
In a conventional read-only medium having a phase pit, when the refractive index of the substrate on which the phase pit is provided is n and the wavelength of the reproduction light is λ, the reproduction output generally has a phase pit depth of λ / 4n. Sometimes known to be the largest. When the push-pull method is used for tracking, the tracking error signal (push-pull signal) becomes maximum when the phase pit depth is λ / 8n, and becomes zero when λ / 4n. It has been known. Therefore, in the conventional read-only medium, the depth of the phase pit is generally set to λ / 6n, which is between the two.

  On the other hand, in the medium of the present invention having the above functional layer, the pit depth at which the reproduction output is maximized is different from the conventional read-only medium. FIG. 34 shows the relationship between the pit depth and C / N in the medium of the present invention. In the experiment whose result is shown in FIG. 34, an optical disk sample having the structure shown in FIG. 2 was used. The substrate 2 was a disk-shaped polycarbonate (refractive index n = 1.58) having a diameter of 120 mm and a thickness of 1.2 mm, on which phase pits were simultaneously formed by injection molding. Three types of pit lengths of 0.29 μm, 0.37 μm, and 0.44 μm were used. The space between adjacent pits was the same length as the pits. The pit depth is a value shown on the horizontal axis of the graph of FIG. The pit depth shown in the figure is a value normalized by the wavelength λ of the reproduction light and the refractive index n of the substrate at the wavelength λ. The layer 10 was composed of a Ge layer having a thickness of 15 nm, and the protective layer 6 was composed of an ultraviolet curable resin having a thickness of 10 μm, as in the sample described above.

  In this experiment, a laser wavelength: 680 nm, a numerical aperture NA: 0.55, a reproducible pit length: a short wavelength type reproduction system of 0.31 μm or more, a laser wavelength: 780 nm, a numerical aperture NA: 0.50, a reproduction Possible pit length: Using a long wavelength type reproduction system of 0.39 μm or more, reproduction power is 4 mW for short wavelength type, 7 mW for long wavelength type, and linear velocity is 11 m / s for both types. It was. Since both types of pits having a length of 0.44 μm are larger than the reproduction limit, normal reproduction is possible. A pit having a length of 0.37 μm is normally reproduced in the short wavelength type, and super-resolution reproduction is performed in the long wavelength type. A super-resolution reproduction is performed on a pit having a length of 0.29 μm even in a short wavelength type.

  From FIG. 34, it can be seen that in the case of normal reproduction, the maximum C / N is obtained in the vicinity of λ / 4n as conventionally known. On the other hand, in the case of super-resolution reproduction, it can be seen that C / N is maximized in the vicinity of λ / 8n. That is, in the case of super-resolution reproduction, a higher reproduction output can be obtained by making the pit depth shallower than λ / 6n, which has been conventionally selected in order to ensure both reproduction output and tracking error signal output. Recognize. In the case of super-resolution reproduction, it can be seen that the drop from the maximum C / N is small even when the pit depth is set to λ / 10n which is remarkably shallow compared to the conventional case.

  In FIG. 34, C / N is shown instead of reproduction output, but the pit depth at which reproduction output becomes maximum coincides with the pit depth at which C / N becomes maximum in the above experiment.

From the above experimental results, in the medium of the present invention, when priority is given to the reproduction output of the minute pits to be super-resolution reproduction, the pit depth d is set to λ / 10n ≦ d <λ / 6n in the entire medium. Especially λ / 9n ≦ d ≦ λ / 7n
It is preferable that

  For example, when reproducing light is incident through the substrate 2 in the medium having the structure shown in FIG. 3A, the first dielectric layer 31 is relatively thin, and therefore the first dielectric layer is composed of pits and other regions. The thickness of 31 is the same. Therefore, even when the layer 10 is formed on the substrate 2 via another layer such as the first dielectric layer 31, the preferable range of the pit depth can be expressed by using the refractive index n of the substrate 2. it can.

  Further, in the case where the unevenness of the substrate 2 in FIG. 1 is reversed, and a thin transparent resin layer is provided on the layer 10 and the reproduction light is incident through this transparent resin layer, the calculation of the preferred pit depth described above is performed. The refractive index used for is the refractive index of the transparent resin layer. In that case, when the transparent resin layer is not provided, the refractive index used for calculating the preferable pit depth is the refractive index of air. That is, in these cases, the refractive index of the transparent resin layer or air existing on the reproduction light incident side is regarded as the refractive index of the substrate.

If there are both pits with a length of less than λ / 4NA that require super-resolution playback and pits with a length of λ / 4NA or more that can be normally played back, the depths of both pits are different. As a result, a high reproduction output can be obtained in both pits. In this case, the depth d _S of a pit having a length less than λ / 4NA and the depth d _L of a pit having a length of λ / 4NA or more are:
d _S <d _L
Is set to hold. In order to obtain a high output, d _S is preferably λ / 10n ≦ d _S <λ / 6n, particularly preferably λ / 9n ≦ d _S ≦ λ / 7n. On the other hand, d _L is
λ / 8n <d _L <λ / 4n, especially λ / 7n ≦ d _L ≦ λ / 5n
It is preferable that

  In order to form two types of pits having different depths, for example, two types of photoresists having different sensitivities may be used in mastering using photolithography. In that case, a low-sensitivity photoresist layer is used as the lower layer, and a high-sensitivity photoresist layer is used as the upper layer.When forming a shallow pit pattern, exposure is performed so that only the upper layer is exposed, and a deep pit pattern is formed. When forming, exposure may be performed so that the lower layer is exposed in addition to the upper layer. Alternatively, two types of photoresists having different absorption wavelengths may be used to form a multilayered photoresist layer. In this case, the upper-layer exposure and the upper-layer and lower-layer exposure may be performed independently.

  Note that the above-described pit depth control is applicable not only to a read-only medium but also to an address pit of a recording medium.

It is a fragmentary sectional view which shows the structural example of the optical information medium of this invention. It is a fragmentary sectional view which shows the structural example of the optical information medium of this invention. (A) And (B) is a fragmentary sectional view which shows the structural example of the optical information medium of this invention. (A), (B), and (C) are partial sectional views showing a configuration example of the optical information medium of the present invention. It is a graph which shows the relationship between pit length and C / N. It is a graph which shows the relationship between reproduction power and C / N. It is a graph which shows the relationship between reproduction power and C / N. It is a graph which shows the relationship between reproduction power and C / N. It is a graph which shows the relationship between reproduction power and C / N. It is a graph which shows the relationship between reproduction power and reflected light quantity. It is a graph which shows the relationship between reproduction power and reflected light quantity. It is a graph which shows the relationship between reproduction power and reflected light quantity. It is a graph which shows the relationship between reproduction power and reflected light quantity. It is a graph which shows the relationship between temperature and a reflectance about W layer. It is a graph which shows the relationship between linear velocity and C / N. It is a graph which shows the content of W in a Mo-W alloy, and the relationship between C / N. It is a graph which shows the relationship between reproduction power and C / N. It is a graph which shows the relationship between reproduction power and C / N. It is a graph which shows the relationship between reproduction power and C / N. It is a graph which shows the relationship between reproduction power and reflected light quantity. It is a graph which shows the relationship between reproduction power and reflected light quantity. It is a graph which shows the relationship between reproduction power and reflected light quantity. It is a graph which shows the relationship between the thickness of the layer 10, and C / N. It is a graph which shows the relationship between the frequency | count of reproduction | regeneration, and C / N. It is a graph which shows the relationship between reproducing power and C / N about the case where a protective layer is not provided and the case where it provides. It is a graph which shows the relationship between the frequency | count of reproduction | regeneration, and C / N about the case where a protective layer is not provided and the case where it provides. It is a graph which shows the relationship between reproduction power and C / N, (A) is a case where a metal layer is not provided, (B) is a case where a metal layer is provided. It is a graph which shows the relationship between reproduction power and C / N. It is a graph which shows the relationship between a linear velocity and C / N, (A) is a case where a metal layer is not provided, (B) is a case where a metal layer is provided. It is a graph which shows the relationship between the ultimate temperature of the layer 10, and C / N. It is a graph which shows the relationship between the ultimate temperature of the layer 10, and C / N. It is a graph which shows the relationship between the ultimate temperature of the layer 10, and C / N. It is a graph which shows the C / N change by the temperature transition of the environment where the optical information medium of this invention was put. It is a graph which shows the relationship between pit depth and C / N. It is a graph which shows the relationship between reproduction power and reflected light quantity. It is a graph which shows the relationship between reproduction power and C / N. It is a graph which shows the relationship between reproduction power and reflected light quantity. It is a graph which shows the relationship between reproduction power and C / N. It is a graph which shows the relationship between reproduction power and C / N.

Explanation of symbols

2 ... Base 21 ... Pit 22 ... Groove 31 ... First dielectric layer 32 ... Second dielectric layer 33 ... Third dielectric layer 4 ... Recording layer 5 ... Metal layer 6 ... Protective layer 10 ... Layer

Claims (8)

It is an optical information medium comprising an information recording surface that has unevenness, can form a recording mark, or has the unevenness and can form a recording mark,
It has a functional layer that has the function of improving the spatial resolution,
This functional layer includes Nb, Mo, W, Mn, Pt, C, Si, Ge, Ti, Zr, V, Cr, Fe, Co, Ni, Pd, Sb, Ta, Al, In, Cu, Sn, Te And a functional layer having a specific thickness corresponding to the composition thereof, wherein the functional layer is composed of a simple substance or an alloy containing at least one element selected from the group consisting of Zn and Bi, or a compound thereof. Optical information medium to be used. It has a base provided with pits for holding information, and has a functional layer on the pit forming surface of this base. 4NA · P _L (P _L is the minimum length of the pit, NA is the aperture of the reproducing optical system) Number) When the reproduction light having a longer wavelength is irradiated, the information held in the pits can be reproduced. When the wavelength of the reproduction light is λ and the refractive index of the substrate is n, the pit depth d Is in the whole medium,
λ / 10n ≦ d <λ / 6n
And
Further, the functional layer includes Nb, Mo, W, Mn, Pt, C, Si, Ge, Ti, Zr, V, Cr, Fe, Co, Ni, Pd, Sb, Ta, Al, In, Cu, Sn And a functional layer having a specific thickness corresponding to the composition of the element or alloy containing at least one element selected from the group consisting of Te, Zn and Bi, or a compound thereof. Characteristic optical information medium. It is an optical information medium comprising an information recording surface that has unevenness, can form a recording mark, or has the unevenness and can form a recording mark,
It has a functional layer that has the function of improving the spatial resolution,
This functional layer is composed of any one of the following elements, and has the following thickness corresponding to the element.
Nb: 2 to 100 nm
Mo: 2 to 70 nm
W: 2 to 70 nm
Mn: 2 to 100 nm
Pt: 2 to 40 nm
C: 2 to 100 nm
Si: 2 to 100 nm
Ge: 2 to 100 nm
Ti: 2 to 100 nm
Zr: 2 to 100 nm
V: 2 to 100 nm
Cr: 2 to 30 nm
Fe: 2 to 80 nm
Co: 2 to 70 nm
Ni: 2 to 70 nm
Pd: 2 to 40 nm
Sb: 2 to 100 nm
Ta: 2 to 100 nm
Al: 2 to 20 nm
In: 2 to 100 nm
Cu: 2 to 10 nm
Sn: 2 to 40 nm
Te: 2 to 70 nm
Zn: 40 to 90 nm
Bi: 45-70 nm It is an optical information medium comprising an information recording surface that has unevenness, can form a recording mark, or has the unevenness and can form a recording mark,
It has a functional layer that has the function of improving the spatial resolution,
This functional layer is configured by adding at least one element selected from the group consisting of nitrogen, oxygen, fluorine, sulfur and carbon to any of the following elements, and includes the following elements contained in this functional layer: An optical information medium characterized by having the following thickness corresponding to:
Nb: 2 to 100 nm
Mo: 2 to 70 nm
W: 2 to 70 nm
Mn: 2 to 100 nm
Pt: 2 to 40 nm
C: 2 to 100 nm
Si: 2 to 100 nm
Ge: 2 to 100 nm
Ti: 2 to 100 nm
Zr: 2 to 100 nm
V: 2 to 100 nm
Cr: 2 to 30 nm
Fe: 2 to 80 nm
Co: 2 to 70 nm
Ni: 2 to 70 nm
Pd: 2 to 40 nm
Sb: 2 to 100 nm
Ta: 2 to 100 nm
Al: 2 to 20 nm
In: 2 to 100 nm
Cu: 2 to 10 nm
Sn: 2 to 40 nm
Te: 2 to 70 nm
Zn: 40 to 90 nm
Bi: 45-70 nm It has a base provided with pits for holding information, and has a functional layer on the pit forming surface of this base. 4NA · P _L (P _L is the minimum length of the pit, NA is the aperture of the reproducing optical system) Number) When the reproduction light having a longer wavelength is irradiated, the information held in the pits can be reproduced. When the wavelength of the reproduction light is λ and the refractive index of the substrate is n, the pit depth d Is in the whole medium,
λ / 10n ≦ d <λ / 6n
And
Furthermore, the functional layer is composed of any one of the following elements, and has the following thickness corresponding to the element.
Nb: 2 to 100 nm
Mo: 2 to 70 nm
W: 2 to 70 nm
Mn: 2 to 100 nm
Pt: 2 to 40 nm
C: 2 to 100 nm
Si: 2 to 100 nm
Ge: 2 to 100 nm
Ti: 2 to 100 nm
Zr: 2 to 100 nm
V: 2 to 100 nm
Cr: 2 to 30 nm
Fe: 2 to 80 nm
Co: 2 to 70 nm
Ni: 2 to 70 nm
Pd: 2 to 40 nm
Sb: 2 to 100 nm
Ta: 2 to 100 nm
Al: 2 to 20 nm
In: 2 to 100 nm
Cu: 2 to 10 nm
Sn: 2 to 40 nm
Te: 2 to 70 nm
Zn: 40 to 90 nm
Bi: 45-70 nm It has a base provided with pits for holding information, and has a functional layer on the pit forming surface of this base. 4NA · P _L (P _L is the minimum length of the pit, NA is the aperture of the reproducing optical system) Number) When the reproduction light having a longer wavelength is irradiated, the information held in the pits can be reproduced. When the wavelength of the reproduction light is λ and the refractive index of the substrate is n, the pit depth d Is in the whole medium,
λ / 10n ≦ d <λ / 6n
And
Furthermore, the functional layer is configured by adding at least one element selected from the group consisting of nitrogen, oxygen, fluorine, sulfur, and carbon to any of the following elements, and included in the functional layer: An optical information medium having the following thickness corresponding to the element:
Nb: 2 to 100 nm
Mo: 2 to 70 nm
W: 2 to 70 nm
Mn: 2 to 100 nm
Pt: 2 to 40 nm
C: 2 to 100 nm
Si: 2 to 100 nm
Ge: 2 to 100 nm
Ti: 2 to 100 nm
Zr: 2 to 100 nm
V: 2 to 100 nm
Cr: 2 to 30 nm
Fe: 2 to 80 nm
Co: 2 to 70 nm
Ni: 2 to 70 nm
Pd: 2 to 40 nm
Sb: 2 to 100 nm
Ta: 2 to 100 nm
Al: 2 to 20 nm
In: 2 to 100 nm
Cu: 2 to 10 nm
Sn: 2 to 40 nm
Te: 2 to 70 nm
Zn: 40 to 90 nm
Bi: 45-70 nm   An optical information medium, wherein a protective layer made of a material having a higher thermal conductivity than air is provided on the functional layer of the optical information medium according to claim 1. In claim 7,
An optical information medium, wherein the protective layer is made of a resin.

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