JP4372776B2 - Optical information recording medium and optical information recording medium reproducing apparatus - Google Patents

Description

  The present invention relates to an optical information recording medium on which information is optically recorded and reproduced, and an optical information recording medium reproducing apparatus for reproducing information recorded on the optical information recording medium.

  In recent years, in an optical information recording medium, it is required to increase the information recording density more and more in order to process enormous information such as images. As one of the solutions, there is a super-resolution reproduction technique which is one of information processing improvement techniques during reproduction. The super-resolution reproduction technique is a technique for reproducing a signal having a mark length (determined by the laser wavelength and the numerical aperture of the optical system) that is less than or equal to the optical resolution limit of the reproduction apparatus. By using such a super-resolution reproduction technique, recording using a smaller mark length becomes possible, and the substantial recording density increases. This means that the problem in increasing the density is not the recording technique but the reproduction technique.

  As another solution for increasing the information recording density, there is a multilayer optical information recording medium in which information recording layers are multilayered and information is recorded / reproduced on / from each information recording layer.

  Further, it is considered to combine these super-resolution reproduction techniques and multilayer optical information recording medium techniques. For example, Patent Document 1 discloses a laminated optical information recording medium in which information recording layers capable of super-resolution reproduction are multilayered. Hereinafter, the super-resolution reproduction technique and the multilayer optical information recording medium technique will be described with reference to Patent Document 1.

  As described above, the super-resolution reproduction technique is a technique for reproducing a signal having a mark length less than or equal to the optical system resolution limit of the reproduction apparatus. In the case of Patent Document 1, the optical constant of a part of the super-resolution reproduction layer is changed in accordance with the intensity distribution of the reproduction laser light (intensity increases as the distance from the center is increased) to function as an optical mask or an optical aperture. Thus, it is possible to substantially reduce the reproduction spot and reproduce a minute recording mark with high resolution.

  As examples of the super-resolution reproducing layer, a phase change material and a semiconductor material in which photon mode absorption saturation occurs are disclosed. For example, in the case of a phase change material, the optical constant is changed by the phase change of the crystal state, the light transmittance is high (or low) in the crystal state at room temperature, and the phase change to the molten state by heating due to light irradiation or the like. In this case, super-resolution reproduction is performed by decreasing (/ increasing) the light transmittance.

When the absorption saturation of the semiconductor material is used, the super-resolution reproduction layer has a configuration in which semiconductor fine particles are dispersed in a glass matrix such as SiO ₂ . When light having a wavelength slightly shorter than the wavelength corresponding to the band gap energy of the semiconductor is irradiated, electrons are excited, absorption saturation occurs, and transmittance changes. Since this phenomenon depends on the light intensity (photon mode), super-resolution reproduction is performed using the change in the transmittance of the super-resolution reproduction layer with respect to the light intensity.

  Next, the multilayer optical information recording medium technique used in Patent Document 1 will be described. The information recording layer is provided on the substrate in the order of the first recording portion and the second recording portion from the reproduction light incident surface, and each information layer is separated by an intermediate layer mainly made of resin. In such a structure, except for the information recording layer farthest from the reproducing light incident surface, a semi-transparent layer through which the reproducing light is partially transmitted is formed. Focus on the layer. Therefore, it can be said that this multilayer optical information recording medium is an optical information recording medium capable of increasing the information recording density as the total number of information recording layers increases.

As described above, the above-described two methods and techniques combining them have been proposed for increasing the density of optical information recording media.
JP 2001-84639 A (published on March 30, 2001)

  However, in many optical information recording media using super-resolution reproduction technology (hereinafter referred to as super-resolution media), a layer functioning as an optical mask or an optical aperture (super-resolution reproduction layer in Patent Document 1). A mask layer itself is optically changed by directly absorbing light or heat. Therefore, there is a problem that the burden on the mask layer itself is likely to increase and the reproduction durability is poor.

  Furthermore, the reproduction film used for the super-resolution medium usually has many dyes and phase change materials, and is expensive compared to the film material used for a normal optical information recording medium that does not use the super-resolution technology. is there. Therefore, the super-resolution medium is also more expensive than a normal optical information recording medium having the same number of information recording layers.

  In particular, in the super-resolution reproduction technique described in Patent Document 1, a phase-change medium and an electron-excited absorption saturated semiconductor are used as the super-resolution reproduction layer. That is, since the structure is changed, the reproduction durability is reduced.

  Further, in the case of an electronically excited absorption saturated semiconductor, the optical characteristics are greatly affected by the particle diameter of the semiconductor fine particles, so that the control of the particle diameter is indispensable for controlling the optical characteristics, and the production is difficult. In addition, film formation conditions are limited in order to obtain uniform fine particles, and there have been problems in practical use or mass production. In addition, since fine particles of about 0.1 nm to 50 nm are dispersed in the matrix, the surface area of the fine particles (surface area at the interface with the matrix) is large, and the surface of the fine particles is likely to be oxidized as the temperature rises during regeneration. However, there is a problem that a change with the passage of time such as alteration is likely to occur, and in some cases, fine particles adhere to each other and desired characteristics cannot be obtained.

  In Patent Document 1, a CNR of a pattern in which 0.41 μm long single-size recording marks are periodically arranged at equal intervals is used as an indicator of signal characteristics. However, there are two problems with this evaluation method. .

  One is that the mark length is larger than the resolution limit of the evaluation optical system described in Patent Document 1, and is insufficient for reproduction evaluation of the super-resolution area. The resolution of the reproducing optical system of the optical information recording medium is generally said to be about λ / 2NA due to the limitation of the frequency limit of the detectable signal (λ: reproducing light wavelength, NA. : Lens aperture ratio). The above corresponds to the resolution limit of the periodic size of a pattern composed of a single size recording mark and a repetition of a space, and the resolution limit is about λ / 4NA, which is half the length of the recording mark. (Hereinafter, the resolution limit is assumed to be λ / 4NA). Therefore, the mark length is larger than the resolution limit of the evaluation optical system described in Patent Document 1, and it can be said that the mark length is insufficient for reproduction evaluation of the super-resolution area.

  The other is that a pattern in which single-size recording marks are periodically arranged at equal intervals is an enumeration of equally spaced marks, and it cannot be said that marks based on substantial recording information are evaluated. Actual recording marks of optical information recording media in practical use do not have a single size arranged at regular intervals, but the intervals are random.

  Furthermore, there are roughly two types of recording methods. One is mark position recording, and the other is called mark edge recording. In mark position recording, single-size recording marks are randomly arranged, but this method has a low recording density. In mark edge recording, data to be recorded is modulated and recording marks having different lengths are randomly arranged, and the recording density is higher than that of mark position recording.

  That is, in order to improve the recording density, it is necessary to record by mark edge recording. As an evaluation for that, recording marks having different lengths are recorded at random (hereinafter referred to as “random pattern”). It is necessary to evaluate the reproduction characteristics of the recording mark in (Yes). The fact that mark edge recording with random patterns is advantageous in terms of recording density is that almost all optical information recording media in practical use are capable of data recording with random pattern recording mark arrays (mark edge recording). It is clear from what has been done.

  In addition, since the CNR evaluation of the single size mark row as performed in Patent Document 1 is only the evaluation of the equidistant pattern of the corresponding size, its characteristics are different from the CNR characteristics at other sizes. There is a case. In particular, when super-resolution reproduction is performed, if the recording mark length is changed, the CNR reproduction power dependency and optimum power may be different. However, in order to actually reproduce a random pattern, it is necessary to reproduce recording marks of any size with a common reproduction power. When the reproduction power that optimizes the CNR varies with the size of the recording mark, another evaluation index is necessary to determine the optimum reproduction power as the total random pattern.

  That is, in order to evaluate a random pattern arrangement, CNR evaluation of a single size recording mark row is not sufficient.

  As described above, the conventional optical information recording medium represented by Patent Document 1 has many problems such as problems on these materials and evaluation indexes.

  The present invention has been made in view of the above problems, and is a multilayer light that is inexpensive and uses a super-resolution reproduction technique with excellent reproduction durability and has a good jitter value for random patterns (mark edge recording). The object is to provide an information recording medium.

  In order to solve the above problems, an optical information recording medium according to the present invention is an optical information recording medium in which information is represented by a recording mark pattern including a recording mark length equal to or less than an optical system resolution limit of a reproducing apparatus. The light transmitting layer, the first information recording layer, the intermediate layer, the second information recording layer, and the substrate are laminated in this order from the reproduction light incident side, and the recording mark pattern includes at least the first information. Formed in the recording layer and the second information recording layer, the first information recording layer and the second information recording layer are heated by the absorption film that absorbs the reproduction light and converts it into heat, and the heat generation of the absorption film, A reproducing film capable of reproducing a signal having a recording mark length equal to or less than a resolution limit, wherein the light absorption film of the first information recording layer is made of a simple substance of Si or an alloy containing Si as a main component. The light absorption film of the layer is simple Ge or G It is characterized by comprising a main component and the alloy.

  In the above configuration, when reproducing the information recorded on the first information recording layer, the reproduction light is irradiated from the light transmitting layer and focused on the first information recording layer. In the first information recording layer, the light absorption film absorbs the reproduction light, thereby converting the light into heat and transferring the heat to the reproduction film. Since the medium rotates during reproduction, the temperature at the rear end of the beam spot increases due to the temperature distribution of the laser. That is, the position where the temperature is high deviates from the center. As a result, the transmittance of the reproducing film in the high temperature region changes, and information recorded with a mark length (pit length when the recording mark is a pit) that is less than the resolution limit of the first information recording layer can be read. it can.

  Further, when reproducing the information recorded on the second information recording layer, the reproduction light is irradiated through the translucent layer, the first information recording layer, and the intermediate layer, and is focused on the second information recording layer. Is done. Then, similarly to the first information recording layer, it is possible to read information recorded with a mark length equal to or less than the resolution limit of the second information recording layer. Thereby, in both the first and second information recording layers, the substantial recording density (meaning the reproducible recording density) can be made higher than the recording density regulated by the optical resolution limit.

  As described above, the first and second information recording layers can read information by the super-resolution reproduction effect by using the temperature change of only the central portion where the light intensity is high in the light spot. Thereby, since the recording density of the first and second information recording layers is below the resolution limit, the recording capacity of the optical information recording medium can be improved with respect to the manufacturing cost, and the recording medium has high cost performance. Can be provided.

  Therefore, by providing the first and second information recording layers, when producing a recording medium having the same recording capacity, the number of recording layers can be reduced as compared with a normal multilayer optical information recording medium. Therefore, the number of expensive vacuum devices for forming the recording layer by sputtering in the production line can be reduced, and the production cost of the recording medium accompanying the increase of the recording layer can be greatly reduced.

  In the above configuration, in the first and second information recording layers, a light absorbing film is formed separately from the reproducing film, and the reproducing film and the absorbing film are separately formed. As a result, the reproduction film itself does not change the optical characteristics by absorbing light and changing the molecular structure. Therefore, it is possible to perform super-resolution reproduction without imposing much burden on the reproduction film in the first and second information recording layers, and it is possible to improve reproduction durability.

  In addition, in the above configuration, the light absorption film of the first information recording layer is formed of Si alone or an alloy containing Si as a main component, and the light absorption film of the second information recording layer is formed of Ge alone or an alloy containing Ge as a main component. Formed from.

  Compared with other metal films, Si and Ge alone or alloys containing them as a main component, the temperature is likely to rise when irradiated with reproduction light, and the generated film is efficiently heated by the generated heat. be able to. Therefore, by using the light absorption film made of these, it is possible to obtain optimum characteristics with a lower reproduction power and to improve the reproduction sensitivity.

  In addition, Si simple substance or an alloy mainly composed of Si has higher light utilization efficiency than Ge simple substance or an alloy mainly composed of Ge. Therefore, by using Si alone or an alloy containing it as a main component for the light absorption film of the first information recording layer, it is possible to sufficiently obtain the reproduction light intensity to the second information recording layer with a relatively low reproduction intensity. And optimum characteristics can be obtained with lower reproduction power. In addition, since the light utilization efficiency is high, it is desirable as an absorption film for the information recording layer that needs to transmit the reproduction light to the next information recording layer, particularly in a multilayer optical information recording medium, and power saving is also possible. High light utilization efficiency can increase the degree of freedom in optical design.

  On the other hand, the light absorption film of the second information recording layer obtains optimum characteristics with lower reproduction power by using Ge alone or an alloy containing it as a main component than Si alone or an alloy containing it as a main component. I have confirmed that. In a multilayer optical information recording medium, it can be said that it is desirable to use Ge alone or an alloy containing it as a main component as the absorption film of the information recording layer that does not require the reproduction light to be transmitted to the next information recording layer.

  Therefore, the light absorbing film of the first information recording layer is formed from Si alone or an alloy containing Si as a main component, and the light absorbing film of the second information recording layer is formed of Ge alone or an alloy containing Ge as a main component. Therefore, the optimum characteristics can be obtained with a lower reproduction power, and the reproduction sensitivity can be improved.

  In the optical information recording medium, it is preferable that the recording mark pattern is arranged based on a mark edge recording method, and more specifically, the recording mark pattern includes a recording mark and a space. Therefore, it is preferable that the length of the recording mark and the space in the reading direction is normalized to at least two values.

  If the recording marks are positioned based on the mark edge recording method, the recording density can be increased as compared with the mark position recording method, and a large capacity can be achieved as an optical information recording medium. Further, not only the value of the length in the reading direction of the space but also the length of the recording mark in the same direction is standardized to at least two values as compared with the case where the length of the recording mark is constant. The recording density can be increased, and a large capacity can be achieved as an optical information recording medium.

  In the optical information recording medium, the recording mark pattern can be formed by, for example, prepits and spaces, and in this case, the medium is a read-only medium.

  In the optical information recording medium, it is preferable that the reproduction film in the first information recording layer or the second information recording layer contains a metal oxide as a main component.

  Since the metal oxide film has the characteristic that the optical characteristics change due to the band gap change due to heat, the optical characteristics are changed by the structural change such as the normal composition change and phase change by using such a metal oxide film as the reproduction film. The reproduction durability can be further improved as compared with an optical information recording medium using a reproduction film using a changing dye or a phase change material.

  In the optical information recording medium, it is preferable that the metal oxide of the reproducing film is made of zinc oxide or contains zinc oxide.

  As a result, the cost of the optical information recording medium can be reduced, and further, by including zinc oxide, it is possible to obtain higher super-resolution characteristics than using other metal oxide films. It becomes possible to improve the recording capacity of the information recording medium. Moreover, since it is not necessary to control the particle size as in the fine particle dispersion of the electron excited absorption saturated semiconductor disclosed in Patent Document 1, the production is easy and mass production is possible. In addition, changes over time such as changes in the grain boundaries of the fine particles hardly occur, and the reproduction durability is improved.

  In order to solve the above problems, an optical information recording medium reproducing apparatus according to the present invention applies laser light having a laser power capable of reproducing any of the above optical information recording media to the first or second information recording layer. And an optical reading means for reading the reflected light from the optical information recording medium.

  In this optical information recording medium reproducing device, the reflected light from the optical information recording medium is read by irradiating laser light of a laser power capable of reproducing the optical information recording medium by the optical reading means, so that it is recorded at a higher density. Stable information reproduction from an optical information recording medium is possible. In order to reproduce such an optical information recording medium, the laser power is set to a higher value than the conventional laser power.

  If the optical information recording medium can be reproduced in this way, it can be reproduced on a double-layer super-resolution medium. For example, since the number of layers is reduced as compared with the case of reproducing a normal medium that requires three or more layers with the same recording capacity, the number of information recording layers to be focused is also reduced. The manufacturing cost is reduced by reducing the number of layers. Further, since the number of focus layers is reduced, the focus control of the optical reading device (optical pickup) is simplified, so that an increase in the cost of the optical reading device is suppressed and the time required for focusing is shortened. Response is improved. Therefore, it is possible to provide a high-performance playback device at a lower cost.

  As described above, the optical information recording medium of the present invention is an optical information recording medium in which information is represented by a recording mark pattern including a recording mark length that is less than or equal to the optical system resolution limit of the reproducing apparatus. The light transmitting layer, the first information recording layer, the intermediate layer, the second information recording layer, and the substrate are laminated in this order from the incident side, and the recording mark pattern includes at least the first information recording layer and the first information recording layer. 2 formed on the information recording layer, and the first information recording layer and the second information recording layer are absorbed by the reproducing light and converted into heat, heated by the heat generated by the light absorbing film, and below the resolution limit. And the light absorption film of the first information recording layer is made of a simple substance of Si or an alloy containing Si as a main component, and the light absorption film of the second information recording layer. Is composed of Ge alone or Ge as the main component It is a configuration made of gold.

  As a result, when producing a recording medium having the same recording capacity, the number of recording layers is larger than that of a normal multilayer optical information recording medium in which the recording density of each information recording layer is a recording density regulated by the resolution limit. Can be reduced. Therefore, the recording capacity of the optical information recording medium can be improved with respect to cost.

  In addition, since the light absorption film and the reproduction film are formed separately, super-resolution reproduction can be performed without imposing much burden on the reproduction film itself, which cannot be achieved with the conventional super-resolution multilayer super-resolution medium. The effect that reproduction durability is acquired is also produced.

  Further, the light absorbing film of the first information recording layer is formed from a simple substance of Si or an alloy thereof, and the light absorbing film of the second information recording layer is formed from a simple substance of Ge or an alloy thereof, whereby the first and second information are recorded. The recording layer is made of another metal film, the light absorbing film of the second information recording layer is made of Si alone or an alloy thereof, and the light absorbing film of the first information recording layer is made of Ge alone or an alloy thereof. In comparison, the reproduction sensitivity can be improved and the power can be saved, and the degree of freedom in optical design is increased.

[Embodiment 1]
An embodiment of the present invention will be described with reference to FIGS. 1 to 6 as follows. In the present embodiment, information is recorded in the first and second information recording layers in a concavo-convex shape by prepits.

  FIG. 1 shows a cross-sectional structure of an optical information recording medium 60 according to the embodiment. As shown in FIG. 1, the optical information recording medium 60 includes a light-transmitting layer 10, a first information recording layer 20, an intermediate layer 30, a second information recording layer 40, and a substrate 50, and a light incident surface. Are stacked in this order.

  The light transmissive layer 10 only needs to sufficiently transmit the reproduction light, is formed of a transparent resin, and an ultraviolet curable resin or the like can also be used. Examples of the resin material that can be used for the light transmissive layer 10 include epoxy acrylate, urethane acrylate, polyester acrylate, fluorinated acrylic resin, and epoxy resin. The translucent layer 10 is not limited to a single layer configuration, and may be a two-layer configuration of a transparent resin film such as a polycarbonate film and a transparent adhesive resin layer. Further, a hard coat layer may be provided on the light incident surface of the translucent layer 10.

  The intermediate layer 30 is a light-transmitting resin layer provided between the first information recording layer 20 and the second information recording layer 40. For example, a resin such as a transparent ultraviolet curable resin can be used. Examples of the resin material that can be used for the intermediate layer 30 include epoxy acrylate, urethane acrylate, polyester acrylate, fluorinated acrylic resin, and epoxy resin.

  The substrate 50 is made of a resin such as a polyolefin resin. For the substrate 50, polycarbonate resin, other resins that can be compression-molded, or glass can also be used. In addition, since the substrate 50 does not need to be transparent, a metal or the like can be used.

  Prepits 31 on which information is recorded are formed on the surface of the intermediate layer 30 on the side in contact with the first information recording layer 20 as shown in the enlarged perspective view of FIG. Further, as shown in the enlarged perspective view of FIG. 2B, prepits 51 on which information is recorded are formed on the surface of the substrate 50 on the side in contact with the second information recording layer 40.

  Then, the first information recording layer 20 and the second information recording layer 40 are formed on each surface of the intermediate layer 30 and the substrate 50 where the prepits 31 and 51 are formed, whereby the first information is recorded. In the recording layer 20 and the second information recording layer 40, the prepit 31 and the prepit 51 are transferred as uneven shapes, respectively.

  Accordingly, the optical information recording medium 60 is in a state where the first and second information recording layers 20 and 40 record information as a concavo-convex shape, and is formed as a so-called read-only optical information recording medium.

  The first information recording layer 20 includes a first reproducing film 21 (reproducing film) and a first light absorbing film 22 (light absorbing film) made of Si alone or an alloy containing Si as a main component. The first light absorption film 22 absorbs the reproduction light and converts the light into heat that can heat the first reproduction film 21. When the first reproducing film 21 is heated by the heat generated in the first light absorbing film 22, the optical constant of the first reproducing film 21 changes, so that a signal with a mark (pit) length below the optical system resolution limit of the reproducing apparatus is generated. Make it playable.

  The second information recording layer 40 includes a second reproducing film 41 (reproducing film) and a second light absorbing film 42 (light absorbing film) made of Ge alone or an alloy containing Ge as a main component. The second light absorbing film 42 absorbs the reproduction light and converts the light into heat that can heat the second reproduction film 41. When the second reproducing film 41 is heated by the heat generated by the second light absorbing film 42, the optical constant of the second reproducing film 41 changes, so that a signal with a mark (pit) length below the optical system resolution limit of the reproducing apparatus is generated. Make it playable.

  The first and second reproducing films 21 and 41 and the first and second light absorbing films 22 and 42 are formed by sputtering in a vacuum apparatus.

  The first and second reproduction films 21 and 41 are preferably made of a metal oxide film having a characteristic that optical characteristics change due to a band gap change caused by heat. Thus, the first and second reproducing films 21 and 41 are compared with the reproducing film in the conventional recording medium using a dye or a phase change material whose optical characteristics change due to a structural change such as a normal composition change or phase change. The reproduction durability can be improved. In addition, since the metal oxide film is generally transparent, there is an advantage that the light-absorbing films 22 and 42 operate more efficiently because the metal oxide films are transparent to the first and second light-absorbing films 22 and 42.

  Among metal oxide films, zinc oxide that is relatively inexpensive and abundant is particularly preferable, and the first and second reproduction films 21 and 41 are preferably made of zinc oxide or contain zinc oxide. Thereby, the cost of the optical information recording medium 60 can be reduced. Furthermore, since it is made of zinc oxide or a material containing zinc oxide, higher super-resolution characteristics can be obtained than when other metal oxide films are used, so that the recording capacity of the optical information recording medium 60 can be improved. It becomes possible. Moreover, since it is not necessary to control the particle size as in the fine particle dispersion of the electron excited absorption saturated semiconductor disclosed in Patent Document 1, the production is easy and mass production is possible. In addition, changes over time such as alteration occurring at the grain boundaries are less likely to occur, and the reproduction durability is improved.

Further, the first and second reproduction films 21 and 41 are formed of a metal oxide other than zinc oxide, for example, a material made of TiO ₂ or CeO ₂ or a material mainly containing these metal oxides. In this case, the reproduction durability is equivalent to that of zinc oxide or a material containing the same, but at present, super-resolution characteristics higher than that of zinc oxide have not been obtained.

  As the material of the first and second reproduction films 21 and 41, organic materials such as pigments, phase change materials, materials made of other metal oxides (for example, TiO2, CeO2), and mainly metal oxides. A material or the like may be used. For example, in the case of an organic material such as a dye or a phase change material, the optical information recording medium of Embodiment 1 does not have durability, but at least the light absorption film is separated, so that the reproduction film material itself reproduces it. It can be easily predicted that the reproduction durability is higher than that of a conventional super-resolution film structure that absorbs light. In addition, when a transparent film is used for the first and second reproduction films 21 and 41, there is an advantage that the light-absorbing film works more efficiently because of good permeability to the light-absorbing film.

  As described above, the optical information recording medium 60 includes the first and second light absorbing films 22 and 42 that generate heat by absorbing the reproduction light in the first and second information recording layers 20 and 40, and the first and second information recording layers 20 and 40. First and second reproduction films 21 and 41 are provided that change the optical constant of the heated portion by heating with the light absorption films 22 and 42, respectively.

  Thereby, in both the first and second information recording layers 20 and 40, the substantial recording density (reproducible recording density) can be made higher than the recording density regulated by the resolution limit. Therefore, when producing a recording medium having the same recording capacity, the number of information recording layers to be stacked is smaller than that of a normal multilayer optical information recording medium in which each information recording layer has a recording density regulated by the resolution limit. It becomes possible to decrease. Therefore, in the production line, the number of expensive vacuum apparatuses for forming the information recording layer by sputtering can be reduced, and the production cost of the recording medium accompanying the increase of the information recording layer can be greatly reduced. it can.

  In the above configuration, when reproducing the information recorded on the first information recording layer 20, the reproduction light is irradiated from the light transmitting layer 10 and focused on the first information recording layer 20. In the first information recording layer 20, the light absorption film 22 absorbs the reproduction light to convert the light into heat, and the heat is transmitted to the reproduction film 21. However, since the optical information recording medium 60 is rotated during reproduction, the temperature of the rear end portion of the beam spot becomes high due to the temperature distribution of the laser. That is, the position where the temperature is high deviates from the center. As a result, the transmittance of the reproducing film 21 in the high temperature region changes, and it is considered that information recorded with a mark (pit) length below the resolution limit of the first information recording layer 20 can be read.

  Further, when reproducing the information recorded on the second information recording layer 40, the reproduction light is irradiated through the translucent layer 10, the first information recording layer 20, and the intermediate layer 30 to obtain the second information. The recording layer 40 is focused. Then, similarly to the first information recording layer 20, information recorded with a mark (pit) length equal to or less than the resolution limit of the second information recording layer 40 can be read. Thereby, in both the first and second information recording layers 20 and 40, the substantial recording density (meaning the reproducible recording density) can be made higher than the recording density regulated by the optical resolution limit.

  As described above, the first and second information recording layers 20 and 40 can read information by the super-resolution reproduction effect by using the temperature change of only the central portion where the light intensity is high in the light spot. Thereby, the size of the minimum recording marks (pits) of the first and second information recording layers 20 and 40 can be reduced below the resolution limit, so that the recording density is improved and the recording capacity of the optical information recording medium with respect to the manufacturing cost Can be improved, and a recording medium with high cost performance can be provided.

  Therefore, by providing the first and second information recording layers 20 and 40, when producing a recording medium having the same recording capacity, the number of information recording layers to be stacked is reduced as compared with a normal multilayer optical information recording medium. It becomes possible. Therefore, in the production line, the number of expensive vacuum apparatuses for forming the information recording layer by sputtering can be reduced, and the production cost of the recording medium accompanying the increase of the information recording layer can be greatly reduced. it can.

  Moreover, in the optical information recording medium 60, the first and second light absorbing films 22 and 42 are formed separately from the first and second reproducing films 21 and 41, and the reproducing film and the absorbing film are formed separately. The first and second reproducing films 21 and 41 themselves do not change the optical characteristics by absorbing light and changing the molecular structure. Therefore, super-resolution reproduction is possible without imposing much burden on the first and second reproduction films 21 and 41 in the first and second information recording layers 20 and 40, and reproduction durability can be improved. .

  Further, in the optical information recording medium 60, the light absorption film 22 of the first information recording layer 20 is formed from a simple substance of Si or an alloy containing Si as a main component, and the light absorption film 42 of the second information recording layer 40 is a simple substance of Ge or It is made of an alloy mainly composed of Ge.

  The first light-absorbing film 22 in the first information recording layer 20 on the side close to the surface on which the reproduction light is incident is made of Si alone or an alloy containing Si as a main component, so that the first light-absorbing film 22 is made of another metal film or the like. Compared to the configuration, the temperature easily rises when the reproduction light is irradiated, the first reproduction film 22 can be efficiently heated by the generated heat, and the optimum characteristics are obtained with a lower reproduction power. be able to. That is, the reproduction sensitivity can be improved. In addition, since Si simple substance or an alloy containing Si as a main component has higher light utilization efficiency than Ge simple substance or an alloy containing Ge as a main component, it can be applied to the second information recording layer 40 with a relatively low reproduction strength. A sufficient reproduction light intensity can be obtained, which is particularly desirable as a multilayer optical information recording medium, and can save power. In addition, since the light utilization efficiency is high, there is an effect that the degree of freedom in optical design is increased.

  On the other hand, for the second light-absorbing film 42 of the second information recording layer 40 on the side far from the surface on which the reproduction light is incident, another metal film is used by using Ge alone or an alloy containing Ge as a main component. As compared with the case, the temperature easily rises when the reproduction light is irradiated, and the second reproduction film 41 can be efficiently heated by the generated heat. Then, optimum characteristics can be obtained with a lower reproduction power than when a simple substance of Si or an alloy of Si is used for the second light absorption film 42, and the reproduction sensitivity can be improved.

  Here, an example having the configuration of the optical information recording medium 60 according to the embodiment shown in FIG. 1 will be described. The optical information recording medium 60 of the example includes a polycarbonate film (film thickness: 55 μm) and a transparent adhesive resin layer, film thickness: 20 μm from the light incident side as the light transmitting layer 10, and the first information recording layer 20. The first reproduction film 21 (thickness: 125 nm) made of zinc oxide, the first light absorption film 22 (thickness: 7.5 nm) made of Si, and the transparent ultraviolet curable resin (film thickness: 25 μm) as the intermediate layer 30 A second reproducing film 41 (film thickness: 157 nm) made of zinc oxide as the second information recording layer 40 and a second light-absorbing film 42 (film thickness: 50 nm) made of Ge, and a polyolefin-based resin as the substrate 50 And a substrate that is laminated in this order from the light incident surface. This configuration is referred to as Example 1.

  Here, of the two layers constituting the translucent layer 10, the transparent adhesive resin layer located between the polycarbonate film and the first reproduction film 21 is bonded to both.

  For example, the manufacturing method of Example 1 is as follows. A second light-absorbing film 42 and a second reproduction film 41 are sequentially formed on the substrate 50 provided with the prepits 51 by sputtering, and the liquid intermediate layer 30 is applied after the film formation. Then, the prepit 31 is transferred to the surface of the coated intermediate layer 30 by 2P transfer using a stamper made of a transparent resin, and the intermediate layer 30 is irradiated with ultraviolet rays in this state, so that the intermediate layer 30 is a solid having the prepit 31 on the surface. It becomes resin.

  After the stamper is peeled off, the first light absorption film 22 and the first reproduction film 21 are formed in this order by sputtering, and finally the light transmitting layer 10 (specifically, a laminated structure composed of a polycarbonate film and a transparent adhesive resin layer) is formed in the first reproduction film. Adhere to 21 to complete. As the sputtering target, a ZnO sintered target having a purity of 99.99%, a Ge target having a purity of 99.99%, and a single crystal Si target are used as zinc oxide, and these targets are formed by RF magnetron sputtering. It was. However, in the first embodiment, the above materials and targets are used. However, the materials and targets are not limited to these, and the materials are not limited as long as they satisfy the technical idea and function in the present application.

  On the other hand, FIG. 3 shows a cross-sectional structure of an optical information recording medium 70 having a conventional configuration having two information recording layers as a comparative example 1 with respect to the optical information recording medium 60 of the first embodiment. In the first comparative example, components having functions equivalent to those in the optical information recording medium 60 of the first embodiment are denoted by the same reference numerals.

  As shown in FIG. 3, the optical information recording medium 70 of Comparative Example 1 includes a polycarbonate film 11 (film thickness 55 μm) and a transparent adhesive resin layer 12 (film thickness 20 μm) as the light-transmitting layer 10, and a first information recording layer. 80, a semi-transparent reflective film 81 (Au, film thickness 15 nm), a transparent ultraviolet curable resin layer (film thickness 25 μm) as the intermediate layer 30, and a reflective film 91 (Au, film thickness) as the second information recording layer 90. 50 nm) and a polyolefin-based resin substrate as the substrate 50, and are laminated in this order from the light incident surface.

  The film thickness of the translucent reflective film 81 is set so that the first information recording layer 80 of Comparative Example 1 has the same reflectance as that of the first information recording layer 20 of Example 1 (about 30%). did. Unless otherwise indicated, numerical values such as reflectance and transmittance shown in the present application are spectrophotometers for a sample in which a corresponding film configuration (in this case, only the first information recording layer 20) is formed on a translucent glass substrate. Shows the values of transmittance and reflectance measured at a wavelength of 405 nm. This wavelength of 405 nm is a reproduction wavelength of the disc signal evaluation optical system described later.

  In the case of the first information recording layer 20 of Example 1, the transmittance is 42.8% and the reflectance is 29.1%. In the case of the first information recording layer 80 of Comparative Example 1, the transmittance is 33.5% and the reflectance is 30. 4%. It can be seen that the transmittance of Example 1 is about 10% higher. The first information recording layers 20 and 80 of Example 1 and Comparative Example 1 have the same reflectance and the transmittance is about 10% higher, so that the light utilization efficiency of Example 1 is higher than that of Comparative Example 1. It can be said that it is expensive.

  In addition, the first and second information recording layers 80 and 90 of Comparative Example 1 are formed on the formation surface of the prepits 31 and 51 on which information is recorded in the intermediate layer 30 and the substrate 50. Similarly to the optical information recording medium 60 of the example, also in the optical information recording medium 70 of the comparative example, the first and second information recording layers 80 and 90 are in a state where the unevenness of the corresponding prepits 31 and 51 is transferred. ing. That is, similarly to the optical information recording medium 60, the optical information recording medium 70 is also formed as a so-called read-only optical information recording medium.

  Next, comparison of various characteristics between the optical information recording medium 60 of Example 1 and the optical information recording medium 70 of Comparative Example 1 will be described.

  Reproduction measurement was performed with a disk measuring instrument (DDU1000 manufactured by Pulstec Corp.) having an optical system with a wavelength of 405 nm semiconductor laser and NA (aperture ratio) of 0.85. In addition, as described in the section of [Problems to be Solved by the Invention], in order to study practical application of an optical information recording medium, data to be recorded is modulated to generate a random recording mark pattern ("random pattern"). It is necessary to evaluate the super-resolution reproduction characteristics.

  First, the random pattern will be described in detail here. The pit arrangement (record mark pattern) can be classified into the following three types. "Monotone pattern" in which single size recording marks (pits) are periodically arranged at regular intervals, "Mark position recording method" in which single size recording marks (pits) are randomly arranged at several intervals This is a “mark edge recording method” in which data to be recorded is modulated and randomly arranged as recording marks (pits) of different lengths.

  The random pattern (random recording mark pattern) employed in the present embodiment is a configuration in which the recording marks (pits) have neither a single size nor an arrangement interval, and are arranged based on the mark edge recording method. In mark edge recording, data to be recorded is modulated and recording marks of different lengths are randomly arranged, and the recording density is higher than that of monotone pattern and mark position recording. In other words, this is an advantageous system for practical use, and there are many practical examples.

  For example, in a CD, the boundary between pits and lands (also referred to as spaces) is defined as “1”, and the others are defined as “0”. That is, mark edge recording with the mark edge set to 1. However, if the original data is recorded on the mark edge as it is, when one channel continues, it becomes a recording mark (pit) smaller than the resolution limit of the CD reproducing optical system and cannot normally be detected. Therefore, in order to avoid this problem, a pattern in which 1 data is continuous is actually converted into a pattern including 0 and recorded.

  In the case of a CD, an EFM (8-14) modulation method (Eight to Fourteen Modulation) is adopted for this conversion, and 8-bit data is converted into 14-bit data. Note that DVD, Blu-Ray Disc (BD), and HD DVD use different modulation methods from CD. DVD is EFMPlus (8-16) modulation, BD is 1-7PP modulation, and HD DVD is ETM (8-12) modulation. Are employed, but both are mark edge recording.

  Taking DVD as an example, since EFMPlus (8-16) RLL (2, 10) modulation is employed, a minimum of two and a maximum of ten zeros are inserted between the edges of recording marks. . Accordingly, since the length of the recording mark is the distance between the edges, there are nine types of 3T to 11T, where T is the reference clock time. The length of the space between the recording marks is also the distance between the edges, so that there are nine types. In other mark edge recording modulation systems, the length of the recording mark and the length of the space between the recording marks are similarly standardized to several values. That is, as an evaluation for practical use, it is necessary to evaluate the reproduction characteristics of random pattern recording marks in which recording marks having different lengths are randomly arranged.

  The above-mentioned pre-pits 31 and 51 are provided on the substrate (intermediate layer 30 or substrate 50) as a random pattern with the shortest mark (pit) length of 0.12 μm. The pre-pits of 0.12 μm are about the resolution limit (λ / 4NA) of the evaluation optical system of the present embodiment described above, and in a normal optical information recording medium, a pattern in which pits and spaces of this size are adjacent to each other. Is a size that cannot be detected as an optical system and cannot be reproduced. Of the random pattern, only the shortest mark having a length of 0.12 μm is about the resolution limit of the evaluation optical system, and all the prepits other than the shortest mark are larger than the resolution limit of the optical system. .

  In this embodiment, since the pre-pits 31 and 51 common to Example 1 and Comparative Example 1 are used, the super-resolution reproduction effect of both media can be compared by comparing the reproduction evaluation results of this random pattern. it can.

  In this embodiment, jitter is used as a signal evaluation index. Fluctuation in the time axis direction of the signal actually obtained by disk reproduction by the optical pickup is jitter with respect to the original pattern recorded on the substrate. Specifically, the value of the standard deviation is the reference clock time. The divided value is expressed in%, and the smaller this value, the better.

  This jitter value is generally used as an evaluation index of the signal quality of a random pattern in an optical information recording medium. When this value increases, the quality of the optical information recording medium deteriorates, such as noise and skipping. To do. In this embodiment, since the prepits 31 and 51 common to the first embodiment and the first comparative example are used, the jitter values are compared by comparing the first information recording layers 20 and 80 and the second information recording layers 40 and 90 in each medium. It is equivalent to comparing with each other. Jitter measurement was performed at a linear velocity of about 4 m / s.

  4 (a) and 4 (b) show the first information recording layers 20 and 80 and the second information recording layer 40 and the second information recording layer 40 in each of the first embodiment and the first comparative example, respectively. It is the result of measuring the reproduction power Pr dependence of 90 jitters.

  4A shows the results of the first information recording layers 20 and 80 of Example 1 and Comparative Example 1, respectively, and FIG. 4B shows the results of the second information recording layers 40 and 90, respectively. It should be noted that no plot is made for the case where the jitter value becomes too large, or the result that the signal quality is poor and the measurement cannot be performed well.

  As is clear from FIGS. 4A and 4B, Example 1 includes both the first and second information recording layers 80 and 40 of Comparative Example 1 in both the first and second information recording layers 20 and 40. Compared to 90, the jitter value at the same reproduction power is lower, and the reproduction characteristic of the random pattern, that is, the detection capability is improved.

  Further, in this reproduction power range, the value at which the jitter becomes the smallest in Example 1 (hereinafter referred to as “jitter bottom value”) cannot be achieved by Comparative Example 1. For example, when the first information recording layers 20 and 80 are compared at an optimum reproduction power of 0.7 mW at which Example 1 takes the jitter bottom value, the jitter of Example 1 is 2.6% lower than that of Comparative Example 1. Similarly, in the second information recording layers 40 and 90, the jitter is reduced by 4.6% when compared with the optimum reproduction power of 3.0 mW at which the first embodiment takes the jitter bottom value.

  In the following, the reproduction power when taking the jitter bottom as described above will be expressed as the optimum reproduction power, and when there are a plurality of optimum reproduction powers (when the same jitter bottom is obtained with a plurality of reproduction powers), Of these, the lowest playback power is expressed as the optimum playback power.

  The reason is considered as follows. In Comparative Example 1, the shortest pit having a mark (pit) length of 0.12 μm cannot be detected near the resolution limit of the reproducing optical system, whereas in Example 1, the signal of the shortest pit of 0.12 μm can be detected. it is conceivable that. That is, a signal having a mark (pit) length near the resolution limit that cannot be reproduced in Comparative Example 1 indicates that the signal can be reproduced in Example 1, and a random pattern is reproduced better than in the past. It can be said that it is possible. As seen from the above comparison, in Example 1, the reproduction capability of the mark (pit) length signal near the resolution limit could be improved. In other words, it can be said that the resolution limit can be substantially reduced by the configuration of the present invention. In other words, it is possible to detect and reproduce not only the vicinity of the resolution limit of a reproduction optical system that could not be detected by conventional media but also a signal with a mark (pit) length that is somewhat shorter than the resolution limit. ing.

  Next, the difference between jitter and CNR as an evaluation index will be specifically described. For comparison of both indices, the jitter and CNR of the optical information recording medium for verification were evaluated.

  As shown in FIG. 5, the created and evaluated medium is a verification optical information recording medium 71 having a configuration in which the prepit 31 and the first information recording layer 20 are not provided in the configuration of the first embodiment. Other configurations are the same.

  That is, from the incident light side, a polycarbonate film (film thickness: 55 μm) and a transparent adhesive resin layer (film thickness: 20 μm) as the translucent layer 10, and a transparent ultraviolet curable resin (film thickness: 25 μm) as the intermediate layer 30 A second reproducing film 41 (film thickness: 157 nm) made of zinc oxide as the second information recording layer 40 and a second light-absorbing film 42 (film thickness: 50 nm) made of Ge, and a polyolefin-based resin as the substrate 50 The substrate is formed in order. This optical information recording medium 71 is referred to as Comparative Example 2, and a sectional view thereof is shown in FIG.

  In Comparative Example 2, the second information recording layer 40 was evaluated. In Comparative Example 2, compared with Example 1, since the prepit 31 and the first information recording layer 20 are not provided, the amount of light reaching the second information recording layer 40 is increased even when the reproduction power is the same. Therefore, although the reproduction power sensitivity is good, it can be considered that the same tendency as in Example 1 is shown in terms of comparison between jitter and CNR evaluation.

  In order to evaluate jitter and CNR of the second information recording layer 40, the prepit 51 was provided with the following two types of pattern pits. One is a random pattern similar to that of the first embodiment, the other is a pattern in which single-size pit rows having a mark (pit) length of 0.12 μm are periodically arranged at equal intervals, specifically, 0.12 μm pits, 0. The arrangement is 12 μm space, 0.12 μm pit, 0.12 μm space,. The 0.12 μm long pit is a pit having a size near the optical resolution limit of the evaluation optical system, and is the same size as the shortest pit 0.12 μm in the same random pattern as in the first embodiment. It can be considered that the characteristics can be confirmed.

  FIG. 6 shows the result of performing jitter evaluation of a random pattern and CNR evaluation of a single size pit pattern in the configuration of Comparative Example 2 as described above. The linear velocity at the time of CNR evaluation was 3 m / s.

  FIG. 6 is a graph showing the reproduction power dependency for the second information recording layer 40 of Comparative Example 2 with respect to the random pattern jitter and the CNR of the 0.12 μm single size pit string.

  According to FIG. 6, in this reproduction power range, the CNR takes the highest CNR value when the reproduction power is 1.75 mW, and the signal quality is the best. In contrast, the jitter takes the lowest jitter bottom when the reproduction power is 1.4 to 1.5 mW, and the signal quality is the best. The optimum reproduction power is 1.4 mW. Therefore, it can be seen that the reproduction powers at which the CNR and jitter evaluation indices are optimal do not always match.

  This can be explained as follows. Since the CNR evaluation of a single size pit row is only an evaluation of the corresponding size pattern, its characteristics are not necessarily common to CNR characteristics of other sizes. In particular, when super-resolution reproduction is performed, there is a possibility that the dependency of CNR on reproduction power is different if the pit length is changed. That is, the reproduction power at which the CNR is optimal is often different depending on the pit size.

  On the other hand, the random pattern includes pits of various standardized sizes. When reproducing the random pattern, it is necessary to reproduce pits of various sizes with a constant reproduction power. Therefore, an evaluation index (such as jitter) different from the CNR for determining the optimum reproduction power as the random pattern total is required.

  The random pattern used for jitter evaluation in the present embodiment is closer to the practical use of the optical information recording medium than the single size pit row, and pits and spaces of several mark lengths that are actually expected to be used. Consists of. That is, it is possible to evaluate the total optimum state including the pit length dependency of the super-resolution reproduction characteristics. Random pattern jitter evaluation can evaluate the reproduction characteristics of the optical information recording medium more than CNR evaluation of a single size pit row. Therefore, in this application, jitter evaluation of a random pattern is adopted as an evaluation index.

  Next, the reproduction durability of Example 1 will be described. Both the first reproduction film 21 and the second reproduction film 41 in Example 1 are made of zinc oxide. The first light absorbing film 22 is made of Si, and the second light absorbing film 42 is made of Ge. These materials are made of an inorganic material and have high melting points of 1000 ° C. or higher and are stable materials.

  Compared to the phase change material proposed in Patent Document 1 and the like and the semiconductor fine particle material dispersed in the matrix, the former is not accompanied by the structural change, and the manufacturing condition complexity and material instability as in the latter It is a relatively stable material. For this reason, it is considered that stable reproduction can be realized without deterioration even by continuous reproduction of tens of thousands of times.

  As described above, Example 1 has reproduction durability that cannot be obtained with a normal super-resolution optical information medium, and can be produced by a manufacturing process almost similar to that of a conventional two-layer optical information recording medium. It has been shown.

  When the first regeneration film 21 and the second regeneration film 41 made of metal oxide such as zinc oxide are heated by heat generated in the first light absorption film 22 and the second light absorption film 42, respectively, the first regeneration film 21 and It is considered that a signal having a mark (pit) length less than or equal to the optical system resolution limit of the reproducing apparatus can be reproduced by changing the optical constant of the second reproducing film 41.

  Next, the results of studying the material dependence of the second light-absorbing film 42 based on the configuration of Example 1 will be described. However, in order to compare only the characteristics of the second information recording layer 40, the first information recording layer 20 is not necessarily required. Conversely, the characteristics of the first information recording layer 20 of each optical information recording medium are provided. If they are different, the comparison of the second information recording layer 40 is adversely affected.

  Therefore, in order to compare the second information recording layer 40, the characteristics of the single-layer optical information recording medium from which the first information recording layer 20 was removed were confirmed. Specifically, the second information recording layer 40 is common to the first information recording layer 20 (and the prepits) in the second comparative example, which is the verification optical information recording medium 71 shown in FIG. 31) is present or not. FIG. 7 shows the jitter evaluation results of the second information recording layer 40 for these optical information recording media.

  According to FIG. 7, as a jitter evaluation result of the second information recording layer 40 of Comparative Example 2, the optimum reproduction power was 1.4 mW, and the evaluation result of Example 1 was 3.0 mW. Further, the jitter bottom values of the second information recording layer 40 in Comparative Example 2 and Example 1 were substantially the same.

  The following can be said from these results. Compared to the optimum reproduction power of Comparative Example 2, the optimum reproduction power of Example 1 is twice or more larger. This is because the first information recording layer 20 (and the pre-pit 31) is present in Example 1, and light is lost due to reflection, absorption, and scattering in the first information recording layer 20, and only partially transmitted light is second. This is because the information reaches the information recording layer 40 and is used for reproduction.

  That is, in order to realize the same super-resolution reproduction, it is necessary to make the light equivalent to the case of Comparative Example 2 reach the second information recording layer 40. In addition, a large reproduction power is required. However, if the reproduction power is increased, the obtained jitter bottom value is almost the same value. Therefore, the presence of the first information recording layer 20 reduces the signal quality of the second information recording layer 40. I understand that it is not.

  From the above, it can be considered that the signal characteristics of the second information recording layer 40 are not affected by the presence or absence of the first information recording layer 20 except for the reproduction power dependency. That is, in comparing and examining the characteristics of the second information recording layer 40, even if the comparison is made in the configuration without the first information recording layer 20, the essence is not impaired. In addition, only the second information recording layer 40 can be compared purely without being affected by the first information recording layer 20, and there is no light loss that occurs in the first information recording layer 20, which is relatively low. There is also an advantage that the study can be made with the reproduction power.

  In response to the above, first, in order to confirm the material dependency of the second light absorbing film 42 in the configuration in which the first information recording layer 20 does not exist, the jitter of the second information recording layer 40 is compared with the above-described Comparative Example 2, A new comparative example 3 was created and compared.

  As described above, Comparative Example 2 has a configuration in which the first information recording layer 20 (and the prepit 31) is removed from Example 1, and the second reproduction film 41 is made of zinc oxide and has a film thickness of 157 nm. The second light absorbing film 42 is made of Ge and has a film thickness of 50 nm.

  On the other hand, Comparative Example 3 has the same configuration as Comparative Example 2, and the second regeneration film 41 has a thickness of 170 nm made of zinc oxide, and the second light absorption film 42 has a thickness of 50 nm made of Si.

  FIG. 8A shows the result of evaluating the jitter of the second information recording layer 40 in Comparative Example 2 and Comparative Example 3. For comparison, the evaluation result of a configuration in which Au 50 nm is provided instead of the second information recording layer 40 in the same configuration as that of Comparative Example 2 is also graphed.

  The following can be said from FIG. One is that both Comparative Example 2 and Comparative Example 3 have a low jitter bottom value as compared with Au 50 nm which is a normal medium. That is, super-resolution reproduction can be realized in any case. Second, the optimum reproduction power (1.4 mW) of Comparative Example 2 is smaller than the optimum reproduction power (1.8 mW) of Comparative Example 3, and the jitter bottom value is obtained at a lower reproduction power. That is, the reproduction power sensitivity is good. Furthermore, the jitter bottom value at the time of reproduction at the optimum reproduction power is better in Comparative Example 2 than in Comparative Example 3.

  From the above, it can be said from the comparison between Comparative Example 2 and Comparative Example 3 that the material of the second light-absorbing film 42 is more desirable than Ge because it has lower optimum reproduction power and lower jitter bottom value. Although the thickness of the second reproducing film 41 is not the same in Comparative Example 2 and Comparative Example 3, the difference in film thickness is about 10 nm, which is a fine adjustment for realizing a similar optical interference state at the reproducing wavelength. The difference is such that the jitter value and optimum reproduction power are not affected, and the second reproduction film 41 may be considered to be substantially common. Therefore, it can be considered that the difference in the jitter evaluation results is due to the difference in the material of the second light-absorbing film between Si and Ge. Therefore, the second light absorbing film 42 is preferably made of Ge.

  Next, based on the evaluation results of Comparative Example 2 and Comparative Example 3, comparison was performed on an optical information recording medium having the first information recording layer 20.

  Comparative Example 4 has the same configuration as that of Example 1, and the second reproducing film 41 in the second information recording layer 40 is made of zinc oxide, the film thickness is 170 nm, and the second light absorbing film 42 is made of Si instead of Ge. The film thickness is 50 nm. In other words, the configuration in which the first information recording layer 20 (and the prepit 31) of Example 1 is provided in Comparative Example 3 is referred to as Comparative Example 4.

  Similarly, in another expression, Example 1 can be expressed as a configuration in which the first information recording layer 20 (and the prepit 31) of Example 1 is provided in Comparative Example 2. That is, if Example 1 and Comparative Example 4 are compared, it can be verified that the results obtained in Comparative Example 2 and Comparative Example 3 are also valid in the optical information recording medium 60 having two information recording layers. it can.

  FIG. 8B shows the jitter evaluation results in the second information recording layers 40 and 90 of the first example, the comparative example 4, and the comparative example 1 for comparison.

  The following can be said from FIG. One is that both Example 1 and Comparative Example 4 have a low jitter bottom value as compared with Comparative Example 1 which is a normal medium. That is, super-resolution reproduction can be realized in any case. Second, the optimum reproduction power (3.0 mW) of Example 1 is smaller than the optimum reproduction power (4.0 mW or more) of Comparative Example 4, and the jitter bottom is obtained at a lower reproduction power. That is, the reproduction power sensitivity is good. Furthermore, the jitter bottom value at the time of reproduction at the optimum reproduction power is better in Example 1 than in Comparative Example 4.

  From the above, according to the comparison between Example 1 and Comparative Example 4, even in the optical information recording medium having two information recording layers, the material of the second light absorbing film is lower in Ge than in Si, and the optimum reproduction power is lower. The bottom of the jitter is low, which is more desirable. Although the film thickness of the second reproduction film 41 is not the same in Example 1 and Comparative Example 4, the film thickness difference is about 10 nm, which is a fine adjustment for realizing the same optical interference state at the reproduction wavelength. The difference is such that the jitter value and optimum reproduction power are not affected, and the second reproduction film 41 may be considered to be substantially common. Therefore, it can be considered that the difference in the jitter evaluation results is due to the difference in the material of the second light-absorbing film between Si and Ge. Therefore, the second light absorbing film 42 is preferably made of Ge.

  The reason why Ge is preferable as the material of the second light-absorbing film can be considered as follows. According to Kittel's “Introduction to Kittel Solid Physics (Part 1)” (6th edition, Maruzen Co., Ltd., p.117), the thermal conductivity of bulk materials is introduced. 0.60 (both units are W / (cm · K)) and Ge is less than half of Si. In general, it cannot be said that the thin film state directly reflects the physical property value of the bulk material, but it is presumed that the thermal conductivity of Ge is smaller than that of Si even in the thin film. That is, it is considered that because the thermal conductivity of Ge is lower than that of Si, the heat generated by absorbing the irradiation light is difficult to diffuse and the temperature of the second reproduction film 41 is likely to rise.

  Subsequently, the result of studying the material dependence of the first light-absorbing film of the first information recording layer 20 will be described. The comparison was made in Example 1 and Comparative Example 5. Comparative Example 5 has the same configuration as that of Example 1, and the first reproduction film 21 in the first information recording layer 20 is made of zinc oxide. The film thickness is about 125 nm, and the first light absorption film 22 is replaced with Si instead of Ge. The film thickness is 7.5 nm. That is, the first light-absorbing film 22 has the same configuration as that of Example 1 except that the first light-absorbing film 22 is made of Ge instead of Si.

  The transmittance and reflectance of the first information recording layer 20 of Example 1 and Comparative Example 5 were measured. Actually, a sample in which the corresponding film configuration (in this case, only the first information recording layer 20) was formed on a translucent glass substrate was measured with a spectrophotometer at a reproduction wavelength of 405 nm of the disc signal evaluation optical system. . As a result, in the case of the first information recording layer 20 of Example 1, the transmittance was 42.8% and the reflectance was 29.1%. In the case of the first information recording layer 20 of Comparative Example 5, the transmittance was 30.2%. The reflectivity was 29.0%. Actually, the optical interference state and the reflectance of Comparative Example 5 were adjusted to the same values as in Example 1 by finely adjusting the thickness of the zinc oxide forming the first reproducing layer 21 for comparison.

  From these results, it can be said that the light utilization efficiency is high because the reflectance of the first information recording layer 20 of Example 1 and Comparative Example 5 is the same, and the transmittance of Example 1 is 10% or higher. This result may be considered to be obtained when the first light absorbing film 22 is made of Si with respect to Ge. Therefore, it is desirable that the first light absorption film 22 is made of Si.

  This will be described in more detail. The first light absorbing film 22 is required to have stricter conditions than the second light absorbing film 42. The reason is as follows. For one thing, in order to reproduce the second information recording layer 40, a certain amount of reproduction light must be transmitted, and the first light absorbing film 22 must be a semi-transmissive film. Secondly, it is necessary to make the first light absorbing film 22 as thin as several nm to 30 nm for that purpose, and it is necessary to ensure high durability even with a thin film thickness, and the third satisfies the above two points. It is necessary to obtain good signal characteristics and super-resolution reproduction characteristics. Therefore, it is more desirable that the first light absorption film 22 is made of Si that can increase the transmittance and reflectance of the first information recording layer 20 and further the light utilization efficiency as compared with Ge.

  In addition, even when other films are added to the first and second information recording layers 20 and 40 in the structure of the embodiment described so far, the characteristics as described above are not greatly lost.

  Furthermore, if a balance between cost and recording capacity can be achieved, the present invention can be applied to a multilayer optical information recording medium having three or more information recording layers.

  As optical information recording media, CD-ROM (Compact Disc Read Only Memory), DVD-ROM (Digital Versatile Disc Read Only Memory), BD-ROM (Blu-ray Disc Read Only Memory), HD DVD-ROM ( High definition digital versatile disc read only memory) can be cited as a format of an optical information recording medium to which various optical discs such as an optical reading disc can be applied.

  The present invention does not ask the recording method or size. Further, as is clear from the above description, by reproducing information using the present optical information recording medium 60, stable information reproduction from an optical information recording medium recorded at a higher density is possible. It turns out that it becomes.

[Embodiment 2]
Other embodiments of the present invention will be described. For convenience of explanation, members having the same functions as those used in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 9, the optical information recording medium 61 of the present embodiment includes a transparent substrate 11 instead of the transparent layer 10 made of a transparent resin. The translucent layer 10 may include a transparent substrate 11.

  In such a structure using the transparent substrate 11, the prepits 31 provided in the intermediate layer 30 can be provided on the transparent substrate 11. Here, prepits are provided on the transparent substrate 11, and no prepits are formed on the surface of the intermediate layer 31 on the first information recording layer 20 side. Note that the direction of the prepits on the transparent substrate 11 is opposite to that of the prepits 31.

  In such an optical information recording medium 61, for example, the first reproducing film 21 and the first light absorbing film 22 forming the first information recording layer 20 are sequentially formed on the transparent substrate 11 on which the prepits are formed. The substrate 50 on which the second absorption film 42 and the second reproduction film 41 forming the second information recording layer 40 are formed and the transparent substrate 11 are connected to the surface of the first information recording layer 20 and the second information recording by the intermediate layer 31. The surface of the layer 40 is bonded together.

  In such a configuration, since it is only necessary to bond the two substrates 11 and 50 together, it is necessary to form the prepits 31 in the intermediate layer 30 using 2P transfer that requires a complicated process as in the first embodiment. The optical information recording medium can be manufactured at a lower cost.

  Further, since this structure conforms to the DVD standard, a high-density DVD (HD-DVD) can be provided at low cost.

[Embodiment 3]
The following will describe another embodiment of the present invention with reference to FIGS.

  In the present embodiment, an optical information recording medium reproducing device for reproducing the optical information recording media 60 and 61 described in the first and second embodiments will be described. FIG. 10 is a diagram showing a schematic configuration of the optical information recording medium reproducing apparatus 100. As shown in FIG.

  As shown in FIG. 10, the optical information recording medium reproducing apparatus 100 irradiates the optical information recording medium 60 by irradiating the optical information recording medium 60 (61) with a light beam and detecting the reflected light. A device for reproducing recorded information. In this embodiment, the case where the optical information recording medium 60 is a disc-shaped optical disc will be described. However, the optical information recording medium 60 may not necessarily be a disc-shaped optical disc.

  As shown in FIG. 10, the optical information recording medium reproducing apparatus 100 rotates the optical information recording medium 60 with a spindle motor 101, and reads information from the optical information recording medium 60 with an optical pickup apparatus 102. . Control of the optical pickup device 102 and the spindle motor 101 is performed by the control unit 103.

  The spindle motor 101 scans the optical spot on the optical information recording medium 60 by rotating the optical information recording medium 60. The control unit 103 includes a signal processing unit 103a, a drive control unit 103b, and the like.

  The signal processing unit 103a records on the optical information recording medium 60 by detecting the recording information based on the electrical signal from the optical pickup device 102 obtained from the reflected light from the recording mark on the optical information recording medium 60. Read the information recorded by the mark. Further, the signal processing unit 103a generates a focus error signal and a tracking error signal, which will be described later, based on an electrical signal from the optical pickup device 102 obtained from reflected light from a recording mark on the optical information recording medium 60.

  The drive control unit 103b is a servo circuit for controlling the driving of the spindle motor 101 and the optical pickup device 102 based on an electrical signal read from the optical pickup device 102 and generated by the signal processing unit 103a and an instruction from the outside. have. In particular, the drive control unit 103b corrects the position of the objective lens 102e based on the focus error signal and the tracking error signal from the signal processing unit 103a, and sets a servo circuit for performing autofocus and tracking of the laser light to the above servo. Includes as a circuit.

  FIG. 11 shows a configuration of the optical pickup device 102. As shown in FIG. 11, the optical pickup device 102 includes a semiconductor laser 102a, a collimating lens 102b, a beam shaping prism (prism that makes a beam circular) 102c, a beam splitter 102d, an objective lens 102e, a lens actuator 102f, and a detection optical system. 102g.

  The optical pickup device 102 is a device that shapes laser light emitted from the semiconductor laser 102a, which is a light source, into a beam shape and condenses it on the optical information recording medium 60. In this optical pickup device 102, a semiconductor laser 102a is used as a laser light source. However, the present invention is not limited to this, and other light sources may be used.

  In addition, the laser power of the semiconductor laser 102a can be set higher than the conventional laser power in order to develop the super-resolution characteristics, and can be switched to the conventional laser power. As a result, reproduction on a super-resolution medium having two information recording layers is possible, and therefore a two-layer super-resolution medium having the same recording capacity and lower cost than a normal medium that requires three or more information recording layers. Playback using is possible.

  In addition, since the number of layers is reduced as compared with the case of reproducing a normal medium that requires three or more layers with the same recording capacity, the number of times of focusing on each layer is reduced. Therefore, since the time required for focusing is shortened, the response to the reproduction command is improved.

  Laser light from the semiconductor laser 102a is converted into substantially parallel light by the collimator lens 102b, and shaped so that the light intensity distribution becomes substantially circular by the beam shaping prism 102c. The substantially circular parallel light passes through the beam splitter 102d and is then focused on the optical information recording medium 60 as a light beam (incident light) by the objective lens 102e. The numerical aperture (NA) of the objective lens 102e is set to 0.65 or 0.85.

  The reflected light from the optical information recording medium 60 is branched by the beam splitter 102d and guided to the detection optical system 102g. In the detection optical system 102g, recording information, defocus information, and track position deviation information are identified from a change in the polarization direction of reflected light from the optical information recording medium 60, a change in reflected light intensity (level of reflected light level), and the like. These pieces of information are converted into electric signals. The converted electric signal is sent to the signal processing unit 103a.

  The reflected light includes reflected light from an address information mark constituted by a part of the prepits 31 and 51 provided on the optical information recording medium 60. The detection optical system 102g generates a light spot (light) formed on the light beam irradiation surface of the optical information recording medium 60 from an electrical signal obtained from the reflected light, that is, an electrical signal obtained by reproducing the address information mark. A focus error signal and a tracking error signal for the optical information recording medium 60 of the beam condensing unit are detected.

  The lens actuator 102f corrects the positional deviation of the light spot in the optical axis direction by feeding back the focus error signal. Thereby, the optical pickup device 102 can form a light spot on the desired first information recording layer 20 or the second information recording layer 40 in the optical information recording medium 60. Further, the lens actuator 102f corrects the positional deviation of the light spot in the track width direction by feeding back the tracking error signal. Thereby, the optical pickup device 102 can cause the optical spot to follow the target track in the optical information recording medium 60.

  In the conventional multilayer optical information recording medium reproducing apparatus, it is necessary to improve the pickup performance accompanied by an increase in cost in order to reproduce information by focusing reproducing light on many recording layers. On the other hand, in this optical information recording medium playback apparatus 100, playback is performed using the optical information recording media 60 and 61 of the first and second embodiments, so that the number of information recording layers to be focused is played back only on a normal medium. Since it decreases compared with the conventional apparatus, the cost increase of the pick-up apparatus 102 can be suppressed. That is, a lower cost reproducing apparatus can be realized. Further, the optical information recording medium reproducing apparatus 100 can perform stable information reproduction by using the optical information recording media 60 and 61 recorded at high density.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  In the optical information recording medium of the present invention, in the information recording layer, by providing a light absorption film that collects the reproduction light and converts it into heat, and a reproduction film that changes the light transmittance of the portion heated by the heat, Since the manufacturing cost can be reduced, the information recording density can be improved, and the reproduction durability of the information recording layer can be improved, it can be suitably used for optical density recording.

It is sectional drawing which shows the structure of the optical information recording medium of one Embodiment concerning this invention, and the optical information recording medium of Example 1. FIG. (A) is a perspective view showing a structure of prepits provided in an intermediate layer in the optical information recording medium, and (b) is a perspective view showing a structure of prepits provided on a substrate in the optical information recording medium. 6 is a cross-sectional view showing a structure of an optical information recording medium of Comparative Example 1. FIG. (A) is a characteristic diagram showing the reproduction power Pr dependence of each jitter for the first information recording layer in the optical information recording media of Example 1 and Comparative Example 1, and (b) is a characteristic diagram showing Example 1 and Comparative Example 1. It is a characteristic view which shows the reproduction power Pr dependence of each jitter of the 2nd information recording layer in the optical information recording medium. It is sectional drawing which shows the structure of the optical information recording medium of the comparative example 2 produced for the comparison of the evaluation parameter | index of a jitter and CNR. It is a characteristic view which shows the reproduction laser power dependence of the jitter and CNR about the 2nd information recording layer in the optical information recording medium of the comparative example 2. FIG. It is a characteristic view which shows the reproduction power Pr dependence of the jitter about each 2nd information recording layer in the optical information recording medium of Example 1 and Comparative Example 2. FIG. (A) is the characteristic diagram which shows the reproduction power Pr dependence of each jitter about the 2nd information recording layer in the optical information recording medium of Comparative Example 2, Comparative Example 3, and Au50nm, (b) is Example 1 and a comparison. It is a characteristic view which shows the reproduction power Pr dependence of each jitter of the 2nd information recording layer in the optical information recording medium of Example 1 and Comparative Example 4. It is sectional drawing which shows the structure of the optical information recording medium of other embodiment concerning this invention. It is a figure which shows schematic structure of the optical information recording medium reproducing | regenerating apparatus of embodiment concerning this invention. It is a figure which shows schematic structure of the optical pick-up apparatus in the said optical information recording-medium reproducing | regenerating apparatus.

Explanation of symbols

10 translucent layer 20 first information recording layer 21 first reproducing film (reproducing film)
22 1st light absorption film (light absorption film)
30 Intermediate Layer 31 Prepit 40 Second Information Recording Layer 41 Second Reproduction Film (Reproduction Film)
42 Second light absorption film (light absorption film)
50 substrate 51 pre-pit 60 optical information recording medium 100 optical information recording medium reproducing device 102 optical pickup device (optical reading means)

Claims (7)

An optical information recording medium in which information is represented by a recording mark pattern including a recording mark length that is less than or equal to the optical system resolution limit of the reproducing apparatus,
From the incident side of the reproduction light, a translucent layer, a first information recording layer, an intermediate layer, a second information recording layer, and a substrate are laminated in this order,
The recording mark pattern is formed on at least the first information recording layer and the second information recording layer,
These first information recording layer and second information recording layer are:
An absorption film that absorbs the regenerated light and converts it into heat;
A reproducing film that is heated by the heat generation of the light-absorbing film and that can reproduce a signal having a recording mark length equal to or less than the resolution limit;
The light-absorbing film of the first information recording layer is made of Si alone or an alloy containing Si as a main component,
Ri Do from absorption film of the second information recording layer has a main component alone or Ge of Ge alloys,
An optical information recording medium, wherein the light absorption film of the first information recording layer is thinner than the light absorption film of the second information recording layer .   2. The optical information recording medium according to claim 1, wherein the recording mark pattern is formed by prepits and spaces.   2. The optical information recording medium according to claim 1, wherein the recording marks are arranged in accordance with a mark edge recording method.   2. The optical information recording according to claim 1, wherein the recording mark pattern includes a recording mark and a space, and a length value in a reading direction of the recording mark and the space is normalized to at least two values. Medium.   5. The optical information recording medium according to claim 1, wherein the reproducing film in the first information recording layer or the second information recording layer contains a metal oxide as a main component.   6. The optical information recording medium according to claim 5, wherein the metal oxide is zinc oxide or contains zinc oxide as a main component.   A laser beam having a laser power capable of reproducing the optical information recording medium according to any one of claims 1 to 6 is applied to the first information recording layer or the second information recording layer, and the optical information recording medium is irradiated with the laser light. An optical information recording medium reproducing device comprising optical reading means for reading the reflected light of the optical information recording medium.

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