JP4099549B2 - Optical recording medium and an optical disk drive - Google Patents

Optical recording medium and an optical disk drive Download PDF

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Publication number
JP4099549B2
JP4099549B2 JP13071398A JP13071398A JP4099549B2 JP 4099549 B2 JP4099549 B2 JP 4099549B2 JP 13071398 A JP13071398 A JP 13071398A JP 13071398 A JP13071398 A JP 13071398A JP 4099549 B2 JP4099549 B2 JP 4099549B2
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Japan
Prior art keywords
recording medium
transparent cover
optical recording
layer
optical
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JPH1131337A (en
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勝久 荒谷
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ソニー株式会社
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Description

[0001]
BACKGROUND OF THE INVENTION
The present invention has a transparent cover layer on one main surface side of the recording layer, and information is recorded and / or reproduced by irradiating light from the transparent cover layer side using an objective lens having a numerical aperture of 0.7 or more. The present invention relates to an optical recording medium to be performed. More specifically, the present invention relates to an optical recording medium having a relatively high hardness on the surface side of the transparent cover layer, being hard to break and having high reliability.
[0002]
[Prior art]
In recent years, in the field of information recording, research on optical information recording methods has been promoted in various places. This optical information recording system can perform recording and reproduction without contact, can achieve a recording density higher by one digit or more than the magnetic recording system, and has a memory format of read-only type, write-once type, and rewritable type. It has many advantages such as being compatible, and is considered to be used in a wide range of applications from industrial use to consumer use as a method that enables the realization of inexpensive large-capacity files.
[0003]
In particular, digital audio discs and optical video discs, which are optical discs compatible with a read-only memory format, are widely used.
[0004]
Optical discs such as the above digital audio discs are formed with a reflective film made of a metal thin film such as an aluminum film on one main surface on which a concavo-convex pattern of a transparent substrate on which concavo-convex patterns such as pits and grooves indicating information signals are formed Then, the recording layer is formed, and the reflective film is further converted into atmospheric moisture, O2A protective film for protecting the film is formed on the reflective film.
[0005]
The magneto-optical disk corresponding to the rewritable memory form has the following configuration. That is, a transparent dielectric film such as silicon nitride is formed on one main surface of a transparent substrate, a magneto-optical recording film such as TbFeCo is formed thereon as a recording layer, and a transparent dielectric film such as silicon nitride is further formed. Further, a reflection film such as an aluminum film is formed, and a protective film made of an ultraviolet curable resin or the like is further formed. In this magneto-optical disk, information is recorded and reproduced by irradiating light from the transparent substrate side.
[0006]
By the way, as a method for increasing the recording capacity of an optical recording medium such as an optical disk or a magneto-optical disk as described above, the numerical aperture of the objective lens of the optical pickup is increased to reduce the spot diameter of the reproduction light. A method of increasing the recording density by recording is proposed.
[0007]
Therefore, recently, a DVD (Digital Versatile Disc, hereinafter referred to as DVD) for recording various data such as images, music, and computer data is also on the market. In this DVD, the thickness of the substrate is set to about 0.6 (mm) so as to be compatible with a short wavelength optical system and to be compatible with an optical system with a high numerical aperture so as to increase the recording density. .
[0008]
Under such circumstances, as a next generation optical recording medium, an optical recording medium capable of recording / reproducing for 4 hours by NTSC (National Television System Committee) system on one side as shown in Japanese Patent Application No. 9-109660. Has been proposed.
[0009]
This optical recording medium has a function as a new recording medium to replace a video tape recorder which is currently mainstream by enabling recording and reproduction for 4 hours as a home video disc recorder. It is an object. In addition, this optical recording medium can be designed to be easy to use for users who are familiar with the convenience and usability of digital audio discs by using the same shape and size as digital audio discs on which music data is recorded. ing. Furthermore, in this optical recording medium, the shape of the disk is made into a disk shape, so that the speed of access, which is the greatest feature of the disk shape, is used, and not only a small and simple recording medium, It is also considered to incorporate various functions such as trick play and editing.
[0010]
Therefore, the optical recording medium is required to have a storage capacity of 8 (GB) or more in order to incorporate such various functions.
[0011]
However, in any of the conventional optical recording media, a storage capacity of 8 (GB) has not been achieved particularly in a size equivalent to that of a digital audio disk and having an information recording layer only on one side. For example, even in a DVD having a high storage capacity, the wavelength λ is 0.65 (μm) in the region of the information signal portion, that is, in the range of radius 24 to 58 (mm) from the center, and the aperture of the optical system. The number (hereinafter referred to as NA) is 0.6, and only a storage capacity of 4.7 (GB) is secured.
[0012]
For example, in order to ensure a storage capacity of 8 (GB) or more while keeping the signal format such as ECC (Error Collection Code) and modulation method as the DVD method, it is necessary to satisfy the following formula 1.
[0013]
4.7 × (0.65 / 0.60 × NA / λ)2 ≧ 82 (Formula 1)
From the above formula 1, it is necessary that NA / λ ≧ 1.20. That is, it is necessary to shorten the wavelength or increase the NA.
[0014]
Here, for example, when the NA is increased, it is necessary to reduce the thickness of the portion through which the reproduction light is irradiated and transmitted. This is the angle at which the disk surface deviates from the vertical with respect to the optical axis of the optical pickup as the NA increases (so-called tilt angle, proportional to the square of the product of the reciprocal of the wavelength of the light source and the numerical aperture of the objective lens). This is because the allowable amount of aberration caused by the above becomes small, and this tilt angle is easily affected by the aberration due to the thickness of the substrate. Therefore, the thickness of the substrate is reduced to minimize the influence of aberration on the tilt angle.
[0015]
For the same reason, it is necessary to keep the variation in the thickness of the portion through which the reproduction light is transmitted within a predetermined range.
[0016]
However, it seems that further higher recording density will be required in the future, and further reduction in the thickness of the substrate will be required. Therefore, for example, a recording layer is formed by forming irregularities on one main surface of the substrate, a reflective film is provided on the recording layer, and a light transmissive layer, which is a thin film that transmits light, is provided on the recording layer. An optical recording medium that reproduces information on the recording layer by irradiating the reproducing light from the recording layer, a reflective film is provided on one main surface of the substrate, and a magneto-optical recording film is formed thereon to form a recording layer. An optical recording medium has been proposed in which a light transmission layer, which is a thin film that transmits light, is provided on the recording medium, and information on the recording layer is reproduced by irradiating reproduction light from the light transmission layer side. In this way, the NA of the objective lens can be increased by reducing the thickness of the light transmission layer. Such a light transmission layer is generally formed of an ultraviolet curable resin such as an acrylic polymer material.
[0017]
[Problems to be solved by the invention]
When the numerical aperture of the objective lens of the optical pickup is increased as described above, if the working distance that is the distance between the objective lens and the optical recording medium is the same as that of the conventional objective lens, There are problems that the size becomes very large, the weight becomes heavy, the access time becomes slow, or the tracking and focus servo bands cannot be secured sufficiently.
[0018]
Therefore, reduction in the weight of the objective lens, in other words, downsizing, has been studied. In this case, it is necessary to bring the objective lens closer to the optical recording medium, that is, to reduce the working distance. However, when the working distance is narrowed in this way, it is natural that collision between the optical pickup and the optical recording medium easily occurs.
[0019]
In the optical disk and magneto-optical disk described above, information is reproduced and / or recorded by irradiating light from the transparent substrate side. This transparent substrate is inexpensive and emits a shape such as a guide groove. Since it can be easily formed by molding, it is generally formed of plastic such as polycarbonate.
[0020]
Accordingly, when the optical pickup and the optical recording medium collide as described above, the optical recording medium is often damaged. That is, for example, when the objective lens of the optical pickup collides with the optical recording medium, the transparent substrate is easily made because the plastic such as polycarbonate that forms the transparent substrate is much softer than the glass that forms the objective lens. Deforms, scratches occur and breaks. Also, a holder made of plastic, for example, is provided to hold the objective lens. When the distance between the holder and the optical recording medium is smaller than the distance between the objective lens and the optical recording medium, the holder collides with the transparent substrate. Will be. In this case, since the plastic forming the holder is softer than the glass forming the objective lens, the holder will not damage the transparent substrate, but if dust or micro dust in the atmosphere is sandwiched between the holder and the transparent substrate. These cause damage and damage. Scratches due to dust and fine dust in the atmosphere can be dealt with by signal processing such as error correction when they occur discretely, but if they occur along the track direction, the error length is long, It is not preferable because error correction is difficult and an error signal is continuously given to the tracking or focus servo signal, the servo is removed, and reliability is impaired.
[0021]
Therefore, in a certain type of magneto-optical disk, the displacement in the thickness direction due to changes in environmental temperature and humidity is suppressed to ± 0.2 (mm) or less to suppress the collision with the optical pickup as much as possible. If the distance decreases, collisions are likely to occur.
[0022]
By the way, in the optical recording medium in which a light transmission layer is provided as described above and light is irradiated from the light transmission layer side, the light transmission layer is a thin layer. It becomes difficult to obtain sufficient reliability due to deterioration.
[0023]
In a magnetic disk that is a magnetic recording medium, a fiber called a liner is brought into contact with the surface of the magnetic disk so as to remove dust, and such a method is also very effective in the above optical recording medium, Implementation is desired. However, in this case, it is necessary that the surface of the optical recording medium, here the surface of the light transmission layer, has a strength that is not damaged by the contact of the fiber or the contact of the fiber with dust or dirt in the air sandwiched between them. Such demands are increasing.
[0024]
Further, it is strongly desired to achieve a storage capacity of 8 (GB) or more in an optical recording medium in which such a light transmission layer is provided and light is irradiated from the light transmission layer side.
[0025]
Therefore, the present invention has been proposed in view of the conventional situation, and the transparent cover layer formed on the recording layer such as the transparent substrate or the light transmission layer irradiated with light is hardly damaged and is damaged. It is an object of the present invention to provide an optical recording medium that is difficult and reliable. It is another object of the present invention to provide an optical recording medium that can cope with a particularly high NA, increase the capacity, and record information of, for example, 8 (GB) or more.
[0026]
[Means for Solving the Problems]
As a result of intensive studies by the present inventors in order to solve the above-mentioned problems, the hardness of the surface side of the transparent cover layer that is formed on the recording layer and irradiated with light, such as the transparent substrate or the light transmission layer of the optical recording medium. It has been found that it is possible to suppress the occurrence of scratches on the transparent cover layer, to prevent damage to the optical recording medium, and to ensure reliability by increasing
[0027]
Further, the present inventors have made further studies and made it possible to cope with high NA, increase the capacity, and record appropriate information for an optical recording medium capable of recording information of, for example, 8 (GB) or more. Appropriate conditions for an optical disk device suitable for recording and / or reproduction of a medium have been found.
[0028]
  That is, to achieve the above-mentioned purposeProposedThe present inventionPertaining toOptical recording mediaAn optical recording medium having a transparent cover layer on one main surface side of a recording layer disposed on a support layer, and recording and / or reproducing information by irradiating light from the transparent cover layer side. The surface t of the cover layer is made of a material having a Young's modulus of 70 (GPa) or more, and the thickness t of the transparent cover layer is t = 3 to 177 in at least the information signal area of the recording layer where the information signal is recorded. (Μm), where the thickness unevenness of the transparent cover layer is Δt, the numerical aperture NA of the optical system for irradiating light for recording and / or reproducing the optical recording medium and the wavelength λ of the light In between, Δt ≦ ± 5.26 ( λ / NA 4 ) (Μm). Here, it is desirable to use an optical system having a numerical aperture NA of 0.7 or more.
[0029]
Examples of the surface hardness index include Mohs hardness, Rockwell hardness, pencil hardness, and the like, but there is no unified one and comparison is difficult. Therefore, in the present invention, the bulk Young's modulus (elastic modulus), which is closely related to the hardness of the material, is used as an index.
[0030]
In the optical recording medium of the present invention, the thickness of the transparent cover layer may be 150 (μm) or less.
[0031]
Further, in the optical recording medium of the present invention, if the transparent cover layer is formed by the first layer disposed on the surface side and the second layer disposed on the recording layer side, it is easily formed. preferable.
[0032]
In this case, the first layer is preferably made of a material having a Young's modulus of 150 (GPa) or higher. If the Young's modulus of the first layer is smaller than 150 (GPa), it is difficult to ensure sufficient hardness. Is not preferable. Further, the thickness of the first layer is preferably 2 (nm) or more and 230 (nm) or less, and if the thickness of the first layer is less than 2 (nm), it is difficult to ensure strength. If the thickness of the first layer is greater than 230 (nm), the surface reflection becomes too large, which is not preferable.
[0033]
Furthermore, in the optical recording medium of the present invention, the surface side of the transparent cover layer is C100-XHX(1 (atomic%) <X <45 (atomic%)), SiThreeNFour, MgF2, Al2OThree, SiO2It is preferable that it consists of the material containing at least 1 type of these.
[0034]
In the optical recording medium of the present invention, the recording layer is disposed on the support layer, and the thickness t of the transparent cover layer is at least in the area of the information signal portion where the information signal is recorded in the recording layer. T = 3 to 177 (μm), and when the uneven thickness of the transparent cover layer is Δt, between the numerical aperture NA and the wavelength λ of the optical system for recording and / or reproducing the optical recording medium Δt ≦ ± 5.26 (λ / NAFour) (Μm) relationship is established.
[0035]
In the optical recording medium of the present invention, the track pitch P is P ≦ 0.64 (μm), and the skew Θ is Θ ≦ ± 84.115 ° (λ / NA).Three/ T) is preferably satisfied.
[0036]
Further, the optical recording medium of the present invention is preferably recorded or reproduced by a recording / reproducing optical system in which the wavelength λ satisfies λ ≦ 0.68 (μm) and the numerical aperture NA satisfies NA / λ ≧ 1.20. It is preferable to use an optical disk device including a laser light source having a wavelength of 680 (nm) or less and a lens having a numerical aperture NA of 0.7 or more for converging the laser beam on the signal recording surface.
[0037]
In the optical recording medium of the present invention, since a transparent cover layer made of a material having a Young's modulus of 70 (GPa) or higher is formed on one main surface side of the recording layer, the numerical aperture of 0. Even if a collision with the optical pickup occurs when the working distance is narrowed by using seven or more objective lenses and light is irradiated, the occurrence of scratches on the transparent cover layer can be suppressed and the surface of the optical recording medium can be suppressed. The occurrence of scratches is suppressed. Further, in the optical recording medium of the present invention, even when the transparent cover layer is brought into contact with the fibers used in the magnetic disk to remove dust on the surface, generation of scratches on the transparent cover layer can be suppressed. The occurrence of scratches on the surface of the optical recording medium can be suppressed.
[0038]
In the optical recording medium of the present invention, if the thickness of the transparent cover layer is 150 (μm) or less, it can sufficiently cope with an increase in the numerical aperture of the objective lens of the optical pickup.
[0039]
In the optical recording medium of the present invention, if the transparent cover layer is formed by the first layer disposed on the surface side and the second layer disposed on the recording layer side, the surface side can be easily formed. Hardness is high and a transparent cover layer is easily formed.
[0040]
Further, in the optical recording medium of the present invention, the thickness t of the transparent cover layer is set to t = 3 to 177 (μm) in at least an information signal portion area in the recording layer where an information signal is recorded, When the thickness unevenness of the transparent cover layer is Δt, Δt ≦ ± 5.26 (λ / NA) between the numerical aperture NA and the wavelength λ of the optical system for recording and / or reproducing the optical recording medium.Four) (Μm), the track pitch P is P ≦ 0.64 (μm), and the skew Θ is Θ ≦ ± 84.115 ° (λ / NA).Three/ T), and recording or reproducing is performed with a recording / reproducing optical system in which the wavelength λ satisfies λ ≦ 0.68 (μm) and the numerical aperture NA satisfies NA / λ ≧ 1.20. It can sufficiently cope with NA, and the capacity is increased. For example, a recording capacity of 8 (GB) or more is achieved.
[0041]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments of the present invention will be described in detail.
[0042]
The optical recording medium of this example has a transparent cover layer made of a material having a Young's modulus of 70 (GPa) or more on one main surface side of the recording layer, and a numerical aperture of 0.7 or more from the transparent cover layer side. Information is recorded and / or reproduced by irradiating light using the objective lens.
[0043]
As a first example of the optical recording medium of the present invention, an example in which the present invention is applied to a magneto-optical disk will be described.
[0044]
That is, in the magneto-optical disk of this example, a transparent dielectric film such as silicon nitride is formed on one main surface of a transparent substrate, and a magneto-optical recording film such as TbFeCo is formed thereon as a recording layer. A transparent dielectric film such as silicon is formed, a reflective film such as an aluminum film is formed, and a protective film made of an ultraviolet curable resin or the like is further formed.
[0045]
In the magneto-optical disk of this example, since the light is irradiated from the transparent substrate side, the transparent substrate is formed as a transparent cover layer, and the surface side of the transparent substrate is formed of a material having a Young's modulus of 70 (GPa) or more. It will be.
[0046]
In the magneto-optical disk of this example, the thickness of the transparent cover layer, that is, the transparent substrate is 150 (μm) or less.
[0047]
Further, in the magneto-optical disk of the present invention, the transparent cover layer, that is, the surface side of the transparent substrate is C.100-XHX(1 (atomic%) <X <45 (atomic%)), SiThreeNFour, MgF2, Al2OThree, SiO2The Young's modulus is 70 (GPa) or more as described above.
[0048]
In the magneto-optical disk of this example, a transparent substrate made of a material having a Young's modulus of 70 (GPa) or more on the surface side is used as a transparent cover layer, and working is performed using an objective lens having a numerical aperture of 0.7 or more from the transparent cover layer side. Even if a collision with the optical pickup occurs when the distance is reduced and light is irradiated, damage to the transparent cover layer is suppressed, damage to the magneto-optical disk surface is suppressed, and damage is caused. Is less likely to occur and reliability is ensured.
[0049]
Further, in the magneto-optical disk of this example, even when a fiber called a liner used in the magnetic disk is brought into contact with the transparent cover layer, generation of scratches on the transparent cover layer can be suppressed, and the surface of the magneto-optical disk can be suppressed. The occurrence of scratches is suppressed, damage is unlikely to occur, and reliability is ensured. Further, as the above fibers, it is also possible to use a nonwoven fabric made of rayon, polyester, polypropylene, and nylon. In this case, in order to prevent abrasion of the magneto-optical disk and the nonwoven fabric, the transparent cover of the magneto-optical disk is used. The layer surface or the nonwoven fabric surface may be coated with a lubricating material.
[0050]
In the magneto-optical disk of this example, the thickness of the transparent cover layer, i.e., the transparent substrate, is 150 ([mu] m) or less, which is sufficient for increasing the numerical aperture of the objective lens of the optical pickup.
[0051]
In the above-described example, the transparent substrate which is the transparent cover layer is described as a single layer. However, the transparent substrate is a first layer disposed on the front side and a second layer disposed on the recording layer side. In this way, the hardness on the surface side can be easily increased.
[0052]
In this case, the first layer is preferably made of a material having a Young's modulus of 150 (GPa) or higher. If the Young's modulus of the first layer is smaller than 150 (GPa), sufficient hardness can be secured. It is not preferable. Further, the thickness of the first layer is preferably 2 (nm) or more and 230 (nm) or less, and if the thickness of the first layer is less than 2 (nm), it is difficult to ensure strength. If the thickness of the first layer is greater than 230 (nm), the surface reflection becomes too large, which is not preferable.
[0053]
Furthermore, in this example, an example in which the present invention is applied to a magneto-optical disk has been described. It goes without saying that is also applicable.
[0054]
When the transparent cover layer is made of an ultraviolet curable resin made of an acrylic polymer material or the like, the composition of the ultraviolet curable resin is changed, or particles such as glass are mixed in the ultraviolet curable resin. It is possible to increase the hardness of the surface side.
[0055]
Next, as a second example of the optical recording medium of the present invention, an example in which a light transmission layer is applied to an optical disc that is irradiated with light as a transparent cover layer will be described.
[0056]
The optical disk of this example is similar to the magneto-optical disk described above, and has a transparent cover layer made of a material having a Young's modulus of 70 (GPa) or more on the one main surface side of the recording layer. Information is recorded and / or reproduced by irradiating light from the transparent cover layer side using an objective lens having a numerical aperture of 0.7 or more.
[0057]
In the magneto-optical disk of this example, since light is irradiated from the light transmitting layer side, the light transmitting layer is formed as a transparent cover layer, and the surface side of the light transmitting layer is formed of a material having a Young's modulus of 70 (GPa) or more. Will be.
[0058]
Further, in the optical disk of this example, information of about 8 (GB) can be recorded.
[0059]
First, the thickness of the transparent cover layer will be described. In general, there is a correlation between the disc skew margin Θ, the wavelength λ of the recording / reproducing optical system, the numerical aperture NA, and the thickness t of the transparent cover layer. The relationship between these parameters and the skew Θ on the basis of an example of a compact disk (hereinafter referred to as CD) is disclosed in Japanese Patent Laid-Open No. 3-225650.
[0060]
According to this, Θ ≦ ± 84.115 ° (λ / NAThree/ T), which can be applied to the optical recording medium of the present invention, and is also applied to the optical disk of this example.
[0061]
Here, considering a specific limit value of the skew Θ when the disk is actually mass-produced, it is appropriate to set it to 0.4 °. This is because when mass production is considered, if the size is smaller than this, the yield decreases and the cost becomes expensive. The existing optical recording medium is also set to 0.6 ° for CD and 0.4 ° for DVD. In the optical disk of this example, the skew Θ is set to 0.4 ° or less.
[0062]
Accordingly, when calculating how much the thickness of the light transmission layer should be set in order to cope with the shorter wavelength and higher NA of the laser light used for recording and / or reproduction with Θ = 0.4 °, When λ = 0.65 (μm), NA is required to be NA / λ ≧ 1.20 to 0.78 or more. From this, t ≦ 288 (μm) is derived.
[0063]
Further, assuming that the wavelength is further shortened and λ = 0.4 (μm) in the future, and NA remains NA ≧ 0.78, t = 177 (μm) is obtained. In this case, in consideration of diverting a manufacturing facility such as a CD having a substrate thickness of 1.2 (mm), the maximum thickness of the optical disk to which the present invention is applied is about 1.38 (mm).
[0064]
Further, considering the magnetic field modulation of the magneto-optical recording medium (hereinafter referred to as MO), the transparent cover layer is preferably thin, and for example, when it is set to 30 (μm) or less, recording / reproduction with MO becomes easy.
[0065]
On the other hand, the lower limit of the thickness of the transparent cover layer is determined by the protective function of the transparent cover layer that protects the recording film or the reflection film, and 3 (μm) considering the reliability and the impact of the collision of the two-group lens described later. The above is desirable.
[0066]
As described above, it is indispensable to increase NA / λ in order to increase the recording density. In this case, for example, in order to achieve a storage capacity of 8 (GB), it is necessary to set at least NA to 0.7 or more and the laser wavelength λ to 0.68 (μm) or less. At this time, as described above, there is the relationship described above between the thickness of the transparent cover layer and the skew, but considering that it corresponds from the current red laser to the blue laser that is expected to spread in the future. The thickness of the transparent cover layer is suitably set to 3 to 177 (μm).
[0067]
Therefore, in the optical disk of this example, the thickness t of the transparent cover layer is set to 3 to 177 (μm).
[0068]
Next, the track pitch will be described. In order to achieve a recording capacity of 8 (GB) as in the present invention, it is necessary to change the track pitch P and the linear density d. As the condition, the following formulas 2 and 3 may be satisfied.
[0069]
(0.74 / P) × (0.267 / d) × 4.7 ≧ 8 (Expression 2)
d ≦ 0.1161 / P (μm / bit) (Formula 3)
For example, when P = 0.56 (μm), d ≦ 0.206 (μm / bit), which is based on DVD ROM (Read Only Memory), and advances in signal processing technology for recording and reproduction In consideration of (specifically, application of PRML, reduction of ECC redundancy, etc.), an increase in the line density of about 15 (%) is expected, and the track pitch P can be increased accordingly. . From this, it can be derived that the maximum track pitch P is 0.64 (μm).
[0070]
Therefore, in the optical disc of this example, the track pitch P is set to P ≦ 0.64 (μm).
[0071]
Further, in the optical disc of this example, the tolerance for the track pitch unevenness ΔP also becomes severe. If the recording / reproducing parameters of CD and DVD are directly used, ΔP ≦ ± 0.03P / 0.74 = ± 0.04P from the DVD pitch of 0.74 (μm) and the tolerance of ± 0.03. Therefore, if P = 0.56, ΔP ≦ ± 0.023 (μm).
[0072]
Therefore, in the optical disc of this example, the track pitch unevenness ΔP is set to ΔP ≦ ± 0.04P.
[0073]
Next, the uneven thickness of the transparent cover layer will be described. In the optical disc of this example, higher accuracy is required for the thickness variation Δt of the transparent cover layer.
[0074]
When the thickness of the transparent cover layer deviates from the design center of the reproduction objective lens, the amount of aberration given to the spot by the thickness error is proportional to the fourth power of NA and to the wavelength. Therefore, when increasing the density by increasing the NA or shortening the wavelength, the amount (transparent cover layer thickness unevenness) is more severely limited.
[0075]
When a CD is given as a specific system example, NA = 0.45 is practically used for the CD, and the thickness error standard of the transparent cover layer is ± 100 (μm). In DVD, NA = 0.6 and ± 30 (μm) is specified. That is, the uneven thickness Δt of the transparent cover layer is expressed by the following formula 4 on the basis of an allowable amount ± 100 (μm) in CD.
[0076]
Here, as a result of experiments on the relationship between the transparent cover layer thickness error and the jitter value at the wavelength λ = 0.68 (μm) and NA = 0.875 with respect to the center of the transparent cover layer thickness 100 (μm). Is shown in FIG.
[0077]
From FIG. 1, it can be seen that, for example, in the DVD, when the jitter reference is 8 (%) when there is no perturbation such as skew, it is about ± 7 (μm). The numerical value derived from the above equation is ± 6 (μm), and a good signal can be obtained from a disk medium satisfying this standard.
[0078]
Therefore, as the density increases, the unevenness Δt allowed for the thickness of the transparent cover layer is ± 5.26 × (λ / NAFour) (Μm) or less.
[0079]
Therefore, in the optical disc of this example, when the thickness variation of the transparent cover layer is Δt, Δt ≦ ± 5... Between the numerical aperture NA and the wavelength λ of the optical system for recording and / or reproducing the optical disc. 26 (λ / NAFour) (Μm).
[0080]
Next, the surface roughness Ra of the surface irradiated with the recording and / or reproducing light will be described. The uneven thickness of the transparent cover layer described above is assumed to be uniform within the disk surface irradiated with the laser beam for recording and / or reproduction, and aberrations can be corrected by shifting the focus point. However, if there is uneven thickness of the transparent cover layer in this region (in the spot), it cannot be corrected by adjusting the focus point. This amount needs to be suppressed to ± 3λ / 100 or less with respect to the thickness center value.
[0081]
Therefore, in the optical disk of this example, the surface roughness Ra of the surface irradiated with the recording and / or reproducing light is set to ± 3λ / 100 or less in the spot size region on the surface.
[0082]
Next, eccentricity will be described. Regarding the eccentricity E, E ≦ 50 × P / 0.74 = 67.57 P (μm) with respect to 50 (μm) of DVD.
[0083]
Therefore, in the optical disc of this example, the eccentricity E is set to E ≦ 67.57 P (μm).
[0084]
That is, in the optical disc of this example, the thickness t of the transparent cover layer in the area of the information recording section where at least the information signal is recorded is 3 to 177 (μm), and the thickness variation Δt of the transparent cover layer and the optical disc are Between the numerical aperture NA and the wavelength λ of the optical system for recording and / or reproducing, Δt ≦ ± 5.26 (λ / NAFour) (Μm), track pitch P is set to P ≦ 0.64 (μm), track pitch unevenness ΔP is set to ΔP ≦ ± 0.04P, and linear density d is set to d ≦ 0.1161 / P (μm / bit), and the disk skew θ is θ ≦ ± 84.115 ° (λ / NA)Three/ T), the eccentricity E is E = 67.57 P (μm), the surface roughness Ra within the spot size region is Ra = ± 3λ / 100 or less, and the recording / reproducing optical system has a wavelength λ of λ ≦≦ By satisfying NA / λ ≧ 1.20, which is 0.68 (μm), a recording capacity of 8 (GB) is secured to achieve high density.
[0085]
In order to manufacture the optical disk of this example, a substrate is formed by an injection molding method using a stamper that realizes the pitch and pitch unevenness satisfying the specifications necessary for the optical recording medium of the present invention described above. Such a high-precision stamper with little pitch unevenness is difficult to achieve with a conventional structure in which the feed is performed with a screw, and is thus manufactured with a master exposure apparatus having a feed structure with a linear motor. Further, the optical system is covered with a cover for eliminating air fluctuations, and is created by installing a vibration isolating material between the laser and the exposure apparatus in order to remove the vibration of the cooling water of the exposure laser.
[0086]
In the case of this example, a reflective film or a recording film is formed on the information signal surface of the substrate, and recording / reproduction is performed from the upper side. It is necessary to form pits.
[0087]
For example, in the case of a ROM of 10 (GB) capacity, if the asymmetry of the signal pit when viewed from the substrate side is 25 (%), the asymmetry when viewed from the opposite side of the substrate is 10 (%). . That is, in this example, in order to read a signal from the side opposite to the substrate side, for example, in order to form a pit having an asymmetry of 10 (%) when viewed from the light irradiation side, the pit shape formed on the substrate is set asymmetry. It is necessary to keep it at 25 (%).
[0088]
Similarly, with respect to the guide groove formed on the recording disk, the groove becomes narrower when the groove duty is changed by the recording film, for example, in the case of groove recording (recording / reproducing into the recess as viewed from the recording / reproducing surface), the stamper It is necessary to take measures such as widening the shape of the. For example, in the case of land / groove recording, in order to obtain a land / groove width duty 50 (%) as seen from the light irradiation side, it is preferable to set it to 55 to 65 (%) as seen from the substrate side.
[0089]
It should be noted that this substrate is desirably 0.6 (mm) or more because a certain degree of rigidity is required when a disk is constituted by a single plate. Similarly, in the case of a structure in which two sheets are bonded, it is preferable that the thickness is 0.3 (mm) or more, which is a half of the structure.
[0090]
Next, as shown in FIG. 2, an information recording film or a reflective film is formed on the information signal portion 11 of the substrate 10 to form a recording layer. At this time, the substrate 10 becomes a support layer. For example, when the disk is a ROM, a reflective film such as Al is formed with a thickness of 20 to 60 (nm).
[0091]
As an information recording film, for example, when a phase change material is taken as an example, an Al film, ZnS-SiO2, GeSbTe, ZnS-SiO2Are formed in this order.
[0092]
In the case of a magneto-optical disk, an Al film, SiN, TbFeCo, and SiN are formed in this order.
[0093]
In the case of the write-once type, after sputtering Au or Al, a cyanine or phthalocyanine organic dye film is applied by spin coating and dried.
[0094]
In the example of FIG. 2, the recording / reproducing light is irradiated through the recording / reproducing objective lens L from the side opposite to the substrate 10.
[0095]
Next, as shown in FIG. 3, a transparent cover layer 12 is further formed thereon with an ultraviolet curable resin. For example, the transparent cover layer 12 is created by dropping and stretching an ultraviolet curable resin on the film forming surface of the substrate 10 formed in any structure formed as described above.
[0096]
As the viscosity of the ultraviolet curable resin, a viscosity of 300 (cps) or more and 6000 (cps) or less is suitable for forming the above-described thickness.
[0097]
For example, when an ultraviolet curable resin having a viscosity of 5800 (cps) at 25 (° C.) is applied, after the ultraviolet curable resin is dropped on the substrate, the substrate is rotated at 2000 (rpm) for 11 seconds. Finally, the transparent cover layer 12 of about 100 (μm) can be formed.
[0098]
Here, when the transparent cover layer 12 is formed, when an ultraviolet curable resin is dropped onto the inner peripheral portion of the substrate 10, for example, at a radius of 25 (mm), and rotated and stretched, the thickness increases due to the relationship between centrifugal force and viscous resistance. There is a difference between the inner and outer circumferences. This amount can be 30 (μm) or more and cannot meet the described thickness range.
[0099]
In order to avoid this, it is effective to drop the ultraviolet curable resin while the center hole 13 of the substrate 10 is filled with some means. For example, a polycarbonate sheet with a thickness of 0.1 (mm) is processed into a circular shape with a diameter Φ of 30 (mm) and bonded to the center of the substrate 10, and then an ultraviolet curable resin is dropped from the center and rotated. A method of stretching, irradiating ultraviolet rays to cure the ultraviolet curable resin, and then punching out the central hole is conceivable. According to this process, it is possible to obtain a light transmission layer having a thickness within an inner and outer circumference difference of 10 (μm) pp (peak to peak).
[0100]
In addition, since it is considered that the transparent cover layer 12 protrudes to the outer periphery of the disk, the diameter of the disk is 120 (mm) +5 (mm) on the basis of the diameter of a CD or the like (120 (mm)). The maximum value is desirable.
[0101]
As shown in FIG. 4, for example, the transparent cover layer 12 may be formed by bonding a polycarbonate sheet 14 having a thickness of 100 (μm) with an ultraviolet curable resin 15. In this case, the sum of the thickness unevenness of the sheet 14 and the thickness unevenness of the UV curable resin 15 for adhesion may be 10 (μm) pp (peak to peak) or less.
[0102]
For example, the sheet 14 processed to have the same diameter as the substrate 10 is placed on the substrate 10 via the UV curable resin 15 for bonding and rotated and stretched, so that the sheet 14 becomes a weight of the UV curable resin 15. Thus, an ultrathin UV curable resin layer is formed, and the total thickness unevenness can be reduced to 10 (μm) pp (peak to peak) or less.
[0103]
The present invention provides an optical recording medium having a multilayer structure in which a second recording layer 18 is formed on an intermediate layer 16 on a first recording layer 17 formed on a substrate 10 as shown in FIG. Can also be applied.
[0104]
In the case of the optical disk having the above-described configuration, skew is likely to occur. In the present invention, in order to reduce the skew, as shown in FIG. 6, an ultraviolet curable resin is used as a skew correction member 19 on the surface of the substrate 10 opposite to the surface on which the transparent cover layer 12 is formed. It is effective to apply.
[0105]
In this case, the skew correction member 19 may be formed by coating with the same material as the transparent cover layer 12, or a material having a higher curing shrinkage than the ultraviolet curable resin that is the material of the transparent cover layer 12 is made thinner. It may be formed by coating.
[0106]
In order to record / reproduce the high density optical disc as described above, a pickup having a high NA objective lens described later is required. In this case, as described above, it is desirable that the distance between the objective lens and the disk surface and the working distance be narrower than the conventional distance.
[0107]
In this case, it is expected that the objective lens collides with the disk surface and damages the disk surface.
[0108]
In order to prevent this, a hard coat (pencil hardness H or higher) is formed on the transparent cover layer 12 as shown in FIG. 7 in order to make the surface side hardness of the transparent cover layer relatively high as in the example described above. 20 may be considered. Further, as the thickness of the transparent cover layer 12 decreases, the hard coat 20 may be provided with an antistatic function because it is easily affected by dust. This antistatic can prevent dust from being adsorbed on the optical disk surface.
[0109]
Further, in the optical disk of this example, when the wavelength of the light for recording and / or reproduction is 780 (nm), the in-plane birefringence amount of the transparent cover layer is an average of 15 (nm) or less in the round trip, The variation is preferably 15 (nm) pp (peak to peak) or less.
[0110]
In the optical disk of this example, a recording / reproduction experiment was conducted when a transparent cover layer was formed using, for example, a polycarbonate sheet having a thickness of 100 (μm) and the recording layer was a phase change film. In this case, jitter 8 (%) was obtained at a linear density of 0.21 (μm / bit). Further, the birefringence amount of such an optical disk was measured. The measurement results are shown in FIG. In FIG. 23, the horizontal axis indicates the radial position (mm), and the vertical axis indicates the birefringence amount (nm). In FIG. 23, the distribution is displayed as vertical line segments, and the position of the horizontal line segment crossing each line segment is an average value. The amount of birefringence could average 15 (nm) or less in the round trip, and the fluctuation in the circumference could be 15 (nm) pp (peak-to-peak) or less.
[0111]
Further, in the optical disk of this example, the same applies when the transparent cover layer is formed by applying a liquid photocurable resin on the information recording layer, rotating and then photocuring, and the recording layer is a phase change film. A recording / reproducing experiment was conducted.
[0112]
In this case, jitter 7 (%) was obtained at a linear density of 0.21 (μm / bit). Further, the birefringence amount of such an optical disk was measured. The measurement results are shown in FIG. In FIG. 24, the horizontal axis indicates the radial position (mm), and the vertical axis indicates the birefringence amount (nm). In FIG. 24, the distribution is displayed as vertical line segments, and the horizontal line segment positions crossing each line segment are average values. This amount of birefringence can be further reduced as compared with the case where the transparent cover layer is formed of a polycarbonate sheet. The average of reciprocation is 5 (nm) or less, and the fluctuation in the circumference is 5 (nm) pp (peak to peak). Peak) or less.
[0113]
Thus, it can be seen that the optical disk of this example has stable and excellent characteristics even when compared with the conventional CD or DVD having an in-plane birefringence of 100 (nm).
[0114]
In the optical recording medium of the present invention, the recording layer forming surface may be subjected to silane treatment. By performing the silane treatment in this manner, the adhesion between the ultraviolet curable resin forming the transparent cover layer and the surface of the recording layer can be improved.
[0115]
In the optical recording medium of this example, an antireflection film may be formed on the surface of the transparent cover layer by a method such as sputtering.
[0116]
The refractive index N of the antireflection film is preferably lower than the refractive index of the transparent cover layer, and the thickness of the antireflection film is such that the wavelength of light for recording and / or reproduction is λ. In this case, it is desirable to set it to (λ / 3) / N (nm) or less, more preferably (λ / 4) / N (nm).
[0117]
When the NA is high as in the optical recording medium of this example, the incident angle of the recording / reproducing light for recording and / or reproducing is also increased, so that the reflection of light on the surface of the transparent cover layer cannot be ignored.
[0118]
For example, when NA = 0.45, the incident angle of the recording / reproducing light is 26.7 °, and when NA = 0.6, it is 36.9 °.
[0119]
When NA = 0.8, the incident angle of the recording / reproducing light is also 53.1 °. It has been confirmed that the light reflectance at the surface of the transparent cover layer depends on the incident angle of the recording / reproducing light. When the refractive index of the transparent cover layer is 1.52, for example, The surface reflectance exceeds 15 (%). (Refer to page 168 of “Laser and Optics Guide” published by Kinomeres Grio Co., Ltd.) In this case, there arises a problem of loss of light quantity and a decrease in effective NA.
[0120]
For this reason, in order to avoid such a problem, it is effective to form an antireflection film on the surface of the transparent cover layer.
[0121]
As a material for the antireflection film, it is known that it is ideal to use a material having an optical refractive index of about 1.23 when the refractive index of the transparent cover layer is 1.52. Kyoritsu Publishing Optical Technology Series 11 Optical thin film (see page 28). However, industrially, for example, MgF2Is used. MgF2Has a refractive index N of 1.38.
[0122]
When the wavelength of the recording / reproducing light is 650 (nm), MgF2It can be seen that the thickness of the antireflection film is preferably formed to a thickness of about 120 (nm) by substituting each numerical value into the formula (λ / 4) / N (nm).
[0123]
By the way, the amount of reflection of light on the surface of the transparent cover layer is (λ / 4) / N (when the thickness of the antireflection film is decreased from zero to (λ / 4) / N (nm). nm), it is confirmed that the minimum value is obtained. On the other hand, when the thickness of the antireflection film exceeds (λ / 4) / N (nm), the amount of reflected light increases, and may be maximized when it reaches (λ / 2) / N (nm). It has been confirmed. From this, it was confirmed that the thickness of the antireflection film should be not more than (λ / 3) / N (nm) practically in consideration of the film forming technique industrially.
[0124]
As described above, when the antireflection film is formed on the surface of the transparent cover layer, for example, MgF as an antireflection film on the transparent cover layer having a refractive index of 1.52.2Is formed in a single layer with a thickness of (λ / 4) / N (nm), and when a recording / reproducing light having a wavelength of 550 (nm) is used, the incident angle of the recording / reproducing light is up to about 60 °. Can prevent a reduction in light quantity of 50% or more (see page 174 of “Laser and Optics Guide” published by Kinomeres Grio Co., Ltd.).
[0125]
The present invention is not limited to a single-plate disc, but an optical recording medium having a structure in which two substrates 51 and 52 having a half thickness of the finally obtained substrate 10 are bonded as shown in FIG. It can also be applied to (optical disc). In this case, since a transparent cover layer having a maximum thickness of 170 (μm) is formed and bonded to the substrates 51 and 52 having a thickness of 0.6 (mm), the thickness of the disk is (0.6 + 0.17) × 2 + ( If the thickness of the adhesive layer is 0.06 (mm), the thickness of the optical disk is 1.60 (mm). Further, as shown in FIG. 9, the present invention can also be applied to an optical recording medium (optical disk) having a structure in which an information signal portion and a transparent cover layer 12 are provided on both surfaces of a single substrate 50.
[0126]
An example of manufacturing the above optical disc will be described. As shown in FIG. 10, a polycarbonate sheet 40 having a thickness of, for example, 100 (μm) prepared by extrusion molding or a casting method is prepared, and a stamper 41 heated to a temperature higher than the glass transition point is attached to a roller 42. Crimp by applying pressure. The pressure in this case can be 280 (Kgf), for example.
[0127]
By this operation, the information pits or guide grooves of the stamper 41 are transferred to the sheet 40 as shown in FIG. And after cooling this, a sheet | seat is peeled from the stamper 41 and the thin board | substrate 43 of thickness (100 micrometers) is formed, for example.
[0128]
Subsequently, in the same manner as in the manufacturing method described above, a recording film or a reflective film can be formed to finally obtain a thin optical recording medium.
[0129]
In addition, an optical recording medium having a multilayer structure can be manufactured using the thin plate substrate 43 shown in FIG.
[0130]
In this case, first, as shown in FIG. 12, the liquid ultraviolet curable resin 60 is dropped on the stamper 141, and the thin substrate 43 shown in FIG. 11 is placed with the recording layer side in contact with the liquid ultraviolet curable resin 60. To do.
[0131]
Then, as shown in FIG. 13, the liquid ultraviolet curable resin 60 is stretched by rotating the stamper 141 on which the thin plate substrates 43 are superposed while being arranged on the rotary base 61 via the liquid ultraviolet resin 60. Then, the required thickness is set to 20 (μm), for example, and thereafter ultraviolet light is irradiated from the thin plate substrate 43 side by a lamp 62 as shown in FIG. 14 to photocur the liquid ultraviolet curable resin 60.
[0132]
Subsequently, as shown in FIG. 15, the thin plate substrate 43 and the photocured ultraviolet curable resin 60 having a thickness of, for example, 20 (μm) are integrally peeled from the stamper 141.
[0133]
As described above, a recording layer can be formed by depositing, for example, a metal thin film such as a Si compound, Al, or Au on the fine irregularities transferred to the ultraviolet curable resin 60 by the stamper 141.
[0134]
Further, by repeating the steps described with reference to FIGS. 12 to 15, an optical disc in which three or more information recording films or reflective films and a transparent cover layer are laminated can be manufactured.
[0135]
Then, as shown in FIG. 16, for example, the substrate 10 obtained by injection molding is bonded to the finally obtained recording layer at an interval of, for example, 20 (μm) through the ultraviolet curable resin 60. An optical disk with high rigidity can be obtained.
[0136]
In addition, as shown in FIG. 17, a thin reflective optical disk having a multilayer structure is formed by forming a highly reflective film 70 of, for example, Al, Au or the like on the finally obtained recording layer and further forming a protective film 71. Can be produced.
[0137]
In this case, when the number of recording layers is N, the thickness of the finally obtained optical disk is, for example, 100 (μm) the thickness of the thin plate substrate 43 and N times the ultraviolet curable resin layer between the respective layers. And the sum of the thicknesses of the highly reflective film 70 and the protective film 71, for example, 5 (μm). That is, for example, when the thickness of the ultraviolet curable resin layer between each layer is 20 (μm) and the thickness of the high reflection film 70 and the protective film 71 is 5 (μm), an optical disk having a four-layer structure is manufactured. As a result, the thickness of the entire optical disc is 185 (μm).
[0138]
However, since the optical disk obtained in this way is very low in rigidity, a flexible optical disk is flattened by attaching a thick plate having rigidity to the thin substrate 43 side, or by high-speed rotation during recording and reproduction. Therefore, it is necessary to devise such as recording and reproduction using the above.
[0139]
The numerical value of 20 (μm) in the example of the thickness between the recording layers described above is determined by the number of layers of the optical disk finally obtained and the movable distance of the pickup lens for recording and reproducing the optical disk.
[0140]
For example, when the movable distance of the lens, that is, the distance between the second group lenses is 50 (μm), the substrate 10 and the thin plate substrate 43 are placed at an interval of 50 (μm) with an ultraviolet curable resin as shown in FIG. In addition, when an optical disk having a three-layer structure is manufactured as shown in FIG. 19, a recording layer is formed between the thin plate substrate 43 and the substrate 10 with a spacing of 25 (μm). do it.
[0141]
In addition to the optical disk having the structure described above, the present invention includes, as shown in FIG. 20, a thin plate substrate 43 and a disk-shaped substrate 50 having a thickness of, for example, 1.1 (mm) prepared by injection molding, for example. The present invention can also be applied to an optical disk that is bonded and bonded via an ultraviolet curable resin and bonded by irradiating ultraviolet rays from the transparent substrate side.
[0142]
Furthermore, in the present invention, as shown in FIG. 21, a substrate 50 on which fine irregularities forming recording layers on both sides are transferred by injection molding and a thin substrate 43 are bonded together via an ultraviolet curable resin. The present invention can also be applied to an optical disc having a four-layer structure that is bonded and bonded by irradiating ultraviolet rays from the thin plate substrate 43 side.
[0143]
Next, the depth of pits or grooves formed on the substrate will be described. Hereinafter, the refractive index of the transparent cover layer is N.
[0144]
The depth of the pit or groove that can obtain the highest degree of modulation is (λ / 4) / N, and the ROM or the like is set to this depth.
[0145]
In addition, in groove recording or land recording, when a tracking error signal is to be obtained by push-pull, the push-pull signal becomes maximum when the pit or land depth is (λ / 8) / N.
[0146]
Further, in the land / groove recording, the groove depth should consider the characteristics of the crosstalk and the cross erase as well as the characteristics of the servo signal. Experimentally, the crosstalk is (λ / 6) / N or (λ / 3) It is minimized near / N, and it has been confirmed that the deeper the cross erase, the less the influence. In addition, considering both the groove inclination and the like to satisfy both characteristics, (3λ / 8) / N is optimal in the vicinity. In the present invention, the depth of the pit or groove is preferably within the above range.
[0147]
Next, a description will be given of an example of a lens that can be applied to the optical disk device of the present invention to realize a suitable high NA. FIG. 22 shows a lens configuration for realizing a high NA.
[0148]
That is, the second lens 32 is disposed between the first lens 31 and the optical disc 21. In this way, by using the two-group lens configuration, the NA can be increased to 0.7 or more, and the distance (WD) between the first surface 32a of the second lens 32 and the surface of the optical disc 21 is set. Can be narrowed.
[0149]
The first surface 31a, the second surface 31b, the third surface 32a, and the fourth surface 32b of the first lens 31 and the second lens 32 are preferably aspherical.
[0150]
In the optical disk device using the two-group lens, it is possible to perform high-density recording / reproduction of the optical disk described above.
[0151]
【Example】
Next, in order to confirm the effect of the present invention, the following experiment was conducted.
[0152]
Experimental example 1
In this experimental example, the relationship between the Young's modulus of the material forming the surface side of the transparent cover layer and the ease of occurrence of scratches was investigated.
[0153]
That is, various optical recording media having a radius of 60 (mm) are prepared as optical recording media, and dust JIS-15 defined by the JIS standard on the surface of the transparent substrate or light transmission layer serving as a transparent cover layer of the optical recording medium. A small amount of was placed. Then, a polyester fiber is put on top of this and 0.2 (g / cm2) With the pressure of), and rotated for 1 minute at a rotational speed of 1800 (rpm), and the degree of occurrence of scratches at a position of a radius of 40 (mm) was visually observed.
[0154]
In addition, as the optical recording medium, a transparent cover layer made of polycarbonate and a transparent cover layer made of an ultraviolet curable resin are prepared, and the transparent cover layer made of polycarbonate is made of polycarbonate having a thickness of 100 (μm). What formed the film, what formed the film which consists of a 100-micrometer-thick ultraviolet curable resin on the transparent cover layer which consists of ultraviolet curable resin, and thickness 50 which formed on the transparent cover layer which consists of ultraviolet curable resin (Nm) CH (amorphous hydrogenated carbon) formed by CVD, SiThreeNFour, MgF2, Al2OThree, SiO2Were prepared by sputtering. That is, as a result, the transparent cover layer is constituted by the first layer disposed on the surface side and the second layer disposed on the recording layer side.
[0155]
The results are shown in Table 1.
[0156]
[Table 1]
[0157]
In Table 1, the first layer forming material, the first layer thickness, the first layer forming material Young's modulus, the first layer forming material pencil hardness, the second layer forming material, and the degree of scratches are shown. It will be shown together. However, the Young's modulus indicates the Young's modulus in the bulk state, and the pencil hardness is shown to represent the hardness of the ultraviolet curable resin for which accurate Young's modulus cannot be measured. The pencil hardness indicates the hardness when cured on a glass substrate.
[0158]
From the results shown in Table 1, it can be seen that an optical recording medium in which the first layer on the surface side is formed of a soft material such as polycarbonate or an ultraviolet curable resin, shows very many scratches. However, among these, the occurrence of scratches is suppressed in the optical disk in which the first layer is formed of an ultraviolet curable resin having a relatively high hardness, and the hardness on the surface side of the transparent cover layer causes the scratches. It is understood that it is greatly involved in.
[0159]
Further, from the results of Table 1, the first layer on the surface side is made of SiO having a Young's modulus of 70 (GPa) or more.2, MgF2In the optical recording medium formed by the above, scratches are considerably suppressed, and the first layer on the surface side is made of Al with a Young's modulus of 150 (GPa) or more.2OThree, SiThreeNFour, CH (amorphous hydrogenated carbon) shows that no scratches are generated in the optical recording medium. This seems to be because the surface hardness is sufficiently hard.
[0160]
That is, if the Young's modulus on the surface side of the transparent cover layer is formed of a material of 70 (GPa) or more as in the present invention, the occurrence of scratches on the surface side of the transparent cover layer can be suppressed, and the surface of the optical recording medium can be prevented. It was confirmed that the generation of scratches was suppressed, damage was unlikely to occur, and reliability was ensured.
[0161]
Further, as in the present invention, the transparent cover layer is formed of the first layer disposed on the surface side and the second layer disposed on the recording layer side, and the first layer has a Young's modulus of 150 (GPa) or more. If formed from this material, the generation of scratches on the surface side of the transparent cover layer is further suppressed, the generation of scratches on the optical recording medium surface is further suppressed, damage is less likely to occur, and reliability is further ensured. Was confirmed.
[0162]
Furthermore, the surface side of the transparent cover layer is C as in the present invention.100-XHX(1 (atomic%) <X <45 (atomic%)), SiThreeNFour, MgF2, Al2OThree, SiO2It was confirmed that the hardness of the surface side of the transparent cover layer can be easily improved if it is formed of a material containing at least one of the above.
[0163]
Experimental example 2
In this experimental example, the relationship between the thickness of the first layer on the surface side of the transparent cover layer and the likelihood of scratches, and the relationship between the thickness of the first layer on the surface side of the transparent cover layer and the reflectance. investigated.
[0164]
That is, an optical recording medium having a diameter of 60 mm and a transparent cover layer made of an ultraviolet curable resin is prepared in the same manner as in Experimental Example 1, and SiO 2 is formed on the transparent cover layer made of an ultraviolet curable resin.2On the transparent cover layer made of an ultraviolet curable resin, each of which is formed with a thickness of 1 (nm), 2 (nm), 10 (nm), 50 (nm), and 200 (nm) by sputtering. SiThreeNFourA film having a thickness of 1 (nm), 2 (nm), 10 (nm), and 50 (nm) was prepared.
[0165]
Then, the ease of occurrence of scratches on these optical recording media was investigated in the same manner as in Experimental Example 1. The results are shown in Table 2.
[0166]
[Table 2]
[0167]
In Table 2, the first layer forming material, the first layer thickness, the second layer forming material, and the degree of scratches are also shown.
[0168]
From the results in Table 2, it can be seen that the greater the thickness of the first layer, the less the occurrence of scratches, regardless of the type of the first layer forming material. The first layer forming material is SiThreeNFourIt can be seen that the effect is obtained when the thickness of the first layer is 2 (nm).
[0169]
By the way, the first layer thickness has an upper limit due to optical problems as well as film formation time.
[0170]
That is, since the first layer and the second layer having different refractive indexes are overlapped, the reflected light at the boundary between the atmosphere and the first layer and the reflected light at the boundary between the first layer and the second layer Interference, the reflectivity becomes very high at a certain thickness, and the amount of light reaching the recording layer is reduced. This is because problems such as a decrease in the level of the reproduction signal and a lack of recording power may occur.
[0171]
Therefore, the refractive index of the transparent cover layer with respect to the atmosphere was fixed at 1.52, and the change in reflectance with respect to light having a wavelength of 640 (nm) when the first layer thickness was changed was obtained by calculation. The first layer is MgF2, SiO2, Al2OThree, CH, SiThreeNFourIt was decided to form by each. The results are shown in FIG. In FIG. 25, the horizontal axis indicates the first layer thickness, the vertical axis indicates the reflectance, and x in the figure indicates MgF.2In the figure, ○ indicates SiO2△ in the figure indicates Al2OThreeIn the figure, ◎ indicates the result of CH, and □ in the figure indicates Si.ThreeNFourThe results are shown.
[0172]
The refractive index of each material is MgF21.38, SiO21.46, Al2OThree1.60, CH 1.80, SiThreeNFourIs 2.00.
[0173]
Moreover, the refractive index with respect to the light of wavelength 640 (nm) when the refractive index with respect to the air | atmosphere of a transparent cover layer was fixed to 1.38, and 1st layer thickness was changed was calculated | required. The first layer is SiO2, Al2OThree, CH, SiThreeNFourIt was decided to form by each. The results are shown in FIG. In FIG. 26, the horizontal axis indicates the first layer thickness, the vertical axis indicates the reflectance, and in the figure, ○ indicates SiO.2△ in the figure indicates Al2OThreeIn the figure, ◎ indicates the result of CH, and □ in the figure indicates Si.ThreeNFourThe results are shown.
[0174]
From the results of FIGS. 25 and 26, CH, Si having a high refractive index.ThreeNFourIt can be seen that the reflectance becomes 10 (%) or more depending on the thickness of the first layer. The reflectance of a normal transparent substrate made of polycarbonate is about 5 (%), and the reproduction signal level is 0.95 × 0.95 = 0.90 compared to the case where there is no surface reflection due to surface reflection. If the permissible amount is 10 (%) lower than the conventional value of 0.9, the surface reflectance is allowed up to 10 (%).
[0175]
In order to satisfy this condition, when the refractive index of the first layer forming material is 1.65 or less, or when the refractive index of the first layer forming material is larger than 1.65, for example, the refractive index is 2. In the case of 0, the first layer thickness needs to be 30 (nm) or less, or 130 (nm) or more and 190 (nm) or less.
[0176]
However, in the case of using a material having a refractive index in the range of the refractive index of the material used in this experimental example, the above-mentioned change in surface reflectance and the greater the thickness, the higher the strength. When considered together, the upper limit of the thickness is considered to be about 230 (nm). If the thickness is greater than this, there is a concern that the surface reflectance will not be an allowable value due to thickness fluctuations when a material with a high refractive index is used, and it is not preferable because the film formation time becomes impractical. .
[0177]
That is, from the result of this experimental example, in the optical recording medium of the present invention, when the transparent cover layer is formed by the first layer disposed on the surface side and the second layer disposed on the recording layer side, It was confirmed that the thickness of the first layer is preferably 2 (nm) or more and 230 (nm) or less.
[0178]
【The invention's effect】
As is clear from the above description, in the optical recording medium of the present invention, a transparent cover layer made of a material having a Young's modulus of 70 (GPa) or more is formed on one main surface side of the recording layer. Even if a collision with the optical pickup occurs when the working distance is narrowed by using an objective lens having a numerical aperture of 0.7 or more from the transparent cover layer side and light is irradiated, scratches on the surface of the transparent cover layer occur. Generation is suppressed, generation of scratches on the surface of the optical recording medium is suppressed, damage is unlikely to occur, and reliability is ensured.
[0179]
Further, in the optical recording medium of the present invention, even when a fiber such as that used in a magnetic disk is brought into contact with the transparent cover layer, generation of scratches on the transparent cover layer is suppressed, and scratches on the surface of the optical recording medium are suppressed. Occurrence is suppressed, damage is unlikely to occur, and reliability is ensured.
[0180]
In the optical recording medium of the present invention, if the thickness of the transparent cover layer is 150 (μm) or less, it can sufficiently cope with an increase in the numerical aperture of the objective lens of the optical pickup.
[0181]
In the optical recording medium of the present invention, if the transparent cover layer is formed by the first layer disposed on the surface side and the second layer disposed on the recording layer side, the surface side can be easily formed. Hardness is high and a transparent cover layer is easily formed.
[0182]
Further, in the optical recording medium of the present invention, the thickness t of the transparent cover layer is set to t = 3 to 177 (μm) in at least an information signal portion area in the recording layer where an information signal is recorded, When the thickness unevenness of the transparent cover layer is Δt, Δt ≦ ± 5.26 (λ / NA) between the numerical aperture NA and the wavelength λ of the optical system for recording and / or reproducing the optical recording medium.Four) (Μm), the track pitch P is P ≦ 0.64 (μm), and the skew Θ is Θ ≦ ± 84.115 ° (λ / NA).Three/ T), and recording or reproducing is performed with a recording / reproducing optical system in which the wavelength λ satisfies λ ≦ 0.68 (μm) and the numerical aperture NA satisfies NA / λ ≧ 1.20. It can sufficiently cope with NA, and the capacity is increased. For example, a recording capacity of 8 (GB) or more is achieved. Further, the optical recording medium of the present invention can be increased in capacity as compared with the conventional one with a simple recording / reproducing apparatus.
[Brief description of the drawings]
FIG. 1 shows a relationship between changes in jitter value due to thickness error of a transparent cover layer.
FIG. 2 is a schematic cross-sectional view of an essential part schematically showing a state where a recording layer is formed on a substrate.
FIG. 3 is a schematic cross-sectional view of an essential part schematically showing an example of an optical disc to which the present invention is applied.
FIG. 4 is a schematic cross-sectional view of an essential part schematically showing another example of an optical disc to which the present invention is applied.
FIG. 5 is a schematic cross-sectional view of an essential part schematically showing still another example of an optical disc to which the present invention is applied.
FIG. 6 is a schematic cross-sectional view of an essential part schematically showing still another example of an optical disc to which the present invention is applied.
FIG. 7 is a schematic cross-sectional view of an essential part schematically showing still another example of an optical disc to which the present invention is applied.
FIG. 8 is a schematic cross-sectional view of an essential part schematically showing still another example of an optical disc to which the present invention is applied.
FIG. 9 is a schematic cross-sectional view of an essential part schematically showing still another example of an optical disc to which the present invention is applied.
FIG. 10 is a side view schematically showing a step of pressure-bonding a sheet to a stamper.
FIG. 11 is a side view showing a process of preparing a thin plate substrate.
FIG. 12 is a cross-sectional view schematically showing a process of disposing a thin plate substrate on a stamper via an ultraviolet curable resin.
FIG. 13 is a cross-sectional view schematically showing a process of stretching an ultraviolet curable resin.
FIG. 14 is a cross-sectional view schematically showing a step of curing an ultraviolet curable resin.
FIG. 15 is a cross-sectional view schematically showing a process of peeling from a stamper.
FIG. 16 is a schematic cross-sectional view of an essential part schematically showing still another example of an optical disc to which the present invention is applied.
FIG. 17 is a schematic cross-sectional view of an essential part schematically showing still another example of an optical disc to which the present invention is applied.
FIG. 18 is a schematic cross-sectional view of an essential part schematically showing still another example of an optical disc to which the present invention is applied.
FIG. 19 is a schematic cross-sectional view of an essential part schematically showing still another example of an optical disc to which the present invention is applied.
FIG. 20 is a schematic cross-sectional view of an essential part schematically showing still another example of an optical disc to which the present invention is applied.
FIG. 21 is a schematic cross-sectional view of an essential part schematically showing still another example of an optical disc to which the present invention has been applied.
FIG. 22 is an enlarged view showing a two-group lens used in an optical disk device for recording / reproducing an optical disk to which the present invention is applied.
FIG. 23 shows an example of the measurement result of the birefringence amount of the transparent cover layer of the optical disc to which the present invention is applied.
FIG. 24 shows another example of the measurement result of the birefringence amount of the transparent cover layer of the optical disc to which the present invention is applied.
FIG. 25 is a characteristic diagram showing an example of the relationship between the first layer thickness and the reflectance.
FIG. 26 is a characteristic diagram showing another example of the relationship between the first layer thickness and the reflectance.
[Explanation of symbols]
10, 50, 51, 52 Substrate, 11 Information signal portion, 12 Transparent cover layer, 13 Center hole, 14, 40 sheet, 15 UV curable resin, 16 Intermediate layer, 17 First recording layer, 18 Second recording Layer, 19 skew correction member, 20 hard coat, 21 optical disk, 31 first lens, 32 second lens, 41, 141 stamper, 42 roller, 43 thin plate substrate, 60 liquid ultraviolet curable resin, 61 rotating base, 62 lamp, 70 highly reflective film, 71 protective film

Claims (33)

  1. In an optical recording medium having a transparent cover layer on one main surface side of a recording layer disposed on a support layer, and recording and / or reproducing information by irradiating light from the transparent cover layer side,
    The surface side of the transparent cover layer is made of a material having a Young's modulus of 70 (GPa) or more,
    At least in the information signal area in which the information signal is recorded in the recording layer, the thickness t of the transparent cover layer is t = 3 to 177 (μm), and the uneven thickness of the transparent cover layer is Δt. Then, Δt ≦ ± 5.26 (λ / NA 4 ) (μm) between the numerical aperture NA of the optical system for irradiating light for recording and / or reproducing the optical recording medium and the wavelength λ of the light. An optical recording medium characterized by the following relationship:
  2. 2. The optical recording medium according to claim 1, wherein the numerical aperture NA of the optical system is 0.7 or more.
  3.   2. The optical recording medium according to claim 1, wherein the transparent cover layer comprises a first layer disposed on the surface side and a second layer disposed on the recording layer side.
  4.   4. The optical recording medium according to claim 3, wherein the first layer is made of a material having a Young's modulus of 150 (GPa) or more.
  5. The surface side of the transparent cover layer is at least one of C 100-X H X (1 (atomic%) <X <45 (atomic%)), Si 3 N 4 , MgF 2 , Al 2 O 3 , SiO 2. The optical recording medium according to claim 1, wherein the optical recording medium is made of a material containing
  6. 2. The optical recording medium according to claim 1, wherein P ≦ 0.64 (μm) and Θ ≦ ± 84.115 ° (λ / NA 3 / t) are satisfied, where P is a track pitch and Θ is skew. .
  7. 2. The optical recording medium according to claim 1, wherein the wavelength λ is recorded or reproduced by a recording / reproducing optical system satisfying λ ≦ 0.68 (μm) and the numerical aperture NA satisfying NA / λ ≧ 1.20. .
  8.   2. The optical recording medium according to claim 1, wherein the optical recording medium has a circular shape with an outer diameter of 125 (mm) or less and a thickness of 1.60 (mm) or less.
  9.   2. The optical recording medium according to claim 1, wherein the recording capacity is a linear density of 8 (GB).
  10. 2. The light according to claim 1, wherein the groove or information pit depth is in the range of (λ / 8) / N to (3λ / 8) N, where N is the refractive index of the transparent cover layer. recoding media.
  11.   When the track pitch is P (μm), the track pitch unevenness ΔP is ΔP ≦ ± 0.04 P (μm), the eccentricity E is E ≦ 67.57 P (μm), and the skew is 0.4 ° or less. The optical recording medium according to claim 1.
  12.   2. The optical recording medium according to claim 1, wherein the surface roughness Ra of the surface irradiated with the light to be recorded and / or reproduced is ± 3λ / 100 or less within a spot size region on the surface.
  13.   The support layer is made of a thermoplastic resin and has a thickness of 0.3 to 1.2 (mm). A guide groove is transferred and formed on the substrate, and a multilayer film is sequentially formed on the guide groove. A dye is spin-coated to form a recording layer, on which at least one ultraviolet curable resin is coated with a thickness of 3 to 177 (μm) to form a transparent cover layer. The optical recording medium according to claim 1.
  14.   The support layer is made of a thermoplastic resin and has a thickness of 0.3 to 1.2 (mm). A guide groove is transferred and formed on the substrate, and a multilayer film is sequentially formed on the guide groove. A dye is spin-coated to form a recording layer, and a light-transmitting film is pasted thereon as a transparent cover layer via an ultraviolet curable resin, and the sum of the thicknesses of both is 3 to 177 (μm). The optical recording medium according to claim 1, wherein the optical recording medium is used.
  15.   2. The optical recording medium according to claim 1, wherein the transparent cover layer is obtained by transferring a signal or a guide groove from a master stamper to a sheet made by injection molding or casting by high temperature heating.
  16. 2. The optical recording medium according to claim 1, wherein a support substrate having a thickness of 0.6 to 1.2 (mm) is bonded to the sheet on which the signal or guide groove is transferred.
  17.   The optical recording medium according to claim 16, wherein the support substrate is a transparent plate.
  18.   17. The optical recording medium according to claim 16, wherein the support substrate is bonded to a sheet having a signal or guide groove transferred via an ultraviolet curable resin.
  19.   19. The optical recording medium according to claim 18, wherein the ultraviolet curable resin is applied by spin coating.
  20.   2. The optical recording medium according to claim 1, wherein the optical recording medium has a double-sided structure having an information signal portion and a transparent cover layer on both sides by simultaneous double-side molding or bonding.
  21.   2. The optical recording medium according to claim 1, wherein the optical recording medium has a multilayer structure in which a plurality of information recording films or reflective films and a plurality of transparent cover layers are laminated.
  22.   22. The optical recording medium according to claim 21, wherein the reflectance of the plurality of reflective films is made smaller as it goes toward the light incident side.
  23.   2. The optical recording medium according to claim 1, wherein an ultraviolet curable resin is also applied to a surface opposite to the transparent cover layer.
  24.   24. The optical recording medium according to claim 23, wherein the ultraviolet curable resin applied to the side opposite to the transparent cover layer has a higher curing shrinkage than the material forming the transparent cover layer.
  25.   2. The optical recording medium according to claim 1, wherein the surface of the transparent cover layer is hard-coated.
  26.   14. The optical recording medium according to claim 13, wherein the surface of the recording layer to which the ultraviolet curable resin is applied is subjected to silane treatment.
  27.   15. The optical recording medium according to claim 14, wherein the surface of the recording layer to which the ultraviolet curable resin is applied is subjected to silane treatment.
  28.   2. The optical recording medium according to claim 1, wherein an antireflection film is formed on the surface of the transparent cover layer.
  29.   The refractive index N of the antireflection film is lower than the refractive index of the transparent cover layer, and the thickness of the antireflection film is (λ / 29) The optical recording medium according to claim 28, wherein the optical recording medium is not more than / N (nm).
  30. A transparent cover layer is provided on one main surface side of the recording layer, and the thickness t of the transparent cover layer is t = 3 to 177 (μm) at least in the information signal area of the recording layer where information signals are recorded. An optical disk device for recording and / or reproducing an optical disk,
    A laser light source for emitting laser light having a wavelength of 680 (nm) or less, and an optical system for converging the laser light on the optical disk signal recording surface,
    The optical disk has a numerical aperture NA of the optical system for recording and / or reproducing the optical disk and a wavelength λ of the laser beam, where Δt is the thickness unevenness of the transparent cover layer of the disk, An optical disc device characterized in that a relationship of Δt ≦ ± 5.26 (λ / NA 4 ) (μm) is established.
  31. 31. The optical disk device according to claim 30, wherein the numerical aperture NA of the optical system is 0.7 or more.
  32. The optical disk device according to claim 30, wherein the optical system is a lens having a two-group structure.
  33.   29. The optical disk device according to claim 28, wherein the lens has a numerical aperture NA of 0.78 or more.
JP13071398A 1997-05-16 1998-05-13 Optical recording medium and an optical disk drive Expired - Fee Related JP4099549B2 (en)

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JP9-127498 1997-05-16
JP12749897 1997-05-16
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