JP4328840B2 - Surface readout type optical recording medium - Google Patents

Description

【００２１】
実施例１〜１０において、Ｘ線回折強度比Ｒを４．０×１０^-3以上とすることにより、ノイズが低減し、ＣＮＲが向上している。また、優れたグライドテスト結果が得られ、ヘッド浮上特性も向上している。
また、実施例１１の表面読み出し型光磁気記録媒体に対して、レーザー波長６８０ｎｍ、有効開口数０．８の光学系を有するスライダーヘッドを使用して記録特性を測定したところ、マーク長０．４μｍにおいて４５ｄＢの良好なＣＮＲ値が得られ、オーバーコートを施した表面読み出し型光磁気記録媒体としても使用可能であることが確かめられた。
【００２２】
【発明の効果】
本発明によれば、ＣＮＲなどの記録再生特性、ヘッド浮上性が向上した優れた表面読み出し型光記録媒体を得ることが可能である。本発明の光記録媒体は、表面読み出し型であるため、基板の貼り合わせ工程を必要とせずにディスク両面に記録することができる。そのため、本発明により、ディスク厚さが薄く、工業的に有利な高密度光記録媒体を得ることが可能となる。
【図面の簡単な説明】
【図１】 本発明の表面読み出し型光記録媒体の一例の構造を示す部分断面概略図である。
【図２】 本発明の実施例１の表面読み出し型光記録媒体の構造を示す部分断面概略図である。
【符号の説明】
１１：基板
１２：反射層
１３：記録層
１４：保護層
２１：基板
２２：反射層
２３：記録層
２４：保護層
２５：固体潤滑層
２６：潤滑層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rewritable surface reading type optical recording medium, in particular, a surface reading type magneto-optical recording medium for recording, reproducing and erasing information by a laser beam and a magnetic field, or information recording, reproducing and recording only by a laser beam. The present invention relates to a surface readout type phase change recording medium for performing erasing.
[0002]
[Prior art]
Optical recording media are portable recording media capable of high-capacity and high-density recording, and demand is rapidly increasing as rewritable media for recording large-capacity files and moving images of computers with the recent development of multimedia. .
Among optical recording media, magneto-optical recording media are generally formed by forming a multilayer film including a recording layer on a transparent disc-like substrate such as plastic, and performing recording and erasing by irradiating a laser while applying a magnetic field. Playback with reflected light. Conventionally, the recording method for the magneto-optical recording medium is mainly so-called optical modulation recording in which recording is performed by applying a fixed magnetic field in the opposite direction after erasing by applying a fixed magnetic field. However, in recent years, a magnetic field modulation method that modulates a magnetic field according to a recording pattern while irradiating a laser has attracted attention as a method that can record (direct overwrite) by one rotation and can accurately record even at a high recording density. ing.
In addition, a phase change recording method using a reversible phase change between a crystal phase and an amorphous phase can be directly overwritten and has recently been used.
[0003]
Conventionally, a recording / reproducing laser is irradiated onto a recording film through a substrate. Recently, so-called near-field optical recording, in which an optical head is moved closer to the recording film, is attracting attention as a means for increasing the density. [Appl. Phys. Lett. 68, p. 141 (1996)]. In this recording method, a solid immersion lens (hereinafter abbreviated as “SIL”) head is used to reduce the laser beam spot size, thereby reducing the conventional recording limit (˜λ / 2NA: NA) determined by the laser wavelength (λ) of the light source. Can be reproduced with a mark shorter than the numerical aperture of the objective lens, and recording / reproduction with an ultrahigh recording density can be realized.
In this near-field optical recording, the optical head is brought close to the recording medium, and it is usually necessary to set the interval to about 100 nm or less. Therefore, unlike the conventional optical recording medium, the recording film is irradiated with the laser beam through the substrate. Instead, a method of directly irradiating the recording film with a laser beam without passing through the substrate is used.
[0004]
That is, the structure of the recording film is generally the substrate / first protective layer / recording layer / second protective layer / reflective layer in the conventional optical recording medium, whereas in the near-field optical recording, the substrate / Recording and reproduction are performed by irradiating a laser beam from the film surface side as a film structure having a reverse configuration of reflective layer / first protective layer / recording layer / second protective layer (surface reading type recording). Recently, a surface recording method has been proposed in which recording is performed by irradiating a laser through a protective coating layer on a thin film with a lens NA of 1 or less [J. Magn. Soc. Jpn. 68, S1, p. 269 (1999)].
In near-field optical recording, a floating slider head is often used to bring the recording film close to the SIL head, but the distance between the head and the recording medium is very close due to the reverse structure of the film structure. (˜100 nm), there is a head-recording medium interface problem (head crash etc.) similar to a hard disk drive. Therefore, there is a demand for a head having excellent head flying characteristics without foreign matters such as dust on the disk. In addition, there are problems of deterioration in recording / reproduction characteristics such as CNR (ratio of reproduction signal to noise) due to surface properties of the recording film, and ensuring durability because of direct exposure to the atmosphere.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide an optical recording medium for surface readout type optical recording having low noise, excellent recording / reproducing characteristics, and head flying characteristics, and having a film structure opposite to that of the conventional one.
[0006]
[Means for Solving the Problems]
In light of the above-described present situation, the present inventors have made extensive studies, and as a result, in a surface readout type optical recording medium in which at least a reflective layer, a recording layer, and a protective layer are laminated in this order on a substrate, the reflective layer Is made of a specific metal film, and the X-ray diffraction intensity ratio R of this metal film is found to improve the recording / reproducing characteristics and the head flying property, and the reflective layer is made of a specific alloy. In addition, the inventors have found that the above effect can be further improved by forming a metal film underlayer containing a specific element between the substrate and the reflective layer, and the present invention has been completed.
That is, according to the present invention, in a surface readout type optical recording medium in which at least a reflective layer, a recording layer, and a protective layer are laminated in this order on a substrate, the reflective layer comprises a metal film containing a noble metal and / or Cu. A surface characterized by 4.0 × 10 ⁻³ ≦ R, where R is an X-ray diffraction intensity ratio ((200) / (111)] between the (200) plane and the (111) plane of the film. The present invention relates to a read-type optical recording medium.
In the reflective layer, Au contains at least one element selected from Group 4, Group 5 and Group 6 elements in the periodic table of elements in a range of 0.1 atomic% to 10.0 atomic%. It is preferable that the alloy is included.
Further, a metal film underlayer containing at least one element selected from the elements of Groups 4, 5, and 6 of the periodic table of elements is formed between the substrate and the reflective layer. preferable.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in further detail below.
FIG. 1 shows a partial cross-sectional schematic view of one embodiment of a surface readout type optical recording medium of the present invention. In the optical recording medium of FIG. 1, a reflective layer 12, a recording layer 13, and a protective layer 14 are laminated on a substrate 11.
The material of the substrate 11 is not particularly limited as long as it satisfies the characteristics as a medium substrate such as mechanical characteristics, and glass, polycarbonate, amorphous polyolefin, engineering plastic, and the like can be used.
[0008]
The reflective layer 12 is composed of a metal film containing a noble metal and / or Cu. In the present invention, the metal film containing noble metal and / or Cu is a metal film made of noble metal, a metal film made of Cu, a metal film made of an alloy of noble metal and Cu, a metal film mainly composed of noble metal, Cu It means a metal film mainly composed of a metal film mainly composed of an alloy of noble metal and Cu. The noble metal referred to here is Au, Ag, Pt or other white metal elements, preferably Au, Ag, Pd, Pt. Moreover, a main component means what contains 90 atomic% or more of the said metal or alloy.
The metal film preferably contains an element (additive element) other than the noble metal and Cu. By including the additive element, the hardness of the film is increased, and it is considered that the head flying characteristics are improved. Examples of the additive element include elements of Group 4, Group 5, and Group 6 of the periodic table of elements, and Ta, Ti, W, Cr, Mo, and Zr are particularly preferable. The above additive elements can be used alone or in combination of two or more.
The addition amount of the additive element is preferably 0.1 atomic% to 10.0 atomic%, and if it exceeds 10.0 atomic%, the recording sensitivity becomes too high and becomes impractical.
[0009]
In the reflective layer of the present invention, when the X-ray diffraction intensity ratio [(200) / (111)] between the (200) plane and the (111) plane is R, 4.0 × 10 ⁻³ ≦ R. An X-ray diffraction intensity ratio R of 4.0 × 10 ⁻³ or more generally means that the crystal grain size of the reflective layer is small and the grain size is averaged. It is considered that when the crystal grain size of the reflective layer is small, noise of the optical recording medium is reduced and recording / reproducing characteristics such as CNR are improved, and when the grain size is averaged, the head flying characteristics are improved. When R is less than 4.0 × 10 ⁻³ , the crystal grain size tends to increase, noise of the optical recording medium increases, and CNR tends to decrease. R is preferably as large as possible, but there is no particular upper limit, but if it is too large, the crystal orientation becomes random and the head flying characteristics tend to deteriorate. R of the reflective layer can be adjusted within the range of the present invention by changing the film orientation by adjusting the film forming conditions.
R is preferably 6.0 × 10 ^{−3 to} 1.0.
The thickness of the reflective layer is preferably 20 to 100 nm. If the film thickness is less than 20 nm, the effect as a reflective layer is small. On the other hand, if the film thickness is more than 100 nm, the surface roughness increases, noise increases, and CNR decreases.
[0010]
In the surface reading type optical recording medium of the present invention, a metal film underlayer containing at least one element selected from the elements of Group 4, Group 5 and Group 6 of the periodic table of elements is formed between a substrate and a reflective layer. It is particularly preferable from the viewpoint of improving the head flying property and durability in addition to improving the CNR. The elements contained in the metal film underlayer are preferably Ti, Ta, Cr, Mo, and V.
The thickness of the metal film underlayer is preferably 2 to 20 nm. If the film thickness is less than 2 nm, the effect as the underlayer cannot be obtained. On the other hand, if the film thickness is more than 20 nm, the surface roughness increases, noise increases, and CNR decreases.
[0011]
Any material can be used for the recording layer 13 as long as it is a material having perpendicular magnetization and a large coercive force, but a material mainly composed of TbFeCo or TbFeCo is particularly preferable because it has a large coercive force. The coercive force of the recording layer is preferably as large as possible in order to stably hold the recorded information. However, the magneto-optical recording medium for near-field magneto-optical recording is preferably 5 kOe or more. Further, a phase change recording medium using a reversible phase change between a crystalline phase and an amorphous phase can also be used as the recording layer. In this case, since the heat generated in the recording layer is large, it is preferable to form a protective layer between the reflective layer 12 and the recording layer 13. As the recording layer, a magneto-optical recording medium is more preferable among various recording media from the viewpoint of high recording density technology such as magnetic super-resolution.
[0012]
The protective layer 14 is made of a transparent dielectric material such as SiN, AlN, SiAlON, Ta ₂ O ₅ , a mixed material of ZnS and SiO ₂ . In order to improve the flying characteristics of the slider head, the protective layer 14 may be a laminate of a transparent dielectric layer and a diamond-like carbon (DLC) solid lubricating layer obtained by adding hydrogen or nitrogen to carbon. good. Further, a very thin lubricating layer of a liquid such as perfluoropolyether is formed thereon by a method such as a dip pulling method, so that the flying characteristics of the slider head are further improved.
In addition to the structure described above, the surface readout type optical recording medium of the present invention forms a dielectric on the reflective layer 12 and forms a recording layer thereon, or a dielectric layer on the reflective layer 12 and a second reflective layer. It is also possible to use a layer by laminating layers and forming a recording layer thereon.
A vacuum thin film forming technique such as a vacuum vapor deposition method or a sputtering method can be used to form the underlayer, the reflective layer, the recording layer, the protective layer, and the solid lubricating layer.
[0013]
Further, the surface readout type optical recording medium of the present invention is a surface readout type optical recording medium for an optical system having an NA of 1 or less by forming a protective coating layer made of an acrylic ultraviolet curable resin after the formation of the protective layer 14. Can be used as well. For forming the protective coating layer, a vacuum thin film forming technique, a dip pulling method, a spin coating method, or the like can be used.
[0014]
【Example】
EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited only to these Examples.
Example 1
A surface reading type magneto-optical recording medium having a structure as shown in FIG. 2 was produced. On the polycarbonate substrate 21 with guide grooves having a track pitch of 0.45 μm, an Au film having a film thickness of 50 nm was formed as the reflective layer 22 by sputtering. On top of this, a recording layer 23 made of Tb _0.20 (Fe _0.76 Co _0.20 Ta _0.04 ) _0.80 was formed to a thickness of 20 nm by DC sputtering.
Further thereon, a protective layer 24 made of SiN is formed to a thickness of 230 nm by a reactive DC sputtering method using a Si target in a mixed atmosphere of Ar and N ₂ , and a solid lubricating layer made of diamond-like carbon (DLC) 25 was formed to a thickness of 15 nm by a reactive RF sputtering method using a C target in a mixed atmosphere of Ar and H ₂ . After forming the solid lubricating layer, a perfluoropolyether-based lubricating layer 26 was applied to a thickness of 1 nm by a dip pulling method to produce a magneto-optical recording medium.
[0015]
Examples 2-4
A surface readout type magneto-optical recording medium was manufactured in the same manner as in Example 1 except that the R was adjusted by changing the orientation of the film by changing the sputtering conditions when forming the Au film.
Example 5
A surface readout type magneto-optical recording medium was manufactured in the same manner as in Example 1 except that the material of the reflective layer 22 was changed to Au—Ta alloy [98/2 (atomic%)] (Au _0.98 Ta _0.02 ). .
Example 6
A surface readout type magneto-optical recording medium was produced in the same manner as in Example 1 except that the material of the reflective layer 22 was changed to Au—Ti alloy [98/2 (atomic%)] (Au _0.98 Ti _0.02 ). .
Example 7
A surface readout type magneto-optical recording medium was produced in the same manner as in Example 1 except that the material of the reflective layer 22 was changed to Au—W alloy [98/2 (atomic%)] (Au _0.98 W _0.02 ). .
[0016]
Example 8
A surface readout type magneto-optical recording medium was manufactured in the same manner as in Example 1 except that Ti was formed between the substrate 21 and the reflective layer 22 with a thickness of 10 nm as the metal film underlayer.
Example 9
A surface readout type magneto-optical recording medium was manufactured in the same manner as in Example 1 except that Ta was formed between the substrate 21 and the reflective layer 22 with a thickness of 10 nm as a metal film underlayer.
Example 10
A surface readout type magneto-optical recording medium was manufactured in the same manner as in Example 1 except that Cr was formed between the substrate 21 and the reflective layer 22 with a thickness of 10 nm as the metal film underlayer.
[0017]
Example 11
Using a substrate with a track pitch of 0.55 μm, after forming the DLC layer, a protective coating layer made of an acrylic UV curable resin is formed to a thickness of 10 μm by spin coating, and then a perfluoropolyether lubricating layer A surface readout type magneto-optical recording medium was produced in the same manner as in Example 1 except that 1 nm was applied by a pulling method.
Comparative Example 1
A surface readout type magneto-optical recording medium was produced in the same manner as in Example 1 except that the orientation of the film was changed by changing the sputtering conditions when the Au film was formed, and R was adjusted.
[0018]
X-ray diffraction measurement (film surface side incidence) was performed on the surface readout type magneto-optical recording media of Examples 1 to 11 and Comparative Example 1 to determine the X-ray diffraction intensity ratio (R).
Further, the following recording / reproduction characteristics were measured to obtain CL value, NL value, and CNR value.
A magneto-optical recording medium is set on the spindle and the medium is rotated at a linear velocity of 10 m / s. A slider SIL head having a laser wavelength of 680 nm and an effective numerical aperture of 1.2 is levitated to a height of 100 nm on the thin film surface, and the recording layer is heated to the Curie temperature Tc or higher by irradiating the laser in a pulsed manner. Recording was performed while the magnetic field was modulated at 18.5 MHz (mark length: 0.27 μm). Here, the coil magnetic field at the time of recording was set to 150 Oe. The CNR was measured while changing the recording power, and the value at which the CNR was saturated was defined as the CNR value of the sample. The reproduction power is 0.8 mW. The CL value and the NL value are values when the CNR is saturated.
[0019]
Further, the following glide test was performed on the surface reading type magneto-optical recording medium.
A magneto-optical recording medium was set on the spindle and rotated. First, using a waffle burnish head (manufactured by Glide Height Co., Ltd., flying height: 25 nm), seek was performed once within a radius of 20 to 60 mm. Next, the disk was sought with a glide head with a piezo element (Glide Height, Flying Height: 50 nm), and the voltage value induced in the piezo element was monitored. The voltage value of 500 mV or more was counted as a hit. A hit count number of 0 to 2 was expressed as very good (）), 3 to 5 as good (◯), 6 to 9 as slightly good (Δ), and 10 or more as bad (x).
Table 1 shows X-ray diffraction measurement results, recording / reproduction characteristics measurement results, and glide test results.
[0020]
[Table 1]

[0021]
In Examples 1 to 10, by setting the X-ray diffraction intensity ratio R to 4.0 × 10 ⁻³ or more, noise is reduced and CNR is improved. In addition, excellent glide test results are obtained, and the head flying characteristics are also improved.
Further, when the recording characteristics of the surface readout type magneto-optical recording medium of Example 11 were measured using a slider head having an optical system with a laser wavelength of 680 nm and an effective numerical aperture of 0.8, the mark length was 0.4 μm. As a result, a good CNR value of 45 dB was obtained, and it was confirmed that it could be used as a surface readout type magneto-optical recording medium with an overcoat.
[0022]
【The invention's effect】
According to the present invention, it is possible to obtain an excellent surface reading type optical recording medium having improved recording / reproducing characteristics such as CNR and head flying characteristics. Since the optical recording medium of the present invention is a surface reading type, it can be recorded on both sides of the disk without the need for a substrate bonding step. Therefore, according to the present invention, it is possible to obtain an industrially advantageous high-density optical recording medium with a thin disc thickness.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional schematic diagram showing the structure of an example of a surface readout type optical recording medium of the present invention.
FIG. 2 is a partial cross-sectional schematic view showing the structure of a surface readout type optical recording medium of Example 1 of the present invention.
[Explanation of symbols]
11: substrate 12: reflective layer 13: recording layer 14: protective layer 21: substrate 22: reflective layer 23: recording layer 24: protective layer 25: solid lubricating layer 26: lubricating layer

Claims (3)

In a surface readout type optical recording medium in which at least a reflective layer, a recording layer, and a protective layer are laminated in this order on a substrate, the reflective layer is made of a metal film containing a noble metal and / or Cu, and the (200) plane of this metal film A surface readout type optical recording medium, wherein 4.0 × 10 ⁻³ ≦ R, where R is an X-ray diffraction intensity ratio [(200) / (111)] between the surface and the (111) plane. The reflective layer contains at least one element selected from Group 4, Group 5 and Group 6 elements in the periodic table of elements in a range of 0.1 atomic% to 10.0 atomic% in Au. The surface readout type optical recording medium according to claim 1, further comprising an alloy. 2. A metal film underlayer comprising at least one element selected from elements of Group 4, Group 5 and Group 6 of the periodic table of elements is formed between the substrate and the reflective layer. The surface reading type optical recording medium according to claim 2.

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