JP2004303350A - Information recording medium, and method and device of recording information to the medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an information recording medium capable of maintaining satisfactory recording characteristics in a wide range of linear speed and to provide a recording method and a recording device. <P>SOLUTION: The information recording medium comprises a lower side protective layer 2, a lower side interface layer 3, a recording layer 4 changing between at least two optically detectable states different from each other by light beam irradiation, an upper side interface layer 5, an upper side protective layer 6 and a reflection layer 7 in this order on a transparent substrate 1. At least one selected from the lower side interface layer 3 and the upper side interface layer 5 consists of a material consisting essentially of a carbide of at least one element selected from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W and Si or carbon, and the recording layer 4 contains Ge, Bi and Te. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００７７】
表１より、下側界面層及び上側界面層に炭素または炭化物を適用していない媒体（ディスク）１〜３は、線速度２０．５ｍ／ｓにおいて高い消去率が得られ、高温試験後の低下もほとんどない。しかし、線速度８．２ｍ／ｓにおいてはＣ／Ｎ比が小さく、高温試験後ではさらに小さくなる。
【００７８】
これに対して、下側界面層、上側界面層または両方に炭素または炭化物を適用した媒体４〜１６は、線速度８．２ｍ／ｓにおいて、高温試験前のＣ／Ｎ比は媒体１〜３と比較して大きく、高温試験後のＣ／Ｎ比の低下も０．２ｄＢ以内と小さい。また線速度が２０．５ｍ／ｓにおいて、消去率が高温試験前で３０ｄＢ以上と十分大きな値が得られ低下も小さい。
【００７９】
中でも、特に、下側界面層に炭素または炭化物を適用した媒体４〜８は、上側界面層に適用した媒体９〜１３や両側に適用した媒体１４〜１６と比較するとＣ／Ｎ比がさらに大きい。
【００８０】
このように、Ｇｅ−Ｓｂ−Ｂｉ−Ｔｅからなる記録層を用いた構成で、下側界面層または上側界面層を、中でも、特に下側界面層を炭素または炭化物とすることで、赤色レーザを用いた光学系で広い線速度範囲においてＣ／Ｎ比及び消去率の高い良好な特性が得られる。
【００８１】
（実施例２）
実施例２では、本発明の情報記録媒体の記録再生特性、特にＣ／Ｎ比及び消去率の記録層の材料・組成に対する依存性を示す。
【００８２】
媒体の構成は、実施例１と同様あるが、本実施例では、下側界面層を炭素、上側界面層を（ＺｒＯ_２）_２５（ＳｉＯ_２）_２５（Ｃｒ_２Ｏ_３）_５０とし、表２に示すように記録層がＧｅ_３８Ｓｂ_１０Ｔｅ_５２の媒体（ディスク）１７、Ｇｅの一部をＳｎに置き換えた組成の媒体１８〜２１及びＳｂの一部をＢｉに置き換えた組成の媒体２２〜２５を作製した。下側界面層及び上側界面層は、実施例１と同様にして形成した。
【００８３】
このようにして作製した媒体１７〜２５の特性を、実施例１と同様の方法で測定した。
【００８４】
表２には、記録層の材料・組成に対する線速度８．２ｍ／ｓでの高温試験前のＣ／Ｎ比と高温試験後のＣ／Ｎ比の増減、線速度２０．５ｍ／ｓでの高温試験前の消去率と高温試験後の消去率の増減を示す。ここでは、グルーブとランドで特性に大きな差がなかったのでグルーブの特性のみ示している。
【００８５】
本実施例においても、Ｃ／Ｎ比は線速度２０．５ｍ／ｓの場合のほうが８．２ｍ／ｓの場合よりも高く、高温試験後の低下量も小さかったので、８．２ｍ／ｓの場合のみを示している。消去率は線速度８．２ｍ／ｓの場合のほうが２０．５ｍ／ｓの場合よりも高く、高温試験後の低下量も小さかったので、２０．５ｍ／ｓの場合のみを示している。
【００８６】
【表２】

【００８７】
表２より、記録層がＧｅ_３８Ｓｂ_１０Ｔｅ_５２である媒体１７は、線速度が８．２ｍ／ｓにおいて大きなＣ／Ｎ比が得られ、高温試験後のＣ／Ｎ比の低下もない。しかし、線速度が２０．５ｍ／ｓにおいて、消去率が低く、高温試験後はさらに低下する。記録層にＳｎを添加した媒体１８〜２１では、Ｓｎが少ない場合は、線速度２０．５ｍ／ｓでの消去率が小さく、高温試験後の低下も大きい。逆に、Ｓｎが多い場合は、線速度８．２ｍ／ｓにおいてＣ／Ｎ比が低くなる。
【００８８】
これに対して、記録層にＢｉを添加した媒体２２〜２５は、Ｂｉの添加量により若干の差はあるものの総じて８．２ｍ／ｓで十分なＣ／Ｎ比が得られ、高温試験後のＣ／Ｎ比の低下も小さい。線速度２０．５ｍ／ｓでも消去率は３０ｄＢ以上と十分な値が得られ低下も小さい。
【００８９】
このように、界面層に炭素を用いた構成で、記録層にＧｅ−Ｓｂ−Ｂｉ−Ｔｅ合金を適用することで広い線速度範囲において良好な特性が得られる。
【００９０】
（実施例３）
実施例３では、２つの情報層を持つ本発明の情報記録媒体のレーザ入射側から離れている第２情報層の記録再生特性、特にＣ／Ｎ比及び消去率の界面層材料に対する依存性を示す。
【００９１】
媒体は、透明基板、第１情報層、分離層、第２情報層、保護基板を順に設けた構成とした。媒体の作製方法であるが、保護基板上に、第２情報層、分離層、第１情報層を形成し、その上に、透明基板を貼り合わせた。保護基板には、直径１２ｃｍ、厚さ１．１ｍｍの円盤状であり、グルーブピッチ０．３２μｍ、グルーブ深さ２０ｎｍの案内溝が形成されたものを用いた。
【００９２】
第２情報層として、保護基板に近い側から反射層Ａｇ_９８Ｐｄ_１Ｃｕ_１を８０ｎｍ、上側保護層（ＺｎＳ）_８０（ＳｉＯ_２）_２０を２０ｎｍ、上側界面層を５ｎｍ、記録層Ｇｅ_４５Ｂｉ_４Ｔｅ_５１を１０ｎｍ、下側界面層を５ｎｍ、下側保護層（ＺｎＳ）_８０（ＳｉＯ_２）_２０を６０ｎｍ、この順に形成した。
【００９３】
第２情報層上に紫外線硬化性樹脂を塗布し、その上にグルーブピッチ０．３２μｍ、深さ２０ｎｍの案内溝が形成された溝転写用の異なる基板を貼りあわせ、その状態で樹脂を硬化させる。その後に溝転写用の異なる基板を剥離することによって案内溝が転写された分離層が形成される。分離層の厚さは２５μｍとなるように形成した。
【００９４】
形成時の第２情報層の記録層は、非晶質であるので、分離層側からレーザ光を照射することによって、第２情報層の記録層の全面を結晶相にする初期化処理を行った。
【００９５】
分離層の案内溝が転写された側に第１情報層として、反射層Ａｇ_９８Ｐｄ_１Ｃｕ_１を１０ｎｍ、上側保護層（ＺｎＳ）_８０（ＳｉＯ_２）_２０を２０ｎｍ、上側界面層（ＺｒＯ_２）_２５（ＳｉＯ_２）_２５（Ｃｒ_２Ｏ_３）_５０を５ｎｍ、記録層Ｇｅ_４５Ｂｉ_２Ｓｂ_２Ｔｅ_５１を６ｎｍ、下側界面層（ＺｒＯ_２）_２５（ＳｉＯ_２）_２５（Ｃｒ_２Ｏ_３）_５０を５ｎｍ、下側保護層（ＺｎＳ）_８０（ＳｉＯ_２）_２０を４０ｎｍ、この順に形成した。 さらに、第１情報層上に厚さが０．０７５μｍの透明基板を貼り合わせた。
【００９６】
最後に、形成時の第１情報層の記録層は、非晶質であるので、透明基板側からレーザ光を照射することによって、第１情報層の記録層の全面を結晶相にする初期化処理を行った。
【００９７】
第２情報層の下側界面層と上側界面層としては、実施例１と同様の各材料を用いた。これ等界面層は実施例１と同様にして形成した。
【００９８】
このようにして作製した本実施例の情報記録媒体は、レーザ光の波長４０５ｎｍ、対物レンズのＮＡ０．８５の光学系を用いて、線速度５．０ｍ／ｓ（基準クロックＴ＝１５．０ｎｓ）及び１０．０ｍ／ｓ（基準クロックＴ＝７．５ｎｓ）の条件でマークエッジ記録を行い、以下の測定を行った。いずれの線速度においても、まず、２Ｔマークと２Ｔスペースが連続する信号（以下、２Ｔ信号と表記）と９Ｔマークと９Ｔスペースが連続する信号（以下、９Ｔ信号と表記）とを交互に１１回記録した。そして、２Ｔ信号が記録された状態でこのトラックを再生し、そのＣ／Ｎ比をスペクトラムアナライザーで測定した。さらに、その上に９Ｔ信号を１回記録したときの、２Ｔ信号振幅の減衰比、すなわち消去率をスペクトラムアナライザーで測定した。
【００９９】
信号を記録する際のレーザの変調波形は、いずれの線速度においても、２Ｔ信号を記録する場合には、パルス幅０．５Ｔ（パワーレベルＰ１）の単一矩形パルスを照射した。９Ｔ信号を記録する場合には、８個のパルスからなるパルス列（パワーレベルＰ１）を照射した。このパルス列は、すべてのパルス幅及びパルス間（パワーレベルＰ３）の幅を０．５Ｔとした。マークを記録しない部分では、パワーレベルＰ２の連続光を照射した。パワーレベルの決め方としては、記録パワーレベルＰ１はＣ／Ｎ比が３５ｄＢを超えるパワーの下限値の１．５倍であり、パワーレベルＰ２は消去率が２０ｄＢを超えるパワーの範囲の中央値であり、再生パワーレベルは０．３ｍＷとした。
【０１００】
以上の条件で測定を行った情報記録媒体について、２Ｔ信号が記録されたままの状態で、９０℃・２０％ＲＨの恒温槽で１００時間保持する高温加速試験を行った。高温加速試験後、試験前に記録したトラックを再生し、Ｃ／Ｎ比を測定した。さらに、その上に９Ｔ信号を１回記録したときの消去率も測定した。
【０１０１】
表３には、下側界面層、上側界面層の材料に対する線速度５．０ｍ／ｓでの高温試験前のＣ／Ｎ比と高温試験後のＣ／Ｎ比の増減、線速度１０．０ｍ／ｓでの高温試験前の消去率と高温試験後の消去率の増減を示す。
【０１０２】
なお、Ｃ／Ｎ比は線速度１０．０ｍ／ｓの場合のほうが５．０ｍ／ｓの場合よりも高く、高温試験後の低下量も小さかったので、５．０ｍ／ｓの場合のみを示している。消去率は線速度５．０ｍ／ｓの場合のほうが１０．０ｍ／ｓの場合よりも高く、高温試験後の低下量も小さかったので、１０．０ｍ／ｓの場合のみを示している。
【０１０３】
【表３】

【０１０４】
表３より、下側界面層及び上側界面層に炭素または炭化物を適用していない媒体２６〜２８は、線速度１０．０ｍ／ｓにおいて大きな消去率が得られる。しかし、線速度５．０ｍ／ｓにおいてはＣ／Ｎ比が小さく、高温試験後ではさらに小さくなる。
【０１０５】
これに対して、下側界面層、上側界面層、両方に炭素または炭化物を適用した媒体２９〜４１は、線速度５．０ｍ／ｓにおいて、高温試験前のＣ／Ｎ比は媒体２６〜２８と比較して大きく、高温試験後のＣ／Ｎ比の低下も０．２ｄＢ以内と小さい。また線速度が１０．０ｍ／ｓにおいて、高温試験前の消去率が３０ｄＢ以上と十分大きな値が得られ低下も小さい。
【０１０６】
中でも、特に、上側界面層に炭素または炭化物を適用した媒体３４〜３８は、下側界面層に適用した媒体２９〜３３や両側に適用した媒体３９〜４１と比較するとさらにＣ／Ｎ比が大きい。
【０１０７】
以上のように、Ｇｅ−Ｂｉ−Ｔｅからなる記録層を用いた構成で、下側界面層または上側界面層、中でも特に上側界面層を炭素または炭化物とすることで、青色レーザを用いた光学系で広い線速度範囲においてＣ／Ｎ比及び消去率の高い良好な特性が得られる。
【０１０８】
【発明の効果】
以上のように本発明によれば、広い線速度範囲において、良好な記録再生特性を満たす情報記録媒体を実現することができるという顕著な効果が得られる。また、本発明によれば、異なる線速度で情報の記録再生を信頼性よく容易に行うことができる。
【図面の簡単な説明】
【図１】本発明の情報記録媒体の構成例を示す断面図
【図２】本発明の情報記録媒体の別の構成例を示す断面図
【図３】本発明の情報記録媒体の２つの情報層を含む構成例を示す断面図
【図４】本発明の実施形態におけるパルス列の例を示す図
【図５】本発明の実施に用いる記録再生装置の構成例を示す図
【符号の説明】
１ 透明基板
２ 下側保護層
３ 下側界面層
４ 記録層
５ 上側界面層
６ 上側保護層
７ 反射層
８ 保護基板
９ 光吸収補正層
１０ 第１情報層
１１ 分離層
１２ 第２情報層
１３ グルーブ
１４ ランド[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an information recording medium used for recording or reproducing information by optical means or electric means, particularly to an optical information recording medium such as a phase change type information recording medium.
[0002]
[Prior art]
In the case of a phase-change type information recording medium, for example, in the case of a rewritable type, when a recording layer is irradiated with a laser beam, a reversible phase transformation occurs between a crystalline phase and an amorphous phase in an irradiated region in the recording layer. Recording and erasing of information signals are performed using When recording or erasing an information signal, a laser beam is modulated between high power and low power and is irradiated on the recording layer.
In such an information recording medium, besides the recording layer, it prevents evaporation of the recording layer and thermal deformation of the substrate during repeated recording, and enhances the optical absorptance and optical change of the recording layer by an optical interference effect. For example, protective layers made of a dielectric material with excellent heat resistance are provided above and below the recording layer, and the incident light is used efficiently, the cooling rate is improved, and the amorphous layer is easily formed. It is common to provide a reflective layer made of a metal or alloy material.
[0003]
It has also been proposed to provide an interface layer between the recording layer and the dielectric layer. The interface layer promotes the crystallization of the recording layer, improves the erasing characteristics, prevents the mutual diffusion of atoms and molecules between the recording layer and the dielectric protective layer, and improves the durability in repeated recording. It is desirable to have environmental reliability that does not cause peeling or corrosion between the recording layer and the recording layer.
[0004]
As a basic means for increasing the amount of information that can be stored per one information recording medium, the laser light spot is reduced by shortening the wavelength of the laser light or increasing the numerical aperture of an objective lens that focuses the laser light. There is a method of reducing the diameter and improving the recording surface density. The mainstream in recent years uses an optical system having a wavelength of 660 nm and a numerical aperture of about 0.6, as represented by a recordable DVD. Further, it has been studied to apply a blue laser diode having a wavelength of about 400 nm, which is approaching the stage of practical use, and further increase the numerical aperture to about 0.85. When the numerical aperture is increased in this manner, the tolerance for tilt of the information recording medium is reduced. Therefore, it is also necessary to reduce the thickness of the substrate on the laser beam incident side from 0.6 mm of a recordable DVD to about 0.1 mm. It has been proposed.
[0005]
In order to increase the amount of information that can be handled per medium, a multilayer recording medium in which a plurality of layers for recording and reproducing information are stacked has been proposed. In such a multilayer recording medium, since the information layer on the side closer to the laser light source absorbs light, the information layer on the side farther from the laser light source performs recording / reproduction with attenuated laser light, and the sensitivity during recording is high. The decrease causes a problem of a decrease in the reflectance and amplitude during reproduction. Therefore, in a multilayer recording medium, the information layer closer to the laser light source has a higher transmittance, and the information layer farther from the laser light source has a higher reflectance, a difference in reflectance, and a higher sensitivity. It is necessary to obtain sufficient recording / reproducing characteristics.
[0006]
In the information recording medium, it is important to increase the recording density as described above, but it is also important to increase the recording speed in order to handle a large amount of data in a short time. In order to support high-speed recording, it is necessary to increase the crystallization speed of the recording layer. In order to solve the above-mentioned phenomenon, for example, it has been proposed that the crystallization speed is increased by adding Sn or the like to the Ge—Sb—Te recording layer to obtain good recording characteristics in high-speed recording (for example, Patent Document 1).
[0007]
[Patent Document 1]
JP-A-2002-74739 (pages 4 to 7)
[0008]
[Problems to be solved by the invention]
As described above, the recording speed of a newly developed drive tends to be higher, and a medium corresponding to this is required. At the same time, in order to ensure compatibility with existing drives that can only record at low speeds, it is necessary to be able to record at the low speed on the same medium. In order for the medium to support high-speed recording, it is necessary to use a recording layer with a high crystallization speed as described above. However, if this is used for low-speed recording, the crystallization speed will be too high. That is, there is a problem in that the amorphous phase is hardly formed and the mark is not easily enlarged, so that the signal amplitude is reduced. In particular, when part of Ge is replaced with Sn as described above, the change in the optical constant between the crystal and the amorphous becomes small, and there is a possibility that the signal amplitude is reduced.
[0009]
SUMMARY OF THE INVENTION An object of the present invention is to provide an information recording medium capable of obtaining good recording / reproducing characteristics in a wide linear velocity range.
[0010]
[Means for Solving the Problems]
The present invention is directed to a transparent substrate, from the side close to the transparent substrate, a lower protective layer, a lower interface layer, a recording layer that changes between at least two different states that are optically detectable by light beam irradiation, An upper interface layer, an upper protective layer, and a reflective layer are included in this order, and at least one selected from the lower interface layer and the upper interface layer is Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and W. An information recording medium is provided which is made of a material containing at least one carbide selected from Si or carbon as a main component, wherein the recording layer contains Ge, Bi, and Te. According to this information recording medium, good recording / reproducing characteristics can be obtained in a wide linear velocity range.
[0011]
In this specification, the term “main component” refers to a component occupying 80 atomic% or more. However, in order to eliminate the influence of other components, this component contains 90 atomic% or more, and more preferably 95 atomic% or more. May be occupied.
[0012]
In addition, the present invention includes a plurality of information layers on a transparent substrate via a separation layer, wherein the information layer farthest from the transparent substrate is a lower protective layer, a lower interface, from a side closer to the transparent substrate. A recording layer, an upper interface layer, an upper protective layer, and a reflective layer that change between at least two different states optically detectable by irradiation with a light beam, in this order, the lower interface layer and the upper interface layer. At least one selected from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and Si, or a material containing carbon as a main component, and the recording layer Provides an information recording medium characterized by including Ge, Bi, and Te. According to this information recording medium, good recording / reproducing characteristics can be obtained in a wide linear velocity range, and an information recording medium having a particularly high recording density can be obtained.
[0013]
According to still another aspect of the present invention, there is provided a method and apparatus for recording information using the medium. According to the recording method of the present invention, on a transparent substrate, a lower protective layer, a lower interface layer, and at least two different states that can be optically detected by light beam irradiation are changed from a side near the transparent substrate. A method for recording information on an information recording medium including a recording layer, an upper interface layer, an upper protective layer, and a reflective layer in this order, wherein two or more modes are applied at the time of recording information. The information is recorded by irradiating the medium with a light beam while rotating the medium at a predetermined linear velocity selected from two or more linear velocities.
[0014]
Another recording method of the present invention, on a transparent substrate, including a plurality of information layers via a separation layer, the information layer farthest from the transparent substrate, from the side closer to the transparent substrate, a lower protective layer, Recording information on an information recording medium including a lower interface layer, a recording layer that changes between at least two different states that can be optically detected by light beam irradiation, an upper interface layer, an upper protective layer, and a reflective layer in this order. A method comprising: applying two or more modes when recording information; rotating the medium at a predetermined linear velocity selected from two or more linear velocities corresponding to the two or more modes; The above information is recorded by irradiating a light beam to the.
[0015]
The recording apparatus of the present invention changes between at least two different states that are optically detectable on the transparent substrate from the side close to the transparent substrate from the lower protective layer, the lower interface layer, and light beam irradiation. An apparatus for recording information on an information recording medium including a recording layer, an upper interface layer, an upper protective layer, and a reflective layer in this order, wherein two or more modes are applied when recording information, and the two or more modes are applied. The information is recorded by irradiating the medium with a light beam while rotating the medium at a predetermined linear velocity selected from two or more linear velocities.
[0016]
Another recording device of the present invention, on a transparent substrate, including a plurality of information layers via a separation layer, the information layer farthest from the transparent substrate, from the side closer to the transparent substrate, a lower protective layer, Recording information on an information recording medium including a lower interface layer, a recording layer that changes between at least two different states that can be optically detected by light beam irradiation, an upper interface layer, an upper protective layer, and a reflective layer in this order. An apparatus for applying two or more modes when recording information and rotating the medium at a predetermined linear velocity selected from two or more linear velocities corresponding to the two or more modes; The above information is recorded by irradiating a light beam to the.
[0017]
The recording method and the recording apparatus of the present invention include a recording / reproducing method for reproducing information before and after recording or at the same time as recording, and a recording / reproducing apparatus provided with a reproducing mechanism together with an information recording mechanism.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
In the information recording medium of the present invention, if a light absorption correction layer is further provided between the upper protective layer and the reflective layer, the erasing rate can be increased by preventing the recording mark from being distorted during rewriting.
[0019]
The recording layer may further contain Sb. That is, the recording layer may include a Ge-Bi-Te-based alloy, or may include a Ge-Sb-Bi-Te-based alloy. The recording layer is, specifically, Ge _x (Sb _1-p Bi _p ) _y Te _z It is preferable to include a material represented by However, x + y + z = 100, 20 ≦ x ≦ 50, 0 <y ≦ 25, 45 ≦ z ≦ 60, and 0 <p ≦ 1. When a recording layer having this composition is used, the C / N ratio and the erasing rate can be improved. x is preferably 35 or more (x ≧ 35). Preferred ranges of y, z, and p are 0 <y ≦ 15, 45 ≦ z ≦ 55, and 0.4 ≦ p ≦ 0.8, respectively.
[0020]
In the recording method of the present invention, the two or more different linear velocities may include a first linear velocity and a second linear velocity that is 1.5 times or more the first linear velocity. In other words, this recording method can also be applied when the fastest linear velocity is 1.5 times or more the slowest linear velocity.
[0021]
When the lower interface layer is made of at least one selected from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W and Si, or a material containing carbon as a main component, the wavelength of the light beam Is preferably set to 600 nm or more and 700 nm or less. When the upper interface layer is made of at least one selected from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W and Si, or a material containing carbon as a main component, The wavelength is preferably 450 nm or less. According to these preferred examples, it is easy to obtain a large signal amplitude.
[0022]
Hereinafter, embodiments of the present invention will be further described with reference to the drawings.
[0023]
(Embodiment 1)
FIG. 1 is a sectional view showing a configuration example of the information recording medium of the present invention. FIG. 1 shows a transparent substrate 1 on which a lower protective layer 2, a lower interface layer 3, a recording layer 4, an upper interface layer 5, an upper protective layer 6, a reflective layer 7, and a protective substrate 8 are provided.
[0024]
A laser beam is focused on the information recording medium from the side of the transparent substrate 1 by an objective lens, and the laser beam is irradiated to perform reproduction.
[0025]
Next, several methods for forming each layer will be described.
[0026]
One is that a lower protective layer 2, a lower interface layer 3, a recording layer 4, an upper interface layer 5, an upper protective layer 6, and a reflective layer 7 are sequentially formed on a transparent substrate 1, and a protective substrate 8 is formed thereon. Is a method of bonding.
[0027]
As another forming method, a reflective layer 7, an upper protective layer 6, an upper interface layer 5, a recording layer 4, a lower interface layer 3, and a lower protective layer 2 are sequentially formed on a protective substrate 8, and a transparent layer is formed thereon. This is a method of bonding the substrates 1 together. In this forming method, a transparent substrate 1 having a small thickness can be used. If the transparent substrate 1 is thin, for example, about 0.1 mm, an optical system of an objective lens having a numerical aperture as high as 0.8 or more can be used, which is advantageous for high-density recording.
[0028]
For the transparent substrate 1, it is preferable to use a material that is substantially transparent at the wavelength of the laser light. Generally, a polycarbonate resin, a polymethyl methacrylate resin, a polyolefin resin, a norbornene-based resin, an ultraviolet-curable resin, glass, or a combination thereof as appropriate can be used. Further, the transparent substrate 1 is provided with a guide groove on the surface on which a film is to be formed, as needed, for tracking a light beam. As shown in FIG. 1, it is composed of a groove 13 and a land 14, and it is possible to record information in one of the areas or both areas. On the side of the transparent substrate 1 where the film is not formed, a transparent substrate is used. The thickness of the transparent substrate 1 is not particularly limited, but a thickness of about 0.01 to 1.5 mm can be used.
[0029]
The lower protective layer 2, the lower interface layer 3, the recording layer 4, the upper interface layer 5, the upper protective layer 6, and the reflective layer 7 are formed by a general vapor-phase thin film deposition method, for example, a vacuum deposition method, a sputtering method, It can be formed by a plating method, a CVD (Chemical Vapor Deposition) method, or an MBE (Molecular Beam Epitaxy) method.
[0030]
Among these methods, the sputtering method is preferable in consideration of the film formation rate, the manufacturing cost, the quality of the layer to be formed, and the like. It can be formed by reactive sputtering of a target to be a material in an atmosphere of Ar gas or a mixed gas of Ar gas and a reaction gas.
[0031]
The lower protective layer 2 and the upper protective layer 6 serve to protect the recording layer 4 from mechanical damage from the outside, so that the surface of the transparent substrate 1 becomes rough when recording is repeated, and the recording layer 4 is broken or evaporated. Reduces the thermal damage to increase the number of repetitive recordings, adjusts the optical distance to increase the light absorption efficiency of the recording layer 4, increases the difference in reflectivity before and after recording, and increases the signal amplitude. It has a function of blocking the influence from the outside air and preventing a chemical change of the recording layer 4. It also has the function of adjusting the phases of the amorphous and crystalline phases. Further, it is preferable that the melting points of the lower protective layer 2 and the upper protective layer 6 are higher than the melting point of the recording layer 4. As the lower protective layer 2 and the upper protective layer 6 satisfying these functions, for example, Y, Ce, Ti, Zr, Nb, Ta, Co, Zn, Al, Si, Ge, Sn, Pb, Cr, Sb, Bi , Te, etc., Ti, Zr, Nb, Ta, Cr, Mo, W, B, Al, Ga, In, Si, Ge, Sn, Pb, etc. nitride, Zn, Cd, etc. sulfide or selenium Or a telluride, a fluoride such as La, Mg, Ca, Ce, Er, Gd, Tb, Dy, Nd, Y, Yb, a simple substance such as Si, Ge, or a mixture or a mixture thereof. Similar materials can be used. Among these, particularly transparent materials having low thermal conductivity, such as ZnS and SiO ₂ Are preferred.
[0032]
The lower interface layer 3 and the upper interface layer 5 have a function of preventing mass transfer occurring between the lower protective layer 2 and the recording layer 4 and between the upper protective layer 6 and the recording layer 4 due to repeated recording. For example, the lower protective layer 2 or the upper protective layer 6 may have ZnS-SiO ₂ When S is used, S atoms are prevented from being mixed into the recording layer 4 and characteristic deterioration due to repeated recording is prevented.
[0033]
In the present embodiment, in order to prevent deterioration in characteristics due to repeated recording and to improve characteristics in a wide linear velocity range, one of the lower interface layer 3 and the upper interface layer 5 or both materials are used. A material mainly containing carbon or a carbide of at least one element selected from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W and Si is used.
[0034]
Carbon and carbide can be formed by a vacuum evaporation method, a sputtering method, an ion plating method, a CVD method, or an MBE method. In particular, it is preferable to form the target by a sputtering method in an Ar gas atmosphere using a target made of each material and composition.
[0035]
When only one interface layer is made of the above-mentioned carbide or carbon, various oxides and nitrides may be used as the material of the other interface layer. As a material of the other interface layer, at least one kind selected from Y, Ce, Ti, Zr, Nb, Ta, Co, Zn, Al, Si, Ge, Sn, Pb, Cr, Sb, Bi, and Te Oxide, at least one nitride selected from Ti, Zr, Nb, Ta, Cr, Mo, W, B, Al, Ga, In, Si, Ge, Sn, and Pb, or a mixture thereof. Materials as components are preferred.
[0036]
The thicknesses of the lower interface layer 3 and the upper interface layer 5 are not particularly limited. However, if the thickness is too small, the effect of the interface layer cannot be exerted. If the thickness is too large, the recording sensitivity is reduced. It is preferably 20 nm or less.
[0037]
As a material of the recording layer 4, the ratio of the number of atoms of Ge, Bi, Sb, and Te is Ge: (Bi + Sb): Te = x: y: z (where x + y + z = 100, 20 ≦ x ≦ 50, 0 < Ge ≦ Bi—Te alloy or Ge—Sb—Bi—Te alloy where y ≦ 25, 45 ≦ z ≦ 60) is preferable. When the recording layer 4 contains Bi, the crystallization speed of the recording layer 4 can be increased, and good recording / reproducing characteristics can be obtained at a high linear velocity. The recording layer 4 preferably contains a Ge—Bi—Te alloy or a Ge—Sb—Bi—Te alloy as a main component.
[0038]
The recording layer 4 is made of a metal such as In, Ga, Zn, Cu, Ag, Au, Cr, etc. for the purpose of adjusting the thermal conductivity or the optical constant, or improving the repetition durability, heat resistance or environmental reliability. One or more elements selected from non-metallic elements such as O, N, F, C, S and B may be added to the recording layer 4 as needed. Among them, particularly, N is excellent in improving the repeated durability. However, these added elements are used in an amount of less than 20 at%, more preferably less than 10 at% of the entire recording layer 4 so as not to impair the crystallization speed of the main component.
[0039]
If the thickness of the recording layer 4 is 2 nm or more and 20 nm or less, a sufficient C / N ratio can be obtained. When the thickness of the recording layer 4 is less than 2 nm, a sufficient reflectance and a change in reflectance cannot be obtained, so that the C / N ratio is low. When the thickness exceeds 20 nm, the thermal diffusion in the thin film surface of the recording layer 4 is large. As a result, the C / N ratio becomes low in high-density recording. Further, the thickness of the recording layer 4 is more preferably 4 nm or more and 14 nm or less.
[0040]
The reflection layer 7 has a function of optically increasing the amount of light absorbed by the recording layer 4 and quickly diffusing the heat generated in the recording layer 4 to make the recording layer 4 easily amorphous. Furthermore, it also has a role of protecting the medium from the use environment.
[0041]
As a material of the reflection layer 7, for example, Au, Ag, Cu, Al, Ni, Cr or an alloy material based on these is used. Among them, Ag alloys have particularly high thermal conductivity and reflectivity, and Al alloys are preferable in terms of cost. Further, the reflective layer 7 may be used by combining a plurality of layers.
[0042]
The thickness of the reflective layer 7 is not particularly limited, but is, for example, 40 nm or more and 200 nm or less, preferably 60 nm or more and 160 nm or less.
[0043]
The above-mentioned multilayer thin film is prepared by a method such as Auger electron spectroscopy, X-ray photoelectron spectroscopy or secondary ion mass spectrometry (for example, “Handbook of Thin Film Preparation” edited by Society of Applied Physics / Thin Film and Surface Physics Society, Kyoritsu Shuppan Co., Ltd. Company, 1991) can examine the material and composition of each layer. In the examples of the present application, it was confirmed that the composition of the target material of each layer was substantially equal to the composition of the actually formed thin film.
[0044]
As the material of the protection substrate 8, the same material as that of the transparent substrate 1 can be used. However, the transparent substrate 1 does not need to be made of the same material, and may not be transparent at the wavelength of the laser beam. The protection substrate 8 is provided with a guide groove on the surface on which the film is to be formed, as needed, for tracking the light beam. The thickness of the protection substrate 8 is not particularly limited, but a thickness of about 0.01 to 3.0 mm can be used.
In the initialization of the recording layer 4, the amorphous recording layer 4 is crystallized by irradiating the recording layer 4 with a light beam such as a laser beam.
[0045]
Further, as shown in FIG. 2, a configuration in which a light absorption correction layer 9 is provided between the upper protective layer 6 and the reflective layer 7 may be employed.
[0046]
The light absorption correction layer 9 adjusts the light absorption ratio between the case where the recording layer 4 is in the crystalline phase and the case where the recording layer 4 is in the amorphous state, and prevents the shape of the recording mark from being distorted at the time of rewriting, thereby increasing the erasing rate. In order to increase the difference in reflectance between the case where the recording layer 4 is in the crystalline phase and the case where the recording layer 4 is in the amorphous state, and to increase the signal amplitude and the C / N ratio, the refractive index is high. In other words, for example, when the refractive index n is 3 or more and 6 or less, the extinction coefficient k is 1 or more and 4 or less, more preferably n is 3 or more and 5 or less and k is 1.5 or more and 2.5 or less. Certain materials can be used. Specifically, amorphous Ge alloys and Si alloys such as Ge-Cr, Ge-Mo, Si-Cr, Si-Mo, and Si-W, or Ti, Zr, Nb, Ta, Cr, Mo, W It is preferable to use crystalline metals, semimetals, and semiconductor materials such as SnTe, PbTe, and the like. Above all, a material based on Si has a higher melting point than Ge, so that it has good heat resistance, and also has a high thermal conductivity, so that the C / N ratio becomes large, which is more preferable.
[0047]
(Embodiment 2)
FIG. 3 is a sectional view showing another example of the configuration of the information recording medium of the present invention. FIG. 3 includes a transparent substrate 1, a first information layer 10, a separation layer 11, a second information layer 12, and a protection substrate 8.
[0048]
Here, the first information layer 10 and the second information layer 12 are, as in the multilayer thin-film configuration shown in FIG. , A recording layer 4, an upper interface layer 5, an upper protective layer 6, and a reflective layer 7 in this order.
[0049]
A laser beam is focused on each information layer of the information recording medium from the side of the transparent substrate 1 with an objective lens, and the laser beam is irradiated to perform reproduction. The reflective layer 7 of the first information layer 10 has a sufficient transmittance so that light incident from the transparent substrate 1 can pass through the first information layer 10 and reach the second information layer 12. For example, the film thickness is reduced to 20 nm or less, or omitted, or an optical interference layer having a high refractive index of 2.2 or more is provided on the opposite side of the reflective layer 7 from the transparent substrate 1 in order to improve the transmittance. Is necessary.
[0050]
Next, several methods for forming each layer will be described.
[0051]
One is a method in which a first information layer 10, a separation layer 11, and a second information layer 12 are sequentially formed on a transparent substrate 1, and a protective substrate 8 is bonded thereon.
[0052]
As another forming method, a second information layer 12, a separation layer 11, and a first information layer 10 are sequentially formed on a protective substrate 8, and the transparent substrate 1 is bonded thereon. In this forming method, the first information layer 10 and the second information layer 12 are formed from at least the reflective layer 7, the upper protective layer 6, the upper interface layer 5, the recording layer 4, and the lower interface layer from the side near the protective substrate 8. 3. The lower protective layer 2 is formed in this order. In this forming method, a transparent substrate 1 having a small thickness can be used. If the transparent substrate 1 is thin, for example, about 0.1 mm, an optical system of an objective lens having a numerical aperture as high as 0.8 or more can be used, which is advantageous for high-density recording.
[0053]
As still another forming method, a first information layer 10 is formed on the transparent substrate 1, a second information layer 12 is formed on the protection substrate 8, and the respective film surface sides of the transparent substrate 1 and the protection substrate 8 are formed. This is a method of bonding together via the separation layer 11. Here, the first information layer 10 includes at least a lower protective layer 2, a lower interface layer 3, a recording layer 4, an upper interface layer 5, an upper protective layer 6, and a reflective layer 7 from the side near the transparent substrate 1. They are formed in order. On the other hand, the second information layer 12 includes at least the reflective layer 7, the upper protective layer 6, the upper interface layer 5, the recording layer 4, the lower interface layer 3, and the lower protective layer from the side close to the protective substrate 8. 2 are formed in this order.
[0054]
The first information layer 10 preferably has a transmittance of at least 30% or more, but may be not only a rewritable type but also a write-once type or a read-only type.
[0055]
As the separation layer 11, an ultraviolet curable resin or the like can be used. The thickness of the separation layer 11 is at least equal to the numerical aperture (NA) of the objective lens so that when one of the first information layer 10 and the second information layer 12 is reproduced, crosstalk from the other is reduced. It is necessary that the thickness be equal to or greater than the depth of focus determined by the wavelength (λ) of the laser beam, and that the thickness be such that all the information layers fall within the range where light can be collected. For example, the thickness of the separation layer 11 needs to be 10 μm to 100 μm when λ = 660 nm and NA = 0.6, and 5 μm to 50 μm when λ = 405 nm and NA = 0.85. . However, if an optical system capable of reducing crosstalk between layers is developed, the thickness of the separation layer 11 may be smaller than the above.
[0056]
Although FIG. 3 shows a configuration in which there are two information layers, an additional information layer may be added via a separation layer.
[0057]
(Embodiment 3)
Next, a recording method and a recording device of the information recording medium of the present invention will be described.
[0058]
When recording the information recording medium of the present invention, the laser beam is modulated between a plurality of power levels corresponding to each linear velocity. As shown in FIG. 4, the power level P1 and the power level P3 (where P1 and P2) are used to eliminate the single rectangular pulse of the power level P1 or excessive heat and to make the mark width uniform. > P3) is used as a recording pulse composed of a plurality of pulse trains. Further, a cooling section of the power level P4 may be provided after the last pulse. The power level P2 (where P1> P2) is kept constant for the portion where no mark is formed.
[0059]
Reproduction is performed by irradiating the mark recorded by the recording pulse with a laser beam. At this time, it is necessary to set the power level so that the recording mark is not erased. In this way, recording / reproduction is performed on the information recording medium at least at two or more different linear velocities. With the medium according to the present invention, good characteristics can be obtained even when the fastest linear velocity is 1.5 times or more the slowest linear velocity among different linear velocities.
[0060]
In recording / reproducing with a laser beam having a wavelength of not less than 600 nm and not more than 700 nm, the lower interface layer 3 contains carbon or at least one element selected from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W and Si. If a material containing carbide as a main component is used, the difference in reflectance between the crystalline state and the amorphous state of the recording layer 4 can be increased, that is, a large signal amplitude can be obtained.
[0061]
In recording / reproducing with a laser beam having a wavelength of 450 nm or less, the upper interface layer 5 mainly contains carbon or a carbide of at least one element selected from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W and Si. When a material as a component is used, the difference in reflectance between the crystalline state and the amorphous state of the recording layer 4 can be increased, and a large signal amplitude can be obtained.
[0062]
FIG. 5 is a schematic view showing an example of a minimum required device configuration of a recording / reproducing device for recording / reproducing an information recording medium as an example of the recording device of the present invention. The laser beam 15 emitted from the laser diode 16 is focused on an optical information recording medium (disk) 19 rotated by a motor 18 through a half mirror 17 and an objective lens 21. The reproduction of information is performed by causing reflected light from the medium 19 to enter the photodetector 20 and detecting a signal.
[0063]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to the following Examples.
[0064]
(Example 1)
Example 1 shows the recording / reproducing characteristics of the information recording medium of the present invention, in particular, the dependence of the C / N ratio and the erasing rate on the interface layer material.
[0065]
A transparent substrate having a diameter of 12 cm and a thickness of 0.6 mm and made of a polycarbonate resin was used. A spiral groove having a groove pitch of 1.23 μm and a groove depth of 50 nm is formed on the surface of the transparent substrate on which a film is formed. The opposite surface on which no film is formed is smooth.
[0066]
In the configuration of the first embodiment, the lower protective layer (ZnS) is formed on the surface of the transparent substrate on which the lands and the grooves are formed. ₈₀ (SiO ₂ ) ₂₀ (Mol%; composition ratios are all mol% or at% below): 150 nm, lower interface layer: 2 nm, recording layer Ge ₄₀ Sb ₂ Bi ₆ Te ₅₂ 8 nm, upper interface layer 2 nm, upper protective layer (ZnS) ₈₀ (SiO ₂ ) ₂₀ To 40 nm, the light absorption correction layer Ge ₈₀ Cr ₂₀ 40 nm, reflective layer Ag ₉₈ Pd ₁ Cu ₁ Were formed in this order at 80 nm.
[0067]
An ultraviolet-curing resin was applied on the surface of the multilayer thin film thus formed, and was bonded to a protective substrate by irradiating ultraviolet rays. As the protective substrate, a disk-shaped one having a diameter of 12 cm and a thickness of 0.6 mm and made of a polycarbonate resin was used.
[0068]
As shown in Table 1, the lower interface layer and the upper interface layer are composed of carbon (C), TiC, SiC, (Ge ₉₀ Cr ₁₀ ) ₉₅ N ₅ (Denoted as GeCrN in Table 1), Ta ₂ O ₅ (TaO in Table 1) or (ZrO ₂ ) ₂₅ (SiO ₂ ) ₂₅ (Cr ₂ O ₃ ) ₅₀ (ZrSiCrO in Table 1).
[0069]
In addition, C, TiC, SiC, Ta ₂ O ₃ , (ZrO ₂ ) ₂₅ (SiO ₂ ) ₂₅ (Cr ₂ O ₃ ) ₅₀ Was formed by a sputtering method using a target having a diameter of 100 mm made of each material and composition in an atmosphere having an Ar gas pressure of 0.13 Pa. The input power at this time was 300 W. (Ge ₉₀ Cr ₁₀ ) ₉₅ N ₅ Is a 100 mm diameter Ge ₉₀ Cr ₁₀ Ar gas and N using a target consisting of ₂ It was formed by a sputtering method in a mixed gas atmosphere of gas. The input power at this time was 300 W. At this time, it was confirmed that the composition of the target material was substantially the same as the composition of the actually formed thin film.
[0070]
Further, since the recording layer at the time of formation is amorphous, an initialization process for irradiating a laser from the transparent substrate side to make the entire surface of the recording layer a crystalline phase was performed.
[0071]
The information recording medium of the present example manufactured in this manner uses an optical system having a laser beam wavelength of 650 nm and an objective lens of NA 0.6, and a linear velocity of 8.2 m / s (reference clock T = 17.1 ns). And 20.5 m / s (reference clock T = 6.9 ns), the mark edge recording was performed, and the following measurement was performed. At any linear velocity, a signal in which a 3T mark and a 3T space are continuous (hereinafter referred to as a 3T signal) and a signal in which an 11T mark and an 11T space are continuous (hereinafter referred to as an 11T signal) are alternately repeated eleven times. Recorded. Then, this track was reproduced with the 3T signal recorded, and the C / N ratio was measured with a spectrum analyzer. Furthermore, the attenuation ratio of the 3T signal amplitude when the 11T signal was recorded once thereon, that is, the erasure rate was measured by a spectrum analyzer.
[0072]
Regarding the modulation waveform of the laser at the time of recording the signal, a single rectangular pulse having a pulse width of 1.5T (power level P1) was applied when recording a 3T signal at any linear velocity. When recording an 11T signal, a pulse train (power level P1) consisting of nine pulses was irradiated. In this pulse train, the first pulse width was 1.5T, the width of the second to ninth pulses was 0.5T, and the width between each pulse (power level P3) was 0.5T. In a portion where no mark is recorded, continuous light of power level P2 was irradiated. Here, P3 = P2. As a method for determining each power level, the recording power level P1 is 1.5 times the lower limit value of the power at which the C / N ratio exceeds 45 dB, and the power level P2 is the median value of the power range at which the erasure rate exceeds 20 dB. The reproduction power level was set to 1.0 mW.
[0073]
The information recording medium measured under the above conditions was subjected to a high-temperature acceleration test in which the 3T signal was kept recorded and kept in a constant-temperature bath at 90 ° C. and 20% RH (relative humidity) for 100 hours. After the high temperature acceleration test, the track recorded before the test was reproduced, and the C / N ratio was measured. Furthermore, the erasing rate when the 11T signal was overwritten once on the sample was also measured.
[0074]
Table 1 shows the increase / decrease in the C / N ratio before and after the high temperature test at a linear velocity of 8.2 m / s for the materials of the lower interface layer and the upper interface layer, and the linear velocity of 20.5 m. 4 shows the increase / decrease of the erasing rate before the high-temperature test and the erasing rate after the high-temperature test in / s. Here, only the characteristics of the groove are shown because there is no large difference in characteristics between the groove and the land.
[0075]
The C / N ratio was higher at a linear velocity of 20.5 m / s than at 8.2 m / s, and the decrease after the high-temperature test was smaller, so only the case of 8.2 m / s is shown. ing. The erasure rate was higher at the linear velocity of 8.2 m / s than at the rate of 20.5 m / s, and the decrease after the high-temperature test was smaller, so only the case of 20.5 m / s is shown.
[0076]
[Table 1]

[0077]
From Table 1, it can be seen that mediums (disks) 1 to 3 in which carbon or carbide is not applied to the lower interface layer and the upper interface layer have high erasure rates at a linear velocity of 20.5 m / s and decrease after a high temperature test. There is almost no. However, at a linear velocity of 8.2 m / s, the C / N ratio is small and becomes even smaller after the high temperature test.
[0078]
On the other hand, the media 4 to 16 in which carbon or carbide is applied to the lower interface layer, the upper interface layer, or both have a C / N ratio before the high temperature test of 8.2 to 1 at a linear velocity of 8.2 m / s. And the decrease in the C / N ratio after the high-temperature test is as small as 0.2 dB or less. At a linear velocity of 20.5 m / s, the erasure rate is at least 30 dB before the high-temperature test, a sufficiently large value is obtained, and the decrease is small.
[0079]
Among them, particularly, the media 4 to 8 in which carbon or carbide is applied to the lower interface layer have a larger C / N ratio than the media 9 to 13 applied to the upper interface layer and the media 14 to 16 applied to both sides. .
[0080]
As described above, in the configuration using the recording layer made of Ge—Sb—Bi—Te, the lower interface layer or the upper interface layer, in particular, the lower interface layer is made of carbon or carbide, so that the red laser can be used. Good characteristics with a high C / N ratio and high erasing rate can be obtained in a wide linear velocity range with the used optical system.
[0081]
(Example 2)
Example 2 shows the recording / reproducing characteristics of the information recording medium of the present invention, particularly the dependence of the C / N ratio and the erasing rate on the material and composition of the recording layer.
[0082]
The configuration of the medium is the same as that of the first embodiment. In this embodiment, the lower interface layer is made of carbon, and the upper interface layer is made of (ZrO 2). ₂ ) ₂₅ (SiO ₂ ) ₂₅ (Cr ₂ O ₃ ) ₅₀ And the recording layer is Ge as shown in Table 2. ₃₈ Sb ₁₀ Te ₅₂ Medium (disk) 17, media 18 to 21 having a composition in which part of Ge was replaced with Sn, and media 22 to 25 having a composition in which part of Sb was replaced with Bi. The lower interface layer and the upper interface layer were formed in the same manner as in Example 1.
[0083]
The characteristics of the media 17 to 25 thus manufactured were measured in the same manner as in Example 1.
[0084]
Table 2 shows the increase / decrease of the C / N ratio before the high temperature test at 8.2 m / s and the C / N ratio after the high temperature test with respect to the material / composition of the recording layer, and the linear velocity at 20.5 m / s. The erasure rate before the high temperature test and the increase / decrease of the erasure rate after the high temperature test are shown. Here, only the characteristics of the groove are shown because there is no large difference in characteristics between the groove and the land.
[0085]
Also in this example, the C / N ratio was higher in the case of the linear velocity of 20.5 m / s than in the case of 8.2 m / s, and the amount of decrease after the high temperature test was smaller. Only the case is shown. The erasure rate was higher at the linear velocity of 8.2 m / s than at the rate of 20.5 m / s, and the decrease after the high-temperature test was smaller, so only the case of 20.5 m / s is shown.
[0086]
[Table 2]

[0087]
From Table 2, the recording layer is Ge ₃₈ Sb ₁₀ Te ₅₂ The medium 17 has a large C / N ratio at a linear velocity of 8.2 m / s, and there is no decrease in the C / N ratio after the high temperature test. However, when the linear velocity is 20.5 m / s, the erasing rate is low, and the erasing rate further decreases after the high temperature test. In the media 18 to 21 in which Sn is added to the recording layer, when the content of Sn is small, the erasing rate at a linear velocity of 20.5 m / s is small, and the decrease after the high-temperature test is large. Conversely, when Sn is large, the C / N ratio becomes low at a linear velocity of 8.2 m / s.
[0088]
On the other hand, in the mediums 22 to 25 in which Bi was added to the recording layer, a sufficient C / N ratio was obtained at 8.2 m / s as a whole, although there was a slight difference depending on the amount of added Bi. The decrease in the C / N ratio is also small. Even at a linear velocity of 20.5 m / s, the erasure rate is 30 dB or more, which is a sufficient value and the decrease is small.
[0089]
As described above, by using the Ge-Sb-Bi-Te alloy for the recording layer with the configuration using carbon for the interface layer, good characteristics can be obtained in a wide linear velocity range.
[0090]
(Example 3)
In Example 3, the recording / reproducing characteristics of the second information layer of the information recording medium of the present invention having two information layers, which is remote from the laser incident side, and particularly the dependence of the C / N ratio and the erasure rate on the interface layer material, are shown. Show.
[0091]
The medium had a configuration in which a transparent substrate, a first information layer, a separation layer, a second information layer, and a protection substrate were sequentially provided. Regarding the method for producing a medium, a second information layer, a separation layer, and a first information layer were formed on a protective substrate, and a transparent substrate was bonded thereon. The protective substrate used was a disk-shaped one having a diameter of 12 cm and a thickness of 1.1 mm, on which a guide groove having a groove pitch of 0.32 μm and a groove depth of 20 nm was formed.
[0092]
As a second information layer, a reflective layer Ag is used from the side close to the protective substrate. ₉₈ Pd ₁ Cu ₁ 80 nm, upper protective layer (ZnS) ₈₀ (SiO ₂ ) ₂₀ 20 nm, upper interface layer 5 nm, recording layer Ge ₄₅ Bi ₄ Te ₅₁ 10 nm, lower interface layer 5 nm, lower protective layer (ZnS) ₈₀ (SiO ₂ ) ₂₀ Was formed in the order of 60 nm.
[0093]
An ultraviolet curable resin is applied on the second information layer, and a different substrate for groove transfer having a guide groove with a groove pitch of 0.32 μm and a depth of 20 nm is bonded thereon, and the resin is cured in that state. . Thereafter, by separating the different substrate for groove transfer, a separation layer to which the guide groove is transferred is formed. The thickness of the separation layer was formed to be 25 μm.
[0094]
Since the recording layer of the second information layer at the time of formation is amorphous, the laser beam is irradiated from the separation layer side to perform an initialization process to make the entire surface of the recording layer of the second information layer a crystalline phase. Was.
[0095]
A reflective layer Ag is formed as a first information layer on the side of the separation layer where the guide groove is transferred. ₉₈ Pd ₁ Cu ₁ 10 nm, upper protective layer (ZnS) ₈₀ (SiO ₂ ) ₂₀ To 20 nm, the upper interface layer (ZrO ₂ ) ₂₅ (SiO ₂ ) ₂₅ (Cr ₂ O ₃ ) ₅₀ Is 5 nm and the recording layer Ge is ₄₅ Bi ₂ Sb ₂ Te ₅₁ Is 6 nm, and the lower interface layer (ZrO ₂ ) ₂₅ (SiO ₂ ) ₂₅ (Cr ₂ O ₃ ) ₅₀ 5 nm, lower protective layer (ZnS) ₈₀ (SiO ₂ ) ₂₀ Was formed in the order of 40 nm. Further, a transparent substrate having a thickness of 0.075 μm was bonded on the first information layer.
[0096]
Finally, since the recording layer of the first information layer at the time of formation is amorphous, a laser beam is irradiated from the transparent substrate side to initialize the entire surface of the recording layer of the first information layer to a crystal phase. Processing was performed.
[0097]
The same materials as in Example 1 were used for the lower interface layer and the upper interface layer of the second information layer. These interface layers were formed in the same manner as in Example 1.
[0098]
The information recording medium of the present embodiment manufactured in this manner has a linear velocity of 5.0 m / s (reference clock T = 15.0 ns) using an optical system having a laser beam wavelength of 405 nm and an objective lens of NA of 0.85. And 10.0 m / s (reference clock T = 7.5 ns), the mark edge recording was performed, and the following measurement was performed. At any linear velocity, first, a signal in which a 2T mark and a 2T space are continuous (hereinafter referred to as a 2T signal) and a signal in which a 9T mark and a 9T space are continuous (hereinafter referred to as a 9T signal) are alternately repeated eleven times. Recorded. Then, this track was reproduced with the 2T signal recorded, and its C / N ratio was measured with a spectrum analyzer. Further, the attenuation ratio of the 2T signal amplitude when the 9T signal was recorded once thereon, that is, the erasure rate was measured by a spectrum analyzer.
[0099]
Regarding the modulation waveform of the laser at the time of recording a signal, a single rectangular pulse having a pulse width of 0.5T (power level P1) was applied when recording a 2T signal at any linear velocity. When recording a 9T signal, a pulse train (power level P1) composed of eight pulses was irradiated. In this pulse train, all the pulse widths and the width between the pulses (power level P3) were set to 0.5T. In a portion where no mark is recorded, continuous light of power level P2 was irradiated. As a power level determination method, the recording power level P1 is 1.5 times the lower limit value of the power at which the C / N ratio exceeds 35 dB, and the power level P2 is the median value of the power range at which the erasure rate exceeds 20 dB. And the reproducing power level was 0.3 mW.
[0100]
The information recording medium measured under the above conditions was subjected to a high-temperature acceleration test in which the 2T signal was kept recorded and kept in a thermostat at 90 ° C. and 20% RH for 100 hours. After the high temperature acceleration test, the track recorded before the test was reproduced, and the C / N ratio was measured. Furthermore, the erasure rate when a 9T signal was recorded once thereon was also measured.
[0101]
Table 3 shows the increase / decrease in the C / N ratio before and after the high-temperature test at a linear velocity of 5.0 m / s for the materials of the lower interface layer and the upper interface layer, and the linear velocity of 10.0 m. 4 shows the increase / decrease of the erasing rate before the high-temperature test and the erasing rate after the high-temperature test in / s.
[0102]
The C / N ratio was higher in the case of the linear velocity of 10.0 m / s than in the case of the 5.0 m / s, and the amount of decrease after the high temperature test was smaller. ing. The erasing rate was higher in the case of the linear velocity of 5.0 m / s than in the case of the 10.0 m / s, and the amount of decrease after the high-temperature test was smaller, so only the case of 10.0 m / s is shown.
[0103]
[Table 3]

[0104]
According to Table 3, the mediums 26 to 28 in which carbon or carbide is not applied to the lower interface layer and the upper interface layer can obtain a large erasing rate at a linear velocity of 10.0 m / s. However, at a linear velocity of 5.0 m / s, the C / N ratio is small and becomes even smaller after the high temperature test.
[0105]
On the other hand, the media 29 to 41 in which carbon or carbide is applied to both the lower interface layer and the upper interface layer have a C / N ratio before the high-temperature test at a linear velocity of 5.0 m / s. And the decrease in the C / N ratio after the high-temperature test is as small as 0.2 dB or less. At a linear velocity of 10.0 m / s, the erasure rate before the high-temperature test is 30 dB or more, which is a sufficiently large value and the decrease is small.
[0106]
Among them, particularly, the mediums 34 to 38 in which carbon or carbide is applied to the upper interface layer have a larger C / N ratio as compared with the media 29 to 33 applied to the lower interface layer and the media 39 to 41 applied to both sides. .
[0107]
As described above, an optical system using a blue laser can be formed by using a recording layer made of Ge-Bi-Te and using a lower interface layer or an upper interface layer, particularly an upper interface layer, of carbon or carbide. Thus, good characteristics with a high C / N ratio and high erasing rate can be obtained in a wide linear velocity range.
[0108]
【The invention's effect】
As described above, according to the present invention, a remarkable effect that an information recording medium satisfying good recording / reproducing characteristics can be realized in a wide linear velocity range can be obtained. Further, according to the present invention, it is possible to easily and reliably record and reproduce information at different linear velocities.
[Brief description of the drawings]
FIG. 1 is a sectional view showing a configuration example of an information recording medium of the present invention.
FIG. 2 is a sectional view showing another configuration example of the information recording medium of the present invention.
FIG. 3 is a cross-sectional view showing a configuration example including two information layers of the information recording medium of the present invention.
FIG. 4 is a diagram showing an example of a pulse train in the embodiment of the present invention.
FIG. 5 is a diagram showing a configuration example of a recording / reproducing apparatus used for implementing the present invention.
[Explanation of symbols]
1 Transparent substrate
2 Lower protective layer
3 Lower interface layer
4 Recording layer
5 Upper interface layer
6 Upper protective layer
7 Reflective layer
8 Protection board
9 Light absorption correction layer
10 First information layer
11 Separation layer
12 Second information layer
13 grooves
14 Land

Claims (13)

On a transparent substrate, from the side close to the transparent substrate, a lower protective layer, a lower interface layer, a recording layer that changes between at least two different optically detectable states by light beam irradiation, an upper interface layer, Including the upper protective layer and the reflective layer in this order,
At least one selected from the lower interface layer and the upper interface layer mainly contains at least one carbide selected from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W and Si, or carbon. Consisting of ingredients
An information recording medium, wherein the recording layer contains Ge, Bi, and Te. On a transparent substrate, a plurality of information layers are respectively interposed via a separation layer, and the information layer farthest from the transparent substrate is a lower protective layer, a lower interface layer, and light beam irradiation from a side closer to the transparent substrate. A recording layer, an upper interface layer, an upper protective layer, and a reflective layer, which change between at least two different optically detectable states, in this order,
At least one selected from the lower interface layer and the upper interface layer mainly contains at least one carbide selected from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W and Si, or carbon. Consisting of ingredients
An information recording medium, wherein the recording layer contains Ge, Bi, and Te. 3. The information recording medium according to claim 1, further comprising a light absorption correction layer between the upper protective layer and the reflective layer. 4. The information recording medium according to claim 1, wherein the recording layer further contains Sb. Recording _{layer, Ge x (Sb 1-p} Bi p) information recording medium according to claim 1 comprising the y Te _z material represented by.
However, x + y + z = 100, 20 ≦ x ≦ 50, 0 <y ≦ 25, 45 ≦ z ≦ 60, and 0 <p ≦ 1. 6. The information recording medium according to claim 5, wherein x ≧ 35. On a transparent substrate, from the side close to the transparent substrate, a lower protective layer, a lower interface layer, a recording layer that changes between at least two different optically detectable states by light beam irradiation, an upper interface layer, A method for recording information on an information recording medium including an upper protective layer and a reflective layer in this order,
At the time of recording the information, two or more modes are applied, and while rotating the medium at a predetermined linear velocity selected from two or more linear velocities corresponding to the two or more modes, a light beam is applied to the medium. A method of recording information on an information recording medium, comprising irradiating and recording the information. On a transparent substrate, a plurality of information layers are respectively interposed via a separation layer, and the information layer farthest from the transparent substrate is a lower protective layer, a lower interface layer, and light beam irradiation from a side closer to the transparent substrate. A method for recording information on an information recording medium including a recording layer, an upper interface layer, an upper protective layer, and a reflective layer in this order that changes between at least two different states that are optically detectable by
At the time of recording the information, two or more modes are applied, and while rotating the medium at a predetermined linear velocity selected from two or more linear velocities corresponding to the two or more modes, a light beam is applied to the medium. A method of recording information on an information recording medium, comprising irradiating and recording the information. 9. The information recording medium according to claim 7, wherein the two or more different linear velocities include a first linear velocity and a second linear velocity that is 1.5 times or more the first linear velocity. How information is recorded. The lower interface layer is made of at least one selected from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W and Si, or a material containing carbon as a main component,
The method for recording information on an information recording medium according to any one of claims 7 to 9, wherein a wavelength of the light beam is from 600 nm to 700 nm. The upper interface layer is made of at least one selected from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W and Si, or a material containing carbon as a main component,
The method for recording information on an information recording medium according to any one of claims 7 to 9, wherein the wavelength of the light beam is 450 nm or less. On a transparent substrate, from the side close to the transparent substrate, a lower protective layer, a lower interface layer, a recording layer that changes between at least two different optically detectable states by light beam irradiation, an upper interface layer, An apparatus for recording information on an information recording medium including an upper protective layer and a reflective layer in this order,
At the time of recording the information, two or more modes are applied, and while rotating the medium at a predetermined linear velocity selected from two or more linear velocities corresponding to the two or more modes, a light beam is applied to the medium. An information recording apparatus for recording information on an information recording medium, wherein the information is recorded by irradiation. On a transparent substrate, a plurality of information layers are respectively interposed via a separation layer, and the information layer farthest from the transparent substrate is a lower protective layer, a lower interface layer, and light beam irradiation from a side closer to the transparent substrate. An information recording apparatus for recording information on an information recording medium including a recording layer, an upper interface layer, an upper protective layer, and a reflective layer, which change in at least two different states that are optically detectable in this order,
At the time of recording the information, two or more modes are applied, and while rotating the medium at a predetermined linear velocity selected from two or more linear velocities corresponding to the two or more modes, a light beam is applied to the medium. An information recording apparatus for recording information on an information recording medium, wherein the information is recorded by irradiation.

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