JP2004005767A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording medium having the satisfied sensitivity and repeated recording property and also capable of recording with the high speed and high density, in the phase transition type optical recording medium. <P>SOLUTION: This optical recording medium is constituted so that a lower protective layer 2, a recording layer 3 reversibly changing phase between an amorphous phase and a crystalline phase, an upper protective layer 4, and a reflective layer 5 having the main component such as Ag are laminated in this order on a transparent substrate 1, and the upper protective layer 4 consists of ZrO<SB>2</SB>, SiO<SB>2</SB>, TiO<SB>2</SB>and X<SB>1</SB>, and the X<SB>1</SB>is at least one kind among Y<SB>2</SB>O<SB>3</SB>, CeO, Al<SB>2</SB>O<SB>3</SB>, MgO, CaO, Nb<SB>2</SB>O<SB>5</SB>and rare earth oxides. Also, a lower 2nd protective layer 6 is arranged between the lower protective layer 2 and the recording layer 3, and also for this lower 2nd protective layer 6, the same material as that of the upper protective layer 4 is used. <P>COPYRIGHT: (C)2004,JPO

Description

【００８７】
実施例６〜１０
基板の溝ピッチを０．７４μｍ、溝幅０．２５μｍ、溝深さ２５ｎｍ、厚さ０．６ｍｍのポリカーボネート製基板を用い、この上にスパッタリング方式により各層を積層した。下部保護層は、ＺｎＳ：ＳｉＯ_２＝８０：２０（ｍｏｌ％）のターゲットを使用し、膜厚を６０ｎｍとした。次に、表２に示すような、第２の下部保護層と所定の記録線速で記録可能な記録層を膜厚１７ｎｍとし、順に作製した。ＺｒＯ_２、ＳｉＯ_２、ＴｉＯ_２およびＸ_１（該Ｘ_１はＹ_２Ｏ_３、ＣｅＯ、Ａｌ_２Ｏ_３、ＭｇＯ、ＣａＯ、Ｎｂ_２Ｏ_５および希土類酸化物のうちの少なくとも一種）からなる混合物層を膜厚１２ｎｍとし上部保護層とした。さらにＡｇを膜厚１６０ｎｍとし反射層とした。紫外線硬化樹脂を塗布し、２μｍ厚として保護とした。最後に、膜のないもう一枚の基板を紫外線硬化樹脂で貼合わせて厚さ１．２ｍｍとし、記録媒体とした。
その後、大口径ＬＤ（１μｍ×１００μｍ）を用い、線速３．５ｍ／ｓ、パワー８５０ｍＷで記録層を結晶化させた。記録再生は波長６５５ｎｍ、対物レンズＮＡ０．６５のピックアップヘッドを用いて、記録線速１７ｍ／ｓで記録密度が２６７μｍ／ｂｉｔとなるように記録した。消去パワーは６ｍＷとした。
表３に、初回、繰り返し記録１０００回後のジッターを示す。これら記録媒体を記録後、８０℃、８５％ＲＨの環境に３００時間放置しても、ジッター劣化はほとんどなかった。
【００８８】
【表２】

【００８９】
【表３】

【００９０】
比較例１
基板の溝ピッチを０．７４μｍ、溝幅０．２５μｍ、溝深さ２５ｎｍ、厚さ０．６ｍｍのポリカーボネート製基板を用い、この上にスパッタリング方式により各層を積層する。下部保護層は、ＺｎＳ：ＳｉＯ_２＝８０：２０（ｍｏｌ％）のターゲットを使用し、膜厚を７０ｎｍとした。次に、表２に示すような、所定の記録線速で記録可能な記録層を膜厚１７ｎｍとして作製した。ＺｎＳ：ＳｉＯ_２＝８０：２０（ｍｏｌ％）混合物層を膜厚１２ｎｍとし上部保護層とした。次に、硫化防止層としてＳｉＣ４ｎｍの膜厚にしてつけた。硫化防止層を設けた後、Ａｇを膜厚１６０ｎｍとし反射層とした。紫外線硬化樹脂を塗布し、２μｍ厚として保護層とした。最後に、膜のないもう一枚の基板を紫外線硬化樹脂で貼合わせて厚さ１．２ｍｍとし、記録媒体とした。
その後、大口径ＬＤ（１μｍ×１００μｍ）を用い、線速３．５ｍ／ｓ、パワー７５０ｍＷで記録層を結晶化させた。記録再生は波長６５５ｎｍ、対物レンズＮＡ０．６５のピックアップヘッドを用いて、記録線速１４ｍ／ｓで記録密度が０．２６７μｍ／ｂｉｔとなるように記録した。
【００９１】
比較例１の媒体を実施例１と比較した。その結果、初回記録時のジッターは実施例１では７％台だが、比較例１では８％台であり、また１０００回繰り返し記録時のジッターは、実施例１では１０％台に抑えられているの対して、比較例１では１２％を越えており、いずれの特性も実施例の方が良かった。これは、硫化防止層を設けたことにより、最適な層構成、記録層組成がずれたためと思われる。
また、初回記録時の記録パワー依存性を評価したところ、ジッターを１０％未満とするために、実施例５ではＰｗ１３ｍＷ以上であれば十分であったのに対して、比較例１では１４ｍＷ以上にする必要があった。
またさらに、比較例１においては、硫化防止層を設けるために製膜装置を改造し、あらたに真空チャンバーを設ける必要があった。このため、媒体１枚あたりの製造コストが上昇した。
また、比較例１においては、記録媒体を記録後、８０℃、８５％ＲＨの環境に３００時間放置したところ、製造した媒体のうち１％くらいの割合で、反射面に欠陥が生じる不良媒体が出た。
【００９２】
実施例１１
トラックピッチ０．７４μｍ、直径１２ｃｍ、厚さ０．６ｍｍのポリカーボネート基板上にマグネトロンスパッタリング法にて、下部保護層にＺｎＳ（８０ｍｏｌ％）ＳｉＯ_２（２０ｍｏｌ％）を６５ｎｍ、相変化記録層にＧｅ：Ｓｂ：Ｔｅ＝４．８９：７７．２８：１７．８３（ａｔ％）を１７ｎｍ、上部保護層にＺｒＯ_２−ＳｉＯ_２（２０ｍｏｌ％）−ＴｉＯ_２（２０ｍｏｌ％）−Ｙ_２Ｏ_３（３ｍｏｌ％）を１０ｎｍ、反射放熱層にＡｇを１４０ｎｍ順次積層し、更に反射放熱層上にアクリル系紫外線硬化樹脂をスピンコートし紫外線照射によって形成した有機保護膜を介して直径１２ｃｍ、厚さ０．６ｍｍのポリカーボネート基板を接着シートにより貼り合せることによりディスクを作成した。このディスクを照射ビーム口径１μｍ×１００μｍの光ディスク初期化装置を用い、出力８２０ｍＷ、ビーム送り速度３６μｍ／ｒｏｔ、線速３ｍ／ｓｅｃの条件で初期結晶化を試みたところ、反射率分布の均一な初期結晶化が可能であった。初期結晶化後、光ディスク評価装置（波長６６０ｎｍ、ＮＡ　０．６５）を用いて記録線速１７．５ｍ／ｓにてＥＦＭ＋ランダム信号の繰り返し記録を行い、ジッターを測定した。記録パワーは１９ｍＷ、バイアスパワー０．１ｍＷ、消去パワー６ｍＷとし、記録ストラテジは本試料用に１Ｔ周期ストラテジを最適化したものを用いた。また再生は線速３．５ｍ／ｓ、パワー０．７ｍＷとした。このとき初回及び１０００回オーバーライト後のジッターは、７．８％、９．６％と実用上十分小さく、モジュレーションも６２．２％、６４．１％とそれぞれと非常に良好な値であった。またこのディスクを湿熱オーブンを用いて８０℃、８５ＲＨ、５００時間の加速劣化試験を行い、ジッターや変調度の変化について調査したところ、ジッターの上昇やモジュレーションの変化はほとんど見られず、マーク消失の傾向は見られなかった。
【００９３】
実施例１２
実施例１１の相変化記録層の組成をＧｅ：Ｇａ：Ｓｂ：Ｔｅ＝４．９１：２．９０：７６．０９：１６．１０（ａｔ％）とした他は、実施例１１と同様にして光ディスクを作成した。このディスクを照射ビーム口径１μｍ×１００μｍの光ディスク初期化装置を用い、出力７２０ｍＷ、ビーム送り速度３６μｍ／ｒｏｔ、線速３ｍ／ｓｅｃの条件で初期結晶化を試みたところ、反射率分布の均一な初期結晶化が可能であった。このとき記録可能最高線速は実施例１１に比較し、より高速記録が可能であった。同様にこのディスクを湿熱オーブンを用いて８０℃、８５ＲＨ、５００時間の加速劣化試験を行いジッターや変調度の変化について調査したところ、ジッターの上昇やモジュレーションの変化はほとんど見られずマーク消失の傾向は見られなかった。
尚、記録可能最高線速とは、記録・消去パワー及び記録ストラテジを最適化後、初回記録時のジッターが１０％以下で記録可能な線速度を示す。
【００９４】
実施例１３
実施例１１の上部保護層組成をＺｒＯ_２−ＳｉＯ_２（２０ｍｏｌ％）−ＴｉＯ_２（４０ｍｏｌ％）−Ｙ_２Ｏ_３（３ｍｏｌ％）とした他は、実施例１１と同様にして光ディスクを作成した。このディスクを照射ビーム口径１μｍ×１００μｍの光ディスク初期化装置を用い、出力８００ｍＷ、ビーム送り速度３６μｍ／ｒｏｔ、線速３ｍ／ｓｅｃの条件で初期結晶化を試みたところ、反射率分布の均一な初期結晶化が可能であった。初期結晶化後、同様にしてジッターを測定したところ、初回記録のジッターは８．１％と充分小さい値であった。このディスクを湿熱オーブンを用いて８０℃、８５ＲＨ、５００時間の加速劣化試験を行い、ジッターや変調度の変化について調査したところ、ジッターの上昇やモジュレーションの変化は全く見られなかった。
【００９５】
実施例１４
実施例１１の相変化記録層の組成をＧｅ：Ｇａ：Ｓｂ：Ｔｅ＝３．０２：２．９６：７５．０５：１８．９７（ａｔ％）とした他は、実施例１１と同様にして光ディスクを作成した。このディスクを照射ビーム口径１μｍ×１００μｍの光ディスク初期化装置を用い、出力８４０ｍＷ、ビーム送り速度３６μｍ／ｒｏｔ、線速３ｍ／ｓｅｃの条件で初期結晶化を試みたところ、反射率分布の均一な初期結晶化が可能であった。初期結晶化後、同様にして、ＥＦＭ＋ランダム信号の記録を行いジッターを測定したところ、初回記録のジッターは７．７％と充分小さい値であったが、このディスクを湿熱オーブンを用いて８０℃、８５ＲＨ、１００時間の加速劣化試験を行ったところ、１００時間後に記録マークの消失傾向が見られた。
【００９６】
【発明の効果】
以上のように、請求項１の光記録媒体によれば、特定の層構成及び上部保護層材料としたことから、高線速記録において、優れた記録特性を有する相変化型光記録媒体を得ることができる。
【００９７】
請求項２〜４の光記録媒体によれば、上記記録媒体における上部保護層材料の混合比の範囲又は主成分を限定したことから、高線速、高密度記録において、高感度で、オーバーライト特性及びアモルファスマークの保存信頼性等に優れた記録特性を有する相変化型光記録媒体を得ることができる。
【００９８】
請求項５及び６の光記録媒体によれば、上記記録媒体において特定下部保護層材料としたことから、オーバーライト特性を向上させ、記録マークをより安定して形成することができる。
【００９９】
請求項７の光記録媒体によれば、上記記録媒体において、下部保護層と記録層の間に下部第２保護層を設け、該下部第２保護層も前記上部保護層と同様の材料としたことから、繰り返し記録特性をより改善することができる。
【０１００】
請求項８〜１３の光記録媒体によれば、初期結晶化も容易でオーバーライトによる特性劣化も少ないなど優れた記録層を形成することができ、高線速記録において優れた記録特性と保存特性を有する相変化型光記録材料を得ることができる。
【０１０１】
請求項１４の光記録媒体によれば、記録層を特定の原子及び原子比率のもので形成したことから、高線速、高密度記録において、高感度でオーバーライト特性に優れ、特に記録マークの保存信頼性に優れた相変化型光記録媒体を得ることができる。
【０１０２】
請求項１５の光記録媒体によれば、上記記録層に更に特定の元素を含有させたことから、より高線速記録に適した相変化型光記録媒体を得ることができる。
【０１０３】
請求項１６及び１７の光記録媒体によれば、反射層を最適な材料で形成したことから、記録マークをより安定して形成することができる。特にＡｇを主成分とする反射層としたことにより、感度が向上し、記録マークの形成をさらに安定にすることができる。
【０１０４】
請求項１８及び１９の光記録媒体によれば、上部保護層の膜厚が４ｎｍ〜２０ｎｍ、或いは下部保護層の膜厚が５０ｎｍ〜２００ｎｍであることから、感度が悪化せず、また冷却速度が遅くならず、高密度高線速記録において、優れた記録特性が得られ、しかも保存特性の良好な相変化型光記録媒体を得ることができる。
【０１０５】
請求項２０の光記録媒体によれば、下部第２保護層の膜厚が２ｎｍ〜１０ｎｍであることから、放熱性を悪化させることなく繰り返し記録特性をより改善するなど高密度高線速記録において優れた記録特性と保存特性を有する相変化型光記録媒体を得ることができる。
【０１０６】
請求項２１及び２２の光記録媒体によれば、記録層の膜厚が１２ｎｍ〜２０ｎｍ、或いは反射層の膜厚が９０ｎｍ〜２００ｎｍであることから、いずれも最適膜厚であり、記録特性に優れた相変化型光記録媒体を得ることができる。
【図面の簡単な説明】
【図１】本発明における第一の光記録媒体の例を示す概略断面図。
【図２】本発明における第二の光記録媒体の例を示す概略断面図。
【図３】上部保護層材料がＺｒ_２Ｏ系の場合とＺｎＳ−ＳｉＯ_２の場合のオーバーライト回数によるジッター変化を示すグラフ。
【図４】本発明におけるパルスパターンを模式的に示す図。
【符号の説明】
１　基板
２　下部保護層
３　記録層
４　上部保護層
５　銀あるいは銀合金反射層
６　下部第２保護層[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a phase-change optical recording medium that has excellent recording characteristics at high linear velocity and high density recording, and that can ensure storage reliability. More specifically, the present invention relates to a configuration and a material of a phase change optical recording medium, and the optical recording material can be applied to a large capacity optical file or a DVD + RW disc.
[0002]
[Prior art]
An optical recording medium on which information can be rewritten by irradiating a semiconductor laser beam uses a magneto-optical recording method in which magnetization is reversed using heat to perform recording and erasing, and a reversible phase change between crystalline and amorphous. There is a phase change recording method for performing recording and erasing by utilizing. The latter is capable of single beam overwriting, and is characterized by a simpler optical system on the drive side, and uses the reversible phase change of the crystalline and amorphous phases used for the latter recording method, so-called The phase-change recording medium is applied as a rewritable recording medium as a computer-related recording medium or a video-acoustic recording medium, and has spread worldwide. With the spread of CD-R and CD-RW recording media, high-speed recording is progressing, and the use of phase-change optical recording media is expected to expand to high-density image recording in the future. Increasingly, therefore, high-speed recording is essential.
[0003]
Such a phase-change optical recording medium is composed of a substrate and a recording layer provided on the substrate, and a heat-resistant and light-transmitting dielectric protection layer is provided on both surfaces of the recording layer. ing. On the dielectric layer on the side opposite to the light beam incident direction, a reflective heat dissipation layer such as a metal or an alloy is laminated. Recording and erasing are possible only by changing the power of the laser beam.The recording method generally changes the crystalline state to an unrecorded / erased state, and the formation of recording marks involves heating the crystalline part of the recording layer to a temperature higher than the melting point. After that, it is performed by quenching and making the recording layer amorphous
[0004]
In order to realize high-speed recording, it is necessary to control heating and rapid cooling of the recording layer in a shorter time. This becomes more remarkable as the recording density increases and the pulse frequency of the laser light emission pulse increases. Further, since the pulse width of the light emission pulse applied to the recording layer becomes narrow (because the reference clock (T) becomes small), a higher laser power is required. This is because if the pulse width is widened, the time during which a pulse required for cooling is not emitted becomes shorter, the area and length of the amorphous phase become smaller, and it becomes difficult to form a mark having a desired length. In order to perform heating and rapid cooling in a short time, it is necessary to apply a higher recording power and increase the pulse off time. Then, it is necessary to cope with a decrease in recording sensitivity by increasing the recording power as the recording linear velocity increases.
[0005]
However, when high-speed overwriting is performed while maintaining such high density, the recording layer is heated to a high temperature (above the melting point) in a short time with high laser power, and then repeatedly subjected to thermal stress such as rapid cooling or slow cooling. Deterioration occurs, causing a problem that the overwrite characteristics are deteriorated.
One of the causes of the deterioration of the recording layer is considered to be the movement of the recording layer in the track direction and the radial direction due to repeated recording. That is, the recording film gradually moves to the front and / or rear of the track due to repeated recording, and the recording film accumulates or becomes thinner at the start end and the end end of the recording. It is considered that the recording film in the center portion in the width direction of the track is pushed away and accumulated on the track wall side, so that the recording film in the center portion in the width direction of the track becomes thin. This also causes a decrease in tracking stability.
[0006]
On the other hand, since the heat mode of heating, melting, and cooling is repeated in a short time, not only the recording layer but also the dielectric protection layer that protects the recording layer is locally heated, and the recording layer is thermally expanded. Also, partial thermal deformation occurs in the substrate and pinholes are generated due to the thermal deformation, which also causes a decrease in overwrite characteristics.
[0007]
For this reason, the dielectric protection layer is disposed so as to sandwich the recording layer, controls the heat diffusion of heating and cooling of the recording layer at the time of recording, and also causes the recording layer to move or be moved by the irradiation of the recording beam. It is required to have the effect of preventing holes from being formed. Therefore, the material constituting the dielectric protective layer must be optically transparent to laser light, have sufficient heat resistance and mechanical strength (melting point, softening point, decomposition temperature, hardness, Young's modulus). ), An appropriate material is selected from the viewpoints of a small coefficient of thermal expansion, wettability to the recording layer and the substrate, and easy formation.
[0008]
Conventionally, as a protective layer of a phase change type optical disk, ZnS and SiO2 which are substantially transparent at the recording wavelength and whose refractive index is larger than the refractive index of the transparent substrate and smaller than the refractive index of the recording layer.₂Have been used. This is because the phase change film is protected from deterioration such as oxidation and the resistance to thermal stress when recording is repeated is large. Another advantage is that the heat conductivity is small and the recording sensitivity of the disc can be improved, and the adhesiveness to the recording layer made of a chalcogenide alloy thin film such as GeSbTe is excellent.
[0009]
However, in recent years, when recording is performed at a higher speed and at a higher density, and repeatedly, high-temperature heating and cooling are repeated in a short time with a higher optical power density as described above, so that not only the recording layer but also between the recording layer and the reflective layer. The protective layer also has a large stress due to heat at the time of recording and is more likely to be deteriorated. To improve the overwrite characteristics, the tensile strength and toughness of the protective film are reduced by ZnS-SiO2.₂It is required to be even larger.
[0010]
On the other hand, a recording material having a high crystallization rate is required. Here, the Sb-Te eutectic phase change recording material such as Ag-In-Sb-Te as a phase change recording medium has a high crystallization speed and is capable of high-speed erasing in high linear velocity recording. Attention has been paid. In other words, Sb-Te eutectic phase change recording materials such as Ag-In-Sb-Te have a high crystallization speed and may be promising materials for high-speed erasure in high linear velocity recording. Are known.
[0011]
However, in order to realize high-speed recording, it is not sufficient to simply increase the crystallization speed of the recording layer, and another important issue is to secure recording sensitivity. This is because, when a recording layer material and composition in which high-speed erasure is prioritized is used, mark formation becomes difficult due to a decrease in glass forming ability accompanying an increase in crystallization speed, and a problem of insufficient sensitivity occurs.
[0012]
In recent years, in order to solve the problem of insufficient sensitivity, Ag has come to be used as a reflective heat dissipation layer instead of a conventional Al alloy-based material. Since the Ag reflective heat dissipation layer has extremely high thermal conductivity, a quenched disk structure suitable for forming a recording mark can be realized.
[0013]
However, when the Ag reflective heat dissipation layer is used, there are the following problems.
That is, ZnS.SiO, which has been conventionally used as a protective layer material,₂Is used as a protective layer, the protective layer (ZnS.SiO₂Due to the reaction with sulfur contained in (1), sulfurization of Ag becomes a problem. A method of solving the problem of sulfurization by providing a sulfurization prevention layer made of SiC, Si, Ge or the like can be considered. However, the provision of the sulfurization prevention layer fluctuates the recording characteristics and complicates production management. Problems arise in various points such as cost increase.
[0014]
Therefore, the protective layer does not contain sulfur and the heat resistance of the protective layer is ZnS.SiO.₂As a promising material having a higher (higher melting point), for example, ZrO₂An optical recording medium using the same has been proposed (JP-A-9-138947). ZrO₂Is a material that has extremely high heat resistance and mechanical strength, is resistant to the heat load in repeated recording, and can be expected to improve the repetition characteristics. Further, since the thermal conductivity is extremely low, the temperature reached at the time of recording becomes high even at a low recording power, so that the cooling gradient becomes large and there is a possibility that the sensitivity can be improved.
[0015]
However, according to our knowledge, ZrO₂When is used for the protective layer, there occurs a problem that the storage reliability of the recording mark (amorphous mark) cannot be maintained. That is, when the medium on which information is recorded is placed in a high-temperature, high-humidity environment, the recording marks are crystallized and disappear. This is probably ZrO₂Since the film is in a crystalline state, if left in a high temperature environment for a long time, ZrO₂This is considered to be because the film promotes generation of crystal nuclei and crystal growth of the recording layer, and promotes crystallization of the recording mark (deterioration of the mark).
[0016]
On the other hand, such ZrO₂Or ZrO₂The optical recording medium used for the protective layer material having a composition containing: JP-A-2000-11450, JP-A-05-144085, JP-A-08-180458, JP-A-08-287515, and JP-A-08-287515. It has also been proposed in Japanese Patent Application Laid-Open Nos. 11-039713, 11-339332 and 2850754.
However, this is aimed at improving overwrite characteristics and the like, and nothing is disclosed about the improvement in the storage reliability of recording marks.
[0017]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and to provide a phase-change recording medium with good sensitivity and excellent repetitive recording characteristics, high-speed and high-density recording, overwrite characteristics and amorphous mark storage reliability. An object of the present invention is to provide an optical recording medium excellent in performance.
[0018]
[Means for Solving the Problems]
The above object of the present invention is achieved by the following means.
That is, according to the present invention,
First, an optical recording medium in which a lower protective layer, a recording layer that undergoes a reversible phase change of an amorphous phase and a crystalline phase, an upper protective layer, and a reflective layer are stacked in this order on a transparent substrate, The protective layer is ZrO₂, SiO₂, TiO₂And X₁Consisting of₁Is Y₂O₃, CeO, Al₂O₃, MgO, CaO, Nb₂O₅And an optical recording medium characterized by being at least one of rare earth oxides.
[0019]
Second, the composition of the upper protective layer (ZrO₂) A (SiO₂) B (TiO₂) C (X₁3) The optical recording medium according to the first aspect, wherein each ratio (mol%) in d is as follows.
30 ≦ a <100, 0 <b ≦ 40, 0 <c ≦ 40, 0.1 ≦ d ≦ 10, a + b + c + d = 100
[0020]
Third, the protective layer is made of ZrO.₂The optical recording medium according to the first or second aspect, wherein the optical recording medium is made of a material mainly containing
[0021]
Fourth, the ZrO₂Is a partially stabilized zirconia, wherein the optical recording medium according to the third aspect is provided.
[0022]
Fifth, the lower protective layer is made of ZrO.₂The optical recording medium according to any one of the first to fourth aspects, wherein the optical recording medium is made of a material containing, as a main component.
[0023]
Sixth, the following protective layer is made of ZnS and SiO₂Or ZnS and ZrO₂The optical recording medium according to any one of the first to fourth aspects, wherein the optical recording medium comprises a mixture of
[0024]
Seventh, a lower second protective layer is provided between the lower protective layer and the recording layer, and the lower second protective layer is made of ZrO.₂, SiO₂, TiO₂And X₂Consisting of₂Is Y₂O₃, CeO, Al₂O₃, MgO, CaO, Nb₂O₅The optical recording medium according to any one of the first to sixth aspects, wherein the optical recording medium is at least one of a rare earth oxide and a rare earth oxide.
[0025]
Eighth, the recording layer is at least Ge, Ga and / or In, Sb, Te and X₃And the X₃Is an at least one of Ag, Cu, Dy and Mn. The optical recording medium according to any one of the first to seventh aspects is provided.
[0026]
Ninth, the optical recording medium according to the eighth, wherein the atomic ratio Sb / (Sb + Te) of Sb and Te in the recording layer is 0.65 to 0.85.
[0027]
Tenthly, there is provided the optical recording medium according to the eighth or ninth aspect, wherein the atomic ratio of Ge in the recording layer is 0.04 to 0.07.
[0028]
Eleventh, the optical recording medium according to any one of the eighth to tenth is provided, wherein the atomic ratio of Ga and / or In of the recording layer is 0.02 to 0.07. You.
[0029]
Twelfth, X of the recording layer₃The optical recording medium according to any one of the eighth to eleventh, wherein the atomic ratio of the optical recording medium is 0.01 to 0.1.
[0030]
Thirteenth, X of the recording layer₃Is Mn, the optical recording medium according to any one of the eighth to twelfth aspects, provided.
[0031]
Fourteenth, the recording layer is made of Ge._αSb_βTe_{1- α − β}Wherein each atomic ratio satisfies 0.04 ≦ α ≦ 0.07, 0.65 ≦ β ≦ 0.85, wherein the optical recording medium according to any one of the first to seventh aspects, Provided.
[0032]
Fifteenthly, the optical recording medium according to the fourteenth aspect is provided, wherein the recording layer further contains at least one element of Ga, In, Dy, and Mn.
[0033]
Sixteenth, the optical recording according to any one of the first to fifteenth features, wherein the reflection layer is made of a metal containing at least one of Ag, Au, Cu, and Al as a main component. A medium is provided.
[0034]
Seventeenthly, the optical recording medium according to the sixteenth aspect is provided, wherein the reflective layer is mainly composed of Ag.
[0035]
Eighteenthly, the optical recording medium according to any one of the first to seventeenth features is provided, wherein the thickness of the upper protective layer is 4 nm to 20 nm.
[0036]
Nineteenthly, the optical recording medium according to any one of the first to eighteenth aspects is provided, wherein the thickness of the lower protective layer is 50 nm to 200 nm.
[0037]
Twentieth, the optical recording medium according to any one of the seventh to nineteenth aspects, wherein the lower second protective layer has a thickness of 2 nm to 10 nm.
[0038]
Twenty-first, the optical recording medium according to any one of the first to twentieth, wherein the thickness of the recording layer is 12 nm to 20 nm.
[0039]
Twenty-second, the optical recording medium according to any one of the first to twenty-first, wherein the thickness of the reflective layer is 90 nm to 200 nm.
[0040]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
As described above, the first configuration of the present invention comprises, on a transparent substrate 1, a lower protective layer 2, a recording layer 3 that undergoes a reversible phase change between an amorphous phase and a crystalline phase,₂, SiO₂, TiO₂And X₁(The X₁Is Y₂O₃, CeO, Al₂O₃, MgO, CaO, Nb₂O₅And at least one of rare earth oxides) and an upper protective layer 4 and a reflective layer 5 (see FIG. 1).
[0041]
The second configuration is such that a lower protective layer 2 and a ZrO₂, SiO₂, TiO₂And X₂(The X₂Is Y₂O₃, CeO, Al₂O₃, MgO, CaO, Nb₂O₅And at least one of rare earth oxides), a recording layer 3 that undergoes a reversible phase change between an amorphous phase and a crystalline phase, ZrO.₂, SiO₂, TiO₂And X₁(The X₁Is Y₂O₃, CeO, Al₂O₃, MgO, CaO, Nb₂O₅And at least one of rare earth oxides) and an upper protective layer 4 and a reflective layer 5 in that order (see FIG. 2).
[0042]
The upper protective layer and the lower protective layer are conventionally made of ZnS, SiO₂And a mixture ratio of ZnS: SiO₂= 80: 20 is used. The refractive index is between 2.0 and 2.1. It is known that this material has a higher melting point than the recording layer. In addition, SiO₂It has been known that the thermal expansion coefficient becomes smaller and the thermal conductivity becomes smaller than that of ZnS alone by adding. Therefore, they have been used for the reason that deformation due to repetitive recording and changes in optical constants due to crystallization of ZnS are small without lowering the recording sensitivity.
[0043]
In particular, the upper protective layer between the recording layer and the reflective layer tends to deteriorate as the number of times of recording is increased. In the case of recording at a higher speed, the recording layer is heated at a high speed and rapidly cooled, so that the thermal shock becomes large. Further, the pulse width of the light emission pulse applied to the medium becomes narrower as the clock becomes faster as the reference clock (T) becomes smaller. When the width is increased, the time during which a pulse required for cooling is not emitted is shortened, the area and length of the amorphous phase are reduced, and a mark having a predetermined length is difficult to be formed. That is, higher light emission power is required.
[0044]
Therefore, as the thermal properties of the upper protective layer, a material having not only a high melting point, but also a smaller thermal conductivity, a smaller coefficient of thermal expansion, and a less elastic crack that is unlikely to generate a thermal shock is required. It becomes.
[0045]
ZrO for dielectric material with low thermal conductivity₂There is. Bulk crystals have low thermal conductivity among other ceramics. Relatively high SiC, AlN, Al₂O₃Are 500 W / mK, 200 W / mK and 40 W / mK, respectively, while ZrO₂Is 5 W / mK or less. Moreover, the melting point is as high as 2000 ° C. or more, the refractive index is 2.0 or more, and the absorption is small. Therefore, it can be used for the upper protective layer.
ZrO₂Is chemically very stable, does not have deliquescent properties due to moisture taken in from the environment, and when used as a protective layer material, becomes a protective layer capable of improving both overwrite characteristics and storage reliability.
[0046]
However, ZrO₂When used alone, the film is in a crystalline state, and if left in a high-temperature environment for a long time, the mark is liable to be degraded (crystallized) and the characteristics are deteriorated.₂Is considered to have an undesirable effect of promoting crystallization.
[0047]
Therefore, in the present invention, ZrO₂To X₁(The X₁Is Y₂O₃, CeO, Al₂O₃, MgO, CaO, Nb₂O₅And at least one of rare earth oxides), SiO₂, TiO₂The above problem can be solved by mixing the above.
[0048]
SiO₂And TiO₂And ZrO₂Can be in an amorphous state. Thereby, ZrO₂The crystallization of the recording mark in contact with the film is not promoted, and the deterioration (crystallization) of the mark can be suppressed. In addition, since the formed film is made amorphous to lower the thermal conductivity, the recording sensitivity can be improved.
[0049]
Note that SiO₂Because of its low refractive index, SiO₂Is unfavorable because the refractive index is greatly reduced as the ratio of is increased. TiO, a high refractive index dielectric₂And crystallization can be suppressed while suppressing a decrease in the refractive index.
[0050]
Also, X₁(The X₁Is Y₂O₃, CeO, Al₂O₃, MgO, CaO, Nb₂O₅And at least one of rare earth oxides) can be prevented from cracking a target material used for forming a thin film of these mixtures. ZrO₂It is more preferable as a protective layer material for further lowering the thermal conductivity than a simple substance.
[0051]
Each mixing ratio of the upper protective layer is (ZrO₂) A (SiO₂) B (TiO₂) C (X₁) D, each ratio (mol%) is preferably 30 ≦ a <100, 0 <b ≦ 40, 0 <c ≦ 40, 0.1 ≦ d ≦ 10, and (a + b + c + d = 100) (X₁Is Y₂O₃, CeO, Al₂O₃, MgO, CaO, Nb₂O₅And at least one of rare earth oxides).
[0052]
As described above, a phase-change type optical disc is rewritten by repeating a phase change of a crystal and an amorphous phase in a phase-change recording layer. Repeat the change. Therefore, the protective film is required to have high mechanical strength and toughness. The upper protective layer of the present invention maintains excellent properties of mechanical strength and toughness even when thinned, and suppresses damage to the recording layer caused by repeated melting and cooling during recording, and further suppresses deformation of the protective layer itself. Is possible. Further, since the thermal conductivity is extremely low, the temperature reached at the time of recording is high even at a low recording power, the cooling gradient is increased, the sensitivity is improved, and the conventional ZnS-SiO₂It is possible to improve the overwrite characteristics such as the reduction of the signal amplitude at the time of overwrite and the suppression of the increase of the jitter, as compared with the case of.
[0053]
FIG. 3 shows that the upper protective layer of the present invention is made of ZrO₂An optical recording medium in the case of a dielectric material containing, as a main component, the same recording layer as the optical recording medium, and in the same layer configuration, the upper protective layer is formed of ZnS—SiO 2.₂5 shows a comparison of the increase in jitter due to the number of overwrites of the optical recording medium in the case of FIG.
In the present invention, the term “jitter” refers to a value obtained by normalizing data to clock jitterσ with the detection window width Tw.
[0054]
In the present invention, the upper protective layer is made of ZrO.₂It is preferable to be composed of a material containing as a main component.
The dielectric layer covering the recording layer is ZrO₂In the case of high-speed, high-density recording, the optimum recording layer composition and disk configuration of a phase-change optical recording medium with high sensitivity, overwrite characteristics, and excellent storage reliability of amorphous marks can be determined. To provide.
Further ZrO₂Is a partially stabilized zirconia, for example, a part of zirconia is Y.₂O₃, MgO, CaO, Nb₂O₅, Al₂O₃Partially stabilized zirconia, which is stabilized by adding rare earth oxides and the like by several percent, is a material having particularly excellent stability because of its excellent mechanical properties.
[0055]
The optimum range of the thickness of the upper protective layer is 4 nm to 20 nm.
In particular, the thickness of the upper protective layer has a more direct effect on the cooling of the recording layer, and if the film thickness is less than 4 nm, defects such as cracks occur to obtain good erasing characteristics and repeated durability. And the recording sensitivity is deteriorated. On the other hand, if the thickness is more than 20 nm, the cooling rate of the recording layer becomes slow, so that it is difficult to form an amorphous phase or the area of the mark becomes small, which is not preferable.
[0056]
The lower protective layer is made of ZrO₂Or a conventional ZnS, SiO₂(The ratio is ZnS: SiO₂= 50: 50 to 85:15 is preferred. ) Or ZnS, ZrO₂And the like.
In a phase change optical recording medium, the lower protective layer has heat resistance and is chemically stable, such as ZnS and SiO.₂Of ZnS or ZnS and ZrO₂The use of a mixture of the above results in a phase change optical recording medium in which the residual stress of the film is small and deterioration due to overwriting hardly occurs. By using these dielectric protective layers, heat diffusion from the recording layer is promoted, and stable amorphous marks can be formed.
Also, ZrO₂By sandwiching the protective layer made of a material mainly composed of, the recording sensitivity can be further increased, and a phase-change optical recording medium having a large modulation can be obtained.
[0057]
Further, in the optical recording medium of the present invention, a lower second protective layer made of the same material as the upper protective layer can be provided between the lower protective layer and the recording layer.
By providing the lower second protective layer, the repetitive recording characteristics can be further improved.
[0058]
The thickness of the lower protective layer is preferably 50 nm to 200 nm.
When a lower second protective layer is provided, the lower second protective layer preferably has a thickness of 2 nm to 10 nm.
[0059]
The phase change recording layer is made of Ge, Ga and / or In, Sb, Te and X.₃(X₃Is preferably a material containing at least one of Ag, Cu, Dy and Mn). Further, the atomic ratio Sb / (Sb + Te) of Sb and Te is preferably 0.65 to 0.85. Further, the atomic ratio of Ge is preferably 0.04 to 0.07, and the atomic ratio of Ga and / or In is preferably 0.02 to 0.07. Furthermore, X₃Is preferably 0.01 to 0.1. And X₃Is more preferably Mn.
[0060]
Sb-Te having a composition in the vicinity of Sb0.7Te0.3, in which the molar ratio of Sb to Te is 7: 3, is a phase change recording material that hardly causes composition segregation due to overwriting and has excellent repetitive recording characteristics. The crystallization rate can be adjusted by changing the mixing ratio of Sb and Te, and the crystallization rate can be increased by increasing the ratio of Sb.
[0061]
According to the experiments by the present inventors, if Sb is 65 atom% or more, recording can be performed at least at a linear velocity of 1 × (1.2 m / s) of a CD. If less than this, even at 1.2 m / s, the increase in jitter due to overwriting was large, and good recording could not be performed. As the Sb ratio increases, the crystallization speed also increases, and good recording at a higher linear velocity becomes possible. However, if it exceeds 85 atom%, the rate of increase in the crystallization rate becomes sharp, and the formation of amorphous marks becomes almost impossible. Therefore, the ratio of Sb in the Sb-Te binary system is preferably set to 65 atom% or more and 85 atom% or less.
[0062]
However, even if the crystallization rate is increased only by the amount of Sb, the crystallization temperature is about 100 ° C. in a high-temperature environment, and the mark disappears at a higher temperature, so that the mark can be used as an optical recording medium. Disappears.
[0063]
Therefore, in order to cope with high-speed recording at a recording linear velocity of 20 m / s or more, Ga is added without increasing the amount of Sb very much. This makes it possible to cope with high-speed recording at a recording linear velocity of 20 m / s or more even when the ratio of Sb is 80 atom% or less, suppresses a decrease in glass forming ability, and easily secures storage reliability. . Ga can increase the crystallization speed with a small amount of addition, and also increases the crystallization temperature. Therefore, the stability of the mark can be improved even in a high temperature environment. If the amount of Ga is too large, the crystallization temperature becomes too high, and in the production process, the amorphous state is converted into a crystalline phase in advance, and at the time of initialization in which the phase is changed, a uniform and high reflectance is obtained in a crystalline state. It becomes difficult to do.
[0064]
In has the same effect as Ga, but does not raise the crystallization temperature as much as Ga, and thus is effective for supplementing Ga. However, if the amount is too large, the repetitive recording characteristics deteriorate. The preferred range of Ga and / or In is 2 to 7 atom%.
[0065]
Further, in consideration of the problems of Ga and / or In, it is preferable to add and use one or more third elements that can enhance the stability of the amorphous phase. Ge is effective as a third element for increasing the stability of the amorphous phase. Even with a small addition, storage reliability can be dramatically improved. The addition amount of Ge is preferably 4 to 7 atom%. When the addition amount is 4 atom% or more, an effect of improving the amorphous stability of the recording layer having a high crystallization rate appears, and the effect increases as the addition amount increases. Although increased, the recording sensitivity and the overwrite characteristic are deteriorated if the added amount is too large, so that it is preferable to set the amount to 7 atom% or less at most.
[0066]
Ge has a low crystallization rate when added in a large amount, and there are Cu and Ag as elements to supplement this. The preferable addition range of Cu and Ag is 2 atom% or less.
[0067]
In addition to Ga and the like, Dy and Mn are additional elements that increase the crystallization speed and do not increase the crystallization temperature as much as Ga. Among them, the present inventors have evaluated the recording characteristics by adding various elements, and when Mn is added, it has the effect of increasing the crystallization speed, and does not deteriorate the stability of the amorphous mark. Therefore, it was found that it was not necessary to increase the amount of Ge added. That is, it has been found that by adding Ge and Mn to Sb-Te, it is possible to ensure both sufficient storage reliability and a high erasing rate at about 5 times speed (17.5 m / s) of DVD. At the same time, it was found that the recording layer was an excellent recording layer in which initial crystallization was easy and characteristic deterioration due to overwriting was small. If the addition amount of Mn is lower than 1 atom%, the effect of increasing the crystallization rate is not clear, so the addition is 1 atom% or more. On the other hand, if the addition amount is too large, the reflectance in an unrecorded state (crystal state) becomes too low.
[0068]
As described above, if the amount of Sb is excessive, the rate of increase in the crystallization rate becomes sharp, which makes it difficult to form an amorphous mark and tends to deteriorate the storage reliability. In particular, the material of the protective layer in contact with the recording layer is ZrO.₂ZrO₂Since the film is in a crystalline state, the degree of deterioration is remarkable. In order to improve the storage reliability of the amorphous mark including the data storage after repeated recording, Ge that increases the storage reliability of the amorphous phase is added to the recording layer material at about 2 to 7 at%. However, the present inventors have actually investigated that when the amount of Ge added is less than 4 at%, ZrO₂80 ° C. in the case of a phase change medium using a dielectric material whose main component is a protective film. Under the 85RH storage environment test, the recording mark may almost disappear, which is not preferable.
[0069]
Therefore, the protective layer material is ZrO₂When the recording layer is made of a material containing_αSb_βTe_{1- α − β}It is preferable that each atom ratio satisfies 0.04 ≦ α ≦ 0.07 and 0.65 ≦ β ≦ 0.85.
As in the present invention, the upper protective layer is made of ZrO.₂When the recording layer is made of a recording material having a composition in the vicinity of Sb7Te3 where the molar ratio of Sb to Te is 7: 3, the recording and storage characteristics are improved and the crystallization temperature is kept low. , And Ge were preferably added at least 4 at% or more. Further, Ge is preferably at 7 at% or less because a large amount of Ge lowers the crystallization speed and causes adverse effects such as an increase in jitter due to overwriting. On the other hand, as described above, since the recording linear velocity depends on the Sb / Te ratio, the ratio of Sb to Te can be increased by increasing the amount of Sb to cope with the high linear velocity. If the amount is excessive, the rate of increase in the crystallization rate becomes sharp, making it difficult to form an amorphous mark. In addition, even if Ge is added at 4 at% or more, the storage reliability tends to deteriorate, so the ratio of Sb Cannot be so high, and therefore it is desirable to be in the range of 65 <Sb <85 at%.
[0070]
It is preferable that the recording layer material further contains at least one element of Ga, In, Dy, and Mn.
For example, by adding Ga without increasing the amount of Sb very much, it is possible to provide a phase change optical recording medium having a higher recording linear velocity. When Ga is used, the crystallization speed can be increased with a small amount of addition, and the crystallization temperature also increases. As a result, the stability of the recording mark when placed in a high temperature environment can be improved. However, if the added amount of Ga is too large, the crystallization temperature becomes too high, and it is difficult to obtain a uniform and high-reflectivity crystalline state during initialization in which the amorphous phase is changed into a crystalline phase in advance in the production process. Become. Therefore, the preferable range of the addition amount of Ga is 1 to 7 at%. In has the same effect as Ga, and is effective in supplementing Ga because it does not raise the crystallization temperature as much as Ga. However, when added in a large amount, the repetitive recording characteristics deteriorate. In addition to Ga, Dy and Mn, which have the effect of increasing the crystallization speed and do not increase the crystallization temperature as much as Ga, can also be used as additional elements.
Among them, Mn is particularly preferable, and when Mn is used, excellent characteristics can be exhibited even if the atomic ratio of Ge is less than 0.04.
[0071]
Thus, in the present invention, the recording layer material preferably contains Ge, Ga, Sb, Te, In, Mn, Ag, and the like.
Preferred specific examples of the recording layer material in the invention are shown below.
Ge: Ga: Sb: Te = 4.91: 2.90: 76.09: 16.10 (atom%)
Ge: Sb: Te: Mn = 5.00: 72.00: 18.00: 5.00 (atom%)
Ge: Ga: Sb: Te = 4.00: 2.00: 73.00: 21.00 (atom%)
Ge: Ga: Sb: Te: Mn = 3.00: 3.00: 70.50: 19.50: 4.00 (atom%)
Ge: Ga: Sb: Te: Ag = 5.00: 2.00: 75.00: 17.50: 0.50 (atom%)
Ge: Sb: Te = 4.89: 77.28: 17.83: (atom%)
Ge: Sb: Te: In: Mn = 3.0: 72.00: 18.00: 3.00: 4.00 (atom%)
[0072]
By properly combining the protective layer and the recording layer as described above and adjusting the composition ratio of each, a low linear velocity to a high linear velocity, more specifically, 1 × (3.5 m / s) to 5 × of DVD (17.5 m / s), a recording medium exhibiting good overwrite characteristics and excellent storage characteristics can be formed.
Furthermore, an element such as Se may be added to improve the recording sensitivity.
[0073]
The thickness range of the recording layer is preferably from 10 nm to 25 nm. If it is too thin, the degree of modulation will be small, and if it is too thick, the recording sensitivity and repetitive recording characteristics will be poor.
The thickness of the phase change recording layer is particularly preferably from 12 to 20 nm. When the thickness of the recording layer is thinner than 12 nm, the sensitivity is poor and the modulation is small. When the thickness of the recording layer is thicker than 20 nm, the recording layer is likely to move due to repetitive overwriting, and the deterioration of jitter becomes severe. That's why.
[0074]
The reflective heat dissipation layer that composes the phase-change optical recording medium is composed from the viewpoint of heat conduction such as adjusting the cooling rate of heat generated during recording and the optical viewpoint of improving the signal contrast during reproduction by the optical interference effect. Is done. A metal (alloy) containing at least one of Ag, Au, Cu, and Al as a main component has a high thermal conductivity and a high light reflectivity. The quenching effect by using these reflective heat dissipation layers is optimally combined, so that the amorphous mark can be formed more accurately.
[0075]
In particular, when the reflective layer is made of a material containing Ag as a main component, the sensitivity can be improved as described above. The Ag reflective layer has a very high thermal conductivity and can be a quenched disk suitable for forming recording marks.
Further, in the optical recording medium of the present invention, even when the reflective layer is made of a material containing Ag as a main element, the problem of Ag sulfidation can be solved by providing the protective layer made of the specific material.
[0076]
The thickness of the reflective layer is preferably 50 nm to 250 nm, particularly preferably 90 nm to 200 nm.
In this case, if the thickness of the reflective heat dissipation layer is too small, the quenching effect required for amorphization cannot be obtained, and the reflection efficiency is also reduced. Conversely, if it is too large, the production efficiency will be reduced.
[0077]
As a substrate to be used, a plastic substrate such as polycarbonate (PC) or polymethacrylic acid (PMMA) or a transparent substrate such as glass is used.
[0078]
The first configuration of the optical recording medium of the present invention uses these recording layer, upper protective layer, and lower protective layer materials to form a lower protective layer, a phase change recording layer, a ZrO layer on a transparent substrate.₂, SiO₂, TiO₂And X₁(The X₁Is Y₂O₃, CeO, Al₂O₃, MgO, CaO, Nb₂O₅And at least one of rare earth oxides) and a reflective layer mainly composed of Ag or the like. In the case where an Ag reflective layer is used as the reflective layer in this configuration, cooling after the temperature of the recording layer is once increased by irradiation of recording power is extremely fast, and the quenching effect is high. However, in the case of an alloy containing a large amount of elements to be added to Ag, the thermal conductivity tends to decrease rapidly with the added amount as compared with that of pure Ag. Therefore, the addition amount is preferably several wt%.
[0079]
Further, a second configuration of the optical recording medium of the present invention is such that a lower protective layer, a ZrO 2₂, SiO₂, TiO₂And X₂(The X₂Is Y₂O₃, CeO, Al₂O₃, MgO, CaO, Nb₂O₅And at least one of rare earth oxides), a recording layer that undergoes a reversible phase change between an amorphous phase and a crystalline phase, ZrO.₂, SiO₂, TiO₂And X₁(The X₁Is Y₂O₃, CeO, Al₂O₃, MgO, CaO, Nb₂O₅And at least one of rare earth oxides) and a reflective layer mainly composed of Ag or the like.
[0080]
The upper protective layer material used in the first and second configurations is ZnS, SiO₂When used as a second lower protective layer between the lower protective layer made of and the recording layer, the repetitive recording characteristics can be further improved. However, if the thickness is too large, the heat radiation property deteriorates. Therefore, the thickness of the lower second protective layer is preferably 2 to 10 nm. Furthermore, ZrO₂The protective layer containing₂The preferred range is (ZrO 2) because the crystallization promoting effect of₂) A (SiO₂) B (TiO₂) C (X₂) D, each ratio (mol%) is 30 ≦ a <100, 0 <b ≦ 40, 0 <c ≦ 40, 0.1 ≦ d ≦ 10, and (a + b + c + d = 100) (X₂Is Y₂O₃, CeO, Al₂O₃, MgO, CaO, Nb₂O₅And at least one of rare earth oxides).
[0081]
The phase change recording medium of the present invention is capable of recording and reproduction with a recording wavelength in the range of 400 to 780 nm. To increase the recording density, the aperture ratio of the objective lens is set to 0.60 or more, and the beam diameter of the incident light is reduced. When the wavelength is 650 nm and the aperture ratio of the objective lens is 0.6 to 0.65, the thickness of the substrate is 0.6 mm, the track pitch of the substrate is 0.74 μm or less, the depth of the groove is 15 nm to 60 nm, and the groove is The width is 0.2 to 0.3 μm.
[0082]
When performing high-speed, high-density recording using the optical recording medium of the present invention, the laser light is pulse-width modulated. The power level of the light emission pulse is composed of three levels: recording, erasing, and bias. The recording and erasing powers are higher than the reproducing power, and the bias power is lower than the reproducing power. The bias power is the power after the irradiation of the recording power, and is necessary for forming an amorphous phase.
[0083]
When forming a mark whose recording mark time is nT (n is an integer of 2 or more, T is a reference clock time), the recording power and bias power irradiation times are OPi and Fpi (i is (Number of pulses), and emits light in a pulse pattern in which the number m of pulses is n-1. The sum of OPi and Fpi is 0.5 <Opi + Fpi <1.5. This pulse further includes a first pulse (1 pulse), a plurality of pulse trains, and a last pulse (1 pulse). These light emission patterns are used to sharpen an edge portion of a recording mark, record a position, and record a mark length. Is required to record at a predetermined length. The recording linear velocity is a maximum of 20 m / s in the case of a 4.7 GB DVD, and the recording clock is a maximum of 150 MHz at a linear density of 0.267 μm / bit. FIG. 4 schematically shows a pulse pattern when the optical recording medium of the present invention is used. The modulation method of the recording data is the (8, 16) modulation method.
[0084]
【Example】
Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited by the following examples.
[0085]
Examples 1 to 5
A substrate made of polycarbonate having a groove pitch of 0.74 μm, a groove width of 0.25 μm, a groove depth of 25 nm, and a thickness of 0.6 mm was used, and each layer was laminated thereon by a sputtering method. The lower protective layer is made of ZnS: SiO₂= 80: 20 (mol%), and the film thickness was 70 nm. Next, as shown in Table 1, a recording layer having a film thickness of 17 nm was produced.
The upper protective layer is ZrO₂, SiO₂, TiO₂And X₁(The X₁Is Y₂O₃, CeO, Al₂O₃, MgO, CaO, Nb₂O₅And a mixture target composed of at least one of rare earth oxides). Next, a reflective layer made of an Ag alloy was formed to have a thickness of 160 nm.
Next, an ultraviolet curable resin was applied to form a protective layer having a thickness of 2 μm. Lastly, another substrate without a film was laminated with an ultraviolet curable resin to a thickness of 1.2 mm to obtain a recording medium.
Thereafter, the recording layer was crystallized using a large-diameter LD (1 μm × 100 μm) at a linear velocity of 3.5 m / s and a power of 850 mW. Recording and reproduction were performed using a pickup head having a wavelength of 655 nm and an objective lens NA of 0.65 so that the recording linear velocity was 14 m / s and the recording density was 0.267 μm / bit. The modulation method of the recording data is (8, 16) modulation. The recording power is 20 mW, the bias power is 0.1 mW, and the erasing power is 6 mW.
Table 1 shows the jitters at the first time and after 1000 times of repetitive recording. When these recording media were left in an environment of 80 ° C. and 85% RH for 300 hours after recording, there was almost no jitter deterioration.
[0086]
[Table 1]

[0087]
Examples 6 to 10
A substrate made of polycarbonate having a groove pitch of 0.74 μm, a groove width of 0.25 μm, a groove depth of 25 nm, and a thickness of 0.6 mm was used, and each layer was laminated thereon by a sputtering method. The lower protective layer is made of ZnS: SiO₂= 80: 20 (mol%), and the film thickness was 60 nm. Next, as shown in Table 2, a second lower protective layer and a recording layer capable of recording at a predetermined recording linear velocity were formed to have a film thickness of 17 nm in order. ZrO₂, SiO₂, TiO₂And X₁(The X₁Is Y₂O₃, CeO, Al₂O₃, MgO, CaO, Nb₂O₅And a mixture layer composed of at least one of rare earth oxides) having a film thickness of 12 nm was used as an upper protective layer. Further, Ag was set to a thickness of 160 nm to form a reflection layer. An ultraviolet-curable resin was applied to protect it to a thickness of 2 μm. Lastly, another substrate without a film was laminated with an ultraviolet curable resin to a thickness of 1.2 mm to obtain a recording medium.
Thereafter, the recording layer was crystallized using a large-diameter LD (1 μm × 100 μm) at a linear velocity of 3.5 m / s and a power of 850 mW. Recording and reproduction were performed using a pickup head having a wavelength of 655 nm and an objective lens NA of 0.65 at a recording linear velocity of 17 m / s and a recording density of 267 μm / bit. The erasing power was 6 mW.
Table 3 shows the jitter after the first and 1000 repetitive recordings. Even after recording these recording media in an environment of 80 ° C. and 85% RH for 300 hours, there was almost no jitter deterioration.
[0088]
[Table 2]

[0089]
[Table 3]

[0090]
Comparative Example 1
A substrate made of polycarbonate having a groove pitch of 0.74 μm, a groove width of 0.25 μm, a groove depth of 25 nm, and a thickness of 0.6 mm is used, and each layer is laminated thereon by a sputtering method. The lower protective layer is made of ZnS: SiO₂= 80: 20 (mol%), and the film thickness was 70 nm. Next, as shown in Table 2, a recording layer capable of recording at a predetermined recording linear velocity was formed with a film thickness of 17 nm. ZnS: SiO₂= 80: 20 (mol%) A mixture layer having a thickness of 12 nm was used as an upper protective layer. Next, SiC was applied to a thickness of 4 nm as an anti-sulfuration layer. After the anti-sulfuration layer was provided, the thickness of Ag was set to 160 nm to form a reflection layer. An ultraviolet-curing resin was applied to a thickness of 2 μm to form a protective layer. Lastly, another substrate without a film was laminated with an ultraviolet curable resin to a thickness of 1.2 mm to obtain a recording medium.
Thereafter, the recording layer was crystallized using a large-diameter LD (1 μm × 100 μm) at a linear velocity of 3.5 m / s and a power of 750 mW. Recording and reproduction were performed using a pickup head having a wavelength of 655 nm and an objective lens NA of 0.65 so that the recording linear velocity was 14 m / s and the recording density was 0.267 μm / bit.
[0091]
The medium of Comparative Example 1 was compared with Example 1. As a result, the jitter at the time of the initial recording is of the order of 7% in Example 1, but is of the order of 8% in Comparative Example 1, and the jitter at the time of repetitive recording 1000 times is suppressed to the order of 10% in Example 1. On the other hand, Comparative Example 1 exceeded 12%, and all the characteristics were better in the example. This is presumably because the provision of the anti-sulfuration layer deviated the optimum layer configuration and recording layer composition.
In addition, when the dependence on the recording power at the time of the initial recording was evaluated, the Pw of 13 mW or more was sufficient in Example 5 to reduce the jitter to less than 10%, whereas the Pw of Comparative Example 1 was 14 mW or more. I needed to.
Furthermore, in Comparative Example 1, it was necessary to remodel the film forming apparatus to provide the anti-sulfuration layer and provide a new vacuum chamber. For this reason, the manufacturing cost per medium has increased.
In Comparative Example 1, after recording the recording medium, the recording medium was left in an environment of 80 ° C. and 85% RH for 300 hours. Came out.
[0092]
Example 11
A lower protective layer of ZnS (80 mol%) SiO was formed on a polycarbonate substrate having a track pitch of 0.74 μm, a diameter of 12 cm and a thickness of 0.6 mm by magnetron sputtering.₂(20 mol%) is 65 nm, the phase change recording layer is Ge: Sb: Te = 4.89: 77.28: 17.83 (at%) is 17 nm, and the upper protective layer is ZrO.₂-SiO₂(20mol%)-TiO₂(20 mol%)-Y₂O₃(3 mol%), Ag is sequentially laminated on the reflective heat radiation layer to 140 nm, and an acrylic UV curable resin is spin-coated on the reflective heat radiation layer. A disc was created by laminating a 0.6 mm polycarbonate substrate with an adhesive sheet. Initial crystallization of this disk was performed using an optical disk initialization device with an irradiation beam diameter of 1 μm × 100 μm under the conditions of an output of 820 mW, a beam feed speed of 36 μm / rot, and a linear velocity of 3 m / sec. Crystallization was possible. After the initial crystallization, EFM + random signals were repeatedly recorded at a recording linear velocity of 17.5 m / s using an optical disk evaluation device (wavelength 660 nm, NA 0.65), and jitter was measured. The recording power was 19 mW, the bias power was 0.1 mW, the erasing power was 6 mW, and the recording strategy used was a 1T cycle strategy optimized for this sample. Reproduction was performed at a linear velocity of 3.5 m / s and a power of 0.7 mW. At this time, the jitters at the first time and after overwriting 1000 times are sufficiently small for practical use, 7.8% and 9.6%, and the modulations are also very good values of 62.2% and 64.1%, respectively. . The disc was subjected to an accelerated deterioration test at 80 ° C., 85 RH and 500 hours using a moist heat oven, and the change in jitter and modulation was examined. No trend was seen.
[0093]
Example 12
The same as Example 11 except that the composition of the phase change recording layer of Example 11 was Ge: Ga: Sb: Te = 4.91: 2.90: 76.09: 16.10 (at%). I made an optical disk. Initial crystallization of this disk was performed using an optical disk initialization device with an irradiation beam diameter of 1 μm × 100 μm under the conditions of an output of 720 mW, a beam feed speed of 36 μm / rot, and a linear velocity of 3 m / sec. Crystallization was possible. At this time, the maximum recordable linear velocity was higher than that of Example 11, and higher-speed recording was possible. Similarly, this disc was subjected to an accelerated deterioration test at 80 ° C. and 85 RH for 500 hours using a moist heat oven to examine the change in jitter and modulation. Was not seen.
The maximum recordable linear velocity refers to a recordable linear velocity with a jitter of 10% or less at the time of initial recording after optimizing the recording / erasing power and the recording strategy.
[0094]
Example 13
The composition of the upper protective layer of Example 11 was ZrO₂-SiO₂(20mol%)-TiO₂(40 mol%)-Y₂O₃(3 mol%), except that an optical disc was prepared in the same manner as in Example 11. Initial crystallization of this disk was attempted using an optical disk initialization device with an irradiation beam diameter of 1 μm × 100 μm under the conditions of an output of 800 mW, a beam feed speed of 36 μm / rot, and a linear velocity of 3 m / sec. Crystallization was possible. When the jitter was measured in the same manner after the initial crystallization, the jitter of the first recording was a sufficiently small value of 8.1%. The disk was subjected to an accelerated deterioration test at 80 ° C., 85 RH and 500 hours using a wet heat oven, and the change in jitter and modulation was examined. As a result, no increase in jitter or change in modulation was observed.
[0095]
Example 14
Example 11 was carried out in the same manner as in Example 11 except that the composition of the phase change recording layer was Ge: Ga: Sb: Te = 3.02: 2.96: 75.05: 18.97 (at%). I made an optical disk. Initial crystallization of this disk was attempted using an optical disk initialization device with an irradiation beam diameter of 1 μm × 100 μm under the conditions of an output of 840 mW, a beam feed speed of 36 μm / rot, and a linear velocity of 3 m / sec. Crystallization was possible. After the initial crystallization, the EFM + random signal was recorded in the same manner and the jitter was measured. The jitter of the initial recording was 7.7%, which was a sufficiently small value. , 85RH for 100 hours, a tendency of disappearance of the recorded marks was observed after 100 hours.
[0096]
【The invention's effect】
As described above, according to the optical recording medium of the first aspect, since the specific layer configuration and the material of the upper protective layer are used, a phase-change optical recording medium having excellent recording characteristics at high linear velocity recording is obtained. be able to.
[0097]
According to the optical recording medium of claims 2 to 4, since the range or the main component of the mixing ratio of the upper protective layer material in the recording medium is limited, high sensitivity and overwriting can be achieved at high linear velocity and high density recording. A phase-change optical recording medium having excellent recording characteristics such as characteristics and storage reliability of the amorphous mark can be obtained.
[0098]
According to the optical recording medium of the fifth and sixth aspects, since the specific lower protective layer material is used in the recording medium, the overwrite characteristics can be improved and the recording mark can be formed more stably.
[0099]
According to the optical recording medium of claim 7, in the recording medium, a lower second protective layer is provided between the lower protective layer and the recording layer, and the lower second protective layer is also made of the same material as the upper protective layer. Thus, the repetitive recording characteristics can be further improved.
[0100]
According to the optical recording medium of claims 8 to 13, it is possible to form an excellent recording layer such as easy initial crystallization and little deterioration of characteristics due to overwriting, and excellent recording characteristics and storage characteristics at high linear velocity recording. Can be obtained.
[0101]
According to the optical recording medium of claim 14, since the recording layer is formed of specific atoms and atomic ratios, in high linear velocity, high density recording, it has high sensitivity and excellent overwrite characteristics. A phase-change optical recording medium having excellent storage reliability can be obtained.
[0102]
According to the optical recording medium of the fifteenth aspect, since the recording layer further contains a specific element, a phase-change optical recording medium more suitable for high linear velocity recording can be obtained.
[0103]
According to the optical recording medium of the sixteenth and seventeenth aspects, since the reflective layer is formed of the optimum material, the recording mark can be formed more stably. In particular, by using a reflective layer containing Ag as a main component, the sensitivity is improved, and the formation of recording marks can be further stabilized.
[0104]
According to the optical recording medium of claims 18 and 19, since the film thickness of the upper protective layer is 4 nm to 20 nm or the film thickness of the lower protective layer is 50 nm to 200 nm, the sensitivity does not deteriorate and the cooling rate is reduced. It is possible to obtain a phase-change type optical recording medium having excellent recording characteristics and excellent storage characteristics in high-density high linear velocity recording without delay.
[0105]
According to the optical recording medium of the twentieth aspect, the thickness of the lower second protective layer is 2 nm to 10 nm. A phase-change optical recording medium having excellent recording characteristics and storage characteristics can be obtained.
[0106]
According to the optical recording medium of claims 21 and 22, since the thickness of the recording layer is 12 nm to 20 nm or the thickness of the reflective layer is 90 nm to 200 nm, both are optimal thicknesses and have excellent recording characteristics. A phase-change optical recording medium can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing an example of a first optical recording medium according to the present invention.
FIG. 2 is a schematic sectional view showing an example of a second optical recording medium according to the present invention.
FIG. 3 is Zr for the upper protective layer material₂O-based case and ZnS-SiO₂7 is a graph showing a change in jitter depending on the number of overwrites in the case of FIG.
FIG. 4 is a diagram schematically showing a pulse pattern in the present invention.
[Explanation of symbols]
1 substrate
2) Lower protective layer
3 Recording layer
4 Upper protective layer
5 Silver or silver alloy reflective layer
6 Lower second protective layer

Claims (22)

An optical recording medium in which a lower protective layer, a recording layer that undergoes a reversible phase change between an amorphous phase and a crystalline phase, an upper protective layer, and a reflective layer are laminated in this order on a transparent substrate, wherein the upper protective layer is made of ZrO. ₂ , SiO ₂ , TiO ₂ and X ₁ , wherein X ₁ is at _{least one} of Y ₂ O ₃ , CeO, Al ₂ O ₃ , MgO, CaO, Nb ₂ O ₅ and a rare earth oxide. Characteristic optical recording medium. The composition (ZrO ₂ ) a (SiO ₂ ) b (TiO ₂ ) c (X ₁ ) d of the upper protective layer has the following proportions (mol%) as follows: 2. Optical recording medium.
30 ≦ a <100, 0 <b ≦ 40, 0 <c ≦ 40, 0.1 ≦ d ≦ 10, a + b + c + d = 100 The optical recording medium according to claim 1, wherein the protective layer is made of a material containing ZrO ₂ as a main component. The optical recording medium according to claim 3, wherein said ZrO ₂ is a partially stabilized zirconia. The optical recording medium according to claim 1, wherein the lower protective layer is characterized by comprising the material mainly composed of ZrO _2. The optical recording medium according to any one of claims 1 to 4, characterized in that it consists of the following protective layer is a mixture of ZnS and SiO _2, or a mixture of ZnS and ZrO _2. A lower second protective layer is provided between the lower protective layer and the recording layer, and the lower second protective layer is made of ZrO ₂ , SiO ₂ , TiO ₂ and X ₂ , wherein X ₂ is Y ₂ O ₃ , _{CeO, Al 2 O 3, MgO} , CaO, Nb 2 O 5 and the optical recording medium according to claim 1, characterized in that at least one of a rare earth oxide. The recording layer includes at least Ge, Ga and / or an In, Sb, and Te and _{X 3,} the preceding claims, wherein _{X 3} is characterized in that at least one of a Ag, Cu, Dy and Mn The optical recording medium according to any one of the above. 9. The optical recording medium according to claim 8, wherein an atomic ratio of Sb / Te of the recording layer Sb / (Sb + Te) is 0.65 to 0.85. 10. The optical recording medium according to claim 8, wherein the atomic ratio of Ge in the recording layer is 0.04 to 0.07. The optical recording medium according to any one of claims 8 to 10, wherein the atomic ratio of Ga and / or In in the recording layer is 0.02 to 0.07. The optical recording medium according to any one of claims 8 to 11 atomic ratio of _{X 3} of the recording layer, characterized in that from 0.01 to 0.1. The optical recording medium according to any one of claims 8-12, wherein X ₃ of the recording layer is characterized by a Mn. Claims made _beta, the atomic ratio, characterized in that it is 0.04 ≦ α ≦ 0.07,0.65 ≦ β ≦ 0.85 - the recording layer is _Ge α Sb _β βTe _1- α 8. The optical recording medium according to any one of 1 to 7. The optical recording medium according to claim 14, wherein the recording layer further contains at least one element of Ga, In, Dy, and Mn. 16. The optical recording medium according to claim 1, wherein the reflection layer is made of a metal containing at least one of Ag, Au, Cu, and Al as a main component. The optical recording medium according to claim 16, wherein the reflective layer is mainly composed of Ag. The optical recording medium according to any one of claims 1 to 17, wherein the thickness of the upper protective layer is 4 nm to 20 nm. 19. The optical recording medium according to claim 1, wherein the lower protective layer has a thickness of 50 nm to 200 nm. 20. The optical recording medium according to claim 7, wherein the lower second protective layer has a thickness of 2 nm to 10 nm. 21. The optical recording medium according to claim 1, wherein the thickness of the recording layer is 12 nm to 20 nm. 22. The optical recording medium according to claim 1, wherein the reflective layer has a thickness of 90 nm to 200 nm.

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