JP4631212B2 - Surface reproduction type optical recording medium - Google Patents

Description

浮上性については、いずれの媒体も良好で、透明樹脂保護層を設けた実施例１〜４および比較例２と透明樹脂保護層の代りに薄い固体潤滑層とした比較例１で特に差は認められなかった。表１に記録再生特性の測定結果を示す。高角入射光の反射状態に関しては、実施例１で透明樹脂保護層膜厚が６００ｎｍ以外の場合は良好で、特に実施例２のように誘電体層を屈折率の異なる２層以上にしたり、実施例３、４のように透明樹脂保護層の上に整合層を設けることによりさらに良好になる。ＣＮＲについては、比較例１、２のように透明樹脂保護層の膜厚が薄いほうが、実施例１より良好ではあるが、実施例２〜４のように誘電体層を屈折率の異なる２層以上にしたり、透明樹脂保護層の上に整合層を設けることにより比較例１と同等以上の良好な特性が得られた。
【００９０】
次に最適記録パワーで５万トラックの連続記録を各試料２０回試み、トラッキングがはずれることなく連続試験が完了できた回数を記録した。
【００９１】
連続記録に関してはレーザービームの直径が１．５μｍ以上であれば２０回の試験を最後まで続けることができた。
【００９２】
次に、実施例４で透明樹脂保護層の膜厚が９００ｎｍの媒体に焦点を固定して、透明樹脂保護層の膜厚が６００、７５０、９００、１０５０、１２００ｎｍの媒体のＣＮＲを測定した。表２に結果を示す。
【００９３】
この結果により、記録領域での透明樹脂保護層の膜厚の最大と最小との差（膜厚むら）をλ／ＮＡ²以内とすることにより、フォーカスサーボなしで記録再生が可能であることが確認された。なお、実施例４の光記録媒体は、いずれもこの条件を満たしていた。
【００９４】
【表２】

（実施例５）
図４に示すような構造の近接場記録用の表面再生型光媒体を製造した。ランドとグルーブの幅の比が１：１、グルーブ深さ５０ｎｍ、トラックピッチ０．３３μｍ（ランドとグルーブ間のピッチ）のポリカーボネート製の基板４１上にＡｇ₉₈Ｐｄ₁Ｔｉ₁からなる反射層４２をＤＣスパッタ法で４０ｎｍの膜厚に形成した。この上にＴｂＦｅＣｏからなる記録層４３をＤＣスパッタ法で２０ｎｍの膜厚に形成した。この上に、屈折率２．１のＳｉＮからなる誘電体層４４をＡｒとＮ₂の混合雰囲気中でＳｉターゲットを使用した反応性ＤＣスパッタ法で２３０ｎｍの膜厚に形成した。この上に実施例１で使用したのと同様な紫外線硬化樹脂モノマーからなるコート剤をスピンコート法で塗布し、紫外線照射により重合させることで屈折率ｎ_OC＝１．５で膜厚が４８０ｎｍの透明樹脂保護層４５を形成した。この上に、パーフルオロポリエーテル系液体潤滑層４６を引き上げ法で２ｎｍ塗布して表面再生型光記録媒体を製造した。
【００９５】
これらの媒体では、記録再生のレーザー波長λ＝６８５ｎｍに対して、誘電体層の光学膜厚は０．７１λ、透明樹脂保護層の光学膜厚は、１．０５λであった。また、基板上でグルーブの深さはλ／（９ｎ_OC）であった。この媒体の媒体表面での基板のランドとグルーブによる段差はＡＦＭによる測定で２０ｎｍ以下であった。また、媒体表面でのレーザービームの直径は２．０μｍであった。
【００９６】
（比較例３）
透明樹脂保護層４５の代りに、屈折率２．０のダイヤモンドライクカーボン（ＤＬＣ）からなる固体潤滑層をＡｒとＨ₂の混合雰囲気中でＣターゲットを使用した反応性ＲＦスパッタ法で２０ｎｍの膜厚に形成した他は、実施例５と同じ方法で表面再生型光媒体を製造した。
【００９７】
この媒体の媒体表面での基板のランドとグルーブによる段差はＡＦＭによる測定で５０ｎｍであった。この媒体の媒体表面でのレーザービームの直径は０．４０μｍであった。
【００９８】
（実施例６）
図９に示すような構造の近接場光記録用の表面再生型光記録媒体を製造した。
ランドとグルーブの幅の比が１：１、グルーブ深さ５０ｎｍ、トラックピッチ０．３３μｍ（ランドとグルーブ間のピッチ）のポリカーボネート製の基板１０１上にＡｇ₉₈Ｐｄ₁Ｔｉ₁からなる反射層１０２をＤＣスパッタ法で４０ｎｍの膜厚に形成した。この上にＴｂＦｅＣｏからなる記録層１０３をＤＣスパッタ法で２０ｎｍの膜厚に形成した。この上に、屈折率２．１のＳｉＮからなる第１誘電体層１０４をＡｒとＮ₂の混合雰囲気中でＳｉターゲットを使用した反応性ＤＣスパッタ法で７５ｎｍの膜厚に形成した。この上に屈折率１．８のＳｉＯＮからなる第２誘電体層１０５をＡｒと微量のＮ₂の混合雰囲気中でＳｉＯＮターゲットを使用したＲＦスパッタ法で１７５ｎｍの膜厚に形成した。この上に実施例１で使用したのと同様な紫外線硬化樹脂モノマーからなるコート剤をスピンコート法で塗布し、紫外線照射により重合させることで屈折率１．５で膜厚が４８０ｎｍの透明樹脂保護層１０６を形成した。この上に、パーフルオロポリエーテル系液体潤滑層１０７を引き上げ法で２ｎｍ塗布して表面再生型光記録媒体を製造した。
【００９９】
これらの媒体では、記録再生のレーザー波長λ＝６８５ｎｍに対して、第１誘電体層と第２誘電体層を合わせた光学膜厚は０．６９λ、透明樹脂保護層の光学膜厚は、１．０５λであった。また、基板上でグルーブの深さはλ／（９ｎ_OC）であった。この媒体の媒体表面での基板のランドとグルーブによる段差はＡＦＭによる測定で２０ｎｍ以下であった。また、媒体表面でのレーザービームの直径は２．２μｍであった。
【０１００】
（実施例７）
図１０に示すような構造の近接場光記録用の表面再生型光記録媒体を製造した。ランドとグルーブの幅の比が１：１、グルーブ深さ５０ｎｍ、トラックピッチ０．３３μｍ（ランドとグルーブ間のピッチ）のポリカーボネート製の基板１１１上にＡｇ₉₈Ｐｄ₁Ｔｉ₁からなる反射層１１２をＤＣスパッタ法で４０ｎｍの膜厚に形成した。この上にＴｂＦｅＣｏからなる記録層１１３をＤＣスパッタ法で２０ｎｍの膜厚に形成した。この上に、屈折率２．１のＳｉＮからなる誘電体層１１４をＡｒとＮ₂の混合雰囲気中でＳｉターゲットを使用した反応性ＤＣスパッタ法で２３０ｎｍの膜厚に形成した。この上に実施例１で使用したのと同様な紫外線硬化樹脂モノマーからなるコート剤をスピンコート法で塗布し、紫外線照射により重合させることで屈折率１．５０のポリメタクリル酸メチルを主体とした透明樹脂保護層１１５を６６０ｎｍの膜厚に形成した。その上に同様の方法で屈折率１．６１のポリクロロスチレンを主体とした第１整合層１１６を１１０ｎｍの膜厚に形成し、その上に屈折率１．４５の、フッ素系界面活性剤を０．１ｗｔ％含みメタクリル酸メチルとポリジメチルシロキサンを主体とした第２整合層１１７を１７０ｎｍの膜厚に形成した。この上に、パーフルオロポリエーテル系液体潤滑層１１８を引き上げ法で２ｎｍ塗布して表面再生型光記録媒体を製造した。
【０１０１】
この媒体で、誘電体層の光学膜厚は０．７１λ、透明樹脂保護層の光学膜厚は１．４５λ、第１と第２整合層の合計の光学膜厚は０．６２λであった。また、基板上でグルーブの深さはλ／（９ｎ_OC）であった。この媒体の媒体表面での基板のランドとグルーブによる段差はＡＦＭによる測定で２０ｎｍ以下であった。
媒体表面でのレーザービームの直径は３．６μｍであった。
【０１０２】
（実施例８）
図７に示すような構造の近接場光記録用の表面再生型光記録媒体を製造した。
ランドとグルーブの幅の比が１：１、グルーブ深さ５０ｎｍ、トラックピッチ０．３３μｍ（ランドとグルーブ間のピッチ）のポリカーボネート製の基板７１上にＡｇ₉₈Ｐｄ₁Ｔｉ₁からなる反射層７２をＤＣスパッタ法で４０ｎｍの膜厚に形成した。この上に、屈折率２．０のＳｉＡｌＮからなる下部誘電体層７３をＡｒとＮ₂の混合雰囲気中でＳｉＡｌターゲットを使用した反応性ＤＣスパッタ法で４０ｎｍの膜厚に形成した。この上にＴｂＦｅＣｏからなる記録層７４をＤＣスパッタ法で２０ｎｍの膜厚に形成した。この上に、屈折率２．１のＳｉＮからなる第１誘電体層７５をＡｒとＮ₂の混合雰囲気中でＳｉターゲットを使用した反応性ＤＣスパッタ法で６５ｎｍの膜厚に形成した。この上に屈折率１．８のＳｉＯＮからなる第２誘電体層７６をＡｒと微量のＮ₂の混合雰囲気中でＳｉＯＮターゲットを使用したＲＦスパッタ法で１９０ｎｍの膜厚に形成した。この上に実施例１で使用したのと同様な紫外線硬化樹脂モノマーからなるコート剤をスピンコート法で塗布し、紫外線照射により重合させることで屈折率１．５で膜厚が６００、７５０、９００、１０５０、１２００ｎｍの５種類の透明樹脂保護層７７を形成した。透明樹脂保護層７７の上に、屈折率２．１のＳｉＮからなる第１整合層７８をＡｒとＮ₂の混合雰囲気中でＳｉターゲットを使用した反応性ＤＣスパッタ法で８０ｎｍの膜厚に形成した。その上に屈折率１．４５のＳｉＯ₂からなる第２整合層７９をＳｉＯ₂ターゲットを使用したＲＦスパッタ法で１６５ｎｍの膜厚に形成した。この上に、パーフルオロポリエーテル系液体潤滑層８０を引き上げ法で２ｎｍ塗布して表面再生型光記録媒体を製造した。
【０１０３】
これらの媒体では、記録再生のレーザー波長λ＝６８５ｎｍに対して、第１〜第２誘電体層を合わせた光学膜厚は０．７０λ、第１〜第２整合層を合計した光学膜厚は０．５９λであった。また、基板上でグルーブの深さはλ／（９ｎ_OC）であった。
【０１０４】
透明樹脂保護層７７の光学膜厚は、膜厚６００、７５０、９００、１０５０、１２００ｎｍについて、各々、１．３１、１．６４、１．９７、２．３０、２．６３λであり、媒体表面でのレーザービームの直径は、各々、３．４、３．９、４．４、４．９、５．５μｍであった。また、この媒体の媒体表面での基板のランドとグルーブによる段差はＡＦＭによる測定で２０ｎｍ以下であった。
【０１０５】
（実施例９）
ポリカーボネート製の基板７１をランドとグルーブの幅の比が１：１、グルーブ深さ７５ｎｍ、トラックピッチ０．３３μｍ（ランドとグルーブ間のピッチ）の基板とした他は、実施例８と同様の表面再生型光記録媒体を製造した。基板上でグルーブの深さはλ／（６ｎ_OC）であった。この媒体の媒体表面での基板のランドとグルーブによる段差はＡＦＭによる測定で２０ｎｍ以下であった。但し、透明樹脂保護層の膜厚は９００ｎｍとした。
【０１０６】
（実施例１０）
ポリカーボネート製の基板７１をランドとグルーブの幅の比が１：２、グルーブ深さ６０ｎｍ、トラックピッチ０．４０μｍ（グルーブ間のピッチ）のグルーブ記録用の基板とした他は、実施例８と同様の表面再生型光記録媒体を製造した。この媒体の媒体表面での基板のランドとグルーブによる段差はＡＦＭによる測定で２０ｎｍ以下であった。但し、透明樹脂保護層の膜厚は９００ｎｍとした。
【０１０７】
（実施例１１）
本実施例においては、実施例８の媒体構造に透明樹脂保護層と整合層との界面から媒体表面側に向かって屈折率が段階的に上がる構造を付加した。
【０１０８】
透明樹脂保護層の膜厚を９００ｎｍとし、整合層を２層から３層、すなわち、透明樹脂保護層の上に、屈折率１．４５のＳｉＯ₂からなる第１整合層（膜厚２３０ｎｍ）、屈折率２．１のＳｉＮからなる第２整合層（膜厚７５ｎｍ）、および屈折率１．４５のＳｉＯ₂からなる第３整合層（膜厚１６５ｎｍ）をこの順に形成した他は、実施例８と同様な方法で表面再生型光記録媒体を製造した。
【０１０９】
これらの媒体では記録再生のレーザー波長λ＝６８５ｎｍに対して、第１〜第２誘電体層を合わせた光学膜厚は０．７０λ、第１〜第３整合層を合計した光学膜厚は、１．０８λであった。また、基板上でのグルーブの深さはλ／（９ｎ_OC）であった。また、媒体表面でのレーザービームの直径は、５．４μｍであった。この媒体の媒体表面での基板のランドとグルーブによる段差はＡＦＭによる測定で２０ｎｍ以下であった。
【０１１０】
実施例５〜１０及び比較例３の表面再生型光記録媒体について、線速度１０ｍ／ｓで媒体を回転させて、薄膜面上にレーザー波長６８５ｎｍ、有効開口数１．３のスライダーＳＩＬヘッドを７０ｎｍの高さに浮上させ、各々の媒体に対して手動で最適の位置に焦点合わせを行った後、レーザービームの偏光面をグルーブに対して垂直としてレーザーをランドまたはグルーブに沿って周波数８４ＭＨｚでパルス的に照射して記録層をキュリー温度以上に暖めながら、ＳＩＬヘッド上のコイル磁界を２０ＭＨｚで変調させることでマーク長０．２５μｍの２Ｔ信号を記録した。ここで、磁界の変調幅は±１３０Ｏｅとした。
【０１１１】
記録後にレーザーパワー１ｍＷで再生しながら（レーザービームの偏光面はグルーブに対して垂直）、分解能バンド幅３０ｋＨｚで２１ＭＨｚでのキャリアとノイズを測定し、このキャリアとノイズの比をＣＮＲとした。
【０１１２】
また、両隣接トラックでの２１ＭＨｚの信号のクロストークを調べた。ここで隣接トラックとは実施例５〜９と比較例３については、ランドに記録すれば隣接するグルーブを、グルーブに記録すれば隣接するランドをさし、実施例１０についてはグルーブに記録して隣接するグルーブとした。ここで、実施例５〜８、比較例３については戻り光の位相をランドとグルーブで独立に位相調整して各々ＣＮＲが最も高い位相で再生した。また、実施例９と１０では位相を零に固定して測定した。また、グルーブ記録の時の高角入射光の反射の状態を見るために瞳面上にＣＣＤカメラを設置して反射光量を低角入射光と比較した。結果を表３に示す。
【０１１３】
【表３】

グルーブ記録の時の高角入射光の反射状態に関しては、比較例３以外の場合は良好で、特に実施例６〜１０のように誘電体層や透明樹脂保護層を屈折率の異なる２層以上にしたり、さらに透明樹脂保護層の上に整合層を設けることによりさらに良好になった。
【０１１４】
グルーブ記録でのＣＮＲは、比較例３では著しく低いが、実施例５〜１０では４３ｄＢ以上の良好な値が得られた。実施例６〜１０のように誘電体層や透明樹脂保護層を屈折率の異なる２層以上にしたり、さらに透明樹脂保護層の上に整合層を設けることによりさらに良好となった。クロストークについては、比較例３は−２０ｄＢと大きな値となったが、実施例５〜１０ではいずれも−２５ｄＢ以下の良好な値が得られた。
【０１１５】
次に実施例８で透明樹脂保護層の膜厚が９００ｎｍの媒体に焦点を固定して、透明樹脂保護層の膜厚が６００、７５０、９００、１０５０、１２００ｎｍの媒体のＣＮＲを測定した。表４に結果を示す。
【０１１６】
この結果により、記録領域での透明樹脂保護層の膜厚の最大と最小との差（膜厚むら）をλ／ＮＡ²以内とすることにより、ランド／グルーブ記録でもフォーカスサーボなしで記録再生が可能であることが確認された。なお、実施例８の光記録媒体は、いずれもこの条件を満たしていた。
【０１１７】
【表４】

（実施例１２）
図４に示すような構造の表面再生型光記録媒体を製造した。トラックピッチ０．４μｍの案内溝（グルーブ）の付いたポリカーボネート製の基板４１上にＡｇ₉₈Ｐｄ₁Ｔｉ₁からなる反射層４２をＤＣスパッタ法で４０ｎｍの膜厚に形成した。この上にＴｂＦｅＣｏからなる記録層４３をＤＣスパッタ法で２０ｎｍの膜厚に形成した。この上に、屈折率２．１のＳｉＮからなる誘電体層４４をＡｒとＮ₂の混合雰囲気中でＳｉターゲットを使用した反応性ＤＣスパッタ法で２３０ｎｍの膜厚に形成した。この上に、実施例１と同様の紫外線硬化樹脂モノマーに分散剤を加えて、さらに屈折率２．０のＩＴＯ超微粒子（平均粒径０．０２μｍ）を５０ｗｔ％添加して十分混合した複合コート剤をスピンコート法で塗布し、紫外線照射により重合させることで屈折率１．６５のＩＴＯ超微粒子分散透明樹脂保護層（膜厚８５０ｎｍ）を形成した。
【０１１８】
この上に、パーフルオロポリエーテル系液体潤滑層４６を引き上げ法で２ｎｍ塗布して表面再生型光記録媒体を製造した。
【０１１９】
この媒体では記録再生のレーザー波長λ＝６８５ｎｍに対して、誘電体層の光学膜厚（実際の膜厚×屈折率）は、０．７１λ、透明樹脂保護層の光学膜厚は、２．０６λであった。また、媒体表面でのレーザービームの直径は２．６μｍであった。
【０１２０】
（実施例１３）
屈折率２．４のＺｎＳ−５０ｗｔ％ＴｉＯ₂からなる誘電体層４４をＡｒ雰囲気中でＺｎＳ−ＴｉＯ₂ターゲットを使用したＲＦスパッタ法で２００ｎｍの膜厚に形成し、その上に屈折率１．５の透明樹脂保護層を９４０ｎｍ形成した以外は実施例１と同様の表面再生型光記録媒体を製造した。
【０１２１】
この媒体では記録再生のレーザー波長λ＝６８５ｎｍに対して、誘電体層の光学膜厚（実際の膜厚×屈折率）は、０．７１λ、透明樹脂保護層の光学膜厚は、２．０６λであった。また、媒体表面でのレーザービームの直径は３．５μｍであった。
【０１２２】
（実施例１４）
屈折率２．６のＳｒＮｂ₂Ｏ₆からなる誘電体層４４をＡｒとＯ₂の混合雰囲気中でＳｒＮｂ₂Ｏ₆ターゲットを使用したＲＦスパッタ法で１８５ｎｍの膜厚に形成し、その上に屈折率１．５の透明樹脂保護層を９４０ｎｍ形成した以外は実施例１と同様の表面再生型光記録媒体を製造した。
【０１２３】
この媒体では記録再生のレーザー波長λ＝６８５ｎｍに対して、誘電体層の光学膜厚（実際の膜厚×屈折率）は、０．７１λ、透明樹脂保護層の光学膜厚は、２．０６λであった。また、媒体表面でのレーザービームの直径は３．５μｍであった。
【０１２４】
実施例１２〜１３の表面再生型光記録媒体について、線速度１０ｍ／ｓで媒体を回転させて、薄膜面上にレーザー波長６８５ｎｍ、有効開口数１．３のスライダーＳＩＬヘッドを７０ｎｍの高さに浮上させ各々の媒体に対して手動で最適の位置に焦点合わせを行った後、レーザーを周波数８４ＭＨｚでパルス的に照射して記録層をキュリー温度以上に暖めながら、ＳＩＬヘッド上のコイル磁界を２１ＭＨｚで変調させることでマーク長０．２４μｍの２Ｔ信号を記録した。ここで、磁界の変調幅は±１３０Ｏｅとした。
【０１２５】
記録後にレーザーパワー１ｍＷで再生しながら、分解能バンド幅３０ｋＨｚで２１ＭＨｚでのキャリアとノイズを測定し、このキャリアとノイズの比をＣＮＲとした。
【０１２６】
ＣＮＲは、実施例１２〜１４が各々、４３ｄＢ，４５ｄＢ，４６ｄＢであった。実施例１２は実施例１と同等で、実施例１３および１４は整合層がある実施例３および４の場合に匹敵するＣＮＲが得られた。
【０１２７】
浮上性については、いずれの媒体も良好であった。連続記録に関しては、いずれも２０回の試験を最後まで続けることができた。
【０１２８】
次に、実施例１および１２〜１４の表面再生型光記録媒体を帯電防止機能のないケースに入れたところ、実施例１２では０．３ｋＶしか帯電しなかったが、実施例１、１３および１４は２〜３ｋＶに帯電した。また、実施例１と実施例１２〜１４を表面の鉛筆硬度について比較すると、実施例１ではＨであったものが、実施例１２〜１４では３Ｈが得られており、浮上性や連続記録で特に大きな差はみられなかったものの長期的に考えると、実施例１２〜１４ではヘッドによる媒体の傷発生の確率が低いと考えられる。また、実施例１２では帯電しにくいために異物が付着しにくいと考えられる。
【０１２９】
【発明の効果】
本発明によれば、表面に開口率ＮＡが１を超える光学ヘッドをレーザービームの波長λに対してλ／４以下の高さで浮上させながらレーザービームにより記録再生を行う表面再生型光記録媒体で、基板上に少なくとも記録層および屈折率ｎ_PがＮＡより大きい透明樹脂保護層を有し、媒体表面でのレーザービームの直径が１．５〜３０μｍとすることにより、長期に渡って安定的な連続記録が可能となる。
【０１３０】
また、レーザービームの直径が３０μｍ以下であることにより、光学ヘッドの下面に凸部を設けて光学ヘッドと媒体表面の接触を防ぐことができる。また、記録領域の透明樹脂保護層の膜厚むらをΔｔとしたとき、Δｔ≦λ／ＮＡ²とすることによりフォーカスサーボを省略することが可能となる。
【０１３１】
さらに、記録層の上に屈折率がＮＡより０．４以上大きい誘電体層を設け、誘電体層の屈折率を媒体表面に向かって段階的あるいは連続的に下げたり、透明樹脂保護層の上にレーザー光に対して光学的な整合をとるための整合層を設けることにより、高角入射光に対して低反射条件を満たし、レーザービームを良好に収束させ、高いＳＮＲと解像度が得られる。また、誘電体層の屈折率ｎ_dを２．４以上にすることによっても高いＳＮＲと解像度が得られる。
【０１３２】
また、保護層の透明樹脂には無機超微粒子が含まれていることにより、透明樹脂保護層の硬度を増し、信頼性を高めることができる。
【図面の簡単な説明】
【図１】 本発明の表面再生型光記録媒体の一実施態様で、ＳＩＬヘッドが浮上する状態の断面摸式図である。
【図２】 従来の表面再生型光記録媒体の一例で、ＳＩＬヘッドが浮上する状態の断面摸式図である。
【図３】 図１の断面図の入射光線の状態の拡大図である。
【図４】 基板／反射層／記録層／誘電体層／透明樹脂保護層／液体潤滑層の構成を有する本発明の光記録媒体の一実施態様の部分断面図である。
【図５】 誘電体層を第１誘電体層と第２誘電体層の２層で構成した本発明の光記録媒体の一実施態様の部分断面図である。
【図６】 媒体表面に第１整合層と第２整合層とを形成した本発明の光記録媒体の一実施態様の部分断面図である。
【図７】 記録層の下に下部誘電体層を有する本発明の光記録媒体の一実施態様の部分断面図である。
【図８】 本発明の表面再生型光記録媒体の一実施態様で、下面に凸部を有するＳＩＬヘッドが浮上する状態の断面摸式図である。
【図９】 誘電体層を第１誘電体層と第２誘電体層の２層で構成し、媒体最表面に液体潤滑層を形成した本発明の光記録媒体の一実施態様の部分断面図である。
【図１０】 整合層を第１整合層と第２整合層の２層で構成し、媒体最表面に液体潤滑層を形成した本発明の光記録媒体の一実施態様の部分断面図である。
【符号の説明】
１１、２１、３１、４１、５１、６１、７１、８１、１０１、１１１：基板
４２、５２、６２、７２、１０２、１１２：反射層
７３：下部誘電体層
１２、２２、３２、４３、５３、６３、７４、８２、１０３、１１３：記録層
１３、２３、３３、４４、６４、８３、１１４：誘電体層
５４、７５、１０４：第１誘電体層
５５、７６、１０５：第２誘電体層
１４、３４、４５、５６、６５、７７、８４、１０６、１１５：透明樹脂保護層
６６、７８、１１６：第１整合層
６７、７９、１１７：第２整合層
４６、５７、６８、８０、１０７、１１８：液体潤滑層
１５、２４、８５：エアギャップ
１６、２５、８６：ＳＩＬヘッド
１７、２６、８７：レーザービーム（入射光線）
１８、２７：焦点
３６：誘電体と透明樹脂保護層の界面でのレーザービームの直径Ｌ１
３７、９０：媒体表面でのレーザービームの直径Ｌ２
８８：ＳＩＬヘッド下面の凸部
８９：凸部の大きさ
９１：コイル[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface reproduction type optical recording medium that records and reproduces light by entering light from the surface of the medium among recordable optical recording media.
[0002]
[Prior art]
An optical recording medium is a recording medium capable of large-capacity and high-density recording, and the demand is rapidly increasing as a medium for recording a large-capacity file and a moving image of a computer accompanying the recent development of multimedia.
[0003]
An optical recording medium is generally formed by forming a multilayer film including a recording layer on a transparent disk-shaped substrate such as plastic, performing recording or erasing by irradiating a laser, and reproducing with reflected light of the laser. The optical recording medium includes an erasable that can be rewritten like a magneto-optical recording medium and a phase change recording medium, and a write-once that can be written only once like a CD-R.
[0004]
Conventionally, the magneto-optical recording medium has been centered on so-called optical modulation recording in which recording is performed by applying a fixed magnetic field in the opposite direction after erasing by applying a fixed magnetic field. The magnetic field modulation method that modulates according to the method is attracting attention as a method that can be recorded (direct overwrite) by one rotation and can be recorded accurately even at high recording density.
[0005]
Phase change recording media have been growing significantly in recent years because they can be directly overwritten by optical modulation recording and can be reproduced by the same optical system as CDs and DVDs. Also, write-once CD-Rs are widely popular because they are completely compatible with CDs.
[0006]
Conventionally, as a means for improving the recording density of an optical recording medium, a land / groove recording method in which recording is performed on both a groove which is merely a guide groove and a land which is a recording area has attracted attention (Optical Memory Symposium '94 Technical). Digest p.41 (1994), Jpn.J.Appl.Phys.Vol.37 p.2144 (1998)).
[0007]
In this method, the land and groove widths are approximately equal and the optical depth is approximately 1/6 of the laser wavelength, or the optical depth is approximately 1/8 of the laser wavelength and the phase is independent between the land and groove during reproduction. By combining adjustment, it is possible to reproduce with small crosstalk.
[0008]
Conventionally, a recording / reproducing laser is applied to a recording film through a substrate. Recently, so-called near-field optical recording, in which an optical head is moved close to a recording film, is attracting attention as a means for increasing the density (Appl. Phys. Lett. 68, p. 141 (1996)). In this recording method, a solid immersion lens (hereinafter abbreviated as SIL) head is used to reduce the laser beam spot size, thereby reducing the conventional recording limit determined by the laser wavelength (λ) of the light source (˜λ / 2NA: NA is an objective lens) Can be reproduced with a mark shorter than the numerical aperture), and recording / reproduction with ultrahigh recording density can be realized.
[0009]
In this near-field optical recording, since the optical head needs to be close to the recording medium (200 nm or less), the recording film is not irradiated with the laser beam through the substrate as in the conventional magneto-optical recording medium, but not through the substrate. A method of directly irradiating a recording film with a laser beam is used (surface reading type recording). At this time, it has been proposed to use a floating slider head in order to bring the recording film close to the SIL head.
[0010]
[Problems to be solved by the invention]
The inventors of the present invention manufactured a near-field optical recording medium using SIL as described above and tried a continuous recording / reproducing test. However, if recording is continued for a long time, foreign matter adheres to the SIL head and recording / reproducing is performed. There was a phenomenon that could not be continued.
[0011]
Also, when recording / reproducing was performed with the land / groove recording method, the surface of the groove medium was far from the optical head by the depth of the groove compared to the surface of the land medium. As a result, the light is easily reflected and the light is condensed. As a result, the recording / reproducing characteristics of the groove are deteriorated as compared with the recording / reproducing characteristics of the land.
[0012]
An object of the present invention is to provide an optical recording medium suitable for near-field optical recording, which exhibits high reliability in a continuous recording test and can obtain good recording / reproducing characteristics.
[0013]
Another object of the present invention is to provide an optical recording medium capable of obtaining sufficient recording / reproduction characteristics even in the land / groove recording system.
[0014]
[Means for Solving the Problems]
As a result of intensive studies in view of the above situation, the present inventors have found that the power density is extremely high on the lower surface of the SIL lens and the surface of the medium. If it is on the road, the temperature rises abnormally and a foreign matter is generated. _P The present invention was completed by providing a transparent resin protective layer having a diameter greater than NA and setting the diameter of the laser beam on the medium surface to 1.5 μm or more.
[0015]
That is, the present invention provides at least a recording layer and a refractive index n on a substrate. _P Has a transparent resin protective layer larger than NA, and recording / reproduction is performed with a laser beam while flying an optical head with an aperture ratio NA exceeding 1 on the surface at a height of λ / 4 or less with respect to the wavelength λ of the laser beam. A surface reproduction type optical recording medium, wherein the diameter of a laser beam on the medium surface is 1.5 μm or more and 30 μm or less. In the magneto-optical recording medium and phase change recording medium of the present invention, a dielectric layer having a refractive index 0.4 or more larger than NA is provided on the recording layer, and the transparent resin protective layer is provided thereon. preferable.
[0016]
Further, the present invention provides a surface reproduction type optical recording medium for performing recording and reproduction by a laser beam while flying an optical head having an aperture ratio NA exceeding 1 on the surface at a height of λ / 4 or less with respect to the wavelength λ of the laser beam. And at least the recording layer and the refractive index n on the substrate. _P The surface-reproducing optical recording medium is characterized in that has a transparent resin protective layer larger than NA, and the transparent resin protective layer contains inorganic ultrafine particles having a particle size of 0.05 μm or less.
[0017]
Further, the present invention provides a surface reproduction type optical recording medium for performing recording and reproduction by a laser beam while flying an optical head having an aperture ratio NA exceeding 1 on the surface at a height of λ / 4 or less with respect to the wavelength λ of the laser beam. And at least the recording layer, the dielectric layer and the refractive index n on the substrate. _P Is a surface reproduction type optical recording medium in which transparent resin protective layers having a refractive index larger than NA are laminated in this order, and the refractive index n of the dielectric layer _d Is a surface-reproducing optical recording medium characterized by being 2.4 or more.
[0018]
Furthermore, the present invention provides a surface reproduction type optical recording medium for performing recording and reproduction by a laser beam while flying an optical head having an aperture ratio NA of more than 1 on the surface at a height of λ / 4 or less with respect to the wavelength λ of the laser beam. In the substrate surface, lands and grooves exist, and at least the recording layer and the refractive index n are formed on the substrate. _P The surface-reproducing optical recording medium has a transparent resin protective layer having a surface roughness greater than NA, and a step difference between the land and the groove on the surface of the transparent resin protective layer is λ / 30 or less.
[0019]
Hereinafter, the present invention will be described with reference to the drawings.
[0020]
FIG. 1 is a schematic cross-sectional view of a surface reproduction type optical recording medium according to an embodiment of the present invention in a state in which a SIL head 16 is levitated. A recording layer 12, a dielectric layer 13, and a transparent resin protective layer 14 are laminated on the substrate 11. A laser beam 17 incident on the SIL head 16 from an objective lens (not shown) reaches the medium surface through the air gap 15.
[0021]
SIL head 16 (NA for aperture ratio, n for refractive index) _SIL Critical angle (sin) ^-1 (1 / n _SIL The laser beam exceeding)) reaches the medium surface by the near field by keeping the air gap 15 within approximately ¼ of the wavelength.
[0022]
The laser beam 17 reaching the medium surface reaches the recording layer 12 through the transparent resin protective layer 14 and the dielectric layer 13 and forms a focal point 18. In the present invention, as shown in FIG. 3, the diameter L2 (37 in the figure) of the laser beam 17 on the medium surface is determined from the Snell's law. ₂ , Film thickness d ₂ ) And transparent resin protective layer (refractive index n _Three , Film thickness d _Three ) Of the laser beam 17 at the interface L1 = 2d ₂ ・ Tan (sin ^-1 (NA / n ₂ )), L2 = L1 + 2d _Three ・ Tan (sin ^-1 (NA / n _Three )). Here, the size of the laser beam 17 at the focal point 18 is approximately λ / NA, and is approximately λ / NA also in the depth direction. ² Although it is said that there is a degree of spread, in the present invention, as described above, the recording layer has a dot-like focal point on the top surface, and a dielectric, a transparent resin protective layer, an air gap, and a SIL head on the medium surface are configured. The geometrical size L2 that is uniquely determined by the above is defined as the diameter of the laser beam on the medium surface.
[0023]
If λ / NA <L2, this value may be considered to coincide with the substantial diameter.
In order to collect light up to the size of λ / NA by the groove, it is preferable to make the unevenness of the land and groove on the surface of the medium flat to λ / 30 or less.
[0024]
In the present invention, the optical head means a hemispherical so-called SIL, a super hemispherical SIL, a SIM (Solid Immer Mirror) with a built-in reflecting mirror, and the like, and the NA becomes larger than 1 using a near field as in the SIL. In this way, the optical head has a lens configured to collect light.
[0025]
FIG. 2 is a schematic cross-sectional view showing a state where the SIL head is levitated as an example of a conventional surface reproduction type optical recording medium. Conventionally, since λ / NA> L2, it is considered that the focus of the laser beam is equivalent to being at 27 on the lower surface of the SIL head, and the laser beam of λ / NA reaches the recording layer 22 from the medium surface by the near field. The diameter of the laser beam on the medium surface was approximately λ / NA.
[0026]
In the medium of the present invention, the diameter of the laser beam on the medium surface can be increased to 1.5 μm or more by adjusting the refractive index and film thickness of the dielectric layer and the transparent resin protective layer. The power density decreases, and abnormal temperature rise due to laser power such as foreign matter and defects can be prevented.
[0027]
As shown in FIG. 8, a system for recording / reproducing information on the medium of the present invention has a convex portion 88 on the lower surface of the optical head having a size of 60 μm or less and a substantially circular or oval shape whose center substantially coincides with the center of the optical head. And the focal point of the laser beam is the recording layer 82 and λ / NA ² It is preferable that the aberration due to the film thickness of the protective layer 84 is corrected by correcting the optical system such as the shape of the objective lens or the SIL lens.
[0028]
By forming the convex portion 88, even if the optical head or the medium is inclined, the risk that the portion corresponding to the optical path of the optical head contacts the medium is reduced. In order to perform recording / reproduction with such an optical head, it is necessary to pass a laser beam through the convex portion 88, and it is conceivable that the beam is oscillated within the convex portion 88 for tracking. For this purpose, the diameter of the laser beam on the medium surface is preferably 30 μm or less.
[0029]
In the case of magneto-optical recording, a coil 91 for magnetic field modulation recording is preferably provided around the convex portion on the lower surface of the optical head. In this case, since the coil 91 can be made smaller as the area of the convex portion 88 is smaller, high-speed modulation is possible, and the recording density and transfer rate are improved.
[0030]
FIG. 4 shows a partial sectional view of an embodiment of the optical recording medium of the present invention. On the substrate 41, a reflective layer 42, a recording layer 43, a dielectric layer 44, a transparent resin protective layer 45, and a liquid lubricating layer 46 are laminated.
[0031]
The substrate 41 is not particularly limited as long as it satisfies the characteristics as a medium substrate such as mechanical characteristics, and glass, polycarbonate, amorphous polyolefin, engineering plastic, or the like can be used.
[0032]
The substrate 41 can be provided with grooves and lands. Conventionally, a groove exists only for tracking of an optical head, and information recording / reproduction is performed on a land which is a recording area. However, with the demand for higher recording density, this groove is also used for information recording. Has become involved in recording and playback. In the surface reproduction type optical recording medium of the present invention, in addition to the conventional land recording method as described above, the groove recording method for recording information in the groove and the land / groove recording for recording information in both the land and the groove. It is also applicable to the system.
[0033]
In the case of the groove recording method, a substrate on which a groove wider than the land width may be used. In the case of the land / groove recording method, the ratio of land to groove (land width / groove width) is 0.5 to 1 at half width. 0.5 is preferable, and 0.8 to 1.1 is more preferable.
[0034]
Groove depth on substrate d _G Is the wavelength of light from the optical head, and n is the refractive index of the transparent resin protective layer. _OC Λ / (14n _OC ) ≦ d _G ≦ λ / (5n _OC ) Is preferable. d _G Is λ / (7n _OC ) To λ / (5n _OC ), The crosstalk between the land and the groove can be reduced, and λ / (14n _OC ) To λ / (7n _OC ), The phase of the return light is greatly different between the land and the groove. Therefore, the crosstalk can be reduced by adjusting the phase independently between the land and the groove in the optical system.
[0035]
Further, if the pitch between the land and the groove is 0.7λ / NA or more, the crosstalk does not become so large. Therefore, as long as tracking is possible, the groove depth can be reduced to increase the linear recording density.
[0036]
The reflective layer 42 is made of a material having a high reflectance at a laser wavelength used, such as a noble metal, Cu, or Al. In order to ensure durability, the reflective layer may be an alloy of these metals or an alloy of these metals and other metals. Further, when the recording layer 43 is sufficiently thick, the reflective layer 42 may not be provided.
[0037]
In the case of magneto-optical recording, the recording layer 43 is composed of an amorphous rare earth transition metal film having a large perpendicular magnetic anisotropy such as TbFeCo, TbDyFeCo, or NdDyFeCo, or an artificial lattice film such as Pt / Co. The film thickness of the recording layer 43 is preferably 10 nm or more and 200 nm or less. When the recording layer is a single layer, the film thickness of the recording layer 43 is more preferably 15 nm or more and 40 nm or less in consideration of SNR. The recording layer 43 does not necessarily have to be a single layer film, and may be a laminate with a layer for improving the recording magnetic field sensitivity such as GdFeCo, or a laminate with a magnetic super-resolution intermediate layer or a reproduction layer. Here, a corrosion-resistant element such as Cr, Ti, Zr, Nb, or Ta is added to the recording layer 43 to increase the corrosion resistance, or Nd of several atomic% is added to increase the Kerr rotation angle at a short wavelength. It may be a thing.
[0038]
In the case of phase change recording, the recording layer 43 is made of a material whose optical constant changes between crystalline and amorphous states, such as GeSbTe and AgInSbTe. The film thickness of the recording layer 43 is preferably 10 nm or more and 40 nm or less.
[0039]
In the case of the write-once (write-once type), the recording layer 43 is composed of a dye film such as cyanine, phthalocyanine, or naphthalocyanine, and these can be formed by spin coating or the like.
[0040]
In the case of magneto-optical recording or phase change recording, AlN, SiN, GeN, Ta on the recording layer 43 ₂ O _Five ZnS-SiO ₂ A transparent dielectric layer 44 such as is preferably formed. The film thickness of the dielectric layer 44 is set to such a film thickness that the signal output from the recorded mark increases, and is preferably set in the range of about 10 to 1000 nm. The larger the refractive index of the dielectric layer 44, the greater the effect of increasing the reproduction signal due to multiple reflections, and the difference in the refractive index with the recording layer 43 is reduced, so that the light can be easily guided by the recording layer 43, resulting in a high output. can get. Therefore, it is preferably 0.4 or more larger than the NA of the SIL head, and more preferably 0.3 or more higher than the refractive index of the transparent resin protective layer.
[0041]
In order to increase the effect of increasing the reproduction signal due to multiple reflection, the thickness of the dielectric layer is spread in the depth direction of the laser beam converged on the recording layer. ² More preferably, it is less.
[0042]
Further, the closer the light traveling direction in the dielectric layer is to be perpendicular to the film surface, the greater the effect of increasing the reproduction signal by multiple reflection, and the refractive index of the transparent resin protective layer is about 1.3 to 1.9. Considering that there is a refractive index n of the dielectric layer _d Is preferably 2.4 or more.
[0043]
As a material of such a dielectric layer, (1) ZnS, Nb ₂ O _Five TiO ₂ One or more substances selected from among (2) (MA) ₁ (MB) ₂ O ₆ MA is composed of one or more substances selected from Mg, Ca, Sr, and Ba, and MB is composed of one or more substances selected from V, Nb, and Ta. Double oxides, (3) perovskite compounds and the like are preferred. (MA) ₁ (MB) ₂ O ₆ The material represented by the following formula is expressed as follows: MA: MB: O = 1: x: y (atomic ratio), x and y are not necessarily strictly equal to x = 2 and y = 6. ) ₁ (MB) ₂ O ₆ Any material having a composition represented by In the case of a perovskite compound, it is not always necessary to be composed of only a perovskite compound, and any material containing at least 80% by weight of the perovskite compound may be used.
[0044]
The transparent resin protective layer 45 is made of a transparent polymer such as polyvinylidene chloride, polychlorostyrene, polyvinyl benzoate, polyacrylic ester, polyvinyl acetate, polydimethylsiloxane, or polyfluorinated ethylene, or a copolymer thereof. . These polymers are formed by adding photopolymerization initiators, leveling agents, heat stabilizers, and other materials that adjust hardness, viscosity, etc. to the monomers of each material, applying them by spin coating, and then polymerizing them by UV irradiation. Alternatively, it can be formed by spin-coating a solution obtained by dissolving a polymer in a solvent, or by attaching a polymer sheet with an adhesive.
[0045]
Among these materials, a material mainly composed of polyacrylic acid ester obtained by photopolymerizing an acrylic acid ester derivative is particularly preferable from the viewpoints of hardness, speed of photopolymerization, and the like. Here, as the number of functional groups of the monomer increases, the hardness of the transparent resin protective layer obtained by photopolymerization increases, but considering the fact that it becomes brittle, the monofunctional, bifunctional, and trifunctional acrylics listed below It is preferable to use an acid ester derivative alone or as a mixture as a main component.
[0046]
Monofunctional (meth) acrylic acid ester derivatives include tetrahydrofurfuryl acrylate, tetrahydrofurfuryl methacrylate, 2-acryloyloxyethyl-2-hydroxypropyl phthalate, 2-methacryloyloxyethyl-2-hydroxypropyl phthalate, phenoxyethyl Examples include acrylate and phenoxyethyl methacrylate.
[0047]
Examples of the bifunctional (meth) acrylic acid ester derivatives include ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,3-propanediol diacrylate, 1,3-propanediol dimethacrylate, 1,4-butanediol diacrylate, 1 , 4-butanediol dimethacrylate, 1,5-pentanediol diol diacrylate, 1,5-pentanediol diol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, 1,7- Heptanediol diacrylate, 1,7-heptanediol dimethacrylate, 1,8-octanediol diacrylate, 1,8-octanediol dimethacrylate, 1,9-nonanediol diacrylate, 1,9 Nonanediol dimethacrylate, 1,10-decanediol diacrylate, 1,10-decanediol dimethacrylate, diacrylate or dimethacrylate derived from average molecular weight 200-600 nopolyethylene glycol, bis (hydroxymethyl) -tricyclo [5 .2.1.02,6] decane diacrylate, bis (hydroxymethyl) -tricyclo [5.2.1.02,6] decane dimethacrylate, ethyleneoside adduct diacrylate of bisphenol A, ethylene oxide adduct of bisphenol A A dimethacrylate etc. can be illustrated.
[0048]
Examples of the trifunctional or higher functional (meth) acrylic acid ester derivatives include pentaerythritol triacrylate, pentaerythritol trimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, bis (hydroxymethyl) -tricyclo [5.2.1. Examples include 02,6] decane triacrylate, bis (hydroxymethyl) -tricyclo [5.2.1.02,6] decane trimethacrylate, dipentaerythritol hexaacrylate, dipentaerythritol hexamethacrylate, and the like.
[0049]
In order for the optical head to float stably, the surface of the transparent resin protective layer 45 is preferably hard, and preferably has a pencil hardness of HB or higher. The lower the refractive index of the transparent resin protective layer 45, the easier the beam becomes. However, if the refractive index is too low, light incident from a high angle will not reach the inside of the transparent resin protective layer. Is preferred.
[0050]
In order to increase the hardness of the transparent resin protective layer, the transparent resin of the protective layer preferably contains inorganic ultrafine particles. For example, a nanometer-sized powder of silicon dioxide or aluminum oxide or a sol-gel material can be added to the resin material that is cured with ultraviolet rays. In order to prevent optical scattering, it is preferable that the material of the inorganic ultrafine particles has a refractive index as close as possible to the resin or has a particle diameter of 0.05 μm or less and further improves dispersibility.
[0051]
The inorganic ultrafine particles are ITO, SnO ₂ : Transparent conductive fine particles such as Sb can suppress the adsorption of foreign matters due to static electricity.
[0052]
In addition, if the inorganic ultrafine particles are aluminum oxide, aluminum nitride, boron nitride, silicon carbide, beryllium oxide or diamond, the heat dissipation of the transparent resin protective layer is enhanced, and abnormal heating due to laser power such as foreign matter and defects is increased. Can be suppressed.
[0053]
The film thickness of the transparent resin protective layer 45 is λ / NA ² It is preferable that the diameter of the laser beam on the medium surface is set in the range of 1.5 μm to 30 μm. The film thickness of the transparent resin protective layer 45 is λ / NA ² By setting it as the above, the interference in the transparent resin protective layer 45 of a light beam can be reduced.
[0054]
Further, by providing the transparent resin protective layer 45, the irregularities on the surface of the optical recording medium due to the lands and grooves on the substrate are substantially leveled, and the distance between the medium surface of the lands and grooves and the lower surface of the optical head is substantially constant. Become. Here, when the film thickness unevenness of the transparent resin protective layer in the recording area is Δt, Δt ≦ λ / NA ² Then, the film thickness distribution is within the range of the depth of focus, the flying height is accurately controlled by adjusting the shape of the slider, and the flying property of the medium is improved to drive the drive without a complicated focus servo mechanism. Since it becomes possible to comprise, it is preferable. Here, the film thickness unevenness means a difference between the maximum value and the minimum value of the film thickness in the recording area.
[0055]
The liquid lubricant layer 46 is made of a lubricant such as perfluoroether or silicon oil, and can cope with an instantaneous contact between the head and the medium, which is a concern in a system provided with a flying head. The film thickness of the liquid lubricating layer 46 is preferably 0.2 nm to 5 nm.
[0056]
Further, when the surface of the optical recording medium of the present invention has a transparent resin protective layer 45 or a matching layer described later formed of a resin layer, the resin layer contains a fluorine-based lubricant or a fluorine-based surfactant. Thus, the medium surface may be lubricated.
[0057]
In order for the recording layer 43 to focus the laser beam to a size of approximately λ / NA, it is preferable that the high-angle incident light reaches the recording layer 43 without being reflected halfway. Here, the high-angle incident light is light incident at an angle of NA> 1, and is an outer portion when the pupil plane of the return light is observed with a CCD camera or the like, but has a level equivalent to the brightness of the inner portion. Is preferred. The film thickness of the dielectric layer 44 is λ / NA ² The film thickness of the transparent resin protective layer 45 is λ / NA. ² If it is above, it is preferable to reduce both the reflection of the dielectric layer 44 and the transparent resin protective layer 45 and the reflection of the transparent resin protective layer 45 and the air gap.
[0058]
In the case where the dielectric layer 44 and the transparent resin protective layer 45 are each a single layer as shown in FIG. 4, in order to satisfy such conditions, the optical film thicknesses are approximately (2m + 1) λ / 4 and nλ / 2, respectively. It is preferable that However, m and n are integers of 0 or more. Here, the film thickness of the transparent resin protective layer 45 is λ / NA. ² If it is thick enough, the optical interference between the upper and lower sides of the transparent resin protective layer will be reduced, so the film thickness of the transparent resin protective layer does not necessarily need to satisfy this condition. In this case, it is preferable to add a matching layer on the transparent resin protective layer so as to reduce reflection at the interface between the transparent resin protective layer and the air gap as will be described later.
[0059]
Further, between the recording layer 43 and the reflective layer 42, AlN, SiN, GeN, Ta ₂ O _Five ZnS-SiO ₂ By providing the lower dielectric layer composed of etc., the antireflection effect at the interface between the transparent resin protective layer and the dielectric layer is enhanced.
[0060]
Further, it is preferable because the refractive index of the dielectric layer can be further lowered by stepwise or continuously decreasing toward the medium surface. The refractive index of the dielectric layer varies depending on the wavelength and manufacturing conditions. For example, SiON 1.5 to 1.9, AlN 2.0, SiN 2 to 2.1, ZnS-SiO ₂ A value of about 2.2 is obtained, and a medium satisfying a good low reflection condition for high-angle incident light can be obtained by changing the film formation rate by two or more layers or by simultaneous sputtering. . The minimum unit of the step is preferably about λ / 4. However, when there is no material having an appropriate refractive index, it is possible to substitute by stacking layers having a refractive index that is thinner than λ / 4 and different in refractive index.
[0061]
The above-described hemispherical SIL, super hemispherical SIL, SIM, etc. are all preferably made of a high refractive index glass having a refractive index of 1.7 or more. Even if the gap is zero, reflection is likely to occur. In addition, when the reflected light from the dielectric layer returns beyond the coherence distance in the transparent resin protective layer, reflection from the medium surface is suppressed even if the thickness of the dielectric layer and the refractive index gradient are adjusted. can not cut. Therefore, it is preferable to suppress reflection on the surface of the medium by providing a matching layer for optically matching the laser beam on the transparent resin protective layer.
[0062]
As a condition for such a matching layer, the refractive index of the matching layer is preferably NA or more, and the refractive index is preferably increased stepwise or continuously from the uppermost layer of the matching layer toward the transparent resin protective layer side. Also, the refractive index of the matching layer is greater than or equal to NA, and the refractive index is increased stepwise or continuously from the uppermost layer of the matching layer toward the transparent resin protective layer, and then stepwise or continuously decreased again. Is preferable because the reflectance is further lowered. At this time, the refractive index of the contact portion between the matching layer and the transparent resin protective layer may be lower than the refractive index of the transparent resin protective layer in the range where the refractive index of the matching layer is NA or more. Further, in order to further reduce the reflectance, such a change in the refractive index may be further repeated. The minimum unit of the step is preferably about λ / 4. However, when there is no material having an appropriate refractive index, it is possible to substitute by stacking layers having a refractive index that is thinner than λ / 4 and different in refractive index.
[0063]
The matching layer is made of SiO ₂ , SiON, AlN, SiN, GeN, Ta ₂ O _Five ZnS-SiO ₂ It is composed of dielectric materials having various refractive indexes such as those or a laminate thereof.
[0064]
A part or all of the matching layer may be made of a transparent resin. For example, the refractive index is 1.63 for polyvinylidene chloride, 1.61 for polychlorostyrene, 1.57 for polybenzoate, 1.49 for polymethyl methacrylate, 1.47 for polyvinyl acetate, polydimethyl Combining two or more of these or a copolymer thereof having a value of about 1.40 for siloxane and about 1.35 for polyfluorinated ethylene can provide a medium that satisfies good low reflection conditions for high-angle incident light.
[0065]
In order to increase the hardness of the transparent resin of the matching layer, the transparent resin preferably contains inorganic ultrafine particles having a particle size of 0.05 μm or less.
[0066]
In order to obtain such a high angle low reflection condition, it is preferable that the film thickness distribution of the transparent resin protective layer is within a range of ± 40 nm or less from the optimum condition. However, a matching layer is formed, and the dielectric layer and the transparent layer are transparent. If the layer structure and the refractive index are adjusted so that the reflection at the interface of the resin protective layer is sufficiently small, the allowable value of the film thickness of the transparent resin protective layer is further increased.
[0067]
The laser beam condensed by the medium tends to be slightly larger in the polarization direction than in the direction perpendicular to the polarization. As a reproducing method of the surface reproduction type optical recording medium of the present invention, the linear recording density is improved by making the polarization plane of the laser beam perpendicular to the groove, and the track density is the same as that of the land / groove recording of the present invention. It is possible to increase.
[0068]
In addition, if the phase of the return light can be adjusted separately for the land and the groove, and the phase is adjusted independently for the land and the groove, it is possible to achieve good reproduction with low crosstalk and high SNR. In this case, as described above, λ / (14n _OC ) ≦ d _G ≦ λ / (7n _OC ) Is preferably satisfied.
[0069]
【Example】
Hereinafter, specific embodiments to which the present invention is applied will be described. In each of the examples and comparative examples, the following surface reproduction type optical recording medium was manufactured and evaluated by flying a SIL head having a laser wavelength λ = 685 nm, NA = 1.3, and a refractive index of 2.0.
Where λ / NA ² = 405 nm. In addition, the film thickness in the following examples and comparative examples indicates the film thickness in the vicinity of the center in the radial direction of the recording area of the optical recording medium measured by the SIL head.
[0070]
Example 1
A surface reproduction type optical recording medium having a structure as shown in FIG. 4 was produced. Ag is formed on a polycarbonate substrate 41 having guide grooves (grooves) having a track pitch of 0.4 μm. ₉₈ Pd ₁ Ti ₁ The reflective layer 42 made of was formed to a film thickness of 40 nm by DC sputtering. A recording layer 43 made of TbFeCo was formed thereon with a thickness of 20 nm by DC sputtering. On top of this, a dielectric layer 44 made of SiN having a refractive index of 2.1 is formed between Ar and N. ₂ The film was formed to a thickness of 230 nm by reactive DC sputtering using a Si target in a mixed atmosphere.
[0071]
On top of this, a photopolymerization initiator, a leveling agent, etc. mainly composed of a mixture of acrylic ester derivatives in which the weight ratio of tetrahydrofurfuryl acrylate, 1,6-hexanediol diacrylate and pentaerythritol triacrylate is 1: 1: 4. A transparent resin protective layer having a refractive index of 1.5 was formed by applying an ultraviolet curable resin monomer added with bismuth by spin coating and polymerizing by ultraviolet irradiation.
[0072]
On top of this, a perfluoropolyether liquid lubricant layer 46 was applied by 2 nm by a pulling method to produce a surface reproduction type optical recording medium. Here, the medium was manufactured with three types of transparent resin protective layer 45 having a thickness of 480, 600 and 940 nm.
[0073]
In these media, the optical film thickness (actual film thickness × refractive index) of the dielectric layer is 0.71λ, and the optical film thickness of the transparent resin protective layer is film thickness with respect to the recording / reproducing laser wavelength λ = 685 nm. They were 1.05λ, 1.31λ, and 2.06λ for 480, 600, and 940 nm, respectively. The diameter of the laser beam on the medium surface was 2.0, 2.4, 3.6 μm for the transparent resin protective layer thicknesses of 480, 600, and 940 nm, respectively.
[0074]
(Comparative Example 1)
Instead of the transparent resin protective layer 45, a solid lubricating layer made of diamond-like carbon (DLC) having a refractive index of 2.0 is replaced with Ar and H. ₂ A surface reproduction type optical recording medium was manufactured in the same manner as in Example 1 except that the film was formed to a thickness of 20 nm by a reactive RF sputtering method using a C target in a mixed atmosphere. The diameter of the laser beam on the medium surface of this medium was 0.40 μm.
[0075]
(Comparative Example 2)
A surface reproduction type optical recording medium was manufactured in the same manner as in Example 1 except that the thickness of the transparent resin protective layer 45 was 250 nm. The optical film thickness of the transparent resin protective layer of this medium was 0.55λ, and the diameter of the laser beam on the medium surface was 1.2 μm.
[0076]
(Example 2)
A surface reproduction type optical recording medium having a structure as shown in FIG. 5 was produced. In this embodiment, the dielectric layer has a structure in which the refractive index of the dielectric layer is lowered stepwise toward the medium surface.
[0077]
Ag is formed on a polycarbonate substrate 51 with guide grooves having a track pitch of 0.4 μm. ₉₈ Pd ₁ Ti ₁ The reflective layer 52 made of was formed to a thickness of 40 nm by DC sputtering. A recording layer 53 made of TbFeCo was formed thereon with a thickness of 20 nm by DC sputtering. On top of this, a first dielectric layer 54 made of SiN having a refractive index of 2.1 is formed of Ar and N. ₂ In a mixed atmosphere, a reactive DC sputtering method using a Si target was used to form a film thickness of 75 nm. A second dielectric layer 55 made of SiON having a refractive index of 1.8 is formed thereon with Ar and a small amount of N. ₂ The film was formed to a thickness of 175 nm by RF sputtering using a SiON target in a mixed atmosphere.
[0078]
A coating agent obtained by adding 0.1 wt% of perfluoropolyether to the same ultraviolet curable resin monomer as used in Example 1 is applied by spin coating, and polymerized by ultraviolet irradiation to have a refractive index of 1 .5 transparent resin protective layer 56 was formed to produce a surface reproduction type magneto-optical recording medium.
[0079]
Here, the medium was manufactured with two types of film thicknesses of the transparent resin protective layer 45 of 480 nm and 940 nm. In these media, the optical film thickness of the first dielectric layer and the second dielectric layer is 0.69λ for the recording / reproducing laser wavelength λ = 685 nm, and the optical film thickness of the transparent resin protective layer is the film thickness. They were 1.05λ and 2.06λ for 480 and 940 nm, respectively. The diameter of the laser beam on the surface of the medium is 2.2 and 3.8 μm for the transparent resin protective layer thicknesses 480 and 980 nm, respectively.
[0080]
(Example 3)
A surface reproduction type optical recording medium having a structure as shown in FIG. 6 was produced. In this embodiment, the refractive index of the matching layer is increased stepwise from the medium surface toward the transparent resin protective layer side.
[0081]
Ag is formed on a polycarbonate substrate 61 with guide grooves having a track pitch of 0.4 μm. ₉₈ Pd ₁ Ti ₁ A reflective layer 62 made of a material having a thickness of 40 nm was formed by DC sputtering. A recording layer 63 made of TbFeCo was formed thereon with a thickness of 20 nm by DC sputtering. On top of this, a dielectric layer 64 made of SiN having a refractive index of 2.1 is formed between Ar and N. ₂ The film was formed to a thickness of 230 nm by reactive DC sputtering using a Si target in a mixed atmosphere. On top of this, a coating agent composed of the same ultraviolet curable resin monomer as that used in Example 1 was applied by spin coating, and polymerized by ultraviolet irradiation to mainly consist of polymethyl methacrylate having a refractive index of 1.50. A transparent resin protective layer 65 was formed to a thickness of 660 nm. A first matching layer 66 mainly composed of polychlorostyrene having a refractive index of 1.61 is formed to a thickness of 110 nm by the same method, and a fluorine-based surfactant having a refractive index of 1.45 is formed thereon. A surface reproducing type optical recording medium was manufactured by forming a second matching layer 67 containing 0.1 wt% mainly of methyl methacrylate and polydimethylsiloxane to a thickness of 170 nm.
[0082]
In this medium, the optical film thickness of the dielectric layer is 0.71λ, the optical film thickness of the transparent resin protective layer is 1.45λ, the total optical film thickness of the first and second matching layers is 0.62λ, The diameter of the laser beam was 3.6 μm.
[0083]
Example 4
A surface reproduction type optical recording medium having a structure as shown in FIG. 7 was produced. Ag is formed on a polycarbonate substrate 71 having guide grooves with a track pitch of 0.4 μm. ₉₈ Pd ₁ Ti ₁ A reflective layer 72 made of a material having a thickness of 40 nm was formed by DC sputtering. On this, a lower dielectric layer 73 made of SiAlN having a refractive index of 2.0 is formed with Ar and N. ₂ The film was formed to a thickness of 40 nm by reactive DC sputtering using a SiAl target in a mixed atmosphere. On this, a recording layer 74 made of TbFeCo was formed to a thickness of 20 nm by DC sputtering. On top of this, a first dielectric layer 75 made of SiN having a refractive index of 2.1 is formed of Ar and N. ₂ The film was formed to a thickness of 65 nm by a reactive DC sputtering method using a Si target in a mixed atmosphere.
[0084]
A second dielectric layer 76 made of SiON having a refractive index of 1.8 is formed thereon with Ar and a small amount of N. ₂ The film was formed to a film thickness of 190 nm by RF sputtering using a SiON target in a mixed atmosphere. On top of this, a coating agent composed of the same ultraviolet curable resin monomer as that used in Example 1 was applied by spin coating, and polymerized by ultraviolet irradiation, thereby mainly comprising polymethyl methacrylate having a refractive index of 1.5. A transparent resin protective layer 77 was formed. Here, five types of film thicknesses of the transparent resin protective layer 77 of 600, 750, 900, 1050, and 1200 nm were manufactured.
[0085]
On the transparent resin protective layer 77, a first matching layer 78 made of SiN having a refractive index of 2.1 is formed of Ar and N. ₂ The film was formed to a thickness of 80 nm by a reactive DC sputtering method using a Si target in a mixed atmosphere. On top of that, SiO with a refractive index of 1.45 ₂ The second matching layer 79 made of ₂ The film was formed to a thickness of 165 nm by RF sputtering using a target. On this, a perfluoropolyether-based liquid lubricating layer 80 was applied by 2 nm by a pulling method to produce a surface reproduction type optical recording medium.
[0086]
In these media, for the recording / reproducing laser wavelength λ = 685 nm, the optical thickness of the first and second dielectric layers combined is 0.70λ, and the optical thickness of the transparent resin protective layer 77 is 600, For 750, 900, 1050, and 1200 nm, the total optical thickness of 1.31, 1.64, 1.97, 2.30, 2.63λ, and the first to second matching layers is 0.59λ. The diameter of the laser beam on the surface of the medium was 3.4, 3.9, 4.4, 4.9, 5.5 μm for the transparent resin protective layer thicknesses 600, 750, 900, 1050, 1200 nm, respectively. It was.
[0087]
For the surface reproduction type optical recording media of Examples 1 to 4 and Comparative Examples 1 to 2, a slider SIL head having a laser wavelength of 685 nm and an effective numerical aperture of 1.3 on the thin film surface is rotated at a linear velocity of 10 m / s. The SIL is lifted to a height of 70 nm, and each medium is manually focused at an optimum position. Then, a laser is irradiated in a pulse manner at a frequency of 84 MHz to warm the main recording layer to a temperature above the Curie temperature. A 2T signal having a mark length of 0.24 μm was recorded by modulating the coil magnetic field on the head at 21 MHz. Here, the modulation width of the magnetic field was ± 130 Oe.
[0088]
While reproducing at a laser power of 1 mW after recording, the carrier and noise at a resolution bandwidth of 30 kHz and 21 MHz were measured, and the ratio of this carrier to noise was defined as CNR. In order to see the state of reflection of high-angle incident light, a CCD camera was installed on the pupil surface, and the amount of reflected light was compared with that of low-angle incident light.
[0089]
[Table 1]

As for the floating property, any medium is good, and in Examples 1 to 4 and Comparative Example 2 provided with a transparent resin protective layer and Comparative Example 1 in which a thin solid lubricating layer is used instead of the transparent resin protective layer, a difference is particularly recognized. I couldn't. Table 1 shows the measurement results of the recording / reproducing characteristics. Regarding the reflection state of the high-angle incident light, it is good when the transparent resin protective layer film thickness is other than 600 nm in Example 1, and in particular, the dielectric layer is made of two or more layers having different refractive indexes as in Example 2 As in Examples 3 and 4, it is further improved by providing a matching layer on the transparent resin protective layer. As for CNR, the thinner the transparent resin protective layer as in Comparative Examples 1 and 2 is better than that in Example 1, but the dielectric layers are divided into two layers having different refractive indices as in Examples 2 to 4. As described above, or by providing a matching layer on the transparent resin protective layer, good characteristics equivalent to or better than those of Comparative Example 1 were obtained.
[0090]
Next, continuous recording of 50,000 tracks with the optimum recording power was attempted 20 times for each sample, and the number of times that the continuous test could be completed without losing tracking was recorded.
[0091]
For continuous recording, 20 tests could be continued to the end if the diameter of the laser beam was 1.5 μm or more.
[0092]
Next, the focal point was fixed to a medium having a transparent resin protective layer thickness of 900 nm in Example 4, and the CNR of the medium having a transparent resin protective layer thickness of 600, 750, 900, 1050, and 1200 nm was measured. Table 2 shows the results.
[0093]
Based on this result, the difference (film thickness unevenness) between the maximum and minimum film thicknesses of the transparent resin protective layer in the recording area is expressed as λ / NA. ² It was confirmed that recording and reproduction can be performed without focus servo. All of the optical recording media of Example 4 satisfied this condition.
[0094]
[Table 2]

(Example 5)
A surface reproduction type optical medium for near-field recording having a structure as shown in FIG. 4 was manufactured. On a polycarbonate substrate 41 having a land-to-groove width ratio of 1: 1, a groove depth of 50 nm, and a track pitch of 0.33 μm (pitch between land and groove), Ag is formed. ₉₈ Pd ₁ Ti ₁ The reflective layer 42 made of was formed to a film thickness of 40 nm by DC sputtering. A recording layer 43 made of TbFeCo was formed thereon with a thickness of 20 nm by DC sputtering. On top of this, a dielectric layer 44 made of SiN having a refractive index of 2.1 is formed between Ar and N. ₂ The film was formed to a thickness of 230 nm by reactive DC sputtering using a Si target in a mixed atmosphere. A coating agent comprising an ultraviolet curable resin monomer similar to that used in Example 1 was applied on this by a spin coating method and polymerized by irradiation with ultraviolet rays, whereby the refractive index n _OC = 1.5 and a transparent resin protective layer 45 having a film thickness of 480 nm was formed. On top of this, a perfluoropolyether liquid lubricant layer 46 was applied by 2 nm by a pulling method to produce a surface reproduction type optical recording medium.
[0095]
In these media, the optical film thickness of the dielectric layer was 0.71λ and the optical film thickness of the transparent resin protective layer was 1.05λ with respect to the recording / reproducing laser wavelength λ = 685 nm. The depth of the groove on the substrate is λ / (9n _OC )Met. The step due to the land and groove of the substrate on the surface of the medium was 20 nm or less as measured by AFM. The diameter of the laser beam on the medium surface was 2.0 μm.
[0096]
(Comparative Example 3)
Instead of the transparent resin protective layer 45, a solid lubricating layer made of diamond-like carbon (DLC) having a refractive index of 2.0 is replaced with Ar and H. ₂ A surface reproducible optical medium was manufactured in the same manner as in Example 5 except that the film was formed to a thickness of 20 nm by a reactive RF sputtering method using a C target in a mixed atmosphere.
[0097]
The step due to the land and groove of the substrate on the surface of the medium was 50 nm as measured by AFM. The diameter of the laser beam on the medium surface of this medium was 0.40 μm.
[0098]
(Example 6)
A surface reproduction type optical recording medium for near-field optical recording having a structure as shown in FIG. 9 was produced.
Ag on a polycarbonate substrate 101 having a land-to-groove width ratio of 1: 1, a groove depth of 50 nm, and a track pitch of 0.33 μm (a pitch between the land and the groove). ₉₈ Pd ₁ Ti ₁ The reflective layer 102 made of was formed to a thickness of 40 nm by DC sputtering. A recording layer 103 made of TbFeCo was formed thereon with a thickness of 20 nm by DC sputtering. On top of this, a first dielectric layer 104 made of SiN having a refractive index of 2.1 is formed of Ar and N. ₂ In a mixed atmosphere, a reactive DC sputtering method using a Si target was used to form a film thickness of 75 nm. A second dielectric layer 105 made of SiON having a refractive index of 1.8 is formed thereon with Ar and a small amount of N. ₂ The film was formed to a thickness of 175 nm by RF sputtering using a SiON target in a mixed atmosphere. On top of this, a coating agent composed of the same UV curable resin monomer as used in Example 1 was applied by spin coating and polymerized by UV irradiation to protect transparent resin having a refractive index of 1.5 and a film thickness of 480 nm. Layer 106 was formed. On top of this, a perfluoropolyether liquid lubricant layer 107 was applied by 2 nm by a pulling method to produce a surface reproduction type optical recording medium.
[0099]
In these media, for the recording / reproducing laser wavelength λ = 685 nm, the optical film thickness of the first dielectric layer and the second dielectric layer is 0.69λ, and the optical film thickness of the transparent resin protective layer is 1 .05λ. The depth of the groove on the substrate is λ / (9n _OC )Met. The step due to the land and groove of the substrate on the surface of the medium was 20 nm or less as measured by AFM. The diameter of the laser beam on the medium surface was 2.2 μm.
[0100]
(Example 7)
A surface reproduction type optical recording medium for near-field optical recording having a structure as shown in FIG. 10 was produced. Ag on a polycarbonate substrate 111 having a land-to-groove width ratio of 1: 1, a groove depth of 50 nm, and a track pitch of 0.33 μm (pitch between land and groove). ₉₈ Pd ₁ Ti ₁ The reflective layer 112 made of was formed to a thickness of 40 nm by DC sputtering. A recording layer 113 made of TbFeCo was formed thereon with a thickness of 20 nm by DC sputtering. On top of this, a dielectric layer 114 made of SiN having a refractive index of 2.1 is formed with Ar and N. ₂ The film was formed to a thickness of 230 nm by reactive DC sputtering using a Si target in a mixed atmosphere. On top of this, a coating agent composed of the same ultraviolet curable resin monomer as that used in Example 1 was applied by spin coating, and polymerized by ultraviolet irradiation to mainly consist of polymethyl methacrylate having a refractive index of 1.50. The transparent resin protective layer 115 was formed to a film thickness of 660 nm. A first matching layer 116 mainly composed of polychlorostyrene having a refractive index of 1.61 is formed to a thickness of 110 nm by a similar method, and a fluorine-based surfactant having a refractive index of 1.45 is formed thereon. A second matching layer 117 containing 0.1 wt% and mainly composed of methyl methacrylate and polydimethylsiloxane was formed to a thickness of 170 nm. On this, a perfluoropolyether-based liquid lubricating layer 118 was applied by 2 nm by a pulling method to produce a surface reproduction type optical recording medium.
[0101]
In this medium, the optical film thickness of the dielectric layer was 0.71λ, the optical film thickness of the transparent resin protective layer was 1.45λ, and the total optical film thickness of the first and second matching layers was 0.62λ. The depth of the groove on the substrate is λ / (9n _OC )Met. The step due to the land and groove of the substrate on the surface of the medium was 20 nm or less as measured by AFM.
The diameter of the laser beam on the medium surface was 3.6 μm.
[0102]
(Example 8)
A surface reproduction type optical recording medium for near-field optical recording having a structure as shown in FIG. 7 was manufactured.
Ag on a polycarbonate substrate 71 having a land-to-groove width ratio of 1: 1, a groove depth of 50 nm, and a track pitch of 0.33 μm (pitch between land and groove). ₉₈ Pd ₁ Ti ₁ A reflective layer 72 made of a material having a thickness of 40 nm was formed by DC sputtering. On this, a lower dielectric layer 73 made of SiAlN having a refractive index of 2.0 is formed with Ar and N. ₂ The film was formed to a thickness of 40 nm by reactive DC sputtering using a SiAl target in a mixed atmosphere. On this, a recording layer 74 made of TbFeCo was formed to a thickness of 20 nm by DC sputtering. On top of this, a first dielectric layer 75 made of SiN having a refractive index of 2.1 is formed of Ar and N. ₂ The film was formed to a thickness of 65 nm by a reactive DC sputtering method using a Si target in a mixed atmosphere. A second dielectric layer 76 made of SiON having a refractive index of 1.8 is formed thereon with Ar and a small amount of N. ₂ The film was formed to a film thickness of 190 nm by RF sputtering using a SiON target in a mixed atmosphere. A coating agent composed of the same ultraviolet curable resin monomer as that used in Example 1 was applied thereon by spin coating, and polymerized by irradiation with ultraviolet rays to give a refractive index of 1.5 and a film thickness of 600, 750, 900. Five types of transparent resin protective layers 77 of 1050 and 1200 nm were formed. On the transparent resin protective layer 77, a first matching layer 78 made of SiN having a refractive index of 2.1 is formed of Ar and N. ₂ The film was formed to a thickness of 80 nm by a reactive DC sputtering method using a Si target in a mixed atmosphere. On top of that, SiO with a refractive index of 1.45 ₂ The second matching layer 79 made of ₂ The film was formed to a thickness of 165 nm by RF sputtering using a target. On this, a perfluoropolyether-based liquid lubricating layer 80 was applied by 2 nm by a pulling method to produce a surface reproduction type optical recording medium.
[0103]
In these media, for the recording / reproducing laser wavelength λ = 685 nm, the total optical thickness of the first and second dielectric layers is 0.70λ, and the total optical thickness of the first and second matching layers is It was 0.59λ. The depth of the groove on the substrate is λ / (9n _OC )Met.
[0104]
The optical film thickness of the transparent resin protective layer 77 is 1.31, 1.64, 1.97, 2.30, 2.63λ for film thicknesses 600, 750, 900, 1050, and 1200 nm, respectively. The diameters of the laser beams were 3.4, 3.9, 4.4, 4.9, and 5.5 μm, respectively. Further, the step due to the land and groove of the substrate on the medium surface of this medium was 20 nm or less as measured by AFM.
[0105]
Example 9
A surface similar to that of Example 8 except that the polycarbonate substrate 71 is a substrate having a land-to-groove width ratio of 1: 1, a groove depth of 75 nm, and a track pitch of 0.33 μm (pitch between land and groove). A reproducible optical recording medium was manufactured. The groove depth on the substrate is λ / (6n _OC )Met. The step due to the land and groove of the substrate on the surface of the medium was 20 nm or less as measured by AFM. However, the film thickness of the transparent resin protective layer was 900 nm.
[0106]
(Example 10)
The substrate 71 made of polycarbonate was the same as in Example 8 except that the land-to-groove width ratio was 1: 2, the groove depth was 60 nm, and the track pitch was 0.40 μm (groove pitch). The surface reproduction type optical recording medium was manufactured. The step due to the land and groove of the substrate on the surface of the medium was 20 nm or less as measured by AFM. However, the film thickness of the transparent resin protective layer was 900 nm.
[0107]
(Example 11)
In this example, a structure in which the refractive index increases stepwise from the interface between the transparent resin protective layer and the matching layer to the medium surface side is added to the medium structure of Example 8.
[0108]
The film thickness of the transparent resin protective layer is 900 nm, and the matching layer is 2 to 3 layers, that is, SiO 2 having a refractive index of 1.45 on the transparent resin protective layer. ₂ A first matching layer (thickness 230 nm) made of, a second matching layer (thickness 75 nm) made of SiN having a refractive index of 2.1, and SiO having a refractive index of 1.45. ₂ A surface reproduction type optical recording medium was manufactured in the same manner as in Example 8 except that the third matching layer (film thickness: 165 nm) made of the above was formed in this order.
[0109]
In these media, for the recording / reproducing laser wavelength λ = 685 nm, the optical film thickness of the first and second dielectric layers is 0.70λ, and the total optical film thickness of the first to third matching layers is It was 1.08λ. The depth of the groove on the substrate is λ / (9n _OC )Met. The diameter of the laser beam on the medium surface was 5.4 μm. The step due to the land and groove of the substrate on the surface of the medium was 20 nm or less as measured by AFM.
[0110]
For the surface reproduction type optical recording media of Examples 5 to 10 and Comparative Example 3, the medium was rotated at a linear velocity of 10 m / s, and a slider SIL head having a laser wavelength of 685 nm and an effective numerical aperture of 1.3 was set to 70 nm on the thin film surface. The laser beam is pulsed at a frequency of 84 MHz along the land or groove with the plane of polarization of the laser beam perpendicular to the groove. The 2T signal having a mark length of 0.25 μm was recorded by modulating the coil magnetic field on the SIL head at 20 MHz while warming the recording layer above the Curie temperature by irradiation. Here, the modulation width of the magnetic field was ± 130 Oe.
[0111]
While reproducing at a laser power of 1 mW after recording (the polarization plane of the laser beam is perpendicular to the groove), the carrier and noise at 21 MHz were measured with a resolution bandwidth of 30 kHz, and the ratio of this carrier to noise was defined as CNR.
[0112]
In addition, the crosstalk of the 21 MHz signal in both adjacent tracks was examined. Here, in Examples 5 to 9 and Comparative Example 3, the adjacent track refers to an adjacent groove if recorded on the land, an adjacent land if recorded on the groove, and recorded on the groove in Example 10. Adjacent grooves were used. Here, in Examples 5 to 8 and Comparative Example 3, the phase of the return light was independently adjusted between the land and the groove, and each was reproduced with the phase having the highest CNR. In Examples 9 and 10, the measurement was performed with the phase fixed to zero. In addition, in order to see the state of reflection of high-angle incident light during groove recording, a CCD camera was installed on the pupil surface, and the amount of reflected light was compared with that of low-angle incident light. The results are shown in Table 3.
[0113]
[Table 3]

Regarding the reflection state of the high-angle incident light at the time of groove recording, the cases other than Comparative Example 3 are good, and in particular, as in Examples 6 to 10, the dielectric layer and the transparent resin protective layer are two or more layers having different refractive indexes. Furthermore, it was further improved by providing a matching layer on the transparent resin protective layer.
[0114]
The CNR in groove recording was remarkably low in Comparative Example 3, but good values of 43 dB or more were obtained in Examples 5 to 10. As in Examples 6 to 10, the dielectric layer and the transparent resin protective layer were further improved by forming two or more layers having different refractive indexes, and further providing a matching layer on the transparent resin protective layer. Regarding crosstalk, Comparative Example 3 had a large value of −20 dB, but in Examples 5 to 10, good values of −25 dB or less were obtained.
[0115]
Next, in Example 8, the focus was fixed on a medium having a transparent resin protective layer thickness of 900 nm, and the CNR of the medium having a transparent resin protective layer thickness of 600, 750, 900, 1050, and 1200 nm was measured. Table 4 shows the results.
[0116]
Based on this result, the difference (film thickness unevenness) between the maximum and minimum film thicknesses of the transparent resin protective layer in the recording area is expressed as λ / NA. ² It was confirmed that recording / reproducing can be performed without focus servo even in land / groove recording. All the optical recording media of Example 8 satisfied this condition.
[0117]
[Table 4]

(Example 12)
A surface reproduction type optical recording medium having a structure as shown in FIG. 4 was produced. Ag is formed on a polycarbonate substrate 41 having guide grooves (grooves) having a track pitch of 0.4 μm. ₉₈ Pd ₁ Ti ₁ The reflective layer 42 made of was formed to a film thickness of 40 nm by DC sputtering. A recording layer 43 made of TbFeCo was formed thereon with a thickness of 20 nm by DC sputtering. On top of this, a dielectric layer 44 made of SiN having a refractive index of 2.1 is formed between Ar and N. ₂ The film was formed to a thickness of 230 nm by reactive DC sputtering using a Si target in a mixed atmosphere. A composite coat in which a dispersant is added to the same UV curable resin monomer as in Example 1, and 50 wt% of ITO ultrafine particles (average particle size 0.02 μm) having a refractive index of 2.0 is added and mixed well. The agent was applied by spin coating and polymerized by ultraviolet irradiation to form an ITO ultrafine particle dispersed transparent resin protective layer (film thickness 850 nm) having a refractive index of 1.65.
[0118]
On top of this, a perfluoropolyether liquid lubricant layer 46 was applied by 2 nm by a pulling method to produce a surface reproduction type optical recording medium.
[0119]
In this medium, the optical film thickness (actual film thickness × refractive index) of the dielectric layer is 0.71λ and the optical film thickness of the transparent resin protective layer is 2.06λ with respect to the recording / reproducing laser wavelength λ = 685 nm. Met. The diameter of the laser beam on the medium surface was 2.6 μm.
[0120]
(Example 13)
ZnS-50wt% TiO with a refractive index of 2.4 ₂ A dielectric layer 44 made of ZnS—TiO in an Ar atmosphere ₂ A surface reproduction type optical recording medium similar to that of Example 1 was produced except that a film having a thickness of 200 nm was formed by RF sputtering using a target, and a transparent resin protective layer having a refractive index of 1.5 was formed thereon with a thickness of 940 nm. .
[0121]
In this medium, the optical film thickness (actual film thickness × refractive index) of the dielectric layer is 0.71λ and the optical film thickness of the transparent resin protective layer is 2.06λ with respect to the recording / reproducing laser wavelength λ = 685 nm. Met. The diameter of the laser beam on the medium surface was 3.5 μm.
[0122]
(Example 14)
SrNb with a refractive index of 2.6 ₂ O ₆ A dielectric layer 44 made of Ar and O ₂ SrNb in a mixed atmosphere ₂ O ₆ A surface reproduction type optical recording medium similar to that of Example 1 was manufactured except that a film having a thickness of 185 nm was formed by RF sputtering using a target, and a transparent resin protective layer having a refractive index of 1.5 was formed thereon, and 940 nm was formed thereon. .
[0123]
In this medium, the optical film thickness (actual film thickness × refractive index) of the dielectric layer is 0.71λ and the optical film thickness of the transparent resin protective layer is 2.06λ with respect to the recording / reproducing laser wavelength λ = 685 nm. Met. The diameter of the laser beam on the medium surface was 3.5 μm.
[0124]
The surface reproduction type optical recording media of Examples 12 to 13 were rotated at a linear velocity of 10 m / s, and a slider SIL head having a laser wavelength of 685 nm and an effective numerical aperture of 1.3 was set to a height of 70 nm on the thin film surface. After flying and focusing manually on each medium at an optimal position, the coil magnetic field on the SIL head is set to 21 MHz while the recording layer is heated to the Curie temperature or higher by irradiating the laser in pulses at a frequency of 84 MHz. 2T signal having a mark length of 0.24 μm was recorded. Here, the modulation width of the magnetic field was ± 130 Oe.
[0125]
While reproducing at a laser power of 1 mW after recording, the carrier and noise at a resolution bandwidth of 30 kHz and 21 MHz were measured, and the ratio of this carrier to noise was defined as CNR.
[0126]
CNRs of Examples 12 to 14 were 43 dB, 45 dB, and 46 dB, respectively. Example 12 was equivalent to Example 1, and Examples 13 and 14 gave CNRs comparable to Examples 3 and 4 with matching layers.
[0127]
All the media were good in terms of flying characteristics. For continuous recording, all 20 tests could be continued to the end.
[0128]
Next, when the surface reproduction type optical recording media of Examples 1 and 12 to 14 were put in a case without an antistatic function, only 0.3 kV was charged in Example 12, but Examples 1, 13, and 14 were charged. Was charged to 2-3 kV. Moreover, when Example 1 and Examples 12-14 are compared about the pencil hardness of a surface, 3H was obtained in Example 12-14, although it was H in Example 1, and floatability and a continuous recording were obtained. Although no significant difference was observed, in the long term, in Examples 12 to 14, it is considered that the probability of media damage by the head is low. Further, in Example 12, it is considered that foreign matter is difficult to adhere because it is difficult to be charged.
[0129]
【The invention's effect】
According to the present invention, a surface reproduction type optical recording medium which performs recording / reproduction with a laser beam while flying an optical head having an aperture ratio NA exceeding 1 on the surface at a height of λ / 4 or less with respect to the wavelength λ of the laser beam. And at least the recording layer and the refractive index n on the substrate. _P Has a transparent resin protective layer larger than NA, and the diameter of the laser beam on the medium surface is 1.5 to 30 μm, it is possible to perform stable continuous recording over a long period of time.
[0130]
Further, since the diameter of the laser beam is 30 μm or less, a convex portion can be provided on the lower surface of the optical head to prevent contact between the optical head and the medium surface. Further, when the film thickness unevenness of the transparent resin protective layer in the recording area is Δt, Δt ≦ λ / NA ² By doing so, it becomes possible to omit the focus servo.
[0131]
Further, a dielectric layer having a refractive index 0.4 or more larger than NA is provided on the recording layer, and the refractive index of the dielectric layer is lowered stepwise or continuously toward the medium surface, or the transparent resin protective layer is By providing a matching layer for optically matching the laser beam, the low reflection condition is satisfied for the high-angle incident light, the laser beam is converged well, and a high SNR and resolution can be obtained. Also, the refractive index n of the dielectric layer _d A high SNR and resolution can also be obtained by setting the ratio to 2.4 or more.
[0132]
In addition, since the transparent resin of the protective layer contains inorganic ultrafine particles, the hardness of the transparent resin protective layer can be increased and the reliability can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing a state in which a SIL head is levitated in an embodiment of a surface reproduction type optical recording medium of the present invention.
FIG. 2 is a schematic cross-sectional view showing a state in which a SIL head is levitated in an example of a conventional surface reproduction type optical recording medium.
FIG. 3 is an enlarged view of a state of incident light in the cross-sectional view of FIG. 1;
FIG. 4 is a partial cross-sectional view of an embodiment of the optical recording medium of the present invention having a configuration of substrate / reflective layer / recording layer / dielectric layer / transparent resin protective layer / liquid lubricating layer.
FIG. 5 is a partial cross-sectional view of an embodiment of an optical recording medium of the present invention in which a dielectric layer is composed of two layers, a first dielectric layer and a second dielectric layer.
FIG. 6 is a partial cross-sectional view of an embodiment of the optical recording medium of the present invention in which a first matching layer and a second matching layer are formed on the medium surface.
FIG. 7 is a partial cross-sectional view of an embodiment of an optical recording medium of the present invention having a lower dielectric layer under a recording layer.
FIG. 8 is a schematic cross-sectional view of a state in which a SIL head having a convex portion on the lower surface floats in one embodiment of the surface reproduction type optical recording medium of the present invention.
FIG. 9 is a partial cross-sectional view of an embodiment of an optical recording medium of the present invention in which a dielectric layer is composed of two layers, a first dielectric layer and a second dielectric layer, and a liquid lubricating layer is formed on the outermost surface of the medium. It is.
FIG. 10 is a partial cross-sectional view of an embodiment of the optical recording medium of the present invention in which the matching layer is composed of two layers, a first matching layer and a second matching layer, and a liquid lubricating layer is formed on the outermost surface of the medium.
[Explanation of symbols]
11, 21, 31, 41, 51, 61, 71, 81, 101, 111: substrate
42, 52, 62, 72, 102, 112: reflective layer
73: Lower dielectric layer
12, 22, 32, 43, 53, 63, 74, 82, 103, 113: Recording layer
13, 23, 33, 44, 64, 83, 114: Dielectric layer
54, 75, 104: first dielectric layer
55, 76, 105: second dielectric layer
14, 34, 45, 56, 65, 77, 84, 106, 115: Transparent resin protective layer
66, 78, 116: first matching layer
67, 79, 117: second matching layer
46, 57, 68, 80, 107, 118: Liquid lubricating layer
15, 24, 85: Air gap
16, 25, 86: SIL head
17, 26, 87: Laser beam (incident light)
18, 27: Focus
36: Laser beam diameter L1 at the interface between the dielectric and the transparent resin protective layer
37, 90: Laser beam diameter L2 on the medium surface
88: Convex part on the bottom of the SIL head
89: Projection size
91: Coil

Claims (28)

A surface reproduction type optical recording medium which performs recording / reproduction with a laser beam while flying an optical head having an aperture ratio NA of more than 1 on the surface at a height of λ / 4 or less with respect to the wavelength λ of the laser beam. recording layer and the refractive index n _P has a NA greater than the transparent resin protective layer, the transparent resin protective layer has a thickness such as the diameter of the laser beam on the medium surface is 1.5μm or more 30μm or less A surface reproduction type optical recording medium. ^2. The surface-reproducing optical recording medium according to claim 1, wherein the thickness of the transparent resin protective layer is λ / NA ² or more. 3. The surface reproduction type optical recording medium according to claim 1, wherein Δt ≦ λ / NA ^2, where Δt is a film thickness unevenness of the transparent resin protective layer in the recording region. The surface regenerative light according to any one of claims 1 to 3, wherein a dielectric layer having a refractive index greater than or equal to 0.4 or more than NA is provided between the recording layer and the transparent resin protective layer. recoding media. Resurfacing type optical recording medium according to claim 4, the thickness of the dielectric layer is equal to or less than lambda / NA ^2. 6. The surface reproducing optical recording medium according to claim 4, wherein the refractive index of the dielectric layer decreases stepwise or continuously toward the medium surface. 7. The surface reproduction type optical recording medium according to claim 1, wherein a matching layer for reducing laser reflected light from the surface of the medium is provided on the transparent resin protective layer. 8. The surface regeneration according to claim 7, wherein the refractive index of the matching layer is NA or more, and the refractive index increases stepwise or continuously from the uppermost layer of the matching layer toward the transparent resin protective layer side. Type optical recording medium. The refractive index of the matching layer is greater than or equal to NA. After the refractive index increases stepwise or continuously from the uppermost layer of the matching layer toward the transparent resin protective layer, the refractive index decreases again stepwise or continuously. The surface-reproducing optical recording medium according to claim 7, wherein The surface reproducing type optical recording medium according to any one of claims 7 to 9, wherein a part or all of the matching layer is made of a transparent resin. 11. The surface-reproducing optical recording medium according to claim 10, wherein the transparent resin of the matching layer contains inorganic ultrafine particles having a particle size of 0.05 [mu] m or less. The surface-reproducing optical recording medium according to claim 1, wherein the medium surface comprises a liquid lubricating layer. The surface reproduction type optical recording medium according to any one of claims 1 to 6, wherein the medium surface comprises a transparent resin protective layer containing a fluorine-based lubricant or a fluorine-based surfactant. The surface reproduction type optical recording medium according to any one of claims 7 to 11, wherein the medium surface comprises a matching layer containing a fluorine-based lubricant or a fluorine-based surfactant. 15. The surface reproduction type optical recording medium according to claim 1, wherein lands and grooves exist on the surface of the substrate. 16. The surface reproduction type optical recording medium according to claim 15, wherein the land width / groove width (half-value width ratio) is 0.5 to 1.5. The groove depth d _G on the substrate is λ / (14n _OC ) ≦ d _G ≦ λ / (5n _OC ), where n _OC is the refractive index of the transparent resin protective layer. 15. The surface reproduction type optical recording medium according to 15. A surface reproduction type optical recording medium which performs recording / reproduction with a laser beam while flying an optical head having an aperture ratio NA of more than 1 on the surface at a height of λ / 4 or less with respect to the wavelength λ of the laser beam. recording layer and the refractive index n _P has a NA greater than the transparent resin protective layer, said characterized in that it contains the particle size 0.05μm or less of the inorganic ultrafine particles in a transparent resin protective layer surface reproduction type optical recording Medium. 19. The surface reproduction type optical recording medium according to claim 18, wherein the inorganic ultrafine particles are transparent conductive fine particles. 19. The surface reproducing optical recording medium according to claim 18, wherein the inorganic ultrafine particles are aluminum oxide, aluminum nitride, boron nitride, silicon carbide, beryllium oxide, or diamond. A surface reproduction type optical recording medium which performs recording / reproduction with a laser beam while flying an optical head having an aperture ratio NA of more than 1 on the surface at a height of λ / 4 or less with respect to the wavelength λ of the laser beam. recording layer, dielectric layer and the refractive index n _P is the surface reproducing type optical recording medium obtained by laminating a NA greater than the transparent resin protective layer in this order, the refractive index n _d of the dielectric layer is 2.4 or more A surface reproduction type optical recording medium characterized by the above. The surface reproduction type optical recording medium according to claim 21, wherein the dielectric layer is composed of one or more substances selected from ZnS, Nb ₂ O ₅ , and TiO ₂ . The dielectric layer is a substance having a composition generally represented by (MA) ₁ (MB) ₂ O ₆ , where MA is one or more substances selected from Mg, Ca, Sr and Ba, and MB is V, Nb The surface-reproducing optical recording medium according to claim 21, wherein the surface-reproducing optical recording medium is made of one or more substances selected from Ta. The surface reproduction type optical recording medium according to claim 21, wherein the dielectric layer is composed of a perovskite compound or a material containing at least 80% by weight of the perovskite compound. A surface reproduction type optical recording medium that performs recording and reproduction by a laser beam while flying an optical head having an aperture ratio NA exceeding 1 on the surface at a height of λ / 4 or less with respect to the wavelength λ of the laser beam. and a groove there between, at least a recording layer and a refractive index n _P on the substrate has a NA greater than the transparent resin protective layer, the step of lands and grooves in said transparent resin protective layer surface is lambda / 30 or less A surface reproduction type optical recording medium. 26. The surface reproduction type optical recording medium according to claim 25, wherein the land width / groove width (half-value width ratio) is 0.5 to 1.5. 26. The surface reproduction type optical recording medium according to claim 25, wherein the width of the groove is wider than the width of the land. The groove depth d _G on the substrate is λ / (14n _OC ) ≦ d _G ≦ λ / (5n _OC ), where n _OC is the refractive index of the transparent resin protective layer. 28. The surface reproduction type optical recording medium according to any one of 25 to 27.

Images