JP2004083294A - Glass substrate for magnetic disk, magnetic disk and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass substrate for a magnetic disk capable of obtaining a magnetic disk having high magnetic anisotropy and high recording density even when the glass substrate is used. <P>SOLUTION: The glass substrate for the magnetic disk which has a texture formed on the main surface to give magnetic anisotropy to a magnetic layer provided on the substrate is provided with a main surface shape having a ratio Ra(r)/Ra(c) of 2 or more in at least 3.9-1,000 nm shape wave length region on the main surface of the glass substrate. Where, Ra(c) is center line average roughness in the disk circumferential direction and Ra(r) is center line average roughness in the disk radial direction. <P>COPYRIGHT: (C)2004,JPO

Description

表１の結果より、基板回転速度とテクスチャ加工時間との積が、略３５００（ｒｐｍ×秒）〜１２０００（ｒｐｍ×秒）とした場合において、Ｒａ（ｒ）／Ｒａ（ｃ）の値が２以上となり好適であることが判る。
テクスチャ形状としては、磁性層に対して磁気記録ヘッドの浮上飛行方向に磁気異方性を付与するよう形成することが好ましいが、磁気ディスクの場合、磁気記録ヘッドの走行方向は円周方向であるので、円周状の規則性を持ったテクスチャ、あるいは、これに交差する形状成分を持つクロステクスチャ、楕円状テクスチャ、らせん状テクスチャまたはこれら形状成分の複合形態であってよい。中でも円周状のテクスチャは、磁性粒子を磁気記録ヘッドの走行方向へ配列させる作用が高いので好ましい。
本発明において、前記テクスチャを形成する磁気ディスク主表面の位置については、磁気ディスクの記録再生領域であることが好ましい。ＣＳＳ（Ｃｏｎｔａｃｔ　Ｓｔａｒｔａｎｄ　Ｓｔｏｐ）記録再生方式におけるＣＳＳゾーンやＬＵＬ（Ｌｏａｄ　Ｕｎｌｏａｄ）記録再生方式におけるＬＵＬゾーンなど、記録再生を行わない領域での主表面形状で特定した場合、主表面形状の面内バラツキなどで記録再生領域の形状と異なる場合があるので好ましくない。
【００１６】
なお、ガラス基板として下記の化学強化基板を用いる場合、テクスチャは化学強化後に行うことが好ましい。化学強化においては、イオン交換の過程で、ガラス基板主表面形状が乱される場合がある。
本発明において、ガラス基板に用いる硝種としては特に限定を設けないが、ガラス基板の材質としては、例えば、アルミノシリケートガラス、ソーダライムガラス、ソーダアルミノシリケートガラス、アルミノボロシリケートガラス、ボロシリケートガラス、石英ガラス、チェーンシリケートガラス、又は結晶化ガラス等のガラスセラミックス等が挙げられる。なお、アルミノシリケートガラスは、耐衝撃性や耐振動性に優れるための特に好ましい。アルミノシリケートガラスとしては、ＳｉＯ_２：　６２〜７５ｗｔ％、Ａｌ_２Ｏ_３：　５〜１５ｗｔ％、Ｌｉ_２Ｏ：４〜１０ｗｔ％、Ｎａ_２Ｏ：　４〜１２ｗｔ％、ＺｒＯ_２：　５．５〜１５ｗｔ％を主成分として含有すると共に、Ｎａ_２Ｏ／ＺｒＯ_２の重量比が０．５〜２．０、Ａｌ_２Ｏ_３／ＺｒＯ_２の重量比が０．４〜２．５である化学強化用ガラス等が好ましい。また、ＺｒＯ_２の未溶解物が原因で生じるガラス基板表面の突起を無くすためには、モル％表示で、ＳｉＯ_２を５７〜７４％、ＺｎＯ_２を０〜２．８％、Ａｌ_２Ｏ_３を３〜１５％、ＬｉＯ_２を７〜１６％、Ｎａ_２Ｏを４〜１４％含有する化学強化用ガラス等を使用することが好ましい。
このようなアルミノシリケートガラスは、化学強化することによって、ガラス基板表面に圧縮応力層を設けることができ、抗折強度や、剛性、耐衝撃性、耐振動性、耐熱性に優れ、高温環境下にあってもＮａの析出がないとともに、平坦性を維持し、ヌープ硬度にも優れる。化学強化方法としては、従来より公知の化学強化法であれば特に限定されない。ガラス基板の化学強化は、加熱した化学強化溶融塩にガラス基板を浸漬し、ガラス基板表層のイオンを化学強化溶融塩中のイオンでイオン交換して行う。
【００１７】
ガラス基板の直径サイズついては特に限定はないが、実用上、モバイル用途のＨＤＤとして使用されることの多い２．５インチサイズ以下の小型磁気ディスクに対しては、耐衝撃性が高く、４０Ｇｂｉｔ／ｉｎ^２以上の情報記録密度が得られ、かつ廉価な磁気ディスクを提供できる本発明は有用性が高く好適である。
また、ガラス基板の厚さは、０．１ｍｍ〜１．５ｍｍ程度が好ましい。特に、０．１ｍｍ〜０．９ｍｍ程度の薄型基板により構成される磁気ディスクの場合では、耐衝撃性が高くかつ廉価な磁気ディスクを提供できる本発明は有用性が高く好適である。
前記構成３又は構成６にあるように、本発明の磁気ディスク用ガラス基板上に、少なくとも磁性層を形成することにより、本発明の磁気ディスクが得られる。本発明において、テクスチャを施されたガラス基板上に、成膜を行って磁気ディスクとする場合、以下のように、テクスチャを施されたガラス基板上に、シード層、下地層、オンセット層、磁性層、保護層、潤滑層を設けた磁気ディスクとするのが好適である。
シード層としては、例えば、Ａｌ系合金、Ｃｒ系合金、ＮｉＡｌ系合金、ＮｉＡｌＢ系合金、ＡｌＲｕ系合金、ＡｌＲｕＢ系合金、ＡｌＣｏ系合金、ＦｅＡｌ系合金等のｂｃｃまたはＢ２結晶構造型合金等を用いることにより、磁性粒子の微細化を図ることができる。特に、ＡｌＲｕ系合金、中でもＡｌ：３０〜７０ａｔ％、残部がＲｕの配合量の合金であれば、磁性粒子の微細化作用に優れているので好ましい。
【００１８】
下地層としては、Ｃｒ系合金、ＣｒＭｏ系合金、ＣｒＶ系合金、ＣｒＷ系合金、ＣｒＴｉ系合金、Ｔｉ系合金等の磁性層の配向性を調整する層を設けることができる。特に、ＣｒＷ系合金、中でも、Ｗ：５〜４０ａｔ％、残部がＣｒの配合量の合金は、磁性粒子の配向を整える作用に優れているので好ましい。
オンセット層としては、磁性層と同様の結晶構造をもつ非磁性材料を用いることにより、磁性層のエピタキシャル成長を助けることができる、例えば、磁性層がＣｏ系合金材料からなる場合は、非磁性のｈｃｐ結晶構造をもつ材料、例えば、ＣｏＣｒ系合金、ＣｏＣｒＰｔ系合金、ＣｏＣｒＰｔＴａ系等を用いる。
本発明においては、磁性層はＣｏ系のｈｃｐ結晶構造をもつ合金であることが好ましい。特に、ＣｏＣｒＰｔＢ合金磁性層の場合、前記テクスチャにより磁性粒子グレインが好適に配向するので好ましい。
保護層としては、例えば、カーボン保護膜などが挙げられる。
保護層上には、潤滑層を形成してもよく、潤滑層を形成する潤滑剤としては、ＰＦＰＥ（パーフロロポリエーテル）化合物が好適である。
【００１９】
本発明において、ガラス基板上に各層を成膜する方法については、公知の技術を用いることができる。中でも、スパッタリング法は、各層の膜厚を薄くできるので好ましい。
本発明の磁気ディスクは、磁気抵抗効果（ＭＲ）型再生素子を備える磁気ヘッドに対して用いると有用性が高い。ＭＲ型再生素子は、記録信号に対する感度が高く、高い再生出力が得られるので、４０Ｇｂｉｔ／ｉｎ^２以上の情報記録密度の磁気ディスクに好適である。ＭＲ型再生素子としては、ＡＭＲ素子、ＧＭＲ素子、ＴＭＲ素子等が挙げられる。
なお、本発明において、前述の残留磁化膜厚積Ｍｒｔ（ｃ）とＭｒｔ（ｒ）については適宜設定できるが、双方ともに０．５ｍｅｍｕ／ｃｃ以下であることが望ましい。０．５ｍｅｍｕ／ｃｃを越えると、媒体ノイズが大きくなり、ＭＲ型再生素子には不向きである。
【００２０】
【発明の実施の形態】
以下に実施例を挙げて、本発明の実施の形態についてさらに具体的に説明する。なお、本発明は以下の実施例に限定されるものではない。
実施例１
本実施例の磁気ディスク用ガラス基板１は、化学強化されたアルミノシリケートガラスに研磨及びテクスチャが施された基板である。この磁気ディスク用ガラス基板１を使用した本実施例の磁気ディスク１０は、図２に示すように、シード層２、下地層３、磁性層４、保護層５、潤滑層６を順次積層してなる。
本実施例においては、前述の図１の相関関係に基づいて、ＭｒｔＯＲ＝１．３２が得られるよう、前記Ｒａ（ｒ）／Ｒａ（ｃ）を６と選定し、この表面形状が得られる様に、磁気ディスク用ガラス基板１を製造した。
本実施例では、以下の（１）粗ラッピング工程（粗研削工程）、（２）形状加工工程、（３）精ラッピング工程（精研削工程）、（４）端面鏡面加工工程、（５）第１研磨工程、（６）第２研磨工程、（７）化学強化工程、（８）テクスチャ工程、を経て磁気ディスク用ガラス基板１を製造し、更に、得られた磁気ディスク用ガラス基板１に（９）成膜工程を施すことにより、磁気ディスク１０を製造した。
【００２１】
（１）粗ラッピング工程
まず、溶融ガラスから上型、下型、胴型を用いたダイレクトプレスにより直径６６ｍｍφ、厚さ１．５ｍｍの円盤状のアルミノシリケートガラスからなるガラス基板を得た。なお、この場合、ダイレクトプレス以外に、ダウンドロー法やフロート法で形成したシートガラスから研削砥石で切り出して円盤状のガラス基板を得てもよい。このアルミノシリケートガラスとしては、ＳｉＯ_２：５８〜７５重量％、Ａｌ_２Ｏ_３：５〜２３重量％、Ｌｉ_２Ｏ：３〜１０重量％、Ｎａ_２Ｏ：４〜１３重量％を含有する化学強化ガラスを使用した。次いで、ガラス基板に寸法精度及び形状精度の向上させるためラッピング工程を行った。このラッピング工程は両面ラッピング装置を用い、粒度＃４００の砥粒を用いて行なった。具体的には、はじめに粒度＃４００のアルミナ砥粒を用い、荷重を１００ｋｇ程度に設定して、上記ラッピング装置のサンギアとインターナルギアを回転させることによって、キャリア内に収納したガラス基板の両面を面精度０〜１μｍ、表面粗さ（Ｒｍａｘ）６μｍ程度にラッピングした。
（２）形状加工工程
次に、円筒状の砥石を用いてガラス基板の中央部分に孔を空けると共に、外周端面の研削をして直径を６５ｍｍφとした後、外周端面および内周端面に所定の面取り加工を施した。このときのガラス基板端面の表面粗さは、Ｒｍａｘで４μｍ程度であった。なお、一般に、２．５インチ型ＨＤＤ（ハードディスクドライブ）では、外径が６５ｍｍの磁気ディスクを用いる。
【００２２】
（３）精ラッピング工程
次に、砥粒の粒度を＃１０００に変え、ガラス基板表面をラッピングすることにより、表面粗さをＲｍａｘで２μｍ程度、Ｒａで０．２μｍ程度とした。上記ラッピング工程を終えたガラス基板を、中性洗剤、水の各洗浄槽（超音波印加）に順次浸漬して、超音波洗浄を行なった。
（４）端面鏡面加工工程
次いで、ブラシ研磨により、ガラス基板を回転させながらガラス基板の端面（内周、外周）の表面の粗さを、Ｒｍａｘで１μｍ、Ｒａで０．３μｍ程度に研磨した。そして、上記端面鏡面加工を終えたガラス基板の表面を水洗浄した。
（５）第１研磨工程
次に、上述したラッピング工程で残留した傷や歪みの除去するため第１研磨工程を両面研磨装置を用いて行なった。両面研磨装置においては、研磨パッドが貼り付けられた上下定盤の間にキャリアにより保持したガラス基板を密着させ、このキャリアをサンギアとインターナルギアとに噛合させ、上記ガラス基板を上下定番によって挟圧する。その後、研磨パッドとガラス基板の研磨面との間に研磨液を供給して回転させることによって、ガラス基板が定盤上で自転しながら公転して両面を同時に研磨加工するものである。以下、実施例で使用する両面研磨装置としては同一装置を用いた。具体的には、ポリシャとして硬質ポリシャ（硬質発泡ウレタン）を用い、研磨工程を実施した。研磨条件は、研磨液としては酸化セリウム（平均粒径１．３μｍ）を研磨剤として分散したＲＯ水とし、荷重：１００ｇ／ｃｍ^２、研磨時間：１５分とした。上記第１研磨工程を終えたガラス基板を、中性洗剤、純水、純水、ＩＰＡ（イソプロピルアルコール）、ＩＰＡ（蒸気乾燥）の各洗浄槽に順次浸漬して、超音波洗浄し、乾燥した。
【００２３】
（６）第２研磨工程
次に第１研磨工程で使用したものと同じタイプの両面研磨装置を用い、ポリシャを軟質ポリシャ（スウェードパット）に変えて、第２研磨工程を実施した。この第２研磨工程は、上述した第１研磨工程で得られた平坦な表面を維持しつつ、例えば表面粗さＲａを１．０〜０．３μｍ程度以下まで低減させることを目的とするものである。研磨条件は、研磨液としては酸化セリウム（平均粒径０．８μｍ）を分散したＲＯ水とし、荷重：１００ｇ／ｃｍ^２、研磨時間を５分とした。上記第２研磨工程を終えたガラス基板を、中性洗剤、純水、純水、ＩＰＡ、ＩＰＡ（蒸気乾燥）の各洗浄槽に順次浸漬して、超音波洗浄し、乾燥した。
（７）化学強化工程
次に、上記洗浄を終えたガラス基板に化学強化を施した。化学強化は硝酸カリウムと硝酸ナトリウムの混合した化学強化液を用意し、この化学強化溶液を３８０℃に加熱し、上記洗浄・乾燥済みのガラス基板を約４時間浸漬して化学強化処理を行なった。化学強化を終えたガラス基板を硫酸、中性洗剤、純水、純水、ＩＰＡ、ＩＰＡ（蒸気乾燥）の各洗浄槽に順次浸漬して、超音波洗浄し、乾燥した。
次に、上記洗浄を終えたガラス基板表面の目視検査及び光の反射・散乱・透過を利用した精密検査を実施した。その結果、ガラス基板表面に付着物による突起や、傷等の欠陥は発見されなかった。また、上記工程を経て得られたガラス基板の主表面の表面粗さを原子間力顕微鏡（ＡＦＭ）にて測定したところ、Ｒｍａｘ＝２．１３ｎｍ、Ｒａ＝０．２０ｎｍと超平滑な表面を持つ磁気ディスク用ガラス基板を得た。また、ガラス基板の外径は６５ｍｍ、内径は２０ｍｍ、板厚は０．６３５ｍｍであった。
【００２４】
（８）テクスチャ工程
前述の図３に示したテープ（Ｔａｐｅ）式のテクスチャ装置を用いて、研磨、及び円周状テクスチャ処理を施した。図３の装置において、支点ａを中心とし、ローラ１０４の軸にそれぞれ固定した板状の部材１０５，１０５が動くことによってガラス基板１を挟みつけている。この時、ガラス基板１に負荷される加重は板状の部材１０５間に張られたバネ１０６の力により決定する。加重は張力計１０７により測定される。なお、テープには織物タイプのテープを、硬質研磨剤には平均粒径０．１２５μｍの多結晶ダイヤモンドが分散剤に溶かしてあるスラリーを用いて行った。
このときのテクスチャ加工条件は以下のとおりである。
加工圧力　　１０ｇ／ｍｍ^２
基板回転速度　　１５０ｒｐｍ
テープの送り速度　３ｍｍ／ｓｅｃ
テクスチャ加工時間　５０秒
従ってこのときの、基板回転速度×テクスチャ加工時間は、７５００（ｒｐｍ×秒）である。
テクスチャ加工後、ガラス基板の主表面形状の測定を行った。表面形状は、ＡＦＭ（原子間力顕微鏡）を用いて、高精細な評価のできるタッピングモードで測定した。測定範囲は１μｍ×１μｍの磁気ディスク用ガラス基板主表面である。ＡＦＭ測定に用いたカンチレバー（探針）の先端曲率半径は、高精度の測定結果が得られるよう、１０ｎｍの先端曲率半径を備えるものを選定して測定した。測定結果は、縦横を２５６×２５６個のメッシュに区画し、２５６×２５６個のデータを用いて、表面形状特性値を算出した。
その結果、本実施例の磁気ディスク用ガラス基板表面には円周状のテクスチャが形成されており、後記表２に示すように、Ｒａ（ｒ）／Ｒａ（ｃ）は６．０１であった。なお、中心線平均粗さＲａの定義は、日本工業規格（ＪＩＳ）Ｂ０６０１の規定に従った。表面形状特性値の算出に当たっては、形状波長が３．９ｎｍ〜１０００ｎｍの形状波長帯域にある形状を用いた。また、測定に用いたディスクの半径位置は、２．５インチ型磁気ディスクの記録再生領域である、半径＝２２ｍｍの主表面である。
【００２５】
（９）成膜工程
枚葉式スパッタリング装置を用いて、上記テクスチャを施されたガラス基板上に、シード層２、下地層３、磁性層４、保護層５及び潤滑層６を順次形成した。シード層２は、ＣｒＴｉ薄膜（膜厚３００オングストローム）からなる第１のシード層２ａと、ＡｌＲｕ薄膜（膜厚：４００オングストローム）からなる第２のシード層２ｂを形成した。下地層３は、ＣｒＷ薄膜（膜厚：１００オングストローム）で、磁性層の結晶構造を良好にするために設けた。なお、このＣｒＷ薄膜は、Ｃｒ：９０ａｔ％、Ｗ：１０ａｔ％の組成比で構成されている。
磁性層４は、ＣｏＰｔＣｒＢ合金からなり、膜厚は、２００オングストロームである。この磁性層のＣｏ、Ｐｔ、Ｃｒ、Ｂ　の各含有量は、Ｃｏ：７３ａｔ％、Ｐｔ：７ａｔ％、Ｃｒ：１８ａｔ％、Ｂ：２ａｔ％である。なお、磁性粒子グレインサイズをＴＥＭ（透過型電子顕微鏡）の平面撮影で調査したところ平均７ｎｍであった。
保護層５は、磁性層４が磁気ヘッドとの接触によって劣化することを防止するためのもので、膜厚５０オングストロームの水素化カーボンからなる。潤滑層６は、パーフルオロポリエーテルの液体潤滑剤をディップ法により形成し、膜厚は９オングストロームである。
【００２６】
次に、得られた磁気ディスクの磁気特性及び信頼性を以下のようにして評価した。
〔磁気特性評価〕
磁気特性は、ＶＳＭ（振動試料型磁化測定法）により測定した。磁気ディスクの半径＝２２ｍｍ位置を中心として８ｍｍ直径の円形試料を切り出し、基板の円周方向、基板の半径方向にそれぞれ外部磁場を印加（±１０ｋＯｅ）して磁化曲線を求め、基板の円周方向及び半径方向のＭｒｔ（残留磁化膜厚積）を算出した。
その結果については後記表２に示すように、ＭｒｔＯＲは１．３２を得ることができた。
〔信頼性評価〕
得られた磁気ディスクについて、グライド特性評価を行ったところ、タッチダウンハイトは、４．５ｎｍであった。タッチダウンハイトは、浮上しているヘッドの浮上量を順に下げていき（例えば磁気ディスクの回転数を低くしていく）、磁気ディスクと接触し始める浮上量を求めて、磁気ディスクの浮上量の能力を測るものであるが、通常、４０Ｇｂｉｔ／ｉｎ^２以上の記録密度が求められるＨＤＤでは、タッチダウンハイトは５ｎｍ以下であることが求められる。
また、ヘッド浮上時の浮上量を１２ｎｍとし、７０℃、８０％ＲＨ環境下で、ヘッドのロード・アンロード動作を繰り返して行うＬＵＬ耐久性について試験したところ、６０万回のＬＵＬ連続試験後でも、ヘッドクラッシュや、サーマルアスペリティなどの故障は発生しなかった。通常に使用されるＨＤＤでは、ＬＵＬ回数が６０万回を越えるには１０年間程度の使用が必要とされている。
【００２７】
実施例２
本実施例では、図１の相関関係を基に、ＭｒｔＯＲが１．３を得られるよう、前記Ｒａ（ｒ）／Ｒａ（ｃ）を４と選定し、この表面形状が得られるように磁気ディスク用ガラス基板及び磁気ディスクの製造を行った。具体的には、実施例１のテクスチャ工程において、基板回転速度を１５０ｒｐｍ、テクスチャ加工時間を３０秒とした。従って、本実施例においては、基板回転速度×テクスチャ加工時間は、４５００（ｒｐｍ×秒）である。この点以外は、実施例１と同様にして磁気ディスク用ガラス基板及び磁気ディスクを製造し、実施例１と同様な評価を行った。結果については表２に示す。
実施例３
本実施例では、図１の相関関係を基に、ＭｒｔＯＲが１．２を得られるよう、前記Ｒａ（ｒ）／Ｒａ（ｃ）を２．３と選定し、この表面形状が得られるように磁気ディスク用ガラス基板及び磁気ディスクの製造を行った。具体的には、実施例１のテクスチャ工程において、基板回転速度を１２０ｒｐｍ、テクスチャ加工時間を３０秒とした。従って、本実施例においては、基板回転速度×テクスチャ加工時間は、３６００（ｒｐｍ×秒）である。この点以外は、実施例１と同様にして磁気ディスク用ガラス基板及び磁気ディスクを製造し、実施例１と同様な評価を行った。結果については表２に示す。
【００２８】
比較例１
本比較例では、実施例１のテクスチャ工程において、基板回転速度を１０００ｒｐｍ、テクスチャ加工時間を３０秒とし、基板回転速度×テクスチャ加工時間は、３００００（ｒｐｍ×秒）であること以外は、実施例１と同様にして磁気ディスク用ガラス基板及び磁気ディスクを製造し、実施例１と同様な評価を行った。結果については表２に示す。
比較例２
実施例１においてテクスチャ工程を行わなかった点以外は、実施例１と同様にして磁気ディスク用ガラス基板及び磁気ディスクを製造し、実施例１と同様な評価を行った。結果については表２に示す。
【００２９】
【表２】

表２の結果を対比すると、図１に示された相関関係と同様な、Ｒａ（ｒ）／Ｒａ（ｃ）とＭｒｔＯＲの関係が得られている事が判る。本発明実施例により、前記Ｒａ（ｒ）／Ｒａ（ｃ）を２以上とすることによって、ＭｒｔＯＲは１．２以上が得られるようになり、前記Ｒａ（ｒ）／Ｒａ（ｃ）を４以上とすることによって、ＭｒｔＯＲは１．３以上が得られるようなることが確認された。すなわち、ガラス基板主表面に、所定の形状波長領域における前記Ｒａ（ｒ）／Ｒａ（ｃ）が２以上となる表面形状を設けることにより、高い磁気異方性を有して高密度記録を可能とする磁気ディスクが得られることが判る。
【００３０】
【発明の効果】
以上詳細に説明したように、本発明によれば、ガラス基板上に少なくとも磁性層を形成したときに、磁性層に高い磁気異方性を付与できる磁気ディスク用ガラス基板を提供することができる。また、このようにガラス基板を用いた場合であっても、高い磁気異方性を備えることで高密度記録を達成でき、しかも耐衝撃性に優れ、廉価な磁気ディスクを提供することができる。また、前述の図１のように、前記Ｒａ（ｒ）／Ｒａ（ｃ）とＭｒｔＯＲとの相関関係を予め求めておくことにより、再現性よく、所定のＭｒｔＯＲを備える磁気ディスクを製造する事ができる。
【図面の簡単な説明】
【図１】Ｒａ（ｒ）／Ｒａ（ｃ）とＭｒｔＯＲとの相関関係を示す図である。
【図２】本発明の実施の形態による磁気ディスクの層構成を模式的に示す断面図である。
【図３】実施例で用いるテープ式テクスチャ装置の概略構成を示す（ａ）側面図と（ｂ）斜視図である。
【符号の説明】
１　　磁気ディスク用ガラス基板
２　　シード層
３　　下地層
４　　磁性層
５　　保護層
６　　潤滑層
１０　磁気ディスク[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magnetic recording medium and a glass substrate for a magnetic recording medium, and more particularly to a magnetic disk mounted on an HDD (hard disk drive) or the like and a glass substrate for a magnetic disk.
[0002]
[Prior art]
2. Description of the Related Art Today, information recording technology, particularly magnetic recording technology, is required to undergo dramatic technological innovation with the rapid development of the IT industry. For magnetic disks mounted on HDDs and the like, 40 Gbit / in²~ 100Gbit / in²There is a need for a technology that can achieve the above information recording density.
A magnetic disk is required to have particularly excellent magnetic characteristics in the flying flight direction of a magnetic recording head. For this reason, for example, in Japanese Patent Application Laid-Open No. 62-273819, a magnetic layer is formed on a metal substrate surface of an aluminum alloy or the like by forming a texture for imparting magnetic anisotropy, and then a magnetic layer is formed. Compared to the characteristics, the magnetic characteristics of the magnetic recording head in the flying flight direction have been improved.
By the way, in recent years, due to demands for mobile and miniaturized HDDs, glass substrates that have high rigidity, excellent impact resistance, and high surface smoothness have been receiving attention.
Further, in the case of a glass substrate, since it is excellent in impact resistance, there is no need to apply a metal film such as NiP to reinforce the rigidity as in the case of an aluminum alloy substrate, and the manufacturing process can be shortened. There is an advantage that an inexpensive magnetic disk can be provided and miniaturization is easy.
For example, the present applicant discloses in JP-A-2002-32909 a magnetic recording medium in which a circumferential texture is formed on a glass substrate and a magnetic layer or the like is sputtered thereon.
[0003]
[Problems to be solved by the invention]
Even in the case of a glass substrate, it is desired that the magnetic properties in the circumferential direction be superior to the magnetic properties in the radial direction. For example, 40Gbit / inch²In order to achieve the above recording density, the magnetic anisotropy ratio (MrtOR) based on the product of the residual magnetization film thickness is required to be 1.2 or more. In addition, 50Gbit / inch²In order to obtain the above recording density, MrtOR is 1.3 or more, particularly, 60 Gbit / inch.²In the high recording density region described above, it is considered that MrtOR is desirably 1.35 or more.
The above-mentioned MrtOR is a magnetic anisotropy ratio OR (Oriented Ratio) calculated from the product of the residual magnetization film thickness (Mrt). At any point on the main surface of the magnetic recording medium, when the product of the thickness of the residual magnetization in the circumferential direction is Mrt (c) and the product of the thickness of the residual magnetization in the radial direction is Mrt (r), the relationship to Mrt (r) is obtained. The ratio Mrt (c) / Mrt (r) of Mrt (c) is defined as MrtOR. Here, Mrt is a product of Mr (residual magnetization) and t (magnetic layer thickness of the medium).
That is, if MrtOR is approximately 1, the magnetic recording medium is an isotropic magnetic recording medium having substantially the same magnetic properties in the circumferential direction and the radial direction. As MrtOR exceeds 1 and increases, the magnetic anisotropy in the circumferential direction increases. This indicates that the performance has been improved.
[0004]
However, although the cause is not yet clear, unlike a case where a texture that imparts magnetic anisotropy is formed on a metal surface, such as an aluminum alloy substrate or a substrate on which a metal film such as NiP is applied, glass is used. When a texture for imparting magnetic anisotropy is formed directly on the substrate surface and a magnetic layer is formed thereon, only about 1.0 to 1.1 of MrtOR was obtained. It was a factor that hindered price reduction.
The present invention has been made in view of the above-mentioned problems, and an object of the present invention is that, first, even when a glass substrate is used, an MrtOR of 1.2 or more is obtained, and 40 Gbit / in²To provide a glass substrate for a magnetic disk which can achieve the above recording density, is excellent in impact resistance, and can obtain an inexpensive magnetic disk. Second, even when a glass substrate is used, it is 1.2 or more. Of 40 Gbit / in²An object of the present invention is to provide an inexpensive magnetic disk which can achieve the above recording density, is excellent in impact resistance, and is inexpensive.
[0005]
[Means for Solving the Problems]
As a result of intensive studies on the glass substrate from various viewpoints, the present inventor has found that when a texture for imparting magnetic anisotropy is directly formed on a glass substrate for a magnetic disk, a specific shape among the glass substrate surface shapes is used. It was found that the wavelength was involved in the development of magnetic anisotropy and the level of MrtOR, and the texture was formed directly on the glass substrate by adjusting the surface shape at this specific shape wavelength to a predetermined shape. Even in this case, it has been found that a high magnetic anisotropy ratio can be obtained.
Further, when the bandwidth of the shape wavelength related to the magnetic anisotropy ratio is examined, for example, there is a remarkable correlation between the surface shape in the band of the shape wavelength of 3.9 nm to 1000 nm and MrtOR. I found something.
That is, the present invention has the following configurations in order to solve the above-mentioned problems.
[0006]
(Configuration 1) A glass substrate for a magnetic disk in which a texture for imparting magnetic anisotropy to a magnetic layer provided on the substrate is formed on a main surface, and a shape wavelength of at least 3.9 nm to 1000 nm on the main surface of the glass substrate. Main surface shape in which the ratio Ra (r) / Ra (c) of the center line average roughness Ra (r) in the disk radial direction to the center line average roughness Ra (c) in the disk circumferential direction is 2 or more in the region. A glass substrate for a magnetic disk, comprising:
(Constitution 2) A glass substrate for a magnetic disk in which a texture for imparting magnetic anisotropy to a magnetic layer provided on the substrate is formed on a main surface, and 1 μm × 1 μm × divided into a plurality of sections on the main surface of the glass substrate. The ratio Ra (r) / Ra (c) of the center line average roughness Ra (r) in the disk radial direction to the center line average roughness Ra (c) in the disk circumferential direction in the region of 1 μm is 2 or more. A glass substrate for a magnetic disk having a surface shape.
(Structure 3) A magnetic disk characterized in that at least a magnetic layer is provided on the magnetic disk glass substrate according to structure 1 or 2.
[0007]
(Structure 4) A method for manufacturing a glass substrate for a magnetic disk, comprising a step of forming a texture on a main surface of a glass substrate to impart magnetic anisotropy to a magnetic layer provided on the substrate, wherein the glass substrate is The ratio Ra (r) / of the center line average roughness Ra (デ ィ ス ク r) in the disk radial direction to the center line average roughness Ra (c) in the disk circumferential direction in the shape wavelength region of at least 3.9 nm to 1000 nm on the main surface. A correlation between Ra (c) and magnetic anisotropy is obtained in advance, and the value of Ra (r) / Ra (c) is selected based on the correlation in order to obtain a predetermined magnetic anisotropy. And forming a texture giving a surface shape of the selected value of Ra (r) / Ra (c).
(Structure 5) A method for manufacturing a glass substrate for a magnetic disk, comprising a step of forming a texture on a main surface of a glass substrate to impart magnetic anisotropy to a magnetic layer provided on the glass substrate, wherein the glass substrate is The ratio Ra (r) of the center line average roughness Ra (に 対 す る r) in the disk radial direction to the center line average roughness Ra (c) in the disk circumferential direction in an area of 1 μm × 1 μm allocated to a plurality of sections on the main surface. ) / Ra (c) and the correlation between the magnetic anisotropy and the value of the Ra (r) / Ra (c) based on the correlation in order to obtain a predetermined magnetic anisotropy. And forming a texture giving a surface shape of the selected value of Ra (r) / Ra (c).
(Structure 6) A method for manufacturing a magnetic disk, comprising forming at least a magnetic layer on a glass substrate manufactured by the method for manufacturing a glass substrate for a magnetic disk according to structure 4 or 5.
[0008]
As in Configuration 1, even when a texture for imparting magnetic anisotropy is formed on the main surface of a glass substrate, the center line average roughness in the circumferential direction of the disk in a specific shape wavelength region of the main surface of the glass substrate. High magnetic anisotropy can be obtained by having a main surface shape in which the ratio Ra (r) / Ra (c) of the center line average roughness Ra (r) in the disk radial direction to Ra (c) is 2 or more. .
FIG. 1 shows the results of a study conducted by the present inventor on the correlation between Ra (r) / Ra (c) and MrtOR.
The results indicated by ● in FIG. 1 indicate that the center line average roughness Ra (c) in the circumferential direction of the disk in the band having a shape wavelength of 3.9 nm to 1000 nm among the main surface shapes of the magnetic disk glass substrate. Is the ratio of the center line average roughness Ra (r) in the radial direction to the ratio, Ra (r) / Ra (c), and the relationship between MrtOR provided in the magnetic disk having a layer including a magnetic layer formed on the substrate. Further, the results indicated by ▲ in the figure are the relationship between Ra (r) / Ra (c) and MrtOR in the band of 19.5 nm to 5000 nm, and the results indicated by × in the figure are: It is a relationship between Ra (r) / Ra (c) in a band of 39.0 nm to 10000 nm and MrtOR.
Here, the surface shape is measured using an atomic force microscope (AFM). The results indicated by ● in FIG. 1 are the results in the band having the shape wavelength of 3.9 nm to 1000 nm as described above, and this is obtained by using the atomic force microscope described above. Is a surface shape numerical value calculated based on data obtained by defining 1 μm × 1 μm as a measurement region and dividing the measurement region by a 256 × 256 mesh. The data indicated by ▲ is based on data obtained by partitioning a 5 μm × 5 μm area on the main surface of the glass substrate, and the data indicated by × is obtained by partitioning a 10 μm × 10 μm area with a 256 × 256 mesh. Is the numerical value of the surface shape calculated.
[0009]
From the results shown in FIG. 1, with respect to the magnetic disk glass substrate having the main surface shape indicated by ●, a high correlation is observed between Ra (r) / Ra (c) and MrtOR with good reproducibility. .
On the other hand, with respect to the magnetic disk glass substrate having the main surface shape indicated by ▲, there is a large variation between Ra (r) / Ra (c) and MrtOR, and the magnitude relationship of Ra (r) / Ra (c). It can be seen that the magnitude relationship between MrtOR and MrtOR is in no particular order, and therefore the glass substrate has a shape wavelength that is inappropriate on the main surface of the glass substrate with respect to the causal relationship with MrtOR. Further, even on a glass substrate surface having the same Ra (r) / Ra (c), the variation of MrtOR is large, and the reproducibility is poor.
Further, regarding the glass substrate for a magnetic disk having the shape indicated by x, no causal relationship was observed with MrtOR, and it is considered that many shape wavelengths that do not contribute to MrtOR are included. Further, even on a glass substrate surface having the same Ra (r) / Ra (c), the variation of MrtOR is large, and the reproducibility is poor.
As described above, when the texture is directly formed on the glass substrate, for example, the Ra (r) / Ra (c) has a surface shape of 2 or more in a shape wavelength region of 3.9 to 1000 nm. A glass substrate is preferable. In this case, the reproducibility is good and the MrtOR is 1.2 or more. Further, a glass substrate having a main surface shape of Ra (r) / Ra (c) of 4 or more is preferable. In this case, reproducibility is good and MrtOR is 1.3 or more.
[0010]
Although the reason why a magnetic substrate having a specific surface shape in a specific shape wavelength region and a glass substrate main surface can obtain good magnetic anisotropy has not been elucidated in detail, it has not been elucidated in detail. It is considered that an interaction occurs between the grain size of the magnetic particles constituting the layer and the shape of the main surface of the glass substrate in a specific shape wavelength range.
For example, 40 Gbit / in which requires MrtOR of 1.2 or more²In the case of the magnetic disk having the above recording density, the grain size of the magnetic particles is reduced to about 5 nm to 15 nm. The texture on the glass substrate main surface that imparts magnetic anisotropy to the magnetic layer is considered to act to orient the magnetic particle grains in a predetermined direction, but in the glass substrate of the present invention, of the texture shape, Since the shape frequency band that does not contribute to the grain orientation of the magnetic particles is excluded, that is, the shape of the shape wavelength band that particularly affects the grain orientation of the magnetic particles is specified, it is considered that a high effect can be obtained.
Therefore, the present invention provides a 40 Gbit / in²It is considered that there is an effect of improving the orientation of magnetic particles for achieving the above recording density, and high magnetic anisotropy can be obtained even when a texture is formed directly on a glass substrate. .
[0011]
Further, as in Configuration 2, by having a main surface shape in which Ra (r) / Ra (c) is 2 or more in a 1 μm × 1 μm area allocated to a plurality of sections on the glass substrate main surface. And high magnetic anisotropy can be obtained. As described above, the surface shape in the shape wavelength region of, for example, 3.9 nm to 1000 nm is obtained by dividing the measurement region by a mesh of 256 × 256 with a measurement region of 1 μm × 1 μm of the main surface of the glass substrate. Obtained from the base.
In the present invention, a glass substrate having a surface shape where Ra (r) / Ra (c) is 2 or more on the main surface of the glass substrate in a region of 1 μm × 1 μm is preferable. In this case, the reproducibility is good and MrtOR is 1.2 or more is obtained. Further, a glass substrate having a main surface shape with Ra (r) / Ra (c) of 4 or more is suitable. In this case, reproducibility is good and MrtOR is 1.3 or more. In the present invention, the main surface shape of the glass substrate can be measured by, for example, an atomic force microscope (AFM). This atomic force microscope is suitable because it can measure the shape wavelength region of the main surface shape specified in the present invention with high accuracy. Further, a minute area such as an area of 1 μm × 1 μm can be measured with high accuracy.
In the case of a stylus-type roughness meter using a stylus (a stylus), for example, Taristep manufactured by Rank Taylor Hobson, Tencor, or the like, the tip shape of the stylus is several μm to several tens μm. In the present invention, accurate measurement cannot be performed in the shape wavelength region, and measurement in a region of 1 μm × 1 μm or less cannot be practically performed. In addition, surface roughness meters such as an optical surface roughness meter also have a lower horizontal resolution than an atomic force microscope, so that in practice, the shape wavelength region in the present invention cannot be accurately measured. Actually, measurement in a region of 1 μm × 1 μm or less cannot be performed.
[0012]
An atomic force microscope (AFM) can precisely measure a surface shape by measuring an atomic force between an atom at a tip of a cantilever (probe) and an atom on a measurement surface. In the present invention, the radius of curvature of the tip of the cantilever (probe) of the atomic force microscope (AFM) is preferably 10 nm or less. When the thickness is 10 nm or less, the shape wavelength band of the glass substrate main surface shape specified in the present invention can be measured with high accuracy, and a minute region of 1 μm × 1 μm can be measured with high accuracy.
In the measurement of an area of 1 μm × 1 μm, it is preferable to use a surface shape characteristic value calculated based on data obtained by dividing the measurement area by a mesh of 256 × 256 or more. By performing such measurement, a high correlation can be obtained between Ra (r) / Ra (c) and MrtOR as described above. The surface shape can be specified. Of course, it is preferable to use a result obtained by partitioning the measurement area by, for example, a mesh of 512 × 512 or more, since a more accurate result can be obtained.
[0013]
As described in Configuration 4, in forming a texture on the main surface of the glass substrate, the center line average roughness Ra (in the circumferential direction of the disk) in the shape wavelength region of at least 3.9 nm to 1000 nm on the main surface of the glass substrate in advance. A correlation between the ratio Ra (r) / Ra (c) of the center line average roughness Ra (r) in the disk radial direction to c に 対 す る) and the magnetic anisotropy is obtained in advance to obtain a predetermined magnetic anisotropy. For this purpose, the value of Ra (r) / Ra (c) is selected based on the correlation, and a texture is formed to give a surface shape of the selected value of Ra (r) / Ra (c). Thereby, the glass substrate for a magnetic disk according to the present invention can be manufactured. Here, the correlation between Ra (r) / Ra (c) and the magnetic anisotropy is, for example, the correlation as shown in FIG.
Further, as described in Configuration 5, the center in the disk radial direction with respect to the center line average roughness Ra (c) in the disk circumferential direction in a 1 μm × 1 μm area previously allocated to a plurality of sections on the main surface of the glass substrate. The correlation between the magnetic anisotropy and the ratio Ra (r) / Ra (c) of the linear average roughness Ra (r) is determined in advance, and based on the correlation, a predetermined magnetic anisotropy is obtained. The magnetic disk according to the present invention by selecting the value of Ra (r) / Ra (c) and forming a texture giving the surface shape of the selected value of Ra (r) / Ra (c). Glass substrates can be manufactured.
According to the present invention, when a texture is formed directly on the main surface of a glass substrate and a magnetic layer is formed thereon, a suitable magnetic anisotropy can be obtained, and 40 Gbit / in.²The above high recording density can be achieved. Further, by manufacturing such a glass substrate for a magnetic disk and a magnetic disk according to the present invention, even in the case of mass production, the variation of MrtOR for each individual can be reduced, so that the production yield (inspection yield) is reduced. It is possible to manufacture an inexpensive magnetic disk with improved quality and stability. In particular, by improving the yield, it is possible to reduce the number of magnetic disks that are defective in inspection, thereby suppressing industrial waste and contributing to the preservation of the global environment.
[0014]
In the present invention, in order to obtain a predetermined magnetic anisotropy, the value of Ra (r) / Ra (c) is selected based on the correlation, and the selected value of Ra (r) / Ra (c) is selected. In order to give the surface shape, texture is applied on the main surface of the glass substrate. As a step of forming the texture, it is preferable to form the texture while polishing, for example, using a tape-type single wafer polishing method. In this case, a loose abrasive method or a fixed abrasive method can be used. Examples of the abrasive grains include diamond abrasive grains. When the texture is formed by a single-wafer polishing method using free diamond abrasive grains, it is preferable because a magnetic disk with high in-plane texture uniformity and small in-plane variation of MrtOR can be provided.
As an example of an apparatus for performing the tape-type single wafer polishing method, there is a tape-type texture apparatus (schematic diagram) as shown in FIG. The apparatus shown in FIG. 3 is an apparatus used in embodiments described later. According to this tape-type texturing apparatus, the glass substrate 1 fixed to the spindle 101 is rotated, and at the same time, an abrasive is supplied to the tape 103 from the slurry (abrasive) dropping port 102, and both main surfaces of the glass substrate 1 are A circumferential texture is formed on the main surface of the glass substrate 1 by being sandwiched between the tapes 103 wound around the glass substrate 1. The roller 104 around which the tape 103 is wound is rotating at a constant rotation speed so that a new surface of the tape 103 always contacts the glass substrate 1. In this case, the spindle 101 can be swung.
The main surface shape of the glass substrate can be adjusted by adjusting the substrate rotation speed (spindle rotation speed) and the texturing time in this tape-type texture device. Specifically, by setting the product (rpm × sec) of the substrate rotation speed (rpm) and the texture processing time (sec) in a predetermined range, the value of Ra (r) / Ra (c) is 2 or more. It is possible to adjust the glass substrate main surface shape so that a certain surface shape can be provided. Table 1 below shows the results of the values of Ra (r) / Ra (c) when the substrate rotation speed and the texture processing time were variously adjusted.
[0015]
[Table 1]

From the results in Table 1, when the product of the substrate rotation speed and the texture processing time is approximately 3500 (rpm × sec) to 12000 (rpm × sec), the value of Ra (r) / Ra (c) is 2 As described above, it is understood that the method is preferable.
The texture shape is preferably formed so as to impart magnetic anisotropy to the magnetic layer in the flying flight direction of the magnetic recording head, but in the case of a magnetic disk, the running direction of the magnetic recording head is the circumferential direction. Therefore, it may be a texture having a circumferential regularity, a cross texture having an intersecting shape component, an elliptical texture, a spiral texture, or a composite form of these shape components. Among them, the circumferential texture is preferable because it has a high effect of arranging the magnetic particles in the running direction of the magnetic recording head.
In the present invention, the position of the main surface of the magnetic disk on which the texture is formed is preferably a recording / reproducing area of the magnetic disk. When specified by the main surface shape in a non-recording / reproducing area, such as a CSS zone in a CSS (Contact / Start / Stop) recording / reproducing method or an LUL zone in a LUL (Load / Unload) recording / reproducing method, in-plane variation of the main surface shape, etc. In some cases, the shape may be different from the shape of the recording / reproducing area.
[0016]
When the following chemically strengthened substrate is used as the glass substrate, it is preferable to perform the texture after the chemical strengthening. In chemical strengthening, the shape of the main surface of the glass substrate may be disturbed in the course of ion exchange.
In the present invention, the type of glass used for the glass substrate is not particularly limited, and examples of the material of the glass substrate include, for example, aluminosilicate glass, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, and quartz. Glass, chain silicate glass, glass ceramics such as crystallized glass, and the like are included. In addition, aluminosilicate glass is particularly preferable because it has excellent shock resistance and vibration resistance. As the aluminosilicate glass, SiO₂： 62 ～ 75wt% 、 Al₂O₃： 5 ~ 15wt%, Li₂O: 4 to 10 wt%, Na₂O: 4-12 wt%, ZrO₂: Containing not less than 5.5 to 15 wt% as a main component and Na₂O / ZrO₂Weight ratio of 0.5 to 2.0, Al₂O₃/ ZrO₂Is preferably a glass for chemical strengthening having a weight ratio of 0.4 to 2.5. Also, ZrO₂In order to eliminate protrusions on the glass substrate surface caused by undissolved substances of₂57-74%, ZnO₂0 to 2.8%, Al₂O₃3-15%, LiO₂7-16%, Na₂It is preferable to use glass for chemical strengthening containing 4 to 14% of O.
Such an aluminosilicate glass can be provided with a compressive stress layer on the surface of the glass substrate by chemical strengthening, and is excellent in bending strength, rigidity, impact resistance, vibration resistance, heat resistance, and in high temperature environments. In this case, there is no precipitation of Na, flatness is maintained, and Knoop hardness is excellent. The chemical strengthening method is not particularly limited as long as it is a conventionally known chemical strengthening method. Chemical strengthening of the glass substrate is performed by immersing the glass substrate in a heated chemically strengthened molten salt and ion-exchanging ions in the surface layer of the glass substrate with ions in the chemically strengthened molten salt.
[0017]
There is no particular limitation on the diameter of the glass substrate. However, in practice, a small magnetic disk of 2.5 inches or less, which is often used as a HDD for mobile use, has high impact resistance and 40 Gbit / in.²The present invention, which can provide the above information recording density and can provide an inexpensive magnetic disk, has high utility and is suitable.
Further, the thickness of the glass substrate is preferably about 0.1 mm to 1.5 mm. In particular, in the case of a magnetic disk constituted by a thin substrate having a thickness of about 0.1 mm to 0.9 mm, the present invention, which can provide an inexpensive magnetic disk with high impact resistance, is highly useful and suitable.
As in Configuration 3 or Configuration 6, the magnetic disk of the present invention is obtained by forming at least a magnetic layer on the glass substrate for a magnetic disk of the present invention. In the present invention, when a magnetic disk is formed by forming a film on a textured glass substrate, a seed layer, an underlayer, an onset layer, It is preferable to use a magnetic disk provided with a magnetic layer, a protective layer, and a lubricating layer.
As the seed layer, for example, a bcc or B2 crystal structure type alloy such as an Al alloy, a Cr alloy, a NiAl alloy, a NiAlB alloy, an AlRu alloy, an AlRuB alloy, an AlCo alloy, and an FeAl alloy is used. This makes it possible to reduce the size of the magnetic particles. In particular, an AlRu-based alloy, in particular, an alloy having an Al content of 30 to 70 at% and a balance of Ru is preferable because it is excellent in the effect of miniaturizing the magnetic particles.
[0018]
As the underlayer, a layer for adjusting the orientation of the magnetic layer such as a Cr-based alloy, a CrMo-based alloy, a CrV-based alloy, a CrW-based alloy, a CrTi-based alloy, or a Ti-based alloy can be provided. In particular, CrW-based alloys, particularly alloys with a W content of 5 to 40 at% and the balance of Cr being included, are preferred because they are excellent in adjusting the orientation of the magnetic particles.
By using a nonmagnetic material having the same crystal structure as the magnetic layer as the onset layer, the epitaxial growth of the magnetic layer can be assisted. For example, when the magnetic layer is made of a Co-based alloy material, a nonmagnetic material is used. A material having an hcp crystal structure, for example, a CoCr-based alloy, a CoCrPt-based alloy, a CoCrPtTa-based material, or the like is used.
In the present invention, the magnetic layer is preferably an alloy having a Co-based hcp crystal structure. In particular, in the case of a CoCrPtB alloy magnetic layer, the magnetic particles are preferably oriented by the texture, which is preferable.
Examples of the protective layer include a carbon protective film.
A lubricating layer may be formed on the protective layer, and a PFPE (perfluoropolyether) compound is suitable as a lubricant for forming the lubricating layer.
[0019]
In the present invention, a known technique can be used for forming each layer on a glass substrate. Among them, the sputtering method is preferable because the thickness of each layer can be reduced.
INDUSTRIAL APPLICABILITY The magnetic disk of the present invention is highly useful when used for a magnetic head having a magnetoresistive (MR) reproducing element. Since the MR type reproducing element has high sensitivity to a recording signal and can obtain a high reproducing output, 40 Gbit / in²It is suitable for a magnetic disk having the above information recording density. Examples of the MR reproducing element include an AMR element, a GMR element, a TMR element and the like.
In the present invention, the above-mentioned remnant magnetization film thickness products Mrt (c) and Mrt (r) can be set as appropriate, but it is preferable that both are 0.5 memu / cc or less. If it exceeds 0.5 memu / cc, the medium noise increases, and it is not suitable for an MR reproducing element.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described more specifically with reference to examples. Note that the present invention is not limited to the following examples.
Example 1
The glass substrate 1 for a magnetic disk of the present embodiment is a substrate obtained by polishing and texturing chemically strengthened aluminosilicate glass. As shown in FIG. 2, the magnetic disk 10 of this embodiment using the glass substrate 1 for a magnetic disk has a seed layer 2, an underlayer 3, a magnetic layer 4, a protective layer 5, and a lubricating layer 6, which are sequentially laminated. Become.
In the present embodiment, Ra (r) / Ra (c) is selected to be 6 based on the above-described correlation shown in FIG. 1 so that MrtOR = 1.32, and this surface shape is obtained. Then, a glass substrate 1 for a magnetic disk was manufactured.
In the present embodiment, the following (1) rough lapping step (rough grinding step), (2) shape processing step, (3) fine lapping step (fine grinding step), (4) mirror face end processing step, (5) 1 polishing step, (6) second polishing step, (7) chemical strengthening step, and (8) texturing step, to produce a glass substrate 1 for a magnetic disk. 9) The magnetic disk 10 was manufactured by performing a film forming process.
[0021]
(1) Rough lapping process
First, a disc-shaped glass substrate made of aluminosilicate glass having a diameter of 66 mm and a thickness of 1.5 mm was obtained from a molten glass by direct pressing using an upper mold, a lower mold, and a body mold. In this case, in addition to the direct press, a disk-shaped glass substrate may be obtained by cutting a sheet glass formed by a down-draw method or a float method with a grinding wheel. As this aluminosilicate glass, SiO 2₂: 58-75% by weight, Al₂O₃: 5 to 23% by weight, Li₂O: 3 to 10% by weight, Na₂O: Chemically strengthened glass containing 4 to 13% by weight was used. Next, a lapping process was performed on the glass substrate to improve dimensional accuracy and shape accuracy. This lapping step was performed using a double-sided lapping apparatus and abrasive grains having a grain size of # 400. Specifically, first, using alumina abrasive grains having a grain size of # 400, setting the load to about 100 kg, and rotating the sun gear and the internal gear of the wrapping device, both surfaces of the glass substrate housed in the carrier are exposed. Lapping was performed to an accuracy of 0 to 1 μm and a surface roughness (Rmax) of about 6 μm.
(2) Shape processing process
Next, a hole was made in the central portion of the glass substrate using a cylindrical grindstone, and the outer peripheral end surface was ground to a diameter of 65 mmφ. Then, the outer peripheral end surface and the inner peripheral end surface were subjected to predetermined chamfering. At this time, the surface roughness of the end face of the glass substrate was about 4 μm in Rmax. In general, a 2.5-inch HDD (hard disk drive) uses a magnetic disk having an outer diameter of 65 mm.
[0022]
(3) Fine wrapping process
Next, the particle size of the abrasive grains was changed to # 1000, and the surface of the glass substrate was wrapped to make the surface roughness about 2 μm in Rmax and about 0.2 μm in Ra. The glass substrate after the lapping step was sequentially immersed in each of washing tanks (ultrasonic application) of a neutral detergent and water to perform ultrasonic cleaning.
(4) Mirror finish process
Next, the surface roughness of the end surface (inner circumference, outer circumference) of the glass substrate was polished to about 1 μm in Rmax and about 0.3 μm in Ra while rotating the glass substrate by brush polishing. Then, the surface of the glass substrate which had been subjected to the end surface mirror finishing was washed with water.
(5) First polishing step
Next, a first polishing step was performed using a double-side polishing apparatus in order to remove scratches and distortion remaining in the above-described lapping step. In a double-side polishing apparatus, a glass substrate held by a carrier is brought into close contact between an upper and lower platen to which a polishing pad is attached, and this carrier is meshed with a sun gear and an internal gear, and the glass substrate is pinched by an upper and lower standard. . Then, by supplying a polishing liquid between the polishing pad and the polishing surface of the glass substrate and rotating the glass substrate, the glass substrate revolves while rotating on the surface plate to simultaneously grind both surfaces. Hereinafter, the same apparatus was used as the double-side polishing apparatus used in the examples. Specifically, a polishing step was performed using a hard polisher (hard urethane foam) as the polisher. The polishing conditions were as follows: a polishing liquid was RO water in which cerium oxide (average particle size: 1.3 μm) was dispersed as an abrasive; a load: 100 g / cm²Polishing time: 15 minutes. The glass substrate after the first polishing step was sequentially immersed in each of a cleaning tank of a neutral detergent, pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying), ultrasonically cleaned, and dried. .
[0023]
(6) Second polishing step
Next, a second polishing step was performed using a double-side polishing apparatus of the same type as that used in the first polishing step, and changing the polisher to a soft polisher (Sweed Pad). The second polishing step aims at reducing, for example, the surface roughness Ra to about 1.0 to 0.3 μm or less while maintaining the flat surface obtained in the first polishing step. is there. The polishing conditions were as follows: a polishing liquid was RO water in which cerium oxide (average particle size: 0.8 μm) was dispersed; load: 100 g / cm²The polishing time was 5 minutes. The glass substrate having been subjected to the second polishing step was sequentially immersed in cleaning tanks of a neutral detergent, pure water, pure water, IPA and IPA (steam drying), ultrasonically cleaned, and dried.
(7) Chemical strengthening process
Next, the glass substrate after the above-mentioned cleaning was chemically strengthened. For the chemical strengthening, a chemical strengthening solution in which potassium nitrate and sodium nitrate were mixed was prepared, the chemical strengthening solution was heated to 380 ° C., and the washed and dried glass substrate was immersed for about 4 hours to perform a chemical strengthening treatment. The chemically strengthened glass substrate was sequentially immersed in cleaning tanks of sulfuric acid, a neutral detergent, pure water, pure water, IPA, and IPA (steam drying), ultrasonically cleaned, and dried.
Next, a visual inspection of the surface of the glass substrate after the cleaning and a precision inspection using reflection, scattering, and transmission of light were performed. As a result, no defects such as protrusions and scratches were found on the surface of the glass substrate. When the surface roughness of the main surface of the glass substrate obtained through the above steps was measured by an atomic force microscope (AFM), the glass substrate had an ultra-smooth surface of Rmax = 2.13 nm and Ra = 0.20 nm. A glass substrate for a magnetic disk was obtained. The outer diameter of the glass substrate was 65 mm, the inner diameter was 20 mm, and the plate thickness was 0.635 mm.
[0024]
(8) Texture process
Polishing and circumferential texture processing were performed using the tape-type texture device shown in FIG. In the apparatus shown in FIG. 3, the glass substrate 1 is sandwiched by the movement of plate-like members 105, 105 fixed to the shaft of the roller 104 about the fulcrum a. At this time, the load applied to the glass substrate 1 is determined by the force of the spring 106 stretched between the plate-like members 105. The load is measured by the tensiometer 107. The tape was a woven tape, and the hard abrasive was a slurry in which polycrystalline diamond having an average particle size of 0.125 μm was dissolved in a dispersant.
The texture processing conditions at this time are as follows.
Processing pressure 10g / mm²
Substrate rotation speed @ 150rpm
Tape feed speed 3 mm / sec
Texture processing time 50 seconds
Therefore, the substrate rotation speed × texture processing time at this time is 7500 (rpm × sec).
After the texture processing, the main surface shape of the glass substrate was measured. The surface shape was measured using an AFM (Atomic Force Microscope) in a tapping mode that enables high-definition evaluation. The measurement range is the main surface of the magnetic disk glass substrate of 1 μm × 1 μm. The tip radius of curvature of the cantilever (probe) used in the AFM measurement was measured by selecting a tip having a tip radius of curvature of 10 nm so as to obtain a highly accurate measurement result. The measurement results were obtained by dividing the length and width into 256 × 256 meshes, and calculating the surface shape characteristic values using the 256 × 256 data.
As a result, a circumferential texture was formed on the surface of the glass substrate for a magnetic disk of this example, and as shown in Table 2 below, Ra (r) / Ra (c) was 6.01. . The definition of the center line average roughness Ra conformed to the provisions of Japanese Industrial Standard (JIS) B0601. In calculating the surface shape characteristic value, a shape having a shape wavelength in a shape wavelength band of 3.9 nm to 1000 nm was used. The radial position of the disk used for the measurement is the main surface with a radius of 22 mm, which is the recording / reproducing area of the 2.5-inch magnetic disk.
[0025]
(9) Film forming process
Using a single-wafer sputtering apparatus, a seed layer 2, a base layer 3, a magnetic layer 4, a protective layer 5, and a lubricating layer 6 were sequentially formed on the textured glass substrate. As the seed layer 2, a first seed layer 2a made of a CrTi thin film (thickness: 300 angstroms) and a second seed layer 2b made of an AlRu thin film (thickness: 400 angstroms) were formed. The underlayer 3 was a CrW thin film (thickness: 100 angstroms) and was provided to improve the crystal structure of the magnetic layer. Note that this CrW thin film is composed of a composition ratio of Cr: 90 at% and W: 10 at%.
The magnetic layer 4 is made of a CoPtCrB alloy and has a thickness of 200 angstroms. The contents of Co, Pt, Cr, and B in this magnetic layer are Co: 73 at%, Pt: 7 at%, Cr: 18 at%, and B: 2 at%. The grain size of the magnetic particles was examined by TEM (transmission electron microscope) plane photographing and found to be 7 nm on average.
The protective layer 5 is for preventing the magnetic layer 4 from deteriorating due to contact with the magnetic head, and is made of hydrogenated carbon having a thickness of 50 Å. The lubricating layer 6 is formed by dipping a liquid lubricant of perfluoropolyether and has a thickness of 9 angstroms.
[0026]
Next, the magnetic properties and reliability of the obtained magnetic disk were evaluated as follows.
(Evaluation of magnetic properties)
The magnetic properties were measured by VSM (vibration sample type magnetization measurement method). A circular sample having a diameter of 8 mm is cut out with the radius of the magnetic disk at a position of 22 mm as the center, and an external magnetic field is applied (± 10 kOe) in the circumferential direction of the substrate and in the radial direction of the substrate to determine a magnetization curve. And the radial direction Mrt (residual magnetization film thickness product) was calculated.
As a result, as shown in Table 2 below, MrtOR was able to obtain 1.32.
[Reliability evaluation]
When the glide characteristics of the obtained magnetic disk were evaluated, the touchdown height was 4.5 nm. The touchdown height is obtained by sequentially lowering the flying height of the flying head (for example, by lowering the rotation speed of the magnetic disk), obtaining the flying height at which the magnetic disk starts to contact, and calculating the flying height of the magnetic disk. It measures performance, but usually 40Gbit / in²In the HDD requiring the above recording density, the touchdown height is required to be 5 nm or less.
Further, when the flying height at the time of flying of the head was set to 12 nm and the load and unloading operations of the head were repeated under the environment of 70 ° C. and 80% RH, the LUL durability was tested. No failure such as head crash or thermal asperity occurred. In the case of a HDD that is normally used, it is necessary to use the HDD for about 10 years before the number of LUL operations exceeds 600,000.
[0027]
Example 2
In the present embodiment, the Ra (r) / Ra (c) is selected as 4 based on the correlation shown in FIG. 1 so that MrtOR is 1.3, and the magnetic disk is formed so as to obtain this surface shape. Glass substrates for use and magnetic disks were manufactured. Specifically, in the texture process of Example 1, the substrate rotation speed was 150 rpm, and the texture processing time was 30 seconds. Therefore, in the present embodiment, the substrate rotation speed × texture processing time is 4500 (rpm × sec). Except for this point, a glass substrate for a magnetic disk and a magnetic disk were manufactured in the same manner as in Example 1, and the same evaluation as in Example 1 was performed. Table 2 shows the results.
Example 3
In the present embodiment, Ra (r) / Ra (c) is selected to be 2.3 based on the correlation shown in FIG. 1 so as to obtain MrtOR of 1.2. A glass substrate for a magnetic disk and a magnetic disk were manufactured. Specifically, in the texturing step of Example 1, the substrate rotation speed was 120 rpm, and the texturing time was 30 seconds. Therefore, in this embodiment, the substrate rotation speed × texture processing time is 3600 (rpm × sec). Except for this point, a glass substrate for a magnetic disk and a magnetic disk were manufactured in the same manner as in Example 1, and the same evaluation as in Example 1 was performed. Table 2 shows the results.
[0028]
Comparative Example 1
In this comparative example, in the texturing step of Example 1, the substrate rotation speed was set to 1000 rpm, the texture processing time was set to 30 seconds, and the substrate rotation speed × texture processing time was 30,000 (rpm × second). A glass substrate for a magnetic disk and a magnetic disk were manufactured in the same manner as in Example 1, and the same evaluation as in Example 1 was performed. Table 2 shows the results.
Comparative Example 2
A glass substrate for a magnetic disk and a magnetic disk were manufactured in the same manner as in Example 1 except that the texturing step was not performed in Example 1, and the same evaluation as in Example 1 was performed. Table 2 shows the results.
[0029]
[Table 2]

Comparing the results in Table 2, it can be seen that the same relationship between Ra (r) / Ra (c) and MrtOR as the correlation shown in FIG. 1 is obtained. According to the embodiment of the present invention, by setting the ratio of Ra (r) / Ra (c) to 2 or more, it becomes possible to obtain MrtOR of 1.2 or more, and to set the Ra (r) / Ra (c) to 4 or more. As a result, it was confirmed that MrtOR of 1.3 or more was obtained. That is, by providing the glass substrate main surface with a surface shape in which Ra (r) / Ra (c) is 2 or more in a predetermined shape wavelength region, high density recording is possible with high magnetic anisotropy. It can be seen that a magnetic disk having the following condition is obtained.
[0030]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to provide a glass substrate for a magnetic disk capable of imparting high magnetic anisotropy to a magnetic layer when at least a magnetic layer is formed on the glass substrate. In addition, even when a glass substrate is used, high-density recording can be achieved by providing high magnetic anisotropy, and an inexpensive magnetic disk with excellent impact resistance can be provided. Also, as shown in FIG. 1 described above, by previously obtaining the correlation between Ra (r) / Ra (c) and MrtOR, it is possible to manufacture a magnetic disk having a predetermined MrtOR with good reproducibility. it can.
[Brief description of the drawings]
FIG. 1 is a diagram showing a correlation between Ra (r) / Ra (c) and MrtOR.
FIG. 2 is a cross-sectional view schematically showing a layer configuration of the magnetic disk according to the embodiment of the present invention.
3A is a side view and FIG. 3B is a perspective view showing a schematic configuration of a tape-type texture device used in the embodiment.
[Explanation of symbols]
1 Glass substrate for magnetic disk
2 Seed layer
3 Underlayer
4 Magnetic layer
5 Protective layer
6 Lubricant layer
10 magnetic disk

Claims (6)

A magnetic disk glass substrate in which a texture for imparting magnetic anisotropy to a magnetic layer provided on the substrate is formed on a main surface,
The ratio Ra (r) of the center line average roughness Ra (r) in the disk radial direction to the center line average roughness Ra (c) in the disk circumferential direction in at least the shape wavelength region of 3.9 nm to 1000 nm on the main surface of the glass substrate. r) / Ra (c) is a glass substrate for a magnetic disk, having a main surface shape of 2 or more. A magnetic disk glass substrate in which a texture for imparting magnetic anisotropy to a magnetic layer provided on the substrate is formed on a main surface,
The ratio of the center line average roughness Ra (r) in the disk radial direction to the center line average roughness Ra (c) in the disk circumferential direction in an area of 1 μm × 1 μm allocated to a plurality of sections on the main surface of the glass substrate. A glass substrate for a magnetic disk, having a main surface shape in which Ra (r) / Ra (c) is 2 or more. A magnetic disk, comprising: a glass layer for a magnetic disk according to claim 1, wherein at least a magnetic layer is provided. A method for producing a glass substrate for a magnetic disk, comprising a step of forming a texture on a main surface of a glass substrate to impart magnetic anisotropy to a magnetic layer provided on the substrate,
The ratio of the center line average roughness Ra (r) in the disk radial direction to the center line average roughness Ra (c) in the disk circumferential direction in at least the shape wavelength region of 3.9 nm to 1000 nm on the main surface of the glass substrate. A correlation between Ra (r) / Ra (c) and magnetic anisotropy is obtained in advance, and the Ra (r) / Ra (c) is determined based on the correlation in order to obtain a predetermined magnetic anisotropy. A method for manufacturing a glass substrate for a magnetic disk, comprising: selecting a value of (a) and forming a texture that gives a surface shape of the selected value of Ra (r) / Ra (c). A method for producing a glass substrate for a magnetic disk, comprising a step of forming a texture on a main surface of a glass substrate to impart magnetic anisotropy to a magnetic layer provided on the substrate,
The center line average roughness Ra (r) in the disk radial direction with respect to the center line average roughness Ra (c) in the disk circumferential direction in an area of 1 μm × 1 μm previously allocated to a plurality of sections on the main surface of the glass substrate. The correlation between the ratio Ra (r) / Ra (c) and the magnetic anisotropy is determined in advance, and the Ra (r) / Ra is determined based on the correlation in order to obtain a predetermined magnetic anisotropy. A method for manufacturing a glass substrate for a magnetic disk, comprising selecting a value of (c) and forming a texture giving a surface shape of the selected value of Ra (r) / Ra (c). A method for manufacturing a magnetic disk, comprising: forming at least a magnetic layer on a glass substrate manufactured by the method for manufacturing a glass substrate for a magnetic disk according to claim 4.

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