JP3742116B2 - Method for controlling magnetic anisotropy of magnetic thin film - Google Patents
Method for controlling magnetic anisotropy of magnetic thin film Download PDFInfo
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- JP3742116B2 JP3742116B2 JP19961992A JP19961992A JP3742116B2 JP 3742116 B2 JP3742116 B2 JP 3742116B2 JP 19961992 A JP19961992 A JP 19961992A JP 19961992 A JP19961992 A JP 19961992A JP 3742116 B2 JP3742116 B2 JP 3742116B2
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- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
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Description
【０００１】
【産業上の利用分野】
本発明は平面インダクタや平面トランスなどの平面型磁気素子に用いられる軟磁性薄膜に関する。
【０００２】
【従来の技術】
近年、各種電子機器の小形化が盛んに進められている。しかし、電子機器の電源部の小形化はそれに比較して遅れている。このため、電源部が機器全体に占める容積比率は増大する一方である。電子機器の小形化は各種回路のＬＳＩ化によるところが大きいが、電源部に必須であるインダクタやトランスなどの磁気部品についてはこのような小形化・集積化が遅れており、これが容積比率増大の主因となっている。
【０００３】
この課題を解決するために、平面コイルと磁性体とを組み合わせた平面型の磁気素子が提案され、その高性能化の検討が進められている。これらの磁気素子に用いられる磁性薄膜には１ＭＨｚ以上の高周波領域において高透磁率かつ低損失であることが要求されている。また、最適の磁気素子の設計のためには透磁率が特定の値に制御された薄膜が必要となる。これらの要求は、薄膜磁気ヘッドなどのその他の磁気素子においても共通するものである。
【０００４】
高周波領域では、透磁率は主に回転磁化過程によってまかなわれる。このため、磁化困難軸方向の励磁が重要になり、磁化困難軸方向の高周波透磁率および高周波損失が重要な物性値になる。高周波透磁率は試料の様々な物性と複雑に関連した量であるが、最も相関が高いものとして異方性磁場と局所異方性分散量とが挙げられる。高周波透磁率は、おおむね異方性磁場の逆数に比例して変化し、異方性分散量の増大によって減少する。
【０００５】
従来、異方性磁場が制御された磁性膜を得るために、種々の方法が検討されている。例えば、膜を特定の形状に加工して形状異方性などを利用する方法、斜め蒸着などによる柱状構造などのサブストラクチャーを利用する方法、基板の選択や成膜条件の制御により得られる優先配向膜やエピタキシャル成長膜の結晶磁気異方性を利用する方法、積層や異種磁性体との組み合わせによる方法、磁場中成膜や磁場中熱処理による方法、およびこれらを組み合わせた方法などがある。
【０００６】
このうち、磁場中熱処理としては、膜面内の一方向に磁場を印加する直流磁場中熱処理方法、膜面内で磁場方向を回転させる回転磁場中熱処理方法などが知られている。直流磁場中熱処理方法は、磁区の固着などを防ぎながら、一軸異方性を誘導する方法である。回転磁場中熱処理方法は、すでに試料が持つ面内異方性を低減する方法である。これらの熱処理は、方向性規則配列の理論に準じた構造異方性が誘導される系における磁気異方性制御に特に有効である。
しかし、これらの方法により磁性薄膜の高透磁率および低損失を実現しようとすると以下のような問題が生じる。
【０００７】
面内直流磁場中熱処理により付与される磁気異方性は、主に熱処理の温度によって決定され、印加磁場の大きさには陽には依存しない。この異方性の大きさは一般にその試料に固有の値となり、熱処理温度の上昇とともに減少するため、異方性磁場の制御性がよくない。特に結晶化温度がキュリー温度より低いアモルファス系においては、磁気異方性を結晶化温度直下における磁気異方性より小さくすることは困難であり、より高い透磁率が要求される場合に対応できないことがある。結晶質やキュリー温度と結晶化温度との関係が逆転しているアモルファス系においても、薄膜インダクタや磁気ヘッドなどの磁気素子に実際に適用した場合には磁性体以外の材料の耐熱温度などの制約から所望の高透磁率に対応した低異方性磁場が達成できない場合がある。
【０００８】
回転磁場中熱処理は熱処理前の巨視的な異方性を弱めて、原理的には０にできる方法である。その点、面内直流磁場中熱処理よりも異方性磁場の制御性に優れている。現実には、面内直流磁場中熱処理と回転磁場中熱処理とを適宜組み合わせて異方性磁場を制御し、所望の高周波透磁率を得ている場合が多い。しかし、この方法では巨視的な磁化困難軸方向に高周波で励磁する際に、微視的には局所的に磁化容易軸方向に励磁している可能性があり、高周波特性の劣化、損失の増大を招く場合がある。また、面内に分布する局所異方性分散によっても高周波特性が損なわれるおそれがある。
【０００９】
以上述べたように、小形化対応の磁気素子には高透磁率・低損失の軟磁性体が必要とされ、限定された温度範囲内で低損失性と小異方性磁場とが両立した軟磁性薄膜を制御性よく得ることが求められている。
【００１０】
【発明が解決しようとする課題】
本発明の目的は、限定された温度範囲において、面内異方性磁場の制御が容易で、かつ高周波で高透磁率と低損失とを可能にする異方性が誘導された軟磁性薄膜を提供することにある。
【００１１】
【課題を解決するための手段と作用】
本発明に係る磁性薄膜の磁気異方性の制御方法は、基板上に磁性薄膜および保護膜を形成し、前記磁性薄膜の膜面に対して３０〜７５°傾いた方向に磁場を印加しながら熱処理を行い、前記磁性薄膜の膜面に非平行に膜面内成分を含む誘導磁気異方性を導入するとともに局所異方性分散量を極めて小さくすることを特徴とするものである。
本発明の対象となる磁性薄膜は、柱状構造などのサブストラクチャーを持たず、かつ方向性規則配列に準じた構造異方性が誘導され得る軟磁性薄膜である。
【００１２】
本発明の方法は、例えば、前記磁性薄膜がアモルファス磁性薄膜である場合に有効に適用できる。
【００１３】
以下、本発明を図１および図２を参照してさらに詳細に説明する。図１（ａ）は膜面に対して角度βをなす方向に磁化容易軸を持つ軟磁性薄膜を示す斜視図、図１（ｂ）は磁化ベクトルの極座標表示を示す図である。また、図２（ａ）は磁化ベクトルＩの方向を示す説明図、図２（ｂ）は有効磁場の方向を示す説明図である。これらの図において、Ｋ0 は磁場中熱処理による誘導磁気異方性の一軸異方性エネルギー、Ｉは磁化ベクトル、Ｈd は反磁場、Ｈexは外部磁場、Ｈeff は有効磁場である。図１（ａ）では、Ｋ0 を磁化容易軸方向に平行なベクトルとして表現している。
【００１４】
柱状構造などの３次元的に異方的な構造を持たず、方向性規則配列の理論に準じた構造異方性が誘導され得る系では、図１（ａ）および（ｂ）に示すように、磁場中熱処理または磁場中成膜によって誘導される磁気異方性の磁化容易軸方向は、熱処理時または成膜時の磁化ベクトルＩの方向に一致する。また、図２（ａ）および（ｂ）に示すように、磁化ベクトルＩの方向は、有効磁場Ｈeff の方向とほぼ同じである。図２（ｂ）に示すように、有効磁場Ｈeff は、外部磁場Ｈexと反磁場Ｈd とをベクトル合成したものである。ここで、Ｈd ＝−Ｉｓｉｎφ／μ0 である。したがって、有効磁場Ｈeff の方向が膜面に平行、垂直、またはその中間の傾斜した方向のいずれの方向であっても、誘導される磁気異方性エネルギ−定数Ｋ0 の大きさに差異は生じず、磁化容易軸方向はその有効磁場Ｈeff の方向に平行となる。
【００１５】
図２（ｂ）に示すように、外部磁場Ｈexとして反磁場Ｈd に比較して十分に大きい直流磁場を膜面または基板面に対して角度αの方向に印加し、膜面または基板面に対して角度βの方向に有効磁場Ｈeff が生じるように熱処理または成膜すると、構造異方性による誘導異方性は膜面に対して角度βの方向に形成される。外部直流磁場Ｈexが反磁場Ｈd に対して大きいほどαとβとの差は０に近づく。ただし、磁場誘起方向性規則配列を生じる軟磁性体であって十分な飽和磁化を有する系では、一般に、誘導される異方性よりも形状異方性の効果の方が大きいため、総合的には面内が磁化容易面となる軟磁性薄膜が得られる。したがって、面内の磁化容易軸方向は、初期状態の面内異方性の容易軸方向に保存される。
【００１６】
膜面に対して角度βの方向に磁化容易軸が誘導された軟磁性薄膜の面内の一軸異方性定数Ｋplは以下のようにして導くことができる。ここで、図１（ｂ）に示すように、磁化ベクトルＩが方向（θ，φ）にあるときの磁気異方性エネルギーＥ0 は、磁化ベクトルＩの方向の関数として次のように表せる。
【００１７】
【数１】
【００１８】
【数２】
式（２）から明らかなように、括弧内のＫ0 ｃｏｓ2 βが面内の見掛けの一軸磁気異方性定数として作用し、θ＝０，πの方向が磁化容易軸方向になっている。すなわち、図のｘ軸方向が磁化容易軸方向となり、面内の一軸異方性定数Ｋpl＝Ｋ0 ｃｏｓ2 βとなる。
【００２０】
このうち、特に膜面に垂直な方向の直流磁場中で熱処理または成膜する場合について図３を参照して説明する。図３においては、事前の面内直流磁場中熱処理（成膜手法に起因する場合もある）によって面内磁気異方性Ｋplが誘導されているものとする。また、Ｋpdは膜面に垂直な方向の直流磁場中熱処理による磁気異方性、ｅDOは方向性規則配列による誘導磁気異方性の磁化容易軸を示す。
【００２１】
前述した議論と同様に、外部磁場Ｈexとして反磁場Ｈd に比較して十分に大きい直流磁場を膜面に垂直な方向に印加すると、構造異方性による誘導異方性は膜面に垂直な方向に形成される。このため、事前の面内直流磁場中熱処理に起因する方向性規則配列によって面内磁気異方性が存在していても、熱処理の時間経過に伴い面内の異方性は減少する。これは、磁気異方性が方向性規則配列の規則度パラメータであり、膜面に垂直な方向の規則度が成長するにつれて、膜面内の規則度が減少するためである。図３に示されるように、理想的には平衡状態に達するに十分な時間の熱処理を施せば、膜面内の異方性を０にすることができる。したがって、熱処理時間を制御することにより、面内異方性の大きさを制御できる。
【００２２】
前述したように、本発明の磁性薄膜では面内の一軸異方性定数Ｋpl＝Ｋ0 ｃｏｓ2 βとなる。したがって、図４に示すように、方向性規則配列による誘導磁気異方性の磁化容易軸方向と膜面のなす角度βをπ／２から０まで変化させることにより、面内の見掛けの一軸磁気異方性エネルギーＫplが０からＫ0 まで制御された軟磁性薄膜が得られる。角度βに関しては、簡単な実験装置でも十分によい精度で所望の値に設定できる。このことは、膜面に非平行に磁気異方性を誘導した膜では、膜面に平行に磁気異方性を誘導した膜に比較して、より小さい面内異方性磁場を実現できることを意味する。
【００２３】
この効果を図５のように示すこともできる。この図は、本発明に係る磁性薄膜および従来の磁性薄膜について面内磁気異方性エネルギーの大きさの制御範囲を示すものである。この図では、膜面内の直流磁場中熱処理を施した場合に方向性規則配列に準じた構造異方性により面内に平行に導入される一軸異方性エネルギーの最小値をＫ0minで表す。これに対して、本発明に係る膜面に非平行な誘導磁気異方性の磁化容易軸を有する軟磁性薄膜の面内の誘導磁気異方性エネルギーの大きさの制御範囲を示す。本発明では、より小さい面内異方性に対応でき、より高透磁率に対応できることがわかる。
【００２４】
次に、磁性薄膜を面内の磁化困難軸方向に高周波励磁する場合を考える。本発明の磁性薄膜を得るための熱処理程においては、面内の磁化困難軸方向に有効磁場は生じない。これは、統計力学的観点からは、局所的な微視的磁化容易軸が、巨視的な面内磁化困難軸方向に平行に生じる可能性が非常に低いことを意味する。また、本発明では、回転磁場中熱処理とは異なり、本来の誘導磁気異方性の方位の分散はほとんどないため、局所異方性分散量を極めて小さくできる。
【００２５】
図６に複素透磁率の実数部および虚数部の周波数特性を模式的に示す。この図において、実線は本発明の磁性薄膜、破線は回転磁場中熱処理が施された磁性薄膜である。複素透磁率の虚数部は１ループ当たりの損失に比例する量である。図６に示されるように、巨視的には同じ面内異方性磁場を示す軟磁性薄膜であっても、本発明のものは回転磁場中熱処理が施されたものよりも低損失を実現できる。
【００２６】
以上述べたように本発明によれば、膜面に非平行な直流磁場中での熱処理または成膜により面内の異方性磁場を制御でき、所望の高透磁率に対応した微小な面内異方性磁場を有し、しかも異方性分散が除去された磁性薄膜を得ることができる。その結果、磁化困難軸方向に高周波励磁した場合に高透磁率と低損失とを実現できる。
【００２７】
【実施例】
以下、本発明の実施例を説明する。
【００２８】
以下の実施例および比較例では、ＲＦマグネトロン・スパッタリング法により作製されたアモルファスＣｏＺｒＮｂ薄膜からなる試料を用いた。主な成膜条件は以下の通りである。
・ターゲット：Ｃｏ84Ｚｒ6.2 Ｎｂ9.8 （鋳込み組成）、３インチ径
・基板回転数：１９．５ｒｐｍ
・基板：アモルファスＳｉＯ2 （熱酸化、０．８μｍ厚）／Ｓｉウェハ（１００）、５インチ径
・基板温度：３９〜５５℃
・到達真空度：１〜３×１０-4Ｐａ
・スパッタ条件
ＲＦパワー：１０．５Ｗ／ｃｍ2
雰囲気：Ａｒフロー（０．２０Ｐａ）
成膜時間：６８ｍｉｎ
【００２９】
以上の条件により２．０μｍ厚のＣｏＺｒＮｂ薄膜を得た。引き続き真空を破らずに同一装置で直ちに保護膜としてアモルファスＳｉＯ2 （１μｍ厚）を積層した。この試料の飽和磁化は２０℃で１．０Ｔ、４５０℃で０．６Ｔであった。また、この試料の結晶化温度は５００℃であった。
【００３０】
実施例１
試料に、膜面に対して角度α（α＝３０°、４５°、６０°、６５°、７０°、７５°、９０°）の方向に直流磁場を印加して真空中で熱処理を施した。熱処理装置としては、振動試料型磁力計（東英工業社製、商品名ＶＳＭ−５）を利用した。磁力計を用いたのは、装置に付属する電磁石（最大印加磁場２０ｋＯｅ）を利用して、膜面に垂直な方向の強力な反磁場（６〜１０ｋＯｅ）よりも大きな外部磁場により磁化ベクトルの膜面に対する角度βを制御するためである。印加磁場は１５ｋＯｅ、熱処理温度は４５０℃、熱処理時間は１０ｍｉｎとした。
【００３１】
実施例２
試料を石英管に真空封入し、膜面に平行に２ｋＯｅの直流磁場を印加して熱処理を行った。熱処理温度は４５０℃とした。この熱処理によって成膜直後の異方性分散が除去され、面内で一様な一軸磁気異方性が誘導されたアモルファスＣｏＺｒＮｂ薄膜が得られる。
【００３２】
この試料に、実施例１と同一の装置を用い、膜面に垂直に直流磁場を印加して真空中で熱処理を施した。印加磁場は１３ｋＯｅ、熱処理温度は３５０℃、４００℃または４５０℃、熱処理時間は１０ｍｉｎとした。
【００３３】
比較例１
実施例１と同一の装置を用い、試料に面内直流磁場中熱処理を施した。この際、熱処理温度は３５０℃から試料の結晶化温度である５００℃の直下まで種々変化させた。その他の条件は実施例１と同一である。
【００３４】
比較例２
実施例１と同一の装置を用い、試料に面内直流磁場中熱処理を施した。その他の条件は実施例１と同一である。この後、さらに成瀬科学機械製の回転磁場中熱処理炉を用い、真空雰囲気で面内の回転磁場中熱処理を施した。面内印加磁場は０．３ｋＯｅ、回転速度は１００ｒｐｍとし、熱処理温度は３５０℃から５００℃まで種々変化させた。
以下、これらの磁性薄膜の特性について検討した結果を説明する。
【００３５】
まず、実施例２の磁性薄膜について、第１段の面内直流磁場中熱処理後に、面内の容易軸方向および困難軸方向のそれぞれで磁化曲線を測定した。図１２に磁化困難軸方向の磁化曲線、図１３に磁化容易軸方向の磁化曲線をそれぞれ示す。各図には印加磁場１０Ｏｅおよび２５０Ｏｅの２種の磁化曲線を示した。横軸は外部印加磁場表示である。これらはフルループの磁化環線であるが、保磁力が非常に小さいため往復のヒステリシスはほとんど観察されない。なお、容易軸方向でもほぼ飽和するには２Ｏｅの磁場を要しているが、これは反磁場の影響によるものである。これらの２方向の飽和磁場の差から面内の異方性磁場を評価でき、良好な軟磁性薄膜が得られていることがわかる。
【００３６】
図７に実施例１の磁性薄膜について面内の異方性磁場Ｈｋの熱処理時の印加磁場角度αに対する依存性を示す。この図から明らかなように、角度αの増加とともに、面内の異方性磁場Ｈｋが減少する。図８は横軸を熱処理時の有効磁場角度すなわち熱処理時に形成される磁気異方性の磁化容易軸の膜面に対する角度βとして、図７を表示し直したものである。この図には理論予想値を破線で併記する。面内の異方性磁場Ｈｋの角度βに対する依存性の実測値は理論予測値とよく一致している。このことから、膜面に非平行な直流磁場中熱処理によって、膜面内の異方性磁場を良好に制御できることがわかる。
【００３７】
図９に実施例１の磁性薄膜について面内の磁化困難軸方向の保磁力Ｈｃの角度αに対する依存性を示す。この図から、膜面に対して非平行な方向に磁化容易軸が誘導された軟磁性薄膜において保磁力の劣化が生じないことが確認できる。特に、α＝９０℃の条件で得られた軟磁性薄膜は１ｍＯｅ以下と非常に小さい保磁力を示している。
【００３８】
図１０に実施例１および比較例２の磁性薄膜について周波数１０ＭＨｚで磁化困難軸方向に励磁した際の高周波透磁率虚数部μ''の高周波透磁率実数部μ´に対する依存性を示す。図中、実線は実施例１、破線は比較例２である。また、この図には抵抗率や膜厚などの値から予想される渦電流損失の計算値を併記する。この図から明らかなように、実施例１では比較例２よりも損失が小さく、渦電流損失以外のヒステリシス損失やその他の異常損の影響はほとんどない。このことから、本発明に係る膜面に傾斜した誘導磁気異方性が付与された系においては、良好な磁化困難軸励磁が行われていることが確認できる。
【００３９】
次に、実施例１の軟磁性薄膜（β＝５０°）および膜面に平行な誘導磁気異方性を有する比較例１の軟磁性薄膜（β＝０°）を用いて、それぞれ薄膜インダクタを作製した。図１１にこれらの薄膜インダクタのインダクタンスＬと品質係数Ｑの周波数特性を示す。図中、実線は実施例１、破線は比較例１である。この図から明らかなように、実施例１では比較例１と比較して、より高いＬが得られ、Ｑの劣化も認められない。
【００４０】
図１４に実施例２（２段階熱処理後）および比較例１の磁性薄膜について面内の異方性磁場Ｈｋの熱処理温度依存性を示す。図中、実線は実施例２、破線は比較例１である。熱処理温度の上昇とともに面内の異方性磁場Ｈｋが減少する傾向が認められるが、実施例２は比較例１よりも面内異方性磁場が小さい。
【００４１】
図１５に実施例２（２段階熱処理後）および比較例２の磁性薄膜について面内の磁化困難軸方向の保磁力Ｈｃの熱処理温度依存性を示す。図中、実線は実施例２、破線は比較例２である。実施例２では熱処理温度の上昇とともにＨｃが減少している。一方、比較例２では熱処理温度の上昇とともにＨｃが増加している。理想的な単一磁区を磁化困難軸方向に励磁する場合、回転磁化過程には保磁力が発生しない。したがって、比較例２における保磁力の増加は局所異方性分散量の増加などに対応しているものと推定される。
図１４および図１５から、実施例２では、保磁力の増加を回避しつつ、面内異方性磁場を減少できることがわかる。
【００４２】
図１６に実施例２（２段階熱処理後）および比較例２の磁性薄膜について周波数１０ＭＨｚで磁化困難軸方向に励磁した際のｔａｎδの高周波透磁率実数部μ´に対する依存性を示す。図中、実線は実施例２、破線は比較例２である。この図から明らかなように、実施例２では比較例２よりも損失が小さい。また、比較例２では前述した保磁力の増加に起因して、高周波におけるヒステリシス損失が増加している。
【００４３】
なお、前記実施例では磁性薄膜を成膜後に熱処理を施しているが、基板面に非平行な直流磁場中で磁性薄膜を成膜することにより、膜面に非平行な磁化容易軸を形成してもよい。
【００４４】
【発明の効果】
以上詳述したように本発明によれば、高周波で高透磁率と低損失とを示す軟磁性薄膜を提供でき、平面インダクタや平面トランスなどの平面型磁気素子に有効に適用できる。
【図面の簡単な説明】
【図１】（ａ）は本発明に係る膜面に対して角度βをなす方向に磁化容易軸を持つ磁性薄膜を示す斜視図、（ｂ）は磁化ベクトルの極座標表示を示す図。
【図２】（ａ）は磁化ベクトルの方向を示す説明図、（ｂ）は有効磁場の方向を示す説明図。
【図３】磁性薄膜の膜面に垂直な方向の直流磁場中で熱処理した際、時間経過に伴う方向性規則配列による誘導磁気異方性の磁化容易軸の方向の変化を示す説明図。
【図４】本発明に係る磁性薄膜についてＫpl／Ｋ0 の熱処理時の実効磁場角度βに対する依存性を示す図。
【図５】本発明に係る磁性薄膜および従来の面内直流磁場中熱処理された磁性薄膜について面内磁気異方性エネルギーの大きさの制御範囲を示す図。
【図６】本発明に係る磁性薄膜および従来の面内回転磁場中熱処理が施された磁性薄膜について複素透磁率の実数部および虚数部の周波数特性を示す図。
【図７】実施例１の磁性薄膜について面内の異方性磁場Ｈｋの熱処理時の印加磁場角度αに対する依存性を示す図。
【図８】実施例１の磁性薄膜について面内の異方性磁場Ｈｋの熱処理時の実効磁場角度βに対する依存性を示す図。
【図９】実施例１の磁性薄膜について面内の磁化困難軸方向の保磁力Ｈｃの印加磁場角度αに対する依存性を示す図。
【図１０】実施例１および比較例２の磁性薄膜について周波数１０ＭＨｚで磁化困難軸方向に励磁した際の高周波透磁率虚数部μ''の高周波透磁率実数部μ´に対する依存性を示す図。
【図１１】実施例１および比較例１の磁性薄膜を用いて作製された薄膜インダクタのインダクタンスＬと品質係数Ｑの周波数特性を示す図。
【図１２】実施例２の磁性薄膜について第１段の熱処理後の磁化困難軸方向の磁化曲線を示す図。
【図１３】実施例２の磁性薄膜について第１段の熱処理後の磁化容易軸方向の磁化曲線を示す図。
【図１４】実施例２および比較例１の磁性薄膜について面内の異方性磁場Ｈｋの熱処理温度依存性を示す図。
【図１５】実施例２および比較例２の磁性薄膜について面内の磁化困難軸方向の保磁力Ｈｃの熱処理温度依存性を示す図。
【図１６】実施例２および比較例２の磁性薄膜について周波数１０ＭＨｚで磁化困難軸方向に励磁した際のｔａｎδの高周波透磁率実数部μ´に対する依存性を示す図。[0001]
[Industrial application fields]
The present invention relates to a soft magnetic thin film used for planar magnetic elements such as planar inductors and planar transformers.
[0002]
[Prior art]
In recent years, various electronic devices have been actively miniaturized. However, downsizing of the power supply unit of electronic equipment is delayed compared with that. For this reason, the volume ratio which a power supply part occupies for the whole apparatus is only increasing. The downsizing of electronic equipment is largely due to the use of LSIs for various circuits, but such miniaturization and integration of magnetic parts such as inductors and transformers that are essential for the power supply unit have been delayed, which is the main reason for the increase in volume ratio. It has become.
[0003]
In order to solve this problem, a planar magnetic element in which a planar coil and a magnetic body are combined has been proposed, and studies on its performance have been advanced. Magnetic thin films used for these magnetic elements are required to have high magnetic permeability and low loss in a high frequency region of 1 MHz or higher. Further, in order to design an optimum magnetic element, a thin film whose magnetic permeability is controlled to a specific value is required. These requirements are common to other magnetic elements such as thin film magnetic heads.
[0004]
In the high frequency region, the magnetic permeability is mainly provided by the rotational magnetization process. For this reason, excitation in the hard axis direction is important, and high-frequency permeability and high-frequency loss in the hard axis direction are important physical properties. The high-frequency magnetic permeability is a quantity that is intricately related to various physical properties of the sample, and the one having the highest correlation includes the anisotropic magnetic field and the amount of local anisotropic dispersion. The high-frequency magnetic permeability changes approximately in proportion to the reciprocal of the anisotropic magnetic field, and decreases as the amount of anisotropic dispersion increases.
[0005]
Conventionally, various methods have been studied in order to obtain a magnetic film having a controlled anisotropic magnetic field. For example, a method that uses shape anisotropy by processing a film into a specific shape, a method that uses a substructure such as a columnar structure by oblique deposition, etc., preferential orientation obtained by substrate selection and film formation condition control There are a method using the magnetocrystalline anisotropy of a film or an epitaxially grown film, a method using lamination or a combination with different types of magnetic materials, a method using film formation in a magnetic field or a heat treatment in a magnetic field, or a method combining these.
[0006]
Among these, as the heat treatment in a magnetic field, a direct-current magnetic field heat treatment method in which a magnetic field is applied in one direction in the film surface, a rotating magnetic field heat treatment method in which the magnetic field direction is rotated in the film surface, and the like are known. The DC magnetic field heat treatment method is a method for inducing uniaxial anisotropy while preventing the magnetic domains from sticking. The heat treatment method in a rotating magnetic field is a method for reducing the in-plane anisotropy of the sample. These heat treatments are particularly effective for controlling magnetic anisotropy in a system in which structural anisotropy is induced according to the theory of directional ordered arrangement.
However, the following problems occur when trying to realize high magnetic permeability and low loss of the magnetic thin film by these methods.
[0007]
The magnetic anisotropy imparted by the heat treatment in the in-plane DC magnetic field is mainly determined by the temperature of the heat treatment and does not depend positively on the magnitude of the applied magnetic field. In general, the magnitude of this anisotropy is a value inherent to the sample and decreases with an increase in the heat treatment temperature, so that the controllability of the anisotropic magnetic field is not good. Especially in the amorphous system where the crystallization temperature is lower than the Curie temperature, it is difficult to make the magnetic anisotropy smaller than the magnetic anisotropy just below the crystallization temperature, and it is impossible to cope with the case where higher magnetic permeability is required. There is. Even in amorphous systems where the relationship between crystallinity, Curie temperature and crystallization temperature is reversed, when applied to magnetic elements such as thin-film inductors and magnetic heads, restrictions such as the heat resistance temperature of materials other than magnetic materials Therefore, a low anisotropic magnetic field corresponding to a desired high permeability may not be achieved.
[0008]
Heat treatment in a rotating magnetic field is a method that can reduce the macroscopic anisotropy before the heat treatment to zero in principle. In that respect, the controllability of the anisotropic magnetic field is superior to the heat treatment in the in-plane DC magnetic field. In reality, in many cases, a desired high-frequency magnetic permeability is obtained by controlling an anisotropic magnetic field by appropriately combining in-plane DC magnetic field heat treatment and rotating magnetic field heat treatment. However, in this method, when exciting at a high frequency in the macroscopically difficult axis direction, there is a possibility that the microscopically local excitation is in the easy axis direction, which degrades the high frequency characteristics and increases the loss. May be invited. In addition, high frequency characteristics may be impaired by local anisotropic dispersion distributed in the plane.
[0009]
As described above, a magnetic element compatible with miniaturization requires a soft magnetic material having high permeability and low loss, and a soft element that achieves both low loss and a small anisotropic magnetic field within a limited temperature range. It is required to obtain a magnetic thin film with good controllability.
[0010]
[Problems to be solved by the invention]
An object of the present invention is to provide a soft magnetic thin film in which in-plane anisotropic magnetic field is easily controlled in a limited temperature range, and anisotropy is induced that enables high permeability and low loss at high frequencies. It is to provide.
[0011]
[Means and Actions for Solving the Problems]
The method for controlling the magnetic anisotropy of a magnetic thin film according to the present invention comprises forming a magnetic thin film and a protective film on a substrate and applying a magnetic field in a direction inclined by 30 to 75 ° with respect to the film surface of the magnetic thin film. Heat treatment is performed to introduce induced magnetic anisotropy containing in-film components non-parallel to the film surface of the magnetic thin film, and the amount of local anisotropy dispersion is extremely reduced .
The magnetic thin film that is the subject of the present invention is a soft magnetic thin film that does not have a substructure such as a columnar structure and that can induce structural anisotropy according to a directional ordered array.
[0012]
The method of the present invention can be effectively applied, for example, when the magnetic thin film is an amorphous magnetic thin film.
[0013]
Hereinafter, the present invention will be described in more detail with reference to FIGS. FIG. 1A is a perspective view showing a soft magnetic thin film having an easy magnetization axis in a direction forming an angle β with respect to the film surface, and FIG. 1B is a view showing polar coordinates of magnetization vectors. 2A is an explanatory diagram showing the direction of the magnetization vector I, and FIG. 2B is an explanatory diagram showing the direction of the effective magnetic field. In these figures, K 0 is a uniaxial anisotropic energy of induced magnetic anisotropy by heat treatment in a magnetic field, I is a magnetization vector, H d is a demagnetizing field, H ex is an external magnetic field, and H eff is an effective magnetic field. In FIG. 1A, K 0 is expressed as a vector parallel to the easy axis direction.
[0014]
In a system that does not have a three-dimensional anisotropic structure such as a columnar structure and can induce structural anisotropy according to the theory of directional ordered arrangement, as shown in FIGS. The easy axis direction of magnetic anisotropy induced by heat treatment in a magnetic field or film formation in a magnetic field coincides with the direction of the magnetization vector I at the time of heat treatment or film formation. Further, as shown in FIGS. 2A and 2B, the direction of the magnetization vector I is substantially the same as the direction of the effective magnetic field H eff . As shown in FIG. 2B, the effective magnetic field H eff is a vector composition of the external magnetic field H ex and the demagnetizing field H d . Here, H d = −I sin φ / μ 0 . Therefore, regardless of whether the effective magnetic field H eff is parallel to, perpendicular to the film surface, or in the middle of the inclined direction, there is a difference in the magnitude of the induced magnetic anisotropy energy constant K 0. It does not occur, and the easy magnetization axis direction is parallel to the direction of the effective magnetic field H eff .
[0015]
As shown in FIG. 2B, a DC magnetic field sufficiently larger than the demagnetizing field H d is applied as the external magnetic field H ex in the direction of the angle α with respect to the film surface or the substrate surface. In contrast, when heat treatment or film formation is performed so that an effective magnetic field H eff is generated in the direction of angle β, induced anisotropy due to structural anisotropy is formed in the direction of angle β with respect to the film surface. The difference between α and β approaches zero as the external DC magnetic field H ex is larger than the demagnetizing field H d . However, in a soft magnetic material that generates a magnetic field induced directional ordered array and has sufficient saturation magnetization, the effect of shape anisotropy is generally larger than that of induced anisotropy. Can obtain a soft magnetic thin film whose in-plane is an easily magnetized surface. Therefore, the in-plane easy axis direction is preserved in the initial in-plane anisotropy easy axis direction.
[0016]
The in-plane uniaxial anisotropy constant K pl in which the easy axis of magnetization is induced in the direction of the angle β with respect to the film surface can be derived as follows. Here, as shown in FIG. 1B, the magnetic anisotropy energy E 0 when the magnetization vector I is in the direction (θ, φ) can be expressed as a function of the direction of the magnetization vector I as follows.
[0017]
[Expression 1]
[0018]
[Expression 2]
As is clear from Equation (2), K 0 cos 2 in parentheses β acts as an in-plane apparent uniaxial magnetic anisotropy constant, and the direction of θ = 0, π is the easy axis of magnetization. That is, the x-axis direction in the figure is the easy magnetization axis direction, and the in-plane uniaxial anisotropy constant K pl = K 0 cos 2 β.
[0020]
Among these, a case where heat treatment or film formation is performed in a DC magnetic field in a direction perpendicular to the film surface will be described with reference to FIG. In FIG. 3, it is assumed that the in-plane magnetic anisotropy K pl is induced by the prior in-plane DC magnetic field heat treatment (which may be caused by the film formation method). Further, K pd represents magnetic anisotropy by heat treatment in a DC magnetic field in a direction perpendicular to the film surface, and e DO represents an easy magnetization axis of induced magnetic anisotropy by directional ordered arrangement.
[0021]
Similar to the discussion above, when a sufficiently large DC magnetic field is applied as the external magnetic field Hex compared to the demagnetizing field Hd in the direction perpendicular to the film surface, the induced anisotropy due to the structural anisotropy is perpendicular to the film surface. Formed in any direction. For this reason, even if the in-plane magnetic anisotropy exists due to the directional regular arrangement resulting from the pre-in-plane DC magnetic field heat treatment, the in-plane anisotropy decreases as the heat treatment time elapses. This is because the magnetic anisotropy is a regularity parameter of the directional regular arrangement, and the regularity in the film surface decreases as the regularity in the direction perpendicular to the film surface grows. As shown in FIG. 3, ideally, the anisotropy in the film plane can be reduced to 0 by performing heat treatment for a time sufficient to reach the equilibrium state. Therefore, the magnitude of the in-plane anisotropy can be controlled by controlling the heat treatment time.
[0022]
As described above, in the magnetic thin film of the present invention, the in-plane uniaxial anisotropy constant K pl = K 0 cos 2 β. Therefore, as shown in FIG. 4, by changing the angle β formed between the direction of easy magnetization of the induced magnetic anisotropy by the directional regular array and the film surface from π / 2 to 0, apparent uniaxial magnetism in the plane is obtained. soft magnetic thin film which is controlled from the anisotropy energy K pl is 0 to K 0 is obtained. Regarding the angle β, even a simple experimental device can be set to a desired value with sufficiently good accuracy. This indicates that a film in which magnetic anisotropy is induced non-parallel to the film surface can realize a smaller in-plane anisotropic magnetic field than a film in which magnetic anisotropy is induced parallel to the film surface. means.
[0023]
This effect can also be shown as shown in FIG. This figure shows the control range of the magnitude of the in-plane magnetic anisotropy energy for the magnetic thin film according to the present invention and the conventional magnetic thin film. In this figure, the minimum value of the uniaxial anisotropy energy introduced parallel to the surface due to the structural anisotropy according to the directional ordered arrangement when the heat treatment in the direct current magnetic field is performed in the film surface is represented by K 0min . . On the other hand, the control range of the magnitude | size of the induced magnetic anisotropy energy in the surface of the soft-magnetic thin film which has a magnetization easy axis | shaft of induction magnetic anisotropy non-parallel to the film surface based on this invention is shown. It can be seen that the present invention can cope with smaller in-plane anisotropy and can cope with higher magnetic permeability.
[0024]
Next, consider a case where the magnetic thin film is excited at a high frequency in the in-plane hard axis direction. In the heat treatment process for obtaining the magnetic thin film of the present invention, no effective magnetic field is generated in the in-plane hard axis direction. This means that, from a statistical mechanical point of view, the local microscopic easy magnetization axis is very unlikely to be generated parallel to the macroscopic in-plane magnetization hard axis direction. Further, in the present invention, unlike the heat treatment in the rotating magnetic field, since there is almost no dispersion of the original induced magnetic anisotropy orientation, the amount of local anisotropy dispersion can be made extremely small.
[0025]
FIG. 6 schematically shows the frequency characteristics of the real part and imaginary part of the complex permeability. In this figure, the solid line represents the magnetic thin film of the present invention, and the broken line represents the magnetic thin film that has been heat-treated in a rotating magnetic field. The imaginary part of the complex permeability is an amount proportional to the loss per loop. As shown in FIG. 6, even in the case of a soft magnetic thin film that macroscopically shows the same in-plane anisotropic magnetic field, the present invention can realize a lower loss than that subjected to heat treatment in a rotating magnetic field. .
[0026]
As described above, according to the present invention, an in-plane anisotropic magnetic field can be controlled by heat treatment or film formation in a DC magnetic field that is not parallel to the film surface, and a minute in-plane corresponding to a desired high permeability can be controlled. A magnetic thin film having an anisotropic magnetic field and having anisotropic dispersion removed can be obtained. As a result, high magnetic permeability and low loss can be realized when high-frequency excitation is performed in the hard axis direction.
[0027]
【Example】
Examples of the present invention will be described below.
[0028]
In the following examples and comparative examples, samples made of an amorphous CoZrNb thin film produced by an RF magnetron sputtering method were used. The main film forming conditions are as follows.
-Target: Co 84 Zr 6.2 Nb 9.8 (casting composition), 3 inch diameter-Substrate rotation speed: 19.5 rpm
・ Substrate: Amorphous SiO 2 (thermal oxidation, 0.8 μm thickness) / Si wafer (100), 5 inch diameter ・ Substrate temperature: 39 to 55 ° C.
・ Achieved vacuum: 1-3 × 10 −4 Pa
Sputtering condition RF power: 10.5 W / cm 2
Atmosphere: Ar flow (0.20 Pa)
Deposition time: 68 min
[0029]
Under the above conditions, a CoZrNb thin film having a thickness of 2.0 μm was obtained. Subsequently, amorphous SiO 2 (1 μm thick) was immediately laminated as a protective film with the same apparatus without breaking the vacuum. The saturation magnetization of this sample was 1.0 T at 20 ° C. and 0.6 T at 450 ° C. The crystallization temperature of this sample was 500 ° C.
[0030]
Example 1
The sample was subjected to heat treatment in a vacuum by applying a DC magnetic field in the direction of an angle α (α = 30 °, 45 °, 60 °, 65 °, 70 °, 75 °, 90 °) with respect to the film surface. . As the heat treatment apparatus, a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd., trade name VSM-5) was used. The magnetometer is used by utilizing an electromagnet (maximum applied
[0031]
Example 2
The sample was vacuum-sealed in a quartz tube, and heat treatment was performed by applying a DC magnetic field of 2 kOe parallel to the film surface. The heat treatment temperature was 450 ° C. By this heat treatment, the anisotropic dispersion immediately after film formation is removed, and an amorphous CoZrNb thin film in which uniform uniaxial magnetic anisotropy is induced in the plane is obtained.
[0032]
This sample was heat-treated in a vacuum using the same apparatus as in Example 1 while applying a DC magnetic field perpendicular to the film surface. The applied magnetic field was 13 kOe, the heat treatment temperature was 350 ° C., 400 ° C. or 450 ° C., and the heat treatment time was 10 min.
[0033]
Comparative Example 1
Using the same apparatus as in Example 1, the sample was heat-treated in an in-plane DC magnetic field. At this time, the heat treatment temperature was variously changed from 350 ° C. to just below 500 ° C. which is the crystallization temperature of the sample. Other conditions are the same as those in the first embodiment.
[0034]
Comparative Example 2
Using the same apparatus as in Example 1, the sample was heat-treated in an in-plane DC magnetic field. Other conditions are the same as those in the first embodiment. Thereafter, in-plane rotating magnetic field heat treatment was performed in a vacuum atmosphere using a rotary magnetic field heat treatment furnace manufactured by Naruse Kagaku Kikai. The in-plane applied magnetic field was 0.3 kOe, the rotation speed was 100 rpm, and the heat treatment temperature was variously changed from 350 ° C. to 500 ° C.
Hereinafter, the result of examining the characteristics of these magnetic thin films will be described.
[0035]
First, for the magnetic thin film of Example 2, after the first stage in-plane DC magnetic field heat treatment, the magnetization curves were measured in the in-plane easy axis direction and the hard axis direction, respectively. FIG. 12 shows a magnetization curve in the hard axis direction, and FIG. 13 shows a magnetization curve in the easy axis direction. Each figure shows two types of magnetization curves of applied magnetic fields of 10 Oe and 250 Oe. The horizontal axis is an externally applied magnetic field display. These are full-loop magnetized ring lines, but since the coercive force is very small, little reciprocal hysteresis is observed. It should be noted that a magnetic field of 2 Oe is required to be almost saturated even in the easy axis direction, which is due to the influence of the demagnetizing field. The in-plane anisotropic magnetic field can be evaluated from the difference between the saturation magnetic fields in these two directions, and it can be seen that a good soft magnetic thin film is obtained.
[0036]
FIG. 7 shows the dependence of the in-plane anisotropic magnetic field Hk on the applied magnetic field angle α during the heat treatment for the magnetic thin film of Example 1. As is clear from this figure, the in-plane anisotropic magnetic field Hk decreases as the angle α increases. FIG. 8 is a re-display of FIG. 7 with the horizontal axis representing the effective magnetic field angle during heat treatment, that is, the angle β of the easy axis of magnetic anisotropy formed during heat treatment with respect to the film surface. In this figure, theoretical predicted values are also shown with broken lines. The measured value of the dependence of the in-plane anisotropic magnetic field Hk on the angle β is in good agreement with the theoretically predicted value. From this, it is understood that the anisotropic magnetic field in the film surface can be well controlled by the heat treatment in the DC magnetic field that is not parallel to the film surface.
[0037]
FIG. 9 shows the dependence of the coercive force Hc in the in-plane hard axis direction on the angle α of the magnetic thin film of Example 1. From this figure, it can be confirmed that the coercive force does not deteriorate in the soft magnetic thin film in which the easy magnetization axis is induced in a direction non-parallel to the film surface. In particular, the soft magnetic thin film obtained under the condition of α = 90 ° C. has a very small coercive force of 1 mOe or less.
[0038]
FIG. 10 shows the dependency of the high-frequency permeability imaginary part μ ″ on the high-frequency permeability real part μ ′ when the magnetic thin films of Example 1 and Comparative Example 2 are excited in the hard axis direction at a frequency of 10 MHz. In the figure, the solid line is Example 1, and the broken line is Comparative Example 2. This figure also shows calculated values of eddy current loss predicted from values such as resistivity and film thickness. As is apparent from this figure, the loss in Example 1 is smaller than that in Comparative Example 2, and there is almost no influence of hysteresis loss other than eddy current loss and other abnormal losses. From this, it can be confirmed that in the system in which the induced magnetic anisotropy inclined to the film surface according to the present invention is imparted, good magnetization difficult axis excitation is performed.
[0039]
Next, using the soft magnetic thin film (β = 50 °) of Example 1 and the soft magnetic thin film (β = 0 °) of Comparative Example 1 having induced magnetic anisotropy parallel to the film surface, thin film inductors were respectively formed. Produced. FIG. 11 shows the frequency characteristics of the inductance L and quality factor Q of these thin film inductors. In the figure, the solid line is Example 1, and the broken line is Comparative Example 1. As is clear from this figure, in Example 1, higher L is obtained than in Comparative Example 1, and no deterioration of Q is recognized.
[0040]
FIG. 14 shows the heat treatment temperature dependence of the in-plane anisotropic magnetic field Hk for the magnetic thin films of Example 2 (after two-step heat treatment) and Comparative Example 1. In the figure, the solid line is Example 2, and the broken line is Comparative Example 1. Although an in-plane anisotropic magnetic field Hk tends to decrease with increasing heat treatment temperature, Example 2 has a smaller in-plane anisotropic magnetic field than Comparative Example 1.
[0041]
FIG. 15 shows the heat treatment temperature dependence of the coercive force Hc in the in-plane hard axis direction for the magnetic thin films of Example 2 (after two-step heat treatment) and Comparative Example 2. In the figure, the solid line is Example 2, and the broken line is Comparative Example 2. In Example 2, Hc decreases as the heat treatment temperature increases. On the other hand, in Comparative Example 2, Hc increases as the heat treatment temperature increases. When an ideal single magnetic domain is excited in the hard axis direction, no coercive force is generated in the rotational magnetization process. Therefore, it is estimated that the increase in coercive force in Comparative Example 2 corresponds to an increase in the amount of local anisotropic dispersion.
14 and 15, it can be seen that in Example 2, the in-plane anisotropic magnetic field can be reduced while avoiding an increase in coercive force.
[0042]
FIG. 16 shows the dependence of tan δ on the high-frequency permeability real part μ ′ when the magnetic thin films of Example 2 (after two-stage heat treatment) and Comparative Example 2 are excited in the hard axis direction at a frequency of 10 MHz. In the figure, the solid line is Example 2, and the broken line is Comparative Example 2. As is apparent from this figure, the loss in Example 2 is smaller than that in Comparative Example 2. Further, in Comparative Example 2, hysteresis loss at high frequencies is increased due to the increase in the coercive force described above.
[0043]
In the above embodiment, heat treatment is performed after the magnetic thin film is formed. However, by forming the magnetic thin film in a DC magnetic field that is non-parallel to the substrate surface, an easy magnetization axis that is non-parallel to the film surface is formed. May be.
[0044]
【The invention's effect】
As described above in detail, according to the present invention, a soft magnetic thin film exhibiting high permeability and low loss at a high frequency can be provided, and can be effectively applied to planar magnetic elements such as planar inductors and planar transformers.
[Brief description of the drawings]
FIG. 1A is a perspective view showing a magnetic thin film having an easy axis of magnetization in a direction forming an angle β with respect to a film surface according to the present invention, and FIG. 1B is a diagram showing polar coordinates of magnetization vectors.
2A is an explanatory diagram showing the direction of a magnetization vector, and FIG. 2B is an explanatory diagram showing the direction of an effective magnetic field.
FIG. 3 is an explanatory diagram showing a change in the direction of the easy magnetization axis of induced magnetic anisotropy due to a directional regular arrangement with time when heat treatment is performed in a DC magnetic field in a direction perpendicular to the film surface of a magnetic thin film.
FIG. 4 is a graph showing the dependence of the magnetic thin film according to the present invention on the effective magnetic field angle β during K pl / K 0 heat treatment.
FIG. 5 is a view showing a control range of the magnitude of in-plane magnetic anisotropy energy for a magnetic thin film according to the present invention and a conventional magnetic thin film heat-treated in an in-plane DC magnetic field.
FIG. 6 is a diagram showing the frequency characteristics of the real part and the imaginary part of the complex permeability for the magnetic thin film according to the present invention and the conventional magnetic thin film subjected to heat treatment in an in-plane rotating magnetic field.
7 is a graph showing the dependence of the in-plane anisotropic magnetic field Hk on the applied magnetic field angle α during the heat treatment for the magnetic thin film of Example 1. FIG.
FIG. 8 is a graph showing the dependence of the in-plane anisotropic magnetic field Hk on the effective magnetic field angle β during heat treatment for the magnetic thin film of Example 1.
9 is a graph showing the dependence of the coercive force Hc in the in-plane hard axis direction on the applied magnetic field angle α for the magnetic thin film of Example 1. FIG.
FIG. 10 is a diagram showing the dependence of the high-frequency permeability imaginary part μ ″ on the high-frequency permeability real part μ ′ when the magnetic thin films of Example 1 and Comparative Example 2 are excited in the hard axis direction at a frequency of 10 MHz.
11 is a graph showing frequency characteristics of inductance L and quality factor Q of a thin film inductor manufactured using the magnetic thin film of Example 1 and Comparative Example 1. FIG.
FIG. 12 is a diagram showing a magnetization curve in the hard axis direction after the first stage heat treatment for the magnetic thin film of Example 2.
FIG. 13 is a diagram showing a magnetization curve in the easy axis direction after the first heat treatment of the magnetic thin film of Example 2.
14 is a graph showing the heat treatment temperature dependence of the in-plane anisotropic magnetic field Hk for the magnetic thin films of Example 2 and Comparative Example 1. FIG.
15 is a graph showing the heat treatment temperature dependence of the coercive force Hc in the in-plane hard axis direction for the magnetic thin films of Example 2 and Comparative Example 2. FIG.
FIG. 16 is a graph showing the dependence of tan δ on the high-frequency permeability real part μ ′ when the magnetic thin films of Example 2 and Comparative Example 2 are excited in the hard axis direction at a frequency of 10 MHz.
Claims (2)
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| JP19961992A JP3742116B2 (en) | 1992-07-27 | 1992-07-27 | Method for controlling magnetic anisotropy of magnetic thin film |
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