JP2004055754A - Magnetoresistive effect element and magnetic memory device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetoresistive effect element having proper magnetic characteristics and a magnetic memory device, provided with the magnetoresistive effect element and securing a while margin for a selective recording, by suppressing repeated variations of turnover magnetic field of a free of magnetizing layer. <P>SOLUTION: The magnetoresistive effect element 1, in which a pair of ferromagnetic layers 5, 7 are made to face an intermediate layer 6 and which is constituted to obtain the change of magnetoresistance by conducting an electric current so as to be orthogonal to a film surface, while one of the ferromagnetic layer is formed so as to be a magnetization fixing layer 5 and the other ferromagnetic layer is formed freely magnetized layer 7, is constituted so that the exchange stiffness constant A [erg/cm], saturated magnetizing Ms [emu/cc], the thickness t [nm] of a film and the width W [nm] of the magnetoresistive effect element 1 satisfy the formula: A/(t×Ms<SP>2</SP>) > W/50. Further, the magnetic memory device, equipped with the magnetoresistive effect element 1 of this configuration, a word line and a bit line, is configured. <P>COPYRIGHT: (C)2004,JPO

Description

の関係がある。この曲線は、Ｈｘ−Ｈｙ平面上でアステロイドを形成するため、アステロイド曲線と呼ばれる。
書き込み時のセル選択方法は、このアステロイド曲線を用いて説明することができる。
【００１５】
ワード書き込み線から発生する磁界が磁化容易軸方向とほぼ一致している構成のＭＲＡＭにおいては、ワード書き込み線から発生する磁界により、磁化自由層（情報記録層）の磁化を反転させて記録を行う。
しかしながら、ワード書き込み線から等距離に位置するメモリセルが複数個存在するため、ワード書き込み線に反転磁界以上の磁界を発生する量の電流を流してしまうと、これら等価な複数のメモリセルに同時に記録を行ってしまうことになる。
そこで、選択したいメモリセルに懸かるビット書き込み線に電流を流して磁化困難軸方向の磁界を発生させる。これにより、選択セルの反転磁界を小さくすることができる。このときの反転磁界をＨｃ（ｈ）、ビット書き込み線による磁界が０の場合の反転磁界をＨｃ（０）とすると、ワード書き込み線による磁界ＨをＨｃ（ｈ）＜Ｈ＜Ｈｃ（０）となるように設定することにより、選択的にメモリセルに記録することができる。
このようにして、記録時にセルを選択することができる。
【００１６】
このＭＲＡＭは、構造が単純であるため高集積化が容易であり、かつ磁気モーメントの回転により記録を行うために書き換え可能回数が大である。
また、アクセス時間についても、非常に高速であることが予想され、既にナノ秒台で動作可能であることが確認されている。
【００１７】
従って、ＭＲＡＭは特にランダムアクセス、書き換え可能回数大、高速動作の３点においてフラッシュメモリよりも優れ、またプロセス整合性の点でＦｅＲＡＭより優れている。さらに、ＤＲＡＭ並みの高集積度とＳＲＡＭ並みの高速性を両立できると期待されるため、システムＬＳＩ用混載メモリをすべて置き換える可能性も有している。
【００１８】
【発明が解決しようとする課題】
しかしながら、ＭＲＡＭは、ＤＲＡＭで用いられているようなＭＯＳスイッチ等による選択記録ではなく、直交磁場による選択記録という特徴的な書き込み方法を採用していることにより、固有の課題を有している。
【００１９】
特に、メモリセルを構成するＴＭＲ素子の磁気特性が素子毎にばらつくことや、同一素子を繰り返し使用した場合のばらつきが存在すると、アステロイド特性を使用した選択書き込みが困難になるという問題点がある。
従って、ＴＭＲ素子には、理想的なアステロイド曲線を描かせるための磁気特性も求められる。
【００２０】
ここで、ＴＭＲ素子を備えたＭＲＡＭにおける、理想的なアステロイド曲線を、図８Ａに示す。曲線に歪やばらつきがなく、きれいな曲線となっている。
【００２１】
これに対して、現実の磁気メモリ装置を測定して得られるアステロイド曲線は、図８Ｂのようになる。
この図８Ｂより、反転磁界にばらつきが存在していることがわかる。これは、メモリ装置を構成する多数のトンネル磁気抵抗効果素子（ＴＭＲ素子）において、各素子の反転磁界にばらつきがあるために、アステロイド曲線がばらついているからである。
【００２２】
図８Ｂのようなアステロイド曲線を有する磁気メモリ装置において、選択記録可能な領域は同図に示した通りである。Ｗ０は、“０”を選択記録することが可能な領域を示し、Ｗ１は“１”を選択記録することが可能な領域を示している。
アステロイド曲線にばらつきがあるため、Ｗ１の領域に比較してＷ０の領域が狭くなっていることがわかる。
実際にＭＲＡＭとして動作させるためには、“０”と“１”を共に選択記録できるようにする必要がある。
従って、選択記録のマージンを充分確保できるように、Ｗ０の領域とＷ１の領域とが、いずれも充分広い範囲を有することが求められる。
【００２３】
そして、図８Ｂより明らかなように、選択記録のマージンを広く確保するためには、アステロイド曲線のばらつき、即ち各メモリセルを構成するＴＭＲ素子の反転磁界のばらつきを抑制することが重要である。
【００２４】
反転磁界のばらつきには種々の起源があり、例えば材料の不均一性やプロセス精度に起因するものもあるが、より本質的には磁化反転そのものが必ずしも同じエネルギー状態を経由して起こるものではないという事実がある。これはＭＲＡＭを構成する一つ一つのビットの反転磁界を繰り返し測定した場合に、必ずしもその値が一定とならず、ある分散（繰り返しばらつきと呼ぶ）を有することにより示される。
従って、反転磁界ばらつきの抑制をするために、この繰り返しばらつきを抑制することが求められる。
【００２５】
上述した問題の解決のために、本発明においては、磁化自由層の反転磁界の繰り返しばらつきを抑制することにより、良好な磁気特性を有する磁気抵抗効果素子、並びにこの磁気抵抗効果素子を備えて選択記録のマージンを広く確保することができる磁気メモリ装置を提供するものである。
【００２６】
【課題を解決するための手段】
本発明の磁気抵抗効果素子は、対の強磁性層が中間層を介して対向されてなり、膜面に対して垂直に電流を流すことによって磁気抵抗変化を得る構成あって、対の強磁性層の一方が磁化固定層であり、もう一方が磁化自由層であり、磁化自由層に用いられる材料の交換スティフネス定数Ａ［ｅｒｇ／ｃｍ］、飽和磁化Ｍｓ［ｅｍｕ／ｃｃ］、膜厚ｔ［ｎｍ］、並びに磁気抵抗効果素子の幅Ｗ［ｎｍ］が、式Ａ／（ｔ・Ｍｓ^２）＞Ｗ／５０を満たすものである。
【００２７】
本発明の磁気メモリ装置は、対の強磁性層が中間層を介して対向されてなり、膜面に対して垂直に電流を流すことによって磁気抵抗変化を得る構成の磁気抵抗効果素子と、この磁気抵抗効果素子を厚み方向に挟むワード線及びビット線とを備え、対の強磁性層のうち一方が磁化固定層であり、他方が磁化自由層であり、磁化自由層に用いられる材料の交換スティフネス定数Ａ［ｅｒｇ／ｃｍ］、飽和磁化Ｍｓ［ｅｍｕ／ｃｃ］、膜厚ｔ［ｎｍ］、並びに磁気抵抗効果素子の幅Ｗ［ｎｍ］が、式Ａ／（ｔ・Ｍｓ^２）＞Ｗ／５０を満たすものである。
【００２８】
ここで、上記式に用いられる交換スティフネス定数Ａは、以下に説明されるように定義されるものである（裳華房刊「強磁性体の物理（下）」（近角聡信著）を参照）。
【００２９】
スピンＳ_ｉとスピンＳ_ｊとが角度をなす場合に、これらのスピンの交換エネルギーｗ_ｉｊは、交換積分をＪとして、

で表される。
Ｓ_ｉとＳ_ｊのなす角度φが小さく、Ｓ_ｉとＳ_ｊの大きさが等しいときには、スピンの大きさをＳとして、式（３）は、

と書くことができる。これはφが小さいときに

となるからである。式（４）から交換エネルギーが角度φの２乗に比例して増すことがわかり、バネ等の弾性体の弾性エネルギーが変形の２乗に比例して増すことと類似している。
【００３０】
そして、磁性体内のスピン分布が与えられたとき、そこに貯えられる交換エネルギーは、そのスピン分布によって記述することができる。ある格子点にあるスピンＳ_ｉの向きに平行な単位ベクトルをａ、単位胞に属する原子の数をｎとしたとき、強磁性体内のスピンの単位体積当たりの交換エネルギーＥ_ｅｘは、

と表される。
他方（ａ・ａ）＝１であるから、この両辺をｘで２回微分することにより、次式（７）の関係を得る。ｙとｚについても同様である。

これを用いると、式（６）は、

と変形される。
このうちＡはＡ＝ｎＪＳ^２／ａで定義されるものであり、ａのｘ、ｙ、ｚによる偏微分は弾性体の歪に相当する量となっていることから、式（８）の交換エネルギーの式は、弾性エネルギーが歪テンソルの２次形式で与えられるのと類似している。
このことから、弾性体の変形による弾性エネルギーの式における「スティフネス定数」にならって、磁性体におけるこのＡを交換スティフネス定数（ｅｘｃｈａｎｇｅ
ｓｔｉｆｆｎｅｓｓ　ｃｏｎｓｔａｎｔ　）と称している。
【００３１】
上述の本発明の磁気抵抗効果素子の構成によれば、磁化自由層に用いられる材料の交換スティフネス定数Ａ［ｅｒｇ／ｃｍ］、飽和磁化Ｍｓ［ｅｍｕ／ｃｃ］、膜厚ｔ［ｎｍ］、並びに磁気抵抗効果素子の幅Ｗ［ｎｍ］が、式Ａ／（ｔ・Ｍｓ^２）＞Ｗ／５０を満たす構成となっていることにより、反転磁界の繰り返しばらつきを抑制することが可能になる。
【００３２】
上述の本発明の磁気メモリ装置の構成によれば、上述した本発明の磁気抵抗効果素子を備えていることにより、磁化自由層の反転磁界の繰り返しばらつきが低減されているため、選択記録を行うことを可能にする磁界の範囲（磁化容易軸方向の磁界及び磁化困難軸方向の磁界）を広くすることができる。
【００３３】
【発明の実施の形態】
本発明は、対の強磁性層が中間層を介して対向されてなり、膜面に対して垂直に電流を流すことによって磁気抵抗変化を得る構成の磁気抵抗効果素子であって、対の強磁性層の一方が磁化固定層であり、もう一方が磁化自由層であり、磁化自由層に用いられる材料の交換スティフネス定数Ａ［ｅｒｇ／ｃｍ］、飽和磁化Ｍｓ［ｅｍｕ／ｃｃ］、膜厚ｔ［ｎｍ］、並びに磁気抵抗効果素子の幅Ｗ［ｎｍ］が、式Ａ／（ｔ・Ｍｓ^２）＞Ｗ／５０を満たす磁気抵抗効果素子である。
【００３４】
また本発明は、上記磁気抵抗効果素子において、中間層として絶縁体もしくは半導体から成るトンネルバリア層を用いたトンネル磁気抵抗効果素子である構成とする。
【００３５】
また本発明は、上記磁気抵抗効果素子において、中間層として導電層を用いた巨大磁気抵抗効果素子である
【００３６】
また本発明は、上記磁気抵抗効果素子において、積層フェリ構造を有する構成とする。
【００３７】
本発明は、対の強磁性層が中間層を介して対向されてなり、膜面に対して垂直に電流を流すことによって磁気抵抗変化を得る構成の磁気抵抗効果素子と、この磁気抵抗効果素子を厚み方向に挟むワード線及びビット線とを備え、対の強磁性層のうち一方が磁化固定層であり、他方が磁化自由層であり、磁化自由層に用いられる材料の交換スティフネス定数Ａ［ｅｒｇ／ｃｍ］、飽和磁化Ｍｓ［ｅｍｕ／ｃｃ］、膜厚ｔ［ｎｍ］、並びに磁気抵抗効果素子の幅Ｗ［ｎｍ］が、式Ａ／（ｔ・Ｍｓ^２）＞Ｗ／５０を満たす磁気メモリ装置である。
【００３８】
また本発明は、上記磁気メモリ装置において、磁気抵抗効果素子は、中間層として絶縁体もしくは半導体から成るトンネルバリア層を用いたトンネル磁気抵抗効果素子である構成とする。
【００３９】
また本発明は、上記磁気メモリ装置において、磁気抵抗効果素子は、中間層として導電層を用いた巨大磁気抵抗効果素子である構成とする。
【００４０】
また本発明は、上記磁気メモリ装置において、磁気抵抗効果素子が積層フェリ構造を有する構成とする。
【００４１】
本発明の磁気抵抗効果素子の一実施の形態の概略構成図を図１に示す。この図１に示す実施の形態は、本発明をトンネル磁気抵抗効果素子（以下、ＴＭＲ素子と称する。）に適用した場合を示している。
【００４２】
このＴＭＲ素子１は、シリコン等からなる基板２上に、下地層３と、反強磁性層４と、強磁性層である磁化固定層５と、トンネルバリア層６と、強磁性層である磁化自由層７と、トップコート層８とがこの順に積層されて構成されている。
即ち、強磁性層の一方が磁化固定層５とされ、他方が磁化自由層７とされた、いわゆるスピンバルブ型のＴＭＲ素子を構成しており、一対の強磁性層である磁化固定層５と磁化自由層７とでトンネルバリア層６を挟み込むことにより、強磁性トンネル接合を形成している。
そして、磁気メモリ素子等にこのＴＭＲ素子１を適用した場合には、磁化自由層７が情報記録層となり、そこに情報が記録される。
【００４３】
反強磁性層４は、強磁性層の一方である磁化固定層５と反強磁性的に結合することにより、書き込みのための電流磁界によっても磁化固定層５の磁化を反転させず、磁化固定層５の磁化の向きを常に一定とするための層である。即ち、図１に示すＴＭＲ素子１においては、他方の強磁性層である磁化自由層７だけを外部磁場等によって磁化反転させる。磁化自由層７は、ＴＭＲ素子１を例えば磁気メモリ装置等に適用した場合に情報が記録される層となるため、情報記録層とも称される。
反強磁性層４を構成する材料としては、Ｆｅ、Ｎｉ、Ｐｔ、Ｉｒ、Ｒｈ等を含むＭｎ合金、Ｃｏ酸化物、Ｎｉ酸化物等を使用することができる。
【００４４】
図１に示すスピンバルブ型のＴＭＲ素子１においては、磁化固定層５は、反強磁性層４と反強磁性的に結合することによって磁化の向きを一定とされる。このため、書き込みの際の電流磁界によっても磁化固定層５の磁化は反転しない。
【００４５】
トンネルバリア層６は、磁化固定層５と磁化自由層７とを磁気的に分離するとともに、トンネル電流を流すための層である。
トンネルバリア層６を構成する材料としては、例えばＡｌ、Ｍｇ、Ｓ_ｉ、Ｌｉ、Ｃａ等の酸化物、窒化物、ハロゲン化物等の絶縁材料を使用することができる。
【００４６】
このようなトンネルバリア層６は、スパッタリング法や蒸着法等によって成膜された金属膜を、酸化又は窒化することにより得ることができる。
また、有機金属と、酸素、オゾン、窒素、ハロゲン、ハロゲン化ガス等とを用いるＣＶＤ法によっても得ることができる。
【００４７】
本実施の形態においては、特に、ＴＭＲ素子１を、ＴＭＲ素子１の素子幅Ｗ［ｎｍ］と、磁化自由層７に用いられる強磁性材料の交換スティフネス定数Ａ［ｅｒｇ／ｃｍ］、飽和磁化Ｍｓ［ｅｍｕ／ｃｃ］、膜厚ｔ［ｎｍ］が、次式（１０）を満たす構成とする。
Ａ／（ｔ・Ｍｓ^２）＞Ｗ／５０　（１０）
【００４８】
このように式（１０）を満たす強磁性材料としては、例えばＣｏＦｅＢを挙げることができる。
このＣｏＦｅＢは、組成によって他の特性を大きく損なうことなく飽和磁化Ｍｓ及び交換スティフネス定数Ａを制御できるという観点で、好ましい材料である。
磁化自由層７にＣｏＦｅＢを用いた場合には、後述する範囲の組成とすることにより、ＴＭＲ素子１が式（１０）を満たすようにすることが可能になる。
【００４９】
また、その他の材料系の強磁性材料でも、ＴＭＲ素子１が式（１０）を満たすように構成することが可能な材料であれば、磁化自由層７に使用することが可能である。
この場合でも、組成によって飽和磁化Ｍｓや交換スティフネス定数Ａを制御することが容易な材料系、例えばＣｏＦｅやＣｏＦｅに種々の添加物（Ｃ，Ｓｉ，Ｐ，Ｇａ，Ｇｅ，Ｚｒ，Ｈｆ，Ｙ，Ｔｉ，Ｎｂ，Ｍｎ，Ｃｒ，Ｎｉ，Ｖ，希土類等）を添加したもの、ＮｉＦｅ，ＣｏＮｉもしくはＮｉＦｅ，ＣｏＮｉを主体としてＢ乃至上記添加物を加えたものを使用することが望ましい。
【００５０】
上述の実施の形態のＴＭＲ素子１によれば、ＴＭＲ素子１が式（１０）を満たすことにより、反転磁界（磁化自由層７の磁化が反転する磁界）の繰り返しばらつきを低減することが可能となる。
【００５１】
これにより、例えば多数のＴＭＲ素子を有して成る磁気メモリ装置にＴＭＲ素子１を適用した場合に、多数のＴＭＲ素子１について反転磁界のばらつきを抑制することにつながり、選択記録のマージンを広くすることができる。
また、ＴＭＲ素子を有して成る磁気ヘッドや磁気センサに適用した場合には、反転磁界の設計値からのずれを抑制して、製造歩留まりを向上することや動作不良を防止することが可能になる。
【００５２】
尚、本発明においては、図１に示すような磁化固定層５及び磁化自由層７のそれぞれが単層から構成されたＴＭＲ素子１に限定されない。
例えば図２に示すように、磁化固定層５が、第１の磁化固定層５ａと第２の磁化固定層５ｂとで非磁性導電体層５ｃを挟み込んでなる積層フェリ構造とされる場合であっても、本発明の効果を得ることができる。
【００５３】
図２に示すＴＭＲ素子１０では、第１の磁化固定層５ａが反強磁性層４と接しており、これらの層間に働く交換相互作用によって、第１の磁化固定層５ａは強い一方向の磁気異方性を持つ。また、第２の磁化固定層５ｂは、トンネルバリア層６を介して磁化自由層７と対向し、スピンの向きが磁化自由層７と比較され直接ＭＲ比に関わる強磁性層となるため、参照層とも称される。
【００５４】
積層フェリ構造の非磁性導電体層５ｃに用いられる材料としては、例えばＲｕ、Ｃｕ、Ｃｒ、Ａｕ、Ａｇ等が挙げられる。図２のＴＭＲ素子１０において、その他の層は図１に示したＴＭＲ素子１とほぼ同様の構成であるため、図１と同じ符号を付して詳細な説明を省略する。
【００５５】
この積層フェリ構造を有するＴＭＲ素子１０においても、式（１０）を満たす構成とすることにより、図１に示したＴＭＲ素子１と同様に、反転磁界（磁化自由層７の磁化が反転する磁界）の繰り返しばらつきを低減することが可能となる。
【００５６】
尚、上述の実施の形態では、磁気抵抗効果素子としてＴＭＲ素子（トンネル磁気抵抗効果素子）１，１０を用いたが、本発明は、一対の強磁性層が中間層を介して対向され、膜面に対して垂直に電流を流して磁気抵抗変化を得る構成を有するその他の磁気抵抗効果素子にも適用することができる。
例えば中間層としてＣｕ等の非磁性導電層を用いた巨大磁気抵抗効果素子（ＧＭＲ素子）で、膜面に対して垂直に電流を流して磁気抵抗効果を得る構成、即ちいわゆるＣＰＰ型のＧＭＲ素子にも本発明を適用することができる。
【００５７】
さらに、磁化固定層や反強磁性体の材料、磁化固定層側における積層フェリ構造の有無等は、本発明の本質を損なわない限り種々の変形が可能である。
【００５８】
上述のようなＴＭＲ素子１，１０等の磁気抵抗効果素子は、例えばＭＲＡＭ等の磁気メモリ装置に用いられて好適である。以下、本発明のＴＭＲ素子を用いたＭＲＡＭについて、図を参照しながら説明する。
【００５９】
本発明のＴＭＲ素子を有するクロスポイント型のＭＲＡＭアレイを、図３に示す。このＭＲＡＭアレイは、複数のワード線ＷＬと、これらワード線ＷＬと直交する複数のビット線ＢＬとを有し、ワード線ＷＬとビット線ＢＬとの交点に本発明のＴＭＲ素子が配置されて成るメモリセル１１とを有する。即ち、このＭＲＡＭアレイでは、３×３のメモリセル１１がマトリクス状に配置される。
【００６０】
尚、ＭＲＡＭアレイに用いられるＴＭＲ素子としては、図１に示したＴＭＲ素子１に限定されず、積層フェリ構造を有する図２に示すＴＭＲ素子１０等、膜面に対して垂直に電流を流すことによって磁気抵抗変化を得る構成の磁気抵抗効果素子において式（１０）を満たす構成であればいかなる構成であっても構わない。
【００６１】
また、メモリ素子に多数あるメモリセルから１つのメモリセルを取り出して、断面構造を図４に示す。
各メモリセル１１は、図４に示すように、例えばシリコン基板１２上に、ゲート電極１３、ソース領域１４及びドレイン領域１５からなるトランジスタ１６を有する。ゲート電極１３は、読み出し用のワード線ＷＬ１を構成している。ゲート電極１３上には、絶縁層を介して書き込み用のワード線（前述したワード書き込み線に相当する）ＷＬ２が形成されている。トランジスタ１６のドレイン領域１５にはコンタクトメタル１７が接続され、さらにコンタクトメタル１７には下地層１８が接続されている。この下地層１８上の書き込み用のワード線ＷＬ２の上方に対応する位置に、本発明のＴＭＲ素子１が形成されている。このＴＭＲ素子１上に、ワード線ＷＬ１及びＷＬ２と直交するビット線（前述したビット書き込み線に相当する）ＢＬが形成されている。
また、各ワード線ＷＬ１，ＷＬ２とＴＭＲ素子１とを絶縁するための層間絶縁膜１９及び絶縁膜２０と、全体を保護するパッシベーション膜（図示せず）等を有して成る。
【００６２】
このＭＲＡＭは、式（１０）を満たす構成のＴＭＲ素子１を用いているので、各メモリセル１１の反転磁界の繰り返しばらつきを低減することができる。
これにより、選択記録を行うための反転磁界のマージンを充分に確保することができる。
【００６３】
（実施例）
以下、本発明を適用した具体的な実施例について、実験結果に基づいて説明する。
図２に示した、磁化固定層５に積層フェリ構造５ａ，５ｂ，５ｃを有するＴＭＲ素子１０について、磁気特性を変化させるために磁化自由層７を種々の組成に変更したサンプルを作製した。具体的には、磁化自由層７の組成を（ＦｅｘＣｏ１−ｘ）１−ｙＢｙとして、ｘ及びｙの値（原子％）を表１に示すように変化させた。また、各サンプルのＴＭＲ素子１０を有する図３及び図４に示した構成の磁気メモリ装置を作製した。
【００６４】
＜サンプル１＞
まず、内部が超高真空領域まで排気されたマグネトロンスパッタ装置内で、基板上に、Ｔａ膜を膜厚３ｎｍ、ＰｔＭｎ膜（反強磁性層４）を膜厚３０ｎｍ、ＣｏＦｅ膜（第１の磁化固定層５ａ）を膜厚１．５ｎｍ、Ｒｕ膜（非磁性導電体層５ｃ）を膜厚０．８ｎｍ、ＣｏＦｅ膜（第２の磁化固定層５ｂ）を膜厚２ｎｍ、Ａｌ膜を例えば膜厚１ｎｍ、というように順次成膜した。
尚、第１の磁化固定層５ａ及び第２の磁化固定層（参照層）５ｂのＣｏＦｅ膜は、ターゲット組成をＣｏ７５Ｆｅ２５（原子％）として成膜した。
【００６５】
次に、Ａｌ膜を純酸素中でプラズマ酸化させて、均一なＡｌ酸化膜を得て、ＴＭＲ素子のトンネルバリア層６を形成した。
【００６６】
続いて、マグネトロンスパッタ装置内で、磁化自由層７を膜厚１．５〜６ｎｍ、Ｔａ膜を膜厚５ｎｍ、それぞれ成膜した。
尚、磁化自由層７の組成は、ｘ＝０，ｙ＝５即ちＣｏ９５Ｂ５（原子％）とした。
【００６７】
次に、反強磁性層４のＰｔＭｎ膜を規則合金化するため、磁場中熱処理を行った。この磁場中熱処理の条件は、１０ｋＯｅの磁界中、２８０℃で１時間とした。
さらに、フォトリソグラフィとイオンミリングの組み合わせにより微細加工し、０．１μｍ×０．２μｍ〜０．６μｍ×１．２μｍの楕円形のＴＭＲ素子１０を得た。
【００６８】
＜サンプル２＞
磁化自由層７の組成を、ｘ＝１０，ｙ＝５即ち（Ｆｅ１０Ｃｏ９０）９５Ｂ５（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００６９】
＜サンプル３＞
磁化自由層７の組成を、ｘ＝２５，ｙ＝５即ち（Ｆｅ２５Ｃｏ７５）９５Ｂ５（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００７０】
＜サンプル４＞
磁化自由層７の組成を、ｘ＝５０，ｙ＝５即ち（Ｆｅ５０Ｃｏ５０）９５Ｂ５（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００７１】
＜サンプル５＞
磁化自由層７の組成を、ｘ＝０，ｙ＝１０即ちＣｏ９０Ｂ１０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００７２】
＜サンプル６＞
磁化自由層７の組成を、ｘ＝５，ｙ＝１０即ち（Ｆｅ５Ｃｏ９５）９０Ｂ１０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００７３】
＜サンプル７＞
磁化自由層７の組成を、ｘ＝１０，ｙ＝１０即ち（Ｆｅ１０Ｃｏ９０）９０Ｂ１０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００７４】
＜サンプル８＞
磁化自由層７の組成を、ｘ＝２５，ｙ＝１０即ち（Ｆｅ２５Ｃｏ７５）９０Ｂ１０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００７５】
＜サンプル９＞
磁化自由層７の組成を、ｘ＝３０，ｙ＝１０即ち（Ｆｅ３０Ｃｏ７０）９０Ｂ１０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００７６】
＜サンプル１０＞
磁化自由層７の組成を、ｘ＝３５，ｙ＝１０即ち（Ｆｅ３５Ｃｏ６５）９０Ｂ１０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００７７】
＜サンプル１１＞
磁化自由層７の組成を、ｘ＝４５，ｙ＝１０即ち（Ｆｅ４５Ｃｏ５５）９０Ｂ１０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００７８】
＜サンプル１２＞
磁化自由層７の組成を、ｘ＝５０，ｙ＝１０即ち（Ｆｅ５０Ｃｏ５０）９０Ｂ１０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００７９】
＜サンプル１３＞
磁化自由層７の組成を、ｘ＝０，ｙ＝２０即ちＣｏ８０Ｂ２０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００８０】
＜サンプル１４＞
磁化自由層７の組成を、ｘ＝５，ｙ＝２０即ち（Ｆｅ５Ｃｏ９５）８０Ｂ２０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００８１】
＜サンプル１５＞
磁化自由層７の組成を、ｘ＝１０，ｙ＝２０即ち（Ｆｅ１０Ｃｏ９０）８０Ｂ２０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００８２】
＜サンプル１６＞
磁化自由層７の組成を、ｘ＝２５，ｙ＝２０即ち（Ｆｅ２５Ｃｏ７５）８０Ｂ２０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００８３】
＜サンプル１７＞
磁化自由層７の組成を、ｘ＝３０，ｙ＝２０即ち（Ｆｅ３０Ｃｏ７０）８０Ｂ２０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００８４】
＜サンプル１８＞
磁化自由層７の組成を、ｘ＝３５，ｙ＝２０即ち（Ｆｅ３５Ｃｏ６５）８０Ｂ２０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００８５】
＜サンプル１９＞
磁化自由層７の組成を、ｘ＝４５，ｙ＝２０即ち（Ｆｅ４５Ｃｏ５５）８０Ｂ２０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００８６】
＜サンプル２０＞
磁化自由層７の組成を、ｘ＝５０，ｙ＝２０即ち（Ｆｅ５０Ｃｏ５０）８０Ｂ２０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００８７】
＜サンプル２１＞
磁化自由層７の組成を、ｘ＝０，ｙ＝３０即ちＣｏ７０Ｂ３０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００８８】
＜サンプル２２＞
磁化自由層７の組成を、ｘ＝５，ｙ＝３０即ち（Ｆｅ５Ｃｏ９５）７０Ｂ３０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００８９】
＜サンプル２３＞
磁化自由層７の組成を、ｘ＝１０，ｙ＝３０即ち（Ｆｅ１０Ｃｏ９０）７０Ｂ３０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００９０】
＜サンプル２４＞
磁化自由層７の組成を、ｘ＝２５，ｙ＝３０即ち（Ｆｅ２５Ｃｏ７５）７０Ｂ３０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００９１】
＜サンプル２５＞
磁化自由層７の組成を、ｘ＝３０，ｙ＝３０即ち（Ｆｅ３０Ｃｏ７０）７０Ｂ３０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００９２】
＜サンプル２６＞
磁化自由層７の組成を、ｘ＝３５，ｙ＝３０即ち（Ｆｅ３５Ｃｏ６５）７０Ｂ３０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００９３】
＜サンプル２７＞
磁化自由層７の組成を、ｘ＝４０，ｙ＝３０即ち（Ｆｅ４０Ｃｏ６０）７０Ｂ３０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００９４】
＜サンプル２８＞
磁化自由層７の組成を、ｘ＝０，ｙ＝４０即ちＣｏ６０Ｂ４０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００９５】
＜サンプル２９＞
磁化自由層７の組成を、ｘ＝１０，ｙ＝４０即ち（Ｆｅ１０Ｃｏ９０）６０Ｂ４０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００９６】
＜サンプル３０＞
磁化自由層７の組成を、ｘ＝２０，ｙ＝４０即ち（Ｆｅ２０Ｃｏ８０）６０Ｂ４０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００９７】
＜サンプル３１＞
磁化自由層７の組成を、ｘ＝２５，ｙ＝４０即ち（Ｆｅ２５Ｃｏ７５）６０Ｂ４０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００９８】
＜サンプル３２＞
磁化自由層７の組成を、ｘ＝３０，ｙ＝４０即ち（Ｆｅ３０Ｃｏ７０）６０Ｂ４０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【００９９】
＜サンプル３３＞
磁化自由層７の組成を、ｘ＝３５，ｙ＝４０即ち（Ｆｅ３５Ｃｏ６５）６０Ｂ４０（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【０１００】
＜サンプル３４＞
磁化自由層７の組成を、ｘ＝０，ｙ＝４５即ちＣｏ５５Ｂ４５（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【０１０１】
＜サンプル３５＞
磁化自由層７の組成を、ｘ＝５，ｙ＝４５即ち（Ｆｅ５Ｃｏ９５）５５Ｂ４５（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【０１０２】
＜サンプル３６＞
磁化自由層７の組成を、ｘ＝１０，ｙ＝４５即ち（Ｆｅ１０Ｃｏ９０）５５Ｂ４５（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【０１０３】
＜サンプル３７＞
磁化自由層７の組成を、ｘ＝２５，ｙ＝４５即ち（Ｆｅ２５Ｃｏ７５）５５Ｂ４５（原子％）とした以外はサンプル１と同様にしてＴＭＲ素子１０を得た。
【０１０４】
また、各サンプル１〜サンプル３７のＴＭＲ素子１０から、それぞれＴＭＲ素子１０を１ｋｂｉｔ（キロビット）有する、図３及び図４に示した構成のＭＲＡＭ（磁気メモリ装置）を作製した。
【０１０５】
上述した反転磁界の繰り返しばらつきの抑制効果は、磁化自由層材料の交換スティフネス定数Ａ及び飽和磁化Ｍｓ、膜厚ｔ、並びにＴＭＲ素子のサイズ、具体的にはＴＭＲ素子の素子幅Ｗとの間に、前述した式（１０）の関係が成立する場合に起こる。
【０１０６】
まず、ＣｏＦｅＢの組成を変えたサンプル１〜サンプル３７において、Ｆｅの含有量（原子％）と、Ｂの含有量（原子％）と、磁化自由層の膜厚を１．５ｎｍ（タイプＩ）としたときのＡ／Ｍｓ^２の値と、タイプＩの構成のＴＭＲ素子を有するメモリ装置の反転磁界の繰り返しばらつきＳＦＤ（標準偏差σ／平均値ａｖｅ．）の値とを、それぞれ表１に示す。
交換スティフネス定数Ａはスピン波共鳴により、飽和磁化Ｍｓは振動試料型磁力計により、それぞれ得た値である。
【０１０７】
【表１】

【０１０８】
表１の結果から、上述した反転磁界の繰り返しばらつきと、磁化自由層７のＡ／Ｍｓ^２とがよく対応していることがわかる。
即ち磁化自由層７のＡ／Ｍｓ^２が小さいサンプルは、ＳＦＤ即ち反転磁界の繰り返しばらつきも大きくなっている。
【０１０９】
表１の測定結果に基づき、Ａ／Ｍｓ^２の値と反転磁界の繰り返しばらつき（ＳＦＤ）の関係を図５に示す。
図５から、磁化自由層７のＡ／Ｍｓ^２が小さいと、ＳＦＤ即ち反転磁界の繰り返しばらつきも大きくなっていることがわかる。
【０１１０】
一般のＭＲＡＭにおいて、ビット線やワード線から発生する磁界のばらつきまでも考慮に入れると、反転磁界のばらつきは、標準偏差／平均値で５％以下に抑える必要がある。さらに微細加工プロセス等のばらつきを考慮すると、単一のＴＭＲ素子では反転磁界の繰り返しばらつきを２％以下に抑えなくてはならない。
このように反転磁界の繰り返しばらつきを２％以下にするためには、図５から、Ａ／Ｍｓ^２の値は３×１０^−１４ｃｍ^２以上でなければならないことがわかる。
【０１１１】
また、図６は、同じく表１に示した測定結果に基づき、反転磁界の繰り返しばらつきを２％以下にすることができるＣｏＦｅＢの組成範囲を、状態図内に斜線を付して示したものである。尚、図中の●印は各サンプル１〜３７の組成を示している。
【０１１２】
さらに、より一般的な関係を求めるために、磁化自由層の膜厚を、１．５ｎｍ、３ｎｍ、６ｎｍと変えて、また素子の短軸長さ（素子幅Ｗに相当する）を０．１μｍ、０．２５μｍ、０．４μｍ、０．５μｍ、０．６μｍと変えてＴＭＲ素子１０を作製し、同様に交換スティフネス定数Ａと飽和磁化Ｍｓ、反転磁界の繰り返しばらつきの測定を行った。
【０１１３】
その結果、磁化自由層の膜厚が１．５ｎｍで、ＴＭＲ素子１０の短軸長さが０．１μｍの場合にはＡ／Ｍｓ^２の臨界値が３×１０^−１４ｃｍ^２であったのが、ＴＭＲ素子１０の短軸長さ及び磁化自由層の膜厚に依存してＡ／Ｍｓ^２の臨界値が変化することがわかった。
この関係を図７に示す。図中△印は磁化自由層の膜厚が１．５ｎｍの場合、●印は磁化自由層の膜厚が３ｎｍの場合、○印は磁化自由層の膜厚が６ｎｍの場合を示している。
【０１１４】
図７より、ＴＭＲ素子１０の短軸長さが長くなる即ちＴＭＲ素子１０が大きくなり、磁化自由層７が厚くなるに従って、臨界値が大きくなり、ほぼ直線的に変化することがわかる。
そして、図７から、ＴＭＲ素子の短軸長さＷと磁化自由層の膜厚ｔ、及びＡ／Ｍｓ^２の臨界値との間には次式の関係が成立することがわかる。
Ｃ・Ａ／Ｍｓ^２の臨界値＝Ｗ・ｔ（Ｃは定数）　（１１）
この比例定数Ｃを計算すると、表２のようになり、およそ５０となることがわかる。
従って、反転磁界の繰り返しばらつきを抑制するための条件は、
５０Ａ／Ｍｓ^２＞Ｗｔ　（１２）
となり、この式（１２）から前述した式（１０）即ち
Ａ／（ｔ・Ｍｓ^２）＞Ｗ／５０　（１０）
が導かれる。
【０１１５】
【表２】

【０１１６】
尚、本発明の磁気抵抗効果素子（ＴＭＲ素子等）は、前述した磁気メモリ装置のみならず、磁気ヘッド及びこの磁気ヘッドを搭載したハードディスクドライブや磁気センサ、集積回路チップ、さらにはパソコン、携帯端末、携帯電話を始めとする各種電子機器、電子機器等に適用することができる。
【０１１７】
本発明は、上述の実施の形態に限定されるものではなく、本発明の要旨を逸脱しない範囲でその他様々な構成が取り得る。
【０１１８】
【発明の効果】
上述の本発明の磁気抵抗効果素子によれば、磁化自由層の反転磁界の繰り返しばらつきが充分に抑えられる。
これにより、例えば磁気抵抗効果素子を有して成る磁気メモリ装置に適用した場合において、磁気メモリ装置全体においてメモリセルを構成する磁気抵抗効果素子の磁化自由層の半端磁界のばらつきを抑制することが可能となり、メモリセルの選択記録のマージンを拡大することができる。
また、例えば磁気抵抗効果素子を有して成る磁気ヘッドや磁気センサに適用した場合において、反転磁界の設計値からのずれを抑制して、製造歩留まりを向上することや動作不良を防止することが可能になる。
【０１１９】
また、本発明の磁気メモリ装置によれば、本発明の磁気抵抗効果素子を備えて構成されていることにより、磁気抵抗効果素子の反転磁界の繰り返しばらつきが抑制されているため、メモリセルの選択記録のマージンを広く確保することができ、安定して記録を行うことができる。
【図面の簡単な説明】
【図１】本発明の一実施の形態のＴＭＲ素子の概略構成図である。
【図２】積層フェリ構造を有するＴＭＲ素子の概略構成図である。
【図３】本発明のＴＭＲ素子をメモリセルとして有する、クロスポイント型ＭＲＡＭアレイの要部を示す概略構成図である。
【図４】図３に示すメモリセルの拡大断面図である。
【図５】Ａ／Ｍｓ^２と反転磁界の繰り返しばらつきとの関係を示す図である。
【図６】ＣｏＦｅＢ系における好ましい組成範囲を示す図である。
【図７】磁化自由層の膜厚及びＴＭＲ素子の短軸長さとＡ／Ｍｓ^２の臨界値との関係を示す図である。
【図８】Ａ　単一ＴＭＲ素子の理想的なアステロイド曲線を示した図である。
Ｂ　多数のＴＭＲ素子のアステロイド曲線を重ねて示した図である。
【符号の説明】
１，１０　トンネル磁気抵抗効果素子（ＴＭＲ素子）、２　基板、３　下地層、４　反強磁性層、５　磁化固定層、５ａ　第１の磁化固定層、５ｂ　第２の磁化固定層（参照層）、５ｃ　非磁性導電体層、６　トンネルバリア層、７　磁化自由層、１１　メモリセル、ＷＬ，ＷＬ１，ＷＬ２　ワード線、ＢＬ　ビット線[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magnetoresistive element and a magnetic memory device including the magnetoresistive element.
[0002]
[Prior art]
With the rapid spread of information and communication devices, especially small personal devices such as mobile terminals, devices such as memories and logics have higher performance such as higher integration, higher speed and lower power consumption. Has been requested. In particular, increasing the density and capacity of non-volatile memories has become increasingly important as a technology for replacing hard disks and optical disks, which cannot be reduced in size essentially due to the existence of movable parts.
[0003]
Examples of the nonvolatile memory include a flash memory using a semiconductor and an FRAM (Ferroelectric Random Access Memory) using a ferroelectric.
However, the flash memory has a drawback that the writing speed is as slow as the order of microsecond. On the other hand, it has been pointed out that the FRAM has a problem that the number of rewritable times is small.
[0004]
As a non-volatile memory which does not have these disadvantages, for example, an MRAM (Magnetic Random Access Memory) as described in “Wanget al., IEEE Trans. Magn. 33 (1997), 4498” has been noted. This is called a magnetic memory. This MRAM has a simple structure, so that high integration is easy, and since the recording is performed by rotating the magnetic moment, the number of rewritable times is large. The access time is also expected to be very fast, and it has already been confirmed that operation is possible on the order of nanoseconds.
[0005]
A magnetoresistive element, particularly a tunnel magnetoresistive (TMR) element, used in this MRAM is basically formed of a laminated structure of ferromagnetic layer / tunnel barrier layer / ferromagnetic layer. In this device, when an external magnetic field is applied between the ferromagnetic layers in a state where a constant current flows between the ferromagnetic layers, a magnetoresistance effect appears according to the relative angle of the magnetization of the two magnetic layers. When the magnetization directions of the two ferromagnetic layers are antiparallel, the resistance value is maximum, and when the magnetization directions are parallel, the resistance value is minimum. The function as a memory element is provided by creating an antiparallel state and a parallel state by an external magnetic field.
[0006]
In particular, in a spin valve type TMR element, one of the ferromagnetic layers is antiferromagnetically coupled to an adjacent antiferromagnetic layer to form a fixed magnetization layer in which the direction of magnetization is always constant. The other ferromagnetic layer is a magnetization free layer whose magnetization is easily inverted by an external magnetic field or the like. Then, this magnetization free layer becomes an information recording layer in the magnetic memory.
[0007]
In the spin valve type TMR element, the rate of change of the resistance value is represented by the following equation (1), where the spin polarizabilities of the ferromagnetic layers are P1 and P2.
2P1P2 / (1-P1P2) (1)
As described above, the larger the respective spin polarizabilities, the larger the resistance change rate.
[0008]
Incidentally, the basic configuration of the MRAM is, for example, as disclosed in JP-A-10-116490, a plurality of bit write lines (so-called bit lines) and a plurality of words orthogonal to the plurality of bit write lines. A write line (a so-called word line) is provided, and a TMR element as a magnetic memory element is arranged at an intersection of the bit write line and the word write line. When recording is performed with such an MRAM, selective writing is performed on the TMR element using the asteroid characteristic.
[0009]
Here, the operation principle of the MRAM using the TMR element will be briefly described.
The MRAM has a structure in which minute storage carriers (magnetic storage carriers) made of a magnetic material are regularly arranged, and wiring is provided so that each of them can be accessed. When a TMR element is used, a magnetization free layer of the TMR element serves as a magnetic storage carrier, and a memory cell is configured by the TMR element.
[0010]
Information is written by controlling the magnetization of the magnetization free layer of the TMR element constituting each memory cell by using a combined current magnetic field generated by applying a current to both the word write line and the bit read line. Do.
[0011]
Generally, “0” information and “1” information are stored according to the direction of magnetization.
Specifically, for example, the case where the magnetization direction of the magnetization free layer and the magnetization direction of the magnetization fixed layer are antiparallel and the resistance value is high is, for example, “1”, and conversely, when the magnetization directions are parallel. Is set to “0”. Conversely, it is also possible to set “0” when antiparallel.
[0012]
In reading information, a memory cell is selected using an element such as a transistor, and the direction of magnetization is extracted as a voltage signal by a magnetoresistance effect.
[0013]
The TMR element constituting the memory cell has a three-layered structure of ferromagnetic material / insulator / ferromagnetic material, that is, a structure including a ferromagnetic tunnel junction (MTJ). The magnetization fixed layer and the other ferromagnetic layer become a magnetization free layer. Then, by using the magnetization fixed layer as a fixed reference layer (pinned / reference layer) and using the magnetization free layer (free layer) as the information recording layer, the magnetization of the magnetization free layer (information recording layer) is increased by the tunnel magnetoresistance effect. Is made to correspond to the voltage signal.
[0014]
Next, a cell selection method at the time of writing will be described.
Generally, when a magnetic field is applied in the direction of the easy axis of the ferromagnetic material in the direction opposite to the magnetization, the magnetization is reversed in the direction of the magnetic field at a certain magnetic field value ± Hc, that is, a reversal magnetic field. The value of the reversal magnetic field can theoretically be obtained from the condition of the minimum energy.
Further, it is known that when a magnetic field is applied not only in the easy axis direction but also in the hard axis direction, the absolute value of the reversal magnetic field Hc decreases. This can also be obtained from the minimum energy condition. If the magnetic field applied in the direction of the hard axis is Hx, the reversal magnetic field Hy at this time is:

There is a relationship. This curve is called an asteroid curve because it forms an asteroid on the Hx-Hy plane.
The cell selection method at the time of writing can be explained using this asteroid curve.
[0015]
In an MRAM having a configuration in which the magnetic field generated from the word write line is substantially coincident with the direction of the axis of easy magnetization, recording is performed by reversing the magnetization of the magnetization free layer (information recording layer) by the magnetic field generated from the word write line. .
However, since there are a plurality of memory cells located at the same distance from the word write line, if a current of an amount that generates a magnetic field more than the reversal magnetic field is applied to the word write line, the equivalent plurality of memory cells are simultaneously transmitted. Recording will be done.
Therefore, a current is caused to flow through a bit write line hanging on a memory cell to be selected to generate a magnetic field in a hard axis direction. Thus, the switching magnetic field of the selected cell can be reduced. Assuming that the reversal magnetic field at this time is Hc (h) and the reversal magnetic field when the magnetic field by the bit write line is 0 is Hc (0), the magnetic field H by the word write line is Hc (h) <H <Hc (0). By setting as follows, it is possible to selectively record data in a memory cell.
Thus, a cell can be selected at the time of recording.
[0016]
This MRAM has a simple structure, so that high integration is easy, and since the recording is performed by rotating the magnetic moment, the number of rewritable times is large.
The access time is also expected to be very high, and it has already been confirmed that operation is possible on the order of nanoseconds.
[0017]
Therefore, the MRAM is superior to the flash memory particularly in the three points of random access, large number of rewritable times, and high-speed operation, and is superior to the FeRAM in process consistency. Further, since it is expected that high integration similar to DRAM and high speed comparable to SRAM can be achieved at the same time, there is also a possibility of replacing all embedded memories for system LSI.
[0018]
[Problems to be solved by the invention]
However, the MRAM has an inherent problem because it employs a characteristic writing method such as selective recording using an orthogonal magnetic field instead of selective recording using a MOS switch or the like used in a DRAM.
[0019]
In particular, if the magnetic characteristics of the TMR elements constituting the memory cell vary from one element to another, or if there is a variation when the same element is repeatedly used, there is a problem that it is difficult to perform selective writing using the asteroid characteristic. .
Therefore, the TMR element is also required to have magnetic properties for drawing an ideal asteroid curve.
[0020]
Here, FIG. 8A shows an ideal asteroid curve in the MRAM having the TMR element. There is no distortion or variation in the curve, and it is a beautiful curve.
[0021]
On the other hand, an asteroid curve obtained by measuring an actual magnetic memory device is as shown in FIG. 8B.
From FIG. 8B, it can be seen that there is variation in the switching field. This is because in many tunnel magnetoresistive elements (TMR elements) constituting the memory device, the asteroid curve varies because the switching field of each element varies.
[0022]
In the magnetic memory device having an asteroid curve as shown in FIG. 8B, the selectively recordable area is as shown in FIG. W0 indicates an area where "0" can be selectively recorded, and W1 indicates an area where "1" can be selectively recorded.
It can be seen that the area of W0 is narrower than the area of W1 because of the variation in the asteroid curve.
In order to actually operate as an MRAM, it is necessary to selectively record both “0” and “1”.
Therefore, it is required that both the area W0 and the area W1 have a sufficiently wide range so that a sufficient margin for selective recording can be secured.
[0023]
As is clear from FIG. 8B, in order to secure a wide margin for selective recording, it is important to suppress variations in the asteroid curve, that is, variations in the switching field of the TMR elements constituting each memory cell. .
[0024]
Variations in the switching field can be of various origins, for example due to material inhomogeneities or process accuracy, but more essentially the magnetization reversal itself does not necessarily occur via the same energy state There is a fact that. This is indicated by the fact that when the reversal magnetic field of each bit constituting the MRAM is repeatedly measured, the value is not always constant and has a certain dispersion (referred to as repetition variation).
Therefore, in order to suppress the switching field variation, it is required to suppress the repetition variation.
[0025]
In order to solve the above-described problem, the present invention suppresses the repetitive variation of the reversal magnetic field of the magnetization free layer, thereby providing a magnetoresistive element having good magnetic characteristics, and selecting the magnetoresistive element including the magnetoresistive element. An object of the present invention is to provide a magnetic memory device capable of securing a wide recording margin.
[0026]
[Means for Solving the Problems]
The magnetoresistive element of the present invention has a configuration in which a pair of ferromagnetic layers are opposed via an intermediate layer, and a magnetoresistance change is obtained by flowing a current perpendicular to the film surface. One of the layers is a fixed magnetization layer and the other is a free magnetization layer. The material used for the free magnetization layer has an exchange stiffness constant A [erg / cm], a saturation magnetization Ms [emu / cc], and a film thickness t [ nm] and the width W [nm] of the magnetoresistive element satisfy the formula A / (t · Ms ² )> W / 50.
[0027]
A magnetic memory device according to the present invention includes a magnetoresistive element having a configuration in which a pair of ferromagnetic layers are opposed to each other with an intermediate layer interposed therebetween to obtain a magnetoresistance change by flowing a current perpendicular to a film surface; A word line and a bit line sandwiching the magnetoresistive element in the thickness direction; one of the pair of ferromagnetic layers is a magnetization fixed layer, the other is a magnetization free layer, and a material used for the magnetization free layer is exchanged. The stiffness constant A [erg / cm], the saturation magnetization Ms [emu / cc], the film thickness t [nm], and the width W [nm] of the magnetoresistive element are expressed by the formula A / (t · Ms ² )> W / It satisfies 50.
[0028]
Here, the exchange stiffness constant A used in the above equation is defined as described below (see “Physics of ferromagnetic material (lower)” published by Shokabo, written by Toshinobu Chikaku) .
[0029]
When the spin S _i and the spin S _j make an angle, the exchange energy w _ij of these spins is expressed as

Is represented by
When the angle φ between S _i and S _j is small and the magnitudes of S _i and S _j are equal, the magnitude of the spin is S, and equation (3)

Can be written. This is when φ is small

This is because Equation (4) shows that the exchange energy increases in proportion to the square of the angle φ, which is similar to the case where the elastic energy of an elastic body such as a spring increases in proportion to the square of the deformation.
[0030]
When the spin distribution in the magnetic body is given, the exchange energy stored therein can be described by the spin distribution. Assuming that a is a unit vector parallel to the direction of the spin S _i at a certain lattice point and n is the number of atoms belonging to a unit cell, the exchange energy E _ex of spin in the ferromagnetic material per unit volume is

It is expressed as
On the other hand, since (a · a) = 1, the following equation (7) is obtained by differentiating both sides twice with x. The same applies to y and z.

Using this, equation (6) becomes

Is transformed.
Among them, A is defined by A = nJS ² / a, and the partial differentiation of a by x, y, and z is an amount corresponding to the strain of the elastic body. The energy equation is similar to that where elastic energy is given in quadratic form of the strain tensor.
From this, following the “stiffness constant” in the equation of elastic energy due to the deformation of the elastic body, this A in the magnetic body is replaced with the exchange stiffness constant (exchange).
stiffness constant).
[0031]
According to the configuration of the magnetoresistance effect element of the present invention described above, the exchange stiffness constant A [erg / cm], the saturation magnetization Ms [emu / cc], the film thickness t [nm] of the material used for the magnetization free layer, and When the width W [nm] of the magnetoresistive effect element satisfies the formula A / (t · Ms ² )> W / 50, it is possible to suppress the repetition variation of the inversion magnetic field.
[0032]
According to the configuration of the magnetic memory device of the present invention described above, since the repetitive variation of the reversal magnetic field of the magnetization free layer is reduced by including the magnetoresistive element of the present invention, selective recording is performed. The range of the magnetic field (the magnetic field in the direction of the easy axis and the magnetic field in the direction of the hard axis) that can perform this can be widened.
[0033]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention relates to a magnetoresistive element having a configuration in which a pair of ferromagnetic layers are opposed to each other with an intermediate layer interposed therebetween to obtain a magnetoresistance change by flowing a current perpendicular to a film surface. One of the magnetic layers is a magnetization fixed layer and the other is a magnetization free layer. The exchange stiffness constant A [erg / cm], the saturation magnetization Ms [emu / cc], and the film thickness t of the material used for the magnetization free layer. [Nm] and the width W [nm] of the magnetoresistive effect element satisfy the formula A / (t · Ms ² )> W / 50.
[0034]
Further, according to the present invention, in the above-mentioned magnetoresistive effect element, the tunnel magnetoresistive effect element uses a tunnel barrier layer made of an insulator or a semiconductor as an intermediate layer.
[0035]
Further, the present invention provides a giant magnetoresistive element using a conductive layer as an intermediate layer in the above magnetoresistive element.
Further, according to the present invention, in the above-described magnetoresistive effect element, a structure having a laminated ferrimagnetic structure is adopted.
[0037]
The present invention provides a magnetoresistive element having a configuration in which a pair of ferromagnetic layers are opposed to each other with an intermediate layer interposed therebetween to obtain a magnetoresistive change by passing a current perpendicular to the film surface, , A word line and a bit line sandwiching the ferromagnetic layer in the thickness direction, one of the pair of ferromagnetic layers is a magnetization fixed layer, the other is a magnetization free layer, and the exchange stiffness constant A [ erg / cm], saturation magnetization Ms [emu / cc], film thickness t [nm], and width W [nm] of the magnetoresistive effect element satisfy the formula A / (t · Ms ² )> W / 50. It is a memory device.
[0038]
Further, according to the present invention, in the magnetic memory device, the magnetoresistive element is a tunnel magnetoresistive element using a tunnel barrier layer made of an insulator or a semiconductor as an intermediate layer.
[0039]
Further, according to the present invention, in the above magnetic memory device, the magnetoresistive element is a giant magnetoresistive element using a conductive layer as an intermediate layer.
[0040]
Further, according to the present invention, in the above magnetic memory device, the magnetoresistive element has a laminated ferri structure.
[0041]
FIG. 1 shows a schematic configuration diagram of an embodiment of the magnetoresistance effect element of the present invention. The embodiment shown in FIG. 1 shows a case where the present invention is applied to a tunnel magnetoresistance effect element (hereinafter, referred to as a TMR element).
[0042]
This TMR element 1 has an underlayer 3, an antiferromagnetic layer 4, a magnetization fixed layer 5 as a ferromagnetic layer, a tunnel barrier layer 6, and a magnetization as a ferromagnetic layer on a substrate 2 made of silicon or the like. The free layer 7 and the top coat layer 8 are laminated in this order.
That is, a so-called spin-valve type TMR element in which one of the ferromagnetic layers is a magnetization fixed layer 5 and the other is a magnetization free layer 7 is formed. By sandwiching the tunnel barrier layer 6 with the magnetization free layer 7, a ferromagnetic tunnel junction is formed.
When the TMR element 1 is applied to a magnetic memory element or the like, the magnetization free layer 7 becomes an information recording layer, and information is recorded thereon.
[0043]
The antiferromagnetic layer 4 is antiferromagnetically coupled to the magnetization fixed layer 5 which is one of the ferromagnetic layers, so that the magnetization of the magnetization fixed layer 5 is not reversed even by a current magnetic field for writing. This is a layer for keeping the magnetization direction of the layer 5 always constant. That is, in the TMR element 1 shown in FIG. 1, only the magnetization free layer 7, which is the other ferromagnetic layer, is inverted by an external magnetic field or the like. The magnetization free layer 7 is also referred to as an information recording layer because it becomes a layer on which information is recorded when the TMR element 1 is applied to, for example, a magnetic memory device or the like.
As a material constituting the antiferromagnetic layer 4, a Mn alloy containing Fe, Ni, Pt, Ir, Rh, etc., a Co oxide, a Ni oxide, or the like can be used.
[0044]
In the spin valve type TMR element 1 shown in FIG. 1, the magnetization fixed layer 5 is antiferromagnetically coupled to the antiferromagnetic layer 4 so that the magnetization direction is constant. Therefore, the magnetization of the magnetization fixed layer 5 is not reversed by the current magnetic field at the time of writing.
[0045]
The tunnel barrier layer 6 is a layer for magnetically separating the magnetization fixed layer 5 and the magnetization free layer 7 and for flowing a tunnel current.
The material constituting the tunnel barrier layer 6, for example Al, Mg, S i, Li, oxides such as _Ca, a nitride, may be used an insulating material such as a halide.
[0046]
Such a tunnel barrier layer 6 can be obtained by oxidizing or nitriding a metal film formed by a sputtering method, an evaporation method, or the like.
Further, it can also be obtained by a CVD method using an organic metal and oxygen, ozone, nitrogen, halogen, halogenated gas or the like.
[0047]
In the present embodiment, particularly, the TMR element 1 is formed by changing the element width W [nm] of the TMR element 1, the exchange stiffness constant A [erg / cm] of the ferromagnetic material used for the magnetization free layer 7, and the saturation magnetization Ms. [Emu / cc] and the thickness t [nm] satisfy the following equation (10).
A / (t · Ms ² )> W / 50 (10)
[0048]
As such a ferromagnetic material satisfying the expression (10), for example, CoFeB can be given.
This CoFeB is a preferable material from the viewpoint that the saturation magnetization Ms and the exchange stiffness constant A can be controlled without significantly impairing other characteristics depending on the composition.
When CoFeB is used for the magnetization free layer 7, the TMR element 1 can satisfy Expression (10) by setting the composition in the range described later.
[0049]
In addition, other ferromagnetic materials can be used for the magnetization free layer 7 as long as the TMR element 1 can be configured so as to satisfy Expression (10).
Even in this case, various additives (C, Si, P, Ga, Ge, Zr, Hf, Y, and Y) can be added to a material system in which the saturation magnetization Ms and the exchange stiffness constant A can be easily controlled by the composition, for example, CoFe or CoFe. It is preferable to use a material to which Ti, Nb, Mn, Cr, Ni, V, rare earth and the like are added, or a material to which NiFe or CoNi or NiFe or CoNi is mainly added and B or the above additives are added.
[0050]
According to the TMR element 1 of the above embodiment, when the TMR element 1 satisfies the expression (10), it is possible to reduce the repetition variation of the reversal magnetic field (the magnetic field in which the magnetization of the magnetization free layer 7 is reversed). Become.
[0051]
As a result, for example, when the TMR element 1 is applied to a magnetic memory device having a large number of TMR elements, it leads to the suppression of the variation of the reversal magnetic field for a large number of TMR elements 1 and widens the margin for selective recording. be able to.
Further, when applied to a magnetic head or a magnetic sensor having a TMR element, it is possible to suppress a deviation of a reversal magnetic field from a design value, thereby improving a manufacturing yield and preventing a malfunction. Become.
[0052]
In the present invention, each of the magnetization fixed layer 5 and the magnetization free layer 7 as shown in FIG. 1 is not limited to the TMR element 1 having a single layer.
For example, as shown in FIG. 2, the magnetization fixed layer 5 has a laminated ferrimagnetic structure in which a nonmagnetic conductor layer 5c is sandwiched between a first magnetization fixed layer 5a and a second magnetization fixed layer 5b. Even so, the effects of the present invention can be obtained.
[0053]
In the TMR element 10 shown in FIG. 2, the first magnetization fixed layer 5a is in contact with the antiferromagnetic layer 4, and the exchange interaction acting between these layers causes the first magnetization fixed layer 5a to have a strong one-way magnetic field. Has anisotropy. The second magnetization fixed layer 5b faces the magnetization free layer 7 via the tunnel barrier layer 6, and is a ferromagnetic layer whose spin direction is compared with the magnetization free layer 7 and is directly related to the MR ratio. Also called a layer.
[0054]
Examples of the material used for the non-magnetic conductive layer 5c having the laminated ferri structure include Ru, Cu, Cr, Au, Ag, and the like. In the TMR element 10 of FIG. 2, the other layers have substantially the same configuration as the TMR element 1 shown in FIG. 1, and therefore, are denoted by the same reference numerals as in FIG.
[0055]
In the TMR element 10 having the laminated ferrimagnetic structure, the reversal magnetic field (the magnetic field in which the magnetization of the magnetization free layer 7 reverses) is obtained by adopting a configuration satisfying the expression (10), similarly to the TMR element 1 shown in FIG. Can be reduced.
[0056]
In the above-described embodiment, the TMR elements (tunnel magnetoresistive elements) 1 and 10 are used as the magnetoresistive elements. However, in the present invention, a pair of ferromagnetic layers are opposed to each other via an intermediate layer. The present invention can also be applied to other magnetoresistive elements having a configuration in which a current flows perpendicularly to the surface to obtain a change in magnetoresistance.
For example, a giant magnetoresistive element (GMR element) using a nonmagnetic conductive layer of Cu or the like as an intermediate layer, in which a current flows perpendicularly to the film surface to obtain a magnetoresistive effect, that is, a so-called CPP type GMR element The present invention can also be applied to
[0057]
Further, the material of the magnetization fixed layer and the antiferromagnetic material, the presence or absence of the laminated ferrimagnetic structure on the magnetization fixed layer side, and the like can be variously modified as long as the essence of the present invention is not impaired.
[0058]
The above-described magnetoresistive elements such as the TMR elements 1 and 10 are suitable for use in a magnetic memory device such as an MRAM. Hereinafter, an MRAM using the TMR element of the present invention will be described with reference to the drawings.
[0059]
FIG. 3 shows a cross-point type MRAM array having the TMR element of the present invention. This MRAM array has a plurality of word lines WL and a plurality of bit lines BL orthogonal to the word lines WL, and the TMR element of the present invention is arranged at an intersection between the word lines WL and the bit lines BL. And a memory cell 11. That is, in this MRAM array, 3 × 3 memory cells 11 are arranged in a matrix.
[0060]
Note that the TMR element used in the MRAM array is not limited to the TMR element 1 shown in FIG. 1, and a current flows perpendicular to the film surface, such as the TMR element 10 shown in FIG. 2 having a laminated ferri structure. Any configuration may be used as long as the configuration satisfies the expression (10) in the magnetoresistance effect element configured to obtain a magnetoresistance change.
[0061]
FIG. 4 shows a cross-sectional structure of one memory cell taken out of many memory cells in the memory element.
As shown in FIG. 4, each memory cell 11 has, for example, a transistor 16 including a gate electrode 13, a source region 14 and a drain region 15 on a silicon substrate 12. The gate electrode 13 constitutes a read word line WL1. On the gate electrode 13, a write word line (corresponding to the above-described word write line) WL2 is formed via an insulating layer. A contact metal 17 is connected to the drain region 15 of the transistor 16, and a base layer 18 is connected to the contact metal 17. The TMR element 1 of the present invention is formed on the underlayer 18 at a position corresponding to above the write word line WL2. On this TMR element 1, a bit line (corresponding to the above-described bit write line) BL orthogonal to the word lines WL1 and WL2 is formed.
Further, it has an interlayer insulating film 19 and an insulating film 20 for insulating the word lines WL1 and WL2 from the TMR element 1, and a passivation film (not shown) for protecting the whole.
[0062]
Since the MRAM uses the TMR element 1 having a configuration satisfying the expression (10), it is possible to reduce the repetition variation of the switching magnetic field of each memory cell 11.
As a result, a sufficient margin of the reversal magnetic field for performing selective recording can be secured.
[0063]
(Example)
Hereinafter, specific examples to which the present invention is applied will be described based on experimental results.
With respect to the TMR element 10 shown in FIG. 2 having the laminated ferrimagnetic structures 5a, 5b, and 5c in the magnetization fixed layer 5, samples were prepared in which the magnetization free layer 7 was changed to various compositions in order to change the magnetic characteristics. Specifically, the composition of the magnetization free layer 7 was (FexCo1-x) 1-yBy, and the values (atomic%) of x and y were changed as shown in Table 1. Further, a magnetic memory device having the configuration shown in FIGS. 3 and 4 having the TMR element 10 of each sample was manufactured.
[0064]
<Sample 1>
First, in a magnetron sputtering apparatus whose inside is evacuated to an ultra-high vacuum region, a Ta film is formed to a thickness of 3 nm, a PtMn film (antiferromagnetic layer 4) is formed to a thickness of 30 nm, and a CoFe film (first magnetization) is formed on a substrate. The fixed layer 5a) has a thickness of 1.5 nm, the Ru film (the nonmagnetic conductive layer 5c) has a thickness of 0.8 nm, the CoFe film (the second magnetization fixed layer 5b) has a thickness of 2 nm, and the Al film has a thickness of, for example. Films were sequentially formed to a thickness of 1 nm.
The CoFe films of the first magnetization fixed layer 5a and the second magnetization fixed layer (reference layer) 5b were formed with a target composition of Co75Fe25 (atomic%).
[0065]
Next, the Al film was plasma-oxidized in pure oxygen to obtain a uniform Al oxide film, and the tunnel barrier layer 6 of the TMR element was formed.
[0066]
Subsequently, in the magnetron sputtering apparatus, the magnetization free layer 7 was formed to a thickness of 1.5 to 6 nm, and the Ta film was formed to a thickness of 5 nm.
The composition of the magnetization free layer 7 was x = 0, y = 5, that is, Co95B5 (atomic%).
[0067]
Next, a heat treatment in a magnetic field was performed to form the PtMn film of the antiferromagnetic layer 4 into an ordered alloy. The conditions of the heat treatment in a magnetic field were set to 280 ° C. for 1 hour in a magnetic field of 10 kOe.
Further, fine processing was performed by a combination of photolithography and ion milling to obtain an elliptical TMR element 10 of 0.1 μm × 0.2 μm to 0.6 μm × 1.2 μm.
[0068]
<Sample 2>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 10, y = 5, that is, (Fe10Co90) 95B5 (atomic%).
[0069]
<Sample 3>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 25, y = 5, that is, (Fe25Co75) 95B5 (atomic%).
[0070]
<Sample 4>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 50, y = 5, that is, (Fe50Co50) 95B5 (atomic%).
[0071]
<Sample 5>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 0, y = 10, that is, Co90B10 (atomic%).
[0072]
<Sample 6>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was x = 5, y = 10, that is, (Fe5Co95) 90B10 (atomic%).
[0073]
<Sample 7>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 10, y = 10, that is, (Fe10Co90) 90B10 (atomic%).
[0074]
<Sample 8>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 25, y = 10, that is, (Fe25Co75) 90B10 (atomic%).
[0075]
<Sample 9>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 30, y = 10, that is, (Fe30Co70) 90B10 (atomic%).
[0076]
<Sample 10>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 35, y = 10, that is, (Fe35Co65) 90B10 (atomic%).
[0077]
<Sample 11>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was x = 45, y = 10, that is, (Fe45Co55) 90B10 (atomic%).
[0078]
<Sample 12>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 50, y = 10, that is, (Fe50Co50) 90B10 (atomic%).
[0079]
<Sample 13>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 0, y = 20, that is, Co80B20 (atomic%).
[0080]
<Sample 14>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 5, y = 20, that is, (Fe5Co95) 80B20 (atomic%).
[0081]
<Sample 15>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 10, y = 20, that is, (Fe10Co90) 80B20 (atomic%).
[0082]
<Sample 16>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was x = 25, y = 20, that is, (Fe25Co75) 80B20 (atomic%).
[0083]
<Sample 17>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 30, y = 20, that is, (Fe30Co70) 80B20 (atomic%).
[0084]
<Sample 18>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 35, y = 20, that is, (Fe35Co65) 80B20 (atomic%).
[0085]
<Sample 19>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 45, y = 20, that is, (Fe45Co55) 80B20 (atomic%).
[0086]
<Sample 20>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was x = 50, y = 20, that is, (Fe50Co50) 80B20 (atomic%).
[0087]
<Sample 21>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 0, y = 30, that is, Co70B30 (atomic%).
[0088]
<Sample 22>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 5, y = 30, that is, (Fe5Co95) 70B30 (atomic%).
[0089]
<Sample 23>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 10, y = 30, that is, (Fe10Co90) 70B30 (atomic%).
[0090]
<Sample 24>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 25, y = 30, that is, (Fe25Co75) 70B30 (atomic%).
[0091]
<Sample 25>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was x = 30, y = 30, that is, (Fe30Co70) 70B30 (atomic%).
[0092]
<Sample 26>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was x = 35, y = 30, that is, (Fe35Co65) 70B30 (atomic%).
[0093]
<Sample 27>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 40, y = 30, that is, (Fe40Co60) 70B30 (atomic%).
[0094]
<Sample 28>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 0, y = 40, that is, Co60B40 (at%).
[0095]
<Sample 29>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 10, y = 40, that is, (Fe10Co90) 60B40 (atomic%).
[0096]
<Sample 30>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 20, y = 40, that is, (Fe20Co80) 60B40 (atomic%).
[0097]
<Sample 31>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 25, y = 40, that is, (Fe25Co75) 60B40 (atomic%).
[0098]
<Sample 32>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 30, y = 40, that is, (Fe30Co70) 60B40 (atomic%).
[0099]
<Sample 33>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 35, y = 40, that is, (Fe35Co65) 60B40 (atomic%).
[0100]
<Sample 34>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 0, y = 45, that is, Co55B45 (atomic%).
[0101]
<Sample 35>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 5, y = 45, that is, (Fe5Co95) 55B45 (atomic%).
[0102]
<Sample 36>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 10, y = 45, that is, (Fe10Co90) 55B45 (atomic%).
[0103]
<Sample 37>
A TMR element 10 was obtained in the same manner as in Sample 1, except that the composition of the magnetization free layer 7 was changed to x = 25, y = 45, that is, (Fe25Co75) 55B45 (atomic%).
[0104]
Further, from the TMR elements 10 of the samples 1 to 37, MRAMs (magnetic memory devices) each having the TMR element 10 of 1 kbit (kilobits) and having the configuration shown in FIGS. 3 and 4 were manufactured.
[0105]
The effect of suppressing the repetition variation of the switching magnetic field described above depends on the exchange stiffness constant A and saturation magnetization Ms of the material of the magnetization free layer, the thickness t, and the size of the TMR element, specifically, the element width W of the TMR element. Occurs when the relationship of the above-described expression (10) is established.
[0106]
First, in Samples 1 to 37 in which the composition of CoFeB was changed, the Fe content (atomic%), the B content (atomic%), and the thickness of the magnetization free layer were 1.5 nm (type I). Table 1 shows the value of A / Ms ^{2 and} the value of the repetition variation SFD (standard deviation σ / average value ave.) Of the reversal magnetic field of the memory device having the TMR element having the type I configuration.
The exchange stiffness constant A is a value obtained by spin wave resonance, and the saturation magnetization Ms is a value obtained by a vibrating sample magnetometer.
[0107]
[Table 1]

[0108]
From the results in Table 1, it can be seen that the above-described repetition variation of the switching field and A / Ms ² of the magnetization free layer 7 correspond well.
That is, in the sample having a small A / Ms ² of the magnetization free layer 7, the SFD, that is, the repetition variation of the switching magnetic field is large.
[0109]
FIG. 5 shows the relationship between the value of A / Ms ² and the repetition variation (SFD) of the switching field based on the measurement results in Table 1.
From FIG. 5, it is understood that when A / Ms ² of the magnetization free layer 7 is small, the SFD, that is, the repetition variation of the switching magnetic field is also large.
[0110]
In a general MRAM, when the variation of the magnetic field generated from the bit line or the word line is also taken into consideration, the variation of the switching magnetic field needs to be suppressed to 5% or less in standard deviation / average value. Further, in consideration of variations in the fine processing process and the like, the repetition variation of the reversal magnetic field must be suppressed to 2% or less in a single TMR element.
FIG. 5 shows that the value of A / Ms ² must be 3 × 10 ⁻¹⁴ cm ² or more in order to reduce the repetition variation of the switching field to 2% or less.
[0111]
FIG. 6 also shows the composition range of CoFeB in which the repetition variation of the reversal magnetic field can be reduced to 2% or less based on the measurement results also shown in Table 1, with hatching in the phase diagram. is there. In addition, the mark ● in the figure indicates the composition of each of Samples 1 to 37.
[0112]
Further, in order to obtain a more general relationship, the thickness of the magnetization free layer was changed to 1.5 nm, 3 nm, and 6 nm, and the minor axis length (corresponding to the element width W) of the element was set to 0.1 μm. , 0.25 μm, 0.4 μm, 0.5 μm, and 0.6 μm, the TMR element 10 was fabricated, and the exchange stiffness constant A, the saturation magnetization Ms, and the repetition variation of the reversal magnetic field were similarly measured.
[0113]
As a result, when the thickness of the magnetization free layer was 1.5 nm and the minor axis length of the TMR element 10 was 0.1 μm, the critical value of A / Ms ² was 3 × 10 ⁻¹⁴ cm ² . However, it was found that the critical value of A / Ms ² changes depending on the minor axis length of the TMR element 10 and the thickness of the magnetization free layer.
This relationship is shown in FIG. In the figure, the symbol △ indicates the case where the thickness of the magnetization free layer is 1.5 nm, the symbol ● indicates the case where the thickness of the magnetization free layer is 3 nm, and the mark ○ indicates the case where the thickness of the magnetization free layer is 6 nm.
[0114]
From FIG. 7, it can be seen that as the short axis length of the TMR element 10 becomes longer, that is, the TMR element 10 becomes larger, and the thickness of the magnetization free layer 7 becomes larger, the critical value becomes larger and changes almost linearly.
Then, from FIG. 7, it can be seen that the formula of the relationship between the minor axis length W and the thickness t of the magnetization free layer, and the critical value of the A / Ms ² of TMR elements is established.
Critical value of C · A / Ms ² = W · t (C is a constant) (11)
When this proportionality constant C is calculated, it becomes as shown in Table 2, and it is understood that it becomes about 50.
Therefore, the conditions for suppressing the repetition variation of the switching field are as follows:
50A / Ms ² > Wt (12)
From this equation (12), the above-mentioned equation (10), that is, A / (t · Ms ² )> W / 50 (10)
Is led.
[0115]
[Table 2]

[0116]
The magnetoresistive effect element (TMR element, etc.) of the present invention is not limited to the above-described magnetic memory device, but also includes a magnetic head, a hard disk drive or a magnetic sensor, an integrated circuit chip, and a personal computer, a portable terminal equipped with the magnetic head. The present invention can be applied to various electronic devices such as mobile phones, electronic devices, and the like.
[0117]
The present invention is not limited to the above-described embodiment, and may take various other configurations without departing from the gist of the present invention.
[0118]
【The invention's effect】
According to the above-described magnetoresistance effect element of the present invention, the repetition variation of the reversal magnetic field of the magnetization free layer can be sufficiently suppressed.
Thus, for example, when applied to a magnetic memory device having a magnetoresistive effect element, it is possible to suppress variations in the terminal magnetic field of the magnetization free layer of the magnetoresistive effect element forming the memory cell in the entire magnetic memory device. As a result, the margin for selective recording of memory cells can be expanded.
Further, for example, when applied to a magnetic head or a magnetic sensor having a magnetoresistive effect element, it is possible to suppress a deviation of a reversal magnetic field from a design value, thereby improving a manufacturing yield and preventing operation failure. Will be possible.
[0119]
Further, according to the magnetic memory device of the present invention, since the magnetic memory device is configured to include the magnetoresistive effect element of the present invention, the repetitive variation of the switching field of the magnetoresistive effect element is suppressed. A wide recording margin can be secured, and stable recording can be performed.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a TMR element according to an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram of a TMR element having a laminated ferri structure.
FIG. 3 is a schematic configuration diagram showing a main part of a cross-point type MRAM array having a TMR element of the present invention as a memory cell.
FIG. 4 is an enlarged sectional view of the memory cell shown in FIG. 3;
FIG. 5 is a diagram illustrating a relationship between A / Ms ² and a repetition variation of a switching magnetic field.
FIG. 6 is a diagram showing a preferable composition range in a CoFeB system.
7 is a diagram showing the relationship between the minor axis length and the critical value of A / Ms ² of film thickness and TMR elements the magnetization free layer.
FIG. 8 is a diagram showing an ideal asteroid curve of a single TMR element.
B is a diagram in which asteroid curves of a large number of TMR elements are superimposed.
[Explanation of symbols]
1,10 Tunnel magnetoresistive element (TMR element), 2 substrate, 3 underlayer, 4 antiferromagnetic layer, 5 fixed magnetization layer, 5a first fixed magnetization layer, 5b second fixed magnetization layer (reference layer) 5c nonmagnetic conductor layer, 6 tunnel barrier layer, 7 magnetization free layer, 11 memory cells, WL, WL1, WL2 word lines, BL bit lines

Claims (8)

A magnetoresistive element having a configuration in which a pair of ferromagnetic layers are opposed to each other with an intermediate layer interposed therebetween and a magnetoresistance change is obtained by flowing a current perpendicular to the film surface,
One of the pair of ferromagnetic layers is a magnetization fixed layer, the other is a magnetization free layer,
The exchange stiffness constant A [erg / cm], the saturation magnetization Ms [emu / cc], the film thickness t [nm] of the material used for the magnetization free layer, and the width W [nm] of the magnetoresistive element are expressed by the following formula A: / (T · Ms ² )> W / 50
A magnetoresistance effect element characterized by satisfying the following. 2. A magnetoresistive element according to claim 1, wherein the intermediate layer is a tunnel magnetoresistive element using a tunnel barrier layer made of an insulator or a semiconductor. The magnetoresistive element according to claim 1, wherein the element is a giant magnetoresistive element using a conductive layer as the intermediate layer. 2. The magnetoresistive element according to claim 1, having a laminated ferrimagnetic structure. A magnetoresistive element having a configuration in which a pair of ferromagnetic layers are opposed to each other via an intermediate layer, and a magnetoresistance effect is obtained by flowing a current perpendicular to the film surface;
Word lines and bit lines sandwiching the magnetoresistive element in the thickness direction,
One of the pair of ferromagnetic layers is a magnetization fixed layer, the other is a magnetization free layer,
The exchange stiffness constant A [erg / cm], the saturation magnetization Ms [emu / cc], the film thickness t [nm] of the material used for the magnetization free layer, and the width W [nm] of the magnetoresistive element are expressed by the following formula A: / (T · Ms ² )> W / 50
A magnetic memory device characterized by satisfying the following. 6. The magnetic memory device according to claim 5, wherein the magnetoresistance effect element is a tunnel magnetoresistance effect element using a tunnel barrier layer made of an insulator or a semiconductor as the intermediate layer. 6. The magnetic memory device according to claim 5, wherein the magnetoresistive element is a giant magnetoresistive element using a conductive layer as the intermediate layer. 6. The magnetic memory device according to claim 5, wherein said magnetoresistive element has a laminated ferrimagnetic structure.

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