JP3673661B2 - Magnetic memory element - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は磁気メモリ素子に関するものであり、好適な印加磁界で動作し、かつ高い磁気抵抗変化率を示すとともに高記録密度化が可能な非破壊型磁気メモリ素子に関するものである。
【０００２】
【従来の技術】
磁気抵抗効果型メモリ素子は、磁性層の磁化方向をディジタル情報に対応させ記録を行うものである。従って、記録の保持に外部からのエネルギー供給を必要としない。また、半導体メモリと比較して製造工程が簡素であり、特に基板材料を限定するものではないため、安価な大容量不揮発性メモリとして期待される。磁気抵抗効果型メモリ素子は、図１に示すように基本的に２層の強磁性層の間に非磁性層を有したサンドイッチ構造である。二つの強磁性層の保磁力は異なり、保磁力の比較的小さな層を検出層、保磁力の比較的大きな層をメモリ層とする。図においてはメモリ層を非磁性層の下側に、検出層を非磁性層の上側に配しているが、メモリ層と検出層の位置が逆になっていても構わない。
【０００３】
記録はメモリ層の磁化反転磁界よりも大きな磁界（Ｈｗ）を印加し、この記録磁界の方向にメモリ層の磁化を平行に向けることで達成される。例えば図２に．示したようにメモリ層の磁化が左向きの場合を『０』、右向きの場合を『１』とする。ただし、検出層の磁化反転磁界はメモリ層の磁化反転磁界よりも小さいので、記録直後は両層の磁化方向は平行である。検出は、メモリ素子に一定の大きさの直流電流を流すとともに、検出層の磁化反転磁界よりも大きく、メモリ層の磁化反転磁界よりも小さな磁界（Ｈａ）を印如し、検出層の磁化反転に伴う電位の変化を調べることにより行われる。両磁性層の磁化方向が平行である場合、そのメモリ素子の抵抗率は、磁化方向が反平行である場合と比べて小さい。
【０００４】
図３に示すように、『０』，が記録されたメモリ素子に＋Ｈａの検出磁界を印加すると両磁性層の磁化方向は反平行となって電位は高くなり、次いで一Ｈａを印加すると両磁性層の磁化方向は平行となって電位は低くなる。このようにして得られた信号を微分回路に通すことで負のパルスが得られる。同様に『１』が記録されたメモリ素子では逆に正のパルスが得られる。また、この検出方式では検出された信号が、検出前の検出層の磁化方向に無関係である。
【０００５】
検出層とメモリ層の磁化反転磁界に差を持たせるために、例えば検出層にはＮｉＦｅ等の保磁力の小さな材料を用い、メモリ層にはＣｏＦｅ等の保磁力の大きな材料を用いるが、両強磁性層問には、お互いの磁化の方向を平行に向けようとする静磁結合力が働いていているため、メモリ素子として動作させるためには、２つの層の保磁力の差がこの静磁結合力よりも大きくなければならない。
【０００６】
【発明が解決しようとしている課題】
検出層とメモリ層の間に形成された非磁性層が金属層である場合、その膜厚が薄い方がより大きな磁気抵抗変化率が得られるので好ましい。ところが非磁性金属層の薄膜化により静磁結合力が増加し、磁化の反平行状態が得られなくなってしまう。
【０００７】
また、面積の小さなメモリ素子では、反磁界の影響により大きな保磁力を維持することが困難となる。これは非磁性層が絶縁膜であるスピントンネル型のメモリ素子においても問題となる。ところが非破壊型磁気メモリ素子のメモリ層の材料として十分な大きさの保磁力を有する材料はいまだ提案されていない。
【０００８】
【課題を解決するための手段】
本発明は、少なくとも、反強磁性層と、第１の強磁性層と、非磁性層と、第２の強磁性層とをこの順に配置し、該反強磁性層は、第１の強磁性層と交換結合しており、前記第１の強磁性層の磁化方向を情報に応じて変化させて記録を行う磁気メモリ素子であって、前記反強磁性層の一方向異方性の向きは、前記第１の強磁性層の磁化方向と平行であり、該第１の強磁性層の磁化方向が反転することにより、反転することを特徴とする磁気メモリ素子を特徴とするものである。なお、前記反強磁性層は、絶縁体であってもよい。
【０００９】
【発明の実施の形態】
以下、本発明を図面を参照してさらに、詳細に説明する。
図４（ａ）に本発明の磁気メモリ素子の膜構成断面図を示す。１は基板、２は反強磁性層、３は第１の強磁性層、４は非磁性層、５は第２の強磁性層である。
【００１０】
また、図４（ｂ）に示すように積層順序を逆にしてもよい。反強磁性層にはＭｎＦｅ、ＭｎＩｒ、ＭｎＰｔ、ＭｎＰｔＣｒ、ＡｌＣｒ等のＭｎ系あるいはＣｒ系反強磁性体やＮｉＯ、α−Ｆｅ2０3等の酸化物反強磁性体が用いられ、ネール点が動作温度より高いものが好ましい。特に酸化物反強磁性体を用いた磁気メモリ素子は反強磁性体中の電子の分流が無いので高い磁気抵抗変化率が期待できる。第１および第２の強磁性層にはＣｏ、ＣｏＦｅ、Ｆｅ、ＮｉＦｅ等が使用可能である。非磁性層にはＣｕやＡｌ2０3等が用いられる。
【００１１】
反強磁性層の一方向異方性の反転は、交換結合している第１の強磁性層の磁化を介して行われる。
【００１２】
すなわち、反強磁性層の一方向異方性の方向と第１の強磁性層の磁化方向が平行である状態で、これらの方向と反平行に外部磁界を印加すると、第１の強磁性層の磁化が反転し、これと交換結合している反強磁性層の原子の磁気モーメントも反転し、さらに相互作用によって反強磁性層内の原子の磁気モーメントが順次反転することにより反強磁性層の一方向異方性が反転する。
【００１３】
本発明における第１の強磁性層の保磁力は、第１の強磁性層の膜厚、第１の強磁性層と反強磁性層の間の交換結合力あるいは反強磁性層の膜厚によって変化する。
特に第１の強磁性層あるいは反強磁性層の膜厚を適当に選ぶことにより容易に保磁力を調節することが可能である。図５に第１の磁性層の膜厚による保磁力の変化を示す。ただし、測定に用いたサンプルは、ガラス基板上に反強磁性層として１０ｎｍのＮｉＯ層、第１の強磁性層としてＣｏＦｅ層、非磁性層として５ｎｍのＣｕ層、第２の強磁性層として５ｎｍのＮｉＦｅ層を順次積層した磁気メモリ素子である。この図からわかるように第１の強磁性層の保磁力は膜厚にほぼ反比例している。また、図６は上記磁気メモリ素子において、ＦｅＣｏ層の膜厚を５ｎｍ一定とし、ＮｉＯ層の膜厚を変えた場合の第１磁性層の保磁力の変化を示したものである。ＮｉＯ層の膜厚が厚くなるに従って、第１の強磁性層の保磁力が大きくなり、ＮｉＯ層の膜厚を変えることによっても第１の強磁性層の保磁力を調節できることがわかる。ただし、この磁気メモリ素子では、ＮｉＯ層の膜厚が２０ｎｍになると磁化曲線や磁気抵抗曲線において磁界方向のシフトが見られ、ＮｉＯ層の一方向異方性の反転が不完全になっている。
【００１４】
第１の強磁性層、非磁性層、第２の強磁性層、反強磁性層が順次積層された磁気メモリ素子は例えば特開平６−２９５４１９号公報で提案されている。しかし、この公報で提案されている磁気メモリ素子は、反強磁性層と結合している第２の強磁性層の磁化方向は固定されており、反強磁性の一方向異方性も反転しないものである。また、特開平９−１３９０６８号公報では反強磁性と交換結合している強磁性層の磁化方向が反転する磁気メモリ素子が開示されているが、反強磁性の一方向異方性が反転しないものであるために印加磁界の方向によって、磁化が反平行になる磁界の大きさが異なっている。このような磁気メモリ素子は、記録磁界あるいは検出磁界の大きさがそれぞれ印加する方向により異なるので、磁界印加回路が煩雑になり好ましくない。反強磁性層の一方向異方性を反転させるためには、反強磁性層内に交換エネルギーを蓄積し得ないように反強磁性層の膜厚を選ぶことが必要である。ただし、そのような膜厚は、反強磁性層の材料や構造により異なる。
【００１５】
図７に本発明の磁気メモリ素子の磁気抵抗曲線と、対応する強磁性層の磁化方向と反強磁性層の一方向異方性の方向の変化の様子を示す。印加磁界ＨがＨ＜−Ｈ1である場合を初期状態とする。このときの各層の磁化および一方向異方性の方向は（ａ）のようにすべて印加磁界の方向と平行である。この状態から印加磁界をＨ2＜Ｈ＜Ｈ1とすると比較的保磁力の小さな第２の強磁性層の磁化が反転し第１の強磁性層と第２の強磁性層の磁化方向が反平行となり抵抗率が高くなる。Ｈ2は第２の強磁性層が有する本来の保磁力Ｈc2と両強磁性層の間に働く静磁結合力Ｈsの和で表される。さらに印加磁界を大きくしＨ1＜Ｈとすると第１の強磁性層の磁化と反強磁性層の一方向異方性が同時に反転し、抵抗率は再び小さくなる。Ｈ2は第１の強磁性層の本来の保磁力Ｈc1と反強磁性層との間に働く交換結合力Ｈｅｘの和から第２の強磁性層との間に働く静磁結合力Ｈsを引いた形で表される。さらに、印加磁界を−Ｈ1＜Ｈ＜−Ｈ2とすると第２の強磁性層の磁化が反転し、さらに印加磁界をＨ＜一Ｈ1とすることで初期状態に戻る。
【００１６】
【実施例】
以下、本発明を実施例によりさらに具体的に説明する。
（実施例１）
ガラス基板上に第２の強磁性層として５nmのＮｉ80Ｆｅ20層、非磁性層として２．２ｎｍのＣｕ層、第１の強磁性層として５ｎｍのＣｏ90Ｆｅ10層、反強磁性層として３ｎmのＩｒ50Mn50層を真空を破ることなくスパッタリングによって順次積層した。強磁性層の磁化反転を急峻にするために、各層成膜中に検出および記録磁界印加方向に平行に約６ｋＡ／mの直流磁界を印加し、面内一軸磁気異方性を誘起させた。
【００１７】
図８は上記のようにして作成した磁気メモリ素子の磁気抵抗変化率の測定結果である。２ｋＡ／mから６ｋＡ／mの磁界範囲で磁化が反平行となり、約５．９％の高い磁気抵抗変化率が得られている。
（実施例２）
ガラス基板上に反強磁性層として１０ｎmのNｉ50O50層、第１の強磁性層として３nmのＣｏ90Ｆｅ10層、非磁性層として２．４ｎmのＣｕ層、第２の強磁性層として３nmのＮｉ80Ｆｅ20層を真空を破ることなくスパッタリングによって順次積層した。強磁性層の磁化反転を急峻にするために、各層成膜中に検出および記録磁界印加方向に平行に約６ｋＡ／mの直流磁界を印加し、面内一軸磁気異方性を誘起させた。
【００１８】
図９は上記のようにして作成した磁気メモリ素子の磁気抵抗変化率の測定結果である。２ｋＡ／mから６．５ｋＡ／mの磁界範囲で磁化が反平行となり、約５．５％の高い磁気抵抗変化率が得られている。
（実施例３）
ガラス基板上に反強磁性層として１５ｎｍのＮｉ50Ｏ50層、第１の強磁性層として１０ｎｍのＣｏ90ＦｅlO層、２ｎｍのＡｌ層を順次積層した後、チヤンバー内に酸素ガスを導入し、該Ａｌ層を酸化させ非磁性酸化物層とした。再びチヤンバー内を十分に真空引きした後、第２の強磁性層として１０ｎｍのＮｉ80Ｆｅ20層を形成した。このようにして得られたスピントンネル膜をリソグラフイープロセスによって１０μｍ角の大きさに加工した後、フォーカスイオンビーム加工装置によって電極を作成し、微少磁気メモリ素子とした。強磁性層の磁化反転を急峻にするために、各層成膜中に検出おまび記録磁界印加方向に平行に約６ｋＡ／ｍの直流磁界を印加し、面内一軸磁気異方性を誘起させた。
【００１９】
図１０は上記のようにして作成した磁気メモリ素子の磁気抵抗変化率の測定結果である。０．５ｋＡ／ｍから４ｋＡ／ｍの磁界範囲で磁化が反平行となり、約１１．５％の高い磁気抵抗変化率が得られている。
〔比較例〕
比較例一１
ガラス基板上に第２の強磁性層として５ｎｍのＮｉ80Ｆｅ20層、非磁性層として２．２ｎｍのＣｕ層、第１の強磁性層として５ｎｍのＣｏ90Ｆｅ10層を、反強磁性層として５０ｎｍのＩｒ50Ｍｎ50層を真空を破ることなくスパッタリングによって順次積層した。強磁性層の磁化反転を急峻にするために、各層成膜中に検出および記録磁界印加方向に平行に約６ｋＡ／ｍの直流磁界を印加し、面内一軸磁気異方性を誘起させた。
【００２０】
図１１は上記のようにして作成した磁気メモリ素子の磁気抵抗変化率の測定結果である。この磁気メモリ素子は、反磁性層の膜厚が厚いために一方向異方性が反転せず、磁気抵抗変化率曲線がＹ軸に対して非対称である。
比較例−２ ．
ガラス基板上に第１の強磁性層として３ｎｍのＣｏ90Ｆｅ10層、非磁性層として２．２ｎmのＣｕ層、第２の強磁性層として３ｎmのＮｉ80Ｆｅ20層を真空を破ることなくスパッタリングによって順次積層した。強磁性層の磁化反転を急峻にするために、各層成膜中に検出および記録磁界印加方向に平行に約６ｋＡ／ｍの直流磁界を印加し、面内一増由磁気異方性を誘起させた。
【００２１】
図１２は上記のようにして作成した磁気メモリ素子の磁気抵抗変化率の測定結果である。両磁性層の磁化反転がほぼ同時に起きているため、高い磁気抵抗変化率は得られていない。
比較例−３
ガラス基板上に第１の強磁性層として３ｎｍのＣｏ90ＦｅlO層、非磁性層として５ｎｍのＣｕ層、第２の強磁性層として３ｎｍのＮｉ80Ｆｅ20層を真空を破ることなくスパッタリングによって順次積層した。
強磁性層の磁化反転を急峻にするために、各層成膜中に検出および記録磁界印加方向に平行に約６ｋＡ／ｍの直流磁界を印加し、面内一軸磁気異方性を誘起させた。
【００２２】
図１３は上記のようにして作成した磁気メモリ素子の磁気抵抗変化率の測定結果である。
０・３ｋＡ／ｍから１・４ｋＡ／ｍの磁界範囲で磁化が反平行となっているが、非磁性金属層の膜厚が厚いため、磁気抵抗変化に関与する電子の割合が減少し、磁気抵抗変化率は約２．７％と低い。
比較例−４
ガラス基板上に第１の強磁性層として１０ｎｍのＣｏ90ＦｅlO層、２ｎｍのＡｌ層を順次積層した後、チヤンバー内に酸素ガスを導入し、該Ａｌ層を酸化させ非磁性酸化層とした。
【００２３】
再びチヤンバー内を十分に真空引きした後、第２の強磁性層として１０ｎｍのＮｉ88Ｆｅ20層を形成した。このようにして得られたスピントンネル膜をリソグラフイープロセスによって１０μm角の大きさに加工した後、フォーカスイオンビーム加工装置によって電極を作成し、微小磁気メモリ素子とした。強磁性層の磁化反転を急峻にするために、各層成膜中に検出および記録磁界印加方向に平行に約６ｋＡ／ｍの直流磁界を印加し、面内一軸磁気異方性を誘起きせた。
【００２４】
図１４は上記のようにして作成した磁気メモリ素子の磁気抵抗変化率の測定結果である。両磁性層の磁化反転磁界の差が小さいため、磁化の反平行状態が
不十分となり、磁気抵抗変化率は約１．２５％と小さい。
【００２５】
【発明の効果】
上記のように本発明の磁気メモリ素子は第１の強磁性層の保磁力を容易に調整することが可能であり、磁気メモリ素子のサイズを小さくしても反磁界による保磁力の減少を相殺でき、記録密度の高い磁気メモリチップを提供できる。
また、強磁性層の間に形成された非磁性金属層の膜厚を薄くすることが可能であり、高い磁気抵抗変化率を有する磁気メモリ素子を得ることができる。
【図面の簡単な説明】
【図１】従来の磁気メモリ素子の基本膜構成の断面図である。
【図２】従来の磁気メモリ素子の記録後の磁化方向を示す図である。
【図３】従来の磁気メモリ素子の検出方法を示す図である。
【図４】本発明の磁気メモリ素子の基本膜構成の断面図である。
【図５】本発明の磁気メモリ素子の第１の磁性層の膜厚に対する第１の磁性層の保磁力の変化を示すグラフである。
【図６】本発明の磁気メモリ素子の反強磁性層の膜厚に対する第１の磁性層の保磁力の変化を示すグラフである。
【図７】本発明の磁気メモリ素子の磁気抵抗曲線と磁化の方向および反強磁性層の一方向異方性の方向を示す図である。
【図８】実施例１の磁気メモリ素子の磁気抵抗変化率曲線を示すグラフである。
【図９】実施例２の磁気メモリ素子の磁気抵抗変化率曲線を示すグラフである。
【図１０】実施例３の磁気メモリ素子の磁気抵抗変化率曲線を示すグラフである。
【図１１】比較例１の磁気メモリ素子の磁気抵抗変化率曲線を示すグラフである。
【図１２】比較例２の磁気メモリ素子の磁気抵抗変化率曲線を示すグラフである。
【図１３】比較例３の磁気メモリ素子の磁気抵抗変化率曲線を示すグラフである。
【図１４】比較例４の磁気メモリ素子の磁気抵抗変化率曲線を示すグラフである。
【符号の説明】
１．基板
２．反強磁性層
３．第１の強磁性層
４．非磁性層
５．第２の強磁性層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic memory element, and more particularly to a nondestructive magnetic memory element that operates with a suitable applied magnetic field, exhibits a high magnetoresistance change rate, and can achieve a high recording density.
[0002]
[Prior art]
The magnetoresistive effect memory element performs recording by making the magnetization direction of the magnetic layer correspond to digital information. Therefore, no external energy supply is required for record keeping. In addition, the manufacturing process is simple compared to a semiconductor memory, and the substrate material is not particularly limited. Therefore, it is expected as an inexpensive large-capacity nonvolatile memory. As shown in FIG. 1, the magnetoresistive effect memory element basically has a sandwich structure having a nonmagnetic layer between two ferromagnetic layers. The two ferromagnetic layers have different coercive forces, and a layer having a relatively small coercive force is a detection layer and a layer having a relatively large coercive force is a memory layer. In the figure, the memory layer is disposed below the nonmagnetic layer and the detection layer is disposed above the nonmagnetic layer. However, the positions of the memory layer and the detection layer may be reversed.
[0003]
Recording is achieved by applying a magnetic field (Hw) larger than the magnetization reversal magnetic field of the memory layer and directing the magnetization of the memory layer parallel to the direction of the recording magnetic field. For example in FIG. As shown, the case where the magnetization of the memory layer is leftward is “0”, and the case where it is rightward is “1”. However, since the magnetization reversal field of the detection layer is smaller than the magnetization reversal field of the memory layer, the magnetization directions of both layers are parallel immediately after recording. In the detection, a certain amount of direct current is passed through the memory element, and a magnetic field (Ha) that is larger than the magnetization reversal magnetic field of the detection layer and smaller than the magnetization reversal magnetic field of the memory layer is applied. This is done by examining the change in potential associated with. When the magnetization directions of both magnetic layers are parallel, the resistivity of the memory element is smaller than when the magnetization directions are antiparallel.
[0004]
As shown in FIG. 3, when a + Ha detection magnetic field is applied to a memory element in which “0” is recorded, the magnetization directions of both magnetic layers become antiparallel and the potential becomes high. The magnetization direction of the layers becomes parallel and the potential is lowered. By passing the signal thus obtained through a differentiating circuit, a negative pulse is obtained. Similarly, a positive pulse is obtained in the memory element in which “1” is recorded. In this detection method, the detected signal is independent of the magnetization direction of the detection layer before detection.
[0005]
In order to give a difference between the magnetization reversal fields of the detection layer and the memory layer, for example, a material having a small coercive force such as NiFe is used for the detection layer, and a material having a large coercive force such as CoFe is used for the memory layer. The ferromagnetic layer has a magnetostatic coupling force that tries to make the directions of magnetizations parallel to each other. Therefore, in order to operate as a memory element, the difference in coercive force between the two layers is the static layer. Must be greater than the magnetic coupling force.
[0006]
[Problems to be solved by the invention]
When the nonmagnetic layer formed between the detection layer and the memory layer is a metal layer, it is preferable that the film thickness is smaller because a larger magnetoresistance change rate can be obtained. However, the magnetostatic coupling force increases due to the thinning of the nonmagnetic metal layer, and the antiparallel state of magnetization cannot be obtained.
[0007]
In addition, in a memory element having a small area, it is difficult to maintain a large coercive force due to the influence of a demagnetizing field. This is also a problem in a spin tunnel type memory element in which the nonmagnetic layer is an insulating film. However, a material having a sufficiently large coercive force as a material for a memory layer of a nondestructive magnetic memory element has not been proposed yet.
[0008]
[Means for Solving the Problems]
The present invention is, at least, an antiferromagnetic layer, a first ferromagnetic layer, a nonmagnetic layer, a second ferromagnetic layer in this order placed, the antiferromagnetic layer, a first ferromagnetic layers and are exchange coupled, I Oh in the magnetic memory device for recording by by changing depending the magnetization direction of the first ferromagnetic layer to the information, the orientation of the unidirectional anisotropy of the antiferromagnetic layer , the Ri first parallel der the magnetization direction of the ferromagnetic layer, Ri by that magnetization direction of the first ferromagnetic layer is reversed, and wherein the magnetic memory device characterized by reversed Monodea Ru. Incidentally, the antiferromagnetic layer may me insulation der.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to the drawings.
FIG. 4A shows a sectional view of the film structure of the magnetic memory element of the present invention. 1 is a substrate, 2 is an antiferromagnetic layer, 3 is a first ferromagnetic layer, 4 is a nonmagnetic layer, and 5 is a second ferromagnetic layer.
[0010]
Further, the stacking order may be reversed as shown in FIG. For the antiferromagnetic layer, Mn-based or Cr-based antiferromagnetic materials such as MnFe, MnIr, MnPt, MnPtCr, and AlCr, and oxide antiferromagnetic materials such as NiO and α-Fe 2 O 3 are used. Higher than the operating temperature is preferred. In particular, a magnetic memory element using an oxide antiferromagnetic material can be expected to have a high rate of change in magnetoresistance because there is no splitting of electrons in the antiferromagnetic material. Co, CoFe, Fe, NiFe, or the like can be used for the first and second ferromagnetic layers. For the nonmagnetic layer, Cu, Al 2 O 3 or the like is used.
[0011]
The reversal of the unidirectional anisotropy of the antiferromagnetic layer is performed via the magnetization of the first ferromagnetic layer that is exchange coupled.
[0012]
That is, when an external magnetic field is applied antiparallel to these directions in a state where the direction of unidirectional anisotropy of the antiferromagnetic layer is parallel to the magnetization direction of the first ferromagnetic layer, the first ferromagnetic layer Is reversed, the magnetic moment of the atoms in the antiferromagnetic layer exchange-coupled with it is also reversed, and the magnetic moment of the atoms in the antiferromagnetic layer is sequentially reversed by the interaction. Reverses the unidirectional anisotropy.
[0013]
The coercive force of the first ferromagnetic layer in the present invention depends on the film thickness of the first ferromagnetic layer, the exchange coupling force between the first ferromagnetic layer and the antiferromagnetic layer, or the film thickness of the antiferromagnetic layer. Change.
In particular, the coercive force can be easily adjusted by appropriately selecting the thickness of the first ferromagnetic layer or the antiferromagnetic layer. FIG. 5 shows the change in coercive force depending on the thickness of the first magnetic layer. However, the sample used for the measurement was a 10 nm NiO layer as an antiferromagnetic layer on a glass substrate, a CoFe layer as a first ferromagnetic layer, a 5 nm Cu layer as a nonmagnetic layer, and a 5 nm as a second ferromagnetic layer. This is a magnetic memory element in which NiFe layers are sequentially stacked. As can be seen from this figure, the coercive force of the first ferromagnetic layer is almost inversely proportional to the film thickness. FIG. 6 shows the change in the coercive force of the first magnetic layer when the thickness of the FeCo layer is kept constant at 5 nm and the thickness of the NiO layer is changed in the magnetic memory element. It can be seen that as the thickness of the NiO layer increases, the coercivity of the first ferromagnetic layer increases, and the coercivity of the first ferromagnetic layer can also be adjusted by changing the thickness of the NiO layer. However, in this magnetic memory element, when the thickness of the NiO layer reaches 20 nm, a shift in the magnetic field direction is observed in the magnetization curve and the magnetoresistance curve, and the inversion of the unidirectional anisotropy of the NiO layer is incomplete.
[0014]
A magnetic memory element in which a first ferromagnetic layer, a nonmagnetic layer, a second ferromagnetic layer, and an antiferromagnetic layer are sequentially laminated is proposed in, for example, Japanese Patent Laid-Open No. 6-295419. However, in the magnetic memory element proposed in this publication, the magnetization direction of the second ferromagnetic layer coupled to the antiferromagnetic layer is fixed, and the antiferromagnetic unidirectional anisotropy is not reversed. Is. Japanese Patent Laid-Open No. 9-139068 discloses a magnetic memory element in which the magnetization direction of a ferromagnetic layer exchange-coupled with antiferromagnetism is reversed, but the antiferromagnetic unidirectional anisotropy is not reversed. Therefore, the magnitude of the magnetic field in which the magnetization becomes antiparallel differs depending on the direction of the applied magnetic field. In such a magnetic memory element, since the magnitude of the recording magnetic field or the detection magnetic field varies depending on the direction of application, the magnetic field application circuit becomes complicated, which is not preferable. In order to reverse the unidirectional anisotropy of the antiferromagnetic layer, it is necessary to select the thickness of the antiferromagnetic layer so that exchange energy cannot be accumulated in the antiferromagnetic layer. However, such a film thickness varies depending on the material and structure of the antiferromagnetic layer.
[0015]
FIG. 7 shows a magnetoresistive curve of the magnetic memory element of the present invention, and a change in the magnetization direction of the corresponding ferromagnetic layer and the direction of unidirectional anisotropy of the antiferromagnetic layer. A case where the applied magnetic field H is H <−H 1 is defined as an initial state. At this time, the magnetization and the direction of unidirectional anisotropy of each layer are all parallel to the direction of the applied magnetic field as shown in FIG. In this state, when the applied magnetic field is H 2 <H <H 1 , the magnetization of the second ferromagnetic layer having a relatively small coercive force is reversed, and the magnetization directions of the first and second ferromagnetic layers are reversed. Parallel and higher resistivity. H 2 is represented by the sum of the original coercive force H c2 of the second ferromagnetic layer and the magnetostatic coupling force H s acting between the two ferromagnetic layers. When the applied magnetic field is further increased and H 1 <H, the magnetization of the first ferromagnetic layer and the unidirectional anisotropy of the antiferromagnetic layer are simultaneously reversed, and the resistivity decreases again. H 2 represents the magnetostatic coupling force H s acting between the second ferromagnetic layer and the sum of the exchange coupling force Hex acting between the original coercive force H c1 of the first ferromagnetic layer and the antiferromagnetic layer. It is expressed by subtracting. Further, when the applied magnetic field is −H 1 <H <−H 2 , the magnetization of the second ferromagnetic layer is reversed, and when the applied magnetic field is set to H <one H 1 , the initial state is restored.
[0016]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples.
(Example 1)
On the glass substrate, a 5 nm Ni 80 Fe 20 layer as a second ferromagnetic layer, a 2.2 nm Cu layer as a nonmagnetic layer, a 5 nm Co 90 Fe 10 layer as a first ferromagnetic layer, and an
[0017]
FIG. 8 shows the measurement results of the magnetoresistance change rate of the magnetic memory element produced as described above. Magnetization becomes antiparallel in a magnetic field range of 2 kA / m to 6 kA / m, and a high magnetoresistance change rate of about 5.9% is obtained.
(Example 2)
A 10 nm Ni 50 O 50 layer as an antiferromagnetic layer on a glass substrate, a 3 nm Co 90 Fe 10 layer as a first ferromagnetic layer, a 2.4 nm Cu layer as a nonmagnetic layer, and a second
[0018]
FIG. 9 shows the measurement results of the magnetoresistance change rate of the magnetic memory element produced as described above. Magnetization becomes antiparallel in the magnetic field range of 2 kA / m to 6.5 kA / m, and a high magnetoresistance change rate of about 5.5% is obtained.
(Example 3)
A 15 nm Ni 50 O 50 layer as an antiferromagnetic layer and a 10 nm Co 90 Fe lO layer as a first ferromagnetic layer and a 2 nm Al layer are sequentially laminated on a glass substrate, and oxygen gas is introduced into the chamber. The Al layer was oxidized to form a nonmagnetic oxide layer. After sufficiently evacuating the inside of the chamber again, a 10 nm Ni 80 Fe 20 layer was formed as the second ferromagnetic layer. The spin tunnel film thus obtained was processed to a size of 10 μm square by a lithographic process, and then an electrode was formed by a focused ion beam processing apparatus to obtain a micro magnetic memory element. In order to make the magnetization reversal of the ferromagnetic layer steep, a DC magnetic field of about 6 kA / m was applied in parallel to the direction of detection and recording magnetic field application during each film formation to induce in-plane uniaxial magnetic anisotropy. .
[0019]
FIG. 10 shows the measurement results of the magnetoresistance change rate of the magnetic memory element produced as described above. Magnetization becomes antiparallel in the magnetic field range of 0.5 kA / m to 4 kA / m, and a high magnetoresistance change rate of about 11.5% is obtained.
[Comparative example]
Comparative Example 1-1
A 5 nm Ni 80 Fe 20 layer as a second ferromagnetic layer, a 2.2 nm Cu layer as a nonmagnetic layer, a 5 nm Co 90 Fe 10 layer as a first ferromagnetic layer, and an antiferromagnetic layer on a glass substrate As an Ir 50 Mn 50 layer of 50 nm was sequentially laminated by sputtering without breaking the vacuum. In order to make the magnetization reversal of the ferromagnetic layer steep, a DC magnetic field of about 6 kA / m was applied in parallel with the direction of detection and recording magnetic field application during each layer formation to induce in-plane uniaxial magnetic anisotropy.
[0020]
FIG. 11 shows the measurement results of the magnetoresistance change rate of the magnetic memory element produced as described above. In this magnetic memory element, since the diamagnetic layer is thick, the unidirectional anisotropy is not reversed, and the magnetoresistance change rate curve is asymmetric with respect to the Y axis.
Comparative Example-2.
A 3 nm Co 90 Fe 10 layer as a first ferromagnetic layer, a 2.2 nm Cu layer as a nonmagnetic layer, and a 3 nm Ni 80 Fe 20 layer as a second ferromagnetic layer on a glass substrate without breaking the vacuum. The layers were sequentially laminated by sputtering. In order to make the magnetization reversal of the ferromagnetic layer steep, a DC magnetic field of about 6 kA / m is applied in parallel to the detection and recording magnetic field application direction during film formation of each layer to induce in-plane increased magnetic anisotropy. It was.
[0021]
FIG. 12 shows the measurement results of the magnetoresistance change rate of the magnetic memory element produced as described above. Since the magnetization reversal of both magnetic layers occurs almost simultaneously, a high magnetoresistance change rate is not obtained.
Comparative Example-3
Sputtering a 3 nm Co 90 Fe 1O layer as a first ferromagnetic layer, a 5 nm Cu layer as a nonmagnetic layer, and a 3 nm Ni 80 Fe 20 layer as a second ferromagnetic layer on a glass substrate without breaking the vacuum. Laminated sequentially.
In order to make the magnetization reversal of the ferromagnetic layer steep, a DC magnetic field of about 6 kA / m was applied in parallel with the direction of detection and recording magnetic field application during each layer formation to induce in-plane uniaxial magnetic anisotropy.
[0022]
FIG. 13 shows the measurement results of the magnetoresistance change rate of the magnetic memory element produced as described above.
Magnetization is antiparallel in the magnetic field range of 0.3 kA / m to 1.4 kA / m. However, since the nonmagnetic metal layer is thick, the proportion of electrons involved in the magnetoresistance change decreases, and The resistance change rate is as low as about 2.7%.
Comparative Example-4
After sequentially laminating a 10 nm Co 90 Fe lO layer and a 2 nm Al layer as a first ferromagnetic layer on a glass substrate, oxygen gas was introduced into the chamber to oxidize the Al layer to form a nonmagnetic oxide layer. .
[0023]
After sufficiently evacuating the inside of the chamber again, a 10 nm Ni 88 Fe 20 layer was formed as the second ferromagnetic layer. The spin tunnel film thus obtained was processed to a size of 10 μm square by a lithographic process, and then an electrode was formed by a focused ion beam processing apparatus to obtain a micro magnetic memory element. In order to make the magnetization reversal of the ferromagnetic layer steep, a DC magnetic field of about 6 kA / m was applied in parallel to the direction of detection and recording magnetic field application during film formation of each layer to induce in-plane uniaxial magnetic anisotropy.
[0024]
FIG. 14 shows the measurement results of the magnetoresistance change rate of the magnetic memory element produced as described above. Since the difference in magnetization reversal field between the two magnetic layers is small, the antiparallel state of magnetization becomes insufficient, and the magnetoresistance change rate is as small as about 1.25%.
[0025]
【The invention's effect】
As described above, the magnetic memory element of the present invention can easily adjust the coercive force of the first ferromagnetic layer, and even if the size of the magnetic memory element is reduced, the decrease in the coercive force due to the demagnetizing field is offset. And a magnetic memory chip having a high recording density can be provided.
Further, the film thickness of the nonmagnetic metal layer formed between the ferromagnetic layers can be reduced, and a magnetic memory element having a high magnetoresistance change rate can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a basic film configuration of a conventional magnetic memory element.
FIG. 2 is a diagram showing a magnetization direction after recording of a conventional magnetic memory element.
FIG. 3 is a diagram illustrating a conventional method for detecting a magnetic memory element.
FIG. 4 is a cross-sectional view of the basic film configuration of the magnetic memory element of the present invention.
FIG. 5 is a graph showing a change in coercive force of the first magnetic layer with respect to the thickness of the first magnetic layer of the magnetic memory element of the present invention.
FIG. 6 is a graph showing a change in coercivity of the first magnetic layer with respect to the film thickness of the antiferromagnetic layer of the magnetic memory element of the present invention.
FIG. 7 is a diagram showing a magnetoresistive curve, a magnetization direction, and a direction of unidirectional anisotropy of an antiferromagnetic layer of the magnetic memory element of the present invention.
8 is a graph showing a magnetoresistance change rate curve of the magnetic memory element of Example 1. FIG.
9 is a graph showing a magnetoresistance change rate curve of the magnetic memory element of Example 2. FIG.
10 is a graph showing a magnetoresistance change rate curve of the magnetic memory element of Example 3. FIG.
11 is a graph showing a magnetoresistance change rate curve of a magnetic memory element of Comparative Example 1. FIG.
12 is a graph showing a magnetoresistance change rate curve of a magnetic memory element of Comparative Example 2. FIG.
13 is a graph showing a magnetoresistance change rate curve of a magnetic memory element of Comparative Example 3. FIG.
14 is a graph showing a magnetoresistance change rate curve of a magnetic memory element of Comparative Example 4. FIG.
[Explanation of symbols]
1.
Claims (5)
前記第１の強磁性層の磁化方向を情報に応じて変化させて記録を行う磁気メモリ素子であって、
前記反強磁性層の一方向異方性の向きは、前記第１の強磁性層の磁化方向と平行であり、該第１の強磁性層の磁化方向が反転することにより、反転することを特徴とする磁気メモリ素子。At least an antiferromagnetic layer, a first ferromagnetic layer, a nonmagnetic layer, and a second ferromagnetic layer are arranged in this order, and the antiferromagnetic layer is exchange coupled with the first ferromagnetic layer. And
A magnetic memory element that performs recording by changing the magnetization direction of the first ferromagnetic layer according to information,
The direction of unidirectional anisotropy of the antiferromagnetic layer is parallel to the magnetization direction of the first ferromagnetic layer, and is reversed when the magnetization direction of the first ferromagnetic layer is reversed. A magnetic memory element.
前記第２の強磁性層を、前記第１の強磁性層に記録された情報を読み出すための検出層として行うことを特徴とする請求項１〜４のいずれか１項に記載の磁気メモリ素子。Reading information recorded in the magnetic memory element by changing the magnetization direction of the first ferromagnetic layer according to the information,
5. The magnetic memory element according to claim 1, wherein the second ferromagnetic layer is used as a detection layer for reading information recorded in the first ferromagnetic layer. 6. .
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP34902098A JP3673661B2 (en) | 1998-12-08 | 1998-12-08 | Magnetic memory element |
| US09/457,084 US6215695B1 (en) | 1998-12-08 | 1999-12-07 | Magnetoresistance element and magnetic memory device employing the same |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP34902098A JP3673661B2 (en) | 1998-12-08 | 1998-12-08 | Magnetic memory element |
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| JP3673661B2 true JP3673661B2 (en) | 2005-07-20 |
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