JP6967259B2 - High-sensitivity surface direct energization giant magnetoresistive element and its applications - Google Patents
High-sensitivity surface direct energization giant magnetoresistive element and its applications Download PDFInfo
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Description
本発明は、基体上に強磁性層と非磁性層とが交互に積層された構造を持つ磁気抵抗素子に関し、より具体的には、特定の構造(層数、層厚さ)を有することにより優れた感度(高いMR比)、を示す面直通電巨大磁気抵抗素子に関する。
The present invention relates to a magnetoresistive element having a structure in which ferromagnetic layers and non-magnetic layers are alternately laminated on a substrate, and more specifically, by having a specific structure (number of layers, layer thickness). It relates to a surface direct current giant magnetoresistive element exhibiting excellent sensitivity (high MR ratio).
面直電流巨大磁気抵抗(CPP−GMR)素子は強磁性層/非磁性層/強磁性層の積層膜をサブμm以下のサイズにピラー化させた構造を持つ。ピラーに対して電流を流した際、2つの強磁性層の磁化の相対角度によって電気抵抗が変化するため、磁場を電気的に検出することができる。しかしながら、CoFeなど一般的な強磁性体を利用した場合においては磁気抵抗(MR)比が3%程度であり(例えば、非特許文献1参照。)、センサーとしての感度が低いことが課題であった。ところが近年、高いスピン偏極率を有するCo基ホイスラー合金(Co2MnSi、Co2(Fe0.4Mn0.6)Si、Co2Fe(Ga0.5Ge0.5)など)を強磁性層とし、格子整合性の良いAg非磁性層を用いた(001)配向ホイスラー/Ag/ホイスラーエピタキシャルCPP−GMR素子で、30−60%ものMR比と、抵抗変化面積ΔRA=10Ωμm2が実現されている(例えば、非特許文献2から4参照。)。
電流センサーや地磁気センサー等に磁気抵抗素子を用いる場合、外部磁場に対してセンサー素子の直線的な応答が重要となる。さらに、高い感度のセンサーを実現するために、外部磁場に対してセンサー素子からの大きな電気的応答、つまり大きなMR比が求められる。トンネル磁気抵抗素子を用いて、上下の強磁性層の磁気モーメントが直行する様に積層膜を作成し、フリー層に対して垂直な外部磁場を与えることで直線的な応答と高いMR比(110%)が可能となることが報告されているが(例えば、非特許文献5参照)、その検知可能磁場範囲は±10mT程度と狭く、耐熱性も250℃程度までと低い。また、非特許文献6によれば、トンネル磁気抵抗素子を用いて、上下の強磁性層の磁気モーメントが直行する様に積層膜を作成し、フリー層厚を減少させることで直線応答性の改善を図っているが、直線応答性の改善に伴って、MR比が減少してしまうという欠点がある。
それに対して、ホイッスラー合金(Co2Fe(Al0.5Si0.5))とAgを用いた面直電流巨大磁気抵抗(CPP−GMR)素子において、Ag層の厚さを変えることで、上下の強磁性層の相関交換結合の強さが変わることが報告されており(例えば、非特許文献7参照)、反強磁性結合をとるようなAg膜厚を用いた場合に、検知可能磁場範囲を±40mT程度と広くすることができ、450℃と良好な素子の耐熱性も実現できている。
しかし、より高い感度の磁気センサー等が要求されており、更なる高感度化(MR比の向上)が求められていた。
The surface direct current giant magnetoresistive (CPP-GMR) element has a structure in which a laminated film of a ferromagnetic layer / a non-magnetic layer / a ferromagnetic layer is pillared to a size of sub μm or less. When a current is passed through the pillars, the electrical resistance changes depending on the relative angle of magnetization of the two ferromagnetic layers, so the magnetic field can be detected electrically. However, when a general ferromagnet such as CoFe is used, the magnetic resistance (MR) ratio is about 3% (see, for example, Non-Patent Document 1), and the problem is that the sensitivity as a sensor is low. rice field. However, in recent years, Co-based Whistler alloys (Co 2 MnSi, Co 2 (Fe 0.4 Mn 0.6 ) Si, Co 2 Fe (Ga 0.5 Ge 0.5 ), etc.) having high spin polarization have been strengthened. The (001) oriented Hoisler / Ag / Hoisler epitaxial CPP-GMR element using an Ag non-magnetic layer with good lattice consistency as the magnetic layer realizes an MR ratio of 30-60% and a resistance change area ΔRA = 10Ωμm 2. (See, for example, Non-Patent
When a magnetoresistive element is used for a current sensor, a geomagnetic sensor, or the like, the linear response of the sensor element to an external magnetic field is important. Further, in order to realize a sensor with high sensitivity, a large electrical response from the sensor element to an external magnetic field, that is, a large MR ratio is required. Using a tunnel magnetoresistive element, a laminated film is created so that the magnetic moments of the upper and lower ferromagnetic layers are orthogonal, and an external magnetic field perpendicular to the free layer is applied to provide a linear response and a high MR ratio (110). %) Is possible (see, for example, Non-Patent Document 5), but its detectable magnetic field range is as narrow as about ± 10 mT, and its heat resistance is as low as about 250 ° C. Further, according to Non-Patent Document 6, using a tunnel magnetoresistive element, a laminated film is formed so that the magnetic moments of the upper and lower ferromagnetic layers are orthogonal to each other, and the free layer thickness is reduced to improve the linear responsiveness. However, there is a drawback that the MR ratio decreases as the linear response is improved.
On the other hand, in a face-to-face current giant magnetoresistive (CPP-GMR) element using a Whistler alloy (Co 2 Fe (Al 0.5 Si 0.5)) and Ag, by changing the thickness of the Ag layer, It has been reported that the strength of the correlation exchange bond between the upper and lower ferromagnetic layers changes (see, for example, Non-Patent Document 7), and a detectable magnetic field is used when an Ag film thickness that forms an antiferromagnetic bond is used. The range can be widened to about ± 40 mT, and good heat resistance of the element of 450 ° C. can be realized.
However, there is a demand for a magnetic sensor having higher sensitivity, and further improvement in sensitivity (improvement of MR ratio) is required.
本発明は、上記の背景技術に鑑み、従来技術より一層高いMR比を有し、高い感度を有する、面直通電巨大磁気抵抗素子(CPP−GMR)を提供すること、及びその関連技術を開発することを課題としている。
In view of the above background art, has a higher MR ratio than the prior art, has high sensitivity, to provide a surface direct electrostatic giant magnetoresistive element (CPP-GMR), and develop related technologies The challenge is to do.
本発明者らは、鋭意検討の結果、特定の構造、より具体的には磁気フリー層の層数が奇数であり、かつ特定の非磁性層の層厚さを有する面直通電巨大磁気抵抗素子(CPP−GMR)を用いることで、高いMR比を実現でき、上記課題を解決しうることを見い出し、本発明を完成するに至った。
すなわち本発明は、
[1] 基体と、
該基体上に設けられ、n層の磁気フリー層と、n−1層の非磁性層とを交互に積層してなる積層部と、
を有する面直通電巨大磁気抵抗素子であって、
nが奇数であり、
少なくとも1つの該非磁性層が、その両面に接する磁気フリー層のペアの間に反強磁性層間交換結合が形成される厚さを有すると共に、磁気固定層を有しない、上記面直通電巨大磁気抵抗素子、である。
As a result of diligent studies, the present inventors have found that a surface-directed giant magnetoresistive element having a specific structure, more specifically, an odd number of magnetic free layers and a specific non-magnetic layer thickness. By using (CPP-GMR ), it was found that a high MR ratio could be realized and the above-mentioned problems could be solved, and the present invention was completed.
That is, the present invention
[1] The substrate and
A laminated portion provided on the substrate and formed by alternately laminating n-layer magnetic free layers and n-1 non-magnetic layers.
It is a surface direct energization giant magnetoresistive element having
n is an odd number
The surface direct energization giant magnetoresistor having a thickness at which at least one non-magnetic layer forms an antiferromagnetic interlayer exchange bond between a pair of magnetic free layers in contact with both sides thereof and having no magnetic fixing layer. The element .
以下、[2]から[12]は、それぞれ本発明の好ましい実施形態の一つである。
[2] 前記非磁性層の全てが、その両面に接する磁気フリー層のペアの間に反強磁性層間交換結合が形成される厚さを有する、[1]に記載の面直通電巨大磁気抵抗素子。
[3] 反強磁性層間交換結合が形成されている1つの非磁性層、及びその両面に接する磁気フリー層のペアについて面内方向に測定した残留磁化/飽和磁化の比が0.8以下である、[1]又は[2]に記載の面直通電巨大磁気抵抗素子。
[4] 前記非磁性層を介して反強磁性層間交換結合を形成する前記磁気フリー層のペアが、同一又は略同一の総磁気モーメントを有する、[1]から[3]のいずれか一項に記載の面直通電巨大磁気抵抗素子。
[5] 前記磁気フリー層が、Co基ホイスラー合金系ハーフメタル材料を含む、[1]から[4]のいずれか一項に記載の面直通電巨大磁気抵抗素子。
[6] 前記Co基ホイスラー合金系ハーフメタル材料が、Co2YZ(ここで、Yは、Ti、V、Cr、Mn、及びFeからなる群より選ばれる少なくとも1種の元素であり、Zは、Al、Si,Ga,Ge、In、及びSnからなる群より選ばれる少なくとも1種の元素である。)で表される組成を有する、[5]に記載の面直通電巨大磁気抵抗素子。
[7] 前記非磁性層が、スピン拡散長が30nm以上である材料系で構成される、[1]から[6]のいずれか一項に記載の面直通電巨大磁気抵抗素子。
[8] 前記非磁性層が、Cu、Al、Ag、及びZnからなる群より選ばれる少なくとも1種の元素を含有する、[1]から[7]のいずれか一項に記載の面直通電巨大磁気抵抗素子。
[9] バッファー/電極層及びキャップ層を更に有する、[1]から[8]のいずれか一項に記載の面直通電巨大磁気抵抗素子。
[10] [1]から[9]のいずれか一項に記載の面直通電巨大磁気抵抗素子を備える、地磁気センサー、電流センサー、又は磁気ヘッド。
Hereinafter, [2] to [12] are each one of the preferred embodiments of the present invention.
[2] The surface direct conduction giant magnetoresistor according to [1] , wherein all of the non-magnetic layers have a thickness at which an antiferromagnetic interlayer exchange bond is formed between a pair of magnetic free layers in contact with both sides thereof. Element .
[3] When the ratio of residual magnetization / saturation magnetization measured in the in-plane direction for one non-magnetic layer on which an antiferromagnetic interlayer exchange bond is formed and a pair of magnetic free layers in contact with both sides thereof is 0.8 or less. The surface direct current enormous magnetoresistive element according to [1] or [2].
[4] Any one of [1] to [3], wherein the pair of the magnetic free layers forming the antiferromagnetic interlayer exchange bond via the non-magnetic layer has the same or substantially the same total magnetic moment. The surface direct energization giant magnetoresistive element described in 1.
[5] The surface direct energization giant magnetoresistive element according to any one of [1] to [4], wherein the magnetic free layer contains a Co-based Hoisler alloy-based half metal material.
[6] The Co-based Whistler alloy-based half-metal material is Co 2 YZ (where Y is at least one element selected from the group consisting of Ti, V, Cr, Mn, and Fe, and Z is , Al, Si, Ga, Ge, In, and Sn), which is at least one element selected from the group.). The surface direct energization giant magnetic resistance element according to [5].
[7] The surface direct energization giant magnetoresistive element according to any one of [1] to [6], wherein the non-magnetic layer is composed of a material system having a spin diffusion length of 30 nm or more.
[8] The surface direct energization according to any one of [1] to [7], wherein the non-magnetic layer contains at least one element selected from the group consisting of Cu, Al, Ag, and Zn. Giant magnetoresistive element .
[9] The surface direct energization giant magnetoresistive element according to any one of [1] to [8], further comprising a buffer / electrode layer and a cap layer.
[10] A geomagnetic sensor, a current sensor, or a magnetic head comprising the surface direct energization giant magnetoresistive element according to any one of [1] to [9].
本発明の面直通電巨大磁気抵抗素子によれば、従来技術では実現し得なかった高いMR比得られるので、高い感度を有する、面直通電巨大磁気抵抗素子(CPP−GMR)を実現できる。本発明の面直通電巨大磁気抵抗素子は、その積層部の層数を増加させることで、比較的容易に外部磁場と抵抗値との直線性を向上することができるので、高い感度と直線性とを両立した面直通電巨大磁気抵抗素子を実現することができる。
According to the surface direct energization giant magnetoresistive element of the present invention, a high MR ratio that could not be realized by the prior art can be obtained, so that a surface direct energization giant magnetoresistive element (CPP-GMR) having high sensitivity can be realized. The surface direct energization giant magnetoresistive element of the present invention can improve the linearity between the external magnetic field and the resistance value relatively easily by increasing the number of layers of the laminated portion, and thus has high sensitivity and linearity. It is possible to realize a surface direct energization giant magnetoresistive element that achieves both.
基体と、
該基体上に設けられ、n層の磁気フリー層と、n−1層の非磁性層とを交互に積層してなる積層部と、
を有する面直通電巨大磁気抵抗素子であって、
nが奇数であり、
少なくとも1つの該非磁性層が、その両面に接する磁気フリー層のペアの間に反強磁性層間交換結合が形成される厚さを有する、上記面直通電巨大磁気抵抗素子、である。
With the substrate
A laminated portion provided on the substrate and formed by alternately laminating n-layer magnetic free layers and n-1 non-magnetic layers.
It is a surface direct energization giant magnetoresistive element having
n is an odd number
The surface direct energization giant magnetoresistive element , wherein the at least one non-magnetic layer has a thickness at which an antiferromagnetic interlayer exchange bond is formed between a pair of magnetic free layers in contact with both sides thereof.
基体
本発明においては、基体上に、複数の磁気フリー層と複数の非磁性層とを交互に積層してなる積層部が設けられる。
基体は、その上に通常強磁性材料からなる磁気フリー層、及び非磁性材料からなる非磁性を積層することができるものであれば特に制限は無いが、例えば単結晶MgO基体を好ましく用いることができる。あるいは、好ましくはホイスラー合金を含む磁気フリー層が
多結晶となるような、Siや金属、合金等を基体として使ってもよい。コストの観点からは、表面酸化Si基体が安価なため基体として好ましいが、半導体製造用のシリコン基体を用いてもよく、またガラス基体や金属基体を用いてもよい。これらのいずれの材料を基体に用いても、本発明の構成を具備し、かつ適切な設計を行うことで、優れた外部磁場と抵抗値との直線性を示す一方で高い感度を有する、面直通電巨大磁気抵抗素子(CPP−GMR)用積層膜を得ることができる。
基体の厚さには特に限定は無く、本発明の目的に反しない限りにおいて当業者が適宜設定すればよいが、機械的強度、磁気抵抗素子製造プロセスにおける取り扱いの容易さ等の観点から、0.1〜1mmであることが好ましく、0.2〜0.5mmであることが特に好ましい。
Substrate In the present invention, a laminated portion formed by alternately laminating a plurality of magnetic free layers and a plurality of non-magnetic layers is provided on the substrate.
The substrate is not particularly limited as long as it can be laminated with a magnetic free layer usually made of a ferromagnetic material and a non-magnetic material made of a non-magnetic material, but for example, a single crystal MgO substrate is preferably used. can. Alternatively, Si, a metal, an alloy, or the like, which preferably forms a polycrystal in the magnetic free layer containing a Whistler alloy, may be used as the substrate. From the viewpoint of cost, the surface oxide Si substrate is preferable as a substrate because it is inexpensive, but a silicon substrate for semiconductor production may be used, or a glass substrate or a metal substrate may be used. Regardless of which of these materials is used as the substrate, a surface having the configuration of the present invention and having high sensitivity while exhibiting excellent linearity between the external magnetic field and the resistance value by appropriately designing the substrate. A laminated film for a directly energized giant magnetoresistive element (CPP-GMR) can be obtained.
The thickness of the substrate is not particularly limited and may be appropriately set by those skilled in the art as long as it does not contradict the object of the present invention. .1 to 1 mm is preferable, and 0.2 to 0.5 mm is particularly preferable.
積層部
本発明において基体上に設けられる積層部は、n層の磁気フリー層とn−1層の非磁性層とを交互に積層したものである。
ここで、nは奇数であり、また非磁性層は、その両面に接する磁気フリー層のペアの間に挟まれるものであるので、フリー層は複数存在するものである。従って、磁気フリー層は、少なくとも3層設けられるものである。この結果、2つの磁気フリー層の間に挟まれる非磁性層は、少なくとも2層設けられる。
磁気フリー層の層数は5層以上であることがより好ましい。磁気フリー層の層数が多いほど、本発明の面直通電巨大磁気抵抗素子用積層膜を用いた面直通電巨大磁気抵抗素子は、外部磁場と抵抗値との直線性に優れる傾向があるためである。
Laminated portion In the present invention, the laminated portion provided on the substrate is formed by alternately laminating n layers of magnetic free layers and n-1 layers of non-magnetic layers.
Here, n is an odd number, and the non-magnetic layer is sandwiched between a pair of magnetic free layers in contact with both sides thereof, so that there are a plurality of free layers. Therefore, at least three magnetic free layers are provided. As a result, at least two non-magnetic layers sandwiched between the two magnetic free layers are provided.
It is more preferable that the number of magnetic free layers is 5 or more. As the number of magnetic free layers increases, the surface direct energization giant magnetoresistive element using the laminated film for the surface direct energization giant magnetoresistive element of the present invention tends to have excellent linearity between the external magnetic field and the resistance value. Is.
本発明において基体上に設けられる積層部は、磁気フリー層の層数が奇数である。磁気フリー層の層数が奇数であることにより、高い磁気抵抗(MR)比を得ることができる。磁気フリー層の層数が奇数であることにより高い磁気抵抗(MR)比が得られるメカニズムは必ずしも明らかではないが、磁気フリー層の層数が奇数の場合には、隣接する磁気フリー層同士の磁化の方向が相互に完全に反転している状態が熱的に安定であり、外部磁場がゼロのときにこの熱的に安定な状態となって高い電気抵抗を示すことと、何らかの関連があるものと推測される。 In the laminated portion provided on the substrate in the present invention, the number of layers of the magnetic free layer is an odd number. Since the number of magnetic free layers is an odd number, a high reluctance (MR) ratio can be obtained. The mechanism by which a high reluctance (MR) ratio is obtained due to the odd number of layers of the magnetic free layer is not always clear, but when the number of layers of the magnetic free layer is odd, the adjacent magnetic free layers are connected to each other. It is thermally stable when the directions of magnetization are completely reversed from each other, and it has something to do with this thermally stable state when the external magnetic field is zero and showing high electrical resistance. It is presumed to be.
本発明の面直通電巨大磁気抵抗素子用積層膜を構成する積層部においては、非磁性層を介して隣接する2つの磁気フリー層によって構成される磁気フリー層のペアのうち少なくとも1つのペアの間に、反強磁性層間交換結合が形成される。反強磁性層間交換結合が形成されているか否かは、1つの非磁性層及びその両面に接する磁気フリー層のペアについて面内方向に測定した残留磁化/飽和磁化の比で判断することができる。すなわち、磁気フリー層のペアの間に反強磁性層間交換結合が形成されることで、当該磁気フリー層のペア及びその間の非磁性層の面内方向の飽和磁界は増大し、これに伴い残留磁化/飽和磁化の比は反強磁性層間交換結合が形成されていない場合と比較して減少するので、これを測定することで、当該磁気フリー層のペアの間に反強磁性層間交換結合が形成されているか否かを判断することができる。
磁気フリー層のペアの間に、反強磁性層交換結合が形成されるか否かは、磁気フリー層及び非磁性層の材料が特定されている場合、非磁性層の厚さに依存するので、磁気フリー層のペアの間に反強磁性層交換結合が形成されるということは、非磁性層が、その両面に接する磁気フリー層のペアの間に反強磁性層間交換結合が形成される厚さを有することを意味する。非磁性層の厚さは、磁気フリー層のペアの間の強磁性交換結合の強度が最小となり、かつ、それらの間の反強磁性層間交換結合の強度が最大となるような厚さであることが好ましい。
強磁性交換結合の強度が小さいことは、ノイズ低減の観点からも好ましい。
In the laminated portion constituting the laminated film for the surface direct energization giant magnetoresistive element of the present invention, at least one pair of magnetic free layers composed of two adjacent magnetic free layers via a non-magnetic layer. An antiferromagnetic interlayer exchange bond is formed between them. Whether or not an antiferromagnetic interlayer exchange bond is formed can be determined by the ratio of residual magnetization / saturation magnetization measured in the in-plane direction for one non-magnetic layer and a pair of magnetic free layers in contact with both sides thereof. .. That is, by forming an antiferromagnetic interlayer exchange bond between the pairs of magnetic free layers, the saturated magnetic field in the in-plane direction of the pair of magnetic free layers and the non-magnetic layer between them increases, and remains accordingly. Since the ratio of magnetization / saturation magnetization is reduced as compared with the case where the antiferromagnetic interlayer exchange bond is not formed, by measuring this, the antiferromagnetic interlayer exchange bond is formed between the pair of the magnetic free layers. It is possible to judge whether or not it is formed.
Whether or not an antiferromagnetic layer exchange bond is formed between a pair of magnetic free layers depends on the thickness of the non-magnetic layer, if the material of the magnetic free layer and the non-magnetic layer is specified. The formation of an anti-ferrometric layer exchange bond between a pair of magnetic free layers means that the non-magnetic layer forms an anti-ferrometric interlayer exchange bond between the pair of magnetic free layers in contact with both sides thereof. Means to have a thickness. The thickness of the non-magnetic layer is such that the strength of the ferromagnetic exchange bond between the pair of magnetic free layers is the minimum and the strength of the antiferromagnetic interlayer exchange bond between them is the maximum. Is preferable.
The low strength of the ferromagnetic exchange coupling is also preferable from the viewpoint of noise reduction.
非磁性層を介して隣接する2つの磁気フリー層によって構成される磁気フリー層のペア間に反強磁性層間交換結合が形成されることで、高い感度を有する、面直通電巨大磁気抵抗素子を実現することができる。また、外部磁場と抵抗値との直線性を向上させることも、比較的容易になる。
本発明の面直通電巨大磁気抵抗素子用積層膜を構成する積層部においては、非磁性層を介して隣接する2つの磁気フリー層によって構成される磁気フリー層のペアのうち少なくとも1つのペアの間に反強磁性層間交換結合が形成されるが、積層部に存在する全ての磁気フリー層のペアの間に反強磁性層間交換結合が形成されることが好ましく、言い換えれば、積層部に存在する非磁性層の全てが、その両面に接する磁気フリー層のペアの間に反強磁性層間交換結合が形成される厚さを有することが好ましい。この様な構成を採用した実施形態においては、磁気抵抗(MR)比は、更に優れたものとなる。
An antiferromagnetic interlayer exchange bond is formed between a pair of magnetic free layers composed of two adjacent magnetic free layers via a non-magnetic layer, so that a surface direct current giant magnetoresistive element having high sensitivity can be obtained. It can be realized. It is also relatively easy to improve the linearity between the external magnetic field and the resistance value.
In the laminated portion constituting the laminated film for the surface direct energization giant magnetic resistance element of the present invention, at least one pair of magnetic free layers composed of two adjacent magnetic free layers via a non-magnetic layer. Anti-ferrometric interlayer exchange bonds are formed between them, but it is preferable that anti-ferrometric interlayer exchange bonds are formed between all the pairs of magnetic free layers existing in the laminated portion, in other words, they are present in the laminated portion. It is preferable that all of the non-magnetic layers to be magnetized have a thickness at which an anti-ferrometric interlayer exchange bond is formed between a pair of magnetic free layers in contact with both sides thereof. In the embodiment adopting such a configuration, the reluctance (MR) ratio becomes further excellent.
非磁性層を介して反強磁性層間交換結合を形成する前記磁気フリー層のペアは、同一又は略同一の総磁気モーメントを有することが好ましい。磁気フリー層のペアは、同一又は略同一の総磁気モーメントを有することで、ペア全体としての磁気モーメントが相殺され、当該ペアを構成する磁気フリー層以外の磁気フリー層に与える影響が低減されるため、外部磁場と抵抗値との直線性の向上に寄与しうるので好ましい。 The pair of magnetic free layers forming an antiferromagnetic interlayer exchange bond via a non-magnetic layer preferably has the same or substantially the same total magnetic moment. By having the same or substantially the same total magnetic moment in the pair of magnetic free layers, the magnetic moments of the pair as a whole are canceled out, and the influence on the magnetic free layers other than the magnetic free layers constituting the pair is reduced. Therefore, it is preferable because it can contribute to the improvement of the linearity between the external magnetic field and the resistance value.
磁気フリー層
本発明の面直通電巨大磁気抵抗素子用積層膜の積層部を構成する磁気フリー層は、強磁性材料を含む層である点で、いわゆる固定層と共通するが、その磁化の方向が固定されていない点で、いわゆる固定層と区別される。
すなわち、いわゆる固定層は、隣接又は近接するする別の強磁性層(ピニング層ともいう)でその磁化の方向が固定されているのに対して、磁気フリー層は、その磁化の方向が固定されておらず、磁化の方向が外部磁場によって応答可能な構成となっている。
Magnetic-free layer The magnetic-free layer that constitutes the laminated portion of the laminated film for the surface-directed magnetoresistive element of the present invention is a layer containing a ferromagnetic material, and is common with a so-called fixed layer, but its magnetization direction. Is not fixed, which distinguishes it from the so-called fixed layer.
That is, the so-called fixed layer has its magnetization direction fixed by another ferromagnetic layer (also called a pinning layer) adjacent to or adjacent to it, whereas the magnetic free layer has its magnetization direction fixed. However, the direction of magnetization is responsive to an external magnetic field.
磁気フリー層は、他の磁気フリー層と反強磁性層間交換結合を形成しうるものであればよく、通常は強磁性材料からなる、又は強磁性材料を含んでなるものであり、例えば鉄(Fe),コバルト(Co),ニッケル(Ni),硼素(B),マンガン(Mn),クロム(Cr),ハフニウム(Hf),銅(Cu),ジルコニウム(Zr),タンタル(Ta),チタン(Ti)およびそれらの合金のうちの1種または2種以上によって構成することができる。
巨大磁気抵抗素子の感度の点などから、磁気フリー層は、Co基ホイスラー合金系ハーフメタル材料を含むものであることが好ましい。
The magnetic free layer may be any one capable of forming an antiferromagnetic interlayer exchange bond with another magnetic free layer, and is usually made of a ferromagnetic material or contains a ferromagnetic material, for example, iron ( Fe), cobalt (Co), nickel (Ni), boron (B), manganese (Mn), chromium (Cr), hafnium (Hf), copper (Cu), zirconium (Zr), tantalum (Ta), titanium ( It can be composed of one or more of Ti) and their alloys.
From the viewpoint of the sensitivity of the giant magnetoresistive element, the magnetic free layer preferably contains a Co-based Rousser alloy-based half-metal material.
ホイスラー合金としては、組成式例えば
Co2XY(X=Mn,Fe、Y=Si,Ge,Al,Ga,Sn,As,Ti,V,Cr)、
Co2CrZ(Z=Si,Ge,Al,Ga,Sn,As,Ti,V,)、
Co2FeAl0.5Si0.5、
Co2FeCr0.5Al0.5
である合金が知られている。
ホイスラー合金は、Co2MnGeを例に取ると、三つの元素がランダムに配置するA2構造、bcc(体心立方格子)の四隅にCoが配置され、中心にMnとGeがランダムに配置するB2構造とCoが四隅にあってMnとGeが交互に配置するL21構造の3つの状態を持つ。この規則化度がA2構造からB2構造へ、B2構造からL21構造へと進むにつれてハーフメタルの性質を示す分極率が増加する
本実施形態において特に好ましいCo基ホイスラー合金系ハーフメタル材料としては、Co2YZ(ここで、Yは、Ti、V、Cr、Mn、及びFeからなる群より選ばれる少なくとも1種の元素であり、Zは、Al、Si,Ga,Ge、In、及びSnからなる群より選ばれる少なくとも1種の元素である。)で表される組成を有するものを挙げることができる。
層間交換結合は、磁気フリー層と非磁性層との間に形成される量子井戸状態に起因することが報告されており、電子状態が類似する材料であれば同様の効果が得られることが合理的に推定される。上記の材料は、実験的に本発明の効果が確認されているCo基ホイスラー合金系ハーフメタル材料と電子状態が類似しており、同様の効果が得られるであろうことが当業者により合理的に理解される。
The whisler alloy has a composition formula of, for example, Co 2 XY (X = Mn, Fe, Y = Si, Ge, Al, Ga, Sn, As, Ti, V, Cr).
Co 2 CrZ (Z = Si, Ge, Al, Ga, Sn, As, Ti, V,),
Co 2 FeAl 0.5 Si 0.5 ,
Co 2 FeCr 0.5 Al 0.5
Alloys are known.
Taking Co 2 MnGe as an example, the Whisler alloy has an A2 structure in which three elements are randomly arranged, Co is arranged at the four corners of bcc (body-centered cubic lattice), and Mn and Ge are randomly arranged in the center of B2. It has three states: the structure and the L21 structure in which Co is at the four corners and Mn and Ge are arranged alternately. As the degree of regularity progresses from the A2 structure to the B2 structure and from the B2 structure to the L21 structure, the polarization rate indicating the properties of the half metal increases. 2 YZ (Here, Y is at least one element selected from the group consisting of Ti, V, Cr, Mn, and Fe, and Z is composed of Al, Si, Ga, Ge, In, and Sn. It is an element having a composition represented by at least one element selected from the group).
It has been reported that the interlayer exchange bond is caused by the quantum well state formed between the magnetic free layer and the non-magnetic layer, and it is rational that the same effect can be obtained if the materials have similar electronic states. Is estimated. It is reasonable by those skilled in the art that the above materials have similar electronic states to the Co-based Whistler alloy-based half-metal materials for which the effects of the present invention have been experimentally confirmed, and similar effects will be obtained. Understood by.
磁気フリー層の厚さには特に限定が無く、磁気フリー層及び非磁性層の材料、層数に応じて、本発明の目的との関係において適切な厚さを選択すればよいが、0.5〜50nmであることが好ましく、1〜20nmであることが特に好ましい。
一例として磁気フリー層がCFAS(Co2FeAl0.5Si0.5の組成のホイスラー合金)、非磁性層がAgである4から6層構成の積層部を有する場合には、磁気フリー層の厚さは、1〜50nmであることが好ましく、1〜20nmであることが特に好ましい。膜厚が0.5nm以上、より好ましくは1nm以上であることで、成膜の制御が容易になり、50nm以下、より好ましくは20nm以下であることで、その後の微細加工が容易になる。
The thickness of the magnetic free layer is not particularly limited, and an appropriate thickness may be selected in relation to the object of the present invention according to the material and the number of layers of the magnetic free layer and the non-magnetic layer. It is preferably 5 to 50 nm, and particularly preferably 1 to 20 nm.
As an example, when the magnetic free layer has a CFAS ( Whisler alloy having a composition of Co 2 FeAl 0.5 Si 0.5 ) and the non-magnetic layer has a laminated portion having a structure of 4 to 6 layers of Ag, the magnetic free layer has a laminated portion. The thickness is preferably 1 to 50 nm, particularly preferably 1 to 20 nm. A film thickness of 0.5 nm or more, more preferably 1 nm or more facilitates control of film formation, and a film thickness of 50 nm or less, more preferably 20 nm or less facilitates subsequent microfabrication.
非磁性層
本発明の面直通電巨大磁気抵抗素子用積層膜の積層部を構成する非磁性層は、非磁性層を介して隣接する2つの磁気フリー層間の反強磁性層間交換結合を維持することができる材料で構成されていればよく、それ以外の制限は無いが、面直方向の電気抵抗を測定することを考慮すれば、非磁性金属元素で構成されることが好ましい。
また、積層部の製造の容易さや、格子不整合による歪等の影響を抑制する観点からは、非磁性層は磁気フリー層と良好な格子整合性を有する材料で構成することが好ましい。
更に、磁気抵抗素子の感度や直線性の観点からは、磁気フリー層の磁化の方向の変化によるスピン散乱の変化をより明確に検出できることが好ましく、従って非磁性層は、スピン緩和が小さな材料、例えばスピン拡散長が30nm以上の材料で構成されることが好ましい。スピン拡散長が100nm以上の材料で構成されることが、より好ましい。
Non-magnetic layer The non-magnetic layer constituting the laminated portion of the laminated film for the surface direct energization giant magnetic resistance element of the present invention maintains an antiferromagnetic interlayer exchange bond between two adjacent magnetic-free layers via the non-magnetic layer. It suffices to be made of a material that can be used, and there are no other restrictions, but it is preferably made of a non-magnetic metal element in consideration of measuring the electrical resistance in the direction perpendicular to the plane.
Further, from the viewpoint of ease of manufacturing the laminated portion and suppressing the influence of strain and the like due to lattice mismatch, it is preferable that the non-magnetic layer is made of a material having good lattice consistency with the magnetic free layer.
Further, from the viewpoint of the sensitivity and linearity of the magnetoresistive element, it is preferable that the change in spin scattering due to the change in the magnetization direction of the magnetic free layer can be detected more clearly. For example, it is preferably composed of a material having a spin diffusion length of 30 nm or more. It is more preferable that the material is composed of a material having a spin diffusion length of 100 nm or more.
上記観点から、非磁性層は、銅(Cu)、アルミニウム(Al)、銀(Ag)、及び亜鉛(Zn)からなる群より選ばれる少なくとも1種の元素を含有することが特に好ましい。
また、金(Au),ルテニウム(Ru)およびマグネシウム(Mg)のうちの少なくとも1種を含有していてもよい。
From the above viewpoint, it is particularly preferable that the non-magnetic layer contains at least one element selected from the group consisting of copper (Cu), aluminum (Al), silver (Ag), and zinc (Zn).
Further, it may contain at least one of gold (Au), ruthenium (Ru) and magnesium (Mg).
非磁性層を介して隣接する2つの磁気フリー層の間には、非磁性層を介して反強磁性(AFM)結合磁場が発生している。非磁性層は、磁気フリー層のペア間の強磁性結合の強度が最小となり、かつ、それらの相互間に反強磁性結合が生じるような厚さを有していることが好ましい。この様な好適な非磁性層の厚さは、磁気フリー層及び非磁性層の構成元素、組成、結晶系等によっても変化し得るが、通常、0.1から10nmの範囲内である。 An antiferromagnetic (AFM) coupled magnetic field is generated via the non-magnetic layer between two magnetic free layers adjacent to each other via the non-magnetic layer. It is preferable that the non-magnetic layer has a thickness such that the strength of the ferromagnetic bond between the pair of magnetic free layers is minimized and the antiferromagnetic bond is formed between them. The thickness of such a suitable non-magnetic layer may vary depending on the constituent elements, composition, crystal system, etc. of the magnetic free layer and the non-magnetic layer, but is usually in the range of 0.1 to 10 nm.
磁気フリー層の間の層間結合は、非磁性層の膜厚に対して周期的に強磁性・反強磁性を繰り返すので、実験的に最適な非磁性層の膜厚を設定することも可能であり、また好ましい。反強磁性層間交換結合が形成される場合、面内方向の飽和磁界が増大するので、例えば非磁性層の膜厚を変化させて該非磁性層及びその両面に接する磁気フリー層のペアについて面内方向の残留磁化/飽和磁化の比を測定することで、実験的に最適な非磁性層の膜厚を決定することが可能である。磁気フリー層のペアの間に反強磁性層間交換結合が形成される場合、当該磁気フリー層のペア及びその間の非磁性層の面内方向の飽和磁界は増大するので、これに伴い残留磁化/飽和磁化の比が、反強磁性層間交換結合が形成されていない場合と比較して減少する。面内方向の残留磁化/飽和磁化の比自体の数値としては、例えば0.8以下となっていれば、反強磁性層間交換結合が形成される膜厚となっていると判断することができる。面内方向の残留磁化/飽和磁化の比は、0.5以下であればより好ましく、0.2以下であれば更に好ましい。
例えば、磁気フリー層がCFAS(Co2FeAl0.5Si0.5の組成のホイスラー合金)、非磁性層がAgである場合は、Ag層の膜厚に対して周期的に強磁性・反強磁性を繰り返す現象は、Ag層の膜厚が例えば5nmを超えると見られなくなる。一方、Ag層の膜厚が例えば0.5nm未満の場合には、膜の不連続性などにより強磁性的結合が現れるおそれがある。従って、この材料系の場合には、例えば膜厚0.5から5nmの範囲で、実験的又はシミュレーションなどにより最適なAg層の膜厚を設定することが好ましい。
Since the interlayer coupling between the magnetic free layers periodically repeats ferromagnetism and antiferromagnetism with respect to the film thickness of the non-magnetic layer, it is possible to set the optimum film thickness of the non-magnetic layer experimentally. Yes and preferred. When an antiferromagnetic interlayer exchange bond is formed, the saturated magnetic field in the in-plane direction increases. By measuring the ratio of residual magnetization / saturation magnetization in the direction, it is possible to experimentally determine the optimum thickness of the non-magnetic layer. When an antiferromagnetic interlayer exchange bond is formed between a pair of magnetic free layers, the saturated magnetic field in the in-plane direction of the pair of magnetic free layers and the non-magnetic layer between them increases, and the residual magnetization / The ratio of saturation magnetization is reduced as compared to the case where the antiferromagnetic interlayer exchange bond is not formed. If the numerical value of the ratio of residual magnetization / saturation magnetization in the in-plane direction itself is, for example, 0.8 or less, it can be determined that the film thickness is such that an antiferromagnetic interlayer exchange bond is formed. .. The ratio of residual magnetization / saturation magnetization in the in-plane direction is more preferably 0.5 or less, and even more preferably 0.2 or less.
For example, when the magnetic free layer is CFAS ( Whisler alloy having a composition of Co 2 FeAl 0.5 Si 0.5 ) and the non-magnetic layer is Ag, it is cyclically ferromagnetic / antiferromagnetic with respect to the film thickness of the Ag layer. The phenomenon of repeating ferromagnetism disappears when the thickness of the Ag layer exceeds, for example, 5 nm. On the other hand, when the film thickness of the Ag layer is, for example, less than 0.5 nm, a ferromagnetic bond may appear due to the discontinuity of the film or the like. Therefore, in the case of this material system, it is preferable to set the optimum film thickness of the Ag layer by experiment or simulation, for example, in the range of 0.5 to 5 nm.
それ以外の層
本発明の面直通電巨大磁気抵抗素子用積層膜及びそれを用いた面直通電巨大磁気抵抗素子は、本発明の目的に反しない限りにおいて、上述の基体、磁気フリー層、及び非磁性層以外の層を有していてもよい。
Other Layers The laminated film for the surface direct energization giant magnetoresistive element of the present invention and the surface direct energization giant magnetoresistive element using the same are the above-mentioned substrate, the magnetic free layer, and the magnetic free layer, as long as it does not contradict the object of the present invention. It may have a layer other than the non-magnetic layer.
例えば、バッファー/電極層(下地層)、キャップ層等を、必要に応じて設けることが好ましい。
ここでいうバッファー/電極層(下地層)は、磁気抵抗(MR)センサー素子の下地となる層ではなく、センサーの構成の中にある層であり、上記基体と積層部との間に設けられるものである。
バッファー/電極層は、基体と積層部との間の格子整合をとる機能、及び/又は磁気抵抗測定用の電極となる機能を有するものであり、前者の機能を有するときには単にバッファー層と称することもあり、後者の機能を有するときには単に電極層と称することもあり、両機能を総称してバッファー層/電極層と称することもある。また、慣用的に下地層と称することもある。
バッファー層/電極層は、1層で両機能を有するものであってもよく、バッファー層の機能を有する層と、電極層の機能を有する層との積層体であっても良く、好ましい例としてCr/Agの積層体を挙げることができる。
電極層としての機能を有する場合のバッファー/電極層は、磁気抵抗測定用の電極となるものであり、例えばAg、Al、Cu、Au、Cr等から選ばれる少なくとも一種類の金属や、これらの金属元素の合金を好ましく用いることができるが、これらには限定されない。
なお、バッファー/電極層を、複数の金属・合金層から構成される2層構造や、3層以上の多層構造としてもよい。
バッファー/電極層の厚さには特に限定は無く、本発明の目的に反しない限りにおいて当業者が適宜設定すればよいが、導電性確保や、磁性フリー層及び非磁性層への影響を限定する等の観点から、5〜1000nmであることが好ましく、20〜500nmであることが特に好ましい。
For example, it is preferable to provide a buffer / electrode layer (base layer), a cap layer, and the like as needed.
The buffer / electrode layer (base layer) referred to here is not a layer that serves as a base for the magnetoresistive (MR) sensor element, but a layer that is included in the sensor configuration, and is provided between the base and the laminated portion. It is a thing.
The buffer / electrode layer has a function of performing lattice matching between the substrate and the laminated portion and / or a function of serving as an electrode for measuring magnetic resistance, and when it has the former function, it is simply referred to as a buffer layer. When it has the latter function, it may be simply referred to as an electrode layer, and both functions may be collectively referred to as a buffer layer / electrode layer. It may also be commonly referred to as a base layer.
The buffer layer / electrode layer may be one layer having both functions, or may be a laminate of a layer having the function of the buffer layer and a layer having the function of the electrode layer, and is a preferable example. A Cr / Ag laminate can be mentioned.
When the buffer / electrode layer has a function as an electrode layer, the buffer / electrode layer serves as an electrode for measuring magnetic resistance, and for example, at least one kind of metal selected from Ag, Al, Cu, Au, Cr and the like, and these. Alloys of metallic elements can be preferably used, but are not limited thereto.
The buffer / electrode layer may have a two-layer structure composed of a plurality of metal / alloy layers or a multi-layer structure having three or more layers.
The thickness of the buffer / electrode layer is not particularly limited and may be appropriately set by those skilled in the art as long as it does not contradict the object of the present invention, but the effect on ensuring conductivity and the magnetic free layer and the non-magnetic layer is limited. From the viewpoint of magnetism and the like, it is preferably 5 to 1000 nm, and particularly preferably 20 to 500 nm.
バッファー層を電極層の下側(基体側)に設けてもよい。このときバッファー層は配向層とも称することができ、フリー磁性層に所望の配向、例えば(001)方向への配向、を与える作用を持つもので、例えばAg、Al、Cu、Au、Cr合金の少なくとも一種類を含むものを用いることが好ましいが、これらには限定されない。
バッファー層(配向層)の厚さには特に限定は無く、本発明の目的に反しない限りにおいて当業者が適宜設定すればよいが、フリー磁性層を適切に配向させる等の観点から、0.1〜100nmであることが好ましく、0.1〜20nmであることが特に好ましい。
なお、実施例等には(001)方向に配向した磁気抵抗素子の結果を示したが、本願請求項1に規定する要件を満たす磁気フリー層及び非磁性層であれば素子の成長結晶方位に依存せず(110)、(211)方位などでも同様の効果が得られる。
The buffer layer may be provided on the lower side (base side) of the electrode layer. At this time, the buffer layer can also be referred to as an alignment layer, which has an action of giving a desired orientation to the free magnetic layer, for example, orientation in the (001) direction, and is, for example, an Ag, Al, Cu, Au, Cr alloy. It is preferable to use one containing at least one kind, but the present invention is not limited thereto.
The thickness of the buffer layer (alignment layer) is not particularly limited and may be appropriately set by those skilled in the art as long as it does not contradict the object of the present invention. It is preferably 1 to 100 nm, and particularly preferably 0.1 to 20 nm.
Although the results of the magnetoresistive element oriented in the (001) direction are shown in Examples and the like, if the magnetic free layer and the non-magnetic layer satisfy the requirements specified in claim 1 of the present application, the growth crystal orientation of the element can be set. The same effect can be obtained with the (110) and (211) orientations that do not depend on each other.
キャップ層は表面の保護のための金属又は合金を含んでなる層である。キャップ層も、センサーの構成の中にある層であり、強磁性層のふた、とも称することができる。
キャップ層は、例えばAg、Al、Cu、Au、Cr 等から選ばれる少なくとも一種類の金属を含んでいてもよく、またこれら金属元素の合金を用いてもよい。
キャップ層の厚さには特に限定は無く、本発明の目的に反しない限りにおいて当業者が適宜設定すればよいが、表面を十分に保護する等の観点から、1〜100nmであることが好ましく、3〜20nmあることが特に好ましい。
キャップ層は、1種類の材料を用いてもよいし、2種類以上の材料を積層させたものでもよい。
The cap layer is a layer containing a metal or alloy for surface protection. The cap layer is also a layer in the sensor configuration and can also be referred to as a ferromagnetic layer lid.
The cap layer may contain at least one kind of metal selected from, for example, Ag, Al, Cu, Au, Cr and the like, or an alloy of these metal elements may be used.
The thickness of the cap layer is not particularly limited and may be appropriately set by those skilled in the art as long as it does not contradict the object of the present invention, but it is preferably 1 to 100 nm from the viewpoint of sufficiently protecting the surface. It is particularly preferably 3 to 20 nm.
As the cap layer, one kind of material may be used, or two or more kinds of materials may be laminated.
磁気フリー層間に十分な強さの反強磁性層間交換結合を確実にかつ安定的に実現する観点からは、バッファー/電極層表面、磁気フリー層と非磁性層との界面、及びキャップ層表面の少なくとも一つは平滑度が高いものであることが好ましい。
磁気フリー層(強磁性層)間の反強磁性層間交換結合の強度及び安定性の観点からは、重要なのは磁気フリー層/非磁性層の界面の平滑性であるが、それを実現するためにはバッファー/電極層表面の平滑性が重要であり、多くの場合バッファー/電極層表面が高い平滑性を有することが必要となる。なお、バッファー/電極層表面、及び磁気フリー層/非磁性層の界面の平滑性が良い場合には、殆どの場合にキャップ層表面の平滑性も向上するので、キャップ層表面の平滑性を評価することで、磁気フリー層/非磁性層の界面の平滑性を、間接的に評価することができる。
より具体的には、バッファー/電極層表面、磁気フリー層と非磁性層との界面、及びキャップ層表面の少なくとも一つの平滑度Raは、0.75nm以下であることが好ましく、0.5nm以下であることがより好ましく、0.25nm以下であることが特に好ましい。これら表面、界面の全ての平滑度Raが上記条件を満たしていることが、とりわけ好ましい。
バッファー/電極層表面、磁気フリー層と非磁性層との界面、及びキャップ層表面の少なくとも一つの平滑度Raには特に下限は存在しないが、通常のプロセスで得られる平滑度としては、Raが0.1nm以上であることが現実的である。
本願においては、界面平滑性の指標として、50nm×50nm以上のエリアについて測定した算術平均粗さRaを用いる。界面平滑性を測定する方法には特に限定は無く、当該技術分野において用いられている評価方法を適宜使用することができるが、例えば、TEM(透過型電子顕微鏡)による断面観察、AFM(原子間力顕微鏡)による平滑性評価等により測定することができる。
From the viewpoint of reliably and stably realizing a sufficiently strong antiferromagnetic interlayer exchange bond between the magnetic-free layers, the buffer / electrode layer surface, the interface between the magnetic-free layer and the non-magnetic layer, and the cap layer surface. It is preferable that at least one has high smoothness.
From the viewpoint of the strength and stability of the antiferromagnetic interlayer exchange bond between the magnetic free layers (ferromagnetic layers), the smoothness of the interface between the magnetic free layer and the non-magnetic layer is important, but in order to realize it. The smoothness of the buffer / electrode layer surface is important, and in many cases, the buffer / electrode layer surface needs to have high smoothness. When the smoothness of the interface between the buffer / electrode layer surface and the magnetic free layer / non-magnetic layer is good, the smoothness of the cap layer surface is also improved in most cases, so the smoothness of the cap layer surface is evaluated. By doing so, the smoothness of the interface between the magnetic free layer / non-magnetic layer can be indirectly evaluated.
More specifically, the smoothness Ra of at least one of the buffer / electrode layer surface, the interface between the magnetic free layer and the non-magnetic layer, and the cap layer surface is preferably 0.75 nm or less, preferably 0.5 nm or less. Is more preferable, and 0.25 nm or less is particularly preferable. It is particularly preferable that all the smoothness Ras of these surfaces and interfaces satisfy the above conditions.
There is no particular lower limit to the smoothness Ra of at least one of the buffer / electrode layer surface, the interface between the magnetic free layer and the non-magnetic layer, and the surface of the cap layer, but Ra is the smoothness obtained by a normal process. It is realistic that it is 0.1 nm or more.
In the present application, the arithmetic average roughness Ra measured for an area of 50 nm × 50 nm or more is used as an index of interfacial smoothness. The method for measuring the interfacial smoothness is not particularly limited, and the evaluation method used in the art can be appropriately used. For example, cross-sectional observation by a TEM (transmission electron microscope) or AFM (atomic force) can be used. It can be measured by smoothness evaluation with a force microscope).
すなわち、製造工程においては、表面平滑性及び界面平滑性を、積層膜上部のAFM等による平滑性評価によって求めることができる。このとき、50nm×50nm以上のエリアにて、Raを測定・計測する。エリアが狭すぎる場合、Raが極端に小さくなってしまうことがあるからである。また、完成した素子においては、原子分解能を持つTEMによる断面観察により、平滑性を測定することが出来る。
TEMによる断面観察による、積層部等の界面の算術平均粗さRaの測定法の一例について、以下に説明する。
HAADF−STEM( High−angle Annular Dark Field Scanning TEM)と、EDS(エネルギー分散型X線分光器)による元素分析とを併用し、観察試料を調整することで、試料断面の原子レベルの成分分析が可能となる。これを利用して界面付近の成分分析を行い、上層の元素成分と、下層の元素成分とが混在している混合領域の素子厚み方向の厚さを測定し、これから界面平滑性(算術平均粗さ)Raを推定することができる。界面の凹凸があることで、素子厚み方向の同じ位置に、上層の元素成分と下層の元素成分の両者が混在することになるので、Raが大きいほど混在領域の素子厚み方向の厚さが大きくなるためである。
より具体的には、上記方法を用い、素子の断面の観察・元素マッピングを行うと、図4に模式的に示すような、断面解析が可能となる。 図4(a)に示す素子は、上層が成分a、下層が成分bからなる2層構造であり、その界面付近の素子厚み方向に、実線abで示す測定領域について、観察・元素マッピングを行うと、図4(b)に模式的に示すような、素子厚み方向の成分分布が得られる。図4(b)中、横軸は素子厚み方向の位置(任意目盛)であり、基板からの距離を示す。縦軸は、成分比(%)であり、実線が成分a、点線が成分bの割合を表す。横軸(素子厚み方向)で基板に近い左側は下層であり、成分bが大半を占める。横軸(素子厚み方向)で基板から隔たった右側は上層であり、成分aが大半を占める。図中、成分比でa(上層)成分20〜80%の部分は、b(下層)成分も20〜80%となり、これを混在領域と定義する。上述の様に、混在領域は界面の凹凸を示すものとして評価でき、混在領域の素子厚み方向の厚さは界面平滑性Raの2倍となるので、上記測定で得られた混在領域の素子厚み方向の厚さを2で除することで、界面平滑性Raを特定することができる。
この測定法は、間接的に界面平滑性Raを評価するものであり、若干の誤差を含むものではあるが、AFM等による平滑性評価と20%程度以内の精度で一致するものである。
上記方法による、実際の素子の断面観察・元素マッピング結果の例は、Jung et al.,Appl.Phys.Lett.,108,102408(2016)のFIG.4等に記載されている。
上記評価方法に用いるTEMは、原子レベルの分解能をもつものであることが好ましく、例えばFEI Company社製 Titan G2等を好適に使用することができる。
上述のHAADF−STEM(High−angle Annular Dark Field Scanning TEM)像は、細く絞った電子線を試料に走査させながら当て、透過電子のうち高角に散乱したものを環状の検出器で検出することにより得られものである。
試料は一般に数〜数十ナノメートルのTEM試料厚さ(試料の厚み方向は、磁気フリー層/非磁性層等の界面の面内方向に相当)に調整される。本発明の積層部を構成する磁気フリー層/非磁性層として典型的なホイスラー合金/Agのケースでは、一般にTEM試料厚さを30nm〜50nmの範囲で調整する。このとき、解析エリアを本願における界面/表面平滑性測定の際に必要な50nm×50nm以上のエリアとするため、幅70nm以上の界面にて、界面平滑性を評価する
That is, in the manufacturing process, the surface smoothness and the interfacial smoothness can be obtained by the smoothness evaluation by AFM or the like on the upper part of the laminated film. At this time, Ra is measured and measured in an area of 50 nm × 50 nm or more. This is because if the area is too small, Ra may become extremely small. Further, in the completed device, the smoothness can be measured by observing the cross section by TEM having atomic resolution.
An example of a method for measuring the arithmetic mean roughness Ra of an interface such as a laminated portion by observing a cross section by TEM will be described below.
By using HAADF-STEM (High-angle Anal Dark Field Scanning TEM) and elemental analysis by EDS (Energy Dispersive X-ray Spectroscopy) in combination to prepare the observation sample, atomic-level component analysis of the sample cross section can be performed. It will be possible. Using this, component analysis near the interface is performed, and the thickness in the element thickness direction of the mixed region where the elemental components of the upper layer and the elemental components of the lower layer are mixed is measured, and then the interface smoothness (arithmetic mean roughness) is measured. S) Ra can be estimated. Due to the unevenness of the interface, both the elemental component of the upper layer and the elemental component of the lower layer are mixed at the same position in the element thickness direction. Therefore, the larger Ra, the larger the thickness of the mixed region in the element thickness direction. This is to become.
More specifically, by observing the cross section of the device and mapping the elements using the above method, the cross section analysis as schematically shown in FIG. 4 becomes possible. The element shown in FIG. 4A has a two-layer structure in which the upper layer is composed of the component a and the lower layer is composed of the component b, and observation / element mapping is performed on the measurement region shown by the solid line ab in the element thickness direction near the interface. And, the component distribution in the element thickness direction as schematically shown in FIG. 4B can be obtained. In FIG. 4B, the horizontal axis is a position (arbitrary scale) in the element thickness direction, and indicates a distance from the substrate. The vertical axis is the component ratio (%), and the solid line represents the ratio of the component a and the dotted line represents the ratio of the component b. The left side near the substrate on the horizontal axis (in the element thickness direction) is the lower layer, and the component b occupies most of it. The right side separated from the substrate on the horizontal axis (in the element thickness direction) is the upper layer, and the component a occupies most of it. In the figure, the portion of the a (upper layer) component of 20 to 80% in the component ratio also has the b (lower layer) component of 20 to 80%, which is defined as a mixed region. As described above, the mixed region can be evaluated as indicating the unevenness of the interface, and the thickness of the mixed region in the element thickness direction is twice the interfacial smoothness Ra. Therefore, the element thickness of the mixed region obtained by the above measurement is obtained. The interfacial smoothness Ra can be specified by dividing the thickness in the direction by 2.
This measuring method indirectly evaluates the interfacial smoothness Ra, and although it includes some errors, it matches the smoothness evaluation by AFM or the like with an accuracy of about 20% or less.
Examples of actual element cross-section observation and element mapping results by the above method are described in Jung et al. , Apple. Phys. Let. , 108, 102408 (2016) FIG. It is described in 4th grade.
The TEM used in the above evaluation method preferably has atomic-level resolution, and for example, Titan G2 manufactured by FEI Company can be preferably used.
The above-mentioned HAADF-STEM (High-angle Anal Dark Field Scanning TEM) image is obtained by applying a finely focused electron beam to a sample while scanning it, and detecting the transmitted electrons scattered at a high angle with an annular detector. It is obtained.
The sample is generally adjusted to a TEM sample thickness of several to several tens of nanometers (the thickness direction of the sample corresponds to the in-plane direction of the interface such as a magnetic free layer / non-magnetic layer). In the case of the Whistler alloy / Ag typical as the magnetic free layer / non-magnetic layer constituting the laminated portion of the present invention, the TEM sample thickness is generally adjusted in the range of 30 nm to 50 nm. At this time, in order to set the analysis area as an area of 50 nm × 50 nm or more required for the interface / surface smoothness measurement in the present application, the interface smoothness is evaluated at the interface having a width of 70 nm or more.
本発明は、強磁性を示す層として、3層以上の奇数の磁気フリー層を有するものであり、3層以上の奇数の磁気フリー層によって所期の効果を実現するものであるので、固定層を必要としない。
In the present invention, as a layer exhibiting ferromagnetism, an odd number of magnetic free layers having three or more layers is provided, and the desired effect is realized by an odd number of magnetic free layers having three or more layers. that it does not require.
製造方法
本発明の面直通電巨大磁気抵抗素子用積層膜、及びこれを備える面直通電巨大磁気抵抗素子の製造方法には特に制限は無く、金属薄膜、金属化合物薄膜を精密に積層できる方法を当業者が適宜選択すればよいが、スパッタ法により製造することが好ましい。
Manufacturing Method There is no particular limitation on the manufacturing method of the laminated film for the surface direct energization giant magnetoresistive element of the present invention and the surface direct energization giant magnetoresistive element provided with the same, and a method capable of precisely laminating a metal thin film or a metal compound thin film can be used. It may be appropriately selected by a person skilled in the art, but it is preferably produced by a sputtering method.
本発明の面直通電巨大磁気抵抗素子用積層膜の一部又は全部の成膜後に、適宜アニールを行うことが可能である。アニールのタイミングには特に制限は無く、アニール温度、各層の耐熱性等に応じて適切なタイミングでアニールを行うことが好ましい。本実施形態においては通常、基体上に、バッファー/電極層、積層部(交互に磁性フリー層及び非磁性層)、並びにキャップ層を成膜していくので、少なくとも積層部の成膜を行った後にアニールを行うことが好ましい。更にキャップ層を成膜した後にアニールを行ってもよいし、アニール温度が高温、例えば600℃以上の場合には、積層部まで成膜した後にアニールを行い、その後にキャップ層を成膜してもよい。
アニールの温度には特に制限は無いが、例えば300℃以上、好ましくは350℃以上、より好ましくは、400℃以上の温度で行うことで、結晶性を向上させることができる。
It is possible to appropriately perform annealing after forming a part or all of the laminated film for the surface direct energization giant magnetoresistive element of the present invention. The timing of annealing is not particularly limited, and it is preferable to perform annealing at an appropriate timing according to the annealing temperature, heat resistance of each layer, and the like. In the present embodiment, the buffer / electrode layer, the laminated portion (alternately magnetic-free layer and non-magnetic layer), and the cap layer are formed on the substrate, so that at least the laminated portion is formed. It is preferable to perform annealing later. Further, annealing may be performed after forming the cap layer, or when the annealing temperature is high, for example, 600 ° C. or higher, the film is formed up to the laminated portion and then annealed, and then the cap layer is formed. May be good.
The temperature of annealing is not particularly limited, but the crystallinity can be improved by performing the annealing at a temperature of, for example, 300 ° C. or higher, preferably 350 ° C. or higher, more preferably 400 ° C. or higher.
用途
本発明の面直通電巨大磁気抵抗素子用積層膜を用いた磁気抵抗素子は、高い感度を実現することができ、また外部磁場と抵抗値との直線性を向上させることが比較的容易なので、高感度が求められるHDD用リードヘッド、高感度電流センサー等や、外部磁場と抵抗値との直線性が求められる、地磁気センサー、電流センサー等において、特に好適に使用することができる。
Applications The magnetoresistive element using the laminated film for the surface direct current enormous magnetic resistance element of the present invention can realize high sensitivity and it is relatively easy to improve the linearity between the external magnetic field and the resistance value. It can be particularly preferably used in HDD lead heads, high-sensitivity current sensors, etc., which require high sensitivity, and geomagnetic sensors, current sensors, etc., which require linearity between an external magnetic field and a resistance value.
以上、特定の実施の形態を例に本発明を説明したが、本発明は上記実施の形態において説明した態様に限定されず、本発明の趣旨から外れることがない限りにおいて、種々の変形が可能である。 Although the present invention has been described above by taking a specific embodiment as an example, the present invention is not limited to the embodiments described in the above-described embodiment, and various modifications can be made as long as it does not deviate from the gist of the present invention. Is.
以下、実施例/比較例を参照しながら、本発明を具体的に説明する。なお、本発明はいかなる意味においても、以下の実施例によって限定されるものではない。 Hereinafter, the present invention will be specifically described with reference to Examples / Comparative Examples. The present invention is not limited to the following examples in any sense.
(実施例1)
磁気フリー層5層、非磁性層4層(Ag、厚さ:2nm)を有する積層膜
実施例1としてCo2Fe(Al0.5Si0.5))(以下、「CFAS」とも言う。)とAgを用いた面直電流巨大磁気抵抗(CPP−GMR)用積層膜を作製した。磁気フリー層の層数nは奇数である5層とした。Ag層(非磁性層)の膜厚は、反強磁性層間交換結合を示す厚さである2nmとし、その層数(n−1)は、4層とした。
図1に、作製した面直通電巨大磁気抵抗素子用積層膜の層構成(CFAS:5層)を示す。MgO基板/Cr(10nm)/Ag(100nm)/CFAS(3nm)/(Ag(2nm)/CFAS(3nm))n−2/Ag(2nm)/CFAS(3nm)/Ag(5nm)/Ru(8nm)と(001)配向した単結晶CPP−GMR用積層膜を作製した。
磁気フリー層の層数は5層(n=5)とした。
積層膜の熱処理は上部Ru層を積層後に400℃で30分間行った。さらに、フォトリソグラフィーを用いて、200×100nmサイズのピラーを作成した。図2にピラーの断面構造を示す。
磁気抵抗の測定は、フォトリソグラフィーにより得られた長方形の短軸方向に加える磁場を変化させながら、直流4端子法によって電気抵抗を測定することにより行った。磁気抵抗の測定結果を図3に示す。図3中、直線的な応答を示す部分を直線に近似し、下記(式)に従って当該部分の近似直線からのずれである非直線性(Non−linearity)を計算したところ、0.4%FSという良好な直線性を示した。
(Example 1)
As Example 1 of a laminated film having 5 magnetic free layers and 4 non-magnetic layers (Ag, thickness: 2 nm), Co 2 Fe (Al 0.5 Si 0.5 )) (hereinafter, also referred to as “CFAS”. ) And Ag were used to prepare a laminated film for surface direct current giant magnetic resistance (CPP-GMR). The number n of the magnetic free layers was set to 5 which is an odd number. The film thickness of the Ag layer (non-magnetic layer) was 2 nm, which is a thickness indicating an antiferromagnetic interlayer exchange bond, and the number of layers (n-1) was four.
FIG. 1 shows the layer structure (CFAS: 5 layers) of the produced laminated film for a surface direct energization giant magnetoresistive element. MgO substrate / Cr (10 nm) / Ag (100 nm) / CFAS (3 nm) / (Ag (2 nm) / CFAS (3 nm)) n-2 / Ag (2 nm) / CFAS (3 nm) / Ag (5 nm) / Ru ( A laminated film for single crystal CPP-GMR oriented at 8 nm) and (001) was prepared.
The number of magnetic free layers was 5 (n = 5).
The heat treatment of the laminated film was performed at 400 ° C. for 30 minutes after laminating the upper Ru layer. Furthermore, using photolithography, pillars having a size of 200 × 100 nm were created. FIG. 2 shows the cross-sectional structure of the pillar.
The magnetic resistance was measured by measuring the electrical resistance by the DC 4-terminal method while changing the magnetic field applied in the minor axis direction of the rectangular shape obtained by photolithography. The measurement result of the magnetic resistance is shown in FIG. In FIG. 3, the portion showing a linear response was approximated to a straight line, and the non-linearity, which is the deviation from the approximate straight line of the portion, was calculated according to the following (formula). It showed good linearity.
(式)
R(meas): 抵抗Rの測定値
R(fit): 抵抗Rの近似値
(R(meas)−R(fit))max:
直線近似範囲におけるR(meas)−R(fit)の最大値
R(max): 直線近似範囲における抵抗Rの測定値の最大値
R(min): 直線近似範囲における抵抗Rの測定値の最少値
(formula)
R (meas): Measured value of resistor R R (fit): Approximate value of resistor R (R (meas) -R (fit)) max:
Maximum value of R (meas) -R (fit) in the linear approximation range R (max): Maximum value of the measured value of resistance R in the linear approximation range R (min): Minimum value of the measured value of resistance R in the linear approximation range
また、磁気抵抗(MR)比を、素子の外部磁場に対する抵抗値の変化から、以下の式に従って計算したところ、MR比は60%と、極めて高い値を示した。
(比較例1)
磁気フリー層6層、非磁性層5層(Ag、厚さ:2nm)を有する積層膜
磁気フリー層の層数nを偶数である層とし、Ag層(非磁性層)の層数(n−1)を5層とした他は、実施例1と同様にしてCFASとAgを用いた面直電流巨大磁気抵抗(CPP−GMR)用積層膜を作製した。
図3(b)にピラーの外部磁場に対する抵抗値の変化を示す。非直線性は0.5%FSであり良好な直線性を示したが、MR比は39%であり、実施例1と比較して顕著に低い値であった。
(Comparative Example 1)
Laminated film having 6 magnetic free layers and 5 non-magnetic layers (Ag, thickness: 2 nm) The number of layers n of the magnetic free layers is an even number, and the number of Ag layers (non-magnetic layers) (n−). A laminated film for surface direct current giant magnetoresistance (CPP-GMR) using CFAS and Ag was produced in the same manner as in Example 1 except that 1) was made into 5 layers.
FIG. 3B shows the change in the resistance value of the pillar with respect to the external magnetic field. The non-linearity was 0.5% FS, showing good linearity, but the MR ratio was 39%, which was significantly lower than that of Example 1.
本発明の面直通電巨大磁気抵抗素子は、従来技術では実現し得なかった高い感度を有するうえ、比較的容易に外部磁場と抵抗値との直線性を向上することができるので、高い感度と直線性とを両立した面直通電巨大磁気抵抗素子を実現することができるなど、実用上高い価値を有するものであり、電気電子機器、情報通信、輸送機器における航法などの産業の各分野において高い利用可能性を有する。 The surface direct energization giant magnetoresistive element of the present invention has high sensitivity that could not be realized by the prior art, and can improve the linearity between the external magnetic field and the resistance value relatively easily, so that the sensitivity is high. It has high practical value, such as being able to realize a surface-directed giant magnetoresistive element that achieves both linearity, and is high in various fields of industry such as navigation in electrical and electronic equipment, information communication, and transportation equipment. Has availability.
Claims (10)
該基体上に設けられ、n層の磁気フリー層と、n−1層の非磁性層とを交互に積層してなる積層部と、
を有する面直通電巨大磁気抵抗素子であって、
nが奇数であり、
少なくとも1つの該非磁性層が、その両面に接する磁気フリー層のペアの間に反強磁性層間交換結合が形成される厚さを有すると共に、磁気固定層を有しない、
上記面直通電巨大磁気抵抗素子。 With the substrate
A laminated portion provided on the substrate and formed by alternately laminating n-layer magnetic free layers and n-1 non-magnetic layers.
It is a surface direct energization giant magnetoresistive element having
n is an odd number
The at least one non-magnetic layer has a thickness at which an antiferromagnetic interlayer exchange bond is formed between a pair of magnetic free layers in contact with both sides thereof, and has no magnetic fixing layer.
The above-mentioned surface direct energization giant magnetoresistive element .
A geomagnetic sensor, a current sensor, or a magnetic head comprising the surface direct energization giant magnetoresistive element according to any one of claims 1 to 9.
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