Magnetic laminate, tmr sensor, and method for manufacturing magnetic laminate

Abstract

The purpose of one aspect of the present invention is to control a dynamic range and to reduce magnetic hysteresis. According to one aspect of the present invention, a magnetic laminate according to the present invention comprises: a first ferromagnetic layer in which magnetization is fixed in a first direction; a spacer layer; a second ferromagnetic layer that is magnetically coupled to the first ferromagnetic layer with the spacer layer interposed therebetween, and has magnetization in a second direction oriented at an angle greater than 0° but smaller than 180° from the first direction; a non-magnetic layer; and a third ferromagnetic layer that is ferromagnetically coupled to the second ferromagnetic layer with the non-magnetic layer interposed therebetween.

Description

Magnetic laminate, TMR sensor, and method for manufacturing magnetic laminate

[0001] The present invention relates to a magnetic laminate, a TMR sensor, and a method for manufacturing a magnetic laminate.

[0002] TMR (Tunnel Magneto Resistance) sensors have a larger output voltage than Hall sensors and giant magneto-resistance (GMR) sensors, and are therefore being applied to a variety of magnetic sensors. TMR sensors have a spin-valve structure with a tunnel barrier layer between a free layer and a reference layer, and detect external magnetic fields based on the electrical resistance between the free layer and the reference layer. Both the free layer and the reference layer are ferromagnetic layers, and the magnetization direction of the reference layer remains fixed even when an external magnetic field is applied. In contrast, the magnetization of the free layer is biased in a certain direction and rotates from that direction when an external magnetic field is applied. Therefore, the angle between the magnetizations of the reference layer and the free layer changes with the external magnetic field, and the external magnetic field can be detected based on the resistance change associated with this angle change.

[0003] Furthermore, in a TMR sensor, by orthogonally ...

[0004] As described above, one method for orthogonally orthogonalizing the magnetizations of the free layer and the pinned layer is a two-step heat treatment, in which the free layer and the pinned layer are subjected to heat treatment in a magnetic field at different temperatures to impart magnetic anisotropy to each of them. However, in the two-step heat treatment, the saturation magnetic field of the free layer is determined to a value of about several mT by the induced magnetic anisotropy inherent to the material, and it is difficult to make it smaller or larger than this value, making it difficult to control the dynamic range.

[0005] Furthermore, this method results in uniaxial magnetic anisotropy of the free layer, and when the external magnetic field is zero, the free layer has a multi-domain structure with a mixture of parallel and antiparallel magnetization. The domain walls that make up each domain move in response to the external magnetic field, but the domain structure does not necessarily return to its original state after the external magnetic field is removed, causing the free layer to exhibit magnetic hysteresis. As a result, even if the external magnetic field strength is the same, the sensor's resistance value changes with each measurement, making it difficult to accurately measure the external magnetic field.

[0006] Another method to obtain a linear response is to place a permanent magnet around the TMR sensor and apply a bias field to the free layer using the leakage field from the permanent magnet, without performing the magnetic field heat treatment described above. In this case, the dynamic range of the sensor can be controlled by the strength of the leakage field from the permanent magnet, but the sensor manufacturing process becomes complicated and the sensor area becomes large.

[0007] Another known method involves inserting a spacer layer of a RuFe alloy between two cobalt layers and utilizing non-collinear interlayer exchange coupling between the spacer layer and each cobalt layer to control the magnetization angle of the cobalt layer between 0° and 180° (Patent Document 1, Non-Patent Document 1). Another known method involves stacking a ferromagnetic layer, an AgSn layer, and a free layer in this order, and controlling the ferromagnetic coupling strength between the ferromagnetic layer and the free layer by adjusting the thickness of the AgSn layer (Non-Patent Document 2).

[0008] International Publication No. 2018 / 161146

[0009] Zachary R. Nunn and 3 others, “Control of the noncollinear interlayer exchange coupling”, Science Advances, Vol. 6, p. eabd8861, 2020 Tomoya Nakatani and 1 other person, “Tunnel magnetoresistance sensors with dual soft-pinned free layers exhibiting highly symmetrical resistance-field response curves”, Journal of Applied Physics, Volume 132, Page 223904, 2022

[0010] In one aspect, the present invention aims to enable control of the dynamic range and suppression of magnetic hysteresis.

[0011] According to one aspect, a magnetic stack includes a first ferromagnetic layer having a magnetization fixed in a first direction, a spacer layer, a second ferromagnetic layer magnetically coupled to the first ferromagnetic layer via the spacer layer and having a magnetization oriented in a second direction that forms an angle with the first direction greater than 0° and less than 180°, a nonmagnetic layer, and a third ferromagnetic layer ferromagnetically coupled to the second ferromagnetic layer via the nonmagnetic layer.

[0012] The magnetic laminate may further include a first antiferromagnetic layer exchange-coupled with the first ferromagnetic layer.

[0013] The magnetic stack may further include a tunnel barrier layer and a fourth ferromagnetic layer that faces the third ferromagnetic layer via the tunnel barrier layer and has a magnetization fixed in a third direction.

[0014] The magnetic laminate may further include an antiparallel coupling layer, and a fifth ferromagnetic layer exchange-coupled to the fourth ferromagnetic layer via the antiparallel coupling layer.

[0015] The magnetic laminate may further include a second antiferromagnetic layer exchange-coupled with the fifth ferromagnetic layer.

[0016] The magnetic stack may further include a tunnel barrier layer and a fifth ferromagnetic layer that faces the third ferromagnetic layer via the tunnel barrier layer and has a magnetization fixed in a fourth direction.

[0017] In the magnetic laminate, the spacer layer may be made of a mixture of a non-magnetic material and a ferromagnetic material.

[0018] In the magnetic laminate, the nonmagnetic material may be any one of Ru, Rh, Cr, and Ir, and the ferromagnetic material may be any one of Fe, Co, and Ni.

[0019] In the magnetic laminate, the material of the non-magnetic layer may be any one of Cu, Ag, Cr, Ru, and an AgSn alloy.

[0020] In the above magnetic laminate, the third ferromagnetic layer may contain either a CoFe alloy or a CoFeB alloy.

[0021] According to another aspect, a TMR sensor includes a first electrode, a first ferromagnetic layer electrically connected to the first electrode and having a magnetization fixed in a first direction, a spacer layer, a second ferromagnetic layer magnetically coupled to the first ferromagnetic layer via the spacer layer and having a magnetization oriented in a second direction that forms an angle with the first direction greater than 0° and less than 180°, a nonmagnetic layer, a third ferromagnetic layer magnetically coupled to the second ferromagnetic layer via the nonmagnetic layer, a tunnel barrier layer, a fourth ferromagnetic layer facing the third ferromagnetic layer via the tunnel barrier layer and having a magnetization fixed in a third direction, and a second electrode electrically connected to the fourth ferromagnetic layer.

[0022] In the above TMR sensor, the width of each of the tunnel barrier layer and the fourth ferromagnetic layer may be narrower than the width of the third ferromagnetic layer in a cross-sectional view.

[0023] According to yet another aspect, a method for manufacturing a magnetic laminate includes forming a first ferromagnetic layer, forming a spacer layer, forming a second ferromagnetic layer magnetically coupled to the first ferromagnetic layer via the spacer layer, forming a nonmagnetic layer, forming a third ferromagnetic layer magnetically coupled to the second ferromagnetic layer via the nonmagnetic layer, and performing a heat treatment on the first ferromagnetic layer in a magnetic field oriented in a first direction, thereby fixing the magnetization of the first ferromagnetic layer in the first direction and orienting the magnetization of the second ferromagnetic layer in a second direction that forms an angle with the first direction greater than 0° and less than 180°.

[0024] The method for manufacturing a magnetic laminate may further include forming an antiferromagnetic layer exchange-coupled with the first ferromagnetic layer.

[0025] The method for manufacturing the magnetic laminate may further include forming a tunnel barrier layer, and forming a fourth ferromagnetic layer that faces the third ferromagnetic layer via the tunnel barrier layer and has its magnetization fixed in a third direction.

[0026] According to the present invention, it is possible to control the dynamic range and suppress magnetic hysteresis.

[0027] FIG. 1(a) is a cross-sectional view of the spin valve structure of the TMR sensor used in the study, and FIG. 1(b) is a plan view showing the magnetization direction of the spin valve structure when the external magnetic field is zero. FIG. 2 is a resistance-magnetic field curve of the spin valve structure. FIG. 3(a) is a schematic diagram of the sample used in the study, and FIG. 3(b) is a plan view showing the direction of each magnetization of the sample. FIG. 4 is a graph obtained by measuring the GMR ratio of the sample of FIG. 3(a) while rotating the external magnetic field in the plane. FIG. 5 is a graph showing the composition of Ru and Fe in the spacer layer and the magnetization M ｐｉｎ and M ｒｅｆ 6 shows the relationship between the composition of Ru and Fe in the spacer layer and the angle α between the two energy components J １ , J ２These figures were obtained by experimentally investigating the relationship between the resistance and magnetic field. FIGS. 7(a) and (b) are cross-sectional views (part 1) of the TMR sensor according to the first embodiment during manufacturing. FIGS. 8(a) and (b) are cross-sectional views (part 2) of the TMR sensor according to the first embodiment during manufacturing. FIGS. 9(a) and (b) are cross-sectional views (part 3) of the TMR sensor according to the first embodiment during manufacturing. FIG. 10 is a cross-sectional view (part 4) of the TMR sensor according to the first embodiment during manufacturing. FIG. 11(a) is a schematic diagram of the TMR sensor according to the first embodiment, and FIG. 11(b) is a plan view of the magnetization directions in the TMR sensor as viewed from the stacking direction z. FIG. 12 is a schematic diagram of a TMR sensor according to a comparative example. FIG. 13(a) is a resistance-magnetic field curve obtained by numerical calculation, and FIG. 13(b) is a sensitivity-magnetic field curve obtained by dividing the differential value of the resistance-magnetic field curve in FIG. 13(a) by the electrical resistance. Figure 14 shows the materials and thicknesses of the layers used in the investigation. Figures 15(a) to 15(c) show the composition of the spacer layer, respectively, of Ru. ４０ Fe ６０ , Ru ３５ Fe ６５ , Ru ３０ Fe ７０ 16A and 16B are diagrams showing the results of investigation of resistance-magnetic field curves when the TMR sensor according to the second embodiment is fabricated. FIGS. 16A and 16B are cross-sectional views (part 1) of the TMR sensor according to the second embodiment during fabrication. FIG. 17 is a cross-sectional view (part 2) of the TMR sensor according to the second embodiment during fabrication. FIG. 18A is a schematic diagram of the TMR sensor according to the first modification, and FIG. 18B is a plan view showing the magnetization directions in the TMR sensor according to this modification as viewed from the stacking direction. FIG. 19 is a schematic diagram of the TMR sensor according to the second modification.

[0028] Prior to describing the present embodiment, the matters considered by the inventors of the present invention will be described.

[0029] FIG. 1( a) is a cross-sectional view of the spin valve structure 9 of the TMR sensor used in the study. As shown in FIG. 1( a), this spin valve structure 9 is formed by stacking a reference layer 4, a tunnel barrier layer 5, and a free layer 6 in this order. Of these, the reference layer 4 and the free layer 6 are both ferromagnetic layers such as CoFe alloy layers. On the other hand, the tunnel barrier layer 5 is an insulating layer such as an MgO layer. In the spin valve structure 9, a tunnel current I is passed between the reference layer 4 and the free layer 6, and the magnitude of an external magnetic field is detected based on the electrical resistance sensed by the tunnel current I.

[0030] FIG. 1(b) is a plan view showing the direction of magnetization of the spin valve structure 9 when the external magnetic field is zero.

[0031] As shown in FIG. 1B, the magnetization M ｒｅｆ is fixed in a certain direction regardless of the direction or magnitude of the external magnetic field. ｆｒｅｅ is the magnetization M of the reference layer 4 when the external magnetic field is zero. ｒｅｆ In this way, each magnetization M ｒｅｆ , M ｆｒｅｅ As a method for orthogonalizing the magnetization M, for example, the two-step heat treatment described above is used. ｆｒｅｅ rotates in the plane of the free layer 6, and each magnetization M ｒｅｆ , M ｆｒｅｅ The electrical resistance changes depending on the angle between the electrodes.

[0032] 2 shows the resistance-magnetic field curve of the spin valve structure 9. The horizontal axis of FIG. 2 is the magnetization M of the reference layer 4. ｒｅｆ The strength of the external magnetic field applied along the direction of magnetization M ｒｅｆ The strength of the external magnetic field parallel to the magnetization M ｒｅｆ The strength of the external magnetic field antiparallel to the direction of the magnetic field is taken as negative. The vertical axis in FIG. 2 represents the electrical resistance.

[0033] As shown in Figure 1(b), when the external magnetic field is zero, each magnetization M ｒｅｆ , M ｆｒｅｅ When the resistance-magnetic field curve 7 is perpendicular to the magnetization M ｒｅｆ The electrical resistance differs between an external magnetic field parallel to the electrode and an external magnetic field antiparallel to the electrode, making it possible to distinguish the direction of the external magnetic field.

[0034] In addition, the range of the magnetic field in which the resistance changes linearly on the resistance-magnetic field curve 7 is a dynamic range D in which the resistance reacts sensitively to changes in the external magnetic field, and the magnetic field H at the boundary of this dynamic range D is １ , H ２ is equal to the saturation magnetic field of the free layer 6.

[0035] To realize further application development of the TMR sensor, it is desirable to be able to control the width of the dynamic range D.

[0036] Furthermore, as mentioned above, the two-step heat treatment causes magnetic hysteresis in the free layer 6, which results in the appearance of a hysteresis curve 7a in the resistance-magnetic field curve 7. Therefore, it is also desirable to suppress the occurrence of magnetic hysteresis and accurately measure the external magnetic field.

[0037] Therefore, the inventors of the present invention have developed a method for producing a magnetized magnet without using a two-stage heat treatment. ｒｅｆ , M ｆｒｅｅ In order to find a way to determine the orientation of the

[0038] 3A is a schematic diagram of the sample S used in the investigation. In the following, the z direction of the xyz Cartesian coordinate system will be referred to as the stacking direction, and the plane perpendicular to the z direction will be simply referred to as the in-plane direction.

[0039] Sample S is formed by laminating an antiferromagnetic layer 1, a fixed layer 2, a spacer layer 3, a reference layer 4, a non-magnetic layer 8, and a free layer 6 in this order in the lamination direction.

[0040] The antiferromagnetic layer 1 is a 6-nm-thick IrMn alloy layer, the pinned layer 2 is a 2-nm-thick ferromagnetic layer made of a Co layer, the spacer layer 3 is a 1-nm-thick RuFe alloy layer, and the reference layer 4 is a 3-nm-thick ferromagnetic layer made of a Co layer, the nonmagnetic layer 8 is a 3-nm-thick Cu layer, and the free layer 6 is a 5-nm-thick ferromagnetic layer made of a CoFe alloy layer.

[0041] Then, by subjecting this sample S to a heat treatment in a magnetic field, the magnetization M of the pinned layer 2 is increased by the exchange coupling between the antiferromagnetic layer 1 and the pinned layer 2. ｐｉｎ was fixed in the in-plane direction.

[0042] In this sample S, by using a RuFe alloy layer as the spacer layer 3, the fixed layer 2 and the reference layer 4 are magnetically coupled as taught in Patent Document 1 and Non-Patent Document 1, and the magnetization M of the reference layer 4 is ｒｅｆ rotates in the plane and magnetization M ｐｉｎ This type of magnetic interaction is called non-collinear interlayer exchange coupling.

[0043] On the other hand, the free layer 6 is separated from the reference layer 4 by the nonmagnetic layer 8, and therefore its magnetization M ｆｒｅｅ is saturated by the external magnetic field H, and the magnetization M ｆｒｅｅ The direction of the magnetic field H is the same as that of the external magnetic field H.

[0044] 3B is a plan view showing the magnetization directions of the sample S. As shown in FIG. 3B, the magnetization M ｒｅｆ is the magnetization M of the pinned layer 2, regardless of the direction of the external magnetic field H, due to the non-collinear interlayer exchange coupling. ｐｉｎ Therefore, each magnetization M ｒｅｆ , M ｐｉｎ The angle α between the external magnetic field H and the magnetization M is greater than 0° and smaller than 180°. ｐｉｎ The angle between the two is represented by θ.

[0045] When a current I flows in the stacking direction of the sample S, the electrical resistance felt by the current I is proportional to the magnetization M of the free layer 6. ｆｒｅｅ and the magnetization M of the reference layer 4 ｒｅｆ The magnetization M of the free layer 6 ｆｒｅｅ The direction of is equal to the direction of the external magnetic field H as described above.

[0046] The inventors of the present application have determined that the magnetization M ｒｅｆ and the magnetization M of the fixed layer 2 ｐｉｎ The following experiment was carried out to determine the angle α.

[0047] 4 is a graph obtained by measuring the GMR ratio of the sample shown in FIG. 3(a) while rotating the external magnetic field H in the plane. The horizontal axis of FIG. 4 represents the angle θ of FIG. 3(b), and the vertical axis represents the GMR ratio. In this experiment, the RuFe alloy of the spacer layer 3 was Ru. ３３ Fe ６７The angle θ at which the GMR ratio becomes zero is shown in FIG. ＩＥＣ The GMR ratio at a certain angle θ is expressed as R, the resistance value at that angle θ, and the minimum resistance value in the entire range of the angle θ. ｍｉｎ Then, (R-R ｍｉｎ ) / R ｍｉｎ It is defined as x100.

[0048] As shown in FIG. ＩＥＣ = 77°. The GMR ratio becomes zero when the magnetization M ｆｒｅｅ and the magnetization M of the reference layer 4 ｒｅｆ As described above, the magnetization M of the free layer 6 ｆｒｅｅ The direction of the magnetization M of the fixed layer 2 is equal to the direction of the external magnetic field H. ｐｉｎ and the magnetization M of the reference layer 4 ｒｅｆ The angle α is the angle θ ＩＥＣ Therefore, when the spacer layer 3 is Ru, ３３ Fe ６７ It was found that when the angle is

[0049] The inventors of the present invention conducted an experiment to investigate how the angle α changes depending on the composition of Ru and Fe in the spacer layer 3. The results of the experiment are shown in FIG.

[0050] FIG. 5 shows the relationship between the composition of Ru and Fe in the spacer layer 3 and the magnetization M ｐｉｎ and M ｒｅｆ This is a diagram obtained by investigating the relationship between the angle α and the

[0051] In this experiment, the Fe composition was varied within a range of 54 atomic % to 70 atomic %. The experimental results revealed that the angle α can be controlled within a range of 50° to 132° by adjusting the Fe composition. Furthermore, according to Patent Document 1, when the Fe composition is 0 atomic %, α = 180°, and when the Fe composition is 100 atomic %, α = 0°. Therefore, by varying the Fe composition within a range greater than 0 atomic % and less than 100 atomic %, the angle α can be controlled within a range greater than 0° and less than 180°.

[0052] The non-collinear interlayer exchange coupling energy is a first energy component J that describes the interlayer coupling due to either antiferromagnetic or ferromagnetic coupling. １ and the second energy component J describing the 90° interlayer bond. ２ It can be divided into:

[0053] First energy component J １ When the value is negative, the magnetization M of the fixed layer 2 and the reference layer 4 ｐｉｎ , M ｒｅｆ The first energy component J １ When the value of is positive, the magnetization M of the fixed layer 2 and the reference layer 4 ｐｉｎ , M ｒｅｆ 10 shows that the layers 2 and 4 are magnetically coupled by ferromagnetic coupling in which the directions are parallel.

[0054] On the other hand, the second energy component J ２ is the magnetization M of the fixed layer 2 and the reference layer 4 ｐｉｎ , M ｒｅｆ This component indicates that the layers 2 and 4 are magnetically coupled by interlayer coupling where the angle between the layers is 90°.

[0055] The inventors of the present invention have determined the composition of Ru and Fe in the spacer layer 3 and the composition of each component J １ , J ２ The relationship between the two was investigated through experiments, and the results are shown in Figure 6.

[0056] FIG. 6 shows the relationship between the composition of Ru and Fe in the spacer layer 3 and each energy component J １ , J ２ This is a diagram obtained by experimentally investigating the relationship between

[0057] As shown in FIG. 6, the second energy component J ２ is approximately constant regardless of the Fe composition, whereas the first energy component J １ It was revealed that the amount of these components J varies greatly depending on the Fe composition. １ , J ２ By the competition between the magnetization M ｐｉｎ , M ｒｅｆ It is considered that the angle α between the two changes depending on the Fe composition, as shown in FIG.

[0058] From the above results, it is clear that the magnetization M of the reference layer 4 can be reduced without performing a two-stage heat treatment in a magnetic field. ｒｅｆ and the magnetization M of the fixed layer 2 ｐｉｎ can be non-collinear (see FIG. 4), and further each magnetization M ｒｅｆ , M ｐｉｎ It has been confirmed that the angle α between the magnetic layers can be controlled by the composition of the spacer layer 3. In the following embodiments, by utilizing such non-collinear exchange interlayer coupling, it is possible to control the dynamic range and suppress magnetic hysteresis.

[0059] First Embodiment FIGS. 7 to 10 are cross-sectional views of a TMR sensor according to a first embodiment during its manufacture.

[0060] 7A, a process for obtaining the cross-sectional structure shown in FIG. 1A is described. First, a silicon substrate 10 having a thermal oxide film (not shown) formed on its surface is prepared, and a copper layer is formed thereon as a lower electrode layer 11 to a thickness of 10 nm to 1000 nm.

[0061] Furthermore, a Ta layer and a Ru layer are formed in this order as an underlayer 12 on the lower electrode layer 11. The thickness of each layer is not particularly limited, and the Ta layer is formed to a thickness of 1 nm or more and 10 nm or less, and the Ru layer is formed to a thickness of 1 nm or more and 10 nm or less.

[0062] Thereafter, a first antiferromagnetic layer 13 made of Ir １－ｘ Mn ｘ (0.7≦x≦0.9) layer is formed to a thickness of 5 nm to 20 nm. At this time, the Ru layer of the underlayer 12 functions to enhance the orientation of the first antiferromagnetic layer 13, making it possible to form a first antiferromagnetic layer 13 with excellent orientation. Furthermore, the underlayer 12 also functions as an adhesion layer, making it possible to enhance the adhesion strength between the lower electrode layer 11 and the first antiferromagnetic layer 13.

[0063] Each of the layers 11 to 13 is formed by DC (Direct Current) magnetron sputtering using Ar gas as the sputtering gas under the condition that the substrate temperature is room temperature (300K).

[0064] Next, the process for obtaining the cross-sectional structure shown in FIG. 7B will be described. First, a Co ｘ Fe １－ｘ A (0.05≦x≦0.95) layer and a Co layer are formed in this order, and these laminated films are used as the first pinned layer 14. The first pinned layer 14 is an example of a first ferromagnetic layer, and its thickness is not particularly limited. For example, ｘ Fe １－ｘ The thickness of the layer is greater than 0 nm and less than or equal to 10 nm, and the thickness of the Co layer is greater than or equal to 0.5 nm and less than or equal to 10 nm, for example, 2 nm.

[0065] Furthermore, a RuFe alloy layer is formed as a spacer layer 15 on the first fixed layer 14 to a thickness of 0.5 nm to 3.0 nm, for example, 1 nm.

[0066] Next, a Co layer is formed as a second pinned layer 16 to a thickness of 1 nm or more and 10 nm or less on the spacer layer 15. The second pinned layer 16 is an example of a second ferromagnetic layer.

[0067] Next, Ag is deposited on the second pinned layer 16 as a non-magnetic layer 17. ｘ Sn １－ｘ The (0.70≦x≦0.98) layer is formed to a thickness of 1.5 nm or more and 4.0 nm or less, for example, 2.5 nm.

[0068] Thereafter, a free layer 18 made of Co was formed on the non-magnetic layer 17. ｘ Fe １－ｘ (0.05≦x≦0.95) layer, Co ｘ Fe ｙ B ｚ Ta ｗ (x+y+z+w=1, 0≦x≦0.8, 0≦y≦0.8, 0.1≦z≦0.3, 0.1≦w≦0.15) layer, a Ta layer, and a Co ｘ Fe ｙ B ｚ (x+y+z=1, 0≦x≦0.8, 0≦y≦0.8, 0.1≦z≦0.3) layers are formed in this order.

[0069] The thickness of the free layer 18 is not particularly limited. ｘ Fe １－ｘ The layer is formed to a thickness of 0.5 nm to 10 nm, and Co ｘ Feｙ B ｚ Ta ｗ The Ta layer is formed to a thickness of more than 0 nm and not more than 50 nm, and the Co layer is formed to a thickness of more than 0 nm and not more than 0.4 nm. ｘ Fe ｙ B ｚ The free layer 18 is an example of a third ferromagnetic layer.

[0070] Each of the above layers 14 to 18 is formed by DC magnetron sputtering using Ar gas as the sputtering gas under conditions where the substrate temperature is room temperature (300K).

[0071] By the steps up to this point, the basic structure of the magnetic laminate 28 made up of the layers 14 to 18 is completed.

[0072] 8A, an MgO layer is formed as the tunnel barrier layer 19 on the free layer 18 to a thickness of 1 nm to 3 nm by RF (Radio Frequency) magnetron sputtering using Ar gas as the sputtering gas. The substrate temperature during the deposition of the tunnel barrier layer 19 is set to, for example, room temperature (300 K).

[0073] Next, the process for obtaining the cross-sectional structure shown in FIG. 8B will be described. First, a Co layer is formed on the tunnel barrier layer 19 as a reference layer 20. ｘ Fe ｙ B ｚ (x+y+z=1, 0≦x≦0.8, 0≦y≦0.8, 0.1≦z≦0.3) layer, Ta layer, Co ｘ Fe ｙ B ｚ (x+y+z=1, 0≦x≦0.8, 0≦y≦0.8, 0.1≦z≦0.3) layer, and Co ｘ Fe １－ｘ (0.05≦x≦0.95) The layers are formed in this order.

[0074] The thickness of the reference layer 20 is not particularly limited. ｘ Fe ｙ B ｚ The Ta layer is formed to a thickness of 0 nm to 0.4 nm.ｘ Fe ｙ B ｚ The layer is formed to a thickness of more than 0 nm and 1 nm or less. ｘ Fe １－ｘ The layer is formed to a thickness of 0.2 nm to 10 nm. Reference layer 20 is an example of a fourth ferromagnetic layer.

[0075] Subsequently, a non-magnetic Ru layer is formed as an antiparallel coupling layer 21 on the reference layer 20 to a thickness of 0.7 nm to 0.9 nm.

[0076] Next, a Co layer was formed on the antiparallel coupling layer 21 as a third pinned layer 22. ｘ Fe １－ｘ (0.05≦x≦0.95) The layer is formed to a thickness of 1 nm or more and 10 nm or less. The third pinned layer 22 is an example of the fifth ferromagnetic layer.

[0077] Then, a second antiferromagnetic layer 23 made of Ir was formed on the third pinned layer 22. １－ｘ Mn ｘ (0.7≦x≦0.9) The layer is formed to a thickness of 5 nm to 20 nm.

[0078] Thereafter, a Ru layer is formed as a cap layer 24 on the second antiferromagnetic layer 23 to a thickness of 2 nm to 20 nm.

[0079] Each of the layers 20 to 24 is formed by DC magnetron sputtering using Ar gas as the sputtering gas under the condition that the substrate temperature is room temperature (300K).

[0080] 3A, the z direction of the xyz Cartesian coordinate system will be referred to as the stacking direction, and the plane perpendicular to the z direction will be simply referred to as the in-plane direction. The stacking direction is the normal direction to the surface of the substrate 10, and is the same as the direction in which the layers 11 to 24 are stacked.

[0081] 9A, a magnetic field heat treatment is performed to heat each of the layers 11 to 24 while applying a magnetic field H in the in-plane direction y (first direction), thereby fixing the magnetization direction of each of the first pinned layer 14 and the third pinned layer 22 in the in-plane direction y (first direction). The conditions for this magnetic field heat treatment are not particularly limited. In this example, the strength of the magnetic field H is set to 7 kOe and the magnetization direction is set to 1×10 -3The heat treatment in the magnetic field is carried out for one hour under the conditions of a reduced pressure atmosphere of 350° C. or less and a substrate temperature of 350° C.

[0082] 9B, a photoresist is applied onto the cap layer 24, and then exposed and developed to form a first resist pattern 25. In this embodiment, since the cap layer 24 is formed on the second antiferromagnetic layer 23, the second antiferromagnetic layer 23 can be prevented from being corroded by the developer.

[0083] Then, using the first resist pattern 25 as a mask, each of the layers 12 to 24 is patterned by Ar ion milling to form an element portion 29 of the TMR sensor made up of each of the layers 12 to 24. During this patterning, the side surfaces of the first resist pattern 25 are recessed, so that the side surfaces of the element portion 29 are inclined from the stacking direction z.

[0084] Next, a process for obtaining the cross-sectional structure shown in Fig. 10 will be described. First, a SiO2 insulating layer 26 is formed on each of the lower electrode layer 11 and the first resist pattern 25 by sputtering. ２ A layer is formed on the insulating layer 26, and the space next to the element portion 29 is filled with the insulating layer 26. Next, the first resist pattern 25 is ultrasonically cleaned in an organic solvent. As a result, the organic solvent penetrates into the first resist pattern 25 through pinholes (not shown) in the insulating layer 26, or the first resist pattern 25 is broken by the ultrasonic waves, thereby removing the first resist pattern 25 and exposing the surface of the cap layer 24. Thereafter, a gold layer is formed on each of the cap layer 24 and the insulating layer 26 as the upper electrode layer 27 to a thickness of 10 nm to 1000 nm. Note that a copper layer may be formed as the upper electrode layer 27 instead of the gold layer.

[0085] This completes the basic structure of the TMR sensor 30 according to this embodiment. In this TMR sensor 30, the layers 12 to 18 below the tunnel barrier layer 19 are electrically connected to the lower electrode layer 11, and the layers 20 to 24 above the tunnel barrier layer 19 are electrically connected to the upper electrode layer 27. When a potential difference is applied between the lower electrode layer 11 and the upper electrode layer 27, the magnitude of the external magnetic field can be measured from the magnitude of the tunnel current that flows through the tunnel barrier layer 19.

[0086] FIG. 11A is a schematic diagram of the TMR sensor 30, and FIG. 11B is a plan view showing the magnetization directions of the TMR sensor 30 as viewed from the stacking direction z.

[0087] As shown in FIG. 11A, the first pinned layer 14 is exchange-coupled with the first antiferromagnetic layer 13 by the above-mentioned heat treatment in a magnetic field (see FIG. 9A), and the magnetization M of the first pinned layer 14 is ｐｉｎ＿１ Similarly, the third pinned layer 22 is exchange-coupled with the second antiferromagnetic layer 23, and the magnetization M of the third pinned layer 22 is fixed in the in-plane direction y (first direction) regardless of the presence or absence of an external magnetic field. ｐｉｎ＿３ is fixed in the in-plane direction y (first direction).

[0088] Furthermore, in this example, since a RuFe alloy is used as the material of the spacer layer 15, when the magnetization of the first pinned layer 14 is pinned by the heat treatment in a magnetic field as shown in FIG. 9( a), the first pinned layer 14 and the second pinned layer 16 are magnetically coupled by the non-collinear interlayer exchange coupling described above.

[0089] As a result, as shown in FIG. 11B, the magnetization M of the second pinned layer 16 remains constant regardless of the presence or absence of an external magnetic field. ｐｉｎ＿２ The direction of the magnetization M of the first fixed layer 14 ｐｉｎ＿１ The magnetization M of the second pinned layer 16 is fixed in a second direction in which the angle α between the first pinned layer 16 and the second pinned layer 16 is greater than 0° and smaller than 180°. ｐｉｎ＿２ The direction of the magnetic field can be fixed, and the occurrence of magnetic hysteresis can be suppressed.

[0090] The material of the spacer layer 15 that generates non-collinear interlayer exchange coupling is not limited to RuFe alloy. As shown in FIG. 6 , non-collinear interlayer exchange coupling is realized by competition between interlayer coupling due to either antiferromagnetic coupling or ferromagnetic coupling and 90° interlayer coupling. Therefore, it is believed that non-collinear interlayer exchange coupling can occur in any material that is a mixture of a ferromagnetic material and a non-magnetic material that exhibits antiferromagnetic coupling. Non-magnetic materials that exhibit antiferromagnetic coupling include Ru, Rh, Cr, and Ir. Ferromagnetic materials include Fe, Co, and Ni. Any combination of these non-magnetic and ferromagnetic materials can be used as the material of the spacer layer 15.

[0091] On the other hand, the second pinned layer 16 and the free layer 18 are ferromagnetically coupled via the nonmagnetic layer 17. Therefore, when the external magnetic field is zero, the magnetization M of the free layer 18 ｆｒｅｅ is the magnetization M of the second pinned layer 16 ｐｉｎ＿２ The CoFe alloy layer included in the free layer 18 strengthens the ferromagnetic coupling between the second pinned layer 16 and the free layer 18, thereby increasing the magnetization M ｆｒｅｅ Magnetization M ｐｉｎ＿２ contributes to pointing in the same direction.

[0092] In addition, the CoFeB layer included in the free layer 18, together with the MgO layer of the tunnel barrier layer 19 and the CoFeB layer of the reference layer 20 thereon, constitutes a ferromagnetic tunnel junction of CoFeB / MgO / CoFeB, thereby achieving a high TMR ratio.

[0093] When an external magnetic field is applied, the magnetization M ｆｒｅｅ The CoFeBTa alloy layer included in the free layer 18 serves to improve the soft magnetic properties of the free layer 18.

[0094] The reference layer 20 is exchange-coupled with the third fixed layer 22 via the antiparallel coupling layer 21 so that the magnetization directions are opposite to each other. ｒｅｆ is the magnetization M of the third pinned layer 22 regardless of the presence or absence of an external magnetic field. ｐｉｎ＿３ It faces in a third direction opposite to the above.

[0095] In the TMR sensor 30, the reference layer 20 faces the free layer 18 via the tunnel barrier layer 19, and the magnetization M of each layer changes in response to an external magnetic field. ｒｅｆ , M ｆｒｅｅ The angle φ between the lower electrode layer 11 and the upper electrode layer 27 changes. Therefore, when a tunnel current I is passed between the lower electrode layer 11 and the upper electrode layer 27, the electrical resistance changes depending on the angle φ, and the magnitude of the external magnetic field can be measured based on this electrical resistance.

[0096] Furthermore, the inclusion of a Ta layer in the free layer 18 can improve the TMR ratio of the TMR sensor 30. The TMR ratio is determined by the ratio of the magnetization M of the free layer 18 and the reference layer 20. ｆｒｅｅ , M ｒｅｆ The electrical resistance of the TMR sensor when is parallel and antiparallel is R Ｐ and R ＡＰ Then, 100 × (R ＡＰ -R Ｐ ) / R Ｐ The larger this value, the greater the change in electrical resistance with respect to a change in the external magnetic field, and the better the performance of the TMR sensor 30. To increase the TMR ratio, a W layer may be included in the free layer 18 instead of the Ta layer.

[0097] Moreover, in this embodiment, by changing the film thickness of the nonmagnetic layer 17, the magnetic coupling strength J between the second pinned layer 16 and the free layer 18 can be adjusted. ｓｐ Therefore, the dynamic range in which the resistance changes approximately linearly in the resistance-magnetic field curve of the TMR sensor 30 can be controlled.

[0098] The inventors of the present invention performed numerical calculations to confirm that the dynamic range can be controlled by changing the film thickness of the nonmagnetic layer 17. In the numerical calculations, comparative examples were also investigated.

[0099] 12 is a schematic diagram of a TMR sensor according to a comparative example. In the comparative example, the second pinned layer 16 and the non-magnetic layer 17 are omitted, and the free layer 18 is formed directly on the spacer layer 15. The other configurations are the same as those shown in FIG. 11. In this case, the first pinned layer 14 and the free layer 18 are magnetically coupled by non-collinear interlayer coupling via the spacer layer 15, and the magnetization M of the free layer 18 is ｆｒｅｅis the magnetization M of the first pinned layer 14 ｐｉｎ＿１ The sensor is fixed in a position facing diagonally relative to the sensor.

[0100] In both the present embodiment and the comparative example, each energy component J included in the non-collinear interlayer exchange coupling energy １ , J ２ (See FIG. 6) is the value (J １ =0.12erg / cm ２ , J ２ =-0.28erg / cm ２ ) was used.

[0101] Furthermore, in both this embodiment and the comparative example, the magnetic moments of the first pinned layer 14 and the free layer 18 were set to 5 Tnm and 10 Tnm, respectively. Note that the magnetic moment is defined as the product of the volume magnetization and the film thickness. In this embodiment, the magnetic moment of the second pinned layer 16 was set to 5 Tnm. Note that in both this embodiment and the comparative example, the TMR ratio was 200%.

[0102] 13A shows the resistance-magnetic field curve obtained by this numerical calculation. In this numerical calculation, the magnetic coupling strength J between the second pinned layer 16 and the free layer 18 is changed to simulate the change in the thickness of the non-magnetic layer 17. ｓｐ -0.02 erg / cm ２ , -0.05erg / cm ２ , -0.10erg / cm ２ The electrical resistance is measured by changing the magnetization M of the second pinned layer 16 when the external magnetic field is applied. ｐｉｎ＿２ The values ​​are normalized by the values ​​when parallel to the axis.

[0103] As shown in FIG. 13A, in both the present embodiment and the comparative example, the resistance-magnetic field curve is an odd function due to the non-collinear interlayer exchange coupling via the spacer layer 15, but the slope of the curve near zero external magnetic field is significantly different.

[0104] In particular, in this embodiment, the magnetic coupling strength J ｓｐThe range of the external magnetic field in which the resistance-magnetic field curve changes approximately linearly changed depending on the thickness of the nonmagnetic layer 17. From this result, it was confirmed that the dynamic range of the TMR sensor 30 can be controlled by changing the thickness of the nonmagnetic layer 17.

[0105] In this example, an AgSn alloy is used as the material for nonmagnetic layer 17, but the material for nonmagnetic layer 17 is not limited to this. By using any of Cu, Ag, Cr, Ru, and an AgSn alloy as the material for nonmagnetic layer 17, the dynamic range can be controlled by the film thickness of nonmagnetic layer 17, as described above.

[0106] On the other hand, since the comparative example did not have the nonmagnetic layer 17, it was not possible to control the dynamic range by changing the film thickness of the nonmagnetic layer 17.

[0107] FIG. 13(b) shows a sensitivity-magnetic field curve obtained by dividing the differential value of the resistance-magnetic field curve of FIG. 13(a) by the electrical resistance.

[0108] As shown in FIG. 13B, the maximum sensitivity is 1.2% / mT in the comparative example, whereas in this embodiment, ｓｐ is -0.02 erg / cm ２ , -0.05erg / cm ２ , -0.10erg / cm ２ The maximum sensitivities are 23% / mT, 10% / mT, and 6% / mT, respectively. In this way, the sensitivity of the TMR sensor in this embodiment can be significantly increased compared to the comparative example. Moreover, the sensitivity value varies depending on the ferromagnetic coupling strength J depending on the film thickness of the nonmagnetic layer 17. ｓｐ It can be varied by controlling

[0109] The inventors of the present invention conducted an experiment to investigate how the resistance-magnetic field curve of the TMR sensor 30 changes depending on the composition of the spacer layer 15 .

[0110] FIG. 14 shows the materials and thicknesses of each layer used in the investigation.

[0111] 15(a) to 15(c) show the composition of the spacer layer 15, respectively. ４０ Fe ６０ , Ru ３５ Fe ６５ , Ru３０ Fe ７０ 15(a) to 15(c) show the results of investigating the resistance-magnetic field curves when the resistance-magnetic field curve is 1. In Figures 15(a) to 15(c), the electrical resistance is expressed as the TMR ratio. Also shown in Figures 15(a) to 15(c) are the sensitivity-magnetic field curves obtained from the resistance-magnetic field curves.

[0112] As shown in Figures 15(a) to (c), it was confirmed that the resistance-magnetic field curves did not show magnetic hysteresis for any of the RuFe compositions. ４０ Fe ６０ (Fig. 15(a)) and Ru ３０ Fe ７０ In the case of (FIG. 15(c)), the maximum sensitivity is obtained when the external magnetic field is near zero, and it is clear that desirable characteristics are achieved for the magnetic sensor, similar to the numerical calculation results in FIGS. 13(a) and 13(b).

[0113] Second Embodiment In this embodiment, the occurrence of magnetic hysteresis in the resistance-magnetic field curve is more effectively suppressed as follows.

[0114] 16 and 17 are cross-sectional views of the TMR sensor according to this embodiment during its manufacture. In these figures, the same elements as those described in the first embodiment are denoted by the same reference numerals, and their description will be omitted below.

[0115] 7A to 9B of the first embodiment are performed to obtain the element portion 29 as shown in Fig. 16A. Thereafter, the first resist pattern 25 used for patterning the element portion 29 is removed.

[0116] Next, the process for obtaining the cross-sectional structure shown in Figure 16(b) will be described. First, a second resist pattern 33, which is narrower in cross-section than the first resist pattern 25, is formed on the cap layer 24. Then, using the second resist pattern 33 as a mask, each of the layers 19 to 24 is patterned by Ar ion milling. As a result, the width of each of the tunnel barrier layer 19 and reference layer 20 in cross-section becomes narrower than the width of the free layer 18, and the top surface 18a of the free layer 18 near the side of the element portion 29 is exposed.

[0117] Thereafter, the process of FIG. 10 of the first embodiment is carried out to complete the basic structure of the TMR sensor 40 according to this embodiment, as shown in FIG.

[0118] 10, the upper surface 18a of the free layer 18 near the side surface of the element portion 29 is not covered with the tunnel barrier layer 19. Therefore, even if the magnetic domain of the free layer 18 at the upper surface 18a does not return to its original state after the external magnetic field is removed, magnetic hysteresis is unlikely to occur in the resistance-magnetic field curve because the area near the side surface of the element portion 29 is a region through which almost no current flows.

[0119] (Modifications) Next, modifications of the above embodiments will be described.

[0120] 18A is a schematic diagram of a TMR sensor according to a first modification. In the first modification, the reference layer 20 and the anti-parallel coupling layer 21 are omitted, and the third fixed layer 22 is formed directly on the tunnel barrier layer 19, so that the third fixed layer 22 faces the free layer 18 via the tunnel barrier layer 19. In this case, as in the first embodiment, the third fixed layer 22 is exchange-coupled with the second antiferromagnetic layer 23, and the magnetization M of the third fixed layer 22 changes regardless of the presence or absence of an external magnetic field. ｐｉｎ＿３ is fixed in the in-plane direction y (fourth direction).

[0121] FIG. 18B is a plan view showing the magnetization directions of the TMR sensor according to this modification as viewed from the stacking direction z.

[0122] As shown in FIG. 18B, the magnetization M of the first fixed layer 14 ｐｉｎ＿１ and the magnetization M of the second pinned layer 16 ｐｉｎ＿２ The angle α between is fixed by non-collinear interlayer coupling via the spacer layer 15, as in the first embodiment.

[0123] On the other hand, the magnetization M of the free layer 18 ｆｒｅｅ is rotated by the external magnetic field and points in the same direction as the external magnetic field. ｆｒｅｅ and magnetization M ｐｉｎ＿３ The angle between the two electrodes changes depending on the external magnetic field, and the magnitude of the external magnetic field can be measured based on the resulting change in electrical resistance.

[0124] 19 is a schematic diagram of a TMR sensor according to a second modification. In the second modification, the stacking order of the layers 13 to 23 is reversed from that of the first embodiment (FIG. 11A). This structure also makes it possible to control the dynamic range and suppress magnetic hysteresis for the same reasons as in the first embodiment.

[0125] 1...antiferromagnetic layer, 2...fixed layer, 3...spacer layer, 4...reference layer, 5...tunnel barrier layer, 6...free layer, 7...resistance-magnetic field curve, 7a...hysteresis curve, 8...non-magnetic layer, 10...silicon substrate, 11...lower electrode layer, 12...underlayer, 13...first antiferromagnetic layer, 14...first fixed layer, 15...spacer layer, 16...second fixed layer, 17...non-magnetic layer, 18...free layer, 19...tunnel barrier layer, 20...reference layer, 21...antiparallel coupling layer, 22...third fixed layer, 23...second antiferromagnetic layer, 24...cap layer, 25...first resist pattern, 26...insulating layer, 27...upper electrode layer, 28...magnetic stack, 29...element portion, 30, 40...TMR sensor, 33...second resist pattern.

Claims

1. A magnetic stack comprising: a first ferromagnetic layer whose magnetization is fixed in a first direction; a spacer layer; a second ferromagnetic layer magnetically coupled to the first ferromagnetic layer via the spacer layer and whose magnetization is oriented in a second direction that forms an angle with the first direction greater than 0° and less than 180°; a nonmagnetic layer; and a third ferromagnetic layer ferromagnetically coupled to the second ferromagnetic layer via the nonmagnetic layer.

2. The magnetic stack according to claim 1, further comprising a first antiferromagnetic layer exchange-coupled with said first ferromagnetic layer.

3. The magnetic stack according to claim 1 or 2, further comprising: a tunnel barrier layer; and a fourth ferromagnetic layer that faces the third ferromagnetic layer via the tunnel barrier layer and has its magnetization fixed in a third direction.

4. The magnetic laminate according to claim 3, further comprising: an antiparallel coupling layer; and a fifth ferromagnetic layer exchange-coupled to the fourth ferromagnetic layer via the antiparallel coupling layer.

5. The magnetic stack according to claim 4, further comprising a second antiferromagnetic layer exchange-coupled with said fifth ferromagnetic layer.

6. The magnetic stack according to claim 1 or 2, further comprising: a tunnel barrier layer; and a fifth ferromagnetic layer that faces the third ferromagnetic layer via the tunnel barrier layer and has its magnetization fixed in a fourth direction.

7. The magnetic laminate according to any one of claims 1 to 6, wherein the spacer layer is made of a mixture of a non-magnetic material and a ferromagnetic material.

8. The magnetic laminate according to claim 7, wherein the nonmagnetic material is any one of Ru, Rh, Cr, and Ir, and the ferromagnetic material is any one of Fe, Co, and Ni.

9. The magnetic laminate according to any one of claims 1 to 8, wherein the material of the non-magnetic layer is any one of Cu, Ag, Cr, Ru, and an AgSn alloy.

10. The magnetic stack according to any one of claims 1 to 9, wherein the third ferromagnetic layer contains either a CoFe alloy or a CoFeB alloy.

11. A TMR sensor comprising: a first electrode; a first ferromagnetic layer electrically connected to the first electrode and having a magnetization fixed in a first direction; a spacer layer; a second ferromagnetic layer magnetically coupled to the first ferromagnetic layer via the spacer layer and having a magnetization oriented in a second direction that forms an angle with the first direction greater than 0° and less than 180°; a nonmagnetic layer; a third ferromagnetic layer magnetically coupled to the second ferromagnetic layer via the nonmagnetic layer; a tunnel barrier layer; a fourth ferromagnetic layer facing the third ferromagnetic layer via the tunnel barrier layer and having a magnetization fixed in a third direction; and a second electrode electrically connected to the fourth ferromagnetic layer.

12. The TMR sensor according to claim 11, wherein, in a cross-sectional view, the width of each of the tunnel barrier layer and the fourth ferromagnetic layer is narrower than the width of the third ferromagnetic layer.

13. A method for manufacturing a magnetic laminate, comprising: forming a first ferromagnetic layer; forming a spacer layer; forming a second ferromagnetic layer magnetically coupled to the first ferromagnetic layer via the spacer layer; forming a nonmagnetic layer; forming a third ferromagnetic layer magnetically coupled to the second ferromagnetic layer via the nonmagnetic layer; and performing a heat treatment on the first ferromagnetic layer in a magnetic field oriented in a first direction, thereby fixing the magnetization of the first ferromagnetic layer in the first direction and orienting the magnetization of the second ferromagnetic layer in a second direction that forms an angle with the first direction greater than 0° and less than 180°.

14. The method for manufacturing a magnetic laminate according to claim 13, further comprising forming an antiferromagnetic layer exchange-coupled with said first ferromagnetic layer.

15. A method for manufacturing a magnetic laminate according to claim 13 or 14, further comprising: forming a tunnel barrier layer; and forming a fourth ferromagnetic layer that faces the third ferromagnetic layer via the tunnel barrier layer and has its magnetization fixed in a third direction.

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