Patent ID: 12256644

DESCRIPTION OF THE EMBODIMENTS

The magnetoresistive sensor described in the present disclosure includes a combination of magnetoresistive devices having different phases. As an example, the magnetoresistive sensor described herein may include at least one wheatstone bridge. Magnetoresistive devices in the wheatstone bridge are connected with one another and have different phases. Electrical resistances of the magnetoresistive devices may vary in corresponding to variation of external magnetic field, thus an output terminal of the wheatstone bridge can be altered.

FIG.1Ais a schematic diagram illustrating a magnetoresistive sensor100, according to some embodiments of the present disclosure.

Referring toFIG.1A, the magnetoresistive sensor100includes a wheatstone bridge102and a wheatstone bridge104. As will be further described, the wheatstone bridge102and the wheatstone bridge104respectively include multiple magnetoresistive devices MR having different phases, and the magnetoresistive devices MR of the wheatstone bridge102have phase differences with respect to the magnetoresistive devices MR of the wheatstone bridge104. It should be noted that, the phase of each magnetoresistive device MR indicates a relationship between resistance variation of the magnetoresistive device MR with respect to variation of an external magnetic field, and such relationship is dependent on a magnetization direction of its reference layer (as indicated by the arrow in each magnetoresistive device MR inFIG.1A). In other words, the phase of each magnetoresistive device MR is related to the magnetization direction of its reference layer. When two magnetoresistive devices MR are described as having a phase difference with each other in the present disclosure, the reference layers of these magnetoresistive devices MR have different magnetization directions.

In some embodiments, the wheatstone bridge102is a full bridge. In these embodiments, the wheatstone bridge102includes four magnetoresistive devices MR each having an electrical resistance varying with respect to variation of the external magnetic field. The four magnetoresistive devices MR include a magnetoresistive device MR1, a magnetoresistive device MR2, a magnetoresistive device MR3and a magnetoresistive device MR4. The magnetoresistive devices MR1, MR2are in serial connection, and have a phase difference of about 180° with each other (i.e., the magnetization directions of the reference layers in the magnetoresistive devices MR1, MR2are about 180° different from each other). Similarly, the magnetoresistive devices MR3, MR4are in serial connection as well, and also have a phase difference of about 180° with each other (i.e., the magnetization directions of the reference layers in the magnetoresistive devices MR3, MR4are about 180° different from each other). Accordingly, two of the magnetoresistive devices MR1-MR4may have a phase, while the other two of the magnetoresistive devices MR1-MR4may have another phase. For instance, the magnetoresistive device MR1and the magnetoresistive device MR3have a first phase, while the magnetoresistive device MR2and the magnetoresistive device MR4have a second phase different from the first phase by about 180°.

Further, the serially connected magnetoresistive devices MR1, MR2and the serially connected magnetoresistive devices MR3, MR4are connected in parallel between an input terminal VINand a reference voltage terminal VR. In addition, an output terminal VOUT1of the wheatstone bridge102is connected to a node between the serially connected magnetoresistive devices MR1, MR2and a node between the serially connected magnetoresistive devices MR3, MR4. In some embodiments, the magnetoresistive devices MR1, MR4with a phase difference of about 180° are connected between the input terminal VINand the output terminal VOUT1, whereas the magnetoresistive devices MR2, MR3with a phase difference of about 180° are connected between the reference voltage terminal VRand the output terminal VOUT1.

Similarly, in some embodiments, the wheatstone bridge104is a full bridge as well. In these embodiments, the wheatstone bridge104includes four magnetoresistive devices MR each having an electrical resistance varying with respect to variation of the external magnetic field. The four magnetoresistive devices MR include a magnetoresistive device MR5, a magnetoresistive device MR6, a magnetoresistive device MR7and a magnetoresistive device MR8. The magnetoresistive devices MR5, MR6are in serial connection, and have a phase difference of about 180° with each other (i.e., the magnetization directions of the reference layers in the magnetoresistive devices MR5, MR6are about 180° different from each other). Similarly, the magnetoresistive devices MR7, MR8are in serial connection as well, and also have a phase difference of about 180° with each other (i.e., the magnetization directions of the reference layers in the magnetoresistive devices MR7, MR8are about 180° different from each other). Accordingly, two of the magnetoresistive devices MR5-MR8may have a phase, while the other two of the magnetoresistive devices MR5-MR8may have another phase. Moreover, as described above, the magnetoresistive devices MR5-MR8of the wheatstone bridge104have a phase difference (e.g., a phase difference of about 90°) with respect to the magnetoresistive devices MR1-MR4of the wheatstone bridge102, respectively. For instance, the magnetoresistive devices MR5, MR7have a third phase, which is different from the first and second phases of the magnetoresistive devices MR1, MR3and the magnetoresistive devices MR2, MR4in the wheatstone bridge102by about 90°, respectively. In addition, the magnetoresistive devices MR6, MR8of the wheatstone bridge104have a fourth phase different from the third phase by about 180°, and different from the first and second phases of the magnetoresistive devices MR1, MR3and the magnetoresistive devices MR2, MR4in the wheatstone bridge102by about 90°, respectively.

In some embodiments, the wheatstone bridges102,104are connected in parallel between the input terminal VINand the reference voltage terminal VR. In these embodiments, the serially connected magnetoresistive devices MR5, MR6and the serially connected magnetoresistive devices MR7, MR8may be connected in parallel between the input terminal VINand the reference voltage terminal VRshared with the wheatstone bridge102. In addition, an output terminal VOUT2of the wheatstone bridge104is connected to a node between the serially connected magnetoresistive devices MR5, MR6and a node between the serially connected magnetoresistive devices MR7, MR8. In some embodiments, the magnetoresistive devices MR5, MR8with a phase difference of about 180° are connected between the input terminal VINand the output terminal VOUT2, whereas the magnetoresistive devices MR6, MR7with a phase difference of about 180° are connected between the reference voltage terminal VRand the output terminal VOUT2.

FIG.1Bis a schematic cross-sectional view illustrating a basic structure of each magnetoresistive device MR in the magnetoresistive sensor100shown inFIG.1A.

Referring toFIG.1B, each magnetoresistive device MR may be a spin valve, and includes a spacer layer106, a reference layer108and a free layer110separated from the reference layer108by the spacer layer106. The reference layer108and the free layer110each include a ferromagnetic material. As compared to the free layer110, the reference layer108may be configured to have a greater coercivity, such that a magnetization direction of the reference layer108is less likely to be altered in corresponding to variation of the external magnetic field, and is indicated by a unidirectional arrow shown inFIG.1B. On the other hand, the free layer110has a relatively low coercivity, and a magnetization direction of the free layer110is dependent on variation of the external magnetic field, as indicated by a bi-directional arrow shown inFIG.1B. An angle between the magnetization direction of the reference layer108and the magnetization direction of the free layer110(i.e., a direction of the external magnetic field) determines an electrical resistance across the magnetoresistive device MR. For instance, when the magnetization direction of the reference layer108is aligned with the magnetization direction of the free layer110, the magnetoresistive device MR is in a parallel state, and has a low electrical resistance. On the other hand, when the magnetization direction of the reference layer108is opposite to the magnetization direction of the free layer110, the magnetoresistive device MR is in an anti-parallel state, and has a high electrical resistance. As a result that the electrical resistances of the magnetoresistive devices MR change in corresponding to the external magnetic field, each wheatstone bridge102/104outputs different voltages in corresponding to variation (e.g., magnitude, direction . . . etc.) of the external magnetic field.

In some embodiments, the magnetoresistive device MR is a giant magnetoresistive (GMR) spin valve. In these embodiments, the spacer layer106may be formed by a non-magnetic conductive material. For instance, the non-magnetic conductive material may include Cu, Ag, Cr, other non-magnetic metals or alloys formed of combinations of these non-magnetic metals. In alternative embodiments, the magnetoresistive device MR is a tunneling magnetoresistive (TMR) spin valve. In these alternative embodiments, the spacer layer106may be formed of an insulating material. For instance, the insulating material may include magnesium oxide, aluminum oxide, other insulating materials or combinations thereof.

The reference layer108, the spacer layer106and the free layer110may stack along a vertical direction, to form a stacking structure. According to some embodiments, as shown inFIG.1B, the reference layer108lies below the spacer layer106, while the free layer110is located above the spacer layer106. However, in alternative embodiments, the reference layer108may be located above the spacer layer106, whereas the free layer110may lie under the spacer layer106.

FIG.1Cis a schematic cross-sectional view illustrating a detailed structure of a reference layer108, according to some embodiments of the present disclosure.

Referring toFIG.1C, in some embodiments, the reference layer108is a multilayer structure, which includes a ferromagnetic layer108aand an antiferromagnetic layer108b. Due to an exchange bias coupling effect at an interface between the ferromagnetic layer108aand the antiferromagnetic layer108b, a magnetic hysteresis loop of the ferromagnetic layer108ashifts, such that the ferromagnetic layer108ahas a greater coercivity. Accordingly, spin directions in the ferromagnetic layer108amay be described as being pinned to a certain direction (as indicated by multiple arrows in the ferromagnetic layer108ashown inFIG.1C), which is also referred to as an exchange bias coupling direction EB. The exchange bias coupling direction EB determines the magnetization direction of the reference layer108, and defines the phase of the magnetoresistive device MR. On the other hand, as indicated by multiple arrows in the antiferromagnetic layer108bshown inFIG.1C, spin directions in a thin region of the antiferromagnetic layer108bclosest to the ferromagnetic layer108amay be aligned with the exchange bias coupling EB direction, and spin directions in rest portion of the antiferromagnetic layer108bmay be alternately oriented as opposite directions along a direction away from the ferromagnetic layer108a, in order to maintain antiferromagnetic characteristic. In some embodiments, the ferromagnetic material for forming the ferromagnetic layer108aincludes a Ni—Fe alloy, a Co—Fe—B alloy, a Co—Fe alloy, Co or other ferromagnetic metals, metal alloys or metallic compounds, while the antiferromagnetic material for forming the antiferromagnetic layer108bincludes an Ir—Mn alloy, a Pt—Mn alloy or the like.

FIG.1Dis a schematic plan view illustrating magnetoresistive devices MR with different phases, according to some embodiments of the present disclosure.

Referring toFIG.1D, each magnetoresistive device MR may be formed in an annular sector shape. The reference layers108of the magnetoresistive devices MR with different phases may be separate annular sector portions singulated from a single initial reference layer formed in an annular shape. This initial reference layer in annular shape may have an exchange bias coupling direction following a vortex path or a loop. Accordingly, when the annular sector portions of the annular initial reference layer are singulated, these reference layers108in annular sector shapes have different exchange bias coupling directions along the vortex path or loop of the original exchange bias coupling direction. Therefore, the magnetoresistive devices MR including these reference layers108may have various phases.

For instance, the reference layers of the magnetoresistive device MR1with the first phase, the magnetoresistive device MR2with the second phase, the magnetoresistive device MR5with the third phase and the magnetoresistive device MR6with the fourth phase may be formed by singulating four separate annular sector portions from a single initial reference layer in annular shape, and are arranged along a vortex path or a loop. The first phase of the magnetoresistive device MR1is indicated by a first exchange bias coupling direction EB1; the second phase of the magnetoresistive device MR2is indicated by a second exchange bias coupling direction EB2; the third phase of the magnetoresistive device MR5is indicated by a third exchange bias coupling direction EB3; and the fourth phase of the magnetoresistive device MR6is indicated by a fourth exchange bias coupling direction EB4. In some embodiments, as shown inFIG.1D, the first exchange bias coupling direction EB1, the third exchange bias coupling direction EB3, the second exchange bias coupling direction EB2and the fourth exchange bias coupling direction EB4are arranged along a clockwise path. In alternative embodiments, the first through fourth exchange bias coupling directions EB1-EB4are arranged along a counterclockwise path.

Although not shown, the magnetoresistive device MR3with the first phase, the magnetoresistive device MR4with the second phase, the magnetoresistive device MR7with the third phase and the magnetoresistive device MR8with the fourth phase may also be formed by singulating four separate annular sector portions from a single initial reference layer in annular shape, and are arranged along a vortex path or a loop as well. In addition, the exchange bias coupling directions of these magnetoresistive devices MR may be arranged along a clockwise path. Alternatively, the exchange bias coupling directions of these magnetoresistive devices MR may be arranged along a counterclockwise path.

FIG.2is a flow diagram illustrating a method for manufacturing the magnetoresistive devise MR with different phases, according to some embodiments of the present disclosure.FIG.3AthroughFIG.3Fare schematic plan views illustrating intermediate structures at various stages during the manufacturing process shown inFIG.2.FIG.4AthroughFIG.4Fare schematic cross-sectional views illustrating the intermediate structures at various stages during the manufacturing process shown inFIG.2.

Referring toFIG.2,FIG.3AandFIG.4A, step S200is performed, and a stacking structure including an antiferromagnetic material layer302, a ferromagnetic material layer304and a mask layer306is formed on a substrate300. The substrate300may be a semiconductor substrate, such as a silicon substrate. However, the present disclosure is not limited to a material of the substrate300. In addition, material layer(s) (e.g., wiring layers) may be preliminarily formed on the substrate300before formation of the stacking structure. The antiferromagnetic material layer302will be patterned to form the antiferromagnetic layer108bdescribed with reference toFIG.1C, and the ferromagnetic material layer304will be patterned to form the ferromagnetic layer108adescribed with reference toFIG.1C. According to some embodiments, a method for forming the antiferromagnetic material layer302and a method for forming the ferromagnetic material layer304respectively include a deposition process, such as a physical vapor deposition (PVD) process. Further, the mask layer306may be a photoresist layer. In some embodiments, the antiferromagnetic material layer302, the ferromagnetic material layer304and the mask layer306are sequentially formed on the substrate300.

Referring toFIG.2,FIG.3BandFIG.4B, step S202is performed, and the mask layer306is patterned to form a mask pattern308. The mask pattern308will be used as a shadow mask during a subsequent etching process for patterning the antiferromagnetic material layer302and the ferromagnetic material layer304. In some embodiments, the mask pattern308is formed as a closed annulus pattern. In those embodiments where the mask layer306is a photoresist layer, a method for patterning the mask layer306to form the mask pattern308may include an exposure process and a development process.

Referring toFIG.2,FIG.3CandFIG.4C, step S204is performed, and the antiferromagnetic material layer302and the ferromagnetic material layer304are patterned to form an initial antiferromagnetic layer310and an initial ferromagnetic layer312, respectively. A stacking structure including the initial antiferromagnetic layer310and the initial ferromagnetic layer312may be referred to as an initial reference layer314. In some embodiments, such patterning step is performed by using an etching process. During the etching process, the mask pattern308shown inFIG.3BandFIG.4Bmay be functioned as a shadow mask, for defining a boundary of the initial reference layer314. In other words, in those embodiments where the mask pattern308is formed as a closed annulus pattern, the initial reference layer314is also formed as a closed annulus pattern. The mask pattern308may be removed after such patterning step by using a method such as a stripping process or an ashing process.

In the embodiments described above, the initial reference layer314is formed by patterning the antiferromagnetic material layer302and the ferromagnetic material layer304using a subtractive lithography process. However, in alternative embodiments, an additive lithography process may be used for patterning the antiferromagnetic material layer302and the ferromagnetic material layer304to form the initial reference layer314. As an example, the additive lithography process may be a lift-off lithography process. In these alternative embodiments, a mask pattern may be formed on the substrate300before formation of the antiferromagnetic material layer302and the ferromagnetic material layer304. After forming the antiferromagnetic material layer302and the ferromagnetic material layer304, the mask pattern and a portion of the antiferromagnetic material layer302as well as a portion of the ferromagnetic material layer304overlying the mask pattern are lifted off from the substrate300. Remained portion of the antiferromagnetic material layer302and remained portion of the ferromagnetic material layer304form the initial antiferromagnetic layer310and the initial ferromagnetic layer312, respectively.

Referring toFIG.2,FIG.3DandFIG.4D, step S206is performed, and the initial reference layer314is subjected to a heat treatment. During the heat treatment, the initial reference layer314is entirely heated over a blocking temperature. When the temperature of the initial reference layer314is higher than the blocking temperature, the exchange bias coupling between the initial antiferromagnetic layer310and the initial ferromagnetic layer312may weaken or no longer exist. As being formed in an annular shape, the initial ferromagnetic layer312may be magnetized with a magnetization direction along a vortex path or a loop, for overcoming a demagnetizing energy. During a cooling step after the heating step, the temperature of the initial reference layer314falls below the blocking temperature. At this time, spin directions of a thin portion of the initial antiferromagnetic layer310closest to the initial ferromagnetic layer312are aligned with the magnetization direction of the initial ferromagnetic layer312, which is oriented along a vortex path or a loop. As a result, an exchange bias oriented along an initial exchange bias coupling direction EB′ following a vortex path or a loop is obtained. According to some embodiments, as shown inFIG.3D, the initial exchange bias coupling direction EB′ is clockwise. In alternative embodiments, the initial exchange bias coupling direction EB′ is counterclockwise. Further, in some embodiments, an external magnetic field may be applied on the initial reference layer314during the cooling step of the heat treatment, for ensuring that the initial exchange bias coupling direction EB′ obtained every time would be consistently clockwise or counterclockwise. In alternative embodiments, an external magnetic field may be absent during the cooling step of the heat treatment. Moreover, in some embodiments, a thickness of the initial ferromagnetic layer312has to be greater than a critical thickness of about 15 nm, for ensuring an exchange bias following a vortex path or a loop can be obtained. However, the critical thickness may vary according to dimension (e.g., thickness) and material selection of the initial reference layer314, the present disclosure is not limited to the value of the critical thickness.

Referring toFIG.2,FIG.3EandFIG.4E, step S208is performed, and the initial reference layer314is patterned to form separate reference layers108each in an annular sector shape. In the current step, the initial antiferromagnetic layer310of the initial reference layer314is patterned to form antiferromagnetic layers108beach in an annular sector shape, while the initial ferromagnetic layer312of the initial reference layer314is patterned to form ferromagnetic layers108aeach in an annular sector shape. A thickness of the antiferromagnetic layers108bis substantially identical with the thickness of the initial antiferromagnetic layer310, and the antiferromagnetic layers108bare arranged along the annular boundary of the initial antiferromagnetic layer310. Similarly, a thickness of the ferromagnetic layers108ais substantially identical with the thickness of the initial ferromagnetic layer312, and the ferromagnetic layers108aare arranged along the annular boundary of the initial ferromagnetic layers312. One of the antiferromagnetic layers108band the ferromagnetic layer108ain contact with each other are collectively referred to as one of the reference layers108. The reference layers108have exchange bias coupling directions EB along a vortex path or a loop, along which the initial exchange bias coupling direction EB′ follows. For instance, four separate reference layers108are obtained from the current patterning step, and the four reference layers108have the first exchange bias coupling direction EB1, the second exchange bias coupling direction EB2, the third exchange bias coupling direction EB3and the fourth exchange bias coupling direction EB4, respectively. In those embodiments where the initial exchange bias coupling direction EB′ follows a clockwise vortex path or loop, the first through fourth exchange bias coupling directions EB1-EB4may be arranged along this clockwise vortex path or loop. In other embodiments where the initial exchange bias coupling direction EB′ follows a counterclockwise vortex path or loop, the first through fourth exchange bias coupling directions EB1-EB4may be arranged along this counterclockwise vortex path or loop. Furthermore, in some embodiments, a method for patterning the initial reference layer314to form the reference layers108each in an annular sector shape includes a lithography process and an etching process.

Referring toFIG.2,FIG.3FandFIG.4F, step S210is performed, and a spacer layer106as well as a free layer110are formed on each of the reference layer108. The spacer layers106and the free layers110may be respectively formed in a shape identical with the shape of the underlying reference layers108(i.e., the annular sector shape), and may be substantially aligned with the underlying reference layers108. In this way, the magnetoresistive devices MR each in an annular sector shape and include one of the reference layers108, the free layer110overlapped with this reference layer108and the spacer layer106lying between this reference layer108and this free layer110. The reference layers108have different exchange bias coupling directions EB, thus the magnetoresistive devices MR have different phases. According to some embodiments, a method for forming the spacer layers106and the free layers110includes globally forming material layers, and patterning these material layers to form the spacer layers106and the free layers110by a lithography process and at least one etching process.

Up to here, the magnetoresistive devices MR have been formed on the substrate300. The magnetoresistive devices MR are arranged along a single annular path, and have different phases. For instance, four magnetoresistive devices MR having different phases are arranged along a single annular path. However, although not shown, more magnetoresistive devices MR arranged along multiple annular shapes can be simultaneously formed on the substrate300. Further, the magnetoresistive devices MR may be routed and interconnected to form the magnetoresistive sensor100including the wheatstone bridges102,104, as shown inFIG.1A.

In alternative embodiments where the free layer110is located below the spacer layer106and the reference layer108lies above the spacer layer106, an initial free layer and an initial spacer layer may be globally formed on the substrate300before the step S200described with reference toFIG.3AandFIG.4A, and the initial free layer and the initial spacer layer are pattered to form separate free layers and separate spacer layers during the step S204described with reference toFIG.3CandFIG.4C. In addition, the step S210described with reference toFIG.3FandFIG.4Fmay be omitted.

As described above, the magnetoresistive devices MR having different phases can be formed by a manufacturing process including a single heat treatment step. Therefore, manufacturing of the magnetoresistive sensor including the magnetoresistive devices MR having different phases (e.g., the magnetoresistive sensor100) can be significantly simplified.

A test structure will be used for verification.FIG.5Ais a schematic plan view illustrating a test device500formed on the substrate300.FIG.5Bis a schematic cross-sectional view along an A-A′ line shown inFIG.5A.FIG.5CandFIG.5Dare images taken on the test structure500by a magnetic force microscopy (MFM).

Referring toFIG.5AandFIG.5B, a test structure500including an initial reference layer is measured to verify if the initial reference layer314could have the initial exchange bias coupling direction EB′ as shown inFIG.3DandFIG.4D. The test structure is similar to the initial reference layer314as shown inFIG.3DandFIG.4Din terms of structure (stacking, thickness and so forth), but is formed as an open annulus pattern rather than a closed annulus pattern. For instance, as shown inFIG.5A, the test structure500including the initial antiferromagnetic layer310and the initial ferromagnetic layer312may be formed as a C-shaped annulus pattern. If the test structure500was formed as a closed annulus pattern, a stray field may be absent, thus the exchange bias coupling direction of the test structure500may be difficult to be observed by MFM. In other words, the test structure500formed as an open annulus pattern can have stray field, thus the exchange bias coupling direction of the test structure500can be observed by MFM, and the initial exchange bias coupling direction EB′ of the initial reference layer314as shown inFIG.3DandFIG.4Dcan be verified.

A first external magnetic field is applied to the test structure500until magnetic saturation is reached, then the first external magnetic field is removed and the test structure500is observed by MFM. The result is shown inFIG.5C. As shown inFIG.5C, a bright region BR1and a dark region DR1are located at two end portions EP1, EP2of the test structure500, respectively. In addition, an apparent bright/dark contrast is absent along a connecting portion CN1extending between the end portions EP1, EP2of the test structure500. This indicates that the magnetization direction of the ferromagnetic layer in the test structure500(i.e., the initial ferromagnetic layer312) resulted from the first external magnetic field is directed from the end portion EP1toward the end portion EP2along the connecting portion CN1. Therefore, the magnetization direction of the test structure500in corresponding to the first external magnetic field follows a vortex path or a loop.

In addition, a second external magnetic field opposite to the first external magnetic field is applied to the test structure500until magnetic saturation is reached, then the second external magnetic field is removed and the test structure500is observed by MFM. The result is shown inFIG.5D. As shown inFIG.5D, a bright region BR2and a dark region DR2are located at two end portions EP1, EP2of the test structure500. In addition, an apparent bright/dark contrast is absent along the connecting portion CN1extending between the end portions EP1, EP2of the test structure500. As opposite to the result shown inFIG.5C,FIG.5Dshows that the bright region BR2is located at the end portion EP1and the dark region DR2is located at the end portion EP2. Since a probe of the MFM is magnetized along with the test structure500by the first and second external magnetic fields opposite to each other, the opposite results shown inFIG.5CandFIG.5D(as indicated by the arrows along the connecting portion CN1as shown inFIG.5CandFIG.5D) indicate that the magnetization direction of the ferromagnetic layer remains unchanged when subjected to opposite external magnetic fields. This proves establishment of exchange bias. Further, a direction of the exchange bias (i.e., the exchange bias coupling direction described in the present disclosure) follows the connecting portion CN1as a part of a vortex path or a loop along.

Furthermore, the test structure500is patterned to form a test structure in an annular sector shape, and the test structure in annular sector shape is measured by MFM.FIG.6Ais a schematic plan view illustrating a test structure600in annular sector shape and located on the substrate300.FIG.6BandFIG.6Care images taken on the test structure600in annular sector shape by MFM.

Referring toFIG.6A, the test structure600in annular sector shape is obtained by patterning the test structure500formed as an open annulus pattern (shown inFIG.5Aand FIG.5B). Therefore, the test structure600still extend along a vortex path or a loop followed by the test structure500, and a central angle of the test structure600in annular sector shape should be less than a central angle of the test structure500as an open annulus pattern.

A first external magnetic field is applied to the test structure600until magnetic saturation is reached, then the first external magnetic field is removed and the test structure600is observed by MFM. The result is shown inFIG.6B. In addition, a second external magnetic field opposite to the first external magnetic field is applied to the test structure600until magnetic saturation is reached, then the second external magnetic field is removed and the test structure600is observed by MFM. The result is shown inFIG.6C. Referring toFIG.6BandFIG.6C, the test structure600in annular sector shape has an end portion EP3and an end portion EP4. According to the result shown inFIG.6B, a bright region BR3is located at the end portion EP3, while a dark region DR3is located at the end portion EP4. On the other hand, in the result shown inFIG.6C, a dark region DR4is located at the end portion EP3, while a bright region BR4is located at the end portion BR4. Since a probe of the MFM is magnetized along with the test structure600by the first and second external magnetic fields opposite to each other, the opposite results shown inFIG.6BandFIG.6C(as indicated by the arrows along a connecting portion CN2extending between the end portions EP3, EP4as shown inFIG.6BandFIG.6C) indicates that the magnetization direction of the ferromagnetic layer remain unchanged when subjected to opposite external magnetic fields. This proves establishment of exchange bias. Further, a direction of the exchange bias (i.e., the exchange bias coupling direction described in the present disclosure) still follows a vortex path or a loop.

The results shown inFIG.6BandFIG.6Cproves that the reference layers108separated from the initial reference layer314(as shown inFIG.3EandFIG.4E) have exchange bias coupling directions EB following an extending path of the initial reference layer314. In other words, by forming an initial reference layer with an initial exchange bias coupling direction following a vortex path or a loop and patterning this initial reference layer to form separate portions, reference layers with different exchange bias coupling directions can be simply manufactured. Subsequently, these reference layers may be subjected to further processes for forming magnetoresistive devices with different phases.

Moreover, the results also indicate that the initial reference layer is not limited to a closed annulus pattern. In alternative embodiments, the reference layers each in annular sector shape can be formed by patterning an initial reference layer as an open annulus pattern, and these reference layers may be subjected to further processes for forming magnetoresistive devices with different phases. In some embodiments, a central angle of the initial reference layer formed as an open annulus pattern is sufficiently large, such that the initial reference layer can be patterned to form a sufficient amount of the reference layers with different exchange bias coupling directions. As an example, the central angle of the initial reference layer formed as an open annulus pattern may be greater than about 180°.

In addition, more results show that initial reference layers formed as other open/closed annulus patterns also have exchange bias coupling directions respectively following a vortex path or a loop, and can be patterned to form separate reference layers with different exchange bias coupling directions. The reference layers may be subjected to further processes for forming magnetoresistive devices with different phases, and are applicable to a magnetoresistive sensor requiring magnetoresistive devices having different phases. For instance, the open/closed annulus pattern of the initial reference layer may include a triangular annulus pattern, a rectangular annulus pattern, a polygonal annulus pattern, an elliptical annulus pattern or so forth, and the reference layers separated from these initial reference layer may respectively have a curved shape, or an annular sector shape with one or more corners.

As above, a manufacturing method for forming magnetoresistive devices having different phases is provided. The method includes forming an initial reference layer as an open/close annulus pattern. By performing a heat treatment on the initial reference layer, the initial reference layer can have an exchange bias oriented along a vortex path or a loop. In a subsequent process step, the initial reference layer is patterned to form separate reference layers. Exchange bias coupling directions of these reference layers are arranged along the vortex path or loop, and are different from one another. Further, these reference layers may be subjected to further processes for forming magnetoresistive devices with different phases. As comparing to other processes using multiple local heat treatments or multiple field depositions, the method for forming the magnetoresistive devices having different phases according to various embodiments of the present disclosure requires only a single global heat treatment, thus process complexity can be significantly reduced.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure covers modifications and variations provided that they fall within the scope of the following claims and their equivalents.