Patent Publication Number: US-2011068786-A1

Title: Magnetic sensor and manufacturing method thereof

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a magnetic sensor capable of detecting a change in a magnetic field highly sensitively, and to a manufacturing method thereof. 
     2. Description of the Related Art 
     In general, when accurately detecting a minute control current flowing in a circuit of a control device, a method is used, where resistors are connected in series in the circuit and a voltage drop of the resistors is measured. However, this may cause some adverse effect on a control system, since a load different from that of the control system is applied. Thus, a method which performs indirect measurement by detecting a gradient of a current magnetic field generated by a control current has been used. For example, the indirect measurement method is achieved by winding a measurement line around a toroidal core, and supplying a control current to the measurement line, to detect a magnetic flux generated in a central part of the toroidal core with a Hall element. 
     It has been pointed out, however, that a current sensor which achieves the method described above has disadvantages, in that a reduction in size is difficult, and that such a current sensor is insufficient in terms of a linearity or a high-frequency response property, and so forth. To address these issues, a magnetic sensor has been proposed, in which a giant magnetoresistive element (which may be hereinafter referred to as a “GMR element”) exhibiting a giant magnetoresistive effect is disposed in an induction magnetic field generated by a control current, and a gradient of the induction magnetic field is detected, as disclosed in U.S. Pat. No. 5,621,377, for example. Also, in this connection, a technology which utilizes a magnetic sensor provided with a GMR element to detect a flaw on a surface of a metal substrate, for example, is known. The magnetic sensor utilizing the GMR element makes it possible to relatively improve a detection sensitivity and a response property, and to obtain detection characteristics which are stable even in a temperature variation. In particular, when the detection of the induction magnetic field is performed with a Wheatstone bridge circuit which includes four GMR elements, a sensitivity and an accuracy can be further improved as compared with a case where only one GMR element is used. 
     On the other hand, the Wheatstone bridge circuit should be so configured that two GMR elements (i.e., first and second GMR elements) among the four GMR elements exhibit a behavior opposite to that of the remaining two GMR elements (i.e., third and fourth GMR elements). That is, a magnetization of a pinned layer in each of the first and the second GMR elements and a magnetization of a pinned layer in each of the third and the fourth GMR elements should be fixed in directions opposite to each other, for example. Also, it is desirable that the four GMR elements structuring the Wheatstone bridge circuit each have a mutually-uniform magnetic property as much as possible. In view of such circumstances, the applicant (the assignee) of this application has previously proposed a magnetic sensor, in which a plurality of GMR elements are collectively formed on the same wafer, then both the GMR elements and the wafer are cut out individually, and four GMR elements, which are selected among those GMR elements, are then so disposed on a substrate as to be appropriately oriented on the substrate, as disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2008-111801. For example, JP2003-502674A (Published Japanese Translation of PCT Application) proposes a method of manufacturing a magnetic sensor, in which two GMR elements are deposited under a magnetic field having a first direction, and remaining two GMR elements are deposited under a magnetic field having an opposite direction to the first direction. Also, JP2003-502876A (Published Japanese Translation of PCT Application) proposes a method in which an annealing process (a process of irradiating a laser pulse, an electron beam, or the like in this method) is separately performed under an application of an external magnetic field in a predetermined direction to allow magnetizations of pinned layers in the four GMR elements to be appropriately oriented, respectively, for example. 
     SUMMARY OF THE INVENTION 
     A magnetic sensor described in JP2008-111801A has a somewhat complicated manufacturing process, and has room for improvement in productivity. A magnetic sensor or the like disclosed in JP2003-502674A has drawbacks in that a manufacturing process is cumbersome, and thus productivity is disadvantageous. In particular, JP2003-502674A has a problem in that an orientation of a magnetization of a pinned layer in each GMR element formed in advance may be influenced by a magnetic field in an opposite direction which is applied in subsequent formation of remaining GMR elements, and thereby the magnetizations of the GMR elements may be deviated from their predetermined orientations. Also, a method described in JP2003-502876A requires special facilities such as a laser irradiation apparatus, an electron beam irradiation apparatus and so forth, and yet still disadvantageous in productivity. 
     It is therefore desirable to provide a magnetic sensor having a compact configuration and superior detection performance of a magnetic field, and which is yet easily manufacturable. It is also desirable to provide a method of manufacturing a magnetic sensor capable of manufacturing such magnetic sensor in a simplified fashion. 
     A magnetic sensor according to an embodiment includes: a first magnetoresistive element and a second magnetoresistive element each including, in order: a magnetization free layer in which orientation of magnetization changes in response to a signal magnetic field; a nonmagnetic spacing layer; a magnetization pinned layer having one or more first layers of a first group of ferromagnetic layers, and one or more second layers of a second group of ferromagnetic layers, the first layer and the second layer being stacked alternately with a nonmagnetic coupling layer in between, and being so antiferromagnetically coupled to each other as to have magnetizations which are opposite in direction to each other; and an antiferromagnetic layer pinning orientation of magnetization in the one or more first layers and orientation of magnetization in the one or more second layers. The magnetization pinned layer in the first magnetoresistive element includes the first layers, which are one more in number than the number of the one or more second layers, and the magnetization pinned layer in the second magnetoresistive element includes the one or more second layers and the one or more first layers in order from the magnetization free layer, and the number of the one or more first layers equals the number of the one or more second layers. 
     A magnetic sensor according to an embodiment includes: a first magnetoresistive element, a second magnetoresistive element, a third magnetoresistive element, and a fourth magnetoresistive element each including, in order: a magnetization free layer in which orientation of magnetization changes in response to a signal magnetic field; a nonmagnetic spacing layer; a magnetization pinned layer having one or more first layers of a first group of ferromagnetic layers, and one or more second layers of a second group of ferromagnetic layers, the first layer and the second layer being stacked alternately with a nonmagnetic coupling layer in between, and being so antiferromagnetically coupled to each other as to have magnetizations which are opposite in direction to each other; and an antiferromagnetic layer pinning orientation of magnetization in the one or more first layers and orientation of magnetization in the one or more second layers. The magnetization pinned layer in each of the first magnetoresistive element and the third magnetoresistive element includes the first layers, which are one more in number than the number of the one or more second layers. The magnetization pinned layer in each of the second magnetoresistive element and the fourth magnetoresistive element includes the one or more second layers and the one or more first layers in order from the magnetization free layer, in which the number of the one or more first layers equals the number of the one or more second layers. A first end of the first magnetoresistive element and a first end of the second magnetoresistive element are connected together in a first connection point, a first end of the third magnetoresistive element and a first end of the fourth magnetoresistive element are connected together in a second connection point, a second end of the first magnetoresistive element and a second end of the fourth magnetoresistive element are connected together in a third connection point, and a second end of the second magnetoresistive element and a second end of the third magnetoresistive element are connected together in a fourth connection point, to establish a bridge circuit. 
     In the magnetic sensor according to the embodiments, the magnetization pinned layer having the one or more first layers of the first group of ferromagnetic layers and the one or more second layers of the second group of ferromagnetic layers, in which the first layer and the second layer are stacked alternately with the nonmagnetic coupling layer in between and so antiferromagnetically coupled each other as to have the magnetizations opposite in direction to each other, is provided to be adjacent to the antiferromagnetic layer. Also, in the first magnetoresistive element (or the first and the third magnetoresistive elements), the magnetization pinned layer includes the first layers, which are one more in number than the number of the one or more second layers. On the other hand, in the second magnetoresistive element (or the second and the fourth magnetoresistive elements), the number of the one or more first layers and the number of the one or more second layers are the same. Further, in the first magnetoresistive element (or the first and the third magnetoresistive elements), the first layer is positioned nearer to the magnetization free layer than the second layer, whereas in the second magnetoresistive element (or the second and the fourth magnetoresistive elements), the second layer is positioned nearer to the magnetization free layer than the first layer. Thus, the first magnetoresistive element (or the first and the third magnetoresistive elements), and the second magnetoresistive element (or the second and the fourth magnetoresistive elements) exhibit resistance changes in directions (i.e., increasing/decreasing direction) opposite to each other in response to the signal magnetic field. As used herein, the term “resistance change” refers to an increase or decrease in resistance. In other words, the wording “exhibit resistance changes in directions opposite to each other” refers to a relationship where, for example, when a resistance of the first magnetoresistive element increases in response to application of the signal magnetic field, a resistance of the second magnetoresistive element decreases, and vice versa. In the magnetic sensor according to the embodiments described above, a thermal annealing process may be performed under application of a magnetic field in one given direction, to allow the magnetizations in one or more first ferromagnetic layers and the one or more second ferromagnetic layers in each of the magnetization pinned layers to have predetermined orientations by one operation. 
     Advantageously, the first magnetoresistive element and the second magnetoresistive element (or the first magnetoresistive element to the fourth magnetoresistive element) are provided on a same substrate. 
     A method of manufacturing a magnetic sensor according to an embodiment includes the steps of: selectively forming, on a substrate, a first magnetoresistive element and a second magnetoresistive element in respective regions different from each other, the first magnetoresistive element and the second magnetoresistive element each including, in order: an antiferromagnetic layer; a magnetization pinned layer having a plurality of ferromagnetic layers which are antiferromagnetically coupled to each other with a nonmagnetic coupling layer in between; a nonmagnetic spacing layer; and a magnetization free layer in which orientation of magnetization changes in response to a signal magnetic field; and heating the first magnetoresistive element and the second magnetoresistive element while applying thereto a magnetic field in one given direction, thereby allowing orientation of magnetization in all of the plurality of ferromagnetic layers of the magnetization pinned layers in the first magnetoresistive element and the second magnetoresistive element to be secured by one operation, wherein the magnetization pinned layer in the first magnetoresistive element is so formed as to include the odd number of the ferromagnetic layers, and the magnetization pinned layer in the second magnetoresistive element is so formed as to include the even number of the ferromagnetic layers. 
     In the method of manufacturing the magnetic sensor according to the embodiment, the magnetization pinned layer in the first magnetoresistive element is so formed as to include the odd number of the ferromagnetic layers, and the magnetization pinned layer in the second magnetoresistive element is so formed as to include the even number of the ferromagnetic layers. Thus, the orientation of the magnetization in the ferromagnetic layer, located nearest to the magnetization free layer in the magnetization pinned layer of the first magnetoresistive element, becomes opposite to the orientation of the magnetization in the ferromagnetic layer, located nearest to the magnetization free layer in the magnetization pinned layer of the second magnetoresistive element. Thus, the first magnetoresistive element and the second magnetoresistive element exhibit resistance changes in directions (i.e., increasing/decreasing direction) opposite to each other in response to the signal magnetic field. 
     Advantageously, the magnetization pinned layer in the first magnetoresistive element is formed to have a five-layer structure including a first ferromagnetic layer having magnetization in a first direction as one of the plurality of ferromagnetic layers, a first coupling layer, a second ferromagnetic layer having magnetization in a second direction opposite to the first direction as another one of the plurality of ferromagnetic layers, a second coupling layer, and a third ferromagnetic layer having magnetization in a first direction as still another one of the plurality of ferromagnetic layers, and the magnetization pinned layer in the second magnetoresistive element is formed to have a three-layer structure including a fourth ferromagnetic layer having magnetization in a second direction as still another one of the plurality of ferromagnetic layers, a third coupling layer, and a fifth ferromagnetic layer having magnetization in a first direction as still another one of the plurality of ferromagnetic layers, which are arranged in order from the magnetization free layer. 
     According to the magnetic sensor of the embodiments, the numbers of the first layers and the second layers, which are so antiferromagnetically coupled to each other as to have the magnetizations opposite in direction to each other, are adjusted to allow the first magnetoresistive element (or the first and the third magnetoresistive elements) and the second magnetoresistive element (or the second and the fourth magnetoresistive elements) to exhibit the resistance changes in directions (i.e., increasing/decreasing direction) opposite to each other in response to the signal magnetic field. Thus, it is possible to achieve the magnetic sensor having superior detection performance of a magnetic field while ensuring a compact configuration and which is yet easily manufacturable, by connecting the first and the second magnetoresistive elements in a half-bridge configuration or connecting the first to the fourth magnetoresistive elements in a full-bridge configuration. Also, according to the method of manufacturing the magnetic sensor of the embodiment, it is possible to manufacture the magnetic sensor with high degree of accuracy in a simplified fashion. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the specification, serve to explain the principles of the invention. 
         FIG. 1  is a plan view illustrating an overall configuration of a magnetic sensor according to an embodiment of the invention. 
         FIG. 2  is an enlarged perspective view illustrating a main configuration of the magnetic sensor illustrated in  FIG. 1 . 
         FIG. 3A  and  FIG. 3B  are cross-sectional views illustrating laminated structures of stacked bodies included in first to fourth MR elements illustrated in  FIG. 2 . 
         FIG. 4  is a circuit diagram illustrating a configuration of a magnetic field detecting circuit in the magnetic sensor illustrated in  FIG. 1 . 
         FIG. 5  is a cross-sectional view illustrating a process in a method of manufacturing the magnetic sensor illustrated in  FIG. 1 . 
         FIG. 6  is a cross-sectional view illustrating a process subsequent to that in  FIG. 5 . 
         FIG. 7A  and  FIG. 7B  are a plan view and a cross-sectional view illustrating a process subsequent to that in  FIG. 6 , respectively. 
         FIG. 8A  and  FIG. 88  are a plan view and a cross-sectional view illustrating a process subsequent to that in  FIGS. 7A and 7B , respectively. 
         FIG. 9A  and  FIG. 9B  are a plan view and a cross-sectional view illustrating a process subsequent to that in  FIGS. 8A and 8B , respectively. 
         FIG. 10A  and  FIG. 10B  are a plan view and a cross-sectional view illustrating a process subsequent to that in  FIGS. 9A and 9B , respectively. 
         FIG. 11A  and  FIG. 11B  are a plan view and a cross-sectional view illustrating a process subsequent to that in  FIGS. 10A and 10B , respectively. 
         FIG. 12A  and  FIG. 12B  are a plan view and a cross-sectional view illustrating a process subsequent to that in  FIGS. 11A and 11B , respectively. 
         FIG. 13A  and  FIG. 13B  are a plan view and a cross-sectional view illustrating a process subsequent to that in  FIGS. 12A and 12B , respectively. 
         FIG. 14A  and  FIG. 14B  are a plan view and a cross-sectional view illustrating a process subsequent to that in  FIGS. 13A and 13B , respectively. 
         FIG. 15A  and  FIG. 15B  are a plan view and a cross-sectional view illustrating a process subsequent to that in  FIGS. 14A and 14B , respectively. 
         FIG. 16A  and  FIG. 16B  are a plan view and a cross-sectional view illustrating a process subsequent to that in  FIGS. 15A and 15B , respectively. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, an embodiment of the invention will be described in detail with reference to the accompanying drawings. 
     First, a configuration of a magnetic sensor according to one embodiment of the invention will be described with reference to  FIGS. 1 to 16B .  FIG. 1  is a plan view illustrating an overall configuration of the magnetic sensor according to the embodiment.  FIG. 2  is an enlarged perspective view illustrating a main configuration of the magnetic sensor. 
     The magnetic sensor according to this embodiment includes first to fourth magnetoresistive (MR: Magneto-Resistive effect) elements  1  to  4  (hereinafter may be simply referred to as “MR elements”), pads  51  to  54 , interconnections L 1  to L 6 , and a difference detector AMP (described later), and so forth, which are provided on a substrate  100 . The magnetic sensor may detect a magnitude of a signal magnetic field Hm applied in a plus Y direction, for example. More specifically, the magnetic sensor may be used as a current sensor, which is disposed near an unillustrated conductor extending, for example, in an X-axis direction and which detects an induction magnetic field induced by a current flowing in the conductor as the signal magnetic field Hm to indirectly measure that current. For example, the pad  51  is connected to a power source Vcc which will be described later, and the pad  52  is grounded. Each of the pads  53  and  54  is connected to an input terminal of the difference detector AMP, for example. 
     The substrate  100  may be a rectangular member which supports the magnetic sensor as a whole, and may be configured of ceramics. The ceramics of the substrate  100  can be glass, silicon (Si), aluminum oxide (Al 2 O 3 ), AlTiC (Al 2 O 3 -TiC), or other suitable material. An insulating layer (not illustrated) containing ceramics such as silicon oxide (SiO 2 ), aluminum oxide, and so forth may be provided to cover the substrate  100 . 
     The first to the fourth MR elements  1  to  4  include a plurality of stacked bodies  11 ,  21 ,  31 , and  41 , respectively. In the exemplary embodiment illustrated in  FIGS. 1 and 2 , the first to the fourth MR elements  1  to  4  include eight stacked bodies  11 ,  21 ,  31 , and  41 , respectively, although it is not limited thereto. When the signal magnetic field Hm is applied, a resistance of each of the first and the third MR elements  1  and  3  changes in the same direction (i.e., the same increasing/decreasing direction) in response to the signal magnetic field Hm, and a resistance of each of the second and the fourth MR elements  2  and  4  changes in a direction (i.e., an increasing/decreasing direction) opposite to that of the first and the third MR elements  1  and  3  in response to the signal magnetic field Hm. Note that the first to the fourth MR elements  1  to  4  each have a substantially similar configuration to one another, except for a configuration of the stacked bodies  11 ,  21 ,  31 , and  41 . In the following, the description will be made based on the first MR element  1  on behalf of the first to the fourth MR elements  1  to  4  with reference mainly to  FIG. 2 , except for the description on the stacked bodies  11 ,  21 ,  31 , and  41 . 
     Referring to  FIG. 2 , the first MR element  1  has a configuration in which the plurality of stacked bodies  11  (stacked bodies  11 A to  11 H) are disposed in a sandwich-like manner between top electrodes  12  (top electrodes  12 A to  12 H) and bottom electrodes  13  (bottom electrodes  13 A to  13 H) in a thickness direction (i.e., a stack direction). The stacked body  11  connects one end of the top electrode  12  and one end of the bottom electrode  13  therethrough. The other end the top electrode  12 , whose one end is connected to the stacked body  11 , is connected, through a columnar connector  14  (connectors  14 A to  14 H), to the other end of the bottom electrode  13 , whose one end is connected to the adjacent stacked body  11 . Thus, all of the stacked bodies  11 A to  11 H are connected or combined in series to one another through the top electrodes  12 A to  12 H, the bottom electrodes  13 A to  13 H, and the connectors  14 A to  14 H. The top electrode  12 A located at one end of the first MR element  1  is connected with the stacked body  11 A, and is also connected to the interconnection L 1  illustrated in  FIG. 1 . The bottom electrode  13 H located at the other end of the first MR element  1  is connected with the stacked body  11 H, and is also connected to the interconnection L 2  illustrated in  FIG. 1 . With this configuration, a current supplied from the interconnection L 1  flows successively through the stacked bodies  11 A to  11 H to the interconnection L 2 . At this time, the current flows in each of the stacked bodies  11 A to  11 H in a direction going from the top electrodes  12  to the bottom electrodes  13  (i.e., in a minus Z direction). Each of the top electrodes  12 , the bottom electrodes  13 , and the connectors  14  is configured of a nonmagnetic material having high-electrical conductivity, which can be copper (Cu), or other suitable material. 
     As illustrated in  FIG. 1 , the second to the fourth MR elements  2  to  4  are provided with top electrodes  22 ,  32 , and  42 , bottom electrodes  23 ,  33 , and  43 , and connectors  24 ,  34 , and  44 , corresponding to the top electrodes  12 , the bottom electrodes  13 , and the connectors  14  in the first MR element  1 , respectively. In the second MR element  2 , the top electrode  22  located at one end of the second MR element  2  is connected to the interconnection L 1 , and the bottom electrode  23  located at the other end of the second MR element  2  is connected to the interconnection L 3 . In the third MR element  3 , the top electrode  32  located at one end of the third MR element  3  is connected to the interconnection L 3 , and the bottom electrode  33  located at the other end of the third MR element  3  is connected to the interconnection L 4 . In the fourth MR element  4 , the top electrode  42  located at one end of the fourth MR element  4  is connected to the interconnection L 2 , and the bottom electrode  43  located at the other end of the fourth MR element  4  is connected to the interconnection L 4 . Also, the interconnection L 2  is connected to the pad  53  through the interconnection L 5 , and the interconnection L 3  is connected to the pad  54  through the interconnection L 6 . 
     Each of the interconnections L 1  to L 6  is configured of a nonmagnetic material having high-electrical conductivity, which can be copper (Cu), or other suitable material. The interconnections L 1  and L 3  to L 6  are located on a same level as the top electrodes  12 ,  22 ,  32 , and  42 , and the interconnection L 2  is located on a same level as the bottom electrodes  13 ,  23 ,  33 , and  43 , for example. Although the interconnections L 2  and L 5  are located on the different levels from each other, the interconnections L 2  and L 5  are joined each other in the thickness direction through a columnar member (not illustrated) configured of copper, for example. 
     Now, a configuration of the stacked bodies  11 ,  21 ,  31 , and  41  will be described with reference to  FIGS. 3A and 3B .  FIG. 3A  illustrates a schematic cross-sectional configuration of the stacked bodies  11  and  31 , whereas  FIG. 3B  illustrates a schematic cross-sectional configuration of the stacked bodies  21  and  41 . Each of the stacked bodies  11 ,  21 ,  31 , and  41  includes a magnetization free layer  61 , an spacing layer  62 , a magnetization pinned layer  63 , and an antiferromagnetic layer  64  in this order from a side on which the top electrodes  12 ,  22 ,  32 , and  42  are provided. In one embodiment, an overcoat film may be so provided as to cover a surface of the magnetization free layer  61  facing the top electrodes  12 ,  22 ,  32 , and  42  side. Also, in one embodiment, a seed layer may be provided between the antiferromagnetic layer  64  and the substrate  100 . 
     The magnetization free layer  61  is a soft ferromagnetic layer in which a magnetization direction J 61  changes in response to an external magnetic field such as the signal magnetic field, and has a magnetization easy axis in an X-axis direction, for example. The magnetization free layer  61  is configured of a cobalt-iron alloy (CoFe), a nickel-iron alloy (NiFe), a cobalt-iron-boron alloy (CoFeB), or other suitable material, for example. 
     The spacing layer  62  is a nonmagnetic tunnel barrier layer configured of a magnesium oxide (MgO), for example. The spacing layer  62  has a thickness which is thin enough that a quantum mechanical tunneling current is possible to pass therethrough. The tunnel barrier layer configured of MgO is obtained by a sputtering process involving an MgO target, an oxidation process of a magnesium (Mg) thin-film, a reactive sputtering process involving a sputtering of magnesium under an oxygen atmosphere, or other suitable process. Other than MgO, a material of the spacing layer  62  can be an oxide or a nitride of aluminum (Al), tantalum (Ta), hafnium (Hf) or the like. 
     The magnetization pinned layer  63  has a synthetic structure in which a first ferromagnetic layer  631  and a second ferromagnetic layer  632  are stacked alternately with a nonmagnetic coupling layer  633  in between, and are so antiferromagnetically coupled to each other as to have magnetizations which are opposite in direction to each other. The magnetization pinned layer  63  has one or more first ferromagnetic layers  631  belonging to a first group of ferromagnetic layers, and one or more second ferromagnetic layers  632  belonging to a second group of ferromagnetic layers. It is to be noted that the number of first ferromagnetic layers  631  and the number of second ferromagnetic layers  632  structuring the magnetization pinned layer  63  differ between the magnetization pinned layer  63  in the stacked bodies  11  and  31  and the magnetization pinned layer  63  in the stacked bodies  21  and  41 . 
     For example, the magnetization pinned layer  63  in each of the stacked bodies  11  and  31  includes the first ferromagnetic layers  631 , which are larger in number by one layer than the second ferromagnetic layer  632 . That is, the magnetization pinned layer  63  in each of the stacked bodies  11  and  31  has a five-layer structure including a first ferromagnetic layer  631 A (a first ferromagnetic layer as one of the first ferromagnetic layers  631  of the first group), the coupling layer  633  (a first coupling layer), the second ferromagnetic layer  632  (a second ferromagnetic layer as the second ferromagnetic layer  632  of the second group), the coupling layer  633  (a second coupling layer), and a first ferromagnetic layer  631 B (a third ferromagnetic layer as another one of the first ferromagnetic layers  631  of the first group), which are stacked in order from the magnetization free layer  61  side. An orientation of a magnetization J 631  of the first ferromagnetic layer  631  (i.e., the first ferromagnetic layers  631 A and  631 B) is antiparallel to an orientation of a magnetization J 632  of the second ferromagnetic layer  632  in a lamination plane. It should be understood that, although  FIG. 3A  illustrates an example where the magnetization pinned layer  63  in each of the stacked bodies  11  and  31  includes the five-layer structure, the configuration of the magnetization pinned layer  63  is not limited thereto. The number of layers in the magnetization pinned layer  63  in each of the stacked bodies  11  and  31  can be optional as long as the number of the first ferromagnetic layers  631  is larger by one layer than the number of the second ferromagnetic layers  632 , such as a nine-layer structure including the coupling layers  633 . 
     On the other hand, the magnetization pinned layer  63  in each of the stacked bodies  21  and  41  has a configuration in which the second ferromagnetic layer  632  (a fourth ferromagnetic layer as the second ferromagnetic layer  632  of the second group) and the first ferromagnetic layer  631  (a fifth ferromagnetic layer as the first ferromagnetic layer  631  of the first group) are stacked alternately in order from the magnetization free layer  61  side with the coupling layer  633  (a third coupling layer) in between, and in which the number of the first ferromagnetic layers  631  is same as (i.e., equals) the number of the second ferromagnetic layers  632 . That is, the magnetization pinned layer  63  in each of the stacked bodies  21  and  41  has the synthetic structure in which the first ferromagnetic layer  631  and the second ferromagnetic layer  632  are so antiferromagnetically coupled to each other as to have magnetizations opposite in direction to each other. It should be understood that, although  FIG. 3B  illustrates an example where the magnetization pinned layer  63  in each of the stacked bodies  21  and  41  includes three-layer structure in which one layer of the first ferromagnetic layer  631  and one layer of the second ferromagnetic layer  632  are so provided as to sandwich the coupling layer  633  in between, the configuration of the magnetization pinned layer  63  is not limited thereto. The magnetization pinned layer  63  in each of the stacked bodies  21  and  41  may include a plurality of first ferromagnetic layers  631  and a plurality of second ferromagnetic layers  632 . That is, the number of layers in the magnetization pinned layer  63  in each of the stacked bodies  21  and  41  can be optional, as long as the second ferromagnetic layer  632  is positioned nearer to the magnetization free layer  61  than the first ferromagnetic layer  631 , and as long as the number of the first ferromagnetic layers  631  and the number of the second ferromagnetic layers  632  are the same, such as a seven-layer structure including the coupling layers  633 . 
     According to this embodiment, the magnetization pinned layer  63  in each of the stacked bodies  11  and  31  includes, on a side nearest to the magnetization free layer  61 , the first ferromagnetic layer  631  having the magnetization J 631  pinned in a minus Y direction, whereas the magnetization pinned layer  63  in each of the stacked bodies  21  and  41  includes, on a side nearest to the magnetization free layer  61 , the second ferromagnetic layer  632  having the magnetization J 632  pinned in a plus Y direction. Thus, the stacked bodies  11  and  31 , and the stacked bodies  21  and  41  exhibit resistance changes in directions (i.e., increasing/decreasing direction) opposite to each other in response to the signal magnetic field Hm. That is, in the stacked bodies  11  and  31 , the magnetization J 61  is oriented in the direction antiparallel to the direction of the magnetization J 631  to have a high resistance state, whereas in the stacked bodies  21  and  41 , the magnetization J 61  is oriented in the direction parallel to the direction of the magnetization J 632  to have a low resistance state, when the signal magnetic field Hm in the plus Y direction is applied, for example. Therefore, in the magnetic sensor according to this embodiment, the resistance of each of the first and the third MR elements  1  and  3  indicates a change in the orientation opposite to the orientation indicated by the resistance of each of the second and the fourth MR elements  2  and  4  in application of the signal magnetic field Hm. Incidentally, it is preferable, but not required, that a sum of a total magnetic moment in all of the first ferromagnetic layers  631  and a sum of a total magnetic moment in all of the second ferromagnetic layers  632  both be equal between the magnetization pinned layer  63  in the stacked bodies  11 ,  31  and the magnetization pinned layer  63  in the stacked bodies  21 ,  42 , since this improves a detection accuracy for the magnetic sensor. As used herein, the term “total magnetic moment” refers to a product of a “magnetic moment per unit volume” of respective materials structuring the ferromagnetic layers thereof and a volume of the ferromagnetic layers thereof (i.e., the “magnetic moment per unit volume” multiplied by the “volume”). 
     The first ferromagnetic layer  631  and the second ferromagnetic layer  632  are each configured of a ferromagnetic material, which can be cobalt (Co), a cobalt-iron alloy (CoFe), a cobalt-iron-boron alloy (CoFeB), or other suitable material. The coupling layer  633  is configured of a nonmagnetic material having high-electrical conductivity, which can be ruthenium (Ru), or other suitable material. The magnetization pinned layer  63  in each of the stacked bodies  11  and  31  and the magnetization pinned layer  63  in each of the stacked bodies  21  and  41  respectively have the following preferred, but not required, configurations. 
     [Magnetization Pinned Layer  63  in Stacked Bodies  11  and  31 ] 
     First ferromagnetic layer  631 B: CoFe layer (1.5 nm thick) 
     Coupling layer  633 : Ru layer (0.8 nm thick) 
     Second ferromagnetic layer  632 : CoFe layer (3.0 nm thick) 
     Coupling layer  633 : Ru layer (0.8 nm thick) 
     First ferromagnetic layer  631 A: CoFe layer (2.0 nm thick) 
     [Magnetization Pinned Layer  63  in Stacked Bodies  21  and  41 ] 
     First ferromagnetic layer  631 : CoFe layer (2.5 nm thick) 
     Coupling layer  633 : Ru layer (0.8 nm thick) 
     Second ferromagnetic layer  632 : CoFe layer (2.0 nm thick) 
     The antiferromagnetic layer  64  is configured of an antiferromagnetic material, which can be a platinum-manganese alloy (PtMn), an iridium-manganese alloy (IrMn), or other suitable material. The antiferromagnetic layer  64  has a state in which a spin magnetic moment in a plus Y direction and a spin magnetic moment in a minus Y direction are completely offset each other, and acts to pin the orientation of the magnetization J 631  of the first ferromagnetic layer  631  and the orientation of the magnetization J 632  of the second ferromagnetic layer  632  in the adjacent magnetization pinned layer  63  in the plus Y direction or in the minus Y direction. 
       FIG. 4  schematically illustrates a configuration of a magnetic field detecting circuit in the magnetic sensor. One end of the first MR element  1  and one end of the second MR element  2  are connected together in a first connection point P 1 , and one end of the third MR element  3  and one end of the fourth MR element  4  are connected together in a second connection point P 2 . Further, the other end of the first MR element  1  and the other end of the fourth MR element  4  are connected together in a third connection point P 3 , and the other end of the second MR element  2  and the other end of the third MR element  3  are connected together in a fourth connection point P 4 , to establish a bridge circuit. The first connection point P 1  is connected to the power source Vcc through the interconnection L 1 , and the second connection point P 2  is grounded through the interconnection L 4 . The third connection point P 3  and the fourth connection point P 4  are connected to input terminals of the difference detector AMP through the interconnection L 5  and the interconnection L 6 , respectively. The difference detector AMP detects a potential difference developed between the third connection point P 3  and the fourth connection point P 4  when a voltage is applied between the first connection point P 1  and the second connection point P 2  (i.e., a difference in a voltage drop generated in each of the first and the second MR elements  1  and  2 ), and outputs the detected potential difference as a difference signal SS. 
     Now, a detecting method, based on the difference signal SS, of the signal magnetic field Hm as a detection target by using the magnetic sensor according to this embodiment will be described. 
     Referring to  FIG. 4 , the description will be given first on a state where the signal magnetic field Hm is not applied. In the following, the resistances of the first to the fourth MR elements  1  to  4  when a read-out current I 1  is caused to flow from the power source Vcc are referred to as r 1  to r 4 , respectively. The read-out current I 1  from the power source Vcc is divided into a read-out current I 1  and a read-out current I 2  in the first connection point P 1 . Thereafter, the read-out current I 1 , having passed through the first MR element  1  and the third MR element  3 , and the read-out current I 2 , having passed through the second MR element  2  and the fourth MR element  4 , are merged at the second connection point P 2 . Here, a potential difference V between the first connection point P 1  and the second connection point P 2  is expressed as follows. 
     
       
         
           
             
               
                 
                   
                     
                       
                         V 
                         = 
                         
                           
                             I 
                              
                             
                                 
                             
                              
                             1 
                             × 
                             r 
                              
                             
                                 
                             
                              
                             4 
                           
                           + 
                           
                             I 
                              
                             
                                 
                             
                              
                             1 
                             × 
                             r 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             I 
                              
                             
                                 
                             
                              
                             2 
                             × 
                             r 
                              
                             
                                 
                             
                              
                             3 
                           
                           + 
                           
                             I 
                              
                             
                                 
                             
                              
                             2 
                             × 
                             r 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           I 
                            
                           
                               
                           
                            
                           1 
                            
                           
                             ( 
                             
                               
                                 r 
                                  
                                 
                                     
                                 
                                  
                                 4 
                               
                               + 
                               
                                 r 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           I 
                            
                           
                               
                           
                            
                           2 
                            
                           
                             ( 
                             
                               
                                 r 
                                  
                                 
                                     
                                 
                                  
                                 3 
                               
                               + 
                               
                                 r 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
       
     
     Also, a potential V 1  at the third connection point P 3  and a potential V 2  at the fourth connection point P 4  are each expressed as follows. 
     
       
         
           
             
               
                 
                   
                     V 
                      
                     
                         
                     
                      
                     1 
                   
                   = 
                   
                     V 
                     - 
                     
                       V 
                        
                       
                           
                       
                        
                       4 
                     
                   
                 
               
             
             
               
                 
                   = 
                   
                     V 
                     - 
                     
                       I 
                        
                       
                           
                       
                        
                       1 
                       × 
                       r 
                        
                       
                           
                       
                        
                       4 
                     
                   
                 
               
             
           
         
       
       
         
           
             
               
                 
                   
                     V 
                      
                     
                         
                     
                      
                     2 
                   
                   = 
                   
                     V 
                     - 
                     
                       V 
                        
                       
                           
                       
                        
                       3 
                     
                   
                 
               
             
             
               
                 
                   = 
                   
                     V 
                     - 
                     
                       I 
                        
                       
                           
                       
                        
                       2 
                       × 
                       r 
                        
                       
                           
                       
                        
                       3 
                     
                   
                 
               
             
           
         
       
     
     Therefore, a potential difference V 0  between the third connection point P 3  and the fourth connection point P 4  is expressed as follows. 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           V 
                            
                           
                               
                           
                            
                           0 
                         
                         = 
                         
                           
                             V 
                              
                             
                                 
                             
                              
                             1 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             ( 
                             
                               V 
                               - 
                               
                                 I 
                                  
                                 
                                     
                                 
                                  
                                 1 
                                 × 
                                 r 
                                  
                                 
                                     
                                 
                                  
                                 4 
                               
                             
                             ) 
                           
                           - 
                           
                             ( 
                             
                               V 
                               - 
                               
                                 I 
                                  
                                 
                                     
                                 
                                  
                                 2 
                                 × 
                                 r 
                                  
                                 
                                     
                                 
                                  
                                 3 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             I 
                              
                             
                                 
                             
                              
                             2 
                             × 
                             r 
                              
                             
                                 
                             
                              
                             3 
                           
                           - 
                           
                             I 
                              
                             
                                 
                             
                              
                             1 
                             × 
                             r 
                              
                             
                                 
                             
                              
                             4 
                           
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     2 
                     ) 
                   
                 
               
             
           
         
       
     
     Here, a following Equation (3) is established from the Equation (1). 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           V 
                            
                           
                               
                           
                            
                           0 
                         
                         = 
                         
                           
                             r 
                              
                             
                                 
                             
                              
                             
                               3 
                               / 
                               
                                 ( 
                                 
                                   
                                     r 
                                      
                                     
                                         
                                     
                                      
                                     3 
                                   
                                   + 
                                   
                                     r 
                                      
                                     
                                         
                                     
                                      
                                     2 
                                   
                                 
                                 ) 
                               
                             
                             × 
                             V 
                           
                           - 
                           
                             r 
                              
                             
                                 
                             
                              
                             
                               4 
                               / 
                               
                                 ( 
                                 
                                   
                                     r 
                                      
                                     
                                         
                                     
                                      
                                     4 
                                   
                                   + 
                                   
                                     r 
                                      
                                     
                                         
                                     
                                      
                                     1 
                                   
                                 
                                 ) 
                               
                             
                             × 
                             V 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             { 
                             
                               
                                 r 
                                  
                                 
                                     
                                 
                                  
                                 
                                   3 
                                   / 
                                   
                                     ( 
                                     
                                       
                                         r 
                                          
                                         
                                             
                                         
                                          
                                         3 
                                       
                                       + 
                                       
                                         r 
                                          
                                         
                                             
                                         
                                          
                                         2 
                                       
                                     
                                     ) 
                                   
                                 
                               
                               - 
                               
                                 r 
                                  
                                 
                                     
                                 
                                  
                                 
                                   4 
                                   / 
                                   
                                     ( 
                                     
                                       
                                         r 
                                          
                                         
                                             
                                         
                                          
                                         4 
                                       
                                       + 
                                       
                                         r 
                                          
                                         
                                             
                                         
                                          
                                         1 
                                       
                                     
                                     ) 
                                   
                                 
                               
                             
                             } 
                           
                           × 
                           V 
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     3 
                     ) 
                   
                 
               
             
           
         
       
     
     In the bridge circuit described above, an amount of resistance change is obtained by measuring the potential difference V 0  between the third and the fourth connection points P 3  and P 4  expressed by the Equation (3) when the signal magnetic field Um is applied. Here, when assuming that the resistances r 1  to r 4  increase by change amounts ΔR 1  to ΔR 4  at the time when the signal magnetic field Um is applied, respectively, that is, when resistances R 1  to R 4  at the time of the application of the signal magnetic field Hm are expressed as: R 1 =r 1 +ΔR 1 ; R 2 =r 2 +ΔR 2 ; R 3 =r 3 +ΔR 3 ; and R 4 =r 4 +ΔR 4 , respectively, the potential difference V 0  at the time when the signal magnetic field Hm is applied is expressed, from the Equation (3), as follows. 
         V 0={( r 3 +ΔR 3)/( r 3 +ΔR 3+ r 2+Δ R 2)−( r 4 +ΔR 4)/( r 4 +ΔR 4+ r 1+Δ R 1)}× V   Equation (4)
 
     As already described above, since, in the magnetic sensor according to this embodiment, the resistances R 1  and R 3  of the first and the third MR elements  1  and  3 , and the resistances R 2  and R 4  of the second and the fourth MR elements  2  and  4 , change in the directions opposite to each other, the change amount ΔR 3  and the change amount ΔR 2  offset each other, and the change amount ΔR 4  and the change amount ΔR 1  offset each other. Thus, there is hardly any increase in denominator in each term in the Equation (4) when comparing a state before the application of the signal magnetic field Hm and a state after the application of the signal magnetic field Hm. On the other hand, as for numerator in each term in the Equation (4), since the change amount ΔR 3  and the change amount ΔR 4  both have opposite signs to each other, the change amount ΔR 3  and the change amount ΔR 4  do not offset each other and thus increase or decrease appears in the numerator. This is because, by the application of the signal magnetic field Urn, the resistances of the second and the fourth MR elements  2  and  4  change by the change amounts ΔR 2  and ΔR 4  (ΔR 2 , ΔR 4 &lt;0), respectively (i.e., the resistances thereof substantially decrease), whereas the resistances of the first and the third MR elements  1  and  3  change by the change amounts ΔR 1  and ΔR 3  (ΔR 1 , ΔR 3 &gt;0), respectively (i.e., the resistance values thereof substantially increase). 
     When assuming that all of the first to the fourth MR elements  1  to  4  have completely the same characteristics, that is, if: r 1 =r 2 =r 3 =r 4 =R; and ΔR 1 =−ΔR 2 =ΔR 3 =ΔR 4 =ΔR are established, the Equation (4) is expressed as follows. 
     
       
         
           
               
             
               
                 
                   
                     
                       
                         
                           
                             V 
                              
                             
                                 
                             
                              
                             0 
                           
                           = 
                           
                             
                               { 
                               
                                 
                                   
                                     ( 
                                     
                                       R 
                                       + 
                                       
                                         Δ 
                                          
                                         
                                             
                                         
                                          
                                         R 
                                       
                                     
                                     ) 
                                   
                                   / 
                                   
                                     ( 
                                     
                                       2 
                                       · 
                                       R 
                                     
                                     ) 
                                   
                                 
                                 - 
                                 
                                   
                                     ( 
                                     
                                       R 
                                       - 
                                       
                                         Δ 
                                          
                                         
                                             
                                         
                                          
                                         R 
                                       
                                     
                                     ) 
                                   
                                   / 
                                   
                                     ( 
                                     
                                       2 
                                       · 
                                       R 
                                     
                                     ) 
                                   
                                 
                               
                               } 
                             
                             × 
                             V 
                           
                         
                       
                     
                     
                       
                         
                           = 
                           
                             
                               ( 
                               
                                 Δ 
                                  
                                 
                                     
                                 
                                  
                                 
                                   R 
                                   / 
                                   R 
                                 
                               
                               ) 
                             
                             × 
                             V 
                           
                         
                       
                     
                   
                 
                 
                   
                     Equation 
                      
                     
                         
                     
                      
                     
                       ( 
                       5 
                       ) 
                     
                   
                 
               
             
           
         
       
     
     Consequently, it is possible to measure the magnitude of the signal magnetic field Hm based on the Equation (4) or the Equation (5), by using the first to the fourth MR elements  1  to  4  in which a relationship between the signal magnetic field Hm and the amounts of resistance changes ΔR (or ΔR 1  to ΔR 4 ) is known. 
     Now, a method of manufacturing the magnetic sensor will be described with reference to  FIGS. 5 to 16B .  FIGS. 5 to 16B  each illustrate a region near a boundary between the first MR element  1  and the second MR element  2  in an expanded manner.  FIGS. 7A to 16A  are views as seen from above, and  FIGS. 7B to 16B  are cross-sectional views corresponding to sectional lines illustrated in  FIGS. 7A to 16A , respectively. 
     Referring to  FIG. 5 , the substrate  100  which may be configured of the material described above is provided, and as needed, an insulating layer Z 1  is provided on a surface of the substrate  100 . Then, a metal film M 1 , which will eventually become the bottom electrodes  13 ,  23 ,  33 , and  43 , is so formed as to cover throughout a surface of the substrate  100  or the insulating layer Z 1  by using a material such as copper. Further, an MR film S 1 , which will eventually become the stacked bodies  11  and  31 , is so formed as to cover throughout a surface of the metal film M 1 . The MR film S 1  is obtained by stacking the antiferromagnetic layer  64 , the magnetization pinned layer  63 , the spacing layer  62 , and the magnetization free layer  61  sequentially on the metal film M 1  by using a sputtering method and the materials described above, for example. Herein, the magnetization pinned layer  63  is so formed that an odd number of ferromagnetic films (not illustrated), which will eventually become the first and the second ferromagnetic layers  631  and  632 , are included therein. For example, a ferromagnetic film, a nonmagnetic film, a ferromagnetic film, a nonmagnetic film, and a ferromagnetic film are subsequently stacked on the antiferromagnetic layer  64  to obtain the magnetization pinned layer  63 . After forming the MR film S 1 , as needed, a hard mask such as a carbon may be so formed, as a protecting film C, to cover throughout a surface of the MR film S 1 . 
     Then, as illustrated in  FIG. 6 , a resist mask RM 1  is so selectively formed as to cover only a region R 1  in which the first MR element  1  and the third MR element  3  will eventually be formed. Then, as illustrated in  FIGS. 7A and 7B , the protecting film C and the MR film S 1  in an exposed region are so selectively removed as to leave the protecting film C and the MR film S 1  in the region R 1 , by using a milling process. The milling process performed here finishes when the milling process reaches the metal film M 1 . 
     Then, the resist mask RM 1  is dissolved to remove the same, and a MR film S 2 , which will eventually become the stacked bodies  21  and  41 , is thereafter so formed as to cover throughout a surface as illustrated in  FIGS. 8A and 8B . The MR film S 2  may be formed by a process procedure similar to that of the MR film S 1 , for example. However, it is to be noted that the process procedure of the MR film S 2  differs from that of the MR film S 1 , in that the magnetization pinned layer  63  is so formed that an even number of ferromagnetic films (not illustrated), which will eventually become the first and the second ferromagnetic layers  631  and  632 , are included therein. 
     Then, after the MR film S 2  is formed, a resist mask RM 2  is so selectively formed as to cover only a region R 2  in which the second MR element  2  and the fourth MR element  4  will eventually be formed, as illustrated in  FIGS. 9A and 9B . Then, as illustrated in  FIGS. 10A and 10B , the MR film S 2  in an exposed region is so selectively removed as to leave the MR film S 2  in the region R 2 , by using a milling process. The milling process performed here finishes when the milling process reaches the metal film M 1  or the protecting film C. 
     Then, as illustrated in  FIGS. 11A and 11B , the resist mask RM 2  is dissolved to remove the same, and the protecting film C is removed by using an aching process. Thereafter, the annealing process is performed on the MR films S 1  and S 2 . For example, a heating is performed on the MR films S 1  and S 2  at a predetermined temperature of 280 degrees centigrade while applying an applied magnetic field H 1  in the plus Y direction, to allow the direction of the magnetization J 631  and the direction of the magnetization J 632  in the magnetization pinned layer  63  to be secured by one operation. Thus, a ferromagnetic layer adjacent to the antiferromagnetic layer  64  in all of the magnetization pinned layers  63  among the stacked bodies  11 ,  21 ,  31 , and  41  turns into the first ferromagnetic layer  631  having the magnetization J 631  in the minus Y direction following the annealing process. More specifically, in the magnetization pinned layer  63  of the stacked bodies  11  and  31  including the odd number of ferromagnetic films, the first ferromagnetic layer  631 B having the magnetization J 631  in the minus Y direction is located at a position nearest to the antiferromagnetic layer  64 , while the first ferromagnetic layer  631 A also having the magnetization J 631  in the minus Y direction is located at a position nearest to the magnetization free layer  61 . Also, in the magnetization pinned layer  63  of the stacked bodies  11  and  31 , the first ferromagnetic layers  631 , each having the magnetization J 631  in the minus Y direction, are provided more by one layer than the second ferromagnetic layer  632  having the magnetization J 632  in the plus Y direction. On the other hand, in the magnetization pinned layer  63  of the stacked bodies  21  and  41  including the even number of ferromagnetic films, the same number of the first ferromagnetic layer  631  having the magnetization J 631  in the minus Y direction and the second ferromagnetic layer  632  having the magnetization J 632  in the plus Y direction are provided. Also, the first ferromagnetic layer  631  having the magnetization J 631  in the minus Y direction is located at a position nearest to the antiferromagnetic layer  64 , while the second ferromagnetic layer  632  having the magnetization J 632  in the plus Y direction is located at a position nearest to the magnetization free layer  61 . It is preferable, but not required, that the applied magnetic field H 1  here have an intensity larger than that of an exchange coupling magnetic field in the synthetic structure of the magnetization pinned layer  63 , that is, larger than the exchange coupling magnetic field between the first ferromagnetic layer  631  and the second ferromagnetic layer  632 . 
     Then, as illustrated in  FIGS. 12A and 12B , after performing the annealing process, the MR films S 1  and S 2  are patterned to form, at predetermined positions, the columnar stacked bodies  11 ,  21 ,  31 , and  41  each having a predetermined planar configuration and size. Further, as illustrated in  FIGS. 12A and 12B , an insulating layer Z 2  is so formed as to embed around the columnar stacked bodies  11 ,  21 ,  31 , and  41 , by using a material such as Al 2 O 3 , for example. Incidentally, the stacked bodies  31  and  41  are not illustrated in  FIGS. 12A and 1213 . Also, although the MR films S 1  and S 2  are patterned after performing the annealing process in this embodiment, the patterning process of the MR films S 1  and S 2  and the annealing process may be reversed in order. In one embodiment, the MR films S 1  and S 2  are patterned to form the columnar stacked bodies  11 ,  21 ,  31 , and  41 , following which the annealing process is performed on those columnar stacked bodies  11 ,  21 ,  31 , and  41 . 
     Then, as illustrated in  FIGS. 13A and 13B , the connectors  14 ,  24 ,  34 , and  44  are so formed as to stand at predetermined positions (the connectors  34  and  44  are not illustrated in  FIGS. 13A and 13B ). Then, as illustrated in  FIGS. 14A and 14B , the stacked bodies  11  to  41 , the connectors  14  to  44 , and neighborhood regions thereof are selectively covered by a resist mask RM 3 , to perform a milling process on the metal film M 1  located in unprotected regions. As a result, the bottom electrodes  13 ,  23 ,  33 , and  43 , and the interconnection L 2  are obtained. 
     Then, as illustrated in  FIGS. 15A and 15B , an insulating layer Z 3  is so formed as to embed the regions in which the metal film M 1  is removed by the milling process, by using material such as Al 2 O 3 , for example. Thereafter, the resist mask RM 3  is dissolved to remove the same. 
     Then, as illustrated in  FIGS. 16A and 16B , the top electrodes  12 ,  22 ,  32 , and  42  (only the upper electrodes  12  and  22  are illustrated in  FIGS. 16A and 16B ), each having a predetermined shape, are so formed as to contact with the upper surface of the stacked bodies  11  to  41  and the upper surface of the connectors  14  to  44 . Also, the interconnections L 1  and L 3  to L 6  (only the interconnection L 3  is illustrated in  FIGS. 16A and 16B ) are formed. Finally, a predetermined process, such as a forming process of the pads  51  to  54  and so forth, is performed to complete the magnetic sensor according to this embodiment. 
     Therefore, according to this embodiment, the numbers of the first ferromagnetic layers  631  and the second ferromagnetic layers  632 , which are antiferromagnetically coupled to each other, are adjusted to allow each of the first and the third MR elements  1  and  3  and each of the second and the fourth MR elements  2  and  4  to exhibit the resistance changes in directions (i.e., increasing/decreasing direction) opposite to each other in response to the signal magnetic field Hm. Thus, the magnetic sensor according to this embodiment enables a compact configuration having the magnetic field detecting circuit including the first to the fourth MR elements  1  to  4  which are connected in a full-bridge configuration on the same substrate  100 , and yet enables a high-accuracy detection of magnetic field. Also, the method of manufacturing the magnetic sensor according to this embodiment enables to manufacture the magnetic sensor with high degree of accuracy in a simplified fashion, since the magnetization directions of the magnetization pinned layer  63  are settable by performing the annealing process while applying the unidirectional applied magnetic field H 1 , without using special facilities such as a laser irradiation system, an electron beam irradiation system and so forth. 
     It is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments and modifications will be apparent to those of skill in the art upon reviewing the above description. For example, in the embodiment described above, the detection circuit including the four MR elements (i.e., a full-bridge circuit) is used to detect the signal magnetic field, although it is not limited thereto. In one embodiment, a detection circuit provided with the first and the second MR elements, exhibiting resistance changes in directions (i.e., increasing/decreasing direction) opposite to each other in response to a signal magnetic field (i.e., a so-called half-bridge circuit) may be used to detect the signal magnetic field. 
     Also, in the embodiment described above, the description has been given with reference to a tunnel MR element having a magnetic tunnel junction structure as the MR element. However, a current-in-plane (CIP) or a current-perpendicular-to-plane (CPP) GMR element may be employed in one embodiment, where the spacing layer may be replaced by a nonmagnetic material layer having high-electrical conductivity, such as copper (Cu), gold (Au), chromium (Cr), and so forth, instead of the tunnel barrier layer, for example. 
     Further, in the embodiment described above, the description has been given with reference to the magnetic sensor which detects the magnitude of the signal magnetic field applied in one given direction, although it is not limited thereto. The magnetic sensor according to the embodiment may be utilized as an angle sensor which detects an orientation or direction of a signal magnetic field rotating in a certain plane of rotation (a plane parallel to the lamination plane of the MR elements). In this one embodiment, since an amount of resistance change varies depending on a relative angle between a direction of application of the signal magnetic field and an orientation of magnetization of the magnetization pinned layer in each of the MR elements as long as a magnitude of the signal magnetic field is constant, this relationship is utilized to obtain an angle of rotation of the signal magnetic field. 
     It should be appreciated that variations may be made in the described embodiments by persons skilled in the art without departing from the scope of the invention as defined by the following claims. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in the specification or during the prosecution of the application, and the examples are to be construed as non-exclusive. For example, in the disclosure, the term “preferably”, “preferred” or the like is non-exclusive and means “preferably”, but not limited to. The use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Moreover, no element or component in the disclosure is intended to be dedicated to the public regardless of whether the element or component is explicitly recited in the following claims. 
     This application is based on and claims priority from Japanese Patent Application No. 2009-217926, filed in the Japan Patent Office on Sep. 18, 2009, the disclosure of which is hereby incorporated by reference in its entirety.