Patent Publication Number: US-7723984-B2

Title: Magnetic sensor and current sensor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates a magnetic sensor capable of detecting a variation of a magnetic field with high sensitivity, and a current sensor capable of detecting a variation of a current flowing through a conductor line with high sensitivity. 
     2. Description of the Related Art 
     In measuring correctly a control current which flows into a circuit of control equipment, a method where resistances are connected in series within the circuit to measure a voltage drop of the resistances is applied generally. In this case, however, a load different from the control system is given, and there is a possibility that an adverse influence may be exerted on the control system. Consequently, a method of indirectly measuring a control current by detecting the gradient of a current magnetic field generated by the control current has been used. Specifically, a control current is supplied to a U-shaped, curved conductor line, and variation of current magnetic fields produced around the curved conductor line is detected by use of a Hall device (for example, refer to Japanese Unexamined Patent Publication No.H07-123090). 
     However, the above-described current sensor has problems that a miniaturization is difficult and that the linearity of detection sensitivity to the change of magnetic field or high-frequency response are inadequate and so on. For this reason, a current sensor, in which a giant magnetoresistive element developing a Giant Magneto-Resistive effect (hereinafter referred to as GMR element) is arranged in a current magnetic field generated by the control current in order to detect its gradient instead of the Hall element, is proposed. That current sensor using such a GMR element can improve the detection sensitivity and high-frequency response, and what is more, a detection characteristic that is stabilized against a temperature change is obtainable. 
     SUMMARY OF THE INVENTION 
     In these days, a current sensor capable of conducting a more precise current measurement is strongly desired. Therefore, it is necessary to secure the linearity of a resistance change of the GMR elements to a variation of current magnetic fields more strictly and with more stably. On the other hand, a current sensor of much more compact whole configuration is also desired. 
     The present invention has been achieved in consideration of such problems, and it is desirable to provide a more miniaturized and simple current sensor capable of measuring a current to be detected with high precision and stability. 
     According to an embodiment of the present invention, there is provided a magnetic sensor including: an element substrate including a magnetoresistive element, the magnetoresistive element having a pinned layer with a magnetization direction pinned to a direction, an intermediate layer, and a free layer whose magnetization direction changes according to an external magnetic field; and a magnetic sheet attached on one side of the element substrate so as to apply a bias magnetic field to the magnetoresistive element. Here, the magnetic sheet may be attached on the side of substrate in the element substrate, or may be attached on the side opposite to the substrate. The attachment between the element substrate and the magnetic sheet may be direct, or may be indirect. 
     Since the magnetic sensor of an embodiment of the present invention is configured in such a way that the magnetic sheet is attached directly or indirectly onto the element substrate having a magnetoresistive element so that the magnetic sheet may apply a bias magnetic field to the magnetoresistive element, it is possible to reduce an influence of unnecessary turbulence magnetic fields applied from the outside. For this reason, the magnetoresistive element shows an accurate and stable resistance change which is excellent in linearity, based on a magnetic field to be detected. Moreover, the arrangement of the magnetic sheet can use a space in a more effective way, compared with a case where permanent magnets or coils are arranged on both sides of the magnetoresistive element. 
     According to an embodiment of the present invention, there is provided a first current sensor including: a conductor line generating a current magnetic field according to a supplied current to be detected; an element substrate including a magnetoresistive element disposed along with the conductor line so that a resistance value of the magnetoresistive element changes according to the current magnetic field; and a magnetic sheet attached on one side of the element substrate so as to apply a bias magnetic field to the magnetoresistive element. 
     According to an embodiment of the present invention, there is provided a second current sensor including: a conductor line generating a current magnetic field according to a supplied current to be detected; a pair of element substrates each including a magnetoresistive element disposed along with the conductor line; a pair of magnetic sheets each attached on one side of each of the element substrates, respectively, so as to apply a bias magnetic field to each of the magnetoresistive elements; a pair of constant current sources each supplying a constant current of a common magnitude to each of the magnetoresistive elements; and a difference detector detecting a difference in the voltage drops resulting from the constant current in each of the magnetoresistive elements. Here, the magnetoresistive elements are set so that a resistance value of one of the magnetoresistive elements changes in a direction opposite to that of resistance-value-change of the other magnetoresistive element according to the current magnetic field, and the current Im to be detected can be measured on the basis of the difference in the voltage drops. 
     According to an embodiment of the present invention, there is provided a third current sensor including: a conductor line generating a current magnetic field according to a supplied current to be detected; first through fourth element substrates disposed along with the conductor line, each of the element substrates including a magnetoresistive element whose resistance value changes according to the current magnetic field; and first through fourth magnetic sheets each attached on one side of each of the first through fourth element substrates, respectively, so as to apply a bias magnetic field to each of the magnetoresistive elements. Here, one end of the magnetoresistive element in the first element substrate and one end of the magnetoresistive element in the second element substrate are connected each other in a first junction point, one end of the magnetoresistive element in the third element substrate and one end of the magnetoresistive element in the fourth element substrate are connected each other in a second junction point, the other end of magnetoresistive element in the first element substrate and the other end of the magnetoresistive element in the fourth element substrate are connected each other in a third junction point, and the other end of magnetoresistive element in the second element substrate and the other end of the magnetoresistive element in the third element substrate are connected each other in a fourth junction point. As a result, a bridge circuit is formed. 
     In the first through third current sensors of an embodiment of the present invention, since the magnetic sheet (the first through fourth magnetic sheets) is attached directly or indirectly onto the element substrate (the first through fourth element substrates) including a magnetoresistive element disposed along with a conductor line used as the path of the current to be detected so that the magnetic sheet applies a bias magnetic field to the magnetoresistive element, it is possible to reduce an influence of unnecessary turbulence magnetic fields applied from the outside. For this reason, the magnetoresistive element shows an accurate and stable resistance change which is excellent in linearity, based on a magnetic field to be detected. Moreover, the arrangement of the magnetic sheet can use a space in a more effective way, compared with a case where permanent magnets or coils are arranged on both sides of the magnetoresistive element. 
     In the first through third current sensors of an embodiment of the present invention, the magnetoresistive element preferably includes in order: a pinned layer having a magnetization direction pinned to a direction; an intermediate layer; and a free layer whose magnetization direction changes according to an external magnetic field, while the magnetization direction under no external magnetic field is parallel or antiparallel to the direction in which the conductor line is extending. It is desirable that the magnetization direction of the pinned layer is orthogonal to or parallel to the magnetization direction of the free layer under no external magnetic field. In the mutually orthogonal case, it is preferable to apply a bias magnetic field in the same direction as the magnetization direction of the free layer under no external magnetic field by use of the magnetic sheet. On the other hand, in the mutually parallel case, it is preferable to apply a bias magnetic field having both a parallel component parallel to the magnetization direction of the pinned layer and a perpendicular component orthogonal to the parallel component by use of the magnetic sheet. Examples of the external magnetic field here include the current magnetic field generated by the current to be detected, the bias magnetic field applied by the magnetic sheet or any external noise. 
     In the third current sensor of an embodiment of the present invention, it is preferable to have further a difference detector detecting a potential difference between the third junction point and the fourth junction point when voltage is applied between the first junction point and the second junction point. In addition, preferably, resistance values of the magnetoresistive elements in the first and third element substrates change in the same direction according to the current magnetic fields, while resistance values of the magnetoresistive elements in the second and fourth element substrates change in the direction opposite to that of resistance-value-change of the magnetoresistive elements in the first and third element substrates according to the current magnetic fields. 
     According to an embodiment of the present invention, there is provided a method of manufacturing a magnetic sensor including the steps of forming a laminated product by applying adhesives to the back of a substrate and sticking a magnetic sheet on the back, the substrate being provided with a plurality of magnetoresistive elements formed on the front surface thereof; setting a magnetization direction of the magnetic sheet; and cutting the laminated product to divide into pieces so that each piece includes a magnetoresistive element. 
     According to the method of manufacturing the magnetic sensor of an embodiment of the present invention, the magnetic sheet is stuck on the back of the substrate provided with a plurality of magnetoresistive elements are formed, then a magnetization direction of the magnetic sheet is set and after that, the laminated product is cut to divide into pieces so that each piece includes a magnetoresistive element. In this manner, a plurality of magnetic sensors having a magnetoresistive element to which a bias magnetic field is applied in a direction can be formed at a time in a simple and easy way. 
     In the method of manufacturing the magnetic sensor of an embodiment of the present invention, it is preferable to further includes a step of grinding the back of the substrate into a predetermined thickness, after forming a plurality of magnetoresistive elements thereon and before sticking the magnetic sheet thereto. 
     In the method of manufacturing the magnetic sensor of an embodiment of the present invention, it is preferable to further includes a step of grinding the magnetic sheet to adjust strength of a bias magnetic field applied from the magnetic sheet to the magnetoresistive elements. 
     According to the magnetic sensor of an embodiment of the present invention, since an element substrate having a magnetoresistive element and a magnetic sheet are unified by bonding together directly or indirectly so that the magnetic sheet can apply a bias magnetic field to the magnetoresistive element, there is an effect that an influence of unnecessary turbulence magnetic fields from the outside can be fully avoided while a magnetic field to be detected can be detected with precision and stability. Moreover, the whole configuration can be made smaller and more simple using a space effectively, compared with a case where permanent magnets or coils are arranged on both sides of the magnetoresistive element for applying a bias magnetic field. 
     According to the first through third current sensors of an embodiment of the present invention, an element substrate (a first through fourth element substrates) having a magnetoresistive element and a magnetic sheet (a first through fourth magnetic sheets) are unified by bonding together and are disposed along with a conductor line that is used as the path of a current to be detected, so that the magnetic sheet can apply a bias magnetic field to the magnetoresistive element. In this manner, there is an effect that an influence of unnecessary turbulence magnetic fields from the outside can be fully avoided while a current magnetic field generated on the basis of a current to be detected can be detected with precision and stability. Moreover, the whole configuration can be made smaller and more simple using a space effectively, compared with a case where permanent magnets or coils are arranged on both sides of the magnetoresistive element for applying a bias magnetic field. Therefore, there is an effect of being able to attain a miniaturization while capable of measuring the current to be detected with high precision and stability. 
     According to the method of manufacturing the magnetic sensor of an embodiment of the present invention, after grinding the back of a substrate provided with a plurality of magnetoresistive elements are formed, a magnetic sheet is stuck on the back of the substrate, then a magnetization direction of the magnetic sheet is set and after that, the laminated product is cut to divide into pieces so that each piece includes a magnetoresistive element. In this manner, there is an effect that a plurality of magnetic sensors having a magnetoresistive element to which a bias magnetic field is applied in a direction can be formed at a time and in a simple and easy way. 
     Other and further objects, features and advantages of the invention will appear more fully from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a configuration of a current sensor according to a first embodiment of the present invention. 
         FIG. 2  is a circuit diagram corresponding to the current sensor appearing in  FIG. 1 . 
         FIG. 3  is an exploded perspective view showing the configuration of a magnetoresistive element that is the principal part of the current sensor appearing in  FIG. 1 . 
         FIGS. 4A and 4B  are conceptual diagrams for explaining a state of magnetization directions, current magnetic fields and bias magnetic fields in the current sensor appearing in  FIG. 1 . 
         FIG. 5  is a perspective view for explaining a step of a manufacturing method of the current sensor appearing in  FIG. 1 . 
         FIG. 6  is a perspective view indicative of a next step following  FIG. 5 . 
         FIG. 7  is a perspective view indicative of a next step following  FIG. 6 . 
         FIG. 8  is a perspective view indicative of a next step following  FIG. 7 . 
         FIGS. 9A and 9B  are conceptual diagrams for explaining a state of magnetization directions, current magnetic fields and bias magnetic fields in a modification of the current sensor appearing in  FIG. 1 . 
         FIG. 10  is a characteristic diagram showing the dependency of a resistance change ratio on a magnetic field in the modification as shown in  FIGS. 9A and 9B . 
         FIGS. 11A and 11B  are conceptual diagrams for explaining a state of magnetization directions, current magnetic fields and bias magnetic fields in a current sensor according to a second embodiment of the present invention. 
         FIGS. 12A and 12B  are conceptual diagrams for explaining a state of magnetization directions, current magnetic fields and bias magnetic fields in a modification of the current sensor appearing in  FIGS. 11A and 11B . 
         FIG. 13  is a conceptual diagram for explaining a state of magnetization directions, current magnetic fields and bias magnetic fields in a current sensor according to a third embodiment of the present invention. 
         FIG. 14  is a circuit diagram corresponding to the current sensor shown in  FIG. 13 . 
         FIG. 15  is a characteristic diagram indicating a distribution of bias magnetic fields Hx in a magnetic sheet of the current sensor shown in  FIGS. 9A and 9B . 
         FIG. 16  is another characteristic diagram indicating a distribution of bias magnetic fields Hx in the magnetic sheet of the current sensor shown in  FIGS. 9A and 9B . 
         FIG. 17  is a characteristic diagram indicating a distribution of bias magnetic fields Hy in the magnetic sheet of the current sensor appearing in  FIGS. 9A and 9B . 
         FIG. 18  is a schematic diagram showing a first modification of a conductor used in the current sensor appearing in  FIG. 1 . 
         FIG. 19  is a schematic diagram showing a second modification of a conductor used in the current sensor appearing in  FIG. 1 . 
         FIG. 20  is a schematic diagram showing a third modification of a conductor used in the current sensor appearing in  FIG. 1 . 
         FIG. 21  is a schematic diagram showing a configuration of the conductor in a current sensor of related arts. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described in detail hereinbelow with reference to the drawings. 
     First Embodiment 
     First, a configuration of a current sensor according to a first embodiment of the present invention will be explained with reference to  FIG. 1  and  FIG. 2 .  FIG. 1  is a schematic diagram showing a perspective configuration of a current sensor  10  according to the present embodiment, and  FIG. 2  expresses a circuit configuration of the current sensor  10  appearing in  FIG. 1 . Directions of all the arrows in  FIG. 2  representing a current to be detected Im, a compensating current Id, current magnetic fields HmA and HmB, compensating current magnetic fields Hd, bias magnetic fields Hb 1  and Hb 2 , and a current  10  indicate a relative direction with respect to a first and a second magnetoresistive elements  3 A and  3 B (which will be described later). 
     The current sensor  10  is an ammeter for measuring a current to be detected Im supplied to a conductor  2  formed on a substrate  1 , and is provided with magnetic sensors  7 A and  7 B including a first and second magnetoresistive elements  3 A and  3 B (hereinafter just referred to as MR elements  3 A and  3 B). The MR elements  3 A and  3 B are connected each other at a first junction point P 1 , and arranged symmetrically with respect to a central line CL that passes along the midpoint on a virtual straight-line connecting the MR elements  3 A and  3 B each other (refer to  FIG. 2 ). 
     The conductor  2  is a V-shaped configuration having a pair of straight-line portions  2 A and  2 B, and a folded portion  2 C for connecting these straight-line portions. The ends of the conductor  2  are connected to pads  2 D and  2 E. The straight-line portions  2 A and  2 B are arranged axisymmetrically with respect to the central line CL (symmetry axis, refer to  FIG. 2 ) in a plane parallel to the plane containing the MR elements  3 A and  3 B, and they are extending so as to make an angle of 45 degrees each other for example (that is, orthogonal to each other), in the x-axis direction and in the y-axis direction, respectively. On the straight-line portions  2 A and  2 B are provided the magnetic sensors  7 A and  7 B, respectively. Details of the magnetic sensors  7 A and  7 B will be described later. 
     As for the straight-line portions  2 A and  2 B, the areas of cross sections thereof orthogonal to the extending directions are uniform and equal to each other. Thereby, synthetic magnetic fields Hm 1  and Hm 2  of current magnetic field HmA and current magnetic field HmB generated when a current to be detected Im flows into the conductor  2  from the pad  2 D toward the pad  2 E, for example, are respectively applied to the MR elements  3 A and  3 B in the directions shown by arrows in  FIG. 2 . Here, the current magnetic field HmA is generated in the +Y direction in the straight-line portion  2 A, and the current magnetic field HmB is generated in the +X direction in the straight-line portion  2 B. Since the current magnetic fields HmA and HmB, although having different directions mutually, are generated by the same current to be detected Im and the areas of the cross sections of the straight-line portions  2 A and  2 B are equally uniformed mutually, the intensity (absolute value) of these current magnetic fields HmA and HmB are mutually equal. However, since the MR element  3 A is arranged close to the straight-line portion  2 A, the influence of the current magnetic fields HmB is smaller than the influence of the current magnetic fields HmA. For this reason, the direction of the synthetic magnetic field Hm 1  applied to the MR element  3 A is slightly tilted (rotated) from the +Y direction to the +X direction, that is, a Y 2  direction. Similarly, since the MR element  3 B is arranged close to the straight-line portion  2 B, the influence of the current magnetic field HmA is small. For this reason, the direction of the synthetic magnetic field Hm 2  applied to the MR element  3 B is slightly tilted (rotated) from the +X direction to the +Y direction, that is, an X 2  direction. Furthermore, the distance from the straight-line portion  2 A to the MR element  3 A and the distance from the straight-line portion  2 B to the MR element  3 B are mutually equal, while the distance from the straight-line portion  2 A to the MR element  3 B and the distance from the straight-line portion  2 B to the MR element  3 A are mutually equal. As a result of that, the intensity (absolute value) of the synthetic magnetic field Hm 1  applied to the MR element  3 A and the intensity (absolute value) of the synthetic magnetic field Hm 2  applied to the MR element  3 B are mutually equal. The MR elements  3 A and  3 B are formed so that each resistance R 1  and R 2  (which will be described later) can develop an opposite directional change each other by the existence of synthetic magnetic fields Hm 1  and Hm 2  when the current sensor  10  is driven. 
     The magnetic sensors  7 A and  7 B are stuck on the straight-line portions  2 A and  2 B with a 51 μm-10 μm thick adhesive layer (not shown) in between, respectively. More specifically, the magnetic sensors  7 A and  7 B are formed by laminating magnetic sheets  6 A and  6 B and element substrates  5 A and  5 B in order on the straight-line portions  2 A and  2 B, respectively, as appearing in  FIG. 1 . The adhesive layers of 5 μm-10 μm in thickness (not shown) are provided between the magnetic sheets  6 A and  6 B and the element substrates  5 A and  5 B, respectively. The element substrates  5 A and  5 B have a structure in which the MR elements  3 A and  3 B are provided on substrates  4 A and  4 B made of a silicon wafer of the order of 100 μm thick, respectively. The magnetic sheets  6 A and  6 B apply bias magnetic fields Hb 1  and Hb 2  (refer to  FIG. 2 ) to the MR elements  3 A and  3 B, respectively. Here, the direction of the bias magnetic field Hb 1  is an X 3  direction (direction tilted slightly from the +X direction to the −Y direction) which intersects perpendicularly with the Y 2  direction, and the direction of the bias magnetic field Hb 2  is a Y 3  direction (direction tilted slightly from the +Y direction to the −X direction) which intersects perpendicularly with the X 2  direction. It is to be noted that the directions of the bias magnetic fields Hb 1  and Hb 2  are determined with reference to the magnetization directions of each pinned layer  13  (which will be described later) of the MR elements  3 A and  3 B besides with reference to the synthetic magnetic fields Hm 1  and Hm 2 . The magnetic sheets  6 A and  6 B are made of a barium strontium ferrite [(Ba—Sr)Fe 2 O 4 ], for example, and have a thickness of 75 μm-95 μm. It is to be noted that the material for the magnetic sheets  6 A and  6 B is not limited to that, but other ferromagnetic materials capable of becoming a permanent magnet can also be used. Preferably, the magnetic sheets  6 A and  6 B have a bigger area than the MR elements  3 A and  3 B so that application of the bias magnetic fields Hb 1  and Hb 2  can be stabilized. 
     The current sensor  10  further includes a constant current source CG 1  (a first constant current source) and a constant current source CG 2  (a second constant current source) the ends of which are connected each other in a second junction point P 2  ( FIG. 2 ). The constant current source CG 1  is connected to the MR element  3 A in a third junction point P 3  by one end opposite to the first junction point P 1 , and the constant current source CG 2  is connected to the MR element  3 B in a fourth junction point P 4  by one end opposite to the first junction point P 1 . Namely, the MR element  3 A and the constant current source CG 1  are connected in series, and the MR element  3 B and the constant current source CG 2  are connected in series, while both of the series connections are then connected in parallel each other axisymmetrically with respect to the central line CL (symmetry axis). Here, the constant current source CG 1  and the constant current source CG 2  are formed so as to supply a constant current  10  of mutually equal value to the MR element  3 A and the MR element  3 B, respectively. It is to be noted that the constant current sources CG 1  and CG 2  are arranged in the inside of a circuit board  9  provided on the substrate  1  (not shown in  FIG. 1 ). 
     The current sensor  10  is further provided with a compensating current line C. If voltage is applied between the first junction point P 1  and the second junction point P 2 , a compensating current Id based on the potential difference between the third junction point P 3  and the fourth junction point P 4  will be supplied to the compensating current line C ( FIG. 2 ). One end of the compensating current line C is connected to the output side of a differential amplifier AMP as a difference detector whose input side is connected to the third and fourth junction points P 3  and P 4 , and the other end of the compensating current line C is grounded via a resistor RL. A compensating current detector S is connected to the resistor RL at a junction point T 1  on the differential amplifier AMP side. Here, the compensating current line C is arranged so that compensating current magnetic fields Hd 1  and Hd 2 , which are respectively opposite to the current magnetic fields Hm 1  and Hm 2 , may be generated when the compensating current Id flows. Namely, the compensating current magnetic field Hd 1  is generated in the −Y direction, while the compensating current magnetic field Hd 2  is generated in the −X direction, consequently having an effect of canceling the current magnetic fields Hm 1  and Hm 2 , respectively. 
     The MR elements  3 A and  3 B have a structure in which an insulating film, a GMR film developing Giant Magneto-Resistive effect, an insulating film, and a pad are laminated in order on the substrates  4 A and  4 B, respectively. Here, the insulating films are made of aluminum oxide (Al 2 O 3 ) etc., for example. The pad is an electrode for supplying a sense current in reading a resistance change of the GMR film. The GMR film will be explained in more detail with reference to  FIG. 3 .  FIG. 3  is an exploded perspective view disassembling and showing the configuration of the GMR film which is included in each of the MR elements  3 A and  3 B. 
     As shown in  FIG. 3 , the GMR film in each of the MR elements  3 A and  3 B has a spin valve structure in which a plurality of function films including magnetic layers are laminated. Specifically, the GMR film includes: a pinned layer  11  having a magnetization direction J 11  which is pinned to a certain direction; an intermediate layer  12  exhibiting no specific magnetization directions; and a free layer  13  having a magnetization direction J 13  whose direction changes according to external magnetic fields H such as the synthetic magnetic fields Hm 1  and Hm 2 , in order. It is to be noted that  FIG. 3  shows an unloaded condition (namely, the state that no external magnetic field H is applied) in which the synthetic magnetic fields Hm 1  and Hm 2  are zero (Hm 1 , Hm 2 =0), and the bias magnetic fields Hb 1  and Hb 2  generated by the magnetic sheets  6 A,  6 B are not applied. In this case, the magnetization direction J 13  of the free layer  13  are in parallel with its own easy magnetization direction AE 13 , while it is orthogonal to the magnetization direction J 11  of the pinned layer  11 . 
     The free layer  13  is made of a soft magnetic material such as nickel iron alloy (NiFe). The intermediate layer  12  is made of copper (Cu), its top face being in contact with the pinned layer  11 , its under face being in contact with the free layer  13 . The intermediate layer  12  may be made of, besides copper, a nonmagnetic metal having high conductivity such as gold (Au). The top face of the pinned layer  11  (the face on the side opposite to the intermediate layer  12 ) and the under face of the free layer  13  (the face on the side opposite to the intermediate layer  12 ) are protected with a protection film (not shown), respectively. An exchange bias magnetic field Hin in the magnetization direction J 11  is generated between the pinned layer  11  and the free layer  13 , working on each other with the intermediate layer  12  in between. The intensity of the exchange bias magnetic field Hin changes as the spin direction in the free layer  13  rotates according to the interval between the pinned layer  11  and the free layer  13  (that is, the thickness of the intermediate layer  12 ). Although  FIG. 3  shows one example of configuration in which the free layer  13 , the intermediate layer  12 , and the pinned layer  11  are laminated in order from bottom up, it is not limited to the configuration but may be made in such a way as laminating in the opposite order. 
     In the GMR film of the MR elements  3 A and  3 B having the foregoing structure, the magnetization direction J 13  of the free layer  13  rotates by applying the synthetic magnetic fields Hm 1  and Hm 2 , and consequently the relative angle of the magnetization direction J 13  and the magnetization direction J 11  changes. The relative angle is decided by the magnitudes and directions of the synthetic magnetic fields Hm 1  and Hm 2 . 
     A relation among the magnetization directions J 11  and J 13  of the GMR films, the bias magnetic fields Hb 1  and Hb 2 , and the synthetic magnetic fields Hm 1  and Hm 2  will be explained herein with reference to  FIGS. 4A and 4B .  FIGS. 4A and 4B  are conceptual diagrams indicating a relation among the current direction, the magnetic field direction, and the magnetization direction in the current sensor  10 . For example, supposing a current to be detected Im flows along the extending direction of the conductor  2  as shown by arrows, a current magnetic field HmA is generated around the straight-line portion  2 A, and a current magnetic field HmB is generated around the straight-line portion  2 B. In this case, the synthetic magnetic field Hm 1  applied to the MR element  3 A is a resultant force between a magnetic field component HmA 1  in the +Y direction caused by the current magnetic field HmA and a magnetic field component HmB 2  in the +X direction caused by the current magnetic field HmB, as shown by vectors. On the other hand, the synthetic magnetic field Hm 2  applied to the MR element  3 B is a resultant force between a magnetic field component HmA 2  in the +Y direction caused by the current magnetic field HmA and a magnetic field component HmB 1  in the +X direction caused by the current magnetic field HmB, as shown by vectors. Here, in the MR elements  3 A and  3 B, the magnetization directions J 11 A and J 11 B of the pinned layers  11  are pinned in the direction parallel or antiparallel with the synthetic magnetic fields Hm 1  and Hm 2 , respectively. When no external magnetic field H is applied, magnetization directions J 13 A and J 13 B of the free layers  13  are in a state orthogonal to the synthetic magnetic fields Hm 1  and Hm 2 , respectively. Namely, when no external magnetic field H is applied, the magnetization directions J 13 A and J 13 B are in a state orthogonal to the magnetization directions J 11 A and J 13 B, respectively. Therefore, when the current to be detected Im is supplied to the conductor  2  and the synthetic magnetic fields Hm 1  and Hm 2  are generated consequently, the magnetization directions J 13 A and J 13 B are coming to be in parallel (low resistance), or antiparallel (high resistance) to the magnetization directions J 11 A and J 11 B, more and more. The MR element  3 A and the MR element  3 B are set so that their own resistances R 1  and R 2  may changes oppositely each other according to the synthetic magnetic fields Hm 1  and Hm 2 . Specifically, as shown in  FIG. 4  A, in the MR element  3 A, the magnetization direction J 11 A is in the +Y 2  direction while the magnetization direction J 13 A under no external magnetic field H is in the +X 3  direction, for example. On the other hand, in the MR element  3 B, the magnetization direction J 11 B is in the −X 2  direction while the magnetization direction J 13 B under no external magnetic field H is in the +Y 3  direction. In this case, when the current to be detected Im flows in the direction of the arrow to generate the synthetic magnetic fields Hm 1  and Hm 2 , the magnetization direction J 13 A rotates counterclockwise (on the drawing sheet) to come to be in parallel with the magnetization direction J 11 A while the magnetization direction J 13 B rotates clockwise (on the drawing sheet) to come to be in antiparallel with the magnetization direction J 11 B. As a result, the resistance R 1  of the MR element  3 A decreases, and the resistance R 2  of the MR element  3 B increases. Or it is also possible that, as shown in  FIG. 4B , in the MR element  3 A, the magnetization direction J 11 A is set in the +Y 2  direction and the magnetization direction J 13 A under no external magnetic fields H is set in the −X 3  direction, while in the MR element  3 B, the magnetization direction J 11 B is set in the −X 2  direction and the magnetization direction J 13 B in the case the external magnetic field H are zero is set in the +Y 3  direction. In this case, when the current to be detected Im flows in the direction indicated by the arrow to generate the synthetic magnetic fields Hm 1  and Hm 2 , the magnetization direction J 13 A rotates clockwise to come to be in parallel with the magnetization direction J 11 A, while the magnetization directions J 13 B rotates clockwise to be in antiparallel with the magnetization direction J 11 B. As a result, the resistance R 1  of the MR element  3 A also decreases, and the resistance R 2  of the MR element  3 B also increases. Although, in both cases of  FIGS. 4A and 4B , the resistance R 1  of the MR element  3 A decreases and the resistance R 2  of the MR element  3 B increases, it is not limited to that, and it is also possible that the resistance R 1  may increase and the resistance R 2  may decrease. 
     It is to be noted that in both of  FIG. 4A  and  FIG. 4B , the magnetic sheets  6 A and  6 B are set so as to apply bias magnetic fields Hb 1  and Hb 2  having the same direction as the magnetization directions J 13 A and J 13 B in the case of no external magnetic field H. Therefore, the bias magnetic fields Hb 1  and Hb 2 , which are corresponding to an anisotropic magnetic field, strengthen the uniaxial anisotropy of the free layer  13  to contribute to stabilization of the magnetic field detecting operation in the MR elements  3 A and  3 B. In related arts, shape anisotropy has been increased by way of developing the shape of the MR element itself long and slender, and further, a resistance change ratio has been raised by way of arranging two or more of the MR elements with a predetermined gap, respectively. In this manner, however, a comparatively big space is required and furthermore a compensating current line has to be enlarged. On the other hand, according to the current sensor  10  of the present embodiment, the flexibility of the shape of the MR elements  3 A and  3 B is high because shape anisotropy is not used, and there is no need of dividing each elements into two or more. As a result, a more compact configuration is realized. 
     What is more, in the current sensor  10 , the conductor  2  is formed of a V-shaped configuration including the straight-line portion  2 A and the straight-line portion  2 B which are orthogonal to each other. In this manner, compared with a current sensor of related arts in which a U-shaped conductor  102  including a pair of parallel straight-line portions  102 A and  102 B as shown in  FIG. 21  is used, current measurement can be conducted more precisely, and what is more, miniaturization of the entire configuration can be realized. That is to say, in the case of the U-shaped conductor  102 , an interaction occurs between a current magnetic field Hm 101  and a current magnetic field Hm 102  to cancel each other when the straight-line portion  102 A and the straight-line portion  102 B are disposed closer, since the flowing directions of the current to be detected Im are certainly made opposite between the straight-line portion  102 A and the straight-line portion  102 B. In order to reduce such an interaction, preferably, a gap W 103  of the MR elements  103 A and the  103 B is kept beyond a certain distance. The conductor  102  further has a problem that the dimension of a folded portion  102 C tends to become large. On the contrary, in the case of the current sensor  10  of the present embodiment, the directions of the current to be detected Im flowing through each of the straight-line portion  2 A and the straight-line portion  2 B are not completely reversed each other (in this case, an angle of 45 degrees exists). As a result, the interaction between the current magnetic field Hm 1  produced from the straight-line portion  2 A and the current magnetic field Hm 2  produced from the straight-line portion  2 B is relatively weak. For this reason, even when the gap W 3  of the MR elements  3 A and  3 B is made small, the current magnetic fields Hm 1  and Hm 2  having a sufficient intensity for detecting operation can be applied to each of the MR elements  3 A and  3 B. Thereby, more precise current measurement becomes possible. Further, since the dimension for the folded portion  2 C can also be made relatively small, height  2 L of the whole conductor  2  can be made smaller than height  102 L of the conductor  102 . Namely, the current sensor  10  having a more compact whole configuration can be realized while maintaining the dimension of the MR elements  3 A and  3 B. Thereby, the measurement error caused by the difference in temperature between the MR elements  3 A and  3 B can also be reduced, and consequently more precise and stable current measurement is possible. 
     In the current sensor  10  having such a configuration, when voltage is applied between the first junction point P 1  and the second junction point P 2 , a compensating current Id based on a potential difference V 0  (difference in the voltage drops produced in each of the MR elements  3 A and  3 B) between the third junction point P 3  and the fourth junction point P 4  flows through the compensating current line C via the differential amplifier AMP (difference detector). The compensating current Id is detected by the compensating current detector S. The differential amplifier AMP has a function of adjusting the compensating current Id so that a value of the difference V 0  becomes zero. 
     Hereafter, a method of measuring the current magnetic fields HmA and HmB generated by the current to be detected Im will be explained with reference to  FIG. 2 . 
     In  FIG. 2 , constant current from the constant current sources CG 1  and CG 2  at the time of applying a predetermined voltage between the first junction point P 1  and the second junction point P 2  is indicated as  10 , and the resistances of the MR elements  3 A and  3 B are indicated as R 1  and R 2 , respectively. When current magnetic fields HmA and HmB are not applied, potential V 1  in the third junction point P 3  is V 1 =I 0 ×R 1 , and potential V 2  in the fourth junction point P 4  is set to V 2 =I 0 ×R 2 . Therefore, the potential difference between the third junction point P 3  and the fourth junction point P 4  is 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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     In this circuit, the amount of resistance change can be obtained by measuring the potential difference V 0  when the current magnetic fields HmA and HmB are applied. For example, when the current magnetic fields HmA and HmB are applied, supposing that the resistance R 1  and R 2  respectively increase by variation amounts ΔR 1  and ΔR 2 , Equation (1) is rewritten as follows: 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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     As already stated, since the MR elements  3 A and  3 B are arranged so that the resistances R 1  and R 2  show an opposite directional variation each other by the current magnetic fields HmA and HmB, the variation amounts ΔR 1  and ΔR 2  have an opposite positive/negative sign each other. Therefore, in Equation (2), R 1  and R 2  (resistance values before application of the current magnetic fields HmA and HmB) cancel out each other while the variation amounts ΔR 1  and ΔR 2  remain as they are. 
     Suppose that both of the MR elements  3 A and  3 B have the completely same characteristics, that is, letting R 1 =R 2 =R and ΔR 1 =−ΔR 2 =ΔR, Equation (2) is re-expressed as follows: 
                           V   ⁢           ⁢   0     ⁢           =           ⁢     I   ⁢           ⁢   0   ×     (       R   ⁢           ⁢   1     +     Δ   ⁢           ⁢   R   ⁢           ⁢   1     -     R   ⁢           ⁢   2     -     Δ   ⁢           ⁢   R   ⁢           ⁢   2       )                   =     I   ⁢           ⁢   0   ×     (     R   +     Δ   ⁢           ⁢   R     -   R   +     Δ   ⁢           ⁢   R       )                   =     I   ⁢           ⁢   0   ×     (     2   ⁢           ⁢   Δ   ⁢           ⁢   R     )                     (   3   )               
Therefore, if the MR elements  3 A and  3 B whose relation between an external magnetic field and their resistance variation amounts is already known are used, the intensity of the current magnetic fields HmA and HmB can be measured and the magnitude of current to be detected Im that generates the current magnetic fields HmA and HmB can be estimated. In this case, since sensing is performed using two of the MR elements  3 A and  3 B, twice as much resistance variation can be obtained as compared with the case where sensing is performed using either one of the MR element  3 A or the MR element  3 B independently. Thereby, it is advantageous for obtaining more accurate measurement value. Since discrepancies in the characteristics of MR elements and dispersion in the connection resistances, etc. can be reduced compared with a case where sensing is performed by way of configuring a bridge circuit using four MR elements, balance adjustment is made easy even if an MR element with high sensitivity is used. In addition, since the number of the MR elements itself can be reduced, the number of terminals naturally becomes fewer, which is advantageous for space-saving.
 
     In the current sensor  10 , the potential V 1  detected in the third junction point P 3  and the potential V 2  detected in the fourth junction point P 4  are supplied to the differential amplifier AMP, and the compensating current Id making the difference (potential difference V 0 ) zero is outputted. The compensating current Id from the differential amplifier AMP produces a compensating current magnetic field Hd having a direction opposite to the current magnetic field HmA and HmB by flowing near the MR elements  3 A and  3 B in the direction opposite to the current to be detected Im, thereby canceling errors caused by dispersion in the connection resistances in the circuit, discrepancies in the mutual characteristics of the MR elements  3 A and  3 B, deviation of temperature distribution, or the disturbance magnetic fields from the outside, etc. As a result, it is possible to get closer to an intensity which is proportional only to the current magnetic fields HmA and HmB. Therefore, by measuring an output voltage Vout and computing the value of the compensating current Id in view of the relation with the known resistor RL in the compensating current detector S, the value of the current magnetic fields HmA and HmB can be calculated with more precision and the magnitude of the current Im to be detected can be estimated with high precision as a result. 
     Next, the method of manufacturing the current sensor  10  will be explained with reference to  FIGS. 5 through 8 . 
     Here, first, as shown in  FIG. 5 , a plurality of MR elements  3  are formed on a face  4 S of a substrate  4 Z (such as a silicon wafer, etc.) which has a thickness of the order of 2 mm. The back of the substrate  4 Z is then ground until it becomes a thickness of, for example 100 μm as shown in  FIG. 6 . Then a magnetic sheet  5 Z is stuck on the back of the substrate  4 Z by applying adhesives thereto, for forming a laminated product  20  ( FIG. 7 ). The magnetization direction of the magnetic sheet  5 Z is set (magnetizing) under room temperature and then the magnetic field intensity applied to the MR elements  3  is adjusted by grinding the back of the magnetic sheet  5 Z as necessary. Subsequently, as shown in  FIG. 8 , a plurality of magnetic sensors  7  are formed by cutting the laminated product  20  to divide into pieces so that each piece includes an MR element  3 . Finally, two magnetic sensors  7  are mounted on a circuit board  8  and then arranged them in the position corresponding to the straight-line portions  2 A and  2 B of the conductor  2 , thereby completing the current sensor  10  by using predetermined steps as described above. 
     As explained above, according to the current sensor  10  of the present embodiment, the MR elements  3 A and  3 B and magnetic sheets  6 A and  6 B, which is disposed along with the conductor line  2  used as the path of the current to be detected Im, are bonded with the substrates  4 A and  4 B in between so that the magnetic sheets  6 A and  6 B apply the bias magnetic fields Hb 1  and Hb 2 . As a result, sufficient stabilization can be attained in the detecting operation while using a space in a more effective way, compared with a case where permanent magnets or coils are arranged on both sides of an MR element. Namely, since the magnetic sheets  6 A and  6 B can be arranged in a nearer position to each of the MR elements  3 A and  3 B, even with a relatively small dimension made of the same materials, bias magnetic fields Hb 1  and Hb 2  can be secured sufficiently for a stable detecting operation. What is more, in addition to the advantage that bulk formation is easy because of the simple configuration, even if the directions of the magnetization directions J 11 A and J 11 B in the MR elements  3 A and  3 B are not equal to each other, the bias magnetic field Hb 1  and Hb 2  can be easily applied to a suitable direction respectively corresponding to each of the magnetization directions J 11 A and J 11 B. 
     In addition, the magnetic sheets  6 A and  6 B are set in such a way as applying the bias magnetic fields Hb 1  and Hb 2  in the same direction as the magnetization directions J 13 A and J 13 B under no external magnetic field H to the MR elements  3 A and  3 B. In this manner, uniaxial anisotropy of the free layer  13  is increased, and the stabilization of magnetic field detecting operation in the MR elements  3 A and  3 B can be efficiently attained. Here, since shape anisotropy is not used, the shape of the MR elements  3 A and  3 B can be decided in more flexible way, and since they do not have to be divided into two or more pieces, a compact configuration can be realized. 
     Further, since the V-shaped conductor line  2  including the straight-line portions  2 A and the straight-line portion  2 B which are orthogonal to each other is employed, a more compact whole configuration can be realized compared with a case where the U-shaped conductor line including a pair of parallel straight-line portions is used. 
     Thus, according to the current sensor  10  of the present embodiment, measurement of the current to be detected Im can be performed with high precision and full stability while realizing a more compact configuration. 
     In addition, the current sensor  10  includes: the MR elements  3 A and  3 B disposed along with the conductor line  2  while mutually connected in parallel so that the resistances R 1  and R 2  can show mutually opposite directional changes by the current magnetic fields HmA and HmB generated by the current to be detected Im flowing through the conductor line  2 ; the constant current source CG 1  connected in series to the MR element  3 A in the third junction point P 3 ; and the constant current source CG 2  connected in series to the MR element  3 B in the fourth junction point P 4 , while the constant current source CG 1  and the constant current source CG 2  are connected in the second junction point P 2 , and the current to be detected Im is detected based on the potential difference V 0  between the third junction point P 3  and the fourth junction point P 4  produced when voltage is applied between the first junction point P 1  and the second junction point P 2 . In this way, the adjustment of an offset value in a zero-magnetic field can become more simple than a case where four magnetoresistive elements are used, and sensitivity of the MR elements  3 A and  3 B to be used can become higher. Further, a stabilized current can be supplied equally to both of the MR elements  3 A and  3 B. Therefore, even if the current to be detected Im is weak, its current magnetic fields HmA and HmB can be detected with high sensitivity and high precision. It is to be noted that a balance adjustment including the MR elements  3 A and  3 B is needed because of the existence of the constant current sources CG 1  and CG 2 . However, since it is electrically controllable, the balance adjustment in the foregoing case is easier than a case where four magnetoresistive elements are used. 
     In particular, the current sensor  10  further has the compensating current line C to which the compensating current Id is supplied based on a difference (difference in the voltage drops produced in each of the MR elements  3 A and  3 B) V 0  between the potential V 1  detected in the third junction point P 3  and the potential V 2  detected in the fourth junction point P 4  so that the compensating current Id applies the compensating current magnetic fields Hd having a direction opposite to the current magnetic fields HmA and HmB to the MR elements  3 A and  3 B, respectively. In this way, changes of the output voltage Vout caused by the discrepancies of the characteristics of the MR element  3 A and  3 B, dispersion of the connection resistances in the circuit or temperature distribution, etc. can be cancelled, and detection of the current magnetic fields HmA and HmB can be attained with higher sensitivity and higher precision. 
     In addition, the MR elements  3 A and  3 B, the constant current sources CG 1  and CG 2 , and the compensating current line C are provided so as to be axisymmetrically arranged with respect to the central line CL in the current sensor  10 , while the pair of straight-line portions  2 A and  2 B in the conductor line  2  are arranged axisymmetrically with respect to the central line CL in a plane parallel to the plane including the MR elements  3 A and  3 B. In this manner, the temperature distribution thereof can become symmetrical with respect to the central line CL. Therefore, the zero-point drift depending on the temperature distribution can be controlled. 
     &lt;Modification 1&gt; 
     Herein, a modification of the current sensor according to the present embodiment is explained with reference to  FIG. 9 . 
     As shown in  FIGS. 4  A and B, the current sensor according to the foregoing first embodiment is configured so that the magnetization directions J 13 A and J 13 B of the free layer  13  are orthogonal to the magnetization directions J 11 A and J 11 B of the pinned layer  11  when no external magnetic field H is applied. However in the present invention, as shown in the modifications shown in  FIGS. 9A and 9B , the current sensor may also be configured in such a way that magnetization directions J 13 A 0  and J 13 B 0  of the free layer  13  are parallel to the magnetization directions J 11 A and J 11 B of the pinned layer  11 , respectively when no external magnetic field H is applied. Specifically, in  FIG. 9A , the magnetization direction J 11 A and the magnetization direction J 13 A 0  of the MR element  3 A are both in the +X 3  direction orthogonal to the synthetic magnetic field Hm 1 , and the magnetization direction J 11 B and the magnetization direction J 13 B 0  of the MR element  3 B are both in the +Y 3  direction orthogonal to the synthetic magnetic field Hm 2 . In  FIG. 9B , the magnetization direction J 11 A and the magnetization direction J 13 A 0  of the MR element  3 A are both in the +X 3  direction orthogonal to the synthetic magnetic field Hm 1 , and the magnetization direction J 11 B and the magnetization direction J 13 B 0  of the MR element  3 B are both in the −Y 3  direction orthogonal to the synthetic magnetic field Hm 2 . However, in these cases, it is preferable that the bias magnetic fields Hb 1  and Hb 2  are applied in an oblique direction to the magnetization directions J 11 A and J 11 B. Namely, it is desirable to apply the bias magnetic fields Hb 1  and Hb 2  which have both of a parallel component parallel to the magnetization directions J 11 A and J 11 B and a perpendicular component orthogonal to each of the parallel components. Specifically, as for  FIG. 9  A, it is preferred that a bias magnetic field Hb 1  having the −Y 3  direction is applied to the MR element  3 A, and a bias magnetic field Hb 2  having the +Y 2  direction is applied to the MR element  3 B. As for  FIG. 9B , it is preferred that a bias magnetic field Hb 1  having the −Y 3  direction is applied to the MR element  3 A, and a bias magnetic field Hb 2  having the +X 3  direction is applied to the MR element  3 B. Herein, the parallel components of the bias magnetic fields Hb 1  and Hb 2 , corresponding to an anisotropic magnetic field, increase the uniaxial anisotropy of the free layers  13  as described in the foregoing first embodiment, consequently contributing to stabilization of the magnetic field detecting operation in the MR elements  3 A and  3 B. On the other hand, the perpendicular components orthogonal to the parallel components are needed because of the following reasons. 
     If the external magnetic field H is applied in the direction orthogonal to the magnetization directions J 11 A and J 11 B respectively to the magnetoresistive elements  3 A and  3 B that are set so that the magnetization directions J 13 A 0 , J 13 B 0  and the magnetization directions J 11 A and J 11 B are mutually parallel in an unloaded state characteristic as shown in  FIG. 10  will be obtained.  FIG. 10  shows a relation between the external magnetic field H and a resistance change ratio ΔR/R letting the external magnetic field H in the +Y direction be a positive external magnetic field H. As shown herein, the relation therebetween is expressed by one curve C 1  in which the value becomes the minimum (ΔR/R=0) when the external magnetic field H=0 and which hardly shows hysteresis. In this case, since 1/f noise caused by hysteresis is extremely small, highly-sensitive and stable sensing can be realized. However, as is clear from  FIG. 10 , a linear variation is not obtained around no external magnetic field H (H=0). For this reason, bias magnetic fields Hb 1  and Hb 2  having a perpendicular component orthogonal to the magnetization directions J 11 A and J 11 B are applied to the MR elements  3 A and  3 B in actually measuring the current magnetic fields HmA and HmB so that the magnetization directions J 13 A 0  and J 13 B 0  may be rotated, for example, by 45 degrees to become magnetization directions J 13 A 1  and J 13 B 1  ( FIGS. 9A and 9B ). In this manner, variation of the current magnetic fields HmA and HmB is detectable with sufficient precision in the linear areas L 1  and L 2  including bias points BP 1  and BP 2  as their midpoints, as indicated in  FIG. 10 . 
     It is to be noted that in the present modification, by applying the bias magnetic fields Hb 1  and Hb 2  in suitable directions, resistance R 1  of the MR element  3 A and resistance R 2  of the MR element  3 B shows a mutually opposite variation when current magnetic fields HmA and HmB is generated. Therefore, current to be detected Im can be measured by supplying a constant current of a mutually equal value to the MR elements  3 A and  3 B, and by detecting the difference in voltage drops produced in the MR elements  3 A and  3 B by the constant current. 
     Second Embodiment 
     A current sensor as a second embodiment according to the present invention will be explained next. Although in the foregoing first embodiment is explained the case in which the conductor line  2  of V-shaped configuration in plan view is used, in the present embodiment is explained a case in which a straight-line shaped conductor line  21  is employed. 
     Since the current sensor of the present embodiment has the same configuration as that of the above-mentioned first embodiment substantially except for the conductor line  21 , here is explained the relation among the magnetization directions J 11  and J 13  of the GMR films in the MR elements  3 A and  3 B, the bias magnetic field Hb, and the current magnetic field Hm with reference to  FIGS. 11A and 11B .  FIGS. 11A and 11B  are conceptual diagrams about the relation among the current direction, the magnetic field direction, and the magnetization direction according to the current sensor of the present embodiment. Here, a current to be detected Im is flowing along the extending direction of the conductor line  21  and the magnetization directions J 11  of the pinned layers  11  are pinned in the direction orthogonal to the current to be detected Im, respectively. On the other hand, the magnetization directions J 13  of the free layers  13  are either parallel or antiparallel to the flowing direction of the current to be detected Im when no external magnetic field H is applied. Namely, when no external magnetic field H is applied, the magnetization directions J 13  of the free layers  13  are orthogonal to the magnetization directions J 11  of the pinned layers  11 . Therefore, when the current magnetic fields Hm is generated, the magnetization directions J 13  come near to a parallel state (low resistance) or antiparallel state (high resistance) with respect to the magnetization directions J 11 . Here, the MR element  3 A and MR element  3 B are set so that their resistances R 1  and R 2  develop an opposite-directional variation each other according to the current magnetic field Hm. Specifically, as shown in  FIG. 11A , the MR element  3 A has the magnetization direction J 11 A in the −y direction and the magnetization direction J 13 A in the −x direction when no external magnetic field H is applied for example. On the other hand, the MR element  3 B has the magnetization direction J 11 B in the +y direction and the magnetization direction J 13 B in the +x direction when no external magnetic field H is applied. In this case, when the current to be detected Im flows as indicated by arrows to generate the current magnetic field Hm, the magnetization direction J 13 A is rotated counterclockwise (on the drawing sheet) to be parallel to the magnetization direction J 11 A, while the magnetization direction J 13 B is rotated clockwise (on the drawing sheet) to be antiparallel to the magnetization direction J 11 B. Or as shown in  FIG. 11B , the magnetization direction J 11 A may be in the −y direction while the magnetization direction J 13 A when no external magnetic field H is applied may be in the +x direction in the MR element  3 A, while the magnetization direction J 11 B may be in the +y direction and the magnetization direction J 13 B when no external magnetic field H is applied may be in the +x direction. In this case, when current to be detected Im flows in the direction of arrows to generate the current magnetic field Hm, the magnetization direction J 13 A is rotated clockwise to come to a state parallel to the magnetization direction J 11 A, while the magnetization direction J 13 B is rotated clockwise to come to a state of antiparallel to the magnetization direction J 11 B. 
     In any case, the bias magnetic fields Hb 1  and Hb 2  are set so as to be in the same direction with the magnetization directions J 13 A and J 13 B when no external magnetic field H is applied, respectively. Therefore, the bias magnetic fields Hb 1  and Hb 2  increase the uniaxial anisotropy of the free layer  13  as corresponding to an anisotropic magnetic field, consequently contributing to stabilization of the magnetic field detecting operation in the MR elements  3 A and  3 B. In particular, since the current sensor of the present embodiment employs the straight-line conductor line  21 , the current magnetic field Hm of a generally uniformed quality can be generated without producing an interaction like in the case of the U-shaped or V-shaped conductor lines. For this reason, the current magnetic field Hm extends efficiently to the MR elements  3 A and  3 B, and current measurement can be made with higher precision. If the magnetization directions J 11 A and J 11 B are arranged so as to be orthogonal to the flowing direction of the current to be detected Im (namely, the extending direction of the conductor line  21 ), the highest sensitivity measurement can be attained. Therefore, when the V-shaped conductor line  2  is used (the first embodiment), the magnetic sensors  7 A and  7 B are leaned along to the extending direction of the conductor line  2  but it is not necessary in the present embodiment, and the magnetic sensors  7 A and  7 B can be installed simply. 
     Further, in the current sensor of the present embodiment, since the conductor line  21  has a straight-line configuration, two-dimensional spread can be prevented compared with the above-mentioned first embodiment using the V-shaped conductor line  2 , the whole configuration can be made more compact. However, since the magnetization direction J 11 A and the magnetization direction J 11 B are in antiparallel mutually as is clear from  FIGS. 11A and 11B , the interval between the MR element  3 A and the MR element  3 B is needed to be larger than the interval W 3  shown in  FIGS. 4A and 4B  in order to avoid interaction of the bias magnetic field Hb 1  and the bias magnetic field Hb 2 . 
     As described above, according to the present embodiment, since the conductor line  21  of straight-line configuration in plan view is employed and the element substrates  5 A and  5 B including the MR elements  3 A and  3 B are disposed along with the conductor line  21 , the interval between the MR elements  3 A and  3 B can be made smaller than the case of the U-shaped conductor line while capable of maintaining the dimension of the MR elements  3 A and  3 B as they are. Further, since the straight-line conductor line has no turning portion unlike the U-shaped conductor line, the dimension of the conductor line  21  can be made smaller. Therefore, a more compact whole configuration can be realized while maintaining the dimensions of the MR elements  3 A and  3 B. What is more, the error of measurement based on temperature difference between the MR elements  3 A and  3 B can be reduced, and current measurement with sufficient precision and stability can be realized. 
     &lt;Modification 2&gt; 
     Subsequently, a modification in the current sensor of the present embodiment will be explained with reference to  FIGS. 12A and 12B . According to the above-mentioned second embodiment, as shown in  FIGS. 11A and 11B , the current sensor is configured in such a way that the magnetization directions J 13 A and J 13 B of the free layers  13  and the magnetization directions J 11 A and J 11 B of the pinned layers  11  are orthogonal to each other when no external magnetic field H is applied. However, like the modification shown in  FIGS. 12A and 12B , the current sensor may be configured in such a way that the magnetization directions J 13 A 0 , J 13 B 0  of the free layers  13  and the magnetization directions J 11 A and J 11 B of the pinned layers  11  are parallel to each other when no external magnetic field H is applied. Specifically, as shown in  FIG. 12A , the magnetization direction J 11 A and the magnetization direction J 13 A 0  of the MR element  3 A are both in the −x direction orthogonal to the current magnetic field Hm, and the magnetization direction J 11 B and the magnetization direction J 13 B 0  of the MR element  3 B are both in the +x direction orthogonal to the current magnetic field Hm. In  FIG. 12B , all of the magnetization direction J 11 A and the magnetization direction J 13 A 0  of the MR element  3 A and the magnetization direction J 11 B and the magnetization direction J 13 B 0  of the MR element  3 B are in the +x direction. However, in these cases, it is desirable to apply the bias magnetic fields Hb 1  and Hb 2  in an oblique direction to the magnetization directions J 11 A and J 11 B. Namely, it is desirable to apply the bias magnetic fields Hb 1  and Hb 2  having both of a parallel component parallel to the magnetization directions J 11 A or J 11 B and a perpendicular component orthogonal to each of the parallel components. In this manner, the free layers  13  come to develop magnetization directions J 13 A 1  and J 13 B 1  inclined at 45 degrees to the magnetization directions J 11 A and J 11 B, for example. As a result, variation of the current magnetic fields Hm is detectable with sufficient precision in the linear areas L 1  and L 2  including the bias points BP 1  and BP 2  as their midpoints, as shown in  FIG. 10 . 
     Third Embodiment 
     Next, a current sensor as a third embodiment according to the present invention will be explained. In the first embodiment as described above is explained the case of arranging the two MR elements  3 A and  3 B on the straight-line portions  2 A and  2 B of the conductor line  2 . On the other hand, in the present embodiment, four MR elements  3 A- 3 D are arranged on one conductor line  2 . Explanation will be made hereinbelow with reference to  FIG. 13 . Since its configuration is substantially similar to that of the above-mentioned first embodiment except for the point that the four MR elements  3 A- 3 D are arranged, descriptions will be omitted suitably according to circumstances. 
       FIG. 13  is a conceptual diagram showing the relation among the current direction, magnetic field direction, and magnetization direction of the current sensor according to the present embodiment. As shown in  FIG. 13 , in the current sensor of the present embodiment, the straight-line portion  2 A is provided with the MR element  3 A and the MR element  3 C along with the extending direction of the straight-line portion  2 A (in the x-axis direction). On the other hand, the straight-line portion  2 B is provided with the MR element  3 B and the MR element  3 D along with the extending direction of the straight-line portion  2 B (in the y-axis direction). It is to be noted that each of the MR elements  3 A- 3 D is disposed on a substrate (not shown) respectively to form an element substrate. Further, a magnetic sheet (not shown) is provided between the substrate and the conductor line  2  so as to apply bias magnetic fields Hb 1 -Hb 4  to the MR elements  3 A- 3 D, respectively. 
     For example, supposing a current to be detected Im flows along the extending direction of the conductor line  2  as shown by arrows, a current magnetic field HmA is generated around the straight-line portion  2 A, and a current magnetic field HmB is generated around the straight-line portion  2 B. In this case, as indicated by vectors, a synthetic magnetic field Hm 1 , which is a resultant force of a magnetic field component HmA 1  in the +Y direction caused by the current magnetic field HmA and a magnetic field component HmB 2  in the +X direction caused by the current magnetic field HmB, is applied to the MR element  3 A. Similarly, a synthetic magnetic field Hm 2 , which is a resultant force of a magnetic field component HmA 2  in the +Y direction caused by the current magnetic field HmA and a magnetic field component HmB 1  in the +X direction caused by the current magnetic field HmB, is applied to the MR element  3 B. To the MR element  3 C, a synthetic magnetic field Hm 3 , which is a resultant force of the magnetic field component HmA 1  in the +Y direction caused by the current magnetic field HmA and a magnetic field component HmB 3  in the +X direction caused by the current magnetic field HmB, is applied. To the MR element  3 D, a synthetic magnetic field Hm 4 , which is a resultant force of a magnetic field component HmA 3  in the +Y direction caused by the current magnetic field HmA and the magnetic field component HmB 1  in the +X direction caused by the current magnetic field HmB, is applied. Here, since the MR elements  3 C and  3 D are located in the position far from the center position CL compared with the MR elements  3 A and  3 B, they are less influenced by the interaction of the current magnetic field HmA and the current magnetic field HmB than the MR elements  3 A and  3 B. Namely, the magnetic field component Hm 3  is smaller than the magnetic field component Hm 2  (Hm 3 &lt;Hm 2 ), and the magnetic field component HmA 3  is smaller than the magnetic field component HmA 2  (HmA 3 &lt;HmA 2 ). Therefore, the synthetic magnetic field Hm 3  has a direction nearer to the +Y direction than the synthetic magnetic field Hm 1 , and the synthetic magnetic field Hm 4  has a direction nearer to the +X direction than the synthetic magnetic field Hm 2 . 
     As for the MR elements  3 A and  3 C, the magnetization directions J 11 A and J 11 C of the pinned layers  11  are pinned in a direction so as to be parallel to the synthetic magnetic fields Hm 1  and Hm 3 , respectively. As for the MR elements  3 B and  3 D, on the other hand, the magnetization directions J 11 B and J 11 D of the pinned layers  11  are pinned so as to be antiparallel to the synthetic magnetic fields Hm 2  and Hm 4 , respectively. When no external magnetic field H is applied, the magnetization directions J 13 A and J 13 C of the free layer  13  are in a state of slightly tilting in the −Y direction from +X direction so as to be orthogonal to the synthetic magnetic fields Hm 1  and Hm 3 , respectively. The magnetization directions J 13 B and J 13 D are in the state of slightly tilting in the −X direction from +Y direction so as to be orthogonal to the synthetic magnetic fields Hm 2  and Hm 4 , respectively. Namely, when no external magnetic field H is applied, the magnetization directions J 13 A-J 13 D are in a state of being orthogonal to the magnetization directions J 11 A-J 13 D, respectively. Therefore, if a current to be detected Im is supplied to the conductor line  2  to generate the synthetic magnetic fields Hm 1 -Hm 4 , the magnetization directions J 13 A and J 13 C approach a state of being parallel (low resistance) to the magnetization directions J 11 A and J 11 C, respectively, and the magnetization directions J 13 B and J 13 D approach a state of being antiparallel (high resistance) to the magnetization directions J 11 B and J 11 D, respectively. Therefore, resistances R 1  and R 3  of the MR elements  3 A and  3 C are reduced, and resistances R 2  and R 4  of the MR elements  3 B and  3 D are increased. 
     As shown in  FIG. 14 , in the current sensor of the present embodiment, ends of the MR elements  3 A and  3 B are connected each other in a first junction point P 1 , ends of the MR elements  3 C and  3 D are connected each other in a second junction point P 2 , the other end of the MR element  3 A and the other end of the MR element  3 D are connected each other in a third junction point P 3 , and the other end of the MR element  3 B and the other end of the MR element  3 C are connected each other in a fourth junction point P 4 . Consequently, a bridge circuit is configured. It is to be noted that  FIG. 14  expresses a circuit configuration in the current sensor of the present embodiment. 
     Hereafter, a method of measuring the current magnetic fields H 1 A and HmB generated by the current to be detected Im will be explained with reference to  FIG. 14 . 
     In  FIG. 14 , a state where the external magnetic field H is not applied is considered first. Each resistance of the MR elements  3 A- 3 D in sending a read current i 0  is expressed by r 1 -r 4 . The read current i 0  flowing from a power supply Vcc is split into two, a read current i 1  and a read current i 2 , in the second junction point P 2 . Then, the read current i 1  which passed the MR element  3 C and the MR element  3 B, and the read current i 2  which passed the MR element  3 D and the MR element  3 A join in the first junction point P 1 . In this case, potential difference V between the second junction point P 2  and the first junction point P 1  is expressed as follows: 
                         V   =         i   ⁢           ⁢   1   ×   r   ⁢           ⁢   3     +     i   ⁢           ⁢   1   ×   r   ⁢           ⁢   2       =       i   ⁢           ⁢   2   ×   r   ⁢           ⁢   4     +     i   ⁢           ⁢   2   ×   r   ⁢           ⁢   1                     =       i   ⁢           ⁢   1   ×     (       r   ⁢           ⁢   3     +     r   ⁢           ⁢   2       )       =     i   ⁢           ⁢   2   ×     (       r   ⁢           ⁢   4     +     r   ⁢           ⁢   1       )                       (   4   )               
Potential V 3  in the fourth junction point P 4  and potential V 4  in the third junction point P 3  can be expressed as follows:
   V 3 =V−i 1 ×r 3   V 4 =V−i 2 ×r 4, 
Therefore, potential difference V 0  of the fourth junction point P 4  and the third junction point P 3  is expressed as follows:
 
                           V   ⁢           ⁢   0     =       V   ⁢           ⁢   4     -     V   ⁢           ⁢   3                   =       (     V   -     i   ⁢           ⁢   2   ×   r   ⁢           ⁢   4       )     -     (     V   -     i   ⁢           ⁢   1   ×   r   ⁢           ⁢   3       )                   =       i   ⁢           ⁢   1   ×   r   ⁢           ⁢   3     -     i   ⁢           ⁢   2   ×   r   ⁢           ⁢   4                     (   5   )               
Here, it can be rewritten as follows based on the equation (4):
 
                           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                   (   6   )               
In this bridge circuit, resistance variation amount can be obtained by measuring the potential difference V 0  between the fourth junction point P 4  and the third junction point P 3  as expressed with the above-mentioned equation (6) when the current magnetic fields HmA and HmB which are an external magnetic field is applied. Here, supposing the resistances R 1 -R 4  are changed by the variation amount of ΔR 1 -ΔR 4 , respectively when the current magnetic fields HmA and HmB are applied, that is, letting each of the resistance values R 1 -R 4  after application of the current magnetic fields HmA and HmB be
   R 1 =r 1 +ΔR 1   R 2 =r 2 +ΔR 2   R 3 =r 3 +ΔR 3   R 4 =r 4 +ΔR 4, 
the potential difference V 0  at the time of the application of the current magnetic fields HmA and HmB can be expressed as follows based on the equation (6):
   V 0={( r 3 +ΔR 3)/( r 3 +ΔR 3 +r 2 +ΔR 2)−( r 4 +ΔR 4)/( r 4 +ΔR 4 +r 1 +ΔR 1)}× V   (7) 
Since the current sensor is configured so as to show a mutually opposite-directional variation between the resistances R 1  and R 3  of the MR elements  3 A and  3 C and the resistances R 2  and R 4  of the MR elements  3 B and  3 D the values of variation ΔR 4  and variation ΔR 1  cancel each other, and variation ΔR 3  and variation ΔR 2  cancel each other. For this reason, in comparing values before/after the application of the current magnetic fields HmA and HmB, the denominator values in each term are scarcely increased in the equation (7). On the other hand, as for the numerator value in each term, increase or decrease appears since variation ΔR 3  and variation ΔR 1  have mutually opposite positive/negative signs without fail.
 
     Supposing that all the MR elements  3 A- 3 D have the same characteristics completely, that is, letting r 1 =r 2 =r 3 =r 4 =R and ΔR 1 =−ΔR 2 =ΔR 3 =−ΔR 4 =ΔR, the equation (7) is given as follows: 
     
       
         
           
             
               
                 
                   
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     Thus, if the MR elements  3 A- 3 D whose characteristic values, such as ΔR/R, are known are used, the intensity of the current magnetic fields HmA and HmB can be measured and consequently, the magnitude of current to be detected Im generating the current magnetic fields HmA and HmB can be estimated. In particular, since sensing is performed using the four MR elements  3 A- 3 D, measurement with higher precision can be realized compared with a case where sensing is performed using only two MR elements  3 A and  3 B. 
     Although the case of using the conductor line  2  of V-shaped configuration in plan view is explained in the present embodiment, the present invention is not limited to this and it is also possible to arrange the four MR elements  3 A- 3 D along with the straight-line shaped conductor line  21  explained in the second embodiment for example. 
     EXAMPLE 
     Next, an example of the present invention will be explained hereinbelow. 
     In the present example, a sample was produced corresponding to the MR element  3 B in the above-mentioned second embodiment ( FIGS. 11A and 11B ), and distribution of the bias magnetic field produced by the magnetic sheet was investigated with regard to the sample. Herein, based on a micromagnetics simulation, a bias magnetic field Hx as a magnetic field component in the x-axis direction orthogonal to the magnetization direction of the pinned layer, and a bias magnetic field Hy as a magnetic field component in the y-axis direction parallel to the magnetization direction of the pinned layer were respectively calculated on the basis of the magnetic sheet face. The result is shown in  FIGS. 15-17 . It is to be noted that the magnetic sheet was magnetized in the x-axis direction to have a function of securing the operation stability of the MR elements by applying the bias magnetic field in the direction of x (orthogonal to the magnetization direction of the pinned layer) to the MR elements. The simulation was performed under the condition that the x directional dimension of the magnetic sheet was 0.37 mm and the y directional dimension of the magnetic sheet was 0.26 mm. Only an area of 0.2 mm (in the x-axis direction)×0.2 mm (in the y-axis direction) including the center positions thereof is shown in  FIGS. 15-17 . 
       FIG. 15  shows a distribution of the bias magnetic field Hx in the y-axis direction. Here, the horizontal coordinate represents positions (mm) in the y-axis direction passing through the center position of the magnetic sheet, and the vertical coordinate expresses the bias magnetic field Hx. Here, three thickness levels of magnetic sheets (75 μm, 85 μm, and 95 μm) were prepared. As shown in  FIG. 15 , every thickness level shows a similar distribution state of gentle convex shape having the center position  0  as its peak for indicating the intensity of the bias magnetic field Hx. It was also confirmed that the intensity of the bias magnetic field Hx could be increased by enlarging the thickness, and the intensity of the bias magnetic field Hx could be reduced by reducing the thickness. 
       FIG. 16  is a characteristic diagram showing a distribution of bias magnetic field Hx developed by the magnetic sheet which has a thickness of 85 μm, in the y-directional positions (mm) and in the x-directional positions (mm). In  FIG. 16 , the center position in each of the x axis and the y axis was set to the origin (zero point). As shown in  FIG. 16 , the distribution of the bias magnetic field Hx was a shape of curved surface within a range from 32×10 −4  [T] to 43×10 −4  [T], in which the cross-point of each of the center positions (namely, the zero points) in both of the x-axis direction and the y-axis direction of the magnetic sheet was the apex. Namely, it proved that the biggest bias magnetic field Hx was obtained in the center position of the magnetic sheet. 
       FIG. 17  shows a distribution of bias magnetic field Hy in the y axis direction and the x axis direction. Here, the center position in each of the x axis and the y axis directions was set as the origin (zero point) similar to the bias magnetic field Hx. Here, in order to secure the operational stability of the MR elements, it is desirable that intensity of the bias magnetic field Hy is zero. As shown in  FIG. 17 , it proved that the bias magnetic field Hy was zero in the center position of the magnetic sheet, but the absolute value of the bias magnetic field Hy was slightly increasing as going to the periphery. However, the absolute value of the bias magnetic field Hy was a very small value less than 10×10 −4  [T], with which level no practical problem would occur. It is to be noted that in  FIG. 17 , the bias magnetic field Hy in the positive area (from 0 mm to −0.1 mm) and the bias magnetic field Hy in the negative area (from 0 mm to 0.1 mm) of the x axis direction show the mutually opposite positive/negative signs. The phenomenon means that the bias magnetic field Hy has a mutually opposite direction on both sides of the center position of the x axis on the magnetic sheet. Similarly, the bias magnetic field Hy in the positive area (from 0 mm to −0.1 mm) and the bias magnetic field Hy in the negative area (from 0 mm to 0.1 mm) of the y axis direction show the mutually opposite positive/negative signs. The phenomenon means that the bias magnetic field Hy has a mutually opposite direction on both sides of the center position of the y axis on the magnetic sheet. 
     As a result of  FIGS. 15-17 , it proved that a bias magnetic field component (the bias magnetic field Hx) in the originally necessary direction could be applied most efficiently if the MR element was arranged in the center position of the magnetic sheet, and what is more, the influence of the bias magnetic field component (bias magnetic field Hy) in the unnecessary direction could be reduced. It was also confirmed that the bias magnetic field of a desired intensity could be given to the magnetoresistive element by selecting a thickness of the magnetic sheet. 
     As mentioned above, although the present invention has been explained with reference to some embodiments and modifications, the present invention is not limited to the above-mentioned embodiments etc. and various kinds of modifications are possible. For example, in the above-mentioned embodiments, there is explained a case of V-shaped conductor line having two straight-line portions orthogonal to each other, but V-shaped conductor lines are not limited to this. Namely, if a conductor line having two straight-line portions has a mutual angle of more than zero and less than 180 degrees, the conductor line corresponds to “the V-shaped conductor line” according to the present invention. Further, a conductor line  22  including a semicircle as shown in  FIG. 18 , and a conductor line  23  including a part of an ellipse as shown in  FIG. 19  are also included in the concept of the “V-shaped conductor line” of the present invention. Still more, a conductor line  24  including only of straight-line portions as shown in  FIG. 20  is also included in the “V-shaped conductor line” of the present invention. 
     Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.