Current sensor

Abstract

To suppress a magnetic field voltage.SOLUTION: A current sensor comprises: a conductor 24 having a shape extending from one side to the other side along a reference line L1, bent on the other side to cross the reference line L1, and extending from the other side to the one side along the reference line L1, in which conductor a current to be measured flows; a galvanomagnetic transducer 34 located in a gap region enclosed by the conductor in a top view and having an active layer 34a on a substrate that is formed to be substantially cross-shaped symmetrical to a reference line L2; and a package for encapsulating the conductor and the galvanomagnetic transducer. The reference line L1 and the reference line L2 are appropriately parallel, or a distance d3 between the reference line L1 and the reference line L2 is 1 / 2 or less of the size of the substrate. It is thereby possible to suppress a magnetic field voltage generated by stresses that the galvanomagnetic transducer receives via the package material from its vicinity.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a current sensor. [Background technology]

[0002] There is a known current sensor that measures the amount of current by passing a current to be measured through a conductor and detecting the magnetic field generated around the conductor using a magnetoelectric conversion element arranged in parallel with the conductor (see, for example, Patent Document 1). In order to improve the sensitivity of such a current sensor, it is desirable to place the magnetoelectric conversion element close to the conductor within the gap of the conductor. However, if the position of the magnetoelectric conversion element is shifted from the center of the gap, there is a risk that the zero magnetic field voltage will increase. Patent Document 1: JP 2015-045634 A Summary of the Invention [Means for solving the problem]

[0003] In one aspect of the present invention, there is provided a current sensor comprising: a conductor having a shape extending from one side to the other side along a first reference line, bending at the other side and intersecting the first reference line, and extending from the other side to the one side along the first reference line, wherein a current to be measured flows through the conductor; a magneto-electric conversion element arranged in a gap region surrounded by the conductor in a top view, the magneto-electric conversion element having an active layer formed in an approximately cross shape symmetrical with respect to a second reference line on a substrate; and a package that seals the conductor and the magneto-electric conversion element, wherein the first reference line and the second reference line are approximately parallel or the distance between the first reference line and the second reference line is less than half the size of the substrate.

[0004] The above summary of the invention does not list all of the features of the present invention. Also, subcombinations of these features may also be inventions. [Brief description of the drawings]

[0005] [Figure 1A] 3 shows an internal configuration of the current sensor as viewed from above. [Figure 1B] 3 shows the internal configuration of the current sensor as viewed from the side. [Diagram 2] The conductor configuration and the arrangement of magnetoelectric conversion elements are shown. [Figure 3A] 1 shows a top view of the conductor configuration and the arrangement of magnetoelectric conversion elements in a simulation model. [Figure 3B] 1 shows a side view of the conductor configuration and the arrangement of magnetoelectric conversion elements in a simulation model. [Figure 3C] Simulation parameters are shown. [Figure 4] The results of an analysis of the strength distribution of the Z-direction magnetic field generated around the conductor are shown below. [Figure 5A] A hard sphere model for applying local stress (normal stress in the X-axis direction σx) to a magnetoelectric conversion element is shown. [Figure 5B] A hard sphere model for applying local stress (normal stress σy in the Y-axis direction) to a magnetoelectric conversion element is shown. [Figure 5C] A hard sphere model for applying local stress (XY-direction shear stress Txy) to a magnetoelectric conversion element is shown. [Figure 6] An equivalent bridge circuit including four regions of magnetoelectric transducers and four resistor arms is shown. [Figure 7] The figure shows the rotation of the active layer in the magnetoelectric transducer and the positional relationship between the four regions. [Figure 8] 1 shows the analysis results of the zero magnetic field voltage generated in the magnetoelectric conversion element versus the distance of the hard sphere from the center of the magnetoelectric conversion element. [Figure 9] The analysis results of the zero magnetic field voltage generated in the magnetoelectric conversion element due to the shear stress Txy in the XY direction versus the distance of the hard sphere from the gap symmetry line are shown. [Figure 10A] 1 shows an example of the stress distribution applied to the magnetoelectric conversion element when the Young's modulus of the molding resin is smaller than the Young's modulus of the magnetoelectric conversion element. [Figure 10B] 1 shows an example of the stress distribution applied to the magnetoelectric conversion element when the Young's modulus of the molding resin is approximately equal to the Young's modulus of the magnetoelectric conversion element. [Figure 11]13 shows the analysis results of the zero magnetic field voltage generated in a magnetoelectric transducer versus the Young's modulus of the substrate of the magnetoelectric transducer. [Figure 12] 1 shows the analysis results of the zero magnetic field voltage generated in the magnetoelectric conversion element versus the Young's modulus of the molding resin. [Figure 13] The graph shows the analysis results of the zero magnetic field voltage generated in the magnetoelectric conversion element versus the Young's modulus of the substrate of the magnetoelectric conversion element / Young's modulus of the mold resin. [Figure 14] 1 shows the analysis results of the zero magnetic field voltage generated in the magnetoelectric conversion element versus the rotation angle of the magnetoelectric conversion element. [Figure 15A] 13 shows the analysis results of the zero magnetic field voltage generated in the magnetoelectric transducer with respect to the distance from the gap symmetry line to the substrate center of the magnetoelectric transducer. [Figure 15B] The distance d3 and directions 1 to 3 in the simulation model are shown. [Figure 16A] 1 shows a state of a lead frame forming step in the manufacturing flow of the current sensor. [Figure 16B] 1 shows a state of a die bonding process in the manufacturing flow of the current sensor. [Figure 16C] 1 shows a state of a wire bonding process in the manufacturing flow of the current sensor. [Figure 16D] 1 shows a state of a molding process in the manufacturing flow of the current sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] The present invention will be described below through embodiments of the invention, but the following embodiments do not limit the scope of the invention according to the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention.

[0007] 1A and 1B show the internal structure of the current sensor 100 in a top view and a side view, respectively, through the package 9. Here, FIG. 1B shows a cross-sectional structure of the current sensor 100 with respect to a reference line BB in FIG. 1A. The up-down direction in FIG. 1A is the vertical direction, the left-right direction in FIG. 1A and FIG. 1B is the horizontal direction, and the up-down direction in FIG. 1B is the height direction. The current sensor 100 is a sensor that measures the amount of current by detecting a magnetic field generated around a conductor 24 when a current to be measured flows through the conductor 24 using a magnetoelectric conversion element 34, and in particular, suppresses a zero magnetic field voltage generated by applying a stress from the package 9 to the magnetoelectric conversion element 34. The current sensor 100 includes a package 9, a frame 10, a plurality of device terminals 17, an insulating member 18, a conductor 24, a magnetoelectric conversion element 34, and a signal processing device 44.

[0008] The package 9 is a member that seals and protects the components of the current sensor 100, including the conductor 24 and the magnetoelectric conversion element 34, except for two device terminals 15 and 16, a plurality of device terminals 17, and the respective terminal portions of the conductor 24, which are provided on the frame 10 described later. The package 9 is formed into a flat rectangular parallelepiped by molding using a sealing resin with excellent insulating properties, such as epoxy.

[0009] The frame 10 is a plate-like member that supports the signal processing device 44 and to which the insulating member 18 is fixed. The frame 10 is formed into a plate shape using, for example, a metal with high thermal conductivity in order to dissipate heat generated particularly by the signal processing device 44. The frame 10 has a main body 11, protrusions 12 and 14, and device terminals 15 and 16.

[0010] The main body 11 is a portion that supports the signal processing device 44. The main body 11 has, for example, a substantially rectangular shape large enough to support the signal processing device 44 in a plan view.

[0011] The protrusions 12 and 14 are portions to which the insulating member 18 is fixed. The protrusions 12 and 14 extend rightward from one end (i.e., the upper end in FIG. 1A) and the other end (i.e., the lower end in FIG. 1A) of one lateral side (i.e., the right side in FIG. 1A) of the main body 11, respectively.

[0012] The device terminals 15, 16 are terminal portions for outputting the detection result of the current under measurement output from the signal processing device 44 to an external device. The device terminals 15, 16 extend leftward from one end (i.e., the upper end in FIG. 1A) and the other end (i.e., the lower end in FIG. 1A) of the other lateral side (i.e., the left side in FIG. 1A) of the main body 11. The device terminals 15, 16 are bent downward at their ends by bending, and further bent horizontally at their tips, to form terminal portions 15a, 16a at their ends, respectively.

[0013] The frame 10 is sealed within the package 9 with terminal portions 15a, 16a of the device terminals 15, 16 protruding from the side surfaces of the package 9.

[0014] The device terminals 17, together with the device terminals 15 and 16, are secondary conductors for outputting the detection result of the current to be measured output from the signal processing device 44 to an external device. In addition, the device terminals 17, together with the device terminals 15 and 16, are used to provide power or operating parameters to the signal processing device 44. In this embodiment, as an example, three device terminals 17 are arranged at equal intervals between the device terminals 15 and 16 of the frame 10 with their longitudinal sides facing horizontally. The device terminals 17 are formed into a rectangular plate shape using metal, and, like the device terminals 15 and 16, their ends are bent downward by bending processing, and their tips are further bent horizontally to form terminal portions 17a at each end.

[0015] The insulating member 18 is a rectangular sheet or film that supports the magnetoelectric conversion element 34, and is made of a material with high dielectric strength, such as polyimide tape, for example. The insulating member 18 is held by the frame 10 with its longitudinal side oriented vertically and one end and the other end of the longitudinal side attached to the lower surfaces of the protruding parts 12, 14 of the frame 10, respectively, to bridge the gap between the protruding parts 12, 14.

[0016] The conductor 24 is a primary conductor that forms a current path through which the current to be measured flows. It has a shape that runs from a current terminal 24a provided on one side of the right side of the package 9 (i.e., the upper side in FIG. 1A) through the inside of the package 9, returns to the right side, and reaches a second current terminal 24e provided on the other side of the right side (i.e., the lower side in FIG. 1A). The conductor 24 is formed using a metal.

[0017] 2 shows the configuration of the conductor 24 and the arrangement of the magnetoelectric conversion element 34. The conductor 24 is formed substantially symmetrically with respect to a reference line (also called a gap symmetry line) L1 extending in the horizontal direction. Here, the direction parallel to the reference line L1 is the Y-axis direction, and the direction perpendicular thereto is the X-axis direction. The conductor 24 extends along the reference line L1 from the -Y side (the right side of the package 9 in FIG. 1A) to the +Y side (the center right of the package 9 in FIG. 1A), bends on the +Y side, intersects with the reference line L1, and has a substantially U-shaped shape extending from the +Y side to the -Y side along the reference line L1. The conductor 24 includes current terminals (also called simply terminal portions) 24a and 24e, body portions 24b and 24d, and a curved portion 24c.

[0018] The terminals 24a and 24e protrude from the right side of the package 9, and are bent at their ends downward by bending, and further bent at their tips horizontally to form terminal portions for inputting a current.

[0019] The body portions 24b and 24d are portions that connect the terminal portions 24a and 24e to the curved portion 24c. As an example, the body portions 24b and 24d are formed in a rectangular shape, and the two terminal portions 24a and 24e are connected to the right sides of the body portions 24b and 24d at a distance from each other, and the legs of the curved portion 24c are connected to the left sides of the body portions 24b and 24d.

[0020] The curved portion 24c has two legs and a connecting portion connecting these two legs. The two legs extend along the reference lines L11 and L12, respectively, and have a rectangular shape with a width smaller than that of the body portions 24b and 24d. Here, the reference lines L11 and L12 are parallel to the reference line L1, and are separated by a distance W on the ±X side from the reference line L1. The connecting portion connects to the +Y ends of the two legs and extends in the X-axis direction. Here, the connecting portion may extend from the leg on the +X side to the leg on the -X side, and may further extend beyond this to the -X side to form the protruding side 24c0. Here, the distance 2W between the two reference lines L11 and L12 (and the distance in the X-axis direction between the two legs) is greater than the width w of the magnetoelectric conversion element 34. The connecting portion may be curved into a substantially U-shape. The conductor 24 has a shape that is line-symmetric or approximately line-symmetric (i.e., line-symmetric within the range of manufacturing tolerance) with respect to the reference line L1 in the region between the reference lines L11 and L12. As a result, the conductor 24 has a shape that is line-symmetric or approximately line-symmetric (i.e., line-symmetric within the range of manufacturing tolerance) with respect to the reference line L1 at least within a distance from the reference line L1 that is equal to the size (w) of the substrate of the magneto-electric conversion element 34.

[0021] Here, the curved portion 24c of the conductor 24 is raised relative to the body portions 24b, 24d by providing a step in the height direction by step processing (e.g., half-punching, etching, forming, coining, etc.). As a result, the bottom surface of the curved portion 24c is higher than the upper surface of the insulating member 18 attached to the bottom surfaces of the protruding portions 12, 14 of the frame 10, and the primary conductor including the conductor 24 is separated from the insulating member 18 connected to the secondary conductor including the device terminals 15, 16, 17, thereby obtaining a high dielectric strength voltage between the primary conductor and the secondary conductor in the package 9.

[0022] The conductor 24 is sealed within the package 9 with the bent portion 24c disposed between the protruding portions 12 and 14 of the frame 10 and the tips of the terminal portions 24a and 24e protruding from the right side of the package 9.

[0023] The magnetoelectric conversion element 34 is a sensor disposed in a gap region surrounded by the conductor 24 in top view, and detects a magnetic field generated by a current to be measured that is passed through the conductor 24. The magnetoelectric conversion element 34 has an active layer 34a formed on a substrate in a substantially cross shape symmetrical with respect to a reference line L2. Here, the active layer 34a has a first rectangular portion extending parallel to the reference line L2 and a second rectangular portion extending in a direction intersecting (perpendicular to) the reference line L2, forming a substantially cross shape symmetrical with respect to the reference line L2. The active layer 34a is formed containing any of indium arsenide (InAs), indium antimony (InSb), and gallium arsenide (GaAs). The magnetoelectric conversion element 34 can be disposed away from the reference axis L1 in top view, and has a width w in the direction in which the reference lines L1 and L2 are separated from each other (i.e., the X-axis direction). This width w is also called the substrate size.

[0024] The magnetoelectric conversion element 34 is disposed on the insulating member 18 in a gap region surrounded by the curved portion 24c of the conductor 24 in a top view, spaced apart from the conductor 24. Here, in this embodiment, the magnetic sensing surface (i.e., the detection surface for detecting a magnetic field) of the magnetoelectric conversion element 34 is provided on the upper surface of the magnetoelectric conversion element 34. As an example, the magnetoelectric conversion element 34 is positioned so that its upper surface is located at the center in the thickness direction of the conductor 24 in a side view. The magnetoelectric conversion element 34 is connected to the signal processing device 44 by wire bonding, and outputs a voltage according to the strength of the detected magnetic field to the signal processing device 44 as an output signal.

[0025] As an example, the magnetoelectric conversion element 34 is disposed so that the reference line L1 and the reference line L2 are parallel. When the reference line L1 and the reference line L2 are parallel and do not overlap, the distance d indicating the positional deviation of the magnetoelectric conversion element 34 is regarded as the distance between the reference line L1 and the reference line L2. Here, the distance d may be equal to or less than half the board size w. On the other hand, the distance d may be greater than one-fifth of the board size w. As described later, by making the distance d greater than one-fifth of the board size w, the magnetoelectric conversion element 34 can be disposed near the inner surface of the conductor 24, which has a strong magnetic field strength. This arrangement makes the magnetic field strength 3% or more stronger than when the distance d is zero, and a highly accurate current sensor 100 can be provided.

[0026] When the active layer 34a formed on the magnetoelectric conversion element 34 rotates, that is, when the reference line L1 and the reference line L2 are not parallel, the distance d indicating the positional deviation of the magnetoelectric conversion element 34 is expressed as the distance between the rotation center of the active layer 34a and the reference line L1. In this case, the distance between the first reference line and the second reference line may be interpreted as the distance d indicating the positional deviation of the magnetoelectric conversion element 34, and the size of the substrate in the direction in which the first reference line L1 and the second reference line L2 move away from each other may be interpreted as the size in the direction parallel to the perpendicular line from the active layer 34a to the reference line L1, that is, the substrate size w. Here, the distance d may be half or less. On the other hand, the distance d may exceed one fifth of the substrate size w. As described later, by making the distance d larger than one fifth of the substrate size w, the magnetoelectric conversion element 34 can be disposed near the inner surface of the conductor 24 with a strong magnetic field strength. With this arrangement, the magnetic field strength becomes 3% or more stronger than when the distance d is zero, and a highly accurate current sensor 100 can be provided.

[0027] The signal processing device 44 is a device that processes the output signal of the magnetoelectric conversion element 34 to calculate the amount of the current to be measured flowing through the conductor 24. The signal processing device 44 may incorporate a memory, a sensitivity correction circuit, an offset correction circuit that corrects the offset of the output, an amplifier circuit that amplifies the output signal from the magnetoelectric conversion element 34, and a temperature correction circuit that corrects the output according to temperature. The signal processing device 44 is supported on the main body 11 of the frame 10, and is connected to the device terminals 15, 16 and three device terminals 17 of the frame 10 by wire bonding. Thus, the signal processing device 44 outputs the calculation result of the amount of the current to be measured flowing through the conductor 24 via the device terminals 15, 16, and 17.

[0028] 3A and 3B show the configuration of the conductor 24 and the arrangement of the magnetoelectric conversion element 34 in the simulation model 100d, respectively, in top and side views. Here, FIG. 3B shows the cross-sectional structure of the simulation model 100d with respect to the reference line BB in FIG. 3A. The simulation model includes the conductor 24 formed in a U-shape, the magnetoelectric conversion element 34 arranged in the gap region thereof, and a package 9 that seals them. The conductor 24 is symmetrical with respect to the reference line L1, and has two body parts 24b and 24d that extend along reference lines L11 and L12 parallel to the reference line L1, and a curved part 24c that curves and connects them in an arc shape. Here, the width and thickness of the body parts 24b and 24d and the curved part 24c are 0.4 mm and 0.4 mm, respectively, the distance from the reference line L1 to the inner surfaces of the body parts 24b and 24d is 0.35 mm, and the radius of curvature of the inner surface of the curved part 24c is 0.35 mm. The magnetoelectric conversion element 34 has an active layer 34a in a substantially cross shape provided on a square substrate with a side length of 0.28 mm. The height is 0.28 mm. In this example, the element is disposed at the center of curvature of the curved portion 24c of the conductor 24. The package 9 uses a molding resin to seal the conductor 24 and the magnetoelectric conversion element 34 except for the -Y end of the conductor 24. It covers a three-dimensional range of 0.05 mm from the outer surface of the body 24b, 24d of the conductor 24 to the ±X side, 0.05 mm from the +Y end of the curved portion 24c to the +Y side, and 1.1 mm above and below the center of the thickness of the conductor 24.

[0029] 3C shows the simulation parameters. The Young's modulus and linear expansion coefficient of the substrate 34b of the magnetoelectric conversion element 34, the package 9, and the conductor 24, and the piezoresistance coefficient of the active layer 34a of the magnetoelectric conversion element 34 are used as the simulation parameters. Here, the parameters are given assuming that the substrate 34b is made of GaAs, the conductor 24 is made of Cu, and the active layer 34a is made of InAs.

[0030] FIG. 4 shows an analysis result of the strength distribution of the Z-direction magnetic field generated around the conductor 24 when a unit current is applied to the conductor 24. The strength distribution of the magnetic field is shown on the reference line BB shown in FIG. 3A, that is, the distribution in the X-axis direction passing through the center of the magnetoelectric conversion element 34. The magnetic field strength is strongest on the inner surface of the conductor 24, slightly weaker in the gap between the inner surfaces, and weakest on the outer surface. From this result, in order to provide a highly accurate current sensor 100, it is desirable to dispose the magnetoelectric conversion element 34 near the inner surface of the conductor 24 where the magnetic field strength is strongest, rather than at the center of the gap of the conductor 24. However, there is a risk that the zero magnetic field voltage will increase if the magnetoelectric conversion element 34 sealed in the package 9 receives a non-uniform pressure, i.e., hydrostatic pressure, from the package 9. Here, the zero magnetic field voltage is an offset voltage generated between a pair of output electrodes when a drive voltage is applied between a pair of input electrodes of the magnetoelectric conversion element 34 to drive the element in a magnetic field-free state. Note that the zero magnetic field voltage is desirably 1.3 mV / V or less from the viewpoint of sensor accuracy.

[0031] The stress experienced by the magnetoelectric conversion element 34 can be given as a superposition of a thermal stress field experienced from a structure far from the element and a thermal stress field caused by a structure near the element. We analyze the zero magnetic field voltage generated in the magnetoelectric conversion element 34 due to the non-uniformity of these two thermal stress fields, and consider a means of suppressing this.

[0032] 5A to 5C show a hard sphere model for applying local stresses, namely, X-axis direction normal stress σx, Y-axis direction normal stress σy, and XY direction shear stress Txy, to the magnetoelectric conversion element 34. The hard sphere model reproduces a non-uniform thermal stress field caused by a structure far from the element by placing two hard spheres RS with a diameter of 50 μm near the magnetoelectric conversion element 34 and applying a forced displacement. In the model shown in FIG. 5A, the two hard spheres RS are placed at a distance d1 on the ±X side from the magnetoelectric conversion element 34, and the X-axis direction normal stress σx is applied to the magnetoelectric conversion element 34. In the model shown in FIG. 5B, the two hard spheres RS are placed at a distance d1 on the ±Y side from the magnetoelectric conversion element 34, and the Y-axis direction normal stress σy is applied to the magnetoelectric conversion element 34. In the model shown in Fig. 5C, two rigid spheres RS are placed at a distance d1 on the ±XY side (diagonal direction) from the magnetoelectric conversion element 34, and a shear stress Txy in the XY axis direction is applied to the magnetoelectric conversion element 34. A stress of 20 MPa is applied to the center of the magnetoelectric conversion element 34 by the two rigid spheres RS. The stress of 20 MPa corresponds to the pull strength of the wire connecting the magnetoelectric conversion element 34 and the signal processing device 44, as defined by the MIL standard (MIL-STD-883H). In other words, a strength equivalent to the breaking stress of the wire is considered as the case in which the stress applied to the magnetoelectric conversion element 34 is at its maximum.

[0033] The left side of FIG. 6 shows four regions of the magnetoelectric conversion element 34, and the right side shows an equivalent bridge circuit including four resistance arms. When a driving voltage is applied to a pair of electrodes of the active layer 34a of the magnetoelectric conversion element 34, current density is concentrated near the four corners around the center of the cross shape. Therefore, the active layer 34a can be approximated by a Wheatstone bridge (also simply called a bridge circuit) consisting of four resistors R1 to R4. Resistance R1 represents the resistance of the active layer 34a in the region E1, and is particularly dominated by the resistance of the active layer 34a near the corners. Resistance R2 represents the resistance of the active layer 34a in the region E2, and is particularly dominated by the resistance of the active layer 34a near the corners. Resistance R3 represents the resistance of the active layer 34a in the region E3, and is particularly dominated by the resistance of the active layer 34a near the corners. Resistance R4 represents the resistance of the active layer 34a in region E4, and is dominated by the resistance of the active layer 34a in particular near the corners.

[0034] The zero magnetic field voltage generated by the stress field applied to the magnetoelectric conversion element 34 and its non-uniformity is calculated as follows. The hydrostatic pressure distribution applied to the magnetoelectric conversion element 34 shown in FIG. 6 is calculated by a simulation using the finite element method, and average values ​​p1 to p4 in each of the four regions E1 to E4 separated by dashed lines are calculated. Using the calculated average values ​​p1 to p4 of the hydrostatic pressure, resistances Ri (i=1 to 4) corresponding to the four regions Ei (i=1 to 4) are calculated by the formula Ri=R(1+πpi). Here, π is the piezoresistance coefficient, and R is the resistance value in a stress-free state. The zero magnetic field voltage Vu when the driving voltage Vin is applied is calculated by the formula Vu=(R1R3-R2R4) / ((R1+R2)(R3+R4))×Vin. The driving voltage Vin=1V. As long as the resistors R1 to R4 are balanced, that is, R1R3=R2R4, no zero magnetic field voltage is generated. However, if the balance of the resistors R1 to R4 is lost and R1R3≠R2R4, an offset voltage will be generated.

[0035] 7 shows the positional relationship between the rotation of the active layer 34a in the magnetoelectric conversion element 34 and the four regions E1 to E4. In the upper left, upper right, lower left, and lower right models, the active layer 34a is rotated to rotation angles of 0 degrees, 15 degrees, 30 degrees, and 45 degrees, respectively, in the magnetoelectric conversion element 34. In each rotation state, the average value of the hydrostatic pressure in the regions E1 to E4 separated by the dashed dotted lines is calculated, and the zero magnetic field voltage Vu is calculated using the above-mentioned formula for resistance Ri and formula for zero magnetic field voltage Vu.

[0036] 8 shows the analysis result of the zero magnetic field voltage Vu generated in the magnetoelectric conversion element 34 with respect to the distance d1 of the hard sphere RS from the center of the magnetoelectric conversion element 34. Here, the magnetoelectric conversion element 34 is located at the gap center of the conductor 24, that is, the reference line L2 coincides with the reference line L1, and the rotation of the active layer 34a in the magnetoelectric conversion element 34 is 0 degrees. In the X-axis direction normal stress σx and the Y-axis direction normal stress σy, the hydrostatic pressures applied to the regions E1 and E2 are equal, and the hydrostatic pressures applied to the regions E3 and E4 are equal, so that R1=R2 and R3=R4. Therefore, the zero magnetic field voltage is almost zero with respect to the distance d1 of the hard sphere RS. In the XY direction shear stress Txy, the hydrostatic pressures applied to the regions E1 and E3 are equal, and the hydrostatic pressures applied to the regions E2 and E4 are equal, so that R1=R3≠R2=R4. Therefore, the zero magnetic field voltage is generated. However, when the distance d1 of the hard sphere RS becomes large, even though the stress applied to the element center is constant at 20 MPa, it falls short of the required level at d1>w=280 μm, where w is the size of the element substrate.

[0037] 9 shows the analysis result of the zero magnetic field voltage generated in the magnetoelectric conversion element 34 by the XY direction shear stress Txy for the distance d2 of the hard sphere RS from the gap symmetry line (reference line L1). As mentioned above, the zero magnetic field voltage decreases as the distance d2 increases, and decreases to a negligible level when the size of the element substrate is 280 μm or more. Even if a non-uniform stress field is generated by the hard sphere RS, when the distance d2 increases, the stress spreads by the Saint-Venant principle before reaching the magnetoelectric conversion element 34 through the package 9, and becomes approximately uniform at a distance approximately equal to the size of the element substrate (w=280 μm). Therefore, even if a stress that is high enough to cause wire breakage is applied to the magnetoelectric conversion element 34 from the structure in the package 9 that is away from the reference line L1 by the size w of the element substrate or more, the generated zero magnetic field voltage is below the required level.

[0038] On the other hand, the stress applied to the magnetoelectric conversion element 34 from the structure within a distance equal to the size w of the element substrate from the reference line L1 may generate a zero magnetic field voltage larger than the required level. Therefore, the conductor 24, which is a structure close to the magnetoelectric conversion element 34, has a shape that is line-symmetric or approximately line-symmetric (for example, symmetric within the range of manufacturing tolerance) with respect to the reference line L1 at least within a distance equal to the size w of the element substrate from the reference line L1. As a result, the thermal stress caused by the structure within a distance equal to the size w of the element substrate from the reference line L1 becomes line-symmetric or approximately line-symmetric with respect to the reference line L1. Furthermore, the thermal stress caused by the structure far from the element, which is a distance equal to or greater than the size w of the element substrate from the reference line L1, becomes uniform before being propagated to the magnetoelectric conversion element, even if the structure is asymmetric with respect to the reference line and therefore generates thermal stress asymmetric with respect to the reference line. Therefore, the balance of the stress field applied to the magnetoelectric conversion element 34 is maintained, and the zero magnetic field voltage can be suppressed.

[0039] 10A shows an example of the stress distribution applied to the magnetoelectric conversion element 34 when the Young's modulus of the molded resin forming the package 9 is sufficiently smaller than that of the magnetoelectric conversion element 34. The XY-direction shear stress Txy generated by the hard sphere RS propagates toward the magnetoelectric conversion element 34 without being dispersed significantly within the package 9. As a result, stress is concentrated in the regions E1 and E3 of the magnetoelectric conversion element 34, and it is expected that the balance of the stress field applied to the magnetoelectric conversion element 34 will be lost and the zero magnetic field voltage will increase.

[0040] 10B shows an example of the stress distribution applied to the magnetoelectric conversion element 34 when the Young's modulus of the molded resin forming the package 9 is approximately equal to the Young's modulus of the magnetoelectric conversion element 34. The XY-direction shear stress Txy generated by the hard sphere RS is dispersed over a wide range within the package 9 and propagates toward the entire magnetoelectric conversion element 34. As a result, stress is applied approximately uniformly to the regions E1 to E4 of the magnetoelectric conversion element 34, and it is expected that the balance of the stress field applied to the magnetoelectric conversion element 34 will be maintained and the zero magnetic field voltage will be suppressed.

[0041] FIG. 11 shows the analysis results of the zero magnetic field voltage generated in the magnetoelectric conversion element 34 versus the Young's modulus of the substrate of the magnetoelectric conversion element 34. Here, the Young's modulus of the molding resin forming the package 9 is set to 21 GPa. The zero magnetic field voltage increases as the Young's modulus of the substrate increases, and saturates at approximately 1.4 mV / V at 700 GPa or more. The zero magnetic field voltage is below the required level when the Young's modulus of the substrate is 550 GPa or less. From this result, by using an element substrate having a Young's modulus of 550 GPa or less, the zero magnetic field voltage can be suppressed to below the required level even if a non-uniform stress field is applied to the magnetoelectric conversion element 34. In addition, the substrate material can be selected from gallium arsenide (Young's modulus 85 GPa for GaAs), silicon (Young's modulus 166 GPa for Si), gallium nitride (Young's modulus 293 GPa for GaN), aluminum nitride (Young's modulus 332 GPa for AlN), sapphire (Young's modulus 335 GPa for Al2O3), and silicon carbide (Young's modulus 550 GPa for SiC).

[0042] FIG. 12 shows the analysis result of the zero magnetic field voltage generated in the magnetoelectric conversion element 34 with respect to the Young's modulus of the molded resin forming the package 9. Here, the Young's modulus of the substrate of the magnetoelectric conversion element 34 is set to 85 Gpa for GaAs as an example. The zero magnetic field voltage decreases as the Young's modulus of the molded resin increases, and becomes below the required level (about 1.4 mV / V) at 3 GPa or more, at least 5 GPa or more, and becomes constant at about 0.3 mV / V at 100 GPa or more. From this result, by forming the package 9 with a molded resin having a Young's modulus of 5 GPa or more, the zero magnetic field voltage can be suppressed to below the required level even if a non-uniform stress field is applied to the magnetoelectric conversion element 34. In addition, most of the commercially available molded resins can be selected as the material of the package 9.

[0043] FIG. 13 shows an analysis result of the zero magnetic field voltage generated in the magnetoelectric conversion element 34 with respect to the ratio (also called Young's modulus ratio) of the Young's modulus (Esubst) of the substrate of the magnetoelectric conversion element 34 based on the Young's modulus (Eresin) of the mold resin forming the package 9. The Young's modulus ratio is given by Esubst / Eresin. The analysis result is obtained by compiling the results given in FIG. 11 and FIG. 12 with respect to the Young's modulus ratio. The zero magnetic field voltage increases with an increase in the Young's modulus ratio, exceeds the required level (about 1.4 mV / V) at about 30, and becomes constant at 1.4 mV / V at 50 or more. From this result, by setting the Young's modulus ratio to 30 or less, the zero magnetic field voltage can be suppressed to below the required level even if a non-uniform stress field is applied to the magnetoelectric conversion element 34.

[0044] These conditions make it possible to block the generation of zero magnetic field voltage due to stress from a package structure that is located at a distance equal to or greater than the board size w from the reference line L1.

[0045] FIG. 14 shows the analysis result of the zero magnetic field voltage generated in the magnetoelectric conversion element 34 with respect to the rotation angle of the magnetoelectric conversion element 34. Here, the package structure within a distance equal to the board size w from the reference line L1 is symmetrical with respect to the reference line L1. The magnetoelectric conversion element 34 is placed at the gap center (on the reference line L1) of the conductor 24, and the rotation angles are selected as 0, 15, 30, and 45 degrees. When the rotation angle is 0 degrees, the stress applied to the element from the structure adjacent to the magnetoelectric conversion element 34 is symmetrical with respect to the reference line L2, and at this time, the stress in the regions E1 and E2 is approximately equal, and the stress in the regions E3 and E4 is approximately equal. Therefore, since R1=R2≠R3=R4, the zero magnetic field voltage generated is approximately zero. However, as the rotation angle increases to 15, 30, and 45 degrees, the stress applied to the element becomes asymmetric with respect to the reference line L2, with R1=R3≠R2=R4, and the zero magnetic field voltage increases to 0.16, 0.28, and 0.46 mV / V. From this result, it is possible to suppress the zero magnetic field voltage generated in the magnetoelectric conversion element 34 by making the rotation angle of the magnetoelectric conversion element 34 approximately zero (for example, zero within the range of manufacturing tolerance), that is, by making the reference lines L1 and L2 approximately parallel (for example, parallel within the range of manufacturing tolerance).

[0046] 15A shows the analysis result of the zero magnetic field voltage generated in the magnetoelectric conversion element 34 with respect to the distance d3 from the gap symmetry line (reference line L1) to the substrate center (reference line L2) of the magnetoelectric conversion element 34 when the rotation angle is 0 degrees. Here, the package structure within a distance equal to the substrate size w from the reference line L1 is symmetrical with respect to the reference line L1. For each of the rotation angles of 0 and 45 degrees of the magnetoelectric conversion element 34, the magnetoelectric conversion element 34 was translated in three directions (directions 1 to 3) from the gap center (on the reference line L1) of the conductor 24, and the zero magnetic field voltage generated in the magnetoelectric conversion element 34 was analyzed. Note that the distance d3 and the directions 1 to 3 are shown in FIG. 15B.

[0047] When the rotation angle is 0 degrees (reference lines L1, L2 are approximately parallel), the magnetoelectric conversion element 34 approaches the conductor 24, and receives non-uniform stress from the conductor 24, generating a zero magnetic field voltage. However, because the rotation angle is 0 degrees, the stress applied to regions E1, E4 approaching the conductor 24 increases equally regardless of the translation direction, and as a result, the resistances R1, R4 fluctuate equally, and R1=R4≠R2=R3 is satisfied, and the zero magnetic field voltage is suppressed to 0.2 mV / V or less.

[0048] When the rotation angle is 45 degrees, the magnetoelectric conversion element 34 approaches the conductor 24, and receives non-uniform stress from the conductor 24, generating a zero magnetic field voltage. The zero magnetic field voltage increases more rapidly with increasing distance d3 in direction 2 relative to direction 3, and in direction 1 relative to direction 2. However, even when the rotation angle is 45 degrees, the zero magnetic field voltage is generally below the required level when the distance d3 is within a range of half the board size w or less.

[0049] These conditions make it possible to block the generation of zero magnetic field voltage due to stress from the package structure within a distance equal to the board size w from the reference line L1.

[0050] A method for manufacturing the current sensor 100 will now be described.

[0051] 16A, first, a single metal plate is pressed to form a pattern of frame 10, multiple device terminals 17, and conductors 24. This pattern includes frame 10, multiple device terminals 17, and conductors 24, with their terminal portions connected to the inside of a rectangular frame (not shown).

[0052] Next, the pattern is subjected to step processing to provide steps at the device terminals 15 and 16 of the frame 10, the multiple device terminals 17, and the conductor 24. This raises the inner portion of the pattern relative to the frame and those terminal portions connected to the frame.

[0053] 16B, next, the magnetoelectric conversion element 34 and the signal processing device 44 are installed. Here, the magnetoelectric conversion element 34 is placed on the insulating member 18 that is hung between the protruding parts 12 and 14. The signal processing device 44 is placed on the main body 11 of the frame 10.

[0054] As shown in FIG. 16C, next, the magnetoelectric conversion element 34 and the signal processing device 44 are connected by wire bonding, and the signal processing device 44 and the device terminals 15, 16, and 17 are connected.

[0055] 16D, the pattern is then molded, leaving only the frame and the frame 10 connected thereto, the device terminals 17, and the terminal portions of the conductors 24. As a result, the package 9 is formed, and the magnetoelectric conversion element 34, the signal processing device 44, and the inner portion of the pattern in which these are installed are sealed therein.

[0056] Finally, the frame exposed from the package 9 is cut from the pattern. As a result, the frame 10, the multiple device terminals 17, and the conductors 24 are separated from one another, and the current sensor 100 is completed.

[0057] The current sensor 100 of this embodiment comprises a conductor 24 having a shape extending from one side to the other along a reference line L1, bending at the other side to intersect with the reference line L1, and extending from the other side to one side along the reference line L1, the conductor 24 through which the current to be measured flows, a magnetoelectric conversion element 34 arranged in a gap region surrounded by the conductor 24 when viewed from above, the magnetoelectric conversion element 34 having an active layer 34a formed in an approximately cross shape symmetrical with respect to the reference line L2 on a substrate, and a package 9 that seals the conductor 24 and the magnetoelectric conversion element 34, wherein the reference line L1 and the reference line L2 are approximately parallel, or the separation distance d3 between the reference line L1 and the reference line L2 is less than half the size w of the substrate. As a result, by having the reference line L1 of the conductor 24 and the reference line L2 of the magneto-electric conversion element 34 arranged in the gap region inside the conductor 24 be approximately parallel, or by having the distance d3 between the reference line L1 and the reference line L2 be less than half the size w of the substrate of the magneto-electric conversion element 34, the zero magnetic field voltage generated by the stress that the magneto-electric conversion element 34 receives from its vicinity via the packaging material can be suppressed.

[0058] In the current sensor 100 of this embodiment, the current flowing through the conductor 24 may be either direct current or alternating current. In the case of direct current, the direction of the flowing current may be determined arbitrarily.

[0059] Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It is clear to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the description of the claims that such modifications and improvements can also be included in the technical scope of the present invention.

[0060] It should be noted that the order of execution of each process, such as operations, procedures, steps, and stages, in the devices, systems, programs, and methods shown in the claims, specifications, and drawings is not specifically stated as "before," "prior to," etc., and may be realized in any order unless the output of a previous process is used in a later process. Even if the operational flow in the claims, specifications, and drawings is explained using "first," "next," etc. for convenience, it does not mean that it is essential to perform the process in this order. [Explanation of symbols]

[0061] 9...package, 10...frame, 11...main body, 12, 14...protruding portion, 15, 16, 17...device terminal, 15a, 16a, 17a...terminal portion, 18...insulating member, 24...conductor, 24a...current terminal, 24a, 24e...terminal portion, 24b, 24d...body portion, 24c...curved portion, 24c0...protruding edge, 34...magnetoelectric conversion element, 34a...active layer, 44...signal processing device, 100...current sensor, 100d...simulation model, E1 to E4...area, L1, L11, L12, L2...reference line, R1 to R4...resistor, RS...hard sphere.

Claims

1. a conductor having a shape extending from one side to the other side along a first reference line, bending at the other side to intersect with the first reference line, and extending from the other side to the one side along the first reference line, wherein a current to be measured flows through the conductor; a magnetoelectric transducer disposed in a gap region surrounded by the conductor in a top view, the magnetoelectric transducer having an active layer formed on a substrate in a substantially cross shape symmetrical with respect to a second reference line; a package that encapsulates the conductor and the magnetoelectric conversion element; wherein the first reference line and the second reference line are substantially parallel, or a distance between the first reference line and the second reference line is equal to or less than half a size of the substrate in a direction in which the first reference line and the second reference line are separated.

2. The current sensor according to claim 1 , wherein the conductor has a shape that is axisymmetric with respect to the first reference line at least within a distance from the first reference line that is equal to a size of the substrate.

3. 2. The current sensor according to claim 1, wherein the active layer of the magnetoelectric conversion element has a first portion extending parallel to the second reference line and a second portion extending in a direction intersecting the second reference line, and has a generally cross shape that is axisymmetric with respect to the second reference line.

4. The current sensor of claim 1 , wherein the distance between the first and second reference lines is greater than one-fifth of a size of the substrate in a direction in which the first and second reference lines are separated.

5. 2. The current sensor according to claim 1, wherein the active layer of the magnetoelectric transducer includes any one of indium arsenide (InAs), indium antimony (InSb), and gallium arsenide (GaAs).

6. The current sensor of claim 1 , wherein the substrate has a Young's modulus of less than or equal to 550 GPa.

7. The substrates are made of gallium arsenide (GaAs), silicon (Si), gallium nitride (GaN), aluminum nitride (AlN), sapphire (Si ２ O ３ 7. The current sensor according to claim 6, wherein the material is one of silicon carbide (SiC).

8. The current sensor of claim 1 , wherein the package has a Young's modulus of 5 GPa or greater.

9. The current sensor of claim 1 , wherein a ratio of the Young's modulus of the substrate to the Young's modulus of the package is 30 or less.

10. a signal processing device for processing an output signal of the magnetoelectric conversion element; a frame supporting the signal processing device; The current sensor of claim 1 further comprising:

Images