JPH09318720A - Flux gate magnetic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flux gate magnetic sensor which is so arranged to facilitate higher sensitivity even in the same sensor size as compared to the conventional ring core type sensor. SOLUTION: Two detection coils 3a and 3b are wound on two side parts as opposed to each other along the long shaft of an oval or rectangular core 1 comprising a magnetic body and all of turns of the detection coils 3a and 3b are made to cross a sensitivity axis, thereby enabling increase in the number of effective turns of the detection coils as compared to the conventional sensor using a ring core.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluxgate magnetic sensor used to measure a magnetic field generated from, for example, geomagnetism or a minute current.

[0002]

2. Description of the Related Art A fluxgate magnetic sensor has a core 11 made of a magnetic material and one excitation coil 12 and two detection coils 13a and 13b wound around it, as schematically shown in FIG. The coils 13a and 13b are differentially connected to each other, that is, one ends of the coils 13a and 13b are connected to each other while being wound in opposite directions.

In such a fluxgate magnetic sensor, an AC magnetic flux generated along the core 11 when an AC current (excitation current) is passed through the excitation coil 12 causes
The insides of the detection coils 13a and 13b are penetrated in opposite directions. When external magnetism acts on the sensor in this state, the magnetic flux due to the magnetism is generated in the detection coils 13a and 13b.
Acting in the same direction with respect to each detection coil 13a,
The AC magnetic flux penetrating the 13b eventually becomes biased in the opposite directions by the external magnetism, and is proportional to the external magnetism from both ends of the detection coils 13a and 13b and has a frequency twice that of the excitation current. The AC voltage signal can be taken out. A voltage signal proportional to the external magnetism can be obtained by amplifying this AC voltage signal with an AC amplifier, rectifying it, and then detecting it.

In addition to a so-called solenoid type magnetic sensor having a rod-shaped core 11 as shown in FIG. 7, a magnetic sensor of this type has a true circular ring-shaped core 21 as shown in FIG. There is a so-called ring core type. In FIG. 8, the excitation coil is not shown in order to avoid complication of the drawing, but in actuality, in order to uniformly excite the core 21, the excitation coil is provided over the entire core 21 with each detection coil. It is wound so as to draw an alternate spiral with the spirals of 23a and 23b. This ring core type fluxgate magnetic sensor has an advantage that it is not necessary to consider the influence of the demagnetizing field when exciting the core.

Further, in such a ring core type fluxgate magnetic sensor, the sensor element is miniaturized by forming the ring core, the excitation coil and the respective detection coils by a thin film by utilizing the semiconductor manufacturing technology.
In addition, a so-called thin film fluxgate magnetic sensor having improved magnetic detection characteristics has been proposed (JP-A-7-1).
91118).

[0006]

By the way, in the fluxgate magnetic sensor, when the magnetic field sensitivity under the optimum excitation condition is a, a = 8NAμ _r f ··· (1) (for example, T. Sistz, Sensors and Actuators, A21
-A23, 799 (1990)). Here, N is the number of turns of the detection coil, A is the cross-sectional area of the core, μ _r is the effective relative permeability, and f is the excitation frequency. As is clear from the equation (1), if the excitation frequency, the cross-sectional area of the core and the magnetic permeability are the same, the number of turns of the detection coil is increased as much as possible to improve the magnetic field detection sensitivity.

However, in the conventional ring core type sensor shown in FIG. 8, the number of turns of the detection coil is limited for the following reason. That is, in the fluxgate magnetic sensor, the magnetic flux of the external magnetic field cannot be detected unless it penetrates the inside of the detection coil. Therefore, in this type of sensor, the sensitivity axis exists, but the ring core type shown in FIG. In this sensor, since the detection coils 23a and 23b in the region shown by the broken line in the figure do not intersect the magnetic field to be measured, they do not substantially function as detection coils.

Further, in order to increase the number of turns of the detection coils 23a and 23b, it is effective to reduce the line and space of the conducting wire.
Since the turns a and 23b are radial with respect to the ring core in a plan view, the number of turns thereof is restricted by the inner diameter of the ring core 21.

Therefore, if only the inner diameter of the ring core 21 is increased, the cross-sectional area of the core 21 is reduced and the sensitivity is lowered. Further, if the inner and outer diameters of the core 21 are both increased, the entire sensor is reduced. There is a problem that the size becomes large.

The present invention has been made in view of the above circumstances, and it is not necessary to consider the influence of the demagnetizing field at the time of exciting the core as in the conventional ring core type sensor, and the conventional ring core type sensor can be used. On the other hand, it is an object of the present invention to provide a fluxgate magnetic sensor having a structure in which the sensitivity can be easily increased even with the same sensor size.

[0011]

In order to achieve the above object, the fluxgate magnetic sensor of the present invention adopts the following configuration.

That is, the core is formed into an elliptical or rectangular loop shape, and two detection coils are wound around two opposite side portions along the long axis of the loop.

In the present invention, the two side portions of the elliptical or rectangular loop which are opposed to each other along the long axis of the loop are two of the rectangular shape when the core is rectangular.
When the core has an elliptical shape, it means a region with a relatively small curvature on both sides of the long axis when the core has an elliptical shape. Further, the elliptical shape mentioned here includes not only an ellipse defined mathematically but also a so-called elliptical shape in which a circle is crushed in its diameter direction.

According to the fluxgate magnetic sensor of the present invention as described above, the two detection coils are wound around the two sides along the major axis of the elliptical or rectangular loop-shaped core. The direction along the long axis becomes the sensitivity axis, and the effective number of turns of the detection coil, that is, the number of turns intersecting the measured magnetic flux in the direction of the sensitivity axis is increased compared to the case of using a perfect circular ring core. This is possible.

Further, since the detection coil is wound around a straight part of the core or a part having a small curvature close to the straight line, the detection coil shown in FIG.
Unlike the winding on the true circular ring core shown in Fig. 3, it does not become radial in a plan view, and therefore the contribution to the increase in the number of turns is increased by reducing the line and space of the detection coil.

[0016]

FIG. 1 is a block diagram of an embodiment of the present invention. (A) shows a state where only detection coils 3a and 3b are wound around a core 1, and (B) shows an excitation coil 2 around the core 1. The state in which only the coil is wound is shown schematically.

The core 1 made of a magnetic material is in the shape of a rectangular loop, and the loop cores 1 facing each other 2
The detection coil 3a is wound around one of the two long sides, and the detection coil 3b is wound around the other of the long sides in a reverse winding.

Further, as shown in (B), the excitation coil 2 is uniformly wound around the entire circumference of the loop core 1. Here, in FIG. 1, the detection coils 3a and 3b and the excitation coil 2 are individually wound around (A) and (B) in order to avoid complication of the drawing. 3a and 3b and the excitation coil 2 are wound in a state where one loop core 1 is shared.

In such an embodiment of the present invention, the detection coils 3a and 3b are rectangular loop cores 1.
The coil is wound around linear coil central axes that are parallel to each other along the two long sides, and the direction along the long sides is the sensitivity axis.

According to such an embodiment of the present invention,
All the turns of the detection coils 3a and 3b intersect the sensitivity axis, so that all the turns are effective turns. Further, since the turns of the detection coils 3a and 3b are parallel to each other, the density of the turns of the detection coils 3a and 3b is larger than that of the turns of the detection coils 3a and 3b which are radial in a plan view using a ring core having a perfect circular shape. Even if the wire diameter of 3b and its interval (line and space) are made equal, it can be made denser, and the pitch between the turns can be made substantially finer. Therefore, in this embodiment, when the number of effective turns of the detection coils 3a and 3b is the same, the sensor size can be reduced, and the sensor size can be reduced as compared with the case of using a perfect circular ring core. If the two are equal, the number of effective turns of the detection coils 3a and 3b is increased to obtain a highly sensitive magnetic sensor.

FIG. 2 is an explanatory view of another embodiment of the present invention, in which the excitation coil is not shown. The feature of this embodiment is that the loop core 1 has an elliptical shape, and the detection coils 3a and 3b are wound around both sides of the loop core 1 on both sides of the major axis of the ellipse.

In the embodiment of FIG. 2 as well, similar to the embodiment of FIG. 1, all the turns of the detection coils 3a and 3b intersect the sensitivity axis (the long axis direction of the ellipse), and the shape is a perfect circle. Compared with the case of using the ring core described above, since the turns are closer to each other in parallel, the same operational effect as the embodiment of FIG. 1 can be obtained.

Next, a case where the present invention is applied to a thin film fluxgate magnetic sensor will be described. In this case, since the schematic structure of the sensor is the same as that shown in FIG. 1 or 2, detailed description of the structure is omitted, and here, the schematic structure equivalent to that shown in FIG. A method of manufacturing a thin film fluxgate magnetic sensor having the above and materials of each part will be described.

FIG. 3 is an explanatory view of the manufacturing procedure. First, as shown in (A), for example, a Cu thin film is formed (film thickness 2 μm) on the surface of a substrate 40 made of, for example, fused silica by dc magnetron sputtering or the like, and patterned by, for example, photolithography and ion beam etching. The lower wiring layer 41 of the detection coils 3a and 3b and the excitation coil 2 is formed, and the groove between the wirings is filled with, for example, a vapor-deposited SiO ₂ film and flattened by a lift-off method. The pattern of the lower wiring layer 41 is partially shown in, for example, FIG. 4A. In this figure, 41a is a pattern for excitation coil, 41b is a pattern for detection coil, and the pattern 41a for excitation coil is as follows. Magnetic core layer 4
While the rectangular loop core pattern formed in 3 is formed uniformly over the entire circumference, the detection coil pattern 41b is formed only in the portions along the two long sides of the rectangular pattern.

Next, for example, SiO ₂ and permalloy are sequentially formed by a sputtering method, and the permalloy is patterned by the same method as described above to form a lower insulating layer 42 and a magnetic core layer 43 as shown in (B). To do. The pattern of the magnetic core layer 43 has a rectangular loop shape as illustrated in FIG.

Next, for example, SiO ₂ is sputter-deposited to form an upper insulating layer 44 as shown in (C), and with respect to the upper insulating layer 44 and the lower insulating layer 42, as shown in (D), For example, by ion beam etching, the lower wiring layer 4
After forming the contact holes 45 at positions corresponding to one ends of the patterns 41a and 41b of No. 1, a Cu thin film 46 is formed by sputtering. Thereafter, the Cu thin film 46 is patterned by photolithography, ion beam etching and the like to form the upper wiring layer 47 as shown in (E). The pattern of the upper wiring layer 47 is as partially illustrated in FIG. 4B. In this figure, 47a is an excitation coil pattern and 47b is a detection coil pattern. It is formed at a position corresponding to the layer 41.

Through the above steps, the excitation coil pattern 4 in the lower wiring layer 41 and the upper wiring layer 47 is formed.
1a and 47a, and detection coil patterns 41b and 4
7b are connected to each other by Cu in the contact hole 45 to form a coil-shaped three-dimensional pattern as shown in the schematic partial perspective views of FIGS. 5A and 5B, and each of the upper and lower wiring layers 41. The thin film fluxgate magnetic sensor having the schematic structure shown in FIG. 1 is obtained in a state in which the pattern of the magnetic core layer 43 sandwiched between the magnetic pole layers 47 and 47 is wound into a spiral shape.

A partially enlarged plan view of the thin film fluxgate magnetic sensor thus obtained is shown in FIG. 6 (A) with the excitation coil omitted, and in FIG. 6 (B), a true example is shown as a comparative example. A partially enlarged plan view of a conventional thin film fluxgate magnetic sensor using a circular ring core is shown with the excitation coil being omitted. As is apparent from FIG. 6, in the thin film fluxgate magnetic sensor to which the present invention is applied, since the turns are parallel to each other, the pitch between the turns of the detection coil is reduced by the amount that the turns are not radial as in the conventional case. Can be substantially miniaturized.

The material of the core and the material of the coil in the thin film fluxgate magnetic sensor to which the present invention is applied are
The material is not limited to the embodiment described above, and any material can be used as long as it is a magnetic body and a conductor having a relatively high magnetic permeability.

[0030]

As described above, according to the present invention, the core around which the excitation coil and the detection coil are wound is formed into an elliptical or rectangular loop shape, and the two detection coils are arranged on two sides along the major axis thereof. Since it is wound around, the effective number of turns of the detection coil that intersects with the sensitivity axis can be more improved when the sensor size is made equal compared to the conventional one using a perfect circular ring core. It is possible to increase the sensitivity and improve the sensitivity, and conversely, it is possible to reduce the sensor size if the number of effective turns is equivalent, which increases throughput and contributes to cost reduction of the sensor. You can

[Brief description of drawings]

FIG. 1 is a configuration explanatory view of an embodiment of the present invention, (A) shows a state in which only a detection coil 3a, 3b is wound around a core 1,
FIG. 3B is a diagram schematically showing a state in which only the excitation coil 2 is wound around the core 1.

FIG. 2 is a structural explanatory view of another embodiment of the present invention in a state where an exciting coil is omitted.

FIG. 3 is an explanatory view of a sensor manufacturing process when the present invention is applied to a thin film fluxgate magnetic sensor.

4 is a lower wiring layer 41 formed in the process of FIG.
3A is an explanatory view of an example of a partial pattern of FIG.
Explanatory drawing of the example of the partial pattern of the upper wiring layer 47 created in the process of (B)

5A and 5B are explanatory diagrams of a three-dimensional pattern of the excitation coil formed by the process of FIG. 3 and explanatory diagrams of a three-dimensional pattern of the detection coil formed at the same time.

6 is a partially enlarged plan view (A) of a thin film fluxgate magnetic sensor obtained by the process of FIG. 3 and a partially enlarged plan view (B) of a thin film fluxgate magnetic sensor using a perfect circular ring core as a comparative example. ) In the figure, with the excitation coil omitted

FIG. 7 is a schematic configuration diagram of a conventional solenoid type fluxgate magnetic sensor.

FIG. 8 is a schematic configuration diagram of a conventional ring core type fluxgate magnetic sensor.

[Explanation of symbols]

 1 Loop Core 2 Excitation Coil 3a, 3b Detection Coil 41 Lower Wiring Layer 41a Excitation Coil Pattern 41b Detection Coil Pattern 43 Magnetic Core Layer 45 Contact Hole 47 Upper Wiring Layer 47a Excitation Coil Pattern 47b Detection Coil Pattern

Claims (1)

[Claims] 1. A fluxgate magnetic sensor in which two detection coils, which are reversely wound and are connected to each other, and an excitation coil are wound around a core made of a magnetic material, and the core has an elliptical or rectangular loop. A fluxgate magnetic sensor, characterized in that each of the two detection coils is wound around two opposite side portions along the long axis of the loop.