WO2012063584A1

WO2012063584A1 - Current sensor

Info

Publication number: WO2012063584A1
Application number: PCT/JP2011/073219
Authority: WO
Inventors: 高橋　彰; 雅博飯塚; 斎藤　正路
Original assignee: アルプス・グリーンデバイス株式会社
Priority date: 2010-11-09
Filing date: 2011-10-07
Publication date: 2012-05-18

Abstract

The objective of the present invention is to provide a current sensor having a simple configuration and that can measure large currents at a high level of precision. The current sensor (1) is characterized by being provided with: magnetoresistive effect elements (12a, 12b) disposed in a manner so that a voltage is output proportional to the induction field from the measured current flowing through a current line (11); and a magnetic shield (14) disposed in a manner so as to cover the magnetoresistive effect elements (12a, 12b) in a plan view. The current sensor (1) is further characterized by the gap between the magnetoresistive effect elements (12a, 12b) and the magnetic shield (14) being 1-40 µm.

Description

Current sensor

The present invention relates to a current sensor that measures current without contact. In particular, the present invention relates to a current sensor having a simple configuration capable of measuring a large current with high accuracy.

In fields such as motor drive technology in electric vehicles and hybrid cars, a relatively large current is handled, and thus a current sensor capable of measuring a large current in a non-contact manner is required for such applications. As such a current sensor, a method of detecting a change in magnetic field caused by a current to be measured by a magnetic sensor has been proposed. For example, Patent Document 1 discloses a current sensor using a magnetoresistive element as an element for a magnetic sensor.

JP 2002-156390 A

By the way, from the viewpoint of improving the controllability of the motor and improving the energy efficiency, there is a case where high current measurement accuracy is desired for the current sensor for large current. However, the current sensor using the magnetoresistive effect element can increase the sensor output, but has a problem that the current measurement region in which the linearity of the sensor output can be ensured is narrow. By adopting a so-called magnetic balance type equipped with a feedback coil, it is possible to achieve both high output and linearity in a wide measurement area to some extent. However, since a feedback coil and a drive circuit for driving the feedback coil are required, the cost is high. End up.

The present invention has been made in view of such a point, and an object thereof is to provide a current sensor having a simple configuration capable of measuring a large current with high accuracy.

The current sensor of the present invention covers a magnetoresistive effect element arranged in a plan view so as to output a voltage proportional to an induced magnetic field from a current to be measured flowing through a current line. And a gap between the magnetoresistive element and the magnetic shield is 1 μm to 40 μm.

According to this configuration, since the magnetoresistive effect element and the magnetic shield are arranged so as to have a predetermined relationship, the measured current region in which the linearity of the output of the current sensor can be obtained is widened. It is possible to measure with high accuracy. That is, it is possible to provide a current sensor that achieves both high accuracy and a wide measurement range with a simple configuration.

In the current sensor of the present invention, the distance between the magnetoresistive element and the magnetic shield may be 1 μm to 8 μm. According to this configuration, since the induced magnetic field received by the magnetoresistive element from the current to be measured can be further reduced, even a large current of 1500 A or more can be accurately measured. Thus, by arranging the magnetoresistive effect element and the magnetic shield more appropriately, it is possible to provide a more excellent current sensor that achieves both high accuracy and a wide measurement range with a simple configuration.

In the current sensor of the present invention, the magnetic shield may be disposed between the current line and the magnetoresistive element. In the current sensor of the present invention, the magnetic shield may be disposed on the opposite side of the magnetoresistive element from the current line.

In the current sensor of the present invention, the magnetic shield and the magnetoresistive effect element are arranged so that the distance between the magnetic shield and the magnetoresistive effect element is 1 μm to 40 μm, and the magnetic shield covers the magnetoresistive effect element. Therefore, the current measurement area where the linearity of the output of the current sensor can be obtained is widened, and a large current can be measured with high accuracy. Thereby, it is possible to provide a current sensor having a simple configuration capable of measuring a large current with high accuracy.

It is a figure shown about the structural example of the magnetic proportional type current sensor which concerns on embodiment. It is a cross-sectional schematic diagram which shows the example of the layer structure of the current sensor which concerns on embodiment. It is a plane schematic diagram which shows the example of the planar view of the current sensor which concerns on embodiment (A) It is a figure which shows the arrangement | positioning model in simulation. (B) It is a figure which shows a simulation result. (A) It is a figure which shows the output characteristic of the current sensor which concerns on embodiment. (B) It is a figure which shows the linearity of the output of the current sensor which concerns on embodiment. It is a schematic diagram which shows the regression line and measurement point which are used for calculation of linearity. (A) It is a figure which shows the output characteristic of the current sensor of a comparative example. (B) It is a figure which shows the linearity of the output of the current sensor of a comparative example. It is a figure which shows the relationship between the magnitude | size of the induced magnetic field which a magnetoresistive effect element receives, and the distance between a magnetic shield and a magnetoresistive effect element.

Hereinafter, embodiments will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a configuration example of a magnetic proportional current sensor according to the present embodiment. A magnetic proportional current sensor 1 shown in FIG. 1 includes a bridge circuit including two

magnetoresistive effect elements

12a and 12b, which are magnetic detection elements, and two

fixed resistance elements

13a and 13b. In addition, the magnetic proportional current sensor 1 includes an induced magnetic field H received by the

magnetoresistive effect elements

12a and 12b by a measured current I flowing through a current line (conductor) 11 disposed in the vicinity of the magnetic proportional current sensor 1. Is provided with a magnetic shield 14 for relaxing the above. The magnetic proportional current sensor 1 is not limited to the one including a bridge circuit as long as a voltage approximately proportional to the induced magnetic field from the current to be measured can be obtained.

In the bridge circuit shown in FIG. 1, the power supply potential Vdd is applied to one terminal of each of the magnetoresistive effect element 12b and the fixed resistance element 13a. Each is given a ground potential (GND). Further, the other terminals of the magnetoresistive effect element 12a and the fixed resistance element 13a are connected to form the first output Out1, and the other terminals of the magnetoresistive effect element 12b and the fixed resistance element 13b are connected to each other. The second output Out2 is set. Since the

magnetoresistive effect elements

12a and 12b have a characteristic that the resistance value is changed by applying the induced magnetic field H from the measured current I, the

magnetoresistive effect elements

12a and 12b are changed according to the induced magnetic field H from the measured current I. The first output and the second output change. The potential difference between the first output and the second output is substantially proportional to the induced magnetic field, and the potential difference (voltage) becomes the output of the magnetic proportional current sensor 1. Note that the configuration of the bridge circuit is not limited to this. For example, a bridge circuit may be configured by combining one magnetoresistance effect element and three fixed resistance elements, or a bridge circuit may be configured by combining four magnetoresistance effect elements.

A magnetic shield 14 is disposed on the current line 11 side of the

magnetoresistive effect elements

12a and 12b and / or on the opposite side of the current line 11 so as to cover the

magnetoresistive effect elements

12a and 12b. The magnetic shield 14 relaxes the induced magnetic field from the current to be measured. Thereby, since the current measurement is performed in a state where the induction magnetic field is substantially weak, the linearity of the sensor output can be maintained even when a large current flows through the current line 11. Note that the magnetic shield 14 may be disposed on either the current line 11 side, the opposite side of the current line 11, or may be disposed on both.

The magnetic shield 14 is desirably arranged at a distance of 1 μm to 40 μm from the

magnetoresistive effect elements

12a and 12b. This is because by arranging the magnetic shield 14 in such a distance range, the influence of the induced magnetic field received by the

magnetoresistive effect elements

12a and 12b due to the current to be measured can be sufficiently mitigated. In such a distance range, the relationship between the distance between the

magnetoresistive effect elements

12a and 12b and the magnetic shield 14 and the induced magnetic field applied to the

magnetoresistive effect elements

12a and 12b is linear, and the design of the current sensor is easy. Because it becomes. In particular, the distance between the

magnetoresistive elements

12a and 12b and the magnetic shield 14 is more preferably 1 μm to 8 μm. This is because the induced magnetic field received by the magnetoresistive effect element from the current to be measured can be further reduced, so that even a large current of 1500 A or more can be measured accurately.

As described above, the magnetic proportional current sensor 1 according to the present embodiment is arranged so that the

magnetoresistive effect elements

12a and 12b and the magnetic shield 14 have a predetermined relationship, so that the output of the current sensor 1 can be reduced. Since the measurement current region where the linearity can be obtained is widened, it is possible to measure a large current with high accuracy. That is, according to the present embodiment, it is possible to provide a current sensor that achieves both high accuracy and a wide measurement range with a simple configuration.

FIG. 2 is a schematic cross-sectional view showing an example of the layer configuration of the magnetic proportional current sensor 1 according to the present embodiment. In FIG. 2, the layer configuration of the region mainly including the

magnetoresistive effect elements

12a and 12b and the magnetic shield 14 is shown. FIG. 2 also shows a current line 11 through which the current to be measured flows in the depth direction of the drawing.

In the current sensor 1 shown in FIG. 2A, an insulating layer 112 is formed on the substrate 111. As the substrate 111, a silicon substrate or the like is used, and as the insulating layer 112, a silicon oxide film, an aluminum oxide film, or the like is used. The silicon oxide film can be formed using a method such as thermal oxidation of a silicon substrate, sputtering, or plasma CVD. The aluminum oxide film can be formed using a method such as sputtering or plasma CVD.

On the insulating layer 112,

magnetoresistive elements

12a and 12b, which are magnetic sensor elements, are formed. In addition, you may form a fixed resistance element (not shown) with the

magnetoresistive effect elements

12a and 12b. For example, when a GMR element is used as the

magnetoresistive effect elements

12a and 12b, a GMR element having a layer configuration including an antiferromagnetic layer, a fixed magnetic layer, a nonmagnetic layer, and a free magnetic layer can be employed.

On the insulating layer 112, electrodes (not shown) may be formed in addition to the

magnetoresistive effect elements

12a and 12b and fixed resistance elements. The electrode is formed, for example, by forming an electrode material layer and then patterning the electrode material layer by photolithography and etching.

An insulating layer 113 is formed on the

magnetoresistive effect elements

12a and 12b, the fixed resistance element, and the electrodes so as to cover them. As the insulating layer 113, a polyimide film, a silicon oxide film, or the like is used. The polyimide film can be formed by applying and curing a polyimide material. The silicon oxide film can be formed using a method such as sputtering or plasma CVD. Here, since the insulating layer 113 is a layer that determines the distance between the

magnetoresistive effect elements

12a and 12b and the magnetic shield 14, the thickness of the insulating layer 113 (the distance between the

magnetoresistive effect elements

12a and 12b and the magnetic shield 14). Is preferably 1 μm to 40 μm. Further, it is more preferable that the thickness of the insulating layer 113 is 1 μm to 8 μm.

A magnetic shield 14 is formed in a region overlapping the

magnetoresistive effect elements

12 a and 12 b on the insulating layer 113. As a material constituting the magnetic shield 14, a high magnetic permeability material such as an amorphous magnetic material, a permalloy magnetic material, or an iron microcrystalline material can be used.

An insulating layer 114 is formed on the insulating layer 113 and the magnetic shield 14. As the insulating layer 114, a polyimide film, a silicon oxide film, or the like is used. The polyimide film can be formed by applying and curing a polyimide material. The silicon oxide film can be formed using a method such as sputtering or plasma CVD.

Contact holes are formed in predetermined regions such as the insulating layer 113 and the insulating layer 114, and electrodes connected to the

magnetoresistive effect elements

12a and 12b, fixed resistance elements, electrodes and the like are formed (not shown). The electrode can be formed by forming an electrode material layer and then patterning the electrode material layer by photolithography and etching.

FIG. 2B shows another example of the layer configuration of the magnetic proportional current sensor 1. In the current sensor 1 shown in FIG. 2B, an insulating layer 212 is formed on the substrate 211. Further, the magnetic shield 14 is formed on the insulating layer 212, and the

magnetoresistive elements

12 a and 12 b are formed via the insulating layer 213 in the region overlapping the magnetic shield 14 on the magnetic shield 14. . An insulating layer 214 is formed on the

magnetoresistive effect elements

12a and 12b.

The main difference between FIG. 2 (a) and FIG. 2 (b) is the position where the magnetic shield 14 is disposed. 2A, the magnetic shield 14 is disposed on the current line 11 side from the

magnetoresistive effect elements

12a and 12b, whereas in FIG. 2B, the magnetic shield 14 is provided with the

magnetoresistive effect elements

12a and 12a. 12b from the current line 11 (on the side substrate 211 side). As described above, as long as the magnetic shield 14 covers the

magnetoresistive effect elements

12 a and 12 b in a plan view, the magnetic shield 14 may be disposed on the current line 11 side or on the opposite side to the current line 11. May be. Of course, the magnetic shield 14 may be arranged on both the current line 11 side and the opposite side of the current line 11. Note that the plan view means a form viewed from a direction perpendicular to the main surfaces of the

substrates

111 and 211.

FIG. 3 is a schematic plan view showing an example of a plan view of the magnetic proportional current sensor 1 according to the present embodiment. In particular, FIG. 3 shows a region where a magnetoresistive effect element and a magnetic shield are formed.

The magnetic proportional current sensor 1 shown in FIG. 3A includes four

magnetoresistive elements

21a, 21b, 21c, and 21d that form a bridge circuit. Arrows attached to the

magnetoresistive effect elements

21a, 21b, 21c, and 21d represent the sensitivity axis directions of the magnetoresistive effect elements. The magnetic proportional current sensor 1 includes a magnetic shield 14 that covers the four

magnetoresistive elements

21a, 21b, 21c, and 21d in a plan view. The magnetic shield 14 is disposed on the front side of the drawing with respect to the

magnetoresistive effect elements

21a, 21b, 21c, and 21d. In FIG. 3A, the configuration disposed on the back side of the drawing sheet by the magnetic shield 14 is also indicated by a solid line.

In the magnetic proportional current sensor 1 shown in FIG. 3A, Vdd is connected to one terminal 22 of the

magnetoresistive effect elements

21a and 21b. Further, GND is connected to one terminal 23 of the magnetoresistive element 21c and one terminal 24 of the magnetoresistive element 21d. The other terminal 25 of the

magnetoresistive effect elements

21a and 21d is the first output. The other terminal 26 of the

magnetoresistive effect elements

21b and 21c becomes the second output. Since the

magnetoresistive effect elements

21a, 21b, 21c, 21d and the magnetic shield 14 are arranged as shown in FIG. 3A, the measurement current region in which the linearity of the output of the current sensor 1 can be ensured is widened. It becomes possible to accurately measure the current.

FIG. 3B shows an example of a plan view of a magnetic proportional current sensor 2 that is different from the magnetic proportional current sensor 1 shown in FIG. The magnetic proportional current sensor 2 shown in FIG. 3B includes four

magnetoresistive elements

31a, 31b, 31c, and 31d that constitute a bridge circuit. Arrows attached to the

magnetoresistive effect elements

31a, 31b, 31c, and 31d represent the sensitivity axis direction of the magnetoresistive effect element. The magnetic proportional current sensor 2 includes a magnetic shield 14 that covers the four

magnetoresistive elements

31a, 31b, 31c, and 31d in a plan view. The magnetic shield 14 is disposed on the front side of the drawing with respect to the

magnetoresistive effect elements

31a, 31b, 31c, and 31d. The magnetic proportional current sensor 2 shown in FIG. 3B is characterized in that it is downsized as compared with the magnetic proportional current sensor 1 shown in FIG. In FIG. 3B, the configuration arranged on the back side of the drawing sheet by the magnetic shield 14 is also shown by a solid line.

In the magnetic proportional current sensor 1 shown in FIG. 3 (b), Vdd is connected to one terminal 32 of the

magnetoresistive effect elements

31a and 31b. Further, GND is connected to one terminal 33 of the magnetoresistive effect element 31c and one terminal 34 of the magnetoresistive effect element 31d. The other terminal 35 of the

magnetoresistive effect elements

31a and 31d is the first output. The other terminal 36 of the

magnetoresistive effect elements

31b and 31c is the second output. Since the

magnetoresistive elements

31a, 31b, 31c, 31d and the magnetic shield 14 are arranged as shown in FIG. 3B, the measurement current region in which the linearity of the output of the current sensor 1 can be secured is widened. It becomes possible to accurately measure the current.

Next, a simulation for confirming the effect of the present invention will be described. First, the magnitude of the induced magnetic field generated by the current to be measured was estimated. FIG. 4A is an arrangement model diagram of a current sensor and a current line assuming an in-vehicle application such as an electric vehicle or a hybrid car. Here, as shown in the arrangement model diagram of FIG. 4A, it is assumed that the current sensor is arranged at a position A 1 mm away from the current line 11 having a width of 25 mm and a thickness of 3 mm. Estimated.

FIG. 4 (b) is a diagram showing a simulation result using the arrangement model of FIG. 4 (a). In the graph shown in FIG. 4B, the horizontal axis indicates the magnitude (A) of the current to be measured flowing through the current line 11, and the vertical axis indicates the magnitude (mT) of the induced magnetic field at the position A. . FIG. 4B shows that an induced magnetic field of about 22 mT is generated at position A when the measured current is about 1000 A. Note that the condition of the current to be measured (about 1000 A) corresponds to the upper limit value of the measurement current required in the current in-vehicle use. However, depending on the application, measurement of a current value of 1500 A or more may be required.

Next, the output characteristics of the current sensor of this embodiment were confirmed. Here, the output characteristics of the current sensor 2 having the structure shown in the plan view of FIG. Further, a GMR element was used as the magnetoresistive effect element, and the distance between the magnetoresistive effect element (GMR element) and the magnetic shield in the current sensor 2 was 17.6 μm.

FIG. 5 is a diagram showing the experimental results. In the graph shown in FIG. 5A, the horizontal axis indicates the magnitude (mT) of the induced magnetic field (magnetic field) received by the current sensor 2, and the vertical axis indicates the output voltage (mV) of the bridge circuit provided in the current sensor 2. Show. In the graph shown in FIG. 5B, the horizontal axis indicates the magnitude (mT) of the induced magnetic field (magnetic field) received by the current sensor 2, and the vertical axis indicates linearity (%). Here, the linearity is an index representing a deviation from a straight line, and means that the smaller the value, the better the linearity. It should be noted that the magnitude of the induced magnetic field on the horizontal axis of the graph shown in FIG. 5 is the magnitude of the magnetic field received by the current sensor 2 and not the magnitude of the magnetic field received by the magnetoresistive element.

Linearity is calculated using a linear regression line obtained from the output voltage of the bridge circuit. FIG. 6 is a schematic diagram showing a regression line and measurement points used for calculation of linearity. In FIG. 6, the horizontal axis indicates the magnetic field, and the vertical axis indicates the voltage that is the sensor output. Moreover, in FIG. 6, a straight line shows a regression line and a black point shows a measurement point. In the regression line, Va is a voltage corresponding to the magnetic field from the upper end to the lower end of the measurement range. The difference between the voltage Vb obtained from the regression line and the measured voltage Vc for each strength of the induced magnetic field (magnetic field) is defined as ΔV. The percentage of ΔV with respect to Va (100 × ΔV / Va) is linearity in each induction magnetic field (magnetic field) strength. In this experiment, the upper end (lower end) of the measurement range is +24 mT (−24 mT).

From FIG. 5A and FIG. 5B, the magnitude of the induced magnetic field received by the current sensor 2 in the present embodiment and the output voltage of the bridge circuit provided in the current sensor 2 are substantially proportional (substantially linear). You can see that In particular, even at 22 mT corresponding to the upper limit value of the current to be measured required for in-vehicle use, the linearity is within 1%, and it can be seen that a large current can be measured accurately.

As a comparative example, the output characteristics of a current sensor having no magnetic shield were confirmed. The measurement conditions are the same as in FIG. 5 except for the presence or absence of a magnetic shield. FIG. 7 shows the simulation result. FIG. 7 (a) corresponds to FIG. 5 (a), and FIG. 7 (b) corresponds to FIG. 5 (b). From FIG. 7A and FIG. 7B, it can be seen that the linearity is greatly deteriorated in the situation where an induced magnetic field exceeding 3 mT is generated.

From the above experimental results and simulation results, the magnetic shield and the magnetoresistive effect element are arranged so that the distance between the magnetic shield and the magnetoresistive effect element is 1 μm to 40 μm, and the magnetic shield covers the magnetoresistive effect element. This shows that the linearity of the output of the current sensor is greatly improved. Thus, a large current can be accurately measured by ensuring linearity in a wide measurement range.

Next, in the current sensor 2, the relationship between the magnitude of the induced magnetic field received by the magnetoresistive effect element (GMR element) and the distance between the magnetic shield and the magnetoresistive effect element was confirmed. Here, assuming a situation where an induced magnetic field of 10 mT is applied to the current sensor 2, how the magnitude of the induced magnetic field received by the magnetoresistive effect element changes in relation to the distance between the magnetic shield and the magnetoresistive effect element. I confirmed.

FIG. 8 is a diagram showing the simulation results. In the graph shown in FIG. 8, the horizontal axis indicates the distance (μm) between the magnetic shield and the magnetoresistive effect element, and the vertical axis indicates the magnitude (mT) of the induced magnetic field received by the magnetoresistive effect element (GMR element). . FIG. 8B is a partially enlarged view of a part of FIG.

FIG. 8 shows that the relationship between the distance between the magnetic shield and the magnetoresistive effect element and the magnitude of the induced magnetic field is represented by a substantially straight line when the distance between the magnetic shield and the magnetoresistive effect element is in the range of 1 μm to 40 μm. . It can also be seen that the induced magnetic field received by the magnetoresistive element is sufficiently relaxed. In other words, by setting the distance between the magnetic shield and the magnetoresistive effect element in the range of 1 μm to 40 μm, it is possible to ensure the linearity of the output of the current sensor in a sufficiently wide range and facilitate the design of the current sensor. it can.

As described above, by arranging the magnetic shield and the magnetoresistive effect element so that the distance between the magnetic shield and the magnetoresistive effect element is 1 μm to 40 μm, and the magnetic shield covers the magnetoresistive effect element, The current measurement area where the linearity of the output of the current sensor can be obtained is widened, and a large current can be accurately measured. Thereby, it is possible to provide a current sensor having a simple configuration capable of measuring a large current with high accuracy.

Note that the present invention is not limited to the above embodiment, and can be implemented with various modifications. For example, the connection relationship, size, and the like of each element in the above embodiment can be changed as appropriate. In addition, the structures described in the above embodiments can be implemented in appropriate combination. In addition, the present invention can be implemented with appropriate modifications without departing from the scope of the present invention.

The current sensor of the present invention can be used, for example, to detect the magnitude of a current for driving a motor of an electric vehicle or a hybrid car.

This application is based on Japanese Patent Application No. 2010-250840 filed on Nov. 9, 2010. All this content is included here.

Claims

A magnetoresistive element arranged to output a voltage proportional to the induced magnetic field from the current to be measured flowing through the current line;
A magnetic shield arranged to cover the magnetoresistive effect element in a plan view;
With
A current sensor characterized in that a distance between the magnetoresistive element and the magnetic shield is 1 μm to 40 μm.
2. The current sensor according to claim 1, wherein a distance between the magnetoresistive element and the magnetic shield is 1 μm to 8 μm.
3. The current sensor according to claim 1, wherein the magnetic shield is disposed between the current line and the magnetoresistive element.
The current sensor according to any one of claims 1 to 3, wherein the magnetic shield is arranged on a side opposite to the current line of the magnetoresistive effect element.