JP2022119745A - Magnetic field sensor device and manufacturing method of magnetic field sensor device - Google Patents

Abstract

To provide a magnetic field sensor device, and a manufacturing method of the magnetic field sensor device.SOLUTION: A magnetic field sensor device having four resistance elements connected to a Wheatstone bridge circuit includes TMR elements in which each resistance element is at least one tunnel magnetic resistor. The respective TMR elements 11 to 14 include a conductive fixed layer 71, a conductive free layer 72, and an electric isolation tunnel barrier for separating the fixed layer 71 and the free layer 72. The free layer 71 includes an anisotropic geometrical shape. An excitation device 2 generates an alternating field. A compensation device 3 generates a DC magnetic field. A measuring device 4 outputs a measurement signal according to a bridge voltage of the Wheatstone bridge circuit. A control device 5 generates a control signal on the basis of a measurement signal outputted from the measuring device so as to perform drive control of the compensation device 3 such that a DC component of the measurement signal can be controlled to have a predetermined value. An evaluation device 6 identifies external magnetic field strength on the basis of an excitation current, and a measurement signal outputted from the measuring device.SELECTED DRAWING: Figure 1

Description

The present invention relates to a magnetic field sensor device and a method of manufacturing a magnetic field sensor device.

With the increase in electrification, the importance of current measurement in automobiles is increasing. A known measuring method uses a measuring shunt and measures the current through the measuring shunt based on the voltage drop. The problem here is that it is frequently necessary to galvanically isolate the measurement and evaluation circuits, which is not possible with this measurement method and must be implemented with additional electronic components.

Therefore, more and more non-contact methods are being used, for example, determining the current generating the magnetic field on the basis of the magnetic field. A magnetic field sensor with improved linearity is known from US2016/0320459. EP 1 450 176 A1 discloses a magnetic field sensor comprising a magnetic field measuring cell and a magnetic shield having at least two parts separated by an air gap and surrounding the magnetic field measuring cell arranged in a cavity of the magnetic shield. Furthermore, from EP 2 423 693 B1 a toroidal core current transformer is known in which the dielectric can be locked to the housing by means of complementary locking elements provided on the dielectric and the housing.

Inductive systems operating on the transformer principle are not suitable for detecting DC components. There are various approaches to non-contact current measurement. Thus, for example, a distinction can be made between linear methods and fluxgate principles.

Linear methods are based on the linear behavior of the current sensor over a defined measurement range. The measured quantity is converted into an electrically detectable quantity, eg voltage, via a substantially linear function.
In contrast, the fluxgate principle specifically exploits the non-linear behavior of the magnetic material of the sensor to specify the required saturation magnetization of the sensor element. It changes in response to the external magnetic field and moves the center point position. Here, the center point position corresponds to the amplitude difference required for saturation in negative and positive magnetic fields.

By generating an oscillating reference magnetic field that periodically saturates the magnetic material by reorienting the field, this center point deviation can be determined and from it the external magnetic field to be measured can be inferred.
Sensors based on, for example, the anisotropic magnetoresistive effect (AMR effect), the giant magnetoresistive effect (GMR effect), the tunnel magnetoresistive effect (TMR effect), etc. can be used for contactless current measurement. . These sensors are used in linear applications, often in measurement bridge applications. There is then the burden of improving the linear characteristic curve of this type of sensor.

The magnetic reversal of the ferromagnetic core within the magnetic core for the fluxgate principle can be detected with a sensor. At this time, a magnetic circuit consisting of an excitation coil and a ferromagnetic core can be used. The sensors use either receive coils or linear magnetic sensors. It may also be envisaged to use one coil wound on a magnetic core simultaneously as exciter and receiver. Additionally, compensation coils can be used to compensate for external magnetic fields, thereby correcting the center point position. The required compensation current then becomes the reference for the external magnetic field.

From document US 2018/0191282 a magnetic field sensor device is known which uses the tunnel magnetoresistive effect (TMR) with two magnetic sensor elements. Further applications of the TMR effect are known from the document US2016/0320462, EP2284553A1.

U.S. Patent Application Publication No. 2016/0320459 EP1450176A1 EP2423693B1 U.S. Patent Application Publication No. 2018/0191282 U.S. Patent Application Publication No. 2016/0320462 EP2284553A1

SUMMARY OF THE INVENTION The present invention provides a magnetic field sensor device and a method for manufacturing a magnetic field sensor device having the features of the independent claims. Furthermore, the invention claims a method of operation of the described magnetic field sensor device.

Preferred embodiments are the subject matter of the respective dependent claims.
According to a first aspect, the invention is a magnetic field sensor device comprising four resistive elements connected in a Wheatstone bridge circuit, each resistive element comprising at least one tunnel magnetoresistive element (TMR element). , each TMR element has an electrically conductive fixed layer, an electrically conductive magnetic free layer, and an electrically insulating tunnel barrier separating the fixed and free layers, the free layer comprising: It relates to a magnetic field sensor device having an anisotropic geometry. The magnetic field sensor device is an excitation device comprising at least one magnetic field device configured to energize the at least one magnetic field device with an excitation current to generate an alternating magnetic field acting on each resistance element. It further comprises an exciter. The magnetic field sensor device further comprises a compensating device configured for each resistive element to generate a DC magnetic field acting on the resistive element. The magnetic field sensor device comprises a measuring device configured to output a measuring signal as a function of the bridge voltage of the Wheatstone bridge circuit. The magnetic field sensor device is configured to generate a control signal based on the measurement signal output from the measurement device for controlling the compensation device such that the DC component of the measurement signal is controlled to a predetermined value. A controller is further provided. Finally, the magnetic field sensor device comprises an evaluation device configured to determine the external magnetic field strength on the basis of the excitation current and the measurement signal output by the measurement device.

According to a second aspect, the invention relates to a method of manufacturing a magnetic field sensor device according to the invention, wherein at least the excitation device and the compensating device are manufactured by thin film processes.

The fluxgate method particularly involves the use of magnetic field sensitive materials (ferromagnetic cores) with a non-linear BH characteristic curve. This generally results in a larger installation space, whose size and position can affect the magnetic field. The magnetic field sensor device according to the invention is constructed such that the sensor elements have geometric anisotropy in order to generate the required non-linearity of the sensor output characteristic curve. Installation space can be saved by incorporating the function of the magnetic field sensitive material into the sensor element.

The idea underlying the present invention is to exploit the geometrically generated non-linearity of magnetic field sensors based on tunnel magnetoresistance in order to provide a highly accurate linear magnetic field sensor device. To this end, the nonlinear TMR elements are connected in a Wheatstone measurement bridge.

Sensors based on TMR are advantageous with respect to the achievable measurement frequencies and are therefore particularly suitable for use in the fluxgate principle. The periodic switching between the two operating points at high frequency places certain demands on the exciter, because when using an exciter coil, the required voltage is highly dependent on the inductance of the exciter coil. is. This also allows high measurement bandwidths to be reached with high precision.

According to a preferred development of the magnetic field sensor device, the free layer is arranged symmetrically with respect to the two main axes, the elongation of the free layer along the main axes being different for the two main axes. The principal axis determines the principal magnetization direction and thus the operating point of the magnetic field sensor device.

According to a preferred development of the magnetic field sensor device, the free layer is elliptically, rectangularly, rhomboidally or lenticularly shaped. The free layer therefore particularly preferably has two axes of symmetry or principal axes.

According to a preferred development of the magnetic field sensor device, the magnetic field device has at least one coil or at least one conductor, and the excitation device has at least one coil or at least one conductor for generating the alternating magnetic field. configured to apply an excitation current to the body;

According to a preferred development of the magnetic field sensor device, the at least one coil or the at least one conductor extends transversely to the magnetization direction of the free layer of the at least one TMR element.

According to a preferred development of the magnetic field sensor device, the excitation device comprises a compensator, the AC component of the excitation current generating an alternating magnetic field and the DC component of the excitation current generating a DC magnetic field. This allows a particularly compact construction.

According to a preferred development of the magnetic field sensor device, each resistive element has a plurality of TMR elements connected in parallel and/or in series. This makes it possible to adjust the sensitivity and effective electrical resistance of the magnetic field sensor device.

According to a preferred development of the magnetic field sensor device, the control device is designed to activate the compensating device in such a way that the measuring signal runs substantially symmetrically about a bridge voltage of zero volts. An evaluation device can determine at which excitation current the Wheatstone measuring bridge switches its operating point. The evaluation device can determine the external magnetic field strength, for example by calculation with a lookup table or a calibration function.

According to a preferred development of the magnetic field sensor device, the evaluation device is further arranged to determine the current strength of the current generating the magnetic field on the basis of the specific strength of the external magnetic field.
According to a preferred development of the magnetic field sensor device, the excitation device and the compensating device are manufactured by thin-film processes. Realizing the exciter and compensator in a thin film process can reduce the current consumption, as the smaller the distance, the smaller the current required to generate the corresponding amplitude of the electric field. Furthermore, preferably, the TMR element may also be manufactured by a thin film process.

According to a preferred development of the magnetic field sensor device, the evaluation device is designed to determine at which excitation current the Wheatstone bridge circuit switches the operating point in order to determine the magnetic field. When an external magnetic field acts on the Wheatstone bridge circuit, the excitation current required for switching the operating point changes. Therefore, the evaluation device can specify the magnetic field strength of the external magnetic field based on the excitation current.

1 is a schematic configuration diagram of a first state of a magnetic field sensor device according to an embodiment of the invention; FIG. The schematic block diagram of the 2nd state of a magnetic field sensor apparatus. Various geometric constructions of the free layer of TMR elements. Schematic diagram illustrating magnetization in a free layer. Schematic diagram of a TMR element. Dependence of resistance on the angle between the magnetization directions of the free and fixed layers of the TMR element. Schematic of a TMR element with a magnetic field device. Schematic which shows the output characteristic curve of the Wheatstone bridge of the magnetic field sensor apparatus which concerns on this invention. FIG. 4 is a flowchart of a method for manufacturing a magnetic field sensor device;

Identical or functionally identical elements and devices are provided with the same reference numerals in all figures. The numbering of process steps is for clarity and generally does not imply any particular chronological order. In particular, several process steps may be performed simultaneously.

FIG. 1 shows a schematic configuration diagram of a magnetic field sensor device 10. As shown in FIG. The Wheatstone bridge circuit comprises four resistive elements R1-R4. Each resistive element R1-R4 consists of a TMR element or TMR cell 11-14 having a fixed layer 71, a free layer 72 and a tunnel barrier (not shown). Free layer 72 has an anisotropic geometry, elliptical in FIG.

The magnetic field sensor device 10 further comprises an excitation device 2 with a magnetic field device. The magnetic field device, which may be configured as a coil or conductor or multiple conductors, is positioned below or above the resistive elements R1-R4. When a current flows through a coil or a conductor, an alternating magnetic field is generated, and the alternating magnetic field acts on resistance elements R1 to R4. The conductor may be manufactured, for example, by a thin film process.

Furthermore, the magnetic field sensor device 10 comprises, for each resistive element R1-R4, a compensating device 3 arranged to generate a DC magnetic field acting on the resistive element. The compensation device 3 and the excitation device 2 may also be implemented by the same component. For example, a coil, a single conductor, or a plurality of parallel conductors extending below or above the TMR elements 11 to 14 may be provided, and an alternating magnetic field is generated by the alternating current component of the excitation current flowing through the coil or conductor. A DC magnetic field is generated by the DC component of the excitation current.

The magnetic field sensor device 10 further comprises a measuring device 4 for measuring the bridge voltage V _DD of the Wheatstone bridge circuit and for outputting a corresponding measuring signal.
The magnetic field sensor device 10 further comprises a control device 5 for receiving measurement signals from the measurement device 4 and for generating control signals based on the measurement signals. Compensator 3 is controlled by this control signal. The control device 5 generates a control signal so that the DC component of the measurement signal is controlled to a predetermined value. In particular, the measurement signal can be controlled to be substantially symmetrical about a bridge voltage of zero volts.

Finally, the magnetic field sensor device 10 comprises an evaluation device 6 for determining the external magnetic field strength on the basis of the excitation current applied by the excitation device 2 and the measurement signal output by the measurement device 4 .
To determine the magnetic field, evaluation device 6 determines the excitation current that switches the operating point of the Wheatstone bridge circuit. When an external magnetic field acts on the Wheatstone bridge circuit, the excitation current required for switching the operating point changes.

As shown in FIG. 1, the magnetization direction of the fixed layer 71 and the magnetization direction of the free layer 72 form an angle. Two of the TMR elements 11 , 14 each have a first free magnetization direction and the other two TMR elements 12 , 13 have a second free magnetization direction that mirrors the magnetization of the free layer 72 . have. The magnetization of the free layer 72 of the TMR elements 11-14 is positively or negatively oriented along the magnetization direction with respect to the two operating points, that is, oriented 180 degrees apart. The magnetization that actually occurs depends on erroneous deviations in the alternating field of the exciter 2 and the DC field of the compensator 3 and the control signal of the controller 6 from the ideal control signal required to compensate for the external magnetic field. .

In the state (first operating point) shown in FIG. 1, the magnetizations of the TMR elements 11 to 14 each exhibit a first direction. The orientation of the TMR elements 11-14 determines the sensing direction x. The magnetic field sensor device 10 can determine the magnetic field strength of the external magnetic field along the sensing direction x.

FIG. 2 shows a further state (second operating point) of the magnetic field sensor device 10 . Here, the magnetizations of the TMR elements 11 to 14 each exhibit a second direction opposite to the first direction.
It should be noted that the present invention is not limited to the illustrated embodiments. In particular, each resistive element R1-R4 may be composed of a plurality of TMR elements 11-14 connected in series and/or in parallel.

FIG. 3 shows various possible geometries of the free layers 72 of the TMR elements 11-14. From left to right, the free layer can be an elliptical free layer 72a, a rectangular free layer 72b, a diamond free layer 72c, or a lenticular free layer 72d.

FIG. 4 is a schematic diagram for explaining the magnetization in the free layer 72. FIG. Axis A, which is the axis of symmetry or principal axis of the free layer 72, is shown. A first orientation of the magnetization of the free layer 72 is illustrated at the bottom left and a second orientation in the opposite direction is illustrated at the bottom right. These magnetization directions of the free layer 72 are periodically switched by an applied alternating magnetic field.

FIG. 5 includes a magnetic pinned layer 71 magnetized along a first direction and a magnetic free layer 72 magnetized along a second direction, either positively or negatively. 2 is a schematic diagram of a TMR element with two directions taking an angle φ; FIG.

Fixed layer 71 has a substantially fixed magnetization that is independent or less dependent on an external magnetic field. The fixed layer 71 and free layer 72 are separated by an electrically non-conductive barrier, also called a blocking layer or tunnel barrier. The pinned layer 71 is magnetically oriented in the preferred direction and the free layer 72 is much more magnetically free. The angle φ between the magnetization directions of the two magnetic layers determines the ohmic resistance of the resulting tunnel magnetoresistance. Depending on the acting magnetic field, this angle φ and thus the resistance change, so that the evaluation device 6 can determine the field strength of the external magnetic field.

FIG. 6 shows the dependence of the resistance R on the angle φ between the magnetization directions of the free and fixed layers of the TMR element. An angle φ of 0 degrees has a first resistance value R↑↑ and corresponds to a parallel orientation of the magnetization directions. As the angle φ increases, the resistance value increases through the resistance value R0 to the maximum value R↑↓ corresponding to the anti-parallel angle of 180 degrees.

FIG. 7 is a schematic diagram of a TMR element with a magnetic field device 21. FIG. The fixed layer 71, the free layer 72, and the parallel conductors forming the magnetic field device 21 and through which the current i flows are shown. The current produces alternating and/or direct magnetic fields that act on the magnetization of the free layer 72 .

To adjust the fixed magnetic reference point, the geometric anisotropy of the free layer 72 is intentionally controlled by the aspect ratio between the length and width of the substantially planar structure not equal to one. adjusted to Withdrawal of the additional magnetic field orients the free layer 72 along the preferred axis set by the anisotropy. Since the anisotropy sets in only one direction, two stable operating points, each twisted 180° to each other, are adjusted.

The stability of the single TMR elements 11-14, ie the amplitude of the magnetic field required to approach each other operating point, is adjusted by the aspect ratio. An elongated free layer 72 has greater stability than a free layer 72 having approximately the same geometric dimensions in both spatial directions.

If a magnetic field of sufficient strength to cyclically alternate between the two operating points of the TMR elements 11-14 is generated using the magnetic field device 21, then in order to approach the respective other operating point The external magnetic field that must first be overcome can be identified by appropriately constructing a Wheatstone bridge circuit with regulated bridge output voltages and knowing the excitation currents required to reach the two operating points.

FIG. 8 is a schematic diagram of the output characteristic curve of the Wheatstone bridge of the magnetic field sensor device 10 according to the invention. The output voltage or bridge voltage V _out is plotted as a function of the magnetic field strength of the external magnetic field B along the sensing direction illustrated in FIG. Saturation voltages V _sat and -V _sat are plotted with the output voltage V _out at zero volts. As the magnetic field increases, the output voltage V _out increases along the arrow direction P starting from the positive saturation voltage V _sat . When the upper magnetic field strength B _flip is positive, the output voltage V _out falls to a negative value and approaches the negative saturation voltage V _sat from the lower side for increasing magnetic field strength B. Conversely, the output voltage V _out decreases from a large magnetic field strength B to a lower negative magnetic field strength B _flip , at which time the magnetic field strength B moves to a positive value. The course of the output voltage V _out exhibits hysteresis.

To determine the magnetic field, the measuring device 4 records the excitation coil current and the bridge voltage of the Wheatstone bridge circuit and describes at which excitation current the Wheatstone bridge circuit switches its operating point. When an external magnetic field acts on the Wheatstone bridge circuit, the exciting current required for switching the operating point changes.

Furthermore, the compensation device 3 controlled by the control device 5 can supply a compensation current such that the operating point is switched symmetrically around zero even in the presence of an external magnetic field.
FIG. 9 is a flow diagram showing a method of manufacturing the magnetic field sensor device 10 according to the present invention.

To this end, in a first process step S1 in thin-film technology, a Wheatstone bridge circuit is provided with four interconnected resistor elements R1-R4, each resistor element having at least one TMR element 11-14.

Furthermore, in process step S2 an excitation device 2 is provided for generating an alternating magnetic field with at least one magnetic field device, such as a coil or a plurality of parallel conductors, which is also preferably manufactured by a thin film process. Furthermore, a compensation device 3 is provided for generating a DC magnetic field. The compensator 3 may comprise separate coils or separate conductors, which are also preferably manufactured by thin film processes. However, the compensator 3 and the exciter 2 may comprise the same components, such as one or more coils or conductors.

In process step S3, a measuring device 4 for measuring the bridge voltage of the Wheatstone bridge circuit is configured. In order to control the compensation device 3 in such a way that the DC component of the measurement signal is controlled to a predetermined value, a control device 5 is arranged which generates a control signal on the basis of the measurement signal output by the measurement device. Finally, an evaluation device is constructed which determines the external magnetic field strength on the basis of the excitation current and the measurement signal output by the measuring device.

2 excitation device 3 compensation device 4 measurement device 5 control device 6 evaluation device 10 magnetic field sensor device 11 TMR cell, TMR element 12 TMR cell, TMR element 13 TMR cell, TMR element 14 TMR cell, TMR element 21 magnetic field device 71 fixed layer 72 Free layer 72a Elliptical free layer 72b Rectangular free layer 72c Diamond free layer 72d Lenticular free layer R1 resistive element R2 resistive element R3 resistive element R4 resistive element S1 process step S2 process step S3 process step

Claims (11)

Four resistive elements (R1-R4) connected to a Wheatstone bridge circuit, each resistive element (R1-R4) having at least one tunnel magnetoresistive TMR element, each TMR element (11-14 ) separates a conductive pinned layer (71), a conductive free layer (72; 72a-72d) and an electrically insulating tunnel barrier separating said pinned layer (71) and said free layer (72; 72a-72d). and wherein said free layers (72; 72a-72d) have an anisotropic geometry;
An excitation device (2) comprising at least one magnetic field device (21), wherein the at least one magnetic field device (21) is energized with an excitation current to cause each resistance element (R1-R4) to an exciter (2) configured to generate an alternating magnetic field acting on (R1-R4);
a compensator (3) configured to generate for each resistive element (R1-R4) a DC magnetic field acting on said resistive element (R1-R4);
a measuring device (4) configured to output a measurement signal in response to the bridge voltage of the Wheatstone bridge circuit;
generating a control signal based on the measurement signal output from the measurement device (4) to drive and control the compensation device (3) so that the DC component of the measurement signal is controlled to a predetermined value; a controller (5) configured in
an evaluation device (6) configured to determine an external magnetic field strength on the basis of the excitation current and the measurement signal output from the measurement device (4);
A magnetic field sensor device (10), comprising: said free layers (72; 72a-72d) are arranged symmetrically with respect to two principal axes, the elongation of said free layers (72; 72a-72d) along said principal axes being different for said two principal axes; Magnetic field sensor device (10) according to claim 1. Magnetic field sensor device (10) according to claim 2, wherein the free layer (72; 72a-72d) is elliptically, rectangularly, rhomboidally or lenticularly shaped. The magnetic field device (21) comprises at least one coil or at least one conductor, and the excitation device (2) comprises the at least one coil or the at least one conductor for generating an alternating magnetic field. 4. The magnetic field sensor device (10) according to any one of claims 1 to 3, arranged to pass an excitation current to the . The magnetic field of claim 4, wherein said at least one coil or said at least one conductor extends transversely to the magnetization direction of said free layer (72) of said at least one TMR element (11-14). A sensor device (10). 6. The excitation device (2) comprises the compensation device (3), the AC component of the excitation current generating the alternating magnetic field and the DC component of the excitation current generating the DC magnetic field. A magnetic field sensor device (10) according to any one of the preceding claims. Magnetic field sensor device (10) according to any one of the preceding claims, wherein each resistive element (R1-R4) comprises a plurality of TMR elements (11-14) connected in parallel and/or in series. . 8. Any of claims 1 to 7, wherein the control device (5) is arranged to drive the compensation device (3) such that the measurement signal extends substantially symmetrically about a bridge voltage of zero volts. Magnetic field sensor device (10) according to claim 1. Magnetic field sensor device (10) according to any one of the preceding claims, wherein the excitation device (2) and the compensation device (3) are manufactured by a thin film process. 10. Method for manufacturing a magnetic field sensor device (10) according to any one of the preceding claims, characterized in that at least the excitation device (2) and the compensation device (3) are manufactured by thin film processes. A method of operating a magnetic field sensor device (10) according to any one of claims 1 to 9, comprising:
The magnetic field sensor device (10)
Equipped with four resistance elements (R1 to R4) connected to a Wheatstone bridge circuit,
an excitation device (2) comprising at least one magnetic field device (21);
a compensator (3);
a measuring device (4);
a controller (5);
an evaluation device (6),
energizing the at least one magnetic field device (21) with an exciting current so as to generate an alternating magnetic field acting on each resistive element (R1-R4);
a step of generating a direct current magnetic field acting on each resistive element (R1-R4);
outputting a measurement signal according to the bridge voltage of the Wheatstone bridge circuit;
generating a control signal based on the measurement signal output from the measurement device (4) to drive and control the compensation device (3) so that the DC component of the measurement signal is controlled to a predetermined value; When,
determining an external magnetic field strength based on said excitation current and said measurement signal output from said measurement device (4).

Images