JP2017211258A - Biological information detector, biological information detection sensor, and method for correcting biological information detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that anything that responds to a magnetic field induced by a coil happens to be detected although it is not a living matter.SOLUTION: A biological information detection sensor 24 includes a support plate 50 and magnetic field detection chips 31, 32. The magnetic field detection chips 31, 32 are arranged on a side face of the support plate so as to be separate from each other in a first direction (direction X) in a first plane. Each of the magnetic field detection chips 31, 32 is configured so that sensitivity to a change of magnetic field in a second direction (direction Y) orthogonal to the first direction (direction X) in the first plane becomes maximum. Since the presence, dimension, position and manner of neural activity of a living matter are detected by detecting a magnetic field generated around by an electric current due to the neural activity of the living matter, i.e., what is called a biomagnetic field, it is possible to easily detect even a human body having a magnetic substance or a conductor.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a biological information detection apparatus that detects a living body using magnetism, a biological information detection sensor, and a correction method for the biological information detection apparatus.

  In Japanese translations of PCT publication No. 2004-529313 (patent document 1), using a magnetic sensor built in a seat of a vehicle or the like, information on a living body sitting on the seat (blood permeance containing iron) is obtained using magnetism. A system for detecting is disclosed. In this system, a coil for applying an alternating magnetic field to the seat and a magnetic sensor for detecting the magnetic field are built in, and the response of the living body to the magnetic field induced by the coil is detected by the magnetic sensor, Detect dimensions, position, etc.

JP-T-2004-529313 (claim 8, paragraph 0032)

  However, in this prior example, if it responds to the magnetic field induced by the coil, it may be detected even if it is not a living body. Examples of such an erroneous detection include an object such as a magnetic body or a ring-shaped conductor.

  An object of the present invention is to provide a biological information detection device, a biological information detection sensor, and a correction method for a biological information detection device that reduce the possibility of erroneous detection of an object other than a living body.

  The present invention is a biological information detection device, and includes a support plate having a first surface, and first and second magnetic field detection units. The first and second magnetic field detectors are arranged on the first surface so as to be separated from each other in the first direction within the first surface. Each of the first and second magnetic field detection units is configured to have a maximum sensitivity to a change in the magnetic field in the second direction orthogonal to the first direction in the first plane.

  According to the present invention, since a living body detects a magnetic field generated by itself without using a magnetic field induced by a coil, noise caused by an object responding to an external magnetic field, such as a magnetic body or a ring-shaped conductor, is detected. Can be less affected.

It is sectional drawing which shows an example of the magnetic thin film structure which comprises a TMR element. It is (A) top view and (B) sectional drawing which show an example of the shape of a TMR element. It is the characteristic view which showed an example of the magnetoresistive characteristic of a TMR element. It is a perspective view which shows the sheet | seat incorporating the biometric information detection sensor which concerns on Embodiment 1. FIG. It is a top view of the sheet | seat incorporating the biometric information detection sensor. FIG. 6 is an enlarged view of the biological information detection sensor 24 of FIG. 5. It is a top view which expands and shows a part of TMR element used for a biological information detection sensor. It is sectional drawing in VIII-VIII of FIG. It is a perspective view which shows the modification of the shape of a support plate. It is a circuit diagram which shows an example of a detection circuit. It is a circuit diagram which shows the 1st modification of a detection circuit. It is a top view which shows the modification of arrangement | positioning of a TMR element. It is a circuit diagram which shows the 2nd modification of a detection circuit. It is a perspective view which shows the sheet | seat incorporating the biometric information detection sensor which concerns on Embodiment 2. FIG. It is a graph which shows the example of analysis which selects a desired signal from the signal of a plurality of living body information detection sensors. It is a graph for demonstrating the influence of the sensitivity variation of the TMR element which comprises a biological information detection sensor. It is a circuit diagram for performing sensitivity correction of a TMR element. It is a perspective view of the sheet | seat incorporating the coil for correction | amendment. It is a top view of the biological information detection sensor provided with the annular current path. It is a graph for demonstrating the characteristic after correction | amendment of the sensitivity variation of the TMR element which comprises a biological information detection sensor. It is a flowchart for demonstrating the content of the correction | amendment process performed using a coil for a correction | amendment and an annular current path. It is a perspective view which shows the modification of the sheet | seat incorporating the biometric information detection sensor. It is a perspective view which shows an example of the bed incorporating the biometric information detection sensor. It is sectional drawing which shows the element arrangement | positioning of the bed incorporating the biometric information detection sensor shown in FIG. It is sectional drawing which shows the modification of the element arrangement | positioning of the bed which incorporates the biometric information detection sensor. It is a figure which shows the modification of a biometric information detection sensor.

  Embodiments of the present invention will be described below with reference to the drawings. The same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

  In the following embodiments, a biological information detection sensor provided with a magnetic sensor built in a portion that comes into contact with a living body, such as the interior of a car seat or a bed, is disclosed. This sensor detects the presence, size, position, and state of nerve activity by detecting the magnetic field generated by the current associated with the nerve activity of the living body, that is, the so-called biomagnetic field. Even a human body can be easily detected.

[Embodiment 1]
In a living body, information is transmitted by a current flowing through a nerve. A magnetic field in which such a current is generated around the living body is called biomagnetic. Biomagnetism is a magnetic field generated when a weak current flows in the direction in which a nerve extends. For the current flowing in the direction in which the nerve extends, a concentric magnetic field surrounding the nerve is generated as shown by the right-handed screw law. In the present embodiment, a biometric information detection apparatus that measures the biomagnetism with a backsheet of a vehicle seat or a biometric information detection sensor (magnetic sensor unit) attached to the inside of a bed will be described. As such a highly sensitive magnetic sensor for detecting biomagnetism, a tunnel magnetoresistance effect element (TMR element) is preferable.

  FIG. 1 is a cross-sectional view showing an example of a magnetic thin film structure constituting a TMR element. The TMR element includes a free layer 4 (upper electrode), a fixed layer 8 (lower electrode), and a tunnel insulating layer 6. A free layer 4 and a ferromagnetic layer called a fixed layer 8 are laminated via a tunnel insulating layer 6, and this laminated film is processed by photolithography or the like. As a result, as shown in FIG. 1, a TMR element is obtained in which the free layer 4 located above and the fixed layer 8 located below are formed with the tunnel insulating layer 6 interposed therebetween.

  The magnetization direction of the fixed layer 8 is fixed in one direction by an exchange coupling magnetic field with the antiferromagnetic layer 10, for example, as shown later in FIG. Alternatively, the magnetization direction of the fixed layer 8 is held in one direction by a magnetic material having a large coercive force.

  On the other hand, the free layer 4 has a spin valve structure in which the magnetization direction is freely rotated by the external magnetic field Hex. The resistance of the TMR element having such a spin valve structure changes according to the angle formed by the magnetization direction of the fixed layer 8 and the magnetization direction of the free layer 4. That is, the resistance of the TMR element changes as the magnetization direction of the free layer 4 changes due to the external magnetic field. For this reason, it is possible to detect a change in the magnetization direction of the free layer 4 due to an external magnetic field in the form of the resistance of the element.

  The pinned layer 8 may include a so-called SAF (Synthetic Anti Ferromagnetic) structure formed of two layers of ferromagnetic thin films stacked via a thin nonmagnetic layer and antiferromagnetically coupled to each other. The free layer 4 may be a single magnetic layer or may have a structure in which two or more kinds of magnetic layers are stacked. As in the structure of the laminated film in FIG. 1, the antiferromagnetic layer 10 may be included in the upper electrode, or may be included in the lower electrode.

For example, a TMR element can be configured by using IrMn as the antiferromagnetic layer 10, CoFe as the fixed layer 8, Al ₂ O ₃ as the tunnel insulating layer 6, and NiFe as the free layer 4. In addition, the antiferromagnetic layer 10 is mainly made of FeMn, IrMn, PtMn, and the material constituting the ferromagnetic material is mainly Co, Ni, Fe such as Co, Fe, CoFe alloy, CoNi alloy, CoFeNi alloy, etc. There are no particular restrictions as long as the material can provide a desired performance for the TMR element, such as a metal contained as a component or a whistler alloy such as NiMnSb or Co ₂ MnGe. The nonmagnetic layer that is the tunnel insulating layer 6 may be an insulator, and may be a metal oxide such as Ta ₂ O ₅ , SiO ₂ , MgO, or a mixture thereof. It may be fluoride.

  Each of the above films is formed by, for example, DC magnetron sputtering. Further, it may be formed by, for example, a molecular beam epitaxy (MBE) method, various sputtering methods, a chemical vapor deposition (CVD) method, or a vapor deposition method.

  In addition, the TMR element is manufactured, for example, by patterning each film by photolithography and reactive ion etching. In that case, for example, first, after forming the films of the free layer 4, the tunnel insulating layer 6 and the fixed layer 8, a desired element pattern is formed by a photoresist. Thereafter, the element shape is obtained by ion milling or reactive ion etching. The element pattern may be formed by electron beam lithography or a focused ion beam.

  Such a TMR element is configured such that when the external magnetic field Hex is not applied, the magnetization direction of the free layer 4 and the magnetization direction of the fixed layer 8 are orthogonal to each other, so that the resistance is linear with respect to the external magnetic field Hex. Can change. For example, when the fixed layer 8 is formed using an antiferromagnetic film, the element is heated and cooled above the blocking temperature of the antiferromagnetic film while applying a sufficiently strong magnetic field (for example, 1 Tesla or more) in a desired direction. Thus, the magnetization direction of the fixed layer 8 can be set to a desired direction.

2A is a top view and FIG. 2B is a cross-sectional view showing an example of the shape of the TMR element.
The magnetization direction of the free layer 4 changes according to the external magnetic field Hex as described above. Here, the magnetization direction of the free layer 4 when the external magnetic field Hex is not applied is defined by making the element pattern viewed from the upper surface of the element formation surface into a horizontally long shape as shown in FIG. can do.

  FIG. 3 is a characteristic diagram showing an example of the magnetoresistance characteristic of the TMR element. When a magnetic field is applied to the TMR element formed in the shape shown in FIG. 2 in a direction parallel to the magnetization direction of the fixed layer 8, the magnetization direction of the free layer 4 changes due to an external magnetic field, and the resistance as shown in FIG. Changes appear. At this time, a saturation region in which the magnetization direction of the free layer 4 and the magnetization direction of the fixed layer 8 are parallel or antiparallel and the resistance does not depend on the external magnetic field, and a linear region having a linear dependence on the external magnetic field appear. . In the TMR element, generally, the resistance is the minimum value when the magnetization direction of the free layer 4 and the magnetization direction of the fixed layer 8 are parallel, and the resistance direction is when the magnetization direction of the free layer 4 and the magnetization direction of the fixed layer 8 are antiparallel. The resistance becomes the maximum value.

  When a sensor that detects a minute magnetic field using such a TMR element is configured, it has been found that when a magnetic field corresponding to the saturation region is applied to the TMR element, the magnetic field cannot be detected.

  If the TMR element is not specially shielded from magnetic fields, the magnetic field of 1e-6 to 1e-5T (hereinafter simply referred to as a static magnetic field) due to the influence of geomagnetism, magnetism from the outside of the vehicle, and magnetization of the magnetized magnetic material in the vehicle. Call). On the other hand, a magnetic field of 1e-10T must be detected as a magnetic field related to biomagnetism (hereinafter referred to as biomagnetic field). The magnitude of the static magnetic field must be assumed to change at a frequency lower than that of the biomagnetic field due to, for example, changes in geomagnetism over time, changes in the direction of the vehicle, changes in the arrangement of magnetic bodies outside the vehicle, and the like. . For example, when the traveling direction of the vehicle changes, the relative direction of the magnetic field applied to the vehicle also changes, and as a result, the static magnetic field applied to the sensor attached to the seat also changes. Further, the magnetic field-resistance characteristics of the TMR element have a saturation region and a linear region as shown in FIG. When a static magnetic field corresponding to the saturation region is applied, even if a change in the magnetic field related to the biomagnetism occurs, the resistance change does not appear, so that the magnetic field cannot be detected.

  In order to solve this problem, it is preferable to use a TMR element having a sufficiently wide magnetic field range in the linear region, and the magnetic field range to be detected by the TMR element is within the linear region of the TMR element characteristics. In the TMR element, the width of the linear region can be increased by increasing the aspect ratio so as to have a horizontally long shape and increasing the shape magnetic anisotropy of the free layer 4 as shown in FIG. Therefore, it is suitable for such a use. Furthermore, the influence of the electrostatic field can be reduced by devising the arrangement of the TMR elements.

  FIG. 4 is a perspective view showing a sheet incorporating the biological information detection sensor according to the first embodiment. FIG. 5 is a top view of a sheet incorporating a biological information detection sensor. FIG. 6 is an enlarged view of the biological information detection sensor 24 of FIG.

  The biological information detection device 20 shown in FIGS. 4 to 6 includes a sheet 22 and a biological information detection sensor 24. The sheet 22 is an example of a structure having a portion that is in close contact with a living body. The support plate 50 is disposed inside such a structure.

  The biological information detection sensor 24 includes a support plate 50 having a first surface (upper surface) and a second surface (back surface), and magnetic field detection chips 31 and 32. The magnetic field detection chips 31 and 32 are arranged on the first surface of the support plate 50 so as to be separated from each other in the first direction (X direction) in the first surface. Each of the magnetic field detection chips 31 and 32 is maximally sensitive to changes in the magnetic field in the second direction (Y direction) orthogonal to the first direction (X direction) in the first plane. Configured. Each of the magnetic field detection chips 31 and 32 is a chip in which a large number of TMR elements connected in series are integrated. The support plate 50 is arranged so that the first direction (X direction in FIG. 6) in which the magnetic field detection chips 31 and 32 are separated from each other coincides with the direction parallel to the backrest surface of the seat 22 (X direction in FIG. 4). .

  As described above, the magnetic field detection chips 31 and 32 including the TMR elements having the same characteristics are arranged at two places where the magnitudes of the static magnetic fields are substantially equal and the magnitudes of the biomagnetic fields are different. By configuring the detection circuit so as to amplify the magnetic field difference, the influence of the static magnetic field can be canceled.

  A magnetic field 30 formed by a current 28 that transmits a nerve extending parallel to the spine is generated on a concentric circle centered around the spine. Here, like the coordinate axes shown in FIG. 4, the vertical direction of the human body 26 (for example, the axis of the spine) is the Z axis, the front of the vehicle is the Y axis, and the axes orthogonal to the Z axis and the Y axis are the X axis. Is defined as an orthogonal coordinate system. As two places where the magnitude of the static magnetic field is substantially the same and the magnitude of the biomagnetic field is different, for example, as shown in the arrangement of the biological information detection sensor 24 in FIGS. Equally, it is a position in the opposite direction when viewed from the spine at approximately the same distance in the X direction on the basis of the spine position.

  FIG. 6 shows the direction of the magnetic field 30 at the element position on the biological information detection sensor 24. Two places where the magnitude of the static magnetic field is substantially the same and the magnitude of the biomagnetic field are different are, for example, the position PA and the position PB. The biological information detection sensor 24 includes a magnetic field detection chip 31 and a magnetic field detection chip 32 that are disposed at the position PA and the position PB, respectively.

  A magnetic field 30 generated at a position PA by a current 28 that transmits a nerve extending through the spine from the head toward the toes has an X component Hx and a Y component Hy. The magnetic field 30 generated by the current 28 at the position PB has an X component Hx ′ and a Y component Hy ′. In this example, the X components Hx and Hx ′ are approximately equal in size and direction, but the Y component Hy and Y component Hy ′ are approximately equal in size and opposite in direction. On the other hand, the Y direction component of the static magnetic field is substantially the same at either position. As a result, the difference between the resistances of the TMR elements at position PA and position PB is proportional to the magnitude of the biomagnetic field. This is output using an appropriate detection circuit.

  Here, magnetic field detection chips 31 and 32, which are formed in the XY plane and integrated with a large number of highly sensitive TMR elements in the Y direction, are arranged at the position PA and the position PB. As the magnetic field detection chips 31 and 32, for example, 1600 unit TMR elements each having an element shape in which the direction of the fixed layer is the plus direction of the Y direction and is long in the X direction can be used.

  FIG. 7 is an enlarged top view showing a part of the TMR element used in the biological information detection sensor. 8 is a cross-sectional view taken along line VIII-VIII in FIG.

  The upper electrode 46, which is a horizontally long island portion of the TMR element 1, has all the laminated structures of magnetic films. The lower electrode 48, which is an island-shaped portion surrounding the two upper electrodes 46, partially cuts the upper part of the laminated structure of the magnetic film by a technique such as ion milling to leave the lowermost conductive layer. And forming a connection portion. Further, the upper electrode 46 is connected to the upper electrode 46 surrounded by another adjacent lower electrode 48 by the aluminum wiring 44 through the contact hole 42. Two upper electrodes 46 surrounded by the same lower electrode 48 are electrically connected to each other via the lower electrode 48.

  In this way, a magnetic sensor is configured in which a plurality of unit TMR elements are connected in series with the aluminum wiring 44 -the upper electrode 46 -the lower electrode 48 -the upper electrode 46 -the aluminum wiring 44. The magnetization direction of the fixed layer (lower electrode 48) is the same in all TMR elements, and is the vertical direction (Y direction) of the drawing. The major axis direction of the upper electrode 46 is aligned in the horizontal direction (X direction) perpendicular to this.

  In this way, the following configuration is realized. That is, each of the magnetic field detection chips 31 and 32 in FIG. 6 includes a plurality of TMR elements 1. Each of the plurality of TMR elements 1 has a horizontally long shape extending in a direction perpendicular to the magnetization direction of the fixed layer 8 as shown in FIG. As shown in FIG. 7, the plurality of TMR elements 1 are arranged side by side in the direction of magnetization of the fixed layer (Y direction), and extend between the directions of magnetization of the fixed layer (Y direction). An aluminum wiring 44 and a lower electrode 48) are connected in series. Each of the plurality of TMR elements 1 and a plurality of contact holes 42 for inter-element wiring are provided.

  In this way, each TMR element is configured such that the free layer has high anisotropy in the X direction and the magnetization of the fixed layer is fixed in the Y direction. Thereby, each of the magnetic field detection chips 31 and 32 in which a plurality of TMR elements are connected in series becomes a magnetic sensor having high sensitivity to the magnetic field in the Y direction. In the example of FIG. 6, the resistance of the TMR element mounted on the magnetic field detection chip 31 disposed at the position PA is high with reference to the resistance value of the TMR element when there is no magnetic field, and the magnetic field detection chip 32 disposed at the position PB has a high resistance. The resistance of the mounted TMR element is lowered. In order to provide a sensitivity difference between the X direction and the Y direction, the aspect ratio of the upper electrode portion of the TMR element is preferably 10: 1 or more, more preferably 100: 1 or more.

  The support plate constituting the biological information detection sensor 24 is a rectangular flat plate made of a nonmagnetic material such as resin, and the positional relationship between the magnetic field detection chips 31 and 32 provided at the position PA and the position PB is changed. It is preferable to hold so that there is no.

  FIG. 9 is a perspective view illustrating a configuration example of the shape of the support plate. The support plate may be a rectangular flat plate, but a protrusion 52 as shown in FIG. 9 is provided on the long side of the support plate 50 so that the positional relationship between the position PA and the position PB does not change due to deformation. May be raised.

  The support plate 50 has holes 56 formed at four corners, for example, and is attached to the structural member of the sheet via a holding mechanism 54 such as a substantially cylindrical rubber inserted into the holes 56. By using the rubber holding mechanism 54, noise such as vibration from the vehicle can be reduced.

  FIG. 10 is a circuit diagram illustrating an example of a detection circuit. The biological information detection sensor 24 includes a magnetic field detection chip 31 disposed at the position PA and a magnetic field detection chip 32 disposed at the position PB. A magnetic field detection chip 31 and a magnetic field detection chip 32 are connected in series in this order between the power supply Vcc and the ground GND. One input terminal of the differential amplifier circuit 64 receives the potential of the connection node between the magnetic field detection chip 31 and the magnetic field detection chip 32. An appropriate reference voltage is applied to the other input terminal of the differential amplifier circuit 64. For example, a circuit in which a resistor 61 and a variable resistor 63 are connected in series between the power supply Vcc and the ground GND is connected in parallel to the magnetic field detection chip 31 and the magnetic field detection chip 32. The resistance value of the variable resistor 62 is adjusted so that the output of the differential amplifier circuit 64 is not saturated, and the origin of the output voltage when there is no biomagnetic input is set.

  When biomagnetism is superimposed on a static magnetic field, a difference occurs between the magnetic fields applied to the position PA and the position PB. Accordingly, the amount of change in the resistance value of the TMR elements of the magnetic field detection chip 31 and the magnetic field detection chip 32 is different, so that the input voltage to one terminal of the differential amplifier circuit 64 changes. As a result, an output corresponding to the magnitude of biomagnetism is obtained. For example, an instrumentation amplifier can be used as the differential amplifier circuit 64. The output of the differential amplifier circuit 64 is converted into a digital signal by the A / D converter 66. This digital signal is used as living body detection information by a controller or the like incorporating a computer.

  FIG. 11 is a circuit diagram showing a first modification of the detection circuit. The detection circuit may be a Wheatstone bridge circuit as shown in FIG. In the detection circuit of this modification, a magnetic field detection chip in which the TMR element 71 and the TMR element 72 are integrated is disposed at the position PA, and a magnetic field detection chip in which the TMR element 73 and the TMR element 74 are integrated is disposed at the position PB. Is done.

  In the first branch constituting the Wheatstone bridge, a TMR element 71 and a TMR element 74 are connected in series between the power supply Vcc and the ground GND in this order. In the second branch, a TMR element 73 and a TMR element 72 are connected in series in this order between the power supply Vcc and the ground GND. One input terminal of the differential amplifier circuit 64 receives the potential of the connection node between the TMR element 71 and the TMR element 74. The other input terminal of differential amplifier circuit 64 receives the potential of the connection node between TMR element 73 and TMR element 72.

  If all the TMR elements 71 to 74 have the same characteristics, the resistance values of the TMR elements 71 to 74 are all the same when the applied magnetic field is the same. Therefore, the voltages at one input terminal and the other input terminal of the differential amplifier circuit 64 are both Vcc / 2.

  When biomagnetism is superimposed on a static magnetic field, there is a difference between the magnetic fields applied to the position PA and the position PB, so that the resistances of the TMR element 71 and the TMR element 72, and the TMR element 73 and the TMR element 74 change with different magnitudes. . For this reason, a difference arises in the voltage of one input terminal of the differential amplifier circuit 64, and the other input terminal, and the output according to the magnitude | size of biomagnetism is obtained.

  At this time, at the position PA and the position PB, the detection accuracy can be improved by devising the arrangement of the unit TMR elements. Here, the reason why the arrangement of the TMR element 71 and the TMR element 72 cannot be the same position will be described.

  When a plurality of TMR elements are formed on the same chip, the magnetic thin film formed on the same surface is partially removed to form a plurality of TMR elements. In this relationship, the positions where the TMR element 71 and the TMR element 72 are formed cannot be exactly the same. Therefore, a difference occurs between the positions of the TMR element 71 and the TMR element 72.

  All the TMR elements described in FIG. 7 are electrically connected in series. Therefore, for example, only the TMR element 71 of FIG. 11 is formed at this position. At this time, the TMR element 72 is formed at a position (not shown in FIG. 7) away from here on the chip. Therefore, the TMR element 71 and the TMR element 72 cannot be arranged closer to the size of the TMR element 71 itself as long as the arrangement of FIG. 7 is adopted. In particular, this effect cannot be ignored in an element having a large in-plane size for a living body.

  FIG. 12 is a top view showing a modified example of the arrangement of the TMR elements. Preferably, for example, as shown in FIG. 12, a magnetic field detection chip in which TMR elements are arranged in a nested manner is used to reduce the influence of the difference in the arrangement positions of the two elements of the TMR element 71 and the TMR element 72. To do.

  In FIG. 12, two rows of TMR elements connected in series are formed on the same chip in a nested manner. These are connected to the positions of the TMR element 71 and the TMR element 72 in FIG. 11, for example. The magnetic field felt by the TMR elements 71 to 72 can be described by the average position of the TMR elements connected in series. For this reason, when the arrangement shown in FIG. 12 is adopted, the difference in position between the TMR elements 71 and 72 can be made smaller than the in-plane size of the element.

  FIG. 13 is a circuit diagram showing a second modification of the detection circuit. This detection circuit includes TMR elements 81 and 82 connected in series, resistors 83 and 84 connected in series, a differential amplifier circuit 85, a time integration circuit 87, and an A / D converter 86. As shown in FIG. 13, the detection circuit may be configured to output a difference from a value obtained by averaging the outputs of the magnetic sensors. In this configuration, a current flows through the resistor 84 in accordance with the output obtained by integrating the output of the differential amplifier circuit 85 by the time integration circuit 87. The amount of current in the resistor 84 increases, and the potential of the connection node between the resistor 83 and the resistor 84 increases. For this reason, the difference between the potential of the connection node of the resistor 83 and the resistor 84 and the potential of the connection node of the TMR element 81 and the TMR element 82 decreases. In this way, the potential of the connection node between the resistor 83 and the resistor 84 approaches the time average value of the intermediate potential of the TMR element 81 and the TMR element 82 that are time averaged.

  As described above, the TMR element disposed at two positions where the static magnetic field is the same and the biomagnetic field is different from each other and the circuit that cancels the influence of the static magnetic field are provided, so that the biomagnetism can be detected with high sensitivity. Is possible.

  A Wheatstone bridge as shown in FIG. 11 or a circuit that obtains a time average as shown in FIG. 13 and inputs it on one side of the bridge corresponds to a “circuit that cancels the influence of a static magnetic field”.

  When there is no saturation of the TMR element and the magnetic field and the TMR element characteristics are almost proportional, even if a Wheatstone bridge as shown in FIG. 11 is used as an input, a time average as shown in FIG. Even in a circuit that obtains the value, it is possible to cancel the influence of the static magnetic field.

[Embodiment 2]
In the first embodiment, an example in which one biological information detection sensor is arranged inside the structure has been described. However, in the second embodiment, more detailed biological information is obtained by using a plurality of biological information detection sensors.

  FIG. 14 is a perspective view showing a sheet incorporating the biological information detection sensor according to the second embodiment. A biological information detection device 120 shown in FIG. 14 includes a sheet 122 and a plurality of biological information detection sensors 131 to 135. Each of the biological information detection sensors 131 to 135 includes magnetic field detection chips 31 and 32 arranged on a support plate as shown in FIG. Similar to FIG. 6, the magnetic field detection chips 31 and 32 having the same characteristics are arranged at two places where the magnitudes of the static magnetic fields are substantially equal and the magnitudes of the biomagnetic fields are different, and the difference between the magnetic fields at the two places is amplified. By configuring the detection circuit to do so, the influence of the static magnetic field can be canceled.

  FIG. 15 is a graph illustrating an analysis example in which a desired signal is selected from signals from a plurality of biological information detection sensors. FIG. 15 shows changes in the elapsed time of outputs from the plurality of biological information detection sensors 131 to 135 of the sheet shown in FIG. The information transmission speed of nerves in the living body is sufficiently slow compared with the transmission speed of electricity and magnetism. Furthermore, the transmission speed differs depending on the type of nerve involved in information transmission. Therefore, a plurality of biological information detection sensors 131 to 135 are arranged in the biological information detection device 120, and magnetic signals obtained from the plurality of biological information detection sensors 131 to 135 are compared with each other.

  There are various methods for discriminating whether a signal is a detection target. For example, a transmission speed obtained by detecting a peak of a signal detected by each biological information detection sensor and calculating a peak interval between the signals. Can be used.

  The output from each biological information detection sensor is differentiated, and the point where the value becomes 0 is defined as the peak position. When the time difference in peak position is compared between each biological information detection sensor, and if the time difference is a value corresponding to the transmission speed of the nerve, it is judged as a detection target signal, and it is shifted Is determined not to be a detection target.

  The calculation used for these determinations can be realized in an analog manner, but the method realized by a computer program is the easiest to understand.

  For example, a data acquisition loop for periodically acquiring the outputs of all units in turn is turned. The first biological information detection sensor 131 determines that the difference from the previous output value has changed from positive to negative as the peak position and sets a flag. The number of times that the data acquisition loop has been turned is counted from the time when the detection waveform of the biological information detection sensor 131 reaches the peak position until the time when the flag of the second biological information detection sensor 132 is reached. If this count value does not deviate from a predetermined predicted value, the process proceeds to a process of measuring the time between the biological information detection sensor 132 and the biological information detection sensor 133. If the count value is different from the predicted value, the flag of the biological information detection sensor 131 is reset, and the process returns to the original data acquisition loop. The processing performed between the biological information detection sensor 131 and the biological information detection sensor 132 as described above is also performed between the biological information detection sensors 132-133, 133-134, and 134-135, and all of these are counted. When the value matches the predicted value, the detected signal is determined as a detection target signal.

  In this way, the transmission speed of the nerve signal can be detected. When the difference Δt1 between the biological information detection sensors at the peak positions of the magnetic signals detected by the plurality of biological information detection sensors matches the preset transmission speed, a desired signal is obtained, and between the biological information detection sensors in FIG. When the difference from the transmission speed set as in the difference Δt2 is large, it is processed as noise. In this way, signals that are not detection targets can be removed. According to the biological information detection apparatus according to Embodiment 2, for example, a signal for moving the limbs and a signal for moving the heart can be distinguished.

[Embodiment 3]
In the sheet with the magnetic sensor as in the first and second embodiments, the plurality of magnetic field detection chips 31 and 32 are arranged apart from each other, so that the reference voltage is corrected.

  This correction is a correction for errors caused by variations in resistance of the TMR element and resistance of wiring for connecting the TMR element and other circuit components cannot be ignored. For example, since the characteristics of the magnetic field detection chip 31 and the magnetic field detection chip 32 in the circuit of FIG. 10 do not match, the resistances of the resistor 61 and the variable resistor 62 are not ideal Vcc / 2. In FIG. 10, the resistance value of the variable resistor 62 can be corrected by shifting it from the resistance value of the resistor 61 by an amount corresponding to the resistance difference between the magnetic field detection chip 31 and the magnetic field detection chip 32. Further, the time integration circuit 87 can also correct the circuit of FIG. In the circuit of FIG. 13, a current is passed through the resistor 84 so that the time average of the output of the differential amplifier circuit 85 becomes 0, and the potential of the connection node between the resistor 83 and the resistor 84 is changed. Even if there is some influence of parasitic resistance, if the magnetic field applied to the TMR elements 81 and 82 is constant for a sufficiently long time with respect to the integration time of the time integration circuit 87, the time integration circuit so that the potential difference of the bridge becomes zero. Is set, so the influence of parasitic resistance is cancelled.

  In the third embodiment, another correction will be described. In this correction, if the sensitivity differs between two magnetic field detection chips provided apart from each other, even if the origin of the sensor output is correctly adjusted with a certain static magnetic field, if the static magnetic field changes, the origin of the sensor output shifts. This is a correction to cope with the problem of end. This problem will be described with reference to FIGS.

  FIG. 16 is a graph for explaining the influence of sensitivity variation of the magnetic field detection chip constituting the biological information detection sensor. In FIG. 16, the difference between the resistances of the magnetic field detection chip 181 and the magnetic field detection chip 182 at a certain static magnetic field value between the magnetic field detection chip 181 and the magnetic field detection chip 182 is indicated by the difference between the slopes of the graphs G1 and G2. ing. For example, in the configuration of FIG. 10, the magnetic field detection chip 181 and the magnetic field detection chip 182 are chips corresponding to the magnetic field detection chip 31 and the magnetic field detection chip 32, respectively.

  If the static magnetic field is constant, correction can be performed by canceling the offset according to the resistance difference in a circuit. However, in the detection of the biomagnetic field, the static magnetic field varies with time, and the change width of the static magnetic field is larger than the magnitude of the biomagnetic field. For this reason, when the static magnetic field fluctuates, the difference in resistance between the magnetic field detection chip 181 and the magnetic field detection chip 182 also fluctuates, so that the output of the magnetic sensor fluctuates even if the biomagnetic field is constant.

  For this reason, it is important to provide a mechanism that adjusts the sensitivity one after the other for the TMR elements placed on the plurality of magnetic field detection chips so as to be exactly the same.

  Such a shift in sensitivity occurs, for example, when the direction of magnetization of the fixed layer with respect to the direction of the static magnetic field differs between the two magnetic field detection chips when a slight shift occurs in the mounting direction of the two magnetic field detection chips. In addition, depending on the location where the apparatus is installed, a difference in temperature between the two sensors may cause a difference in sensitivity related to the temperature characteristics of the TMR element. In addition, when a magnetic material is brought into the room or when the position of the magnetic material changes, a difference in sensitivity also occurs due to a change in the distribution of the static magnetic field depending on the magnetic material.

  FIG. 17 is a circuit diagram for performing sensitivity correction of the TMR element. The circuit diagram of FIG. 17 includes preamplifiers 64A and 64B in addition to the circuit configuration of FIG. 10 in order to correct the difference in sensitivity between the two magnetic field detection chips 31 and 32. By adjusting the gains of the preamplifiers 64A and 64B, the gain is adjusted so that the output when the biomagnetism is not applied becomes the reference voltage. However, with this circuit configuration, it is difficult to cope with a change in sensitivity of the TMR element that occurs according to a factor that changes with time, such as a temperature difference between sensors.

  Therefore, in the biological information detection apparatus of the third embodiment, correction is performed by providing a correction coil and an annular current path and applying a bias magnetic field.

  FIG. 18 is a perspective view of a sheet in which a correction coil is incorporated. FIG. 19 is a top view of a biological information detection sensor having an annular current path. As shown in the perspective view of FIG. 18, the biological information detection apparatus 170 according to the third embodiment includes a sheet 172, a correction coil 190 provided on the back surface of the sheet 172, and a biological information detection sensor 175. As shown in FIG. 19, the biological information detection sensor 175 includes a support plate 183, magnetic field detection chips 181 and 182, signal processing circuits 184 and 185, a differential amplifier 186, an amplifier 187, and an annular current path 188. including. The support plate 183, the magnetic field detection chips 181 and 182 and the differential amplifier 186 have a configuration corresponding to the configuration of the first embodiment. The signal processing circuits 184 and 185 include a low-pass filter and perform signal processing for removing high-frequency noise.

  The biological information detection sensor 175 is provided with an annular current path 188 and an amplifier 187 for applying a magnetic field due to an electric current to the magnetic field detection chip 182 on the support plate 183. Different from the sensor 24. The output current value of the amplifier 187 is determined by a prior calibration.

  It is known that the sensitivity of the TMR element is reduced by applying a magnetic field in a direction parallel to the magnetization direction of the fixed layer of the TMR element.

  Therefore, as shown in FIG. 19, the biological information detection sensor 175 mounted on the biological information detection device 170 has a first surface (upper surface) of the support plate 183 or a second support plate parallel to the first surface. An annular current path 188 is further provided on the surface (back surface). When the sensitivity of the magnetic field detection chip 182 is higher than that of the magnetic field detection chip 181, a predetermined current is passed through the annular current path 188 to reduce the sensitivity of the TMR element of the magnetic field detection chip 182, and the magnetic field detection chip 181 and the magnetic field detection chip 182 are reduced. By aligning the sensitivities of the TMR elements, it is possible to reduce the difference in offset drift caused by the sensor sensitivity shift.

  The annular current path 188 may be formed on one surface of the support plate 183. Further, two annular current paths formed on both surfaces of the support plate 183 may be connected in series, and the direction of current when viewed from one surface may be opposite. For example, the annular current path on the top surface is clockwise and the annular current path on the back surface is counterclockwise. In this case, the magnetic field detection chip 182 has a different distance from the annular current path on the top surface and the back surface. Therefore, the magnitude of the magnetic field generated from the annular current path on the upper surface is different from that of the reverse magnetic field generated from the annular current path on the rear surface. For this reason, a different magnetic field is applied to the magnetic field detection chip 182 at a distance ratio. On the other hand, even when a large magnetic field is applied from the outside, since the external magnetic field generation source is generally farther than the biomagnetic field, the current induced in the upper ring current path and the lower ring current path Are almost equal. Therefore, when the annular current path is provided on both surfaces of the support plate 183, there is an effect that the annular current path does not become a noise generation source.

  When a magnetic field is applied to the above circuit from a distance, the magnetic fields linked to the annular current path on the front surface side and the annular current path on the back surface side are almost the same, so the electromotive forces generated in the two annular current paths cancel each other, It is thought that current due to electromagnetic induction does not flow. On the other hand, when a magnetic field is applied from very close, there is a difference in the magnetic field interlinked between the annular current path on the front surface side and the annular current path on the back surface side, so that a difference occurs in the voltage induced in each annular current path. Current due to electromagnetic induction flows.

  Here, the difference between “far” and “very close” is that the distance from the annular current path on the front side and the annular current path on the back side (that is, the thickness of the support plate) differs from the magnetic field source. Depends on the distance. For example, geomagnetism or a magnetic field from another vehicle corresponds to a magnetic field applied from “far”, and a magnetic field from a living body corresponds to a magnetic field applied from “very close”.

  FIG. 20 is a graph for explaining the characteristic after correcting the sensitivity variation of the TMR elements constituting the biological information detection sensor. By passing an appropriate current through the annular current path, the characteristics of the magnetic field detection chip 182 in FIG. 16 change, and in FIG. 20, the graph G2 has almost the same characteristics as the graph G1.

  FIG. 21 is a flowchart for explaining the content of the correction process performed using the correction coil and the annular current path. Referring to FIG. 12, in the correction method of the biological information detection apparatus, step S <b> 2 in which a uniform static magnetic field is applied to magnetic field detection chips 181 and 182 by correction coil 190 and the outputs of magnetic field detection chips 181 and 182 are acquired. Step S3, Step S4 for controlling the current flowing through the annular current path 188 in accordance with the output acquired at Step S3, and Step S6 for storing the amount of current flowing through the annular current path 188 are provided.

  The point of the processing in FIG. 21 is that a static magnetic field is applied by the correction coil. That is, current is passed through the annular current path so that the output of the zero magnetic field is equal between the two magnetic field detection chips and the output of the two magnetic field detection chips is equal when the external magnetic field Hex is applied by the correction coil. Adjust the sensitivity. If the relationship between the current flowing in the annular current path and the sensitivity of the sensor is known, it should be able to be corrected in one step. However, since the sensitivity of the sensor is actually unknown, the current flowing in the annular current path and the sensor sensitivity The relationship of sensitivity is unknown, and the sensitivity is adjusted in multiple steps.

  Hereinafter, each step will be described in more detail. The biological information detection device 170 is connected to a controller such as a microcomputer. In step S <b> 1, the controller acquires and stores the output of the biological information detection sensor 175 in a state where no current is passed through the correction coil 190.

  In step S <b> 2, the controller passes a desired current through the correction coil 190 to generate a uniform magnetic field for the two magnetic field detection chips on the biological information detection sensor 175. The uniform magnetic field preferably has the same magnitude, but for example, the correction coil 190 applies a magnetic field that gives a change in the same direction to the output of the magnetic field detection chips 181 and 182 to the magnetic field detection chips 181 and 182. It may be configured to do so.

  At this time, the magnetic field generated by the correction coil 190 must be lower than the saturation magnetic field of the TMR element of each chip. The controller waits until the current flowing through the correction coil 190 is stabilized before proceeding to step S3.

  In step S <b> 3, the controller acquires and stores the output difference between the two magnetic field detection chips 181 and 182 of the biological information detection sensor 175. At this time, if the sensitivity of the TMR element of the magnetic field detection chip 182 is higher than the sensitivity of the magnetic field detection chip 181, the output difference is different between step S1 and step S2.

  In step S4, a current corresponding to the difference between the output differences obtained in steps S1 and S2 is passed through the annular current path. The controller waits until the current flowing through the annular current path 188 is stabilized before proceeding to step S5. When a current is passed through the annular current path 188, a magnetic field stronger than the magnetic field detection chip 181 is applied to the magnetic field detection chip 182. That is, the annular current path 188 is configured to generate a non-uniform magnetic field in the magnetic field detection chip 182 rather than the magnetic field detection chip 181.

  In step S5, the output difference between the two magnetic field detection chips when a static magnetic field is applied by passing a current through the correction coil 190 is the output difference when the current of the correction coil 190 in step S1 is zero ( It is determined whether it is equal to (offset). If the value (offset) obtained in step S1 is different from the value obtained in step S3 (output difference when applying a static magnetic field) (NO in S5), the controller returns the process to step S4. If the above values are equal (YES in S5), the controller advances the process to step S6 and performs a process of storing a current value to be passed through the annular current path 188. Thereafter, in step S7, the controller restores the current of the correction coil 190 to complete the correction of the biological information detection sensor 175.

  Thereafter, when detecting biomagnetism, measurement is performed while the current having the current value stored in step S6 is caused to flow through the annular current path 188.

  As described above, by providing the correction coil and the annular current path, the biological information detecting device of the third embodiment can be used even when the characteristics of the two magnetic field detecting chips arranged in the biological information detecting sensor vary. It is possible to correct the characteristics.

[Various modifications]
FIG. 22 is a perspective view showing a modified example of the sheet incorporating the biological information detection sensor. Referring to FIG. 22, the biological information detection device 220 of this modification includes a sheet 222, a correction coil 240, and a plurality of biological information detection sensors 231 to 236. 4, FIG. 14 and FIG. 18 show an example in which two magnetic field detection chips are arranged with the positions PA and PB separated from each other in the direction parallel to the seat back surface (X direction). As shown, biological information detection sensors 231 to 236 are arranged in a direction in which two magnetic field detection chips are arranged apart from each other in the direction intersecting the backrest surface of the seat (Y direction), and a magnetic field difference in the X direction is detected. You may do it.

  In Embodiments 1 to 3, the case where the structure is a sheet is shown, but the structure having a surface to which the living body is in close contact may be a bed. FIG. 23 is a perspective view showing an example of a bed incorporating a biological information detection sensor. FIG. 24 is a cross-sectional view showing the element arrangement of the bed incorporating the biological information detection sensor shown in FIG. The biological information detection device 270 includes a bed 272 and a plurality of biological information detection sensors 281 to 286 that are arranged such that two magnetic field detection chips are separated from each other in the X direction. As shown in FIGS. 22 and 24, a biological information detection sensor may be built in the bed to detect biomagnetism generated by a human body lying on the bed. The support plate 50 in FIG. 6 is arranged so that the direction in which the two magnetic field detection chips are separated (the X direction in FIG. 6) coincides with the direction parallel to the biological contact surface of the bed (the X direction in FIG. 23).

  FIG. 25 is a cross-sectional view showing a modification of the element arrangement of the bed incorporating the biological information detection sensor. The biological information detection device 270A includes a bed 272 and a plurality of biological information detection sensors 281A to 286A each disposed so that two magnetic field detection chips are separated from each other in the Y direction. As shown in FIGS. 23 and 24, the positions PA and PB may be separated in a direction parallel to the biological contact surface of the bed (X direction), or intersect the biological contact surface of the bed as shown in FIG. You may separate in a direction (Y direction).

  FIG. 26 is a diagram illustrating a modification of the biological information detection sensor. Referring to FIG. 26, biological information detection sensor 175A includes a support plate 183, magnetic field detection chips 181 and 182, a differential amplifier 186, amplifiers 187 and 187A, and annular current paths 188 and 188A. The support plate 183, the magnetic field detection chips 181 and 182 and the differential amplifier 186 have a configuration corresponding to the configuration of the first embodiment.

  The biological information detection sensor 175A is provided with an annular current path 188A and an amplifier 187A for applying a magnetic field due to current to the magnetic field detection chip 182 on the support plate 183, and the biological information detection sensor 175 of the third embodiment. And different.

  In FIG. 19 of the third embodiment, the case where the TMR element of the magnetic field detection chip 182 has higher sensitivity has been described for the sake of explanation. However, the magnetic field detection chip 181 may actually have higher sensitivity. In view of this, the biological information detection sensor 175A includes two annular current paths 188 and 188A as shown in FIG.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiment but by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

  1,71,72,73,74,81,82 TMR element, 4 free layer, 6 tunnel insulating layer, 8 fixed layer, 10 antiferromagnetic layer, 20, 120, 170, 220, 270, 270A biological information detection device , 22, 122, 172, 222 sheet, 24, 131, 132, 133, 135, 175A, 231, 236, 281, 281A, 286, 286A biological information detection sensor, 26 human body, 28 current, 30 magnetic field, 31 , 32, 181, 182 Magnetic field detection chip, 42 Contact hole, 44 Aluminum wiring, 46 Upper electrode, 48 Lower electrode, 50, 183 Support plate, 52 Protruding part, 54 Holding mechanism, 56 holes, 61, 83, 84 Resistance, 62, 63 variable resistance, 64, 85 differential amplifier circuit, 64A, 64B preamplifier, 66, 86 converter, 7 hours integrating circuit, 184 a signal processing circuit, 186 a differential amplifier, 187,187A amplifier, 188,188A annular current path, 190,240 correction coils, 272 beds.

Claims (13)

A support plate having a first surface;
A first magnetic field detector and a second magnetic field detector disposed on the first surface so as to be separated from each other in a first direction within the first surface;
Each of the first and second magnetic field detection units is configured to have a maximum sensitivity to a change in a magnetic field in a second direction orthogonal to the first direction in the first plane. A biological information detection device. It further comprises a structure having a portion that adheres to the living body,
The biological information detection apparatus according to claim 1, wherein the support plate is disposed inside the structure. The structure is a sheet,
The biological information detection apparatus according to claim 2, wherein the support plate is disposed such that the first direction is parallel to a backrest surface of the seat. The structure is a bed;
The biological information detection apparatus according to claim 2, wherein the support plate is disposed such that the first direction is parallel to the biological contact surface of the bed. The structure is a sheet,
The biological information detection apparatus according to claim 2, wherein the support plate is arranged so that the first direction is a direction intersecting a backrest surface of the seat. The structure is a bed;
The biological information detection apparatus according to claim 2, wherein the support plate is disposed so that the first direction intersects the biological adhesion surface of the bed.   A correction coil embedded in the structure and configured to apply a magnetic field that applies a change in the same direction to the outputs of the first and second magnetic field detection units to the first and second magnetic field detection units; The living body information detecting device according to claim 2 further provided.   The biological information detection device according to claim 1, further comprising an annular current path disposed on the first surface of the support plate or the second surface of the support plate parallel to the first surface. Each of the first and second magnetic field detectors includes a plurality of TMR elements,
Each of the plurality of TMR elements has a horizontally long shape extending in a direction perpendicular to the magnetization direction of the fixed layer,
The biological information detection apparatus according to claim 1, wherein the plurality of TMR elements are arranged side by side in a direction of magnetization direction of the fixed layer, and are connected in series by inter-element wiring extending in the direction of magnetization direction of the fixed layer. . A support plate having a first surface;
A first magnetic field detector and a second magnetic field detector disposed on the first surface so as to be separated from each other in a first direction within the first surface;
Each of the first and second magnetic field detection units is configured to have a maximum sensitivity to a change in a magnetic field in a second direction orthogonal to the first direction in the first plane. A biological information detection sensor.   The biological information detection sensor according to claim 10, further comprising an annular current path disposed on the first surface of the support plate or the second surface of the support plate parallel to the first surface. Each of the first and second magnetic field detectors includes a plurality of TMR elements,
Each of the plurality of TMR elements has a horizontally long shape extending in a direction perpendicular to the magnetization direction of the fixed layer,
The biological information detection sensor according to claim 10, wherein the plurality of TMR elements are arranged side by side in the direction of magnetization of the fixed layer and are connected in series by inter-element wiring extending in the direction of magnetization of the fixed layer. . A living body comprising a support plate having a first surface and first and second magnetic field detectors arranged on the first surface so as to be separated from each other in a first direction within the first surface. An information detection sensor and a correction method for a biological information detection device in which an annular current path that generates a non-uniform magnetic field in the first and second magnetic field detection units is disposed inside a structure,
The biological information detection apparatus further includes a correction coil embedded in the structure and configured to apply the same magnetic field to the first and second magnetic field detection units,
Each of the first and second magnetic field detection units is configured to have a maximum sensitivity to a change in a magnetic field in a second direction orthogonal to the first direction in the first plane. And
The method
Applying a uniform static magnetic field to the first and second magnetic field detectors with the correction coil;
Obtaining outputs of the first and second magnetic field detectors;
Controlling the current flowing through the annular current path according to the output obtained in the obtaining step;
And a step of storing the amount of current flowing through the annular current path.

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