JP2005090971A - Magnetic sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized high-sensitivity magnetic sensor utilizing a magnetostrictive effect. <P>SOLUTION: This magnetic sensor is constituted of a vibrating body 12 formed from magnetic thin films 11 serving simultaneously as the first electrode 10 and a magnetic film holding substrate, a substrate 14 for supporting the vibrating body 12 formed by laminating the magnetic thin films, and the second electrode 13 arranged on the position opposite to the vibrating body 12. In the sensor, the Young's modulus of the magnetic thin films 11 is changed by the magnetostrictive effect following the change of an external magnetic field in the state where the vibrating body 12 is mechanically vibrated integrally by an electrostatic force generated by a driving voltage applied between the first electrode 10 and the second electrode 13. Therefore, a mechanical resonance frequency of the vibrating body 12 is changed, and a variation of the resonance frequency is used as an output to the external magnetic field based on a detection voltage generated between the first electrode 10 and the second electrode 13. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention mainly relates to a magnetic sensor suitable for use in portable terminal devices, home appliances, and the like.

  In general, a phenomenon in which a magnetic material changes its shape when a magnetic field is applied and magnetized is called “magnetostriction” (Non-Patent Document 1). As an example of a magnetic sensor using the magnetostrictive effect, there is a magnetic sensor provided with means for measuring a deformation amount (displacement amount) of a magnetic material due to the magnetostrictive effect described in Patent Document 1.

  FIG. 4 is a perspective view of a conventional magnetic sensor. This magnetic sensor includes a magnetic thin film 41, a support means 42, a chip 44, a cantilever 45 that supports the chip 44, a piezo element 46, an ammeter 47, and a power supply 48. Specifically, the magnetic material and a support that supports the magnetic material. The magnetic sensor includes means for measuring a deformation amount (displacement amount) of the magnetic material due to the magnetostriction effect when the magnetic field to be measured is applied. In particular, a magnetic thin film is used as a magnetic material, and at least one part of the magnetic thin film is fixed. Further, as a means of measuring the deformation (displacement) of the magnetic thin film, atomic force, tunnel current, light interference, evanescent light, It consists of a displacement meter that uses electrostatic capacity.

  That is, in the magnetic sensor described in Patent Document 1, the deformation amount (displacement amount) of the magnetic material due to the magnetostriction effect is used as means for measuring the magnetic field to be measured.

JP-A-9-243721 Keizo Ota, Basics of Magnetic Engineering 2, Kyoritsu Shuppan, p236

In the magnetic sensor described in Patent Document 1, the amount of displacement with respect to the magnetic field to be measured is 1 nm or less considering that the cantilever length L is 100 nm and the magnetostriction constant λ is −30 × 10 ^−5. . Here, the magnetic field accuracy is determined by a displacement meter, and the displacement meter uses an atomic force, a tunnel current, or the like. Therefore, in order to maintain a desired measurement accuracy, it is indispensable to apply a highly accurate displacement meter, and the measurement system becomes large and complicated.

  Accordingly, an object of the present invention is to provide a highly sensitive small magnetic sensor using the magnetostriction effect that requires a relatively small measurement system.

  In order to solve the above-described problems, according to the present invention, a magnetic thin film that also serves as a first electrode or a vibrating body formed of a first electrode, a magnetic thin film, and a magnetic film holding substrate, and a support for the vibrating body are provided. The vibrating body is formed of a substrate and a second electrode disposed at a position opposite to the vibrating body, and the vibrating body is mechanically integrated with an electrostatic force generated by a driving voltage applied between the first electrode and the second electrode. As the external magnetic field changes in the state of vibration, the Young's modulus of the magnetic thin film changes due to the magnetostrictive effect, whereby the mechanical resonance frequency of the vibrating body changes, and the first electrode Based on the detected voltage generated between the first electrode and the second electrode, a magnetic sensor can be obtained in which the amount of change in the resonance frequency is output with respect to the external magnetic field.

  According to the present invention, in the above magnetic sensor, one end of the support substrate and the vibrating body is integrally formed, both ends of the support substrate and the vibrating body are integrally formed, or the support substrate. And a magnetic sensor having a diaphragm structure in which end portions of the vibrating body are integrally formed.

  Further, in the above magnetic sensor, the support substrate and the magnetic film holding substrate of the vibrator are made of silicon or quartz, and the support substrate and the vibrator are made of a metal thin film or a polysilicon thin film. can get.

  Furthermore, in the above magnetic sensor, it is desirable that the sensor is structured to be wrapped with a structure made of a nonmagnetic metal conductor.

  Further, according to the present invention, a vibrating body formed of a magnetic thin film that also serves as the first electrode or the first electrode, the magnetic thin film, and the magnetic film holding substrate, a substrate for supporting the vibrating body, and the vibrating body And a vibrating body formed of a non-magnetic thin film that also serves as a third electrode and a magnetic film holding substrate, and the non-magnetic thin film and the magnetic film holding substrate. A sensor structure including a substrate for supporting the vibrating body and a fourth electrode disposed at a position opposite to the vibrating body, and is generated by a driving voltage applied between the first electrode and the second electrode. The mechanical resonance frequency of the vibrating body is changed by changing the Young's modulus of the magnetic thin film as the external magnetic field changes while the vibrating body is mechanically vibrated integrally with electric power. Changes, and the first electrode and the second electrode A state in which the vibrator is mechanically vibrated as a whole by an amount of change in the resonance frequency based on a detection voltage generated in between and an electrostatic force generated by a driving voltage applied between the third electrode and the fourth electrode. In the magnetic sensor, the difference between the resonance frequency based on the detection voltage generated between the third electrode and the fourth electrode is output to the external magnetic field.

  In addition, according to the present invention, in the above magnetic sensor, a magnetic sensor in which the second electrode and the fourth electrode are the same can be obtained.

  Furthermore, according to the present invention, in the magnetic sensor, the substrate for supporting the vibrating body on which the magnetic thin film is laminated and the substrate for supporting the vibrating body on which the nonmagnetic thin film is laminated are made the same. It is desirable.

  According to the magnetic sensor of the present invention, it is possible to provide a highly sensitive small-sized magnetic sensor that requires only a relatively small-scale measurement system using the magnetostrictive effect.

  A magnetic sensor according to an embodiment of the present invention will be described below with reference to the drawings.

  The magnetic sensor of the present invention includes a vibrating body formed of a magnetic thin film that also serves as a first electrode and a magnetic film holding substrate, a substrate for supporting the vibrating body, and a first electrode disposed at a position facing the vibrating body. It consists of two electrodes. Since the magnetic thin film also serving as the first electrode is laminated on the magnetic film holding substrate, it is mechanically a single rigid body and can be handled mechanically as a single vibrating body. When the external magnetic field changes, the mechanical resonance frequency of the vibrating body changes, and when the external magnetic field amount vibrates as a whole from the amount of change in the resonance frequency, it is calculated.

(Embodiment 1)
FIG. 1 is a perspective view of the magnetic sensor according to the first embodiment. The magnetic sensor includes a vibrating body 12 in which a magnetic thin film 11 also serving as a first electrode 10 is stacked on a magnetic film holding substrate on a sensor substrate 15 and a substrate for supporting the vibrating body 12 in which the magnetic thin film 11 is stacked. 14 and a second electrode 13 disposed at a position facing the vibrating body 12 (hereinafter referred to as sensor structure). The magnetic film holding substrate of the vibrating body 12 is a conductor layer doped with phosphorus at a high concentration, for example, polysilicon, which is omitted in FIG. 1 but is electrically connected to the electrode portion. Yes. The sensor substrate 15 is made of silicon, quartz, or the like. In the case of silicon, an insulating film such as a thermal oxide film, SiO ₂ , SiN film, or the like is formed on the entire surface in advance.

  Next, the operation of the magnetic sensor according to the present invention will be described. First, the vibrating body 12 is mechanically vibrated integrally by an electrostatic force generated by a driving voltage applied between the first electrode 10 and the second electrode 13. Next, under the state where the vibrating body 12 vibrates at a specific resonance frequency, the Young's modulus of the magnetic thin film 11 changes due to the magnetostrictive effect as the external magnetic field changes, that is, the electrode and the magnetic film are retained. The mechanical resonance frequency of the vibrating body 12 changes due to the stress and the like due to the bonding of the substrates, and the amount of change in the resonance frequency based on the detected voltage generated between the first electrode 10 and the second electrode 13. Is an output for an external magnetic field.

For example, if the vibrating body 12 is polysilicon of about 100 μm × 50 μm × 1 μm, the mechanical resonance frequency is about 10809 (kHz), and the amount of change in the resonance frequency when the external magnetic field changes by about 0.3 (Oe). Is about −3.21 (kHz). Here, a Co—Fe—Zr thin film having a stoichiometric composition ratio of approximately 55:35:15 is used as the magnetic film laminated on the vibrating body 12. The saturation magnetostriction constant λs of the magnetic film is about 25 × 10 ⁻⁶ .

  As a magnetic film in this case, it is desirable to apply a material having as small a coercive force as possible in order to measure a weak magnetic field or a magnetic field in a minute region. When the magnetic sensor according to the present embodiment is manufactured, a standardized two-layer or three-layer polysilicon MEMS process using a combination of a polysilicon structure layer and a sacrificial layer such as silicon dioxide can be used. The compatibility is good and an improvement in the S / N ratio can be expected. As a result, it is advantageous for downsizing the entire sensor module.

  Further, as another manufacturing method, a bulk etching technique using a difference in etching rate depending on a crystal plane of silicon or quartz can be applied, and a substrate 14 for supporting the vibrating body 12 as a magnetic film holding substrate of the vibrating body 12. As, a material similar to that of the vibrating body 12 can be used.

  Furthermore, in addition to the structure in which the substrate 14 for supporting the vibrating body 12 and one end of the vibrating body 12 are integrated as shown in FIG. 1, for example, the structure in which both ends of the substrate 14 and the vibrating body 12 are integrated, or The same effect can be obtained by adopting a diaphragm structure in which the substrate 14 and the end of the vibrating body 12 are integrally formed.

  In the magnetic sensor, by adding a non-magnetic metal conductor having a structure surrounding the sensor structure as an electrostatic shield, noise due to parasitic capacitance is reduced, and accuracy can be improved.

(Embodiment 2)
FIG. 2 is a perspective view of the magnetic sensor according to the second embodiment. The configuration of the magnetic sensor is substantially the same as that of the first embodiment, and in the figure, a structure in which both ends of the substrate 24 and the vibrating body 22 are integrated is shown. In the magnetic sensor according to the present embodiment, the vibrating body 22 in which the first electrode 20 and the magnetic thin film 21 are stacked on the magnetic film holding substrate and the vibrating body 22 in which the magnetic thin film 21 is stacked are supported on the sensor substrate 25. And a second electrode 23 disposed at a position facing the vibrating body 22. The first electrode 20 and the second electrode 23 are made of a metal thin film such as gold, and are omitted from the drawing but are electrically connected to the electrode portion. The sensor substrate 25 is made of silicon, quartz, or the like. In the case of silicon, a thermal oxide film, an insulating film such as a SiO ₂ film or an SiN film formed by LPCVD or the like is previously formed on the entire surface. Of course, when the magnetic thin film 21 is conductive, the magnetic sensor can be configured with the configuration also serving as the first electrode as in the first embodiment.

  When manufacturing the magnetic sensor according to the present embodiment, a MEMS process using a sacrificial layer is used. That is, as a sacrificial layer of the vibrator 22 made of a metal thin film, a photosensitive resist is deposited to a thickness of about 1 μm, and then a metal thin film is deposited to a thickness of about 1 μm using a thin film forming technique such as vacuum evaporation or sputtering. Then, patterning is performed by a known photolithography method. Further, the magnetic thin film 21 is deposited and patterned in the same manner as the metal thin film. Finally, the sacrificial layer can be removed by immersion in an organic solvent such as a resist stripping solution or by a dry etching method so that the vibrator 22 is completely suspended in the air.

(Embodiment 3)
FIG. 3 is a perspective view of the magnetic sensor according to the third embodiment. The magnetic sensor according to the third embodiment includes a vibrating body 32 in which a magnetic thin film 31 also serving as a first electrode 30 is stacked, a substrate 34 for supporting the vibrating body 32 in which the magnetic thin film 31 is stacked, and a vibrating body 32. A structure (hereinafter referred to as a sensor structure having a magnetic film) composed of the second electrodes 33 arranged at opposite positions, a vibrating body 38 in which a nonmagnetic thin film 37 that also serves as the third electrode 36 is stacked, and a nonmagnetic thin film 37 are stacked. The sensor structure (hereinafter referred to as a sensor structure having a nonmagnetic thin film) is composed of a substrate 34 for supporting the vibrating body 38 and a fourth electrode 39 disposed at a position facing the vibrating body 38. Of course, a metal thin film such as gold may be provided as the first electrode 30 in addition to the magnetic thin film 31 as in the second embodiment.

  As the external magnetic field changes while the vibrating body 32 is mechanically vibrated integrally by the electrostatic force generated by the drive voltage applied between the first electrode 30 and the second electrode 33, the magnetic field The mechanical resonance frequency of the vibrating body 32 changes due to a change in the Young's modulus of the thin film 31, and the amount of change in the resonance frequency based on the detected voltage generated between the first electrode 30 and the second electrode 33, and the third The electrostatic force generated by the drive voltage applied between the electrode 36 and the fourth electrode 39 is generated between the third electrode 36 and the fourth electrode 39 while the vibrating body 38 is mechanically vibrated integrally. The difference from the change amount of the resonance frequency based on the detection voltage is set as an output with respect to the external magnetic field.

  Further, it is desirable that the second electrode 33 and the fourth electrode 39 on the sensor substrate 35 have the same wiring and a common ground.

  A mechanical resonance frequency from a sensor structure having a nonmagnetic thin film disposed in the vicinity of a sensor structure having a magnetic thin film is used as a reference for sensor output, and a vibrating body 32 and a nonmagnetic thin film 37 laminated with a magnetic thin film 31 are provided. By using the mechanical resonance frequency difference of the laminated vibrator 38 as a sensor output, it is possible to compensate for a change in Young's modulus of the vibrator 32 and the like due to temperature fluctuation. The accuracy of the shape of the sensor structure having a magnetic film and the nonmagnetic thin film is almost determined by photolithography of the semiconductor manufacturing apparatus, and can be formed with an accuracy of 1 μm or less.

  The vibrating body 32 having the magnetic thin film 31 laminated thereon and the vibrating body 38 having the nonmagnetic thin film 37 laminated are desirably mechanically independent, and the vibrating body in the vicinity of the center of the substrate 34 for supporting each vibrating body. It is optimal to provide a groove between 32 and 38.

1 is a perspective view of a magnetic sensor according to Embodiment 1 of the present invention. The perspective view of the magnetic sensor by Embodiment 2 in this invention. The perspective view of the magnetic sensor by Embodiment 3 in this invention. The perspective view of the magnetic sensor in a prior art.

Explanation of symbols

10, 20, 30 First electrode 11, 21, 31, 41 Magnetic thin film 12, 22, 32, 38 Vibrating body 13, 23, 33 Second electrode 14, 24, 34 Substrate 15 (for supporting the vibrating body) , 25, 35 Sensor substrate 36 Third electrode
37 Nonmagnetic thin film 39 Fourth electrode
42 support means 43 external magnetic field 44 chip 46 piezo element 45 cantilever 47 ammeter 48 power supply 100 driving high frequency power supply

Claims (10)

  A magnetic thin film that also serves as the first electrode or a vibrating body formed by the first electrode, the magnetic thin film, and the magnetic film holding substrate, a substrate for supporting the vibrating body, and a first electrode disposed at a position facing the vibrating body. The external magnetic field is changed in a state where the vibrating body is integrally vibrated by an electrostatic force generated by a driving voltage applied between the first electrode and the second electrode. An amount of change in the mechanical resonance frequency of the vibrating body accompanying the vibration is output to an external magnetic field.   The magnetic sensor according to claim 1, wherein one end of the support substrate and the vibrating body is integrally formed.   The magnetic sensor according to claim 1, wherein both ends of the support substrate and the vibrating body are integrally formed.   The magnetic sensor according to claim 1, wherein a diaphragm structure in which an end portion of the support substrate and the vibrating body is integrally formed.   5. The magnetic sensor according to claim 1, wherein the support substrate and the magnetic film holding substrate of the vibrating body are made of silicon or quartz.   5. The magnetic sensor according to claim 1, wherein the support substrate and the vibrating body are made of a metal thin film or a polysilicon thin film.   The magnetic sensor according to any one of claims 1 to 6, wherein the sensor has a structure wrapped with a structure made of a nonmagnetic metal conductor.   A first vibrating body formed of a magnetic thin film that also serves as a first electrode or a first electrode, a magnetic thin film, and a magnetic film holding substrate; a substrate for supporting the first vibrating body; and the first vibration A second vibration body formed of a second electrode disposed at a position facing the body, a nonmagnetic thin film serving also as a third electrode, and a magnetic film holding substrate; and a substrate for supporting the second vibration body; A sensor structure including a fourth electrode disposed at a position opposite to the second vibrating body, and the first electrostatic force generated by a driving voltage applied between the first electrode and the second electrode causes the first The amount of change in the mechanical resonance frequency of the first vibrating body as the external magnetic field changes while the vibrating body is mechanically vibrated integrally, and between the third electrode and the fourth electrode Due to the electrostatic force generated by the drive voltage applied to the second vibrating body, A magnetic sensor, characterized in that the output for the difference an external magnetic field between the change in the resonance frequency of the second vibrator in a state of being mechanically vibrated at the body.   The magnetic sensor according to claim 8, wherein the second electrode and the fourth electrode are the same in the magnetic sensor.   In the magnetic sensor, the substrate for supporting the first vibrating body on which the magnetic thin film is laminated and the substrate for supporting the second vibrating body on which the nonmagnetic thin film is laminated are the same. The magnetic sensor according to claim 8, wherein the magnetic sensor is a magnetic sensor.

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