JP2016031237A - MEMS piezoelectric sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a MEMS piezoelectric sensor of a structure advantageous for enhancing the sensitivity and allowing multi-axial configuration.SOLUTION: A MEMS piezoelectric sensor 1 comprises a cup-shaped sensor body 2 having a central axial line 20; a supporting structure 3 coupled to the sensor body 2 in a prescribed coupling region 18 including the central axial line 20 and supporting the sensor body 2; a piezoelectric film 6 formed on a surface of the sensor body 2; and a plurality of electrodes Ed and Es arranged radially centering on the central axial line 20 and coupled to a surface of the piezoelectric film 6. The plurality of electrodes Ed and Es include, for instance, a pair of excitation electrodes Ed and a pair of detection electrodes Es. The sensor body 2 includes a discoid bottom 21 and a cylindrical trunk 22. The supporting structure 3 includes a columnar part 25 coupled to the bottom 21 and a support substrate 31 supporting the columnar part.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a MEMS (Micro Electro Mechanical System) piezoelectric sensor. The MEMS piezoelectric sensor includes an angular velocity sensor, a pressure sensor, a microphone, an ultrasonic sensor, an acceleration sensor, a temperature sensor, and the like.

  One prior art of a MEMS piezoelectric sensor is described in Patent Document 1. Patent Document 1 discloses a vibrating gyroscope. The vibrating gyroscope includes a frame-shaped support portion, four flexible portions arranged in a cross shape inside the support portion, a weight portion coupled to each free end of the four flexible portions, and 4 The piezoelectric element for excitation and the piezoelectric element for detection provided in each of the flexible parts are included. The weight portion is coupled only to the free end of the flexible portion. The excitation piezoelectric element drives the weight portion by vibrating the flexible portion. The detection piezoelectric element detects distortion of the flexible portion according to the movement of the weight portion.

  The x-axis is defined along two linearly aligned flexible parts, and the y-axis is defined along two flexible parts linearly aligned so as to be orthogonal thereto, and orthogonal to the x-axis and y-axis. A z-axis is defined. A driving voltage that vibrates at the natural frequency of the flexible portion is applied to the excitation piezoelectric element. Thereby, the weight part vibrates in the z-axis direction. When the sensor die rotates around the y axis, a Coriolis force in the x axis direction acts on the weight portion. This Coriolis force is detected by two detection piezoelectric elements arranged in the x-axis direction. When the sensor die rotates around the x axis, a Coriolis force in the y axis direction acts on the weight portion. This Coriolis force is detected by two detection piezoelectric elements arranged in the y-axis direction. Since the Coriolis force is proportional to the angular velocity, the angular velocity can be obtained based on the detected Coriolis force. When detecting the three-axis component of the angular velocity, for example, a voltage is applied to the excitation piezoelectric element so that the weight portion vibrates in the x-axis direction and the y-axis direction.

JP 2010-122141 A

One embodiment of the present invention provides a MEMS piezoelectric sensor having a structure advantageous for high sensitivity.
Moreover, one embodiment of the present invention provides a MEMS piezoelectric sensor having a structure advantageous for multi-axis.

  One embodiment of the present invention includes a cup-shaped sensor body having a central axis, a support structure coupled to the sensor body in a predetermined coupling region including the central axis, and supporting the sensor body, Provided is a MEMS piezoelectric sensor comprising: a piezoelectric film formed on a surface; and a plurality of electrodes arranged radially about the central axis of the cup shape and bonded to the surface of the piezoelectric film. .

  According to the configuration of this embodiment, the sensor body has a cup shape, and is coupled to and supported by the support structure in a predetermined coupling region including the central axis. Accordingly, the entire sensor body can vibrate while being supported in a region including the central axis. A plurality of electrodes are joined to a piezoelectric film formed on the surface of the sensor body. The plurality of electrodes are arranged radially about the cup-shaped central axis. By using these plural electrodes, it is possible to generate vibrations over almost the entire sensor body or to detect electromotive force generated in the piezoelectric film due to external force or other influences. Since almost the entire sensor body vibrates, detection with high sensitivity is possible. In addition, since the cup-shaped sensor body undergoes three-dimensional deformation according to various physical quantities such as external force, temperature, humidity, acceleration, angular velocity, angular acceleration, etc., it is possible to detect physical quantities related to a plurality of coordinate axis directions. So-called multi-axis can be realized. As described above, the physical quantity includes environmental parameters such as temperature and humidity, and mechanical quantities such as force, acceleration, angular velocity, and angular acceleration.

The coupling region is a region in the vicinity of the central axis, and when viewed along the central axis, it is preferable that the outer edge is inside the outer edge of the sensor body and surrounds the central axis. . Typically, the support structure is coupled to the sensor body on the central axis, but a coupling portion between the sensor body and the support structure may be disposed so as to surround the central axis.
Specifically, the coupling region is preferably a region set in a circle having a diameter equal to or less than ½ of the diameter of a circle passing through the outer edge of the sensor body when viewed along the central axis.

In one embodiment of the present invention, the plurality of electrodes include at least one excitation electrode and at least one detection electrode.
According to this configuration, by applying a driving voltage to the excitation electrode, the piezoelectric film can be expanded and contracted by the inverse piezoelectric effect, and thereby the sensor body can be vibrated. On the other hand, the detection electrode can derive a voltage generated in the piezoelectric film due to the piezoelectric effect. Thereby, since the sensor body can be vibrated and the deformation of the sensor body can be detected, a highly sensitive vibration type sensor can be provided. Also, the three-dimensional deformation that occurs in the cup-shaped sensor body can be detected by the detection electrode, and so-called multi-axis can be realized.

  In one embodiment of the present invention, an excitation piezoelectric element is formed at a place where the excitation electrode is disposed. A detection piezoelectric element is formed at a place where the detection electrode is disposed. The excitation electrode is an upper electrode of the excitation piezoelectric element. The detection electrode is an upper electrode of the detection piezoelectric element. The lower electrode is formed on the surface of the sensor body. A piezoelectric film is formed in contact with the lower electrode. The lower electrode may be a common electrode for the excitation piezoelectric element and the detection piezoelectric element.

In one embodiment of the present invention, the plurality of electrodes include at least a pair of excitation electrodes and at least a pair of detection electrodes.
According to this configuration, by applying a driving voltage to the pair of excitation electrodes, the piezoelectric film can be expanded and contracted by the inverse piezoelectric effect, and thereby the sensor body can be vibrated. On the other hand, the pair of detection electrodes can derive a voltage generated in the piezoelectric film due to the piezoelectric effect. Accordingly, stable vibration can be reliably generated in the sensor body, and deformation of the sensor body can be detected in a systematic manner, so that a vibration sensor with higher sensitivity can be provided.

In an embodiment of the present invention, the plurality of electrodes are provided at positions 2n times symmetrical (where n is a natural number) around the central axis.
According to this configuration, since the plurality of electrodes are provided at a position that is 2n times symmetrical around the central axis, a pair of electrodes can be arranged at symmetrical positions across the central axis. Thereby, the sensor body can be excited effectively, the vibration of the sensor body can be detected with high sensitivity, and an electrode arrangement advantageous for multi-axis can be achieved.

  Note that electrodes need not be provided at all 2n-fold symmetric positions, and electrodes may not be disposed at at least one of the 2n-fold positions. For example, the excitation electrode may be arranged at one or two of six positions that are six-fold symmetric, the detection electrode may be arranged at the other one or two positions, and the remaining positions may be vacant. Further, the excitation electrode may be arranged at two positions out of six positions that are six-fold symmetric, and the detection electrode may be arranged at the remaining four positions. Various other electrode arrangements are possible.

In one embodiment of the present invention, 2n electrodes (where n is a natural number) are provided at 2n times symmetrical positions around the central axis.
According to this configuration, the electrodes are arranged at all positions 2n times symmetrical. Thereby, the sensor body can be excited effectively, the vibration of the sensor body can be detected with high sensitivity, and an electrode arrangement advantageous for multi-axis can be achieved.

For example, the excitation electrodes may be arranged at four positions among the eight positions that are eight-fold symmetric, and the detection electrodes may be arranged at the remaining four positions.
In one embodiment of the present invention, the 2n electrodes include n excitation electrodes and n detection electrodes alternately arranged around the central axis.
According to this configuration, since the excitation electrode and the detection electrode are alternately arranged at 2n times symmetrical positions, the sensor body can be excited effectively, and the vibration of the sensor body can be detected with high sensitivity. It is possible to provide a structure that is advantageous for conversion.

  For example, excitation electrodes may be arranged at every other position among eight positions that are eight-fold symmetric, and detection electrodes may be arranged at every other position. In addition, four positions out of the six positions that are six-fold symmetric are used, and the first excitation electrode, the second detection electrode, the second excitation electrode, and the second detection are arranged at the four positions. Four electrodes may be arranged in the order of the electrodes. In this case, the two positions are empty.

In one embodiment of the present invention, the plurality of electrodes are arranged symmetrically with respect to the cup-shaped central axis and are joined to the surface of the piezoelectric film, and the cup-shaped center. A pair of detection electrodes arranged symmetrically with respect to the axis and joined to the surface of the piezoelectric film.
According to this configuration, since the pair of excitation electrodes are arranged symmetrically with respect to the cup-shaped central axis, the sensor body can be effectively excited and vibrated with a large amplitude. In addition, since the pair of detection electrodes are arranged symmetrically with respect to the cup-shaped central axis, a change in the shape of the sensor body can be detected with high accuracy. Thereby, highly sensitive detection is possible, and a structure advantageous for multi-axis can be provided.

In one embodiment of the present invention, the piezoelectric film is driven by the excitation electrode, whereby stationary vibration is generated in the sensor body, the excitation electrode is disposed on the antinode of the stationary vibration, and the detection wave is detected at the node of the stationary wave. Electrodes are arranged.
According to this configuration, the physical quantity can be detected by the detection electrode in a state where steady vibration is generated in the sensor body by the excitation electrode. Since the detection electrode is disposed at the node of steady vibration, a change occurring in the sensor body can be detected in a state where the influence of vibration generated by the excitation electrode is suppressed.

  For example, when an angular velocity is applied to the MEMS piezoelectric sensor in a state where steady vibration is generated in the sensor body, the steady vibration is changed by the Coriolis force, and a signal representing this change is extracted from the detection electrode. Thereby, the angular velocity can be detected. Since three-dimensional vibrations are generated in the sensor body, it is possible to detect angular velocities about the three axes by performing appropriate processing on the signal extracted from the detection electrodes.

In one embodiment of the present invention, the vibration generated in the sensor body by driving the piezoelectric film by the excitation electrode is a wine glass mode. In the wine glass mode, since the vibration loss is small, the Q value is high and it is difficult to be influenced by external acceleration. As a result, highly sensitive detection is possible, and a structure advantageous for multi-axis can be provided.
In one embodiment of the present invention, the sensor body includes a bottom portion and a trunk portion, and the support structure is coupled to the sensor body at the bottom portion. With this configuration, since the sensor body is supported at the bottom thereof, vibration can be generated in the entire sensor body, so that vibration with a small vibration loss, for example, vibration in a wine glass mode is possible. Thereby, detection with high sensitivity is possible, and a structure advantageous for multi-axis can be provided.

  In one embodiment of the present invention, the support structure includes a columnar portion that is coupled to the bottom portion and extends along the central axis. According to this configuration, the sensor body is supported by the columnar portion coupled to the bottom portion. Thereby, since vibration can be generated in the entire sensor body, vibration with less vibration loss, for example, vibration in a wine glass mode is possible, and a structure advantageous for multi-axis can be provided.

In one embodiment of the present invention, the columnar portion is coupled to the bottom of the sensor body inside the cup shape, and the support structure is coupled to the columnar portion on the opening edge side of the sensor body. including. According to this configuration, since the columnar portion can be arranged inside the cup shape, it is possible to provide a MEMS piezoelectric sensor that is small, highly sensitive, and advantageous for multi-axis use.
The support substrate can be made of any substrate material such as silicon or alumina.

In one embodiment of the present invention, the surface of the support substrate and the opening edge are spaced apart. According to this configuration, since the support substrate and the sensor body are separated from each other, the vibration of the sensor body is not hindered by the support substrate. Thereby, since the sensor body can be vibrated efficiently, it is possible to provide a MEMS piezoelectric sensor that is highly sensitive and advantageous for multi-axis use.
In one embodiment of the present invention, a support portion is provided at a position corresponding to the columnar portion on the surface of the support substrate, and the support is provided at a position facing the opening edge of the sensor body on the surface of the support substrate. A recess deeper than the part is formed.

According to this configuration, while the columnar portion is supported by the support portion on the surface of the support substrate, a recess is formed on the surface of the support substrate at a position facing the opening edge of the sensor body. As a result, the sensor body can be supported in a state in which efficient vibration of the sensor body is ensured.
Further, the columnar part may not protrude outward (in a direction away from the bottom part) of the sensor body from the opening edge of the sensor body in the direction along the central axis. More specifically, the end of the columnar part facing the support substrate may be at the same position as the opening edge of the sensor body in the direction along the central axis. Such a structure is obtained, for example, by etching a substrate such as a silicon substrate to simultaneously form a sensor body and a columnar portion integrated therewith. Therefore, even in the structure in which the sensor body and the columnar part are simultaneously formed in the MEMS process, it is possible to ensure efficient vibration of the sensor body by the recess formed in the support substrate.

In one embodiment of the present invention, a support portion is provided at a position corresponding to the columnar portion on the surface of the support substrate, and straddles the inside and outside of the sensor body along different directions intersecting the support portion. Accordingly, the sensor body includes a plurality of beam portions, and a recess is formed at an opening edge of the sensor body at a position corresponding to the plurality of beam portions.
According to this configuration, since the plurality of beam portions that respectively extend along the intersecting direction in the support portion extend over the inside and the outside of the sensor body, at the time of assembly, the plurality of beam portions are used as marks. The sensor body can be aligned with the support portion. Further, since the contact with the beam portion can be avoided by the concave portion, the opening edge of the sensor body can be disposed at a position closer to the substrate surface than the surface of the beam portion. Thereby, since the sensor body can be enlarged, detection with higher sensitivity becomes possible. The beam portion may be coupled to the support portion or may be separated from the support portion.

In an embodiment of the present invention, the columnar portion and the support substrate are connected by direct bonding of resin (specifically, resin adhesive), metal (for example, solder), or silicon. Thereby, a columnar part and a support substrate can be combined reliably.
In one embodiment of the present invention, circuit wiring is formed on the surface of the support substrate, and the circuit wiring and the electrode are connected by a bonding wire. According to this structure, it is a circuit board which comprises a support substrate, The electrode on a sensor body is connected to the circuit wiring on the circuit board by the bonding wire. That is, the connection between the electrode and the circuit wiring is ensured by wire bonding. Thereby, the electrical connection for stable input / output between the sensor body and the circuit board can be achieved while suppressing the influence on the vibration of the sensor body.

  In one embodiment of the present invention, the support structure is coupled to the bottom of the sensor body outside the cup shape. In this configuration, since the support structure is coupled to the bottom of the sensor body outside the cup shape, it is easy to couple the support structure and the sensor body. Therefore, a MEMS piezoelectric sensor having a simple structure, high sensitivity, and advantageous for multi-axis can be provided.

In one embodiment of the present invention, the support structure includes a support substrate facing the outer surface of the bottom portion of the sensor body. With this configuration, the sensor body can be supported in a state where the outer surface of the bottom of the sensor body faces the support substrate. Therefore, it is possible to provide a MEMS piezoelectric sensor that has high sensitivity and is advantageous for multi-axis use while simplifying the support structure.
In one embodiment of the present invention, circuit wiring is formed on the surface of the support substrate, and the circuit wiring and the electrode are connected by wireless bonding. According to this configuration, since the electrode and the circuit wiring can be connected by wireless bonding, it is possible to provide a MEMS piezoelectric sensor with high sensitivity and advantageous for multi-axis while simplifying the connection structure. Further, since the structure for electrical connection can be used as a part of the support structure of the sensor body, the entire structure can be simplified.

In one embodiment of the present invention, the sensor body includes a flat bottom portion and a cylindrical trunk portion coupled to the bottom portion, and the bottom portion (outer surface or inner surface) or the trunk portion (outer surface). Alternatively, the piezoelectric film is disposed on the inner surface.
Thus, the structure in which the sensor body has a flat bottom and a cylindrical body can be manufactured by a process of etching a substrate such as a silicon substrate. Since the entire cup-shaped sensor body vibrates and deforms, the piezoelectric film may be disposed on either the bottom or the body, and an electrode may be disposed in accordance with the arrangement of the piezoelectric film. That is, the piezoelectric film can be disposed on one or both of the bottom part and the body part. When the piezoelectric film is disposed on the bottom, the piezoelectric film may be disposed on one of the outer surface and the inner surface of the bottom, or may be disposed on both of them. Similarly, when the piezoelectric film is disposed on the body, the piezoelectric film may be disposed on one of the outer surface and the inner surface of the body, or may be disposed on both of them.

The electrode can be arranged on one or both of the flat bottom and the cylindrical body depending on the arrangement of the piezoelectric film. For example, the excitation electrode may be arranged on one of the bottom part and the body part, and the detection electrode may be arranged on the other of them.
In one embodiment of the present invention, the piezoelectric film is disposed on the outer surface of the sensor body. According to this configuration, since the electrodes are arranged outside the sensor body so as to correspond to the arrangement of the piezoelectric film, external connection of the electrodes is facilitated.

In one embodiment of the present invention, the piezoelectric film is disposed on the inner surface of the sensor body. According to this configuration, since the electrodes are arranged inside the sensor body so as to correspond to the arrangement of the piezoelectric film, external connection of the electrodes can be performed inside the sensor body. Thereby, the structure can be reduced in size.
In one embodiment of the present invention, the sensor body is made of a material whose main component is silicon. According to this configuration, the sensor body can be manufactured by processing silicon by the MEMS process.

  In one embodiment of the present invention, the sensor body includes a cylindrical body having a diameter of 0.2 mm or more and 5 mm or less and a wall thickness of 1/20 or less of the diameter. Is 100 μm or more and 1 mm or less. With this configuration, it is possible to provide a MEMS piezoelectric sensor that can efficiently excite the sensor body and that can perform highly sensitive detection and is advantageous for multi-axis use.

By setting the diameter of the sensor body to 0.2 mm or more and 5 mm or less, processing and wiring are easy, and the resonance frequency can be set to a high frequency range in which high sensitivity detection is possible. That is, if the sensor body has a diameter of less than 0.2 mm, cylindrical processing and wiring become difficult. In addition, when the diameter of the sensor body exceeds 5 mm, the resonance frequency is lowered, and there is a concern that sensitivity may be lowered.
As the thickness of the body portion is thinner, the sensitivity is improved. However, if the thickness is too thin, the processed shape becomes unstable and causes variations in sensor characteristics. Therefore, the thickness is preferably 10 μm or more.

If the length of the body portion is too short, there is a concern that the Q value is lowered and the sensitivity is lowered. Therefore, the length is preferably 100 μm or more. On the other hand, if the length of the body is too long, it takes too much processing time and is impractical, so 1 mm or less is preferable.
In one embodiment of the present invention, the sensor body includes a bottom part coupled to the body part, and the support structure is coupled to the bottom part and is more than 1/20 of the cylindrical diameter of the body part. A columnar portion having a circular cross section having a diameter of 2 or less is included. With this configuration, it is possible to provide a MEMS piezoelectric sensor that can efficiently excite the sensor body and that can perform highly sensitive detection and is advantageous for multi-axis use. In particular, the structure in which the cylindrical body portion is supported by the columnar portion having a circular cross section can efficiently vibrate the entire sensor body. In addition, the circular cross section of the columnar part has a shape of a cut surface perpendicular to the central axis.

  By setting the diameter of the columnar portion to be 1/20 or more of the diameter of the cylindrical shape of the body portion, the coupling between the columnar portion and the bottom portion has sufficient strength. In addition, the electrode connection portion can be provided in the coupling region between the columnar portion and the bottom portion, and the wiring connection to the electrode connection portion can be stably performed while being reliably supported by the columnar portion. In addition, by setting the diameter of the columnar part to ½ or less of the cylindrical diameter of the body part, it is possible to suppress vibration restraint by the columnar part, and thus the entire sensor body can be vibrated efficiently.

  In one embodiment of the present invention, the thickness of the piezoelectric film is not less than 0.2 μm and not more than 5 μm. With this configuration, the piezoelectric film generates the necessary reverse piezoelectric effect and piezoelectric effect with almost no restraint on vibration and deformation of the sensor body, so that highly sensitive detection is possible and MEMS is advantageous for multi-axis use. A piezoelectric sensor can be provided. If the film thickness is less than 0.2 μm, there is a risk of leakage, and excitation may not be possible. On the other hand, if the film thickness exceeds 5 μm, fine processing may be difficult.

  In one embodiment of the present invention, the piezoelectric film includes an oxide having a perovskite structure mainly composed of Pb, Zr and Ti, an oxide having a perovskite structure mainly composed of Pb, Mg, Nb and Ti, K, It consists of an oxide having a perovskite structure mainly composed of Na and Nb or an oxide having a perovskite structure mainly composed of Ba, Ca and Ti. With this configuration, since a piezoelectric film made of a piezoelectric thin film material having high piezoelectric characteristics produces a large inverse piezoelectric effect and piezoelectric effect, highly sensitive detection is possible.

  In one embodiment of the present invention, the piezoelectric film is a piezoelectric material film formed by a sol-gel method or a sputtering method. With this configuration, a piezoelectric film having a required film thickness can be formed, so that a highly sensitive detection is possible and a MEMS piezoelectric sensor that is advantageous for multi-axis can be provided.

FIG. 1 is a perspective view of a MEMS piezoelectric sensor according to an embodiment of the present invention. FIG. 2 is a longitudinal sectional view of a main part of the MEMS piezoelectric sensor. FIG. 3 is a perspective view showing a part of the structure of the sensor body of the MEMS piezoelectric sensor. FIG. 4 is a perspective view of a support substrate that supports the sensor body. FIG. 5 is a plan view for explaining the arrangement of electrodes on the sensor body. FIG. 6 is an enlarged cross-sectional view near the center of the bottom of the sensor body. 7A is a plan view of the sensor body, FIG. 7B is a cross-sectional view taken along line BB of FIG. 7A, and FIG. 7C is a cross-sectional view taken along line CC of FIG. 7A. FIG. 8 is a schematic perspective view showing three-dimensional deformation occurring in the sensor body. FIG. 9 is a diagram illustrating forces and displacements generated at the bottom of the sensor body when the sensor body is placed in a motion system that moves with an angular velocity about the central axis. 10A is a plan view of the sensor body, FIG. 10B is a cross-sectional view taken along line BB in FIG. 10A, and FIG. 10C is a cross-sectional view taken along line CC in FIG. 10A when an angular velocity is generated. Indicates the state. 11A to 11C are cross-sectional views for explaining a manufacturing process of the sensor body. 11D to 11F are cross-sectional views for explaining a manufacturing process of the sensor body. 11G to 11I are cross-sectional views for explaining a manufacturing process of the sensor body. 11J to 11L are cross-sectional views for explaining the manufacturing process of the sensor body. 12A to 12D are cross-sectional views for explaining a manufacturing process of the support substrate. 12E to 12G are cross-sectional views for explaining a manufacturing process of the support substrate. FIG. 13 shows the experimental results confirming the vibration of the sensor body. FIG. 14 shows an experimental result of confirming steady vibration in the wineglass mode of the sensor body. FIG. 15 shows the experimental results for confirming the detection operation. FIG. 16A is a diagram illustrating a result of obtaining a relationship of a scale factor with respect to the thickness of the body portion of the sensor body on the assumption that the Q value is constant and the amplitude of the resonance state is proportional to the displacement when the static load is applied. FIG. 16B is a diagram showing the relationship between the thickness of the body portion of the sensor body and the scale factor in the vibration state. FIG. 17 is a schematic cross-sectional view for explaining the configuration of a MEMS piezoelectric sensor according to another embodiment of the present invention. FIG. 18 is a schematic cross-sectional view for explaining the configuration of a MEMS piezoelectric sensor according to still another embodiment of the present invention. FIG. 19A is a perspective view for explaining a configuration of a MEMS piezoelectric sensor according to still another embodiment of the present invention. FIG. 19B is a perspective view for explaining the configuration of a MEMS piezoelectric sensor according to still another embodiment of the present invention. FIG. 20 is a schematic cross-sectional view for explaining the configuration of a MEMS piezoelectric sensor according to still another embodiment of the present invention. FIG. 21A shows a modification regarding the shape of the sensor body. FIG. 21B shows a modification regarding the shape of the sensor body. FIG. 21C shows a modification regarding the shape of the sensor body. FIG. 22 shows a modification regarding the shape of the sensor body. FIG. 23 shows a configuration example in which a piezoelectric element is arranged inside a wine glass-type sensor body.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a perspective view of a MEMS piezoelectric sensor 1 according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the MEMS piezoelectric sensor 1 at a cut surface including the central axis 20. FIG. 3 is a perspective view showing the sensor body 2 of the MEMS piezoelectric sensor 1 with a part cut away. FIG. 4 is a perspective view of the support substrate 31 that supports the sensor body 2.

The MEMS piezoelectric sensor 1 includes a sensor body 2 and a support structure 3 that supports the sensor body 2. The support structure 3 includes a support substrate 31.
In this embodiment, the sensor body 2 is made of silicon. More specifically, the sensor body 2 is manufactured by processing a silicon substrate (more specifically, an SOI (Silicon-On-Insulator) substrate) by a semiconductor process.

  The sensor body 2 has a cup shape. Specifically, the sensor body 2 has a bottom portion 21 and a trunk portion 22. In this embodiment, the bottom portion 21 has a flat plate shape. More specifically, the bottom portion 21 is a disc portion having a disk shape (disc shape) with a uniform thickness. The trunk | drum 22 is a cylinder shape in this embodiment. More specifically, the body portion 22 is a cylinder portion (side wall portion) that is continuous with the periphery of the bottom portion 21 and has a cylindrical shape with a uniform thickness. Therefore, in this embodiment, the sensor body 2 has a rotationally symmetric shape around the central axis 20, and more specifically, is a rotating body around the central axis 20. The sensor body 2 is supported by the support substrate 31 in a state where the bottom 21 is disposed on the side opposite to the support substrate 31.

  A lower electrode 5 and a piezoelectric film 6 are laminated on the outer surface 21 a of the bottom 21 of the sensor body 2. On the piezoelectric film 6, a plurality of electrodes Ed1 to Ed4 and Es1 to Es4 are arranged. The plurality of electrodes Ed <b> 1 to Ed <b> 4, Es <b> 1 to Es <b> 4 are arranged radially about the central axis 20. In this embodiment, eight electrodes Ed1 to Ed4 and Es1 to Es4 are provided. The eight electrodes Ed1 to Ed4 and Es1 to Es4 are arranged at eight-fold symmetrical positions around the central axis 20 respectively.

  In this embodiment, the eight electrodes include four excitation electrodes Ed1 to Ed4 (sometimes referred to as “excitation electrodes Ed” when collectively referred to) and four detection electrodes Es1 to Es4 (hereinafter collectively referred to as “excitation electrodes Ed”). Sometimes "detection electrode Es"). Each of the electrodes Ed1 to Ed4 and Es1 to Es4 is a strip electrode that is linearly arranged along the radius of the bottom portion 21 and has a constant width. A connection portion 8 to the lower electrode 5 is disposed at the center of the bottom portion 21. The inner end of each of the electrodes Ed1 to Ed4 and Es1 to Es4 on the side close to the central axis 20 is a bonding pad 9 for wire bonding.

  In this embodiment, the support substrate 31 is made of silicon. More specifically, the support substrate 31 is manufactured by processing a silicon substrate by a semiconductor process. On the surface 31 a of the support substrate 31, an engraved portion 15 is formed. The dug 15 is a recess dug down from the surface 31 a of the support substrate 31, and has a bottom surface 15 a lower than the surface 31 a of the support substrate 31. In this embodiment, the peripheral edge 15b of the digging portion 15 is circular. The sensor body 2 is disposed in the digging portion 15. The sensor body 2 is supported by the support substrate 31 in the digging portion 15. The sensor body 2 is supported in a posture in which the opening edge 23 is opposed to the bottom surface 15 a of the digging portion 15. A gap 16 is formed between the opening edge 23 and the bottom surface 15 a of the digging portion 15.

  Wiring is formed on the surface of the support substrate 31. The wirings are excitation wirings Wd1 to Wd4 corresponding to the excitation electrodes Ed1 to Ed4 (referred to collectively as “excitation wiring Wd”) and detection wirings Ws1 to Ws4 corresponding to the detection electrodes Es1 to Es4 (referred to as “detection wirings generally”). Ws ”) and a common wiring Wc corresponding to the lower electrode 5. In this embodiment, four excitation wires Wd1 to Wd4 corresponding to the four excitation electrodes Ed1 to Ed4 and four detection wires Ws1 to Ws4 respectively corresponding to the four detection electrodes Es1 to Es4 are provided. ing. The common wiring includes an annular portion 32 formed in an annular shape (annular in this embodiment) along the peripheral edge 15b of the digging portion 15, and a plurality of lead portions 33 drawn from the annular portion 32. have. The plurality of lead portions 33 are routed on the surface 31a of the support substrate 31 so as to divide the adjacent excitation wires Wd1 to Wd4 and the detection wires Ws1 to Ws4.

  A bonding pad 34 is disposed in the middle of one lead portion 33, and an external connection pad 35 is disposed at an end portion of the lead portion 33. The bonding pad 34 and the lower electrode connection portion 8 of the sensor body 2 are connected by a bonding wire Bc. Each excitation wiring Wd1 to Wd4 is provided with a bonding pad 36 at an end portion close to the sensor body 2 and an external connection pad 37 at the opposite end portion. The bonding pads 9 of the excitation electrodes Ed1 to Ed4 and the bonding pads 36 of the corresponding excitation wirings Wd1 to Wd4 are connected by bonding wires Bd1 to Bd4 (referred to collectively as “bonding wires Bd”). Similarly, in each of the detection wirings Ws1 to Ws4, a bonding pad 38 is disposed at an end portion close to the sensor body 2, and an external connection pad 39 is provided at the opposite end portion. The bonding pads 9 of the detection electrodes Es1 to Es4 and the corresponding bonding pads 38 of the detection wirings Ws1 to Ws4 are connected by bonding wires Bs1 to Bs4 (referred to collectively as “bonding wires Bs”).

  A drive circuit 51 is connected to the external connection pads 37 of the excitation wirings Wd1 to Wd4. The drive circuit 51 applies a drive signal between the common wiring Wc and the excitation wirings Wd1 to Wd4. Thereby, a drive voltage is applied between the lower electrode 5 and the excitation electrodes Ed1 to Ed4. The drive signal may be a sine wave signal. The frequency of the drive signal is preferably a natural frequency that allows the sensor body 2 to resonate. A detection circuit 52 is connected to the external connection pads 39 of the detection wirings Ws1 to Ws4. The detection circuit 52 detects, amplifies and outputs the voltage between the common wiring Wc and the detection wirings Ws1 to Ws4 as a detection signal. Thereby, a detection signal generated between the lower electrode 5 and the detection electrodes Es1 to Es4 is extracted.

  A support portion 14 is provided in the center of the dug portion 15. In this embodiment, the support portion 14 has a cylindrical shape. Therefore, the digging portion 15 is formed in an annular shape around the support portion 14 in this embodiment. By forming the annular recess 15 in the support substrate 31, the support 14 integrated with the support substrate 31 can be provided in the center of the recess 15.

  On the other hand, a columnar portion 25 that is coupled to the bottom portion 21 and extends along the central axis 20 is provided inside the sensor body 2. In this embodiment, the columnar portion 25 has a cylindrical shape, and one end thereof is integrated with the bottom portion 21. More specifically, the bottomed cylindrical cup-shaped sensor body 2 is cut out from the SOI substrate 10 for producing the sensor body 2 by etching. At the time of this etching, the columnar portion 25 integrated with the bottom portion 21 can be provided by simultaneously forming the concave portion 26 having an annular cross section inside the sensor body 2. Therefore, the front end surface 25 a of the columnar portion 25 is at the same position as the opening edge 23 of the sensor body 2 with respect to the direction of the central axis 20. The front end surface 25 a of the columnar part 25 is bonded to the surface 14 a of the support part 14 of the support substrate 31. For the bonding, for example, an adhesive 17 made of a resin material may be used. In addition, the columnar portion 25 may be bonded to the support substrate 31 using a metal brazing material (for example, solder), or the columnar portion 25 and the support substrate 31 may be bonded by direct bonding of silicon.

  The opening edge 23 of the sensor body 2 faces the digging portion 15. The bottom surface 15 a of the digging portion 15 is retreated to a position lower than the surface 31 a of the support substrate 31 (a position retreated in a direction away from the sensor body 2), and the opening edge 23 of the sensor body 2 is the front end surface of the columnar portion 25. The gap 16 is formed between the opening edge 23 and the bottom surface 15a of the digging portion 15 because it is at the same height as 25a (the same position in the direction of the central axis 20). Thus, the support structure 31 that supports the sensor body 2 at a position on the central axis 20 is constituted by the support substrate 31 and the columnar portion 25.

  The columnar portion 25 is integrally coupled to the bottom portion 21 at a coupling region 18 including the central axis 20 in a plan view viewed along the central axis 20. The coupling region 18 is a circular region around the central axis 20 and is a region near the central axis 20. The coupling region 18 is on the inner side of the outer edge of the sensor body 2 in a plan view viewed along the central axis 20. More specifically, the diameter of the coupling region 18 is equal to or less than ½ of the diameter of the sensor body 2 in the plan view (equal to the diameters of the bottom portion 21 and the trunk portion 22 in this embodiment). The diameter of the coupling region 18 is preferably 1/20 or more of the diameter of the sensor body 2 in plan view. The columnar portion 25 and the bottom portion 21 are coupled to each other throughout the coupling region 18. Accordingly, the columnar portion 25 is coupled to the bottom portion 21 of the sensor body 2 on the central axis 20. The bonding pads 9 arranged at the inner ends of the electrodes Ed and Es are located in the coupling region 18 in plan view. That is, the bonding pad 9 overlaps the columnar portion 25 in plan view.

  The sensor body 2 is manufactured using, for example, an SOI substrate 10. The SOI substrate 10 includes a silicon substrate 11, an insulating film 12 (typically an oxide film) formed on the surface of the silicon substrate 11, and a silicon layer 13 formed on the surface of the insulating film 12. The annular recess between the columnar part 25 and the body part 22 is formed by etching from the surface of the back surface of the silicon substrate 11 (the side opposite to the insulating film 12). This etching may be performed in the same process as the etching of the outer side of the body part 22 for separating the body part 22 from the silicon.

  As best shown in FIG. 2, the lower electrode 5 is formed on the outer surface of the bottom 21. In this embodiment, the lower electrode 5 is formed over the entire outer surface of the bottom portion 21. A piezoelectric film 6 is formed on the surface of the lower electrode 5. In this embodiment, the piezoelectric film 6 is formed over the entire surface of the lower electrode 5. That is, the piezoelectric film 6 is continuous over the entire outer surface of the bottom 21. Excitation electrodes Ed1 to Ed4 and detection electrodes Es1 to Es4 are formed on the surface of the piezoelectric film 6.

  The excitation electrodes Ed1 to Ed4 are opposed to the lower electrode 5 with the piezoelectric film 6 interposed therebetween. Therefore, in the region where the excitation electrodes Ed1 to Ed4 are in contact with the piezoelectric film 6, the excitation piezoelectric elements Pd1 to Pd4 (piezoelectric actuator: sandwiched between the excitation electrodes Ed1 to Ed4 and the lower electrode 5). Hereinafter, they are collectively referred to as “excitation piezoelectric element Pd”). The detection electrodes Es1 to Es4 are opposed to the lower electrode 5 with the piezoelectric film 6 interposed therebetween. Therefore, in the region where the detection electrodes Es1 to Es4 are in contact with the piezoelectric film 6, the detection piezoelectric elements Ps1 to Ps4 (piezoelectric sensor :) having the piezoelectric film 6 sandwiched between the detection electrodes Es1 to Es4 and the lower electrode 5 Hereinafter, they are collectively referred to as “detection piezoelectric element Ps”).

FIG. 5 is a plan view for explaining the arrangement of the electrodes Ed1 to Ed4 and Es1 to Es4. 2n (n is a natural number, in this embodiment, n = 4) electrodes Ed1 to Ed4 and Es1 to Es4 arranged on the surface of the piezoelectric film 6 are arranged around the central axis 20 at 2n times symmetrical positions. Has been. In other words, 2n electrodes are arranged at equiangular intervals at an angular interval of 360 / 2n degrees (45 degrees when n = 4). N _d (n _d is a natural number. In this embodiment, n _d = 4) excitation electrodes Ed (shown by hatching in FIG. 5 for the sake of clarity) are arranged n _d times around the central axis 20. It is arranged in a symmetrical position. In other words, _{n d} number of excitation electrode Ed are _(at the time of _n d = 4 90 °) 360 / _{n d} of about the central axis 20 are arranged at equal angular intervals in angular spacing. Similarly, _{n s} number _{(n s} is a natural number. In this _{embodiment, n} s = 4) detecting electrode Es of, are disposed at positions of _{n s-fold} symmetry about the central axis 20. In other words, the n _s detection electrodes Es are arranged at equiangular intervals around the central axis 20 at an angular interval of 360 / _ns degrees (90 degrees when n _s = 4). The excitation electrodes Ed and the detection electrodes Es are alternately arranged in the circumferential direction around the central axis 20, and the angular interval between the adjacent excitation electrodes Ed and the detection electrodes Es is 360 / 2n degrees (n = 4). Sometimes 45 degrees). In this embodiment, n = n _d = n _s .

  A pair of excitation electrodes Ed1 and Ed3 arranged symmetrically with respect to the central axis 20 and another pair of excitation electrodes Ed2 and Ed4 arranged symmetrically with respect to the central axis 20 are 90 around the central axis 20. It has a positional relationship of rotational movement. These two pairs of excitation electrodes Ed1, Ed3; Ed2, Ed4 are applied with, for example, drive voltages that are 180 degrees out of phase. Specifically, when + 5V is applied to the first pair of excitation electrodes Ed1 and Ed3 with reference to the potential of the lower electrode 5, the second pair of excitation electrodes Ed2 and Ed4 has the potential of the lower electrode 5 as a reference. A voltage of -5V is applied.

  FIG. 6 is an enlarged cross-sectional view near the center of the bottom 21. In the vicinity of the central axis 20, the piezoelectric film 6 and the silicon layer 13 are removed to form a recess 27. The recess 27 reaches the insulating film 12. The ball 28 of the bonding wire Bc for connection to the lower electrode 5 is disposed in the recess 27. The ball 28 is in contact with the exposed end surface of the silicon layer 13 and the exposed end surface of the lower electrode 5 on the peripheral wall surface 27 a of the recess 27. The ball 28 may be in contact with the piezoelectric film 6 but should not be in contact with either the excitation electrode Ed or the detection electrode Es as the upper electrode.

The bonding wire Bc is in direct contact with and electrically connected to the lower electrode 5, and an energization path reaching the lower electrode 5 through the silicon layer 13 is also formed. The silicon layer 13 is made to have a low resistance by adding impurities, and provides an energization path between the bonding wire Bc and the lower electrode 5.
The electric resistance of the silicon layer 13 may be made sufficiently low, the silicon layer 13 may be used as the lower electrode of the piezoelectric elements Pd1 to Pd4, Ps1 to Ps4, and the lower electrode 5 may be omitted.

  7A is a plan view of the sensor body 2, FIG. 7B is a cross-sectional view taken along line BB in FIG. 7A, and FIG. 7C is a cross-sectional view taken along line CC in FIG. 7A. When a drive voltage having a natural frequency of the sensor body 2 is applied to the excitation electrodes Ed <b> 1 to Ed <b> 4, a wine glass mode standing wave SW is generated in the sensor body 2. Specifically, the bottom 21 is alternately expanded and contracted along the pair of excitation electrodes Ed1 and Ed3 and the other pair of excitation electrodes Ed2 and Ed4 facing each other with the central axis 20 therebetween. Accordingly, the bottom portion 21 is warped and deformed, and the body portion 22 is also deformed in accordance with the warp deformation. As a result, as shown in FIG. 8, the sensor body 2 is three-dimensionally deformed.

  During steady vibration in the wine glass mode, the direction of the pair of excitation electrodes Ed1, Ed3 facing each other across the central axis 20 and the direction of the other pair of excitation electrodes Ed2, Ed4 arranged so as to be orthogonal thereto Becomes an antinode AN of steady vibration. The direction of each of the detection electrodes Es1 to Es4 when viewed from the central axis 20 is a node N of steady vibration. Therefore, when no external force is generated, the detecting piezoelectric elements Ps1 to Ps4 do not detect the deformation of the sensor body 2.

  FIG. 9 shows the force and displacement generated at the bottom 21 of the sensor body 2 when the sensor body 2 is placed in a motion system that moves around the central axis 20 with an angular velocity ω. When steady vibration is occurring in the wineglass mode, the position of the excitation electrode Ed is the vibration antinode AN at the bottom 21 of the sensor body 2, and vibration in the direction along the central axis 20 is generated at the vibration antinode AN. ing. At an arbitrary moment, a displacement toward one side of the central axis 20 occurs in one of the adjacent excitation electrodes Ed, and a displacement toward the other side of the central axis 20 occurs in the other of the excitation electrodes Ed. ing. Therefore, the Coriolis force FC1 in one direction along the circumferential direction around the central axis 20 is applied to one of the two pairs of excitation electrodes Ed1, Ed3; Ed2, Ed4 facing each other with the central axis 20 therebetween. The Coriolis force FC2 in the other direction is generated along the circumferential direction around the central axis 20 with respect to the other pair. Due to the Coriolis forces FC1 and FC2, at the position of one pair Es1 and Es3 of the two pairs of detection electrodes Es facing each other across the center axis 20, the peripheral edge of the bottom 21 is displaced toward one of the center axes 20 DS1 is generated, and at the position of the other pair Es2, Es4, a displacement DS2 in which the peripheral edge of the bottom 21 is directed to the other of the central axis 20 is generated. These displacements DS1 and DS2 are detected by the detection piezoelectric elements Ps1 to Ps4 corresponding to the detection electrodes Es1 to Es4.

  10A is a plan view of the sensor body 2, FIG. 10B is a cross-sectional view taken along line BB in FIG. 10A, and FIG. 10C is a cross-sectional view taken along line CC in FIG. 10A. When the angular velocity ω is generated, the vibration OS is also generated at the position of the detection electrode Es due to the Coriolis force. Specifically, the bottom 21 is alternately expanded and contracted along the pair of detection electrodes Es1, Es3 and the other pair of detection electrodes Es2, Es4 that are opposed to each other with the central axis 20 interposed therebetween. Accordingly, the bottom portion 21 is warped and deformed, and the body portion 22 is also deformed in accordance with the warp deformation. As a result, a complicated three-dimensional deformation is generated in the sensor body 2 by adding vibration due to the Coriolis force in addition to the deformation shown in FIG.

Therefore, when the angular velocity ω is generated, the vibration OS caused by the Coriolis force is detected by the pair of detection piezoelectric elements Ps1 and Ps3 opposed to each other with the central axis 20 interposed therebetween, and another pair arranged in a direction orthogonal thereto. Are detected by the detecting piezoelectric elements Ps2 and Ps4.
11A to 11L are cross-sectional views for explaining the manufacturing process of the sensor body 2.
As shown in FIG. 11A, an SOI substrate 10 is prepared. The SOI substrate 10 includes a silicon substrate 11, an insulating film 12 (so-called buried oxide film) formed on the surface, and a silicon layer 13 (active layer) formed on the surface. The silicon substrate 11 may have a thickness of 525 nm, for example. The insulating film 12 may be a silicon oxide film having a thickness of 1000 nm, for example. The silicon layer 13 is a semiconductor layer imparted with conductivity by adding impurities to reduce resistance, and may have a thickness of 20 μm and a specific resistance of 1 to 10 Ω · cm, for example.

As shown in FIG. 11B, the lower electrode 5 is formed over the entire surface of the silicon layer 13 of the SOI substrate 10, and the piezoelectric film 6 is further laminated on the lower electrode 5. The lower electrode 5 may be composed of, for example, a laminated electrode film in which a Ti layer (adhesion layer) and a Pt layer are sequentially laminated on the surface of the silicon layer 13. A seed layer for forming the piezoelectric film 6 may be further formed on the lower electrode 5. As the seed layer, a (Pa, La) TiO ₃ (PLT) film may be used. The Ti layer, the Pt layer, and the PLT layer can be continuously formed using a multi-source sputtering apparatus. Examples of film forming conditions for each layer are as follows.

  The piezoelectric film 6 is made of, for example, PZT. In general, the piezoelectric film 6 is composed of an oxide having a perovskite structure mainly composed of Pb, Zr and Ti (PZT), an oxide having a perovskite structure mainly composed of Pb, Mg, Nb and Ti (PMNT), K, What is necessary is just to consist of the oxide of the perovskite structure which has Na and Nb (KNN) as a main component, or the oxide of the perovskite structure which has Ba, Ca, and Ti (BCT) as a main component. Such a piezoelectric film 6 can be formed by a sol-gel method or a sputtering method. For example, examples of conditions for forming a PZT film by sputtering are as follows.

Next, as shown in FIG. 11C, a photoresist pattern 61 is formed on the piezoelectric film 6. The photoresist pattern 61 has an opening 62 corresponding to the formation position of the excitation electrode Ed and the detection electrode Es.
As shown in FIG. 11D, an upper electrode film 63 is deposited on the photoresist pattern 61. The upper electrode film 63 is in contact with the piezoelectric film 6 in the opening 62 of the photoresist pattern 61 and is in contact with the surface of the photoresist pattern 61 outside the opening 62. The upper electrode film 63 may be a Pt film, for example. In consideration of later wire bonding, Au (gold) excellent in bondability with a wire may be used. However, when gold is deposited directly on the surface of PZT, the adhesion is poor. Therefore, a Cr film (for example, a film thickness of about 50 nm) is formed as an adhesion layer on the surface of PZT, and then an Au film (for example, a film thickness of about 100 nm). ) Is preferably formed. These films can be formed using a sputtering apparatus.

Next, as shown in FIG. 11E, the photoresist pattern 61 is removed. At this time, the upper electrode film 63 on the surface of the photoresist pattern 61 is lifted off, and only the upper electrode film 63 in the opening 62 of the photoresist pattern 61 is left on the piezoelectric film 6, and the excitation electrode Ed and the detection electrode Es. Configure.
Next, as shown in FIG. 11F, an etching mask layer 65 for selectively etching the silicon layer 13 is formed on the entire surface on the silicon layer 13 side, and an etching mask layer for selectively etching the silicon substrate 11 from the back surface. 66 is formed on the entire back surface of the silicon substrate 11. The etching mask layers 65 and 66 may be made of, for example, a Cr (chrome) film. Since the etching of the silicon layer 13 which is an active layer has a poor selectivity with respect to Cr as compared with the etching of the silicon substrate 11, the thickness of the Cr layer on the silicon layer 13 side (for example, 800 nm) is set to the Cr on the back surface of the silicon substrate 11. It is preferable to make it larger than the thickness of the layer (for example, 500 nm).

  Next, as shown in FIG. 11G, resist patterns 67 and 68 are formed on the surfaces of the etching mask layers 65 and 66, respectively. The resist pattern 67 on the front side has an annular opening 69 that defines the outer peripheral edge of the bottom 21 of the sensor body 2 and a circular opening 70 that corresponds to the recess 27 at the center of the bottom 21. The resist pattern 68 on the back surface side has an annular opening 71 that defines the outer periphery of the body portion 22 of the sensor body 2, and an annular opening 72 that defines the inner periphery of the body portion 22 of the sensor body 2 and the peripheral surface of the columnar portion 25. And have.

  As shown in FIG. 11H, the etching mask layers 65 and 66 are etched using these resist patterns 67 and 68 as a mask (for example, wet etching using a chromium etching solution), and the etching mask layers 65 and 66 are formed into the resist pattern 67. , 68 in the same pattern. The patterned etching mask layer 65 covers the upper surfaces and end surfaces of the electrodes Ed and Es.

  As shown in FIG. 11I, the piezoelectric film 6, the lower electrode 5, and the silicon layer 13 are etched using the etching mask layers 65 and 66 as a mask. Etching of the piezoelectric film 6 (for example, PZT film) may be performed using an NLD-RIE (magnetic neutral loop discharge reactive ion etching) apparatus. NLD-RIE is a method that can generate plasma under a low pressure by generating a magnetic field in a reaction chamber to increase the density of the plasma and improve the in-plane uniformity. The seed layer made of PLT and the lower electrode 5 (Pt / Ti) can also be etched under the same conditions by the same apparatus. Thereafter, the silicon layer 13 is etched. Etching of the silicon layer 13 can also be performed using the same apparatus. Examples of etching conditions for the piezoelectric film 6 (PZT) and the silicon layer 13 are shown below.

Thereafter, as shown in FIG. 11J, the silicon substrate 11 is etched from the back surface side using the etching mask layer 66 as a mask in a state where the pattern on the front surface side is covered with a resist 74. This etching may be, for example, dry etching using an ICP-RIE (Inductively Couple Plasma Reactive Ion Etching) apparatus. More specifically, the Bosch process that achieves a high aspect ratio while suppressing side etching by repeating an etching process using a highly reactive gas and a process of depositing a protective film with a polymer on the Si surface. May be used. For example, SF ₆ may be used for etching silicon, and C ₄ F ₈ may be used for forming a protective film. An example of processing conditions is shown below.

  Thereafter, as shown in FIG. 11K, the sensor body 2 is separated from the SOI substrate 10 by etching away the insulating film 12 outside the bottom portion 21. The etching may be dry etching using, for example, an ICP-RIE apparatus. An example of etching conditions is shown below.

Then, as shown in FIG. 11L, the sensor body 2 is obtained by removing the etching mask layers 65 and 66 (Cr layer) with a chromium etching solution.
12A to 12G are cross-sectional views for explaining the manufacturing process of the support substrate 31.
As shown in FIG. 12A, a silicon substrate 80 having an insulating film 81 (for example, a silicon oxide film formed by thermal oxidation) formed on the surface is prepared. For example, the thickness of the silicon substrate 80 may be about 300 μm, and the thickness of the insulating film 81 may be about 100 nm.

  As shown in FIG. 12B, a resist pattern 83 having openings 82 corresponding to the patterns of the wirings Wd, Ws, Wc is formed on the surface of the insulating film 81. A wiring film 85 is deposited on the entire surface as shown in FIG. 12C. The wiring film 85 may be a laminated film of a Cr film (for example, a film thickness of about 50 nm) as an adhesion layer in contact with the insulating film 81 and an Au film laminated thereon (for example, a film thickness of about 100 nm). These films can be formed using a sputtering apparatus. The wiring film 85 enters the opening 82 of the resist pattern 83 and is formed on the insulating film 81, and is formed on the resist pattern 83 outside the opening 82.

Next, as shown in FIG. 12D, when the resist pattern 83 is removed, the wiring film 85 on the resist pattern 83 is lifted off, so that the wirings Wd, Ws, Wc corresponding to the openings 82 of the resist pattern 83 become the insulating film 81. Left over.
Next, as shown in FIG. 12E, a resist pattern 88 having an annular opening 87 corresponding to the digging portion 15 is formed. Using this resist pattern 88 as a mask, as shown in FIG. 12F, insulating film 81 is etched and silicon substrate 80 is further etched. Thereby, the annular digging portion 15 is formed, and the columnar support portion 14 is formed inside thereof. Thereafter, as shown in FIG. 12G, the support substrate 31 is obtained by removing the resist pattern 88.

  The insulating film 81 may be etched by, for example, wet etching using buffered hydrofluoric acid (BHF). Further, the etching of the silicon substrate 80 may be performed by dry etching using an ICP-RIE apparatus as in the case of the silicon substrate 11 of the sensor body 2. The processing conditions may be the same as those for the silicon substrate 11 of the sensor body 2. The depth of etching can be set by adjusting the number of process cycles, and may be about 150 μm, for example.

After that, the sensor body 2 and the support substrate 31 are coupled via the columnar portion 25 by bonding the columnar portion 25 to the support portion 14. Then, the MEMS piezoelectric sensor 1 is obtained by wire bonding the electrodes Ed, Es, 5 of the sensor body 2 to the wirings Wd, Ws, Wc on the support substrate 31.
FIG. 13 shows the experimental results confirming the vibration of the sensor body 2. The dimensions (see FIG. 2) of each part of the sensor body 2 used in the experiment are as follows. That is, the diameter D1 of the columnar portion 25 is 1 mm, the diameter D2 of the bottom portion 21 is 3 mm, the height H of the trunk portion 22 is 525 μm, the thickness T _D of the bottom portion 21 is 20 μm, and the thickness T _S of the trunk portion 22 is 30 μm. is there. Each electrode Ed, Es is a rectangle having a width of 100 μm and a length of 1100 μm.

While applying a sine wave to the excitation electrodes Ed1 to Ed4 and sweeping the frequency, vibrations in the vicinity of the excitation electrodes Ed1 to Ed4 were measured with a laser Doppler vibrometer. As a result, near the frequency of 34 kHz, the vibration phase was reversed and the amplitude was maximized, confirming resonance.
FIG. 14 shows the experimental results confirming steady vibration in the wine glass mode. The sensor body 2 used in the experiment is the same as in FIG. A sine wave having a frequency of 34 kHz was applied to the excitation electrodes Ed1 to Ed4, and the amplitude at the peripheral edge of the bottom 21 was measured with a laser Doppler vibrometer. The horizontal axis is a position in the x-axis direction defined along a pair of excitation electrodes Ed1, Ed3 facing each other with the central axis 20 therebetween, and the vertical axis is another pair of excitation electrodes Ed2 facing each other with the central axis 20 therebetween. , Ed4, and the origin in the y-axis direction, which is the intersection of the x-axis and the y-axis, corresponds to the central axis 20 of the bottom 21. The distance from the origin represents the amplitude at the peripheral edge in each direction around the central axis 20.

From FIG. 14, it can be seen that the position of the excitation electrode Ed is an antinode of vibration, and the intermediate position between them, that is, the position of the detection electrode Es is a node of vibration. That is, it can be seen that a steady vibration (resonance) in the wine glass mode occurs.
FIG. 15 shows the experimental results for confirming the detection operation. The sensor body 2 used in the experiment is the same as in FIG. Using a frequency response analyzer, a sine wave was applied to the pair of excitation electrodes Ed1 and Ed3, and the frequency was swept while the output signals of the other excitation electrodes Ed2 and Ed4 were detected. As a result, the phase of the detection signal was reversed and the amplitude (arbitrary unit) was maximized around a frequency of 34 kHz, and resonance was confirmed. As a result, it was confirmed that the amplitude could be detected by the piezoelectric element on the sensor body 2.

Table 6, the thickness T _S of the body portion 22 20 [mu] m, to prepare a sample with 30μm and 40 [mu] m, measured natural frequency in wineglass mode, the experimental results obtained the Q value in addition wineglass mode Indicates.

Figure 16A is a constant Q value, assuming that the amplitude of the resonant state is proportional to the displacement at the time of static load is applied to obtain the relationship of the normalized scale factor for the thickness T _S of the body portion 22 (arbitrary units) It is a figure which shows the result. Figure 16B shows the relationship between the normalized scale factor of the vibration state and the thickness T _S of the body portion 22 (arbitrary unit). The scale factor represents the amount of voltage change per degree / second and corresponds to the angular velocity detection sensitivity. In the vibration state, the vibration amplitudes for driving and detection are each multiplied by the Q value. Therefore, with respect to the scale factor of Fig. 16A, multiplied by square of the Q value corresponding to each thickness T _S of Table 6, by normalizing the maximum value, the scale factor of Fig. 16B is obtained.

Higher scale factor greater thickness T _S of the body portion 22 is small, therefore, possible to provide a highly sensitive MEMS piezoelectric sensor 1. That is, as the thickness T _S of the body portion 22 is small, the displacement caused by the Coriolis force increases, accordingly, can realize high-sensitivity sensor. However, it is preferred that the thickness T _S to more than 10 [mu] m, the thinner the thickness T _S of the body portion 22 in the above range 10 [mu] m, can realize high-sensitivity sensor.

As described above, according to the MEMS piezoelectric sensor 1 of this embodiment, the sensor body 2 has a cup shape and is supported by being coupled to the support structure 3 on the central axis 20 thereof. Therefore, the entire sensor body 2 can vibrate while being supported on the central axis 20.
A plurality of electrodes are bonded to the piezoelectric film 6 formed on the surface of the sensor body 2. In this embodiment, the plurality of electrodes includes four excitation electrodes Ed1 to Ed4 and four detection electrodes Es1 to Es4, which are arranged radially around the center axis 20 of the cup shape. . By using these electrodes Ed and Es, it is possible to generate vibration over the entire sensor body 2 or to detect an electromotive force generated in the piezoelectric film 6 due to external force or other influences. Since almost the entire sensor body 2 vibrates, detection with high sensitivity is possible.

In addition, since the cup-shaped sensor body 2 is three-dimensionally deformed according to various physical quantities such as external force, temperature, humidity, acceleration, angular velocity, and angular acceleration, it is possible to simultaneously detect physical quantities in a plurality of coordinate axis directions. And so-called multi-axis can be realized.
In the configuration of this embodiment, by applying a drive voltage to the two pairs of excitation electrodes Ed1, Ed3; Ed2, Ed4, the piezoelectric film 6 is expanded and contracted by the inverse piezoelectric effect, thereby causing the sensor body 2 to vibrate. be able to. On the other hand, the two pairs of detection electrodes Es1, Es3; Es2, Es4 can derive a voltage generated in the piezoelectric film 6 due to the piezoelectric effect. Thereby, since the sensor body 2 can be vibrated and the deformation of the sensor body 2 can be detected, a highly sensitive vibration type sensor can be provided. In addition, three-dimensional deformation that occurs in the cup-shaped sensor body 2 can be detected by the detection electrodes Es1 to Es4, and so-called multi-axis can be realized.

  In this embodiment, the excitation electrode Ed and the detection electrode Es are provided 2n times around the central axis 20 (where n is a natural number; in this embodiment, n = 4). Two pairs of excitation electrodes Ed1, Ed3; Ed2, Ed4 are arranged at symmetrical positions with the central axis 20 in between, and two pairs of detection electrodes Es1, Es3; Es2 at symmetrical positions with the central axis 20 in between. , Es4 are arranged. The excitation electrodes Ed and the detection electrodes Es are alternately arranged at 2n times symmetrical positions. Thereby, the sensor body 2 can be excited effectively and can be vibrated with a large amplitude. In addition, the shape change of the sensor body 2 can be detected with high accuracy, whereby the vibration of the sensor body 2 can be detected with high sensitivity, and the MEMS piezoelectric sensor 1 that is advantageous for multi-axis can be realized.

Furthermore, in this embodiment, a physical quantity can be detected by the detection electrode Es in a state where steady vibration (wineglass mode) is generated in the sensor body 2 by the excitation electrode Ed. Since the detection electrode Es is disposed at the node N of the steady vibration, it is possible to detect a change occurring in the sensor body 2 in a state where the influence of the vibration generated by the excitation electrode Ed is suppressed.
More specifically, in this embodiment, when an angular velocity is applied to the MEMS piezoelectric sensor 1 in a state where steady vibration has occurred in the sensor body 2, the steady vibration changes due to Coriolis force, and a signal representing this change is detected by the detection electrode. Taken from Es. Thereby, the angular velocity can be detected. Since three-dimensional vibration occurs in the sensor body 2, it is possible to detect angular velocities about the three axes at the same time by performing appropriate processing on the signal extracted from the detection electrode Es.

In this embodiment, the steady vibration generated in the sensor body 2 is the wine glass mode. In the wine glass mode, since the vibration loss is small, the Q value is high and it is difficult to be influenced by external acceleration. Thereby, detection with high sensitivity is possible and the MEMS piezoelectric sensor 1 advantageous to multi-axis can be provided.
In this embodiment, the sensor body 2 includes a bottom portion 21 and a body portion 22, and the support structure 3 is coupled to the sensor body 2 at the bottom portion 21. Therefore, since the sensor body 2 is supported by the bottom portion 21, vibration can be generated in the entire sensor body 2, and vibration with a small vibration loss, for example, vibration in a wine glass mode is possible. Thereby, it is possible to provide the MEMS piezoelectric sensor 1 that can detect with high sensitivity and is advantageous for multi-axis.

Specifically, in this embodiment, the sensor body 2 is supported by a columnar portion 25 coupled to the bottom portion 21. Thereby, since vibration can be generated in the entire sensor body 2, vibration with a small vibration loss, for example, vibration in a wine glass mode is possible.
Moreover, in this embodiment, the columnar part 25 is couple | bonded with the bottom part 21 of the sensor body 2 inside a cup shape. The support structure 3 includes a support substrate 31 coupled to the columnar portion 25 on the opening edge 23 side of the sensor body 2. In this configuration, since the columnar portion 25 can be arranged inside the cup shape, it is possible to provide the MEMS piezoelectric sensor 1 that is small and highly sensitive and is advantageous for multi-axis use.

In this embodiment, since the surface of the support substrate 31 and the opening edge 23 of the sensor body 2 are separated from each other, the vibration of the sensor body 2 is not inhibited by the support substrate 31. Thereby, since the sensor body 2 can be vibrated efficiently, the MEMS piezoelectric sensor 1 which is highly sensitive and advantageous for multi-axis can be provided.
Further, in this embodiment, the support portion 14 is provided at a position corresponding to the columnar portion 25 on the surface of the support substrate 31, and is supported at a position facing the opening edge 23 of the sensor body 2 on the surface of the support substrate 31. A dug portion 15 that is dug down from the portion 14 is formed. According to this configuration, the columnar portion 25 is supported by the support portion 14 on the surface of the support substrate 31, while a recess (recessed portion) is formed on the surface of the support substrate 31 at a position facing the opening edge 23 of the sensor body 2. 15) is formed. Thereby, the sensor body 2 can be supported in a state in which efficient vibration of the sensor body 2 is ensured.

  Further, the columnar part 25 may not protrude outward (in a direction away from the bottom part 21) of the sensor body 2 from the opening edge 23 of the sensor body 2 in the direction along the central axis 20. More specifically, the end of the columnar portion 25 facing the support substrate 31 may be at the same position as the opening edge 23 of the sensor body 2 in the direction along the central axis 20. Such a structure is obtained by etching the SOI substrate 10 to simultaneously form the sensor body 2 and the columnar portion 25 integrated therewith. Therefore, with the structure in which the sensor body 2 and the columnar portion 25 are formed at the same time in the MEMS process, the vibration of the sensor body 2 can be ensured by the digging portion 15 formed in the support substrate 31.

  Furthermore, in this embodiment, the support substrate 31 is a circuit board on which circuit wirings Wd, Ws, and Wc are formed, and the electrodes 5 and Ed are bonded to the circuit wirings Wd, Ws, and Wc by bonding wires Bd1 to Bd4 and Bs1 to Bs4. ˜1Ed4, Es1 to Es4 are connected. That is, the connection between the electrode and the circuit wiring is ensured by wire bonding. Since the bottom 21 on which the excitation electrodes Ed1 to Ed4 and the detection electrodes Es1 to Es4 are formed has a flat outer surface 21a, these electrodes 5, Ed to 1Ed4, Es1 to Es4 and wiring on the support substrate 31 Wire bonding can be easily achieved.

  In this embodiment, the sensor body 2 includes a flat bottom portion 21 and a cylindrical body portion 22 coupled to the bottom portion 21. The piezoelectric film 6 is disposed on the outer surface 21 a of the flat bottom 21. As described above, the structure in which the sensor body 2 has the flat bottom portion 21 and the cylindrical body portion 22 can be manufactured by the step of etching the SOI substrate 10. Further, since the electrodes Ed and Es are arranged outside the sensor body 2, external connection of the electrodes Ed and Es is easy.

In this embodiment, since the sensor body 2 is made of a material mainly composed of silicon, the sensor body 2 can be manufactured by processing silicon.
Body 22 of the sensor body 2, 0.2 mm or more 5mm or less in diameter D2, and is preferably thick _{T S} is 1/20 or less of the cylindrical shape of the diameter D2. And it is preferable that the length H of the cylindrical central axis 20 direction is 100 micrometers or more and 1 mm or less. As a result, it is possible to provide the MEMS piezoelectric sensor 1 that can efficiently excite the sensor body 2 and that can perform highly sensitive detection and is advantageous for multi-axis use.

  By setting the diameter D2 of the sensor body 2 to 0.2 mm or more and 5 mm or less, processing and wiring are easy, and the resonance frequency can be set to a high frequency range in which high sensitivity detection is possible. That is, if the diameter D2 of the sensor body 2 is less than 0.2 mm, cylindrical processing and wiring become difficult. In addition, when the diameter D2 of the sensor body 2 exceeds 5 mm, the resonance frequency is lowered, and there is a concern that the sensitivity is lowered.

Since the sensitivity is improved as the thickness TS of the body portion 22 is thinner, the thickness T _S is preferably set to 1/20 or less of the cylindrical diameter D2. However, a machining shape thickness T _S is too thin becomes unstable, so causing variations in sensor characteristics, the wall thickness T _S is preferably at least 10 [mu] m.
If the length H of the body portion 22 is too short, there is a concern that the Q value is lowered and the sensitivity is lowered. Therefore, the length H is preferably set to 100 μm or more. On the other hand, if the length H of the body portion 22 is too long, it takes too much processing time and is impractical, so 1 mm or less is preferable.

  Further, the columnar portion 25 constituting the support structure 3 is preferably a columnar shape having a circular cross section having a diameter D1 of 1/20 or more and 1/2 or less of the cylindrical diameter D2 of the body portion 22. As a result, it is possible to provide the MEMS piezoelectric sensor 1 that can efficiently excite the sensor body 2 and that can perform highly sensitive detection and is advantageous for multi-axis use. In particular, the structure in which the cylindrical body portion 22 is supported by the columnar portion 25 having a circular cross section can vibrate the entire sensor body 2 efficiently. Note that the circular cross section of the columnar portion 25 has a shape of a cut surface perpendicular to the central axis 20.

  By setting the diameter D1 of the columnar part 25 to 1/20 or more of the cylindrical diameter D2 of the body part 22, the coupling between the columnar part 25 and the bottom part 21 has sufficient strength. Further, the bonding pad 9 which is a connection portion of the electrodes Ed and Es can be provided in the coupling region 18 between the columnar portion 25 and the bottom portion 21, and the electrodes Ed and Es are bonded while being reliably supported by the columnar portion 25. Wiring connection (wire bonding) to the pad 9 can be performed stably. In addition, by setting the diameter D1 of the columnar part 25 to be equal to or less than ½ of the cylindrical diameter D2 of the body part 22, vibration restraint by the columnar part 25 can be suppressed, so that the entire sensor body 2 is vibrated efficiently. be able to.

  The film thickness of the piezoelectric film 6 is preferably 0.2 μm or more and 5 μm or less. Thereby, it is possible to avoid the piezoelectric film 6 from constraining vibration and deformation of the sensor body 2, and the piezoelectric film 6 produces the necessary reverse piezoelectric effect and piezoelectric effect. A MEMS piezoelectric sensor 1 that is advantageous for shafting can be provided. If the film thickness is less than 0.2 μm, there is a risk of leakage, and excitation may not be possible. On the other hand, if the film thickness exceeds 5 μm, fine processing may be difficult.

  As described above, the piezoelectric film 6 includes a perovskite structure oxide (PZT) mainly composed of Pb, Zr, Ti, a perovskite structure oxide (PMNT) mainly composed of Pb, Mg, Nb, Ti, It is preferably made of a perovskite structure oxide (KNN) mainly composed of K, Na, Nb or a perovskite structure oxide (BCT) mainly composed of Ba, Ca, Ti. Since these are piezoelectric thin film materials having high piezoelectric characteristics, the piezoelectric film 6 produces a large inverse piezoelectric effect and piezoelectric effect, and therefore, highly sensitive detection is possible.

Such a piezoelectric film 6 can be formed by a sol-gel method or a sputtering method, whereby the piezoelectric film 6 having a required film thickness can be formed. Therefore, it is possible to provide the MEMS piezoelectric sensor 1 that can detect with high sensitivity and is advantageous for multi-axis.
FIG. 17 is a schematic cross-sectional view for explaining the configuration of a MEMS piezoelectric sensor 1A according to another embodiment of the present invention. In FIG. 17, portions corresponding to the respective portions of the above-described embodiment are denoted by the same reference numerals.

  In this embodiment, the cup-shaped sensor body 2 is supported on the support substrate 31 with the bottom 21 facing the support substrate 31 and the opening edge 23 facing away from the support substrate 31. The support substrate 31 has a flat surface 31a on which wirings Wc, Wd, and Ws are formed. A bump 90 is disposed at one end of the wirings Wc, Wd, and Ws. A lower electrode 5 is formed on an outer surface 21 a facing the support substrate 31 at the bottom 21 of the sensor body 2, a piezoelectric film 6 is laminated on the lower electrode 5, and further on the piezoelectric film 6. The excitation electrode Ed and the detection electrode Es are stacked. Bumps 91 are arranged at one end (for example, the end on the inner side) of the electrodes Es and Ed. The bumps 91 are joined to the bumps 90 on the wirings Wd and Ws side. On the other hand, a part of the lower electrode 5 is exposed from the piezoelectric film 6. In this embodiment, the lower electrode 5 is exposed in a region including the central axis 20. Lead wires 93 are drawn from the exposed portions of the lower electrode 5 to the surface of the piezoelectric film 6, and bumps 92 are provided on the lead wires 93. The bump 92 is bonded to the bump 90 provided on the wiring Wc on the support substrate 31.

Thus, in this embodiment, the sensor body 2 is supported by the support substrate 31 in the coupling region 18 in the vicinity of the central axis 20 without providing the columnar portion 25 inside the sensor body 2. In this embodiment, the support structure 3 includes a support substrate 31 and bumps 90 to 92.
In this embodiment, the support structure 3 is coupled to the bottom 21 of the sensor body 2 outside the cup shape. Therefore, since the coupling between the support structure 3 and the sensor body 2 is easy, the MEMS piezoelectric sensor 1A having a simple structure, high sensitivity, and advantageous for multi-axis can be provided.

In addition, since the sensor body 2 can be supported with the outer surface 21a of the bottom 21 of the sensor body 2 facing the support substrate 31, the support structure 3 can be simplified, and the structure is highly sensitive and advantageous for multi-axis use. 1A can be provided.
Circuit wirings Wc, Wd, Ws are formed on the surface 31a of the support substrate 31, and the circuit wirings Wc, Wd, Ws and the electrodes 5, Ed, Es are connected by wireless bonding. Thereby, it is possible to provide the MEMS piezoelectric sensor 1A having high sensitivity and advantageous for multi-axis while simplifying the connection structure. In addition, since the structure for electrical connection can be used as a part of the support structure 3 of the sensor body 2, the entire structure can be simplified.

FIG. 18 is an illustrative cross-sectional view for explaining the configuration of a MEMS piezoelectric sensor 1B according to still another embodiment of the present invention. In FIG. 18, corresponding parts of the respective parts shown in the above-described embodiments are denoted by the same reference numerals.
In this embodiment, a columnar portion 95 is coupled to the outer surface 21 a of the bottom portion 21 of the sensor body 2. The columnar portion 95 extends from the outer surface 21 a of the bottom portion 21 along the central axis 20 of the sensor body 2 in a direction away from the bottom portion 21. The tip of the columnar part 95 is supported on the surface 31 a of the support substrate 31. The columnar part 95 can be produced by processing the silicon layer 13 of the SOI substrate 10, for example.

  In this embodiment, the cup-shaped sensor body 2 is supported on the support substrate 31 with the bottom 21 facing the support substrate 31 and the opening edge 23 facing away from the support substrate 31. The support substrate 31 has a flat surface 31a on which wirings Wc, Wd, and Ws are formed. A bump 90 is disposed at one end of the wirings Wc, Wd, and Ws. A lower electrode 5 is formed on an outer surface 21 a facing the support substrate 31 at the bottom 21 of the sensor body 2, a piezoelectric film 6 is laminated on the lower electrode 5, and further on the piezoelectric film 6. The excitation electrode Ed and the detection electrode Es are stacked.

  One end portion (for example, the end portion on the inner side) of the electrodes Es and Ed has a lead portion 96 that is led out along the side surface of the columnar portion 95 and reaches the tip end surface 95 a of the columnar portion 95. A bump 91 is disposed on the leading end surface 95 a of the columnar portion 95 on the lead portion 96. The bumps 91 are joined to the bumps 90 on the wirings Wd and Ws side. On the other hand, one end portion (for example, the inner end portion) of the lower electrode 5 has a lead portion 97 that is drawn along the side surface of the columnar portion 95 and reaches the tip end surface 95 a of the columnar portion 95. A bump 92 is provided on the leading portion 97 of the columnar portion 95 on the lead portion 97. The bump 92 is bonded to the bump 90 provided on the wiring Wc on the support substrate 31.

Thus, in this embodiment, the sensor body 2 is supported by the support substrate 31 in the coupling region 18 in the vicinity of the central axis 20 through the columnar portion 95 provided outside the sensor body 2. That is, even with this configuration, the sensor body 2 can be supported on the central axis 20 by the support structure 3 provided outside the sensor body 2.
In this embodiment, the support structure 3 includes a support substrate 31, a columnar portion 95, and bumps 90 to 92. By providing the columnar portion 95, the support substrate 31 and the sensor body 2 can be reliably separated.

  19A and 19B are perspective views for explaining the configuration of MEMS piezoelectric sensors 1C and 1D according to still another embodiment of the present invention. In this embodiment, a pair of linear beam portions 101 arranged in a cross shape is formed on the support substrate 31, and the support portion 14 is arranged at the intersection of the pair of beam portions 101. A columnar part 25 formed integrally with the sensor body 2 is bonded onto the support part 14. The beam portion 101 extends linearly across the inside and outside of the sensor body 2 in plan view. Since the beam portion 101 has a cross shape and the support portion 14 is disposed at the intersection, the sensor body 2 is arranged on the support portion 14 and assembled by referring to the beam portion 101 when the sensor body 2 is assembled. The body 2 can be easily and accurately aligned. Thereby, the assembling property of the sensor body 2 is improved and accurate assembling becomes possible.

The beam portion 101 is formed in a dug portion 15 that is a recess dug from the surface 31 a of the support substrate 31.
19A, the height of the beam portion 101 from the bottom surface 15a of the digging portion 15 is lower than the surface 31a of the support substrate 31, and the height of the support portion 14 from the bottom surface 15a is the surface of the support substrate 31. It is the same as 31a. And the lower end of the columnar part 25 of the sensor body 2 and the opening edge 23 are located in the same plane. Accordingly, a gap corresponding to the height difference between the beam portion 101 and the support portion 14 is secured between the opening edge 23 and the beam portion 101.

  On the other hand, in the configuration of FIG. 19B, the height of the beam portion 101 from the bottom surface 15a of the digging portion 15 is the same as the surface 31a of the support substrate, and the height of the support portion 14 is also the same as the surface 31a. The opening edge 23 extends to the lower side (in the direction approaching the support substrate 31) than the lower end of the columnar part 25 of the sensor body 2. On the opening edge 23, notches 24, which are recesses for inserting the beam portion 101, are arranged at locations corresponding to the beam portion 101 (four locations in this embodiment). The beam portion 101 extends through the cutout portion 24 and straddles the inner side and the outer side of the sensor body 2. The notch 24 secures a gap that avoids contact between the sensor body 2 and the beam 101.

The beam portion 101 does not need to cross in a cross shape. If at least two beam portions 101 that cross each other are provided on the surface of the support substrate 31, the beam body 101 serves as a mark when the sensor body 2 is aligned. Can be used.
Thus, in this configuration, a plurality of beam portions 101 extending in different directions (other than 180 degrees) from the support portion 14 provided on the surface 31a of the support substrate 31 are provided. The sensor body 2 extends over the inner side and the outer side. Therefore, at the time of assembly, the sensor body 2 can be aligned with the support portion 14 with the plurality of beam portions 101 as marks.

  In the configuration of FIG. 19B, the opening edge 23 of the sensor body 2 is formed with notches 24 at positions corresponding to the plurality of beams 101, so that contact with the beams 101 is notched 24. Can be avoided. Therefore, the opening edge 23 of the sensor body 2 can be disposed at a position closer to the surface 31 a of the support substrate 31 than the surface of the beam portion 101. Thereby, since the sensor body 2 can be enlarged, detection with higher sensitivity becomes possible.

FIG. 20 is a schematic cross-sectional view for explaining the configuration of a MEMS piezoelectric sensor 1E according to still another embodiment of the present invention. In FIG. 20, the corresponding parts of the respective parts shown in the above-described embodiment are denoted by the same reference numerals.
In this embodiment, piezoelectric elements Pd and Ps are formed on the body portion 22 of the sensor body 2. Specifically, the lower electrode 5 is formed on the outer surface 22 a of the body 22 of the sensor body 2, and the piezoelectric film 6 is laminated on the lower electrode 5, and the excitation electrode is formed on the piezoelectric film 6. Ed and the detection electrode Es are provided. Thereby, the excitation piezoelectric element Pd is formed at the position of the excitation electrode Ed, and the detection piezoelectric element Ps is formed at the position of the detection electrode Es.

  For example, a total of eight excitation electrodes Ed and detection electrodes Es are arranged at eight-fold symmetrical positions around the central axis 20. Specifically, the four excitation electrodes Ed are arranged at a four-fold symmetrical position around the central axis 20. Further, the four detection electrodes Es are arranged at a four-fold symmetrical position around the central axis 20. The excitation electrodes Ed and the detection electrodes Es are alternately arranged along the circumferential direction at eight-fold symmetrical positions around the central axis 20. The excitation electrode Ed and the detection electrode Es are connected to the wirings Wd and Ws on the support substrate 31 by, for example, bonding wires Bd and Bs.

A part of the lower electrode 5 is exposed from the piezoelectric film 6. The exposed portion and the wiring Wc on the support substrate 31 are connected by a bonding wire Bc.
A piezoelectric element can be formed on both the bottom 21 and the body 22 of the sensor body 2.
21A to 21C show modified examples related to the shape of the sensor body 2. In these drawings, the corresponding parts of the above-described embodiments are denoted by the same reference numerals.

In the example of FIG. 21A, the body 22 of the sensor body 2 is inclined with respect to the central axis 20 and is configured in a truncated cone shape (cone shape). More specifically, it has a truncated cone shape (cone shape) that extends from the bottom 21 toward the opening edge 23. The electrodes Ed and Es may be disposed on the bottom portion 21 and may be disposed on the trunk portion 22.
In the example of FIG. 21B, the body portion 22 of the sensor body 2 includes a first portion 221 that is inclined with respect to the central axis 20 at a first inclination angle, and a second portion 222 that is inclined at a second inclination angle. . The first portion 221 has a truncated cone shape (cone shape) that is coupled to the bottom portion 21 and has a side surface that is inclined outwardly away from the central axis 20 as the distance from the bottom portion 21 increases. The second portion 222 has a frustoconical cylinder shape having an outer edge continuous with the outer edge of the first portion 221, and a side surface extending inwardly from the outer edge toward the central axis 20. (Cone shape). In other words, the first portion 221 has a shape that expands outward as it moves away from the bottom portion 21, and the second portion 222 has a shape that narrows inward as it moves away from the bottom portion 21, and their outer edges are joined together. The electrodes Ed and Es may be disposed on the bottom portion 21 and may be disposed on the trunk portion 22 (for example, the first portion 221).

In the example of FIG. 21C, the body portion 22 has a cylindrical shape, and an annular flange portion 223 extending inward along a plane perpendicular to the central axis 20 is coupled to the edge portion on the opposite side to the bottom portion 21. ing. The electrodes Ed and Es may be disposed on the bottom portion 21 and may be disposed on the trunk portion 22.
FIG. 22 shows a modification regarding the shape of the sensor body 2. In this example, the sensor body 2 is formed in a wine glass shape. More specifically, the sensor body 2 is a rotating body around the central axis 20, and along the cut surface including the central axis 20, the bottom portion 21 and the body portion 22 are along a continuous curved line without being separated. For example, the curved line that the bottom 21 and the body 22 follow in the cut surface may be a partial ellipse (specifically, a semi-ellipse). In the example of FIG. 22, a columnar portion 95 is provided integrally with the sensor body 2 along the central axis 20 of the bottom portion 21. In this example, the columnar part 95 is disposed outside the sensor body 2, but a similar columnar part 95 may be provided inside the sensor body 2. In addition, the sensor body 2 can be supported on the support substrate 31 by the support structure 3 similar to that shown in FIG. The electrodes Ed and Es may be disposed on the bottom portion 21 and may be disposed on the trunk portion 22.

  FIG. 23 shows a configuration example in which the piezoelectric elements Pd and Ps are arranged inside the wineglass-type sensor body 2. A lower electrode 5 is formed on the inner surface of the sensor body 2, and a piezoelectric film 6 is laminated on the lower electrode 5. An excitation electrode Ed and a detection electrode Es are disposed on the surface of the piezoelectric film 6. By disposing the piezoelectric elements Pd and Ps inside the sensor body 2, electrical connection with the support substrate 31 can be performed inside the sensor body 2. As a result, the MEMS piezoelectric sensor can be reduced in size.

As mentioned above, although embodiment of this invention has been described, this invention can also be implemented with another form so that it may enumerate next.
(1) The sensor body is not necessarily a rotating body. For example, the sensor body may be constituted by a polygonal cylindrical body, a polygonal frustum cylindrical body, or the like.
(2) The arrangement of the piezoelectric elements inside the sensor body is not limited to the sensor body having the shape shown in FIG. 23, and the piezoelectric elements can be arranged inside the sensor body in other forms.

  (3) There may be at least two upper electrodes (excitation electrodes and detection electrodes) facing the lower electrode with the piezoelectric film interposed therebetween. The at least two upper electrodes preferably include at least one excitation electrode and at least one detection electrode. The number of excitation electrodes and detection electrodes need not be the same. Therefore, the total number of upper electrodes may be odd or even. For example, one excitation electrode and two detection electrodes may be provided, and a total of three upper electrodes may be provided. Further, the plurality of upper electrodes preferably have at least a pair of excitation electrodes and at least a pair of detection electrodes. In this case, at least four upper electrodes are provided.

(4) The excitation electrode and the detection electrode are not necessarily arranged at equivalent positions on the sensor body. For example, the excitation electrode may be disposed at the bottom of the sensor body, and the detection electrode may be disposed at the body of the sensor body, or vice versa.
(5) The coupling region between the sensor body and the support structure is a circular region in which the columnar portion 25 and the bottom portion 21 are coupled in the embodiment of FIG. 1 and the like, and the columnar portion 25 is coupled to the bottom portion 21 in the entire region. ing. On the other hand, in the embodiment shown in FIGS. 17 and 18, the sensor body 2 and the support structure 3 are coupled to each other at the position of the plurality of bumps 90 in the region including the bumps 90 and the like. Since the plurality of bumps 90 are disposed so as to surround the central axis 20, it can be said that the sensor body 2 is substantially coupled to the support structure 3 on the central axis 20. Similar coupling can be achieved when the coupling portion has an arc shape or an annular shape.

  (6) The piezoelectric film 6 may be disposed on only one of the bottom portion 21 and the body portion 22 of the sensor body 2 or may be disposed on both. In addition, the piezoelectric film 6 may be disposed on either the inner surface or the outer surface of the bottom 21 of the sensor body 2, or the piezoelectric film 6 may be disposed on both of them. Similarly, the piezoelectric film 6 may be disposed on either the inner surface or the outer surface of the body portion 22 of the sensor body 2, or the piezoelectric film 6 may be disposed on both of them. Since the entire cup-shaped sensor body 2 vibrates and deforms, the piezoelectric film 6 may be disposed on either the bottom portion 21 or the body portion 22 and an electrode may be disposed in accordance with the arrangement of the piezoelectric film. .

  (6) When the electrodes Ed and Es are arranged at 2n times symmetrical positions around the central axis 20, at least one of the positions may be vacant without arranging the electrodes at all positions. For example, you may arrange | position an electrode only in six places of the 8 times symmetrical positions. Specifically, the excitation electrodes Ed may be arranged at two positions among the eight-fold positions, and the detection electrodes Es may be arranged at four positions among the positions. However, detection with higher sensitivity is possible when the electrodes Ed and Es are arranged at all positions.

(7) The number of excitation electrodes Ed and detection electrodes Es may not be the same. For example, the excitation electrodes Ed may be disposed at two positions out of the six-fold positions around the central axis 20, and the detection electrodes Es may be disposed at four positions, respectively.
In addition, various design changes can be made within the scope of matters described in the claims.

1, 1A, 1B, 1C, 1D, 1E MEMS piezoelectric sensor 2 Sensor body 3 Support structure 5 Lower electrode 6 Piezoelectric film 8 Lower electrode connection portion 9 Bonding pad (upper electrode connection portion)
DESCRIPTION OF SYMBOLS 10 SOI substrate 11 Silicon substrate 12 Insulating film 13 Silicon layer 14 Support part 15 Recessed part (recess)
16 Gap 17 Adhesive 18 Bonding area 20 Center axis 21 Bottom 22 Body 23 Opening edge 24 Notch (recess)
25 Columnar part 28 Ball of bonding wire 31 Support substrate 51 Drive circuit 52 Detection circuit 90-92 Bump 95 Columnar part 101 Beam part 221 1st part 222 2nd part 223 Flange part Ed, Ed1-Ed4 Excitation electrode Es, Es1-Es4 Detection electrodes Pd1-Pd4 Piezoelectric elements for excitation Ps1-Ps4 Piezoelectric elements for detection Wd, Wd1-Wd4 Excitation wiring Ws, Ws1-Ws4 Detection wiring Wc Common wiring Bd, Bd1-Bd4 Bonding wire Bs, Bs1-Bs4 Bonding wire Bc Bonding wire SW Standing wave OS vibration AN Steady vibration antinode N Steady vibration node ω Angular velocity

Claims (29)

A cup-shaped sensor body having a central axis;
A support structure coupled to the sensor body at a predetermined coupling region including the central axis and supporting the sensor body;
A piezoelectric film formed on the surface of the sensor body;
A MEMS piezoelectric sensor, comprising: a plurality of electrodes arranged radially about the central axis of the cup shape and bonded to the surface of the piezoelectric film.   The MEMS piezoelectric sensor according to claim 1, wherein the plurality of electrodes include at least one excitation electrode and at least one detection electrode.   The MEMS piezoelectric sensor according to claim 1, wherein the plurality of electrodes include at least a pair of excitation electrodes and at least a pair of detection electrodes.   4. The MEMS piezoelectric sensor according to claim 1, wherein the plurality of electrodes are provided at positions 2n times symmetrical (where n is a natural number) around the central axis. 5.   2. The MEMS piezoelectric sensor according to claim 1, wherein 2n electrodes (where n is a natural number) are provided at positions 2n times symmetrical about the central axis.   The MEMS piezoelectric sensor according to claim 5, wherein the 2n electrodes include n excitation electrodes and n detection electrodes that are alternately arranged around the central axis. The plurality of electrodes are
A pair of excitation electrodes arranged symmetrically with respect to the cup-shaped central axis and bonded to the surface of the piezoelectric film;
The MEMS piezoelectric sensor according to claim 1, further comprising a pair of detection electrodes arranged symmetrically with respect to the cup-shaped central axis and joined to a surface of the piezoelectric film.   The piezoelectric film is driven by the excitation electrode, whereby stationary vibration is generated in the sensor body, the excitation electrode is disposed at an antinode of the stationary vibration, and the detection electrode is disposed at a node of the stationary wave. Item 8. The MEMS piezoelectric sensor according to Item 2, 3, 6, or 7.   The MEMS piezoelectric sensor according to claim 2, 3, 6, 7, or 8, wherein the vibration generated in the sensor body by driving the piezoelectric film by the excitation electrode is a wine glass mode.   The MEMS piezoelectric sensor according to claim 1, wherein the sensor body includes a bottom portion and a trunk portion, and the support structure is coupled to the sensor body at the bottom portion.   The MEMS piezoelectric sensor according to claim 10, wherein the support structure includes a columnar portion coupled to the bottom portion and extending along the central axis. The columnar part is coupled to the bottom of the sensor body inside the cup shape;
The MEMS piezoelectric sensor according to claim 11, wherein the support structure includes a support substrate coupled to the columnar portion on an opening edge side of the sensor body.   The MEMS piezoelectric sensor according to claim 12, wherein a surface of the support substrate and the opening edge are separated from each other. A support part is provided at a position corresponding to the columnar part on the surface of the support substrate,
The MEMS piezoelectric sensor according to claim 13, wherein a recess is formed deeper than the support portion at a position facing the opening edge of the sensor body on the surface of the support substrate. A support part is provided at a position corresponding to the columnar part on the surface of the support substrate,
A plurality of beam portions respectively extending across the inside and the outside of the sensor body along different directions intersecting in the support portion;
The MEMS piezoelectric sensor according to claim 13, wherein a concave portion is formed at an opening edge of the sensor body at a position corresponding to the plurality of beam portions.   The MEMS piezoelectric sensor according to any one of claims 12 to 15, wherein the columnar portion and the support substrate are connected by direct bonding of resin, metal, or silicon. Circuit wiring is formed on the surface of the support substrate,
The MEMS piezoelectric sensor according to claim 12, further comprising a bonding wire that connects the circuit wiring and the electrode.   12. A MEMS piezoelectric sensor according to claim 10 or 11, wherein the support structure is coupled to the bottom of the sensor body outside the cup shape.   The MEMS piezoelectric sensor according to claim 18, wherein the support structure includes a support substrate facing an outer surface of a bottom portion of the sensor body. Circuit wiring is formed on the surface of the support substrate,
The MEMS piezoelectric sensor according to claim 19, wherein the circuit wiring and the electrode are connected by wireless bonding. The sensor body includes a flat bottom and a cylindrical body coupled to the bottom;
The MEMS piezoelectric sensor as described in any one of Claims 1-20 by which the said piezoelectric material film is arrange | positioned at the said bottom part or the said trunk | drum.   The MEMS piezoelectric sensor according to any one of claims 1 to 21, wherein the piezoelectric film is disposed on an outer surface of the sensor body.   The MEMS piezoelectric sensor according to any one of claims 1 to 21, wherein the piezoelectric film is disposed on an inner surface of the sensor body.   The MEMS piezoelectric sensor according to any one of claims 1 to 23, wherein the sensor body is made of a material mainly composed of silicon.   The sensor body includes a cylindrical body having a diameter of 0.2 mm to 5 mm and a wall thickness of 1/20 or less of the diameter, and the length of the cylindrical shape in the central axis direction is 100 μm to 1 mm. The MEMS piezoelectric sensor according to any one of claims 1 to 24. The sensor body includes a bottom portion coupled to the trunk portion,
The MEMS piezoelectric sensor according to claim 25, wherein the support structure includes a columnar part coupled to the bottom part and having a circular cross section having a diameter of 1/20 or more and 1/2 or less of a cylindrical diameter of the body part. .   The MEMS piezoelectric sensor according to any one of claims 1 to 26, wherein a film thickness of the piezoelectric film is not less than 0.2 µm and not more than 5 µm.   The piezoelectric film has an oxide having a perovskite structure mainly composed of Pb, Zr and Ti, an oxide having a perovskite structure mainly composed of Pb, Mg, Nb and Ti, and mainly composed of K, Na and Nb. The MEMS piezoelectric sensor according to any one of claims 1 to 27, comprising an oxide having a perovskite structure or an oxide having a perovskite structure mainly composed of Ba, Ca, and Ti.   The MEMS piezoelectric sensor according to any one of claims 1 to 28, wherein the piezoelectric film is a piezoelectric material film formed by a sol-gel method or a sputtering method.

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