WO2012153549A1

WO2012153549A1 - Piezoelectric sensor device

Info

Publication number: WO2012153549A1
Application number: PCT/JP2012/052229
Authority: WO
Inventors: 陽平館; 谷本　亮介
Original assignee: 株式会社村田製作所
Priority date: 2011-05-12
Filing date: 2012-02-01
Publication date: 2012-11-15

Abstract

Disclosed is a piezoelectric sensor device with which reduction in device size can be achieved and in which costs can be reduced without requiring precise fixing of the piezoelectric detection element and without needing to provide a space on the opposite side to the detection face. One side face of a piezoelectric detection element (2) of the enclosed energy type is designated as the detection face and a holding member (7) is laminated, with interposition of a joining layer (6), on the face on the opposite side to this detection face. If the acoustic impedance value of the piezoelectric detection element (2) is identified as the first acoustic impedance value Z1, the acoustic impedance value of the joining layer (6) is identified as the second acoustic impedance value Z2, and the acoustic impedance value of the holding member (7) is identified as the third acoustic impedance value Z3, then, for this piezoelectric sensor device (1), it is specified that: Z1 > Z2 < Z3.

Description

Piezoelectric sensor device

The present invention relates to a piezoelectric sensor device used for detection of biochemical substances, inorganic or organic materials, and more particularly, to detect using a change in resonance characteristics due to mass load of a detection substance on a detection surface. The present invention relates to a piezoelectric sensor device that detects a substance.

Conventionally, various sensors using a crystal resonator have been developed. For example, Patent Document 1 below discloses a QCM (Quartz Crystal Microbalance) sensor shown in FIGS. 5 (a) and 5 (b). In the QCM sensor 1001, a crystal resonator 1002 is used. The crystal unit 1002 has a structure in which electrodes are formed on the upper surface and the lower surface of a crystal substrate. When a substance to be detected adheres to the crystal unit 1002, the resonance characteristics of the crystal unit 1002 change. A substance to be detected is detected using the change in the resonance characteristics.

Since the crystal unit 1002 is used, a package structure that does not hinder the vibration of the crystal unit 1002 is necessary. Therefore, the QCM sensor 1001 uses a substantially cylindrical package member 1003. The package member 1003 has a substantially cylindrical shape and has a bottom surface closed. The crystal unit 1002 is fixed in a substantially cylindrical package member 1003 with an adhesive 1004. In this structure, the upper side of the crystal unit 1002 is opened toward the upper end opening of the package member 1003. Accordingly, the substance to be detected can adhere to the upper surface of the crystal unit 1002. On the other hand, a sealed space B is formed below the crystal unit 1002 so as not to disturb vibration.

JP 2008-32617 A

In the QCM sensor 1001, the closed space B had to be formed on the surface opposite to the detection surface of the crystal unit 1002. For this reason, the miniaturization could not be promoted. In addition, the space B must be sealed. Otherwise, the detected substance may enter the space B and the detected substance may not be detected accurately.

Furthermore, the crystal unit 1002 must be accurately fixed to the inner peripheral surface of the package member 1003. That is, if the crystal unit 1002 is not fixed at an accurate position, the detection accuracy decreases. The crystal unit 1002 is fixed to the package member 1003 with an adhesive 1004. However, it is difficult to fix the crystal unit 1002 in an accurate position with the adhesive 1004. Therefore, there is a problem that it takes a cost to manage the fixing accuracy of the crystal unit 1002.

An object of the present invention is to provide a piezoelectric sensor device that can be easily and inexpensively manufactured and can be downsized without requiring a complicated operation for managing accuracy when fixing a piezoelectric detection element. It is to provide.

The piezoelectric sensor device according to the present invention includes a piezoelectric detection element, a bonding layer, and a holding member. The piezoelectric detection element has an open detection surface, and is configured to detect a detection target substance based on a mass change when the detection target substance adheres to the detection surface, and has a first acoustic impedance value Z1. . The bonding layer is laminated on a surface opposite to the detection surface of the piezoelectric detection element, and is made of a material having a second acoustic impedance value Z2 smaller than the first acoustic impedance value Z1. The holding member is bonded to the surface of the bonding layer opposite to the piezoelectric detection element, and is made of a material having a third acoustic impedance value Z3 larger than the second acoustic impedance value Z2.

In a specific aspect of the piezoelectric sensor device of the present invention, a plurality of piezoelectric sensor devices are provided, and the resonance frequencies of the piezoelectric detection elements of the plurality of piezoelectric sensor devices are equalized. In the present invention, the vibration of the piezoelectric detection element is unlikely to leak to other members such as a mounting substrate via the holding member. Therefore, interference between the piezoelectric detection elements of the plurality of piezoelectric sensor devices can be suppressed. Therefore, by mounting a plurality of piezoelectric sensor devices configured using piezoelectric detection elements having the same resonance frequency on, for example, one mounting substrate, a piezoelectric sensor device having a plurality of detection portions can be provided.

In this case, preferably, one of the plurality of piezoelectric sensor devices is a reference piezoelectric sensor device, and the other piezoelectric sensor device is a detection piezoelectric sensor device. In this case, the substance to be detected can be detected with higher accuracy by using the output of the reference piezoelectric sensor device and the output of the detection piezoelectric sensor device.

Further, in another specific aspect of the present invention, a mounting board on which the plurality of piezoelectric sensor devices are mounted is further provided. In this case, the plurality of piezoelectric sensor devices can be mounted on one mounting substrate, and a piezoelectric sensor device having a plurality of detection portions can be configured as a single component.

In another specific aspect of the piezoelectric sensor device according to the present invention, the piezoelectric detection element includes a plurality of electrodes provided to face the piezoelectric substrate via a part or all of the piezoelectric substrate. In this case, a piezoelectric detection element used in the piezoelectric sensor device of the present invention can be configured in the same manner as a known piezoelectric vibrator.

The piezoelectric sensor device according to the present invention can be used for detecting various substances to be detected. However, in yet another specific aspect of the present invention, a biosensor apparatus using a biochemical substance as a substance to be detected is configured. . In that case, according to the present invention, a biochemical substance can be detected with high accuracy, and a small and inexpensive biosensor device can be provided.

In the piezoelectric sensor device according to the present invention, since the acoustic impedance values of the piezoelectric detection element, the bonding layer, and the piezoelectric sensor device are set as described above, vibration of the piezoelectric detection element is hardly hindered by the bonding layer and the holding member. Therefore, the holding member can be bonded via the bonding layer without providing a space on the surface opposite to the detection surface of the piezoelectric detection element.

Therefore, downsizing can be achieved without lowering the detection accuracy of the piezoelectric sensor device. In addition, when the piezoelectric detection element is bonded to the holding member via the bonding layer, highly accurate positioning is not required. Therefore, it is possible to greatly reduce the process and cost necessary for increasing the fixing accuracy of the piezoelectric detection element.

FIG. 1A is a perspective view of a piezoelectric sensor device according to a first embodiment of the present invention, and FIG. 1B is a perspective view showing a piezoelectric detection element used in the piezoelectric sensor device. FIG. 2 is a partially cutaway front sectional view showing a piezoelectric sensor device according to a second embodiment of the present invention. FIGS. 3A and 3B are a plan view for explaining another example of the piezoelectric detection element used in the present invention and a schematic plan view showing the electrode shape on the lower surface through the piezoelectric substrate. . FIG. 4 is a perspective view showing still another example of the piezoelectric detection element used in the piezoelectric sensor device of the present invention. 5 (a) and 5 (b) are a plan view showing a conventional QCM sensor and a cross-sectional view showing a portion along line AA in FIG. 5 (a).

Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

FIG. 1A is a perspective view showing a piezoelectric sensor device according to a first embodiment of the present invention. The piezoelectric sensor device 1 of the present embodiment is a biosensor device that detects biochemical substances such as proteins. However, the piezoelectric sensor device 1 can also be used for measuring a substance to be detected other than a biochemical substance, for example, a chemical substance such as a gas.

The piezoelectric sensor device 1 has a piezoelectric detection element 2. As shown in FIG. 1B, the piezoelectric detection element 2 includes a piezoelectric substrate 3, a first electrode 4 formed on the upper surface of the piezoelectric substrate 3, and a second electrode formed on the lower surface of the piezoelectric substrate 3. And 5.

The piezoelectric substrate 3 is made of a piezoelectric ceramic such as a lead zirconate titanate ceramic. However, the piezoelectric substrate 3 may be formed of a piezoelectric single crystal such as quartz.

In the present embodiment, the piezoelectric substrate 3 is made of piezoelectric ceramics and is polarized in the direction indicated by the arrow P shown in the drawing. The piezoelectric substrate 3 has a strip shape with a rectangular planar shape. The polarization direction P is a direction connecting the first end face 3a and the second end face 3b.

The first electrode 4 extends from the central region toward the second end surface 3b side on the upper surface of the piezoelectric substrate 3, and reaches the edge formed by the upper surface and the second end surface 3b. The second electrode 5 is formed so as to extend from the central region of the lower surface of the piezoelectric substrate 3 to the edge formed by the first end surface 3a and the lower surface. In the central region of the piezoelectric substrate 3, the first electrode 4 and the second electrode 5 are overlapped via the piezoelectric substrate 3. This overlapping portion constitutes a piezoelectric vibration part.

Since the polarization direction P of the piezoelectric substrate 3 is the above direction, when an AC electric field is applied between the first and

second electrodes

4 and 5, the thickness shear vibration mode is excited and confined in the vibration part. That is, the piezoelectric detection element 2 is a piezoelectric element using an energy confinement type thickness-shear vibration mode.

The first and

second electrodes

4 and 5 can be formed of an appropriate metal such as Ag, Au, Cu, Al, or an alloy thereof.

The piezoelectric detection element 2 is made of piezoelectric ceramics, and its acoustic impedance value is defined as a first acoustic impedance value Z1.

In the piezoelectric sensor device 1 shown in FIG. 1A, the upper surface of the piezoelectric detection element 2 is a detection surface. A bonding layer 6 is laminated on the surface of the piezoelectric detection element 2 opposite to the detection surface, that is, the lower surface. In the present embodiment, the bonding layer 6 is made of an insulating adhesive. As such an adhesive, an appropriate adhesive such as an epoxy resin adhesive or a silicone resin adhesive can be used. However, the bonding layer 6 may be an insulating bonding material other than the adhesive as long as it performs the bonding function.

The holding member 7 is laminated on the lower surface of the bonding layer 6. The holding member 7 has a rectangular plate shape. In the present embodiment, the holding member 7 has the same planar shape as the piezoelectric substrate 3. The holding member 7 constitutes a surface on the side where the piezoelectric sensor device 1 is mounted on the mounting substrate. That is, the holding member 7 is bonded via the bonding layer 6 in order to open the detection surface of the piezoelectric detection element 2 so that the substance to be detected can adhere and to seal the opposite surface. As a material constituting the holding member 7, an appropriate material such as an insulating ceramic such as alumina or a synthetic resin such as an epoxy resin can be used. In the present embodiment, the holding member 7 is made of an insulating ceramic.

The acoustic impedance value of the bonding layer 6 is a second acoustic impedance value Z2, and the acoustic impedance value of the holding member 7 is a third acoustic impedance value Z3.

In the piezoelectric detection element 2, a first terminal electrode 8 is formed on the first end face of the laminate composed of the bonding layer 6 and the holding member 7. A second terminal electrode 9 is formed on the opposite end surface facing the first end surface. The first terminal electrode 8 is formed so as to extend from the first end face to the lower face of the laminate. The second terminal electrode 9 is formed so as to reach the upper surface and the lower surface from the second end surface of the laminate. The portion of the second terminal electrode 9 reaching the upper surface of the laminate is in surface contact with the first electrode 4.

The portions of the first terminal electrode 8 and the second terminal electrode 9 reaching the lower surface of the laminate are provided in contact with electrode lands and the like on the mounting substrate described later in surface contact.

In the piezoelectric sensor device 1, when a substance to be detected adheres to the detection surface, that is, the upper surface of the piezoelectric detection element 2, the resonance characteristics of the piezoelectric detection element 2 change. Thereby, the presence or absence of the substance to be detected and the amount of the substance to be detected can be detected.

Conventionally, in a piezoelectric sensor device using a piezoelectric detection element, it has been necessary to provide a space for preventing the vibration of the piezoelectric detection element. That is, the space B shown in FIG. 5 must be formed on the surface opposite to the open detection surface. On the other hand, in the piezoelectric sensor device 1, it is not necessary to form such a space B. That is, as is clear from FIG. 1A, the entire lower surface of the piezoelectric detection element 2 is bonded to the holding member 7 via the bonding layer 6. Therefore, there is no space on the surface opposite to the detection surface of the piezoelectric detection element 2. Therefore, the piezoelectric sensor device 1 can be reduced in size.

In addition, since the piezoelectric sensor device 1 only needs to be laminated and bonded to the holding member 7 via the bonding layer 6, the piezoelectric sensor device 1 can simplify the assembly process. In the conventional QCM sensor 1001, since the space B must be formed, the package structure is complicated, and the accuracy of the fixing position of the crystal unit 1002 must be increased. On the other hand, in the piezoelectric sensor device 1 according to the present embodiment, since it is not necessary to provide a space, it is possible not only to simplify the package structure but also to increase the fixing accuracy of the piezoelectric detection element 2.

Further, in the piezoelectric sensor device 1 of the present embodiment, even if the space is omitted, the resonance characteristics of the piezoelectric detection element 2 are hardly deteriorated. This is because the first acoustic impedance value Z1 to the third acoustic impedance value Z3 have a relationship of Z1> Z2 <Z3. That is, since the first to third acoustic impedance values Z1 to Z3 satisfy such a relationship, the vibration leaked from the piezoelectric detection element 2 to the bonding layer 6 is an interface between the bonding layer 6 and the holding member 7. Reflected by. Therefore, even if the structure does not provide a space, the resonance characteristics of the piezoelectric detection element 2 are unlikely to deteriorate. Therefore, it is possible to measure the presence / absence of the substance to be detected and the amount of the substance to be detected with high accuracy by using the change in resonance characteristics due to the mass load action of the substance to be detected attached to the detection surface.

FIG. 2 is a partially cutaway front sectional view showing a piezoelectric sensor device 16 according to a second embodiment of the present invention. In the second embodiment, a plurality of

piezoelectric sensor devices

1, 1 </ b> A are mounted on the mounting substrate 11. The

piezoelectric sensor devices

1 and 1A are configured in the same manner as the piezoelectric sensor device 1 of the first embodiment.

The mounting substrate 11 is made of an insulating material such as alumina. Electrode lands 12 to 15 are formed on the mounting substrate 11. The first and second

terminal electrodes

8 and 9 of the piezoelectric sensor device 1 are in contact with the electrode lands 12 and 13, respectively. In this way, the piezoelectric sensor device 1 is mounted on the portion where the electrode lands 12 and 13 are formed using a conductive bonding material (not shown) made of solder, conductive adhesive or the like. Similarly, the piezoelectric sensor device 1 </ b> A is mounted on the mounting substrate 11 in a portion where the electrode lands 14 and 15 are provided.

Since the

piezoelectric sensor devices

1 and 1A have the above-described structure, the vibration of the piezoelectric detection element 2 hardly leaks to the holding member 7 side. Therefore, even when the plurality of

piezoelectric sensor devices

1 and 1A are fixed and mounted on the same mounting substrate 11, that is, a single mounting substrate 11, interference between the

piezoelectric sensor devices

1 and 1A hardly occurs.

Therefore, as the piezoelectric sensor device 1 and the piezoelectric sensor device 1A, exactly the same piezoelectric sensor device having the same resonance frequency of the piezoelectric detection element 2 can be used. Thereby, the assembly process of the piezoelectric sensor device 16 according to the second embodiment having the plurality of

piezoelectric sensor devices

1 and 1A can be simplified and the cost can be reduced.

Any of the plurality of

piezoelectric sensor devices

1 and 1A may be used as a detection piezoelectric sensor device. Preferably, one piezoelectric sensor device 1 is used as a reference piezoelectric sensor device, and the other piezoelectric sensor device 1A is used. It is desirable to use a piezoelectric sensor device for detection. Accordingly, the substance to be detected can be measured with higher accuracy based on the output difference between the reference piezoelectric sensor device and the detection piezoelectric sensor device.

Further, when mounting a plurality of piezoelectric sensor devices on the mounting substrate 11, the number of piezoelectric sensor devices is not limited to the illustrated configuration, and three or more piezoelectric sensor devices may be mounted.

In the second embodiment shown in FIG. 2, the plurality of

piezoelectric sensor devices

1 and 1A are mounted on the mounting substrate 11, but only one piezoelectric sensor device 1 is mounted on the mounting substrate. Also good.

Furthermore, in the second embodiment, the resonance frequency of the piezoelectric detection element 2 of the piezoelectric sensor device 1 and the resonance frequency of the piezoelectric detection element 2 of the piezoelectric sensor device 1A are made equal, but they may be different. When the resonance frequencies are different, interference between the

piezoelectric sensor devices

1 and 1A can be more effectively suppressed.

FIGS. 3A and 3B are a plan view showing a modification of the piezoelectric detection element used in the present invention and a schematic plan view showing the electrode shape on the lower surface through the piezoelectric substrate.

3 (a) and 3 (b), the piezoelectric detection element 21 according to this modification has a rectangular plate-shaped piezoelectric substrate 22. The piezoelectric substrate 22 is made of piezoelectric ceramic and is polarized in the thickness direction. A first electrode 23 having a circular planar shape is formed at the center of the upper surface of the piezoelectric substrate 22. A second electrode 24 is formed on the lower surface so as to face the first electrode 23. A portion where the first electrode 23 and the second electrode 24 overlap each other constitutes an energy confinement type piezoelectric vibration portion using a thickness longitudinal vibration mode.

The first electrode 23 is electrically connected via a wiring electrode 25 to a connection electrode 26 provided along the edge formed by the upper surface and one end surface of the piezoelectric substrate 22. Similarly, the second electrode 24 is connected to the connection electrode 28 via the wiring electrode 27. The connection electrode 28 is formed so as to reach the edge formed by the lower surface of the piezoelectric substrate 22 and the other end surface.

As shown in FIG. 3, in the present invention, the piezoelectric detection element may be an energy confinement type piezoelectric element using a thickness longitudinal vibration mode.

FIG. 4 is a perspective view for explaining still another modified example of the piezoelectric detecting element used in the present invention. The piezoelectric detection element 31 of the present modification is an energy confinement type piezoelectric element using a second harmonic of thickness longitudinal vibration. The piezoelectric detection element 31 has a rectangular plate-shaped piezoelectric substrate 32. The piezoelectric substrate 32 is polarized in the thickness direction. A first electrode 33 is formed on the upper surface of the piezoelectric substrate 32, and a second electrode 34 is formed on the lower surface. The first electrode 33 and the second electrode 34 extend from the center of the upper surface and the lower surface of the piezoelectric substrate 32 toward the second end surface 32b.

Furthermore, an internal electrode 35 is formed at an intermediate height position of the piezoelectric substrate 32. The internal electrode 35 overlaps the first electrode 33 and the second electrode 34 with the piezoelectric substrate layer in the central region of the piezoelectric substrate 32. The internal electrode 35 extends from the central portion of the piezoelectric substrate 32 toward the first end face 32a and is drawn out to the first end face 32a.

In the piezoelectric detection element 31, an energy confinement type piezoelectric element using the second harmonic of the thickness longitudinal vibration mode is applied by applying an alternating electric field between the first and

second electrodes

33 and 34 and the internal electrode 35. Works as. In the present invention, an energy confinement type piezoelectric element using such a higher-order mode of the thickness longitudinal vibration mode may be used as the piezoelectric detection element.

As shown in FIGS. 3 and 4, in the present invention, various energy confinement type piezoelectric elements such as a piezoelectric element using a harmonic in the thickness longitudinal vibration mode and the thickness longitudinal vibration mode are not limited to the thickness sliding mode. Can be used as a piezoelectric detection element, and is not particularly limited.

DESCRIPTION OF

SYMBOLS

1,1A ... Piezoelectric sensor apparatus 2 ... Piezoelectric detection element 3 ... Piezoelectric substrate 3a ... 1st end surface 3b ... 2nd end surface 4 ... 1st electrode 5 ... 2nd electrode 6 ... Bonding layer 7 ... Holding member 8 ... 1st terminal electrode 9 ... 2nd terminal electrode 11 ... Mounting board 12-15 ... Electrode land 16 ... Piezoelectric sensor device 21 ... Piezoelectric detection element 22 ... Piezoelectric substrate 23 ... 1st electrode 24 ... 2nd electrode 25 ... Wiring electrode 26 ... Connection electrode 27 ... Wiring electrode 28 ... Connection electrode 31 ... Piezoelectric detection element 32 ... Piezoelectric substrate 32a ... First end face 32b ... Second end face 33 ... First electrode 34 ... Second electrode 35 ... Inside electrode

Claims

A piezoelectric detection element having an open detection surface, configured to detect the detection target material by a mass change when the detection target material adheres to the detection surface, and having a first acoustic impedance value Z1;
A bonding layer made of a material that is laminated on a surface opposite to the detection surface of the piezoelectric detection element and has a second acoustic impedance value Z2 smaller than the first acoustic impedance value Z1,
A piezoelectric sensor comprising: a holding member made of a material having a third acoustic impedance value Z3 larger than the second acoustic impedance value Z2, which is joined to a surface of the joining layer opposite to the piezoelectric detection element; apparatus.
A piezoelectric sensor device comprising a plurality of piezoelectric sensor devices according to claim 1, wherein the resonance frequencies of the piezoelectric detection elements of the plurality of piezoelectric sensor devices are equal.
3. The piezoelectric sensor device according to claim 2, wherein one of the plurality of piezoelectric sensor devices is a reference piezoelectric sensor device, and the other piezoelectric sensor device is a detection piezoelectric sensor device.
The piezoelectric sensor device according to claim 2 or 3, further comprising a mounting substrate on which the plurality of piezoelectric sensor devices are mounted.
The piezoelectric sensor device according to any one of claims 1 to 4, wherein the piezoelectric detection element includes a piezoelectric substrate and a plurality of electrodes provided so as to face each other through part or all of the piezoelectric substrate.
The piezoelectric sensor device according to any one of claims 1 to 5, which is a biosensor device using a biochemical substance as a substance to be detected.