JP2015014480A - Sensing device and piezoelectric sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress adhesion of a solution to an excitation electrode on the other surface side of a quartz oscillator upon sensing an object by supplying a sample solution to one surface side of the quartz oscillator, which is a piezoelectric oscillator.SOLUTION: The other surface side of a quartz oscillator 5 is supported by a wiring substrate 3, and in the wiring substrate 3, an opening part 31 is provided in an area corresponding to excitation electrodes 53A and 53B on the other surface side of the quartz oscillator 5. On an interior side of the opening part 31 as well as on an exterior side of the excitation electrodes 53A and 53B on the other surface side, an annular cover member 4 is provided that surrounds peripheries of the excitation electrodes 53A and 53B, and the annular cover member 4 is provided so that one end side of the cover member closely contacts with the other surface side of a quartz piece 51. Accordingly, even if a solution enters the other surface side of the quartz oscillator 5 from a gap between the quartz oscillator 5 and the wiring substrate 3, intrusion of the solution to an interior side of the cover body 4 is curbed by the cover body 4, and thus, adhesion of the solution to the excitation electrodes 53A and 53B on the other surface side of the quartz oscillator 5 is curbed.

Description

The present invention relates to a sensing device for sensing a sensing object contained in a sample liquid based on an oscillation frequency of a piezoelectric vibrator such as a crystal vibrator and a piezoelectric sensor used in the sensing device.

As a device for detecting a trace substance in a solution or gas, a sensing device using a QCM (Quarts Crystal Microbalance) using a crystal resonator is known. In this type of sensing device, a substance is adsorbed to a quartz crystal resonator by, for example, an antigen-antibody reaction, and a change in the natural frequency of the quartz crystal resonator according to a mass change at this time is used to perform qualitative analysis or quantification of a minute amount of material. Analyzing.

As this type of sensing device, as shown in Patent Document 1, a crystal unit is housed in a sensor unit, a flow path of a sample solution is formed on one side of the crystal unit, and the sample solution is placed in the flow channel. A configuration for detecting a sensing object while flowing is known. As shown in FIG. 6, the crystal resonator 10 is configured by providing excitation electrodes 11 and 12 on the front and back surfaces of the crystal piece 1, and the crystal sensor 14 is attached to the wiring board 13 by attaching the crystal resonator 10 to the wiring substrate 13. It is configured. When the entire periphery of the crystal unit 10 is bonded to the wiring substrate 13, there is a risk that the crystal unit 10 may be distorted. 13 is fixed.
The sensing device is configured to hold the quartz sensor 14 between the support 15 and the flow path forming member 16. In FIG. 6, reference numeral 17 denotes a sealing member. A through hole 18 larger than the excitation electrode 12 on the other surface side is formed in the wiring board 13 in order to secure a region where the crystal resonator 10 vibrates.

  In such a sensor unit, the sample liquid is supplied from one end side of the flow path forming member 16 and discharged from the other end side to the crystal resonator 10 surrounded by the flow path forming member 16 and the wiring substrate 13. The oscillation frequency is acquired while detecting the sensing object. As described above, since the quartz resonator 10 is bonded to the wiring substrate 13 at a plurality of peripheral portions thereof, there is a gap between the quartz resonator 10 and the wiring substrate 13, but the normal sensing is performed. In the inspection of the target object, there is no possibility that the sample liquid may enter the other surface side of the crystal resonator 10 from the gap between the crystal resonator 10 and the wiring substrate 13. However, when the crystal sensor 14 is removed from the sensor unit, or when the liquid remaining on the surface of the crystal unit 10 is blown off by a blower, the liquid enters from the gap between the crystal unit 10 and the wiring board 13. The liquid may adhere to the other surface side of the crystal unit 10.

  Quartz crystal oscillates regardless of whether the excitation electrode on one side (front side) is placed in the gas phase or the liquid phase, but the atmosphere on which the excitation electrode on the other side (back side) is placed is a gas phase. Otherwise, it has the property of not oscillating stably. For this reason, when a liquid adheres to the excitation electrode 12 on the other surface side of the crystal unit 10, the oscillation itself is inhibited or stable oscillation cannot be obtained. Therefore, when liquid adheres to the excitation electrode 12 on the other surface side, for example, air is sent from the opening 18 of the wiring board 13 by a blower to dry and remove the liquid on the other surface side.

  However, when the fundamental frequency is about 30 MHz, for example, the crystal piece 1 constituting the crystal unit 10 has a very thin thickness of 50 μm or less. For this reason, there exists a possibility that the accident that it may be damaged by the impact of the wind of an air blower may generate | occur | produce. Moreover, even if it is not damaged, depending on the nature of the liquid, there is a concern that after adhering to the excitation electrode on the back side, it evaporates and adheres to the excitation electrode 12 to inhibit vibration and stabilize oscillation.

Patent Document 2 proposes a technique in which a piezoelectric plate is fitted and fixed in a recess formed in a substrate so that an electrode provided on the back surface of the piezoelectric plate is covered with a space. A sealing material is provided between the peripheral portion of the piezoelectric plate and the concave portion, and this prevents the liquid from flowing to the back side of the piezoelectric plate, but when the sealing material is provided on the entire peripheral portion of the piezoelectric plate. As described above, the vibration of the piezoelectric plate may be hindered.
Patent Document 3 describes a configuration in which a diaphragm is inserted and fixed in a recess formed in a covering material, and a space filled with gas is formed between the diaphragm and the covering material. The peripheral edge of the diaphragm and the inner wall surface of the covering material are sealed with a sealing material, and the sealing material is also installed outside the space on the back side of the diaphragm. In this configuration, the side surface of the diaphragm is held in contact with the inner wall surface of the covering material, and the peripheral portion of the diaphragm is sealed with the sealing material, which may prevent stable oscillation of the diaphragm. is there.

JP 2011-227033 A (refer to FIG. 7 etc.) JP 2007-93549 A (see paragraphs 0009 and 0010, FIG. 3) WO2002 / 061396 (see FIG. 4 etc.)

  The present invention has been made based on such circumstances, and its purpose is to supply the sample liquid to one surface side of the piezoelectric vibrator to sense the object in the sample liquid. An object of the present invention is to provide a technique for suppressing the adhesion of liquid to the side excitation electrode.

For this reason, the present invention provides a sensing device for sensing a sensing object in a sample liquid by supplying the sample liquid to one surface side of a piezoelectric vibrator provided with excitation electrodes on one surface side and the other surface side of the piezoelectric piece, respectively.
A substrate provided on the other surface side of the piezoelectric vibrator to support the piezoelectric vibrator, and having a larger opening than the excitation electrode in a region corresponding to the excitation electrode on the other surface side;
It is provided inside the opening of the substrate and outside the excitation electrode on the other surface side so as to surround at least the side of the excitation electrode over the entire circumferential direction, and one end side thereof is the other surface side of the piezoelectric piece. An annular cover member provided in close contact with the
The piezoelectric vibrator is provided for sensing a sensing object based on the oscillation frequency when the piezoelectric vibrator is oscillated by an oscillation circuit.

According to another aspect of the present invention, a sample solution is supplied to one surface side of a piezoelectric vibrator having excitation electrodes provided on one surface side and the other surface side of the piezoelectric piece to detect a sensing object in the sample solution. In the piezoelectric sensor used in the device,
A substrate provided on the other surface side of the piezoelectric vibrator to support the piezoelectric vibrator, and having a larger opening than the excitation electrode in a region corresponding to the excitation electrode;
Provided inside the opening and outside the excitation electrode on the other surface side so as to surround at least the side of the excitation electrode over the entire circumferential direction, and one end side thereof is in close contact with the other surface side of the piezoelectric piece. An annular cover member provided so as to
The piezoelectric vibrator is provided for sensing a sensing object based on the oscillation frequency when the piezoelectric vibrator is oscillated by an oscillation circuit.

  In a sensing device that senses a sensing object in a sample liquid by supplying a sample liquid to one surface side of a piezoelectric vibrator having excitation electrodes provided on one side and the other side of the piezoelectric piece, respectively, A substrate for supporting the piezoelectric vibrator is provided on the surface side. In this substrate, an opening larger than the excitation electrode is formed in a region corresponding to the excitation electrode on the other surface side of the piezoelectric vibrator. In addition, an annular cover member is provided inside the opening and outside the excitation electrode on the other surface side so as to surround the periphery of the excitation electrode so that one end side thereof is in close contact with the other surface side of the piezoelectric piece. As a result, even if liquid enters the other surface side of the piezoelectric vibrator from the gap between the piezoelectric vibrator and the substrate, the cover body prevents the liquid from entering the inside of the cover body. The adhesion of the liquid to the excitation electrode on the other surface side is suppressed.

It is a disassembled perspective view which shows an example of the sensing apparatus of this invention. It is a longitudinal section showing an example of a sensing device. It is a top view which shows an example of the crystal oscillator used for a sensing apparatus. It is the schematic which shows the circuit structure in a sensing apparatus. It is a longitudinal cross-sectional view which shows a part of other example of the sensing apparatus of this invention. It is a longitudinal cross-sectional view which shows a part of conventional sensing device.

  An example of the sensing device of the present invention will be described with reference to FIGS. This sensing device is configured by housing a crystal sensor in the sensor unit 2. For example, as shown in FIGS. 1 and 2, the sensor unit 2 includes a support 21, a sealing member 22, a wiring substrate 3 that forms a substrate, a cover member 4, a crystal resonator 5 that is a piezoelectric resonator, and a flow path forming member. 23 and the upper cover 24 are laminated in this order from the lower side. The X axis, the Y axis, and the Z axis shown in FIGS. 1 to 3 indicate an orthogonal coordinate system.

  The crystal sensor 6 forms a piezoelectric sensor, and is configured by providing a crystal resonator 5 on a wiring substrate 3 made of, for example, a glass epoxy substrate. As shown in FIGS. 2 and 3, the crystal resonator 5 is provided with an excitation made of, for example, gold (Au) on the front surface side and the back surface side of a disk-shaped crystal piece 51 that is, for example, an AT-cut piezoelectric piece. An electrode is provided. 3A shows the front surface side (one surface side) of the crystal unit 3, and FIG. 3B shows the back surface side (the other surface side). In this example, as shown in FIGS. 3A and 3B, the first excitation electrode 53A and the second excitation electrode 53B are arranged on the other surface side of the crystal piece 51 so as to be separated from each other, and on the one surface side. The common excitation electrode 52 is disposed in the first and second electrodes. The excitation electrode 52 includes a first excitation electrode 52A and a second excitation electrode 52B that face the excitation electrodes 53A and 53B, respectively. Thus, the first vibration region 5A is formed by the first excitation electrode 53A and the first excitation electrode 52A, and the second vibration region 5B is formed by the second excitation electrode 53B and the second excitation electrode 52B. .

  The first excitation electrode 53A and the second excitation electrode 53B on the other surface side are wired when the crystal sensor 6 is attached to the sensor unit 2 via the extraction electrodes 531 and 532, respectively, as shown in FIG. The conductive paths 32 and 34 routed on the substrate 3 are electrically connected to each other. The common electrode 52 is electrically connected to the conductive path 33 formed on the wiring board 3 when the crystal sensor 6 is mounted on the sensor unit 2 via the extraction electrode 521 formed so as to wrap around to the back surface side. It is connected to the.

  Connection terminals 35 to 37 that are electrically connected to the respective conductive paths 32 to 34 are formed in the end region of the wiring board 3. As shown in FIG. 4, these conductive paths 32 and 34 are connected to the first oscillation circuit 6A and the second oscillation circuit 6B, respectively, and the common excitation electrode 52 is connected to the ground side of the oscillation circuits 6A and 6B. Is done. In addition, an adsorption layer 54 is formed on the surface of the first excitation electrode 52A to bind a sensing object by, for example, an antigen-antibody reaction.

  As shown in FIGS. 1 and 2, the crystal unit 5 is mounted so as to close an opening (through hole) 31 formed in the wiring board 3. The opening 31 is formed to secure a region for sufficiently vibrating the crystal piece 51 when the crystal resonator 5 oscillates, and the inner edge of the opening 31 is outside the excitation electrodes 53A and 53B on the other surface side. It is comprised so that it may be located in. In addition, the crystal unit 5 is bonded and fixed to the wiring substrate 3 at a plurality of, for example, three locations on the peripheral edge of the opening 31 with an adhesive such as a conductive paste. In this bonding, as described in the background art, it is preferable that the bonding area is small so as not to inhibit the vibration of the crystal piece 51, so the crystal piece 51 is between the crystal piece 51 and the wiring substrate 3. A slight gap is formed in most of the circumferential direction.

  As shown in FIGS. 1 and 2, a recess 211 is formed in the support 21 to secure a storage area for the wiring substrate 3, and the peripheral portion of the recess 211 is a stage on which the wiring substrate 3 is placed. The unit 212 is configured. In FIG. 1, for convenience of illustration, the step 212 is omitted. Further, a sealing member 22 is provided in the recess 211 of the support 21 so as to cover the opening 31 of the wiring board 3. As shown in FIGS. 1 and 2, the sealing member 22 is a flat cylindrical body whose other end is closed, and its upper end (one end side) is an annular body. The sealing member 22 is made of an elastic body, and the annular upper end is provided outside the opening 31 of the wiring board 3 so as to be in close contact with the back side of the wiring board 3.

  Further, inside the opening 31 of the wiring board 3 and outside the excitation electrodes 53A and 53B on the other surface side, an annular shape is provided so as to surround at least the sides of the excitation electrodes 53A and 53B over the entire circumferential direction. A cover member 4 is provided. As shown in FIG. 1, the cover member 4 is formed of a flat cylindrical body whose other end is closed, and its upper end (one end side) is an annular body, and the annular upper end is a crystal resonator. 5 is provided so as to be in close contact with the back surface side. Thus, the upper end of the cover member 4 forms a contact surface 41 between the cover member 4 and the crystal unit 5. The contact surface 41 is indicated by a dotted line in FIG. 3B, and the outer peripheral edge of the contact surface 41 is located inside the opening 31 of the wiring board 3, and the inner peripheral edge of the contact surface 41 is the crystal resonator 5. It is comprised so that it may be located in the outer side of excitation electrode 53A, 53B of the back side. The width W of the contact surface 41 is appropriately set according to the size of the opening 31 of the wiring board 3 and the size of the formation region of the excitation electrodes 53A and 53B. Further, the height H of the cover member 4 is set to be smaller than the thickness of the wiring board 3. As an example of the size of the cover member 4, the inner diameter A is about 2.0 mm, the width W is about 0.6 mm, and the height H is about 1.6 mm.

  Such a cover member 4 is made of a material that is in close contact with the crystal piece 5 and does not inhibit the vibration of the crystal piece 5. The close contact here refers to a state in which both are attached so as to suppress the intrusion of the liquid into the contact surface 41 between the cover member 4 and the crystal piece 5, and includes, for example, a case where both are bonded with an adhesive. . Specific examples of the material of the cover member 4 include an elastic body such as polydimethylsiloxane (PDMS). Since PMDS has an adsorptive power to quartz, it sticks to and comes into close contact with the quartz when pressed against the quartz. Further, the upper end of the cover member 4 may be irradiated with plasma to modify the surface of the upper end to improve the adhesion to the crystal piece 51.

  Further, the crystal sensor 6 includes a flow path forming member 23 made of an elastic body, and the flow path forming member 23 and the sealing member 22 press the one surface side (front surface side) and the other surface side (back surface side), respectively. Attached to the sensor unit 2. As shown in FIG. 2, the flow path forming member 23 forms a liquid supply area 27 that forms a reaction flow path in an area where the excitation electrodes 52 </ b> A and 52 </ b> B on one surface side of the crystal unit 5 are formed. The liquid supply region 27 is configured such that liquid is supplied from the liquid supply pipe 25 to one side in the X direction (the length direction of the crystal piece 51) in FIG. 2, and from the other side in the X direction. The liquid is discharged through the liquid discharge pipe 26. As a result, the sample solution flows from one side in the length direction of the crystal unit 5 to the other side on one side of the crystal unit 5.

  The oscillation output (frequency signal) of the first oscillation circuit 6A for oscillating the first oscillation region 5A and the second oscillation circuit 6B for oscillating the second oscillation region 5B are alternately switched by the switch unit 61. The frequency measuring unit 62 is configured to receive the data. The frequency measuring unit 62 is configured to detect the frequency by, for example, a frequency counter or a method for obtaining the speed of the rotation vector as described in, for example, JP-A-2006-258787. The oscillation frequencies of the vibration regions 5A and 5B obtained by the frequency measuring unit 62 are sent to the data processing unit 63, and for example, a difference is taken and displayed.

  In the above-described sensing device, the presence or absence of a sensing object is determined as follows. First, for example, while supplying a buffer solution via the liquid supply pipe 25, the oscillation circuits 6A and 6B oscillate the crystal resonator 5 at a frequency of, for example, 9 MHz, and the frequency measurement unit 62 oscillates the oscillation frequencies of these vibration regions 5A and 5B. To get. The oscillation frequency of the vibration region 5A acquired at this time is set as the first frequency signal. Subsequently, the supply of the buffer solution is stopped, and the sample solution is supplied through the liquid supply pipe 25. As a result, the sample liquid flows through the liquid supply region 27, and when the sensing object X is included in the sample liquid, the sensing object X is quickly adsorbed (bound) to the adsorption layer 54 by the antigen-antibody reaction. ) As described above, when the sensing object X is contained in the sample liquid, the sensing object X is captured by the adsorption layer 54 on the first excitation electrode 52A side, and the first excitation electrode 52A has a mass. Since it is added, the oscillation frequency changes accordingly.

  After supplying the sample liquid in this way, the oscillation frequencies of the vibration regions 5A and 5B are acquired, and the oscillation frequency of the vibration region 5A acquired at this time is used as the second frequency signal. Then, a difference from the first frequency signal acquired before supplying the sample liquid is taken, and compared with a preset threshold value, for example, in the data processing unit 63, and if the frequency data is equal to or higher than the threshold value, the sensing object If X is “present” and less than the threshold, it is determined that the sensing object X is “not present”. In this example, since the oscillation frequency of the second vibration region 5B is due to a disturbance such as a change in temperature, the viscosity of the aqueous solution itself, or adhesion of a substance other than the object, the oscillation frequency of the first vibration region 5A When the oscillation frequency of the second vibration region 5B is subtracted, a frequency difference resulting from the adsorption of the target object that compensates for the frequency fluctuation due to the disturbance is obtained. For this reason, it is possible to perform highly accurate measurement on the presence or absence of the sensing object X.

  According to the above-described embodiment, as described above, the oscillation frequency is acquired while allowing the liquid to flow through the liquid supply region 27 formed between the crystal resonator 5 and the flow path forming member 23. Since the liquid is confined in the liquid supply region 27, it does not leak outward from the region 27, but there is a gap between the peripheral portion of the crystal unit 5 and the wiring board 3 as described above. When the crystal sensor 6 is removed from the sensing device, or when the liquid remaining on the surface of the crystal unit 5 is blown away by a blower, the liquid is removed from the gap between the crystal unit 5 and the wiring substrate 3. There is a possibility that the crystal resonator 5 may go around to the other surface side through the three openings 31.

  However, as described above, the cover member 4 is provided in the opening 31 so as to cover the excitation electrodes 53A and 53B on the other surface side of the crystal resonator 5, and the cover member 4 is in close contact with the crystal resonator 5. Has been. For this reason, even if liquid enters the other surface side of the crystal unit 5 through the gap between the crystal unit 5 and the wiring board 3, it cannot enter between the cover member 4 and the crystal unit 5, so There is no possibility that the liquid adheres to the excitation electrodes 53A and 53B on the other surface side of the child 5. As a result, the atmosphere in which the excitation electrodes 53A and 53B on the other surface side of the crystal unit 5 are placed can always be kept in the gas phase, so that stable oscillation can be ensured. Moreover, since it is not necessary to dry the excitation electrodes 53A and 53B on the other surface side using a blower, there is no concern that an accident such as destruction of a crystal piece will occur. Further, some liquids adhere to the excitation electrode due to drying of the solute. However, since this can be suppressed, stable oscillation can always be performed.

  Furthermore, since the cover member 4 is configured to cover the excitation electrodes 53A and 53B on the other surface side of the crystal resonator 5 through a space, the cover member 4 is used when the crystal sensor 6 is immersed in a sample solution. However, it is possible to prevent the liquid from adhering to the excitation electrodes 53A and 53B on the other surface side. Furthermore, since the cover member 4 is provided inside the opening 31 of the wiring board 3, it is not necessary to change the shape of the wiring board 3 for attaching the cover member 4, and it can be provided in combination with an existing crystal sensor. Therefore, the waterproof structure of the excitation electrode on the other surface side can be secured with an inexpensive and simple structure. Further, when the cover member 4 is made of an elastic body having an adsorptivity with respect to quartz such as PDMS, for example, both can be brought into close contact with each other by pressing the cover member 4 against the quartz vibrator, so that the manufacturing is easy.

  In the above, as shown in FIG. 5, the cover member 7 is located inside the opening 31 of the wiring board 3 and outside the excitation electrodes 53A and 53B on the other surface side of the crystal unit 5. An annular body provided so that the upper end thereof is in close contact with the other surface side of the crystal unit 5 so as to surround the periphery of 53B may be used, and the excitation electrodes 53A and 53B on the other surface side are not necessarily disposed through the space. It may not be configured to cover. When the crystal sensor 6 is not used by being immersed in the sample solution, the cover member 7 is provided in an annular shape so as to surround the excitation electrodes 53A and 53B on the other surface side of the crystal resonator 5, so that the other surface side is provided. This is because the adhesion of the liquid to the excitation electrodes 53A and 53B can be suppressed. Furthermore, when the cover member is brought into close contact with the crystal resonator with an adhesive, the cover member need not be formed of an elastic body, and may be formed of, for example, plastic. In addition to the above PDMS, silicon rubber or the like can be used as the elastic body that is attracted to the piezoelectric piece constituting the cover member.

  Further, the piezoelectric vibrator (quartz crystal vibrator) constituting the piezoelectric sensor (quartz sensor) may include only a reaction excitation electrode provided with an adsorption layer. Furthermore, the piezoelectric sensor is used to supply a liquid to one surface of the piezoelectric sensor, oscillate a piezoelectric vibrator constituting the piezoelectric sensor by an oscillation circuit, and sense a sensing object based on the oscillation frequency. It suffices that the sensor unit is not necessarily used by being incorporated in the sensor unit.

2 Sensor unit 3 Wiring board 31 Opening 4 Cover member 5 Crystal oscillators 52A and 52B Excitation electrodes 53A and 53B on one surface side Excitation electrodes 5A and 5B on the other surface side Vibration region 6 Crystal sensors 6A and 6B Oscillation circuit

Claims (7)

In a sensing device for sensing a sensing object in a sample liquid by supplying a sample liquid to one surface side of a piezoelectric vibrator provided with excitation electrodes on one side and the other side of the piezoelectric piece, respectively,
A substrate provided on the other surface side of the piezoelectric vibrator to support the piezoelectric vibrator, and having a larger opening than the excitation electrode in a region corresponding to the excitation electrode on the other surface side;
It is provided inside the opening of the substrate and outside the excitation electrode on the other surface side so as to surround at least the side of the excitation electrode over the entire circumferential direction, and one end side thereof is the other surface side of the piezoelectric piece. An annular cover member provided in close contact with the
The piezoelectric vibrator is provided for sensing a sensing object based on the oscillation frequency when the piezoelectric vibrator is oscillated by an oscillation circuit. A flow path forming member for forming a reaction flow path in a region facing the one surface side, including a facing surface that is in close contact with the one surface side of the piezoelectric vibrator and faces the piezoelectric vibrator through a gap;
A liquid supply port for supplying a sample solution to the reaction channel;
The sensing device according to claim 1, further comprising a liquid outlet for discharging the sample liquid from the reaction channel. The sensing device according to claim 1, wherein the cover member is configured to cover the excitation electrode on the other surface side of the piezoelectric vibrator through a space. The sensing device according to claim 1, wherein the cover member is configured by an elastic body that is attracted to the piezoelectric piece. In the piezoelectric sensor used in the sensing device for sensing the sensing object in the sample liquid by supplying the sample liquid to one surface side of the piezoelectric vibrator provided with the excitation electrode on each of the one surface side and the other surface side of the piezoelectric piece,
A substrate provided on the other surface side of the piezoelectric vibrator to support the piezoelectric vibrator, and having a larger opening than the excitation electrode in a region corresponding to the excitation electrode;
Provided inside the opening and outside the excitation electrode on the other surface side so as to surround at least the side of the excitation electrode over the entire circumferential direction, and one end side thereof is in close contact with the other surface side of the piezoelectric piece. An annular cover member provided so as to
The piezoelectric vibrator is provided for sensing a sensing object based on an oscillation frequency when the piezoelectric vibrator is oscillated by an oscillation circuit. The piezoelectric sensor according to claim 5, wherein the cover member is configured to cover the excitation electrode on the other surface side of the piezoelectric vibrator through a space. The piezoelectric sensor according to claim 5, wherein the cover member is formed of an elastic body that is attracted to the piezoelectric piece.

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