WO2007032259A1

WO2007032259A1 - Piezoelectric sensor

Info

Publication number: WO2007032259A1
Application number: PCT/JP2006/317811
Authority: WO
Inventors: Morito Akiyama; Naohiro Ueno; Tatsuo Tabaru
Original assignee: National Institute Of Advanced Industrial Science And Technology
Priority date: 2005-09-14
Filing date: 2006-09-08
Publication date: 2007-03-22
Also published as: JP2007108161A; JP4883768B2

Abstract

Disclosed is a piezoelectric sensor (1) comprising a piezoelectric element (10) which receives a pressure at a first surface and generates electrical charges from the pressure. In this piezoelectric sensor (1), a space is formed in a region facing a second surface of the piezoelectric element that is opposite to the first surface.

Description

Specification

Piezoelectric sensor

Technical field

[0001] The present invention relates to a piezoelectric ceramic thin film element that detects a physical quantity such as acoustic emission, vibration, and acceleration in a high temperature environment such as an internal combustion engine or a plant such as a nuclear power plant. It relates to sensors.

Background art

[0002] Sensors are installed inside structures to detect abnormalities in structures that generate high-temperature atmosphere, such as piping and valves in plants such as nuclear power plants, and engines of internal combustion engines. For example, acoustic emission sensors that detect acoustic emissions, which are elastic waves generated when cracks or cracks occur in structures, and piezoelectric vibration sensors that detect abnormal vibration and acceleration information are used. These include various types such as a compression type, a cantilever type, a diaphragm type, and a shear type.

Among these, a compression type thin film type piezoelectric sensor is disclosed in Japanese Patent Publication “JP-A-6-148011 (Publication Date: May 27, 1994)” (hereinafter, Patent Document 1). As shown in Fig. 1, it is composed of a pedestal, a pedestal side electrode, a piezoelectric body, a load body side electrode, and a stacked body in which load bodies are stacked in sequence, and is used by attaching the lower surface of the pedestal to the structure. It is. When vibration is generated in the structure, the vibration is transmitted to the pedestal side of the thin film piezoelectric sensor. The vibration transmitted to the pedestal side of the thin film type piezoelectric sensor is transmitted to the piezoelectric body, and compressive stress or tensile stress proportional to the vibration acceleration is generated in the piezoelectric body. Then, an electric signal (charge) proportional to the stress is generated on both surfaces of the piezoelectric body, and the two electrodes disposed on both sides of the piezoelectric body take out the charge. The magnitude and acceleration of the vibration of the structure can be detected by measuring the extracted electric charge.

[0004] Conventionally, various piezoelectric materials as shown in Table 1 are used for such piezoelectric sensors.

[0005] [Table 1] AIN PZT Quartz LiNb0 ₃ Kyuri-temperature [. c] 300 573 1210 Piezoelectric constant d ₃₃ [pm / V] 4 300 2 6

Voltage output constant ₃ [V- m / N] 0.05 0.02 0.05 0.02

Thin film ○ ○ 厶 Δ

Patent Document 1 and Japanese Patent Laid-Open Publication No. 10-206399 (publication date: August 7, 1998) (hereinafter referred to as Patent Document 2) include lead zirconate titanate (PZT) as a piezoelectric material. ) And an example of a piezoelectric sensor using polyvinylidene fluoride (PVDF). When

§ 厂

However, these piezoelectric materials have a low Curie temperature, and the maximum application temperature is about 300 ° C. In contrast, the inside of the structure has a high combustion temperature (around 500 ° C.). For this reason, the piezoelectric body of the piezoelectric sensor installed inside the structure becomes quite hot (around 400 ° C) and reaches the Curie temperature. If the piezoelectric body is heated to a temperature exceeding the Curie temperature, the piezoelectric characteristics deteriorate and it cannot be used. Therefore, in the case of using a low-curie temperature piezoelectric material as described above, the Japanese Patent Publication “JP-A-5-203665 publication date (August 10, 1993)” (hereinafter, As described in Patent Document 3), it is necessary to separately provide a cooling means for maintaining the piezoelectric body at an appropriate temperature. However, the provision of the cooling means causes a problem that the structure of the piezoelectric sensor is complicated and the cost is increased.

[0006] In order to solve the above problem, a method of using a piezoelectric body in a high temperature environment with a high Curie temperature is conceivable. Japanese Patent Publication “JP-A-5-34230 (Publication Date: Feb. 9, 1993)” (hereinafter referred to as Patent Document 4) describes the use of lithium Niobate (LiNbO) having a high Curie temperature as a piezoelectric material. A method for use as a body is disclosed. Lithium niobate

Three

As shown in Table 1, the Curie temperature is about 1210 ° C, and it can be used in a high-temperature environment without using cooling means. However, lithium niobate is inferior in workability, difficult to form a thin film, and has a problem S that piezoelectric properties cannot be obtained unless it is in a single crystal state. In addition, there is a problem that production and processing are difficult and costly.

[0007] Also, when quartz is used for the piezoelectric body, it is difficult to form a thin film as described above. There is a problem.

[0008] Therefore, an example of a method for solving these problems is disclosed in Japanese Patent Publication “JP 2004-156991 A (publication date: June 3, 2004)” (hereinafter, Patent Document 5). It has been done. The piezoelectric sensor disclosed in Patent Document 5 uses a piezoelectric body having no Curie temperature, such as aluminum nitride (A1N) or zinc oxide (ZnO). Specifically, the piezoelectric sensor is formed by laminating a base layer, a piezoelectric thin film layer (aluminum nitride), and an upper electrode in this order on a metal diaphragm, and extracts charges generated from the piezoelectric thin film layer. A signal output rod is fixed to the upper electrode by pressure bonding. The pressure received by the metal diaphragm from the outside is transmitted to the piezoelectric thin film layer, and the piezoelectric thin film layer generates an electric charge according to the pressure. The pressure is detected by measuring the electric charge through a signal output rod. As a result, it is possible to realize a low-cost piezoelectric sensor that is small and excellent in heat resistance.

[0009] However, in the conventional configuration, the piezoelectric constant d as shown in Table 1 is used as the piezoelectric body of the piezoelectric element.

Since aluminum nitride with a small size of 33 is used, it is not possible to generate a sufficient charge according to the external pressure. In addition, since the piezoelectric element is tightly fixed to the signal output rod, the amount of deformation of the piezoelectric element due to external pressure is limited. Piezoelectric elements are deformed by the pressure of an external force and generate electric charges according to the stress generated inside them. Therefore, if the amount of deformation of the piezoelectric element is small, electric charges are generated accurately according to external pressure. I can't. Therefore, a piezoelectric sensor using such a piezoelectric element has a problem of low sensitivity. In particular, a sensor for detecting an abnormality in a structure needs to detect even a slight abnormality, so its sensitivity is an important issue. In addition, other piezoelectric materials with a large piezoelectric constant d shown in Table 1 cause the above-mentioned problems.

33

Not suitable for use.

Here, the piezoelectric constant d is generated from the piezoelectric body with respect to the pressure applied to the piezoelectric body.

33

This value represents the amount of charge generated. That is, the piezoelectric constant d

33 The larger the value, the more charge is generated. As the amount of generated charge increases, a charge corresponding to the pressure can be generated even if the applied pressure is small. Therefore, this large amount of charge affects the sensitivity of the piezoelectric element. The present invention has been made in view of the above problems, and an object thereof is to provide a piezoelectric sensor that can obtain high sensitivity using a piezoelectric element having low sensitivity.

Disclosure of the invention

[0012] In order to achieve the above object, the piezoelectric sensor of the present invention is a piezoelectric sensor including a piezoelectric element that receives a pressure on the first surface and generates an electric charge by the pressure. It is characterized in that a space is formed in a region facing the second surface opposite to the above.

When the piezoelectric element is deformed by receiving a force from the outside, a compressive stress and a tensile stress are generated inside the piezoelectric element, and an electric charge corresponding to the stress is generated. Therefore, if the amount of deformation is large, the stress generated in the inside becomes large, and more charges are generated.

[0014] According to the above configuration, since the space is formed in the region where the second surface opposite to the first surface of the piezoelectric element faces, the piezoelectric element that has received the pressure is Depending on the pressure, you can rub in the direction. In this way, by forming a space on the surface opposite to the surface that receives pressure, the piezoelectric element can be held in the direction of the space without being obstructed. Thereby, even if the pressure generated outside is slight, the piezoelectric element can be swollen, so that the piezoelectric element can accurately generate charges corresponding to the pressure. Therefore, even if a piezoelectric element with low sensitivity is used, a highly sensitive piezoelectric sensor can be obtained.

[0015] Other objects, features, and advantages of the present invention will be sufficiently enhanced by the following description. The benefits of the present invention will become apparent from the following description with reference to the accompanying drawings.

Brief Description of Drawings

FIG. 1, showing an embodiment of the present invention, is a cross-sectional view showing a schematic configuration of a piezoelectric sensor.

2 is a cross-sectional view showing a piezoelectric element in the piezoelectric sensor shown in FIG.

FIG. 3 is a cross-sectional view showing a relationship between a piezoelectric element and a signal output bar in the piezoelectric sensor shown in FIG.

FIG. 4 (a) is a longitudinal sectional view of a cylindrical signal output rod having a recess.

FIG. 4 (b) is a cross-sectional view of a cylindrical signal output rod having a recess. [4 (c)] is a longitudinal sectional view of a hemispherical signal output bar having a recess.

[4 (d)] is a cross-sectional view of a prismatic signal output rod having a recess.

FIG. 5 is a cross-sectional view showing a schematic configuration of a piezoelectric sensor that extracts electric charges generated from a piezoelectric element using a conducting wire.

FIG. 6 is a cross-sectional view of a piezoelectric element in which the upper electrode is formed only in the outer peripheral side region of the piezoelectric thin film layer in the piezoelectric sensor shown in FIG.

[FIG. 7] A cross-sectional view of the piezoelectric sensor shown in FIG. 1 when sag occurs in the piezoelectric element. 圆 8 (a)] In the piezoelectric sensor shown in FIG. FIG. 5 is a plan view of a piezoelectric element when provided separately in a region closer to the center. [8 (b)] FIG. 8A is a cross-sectional view of the piezoelectric element shown in FIG.

[9 (a)] FIG. 9 is a cross-sectional view of a piezoelectric element formed by dividing a piezoelectric thin film layer and an upper electrode in the piezoelectric sensor shown in FIG.

FIG. 9 (b) is a plan view of the upper electrode shown in FIG. 9 (a).

[10] FIG. 10 is a cross-sectional view of the piezoelectric element in which the piezoelectric thin film layer is formed only in the outer peripheral region in the piezoelectric sensor shown in FIG.

FIG. 11 is a cross-sectional view showing a schematic configuration of the piezoelectric sensor when the piezoelectric thin film layer shown in FIG. 1 is formed directly on the front end wall of the housing.

FIG. 12 is an enlarged cross-sectional view of the case where the piezoelectric thin film layer shown in FIG. 1 is formed directly on the front end wall of the case.

FIG. 13 is a cross-sectional view showing a schematic configuration of the piezoelectric sensor when a recess is provided in the front end wall of the housing on which the piezoelectric thin film layer shown in FIG. 1 is formed.

14] A sectional view showing a schematic configuration of the piezoelectric sensor when the front end wall having the recess shown in FIG. 13 is formed of silicon.

FIG. 15 is a cross-sectional view showing a measurement system for measuring the amount of electric charge generated by the piezoelectric element force with respect to the pressure stored in the piezoelectric element in the piezoelectric sensor acting on this embodiment.

FIG. 16 is a waveform diagram showing the result of measuring the amount of charge taken from the piezoelectric element with an oscilloscope in the measurement system. FIG. 17 is a graph showing the relationship between the force generated by the piezoelectric element in the measurement system and the charge amount obtained from the signal amplitude shown in the waveform diagram measured by the oscilloscope.

FIG. 18 is a graph showing the relationship between the pressure converted to the output voltage and the force obtained from the piezoelectric element in the measurement system and the signal amplitude force shown in the waveform diagram measured by the oscilloscope, and the amount of charge obtained.

FIG. 19 is a cross-sectional view showing a measurement system for measuring the amount of electric charge that also generates the piezoelectric element force with respect to the pressure applied to the piezoelectric element shown in FIGS. 8 (a) and 8 (b).

FIG. 20 is a graph showing a waveform of a voltage output from the piezoelectric element when pressure is applied to the piezoelectric element in the measurement system shown in FIG.

21] A graph showing changes in piezoelectric response to temperature changes of the piezoelectric sensor of this embodiment.

圆 22] A graph showing frequency characteristics of the piezoelectric sensor of the present embodiment.

23 (a)] In the piezoelectric sensor of the present embodiment, it is a plan view showing a schematic configuration of a piezoelectric element when a glass substrate is used as a pressure transmission member.

FIG. 23 (b) is a cross-sectional view showing a measurement system for measuring the amount of charge generated from the piezoelectric element with respect to the pressure applied to the piezoelectric element shown in FIG. 23 (a).

FIG. 24 is a graph showing the amount of charge generated from the piezoelectric thin film layer when pressure is applied to the piezoelectric element in the measurement system shown in FIG. 23 (b).

Explanation of symbols

1 Piezoelectric sensor

2 Signal transmission part

10 Piezoelectric element

10a Near the center

10b Near both ends

11 Metal diaphragm (pressure transmission member)

12 Underlayer

13 Piezoelectric thin film layer

14 Upper electrode 20 enclosure

21 Rear housing

22 Front housing

22d front end wall

30 Signal output rod (conductive member, electrode layer)

32 recess

40 Electric urine column

53 opening

60 conductor

BEST MODE FOR CARRYING OUT THE INVENTION

[0018] An embodiment of the present invention is described below with reference to the drawings.

In the present embodiment, a case where a piezoelectric sensor is applied to an internal combustion engine will be described as an example.

FIG. 1 is a cross-sectional view showing a schematic configuration of the piezoelectric sensor of the present embodiment. The piezoelectric sensor 1 detects an abnormality in the cylinder by detecting the pressure generated in the internal combustion engine cylinder. The piezoelectric sensor 1 includes a signal transmission unit 2 and a piezoelectric element 10.

[0020] The piezoelectric element 10 receives a pressure generated in the cylinder and generates a charge corresponding to the pressure. Details of the piezoelectric element 10 will be described later.

The signal transmission unit 2 includes a housing 20, a signal output rod (conductive member, electrode layer) 30, and an electrical insulating column 40. The signal transmission unit 2 transmits the electric charge generated from the piezoelectric element 10 as a detection signal to a signal carrying cable (not shown) via the signal output rod 30.

The casing 20 includes a front casing 22 and a rear casing 21 in the front and rear in the axial direction, and a shaft hole 50 through which a front end force penetrates to the rear end is formed. The casing 20 is preferably made of a heat-resistant metal because it is provided in an internal combustion engine that is at a high temperature.

[0023] The rear housing 21 includes a large-diameter portion 21a and a small-diameter portion 21b in front and rear in the axial direction, and the large-diameter portion 21a has an inner diameter and an outer diameter larger than those of the small-diameter portion 21b. . Large diameter part 21 A connector for attaching a signal carrying cable (not shown) is fitted inside a.

[0024] The front housing 22 includes a large-diameter portion 22a having a large outer diameter and a small-diameter portion 22b having a small outer diameter at the front and rear in the axial direction. A large-diameter hole 51 constituting a part of the shaft hole 50 is formed inside the front housing 22, and a small-diameter portion 21b of the rear housing 21 is formed in the large-diameter hole 51 of the large-diameter portion 22a. It is fitted by screwing.

[0025] An opening 53 having a smaller diameter than the large-diameter hole 51 is formed in the front end wall 22d of the small-diameter portion 22b in order to take in the pressure of an external force. Further, a step portion 22c for mounting the piezoelectric element 10 is formed around the opening 53 in the inner surface of the front end wall 22d.

[0026] The shaft hole 50 is a connecting hole of a large diameter hole 51 having a large diameter on the small diameter portion 22b side and a small diameter hole 52 having a small diameter on the small diameter portion 21b side. The large-diameter hole 51 is fitted with a cylindrical electric insulating ring column 40 having an outer diameter slightly smaller than the hole diameter of the large-diameter hole 51. A metal hole is inserted into the through-hole of the electric insulating ring column 40. A signal output rod 30 made of steel is installed.

[0027] The signal output rod 30 has a round bar shape, and includes a step portion 31 whose outer diameter on the front end side is larger than that of other portions. Further, a recess 32 is formed in the front end surface of the signal output rod 30. Therefore, the front end surface of the signal output rod 30 is a ring-shaped annular surface. The shape of the recess 32 is not particularly limited, and for example, a cylindrical shape, a prismatic shape, a conical shape, a pyramidal shape, or the like can be selected as appropriate.

[0028] Further, the rear end portion of the signal output rod 30 passes through the small-diameter hole 52 in the small-diameter portion 21b of the rear housing 21, reaches the inside of the large-diameter portion 21a, and is connected to a signal carrying cable (not shown). In addition, a metal electrode 33 is provided on the front end surface of the signal output rod 30, and the electrode 33 is configured to come into contact with the piezoelectric element 10 at the step portion 22 c of the small diameter portion 22 b of the front case 22.

The opening 53 is located inside the cylinder, and the pressure generated inside the cylinder enters from the opening 53 and reaches the piezoelectric element 10. Further, the signal output rod 30 is in contact only with the piezoelectric element 10 and the electrically insulating ring column 40 in the shaft hole 50 and is electrically insulated from the housing 20.

[0030] The piezoelectric sensor 1 is configured as described above. Here, an assembly method of the piezoelectric sensor 1 will be described below. First, the piezoelectric element 10 is placed on the step 22 c of the front housing 22. At this time, the front end surface (first surface) of the piezoelectric element 10 is exposed from the opening 53 of the front housing 22. Next, the signal output rod 30 is inserted into the front housing 22 and comes into contact with and fixed to the rear end surface (second surface) of the piezoelectric element 10. Next, the electrically insulating ring column 40 is inserted into the front housing 22 with the signal output rod 30 inserted therein, and is in contact with and fixed to the step portion 31 at the front end of the signal output rod 30. . Thereafter, the small-diameter portion 21b of the rear housing 21 is inserted into the large-diameter portion 22a of the front housing 22, and the front end wall of the rear housing 21 pushes the rear end wall of the electrical insulating ring column 40. Then, the piezoelectric element 10, the signal output rod 30, and the electrically insulating ring column 40 are fixed in a state where they are crimped inside the front housing 22. The piezoelectric sensor 1 can be formed by the above method.

Next, the piezoelectric element 10 will be described in detail with reference to FIG. FIG. 2 is a cross-sectional view showing the piezoelectric element 10 according to the present embodiment.

The piezoelectric element 10 is formed by forming a base layer 12, a piezoelectric thin film layer 13, and an upper electrode 14 in this order on a metal diaphragm (pressure transmission member) 11.

[0034] For each film formation, a physical vapor deposition (PVD) method, that is, a method of forming a thin film by evaporating a substance by a physical method and condensing on a member to be formed can be used.

. Specifically, for example, vacuum deposition methods such as resistance heating deposition or electron beam heating deposition,

Various sputtering methods such as DC sputtering, high frequency sputtering, RF plasma assisted sputtering, magnetron sputtering, ECR sputtering or ion beam sputtering, high frequency ion plating method, various ion plating such as active ion deposition or arc ion plating Methods, molecular beam epitaxy, laser ablation, ion cluster beam deposition, and ion beam deposition.

[0035] The metal diaphragm 11 is in contact with the space in the cylinder in which pressure is generated, and receives the pressure generated in the cylinder to which the force of the opening 53 has also entered. The metal diaphragm 11 transmits the pressure to the piezoelectric thin film layer 13 through the underlayer 12. The metal diaphragm 11 also has a function as a substrate that supports the piezoelectric element 10. The diaphragm refers to a film-like body that deforms according to an applied pressure. Therefore, the metal diaphragm 11 generates stagnation when the external force is also subjected to pressure. [0036] It should be noted that the metal diaphragm 11 is required to have heat resistance because it is installed in the internal combustion engine cylinder that is at a high temperature. Therefore, the metal diaphragm 11 is preferably made of, for example, a heat resistant metal material equivalent to Inconel or SUS630. In addition, the surface of the metal diaphragm 11 on the side where the piezoelectric thin film layer 13 is formed is polished or chemically treated to prevent cracking or peeling of the piezoelectric thin film layer 13 and to enhance the orientation of the crystal axis. It ’s good to have a specular look by any way!

The foundation layer 12 is a buffer layer between the metal diaphragm 11 and the piezoelectric thin film layer 13 formed on the foundation layer 12. In addition, the underlayer 12 has a role of improving the polar orientation of the piezoelectric thin film layer 13, the orientation of the crystal axis, and the wettability with the metal diaphragm 11. Further, the underlayer 12 has a function as a lower electrode.

[0038] The material of the underlayer 12 is TiN, MoSi2, Si3N4, Cr, Fe, Mg, Mo, Nb, Ta, Ti, Zn, Zr, W, Pt, Al, Ni, Cu, Pd, Rh Ir, Ru, Au, or Ag can be used, and a single layer or a multilayer of two or more layers using a plurality of materials can be used.

The piezoelectric thin film layer 13 has piezoelectric characteristics, and generates electric charges when it receives pressure from an external force. Specifically, stagnation occurs in the piezoelectric thin film layer 13 accompanying the stagnation generated in the metal diaphragm 11. A compressive stress and a tensile stress are generated inside the piezoelectric thin film layer 13 according to the sag of the piezoelectric thin film layer 13. Electric charges are generated from the piezoelectric thin film layer 13 by the action of the internal stress. As described above, the piezoelectric thin film layer 13 receives a pressure and generates a charge corresponding to the pressure. The piezoelectric thin film layer 13 is preferably formed by sputtering using aluminum nitride (A1N) or zinc oxide (ZnO).

The upper electrode 14 takes out the electric charge generated from the piezoelectric thin film layer 13 by the pressure received by the metal diaphragm 11 together with the base layer 12. Then, the extracted electric charge contacts with the upper electrode 14 and is transmitted as a detection signal to the signal carrying cable (not shown) via the signal output rod 30. The material of the upper electrode 14 can be the same material as that of the underlayer 12, but it is not necessary that the upper electrode 14 be the same. The structure may be a single layer or multiple layers. Next, the configuration of the piezoelectric element 10 and the signal output rod 30 will be described with reference to FIG.

[0042] As described above, since the concave portion 32 is formed at the front end portion of the signal output rod 30 in contact with the upper electrode 14 of the piezoelectric element 10, there is no gap between the piezoelectric element 10 and the signal output rod 30. A space is formed. As a result, the piezoelectric element 10 can squeeze in the direction of the space without being disturbed by the signal output rod 30 when an external force is also subjected to pressure.

In the present embodiment, the shape of the recess 32 in the signal output rod 30 is a ring-shaped annular surface as shown in FIGS. 4 (a) and 4 (b). It is not limited. As other shapes, for example, a hemispherical shape may be used as shown in FIG. Further, as shown in FIG. 4 (d), the cross section of the recess 32 in the signal output rod 30 may be square. The depth of the recess 32 is preferably not less than 0. Olmm and not more than 10 mm.

In the present embodiment, the signal output rod 30 is a rod-shaped member having the recess 32, but it may be an annular electrode layer. Thereby, since a hollow space is formed inside the electrode layer, the piezoelectric element 10 can be sandwiched in the space direction of the electrode layer.

Next, the operation of the piezoelectric sensor 1 will be described with reference to FIG.

[0046] First, the metal diaphragm 11 receives pressure generated by vibration or the like inside the internal combustion engine cylinder. In the metal diaphragm 11 that has received the pressure, a sag corresponding to the pressure is generated in the direction in which the pressure is applied, that is, in the space direction of the recess 32 of the signal output rod 30. Then, accompanying the sag of the metal diaphragm 11, the sag occurs in the inner direction of the recess 32 in the base layer 12 and the piezoelectric thin film layer 13 as well. Due to the occurrence of stagnation in the piezoelectric thin film layer 13, stress is generated inside the piezoelectric thin film layer 13. Then, a charge corresponding to the stress generated inside the piezoelectric thin film layer 13 is generated from the piezoelectric thin film layer 13. Next, the base layer 12 and the upper electrode 14 force disposed on both surfaces of the piezoelectric thin film layer 13 take out the charges generated in the piezoelectric thin film layer 13. The extracted charges are transmitted to the electrode 33 and transmitted as a detection signal to a signal carrying cable (not shown) via the signal output rod 30. By measuring this detection signal, the pressure generated in the internal combustion engine cylinder can be detected. As described above, the piezoelectric sensor 1 according to the present embodiment is configured to detect the pressure generated outside by using the stagnation effect of the piezoelectric element 10.

Thus, the piezoelectric element 10 of the present embodiment is recessed without being obstructed by the signal output rod 30. Part 32 can be swept in the direction of the space. Thereby, even if the pressure generated outside is slight, the piezoelectric element 10 can be swollen, and the pressure can be detected based on the charge generated according to this stagnation. Therefore, even when a piezoelectric element with low sensitivity is used, a highly sensitive piezoelectric sensor can be obtained by utilizing the stagnation effect of the piezoelectric element.

Here, a configuration for taking out the electric charge generated from the piezoelectric thin film layer 13 by using a lead wire instead of the signal output rod 30 will be described. FIG. 5 is a cross-sectional view showing a schematic configuration of the piezoelectric sensor 1 that takes out electric charges generated from the piezoelectric thin film layer 13 by a conducting wire.

[0049] The casing 20 in this configuration is preferably a cylindrical member in which only one end surface is released. The one end face is connected to the metal diaphragm 11. Therefore, a sealed space is formed inside the housing 20. In addition, a piezoelectric thin film layer 13 and an upper electrode 14 are formed in this order on the surface of the metal diaphragm 11 on the space side, and a conductive wire 60 is electrically connected to the upper electrode 14.

[0050] Thereby, by receiving the pressure of the external force, the piezoelectric element 10 stagnate in the direction of the space and generates electric charges. Then, this electric charge is taken out by the upper electrode 14 and transmitted as a detection signal to the signal carrying cable via the conducting wire. In this way, by forming a space between the casing 20 and the piezoelectric element 10, the piezoelectric element 10 can be sandwiched in the surface opposite to the surface receiving pressure, that is, in the direction of the space. Therefore, a sufficient charge can be obtained using the stagnation effect of the piezoelectric element 10.

Here, the relationship between the thickness of the metal diaphragm 11 and the amount of charge generated from the piezoelectric thin film layer 13 will be described below.

For example, when the thickness of the metal diaphragm 11 is reduced, the amount of stagnation increases.

Therefore, more charges are generated from the piezoelectric thin film layer 13. Further, when the thickness of the metal diaphragm 11 is increased, the amount of stagnation is reduced. Therefore, the amount of charge generated from the piezoelectric thin film layer 13 is reduced. Thus, by changing the thickness of the metal diaphragm 11, the amount of charge generated from the piezoelectric thin film layer 13 can be changed. In other words, the sensitivity of the piezoelectric sensor 1 can be changed by arbitrarily setting the thickness of the metal diaphragm 11. Here, the upper electrode 14 may be formed so as to take out electric charges generated by compressive stress or tensile stress generated in the piezoelectric thin film layer 13.

In the present embodiment, a configuration will be described in which the upper electrode 14 extracts charges generated by the compressive stress generated in the piezoelectric thin film layer 13. FIG. 6 is a cross-sectional view of the piezoelectric element 10 in which the upper electrode 14 is formed only in the outer peripheral side region of the piezoelectric thin film layer 13.

The piezoelectric thin film layer 13 generates stagnation accompanying the stagnation generated in the metal diaphragm 11, thereby generating compressive stress and tensile stress therein. Specifically, as shown in FIG. 7, the central portion 10 a of the piezoelectric thin film layer 13 is pulled in the both directions by the sag of the metal diaphragm 11. As a result, a tensile stress is generated near the center 10 a of the piezoelectric thin film layer 13. Further, the vicinity 10b of both ends of the piezoelectric thin film layer 13 is compressed in the contraction direction. As a result, compressive stress is generated in the vicinity 10 b of both ends of the piezoelectric thin film layer 13.

Incidentally, the charge generated by the compressive stress and the charge generated by the tensile stress have different polarities. For this reason, if charges generated by both stresses are taken out by the upper electrode 14, they cancel each other out, so that sufficient charges cannot be taken out. Therefore, the upper electrode 14 is formed only in a range where the compressive stress of the piezoelectric thin film layer 13 is generated.

[0057] According to the above configuration, the upper electrode 14 can take out only the charge generated by the compressive stress from the piezoelectric thin film layer 13 without canceling out the charge generated by the tensile stress. Therefore, the upper electrode 14 can extract a sufficient amount of charge from the piezoelectric thin film layer 13. As a result, even if the pressure of the external force transmitted to the metal diaphragm 11 is small, more electric charge can be taken out from the piezoelectric thin film layer 13, so that the slight pressure generated inside the cylinder of the internal combustion engine can be detected. can do. That is, the piezoelectric sensor 1 with further improved detection sensitivity can be realized.

Further, the upper electrode 14 is provided so as to individually take out the electric charge generated by the compressive stress generated in the piezoelectric thin film layer 13 due to the pressure and the electric charge generated by the tensile stress, respectively. Also good. Specifically, as shown in FIGS. 8 (a) and 8 (b), the upper electrode 14 is individually provided in the outer peripheral side region and the central region of the piezoelectric thin film layer 13, respectively. It is the composition which is. In FIGS. 8 (a) and 8 (b), the electrode provided in the outer peripheral region is defined as the external electrode 14b, and the electrode provided in the region closer to the central portion. The pole is shown as the center electrode 14a. In order to take out the electric charge generated from the piezoelectric thin film layer 13, a base layer 12 serving as a lower electrode may be provided on the lower surface of the piezoelectric thin film layer 13, as shown in FIGS. 8 (a) and 8 (b). Thus, the electrode 14c may be provided at an arbitrary position of the metal diaphragm 11. Electrical wiring (not shown) is connected to the electrodes 14a ', 14b, and 14c, respectively.

[0059] Thereby, electric charges generated by the compressive stress acting on the outer peripheral region of the piezoelectric thin film layer 13 are generated by the external electrode 14b and by the tensile stress acting on the region near the center of the piezoelectric thin film layer 13. The charges to be taken out can be taken out individually by the center electrode 14a.

[0060] Therefore, a sufficient amount of charge can be detected by adding the charges taken out individually. In order to obtain the amplified charge (output) by adding both, it is possible to invert the polarity of one charge. Thereby, the sensitivity of the piezoelectric sensor 1 can be further improved.

[0061] In order to form the upper electrode 14 in a range where the compressive stress of the piezoelectric thin film layer 13 is generated, the upper electrode 14 may be formed in an annular shape, or may be divided into two or more. It is good also as a composition.

In the above configuration, since the upper electrodes 14 are provided at both ends of the piezoelectric thin film layer 13, a space is formed between the upper electrodes 14. As a result, the piezoelectric thin film layer 13 can squeeze in the direction of the signal output rod 30 when receiving pressure. Therefore, electric charges can be generated by using the sag of the piezoelectric thin film layer 13 without providing the recess 32 in the signal output rod 30.

Further, the upper electrode 14 may be formed only in a range where the tensile stress of the piezoelectric thin film layer 13 is generated. Thereby, the upper electrode 14 can take out only the electric charge generated from the piezoelectric thin film layer 13 due to the tensile stress. Thereby, the same effect as the case where only the electric charge generated by the compressive stress is taken out can be obtained.

Further, as shown in FIGS. 9 (a) and 9 (b), the piezoelectric thin film layer 13 is formed by dividing the metal diaphragm 11 into ranges where compressive stress and tensile stress are generated, A structure in which the central electrode 14a and the external electrode 14b are formed corresponding to the divided piezoelectric thin film layer 13 may be employed. And charge generated by compressive stress or charge generated by tensile stress The polarity of either one of the charges is reversed. As a result, it is possible to take out a charge obtained by adding up the charge generated by the compressive stress and the charge generated by the tensile stress. Therefore, since the charge that can be taken out from the piezoelectric thin film layer 13 can be further increased, the piezoelectric sensor 1 with higher sensitivity can be realized.

[0065] In the present embodiment, the upper electrode 14 is formed on the piezoelectric thin film layer 13. The force is not particularly limited. The upper electrode 14 and the piezoelectric thin film layer 13 are connected by a signal line. It is also good. Thereby, the electric charge generated by the compressive stress or tensile stress generated in the piezoelectric thin film layer 13 can be detected via the signal line.

Here, as shown in FIG. 10, the piezoelectric thin film layer 13 may be formed only in a range where the compressive stress is generated in the metal diaphragm 11. As a result, only the compressive stress acts on the piezoelectric thin film layer 13, so that the upper electrode 14 can extract only the electric charge generated by the compressive stress from the piezoelectric thin film layer 13. Therefore, as described above, the upper electrode 14 can extract more charges from the piezoelectric thin film layer 13 even if the pressure of the external force transmitted to the metal diaphragm 11 is slight. That is, a highly sensitive piezoelectric sensor 1 can be realized. The shape of the piezoelectric thin film layer 13 may be a ring-shaped configuration, or may be a configuration divided into two or more. Alternatively, the piezoelectric thin film layer 13 may be formed only in a range where tensile stress is generated.

Here, as shown in FIGS. 11 and 12, the piezoelectric thin film layer 13 is directly formed on the front end wall 22d of the front housing 22, and the piezoelectric thin film layer 13 is formed on the front end wall 22d. A configuration may be adopted in which the portion is diaphragm processed. As a result, the piezoelectric thin film layer 13 can be squeezed toward the inside of the recess 32 formed in the signal output rod 30 in association with the sag of the front end wall 22d that receives external pressure. Then, charges are generated according to the sag of the piezoelectric thin film layer 13. Thus, since the housing 20 for mounting the piezoelectric element 10 can also function as the metal diaphragm 11, the metal diaphragm 11 becomes unnecessary. Therefore, since the configuration of the piezoelectric element 10 can be simplified, the piezoelectric sensor can be reduced in size and the cost can be reduced.

[0068] Examples of the diaphragm processing method include machining, chemical etching, electric discharge machining, and laser cage. Then, by the above-mentioned cage, the front end wall 22d The thickness of the portion where the piezoelectric thin film layer 13 is formed is preferably 0.005 mm or more and 10 mm or less.

Further, as shown in FIG. 13, a recess 22e is provided in the front end wall 22d of the front case 22 on which the piezoelectric thin film layer 13 is formed, and the upper electrode 14 is provided only above the edge portion 22f in the recess 22e. It is good also as the provided structure. As a result, when the pressure receiving portion 22g formed on the upper surface in the concave portion 22e receives pressure and stagnation occurs, the piezoelectric thin film layer 13 located above the edge portion 22f generates compressive stress and charges are generated. appear. Then, the upper electrode 14 can take out the charges generated by this compressive stress. Thus, sufficient charges can be taken out by using the stagnation of the casing 20 without using the metal diaphragm 11. Therefore, a highly sensitive piezoelectric sensor 1 can be realized with a simple configuration.

[0070] As described above, since a space is formed between the upper electrodes 14, the piezoelectric thin film layer 13 can be sandwiched in the direction of the signal output rod 30 when receiving pressure. Therefore, the signal output rod 30 is not required to be provided with the recess 32.

Further, the front end wall 22d for forming the piezoelectric thin film layer 13 may be formed of a semiconductor such as silicon. By using silicon, mass production becomes possible, and an inexpensive and small piezoelectric sensor 1 can be realized. FIG. 14 is a cross-sectional view showing a schematic configuration of the piezoelectric sensor 1 when the front end wall 22d shown in FIG. 13 is formed of silicon.

Here, in the present embodiment, the structure in which the piezoelectric thin film layer 13 is formed on the underlayer 12 may be configured such that the piezoelectric thin film layer 13 is directly formed on the metal diaphragm 11. When the base layer 12 is provided as in the present embodiment, the diaphragm is not limited to a metal. For example, a semiconductor such as a polymer, a metal oxide, a metal nitride, or silicon may be used. good.

[0073] The material of the piezoelectric thin film layer 13 used in this embodiment is preferably aluminum nitride (AIN). The reason for this is that aluminum nitride has stable piezoelectric properties even at high temperatures and has little impact on the environment because it does not use heavy metals such as lead. The piezoelectric thin film layer 13 may be made of another material as long as it does not have a Curie temperature. This “piezoelectric material having no Curie temperature” is a material that has piezoelectric characteristics and does not cause polar dislocation as the temperature rises. Examples include substances having a crystalline structure. Specific examples of the substance having the crystal structure of the wurtzite structure include aluminum nitride (A1N) and zinc oxide (ZnO).

[0074] Such a piezoelectric material does not lose its piezoelectric properties until the crystal melts or sublimes. In addition, a substance having a crystal structure of the wurtzite structure has piezoelectric characteristics because there is no symmetry in the crystal, and since it is not a ferroelectric substance, there is no Curie temperature. Therefore, the piezoelectric element made of the above-described piezoelectric material has excellent heat resistance and does not deteriorate the piezoelectric characteristics. Even if it is exposed to a high temperature close to 500 ° C. like the inside of a cylinder of an internal combustion engine, the piezoelectric element As a function never lose. Therefore, it is possible to use the internal combustion engine cylinder without using a piezoelectric element cooling device. As described above, the piezoelectric element made of the above-described piezoelectric material has excellent heat resistance and does not deteriorate the piezoelectric characteristics even at high temperatures. It is also excellent in workability and suitable for thin film production.

Here, the Curie temperature does not exist! A method for forming a thin film of piezoelectric material can be realized by using a known technique. Specifically, oxide-based, carbon-based, nitrogen-based or boride-based ceramic sintered bodies, insulating substrates with quartz glass power, and heat-resistant metal material cards such as Inconel or SUS630. A thin film can be formed on a conductive substrate formed by growing the piezoelectric ceramic into a single crystal while controlling the polarity.

In addition, the thickness of the piezoelectric thin film layer 13 of the piezoelectric sensor 1 of the present invention is preferably in the range of 0.1111 to 100111. Further, it is more preferably 0.5 m or more and 20 μm or less: more preferably m or more and 10 m or less. When the thickness force of the piezoelectric thin film layer 13 is less than 0.1 m and a short circuit occurs between the underlayer 12 and the upper electrode 14, the film thickness becomes longer than 100 μm and the film formation time becomes long. .

In addition, the piezoelectric thin film layer 13 has a dipole orientation degree of preferably 75% or more and more preferably 90% or more in order to maintain good piezoelectric characteristics. The degree of dipole orientation is the proportion of crystal columns that form electric dipoles that are positive or negative in the thin film surface in the same direction. If the polarity direction of the crystal column is completely random, the piezoelectricity of each crystal column cancels each other, and the piezoelectricity disappears in the entire thin film. When the dipole orientation of the piezoelectric thin film layer 13 is less than 75%, the apparent piezoelectric constant The number d is less than half of the dipole orientation degree of 100%, and the pressure of the piezoelectric thin film layer 13 is reduced.

33

This is because the electric characteristics deteriorate and the pressure cannot be detected well. If the dipole orientation degree is 75% or more, sufficient piezoelectric characteristics can be secured.

[0078] In order to set the dipole orientation to 75% or more, it is necessary to easily align the first atoms when the crystal column grows, and the material of the underlayer 12 is the same as the material of the piezoelectric thin film layer 13. When the same component metal, for example, A1N is used for the piezoelectric thin film layer 13, the base layer 12 is preferably Al, and when the piezoelectric thin film layer 13 is ZnO, the base layer 12 is preferably Zn. When the underlayer 12 is a multilayer, it is preferable that the uppermost layer, that is, the layer in contact with the piezoelectric thin film layer 13, be made of a metal having the same component as the material of the piezoelectric thin film layer 13.

In the present embodiment, the pressure is transmitted from the force metal diaphragm 11 using the metal diaphragm 11 as the pressure transmission member to the piezoelectric thin film layer 13 via another member such as a pressure transmission rod. Even so, it is possible to realize a piezoelectric sensor 1 that has excellent heat resistance and does not require a cooling means.

[0080] The pressure transmission member is not limited to the metal diaphragm 11, but may be ceramics such as a glass substrate. Specific ceramics include acid-ceramics such as acid aluminum, acid magnesium, acid zirconium oxide, titanium oxide, yttrium oxide, and oxygen key, aluminum nitride, silicon nitride, Examples thereof include nitride ceramics such as boron nitride and gallium nitride, carbide ceramics such as silicon carbide and tungsten carbide, and silicide ceramics such as molybdenum disilicide. Thereby, compared with a metal, corrosion resistance, heat resistance, pressure resistance, etc. improve. The experimental results of examining the characteristics of the piezoelectric sensor when using a glass substrate will be described later.

Example

[0081] With respect to the piezoelectric sensor 1 according to the present embodiment, an experiment was performed to measure the amount of charge generated from the piezoelectric element 10 with respect to the pressure applied to the piezoelectric element 10.

FIG. 15 shows the measurement system used in this experiment. Specifically, the piezoelectric element 10 is covered with a cylindrical glass tube, and a sealed space equal to the atmospheric pressure is created inside. The upper electrode 14 of the piezoelectric element 10 and the amplifier are connected by a low noise coaxial cable, and the amplifier is connected to the oscilloscope. In this experiment, the thickness of 0.2 mm was measured by sputtering. A type in which an upper electrode 14 having a thickness of 200 nm and aluminum nitride (piezoelectric thin film layer 13) having a thickness of 1 μm are formed on a metal diaphragm 11 of Nconel 601 and the aluminum nitride on the metal diaphragm 11. Two types of piezoelectric elements 10 of type B were used.

[0083] In the above measurement system, the atmospheric pressure in the sealed space is extracted at once and the pressure is rapidly reduced. At this time, the metal diaphragm 11 of the piezoelectric element 10 receives a force in the direction of the sealed space due to the sudden pressure reduction, and stagnation occurs. Then, accompanying the sag of the metal diaphragm 11, the piezoelectric thin film layer 13 swells, and stress is generated inside. Electric charges are generated from the piezoelectric thin film layer 13 by the stress generated in the piezoelectric thin film layer 13. The charge generated at this time is taken out by the upper electrode 14 and can be measured with an oscilloscope.

FIG. 16 is a waveform diagram obtained by measuring the amount of charge taken out from the piezoelectric element 10 when the sealed space is rapidly depressurized. FIG. 17 is a graph showing the relationship between the force applied to the piezoelectric element 10 and the charge amount obtained from the signal amplitude force shown in the waveform diagram of FIG. 16. FIG. 18 shows the relationship between the force and the charge amount. It is the graph which showed the relationship between the pressure and output voltage which converted.

From the results of FIG. 17, it was found that the force applied to the metal diaphragm 11 and the amount of charge taken out from the upper electrode 14 have a proportional relationship. The slope of the straight line indicating this proportional relationship indicates the apparent piezoelectric constant d (pC / N), that is, the piezoelectric constant of the piezoelectric element 10.

33

The Here, in the conventional configuration that does not use the stagnation effect of the piezoelectric element 10, the piezoelectric constant d

33 had d = 2. In contrast, the stagnation effect of the piezoelectric element 10 in the present embodiment

33

Is used, the piezoelectric constant d of the piezoelectric element 10 is d = 30.808 for the A type above.

33 33

In the above B type, d = 22.305. In this way, the stagnation effect of the piezoelectric element 10 is used.

33

As a result, the piezoelectric constant d of the piezoelectric element 10 is greatly increased.

33

Next, the configuration shown in FIGS. 8 (a) and 8 (b), that is, the outer electrode 14b in the outer peripheral region on the upper surface of the piezoelectric thin film layer 13, and the central electrode 14a in the region closer to the center, respectively. An experiment was conducted to measure the voltage output from the piezoelectric element 10 (piezoelectric thin film layer 13) with respect to the pressure applied to the piezoelectric element 10 in a configuration in which the electrode 14c is provided at an arbitrary position of the metal diaphragm 11 provided separately. .

FIG. 19 shows the measurement system used in this experiment. This measurement system is shown in Fig. 15 above. In this case, an aluminum nitride (piezoelectric thin film layer 13) with a thickness of l / zm was formed on a metal diaphragm 11 with a thickness of 0.2 mm, and a thickness of 0.05- A piezoelectric element provided with a 0.3 μm central electrode 14a and an external electrode 14b is used. An electrode 14c having a thickness of 0.05 to 0.3 m is provided at one end of the metal diaphragm. The external electrode 14b and the electrode 14c are connected to the amplifier 1 through a low-noise coaxial cable, and the center electrode 14a and the electrode 14c are connected to the amplifier 2 through a low-noise coaxial cable, and each of the amplifiers 1 and 2 is connected to an oscilloscope. Connect with.

FIG. 20 is a graph showing a waveform of pressure output from the piezoelectric thin film layer 13 when pressure is applied to the piezoelectric element 10 in the measurement system. In the measurement system, the pressure is applied from the direction opposite to the direction applied to the piezoelectric element 10 in order to easily obtain the output characteristics of the piezoelectric element 10.

[0089] As shown in FIG. 20, it was found that the output signal can be detected simultaneously from the external electrode 14b connected to the amplifier 1 and the central electrode 14a connected to the amplifier 2. Thus, it was found that even when a plurality of electrodes were used, the output signal could be detected simultaneously in each. This makes it possible to add individually detected output signals by matching the polarities of the output signals. Therefore, even if the pressure applied from the outside is small, a larger output can be obtained, so that the sensitivity of the piezoelectric sensor can be improved.

[0090] Next, an experiment was conducted to examine the temperature characteristics and frequency characteristics of the piezoelectric sensor 1 that is effective in the present embodiment.

FIG. 21 is a graph obtained by measuring the change in piezoelectric response to the temperature change of the piezoelectric sensor 1. The piezoelectric response can be considered by measuring the amount of charge per 1-Euton (N), that is, the piezoelectric constant. As shown in FIG. 21, it was found that the piezoelectric sensor 1 can maintain stable piezoelectric characteristics up to 600 ° C. Thereby, according to the piezoelectric sensor 1 in the present embodiment, stable measurement can be performed in a high-temperature environment of about 500 ° C. such as inside the structure.

FIG. 22 is a graph showing frequency characteristics in the piezoelectric sensor 1. As shown in FIG. 22, it was found that measurement was possible from 0.3 Hz to: LOOHz. [0093] Next, in the piezoelectric sensor 1 according to the present embodiment, the piezoelectric element 10 (piezoelectric thin film layer 13) cover against the pressure applied to the piezoelectric element 10 when the glass substrate 1la is used as the pressure transmitting member. An experiment was carried out to measure the amount of charge generated from the above.

FIG. 23 (a) is a plan view showing a schematic configuration of the piezoelectric element 10 when the glass substrate 11a is used as the pressure transmission member in the piezoelectric sensor 1, and FIG. It shows the measurement system used. In this measurement system, an aluminum nitride (piezoelectric thin film layer 13) having a thickness of 1 m is formed on a glass substrate 11a having a thickness of 1 mm, and an upper electrode 14 having a thickness of 0.05 to 0. is formed thereon. The provided piezoelectric element is used. A lower electrode 12 is provided between the glass substrate 11a and the piezoelectric thin film layer 13. Then, the lower electrode 12 and the upper electrode 14 are connected to the amplifier by a low noise coaxial cable, and the amplifier is connected to the oscilloscope.

FIG. 24 is a graph showing the amount of charge generated from the piezoelectric thin film layer 13 when pressure is applied to the piezoelectric element 10 in the measurement system. From the results shown in the figure, it was found that the force applied to the glass substrate 11a and the amount of charge taken out from the piezoelectric thin film layer 13 are proportional to each other. The piezoelectric response, ie, the piezoelectric constant d (pCZ

33

When N) is calculated, d = 75.4. Here, a conventional structure using aluminum nitride is used.

33

In the results, d = 2 as described above. In this way, a glass substrate is used for the pressure transmission member

33

Even in such a case, it was found that by using the stagnation effect of the piezoelectric element 10, the value of the piezoelectric constant d of the piezoelectric element 10 was significantly increased.

33

[0096] As described above, the piezoelectric sensor of the present invention is a piezoelectric sensor including a piezoelectric element that receives a pressure on the first surface and generates electric charges by the pressure, and is opposite to the first surface. In this configuration, a space is formed in the region where the second surface faces.

Accordingly, the piezoelectric element can be encased in the space according to the pressure generated outside, and the electric charge according to this stagnation can be generated accurately. Therefore, it is possible to provide a piezoelectric sensor that can obtain high sensitivity by using a piezoelectric element having low sensitivity.

The piezoelectric sensor of the present invention further includes a conductive member on the second surface of the piezoelectric element, and a connection surface where the conductive member is electrically connected to the piezoelectric element is the piezoelectric element. It is preferable that only the region on the outer peripheral side of the second surface of the element is in contact.

[0099] According to the above configuration, since the conductive member is in contact with only the outer peripheral region of the surface that generates the charge opposite to the surface that receives the pressure of the piezoelectric element, the charge generating side of the piezoelectric element is generated. A space is formed. Therefore, the piezoelectric element that has received the pressure can squeeze in the direction of the pressure, that is, the direction of the space, and generates an electric charge according to the stress generated in the inside. Then, the pressure applied to the piezoelectric element can be detected by the conductive member taking out the electric charge generated from the piezoelectric element. In this way, the piezoelectric element can be squeezed in the direction of the space without being obstructed by the conductive member that takes out the electric charge, and therefore it is possible to accurately generate electric charges according to the pressure. Therefore, a highly sensitive piezoelectric sensor can be obtained even when a piezoelectric element with low sensitivity is used.

[0100] In the piezoelectric sensor of the present invention, the conductive member is a conductive rod-shaped member, and one end surface in the axial direction serves as the connection surface, and a recess is formed at a position near the center of the connection surface. I like it! /

[0101] According to the above configuration, the recess is formed in the conductive member at a position near the center of the connection surface between the conductive member and the piezoelectric element. As a result, a space is formed on the side opposite to the surface receiving the pressure of the piezoelectric element. Therefore, when the piezoelectric element receives pressure from the outside, the piezoelectric element can be squeezed in the direction of pressure according to the pressure, that is, in the inner direction of the recess of the conductive member without being obstructed by the conductive member. A stress corresponding to the sag of the piezoelectric element is generated inside the piezoelectric element, and an electric charge corresponding to the stress is generated. In this way, the piezoelectric element can be sandwiched by forming a recess in the conductive member.

[0102] The piezoelectric sensor of the present invention further includes a housing for mounting the piezoelectric element, wherein an opening formed in a front end wall of the housing is located on the first surface, The piezoelectric element is preferably fixed between the front end wall and the rod-shaped member by the rod-shaped member disposed on the second surface.

[0103] According to the above configuration, the opening is formed in the front end wall of the housing for mounting the piezoelectric element, and the opening is located on the first surface. The piezoelectric element is fixed between the front end wall and the rod-shaped member by the rod-shaped member disposed on the second surface. Thus, the piezoelectric element is fixed between the front end wall of the housing where the opening is formed and the rod-shaped member with the pressure receiving surface (first surface) exposed to the opening force. Is done. Therefore, the piezoelectric element can receive pressure from the outside and can squeeze only in the direction of the pressure.

[0105] In the piezoelectric sensor of the present invention, the piezoelectric element includes an upper electrode that extracts electric charges generated from the piezoelectric element, and the upper electrode is generated inside the piezoelectric element by the action of the pressure. It is preferable that an electric charge generated by compressive stress or tensile stress is taken out.

[0106] The piezoelectric element generates a compressive stress and a tensile stress due to stagnation. Specifically, when pressure is applied to the piezoelectric element and stagnation occurs, the vicinity of the center of the piezoelectric element is pulled in both directions. Thereby, tensile stress is generated near the center of the piezoelectric element. On the other hand, the vicinity of both ends of the piezoelectric element is compressed in the contraction direction. As a result, compressive stress is generated near both ends of the piezoelectric element.

By the way, the charge generated by the compressive stress in the piezoelectric element and the charge generated by the tensile stress have different polarities. Therefore, if the electric charges generated by both stresses are taken out by the electrode layer, they cancel each other out, so that it is impossible to take out enough electric charges!

[0108] According to the above configuration, the upper electrode is provided so as to take out the electric charge generated by the compressive stress or tensile stress of the piezoelectric element.

Accordingly, for example, the upper electrode can take out the piezoelectric element force that does not cancel the charge generated by the compressive stress with the charge generated by the tensile stress. Therefore, the upper electrode can extract a sufficient amount of electric charge with the piezoelectric element force. As a result, even if the pressure applied to the piezoelectric element is small, more electric charge can be taken out with the piezoelectric element force, so that even a slight pressure generated outside can be detected.

[0110] In the piezoelectric sensor of the present invention, the piezoelectric element includes a piezoelectric thin film layer that generates a charge upon receiving a pressure, and an upper electrode that extracts the charge generated from the piezoelectric thin film layer. It is preferable that the piezoelectric thin film layer is in contact with only the outer peripheral region of the second surface.

[0111] According to the above configuration, the upper electrode is in contact with only the outer peripheral region of the surface that generates a charge opposite to the pressure receiving surface of the piezoelectric thin film layer. A space is formed on the side where the load is generated. For this reason, the piezoelectric thin film layer that has received the pressure can swell in the direction of pressure, that is, the direction of the space, and generates an electric charge according to the stress generated therein. The pressure applied to the piezoelectric element can be detected by the upper electrode taking out the electric charge generated from the piezoelectric thin film layer.

[0112] The piezoelectric sensor of the present invention includes a housing for mounting the piezoelectric element, and the piezoelectric element includes a piezoelectric thin film layer that generates a charge upon receiving pressure, It is preferable that the film layer is formed on the front end wall of the casing, and the piezoelectric thin film layer on the front end wall is formed, and the portion is covered so as to function as a diaphragm! /. Specifically, the thickness of the front end wall on which the piezoelectric thin film layer is formed is preferably 0.005 mm or more and 10 mm or less.

[0113] According to the above configuration, the piezoelectric thin film layer that generates an electric charge by receiving pressure is directly formed on the front end wall of the casing. The front end wall on which the piezoelectric thin film layer is formed is processed so as to function as a diaphragm. Here, the diaphragm is a film-like body that deforms in response to an applied pressure.

[0114] Thus, the front end wall that receives pressure can be squeezed in the direction of pressure, and the piezoelectric thin film layer can be squeezed along with this stagnation. As described above, since the piezoelectric thin film layer can be formed directly on the housing, the structure of the piezoelectric element can be simplified. Therefore, it is possible to obtain a piezoelectric sensor with a small size, low cost, and high sensitivity.

[0115] The piezoelectric sensor of the present invention includes a housing for mounting the piezoelectric element. The piezoelectric element includes a pressure transmission member positioned on the first surface side and the second surface. A piezoelectric thin film layer that generates a charge upon receiving pressure, and an upper electrode that extracts electric charge generated from the piezoelectric thin film layer, and the housing has an opening, and the pressure transmission The member includes the opening portion so that the piezoelectric thin film layer and the upper electrode are accommodated in the housing, and only a region on the outer peripheral side of the pressure transmission member is in contact with a region around the opening. It is preferred to be provided in.

[0116] According to the above configuration, the pressure transmission member that receives pressure is provided in the opening so as to be in contact with the region around the opening in the housing that accommodates the piezoelectric thin film layer and the upper electrode. [0117] Thus, the casing and the pressure transmission member do not come into contact with each other in the region on the central side other than the region on the outer peripheral side. That is, a space is formed in the inner direction of the housing, that is, on the side where electric charges are generated in the piezoelectric thin film layer. Therefore, the pressure transmission member that has received the pressure can squeeze in the direction of the pressure, that is, the direction of the space, and the piezo-electric thin film layer can squeeze along with the stagnation. Thus, by forming the space on the surface opposite to the surface that receives the pressure, the piezoelectric element can be held in the direction of the space without being obstructed.

[0118] In the piezoelectric sensor of the present invention, it is preferable that a conductive wire is connected to the upper electrode.

[0119] According to the above configuration, since the conducting wire is connected to the upper electrode, the electric charge generated from the piezoelectric thin film layer is taken out by the conducting wire. Then, the pressure applied to the pressure transmission means can be detected by detecting the extracted electric charge.

[0120] In the piezoelectric sensor of the present invention, the upper electrode is an annular member, and one surface serves as a connection surface connected to the piezoelectric thin film layer, and this connection surface is located on the second surface of the piezoelectric thin film layer. It is preferable to touch only the outer peripheral area.

[0121] According to the above configuration, the annular upper electrode is in contact with only the outer peripheral region of the second surface of the piezoelectric thin film layer, so that a hollow space is formed inside the upper electrode. Therefore, the piezoelectric thin film layer can be sandwiched in the spatial direction of the upper electrode.

[0122] In the piezoelectric sensor of the present invention, the piezoelectric element includes an upper electrode that extracts electric charges generated from the piezoelectric element, and the upper electrode is generated inside the piezoelectric element by the action of the pressure. It is preferable that the electric charge generated by the compressive stress and the electric charge generated by the tensile stress are individually taken out.

[0123] The piezoelectric element receives a stagnation caused by an external pressure, and generates a compressive stress and a tensile stress therein. However, the charge generated by the compressive stress in the piezoelectric element and the charge generated by the tensile stress in the piezoelectric element have different polarities, so if the charge generated by both stresses is taken out by the electrode layer, they will cancel each other out. I can't get enough charge.

[0124] On the other hand, according to the above configuration, the upper electrode is provided so as to individually take out the charge generated by the compressive stress and the charge generated by the tensile stress. [0125] Accordingly, since the charge generated by the compressive stress and the charge generated by the tensile stress can be taken out separately, a sufficient amount of charge obtained by adding both can be detected. In order to obtain an amplified charge (output) by adding both, it is possible to invert the polarity of one charge. As a result, even if the pressure applied to the piezoelectric element is small, more electric charge can be taken out with the entire force of the piezoelectric element, so that even a slight pressure generated outside can be detected. That is, the sensitivity of the piezoelectric sensor can be further improved.

[0126] In the piezoelectric sensor of the present invention, the piezoelectric element includes a piezoelectric thin film layer that generates a charge upon receiving a pressure, and an upper electrode that extracts the charge generated from the piezoelectric thin film layer. It is preferable that the piezoelectric thin film layer is individually provided in an outer peripheral region and a central region on the second surface.

[0127] Here, the piezoelectric element is subjected to the stagnation caused by the pressure of an external force, and compressive stress is generated in the outer peripheral side region of the second surface, and the central portion of the second surface is Tensile stress is generated in the region close to it.

[0128] According to the above configuration, the upper electrode is individually provided in the outer peripheral region and the central region on the surface that generates charges opposite to the surface receiving the pressure of the piezoelectric thin film layer. It is possible to individually take out the charge generated by the compressive stress and the charge generated by the tensile stress.

Therefore, a sufficient amount of charges obtained by adding the charges generated by compressive stress and tensile stress can be detected by a method of reversing the polarity of one of the charges. As a result, even if the pressure applied to the piezoelectric element is small, more charges can be taken out from the piezoelectric element, so that even a slight pressure generated outside can be detected. That is, the sensitivity of the piezoelectric sensor can be further improved.

[0130] The specific embodiments or examples made in the detailed description of the invention are to clarify the technical contents of the present invention, and are limited to such specific examples. Therefore, various modifications may be made within the scope of the spirit of the present invention and the claims described below.

Industrial applicability Since the piezoelectric sensor of the present invention can detect the vibration, pressure, etc. of an object to be measured in a high temperature environment, it can be used for measuring pressure fluctuations of high temperature and high pressure fluid in pipes and tanks in plants such as nuclear power plants. Is also applicable.

Claims

The scope of the claims

[1] In a piezoelectric sensor having a piezoelectric element that receives pressure on the first surface and generates electric charge by the pressure,

A piezoelectric sensor characterized in that a space is formed in a region facing a second surface opposite to the first surface.

[2] A conductive member is provided on the second surface of the piezoelectric element, and a connection surface electrically connected to the piezoelectric element of the conductive member is an outer peripheral side of the second surface of the piezoelectric element. The piezoelectric sensor according to claim 1, wherein the piezoelectric sensor is in contact with only the region.

[3] The conductive member is a conductive rod-shaped member, wherein one end surface in the axial direction serves as the connection surface, and a recess is formed at a position near the center of the connection surface. The piezoelectric sensor according to claim 2.

[4] A housing for mounting the piezoelectric element is provided, and an opening formed in a front end wall of the housing is located on the first surface and disposed on the second surface. 4. The piezoelectric sensor according to claim 3, wherein the piezoelectric element is fixed between the front end wall and the rod-shaped member by a rod-shaped member.

[5] The piezoelectric element is provided with an upper electrode for extracting electric charges generated from the piezoelectric element, and the upper electrode is generated by a compressive stress or a tensile stress generated in the piezoelectric element by the action of the pressure. The piezoelectric sensor according to claim 1, wherein the piezoelectric sensor is provided so as to take out a charge to be removed.

[6] The piezoelectric element includes a piezoelectric thin film layer that generates a charge under pressure and an upper electrode that extracts the charge generated from the piezoelectric thin film layer,

3. The piezoelectric sensor according to claim 1, wherein the upper electrode is in contact with only an outer peripheral region of the second surface of the piezoelectric thin film layer.

[7] A housing for mounting the piezoelectric element is provided,

The piezoelectric element includes a piezoelectric thin film layer that generates a charge upon receiving pressure, and the piezoelectric thin film layer is formed on a front end wall of the casing, and the piezoelectric thin film layer is formed on the front end wall. The part is processed to function as a diaphragm. The piezoelectric sensor according to claim 1 or 2, wherein:

[8] includes a housing for mounting the piezoelectric element;

The piezoelectric element is generated from the pressure transmission member located on the first surface side, the piezoelectric thin film layer located on the second surface side, which generates electric charge under pressure, and the piezoelectric thin film layer. And an upper electrode for extracting electric charge,

The casing has an opening, and the pressure transmission member includes the piezoelectric thin film layer and the upper electrode accommodated inside the casing, and only the outer peripheral region of the pressure transmission member is opened. The piezoelectric sensor according to claim 1, wherein the piezoelectric sensor is provided in the opening so as to be in contact with a region around the portion.

[9] A conductor is connected to the upper electrode! The piezoelectric sensor according to claim 8, wherein the piezoelectric sensor is wound.

[10] The upper electrode is an annular member, and one surface serves as a connection surface connected to the piezoelectric thin film layer, and this connection surface is in contact with only the outer peripheral region of the second surface of the piezoelectric thin film layer. The piezoelectric sensor according to claim 9, wherein:

[11] The piezoelectric element includes an upper electrode for extracting electric charges generated from the piezoelectric element, and the upper electrode is charged and tensile generated by compressive stress generated in the piezoelectric element by the action of the pressure. 3. The piezoelectric sensor according to claim 1, wherein the piezoelectric sensor is provided so as to individually take out the electric charges generated by the stress.

[12] The piezoelectric element includes a piezoelectric thin film layer that generates a charge under pressure, and an upper electrode that extracts the charge generated from the piezoelectric thin film layer,

3. The piezoelectric sensor according to claim 1, wherein the upper electrode is individually provided in a region on the outer peripheral side and a region near the center of the second surface of the piezoelectric thin film layer. .