JP7428568B2 - Method for manufacturing piezoelectric element membrane of ultrasonic sensor and ultrasonic sensor - Google Patents

Description

The present disclosure relates to a method for manufacturing a dielectric material, a dielectric material, and an ultrasonic sensor.

A piezoelectric element used in an ultrasonic sensor or the like is made of a dielectric material. Lithium niobate (LiNbO ₃ ) is known as a dielectric material that has a high Curie point and is suitable for use in high-temperature environments.

Patent Document 1 discloses an ultrasonic thickness sensor including a piezoelectric film made of lithium niobate. Furthermore, Patent Document 1 discloses that powders of niobium oxide (Nb ₂ O ₃ ) and lithium carbonate (Li ₂ CO ₃ ) are blended to have a target lithium niobate composition, mixed, and then fired. , it is described that lithium niobate powder is obtained.

Japanese Patent Application Publication No. 2013-197541

By the way, the product (dielectric material) obtained by firing (synthesizing) a mixture of lithium carbonate and niobium oxide is lithium niobate (dielectric material) having a composition in which the molar ratio of lithium and niobium is Li:Nb = 1:1. It is known that the higher the content of LiNbO ₃ ), the higher the polarization efficiency. In order to obtain a product with high polarization efficiency, the raw materials lithium oxide carbonate powder and niobium oxide powder are blended so that the molar ratio of lithium and niobium is Li:Nb = 1:1. It was thought that firing (synthesis) would be sufficient. However, in this case, it was found that a fired product (dielectric material) having a polarization efficiency as high as expected could not be obtained.

When the polarization efficiency of a dielectric material is low, the piezoelectric performance of a piezoelectric material obtained by polarizing the dielectric material is relatively low, and it is difficult to improve the sensitivity of an ultrasonic sensor using the piezoelectric material.

In view of the above circumstances, it is an object of at least one embodiment of the present invention to provide a method for manufacturing a dielectric material, a dielectric material, and an ultrasonic sensor that can produce an ultrasonic sensor with good sensitivity. .

A method for manufacturing a dielectric material according to at least one embodiment of the present invention includes:
mixing lithium carbonate and niobium oxide to obtain a mixture such that the molar ratio of lithium to niobium is greater than 50/50 and less than or equal to 56/44;
firing the mixture to obtain a fired product in which LiNbO ₃ crystals and Li ₃ NbO ₄ crystals coexist;
Equipped with.

Further, the dielectric material according to at least one embodiment of the present invention is
LiNbO ₃ crystals and Li ₃ NbO ₄ crystals coexist.

Further, an ultrasonic sensor according to at least one embodiment of the present invention includes:
It includes a piezoelectric element made of the dielectric material described above and configured to generate ultrasonic waves when driven by an electrical signal.

According to at least one embodiment of the present invention, a method for manufacturing a dielectric material, a dielectric material, and an ultrasonic sensor that can produce an ultrasonic sensor with good sensitivity are provided.

FIG. 1 is a schematic configuration diagram of an ultrasonic sensor according to an embodiment. 1 is a diagram showing a part of a phase diagram of an oxide (Li--Nb--O system) containing lithium and niobium. This is an example of an X-ray diffraction chart of a fired product obtained by firing a raw material mixture. This is an example of an X-ray diffraction chart of a fired product obtained by firing a raw material mixture. It is a graph showing the relationship between the molar ratio of lithium and niobium in the raw material mixture and the polarization efficiency of the sintered body.

Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described as the embodiments or shown in the drawings are not intended to limit the scope of the present invention thereto, and are merely illustrative examples. do not have.

In this specification, a dielectric material refers to a material that has dielectric properties, and is a concept that also includes materials that have piezoelectric properties. That is, the piezoelectric body used for producing the piezoelectric element, the sintered body before polarization treatment, the molded body before sintering, and the fired product before molding are all included in the "dielectric material."

(Configuration of ultrasonic sensor)
FIG. 1 is a schematic configuration diagram of an ultrasonic sensor including a piezoelectric element formed of a dielectric material according to an embodiment. The ultrasonic sensor 1 shown in FIG. 1 is an ultrasonic sensor for inspecting an object to be inspected 30, and includes a piezoelectric element 2, a pair of electrodes 4 and 5, and lead wires 6 and 8. The ultrasonic sensor 1 may be a thickness measurement sensor configured to measure the thickness (wall thickness) of the inspection object 30 (for example, piping).

The piezoelectric element 2 has a membrane shape and is provided so as to be sandwiched between a pair of electrodes 4 and 5. That is, the membrane-type piezoelectric element 2 is formed on the surface of the thin plate-like electrode 5, and the other electrode 4 is formed on the surface of the piezoelectric element 2. Note that the ultrasonic sensor 1 connects the test object to the test object through an adhesive layer (not shown) provided between one of the pair of electrodes 4 and 5 (electrode 5 in the illustrated example) and the test object 30. It may be attached to the object 30.

Lead wires 6 and 8 are connected to the pair of electrodes 4 and 5, so that an electric signal (voltage) can be applied to the piezoelectric element 2 via the pair of electrodes 4 and 5. The piezoelectric element 2 is configured to be driven by an applied electric signal to generate ultrasonic waves, and to irradiate the object to be inspected 30 with the ultrasonic waves.

In the ultrasonic sensor 1 having such a configuration, as described above, an electric signal (voltage) is applied to the piezoelectric element 2 to generate an ultrasonic wave, which is emitted to the object to be inspected 30, and the object to be inspected 30 is emitted from the object to be inspected. The piezoelectric element 2 receives the reflected waves (ultrasonic waves) and detects the potential. Then, the thickness of the object to be inspected 30 can be measured based on the time from when the piezoelectric element 2 emits an ultrasonic wave to when the reflected wave is received, and the speed of sound in the object to be inspected 30 .

The dielectric material constituting the piezoelectric element 2 described above is characterized in that LiNbO ₃ crystals and Li ₃ NbO ₄ crystals coexist in the dielectric material. A method for manufacturing this dielectric material will be described below.

(Method for manufacturing dielectric material)
A method for manufacturing a dielectric material according to an embodiment includes firing a mixture of lithium carbonate (Li ₂ CO ₃ ) powder and niobium oxide (Nb ₂ O ₅ ) powder as raw material powder to produce a fired product (dielectric material). (firing step).
The method for manufacturing a dielectric material according to one embodiment may further include a step of molding the above-described fired product to obtain a molded body (dielectric material) (molding step).
Further, the method for manufacturing a dielectric material according to one embodiment may further include a step of firing the above-described molded body to obtain a sintered body (dielectric material) (sintering step).
Further, the method for manufacturing a dielectric material according to one embodiment may further include a step of subjecting the above-mentioned sintered body to a polarization treatment to obtain a piezoelectric material (dielectric material) (polarization step).
Note that the piezoelectric element 2 described above may be manufactured using the piezoelectric body obtained in this manner.

(Baking step)
In the firing step, lithium carbonate (Li ₂ CO ₃ ) powder and niobium oxide (Nb ₂ O ₅ ) powder, which are raw material powders, are mixed in a prescribed mixing ratio to obtain a mixture, and the mixture is fired. The above-mentioned compounding ratio is such that the molar ratio of lithium to niobium is more than 50/50 and less than 56/44, or the molar ratio of lithium to niobium is more than 51/49 and less than 56/44. Lithium (Li ₂ CO ₃ ) powder and niobium oxide (Nb ₂ O ₅ ) powder are mixed to obtain a mixture. By firing a mixture having the above-mentioned mixing ratio, a fired product in which LiNbO ₃ crystals and Li ₃ NbO ₄ crystals coexist can be obtained.

Here, FIG. 2 is a diagram showing a part of a phase diagram of an oxide (Li--Nb--O system) containing lithium and niobium. The horizontal axis indicates the molar ratio of niobium to the total amount of lithium and niobium contained in the oxide. For example, when the value on the horizontal axis is 46, the molar ratio of lithium to niobium is 54/46.

In an oxide containing lithium (Li) and niobium (Nb), a region where the molar ratio of Nb to Li is 50/50 or less is a region in which LiNbO ₃ with a non-stoichiometric composition is generated (region in the phase diagram of FIG. 2). (a)) is included. Therefore, when the blending ratio of lithium and niobium in the raw material powder is within this range (a), the amount of LiNbO ₃ produced in the fired product having a composition in which the molar ratio of lithium and niobium is 1:1 is reduced. Furthermore, since lithium has a small atomic weight and easily volatizes during high-temperature synthesis (during firing), some Li atoms are removed from the LiNbO ₃ crystal structure. Therefore, if a raw material mixture in which the molar ratio of lithium and niobium is Li:Nb=1:1 (that is, the molar ratio of Li to Nb is 50/50) is fired (synthesized), the fired product will contain LiNbO ₃ ( It is considered that the content of crystals with a composition of Li:Nb=1:1) becomes unexpectedly small.

If the content ratio of LiNbO ₃ in the fired product is low, the polarization efficiency will be low, and in this case, the piezoelectric performance of the piezoelectric body obtained by polarizing the sintered body obtained from the fired product will be relatively low.

On the other hand, in the phase diagram of FIG. 2, the region (b) where the molar ratio of lithium (Li) to niobium (Nb) is larger than 50/50 is a region where LiNbO ₃ crystals and Li ₃ NbO ₄ crystals coexist. It is. Although not shown in FIG. 2, region (b) is a region where the molar ratio of lithium (Li) to niobium (Nb) is greater than 50/50 and less than or equal to about 75/25 (that is, the Nb concentration is about 25%). 50% or more).

Within the above-mentioned region (b), the ratio of LiNbO ₃ crystals to Li ₃ NbO ₄ crystals is determined depending on the ratio of lithium to niobium, and the smaller the molar ratio of lithium (Li) to niobium (Nb), the more ( That is, the larger the Nb concentration), the larger the proportion of LiNbO ₃ becomes. Therefore, if the molar ratio of lithium (Li) to niobium (Nb) is greater than 50/50 and less than or equal to 56/44, or within the range of greater than or equal to 51/49 and less than or equal to 56/44, LiNbO _{3 is} present in the fired product. and Li ₃ NbO ₄ crystals are included in a predetermined ratio, and the amount of LiNbO ₃ crystals produced is relatively large.

Note that FIGS. 3 and 4 are examples of X-ray diffraction charts of a fired product obtained by firing a mixture of lithium carbonate powder and niobium oxide powder, respectively. Figure 3 shows the X-ray diffraction results obtained under conditions where the molar ratio of lithium to niobium in the mixture was 51.5/48.5, and Figure 4 shows the X-ray diffraction results obtained under the conditions where the molar ratio of lithium to niobium in the mixture was 50/50. It is a chart. In the charts of FIGS. 3 and 4, the peaks marked with the symbol "A" indicate the presence of LiNbO ₃ crystals, and the peaks with the symbol "B" indicate the presence of Li ₃ NbO ₄ crystals. It is.

In the X-ray diffraction chart of FIG. 3, there are both a peak indicating the presence of LiNbO ₃ crystals (peak with symbol A) and a peak indicating the presence of Li ₃ NbO ₄ crystals (peak with symbol B). exist. Therefore, under conditions where the molar ratio of lithium to niobium in the raw material mixture is 51.5/48.5 (within region (b) in FIG. 2), both LiNbO ₃ crystals and Li ₃ NbO ₄ crystals are formed by firing. is shown to be generated. On the other hand, in the X-ray diffraction chart of FIG. 4, although there is a peak indicating the presence of LiNbO ₃ crystals (the peak with the symbol A), there is a peak indicating the presence of Li ₃ NbO ₄ crystals (see FIG. ) does not exist. Therefore, under conditions where the molar ratio of lithium to niobium in the raw material mixture is 50/50 (within region (a) in FIG. 2), LiNbO ₃ crystals are generated by firing, but Li ₃ NbO ₄ crystals are not generated. It has been shown that

In addition, Figure 5 shows the molar ratio of lithium and niobium in the raw material mixture (mixture of lithium carbonate powder and niobium oxide powder) and the predetermined temperature (above room temperature and below 200°C) of the sintered body obtained from the fired product of the raw material mixture. FIG. The horizontal axis of the graph in FIG. 5 shows the ratio of lithium in the raw material mixture (the ratio of the molar amount of lithium to the molar amounts of lithium and niobium), and the vertical axis shows the piezoelectric constant d33. Note that the larger the piezoelectric constant d33, the higher the piezoelectric efficiency.

From the graph of FIG. 5, in the region where the molar ratio of lithium to niobium in the raw material mixture exceeds 50/50 (region where the Li ratio on the horizontal axis is greater than 50; region (b) in FIG. 2), the molar ratio It can be seen that d33 is larger than the region where Li ratio is 50/50 or less (region where the Li ratio on the horizontal axis is 50 or less; region (b) in FIG. 2), and the piezoelectric efficiency of the sintered body is high. In particular, it can be seen that when the above-mentioned molar ratio (Li/Nb) is within the range of 51/49 or more and 56/44 or less, d33 is particularly large and the piezoelectric efficiency is also particularly high.

In the above-described embodiment, the molar ratio of lithium (Li) to niobium (Nb) is greater than 50/50 and less than or equal to 56/44, or the above-mentioned molar ratio is greater than or equal to 51/49 and less than or equal to 56/44. The mixture obtained by mixing raw material powders (lithium carbonate powder and niobium oxide powder) is fired (synthesized). As a result, a fired product in which LiNbO ₃ crystals and Li ₃ NbO ₄ crystals coexist in a predetermined ratio and has a relatively high content of LiNbO ₃ (the molar ratio of Li and Nb is Li:Nb=1:1) is obtained. is obtained, that is, a fired product with relatively high polarization efficiency is obtained. Therefore, by using this fired product, a piezoelectric body with good piezoelectric performance can be obtained, and an ultrasonic sensor with good sensitivity can be manufactured using this piezoelectric body.

The temperature at which the raw material powder mixture is fired may be, for example, in the range of 950°C or higher and 1140°C or lower. By performing the firing under high temperature conditions in this way, the reaction between the raw materials lithium carbonate and niobium oxide is promoted, and a fired product in which LiNbO ₃ crystals and Li ₃ NbO ₄ crystals coexist can be efficiently obtained. Can be done.

(molding step)
In the step of obtaining a molded body, for example, a slurry is prepared by kneading the fired product obtained in the firing step and a binder sol, and the slurry is formed into a film shape to obtain a film-like molded product. You may also obtain Note that a thin ultrasonic sensor including a piezoelectric body obtained from a film-like molded body has excellent flexibility and is therefore suitable for measuring the thickness of a measurement object (for example, a pipe) having a curved surface. In addition, such a thin ultrasonic sensor is easy to always install on a measurement target object, so it is easy to continuously measure the measurement target object, or it is possible to suppress variations in measurement accuracy over time.

The above slurry may be prepared by adding a binder sol to the fired product and kneading it using a roll mill, a ball mill, or the like. Furthermore, a rotary evaporator or the like may be used to perform a desolvent treatment (volatization removal of the solvent) at the same time as the defoaming treatment to obtain a slurry of a predetermined viscosity. The viscosity of the slurry may be a viscosity suitable for forming a film-like molded body, and may be, for example, 1,500 mPa·s or more and 20,000 mPa·s or less.

As the binder sol, a liquid mixture of metal alkoxides and carboxylates constituting the dielectric substance may be used. For example, a mixed solution of titanium butoxide, zirconium butoxide, and lead acetate, which are metal alkoxides and carboxylates constituting the dielectric material PTZ (lead zirconate titanate), may be used as a binder sol. good. By using such a binder sol, during sintering in the subsequent sintering step, a portion of the sol forms a dielectric material (eg, lead zirconate titanate), which acts as a binder. Further, this dielectric material is polarized in the same way as lithium niobate by performing polarization treatment in a polarization step after firing, and exhibits piezoelectric performance. Therefore, it can contribute to improving the piezoelectric performance of the piezoelectric body obtained.

When a film-like molded body is produced in the molding step, the film thickness of the molded body may be 60 μm or more and 80 μm or less. By setting the film thickness of the film-like molded body to 60 μm or more, the detection accuracy of an ultrasonic sensor using this film-like molded body can be improved. In addition, by setting the film thickness of the film-like molded body to 80 μm or less, the flexibility of the film-like molded body becomes appropriate, so that, for example, an ultrasonic sensor can be appropriately installed on an inspection target having a curved surface. Can be done.

In addition, when producing a film-like molded body in the molding step, the above-mentioned slurry can be spray-coated, or the above-mentioned slurry can be used to perform screen printing or stencil printing to produce a film-like molded body (for example, a thin plate-like molded body). A film-like molded body may be obtained by forming a film of slurry on the electrode 5 (see FIG. 1) and drying this film.

In some embodiments, the average particle size of the fired product may be adjusted to 2 μm or more and 5 μm or less before the molding step (before obtaining the molded body or preparing the slurry).

If the average particle diameter of the fired product before obtaining the molded body is 10 μm or more, the specific surface area of the particles is not too large, and therefore volatile components (sol, etc.) can be evaporated during sintering in the subsequent sintering step. This reduces the impact of shrinkage caused by cracks, making it less likely that cracks will occur. Furthermore, if the above-mentioned average particle diameter is 40 μm or less, the specific surface area of the particles is not too small, so it becomes easy to secure a contact area with the binder component (sol, etc.), and the binder component can be effective as a binder. This makes it easier for cracks to occur during sintering. Therefore, according to the above-described embodiment, a crack-free sintered body can be easily obtained, and the quality of the sintered body can be made good.

In addition, in this specification, "average particle diameter" means the particle diameter (D50) at 50% of the integrated value in the particle size distribution determined by laser diffraction/scattering method.

In some embodiments, before the molding step (before obtaining a molded body or preparing a slurry), the particle size distribution of the fired product is adjusted so that D50 is 2 μm or more and 5 μm or less. You may also do so. By setting the particle size distribution of the fired product within the above range, cracking and peeling during sintering of the molded body can be effectively suppressed. Moreover, especially when obtaining a film-like molded body and a sintered product, the flexibility of the sintered product can be made appropriate.

In addition, the above-mentioned D50 means the particle diameter at 50% of the integrated value in the particle size distribution determined by the laser diffraction/scattering method.

(Sintering step)
In the sintering step, the molded body obtained in the molding step may be sintered at a temperature of, for example, 600° C. or higher and 700° C. or lower. By sintering the molded body, the particles are bonded to each other and baked and solidified, and a sintered body is obtained.

(Polarization step)
In the polarization step, a piezoelectric body is obtained by subjecting the sintered body obtained in the sintering step to polarization treatment. The polarization treatment can be performed by providing a pair of electrodes (see, for example, FIG. 1) on the sintered body and applying a voltage between these electrodes.

The sintered body obtained from the fired product obtained in the above-mentioned firing step has a relatively high polarization efficiency. Therefore, by subjecting such a sintered body to polarization treatment, a piezoelectric body can be efficiently obtained. In addition, since it is possible to polarize appropriately with relatively low voltage and current, even if it is a film-like sintered material that is easily damaged when high voltage is applied, it is possible to polarize it appropriately. can. Therefore, by using a piezoelectric material obtained by polarization treatment, an ultrasonic sensor having good sensitivity can be manufactured.

The contents described in each of the above embodiments can be understood as follows, for example.

(1) A method for manufacturing a dielectric material according to at least one embodiment of the present invention includes:
mixing lithium carbonate and niobium oxide to obtain a mixture such that the molar ratio of lithium to niobium is greater than 50/50 and less than or equal to 56/44;
firing the mixture to obtain a fired product in which LiNbO ₃ crystals and Li ₃ NbO ₄ crystals coexist;
Equipped with.

In an oxide containing lithium (Li) and niobium (Nb), a region where the molar ratio of Nb to Li is 50/50 or less includes a region where LiNbO ₃ having a non-stoichiometric composition is generated. In addition, lithium has a small atomic weight and easily volatizes during synthesis (calcination) at high temperatures. Therefore, if a raw material mixture in which the molar ratio of lithium and niobium is Li:Nb=1:1 (that is, the molar ratio of Li to Nb is 50/50) is fired (synthesized), the fired product will contain LiNbO ₃ ( It is considered that the content of crystals with a composition of Li:Nb=1:1) becomes unexpectedly small.

In this regard, according to method (1) above, the raw materials (lithium carbonate and niobium oxide) are mixed so that the molar ratio of lithium (Li) to niobium (Nb) is greater than 50/50 and less than 56/44. Since the resulting mixture is fired (synthesized), LiNbO ₃ crystals and Li ₃ NbO ₄ crystals coexist in a predetermined ratio, and LiNbO ₃ (the molar ratio of Li and Nb is Li:Nb=1). A fired product (dielectric material) having a relatively high content of :1) can be obtained, that is, a fired product (dielectric material) having a relatively high polarization efficiency can be obtained. Therefore, by using the fired product (dielectric material), a piezoelectric body with good piezoelectric performance can be obtained, and an ultrasonic sensor with good sensitivity can be produced using this piezoelectric body. .

(2) In some embodiments, in the method of (1) above,
In the step of obtaining the mixture, the mixture is obtained by mixing lithium carbonate and niobium oxide such that the molar ratio of lithium to niobium is 51/49 or more.

According to method (2) above, a mixture of raw materials (lithium carbonate and niobium oxide) is obtained such that the molar ratio of lithium to niobium is 51/49 or more, so LiNbO ₃ crystals and Li ₃ NbO It is possible to more reliably obtain a fired product in which the _four crystals coexist in a predetermined ratio and have a relatively high content of LiNbO ₃ (the molar ratio of Li and Nb is Li:Nb=1:1). Therefore, it becomes easier to obtain an ultrasonic sensor with good sensitivity.

(3) In some embodiments, in the method (1) or (2) above,
The method for manufacturing the dielectric material includes:
a step of molding the fired product to obtain a molded body;
Sintering the molded body to obtain a sintered body;
Equipped with.

According to the method (3) above, a sintered body (ceramic; dielectric material) is obtained by sintering the compact of the fired product (dielectric material) obtained by the method (1) above. By using a piezoelectric element obtained from the sintered body, an ultrasonic sensor having good sensitivity can be manufactured.

(4) In some embodiments, in the method of (3) above,
In the step of obtaining the molded body, the slurry obtained by kneading the fired product and the binder sol is formed into a film shape to obtain the molded body.

According to the method (4) above, since a film-like molded body is obtained from a slurry containing a fired product (dielectric material) and a binder sol, a film obtained from a sintered product of the molded body is A thin ultrasonic sensor can be manufactured using a piezoelectric element like this.
Further, since the above-mentioned fired product (dielectric material) has a relatively high polarization efficiency, it is possible to appropriately polarize it with a relatively low voltage and current. Therefore, according to the method (4) above, even if the film-like sintered material (dielectric material) is easily damaged when a high voltage is applied, polarization treatment can be performed appropriately.

(5) In some embodiments, in the method (3) or (4) above,
The method for manufacturing the dielectric material includes:
Before obtaining the molded body, the method includes a step of adjusting the average particle size of the fired product to 2 μm or more and 5 μm or less.

According to the method (5) above, since the average particle diameter of the fired product (dielectric material) before obtaining the molded body is set to 10 μm or more, the specific surface area of the particles is not too large, and therefore, during sintering. Since the effect of shrinkage due to volatilization of volatile components (sol, etc.) can be reduced, cracks are less likely to occur. In addition, according to method (5) above, since the average particle diameter is set to 40 μm or less, the specific surface area of the particles is not too small, and therefore, it is easy to secure the contact area with the binder component (sol, etc.). Since the binder component becomes more effective as a binder, cracks are less likely to occur during sintering. Therefore, according to the method (5) above, a crack-free sintered body can be easily obtained, and the quality of the sintered body (dielectric material) can be made good.

(6) In some embodiments, in any of the methods (3) to (5) above,
The method for manufacturing the dielectric material includes:
Before obtaining the molded body, the method includes a step of adjusting the particle size distribution of the fired product so that D50 is 2 μm or more and 5 μm or less.

According to the method (6) above, since the fired product has the above-mentioned particle size distribution, cracking and peeling when sintering the molded body can be suppressed. Moreover, especially when obtaining a film-like molded body and a sintered product, the flexibility of the sintered product can be made appropriate.

(7) In some embodiments, in any of the methods (3) to (6) above,
The method for manufacturing the dielectric material includes:
The method further includes a step of subjecting the sintered body to polarization treatment.

According to the method (7) above, since the polarization treatment is performed on a sintered body with relatively high polarization efficiency, a piezoelectric body can be efficiently obtained. In addition, since it is possible to polarize appropriately with relatively low voltage and current, even if it is a film-like sintered material that is easily damaged when high voltage is applied, it is possible to polarize it appropriately. can. Therefore, by using a piezoelectric material (dielectric material) obtained by polarization treatment, an ultrasonic sensor having good sensitivity can be manufactured.

(8) The dielectric material according to at least one embodiment of the present invention is
LiNbO ₃ crystals and Li ₃ NbO ₄ crystals coexist.

The dielectric material having the structure (8) above is a lithium/niobium oxide in a lithium/niobium molar ratio region (concentration region) in which LiNbO ₃ crystals and Li ₃ NbO ₄ crystals coexist. In the dielectric material, LiNbO ₃ (Li:Nb=1:1) crystals are not generated in a non-stoichiometric ratio, but LiNbO ₃ crystals and Li ₃ NbO ₄ crystals coexist in a predetermined ratio. That is, since the dielectric material having the configuration (8) above reliably contains LiNbO ₃ at a predetermined ratio, this dielectric material has relatively high polarization efficiency. Therefore, by using this dielectric material (fired product, molded body, sintered body, piezoelectric body, etc.), an ultrasonic sensor having good sensitivity can be manufactured.

(9) The ultrasonic sensor (1) according to at least one embodiment of the present invention includes:
The piezoelectric element (2) is formed from the dielectric material described in (8) above and is configured to generate ultrasonic waves when driven by an electric signal.

According to the configuration (9) above, since the piezoelectric element is formed of a dielectric material having relatively high polarization efficiency, it is possible to produce an ultrasonic sensor equipped with the piezoelectric element and having good sensitivity. can.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and also includes forms in which modifications are made to the above-described embodiments and forms in which these forms are appropriately combined.

In this specification, expressions expressing relative or absolute arrangement such as "in a certain direction", "along a certain direction", "parallel", "perpendicular", "center", "concentric", or "coaxial" are used. shall not only strictly represent such an arrangement, but also represent a state in which they are relatively displaced with a tolerance or an angle or distance that allows the same function to be obtained.
For example, expressions such as "same,""equal," and "homogeneous" that indicate that things are in an equal state do not only mean that things are exactly equal, but also have tolerances or differences in the degree to which the same function can be obtained. It also represents the existing state.
In addition, in this specification, expressions expressing shapes such as a square shape or a cylindrical shape do not only mean shapes such as a square shape or a cylindrical shape in a strict geometric sense, but also within the range where the same effect can be obtained. , shall also represent shapes including uneven parts, chamfered parts, etc.
Furthermore, in this specification, the expressions "comprising,""including," or "having" one component are not exclusive expressions that exclude the presence of other components.

1 Ultrasonic sensor 2 Piezoelectric element 4 Electrode 5 Electrode 6 Lead wire 8 Lead wire 30 Inspection object

Claims (6)

A method for manufacturing a piezoelectric element membrane for an ultrasonic sensor, the method comprising:
mixing lithium carbonate and niobium oxide to obtain a mixture such that the molar ratio of lithium to niobium is greater than 51/49 and less than or equal to 56/44;
firing the mixture to obtain a fired product in which LiNbO ₃ crystals and Li ₃ NbO ₄ crystals coexist;
obtaining the piezoelectric element film by performing a polarization treatment on a film containing the fired product in which the LiNbO ₃ crystal and the Li ₃ NbO ₄ crystal coexist;
A method for manufacturing a piezoelectric element film for an ultrasonic sensor comprising: In the step of obtaining the mixture, lithium carbonate and niobium oxide are mixed so that the molar ratio of lithium to niobium is 51/49 or more. Production method. a step of molding the fired product to obtain a molded body;
Sintering the molded body to obtain a sintered body as the film;
A method for manufacturing a piezoelectric element film for an ultrasonic sensor according to claim 1 or 2, comprising: The piezoelectric element of the ultrasonic sensor according to claim 3, wherein in the step of obtaining the molded body, the slurry obtained by kneading the fired product and a binder sol is formed into a film shape to obtain the molded body. Membrane manufacturing method. 5. The method for manufacturing a piezoelectric element film for an ultrasonic sensor according to claim 3, further comprising the step of adjusting an average particle diameter of the fired product to 2 μm or more and 5 μm or less before obtaining the molded body. The piezoelectric ultrasonic sensor according to any one of claims 3 to 5, comprising a step of adjusting the particle size distribution of the fired product so that D50 is 2 μm or more and 5 μm or less before obtaining the molded body. Method of manufacturing element film.

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