JP2021057388A - Piezoelectric single crystal element, manufacturing method thereof, and application thereof - Google Patents

Abstract

To provide a piezoelectric single crystal element capable of increasing the manufacturing yield of an applicable device and capable of improving the dielectric property and the piezoelectric property, a manufacturing method thereof, and an application thereof.SOLUTION: A piezoelectric single crystal element 1 includes electrodes on both main surfaces of a rectangular single crystal plate composed of a lead composite perovskite composition containing magnesium oxide, niobium oxide, and lead titanate, in the single crystal plate 2, the (001) plane is the main plane, and the (100) plane and the (010) plane are the side surfaces, and the ratio L/W of the length L of the (100) orientation to the width W of the (010) orientation is 4 to 20. The frequency constant N31 represented by the product of the resonance frequency fr in the lateral vibration mode orthogonal to the polarization direction and the length l in the vibration direction is 520 to 700 Hz m at 25°C.SELECTED DRAWING: Figure 1

Description

The present invention relates to a piezoelectric single crystal device capable of increasing the manufacturing yield of the applicable device and also improving the dielectric property and the piezoelectric property, a method for manufacturing the same, and an application of the piezoelectric single crystal device.

In various ultrasonic diagnostic devices and ultrasonic image inspection devices, an electronically operated array type ultrasonic probe having an ultrasonic transmission / reception function equipped with an ultrasonic transmission / reception element having a piezoelectric element is mainly used.

In a general ultrasonic probe, as described in Patent Document 1, a piezoelectric element formed by forming electrodes on both sides of a piezoelectric body is bonded onto a backing material, and an acoustic matching layer is bonded onto the piezoelectric element. After that, a plurality of channels are formed by array processing, and an acoustic lens is further formed on the acoustic matching layer. In such an ultrasonic probe, each electrode of the piezoelectric element is a device of a medical ultrasonic diagnostic apparatus and an ultrasonic image inspection apparatus via a control signal board (flexible printed wiring board, FPC) and a cable. It is connected to the main body.

The piezoelectric element used in the ultrasonic probe is required to have a large relative permittivity and a piezoelectric constant and a small dielectric loss. In addition, it is required that the piezoelectric characteristics such as the dielectric constant and the dielectric loss and the piezoelectric characteristics such as the piezoelectric constant are uniform inside the piezoelectric element and between the plurality of piezoelectric elements. Piezoelectric ceramics and those using a composite piezoelectric material composed of the piezoelectric ceramics / resin composite have been the mainstream, but it is not easy to meet the above demands with these elements, and in recent years, a single crystal plate. It has been studied to improve the performance of the piezoelectric element by adopting.

Examples of such a single crystal plate include lead titanate (PbTiO ₃ ) and Pb (B ¹ Nb) O ₃ (B ¹ is at least one of Mg, Zn, In, Sc, Yb, etc.). Those composed of a relaxa-based lead composite perovskite composition composed of, and those composed of a material obtained by adding a small amount of manganese oxide, zirconium oxide, or the like to the composition are used.

In a piezoelectric element using a single crystal plate as described above, usually, the single crystal plate is cut to a predetermined size, polished to a predetermined thickness as necessary, and then formed on both main surfaces (flat plate surfaces). It is manufactured by obtaining a step of forming an electrode and then performing a polarization treatment by applying a DC electric field.

Attempts have also been made to improve the polarization treatment of the piezoelectric element. For example, Patent Document 2 shows that the electromechanical coupling coefficient and frequency constant of a piezoelectric element can be improved by performing a heating / cooling treatment under various conditions and then a polarization treatment under specific conditions.

On the other hand, Patent Documents 3 and 4 show that the dielectric constant and the piezoelectric constant of the device can be improved by manufacturing the piezoelectric element through a polarization process in which an AC electric field is applied instead of a DC electric field.

Japanese Unexamined Patent Publication No. 7-50898 Japanese Unexamined Patent Publication No. 2003-282986 Japanese Unexamined Patent Publication No. 2014-045411 Japanese Unexamined Patent Publication No. 2014-187285

For example, with the techniques described in Patent Documents 3 and 4, although a certain effect can be expected, microcracks from the machined surface due to stress during polarization due to insufficient performance of the single crystal plate and high polarization reversal speed due to high AC frequency. May occur. When, for example, an ultrasonic probe is manufactured using a piezoelectric element having a single crystal plate in which such microcracks are generated, the piezoelectric element is damaged when it is bonded to an FPC, a backing material, or an acoustic matching layer. This will reduce the manufacturing yield of the ultrasonic probe. The decrease in the manufacturing yield of the applicable equipment due to the microcracks generated during the polarization treatment during the production of the piezoelectric element becomes a particular problem in a large piezoelectric element having ^{an electrode area of more than 2 cm 2.}

The present invention has been made in view of the above circumstances, and an object of the present invention is a piezoelectric single crystal device capable of increasing the manufacturing yield of the applicable device and improving the dielectric property and the piezoelectric property, a method for manufacturing the piezoelectric single crystal device, and a method thereof. It is an object of the present invention to provide the use of the piezoelectric single crystal element.

The piezoelectric single crystal element of the present invention comprises electrodes on both main surfaces of a rectangular single crystal plate composed of a lead composite perovskite composition containing magnesium oxide, niobium oxide and lead titanate. With the (001) plane as the main plane and the (100) plane and the (010) plane as the side surfaces, the ratio L / W of the length L of the (100) orientation to the width W of the (010) orientation is 4 to 4. _{20 and the frequency constant N 31} represented by the product of the resonance frequency fr in the lateral vibration mode orthogonal to the polarization direction and the length l in the vibration direction is 520 to 700 Hz · m at 25 ° C. It is characterized by.

The piezoelectric single crystal element of the present invention comprises an electrode forming step of forming electrodes on both main surfaces of a rectangular single crystal plate composed of a lead composite perovskite composition containing magnesium oxide, niobium oxide and lead titanate, and the above-mentioned electrodes. An AC electric field at a frequency of 0.0001 Hz or more and less than 0.1 Hz is applied to the single crystal plate after the forming step for 3 to 50 cycles at room temperature or higher and at a phase transition temperature Tf that causes a phase transition from pseudo-cubic crystals. It can be produced by the production method of the present invention having a polarization treatment step of performing a polarization treatment.

The lead composite perovskite composition has two types of phase transitions depending on the content of lead titanate. As the first form, it may have a phase transition temperature Trt that undergoes a phase transition from pseudo-cubic to tetragonal, and as a second form, it may have a phase transition temperature Trm that undergoes a phase transition from pseudo-cubic to monooblique. The phase transition temperature is in the range of 70 ° C. or higher and 110 ° C. or lower. In the present specification, the phase transition temperature from the above-mentioned pseudo-standing crystal is generically referred to as the phase transition temperature Tf.

The present invention also includes an ultrasonic transmission / reception element and an ultrasonic probe having the piezoelectric single crystal element of the present invention.

According to the present invention, it is possible to provide a piezoelectric single crystal element capable of increasing the yield of the applicable device and improving the dielectric property and the piezoelectric property, a method for producing the same, and an application of the piezoelectric single crystal element.

It is a perspective view which shows an example of the piezoelectric single crystal element of this invention schematically. It is a graph which shows an example of the processing conditions at the time of performing the polarization processing on the single crystal plate after electrode formation.

As described above, the piezoelectric element is usually manufactured through a polarization treatment by a DC electric field, but it is difficult to sufficiently improve the performance of the piezoelectric element obtained in this way. On the other hand, as described above, there is also a proposal to manufacture a piezoelectric element through polarization treatment with an AC electric field, but in this case, microcracks are formed in the single crystal plate constituting the element.

Since precision processing is required in the manufacture of a piezoelectric single crystal element or an ultrasonic probe using a piezoelectric single crystal element, such microcracks may cause a decrease in the manufacturing yield of the applicable equipment.

The present inventors can obtain a piezoelectric single crystal device that can suppress the occurrence of microcracks in a single crystal plate and has high flexibility by applying an AC electric field under a specific frequency condition to perform a polarization treatment. In addition to improving the dielectric properties and piezoelectric properties of the piezoelectric single crystal device thus obtained, other members (backing material, backing material, etc.) for manufacturing the device to which the device is applied (ultrasonic probe, etc.) It has been found that when it is bonded to and processed with (FPC, acoustic matching layer, etc.), it is unlikely to be damaged and the manufacturing yield of the applicable device can be increased, and the present invention has been completed.

The piezoelectric single crystal element of the present invention has electrodes on both main surfaces of a rectangular single crystal plate composed of a lead composite perovskite composition containing magnesium oxide, niobium oxide and lead titanate.

FIG. 1 shows a perspective view schematically showing an example of the piezoelectric single crystal element of the present invention. However, FIG. 1 is for facilitating the understanding of the structure of the piezoelectric single crystal element, and the size of each element is not always accurate. The piezoelectric single crystal element 1 has both main surfaces [(001) surfaces of the single crystal plate 2. Upper and lower surfaces in the figure. ] Has electrodes 3 and 3. The horizontal arrows in the figure mean the direction of the horizontal vibration mode 31 to be measured when the frequency constant N ₃₁ is obtained, and the arrows from top to bottom in the figure are AC electric fields applied during the polarization process. It means the direction of E. The crystal orientation is shown on the left side of the figure.

The lead composite perovskite composition constituting the single crystal plate includes magnesium oxide, niobium oxide and lead titanate, for example, Pb (Mg _1/3 Nb _2/3 ) O _3- PbTiO ₃ ] (PMN-PT). ). The lead composite perovskite composition may contain a small amount of manganese oxide or zirconium oxide as long as the effects of the present invention are not impaired.

The Curie temperature of the single crystal plate is preferably 128 ° C. or higher, more preferably 130 ° C. or higher, more preferably 140 ° C. or lower, and further preferably 136 ° C. or lower. By using a single crystal plate having such a Curie temperature, the dielectric property and the piezoelectric property of the device become better, and the device can be used in a wider temperature range. The Curie temperature can be adjusted by adjusting the component composition (particularly the ratio of lead titanate) of the lead composite perovskite composition constituting the single crystal plate. Specifically, the Curie temperature can be adjusted to the above range by setting the ratio of lead titanate in the lead composite perovskite composition constituting the single crystal plate to 27 to 30 mol%.

The Curie temperature of the single crystal plate referred to in the present specification is obtained from the maximum value of the capacitance measured by placing the sample in a constant temperature bath, raising the temperature at a frequency of 1 kHz and 1 ° C./min, and using an LCR meter. This is the required value.

The single crystal plate is rectangular. The main surface (flat plate surface) of the single crystal plate is the (001) surface, and the side surfaces are the (100) surface and the (010) surface from the viewpoint of improving the characteristics of the piezoelectric single crystal element.

If the ratio L / W of the length L of the (100) orientation and the width W of the (010) orientation is too large, the single crystal plate may be used for joining with other members in the equipment to which the piezoelectric single crystal element is applied. , The element is more easily damaged. Therefore, from the viewpoint of suppressing the above-mentioned damage, the ratio L / W in the single crystal plate is set to 20 or less. On the other hand, the piezoelectric single crystal element of the present invention has a specific frequency constant, but if the ratio L / W is too small, an accurate frequency constant cannot be obtained. Therefore, the L / W in the single crystal plate is 4 That's all.

The single crystal plate related to the piezoelectric single crystal element can be obtained, for example, by using a commercially available raw material single crystal plate, cutting the single crystal plate to a predetermined size, and then polishing the surface as necessary to adjust the thickness. ..

Specific examples of commercially available products that can be used as raw material single crystal plates include "X2B (trade name)" (PMN-PT) manufactured by TS Technologies, Inc. and PMN-28PT (Type) manufactured by CTS Corporation. A), PMN-32PT (Type B) and the like can be mentioned.

The method for cutting the raw material single crystal plate is not particularly limited, and it may be cut using a precision cutting device such as a dicing saw. Since the main surface (flat plate surface) of the commercially available single crystal plate is the (001) surface, the single crystal plate is cut so that the cut surface is the (100) surface and the (010) surface.

The thickness of the single crystal plate is preferably 0.1 mm or more, preferably 0.5 mm or less, and more preferably 0.45 mm or less. When the raw material single crystal plate is thicker than this, the surface may be polished with a grinder or the like to adjust the thickness to the above value.

It is preferable to heat-treat the single crystal plate obtained by the above-mentioned cutting and polishing in the air. By this heat treatment, the stress applied to the single crystal plate during cutting and polishing can be relaxed, and the mechanical strength of the single crystal plate can be increased.

The heat treatment method for the single crystal plate is not particularly limited. For example, the single crystal plate can be enclosed in a firing container such as an alumina or magnesia saggar, and the heat treatment can be performed in a small electric furnace.

The heat treatment temperature is preferably 200 ° C. or higher, preferably 800 ° C. or lower, and more preferably 600 ° C. or lower. The heat treatment time is preferably 30 minutes or more, and preferably 24 hours or less.

A piezoelectric single crystal device can be obtained by forming electrodes on both main surfaces (flat plate surfaces) of the single crystal plate as described above in the electrode forming step and then subjecting the polarization treatment in the polarization treatment step.

The electrodes are formed on both main surfaces of the single crystal plate by, for example, a metal such as Ni, Cr, Ti, Au, Pt, Pd, Ag, Cu, and Al by a sputtering method, a plating method, a vapor deposition method, or the like. be able to. The thickness of the electrode is preferably 100 to 2000 nm.

After forming electrodes on both main surfaces of the single crystal plate, polarization treatment is performed in the polarization treatment step.

The polarization treatment is carried out at room temperature or higher and at a temperature equal to or lower than the phase transition temperature Tf at which the phase transitions from the pseudo-cubic crystal. As used herein, "room temperature" means 25 ° C. If the temperature during the polarization treatment is too high, the dielectric characteristics and piezoelectric characteristics of the piezoelectric single crystal element cannot be sufficiently secured.
The temperature is Tf or less.

The phase transition temperature Tf (also referred to as "practical limit temperature") of the single crystal plate referred to in the present specification for the phase transition from the pseudo-cubic is such that the sample is placed in a constant temperature bath and the frequency is 1 kHz and 1 ° C./min. It is a value obtained as a temperature when the temperature is raised and the maximum value of the capacitance in the temperature range of 70 ° C. or higher and 110 ° C. or lower is shown, which is measured using an LCR meter.

FIG. 2 shows a graph showing an example of processing conditions when the single crystal plate after electrode formation is subjected to the polarization treatment. In the graph of FIG. 2, the vertical axis represents the electric field strength and the horizontal axis represents the time (processing time). After applying the same frequency and AC electric field for the first few cycles, the frequency and electric field are changed. The conditions for applying an AC electric field are shown. As shown in FIG. 2, it is one cycle of the AC electric field that the electric field strength reaches the maximum value in the positive direction from 0, reaches the minimum value in the negative direction, and then returns to 0, and the time required for this one cycle. The longer the value, the lower the frequency of the AC electric field. Then, in FIG. 2, V1 and Vn indicate the strength of the applied electric field.

If the frequency of the AC electric field applied during the polarization treatment is too high, microcracks will occur in the single crystal plate. Therefore, from the viewpoint of suppressing this, it is preferably less than 0.1 Hz and preferably 0.05 Hz or less. However, if the frequency of the AC electric field applied during the polarization treatment is too low, the polarization treatment for a very long time is required, and the productivity of the device is lowered. Therefore, from the viewpoint of enabling the piezoelectric single crystal element to be produced with good productivity, the frequency of the AC electric field applied during the polarization treatment is 0.0001 Hz or higher, preferably 0.002 Hz or higher.

The cycle of the AC electric field during the polarization treatment is 3 cycles or more from the viewpoint of sufficiently ensuring the effect of the polarization treatment and satisfactorily enhancing the dielectric characteristics and the piezoelectric characteristics of the device, and the occurrence of discharge failure during the polarization treatment is caused. From the viewpoint of suppressing, the number of cycles is 50 or less.

When applying an AC electric field, the peak-to-peak electric field is preferably 0.3 kV / mm or more from the viewpoint of sufficiently ensuring the effect of the polarization treatment and satisfactorily enhancing the dielectric characteristics and piezoelectric characteristics of the device. From the viewpoint of suppressing the occurrence of discharge breakdown during the polarization treatment, the peak-to-peak electric field is preferably 4 kV / mm or less.

In the polarization treatment step, it is desirable to change the AC electric field and frequency at least once. As for the change of the AC electric field, it is preferable to include at least one change in which the AC electric field in the later cycle is made stronger than the AC electric field in the earlier cycle. Further, regarding the frequency change, it is preferable to include at least one change in which the frequency in the later cycle is lower than the frequency in the earlier cycle.

As described above, the frequency of the AC electric field in the polarization treatment is preferably low, but the polarization treatment time is long in order to obtain an element having good dielectric properties and piezoelectric characteristics. Therefore, the frequency at any stage during the polarization process is set to a relatively high value within the above range, an AC electric field of several cycles (for example, 3 cycles or more) is applied, and then the frequency is changed to a low frequency. By applying an AC electric field for several cycles (for example, 3 cycles or more), the polarization processing time can be shortened as much as possible while suppressing the occurrence of microcracks in the piezoelectric single crystal element, and its productivity. Can also be increased.

As for the AC electric field in the polarization treatment, the AC electric field at any stage during the polarization treatment is set lower than the above range and applied for several cycles (for example, 3 cycles or more), followed by a strong AC electric field. By changing to and applying several cycles (for example, 3 cycles or more), the dielectric characteristics and the piezoelectric characteristics of the obtained piezoelectric single crystal element can be further improved.

In the polarization processing step, the number of times the AC electric field and frequency are changed is not particularly limited and may be 1, 2, 3, or more, but the number of changes can be up to 2 times (that is, once). The electric field and frequency conditions used in the polarization treatment of the above are usually 3 or less). When the number of changes of the electric field and the frequency is two or more, each electric field is preferably stronger than the electric field immediately before the change, and each frequency is preferably lower than the frequency immediately before the change. Further, the AC electric field under each condition is preferably applied for 3 cycles or more, but the total number of cycles under each condition should be 50 cycles or less.

Further, when changing the electric field and frequency conditions, both may be changed at the same time (in the same cycle), or they may be changed in different cycles, but usually they are changed at the same time.

Further, as the waveform of the AC electric field, not only a triangular wave but also a sine wave, a trapezoidal wave, or the like may be used.

After applying the AC electric field, a DC electric field of 50% or more of the peak-to-peak electric field may be applied. This is because the optimum dielectric characteristics and piezoelectric characteristics can be secured by applying a DC electric field after the AC electric field to perform the polarization treatment.

_{The piezoelectric single crystal element thus obtained has a frequency constant N 31} represented by the product of the resonance frequency fr in the lateral vibration mode orthogonal to the polarization direction and the length l in the vibration direction at 25 ° C. It will be 700 Hz / m or less. The piezoelectric single crystal element having such a low frequency constant N ₃₁ was obtained through a polarization treatment in which a DC electric field is applied, or a polarization treatment in which an AC electric field is applied under known conditions. It is considered that the flexibility is improved by changing the domain wall density as compared with the piezoelectric single crystal element. Therefore, when it is bonded and processed with other members (backing material, FPC, acoustic matching layer, etc.) in order to manufacture the applicable equipment (ultrasonic probe, etc.), it is less likely to be damaged and the yield of the applicable equipment is increased. Also, it has excellent dielectric properties and piezoelectric properties.

However, if the frequency constant N ₃₁ of the piezoelectric single crystal element is too low, the reproducibility of the dielectric characteristics and the piezoelectric characteristics may deteriorate, and the operating temperature range is limited to 70 ° C. or lower. The frequency constant N ₃₁ is 520 Hz · m or more, and preferably 600 Hz · m or more. By adopting the manufacturing method and conditions _{described above, a piezoelectric single crystal device having a frequency constant N 31 of} not more than the above upper limit value and not more than the above lower limit value can be obtained.

The piezoelectric single crystal element of the present invention is suitable for an ultrasonic transmission / reception element of a device such as a medical ultrasonic diagnostic apparatus or an ultrasonic probe of an ultrasonic image inspection apparatus to which a piezoelectric single crystal element has been conventionally applied. , It can be applied to other applications to which the conventional piezoelectric element is applied.

Further, according to the manufacturing method of the present invention, since a piezoelectric single crystal device in which the generation of microcracks and electrode peeling are suppressed can be obtained, element breakage and chipping when attaching the matching layer are reduced, and the applicable device is manufactured. A piezoelectric single crystal device capable of increasing the yield can be manufactured. Moreover, according to the manufacturing method of the present invention, the dielectric property and the piezoelectric property of the device can be significantly improved at low cost, and therefore the industrial importance thereof is extremely high.

Hereinafter, the present invention will be described in detail based on Examples. However, the following examples do not limit the present invention.

Example 1
Both main surfaces [(001 surface)] of the raw material single crystal plate of Pb (Mg _1/3 Nb _2/3 ) O _3- PbTiO _{3 (PMN-PT) were polished with a grinder (manufactured by DISCO Corporation).} The thickness was set to 0.30 mm. This single crystal plate is cut using a dicing saw (manufactured by Disco Corporation) so that the cut surfaces are the (100) plane and the (010) plane, and the length L in the (100) orientation is 20 mm. 010) A single crystal plate having an orientation width W of 5 mm was obtained. Table 1 shows the Curie temperature Tc, the practical limit temperature Tf, and the size of the single crystal plate of the raw material single crystal plate.

The obtained single crystal plate was sealed in a magnesia saggar and heat-treated in the air at 300 ° C. for 5 hours using a small electric furnace. An electrode having a base layer made of chromium having a thickness of 50 nm and an upper layer made of gold having a thickness of 200 nm is formed on both main surfaces [(001 surface)] of the single crystal plate after the heat treatment by using a sputtering device. did. Then, the single crystal plate on which the electrodes were formed was subjected to polarization treatment by applying an AC electric field at 25 ° C. under the conditions shown in Table 2 to obtain a piezoelectric single crystal element having the appearance shown in FIG.

Examples 2-12, Comparative Examples 1-5
Piezoelectric single crystals were used in the same manner as in Example 1 except that the raw material single crystal plates at the Curie temperature shown in Table 1 were used, the single crystal plates had the sizes shown in Table 1, and an AC electric field was applied under the conditions shown in Table 2. Obtained an element.

The number of "steps" shown in Table 2 means the number of AC electric field and frequency conditions adopted during the polarization treatment, "Step 1" is the condition adopted first, and "Step 2" is the second. "Step 3" shows the conditions adopted in the third, respectively. Further, the “electric field” in Table 2 means a peak-to-peak electric field.

For each of the piezoelectric single crystal elements of Examples and Comparative Examples, the following measurements were performed after 24 hours or more had passed from the polarization treatment. Each measurement was carried out at room temperature by the following method. However, in Comparative Example 5 in which the polarization treatment was performed with the initial frequency set to 10 Hz and the changed frequency set to 100 Hz, the following measurements were not performed because dielectric breakdown occurred during the treatment.

<Frequency constant N ₃₁ >
_{The frequency constant N 31} of each of the piezoelectric single crystal elements of the examples and the comparative examples is the lateral vibration mode 31 (horizontal in FIG. 1) obtained by using the “impedance analyzer 4294A (trade name)” manufactured by KeySight Technology Co., Ltd. It was calculated by the following formula from the resonance frequency fr of (arrow) and the length l of the piezoelectric single crystal element in the vibration direction (that is, the length L of the single crystal plate).

N ₃₁ = fr x l

<Relative permittivity>
The relative permittivity of each of the piezoelectric single crystal elements of Examples and Comparative Examples was calculated by the following formula from the capacitance measured using "Impedance Analyzer 4294A (trade name)" manufactured by KeySight Technology Co., Ltd.

Relative permittivity = Capacitance x Single crystal plate thickness
÷ (Vacuum permittivity x length of single crystal plate L x width of single crystal plate W)

<Piezoelectric constant>
The piezoelectric constants of each of the piezoelectric single crystal elements of Examples and Comparative Examples were _{measured using "Piezo d 33} meter (trade name)" manufactured by the Vocal Research Institute of the Chinese Academy of Sciences. The measurement was carried out for all three samples in both Examples and Comparative Examples, and the average value thereof was taken as the piezoelectric constant of each piezoelectric single crystal element.

Table 3 shows the above evaluation results of the piezoelectric single crystal elements of Examples 1 to 3 and Comparative Examples 1 and 2 using a single crystal plate having a Curie temperature of 128 ° C.

As shown in Table 3, the piezoelectric single crystal elements of Examples 1 to 3 obtained by being manufactured through a polarization treatment step of applying an AC electric field under appropriate frequency conditions _{and having an appropriate frequency constant N 31 have a relative permittivity.} , The piezoelectric constant d ₃₃ was high, and the dielectric property and the piezoelectric property were excellent. Further, in the element of Example 2 in which the electric field and frequency conditions are changed once while the AC electric field is being applied and the polarization treatment is performed, the AC electric field is applied and polarized without changing the electric field and frequency conditions. The element of Example 3 which was treated is superior in dielectric property and piezoelectric property to the element of Example 1, and the polarization treatment was performed by changing the electric field and frequency conditions twice while applying the AC electric field. The element was more excellent in dielectric property and piezoelectric property than the element of Example 2.

On the other hand, the piezoelectric single crystal element of Comparative Example 1 manufactured by applying only a DC electric field and performing a polarization treatment, and the element of Comparative Example 2 manufactured by performing a polarization treatment in which an AC electric field is applied at a high frequency are used. The frequency constant N ₃₁ could not be lowered, both the relative permittivity and the piezoelectric constant d ₃₃ were low, and the dielectric characteristics and the piezoelectric characteristics were inferior.

Table 4 shows the above evaluation results of the piezoelectric single crystal elements of Examples 4 to 12 and Comparative Examples 3 and 4 using a single crystal plate having a Curie temperature other than 128 ° C.

As shown in Table 4, the piezoelectric single crystal devices of Examples 4 to 12 obtained by manufacturing through a polarization treatment step of applying an AC electric field under appropriate frequency conditions _{and having an appropriate frequency constant N 31 are described in Example 1.} Similar to the elements of ~ 3, both the relative permittivity and the piezoelectric constant d ₃₃ were high, and the dielectric characteristics and the piezoelectric characteristics were excellent. Further, when comparing the elements of Examples 4 to 6, the elements of Examples 7 to 9, and the elements of Examples 10 to 12 using single crystal plates having the same Curie temperature, with some exceptions, As in the cases of Examples 1 to 3, it was confirmed that the more the frequency and the electric field conditions were changed during the application of the AC electric field, the better the dielectric characteristics and the piezoelectric characteristics.

On the other hand, the elements of Comparative Examples 3 and 42 manufactured by performing the polarization treatment of applying an AC electric field at a high frequency _{cannot lower the frequency constant N 31} like the elements of Comparative Example 2, and have a relative ratio. Both the dielectric constant and the piezoelectric constant d ₃₃ were low, and the dielectric characteristics and the piezoelectric characteristics were inferior.

<Yield evaluation when a piezoelectric single crystal element is bonded to a member for applicable equipment and processed>
For each of the piezoelectric single crystal elements of Examples 3, 4, 8 and Comparative Example 1, a backing material for an ultrasonic transmission / reception element using a conductive epoxy resin (EVA rubber-based shore A hardness of 70, acoustic impedance). Was adhered to the material of 4M Rayls) and slitted with the above dicing saw at a pitch of 1.2 mm to divide the piezoelectric single crystal element portion into 50 parts. The capacitance of each divided channel was measured using an LCR meter, and the manufacturing yield of the applicable equipment was evaluated from the result and the visual observation of defects such as cracks during the division process. The evaluation was performed on one of each of Examples and Comparative Examples, and the ratio (%) excluding the number of defective products was taken as the manufacturing yield. These results are shown in Table 5.

As shown in Table 5, the piezoelectric single crystal device of Example 3, 4, and 8 having the proper frequency constant N _31, as compared to a device having a frequency constant N ₃₁ is high Comparative Example 1, high manufacturing yield of applied equipment It was.

The present invention can be implemented in forms other than the above, as long as the gist of the present invention is not deviated. The embodiments disclosed in the present application are examples, and the present invention is not limited to these embodiments. The scope of the present invention is construed in preference to the description of the attached claims over the description of the above specification, and all changes within the scope of the claims are patent claims. Is included in the range of.

1 Piezoelectric single crystal element 2 Single crystal plate 3 Electrode

Claims (7)

A piezoelectric single crystal device having electrodes on both main surfaces of a rectangular single crystal plate composed of a lead composite perovskite composition containing magnesium oxide, niobium oxide and lead titanate.
The single crystal plate has the (001) plane as the main surface and the (100) plane and the (010) plane as the side surfaces, and the ratio L / of the length L in the (100) orientation to the width W in the (010) orientation. W is 4 to 20
_{The frequency constant N 31} represented by the product of the resonance frequency fr in the lateral vibration mode orthogonal to the polarization direction and the length l in the vibration direction is 520 to 700 Hz · m at 25 ° C. Piezoelectric single crystal element. The piezoelectric single crystal element according to claim 1, wherein the Curie temperature is 128 to 140 ° C., and the frequency constant N _{31 is 600 to 700 Hz · m at 25 ° C.} The method for manufacturing a piezoelectric single crystal element according to claim 1 or 2.
An electrode forming step of forming electrodes on both main surfaces of a rectangular single crystal plate composed of a lead composite perovskite composition containing magnesium oxide, niobium oxide and lead titanate.
0.0001 Hz or higher at room temperature or higher, at a temperature of 0.0001 Hz or higher, which is the phase transition temperature Tf or lower, which indicates the maximum capacitance observed in the temperature range of 70 ° C. or higher and 110 ° C. or lower from the pseudo-cubic crystal on the single crystal plate after the electrode forming step A method for manufacturing a piezoelectric single crystal element, which comprises a polarization treatment step of applying an AC electric field at a frequency of less than 0.1 Hz for 3 to 50 cycles to perform a polarization treatment. The method for manufacturing a piezoelectric single crystal element according to claim 3, wherein the AC electric field in the polarization treatment step is a peak-to-peak electric field of 0.3 to 4 kV / mm. In the polarization treatment step, the AC electric field and frequency are changed at least once.
The change in the AC electric field includes at least one change to make the AC electric field in the later cycle stronger than the AC electric field in the earlier cycle.
The method for manufacturing a piezoelectric single crystal device according to claim 3 or 4, wherein in the frequency change, the frequency in the later cycle is changed to be lower than the frequency in the earlier cycle at least once. An ultrasonic transmission / reception element comprising the piezoelectric single crystal element according to claim 1 or 2. An ultrasonic probe comprising the piezoelectric single crystal element according to claim 1 or 2.

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