JP7369504B2 - Method of manufacturing piezoelectric single crystal element, method of manufacturing ultrasonic transmitting/receiving element, and method of manufacturing ultrasonic probe - Google Patents

Description

The present invention relates to a piezoelectric single crystal element that can increase the production yield of applied equipment and improve dielectric properties and piezoelectric properties, a method for manufacturing the piezoelectric single crystal element, and uses of the piezoelectric single crystal element.

2. Description of the Related Art Electronically operated array-type ultrasound probes having an ultrasound transmission/reception function and equipped with ultrasound transmission/reception elements having piezoelectric elements are mainly used in various ultrasound diagnostic apparatuses and ultrasound imaging apparatuses.

As described in Patent Document 1, a typical ultrasonic probe has a piezoelectric element formed by forming electrodes on both sides of a piezoelectric body bonded onto a backing material, and an acoustic matching layer bonded onto the piezoelectric element. Then, array processing is performed to form a plurality of channels, and an acoustic lens is further formed on the acoustic matching layer. In this type of ultrasonic probe, each electrode of the piezoelectric element is connected to a medical ultrasonic diagnostic device and an ultrasonic image inspection device via a control signal board (flexible printed wiring board, FPC) and a cable. Connected to the main unit.

A piezoelectric element used in an ultrasonic probe is required to have a large relative dielectric constant and piezoelectric constant, and a small dielectric loss. In addition, dielectric properties such as dielectric constant and dielectric loss, and piezoelectric properties such as piezoelectric constant are required to be uniform inside a piezoelectric element and between multiple piezoelectric elements. The mainstream was to use piezoelectric ceramics or composite piezoelectric materials made of the piezoelectric ceramic/resin composite described above, but it is not easy to meet the above requirements with these devices, and in recent years single crystal plates have been used. Studies have been conducted to improve the performance of piezoelectric elements by adopting .

Such single crystal plates include, for example, lead titanate (PbTiO ₃ ), Pb(B ¹ Nb)O ₃ (B ¹ is at least one of Mg, Zn, In, Sc, Yb, etc.). Some are made of a relaxer-based lead composite perovskite composition, and others are made of a material in which small amounts of manganese oxide, zirconium oxide, etc. are added to the above composition.

A piezoelectric element using a single-crystal plate as described above is usually made by cutting the single-crystal plate to a predetermined size, polishing it to a predetermined thickness as necessary, and then cutting the single-crystal plate to a predetermined thickness. It is manufactured by forming an electrode and then performing a polarization process by applying a DC electric field.

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

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

Japanese Patent Application Publication No. 7-50898 JP2003-282986A JP2014-045411A Japanese Patent Application Publication No. 2014-187285

For example, the techniques described in Patent Documents 3 and 4 can be expected to have certain effects, but due to the insufficient performance of the single crystal plate and the fast polarization reversal speed due to high AC frequencies, micro cracks occur from the machined surface due to stress during polarization. There is a possibility that this may occur. If, for example, an ultrasonic probe is manufactured using a piezoelectric element having a single crystal plate with such microcracks, the piezoelectric element may be damaged when it is bonded and processed to an FPC, backing material, or acoustic matching layer. As a result, the manufacturing yield of ultrasonic probes decreases. Decreased manufacturing yield of applied equipment due to microcracks generated during polarization treatment during piezoelectric element manufacturing is particularly problematic in large piezoelectric elements with electrode areas exceeding 2 cm ² .

The present invention has been made in view of the above circumstances, and its purpose is to provide a piezoelectric single crystal element capable of increasing the production yield of applied equipment and improving dielectric properties and piezoelectric properties, a method for producing the same, and An object of the present invention is to provide uses of the piezoelectric single crystal element.

The piezoelectric single crystal element of the present invention has electrodes on both main surfaces of a rectangular single crystal plate made of a lead composite perovskite composition containing magnesium oxide, niobium oxide, and lead titanate, and the single crystal plate has electrodes on both main surfaces. has the (001) plane as the main plane, the (100) plane and the (010) plane as the side faces, and the ratio L/W of the length L in the (100) direction to the width W in the (010) direction is 4 to 20, and the frequency constant N ₃₁ expressed as the product of the resonance frequency fr of the transverse vibration mode perpendicular 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 made of a lead composite perovskite composition containing magnesium oxide, niobium oxide and lead titanate; After the formation process, an alternating current electric field at a frequency of 0.0001 Hz or more and less than 0.1 Hz is applied for 3 to 50 cycles to the single crystal plate after the formation process at a temperature of room temperature or higher and a phase transition temperature Tf at which the phase transition from pseudo cubic crystal occurs. It can be manufactured by the manufacturing method of the present invention, which includes a polarization treatment step of performing polarization treatment.

The lead composite perovskite composition has two types of phase transition forms depending on the content of lead titanate. The first form may have a phase transition temperature Trt at which the phase transitions from pseudocubic to tetragonal, and the second form may have a phase transition temperature Trm at which the phase transitions from pseudocubic to monoclinic. The phase transition temperature is within the range of 70°C or higher and 110°C or lower. In this specification, the above-mentioned phase transition temperatures from pseudo-orectic crystals are collectively referred to as phase transition temperatures Tf.

Further, the present invention also includes an ultrasonic transmitting/receiving 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 that can increase the yield of applied equipment and improve dielectric properties and piezoelectric properties, a method for manufacturing the piezoelectric single crystal element, and uses of the piezoelectric single crystal element.

FIG. 1 is a perspective view schematically showing an example of a piezoelectric single crystal element of the present invention. It is a graph showing an example of processing conditions when polarizing a single crystal plate after electrode formation.

As mentioned above, piezoelectric elements are usually manufactured through polarization treatment using a direct current electric field, but it is difficult to sufficiently improve the performance of piezoelectric elements obtained in this way. On the other hand, as mentioned above, there is also a proposal to manufacture a piezoelectric element through polarization treatment using an alternating current electric field, but in this case, microcracks will occur in the single crystal plate constituting the element.

In the manufacture of piezoelectric single crystal elements or ultrasonic probes using piezoelectric single crystal elements, precise processing is required, and therefore, such microcracks may cause a decrease in the manufacturing yield of applied equipment.

The present inventors have discovered that by applying an alternating current electric field under specific frequency conditions and performing polarization treatment, it is possible to suppress the generation of microcracks in a single crystal plate and to obtain a piezoelectric single crystal element with high flexibility. In addition to improved dielectric and piezoelectric properties, the piezoelectric single crystal element thus obtained has improved dielectric properties and piezoelectric properties. The present inventors have discovered that when bonded to FPC (FPC, acoustic matching layer, etc.) and processed, breakage is less likely to occur and the manufacturing yield of applicable devices can be increased, leading to the completion of the present invention.

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

FIG. 1 is a perspective view schematically showing an example of the piezoelectric single crystal element of the present invention. However, FIG. 1 is provided to facilitate understanding of the structure of the piezoelectric single crystal element, and the size of each element is not necessarily accurate. The piezoelectric single crystal element 1 has both main surfaces of a single crystal plate 2 [(001) plane. Upper and lower surfaces in the figure. ] has electrodes 3, 3. The horizontal arrow in the figure indicates the direction of the transverse vibration mode 31 measured when determining the frequency constant _N31 , and the arrow from top to bottom in the figure indicates the AC electric field applied during polarization processing. It means the direction of E. Further, the left side of the figure shows the crystal orientation.

The lead composite perovskite composition constituting the single crystal plate includes one containing 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, further preferably 140°C or lower, and even more preferably 136°C or lower. By using a single crystal plate having such a Curie temperature, the dielectric properties and piezoelectric properties of the element will be better, and the element can be used in a wider temperature range. Note that by adjusting the component composition (particularly the proportion of lead titanate) of the lead composite perovskite composition constituting the single crystal plate, its Curie temperature can be adjusted. Specifically, by setting the proportion of lead titanate in the lead composite perovskite composition constituting the single crystal plate to 27 to 30 mol %, the Curie temperature can be adjusted within the above range.

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

The single crystal plate is rectangular. In order to improve the characteristics of the piezoelectric single crystal element, the single crystal plate has a main surface (flat plate surface) of a (001) plane, and side surfaces of a (100) plane and a (010) plane.

If the ratio L/W of the length L in the (100) direction and the width W in the (010) direction is too large, the monocrystalline plate may be difficult to bond to other components in equipment to which the piezoelectric single crystal element is applied. , the element is more likely to be 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. The above shall apply.

A single crystal plate related to a piezoelectric single crystal element can be obtained, for example, by using a commercially available raw material single crystal plate, cutting it into 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 A) and PMN-32PT (Type B).

There are no particular restrictions on the method of cutting the raw material single crystal plate, and a precision cutting device such as a dicing saw may be used to cut it. Note that the commercially available single crystal plate has a main surface (flat plate surface) that is a (001) plane, and therefore is cut so that the cut planes are a (100) plane and a (010) plane.

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

The single crystal plate obtained through the above cutting and polishing is preferably subjected to heat treatment in the atmosphere. This heat treatment makes it possible to relieve the stress applied to the single crystal plate during cutting and polishing, thereby increasing the mechanical strength of the single crystal plate.

There are no particular restrictions on the method of heat treatment of the single crystal plate; for example, the single crystal plate may be sealed in a firing container such as an alumina or magnesia sagger, and heat treated 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. Further, the heat treatment time is preferably 30 minutes or more, and preferably 24 hours or less.

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

The electrodes are formed on both main surfaces of the single crystal plate by sputtering, plating, vapor deposition, etc. using metals such as Ni, Cr, Ti, Au, Pt, Pd, Ag, Cu, and Al. 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 a polarization treatment step.

The polarization treatment is carried out at a temperature above room temperature and below the phase transition temperature Tf at which phase transition from pseudo cubic crystal occurs. "Room temperature" as used herein means 25°C. Note that if the temperature during polarization treatment is too high, the dielectric and piezoelectric properties of the piezoelectric single crystal element cannot be maintained sufficiently.
The temperature shall be below Tf.

In this specification, the phase transition temperature Tf (also referred to as "practical limit temperature") at which a single crystal plate undergoes a phase transition from a pseudo-cubic crystal is determined by placing a sample in a constant temperature bath and heating at a frequency of 1 kHz and 1°C/min. This value is determined as the temperature at which the capacitance reaches the maximum value within a temperature range of 70° C. or higher and 110° C. or lower, which is measured using an LCR meter when the temperature is increased.

FIG. 2 shows a graph showing an example of processing conditions when polarizing a single crystal plate after electrode formation. In the graph in Figure 2, the vertical axis represents electric field strength and the horizontal axis represents 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 alternating current electric field are shown. As shown in Figure 2, one cycle of the AC electric field is when the electric field strength reaches the highest value in the positive direction from 0, reaches the lowest value in the negative direction, and then returns to 0, and the time taken for this one cycle. The longer the value, the lower the frequency of the alternating current electric field. In FIG. 2, V1 and Vn indicate the strength of the applied electric field.

If the frequency of the alternating current electric field applied during the polarization treatment is too high, microcracks will occur in the single crystal plate, so 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 alternating current electric field applied during the polarization process is too low, the polarization process will be required for a very long time, reducing device productivity. Therefore, from the viewpoint of producing piezoelectric single crystal elements with good productivity, the frequency of the alternating current electric field applied during the polarization treatment is preferably 0.0001 Hz or more, and preferably 0.002 Hz or more.

The cycle of the alternating current electric field during the polarization process is three or more cycles in order to ensure the sufficient effect of the polarization process and improve the dielectric and piezoelectric properties of the element. From the viewpoint of suppression, it is 50 cycles or less.

When applying an alternating current 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 polarization treatment and improving the dielectric properties and piezoelectric properties of the element. From the viewpoint of suppressing the occurrence of discharge breakdown during polarization treatment, the peak-to-peak electric field is preferably 4 kV/mm or less.

In the polarization process, it is desirable to change the alternating current electric field and frequency at least once. Regarding the change in the alternating current electric field, it is preferable to include at least one change in which the alternating current electric field in a later cycle is made stronger than the alternating current electric field in an earlier cycle. Regarding the change in frequency, it is preferable to include at least one change in which the frequency in a later cycle is lower than the frequency in an earlier cycle.

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

In addition, the AC electric field in the polarization process is applied at any stage during the polarization process by setting the AC electric field lower than the above range and applying it for several cycles (for example, 3 cycles or more), followed by applying a strong AC electric field. The dielectric properties and piezoelectric properties of the piezoelectric single crystal element obtained can be further improved by changing the temperature and applying it for several cycles (for example, three or more cycles).

In the polarization process, the number of times the AC electric field and frequency are changed is not particularly limited and can be changed once, twice, three times, or more. The electric field and frequency conditions employed in the polarization process are usually 3 or less. When the electric field and frequency are changed two or more times, each electric field is preferably stronger than the electric field immediately before changing, and each frequency is preferably lower than the frequency before changing. Further, it is preferable that the alternating current electric field is applied for three or more cycles under each condition, but the total number of cycles under each condition is set to be 50 cycles or less.

Further, when changing the electric field and frequency conditions, they may be changed at the same time (in the same cycle) or 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, etc. 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 optimal dielectric properties and piezoelectric properties can be ensured by applying a direct current electric field after an alternating current electric field to perform polarization treatment.

The piezoelectric single crystal element thus obtained has a frequency constant N ₃₁ expressed as the product of the resonance frequency fr of the transverse vibration mode perpendicular to the polarization direction and the length l in the vibration direction at 25°C. It becomes 700Hz・m or less. A piezoelectric single crystal element having such a low frequency constant _N31 is a piezoelectric single crystal element obtained through a polarization process that applies a direct current electric field, or a piezoelectric single crystal element obtained through a polarization process that applies an alternating current electric field under known conditions. Compared to piezoelectric single-crystal devices, the change in domain wall density is thought to improve flexibility. Therefore, when it is bonded and processed with other parts (backing material, FPC, acoustic matching layer, etc.) in order to manufacture applied equipment (ultrasonic probes, etc.), damage is less likely to occur, increasing the yield of applied equipment. It also has excellent dielectric and piezoelectric properties.

However, if the frequency constant N ₃₁ of the piezoelectric single crystal element is too low, there is a risk that the reproducibility of dielectric properties and piezoelectric properties will decrease, and the operating temperature range will be limited to 70°C or less. The frequency constant N ₃₁ is 520 Hz·m or more, preferably 600 Hz·m or more. By employing the manufacturing method and conditions described above, it is possible to obtain a piezoelectric single crystal element in which the frequency constant N ₃₁ is less than or equal to the upper limit value and greater than or equal to the lower limit value.

The piezoelectric single crystal element of the present invention is suitable for ultrasonic transmitting and receiving elements of devices such as medical ultrasound diagnostic equipment and ultrasound probes of ultrasound imaging equipment, to which piezoelectric single crystal elements have been conventionally applied, and , it can also be applied to other applications where conventional piezoelectric elements are applied.

Furthermore, according to the manufacturing method of the present invention, a piezoelectric single crystal element with suppressed occurrence of microcracks and electrode peeling can be obtained, which reduces element folding and chipping when pasting a matching layer, and manufactures applicable equipment. A piezoelectric single crystal element can be manufactured with improved yield. Moreover, according to the manufacturing method of the present invention, the dielectric properties and piezoelectric properties of the element can be significantly improved at low cost, and therefore its industrial importance 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 plane)] of a 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 Co., Ltd.). The thickness was set to 0.30 mm. This single crystal plate was cut using a dicing saw (manufactured by DISCO Co., Ltd.) so that the cut planes were (100) plane and (010) plane, and the length L in the (100) direction was 20 mm, ( 010) A single crystal plate with an orientation width W of 5 mm was obtained. Table 1 shows the Curie temperature Tc, practical limit temperature Tf, and size of the single crystal plate of the raw material single crystal plate.

The obtained single-crystal plate was sealed in a magnesia sagger, and heat-treated in the atmosphere at 300° C. for 5 hours using a small electric furnace. Electrodes having a base layer made of chromium with a thickness of 50 nm and a top layer made of gold with a thickness of 200 nm are formed on both main surfaces [(001 plane)] of the single crystal plate after heat treatment using a sputtering device. did. Then, the single crystal plate on which the electrodes were formed was subjected to polarization treatment by applying an alternating current 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. 1.

Examples 2 to 12, Comparative Examples 1 to 5
A piezoelectric single crystal was prepared in the same manner as in Example 1, except that a raw material single crystal plate having the Curie temperature shown in Table 1 was used, the single crystal plate was made to have the size shown in Table 1, and an AC electric field was applied under the conditions shown in Table 2. I got the element.

The number of "steps" listed in Table 2 means the number of AC electric field and frequency conditions adopted during the polarization process, with "Step 1" being the first condition adopted, and "Step 2" being the second condition. "Step 3" shows the conditions adopted in the third step, and "Step 3" shows the conditions adopted in the third step. Moreover, "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 24 hours or more after the polarization treatment. Each measurement was performed at room temperature using the following method. However, in Comparative Example 5, in which polarization treatment was performed with the initial frequency at 10 Hz and the changed frequency at 100 Hz, dielectric breakdown occurred during the treatment, so the following measurements were not performed.

<Frequency constant N ₃₁ >
The frequency constant N ₃₁ of each piezoelectric single crystal element in Examples and Comparative Examples is determined using the “Impedance Analyzer 4294A (trade name)” manufactured by Keysight Technologies Inc. It was calculated by the following formula from the resonance frequency fr of the 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).

_N31 = fr × l

<Relative dielectric constant>
The relative permittivity of each piezoelectric single crystal element in the Examples and Comparative Examples was calculated by the following formula from the capacitance measured using "Impedance Analyzer 4294A (trade name)" manufactured by Keysight Technologies.

Relative permittivity = capacitance x thickness of single crystal plate
÷ (vacuum permittivity x length of single crystal plate L x width of single crystal plate W)

<Piezoelectric constant>
The piezoelectric constant of each piezoelectric single crystal element of Examples and Comparative Examples was measured using "Piezo D ₃₃ Meter (trade name)" manufactured by the Institute of Vocal Music, Chinese Academy of Sciences. Measurements were carried out on 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 for the piezoelectric single crystal elements of Examples 1 to 3 and Comparative Examples 1 and 2 in which single crystal plates with a Curie temperature of 128° C. were used.

As shown in Table 3, the piezoelectric single crystal elements of Examples 1 to 3, which were manufactured through a polarization process in which an alternating current electric field was applied under appropriate frequency conditions and had an appropriate frequency constant N ₃₁ , had a relative dielectric constant of , piezoelectric constant _d33 were high, and the dielectric properties and piezoelectric properties were excellent. In addition, the device of Example 2, which was polarized by changing the electric field and frequency conditions once while applying an AC electric field, was polarized by applying an AC electric field without changing the electric field and frequency conditions. The dielectric properties and piezoelectric properties are better than those of Example 1, which was subjected to the treatment, and the element of Example 3, in which the polarization treatment was performed by changing the electric field and frequency conditions twice during the application of an alternating electric field. The device had even better dielectric and piezoelectric properties than the device of Example 2.

On the other hand, the piezoelectric single crystal element of Comparative Example 1, which was manufactured by performing polarization treatment by applying only a DC electric field, and the element of Comparative Example 2, which was manufactured by performing polarization treatment by applying AC electric field at a high frequency, The frequency constant N ₃₁ could not be lowered, both the dielectric constant and the piezoelectric constant d ₃₃ were low, and the dielectric properties and piezoelectric properties were poor.

Further, Table 4 shows the above evaluation results for the piezoelectric single crystal elements of Examples 4 to 12 and Comparative Examples 3 and 4 in which single crystal plates other than those having a Curie temperature of 128° C. were used.

As shown in Table 4, the piezoelectric single crystal elements of Examples 4 to 12, which were manufactured through a polarization process in which an alternating current electric field was applied under appropriate frequency conditions and had an appropriate frequency constant N ₃₁ , were Similar to the elements No. 3 to 3, both the relative permittivity and piezoelectric constant _d33 were high, and the dielectric and piezoelectric properties were excellent. Furthermore, when comparing the devices of Examples 4 to 6, the devices of Examples 7 to 9, and the devices of Examples 10 to 12, which used single crystal plates with the same Curie temperature, with some exceptions, As in Examples 1 to 3, it was confirmed that the more times the frequency and electric field conditions were changed during application of the AC electric field, the better the dielectric and piezoelectric properties were.

On the other hand, the elements of Comparative Examples 3 and 42, which were manufactured by performing polarization treatment by applying an alternating electric field at a high frequency, could not lower the frequency constant N ₃₁ as well as the element of Comparative Example 2, and Both the dielectric constant and the piezoelectric constant _d33 were low, and the dielectric properties and piezoelectric properties were poor.

<Yield evaluation when piezoelectric single crystal elements are bonded and processed to applicable equipment components>
Each of the piezoelectric single crystal elements of Examples 3, 4, 8 and Comparative Example 1 was coated with a backing material for ultrasonic transmitting and receiving elements (EVA rubber based, Shore A hardness 70, acoustic impedance (4MRayls material), and slits were processed at a pitch of 1.2 mm using the above-mentioned dicing saw to divide the piezoelectric single crystal element into 50 parts. The capacitance of each divided channel was measured using an LCR meter, and the manufacturing yield of the applied equipment was evaluated based on the results and visual observation of defects such as cracks during the dividing process. The evaluation was performed on one product in both Examples and Comparative Examples, and the manufacturing yield was determined by excluding the number of defective products. These results are shown in Table 5.

As shown in Table 5, the piezoelectric single crystal elements of Examples 3, 4, and 8 having appropriate frequency constants _N31 had a higher manufacturing yield of applied equipment than the element of Comparative Example 1 having a high frequency constant _N31 . Ta.

The present invention can be implemented in forms other than those described above without departing from the spirit thereof. The embodiments disclosed in this application are merely examples, and the present invention is not limited to these embodiments. The scope of the present invention shall be interpreted with priority given to the description of the appended claims rather than the description of the foregoing specification, and all changes within the scope of equivalency to the claims shall be interpreted as included in the range.

1 piezoelectric single crystal element 2 single crystal plate 3 electrode

Claims (6)

A method for manufacturing a piezoelectric single crystal element having electrodes on both main surfaces of a rectangular single crystal plate made of a lead composite perovskite composition containing magnesium oxide, niobium oxide, and lead titanate, the method comprising:
The lead composite perovskite composition is Pb(Mg _1/3 Nb _2/3 )O ₃ -PbTiO ₃ ,
The single crystal plate has a (001) plane as its main surface, a (100) plane and a (010) plane as its side surfaces, and has a ratio L/of the length L in the (100) direction and the width W in the (010) direction. W is 4 to 20,
The frequency constant N ₃₁ expressed as the product of the resonance frequency fr of the transverse vibration mode perpendicular to the polarization direction and the length l in the vibration direction is 520 to 700 Hz m at 25°C ,
an electrode forming step of forming electrodes on both main surfaces of a rectangular single crystal plate made of the lead composite perovskite composition;
After the above electrode forming step, the single crystal plate is heated at 0.0001 Hz or higher at a temperature higher than room temperature and lower than the phase transition temperature Tf which exhibits the maximum capacitance observed in the temperature range from 70°C to 110°C from pseudo cubic crystal. 0. A method for manufacturing a piezoelectric single crystal element, comprising a polarization treatment step of applying an alternating current electric field at a frequency of 0.08 Hz or less for 3 to 50 cycles to perform polarization treatment. The method for manufacturing a piezoelectric single crystal element according to claim 1, wherein the alternating current electric field in the polarization treatment step is 0.3 to 4 kV/mm in peak-to-peak electric field. In the polarization treatment step, changing the alternating current electric field and frequency at least once,
The change in the alternating current electric field includes at least one change in which the alternating current electric field in a later cycle is made stronger than the alternating current electric field in an earlier cycle;
3. The method for manufacturing a piezoelectric single crystal element according to claim 1 , wherein the frequency change includes at least one change in which the frequency in a later cycle is lower than the frequency in an earlier cycle. The piezoelectric single crystal element has a Curie temperature of 128 to 140°C and a frequency constant of N ₃₁ is 600 to 700 Hz·m at 25°C, the method for manufacturing a piezoelectric single crystal element according to any one of claims 1 to 3. A method for manufacturing an ultrasonic transceiver element, comprising using a piezoelectric single crystal element manufactured by the method for manufacturing a piezoelectric single crystal element according to any one of claims 1 to 4 . A method for manufacturing an ultrasonic probe, comprising using a piezoelectric single crystal element manufactured by the method for manufacturing a piezoelectric single crystal element according to any one of claims 1 to 4 .

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