JP3397538B2 - Manufacturing method of oxide piezoelectric single crystal - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an oxide piezoelectric single crystal used for an ultrasonic probe which is an ultrasonic transmitting / receiving element of an ultrasonic diagnostic apparatus, an ultrasonic flaw detector, or the like.

[0002]

2. Description of the Related Art An ultrasonic probe used in an ultrasonic diagnostic apparatus, an ultrasonic flaw detector, etc., is mainly composed of a piezoelectric element and radiates ultrasonic waves toward an object to detect the acoustic impedance of the object. The internal state of the object can be imaged by receiving reflected echoes from different interfaces. Conventionally, as a vibrator, lead zirconate titanate having a large electromechanical coupling coefficient (k ₃₃ ′, kt, etc.) and a large permittivity that is easy to match with a transmission / reception circuit with little loss due to a cable or device stray capacitance PZT) -based ceramics are used.

Currently, ultrasonic probes have a thickness of several tens of μm.
An array probe in which approximately 10 to 200 strip-shaped oscillators each having a size of several 100 μm are arranged is the mainstream, and the number of oscillators tends to increase with the demand for higher resolution. Further, in response to the demand for higher sensitivity and wider band of the ultrasonic probe, improvement in piezoelectric characteristics of the piezoelectric element itself is required. Pb having a large electromechanical coupling coefficient for these requirements
[(Zn _1/3 Nb _2/3 ) _1-x Ti _x ] O ₃ , Pb [(M
g _1/3 Nb _2/3 ) _1-y Ti _y ] O ₃ , Pb [(Ni _1/3
Nb _2/3 ) _1-z Ti _z ] O ₃ , Pb [(Co _1/3 Nb
_2/3 ) _1-u Ti _u ] O ₃ , Pb [(A _1/2 Nb _1/2 ).
_1-w Ti _w ] O ₃ (where A is Sc, In, Fe, Y
And a complex oxide containing a trivalent metal element such as one selected from rare earth elements), and Nb in these complex oxides.
An ultrasonic probe using a perovskite type oxide single crystal such as a composite oxide of tantalic acid-lead titanate in which a part of the above is substituted with Ta, and a composite oxide combining these is expected.

By the way, the piezoelectric material used for the transducer of the ultrasonic probe is a plate having a size of 10 mm square or more, and has a large electromechanical coupling coefficient (for example, k ₃₃ ′> 7).
5%) and a high dielectric constant, and it is desired that the characteristics of the piezoelectric / dielectric body be uniform in each vibrator. Usually, the oxide piezoelectric single crystal is grown by a so-called flux method in which lead oxide, boron oxide, etc. are used as a flux, and each component of the oxide piezoelectric single crystal is used as a raw material. In this flux method, the flux and the raw material of the piezoelectric oxide single crystal are melted at a temperature of 900 ° C. or higher,
This is a simple growth method in which a single crystal is precipitated by simply slowly cooling it to near the eutectic temperature of 850 ° C. or less.

However, when the perovskite type oxide single crystal containing the lead oxide is grown from the solution by the flux method, an unusable low dielectric constant lead oxide and niobium oxide piechlore type oxide single crystal is generated. easy.
Furthermore, the perovskite type oxide single crystal is <11
Since the 1> orientation is the most dominant growth orientation, <111>
Easy to grow fast in the direction. In particular, when the growth in the <111> direction is remarkable, a pichlore type oxide single crystal is likely to be generated. In such a case, an arrowhead-shaped single crystal extending in the <111> orientation is likely to be formed, and inclusions called inclusions made of flux components inside the single crystal during growth, growth stress strain, twin crystals, etc. Defects are likely to occur. When such a defect occurs, the piezoelectric / dielectric characteristics vary when a large single crystal having a size of 10 mm or more necessary for manufacturing an ultrasonic probe is grown. Furthermore, since all of the oxide piezoelectric single crystals are solid solution type oxides, when crystal growth is performed by slow cooling, the composition gradually changes with it,
When it is used as an oscillator of an ultrasonic probe, the characteristics become non-uniform. As a result, there arise problems that the sensitivity of the ultrasonic probe is substantially lowered and the band is narrowed.

[0006]

SUMMARY OF THE INVENTION According to the present invention, defects such as inclusions, growth stress strains, and twins do not occur inside a single crystal even if the area is large, and the piezoelectric and dielectric characteristics are excellent and uniform. An object of the present invention is to provide a method for producing an oxide piezoelectric single crystal having a composition.

[0007]

A method of manufacturing an oxide piezoelectric single crystal according to the present invention is carried out by using Pb [(Zn _1/3 Nb _2/3 ) _1-x T
i _x ] O ₃ (where x is 0.05 ≦ x ≦ 0.20), Pb [(Mg _1/3 Nb _2/3 ) _1-y Ti _y ] O ₃ (where y is 0. 20 ≦ y ≦ 0.40), Pb [(N
_{i 1/3 Nb 2/3) 1-z} Ti z] O 3 ( however, z is 0.30
≦ z ≦ 0.50), Pb [(Co _1/3 Nb _2/3 ).
_1-u Ti _u ] O ₃ (where u is 0.10 ≦ u ≦ 0.30
, Pb [(A _1/2 Nb _1/2 ) _1-w Ti _w ] O ₃ (where A is one selected from Sc, In, Fe, Y and rare earth elements, and w is 0.30). ≦ w ≦ 0.50),
Or a perovskite-type composite oxide in which a part of Nb in the above formula is replaced by Ta, or a part of Pb in the above formula is 10 mol%
In manufacturing a piezoelectric single crystal composed of a perovskite-type composite oxide substituted with at least one of Na, Sr, Ca, and La by the flux method, a bottomed cylindrical shape having a bottom radius of curvature of at least 10 mm or more Flux mainly containing lead oxide in the container, a step of containing each component of the piezoelectric single crystal as a raw material, and lowering the temperature downward,
The bottomed tubular container is placed in an electric furnace having a temperature gradient of 0.05 to 20 ° C./mm, the flux and the raw material in the bottomed tubular container are melted, and then the bottomed tubular container is The container has an electric furnace area having the temperature gradient of 0.05 to 10 m.
A step of generating a <100> orientation single crystal nucleus at the bottom position of the bottomed cylindrical container by lowering at a speed of m / hr, and growing a single crystal in the <100> orientation from this single crystal nucleus. It is characterized by including and.

According to the present invention, the growth of the <111> orientation is suppressed, preferentially the single crystal nuclei of the <100> orientation are generated, and the single crystal nuclei are continuously oriented in the <100> orientation. It is difficult to generate the above-mentioned Pychlore type oxide single crystal because it is grown, and inclusion defects inside the single crystal, growth stress strain, twin defects, etc. found in the conventional flux method do not occur. At the same time, the composition fluctuation inside the single crystal is extremely small, and it is possible to manufacture an oxide piezoelectric single crystal having a uniform composition having excellent piezoelectric characteristics and dielectric characteristics even in a large area.

In particular, a perovskite type oxide piezoelectric single crystal having a rectangular parallelepiped shape and a growth edge of three-fold symmetry with a length of 3 mm or more with respect to the <111> axis of the single crystal is formed inside the single crystal. There will be no defects in the material.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for manufacturing an oxide piezoelectric single crystal according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing an apparatus for growing an oxide piezoelectric single crystal. Reference numeral 1 in the figure is a vertical tubular electric furnace in which a heater 2 is embedded in the vertical direction. Reference numeral 3 in the drawing denotes a bottomed cylindrical container which is vertically movable in the electric furnace 1.

First, a raw material containing lead oxide as a main component and at least one selected from niobium oxide and tantalum oxide is placed in a bottomed cylindrical container 3. This bottomed cylindrical container 3
Is set to have the highest temperature in the central portion by the heater 2 and to be lowered as it goes upward and downward, that is, is suspended in the electric furnace 1 having a temperature gradient. Then, after melting the raw material and the flux in the bottomed cylindrical container 3 in the electric furnace 1, the container 3 containing the solution 4 is locally cooled at a low temperature by gradually lowering the container 3. Then, a single crystal nucleus of <100> orientation is generated at the bottom position, and the single crystal 5 is grown in the <100> orientation from this single crystal nucleus.

The oxide piezoelectric single crystal grown by the above method is Pb [(Zn _1/3 Nb _2/3 ) _1-x Ti _x ] O ₃ (where x is 0.05 ≦ x ≦ 0.20). ), Pb
[(Mg _1/3 Nb _2/3 ) _1-y Ti _y ] O ₃ (where y is 0.20 ≦ y ≦ 0.40), Pb [(Ni _1/3 N
b _2/3 ) _1-z Ti _z ] O ₃ (where z is 0.30 ≦ z ≦
0.50), Pb [(Co _1/3 Nb _2/3 ) _1-u T
i _u ] O ₃ (where u represents 0.10 ≦ u ≦ 0.30), Pb [(A _1/2 Nb _1/2 ) _1-w Ti _w ] O ₃ (where A is Sc, One kind selected from In, Fe, Y and rare earth elements, w is 0.30 ≦ w ≦ 0.50), or a part of Nb in the above formula is Ta. Or a perovskite-type composite oxide in which a part of Pb in the above formula is replaced with at least one of Na, Sr, Ca, and La in an amount of 10 mol% or less.

The solution composition for growing the single crystal of the perovskite type composite oxide is composed of a single crystal composition to be grown (eg, a perovskite type oxide piezoelectric single crystal of lead zinc niobium-lead titanate is abbreviated as PZN-PT) and oxidation. It is preferable that the composition ratio with respect to the flux composition containing lead (PbO) as the main component (abbreviated as Flux) is PZN-PT / Flux = 20/80 or more in molar ratio. In the Bridgman method, the molar ratio is preferably in the range of PZN-PT / Flux = 30/70 to 95/5. The flux component is mainly an oxide (A; Zn,) of lead oxide (PbO), boron oxide (B ₂ O ₃ ) and at least one element (A) of a single crystal component.
At least one element selected from rare earth elements such as Mg, Ni, Fe, Co, Sc and In), and its flux composition is PbO = 60 to 100 mol%, B
₂ O ₃ = 0 to 40 mol%, oxide of A = 0 to 40 mol%
Is preferred. Part of the PbO is PbF
Allowed to be replaced by lead compounds such as ₂ , PbO ₂ and Pb ₃ O ₄ . Moreover, as other additives, Li ₂
O, K ₂ O, CaO, SrO, MnO, CuO, Al _{2
O 3, Ga 2 O 3,} Bi 2 O 3, La 2 O 3, Nd 2 O
₃ , SiO ₂ , GeO ₂ , SnO ₂ , ZrO ₂ , HfO
₂ , V ₂ O ₅ , Sb ₂ O ₅ , and Ta ₂ O ₅ are allowed to be used within the range of 5 mol%. Perovstokite type oxide piezoelectric single crystals other than PZN-PT are also grown by the same method as described above.

The container is preferably made of a noble metal such as Pt or Rh. Such a container preferably has a flat bottom. In particular, when the bottom of the container has the lowest temperature and the area is 5 mm or more in diameter and the radius of curvature is at least 10 mm or more, nucleation in the <100> orientation is likely to occur.

The growth rate of the oxide piezoelectric single crystal is 0.
It is preferably from 05 to 5 mm / hr. This is due to the following reasons. That is, if the growth rate is less than 0.05 mm / hr, compositional variation will be large, and it will be difficult to manufacture an oxide piezoelectric single crystal having uniform piezoelectric characteristics and dielectric characteristics. On the other hand, if the growth rate exceeds 5 mm / hr, the growth becomes dominant in the <111> orientation, and defects such as inclusions, growth stress strain, and twins are likely to occur inside the single crystal.

[0016]

The temperature gradient by the heater of the electric furnace and the descending speed of the container are 0.05 to 20 ° C./m, respectively.
m, 0.05 to 10 mm / hr. By setting such conditions, the growth rate of the above-described oxide piezoelectric single crystal can be set to 0.05 to 5 mm / hr.

It is also possible to cool the local portion of the bottom of the container by moving the container in the electric furnace having such a temperature gradient, but by bringing a cooling rod into contact with a point on the bottom of the container, this one point can be cooled. Only the more efficient cooling becomes possible.

The container was lowered during the growth of the single crystal, because the flux containing PbbO as the main component usually has a larger specific gravity than the piezoelectric single crystal. If the specific gravity of the flux containing PbO as the main component is smaller than that of the piezoelectric single crystal, it is necessary to raise the container in the electric furnace for crystal growth.

An ultrasonic probe manufactured by using the oxide piezoelectric single crystal according to the present invention will be described in detail below with reference to FIG. Plural piezoelectric bodies 1 made of oxide piezoelectric single crystal
1 are separated and adhered to each other on the backing material 12. Each of the piezoelectric bodies 11 vibrates in the direction of arrow A in the figure. The first electrode 13 is formed from the ultrasonic wave transmitting / receiving surface of each piezoelectric body 11 to the side surface thereof and a part of the surface opposite to the transmitting / receiving surface. The second electrode 14 is formed on the surface of each of the piezoelectric bodies 11 opposite to the transmitting / receiving surface at a desired distance from the first electrode 13. Such piezoelectric body 11, the first,
The second electrodes 13 and 14 form an ultrasonic transmitting / receiving element. The acoustic matching layer 15 includes the first electrodes 1
3 is formed on each ultrasonic wave transmitting / receiving surface of each piezoelectric body 11. The acoustic lens 16 is formed over the entire acoustic matching layer 15. The flexible printed wiring board 18 is connected to each of the first electrodes 13. The ground electrode plate 17 includes the second electrodes 4
Are connected by soldering, for example. A plurality of conductors (cables) not shown are connected to the flexible printed wiring board 18 and the ground electrode board 17, respectively.

The ultrasonic probe having the structure shown in FIG. 2 is manufactured by the following method, for example. First,
A conductive film is deposited on the oxide piezoelectric single crystal by a sputtering method,
The conductive film is left on the ultrasonic wave transmitting / receiving surface and the surface opposite to the transmitting / receiving surface by the selective etching technique. Subsequently, an acoustic matching layer is formed on the surface of the single crystal piece that serves as the ultrasonic wave transmitting / receiving surface, and these are bonded onto the backing material 12. Subsequently, a plurality of piezoelectric bodies 11 having first and second electrodes 13 and 14 on the backing material 12 are separated from each other by cutting the acoustic matching layer from the acoustic matching layer a plurality of times using a blade. And each piezoelectric body 11
A plurality of acoustic matching layers 15 respectively arranged on the above are formed. Next, after forming the acoustic lens 16 on the acoustic matching layer 15, the flexible printed wiring board 18 is formed.
Are connected to the first electrode 13 respectively, and the second electrode 1
4, an earth electrode plate 17 is connected by, for example, soldering, and a plurality of conductors (cables) (not shown) are connected to the flexible printed wiring board 18 and the earth electrode plate 17, respectively, to produce an ultrasonic probe.

[0022]

The preferred embodiments of the present invention will be described in detail below. (Example 1) First, PbO, Z having a purity of 99.9% or more
The molar ratio of nO, Nb ₂ O ₅ and TiO ₂ between lead niobate zincate (Pb [Zn _1/3 Nb _2/3 ] O ₃ ; abbreviated as PZN) and lead titanate (PbTiO ₃ ; abbreviated as PT). Is 9
1: 9 (that is, Pb [(Zn _1/3 Nb _2/3 ) _1-x Ti
_x ] O ₃ , x = 0.09), this 91PZN-9PT
And lead oxide (PbO) as a flux in a molar ratio of 8
Weighed to be 5:15. Pure water was added to these powders and mixed with a zirconia ball in a ball mill for 12 hours. The mixture was dried, thoroughly mixed and pulverized with a liquor machine, put in a rubber container, and subjected to isostatic pressing at a pressure of 2 ton / cm ² to mold the mixture. This lump 1.0
1 kg was put into the above-mentioned bottomed cylindrical platinum container 3 having an inner diameter of 30 mm and a diameter of 200 cc. Subsequently, the temperature of the central portion is 1230 ° C., the vertical temperature is 1 ° C./mm, and the vertical temperature is 1230 ° C. The heater 2 is divided into four parts. 3 was hung up and the temperature was raised to 1230 ° C. for 6 hours, then 12
Solution 4 was prepared by holding for a period of time to dissolve the flux and the raw material in the container 3. Then, the platinum container 3 is moved toward the temperature gradient part below the center of the electric furnace 1 by 1 mm.
It was lowered to about 500 mm at a speed of / hr and then allowed to cool to room temperature. The platinum container 3 was boiled with 20% nitric acid for 8 hours, the flux was melted and the crystals were taken out.

The obtained crystal was a block of a substantially rectangular parallelepiped having a pale yellow color tone and a size of 25 mm square × 75 mm L. This crystal structure was investigated by X-ray diffraction. As a result, it was found to have a rhombohedral perovskite structure at room temperature.

Further, when the crystal structure of the crystal was examined by an X-ray Laue photograph, it was confirmed that the crystal was a single crystal showing clear Laue spots and extending in the <100> direction in the longitudinal direction. That is, the vertical direction to the bottom surface of the platinum container is the <100> orientation of the single crystal, and the nucleation of the <100> orientation perpendicular to this surface occurs on the bottom surface of the platinum container, and the axial direction of the platinum container ( It was found that the single crystal grew in the <100> orientation in the direction perpendicular to the bottom surface). The surface stuck to the bottom surface of the platinum container was the {100} surface.
A growth surface that appeared to be a crystal habit appeared on the surface of the single crystal. However, this plane was not the {100} plane. When the single crystal was observed, a growth edge having three-fold symmetry with respect to four <111> orientations appeared. The length of this growth edge is 3 to 30
It was mm. The growth rate of a single crystal is 0.1 from the growth time.
It was found to be 5 mm / hr. Also, from the chemical analysis of the single crystal powder by ICP, the above composition: Pb
The x value of [(Zn _1/3 Nb _2/3 ) _1-x Ti _x ] O ₃ is 0.
It was confirmed to be 09.

Then, using the X-ray Laue camera, the <100> orientation axis was set for the obtained single crystal, and a {100} plane single crystal plate having a thickness of 1 mm was cut out by a cutter perpendicular to this axis and polished. To a thickness of 0.3 mm. The inside of this plate-shaped single crystal was observed. As a result, it was confirmed that defects such as inclusion (inclusion) and growth strain were not included at all. Subsequently, a silver electrode and a Ti / Au electrode were formed on both surfaces of the plate-like single crystal by a sputtering method, and 15
An electric field of 1 kV / mm is applied in insulating oil at 0 to 250 ° C for 3
After applying for 0 minutes, electric field cooling was performed to perform polarization. This was used as a 10 mm square plate and the capacitance was measured using an LCR meter. As a result, the relative dielectric constant was 3,500. The plate-shaped single crystal with electrodes has a width of 0.15 mm and a thickness of 0.3 m.
The sample was cut into strips of m and 10 mm in length, and the resonance and antiresonance frequencies were measured. As a result, the electromechanical coupling coefficient k ₃₃ ′ is 8
It was confirmed that the range of 6 to 87% had a variation of 1% or less, and had good piezoelectric characteristics.

Further, as shown in FIG.
An array type ultrasonic probe shown in Fig. 3 was produced. That is,
The piezoelectric single crystal of 91PZT-9PT is processed to have a thickness of 2
A square plate of 00 μm was produced. A Ti / Au conductor film is deposited on the upper and lower surfaces and side surfaces of the obtained square plate by a sputtering method,
By the selective etching technique, the conductive film portion located on one side surface of the square plate and a part of the conductive film located on the surface opposite to the surface serving as the ultrasonic transmission / reception surface were removed. Subsequently, after forming an acoustic matching layer on the surface of the rectangular plate that serves as the ultrasonic wave transmitting / receiving surface, the flexible printed wiring board 18 is firstly attached.
The conductive film portion provided for the electrode was connected by soldering. Further, the ground electrode 17 was connected to the conductive film portion serving as the second electrode by soldering, and these were bonded onto the backing material 12. The flexible printed wiring board 18 and the ground electrode 17 may be connected to the conductor film using a conductive paste. Subsequently, a diamond blade was used to cut from the acoustic matching layer to the square plate, and cut into strips with a width of 100 μm. By this cutting, the piezoelectric bodies 1 having the first and second electrodes 13 and 14 separated from each other on the backing material 12 and a plurality of acoustic matching layers 15 respectively arranged on the respective piezoelectric bodies 1 were formed. . Next, after forming the acoustic lens 16 on the acoustic matching layer 15, the flexible printed wiring board 18 is soldered and connected to each of the first electrodes 3, and the ground electrode plate 17 is soldered to each of the second electrodes 14. 110pF / m, not shown,
An array type ultrasonic probe was manufactured by connecting a plurality of conductors (cables) having a length of 2 m to the flexible printed wiring board 18 and the ground electrode board 17, respectively.

With respect to the obtained array type ultrasonic probe, the reflection echo was measured by the pulse echo method. As a result, an echo with a center frequency of 3.5 MHz was obtained over all the elements. Moreover, the sensitivity is 5 compared with conventional ceramics.
It was found that the frequency band was high, the frequency band was -6 dB, and the relative bandwidth was 92%.

Example 2 First, PbO, MgO, Nb ₂ O ₅ , TiO ₂ and B ₂ O having a purity of 99.9% or more.
₃ is lead magnesium niobate (Pb [Mg _1/3 Nb
_2/3 ] O ₃ ; abbreviated as PMN) and lead titanate (PbTiO 2
₃ ; molar ratio of PT is 67:33 (that is, Pb
[(Mg _1/3 Nb _2/3 ) _1-x Ti _x ] O ₃ , x = 0.3
In 3), this 67 PMN-33PT and flux (FL
UX = PbO + MgO + B ₂ O ₃ , molar ratio of PbO / M
gO / B ₂ O ₃ = 6/3/1) and [67 PMN-33
PT / (PbO + MgO + B ₂ O ₃ )] at a molar ratio of 6
Weighed to be 0:40. These powders were treated in the same manner as in Example 1 to prepare lumps. This lump 1.
3 kg was put into the 200 cc bottomed cylindrical platinum container 3 having an inner diameter of 30 mm shown in FIG. Next, the vertical tubular electric furnace 1 having the dimensions described in Example 1 was set such that the temperature of the central portion was 1200 ° C. and the average temperature gradient in the vertical direction was 5 ° C./mm by the heater 2 divided into four vertically. After suspending the platinum container 3 and raising the temperature to 1200 ° C. for 6 hours, 12
Solution 4 was prepared by holding for a period of time to dissolve the flux and the raw material in the container 3. Then, the platinum container 3 is moved to the temperature gradient part below the center of the electric furnace 1 by 2 mm.
It was lowered to about 400 mm at a speed of / hr and then allowed to cool to room temperature. The platinum container 3 was boiled with 20% nitric acid for 8 hours, the flux was melted and the crystals were taken out.

The obtained crystal was a block of a substantially rectangular parallelepiped having a light yellow color tone and a size of 25 mm square × 50 mmL. This crystal structure was investigated by X-ray diffraction. As a result, it was found to have a rhombohedral perovskite structure at room temperature.

When the crystal structure of the crystal was examined by an X-ray Laue photograph, it was confirmed that the crystal was a single crystal showing clear Laue spots and extending in the <100> orientation in the longitudinal direction. That is, in the single crystal grown in the <100> orientation, the plane in which the single crystal appeared (that is, the crystal habit) was the {100} plane. When the single crystal was observed, a growth edge having three-fold symmetry with respect to four <111> orientations appeared. The length of this growth edge was 20 to 40 mm. From the growth time, it was found that the growth rate of the single crystal was 0.25 mm / hr. Further, from the chemical analysis by ICP of the single crystal powder, the composition: Pb [(Mg _1/3 Nb _2/3 ) _1-x Ti _x ].
It was confirmed that the x value of O ₃ was 0.33.

Then, using the X-ray Laue camera, the <100> orientation axis of the obtained single crystal was taken out, and a {100} plane single crystal plate having a thickness of 1 mm was cut out by a cutter perpendicular to this axis and polished. To a thickness of 0.3 mm. The inside of this plate-shaped single crystal was observed. As a result, it was confirmed that defects such as inclusion (inclusion) and growth strain were not included at all. Subsequently, a silver electrode and a Ti / Au electrode were formed on both surfaces of the plate-like single crystal by a sputtering method, and 15
An electric field of 1 kV / mm is applied in insulating oil at 0 to 250 ° C for 3
After applying for 0 minutes, electric field cooling was performed to perform polarization. This was used as a 10 mm square plate and the capacitance was measured using an LCR meter. As a result, the relative dielectric constant was 3,200. ,
The plate-shaped single crystal with an electrode was 0.15 mm wide and 0.3 mm thick.
Resonance and anti-resonance frequencies were measured by cutting into strips each having a length of 10 mm and a length of 10 mm. As a result, it was confirmed that the electromechanical coupling coefficient k ₃₃ ′ was 84% to 85%, which had good piezoelectric characteristics.

Example 3 First, PbO, Sc ₂ O ₃ , Nb ₂ O ₅ , TiO ₂ and B having a purity of 99.9% or more are prepared.
₂ O ₃ , lead scaniodate niobate (Pb [Sc _1/2
Nb _1/2 ] O ₃ ; abbreviated as PSN) and lead titanate (PbT
The molar ratio of iO ₃ ; PT is 58:42 (that is, P).
b [(Sc _1/2 Nb _1/2 ) _1-x Ti _x ] O ₃ , x = 0.
42), this 58PSN-42PT and flux (P
bO + B ₂ O ₃ , molar ratio of PbO / B ₂ O ₃ = 8/2)
Doo is _{[67 PMN-33PT/ (PbO + B 2} O 3)]
Was weighed so that the molar ratio was 30:70. These powders were treated in the same manner as in Example 1 to prepare lumps. 1.5 kg of this lump is used for the 2 mm of inner diameter 30 mm of FIG.
It was put in a bottomed cylindrical platinum container 3 of 00 cc. Continuing,
The platinum container 3 was placed in the vertical tubular electric furnace 1 having the dimensions described in Example 1 in which the temperature of the central portion was 1280 ° C. and the average temperature gradient in the vertical direction was 2 ° C./mm by the heater 2 divided into four parts. Was hung up, the temperature was raised to a temperature of 1280 ° C. for 6 hours, and then held for 12 hours to dissolve the flux and the raw material in the container 3 to prepare a solution 4. Next, the platinum container 3 was lowered from the center of the electric furnace 1 toward a temperature gradient portion below the electric furnace 1 at a speed of 0.5 mm / hr to about 400 mm, and then allowed to cool to room temperature. 20 for the platinum container 3
% Nitric acid, the mixture was boiled for 8 hours, the flux was dissolved and the crystals were taken out.

The obtained crystal was a block of a substantially rectangular parallelepiped having a pale yellow color tone and a size of 25 mm square × 45 mm L. This crystal structure was investigated by X-ray diffraction. As a result, it was found to have a rhombohedral perovskite structure at room temperature.

When the crystal structure of the crystal was examined by an X-ray Laue photograph, it was confirmed that the crystal was a single crystal showing clear Laue spots and extending in the <100> orientation in the longitudinal direction. That is, <1 that grew in the axial direction of the platinum container
It was confirmed that the crystal was a single crystal of 00> orientation. When the single crystal was observed, a growth edge having three-fold symmetry with respect to four <111> orientations appeared. The length of this growth edge is 10-3
It was 0 mm. The growth rate of the single crystal was 0.
It was found to be 08 mm / hr. Also, from the chemical analysis of the single crystal powder by ICP, the above composition: Pb
The x value of [(Sc _1/2 Nb _1/2 ) _1-x Ti _x ] O ₃ is 0.
It was confirmed to be 42.

Then, using the X-ray Laue camera, the <100> orientation axis of the obtained single crystal was taken out, and a {100} plane single crystal plate having a thickness of 1 mm was cut out by a cutter perpendicular to this axis and polished. To a thickness of 0.3 mm. The inside of this plate-shaped single crystal was observed. As a result, it was confirmed that defects such as inclusion (inclusion) and growth strain were not included at all. Subsequently, a silver electrode and a Ti / Au electrode were formed on both surfaces of the plate-like single crystal by a sputtering method, and 15
An electric field of 1 kV / mm is applied in insulating oil at 0 to 250 ° C for 3
After applying for 0 minutes, electric field cooling was performed to perform polarization. This was used as a 10 mm square plate and the capacitance was measured using an LCR meter. As a result, the relative dielectric constant was 2,600. ,
The plate-shaped single crystal with an electrode was 0.15 mm wide and 0.3 mm thick.
Resonance and anti-resonance frequencies were measured by cutting into strips of 10 mm in length and 10 mm in length. As a result, it was confirmed that the electromechanical coupling coefficient k ₃₃ ′ was 85 to 86%, and had good piezoelectric characteristics with little variation.

Example 4 First, PbO, ZnO, NiO, MnO, Sc ₂ O ₃ and Yb _{2 having} a purity of 99.9% or more.
O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ , TiO ₂ and Zr
O ₂ is replaced by Pb [{Zn _1-QR Ni _Q Mn _R ).
_{1 / 3-2W / 3} (Sc _1-S Yb _S ) _W (Nb _1-T Ta _T )
_{2 / 3-W / 3} } _1-X (Ti _1-U Zr _U ) _X ] O ₃ (Q = 0.
10, R = 0.05, S = 0.30, T = 0.05, U
= 0.01, W = 0.08, X = 0.22; PZSNT
Z) and flux (FLUX = PbO + ZnO +)
B ₂ O ₃ , PbO / ZnO / B ₂ O ₃ = 7/2 in molar ratio
/ 1) is a molar ratio of PZSNTZ / FLUX = 5: 0 /
Weighed to 50. These powders were treated in the same manner as in Example 1 to prepare lumps. This chunk 1.5k
1 g was placed in the bottomed cylindrical platinum container 3 of 200 cc having an inner diameter of 30 mm shown in FIG. Next, the temperature in the center is 1
The platinum container 3 is hung from a vertical tubular electric furnace 1 having an inner diameter of 80 mm and a length of 1000 mm, which has an average temperature gradient of 3 ° C./mm in the up-down direction by a heater 2 which is divided into four vertically at 1260 ° C. After the temperature was raised to 6 ° C. for 6 hours, it was kept for 12 hours to dissolve the flux and the raw material in the container 3 to prepare a solution 4. Then, the platinum container 3 was moved toward the temperature gradient portion below the center of the electric furnace 1 by 1 mm /
It was lowered to about 500 mm at a speed of hr and then left to cool to room temperature. The platinum container 3 was boiled with 20% nitric acid for 8 hours, the flux was melted and the crystals were taken out.

The obtained crystal was a block of a substantially rectangular parallelepiped having a pale yellow color tone and a size of 25 mm square × 30 mmL. This crystal structure was investigated by X-ray diffraction. As a result, it was found to have a rhombohedral perovskite structure at room temperature.

When the crystal structure of the crystal was examined by an X-ray Laue photograph, it was confirmed that the crystal was a single crystal showing clear Laue spots and extending in the <100> direction in the longitudinal direction. That is, a single crystal is <1 in the axial direction of the platinum container.
It was growing in the 00> direction. A growth plane that appeared to be a crystal habit appeared on the surface of this single crystal, but this plane was not the {100} plane. Observing the single crystal, four <111>
A growth edge symmetrical with respect to the azimuth three times appeared. The length of this growth edge was 3 to 7 mm. From the growth time, it was found that the growth rate of the single crystal was 0.05 mm / hr.
In addition, the single crystal powder was chemically analyzed by ICP. As a result, the composition value is close to the composition (± 3%
Within).

Then, using the X-ray Laue camera, the <100> orientation axis of the obtained single crystal was taken out, and a {100} plane single crystal plate having a thickness of 1 mm was cut out by a cutter perpendicular to this axis and polished. To a thickness of 0.3 mm. The inside of this plate-shaped single crystal was observed. As a result, it was confirmed that defects such as inclusion (inclusion) and growth strain were not included at all. Subsequently, a silver electrode and a Ti / Au electrode were formed on both surfaces of the plate-like single crystal by a sputtering method, and 15
An electric field of 1 kV / mm is applied in insulating oil at 0 to 250 ° C for 3
After applying for 0 minutes, electric field cooling was performed to perform polarization. This was used as a 10 mm square plate and the capacitance was measured using an LCR meter. As a result, the relative dielectric constant was 3,500. The plate-shaped single crystal with electrodes has a width of 0.15 mm and a thickness of 0.3 m.
The sample was cut into strips of m and 10 mm in length, and the resonance and antiresonance frequencies were measured. As a result, the electromechanical coupling coefficient k ₃₃ ′ is 8
It was confirmed that 7 to 89% had good piezoelectric characteristics with little variation.

Further, as shown in FIG.
An array type ultrasonic probe shown in Fig. 3 was produced. That is,
The PZSNTZ piezoelectric single crystal is processed to a thickness of 200 μm.
A square plate of m was prepared. A Ti / Au conductor film was vapor-deposited on the upper and lower surfaces and side surfaces of the obtained square plate by a sputtering method, and the conductive film portion located on one side surface of the square plate and a surface to be an ultrasonic wave transmitting / receiving surface were formed by a selective etching technique. A part of the conductive film located on the opposite surface was removed. Continuing,
After forming an acoustic matching layer on the surface of the square plate that serves as the ultrasonic transmission / reception surface, the flexible printed wiring board 18 was connected to the conductive film portion serving as the first electrode by soldering. Further, the ground electrode 17 is connected to the conductive film portion provided for the second electrode by soldering, and these are connected to the backing material 1.
Glued on 2. The flexible printed wiring board 18 and the ground electrode 17 may be connected to the conductor film using a conductive paste. Subsequently, a diamond blade was used to cut from the acoustic matching layer to the square plate, and cut into strips with a width of 100 μm. By this cutting, the first and second electrodes 1 are formed on the backing material 12.
Separated piezoelectric bodies 1 having 3 and 14 and a plurality of acoustic matching layers 15 respectively arranged on the piezoelectric bodies 1 were formed. Then, the acoustic matching layer 15
After forming the acoustic lens 16 on each of them, the flexible printed wiring board 18 is connected to each of the first electrodes 3 by soldering, and the ground electrode plate 17 is connected to each of the second electrodes 14 by soldering. An array type ultrasonic probe was manufactured by connecting a plurality of conductors (cables) having a length of 110 pF / m and a length of 2 m to the flexible printed wiring board 18 and the ground electrode board 17, respectively.

The reflection echo of the obtained array type ultrasonic probe was measured by the pulse echo method. As a result, an echo with a center frequency of 3.5 MHz was obtained over all the elements. Also, the sensitivity is 6 compared with conventional ceramics.
It was found that the frequency band was high, the frequency band was -6 dB, and the relative bandwidth was 87%.

Comparative Example 1 First, PbO, ZnO, Nb ₂ O ₅ and TiO ₂ having a purity of 99.9% or more were mixed with lead niobate zincate (Pb [Zn _1/3 Nb _2/3 ] O _3). ; PZN
(Abbreviated as) and lead titanate (PbTiO ₃ ; abbreviated as PT) have a molar ratio of 91: 9 (that is, Pb [(Zn _1/3 Nb _2/3 )).
_1-x Ti _x ] O ₃ , x = 0.09), and this 91PZN
-9PT and lead oxide (PbO) as a flux were weighed so that the molar ratio was 80:20. These powders were treated in the same manner as in Example 1 to prepare lumps. Approximately 1.0 kg of this lump is 200 with an inner diameter of 30 mm shown in FIG.
It was put in a bottomed cylindrical platinum container 3 of cc. Subsequently, the temperature of the central portion is 1220 ° C., the vertical temperature is 20 ° C./mm by the heater 2 divided into four vertically, and the platinum container is placed in the vertical tubular electric furnace 1 having an inner diameter of 80 mm and a length of 1000 mm. After suspending 3 and raising the temperature to 1230 ° C. for 6 hours, it was kept for 12 hours to dissolve the flux and the raw materials in the container 3 to prepare a solution 4. Next, the platinum container 3 was lowered from the center of the electric furnace 1 toward a temperature gradient portion below the electric furnace 1 at a speed of 1 mm / hr to about 500 mm, and then allowed to cool to room temperature. 20% of the platinum container 3
It was boiled in nitric acid for 8 hours, the flux was dissolved and the crystals were taken out.

The obtained crystals were light yellow in color and were substantially arrowhead-shaped blocks having a size of 15 mm square × 100 mmL. This crystal structure was investigated by X-ray diffraction. As a result, it was found to have a rhombohedral perovskite structure at room temperature.

When the crystal structure of the crystal was examined by an X-ray Laue photograph, it was confirmed that the crystal was a single crystal showing clear Laue spots and extending in the <111> direction in the longitudinal direction. That is, the vertical direction (axial direction) to the bottom surface of the platinum container is the <111> orientation of the single crystal, the nucleation of the <111> orientation occurs from the bottom surface of the platinum container, and the axial direction of the platinum container (bottom surface and <11 in the vertical direction)
It was found that the grains grew in the 1> orientation. The surface stuck to the bottom surface of the platinum container was the {111} surface. Moreover, the growth edge as in Example 1 was not observed. From the growth time, it was found that the growth rate of the single crystal was 15 mm / hr. Further, when the single crystal powder was subjected to a chemical analysis by ICP, the composition: Pb between the nucleation point and the growth end point;
The x value of [(Zn _1/3 Nb _2/3 ) _1-x Ti _x ] O ₃ is 0.
It was found that there was a large variation from 080 to 0.105.

Then, using the X-ray Laue camera, the <001> azimuth axis of the obtained single crystal was taken out, and a 1 mm-thick single crystal plate was cut out with a cutter perpendicular to this axis and polished to 0.3 mm. Finished to thickness. The inside of this plate-shaped single crystal was observed. As a result, many inclusions and twins were observed. Subsequently, a silver electrode and a Ti / Au electrode were formed on both surfaces of the plate-shaped single crystal by a sputtering method, and an electric field of 1 kV / mm was applied for 30 minutes in insulating oil at 150 to 250 ° C., followed by electric field cooling and polarization. Was done. This was used as a 10 mm square plate and the capacitance was measured using an LCR meter. As a result, the relative dielectric constant was 3,500. The plate-shaped single crystal with electrodes was cut into strips having a width of 0.15 mm, a thickness of 0.3 mm, and a length of 10 mm, and resonance was performed.
The anti-resonance frequency was measured. As a result, the electromechanical coupling coefficient k ₃₃ ′ was 70% to 82% with large variations and poor piezoelectric properties.

Further, an array-type ultrasonic probe shown in FIG. 2 was prepared by selecting a portion having no inclusion and using the single crystal. That is, the 91PZT-9
A piezoelectric single crystal of PT was processed to form a square plate having a thickness of 200 μm. Ti / Au was formed on the upper and lower surfaces and side surfaces of the obtained square plate.
A conductive film is vapor-deposited by a sputtering method, and the conductive film portion located on one side surface of the square plate and a part of the conductive film located on a surface opposite to an ultrasonic transmitting / receiving surface are selectively etched. Removed. Subsequently, after forming an acoustic matching layer on the surface of the square plate to be the ultrasonic wave transmitting / receiving surface,
The flexible printed wiring board 18 was connected to the conductive film portion serving as the first electrode by soldering. Further, the ground electrode 17 was connected to the conductive film portion serving as the second electrode by soldering, and these were bonded onto the backing material 12. The flexible printed wiring board 18 and the ground electrode 17 may be connected to the conductor film using a conductive paste. Subsequently, a diamond blade is used to cut from the acoustic matching layer to the square plate, and 10
It was cut into strips with a width of 0 μm. By this cutting, the piezoelectric bodies 1 having the first and second electrodes 13 and 14 separated from each other on the backing material 12 and a plurality of acoustic matching layers 15 respectively arranged on the respective piezoelectric bodies 1 were formed. . Then, the acoustic lens 1 is formed on the acoustic matching layer 15.
After forming 6, the flexible printed wiring board 18 is connected to each of the first electrodes 3 by soldering, and the ground electrode board 17 is connected to each of the second electrodes 14 by soldering,
Furthermore, an array-type ultrasonic probe was manufactured by connecting a plurality of conductors (cables) (not shown) having a length of 2 m and 110 pF / m to the flexible printed wiring board 18 and the ground electrode board 17, respectively.

The reflection echo of the obtained array type ultrasonic probe was measured by the pulse echo method. As a result, an echo with a center frequency of 3.5 MHz was obtained over all the elements. Moreover, the sensitivity is 2 compared with conventional ceramics.
Higher dB, but sensitivity variation is maximum 6d with 40 array elements
It was as big as B. Also, the frequency band was -6 dB, the average value of the ratio band was as narrow as 60%, and the variation was 50 to 80%.

[0048]

As described above, according to the method for producing an oxide piezoelectric single crystal according to the present invention, defects such as inclusions, growth stress strains and twins are generated inside the single crystal even if the area is large. In addition, it is possible to obtain an oxide piezoelectric single crystal having excellent piezoelectric and dielectric properties and a uniform composition, and as a result, as an ultrasonic probe, which is an ultrasonic transmitting / receiving element for ultrasonic diagnostic equipment and ultrasonic flaw detectors. It has remarkable effects such as effective use.

[Brief description of drawings]

FIG. 1 is a schematic view showing a growing apparatus for producing an oxide piezoelectric single crystal according to the present invention.

FIG. 2 is a perspective view showing an ultrasonic probe incorporating an oxide piezoelectric single crystal manufactured according to the present invention.

[Explanation of symbols]

1 ... Electric furnace, 2 ... Heater, 3 ... Platinum container, 4 ... Solution, 5
... single crystal, 11 ... piezoelectric body, 12 ... backing material, 13,
14 ... Electrode, 15 ... Acoustic matching layer, 16 ... Acoustic lens, 17 ... Ground electrode, 18 ... Flexible printed wiring board.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H01L 41/18 H01L 41/18 101A (72) Inventor Mamoru Izumi 1 Komukai Toshiba Town, Kawasaki City, Kanagawa Prefecture Toshiba Research Co., Ltd. Development Center (72) Inventor Masaru Kawauchi 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Toshiba Research and Development Center (72) Inventor Yohachi Yamashita 70 Yanagi-cho, Sachi-ku, Kawasaki-shi, Kanagawa Toshiba Corporation Yanagimachi Factory (56) Reference JP-A-6-122594 (JP, A) JP-A-5-139878 (JP, A) JP-A-6-345581 (JP, A) JP-A-6-38963 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 41/24

Claims (2)

(57) [Claims] 1. Pb [(Zn _1/3 Nb _2/3 ) _1-x Ti _x ] O
₃ (where x is 0.05 ≦ x ≦ 0.20), Pb [(Mg _1/3 Nb _2/3 ) _1-y Ti _y ] O ₃ (however, y
Represents 0.20 ≦ y ≦ 0.40), Pb [(Ni _1/3 Nb _2/3 ) _1-z Ti _z ] O ₃ (however, z
Indicates 0.30 ≦ z ≦ 0.50), Pb [(Co _1/3 Nb _2/3 ) _1-u Ti _u ] O ₃ (however, u
Is 0.10 ≦ u ≦ 0.30), Pb [(A _1/2 Nb _1/2 ) _1-w Ti _w ] O ₃ (where A is Sc, In, Fe, Y and a rare earth element) 1 chosen
Seed, w represents 0.30 ≦ w ≦ 0.50), or a perovskite-type composite oxide represented by: or a perovskite-type composite oxide in which a part of Nb in the above formula is replaced by Ta, or 10 mol% of a part of Pb in the formula
In producing a piezoelectric single crystal composed of a perovskite-type composite oxide substituted with at least one of Na, Sr, Ca, and La by the flux method, a bottomed cylindrical shape with a radius of curvature of at least 10 mm or more A step of accommodating mainly lead oxide as a raw material and each component of the piezoelectric single crystal as a raw material in a container, and lowering the temperature downward to obtain a temperature gradient of 0.05 to 2
The bottomed tubular container is placed in an electric furnace set to 0 ° C./mm, the flux and the raw material in the bottomed tubular container are melted, and then the bottomed tubular container is subjected to an electric treatment with the temperature gradient. By lowering the furnace region at a speed of 0.05 to 10 mm / hr, single crystal nuclei of <100> orientation are generated at the bottom position of the bottomed cylindrical container, and <10> is generated from the single crystal nuclei.
And a step of growing the single crystal in the 0> orientation. 2. The growth of a single crystal of <100> orientation is less than 0.
The method for producing an oxide piezoelectric single crystal according to claim 1, wherein the method is performed at a speed of 05 to 5 mm / hr.