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DESCRIPTION JP2005005698

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DESCRIPTION JP2005005698
PROBLEM TO BE SOLVED: To provide a piezoelectric single crystal device (device) positively
utilizing an electromechanical coupling coefficient k in a direction (lateral vibration mode)
orthogonal to a polarization direction. When a polarization direction 3 is a pseudo cubic [001]
axis, a normal direction 1 of an end face of a piezoelectric element is in a crystal plane including
[010] and [100] axes orthogonal to the polarization direction 3. It is characterized in that it is in
the range of 0 to 15 ° or in the range of 40 to 50 ° with respect to the direction n orthogonal
to the existing domain structure. [Selected figure] Figure 9
Piezoelectric single crystal device and method of manufacturing the same
[0001]
The present invention relates to a piezoelectric single crystal device and a method of
manufacturing the same. More specifically, it is an element made of a piezoelectric single crystal
material, and the piezoelectric single crystal element focusing on the electromechanical coupling
coefficient k31 of the vibration mode in the direction perpendicular to the polarization direction,
ie, the transverse direction, and the domain structure in the direction The present invention
relates to a method of manufacturing a single crystal element. That is, the present invention
properly controls the domain structure (the extending direction of the striped pattern on the
surface of the element) focusing on the electromechanical coupling coefficient k31 in the
direction (lateral vibration mode) orthogonal to the polarization direction. And a method of
manufacturing the piezoelectric single crystal device.
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[0002]
For example, as shown in FIG. 1, the longitudinal direction of the piezoelectric single crystal
element is a polarization direction 3 and the polarization direction 3 for a rod-like body (a = b)
having an aspect ratio: L / a of 3 or more. Represents the magnitude of the vibration in the
polarization direction 3 (longitudinal vibration) when the voltage is applied, and is expressed by
the electromechanical coupling coefficient k33 of the longitudinal vibration mode which is
proportional to the square root of the conversion efficiency of electrical energy and mechanical
energy. The higher the number, the better the efficiency. Further, as shown in FIG. 2A, a platelike piezoelectric single crystal element (a >> L, b >> L) having an aspect ratio (aspect ratio: a / b)
of 2.5 or more is orthogonal to its polarization direction 3 The electromechanical coupling
coefficient k31 in the direction 1 (lateral vibration mode) also means that the larger the value,
the better the efficiency. The piezoelectric single crystal element may have a shape such as a
rectangular plate or a disk other than the above-mentioned rod-like body or plate-like body, and
the electromechanical coupling coefficient can be obtained similarly for each shape.
[0003]
As the most well-known piezoelectric single crystal material, a solid solution of lead zinc niobate
Pb (Zn1 / 3Nb2 / 3) O3 and lead titanate PbTiO3 (referred to as PZN-PT or PZNT) or lead
magnesium niobate There is a piezoelectric single crystal material consisting of a solid solution
(referred to as PMN-PT or PMNT) of Pb (Mg1 / 3Nb2 / 3) O3 and lead titanate PbTiO3.
[0004]
For example, Patent Document 1 discloses an ultrasonic probe using a piezoelectric substance
consisting of a solid solution single crystal of lead zinc niobate-lead titanate (PZN-PT).
In this technology, such a piezoelectric body has an electromechanical coupling coefficient k33
as large as 80 to 85% in the polarization direction 3 (so-called longitudinal 3 vibration mode),
and by using this single crystal, a probe with high sensitivity is obtained. It shows that it is
possible. Heretofore, although a single-crystal piezoelectric element has thus been studied with
regard to the electromechanical coupling coefficient k33 in the polarization direction 3 and
various applications have been developed, unexplored technologies have been developed for
characteristics in the direction orthogonal to the polarization direction 3 It is a field. JP-A-638963
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[0005]
As an example of developing a piezoelectric element in which the electromechanical coupling
coefficient k31 in the direction 1 (lateral vibration mode) orthogonal to the polarization direction
3 is as large as 80%, see Non-Patent Documents 1 and 2 of Ogawa et al. Have been described.
Jpn. J. Appl. Phys. 41 (2002) L55 Jpn. J. Appl. Phys. 41 (2002) pp. 7108-7112
[0006]
However, in any such non-patent documents, as described above, the electromechanical coupling
coefficient k31 in the direction 1 (lateral vibration mode) orthogonal to the polarization direction
3 is related to the domain structure or k31 exceeds 80% Since there is no description about the
reproducibility of things, it is considered to be experimental data obtained by chance without
reproducibility as in the other known documents.
[0007]
Here, when the single crystal is cut into a size suitable for the device, the domain structure is, as
shown in FIGS. 7 (b), 7 (c) and 9 (b), on the surface of the single crystal material. It is a striped
pattern that can be observed with the naked eye or with a stereomicroscope.
This stripe pattern is a light and dark stripe, and the distance is several micrometers to one
hundred and several tens of micrometers, but it has also been observed that the distance is 1 mm
or more. Hereinafter, in the present invention, “domain structure” means “extending
direction of stripe lines on the device surface” unless otherwise specified.
[0008]
An object of the present invention is to provide a piezoelectric single crystal device in which the
direction of such domain structure (the extending direction of the stripe pattern of the device
surface) is properly controlled, and a method of manufacturing the same.
[0009]
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In order to achieve the above object, the gist of the present invention is as follows.
(1)When the polarization direction is a pseudo cubic [001] axis, a domain structure in which a
normal direction of the end face of the piezoelectric element exists in a crystal plane including
[010] and [100] axes orthogonal to the polarization direction In the direction perpendicular to
the polarization direction which is in the range of 0 to 15 ° or in the range of 40 to 50 ° with
respect to the direction orthogonal to the extending direction of the stripe pattern visible in the
plane) It is a piezoelectric single crystal device excellent in mechanical coupling coefficient k31.
[0010]
(2)
In the above (1), the piezoelectric single crystal device is formed of xPb (A1, A2,..., B1, B2,...) O3 +
(1-x) PbTiO3 (where x is a mole fraction, 0 <x <1). I assume. And the like, wherein A1, A2,... Are
composed of one or more elements selected from the group consisting of Zn, Mg, Ni, Lu, In and
Sc, and B1, B2. And W is one or more elements selected from the group consisting of W, and is a
piezoelectric single crystal element made of a piezoelectric single crystal material having a
complex perovskite structure.
[0011]
(3)In the above (2), the piezoelectric single crystal element further includes one or more
elements selected from the group consisting of Mn, Cr, Sb, Ca, W, Al, La, Li and Ta in the solid
solution by 0.5. It is a piezoelectric single crystal element containing mass ppm to 5 mass%.
[0012]
(4)A method of manufacturing a piezoelectric single crystal element according to the above
(1), (2) or (3), which comprises: cutting out a piezoelectric single crystal material of a
predetermined shape from a single crystal ingot having a domain structure in a predetermined
direction; A main polarization process of applying an electric field under a predetermined
condition to polarize the piezoelectric single crystal material in the [001] direction of the
piezoelectric single crystal material, and manufacturing the piezoelectric single crystal device.
[0013]
(5)In the above (4), the main polarization step is a step of applying a DC electric field of 350
to 1500 V / mm in a temperature range of 20 to 200 ° C. in the [001] direction of the cut out
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piezoelectric single crystal material It is a manufacturing method of an element.
[0014]
(6)In the above (4), the main polarization step applies a DC electric field of 250 to 500 V /
mm at a temperature higher than the Curie temperature (Tc) of the piezoelectric single crystal
material in the [001] direction of the cut out piezoelectric single crystal material. It is a
manufacturing method of a piezoelectric single crystal element which is a process of cooling to
room temperature as it is.
[0015]
(7)In the above (4), (5) or (6), manufacturing of a piezoelectric single crystal device further
including an auxiliary polarization step of applying an electric field in a direction orthogonal to
the polarization direction to polarize either before or after the main polarization step. It is a
method.
[0016]
In addition, “pseudo cubic crystal” as referred to herein is not only cubic crystals but also
rhombohedral crystals having an angle formed by crystallographic three axes within 90 ° ± 1
°, and a mixture of rhombohedral crystals and tetragonal crystals. To be present, it is intended
to include crystals that can be treated as cubic crystallographically.
Also, in the “perovskite structure”, as the unit cell of the solid solution single crystal is
schematically shown in FIG. 3, R ions are located at the corners of the unit cell, and oxygen ions
are located at the face center of the unit cell. Mean that the M ion has a structure (RM03) located
in the body center of the unit cell.
In the “composite perovskite structure” to which the present invention is applied, the M ion at
the body-centered position in FIG. 3 is not one type of element ion, but two or more types of
element ions (A1, A2, ... , B1, B2, ...) is said to be composed of any element.
[0017]
According to the present invention, for applications such as an actuator or a transducer used for
position control of a precision machine, for example, which actively utilizes the
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electromechanical coupling coefficient k31 in a direction (lateral vibration mode) orthogonal to
the polarization direction. It is possible to manufacture the used piezoelectric single crystal
element (device).
[0018]
The inventors of the present invention have the electromechanical coupling coefficient k33 of the
polarization direction 3 (longitudinal vibration mode) of the piezoelectric single crystal element
having a value of 80% or more, thereby being used for various applications, The
electromechanical coupling coefficient k 31 in the direction 1 (lateral vibration mode) orthogonal
to the polarization direction 3 is, for example, described in the document IEEE Proc.
As shown in MEDICAL IMAGING 3664 (1999) pp. 239 and other documents, it has a lower value
than the electromechanical coupling coefficient k33 of 49 to 62% and polarization direction 3
(longitudinal vibration mode), and It paid attention to showing a value with variation by.
[0019]
And as a result of earnestly researching, while the piezoelectric single crystal element has a large
electromechanical coupling coefficient k33 in the polarization direction 3 (longitudinal vibration
mode), an electric machine in the direction 1 (lateral vibration mode) orthogonal to the
polarization direction 3 Because the coupling coefficient k31 is small, the value is not repeatable,
and the variation is large, the reason why it is not suitable as a piezoelectric single crystal device
utilizing a lateral vibration mode is the polarization direction of the polarized piezoelectric single
crystal device 3 When the domain structure (the extending direction of the stripe line of the
element surface) formed by the electric dipoles in the direction 1 orthogonal to the direction 1
does not have an appropriate direction with respect to the vibration direction 1 of the lateral
vibration. I discovered that
[0020]
Also, conversely, the electromechanical coupling coefficient k 31 in the direction 1 (lateral
vibration mode) orthogonal to the polarization direction 3 is large, and the value is reproducible
as a piezoelectric single crystal device using the lateral vibration mode. To be suitable, the
domain structure (the extending direction of the striped lines on the surface of the element)
formed by the electric dipoles in the direction orthogonal to the polarization direction 3 of the
polarized piezoelectric single crystal element is It has been found that for the vibration direction
1 of the directional vibration, it must have a proper direction.
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[0021]
Hereinafter, the present invention will be described in detail.
For example, a solid solution single crystal of lead zinc niobate-lead titanate (referred to as PZNPT or PZNT) has a complex perovskite structure (the unit cell is located at the corner of the unit
cell as schematically shown in FIG. 3). There is a Pb ion, and it has a structure in which an
element ion of any of Zn, Nb, and Ti is present at the body-center position of the unit cell.
FIG. 4 shows a phase diagram according to the composition ratio of lead zinc niobate (PZN) and
lead titanate (PT).
In addition, FIG. 4 is Nomura et al., J. Phys.
(1969)It is quoted from etc.
In addition, the ○ marks in FIG. 4 represent the piezoelectric singlets of 0.91 lead zinc niobate
(PZN) +0.09 lead titanate (PT) (expressed as a molar fraction of x = 0.91) used in Examples 1 to
4. It is an example of the composition of a crystal element (0.91 PZN-0.09 PT). Tc in FIG. 4
indicates the Curie temperature, and Trt indicates the phase transition temperature from
rhombohedral (in a broad concept, pseudo cubic) to tetragonal.
[0022]
In particular, a rhombohedral PZN-PT such as 0.91 PZN-0.09 PT has spontaneous polarization
equivalent to an electric dipole in eight directions of <111> orientation of the crystal when
viewed as pseudo cubic. ing. Moreover, these spontaneous polarizations do not exist separately in
the crystal, but form a structure (domain structure) in which small regions (domains) in which
spontaneous polarizations are aligned contact each other continuously. This structure exists as a
set of planes parallel to one of six {110} planes when the solid solution single crystal is regarded
as pseudo cubic. As described above, when a single crystal is cut out to a size suitable for an
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element to make an element material as described above, stripes are formed on the surface of the
element material, as shown on the surface of the pseudo cubic crystal in FIG. It can be observed
with the naked eye or with a stereomicroscope (see FIG. 7 (b), FIG. 7 (c) and FIG. 9 (b)). This
stripe pattern is a light and dark stripe, and the distance is several micrometers to one hundred
and several tens of micrometers, but it has also been observed that the distance is 1 mm or more.
[0023]
When this single crystal is cut into a cube surrounded by six {100} planes, with the [100], [010],
and [001] axes of the pseudo cubic crystal as independent orthogonal axes, for example, as
shown in FIG. Thus, in the (001), (00-1), (100) and (-100) planes, the direction of the stripes is
parallel to the [010] axis, and in the (010) and (0-10) planes, the direction of the stripes is The
direction indicates a fixed direction such as being parallel to the [10-1] axis.
[0024]
That is, in the cubic sample as described above, the extending direction of the striped line on the
surface corresponding to the domain structure is four {100} planes (specifically, (001), (00-1) ,
(100), (-100) planes are parallel to the <100> axis (specifically, the [010] axis) direction, and the
remaining two {100} planes (specifically, (010), ( 0-10) is parallel to the <110> axis (specifically,
the [10-1], [101] axes).
That is, at each surface of the cube, the domain structure (the extending direction of the streaked
lines) forms an angle parallel or orthogonal or 45 ° with the <100> axis orientation.
[0025]
In such a spontaneous polarization state, even when an electric field is applied in the <100> axis
direction (for example, the [001] axis) without considering the domain structure, the electric
dipole is applied in the electric field application direction (polarization direction 3, for example
[001 ), And the spontaneous polarization directions become aligned.
[0026]
However, in the alignment of the spontaneous polarization direction, various states occur due to
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the domain structure of the element material and the mode of application of the electric field, etc.
As a result, for example, in the case of lead zinc niobate-lead titanate (PZN-PT) In the above,
although the electromechanical coupling coefficient k33 in the polarization direction 3 has a
value of 80% or more, the electromechanical coupling coefficient k31 in the direction 1
orthogonal to the polarization direction 3 is the same as that described in the aforementioned
document (IEEE Proc.
According to MEDICAL IMAGING 3664 (1999) pp. 239), it was found to be distributed with
variation in the range of 49 to 62%.
[0027]
The value of the electro-mechanical coupling coefficient k31 of such a transverse vibration mode
is used for applications such as actuators and transducers used for position control of precision
machines that actively utilize the electro-mechanical coupling coefficient k31. It is difficult to
fabricate a piezoelectric single crystal device (device).
[0028]
The factors that give this result are explained as follows by considering the above-mentioned
domain structure.
That is, in the single crystal cut out from the single crystal ingot after growth, the direction of the
electric dipole in the domain consisting of a set of electric dipoles in the same direction in the
polarization direction 3 and the direction orthogonal to this is per domain It does not exhibit
piezoelectricity and is in an unpolarized state, because it is oriented in various directions.
[0029]
By selecting the polarization processing temperature and applied electric field, which are
generally used polarization conditions, and applying an electric field in the polarization direction
3 for polarization, electric dipoles in many domains that are directed in various directions for
each domain for the first time The orientation of the child can be aligned with the polarization
direction 3 (one direction). As a result, the electromechanical coupling coefficient k33 in the
polarization direction 3 exhibits, for example, a large value of 80% or more in the case of lead
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zinc niobate-lead titanate (PZN-PT). However, the arrangement of domains in the direction
orthogonal to the polarization direction 3 can not be controlled by the above-mentioned
polarization process. Inherently, proper selection of the domain structure in the plane orthogonal
to the polarization direction 3 of the cut out element material and the polarization condition in
the polarization direction 3, that is, control only within an appropriate range of polarization
temperature and applied electric field It is possible.
[0030]
Hereinafter, the reasons for limitation of the piezoelectric single crystal device of the present
invention will be described. (1) Crystal Structure of Piezoelectric Single Crystal Device
(Pseudocubic Complex Perovskite Structure): The “pseudocubic crystal” targeted by the
present invention has a 90 ° angle formed by crystallographic three axes in addition to cubic
crystal. It includes rhombohedral crystals which are within ± 1 ° and crystals which can be
treated as cubic crystals crystallographically because rhombohedral crystals and tetragonal
crystals are present in mixture. Further, as the unit cell of the solid solution single crystal is
schematically shown in FIG. 3, Pb ions are located at the corners of the unit cell, oxygen ions are
located at the face center of the unit cell, and M ions are for the unit cell. It is a perovskite
structure (RMO3) that is located in the body center, and furthermore, the M ion at the body
center position in FIG. 3 is not one type of element ion but two or more element ions (A1, A2 ... ,
B1, B2...) Is required to be a complex perovskite structure.
[0031]
(2) Shape of Single-Crystal Element The shape of the “piezoelectric single-crystal element” to
which the present invention is applied is a plate 1 as shown in FIG. In the case of using the
electromechanical coupling coefficient k31 of mode), it is desirable because the effect is most
greatly exhibited. In particular, the shape of the desired element is a plate-like body (a >> L, b >>
L) having an elongated ratio (aspect ratio: a / b) of 2.5 or more, more preferably, an elongated
ratio (aspect ratio: a / b) ) Is three or more plate-like bodies. In addition, according to a use, the
shape of the both ends (short side b) of the plate-like body of this invention is convexly curved b
'(broken line) as shown in FIG.2 (b) or concavely curved b' It may be '(dotted line). Also, it may be
a square plate of a = b. The element end face referred to in the present invention means a short
side b perpendicular to the long side a in FIG. 2 (b). Therefore, the normal direction 1 of the
element end face (b) is parallel to the long side a of the element.
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[0032]
(3) The normal direction 1 of the end face of the piezoelectric element is 0 to 15 ° with respect
to the direction n orthogonal to the domain structure present in the crystal plane including the
[010] and [100] axes orthogonal to the polarization direction 3 or Within the range of 40 ° to
50 °: The reason why the normal direction 1 of the end face of the element utilizing transverse
vibration is limited to such an angle range is considered as follows. That is, with respect to the
direction n orthogonal to the domain structure existing in the crystal plane including the [010]
and [100] axes orthogonal to the [001] axis which is the polarization direction 3 which is the
range of the angle θ other than the above range In the range of 15 ° <θ <40 ° and 50 ° <θ
<75 °, the <100> direction (for example, [010] direction) is in the plane orthogonal to the
polarization direction <100> axis (for example, the [001] axis) Crystal axis orientations of low
index such as <310>, <210>, <320> exist between the <110> direction (for example, the [110]
direction), and transverse vibration modes are dispersed in these directions. As a result, spurious
(disturbance of the curve) occurs in the impedance curve of the transverse vibration mode, and
the frequency range of the transverse vibration mode (more specifically, the difference between
the resonant frequency fR and the antiresonant frequency fA) narrows. As a result, it is
considered that the electromechanical coupling coefficient k31 in the lateral vibration mode
decreases. As described in (4) below, an angular range of 0 ° to -15 ° or -40 ° to -50 ° is also
within the scope of the present invention from the symmetry of cubic crystals.
[0033]
(4) Composition and Structure of Single-Crystal Element: The composition of the piezoelectric
single-crystal element of the present invention is xPb (A1, A2,..., B1, B2,...) O3 + (1-x) PbTiO3
(where x is a mole fraction) It is a rate, and 0 <x <1. And the like, wherein A1, A2,... Consist of one
or more elements selected from the group consisting of Zn, Mg, Ni, Lu, In and Sc, and B1, B2.
When a single crystal of a complex perovskite structure composed of one or more elements
selected from the group consisting of Mo, W and W is used, the element is suitable for the
transverse vibration mode. That is, as the unit cell of the solid solution single crystal is
schematically shown in FIG. 3, the Pb ion is located at the corner of the unit cell, the oxygen ion
is located at the face center of the unit cell, and the M ion is the unit cell The perovskite structure
(RMO3) is located in the body center of the body, and furthermore, the M ion at the body center
position in FIG. 3 is not one kind of elemental ion, but from Zn, Mg, Ni, Lu, In and Sc It is
necessary that the composite perovskite structure has any one or more elements selected from
the group consisting of: and one or more elements selected from the group consisting of Nb, Ta,
Mo and W. In particular, in the case of using lead zinc niobate-lead titanate (PZN-PT) as a solid
solution single crystal, the molar fraction x is preferably in the range of 0.80 to 0.98, more
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preferably 0.89 to 0.95. . In addition, when using magnesium niobate-lead titanate (PMN-PT) as
the solid solution single crystal, the molar fraction x may be in the range of 0.60 to 0.98, and
more preferably 0.60 to 0.80. preferable. In the case of using indium / lead magnesium oxidelead titanate (PIMN-PT) as the solid solution single crystal, the mole fraction x is preferably in the
range of 0.60 to 0.80, more preferably 0.64 to 0.76. Is preferred. Furthermore, when it is
necessary to increase the relative dielectric constant rr and the mechanical quality factor Qm, the
composition of the above-mentioned piezoelectric single crystal device may be Mn, Cr, Sb, Ca, W,
Al, La, Li. And Ta may be added in an amount of 0.5 mass ppm to 5 mass%, respectively. In total,
addition of more than 5% by mass makes it difficult to form single crystals and may result in
polycrystals. The effect of adding these elements is, for example, by adding Mn and Cr, it is
possible to improve the mechanical quality factor Qm and suppress deterioration with time.
In addition, the addition of Sb, La, W and Ta improves the relative dielectric constant εr.
[0034]
Next, a preferred method of manufacturing the piezoelectric single crystal device of the present
invention will be described. The method of manufacturing a piezoelectric single crystal device
according to the present invention comprises the steps of manufacturing a single crystal ingot
having a domain structure, cutting out a piezoelectric single crystal material of a predetermined
shape from the single crystal ingot in a predetermined direction, and the piezoelectric single
crystal It is characterized by having a main polarization step of applying an electric field under
predetermined conditions in the [001] direction of the material to polarize the piezoelectric
single crystal material, or an auxiliary polarization step before and after the main polarization
step. . Hereinafter, the reasons for limitation of the manufacturing method of the present
invention in each step will be described.
[0035]
(5) Production of single crystal ingot having domain structure: xPb (A1, A2, ..., B1, B2, ...) O3 + (1x) PbTiO3 (where x is a mole fraction, 0 <x <1 I assume. And the like, wherein A1, A2,... Are
composed of one or more elements selected from the group consisting of Zn, Mg, Ni, Lu, In and
Sc, and B1, B2. And W, or a single crystal of one or more elements selected from the group
consisting of Mn, Cr, Sb, Ca, W, Al, La, Li, and Ta in the above composition. The method of
manufacturing a single crystal ingot in which 0.5 mass ppm to 5 mass% of the element is added
is a method of dissolving the raw material adjusted to the above composition in a flux and then
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lowering the temperature to solidify it or heating to a melting point or more There is a method of
obtaining a single crystal by solidifying in one direction after melting. The former method
includes the flux method, the melt bridgeman method, or the TSSG method (Top Seeded Solution
Growth), and the latter method includes the horizontal melting bridgeman method, the CZ
method (Czochralski method), etc. However, in the present invention, it is not particularly
defined.
[0036]
(6) Determination of Crystallographic Orientation of Single Crystal Ingot: The [001] axis
orientation of a single crystal ingot is roughly determined by the Laue method, and at the same
time, the [010] axis orientation and the [100] axis orthogonal to the [001] axis orientation.
Orientation or approximately determines the crystallographic orientation, such as the [110],
[101], [011] axis orientation as required. Furthermore, the crystallographic plane {100} plane
orthogonal to any crystal axis such as [001] axis, [010] axis and [100] axis is polished, and the
correct orientation is obtained using an X-ray direction measuring machine etc. Determine and
correct the above-mentioned deviation of the polished surface.
[0037]
(7) Rough cutting (cutting into a wafer of appropriate thickness): Cutting a single crystal ingot
with a wire saw or an inner edge cutting machine etc. parallel or orthogonal to the polished
surface {100} of the above single crystal ingot Cut using a machine to obtain a plate material
(wafer) of appropriate thickness. In addition, the process of chemical-etching using etching
solution can also be included after cutting as needed.
[0038]
(8) Polishing (cutting into a wafer of a predetermined thickness): The above-mentioned wafer is
ground or polished by a grinder or polishing machine such as a lapping machine, a polishing
machine or the like to obtain a wafer of a desired thickness. In addition, the process of chemicaletching using etching liquid as needed can also be included after grinding and grinding |
polishing.
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[0039]
(9) Fabrication of Piezoelectric Single Crystal Material: The above wafer has a {100} plane on the
wafer surface (the widest surface). The domain structure (the extending direction of the streaked
lines) of this wafer, as shown in FIG. 5, forms an angle parallel or perpendicular (FIG. 7A) or 45
° with the [100] axis orientation. {100}With respect to the direction n orthogonal to the
domain structure (the extending direction of the striped line) existing in the plane, the normal
direction 1 of the element end face is 0 to 15 ° or 40 to 50 °. From a wafer, a piezoelectric
single crystal material of a predetermined shape is cut out and manufactured using a precision
cutting machine such as a dicing saw or a cutting saw.
[0040]
(10)
Preparation of Electrodes: It is necessary to prepare in advance the electrodes necessary for
applying an applied electric field in the main polarization treatment or in addition, in the
auxiliary polarization treatment. Before main polarization treatment, Cr-Au coating (Cr layer of
1st layer: thickness about 50 Å, Au layer of 2nd layer) by sputtering method on the upper and
lower surfaces which are opposite {100} faces of the produced piezoelectric single crystal
material : Form a gold film by plasma deposition or form a silver film by screen printing, and
then bake to form an electrode. In addition, before the auxiliary polarization treatment,
electrodes are formed in the same manner as described above on two opposing surfaces
perpendicular to the auxiliary polarization direction. When the main polarization treatment is
performed after the auxiliary polarization treatment, or when the auxiliary polarization treatment
is performed after the main polarization treatment, if the electrode used for the first polarization
treatment remains, the subsequent polarization treatment becomes unstable. The electrode
should be completely removed with an appropriate chemical etchant and acid.
[0041]
(11)
Main polarization treatment step: Single crystal cut out from the grown single crystal ingot, as it
is, the direction of the electric dipole in the domain consisting of a set of electric dipoles in the
same direction in the polarization direction 3 and the direction orthogonal thereto. Because they
are oriented in various directions in each domain, they do not exhibit piezoelectricity and are in
an unpolarized state. By selecting the polarization processing temperature and applied electric
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field, which are generally used polarization conditions, and applying an electric field in the
polarization direction 3 for polarization, electric dipoles in many domains that are directed in
various directions for each domain for the first time The orientation of the child can be aligned
with the polarization direction 3 (one direction). As a result, the electromechanical coupling
coefficient k33 in the polarization direction 3 exhibits a large value of 80% or more, for example,
in the case of lead zinc niobate-lead titanate. However, the arrangement of domains in the
direction orthogonal to the polarization direction 3 can not be controlled by the above-mentioned
polarization process. Proper selection of the domain structure in the plane orthogonal to the
polarization direction 3 of the originally cut out element material, and the polarization conditions
in the polarization direction 3, that is, within the appropriate range of polarization temperature
and applied electric field and polarization time It is possible to control only with.
[0042]
In the main polarization step of the present invention, it is preferable to apply a DC electric field
of 350 to 1500 V / mm in a temperature range of 20 to 200 ° C. in the polarization direction 3
of the cut out piezoelectric single crystal material. That is, in the case of less than 20 ° C. which
is the lower limit value of the above preferable temperature range or less than the lower limit
value 350 V / mm of the applied electric field range, the polarization is insufficient. When the
temperature exceeds the upper limit of 200 ° C. of the above preferable temperature range or
exceeds the upper limit of 1500 V / mm of the applied electric field range, hyperpolarization
(over pole) occurs to deteriorate the piezoelectric characteristics of the piezoelectric single
crystal device. Let In addition, an excessive electric field may increase strain in the crystal to
cause breakage, which may cause a crack in the piezoelectric single crystal device.
[0043]
In addition, it is preferable to adjust the polarization time in accordance with the polarization
processing temperature and the applied electric field selected within the above preferable range.
The polarization time is at most 180 minutes. Alternatively, the main polarization step may be
performed at a temperature higher than the Curie temperature Tc of the piezoelectric single
crystal material in the polarization direction 3 of the cut out piezoelectric single crystal material,
preferably 250 to 500 V / mm in a temperature range of 180 to 300 ° C. It may be cooled
(electric field cooling) to room temperature while applying a direct current electric field. By
setting the temperature higher than the Curie temperature, the presence of the electric dipole is
once eliminated, and then, by cooling to a temperature lower than the Curie temperature, the
directions of the electric dipoles are aligned more clearly. If the temperature is lower than the
13-04-2019
15
Curie temperature, an electric dipole remains in part, and the polarization becomes insufficient.
In addition, in the case where the lower limit value of the preferable applied electric field range is
less than 250 V / mm, the polarization is insufficient. When the upper limit 500 V / mm of the
preferable applied electric field range is exceeded, hyperpolarization (over pole) occurs to
deteriorate the piezoelectric characteristics of the piezoelectric single crystal element. In addition,
an excessive electric field may increase strain in the crystal, causing a crack in the piezoelectric
single crystal element, which may cause breakage. The cooling rate is preferably a rate at which
no crack occurs in the element during cooling. The Curie temperature is a transition temperature
at which the electric dipoles do not align in random directions and become non-piezoelectric or
ferroelectric. This is determined by the composition and the structure of the substance.
[0044]
(12)
Auxiliary polarization treatment step: The above-mentioned main polarization step is a step of
performing main polarization of the piezoelectric single crystal element, preferably before or
after the main polarization step, in a direction orthogonal to the above polarization direction 3,
preferably It is also effective to apply an electric field in the transverse vibration direction 1 to
control the alignment state of the ferroelectric domains in the direction orthogonal to the
polarization direction 3 described above. Types of electric field applied in the direction
orthogonal to the polarization direction 3 include DC electric field, pulse electric field, AC electric
field, and steady electric field of these electric fields, and attenuation electric field etc. There are
appropriate conditions depending on the characteristics of the individual piezoelectric single
crystal elements and the desired value of the electromechanical coupling coefficient k31 in the
direction orthogonal to the polarization direction. These can be determined by experiments and
the like. In order to obtain the effect of the auxiliary polarization, the auxiliary polarization
temperature is preferably 25 ° C. to a phase transition temperature (for example, Trt line shown
in FIG. 4) or less, and the applied electric field range is preferably 350 to 1500 V / mm. In
addition, although it is preferable to adjust polarization time according to the polarization
process temperature and application electric field which were chosen within said suitable range,
10 minutes-2 hours are desirable especially. Further, as the pulse electric field, unipolar and
bipolar pulses such as an AC triangular wave as shown in FIG. 10 can be used in addition to the
rectangular wave.
[0045]
Domain structure (parallel light and shade on the crystal plane) to obtain a piezoelectric single
crystal element with high electromechanical coupling coefficient k31 suitable as a piezoelectric
single crystal element utilizing a direction (lateral vibration mode) orthogonal to the polarization
13-04-2019
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direction In the following, the method of selecting the stripe pattern and controlling the
polarization conditions will be described by way of examples.
[0046]
(Example 1) 0.91 lead zinc niobate (PZN) + 0.09 lead titanate (PT) (represented by mole fraction
with x = 0.91) used piezoelectric single crystal element (Curie temperature Tc = 175 ° C,
element) Shape: The shape of 13 mm in length × 4 mm in width × 0.36 mm in thickness is
shown in FIG.
[0047]
In addition, according to the manufacturing method described above, the piezoelectric single
crystal element is manufactured so as to have a composition of 0.91 lead zinc niobate (PZN) +
0.09 lead titanate (PT) (expressed as a molar fraction of x = 0.91) After being adjusted, a single
crystal ingot was obtained by the above-mentioned melt Bridgman method.
Next, the exact crystallographic orientation of this single crystal ingot was determined and
polished, and the single crystal ingot was cut with a wire saw orthogonal to this polished surface
{100} plane to obtain a plate of 0.5 mm thickness .
The plate was polished by a polishing machine to obtain a 0.36 mm thick wafer. A piezoelectric
single crystal material of element shape: 13 mm long × 4 mm wide × 0.36 mm thick was cut
out from this wafer using a dicing saw. In the piezoelectric single crystal materials 10 and 11 in
which six manufactured faces are surrounded by {100} planes, the polarization direction is the
[00-1] axial direction between the upper surface 10a or 11a and the lower surface 10b or 11b
(FIG. 6 (a In the vertical direction).
[0048]
In the piezoelectric single crystal material 10, the direction n orthogonal to the domain structure
(the extending direction of the striped pattern on the surface) of the upper surface 10a is
orthogonal to the normal direction 1 of the device end face 10c (FIG. 6 (b 7A and 7B, the single
crystal wafer 12 shown in FIG. 7A is cut out using a dicing saw, and the piezoelectric single
crystal material 11 has the domain structure of the upper surface 11a (surface As shown in FIG.
7A, the direction n orthogonal to the extending direction of the upper striped line is parallel to
the normal direction 1 of the element end face 11c (FIGS. 6C and 7C). A large single crystal wafer
13-04-2019
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12 shown in FIG. 1 is cut out using a dicing saw.
[0049]
Cr-Au coating (Cr layer in the first layer: about 50 Å thick) by sputtering on upper and lower
surfaces 10a and 10b or 11a and 11b which are opposite {100} faces of each of the prepared
piezoelectric single crystal materials 10 and 11 Au layer: about 100 to 200 Å thick) to form a
gold electrode, and by applying a DC electric field of 700 V / mm for 60 minutes in the air at 25
° C. for polarization, a piezoelectric single crystal is formed. Devices 10 'and 11' were
manufactured.
[0050]
The impedance curve and phase of the k31 mode obtained using the impedance phase gain
analyzer (manufactured by HP, device number: HP4912) for the two types of polarizationprocessed piezoelectric single crystal devices 10 'and 11' manufactured. Are shown in FIGS. 8 (a)
and 8 (b), respectively.
In FIGS. 8A and 8B, the electromechanical coupling coefficient k31 increases as the difference
between the two frequencies when the phase is 0 °, that is, the resonance frequency fR and the
antiresonance frequency fA increases. Indicates that is large.
In addition, k31 was calculated by a known calculation formula (refer to the standard of
electronic material industry association: EMAS-6008, 6100). The measurement results are shown
in Table 1.
[0051]
[0052]
The angle n between the direction n orthogonal to the piezoelectric single crystal element 10
'(the domain structure of the upper surface 10a (the extending direction of the striped pattern on
the surface) shown in FIG. 8A) and the normal direction 1 of the element end face 10c. Is 90 °,
the electromechanical coupling coefficient k31 in the direction (lateral vibration mode)
orthogonal to the polarization direction is 50.7% and 55% or less, which is insufficient as the
characteristic of the element for the lateral vibration mode (Fig. 8 (a)).
13-04-2019
18
[0053]
On the other hand, the direction n orthogonal to the piezoelectric single crystal element 11 '(the
domain structure of the upper surface 11a (the extending direction of the striped pattern on the
surface) shown in FIG. When the angle formed is 0 °, the electromechanical coupling coefficient
k31 in the direction (lateral vibration mode) orthogonal to the polarization direction is also
86.2% and 80% or more, which is sufficient as the characteristic of the element for the lateral
vibration mode (Fig. 8 (b)).
[0054]
In addition, Mn, Cr, Sb, Ca, W, Al, La, Li and a solid solution of 0.91 lead zinc niobate (PZN) +
0.09 lead titanate (PT) (represented by mole fraction with x = 0.91) Also for a composition
further containing 0.5 mass ppm to 5 mass% of one or more elements selected from the group
consisting of Ta, a device is manufactured by the same manufacturing method as 0.91 PZN-0.09
PT, 0.91 PZN-0.09 PT When the electromechanical coupling coefficient k31 was examined under
the same test conditions as in Table 1, as shown in Table 1, in each case the piezoelectric single
crystal element 11 '(domain structure of its upper surface 11a A high electromechanical coupling
coefficient k31 is obtained when the direction n orthogonal to the above is 1 and 0 ° in the
normal direction of the device end face 11c.
In particular, when Mn or Cr is added, the mechanical quality factor Qm is significantly improved
from 65.0 to 120.0 to 150.0, and the addition of Sb, W, La, and Ta results in a relative dielectric
constant εr of 3500 to 4300 to Significantly improved with 4700.
The mechanical quality factor Qm and the relative dielectric constant εr are determined using
an impedance analyzer (manufactured by HP, device number: HP4192A) in accordance with the
Electronic Materials Industry Association Standard (refer to: EMAS-6008, 6100). The
[0055]
Example 2 In order to investigate in detail the correlation between the end face orientation 1
(more strictly, the normal direction of the end face) of the element using the transverse vibration
mode and the domain structure, the inventor further examined FIG. As shown in a), with respect
13-04-2019
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to the direction n orthogonal to the domain structure (the extending direction of the streaked line
on the surface), the normal direction 1 of the end face 11c of the element using transverse mode
is 0 ° (figure Various single crystal element materials 11 cut out using a dicing saw while
changing from [100] direction shown in 9 (a) to 90 ° ([010] direction shown in FIG. 9A) every 5
° , 13 and the like, and polarized in a direction perpendicular to the paper surface of FIG. 9A by
using a polarization method of applying a DC electric field of 700 V / mm for 60 minutes in the
atmosphere at 25 ° C. After setting ', 13', the electromechanical coupling coefficient k31 for the
transverse vibration mode was measured.
The measurement results are shown in Table 2. The method of manufacturing the piezoelectric
single crystal device, the device dimensions, and the test conditions were the same as in Example
1.
[0056]
Here, the [100] axis direction in the plane orthogonal to the polarization direction (in the plane of
the drawing in FIG. 9A, strictly speaking, in the crystal plane including the [010] axis and the
[100] axis orthogonal to the polarization direction 3). The selection of the range of 0 ° to 90 °
with respect to, from the symmetry of cubic crystal, makes the angle range necessary and
sufficient for obtaining information on all directions in the {100} plane orthogonal to the
polarization direction. It is for.
[0057]
[0058]
From the results shown in Table 2, 0.91 lead zinc niobate (PZN) + 0.09 lead titanate at 0 ° to 15
° and 40 to 50 ° with respect to the [100] axis direction in the plane orthogonal to the
polarization direction 3 It can be seen that (PT) exhibits an electromechanical coupling
coefficient k31 of 70% or more for the lateral vibration mode, and is suitable as a device for
lateral use.
FIG. 9B is a surface photograph of a single crystal element cut out using a dicing saw so that the
normal direction 1 of the element end face with respect to the direction n orthogonal to the
domain structure is 48 °.
13-04-2019
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[0059]
Furthermore, in the range of angle 0 to 15 ° and angle 40 to 50 °, the angle is not in steps of 5
°, and k31 is measured in detail also for the angle between them. It was also confirmed that the
electromechanical coupling coefficient k31 of was always 70% or more.
[0060]
In addition, in the case where the mole fraction x of lead zinc niobate (PZN) of lead x zinc niobate
(PZN) + (1-x) lead titanate (PT) (PZN-PT) is 0.80 or 0.95 ( Lead-magnesium niobate (PMN) + lead
titanate (PT) (PMN-PT) of materials other than 0.80 PIMN-0.20 PT and 0.95 PZN-0.05 PT) and
lead zinc niobate Also for (PIMN) + lead titanate (PT) (PIMN-PT), a device is manufactured by the
same manufacturing method as 0.91 PZN-0.09 PT, and an electromechanical coupling coefficient
k31 under the same test conditions as 0.91 PZN-0.09 PT. As shown in Table 2, a high
electromechanical coupling coefficient k31 was obtained in the range of angle 0 to 15 ° and the
range of angle 40 to 50 °.
Here, 0.70 PMN-0.30 PT has a molar fraction x of magnesium lead niobate (PMN) of 0.70, and
0.70 PIMN-0.30 PT has a molar fraction of lead magnesium niobate (PIMN) x Is 0.70.
[0061]
On the other hand, in the appropriate range consisting of the range of 0 to 15 ° and the range
of 40 to 50 ° with respect to the [100] axis direction in the plane orthogonal to the polarization
direction 3, the transverse vibration mode is dispersed and generated It is considered that an
electromechanical coupling coefficient k31 of a high transverse vibration mode can be obtained
because there is no crystal axis orientation of low index such as <310>, <210>, <320>.
When the range of the angle θ is in the range of 75 ° ≦ θ ≦ 90 °, the correlation between
the domain structure and the normal direction of the end face of the device utilizing the
transverse vibration is a reverse correlation to 0 ≦ θ ≦ 15 °. Therefore, it is considered that
only the electromechanical coupling coefficient k31 of the low transverse vibration mode can be
obtained.
13-04-2019
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[0062]
Example 3 Next, a preferred polarization treatment method for producing a piezoelectric single
crystal element suitable for use in the transverse vibration mode will be described using Example
3. Table 3 shows the measurement results of the electromechanical coupling coefficient k31 of
the lateral vibration mode of the piezoelectric single crystal devices 10 'and 11' manufactured
under various polarization processing conditions. The method of manufacturing the piezoelectric
single crystal device, the device dimensions, and the test conditions were the same as in Example
1. The same composition as in Example 2 was used for the composition of the piezoelectric single
crystal element. The measurement results are shown in Table 3.
[0063]
[0064]
The polarization treatment temperature of the crystal 11 suitable for utilizing the transverse
mode manufactured in the same manner as in Example 1 is 25 ° C., the applied electric field is
320 V / mm below the lower limit of the range of the present invention, and the application time
is 30 minutes In the case of several points between 180 minutes, the electric machine in the
direction (lateral vibration mode) orthogonal to the polarization direction is shown as a
representative of the case where the application time is the longest 180 minutes in (1) of Table 3
The coupling coefficient k31 was 58% and 60% or less for lead 0.91 zinc niobate (PZN) and lead
0.09 titanate (PT), and the characteristics of the device for the transverse vibration mode were
insufficient.
180In the application time shorter than a minute, only a lower electromechanical coupling
coefficient k31 was obtained. This is considered to be due to insufficient polarization under the
conditions.
[0065]
On the other hand, in the crystal 10 which is not suitable for the use of the transverse mode
manufactured by the same method as the first embodiment, in any case, the electromechanical
coupling coefficient k31 in the direction (lateral vibration mode) orthogonal to the polarization
direction is 0.91. Zinc lead niobate (PZN) + 0.09 lead titanate (PT) was 55% or less, and no
improvement in polarization treatment conditions was obtained.
13-04-2019
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[0066]
The temperature of the crystal 11 suitable for use in the transverse vibration mode
manufactured in the same manner as in Example 1 is 40 ° C., the applied electric field is 1700 V
/ mm exceeding the upper limit of the range of the present invention, and the application time is
In the case where the number of points is between 30 minutes and 180 minutes, as shown in (9)
of Table 3 as a representative case where the application time is at a minimum of 30 minutes,
electricity in the direction orthogonal to the polarization direction (lateral vibration mode) The
mechanical coupling coefficient k31 was 53% for lead 0.91 zinc niobate (PZN) + lead 0.09
titanate (PT).
In addition, when the application time exceeds 30 minutes, there are many cases where a crack is
generated in the piezoelectric single crystal element during or immediately after the application
is completed.
[0067]
It is considered that under this condition, hyperpolarization (over pole) occurs to degrade the
piezoelectric characteristics of the piezoelectric single crystal device. Further, the generation of
the crack in the piezoelectric single crystal element is considered to be that the strain in the
crystal 11 is increased by the excessive electric field and the breakage is caused. In either case, in
crystal 10, the electromechanical coupling coefficient k31 in the direction <lateral vibration
mode> orthogonal to the polarization direction is 55% or less for lead 0.91 zinc niobate (PZN) +
lead 0.09 titanate (PT) No improvement was obtained under the polarization conditions.
[0068]
Furthermore, the crystal 11, which is suitable for use in the transverse vibration mode, is applied
for 120 minutes in a silicone oil of 200 ° C. higher than the Curie temperature Tc shown in FIG.
4 while applying a DC electric field of 400 V / mm. When the temperature of the silicone oil is
lowered to room temperature (25 ° C.), as shown in (10) of Table 3, the electromechanical
coupling coefficient k31 in the direction (lateral vibration mode) orthogonal to the polarization
direction is 0.91 zinc niobium In lead acid (PZN) + 0.09 lead titanate (PT), it was 80% and 70% or
13-04-2019
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more. This indicates that the method of cooling with an applied electric field (electric field
cooling) is effective. However, in the crystal 10, under the conditions, the electromechanical
coupling coefficient k31 in the direction (lateral vibration mode) orthogonal to the polarization
direction is 55% or less, and no improvement under the polarization treatment condition by
electric field cooling is obtained.
[0069]
In (2) to (8) of Table 3, piezoelectric single crystal devices were manufactured under polarization
processing conditions in which a DC electric field of 350 to 1500 V / mm was applied in a range
of 30 minutes to 180 minutes in a temperature range of 25 to 60 ° C. That's the case. In this
case, the electromechanical coupling coefficient k31 in the direction (lateral vibration mode)
orthogonal to the polarization direction of the crystal 11 suitable for use in the horizontal
vibration mode is 0.91 lead zinc niobate (PZN) + 0.09 lead titanate ( In PT), 78 to 86% and 70%
or more of all. However, in the crystal 10, under the above conditions, the electromechanical
coupling coefficient k31 in the direction (lateral vibration mode) orthogonal to the polarization
direction is 55 for 0.91 lead niobate (PZN) + 0.09 lead titanate (PT). % Or less, and no
improvement in polarization treatment conditions was obtained.
[0070]
In addition, when x mole fraction of lead zinc niobate (PZN) of lead x zinc niobate (PZN) + (1-x)
lead titanate (PT) (PZN-PT) is 0.80 or 0.95 Lead-magnesium niobate (PMN) + lead titanate (PT)
(0.70 PMN-0.30) using 0.80 PZN-0.20 PT and 0.95 PZN-0.05 PT) and magnesium niobate
instead of lead zinc niobate The same manufacturing method as 0.91PZN-0.09PT is also used for
PT) and lead indium magnesium oxide (PIMN) + lead titanate (PT) (0.70PIMN-0.30PT) in which
indium is added to magnesium and lead niobate The element was fabricated, and the
electromechanical coupling coefficient k31 was examined under the same test conditions as 0.91
PZN-0.09 PT. As shown in Table 3, the crystal 11 which is suitable for use in the transverse
vibration mode is better than the crystal 10 The electromechanical coupling coefficient k31 is
also high, and in a DC electric field of 350 to 1500 V / mm in a temperature range of 25 to 60 °
C., An element having a high electromechanical coupling coefficient k31 was obtained. Thus, the
same results as in 0.91 lead niobate (PZN) + 0.09 lead titanate (PT) were obtained in all devices
having compositions other than 0.91 PZN-0.09 PT. Here, 0.70 PMN-0.30 PT has a molar fraction
x of magnesium lead niobate (PMN) of 0.70, and 0.70 PIMN-0.30 PT has a molar fraction of lead
magnesium niobate (PIMN) x Is 0.70.
13-04-2019
24
[0071]
Example 4 Next, a suitable auxiliary polarization treatment method for manufacturing a
piezoelectric single crystal element suitable for use in the transverse vibration mode will be
described using Example 4. Table 4 shows the measurement results of the electromechanical
coupling coefficient k31 of the transverse vibration mode of the piezoelectric single crystal
element 11 'manufactured under various auxiliary polarization conditions. The method of
manufacturing the piezoelectric single crystal element 11, the element dimensions, and the test
conditions were the same as in Example 1. The same composition as in Example 2 was used for
the composition of the piezoelectric single crystal element. The element shape is such that the
normal direction 1 of the element end face 11c is 15 ° with respect to the direction n
orthogonal to the domain structure (the extending direction of the striped line) present in the
{100} plane: A 13 mm long × 4 mm wide × 0.36 mm thick piezoelectric single crystal material
was cut out and fabricated using a dicing saw.
[0072]
[0073]
Cr-Au coating (Cr layer of about 50 Å thickness in the first layer, Au of the second layer) on both
end faces 11c of the crystal 11 suitable for utilizing the transverse mode manufactured by the
same method as in Example 1 by sputtering Layer: a thickness of about 100 to 200 .ANG.) To
form an electrode, the auxiliary polarization temperature is 25 to 40.degree. C., the DC applied
electric field is 320 to 1700 V / mm, and the application time is 10 to 150 minutes. Auxiliary
polarization treatment was performed.
Thereafter, the above electrode is completely dissolved and removed with a chemical etching
solution and an acid, and Cr-Au coating (1) is sputtered on upper and lower surfaces 11a and
11b which are opposite {100} faces of piezoelectric single crystal material 11. An electrode is
prepared by forming a Cr layer of about 50 Å in thickness and an Au layer of about 100 to 200 Å
in thickness for the second layer, and the main polarization process produces a DC electric field
of 700 V / mm in air at 25 ° C. Was applied for 60 minutes. The electromechanical coupling
coefficient k31 in the direction (lateral vibration mode) orthogonal to the polarization direction is
shown in Table 4. In (2) to (6) of Table 4, a piezoelectric single crystal element is manufactured
under auxiliary polarization processing conditions in which a DC electric field of 350 to 1500 V /
13-04-2019
25
mm is applied in a range of 10 minutes to 120 minutes in a temperature range of 25 to 60 ° C.
It is the case. In this case, the electromechanical coupling coefficient k31 in the direction (lateral
vibration mode) orthogonal to the polarization direction of the crystal 11 suitable for use in the
horizontal vibration mode is 0.91 lead zinc niobate (PZN) + 0.09 lead titanate ( In PT), k 31 in the
case of (11) in Table 4 which was not subjected to the auxiliary polarization treatment was 74%,
but all were 78% or more. By this auxiliary polarization process, an even higher
electromechanical coupling coefficient k31 was obtained. In addition, in the case of (8) in Table 4
in which the auxiliary polarization process was performed under the same conditions as (3) in
Table 4 after the main polarization step, a high electromechanical coupling coefficient k31 was
obtained as high as 83%.
[0074]
In addition, as shown in (9) and (10) of Table 4, a high electromechanical coupling coefficient
k31 was obtained also when a bipolar triangular wave pulse electric field as shown in FIG. 10
was applied for 10 minutes before and after the main polarization step. .
[0075]
Furthermore, in the two cases where the mole fraction x of lead zinc niobate (PZN) of lead x zinc
niobate (PZN) + (1-x) lead titanate (PT) (PZN-PT) is 0.80 and 0.95 ( Lead Magnesium Niobate
(PMN) + Lead Titanate (PT) (0.70 PMN-0.30) using 0.80 PZN-0.20 PT and 0.95 PZN-0.05 PT)
and magnesium niobate instead of zinc niobate The same manufacturing method as 0.91PZN0.09PT is also used for PT) and lead indium magnesium oxide (PIMN) + lead titanate (PT)
(0.70PIMN-0.30PT) in which indium is added to magnesium and lead niobate The element was
fabricated, and the electromechanical coupling coefficient k31 was examined under the same test
conditions as 0.91 PZN-0.09 PT. As shown in Table 4, in the crystal 11 suitable for use in the
transverse vibration mode, before and after the main polarization treatment DC electric field
range of 350 to 1500 V / mm in the temperature range of 25 to 40 ° C under the auxiliary
polarization conditions performed in At an applied electric field treatment by the bipolar
triangular wave pulse electric field, the electromechanical coupling factor k31 was improved.
Thus, the same results as in 0.91 lead niobate (PZN) + 0.09 lead titanate (PT) were obtained in all
devices having compositions other than 0.91 PZN-0.09 PT. Here, 0.70 PMN-0.30 PT has a molar
fraction x of magnesium lead niobate (PMN) of 0.70, and 0.70 PIMN-0.30 PT has a molar
fraction of lead magnesium niobate (PIMN) x Is 0.70.
13-04-2019
26
[0076]
According to the present invention, for applications such as an actuator or a transducer used for
position control of a precision machine, for example, which actively utilizes the
electromechanical coupling coefficient k31 in a direction (lateral vibration mode) orthogonal to
the polarization direction. It is possible to manufacture the used piezoelectric single crystal
element (device).
[0077]
It is an example which shows the direction and shape of a piezoelectric single crystal element
using electromechanical coupling coefficient k33 of a longitudinal direction vibration mode.
(a) is an example showing the orientation and shape of a piezoelectric single crystal element
using the electromechanical coupling coefficient k31 in a direction 1 (lateral vibration mode)
orthogonal to the polarization direction 3; (b) is a polarization direction 3 Is a diagram showing
the shape of the end face of a piezoelectric single crystal element using an electromechanical
coupling coefficient k31 in a direction 1 (lateral vibration mode) orthogonal to the direction. It is
a typical perspective view of perovskite crystal structure (RM03). It is a phase diagram of PZN-PT
(PZNT). It is a schematic diagram of the domain structure of the cube surface whose six faces are
{100} faces. (a) is an explanatory view when a direct current electric field is applied to a single
crystal, (b) is an angle between a normal direction 1 of the end face 10c of the piezoelectric
single crystal material 10 and a direction n orthogonal to the domain structure Is a diagram
showing 90 °, and (c) is a diagram showing an angle of 0 ° between the normal direction 1 of
the end face 11 c of the piezoelectric single crystal material 11 and the direction n orthogonal to
the domain structure. (a) is a diagram showing the relationship between the piezoelectric single
crystal materials 10 and 11 having a (001) plane (paper surface) orthogonal to the polarization
direction 3 and the domain structure, and (b) is a diagram of the piezoelectric single crystal
material 10 Surface photograph showing domain structure (one square of background squared
paper is 1 mm), (c) is surface photograph showing domain structure of piezoelectric single
crystal material 11 (one square of background squared paper is 1 mm) It is. (a) is a figure which
shows the impedance curve and phase of k31 vibration mode in the case of piezoelectric single
crystal element 10 ', (b) is the impedance curve and phase of k31 vibration mode in the case of
piezoelectric single crystal element 11' FIG. (a) illustrates the direction in which various
piezoelectric single crystal materials are cut out from the single crystal wafer 12 in the normal
direction 1 of the device end face (11c, 13c) with respect to the direction n orthogonal to the
domain structure 1 to 90 °. (B) is a surface photograph of a single crystal element cut out so
that the normal direction 1 of the end face of the element with respect to the direction n
orthogonal to the domain structure is 48.degree. One square is 1 mm). It is a wave form diagram
13-04-2019
27
of a bipolar triangular wave pulse.
Explanation of sign
[0078]
10、11、13 Single crystal element material 10a, 11a electrode face (001) 10b, 11b electrode
face (00-1) 10c, 11c cut end face of piezoelectric single crystal material 12 single crystal wafer
10 ', 11', 13 ': after polarization treatment Piezoelectric single crystal material a Horizontal
direction (direction 1 of transverse vibration) dimension of single crystal device b (depth
(direction 2)) dimension of end surface of single crystal device b ′ convex end surface of single
crystal device b ′ ′ single crystal device Concave end face L: longitudinal direction of single
crystal element (direction of polarization 3) dimension V: DC voltage 1: normal direction of
element end face (transverse vibration direction) 3: polarization direction (longitudinal vibration
direction) n: domain structure Direction perpendicular to the extending direction of the striped
line)
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