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DESCRIPTION JP2006147840

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DESCRIPTION JP2006147840
A piezoelectric / electrostrictive device capable of effectively preventing vibration damping of a
thin-walled diaphragm portion, maintaining high displacement (amplitude) and having excellent
response and capable of highly accurate (high resolution, high sensitivity) detection. provide. A
ceramic substrate 1 having a thick portion 11 and a thin diaphragm portion 12 and a
piezoelectric / electrostrictive element 2 having a layer structure including a lower electrode 21,
a piezoelectric / electrostrictive film 22 and an upper electrode 23. In addition, the thin-walled
diaphragm portion 12 of the ceramic base 1 is vibrated in conjunction with the drive of the
piezoelectric / electrostrictive element 2, and the shape and dimensions defined in the following
(A) to (C) Configure to meet the relationship. (A) The shape of the thin diaphragm portion 12 is
an outwardly convex arch shape, and the amount of outward projection of the arch shape is 5 to
50 μm. (B) The installation width of the thin diaphragm portion is 600 to 2000 μm, and (C) the
ratio (height / width) of the height of the thick part to its width is 0.25 to 3. [Selected figure]
Figure 1
Piezoelectric / electrostrictive device
[0001]
The present invention relates to a piezoelectric / electrostrictive device. More specifically, the
present invention relates to a piezoelectric / electrostrictive device used as an actuator utilizing
bending displacement, or various sensors (for example, a sensor for a microphone, a viscosity
sensor, etc.) for detecting fluid characteristics, sound pressure, minute weight, acceleration, etc. .
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1
[0002]
Piezoelectric / electrostrictive devices are used as actuators and various sensors. As such a
piezoelectric / electrostrictive device, for example, one used for measurement of characteristics
such as density, concentration, and viscosity of a fluid is disclosed (see Patent Document 1). Such
a piezoelectric / electrostrictive device is a sensor utilizing the correlation between the amplitude
of the piezoelectric / electrostrictive device as a vibrator and the viscosity resistance of the fluid
in contact with the piezoelectric / electrostrictive device (vibrator) It is used as
[0003]
In general, the vibration mode in a mechanical system such as vibration of a vibrator can be
replaced by an equivalent circuit in an electric system, and a piezoelectric / electrostrictive
device (vibrator) is vibrated in a fluid, and the vibrator is a fluid Properties of the fluid, such as
viscosity, density, concentration, etc., by using the change of the electrical constant of the
equivalent circuit of the piezoelectric / electrostrictive element constituting the vibrator by
receiving mechanical resistance based on the viscosity resistance of It is measuring. Here, as the
fluid which can be measured, liquid and gas can be mentioned. Such a liquid may consist of a
single component such as water, alcohol, oil, etc. A solution, a mixture or a suspension of a
medium soluble or insoluble in these, a slurry, a paste Or the like.
[0004]
Moreover, as an electrical constant to be detected, for example, loss factor, phase, resistance,
reactance, conductance, susceptance, inductance, capacitance and the like can be mentioned, and
in particular, a maximum or minimum change point near the resonance frequency of the
equivalent circuit. A loss factor or phase having one is preferably used. Thus, not only the
viscosity of the fluid but also the density and concentration (for example, the concentration of
sulfuric acid in an aqueous sulfuric acid solution) can be measured. In addition to the electrical
constant, the change in resonance frequency may be used as an index for detecting the change in
vibration mode, as long as there is no particular problem in terms of measurement accuracy and
durability. When a ferroelectric is used as a piezoelectric / electrostrictive element, after applying
a pulse-like electric field, the charge generated due to the delay of the dipole moment of the
ferroelectric is detected as a voltage. You can also use changes in
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[0005]
As such a piezoelectric / electrostrictive device, a ceramic substrate having a thick portion and a
thin diaphragm portion integrally formed with the thick portion to form a cavity, and a
piezoelectric / electrostrictive element fixed to the outer surface thereof , And an auxiliary
electrode is formed at a position independent of the lower electrode constituting the piezoelectric
/ electrostrictive element, and a portion of the auxiliary electrode is inserted into a lower portion
of the piezoelectric / electrostrictive film. What was formed is disclosed (refer patent document
2). With this configuration, the upper electrode can be formed continuously without
disconnection on the surface of the auxiliary electrode and the piezoelectric / electrostrictive
element, and the reliability of connection of the upper electrode can be improved. . The fluid to
be measured is introduced and filled into the cavity via the through hole. Furthermore, by
forming the auxiliary electrode continuously not only on the outer surface of the thin-walled
diaphragm portion but also on the thick-walled portion, stable device characteristics and a
piezoelectric / electrostrictive device that is not easily restricted by use conditions are obtained.
be able to. JP-A-8-201265 JP-A-2002-261347
[0006]
However, in the piezoelectric / electrostrictive device and the like disclosed in the abovementioned patent documents, only the thin diaphragm portion is vibrated in conjunction with the
driving of the piezoelectric / electrostrictive element, but in fact, the thin diaphragm portion Not
only that, but also the thick-walled part is vibrated, the vibration energy of the thin-walled
diaphragm part is attenuated, the displacement (amplitude) is reduced and the responsiveness is
reduced, and high accuracy (high resolution There is a problem that high sensitivity detection
becomes difficult.
[0007]
The present invention has been made in view of the above problems, and damping of vibration of
a thin-walled diaphragm portion is effectively prevented, displacement (amplitude) is maintained
high, response is excellent, high accuracy (high resolution, high) It is an object of the present
invention to provide a piezoelectric / electrostrictive device capable of detecting sensitivity.
[0008]
In order to achieve the above object, according to the present invention, the following
piezoelectric / electrostrictive device is provided.
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[0009]
[1] A ceramic base having a thick-walled portion and a thin-walled diaphragm portion integrally
installed on an end face of the thick-walled portion, wherein a cavity communicating with the
outside is formed by the thick-walled portion and the thin-walled diaphragm portion And a
piezoelectric / electrostrictive element having a layer structure including a lower electrode, a
piezoelectric / electrostrictive film, and an upper electrode fixed on the outer surface of the thinwalled diaphragm portion of the ceramic substrate, the piezoelectric / electrostrictive element A
piezoelectric / electrostrictive device capable of vibrating the thin-walled diaphragm portion of
the ceramic base in conjunction with driving of the ceramic substrate, and satisfying the shape
and size relationships defined in the following (A) to (C): Piezoelectric / electrostrictive device.
(A) The shape of the thin diaphragm portion is an outwardly convex arch shape, and the amount
of outward projection of the arch shape is 5 to 50 μm. (B) Construction of the thin diaphragm
portion The width is 600 to 2000 μm, and (C) the ratio (height / width) of the height of the thick
portion to the width is 0.25 to 3.
[0010]
[2] Each of the thin diaphragm portion and the thin diaphragm portion has two or more
piezoelectric / electrostrictive elements fixed on the outer surface, and the thin diaphragm
portion and the piezoelectric / electrostrictive element are on the first plane and The
piezoelectric / electrostrictive device according to [1], which is disposed on a second plane
parallel to the first plane.
[0011]
[3] Each of the thin diaphragm portion and the thin diaphragm portion has two or more
piezoelectric / electrostrictive elements fixed on the outer surface, and the thin diaphragm
portion and the piezoelectric / electrostrictive element are on the first plane, The piezoelectric /
electrostrictive device according to [1], which is disposed on a second plane parallel to the first
plane and / or on a third plane perpendicular to the first plane.
[0012]
[4] The piezoelectric / electrostrictive element is formed by a film forming method, and after the
constituent material of the piezoelectric / electrostrictive element is disposed on the outer
surface of the thin diaphragm portion, The piezoelectric / electrostrictive device according to any
one of the above [1] to [3], which is obtained by being heat-treated and fixed on the outer surface
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of the thin-walled diaphragm part.
[0013]
According to the present invention, a piezoelectric / electrostrictive device capable of effectively
preventing vibration damping of a thin-walled diaphragm portion, maintaining high displacement
(amplitude) and having excellent response and capable of highly accurate (high resolution, high
sensitivity) detection. Is provided.
[0014]
Hereinafter, the best mode for carrying out the piezoelectric / electrostrictive device of the
present invention will be described with reference to the drawings.
[0015]
FIG. 1 is an explanatory view schematically showing one embodiment of the piezoelectric /
electrostrictive device of the present invention, and FIG. 2 is a diagram showing the shape and
one embodiment of the piezoelectric / electrostrictive device shown in FIG. It is explanatory
drawing which shows a dimensional relationship typically.
[0016]
As shown in FIGS. 1 and 2, the piezoelectric / electrostrictive device of the present embodiment
has a thick portion 11 and a thin diaphragm portion 12 integrally mounted on the end face of
the thick portion 11. A ceramic substrate 1 in which a cavity 13 communicating with the outside
is formed by a thick portion 11 and a thin diaphragm portion 12, and a lower electrode 21 fixed
to the outer surface of the thin diaphragm portion 12 of the ceramic substrate 1 And
piezoelectric / electrostrictive element 2 having a layer structure including upper electrode 23
and piezoelectric / electrostrictive element 2 capable of vibrating thin diaphragm portion 12 of
ceramic substrate 1 in conjunction with driving of piezoelectric / electrostrictive element 2 The
electrostrictive device 10 is characterized by satisfying the shape and size relationships defined
in the following (A) to (C).
(A) The shape of the thin-walled diaphragm portion 12 is an outwardly convex arch shape, and
the protruding amount (h) of the arch shape outward is 5 to 50 μm, (B) of the thin-walled
diaphragm portion The installation width (m) is 600 to 2000 μm, and (C) the ratio (height /
width) of the height of the thick portion to the width is 0.25 to 3.
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[0017]
In the present embodiment, as described above, the shape of the thin-walled diaphragm portion
12 (A) is an outwardly convex arch shape, and the amount (h) of outward projection of the arch
shape is five to five. It needs to be 50 μm, preferably 5 to 30 μm.
By forming the outwardly convex arch shape, it is possible to efficiently change the distortion
and stress generated in the piezoelectric / electrostrictive element 2 into displacement.
That is, the piezoelectric / electrostrictive element 2 formed on the outer surface of the
outwardly projecting arch-shaped thin diaphragm portion 12 is driven in the direction (X
direction) perpendicular to the outer surface of the thin diaphragm portion 12 by being driven.
Since it is displaced, the thin-walled diaphragm portion 12 of the ceramic substrate 1 also
vibrates in the direction (X direction) perpendicular to the outer surface while changing the
internal volume of the cavity 13 in conjunction with the drive of the piezoelectric /
electrostrictive element 2 The piezoelectric / electrostrictive element 2 (specifically, at least the
lower electrode 21 and the piezoelectric / electrostrictive film 22) is against the outer surface of
the arch shape convex outward of the thin-walled diaphragm portion 12. By being formed, the
rigidity of the portion of the thin-walled diaphragm portion 12 where the piezoelectric /
electrostrictive element 2 is formed can be effectively improved.
In addition, the thin diaphragm portion 12 having an outwardly convex arch shape can improve
mechanical strength against pressure from the outer surface side of the thin diaphragm portion
12.
Furthermore, it is also possible to increase the natural frequency and response speed of the thinwalled diaphragm portion 12 in which the piezoelectric / electrostrictive element 2 is formed.
In addition, when the amount (h) of outward protrusion of the arch shape is out of the range of 5
to 50 μm, as shown in FIGS. 3 (a) and 3 (b), it is necessary to output a strong and clear signal. It
becomes difficult to secure a sufficiently large displacement and a vibration mode that is hard to
damp.
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As the protrusion amount (h) increases, the displacement decreases and unnecessary
deformation easily occurs, so the S / N ratio of the output signal decreases, but the protrusion
amount (h) is in the range of 5 to 30 μm. If it is inside, it is preferable because a clear output
signal can be obtained with certainty.
That is, FIG. 3 (a) is a graph showing the relationship between the amount of protrusion (h) of the
thin diaphragm portion and the displacement of the thin diaphragm portion, and when the
amount of protrusion (h) is out of the range of 5 to 50 μm, the displacement is It shows that it
becomes sharply smaller. FIG. 3 (b) is a graph showing the relationship between the amount of
protrusion (h) of the thin-walled diaphragm portion and the opening of the thick portion, and
when the amount of protrusion (h) is less than 5 μm, the thick portion is on the cavity side If it
falls over and exceeds 50 μm, the rigidity of the thin-walled diaphragm decreases, and the
desired deformation does not occur (for example, the first mode in the case of vibration is the
center) of the thin-walled diaphragm This indicates that the opening of the thick part does not
change when the amount (h) exceeds 50 μm). Note that “the opening of the thick portion”
means an amount by which the reference point T shown in FIG. 2 moves in the width (q)
direction of the thick portion 11 and moves outward in the width (q) direction ( In the figure, a
positive amount is indicated when moving to the right), and a negative amount is indicated when
moving inward in the width (q) direction (to the left in the figure).
[0018]
Moreover, the installation width (m) of (B) thin-walled diaphragm part needs to be 600-2000
micrometers, and it is preferable that it is 600-1500 micrometers. Here, the installation width
(m) of the thin-walled diaphragm portion means the length in the short direction of the cavity 13.
For example, in the case where the shape of the cavity 13 (cross-sectional shape perpendicular to
the X direction) is circular In the case of its diameter, in the case of a rectangle, its short side
length, in the case of an elliptical shape, it means a length corresponding to its short axis length
or the like. As shown in FIGS. 4A and 4B, when the installation width (m) of the thin diaphragm
portion is less than 600 μm, the flow path resistance increases and the displacement decreases,
and when it exceeds 2000 μm, the thin wall portion becomes thin. Since the rigidity of the
diaphragm portion is lowered and the natural frequency is lowered and it is easily attenuated, a
sufficient output signal can not be obtained. If the installation width (m) exceeds 1500 μm,
unnecessary deformation is likely to occur, so the S / N ratio of the output signal may be small
(the installation width (m) is unnecessary up to 2000 μm). Although it is likely to occur, it is
preferable that the installation width (m) is in the range of 600 to 1500 μm because a clear
output signal can be obtained with certainty. That is, FIG. 4A is a graph showing the relationship
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between the installation width (m) of the thin diaphragm portion and the displacement of the thin
diaphragm portion, and the displacement becomes smaller when the installation width (m) is less
than 600 μm. It indicates that a sufficient output signal can not be obtained. FIG. 4 (b) is a graph
showing the relationship between the installation width (m) of the thin diaphragm portion and
the attenuation, and when the installation width (m) exceeds 2000 μm, the rigidity of the thin
diaphragm portion decreases to lower the natural frequency Also, it is susceptible to the
unnecessary vibration mode, so that it is easy to be damped, indicating that a sufficient output
signal can not be obtained. Also, if the installation width (m) is less than 600 μm, the mass of the
thin-walled diaphragm becomes small and easily influenced by the restraint at both ends, which
indicates that attenuation easily occurs and a sufficient output signal can not be obtained. . In the
graph of FIG. 4A, the case where the protrusion amount (h) of the thin-walled diaphragm portion
is 50 μm is indicated by 場合, the case of 20 μm is indicated by □, and the case of 0 μm is
indicated by Δ. Further, the specific scale of the attenuation on the vertical axis in FIG. 4B is
indicated by the value of the ratio of the vibration wave amplitude = [(10th vibration wave
amplitude / 5th vibration wave amplitude) × 100 (%)]. . Here, the fifth vibration wave amplitude
means the fifth one of the amplitude generated by the free vibration, and the tenth vibration
wave amplitude means the tenth one of the amplitude generated by the free vibration. .
When the fifth vibration wave amplitude is represented by V5 and the tenth vibration wave
amplitude is represented by V10, the value of the ratio of the vibration wave amplitude is
represented by [(V10 / V5) × 100 (%)].
[0019]
In addition, the ratio (height (p) / width (q)) to the width (q) of the height (p) of the thick part (C)
needs to be 0.25 to 3, 0 It is preferable that it is 25-1.5. As shown in FIGS. 5A and 5B and FIGS.
6A and 6B, when this ratio is less than 0.25, the X direction vibration of the device end E due to
the drive of the thin diaphragm portion It becomes easy to be excited and causes damping of thin
diaphragm part vibration. Further, if the ratio is greater than 3, vibration in the width direction of
the device end E is easily excited when the thin diaphragm portion is driven, which causes
damping of the thin diaphragm portion vibration. Note that if the ratio (height (p) / width (q))
exceeds 1.5, high-order deformation of thick parts tends to occur and the S / N ratio of the
output signal may decrease. The ratio (height (p) / width (q)) is preferably in the range of 0.25 to
1.5 because a clear output signal can be obtained with certainty. That is, FIG. 5A shows that the
ratio (height (p) / width (q)) of the height (p) of the thick portion to its width (q) is small (shown
by a solid line in the figure) An explanatory view schematically showing that the X direction
vibration of the device end E is greatly excited (when the ratio is large (indicated by a broken line
in the figure, the X direction vibration of the device end E is small). 5 (b) is a graph showing the
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relationship between the height (p) / width (q) and the displacement of the device end E in the X
direction (see FIG. 1), and the height (p) When the width / q) is less than 0.25, it is shown that Xdirection vibration of the device end E is excited to cause damping of thin-walled diaphragm
portion vibration. In FIG. 6 (a), if the height (p) / width (q) is so large as to exceed 3 (indicated by
a broken line in the figure), the vibration in the width direction of the device end E is greatly
excited (the proportion is small FIG. 6B is an explanatory view schematically showing that the
vibration in the width direction of the device end E is small (when shown by a solid line in the
figure), and FIG. 6B shows height (p) / width It is a graph which shows the relationship between
(q) and the displacement amount of the width direction of the device edge part E, and when
height (p) / width (q) exceeds 3, a thick part will deform and thin diaphragm It is shown to cause
damping of the head vibration.
[0020]
Since the piezoelectric / electrostrictive device of this embodiment has the above-mentioned
configuration, damping of vibration of the thin-walled diaphragm portion is effectively prevented,
displacement (amplitude) is maintained high, response is excellent, and high accuracy ( High
resolution, high sensitivity) detection is possible.
[0021]
In the embodiment shown in FIGS. 1 and 2, on the outer surface of the thin diaphragm portion
12 and the thin diaphragm portion 12 integrally constructed on the end faces (on the first plane
A) of the two thick portions 11. Although the case where one fixed piezoelectric / electrostrictive
element 2 is disposed has been described, as shown in FIGS. 7 to 10, as another embodiment, a
thin diaphragm portion 12 and a piezoelectric / electrostrictive element 2 are provided. May be
disposed on the first plane A and / or on the second plane B parallel to the first plane A,
respectively.
In FIG. 7, the thin-walled diaphragm portion 12 and the piezoelectric / electrostrictive element 2
are disposed on both end surfaces of the two thick portions 11 (a second flat surface B parallel to
the first flat surface A and the first flat surface A The upper one shows the case where one is
provided. In FIG. 8, the thin-walled diaphragm portion 12 and the piezoelectric / electrostrictive
element 2 are on both end surfaces of one thick portion 11 (on the first plane A and on the
second plane B parallel to the first plane A) Shows the case where one of them is disposed in a
cantilever state. FIG. 9 shows a case where three thin-walled diaphragm portions 12 and three
piezoelectric / electrostrictive elements 2 are disposed on one end face of each of the four thick
portions 11 (on the first plane A). In FIG. 10, the thin-walled diaphragm portion 12 and the
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piezoelectric / electrostrictive element 2 are disposed on both end faces of the four thick
portions 11 (a second plane B parallel to the first plane A and the first plane A). The upper case
shows the case where three pieces in total and six pieces in total are arranged.
[0022]
Further, as shown in FIG. 11, as another embodiment, in the case where each of two or more
piezoelectric / electrostrictive elements 2 fixed on the outer surface of the thin diaphragm
portion 12 and the thin diaphragm portion 12 is provided, the thin diaphragm portion And the
piezoelectric / electrostrictive element is disposed on a first plane A, on a second plane B parallel
to the first plane A, and / or on a third plane C perpendicular to the first plane A. It may be
provided. In FIG. 11, the thin-walled diaphragm portion 12 and the piezoelectric / electrostrictive
element 2 are formed on both end faces parallel to one another and four end faces perpendicular
to each other of the four thick portions 11 (on the first plane A, the first plane A). In the case of a
total of four, one on each of a second plane B parallel to the third plane C and a third plane C
(two planes having two planes C) perpendicular to the first plane A, respectively.
[0023]
The graphs shown in FIGS. 3 to 6 are obtained by vibrating the thin diaphragms 12
independently of each other in the case of the piezoelectric / electrostrictive device having a
configuration having two or more thin diaphragms as shown in FIGS. Created on the basis of
These graphs show an example, and have a dimensional relationship of thickness 14 μm of thinwalled diaphragm part, protrusion 20 μm, installation width 1500 μm, height 800 μm of thick
part and width 800 μm of thick part. FIG. 8 is a graph created based on a device having two
symmetrically arranged thin diaphragm portions as shown in FIG. 7.
[0024]
In the present embodiment, the piezoelectric / electrostrictive element 2 is formed by the film
forming method, and the constituent material of the piezoelectric / electrostrictive element 2 is
disposed on the outer surface of the thin diaphragm portion 12. In the case where it is obtained
by heat treatment and being fixed on the outer surface of the thin-walled diaphragm portion 12,
it is possible to improve the bondability between the layers, and the effect is most effective. It can
be demonstrated.
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[0025]
Hereinafter, each component used for the piezoelectric / electrostrictive device of the present
invention will be specifically described.
[0026]
The material of the ceramic substrate 1 used in the present invention is preferably one having
heat resistance, chemical stability, and insulation.
The heat treatment may be performed as described above when fixing the piezoelectric /
electrostrictive element 2 (including the lower electrode 21, the piezoelectric / electrostrictive
film 22, and the upper electrode 23 described later) on the outer surface thereof. This is because
if the piezoelectric / electrostrictive device is used as a sensor element for sensing the
characteristics of the liquid, the liquid may have conductivity or corrosion.
[0027]
From such a point of view, examples of the ceramic preferably used as a constituent material of
the ceramic substrate 1 include stabilized zirconium oxide, aluminum oxide, magnesium oxide,
mullite, aluminum nitride, silicon nitride, glass and the like. .
Among them, stabilized zirconium oxide is more preferable because it can maintain high
mechanical strength even when the thin diaphragm portion 12 is thinly formed, and is excellent
in toughness and the like.
[0028]
The thickness of the thin-walled diaphragm portion 12 of the ceramic substrate 1 is usually 100
μm or less, preferably 30 μm or less, more preferably 15 μm or less, so as not to restrict
driving of the piezoelectric / electrostrictive element 2.
[0029]
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In addition, the external shape of the thin-walled diaphragm portion 12 is any shape such as a
rectangle, square, triangle, oval, or perfect circle corresponding to the shape of the frame or Ushaped body of the thick portion 11 Although it is good, as shown in FIG. 1, the thick part 11 and
the thin diaphragm part 12 form a cavity 13 and at the same time a through hole 14 is formed,
and the fluid to be measured is made through the through hole 14. In the case of feeding and
discharging, it is preferable that the shape is rectangular, oval or oval.
In order to obtain an ideal vibration (displacement), it is more preferable that the aspect ratio is a
rectangle, an oval, or an oval with an aspect ratio of 1.5 or more. Further, the thick portion may
be provided with a hole or a hole used for attachment, positioning and the like of the device.
[0030]
The piezoelectric / electrostrictive element 2 (including the lower electrode 21 and the
piezoelectric / electrostrictive film 22 upper electrode 23) used in the present invention is fixed
on the outer surface of the thin diaphragm portion 12. The lower electrode 21 constituting the
piezoelectric / electrostrictive element 2 is formed on the outer surface of the thin-walled
diaphragm portion 12 in the same size as the size in which the piezoelectric / electrostrictive film
22 is to be formed. In this case, the width in the short direction of the lower electrode 21 may be
larger than that of the thin diaphragm portion 12 or smaller than the width of the piezoelectric /
electrostrictive film 22.
[0031]
An auxiliary electrode (not shown) may be provided in order to enhance the reliability of the
electrical connection of the upper electrode. The auxiliary electrode can be formed continuously
at a predetermined position on the outer surface of the thin-walled diaphragm portion 12. The
lower electrode 21 and the auxiliary electrode may be made of different materials or the same
material, and it is preferable that the lower electrode 21 and the auxiliary electrode be a
conductive material having a good bonding property with any of the ceramic substrate 1 and the
piezoelectric / electrostrictive film 22. Specifically, an electrode material containing platinum,
palladium, rhodium, silver, or an alloy of these as a main component can be mentioned. In
particular, when heat treatment for sintering is performed when forming the piezoelectric /
electrostrictive film 22, an electrode material mainly composed of platinum or an alloy thereof is
more preferable. Various known film forming methods can be used to form the lower electrode
21 and the auxiliary electrode. As such a film forming method, for example, thin film forming
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methods such as ion beam, sputtering, vacuum evaporation, CVD, ion plating, plating, etc., and
thick film forming methods such as screen printing, spray, dipping etc. can be mentioned. .
Among them, sputtering and screen printing are preferred.
[0032]
A bonding layer (not shown) for bonding the piezoelectric / electrostrictive film 22 and the thin
diaphragm portion 12 may be provided between the lower electrode 21 and the auxiliary
electrode. In this case, the bonding layer is formed prior to the formation of the piezoelectric /
electrostrictive film 22. By forming such a bonding layer, the rigidity of the piezoelectric /
electrostrictive element 2 on the outer surface of the thin-walled diaphragm portion 12 becomes
uniform, which is preferable in obtaining ideal vibration (displacement). The bonding layer may
be either an organic material or an inorganic material as long as it has an insulating property and
has high adhesion and bondability with any of the piezoelectric / electrostrictive film 22 and the
ceramic substrate 1. In addition, it is possible to obtain a reliable bond because the thermal
expansion coefficient of the material forming the bonding layer has an intermediate value of the
thermal expansion coefficients of the constituent materials of the ceramic substrate 1 and the
piezoelectric / electrostrictive film 22. Preferred. When the piezoelectric / electrostrictive film 22
is heat-treated for sintering, the material of the piezoelectric / electrostrictive film 22 to which a
small amount of glass component is added, or the softening of the piezoelectric / electrostrictive
film 22 or more at the heat treatment temperature A glass material having a point is preferable
because it has high adhesion and bondability with any of the piezoelectric / electrostrictive film
22 and the ceramic substrate 1.
[0033]
Further, the constituent material of the piezoelectric / electrostrictive film 22 described later is
(Bi0.5Na0.5) TiO3 or a material containing this as a main component, or (1-x) (Bi0.5Na0.5) TiO3xKNbO3 (x Is a molar fraction 0 ≦ x ≦ 0.06) or a material having this as a main component, (1x) (Bi0.5Na0.5) TiO3-xKNbO3 (x is a molar fraction 0 Adhesion of both the piezoelectric /
electrostrictive film 22 and the ceramic substrate 1 is high when a small amount of glass
component is added to a material having <x ≦ 0.5) as the main component, and the piezoelectric
/ electrostrictive film during heat treatment 22 and the ceramic substrate 1 can be suppressed,
which is preferable. That is, by forming the bonding layer into (1-x) (Bi0.5Na0.5) TiO3-xKNbO3 (x
is a molar fraction of 0 <x ≦ 0.5) to which a small amount of glass component is added,
piezoelectric / electric Since the component similar to that of the strained film 22 is included, the
adhesion with the piezoelectric / electrostrictive film 22 is high, and the problem due to the
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diffusion of different elements which easily occurs when glass is used alone is eliminated.
Therefore, the reactivity with the ceramic substrate 1 is high and a strong bond is possible. When
the main component of the bonding layer is (1-x) (Bi0.5Na0.5) TiO3-xKNbO3 (where x is a mole
fraction of 0.08 ≦ x ≦ 0.5), the piezoelectric characteristics Since almost nothing is shown,
stable device characteristics can be obtained without generating vibration (displacement), stress
and the like with respect to the electric field generated in the lower electrode 21 and the
auxiliary electrode at the time of use.
[0034]
For forming the bonding layer, the usual thick film method is used, and in particular, the
stamping method, the screen printing method, the ink jet method is suitably used when the size
of the portion to be formed is about several 10 μm to several 100 μm. . If heat treatment of the
bonding layer is required, heat treatment may be performed before the formation of the
piezoelectric / electrostrictive film 22, or heat treatment may be performed simultaneously with
the formation of the piezoelectric / electrostrictive film 22.
[0035]
The piezoelectric / electrostrictive film 22 constituting the piezoelectric / electrostrictive element
2 is formed to be mounted on the outer surface of the lower electrode 21 (the auxiliary electrode
and the bonding layer as needed). The constituent material of the piezoelectric / electrostrictive
film 22 is not particularly limited as long as it exhibits a piezoelectric / electrostrictive effect. For
example, lead-based materials such as lead zirconate, lead titanate, and lead zirconate titanate
(PZT) Ceramic piezoelectric / electrostrictive materials; barium titanate and titavari ceramic
ferroelectrics mainly composed of it; polymer piezoelectrics represented by polyvinylidene
fluoride (PVDF); represented by (Bi0.5Na0.5) TiO3 Bi-based ceramic piezoelectric body; Bilayered ceramic and the like can be mentioned. These mixtures, solid solutions, those to which
additives are added, and the like may be used, in which the piezoelectric / electrostrictive
properties are improved.
[0036]
The PZT-based ceramic piezoelectric / electrostrictive material is suitably used as a material of a
sensor having high piezoelectric characteristics and capable of high sensitivity detection. Among
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them, it is composed of a material having at least one selected from the group consisting of lead
titanate, lead zirconate, lead magnesium niobate and lead nickel niobate as a main component,
and the reactivity with the constituent material of the ceramic substrate 1 Is low, segregation of
components during heat treatment does not easily occur, treatment for maintaining the
composition is smoothly performed, and desired composition and crystal structure are easily
obtained.
[0037]
When platinum or an alloy containing platinum as a main component is used as a constituent
material of the lower electrode 21 and the auxiliary electrode, the bonding property with these is
higher, the variation in the characteristics of the piezoelectric / electrostrictive device is reduced,
and the ratio is high. (Bi0.5Na0.5) TiO3 or a material containing this as a main component is
preferably used because reliability can be obtained. Above all, (1-x) (Bi0.5Na0.5) TiO3-xKNbO3 (x
is 0 ≦ x ≦ 0.06 in mole fraction) or a material containing this as a main component has
relatively high piezoelectric properties It is preferable from Various known film forming methods
can be used to form the piezoelectric / electrostrictive film 22 similarly to the lower electrode 21
and the auxiliary electrode. Among them, screen printing is preferable from the viewpoint of cost
reduction.
[0038]
The piezoelectric / electrostrictive film 22 formed by the above-described method is heat-treated
as needed, and integrated with the lower electrode 21 (the auxiliary electrode and the bonding
layer as needed). In order to suppress the variation of the characteristics of the piezoelectric /
electrostrictive device and to improve the reliability, it is necessary to make the bonding property
of the piezoelectric / electrostrictive film 22 and the lower electrode 21 (auxiliary electrode and
bonding layer as needed) stronger. (Bi0.5Na0.5) TiO3 or a material containing this as a main
component, in particular, (1-x) (Bi0.5Na0.5) TiO3-xKNbO3 (x is 0 ≦ x in mole fraction) It is
preferable to heat-process at the temperature of 900-1400 degreeC, preferably 1000-1300
degreeC using the material which has ≦ 0.06) or this as a main component. The same applies to
the case of using a PZT-based ceramic piezoelectric / electrostrictive material. At this time, heat
treatment is preferably performed while controlling the atmosphere together with the
evaporation source of the ceramic piezoelectric / electrostrictive material so that the
piezoelectric / electrostrictive film 22 does not become unstable at high temperature.
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[0039]
The upper electrode 23 constituting the piezoelectric / electrostrictive element 2 is formed to be
placed on the outer surface of the piezoelectric / electrostrictive film 22 formed as described
above. As a material of the upper electrode 23, a conductive material having high bonding
property with the piezoelectric / electrostrictive film 22 is used, and it is formed by the same film
forming method as the lower electrode 21 and the auxiliary electrode. Further, after the film
formation, the upper electrode 23 is heat-treated as needed, and is bonded to the piezoelectric /
electrostrictive film 22 and the auxiliary electrode to form an integral structure. It is the same as
the case of the lower electrode 21 that such heat treatment is not necessarily required. In order
to realize an ideal drive (displacement), it is preferable that the rigidity be uniform on the thinwalled diaphragm part 12. For this purpose, the lower electrode 21, the piezoelectric /
electrostrictive film 22 and the upper electrode 23 are bonded It is preferable to be integrated
with the thin diaphragm portion 12 by heat treatment rather than bonding using an agent.
Further, in order to obtain a sharp peak, the shape in the width direction of the upper electrode
23 is preferably line symmetrical. By making it symmetrical, only the inherent vibration can be
emphasized and vibrated. Furthermore, it is preferable that the centers of the upper electrode 23
and the thin-walled diaphragm portion 12 coincide with each other, but the deviation from the
center is 5% or less of the length of the thin-walled diaphragm portion 12 in the length direction
of the thin-walled diaphragm portion 12 The width is preferably 10% or less of the width of the
thin diaphragm portion 12 in the width direction. The ratio of the area effective for driving the
upper electrode 23 to the area of the thin diaphragm portion 12 is preferably 15 to 40%. Within
this range, the vibration necessary for sensing can be obtained, and an advantageous rigidity for
vibrating can be obtained.
[0040]
When the lower electrode 21, the bonding layer, the piezoelectric / electrostrictive film 22, and
the upper electrode 23 are bonded by heat treatment as needed, the heat treatment may be
performed for each formation, and each of them is sequentially formed After the heat treatment,
heat treatment may be performed simultaneously. In heat treatment, it is preferable to select a
suitable heat treatment temperature in order to suppress good bondability and deterioration due
to diffusion of constituent elements. Although FIG. 1 shows the case where the through hole 14 is
formed in the cavity 13, the structure of the cavity 13 or the like in which the piezoelectric /
electrostrictive device is in contact with the fluid may be a simple cavity structure. There is no.
Furthermore, the end of the piezoelectric / electrostrictive film 22 in the longitudinal direction
may have a length not exceeding the thin diaphragm portion 12, and the piezoelectric /
electrostrictive film 22 may not be extended to the thick portion 1.
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[0041]
EXAMPLES Hereinafter, the present invention will be more specifically described by way of
examples; however, the present invention is not limited by these examples.
[0042]
(Example 1) One thin-walled diaphragm part (thickness 14 μm, protrusion amount 20 μm,
installation width 1500 μm) and two thick-walled parts (height 800 μm of thick-walled part,
width 800 μm of thick-walled part, (thick-walled part) Height / width of thick part) = 1.0) and
one piezoelectric / electrostrictive element (lower electrode thickness 4 μm, piezoelectric /
electrostrictive film thickness 20 μm, upper electrode thickness 0.5 μm) A piezoelectric /
electrostrictive device was prepared.
In addition, the protrusion amount of the arch shape in the thin-walled diaphragm part which
comprises the piezoelectric / electrostrictive device obtained in Example 1 was confirmed by
measuring the cut surface of a piezoelectric / electrostrictive device with an optical measurement
microscope.
[0043]
(Measurement of Characteristics of Thin-Walled Diaphragm Section) The vibration characteristic
of the thin-walled diaphragm section constituting the piezoelectric / electrostrictive device
obtained in Example 1 is cut off from the state where a voltage of 50 V is applied to the
piezoelectric / electrostrictive device The moment at which this was done was taken as the origin
of time, and the change over time of the position of the vibrating thin diaphragm part at that time
was measured by a laser Doppler measuring device for 20 cycles. As a result, the fifth vibration
wave amplitude (V5) is 2.70 μm, the tenth vibration wave amplitude (V10) is 2.45 μm, and the
ratio of the vibration wave amplitude = [(V10 / V5) × 100 (%)] , 90.7%, it was found that the
damping of the vibration is small.
[0044]
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Comparative Example 1 The vibration characteristics were similarly measured in the same
manner as in Example 1 except that the thin-walled diaphragm portion was not formed into an
arch shape (protrusion amount was 0 μm) in Example 1. As a result, the fifth oscillatory wave
amplitude is 2.43 μm, the tenth oscillatory wave amplitude is 1.93 μm, and the ratio of the
oscillatory wave amplitude = [(V10 / V5) × 100 (%)] is 79.4%. The vibration damping was found
to be large.
[0045]
Comparative Example 2 The vibration characteristics were similarly measured in the same
manner as in Example 1 except that the protrusion of the arch shape in the thin-walled
diaphragm portion was 4 μm in Example 1. As a result, the fifth oscillatory wave amplitude is
2.31 μm, the tenth oscillatory wave amplitude is 1.95 μm, and the ratio of the oscillatory wave
amplitude = [(V10 / V5) × 100 (%)] is 84.4%. The vibration damping was found to be large.
[0046]
Comparative Example 3 The vibration characteristics were similarly measured in the same
manner as in Example 1 except that the amount of protrusion of the arch shape in the thinwalled diaphragm portion was set to 60 μm. As a result, the fifth vibration wave amplitude is
1.31 μm, the tenth vibration wave amplitude is 0.79 μm, and the ratio of the vibration wave
amplitude = [(V10 / V5) × 100 (%)] is 60.3%. The vibration damping was found to be large.
[0047]
Comparative Example 4 The vibration characteristics were measured in the same manner as in
Example 1 except that the installation width of the thin-walled diaphragm portion was 300 μm
and the amount of protrusion was 0 μm in Example 1. As a result, the fifth vibration wave
amplitude is 0.4 μm, the tenth vibration wave amplitude is 0.29 μm, and the ratio of the
vibration wave amplitudes = [(V10 / V5) × 100 (%)] is 72.5%. The vibration damping was found
to be large.
[0048]
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Comparative Example 5 The vibration characteristics were similarly measured in the same
manner as in Example 1 except that the installation width of the thin-walled diaphragm portion
in Example 1 was 2500 μm. As a result, the fifth vibration wave amplitude is 3.71 μm, the tenth
vibration wave amplitude is 2.73 μm, and the ratio of the vibration wave amplitude = [(V10 /
V5) × 100 (%)] is 73.6%. The vibration damping was found to be large.
[0049]
Comparative Example 6 Example 1 except that the thickness of the thick portion is 200 μm, the
width of the thick portion is 1500 μm, and the (height of the thick portion / width of the thick
portion) is 0.13. The vibration characteristics were measured in the same manner as in Example
1. As a result, the fifth oscillatory wave amplitude is 2.40 μm, the tenth oscillatory wave
amplitude is 1.94 μm, and the ratio of the oscillatory wave amplitude = [(V10 / V5) × 100 (%)]
is 80.1%. The vibration damping was found to be large.
[0050]
Comparative Example 7 Example 1 except that the thickness of the thick portion is 1200 μm,
the width of the thick portion is 200 μm, and the (height of the thick portion / width of the thick
portion) = 6.0. The vibration characteristics were measured in the same manner as in Example 1.
As a result, the fifth vibration wave amplitude is 2.36 μm, the tenth vibration wave amplitude is
1.88 μm, and the value of the ratio of the vibration wave amplitude = [(V10 / V5) × 100 (%)] is
79.7%. The vibration damping was found to be large.
[0051]
The piezoelectric / electrostrictive device of the present invention is an actuator utilizing bending
displacement; various sensors for detecting fluid characteristics, sound pressure, minute weight,
acceleration, etc. such as a sensor for a microphone, a viscosity sensor, etc .; filters; transformers;
Sound generators such as: Vibrators and oscillators for power and communication; Displays;
Piezoelectric / electrostrictive types that generate bending displacements such as unimorph type
used for servo displacement elements, pulse drive motors, ultrasonic motors etc. It is effectively
used in various industrial fields that require film-type actuators (refer to Kenji Uchino (ed., Japan
Industrial Technology Center) "Piezoelectric / electrostrictive actuators: from foundation to
application" (Morikita Press)).
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[0052]
It is an explanatory view showing typically one embodiment of a piezoelectric / electrostrictive
device of the present invention.
It is explanatory drawing which shows typically the shape and dimensional relationship in
embodiment shown in FIG. FIG. 3 (a) is a graph showing the relationship between the amount of
protrusion (h) of the thin diaphragm portion and the displacement of the thin diaphragm portion,
and FIG. 3 (b) shows the amount of protrusion (h) of the thin diaphragm portion and thick It is a
graph which shows a relation with opening of a department. FIG. 4A is a graph showing the
relationship between the installation width (m) of the thin diaphragm portion and the
displacement of the thin diaphragm portion, and FIG. 4B shows the installation width (m) of the
thin diaphragm portion and the vibration wave It is a graph which shows the relation of the ratio
of amplitude. FIG. 5 (a) shows the X direction vibration of the device edge E when the ratio
(height (p) / width (q)) of the height (p) of the thick portion to its width (q) is small Is
schematically illustrated (when the value is large, the vibration of the device end E is small). FIG.
5 (b) shows the height (p) / width (q). It is a graph which shows the relationship with the
displacement amount of the X direction of the device edge part E. FIG. In FIG. 6A, when the
height (p) / width (q) is large, the width direction vibration of the device end E is excited greatly
(when the ratio is small, the width direction vibration of the device end E is small 6 (b)
schematically shows the relationship between the height (p) / width (q) and the amount of
displacement of the device end E in the width direction. It is a graph. FIG. 16 is an explanatory
view schematically showing another embodiment of the piezoelectric / electrostrictive device of
the present invention, in which the thin diaphragm portion and the piezoelectric / electrostrictive
element are provided on both end faces of two thick portions (first The case where only one each
is disposed on the plane and on the second plane parallel to the first plane) is shown. FIG. 16 is
an explanatory view schematically showing another embodiment of the piezoelectric /
electrostrictive device of the present invention, in which the thin diaphragm portion and the
piezoelectric / electrostrictive element are on both end faces of one thick portion (on the first
plane And one in a second plane parallel to the first plane), each being disposed in a cantilever
manner. FIG. 8 is an explanatory view schematically showing another embodiment of the
piezoelectric / electrostrictive device of the present invention, in which the thin-walled
diaphragm portion and the piezoelectric / electrostrictive element are formed on one end face of
each of four thick portions (first 3) is disposed on the plane of FIG. 16 is an explanatory view
schematically showing another embodiment of the piezoelectric / electrostrictive device of the
present invention, in which the thin diaphragm portion and the piezoelectric / electrostrictive
element are provided on both end faces of four thick portions (first 6 shows a case where three
in total and six each in the second plane parallel to the first plane and the second plane) are
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provided.
FIG. 8 is an explanatory view schematically showing another embodiment of the piezoelectric /
electrostrictive device of the present invention, wherein the thin diaphragm portion and the
piezoelectric / electrostrictive element are both end faces parallel to each other and
perpendicular to each other of four thick portions. One on each of the two end faces (on the first
plane, on the second plane parallel to the first plane, and on the third plane (this plane is two)
perpendicular to the first plane) , In the case of a total of four disposed.
Explanation of sign
[0053]
DESCRIPTION OF SYMBOLS 1 ... Ceramic base | substrate, 2 ... Piezoelectric / electrostrictive
element, 11 ... Thick part, 12 ... Thin-walled diaphragm part, 13 ... Cavity, 14 ... Through hole, 21
... Lower electrode, 22 ... Piezoelectric / electrostrictive film, 23 ... Top Electrode, X: direction
perpendicular to the outer surface of the thin-walled diaphragm, h: protruding amount of the
thin-walled diaphragm, m: installation width of the thin-walled diaphragm, p: height of the thickwalled portion, q: width of the thick-walled portion, A: first plane B: second plane parallel to the
first plane C: third plane perpendicular to the first plane T: reference point in the concept of
opening of the thick part E: Device edge.
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