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DESCRIPTION JPH06275885

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DESCRIPTION JPH06275885
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
piezoelectric element and a method of manufacturing the same.
[0002]
2. Description of the Related Art For example, as shown in FIGS. 5 (A) and 5 (B), a piezoelectric
element used as an electroacoustic transducer includes a polymer containing vinylidene fluoride,
vinylidene cyanide or the like as a monomer, or repetitively. Upper and lower circular electrodes
2 and 3 are formed on the upper and lower surfaces of a disk-shaped piezoelectric film 1 made of
a polymer material having a spontaneous polarization (intramolecular dipole moment) such as a
copolymer containing them as unit main components There is a structure of the provided. Among
them, the piezoelectric film 1 is formed with a spontaneous polarization directed upward in the
film thickness direction as shown by an arrow in FIG. In this piezoelectric element, in order to
convert the movement direction of the piezoelectric film 1 into the vibration direction of air, as
shown in FIG. 5B, it is appropriately curved in the direction of projecting upward in advance.
Then, when the direction of the electric field generated by the voltage applied between the pair
of electrodes 2 and 3 is the same as the direction of the spontaneous polarization, the
piezoelectric film 1 shrinks as shown in FIG. If it is not shown, it will extend. Such conversion of
electrical energy into mechanical displacement causes the piezoelectric element to be distorted
and to generate a sound.
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[0003]
By the way, in such a piezoelectric element, the maximum mechanical displacement at the time of
converting electric energy into mechanical displacement is obtained when the maximum voltage
is applied to the piezoelectric film 1 in the range where the dielectric breakdown does not occur.
Therefore, there is a limit to the maximum voltage to be applied, so that the above-described
conventional piezoelectric element can not obtain sufficient mechanical displacement, and there
is a problem that the acoustic characteristics are not good.
[0004]
On the other hand, a piezoelectric element having a bimorph structure as shown in FIGS. 6A and
6B is known as a piezoelectric element capable of obtaining a larger mechanical displacement. In
this piezoelectric element, the intermediate electrode 13 is interposed between the upper and
lower piezoelectric films 11 and 12, the upper electrode 14 is provided on the upper surface of
the upper piezoelectric film 11, and the lower electrode 15 is provided on the lower surface of
the lower piezoelectric film 12. It has a structure. The directions of the spontaneous polarization
of the two piezoelectric films 11 and 12 are both downward as shown by the arrows in FIG. 6 (B).
Then, as shown in FIG. 6C, when a positive voltage is applied to the intermediate electrode 13
and a negative voltage is applied to the upper and lower electrodes 14 and 15, the upper
piezoelectric film 11 expands and the lower piezoelectric film 12 contracts. Thus, even if the
voltage applied to each of the piezoelectric films 11 and 12 is the same as in the case shown in
FIG. 5C, it is distorted more largely, and thus a larger mechanical displacement can be obtained,
and acoustic characteristics can be improved. it can.
[0005]
However, such a conventional piezoelectric element has a structure in which two piezoelectric
films 11 and 12 are laminated, which not only complicates the structure but also structurally
improves the adhesive property. There is another problem in that it is used and laminated, and
hence the electroacoustic conversion efficiency is dependent on the elastic modulus of the
adhesive. An object of the present invention is to provide a piezoelectric element capable of
obtaining a larger mechanical displacement despite the simple structure using a single
piezoelectric film, and a method of manufacturing the same.
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2
[0006]
A piezoelectric element according to a first aspect of the present invention is provided with a
piezoelectric film in which the direction of spontaneous polarization is a single direction, and
corresponding portions of both surfaces of the piezoelectric film. A pair of first electrodes and a
pair of second electrodes provided on corresponding portions of both surfaces of the
piezoelectric film are provided, and between the pair of first electrodes and the pair of second
electrodes Electric fields reverse to each other are applied between the electrodes. The
piezoelectric element according to claim 2 comprises a piezoelectric film in which the direction of
spontaneous polarization is opposite to each other between one portion and the other portion,
and a pair of electrodes provided on both sides of the piezoelectric film. It is. According to the
third aspect of the present invention, in the production of the piezoelectric element according to
the second aspect, an electric field in the opposite direction is applied to one portion and the
other portion of the piezoelectric film to thereby obtain one portion of the piezoelectric film. And
other parts form spontaneous polarizations in which the directions are opposite to each other.
According to a fourth aspect of the present invention, in manufacturing the piezoelectric element
according to the second aspect, an electric field in one direction is applied to at least one part of
the piezoelectric film, whereby the one direction is applied to at least one part of the piezoelectric
film. By forming a spontaneous polarization in the same direction and then applying an electric
field in the opposite direction to the one direction only to the other part of the piezoelectric film,
only the other part of the piezoelectric film in the opposite direction It is intended to form
spontaneous polarization.
[0007]
According to the piezoelectric element of the first aspect of the invention, when voltages in
opposite directions are applied between the pair of first electrodes and the pair of second
electrodes, for example, between the pair of first electrodes The piezoelectric film in the case is
contracted by applying an electric field in the same direction as the direction of spontaneous
polarization, and the piezoelectric film between the pair of second electrodes is extended by
applying an electric field in the reverse direction to the direction of spontaneous polarization.
Distortion substantially equivalent to that of the conventional bimorph piezoelectric element can
be obtained, and therefore, despite the simple structure using a single piezoelectric film, larger
mechanical displacement can be obtained. According to the piezoelectric element of the second
aspect, since the directions of the spontaneous polarization are opposite to each other between
one portion and the other portion of the piezoelectric film, a voltage in a single direction is
applied between the pair of electrodes. Then, for example, the piezoelectric film at one portion is
contracted by applying an electric field in the same direction as the direction of spontaneous
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polarization, and the piezoelectric film at the other portion is expanded by applying an electric
field in the opposite direction to the direction of spontaneous polarization. Therefore, distortion
equivalent to that of the conventional bimorph piezoelectric element can be obtained, and
therefore, despite the simple structure using a single piezoelectric film, larger mechanical
displacement can be obtained. In this case, when the invention according to claim 3 or 4 is used,
it is possible to easily manufacture a piezoelectric element provided with a piezoelectric film in
which the direction of spontaneous polarization is opposite to each other in one part and the
other part. it can.
[0008]
1 (A) and 1 (B) show a piezoelectric element according to an embodiment of the present
invention. In this piezoelectric element, a circular upper center electrode 22 and a lower center
electrode 23 are provided on the upper surface central portion and the lower surface central
portion of one disk-shaped piezoelectric film 21, and the upper surface peripheral portion and
the lower surface periphery of the piezoelectric film 21 are provided. A ring-shaped upper
peripheral electrode 24 and a lower peripheral electrode 25 are provided in the part, and the
structure is appropriately curved in the direction of projecting upward as a whole. Among them,
the piezoelectric film 21 is formed with a spontaneous polarization directed upward in the film
thickness direction as indicated by an arrow in FIG.
[0009]
In this piezoelectric element, for example, as shown in FIG. 1C, a voltage is applied so that an
electric field in the direction opposite to the direction of the spontaneous polarization of the
piezoelectric film 21 is formed between the pair of center electrodes 22 and 23. When a voltage
is applied so that an electric field in the same direction as the spontaneous polarization direction
of the piezoelectric film 21 is formed between the pair of peripheral electrodes 24 and 25, the
central portion of the piezoelectric film 21 expands and the peripheral portion contracts.
Therefore, even if the voltage applied to the central portion and the peripheral portion of the
piezoelectric film 21 is the same as in the case shown in FIG. 5C, it is distorted more largely, a
larger mechanical displacement is obtained, and the acoustic characteristics are improved. Can.
Further, in this piezoelectric element, since only one piezoelectric film 21 is used, not only the
structure is simple as compared with the conventional one shown in FIGS. There is no need to
laminate with an agent, so the electroacoustic conversion efficiency does not depend on the
modulus of the adhesive.
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[0010]
Next, FIGS. 2A and 2B show a piezoelectric element in another embodiment of the present
invention. In this piezoelectric element, a circular upper electrode 32 and a lower electrode 33
are provided on the upper and lower surfaces of one disk-shaped piezoelectric film 31, and the
structure is appropriately curved in a direction projecting upward as a whole. It has become.
Among them, the central portion 31a of the piezoelectric film 31 has a spontaneous polarization
directed downward in the film thickness direction, as shown by the arrow in FIG. It is formed. In
the peripheral portion 31b of the piezoelectric film 31, a spontaneous polarization upward in the
film thickness direction is formed as shown by an arrow in FIG. 2B by the stretching treatment
applied in advance and the electric field alignment described later. ing.
[0011]
In this piezoelectric element, for example, as shown in FIG. 2C, when a negative voltage is applied
to the upper electrode 32 and a positive voltage is applied to the lower electrode 33, the
direction of spontaneous polarization is generated at the central portion 31a of the piezoelectric
film 31. An electric field in the reverse direction is applied to extend, and an electric field in the
same direction as the direction of the spontaneous polarization is applied to contract in the
peripheral portion 31b of the piezoelectric film 31. Therefore, also in this case, even if the
voltage applied to the piezoelectric film 31 is the same as the case shown in FIG. 5C, it is
distorted more largely, a larger mechanical displacement can be obtained, and the acoustic
characteristics can be improved. . In addition, also in this piezoelectric element, since only one
piezoelectric film 31 is used, not only the structure is simple as compared with the conventional
one shown in FIGS. There is no need to laminate with an agent, so the electroacoustic conversion
efficiency does not depend on the modulus of the adhesive.
[0012]
Next, an example of a method of manufacturing the piezoelectric element shown in FIGS. 2A and
2B will be described with reference to FIG. In this case, first, a circular upper central electrode 42
and a central lower surface of a disk-shaped film 41 formed by stretching a polymer made of a
monomer such as vinylidene fluoride or vinylidene cyanide and the like. A lower center electrode
43 is provided, and a ring-shaped upper peripheral electrode 44 and a lower peripheral electrode
45 are provided on the upper surface peripheral portion and the lower surface peripheral
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portion of the film 41. Next, when a positive voltage is applied to the upper center electrode 42
and the lower peripheral electrode 45 while a negative voltage is applied to the lower center
electrode 43 and the upper peripheral electrode 44 while heating, the central portion of the film
41 is shown in FIG. The downward spontaneous polarization is formed in the film thickness
direction as indicated by the arrow in FIG. 3, and the upward spontaneous polarization is formed
in the film thickness direction as indicated by the arrow in FIG. Thereafter, the upper electrodes
42 and 44 are connected to each other, the lower electrodes 43 and 45 are connected to each
other, and an appropriate bending process is performed. As a result, piezoelectric elements as
shown in FIGS. 2A and 2B are obtained. Is obtained. Therefore, it is possible to easily
manufacture a piezoelectric element provided with the piezoelectric film 31 in which the
directions of spontaneous polarization in the central portion 31a and the peripheral portion 31b
are opposite to each other.
[0013]
Next, another example of the method of manufacturing the piezoelectric element shown in FIGS.
2 (A) and 2 (B) will be described with reference to FIGS. 4 (A) and 4 (B). In this case, first, as
shown in FIG. 4A, circular upper portions are formed on the upper and lower surfaces of a diskshaped film 51 formed by stretching a polymer made of a monomer such as vinylidene fluoride
or vinylidene cyanide. An electrode 52 and a lower electrode 53 are provided. Next, when a
positive voltage is applied to the upper electrode 52 and a negative voltage is applied to the
lower electrode 53 while heating, the film 51 is in the film thickness direction as shown by the
arrows in FIG. A downward spontaneous polarization is formed. Next, while similarly heating, as
shown in FIG. 4B, when applying a negative voltage to the periphery of the upper electrode 52
and applying a positive voltage to the periphery of the lower electrode 53, the periphery of the
film 51 is obtained. As shown by the arrows in FIG. 4B, spontaneous polarization in the film
thickness direction and upward is formed only in the portion. Thereafter, when a suitable
bending process is performed, a piezoelectric element as shown in FIGS. 2A and 2B is obtained.
Therefore, also in this case, it is possible to easily manufacture a piezoelectric element provided
with the piezoelectric film 31 in which the directions of spontaneous polarization in the central
portion 31a and the peripheral portion 31b are opposite to each other.
[0014]
As described above, according to the invention described in claim 1 or 2, since distortion
substantially equivalent to that of the conventional bimorph piezoelectric element can be
obtained, it is easy to use a single piezoelectric film. In spite of the structure, larger mechanical
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displacement can be obtained and the acoustic characteristics can be improved. According to the
third and fourth aspects of the present invention, it is possible to easily manufacture a
piezoelectric element provided with a piezoelectric film in which the directions of spontaneous
polarization in one part and the other part are opposite to each other.
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