JPH06275884A - Piezoelectric element - Google Patents

Abstract

(57) [Abstract] [Purpose] The structure in a normal state can be a planar structure, and a large volume can be produced. [Structure] Piezoelectric bodies 22 and 23 having a bimorph structure are provided on both surfaces of a flexible support film 21.
As described above, since the piezoelectric bodies 22 and 23 having the bimorph structure are provided, the structure in a normal state can be a planar structure. When the piezoelectric element has a certain degree of rigidity, the inexpensive support film 21 can have a certain degree of rigidity. Therefore, the electrode layers 22a, 22
It is not necessary to thicken c, 22e, 23a, 23c, 23e and the like, and therefore, it is inexpensive, easy to vibrate, and capable of producing a large volume.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric element.

[0002]

2. Description of the Related Art For example, in a piezoelectric element used as an electroacoustic transducer, an upper electrode layer 2 and a lower electrode layer 3 are provided on the upper and lower surfaces of a piezoelectric film 1 made of a ferroelectric polymer, as shown in FIG. There is a structure. Of these, the piezoelectric film 1
The spontaneous polarization direction of is in the film thickness direction and is upward. In this piezoelectric element, in order to convert the movement direction of the piezoelectric film 1 shown by the arrow A into the vibration direction of air shown by the arrow B, the piezoelectric element is appropriately curved in a direction projecting upward. Then, when an AC signal is applied from the amplifier 4 between the two electrode layers 2 and 3, when the direction of the electric field generated by the voltage applied between the two electrode layers 2 and 3 is opposite to the direction of spontaneous polarization, piezoelectric The film 1 extends in the direction of arrow A, and if it is in the same direction, it contracts in the direction of arrow A. The conversion of such electrical energy into mechanical displacement causes the piezoelectric element to vibrate and generate sound.

By the way, in such a piezoelectric element, in order to convert the movement direction of the piezoelectric film 1 shown by the arrow A into the vibration direction of air shown by the arrow B, the piezoelectric element is appropriately curved in a direction projecting upward. Therefore, there is a problem in that the structure in a normal state cannot be a planar structure.

On the other hand, a piezoelectric element having a bimorph structure as shown in FIG. 5 is known as a piezoelectric element having a planar structure in a normal state. In this piezoelectric element, the intermediate electrode layer 13 is interposed between the upper and lower piezoelectric films 11 and 12,
The upper electrode layer 14 is provided on the upper surface of the upper piezoelectric film 11, and the lower electrode layer 15 is provided on the lower surface of the lower piezoelectric film 12. The directions of spontaneous polarization of the piezoelectric films 11 and 12 are both in the film thickness direction and are upward. Then, as shown in FIG. 5, when a negative voltage is applied from the amplifier 16 to the intermediate electrode layer 13 and a positive voltage is applied to the upper and lower electrode layers 14 and 15, the upper piezoelectric film 11 expands, and the lower piezoelectric film 12. Is contracted, the whole is curved in a direction projecting upward, and when a reverse voltage is applied, it is curved in the opposite direction.

By the way, in such a piezoelectric element, it is necessary to have a certain degree of rigidity in structure, and therefore the electrode layers 13, 14, 15 are made thick. However, if the electrode layers 13, 14 and 15 are made thick, there is a problem that it becomes difficult to vibrate and it becomes impossible to produce a very large volume. The electrode layers 13, 14, 15
The piezoelectric films 11 and 12 may be thickened instead of being thickened. In this case, the relatively expensive piezoelectric films 11 and 12 are used.
Therefore, there is another problem that the cost becomes high.

[0006]

As described above, in the case of the conventional piezoelectric element shown in FIG. 4, there is a problem in that the structure in the normal state cannot be made into a planar structure. On the other hand, as shown in FIG. In the case of the conventional piezoelectric element, there is a problem that it becomes difficult to vibrate and it becomes impossible to produce a very large volume. An object of the present invention is to provide a piezoelectric element which can be made to have a planar structure in a normal state and which can easily vibrate and generate a large volume.

[0007]

According to the present invention, a piezoelectric film having a bimorph structure is provided on at least one surface of a flexible support film.

[0008]

According to the present invention, since the piezoelectric body having the bimorph structure is provided, it is possible to make the structure in a normal state a planar structure, and an inexpensive supporting film having flexibility is provided to the whole piezoelectric element to some extent. Since it is possible to provide rigidity, it is not necessary to thicken the electrode layer and the piezoelectric film, and therefore, it is inexpensive, easy to vibrate, and large volume can be produced.

[0009]

1 shows a piezoelectric element according to a first embodiment of the present invention. This piezoelectric element has a structure in which bimorph piezoelectric bodies 22 and 23 are provided on the upper and lower surfaces of a support film 21 made of a flexible polymer film such as PET. In this case, as an example, first, a thin electrode layer 22 is formed on the upper and lower surfaces of the support film 21 by a method such as sputtering, vapor deposition, printing, and coating.
a and 23a are formed. Next, each surface of the electrode layers 22a and 23a is coated with a coatable ferroelectric polymer such as vinylidene fluoride copolymer or trifluoroethylene copolymer to form piezoelectric films 22b and 23b. Next, thin electrode layers 22c and 23c are formed on the respective surfaces of the piezoelectric films 22b and 23b by the same method as described above. Next, the piezoelectric films 22d and 23d are formed on the respective surfaces of the electrode layers 22c and 23c by the same method as described above.
Finally, thin electrode layers 22e and 23e are formed on the respective surfaces of the piezoelectric films 22d and 23d by the same method as described above.

Therefore, in the upper piezoelectric body 22, the intermediate electrode layer 22c is interposed between the two piezoelectric films 22b and 22d, the lower electrode layer 22a is provided on the lower surface of the lower piezoelectric film 22b, and the upper piezoelectric film 22d is formed. It has a bimorph structure in which an upper electrode layer 22e is provided on the upper surface. In the lower piezoelectric body 23, the intermediate electrode layer 23c is interposed between the two piezoelectric films 23b and 23d, the upper electrode layer 23a is provided on the upper surface of the upper piezoelectric film 23b, and the lower electrode is formed on the lower surface of the lower piezoelectric film 23d. It has a bimorph structure in which the electrode layer 23e is provided. The directions of spontaneous polarization of the piezoelectric films 22b, 22d, 23b, and 23d are all in the film thickness direction and are upward.

In this piezoelectric element, as shown in FIG. 1, a negative voltage is applied from the amplifier 24 to the intermediate electrode layers 22c and 23c and the remaining electrode layers 22a, 22e and 23 are applied.
When a + voltage is applied to a and 23e, the upper piezoelectric film 22
As d and 23b expand and the lower piezoelectric films 22b and 23d contract, they bend in the direction of projecting upward as a whole, and when the reverse voltage is applied, they bend in the opposite direction.

By the way, since this piezoelectric element is provided with the piezoelectric bodies 22 and 23 having a bimorph structure, the structure in a normal state can be a planar structure. Further, since the support film 21 having flexibility can be given a certain degree of rigidity, the electrode layers 22a, 22c, 22
It is not necessary to increase the thickness of e, 23a, 23c, and 23e, and therefore, it is easy to vibrate and a large volume can be produced.
Particularly, in the case of this embodiment, since the piezoelectric films 22 and 23 having the bimorph structure are provided on both surfaces of the supporting film 21, it is attempted to vibrate as compared with a normal piezoelectric element having the bimorph structure as shown in FIG. 5, for example. The force exerted is stronger, and therefore vibrates more and produces a louder volume.

The present invention is not limited to the above-mentioned first embodiment. For example, as in the second embodiment shown in FIG. 2, a plurality of grooves (recesses) 25 having a V-shaped cross section may be provided in a grid pattern on both surfaces (or one surface) of the support film 21, and as shown in FIG. As in the third embodiment, the support film 21 may be provided with a plurality of through holes 26. By doing so, even if the support film 21 is thickened, its rigidity can be appropriately suppressed. However, in this case, the electrode layers 22a and 23a provided on both surfaces of the support film 21 are adhered by an adhesive or the like. Further, in the above-mentioned embodiment, the piezoelectric films 22 and 23 having the bimorph structure are provided on both surfaces of the support film 21, but they may be provided on only one surface. Also,
In the above-described embodiments, the piezoelectric element has a planar structure in a normal state, but the piezoelectric element is not limited to this and may be curved.

[0014]

As described above, according to the present invention, since the piezoelectric body having the bimorph structure is provided, it is possible to make the structure in a normal state a plane structure, and also it is flexible and inexpensive. Since the film can give the entire piezoelectric element a certain degree of rigidity, it is not necessary to increase the thickness of the electrode layer or the piezoelectric film, and therefore the cost is low, the vibration is easy, and a large volume can be produced.

[Brief description of drawings]

FIG. 1 is a side view of a piezoelectric element according to a first embodiment of the present invention.

FIG. 2 is a side view of the piezoelectric element according to the second embodiment of the present invention.

FIG. 3 is a side view of a piezoelectric element according to a third embodiment of the present invention.

FIG. 4 is a side view of an example of a conventional piezoelectric element.

FIG. 5 is a side view of another example of a conventional piezoelectric element.

[Explanation of symbols]

 21 Support Films 22 and 23 Bimorph Piezoelectric Body 25 Groove (Recess) 26 Through Hole

Claims (3)

[Claims] 1. A piezoelectric element comprising a flexible support film and a piezoelectric material having a bimorph structure provided on at least one surface of the flexible support film. 2. The support film is provided with a plurality of recesses on at least one surface thereof.
The piezoelectric element described. 3. The piezoelectric element according to claim 1, wherein the support film is provided with a plurality of through holes.