JP2014068225A - Piezoelectric vibration element, and piezoelectric vibration device using the same and portable terminal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric vibration element which can transmit strong vibration to a diaphragm even if the diaphragm is bonded directly to the surface, and to provide a piezoelectric vibration device using the same, and a portable terminal.SOLUTION: A piezoelectric vibration element includes at least a plurality of electrodes 21-25 arranged alternately along the first direction, and a plurality of piezoelectric layers 27, where the average of magnitude of voltages applied between adjoining electrodes on one side in the first direction is smaller than the average of magnitude of voltages applied between adjoining electrodes on the other side in the first direction. A piezoelectric vibration device using the same, and a portable terminal are also provided. A piezoelectric vibration element that can transmit strong vibration to a diaphragm even if the diaphragm is bonded directly to the surface, and a piezoelectric vibration device using the same and a portable terminal can be obtained.

Description

  The present invention relates to a piezoelectric vibration element, a piezoelectric vibration device using the same, and a portable terminal.

  Conventionally, a plate-like piezoelectric bimorph element and a vibration plate are arranged with a space therebetween, and one end in the length direction of the piezoelectric bimorph element is fixed to the vibration plate via a fixing jig, thereby vibrating the piezoelectric bimorph element. There is known a piezoelectric vibration device that transmits a vibration to a diaphragm (see, for example, Patent Document 1).

JP 2006-238072 A

  However, the above-described conventional piezoelectric vibration device requires a sufficient space between the piezoelectric bimorph element and the diaphragm so that the piezoelectric bimorph element and the diaphragm do not contact even when an impact is applied. There is a problem that it is difficult to reduce the thickness. In addition, the inventors have clarified that it is difficult to transmit strong vibration to the diaphragm when one main surface of the diaphragm is directly joined to one main surface of the piezoelectric bimorph element in order to reduce the thickness.

  The present invention has been devised in view of such problems, and an object of the present invention is to provide a piezoelectric vibration element capable of transmitting strong vibration to a vibration plate even when the vibration plate is directly bonded to the surface, and the piezoelectric vibration element. Another object is to provide a piezoelectric vibration device and a portable terminal using the above.

  The piezoelectric vibration element according to the present invention includes at least a plurality of electrodes and a plurality of piezoelectric layers arranged alternately along the first direction, and the adjacent electrodes on one side in the first direction. The average of the magnitudes of the voltages applied between them is smaller than the average of the magnitudes of the voltages applied between the adjacent electrodes on the other side in the first direction.

  The piezoelectric vibration device of the present invention includes at least the piezoelectric vibration element and a vibration plate having one main surface bonded to the surface on the one side in the first direction of the piezoelectric vibration element. It is. The portable terminal according to the present invention includes at least the piezoelectric vibration device and an electronic circuit that generates an electric signal input to the piezoelectric vibration element.

  According to the piezoelectric vibration element of the present invention, it is possible to obtain a piezoelectric vibration element that can transmit strong vibration to the vibration plate even if the vibration plate is directly bonded to the surface. According to the piezoelectric vibration device of the present invention, a thin piezoelectric vibration device capable of transmitting strong vibration can be obtained. According to the mobile terminal of the present invention, a thin mobile terminal capable of transmitting strong vibrations can be obtained.

1 is a perspective view schematically showing a piezoelectric vibration element of a first example of an embodiment of the present invention. (A)-(e) is a top view for demonstrating the structure of the piezoelectric vibration element shown in FIG. It is a figure for demonstrating the structure of the piezoelectric vibration element shown in FIG. It is a figure for demonstrating the voltage applied between the electrodes of the piezoelectric vibration element shown in FIG. It is a figure for demonstrating the voltage applied between the electrodes of the piezoelectric vibration element of the 2nd example of embodiment of this invention. It is a perspective view which shows typically the piezoelectric vibration apparatus of the 3rd example of embodiment of this invention. It is a perspective view which shows typically the portable terminal of the 4th example of embodiment of this invention. FIG. 8 is a cross-sectional view taken along line A-A ′ in FIG. 7. FIG. 8 is a sectional view taken along line B-B ′ in FIG. 7.

  Hereinafter, a piezoelectric vibration element of the present invention, a piezoelectric vibration device using the same, and a portable terminal will be described in detail with reference to the accompanying drawings.

(First example of embodiment)
FIG. 1 is a perspective view schematically showing a piezoelectric vibration element 14 which is a first example of an embodiment of the present invention. As shown in FIG. 1, the piezoelectric vibration element 14 of this example has a first direction (z-axis direction in the drawing) as a thickness direction, and an x-axis direction in the drawing perpendicular to the first direction as a length direction. There is a rectangular parallelepiped shape in which the first direction and the y-axis direction in the drawing perpendicular to the x-axis direction in the drawing are the width direction. The piezoelectric vibration element 14 includes the laminate 20, the first external terminal 41, the second external terminal 42, the third external terminal (not shown), and the fourth external terminal (not shown). ) And a fifth external terminal (not shown).

  As shown in FIG. 1, an electrode 23 is disposed on the end surface of the laminate 20 on one side in the first direction (+ z direction side in the drawing), and on the end surface in the + x direction of the laminate 20 in the drawing. The 1st external terminal 41 and the 2nd external terminal 42 are arrange | positioned. Although not shown in FIG. 1, an electrode 25 (see FIG. 2) is disposed on the other end face in the first direction (the −z direction side in the drawing) of the stacked body 20. The third to fifth external terminals (not shown) are arranged on the end surface in the −x direction in FIG.

  2A to 2E are plan views schematically showing the shapes of the electrodes 21 to 25 included in the piezoelectric vibration element 14. FIG. 3 shows the basic positional relationship of the electrodes 21 to 25 in the first direction (the z-axis direction in the drawing) and the polarization state of the piezoelectric layer 27 disposed between the electrodes 21 to 25. It is a figure shown typically. In FIG. 3, the first to fifth external terminals and the piezoelectric layer 27 are not shown. As shown in FIGS. 2 and 3, the stacked body 20 includes a plurality of piezoelectric layers 27 polarized in a first direction (z-axis direction in the figure) and a plurality of flat electrodes 21 to 25. They are arranged alternately along the first direction.

The electrode 21 has a structure in which one end of a rectangular lead portion 21b is connected to one end of a rectangular main body portion 21a formed at a distance from the side surface of the laminate 20. The other end of the lead portion 21 b is connected to the first external terminal 41. The electrode 22 has a structure in which one end of a rectangular lead portion 22b is connected to one end of a rectangular main body portion 22a formed at a distance from the side surface of the laminate 20. The other end of the lead portion 22 b is connected to the second external terminal 42. The electrode 23 has a structure in which one end of a rectangular lead portion 23b is connected to one end of a rectangular main body portion 23a formed at a distance from the side surface of the laminate 20. The other end of the lead portion 23b is connected to a third external terminal (not shown). The electrode 24 has a structure in which one end of a rectangular lead portion 24b is connected to one end of a rectangular main body portion 24a formed at a distance from the side surface of the laminate 20. The other end of the lead portion 24b is connected to a fourth external terminal (not shown). The electrode 25 has a structure in which one end of a rectangular lead portion 25b is connected to one end of a rectangular main body portion 25a formed at a distance from the side surface of the laminate 20. The other end of the lead portion 25b is connected to a fifth external terminal (not shown).

  Further, the piezoelectric layer 27 disposed between the electrodes 21 to 25 is polarized as shown by arrows in FIG. Arrows P1 to P4 indicate the macroscopic polarization state of each piezoelectric layer 27 as a vector, the direction of the arrow indicates the direction of polarization, and the magnitude of the arrow indicates the strength of the polarization. Show. As shown in FIG. 3, each piezoelectric layer 27 is polarized with substantially equal strength.

  As shown in FIG. 3, the piezoelectric layer 27 is polarized in the direction from the electrodes 24 and 25 toward the electrode 22 on the other side in the first direction (the −z direction side in the drawing). Is polarized in the direction from the electrode 21 toward the electrodes 23 and 24 on one side (the + z direction side in the figure).

  When the piezoelectric vibration element 14 is vibrated, the potential of the electrode 23, the potential of the electrode 24, and the potential of the electrode 25 become higher than the potential of the electrode 21 and the potential of the electrode 22 at a certain moment. The electrodes 21 to 21 are connected via the first to fifth external terminals so that the potential of the electrode 23, the potential of the electrode 24, and the potential of the electrode 25 are lower than the potential of the electrode 21 and the potential of the electrode 22. An AC voltage is applied to 25. Thereby, the piezoelectric vibrating element 14 is configured such that the polarization direction with respect to the direction of the electric field applied at a certain moment is reversed between one side and the other side in the first direction (z-axis direction in the figure).

  Therefore, when an electrical signal is applied and one side (the + z-direction side in the figure) of the first direction extends in the length direction (the x-axis direction in the figure) of the piezoelectric vibration element 14 at a certain moment, the first The other side of this direction (the −z direction side in the figure) is configured to shrink in the length direction of the piezoelectric vibration element 14. Thereby, the piezoelectric vibration element 14 is flexibly vibrated in the first direction (the z-axis direction in the figure) so that the amplitude changes in the x-axis direction in the figure when an electric signal is applied. Thus, the piezoelectric vibration element 14 is configured by a piezoelectric body (piezoelectric bimorph element) having a bimorph structure.

  FIG. 4 is a diagram for explaining a voltage applied between the electrodes 21 to 25 of the piezoelectric vibration element 14 when the piezoelectric vibration element 14 shown in FIG. 1 is vibrated. Arrows E1 to E4 indicate the state of a macroscopic electric field between adjacent electrodes at a certain moment as a vector, the direction of the electric field is indicated by the direction of the arrow, and the strength of the electric field is indicated by the size of the arrow. It shows.

  As shown in FIG. 4, the magnitude of the electric field E1 between the adjacent electrodes 25 and 22 at a certain moment is | E1 |, the magnitude of the electric field E2 between the adjacent electrodes 22 and 24 is | E2 | If the magnitude of the electric field E3 between the matching electrodes 24 and 21 is | E3 | and the magnitude of the electric field E4 between the adjacent electrodes 21 and 23 is | E4 |, then | E1 |> | E2 |> | E3 |> A voltage is applied between adjacent electrodes so that | E4 |.

Here, the areas where the adjacent electrodes face each other are all set to be approximately equal, the intervals between the adjacent electrodes are all set to be approximately equal, and the dielectric constant of the piezoelectric layer 27 located between the adjacent electrodes is also set. It is set approximately equal. Therefore, the magnitude of the voltage V1 applied between the adjacent electrodes 25, 22 is | V1 |, the magnitude of the voltage V2 applied between the adjacent electrodes 22, 24 is | V2 |, and the adjacent electrodes 24, 21 are used. If the magnitude of the voltage V3 applied between them is | V3 | and the magnitude of the voltage V4 applied between the adjacent electrodes 21 and 23 is | V4 |, then | E1 |> | E2 |> | E3 |> | The voltage applied so that E4 | becomes | V1 |> |
V2 |> | V3 |> | V4 |.

  When the piezoelectric vibration element 14 is vibrated, an alternating voltage is applied between adjacent electrodes of the piezoelectric vibration element 14 as described above. Therefore, the voltages V1, V2, V3, and V4 are alternating voltages, and their magnitudes and signs change periodically, but their frequencies and phases are equal to each other. Therefore, the magnitude relationship among | V1 |, | V2 |, | V3 |, and | V4 | is the magnitude relationship between the effective values, but is also the magnitude relationship between the instantaneous values at any moment except when the value becomes zero. It is also the relationship between the maximum values.

  In the piezoelectric vibration element 14 of this example, the average magnitude of the voltage applied between adjacent electrodes on one side in the first direction (the + z direction side in the figure) is the other side in the first direction (see the figure). Of the voltage applied between adjacent electrodes on the -z direction side). Note that one side in the first direction is a part on one side of the center in the first direction, and the other side in the first direction is a part on the other side of the center in the first direction. is there. In the piezoelectric vibration element 14 of this example, the electrode 24 is located at the center of the first direction (z-axis direction in the drawing) of the piezoelectric vibration element 14.

  That is, if the average of the magnitudes of voltages applied between adjacent electrodes on the other side in the first direction is A1, A1 = (| V1 | + | V2 |) / 2, and one side in the first direction If the average of the magnitudes of voltages applied between adjacent electrodes in A is A2, then A2 = (| V3 | + | V4 |) / 2. In the piezoelectric vibration element 14 of this example, the average A2 of the magnitude of the voltage applied between the adjacent electrodes on one side in the first direction is applied between the adjacent electrodes on the other side in the first direction. It is smaller than the average A1 of the magnitude of the voltage. Thus, the vibration device is configured to join the main surface of the vibration plate to the surface of the piezoelectric vibration element 14 on one side in the first direction (+ z direction side in the drawing) and transmit the vibration of the piezoelectric vibration element 14 to the vibration plate. When it is done, strong vibration can be transmitted to the diaphragm.

  The reason why this effect is obtained can be estimated as follows. That is, for example, when the piezoelectric vibration element 14 is bent so that the −z direction side is convex, as described above, the + z direction side of the piezoelectric vibration element 14 contracts in the x-axis direction. Then, since the surface of the vibration plate (the surface on the −z direction side) joined to the surface on the + z direction side of the piezoelectric vibration element 14 also contracts in the x axis direction, the vibration plate will be deformed so that the + z direction side is convex. And Therefore, the direction in which the piezoelectric vibration element 14 tries to bend and the direction in which the vibration plate tries to bend are reversed, the vibration of the piezoelectric vibration element 14 is hindered, and the vibration of the piezoelectric vibration element 14 is weakened. Thereby, the vibration transmitted to the diaphragm is weakened.

  On the other hand, in the piezoelectric vibrating element 14 of this example, the average magnitude of the voltage applied between adjacent electrodes on one side in the first direction (the + z direction side in the figure) is the other in the first direction. It is smaller than the average of the magnitude | sizes of the voltage applied between the adjacent electrodes in the side (-z direction side of a figure). As a result, the average magnitude of the electric field between the adjacent electrodes on one side in the first direction (+ z direction side in the figure) is equal to that on the other side in the first direction (on the −z direction side in the figure). It is smaller than the average of the magnitude of the electric field between the mating electrodes.

  That is, assuming that the average electric field between adjacent electrodes on the other side in the first direction is B1, B1 = (| E1 | + | E2 |) / 2, and the adjacent on one side in the first direction. B2 = (| E3 | + | E4 |) / 2 when the average magnitude of the electric field between the matching electrodes is B2, but adjacent electrodes on one side in the first direction (+ z direction side in the figure) The average electric field magnitude B2 between them is smaller than the average electric field magnitude B1 between adjacent electrodes on the other side in the first direction (the −z direction side in the figure). In the piezoelectric vibration element 14 of this example, as described above, the polarization strengths of the plurality of piezoelectric layers 27 are substantially equal.

  Therefore, when the piezoelectric vibration element 14 of this example vibrates by being given an electric signal, the amount of expansion / contraction on one side in the first direction is smaller than the amount of expansion / contraction on the other side in the first direction. As a result, the force to bend the vibration plate bonded to the surface of the piezoelectric vibration element 14 on one side in the first direction in the direction opposite to that of the piezoelectric vibration element 14 is reduced. Accordingly, the action of preventing the vibration of the piezoelectric vibration element 14 is reduced, the piezoelectric vibration element 14 can vibrate strongly, and the strong vibration can be transmitted to the diaphragm. In addition, since the deformation on one side in the first direction when the piezoelectric vibration element 14 undergoes flexural vibration is smaller than the deformation on the other side in the first direction, the surface on the one side in the first direction Even when the vibration of the bonded diaphragm is suppressed, the vibration of the piezoelectric vibration element 14 is not significantly suppressed, and a strong vibration can be transmitted to the diaphragm.

  For example, when the center in the first direction (the z-axis direction in the drawing) is located in one piezoelectric layer 27A, the piezoelectric layer 27A may be excluded. That is, the average of the magnitudes of voltages applied between adjacent electrodes located on one side in the first direction (the + z direction side in the figure) with respect to the piezoelectric layer 27A is expressed as “adjacent one side in the first direction. The average of the magnitude of the voltage applied between the matching electrodes ”, and the voltage applied between the adjacent electrodes located on the other side in the first direction (the −z direction side in the figure) of the piezoelectric layer 27A. May be set to “average of magnitudes of voltages applied between adjacent electrodes on the other side in the first direction”.

  Further, in the piezoelectric vibration element 14 of this example, the magnitude of the voltage applied between the adjacent electrodes from the other side in the first direction (the −z direction side in the figure) to the one side (the + x direction side in the figure). When the lengths are sequentially described, | V1 |, | V2 |, | V3 |, and | V4 |, but the relationship between these sizes is | V1 |> | V2 |> | V3 |> | V4 | ing. That is, in the piezoelectric vibration element 14 of the present example, the magnitude of the voltage applied between the adjacent electrodes gradually decreases toward the one side in the first direction (the + z direction side in the figure).

  Then, by sequentially describing the magnitude of the electric field between the adjacent electrodes from the other side in the first direction (the −z direction side in the drawing) to the one side (the + x direction side in the drawing), | E1 |, | E2 |, | E3 |, and | E4 |, but the relationship between these sizes is | E1 |> | E2 |> | E3 |> | E4 |. That is, in the piezoelectric vibration element 14 of this example, the magnitude of the electric field between the adjacent electrodes gradually decreases toward one side in the first direction (the + z direction side in the figure).

  As a result, the amount of expansion / contraction of each piezoelectric layer 27 when the piezoelectric vibration element 14 undergoes flexural vibration gradually decreases toward one side in the first direction, so that the piezoelectric layer within the piezoelectric vibration element 14 The stress generated in the portion where the amount of expansion and contraction 27 changes can be reduced. Thereby, problems, such as generation | occurrence | production of a microcrack, can be reduced.

  In the piezoelectric vibration element 14 of this example, the laminate 20 can have a length of about 18 mm to 28 mm, a width of about 1 mm to 6 mm, and a thickness of about 0.2 mm to 1.0 mm, for example. The length of the main body of the electrodes 21 to 25 can be about 17 mm to 25 mm, for example, and the width of the main body of the electrodes 21 to 25 can be about 0.5 mm to 1.5 mm, for example.

The piezoelectric layer 27 constituting the stacked body 20 can be formed using a piezoelectric material. For example, a lead-free piezoelectric material such as lead titanate (PT), lead zirconate titanate (PZT), Bi layered compound, tungsten bronze structure compound, or the like can be suitably used. The thickness of one layer of the piezoelectric layer 27 can be set to, for example, about 0.01 to 0.1 mm. The electrodes 21, 22, and 24 can be formed using a known metal material. For example, in addition to a metal component such as silver or an alloy of silver and palladium, a material containing a ceramic component or a glass component can be preferably used. The electrodes 23 and 25 and the first to fifth external terminals can be formed using a known metal material, but preferably contain, for example, a metal component made of silver and a glass component.

  Such a piezoelectric vibration element 14 can be manufactured by the following method, for example. First, a binder, a dispersant, a plasticizer, and a solvent are added to the piezoelectric material powder, and the mixture is agitated to produce a slurry. The obtained slurry is formed into a sheet shape to produce a green sheet. Next, a conductive paste is printed on the green sheet to form electrode patterns to be the electrodes 21, 22, and 24. The green sheets on which the electrode patterns are formed are stacked and pressed using a press device to form a laminated molded body Is made. Then, degreasing and baking are performed, and a laminated body is obtained by cutting to a predetermined dimension. Next, a conductor paste for forming the electrodes 23 and 25, the first external terminal 41, the second external terminal 42, and the third to fifth external terminals (not shown) is printed at a predetermined temperature. After baking, the piezoelectric layer 27 is polarized by applying a DC voltage through the first to fifth external terminals. In this way, the piezoelectric vibration element 14 can be obtained.

  For example, when a problem occurs when the electrode is exposed at the end face in the first direction (z-axis direction in the drawing) of the stacked body 20, a protective layer made of a piezoelectric body or the like may be provided. In that case, it is desirable to sufficiently reduce the thickness of the protective layer.

(Second example of embodiment)
FIG. 5 is a diagram for explaining a voltage applied between the electrodes of the piezoelectric vibration element according to the second example of the embodiment of the present invention. In FIG. 5, the illustration of the piezoelectric layer and the first to fifth external terminals is omitted to simplify the illustration. Moreover, in this example, a different point from the 1st example of embodiment mentioned above is demonstrated, the same referential mark is attached | subjected to the same component and the overlapping description is abbreviate | omitted.

  The piezoelectric vibration element 14a of this example is added between adjacent electrodes on one side in the first direction (the + z direction side in the drawing), similarly to the piezoelectric vibration element 14 of the first example of the above-described embodiment. The average voltage magnitude A2 = (| V3 | + | V4 |) / 2 is the average voltage magnitude applied between adjacent electrodes on the other side in the first direction (the −z direction side in the figure). It is smaller than A1 = (| V1 | + | V2 |) / 2.

  Thus, the average B2 = (| E3 | + | E4 |) / 2 of the magnitude of the electric field between the adjacent electrodes on one side in the first direction (+ z direction side in the figure) is the first direction. Smaller than the average B1 = (| E1 | + | E2 |) / 2 of the magnitude of the electric field between the adjacent electrodes on the other side (the −z direction side in the figure). In the piezoelectric vibration element 14a of this example, the polarization strengths of the plurality of piezoelectric layers 27 are substantially equal to each other, like the piezoelectric vibration element 14 of the first example of the embodiment described above.

  As a result, when a vibration device is constructed in which the main surface of the diaphragm is joined to the surface on one side in the first direction (the + z direction side in the figure) and the vibration of the piezoelectric vibration element 14a is transmitted to the diaphragm. Strong vibration can be transmitted to the board. Further, even when vibration of the diaphragm is suppressed, strong vibration can be transmitted to the diaphragm.

  Further, in the piezoelectric vibration element 14a of this example, the relationship of | V1 | = | V2 |> | V3 |> | V4 | is established in the magnitudes V1, V2, V3, and V4 of voltages applied between adjacent electrodes. ing. That is, the magnitude of the voltage applied between adjacent electrodes is constant on the other side in the first direction (the −z direction side in the figure) and on the one side in the first direction (the + z direction side in the figure). , And gradually decreases toward one side of the first direction.

As a result, the piezoelectric vibration element 14a of the present example has an electric field magnitude E between adjacent electrodes.
In E1, E2, E3, and E4, the relationship | E1 | = | E2 |> | E3 |> | E4 | That is, the magnitude of the electric field between adjacent electrodes is constant on the other side in the first direction (the −z direction side in the figure), and on the one side in the first direction (the + z direction side in the figure) As it goes to one side in the direction of 1, it becomes smaller in steps.

  Since such a configuration is provided, the piezoelectric vibration element 14a of the present example can ensure a large amount of deformation on the other side in the first direction. As a result, when a piezoelectric vibration device in which the main surface of the diaphragm is attached to the surface on one side in the first direction (+ z direction side in the figure), stronger vibration can be transmitted to the diaphragm.

(Third example of embodiment)
FIG. 6 is a perspective view schematically showing a piezoelectric vibration device 15 according to a third example of the embodiment of the present invention. In FIG. 6, the detailed structure of the piezoelectric vibration element 14 is not shown in order to facilitate drawing. Moreover, in this example, a different point from the 1st example of embodiment mentioned above is demonstrated, the same referential mark is attached | subjected to the same component and the overlapping description is abbreviate | omitted. The piezoelectric vibration device 15 of this example includes the piezoelectric vibration element 14 and the diaphragm 12 of the first example of the above-described embodiment.

  The diaphragm 12 has a rectangular thin plate shape, and has one main surface (on the −z direction side in the figure) on the surface of one side (the + z direction side in the figure) of the piezoelectric vibration element 14 in the first direction. Are joined using an adhesive or the like. Such a diaphragm 12 can be preferably formed using a material having high rigidity and elasticity, such as acrylic resin or glass. Moreover, the thickness of the diaphragm 12 is set to about 0.4 mm to 1.5 mm, for example. The piezoelectric vibration device 15 of this example having such a configuration functions as a piezoelectric vibration device that flexibly vibrates the piezoelectric vibration element 14 by applying an electric signal and transmits the vibration to the vibration plate 12.

  In the piezoelectric vibration device 15 of this example, one main surface of the vibration plate 12 is bonded to the surface of one side (the + z direction side in the drawing) of the piezoelectric vibration element 14 in the first direction. In addition, the piezoelectric vibration element 14 has an average of magnitudes of voltages applied between adjacent electrodes on one side in the first direction (+ z direction side in the figure), and the other side in the first direction (−z in the figure). Smaller than the average of the magnitudes of voltages applied between adjacent electrodes on the direction side). Thereby, even when the diaphragm 12 can vibrate freely, even when the vibration of the diaphragm 12 is suppressed, a thin piezoelectric vibration device that can transmit strong vibration to the diaphragm 12 can be obtained.

(Fourth example of embodiment)
FIG. 7 is a perspective view schematically showing a portable terminal of the fourth example of the embodiment of the present invention. 8 is a cross-sectional view taken along line AA ′ in FIG. 9 is a cross-sectional view taken along line BB ′ in FIG. 8 and 9, the detailed structure of the piezoelectric vibration element 14 is not shown. Moreover, in this example, a different point from the 3rd example of embodiment mentioned above is demonstrated, the same referential mark is attached | subjected to the same component and the overlapping description is abbreviate | omitted. The portable terminal of this example includes the piezoelectric vibration device 15 of the third example of the embodiment shown in FIG. 6, an electronic circuit 17, a display 18, and a housing 19.

  The electronic circuit 17 generates an electrical signal that is input to the piezoelectric vibration element 14. The electronic circuit 17 may include other circuits such as a circuit for processing image information to be displayed on the display 18 and a communication circuit. The electronic circuit 17 and the piezoelectric vibration element 14 are connected via a wiring (not shown).

The display 18 is a display device having a function of displaying image information. For example, a known display such as a liquid crystal display, a plasma display, and an organic EL display can be suitably used. The display 18 may have an input device such as a touch panel.

  The housing 19 has a box shape with one surface opened. The casing 19 can be formed using a material such as a synthetic resin having high rigidity and elasticity, for example, but may be formed using other materials such as a metal.

  In the portable terminal of this example, the diaphragm 12 is disposed outside the display 18 and integrated with the display 18, and functions as a cover that protects the display 18. Further, the diaphragm 12 has only one main surface (main surface on the −z direction side in the figure) around the casing 19 joined to the casing 19 with an adhesive or the like, and is attached to the casing 19 so as to vibrate. . The diaphragm 12 may have an input device such as a touch panel.

  The mobile terminal of this example having such a configuration can generate sound by vibrating the diaphragm 12 by vibrating the piezoelectric vibrating element 14. And the sound information can be transmitted to a person by this sound. In addition, audio information may be transmitted by transmitting vibration by bringing the diaphragm 12 or the casing 19 into contact with a part of a human body such as an ear directly or via another object.

  The portable terminal of this example uses a thin piezoelectric vibration device that can transmit strong vibration to the diaphragm 12 even when the diaphragm 12 can vibrate freely or when vibration of the diaphragm 12 is suppressed. ing. Thereby, even when the diaphragm 12 can vibrate freely, even when the vibration of the diaphragm 12 is suppressed, a thin mobile terminal capable of transmitting strong vibration to the diaphragm 12 can be obtained. Therefore, according to the portable terminal of this example, even when the diaphragm 12 is brought into contact with a human body such as an ear, strong vibration can be transmitted to the diaphragm 12 and voice information can be transmitted satisfactorily. A thin portable terminal can be obtained.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications and improvements can be made without departing from the scope of the present invention.

  For example, in the first and second examples of the above-described embodiment, the example in which the piezoelectric vibration element 14 has the five electrodes 21 to 25 is shown in order to simplify the illustration. However, the present invention is not limited to this, and a configuration having more electrodes may be used.

  In the third and fourth examples of the above-described embodiment, the example having the piezoelectric vibration element 14 of the first example of the embodiment has been described. However, the present invention is not limited to this. You may have the piezoelectric vibration element 14a of the 2nd example of embodiment, and the piezoelectric vibration element of another form.

  In the fourth example of the above-described embodiment, the example in which the cover of the display 18 functions as the diaphragm 12 is shown, but the present invention is not limited to this. For example, the display 18 itself may function as the diaphragm 12.

12: Vibration plates 14 and 14a: Piezoelectric vibration element 15: Piezoelectric vibration device 17: Electronic circuits 21, 22, 23, 24, 25: Electrode 27: Piezoelectric layer

Claims (5)

  A voltage level applied between adjacent electrodes on one side in the first direction, having at least a plurality of electrodes and a plurality of piezoelectric layers arranged alternately along the first direction. Is smaller than the average of the magnitudes of the voltages applied between the adjacent electrodes on the other side in the first direction.   2. The piezoelectric vibration element according to claim 1, wherein the magnitude of the voltage applied between the adjacent electrodes decreases stepwise toward the one side in the first direction.   The magnitude of the voltage applied between the adjacent electrodes is constant on the other side in the first direction, and toward the one side in the first direction on the one side in the first direction. The piezoelectric vibration element according to claim 2, wherein the piezoelectric vibration element decreases in a stepwise manner.   The piezoelectric vibration element according to any one of claims 1 to 3, and a vibration plate having at least one main surface bonded to the surface on the one side in the first direction of the piezoelectric vibration element. A characteristic piezoelectric vibration device.   5. A portable terminal comprising at least the piezoelectric vibration device according to claim 4 and an electronic circuit that generates an electric signal input to the piezoelectric vibration element.

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