JP2015046947A - Piezoelectric sounder and electronic apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable prevention of characteristic deterioration and downsizing by minimizing a flowing current value without impairing a displacement amount as an element of a piezoelectric sounder.SOLUTION: A piezoelectric driving element 10 used for a piezoelectric sounder includes: piezoelectric layers 20, 22, 24, 30, 32 and 34; electrode layers 40, 42, 44, 52 and 54 between the piezoelectric layers; and electrode layers 46 and 56 on the surfaces of a laminate. The piezoelectric layers 20, 22 and 24, and the piezoelectric layers 30, 32 and 34 are arranged on an upper side and on a lower side of the electrode layer 40 at a center in the thickness direction, respectively. The piezoelectric layers on the upper side and the piezoelectric layers on the lower side are polarized in opposite directions to each other. The piezoelectric layers 20 and 30 in a center portion having the smallest displacement amount are thickest, and are reduced in thickness at a predetermined rate as it goes toward the outside. The piezoelectric layers 22 and 32 have the same thickness and the piezoelectric layers 24 and 34 have the same thickness. The piezoelectric driving element 10 is attached to a support plate 70 and supported by a frame 80 to form the piezoelectric sounder.

Description

  The present invention relates to a piezoelectric sounding body and an electronic device using the piezoelectric sounding body, and more specifically to an improvement of a piezoelectric sounding body suitable for mounting on a small device or the like.

  In recent years, mobile phones, smartphones, and the like have been enhanced not only with call functions but also with functions as portable personal information terminals. Among them, regarding the size of the device itself, there is a strong demand for downsizing, thinning, and weight reduction, and accordingly, there is an increasing demand for downsizing, thinning, and weight reduction of components to be used. The same requirements apply to loudspeakers, but piezoelectric loudspeakers that use the displacement of the piezoelectric element in the 31 direction and expand the displacement using bending displacements are easy to make thin and structurally have high sound pressure. Since it can be secured, it has been used for portable devices. In addition, since the piezoelectric speaker is a voltage-driven type, it has an advantage that it consumes less power than a dynamic speaker, and is suitable as a component used in a portable device in which battery life is important.

  These piezoelectric speakers are formed of a laminate of up to about eight layers, particularly from the viewpoint of reducing driving voltage, and are used by being attached to shim plates such as metal plates. At this time, a single laminated piezoelectric material attached to a metal plate is called a unimorph type, and a laminated piezoelectric material polarized in opposite directions on both sides of a metal plate is called a bimorph type. As such a unimorph type and bimorph type piezoelectric speaker, for example, there is a technique described in Patent Document 1. In the case of the bimorph type, there is also a method of realizing the bimorph type with one element by reversing the polarization direction between the upper half and the lower half of the laminated piezoelectric element without using a metal plate. Since this integrated bimorph element does not include an extra structure such as a metal plate, the bending displacement efficiency is relatively high.

JP 2003-259488 A

  A piezoelectric speaker is a capacitive element, and from the viewpoint of effective power consumption, as described above, it consumes much less power than a dynamic speaker and can extend the duration of a battery. . However, particularly at 10 to 20 kHz, which is near the upper limit of the audible sound range, the impedance decreases, so the value of the flowing current increases. When the current value increases as described above, although the effective power consumption is small, there arises a problem that heat is generated in a place having a higher resistance value compared to other parts, such as a connecting portion of a conducting wire constituting the speaker. And since deterioration of a piezoelectric element is accelerated by heat_generation | fever, there exists a possibility of causing characteristic deterioration in the time after a design. In addition, since it is necessary to consider that a large current flows also in a circuit for driving the speaker, it is necessary to use a thick conductor or the like, which causes a problem that hinders downsizing of portable devices and the like.

  The present invention focuses on the above points, and provides a piezoelectric sounding body capable of preventing characteristic deterioration and miniaturization by keeping the flowing current value low without impairing the amount of displacement as an element. The purpose is to do. Another object is to provide an electronic device using the piezoelectric sounding body.

The piezoelectric sounding body of the present invention is a piezoelectric sounding body in which a bimorph type piezoelectric driving element in which four or more piezoelectric layers that contribute to displacement are stacked is supported by a support plate, and the plurality of piezoelectric members An electrode layer is formed between the layers, and the same number of upper and lower piezoelectric layers are polarized in opposite directions with the center in the stacking direction as a boundary, and the center portion in the stacking direction is a non-polarized layer, and the stacking direction from the center The thickness of the piezoelectric layer is gradually reduced in the vertical direction, and the thickness of the piezoelectric layer is the same when the upper and lower stacking positions are the same from the central boundary, and contributes to displacement. Among the piezoelectric layers to be used, when the thickness of the thickest piezoelectric layer is t _dmost , n layers (n is a natural number) from the base point with the surface on the central boundary side of the thickest piezoelectric layer as a base point the thickness of _until, satisfy the _{t dmost} × (√n) And wherein the Succoth

A piezoelectric sounding body according to another aspect of the invention is a piezoelectric sounding body in which a bimorph type piezoelectric driving element in which four or more piezoelectric layers contributing to displacement are laminated and supported by a support plate is supported by the support plate. An electrode layer is formed between the body layers, and the same number of upper and lower piezoelectric layers are polarized in the opposite direction with the center in the stacking direction as a boundary, and the center portion in the stacking direction is formed of a shim plate. The thickness of the piezoelectric layer is gradually reduced in the vertical direction, and the thickness of the piezoelectric layer is the same when the upper and lower stacking positions are the same from the central boundary, and contributes to displacement. Among the piezoelectric layers to be used, when the thickness of the thickest piezoelectric layer is t _dmost , n layers (n is a natural number) from the base point with the surface on the central boundary side of the thickest piezoelectric layer as a base point the thickness of _until, less than a _{t dmost} × (√n) It is characterized in. One of the main forms is that when the thickness of the thickest piezoelectric layer among the piezoelectric layers contributing to displacement is t _dmost and the number of piezoelectric layers contributing to displacement is 2n, the total thickness is Is 2 × t _dmost × (√n).

Still another piezoelectric sounding body is a piezoelectric sounding body in which a bimorph type piezoelectric driving element in which four or more piezoelectric layers that contribute to displacement are stacked is supported by a support plate, and the plurality of piezoelectric members An electrode layer is formed between the layers, and the same number of upper and lower piezoelectric layers are polarized in opposite directions with the center in the stacking direction as a boundary, and the center portion in the stacking direction is a non-polarized layer, and the stacking direction from the center The thickness of the piezoelectric layer is gradually reduced toward the upper and lower sides, and the thickness of the piezoelectric layer is the same when the upper and lower stacking positions are the same with respect to the central boundary. Among the piezoelectric layers contributing to the above, when the thickness of the thickest piezoelectric layer is t _dmost and the thickness of the electrode layer of the nth layer (n is a natural number) from the central boundary is t _ie (n) , With the central boundary side surface of the thickest piezoelectric layer as a base point, The thickness from the base point to the n _layer, characterized in that it is a _{t dmost × (√n) + Σ} ie (n-1).

Still another piezoelectric sounding body is a piezoelectric sounding body in which a bimorph type piezoelectric driving element in which four or more piezoelectric layers that contribute to displacement are stacked is supported by a support plate, and the plurality of piezoelectric members An electrode layer is formed between the layers, and the same number of upper and lower piezoelectric layers are polarized in the opposite direction with respect to the center in the stacking direction, and the central portion in the stacking direction is formed of a shim plate. The thickness of the piezoelectric layer is gradually reduced toward the surface, and the thickness of the piezoelectric layer is the same when the upper and lower stacking positions are the same with respect to the central boundary. Among the contributing piezoelectric layers, when the thickness of the thickest piezoelectric layer is t _dmost and the thickness of the electrode layer of the nth layer (n is a natural number) from the center boundary is t _ie (n), Starting from the central boundary side surface of the thickest piezoelectric layer, the base Thickness from up to n _layers, characterized in that it is a _{t dmost × (√n) + Σ} ie (n-1). One of the main forms is characterized in that an error of ± 10% is allowed for the thickness of each layer of the piezoelectric layer with respect to the ratio. An electronic apparatus according to the present invention uses any one of the piezoelectric sounding bodies described above. The above and other objects, features and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings.

  According to the present invention, in a piezoelectric sounding body using a piezoelectric driving element in which a plurality of piezoelectric layers are stacked, the thickness of the piezoelectric layer with the smallest amount of displacement is maximized, and the piezoelectric layers are sequentially formed outward. It was decided to form thinly. As a result, the capacitance can be reduced and the flowing current value can be kept low without impairing the amount of displacement as the element. As a result, it is possible to prevent the occurrence of a failure due to heat generation and to reduce the size because it is not necessary to use a thick conductor in the drive circuit.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows Example 1 of this invention, (A) is sectional drawing which shows the laminated structure of a piezoelectric drive element, (B) and (C) are sectional drawings which show the state which the piezoelectric drive element bent, (D) And (E) are diagrams showing an example of a frame that supports the piezoelectric driving element. It is sectional drawing which shows the structure of the electrode layer of the 4-8 layer laminated bimorph type piezoelectric drive element of this invention, (A-1)-(A-3) shows the electrode structure at the time of polarization operation, (B -1) to (B-3) show electrode configurations during driving. It is a top view which shows the internal electrode pattern of the piezoelectric drive element of this invention. It is explanatory drawing which shows the definition of the thickness of a piezoelectric drive element in consideration of the thickness of an internal electrode layer. It is a figure which shows the other Example of this invention.

  Hereinafter, the best mode for carrying out the present invention will be described in detail based on examples. 1A is a cross-sectional view showing a laminated structure of piezoelectric drive elements, FIGS. 1B and 1C are cross-sectional views showing a state in which the piezoelectric drive element is bent, and FIGS. 1D and 1E support a piezoelectric drive element. It is a figure which shows an example of the frame to do. FIG. 2 is a cross-sectional view showing the configuration of the electrode layer of the 4- to 8-layer laminated bimorph type piezoelectric driving element of the present invention, and (A-1) to (A-3) show the electrode configuration during polarization operation. (B-1) to (B-3) show electrode configurations during driving. FIG. 3 is a plan view showing an internal electrode pattern of the piezoelectric driving element of the present invention. FIG. 4 is an explanatory diagram showing the definition of the thickness of the piezoelectric driving element when the thickness of the internal electrode layer is taken into consideration. The piezoelectric sounding body 10 of this embodiment is used as a speaker of a mobile communication terminal represented by a mobile phone or a smartphone, for example.

  As shown in FIGS. 1A and 1D, the piezoelectric driving element 10 used in the piezoelectric sounding body of the present embodiment is a bimorph type and is generally rectangular. The piezoelectric driving element 10 includes six piezoelectric layers 20, 22, 24, 30, 32, 34, and electrode layers 40, 42, 44, 52, 54 provided between the piezoelectric layers, It is comprised by the electrode layers 46 and 56 formed in the laminated body surface. In this embodiment, three piezoelectric layers are formed on the upper and lower sides with the electrode layer 40 at the center in the thickness direction as a boundary. The piezoelectric layer 20, 22, 24 forms the upper laminated piezoelectric material 12, and the piezoelectric material layers 30, 32, 34 form the lower laminated piezoelectric material 14.

  In the present embodiment, the piezoelectric layers 20 and 30 are formed to have the largest thickness at the portion where the displacement of the piezoelectric driving element 10 is the smallest (the portion where the lateral expansion and contraction is the smallest). The piezoelectric layers 20, 22, and 24 are thinned in the order, and the piezoelectric layers 30, 32, and 34 are thinned in the order. The piezoelectric layers 20 and 30 have the same thickness, the piezoelectric layers 22 and 32 have the same thickness, and the piezoelectric layers 24 and 34 have the same thickness. That is, the thickness of each piezoelectric body layer is set so that the electrode layer 40 has a symmetrical plane and the layer structure and thickness are symmetrical. Therefore, when the bimorph structure is employed as in the present embodiment, the piezoelectric layer (piezoelectric layer contributing to displacement) constituting the piezoelectric drive element is always an even number layer of four or more layers. The thickness ratio between the piezoelectric layers will be described in detail later.

  The piezoelectric drive element 10 can be manufactured by using a normal method in which a piezoelectric body such as PZT is formed into a sheet, a paste including electrodes is printed on the sheet, laminated and pressed, and then fired at a predetermined temperature. . There are no particular restrictions on the dimensions in the surface direction of the element, but assuming use in a normal portable device, a circle with a diameter of about 20 to 25 mm or a rectangle with a side of about 15 to 20 mm is preferable. In this embodiment, it is rectangular. In the example of FIG. 1A, the piezoelectric layer 34, the electrode layer 54, the piezoelectric layer 32, the electrode layer 52, the piezoelectric layer 30, the electrode layer 40, the piezoelectric layer 20, the electrode layer 42, and the piezoelectric layer from the bottom. 22, the electrode layer 44, and the piezoelectric layer 24 are laminated in this order. The outermost electrode layers 46 and 56 may be printed with a paste in the same manner as the internal electrode layers and fired at the same time as the laminate, or may be applied and baked after firing the laminate. Or you may form by low temperature processes, such as vapor deposition, a sputter | spatter, and plating.

  Next, a voltage for polarization is applied to the piezoelectric layers 20 to 24 and 30 to 34 of the laminated body thus formed by using the electrode layers 40 to 46 and 52 to 56 to perform predetermined polarization. Is done. For example, in the example shown in FIG. 2A-2, the electrode layer 42 and the electrode layer 46 are connected by the side electrode 62 as a positive electrode pattern, and the electrode layer 52 and the electrode layer 56 are connected by a side electrode 64 as a negative electrode pattern. To do. The electrode layers 40, 44 and 54 are connected by the side electrode 60 as a common pattern. Examples of these positive electrode pattern, negative electrode pattern, and common pattern are shown in FIGS. The side electrodes 60, 62, and 64 are formed by, for example, a method of applying a paste to the side surface of the laminated body or a method using a low temperature process such as vapor deposition, sputtering, or plating. Alternatively, it is possible to connect by a conventionally used method such as a method of using a through hole that opens a hole in a piezoelectric sheet and connects electrode layers during paste printing without connecting on the external side surface.

  When the piezoelectric driving element 10 has a four-layer structure, the electrode layer 42 has a positive electrode pattern and the electrode layer 52 has a negative electrode pattern, as shown in FIG. The electrode layers 40, 44, and 54 are connected by the side electrode 60 as a common pattern. When the piezoelectric driving element 10 has an eight-layer structure, as shown in FIG. 2 (A-3), the electrode layer 42 and the electrode layer 46 are connected by a side electrode 62 as a positive electrode pattern, and the electrode layer 52 and the electrode are connected. The layer 56 is connected by a side electrode 64 as a negative electrode pattern. Further, the electrode layers 40, 44, 48, 54, 58 are connected by the side electrode 68 as a common pattern.

  Polarization is performed after firing the laminate and forming the electrodes. As the polarization voltage, a voltage higher than the coercive electric field of the material is applied. At this time, it is necessary to apply a voltage in accordance with the thickest layer thickness. Further, the voltage may be lowered by increasing the temperature during polarization. At the time of polarization, as shown in FIGS. 2 (A-1) to (A-3), using a positive electrode pattern, a negative electrode pattern, and a common pattern, polarization is performed using three common electrodes of positive and negative voltages and 0V. At this time, the positive and negative voltages need to be the same and must be applied simultaneously. If the voltages are different or not applied at the same time, the element will be deformed abnormally, causing cracks due to stress. After the polarization is completed, as shown in FIGS. 2B-1 to 2B-3, positive and negative electrodes are connected to form one electrode. In the example of the four-layer structure shown in FIG. 2 (B-1), the electrode layers 42 and 52 are connected by the side electrode 66. In the example of the 6-layer structure shown in FIG. 2 (B-2) and the 8-layer structure shown in FIG. 2 (B-3), the electrode layers 42, 46, 52, and 56 are connected by the side electrode 50.

  Then, by inputting a signal to the connected electrode and common electrode, the piezoelectric drive element 10 expands and contracts in the opposite direction in the upper half and the lower half, resulting in bending displacement. In the example of the six-layer structure in FIG. 1A, the polarization directions of the piezoelectric layers 30, 32, and 34 of the lower stacked piezoelectric body 14 are the same as those of the piezoelectric layers 20, 22, and 24 of the upper stacked piezoelectric body 12. It is opposite to the polarization direction. On the other hand, a driving voltage such as an audio signal is applied to the electrode layers 42, 46, 52, and 56, and the other electrode layers 40, 44, and 54 are grounded. For this reason, the expansion / contraction of the multilayer piezoelectric body 12 in the direction of the arrow FA and the expansion / contraction of the multilayer piezoelectric body 14 in the direction of the arrow FC are opposite to each other. That is, as shown in FIG. 1B, when the laminated piezoelectric body 12 extends in the direction of the arrow FA, the laminated piezoelectric body 14 contracts in the direction of the arrow FC. Conversely, as shown in FIG. 1C, when the laminated piezoelectric body 12 contracts in the direction of the arrow FA, the laminated piezoelectric body 14 extends in the direction of the arrow FC. For this reason, it vibrates in the direction of arrow FB as a whole.

  The total thickness of the piezoelectric driving element 10 is 50 to 200 μm. If the thickness is less than this, a sufficient force is not generated, so that the air and the rigidity of the support plate 70 described later are lost, and the displacement cannot be sufficiently performed. If it is thicker than this, the rigidity of the piezoelectric drive element 10 itself is too high, so that it cannot be sufficiently displaced. In the example of FIG. 1 (A), there are six piezoelectric layers, but it may be an even number layer of four or more, and the four-layer structure shown in FIGS. 2 (A-1) and (B-1) is also possible. Alternatively, an eight-layer structure shown in FIGS. 2A-3 and B-3 may be employed. In any case, the layers are laminated so that the top and bottom are symmetrical with respect to the center in the thickness direction (the electrode layer 40 in this embodiment).

When the thickness ratio of the plurality of piezoelectric layers is considered to cause bending displacement, the total number of layers is calculated as 2n (n is a natural number) from the necessary expansion / contraction amount calculated from the radius of curvature. This can be expressed by Equation 1.

Using Equation 1, the number of piezoelectric layers stacked is
In the case of 4 layers (n = 2), the thickness ratio of the piezoelectric body is, in order from the lower layer,
√2-1: 1: 1: √2-1
It becomes.
For 6 layers (n = 3)
√3-√2: √2-1: 1: 1: √2-1: √3-√2
And
For 8 layers (n = 4)
2-√3: √3-√2: √2-1: 1: 1: √2-1: √3-√2: 2-√3
It becomes. The thickness of each layer is allowed to have an error of ± 10% with respect to the above ratio. The total thickness when the thicknesses of the respective layers having such an ideal thickness ratio are totaled is the piezoelectric layer contributing to the displacement, where t _dmost is the thickness of the thickest piezoelectric layer among the piezoelectric layers contributing to the displacement. When the number of body layers is 2n,
2 x t _dmost x (√n)
It has been found that In other words, of the piezoelectric layers that contribute to displacement, when the thickness of the thickest piezoelectric layer is t _dmost , the boundary surface between the thickest piezoelectric layer and the central electrode layer is used as a base point, and from this base point The thickness up to n layers (n is a natural number)
t _dmost × (√n)
Will be satisfied. Since the piezoelectric driving element of the present embodiment has a bimorph structure, the thickness of the piezoelectric layer as the entire element is twice that, which is 2 × t _dmost × (√n) as described above.

  However, in an actual laminate, an electrode layer must be formed between each layer. Since this electrode needs to be formed simultaneously with the sintering of the ceramic (piezoelectric layer), silver, platinum, palladium, an alloy thereof, or the like that does not melt at the sintering temperature of the ceramic but only causes the sintering is used. Unlike the piezoelectric layer, the electrode layer is not deformed by a voltage, and thus the above Equation 1 is corrected by the presence of the electrode layer. As described above, since the displacement amount of the piezoelectric driving element 10 is suppressed due to the presence of the electrode layer, the thickness of the electrode layer is preferably as thin as possible, for example, 1 to 2 μm according to the printing method. Further, since the electrode ratio increases as the number of layers increases, the actual number of stacked piezoelectric layers is up to eight. In addition, since there is no inclination or difference between the two layers, the minimum number of layers is four.

Here, the thickness of the electrode layer is t _ie , the thickness of the thickest piezoelectric layer is t _dmost, and the ratio A of the thickness of the electrode layer to the thickness of the thickest piezoelectric layer is A = (t _ie / t _dmost ) In this way, the above Equation 1 can be corrected in consideration of the increase in the overall thickness and the increase in bending rigidity, but the solution cannot be derived analytically. However, if the Young's modulus of the electrode material is 50 to 150 GPa, the total thickness of the piezoelectric driving element 10 is 50 to 200 μm, and the electrode thickness is 5 μm at maximum, the calculation can be made approximately. Optimum characteristics can be obtained when the thickness of the piezoelectric layers 32, 30, 20, 22 when the number of stacked piezoelectric layers is four is set to the ratio of Equation 2 below.

Similarly, the thickness ratio of the piezoelectric layers 34, 32, 30, 20, 22, and 24 that provides optimum characteristics when the number of stacked piezoelectric layers is 6 is expressed by the following Equation 3.

Furthermore, the thickness ratio of the piezoelectric layers 36, 34, 32, 30, 20, 22, 24, and 26 that provides the optimum characteristics when the number of stacked piezoelectric layers is 8 is shown in the following Equation 4.

  If the error is up to ± 10% for each piezoelectric layer, the effect of the present invention can be exhibited. However, since the present embodiment is a bimorph type, the thickness of the outer layer must be smaller than the thickness of the inner layer. If it is out of the range, the element capacitance increases, the current value at the time of driving increases, and the desired effect cannot be obtained.

When the thickness of the electrode layer is also taken into consideration in this way, among the piezoelectric layers contributing to displacement, the thickness of the thickest piezoelectric layer is t _dmost, and the boundary surface between the thickest piezoelectric layer and the center electrode layer is the base point. , Expressing the thickness from the base point to the n layer,
t _dmost × (√n) + _{Σt ie} (n-1)
It has been found to be shown in the relationship.

This will be specifically described with reference to FIG. FIG. 4 shows the multilayer piezoelectric body 12 side at the top of the piezoelectric driving element 10. The piezoelectric layer 20 in contact with the central electrode layer 40 contributes most to the displacement. In this example, base thickness (the piezoelectric layer 20 and the boundary surface of the electrode layer 40) from the first layer of the piezoelectric layer, when applying the above equation of _{t DMOST} × _(√n), a _{t DMOST.} Next, the thickness up to the second layer (n = 2) is _obtained by adding the thickness t _ie (1) of the electrode layer 42 to t _dmost × (√2) to obtain td _most × (√2) + t _ie (1) It becomes. Further, the thickness of up to the third layer (n = 3), in addition the thickness of the second layer of the electrode layer _{44, t dmost × (√3)} + t ie (1) + t becomes _ie (2). That is, since there are (n-1) electrode layers between the n piezoelectric layers, the thickness from the base point to the n layer is increased by adding the corresponding thickness to t _dmost × it can be expressed as _{(√n) + Σt ie (n} -1).

  The piezoelectric drive element 10 is attached to a support plate 70 as shown in FIG. The support plate 70 is made of a material that is as soft as possible. For example, rubber or urethane is suitable. The thickness of the support plate 70 is 50 to 200 μm, which is the same as that of the piezoelectric drive element 10. Below this, the element cannot be supported sufficiently, and there is a possibility of damaging the element during vibration. Above this, the vibration of the element is hindered and the sound pressure is lowered. Then, the support plate 70 to which the piezoelectric driving element 10 is attached is attached to a metal or plastic frame, and electrodes are connected to a terminal plate or the like to obtain a piezoelectric sounding body. At this time, a lead or the like may be used, or a conductive paste or the like that is heat-cured may be used.

  The frame may have a shape like a lid in addition to a simple frame shape having an opening 82 like the frame 80 shown in FIG. However, it is necessary to leave a sufficient gap between the upper portion of the lid, the element, and the diaphragm so as not to contact by vibration. For example, the frame 90 shown in FIG. 1 (E) is the lid type described above, has a sufficient space 92 that does not hinder the vibration of the element, and a plurality of sound emitting holes 96 on the bottom surface 94 of the lid portion. Is provided. The piezoelectric sounding body obtained in this way has a current value that is 50% to 60% lower than that obtained by simply stacking piezoelectric bodies of the same thickness, although the sound pressure does not change. It is possible to suppress the heat generation at the portion and to use a small and low-cost component as a component of the drive circuit.

表１の実験例１〜４，比較例１〜６の結果から分かる通り、本発明の範囲内であれば、十分流れる電流は小さいが、範囲外の素子では電流値が大きく、所望の効果を得ることが出来ないことが確認された。 Table 1 below shows the sound pressure (average sound pressure of 800, 1000, 1500, 2000 Hz) and the current value during driving of the speaker manufactured by such a method. The element used for the test has a size of 14 × 18 mm, and an elastomer having a thickness of 100 μm is used for the support plate 70 and is attached to a metal frame 90 with a lid shape as shown in FIG. And Experimental Examples 1-4 which changed the number of layers and layer structure were produced, and the test was done. Further, as Comparative Examples 1 to 6, a similar test was performed on speakers similarly produced using elements having a layer thickness configuration outside the scope of the present invention, and the results are shown in Table 1.

As can be seen from the results of Experimental Examples 1 to 4 and Comparative Examples 1 to 6 in Table 1, the current flowing sufficiently is small within the range of the present invention, but the current value is large in the element outside the range, and the desired effect is obtained. It was confirmed that they could not be obtained.

  As described above, according to the first embodiment, in the piezoelectric sounding body using the bimorph type piezoelectric driving element 10 in which a plurality of piezoelectric layers are stacked, the thickness of the piezoelectric layer in the central portion with the smallest amount of displacement is maximized. . Then, with the center in the thickness direction as the boundary, the number of stacked layers is the same as the upper and lower layers, and the layer structure is vertically symmetrical, and the thickness of the piezoelectric layer is decreased from the center toward the outside. For this reason, the capacitance can be reduced without impairing the amount of displacement as an element, and the value of the current that flows even when a high-frequency signal is input can be kept low. As a result, it is possible to prevent the occurrence of a failure due to heat generation and to reduce the size because it is not necessary to use a thick conductor in the drive circuit.

  <Modification 1> Next, Modification 1 of the present embodiment will be described with reference to FIG. In the piezoelectric driving element 10 shown in FIG. 1 (A), an upper laminated piezoelectric body 12 and a lower laminated piezoelectric body 14 are formed with an electrode layer 40 interposed therebetween, but the piezoelectric shown in FIG. 5 (A). In the drive element 100, the laminated piezoelectric body 12 and the laminated piezoelectric body 14 are formed symmetrically with an inactive layer (non-polarized layer) 102 other than the electrode layer interposed therebetween. Even in such a case, the same effect as the above-described embodiment can be obtained.

  <Modification 2> Next, Modification 2 of the present embodiment will be described with reference to FIG. The piezoelectric driving element 10 shown in FIG. 1A is a bimorph type that does not use a shim plate. However, like the piezoelectric driving element 110 shown in FIG. 5B, a shim plate 112 such as a metal plate is used. It is good also as a structure which affixes the laminated piezoelectric body 12 and the laminated piezoelectric body 14 on and under. In this case, the piezoelectric sounding body can be configured by supporting the shim plate 112 by the frames 80 and 90 shown in FIG. 1D or FIG. 1E, and the same effects as those of the first embodiment described above can be obtained.

  Next, Embodiment 2 of the present invention will be described with reference to FIG. In the first embodiment, the piezoelectric driving element is a bimorph type, but the present invention can also be applied to a unimorph type. The piezoelectric driving element 120 shown in FIG. 5C has a configuration in which a laminated piezoelectric body 12 having a four-layer structure is attached to one main surface of a diaphragm 122 made of a metal material. And this is attached to the said frame 80 or 90, and a piezoelectric sounding body is comprised. In the unimorph type as in the present embodiment, the piezoelectric layer with the least displacement (the portion with the smallest expansion and contraction in the lateral direction), that is, the piezoelectric layer 20 on the vibration plate 122 side is the thickest, and the upper direction in the stacking direction. The thickness decreases in the order of the piezoelectric layers 22, 24, and 26 as it goes.

更に、変位に寄与する圧電体層のうち、最も厚い圧電体層の厚みをｔ_{ｄｍｏｓｔ}とし、変位に寄与する圧電体層の層数をｎとしたときに、
全層厚が、
ｔ_{ｄｍｏｓｔ}×（√n）
となるように規定するとよい。 The number of piezoelectric layers may be two or more. For example, when the number of stacked layers is n (n is a natural number), the thickness ratio of the piezoelectric layers from the diaphragm 122 side to the upper layer is Ideally, the ratio is expressed by the following formula 5. Of course, the ratio of each piezoelectric layer is allowed to be ± 10% as in the first embodiment. In order to apply the following formula 5, a diaphragm having a Young's modulus of 50 to 200 GPa and a thickness less than half that of the laminated piezoelectric body 12 is used as the diaphragm 122.

Furthermore, among the piezoelectric layers contributing to displacement, when the thickness of the thickest piezoelectric layer is t _dmost and the number of piezoelectric layers contributing to the displacement is n,
The total thickness is
t _dmost × (√n)
It is good to stipulate that

Further, as in Embodiment 1, the ratio A of the thickness of the thickest piezoelectric layer electrode layer to the thickness _{(t DMOST)} of _{(t ie),} by defining the _{A = (t ie / t dmost} ), The above Equation 5 can be corrected due to the presence of the electrode layers between the piezoelectric layers. For example, when the Young's modulus of the electrode material is 50 to 150 GPa, the total thickness of the piezoelectric driving element 120 is 50 to 200 μm, and the electrode thickness is 5 μm at maximum, the calculation can be performed approximately. Optimum characteristics can be obtained when the thickness of the piezoelectric layers 20 and 22 when the number of stacked piezoelectric layers is two is set to the ratio of the following formula 6.

Similarly, the thickness ratio of the piezoelectric layers 20, 22, and 24 that provides optimum characteristics when the number of stacked piezoelectric layers is 3 is shown in Equation 7 below.

Furthermore, the thickness ratio of the insulator layers 20, 22, 24, and 26 that provides optimum characteristics when the number of stacked piezoelectric layers is four is shown in the following Equation 8.

If the thickness error of each piezoelectric layer is up to ± 10%, the effect of the present invention can be exhibited. However, since this embodiment is a unimorph type, the thickness of the outer layer must be smaller than the thickness of the piezoelectric layer 20 on the diaphragm 122 side. If it is out of the range, the element capacitance increases, the current value at the time of driving increases, and the desired effect cannot be obtained. If these points can be satisfied, even if a unimorph type is used as in the present embodiment, the same effect as in the first embodiment can be obtained. The thickness from the base point in consideration of the thickness of the electrode layer (the boundary surface between the diaphragm 122 and the piezoelectric layer 20 in this embodiment) to the nth layer is t _dmost as in the first embodiment. X (√n) + Σt _ie (n−1)

In addition, this invention is not limited to the Example mentioned above, A various change can be added in the range which does not deviate from the summary of this invention. For example, the following are included.
(1) The shape of the piezoelectric driving element shown in the above embodiment is also an example, and may be appropriately changed as necessary, such as a circular shape.
(2) The dimension in the surface direction of the piezoelectric drive element shown in the above embodiment is also an example, and the design can be appropriately changed as necessary.
(3) The materials shown in the above embodiments are also examples, and various known materials may be used.
(4) The support mechanism of the piezoelectric drive element by the support plate 70 and the frame 80 or 90 shown in the first embodiment is also an example, and the design can be changed as appropriate within a range where the same effect can be obtained.
(5) The method for laminating the piezoelectric driving elements shown in the first embodiment is also an example, and may be changed as appropriate. As shown in FIG. 5D, when the bimorph type has a four-layer structure, the thickness of the piezoelectric layers 20 and 30 on the center side is approximately twice the thickness of the piezoelectric layers 22 and 32 on the outer side. The piezoelectric layers 20 and 30 are formed by stacking two piezoelectric sheets used as the piezoelectric layers 22 and 32. If the thickness of the piezoelectric layer can be adjusted by adjusting the number of laminated sheets as described above, the manufacturing becomes easy.
(6) In the above embodiment, the speaker mounted on a mobile phone or the like has been described as an example, but the present invention is applied as a piezoelectric sounding body used in various other known electronic devices such as a receiver of a mobile phone. Is possible.

  According to the present invention, in a piezoelectric sounding body using a piezoelectric driving element in which a plurality of piezoelectric layers are stacked, the thickness of the piezoelectric layer with the smallest amount of displacement is maximized, and the piezoelectric layers are sequentially formed outward. It was decided to form thinly. As a result, the capacity of the piezoelectric sounding body can be reduced without sacrificing the amount of displacement as an element, and the current value can be kept low, preventing the occurrence of failure and downsizing. Applicable to. In particular, it is suitable for use in portable electronic devices such as mobile phones and smartphones.

DESCRIPTION OF SYMBOLS 10: Piezoelectric drive element 12, 14: Laminated piezoelectric material 20-26, 30-36: Piezoelectric layer 40-46, 52-58: Electrode layer 50, 60-68: Side electrode 70: Support plate 80, 90: Frame 82: Opening 92: Space 94: Bottom 96: Sound emitting hole 100: Piezoelectric drive element 102: Inactive layer 110: Piezoelectric drive element 112: Shim plate (support plate)
120: Piezoelectric drive element 122: Diaphragm

Claims (7)

A piezoelectric sounding body in which a piezoelectric layer that contributes to displacement is supported by a support plate with a bimorph type piezoelectric driving element in which four or more layers and even layers are laminated,
An electrode layer is formed between the plurality of piezoelectric layers,
With the center in the stacking direction as a boundary, the same number of piezoelectric layers are polarized in the opposite direction,
The central part in the stacking direction is a non-polarized layer,
The thickness of the piezoelectric layer is gradually reduced from the center upward and downward in the stacking direction, and
The thickness of the piezoelectric layer has the same thickness when the upper and lower lamination positions are the same from the central boundary,
Among the piezoelectric layers contributing to displacement, when the thickness of the thickest piezoelectric layer is t _dmost , the nth layer (n Is a natural number)
t _dmost × (√n)
A piezoelectric sounding body characterized by satisfying A piezoelectric sounding body in which a piezoelectric layer that contributes to displacement is supported by a support plate with a bimorph type piezoelectric driving element in which four or more layers and even layers are laminated,
An electrode layer is formed between the plurality of piezoelectric layers,
With the center in the stacking direction as a boundary, the same number of piezoelectric layers are polarized in the opposite direction,
The central part in the stacking direction consists of shim plates,
The thickness of the piezoelectric layer is gradually reduced from the center upward and downward in the stacking direction, and
The thickness of the piezoelectric layer has the same thickness when the upper and lower lamination positions are the same from the central boundary,
Among the piezoelectric layers contributing to displacement, when the thickness of the thickest piezoelectric layer is t _dmost , the nth layer (n Is a natural number)
t _dmost × (√n)
A piezoelectric sounding body characterized by satisfying Of the piezoelectric layers contributing to displacement, when the thickness of the thickest piezoelectric layer is t _dmost and the number of piezoelectric layers contributing to displacement is 2n,
The total thickness is
2 x t _dmost x (√n)
The piezoelectric sounding body according to claim 1 or 2, wherein A piezoelectric sounding body in which a piezoelectric layer that contributes to displacement is supported by a support plate with a bimorph type piezoelectric driving element in which four or more layers and even layers are laminated,
An electrode layer is formed between the plurality of piezoelectric layers,
With the center in the stacking direction as a boundary, the same number of piezoelectric layers are polarized in the opposite direction,
The central part in the stacking direction is a non-polarized layer,
The thickness of the piezoelectric layer is gradually reduced from the center upward and downward in the stacking direction, and
The thickness of the piezoelectric layer has the same thickness when the upper and lower lamination positions are the same from the central boundary,
Of the piezoelectric layers contributing to displacement, the thickness of the thickest piezoelectric layer is t _dmost, and the thickness of the electrode layer of the nth layer (n is a natural number) from the central boundary is t _ie (n) In addition,
Starting from the central boundary side surface of the thickest piezoelectric layer, the thickness from the base point to the n layer is as follows:
t _dmost × (√n) + Σ _ie (n−1)
A piezoelectric sounding body characterized by being. A piezoelectric sounding body in which a piezoelectric layer that contributes to displacement is supported by a support plate with a bimorph type piezoelectric driving element in which four or more layers and even layers are laminated,
An electrode layer is formed between the plurality of piezoelectric layers,
With the center in the stacking direction as a boundary, the same number of piezoelectric layers are polarized in the opposite direction,
The central part in the stacking direction consists of shim plates,
The thickness of the piezoelectric layer is gradually reduced from the center upward and downward in the stacking direction, and
The thickness of the piezoelectric layer has the same thickness when the upper and lower lamination positions are the same from the central boundary,
Of the piezoelectric layers contributing to displacement, the thickness of the thickest piezoelectric layer is t _dmost, and the thickness of the electrode layer of the nth layer (n is a natural number) from the central boundary is t _ie (n) In addition,
Starting from the central boundary side surface of the thickest piezoelectric layer, the thickness from the base point to the n layer is as follows:
t _dmost × (√n) + Σ _ie (n−1)
A piezoelectric sounding body characterized by being.   The piezoelectric sounding body according to claim 1, wherein an error of ± 10% is allowed for the thickness of each layer of the piezoelectric body layer with respect to the ratio.   An electronic apparatus using the piezoelectric sounding body according to any one of claims 1 to 6.

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