JP2006287725A - Piezoelectric acoustic element and piezoelectric acoustic generating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acoustic generating device with high acoustic generation efficiency and small energy loss. <P>SOLUTION: This piezoelectric acoustic generation device 10 having a piezoelectric acoustic element 17 and a panel 12 fixed via a piezoelectric drive element 20 of the piezoelectric acoustic element 17 and generating sound from the panel 12 is provided. The piezoelectric acoustic element 17 constituting the piezoelectric acoustic generating device 10 has the columnar piezoelectric drive element 20 constituted of a plurality of piezoelectric layers and a plurality of electrode layers which are alternately laminated and an elastic body board 11 of which a part is fixed to the piezoelectric drive body 20 and at least one end is a free end. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a piezoelectric acoustic element having a piezoelectric drive body as a vibration generation source and a plate-like elastic body as a vibration amplifier, and transmits the vibration generated and amplified by the piezoelectric acoustic element to the panel to generate the sound. The present invention relates to a piezoelectric acoustic generator used as a source.

  In recent years, in portable electronic devices such as mobile phones, digital cameras, and PDAs (personal digital assistants), miniaturization and weight reduction are accelerating, and a sound generator suitable as a sound source is awaited. ing. Such a sound generator needs to be suitable for downsizing and weight reduction, to achieve high acoustic conversion efficiency and to have a wide reproduction frequency band. Advancing and proposing.

  For example, Patent Document 1 describes an acoustic generator having a structure in which a piezoelectric element (transducer, piezoelectric bimorph) is fixed to a column on a panel (see FIG. 1 of Patent Document 1). This has a structure in which a piezoelectric element is fixed on the panel through a small support member that does not have a driving force and does not generate vibration, and the piezoelectric element is a vibration source (driving source) and has a reproduction frequency characteristic. It also functions as a diaphragm that determines

  Patent Document 2 describes a sound generator that generates sound pressure in a device having a liquid crystal display device and its protective panel. This is a structure in which a piezoelectric bimorph element and an elastic plate are arranged in parallel at a predetermined interval on a column fixed to a specific portion of a liquid crystal protection panel, and a single piezoelectric bimorph element is a vibration generating source ( In order to improve the frequency characteristics in the case of a driving source), an elastic body plate which itself does not have a driving force and does not generate vibration is combined to achieve a flat frequency characteristic.

Further, Patent Document 3 describes a structure of a piezoelectric actuator for generating a sound wave by vibrating a transparent panel covering a display surface of a mobile phone or the like. This is intended to prevent damage due to impact such as dropping by disposing an impact absorbing material on a plate-like piezoelectric diaphragm fixed on a panel.
International Publication No. 01/54450 Pamphlet JP 2005-26754 A JP 2004-104327 A

  However, in the conventional acoustic generator described above, when the piezoelectric bimorph element is evaluated as expressing the function of the elastic body plate, the piezoelectric ceramic material constituting the piezoelectric bimorph element has a large energy loss during vibration. There was a problem that the generation efficiency was not sufficient.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a sound generator having high sound generation efficiency and low energy loss. As a result of repeated research, in the structure where the piezoelectric bimorph element not only serves as a drive source but also serves as an elastic plate that determines the frequency characteristics of sound generation, as in conventional sound generators, the efficiency of sound generation is improved. It was thought that there was a limit. Then, in the sound generator that transmits vibration to the panel and generates sound from the panel, the above object is achieved by separating the functions of the driving source for generating vibration and the diaphragm for realizing the desired frequency characteristics. This has been found to be achieved and the present invention has been completed.

  First, according to the present invention, a columnar piezoelectric driving body composed of a plurality of alternately stacked piezoelectric layers and a plurality of electrode layers, a part of which is fixed to the piezoelectric driving body, and at least one end is a free end. A piezoelectric acoustic element including a plate-like elastic body (also referred to as an elastic plate) is provided.

  In the piezoelectric acoustic element according to the present invention, since the plate-like elastic body is supported so that at least one end is a free end, it is preferable that the material used therefor has high impact resistance. The metal or resin can be shown as a preferable material used for the plate-like elastic body.

  The columnar piezoelectric driving body in the piezoelectric acoustic element according to the present invention serves as a vibration generation source by repeated displacement of the piezoelectric layer based on electric field induced strain, and the plate-like elastic body has a role of the vibration generation source. First, it is vibrated by the piezoelectric driving body and serves exclusively as a diaphragm that lowers the resonance frequency or flattens the frequency characteristics.

  The displacement generated by the piezoelectric driving body (piezoelectric layer) may be either the longitudinal effect of electric field induced strain or the lateral effect of electric field induced strain. The longitudinal effect of electric field induced strain is a phenomenon in which when an electric field is applied in the same direction as the polarization direction of the piezoelectric layer, the piezoelectric driver (piezoelectric layer) also deforms to expand and contract in the same direction. The effect is a phenomenon in which when an electric field is applied in the same direction as the polarization direction of the piezoelectric layer, the piezoelectric driving body (piezoelectric layer) is deformed so as to expand and contract in a direction perpendicular to the direction.

  In addition, the piezoelectric acoustic element according to the present invention is expressed as piezoelectric, but is an acoustic element that utilizes distortion induced by an electric field as described above, and in a narrow sense, is a distortion approximately proportional to an applied electric field. It is not limited to an acoustic element that uses the piezoelectric effect to generate a quantity, but to an electrostrictive effect that generates a distortion amount that is roughly proportional to the square of the applied electric field, a polarization reversal that appears in all ferroelectric materials, and an antiferroelectric material. Also included is an acoustic element that utilizes a phenomenon such as a phase transition between an antiferroelectric phase and a ferroelectric phase. Whether or not the polarization process is performed in the production is also appropriately determined based on the property of the material applied to the piezoelectric layer that is the main component of the piezoelectric acoustic element. The piezoelectric layer refers to a layered piezoelectric material (also not strictly narrow).

  Although the piezoelectric acoustic element which concerns on this invention is not limited, It is preferable that each thickness of the several piezoelectric layer concerning a piezoelectric drive body is 5-200 micrometers. More preferably, it is 5-100 micrometers. By thinning the piezoelectric layer in this way, it is possible to stack more piezoelectric layers (in the order of several tens to several hundreds) with a constant thickness (height or width). In the same manner, compared with a piezoelectric driving body having a thicker one piezoelectric layer and a smaller number of stacked layers, the electric field strength is increased even with the same driving voltage, and a relatively larger displacement and higher generation force can be obtained. Further, if the amount of displacement and the generated force are the same, a lower drive voltage can be obtained, and energy saving can be achieved. The number of layers of the plurality of piezoelectric layers applied to the piezoelectric driver is not limited, but is preferably 2 to 100 layers. This is because sufficient generation force can be obtained for application as a piezoelectric acoustic element.

  The thickness of the plurality of electrode layers applied to the piezoelectric driving body is not limited and may be an appropriate thickness depending on the application, but a uniform electrode layer can be formed on the surface of the piezoelectric layer. In particular, the thickness is preferably 10 μm or less. More preferably, it is formed with a thickness of 5 μm or less. If the thickness is greater than 10 μm, it is difficult to deform the electrode itself, and displacement (vibration) as a piezoelectric driving body may be hindered and energy loss may increase.

  The piezoelectric acoustic element according to the present invention is not limited, but is preferably formed by firing and integrating at least the piezoelectric driving body. Even if displacement occurs repeatedly due to vibration generation, structural changes such as peeling between the piezoelectric layer and electrode layer are difficult to occur, long-term reliability is excellent, and stable quality vibration as a vibration source is a plate-like elastic body This is because the desired frequency characteristic provided by the plate-like elastic body can be stably realized. The shape of the piezoelectric driving body is not limited as long as it is columnar, and the shape may be determined in relation to the panel in the piezoelectric acoustic generator according to the present invention using this piezoelectric acoustic element. As a preferable shape, a rectangular parallelepiped shape which is a prism shape is exemplified.

  In the piezoelectric acoustic element according to the present invention, the shape of the plate-like elastic body is determined based on a desired (reproduction) frequency characteristic, and there is no limitation under other conditions, such as a circle, an ellipse, a square, etc. Alternatively, an asymmetric shape may be used, but a more preferable shape is a rectangle. Further, the plate-like elastic body is fixed to the piezoelectric drive body so that at least one end is a free end in order to fulfill the function as a vibration plate. The connection mode with the driving body is not limited. For example, when the plate-like elastic body is rectangular, the one is fixed to the piezoelectric driving body at one end in the longitudinal direction and the other end is a free end. Similarly, when the plate-like elastic body is rectangular, it is fixed to the piezoelectric driving body at the center in the longitudinal direction and both ends are free ends.

  In the piezoelectric acoustic element according to the present invention, the number of plate-like elastic bodies is not limited, and may be one or two or more. In the case of two or more sheets, FIG. 9 and FIG. An embodiment like 12a can be taken.

  Next, according to the present invention, the piezoelectric acoustic element described above and a panel fixed via the piezoelectric driving body of the piezoelectric acoustic element are provided, and a plurality of electrode layers of the piezoelectric driving body are provided on one layer. A piezoelectric sound generating device is provided that includes a pair of signal input units connected to each other, and an electric signal is input to the signal input unit to generate sound from the panel.

  The panel is specified as a sound generation source in the piezoelectric sound generation device according to the present invention, and a specific aspect of the panel is a design of a portable electronic device to which this piezoelectric sound generation device is applied (for example). Should be specified by. Usually, it is preferable to listen to the sound while watching the liquid crystal screen, and therefore, an embodiment using a liquid crystal protection panel as the panel is exemplified. However, it is not limited, and may be a part of the case of the portable electronic device provided in a predetermined place of the portable electronic device.

  The piezoelectric acoustic generator according to the present invention is specific if a part of the plate-like elastic body is fixed to the piezoelectric driving body so that at least one end is a free end, and the panel is fixed via the piezoelectric driving body. Although there is no restriction | limiting of an aspect, As a preferable aspect, what uses the support | pillar part of a plate-shaped elastic body and a (plate-shaped) panel as a piezoelectric drive body can be illustrated.

  In the piezoelectric acoustic generator according to the present invention, it is preferable that a wiring pattern for inputting an electric signal to the pair of signal input portions is formed on the panel.

  The piezoelectric acoustic element according to the present invention includes a columnar piezoelectric driving body and a plate-like elastic body, and the piezoelectric driving body has a function of a vibration generation source (driving source), The elastic body has no role as a vibration source, and has one end as a free end, which exclusively amplifies vibration and flattens the frequency characteristics, or improves the acoustic characteristics in the low frequency range, etc. Take on. In this way, the piezoelectric acoustic element according to the present invention suppresses energy loss by completely separating the vibration generating function part and the acoustic frequency characteristic forming function part for realizing a desired frequency characteristic, and is high. Sound generation efficiency can be realized.

  The piezoelectric acoustic generator according to the present invention generates sound from the panel by fixing the panel via the piezoelectric driving body of the piezoelectric acoustic element according to the present invention. A plate-like elastic body is not used as a vibration generation source (drive source). For example, a panel and a plate-like elastic body are fixed with a support column, and the column portion is a columnar piezoelectric drive unit that is a vibration generation source. In addition to amplifying minute vibrations generated by the piezoelectric driving body with a plate-like elastic body, a desired acoustic frequency characteristic can be realized. In order to realize a small acoustic generator with high acoustic conversion efficiency, it is desirable that the resonance frequency of the vibration generated by the vibration source matches the relatively low sound range of the reproduction frequency band. The sound generator can realize such frequency characteristics. Further, in the piezoelectric sound generating device according to the present invention, the wiring pattern for the electric signal input to generate sound from the panel is formed on the panel itself, and no lead wire is used. It is possible to suppress the loss of vibration energy and the influence on the vibration characteristics of the piezoelectric driving body that may occur when using.

  Hereinafter, embodiments of the present invention will be described with appropriate reference to the drawings, but the present invention should not be construed as being limited thereto. Various changes, modifications, improvements, and substitutions can be added based on the knowledge of those skilled in the art without departing from the scope of the present invention. For example, the drawings show preferred embodiments of the present invention, but the present invention is not limited by the modes shown in the drawings or the information shown in the drawings. In practicing or verifying the present invention, the same means as described in this specification or equivalent means can be applied, but preferred means are those described below.

  FIG. 1 is a perspective view schematically showing one embodiment of a piezoelectric acoustic generator according to the present invention including the piezoelectric acoustic element according to the present invention, and FIG. 2 is a partial view of FIG. FIG. A piezoelectric acoustic generator 10 shown in FIG. 1 includes a prismatic piezoelectric driving body 20 and a metal elastic plate 11 (for example, plate-like) fixed at an upper portion (in the drawing) of the piezoelectric driving body 20. The device includes a piezoelectric acoustic element 17 formed of an elastic body and an acrylic panel 12 (for example) fixed at a lower portion (in the drawing) of the piezoelectric driving body 20, and generates sound 18 from the panel 12.

  The rectangular elastic body plate 11 is fixed by the piezoelectric driving body 20 at a substantially central portion thereof, and both ends thereof are free ends, and are easily vibrated. In the piezoelectric acoustic generator 10 (piezoelectric acoustic element 17), common electrodes 78 and 79 as a pair of signal input units connected to every other electrode layers 48 and 49 of (for example) 14 layers of the piezoelectric driving body 20. When an electrical signal is input to the electrode, a voltage is applied between the opposing electrode layers 48 and 49 that are conducted to form an electric field. Then, a displacement based on the electric field induced strain occurs in the piezoelectric layer 44 sandwiched between the electrode layers 48 and 49, and the entire piezoelectric driving body 20 formed by laminating the piezoelectric layer 44 generates vibration due to the repetition of the displacement. The polarization direction of the piezoelectric layer 44 is the same S1 direction as the stacking direction (see FIG. 2). When an electric field is applied in the same direction, the piezoelectric driver 20 (piezoelectric layer 44) expands and contracts in the same S2 direction as the S1 direction. To do. That is, in the piezoelectric driving body 20, the displacement of the piezoelectric layer 44 is based on the longitudinal effect of the electric field induced strain.

  The elastic plate 11 itself does not generate vibration but is vibrated by vibration generated by the piezoelectric driving body 20 and plays a role of flattening frequency characteristics. In the piezoelectric acoustic generator 10, since the wiring patterns 21 and 22 for inputting electric signals to the common electrodes 78 and 79 (a pair of signal input portions) are formed on the panel 12, the piezoelectric driver 20 itself wakes up. Due to the vibration and the vibration of the elastic plate 11 caused by the vibration, the wiring portion applied to the electric signal does not vibrate or shake.

  In the piezoelectric acoustic generator 10, the columnar piezoelectric driver 20 including a plurality of piezoelectric layers 44 and a plurality of electrode layers 48 and 49 that are alternately stacked is formed by firing and integration. On the other hand, the means for fixing the elastic plate 11 that is a metal plate to the upper portion of the piezoelectric drive body 20 and the means for fixing the panel 12 that is an acrylic plate to the lower portion of the piezoelectric drive body 20 are adhesion.

  Next, FIG. 3 is a partially enlarged perspective view showing the piezoelectric driving body in an enlarged manner in the piezoelectric acoustic generating apparatus in which only the piezoelectric driving body of the piezoelectric acoustic element is different from the piezoelectric acoustic generating apparatus 10. In the prismatic piezoelectric driving body 30 employed in this piezoelectric acoustic generator, a common electrode 78 as a pair of signal inputs connected to (for example) electrode layers 48 and 49 each consisting of eight layers. When an electrical signal is input to 79, a voltage is applied between the opposing electrode layers 48 and 49 conducted therethrough to form an electric field. Similarly to the piezoelectric driving body 20, a displacement based on the electric field induced strain occurs in the piezoelectric layer 44 sandwiched between the electrode layers 48 and 49, and the piezoelectric driving body formed by laminating the piezoelectric layers 44 by repeating this displacement. The whole 20 generates vibration. In the piezoelectric driving body 30, the polarization direction of the piezoelectric layer 44 is the same S3 direction (see FIG. 3) as the stacking direction, and when an electric field is applied in the same direction, the piezoelectric driving body 30 (piezoelectric layer 44) It expands and contracts in the S4 direction orthogonal to the direction. That is, in the piezoelectric driving body 30, the displacement of the piezoelectric layer 44 is based on the lateral effect of the electric field induced strain.

  Next, a method for manufacturing the piezoelectric acoustic element and the piezoelectric acoustic generator of the present invention will be described. First, a method for producing a plate-like elastic body will be described. The manufacturing method of the plate-like elastic body is not limited. For example, a commercially available metal plate having a desired thickness can be produced by punching, cutting, etching, or the like.

  Next, a method for manufacturing a piezoelectric driving body will be described. A piezoelectric driving body composed of a plurality of piezoelectric layers and electrode layers can be manufactured by appropriately forming and laminating piezoelectric layers and electrode layers in accordance with various known film forming methods and sheet laminating methods as appropriate. As the film forming method, for example, a thick film forming method such as screen printing, spraying, dipping, coating, electrophoresis, etc., and a thin film forming method such as ion beam, sputtering, vacuum deposition, ion plating, CVD, plating, etc. are appropriately selected. Is done. Note that the same means is employed for forming the common electrode and forming the wiring pattern on the panel.

  In particular, for forming the piezoelectric layer, a thick film forming method by screen printing, spraying, dipping, coating, or the like, or a sheet forming method such as a doctor blade method or a reverse roll coater method is suitably employed.

  The electrode layer and the piezoelectric layer formed by the above method may be fired (heat treatment) each time the respective layers are formed, or after all the layers are formed and the common electrode is formed, they are fired simultaneously. Each layer may be integrated at the same time. The firing (heat treatment) temperature for integrating the electrode layer and the piezoelectric layer formed in this way is generally a temperature of about 800 ° C. to 1400 ° C., preferably a temperature in the range of 900 ° C. to 1200 ° C. Is advantageously selected. Further, when firing the piezoelectric layer, it is preferable to perform firing while controlling the atmosphere together with the evaporation source of the piezoelectric material forming the piezoelectric layer so that the composition of the piezoelectric layer does not become unstable at high temperatures.

  A piezoelectric acoustic element according to the present invention can be obtained by fixing a plate-like elastic body to the piezoelectric driving body thus obtained using an adhesive. The adhesive may be any of thermoplastic, thermosetting, and synthetic rubber, and can be selected based on the use atmosphere. For example, it is preferable to employ a thermosetting resin such as an epoxy resin.

  Next, a method for manufacturing a panel will be described. The panel is not limited in its manufacturing method. For example, a commercially available glass plate having a desired thickness or a thin plate made of a resin-based material such as acrylic is processed into a predetermined shape by molding, punching, and cutting. Can be produced.

  The panel is fixed to the previously produced piezoelectric acoustic element using an adhesive or an adhesive tape, and a conductive material is used to form a wiring pattern on the panel so as to conduct to the common electrode of the piezoelectric actuator of the piezoelectric acoustic element. Thus, the piezoelectric acoustic generator according to the present invention is obtained. As the adhesive for fixing the panel, the same adhesive as that used for bonding the piezoelectric driving body and the plate-like elastic body can be adopted.

  Although the manufacturing method has been described above, materials used for the piezoelectric acoustic element and the piezoelectric acoustic generator according to the present invention will be described below. First, a material for forming a plate-like elastic body will be described. Elasticity means elasticity against plasticity, and the material of a plate-like elastic body is limited as long as it has the property of deforming when applying force from the outside to the object and returning to its original shape when removing the force. Is not to be done. For example, a metal material such as aluminum or stainless steel, a ceramic material such as alumina or zirconia, or a resin material such as polyimide is used. More preferred is a metal material.

  Next, the materials of the piezoelectric layer and the electrode layer constituting the piezoelectric driver will be described. First, as a piezoelectric material forming the piezoelectric layer, a material having a high piezoelectric constant and a high electromechanical coupling coefficient is preferable. Specifically, lead zirconate, lead manganese tungstate, sodium bismuth titanate, bismuth ferrate, Sodium potassium niobate, strontium bismuth tantalate, lead magnesium niobate, lead nickel niobate, lead zinc niobate, lead manganese niobate, lead magnesium tantalate, lead nickel tantalate, lead antimony stannate, lead titanate, titanium Examples thereof include barium oxide, barium copper tungstate, lead magnesium tungstate, lead cobalt niobate, and composite oxides composed of two or more of these.

  These piezoelectric materials include lanthanum, calcium, strontium, molybdenum, tungsten, barium, niobium, zinc, nickel, manganese, cerium, cadmium, chromium, cobalt, antimony, iron, yttrium, tantalum, lithium, bismuth and tin. An oxide such as copper may be dissolved.

  Furthermore, lithium bismutate or lead germanate is added to a material obtained by adding lithium bismutate, lead germanate, or the like to the above materials, for example, a composite oxide of lead zirconate, lead titanate, and lead magnesium niobate. Material can be adopted. These materials can exhibit high material properties while realizing low-temperature firing of the piezoelectric layer.

  Next, the material for forming the electrode layer is preferably made of a metal that is solid at room temperature and has excellent conductivity. For example, aluminum, titanium, chromium, iron, cobalt, nickel, copper, zinc, A simple metal such as niobium, molybdenum, ruthenium, palladium, rhodium, silver, tin, tantalum, tungsten, iridium, platinum, gold, lead, or an alloy thereof is used. Further, a cermet material in which the same material as the piezoelectric layer or shim plate is dispersed may be used. In this case, it is preferable to disperse the cermet material at a ratio of about 5 to 30% by volume. Note that the same material can be selected for the wiring pattern.

  Next, materials for forming the panel will be described. The material of the panel is not limited as long as it can generate sound. For example, resin materials such as acrylic, ABS, and polycarbonate, glass materials such as phosphoric acid-silicate glass, carbon fiber materials, metal materials such as aluminum and stainless steel, and the like are used.

  The piezoelectric acoustic element of the present invention and the piezoelectric acoustic generator using the piezoelectric acoustic element are incorporated in portable electronic devices that are selectively equipped with functions of a notebook computer, telephone, camera, GPS, radio, television, etc. Used instead of a speaker. For example, a liquid crystal protection panel of a portable electronic device is adopted as a panel in the piezoelectric sound generating device according to the present invention, and the piezoelectric sound generating device according to the present invention is incorporated into the portable electronic device, so that the panel itself protecting the liquid crystal screen can be improved The sound can be generated.

1 is a perspective view schematically showing one embodiment of a piezoelectric acoustic generator according to the present invention. FIG. 2 is a partially enlarged perspective view in which a part (piezoelectric drive body) of FIG. 1 is enlarged. It is a figure which shows typically other embodiment of the piezoelectric acoustic generator which concerns on this invention, and is the partial expansion perspective view which expanded a part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Piezoelectric sound generator, 11 ... Elastic board (plate-shaped elastic body), 12 ... Panel, 17 ... Piezoelectric acoustic element, 18 ... Sound, 20, 30 ... Piezoelectric drive body, 21,22 ... Wiring pattern, 44 ... Piezoelectric layer, 48, 49 ... Electrode layer, 78, 79 ... Common electrode.

Claims (4)

  A columnar piezoelectric driving body composed of a plurality of alternately laminated piezoelectric layers and a plurality of electrode layers, and a plate-like elastic body having a part fixed to the piezoelectric driving body and having at least one free end. A piezoelectric acoustic element provided.   The piezoelectric acoustic element according to claim 1, wherein a material used for the plate-like elastic body is a metal or a resin.   A piezoelectric acoustic element according to claim 1 and a panel fixed via the piezoelectric driving body of the piezoelectric acoustic element, and connected to a plurality of electrode layers of the piezoelectric driving body every other layer. A piezoelectric acoustic generator that includes a pair of signal input units and generates sound from the panel when an electric signal is input to the signal input unit.   The piezoelectric acoustic generator according to claim 3, wherein a wiring pattern for inputting the electric signal to the pair of signal input portions is formed on the panel.

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