JP5923849B2 - Method for manufacturing piezoelectric element - Google Patents

Description

  The present invention relates to an oscillation device and a method for manufacturing a piezoelectric element.

  An electromagnetic actuator is often used as a drive source for an acoustic element such as a speaker because of its ease of handling. The electromagnetic actuator is composed of a permanent magnet and a voice coil, and generates vibration by the action of the magnetic circuit of the stator using the magnet. An electromagnetic speaker using an electromagnetic actuator as a drive source generates sound when a low-rigidity diaphragm such as an organic film, which is fixed to a vibration part of the electromagnetic actuator, vibrates.

  In recent years, the demand for mobile phones and notebook personal computers has increased, and accordingly, the demand for small and power-saving actuators is increasing. However, the electromagnetic actuator has a problem in power saving because it requires a large amount of current to flow to the voice coil during operation. Further, the electromagnetic actuator is not suitable for miniaturization and thinning due to its structure.

  On the other hand, in recent years, piezoelectric actuators using piezoelectric elements such as piezoelectric ceramics as drive sources have been developed as thin vibration parts that replace electromagnetic actuators (for example, Patent Documents 1 to 5). The piezoelectric actuator generates mechanical vibration using a piezoelectric element, and has, for example, a structure in which a piezoelectric ceramic element (also simply referred to as “piezoelectric element”) and a support member are joined. The piezoelectric actuator has features such as small size and light weight, power saving, and no leakage magnetic flux.

  By the way, although a piezoelectric actuator is advantageous for thickness reduction, it has one aspect that it is inferior in acoustic performance as an acoustic element (for example, a speaker) as compared with an electromagnetic actuator. Specifically, since the piezoelectric element itself is highly rigid and has a high mechanical Q value, a large amplitude can be obtained in the vicinity of the resonance frequency compared to the electromagnetic actuator, but the amplitude is small in a band other than the resonance frequency. End up.

  Patent Documents 1 and 2 disclose a configuration in which the outer peripheral portion of the support member is supported by a relatively easily deformable beam in order to increase the vibration amplitude of the actuator. Further, Patent Document 3 discloses a technique in which a leaf spring having slits along the circumference is formed in the peripheral portion of the support member to obtain a large vibration amplitude for the same purpose. Patent Document 4 discloses a technique for broadening the frequency characteristics by joining the outer peripheral portion of the support member and the support through a curved support. The techniques described in Patent Documents 1 to 3 are techniques when using a piezoelectric actuator as a vibrator.

JP-A-61-168971 JP 2000-140759 A JP 2001-17917 A Japanese Patent Laid-Open No. 2001-39791 International Publication No. 2007/060768 Pamphlet

  As described above, there are cases where it is preferable not to give the oscillation characteristics frequency dependency, for example, when a piezoelectric element is used as an oscillation source of a speaker. However, it has been difficult to reduce the frequency dependence of the oscillation characteristics and increase the oscillation output. In order to reduce the frequency dependence of the oscillation characteristics and increase the oscillation output, it is preferable to fabricate an oscillation device having a novel structure.

  An object of the present invention is to provide an oscillation device using a piezoelectric element and having a novel structure, and a method for manufacturing the piezoelectric element.

According to the present invention, a piezoelectric body ;
A support member for supporting the front Symbol piezoelectric,
A method of manufacturing a piezoelectric element having
Disposing a resin material having a piezoelectric effect in the opening of the support member having an opening;
Forming the piezoelectric body made of a resin material in close contact with the inner peripheral surface of the opening by melting and then solidifying the resin material;
A method for manufacturing a piezoelectric element comprising:

  According to the present invention, it is possible to provide an oscillation device that uses a piezoelectric element and has a novel structure, and a method of manufacturing the piezoelectric element.

It is a top view which shows the structure of the oscillation apparatus which concerns on 1st Embodiment. It is AA 'sectional drawing of FIG. It is a figure which shows the chemical formula of a polyvinylidene fluoride. It is a top view which shows the modification of FIG. FIG. 3 is a cross-sectional view showing a method for manufacturing the oscillation device shown in FIG. 1. FIG. 3 is a cross-sectional view showing a method for manufacturing the oscillation device shown in FIG. 1. It is sectional drawing which shows the modification of FIG. It is sectional drawing which shows the structure of the oscillation apparatus which concerns on 2nd Embodiment. It is sectional drawing which shows the structure of the oscillation apparatus which concerns on 3rd Embodiment. It is the schematic which shows the structure of a portable communication terminal.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

(First embodiment)
FIG. 1 is a plan view showing the configuration of the oscillation device according to the first embodiment. 2 is a cross-sectional view taken along the line AA ′ of FIG. This oscillation device includes a support member 40, a piezoelectric film (piezoelectric body) 22, a first electrode 24, and a second electrode 26 (shown in FIG. 2). The support member 40 has an opening 42. The piezoelectric film 22 is in close contact with the inner peripheral surface of the opening 42 and is made of a resin material having a piezoelectric effect. The first electrode 24 is in contact with one surface of the piezoelectric film 22, and the second electrode 26 is in contact with the other surface of the piezoelectric film 22. This oscillation device is used, for example, as an oscillation source of a parametric speaker or an oscillation source of a sound wave sensor. The parametric speaker here is used, for example, as a sound source of an electronic device (for example, a mobile phone, a laptop personal computer, a small game device, etc.). Details will be described below.

  In the present embodiment, the openings 42 are formed in the support member 40 in a plurality of matrix shapes. The piezoelectric film 22 is formed in each of the plurality of openings 42. The piezoelectric film 22 adheres to the inner peripheral surface of the opening 42 over the entire circumference by welding to the inner wall of the opening 42.

  In the example shown in FIG. 1, the planar shapes of the opening 42 and the piezoelectric film 22 are rectangular, but the planar shapes of the opening 42 and the piezoelectric film 22 are not limited to this, and may be, for example, circular as shown in FIG. 4. Good.

  The piezoelectric film 22 is made of a resin material having a piezoelectric effect as described above, and is polarized in the thickness direction. The resin material is not particularly limited as long as it has a piezoelectric effect, but a material having high mechanical conversion efficiency, for example, polyvinylidene fluoride having a chemical formula shown in FIG. 3, polyvinyl chloride, or the like can be used. The thickness of the piezoelectric film 22 is not particularly limited, but is preferably 5 μm or more and 1 mm or less. When the thickness of the piezoelectric film 22 is less than 5 μm, variations in thickness are likely to occur due to the manufacturing process. Moreover, when the thickness of the piezoelectric film 22 exceeds 1 mm, the thickness of the oscillation device increases.

A first electrode 24 is formed on one surface of the piezoelectric film 22, and a second electrode 26 is formed on the other surface of the piezoelectric film 22. The piezoelectric element 20 is formed by the piezoelectric film 22, the first electrode 24, and the second electrode 26. Although the material which comprises the 1st electrode 24 and the 2nd electrode 26 is not specifically limited, For example, silver and silver / palladium can be used. Since silver is used as a general-purpose electrode material with low resistance, it has advantages in manufacturing process and cost. Since silver / palladium is a low-resistance material excellent in oxidation resistance, there is an advantage from the viewpoint of reliability. The thickness h ₂ of the first electrode 24 and the second electrode 26 is not particularly limited, the thickness is preferably at 1μm or more 100μm or less. If the thickness is less than 1 μm, it is difficult to uniformly mold the first electrode 24 and the second electrode 26, and as a result, the electromechanical conversion efficiency may be reduced. Moreover, when the film thickness of the 1st electrode 24 and the 2nd electrode 26 exceeds 100 micrometers, the 1st electrode 24 and the 2nd electrode 26 become a constraining surface with respect to the piezoelectric film 22, and may reduce energy conversion efficiency. Sex comes out.

  Further, the oscillation device includes a control unit 50 and a signal generation unit 52 as an oscillation circuit. The signal generator 52 generates an electrical signal input to the first electrode 24 and the second electrode 26 of the piezoelectric element 20, for example, a modulation signal in a parametric speaker. The transport wave of the modulation signal is an ultrasonic wave having a frequency of 20 kHz or higher, for example, an ultrasonic wave having a frequency of 100 kHz. The control unit 50 controls the signal generation unit 52 based on information input from the outside. When the oscillation device is used as a speaker, information input to the control unit 50 is an audio signal.

  Next, a case where the oscillation device according to the present embodiment is used as a parametric speaker will be described.

  First, the principle of a general parametric speaker will be described. A parametric speaker emits ultrasonic waves (transport waves) subjected to AM modulation, DSB modulation, SSB modulation, and FM modulation from each of a plurality of oscillation sources into the air, and due to nonlinear characteristics when the ultrasonic waves propagate into the air. , To make an audible sound appear. Non-linear here means that the flow changes from laminar flow to turbulent flow when the Reynolds number indicated by the ratio between the inertial action and the viscous action of the flow increases. Since the sound wave is slightly disturbed in the fluid, the sound wave propagates nonlinearly. In particular, in the ultrasonic frequency band, the nonlinearity of sound waves can be easily observed. And when an ultrasonic wave is radiated in the air, harmonics accompanying the nonlinearity of the sound wave are remarkably generated. The sound wave is a dense state where the density of the molecular density is generated in the air. When it takes time for air molecules to recover from compression, air that cannot be recovered after compression collides with air molecules that continuously propagate, and a shock wave is generated. An audible sound is generated by this shock wave.

  5 and 6 are cross-sectional views showing a method for manufacturing the oscillation device shown in FIG. The cross sections shown in these figures correspond to the AA ′ cross section of FIG.

  First, as shown in FIG. 5A, the support member 40 is placed on the stage 100. Next, as shown in FIG. 5B, a resin material 200 having a piezoelectric effect is disposed in each of the plurality of openings 42 of the support member 40.

  Next, as shown in FIG. 6, the resin material 200 is melted while pressing the upper surface of the resin material 200 toward the stage 100 using the pressing member 110. Thereby, the resin material 200 is filled in the opening 42. For example, the resin material 200 is melted by heat from a heater provided on at least one of the stage 100 and the pressing member 110. Thereafter, the molten resin material 200 is cooled and solidified. Thereby, the plurality of piezoelectric films 22 are collectively formed in a state where they are welded over the entire circumference of the inner peripheral surface of the opening 42.

  Thereafter, the first electrode 24 is formed on one surface of the piezoelectric film 22, and the second electrode 26 is formed on the other surface of the piezoelectric film 22.

  In the step shown in FIG. 6, as shown in FIG. 7, a convex portion 112 may be provided in a portion of the pressing member 110 that faces the opening 42. In this case, the resin film 200 can be efficiently melted to form the piezoelectric film 22 by providing the protrusion 112 with a heater.

  Next, the operation and effect of this embodiment will be described. According to this embodiment, it is possible to provide an oscillation device that uses a piezoelectric element and has a novel structure, and a method for manufacturing the piezoelectric element. In the structure according to this embodiment, the piezoelectric body of the piezoelectric element 20 is the piezoelectric film 22 made of a resin material. For this reason, compared with the case where a piezoelectric material is ceramics, impact resistance improves and the mechanical quality factor Q of the piezoelectric element 20 also falls.

  Further, in order to increase the output while maintaining the basic resonance circumference of the piezoelectric element 20 at a desired value, the sizes of the opening 42 and the piezoelectric film 22 are set so that the basic resonance circumference is a desired value. In addition, it is necessary to provide a plurality of openings 42 and piezoelectric films 22. However, in this embodiment, since the piezoelectric film 22 can be simultaneously formed in the plurality of openings 42 of the support member 40, even if a plurality of openings 42 and the piezoelectric film 22 are provided, an increase in manufacturing cost is suppressed. it can.

  Further, the size of the piezoelectric film 22 can be changed only by changing the size of the plurality of openings 42. Since the plurality of openings 42 and the piezoelectric film 22 can be provided for one support member 40, the oscillation device can be easily provided with a plurality of basic resonance peripheral numbers.

(Second Embodiment)
FIG. 8 is a cross-sectional view showing the configuration of the oscillation device according to the second embodiment, and corresponds to FIG. 2 in the first embodiment. The oscillation device according to the present embodiment has the same configuration as the oscillation device according to the first embodiment except for the following points.

  First, irregularities 44 are formed on the inner peripheral surface of the opening 42 of the support member 40. The piezoelectric film 22 enters the unevenness 44 when the resin material 200 is melted, and is in close contact with the surface of the unevenness 44.

  Also according to this embodiment, the same effect as that of the first embodiment can be obtained. Moreover, since the unevenness | corrugation 44 was formed in the internal peripheral surface of the opening 42, the adhesiveness of the piezoelectric film 22 and the internal peripheral surface of the opening 42 improves.

(Third embodiment)
FIG. 9 is a cross-sectional view showing the configuration of the oscillation device according to the third embodiment, and corresponds to FIG. 2 in the first embodiment. The oscillation device according to the present embodiment has the same configuration as the oscillation device according to the first embodiment except for the following points.

  First, a covering portion 46 is disposed above the plurality of piezoelectric films 22. The covering portion 46 is formed integrally with the support member 40. Specifically, the support member 40 protrudes upward and is connected to the lower surface of the covering portion 46.

  A through hole 48 is formed in the covering portion 46. The through hole 48 is provided to face each of the plurality of piezoelectric films 22.

  Also according to this embodiment, the same effect as that of the first embodiment can be obtained. Further, the directivity of the ultrasonic wave radiated from each piezoelectric element 20 through the through hole 48 is further improved. Further, since the piezoelectric elements 20 are separated from each other by the support member 40, it is possible to prevent the sound waves generated by the adjacent piezoelectric elements 20 from interfering with each other.

  In the oscillation device shown in the second embodiment, the covering portion 46 and the through hole 48 shown in this embodiment may be provided.

(Example)
The oscillation devices shown in FIGS. 2, 4, 8, and 9 were prepared, and the characteristics of the oscillation devices were examined (Examples 1 to 4). In this embodiment, the oscillation device functions as a parametric speaker. As a comparative example, an electrodynamic oscillation device having the same plane area as in Examples 1 to 4 was prepared and the characteristics were examined. The evaluation items are as follows.

(Evaluation 1: Measurement of sound pressure level frequency characteristics)
The sound pressure level when an AC voltage of 1 V was input was measured with a microphone placed at a position away from the element by a predetermined distance. The predetermined distance is 10 cm unless otherwise specified, and the frequency measurement range is 10 Hz to 10 kHz.

(Evaluation 2: Drop impact test)
The mobile phone equipped with the oscillation device was naturally dropped 5 times from directly above 50 cm, and a drop impact stability test was performed. Specifically, the presence or absence of breakage such as cracks after the drop impact test was visually confirmed, and the sound pressure characteristics after the test were further measured. As a result, the sound pressure level difference (referring to the difference between the sound pressure level before the test and the sound pressure level after the test) was less than 3 dB, and 3 dB or more was rated as x.

  The evaluation results are shown in Table 1.

  From this table, it was shown that the oscillation device according to each example had a large output, a flat frequency characteristic, and was strong against an impact when dropped compared to the oscillation device according to the comparative example.

  As shown in FIG. 10, the oscillation device according to Examples 1 to 4 was used as the speaker 302 of the mobile communication terminal 300. The speaker 302 was attached to the inner surface of the casing of the mobile communication terminal 300. Table 2 shows the characteristics of the speaker 302 when each embodiment is used.

  From this table, it was shown that the speaker 302 according to each example has a flat frequency characteristic and is strong against an impact when dropped.

  As mentioned above, although embodiment of this invention was described with reference to drawings, these are the illustrations of this invention, Various structures other than the above are also employable.

20 Piezoelectric element 22 Piezoelectric film 24 First electrode 26 Second electrode 40 Support member 42 Opening 44 Concavity and convexity 46 Covering part 48 Through hole 50 Control part 52 Signal generating part 100 Stage 110 Pressing member 112 Convex part 200 Resin material 300 Portable communication terminal 302 Speaker

Claims (1)

A piezoelectric body ;
A support member for supporting the front Symbol piezoelectric,
A method of manufacturing a piezoelectric element having
Disposing a resin material having a piezoelectric effect in the opening of the support member having an opening;
Forming the piezoelectric body made of a resin material in close contact with the inner peripheral surface of the opening by melting and then solidifying the resin material;
A method for manufacturing a piezoelectric element comprising:

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