JPS6165599A - Piezo-electric speaker and method for producing the same - Google Patents

Abstract

PURPOSE:To attain a compact size and a smooth output sound pressure characteristic in a wide zone by producing a plate having a dome like curved portion with a flat surface shape of circle or ellipsoid, applying zircon-lead titanate forming organic precarser metal solution immediately or through an electrode to a surface of the plate, and making a thermally processing to said applied film. CONSTITUTION:On a surface and a rear surface of a metal plate (Ni plate) having a dome like curved portion of an outer diameter of 40mm and a thickness of 40mum and an edge side thereof being on a flat surface and a flat surface shape of said curved portion being circle, zircon-lead titanate piezo-electric layers 32, 33 having a thickness of 15mum produced from an organic metal compound are formed. As the organic metal compound solution, a solution for forming a piezo-electric film of PbZr0.52Ti0.48O3 is used. This applied by a dipping method and the organic compound is decomposed in an air at a temperature of 400 deg.C after drying, and thereafter thermal ly processed at a temperature of 600 deg.C for 10min to form a thin film of PbZr0.52Ti0.48O3 on the metal plate. On this metal plate, an electrodes composed of Au/Cr 34, 35 are vaporized, a circumference is fixed and a piezo-electric speaker is obtained. The piezo-electric layers 32, 33 are polarized and an oscillation in a diametrically extending direction is employed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field of the Invention) The present invention relates to a piezoelectric speaker used in telephones and the like.

(Prior Art) Conventionally, a piezoelectric speaker has a piezoelectric ceramic plate 1 mounted on a flat metal plate 11 made of brass, stainless steel, etc., as shown in FIG.
Bimorph circular flat plate vibrators in the form of 2 bonded together are exclusively used, and those in which the bimorph disk is directly used as a sounding body, or those in which the former middle and high school, Sawara, and former sites are published in the Proceedings of the Acoustical Society of Japan (October 1982) ) As described in "Piezoelectric Speaker" on pages 289 to 290, there are devices that use the bimorph disk as a driving element, such as high-pitched speakers,
Buzzers and the like are generally used in a relatively high audible frequency range of IKHz or higher.

Apart from this, as shown in Figure 8, there is also a pressure
A disc made of only a box is used as the vibrating body 21,
A speaker has been proposed in which the circumferential portion of the disk 21 is bonded to a rigid wall 22 by slightly curving the disk 21, and the disk 21 is used in a radial expansion/contraction mode.

(Problems with the Prior Art) In recent years, as the performance of speakers has improved, there has been a strong demand for piezoelectric speakers to have wideband reproduction that can cover the human voice band of 300 Hz to 3500 Hz, especially low frequency reproduction.

In order to sufficiently cover the audio band with a conventional piezoelectric speaker using a piezoelectric bimorph disk shown in FIG. 7, it is important to lower the resonance frequency ft of the bimorph vibrator. In order to lower the resonant frequency ft of the bimorph resonator, the diameter of the disc may be increased or the thickness of the bimorph resonator may be reduced. However, if it is attempted to widen the band by increasing the diameter of the disc, it becomes impossible to downsize the speaker. Therefore, it becomes impossible to use it as a handset for a talk set. When downsizing a bimorph resonator, it is extremely important to reduce the thickness of the resonator. The piezoelectric ceramic disk 11 shown in FIG. 7 is manufactured by thin plate processing by lapping), and the maximum plate thickness after polishing is 0.11111 mm. In the bimorph structure shown in FIG. 1, it is essential to flex the diaphragms 11 and 12 sufficiently to radiate sound efficiently, so the thickness of the metal plate 12 bonded to the piezoelectric ceramic disk 11 is also Q. It reaches about 1m. In other words, no matter how thin the piezoelectric bimorph diaphragm is, considering the production yield based on current processing technology, the total thickness of the plate is more than 0.2M11, which is necessary for wideband reproduction that can sufficiently cover audio frequencies. The diameter of the disk is small, so 75α is required.

Regarding performance, when a pressure-sensing speaker is constructed using a bimorph circular plate vibrator as shown in Figure 7, the second and third order high-order resonances near the fundamental resonance frequency of the diaphragm are noticeable within the audio frequency. This method has the disadvantage of causing large peaks and deteriorating call quality.

On the other hand, in the piezoelectric speaker having the structure shown in FIG. 8, the diaphragm is made of the piezoceramic itself, which has drawbacks such as lack of reliability due to mechanical brittleness K and difficulty in molding.

(Objective of the Invention) An object of the present invention is to realize a piezoelectric speaker which is miniaturized and has a flat output sound pressure characteristic over a wide band.

(Structure of the Invention) That is, the present invention provides a plate having a dome-shaped curved portion, the planar shape of the dome-shaped curved portion being a circle or an ellipse,
A piezoelectric speaker characterized by having a diaphragm having a structure in which a thin film of zircon-lead titanate is formed on at least one surface of the diaphragm through an electrode or directly, and a piezoelectric speaker having a planar shape of a circle or an ellipse. A step of producing a plate having a female dome-shaped curved part, a step of applying an organometallic solution of a zircon/lead titanate forming precursor to at least one surface of the plate via an electrode or directly, and applying the coating film. 1. A method of manufacturing a piezoelectric speaker, characterized by comprising a step of heat treatment.

(Description of Structure) The present invention improves the problems of the prior art by adopting the above structure using a piezoelectric ceramic produced from an organometallic compound. First, a method for manufacturing a piezoelectric speaker according to the present invention will be described below.

A dome-shaped metal plate such as Ni or an insulating plate such as alumina is immersed in an organic metal compound solution that becomes zircon-lead titanate by thermal decomposition, and is slowly pulled up and dried.

Zircon-lead titanate having various composition ratios can be made from K by adjusting the organometallic compound solution.

The organic metal compound solution can be applied by a dipping method, a spray method, a spinner method, a screen printing method, or any other method commonly used in painting or printing.

Furthermore, if a part of the piezoelectric layer is not coated, it is possible to partially form the entire piezoelectric layer by a commonly used masking method.

As is well known, piezoelectricity can be imparted to the piezoelectric layer by polarizing it with a high DC electric field. 1(a) to 1) show piezoelectric layers 32 on the front and back surfaces of a metal plate 310 formed into a dome shape.
33 and further provided with electrodes 34.3Fl, it is possible to strongly excite radial elongation vibration or bending vibration depending on the polarization direction shown by the arrow and the way the electric terminals are arranged. In Figure 1 (a).

(b) can be excited with radial elongation vibration, and g) and ni) can be excited with bending vibration. In the case of camera elements (a) and (b)) that utilize radial expansion vibration, the periphery must be fixed if they are to be operated as a speaker, but for the camera elements (c) and (b) that utilize flexural vibration, In the case of a child, either a method of fixing the periphery or supporting a vibration node is possible. Furthermore, as shown in FIG. 2, when the piezoelectric layer 32 is provided only on one side of the dome-shaped molded metal plate 310 and the electrode 34 is further provided, both the radial elongation vibration and the bending vibration can be excited. The conversion efficiency is slightly inferior to that of the vibrator shown in FIG. 1 in which the piezoelectric layer 32.33t is provided on both sides of the molded plate 310. However, it is somewhat advantageous for lowering frequencies because it is easier to process thinner overall.

Furthermore, when the molded diaphragm 51 is an insulator as shown in FIG.
2.53 is provided by a method such as plating or vapor deposition, and if necessary, the electrodes 52 and 53 are short-circuited and electrically connected to the piezoelectric layer 32゜33. , 34, 35, it is clear that the transducer operates exactly the same as the vibrator shown in FIGS. 1 and 2.

The piezoelectric speaker according to the present invention has the following excellent features. First, a formed metal plate 31,
The connecting plate 51 can be easily formed into a thin dome by a method such as pressing or plasma spraying, and the piezoelectric layer 34 formed on one or both sides of the forming plate 31 or 51 can be easily formed into a thin dome.
．． Since the diaphragm 35 can also be made into an extremely thin film of several μm to several tens of μm, the thickness of the diaphragm can be easily made thinner than that of conventional diaphragms, making it possible to reduce the size and frequency. With the conventional method of manufacturing bimorph resonators by bonding piezoelectric ceramic plates to flat metal plates, it is impossible to form a piezoelectric layer on the surface of a dome-shaped molded plate, and this has been achieved for the first time with the present invention. It's watery.

Furthermore, since the diaphragm is formed into a dome shape, the fundamental resonance frequency /rl and the second and third higher mode resonance frequencies fr2. As long as fr3 is present at a considerable level, a piezoelectric speaker with a flat audio band and good speech quality can be realized. Although it is desirable that the planar shape of the dome-shaped curved portion be circular, the effect of the invention will not be lost even if it is oval.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. As an embodiment of the present invention, as shown in FIG. 4, a metal plate (Ni plate) having an outer diameter of 4Qm and a thickness of 40μm, the edge of the dome-shaped curved part is flat, and the planar shape of the dome-shaped curved part is a circle. ) produced from organometallic compounds on the front and back surfaces of
Zircon/lead titanate piezoelectric layers 32 and 33 having a μ-thickness were formed.

The organometallic compound solution is PbZr□, 52 Tio, 48
A solution that forms a 0s piezoelectric film was used. This organometallic compound solution is synthesized by the following process.

Lead oxide, zirconium acetylacetate, and tetrabutoxytitanium f, PbT to /PbZrO3 were weighed so that the molar ratio was 48152, heated in acetylacetone at a temperature of 100 to 110 °C, and reacted to form a complex metal oxide equivalent. A lead zirconate titanate precursor core 8X having a concentration of 12.5% by weight was prepared. This was applied by a dipping method, and after drying, the organic matter was decomposed in the air at a temperature of 400°C, and then heat treated at a temperature of 600'C for 10 minutes. A thin film was formed. Electrodes 3'4 and 35f made of Au/lr were deposited on this film, and the peripheral portions were fixed to fabricate a piezoelectric speaker. Zircon lead titanate piezoelectric layer 32°33
In this case, Fi is polarized in the direction of the arrow and the radial elongation vibration IIh is actively utilized. The fundamental resonance frequency is approximately 1.3
It is KHz. When the metal plate 31 extends in the radial direction, this piezoelectric speaker vibrates like a piston in a direction perpendicular to the surface because the periphery is fixed. Further, the fact that the edge portion of the dome-shaped molded body is flat is extremely effective for stabilizing the support and lowering the frequency.

Next, a diaphragm according to the present invention was housed in a cabinet having three degrees of freedom for an acoustic vibration system as shown in FIG. 5 to construct a speaker system. In FIG. 5, 70 is a diaphragm, 71
is the cabinet, 72f′i front air chamber, 73 is the rear air chamber, 7
4 is a sound absorbing material, 75 is an earpiece, and 76 is a small hole.

Of these, it has 74, 75, and 76 tri acoustic resistance components, and is effective in damping the resonance of the entire speaker system and flattening the output sound pressure characteristics. The frequency characteristic of the voltage sensitivity of the piezoelectric speaker of the present invention shown in FIG. 5 is shown by a solid line in FIG. In addition, a conventional piezoelectric speaker in which a zircon-lead titanate-based piezoelectric ceramic plate having a thickness of Q, lax was adhered to a Ni metal plate with a diameter of 4 mm and a thickness of 0.1 jIIN was housed in a cabinet similar to that shown in Fig. 5. When the voltage sensitivity frequency characteristic is shown by the dashed line.

It is clear that, compared to the conventional piezoelectric bimorph speaker, the output sound pressure characteristic of the speaker according to the present invention is flatter over a wide range, and a remarkable improvement is particularly observed in the bass range.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to realize a piezoelectric speaker that is small and has flat output sound pressure characteristics over a wide band, and can be installed in a large number of industries.

[Brief explanation of drawings]

Figures 1 (a) to (e), Figure 2, Figures 3 (a) to (e), and Figure 4 are diagrams showing examples of the diaphragm according to the present invention, and Figure 5 is a schematic diagram of a piezoelectric speaker cabinet. FIG. 6 is an output sound pressure characteristic diagram of a piezoelectric speaker, FIG. 7 is a diagram showing a conventional bimorph piezoelectric vibrator, and FIG. 8 is a diagram showing a disk vibrating body made only of piezoelectric ceramics. In the figure, 11 is 4 flat metal plates, 12 is a piezoelectric ceramic plate, 2
1 is a curved piezoelectric ceramic disk, 22 is a rigid wall, 311 is a metal plate formed into a dome shape, 32.33 is a piezoelectric layer, 34° 35. 52.53 is an electrode, 51 is formed into a dome shape. Insulating plate, 70 is a diaphragm, 71 is a cabinet, 72 is a front air chamber, 73 is a rear air chamber, 74 is a sound absorbing material, 751- is an earpiece, and 76 is a small hole.

Claims (3)

[Claims] (1) A plate having a dome-shaped curved portion, the planar shape of the dome-shaped curved portion being circular or elliptical, and at least one surface of which is connected via an electrode or directly to zircon-lead titanate. 1. A piezoelectric speaker comprising a diaphragm having a structure in which a thin film is formed. (2) The piezoelectric speaker according to claim 1, wherein the outer edge of the dome-shaped curved portion is flat. (3) A step of producing a plate having a dome-shaped curved portion having a circular or elliptical planar shape, and applying an organic zircon/lead titanate forming precursor to at least one surface of the plate via an electrode or directly. A method for manufacturing a piezoelectric speaker, comprising the steps of applying a metal solution and heat-treating the applied film.