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DESCRIPTION JPS61182400

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DESCRIPTION JPS61182400
[0001]
TECHNICAL FIELD The present invention relates to an improvement of a method of
manufacturing a piezoelectric diaphragm having a bimorph structure in which a piezoelectric
element is joined to a thin metal plate. [Prior Art] Generally, a piezoelectric diaphragm having a
bimorph structure in which a piezoelectric ceramic plate or a piezoelectric film such as a
piezoelectric ceramic plate is joined to a thin metal plate has many advantages such as long life,
low current drive, il type and light weight. Therefore, it is used as a sound generator for various
devices such as a clock, a voice synthesis device, and a telephone. In this case, it is desirable that
the above-mentioned sounding body can obtain high sound pressure at the lowest possible
frequency. As a means of obtaining such a sounding body, it has been attempted to manufacture
a low frequency, high sound pressure sounding body by thinning a metal plate and a
piezoelectric ceramic. In this method of producing the sounding body, for example, a lead
zirconate titanate (PZT) green sheet is formed to a thickness of about 70 μm by a method such
as a doctor blade or extrusion, and punched to a desired size (eg, 20 mφ) to form a thin metal
plate Do. Then, the thin metal plate is fired at a temperature of 1200 to 1300 ° C. in a lead
oxide atmosphere, and a metal such as silver, gold or nickel is deposited on both sides by
sputtering or vacuum evaporation to form an electrode, 3 kV / After polarization with a DC
electric field of about mm, the above-mentioned gold II thin plate is cracked. This is a method in
which a low viscosity epoxy adhesive or the like is adhered by applying pressure, heat, and
curing while paying attention not to cause a crack. However, the above manufacturing method
has the following disadvantages. That is, a large number of bores are contained in the
piezoelectric ceramic, and when thinned, the bores become through holes, which may cause a
short circuit at the time of polarization. Therefore, there is a limit to thinning. Bore-free
piezoelectric ceramics can be obtained by hot-pressing or firing in an oxygen atmosphere, but it
is still impossible to completely eliminate the bores. In addition, the above method is expensive in
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cost, and by bonding the thin-walled ceramic, it is likely to cause defective products such as
cracks, chips and cracks, which has a major drawback of leading to a reduction in yield. Further,
as another means for obtaining the above-mentioned sounding body, thin film formation of zinc
oxide (ZnO) or aluminum nitride (AffiN) on a thin metal plate such as a titanium metal plate or a
polymer film by a method such as sputtering or ion plating. It is also attempted to produce a low
frequency, high sound pressure sounding body by doing this. The method for producing this
sounding body is, for example, a method of forming a zinc oxide film oriented by high frequency
sputtering on a titanium metal thin plate, a thin glass plate or the like, using zinc oxide ceramics
as a target.
However, the above manufacturing method has the following disadvantages. That is, the
thickness of the zinc oxide film formed by the above-mentioned manufacturing method becomes
very thin. In general, the resonant frequency f of a thin circular diaphragm is fo-(αt / 2a2) / 2. Q
(1-62) ... (1) It represents. In equation (1), α is a constant determined by the supporting method,
t is the thickness, a is the radius of the disk, E is the Young's modulus, ρ is the density, and δ is
the Poisson's ratio. Therefore, as apparent from the above equation (1), if the thickness t is thin,
the resonance frequency fo decreases and it becomes preferable as a low frequency sound
generator, but if the film thickness leaks too much, heat resistance, mechanical strength, etc.
Various problems will occur at this point. However, it takes a long time to achieve the required
thickness, which causes problems in cost. In addition, this type of sounding body is likely to
generate high-order flexible imaging motion, and if a high frequency component is superimposed
on this flexural vibration, the sounding frequency will increase even if a low frequency voltage is
applied. There was also a problem of that. As means for removing the high frequency component,
it is conceivable to increase the dielectric constant of the piezoelectric body. However, since the
film formed of zinc oxide or aluminum nitride has a low dielectric constant, the high frequency
component can not be removed. In addition, since the dielectric constant is low, the impedance at
low frequencies (0 to 2 kHz>) is too high, and it has a disadvantage that it can not be driven by a
circuit having a normal output impedance. Conventionally, a piezoelectric imaging plate having a
bimorph structure is generally a thin piezoelectric ceramic flat plate bonded to a metal plate. For
example, joining a piezoelectric body along a curved surface inside a cylinder is not possible. It
was possible. Therefore, it has not been possible to obtain a bent type sounding body having
various shapes. Also, the directivity control of the sound wave can not be performed by the
piezoelectric diaphragm of the bimorph structure itself. Recently, a flexible polymer piezoelectric
film has been developed, but because the impedance at low frequency is too high, effective
voltage driving can not be performed. [Objective] The present invention has been made based on
the above-mentioned circumstances, and its object is to obtain a high sound pressure at a low
frequency and to control directivity of a bending type sounding body having various shapes or
sound waves. It is an object of the present invention to provide a method of manufacturing a
piezoelectric diaphragm capable of easily, stably, and inexpensively producing possible sounding
members and the like. [Summary] The present invention is characterized as follows in order to
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achieve the above object.
That is, an alkoxide compound having a high piezoelectric constant and a high dielectric constant
is attached by subjecting the thin metal plate to hydrolysis and heat treatment, and then the
alkoxide compound attached to the thin metal plate is hydrolyzed and heat treated in an oxygen
atmosphere. Further, the present invention is characterized in that the electrode is formed on the
thin metal plate to which the above-mentioned alkoxide compound is attached, and then
polarized. An embodiment of the present invention will be described below with reference to FIG.
First, a metal thin plate made of a metal having a thermal expansion coefficient close to that of
PLZT, that is, ((Pb1-xLax) (Zr'x-yT'1y) 03), for example, titanium, is ultrasonically cleaned using
acetone, trichlene or the like. Then, the titanium thin metal plate is dipped in an alkoxide
compound having high viscosity, or the alkoxide compound is applied to the titanium thin metal
plate by means of coating, printing, spraying or the like. The alkoxide compound is formed as
follows. First, 0.93 mol% of Pb (i-0C3H7) 2, 0.07 mol% of La (OC2H5) 3, and 0.65-E / L /% of Zr
(OC2H5) 4 and Ti (OC2H5) Ethyl alcohol (C2H50H) is added at a ratio of about 5: 3 to PLZT
solution A in which 4) is mixed with 0.35 mol% of the mixed solution B. Then, to the above mixed
solution B, an alcohol solution C in which ethyl alcohol, water and acetic acid are mixed in a ratio
of about 39: 6'O: 1 is added while being well stirred in a ratio of about 1: 1, and then 30.degree.
Leave at temperature for 10 to 50 hours. As a result, an alkoxide compound having a viscosity
increased to 1 to 10 centipoise is obtained. Therefore, the alkoxide compound solution is
dropped onto a titanium metal thin plate on a spinner with a thickness of 30 μm and a diameter
of 25 mmφ, and the spinner is rotated at 1000 to 8000 rpm. By this, a uniform film is formed on
the titanium thin metal plate. Next, the complex as described above is hydrolyzed by heating at
130 to 180 ° C. for 10 to 20 minutes to obtain (Pt) o, g s Lao, o 7) (Zrn, 5sTia, 3s) Os. A
transparent amorphous film (amorphous film) as a component is formed on the titanium thin
metal plate. At this time, the thickness which can be coated in one film formation is related to the
viscosity of the solution of the aluroxide compound. That is, when the viscosity is small, the film
thickness of one time becomes thin, and when the viscosity is high, the film thickness of one time
becomes large. Next, the titanium metal thin plate on which the above amorphous film is formed
is first preheated at 80 to 150 ° C. in an oxygen atmosphere, and then heat treated at 50 to 500
° C. to 900 ° C. for 2 hours.
Then, upon slow cooling in an oxygen atmosphere, the film formed on the titanium sheet metal
crystallizes from amorphous and simultaneously becomes opaque. However, since the crystal
nuclei are not uniformly present at this stage, titanium gold r! A thin plate is again coated with an
alkoxide compound solution using a spinner, hydrolyzed, and then heat-treated at 500 to 900 °
C. for 2 hours. Thereafter, the above operation is repeated until crystal nuclei are uniformly
present and the thickness of the film to be coated becomes about 20 to 30 μm. After that, as in
the prior art, the electrodes are formed by means of vacuum evaporation, plating, sputtering or
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the like, and then polarized. By doing this, it is possible to manufacture a piezoelectric diaphragm
in which the piezoelectric crystal structure 2 obtained by hydrolyzing and heat-treating the
alkoxide compound solution on the titanium metal thin plate 1 as shown in FIG. 2 is joined. The
alkoxide compound has a high piezoelectric constant and a high dielectric constant by hydrolysis
and heat treatment. Therefore, according to this embodiment, low frequency. It can be
manufactured. Further, the processing temperature for crystallizing the alkoxide compound can
be lowered by 200 to 400 ° C. in this embodiment, while it is about several hundred degrees in
the conventional baking method. . Therefore, titanium metal having a thermal expansion
coefficient close to PLZT and a high melting point can be used for the substrate. FIG. 3 is a crosssectional view showing an example of a piezoelectric diaphragm manufactured by applying the
present invention to a titanium metal thin plate 11 having a curved surface. The piezoelectric
crystal structure 12 is joined to the curved surface of the titanium thin metal plate 11 by the
method according to the present invention, and the electrode 13 is further formed. When a
voltage is supplied to the piezoelectric diaphragm having this bimorph structure through the lead
wires 14a and 14b, the piezoelectric diaphragm is curved from the position indicated by the
broken line as indicated by an arrow X in FIG. Therefore, directivity control can be performed
such that the sound wave M converges to, for example, the point P, and new acoustic effects can
be expected. The present invention is not limited to the above embodiment. For example,
although the case where the sheet metal plate as a substrate is a flat plate and the case of a
curved plate is illustrated in the above embodiment, the present invention can be applied to a
sheet metal having a more complicated shape. Further, in the above embodiment, although one
combination using a titanium metal thin plate is shown as a metal thin plate having a thermal
expansion coefficient close to that of PLZT, a metal thin plate made of tantalum metal or nickel
metal may be applied. Of course, various modifications can be made without departing from the
scope of the present invention.
[Effects of the Invention] As described above, according to the present invention, the thin metal
sheet is subjected to hydrolysis and heat treatment to obtain a high piezoelectric constant. After
depositing an alkoxide compound having a high dielectric constant, and then hydrolyzing the
alkoxide compound attached to the thin metal plate and performing heat treatment in an oxygen
atmosphere, and further forming an electrode on the thin metal plate to which the alkoxide
compound is attached Since the polarization is performed, high sound pressure can be obtained
at a low frequency, and a flexible sounding body having various shapes or a sounding body
capable of controlling directivity of sound waves can be manufactured easily, stably and at low
cost. It is possible to provide a method of manufacturing a possible piezoelectric diaphragm.
[0002]
Brief description of the drawings
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[0003]
FIG. 1 is a flow chart for explaining an embodiment of the present invention, and FIGS. 2 and 3
are sectional views showing a piezoelectric diaphragm manufactured according to the
embodiment.
1.11 ... titanium metal thin plate, 2.12 ... piezoelectric crystal structure, 13 ... electrode, 14a, 14b
... lead wire. Applicant agent Patent attorney Atsushi Tsuboi Figure 2
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