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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
piezoelectric speaker, and more particularly to a piezoelectric speaker used as a piezoelectric
buzzer or a piezoelectric speaker. [Prior Art] A piezoelectric sounding body obtained by bonding
two sheets of piezoelectric material having electrodes formed on both sides is connected to
electrodes so as to be opposite to each other with respect to the polarization direction, so that an
AC voltage is generated between the electrodes. When is applied, the respective bonded
piezoelectric materials expand and contract in the opposite direction to cause warping alternately
in the vertical direction centering on the bonded surface. Therefore, if the outer peripheral
portion is fixed in a circular shape, this warpage causes the central portion to be displaced up
and down to become a vibrator that vibrates at the frequency of the applied AC signal. Is the
sounding body that produces the sound by creating a compressional wave of air. [Problems to be
Solved by the Invention] In the above-described sounding body, if the displacement of the central
portion is large, the sound produced is also large, and a structure having a large displacement of
the central portion is desired. However, in the case where the piezoelectric material is a ceramic
sintered body, the material itself does not have flexibility, so if the periphery is fixed, the
movement of the central portion is also suppressed. As a result, the peripherally fixed bimorph
piezoelectric sounding body formed entirely of ceramics can only be a sounding body having a
small sound pressure level. FIG. 4 is a partially cutaway perspective view of a bimorph type
sounding body showing a portion of a conventional piezoelectric sounding body. As shown in
FIG. 4, the piezoelectric sounding body has the metal plate 41 as its center, the piezoelectric
members 42 and 43 are attached to both sides, and the electrodes 44 are mutually connected
opposite to each other in polarization. It is a thing. By sticking the metal plate 41 to the metal
plate 41 in this manner, the portion of the metal plate 41 secures flexibility with the support 45
of the peripheral fixed portion, so that the warpage generated in the portion of the piezoelectric
material 42 displaces the whole. This makes it vibrate and produces sound efficiently. However,
the sounding body attached to such a metal plate requires a step of affixing a piezoelectric
material to a metal plate and a step of connecting electrodes, and furthermore, the upper and
lower positions of the metal plate are perfectly aligned and bonded. However, this alignment
process is not easy and increases the cost. An object of the present invention is to provide a
piezoelectric sounding body with an efficient and easy method by which these conventional
drawbacks can be eliminated and integrated firing can be performed. [Means for Solving the
Problems] The piezoelectric sounding body according to the present invention is a piezoelectric
bimorph type obtained by fixedly supporting a part of a laminate of two layers of piezoelectric
ceramics sandwiched by at least three layers of electrodes. In the sound-producing body of the
present invention, the thickness of the boundary portion between the fixed support portion and
the free portion or the free state portion adjacent thereto is thinner than the thickness of the
bimorph-formed portion, and the electrode of this bimorph-formed portion is through-hole
connected Are connected to the first layer, and the second layer is up to the end face of the
electrode forming portion.
[Operation] The piezoelectric sounding body according to the present invention is a bimorphtype laminated body in which three electrode layers are formed, but before being laminated as
this laminated body, holes are formed at positions where the outer periphery fixing portion is
formed as the sounding body. In this layer, the upper layer and the lower layer are shifted by 1 /
′ ′ 2 pitch, and by this lamination, a groove is formed at the position of the outer peripheral
fixing portion, and the outer peripheral fixing is performed. The thickness of the portion is
reduced to one layer. As a result, the thickness of the peripheral portion can be reduced
compared to the case where the conventional piezoelectric ceramic plates are stacked and fixed
in the periphery, and this thinness facilitates movement as a diaphragm despite the upper mix. .
For this reason, even if the same power is supplied, the diaphragm of the present invention is
efficiently displaced and becomes a sounding body having a high sound pressure level.
Therefore, as in the conventional case, due to the problem of efficiency, electrode formation on a
piezoelectric plate, adhesion to a metal plate, attachment to a case support, electrode connection
with an external terminal, etc. The piezoelectric sounding body can be obtained by a simple
process of simply laminating and integrally firing without requiring any process. Next, the
piezoelectric sounding body of the present invention will be described with reference to the
drawings. FIG. 1 is a partially cutaway perspective view of a piezoelectric speaker according to an
embodiment of the present invention. In the diaphragm, electrodes 13 are formed on two layers
of piezoelectric ceramics 11 and 12 in all three layers of upper and lower and inside, and this
electrode is connected to the first extraction electrode 14 with a through hole and the outer
periphery It is drawn out in three directions of the fixed body 15 and connected to the external
electrode 16. The piezoelectric ceramic sock 11, which is the upper layer, is in the form of a
small disk having only the portion where the electrode 13 is formed, and is 60% to 80% of the
diameter of the outer peripheral fixed body 15. FIG. 2 is a plan view showing an example of a
pattern formed on a piezoelectric material green sheet for obtaining the piezoelectric sounding
body of the present invention and an example of a drilling state, and the piezoelectric material
shown in FIG. Electrodes 13 are formed on the front side of the green sheet 11 and the front and
back sides of the piezoelectric material green sheet 12 shown in FIG. 2 (b), and the extraction
electrode 14 is formed on the piezoelectric material green sheet 12 which is the lower side
during lamination. Each is pulled out in three different directions. Also, as shown in FIG. 2 (c), at
the position of radius R2 (FIG. 2 (a)) where the radius is 50% to 80% of the position of radius R1
at which the outer peripheral fixed body is formed. The piezoelectric green sheet 11 to be the
upper side is punched out, the center is aligned with the piezoelectric green sheet 12 to be the
lower side, and temporary pressure bonding is performed.
At this time, at the electrode end of the upper piezoelectric material green sheet 11, there are
through holes 21 and connection electrodes 22 for connecting to the extraction electrode 1 = i
formed on the lower sheet 12. The two piezoelectric green sheets obtained in this way are
laminated and pressed as they are and fired through a binder removal step, replacing only a
simple diaphragm, and incorporating it into the fixing portion and case as a sound generator.
Although two green sheets 23 each having a hole of radius R1 may be formed on the upper and
lower sides of the two sheets, and after these are stacked and temporarily fixed, as shown in FIG.
Thus, an integral product with the outer peripheral fixed body is obtained by laminating and
pressing, and a piezoelectric sounding body obtained by integral firing is obtained through one
binder removal step and a firing process. FIG. 3 is a side view showing a configuration example
when the piezoelectric sounding body of the present invention is laminated. In the piezoelectric
sounding body configured in this manner, the peripheral fixing portion becomes approximately
20 μm to 50 μm thick for the Green Sea 1-1 layer, and therefore, although it is a ceramic
sintered body in this portion, flexibility − Since the vertical deflection generated in the central
electrode formation portion is obtained in a state close to the free state, the efficiency drop due
to the peripheral fixation is much less and the sound producing body has a high sound pressure
level. In addition, since the piezoelectric sounding body of the present invention is obtained only
by drilling and printing of a green sheet, and laminating, removing binder and firing, as in the
prior art, alignment and bonding of a metal plate and a piezoelectric material and externalization
of electrodes No need for wiring for taking out, etc., and the manufacturing process of a typical
multilayer ceramic capacitor can be used as it is, so the cost reduction effect can be easily
obtained. 5 The piezoelectric green sheet used here is made of magnesium niobate , Pb (Mg 1 □,
· N b 2. 3) A powder of an electrostrictive material whose main component is 03 is dispersed in a
solvent together with an organic binder to form a slurry. This is made into the ceramic green
sheet of uniform thickness 20 micrometers-200 micrometers by the slip casting method using a
doctor blade. The ceramic green sheet is punched to a prescribed size, and holes for through hole
formation are formed by a punch and a die. Next, a screen printer is used to print an electrode
paste on the processed piezoelectric material green sheet including the drilling. At this time, the
electrode paste is also embedded in the through hole simultaneously. A green sheet on which the
second layer having the through-hole connection and the electrode pattern obtained in this way
is temporarily pressure-bonded is stacked and heated at a temperature around 100 ° C. and
pressure-bonded at a pressure of about 250 kg / cm 2 Get the body.
Next, this laminated wood is cut into a predetermined size as required, and first, the organic
matter present in the cavity pattern or the ceramic green sheet is slowly heated in an oxidizing
atmosphere in one binder removal step to decompose and disappear. Usually, these organic
substances are completely decomposed and oxidized up to 500 ° C to 600 ° C, but if the
temperature is rapidly raised to the decomposition temperature, the laminate will break, so 25 °
C / hour or more may be used. The temperature is raised at the rate of temperature rise, and the
organic matter is completely eliminated by maintaining the temperature at 500 ° C. to 600 ° C.
for a sufficiently long time. Thereafter, by firing at a temperature of 900 ° C. to 1200 ° C., the
above-described piezoelectric sounding body can be obtained. In the present embodiment, the
diaphragm forming the bimorph is made circular, and the second layer is punched out into a
circular shape to obtain it. However, the shape of the diaphragm is not limited to a circle, for
example, a rectangular shape In the bimorph diaphragm, both ends are configured as support
parts, but in order to make the fixed part of the both ends be the thickness of one layer of the
piezoelectric green sheet, the electrode of the through hole connection is connected to the upper
piezoelectric green sheet A green sheet which is formed and smaller than the size of the fixed
portion may be temporarily pressure-bonded. [Effects of the Invention] As is apparent from the
above description, in the piezoelectric sounding body according to the present invention, the
second layer of electrode connection is laminated at the boundary between the free state portion
displaced as the diaphragm and the stationary portion supporting the diaphragm. Is connected to
the first layer by through holes, so only one layer may be required at this boundary, and thin fhis region of this part can be performed, although it is a ceramic sintered body obtained
integrally from the diaphragm to the fixed body. In addition, the displacement of the diaphragm
can be increased as much as the displacement generated by the diaphragm becomes close to the
free state, and there is an effect that a sounding body having a high sound pressure level can be
Brief description of the drawings
FIG. 1 is a partially cutaway perspective view of a piezoelectric sounding body showing one
embodiment of the present invention, and FIG. 2 is an example of a pattern formed on a
piezoelectric material green sheet to obtain the piezoelectric sounding body of the present
invention FIG. 3 is a side view showing an example of the constitution when the piezoelectric
sounding body of the present invention is laminated, and FIG. 4 is a partially cutaway perspective
view of a bimorph type sounding body showing an example of a conventional piezoelectric
sounding body. is there.
11.12 ··· Piezoelectric ceramics (piezoelectric material green sheet), 13.44 ··· Electrodes 14 ···
Extraction electrodes, 15 ··· Peripheral fixed body, 16 ··· External electrode, R1 ··· Fixed The radius
of the position of the body, R2: punching radius of the second layer, 21: through hole, 22:
connecting electrode, 23: green sheet, 31: peeling film, 32. Spacer, 41: metal plate, 42.43:
piezoelectric material, 45: support. --1