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The present invention relates to an improvement of a piezoelectric diaphragm in which a thin
metal plate and a piezoelectric element plate are bonded. Prior art piezoelectric diaphragms
include not only simple elements that use the induced strain of the ferroelectric itself as they are,
but also composite elements that spatially expand the amount of displacement by combining with
other elastic materials and the like. The composite element includes a bimorph type in which a
metal plate is adhered between two piezoelectric element plates, and a unimorph type in which a
metal plate is adhered to one side of the piezoelectric element plate. For example, as a unimorph
type, as shown in FIG. 1, electrodes 2 and 2 made of a metal material are provided on both sides
of a piezoelectric plate 1 made of an oxide ceramic material to form a piezoelectric element plate
1. Usually, a metal thin plate 3 is adhered to the electrode 2 ′ ′ by a conductive adhesive layer
4 and a lead wire 4 is connected to the metal plate 4 and the electrode 2. Such a piezoelectric
diaphragm fixes one end and allows the other end to be displaced, detects mechanical
displacement as an electrical signal, or reversely gives an electrical signal to cause mechanical
displacement. The disk-shaped piezoelectric vibrating plate is used as a displacement device or a
disk-like piezoelectric diaphragm fixed in its periphery and incorporated in a resonance box or
the like to be used as a piezoelectric buzzer or a piezoelectric speaker device that converts an
electrical signal into an audio signal. However, when a piezoelectric buzzer or a piezoelectric
speaker element is designed using the piezoelectric diaphragm having the above structure, the
adhesive layer between the piezoelectric element and the thin metal plate is made of a
conductive material (eg, silver, etc.) The acoustic element is formed by using a conductive
adhesive in which carbon or the like is mixed with an organic substance such as a resin solution
(for example, a solution such as an epoxy resin or a polyester resin). Adversely affect the sound
pressure and other characteristics of the That is, first of all, mechanical vibration energy
generated from the piezoelectric element is partially due to the structure in which the organic
substance having a large stress relaxation intervenes between inorganic materials such as
piezoelectric elements and metal thin plates having small stress relaxation and metal materials. Is
absorbed by the organic layer and is not efficiently transmitted to the thin metal plate. Second,
the organic layer has a large temperature dependence of stress relaxation, and it is easy to
relieve stress as the temperature rises. That is, the sound pressure tends to fluctuate with
temperature change, and as the temperature rises, mechanical vibration energy is easily
absorbed, and the sound pressure becomes low. Thirdly, the organic layer is weak against various
environmental factors such as moisture resistance, organic solvent resistance, light resistance
and the like, which are peculiar to organic substances. Although there is a problem with the
adhesive layer having an organic layer as described above, the bonding method for bonding the
piezoelectric element and the metal thin plate is merely required to apply the conductive
adhesive and to overlap the bonding surfaces, so that It is often used conventionally because of
its ease.
However, further improvement in performance of the piezoelectric buzzer and the piezoelectric
speaker element is required, and the improvement is desired. Means for Solving the Problems In
the present invention, in order to solve the above problems, in the piezoelectric diaphragm in
which a piezoelectric element plate is adhered to a thin metal plate through an adhesive layer,
the adhesive layer is made of an inorganic material. The present invention provides a
piezoelectric diaphragm characterized by Next, the present invention will be described in detail.
In the present invention, the adhesive layer is made of an inorganic material, and it is desirable
that the adhesive layer has conductivity to the extent that the electric or mechanical properties of
the piezoelectric diaphragm are not adversely affected. Examples of the inorganic material
include nonmetallic materials and metallic materials, and as the nonmetallic material, one or
more metal powders such as 8 g, Pd, PL, Ni, Cu, Co, etc. are used. Contained in glass, strontium
chromate (SrCr03), strontium ferrate molybdate (Sr 2 (Fe, Mo) 06), barium ferrate rhenate (Ba 2
(Fe, Re) O, etc.) 1 type or 2 or more Glass-based materials such as those obtained by mixing
conductive oxide powder into glass, electron conductive glass such as v2o5-p2o5 glass, or alkali
silicate ion conductive glass such as Na2O-5i02- to 1203; As metal-based materials, Pb-5n, PbAg, Pb-Cd. Solders such as low melting point B1-Pb-5n alloys containing a large amount (40 to
70%) of Pb-In, Pb-Cd-Zn alloy, 5n-Cd, etc. or mainly Ag and Cu, Examples of materials added with
Zn, Cd and others, and silver brazing materials exemplified as a melting point of 600 to 1000 °
C., and brazing materials such as gold brazes mainly containing sieve and added with about 20%
of Cu, Ni, In etc. Be When aluminum sheet metal is used, Al containing a small amount of Cu, Sn,
or Zn as the main component, Zn, Sn, Cd, or Pb containing low melting point metal as the main
component, Cu, ^ 1! Al solder containing a small amount of Ag, Sb, etc. is used. The above
inorganic materials can be made into an adhesive layer by sandwiching and melting a mixture of
the respective constituent components as a powder on the adhesive surface, and a mixed powder
containing a solvent such as butyl alcohol and an organic binder such as ethyl cellulose The
paste may be applied to one or both of the adhesive surfaces, the solvent may be evaporated, and
then the adhesive surfaces may be combined and melted to form an adhesive layer. In these
cases, the coatability can be improved by adding an organic substance such as a resin. In this
case, the organic substance is decomposed or burnt after application, and thereafter, the abovedescribed melting does not cause the organic substance to remain in the adhesive layer. Is
Note that either heating or ultrasonic waves can be used for melting. In the present invention, the
piezoelectric material of the piezoelectric element is PZT (Pb (Zr, Ti) 03), PLZT (Pb, La) (Zr, Ti)
03), PT (PbTi 03), or a three component based on PZT. The thing using piezoelectric materials,
such as a system, is mentioned. In the present invention, examples of the metal sheet include
nickel sheet, brass sheet, stainless steel sheet and the like. In the present invention, although the
piezoelectric element may have electrodes only on the surface opposite to the thin metal plate, it
has electrodes on both sides as in the case of FIG. A thin metal plate may be adhered to the above
through the above-mentioned inorganic adhesive layer. Such an electrode is formed by vacuum
deposition, sputtering, electroless plating, or a mixture of metal materials such as Ag, Pd5Pt,
Ni5Cu, Co, etc. with glass to form a paste, and this paste is applied and melted by screen printing
etc. It is formed by Since an inorganic material is used in the adhesive layer for bonding the
working piezoelectric element and the metal thin plate, the stress relaxation property can be
made closer to that of the piezoelectric element or the metal thin plate than the conventional
organic substance, and environmental factors such as heat You can maintain this without being
affected by EXAMPLE Next, an example of the present invention will be described with reference
to the drawings. Example 1 A green sheet is prepared by a doctor blade method using Pb (Mgl /
3Nba'3) 0.375 TIo, 375 Zr (raw material powder having a composition of L25003), and fired at
1300 ° C. for 2 hours for thickness A sheet-like piezoelectric sintered body having a diameter of
25 μm and a temperature of 100 μm was obtained (corresponding to the piezoelectric plate 1
in FIG. 1). While leaving side margins 1 fl on both sides of this piezoelectric plate, silver paste for
piezoelectrics (manufactured by Shoei Kagaku Co., Ltd.) is applied by screen printing, and heat
treatment is applied at 800 ° C. for 15 minutes to form electrodes (FIG. 2) to obtain a sheet-like
piezoelectric element. Next, 100 parts of stainless steel, 1) 35 mm diaphragm (corresponding to
the thin metal plate 3 in FIG. 1) E 100 parts of Ag powder (average particle diameter 2.0 #m),
PbO-8203 solder glass (Toshiba) Adhesive paste having a composition of 10 parts of Glass M, 30
parts of butyl alcohol and 3 parts of ethylcellulose is applied by screen printing concentrically to
a diameter of 23 n (FIG. 1 piezoelectric plate 1 deposition (organic type) 4 Then, the sheet-like
piezoelectric element was placed on the printing surface, and magnesia porcelain was placed
thereon as a weight, and heat treatment was performed at 450 ° C. for 10 minutes to obtain a
piezoelectric diaphragm.
A lead wire is attached to the obtained piezoelectric diaphragm using solder paste like lead wire
5 in FIG. 1 to make a piezoelectric buzzer, and this piezoelectric buzzer is placed in an anechoic
chamber with a dark noise of 40 dB (A range). The sound pressure level was measured by a noise
level meter while maintaining the distance between the noise level meter and 10CI1), inputting a
10 vpp sine wave reference signal into the lead wire. The results obtained by changing the
measurement temperature are shown by lines in FIG. Example 2 In Example 1, 100 parts of
strontium ferrate molybdate powder (average particle diameter 1.5 μm), 10 parts of PbO-8203
solder glass (manufactured by Toshiba Glass Co., Ltd.), and 30 parts of butyl alcohol were used as
the adhesive paste. A piezoelectric buzzer was produced in the same manner except that one
having a composition of 3 parts of ethyl cellulose was used. Example 3 In Example 1, an adhesive
paste was used having a composition of 100 parts of powder glass (average particle diameter 3.0
μm) containing 30 parts by weight of v 2 O 5 and P 2 O 5, 30 parts of butyl alcohol and 3 parts
of ethylcellulose, A piezoelectric buzzer was similarly manufactured except that the heat
treatment condition of the coated material was changed to 400 ° C. for 10 minutes. EXAMPLE 4
In Example I, 1 to the adhesive paste. A piezoelectric buzzer was prepared in the same manner as
that of the composition having a composition of 100 parts of bAg 415 powder (average particle
diameter 25 μm), 30 parts of butyl alcohol and 3 parts of ethylcellulose, and the heat treatment
condition of the coated material was 400 ° C. for 10 minutes. Made. Example 5 In Example 1, an
adhesive paste was used having a composition of 100 parts of Pb5n (composition Pb / Sn =
37/63) alloy powder (average particle diameter 10 μm), 30 parts of butyl alcohol and 3 parts of
ethylcellulose. A piezoelectric buzzer was produced in the same manner as in the above except
that the heat treatment conditions of the coated material were changed to 200 ° C. and 10
minutes. The sound pressure levels of the piezoelectric buzzers of Examples 2 to 5 were also
measured in the same manner as in Example 1. As a result, the sound pressure level was high as
in Example 1, and stable against temperature changes. Comparative Example In Example 1, a
conductive paste (for example, 70 parts of Ag and 30 parts of epoxy-polyamide as main solids)
was used as the adhesive paste, and the coated product was cured at 60 to 100 ° C. A
piezoelectric buzzer was produced in the same manner except for the above. The sound pressure
level of this piezoelectric buzzer is also measured in the same manner as in Example 1. The result
is shown in FIG. 2B. From these results, it can be seen that the piezoelectric diaphragm of the
example has a higher sound pressure level than that of the comparison 1), and its temperature
dependency is also small. According to the present invention, since the piezoelectric element and
the thin metal plate are adhered by the adhesive layer made of an inorganic material, the stress
relaxation property is smaller than that of the organic material, close to the piezoelectric element
and the thin metal plate On the other hand, since the piezoelectric diaphragm can be stably
maintained, the sound pressure is improved when the piezoelectric diaphragm is used for an
acoustic element such as a piezoelectric speaker, there is no fluctuation of the sound pressure
due to the change of operating temperature, moisture resistance, organic solvent resistance, light
resistance Resistance to operating environment conditions such as
Brief description of the drawings
FIG. 1 is a cross-sectional view of a piezoelectric diaphragm, and FIG. 2 is an IKI 17.I. of a
piezoelectric buzzer prepared using an embodiment of the present invention and a conventional
piezoelectric diaphragm.
It is the graph which showed the temperature dependence of the sound pressure in. In the figure,
1 is a piezoelectric element plate, 2.2 'is an electrode, 3 is a thin metal plate, and 4 is a
conductive adhesive. 1 in December 25, 1987