JPH0554319B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an improved piezoelectric diaphragm made by laminating a thin metal plate and a piezoelectric element plate.

PRIOR ART Piezoelectric diaphragms include simple elements that utilize the induced strain of the ferroelectric itself as is, as well as composite elements that spatially expand the amount of displacement by combining with other elastic materials. This composite type element includes a bimorph type in which a metal plate is bonded between two piezoelectric diaphragms, and a unimorph type in which a metal plate is bonded to one side of a piezoelectric element plate.

For example, in the case of 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. A structure in which a thin metal plate 4 is bonded to the electrode 2' with a conductive adhesive layer 3, and a lead wire 5 is connected to the thin metal plate 3 and the electrode 2 is usually used.

Such a piezoelectric diaphragm is a micro-displacement element that has one end fixed and the other end movable, and can detect mechanical displacement as an electrical signal, or conversely, generate mechanical displacement by applying an electrical signal. In addition, a disc-shaped piezoelectric diaphragm has a fixed periphery and is incorporated into a resonance box or the like to be used as a piezoelectric buzzer or piezoelectric speaker element that converts an electric signal into an audio signal.

Problems to be Solved by the Invention However, when a piezoelectric buzzer or a piezoelectric speaker element is designed using a piezoelectric diaphragm having the above structure, the adhesive layer between the piezoelectric element and the thin metal plate is made of a conductive material (for example, silver, Carbon, etc.) into a resin solution (e.g. epoxy resin, polyester resin, etc. solution)
Since the acoustic element is formed by using a conductive adhesive mixed with an organic material such as, the organic material layer that occupies most of the organic material layer has an undesirable effect on the sound pressure and other characteristics of the acoustic element.

That is, first of all, because of the structure in which an organic substance with a large stress relaxation is interposed between inorganic materials or metal materials such as piezoelectric elements and thin metal plates with a small stress relaxation,
Part of the mechanical vibration energy generated from the piezoelectric element is absorbed by the organic layer and is not efficiently transmitted to the thin metal plate. Secondly, the stress relaxation of the organic layer has a large temperature dependence, and stress relaxation becomes easier as the temperature rises. That is, the sound pressure tends to fluctuate in response to temperature changes, and as the temperature rises, mechanical vibration energy is more easily absorbed and the sound pressure becomes lower.
Thirdly, the organic material layer has weak resistance to various environmental factors such as moisture resistance, organic solvent resistance, light resistance, etc., which are inherent to organic materials.

Despite these problems with adhesive layers containing organic layers, the method of bonding piezoelectric elements and thin metal plates simply involves applying a conductive adhesive and overlapping the adhesive surfaces, making it easier to manufacture. It has been commonly used due to its simplicity. However, there has been a demand for further improvements in the performance of piezoelectric buzzers and piezoelectric speaker elements, and improvements have been desired.

As one of the improvements, for example,
As described in Publication No. 75648, it is also known that a piezoelectric ceramic material and an electrode are bonded using silver solder or gold solder. For example, silver solder has a high melting point of 600 to 1000°C, When forming a piezoelectric diaphragm, other metal members may oxidize, and the bonding layer may deteriorate or corrode under high temperature and high humidity conditions, causing problems in maintaining the performance of the piezoelectric diaphragm and using it for a long time. It was hot.

Means for Solving the Problems In order to solve the above problems, the present invention provides a piezoelectric diaphragm in which a piezoelectric element plate is adhered to a thin metal plate through an adhesive layer, the adhesive layer being made of a conductive glass-based material. The present invention provides a piezoelectric diaphragm characterized by comprising:

Next, the present invention will be explained in detail.

In the present invention, as the material used for the adhesive layer, a glass-based material is used that has electrical conductivity to the extent that it does not adversely affect the electrical or mechanical properties of the piezoelectric diaphragm. For example, Ag, Pd, Pt, Ni, Cu,
Materials in which one or more metal powders such as Co are mixed into glass, strontium chromate (SrCrO ₃ ), strontium ferrate molybdate (Sr ₂ (Fe,Mo)O ₆ , barium rhenate ferrate (Ba ₂ Material in which one or more conductive oxide powders such as (Fe,Re)O ₆ are mixed into glass, V ₂ O ₅ −
Electron conductive glass such as P ₂ O ₅ glass or Na ₂
Glass-based materials such as alkali silicate-based ion conductive glasses such as O-SiO ₂ -Al ₂ O ₃ are exemplified.

The above-mentioned inorganic materials can also be made into an adhesive layer by sandwiching and melting a mixture of each constituent component as a powder between adhesive surfaces, or by adding a solvent such as butyl alcohol and an organic binder such as ethyl cellulose to the mixed powder. It is also possible to form an adhesive layer by applying a paste to one or both of the adhesive surfaces, volatilizing the solvent, and then melting the adhesive surfaces together. In these cases, it is also possible to add an organic substance such as a resin to improve its applicability. In this case, the organic substance is decomposed or burned after application, and then melted as described above to prevent the organic substance from remaining on the adhesive layer. It is preferable. Note that either heating or ultrasonic waves can be used for melting.

In addition, in the present invention, the piezoelectric material of the piezoelectric element is PZT (Pb (Zr, Ti) O ₃ ), PLZT (Pb, La).
(Zr,Ti)O ₃ ), PT (PbTiO ₃ ) system, or PZT
Examples include those using piezoelectric materials such as three-component systems based on .

Further, in the present invention, examples of the metal thin plate include a nickel thin plate, a brass thin plate, a stainless steel thin plate, and the like.

In addition, in the present invention, the piezoelectric element may have electrodes only on the surface opposite to the thin metal plate, but it has electrodes on both sides as in the case of FIG. A thin metal plate may be bonded to the above-mentioned inorganic adhesive layer. Such electrodes can be made by vacuum evaporation, sputtering, electroless plating of metal materials such as Ag, Pd, Pt, Ni, Cu, Co, etc., or by mixing these metal materials with glass to form a paste, and then making this paste by screen printing, etc. It is formed by coating and melting.

Function Since a conductive glass-based material is used for the adhesive layer that adheres the piezoelectric element plate and the metal thin plate, the glass component can have a lower melting point than metals such as silver solder, so it forms the adhesive layer. At the same time, the heat treatment temperature of the coated material can be lowered, and oxidation of the metal member can be suppressed when joining the thin metal plate to the piezoelectric element plate. In addition, glass is resistant to oxidation and corrosion even in high temperature and humid atmospheres, and when glass-based materials contain metal, the adhesive layer formed by melting the metal covers the metal with glass, preventing oxidation and corrosion. be done. Further, the stress relaxation property can be made closer to that of a piezoelectric element or a thin metal plate than that of conventional organic materials, and this property can be maintained without being affected by environmental factors such as heat.

Example Next, embodiments of the present invention will be described with reference to the drawings.

Example 1 A green sheet was prepared using a doctor blade method using a raw material powder having the composition of Pd (Mg _1/3 Nb _2/3 ) _0.375 Ti _0.375 Zr _0.250 O ₃ and was baked at 1300°C for 2 hours to make a thick sheet. A sheet-shaped piezoelectric sintered piezoelectric plate (corresponding to piezoelectric plate 1 in Figure 1) having a length of 100 μm and a diameter of 25 mm was obtained.
Leave a side margin of 1 mm on both sides of this piezoelectric plate,
Piezoelectric silver paste (manufactured by Shoei Kagaku Co., Ltd.) was applied using a screen printing method, and heat treated at 800°C for 15 minutes to form electrodes (corresponding to electrodes 2 and 2' in Figure 1).
A sheet-like piezoelectric element was obtained.

Next, 100 parts of Ag powder (average particle size 2.0 μm) and PbO・B ₂ O ₃ based solder glass (Toshiba Glass Co., Ltd. After applying an adhesive paste having a composition of 10 parts (manufactured by S.A.), 30 parts of butyl alcohol, and 3 parts of ethyl cellulose in concentric circles with a diameter of 23 mm using a screen printing method (corresponding to the conductive adhesive layer 3 in Figure 1), The sheet-like piezoelectric element was placed on the printed surface, 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 piezoelectric buzzer was created by attaching a lead wire as lead wire 5 in Figure 1 to the obtained piezoelectric diaphragm using solder paste, and the piezoelectric buzzer was placed in an anechoic chamber with a background noise of 40 dB (A range). The sound pressure level was measured using the sound level meter by installing it at a distance of 10 cm from the sound level meter and inputting a 10Vpp sine wave reference signal to the lead wire. The results obtained by varying the measurement temperature are shown in FIG. 2 by line A.

Example 2 In Example 1, strontium ferrate molybdate powder (average particle size 1.5μ) was added to the adhesive paste.
A piezoelectric buzzer was produced in the same manner except that a material having a composition of 100 parts of PbO·B ₂ O ₃ solder glass (manufactured by Toshiba Glass Co., Ltd.), 30 parts of butyl alcohol, and 3 parts of ethyl cellulose was used.

Example 3 In Example 1, V ₂ O ₅ was added to the adhesive paste.
Powdered glass containing equivalent amounts of P ₂ O ₅ (average particle size 3.0 μ
A piezoelectric buzzer was produced in the same manner except that the coating was heat-treated at 400° C. for 10 minutes using a product having a composition of 100 parts m), 30 parts butyl alcohol, and 3 parts ethyl cellulose.

Example 4 In Example 1, adhesive paste
Using a powder with a composition of 100 parts of RbAg ₄ I ₅ powder (average particle size 25 μm), 30 parts of butyl alcohol, and 3 parts of ethyl cellulose, the heat treatment conditions for the applied material were set to 400
A piezoelectric buzzer was fabricated in the same manner except that the temperature was 10 minutes.

Example 5 In Example 1, PbSn was added to the adhesive paste.
(Composition Pb/Sn=37/63) Alloy powder (average particle size 10μ
A piezoelectric buzzer was produced in the same manner except that the coating had a composition of 100 parts m), 30 parts of butyl alcohol, and 3 parts of ethyl cellulose, and the heat treatment conditions for the applied product were 200° C. and 10 minutes.

Example 1 also applies to the piezoelectric buzzers of Examples 2 to 5.
As a result of measuring the sound pressure level in the same manner as in Example 1, the sound pressure level was high as in Example 1, and was stable against temperature changes.

Comparative Example In Example 1, a conductive paste (for example, 70 parts of Ag and 30 parts of epoxy-polyamide were used as the main solids) was used as the adhesive paste, and the applied product was cured at 60 to 100°C. A piezoelectric buzzer was produced in the same manner.

The sound pressure level of this piezoelectric buzzer was also measured in the same manner as in Example 1, and the results are shown by line B in FIG.

From these results, it can be seen that the piezoelectric diaphragm of the example has a higher sound pressure level than that of the comparative example, and its temperature dependence is also small.

Effects of the Invention According to the present invention, since the piezoelectric element plate and the thin metal plate are bonded together using an adhesive layer made of a conductive glass material, the heat treatment temperature during melting of the applied glass material during the formation of the adhesive layer can be reduced. By lowering the temperature, it is possible to suppress oxidation of metal members such as thin metal plates and improve workability. Furthermore, when the glass material contains metal, the adhesive layer formed by melting the metal covers the metal with glass to prevent oxidation and corrosion even under high temperature and high humidity conditions. In addition, the stress relaxation property is smaller than that of organic materials, making it similar to piezoelectric elements and thin metal plates, and it can maintain stability against heat, etc., so when piezoelectric diaphragms are used in acoustic elements such as piezoelectric speakers, the sound pressure can be improved. However, there is no change in sound pressure due to changes in operating temperature, and resistance under operating environmental conditions such as moisture resistance, organic solvent resistance, and light resistance can be improved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a piezoelectric diaphragm, and FIG. 2 is a graph showing the temperature dependence of sound pressure at 1 KHz of piezoelectric buzzers made using an embodiment of the present invention and a conventional piezoelectric diaphragm. In the figure, 1 is a piezoelectric element plate, 2 and 2' are electrodes, 3 is a conductive adhesive layer, and 4 is a thin metal plate.

Claims (1)

[Claims] 1. A piezoelectric diaphragm in which a piezoelectric element plate is bonded to a thin metal plate via an adhesive layer, wherein the adhesive layer is made of a conductive glass-based material.