JPS6133509B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a piezoelectric electroacoustic transducer made of a flexible polymer piezoelectric sheet. Piezoelectric electroacoustic transducers using polymer piezoelectric sheets are widely used in speakers, microphones, pickups, and the like. These diaphragms are constructed by laminating one or more piezoelectric sheets together to form a bimorph. As shown in FIG. 1, the bimorph diaphragm is made by pasting two piezoelectric sheets 1 ₁ and 1 ₂ so that their polarization directions (indicated by arrows) are opposite to each other, and attaching external electrodes 2 ₁ on the front and back sides. , 2 A series type in which electrode terminals are derived from ₂ ;
As shown in Fig. 2, two piezoelectric sheets 1 ₁ , 1
₂ are pasted together so that their polarization directions are in the same direction,
It is also well known that there is a parallel type in which the front and back external electrodes 2 ₁ and 2 ₂ are commonly connected to lead out one electrode terminal, and the other electrode terminal is led out from the internal electrode 3. When an inorganic ferroelectric material such as lithium tantalate or lead titanium zirconate is used as the piezoelectric sheet material constituting these diaphragms, a conductive paste is coated by a printing method etc. to install the electrodes. Then, a method of baking has been adopted. For this reason, the adhesiveness of the electrodes is good, and the resin that serves as a binder can also serve as a protective layer, and the electrode terminals can also be soldered to one point on the electrode, making it highly reliable as a diaphragm. was in good condition. However, inorganic ferroelectric materials are hard and brittle, and lack workability, making it difficult to obtain thin, large-area, and highly sensitive materials. In contrast, flexible piezoelectric sheets made of polyvinylidene fluoride, copolymers thereof, or composite materials in which fine inorganic ferroelectric powder is filled in a polymer matrix of these materials, and In the bimorph constructed, the electrode installation method is as follows.
Since piezoelectric sheets soften at temperatures of about 170 to 180°C, it is difficult to apply metal paste or bake them, so vapor deposition and sputtering are widely used. However, since the electrodes provided by these methods are extremely thin, they are susceptible to oxidative corrosion, and the electrodes deteriorate significantly in humid atmospheres. In addition, the adhesion between the piezoelectric sheet and the electrodes is poor, and if you try to form an arbitrary electrode pattern on the piezoelectric sheet by etching, etc., the etching solution will seep in, making the adhesion between the electrodes and the piezoelectric sheet even worse. do. Furthermore, even if it is attempted to stack a metal layer directly on the electrode and the electrode terminal by plating or the like to prevent deterioration of the electrode due to oxidative corrosion, peeling occurs between the piezoelectric sheet and the electrode due to penetration of the plating liquid. For these reasons, it has conventionally been difficult to obtain a highly reliable diaphragm using a piezoelectric sheet using a polymer material. The present invention solves the above-mentioned drawbacks and provides a piezoelectric electroacoustic transducer in which a highly reliable diaphragm is constructed of a flexible piezoelectric sheet made of a polymeric material. In the present invention, the electrodes of the diaphragm are coated with an organic protective layer using a spin coating method to improve the adhesion between the electrodes and the polymer piezoelectric sheet and prevent oxidation corrosion of the electrodes. . In this case, in order to clamp the periphery of the diaphragm, the diameter of the electrode is made smaller than the diameter of the piezoelectric sheet, and the diameter of the organic protective layer is made larger than the diameter of the electrode and equal to or smaller than the clamp diameter. In particular, when the diaphragm has a bimorph structure and the periphery of the diaphragm is clamped, the outer electrode diameter is smaller than the diameter of the piezoelectric sheet; Cover with an organic protective layer. Further, the electrodes are formed by vapor deposition, sputtering, etc. At the same time, electrode terminals are integrally formed around the diaphragm and led out.
A metal plating layer is overlaid on the portion of the electrode terminal that is not covered with the organic protective layer. This prevents oxidation corrosion of the electrode terminals. Furthermore, even when a metal plating layer is provided on an electrode terminal, in the present invention, since the electrode portion is covered with an organic protective layer, a situation where the electrode peels off due to penetration of the plating solution is prevented. Examples of the organic protective layer used in the present invention include a copolymer of vinyl chloride and vinyl acetate, polyvinyl chloride, polyvinyl acetate, acetyl cellulose, polyethylene terephthalate, polyimide, polyurethane, polyvinylidene fluoride, polyvinyl butyral, polyvinyl formal, Polyvinyl alcohol, polyvinylidene chloride, polyethylene, polyvinylpyrrolidone, polyvinyl acrylamide, nylon, polycarbonate, polypropylene, polystyrene, polybutene, polytrifluorochloroethylene, copolymer of tetrafluoroethylene and hexafluoropropylene, polytetrafluoride Thermoplastic resins such as ethylene, copolymers of trifluorochloroethylene and vinylidene fluoride, and thermosetting resins such as epoxy are used. Further, the organic protective layer used in the present invention may be formed by any method such as spin coating, dipping, plasma, sputtering, etc. Examples of the present invention will be described below. Figure 3a
is a plan view of the bimorph diaphragm of one embodiment, and b and c of the same figure are X-X' and Y- of a, respectively.
It is a Y′ cross-sectional view. 11 ₁ and 11 ₂ are made of polymer materials that are polarized in advance in a predetermined thickness direction and have an outer diameter of 20
It is a flexible piezoelectric sheet with a diameter of mm, and is made of a composite material in which polyvinylidene fluoride, a copolymer thereof, or a matrix thereof is filled with inorganic ferroelectric powder. This equivalent piezoelectric sheet 11 ₁ , 1
1 ₂ is provided with external electrodes 12 ₁ , 12 ₂ , internal electrodes 13 ₁ , 13 ₂ , and an organic adhesive 14 .
are overlapped in the thickness direction. External electrode 12
₁ , 12 ₂ is 3μm by vapor deposition or sputtering
It consists of an Al film with a thickness of 11mmφ. As the adhesive 14, Epotek 301-2 (an epoxy adhesive under the trade name of Epotek Technology Co., Ltd.) was used. 12
₁₁ , 12 ₁₂ and 12 ₂₁ , 12 ₂₂ are electrode terminals integrally formed with the external electrodes 12 ₁ and 12 ₂ , respectively. The external electrodes 12 ₁ , 12 ₂ have organic protective layers 15 ₁ ,
₁₅₂ coated. Specifically, an epoxy resin was applied by spin coating to form organic protective layers 15 ₁ and 15 ₂ of 20 μm and 15 mmφ. Next, _metal plating layers 16 ₁₁ , 16 ₁₂ , 16 ₂₁ , 16 ₂₂ with a thickness of 6 μm are formed on the electrode terminals 12 ₁₁ , _{12 12} , 12 _{21 , 12 22 that are not covered with the organic protective layers 15 1} , 15 ₂ .
A thick Cr layer was provided. The bimorph diaphragm thus obtained was clamped with a 17 mmφ clamp jig to construct a piezoelectric electroacoustic transducer. As a result of heat shock testing of this converter at -40°C to 70°C and 95% RH, it was confirmed that it is extremely stable with no oxidation corrosion or peeling of the electrodes even after 3 x ¹⁰³ cycles. Ta. FIG. 4 shows the change in sound pressure at the resonance frequency during this test, and in the example, the sound pressure level was kept constant over a long period of time. Comparative Example 1 in Figure 4 shows the test results for a converter configured exactly the same as the example except that the organic protective layer and metal plating layer were not provided, and the external electrodes and electrode terminals were oxidized after about 3 cycles. Completely disappeared due to corrosion. In addition, Comparative Example 2 has a smaller external electrode and electrode terminal than Comparative Example 1.
This is the case of a converter with a thick Al film (9 μm), and although it has a longer life than Comparative Example 1, the electrodes completely disappeared after about 20 cycles. Next, test data on the peeling resistance of the external electrode due to the organic protective layer are shown in the table below. For comparison, tests were conducted on three types with different diameters of the organic protective layer and one without the organic protective layer. As is clear from the table, it can be seen that by making the diameter of the organic protective layer larger than the diameter of the external electrode, the adhesion of the external electrode is greatly improved.

[Table] As explained above with specific data, according to the present invention, a bimorph diaphragm is constructed from a flexible piezoelectric sheet using a polymer material, and therefore external electrodes and electrode terminals are Even when using a thin metal film by vapor deposition or sputtering,
By covering the external electrode with an organic protective layer, electrode deterioration due to oxidation and corrosion can be prevented, and the adhesion of the electrode can be improved. Further, by providing a metal plating layer on the electrode terminal, oxidation corrosion of the electrode terminal is prevented. Furthermore, even when this metal plating layer is provided, in this invention, the external electrodes are covered with an organic protective layer, so the plating liquid does not seep between the external electrodes and the piezoelectric sheet, and in this respect, the bimorph diaphragm is also advantageous. Reliability will be improved. Note that this invention is not limited to the above embodiments. For example, Al as external electrode and electrode terminal.
In addition to Cr, other metals such as Ni may be used as the metal plating layer provided on the electrode terminal. It is sufficient that the metal plating layer has a thickness of about 5 μm or more.

[Brief explanation of the drawing]

1 and 2 are diagrams showing the basic configuration of a series-type and parallel-type bimorph diaphragm, respectively, FIG. 3 is a diagram showing the configuration of a bimorph diaphragm in an embodiment of the present invention, and FIG. FIG. 6 is a diagram showing heat shock test results of a piezoelectric electroacoustic transducer using a diaphragm, together with a comparative example. 11 ₁ , 11 ₂ ... Flexible piezoelectric sheet, 12
₁ , 12 ₂ ... external electrode, 12 ₁₁ , 12 ₁₂ , 12
₂₁ , 12 ₂₂ ... Electrode terminal, 13 ₁ , 13 ₂ ... Internal electrode, 14 ... Adhesive, 15 ₁ , 15 ₂ ... Organic protective layer, 16 ₁₁ , 16 ₁₂ , 16 ₂₁ , 16 ₂₂ ... Metal Metsuki layer.

Claims (1)

[Claims] 1. In a piezoelectric electroacoustic transducer configured by integrally forming an electrode and an electrode terminal on the surface of a diaphragm made of a polymeric material and clamping the periphery, the diameter of the electrode is defined as the diameter of the diaphragm. The diaphragm is smaller in size, and the electrode is covered with an organic protective layer having a diameter larger than the diameter of the electrode and smaller than the diameter of the diaphragm, and a metal plating layer is provided on the electrode terminal portion that is not covered with the organic protective layer. A piezoelectric electroacoustic transducer. 2. The diaphragm made of a polymeric material is a piezoelectric type according to claim 1, which is made of polyvinylidene fluoride, a copolymer thereof, or a composite in which inorganic ferroelectric fine particles are dispersed using polyvinylidene fluoride as a matrix. Electroacoustic transducer.