JPS6133512B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic transducer that is highly water resistant, wear resistant, and has an electrically stable structure.

Inorganic piezoelectric materials or so-called polymer piezoelectric materials that become piezoelectric through poling can effectively transmit and receive ultrasonic waves.
Used as an ultrasonic transducer.

In particular, polymer piezoelectric films have various advantages over inorganic piezoelectric materials, such as low acoustic impedance, flexibility, and high workability, so they are useful for ultrasonic flaw detection, ultrasonic diagnosis, acousto-optic, etc. It is extremely useful as a transducer used in the field.

In order to operate a polymeric piezoelectric film as such a transducer, electrodes are required on both sides of the piezoelectric film, either directly or via an intermediate layer. This electrode is
It is formed by adhering a metal plate or metal foil, or by attaching a metal thin film to the piezoelectric film by a method such as vapor deposition, sputtering, or plating, or by applying a conductive paint.

FIG. 1 shows an example of the basic structure of a conventional ultrasonic transducer using a polymer piezoelectric film.

Figure 1A shows a polymer piezoelectric film 3 on a metal block 2.
is adhered to the piezoelectric film, and an electrode 4 on the operating surface side is formed on the piezoelectric film. The metal block 2 functions to operate the piezoelectric film at 1/4λ and is also used as a back electrode. In FIG. 1B, the metal film 2' provided as the electrode on the back side of the polymer piezoelectric film 3 forms a sandwich-like structure between the metal film 2' and the electrode 4 on the active surface side, and this serves as a support substrate (sound absorber). It is glued on top of 1. The active surface side electrode 4 is usually provided on the polymer piezoelectric film 3 using a method such as vapor deposition, sputtering, plating, etc., or the piezoelectric film 3 is placed on the supporting substrate 1. Or after gluing onto 2, it is provided by the same means as above.
To connect to the power supply, connect the lead wire with electrode 4 using conductive paste.
This is done by connecting to.

However, the transducer with the above structure is
It cannot be put to practical use due to the following major drawbacks. That is, for example, transducers used for ultrasonic flaw detection and ultrasonic diagnosis are often used underwater, so the electrode 4 on the operating surface side may deteriorate due to water or oxygen, and mechanical friction may occur. Furthermore, since the polymer piezoelectric film on which the active surface side electrode 4 is formed has no heat resistance, the electrode and the power supply circuit system, or the electrode and the reception/amplification circuit It is generally difficult to establish electrical continuity with the system by soldering, and therefore, the adhesive strength between the electrode and the lead wire is weak.

The present inventors have developed an ultrasonic transducer to solve the above-mentioned drawbacks by using a polymer film having a certain thickness in contact with an electrode in order to control the resonance frequency of a polymer piezoelectric material. This addition was already disclosed in Japanese Patent Application No. 55-15860, and a practical ultrasonic transducer as shown in FIG. 2 was exemplified.

That is, the transducer of FIG.
The transducer shown in the figure is improved in the following points.

(i) By providing the surface additional film 5, the active surface side electrode 4 deposited on the surface of the polymer piezoelectric film 3 is protected, and its durability against water and friction is improved.

(ii) By providing the surface additional film 5, the active surface side electrode 4 is insulated from the outside (this is important for ultrasonic diagnostic applications where safety is strongly required).

(iii) The metal case 6 is the piezoelectric film 3 on which the electrode 4 is deposited
to prevent the piezoelectric film from peeling off from the support substrate 1, and to contact the electrode 4 over a wide area (if necessary, use a conductive adhesive or flexible metal foil (Sn, In, etc.) between 4 and 6. ), a stable electrical connection can be achieved.

(iv) By providing an insulating case 7, electrical insulation from the outside has been achieved completely.

(v) By using an appropriate auxiliary jig, the supporting substrate 1, the back electrode 2, the polymer piezoelectric film 1 on which the active surface side electrode 4 is vapor-deposited, the surface additional film 5, the metal case 6, and The plastic case 7 can be bonded in sequence, and the process of assembling and manufacturing the transducer can be simplified.

etc.

However, the biggest drawback of the conventional ultrasonic transducer disclosed above is that the active surface side electrode 4 is provided on the polymer piezoelectric film 3 in advance, so the limited amount of the polymer piezoelectric film 3 is 3. For example, the selection of preferred combinations of fluorine-based polymers and electrodes from the viewpoint of adhesion strength is limited, and the adhesion strength remains low. Therefore, after depositing the electrode 4 on the surface of the piezoelectric film, if the piezoelectric film 3 is pre-cleaned, the electrode 4 may peel off, or if the polymer piezoelectric film 3 is bent at an appropriate curvature as necessary during assembly, the electrode 4 may peel off. 4 peeling often occurs.

Furthermore, due to the application of high temperature and high pressure conditions during the poling process, the electrodes 4 deposited on the surface in advance may be destroyed, or after assembly, the bonded portion via the silver paste may be damaged. Peeling from the edges of the metal case may occur, etc.
Since the electrode 4 was previously provided on the polymeric piezoelectric film 3, it had various drawbacks.

The present invention has been made to eliminate these drawbacks and is constructed as follows. That is,
In an ultrasonic transducer in which a piezoelectric film or plate, an electrode on the active side of this film or plate, and a surface-added film are laminated in this order, the active-side electrode is placed on the surface-added film. An ultrasonic transducer structure which is preformed and then bonded to the piezoelectric membrane or plate.

Next, the present invention will be explained in more detail using FIG. In FIG. 3, the method of adhering the active surface side electrode 4' to the surface additional film 5 used in the present invention is as follows.
General methods known in the art are used.
In other words, the methods include vapor deposition, sputtering, CVD, electrolytic plating, chemical plating, coating, etc., and the types of electrodes include Al, Cu, Au, Ag, In,
It may be a metal such as Cr, Co, Ni, Pt, Sn, or any alloy thereof, or a conductive paint such as silver paste. Alternatively, it may be a metal foil.

Further, as the material for the surface additional film 5, any material can be used as long as the active surface side electrode 4' is firmly attached, but generally heat-resistant polymers such as polyester, aromatic polyamide, polyimide, etc.
Polyphenylene, polyethylene, polypropylene, etc. can be selected depending on the purpose.

In this example, the case where the transducer is made of one element has been described, but it goes without saying that the present invention can also be applied to a transducer made of multiple elements (for example, a linear array, an annular array, etc.).

In addition, according to the structure of the present invention, since the conductive thin film formed in advance on the surface addition film 5 acts as an electrode on the operating surface side of the piezoelectric film, in some cases, the piezoelectric film may be removed during poling as shown in FIG. The electrode 4 attached thereto may be omitted.

The effects obtained by the present invention in which the active surface side electrode 4' is previously provided on the inner surface of the surface-added film are as follows.

(1) The surface additional film 5 is a piezoelectric film 3 whose object is limited.
Unlike the above, it is possible to select from among many types according to the application, and a combination of the active surface side electrode 4' and the surface additional film 5 with strong adhesion strength can be arbitrarily selected. Strong adhesion strength means that
This means that in the present invention, the peeling of the electrodes that occurs in the conventional transducer described above, especially during assembly, does not occur, and in fact, since there is no peeling of the electrodes 4', handling becomes easier. , the assembly and manufacturing process of the transducer can be extremely simplified.

(2) When a heat-resistant surface-added film such as polyester or polyimide is used, soldering can be performed between the active surface side electrode 4' on the surface-added film and the metal case or other conductor. This makes the electrical connection highly reliable and contributes to improving water resistance, chemical resistance, etc.
That is, according to this aspect of the present invention, the electrode 4 is eroded due to water (or chemicals) entering from the bonded portion between the metal case 6 and the surface-added film 5, and the conduction does not work sufficiently, resulting in a decrease in function. The drawbacks of conventional ultrasonic transducer structures can be covered.

(3) Since the conductive thin film that becomes the electrode on the active side is adhered to the piezoelectrically inactive surface-added film,
For example, etching processing of the conductive thin film on the surface-added film becomes possible, and conductive thin films having various pattern shapes depending on the purpose can be created.

(4) The size of the surface additional film 5 and the active surface side electrode 4' formed on the film is the same as that of the conductive metal case 6.
Since the electrical connection can be selected as arbitrarily as possible in relation to the location of the electrical connection, there is a degree of freedom in the contact point, which is advantageous in manufacturing the transducer.

Further, if necessary, a part of the surface additional film 5 to which the operating surface side electrode 4' is adhered can be used as a flexible conductive cable. In this case, even if the wiring is complicated, wiring work becomes easy and , compactness can be achieved.

(5) In the case of a conventional ultrasonic transducer structure in which electrical contact is made on the thin film electrode 4 attached to the piezoelectric film, the piezoelectric film is connected to the electrical contact point, that is, the metal case. However, in the present invention, this is not necessary and the piezoelectric film can be limited to the minimum necessary size. Therefore, the number of processing steps such as bending the piezoelectric film is reduced, resulting in a highly reliable transducer.

As described above, the electrode formation according to the present invention not only helps improve the stability, reliability, and lifespan of the transducer, but also reduces limitations on the structure of the transducer, allowing transducers of various structures and shapes to be used. This makes it easy to manufacture.

Although the present invention has been described with respect to the case where a polymeric piezoelectric film is used as a vibrator, the present technology can generally be applied to a transducer that uses an inorganic piezoelectric material as a vibrator.

[Brief explanation of the drawing]

Fig. 1 shows an example of the basic structure of a conventional ultrasonic transducer using a polymer piezoelectric film, and Fig. 2 shows an improvement on Fig. a diagram showing an ultrasound transducer;
FIG. 3 is a diagram showing the structure of an ultrasonic transducer according to the present invention. Explanation of symbols: 1: Support substrate, 2, 2': Back side electrode, 3: Polymer piezoelectric film, 4, 4': Operating side electrode, 5: Surface protective film, 6: Metal case, 7: Plastic case , 8: Conductor.

Claims (1)

[Claims] 1. In an ultrasonic transducer in which a piezoelectric film or plate, an electrode on the active side of this film or plate, and a surface-added film are laminated in this order, the electrode on the active side is laminated on the surface-added film. an ultrasonic transducer structure formed by forming the electrode in advance and then bonding the electrode and the piezoelectric film or plate.