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DESCRIPTION JP2001298796

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DESCRIPTION JP2001298796
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
composite piezoelectric transducer plate useful for producing an ultrasonic probe and a method
for producing the same.
[0002]
2. Description of the Related Art A composite piezoelectric material used in the preparation of a
composite piezoelectric transducer plate comprises a piezoelectric ceramic having a high
electromechanical coupling coefficient and a polymer material having a low acoustic impedance,
and the composite piezoelectric transducer plate is Electrodes are formed on upper and lower
surfaces of a composite piezoelectric body, and the composite piezoelectric body is manufactured
by polarization.
[0003]
This type of composite piezoelectric oscillator plate has a high electromechanical coupling
coefficient because it is a composite of the piezoelectric ceramic having a high electromechanical
coupling coefficient as described above and a polymer material having a low acoustic impedance.
And, as a piezoelectric transducer plate having a low acoustic impedance, it has been found to be
very useful in the production of an ultrasonic probe.
[0004]
As shown in FIGS. 4 and 5, an ultrasonic probe using the above composite piezoelectric vibrator
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plate converts the electric pulse into an ultrasonic wave and converts the ultrasonic pulse into an
electric signal. A plate 1, an acoustic matching layer 8 for efficiently emitting a short waveform
ultrasonic wave to a human body, a packing material 7 for acoustically damping the back surface
of the composite piezoelectric vibrator plate 1, an ultrasonic wave An acoustic lens 9 or the like
for converging a beam is configured as a main component.
[0005]
That is, as shown in FIG. 4, in the ultrasonic probe, the ground lead frame 5 and the signal lead
are formed on the electrode 3 of the composite piezoelectric vibrator plate 1 formed by forming
the electrodes 3 on the upper and lower surfaces of the composite piezoelectric body 2. The
frame 6 is bonded by the bonding material 4, and electrical conduction is established between
one electrode 3 and the ground lead frame 5 and between the other electrode 3 and the signal
lead frame 6. In addition, as shown in FIG. 5, the one with the acoustic matching layer 8 adhered
to the electrode 3 on the upper surface is sliced at a constant width and manufactured by
attaching the acoustic lens 9 on the entire top of them. .
However, in FIG. 5, illustration of the bonding material 4 is omitted in order to avoid
complication.
[0006]
However, although the composite piezoelectric vibrator plate has the above-mentioned excellent
properties, it has a matrix structure with a polymer material, so it has poor heat resistance and
has a property of being soft and easily deformed. Therefore, there was a problem as shown below
in the case of the assembly to the ultrasonic probe manufactured by requiring the above
complicated processes.
[0007]
The electrodes of the composite piezoelectric vibrator plate are formed of gold or the like by a
sputtering method that is relatively resistant to heat, and generally has a structure as shown in
FIG.
That is, as shown in FIG. 1, the composite piezoelectric body is composed of a composite of the
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piezoelectric ceramic 2a and the polymer material 2b, and as shown in FIG. 2, the electrode 3 is
the piezoelectric ceramic 2a of the composite piezoelectric body 2. In both the part of and the
part of the polymer material 2b, metal layers of the same material are used.
[0008]
However, in the electrode formation by the sputtering method as described above, since the
adhesion strength between the electrode 3 and the piezoelectric ceramic 2a or the polymer
material 2b is weak, the electrode is peeled off during the process of assembling the ultrasonic
probe, and finally the slice is sliced. The electrodes of each cut unit may be interrupted, and a
unit having an electrode of a predetermined area can not be obtained.
[0009]
With regard to the polymer part of the composite piezoelectric vibrator plate, there is no
functional problem as long as it is connected in parallel to the slice direction, but if the electrode
on the piezoelectric ceramic surface is peeled off, peeling is only partial. However, since the main
source of piezoelectric characteristics is ceramics, it causes a major problem in function.
[0010]
In particular, since the lead-out portion of the electrode is at the end, if the electrode peels off at
a length greater than the slice width at right angles to the slice direction, such peeling may occur
at a portion near the lead-out portion The unit will not perform any function at all.
[0011]
In order to minimize the loss of the high electromechanical coupling coefficient of the
piezoelectric ceramic, it is preferable that the hardness of the polymer used be as low as possible.
Also, depending on the application, it may be desirable to arrange the composite piezoelectric
oscillator plate on a curved surface, so it is preferable in terms of performance or function that
the composite piezoelectric body itself is soft, but the electrodes are simple because of the
softness of conventional electrodes. (Ie, when the composite piezoelectric body is bent and
deformed, the electrode can not follow the deformation, and the electrode may be peeled or
broken).
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[0012]
In the case of the sputtering method, it is likely that shadows are easily generated during
sputtering. This is probably because the thickness of the electrode is partially reduced, or the
piezoelectric ceramic portion is hard and the polymer material portion is soft. The abovementioned peeling of the electrode and the like particularly frequently occur at the boundary
between the polymer and the polymer material.
[0013]
As a countermeasure for the above problems, it is conceivable to make the thickness of the
electrode thicker than necessary by prolonging the sputtering time, but this is expensive and not
practical.
[0014]
SUMMARY OF THE INVENTION The present invention solves the problems of the prior art as
described above, and even if it is made of a soft composite piezoelectric material, it has excellent
adhesion to electrodes and is equivalent to the prior art. An object of the present invention is to
provide a composite piezoelectric vibrator plate having an electromechanical coupling coefficient
and capable of manufacturing an ultrasonic probe more reliably and more reliably.
[0015]
According to one aspect of the present invention, there is provided a composite piezoelectric
body of a piezoelectric ceramic and a polymer material, and electrodes formed on the upper and
lower surfaces thereof. A composite piezoelectric vibrator plate comprising the electrode is
characterized by comprising a gold layer or a copper layer formed by electroless plating.
[0016]
Another subject matter of the present invention is, as set forth in claim 3, a composite
piezoelectric vibrator comprising a composite piezoelectric material of a piezoelectric ceramic
and a polymer material, and electrodes formed on the upper and lower surfaces thereof. In the
plate, at least one of the electrodes is a nickel layer formed by electroless plating on the surface
of the piezoelectric ceramic portion and a gold layer or a copper layer formed directly on the
nickel layer or through the nickel-chromium layer. And, on the surface of the polymer part, it is
characterized in that it is composed of a gold layer or a copper layer or a gold layer or copper
layer formed via a nickel-chromium layer. According to the fifth aspect of the present invention,
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the composite piezoelectric vibrator plate is formed by: forming a nickel layer on the
piezoelectric ceramic by electroless plating of nickel; A second step of forming a composite with
a child material, and forming a gold layer or a copper layer directly or through a nickelchromium layer on the composite piezoelectric body of the piezoelectric ceramic and the
polymer material obtained in the second step It is a method of manufacturing through three
steps.
In the latter case of the composite piezoelectric vibrator plate in which the configuration of the
electrode is changed between the piezoelectric ceramic portion and the polymer portion, for
example, as shown in FIG. 3, the electrode 3 is formed by electroless plating on the surface of the
piezoelectric ceramic 2a portion And the gold layer or copper layer 3b formed on the nickel layer
3a, and only the gold layer or copper layer 3b on the surface of the polymer material 2b.
[0017]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention,
piezoelectric ceramics include lead zirconate titanate (PZT), barium titanate (BT), lead titanate
(PT) and bismuth titanate (BIT). However, lead zirconate titanate piezoelectric ceramics are
particularly preferable in that they have higher electromechanical coupling coefficient and
dielectric constant.
[0018]
In the present invention, as the polymer material, for example, polyurethane resin, epoxy resin,
acrylic resin and the like can be used, but particularly when a polymer material having a Shore A
hardness of 70 or less is used, a soft composite piezoelectric material is produced. As such a
polymer material having a Shore A hardness of 70 or less, a silicone rubber-based polymer
material is particularly preferably used.
In addition, a hollow resin bead or the like having a small specific gravity may be added to the
polymer material for the purpose of lowering the acoustic impedance.
The lower the hardness of the polymer material, the more suitable for producing a soft composite
piezoelectric material. However, if the hardness of the polymer material is too low, the composite
piezoelectric material tends to be too soft and the electrode tends to peel off. For this reason, the
hardness of the polymer material is preferably 70 or less and 20 or more in Shore A hardness.
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The Shore A hardness in the present specification is the Shore A hardness defined in JIS K 7215.
[0019]
According to the present invention, even in the case of a composite piezoelectric body
constituted by using the above-mentioned soft polymer material, the piezoelectric properties
inherent to the piezoelectric ceramic are not impaired, and the adhesion of the electrode is
excellent. A composite piezoelectric vibrator plate is obtained.
[0020]
In the present invention, when the electrode is formed of a gold layer or a copper layer formed
by electroless plating, the thickness of the gold layer or the copper layer is preferably 0.2 μm to
3 μm.
By setting the thickness of the gold layer or copper layer to 0.2 μm or more, good adhesion
between the gold layer or copper layer and the piezoelectric ceramic is secured, and by setting
the thickness to 3 μm or less, the electromechanical coupling coefficient is reduced. Can be
prevented.
[0021]
In the present invention, the thickness of the nickel layer formed by electroless plating is
preferably 0.1 μm to 2 μm.
By setting the thickness of the nickel layer to 0.1 μm or more, good adhesion between the nickel
layer and the piezoelectric ceramic can be secured, and by setting the thickness to 2 μm or less,
reduction of the electromechanical coupling coefficient can be prevented. .
[0022]
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The thickness of the gold layer or copper layer formed directly on the nickel layer formed by
electroless plating or via a nickel-chromium layer is preferably 0.1 μm to 3 μm.
By making the thickness of the gold layer or the copper layer within the above thickness range, it
is possible to avoid the cost increase due to the excessive thickness while securing the good
adhesion.
[0023]
In the present invention, at least one of the electrode layers is a nickel layer formed by
electroless plating on the surface of the piezoelectric ceramic portion and a gold layer or a gold
layer formed directly on the nickel layer or via a nickel-chromium layer. A composite
piezoelectric vibrator plate composed of a copper layer and composed of a gold layer or a copper
layer or a gold layer or a copper layer formed via a nickel-chromium layer on the surface of the
polymer part has no electrode. There is some deformation in the composite piezoelectric vibrator
plate at the boundary between the piezoelectric ceramic and the polymer material that is most
likely to cause cutting of the electrode compared to the composite piezoelectric vibrator plate
made of gold layer or copper layer formed by electrolytic plating. When it happens, it has the
characteristic advantage that it is difficult for the electrode to be cut and the adhesion strength
between the electrode and the piezoelectric ceramic is high. When a method for manufacturing a
composite piezoelectric transducer plate to change the configuration of electrodes in the box part
and the polymer material portion is as follows.
[0024]
In order to manufacture the composite piezoelectric vibrator plate, first, in the first step,
electroless plating of nickel is performed on the piezoelectric ceramic to form a nickel layer on
the surface of the piezoelectric ceramic.
Next, as a second step, the piezoelectric ceramic on which the nickel layer is formed by
electroless plating as described above and the polymer material are combined.
Then, as a third step, the nickel layer formed on the surface of the piezoelectric ceramic portion
of the composite piezoelectric body of the piezoelectric ceramic and the polymer material
obtained in the second step and the surface of the polymer layer directly or A gold or copper
layer is formed through the nickel-chromium layer to form an electrode.
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For the formation of the gold layer or the copper layer in the third step, either sputtering or
electroless plating can be employed, but from the viewpoint of cost reduction and better
adhesion than sputtering, no It is preferable to adopt the electrolytic plating method, and in
particular, it is preferable to adopt the electroless plating method of copper.
In that case, in order to improve the corrosion resistance, a gold layer or a silver layer may be
further formed on the copper layer, and the copper layer may be coated with the gold layer or
the silver layer. Electrolytic plating is suitable as a method of forming a gold layer or a silver
layer at that time. In the case where the gold layer or copper layer is formed by electroless
plating in the third step, a nickel layer or polymer formed by electroless plating on the surface of
the piezoelectric ceramic portion without interposing the nickel-chromium layer. When the gold
layer or copper layer is formed by sputtering, a nickel-chromium layer is first formed by
sputtering, and gold is formed via the nickel-chromium layer. The formation of a layer or copper
layer provides higher adhesion than direct gold or copper layer formation by sputtering.
However, a gold layer or a copper layer can also be formed directly on the nickel layer or the
polymer material by sputtering.
[0025]
EXAMPLES The present invention will be described in more detail with reference to the following
examples. However, the present invention is not limited to those examples.
[0026]
Examples 1-1 to 1-7 A lead zirconate titanate piezoelectric ceramic plate having an
electromechanical coupling coefficient k33 of 80% and a thickness of 0.6 mm is 35 μm wide at
intervals of 150 μm in a direction orthogonal to the slice direction by a dicing machine. A
groove was formed. After that, silicone rubber-based polymer material of Shore A hardness 40
with hollow resin beads added is poured into the grooves, and after the polymer material is
cured, grooves with a width of 35 μm at intervals of 150 μm in the slice direction are diced by
a dicing machine It formed. Thereafter, a silicone rubber-based polymer material to which the
hollow resin beads are added is poured into the groove, the polymer material is cured, and
polished to a predetermined thickness to obtain zirconate titanate 150 μm × 150 μm × 370
μm. A composite piezoelectric body having a structure in which a silicone rubber-based polymer
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material is covered with a width of 35 μm around a thin rod of lead-based piezoelectric ceramics
(in this example, a prism, but the shape is not limited) is obtained.
[0027]
Next, after chemically pre-treating the above-mentioned composite piezoelectric material
according to a conventional method, as shown below, electroless plating was carried out while
changing metal species and thickness.
[0028]
Electroless plating treatment of gold: The above composite piezoelectric body is immersed in a
commercially available electroless gold plating solution (manufactured by Uemura Kogyo Co.,
Ltd., GOBEL-2M (trade name)) at a bath temperature of 60 ° C. A gold layer was formed by
electroless plating.
However, the immersion time was variously changed according to the thickness of the gold layer
to be obtained.
[0029]
Electroless plating treatment of copper: The above composite piezoelectric body is immersed in a
commercially available electroless copper plating solution (Sulcup PEA (trade name)
manufactured by Kamimura Kogyo Co., Ltd.) at a bath temperature of 30 to 40 ° C. A copper
layer was formed by electroless plating of copper. However, the immersion time was variously
changed according to the thickness of the copper layer to be obtained.
[0030]
The composite piezoelectric material subjected to the electroless plating process is polished on
the side surface to remove the plated layer on the side surface, leaving only the plated layer on
the upper surface and the lower surface of the composite piezoelectric material, and the DC
voltage is composed of the plated layer A composite piezoelectric vibrator plate was obtained by
applying a voltage between upper and lower electrodes to polarize the composite piezoelectric
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body. The cross section of the main part of this composite piezoelectric vibrator plate is as shown
in FIG. 2. In the composite piezoelectric vibrator plate of this first embodiment series, the
piezoelectric ceramic 2a and the polymer material 2b constituting the composite piezoelectric
body 2 are used. Electrodes 3 made of metal layers of the same material are formed on the
respective surfaces.
[0031]
The resulting composite piezoelectric vibrator plate was pre-soldered at a solder iron tip
temperature of 250 ° C. using solder of # KR-19, 60A (trade name) made by Nippon Arumito,
and then a lead made of solder-plated copper foil Soldered the foil. Then, the lead foil is pulled in
the direction opposite to the drawing direction by 180 °, and the maximum load at that time is
measured with a strength tester (manufactured by Shimadzu Corporation, AGS-500B (trade
name)). The peel resistance was examined. The results are shown in Table 1.
[0032]
The electromechanical coupling coefficient k33 'of the longitudinal vibration of the composite
piezoelectric body is a sample having a size of 10 mm × 60 mm, and the resonance frequency of
the longitudinal vibration is measured by the impedance analyzer 4194A (trade name,
manufactured by Hewlett Packard Co.) The fr and the anti-resonance frequency fa were
measured and calculated from the following formula. k33 '= [(fa−fr) / (0.405 × fr + 0.81 ×
(fa−fr))] 1 / 2
[0033]
The electromechanical coupling coefficient k33 'obtained in this manner is shown in Table 1.
However, when displaying the electromechanical coupling coefficient k33 'in Table 1, it is
simplified and shown only by k33'.
[0034]
Comparative Examples 1-1 to 1-2 After forming a nickel-chromium layer with a thickness of 0.02
μm on a composite piezoelectric body similar to that used in Example 1 by a sputtering method,
the gold layer and the copper layer are respectively separated. Formed by sputtering.
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[0035]
The peel resistance and the electromechanical coupling coefficient k33 'were examined in the
same manner as in Example 1 for the obtained composite piezoelectric vibrator plate.
The results are shown in Table 1 together with the results of Examples 1-1 to 1-7. In addition, in
displaying the electromechanical coupling coefficient k33 'in Table 1 in Table 1, it simplifies and
shows only by k33'.
[0037]
As shown in Table 1, in Examples 1-1 to 1-7, although the electromechanical coupling coefficient
k33 'was equivalent to Comparative Examples 1-1 to 1-2, the peeling resistance of the electrode
The indicated values were much higher than in Comparative Examples 1-2. From these results, it
can be seen that, in the composite piezoelectric electron diaphragms of Examples 1-1 to 1-7 of
the present invention, the adhesion of the electrodes is improved without impairing the
piezoelectric characteristics of the composite piezoelectric material.
[0038]
Examples 2-1 to 2-By applying lead-free zirconate titanate piezoelectric ceramic plate having an
electromechanical coupling coefficient k33 of 80% and a thickness of 0.37 mm by electroless
plating of nickel and controlling the plating time Then, nickel layers of various thicknesses shown
in Table 2 were formed on the surface of a lead zirconate titanate piezoelectric ceramic plate.
[0039]
The above electroless plating treatment of nickel is carried out by chemically pretreating the
above piezoelectric ceramic plate according to a conventional method, and then a commercially
available phosphorus-based nickel plating solution [Nimuden LPX (trade name) manufactured by
Uemura Kogyo Co., Ltd.] The above-mentioned piezoelectric ceramic plate was immersed at a
bath temperature of 90 ° C., and a nickel layer was formed on the surface thereof by electroless
plating of nickel.
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However, the immersion time was variously changed according to the thickness of the nickel
layer to be obtained.
[0040]
Next, using a dicing machine, grooves having a width of 35 μm were formed at intervals of 150
μm in the direction orthogonal to the slice direction in the lead zirconate titanate piezoelectric
ceramic plate on which the above-mentioned nickel layer was formed. After that, a silicone
rubber-based polymer material of Shore A hardness 40 with hollow resin beads added is poured
into the groove, and after the polymer material is cured, grooves 35 μm wide at intervals of 150
μm in the slicing direction are used as dicing machines. It formed. After that, a silicone rubberbased polymer material of Shore A hardness 40 with the same hollow resin beads as above added
to the grooves is poured, and the polymer material is cured to form lead zirconate titanate 150
μm × 150 μm × 370 μm. A composite piezoelectric body having a structure in which a
silicon rubber-based polymer material is covered with a width of 35 μm around a thin rod of a
piezoelectric ceramic and having a nickel layer formed on the upper and lower surfaces of the
piezoelectric ceramic portion was obtained.
[0041]
Next, the composite piezoelectric body is subjected to electroless plating of gold or copper by the
same electroless plating method as in Example 1, and the plating time is adjusted to obtain gold
layers of various thicknesses shown in Table 2. Or formed a copper layer.
[0042]
Then, the side surface is polished to remove the plating layer on the side surface, and a direct
current voltage is applied between the upper and lower electrodes on the upper surface and the
lower surface composed of nickel layer-gold layer and gold layer or nickel layer-copper layer and
copper layer. A composite piezoelectric vibrator plate was obtained by applying and polarizing
the composite piezoelectric body.
[0043]
The peel resistance and the electromechanical coupling coefficient k33 'of the obtained
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composite piezoelectric vibrator plate were examined in the same manner as in Example 1-1.
The results are shown in Table 2.
The cross section of the main part of this composite piezoelectric vibrator plate is as shown in
FIG. 3, and in the composite piezoelectric vibrator plate of this embodiment 2-1 to 2-10, the
portion of the piezoelectric ceramic 2a of the composite piezoelectric body 2 is The electrode 3 is
composed of the nickel layer 3a and the gold layer or copper layer 3b formed on the nickel layer
3a, and the electrode 3 is made of only the gold layer or copper layer in the portion of the
polymer material 2b of the composite piezoelectric body 2. Is configured. In this composite
piezoelectric vibrator plate, the nickel layer 3a is formed on the portion of the piezoelectric
ceramic 2a and then composited with the polymer material 2b to produce the composite
piezoelectric body 2.
[0044]
Examples 2-1 to 2-13 A nickel-chromium layer having a thickness of 0.02 μm was formed on
the above-mentioned nickel layer after carrying out in the same manner as in Example 2-1 until
the formation of nickel layers on the upper and lower surfaces of the composite piezoelectric
material. A composite piezoelectric vibrator is formed in the same manner as in Example 2-1
except that a gold layer or a copper layer is formed on the nickel-chromium layer by sputtering
so as to have various thicknesses shown in Table 2. I got a board. The thickness of the gold layer
or copper layer was adjusted by adjusting the sputtering time.
[0045]
The peel resistance and the electromechanical coupling coefficient k33 'of the obtained
composite piezoelectric vibrator plate were examined in the same manner as in Example 1-1. The
results are shown in Table 2.
[0046]
Comparative Examples 2-1 to 2-2 A composite piezoelectric according to Example 2-1, except
that the lead zirconate titanate piezoelectric ceramic plate similar to Example 2-1 was not
subjected to electroless plating of nickel. A nickel-chromium layer was formed to a thickness of
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0.02 μm on the surface by sputtering, and then a gold layer and a copper layer were separately
formed by sputtering.
[0047]
Thereafter, the plating layer on the side surface was removed and polarized in the same manner
as in Example 2-1 to obtain a composite piezoelectric vibrator plate.
[0048]
The peel resistance and the electromechanical coupling coefficient k33 'of the obtained
composite piezoelectric vibrator plate were examined in the same manner as in Example 1-1.
The results are shown in Table 2.
Note that the electromechanical coupling coefficient k33 'is displayed in Table 2 in a simplified
manner by using only k33'.
[0050]
As shown in Table 2, in Examples 2-1 to 2-13, the electromechanical coupling coefficient k33
'was equivalent to Comparative Examples 2-1 and 2-2, but the peeling resistance of the electrode
The indicated values were much higher than in Comparative Examples 2-1 and 2-2. From these
results, it can be seen that in the composite piezoelectric vibrator plates of Examples 2-1 to 2-13
of the present invention, the adhesion of the electrodes is improved without impairing the
piezoelectric characteristics of the composite piezoelectric body.
[0051]
As described above, according to the present invention, even if it is made of a soft composite
piezoelectric material, the adhesion of the electrode is excellent, and it has an electromechanical
coupling coefficient equivalent to that of the prior art, Provided is a composite piezoelectric
transducer plate capable of manufacturing an ultrasonic probe more reliably and reliably.
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