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DESCRIPTION JP2001102651

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DESCRIPTION JP2001102651
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
piezoelectric element and an ultrasonic oscillator, and more particularly to a piezoelectric
element using a piezoelectric single crystal and an ultrasonic oscillator suitable for an ultrasonic
probe using the piezoelectric element. .
[0002]
2. Description of the Related Art In general, a lead zirconate titanate (PZT) -based piezoelectric
ceramic material having an electromechanical coupling coefficient k33 of about 70% is used as
an ultrasonic probe of a medical ultrasonic diagnostic apparatus.
[0003]
In general, in an ultrasonic probe of a medical ultrasonic diagnostic apparatus, a piezoelectric
element having a pair of electrodes formed on such a piezoelectric ceramic material is formed in
a strip shape, and a plurality of strip-shaped piezoelectric elements are prepared. They are
arranged in an array, electronically controlled ultrasonic electron beams, and acquired in real
time high-resolution tomograms.
[0004]
Here, FIG. 6 shows a cross-sectional view of the array type ultrasonic probe as viewed from the
array direction of the array.
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[0005]
The ultrasonic probe forms a piezoelectric element in which a piezoelectric material 62 is
sandwiched between a pair of electrodes consisting of a lower electrode 63 and an upper
electrode 64 on the surface of a substrate 61 such as a backing material, and an acoustic
matching layer on the piezoelectric element. 65 and an acoustic lens 66 are formed.
Further, a flexible printed circuit 68 (FPC) is joined to the pair of electrodes 63 and 64 using a
solder 67 or the like.
[0006]
In such an ultrasonic probe, when all of the piezoelectric material 62 is polarized to have
piezoelectric characteristics, the piezoelectric characteristics are not symmetrical at the junction
due to the influence of the solder and the conductive layer.
[0007]
Therefore, conventionally, the lower electrode 63 is not formed on the entire lower surface of the
piezoelectric material but only in the central portion, and an end electrode 63 'not electrically
connected to the lower electrode is separately formed. To produce a piezoelectric element in
which only the central portion (hatched portion in the piezoelectric material 62) functions as a
vibrator without making the end of the piezoelectric element function as a vibrator, and this
polarized piezoelectric element Was formed on the backing material 61 to produce an ultrasonic
probe.
That is, by doing this, the amount of adhesion of the conductive layer, the solder and the like is
reduced in the portion functioning as the vibrator, and the symmetry of the sound field is
maintained.
[0008]
On the other hand, a piezoelectric single crystal using Pb ((Zn1 / 3Nb2 / 3) 0.91Ti0.09) 3 which
is a solid solution of lead zinc niobate and lead titanate as a piezoelectric material has a large
electromechanical coupling coefficient and is very It is a material that is excellent in efficiency,
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and is expected to improve the characteristics of ultrasonic probes.
[0009]
Since this piezoelectric single crystal has a low Curie point, it is depolarized by soldering or heat
generated when the piezoelectric element is cut into an array.
Therefore, it is necessary to repolarize after incorporating the piezoelectric element in the
ultrasonic probe.
[0010]
However, in an ultrasonic oscillator such as a conventional ultrasonic probe, it is difficult to
polarize only the central portion of the piezoelectric element after assembly, and even the
soldered portion or the conductive layer portion is polarized, and as a vibrator There is a
problem in that it functions and loses the symmetry of the sound field generated by the strip-like
piezoelectric element.
[0011]
In addition, since the piezoelectric single crystal has lower mechanical strength than the
piezoelectric ceramic, it causes cracks due to heat shock due to local heating by soldering, and
along the backing material side of the FPC before array processing When bending is carried out
substantially at a right angle, pressure is applied to the end of the soldered vibrator to cause a
crack in the area to which the FPC is soldered.
When the electrodes of the vibrator are divided due to these cracks, there is a problem that the
disconnection failure occurs and the yield of the probe is lowered.
[0012]
As described above, in an ultrasonic oscillator such as an ultrasonic probe, a conductive layer to
be bonded to a piezoelectric element or a solder for bonding when the piezoelectric element to
be used is repolarized. The problem of the problem that the symmetry of the sound field can not
be obtained has arisen by
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[0013]
In addition, in the joint between the piezoelectric element and the conductive layer, there is a
problem that a crack is generated in the piezoelectric material due to heat shock at the time of
soldering, processing of the conductive layer, or the like.
[0014]
The present invention has been made in view of such problems, and it is an object of the present
invention to provide a piezoelectric element and an ultrasonic oscillator that can maintain the
symmetry of the sound field even after repolarization.
Alternatively, it is an object of the present invention to provide a piezoelectric element and an
ultrasonic oscillator that reduce the occurrence of a crack at the joint between the piezoelectric
element and the conductive layer.
[0015]
The present invention will be described below.
[0016]
According to a first aspect of the invention, there is provided a reinforcement comprising a first
electrode, a piezoelectric material disposed on the first electrode, and a material different from
the piezoelectric material juxtaposed to the piezoelectric material on the first electrode. It is a
piezoelectric element characterized by having a material and a counter electrode formed on the
above-mentioned piezoelectric material.
[0017]
That is, since the lead wire for applying a voltage can be joined on the reinforcing material
through the electrode, there is no need to dispose a bonding material such as solder or a lead
wire right above the piezoelectric material, and the bonding material or lead wire is used. The
change in vibration of the piezoelectric element is suppressed, and the symmetry of the
ultrasonic wave formed by the ultrasonic wave generated from the piezoelectric element is
improved.
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[0018]
Moreover, since it is not necessary to form an end electrode etc. separately from the said
electrode, a structure is simplified and a manufacturing process can also be simplified.
[0019]
In addition, by providing a reinforcing material at the end of the piezoelectric element, it is
possible to reduce the occurrence of cracks in the piezoelectric single crystal at the end of the
piezoelectric element at which cracks easily occur during processing of the lead wire or the
piezoelectric element. .
[0020]
Further, a piezoelectric single crystal can be used as the piezoelectric material.
[0021]
The piezoelectric single crystal has good piezoelectric characteristics, but on the other hand, it is
a material that is easily depolarized by heating such as soldering, so it is necessary to repolarize
after solder bonding.
According to the piezoelectric element of the present invention, since no bonding material such
as solder adheres to the vibrating portion of the piezoelectric element even when repolarization
is performed, the symmetry of the ultrasonic wave generated from the piezoelectric vibrator is
good. Can be maintained.
[0022]
Preferably, the reinforcing material is a non-piezoelectric material.
[0023]
If the reinforcing material is different from the piezoelectric material in resonance frequency, the
above-mentioned effects can be obtained, but in order to suppress the vibration due to the
reinforcing material more reliably, the reinforcing material should be selected from materials
having no piezoelectric property. Is desirable.
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[0024]
Further, according to the present invention, the main surface of the piezoelectric material portion
is fixed to at least a part of a plate-like or rod-like piezoelectric material portion having at least
two main surfaces oscillating ultrasonic waves, and the side edge of the piezoelectric material
portion. A non-piezoelectric material portion having a common surface with the conductor
portion, which is formed from the piezoelectric material portion to the non-piezoelectric material
portion along the two main surfaces and serves as an electrode for applying a voltage across the
piezoelectric material portion It is a piezoelectric element characterized by having.
[0025]
A second invention comprises a substrate, a first electrode, a piezoelectric material disposed on
the first electrode, and a material different from the piezoelectric material juxtaposed to the
piezoelectric material on the first electrode. It has a reinforcing material, the piezoelectric
material, and a counter electrode formed on the surface of the reinforcing material, and includes
a piezoelectric element formed on the substrate and an acoustic lens formed on the piezoelectric
element. Is an ultrasonic oscillator.
[0026]
That is, the piezoelectric element of the first aspect of the invention is particularly effective for an
ultrasonic wave generator that focuses ultrasonic waves generated from the piezoelectric
element using an acoustic lens.
Furthermore, it is suitably used for an ultrasonic probe that oscillates and receives ultrasonic
waves.
[0027]
The ultrasonic oscillator has a lead wire having one end connected to the drive circuit and the
other end joined to the reinforcing material via the first electrode or the counter electrode, and
the piezoelectric material via the lead wire. By applying a predetermined voltage, the
piezoelectric material can be polarized, the piezoelectric element can be vibrated, and an
ultrasonic wave can be oscillated.
[0028]
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According to a third aspect of the present invention, there is provided a step of forming a pair of
electrodes sandwiching a piezoelectric material and a reinforcing material provided adjacent to
the piezoelectric material, a step of bonding a lead wire to the pair of electrodes on the
reinforcing material, and And D. applying a predetermined electric field between the pair of
electrodes to polarize the piezoelectric material.
[0029]
DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 is a plan view
showing an example of a method of manufacturing a piezoelectric element according to the
present invention.
[0030]
Reinforcing materials 2 are disposed at both ends of the piezoelectric single crystal 1, and they
are joined via an adhesive (not shown) (FIG. 1a).
Furthermore, on both main surfaces of the piezoelectric single crystal 1 and the connected
reinforcing material 2, electrodes 6 and 7 made of a conductive layer are formed to form a
piezoelectric element (FIG. 1b).
[0031]
The piezoelectric element is cut to a desired width to form an array of a plurality of strip-shaped
piezoelectric elements (FIG. 1c).
[0032]
The piezoelectric material is not particularly limited as long as it is a piezoelectric material in the
present invention, but it is desirable to use a large piezoelectric single crystal of k33.
The piezoelectric single crystal is not particularly limited as long as it is a single crystal used as a
piezoelectric element.
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For example, a composite perovskite-type piezoelectric single crystal composed of a solid
solution of lead (zinc niobate) and lead titanate such as Pb ((Zn1 / 3Nb2 / 3) 0.91Ti0.09) 3, and
lead magnesium niobate and lead titanate And a single crystal composed of a solid solution of
lead scandium niobate and lead titanate.
[0033]
Further, as the adhesive, it is desirable to select a material that can withstand a high temperature
of about 200 ° C. when soldering a lead such as a FPC (flexible printed circuit) and the electrode
6 or 7, for example, an epoxy for high temperature It is desirable to use an adhesive or sealing
glass.
[0034]
Further, as the reinforcing material 2 according to the present invention, it is desirable to use one
having the same thickness as the piezoelectric single crystal 1 from the viewpoint of adaptability
to a manufacturing surface or an ultrasonic oscillator or the like.
[0035]
Further, the reinforcing material 2 supports an electrode to be described later, as long as the
material does not resonate at the resonance frequency of the piezoelectric single crystal 1, that
is, it is particularly limited as long as it is a member different from the piezoelectric single crystal.
It can be used without
However, in order to reliably suppress the vibration of the reinforcing member 2, it is desirable
to use a material other than the piezoelectric material.
It is also desirable to select a material that can withstand the soldering temperature as well as the
adhesive.
Specifically, for example, ceramics such as alumina, glass or epoxy resin for high temperature
may be mentioned.
[0036]
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Further, as the reinforcing material 2, it is desirable to use a machinable ceramic material such as
Macor (manufactured by Ishihara Pharmaceutical Co., Ltd.) or Macerite (manufactured by Mitsui
Mining & Materials Co., Ltd.).
When cutting piezoelectric elements into an array, a dicer etc. is used, but since a piezoelectric
single crystal etc. starts cutting and cracks are likely to occur at the end of cutting, machining is
performed by placing a machinable ceramic at the end. It is possible to reduce the occurrence of
cracks at the time of
[0037]
The electrode according to the present invention is not particularly limited as long as it is a
conductive material, but it is desirable to form a metal layer containing copper or nickel as a
main component and having good solderability.
In addition, a Ti layer can be formed as a base layer, or a surface layer of gold or the like can be
formed as an oxidation preventing layer, in consideration of the adhesion to the piezoelectric
body.
[0038]
When applying a voltage with a predetermined potential difference between both electrodes 6
and 7 of this piezoelectric element, the piezoelectric material is made by connecting a terminal
only with solder or the like on the reinforcing material via the electrodes 6 and 7. Polarize.
In the element obtained in this manner, the vibration part has a uniform configuration, and the
sound field emitted from each piezoelectric element has good symmetry.
[0039]
Second Embodiment FIG. 2 shows a plan view of a piezoelectric element for explaining a second
embodiment.
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[0040]
In the first embodiment, the reinforcing material is formed only at both ends of the piezoelectric
single crystal, but in the present embodiment, the reinforcing material 2 is formed on all four
sides surrounding the piezoelectric single crystal 1.
As in the first embodiment, this piezoelectric element is obtained by forming electrodes on both
sides of the piezoelectric element 8 (not shown).
[0041]
Further, the flexible substrate 9 and the FPC 11 in which the lead wiring composed of the
conductive layer 10 is formed are joined to the electrodes of the piezoelectric element 8 (the FPC
is also joined to the lower surface side of the piezoelectric element). , Omitted in FIG.
Then, the piezoelectric element 8 is cut at the position indicated by the dotted line to form an
array of piezoelectric elements.
[0042]
In general, when producing an ultrasonic probe, the piezoelectric element 11 prepares a
transducer larger than the width W used as a probe, and uses the region protruding on both
sides than the width W for fixing at the time of processing, etc. It is a useless area that is cut off
during array processing and discarded when used as a probe.
In the case of a piezoelectric single crystal, it is difficult to grow a single crystal to a large size,
and as the size of the vibrator increases, the mass productivity decreases.
[0043]
Therefore, as shown in FIG. 2, by forming the reinforcing material 2 on all four sides surrounding
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the piezoelectric single crystal 1, it is possible to miniaturize the piezoelectric single crystal to be
used, and thus to improve its productivity. Is possible.
[0044]
Third Embodiment FIG. 3 shows a cross-sectional view of an ultrasonic oscillator according to the
present invention in which an FPC is connected to a piezoelectric element.
[0045]
A piezoelectric element as shown in FIG. 1 (b) was polarized once on the surface of the backing
material 3, and FPCs were soldered to the electrodes 6, 7, respectively.
At this time, solder bonding was performed so as to be formed on the reinforcing material so as
not to protrude onto the piezoelectric single crystal 1.
[0046]
Furthermore, after providing acoustic matching layers 4 and 4 'on the surface of the electrode 6,
as shown in FIG. 1C, the piezoelectric elements were divided together with the FPC and the
acoustic matching layer, and processed into an array.
[0047]
Thereafter, the FPC was bent along the backing material, but no cracks were observed in the
piezoelectric single crystal 1 or the electrode bonding support.
[0048]
Furthermore, a silicon adhesive was filled and fixed between the arrayed piezoelectric single
crystals, and then an acoustic lens 12 made of silicon was formed on the surface of the acoustic
matching layer.
[0049]
After producing the ultrasonic oscillator in this manner, an electric field of 1 kV / mm was
applied from the end terminal of the FPC to repolarize the piezoelectric element in the normal
temperature atmosphere.
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[0050]
In the ultrasonic oscillator thus obtained, since the piezoelectric single crystal is not present at
the end heated by the solder joint, the reinforcing material is not polarized at the time of
repolarization, and does not vibrate at the time of driving the ultrasonic oscillator.
Therefore, it becomes possible to transmit the ultrasonic wave which maintained symmetry.
[0051]
Further, by providing the reinforcing material at the end of the piezoelectric element in this way,
it is not necessary to provide an end electrode separately from the electrode formed on the
vibrating surface of the piezoelectric element, so the configuration of the ultrasonic oscillator can
be simplified. The manufacturing process can also be simplified.
[0052]
Using this ultrasonic oscillator as an ultrasonic probe, ultrasonic waves were transmitted and
received, and the sound field generated by this ultrasonic oscillator was measured, but it showed
a symmetrical sound field without disturbance.
In addition, there were no breaks due to cracks.
[0053]
Comparative Example An ultrasonic oscillator was manufactured in the same manner as the
second embodiment except that a piezoelectric element in which an electrode was formed on the
entire main surface of a piezoelectric single crystal was used without using an electrode bonding
member.
[0054]
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In this ultrasonic oscillator, about 20% of cracks occurred at the time of soldering of the FPC.
Furthermore, the crack was further added to about 30% at the time of FPC bending.
[0055]
Moreover, although the ultrasonic oscillator was driven using the piezoelectric element which the
crack did not generate | occur | produce, the obtained sound field was a thing without symmetry.
[0056]
Fourth Embodiment FIG. 4 is a schematic sectional view using an ultrasonic oscillator as an
ultrasonic probe, and FIG. 4 (a) is a sectional view in the array direction of the array, and FIG. 4
(b) is a sectional view. It is sectional drawing of the orthogonal direction of (a).
[0057]
In FIG. 4, the FPC shown in FIG. 4 is bent to the backing material side, and the ultrasonic
oscillator shown in FIG.
The FPC is fixed by an adhesive 14, and the ultrasonic oscillator and the case 13 are fixed by this
adhesive (the explanation of the reference numerals overlapping those in FIG. 2 is omitted).
[0058]
Further, in the present embodiment, the reinforcing material at the end in the array direction is
left in the probe using the piezoelectric element shown in FIG.
[0059]
Usually, as shown in FIG. 4, an ultrasonic oscillator is housed in case 13 and used.
[0060]
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The ultrasonic waves generated from the ultrasonic generator mainly travel in the lens direction,
but a part is reflected by the case 13.
In the ultrasonic probe, since the piezoelectric element receives the ultrasonic wave reflected by
the object to be measured which has passed through the lens, the piezoelectric element receives
the ultrasonic wave reflected by the case 13 as noise.
[0061]
According to the present invention, since the reinforcing material is present at the end of the
piezoelectric element, the distance between the piezoelectric element and the case is expanded,
so that it is possible to reduce the reflected wave by the case 13 received by the piezoelectric
element. Become.
[0062]
Moreover, FIG. 6 is a modification of the ultrasonic oscillator of this invention.
[0063]
In FIG. 6, the lead wiring 10 is disposed not only on the reinforcing member 2 but also on the
piezoelectric material 1.
Since the connecting portion between the piezoelectric material 1 and the reinforcing member 2
is likely to have a step, in the thin film in which the electrodes 6 and 7 are formed by sputtering
or the like, disconnection is likely to occur at this connecting portion. The connection to the
upper side can prevent the disconnection of the connection portion.
[0064]
According to the present invention, the piezoelectric material is not disposed at the position
corresponding to the bonding portion between the piezoelectric element and the lead wire, so
that the bonding portion can be driven as a vibrator even if the piezoelectric element is
repolarized. As a result, it becomes possible to generate an ultrasonic wave with good symmetry
from the piezoelectric element.
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[0065]
Another effect is that it is possible to reduce the occurrence of cracks at the end of the
piezoelectric element when processing the piezoelectric element or processing a lead wire
bonded to the piezoelectric element.
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