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DESCRIPTION JP2000125393

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DESCRIPTION JP2000125393
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic transducer used in a medical ultrasonic diagnostic apparatus or an ultrasonic
diagnostic apparatus for nondestructive inspection.
[0002]
2. Description of the Related Art Ultrasonic transducers are, for example, acoustic lenses, acoustic
matching devices, as shown in the "medical handbook" (Nippon Electronic Machinery Industries
Association, Corona, p. 186. 1985. 4.20). The layer, the piezoelectric element (unit element) and
the backing material are integrated. The piezoelectric element is formed of a piezoelectric body
such as a piezoelectric ceramic having electrodes formed on both sides.
[0003]
The ultrasonic transducer having the above configuration is driven as follows. That is, a driving
pulse voltage of about 100 to several hundred volts generated by a pulse generator is applied to
the piezoelectric element to rapidly deform the piezoelectric element by the reverse piezoelectric
effect. The ultrasonic pulse excited by this deformation is emitted to the outside through the
acoustic matching layer and the acoustic lens.
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[0004]
The emitted ultrasonic pulse is reflected at the interface of each tissue in the body in medical
applications, and in non-continuous portions such as flaws inside the object to be measured in
nondestructive testing applications. The reflected ultrasonic pulse reenters the piezoelectric
element through the acoustic lens and the acoustic matching layer, and vibrates the piezoelectric
body. This mechanical vibration is converted into an electrical signal by the piezoelectric effect,
and the electrical signal is sent to the observation device through the electrode. Thus, the
piezoelectric element functions as an electro-mechanical energy converter. In addition, when
transmitting and receiving ultrasonic waves, the free vibration of the piezoelectric element is
restricted by the back load member, so that the resolution in the traveling direction of the
ultrasonic waves is improved.
[0005]
Conventionally, the piezoelectric element and the acoustic matching layer of the ultrasonic
transducer have been bonded by an epoxy resin-based adhesive as disclosed in Japanese Utility
Model Application Publication No. 1-148832.
[0006]
The prior art has the following problems.
First, adhesion at the bonding interface between the piezoelectric element and the acoustic
matching layer, and more specifically, between the front electrode of the piezoelectric element
and the acoustic matching layer was low. The reason for the low adhesion is that the adhesion
between the resin adhesive and the electrode is low because the electrode is made of an
inorganic material such as metal.
[0007]
Due to the low adhesive strength at the bonding interface, peeling may occur at the bonding
interface due to changes with time of the ultrasonic transducer, stress during driving, or changes
due to sudden temperature differences during transport storage, etc. The When peeling or the
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like occurs at the bonding interface, the excited ultrasonic waves are not efficiently transmitted
to the object to be measured, and thus the image quality is deteriorated such as the reduction of
the resolution and the deterioration of the reliability of the image.
[0008]
In addition, since the adhesion at the bonding interface is low, the resistance of the bonding
interface such as chemical resistance and weather resistance is low. Due to the low resistance,
the aging of the ultrasonic transducer has become significant.
[0009]
Second, when ultrasonic waves pass through the bonding interface, diffuse reflection at the
bonding interface is large. Diffuse reflection is large because the acoustic impedance of the
adhesive made of resin and the acoustic impedance of the acoustic matching layer and the
piezoelectric body are largely different. Since the diffuse reflection is large, the sensitivity and the
S / N ratio as an ultrasonic transducer are lowered, and the image quality of the ultrasonic image
is deteriorated.
[0010]
SUMMARY OF THE INVENTION The present invention provides an ultrasonic transducer capable
of improving adhesion and resistance at the interface between a piezoelectric element and an
acoustic matching layer and reducing diffuse reflection of ultrasonic waves. The purpose is
[0011]
In order to solve the above problems, in the present invention, the present invention includes at
least one transducer element, which comprises an acoustic matching layer made of an inorganic
material, a piezoelectric element, and a back load. There is provided an ultrasonic transducer
comprising a material, wherein the acoustic matching layer and the piezoelectric element are
bonded to each other through a bonding layer made of an inorganic conductive material.
[0012]
Furthermore, according to the present invention, the transducer element includes at least one
transducer element, the transducer element comprising an acoustic matching layer made of an
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inorganic material, a piezoelectric element, and a backing material, and the front electrode of the
piezoelectric element is an inorganic conductive material. An ultrasonic transducer is provided,
characterized in that the acoustic matching layer is bonded to the piezoelectric element by the
inorganic conductive material.
[0013]
In the present invention, it is preferable that the inorganic conductive material comprises indium
and at least one element selected from the group consisting of gold, platinum, silver, palladium
and bismuth.
[0014]
DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below with
reference to the drawings.
(I) Structure of Ultrasonic Transducer According to the Present Invention First, the structure of
the ultrasonic transducer according to the present invention will be described.
[0015]
In the ultrasonic transducer according to the present invention, (A) the type in which the acoustic
matching layer and the piezoelectric element are bonded via the bonding layer, and (B) the
acoustic matching layer and the piezoelectric element are not via the bonding layer Includes
types that are bonded to.
[0016]
Each type is described below.
(A) A type of ultrasonic transducer in which an acoustic matching layer and a piezoelectric
element are bonded via a bonding layer is an ultrasonic transducer of at least one transducer
element and, if necessary, ultrasonic transducer elements. It includes an acoustic lens or the like
disposed on the surface.
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[0017]
The transducer element includes an acoustic matching layer made of an inorganic material, a
piezoelectric element, and a backing material. The acoustic matching layer and the piezoelectric
element are bonded to each other through a bonding layer made of an inorganic conductive
material.
The acoustic matching layer, the bonding layer, the piezoelectric element, and the back load
material are stacked, for example, in this order, in the order.
The front surface of the acoustic matching layer is an ultrasonic transmission / reception surface.
[0018]
The number of transducer elements is one or more.
When a plurality of transducer elements are included, these transducer elements are, for
example, linearly arranged in the scanning direction via the insulating layer. The scanning
direction is, for example, the direction in which the drive of the transducer element is scanned in
order to scan the transmission and reception of ultrasound to obtain a real time ultrasound
image.
[0019]
The insulating layer is formed of, for example, an electrically insulating resin. Examples of the
electrically insulating resin include gelled epoxy resins and urethane resins. Moreover, you may
use what mixed the glass balloon with the gel-like epoxy resin as a filler.
[0020]
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The acoustic lens is for focusing the emitted ultrasonic waves, and is formed of an insulator such
as silicone rubber, for example. The acoustic matching layer of the transducer element is for
efficiently transmitting and receiving ultrasonic waves by matching the acoustic impedance
between the object to be measured that is the other of transmitting and receiving ultrasonic
waves and the piezoelectric body described later.
[0021]
The acoustic matching layer may have only one layer or two or more layers. The acoustic
matching layer is formed of an inorganic material. Examples of the inorganic material include
ceramics. The ceramic is preferably a machinable ceramic. By forming the free-cutting ceramic, it
is easy to process the acoustic matching layer into a desired shape.
[0022]
The shape of the piezoelectric element is not particularly limited, and may be rectangular,
circular or the like. Further, by combining the curvature of the piezoelectric element and the
curvature of the acoustic matching layer, a concave or bowl-like ultrasonic transducer element
can be formed.
[0023]
The piezoelectric element includes a piezoelectric body, a front electrode formed on the front
surface of the piezoelectric body, and a back electrode formed on the back surface facing the
front surface. Ultrasonic waves are transmitted and received through the front surface of the
piezoelectric body.
[0024]
Examples of the piezoelectric body include piezoelectric inorganic materials such as piezoelectric
ceramics such as PZT (lead zirconate titanate). Various front and back electrodes are known in
the art and are not particularly limited. For example, a silver (Ag) baked electrode, a silver
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palladium (Ag-Pd) baked electrode, nickel (Ni) or Electrode made of inorganic conductive
material such as electrode by electroless plating of gold (Au), electrode by deposition of gold or
copper (Cu) or platinum (Pt) or chromium (Cr) / silver or copper / chromium / gold or sputtering
or the like Etc. Alternatively, the front and back electrodes may be formed of an inorganic
conductive material used for a bonding layer described later.
[0025]
A voltage for oscillation is applied between the front and back electrodes to oscillate the
piezoelectric body to generate an ultrasonic wave. Also, a voltage signal induced in the
piezoelectric body by the ultrasonic wave reflected from the object to be measured and incident
on the ultrasonic transducer is sent to the external measuring instrument through the front and
back electrodes.
[0026]
The backing material is bonded to the back electrode of the piezoelectric element by an epoxy
resin. The back load member regulates free vibration of the piezoelectric element when the
piezoelectric element transmits and receives ultrasonic waves, and improves the resolution in the
traveling direction of the ultrasonic wave. As a back load material, insulators, such as resin which
mixed tungsten powder or ferrite powder etc., or rubber, etc. are mentioned, for example.
[0027]
The above-mentioned acoustic matching layer and the piezoelectric element are bonded to each
other with good adhesion by the bonding layer. More specifically, the acoustic matching layer
and the front electrode of the piezoelectric element are bonded to each other by the bonding
layer.
[0028]
The bonding layer is formed of an inorganic conductive material. Examples of the inorganic
conductive material include indium-based alloys and silver-based compounds. Examples of the
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indium-based alloy include, for example, indium (In) as a main component to which lead (Pb),
silver (Ag), tin (Sn) or the like is added.
[0029]
Or indium (In) as a main component, to which gold (Au), platinum (Pt), silver (Ag), palladium (Pd),
bismuth (Bi), aluminum (Al), titanium (Ti), nickel ( What added at least 1 sort (s) of element
chosen from the group which consists of Ni) etc. is mentioned.
[0030]
In particular, it is preferable to use indium (In) as a main component and at least one element
selected from the group consisting of gold, platinum, silver, palladium, and bismuth.
That is because the melting point can be adjusted and the durability is improved.
[0031]
Examples of the silver-based compound include paste-like compounds in which silver is a main
component and a glass component such as an oxide of zinc-boron (Zn-B) is mixed therewith. In
addition to this, bismuth for improving wettability with solder, boron for lowering the melting
point, manganese (Mn) for vitrifying, nickel for alloying with silver to reduce solder cracking, etc.
You may add it.
[0032]
The thickness of the bonding layer is preferably as small as possible at least at 1/8 λ or less
with respect to the wavelength λ obtained by dividing (sound velocity determined by the
material) by (frequency of the ultrasonic wave to oscillate). The reason is that when the thickness
of the bonding layer exceeds 1/8 λ, the reflection of ultrasonic waves by the bonding layer
increases, and the smaller the thickness of the bonding layer, the smaller the reflection of
ultrasonic waves by the bonding layer.
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[0033]
In the ultrasonic transducer having the above-described configuration, the ultrasonic wave
emitted from the front surface of the oscillated piezoelectric material is emitted toward the
external object through the bonding layer and the acoustic matching layer (one or more layers).
Be done. Then, a voltage signal induced in the piezoelectric body by the ultrasonic wave reflected
from the object to be measured and incident on the ultrasonic transducer element is sent to the
external measuring instrument through the front electrode and the back electrode. The drive of
each ultrasonic transducer element is scanned in the array direction of the element, so that the
emission of ultrasonic waves is performed while being scanned.
[0034]
In the present invention, the bonding layer is conductive because it is formed of an inorganic
conductive material. Therefore, the bonding layer is electrically connected to the front electrode
of the piezoelectric element, and wiring to the front electrode can be performed by connecting to
the bonding layer.
[0035]
Further, since the bonding layer is made of an inorganic conductive material, adhesion at the
bonding interface between the acoustic matching layer made of inorganic material and the
bonding layer, and at the bonding interface between the front electrode made of inorganic
conductive material and the bonding layer Is high.
[0036]
Due to the high adhesive strength at the bonding interface, it is difficult for peeling to occur at
the bonding interface due to changes with time of the ultrasonic transducer, stress during
driving, or changes due to rapid temperature differences during transport storage .
Since peeling does not easily occur, the ultrasonic wave excited by the piezoelectric element is
efficiently transmitted to the object to be measured.
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[0037]
In addition, since the adhesive strength at the bonding interface is high, the resistance of the
bonding interface such as chemical resistance and weather resistance is high, and the timedependent change of the ultrasonic transducer is reduced. Furthermore, the acoustic impedance
of the bonding layer made of an inorganic conductive material is close to the acoustic impedance
of the acoustic matching layer made of an inorganic material. Therefore, diffuse reflection of
ultrasonic waves is reduced at the interface between the acoustic matching layer and the bonding
layer.
[0038]
In addition, the bonding layer made of an inorganic conductive material has small attenuation of
ultrasonic waves and high sound velocity of ultrasonic waves. Therefore, the thickness of the
bonding layer becomes negligible with respect to the wavelength of the ultrasonic wave, and the
ultrasonic wave is generated at the interface between the acoustic matching layer and the
bonding layer and at the interface between the bonding layer and the piezoelectric material.
Diffuse reflection is reduced.
[0039]
As a result of the reduced diffuse reflection of ultrasonic waves as described above, the
sensitivity and the S / N ratio as an ultrasonic transducer are improved, and the image quality of
the ultrasonic image is improved. In the ultrasonic transducer according to the present invention,
when there are a plurality of ultrasonic transducer elements, the elements are separated from
each other by the insulating layer. Along with each element, an acoustic matching layer having a
large acoustic impedance is also separated from each other by the insulating layer. Therefore,
ultrasonic vibration does not directly propagate through the acoustic matching layer between
adjacent ultrasonic transducer elements. As a result, mechanical crosstalk between adjacent
ultrasonic transducer elements is reduced, the S / N ratio as an ultrasonic transducer is
improved, and the accuracy of ultrasonic images is enhanced.
[0040]
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In addition, since the acoustic matching layer is separated by the insulating layer, the width of
the ultrasonic transmission / reception surface is narrow. Therefore, the directivity of the
ultrasonic wave emitted from the acoustic matching layer is broadened, and the ultrasonic
transducer is an effective ultrasonic transducer for an observation apparatus using a method
such as aperture synthesis.
[0041]
Ultrasonic transducers of this type include, for example, the first to fourth embodiments
described below. Among these, the ultrasonic transducers of the first to third embodiments are
composed of a plurality of ultrasonic transducer elements linearly arranged in the scanning
direction. This type of ultrasound transducer is generally referred to as electronic linear
scanning.
[0042]
The ultrasonic transducer of the fourth embodiment consists of one ultrasonic transducer
element. First Embodiment of the Present Invention FIG. 1 is a schematic perspective view
showing an example of the first embodiment.
[0043]
In the ultrasonic transducer of the first embodiment, a plurality of ultrasonic transducer elements
60 are linearly arranged in the scanning direction via the insulating layer 5. FIG. 2 is a schematic
cross-sectional view along line A-A 'of FIG. 1 to show the cross section of one ultrasonic
transducer element 60. As shown in FIG.
[0044]
In each ultrasonic transducer element 60, an acoustic lens (not shown), an acoustic matching
layer 1, a bonding layer 2 made of the inorganic conductive material of the present invention, a
piezoelectric element 3 and a backing material 4 are stacked in this order Form a structure.
[0045]
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The back load member 4 is a member common to the ultrasonic transducer elements 60.
The back load member 4 has a rectangular parallelepiped shape, and the longitudinal direction of
the rectangular parallelepiped is the scanning direction of the ultrasonic wave. A plurality of sets
of the acoustic matching layer 1, the bonding layer 2 and the piezoelectric element 3 stacked one
on top of the other on the back load material 4 are arranged via the insulating layer 5 in the
longitudinal direction of the rectangular parallelepiped. One ultrasonic transducer element 60 is
constituted by a pair of the acoustic matching layer 1 separated by the insulating layer 5, the
bonding layer 2 and the piezoelectric element 3, and the backing material 4 under the
piezoelectric element 3. .
[0046]
The acoustic matching layer 1 of each ultrasonic transducer element 60 is smaller than the
piezoelectric element, and the lead 7 which is a common electrode is connected to the exposed
bonding layer 2 material by the low temperature solder 14.
[0047]
The conductor 7 is usually a GND (ground) line.
The conducting wire 7 is formed of, for example, copper, phosphor bronze, silver or the like. The
conducting wire 7 is prepared such that the acoustic matching layer 1 of each element 60 is
smaller than the piezoelectric element, and is connected to each bonding layer 2 material along
the arrangement direction of the elements 60. Since the bonding layer 2 is electrically connected
to the front electrode 12 of the piezoelectric element 3, the front electrode 12 of each element
60 is electrically connected to each other through the bonding layer 2 by the conducting wire 7.
[0048]
The piezoelectric element 3 includes a front electrode 12, a piezoelectric body 11, and a back
electrode 13. Usually, the front electrode 12 is connected to the GND line as described above,
and the back electrode 13 is connected to the voltage signal line.
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[0049]
The electrode of the flexible printed circuit board 8 on which the electrode pattern is printed is
connected to the back electrode 13 exposed by removing a part of the back load material 4 of
each ultrasonic transducer element 60 by low temperature solder 15. More specifically, each
electrode printed on the flexible printed circuit board 8 is connected to one or more back
electrodes 13. As described above, usually, the electrodes of the flexible printed circuit board
connected to the back electrode 13 are voltage signal lines. Epoxy resin or the like 16 is filled
around the exposed back electrode 13 to cover the low temperature solder 15.
[0050]
The flexible printed circuit board 8 may be connected to the back electrode 13 using an
anisotropic conductive film instead of the low temperature solder 15. As an anisotropic
conductive film, the conductive film etc. which consist of metal film covering plastic particles
which performed Ni-Au plating processing to particles, such as polystyrene and epoxy, are
mentioned, for example.
[0051]
FIG. 3 shows an example of the electrode pattern printed on the flexible printed circuit board 8. A
plurality of electrode portions 9 are printed on the insulating film 10. The respective electrode
parts 9 are printed apart from each other in alignment with the arrangement interval of the
ultrasonic transducer elements 60, and are connected to one or more back electrodes 13.
[0052]
The entire structure described above is covered with a sealing epoxy resin or the like. This resin
forms another acoustic matching layer, ie, the second acoustic matching layer 17 on the front
surface of the acoustic matching layer 1. The second acoustic matching layer 17 is for enhancing
the efficiency of transmission of the ultrasonic wave to the object and improving the chemical
resistance. In addition, this resin for sealing is abbreviate | omitted in FIG.
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[0053]
The above-described structure covered with the sealing resin is housed in a case (not shown), and
cables (not shown) for connecting to the above-described conductive wires 7 are wired.
[0054]
Second Embodiment of the Present Invention FIG. 4 is a schematic perspective view showing an
example of the second embodiment.
In the ultrasonic transducer of the second embodiment, a plurality of ultrasonic transducer
elements 61 are linearly arranged in the scanning direction via the insulating layer 5.
[0055]
FIG. 5 is a schematic cross-sectional view along line B-B 'of FIG. 4 for showing a cross section of
one ultrasonic transducer element 61. As shown in FIG. Each ultrasonic transducer element 61
has the same structure as the ultrasonic transducer element 60 shown in FIG. 2 except that the
shape of the bonding layer 2 and the way of connecting the common electrode to the bonding
layer 2 are different.
[0056]
That is, in each ultrasonic transducer element 61, the bonding layer 2 is extended not only
between the acoustic matching layer 1 and the piezoelectric element 3 but also to the side
surface along the scanning direction of the acoustic matching layer 1, ie, the longitudinal
direction of the rectangular parallelepiped. It is formed out.
[0057]
In each of the ultrasonic transducer elements 61, a flexible printed circuit board 18 on which an
electrode pattern as shown in FIG. 3 is formed instead of the conductive wire 7 used in the
element 60 shown in FIGS. It is used as a common electrode.
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More specifically, the electrode portion 9 formed on the circuit board 18 is connected to the
bonding layer 2 formed on the side surface of the one or more acoustic matching layers 1. An
electrode pattern may be formed on the entire surface of the flexible printed circuit board 18 for
the common electrode.
[0058]
The flexible printed circuit board 18 is connected using low temperature solder 14 or an
anisotropic conductive film as shown in FIG. The front electrodes 12 of the respective elements
61 are electrically connected to each other through the bonding layer 2 by the circuit board 18.
[0059]
The flexible printed circuit board 8 connected to the back electrode 13 of the piezoelectric
element 3 and the flexible printed circuit board 18 connected to the bonding layer 2 are
combined in a double-layered flexible printed circuit board and connected to the outside. .
[0060]
In the present embodiment, by connecting to each bonding layer 2 formed on the side surface of
the acoustic matching layer 1, wiring to the front electrode 12 of each element 61 can be
performed.
Since wiring can be performed by wire connection on the side surface of the acoustic matching
layer 1, a member for wiring, for example, the flexible printed circuit board 18 or the low
temperature solder 14 is not disposed on the ultrasonic wave transmitting / receiving surface of
the piezoelectric element 3. Therefore, the area of the ultrasonic transmitting / receiving surface
of the piezoelectric element 3 and the acoustic matching layer 1 can be effectively used, and the
sensitivity as an ultrasonic transducer is improved. In addition, since there is no excess on the
ultrasonic wave transmission / reception surface, unnecessary vibration mixed in the emitted
ultrasonic waves is reduced, the S / N ratio is improved, and the image quality of the ultrasonic
image is improved.
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[0061]
Third Embodiment of the Present Invention FIG. 6 is a schematic perspective view showing an
example of the third embodiment. In the ultrasonic transducer of the third embodiment, a
plurality of ultrasonic transducer elements 62 are linearly arranged in the scanning direction via
the insulating layer 5.
[0062]
FIG. 7 is a schematic cross-sectional view along line C-C 'of FIG. 6 for showing a cross section of
one ultrasonic transducer element 62. As shown in FIG. Each ultrasonic transducer element 62
has the same structure as the ultrasonic transducer element 60 shown in FIG. 2 except that the
shape of the bonding layer 2 and the way of connecting common electrodes to the bonding layer
2 are different.
[0063]
That is, in each ultrasonic transducer element 62, the bonding layer 2 is not only between the
acoustic matching layer 1 and the piezoelectric element 3 but also a side surface along the
scanning direction of the acoustic matching layer 1 and a part of the front face of the acoustic
matching layer It is also extended and formed.
[0064]
The bonding layer 2 formed on the front surface of each acoustic matching layer 1 is bonded
using a low temperature solder 14 by a conducting wire 7 which is a common electrode.
The front electrodes 12 of the respective elements 62 are electrically connected to each other
through the bonding layer 2 by the conductive wire 7.
[0065]
In the present embodiment, by connecting to each bonding layer 2 formed on the front surface of
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the acoustic matching layer 1, wiring to the front electrode 12 of each element 61 can be
performed. Wiring to the bonding layer 2 on the front surface of the acoustic matching layer 1 is
easy, so wiring to the front electrode 12 of each element 62 is facilitated.
[0066]
In addition, since the conducting wire 7 is connected to the bonding layer 2 on the front surface
of the acoustic matching layer 1, the acoustic matching layer 1 may be of the same size as the
piezoelectric element 3. Since the dimensions of the acoustic matching layer 1 are the same as
the dimensions of the piezoelectric element 3, the sensitivity and the S / N ratio as an ultrasonic
transducer are improved, and the image quality of the ultrasonic image is improved.
[0067]
Fourth Embodiment of the Present Invention FIG. 8 is a schematic perspective view showing an
example of the fourth embodiment. The ultrasonic transducer of the fourth embodiment consists
of one ultrasonic transducer element. The ultrasonic transducer element includes one disk-like
piezoelectric element.
[0068]
The ultrasonic transducer of this embodiment has a structure in which an acoustic lens 19, an
acoustic matching layer 1, a bonding layer 2, a piezoelectric element 3, a backing material 4 and
an insulating sealing resin 20 are laminated in this order. The acoustic lens 19 has a disk shape
whose front surface is concave, the acoustic matching layer 1, the bonding layer 2, and the
piezoelectric element 3 have a disk shape, and the back load material 4 and the insulating sealing
resin 20 have a cylindrical shape.
[0069]
The acoustic lens 19 made of epoxy resin has the function of the second acoustic matching layer
17 described above and the function of focusing the ultrasonic beam. Similar to the bonding
layer 2 in the third embodiment shown in FIGS. 6 and 7, the bonding layer 2 is formed to extend
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also to part of the side surface and the front surface of the acoustic matching layer 1.
[0070]
The piezoelectric element 3 is composed of a piezoelectric body 11 in which a front electrode 12
and a back electrode 13 are formed. The acoustic matching layer 1, the bonding layer 2, the
piezoelectric element 3 and the backing material 4 are accommodated in a cylindrical metallic
housing 22 via a cylindrical insulating layer 21. An acoustic lens 19 is disposed in front of the
acoustic matching layer 1 to cover the housing 22. The insulating sealing resin 20 is
accommodated in the housing 22 so as to be located on the back surface of the backing material
4 and the insulating layer 21.
[0071]
The bonding layer 2 formed on the front surface of the acoustic matching layer 2 is connected to
the metal housing 22 through the solder 14. The electrode 13 formed on the back side of the
piezoelectric body 11 is connected to the signal line of the cable 23 through the solder 15. The
cable 23 penetrates the backing material 4 and the insulating sealing resin 20 and communicates
with the outside. Further, the housing 22 is connected to the GND (ground) line of the cable 23
through the solder 15. Thus, the ultrasonic transmission / reception surface side of the
piezoelectric body 11 is connected to the GND line through the front electrode 12, the bonding
layer 2 and the housing 22.
[0072]
By applying a predetermined voltage between the signal line of the cable 23 and the GND line,
ultrasonic waves can be oscillated from the piezoelectric element 3. The oscillated ultrasonic
waves are emitted through the acoustic lens 19 to the object to be measured. Further, the voltage
induced in the piezoelectric element 3 by the ultrasonic wave reflected from the object to be
measured and incident through the acoustic lens 19 can be sent to the outside by the signal line
and the GND line.
[0073]
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In the ultrasonic transducer of the present embodiment, wiring to the front electrode 12 of the
piezoelectric body 11 is performed by connecting to the bonding layer 2 on the front surface of
the acoustic matching layer 1 as in the third embodiment described above. be able to. Wiring to
the bonding layer 2 on the front surface of the acoustic matching layer 1 is easy, so wiring to the
front electrode 12 is facilitated.
[0074]
Further, since the wire connection to the bonding layer 2 is performed on the front surface of the
acoustic matching layer 1, the acoustic matching layer 1 may have the same dimension as that of
the piezoelectric element 3. Since the dimensions of the acoustic matching layer 1 are the same
as the dimensions of the piezoelectric element 3, the sensitivity and the S / N ratio as an
ultrasonic transducer are improved, and the image quality of the ultrasonic image is improved.
[0075]
(B) Type of Ultrasonic Transducer in Which Acoustic Matching Layer and Piezoelectric Element
are Bonded Without a Bonding Layer This type of ultrasonic transducer includes at least one
transducer element and, if necessary, an acoustic lens.
[0076]
The transducer element includes an acoustic matching layer made of an inorganic material, a
piezoelectric element, and a backing material.
The front electrode of the piezoelectric element is formed of an inorganic conductive material,
and the acoustic matching layer is bonded to the piezoelectric element by the inorganic
conductive material.
[0077]
That is, in the ultrasonic transducer of this type, the acoustic matching layer and the piezoelectric
element are directly bonded without interposing the bonding layer. The front electrode of the
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piezoelectric element is formed of an inorganic conductive material that forms the bonding layer
described in detail in the description of type (A). Other than that, it has the same structure as an
ultrasonic transducer of type (A).
[0078]
In this type of ultrasonic transducer, since the front electrode of the piezoelectric element is
made of an inorganic conductive material, the adhesion at the bonding interface with the acoustic
matching layer made of an inorganic material is high.
[0079]
Due to the high adhesive strength at the bonding interface, it is difficult for peeling to occur at
the bonding interface due to changes with time of the ultrasonic transducer, stress during
driving, or changes due to rapid temperature differences during transport storage .
Since peeling does not easily occur, the ultrasonic wave excited by the piezoelectric element is
efficiently transmitted to the object to be measured.
[0080]
In addition, since the adhesive strength at the bonding interface is high, the resistance of the
bonding interface such as chemical resistance and weather resistance is high, and the timedependent change of the ultrasonic transducer is reduced. Furthermore, since there is no
bonding layer, the acoustic matching layer and the piezoelectric body are directly bonded. The
acoustic matching layer and the piezoelectric body are each formed of an inorganic material, and
their acoustic impedances are close to each other. Therefore, irregular reflection at the bonding
interface between the two decreases.
[0081]
The ultrasonic transducer of this type includes, for example, the fifth embodiment described
below. <Fifth Embodiment of the Present Invention> In the ultrasonic transducer of the fifth
embodiment, a plurality of ultrasonic transducer elements are insulating layers as in the
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ultrasonic transducers of the first to third embodiments. Are linearly arranged in the scanning
direction.
[0082]
FIG. 9 is a schematic cross section to show one ultrasonic transducer element 63. In each
ultrasonic transducer element 63, the acoustic matching layer 1 and the piezoelectric element 3
are directly bonded. More specifically, the acoustic matching layer 1 is directly bonded to the
front electrode 12 of the piezoelectric element 3. The other structure is the same as that of the
ultrasonic transducer element 60 of the first embodiment shown in FIG.
[0083]
(II) Method of Manufacturing Ultrasonic Transducer According to the Present Invention Next, a
method of manufacturing the ultrasonic transducer according to the first to fifth embodiments
described above will be described.
[0084]
Method of Manufacturing Ultrasonic Transducer of First Embodiment An example of a method of
manufacturing the ultrasonic transducer of the first embodiment shown in FIGS. 1 and 2 will be
described with reference to FIG.
[0085]
(A) First, the piezoelectric body 11 is ground to a predetermined thickness using a lapping
machine or the like.
The front electrode 12 and the back electrode 13 are formed on each surface of the ground
piezoelectric body 11 to produce the piezoelectric element 3.
The formation of the electrode is performed, for example, by silver baking or the like.
[0086]
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(B) Next, to form the bonding layer 2 on the front electrode 12, for example, a paste-like
inorganic conductive material containing indium as a main component and lead, silver and tin
added thereto is placed on the front electrode 12 Apply As a method of application, a method of
applying an inorganic conductive material on the paste by screen printing, a method of applying
a melted inorganic conductive material using a brush, and the like can be mentioned. The
application may be performed on the piezoelectric element 3 as described above, or may be
performed on a plate made of an inorganic material for forming the acoustic matching layer 1
described later.
[0087]
(C) A plate made of an inorganic material for forming the acoustic matching layer 1 is bonded
onto the applied inorganic conductive material to prepare a laminate. The plate made of this
inorganic material has a smaller size than the bonding layer 2 so that the periphery of the
bonding layer 2 is exposed. The top view which shows an example of this laminated body is
shown to Fig.10 (a), and sectional drawing is shown in FIG.10 (b).
[0088]
(D) The above-mentioned laminate is put into a reflow furnace having a peak temperature of 200
° C., for example, to dry the inorganic conductive material, and the acoustic matching layer 1
and the piezoelectric element 3 are joined. In addition, as a method of joining the acoustic
matching layer 1 and the piezoelectric element 3 using the joining layer 2, in addition to the
above, materials having similar coefficients of linear expansion were selected for the acoustic
matching layer 1 and the piezoelectric element 3 respectively. After that, a method may be used
in which so-called baking is performed to heat the laminated body to a high temperature.
[0089]
Alternatively, after a thin foil such as a metal foil is produced from the material forming the
bonding layer 2 and this foil is sandwiched between the acoustic matching layer 1 and the
piezoelectric element 3, the acoustic matching layer 1 and the piezoelectric element 3 are It may
be a method of heating and joining while pressing from both sides.
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[0090]
(E) The above-described laminate is cut in accordance with the desired size of the piezoelectric
element 3.
The cutting is performed, for example, by cutting off the peripheral portion of the laminate.
However, it cuts so that the joining layer 2 to expose remains. An example of the location to be
cut is shown by a dotted line in FIG. A plan view of the laminate cut in this manner is shown in
FIG. 10 (c) and a cross-sectional view is shown in FIG. 10 (d).
[0091]
(F) The piezoelectric element 3 is subjected to polarization processing. The polarization process is
performed, for example, by placing the cut laminate in silicon oil at about 100 ° C. and applying
a predetermined voltage to the electrodes 12 and 13 on both sides of the piezoelectric body 11.
[0092]
It should be noted that instead of polarization treatment of the piezoelectric element 3 in this
step, the above-described steps (a) are carried out using the piezoelectric element 3 subjected to
polarization treatment as described above after forming the electrodes 12 and 13 on both sides
of the piezoelectric body You may go from). As a result, since the piezoelectric element alone is
subjected to polarization treatment, stress breakdown at the time of polarization and residual
stress after polarization are reduced, and a highly reliable transducer can be obtained. However,
as described above, when bonding the acoustic matching layer 1 to the piezoelectric element 3,
the piezoelectric element 3 is heated to 200 ° C. Therefore, it is necessary that the Curie point
of the piezoelectric body 11 be sufficiently high so that the piezoelectricity of the piezoelectric
element 3 subjected to the polarization process does not deteriorate even at such a high
temperature.
[0093]
(G) The flexible printed circuit board 8 is bonded to the back electrode 13 of the piezoelectric
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element 3 using a low temperature solder or an anisotropic conductive film. When bonding using
an anisotropic conductive film, after the ribbon-like anisotropic conductive film is temporarily
fixed to the piezoelectric element 3, the flexible printed circuit board 8 is positioned and fixed,
and pressure is applied to heat and bond .
[0094]
(H) The backing material 4 is bonded to the back electrode 13 using an epoxy adhesive. (I) After
the backing material 4 is joined, a plurality of grooves for dividing the piezoelectric element 3 are
formed according to the electrode pattern of the flexible printed circuit board 8 using, for
example, a precision cutter. The plurality of grooves form a plurality of ultrasonic transducer
elements 60 divided from one another.
[0095]
Specifically, a plurality of grooves are formed to reach a part of the backing material 4 from the
side of the acoustic matching layer 1 through the acoustic matching layer 1, the bonding layer 2,
and the piezoelectric element 3. The grooves are formed such that one or more ultrasonic
transducer elements 60 are connected to each electrode portion 10 of the flexible printed circuit
board 8.
[0096]
After the grooves are formed in this way, the grooves are filled with an electrically insulating
resin or the like and hardened to form the insulating layer 5. It should be noted that, before
bonding the backing material 4 to the back electrode 13, a plurality of grooves may be formed in
accordance with the electrode pattern of the flexible printed circuit board 8 to form the
ultrasonic transducer elements 6 divided from each other. good. That is, the groove is formed to
reach a part of the acoustic matching layer 1 from the side of the back electrode 13 of the
piezoelectric element 3 through the piezoelectric element 3 and the bonding layer 2. The
formation of the grooves is also performed such that one or more ultrasonic transducer elements
60 are connected to each electrode of the flexible printed circuit board 8. After the electrically
insulating resin or the like is filled in the formed groove and cured to form the insulating layer 5,
the back load material 4 is bonded to the back electrode 13.
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[0097]
(J) The low temperature solder 14 is used to bond the conducting wire 7 as a common electrode
on the exposed bonding layer 2 or the front electrode 12 of the piezoelectric element 3. (K) The
structure obtained as described above is covered and sealed with an epoxy resin to form a
second acoustic matching layer 17.
[0098]
As a method of sealing with an epoxy resin, for example, after putting the epoxy resin in a mold
of a predetermined shape coated with a mold release agent, the above structure is inserted into
the resin while performing alignment. And then curing the resin to take out this structure.
[0099]
(L) Attach an acoustic lens (not shown), connect wiring cables, and put in a case to complete an
ultrasonic transducer.
Method of Manufacturing Ultrasonic Transducer of Second Embodiment An example of a method
of manufacturing the ultrasonic transducer of the second embodiment shown in FIGS. 4 and 5
will be described.
[0100]
(A) After the piezoelectric body 11 is ground to a predetermined thickness, the electrodes 12 and
13 are formed on both sides to manufacture the piezoelectric element 3. The formation of the
electrode is performed, for example, by silver baking. Then, a plate made of an inorganic material
for forming the acoustic matching layer 1 is cut in accordance with the size of the piezoelectric
element 3.
[0101]
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(B) Apply an inorganic conductive material to the side and back of the cut acoustic matching
layer 1. After drying the inorganic conductive material, the back surface of the acoustic matching
layer 1 is bonded to the piezoelectric element 3 and baked and bonded. Thus, the bonding layer
2 is formed on the back surface and the side surface of the acoustic matching layer 1.
[0102]
(C) A polarization process is performed on the piezoelectric element 3. (D) The flexible printed
circuit board 8 is bonded to the back electrode 13 of the piezoelectric element 3 by low
temperature solder 15 or an anisotropic conductive film. Similarly, the flexible printed circuit
board 18 is bonded to the bonding layer 2 on the side of the acoustic matching layer 1.
[0103]
(E) The backing material 4 is bonded to the back electrode 13. Then, after grooves for dividing
the piezoelectric element 3 are formed, the insulating layer 5 is formed, and the ultrasonic
transducer element 61 is formed. Next, the whole is covered with a resin to form a second
acoustic matching layer 17, and then an acoustic lens is attached to complete an ultrasonic
transducer.
[0104]
Method of Manufacturing Ultrasonic Transducer of Third Embodiment An example of a method
of manufacturing the ultrasonic transducer of the third embodiment shown in FIGS.
[0105]
(A) First, the piezoelectric body 11 is ground to a predetermined thickness.
Electrodes 12 and 13 are formed on both sides of the ground piezoelectric body 11 to produce a
piezoelectric element 3. The formation of the electrode is performed, for example, by silver
baking.
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[0106]
(B) The acoustic matching layer 1 is cut in accordance with the size of the piezoelectric element
3. (C) Apply an inorganic conductive material for the bonding layer 2 continuously over the back
surface, side surface and part of the front surface of the acoustic matching layer 1. As the
inorganic conductive material, for example, a paste-like conductive material containing a glass
component containing silver as a main component is used. An inorganic conductive material is
applied to the front surface of the acoustic matching layer 1 and the back surface to be bonded
to the piezoelectric element 3 by screen printing. An inorganic conductive material is applied to
the side surface of the acoustic matching layer 1 using a brush or the like. After drying the
applied inorganic conductive material, the piezoelectric element 3 is bonded to the back surface
of the acoustic matching layer 1, and is baked and bonded. More specifically, in the case of
containing the organic substance for facilitating the screen printing of the above-mentioned
inorganic conductive material, the temperature rising rate is lowered up to 550 ° C. to burn the
organic substance, and the baking is performed at 650 ° C. Joint.
[0107]
(D) The piezoelectric element 3 is polarized. After the polarization processing, the flexible printed
circuit board 8 is bonded to the back electrode 13 of the piezoelectric element 3, and the back
load material 4 is bonded to the back electrode 13. Next, grooves for dividing the piezoelectric
element 3 are formed, the insulating layer 5 is formed, and the ultrasonic transducer element 62
is manufactured.
[0108]
(E) The lead 7 is connected to each bonding layer 2 formed on the front surface of the acoustic
matching layer 1 using the low temperature solder 14. (F) The whole is covered with a resin to
form a second acoustic matching layer 17, and then an acoustic lens is attached to complete an
ultrasonic transducer.
[0109]
Method of Manufacturing Ultrasonic Transducer of Fourth Embodiment An example of a method
of manufacturing the ultrasonic transducer of the fourth embodiment shown in FIG. 8 will be
described.
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[0110]
(A) First, the disk-shaped piezoelectric body 11 is ground to a predetermined thickness.
Next, the electrodes 12 and 13 are formed on the ground piezoelectric element. The formation of
the electrode is carried out, for example, by baking a silver palladium paste-like electrode
material.
[0111]
(B) The first acoustic matching layer 1 is processed in accordance with the size of the
piezoelectric element. (C) A paste-like conductive material containing In as a main component
and Pb and Ag added thereto is applied to the first acoustic matching layer 1. The conductive
material is applied to form the bonding layer 2 on the entire surface on one side of the matching
layer 1 and the bonding layer 2 folded back on the side surface.
[0112]
(D) The surface of the first matching layer 1 coated with the conductive material is bonded to the
piezoelectric element 3 and placed in a reflow furnace with a peak temperature of 200 ° C. to
laminate the piezoelectric element 3 and the first acoustic matching layer 1 Make a body.
[0113]
(E) Thereafter, the piezoelectric element 3 is subjected to polarization processing.
(F) On the other hand, the insulating layer 21 is fixed to the metal housing 22 with an adhesive. A
groove in which the piezoelectric element 3 can be attached is formed in the insulating layer 21
so that the piezoelectric element 3 can be easily positioned.
[0114]
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(G) An adhesive is applied to the groove portion of the insulating layer 21 in which the
piezoelectric element 3 is inserted, and a laminate of the first acoustic matching layer 1 and the
piezoelectric element 3 is mounted and adhered by the adhesive. (H) Next, a low temperature
solder 14, a wire, and a conductive adhesive are used to connect the housing 22 with the
bonding layer 2 folded at the side of the first acoustic matching layer 1.
[0115]
(I) Next, the second acoustic matching layer 19 also serving as an acoustic lens is formed. As a
forming method, for example, an appropriate amount of resin such as epoxy is placed on the
surface of the first acoustic matching layer 1, and curing is performed using a mold having good
releasability.
[0116]
(J) Thereafter, the signal line of the cable 23 is connected to the back side of the piezoelectric
element 3 and the GND line of the cable 23 is connected to the inner wall of the metal housing
22 by solder 15 or the like. Next, the insulating layer 21 is filled with a resin mixed with tungsten
powder that is the base of the backing material 4 and cured. Thereafter, an insulating resin 20
made of epoxy resin or the like is filled to complete the ultrasonic transducer shown in FIG.
[0117]
Method of Manufacturing Ultrasonic Transducer of Fifth Embodiment An example of a method of
manufacturing the ultrasonic transducer of the fifth embodiment shown in FIG. 9 will be
described.
[0118]
(A) Grind the piezoelectric body 11 to a predetermined thickness.
(B) An inorganic conductive material for forming the front electrode 12 is applied to the ground
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piezoelectric body 11, and the acoustic matching layer 1 is joined. As the inorganic conductive
material, for example, a paste-like conductive material containing indium as a main component
and added with lead, silver, tin or the like is used. The inorganic conductive material is melted,
for example, under atmospheric pressure, and then applied to the front surface of the
piezoelectric body 11 using a metal mask which is a screen printing method.
[0119]
Specifically, while heating the piezoelectric body 11 to about 200 ° C., the melted inorganic
conductive material is applied to the front surface of the piezoelectric body 11. The acoustic
matching layer 1 is bonded to the front surface of the piezoelectric body 11 while the inorganic
conductive material is melted without being solidified by heating. After that, the inorganic
conductive material is solidified to form the front electrode 12, and the acoustic matching layer 1
is bonded to the front surface of the piezoelectric body 11.
[0120]
Next, the molten inorganic conductive material is applied to the back side of the piezoelectric
body 11 without heating the piezoelectric body 11. The inorganic conductive material is
solidified to form the back electrode 13. Thus, a laminate composed of the acoustic matching
layer 1, the bonding layer 2 and the piezoelectric element 3 is produced.
[0121]
(C) The laminate is cut to fit the desired size of the piezoelectric element 3. (D) Polarize the
piezoelectric element 3. Note that the process may be started from the above step (a) using the
piezoelectric element 3 which has been subjected to polarization treatment in advance. At that
time, when grinding the piezoelectric element 3 in the above-mentioned step (a), only the front
side of the piezoelectric body 11 including the front electrode 12 may be ground and removed,
and the rear side may be left as it is without grinding . If at least the front surface side of the
piezoelectric body 11 is ground, the acoustic matching layer 1 can be bonded together with the
reformation of the front electrode 12 in the above-described step (b).
[0122]
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(E) The flexible printed circuit board 8 is bonded to the back electrode 13 of the piezoelectric
element 3. (F) The backing material 4 is bonded to the back electrode 13.
[0123]
(G) A groove for dividing the piezoelectric element 3 is formed to form the insulating layer 5, and
the ultrasonic transducer element 63 is manufactured. (H) After connecting the lead 7 to the
front electrode 12, the whole is covered with a resin to form a second acoustic matching layer
17, and then an acoustic lens is attached to complete the ultrasonic transducer.
[0124]
As described above in detail, according to the present invention, ultrasonic waves capable of
improving the adhesion and resistance and reducing irregular reflection of ultrasonic waves at
the bonding interface between the piezoelectric element and the acoustic matching layer. A
transducer is provided.
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