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JP2005117159

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DESCRIPTION JP2005117159
PROBLEM TO BE SOLVED: To provide an ultrasonic transducer array etc. capable of forming an
ultrasonic beam with reduced side lobes without putting an excessive load on electronic circuits.
SOLUTION: An ultrasonic transducer array is a plurality of groups of ultrasonic transducers
vibrating at different amplitudes with respect to the same applied voltage, and a plurality of
ultrasonic transducers are arranged in different arrangements according to the amplitudes of the
respective groups. A group of ultrasonic transducers 10, 11, ..., and a filler 18 holding a plurality
of groups of ultrasonic transducers. [Selected figure] Figure 1
Ultrasonic transducer array and method of manufacturing the same
[0001]
The present invention relates to an ultrasonic transducer array that transmits and receives
ultrasonic waves in medical and structural flaw detection ultrasonic imaging devices.
[0002]
Conventionally, a piezoelectric ceramic represented by PZT (lead zirconate titanate: Pb (lead)
zirconate titanate) or PVDF (polyvinylidene fluoride: polyvinylidene difluoride) has been used as
an element (vibrator) used for transmission and reception of ultrasonic waves. A piezoelectric
element including a polymeric piezoelectric element represented by the above has generally been
used.
03-05-2019
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When a voltage is applied to such a piezoelectric element through an electrode, the piezoelectric
element expands and contracts due to the piezoelectric effect to generate an ultrasonic wave.
Therefore, by arranging a plurality of such piezoelectric elements (vibrators) in one or two
dimensions, and driving each of the transducers with a predetermined delay, an ultrasonic beam
transmitted in a desired direction is obtained. It can be formed.
[0003]
By the way, when an ultrasonic beam is transmitted from a transducer array in which a plurality
of such transducers are arranged, in addition to the high sound pressure area (main lobe) formed
in the transmission direction and the angular range in the vicinity thereof, A high sound pressure
area is also formed in a plurality of angular ranges. These high sound pressure areas formed
laterally are called side lobes and are factors that lower the SN ratio in the ultrasonic detection
signal.
[0004]
The side lobes are mainly caused by a truncation error caused by breaking the distribution
function of the voltage applied to the plurality of transducers in accordance with the opening of
the transducer array. Therefore, theoretically, it is possible to eliminate side lobes by using an
infinite aperture array. However, in practice, since the aperture of the transducer array is finite,
the side lobe can not be eliminated at all. Therefore, conventionally, with respect to each of the
plurality of vibrators, the side lobe is canceled or reduced by controlling the amplitude of the
vibration in a circuit to reduce the truncation of the distribution function. However, with the
recent miniaturization and high integration of vibrators, it is burdensome for the circuit side to
control a large number of vibrators in a circuit. In particular, in the case of using a twodimensional array, the number of transducers increases in a square law manner, and the load on
the circuit side increases dramatically.
[0005]
In order to solve such a problem, in Patent Document 1, a plurality of internal electrode layers
and vibrator elements having a laminated structure formed by alternately laminating a plurality
of vibrator layers are arranged in an array. The ultrasonic probe is characterized in that the
number of layers of the ultrasonic element to be driven is large at the central portion in the
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2
longitudinal direction of the transducer element and decreases toward both ends. The child is
disclosed. However, as shown on page 1 of Patent Document 1, a vibrator element having such a
structure is considered to be structurally fragile because continuous vibrators are sandwiched
between different electrode layers. As a result, it is also conceivable that the resonance converges
to a region where the sound pressure level is large. JP-A-2000-88822 (Page 1)
[0006]
In view of the above, it is an object of the present invention to provide an ultrasonic transducer
array capable of forming an ultrasonic beam with reduced side lobe levels without placing an
excessive burden on the electronic circuit. .
[0007]
In order to solve the above problems, an ultrasonic transducer array according to the present
invention is a plurality of groups of ultrasonic transducers vibrating at different amplitudes with
respect to the same applied voltage, and different from each other according to the amplitude of
each group A plurality of ultrasonic transducers arranged in an array, and a filler holding the
plurality of ultrasonic transducers.
[0008]
In the method of manufacturing an ultrasonic transducer array according to the first aspect of
the present invention, a plurality of ultrasonic transducers, which vibrate at different amplitudes
with respect to the same applied voltage, for each group, a plurality of substrates or Step (a) of
fabricating a plurality of element arrays by arranging them in mutually different arrangements
on the main surfaces of a plurality of base materials that can be peeled off, and bonding the
plurality of element arrays facing each other Arranging a plurality of ultrasonic transducers
arranged in the element array on the same surface on the same surface, and removing the
substrate or the substrate included in one of the bonded element arrays (c). Before or after the
step (c), the step of (d) filling the filler between a plurality of ultrasonic transducers arranged on
the same surface.
[0009]
Further, in the method of manufacturing an ultrasonic transducer array according to the second
aspect of the present invention, each of a plurality of groups of ultrasonic transducers vibrating
at different amplitudes with respect to the same applied voltage is specified by a material serving
as a filler. Forming a coating layer having a thickness and a shape of each of the plurality of
ultrasonic transducers, arranging a plurality of ultrasonic transducers having the coating layer in
different arrangements according to the amplitudes of the respective groups, and Integrating the
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plurality of coating layers respectively formed on the acoustic transducer.
[0010]
Furthermore, in the method of manufacturing an ultrasonic transducer array according to the
third aspect of the present invention, a step (a) of forming a first piezoelectric material layer on a
substrate so as to change its thickness; A step (b) of forming a continuous body of the laminate
by forming an electrode layer in the upper layer of the layer, and dividing the continuous body of
the laminate into an element shape, it is arranged in a predetermined arrangement on the
substrate Step (c) of forming a plurality of elements, and step (d) of disposing a filler between the
plurality of elements and removing the substrate, thereby forming an electrode on the end face
of the plurality of elements exposed thereby Do.
[0011]
According to the present invention, the ultrasonic transducers of a plurality of groups vibrating
at different amplitudes with respect to the same applied voltage are arranged in accordance with
the amplitudes of the respective groups. An ultrasound beam can be formed with reduced lobe
levels.
Therefore, the image quality of the ultrasonic image can be improved by increasing the SN ratio
(signal-to-noise ratio) and DU ratio (desired wave to unnecessary wave ratio) caused by the side
lobes.
[0012]
The best mode for carrying out the present invention will be described in detail below with
reference to the drawings.
The same reference numerals are given to the same components, and the description will be
omitted.
FIG. 1 is a perspective view showing an ultrasonic transducer array according to a first
embodiment of the present invention.
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The ultrasonic transducer array 100 according to the present embodiment includes a plurality of
groups of ultrasonic transducers (hereinafter also referred to simply as elements ) 10, 11,...
Arranged in a two-dimensional matrix, between and around them. And the filler 18 disposed.
[0013]
Each of the plurality of groups of elements 10, 11,... Is, for example, a minute columnar structure
having a bottom width of about 0.2 to 1.0 mm and a height of about 1.0 mm.
The respective groups of elements 10, 11, ... have different piezoelectric distortion constants (m /
V). Here, the piezoelectric strain constant is represented by (the generated strain) / (the strength
of the applied electric field). That is, the plurality of groups of elements 10, 11,... Vibrate with
different amplitudes by expanding and contracting by different displacement amounts with
respect to the applied drive voltage. A common electrode 19 is provided to the plurality of
groups of elements 10, 11,. The filler 18 is, for example, an epoxy resin material, and holds a
plurality of groups of elements 10, 11,.
[0014]
FIG. 2 is an enlarged view of a part of a cross section taken along line II-II of FIG. As shown in
FIG. 2, for example, the element 10 includes a plurality of piezoelectric material layers 10 a and a
plurality of internal electrode layers 10 b alternately stacked, and two side electrodes 10 c
provided on opposite sides of the element 10. It is. Further, an upper electrode 10 d is provided
on the upper surface of the element 10.
[0015]
As the piezoelectric material layer 10a, a piezoelectric ceramic typified by PZT (lead zirconate
titanate: Pb (lead) zirconate titanate) or a polymer piezoelectric element typified by PVDF
(polyvinylidene fluoride: polyvinylidene fluoride) is used. Be In addition, insulating regions 10 e
are provided alternately at left and right ends of each of the plurality of internal electrode layers
10 b. As a result, the internal electrode layer 10b is connected to one of the side electrodes 10c
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and insulated from the other, so that the electrodes sandwiching each of the plurality of
piezoelectric material layers 10a are connected in parallel. In the structure having such a
laminated structure, the electrical impedance can be reduced because the area of the facing
electrodes is increased as compared with the single layer structure. Therefore, it operates more
efficiently for the applied drive voltage than a single-layer structure. In order to insulate the
internal electrode layer from the side electrode, a method may be used in which the end surface
of the internal electrode layer exposed on the side surface is covered with an insulating material
instead of providing the insulating region.
[0016]
The other groups of elements 11, 12 also have the same laminated structure as the element 10,
but the number of laminated piezoelectric material layers and internal electrode layers, in other
words, the thickness of the piezoelectric material layers (lamination interval) Are different from
each other. As described above, when the same drive voltage is applied, the magnitudes of
effective electric fields that contribute to the expansion and contraction of the piezoelectric
material layer differ between elements having different lamination intervals. That is, each
element will have different piezoelectric strain constants. Here, it is known that the lamination
interval D (x) of the element and the amplitude a (x) when a predetermined voltage is applied are
inversely proportional, and the relationship between them is expressed by the following equation
. D (x) ∝1 / a (x) where x is the distance from the center to the end of the ultrasonic transducer
array, and by adjusting the value of D (x) as in the following equation The amplitude a (x) when a
predetermined voltage is applied can be made close to a desired value. a(x)∝1/D(x)
[0017]
FIG. 3 shows the amplitude distribution of the elements used in designing the arrangement of the
elements. The elements 10, 11,... Are arranged according to their respective piezoelectric strain
constants so as to vibrate with the amplitude shown in FIG. 3 when a predetermined drive
voltage is applied. That is, near the center of the ultrasonic transducer array 100, an element 10
vibrating at an amplitude a10 is disposed. In addition, the element 11 vibrating at an amplitude
a11 is disposed at a position separated by a distance L11 from the center of the array. Similarly,
an element 12 oscillating with an amplitude a12 is disposed at a position separated by L12 from
the center of the array. By providing the plurality of elements arranged in the ultrasonic
transducer array with such an amplitude distribution, it is possible to reduce side lobes in the
formed ultrasonic beam.
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[0018]
In this embodiment, the element array can be designed based on various other amplitude
distributions. FIG. 4 shows an amplitude distribution used in antenna engineering described in
"Antenna Engineering Handbook" edited by the Institute of Electrical Information and
Communication Engineers (Ohm Company). In FIG. 4, the side lobe level is based on the sound
pressure intensity of the main lobe. Also, L represents the aperture width, λ represents the
wavelength, and θμp represents the beam diameter. These amplitude distributions can also be
applied when forming an ultrasound beam. At that time, as shown in FIG. 4, since the side lobe
level and the gain coefficient are in a contradictory relationship, it is desirable to select an
appropriate amplitude distribution according to the purpose. Besides this, an amplitude
distribution such as a binomial distribution, a Chebykoff distribution, or a Taylor distribution may
be used. When using the Chebykoff distribution, the side lobe level can be kept below a certain
level, and the width of the main beam can be minimized. Moreover, in the case of using the
Taylor distribution, in addition to the advantage of the Chebykov distribution, the unnecessary
ultrasonic irradiation dose can be reduced.
[0019]
Next, a method of manufacturing the ultrasonic transducer array according to the present
embodiment will be described with reference to FIGS. In the present embodiment, in order to
simplify the description, an ultrasonic transducer array in which two groups of elements are
arranged in a 5 × 5 two-dimensional matrix is manufactured. FIG. 5 is a flowchart showing the
method of manufacturing the ultrasonic transducer array according to the present embodiment.
[0020]
In step S11 of FIG. 5, as shown in FIG. 6, an element array is produced for each group based on
the final design of the element array. FIG. 6 shows an element array 21 in which the first
elements 21a are arranged on the substrate 21b, and an element array 22 in which a plurality of
elements 22a are arranged on the substrate 22b. These element arrays 21 and 22 are produced,
for example, as follows. As shown in FIG. 7A, a continuous body of the laminated structure is
formed by alternately laminating the piezoelectric material layer 23a and the intermediate
electrode layer 23b a predetermined number of times on the substrate 22b. The piezoelectric
material layer 23a may be a plate of a piezoelectric material, or a jet deposition method (aerosol
03-05-2019
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deposition method or gas deposition method) in which the material is deposited by blowing
powder of the material toward the lower layer at high speed. It may be formed by using. In this
case, it is desirable to bake the piezoelectric material layer in order to increase the grain size of
PZT. The intermediate electrode layer 23 b can be formed by sputtering or vacuum evaporation.
Next, as shown in FIG. 7B, the continuous body of the laminated structure is divided into element
shapes using, for example, a dicer, and the laminated structure in an unnecessary region is
thinned. Alternatively, by using the sandblasting method, it is possible to easily form a layered
structure having an element shape arranged in a predetermined arrangement. Furthermore, side
electrodes are provided on each of these element-shaped laminated structures. Thereby, the
element array 22 shown in FIG. 6 is produced. In addition, the element array 21 is similarly
manufactured by changing the thickness (stacking interval) and the number of layers of the
piezoelectric material layer.
[0021]
Next, in step S12, as shown in FIG. 8A, the manufactured element arrays 21 and 22 are opposed
to each other, aligned, and attached. Thus, the plurality of groups of elements 21a and 22a are
arranged on the same plane in accordance with the final design of the element arrangement.
[0022]
Next, in step S13, as shown in FIG. 8B, the filler 24 is disposed between the plurality of groups of
elements disposed on the same surface. For that purpose, for example, the one to which the
element arrays 21 and 22 are attached is placed in a container filled with a liquid filler, and the
container is evacuated. Thereby, the filler penetrates between the plurality of elements 21a and
22a. Further, after curing the filler, the element array is removed from the container.
[0023]
In step S14, the substrate is removed by polishing or the like, and electrodes are formed on the
end faces of the plurality of groups of elements 21a and 22a exposed thereby. At that time, as
shown in (c) of FIG. 8, an electrode 25 is formed on each of the end faces of the plurality of
groups of elements 21a and 22a, and a common electrode 26 is formed on the other end face.
This produces an ultrasonic transducer array that includes two groups of elements with different
piezoelectric strain constants.
03-05-2019
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[0024]
In order to manufacture an ultrasonic transducer array including elements of three or more
different groups, the following may be performed. That is, in step S11 of FIG. 4, three or more
different element groups are arranged in different arrangements on the substrate or later
peelable substrate for each group based on the final design of the element array. By arranging, a
plurality of element arrays are manufactured. For example, a transparent adhesive sheet is used
as a substrate that can be peeled off later. Then, in step S12, the element groups arranged in
each element array are bonded to each other while aligning the transparent adhesive sheet or the
like, and the substrate or the base material is removed. By repeating this process, element groups
arranged in a plurality of element arrays are arranged on the same plane. The subsequent steps
are the same as those shown in FIG.
[0025]
As described above, in the present embodiment, the piezoelectric strain constant of the element
is changed by changing the number of laminations and the lamination interval, so that the
amplitude of the vibration of the element can be arbitrarily designed. In addition, since a plurality
of groups of elements designed in such a manner are arranged based on a predetermined
amplitude distribution, side lobes caused by censoring errors of the distribution function are
reduced, and the SN ratio and DU ratio of detection signals are increased. It will be possible to
Furthermore, since the plurality of elements are designed to vibrate at different amplitudes with
respect to the same applied voltage, amplitude modulation can be controlled according to the
element arrangement without increasing the load on the circuit side, It is also possible to cope
with the future increase in elements and higher integration.
[0026]
Next, a method of manufacturing an ultrasonic transducer array according to a second
embodiment of the present invention will be described with reference to FIGS. FIG. 9 is a
flowchart showing a method of manufacturing an ultrasonic transducer array according to the
present embodiment. In step S21 of FIG. 9, a plurality of groups of elements arranged in the
ultrasonic transducer array are manufactured. That is, first, as shown in (a) of FIG. 10, a
continuous body of a laminated structure is manufactured by alternately laminating a plurality of
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piezoelectric material layers 31a and a plurality of internal electrode layers 31b a predetermined
number of times. . For that purpose, for example, a thin film of an internal electrode material is
formed and laminated on a PZT plate material having a predetermined thickness, or a PZT layer
and an internal electrode layer are alternately formed on a substrate using a jet deposition
method. . Next, as shown in (b) of FIG. 10, the insulating material 31c is formed so as to
alternately cover one end surface of the plurality of internal electrode layers 31b on the side
surface of the continuous body of the laminated structure. For that purpose, for example, an
insulating material such as glass is attached to the end face of the internal electrode layer 31 b
using electrophoresis. Next, as shown in (c) of FIG. 10, side electrodes 31 d are formed on the
side surfaces of the continuous body of the laminated structure in which the insulating material
31 c is formed. Further, as shown in (d) of FIG. 10, the continuum of the laminated structure is
cut into element sizes using a dicer. Thus, the element 30 is manufactured. Similarly, plural
groups of elements having different thicknesses (stacking intervals) of the piezoelectric material
layer and the number of stacked layers are manufactured.
[0027]
In step S22 of FIG. 9, as shown in (a) of FIG. 11, each of the plurality of groups of elements 30 is
coated with the material of the filler 18 (FIG. 1). The thickness and shape of the coating layer 32
are determined according to the arrangement of the elements in the ultrasonic transducer array.
As a method of coating, for example, (1) a method of wrapping the element with a resin material
formed into a film, (2) a method of immersing the element in a liquid coating material, and (3)
arranging the element in a mold A method of injecting and curing a liquid coating material, a
method of (4) spraying a liquid coating material onto the element, and a method of applying with
a brush may be considered. The thickness of the coating layer can be controlled by the thickness
of the film, the viscosity of the liquid coating material, the shape and surface properties of the
element, the number of coating operations, and the like. In addition, when not only the side
surface of the element but also the bottom surface is covered with the coating material by the
coating operation, the coating material is removed by polishing the surface or the like.
[0028]
Next, in step S23, as shown in (b) of FIG. 11, a plurality of groups of coated elements 33, 34, 35
obtained by coating each of the plurality of elements are subjected to the final design of the
element array. Arrange based on As a placement method, a method of bundling a plurality of
groups of coated elements, bringing them close to a jig, or using a bonder to suction each of the
coated elements to place it at a predetermined position is used.
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[0029]
Furthermore, in step S24, for example, the coating layers of the plurality of groups of coated
elements are integrated by heating. Furthermore, as shown in (c) of FIG. 11, the upper electrode
36 is formed on the end face of each of the plurality of groups of elements, and the common
electrode 37 is formed, thereby including a plurality of groups of elements having different
piezoelectric distortion constants. An ultrasonic transducer array is manufactured.
[0030]
According to this embodiment, even if the types of elements included in the ultrasonic transducer
array increase, the ultrasonic transducer array can be easily manufactured without significantly
increasing the number of manufacturing processes. Further, according to the present
embodiment, the arrangement of the elements in the ultrasonic transducer array is determined
by the thickness and shape of the coating layer, so that it is not necessary to perform precise
alignment on the substrate, and the manufacturing process is simplified. Can.
[0031]
As a modification of the method of manufacturing an ultrasonic transducer array according to
the present embodiment, the following method may be used. In step S22 of FIG. 9, each of the
plurality of groups of elements is coated with a material that can be removed by a physical or
chemical action such as chemicals, heating, cooling, or weathering in a later step. As such a
material, for example, epoxy-based, polyimide-based, and PMMA (poly methyl methacrylate) based resist materials which are decomposed by thermal oxidation can be mentioned. Next, a
plurality of sets of coated elements are placed and fixed on the substrate. Next, the coating layer
of the coated element is removed by physical or chemical action, and a filler is placed between
and around the plurality of elements exposed on the substrate. Further, the substrate is removed,
and the upper electrode and the common electrode are arranged in a plurality of groups of
elements. According to this modified example, even a material which can not reversibly repeat
changes such as melting and curing can be used as a filler.
[0032]
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11
Next, an ultrasonic transducer array according to a third embodiment of the present invention
will be described. FIG. 12 shows a part of an ultrasonic transducer array according to the present
embodiment. Here, in the ultrasonic transducer array shown in FIG. 1, the piezoelectric strain
constants in the plurality of elements are mutually changed by changing the number of
laminations (lamination interval), thereby controlling the amplitude of vibration in the elements.
ing. However, a plurality of elements having substantially different piezoelectric distortion
constants can also be realized by the following configuration.
[0033]
As shown in FIG. 12, the ultrasonic transducer array according to the present embodiment
includes a plurality of groups of ultrasonic transducers (elements) 41, 42,. These elements 41,
42, ... include lower electrodes 41a, 42a, ..., piezoelectric material layers 41b, 42b, ..., and upper
electrodes 41c, 42c, ... respectively. In addition, piezoelectric material layers 41 d, 42 d,... Are
provided in the upper layer of the upper electrodes 41 c, 42 c,.
[0034]
Each of the piezoelectric material layers 41b, 42b,... Has a predetermined thickness distribution
according to the element arrangement. As described above, in the present embodiment, by
providing the thickness of the piezoelectric material layer with a distribution in each element, the
lamination distance is adjusted to change the piezoelectric strain constant.
[0035]
FIG. 13 is a diagram for explaining the method of manufacturing the ultrasonic transducer array
according to the present embodiment. First, as shown in (a) of FIG. 13, the piezoelectric material
layer 45 is formed on the substrate 44 so as to change its thickness. At that time, the thickness of
the piezoelectric material layer 45 can be easily controlled by using the jet deposition method.
Next, the electrode layer 46 is formed on the surface of the piezoelectric material layer 45. Next,
as shown in (c) of FIG. 13, the piezoelectric material layer 47 is formed on the electrode layer 46
using a jet deposition method to form a continuous continuum of height. Next, as shown in (d) of
FIG. 13, the continuous body shown in (c) of FIG. 13 is divided into element shapes by sub-die
03-05-2019
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processing. Furthermore, an ultrasonic transducer array is manufactured by arranging a filler
between a plurality of elements, removing the substrate, and thereby forming an electrode on the
exposed end face of the elements. In the present embodiment, the jet deposition method is used
to change the thickness of the piezoelectric material layer, but in addition, for example, the
piezoelectric material having a flat surface is sloped by forming a recess by countersinking. A
method may be used. Alternatively, the lower electrodes 41a, 41b,... (FIG. 12) may be
manufactured by forming an electrode layer on the substrate 44 in advance before forming the
piezoelectric material layer 45.
[0036]
An ultrasonic transducer array according to a fourth embodiment of the present invention will be
described. FIG. 14 shows a part of an ultrasonic transducer array according to the present
embodiment. As shown in FIG. 14, the ultrasonic transducer array according to the present
embodiment includes a plurality of groups of ultrasonic transducers (elements) 51, 52,. Each of
the plurality of groups of elements 51, 52, ... includes a plurality of piezoelectric material layers
51a, 52a, ..., a plurality of internal electrode layers 51b, 52b, ..., side electrodes 51c, 52c, ..., and
an upper electrode 51d, 52 d, ... is included. These elements 51, 52,... Are provided with a
common electrode 54.
[0037]
The plurality of groups of elements 51, 52, ... have the same number of layers, but the internal
electrode layers 51b, 52b, ... included in them have different thicknesses. By this, the lamination
distance in the elements 51, 52,... Is adjusted to change the piezoelectric distortion constant. In
order to produce an element having a different thickness of the internal electrode layer, for
example, the electrode layer is formed on the piezoelectric material layer formed on the substrate
so that the thickness changes in the plane. Such an electrode layer and a piezoelectric material
layer formed thereon can be easily formed, for example, by using a jet deposition method.
[0038]
Next, an ultrasonic transducer array according to a fifth embodiment of the present invention will
be described. As shown in (a) of FIG. 15, the ultrasonic transducer according to the present
embodiment includes a plurality of groups of ultrasonic transducers (elements) 61, 62,. Each of
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these elements 61, 62, ... includes a piezoelectric material layer (for example, the piezoelectric
material layer 65a in the element 65) and an upper electrode (for example, the upper electrode
65b in the element 65). Further, the common electrode 66 is provided in the plurality of groups
of elements 61, 62,..., And the filler 67 is disposed between the elements 61, 62,.
[0039]
The plurality of piezoelectric material layers respectively included in the plurality of groups of
elements 61, 62,... Are formed of materials different from each other depending on the
arrangement of the elements. FIG. 15 (b) shows the relationship between the arrangement of
elements and the composition of the material forming the piezoelectric material. As shown in (a)
and (b) of FIG. 15, a piezoelectric material layer formed mostly of the raw material A is used for
an element (for example, the element 61) disposed near the center of the ultrasonic transducer
array. ing. On the contrary, in the element (for example, the element 64) close to the peripheral
portion, the piezoelectric material layer in which the proportion of the raw material A is reduced
and the proportion of the raw material B is increased accordingly is used. In this way, materials
that change the function of the material continuously or stepwise by changing the composition of
the raw materials are called functionally graded materials. In the present embodiment, the
piezoelectric strain constant is changed by adjusting the blending of the raw materials A and B.
[0040]
FIG. 16 is a diagram for explaining a method of manufacturing the ultrasonic transducer array
shown in FIG. As shown in FIG. 16A, the piezoelectric material layer 71 is formed on the
substrate 70 by the jet deposition method using two nozzles. At that time, by controlling the
positions of the nozzle 72 for jetting the raw material A and the nozzle 73 for jetting the raw
material B, the composition on the raw materials A and B is adjusted according to the position on
the substrate 70 by scanning the substrate. Change. Next, as shown in (b) of FIG. 16, the
piezoelectric material layer 71 is divided, and after the filler is disposed, the substrate 70 is
removed and the upper electrode and the common electrode are disposed (see (a) of FIG. 15). ).
In addition, before forming the piezoelectric material layer 71, a lower electrode may be provided
on each element by forming an electrode layer on the substrate 70 in advance.
[0041]
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In this embodiment, as shown in (b) of FIG. 15, although the functionally gradient material in
which the composition of the raw materials A and B changes continuously, the functionally
gradient material in which the composition of these materials is stepwise changed May be used.
Alternatively, polarization processing (Polling) may be used as a method of changing the
piezoelectric strain constant of each element. Here, it is known that the piezoelectric strain
constant of the device changes due to the polarization process in which the voltage applied per
unit length is different. Therefore, the ultrasonic transducer array may be manufactured by
arranging a plurality of groups of elements subjected to different polarization processes in an
array in accordance with the polarization processes. Alternatively, a plurality of groups of
elements made of the same material may be arranged in an array, and each group may be
subjected to different polarization treatments depending on the arrangement.
[0042]
In the first to fifth embodiments described above, when the piezoelectric material layer or the
electrode layer is formed using the jet deposition method, the powder of the material bites into
the lower layer of those layers by collision. Anchoring occurs. The depth of the anchor layer (the
layer into which the powder bites in) varies depending on the density of the lower layer, the
velocity of the powder, and the like, but is usually about 10 nm to 100 nm. Therefore, by
observing the interface of the layers included in each ultrasonic transducer, it is possible to
determine whether or not the layer is formed using the jet deposition method.
[0043]
In the first to fifth embodiments of the present invention, an ultrasonic transducer array has been
described in which a plurality of groups of elements having square bottoms are arranged in a
two-dimensional matrix. However, the arrangement of the plurality of groups of elements is not
limited to this. For example, the annular array may be manufactured by arranging the plurality of
groups of elements concentrically according to the piezoelectric strain constant of each group.
Alternatively, as shown in (a) of FIG. 17, a one-dimensional ultrasonic transducer is provided by
arranging a plurality of groups of elements 81, 82,... Having rectangular bottoms in one
dimension in accordance with the respective piezoelectric strain constants. Arrays may be made.
Alternatively, as shown in FIG. 17B, a plurality of one-dimensional ultrasonic transducer arrays
may be arranged in one direction to produce a 1.5-dimensional ultrasonic transducer array.
[0044]
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An ultrasonic probe can be manufactured using the ultrasonic transducer array according to the
first to fifth embodiments of the present invention described above. FIG. 18 is a partial crosssectional perspective view showing an ultrasonic probe according to an embodiment of the
present invention. As shown in FIG. 18, the ultrasound probe includes an ultrasound transducer
array 100, a backing layer 2, an acoustic matching layer 3, and an acoustic lens 4. These units
are housed in the housing 5. Further, the wiring drawn out from the ultrasonic transducer array
100 is connected to an electronic circuit included in the ultrasonic imaging apparatus main body
via the cable 6.
[0045]
The backing layer 2 is formed of, for example, an epoxy resin containing powder of metal powder
such as ferrite or powder of PZT, or a material having high acoustic attenuation such as rubber
containing ferrite powder, and the unnecessary generated from the ultrasonic transducer array
100 Accelerates the attenuation of ultrasonic waves. Further, the acoustic matching layer 3 is
formed of, for example, Pyrex (registered trademark) glass or an epoxy resin containing metal
powder that easily transmits ultrasonic waves, and the acoustic impedance between the subject
as the living body and the ultrasonic transducer is Eliminate inconsistencies. Thereby, the
ultrasonic wave transmitted from the ultrasonic transducer is efficiently propagated into the
subject. Furthermore, the acoustic lens 4 is made of, for example, silicone rubber, and is
transmitted from the ultrasonic transducer array 100 to focus the acoustic impedance-matched
ultrasonic beam in the acoustic matching layer 3 at a predetermined depth.
[0046]
By driving the ultrasonic transducer array 100, the plurality of groups of elements 10, 11,... (FIG.
1) contained therein vibrate at an amplitude corresponding to the piezoelectric strain constant of
each group to generate ultrasonic waves. . At that time, an ultrasonic beam transmitted in a
desired direction is formed by driving a plurality of groups of elements 10, 11, ... at a
predetermined timing using electronic circuits included in the ultrasonic imaging apparatus main
body. Can. In addition, the plurality of groups of elements 10 expand and contract by receiving
ultrasonic waves, and generate an electric signal (detection signal). Here, when an element
having a large piezoelectric strain constant is used to generate an ultrasonic wave having a large
intensity, the piezoelectric output constant (V · m / N) decreases, and the ultrasonic wave
reception sensitivity of the element is also It will decrease. The piezoelectric output constant is
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represented by (the strength of the generated electric field) / (the applied stress). In particular, in
the case where the number of stacked layers of elements is changed as in the first embodiment,
the tendency is remarkable. Therefore, it is desirable to separately provide an element for
receiving ultrasonic waves. As described in the fifth embodiment, when the piezoelectric strain
constant is increased by changing the material, the sensitivity may be slightly reduced by the
amount of the dielectric constant. It is possible to combine.
[0047]
It is a perspective view showing an ultrasonic transducer array concerning a 1st embodiment of
the present invention. It is a figure which shows a part of cross section in II of the ultrasonic
transducer array shown in FIG. It is a figure which shows the amplitude distribution used when
designing the arrangement ¦ positioning of an element. It is a figure which shows the amplitude
distribution used in antenna engineering. It is a flowchart which shows the manufacturing
method of the ultrasonic transducer array which concerns on the 1st Embodiment of this
invention. It is a figure for demonstrating the manufacturing method of the ultrasonic transducer
array which concerns on the 1st Embodiment of this invention. It is a figure for demonstrating
the manufacturing method of the element array shown in FIG. It is a figure for demonstrating the
manufacturing method of the ultrasonic transducer array which concerns on the 1st Embodiment
of this invention. It is a flowchart which shows the manufacturing method of the ultrasonic
transducer array which concerns on the 2nd Embodiment of this invention. It is a figure for
demonstrating the manufacturing method of the ultrasonic transducer array which concerns on
the 2nd Embodiment of this invention. It is a figure for demonstrating the manufacturing method
of the ultrasonic transducer array which concerns on the 2nd Embodiment of this invention. FIG.
7 is a view showing a part of an ultrasonic transducer array according to a third embodiment of
the present invention. It is a figure for demonstrating the manufacturing method of the ultrasonic
transducer array which concerns on the 3rd Embodiment of this invention. FIG. 7 is a view
showing a part of an ultrasonic transducer array according to a fourth embodiment of the
present invention. It is a perspective view showing the ultrasonic transducer array concerning a
5th embodiment of the present invention. It is a figure for demonstrating the manufacturing
method of the ultrasonic transducer array which concerns on the 5th Embodiment of this
invention. It is a perspective view showing a modification of shape and arrangement of elements
in an ultrasonic transducer array. FIG. 2 is a partial cross-sectional perspective view showing an
ultrasound probe to which the ultrasound transducer array shown in FIG. 1 is applied.
Explanation of sign
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[0048]
Reference Signs List 2 backing layer 3 acoustic matching layer 4 acoustic lens 5 housing 6 cable
10 to 14, 21a, 22a, 30, 41 to 43, 51 to 53, 61 to 65, 81 to 85 ultrasonic transducers (elements)
10a, 23a, 31a, 41b to 43b, 41d to 43d, 51a to 53a, 45, 47, 71 Piezoelectric material layers 10b,
23b, 31b, 51b to 53b Internal electrode layers 10c, 31d, 51c to 53c Side electrodes 10d, 25, 36,
41c -43c, 51d-53d upper electrode 10e insulating region 18, 24, 67 filler 19, 26, 37, 54, 66
common electrode 21, 22 element array 21b, 22b, 44, 70 substrate 31c insulating material 32
coating layer 33- 35 Coated Elements 41a to 43a Lower Electrode 46 Electrode Layer 72, 73
Nozzle 100 ultrasonic transducer array
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