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DESCRIPTION JP2017005661

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DESCRIPTION JP2017005661
Abstract: To provide an ultrasonic transducer and an ultrasonic diagnostic apparatus having a
highly sensitive vibration element without increasing the manufacturing cost. An ultrasonic
transducer has a plurality of laminates in which a diaphragm, a lower electrode, a piezoelectric
film, and an upper electrode are laminated in this order, and the plurality of laminates are
divided into a predetermined number of plural members. In each of at least one of the plurality of
vibration elements, one of the stacks is composed of the lower electrode of a material or material
composition ratio different from that of the lower electrode of any other stack. Have. [Selected
figure] Figure 4
Ultrasonic transducer and ultrasonic diagnostic apparatus
[0001]
The present invention relates to an ultrasonic transducer and an ultrasonic diagnostic apparatus.
[0002]
The ultrasonic diagnostic apparatus transmits ultrasonic pulses from the ultrasonic probe into
the subject, receives echo signals from the inside of the subject with the ultrasonic probe, and
converts the signals into electrical signals.
The ultrasound probe has an ultrasound transducer that converts the electrical signal into
mechanical vibration and vice versa. As the ultrasonic transducer, for example, a vibrating
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element (bulk-type vibrating element) obtained by dividing a bulk-shaped piezoelectric body in
which a piezoelectric material and an electrode material are stacked is used. A large number of
transducer elements are arranged in the longitudinal direction of the ultrasonic probe.
[0003]
In the electronic scanning method, an ultrasonic beam is scanned by sequentially driving the
arranged transducer elements one by one in the longitudinal direction of the ultrasonic probe. An
ultrasonic tomographic image of the subject is obtained based on the echo signal obtained by
scanning the ultrasonic beam.
[0004]
The resolution of the ultrasonic tomographic image depends on the pitch in the scanning
direction of the ultrasonic beam. This pitch is determined by the width of the vibrating element.
Therefore, in order to increase the resolution of ultrasonic tomograms, miniaturization and
densification of the transducer elements are required.
[0005]
Also, in general, when mechanical stress is generated by applying compressive stress, tensile
stress or the like to the vibrating element, polarization occurs in the vibrating element, and a
voltage proportional to the strain is generated. Therefore, it is also required to increase the
sensitivity of the vibrating element by securing the ease of distortion of the vibrating element so
that the voltage upon receiving the ultrasonic pulse changes significantly.
[0006]
In recent years, an ultrasonic probe using a semiconductor microfabrication technology (MEMS
technology) has been proposed in response to the demand for miniaturization and high density
of a vibrating element. For example, a vibration element manufactured by the MEMS technology
described in Patent Document 1 is configured by sequentially forming a piezoelectric film and an
upper electrode on a vibration plate which also serves as the lower electrode.
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[0007]
Further, for example, in Patent Document 2, in order to increase the sensitivity of the vibration
element, the diaphragm is removed, the piezoelectric film is formed into a non-flat shape (for
example, dome shape) which is easily distorted, and a bending mode is added. It has been
described to obtain high electrical opportunity coupling.
[0008]
JP, 2013-93760, A U.S. Patent No. 8767512 specification
[0009]
However, in the vibration element described in Patent Document 1, the piezoelectric film has a
shape formed on a flat diaphragm.
Since this is a shape that is difficult to distort, the vibration element provided with such a
piezoelectric film has a problem in that the sensitivity is lower than that of a bulk type vibration
element.
[0010]
Further, the diaphragm dome shape of the vibrating element described in Patent Document 2 has
a complicated structure, and is difficult to produce by the MEMS technology.
For this reason, there is a problem that the yield is lowered, and a high-level manufacturing
process is required to produce the dome shape.
[0011]
The present invention solves the above-mentioned conventional problems, and an object thereof
is to provide an ultrasonic transducer and an ultrasonic diagnostic apparatus having a highly
sensitive vibrating element without using a complex structure such as a dome shape. .
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[0012]
In order to achieve the above object, an ultrasonic transducer according to the present invention
has a plurality of laminates in which a diaphragm, a lower electrode, a piezoelectric film and an
upper electrode are laminated in this order, and the plurality of laminates are predetermined. A
plurality of vibration elements are divided into a number, and in each of at least one of the
plurality of vibration elements, any one of the laminates is a material different from the lower
electrode of any other laminate. Or it has a lower electrode of material composition ratio.
[0013]
According to the present invention, lower electrodes having different materials or material
composition ratios are mixed in a predetermined number of laminates constituting individual
vibration elements without complicating the structure of the laminates constituting the vibration
elements, and By adjusting the mixture ratio, it becomes possible to appropriately control the
physical properties of the piezoelectric film, in particular, the dielectric constant of the
piezoelectric film, and therefore, downsizing and densification of the laminate without a
complicated structure. In other words, the miniaturization and densification of the vibrating
element become easy, and it is possible to provide the ultrasonic transducer and the ultrasonic
diagnostic apparatus having the highly sensitive vibrating element.
[0014]
BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram which shows the whole structure
of the ultrasound diagnosing device in embodiment of this invention.
It is a circuit diagram of signal detection by MOSFET.
It is a figure which shows the arrangement | sequence of a vibration element.
It is a sectional view showing roughly an example of a layered product group. It is a figure which
shows the mixed ratio of the several laminated body in the same channel. FIG. 6A is a diagram
showing a transducer arrangement, and FIG. 6A is a diagram when a combination of two
laminates is arranged as a laminate group, and FIG. 6B is a diagram when a combination of three
laminates is arranged as a laminate group FIG. 6C is a diagram when arranging a combination of
four laminates as a laminate group. It is a figure which shows the laminated body assembly part
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disperse | distributed and arrange | positioned in a vibrating element. FIG. 8A is a view when the
area of the lower electrode and the upper electrode included in the same laminate are different,
FIG. 8A is a view when the upper electrode is in a small circle shape, and FIG. 8B is a view when
the upper electrode is in a ring shape It is a figure of time.
[0015]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings.
[0016]
FIG. 1 is a block diagram showing an entire configuration of an ultrasonic diagnostic apparatus S
in the present embodiment.
[0017]
The ultrasonic diagnostic apparatus S is composed of an ultrasonic diagnostic apparatus main
body 1 and an ultrasonic probe 2.
The ultrasonic diagnostic apparatus main body 1 includes a control unit 3, a signal processing
unit 14, an image generation unit 15, a display control unit 16, and a user interface UI.
The user interface UI has a display unit 17 and an operation unit 18.
[0018]
The ultrasonic probe 2 has a probe control unit 2A, a transmitting / receiving unit 11, and an
ultrasonic transducer 10. The ultrasonic transducer 10 has a transducer array 20A (described
later) in which a plurality of transducer elements 20 (described later) are arrayed. The ultrasonic
probe 2 is provided with a transmission / reception switching unit (switch) 4 connected to the
transmission unit 12 and the reception unit 13 of the transmission / reception unit 11.
[0019]
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The transmission / reception switching unit 4 switches the connection between each transducer
20 and the transmission unit 12 or the reception unit 13 according to the transmission /
reception switching signal from the probe control unit 2A. Each transducer element 20 is
connected to the transmission unit 12 or the reception unit 13 by switching of the transmission /
reception switching unit 4. The vibrating element 20 connected to the transmitting unit 12
functions as a transmitting vibrating element 20, and generates an ultrasonic pulse by the
voltage pulse supplied from the transmitting unit 12. The vibrating element 20 connected to the
receiving unit 13 functions as a receiving vibrating element 20, receives a reflection (echo) signal
from the subject, and outputs the signal to the receiving unit 13. The transmitting and receiving
unit 11 may be provided in the ultrasonic probe 2 but may be provided in the ultrasonic
diagnostic apparatus main body 1.
[0020]
The receiving unit 13 converts the charge induced by the vibrating element 20 in response to the
reception of the reflection (echo) signal into a voltage signal corresponding to the charge
amount. The receiving unit 13 includes a detection system 130 provided in one-to-one
correspondence with each of the transducer elements 20, and the detection system 130 includes
one or more detection elements. For example, a MOSFET (metal oxide semiconductor field effect
transistor) is used as a detection element. FIG. 2 is a circuit diagram of MOSFET detection in
which the vibration element 20 and the detection system 130 are connected. As shown in FIG. 2,
a voltage signal (V) generated by piezoelectric conversion of the reflection signal received by the
vibrating element 20 is detected by the detection system 130 as a detection signal (Vin). In order
to maximize the sensitivity of the vibrating element 20, match the first capacitance C f on the
vibrating element 20 side with the second capacitance C in (gate capacitance) on the detection
system 130 side. Will be described later.
[0021]
The probe control unit 2A switches each connection in the transmission / reception switching
unit 4 at a predetermined switching timing according to an arrangement pattern indicating the
position of the transmitting vibration element 20 and the receiving vibration element 20, which
are set in advance. Are connected to the transmission unit 12 or the reception unit 13, and the
vibration element 20 is switched for transmission or reception.
[0022]
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The signal processing unit 14 performs various processes such as a process of applying a BPF
(Band Pass Filter) to the voltage signal from the receiving unit 13, a non-linear compression, a
depth correction, a detection process, and the like.
The image generation unit 15 generates image data representing the tissue shape of the subject
based on the data after signal processing. The display control unit 16 receives an input operation
from the operation unit 18 (a keyboard, a mouse, a touch panel or the like), and displays a
tomographic image on a display unit 17 (a liquid crystal screen or the like) based on image data.
[0023]
FIG. 3 is a view schematically showing an example of the ultrasonic transducer 10.
[0024]
As shown in FIG. 3, the transducer array 20A is one in which 128 transducer elements 20 are
arrayed in the longitudinal direction of the ultrasonic probe 2 (scanning direction indicated by X
in FIG. 3).
The vibrating element 20 constitutes one unit (one channel) to which a delay time is given at the
time of electronic scanning. That is, the plurality of transducer elements 20 form an array of a
plurality (here, 128) of channels.
[0025]
Each vibration element 20 has a predetermined number (26 in this case) of laminates having the
same structure, 2 × in the minor axis direction (the elevation direction indicated by Y in FIG. 3)
orthogonal to the major axis direction and the major axis direction. 13 arranged in a matrix form.
In other words, the plurality of stacks are divided into a predetermined number to form the
plurality of vibration elements 20. In addition, each laminate includes a piezoelectric material,
and when manufactured by MEMS technology, this may be referred to as “pMUT cell” (pMUT:
piezoelectric micromachined ultrasound transducer), and such a laminate A set of s may be called
"pMUT cell group".
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[0026]
In the present embodiment, in each vibrating element 20, two types of laminates are mixed in
order to achieve high sensitivity. Hereinafter, the first type of laminate is referred to as a
laminate 30A, and the second type of laminate is referred to as a laminate 30B. In the following
description, a set of two or more stacks (stacks 30A and 30B) is referred to as a stack group 300.
Also, a generic term of the laminates 30A and 30B is referred to as a laminate 30.
[0027]
FIG. 4 is a cross-sectional view schematically showing an example of the laminate group 300. As
shown in FIG. In this example, the stack group 300 includes one stack 30A and a stack 30B.
[0028]
Each of the laminates 30A and 30B has a diaphragm (diaphragm) 32, a lower electrode 33, a
piezoelectric film 34, and an upper electrode 35. The diaphragm 32, the lower electrode 33, the
piezoelectric film 34, and the upper electrode 35 are stacked in this order. Although not shown, a
film for protection and insulation is formed on the upper electrode 35. For this film, for example,
an oxide film such as SiO 2 (silicon oxide) or an organic film such as an epoxy resin or parylene is
used.
[0029]
Both ends of the diaphragm 32 are supported by the substrate 31. The diaphragm 32 is
integrally formed with the substrate 31. For example, the diaphragm 32 is formed in a thin plate
shape by partially thinning a silicon substrate as a material of the substrate 31 by etching.
[0030]
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The lower electrode 33 is deposited on the flat diaphragm 32. Further, the piezoelectric film 34
is formed on the lower electrode 33. Further, the upper electrode 35 is formed on the
piezoelectric film 34. In the present embodiment, since these stacked layers are flat and not
complicated, they can be easily and finely manufactured by the usual film forming technology
and MEMS technology, and therefore, the size reduction and the densification of the stacked
body 30 are realized. As a result, miniaturization and densification of the vibration element 20
can be achieved.
[0031]
As the material of the upper electrode 35, the same material as the material of the lower
electrode 33 described later may be used from the viewpoint of easiness of production, but a
material different from the lower electrode 33 may be used.
[0032]
The material of the piezoelectric film 34 may be a conventionally known material such as lead
zirconate titanate, for example.
[0033]
As shown in FIG. 4, the stacks 30A and 30B have the same structure.
The same structure means that the substrate 31, the diaphragm 32, the lower electrode 33, the
piezoelectric film 34, the upper electrode 35, etc. have the same thickness and sectional shape.
In addition, although the board | substrate 31 contains the location shared between the
laminated body 30A and the laminated body 30B, it is made the same by the structure when it
divides by half. Also, the same range includes manufacturing errors. For example, the
piezoelectric films 34 are made of the same material and have the same thickness. Further, as
described above, the diaphragm 32 is flat. Furthermore, the piezoelectric film 34 and the upper
electrode 35 can be easily manufactured in the same manufacturing process. For this reason, it
becomes easy to manufacture laminated body 30A, 30B, and makes manufacture of the vibration
element 20 easy by extension.
[0034]
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Here, by making the structure of the laminate 30 non-planar, or by making the materials of the
piezoelectric film 34 different between the laminate 30A and the laminate 30B so that the
dielectric constants become different. Although it is conceivable to obtain a highly sensitive
vibrating element 20, this may increase the manufacturing cost of the vibrating element 20.
[0035]
In the present embodiment, the individual vibration elements 20 can be formed without
complicating the structure of the laminate 30 in a non-planar manner and without making the
materials of the piezoelectric films 34 in the laminates 30A and 30B different from each other.
The lower electrodes 33 having different materials or material composition ratios are mixed in
the predetermined number of laminated bodies 30 to be configured, and the physical properties
of the piezoelectric film 34, in particular, the dielectric constant of the piezoelectric film 34 are
adjusted by adjusting the mixture ratio. The relative dielectric constant ε γ) can be
appropriately controlled.
Thereby, the highly sensitive vibration element 20 can be obtained without increasing the
manufacturing cost.
[0036]
The material of the lower electrode 33 is a material that can produce the piezoelectric effect of
the piezoelectric material formed in the upper layer and does not generate a reaction compound
with the component elements in the piezoelectric material, a material with good surface
smoothness, and a material of piezoelectric material It is desirable that the alloy phase is not
precipitated due to film process temperature change. As a result, the piezoelectric film 34 and
the lower electrode 33 are not in close contact with each other and hardly come off, and an effect
of suppressing the time-lapse deterioration of the piezoelectric characteristics is obtained.
[0037]
For example, when a material having a lattice constant of 3.9 to 4.1 [.ANG.] Representing the unit
cell size of a crystal is used as the material of the piezoelectric film 34, the material of the lower
electrode 33 for obtaining the above-mentioned effect As, the thing of the range whose lattice
constant is 3.9-4.1 [Å] is used.
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[0038]
As a material of the lower electrode 33 having such a lattice constant, for example, a perovskite
type compound such as platinum (Pt) or LNO (LaNiO 3), a silver alloy (Ag) containing silver (Ag)
as a main component and palladium (Pd) -Pd) is mentioned.
[0039]
Other examples of materials usable for the lower electrode 33 include copper (Cu), silicon (Si),
chromium (Cr), titanium (Ti), nickel (Ni), gold (Au), platinum (Pt) And silver alloys containing at
least one of aluminum (Al), tantalum (Ta), and cobalt (Co).
[0040]
The material of the lower electrode 33 may be (Ba, La) TiO 3 or (Ba, La) SnO 3 having a lattice
constant of 4.0 to 4.1 Å.
さらに、SrRuO 3 であってもよい。
These materials, like platinum (Pt), LNO, and silver alloy (Ag-Pd), exhibit the piezoelectric effect
of the piezoelectric material.
[0041]
As a method of forming the lower electrode 33 on the vibration plate 32, PVD methods such as
sputtering method, ion plating method, molecular beam epitaxy method, laser ablation method,
ionized cluster beam evaporation method and ion beam evaporation method are used. Be
Note that as a film formation method, it is preferable to use a sputtering method using the abovedescribed material as a target material.
[0042]
If the lower electrode 33 is formed on the vibrating plate 32 by, for example, multi-source
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sputtering, and silver (Ag) and palladium (Pd) are used as the target material, the positional
relationship between the sample and the target material Regions in which the contents of silver
(Ag) and palladium (Pd) are slightly different from each other can be manufactured at one time,
and the fine adjustment of the lattice constant can be easily performed. The lattice constant of
the piezoelectric film 34 and the lattice constant of the lower electrode 33 Can be properly
adjusted and the dielectric constant can be controlled.
[0043]
When the material of the lower electrode 33 is a silver alloy (Ag-Pd), the lower electrode 33 of
one of the stacked bodies 30A, 30B is different from the lower electrode 33 of any of the other
stacked bodies 30A, 30B, It has a composition ratio of silver (Ag) and palladium (PD).
Thereby, the capacitance of the stacked body 30A is different from the capacitance of the
stacked body 30B.
[0044]
The relative dielectric constant ε γ of the piezoelectric film 34 can be confirmed by a known
measurement method.
[0045]
An example of a method of measuring the relative dielectric constant ε γ will be described.
For measurement of the relative dielectric constant ε γ of the piezoelectric film 34, for
example, as a measurement target of the relative dielectric constant ε γ, PZT (Pb (Pb) is used so
that the film thickness of the lower electrode 33 becomes 1 [μm] / 100 [nm]. What formed into
a film (Zr, Ti) O3) / PLT (Pb, La) TiO3) is used. An object to be measured is set in, for example, a
sawer tower circuit, and an alternating current power supply 1 [MHz] is applied to both
electrodes of the piezoelectric film 34. The relative dielectric constant ε γ of the piezoelectric
film 34 is measured based on the voltage applied to the both electrodes of the piezoelectric film
34 and the charge induced on the both electrodes of the piezoelectric film 34.
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[0046]
The relationship between the material or the like of the lower electrode 33 and the relative
dielectric constant ε γ of the piezoelectric film 34 is, for example, as follows. When the material
is platinum (Pt), the relative permittivity ε γ is 480. When the material is LNO (LaNiO 3), the
relative dielectric constant ε γ is 550. Furthermore, in the case of a silver alloy Ag̶Pd (45%)
containing 45% palladium (Pd) whose material composition ratio is silver (Ag) as a main
component, the relative dielectric constant ε γ is 260. Furthermore, in the case of a silver alloy
Ag̶Pd (25%) containing 25% palladium (Pd) whose material composition ratio is silver (Ag) as a
main component, the relative dielectric constant ε γ is 230.
[0047]
From this, even if the laminates 30A and 30B have the same structure, the capacitances of the
laminates 30A and 30B differ because the materials and the like of the lower electrodes 33
thereof are different. Therefore, by adjusting the combination of the stacked bodies 30A and 30B
in the stacked body group 300 connected to the MOSFET (detection element), the capacitance on
the stacked body group 300 (laminated bodies 30A and 30B) side is detected by the detection
system 130. In this case, it is possible to match the capacitance on the input side of the MOSFET
(detection element) electrically connected to the stacked body group 300, and a highly sensitive
vibration element 20 is obtained. In addition, manufacturing tolerance (individual difference) of
the MOSFET can be obtained by adopting a method of matching the first capacitance C f on the
vibration element 20 side with the second capacitance C in on the detection system 130 side in
this manner. Even if the second electrostatic capacitance C in on the detection system 130 side is
not always the same due to the first electrostatic capacitance C f on the vibrating element 20 side
is always matched with the second electrostatic capacitance C in It can be done.
[0048]
FIG. 5 shows an adjustment example of the mixture ratio of the stacked bodies 30A and 30B. The
laminate 30A is indicated by a white circle, and the laminate 30B is indicated by a hatched circle.
In this example, the total number of laminates 30A and 30B in the same channel is 26 and the
mixture ratio of the laminates 30A and 30B is adjusted at "13:13" to "24: 2". It is also possible to
adjust the first electrostatic capacitance C f of the entire vibration element 20 by changing the
mixture ratio of the stacked bodies 30A and 30B as described above.
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[0049]
Next, see Table 1 for matching the first capacitance C f on the laminate group side connected to
the MOSFET (detection element) with the second capacitance C in on the input side of the
MOSFET (detection element) To explain. In order to make the description easy to understand, an
example in which the number of laminates in the laminate group 300 connected to the MOSFET
(detection element) is two to four will be described.
[0050]
Table 1 shows the first capacitance C f on the side of the laminate group 300 manufactured by
changing the material or the material composition ratio of the lower electrode 33. In addition, in
order to facilitate the production of the vibration element 20, since the laminates in the same
channel (the vibration element 20) have the same structure, the thickness d of the piezoelectric
film 34 is the same, and the dimension (for example, the length of the side) ) It is a precondition
that L is identical.
[0051]
[0052]
In Table 1, d is the thickness of the piezoelectric film 34, ε γ is the relative permittivity of the
piezoelectric film 34, and C f is the capacitance of the piezoelectric film 34 (the stacks of the
stacks 300) L is a first electrostatic capacity, and L is a side length of the square piezoelectric
film 34.
In addition, when producing the laminated body for 5 [MHz], the piezoelectric material film 34
whose length L is 53 [micrometers] is used. Further, when producing a laminate for 1 MHz, the
piezoelectric film 34 having a length L of 106 μm is used. By substituting these into the
equation (1), the first capacitance C f of each laminate is calculated. The dielectric constant ε o
of vacuum is set to 8.85 [pF / m]. C f = ε o ε γ L <2> / d (1)
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[0053]
From Table 1, for example, in the case of the piezoelectric film 34 of d = 1 [μm], εγ = 200, L =
53 [μm], the first capacitance C f of the laminated body is 5 [pF]. Further, for example, in the
case of the piezoelectric film 34 of d = 1 [μm], ε γ = 400, and L = 53 [μm], the first
capacitance Cf of the laminated body is 10 [pF]. Note that the thickness d of the piezoelectric film
34 is the same and the side length L is the same according to the above-described conditions.
[0054]
On the other hand, when the second electrostatic capacitance C in at the input side of the
MOSFET (detection element) is 15 [pF], two types of piezoelectric films 34 having the abovementioned two types of first electrostatic capacitances C f are used. When the laminates 30A and
30B are manufactured, the sum of their first capacitances C f is 15 (= 5 + 10) [pF]. A stack group
300 is configured by a combination of the stacks 30A and 30B, and one MOSFET (detection
element) is connected to the stack group 300 to form a first electrostatic of the combined stacks
30A and 30B. The sum of the capacitances C f can be matched to the second capacitance C in on
the input side of the MOSFET (detection element). In addition, when performing said alignment,
although the sum total of 1st electrostatic capacitance Cf was made to correspond to 2nd
electrostatic capacitance Cin, it is not necessary to necessarily make it correspond. Since the sum
of the first capacitances C f indicates a discontinuous numerical value, if it is difficult to match
them, the sum of the first capacitances C f is the second static value so that the vibrating element
20 has high sensitivity. The sum of the first capacitances C f may be matched to be substantially
equal to the second capacitance C in by combining the stacks so as to approach the capacitance C
in. The difference between the sum of the first capacitance C f and the second capacitance C in is
preferably about -20% to + 20%.
[0055]
As described above, when the laminate group 300 is configured by a combination of the
laminates 30A and 30B, the laminates 30A and 30B (shown by A and B in FIG. 6) alternate with
each other as shown in FIG. 6A. Thus, the stacks 300 are arranged in the elevation direction (Y
direction). The reason is that the laminates 30A and 30B having different first capacitances are
mixed as much as possible to achieve uniform acoustic characteristics. In addition, the laminated
body group 300 is shown with a broken line in FIG. 6A. In the stacks 30A and 30B in the stack
group 300, the lower electrodes 33 are connected to each other.
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[0056]
Further, from Table 1, for example, in the case of the piezoelectric film 34 of d = 1 [μm], ε γ =
100, L = 53 [μm], the first capacitance C f of the laminate is 2.5 [pF ]. Further, for example, in
the case of the piezoelectric film 34 of d = 1 [μm], ε γ = 400, and L = 53 [μm], the first
electrostatic capacitance C f of the laminated body is 10 [pF]. Note that the thickness d of the
piezoelectric film 34 is the same and the side length L is the same according to the abovedescribed conditions.
[0057]
On the other hand, when the second electrostatic capacitance C in at the input side of the
MOSFET (detection element) is 22.5 [pF], the piezoelectric film 34 having the two types of the
first electrostatic capacitance C f is used. If two types of laminates are produced, the sum of their
first capacitances C f is 22.5 (= 2.5 + 10 + 10) [pF]. A stacked body group 300 is formed by
combining two stacked bodies 30A and one stacked body 30B, and one MOSFET (detection
element) is connected to the stacked body group 300 to combine the stacked bodies. The sum of
the first electrostatic capacitances C f on the 30A and 30B sides can be made to coincide with the
second electrostatic capacitance C in on the input side of the MOSFET (detection element).
[0058]
As described above, when the laminate group 300 is configured by combining two laminates 30A
and one laminate 30B, as shown in FIG. 6B, in order to make the acoustic characteristics uniform.
The overall shape of the laminate group 300 in which each laminate 30A and one laminate 30B
are combined is, for example, L-shaped, and one laminate 30B is disposed at the corner. The
stacks 300 are arranged in the elevation direction (Y direction) such that the L-shapes combine
with each other. In addition, the laminated body group 300 is shown with a broken line in FIG.
6B. The lower electrodes 33 are connected to each other in the stacked bodies 30A and 30B in
the stacked body group 300.
[0059]
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Although not shown in Table 1, a laminate group 300 is configured by a combination of four
types of laminates 30A, 30B, 30C, and 30D, and one MOSFET (detection element) is connected to
the laminate group 300. As a result, the first capacitance C f on the stacked body group 300
(stacked bodies 30A and 30B) side can be matched with the second capacitance C in on the input
side of the MOSFET (detection element). When the laminate group 300 is configured by
combining four types of laminates 30A, 30B, 30C, and 30D, the overall shape of the laminate
group 300 is as shown in FIG. 6C in order to achieve uniform acoustic characteristics. It becomes
square shape which arranges layered products 30A, 30B, 30C, and 30D in four corners. The
rectangular stacks 300 are arranged in the elevation direction (Y direction). The stack group 300
is shown by a broken line in FIG. 6C. The lower electrodes 33 are connected to each other in the
stacked bodies 30A and 30B in the stacked body group 300.
[0060]
As described above, in accordance with the MOSFET (detection element) in which the second
electrostatic capacitance C in changes according to the area, the first electrostatic capacitance C f
of the stacked body group 300 electrically connected to the MOSFET Can be adjusted. Needless
to say, when the stacks 30 are electrically connected to the individual MOSFETs one by one, if
the capacitances of the respective MOSFETs coincide with each other, these may be electrically
connected one-on-one.
[0061]
As shown in FIGS. 6A to 6C, although different types of stacks 30A and 30B can be dispersedly
arranged in the vibration element 20, the same type of stacks 30A or 30B can be used for
capacitance adjustment. It may be arranged adjacent to each other. An example is shown in FIG.
In this example, a laminate assembly 301 consisting of eight adjacently arranged laminates 30A
and a laminate assembly 301 consisting of eight adjacently arranged laminates 30B are
alternately arranged in the vibration element 20. It is done.
[0062]
In the vibrating element 20 in which the stacked body aggregation portion 301 is arranged in
this manner, the dimension of each of the stacked body aggregation portions 301 is equal to or
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less than the half wavelength of the ultrasonic wave to be received. As shown in FIG. 7, for
example, L is the dimension in the elevation direction (Y direction) of the laminated body
assembly 301 (the assembly of the laminated body 30A or the assembly of the laminated body
30B), λ is the wavelength of the ultrasonic wave to be received In this case, the arrangement
condition of the laminated body assembly portion 301 which is permitted to achieve uniform
acoustic characteristics is L ≦ λ / 2.
[0063]
In the above-described embodiment, the areas of the lower electrode 33 and the upper electrode
35 included in the same laminate 30A, 30B are the same. On the other hand, the sensitivity may
be increased because the areas of the lower electrode 33 and the upper electrode 35 included in
the same stacked body 30A, 30B are different. In order to increase the sensitivity, the area of the
other electrode may be made smaller than the area of one electrode, but here, the area of the
upper electrode 35 is made smaller than the area of the lower electrode 33. The reason is that
since the lower electrode 33 has the piezoelectric film 34 formed thereon, it is necessary to
secure a certain area.
[0064]
For example, as shown in FIG. 8A, by making the diameter R1 of the circle of the upper electrode
35 smaller than the diameter R of the circle of the lower electrode 33, the area of the upper
electrode 35 is made smaller than the area of the lower electrode 33.
[0065]
For example, as shown in FIG. 8B, the lower electrode 33 has a circular shape, the upper
electrode 35 has a ring shape, and the lower electrode 33 has a diameter R2 of a circle and an
outer diameter R3 of a ring shape of the upper electrode 35. When the upper electrode 35 has a
ring shape (shown by an inner diameter R4 of the ring shape), the area of the upper electrode 35
is smaller than the area of the lower electrode 33.
[0066]
In the ultrasonic transducer 10 described above, the laminate includes the laminate 30A
(corresponding to the “first laminate” of the present invention) and the laminate 30B
(corresponding to the “second laminate” of the present invention) When a plurality of
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vibration elements constitute an array of a plurality of channels, it is preferable that the stacked
bodies 30A be arranged not to be adjacent to each other in one channel.
As a result, since the laminate 30A is mixed with a different type of laminate (for example, the
laminate 30B) or the like, the acoustic characteristics can be made uniform.
[0067]
In the ultrasonic transducer 10 described above, the vibration element 20 constitutes one
channel, but a predetermined number of laminated bodies 30A, 30B constituting the vibration
element 20 of the same channel are divided into a plurality of sub-channels It may be done.
At this time, lower electrodes 33 included in the same subchannel among the plurality of
subchannels are electrically connected to each other. The number of stacks in the subchannels
used for electronic scanning is less than the number of stacks in one channel, but it is possible to
scan shallow areas within the object.
[0068]
In addition, any of the above-described embodiments is merely an example of implementation for
carrying out the present invention, and the technical scope of the present invention should not
be interpreted in a limited manner by these. That is, the present invention can be implemented in
various forms without departing from the scope or main features of the present invention.
[0069]
The present invention can be applied to an ultrasonic diagnostic apparatus provided with an
ultrasonic transducer. By using a small-sized, high-density vibrating element, the ultrasonic probe
becomes small and lightweight, and the operability of the ultrasonic probe can be improved.
[0070]
S ultrasonic diagnostic apparatus 1 ultrasonic diagnostic apparatus main body 2 ultrasonic probe
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10 ultrasonic transducer 20A transducer array 20 vibratory element 30 laminate 30A laminate
30B laminate 31 substrate 32 diaphragm 33 lower electrode 34 piezoelectric film 35 upper part
Electrode 130 detection system 300 stack group
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