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JP2012175507

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
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DESCRIPTION JP2012175507
An ultrasonic transducer capable of generating sufficient power at the time of transmission and
obtaining sufficient sensitivity at the time of reception. In addition, an ultrasonic transducer that
does not require a DC bias is configured. An ultrasonic transducer has a plurality of cells. In each
cell 14, a vibrating membrane 22 is provided above the cavity 20, and includes a signal electrode
layer 24 and a ground electrode layer 26. The main body of the vibrating membrane 22 contains
a piezoelectric material, and the voltage generated by the piezoelectric effect there is detected by
the two electrode layers 24, 26. Above the cavity 20, a magnet 30 which moves with the
vibrating membrane 22 is provided, and below it, an electromagnet tip 36 is provided. The
electromagnet tip 36 generates an alternating magnetic field, which causes the magnet 30 to
periodically generate an attracting force and a repulsive force. As a result, the vibrating
membrane 22 vibrates ultrasonically. [Selected figure] Figure 2
Ultrasonic transducer
[0001]
The present invention relates to an ultrasonic transducer, and more particularly to an ultrasonic
transducer having a fine structure manufactured by semiconductor manufacturing technology.
[0002]
Ultrasonic diagnosis is widely used in the field of medicine.
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1
In ultrasonic diagnosis, an ultrasonic probe (probe) is abutted on the surface of a living body to
transmit and receive ultrasonic waves. Transmission and reception of ultrasonic waves is actually
performed by an ultrasonic transducer (ultrasonic transducer) in the ultrasonic probe. A 1D array
transducer or the like is known as an ultrasonic transducer. It is constituted by a plurality of
vibration elements arranged in one dimension. Other types of ultrasound transducers, such as 2D
array transducers, are also in practical use.
[0003]
The ultrasonic transducer is typically made of a piezoelectric ceramic material such as PZT.
Recently, as a new type of ultrasonic transducer, a capacitive ultrasonic transducer (cMUT:
Capacitive Micro-machined Ultrasonic Transducers) manufactured using semiconductor
manufacturing technology has been proposed. The cMUT has a large number of microcells
formed on a silicon substrate. Each cell has a minute gap, on the bottom of which one electrode is
arranged, on the top of which a vibrating membrane provided with the other electrode is
provided. By applying a voltage between the two electrodes, the vibrating film vibrates by
electrostatic action, thereby generating an ultrasonic wave. The reflected wave from the inside of
the living body is received by the vibrating membrane and causes a change in the capacitance
between the pair of electrodes. By detecting it, a received signal is generated.
[0004]
As an ultrasonic transducer other than the above cMUT, pMUT (Piezoelectric Micro-machined
Ultrasonic Transducer) is also known. Similar to the cMUT, this is manufactured using a
semiconductor manufacturing technology, but uses a film having a piezoelectric material as a
vibrating film. For example, at the time of transmission, as in the cMUT, a voltage is applied to
one of the electrodes of the film and the electrode at the bottom of the air gap immediately below
the vibrating film, and the electrostatic action thereby generates ultrasonic vibration. At the time
of reception, an electromotive force generated by the piezoelectric effect is detected between
both surfaces of the film by the film receiving a reflected wave. Patent Document 1 discloses an
ultrasonic transducer in which cMUT and pMUT are complexed. In the ultrasonic transducer, a
piezoelectric material film is used as a vibrating film. It acts as a cMUT at transmit and as a
pMUT at receive.
[0005]
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2
Patent Document 2 discloses a magnetic electromechanical transducer which does not require
DC bias. Although the details of the operation mechanism are unclear, it seems that the vibrating
film is vibrated by using the magnetic force. This is used as a directional speaker sound source,
an impulse signal generator, and is used as a sound source of an ultrasonic sensor or the like.
That is, only transmission of ultrasonic waves is performed. An element functioning for
transmission and reception is not described in this patent document 2.
[0006]
JP, 2007-229328, A JP, 2005-027186, A
[0007]
An object of the present invention is to provide a new type of ultrasonic transducer, and in
particular, to provide an ultrasonic transducer capable of generating sufficient power at
transmission and obtaining sufficient sensitivity at reception. I assume.
[0008]
Another object of the present invention is to provide an ultrasonic transducer that does not
require a DC bias.
[0009]
An ultrasonic transducer according to the present invention includes a plurality of transmission /
reception cells formed on a substrate, and each of the transmission / reception cells includes a
piezoelectric layer containing a piezoelectric material and a pair formed on the front and back of
the piezoelectric layer. And a movable magnetic layer attached to the vibrating film, and a fixed
magnetic layer provided on the back side of the vibrating film so as to be separated from the
vibrating film. And at least one of the movable magnetic layer and the fixed magnetic layer is
configured as a magnetic field generator that generates a magnetic field by a transmission signal,
ultrasonic vibration is caused in the vibrating film by magnetic action during transmission, and
the vibration during reception It is characterized in that the reception signal is generated by the
piezoelectric effect in the film.
[0010]
According to the above configuration, at the time of transmission, a magnetic field is generated in
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at least one of the movable magnetic layer and the fixed magnetic layer, and ultrasonic vibration
is generated in the vibrating film supporting the movable magnetic layer by the magnetic action.
This generates a transmission wave, which is emitted to the living body.
At the time of reception, a voltage is generated between the pair of electrode layers by the
piezoelectric effect in the vibrating film, whereby a reception signal is generated.
The generation of the pre-deformation by means of a DC bias is not always necessary, since it
utilizes the magnetic effect at the time of transmission, ie both the attraction and repulsion
effects are available.
Moreover, since it is easy to cause the vibrating film to vibrate largely by using the magnetic
effect, it is possible to generate large ultrasonic power. At the time of reception, it is possible to
detect a weak signal with high sensitivity using a piezoelectric effect. Even if the vibrating
membrane itself does not vibrate significantly, if distortion occurs in it, it is possible to detect the
received wave. As a modification, it is possible to detect an electromotive force induced between
the magnetic bodies by the vibration of the vibrating film at the time of reception.
[0011]
The above-mentioned ultrasonic transducer can be manufactured using semiconductor
manufacturing technology (specifically, technology such as lithography, etching, deposition, etc.)
or micromachine technology. Preferably, the transmitter and receiver are formed on the
substrate and integrated with the ultrasonic transducer. Examples of the piezoelectric member
constituting the vibrating film include polymeric piezoelectric materials, PZT, and the like.
[0012]
Preferably, one of the movable magnetic layer and the fixed magnetic layer is configured as the
magnetic field generator, the other of the movable magnetic layer and the fixed magnetic layer is
formed of a magnetic material, and the movable magnetic layer Ultrasonic vibration is generated
in the vibrating film by the magnetic attraction and magnetic repulsion between the fixed
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magnetic layer and the magnetic layer. The transmission signal is configured as a magnetically
generated signal having an alternating characteristic.
[0013]
Preferably, the movable magnetic layer is formed of a magnetic material, and the fixed magnetic
layer is formed as the magnetic field generator. According to this configuration, since the
magnetic field generator is on the fixed side, the load on the diaphragm can be reduced. The
magnetic material may be a thin film layer made of a material such as a permanent magnet.
[0014]
Preferably, each of the transmission / reception cells has a cavity provided on the back side of
the vibrating membrane. If a cavity is formed, the motion space of the vibrating membrane can
be secured to promote its motion.
[0015]
In addition, when a vibration element is comprised by several transmission / reception cell, you
may make it electrically connect in common the several electrode which they have. It is also
possible to separately control weighting and variable aperture etc. in the direction orthogonal to
the electronic scanning direction. Instead of the 1D array transducer, a 2D array transducer may
be configured.
[0016]
According to the present invention, a new type of ultrasonic transducer can be provided, and in
particular, an ultrasonic transducer capable of generating sufficient power at the time of
transmission and sufficient sensitivity at the time of reception can be provided. Alternatively,
according to the present invention, an ultrasonic transducer that does not require a DC bias can
be provided.
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[0017]
It is a top view of the ultrasonic transducer concerning the present invention. It is a sectional
view of an ultrasonic transducer concerning the present invention. It is a figure which shows the
ultrasonic transducer | vibrator which concerns on other embodiment.
[0018]
Hereinafter, preferred embodiments of the present invention will be described based on the
drawings.
[0019]
FIG. 1 shows a preferred embodiment of an ultrasonic transducer according to the present
invention, and FIG. 1 is a schematic top view thereof.
The ultrasonic transducer is used in ultrasonic diagnosis of a living body (human body).
Specifically, the ultrasonic transducer is provided in an ultrasonic probe (probe) that is in contact
with the living body to transmit and receive ultrasonic waves. It is a wave. In FIG. 1, the
ultrasonic transducer 10 has a cell array 12. The cell array 12 is composed of a plurality of cells
14 two-dimensionally densely arranged. Each cell 14 constitutes a transducer as a transmission /
reception unit, and in the present embodiment, each cell 14 has a hexagonal shape when viewed
from above. Of course, it may have other shapes.
[0020]
A plurality of hatched cells indicated by reference numeral 16 constitute one vibration element.
That is, it constitutes one unit of electronic control. In FIG. 1, the X direction is an electronic
scanning direction, and the Y direction is an elevation direction orthogonal to the electronic
scanning direction. Electronic control may be applied to each ultrasonic transducer so that
weighting and aperture change can be performed in the elevation direction. The ultrasonic
transducer shown in FIG. 1 is a so-called 1D array transducer, but the present invention is also
applicable to a 1.5D array transducer and a 2D array transducer.
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[0021]
FIG. 2 shows a schematic cross-sectional view of the ultrasonic transducer shown in FIG. The
thickness and size of each member are for the purpose of the description of the invention, and an
appropriate thickness and size are applied at the time of implementation. In FIG. 2, X represents
the electronic scanning direction as described above, and the Z direction is the thickness
direction. The Z direction is the transmission / reception direction, and the upper side in FIG. 2
corresponds to the living body side.
[0022]
The substrate 18 is configured as a flat silicon plate. In the upper layer, a plurality of cells 14 are
manufactured using semiconductor manufacturing technology. The plurality of cells 14 are
partition walls 18A.
[0023]
The structure of each cell 14 will be described below. The cell 14 has a cavity 20 as a cavity. The
cavity 20 has a well-like form. Above the cavity 20, a vibrating film 22 is provided as a thin layer
which spreads in the horizontal direction. The vibrating membrane 22 of each cell may be
connected to form a single membrane, or the vibrating membrane 22 may be provided for each
cell. In FIG. 2, a single vibrating membrane is employed. The vibrating film 22 has a piezoelectric
layer as its main body, and the piezoelectric layer is made of PVDF, PZT or the like. That is, the
piezoelectric layer is configured to include a material that produces a piezoelectric effect. A
signal electrode layer 24 is formed on the lower surface side of the vibrating membrane 22,
specifically, on the bottom portion corresponding to each cell 14. On the other hand, the ground
electrode layer 26 is entirely formed on the upper surface side of the vibrating film 22. A voltage
generated between the signal electrode layer 24 and the ground electrode layer 26 is detected at
the time of reception as described later.
[0024]
The upper side of the vibrating membrane 22 is covered by a protective layer 32. The upper
surface of the protective layer 32 may be in direct contact with the living body, or may be
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7
configured to be in contact with the living body via the matching layer or the casing member.
The protective layer 32 slightly drops toward the cavity 20 for each cell 14 in the protective
layer 32 in response to the central portion of the vibrating membrane 22 in the natural state
being slightly lowered downward for each cell 14. It has a form. However, the upper surface may
be flat as indicated by reference numeral 34.
[0025]
A magnet 30 is provided on the back side of the vibrating film 22, that is, below the insulating
film 28 as a spacer. The magnet 30 is preferably made of a magnetic material, in particular, a
ferromagnetic material. An electromagnet tip 36 is provided on the bottom of the cavity 20. The
electromagnet chip 36 is a magnetic field generator that generates a magnetic field at the time of
transmission. For example, the electromagnet tip 36 has a spiral signal line. An alternating
magnetic field may be generated thereby. In the present embodiment, it is possible to vibrate the
vibrating film 22 up and down for each cell 14 by the magnetic field generated by such an
electromagnet chip 36 at the time of transmission. In that case, it is possible to use a repulsive
force in addition to the suction force. As a result, it is possible to realize a cell structure which
does not require a preliminary suction function or the like by a DC bias as in a conventional
electrostatic transducer.
[0026]
The external electrodes 42 and 44 are connected to the electromagnet chip 36 via the lines 38
and 40, and they are further connected to the transmitter 46. Further, the signal electrode layer
24 and the ground electrode layer 26 in each cell are connected to the receiving unit 48 through
the lines 50 and 52. The transmitting unit 46 supplies a high frequency signal for generating
ultrasonic vibration for each cell at the time of transmission. The high frequency signal is a signal
that generates a high frequency magnetic field. The receiving unit 48 detects a voltage signal as a
result of the piezoelectric effect generated for each cell, thereby generating a reception signal.
Although the transmitter 46 and the receiver 48 are illustrated outside the substrate 18 in FIG. 2,
it is desirable to form the transmitter 46 and the receiver 48 on the substrate 18. That is, it is
desirable to form a transmission amplifier, a reception amplifier, a phasing addition part, etc.
using semiconductor technology.
[0027]
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8
Next, the operation of each cell 14 will be described. At the time of transmission, a high
frequency signal is supplied from the transmission unit 46 to the electromagnet chip 36 in the
cell 14. As a result, a magnetic field is generated in the electromagnet chip 36, and an attraction
force and a repulsion force are alternately generated in the magnet 30 receiving the magnetic
field. Since the vibrating membrane 22 carries the magnet 30, the vibrating membrane 22 itself
ultrasonically vibrates due to the action of such attractive force and repulsive force. It is
transmitted to the living body side and transmitted as an ultrasonic transmission signal.
[0028]
On the other hand, at the time of reception, a reflected wave from the inside of the living body is
detected in each cell 14. Specifically, as a result of ultrasonic vibration of the vibrating film 22,
the piezoelectric action of the piezoelectric material contained therein is developed, and a voltage
is generated between the two electrodes. The voltage is detected by the pair of electrode layers
24 and 26 and amplified at the receiver. Therefore, since the magnetic force can be used at the
time of transmission, there is an advantage that strong transmission power can be easily
obtained. In particular, since the cavity 20 is provided in the present embodiment, the overall
motion of the vibrating membrane 22 can be tolerated, and the advantage that transmission
power can be easily obtained can be obtained. At the time of reception, an advantage is obtained
that minute vibrations can be detected with high sensitivity by the piezoelectric effect. In this
embodiment, since the DC offset is not necessary in any case, it is possible to solve the problem
in the conventional transducer using electrostatic action.
[0029]
The above ultrasonic transducer can be manufactured using semiconductor manufacturing
technology, that is, an ultrasonic transducer can be configured using lithography technology,
etching technology, film forming technology, bonding technology, etc. It is. In that case, a large
number of cells can be formed at one time, and furthermore, the transmitting unit and the
receiving unit can be formed on the same substrate, so that a highly practical ultrasonic
transducer can be configured.
[0030]
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Another embodiment is shown in FIG. In this embodiment, the ultrasound transducer 54
comprises a plurality of cell arrays 56, which comprises a plurality of cells 58. Each cell 58 has a
square shape as viewed from above. Here, reference numerals 60, 62, 64 denote one vibration
element, and the cells 66, 68 existing between them function to prevent acoustic crosstalk. Of
course, those cells may be included to constitute an array transducer.
[0031]
10 ultrasonic transducer, 12 cell array, 14 cell, 16 vibrating element, 18 substrate, 20 cavity, 22
vibrating membrane, 24 signal electrode layer, 26 ground electrode layer, 30 magnet, 36
electromagnet chip.
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