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JP2009050560

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2009050560
PROBLEM TO BE SOLVED: To provide an electrostatic capacitance type ultrasonic transducer
capable of transmitting and receiving ultrasonic waves with sufficient sound pressure and
sensitivity while eliminating the need for applying DC bias voltage by providing an electret, an
ultrasonic diagnostic apparatus, and an ultrasonic diagnostic apparatus Provide an acoustic
microscope. A vibration comprising a first electrode, a vibrating membrane disposed on the first
electrode with a gap therebetween, and a second electrode supported by the vibrating
membrane. In the ultrasonic transducer configured to include a daughter cell and an electret
layer that holds a charge and gives a predetermined potential difference between the first
electrode and the second electrode, the electret layer includes When viewed from the
transmission direction of the ultrasonic wave generated by the vibration of the vibrating
membrane, the vibrating membrane is disposed in a region separated from the transducer cell.
[Selected figure] Figure 5
Ultrasonic transducer, ultrasonic diagnostic apparatus and ultrasonic microscope
[0001]
The present invention relates to a capacitive ultrasonic transducer configured to include an
electret, an ultrasonic diagnostic apparatus, and an ultrasonic microscope.
[0002]
2. Description of the Related Art Ultrasonic diagnostic methods for irradiating a subject with
ultrasonic waves and diagnosing the state of the subject from echo signals thereof are in
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widespread use.
An ultrasonic endoscope used in the medical field is one of the ultrasonic diagnostic apparatuses
used for the ultrasonic diagnostic method.
[0003]
The ultrasonic diagnostic apparatus is used not only in the medical field but also in the industrial
field to diagnose the presence or absence of a defect such as a flaw, a crack, or a cavity generated
in a subject (sample), and these are nondestructive It is known as an inspection device or a
nondestructive testing device.
[0004]
In addition, so-called V (z) curve for quantifying the elastic property of the subject or evaluating
the structure of the thin film by irradiating the subject (sample) with ultrasonic waves and
evaluating the acoustic characteristics of the subject The analysis method by is known.
An ultrasonic microscope is known as an apparatus for analyzing the property of an object from
such a V (z) curve.
[0005]
These ultrasonic diagnostic apparatuses and ultrasonic microscopes are provided with ultrasonic
transducers for converting electric signals into ultrasonic waves and transmitting the ultrasonic
waves, and for receiving ultrasonic waves and converting them into electric signals.
[0006]
Conventionally, a piezoelectric element such as ceramic piezoelectric material PZT (lead zirconate
titanate) has been mainly used as an ultrasonic transducer, but in recent years, micromachining
technology as disclosed in Japanese Patent Application Laid-Open No. 2005-510264. Capacitive
micromachined ultrasonic transducers (hereinafter referred to as c-MUTs) manufactured by
using the U.S. Pat.
[0007]
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The c-MUT is configured to include a pair of flat plate-like electrodes (parallel flat plate
electrodes) facing each other across a gap, and transmits and receives ultrasonic waves by
vibration of a membrane (membrane) including one of the electrodes. To do.
The c-MUT converts an ultrasonic signal into an electrical signal based on a change in
electrostatic capacitance between a pair of electrodes when receiving ultrasonic waves, and in
particular, when receiving, a DC bias voltage between the pair of electrodes Must be applied.
[0008]
In order to solve this problem, a c-MUT (electrostatic ultrasonic transducer) that does not require
application of a DC bias voltage by providing an electret (electret insulating film) between a pair
of electrodes is disclosed in JP-A-2-52599. Is disclosed in Japanese.
Japanese Patent Application Laid-Open No. 2005-510264.
[0009]
By the way, the sound pressure of the ultrasonic wave transmitted by the c-MUT and the
sensitivity to the received ultrasonic wave depend on the capacitance between the pair of
electrodes. For example, FIG. 14 shows an equivalent circuit diagram in the case where the
electret 503 is disposed between parallel plate electrodes composed of a pair of electrodes 501
and 502. In this case, the combined capacitance C1 between the pair of electrodes 501 and 502
is a value obtained by combining the capacitance Cmem of the membrane 506, the capacitance
Ccav of the cavity 504 (air gap), and the capacitance Cele of the electret 503. It becomes.
[0010]
Here, since the thickness of the cavity 504 is determined by the required amplitude of the
membrane 506, it is constant regardless of the presence or absence of the electret 503.
Therefore, when the electret 503 is not disposed between the electrodes 501 and 502, the
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combined capacitance C0 between the electrodes 501 and 502 is larger than the combined
capacitance C1.
[0011]
In other words, in the conventional c-MUT, since the thickness of the cavity 504 is increased by
arranging the electret, the capacitance between the electrodes is reduced as compared with the
case where the electret is not arranged.
[0012]
For example, when the c-MUT is used in a body cavity such as for an ultrasound endoscope, the
c-MUT is preferably driven at a low voltage to ensure insulation.
In order to obtain the capacitance between the electrodes which can realize sufficient acoustic
pressure and sensitivity of ultrasonic waves at the time of this low voltage driving, the interelectrode distance of the c-MUT is made 1 μm or less, preferably 0.5 μm or less Is desirable.
[0013]
On the other hand, an electret formed of, for example, a silicon oxide film needs to have a
thickness of at least 1 μm in order to stably hold charge over a long period.
[0014]
That is, when the electret is disposed between the electrodes, the necessary inter-electrode
distance can not be secured, and it is impossible to transmit and receive ultrasonic waves with
sufficient sound pressure and sensitivity using the conventional c-MUT. Met.
[0015]
The present invention has been made in view of the above problems, and by providing an
electret, it is possible to transmit and receive ultrasonic waves with sufficient sound pressure and
sensitivity while making it unnecessary to apply a DC bias voltage. An object of the present
invention is to provide a capacitive ultrasonic transducer, an ultrasonic diagnostic apparatus and
an ultrasonic microscope.
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[0016]
An ultrasonic transducer according to the present invention comprises a first electrode, a
vibrating membrane disposed on the first electrode with a gap therebetween, and a second
electrode supported by the vibrating membrane. An ultrasonic transducer comprising: a
transducer cell configured as described above; and an electret layer that holds a charge and
applies a predetermined potential difference between the first electrode and the second
electrode, The layer is characterized in that it is disposed in a region separated from the
transducer cell when viewed from the transmission direction of the ultrasonic wave generated by
the vibration of the vibrating film.
[0017]
First Embodiment Hereinafter, a first embodiment of the present invention will be described with
reference to FIGS. 1 to 8.
In each of the drawings used in the following description, the scale of each member is made
different in order to make each member have a size that can be recognized in the drawings.
FIG. 1 is an explanatory view showing a schematic configuration of an ultrasonic endoscope.
FIG. 2 is a perspective view showing the structure of the distal end portion of the ultrasonic
endoscope.
FIG. 3 is a perspective view of the transducer array.
[0018]
In this embodiment, an example in which the present invention is applied to an ultrasonic
endoscope as an ultrasonic diagnostic apparatus will be described. As shown in FIG. 1, the
ultrasonic endoscope 1 according to the present embodiment includes an elongated insertion
portion 2 introduced into a body cavity, an operation portion 3 positioned at a proximal end of
the insertion portion 2, and the operation portion 3. And a universal cord 4 extending from the
side of the main body.
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[0019]
The proximal end of the universal cord 4 is provided with an endoscope connector 4a connected
to a light source device (not shown). The endoscope connector 4a is detachably connected to the
electric cable 5 detachably connected to the camera control unit (not shown) via the electric
connector 5a and the ultrasonic observation apparatus (not shown) via the ultrasonic connector
6a. The ultrasonic cable 6 is extended.
[0020]
The insertion portion 2 is positioned at a distal end rigid portion 20 formed of a hard resin
member in order from the distal end side, a bendable curved portion 8 positioned at the rear end
of the distal end rigid portion 20, and a rear end of the curved portion 8 A flexible tube portion 9
having a small diameter and a long length and extending to the tip end portion of the operation
portion 3 is continuously provided. Further, an ultrasonic wave transmitting / receiving unit 30
for transmitting / receiving an ultrasonic wave described later in detail is provided on the distal
end side of the distal end rigid portion 20.
[0021]
The operation unit 3 has an angle knob 11 for controlling the bending of the bending portion 8
in a desired direction, an air supply / water supply button 12 for performing air supply and
water supply operations, a suction button 13 for performing suction operation, a body cavity The
treatment tool insertion port 14 etc. which become an entrance of the treatment tool to introduce
to are provided.
[0022]
As shown in FIG. 2, the distal end rigid portion 20 includes an illumination lens (not shown) that
constitutes an illumination optical unit that emits illumination light to the observation site, and
an objective that constitutes an observation optical unit that captures an optical image of the
observation site A lens 21, a suction and forceps port 22, which is an opening through which a
portion to be removed is suctioned or a treatment tool protrudes, and an air / water supply port
(not shown) for supplying air and water are provided.
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[0023]
As shown in FIG. 3, the ultrasonic wave transmitting / receiving unit 30 provided at the distal
end of the distal end rigid portion 20 is configured to include the transducer array 31, the drive
circuit 34, and the FPC 35.
The FPC 35 is a wiring board (flexible wiring board) having flexibility and mounting surfaces
formed on both sides, and in the ultrasonic wave transmitting / receiving unit 30, the FPC 35 is
an axis substantially parallel to the insertion axis of the distal end rigid portion 20. Is wound in a
substantially cylindrical shape with the central axis as a center axis.
[0024]
On the outer peripheral surface of the cylindrical FPC 35, a transducer array 31 which is an
ultrasonic transducer array is provided.
The transducer array 31 includes a plurality of transducer units 32, which are the ultrasonic
transducers of the present embodiment, arranged in the circumferential direction on the outer
peripheral surface of the FPC 35. The transducer units 32 have a substantially rectangular shape
as viewed from the normal direction of the outer peripheral surface of the FPC 35, and are
arranged at equal intervals on the outer peripheral surface of the cylindrical FPC 35, with the
short direction as the circumferential direction. The transducer array 31 includes, for example,
several tens to several hundreds of transducer units 32. The transducer array 31 according to
the present embodiment includes 128 transducer units 32. Each transducer unit 32 is provided
with sixteen transducer elements 33.
[0025]
As will be described in detail later, the transducer unit 32 of the present embodiment is a
capacitive ultrasonic transducer formed by micromachining technology on a silicon substrate
made of a silicon semiconductor with low resistance, and so-called MEMS (Micro Electro) It
belongs to the technical scope of Mechanical Systems. A capacitive ultrasonic transducer formed
by such micromachining technology is generally called c-MUT (Capacitive Micromachined
Ultrasonic Transducer).
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[0026]
In the transducer array 31 of the present embodiment, a plurality of transducer elements 33
arranged in one transducer unit 32 constitute a minimum drive unit for transmitting and
receiving ultrasonic waves. The transducer elements 33 transmit ultrasonic waves in the normal
direction of the mounting surface of the FPC 35, that is, outward in the radial direction of the
cylindrical FPC 35.
[0027]
On the other hand, a plurality of drive circuits 34 are mounted on the inner peripheral surface of
the cylindrical FPC 35, that is, on the mounting surface opposite to the mounting surface on
which the transducer array 31 is mounted. The drive circuit 34 has an electric circuit such as a
pulser for driving the transducer element 33 or a selection circuit, and is electrically connected
to each transducer element 33.
[0028]
The drive circuit 34 is also electrically connected to the plurality of signal electrodes 36 and the
ground electrode 37 formed on the outer peripheral surface of the cylindrical FPC 35. The signal
electrode 36 and the ground electrode 37 are inserted in the ultrasonic cable 6 and one end is
electrically connected to the ultrasonic connector 6a. The other end of the coaxial cable is
electrically connected. Thus, the drive circuit 34 is electrically connected to the ultrasonic
observation apparatus.
[0029]
The ultrasonic transmitting and receiving unit 30 having the above-described configuration is
formed on a plane substantially orthogonal to the insertion axis of the distal end rigid portion 20
by the two-dimensional transducer array 31 disposed on the outer peripheral surface of the
cylindrical FPC 35 It is possible to perform electronic radial scanning capable of sector scanning,
which transmits and receives radially based on the above.
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[0030]
Next, the detailed configuration of the transducer unit 32, which is the capacitive ultrasonic
transducer according to the present embodiment, will be described below with reference to FIGS.
FIG. 4 is a top view of the transducer unit 32 as viewed from the ultrasonic wave transmitting
and receiving side. That is, in FIG. 4, ultrasonic waves are transmitted in the direction orthogonal
to the paper surface and away from the paper surface. FIG. 5 is a cross-sectional view taken
along the line V-V of FIG. FIG. 6 is an equivalent circuit diagram of the transducer unit 32. As
shown in FIG. FIG. 7 is a partial cross-sectional view of a region where the electret layer of the
transducer unit is formed.
[0031]
As shown in FIG. 4, the transducer unit 32 of the present embodiment is configured by arranging
a plurality of transducer elements 33. In FIG. 4, an elongated region surrounded by a broken line
indicates one transducer element 33.
[0032]
The transducer element 33 is configured to include a plurality of transducer cells 100. In
addition, the transducer element 33 includes an electret layer 130 electrically connected to each
of the plurality of transducer cells 100 constituting the transducer element 33, a signal electrode
pad 38, and a ground electrode pad 39. Is configured.
[0033]
In the present embodiment, the transducer element 33 includes eight transducer cells 100
linearly arranged in the longitudinal direction of the elongated region, and eight transducer cells
100 arranged at one end of the elongated region. It comprises one electret layer 130 electrically
connected in parallel to all.
[0034]
In the same transducer element 33, the transducer cells 100 are all electrically connected in
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parallel, and drive signals from the ultrasonic observation apparatus are simultaneously input
through the signal electrode pad 38, so that the same signals are simultaneously generated.
Transmit phase ultrasound.
[0035]
As shown in FIG. 5, the transducer element 33 of the present embodiment is a capacitive type
having a laminated structure formed on a silicon substrate 101 made of a silicon semiconductor
with low resistance by a micromachining technology using a semiconductor process or the like.
Ultrasonic transducer.
[0036]
In the following description of the laminated structure, the vertical direction of each layer is such
that the direction of moving away from the surface of the silicon substrate 101 in the normal
direction is the upper direction.
For example, in the cross-sectional view of FIG. 5, the upper electrode 120 is referred to as being
disposed above the lower electrode 110.
The thickness of each layer refers to the dimension of each layer in the direction normal to the
surface of the silicon substrate 101.
In the following description, for convenience, the surface of the silicon substrate 101 on which
the transducer cell 100 is to be formed is referred to as the cell formation surface, and the
surface opposite to the surface on which the transducer cell 100 is to be formed is referred to It
is called the back side.
[0037]
The silicon substrate 101 is made of low resistance silicon having conductivity, and a first
insulating film 102 and a back surface insulating film 109 which are silicon oxide films having
electric insulating properties are formed on both surfaces. The first insulating film 102 and the
back surface insulating film 109 are high temperature oxide films formed by thermally oxidizing
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the silicon substrate 101. The first insulating film 102 and the back surface insulating film 109
may be silicon nitride films.
[0038]
First, the structure of the transducer cell 100 will be described in detail below. The transducer
cell 100 has a lower electrode 110 (first electrode) and an upper electrode 120 (second
electrode), which are a pair of parallel flat plate electrodes facing each other through the cavity
107 which is a substantially cylindrical gap. And be configured. The transducer element 33
configured to include the transducer cell 100 is vibrated by the membrane 100 a (vibrating film)
which is a film-like structure having elasticity including the upper electrode 120 of the
transducer cell 100. It transmits and receives ultrasonic waves.
[0039]
A lower electrode 110 which is a conductive layer is formed on the first insulating film 102 in a
substantially circular shape as viewed from above. The lower electrode 110 is formed by
depositing Mo (molybdenum) by sputtering and patterning. In the lower electrode 110, lower
electrodes 110 of the transducer cells 100 adjacent to each other when viewed from above are
electrically connected by the lower electrode wiring 111.
[0040]
The material of the lower electrode 110 which is the lower layer portion of the laminated
structure and is formed on the silicon oxide film is not limited to Mo, but may be formed of, for
example, W (tungsten), Ti (titanium), Ta (tantalum) or the like. The melting point metal or its
alloy is preferable, but the material is not limited to this as long as high temperature heat
treatment can be avoided in the subsequent manufacturing process, and Al (aluminum), Cu
(copper), etc. It may be The lower electrode 110 may have a multilayer structure in which two or
more conductive materials are stacked.
[0041]
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A wafer penetrating electrode 112 formed through the silicon substrate 101 is formed at an end
opposite to the end where the electret layer 130 is disposed, of the transducer element 33
having an elongated shape as viewed from above. , 33 transducer elements are provided. Wafer
penetrating electrode 112 is electrically insulated from silicon substrate 101 and electrically
connected to lower electrode 110 and signal electrode pad 38 formed on back surface insulating
film 109.
[0042]
That is, all the lower electrodes 110 in the same transducer element 33 are electrically connected
to the signal electrode pads 38 formed on the back surface of the silicon substrate 101 through
the lower electrode wiring 111 and the wafer through electrode 112. There is.
[0043]
A second insulating film 103 having electrical insulation is formed on the lower electrode 110 so
as to cover the lower electrode 110.
The second insulating film 103 is a silicon oxide film in the present embodiment, and is formed
by plasma CVD. The second insulating film 103 may be a silicon nitride film, hafnium nitride
(HfN), hafnium oxynitride (HfON), or the like.
[0044]
On the second insulating film 103, a third insulating film 104 having electrical insulation is
formed over the cavity 107. The third insulating film 104 is a silicon oxide film in the present
embodiment, and is formed by plasma CVD. The third insulating film 104 may be a silicon nitride
film.
[0045]
Between the second insulating film 103 and the third insulating film 104, a cavity 107 which is a
sealed void layer in an atmospheric pressure, pressurized or depressurized state is formed. Here,
the reduced pressure state refers to a state in which the pressure is lower than the atmospheric
04-05-2019
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pressure, and also includes a so-called vacuum state. The cavity 107 has a substantially
cylindrical shape, and is provided substantially concentrically with the lower electrode 110 as
viewed from above.
[0046]
In the present embodiment, the cavity 107 is formed by etching the sacrificial layer, which is a
known technique, and is used to communicate the inside of the cavity 107 used in etching the
sacrificial layer with the upper layer of the third insulating film 104. The layer removal holes are
sealed by plugs (not shown). The cavity 107 may be formed by a method of bonding wafers after
mechanical or chemical microfabrication.
[0047]
On the third insulating film 104, an upper electrode 120 which is a substantially circular
conductive layer as viewed from above is formed. The upper electrode 120 is provided
substantially concentrically with the lower electrode 110 as viewed from above, that is, at a
position facing the lower electrode 110. In the present embodiment, the upper electrode 120 is
formed by depositing and patterning Al by sputtering.
[0048]
The upper electrodes 120 of the transducer cells 100 adjacent to each other when viewed from
above are electrically connected to each other by the upper electrode wiring 121. The material of
the upper electrode 120 may be any material other than Al, for example, one having conductivity
such as Cu, W, Ti, or Ta. The upper electrode 120 may have a multilayer structure in which two
or more conductive materials are stacked.
[0049]
The upper electrode wiring 121 is electrically connected to the through electrode 122 at an end
opposite to the end where the electret layer 130 is disposed, of the transducer element 33
having an elongated shape as viewed from above. There is. The through electrode 122 is formed
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through the first insulating film 102, the second insulating film 103, and the third insulating film
104 in the same process as the upper electrode 120 and the upper electrode wiring 121, and the
through electrode 122 is formed. Are electrically connected to the silicon substrate 101 via the
ohmic contact region 122a.
[0050]
Further, a ground electrode pad 39 is formed on the back surface insulating film 109, and the
ground electrode pad 39 is electrically connected to the silicon substrate 101 through the ohmic
contact region 123a.
[0051]
That is, all the upper electrodes 120 in the same transducer element 33 are electrically
connected to the ground electrode pad 39 formed on the back surface of the silicon substrate
101 via the upper electrode wiring 121, the through electrode 122, and the silicon substrate
101. It is connected.
[0052]
A protective film 105 having electrical insulation is formed on the upper electrode 120.
The protective film 105 is a silicon nitride film in the present embodiment, and is formed by
plasma CVD.
The protective film 105 may be made of a silicon oxide film, hafnium nitride (HfN), hafnium
oxynitride (HfON) or the like in addition to silicon nitride. In particular, HfN and HfON are
preferable as protective films because high density films are obtained.
[0053]
Further, on the protective film 105, a paraxylylene resin film 106 having water resistance,
chemical resistance, and the like and excellent in biocompatibility and electrical insulation is
formed.
[0054]
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The transducer unit 32 is mounted on the FPC 35 by a known method such as solder bonding,
anisotropic conductive film bonding, ultrasonic bonding and the like.
Thereby, the transducer cell 100 of the transducer element 33 described above is electrically
connected to the drive circuit 34 mounted on the opposite side of the FPC 35 through the signal
electrode pad 38 and the ground electrode pad 39.
[0055]
As described above, in the present embodiment, the substrate on which the vibrator cell 100 is
formed is the low resistance silicon substrate 101, and the silicon substrate 101 is set to the
ground potential to shield the noise coming from the back side, thereby further improving the S /
N ratio. It is possible to obtain an ultrasound image with a high ratio. In addition, by providing
the signal electrode pad 38 and the ground electrode pad 39 on the back surface side of the
transducer cell 100, the mounting area can be reduced, and the distal end rigid portion 20 can
be configured to be short. The operability of the mirror 1 is improved.
[0056]
In the configuration described above, the lower electrode 110, the upper electrode 120, and the
cavity 107 have a substantially circular shape when viewed from above, but the shape is not
limited to this embodiment, and may be, for example, a regular hexagon or the like. It may be a
polygonal shape such as a rectangle, or any other shape. The dimensions of the membrane 100a
and the cavity 107 are determined by the wavelength and output of ultrasonic waves used during
observation.
[0057]
Next, the configuration of the region where the electret layer 130 of the ultrasonic transducer of
the present embodiment is disposed will be described in detail below. In the present embodiment,
as described above, the electret layer 130, which is the charge holding means, is disposed at the
end of the transducer element 33 having an elongated shape as viewed from above. The electret
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layer 130 has a function of permanently holding positive or negative charges.
[0058]
The electret layer 130 of the present embodiment is made of an inorganic film, and specifically,
is formed by charging a silicon oxide film formed by a plasma CVD method or the like by corona
discharge. The electret layer 130 may be formed of another inorganic film such as a silicon
nitride film, an HfO 2 film, or a Hf (hafnium) oxide such as an HfAl 2 O 5 film. In addition, the
electret layer 130 may be configured by laminating a plurality of types of the inorganic films.
[0059]
As shown in the equivalent circuit diagram of FIG. 6, in the single transducer element 33, the side
holding the negative charge of the electret layer 130 is electrically connected to the lower
electrode 110 of each of the plurality of transducer cells 100. It is connected to the. Since the
upper electrode 120 of the transducer cell is grounded, the electret layer 130 provides a
potential difference between the lower electrode 110 which is a pair of electrodes of the
transducer cell 100 and the upper electrode 120.
[0060]
That is, the transducer cell 100 is electrically equivalent to the state in which the DC bias voltage
is applied between the lower electrode 110 and the upper electrode 120, and the transducer unit
32 which is the ultrasonic transducer of this embodiment has the DC bias voltage. It becomes
possible to transmit and receive an ultrasonic wave, without applying from the outside. That is,
the voltage effective value of the signal for driving the transducer cell 100 can be reduced.
[0061]
Therefore, the ultrasonic diagnostic apparatus equipped with the transducer cell 32, which is the
ultrasonic transducer of the present embodiment, does not require a circuit or wiring for
applying a DC bias voltage as in the conventional c-MUT, and the apparatus can be miniaturized.
Can be implemented. Further, since the voltage effective value of the drive signal for driving the
04-05-2019
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transducer cell 100 can be suppressed to be low, the current value flowing through the drive
circuit or the wiring can be reduced, and power consumption can be reduced. As a result, it is
possible to further miniaturize the drive circuit and to prevent the characteristic variation of the
transducer cell due to the heat generation of the drive circuit.
[0062]
Specifically, as shown in the partial cross sectional view of FIG. 7, the electret layer 130 of the
present embodiment is a lower conductive layer 114 (first conductive layer) electrically
connected to the lower electrode 110 of the transducer cell 100. And the upper conductive layer
124 (second conductive layer) electrically connected to the upper electrode 120. In the present
embodiment, the lower conductive layer 114 is a conductive layer made of Mo formed by the
same semiconductor process as the lower electrode 110. The upper conductive layer 124 is a
conductive layer made of Al formed by the same semiconductor process as the upper electrode
120.
[0063]
In addition, a void 131 which is an insulating layer is interposed between the electret layer 130
and the upper conductive layer 124. The void portion 131 is formed by sacrificial layer etching
which is a known technique in the present embodiment. The void portion 131 may be another
insulating film such as a silicon oxide film or a silicon nitride film as long as it electrically
insulates the electret layer 130 from the upper conductive layer 124.
[0064]
A protective film 105 having electrical insulation is formed above the upper conductive layer
124 as in the case of the vibrator cell 110. As described above, the protective film 105 is a
silicon nitride film in the present embodiment.
[0065]
Further, in the upper conductive layer 124 and the protective film 105 disposed above the
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electret layer 130, innumerable minute through holes 132 penetrating the upper conductive
layer 124 and the protective film 105 in the thickness direction are formed. It is done. The
through holes 132 are formed only in a region overlapping the electret layer 130 when viewed
from above the upper conductive layer 124 and the protective film 105. In the present
embodiment, the through holes 132 are on the order of μm in diameter (a few μm in diameter),
and are randomly scattered at a predetermined distribution density.
[0066]
The form of the through holes 132 formed in the upper conductive layer 124 and the protective
film 105 is not limited to this embodiment, and the through holes 132 are regularly formed, for
example, in a matrix. It may be.
[0067]
Above the protective film 105, a paraxylylene resin film 106 is formed as in the case of the
transducer cell 110.
[0068]
Further, as shown in FIG. 7, in the transducer element 33, the region where the electret layer 130
is disposed is projected upward (the transmission direction of the ultrasonic wave) than the
region where the transducer cell 100 is formed. Is formed.
Specifically, the thickness We of the region of the transducer element 33 where the electret layer
130 is disposed is larger than the thickness Wc of the region where the transducer cell 100 is
formed.
[0069]
As described above, the transducer unit 32 according to the present embodiment has a
configuration in which the region adjacent to the transducer cell 100 protrudes in the ultrasound
transmission direction more than the region in which the transducer cell 100 is formed. It is
possible to prevent the breakage of the membrane 100 a of the transducer cell 100 due to the
contact with another object.
[0070]
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Further, in the present embodiment, in the region where the electret layer 130 is formed, the
distance De between the upper conductive layer 124 and the lower conductive layer 114 serving
as parallel plate electrodes facing each other is the upper electrode 120 and the lower electrode
of the transducer cell 100. It is formed to be wider than the interval Dc of 110.
For this reason, it is possible to suppress the generation of parasitic capacitance in a region that
does not contribute to the transmission and reception of ultrasonic waves, and to increase the
efficiency of driving the ultrasonic unit.
[0071]
Here, the charging process by corona discharge of the electret layer 130 of the transducer unit
32 which is the ultrasonic transducer of the present embodiment is carried out on the silicon
oxide film to be the electret layer 130, the void 131, the upper conductive layer 124 and the
protective film. This is performed in a state where the through holes 132 are formed, and the
through holes 132 penetrating the upper conductive layer 124 and the protective film 105 in the
thickness direction are further formed.
[0072]
That is, at least part of the electret layer 130 is exposed upward through the through-hole 132
after all the semiconductor processes for forming the layer structure after the electret layer 130
are completed. It takes place in the
[0073]
Then, after the electret layer 130 is charged, the paraxylylene resin film 106 is formed by spin
coating or the like to complete the structure on the cell formation surface side of the transducer
unit 32.
[0074]
The effects of the ultrasonic transducer and the ultrasonic diagnostic apparatus of the present
embodiment having the above-described configuration will be described below.
[0075]
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In the transducer unit 32 of the present embodiment, the electret layer 130 is a transducer cell
when viewed from the transmission direction of ultrasonic waves, that is, the stacking direction
of the lower electrode 110 and the upper electrode 120 which are a pair of electrodes of the
transducer cell 100. They are arranged in mutually separated areas which do not overlap 100.
Therefore, in the vibrator unit 32 according to the present embodiment, the thickness of the
electret layer 130 and the distance between the lower electrode 110 and the upper electrode
120 can be set independently.
[0076]
For example, the transducer unit of the present embodiment is compared to a conventional
capacitive ultrasonic transducer in which the electret 503 is disposed between the electrodes
501 and 502 which are a pair of parallel plate electrodes as shown in FIG. 32 can make the
distance (gap) between a pair of parallel plate electrodes (in the present embodiment, the lower
electrode 110 and the upper electrode 120) smaller, and make the electret layer 130, which is a
charge holding means, thicker.
[0077]
Therefore, according to the present embodiment, the distance between the lower electrode 110
and the upper electrode 120 is made smaller than in the prior art to increase the capacitance
between both electrodes, and the sound pressure of the transmitting ultrasonic wave and the
receiving ultrasonic wave While improving the sensitivity, the thickness of the electret layer 130
can be made such that the electret layer 130 can permanently and stably hold the charge.
[0078]
Further, the transducer unit 32 according to the present embodiment is not disposed by being
stacked on the lower electrode 110 and the upper electrode 120 and the electret layer 130 in
the thickness direction, and therefore, the transducer unit 32 is more than the conventional
capacitive ultrasonic transducer. It is possible to make it thin.
[0079]
Similarly, as compared with the conventional capacitive ultrasonic transducer configured by
laminating the transducer cell and the electret in the thickness direction, the transducer unit 32
of the present embodiment transmits ultrasonic waves. It is possible to make the thickness in the
direction thinner.
04-05-2019
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[0080]
Therefore, the transducer unit 32, which is the ultrasonic transducer of the present embodiment,
is thinner compared to the prior art, and has higher sound pressure of transmission ultrasonic
waves and higher sensitivity of reception ultrasonic waves when driven by a low voltage. In
addition, its properties can be maintained permanently.
[0081]
In other words, the present embodiment maintains the initial performance over a long period of
time in achieving the predetermined sound pressure of the transmission ultrasonic wave and the
sensitivity of the reception ultrasonic wave, and is thinner and lower voltage than before. To
realize a drivable ultrasonic transducer.
[0082]
Further, according to the present embodiment, it is possible to configure an ultrasonic diagnostic
apparatus including the transducer unit 32 which is thin and can be driven by a low voltage, so
as to have a longer life and smaller size than in the prior art. .
For example, in the case of the ultrasonic endoscope 1 as shown in FIG. 1, the outer diameter of
the transducer array 31 can be made smaller than before, and a diagnosis with less burden on
the subject can be realized. Can.
[0083]
Further, in the vibrator unit 32 according to the present embodiment, the upper conductive layer
124 and the protective film 105 disposed on the upper layer of the electret layer 130 are
penetrated through the upper conductive layer 124 and the protective film 105 in the thickness
direction. Holes 132 are formed.
Since the electret layer 130 is disposed in a region separated from the transducer cell 100 when
viewed from the transmission direction of the ultrasonic waves when the process of forming the
upper conductive layer 124 and the protective film 105 is completed, the through holes 132 are
04-05-2019
21
formed. At least a part is exposed upward (transmission direction of ultrasonic waves) via
[0084]
In the vibrator unit 32 according to the present embodiment having such a configuration, the
step of charging the electret layer 130 by corona discharge is easily performed after the upper
conductive layer 124 and the protective film 105 are formed. Is possible.
In this charging process, the charges generated by the corona discharge are not entirely captured
by the upper conductive layer 124 which is a conductive layer covering the electret layer 130,
but a part of the charges is formed on the electret layer 130 through the through holes 132. To
reach.
Then, after the electrification process of the electret layer 130 is completed, the step of forming
the paraxylylene resin film 106 is performed, and the structure on the cell formation surface side
of the transducer unit 32 is completed.
The paraxylylene resin preferably contains fluorine (F) because it has high chemical resistance.
[0085]
In other words, in the present embodiment, the electret process is performed on the electret
layer 130 after the entire layer structure formed by the semiconductor process is formed, and
after the electret process is performed on the electret layer 130, the electret process is
performed. There is no step of raising the temperature of layer 130, such as a step such as CVD.
[0086]
In general, electrets, which are charge holding means, have the property of releasing charges and
lowering the amount of charge held when the temperature is raised.
For example, in the electret layer 130 made of the silicon oxide film of the present embodiment,
when the temperature is approximately 400 ° C. or more, a decrease in the charge amount
04-05-2019
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occurs.
If the amount of charge held by the electret layer 130 decreases, the direct current voltage
component applied between the lower electrode 110 and the upper electrode 120 decreases, so
the sensitivity of the ultrasonic waves received by the transducer unit 32 particularly decreases.
Resulting in.
[0087]
For example, in the case of forming a capacitive ultrasonic transducer in which the electret 503
is disposed between the electrodes 501 and 502 which are a pair of parallel flat plate electrodes
as shown in FIG. 14 in the prior art, the electret 503 is charged. If processing performed at a
temperature of 400 ° C. or higher is used to form the electrode 501 on the upper layer side and
the insulating film after the processing, the electrification amount of the electret 503 decreases
and the sensitivity of the ultrasonic transducer decreases. It will do.
Although it is conceivable to prevent the decrease in the electrification amount of the electret
503 by performing all the manufacturing steps of the ultrasonic transducer at 400 ° C. or lower
after the electret 503 is charged, the usable film forming method is limited. There is a problem
that cost increases because the number of manufacturing apparatuses required increases and the
process becomes complicated.
[0088]
However, the vibrator unit 32 having the configuration of the present embodiment heats the
electret layer 130 after the charging process as described above to a temperature at which the
amount of charge held by the electret layer 130 is reduced. It has the composition which can be
manufactured without.
[0089]
Therefore, the transducer unit 32, which is the ultrasonic transducer of the present embodiment,
can increase the amount of charge held by the electret layer 130 compared to the prior art, and
receive higher when driven by a low voltage. It has ultrasonic sensitivity.
04-05-2019
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In addition, since the vibrator unit 32 of this embodiment does not require a semiconductor
process performed at a relatively low temperature, for example, a processing temperature of 400
° C. or less, it can be manufactured at low cost by a more versatile semiconductor
manufacturing apparatus. It is possible.
[0090]
In the above-described embodiment, the electret layer 130 is described as a single layer or
multilayer inorganic film such as a silicon oxide film, which has been subjected to a charging
process, but the form of the electret layer 130 is not limited thereto. It is not limited.
[0091]
For example, the electret layer 130 may be formed of an organic film, and specifically, may be
formed by charging a fluorocarbon resin generally referred to as FEP by corona discharge, or a
fluorocarbon resin other than FEP, or the like. It may be composed of other organic films such as
polyimide, polypropylene and polymethylpentene.
[0092]
Electrets composed of these organic films are forms conventionally used in other fields, and are
known to be capable of stably holding charges for a long period of time.
However, electrets made of organic films have the property of lowering the amount of charge
held by raising the temperature, and in particular, the decrease in the amount of charge held is
100 ° C. to 100 ° C. lower than electrets made of inorganic films. Since it occurs at about 200
° C., it is difficult to apply to a capacitive ultrasonic transducer formed by a semiconductor
process.
[0093]
However, in the vibrator unit 32 according to the present embodiment, since the electret
charging process is performed after the completion of the semiconductor process as described
above, even if the electret is formed of an organic film, the amount of charge held by the electret
decreases. I will never do it.
04-05-2019
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[0094]
Therefore, according to the present embodiment, the electret of the vibrator unit 32 can be
constituted by an organic film capable of holding charges stably for a long period of time
compared to the prior art, and has a longer life than the prior art. It is possible to provide a
capacitive ultrasonic transducer.
[0095]
Further, in the above-described embodiment, the electret layer 130 holding negative charge is
formed in contact with the lower conductive layer 114 electrically connected to the lower
electrode 110 of the transducer cell 100.
Then, an air gap portion 131 which is an insulating layer is interposed between the electret layer
130 and the upper conductive layer 124.
[0096]
Such a configuration is effective particularly when the voltage signal output from the drive circuit
34 and supplied to the lower electrode 110 at the time of transmission of the ultrasonic waves of
the transducer unit 32 has a negative polarity.
This is because in such a configuration, a DC voltage component of negative polarity is applied
between the lower electrode 110 and the upper electrode 120 by the electret layer 130, and the
upper part where the charge held by the electret layer 130 is the ground potential This is
because it is possible to prevent the conductive layer 124 from flowing out.
[0097]
Further, in order to make the retention of charge by the electret layer 130 more reliable, it is
effective to cover the entire surface around the electret layer 130 with an insulating film.
It goes without saying that the insulating film covering the entire surface around the electret
04-05-2019
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layer 130 may be divided into a plurality of insulating films.
[0098]
For example, as shown in FIG. 8 as a modified example of the present embodiment, insulating
layers 138 and 139 are formed on the lower layer side and the upper layer side of electret layer
130, thereby covering the entire surface around electret layer 130 with an insulating film. With
the configuration, the charge retention by the electret layer 130 can be made more reliable.
In the modification of the present embodiment shown in FIG. 8, when the electret layer 130 is
formed of a silicon oxide film, the second insulating film 104 covering the electret layer 130, the
protective film 105, and the insulating layers 138 and 139 are silicon. It is preferable to be
composed of a nitride film.
[0099]
Note that the polarity of the charge held by the electret layer 130 and the air gap 131 which is
an insulating layer depending on the polarity of the signal output from the drive circuit 34 and
whether the signal is applied to the lower electrode 110 or the upper electrode 120. The position
at which is interposed is appropriately changed, and is not limited to the above-described
embodiment.
[0100]
In addition, in an ultrasonic diagnostic apparatus configured to include an ultrasonic transducer,
a conductive layer electrically grounded independently of the ultrasonic transducer to shield
extraneous noise and improve the S / N ratio. The shield layer may cover the ultrasonic
transducer.
[0101]
When the shield layer is applied to the embodiment described above, for example, if the process
of covering the transducer cell 32 with the shield layer is performed at a temperature at which
the amount of charge held by the electret layer 130 decreases. For example, a through hole is
formed in a region overlapping the electret layer 130 of the shield layer as in the upper
conductive layer 124, and the electret layer 130 is charged through the through hole.
04-05-2019
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[0102]
For example, if the process of covering the transducer cell 32 with a shield layer is performed at
a temperature lower than the temperature at which the amount of charge held by the electret
layer 130 decreases, the shield layer It is not necessary to form a through hole, which is formed
after the charging process is performed.
[0103]
The vibrator unit of the present embodiment is configured using the conductive silicon substrate
101 as a base, but the vibrator unit is made of electrically insulating quartz, sapphire, quartz,
alumina, zirconia, or the like. You may form on the base material comprised with insulating
materials, such as glass and resin.
[0104]
In addition, although the ultrasonic endoscope of the present embodiment is described as
performing electronic radial scanning, the scanning method is not limited to this, and linear
scanning, convex scanning, mechanical scanning, etc. It may be adopted.
The transducer array may be a two-dimensional array in which a plurality of transducer elements
are two-dimensionally arrayed, and not only a form in which the transducer elements are
arrayed, but a single transducer element It may be a form using.
[0105]
Further, the ultrasonic diagnostic apparatus of the present embodiment may be an ultrasonic
probe type without an optical observation window, or may be a capsule type ultrasonic
endoscope.
The ultrasound diagnostic apparatus may be a so-called extracorporeal ultrasound diagnostic
apparatus that performs ultrasound scanning from above the body surface of the subject into the
body cavity.
The ultrasonic diagnostic apparatus may be a nondestructive inspection apparatus or a
04-05-2019
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nondestructive testing apparatus used in the industrial field.
[0106]
Second Embodiment Hereinafter, a second embodiment of the present invention will be described
with reference to FIG.
FIG. 9 is a cross-sectional view of a transducer element according to a second embodiment.
[0107]
The second embodiment differs from the configuration of the first embodiment only in the
configuration of the region in which the electret layer is formed.
Therefore, only the difference will be described below, and the same components as those of the
first embodiment are denoted by the same reference numerals, and the description thereof will
be appropriately omitted.
[0108]
As compared with the first embodiment, as shown in FIG. 9, in the vibrator unit of the present
embodiment, the area where the electret layer 130 of the vibrator element 33a is formed is the
area where the vibrator cell 100 is formed. , And does not protrude in the transmission direction
of the ultrasonic wave.
[0109]
In the transducer element 33a of the present embodiment, the concave portion 101a is formed in
the region of the silicon substrate 101 where the electret layer 130 is formed, thereby
eliminating the unevenness on the surface on the ultrasonic wave transmitting side.
[0110]
With such a configuration, in the transducer unit which is the ultrasonic transducer of the
present embodiment, the accuracy of patterning in the semiconductor process forming the
04-05-2019
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transducer cell 100 is improved.
[0111]
That is, the transducer unit of the present embodiment can improve the dimensional accuracy of
the transducer cell 100 as compared to the first embodiment, and can form the transducer cell
100 having uniform acoustic characteristics. It becomes possible.
[0112]
Third Embodiment Hereinafter, a third embodiment of the present invention will be described
with reference to FIGS. 10 and 11. FIG.
FIG. 10 is a top view of the ultrasonic transducer unit 233 of the present embodiment.
FIG. 11 is a cross-sectional view taken along line XI-XI of FIG.
[0113]
The third embodiment differs from the configuration of the first embodiment only in the
positional relationship between the region in which the transducer cell and the electret layer are
formed.
Therefore, only the difference will be described below, and the same components as those of the
first embodiment are denoted by the same reference numerals, and the description thereof will
be appropriately omitted.
[0114]
As shown in FIG. 10, the transducer unit 233 according to this embodiment includes a plurality
of transducer cells 200 arranged in a matrix when viewed from above (transmission direction of
ultrasonic waves), and the transducer cells 200 are located above And a plurality of electret
04-05-2019
29
layers 230 formed in an area separated from each other.
In FIG. 10, a pattern formed by the same conductive layer as the upper electrode 220 of the
vibrator cell 200 is shown by a solid line, and a pattern formed by the same conductive layer as
the lower electrode 210 is shown by a broken line for the sake of description. Specifically, a
region where the electret layer 130 is disposed is indicated by a two-dot chain line. Specifically,
four transducer cells 200 arranged adjacent to each other in two rows and two columns which
are a part of the transducer unit 233 are shown. In the case where attention is paid to the above,
the electret layer 230 is disposed at the same distance from all of the four transducer cells 200
in the direction orthogonal to the ultrasonic wave transmission direction.
That is, in a cross section (FIG. 11) including a center of two transducer cells 200 located
diagonally of the four transducer cells 200 in 2 rows and 2 columns and parallel to the
transmission direction of the ultrasonic wave In this case, the transducer cells 200 and the
regions in which the electret layers 230 are disposed are alternately arranged.
[0115]
As shown in FIG. 11, as in the first embodiment, the vibrator unit 233 according to the present
embodiment includes a first insulating film 202 and a back surface insulating film 209, which are
silicon oxide films each having an electrical insulating property on both surfaces. Are formed by
a micromachining technique using a semiconductor process or the like on a silicon substrate 201
made of a low-resistance silicon semiconductor on which is formed.
[0116]
The configuration of the region in which the transducer cell 200 and the electret layer 230 are
disposed is the same as that of the first embodiment, and thus the detailed description thereof is
omitted, and only the configuration will be described below.
[0117]
The vibrator cell 200 includes a lower electrode 210 which is a substantially circular conductive
layer when viewed from above, and an upper electrode 220 which is a substantially circular
conductive layer when viewed from above disposed opposite to the lower electrode. And a cavity
207 which is a substantially cylindrical gap interposed between the lower electrode 210 and the
upper electrode 220.
04-05-2019
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Then, for the purpose of electrically insulating the lower electrode 210 and the upper electrode
220, the second insulating film 203 and the third insulating film 204 are disposed on the side of
the cavity 207 of the lower electrode 210 and the upper electrode 220, respectively.
In addition, a protective film 205 and a paraxylylene resin film 206 are disposed on the upper
electrode 220.
[0118]
The transducer cell 200 according to the present embodiment is a film-like structure having
elasticity and configured of the upper electrode 220, the third insulating film 204, the protective
film 205, and the paraxylylene resin film 206 of the transducer cell 200 described above.
Ultrasonic waves are transmitted and received by the vibration of the membrane 200 a (vibration
film).
[0119]
On the other hand, the region where the electret layer 230 is disposed includes the lower
conductive layer 214 electrically connected to the lower electrode 210 of the transducer cell
200, the upper conductive layer 224 electrically connected to the upper electrode 220, and The
electret layer 230 is interposed between the lower conductive layer 214 and the upper
conductive layer 224.
In addition, an air gap portion 231 which is an insulating layer is interposed between the electret
layer 230 and the upper conductive layer 224.
[0120]
Then, in the upper conductive layer 224 and the protective film 205 disposed above the electret
layer 230, innumerable fine through holes 232 penetrating the upper conductive layer 224 and
the protective film 205 in the thickness direction are formed. It is done.
[0121]
Further, as shown in FIG. 10, in the present embodiment, a pattern formed of the same
04-05-2019
31
conductive layer as the upper electrode 220 (in FIG. 10, except for the region where the
transducer cell 200 and the electret layer 230 are disposed). And the pattern (broken line in FIG.
10) formed of the same conductive layer as the lower electrode 210 are arranged so as not to
overlap each other.
[0122]
That is, in the present embodiment, the upper electrode wire 221 electrically connecting the
plurality of upper electrodes 220 and the plurality of upper conductive layers 224, the plurality
of lower electrodes 210 and the plurality of lower conductive layers 214 are electrically
connected. The lower electrode wires 211 to be connected are arranged alternately or at
different angles in different regions as viewed from above.
[0123]
As described above, by arranging the upper conductive layer 224 and the lower conductive layer
214 so as not to overlap with each other as viewed from above, generation of parasitic
capacitance in the wiring portion can be prevented.
[0124]
The vibrator unit of the present embodiment provided with the vibrator element 233 having the
above configuration has the same effects as those of the first embodiment described above, and
further has the following effects.
[0125]
The transducer unit of the present embodiment contributes to the transmission and reception of
ultrasonic waves when the transducer unit is viewed from the transmission direction of
ultrasonic waves by arranging the electret layer 230 between the plurality of transducer cells
200. It is possible to make the area of the non-overlapping region smaller than that of the first
embodiment.
In other words, it is possible to improve the utilization efficiency of the ultrasonic wave
transmitting / receiving surface of the transducer unit.
[0126]
04-05-2019
32
Therefore, the transducer unit of the present embodiment can transmit and receive ultrasonic
waves more efficiently, and can provide a more compact ultrasonic diagnostic apparatus.
[0127]
The electret layer 230 may be any layer as long as it holds an amount of electric charge
sufficient to apply a DC voltage to the transducer cells 200 of the transducer unit, and as shown
in FIG. It does not have to be disposed in all areas.
[0128]
Further, in the above-described embodiment, the electret layer is divided into a plurality of
regions and disposed, but the electret layer is in a separated region different from the region in
which the transducer cell is formed. If it is, it may be arrange | positioned by a single continuous
shape.
[0129]
For example, as shown in FIG. 12, the electret layer 230a may be disposed in a lattice-like area
that fills the area between the plurality of transducer cells 200 arranged in a matrix.
[0130]
Fourth Embodiment Hereinafter, a fourth embodiment of the present invention will be described
with reference to FIG.
The fourth embodiment is an application of the above-described ultrasonic transducer of the
present invention to an ultrasonic microscope.
FIG. 13 is a diagram for explaining the configuration of the ultrasonic microscope of the present
embodiment.
[0131]
The ultrasound microscope 300 applies a high frequency signal generated by the high frequency
04-05-2019
33
oscillator 301 to the ultrasound transducer 303 according to the present invention via the
circulator 302 to convert it into ultrasound.
The ultrasonic waves are converged by the acoustic lens 304, and the sample 305 is placed at
the convergence point.
The sample 305 is held by a sample holder 306, and a coupler 307 such as water is filled
between the sample 305 and the lens surface of the acoustic lens 304.
The reflected wave from the sample 305 is received by the transducer 303 via the acoustic lens
304 and converted into an electrical reflected signal.
An electrical signal corresponding to the received ultrasound output from the ultrasound
transducer 303 is input to the display device 308 via the circulator 302.
The sample holder 306 is driven by the scanning device 310 controlled by the scanning circuit
309 in two horizontal directions of XY in the horizontal plane.
[0132]
The ultrasonic microscope 300 configured as described above quantifies the elastic property of
the sample 305 or evaluates the structure of the thin film by irradiating the sample 305 with
ultrasonic waves to evaluate the acoustic characteristics of the sample 305. It is possible.
[0133]
The following configuration can be proposed based on the embodiment described above.
That is, (Additional remark 1) In a capacitive ultrasonic transducer using a micromachine
process, it is composed of a large number of transducer cells arranged on a substrate, and the
transducer cell is a vibration comprising at least an upper electrode and an insulating film. A
membrane, a gap portion in contact with the vibrating membrane, a lower electrode facing the
upper electrode and disposed across the gap portion, and an electret layer holding a charge,
04-05-2019
34
which is the same substrate as the transducer cell The capacitance type supercapacitor is
characterized in that it is disposed at a position not overlapping the transducer cell and is
sandwiched between the upper electrode and the lower electrode in a direction substantially
perpendicular to the vibrating membrane. Sound transducer.
[0134]
(Supplementary Note 2) The capacitive ultrasonic transducer according to Supplementary Note 1,
wherein the electret layer protrudes toward the acoustic radiation portion with respect to the
vibrating membrane portion.
[0135]
(Supplementary Note 3) The capacitive ultrasonic transducer according to supplementary note 1,
wherein the electret layer is made of a silicon compound or a hafnium compound.
[0136]
(Supplementary Note 4) The capacitive ultrasonic transducer according to supplementary note 1,
wherein the electret layer is made of at least a fluorine-based resin.
[0137]
(Supplementary Note 5) The capacitive ultrasonic transducer according to Supplementary Note 1,
characterized in that the substrate of the electret layer portion is concave and the surface of the
vibrator is substantially flat.
[0138]
(Supplementary Note 6) An intracorporeal insertion type ultrasonic diagnostic apparatus
comprising the capacitive ultrasonic transducer according to supplementary note 1 at the tip of
an insertion portion to be inserted into a body cavity.
[0139]
The present invention is not limited to the above-described embodiment, and can be
appropriately modified without departing from the scope or spirit of the invention as can be read
from the claims and the entire specification, and an ultrasonic wave accompanied by such a
modification. Transducers, ultrasound systems and ultrasound microscopes are also within the
scope of the present invention.
04-05-2019
35
[0140]
It is explanatory drawing which shows schematic structure of an ultrasonic endoscope.
It is a perspective view which shows the structure of the front-end | tip part of an ultrasonic
endoscope.
It is a perspective view of a vibrator array.
It is the top view which looked at a transducer unit from the transmission direction of an
ultrasonic wave.
FIG. 5 is a cross-sectional view taken along the line V-V of FIG. 4;
It is an equivalent circuit schematic of a vibrator unit.
It is a fragmentary sectional view of the field in which the electret layer of vibrator unit was
formed.
It is a fragmentary sectional view of the field in which the electret layer of the modification of a
1st embodiment was formed.
It is sectional drawing of the vibrator | oscillator element of 2nd Embodiment. It is a top view of
the vibrator | oscillator unit of 3rd Embodiment. FIG. 10 is a cross-sectional view taken along the
line XX in FIG. It is a top view of the vibrator | oscillator unit of the modification of 3rd
Embodiment. It is an explanatory view showing a schematic structure of an ultrasonic
microscope. It is an equivalent circuit schematic of the conventional capacitive transducer.
Explanation of sign
04-05-2019
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[0141]
100 vibrator cell, 100a membrane, 101 silicon substrate, 102 first insulating film, 104 second
insulating film, 105 protective film, 107 cavity, 109 back surface insulating film, 110 lower
electrode, 111 lower electrode wiring, 114 lower conductive layer, 120 upper electrode, 121
upper electrode wiring, 124 upper conductive layer, 130 electret layer, 131 air gap, 132 through
hole
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