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JP2011045040

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DESCRIPTION JP2011045040
An electromechanical transducer capable of achieving both reduction of parasitic capacitance
between electromechanical transducers and improvement of a fill factor is provided. An
electromechanical transducer (100) includes a conductive substrate (103) and a plurality of
electromechanical transducers (104) disposed on a first surface of the substrate. The substrate is
formed with a groove 111 extending from the second surface side opposite to the first surface of
the substrate to the first surface side for electrically separating the plurality of electromechanical
transducers from one another. The width of the groove 111 on the first surface side of the
substrate 103 is narrower than the width of the groove 111 on the second surface side of the
substrate 103. [Selected figure] Figure 1
Electromechanical transducing device, and method of manufacturing the electromechanical
transducing device
[0001]
The present invention relates to an electromechanical transducer such as an ultrasonic
transducer and a method of manufacturing the same.
[0002]
An ultrasonic transducer converts electrical signals into ultrasonic waves and converts ultrasonic
waves into electrical signals, and is used as a probe for medical imaging and nondestructive
testing.
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1
One form of ultrasound transducer is the Capacitive Micromachined Ultrasound Transducer
(CMUT). The CMUT comprises, for example, a substrate having a lower electrode, a membrane
supported by a support formed on the substrate, and an upper electrode. One cavity is defined by
a lower electrode, a membrane, an upper electrode, and a support. The CMUT vibrates the
membrane with a voltage applied between the lower electrode and the upper electrode to emit an
acoustic wave. Also, the membrane is vibrated by the received sound wave, and the sound wave
is detected by the change in capacitance between the lower electrode and the upper electrode.
[0003]
Conventionally, CMUTs have been manufactured using so-called surface micromachining, bulk
micromachining and the like. Further, as a wiring method, there is a method of connecting
elements to a circuit substrate by using a plurality of membranes and cavities on a silicon
substrate as one element, and using the silicon substrate itself as a lower electrode and a through
wiring (see Patent Document 1). This method is described in FIG. The CMUT 1007 is composed
of a plurality of elements 1008, and transmits and receives ultrasonic waves by using the
elements as one unit. The element 1008 includes an upper electrode 1000, a membrane 1001, a
cavity 1002, and a lower electrode 1003. A groove 1004 is formed to electrically isolate adjacent
elements 1008 from each other for insulation. The CMUT 1007 is connected to the ASIC
substrate 1006 by the bumps 1005.
[0004]
US-A1-20060075818 specification
[0005]
The conventional CMUT requires a separation groove having a width of several hundreds of
microns to electrically separate an element which is a unit element consisting of one cavity or an
assembly of a plurality of cavities.
However, since the cavities can not be arranged in the part of the separation groove, the number
of cavities that can be arranged per unit area of the substrate is reduced, and the fill factor (here,
the occupation of the electromechanical transducer per unit area of the substrate). (Meaning
rate) decreases. Therefore, the sensitivity of the entire device is likely to be reduced.
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[0006]
In view of the above problems, the electromechanical transducer according to the present
invention includes a conductive substrate, and a plurality of electromechanical transducers, such
as a capacitive type, disposed on the first surface of the substrate. In order to electrically
separate the plurality of electromechanical conversion parts from each other on the substrate,
from the second surface side opposite to the first surface of the substrate to the first surface side
of the substrate An extending groove is formed. The width of the groove on the first surface side
of the substrate is narrower than the width of the groove on the second surface side of the
substrate.
[0007]
Further, in view of the above problems, the method of manufacturing an electromechanical
transducer according to the present invention includes the following steps. Forming a groove in
the silicon substrate by alkaline wet etching to form a plurality of first electrodes separated from
each other; Forming a cavity facing the first electrode; Forming a membrane facing the cavity;
Forming a second electrode on the membrane; The step of forming a plurality of first electrodes
separated from each other by the alkaline wet etching is a step of forming a groove in a silicon
substrate by dry etching a plurality of times and forming a plurality of first electrodes separated
from each other It can also be replaced.
[0008]
According to the present invention, by making the width of the groove on the first surface side of
the substrate narrower than the width of the groove on the second surface side, a plurality of
electromechanical transducers are compared on the first surface side. Can be arranged at a very
high density. Then, by increasing the width of the groove from the first surface side toward the
second surface side, a sufficient width is secured for the whole separation groove, so that
electrical separation between the electromechanical conversion parts is ensured. Can reduce
parasitic capacitance. As a result, the decrease in sensitivity due to the small width of the groove
on the first surface side can be suppressed. Further, since the width of the groove on the first
surface side can be narrowed while suppressing the decrease in sensitivity, the electromechanical
transducer can be arranged at a high density, and the fill factor can be improved. Also from this
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point, the sensitivity of the electromechanical transducer such as the CMUT can be improved. In
other words, according to the present invention, it is possible to simultaneously reduce the
parasitic capacitance between the electromechanical conversion parts and improve the signal
output of the electromechanical conversion device.
[0009]
It is a figure explaining CMUT of Example 1 of this invention. It is process drawing explaining the
manufacturing method of CMUT of Example 2 of this invention. It is a figure explaining CMUT of
Example 3 of this invention. It is a figure explaining the manufacturing method of CMUT of
Example 3 of this invention. It is a figure explaining CMUT of Example 4 of this invention. It is
the schematic explaining the conventional CMUT.
[0010]
Hereinafter, embodiments of the present invention will be described. The features of the
electromechanical transducer of the present invention and the method of manufacturing the
same are as follows. That is, the width (also referred to as the width of the bottom) on the first
surface side of the conductive substrate is greater than the width on the second surface (also
referred to as the width of the opening) corresponding to the arrangement of the plurality of
electromechanical transducers A narrow groove is also formed to divide the substrate into a
plurality of portions, and the plurality of portions of the substrate, which also serve as electrodes,
are isolated from each other.
[0011]
Based on the above concept, the basic form of the electromechanical transducer of the present
invention and the method of manufacturing the same has the configuration as described in the
section for solving the problems. Based on this basic form, embodiments as described below are
possible.
[0012]
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The groove decreases, for example, continuously or discontinuously from the opening to the
bottom (continuously from the first surface side to the second surface side opposite to the first
surface) Can have a non-continuously wide cross-sectional shape. Such a structure is preferable
from the viewpoint of reduction of parasitic capacitance between electromechanical transducers
of the electrostatic capacitance type and the like and improvement of the fill factor of the
electromechanical transducer. In addition, it is a structure that can be easily realized by a method
of forming a groove in a silicon substrate by alkaline wet etching. In this method, it is possible to
form a groove slope that forms an angle of 54.7 degrees with the substrate surface, so it is easy
to make the above groove by appropriately setting the thickness of the substrate and the width
of the opening of the etching mask. (See Example 2 below). In this case, the side wall of the
groove is flat and inclined with respect to the substrate.
[0013]
The side walls of the groove can also be stepped. Such a structure can be easily manufactured by
multiple dry etching, that is, dry multistage etching. That is, after the mask is formed on the
bottom of the silicon substrate with a suitable pattern corresponding to the arrangement of the
plurality of electromechanical conversion parts and the first dry etching is performed, the
opening of the mask is enlarged appropriately to perform the next dry Perform the etching. The
side wall can form a step-like groove by repeating such an etching process while making the
groove stepwise and reaching the other surface of the substrate. Also in this method, the width of
the bottom can be made smaller than the opening.
[0014]
Hereinafter, a plurality of embodiments of the present invention will be described in detail with
reference to the drawings. However, the present invention is not limited to the specific forms of
these examples. Example 1 Example 1 will be described with reference to FIG. Example 1 relates
to a capacitive ultrasonic transducer consisting of a Si substrate in which elements are separated
by grooves, and a device in which the membrane 105 is manufactured by bonding an SOI
(Silicon-on-insulator) substrate. As shown in FIG. 1A of the cross-sectional view of the
electromechanical transducer of the present embodiment, the electromechanical transducer 100
includes a circuit board 101 and a silicon substrate 103. The circuit board 101 is disposed
directly below the silicon substrate 103.
[0015]
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As shown in FIG. 1 (b), which is a top view of FIG. 1 (a), the electro-mechanical transducer device
100 of this embodiment is constituted by 4 × 4 elements 104. The region indicated by 104 in
FIG. 1B is one element. Here, the element 104 which is the capacitive type electromechanical
transducer is one unit that transmits and receives ultrasonic waves. One lower electrode 108 and
a subsequent through wire 109 are disposed per element. Here, 4 × 4 elements 104 are
arranged, but the present invention is not limited to this. The element 104 will be described with
reference to FIG. 1C which is an enlarged view of a part of FIG. 1B and FIG. 1A which is a crosssectional view taken along the line A-A 'of FIG. The element 104 disposed on one surface, which
is the first surface of the substrate 103, includes the membrane 105, the cavity 106, the upper
electrode 107, the lower electrode 108, and the like. As the respective materials, the membrane
is Si, the material around the cavity (except the membrane side) is SiO 2, the upper electrode is
Al, the lower electrode is Si, and the lower lead-out wiring which is a through wiring is Si. The Si
substrate 103 and the circuit substrate 101 are joined via the solder 110 and the electrode pad
116. As described above, in the present embodiment, the element 104 which is an
electromechanical transducer includes a support, a membrane provided on the support, and a
lower electrode which is a first electrode provided to face the membrane. It has an upper
electrode which is a second electrode provided on the membrane. The lower electrode 108 is
electrically connected to a portion (through wiring 109) of the substrate 103 surrounded by the
groove 111. Here, the membrane can also be configured to double as the upper electrode.
Further, in the present embodiment, the lower electrode 108 and the through wiring 109 are
described separately as “electrode” and “wiring”, but in the present invention, the
configuration in which the lower electrode 108 and the through wiring 109 are integrated is
described. It can also be adopted.
[0016]
The groove 111 and the lower electrode 108 will be described. As shown in FIGS. 1A, 1 B, and 1
C, the groove 111 is formed in a portion of the substrate 103 substantially corresponding to the
area between the adjacent elements 104. This is to provide insulation between adjacent elements
104. As shown in FIG. 1A, the groove 111 is required to completely penetrate the lower electrode
108 and the portion of the silicon substrate 103 which is the through wiring 109. The parasitic
capacitance between adjacent elements 104 is reduced by forming the groove 111 so that the
bottom on the first surface side of the substrate is narrower than the opening on the other
surface which is the second surface of the substrate. And, the effective area of one element 104
can be made larger. In the present embodiment, the side wall of the groove 111 is formed by a
plane inclined with respect to the Si substrate 103. Thereby, discharge between the adjacent
elements 104 is less likely to occur. The side wall of the groove cross-sectional shape may be a
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straight or curved continuous sloped surface, for example, a non-continuous stepped surface.
[0017]
The upper electrode 107 will be described with reference to FIGS. 1 (a), (b), and (c). Wirings 112
are formed to electrically connect the upper electrodes 107 formed in the one element 104. In
order to electrically connect the upper electrodes 107 of adjacent elements 104, a wire is formed
on the top of the beam 113 which is a portion of the membrane 105 substantially corresponding
to the groove 111. Finally, all the upper electrodes 107 are connected to the lead wires 114. As
shown in FIG. 1A, the upper electrode 107 is connected to the circuit board 101 via the lead wire
114 and the silicon substrate 103.
[0018]
The dimensions of each part will be described. The width wm of the membrane 105 of each cell
having the cavity 106 is 200 μm, and the thickness tm is 1.5 μm. The width of the cavity 106 is
200 μm like the width of the membrane, and the depth tc is 1 μm. The width wt of the bottom
of the groove 111 is 100 μm, and the depth tt1 is 100 μm. The width we1 of the upper
electrode 107 shown in FIG. 1C is 100 μm, and the thickness te1 is 330 nm. The width we2 of
the wiring 112 connecting the upper electrode 107 shown in FIG. 1C is 10 μm, and the
thickness is the same as that of the upper electrode. The width we3 of the lead wire 114 is 100
μm. The width we 4 of the lower electrode 108 is 900 μm, and the thickness (including the
through wiring 109) is the same as the depth tt 1 of the groove 111. The planar size of the lower
electrode pad 116 is 100 μm × 100 μm, and the thickness is 330 nm. However, these values
are merely examples, and other values can be taken. Also, in the drawings, the ratio of
dimensions of each part is different from the actual one for the sake of clarity. When it is
considered to use anisotropic etching in which the slope of the groove 111 is formed at an angle
of 54.7 degrees with respect to the substrate surface, the width and depth of the bottom of the
groove 111 make the width of the opening of the groove 111 200 μm or more Easily. Thus, a
structure in which the width of the groove 111 on the first surface side is narrower than the
width of the groove 111 on the second surface can be easily formed.
[0019]
The operating principle of the CMUT will be described. When ultrasonic waves are received, the
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membrane 105 is displaced, and the gap between the upper electrode 107 and the lower
electrode 108 changes. An ultrasonic image or the like can be obtained by detecting and
performing signal processing on the amount of change in capacitance. Further, in the case of
transmitting an ultrasonic wave, the membrane 105 is vibrated by applying a modulation voltage
to the upper electrode 107 or the lower electrode 108 from the circuit substrate 101.
[0020]
According to this embodiment, the influence of parasitic capacitance between adjacent elements
can be reduced, and the effective area of one element can be made larger, and the sensitivity of
the CMUT can be improved. Further, the above configuration using the silicon substrate itself as
the wiring is excellent in that either surface micromachining or bulk micromachining described
in the second embodiment can be applied as a method of forming a cavity. As a method of
forming a through wiring, there is a method of forming a through hole in a silicon substrate and
forming polysilicon or the like thereon to form a wiring, or a method of plating Cu or the like to
form a wiring. Is inferior in whether or not the cavity can be formed in various ways.
[0021]
Example 2 Example 2 will be described. The present embodiment relates to the method of
manufacturing the CMUT described in the first embodiment. FIG. 2 is a process diagram for
explaining the method of manufacturing the CMUT of this embodiment, and the process flow of
FIG. 2 shows a cross-sectional view of two elements for simplification of the explanation, but the
other elements are also the same. It is made. Further, in FIG. 2, the same reference numerals are
attached to portions having the same functions as the portions shown in FIG. 1.
[0022]
First, the Si substrate 103 is prepared. Typically, this is single crystal silicon to which
semiconductor processing techniques can be readily applied. Since the Si substrate 103 later
becomes the lower electrode 108 and the through wiring 109, one having a low resistivity (that
is, one having a certain degree of conductivity) is preferable. In the present example, a Si
substrate having a specific resistance of less than 0.02 Ω · cm was used. Next, an oxide film 201
is formed on the Si substrate 103 by pyrogenic oxidation, and a cavity pattern is formed by
photolithography. Further, the oxide film 201 is etched by buffered hydrofluoric acid (BHF) to
04-05-2019
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form a cavity 106. For example, the Si substrate 103 has a thickness of 525 μm, and the oxide
film 201 has a thickness of 1 μm. FIG. 2A is a top view after forming a cavity pattern, and FIG.
2A 'is a cross-sectional view taken along the line A-A'.
[0023]
Next, in order to insulate the bottom of the cavity 106, the substrate 103 is thermally oxidized
again. Thereby, an oxide film 203 is formed to a thickness of 1500 Å. The oxide film 203 is also
formed on the lower surface of the substrate 103. FIG. 2 (B) is a top view after the formation of
the thermal oxide film 203, and FIG. 2 (B ') is a B-B' cross-sectional view.
[0024]
Next, the SOI substrate 205 is bonded to the substrate 103 in FIG. FIG. 2C is a top view after
bonding the SOI substrate, and FIG. 2C 'is a cross-sectional view taken along the line C-C'. The
SOI substrate 205 is configured of a device layer (thickness 1.5 μm), a buried oxide film layer
(thickness 0.4 μm), and a support substrate layer (thickness 500 μm). The bonding process is
as follows. First, the bonding surface of the substrate 103 and the SOI substrate 205 is subjected
to N 2 plasma processing. Next, the substrate 103 and the substrate 205 are aligned with the
orientation flat. Finally, the two are joined in a vacuum chamber under conditions of a
temperature of 300 ° C. and a load of 500N.
[0025]
Next, the supporting substrate layer and the buried oxide film layer of the SOI substrate 205 are
removed by etching. The supporting substrate layer of the SOI substrate 205 is removed by dry
etching using SF6, and the buried oxide film layer is removed by etching using buffered
hydrofluoric acid (BHF). Thereby, the membrane 105 is formed. FIG. 2D is a top view after
etching the supporting substrate layer and the buried oxide film layer of the SOI substrate 205,
and FIG. 2D 'is a cross-sectional view taken along the line D-D'.
[0026]
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Next, the upper electrode lead electrode 114 is formed. A resist pattern of the upper electrode
lead electrode is formed on the membrane 105 side of the substrate 103 manufactured in FIG.
2D by photolithography. Using this resist as a mask, the membrane 105 is etched by dry etching
using CF 4 gas. Similarly, using the resist as a mask, the oxide films 201 and 203 are etched by
dry etching using CF 4 gas. FIG. 2E is a top view after forming the upper electrode extraction
electrode 114, and FIG. 2E 'is a cross-sectional view taken along the line E-E'.
[0027]
Next, the upper electrode 107 is formed. After removing the resist of the substrate manufactured
in FIG. 2 (E), Al is vapor deposited. A resist pattern of the upper electrode is formed on the
surface on which Al is vapor-deposited by photolithography. Finally, the upper electrode 107 is
formed by wet etching Al using the resist pattern as a mask. FIG. 2F is a top view after forming
the upper electrode 107, and FIG. 2F 'is a cross-sectional view taken along the line F-F'.
[0028]
Next, after removing the resist of the substrate manufactured in FIG. 2F, a resist pattern for
separating into 4 × 4 elements 104 is formed by photolithography. Further, after the oxide film
203 is etched by BHF, the resist is removed. The etched oxide film 203 serves as an etching mask
for forming the groove 111. FIG. 2G is a top view after forming the etching mask, and FIG. 2G 'is
a cross-sectional view taken along the line G-G'.
[0029]
Next, the groove 111 is formed in the Si layer 103. FIG. 2H is a top view after forming the
groove, and FIG. 2H 'is a cross-sectional view taken along H-H'. Wet etching of the Si substrate
103 is performed using the oxide film 203 formed in FIG. 2G as an etching mask. The wet
etching uses anisotropic wet etching using an alkaline solution. As the alkaline solution, for
example, an aqueous potassium hydroxide solution or an aqueous tetramethylammonium
hydroxide solution (TMAH) may be used. After the etching, the oxide film 203 is removed. The
cross section of the groove 111 has a trapezoidal shape whose bottom is narrower than the
opening.
04-05-2019
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[0030]
Finally, the substrate manufactured in FIG. 2H and the circuit substrate 101 are bonded. FIG. 2I
is a top view after the circuit board 101 is bonded, and FIG. 2I 'is a cross-sectional view taken
along the line I-I'. Solder is used for bonding. Solder paste is printed on the portion of the
electrode pad 116 of the substrate 101. Next, solder balls are formed by reflowing the solder
paste. Finally, the electrode pad 116 of each circuit element of the circuit substrate 101 and the
lower electrode of the substrate 103 are aligned, and the substrates 101 and 103 are joined by
reflow of the solder 116. Thereby, a configuration that enables signal processing in transmission
and reception of ultrasonic waves is manufactured.
[0031]
In this embodiment, as described above, the step of forming a plurality of lower electrodes by
forming a groove on the substrate by alkaline wet etching, the step of forming a cavity facing the
lower electrode, and the step of forming a membrane facing the cavity , Forming an upper
electrode on the membrane. In this embodiment, a cavity structure is formed on a silicon
substrate, and a method using bulk micromachining for bonding an SOI substrate is used. In the
configuration produced by this method, since a silicon single crystal is used as a membrane,
mechanical properties of the membrane are improved. However, other than this, a fabrication
method using surface micromachining may be used. Specifically, for example, the following is
performed. A silicon nitride film is formed as a membrane on a substrate on which a polysilicon
layer is formed as a sacrificial layer, and etching holes are formed in the portion of the
membrane. The polysilicon layer of the sacrificial layer is etched with an etching solution
through the etching holes to form a cavity. Finally, the etching hole is filled with a silicon nitride
film to form a sealed cavity. Also in this method, the groove may be formed in the substrate on
which the element is formed as described above.
[0032]
Example 3 Example 3 will be described with reference to FIG. 3 (a). The third embodiment is
basically the same as the CMUT described in the first embodiment, but differs in a portion in
which the cross-sectional shape of the groove 111 is stepped. The groove 111 is characterized in
that the width near the element 104 is narrow. With such a cross-sectional shape, it is possible to
arrange more cavities while minimizing an increase in parasitic capacitance generated between
adjacent elements 104. Here, as shown in FIG. 3B, consider a groove whose width is wider at a
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portion far from the element 104. The number of cavities that can be arranged is the same as in
FIG. 3A, but the parasitic capacitance generated between the adjacent elements 104 is increased,
and noise is increased. The larger the groove width averaged in the depth direction, the smaller
the parasitic capacitance generated between the adjacent elements 104. Therefore, by narrowing
the width of the portion near the element 104 of the groove 111 and widening the width of the
other portion, the sensitivity improvement due to the increase in the number of cavities is
realized while minimizing the noise due to the parasitic capacitance. be able to.
[0033]
Next, a method of manufacturing the CMUT of FIG. 3A will be described with reference to FIG.
The basic manufacturing method is the same as that of the second embodiment, except for the
step corresponding to FIG. 2H in which the groove 111 is formed. Here, only the method of
forming the groove will be described. First, a resist mask 301 is formed on the oxide film 203
formed in FIG. 2G, and dry etching is performed halfway through the Si substrate 103 (FIGS. 4A
and 4A '). The feature is that the opening of the resist mask 301 is narrower than the opening of
the oxide film 203. Next, the resist mask 301 is peeled off, a resist mask 302 is formed over the
oxide film 203, and dry etching is performed until the oxide film 201 (see FIG. 2B ') is exposed
(FIG. 4B, (B') )). The dry etching uses a dry etching method called a Bosch process. This method
can achieve both a high etching rate and a high aspect ratio by alternately performing the
etching and the protective film formation. After dry etching, the resist mask 302 is peeled off,
and the oxide film 203 is removed. The cross section of the groove 111 has a step-like shape in
which the bottom surface is greatly narrowed.
[0034]
In the wet etching method of the second embodiment, the arrangement of the groove is restricted
due to the crystal anisotropy of silicon, but in the method using the dry etching of the third
embodiment, such restriction is small. The degree of freedom of arrangement can be made
higher.
[0035]
Example 4 Example 4 will be described with reference to FIGS. 5 (a) and 5 (b).
The fourth embodiment is a modification of the CMUT described in the first embodiment. As
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shown in the cross-sectional view of FIG. 5A, this embodiment has a structure in which an epoxybased filler 117 called an underfill is introduced into the CMUT shown in FIG. 1A. FIG. 5 (b) is a
top view thereof. As shown in FIG. 5A, an underfill 117 as a filler is introduced between the
silicon substrate 103 and the circuit substrate 101, and the silicon substrate 103 and the circuit
substrate 101 are joined with the filler interposed therebetween. There is. The underfill 117 is
used to reinforce a portion that is fragile by forming a trench (groove) structure, and to reduce
distortion generated due to the difference in thermal expansion coefficient between the silicon
substrate 103 and the circuit substrate 101 at the time of solder bonding. It is introduced as a
purpose.
[0036]
Also, the underfill 117 minimizes the influence of the reflection of the ultrasonic waves at the
interface near this region by matching the acoustic impedance in the vicinity of the region
between the silicon substrate 103 and the circuit substrate 101 in this ( It is also introduced for
the purpose of suppressing reflections. In order to adjust acoustic impedance, fine particles of
tungsten or alumina are mixed with epoxy-based material DEVCON-B (registered trademark) to
match the target impedance. For example, while the acoustic impedance of the circuit board 101
is 5.6 kg / s · cm <2>, the acoustic impedance of DEVCON-B is 4.7 kg / s · cm <2>. For example, a
target acoustic impedance of 5.6 kg / s · cm <2> can be realized by mixing approximately 40% of
tungsten in DEVCON-B by mass ratio and evenly dispersing. However, since the viscosity
increases as the content of tungsten increases, air bubbles may be included when introduced. In
vertical trenches where air escapes poorly, bubbles may remain, which may cause acoustic
problems. That is, when there is a bubble, most of the ultrasonic waves flying from the upper
part of FIG. 5 (a) are reflected at the bubble due to the difference in acoustic impedance between
the bubble and the epoxy I will do it. It becomes noise and causes a reduction in signal strength,
or interferes with the originally desired signal to strengthen or weaken the signal.
[0037]
Therefore, in the case of this embodiment having a tapered trench structure, when the epoxy is
introduced, the epoxy flows along the side wall of the groove 111. At this time, even if the epoxy
droplets become large due to viscosity, they are introduced without clogging at the introduction
port of the opening of the groove 111 because the groove 111 is tapered. Also, it is conceivable
to perform plasma treatment to activate the surface of the trench 111 of the trench structure in
order to assist the introduction of epoxy. Also in this case, since the taper is attached, the plasma
itself can easily enter the bottom of the groove 111, and as a result, the epoxy can be easily
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introduced to the bottom of the groove 111. Furthermore, the taper allows the epoxy to be
introduced such that the air escapes while maintaining the gap between the sidewall of the
groove 111 and the epoxy. As a result, air is less likely to be left and bubbles are less likely to be
generated, acoustic problems can be reduced or almost eliminated, and broadband characteristics
can be realized. That is, originally, the capacitance type electromechanical transducer as in this
embodiment has a wide band characteristic that the frequency band is wide even in water and air
as compared with the piezoelectric type, but this feature is further assured and It can be realized
stably.
[0038]
100 ... CMUT (electro-mechanical transducer), 103 ... silicon substrate (conductive substrate),
104 ... element (electromechanical transducer), 111 ... groove
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