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JP2010074538

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DESCRIPTION JP2010074538
[PROBLEMS] In manufacturing, it is possible to omit the step of separately providing a metallic
electrode on the substrate side, and to select ceramics as the material of the vibrating membrane
or the sacrificial layer which requires treatment at high temperature. Provided is an ultrasonic
transducer with an increased degree of freedom in the process. SOLUTION: A vibrating electrode
4 fixed to a vibrating membrane 1 and vibrating with the vibrating membrane, and a vibrating
membrane supporting portion 2 supporting the vibrating membrane 1 so that the vibrating
membrane 1 faces the substrate 3 is provided. For example, when the vibrating film 1 vibrates
due to the reception of an ultrasonic wave, by forming a conductor in a portion facing the
vibrating electrode 4 or making the whole of the substrate 3 a conductor, the vibrating electrode
4 and the substrate 3 are provided. Using the change in capacitance generated with (or a
conductor), an electrical signal related to the received ultrasonic wave is acquired. [Selected
figure] Figure 2
Ultrasonic transducer
[0001]
The present invention relates to an ultrasonic transducer provided with a vibrating film that
transmits and receives ultrasonic waves.
[0002]
FIG. 5 is a cross-sectional view showing the configuration of a conventional ultrasonic transducer.
04-05-2019
1
The conventional ultrasonic transducer includes a vibrating membrane 100 for transmitting and
receiving ultrasonic waves, and a vibrating membrane support portion 101 provided on one
surface of the substrate 104 and supporting the vibrating membrane 100 so as to face the
substrate 104. In addition, a pair of electrodes 102 and 103 are provided, one of the electrodes
102 is formed on the vibrating film 100, and the other electrode 103 is formed on the substrate
104.
[0003]
In such a conventional ultrasonic transducer, the vibrating film 100 and the one electrode 102
are vibrated by the received ultrasonic wave (sound pressure), and the capacitance change
between the pair of electrodes 102 and 103 occurs at this time The vibration film 100 is vibrated
by transmitting an ultrasonic wave by acquiring an electric signal related to the received
ultrasonic wave, or by applying a direct current voltage and an alternating current voltage
between the pair of electrodes 102 and 103.
[0004]
Further, Non-Patent Document 1 discloses such a conventional ultrasonic transducer and a
method of manufacturing the same.
In the ultrasonic transducer of Non-Patent Document 1, after an insulating layer of oxide is
formed on a silicon substrate, and a metallic electrode is deposited on the insulating layer, a socalled sacrificial material made of polyimide surrounding the electrode is covered. Coat the layer.
Thereafter, a vibrating film and a vibrating film support made of Si3N4 are co-deposited on the
sacrificial layer, and another electrode is deposited on the vibrating film, and then a plurality of
electrodes penetrating the electrode and the vibrating film are formed. It is manufactured by
providing a hole and etching the sacrificial layer through the hole. "Nobel, Wide Bandwidth,
Micromachined Ultrasonic Transducers", IEEE TRANSACTIONS ON ULTRASONICS, FERRO
ELECTRICS, AND FREQUENCY CONTROL, USA, IEEE Publications, November, VOL. 48, NO. 6, p.
1495-1507
[0005]
04-05-2019
2
However, in the above-described conventional ultrasonic transducer, since the vibrating
membrane supporting portion has a cylindrical shape having a thickness substantially equal to
the thickness of the vibrating membrane, the mechanical strength is low, and damage in the case
of long-term use In addition, there is a problem that free handling is restricted, and the vibration
of the vibrating membrane can not be stably supported, and noise may be mixed in the obtained
electric signal. In addition, since the electrode provided on the substrate side is metallic, material
selection of the ceramic vibrating film or the sacrificial layer generally required to be processed
at high temperature is limited, and there is also a problem that the degree of freedom in the
manufacturing process is poor. there were. However, such a problem can not be solved by the
ultrasonic transducer of Non-Patent Document 1.
[0006]
The present invention has been made in view of such circumstances, and an object of the present
invention is to provide a vibrating electrode which is fixed to a vibrating film and vibrates
together with the vibrating film, and the vibration so that the vibrating film faces the substrate. A
vibrating membrane supporting portion for supporting a membrane, and the conductor having a
conductor in a portion facing the vibrating electrode, for example, when the vibrating membrane
vibrates due to the reception of an ultrasonic wave, the vibrating electrode and the vibrating
membrane Capacitance change with the substrate (or conductor) can be used to obtain an
electrical signal related to the received ultrasonic wave, eliminating the step of providing a
metallic electrode on the substrate side in the manufacturing process. Another object of the
present invention is to provide an ultrasonic transducer which can be selected as a material of a
vibrating membrane or a sacrificial layer and which can be treated at a high temperature, and
which has a high degree of freedom in the manufacturing process.
[0007]
In addition, another object of the present invention is to increase the mechanical strength of the
vibrating membrane support portion by providing a tubular vibrating membrane support portion
having a thickness of 50 times to 600 times the thickness of the vibrating membrane, and the
durability thereof. An ultrasonic transducer capable of improving the degree of freedom of
handling.
[0008]
In addition, another object of the present invention is to form a ceramic film on the inner
peripheral surface of the vibrating membrane supporting portion so that the etchant can be in
contact with the vibrating membrane supporting portion when removing the sacrificial layer by
etching. It is an object of the present invention to provide an ultrasonic transducer which is
blocked, has no restriction on the choice of etching agent, and has a high degree of freedom in
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3
the manufacturing process.
[0009]
In addition, another object of the present invention is to transmit and receive ultrasonic waves
accurately even when used in a high frequency range by configuring the vibrating film to be
made of silicon nitride having a residual tensile stress of 50 MPa or less. An ultrasonic
transducer that can be
[0010]
The ultrasonic transducer according to the present invention is provided on a surface of a
substrate, a vibrating film vibrating when transmitting and receiving ultrasonic waves, a vibrating
electrode fixed to the vibrating film, and the vibration so as to face the substrate. In an ultrasonic
transducer provided with a vibrating membrane support portion for supporting a membrane, the
substrate is characterized by having a conductor at a portion facing the vibrating electrode.
[0011]
The ultrasonic transducer according to the present invention is characterized in that the
vibrating membrane support portion is made of a material different from that of the vibrating
membrane, and has a tubular shape having a thickness 50 to 600 times that of the vibrating
membrane.
[0012]
The ultrasonic transducer according to the present invention is characterized in that a ceramic is
formed on the inner circumferential surface of the vibrating membrane support.
[0013]
The ultrasonic transducer according to the present invention is characterized in that the
vibrating film is made of silicon nitride having a residual tensile stress of 50 MPa or less.
[0014]
The ultrasonic transducer according to the present invention is characterized by having a
plurality of through holes penetrating both the vibrating membrane and the vibrating electrode.
[0015]
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The ultrasonic transducer according to the present invention is characterized in that the
vibrating membrane support portion is made of polysilicon, and silicon oxide is formed on the
inner peripheral surface of the vibrating membrane support portion.
[0016]
In the present invention, when an ultrasonic wave is received, the vibrating membrane vibrates,
and the vibrating electrode fixed to the vibrating membrane also vibrates.
At this time, since the distance between the vibrating electrode and the conductor of the
substrate (or the conductor) changes, the capacitance between the vibrating electrode and the
substrate changes.
Therefore, based on the change in capacitance, an electrical signal related to the received
ultrasonic wave can be obtained.
[0017]
In the present invention, the vibrating membrane supporting portion is made of, for example,
polysilicon, and the thickness thereof is set to be 50 times to 600 times that of the vibrating
membrane, thereby enhancing the mechanical strength of the vibrating membrane supporting
portion. Improve durability and freedom of handling.
In addition, since the vibration of the vibrating membrane is stably supported and the number of
obtained vibrating membranes becomes uniform, the vibration of the membrane and the output
electric signal become stable.
[0018]
In the present invention, a ceramic, for example, silicon oxide is deposited on the inner peripheral
surface of the vibrating film support, and the etching film corrodes the vibrating film support
when the so-called sacrificial layer is removed by etching. To prevent
04-05-2019
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[0019]
In the present invention, silicon nitride having a residual tensile stress of 50 MPa or less is used
as the vibrating film.
That is, in addition to using silicon nitride having a high Young's modulus, the residual tensile
stress is as low as 50 MPa or less, thereby enhancing the mechanical (vibration) -electrical
energy (electrical signal) conversion efficiency and minimizing the deflection of the vibrating film
due to stress. To limit.
[0020]
In the present invention, a plurality of through holes which penetrate both the vibrating
membrane and the vibrating electrode are provided.
During removal of the sacrificial layer, an etchant is injected through the through holes to etch
the sacrificial layer.
[0021]
According to the present invention, when the vibrating membrane vibrates due to the reception
of the ultrasonic wave, an electric signal related to the ultrasonic wave received using the change
in capacitance generated between the vibrating electrode and the substrate (conductor) As the
vibration film can be vibrated and ultrasonic waves can be transmitted by applying a direct
current voltage and an alternating current voltage between the vibrating electrode and the
substrate (or conductor), it is possible to obtain a metal on the substrate side. It is not necessary
to separately provide the gender electrode, the structure is simplified, the selection of the
ceramic vibrating film or the sacrificial layer requiring the treatment at high temperature is made
possible, and the degree of freedom in the manufacturing process is increased.
[0022]
According to the present invention, since the vibrating membrane supporting portion having a
cylindrical shape having a thickness of 50 to 600 times that of the vibrating membrane is
provided to increase the mechanical strength of the vibrating membrane supporting portion, the
durability and the freedom of handling The yield can be improved.
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[0023]
According to the present invention, since the ceramic film is formed on the inner peripheral
surface of the vibrating membrane support portion, the contact between the etching agent and
the vibrating membrane support portion is blocked when the sacrificial layer is removed by
etching. The choice of is not limited, and the degree of freedom in the manufacturing process is
increased.
[0024]
According to the present invention, since the vibration film is silicon nitride having a residual
tensile stress of 50 MPa or less, the energy conversion efficiency is high, and the vibration film
can be maintained in a horizontal state without warp, so that it is accurate. Can transmit and
receive ultrasonic waves.
[0025]
Hereinafter, an ultrasonic transducer according to the present invention will be specifically
described based on the drawings.
FIG. 1 is a plan view of an ultrasonic transducer according to the present invention, and FIG. 2 is
a longitudinal sectional view taken along the line A-B of FIG.
[0026]
The ultrasonic transducer according to the present invention comprises a vibrating membrane 1
for transmitting and receiving ultrasonic waves, a vibrating membrane support portion 2 for
supporting the vibrating membrane 1, and a substrate 3 provided with the vibrating membrane
support portion 2 on one side. There is.
Further, on one surface of the vibrating membrane 1, a vibrating electrode 4 vibrating with the
vibrating membrane 1 is formed.
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[0027]
An insulating film 5 made of a ceramic (for example, silicon oxide) is formed on the one surface
of the substrate 3, and a vibrating film supporting portion 2 is provided on the upper surface of
the insulating film 5.
The vibrating film support 2 has, for example, a cylindrical shape, and is erected so that the
peripheral edge of one end is in contact with the insulating film 5.
Further, on the inner peripheral surface of the vibrating membrane support portion 2, a
corrosion resistant film 6 made of a ceramic excellent in corrosion resistance, for example, silicon
oxide is formed.
[0028]
The vibrating membrane 1 is provided so as to cover the vibrating membrane support 2.
Accordingly, the space portion 7 is formed by the insulating film 5, the inner peripheral surface
(the corrosion resistant film 6) of the vibrating film support portion 2, and the vibrating film 1.
[0029]
The vibrating film 1 has a thickness of 0.5 to 3 μm, and is made of, for example, silicon nitride
having a residual tensile stress of 50 MPa or less and having excellent insulating properties.
In addition, the vibrating membrane 1 vibrates in the vibrating portion 11 (lines A2 to B2 in the
figure, A2 to B2), and the fixed portion 12 held by the vibrating membrane support portion 2
(line AB in the figure). And A1 to A2 and B1 to B2).
The vibrating portion 11 has a gear shape in a plan view, and the fixing portion 12 has a disk
shape having a central portion rounded off.
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The vibrating portion 11 has a disk shape, and connects the central portion 111 (A3 to B3 in the
line A-B in the figure) and the central portion 111 to the fixed portion 12 on which the vibrating
electrode 4 is vapor-deposited. Six connecting portions 112, 112, 112, ... (A2-B in the drawing,
A2-A3 and B2-B3).
The connection portions 112, 112, 112,... Are disposed at equal intervals on the peripheral edge
portion of the central portion 111, and extend in the radial direction of the central portion 111.
The diameter of the vibrating membrane 1 (A2 to B2 on the line A-B in the figure) is 600 to 700
μm. The vibrating portion 11 and the fixing portion 12 are integrally formed. In the present
embodiment, although the case where the diameter of the vibrating membrane 1 is 600 to 700
μm is taken as an example, the diameter of the vibrating membrane 1 is determined by the
frequency and the band.
[0030]
As described above, the vibrating membrane support 2 is cylindrical and made of, for example,
polysilicon which is a different material from the vibrating membrane. The vibrating membrane
supporting portion 2 has a dimension in the axial length direction (in other words, a distance
between the vibrating membrane 1 and the insulating film 5) of 2 to 3 μm, and an outer
diameter of 600 to 700 μm equal to the diameter of the vibrating membrane 1 . In addition, the
vibrating membrane support portion 2 has a thickness of 50 times to 600 times the thickness of
the vibrating membrane 1.
[0031]
The substrate 3 is, for example, a silicon wafer having a resistance value of 0.1 Ωcm or less in
which a conductive impurity is doped in n-type or p-type. On the other hand, the vibrating
electrode 4 is made of a metal thin film and is vapor-deposited on the central portion 111 of the
vibrating film 1. The vibrating electrode 4 is in the form of a disk having the same size as the
central portion 111, and a strip-like lead pad 41 extending in the radial direction is provided at
the peripheral edge on one side of the vibrating electrode 4. The lead pad 41 is deposited on any
one of the connection parts 112. The substrate 3 and the vibrating electrode 4 are each
04-05-2019
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electrically connected to an external device, and an electrical signal related to the change in
capacitance between the substrate 3 and the vibrating electrode 4 is output. The substrate 3 has
a cavity (not shown) inside. The cavity is formed by anisotropic etching (or dry etching) from the
other surface side of the substrate 3. The hollow has a size substantially the same as that of the
vibrating membrane 1 in plan view, and is formed so as to be aligned with the vibrating
membrane 1. Further, a through hole (not shown) which penetrates the insulating film 5 is
provided on one surface side of the substrate 3, and the hollow and the space 7 are
communicated with each other by the through hole. A hole is formed on the other surface of the
substrate 3 during the anisotropic etching, but is sealed after the etching process.
[0032]
As described above, the ultrasonic transducer according to the present invention uses silicon
nitride having a residual tensile stress of 50 MPa or less as the vibrating film 1, and silicon
nitride has a higher Young's modulus than other vibrating film materials. Thus, the conversion
efficiency between the vibration and the electrical signal is high. In addition to being able to cope
with use in the high frequency range, the shape of the vibrating membrane 1 is maintained as
designed (horizontally), accurate ultrasonic wave transmission / reception is possible, and stable
electronic signal sensing (output) is possible. It is possible.
[0033]
The ultrasonic transducer according to the present invention can solve the instability of the
support of the vibrating membrane 1 which may occur when the thickness of the vibrating
membrane support 2 is thin, and the thickness of the vibrating membrane support 2 is thick. It is
possible to prevent the decrease in sensitivity that may occur if the amount is too high. For
example, as in the conventional ultrasonic transducer, the mechanical strength is low when the
thickness of the vibrating membrane support is approximately equal to the thickness of the
vibrating membrane, and when using for a long time, the vibrating membrane support and the
vibration There is a possibility that the fixed or vibrating membrane support of the membrane
may be broken, and the free handling is restricted, the yield is lowered, and the vibration of the
vibrating membrane can not be stably supported, and the obtained electric signal And other
problems such as noise mixing. In addition, when the thickness of the vibrating membrane
support 2 is too thick, a stress is generated in the vibrating membrane support 2 to disturb the
vibration of the vibrating membrane, causing a problem of reducing the sensitivity. However,
since the vibrating membrane support portion 2 of the ultrasonic transducer according to the
present invention has a thickness of 50 to 600 times the thickness of the vibrating membrane 1,
04-05-2019
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such a problem can be solved.
[0034]
In the ultrasonic transducer according to the present invention, since the silicon wafer is used as
the substrate 3, the silicon wafer serves as a ground, and the noise of the electric signal obtained
from the received ultrasonic wave is reduced, and S / N The ratio improves.
[0035]
The vibrating membrane 1 and the vibrating electrode 4 and the lead pad 41 are penetrated in
the thickness direction, for example, by a plurality of through holes 8, 8, 8.
Therefore, the air existing in the space 7 can be moved in and out through the through holes 8,
8, 8,..., And the resistance by the air in the space 7 that occurs when the vibrating membrane 1
vibrates can be alleviated. It can. In addition, etching of the sacrificial layer described later is
performed using through holes 8, 8, 8,.
[0036]
Hereinafter, the operation of the ultrasonic transducer according to the present invention will be
described. For convenience of explanation, the case of receiving an ultrasonic wave from the
outside will be described as an example.
[0037]
When the ultrasonic transducer according to the present invention receives an ultrasonic wave
from the outside, the vibrating film 1 vibrates by the ultrasonic wave (sound pressure). When the
vibrating membrane 1 vibrates, the vibrating electrode 4 vapor-deposited on the vibrating
membrane 1 also vibrates, so the distance between the vibrating electrode 4 and the substrate 3
changes. Accordingly, the capacitance between the vibrating electrode 4 and the substrate 3 is
changed. Based on the change in capacitance between the vibrating electrode 4 and the substrate
3, an electrical signal related to the received ultrasonic wave can be obtained.
04-05-2019
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[0038]
On the other hand, the transmission of the ultrasonic wave is performed by vibrating the
diaphragm 1 by applying a direct current and an alternating voltage between the vibrating
electrode 4 and the substrate 3, and other actions are the same as in the case of receiving the
ultrasonic wave. The detailed description is omitted.
[0039]
3 and 4 are explanatory views showing a method of manufacturing an ultrasonic transducer
according to the present invention.
Hereinafter, a method of manufacturing an ultrasonic transducer according to the present
invention will be described.
[0040]
First, a ceramic (for example, silicon oxide) film 5 is formed on a substrate 3 made of, for
example, a silicon wafer, and a material (for example, polysilicon) layer 2lay different from the
vibrating film 1 (silicon nitride) is formed on the insulating film 5. (FIG. 3 (a)). Hereinafter, for
convenience of description, the different material layer 2lay will be referred to as the different
layer 2lay for short.
[0041]
Thereafter, a groove forming process is performed. In the groove forming step, the dissimilar
layer 2lay is hollow-patterned to follow the inner peripheral edge of the vibrating membrane
support 2 in plan view, thereby forming the groove 21 in the dissimilar layer 2lay (FIG. 3 (b)).
After the groove forming step, the dissimilar layer 2lay is divided into an inner portion 2in of the
groove 21 surrounded by the groove 21 and an outer portion 2out of the groove 21. The inner
portion 2 in is a so-called sacrificial layer in forming the vibrating film 1 and is removed in an
etching process described later. In addition, a part of the outer portion 2 out becomes the
vibrating membrane support portion 2.
04-05-2019
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[0042]
Next, a embedding process is performed to embed a ceramic (for example, silicon oxide) having
excellent corrosion resistance in the grooves 21 using a chemical vapor deposition method (HDP
CVD) with high density plasma (FIG. 3C). Silicon oxide can be embedded in the groove 21 by such
an embedding step, and the corrosion resistant film 6 will be formed.
[0043]
Thereafter, an excess removing step is performed to remove the portion other than the portion
corresponding to the thickness of the vibrating membrane support portion 2 from the outer
portion 2out (FIG. 4 (d)). The surplus removing step is a step of removing the outer portion 2out
except the portion from the inner periphery to the position to become the outer peripheral edge
when the groove 21 is the inner periphery of the vibrating membrane support 2. The vibrating
membrane support portion 2 is formed by the surplus removing step.
[0044]
Subsequently, the vibrating film 1 is formed on the inner portion 2in and the outer portion 2out
(the vibrating film support portion 2) (FIG. 4E). The vibrating film 1 is made of, for example,
silicon nitride, and is performed using low pressure chemical vapor deposition (LPCVD).
Thereafter, patterning is performed on the deposited silicon nitride, and as described above, the
vibration in which the substantially gear-like vibrating portion 11 and the disk-like fixed portion
12 having the central portion rounded off is integrated. A membrane 1 is obtained.
[0045]
Next, in order to provide the vibrating electrode 4, Al, Pt / Ti, Cr or the like is vapor-deposited on
the vibrating film 1 using a low pressure chemical vapor deposition method. Thereafter,
patterning is performed, and as described above, strip-shaped lead pads 41 extending in the
radial direction are formed at the peripheral portion on one side of the disc-shaped vibrating
electrode 4 and the vibrating electrode 4. Thereafter, patterning for providing a plurality of
through holes 8, 8, 8,... Penetrating both the vibrating membrane 1 and the vibrating electrode 4
04-05-2019
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is further performed (FIG. 4 (f)).
[0046]
Thereafter, an etching process is performed to remove the inner portion 2 in of the groove 21
surrounded by the groove 21, that is, the sacrificial layer by dry etching. In the etching step, an
etchant is injected through the through holes 8, 8, 8,... To etch the inner portion 2 in (sacrifice
layer). As can be seen from (d) to (g) in FIGS. 3 and 4, a corrosion resistant film 6 is interposed
between the inner portion 2 in and the vibrating membrane support portion 2, and between the
inner portion 2 in and the substrate 3. Since the silicon oxide excellent in corrosion resistance
intervenes as the insulating film 5, the inner portion 2in is surrounded by the films (corrosion
resistant film 6 and insulating film 5) excellent in corrosion resistance. Therefore, in the case of
the dry etching, the corrosion resistant film 6 and the insulating film 5 play a role of a stopper
for the etching agent to protect the vibrating film support 2 and the substrate 3. The ultrasonic
transducer according to the present invention can be obtained by the above steps (FIG. 4 (g)).
[0047]
In the conventional ultrasonic transducer manufacturing method, not dry etching but wet etching
is used, so the warpage of the vibrating film due to the surface tension of the etching solution or
so-called stiction in which the vibrating film sticks to the substrate side Problems have occurred.
Since the ultrasonic transducer according to the present invention uses dry etching as described
above, the occurrence of such a problem can be prevented. The thickness of the diaphragm
supporting portion 2 can be changed by controlling the groove forming step (FIG. 3B) or the
excess removing step (FIG. 4D).
[0048]
As described above, in the ultrasonic transducer according to the present invention, since the
sacrificial layer (inner portion 2 in) and the vibrating membrane support portion 2 (outer portion
2 out) are both formed based on the dissimilar layer 2 lay, the sacrificial layer The manufacturing
process can be simplified, as it is not necessary to provide a separate process for forming.
[0049]
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In the above description, although the case where the substrate 3 is a silicon wafer and the whole
is a conductor has been described as an example, the present invention is not limited to this.
For example, in the substrate 3, only the portion facing the vibrating electrode 4 may be a
conductor, or only a part of the facing portion may be a conductor.
[0050]
It is a top view of the ultrasonic transducer concerning the present invention. It is a longitudinal
cross-sectional view by the AB line of FIG. It is an explanatory view showing the ultrasonic
transducer manufacturing method concerning the present invention. It is an explanatory view
showing the ultrasonic transducer manufacturing method concerning the present invention. It is
sectional drawing which shows the structure of the conventional ultrasonic transducer | vibrator.
Explanation of sign
[0051]
DESCRIPTION OF SYMBOLS 1 vibrating film 2 vibrating film support part 3 board | substrate 4
vibrating electrode 5 insulation film 6 corrosion-resistant film 7 space part 8 through-hole 41
lead pad
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