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JP2014212449

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2014212449
[Problem] In the case where gaps between all cells in an element are connected by an etching
path, if sealing failure occurs in one etching hole, the conversion efficiency of the element may
be significantly reduced. SOLUTION: The transducer according to the present invention is a
transducer comprising one or more elements, wherein the elements comprise a plurality of cells,
and each cell comprises one of a pair of electrodes spaced apart from one another. And the first
cell and the second cell of the plurality of cells in the element are in communication with each
other, and the first cell and the third cell are thirdly structured. And the cells are not connected
to each other. [Selected figure] Figure 1
Transducer, method of manufacturing transducer, and subject information acquiring apparatus
[0001]
The present invention relates to a transducer, a method of manufacturing a transducer, and an
object information acquiring apparatus. In particular, the present invention relates to a capacitive
transducer used as an ultrasonic transducer or the like, a method of manufacturing the same, and
an object information acquiring apparatus.
[0002]
Capacitive micromachined ultrasonic transducers (CMUTs), which are capacitive transducers
using micromachining technology, are being investigated as alternatives to piezoelectric
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1
elements. Such capacitive transducers can transmit or receive ultrasonic waves using the
vibration of the vibrating membrane.
[0003]
Each element of the CMUT is composed of a plurality of cells, and the gaps (cavities) in each cell
can be formed by etching the sacrificial layer through the etching holes. Thereafter, the etching
holes are sealed by being filled. In Patent Document 1, a plurality of etching holes are formed for
each cell, and a gap of one cell is formed by etching through the plurality of etching holes. Also,
the gaps between the cells are sealed and the gaps do not communicate with each other.
Moreover, in patent document 2, one etching hole is formed with respect to several cells. Then,
the etching holes are arranged such that the front lines on which the respective etching
progresses do not intersect in the region under the vibrating film by the etching solution that has
entered from the plurality of adjacent etching holes. By arranging in this manner, etching
residues are prevented from remaining in the gap.
[0004]
JP, 2008-98697, A JP, 2011-254281, A
[0005]
When forming an etching hole for every cell and removing a sacrificial layer like patent
document 1, since many etching holes exist, it is difficult to arrange a cell with high density.
Therefore, the transmission efficiency and the reception sensitivity, that is, the conversion
efficiency of the transducer are reduced as compared to the transducer in which the cells are
arranged at high density.
[0006]
In Patent Document 2, since one etching hole is shared by a plurality of cells, it is possible to
arrange the cells at a high density. However, in the case of Patent Document 2, the gaps between
all the cells in the element are connected by the etching path. Therefore, if a sealing failure
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2
occurs in one etching hole, it causes a significant decrease in transmission efficiency and
reception sensitivity of the element. In particular, when a transducer is used in liquid, water may
intrude into the gap, which may cause greater transmission efficiency and lower reception
sensitivity.
[0007]
Therefore, the present invention is characterized by providing a transducer that is less likely to
cause a significant reduction in conversion efficiency, and a method of manufacturing the same.
[0008]
The transducer according to the present invention is a transducer comprising one or more
elements, wherein the elements comprise a plurality of cells, and each cell is a vibrating
membrane including one of a pair of electrodes spaced apart from one another. The first cell and
the second cell in the plurality of cells in the element communicate with each other, and the first
cell and the third cell are configured to be vibratably supported. It is characterized in that the
respective gaps do not communicate with each other.
[0009]
According to the present invention, it is possible to provide a transducer which is less likely to
cause a significant reduction in conversion efficiency, and a method of manufacturing the same.
[0010]
It is a schematic diagram for demonstrating the transducer of one Embodiment of this invention.
It is a top view for demonstrating the transducer of Example 2 of this invention.
It is an AB sectional view for explaining a manufacturing method of a transducer of one
embodiment of the present invention.
It is a schematic diagram for demonstrating the to-be-tested object information acquisition
apparatus of one Embodiment of this invention.
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3
[0011]
Hereinafter, embodiments of the present invention will be described using the drawings.
[0012]
(Structure of Transducer) First, the transducer of the present embodiment will be described with
reference to FIG.
FIG. 1 (a) is a top view of a capacitive transducer, and FIG. 1 (b) is a cross-sectional view taken
along the line A-B of FIG. 1 (a). The capacitance type transducer according to the present
embodiment includes a plurality of cells 12. Each cell 12 is vibrated by a vibrating membrane 9
including one of a pair of electrodes separated by a cavity as a gap. It is a supported structure.
Specifically, each cell 12 includes the first electrode 1 and the vibrating film 9 including the
second electrode 2 opposed to the first electrode 1 with the gap 3 interposed therebetween.
[0013]
In FIG. 1, a plurality of cells 12 constitute one element 14, and the capacitive transducer
performs signal input and output in units of this element. That is, when one cell is considered as
one capacity, the capacities of a plurality of cells in the element are electrically connected in
parallel. In addition, when there are a plurality of elements 14, the elements are electrically
separated. In FIG. 1, the first electrode 1 is an electrode to which a bias voltage is applied, and
the second electrode 2 is a signal extraction electrode. That is, in the case of having a plurality of
elements 14, at least the second electrode 2 functioning as a signal extraction electrode needs to
be electrically separated for each element. The signal (electrical signal) output from the second
electrode 2 is extracted by the extraction wiring 16. The first electrode 1 to which a bias voltage
is applied may be electrically connected to each other by a plurality of elements, or may be
separated for each element. Also, as a matter of course, the functions of the first electrode 1 and
the second electrode 2 may be reversed. That is, the lower first electrode 1 may be a signal
extraction electrode, and the second electrode 2 on the vibrating film side may be an electrode to
which a bias voltage is applied. As the wiring, not a lead wiring 16 but a through wiring or the
like may be used.
[0014]
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The vibrating membrane is composed of the first membrane 7, the second membrane 8 and the
second electrode 2 sandwiched therebetween in FIG. 1, but has at least a second electrode and is
a vibrating membrane Should just be the structure which can be vibrated. For example, the
vibrating membrane may be configured with only the second electrode, or the vibrating
membrane may be configured with only the first membrane and the second electrode.
[0015]
Further, in the present embodiment, the first electrode 1 is provided on the substrate 10 via the
first insulating film 11, and the second insulating film 15 is provided on the first electrode 1.
However, the first electrode 1 may be provided directly on the substrate 10 without interposing
the first insulating film 11, and the second insulating film 15 is not provided on the first
electrode 1, so that the first electrode 1 is not provided. One electrode 1 may be exposed.
[0016]
(Driving Principle of Transducer) Here, the driving principle of the capacitive transducer will be
described. When an ultrasonic wave is received by a capacitive transducer, a DC voltage is
applied to the first electrode 1 from voltage application means (not shown) so that a potential
difference is generated between the first electrode 1 and the second electrode 2 Make it in the
When an ultrasonic wave is received in that state, the vibrating film 9 having the second
electrode 2 vibrates, so the distance between the second electrode 2 and the first electrode 1
changes, and the capacitance changes. Due to this change in capacitance, a signal (current) is
output from the second electrode 2 and a current flows in the lead-out wiring 16. This current is
converted into a voltage by a current-voltage conversion element (not shown) to obtain an
ultrasonic reception signal. As described above, the DC voltage may be applied to the second
electrode 2 and the signal may be extracted from the first electrode 1 by changing the
configuration of the lead wiring 16.
[0017]
In addition, when transmitting an ultrasonic wave, while applying a DC voltage to the first
electrode 1, an AC voltage is applied to the second electrode 2, or a DC voltage and an AC voltage
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are applied to the second electrode 2. A superimposed voltage (that is, an AC voltage whose
positive and negative are not reversed) is applied to vibrate the vibrating film 9 by electrostatic
force. An ultrasonic wave can be transmitted by this vibration. Also in the case of transmitting an
ultrasonic wave, an alternating voltage may be applied to the first electrode 1 to vibrate the
vibrating film 9 by changing the configuration of the lead wire 16. The capacitive transducer of
this embodiment can perform at least one of transmission and reception of ultrasonic waves
(acoustic waves).
[0018]
(Relationship between Element and Cell) In the present embodiment, among the plurality of cells
12 included in the element 14, n (n is an integer of 2 or more) cells 12 constitute one cell group
13. A cell group is a structure provided with two or more (plural) cells. Typically, gaps between
all cells in a cell group are in communication (spaces are connected). In particular, when one
etching hole is shared by three cells as shown in FIG. 1, etc., the gaps between the cells in the cell
group are common etchings provided to form the gaps between the cells. It is spatially connected
to the seal that seals the hole. In addition, one element 14 includes a plurality of cell groups 13,
and the respective gaps do not communicate between the cell groups.
[0019]
In FIG. 1, the element 14 comprises six cell groups 13, and each cell group 13 is composed of
three cells 12. The gap 3 in the cell group 13 is formed by etching through the etching hole 5,
and the etching hole 5 is sealed by the sealing portion 6. The gaps 3 in the cell group 13
communicate with each other through the etching path 4 formed in the etching step, but the
gaps between the adjacent cell groups 13 do not communicate with each other.
[0020]
The sealing portion 6 is provided to bury and seal the etching hole 5 so that liquid and outside
air do not enter the gap 3. In particular, when sealing is performed under reduced pressure, the
vibrating film 9 is deformed by atmospheric pressure, and the distance between the first
electrode 1 and the second electrode 2 becomes short. Since the transmission efficiency or
reception sensitivity is proportional to the 1.5th power of the effective distance between the first
electrode 1 and the second electrode 2, sealing is performed under reduced pressure, and the
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pressure inside the gap 3 is lower than atmospheric pressure In this case, transmission efficiency
or reception sensitivity (ie, conversion efficiency) can be improved. The effective distance is the
sum of the value obtained by dividing the insulating film present between the first electrode 1
and the second electrode 2 by the relative dielectric constant and the distance in the depth
direction of the gap 3. is there.
[0021]
As described above, in the present embodiment, in one element, the cells in the first cell group
(including the first cell and the second cell) communicate with each other through the gaps. The
first cell (the cell in the first cell group) and the third cell (typically the cell in the second cell
group) that does not constitute the first cell group are There is no communication between each
other. Such a configuration reduces the possibility of causing a significant reduction in the
conversion efficiency of the element, even when the etching holes 5 are shared for high density
arrangement of cells. That is, even if a sealing failure occurs in one etching hole 5, the conversion
efficiency is affected only by the cells in which the gaps communicate with each other, and in the
cells in which the gaps do not communicate with each other. Absent.
[0022]
In particular, despite the fact that the etching hole 5 is sealed under reduced pressure, the
distance between the first and second electrodes of the cell in which the pressure in the gap
becomes equal to the outside air due to sealing failure is reduced in the gap. It is greater than the
distance between the first and second electrodes of the cell in state. Therefore, the conversion
efficiency of the cell whose gap is communicated with the outside air is reduced. In addition,
when a capacitive transducer is used in liquid, water may intrude into the gap connected to the
etching hole of sealing failure, which may cause a reduction in conversion efficiency or an
insulation failure. is there. However, in the case of the configuration of the present embodiment,
even if the sealing failure of a part of the etching holes occurs, only the cell group in which the
gap and the etching hole of the sealing failure are connected becomes a failure. Does not cause
Therefore, a significant reduction in conversion efficiency of the element can be avoided. In
addition, the yield due to sealing failure can be improved.
[0023]
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7
In the present embodiment, the number of etching holes 5 and the number of sealing portions 6
in the cell group 13 are preferably smaller than the number of cells constituting the cell group.
With such a configuration, the number of etching holes relative to the number of cells can be
reduced, so that a plurality of cells can be arranged at high density, and transmission efficiency
and reception sensitivity can be improved. In particular, when the cells are arranged closer than
the inter-cell distance in FIG. 1, it is preferable that the number of etching holes be small with
respect to the number of cells in the cell group. In addition, the etching hole and the sealing
portion are preferably arranged inside the envelope of one cell group. The envelope of a cell
group is a curve that shares the tangent of all the cells on the outer peripheral side among the
cells that constitute the cell group, and all the cells that constitute the cell group enter inside the
envelope. When the number of etching holes for the cells increases, the etching holes are
disposed outside the envelope of one cell group, and it is difficult to bring the cell groups close to
each other. In the case where the number of etching holes relative to the number of cells in a cell
group is small, the etching holes are arranged inside the envelope forming one cell group, so that
the cell groups can be brought close to each other. In addition, when the number of cells in a cell
group is two and the gap between the cells is minimized, the cell groups can not be placed close
to each other because they are disposed outside the envelope of the cell group. The number of
cells is preferably three or more.
[0024]
Furthermore, one cell group is composed of three or more cells, and at least one of each of the
etching holes and the sealing portion of one cell group is arranged at an equal distance from the
center of each cell. preferable. By arranging one of the etching holes at a position equidistant
from the centers of all the cells in the cell group, the etching time of all the cells can be made
uniform. Thus, overetching of the cell gap can be prevented. Here, the “equidistant positions”
include not only strictly equidistant positions but also substantially equidistant positions where
the etching time for forming the gaps between the cells can be regarded as the same.
[0025]
Further, in order to stably and easily realize the formation of the sealing portion 6, it is preferable
to make the width of the etching path 4 in the region where the etching hole 5 is formed wider
than the width of the etching hole 5. In addition, it is preferable that the width of the etching
holes 5 be smaller because the cells can be arranged more closely. Specifically, in FIG. 1, the size
of the orthographic projection of the etching path 4 on the substrate 10 in the region where the
etching hole 5 is formed is larger than the size of the orthographic projection of the etching hole
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5 on the substrate 10. In addition, since the cross section of the structure in the vicinity of the
etching hole 5 is rotationally symmetric, sealing can be stably and easily realized, and the yield
can be improved. That is, compared to the case where the cross section of the structure in the
vicinity of the etching hole 5 is not rotationally symmetrical, the gas inflow conditions such as
CVD become uniform in the case of the configuration of FIG. Therefore, the sealing conditions
become uniform, and sealing defects are less likely to occur.
[0026]
However, in the case where the width of the etching path 4 is wider than the width of the etching
hole 5, sealing is stable, but if sealing failure occurs, conversion efficiency is likely to be reduced.
That is, as shown in FIG. 1, since the etching path 4 is wide, even if the etching hole 5 is
embedded, the space between the cells is connected by the space of the etching path around the
embedded (side of the sealing portion). Therefore, the cell group in which the gaps communicate
with each other through the etching path 4 is likely to be affected by one sealing portion failure.
Therefore, particularly in the case of such a configuration, in one element, the cells in the first
cell group communicate with each other, and the cells in the first cell group and the cells of the
second cell group Preferably, the gaps do not communicate with each other.
[0027]
Further, the region of the etching path 4 which is in communication with the gap 3 is narrower
than the region where the etching hole 5 is formed. This is to increase the area for supporting
the vibrating membrane 9.
[0028]
It is preferable that the sealing part 6 of this embodiment is arrange | positioned in the position
of equal distance from each center part of the some cell connected with the sealing part 6. As
shown in FIG. With this configuration, since the etching holes 5 are equidistant from the centers
of the cells surrounding the etching holes 5, the etching time for forming the gap 3 is the same
between the cells. If the time for forming the gap is the same, even if the etching holes 5 are
shared between the cells, the etching residue that causes the variation of the conversion
efficiency hardly remains in the gap. Also, by arranging the sealing portion 6 at the shortest
distance from each cell in the periphery, the cells can be arranged with high density. Here, the
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“equidistant positions” include not only strictly equidistant positions but also substantially
equidistant positions where the etching time for forming the gaps 3 of the respective cells can be
regarded as the same.
[0029]
Furthermore, in the present embodiment, it is preferable that one cell group is composed of three
cells, and the center of each cell is disposed at a position corresponding to the vertex of an
equilateral triangle. With this configuration, a plurality of cells in the element can be arranged
substantially in a honeycomb shape, so the cells can be arranged at the highest density, and the
conversion efficiency of the element can be improved. In this configuration, the sealing portion 6
is preferably located at the center of the equilateral triangle. Here, “a position corresponding to
the vertex of an equilateral triangle” means not only the position of “a vertex of an equilateral
triangle” but also a substantially equilateral triangle within a range that does not affect the case
of arranging a plurality of cells in a substantially honeycomb shape. Contains the position of the
top of. The “central part of the equilateral triangle” is not only the position of the “center of
the equilateral triangle” but also “the equilateral triangle if the etching time for forming the
gaps 3 of the three cells can be considered to be the same. Approximately the center of the
[0030]
Further, in the present embodiment, although the plurality of cell groups in the element are all
configured by the same number of cells, as shown in Example 2 described later, the number of
cells constituting the cell group configuration is different 2 It is also possible to have a
configuration having more than types of cells. That is, the element includes at least the first cell
group and the second cell group in an element, and n cells (n is an integer of 2 or more) included
in the first cell group are included in the second cell group Let m cells (m is an integer of 2 or
more). In this case, if n = m, the configuration shown in FIG. 1 is included, and if n ≠ m, the
configuration shown in FIG. 2 is included. As shown in FIG. 2, by combining cells having different
numbers of cells, the cells can be arranged more closely, and the conversion efficiency of the
element can be further improved.
[0031]
Further, the number of cell groups included in the element may be any number as long as it is
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plural. The number of elements may be any number as long as it is one or more, and in the case
of acquiring information of a wide area in a subject, it is better to provide a plurality of elements.
[0032]
(Method of Manufacturing Transducer) Next, a method of manufacturing the transducer of this
embodiment will be described with reference to FIG. FIG. 3 is a cross-sectional view showing the
method of manufacturing the capacitive transducer of the present embodiment, and FIG. 3
corresponds to the cross-sectional view along the line A-B in FIG. Even when the same members
as in FIG. 1 are shown, the same reference numerals may be used for the description.
[0033]
First, as shown in FIG. 3A, the first insulating film 51 is formed on the substrate 50, and the first
electrode 41 is formed on the first insulating film 51. A silicon substrate can be used as the
substrate 50, and the first insulating film 51 is provided to insulate the substrate 50 from the
first electrode 41. When the substrate 50 is an insulating substrate such as a glass substrate, the
first insulating film 51 may not be formed. The substrate 50 is preferably a substrate having a
small surface roughness. When the surface roughness is large, the surface roughness is
transferred also in the film forming step after the present step, and the first electrode 41 and the
second electrode 42 (FIG. 3 (e)) by the surface roughness. The distance between them (see
reference) varies between cells and between elements. This variation leads to variation in
conversion efficiency. Therefore, the substrate 50 is preferably a substrate having a small surface
roughness. Further, it is preferable that the first insulating film 51 and the first electrode 41 also
have a small surface roughness. For example, a silicon nitride film, a silicon oxide film or the like
can be used for the first insulating film 51, and titanium, aluminum or the like can be used for
the first electrode 41, for example.
[0034]
Next, as shown in FIG. 3B, the second insulating film 52 is formed on the first electrode. The
second insulating film 52 is formed to prevent an electrical short circuit or a dielectric
breakdown between the electrodes when a voltage is applied between the first electrode 41 and
the second electrode 42. However, when driving with a low voltage, since the first membrane 47
described later is an insulator, the second insulating film 52 may not be formed. The second
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insulating film 52 is preferably an insulating material having a small surface roughness like the
substrate 50, and for example, a silicon nitride film, a silicon oxide film or the like can be used.
[0035]
Next, as shown in FIG. 3C, a sacrificial layer 43 is formed. The sacrificial layer 43 is also
preferably a material with a small surface roughness. Moreover, in order to shorten the etching
time of the sacrificial layer 43, a material having a high etching rate is preferable. Furthermore,
the second insulating film 52, the first membrane 47 (see FIG. 3D), and the second electrode 42
are hardly etched by the etchant or etching gas for removing the sacrificial layer 43. Sacrificial
layer materials are preferred. This is because when the second insulating film 52, the first
membrane 47, and the second electrode 42 are partially etched by the etchant or etching gas for
removing the sacrificial layer 43, the thickness of the vibrating film is This is because the
variation in distance and the variation in distance between electrodes occur. When the second
insulating film 52 and the first membrane 47 are formed of a silicon nitride film or a silicon
oxide film, the sacrificial layer 43 is preferably formed of chromium. This is because chromium
can be etched using an etching solution in which the surface roughness is small and the second
insulating film 52, the first membrane 47, and the second electrode 42 are not etched.
[0036]
Next, as shown in FIG. 3D, the first membrane 47 is formed on the sacrificial layer. The first
membrane 47 preferably has low tensile stress. For example, a tensile stress of 300 MPa or less
is good. As the first membrane 47, a silicon nitride film is preferable because stress control is
possible and a low tensile stress of 300 MPa or less can be achieved. If the first membrane 47
has a compressive stress, the first membrane 47 may cause sticking or buckling and may be
significantly deformed. Sticking means that the vibrating membrane including the first
membrane 47 adheres to the substrate side after removing the sacrificial layer. Also, in the case
of having a large tensile stress, the first membrane 47 may be broken. Therefore, the first
membrane 47 preferably has a low tensile stress.
[0037]
Next, as shown in FIG. 3E, the second electrode 42 is formed on the first membrane 47, and the
etching hole 45 is further formed. Thereafter, the sacrificial layer 43 is removed through the
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etching holes 45. The second electrode 42 is preferably a material having a small residual stress
so as not to cause a large deformation of the vibrating membrane. Furthermore, the second
membrane 48 (see FIG. 3F) or a heat resistance that does not cause deterioration or increase in
stress due to a temperature at the time of forming a sealing layer for forming the sealing portion
46 or the like. Materials are preferred. When the sacrificial layer is removed while the second
electrode 42 is exposed, the sacrificial layer may be etched while a photoresist or the like for
protecting the second electrode 42 is applied. However, in this case, the stress of the photoresist
or the like makes the first membrane 47 easy to stick. Therefore, the second electrode 42
preferably has etching resistance so that the sacrificial layer can be etched without the
photoresist and the second electrode 42 exposed. Specifically, it is preferable to use titanium, an
aluminum silicon alloy, or the like as the second electrode 42.
[0038]
Next, as shown in FIG. 3F, a second membrane 48 is formed. In this step, the step of forming the
second membrane 48 on the second electrode 42 and the step of forming the sealing portion 46
for sealing the etching hole 45 are both performed. By forming the second membrane 48, a
vibrating membrane having a desired spring constant can be obtained, and the etching hole 45
can be sealed by the second membrane 48. When the sealing process of the etching hole 45 and
the process of forming the second membrane 48 are the same as this process, the vibrating film
can be formed only by the film forming process. Therefore, the thickness of the vibrating film can
be easily controlled, and the variation in the spring constant or the deflection of the vibrating
film due to the thickness variation can be suppressed, so that the variation in conversion
efficiency between cells or elements can be reduced. it can.
[0039]
However, in the present embodiment, the step of sealing the etching hole 45 and the step of
forming the second membrane 48 can be separate steps. That is, the second membrane 48 can
be formed after forming the second membrane 48, or the second membrane 48 can be formed
after forming the sealing portion 46. Alternatively, the etching holes 45 may be formed after the
second electrode 42 is formed and the second membrane 48 is formed. After the etching holes
45 are formed, the sacrificial layer 43 is removed through the etching holes 45 and finally
sealed. The sealing layer 46 can also be used as a third membrane.
[0040]
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The second membrane 48 is preferably a material having low tensile stress. As with the first
membrane 47, if the second membrane 48 has compressive stress, it causes sticking or buckling
and is greatly deformed. Also, in the case of a large tensile stress, the second membrane 48 may
be broken. Thus, the second membrane 48 preferably has low tensile stress. Specifically, as the
second membrane 48, it is preferable to use a silicon nitride film that can be stress-controlled
and can have a low tensile stress of 300 MPa or less.
[0041]
After this process, wiring not connected to the first electrode and the second electrode is formed
by a process not shown. The wiring material may be aluminum or the like.
[0042]
(Object Information Acquisition Device) The transducer described in the above embodiment can
be applied to an object information acquisition device using an acoustic wave including an
ultrasonic wave. Acoustic waves from the subject are received by the transducer, and subject
information reflecting the optical characteristic value of the subject such as light absorption
coefficient using the electrical signal output from the transducer, and subject reflecting the
difference in acoustic impedance. Sample information can be acquired.
[0043]
FIG. 4A shows an object information acquisition apparatus using the photoacoustic effect. The
pulsed light generated from the light source 2010 is irradiated to the subject 2014 via the
optical member 2012 such as a lens, a mirror, and an optical fiber. The light absorber 2016
inside the object 2014 absorbs the energy of the pulsed light and generates a photoacoustic
wave 2018 which is an acoustic wave. The transducer 2020 in the probe 2022 receives the
photoacoustic wave 2018, converts it into an electrical signal, and outputs the signal to the
signal processing unit 2024. The signal processing unit 2024 performs signal processing such as
A / D conversion and amplification on the input electric signal, and outputs the signal processing
to the data processing unit 2026. The data processing unit 2026 acquires object information
(characteristic information reflecting the optical characteristic value of the object such as a light
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absorption coefficient) as image data using the input signal. Here, the signal processing unit
2024 and the data processing unit 2026 are collectively referred to as a processing unit. The
display unit 2028 displays an image based on the image data input from the data processing unit
2026.
[0044]
FIG. 4B shows a subject information acquiring apparatus such as an ultrasonic echo diagnostic
apparatus using reflection of acoustic waves. The acoustic wave transmitted from the transducer
2120 in the probe to the subject 2114 is reflected by the reflector 2116. The transducer 2120
receives the reflected acoustic wave 2118, converts it into an electrical signal, and outputs the
electrical signal to the signal processing unit 2124. The signal processing unit 2124 performs
signal processing such as A / D conversion and amplification on the input electric signal, and
outputs the signal processing to the data processing unit 2126. The data processing unit 2126
acquires object information (characteristic information reflecting a difference in acoustic
impedance) as image data using the input signal. Here, the signal processing unit 2124 and the
data processing unit 2126 are collectively referred to as a processing unit. The display unit 2128
displays an image based on the image data input from the data processing unit 2126.
[0045]
The probe may be one that scans mechanically or one that is moved by a user such as a doctor or
an engineer relative to the subject (handheld type). Moreover, in the case of the apparatus using
a reflected wave like FIG.4 (b), you may provide the probe which transmits an acoustic wave
separately from the probe which receives.
[0046]
Furthermore, it is an apparatus having both the functions of the apparatus shown in FIGS. 4A and
4B, object information reflecting the optical characteristic value of the object, and object
information reflecting the difference in acoustic impedance. , And may be acquired. In this case,
the transducer 2020 in FIG. 4A may transmit not only the photoacoustic wave but also the
acoustic wave and the reflected wave.
04-05-2019
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[0047]
Next, the transducer of the present embodiment will be described in more detail in more specific
examples.
[0048]
A first embodiment will be described with reference to FIG.
The capacitive transducer of the present embodiment has one element, and the element has six
cell groups 13 composed of three cells 12. The cell 12 includes a first electrode 1 and a vibrating
membrane 9 including the second electrode 2 provided with the first electrode 1 and the gap 3
interposed therebetween, and the vibrating membrane 9 is vibratably supported There is. The
vibrating membrane 9 includes a first membrane 7, a second membrane 8 and a second
electrode 2. The first electrode 1 is an electrode for applying a bias voltage, and the second
electrode 2 is a signal extraction electrode. The shape of the vibrating film in this embodiment is
circular, but the shape may be rectangular, hexagonal or the like. In the case of a circular shape,
the vibration mode is axisymmetric, which is preferable because the vibration of the vibrating
film due to the unnecessary vibration mode can be suppressed.
[0049]
The first insulating film 11 on the substrate 10 which is a silicon substrate is a silicon oxide film
with a thickness of 1 μm formed by thermal oxidation. The second insulating film 15 is a silicon
oxide film formed by Prasma Enhanced Chemical Vapor Deposition (PE-CVD). The first electrode
1 is titanium with a thickness of 50 nm, and the second electrode 2 is titanium with a thickness
of 100 nm. The first membrane 7 and the second membrane 8 are silicon nitride films produced
by PE-CVD, and are formed with a tensile stress of 200 MPa or less. The diameters of the first
membrane 7 and the second membrane 8 are 25 μm, and the thicknesses thereof are 0.4 μm
and 0.7 μm. The depth of the gap 3 is 0.2 μm.
[0050]
In the cell group 13, an etching path 4 and an etching hole 5 for forming a gap 3 of three cells
constituting the cell group 13 are disposed, and the etching hole 5 is sealed by a sealing portion
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6. . The inside of the gap can be maintained at 200 Pa because it is shut off from the outside air
by the sealing portion 6. Further, in order to prevent the outside air from entering the gap 3, the
thickness of the sealing portion 6 is preferably 2.7 times or more the depth of the gap 3. In
particular, PE-CVD should have a thickness of the sealing portion 6 2.7 times or more the depth
of the gap 3 because the uniformity of film formation is low compared to Low Pressure Chemical
Vapor Deposition (LPCVD). Is preferred.
[0051]
The width of the etching path 4 in the region where the etching hole 5 is formed is 6 μm, and
the diameter of the etching hole 5 is 4 μm. Since the size of the etching hole 5 is smaller than
the width of the etching path 4 and the cross section of the etching hole 5 is rotationally
symmetrical, the sealing portion 6 can be easily formed. In the case of combining the second
membrane 8 and the sealing step, the sealing portion 6 can also be formed by depositing the
second membrane 8 having a thickness of 0.7 μm.
[0052]
When the gaps 3 of three cells are etched through one etching hole 5 as in this embodiment, the
cells in the cell group can be arranged at high density. Therefore, for example, the number of
cells can be increased by 40% or more, and the conversion efficiency can be improved by 40%, as
compared with the case where the sealing portion is provided for each cell (one etching hole per
cell). is there. Here, the comparison result in the case where the distance relationship between
the cell and the sealing portion is the same is shown.
[0053]
Further, the element 14 of the present embodiment is constituted by a plurality of cell groups 13,
and since the cells 3 do not have the gap 3 communicating with each other, the sealing failure
occurs even if a failure occurs in one sealing portion 6. Only the cells connected to the part
become defective and do not cause a defect as the element 14. Therefore, the conversion
efficiency of the transducer is not significantly reduced, and the yield can be improved.
[0054]
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Next, the configuration of the capacitive transducer of the second embodiment will be described
with reference to FIG. FIG. 2 is a top view of the capacitive transducer of this embodiment. The
configuration of the capacitive transducer of the second embodiment is different from that of the
first embodiment in that there are two types of plural cell groups constituting an element.
[0055]
The capacitive transducer according to this embodiment includes an element including a plurality
of first cell groups 33 each composed of three cells 32 and a second cell group 35 composed of
four cells 32. There are two 34. The configuration of the cell 32 and the configuration of the first
cell group 33 are substantially the same as those of the cell group 13 of the first embodiment,
and therefore the description thereof is omitted.
[0056]
The second cell group 35 is composed of four cells 32, and a gap 23 of the four cells 32 is
formed by etching through two etching holes 25. The width of the etching path 24 is 6 μm, and
the diameter of the etching hole 25 is 4 μm. Since the size of the etching hole 25 is smaller than
the width of the etching path 24 and the cross section of the etching hole 25 is rotationally
symmetrical, the formation of the sealing portion 26 is facilitated. Also in the present
embodiment, the sealing portion 26 is also formed by depositing a second membrane layer
having a thickness of 0.7 μm.
[0057]
Thus, the element of this embodiment includes the first cell group 33 composed of three cells,
and the second cell group 35 composed of four cells, Cell group 35 are arranged in the outer
region (peripheral portion) in the element. With this configuration, as compared to the first
embodiment, the cells can be disposed in the peripheral space in the element, and therefore,
more cells can be disposed in the element. Therefore, the capacitive transducer of this
configuration can further improve the conversion efficiency.
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[0058]
DESCRIPTION OF SYMBOLS 1 first electrode 2 second electrode 3 gap 4 etching path 5 etching
hole 6 sealing part 7 first membrane 8 second membrane 9 vibrating membrane 10 substrate 11
first insulating film 12 cell 13 cell group 14 element 15 Second insulating film
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