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JP2013126069

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DESCRIPTION JP2013126069
Abstract: The present invention provides an electromechanical transducer capable of determining
a drive bias voltage of a sensor element without impairing the conversion characteristics of the
sensor element, and a method of manufacturing the same. An electromechanical transducer
(101) has a sensor element (103) including a cell (104) having a first electrode (109) and a
second electrode (105) provided with a first electrode (109) and a gap (107). In addition to the
sensor element, it has a monitor element 110 for measuring a pull-in voltage, which includes a
cell 111 having a first electrode 116 and a second electrode 112 provided therebetween. The
two elements 103 and 110 are formed such that the pull-in voltage of the monitor element 110
and the drive bias voltage for driving the sensor element 103 have a predetermined relationship.
[Selected figure] Figure 1-1
Electromechanical converter and method of manufacturing the same
[0001]
The present invention relates to a capacitive electromechanical transducer capable of
transmitting and / or receiving acoustic waves, such as a capacitive ultrasonic transducer that
can be manufactured using a semiconductor process. In the present specification, the acoustic
wave includes what are called sound waves, ultrasonic waves, and photoacoustic waves. For
example, the inside of the subject is irradiated with light (electromagnetic wave) such as visible
light or infrared light to generate an acoustic wave generated inside the subject, or the acoustic
wave is transmitted inside the subject and reflected acoustic wave reflected inside the subject
including.
04-05-2019
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[0002]
Using Capacitive Micromachined Ultrasonic Transducers (CMUTs) using a capacitance method as
described in Patent Document 1 and Non-patent Document 1 to obtain an image of tissue inside
a living body using ultrasonic waves. Has been proposed. As illustrated in FIG. 7A, in the CMUTs
901, elements 902 for receiving or transmitting ultrasonic signals are arranged in a twodimensional direction. Further, as shown in FIG. 7-2, the element 902 is composed of a plurality
of cells 903. The cell includes, for example, a membrane 905 having an upper electrode (second
electrode to be described later) 904, and a lower electrode (a first electrode to be described
below) disposed directly below the membrane via a support member 910, a cavity 906 and an
insulating film 907. An electrode 908 is a structure fabricated on a substrate 909. Here, upper
electrodes between cells in the element 902 and lower electrodes are electrically connected to
each other. In FIG. 7B, the upper electrodes 904 between the cells 903 are electrically connected
to each other by the wire 911, and for the lower electrode 908, one electrode uniformly formed
in the element 902 is used as all the cells. 903 is sharing. On the other hand, between the
elements 902, at least one of the upper electrodes and the lower electrodes is electrically isolated
from each other. In this example, although not shown in FIG. 7B, all the elements 902 of the
CMUTs 901 share one uniformly formed electrode as the lower electrode 908.
[0003]
A method of receiving ultrasound signals using CMUTs, ie, a method of converting ultrasound
signals into electrical signals, is shown below. As shown in FIG. 8, a drive bias voltage is applied
between the upper electrode 1001 and the lower electrode 1002 of each element using a drive
bias voltage source 1003. Here, the bias voltage refers to a DC voltage, and the drive bias voltage
refers to a constant DC voltage applied to drive the CMUTs. In this state, when the ultrasonic
signal p (t) is input from the ultrasonic signal source 1004 to the CMUTs, the membrane 1005
integral with the upper electrode 1001 vibrates, and the space between the upper electrode
1001 and the lower electrode 1002 of each element is vibrated. The capacitance changes.
Thereby, an electric signal i (t) corresponding to the ultrasonic signal can be obtained from the
upper electrode 1001 of each element. On the other hand, when transmitting ultrasonic signals
using CMUTs, the membrane 1005 may be vibrated by applying a drive bias voltage and an
electric signal corresponding to the ultrasonic signals between both electrodes of each element.
[0004]
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In conventional CMUTs, one of the upper electrode and the lower electrode is often a common
electrode electrically connected between all the elements. At this time, the other electrode is
connected to the input terminal of the signal current detection circuit, and is often virtually equal
to the reference potential of the entire CMUTs. In such an electrode configuration, the same drive
bias voltage is applied between both electrodes of all elements.
[0005]
U.S. Pat. No. 6,430,109
[0006]
Zuang.et.al., IEEE Trans.
Ultrason. Ferroelectr. Freq. Control, vol.56,
No.1, pp.182−192, 2009.
[0007]
In the above configuration, there may be a deviation in the pull-in voltage of the element. In such
a case, it is desirable to be able to determine the drive bias voltage without changing the
conversion characteristics of the element. Here, the conversion characteristic refers to the
magnitude of the current signal output from the element for a given ultrasound signal input.
When the bias voltage of the element exceeds a certain value, a phenomenon called pull-in
occurs in which the membrane instantaneously contacts the bottom of the cavity. The bias
voltage at this time is defined as a pull-in voltage. The value of the pull-in voltage depends on the
structural parameters of the element such as the size and thickness of the membrane, the depth
of the cavity and the like. When pull-in occurs, the conversion characteristic of the element
changes. This is because a sudden change in electric field strength occurs, and the membrane
and the insulating layer are charged by contact and the drive bias voltage is weakened.
Therefore, in order to obtain CMUTs having desired conversion characteristics, it is desirable that
a bias voltage higher than the pull-in voltage is not applied between both electrodes of the
element.
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[0008]
On the other hand, since the conversion characteristics of the element increase with the increase
of the drive bias voltage, it is desirable that the drive bias voltage be large. However, for the
above reason, the drive bias voltage should be less than the pull-in voltage. Therefore, in order to
determine the optimum drive bias voltage, it is necessary to know the pull-in voltage. As a
method of knowing the pull-in voltage, there is also a method of using the predicted value of the
pull-in voltage calculated from the structural parameter of the element. However, in view of the
deviation of structural parameters at the time of manufacture, in order to reliably avoid pull-in, it
is desirable to determine the drive bias voltage based on the pull-in voltage of the element
actually manufactured. In order to obtain the pull-in voltage of an actually manufactured
element, the method of measuring the bias voltage when pull-in actually occurs is the most
reliable. However, in this method, since the membrane comes in contact with the bottom of the
cavity and pull-in occurs, the conversion characteristics of the element change, and it is difficult
to obtain CMUTs having the desired conversion characteristics.
[0009]
In view of the above problems, an electromechanical transducer according to the present
invention includes a sensor element including at least one cell having a first electrode and a
second electrode opposed to the first electrode with a gap therebetween. Have. And for
measuring a pull-in voltage including at least one cell having a first electrode and a second
electrode opposite to the first electrode with a gap in addition to the sensor element. The monitor
element and the sensor element are formed such that a monitor element is provided, and a pullin voltage of the monitor element and a drive bias voltage for driving the sensor element have a
predetermined relationship.
[0010]
Further, in view of the above problems, according to the method of manufacturing an
electromechanical transducer according to the present invention, at least a cell having a first
electrode and a second electrode provided opposite to the first electrode with a gap
therebetween is provided. A cell having a first step of forming a sensor element including one,
and a second electrode provided opposite to the first electrode with a gap between the first
electrode and the first electrode in addition to the sensor element And a second step of forming a
monitor element for measuring a pull-in voltage including at least one. Then, in the first step and
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the second step, the monitor element and the sensor element are formed such that the pull-in
voltage of the monitor element and the drive bias voltage of the sensor element have a
predetermined relationship.
[0011]
According to the present invention, since the monitor element is formed such that the pull-in
voltage has a predetermined relationship with the drive bias voltage for driving the sensor
element, the drive bias of the sensor element is not impaired. The voltage can be determined.
[0012]
The top view which shows CMUTs of 1st Example of the electro-mechanical transducer of this
invention.
The figure explaining the sensor element of a 1st Example. The figure explaining the monitor
element of a 1st Example. FIG. 7 is a plan view illustrating another example of the monitor
element according to the first embodiment of the present invention. The top view which shows
the structure of CMUTs in a 2nd Example. The figure which shows an example of distribution of
the thickness of the insulating layer on CMUTs, and distribution of the pull-in voltage of the
sensor element corresponding to it. The figure which shows another example of distribution of
the pull in voltage of a sensor element. The top view which shows the structure of CMUTs in 3rd
Example. A figure explaining CMUTs in a 4th example. The top view which shows the structure of
conventional CMUTs. The figure explaining the element of conventional CMUTs. The figure
explaining the drive principle of CMUTs. FIG. 2 is a diagram showing an example of an object
information acquiring apparatus using the electro-mechanical transducer according to the
present invention.
[0013]
The feature of the present invention is, in addition to the sensor element, to provide a monitor
element for measuring the pull-in voltage which has basically the same structure as the sensor
element. Then, both elements are formed such that the pull-in voltage of the monitor element and
the drive bias voltage for driving the sensor element have a predetermined relationship. Based on
this concept, the electromechanical transducer and the method of manufacturing the same
according to the present invention have the basic configuration as described in the means for
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solving the above problems. In the present invention of this configuration, since the pull-in
voltage is equal to or higher than the drive bias voltage, typically both elements are configured
such that the pull-in voltage of the monitor element is smaller than the pull-in voltage of the
sensor element. However, if the relationship between the pull-in voltage of the monitor element
and the drive bias voltage of the sensor element is known, the drive bias voltage of the sensor
element can be calculated from the measured value of the pull-in voltage of the monitor element.
Therefore, there is no limitation on how to set the magnitude relationship between the pull-in
voltages of both elements. However, if the structural parameters of both elements are set so that
the pull-in voltage of the monitor element is equal to or higher than the pull-in voltage of the
sensor element, both elements should not be pulled in when measuring the pull-in voltage of the
monitor element. At least one of the first and second electrodes needs to be electrically separated
between the two elements. Here, structural parameters are elements such as thickness and
Young's modulus of membrane, thickness and dielectric constant of insulating layer under cavity,
depth of cavity, electrode area, area of movable part of membrane, etc. It refers to the dimensions
and material constants of the members that make up the included cell.
[0014]
Hereinafter, specific embodiments of the electro-mechanical transducer and the method of
manufacturing the same will be described. First Embodiment CMUTs 101 according to the
present embodiment, which is an example of the electromechanical transducer according to the
present invention, is arranged in a two-dimensional direction inside sensor area 102 on its main
surface as shown in FIG. And a plurality of sensor elements 103. Further, the CMUTs 101 of the
present embodiment have monitor elements 110 at the periphery of the sensor area 102. Here,
the main surface refers to the surface of the CMUTs 101 that faces the subject on which an
ultrasonic image or the like is to be acquired. Further, the peripheral portion of the sensor area
102 refers to an area surrounded by the boundary of the sensor area 102 and the outline of the
CMUTs 101. The sensor element 103 has, for example, the same structure as the element of the
conventional CMUTs described above. That is, as shown in FIGS. 1-2 (a) and (b), the membrane
106 having the upper electrode (second electrode) 105 and the cavity (gap) 107 and the
insulating film 108 directly below the membrane 106 are disposed. And a plurality of cells 104
each having a lower electrode (first electrode) 109. The monitor element 110 basically has the
same structure as the sensor element 103. That is, as shown in FIGS. 1-3 (a) and (b), a membrane
113 having a second electrode 112, and a first electrode 116 disposed directly below the
membrane via a cavity 114 and an insulating film 115. And a plurality of cells 111 having In the
present embodiment, the monitor element 110 differs from the sensor element 103 in that the
structure parameter is set such that the pull-in voltage is smaller than the pull-in voltage of the
sensor element 103. That is, for example, the structure parameter is set such that the ratio of the
pull-in voltage of the monitor element 110 to the pull-in voltage of the sensor element 103
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becomes a predetermined value (value smaller than 1). The pull-in voltage of the monitor
element 110 can be measured, and the drive bias voltage of the sensor element 103 can be
determined based on the measured value. Thus, the drive bias voltage can be determined without
pulling in the sensor element 103. In this case, when the pull-in voltage of the monitor element
110 is measured, the sensor element 103 can not be pulled in by design, so the sensor element
and the first and second electrodes of the monitor element are electrically connected. It is also
good.
However, since there may be manufacturing errors, at least one of the first and second electrodes
is electrically separated between the two elements in order to ensure that the sensor element
does not pull in on the safe side. It is desirable to be done.
[0015]
In order to make the pull-in voltage of the monitor element smaller than the pull-in voltage of the
sensor element, the above-mentioned structural parameters of the monitor element may be
determined as follows. The pull-in voltage Vp and the spring constant K of the membrane, which
is a structural parameter of the element, the vacuum equivalent distance d between the first
electrode and the second electrode, and the area A of the second electrode approximately There
is a relationship as shown in the following equation (1). Here, the spring constant of the
membrane refers to a constant representing how many times the external force applied in the
direction perpendicular to the main surface of the membrane is the displacement of the
membrane in that direction. In addition, the vacuum equivalent distance d is expressed by the
equation (where the cavity depth is dc, the thickness of the insulating layer is di, the relative
permittivity of the insulating layer is ki, the thickness of the membrane is dm, and the relative
permittivity of the membrane is km It is expressed as 2). Vp∝K<0.5>d<1.5>A<−0.5>・
・・(1) d=dc+(di/ki)+(dm/km)・・・(2)
[0016]
Therefore, for example, in order to make the pull-in voltage Vpm of the monitor element 80% of
the pull-in voltage Vps of the sensor element, the structural parameter of the monitor element
may be determined as follows. In the first example, as shown in FIGS. 1-3, the depth of the cavity
114 and the thickness of the insulating layer 115 are adjusted, and the vacuum equivalent
distance between the electrodes of the monitor element 110 is the vacuum equivalent between
the electrodes of the sensor element It should be 86.2% of the distance. As a second example, as
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shown in FIG. 1-4 (a), the area of the second electrode 118 of the monitor element 117 may be
156.3% of the second electrode 105 of the sensor element. As a third example, the spring
constant of the membrane 113 of the monitor element 110 may be 89.4% of the spring constant
of the membrane 106 of the sensor element 103. In order to reduce the membrane's spring
constant, it is easiest to increase the area of the vibrating part 120 of the membrane of the
monitor element 119 as shown in Fig. 1-4 (b), but the thickness of the membrane is thin. It is also
possible by doing.
[0017]
In order to determine the drive bias voltage, the pull-in voltage of the monitor element is
measured, and typically, the product of the pull-in voltage and a predetermined constant may be
used as the drive bias voltage. This constant is determined from the ratio of the drive bias voltage
to the pull-in voltage of the monitor element. In particular, if the design is determined such that
the pull-in voltage of the monitor element is equal to the drive bias voltage, this constant is 1.
That is, the pull-in voltage of the monitor element can be used as the drive bias voltage as it is.
[0018]
The method of measuring the pull-in voltage of the monitor element is as follows. While applying
a gradually increasing bias voltage from 0 between the electrodes of the monitor element,
observe whether or not pull-in occurs, and let the bias voltage at the time of pull-in occurrence
be the pull-in voltage. In order to determine the pull-in of the monitor element, the change in the
characteristic value of the monitor element with respect to the bias voltage may be measured.
The characteristic values to be measured include, for example, impedance characteristics
between electrodes and displacement of the membrane. The method of determining the
occurrence of pull-in using each characteristic value is shown below. The impedance
characteristic between the electrodes with respect to frequency has a singular point where the
characteristic changes largely in the vicinity of the resonant frequency of the membrane. When
pull-in occurs, the central portion of the membrane is fixed to the bottom of the cavity, and the
resonant frequency of the membrane changes largely to the higher side. Along with this, the
position of the singular point of the impedance characteristic also largely changes toward the
higher frequency. Therefore, the position of the singular point of the impedance characteristic is
observed using an impedance analyzer or the like, and it may be determined that the pull-in has
occurred if the singular point of the impedance characteristic is largely changed to the higher
one. Also, the displacement of the membrane changes greatly from about one third of the
vacuum equivalent distance between the electrodes to the same size as the depth of the cavity at
04-05-2019
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the moment of pull-in. Therefore, the displacement of the membrane may be observed using an
optical interferometer or the like, and it may be determined that pull-in has occurred if the
displacement of the membrane changes significantly.
[0019]
In order to measure the pull-in voltage and calculate the drive bias voltage as described above,
the pull-in voltage measurement means and the drive control means may be provided. The pull-in
voltage measuring means measures the pull-in voltage of the monitor element as described
above. The drive control means determines the drive bias voltage by arithmetically processing
the pull-in voltage of the monitor element obtained by the pull-in voltage measurement means,
and drives the sensor element with the voltage in use. Further, the above-described
electromechanical transducer can be manufactured by a manufacturing method having the
following first step and second step. In the first step, a sensor element including at least one cell
having a first electrode and a second electrode opposed to the first electrode with a gap is
formed. In the second step, in addition to the sensor element, there is provided a pull-in voltage
comprising at least one cell having a first electrode and a second electrode opposed to the first
electrode with a gap therebetween. Form a monitor element to measure. Then, in the first step
and the second step, both elements are formed such that the pull-in voltage of the monitor
element and the drive bias voltage of the sensor element have a predetermined relationship.
Furthermore, a third step of measuring the pull-in voltage of the monitor element, and a fourth
step of calculating the pull-in voltage of the monitor element measured in this step to determine
a drive bias voltage for driving the sensor element You may have. When manufacturing the
device, the drive bias voltage of the drive control means may be fixedly set to a voltage value
determined by measuring the pull-in voltage of the monitor element and arithmetically
processing the measured pull-in voltage. In this case, the monitor element may be disconnected
from the device after device manufacture. Alternatively, the apparatus may be configured such
that the drive bias voltage of the drive control means can be reset to the voltage value obtained
by measuring the pull-in voltage of the monitor element and processing the pull-in voltage after
the manufacture. The monitor element can be arranged on the same substrate as the substrate on
which the sensor element is formed, and at the periphery of the sensor area in which the sensor
element is formed, as shown in FIG. Such an arrangement is excellent in terms of ease of
manufacture, ease of setting and separating the structural parameters of both elements, and ease
of measurement of the pull-in voltage of the monitor element, but the monitor element is not
necessarily on the periphery of the sensor area. It does not have to be deployed.
If the pull-in voltage of the monitor element can be measured without causing pull-in of the
sensor element, for example, an element of a part (for example, a part of an edge) of the element
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arranged in the sensor area can be configured as a monitor element.
[0020]
Second Embodiment The CMUTs 201 of the present embodiment are dispersed at a plurality of
locations on the periphery of the sensor area 202 as shown in FIG. 2, and are appropriately
arranged according to the distribution tendency of the pull-in voltage of the sensor element 203.
The monitor element 204 is provided. Here, it is assumed that it is known in advance that the
distribution tendency of the pull-in voltage of the sensor element 203 is a monotonous
distribution tendency having neither a maximum value nor a minimum value as shown in FIG. 2B.
In order to determine the drive bias voltage, the pull-in voltage of each of the monitor elements
204 may be measured simultaneously, for example, the minimum value thereof may be used as
the drive bias voltage of the sensor element 203. If the pull-in voltage of each of the monitor
elements 204 can not be measured simultaneously, the characteristic values of all the monitor
elements 204 may be measured each time the bias voltage is changed by a small amount. In the
present embodiment, the pull-in voltage of all the monitor elements 204 is configured to be
smaller than the pull-in voltage of the sensor element 203. Therefore, the minimum value of the
pull-in voltage of the monitor element 204 is always smaller than the minimum value of the pullin voltage of the sensor element 203. As described above, even when there is a deviation in the
pull-in voltage between the elements on the CMUTs, the drive bias voltage can be determined
without pulling in the sensor element 203.
[0021]
The reason why the above effects can be obtained will be described below. For example, as
shown in FIG. 3A, consider the case where the thickness of the insulating layer of CMUTs has a
distribution monotonously decreasing from point A to point B. From the above equation (1), the
pull-in voltage decreases as the insulating layer becomes thinner. Therefore, as shown in FIG. 3B,
the pull-in voltage of the sensor element 203 has a monotonically decreasing distribution along
the direction from point A to point B, and the pull-in voltage of the sensor element 203 at point C
is minimized. . Therefore, by disposing the monitor element 204 near the sensor element 203 at
the point C, it is guaranteed by design that the pull-in voltage is smaller than the minimum value
of the pull-in voltages of all the sensor elements 203.
[0022]
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Furthermore, even in the case where the pull-in voltage of the sensor element 203 has a
distribution as shown in FIGS. 4A to 4C, the monitor element 204 may be disposed in the vicinity
of the sensor element 203 at point D, point E, and point F. Similar guarantees are obtained. Now,
consider the case where the monitor element 204 is disposed in the vicinity of the sensor
element 203 at point C, point D, point E, and point F in FIG. In this case, for example, if the
minimum value of the pull-in voltages is a drive bias voltage, the drive bias voltage is smaller
than the minimum value of the pull-in voltages of the sensor elements regardless of the direction
of distribution of the thickness of the insulating layer. Is guaranteed. In the above description, the
same conclusion can be obtained by replacing the insulating layer with a membrane.
[0023]
The distribution as described above will be described as occurring even if it is not intended in
design. That is, it may happen that CMUTs having the distribution tendency of the structural
parameters as described above are actually produced. Generally, these deviations depend on the
deviation of the film thickness at the time of film formation and the etching amount at the time of
etching. The film forming apparatus and the etching apparatus often exhibit a monotonous
distribution of film thickness and etching amount from the center to the end of the chamber.
Therefore, by arranging the substrate on which the CMUTs are made at appropriate places in the
above apparatus, the CMUTs in which the structural parameters in the element show a
monotonous distribution as described above will be made. In the present embodiment, the design
of the electromechanical transducer is devised so that the characteristics of the film forming
apparatus and the etching apparatus do not become apparent as defects of the manufactured
electromechanical transducer.
[0024]
Third Embodiment The CMUTs 301 of this embodiment, as shown in FIG. 5, have a monitor
element group 304 in which a plurality of monitor elements 303 are arranged adjacent to each
other at the periphery of the sensor area 302. According to the present embodiment, for
example, even when one of the monitor elements 303 does not operate normally due to an
accidental abnormality, the pull-in voltage of the other monitor elements 303 of the monitor
element group 304 is measured to cause this situation. We can avoid trouble. As described
above, the possibility of determining the drive bias voltage of the sensor element can be
increased, even when the monitor element 303 accidentally malfunctions. The other points are
the same as in the first embodiment.
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[0025]
Fourth Embodiment The CMUTs 401 of this embodiment have monitor element groups 404 each
including a plurality of monitor elements 403 at the periphery of the sensor area 402 as shown
in FIG. 6A. Hereinafter, for convenience, each of the monitor elements 403 will be described with
names G, H, I, J. The pull-in voltage of each of the monitor elements 403 is different from each
other, and the pull-in voltage of all monitor elements 403 is equal to or higher than the drive bias
voltage and smaller than the pull-in voltage of the sensor element 405. For example, the pull-in
voltages Vpg, Vph, Vpi, Vpj of the monitor elements G to J are configured to have a relationship
as shown in Formula (3) with respect to the drive bias voltage Vdb and the pull-in voltage Vp of
the sensor element 405. Vdb = Vpg <Vph <Vp <Vpj <Vp (3) Further, the coefficients αg to αj for
determining the drive bias voltage from the pull-in voltages of the monitor elements G to J can be
expressed by the equations (4) to (7) It is designed to be determined in the same way. αg = Vpg
/ Vdb = 1 (4) αh = Vph / Vdb (5) αi = Vpi / Vdb (6) αj = Vpj / Vdb (7)
[0026]
An example of a method of measuring the time-dependent change of the pull-in voltage of the
sensor element 405 using the above-mentioned monitor element group 404 will be described
with reference to FIG. For each of the monitor elements G to J, the measurement time of the pullin voltage according to the usage time of the CMUTs 401 is determined in advance. For example,
the use times are 0, th, ti, and tj for the monitor elements G to J, respectively. ただし、
0<th<ti<tjである。 Here, the use time refers to a value obtained by accumulating the
time when the CMUTs 401 were driven, that is, the time when the drive bias voltage was applied
to the CMUTs 401. The reason for determining the order of measuring the pull-in voltages of the
monitor elements in the ascending order of the pull-in voltages is to prevent pull-in from
occurring in other monitor elements when measuring the pull-in voltages of the monitor
elements. If pull-in occurs in another monitor element before measuring the pull-in voltage, a
residual electric field is generated due to charging or the like, and it becomes difficult to measure
the correct pull-in voltage of the other monitor element.
[0027]
Before using the CMUTs 401 for the first time, the drive controller 407 sends a command signal
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to the pull-in voltage measuring device 406 to measure the pull-in voltage of the monitor
element G. The pull-in voltage measuring device 406 measures the pull-in voltage of the monitor
element G, and transmits the measured value to the drive controller 407. The drive controller
407 drives the CMUTs 401 using the measured value as a drive bias voltage. Thereafter, the
CMUTs 401 are driven while measuring the usage time using the timer 408, and when the usage
time reaches th, the drive controller 407 temporarily stops the driving of the CMUTs 401. At this
time, a transmitter 410 such as light or voice may be used to notify the user 409 to stop using
the CMUTs 401. Thereafter, the drive controller 407 obtains the measurement value of the pullin voltage of the monitor element H in the same manner as described above, and updates the
value obtained by multiplying the measurement value by the coefficient αh of equation (5) as
the drive bias voltage. , Drive the CMUTs 401 again. Also at use times ti and tj, the drive
controller 407 updates the drive bias voltage and drives the CMUTs in the same manner as
described above. As described above, it is possible to correct the change of the conversion
characteristic due to the time-dependent change of the pull-in voltage at each predetermined
time.
[0028]
As described above, in the electromechanical transducer of this embodiment, the plurality of
monitor elements belonging to the monitor element group have different pull-in voltages, and are
provided with the following clock means, pull-in voltage measuring means, and drive control
means. The clock means measures the time to measure the pull-in voltage of each of the plurality
of monitor elements. The pull-in voltages of the plurality of monitor elements are measured at
respective predetermined times measured by the pull-in voltage measurement means and the
clock means. The drive control means determines a drive bias voltage by processing each pull-in
voltage obtained by the pull-in voltage measurement means, and drives the sensor elements with
the drive bias voltage.
[0029]
Fifth Embodiment The electromechanical transducer described in the above embodiments can be
applied to an object information acquiring apparatus using an acoustic wave. An acoustic signal
from an object is received by an electro-mechanical transducer, and an object obtained by
reflecting an optical characteristic value of the object such as a light absorption coefficient or the
like or an object reflecting an acoustic impedance difference using an output electric signal
Information can be obtained. FIG. 9A shows the object information acquiring apparatus of the
present embodiment using the photoacoustic effect. The pulsed light generated from the light
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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. A probe
(probe) provided with an electromechanical transducer 2020 and a housing 2022 for housing
the same receives the photoacoustic wave 2018, converts it into an electric 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 (object information reflecting the optical characteristic value of the object
such as a light 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.
[0030]
FIG. 9B shows a subject information acquiring apparatus such as an ultrasonic echo diagnostic
apparatus using reflection of acoustic waves. An acoustic wave transmitted from the probe
having the electromechanical transducer 2120 and a housing 2122 accommodating the same to
the subject 2114 is reflected by the reflector 2116. The probe receives the reflected acoustic
wave 2118 (reflected wave), converts it into an electrical signal, and outputs the 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
(object information reflecting the 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. 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). Further, in the case of an apparatus using a reflected wave as shown in FIG. 9B, the probe
for transmitting the acoustic wave may be provided separately from the probe for receiving.
[0031]
101 ... CMUTs (electro-mechanical transducer), 102 ... sensor area, 103 ... sensor element, 104,
111 ... cell, 105, 112 ... second electrode 106, 113 ... · Membrane, 107, 114 · · · Cavity (gap), 109,
116 · · · First electrode, 110 · · · Monitor element
04-05-2019
14
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