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DESCRIPTION JP2015173682

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DESCRIPTION JP2015173682
Abstract: An acoustic sensor, an ultrasonic probe and an ultrasonic diagnostic apparatus capable
of easily forming a piezoelectric member with high accuracy. Kind Code: A1 A piezoelectric thin
film is stacked on a semiconductor substrate directly or indirectly, and the semiconductor
substrate is based on the amount of charge induced in the piezoelectric thin film according to the
sound pressure incident on the piezoelectric thin film. The semiconductor device is provided with
a semiconductor chip that changes a current flow in a predetermined area and outputs a signal
according to the current flow. [Selected figure] Figure 4
Acoustic sensor, ultrasonic probe and ultrasonic diagnostic apparatus
[0001]
The present invention relates to an acoustic sensor, an ultrasonic probe, and an ultrasonic
diagnostic apparatus.
[0002]
2. Description of the Related Art Conventionally, there is an ultrasonic diagnostic apparatus that
inspects an internal structure by irradiating ultrasonic waves into the inside of a subject and
receiving and analyzing the reflected waves.
In ultrasonic diagnosis, since a subject can be nondestructively and noninvasively examined, it is
widely used in various applications such as examination for medical purposes and examination of
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1
the inside of a building.
[0003]
In the ultrasound diagnostic apparatus, the received ultrasound is converted into an electrical
signal according to the intensity and acquired. A transducer (transducer) using a piezoelectric
body is used as an acoustic sensor for receiving the ultrasonic wave, and an electrical signal
corresponding to the amount of mechanical deformation (stretching) of the piezoelectric body
due to the sound pressure of the ultrasonic wave It is converted to (charge amount) and detected.
In this acoustic sensor, conventionally, a vibrator including a piezoelectric body is formed, for
example, in a plate shape or thick film shape (usually 10 μm or more, generally 100 μm or
more) such as a laminated substrate using a thick film coating technique. The ultrasonic intensity
is measured by detecting the deformation in the thickness direction due to the ultrasonic wave
incident on the plate surface.
[0004]
The piezoelectric body includes a ferroelectric such as PZT (lead zirconate titanate).
Conventionally, ferroelectrics are used in non-volatile memory (ferroelectric memory, FeRAM)
using their polarization characteristics with hysteresis. In a ferroelectric memory, a ferroelectric
thin film is provided between a gate electrode and a channel region between the drain and the
source, and a voltage is applied to the ferroelectric thin film to maintain a polarization state
corresponding to one of binary values. The electric conductivity of the channel region is changed
by causing the electric field to flow, and binary data is read by measuring the conduction state
between the drain and the source (for example, Patent Document 1).
[0005]
U.S. Pat. No. 3,832,700
[0006]
However, with the increase in resolution and sensitivity of ultrasonic diagnostic apparatuses,
ultrasonic probes with higher accuracy are required.
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At this time, in order to form the piezoelectric member of the acoustic sensor used for ultrasonic
wave reception with high accuracy in the present mode in the conventional ultrasonic probe,
there is a problem that complicated and large-sized manufacturing process is required. There is.
[0007]
An object of the present invention is to provide an acoustic sensor, an ultrasonic probe and an
ultrasonic diagnostic apparatus capable of easily forming a piezoelectric member with high
accuracy.
[0008]
In order to achieve the above object, according to the first aspect of the present invention, the
piezoelectric thin film is directly or indirectly stacked on the semiconductor substrate, and the
piezoelectric thin film is formed according to the sound pressure incident on the piezoelectric
thin film. An acoustic sensor comprising: a semiconductor chip that changes a conduction state of
a predetermined region of the semiconductor substrate based on an amount of induced charge,
and outputs a signal according to the conduction state.
Here, the thin film refers to those formed by various thin film manufacturing processes such as a
sputtering method, a CVD method, and a sol-gel method.
[0009]
The invention according to claim 2 relates to the acoustic sensor according to claim 1, wherein
the electric conductivity of the channel region provided in the semiconductor substrate is
changed by an electric field generated by the induced charge, so that the electric field of the
channel region is changed. It is characterized in that the current-carrying state is changed.
[0010]
The invention according to claim 3 is the acoustic sensor according to claim 1, wherein the
semiconductor chip is provided with an electrode for switching whether or not the channel
region provided in the semiconductor substrate is conductive, and the channel region is in a
conductive state. In this case, the piezoelectric thin film may be connected to one end of the
channel region such that the conduction state is changed by the charge corresponding to the
amount of the induced charge flowing in the channel region. It is characterized.
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[0011]
The invention according to claim 4 is the acoustic sensor according to any one of claims 1 to 3,
wherein the piezoelectric thin film is divided into a plurality of blocks and arranged in at least
one direction, and the semiconductor chip is The signal is output for each of one or more of the
blocks.
[0012]
The invention according to claim 5 is the acoustic sensor according to any one of claims 1 to 4,
wherein the piezoelectric thin film is a semiconductor chip in which a coercive electric field
voltage reverses its polarization state by a ferroelectric member. It is characterized in that it is
formed to be less than the withstand voltage of
[0013]
The invention according to claim 6 is the acoustic sensor according to claim 5, wherein the
semiconductor chip is provided with a voltage application circuit for setting the polarization state
of the piezoelectric thin film.
[0014]
The invention according to claim 7 relates to the acoustic sensor according to claim 6, wherein
the piezoelectric thin film is divided into a plurality of blocks and arranged in at least one
direction, and the semiconductor chip is provided for each of one or more of the blocks. The
signal output circuit is characterized in that the voltage application circuit is capable of setting
the polarization state for each of the blocks.
[0015]
The invention according to claim 8 is the acoustic sensor according to claim 6 or 7, wherein a
control unit for determining the polarization state of the piezoelectric thin film and controlling
the operation of the voltage application circuit according to the determined polarization state is
provided. It is characterized by having.
[0016]
The invention according to claim 9 is the acoustic sensor according to claim 8, characterized in
that the control unit determines a polarization state according to processing relating to a
predetermined spatial correlation performed on a received sound wave. There is.
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[0017]
The invention according to claim 10 is an ultrasonic probe using the acoustic sensor according to
any one of claims 1 to 9.
[0018]
The invention according to claim 11 includes: the ultrasonic probe according to claim 10; a
signal processing unit that analyzes a signal related to the ultrasonic wave received by the
ultrasonic probe; and an analysis of the signal processing unit An output unit configured to
output a result in a predetermined manner, and an ultrasonic diagnostic apparatus characterized
by comprising:
[0019]
The invention according to claim 12 is an ultrasonic probe using the acoustic sensor according to
claim 6 or 7, a signal processing unit for analyzing a signal related to an ultrasonic wave received
by the ultrasonic probe. An output unit that outputs the analysis result of the signal processing
unit in a predetermined format; a control unit that determines the polarization state of the
piezoelectric thin film and controls the operation of the voltage application circuit according to
the determined polarization state; An ultrasonic diagnostic apparatus comprising:
[0020]
According to the present invention, it is possible to easily form a piezoelectric member for
receiving an ultrasonic wave with high accuracy.
[0021]
FIG. 1 is an overall view showing an ultrasonic diagnostic apparatus according to an embodiment
of the present invention.
It is a block diagram which shows the internal structure of an ultrasound diagnosing device.
It is a figure explaining the example of transducer arrangement.
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It is a schematic diagram which shows the cross-section of a vibrator | oscillator.
It is a schematic diagram which shows the setting of the polarization state in vibrator | oscillator
arrangement | sequence.
It is a schematic diagram which shows the cross-section of the vibrator | oscillator of 2nd
Embodiment.
[0022]
Hereinafter, embodiments of the present invention will be described based on the drawings.
First Embodiment FIG. 1 is an overall view of an ultrasonic diagnostic apparatus S provided with
an ultrasonic probe using the acoustic sensor of the present embodiment.
FIG. 2 is a block diagram showing an internal configuration of the ultrasonic diagnostic
apparatus S.
[0023]
As shown in FIG. 1, the ultrasonic diagnostic apparatus S includes an ultrasonic diagnostic
apparatus main body 1 and an ultrasonic probe 2 (ultrasound probe) connected to the ultrasonic
diagnostic apparatus main body 1 via a cable 22. Equipped with
The ultrasonic diagnostic apparatus main body 1 is provided with an operation input unit 18 and
an output display unit 19.
The control unit 15 of the ultrasonic diagnostic apparatus main body 1 outputs a drive signal to
the ultrasonic probe 2 to output an ultrasonic wave based on an input operation from the outside
to an input device such as a keyboard or a mouse of the operation input unit 18 Also, a reception
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signal related to ultrasonic wave reception is acquired from the ultrasonic probe 2 and various
processing is performed, and the result etc. are displayed on the liquid crystal screen of the
output display unit 19 as necessary.
[0024]
As shown in FIG. 2, the ultrasonic diagnostic apparatus main body 1 includes a transmitting unit
12, a receiving unit 13, a transmission / reception switching unit 14, a control unit 15, an image
processing unit 16 (signal processing unit), and a storage unit 17. , An operation input unit 18,
an output display unit 19 (output unit), and the like.
[0025]
The transmission unit 12 outputs a pulse signal supplied to the ultrasound probe 2 in accordance
with a control signal input from the control unit 15, and causes the ultrasound probe 2 to
generate an ultrasound wave.
The transmission unit 12 includes, for example, a clock generation circuit, a pulse generation
circuit, a pulse width setting unit, and a delay circuit.
The clock generation circuit is a circuit that generates a clock signal that determines the
transmission timing and transmission frequency of the pulse signal.
The pulse generation circuit is a circuit that generates a bipolar rectangular wave pulse of a
preset voltage amplitude at a predetermined cycle.
The pulse width setting unit sets the pulse width of the rectangular wave pulse output from the
pulse generation circuit. Before or after the input to the pulse width setting unit, the rectangular
wave pulse generated by the pulse generation circuit is separated into different wiring paths for
each transducer 21 of the ultrasonic probe 2. The delay circuit is a circuit that delays and
outputs the delay time set for each of these wiring paths in accordance with the timing of
transmitting the generated rectangular wave pulse to each of the transducers 21.
[0026]
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The receiving unit 13 is a circuit that acquires the reception signal input from the ultrasound
probe 2 according to the control of the control unit 15. The receiving unit 13 includes, for
example, an amplifier, an A / D conversion circuit, and a phasing addition circuit. The amplifier is
a circuit that amplifies the received signal corresponding to the ultrasonic wave received by each
transducer 21 of the ultrasonic probe 2 at a predetermined amplification factor set in advance.
The A / D conversion circuit is a circuit that converts the amplified reception signal into digital
data at a predetermined sampling frequency. The phasing addition circuit gives a delay time to
the A / D converted received signal for each wiring path corresponding to each vibrator 21 to
adjust the time phase, and adds them (phasing addition) to obtain a sound. It is a circuit that
generates line data.
[0027]
The transmission / reception switching unit 14 transmits a drive signal from the transmission
unit 12 to the vibrator 21 when oscillating the ultrasonic wave from the vibrator 21 based on the
control of the control unit 15, while the ultrasonic wave emitted by the vibrator 21. When
acquiring such a signal, a switching operation is performed to cause the reception unit 13 to
output the reception signal.
[0028]
The control unit 15 includes a central processing unit (CPU), a hard disk drive (HDD), a random
access memory (RAM), and the like.
The CPU reads out various programs stored in the HDD, expands them in the RAM, and generally
controls the operation of each part of the ultrasonic diagnostic apparatus S according to the
expanded programs. The HDD stores a control program and various processing programs for
operating the ultrasound diagnostic apparatus S, various setting data, and the like. These
programs and setting data may be stored in an auxiliary storage device using a non-volatile
memory such as a flash memory other than the HDD, for example, so as to be readable and
writable. The RAM is volatile memory such as SRAM or DRAM, provides a working memory space
to the CPU, and stores temporary data.
[0029]
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The image processing unit 16 performs arithmetic processing for creating a diagnostic image
based on the received data of ultrasonic waves separately from the CPU of the control unit 15.
The diagnostic image may include image data to be displayed on the output display unit 19 in
substantially real time, a series of moving image data, still image data of a snapshot, and the like.
Note that this arithmetic processing may be performed by the CPU 15.
[0030]
The storage unit 17 is, for example, a volatile memory such as a dynamic random access memory
(DRAM). Alternatively, various nonvolatile memories that can be rewritten at high speed may be
used. The storage unit 17 stores diagnostic image data for real-time display processed by the
image processing unit 16 in frame units. The ultrasonic diagnostic image data stored in the
storage unit 17 is read according to the control of the control unit 15 and transmitted to the
output display unit 19 or to the outside of the ultrasonic diagnostic apparatus S via a
communication unit (not shown). It is output. At this time, if the display mode of the output
display unit 19 is a television system, a DSC (Digital Signal Converter) is provided between the
storage unit 17 and the output display unit 19 and the scan format is converted and then output.
It should be done.
[0031]
The operation input unit 18 includes a push button switch, a keyboard, a mouse, or a trackball,
or a combination of these, converts the user's input operation into an operation signal, and inputs
the operation signal to the ultrasonic diagnostic apparatus main body 1.
[0032]
The output display unit 19 is a display using any of various display methods such as a liquid
crystal display (LCD), an organic electro-luminescent (EL) display, an inorganic EL display, a
plasma display, and a cathode ray tube (CRT) display. It has a screen and its drive unit.
The output display unit 19 generates a drive signal of the display screen (each display pixel)
according to the control signal output from the CPU 15 or the image data generated by the
image processing unit 16, and a menu related to ultrasonic diagnosis on the display screen. ,
Status, and display of measurement data based on the received ultrasound.
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[0033]
The operation input unit 18 and the output display unit 19 may be integrally provided in the
casing of the ultrasonic diagnostic apparatus main body 1, or may be externally attached via a
USB cable or the like. It may be. Further, as long as the ultrasonic diagnostic apparatus main
body 1 is provided with an operation input terminal and a display output terminal, peripheral
devices for conventional operation and display may be connected to these terminals for use.
[0034]
The ultrasound probe 2 oscillates an ultrasonic wave (here, about 1 to 30 MHz) and emits it to a
subject such as a living body, and a reflected wave (a reflected wave reflected by the subject
among the emitted ultrasonic waves) Functions as an acoustic sensor that receives echoes and
converts them into electrical signals. The ultrasonic probe 2 includes a transducer array 210
which is an array of a plurality of transducers 21 for transmitting and receiving ultrasonic waves,
and a cable 22. The cable 22 has a connector (not shown) with the ultrasonic diagnostic
apparatus main body 1 at one end thereof, and the ultrasonic probe 2 is configured to be
detachable from the ultrasonic diagnostic apparatus main body 1 by the cable 22. ing.
[0035]
The vibrator array 210 is an array of a plurality of vibrators 21 including a piezoelectric element
having a piezoelectric body and electrodes provided at both ends at which charges appear due to
deformation (expansion and contraction). , Are arranged two-dimensionally in one plane. By
supplying a voltage pulse (pulse signal) to the vibrator 21, the piezoelectric body is deformed
according to the electric field generated in each piezoelectric body, and an ultrasonic wave is
transmitted. Further, when an ultrasonic wave of a predetermined frequency band is incident on
the vibrator 21, the thickness of the piezoelectric body fluctuates (oscillates) due to the sound
pressure, so that the electric charge corresponding to the fluctuation amount is in the thickness
fluctuation direction both ends In the electrodes at both ends of the piezoelectric element, a
charge corresponding to the charge is induced. Here, a ferroelectric is used as the piezoelectric
body. The electric field generated in the ferroelectric during transmission and reception of
ultrasonic waves is smaller than the coercive electric field strength of the ferroelectric.
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[0036]
FIG. 3 is a view for explaining an example of the transducer array 210 in the ultrasound probe 2.
In the ultrasound probe 2 according to the present embodiment, for example, the transducer
array 210 includes 3 (width direction) × 192 (scanning direction) = 576 transducers 21
arranged in a two-dimensional array. Be Alternatively, the transducers 21 may be onedimensionally arranged in the scanning direction. In addition, the number of transducers 21 can
be set arbitrarily. The ultrasound probe 2 may employ either an electronic scanning method or a
mechanical scanning method, and may adopt any of a linear scanning method, a sector scanning
method or a convex scanning method as a scanning method. It may be Moreover, the bandwidth
of the reception frequency of the ultrasonic wave in the ultrasonic probe 2 can be set arbitrarily.
Further, the ultrasonic diagnostic apparatus S can be configured to be able to connect and use
any one of a plurality of different ultrasonic probes 2 according to the diagnosis object to the
ultrasonic diagnostic apparatus main body 1.
[0037]
FIG. 4 shows the cross-sectional structure of one transducer 21 involved in transmission and
reception of ultrasonic waves. The vibrator 21 of the present embodiment is formed as a
semiconductor chip in which the ferroelectric thin film layer 112 (piezoelectric thin film) and the
gate electrode 113 are stacked and arranged on the semiconductor substrate 100 with the gate
insulating film 111 interposed therebetween. . Side walls 114 and 115 are provided on both
sides of the ferroelectric thin film layer 112. On the upper surface of the semiconductor
substrate 100, extension regions 116 and 117 (conductive regions), a source region 101 and a
drain region 102 are formed with a region under the gate electrode 113 (a predetermined region
and a portion to be a channel region) interposed therebetween. Ru. Source region 101 and drain
region 102 are connected to metal interconnections 103 and 104, respectively.
[0038]
The semiconductor substrate 100 is, for example, a p-type silicon substrate. By implanting n-type
ions such as phosphorus or arsenic into the semiconductor substrate 100, the extension regions
116 and 117 are formed, and further, the source region 101 and the drain region 102 are
formed.
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[0039]
Source region 101 is grounded via metal wire 103. The drain region 102 is connected to the
signal output via the metal wire 104. The voltage supply unit can be connected to the gate
electrode 113 through a voltage application circuit (not shown) provided on the semiconductor
substrate 100, and a bias voltage between the gate and the source is supplied to the gate
electrode 113. By applying this bias voltage to the ferroelectric thin film layer 112, the
polarization state is changed according to the bias voltage. On the other hand, normally, the gate
electrode 113 is kept in the floating state or in the ground state, and when the ultrasonic wave is
incident on the ferroelectric thin film layer 112, the ultrasonic wave intensity (sound pressure)
and the polarization state are Charges are generated at both ends (both sides) of the ferroelectric
thin film layer 112 according to the above. In the semiconductor substrate 100, the conduction
state in the channel region between the source region 101 and the drain region 102 changes
according to the charge generated on the side of the gate insulating film 111 of the ferroelectric
thin film layer 112, and between the source and drain The charge that has flowed is output as a
signal from the drain region 102.
[0040]
The ferroelectric thin film layer 112 is, for example, a thin film (usually less than 10 μm, more
preferably less than 1 μm) using a ferroelectric member such as PZT (lead zirconate titanate),
and the source region 101 and the drain region 102 The surface area and the thickness are set
to values corresponding to the reception frequency of the ultrasonic waves while keeping the
channel length between them appropriately. As the ferroelectric member, in addition to PZT,
ferroelectrics having various perovskite structures, ferroelectrics having a tungsten-bronze
structure, ferroelectrics having a bismuth layer structure, PVDF (polyvinylidene fluoride), or
PVDF-based copolymer Organic ferroelectrics as described above, or composite materials using
these in combination may be used. These ferroelectrics usually have a multi-domain and / or
polycrystalline structure.
[0041]
The ferroelectric thin film layer 112 and the gate electrode 113 are formed on the
semiconductor substrate 100 by sputtering (PVD (physical vapor deposition)), sol-gel method,
CVD (chemical vapor deposition), etc. Then, it is formed by etching back using a mask (such as a
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photoresist pattern) in accordance with the structure of the structure. Next, sidewalls 114 and
115 are also formed by etching after forming an insulating film (for example, silicon dioxide
SiO2) on semiconductor substrate 100, ferroelectric thin film layer 112, and gate electrode 113
using a CVD method or the like. . The source region 101 and the drain region 102 are formed by
performing ion implantation by self alignment using the gate electrode 113 and the sidewalls
114 and 115 as a mask. Then, metal wires 103 and 104 connected to the gate electrode 113, the
source region 101 and the drain region 102 are provided. The plurality of transducers 21 and
the ferroelectric thin film layer 112 (block) corresponding to each may be separately formed, but
a plurality thereof may be collectively formed on one or a small number of wafers. Thus, the
transducer array 210 can be formed easily and at low cost while arranging the plurality of
transducers 21 with high accuracy.
[0042]
As described above, by using the ferroelectric thin film layer 112 for the transducer 21 of the
ultrasonic probe 2, the ferroelectric layer is uniformly formed, and the polarization with high
accuracy corresponding to the incident ultrasonic intensity occurs. . Further, by using such a thin
film, the voltage (coercive field voltage) for generating a coercive electric field necessary for
polarization inversion is sufficiently reduced, so that it is easy even after the circuit formation of
the vibrator 21. A voltage can be applied to the ferroelectric thin film layer 112 to change the
polarization state. At this time, in the vibrator 21, the withstand voltage of each part, for example,
the dielectric breakdown voltage of the gate insulating film, the withstand voltage between the
drain and the source, the withstand voltage between the P and N wells, the withstand voltage
between the well and the semiconductor substrate, etc. The film thickness of the ferroelectric
thin film layer 112 needs to be determined so as to be equal to or higher than the maximum
applied voltage for causing the ferroelectric thin film layer 112 to generate a coercive electric
field. In general, the withstand voltage is 10 to several tens of volts or less, and the coercive field
voltage may be smaller than this. The coercive electric field is about MV / m depending on the
ferroelectric material, composition ratio, crystal system, etc., and in order to make the coercive
electric field voltage less than the withstand voltage, including the influence of the thickness of
the gate insulating film The thickness of the ferroelectric thin film layer 112 is on the order of
μm or less. In addition, here, when ultrasonic wave transmission is performed using the
ferroelectric thin film layer 112, the voltage applied at the time of transmission can be reduced
according to the film thickness, but polarization is performed in a range smaller than the coercive
electric field voltage. The value can be set to an appropriate value as long as the heat generation
amount is not a problem without changing the state.
[0043]
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The vibrator 21 according to the present embodiment is not limited to the state in which the
polarization directions of the respective regions are aligned, and ultrasonic waves can be
received by setting various polarization states. When an ultrasonic wave is incident on the
ferroelectric thin film layer 112 in a state in which the polarization direction is completely
aligned, a deformation according to the sound pressure of the ultrasonic wave occurs in the
entire ferroelectric thin film layer 112 as in a normal piezoelectric material. Therefore, charges
corresponding to the deformation are generated at both ends. On the other hand, when
ultrasonic waves are incident on the ferroelectric thin film layer 112 in a state in which the
polarization directions of the multi-area and poly-crystalline areas are not aligned, no stretch
deformation occurs in the ferroelectric thin film layer 112 as a whole. That is, no charge
corresponding to the deformation is generated at both ends. In the polarization state between
these, the amount of charge generated also becomes an intermediate value.
[0044]
However, when the polarization state of the ferroelectric thin film layer 112 is changed, the
magnitude of the electric field generated in the ferroelectric thin film layer 112 is not
proportional to the polarization state. Therefore, the correspondence relationship between the
polarization state to be set and the electric field (applied voltage) for changing to the polarization
state can be stored in a table in advance in the HDD of the control unit 15 or the like. When
changing the polarization state of the ferroelectric thin film layer 112, referring to this table, the
applied voltage corresponding to the change from the current polarization state to the desired
polarization state is acquired, and the source region 101 and the drain region are obtained. This
applied voltage may be supplied from the voltage supply unit to the gate electrode 113, with 102
in a grounded state. Alternatively, once the current polarization state is changed to a
predetermined polarization state, only the table corresponding to the change from the
predetermined polarization state is stored by changing the predetermined polarization state to a
desired polarization state. It can be done.
[0045]
In the ultrasound probe 2 of the present embodiment, the polarization state can be set
independently for each transducer 21 of the transducer array 210. That is, at least a part of the
gate electrode 113 side is separately provided for the wiring between the voltage supply unit and
the gate electrode 113, and switching signals can be switched on / off by the control signal from
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the control unit 15 or the like. The voltage can be supplied only to the desired vibrator 21.
Alternatively, a voltage dividing circuit or the like may be provided in the middle of the individual
wiring, and a desired voltage division may be applied to the ferroelectric thin film layer 112 of
each vibrator 21 with respect to the predetermined voltage output from the voltage supply unit.
It may be In this case, if a resistive element is provided in the ultrasonic probe 2 as a load for
voltage division, the size tends to be large compared to the semiconductor chip, so a plurality of
small capacity capacitors are combined to generate an appropriate voltage Also good.
Alternatively, partial pressures may be generated by the ultrasonic diagnostic apparatus main
body 1 and supplied to the respective ferroelectric thin film layers 112 of the ultrasonic probe 2.
[0046]
Various patterns can be used as the setting pattern of the polarization state for each vibrator 21.
For example, by changing the polarization state of each transducer 21 for each position, the
reception sensitivity of each transducer 21 can be weighted. That is, in the prior art, the process
(especially apodization) relating to spatial correlation such as weighting for each transducer 21
and formation of a reception window, which were performed by individually changing the
amplification factor of the amplifier, is not affected by adjustment of the amplification factor. You
can do it. Also, in particular, to reduce the reception sensitivity of the transducer 21 at a position
that you do not want to receive to reduce the influence of artifacts etc. to zero level, change the
polarization state to form a reception window (for example, a Hanning window) Can do.
[0047]
FIG. 5 is a view schematically showing setting of polarization states of the respective transducers
21 of the two-dimensionally arranged transducer array 210. As shown in FIG. Here, the tendency
of the magnitude of the polarization amount is shown by the length of both arrows. In this
transducer array 210, the polarization amount of the ferroelectric thin film layer 112 related to
the transducer 21 in the vicinity of the center is set to be large, that is, the polarization directions
of the multiregions and poly regions (grains) are aligned. It is set such that the polarization
amount gradually decreases toward the ferroelectric thin film layer 112 related to the vibrators
21 at four corners, that is, the polarization directions of the respective domains and the crystal
regions are not aligned. As a result, the reception sensitivity by the transducers 21 near the
center is high, and the apodization setting is performed so as to reduce the reception sensitivity
by the transducers 21 at the four corners. Here, although the polarization amount (reception
sensitivity) is set to be smaller from the center toward the end in any two-dimensional direction,
the polarization amount may be changed only in the scanning direction.
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[0048]
As described above, in the acoustic sensor used in the ultrasonic probe 2 of the present
embodiment, the ferroelectric thin film layer 112 (piezoelectric thin film) is directly or indirectly
stacked on the semiconductor substrate 100, and The conduction state of the channel region in
the semiconductor substrate 100, that is, the amount of flowing charge changes based on the
amount of charge induced in the ferroelectric thin film layer 112 according to the sound
pressure incident on the ferroelectric thin film layer 112. And a vibrator 21 for outputting a
signal according to the current-carrying state. As described above, by receiving an ultrasonic
wave using a thin film formed using a sputtering method or the like, a piezoelectric layer with
higher accuracy can be formed, so data of high resolution and high resolution can be easily
obtained. It can be acquired.
[0049]
Further, the electric conductivity of the channel region provided in the semiconductor substrate
100 is changed by the electric field generated by the charge induced in the ferroelectric thin film
layer 112 in response to the incidence of the ultrasonic wave, whereby the conduction state of
this channel region is obtained. Because of the varying structure, such acoustic sensors can be
easily and inexpensively manufactured using conventional FeRAM manufacturing processes.
[0050]
Further, the transducers 21 each having the ferroelectric thin film layer 112 are arranged in a
plurality of two-dimensional arrays or one-dimensionally, and each transducer 21 is configured
to output a signal related to the reception intensity of ultrasonic waves. The transducer array
210 can be formed compactly.
In addition, since such vibrators 210 can be formed on one or a small number of wafers, the
vibrator array 210 can be formed easily and at low cost while arranging the plurality of vibrators
21 with high accuracy. I can do it.
[0051]
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Further, the ferroelectric thin film layer 112 is formed by a ferroelectric member such as PZT so
as to have a coercive electric field voltage for reversing its polarization state lower than the
withstand voltage of the vibrator 21 formed. By adjusting the ferroelectric thin film layer 112 to
an appropriate polarization state, ultrasonic waves can be received by the vibrator 21 with an
appropriate sensitivity. Further, since such setting of the polarization state can be performed
after the formation of the transducers 21 and the transducer array 210, it is possible to easily
cope with the secular change of the reception sensitivity.
[0052]
Further, the vibrator 21 is provided with a voltage application circuit for setting the polarization
state of the ferroelectric thin film layer 112, and each of the elements can be easily controlled by
internal control of the ultrasonic probe 2 and the ultrasonic diagnostic apparatus 1. The
polarization state of the ferroelectric thin film layer 112 can be adjusted.
[0053]
Further, since the voltage application circuit is provided to be able to set the polarization state
individually for each of the vibrators 21, it is possible to easily adjust the sensitivity between the
respective vibrators 21.
Moreover, since weighting of spatial sensitivity, formation of a receiving window, etc. can be
performed according to the reception situation, it is possible to reduce artifacts, and to perform
processing that has conventionally been performed by adjusting the amplification factor of the
conventional amplifier. It will be possible to do it on the 21 side.
[0054]
Further, the control unit 15 determines the polarization state of the ferroelectric thin film layer
112, and controls the operation of the voltage application circuit according to the determined
polarization state. Therefore, fine setting such as weighting of the sensitivity of each vibrator 15
can be performed easily, frequently, and at high speed.
[0055]
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In addition, since the control unit 15 can determine the polarization state according to the
processing relating to spatial correlation such as apodization to be performed on the received
sound wave, switching of the output availability of the received signal by the switching element
or the amplifier It is possible to simplify or omit the process of adjusting the amplification factor.
[0056]
In addition, by using the acoustic sensor as described above for the ultrasonic probe 2, the
ultrasonic probe 2 can be formed with a lightweight, compact, high sensitivity, and high
resolution.
[0057]
The image processing unit 16 analyzes the signal related to the ultrasonic wave received by the
above-mentioned ultrasound probe 2, and the output display unit 19 outputs the analysis result
of the image processing unit 16 in a predetermined format. The ultrasonic diagnostic apparatus S
enables the user to perform ultrasonic diagnosis based on an ultrasonic diagnostic image with
high accuracy and high sensitivity easily and at low cost.
[0058]
Second Embodiment Next, an ultrasound probe 2 according to a second embodiment will be
described.
The ultrasonic probe 2 is the same as the ultrasonic probe 2 of the first embodiment except that
the structure of the transducer 21 b is different from that of the transducer 21, and the same
components are denoted by the same reference numerals. And the explanation is omitted.
[0059]
FIG. 6 is a view for explaining the cross-sectional structure of one transducer 21b related to
transmission and reception of ultrasonic waves in the ultrasonic probe 2 of the second
embodiment.
[0060]
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In the ultrasonic probe 2 of the present embodiment, the gate electrode 112 b (electrode) and
the metal wiring 113 b are provided on the p-type semiconductor substrate 100 via the gate
insulating film 111.
Further, the structure relating to the gate electrode is embedded by the insulating films 121 and
131.
In the source region 101, a contact plug 103b provided through the insulating films 121 and
131 is connected.
Further, here, the drain region 102 is adjacent to the arranged transfer electrode 118.
[0061]
A ferroelectric thin film layer 132 is sandwiched between the electrodes 133 and 134 and
stacked on the insulating film 121 to form a ferroelectric capacitor as a piezoelectric element.
One of the electrodes 133 and 134 is used. Here, the electrode 134 is connected to the contact
plug 103 b via the metal wire 135.
[0062]
The transfer electrode 118 is formed of a metal member or the like, and an on voltage is
sequentially applied to form a potential well in the semiconductor substrate 100 below the
transfer electrode 118.
The charge flowed into the drain region 102 is transferred along the well of the formed potential
by transferring the semiconductor substrate 100 according to the principle of charge coupled
device (CCD). To go.
[0063]
The gate electrode 112b is formed of, for example, polysilicon, and a desired voltage is supplied
from a voltage supply unit connected via the metal wiring 113b, whereby the voltage is applied
between the gate and the source, and the semiconductor substrate 100 is formed. The
conduction state of the channel region between the source region 101 and the drain region 102
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19
is changed under the gate electrode 112b.
[0064]
As the insulating films 121 and 131, silicon insulating films using silicon dioxide are used.
After the formation of the insulating films 121 and 131, a mask is formed using a photoresist or
the like, a contact hole is provided by etching, tungsten or the like is implanted into the contact
hole, and then polishing by etch back or CMP (chemical mechanical polishing) Form the contact
plug 103b.
[0065]
The electrode 134 provided on the ferroelectric capacitor is kept at the ground state. On the
other hand, the electrode 133 is connected to the source region 101 and charges are generated
at both ends of the ferroelectric thin film layer 132 when an ultrasonic wave is incident on the
ferroelectric thin film layer 132. Current flows between the By applying a predetermined voltage
to metal interconnection 113b and gate electrode 112b at the time of ultrasonic wave reception
to make the channel region conductive, this current is further transmitted from drain region 102
to the signal output through the channel region. .
[0066]
The electrode 133 is further connectable to a voltage supply unit, and an electric field is
generated between the electrodes 133 and 134 by supplying a desired voltage from the voltage
supply unit, and the polarization state of the ferroelectric thin film layer 132 is generated. Can be
changed.
[0067]
For the ferroelectric thin film layer 132, the same ferroelectric as the ferroelectric thin film layer
112 in the vibrator 21 of the ultrasonic probe 2 of the first embodiment can be used.
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The ferroelectric thin film layer 132 relating to this ferroelectric capacitor is formed with an area
corresponding to the reception frequency of the ultrasonic wave. At this time, the ferroelectric
thin film layer 132 has no limitation on the channel length, but has an appropriate shape and
arrangement according to the spatial resolution of the ultrasound probe 2 related to the plurality
of transducers 21 b. In FIG. 6, the ferroelectric capacitor and the FET are drawn in the same size,
but this is schematic. In fact, while it is possible to miniaturize the FET, it is not possible to
miniaturize the size of the ferroelectric capacitor relative to the reception frequency of the
ultrasonic wave, so the ferroelectric capacitor is larger. Become.
[0068]
As described above, the ultrasonic probe 2 of the second embodiment is provided with the gate
electrode 112b for switching the conduction of the channel region provided in the
semiconductor substrate 100, and a predetermined voltage is applied to the gate electrode 112b.
When the channel region is in the conductive state, charges corresponding to the amount of
charges induced in the ferroelectric thin film layer 132 by the incidence of the ultrasonic waves
flow in the channel region, whereby the amount of charges flowing in the channel region The
ferroelectric thin film layer 132 is connected to one end of the channel region via the electrode
134, the metal wiring 135, and the contact plug 103b so as to change. Thus, by providing the
ferroelectric capacitor and guiding it to the channel region, the FET related to the signal output
while the size of the ferroelectric capacitor (ferroelectric thin film layer 132) related to the
ultrasonic wave reception is matched to the size of the reception frequency. The structure can be
easily miniaturized. Further, since the ferroelectric is formed of a thin film at this time, a highly
accurate acoustic sensor can be provided while being stacked on the FET structure without
taking up a place.
[0069]
The present invention is not limited to the above embodiment, and various modifications are
possible. For example, although the ferroelectric thin film layer is used in the above embodiment,
the present invention is similarly applied to the case of forming an acoustic sensor using a thin
film of a normal piezoelectric material having no or weak ferroelectricity. I can do it. In this case,
since the desired polarization state can not be maintained, there is no need to provide a
configuration for setting the polarization state by applying a voltage between the voltage supply
unit and the gate-source. On the other hand, when performing apodization etc., it is necessary to
cope with it by changing the amplification level of an amplifier etc. as usual.
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[0070]
In addition, even in the case of using a ferroelectric thin film, adjustment of the polarization state
is performed only in response to long-term changes due to aging or the like, and usually, the
change in amplification level of the amplifier or the switching element Apodization or window
setting may be performed by switching or the like.
[0071]
In the first embodiment, although the gate oxide film is sandwiched between the ferroelectric
thin film layer and the silicon substrate, the ferroelectric thin film layer is directly formed
without sandwiching the gate oxide film as in the MFSFET structure. It may be laminated on a
silicon substrate.
[0072]
In the second embodiment, the conduction state is controlled via the FET type transistor, but it
may be a bipolar type transistor.
In this case, the ferroelectric thin film is connected to the emitter instead of the source region.
Further, the withstand voltage to be compared with the coercive electric field voltage includes
the withstand voltage between each region of the base, the emitter, and the collector.
[0073]
Further, in the second embodiment, the form in which the charge related to one ferroelectric
capacitor is supplied to the channel region of one FET is described as an example. It may be. In
this case, it is also possible to output charge signals from the n-channel FET and the p-channel
FET by using two ferroelectric capacitors whose polarization states are aligned in the same
direction. Alternatively, when the polarization states of the two ferroelectric capacitors are
reversed, charge signals corresponding to the amplitude intensity of the ultrasonic wave are
output in a rectified form from the n-channel FET and the p-channel FET.
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[0074]
In the above embodiment, the ultrasonic probe according to the medical ultrasonic diagnostic
apparatus has been described as an example, but the ultrasonic diagnostic apparatus may be
used for diagnosis of the inside of the building structure, etc. . In this case, the acoustic sensor
portion for transmitting and receiving the ultrasonic wave does not have to be provided outside
the ultrasonic diagnostic apparatus main body as an ultrasonic probe, and may be integrally
provided in the ultrasonic diagnostic apparatus main body.
[0075]
Further, the transducer as the acoustic sensor of the present invention does not have to be used
in an ultrasonic diagnostic apparatus, and may be used in a measurement apparatus that simply
measures the reception intensity of ultrasonic waves. In such a case, only a single acoustic sensor
may be provided without providing a plurality of acoustic sensors.
[0076]
In the above embodiment, although the case of receiving ultrasonic waves of 1 to 30 MHz has
been described, an acoustic sensor that receives sound waves in a frequency band that can be
received when the piezoelectric member is formed by a thin film manufacturing process will be
described. The invention can be applied.
[0077]
Further, in the above embodiment, the control unit is provided only in the ultrasonic diagnostic
apparatus main body 1 and the control signal is sent to the ultrasonic probe 2. However, partial
control may be performed depending on power consumption, size, weight, etc. The control may
be performed by the ultrasound probe 2.
Thus, the amount of control signal passing through the cable 22 can be reduced. Alternatively,
the setting data is held by the ultrasonic probe 2 and the polarization state is set using the
setting data in the ultrasonic probe 2 based on the control signal from the ultrasonic diagnostic
apparatus main body 1 It is good as well. In addition, specific details such as the configuration
and the structure shown in the above embodiment can be appropriately changed without
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departing from the scope of the present invention.
[0078]
DESCRIPTION OF SYMBOLS 1 ultrasound diagnostic apparatus main body 2 ultrasound probe 12
transmission unit 13 reception unit 14 transmission / reception switching unit 15 control unit
16 image processing unit 17 storage unit 18 operation input unit 19 output display unit 21
vibrator 21 b vibrator 22 cable 100 semiconductor Substrate 101 source region 102 drain
region 103 metal wiring 103 b contact plug 104 metal wiring 111 gate insulating film 112
ferroelectric thin film layer 112 b gate electrode 113 gate electrode 113 b metal wiring 114,
115 side wall 116, 117 extension region 118 transfer electrode 121, 131 Insulating film 132
Ferroelectric thin film layer 133 Electrode 134 Electrode 135 Metal wiring 210 Vibrator
arrangement S Ultrasonic diagnostic device
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