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JPH01269080

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DESCRIPTION JPH01269080
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic transducer, for example, a high-performance, compact, lightweight electrostatic
ultrasonic wave that can be used for detection of a proximity chamber of an industrial robot, a
back sensor of an automobile, etc. The present invention relates to the structure of a transducer
and a method of manufacturing the same. (Conventional art) Conventionally, in the field of
industrial robots, a sensor that is an object is used when the object is transparent, or when the
medium between the sensor and the object is dirty with dust or the like There is a drawback that
it can not do. Therefore, in recent years, a technology has emerged that attempts to use
ultrasound for recognition of an object instead of visible light. In ultrasonic transducers, since
ultrasonic waves are transmitted and received by one or more devices, the mechanical elements
that transmit and receive ultrasonic waves, and the electrical circuits such as the oscillating
circuit and receiving circuit that support the mechanical elements. The elements need to be
combined well. In particular, when a surface is vibrated to emit ultrasonic waves into the air, the
response of the air (acoustic impedance) to the surface is very small compared to liquid or solid,
so the emission of ultrasonic waves with large intensity Is difficult. Therefore, it is necessary not
only to design ultrasonic waves to be emitted efficiently in the mechanical elements described
above, but also in the electrical elements, it is necessary to contrive small signals by the
amplification compensation circuit and receive them etc. . However, the ultrasonic transducers
generally used at present have a considerable device-to-device variation in the characteristics of
this mechanical element and can not necessarily be designed optimally. Furthermore, the
mechanical and electrical elements are not integrated into one unit, which makes it difficult to
reduce the size and weight of the device. Hereinafter, the conventional example will be described
with reference to the drawings. FIG. 4 is a view showing a cross section of a configuration
example of a conventional ultrasonic transducer. In the figure, 47 is a circular aluminum alloy
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plate, and a plurality of holes 101 having a depth of several to several tens of pm are formed on
the surface by machining. On the upper surface of the hole 101, a polyester film 48 with a
thickness of about 12 yen and 1 m is fixed by being sandwiched between the metal case 41 and
the plate 47 of aluminum alloy. An upper electrode 49 of gold or the like is vapor-deposited on
the surface of the polyester film 48 opposite to the surface in contact with the aluminum alloy
plate 47. A protective screen 43 is fixed to the metal case 41 by a protective screen to prevent
the polyester film 48 from being damaged from the outside. On the other hand, a plate spring 46
made of metal is attached to the back surface of the aluminum alloy plate 47, and the aluminum
alloy plate 47 is pressed against the metal case 41.
Further, the leaf spring 46 is fixed to the plastic case 42. The reference numeral 44.45 is an
electrode terminal, 44 is integrally formed with the plate spring 46, while 45 is integrally formed
with the metal case 41. Accordingly, the potential of the electrode terminal 44 is equal to that of
the aluminum alloy plate 47 through the plate spring 46, while the potential of the electrode
terminal 45 is equal to that of the upper electrode 49 through the metal case 41. FIG. 5 is a view
for explaining the operation principle of the electrostatic ultrasonic transducer described in FIG.
4, which is composed of a mechanical element 51 for generating vibration and other electric
elements 52. The mechanical element 51 is composed of a diaphragm 51a and a fixed plate 51b,
and has, for example, the structure shown in FIG. On the other hand, the electrical element 52 is
composed of a bias power supply 53, a resistor 54 and an oscillation circuit 55 in the case of
ultrasonic wave transmission. Now, when no signal is generated from the oscillation circuit 55,
the diaphragm 51a is pulled and bent to the fixed plate 51b by the bias voltage applied by the
bias power supply 53. Subsequently, when an AC voltage having a smaller amplitude than the
bias voltage is applied to the oscillation circuit 55, the polarity changes according to the polarity
of the voltage across the oscillation circuit 55 as follows. That is, when the polarity of the voltage
applied to both ends of the oscillation circuit 55 is the same as the bias voltage, a potential
difference equal to the sum of these voltages is applied to the diaphragm 51a and the fixed plate
51b to cause vibration. Therefore, when the voltage across the oscillating circuit is periodically
changed by the oscillating circuit 55, the diaphragm 51a vibrates and an ultrasonic wave is
emitted to the front. The resistor 54 has a function of protecting the circuit so that a large
current does not flow in the circuit when a discharge or the like occurs between the diaphragm
51a and the fixed plate 51b. Although the case of transmission of ultrasonic waves has been
described above, in the case of delivery, 55 in FIG. 5 may be a receiving circuit that performs
amplification compensation and the like. At this time, the diaphragm 51a is vibrated by the
ultrasonic wave that has entered from the outside, and the capacity between the diaphragm 51a
and the fixed plate 51b is changed. Therefore, an alternating current flows in the receiving circuit
55, and amplification can be compensated for the delivery of ultrasonic waves. (Problems to be
Solved by the Invention) In the above, the conventional electrostatic ultrasonic transducer has
been described using an example. Among them, when machining the hole 101 shown in FIG. 4,
the variation by the size and shape of the hole can not be avoided by the conventional machining
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method. The hole 101 corresponds to the gap between the diaphragm 51a and the fixed plate
51b shown in FIG. 5, and when the dimensions and the outer shape thereof vary, the force for
driving the diaphragm 51a varies, eventually resulting in ultrasonic waves. There is a drawback
that transmission and reception characteristics are not constant.
The thinner the film 48 (FIG. 4) of polyester, the higher the sensitivity. That is, the distance
between the upper electrode 49 and the aluminum alloy plate 47 which is the lower electrode is
reduced. However, as the polyester film 48 is made thinner, minute holes are produced in the
film, and a high bias voltage causes a discharge between the upper electrode 49 and the
aluminum alloy plate 47, which causes the device to break down. It often happened. For this
reason, there is a problem that the thickness of the polyester film 48 can not be reduced and the
sensitivity can not be increased. Also, when the temperature in the atmosphere changes, the
volume of air confined in the hole 101 provided between the polyester film 48 and the aluminum
alloy plate 47 in FIG. 4 changes. This directly affects the transmission and reception
characteristics of the transducer because it changes the tension of the polyester film 48 and the
distance between the polyester film 48 and the aluminum alloy plate 47. Therefore, there was a
need to reduce the temperature dependence of the transducer. Furthermore, as mentioned above,
in ultrasonic transducers, a combination of mechanical and electrical elements is inevitable, and
when attempting to realize higher performance devices using conventional structures, There was
a tendency that the area occupied by the electrical elements became larger and the apparatus
became larger. In fact, the wires connecting the electrodes of the arrayed transducers are known
to be quite large by themselves. As described above, in the prior art, there is a disadvantage that
the device can not be reduced in size and weight even if a device with higher performance is
manufactured. The object of the present invention is to eliminate the above-mentioned
drawbacks of the prior art, and to reduce the temperature dependency of the transmission and
reception characteristics of the ultrasonic transducer, and to make the characteristics uniform
and yet highly sensitive, small and lightweight. And providing a method of manufacturing the
same. (Means for Solving the Problems) According to the present invention, a thin film having a
first electrode on one surface and a second electrode provided on the surface of a semiconductor
substrate having a hole on the surface are provided. An ultrasonic transducer characterized by
one electrode and the same is obtained. Furthermore, according to the present invention, a thin
film having a first electrode on one surface and a second electrode provided on the surface of a
semiconductor substrate having a hole on the surface are provided, the first electrode and the
second electrode. In the method of manufacturing an ultrasonic transducer in which an
insulating film is provided so as to adhere to the second electrode between the electrode and the
electrode, the hole is formed from the back side of the substrate simultaneously with the
formation of the hole using anisotropic etching technology. A method of manufacturing an
ultrasonic transducer is provided, including the steps of forming the through holes to form
through holes and mounting the substrate on a holed base.
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Furthermore, according to the present invention, a thin film having a first electrode on one
surface and a second electrode provided on the surface of a semiconductor substrate having a
hole on the surface are provided, the first electrode and the second electrode. In an ultrasonic
transducer in which an insulating film is fixed to a second electrode between the electrode and
the electrode, the hole is a through hole communicating with the back surface of the
semiconductor substrate, and the hole is communicated with the outside world. A plurality of
ultrasonic transducers are arranged in an array so that electrical signals independent of each
other can be input / output to electrodes on at least one side of the first and second electrodes of
each ultrasonic transducer 1 An ultrasound transducer characterized by the above is obtained.
(Operation) The ultrasonic transducer according to the present invention is an electrostatic
ultrasonic transducer which enables integration of a manufacturing method and peripheral
circuits conforming to IC process technology such as silicon, and, for example, elastic vibration as
shown in FIG. By moving the organic thin film 10 as a body up and down according to the change
in the potential difference applied to the upper and lower electrodes 49.6 of the 5102 film 3
provided on the silicon substrate 1, ultrasonic waves are transmitted. On the other hand, when
this device is used for receiving ultrasonic waves, the organic thin film 10 vibrates due to the
pressure of the external ultrasonic wave, and as a result, the capacitance between the upper and
lower electrodes of the SiO 2 film 3 changes. It is possible to detect the pressure of the external
supersonic wave as a change in the value of the current flowing in the electric circuit (bias
voltage is applied). At this time, in order to increase the sensitivity of the transmission and
reception characteristics of the transducer, it is necessary to reduce the distance between the
upper electrode 49 and the lower electrode 6 provided on the silicon substrate 1. In the present
invention, as shown as an example in FIG. 1, the surface of the lower electrode 6 is covered with
an insulating film such as a SiO 2 film 3 to maintain good insulation between the upper electrode
and the lower electrode while keeping the distance between them. It is possible to reduce the
sensitivity to increase. In addition, the etching hole 12 is connected to the rear hole 22 to be a
through hole and communicate with the outside world, and the air that has conventionally been
confined in the etching hole 12 can move in and out of the outside world. It can be reduced.
Furthermore, since the ultrasonic transducer according to the present invention uses the
semiconductor substrate, (1) the etching hole 12 and the back hole 22 can be simultaneously
formed precisely on the semiconductor substrate using the fine etching technology of the
semiconductor, (2) oscillation circuit and reception circuit can be integrated using semiconductor
IC process technology, and thus high-performance ultrasonic transducers It became possible to
manufacture in a small size and light weight.
An electrostatic ultrasonic transducer according to an embodiment of the present invention will
be described below with reference to the drawings. 1 and 2 show an embodiment of the present
invention and are a cross-sectional view and a plan view, respectively. In this embodiment, an
upper electrode 49 of gold, aluminum or the like is vapor-deposited on the lower surface of the
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organic thin film 10 of polyester or the like for transmitting and receiving ultrasonic waves. The
organic thin film 10 vibrates up and down on etching holes 12 regularly formed in a silicon
substrate 1 as shown in FIG. 2 to transmit and receive ultrasonic waves. The upper electrode 49
and the lower electrode 6 are disposed on both sides of the SiO 2 film 3 provided on the lower
surface of the organic thin film 10, and when transmitting waves, an alternating voltage is
applied to vibrate the organic thin film 10. At the time of delivery, the organic thin film 10
vibrates to generate a voltage. The SiO 2 film 3 provided between the lower electrode 6 and the
upper electrode 49 helps to maintain good electrical insulation between the two. Furthermore,
when the thickness of the SiO □ film 3 is about 111 m, the spatial distance between the upper
electrode 49 and the lower electrode 6 is also about 111 m, and conventionally, as shown in FIG.
The distance between the electrodes is advantageously reduced as compared with the thickness
of the polyester film 48 (1211 m). Since the electrostatic force acting on the organic thin film 10
is approximately inversely proportional to the square of the distance between the two electrodes
49 and 6, the sensitivity of the transmission and reception characteristics of the device can be
increased. The SiO 2 film 20 is also inserted between the lower electrode 6 and the silicon
substrate 1 to prevent current from leaking between the lower electrode 6 and the silicon
substrate 1. Lower electrode 6 is electrically connected to integrated circuit 8 for driving and
receiving fabricated on silicon substrate 1 via an aluminum wiring (not shown) also formed on
SiO 2 film 3. . Further, the etching hole 12 is in communication with the rear hole 22 so as to be
a through hole so that the air sealed therein can enter and leave the outside. The etching holes
12 and the back holes 22 are manufactured by applying anisotropic etching technology of silicon
in order to precisely finish the size and shape. This uses, for example, a pattern of a plurality of
square 5i02 films whose side is meshed in the <110> direction on one surface of the silicon
substrate 1 having the main surface in the (100) direction using photolithography technology
The sample is then immersed in an anisotropic etching solution such as hydrazine.
In this case, there is a feature that the etching of the silicon automatically stops at the stage
where the etching holes 12 and the rear holes 22 in the shape of a pyramidal quadrangular
pyramid are formed. Therefore, when the shapes of the etching holes 12 and the rear holes 22
are formed by photolithography, fine shapes can be formed with high accuracy, and furthermore,
the sample is immersed in liquid to perform etching. It has the advantage of being able to process
large quantities of samples each time. FIGS. 3 (a)-(e) are cross-sectional views showing an
example of the procedure for manufacturing an ultrasonic transducer having an embodiment of
the present invention. In the drawings, the same reference numerals as in FIGS. 1 and 2 shown as
one embodiment of the present invention denote the same components. FIG. 2A shows the
etching holes 12 of FIG. 2 on one side of the silicon substrate 1 having a (100) surface by using a
photolithographic technique for all 20 of the Sio 2 film 20 by the thermal oxidation method. In
the same shape, a square opening 30 having a length of several tens of pm and a rear opening
31 having a rectangular shape with a size of several hundreds of pm are formed on the other
side. The rear openings 31 are dimensioned so that the holes provided on the front and back of
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the substrate 1 pass through each other after etching. When forming the opening 30131, it is
necessary to arrange so that the sides of the etching hole 12 and the rear hole 22 in FIG. 2 face
in the <110> direction. This sample is immersed in an aqueous solution such as FDP
(ethylenediamine pyrocatechol) or hydrazine, and the etching ratio to the (100) plane is
significantly larger than the etching ratio to the (111) plane of the silicon anisotropic etching
hole ( Anisotropy). Therefore, by immersing the sample shown in FIG. 6A in the aqueous solution,
the etching hole 12 and the rear hole 22 shown in FIG. 6B can be produced. In the drawing, the
angles 12 and 22 are different, but in fact both are the same angle, and the angle with the
horizontal plane of the silicon substrate 1 is about 70 degrees. Subsequently, the sample is
thermally oxidized again to completely etch the SiO 2 film 20 on the surfaces of the etching holes
12 and the rear holes 22 and then, using the usual silicon IC process technology, the integrated
circuit 8 for transmission and reception is formed Figure (C)). Subsequently, in order to form a
lower electrode 6 and a wire (not shown) connected to the integrated circuit 8, the 5102 film 20
on the integrated circuit 8 is partially removed to deposit aluminum, and the wire is formed using
ordinary photolithography technology. Pattern it.
Thereafter, the 8102 film 3 is formed by the CVD method (FIG. 3D). The lower electrode 6 is to
improve the adhesion to the SiO 2 film 3 (the same figure (e)). After that, it is mounted on a
pedestal 35 (stem) with holes in order to communicate with the outside world. In the
embodiment of the present invention shown in FIGS. 1 and 2, the structure in which the upper
electrode 49 is in direct contact with the SiO 2 film 3 is shown. On the other hand, a
configuration similar to that of the conventional example shown in FIG. 4 by reversing the
positional relationship between the upper electrode 49 and the organic thin film 10 is also
included in the present invention. In this case, the distance between the upper electrode 49 and
the lower electrode 6 is larger than that in the previous embodiment, so that the sensitivity is
lowered. However, both the SiO2 film 3 and the organic thin film 10 are present between the
picture electrodes. As a result, the electrical insulation between the two electrodes is sufficiently
compensated. Therefore, short circuit between the two electrodes is reduced, and device
reliability is improved. In addition, since the thickness of the organic thin film 10 can be reduced
because of the presence of the SiO 3 film 3, the sensitivity can be increased as compared with the
prior art. In addition, since the thickness of the organic thin film can be made thick or thin, there
is an advantage that design freedom is increased. Moreover, it is also possible to use metal thin
films such as gold and titanium instead of the organic thin film 10. At this time, since the melting
point of the metal is higher than that of the organic substance, it is a high temperature plan view.
In the figure, the same reference numerals as in FIGS. 1 and 2 denote the same components. In
these embodiments, a rectangle 70 indicated by a broken line indicates a vibrator element
included on the same lower electrode 6 shown in FIGS. 1 and 2. However, integrated circuit 8 is
not included. Further, the electrodes formed on the upper and lower surfaces of the vibrator
element 70 are connected to a part of the integrated peripheral circuit 8 'through aluminum
wiring (not shown). When a plurality of vibrator elements 70 are arranged as shown in the
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embodiment of FIGS. 6 and 7, ultrasonic waves are emitted strongly at a small angle on the front
surface, or ultrasonic waves at only a small angle on the front surface are strongly received. You
will be less likely to be confused by ambient noise. In addition, using the above-described
technology for anisotropic etching of silicon, it is possible to simultaneously form vibrator
elements 70 of exactly the same shape, so that the quality is stable and the time required for
manufacture is short. In addition to the embodiment shown here, there is also an embodiment in
which the area of the central oscillator element 70 is increased and the area of the oscillator
element 70 is decreased toward the periphery (not shown). In this case, there is an advantage
that the directivity described above is further improved, and a high-quality device with less noise
can be provided.
FIG. 8 is a plan view of the third embodiment of the present invention. In the figure, the same
reference numerals as in FIG. 6 indicate the same components. The embodiment of the present
invention is characterized in that the lower electrodes 6 formed on the vibrator element 70 are
disposed separately from each other, and are connected to the peripheral circuit 8 ′ ′ via
aluminum wiring, respectively. Therefore, in the ultrasonic transducer having the configuration
of the present embodiment, it is possible to apply a voltage having a different strength and phase
to each vibrator element 70. In particular, by applying voltages having different phases to each
of the oscillator elements 70, the directions of transmission and reception of ultrasonic waves
can be changed, and thus, a high-performance ultrasonic transducer that performs electrical
scanning. Can provide Although FIG. 8 shows an array of ultrasonic transducers in one row and
five columns, the number of vibrator elements 70 need not be limited at all. For example, in the
embodiment of FIG. 7, the electrodes on the upper and lower surfaces of the vibrating element
70 are separately disposed for each vibrating element 70, and when the respective electrodes are
connected to the peripheral circuit 8 ' It is possible to realize a two-dimensional ultrasonic
transducer that can be scanned in Further, in the ultrasonic transducer described in the present
embodiment, the lower electrode of each vibrator element 70 can be simultaneously and easily
formed using the normal IC process technology, which is a great advantage over the prior art. It
is. In the embodiment in which the lower electrode is separated, one vibrating body element 70
has been described as having a plurality of etching holes as shown in FIGS. 1 and 2, but not
limited thereto. It may be considered that the etching holes in the two figures correspond to one
vibrator element. The present invention has been described above in detail by way of examples.
The configuration of the present invention holds regardless of whether the ultrasonic wave used
as a signal changes continuously, or changes in a pulsed manner with only a few wavelengths or
the like. In addition, the same holds true regardless of whether the wavelength of ultrasonic
waves is single or plural. Furthermore, there is also a configuration in which the influence of the
back side of the device is reduced by placing a sound absorbing material such as a sponge
outside the rear hole, and a configuration in which a horn is placed in front of the vibrating body
to increase sensitivity. Included in the present invention. The sensitivity of the transmission and
reception of the ultrasonic waves can be increased by increasing the area of the metal thin film
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or the organic thin film contributing to vibration or reducing the thickness in the above
embodiment.
Furthermore, the sensitivity can also be increased by thinning the 8102 film between the organic
thin film and the lower electrode. However, in this case, changes in the frequency characteristics
of the device and the like occur simultaneously. Therefore, when designing the ultrasonic sensor,
the sensitivity, frequency characteristics, electro-acoustic conversion efficiency, etc. are
optimized in consideration of the above effects. The dimensions of the vibrating body and the
5102 membrane must be determined to Although the 5102 film 3 is used in the above
embodiment, the present invention is not limited to this, and any film can be used if it can be
fixed to the surface of the lower electrode, such as Si3N4.5tOxNy or polyimide, in a thin film by a
method such as CVD, (Effects of the Invention) As described above, according to the present
invention, it has become possible to supply an integrated ultrasonic transducer with high
sensitivity, small size and light weight with small variation in characteristics due to temperature
change and small variation in characteristics. As a result, in the field of industrial robots and the
like, high-performance ultrasonic transducers can be used to detect proximity chambers and the
like. In addition, since the ultrasonic transducer of the present invention can be manufactured in
large quantities by the manufacturing method in accordance with the conventional
semiconductor IC manufacturing process technology, the manufacturing cost can be reduced.
These effects are remarkable, and the present invention is effective.
[0002]
Brief description of the drawings
[0003]
1 and 2 are a sectional view and a plan view, respectively, of an embodiment of the first
invention of the present application, and FIGS. 3 (a) to 3 (e) are a method of manufacturing the
embodiment of the first invention of the present application. FIG. 4 is a cross-sectional view of a
conventional ultrasonic transducer, FIG. 5 is a principle diagram of a conventional electrostatic
transducer, and FIGS. 6 and 7 are other embodiments of the present invention. FIG. 8 is a plan
view showing an embodiment of an ultrasonic transducer array according to the third invention
of the present application.
DESCRIPTION OF SYMBOLS 1 ... Silicon substrate, 3, 20 ... SiO2 film | membrane 6. Lower part
electrode 8 ... Integrated circuit, 8 '... Peripheral circuit, 10 ... Organic thin film, 12 ... Etching hole,
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22 ... back hole, 30 ... opening, 31 ... back opening, 35 ... pedestal, 41 ... metal case, 42 ... plastic
case, 43 ... protection slip 1r-n, required 45: electrode terminal 46: leaf spring 47: aluminum
alloy plate 48. · · · Polyester film, 49 · · · upper electrode, 51 · · · mechanical elements, 51a · · ·
diaphragm, 51b · · · fixed plate, 52 · · · electrical elements, 53 · · · bias power supply, 54:
resistance, 55: oscillation circuit (or reception circuit), 70: vibrator element. Patent Assignee
General Manager, Industrial Technology Institute Kozo Iizuka Figure 1 Figure 2 Figure 3 Figure 4
Figure 6 Figure 7 Figure 8
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