JPS62284600

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DESCRIPTION JPS62284600
[0001]
FIELD OF THE INVENTION The present invention relates to ultrasonic transducers, and in
particular to the construction of a high performance, compact and lightweight electrostatic
airborne ultrasonic transducer that can be used to detect proximity parties in industrial robots. It
is about (Conventional art) Conventionally, in the field of industrial robots, a solid-state image
sensor using visible light such as COD has often been used to recognize the distance, size, shape,
etc. of a target object. However, sensors using visible light have the disadvantage that they can
not be used when the target object is transparent or when the medium between the sensor and
the target object is contaminated with dust or the like. Therefore, in recent years, a technology
has emerged that attempts to use ultrasound for recognition of an object instead of visible light.
In an ultrasonic transducer, since ultrasonic waves are transmitted and received by one or a
plurality of devices, the mechanical elements performing the oscillation and reception of the
ultrasonic waves, and the electrical circuits such as the oscillation circuit and the reception
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 considerably large device-to-device variation of the characteristics of this
mechanical element, and can not be said to be necessarily optimally designed. 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. In the following, the prior art will be described with
reference to the drawings and at the same time its drawbacks will be described. FIG. 4 is a view
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showing a cross section of a configuration example of a conventional ultrasonic transducer. In
the figure, 47 is a circular aluminum alloy 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 film 48 of polyester having a thickness of 6 to 20 pm is held and fixed by a metal
case 41 and a plate 47 of an aluminum alloy. On the surface of the polyester film 48, an
electrode 49 made of gold foil or the like is vapor-deposited on the surface opposite to the left
contact surface of 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. A tool 45 is an electrode terminal, and
44 is integrally formed with the plate spring 46, while 45 is formed integrally with the metal
case 41. Therefore, the potential of the electrode terminal 44 is equal to the plate 47 of
aluminum alloy through the plate spring 46, while the potential of the electrode terminal 45 is
equal to the electrode 49 through the metal case 41. Thus, when a voltage is applied to the
electrode terminal 44 ° 45, a voltage equal to this applied voltage is generated between the
aluminum alloy plate 47 and the electrode 49, and the polyester film 48 is bent by electrostatic
force. Therefore, when the voltage applied to the electrode terminal 44. 45 changes with
alternating current, the electrostatic force acting on the polyester film 48 also changes with
alternating current, causing the polyester film 48 to vibrate, and as a result, ultrasonic waves are
radiated to the front surface. Be done. FIG. 5 is a view showing the 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 voltage 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 to the fixed plate 51b by
the bias voltage 53 and bent. Subsequently, when an AC voltage smaller than the bias voltage 53
is generated in the oscillation circuit 55, the polarity changes according to the polarity of the
voltage generated at both ends of the oscillation circuit 55 as follows. That is, when the polarity
of the voltage generated at both ends of the oscillation circuit 55 is the same as the bias voltage
53, the deflection of the diaphragm 51a becomes large because a potential difference equal to
the sum of these voltages is applied to the diaphragm 51a and the fixed plate 51b. On the other
hand, when the polarity of the voltage of the oscillation circuit 55 is opposite to that of the bias
voltage 53, the deflection of the diaphragm 51a is reduced because a potential difference equal
to the difference between these voltages is applied to the diaphragm 51a and the fixed plate 51b.
Therefore, when the oscillating circuit 55 periodically changes the voltage at both ends of the
oscillating circuit, 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
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circuit when a discharge or the like occurs between the diaphragm 51a and the fixed plate 51b.
Although the case of transmitting 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 5ia is vibrated by the ultrasonic wave that has entered from
the outside, and the capacity between the diaphragm 51a and the fixed plate 51b changes.
Therefore, an alternating current flows in the receiving circuit 55, and amplification
compensation is performed to enable reception of ultrasonic waves. (Problems to be Solved by
the Invention) In the above, the description has been made of the conventional electrostatic
ultrasonic transducer using an example. Among them, when machining the hole 101 shown in
FIG. 4, some variation in the size and shape of the hole can not be avoided by the conventional
machining 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 the transmission and reception characteristics are not constant. In addition, as
described above, in ultrasonic transducers, the combination of mechanical and electrical
elements is inevitable, and when attempting to realize a more sophisticated device using a
conventional channel, Increasingly, the area occupied by this electrical element has tended to
increase the size of the device. 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. SUMMARY OF THE INVENTION It is an object of the
present invention to eliminate the drawbacks of the prior art and to provide a high performance,
compact and lightweight airborne ultrasonic transducer with uniform characteristics. SUMMARY
OF THE INVENTION According to the present invention, in an electrostatic transducer provided
with an organic thin film having a first electrode on one side, a silicon substrate having a
plurality of holes for the second electrode is provided. An ultrasonic transducer characterized in
that it is provided on a surface, and at least the first and second electrodes of the electrostatic
transducer comprising an organic thin film having a first electrode on one side. According to the
present invention, there is provided an ultrasonic transducer characterized in that independent
electrical signals can be input to and output from electrodes on one side. (Operation) The
ultrasonic transducer according to the present invention is an electrostatic ultrasonic transducer
capable of integrating a manufacturing method and peripheral circuits in conformity with silicon
IC process technology, and as shown in FIG. 2, it is an elastic vibrator. A polyester film is
designed to move up and down according to the change in the potential difference applied to the
electrodes above and below the polyester film to transmit ultrasonic waves.
In addition, when this device is used for delivery of ultrasonic waves, the change in the potential
difference between the upper and lower electrodes of the polyester film when the polyester film
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vibrates due to external ultrasonic waves is used to It can be read out as a change. In addition,
since the ultrasonic transducer according to the present invention uses a silicon substrate, (1)
holes can be precisely formed on the silicon substrate by using a fine etching technique of
silicon, and variations in device characteristics may be impaired from the manufacturing process
(2) The oscillator circuit and the receiver circuit can be integrated using silicon IC process
technology, so it becomes possible to manufacture a high-performance ultrasonic transducer in a
compact and lightweight manner. The Embodiments of the present invention will be described
below with reference to the drawings. 1 and 2 show an embodiment of the present invention,
which correspond to a plan view and a sectional view, respectively. An upper electrode 49 of
gold, aluminum or the like is vapor-deposited on the upper surface of the organic thin film
polyester film 48 for transmitting and receiving ultrasonic waves in the present embodiment. The
polyester film 48 vibrates up and down on the unpenetrated etching holes 12 formed in the
silicon substrate 1 to transmit and receive ultrasonic waves. The upper electrode 49 and the
lower type electrode 6 are disposed on both sides of the main surface of the polyester film 48,
and when the polyester film 48 vibrates, different potential differences are applied or generated.
An oxide film 3 is inserted between the lower electrode 6 and the silicon substrate 1 to prevent
current from leaking between the electrode 6 and the substrate 1. The lower electrode 6 is
electrically connected to an integrated circuit 8 for driving and receiving which is produced on
the silicon substrate 1 through an aluminum wiring 21 also placed on the oxide film 3. The
etching hole 12 is manufactured by applying, for example, an anisotropic etching technique of
silicon in order to finish the size and shape with high accuracy. This is done, for example, after
printing a plurality of squares, the sides of which are meshed in the <110> direction, on one
surface of the silicon substrate 1 having the main surface in the (100) direction, using the 7oresist technology, The sample is immersed in an anisotropic etching solution such as hydrazine.
In this case, there is a feature that the etching of silicon automatically stops at the stage where
the etching hole 12 in the shape of a pyramidal four-sided pyramid is formed. Further, as
described above, in order to produce the shape of the etching hole 12 using a photoresist
technique, a fine shape can be formed with high accuracy, and furthermore, the sample is
immersed in liquid to perform etching. As it does, it has the advantage of being able to process a
large number of samples at one time.
FIG. 3 shows an example of the procedure for producing 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. In the
same figure (a), an opening 30 having the same shape as the etching hole 12 of FIG. 1 is formed
by using a photoetching technique in which the oxide film 3 is attached to the front and back of
the silicon substrate 1 having the (100) plane. It is a thing. When forming the opening 30, it is
necessary to arrange so that the side of the etching hole 12 of FIG. 1 faces in the <110>
direction. This sample is immersed in an aqueous solution such as FDP (ethylenediamine
pyrocatechol) or hydrazine to perform anisotropic etching of silicon (FIG. 6 (b)). An aqueous
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solution of FDP, hydrazine or the like has a property (anisotropy) that the etching rate to the
(100) plane is significantly larger than the etching rate to the (111) plane of silicon. Therefore,
by immersing the sample shown in FIG. 5A in the aqueous solution, the etching hole 12 shown in
FIG. 5B can be produced. Subsequently, the sample is again put into the oxidation furnace in
order to apply the oxide film 3 to the etching hole 12, and thereafter, the integrated circuit 8 for
transmission and reception is formed using the normal silicon IC process technology (FIG. (C)). .
Subsequently, an aluminum wiring 21 connected to the lower electrode 6 and the integrated
circuit 8 is formed by vapor deposition or the like (FIG. 6 (d)). The lower electrode is preferably
made of Au on the Cr underlayer in order to improve the bonding with the oxide film 3. However,
the lower electrode is not necessarily limited to this, and metals such as aluminum may be
substituted. Also good. Thereafter, the polyester film 48 on which the upper electrode 49 is
vapor-deposited is adhered to the silicon substrate 1, and then the device is mounted on a
package. 6 and 7 are plan views showing other embodiments of the present invention. In the
figure, the same reference numerals as in FIGS. 1 and 2 denote the same components. In these
embodiments, a plurality of rectangles 70 indicated by broken lines indicate elements included
on the same lower electrode 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 peripheral circuit 8 through an aluminum wiring (not shown).
As shown in the embodiment of FIGS. 6 and 7, when a plurality of the vibrator elements 70 are
arranged, the ultrasonic wave is strongly emitted at a small angle of the front surface, or the
ultrasonic wave of only a small angle of the front surface is strongly received. It has the feature
that it is possible to reduce the amount of confusion by surrounding noise.
Also, using the above-described anisotropic etching technology of silicon, it is possible to
simultaneously form the vibrator element 70 of exactly the same shape, which causes problems
in terms of quality and time required for manufacturing. It has the feature that it does not exist.
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 reduced
toward the periphery (not shown). In this case, there is an advantage that the directivity
described above can be further modified to provide a high-quality device with less noise. FIG. 8 is
another embodiment of the present invention. In the figure, the same reference numerals as in
FIG. 6 indicate the same components. In the embodiment of the present invention, the lower
electrode formed on the vibrator element 7 o is separately disposed for each vibrator element 7
o, and is connected to the peripheral circuit 8 through the aluminum wiring, respectively. There
is a feature. Therefore, in the ultrasonic transducer having the configuration of the present
embodiment, it is possible to apply a voltage having different strength and phase for each of the
vibrator elements 7 o. In particular, by applying a voltage having a different phase to each of the
oscillator elements 70, it is possible to change the direction of transmission and reception of the
ultrasonic waves, and thus, high-performance ultrasonic waves that electrically scan. It has the
feature that it can provide a transducer. In this embodiment, the electrodes on the lower surface
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of the vibrating element 70 are disassembled for each vibrating element 70, but in addition to
the electrodes on the lower surface of each vibrating element 70 in common, the upper surface
of each vibrating element 70 It is possible to realize a device having the same effect as the above
by separating the electrodes (not shown) of each of the vibrator elements 70 separately.
Although FIG. 8 shows the 1-row 5-row ultrasonic transducer array, the number of vibrator
elements 70 need not be limited at all. For example, in the embodiment of FIG. 7, when the
electrodes of the upper and lower surfaces of the vibrator element 70 are separately disposed for
each vibrator element 70 and the respective electrodes are connected to the peripheral circuit 8,
the electricity in the two-dimensional direction It is possible to realize a two-dimensional
ultrasonic transducer that can be scanned in Further, in the ultrasonic transducer array described
in the present embodiment, the lower surface electrode of each vibrator element 70 can be
simultaneously and easily formed using the normal IC process technology, which is also larger
than the prior art. It is an advantage. In the embodiment in which the lower electrode or the
upper electrode is separated, one vibrator element 70 is described as having a plurality of
etching holes as shown in FIG. 1 and FIG. 2, but the present invention is not limited thereto. It
may be considered that the number of etching holes in FIG. 2 corresponds 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 number of wavelengths.
Also, it does not matter whether the wavelength "" of the ultrasonic wave is single or plural. In
the embodiment of the present invention, air was confined in the hole under the vibrator, but in
addition to this configuration, a configuration is also possible in which an open hole is made in
the bottom of the hole to allow air flow. is there. Furthermore, the present invention reduces the
influence of the back side of the device by placing a sound absorbing material such as a sponge
outside the hole and the like, and the configuration in which the horn is placed in front of the
vibrator to increase the sensitivity. include. In the above embodiment, the sensitivity of
transmission and reception of ultrasonic waves can be increased by increasing the area of the
vibrator or reducing the thickness. 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
must be determined to (Effects of the Invention) As described above, according to the present
invention, it has become possible to supply a high-performance, small-sized lightweight
integrated ultrasonic transducer with small variations in characteristics. As a result, it has
become possible to use a high-performance ultrasonic transducer for the detection of a proximity
room etc. in the field of industrial robots etc. In addition, since the ultrasonic transducer of the
present invention can be manufactured in large quantities by a method consistent with the
conventional silicon IC process technology, the manufacturing cost can be reduced. These effects
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are remarkable, and the present invention is effective.
[0002]
Brief description of the drawings
[0003]
1 and 2 are a plan view and a sectional view, respectively, of an embodiment of the present
invention, and FIGS. 3 (a) to 3 (d) are conceptual diagrams showing an embodiment of a method
of manufacturing the embodiment of the present invention. Fig. 4 is a sectional view of a
conventional ultrasonic transducer, Fig. 5 is a principle view of a conventional electrostatic
transducer, and Figs. 6 and 7 are plan views showing other embodiments of the present
invention, Fig. 8 FIG. 1 is a plan view showing an embodiment of an ultrasonic transducer array
according to the present invention.
1 · · · Silicon substrate, 3 · 0. Oxide film 6. Lower electrode 8. Integrated circuit 21 Aluminum
wiring 12. Etching hole 30. Opening 41. Metal case 42. Plastic case , 43: protective screen,
44.45: 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 · · · · · · · · · · · · · · · · · · · · · · · sending and receiving circuits, 70 ··· Vibrator element.
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