JPH0577240B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an ultrasonic transducer, which is a high-performance transducer that can be used, for example, in proximity detection of industrial robots, back sensor of automobiles, etc. This invention relates to the structure of a small and lightweight electrostatic ultrasonic transducer.

(Prior Art) Conventionally, in the field of industrial robots, solid-state image sensors such as CCDs that use visible light have been widely used to recognize the distance, size, shape, etc. of a target object. However, sensors that use visible light have the disadvantage that they cannot be used when the target object is transparent or when the medium between the sensor and the target object is dirty with dust or the like. Therefore, in recent years, a technology has appeared that attempts to use ultrasonic waves instead of visible light to recognize target objects. In an ultrasonic transducer, ultrasonic waves are transmitted and received by one or more devices, so there are mechanical elements that transmit and receive ultrasonic waves, as well as oscillation circuits, receiving circuits, etc. that assist in this process. It is necessary to combine electrical elements appropriately. In particular, when trying to emit ultrasonic waves into the air by vibrating a certain surface, the response (acoustic impedance) of the air to that surface is very small compared to liquids or solids, so ultrasonic waves with high intensity are emitted. is difficult. Therefore, in addition to designing the mechanical elements mentioned above so that ultrasonic waves are emitted efficiently, it is also necessary to devise measures such as using an amplification compensation circuit to compensate for small signals and receive them in the electrical elements. be. However, in the ultrasonic transducers currently in general use, the characteristics of these mechanical elements vary considerably between devices, and it cannot be said that they are necessarily optimally designed. Furthermore, since the mechanical and electrical elements are not integrated, it is difficult to downsize the device. Hereinafter, a conventional example will be explained with reference to figures, and at the same time, its drawbacks will be discussed.

FIG. 4 is a diagram showing a cross section of a configuration example of a conventional ultrasonic transducer. In the figure, reference numeral 47 denotes a circular aluminum alloy plate, on the surface of which a plurality of holes 101 having a depth of several to several tens of micrometers are formed by machining. On the upper surface of this hole 101, a polyester film 48 having a thickness of about 12 μm is fixed between a metal case 41 and an aluminum alloy plate 47. Surface of aluminum alloy plate 47 and polyester film 48
There is only point contact with the bottom surface of the . The surface of the polyester film 48 has an electrode 4 made of gold foil or the like on the surface opposite to the surface in contact with the aluminum alloy plate 47.
9 is deposited. A protective screen 43 in the figure is fixed to the metal case 41 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 presses the aluminum alloy plate 47 against the metal case 41. Further, the leaf spring 46 is attached to the plastic case 42.
Fixed. 44 and 45 are electrode terminals;
4 is constructed integrally with a leaf spring 46, and on the other hand,
45 is constructed integrally with the metal case 41.
Therefore, the potential of the electrode terminal 44 is equal to that of the aluminum alloy plate 47 via the plate spring 46, while the potential of the electrode terminal 45 is equal to that of the electrode 4 via the metal case 41.
It will be equal to 9.

FIG. 5 is a diagram showing the principle of the electrostatic ultrasonic transducer described in FIG. The mechanical element 51 is a diaphragm 51a
and a fixed plate 51b, for example, a fourth
It has the structure shown in the figure. On the other hand, the electrical element 52 is
In the case of ultrasonic wave transmission, it is composed of a bias voltage 53, a resistor 54, and an oscillation circuit 55. Now, when no signal is generated from the oscillation circuit 55, the diaphragm 51a is pulled by the fixed plate 51b by the bias voltage 53 and is bent. Subsequently, when an AC voltage having a smaller amplitude than the bias voltage 53 is applied to the oscillation circuit 55, the polarity of the voltage across the oscillation circuit 55 changes 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 53, a potential difference equal to the sum of these voltages is applied to the diaphragm 51a and the fixed plate 51b, so that the flexure of the diaphragm 51a increases. on the other hand,
When the polarity of the voltage of the oscillation circuit 55 is opposite to the bias voltage 53, a potential difference equal to the difference between these voltages is applied to the diaphragm 51a and the fixed plate 51b.
The deflection of the diaphragm 51a becomes smaller. Therefore, when the oscillation circuit 55 periodically changes the voltage across the oscillation circuit, the diaphragm 51a vibrates and a sound wave is emitted to the front. Note that the resistor 54 has a function of protecting the circuit so that a large current does not flow through the circuit when discharge or the like occurs between the diaphragm 51a and the fixed plate 51b. Although the case of ultrasonic wave transmission has been described above, in the case of wave reception, 55 in FIG. 5 may be a receiving circuit that performs amplification compensation, etc. At this time, due to the ultrasonic waves that entered from the outside,
The diaphragm 51a vibrates, and the capacitance between the diaphragm 51a and the fixed plate 51b changes. Therefore, an alternating current flows through the receiving circuit 55, and by amplifying and compensating this current, it becomes possible to receive ultrasonic waves.

(Problems to be Solved by the Invention) The conventional electrostatic ultrasonic transducer has been described above using examples. Among these, when machining the hole 101 shown in FIG. 4, the conventional machining method could not avoid slight variations in the size and shape of the hole. This hole 101 is the fifth
Between the diaphragm 51a and the fixed plate 51b shown in the figure
When the dimensions and outer shape of the diaphragm 51 vary, the force for driving the diaphragm 51 varies, resulting in a disadvantage that the transmission and reception characteristics of the ultrasonic waves are not constant.

Furthermore, when reducing the thickness of the polyester film 48 (Fig. 4), micro holes are generated in the film during manufacturing, so a high bias voltage 53 (Fig. 5) is applied to the electrode 49 and the aluminum alloy plate. 47, which often caused a discharge to occur, deteriorating the characteristics of the device. For this reason, the thickness of the polyester film 48 is limited, and the degree of freedom in design is restricted.

Furthermore, as mentioned earlier, the combination of mechanical and electrical elements is unavoidable in ultrasonic transducers, and when trying to realize even higher performance devices using conventional structures, There has been a tendency for the area occupied by these electrical elements to become larger and larger, and for devices to become larger. In fact, it is known that the wiring connecting the electrodes of arrayed transducers becomes quite large. As described above, the conventional technology has the disadvantage that even if a device with higher performance is manufactured, it is not possible to reduce the size and weight of the device.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art described above, and to provide an ultrasonic transducer that has uniform characteristics, is highly sensitive, and is small and lightweight.

(Means for Solving the Problems) According to the present invention, an organic 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 combined. An ultrasonic transducer comprising: an insulating film fixed to the surface of the second electrode between the first electrode and the second electrode; and an ultrasonic transducer comprising an organic thin film having a first electrode on one surface and a second electrode provided on a surface of a semiconductor substrate having a hole in the surface, the first electrode and the second electrode, a plurality of ultrasonic transducers are arranged in an array, each having an insulating film fixed to the surface of the second electrode. An ultrasonic transducer is obtained, characterized in that mutually independent electrical signals can be input and output to and from at least one electrode on the second electrode side.

(Function) The ultrasonic transducer of the present invention is an electrostatic ultrasonic transducer that enables the manufacturing method compatible with IC process technology such as silicon and the integration of peripheral circuits, as shown in Fig. 2. The organic thin film 10, which is an elastic vibrating body, moves up and down according to changes in the potential difference applied to the upper and lower electrodes of the CVDSiO ₂ film 3 provided on the silicon substrate 1.
Ultrasonic waves are transmitted. On the other hand, when this device is used to receive ultrasonic waves, the organic thin film 10 vibrates due to the pressure of external ultrasonic waves, and as a result, the capacitance between the upper and lower electrodes of the CVDSiO ₂ film 3 changes. Utilizing this fact, it is possible to detect the pressure of external ultrasonic waves as a change in the value of current flowing through an electric circuit (to which a bias voltage is applied). At this time, in order to increase the sensitivity of the wave transmission and reception characteristics of the transducer, it is possible to reduce the distance between the upper electrode 49 deposited on the organic thin film 10 and the lower electrode 6 provided on the silicon substrate 1. It becomes necessary. In the present invention, as shown in FIG. 2 as an example, by fixing a thin insulating film on the surface of the lower electrode 6 by oxidation, CVD, sputtering, coating, etc., the insulation between the upper electrode 49 and the lower electrode 6 is improved. While keeping the
This made it possible to reduce the distance between the two. Furthermore, since the ultrasonic transducer of the present invention uses a semiconductor substrate, (1) holes can be made with high precision on the semiconductor substrate using semiconductor micro-etching processing technology, and device characteristics resulting from the manufacturing process can be (2) The oscillator circuit and receiver circuit can be integrated using semiconductor IC process technology, making it possible to manufacture high-performance ultrasonic transducers in a compact and lightweight manner. Ta.

(Example) Hereinafter, as an example, an electrostatic airborne ultrasonic transducer, which is a type of ultrasonic transducer, will be described with reference to the drawings.

FIG. 1 and FIG. 2 show one embodiment of the present invention, and correspond to a plan view and a sectional view, respectively. An upper electrode 49 made of gold, aluminum, etc. is deposited on the lower surface of the organic thin film 10, such as a polyester film, which transmits and receives ultrasonic waves in this embodiment. This organic thin film 10 vibrates up and down above a non-penetrating etched hole 12 made in the silicon substrate 1 to transmit and receive ultrasonic waves. An upper electrode 49 and a lower electrode 6 are arranged on both sides of the CVDSiO ₂ film 3 provided on the lower surface of the organic thin film 10, and when transmitting waves, an AC voltage is applied to vibrate the organic thin film 10. let When receiving waves, the organic thin film 10 vibrates to generate a voltage. On one main surface of the silicon substrate 1, a CVDSiO ₂ film 3 is provided between the lower electrode 6 and the upper electrode 49, as shown in FIG. this is,
This serves to maintain electrical insulation between the upper electrode 49 and the lower electrode 6. Furthermore, when the thickness of the CVDSiO ₂ film 3 is about 1 μm, the spatial distance between the upper electrode 49 and the lower electrode 6 is also about 1 μm.
7 was approximately the thickness of the polyester film 48 (approximately 12 μm), the advantage is that the distance between the electrodes can be significantly reduced. Since the electrostatic force acting on the upper electrode 49 is approximately inversely proportional to the square of the distance between the two electrodes 49 and 6, the configuration according to the present invention allows the distance between the electrodes to be reduced, and as a result, , it is possible to increase the sensitivity of the wave transmission and reception characteristics of the device. Note that there is also a gap between the lower electrode 6 and the silicon substrate 1.
A SiO ₂ film 20 is inserted to prevent current from leaking between the lower electrode 6 and the silicon substrate 1. The lower electrode 6 is electrically connected to an integrated circuit 8 for driving and receiving fabricated on the silicon substrate 1 via an aluminum wiring (not shown) also placed on the CVDSiO ₂ film 3. There is. Further, the etching hole 12 is manufactured by applying, for example, silicon anisotropic etching technology in order to finish the etching hole 12 with high accuracy in size and shape. For example, this method uses photolithography technology to form a pattern of multiple square SiO ₂ films with one side aligned in the <110> direction on one side of a silicon substrate 1 whose main surface is in the (100) direction. After the sample is etched, the sample is immersed in an anisotropic etching solution such as hydrazine. This case has the advantage that silicon etching is automatically stopped when the pyramid-shaped etching hole 12 is formed. Furthermore, as mentioned earlier, in order to create the shape of the etched hole 12 using photolithography technology, it is possible to form a minute shape with high precision, and furthermore, the sample is immersed in a liquid and etched. This method has the advantage that a large amount of samples can be processed at once.

FIG. 3 shows an example of a procedure for manufacturing an ultrasonic transducer having an embodiment of the present invention. In the figures, the same reference numerals as in FIGS. 1 and 2, which were previously shown as an embodiment of the present invention, indicate the same components. Figure a shows that a silicon substrate 1 with a (100) plane is placed in an oxidation furnace and SiO ₂ is deposited on the front and back surfaces.
A square opening 30 having the same shape as the etching hole 12 shown in FIG. 1, each side having a length of several tens of micrometers, is formed on the film 20 using photolithography. When forming the opening 30,
It is necessary to arrange the etching hole 12 in FIG. 1 so that the sides thereof face the <110> direction. This sample
Silicon is anisotropically etched by immersing it in an aqueous solution such as EDP (ethylenediamine pyrocatechol) or hydrazine (Figure b). Aqueous solutions such as EDP and hydrazine have a property (anisotropy) in that the etching rate for the (100) plane of silicon is significantly higher than the etching rate for the (111) plane. Therefore, by immersing the sample shown in figure a in the aqueous solution, etching holes 1 shown in figure b can be formed.
2 can be made. Subsequently, the sample is put into the oxidation furnace again to form a SiO ₂ film 20 in the etching hole 12, and then an integrated circuit 8 for transmitting and receiving is formed using a normal silicon IC process technology (FIG. 3(c)). Next, an aluminum thin film that will become the lower electrode 6 and wiring (not shown) connecting it to the integrated circuit 8 is formed on the SiO ₂ film 20 by vapor deposition or the like, and then the sample is placed in a CVD furnace to form the CVDSiO ₂ film 3. (d). The lower electrode preferably has Au on top of a Cr base to improve bonding with the SiO ₂ film 20, but it is not necessarily limited to this, and a metal such as aluminum may be used instead. It's okay. Thereafter, the organic thin film 10 with the upper electrode 49 deposited thereon is adhered to the CVDSiO ₂ film 3, and then the device is mounted in a package (see e in the figure).

In one embodiment of the invention shown in FIGS. 1 and 2, a configuration is shown in which the upper electrode 49 is in direct contact with the CVDSiO ₂ film 3. On the other hand, this upper electrode 4
The present invention also includes a configuration in which the positional relationship between the organic thin film 9 and the organic thin film 10 is reversed to be similar to that of the conventional example shown in FIG. In this case, there is a drawback that the sensitivity is lower than that of this embodiment, but the CVDSiO ₂ film 3 provided between the organic thin film 10 and the lower electrode 6 allows the upper electrode 49 and the lower electrode 6 to Since the electrical insulation is sufficiently compensated, the reliability of the device is improved, and the thickness of the organic thin film 10 can be further reduced, so that the sensitivity can be increased. Furthermore, since the thickness of the organic thin film can be made thick or thin, there is an advantage that the degree of freedom in design is increased.

FIGS. 6 and 7 are plan views showing other embodiments of the present invention. In Figures 1 and 2,
The same numbers as in the figures indicate the same components. In these examples, the rectangle 70 shown in dashed lines
1 and 2 show elements included on the same bottom electrode shown in FIGS. 1 and 2. However, the integrated circuit 8 is not included. Further, electrodes formed on the upper and lower surfaces of the vibrating body element 70 are connected to a part of the peripheral circuit 8 via aluminum wiring (not shown). When a plurality of the vibrating body elements 70 are arranged as shown in the embodiments of FIGS. 6 and 7, ultrasonic waves can be strongly radiated to a small angle in the front, or ultrasonic waves can be strongly received only in a small angle in the front. You can
It has the characteristic of being less distracted by surrounding noise. Furthermore, by using the silicon anisotropic etching technique described above, it is possible to simultaneously form the vibrating body elements 70 with exactly the same shape, so there is no problem in terms of quality and manufacturing time. It has the advantage that there is no In addition to the embodiments shown here, the area of the central vibrating body element 70 is increased, and the vibrating body elements 70 increase as they move toward the periphery.
There is also an embodiment in which the area is reduced (not shown).
In this case, there is an advantage that the above-mentioned directivity is further improved and a high-quality device with less noise can be provided.

FIG. 8 shows a plan view of an embodiment of the second invention of the present application. In the figure, the same numbers 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 vibrating body element 70 are arranged separately from each other, and are each connected to the peripheral circuit 8 via aluminum wiring. Therefore, in the ultrasonic transducer having the configuration of this embodiment, it is possible to apply voltages having different intensities and phases to each vibrating body element 70. In particular, by applying voltages with different phases to each vibrating body element 70, the directions of ultrasonic wave transmission and reception can be changed. It has the feature of being able to provide a sonic transducer. In this embodiment, the electrodes on the bottom surface of each vibrating body element 70 are separated for each vibrating body element 70, but conversely, the electrodes on the bottom surface of each vibrating body element 70 are made common and the electrodes on the top surface of each vibrating body element 70 are separated. Even if the electrode 49 is separated for each vibrator element 70, a device having the same effect as above can be realized. Although FIG. 8 shows an ultrasonic transducer array with one row and five columns, there is no need to limit the number of vibrating body elements 70 at all. For example, in the embodiment shown in FIG. 7, if the electrodes on the upper and lower surfaces of the vibrating body element 70 are arranged separately for each vibrating body element 70 and each electrode is connected to the peripheral circuit 8, electrical power is generated in a two-dimensional direction. A two-dimensional ultrasound transducer capable of scanning can be realized. Furthermore, in the ultrasonic transducer array described in this embodiment, compared to the conventional technology, the lower surface electrodes of each vibrating body element 70 can be formed simultaneously and easily using ordinary IC process technology. This is a big advantage.

In addition, in the embodiment in which the lower electrode or the upper electrode is separated, one vibrating body element 70 is as shown in FIG.
Although the explanation has been made assuming that the etching hole has a plurality of etching holes as shown in Fig. 2, it is not limited to this.
It may be considered that one etched hole in the figure corresponds to one vibrator element.

The present invention has been described in detail by giving examples. The configuration of the present invention is applicable regardless of whether the ultrasonic wave used as a signal changes continuously or changes in a pulsed manner with only one or a few wavelengths. This also holds true regardless of whether the ultrasonic wave has a single wavelength or multiple wavelengths. Furthermore, in the embodiment of the present invention, air was trapped in the hole under the vibrating body;
In addition to this configuration, there is also a configuration in which an opening is made at the bottom of the hole to allow air to flow. Furthermore, the present invention also includes a configuration in which the influence of the back side of the device is reduced by placing a sound-absorbing substance such as a sponge on the outside of the hole, and a configuration in which a horn is placed in front of the vibrating body to increase sensitivity. include.

In the above embodiments, the sensitivity of ultrasonic transmission and reception can be increased by increasing the area or decreasing the thickness of the organic thin film that contributes to vibration. Furthermore, the sensitivity can also be increased by making the CVDSiO ₂ film 3 between the organic thin film and the lower electrode thinner.
However, in this case, changes in the frequency characteristics of the device occur at the same time, so when designing an ultrasonic sensor, take the above effects into account and optimize the sensitivity, frequency characteristics, electroacoustic conversion efficiency, etc. The dimensions of the vibrating body and the CVDSiO ₂ film 3 must be determined so as to

In the above embodiment, the insulating film shown in FIG.
Although CVDSiO ₂ film 3 was used, it is not limited to this.
Any material such as Si ₃ N ₄ , SiO _x N _y , polyimide, etc. that can be adhered to the surface of the lower electrode 6 in a thin film form by CVD, sputtering, coating, or the like can be used.

(Effects of the Invention) As described above, according to the present invention, it has become possible to provide an integrated ultrasonic transducer that is highly sensitive, small in size, and lightweight with little variation in characteristics. As a result, it has become possible to utilize high-performance ultrasonic transducers for detecting proximity sense and the like in fields such as industrial robots. Furthermore, the ultrasonic transducer of the present invention is a conventional semiconductor IC.
Since it can be manufactured in large quantities using a manufacturing method that matches the manufacturing process technology, manufacturing costs can be reduced. These effects are remarkable and the present invention is effective.

[Brief explanation of the drawing]

Figures 1 and 2 are a plan view and a sectional view of an embodiment of the first invention of the present application, respectively, and Figures 3 a to e
4 is a conceptual diagram showing an example of a method for manufacturing the embodiment of the first invention of the present application, FIG. 4 is a sectional view of a conventional ultrasonic transducer, and FIG. 5 is a sectional view of a conventional electrostatic transducer. The principle diagram, FIGS. 6 and 7 are plan views showing other embodiments of the first invention of the present application, and FIG. 8 is a plan view showing an embodiment of the ultrasonic transducer array according to the second invention of the present application. . 1... Silicon substrate, 3... CVDSiO ₂ film, 6
... lower electrode, 8 ... integrated circuit, 10 ... organic thin film, 12 ... etching hole, 20 ... SiO ₂ film,
30... Opening, 41... Metal case, 42... Plastic case, 43... Protective screen, 4
4, 45... Electrode terminal, 46... Leaf spring, 47...
...Aluminum alloy plate, 48...Polyester film,
49... Upper electrode, 51... Mechanical element, 51a
... Vibration plate, 51b ... Fixed plate, 52 ... Electrical element, 53 ... Bias voltage, 54 ... Resistance, 5
5... Transmitting and receiving circuit, 70... Vibrating body element.

Claims (1)

[Claims] 1. An ultrasonic transducer comprising an organic 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, An insulating film is provided between the first electrode and the second electrode so as to be fixed to the surface of the second electrode, and the insulating film is electrically connected between the second electrode and the semiconductor substrate. An ultrasonic transducer characterized in that a second electrode is provided in an area that is insulated and includes at least a side surface of the hole provided on the surface of a semiconductor substrate. 2. The ultrasonic transducer according to claim 1, wherein the first electrode is placed in direct contact with the oxide film. 3 Comprising an organic 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, the first electrode and the second electrode An insulating film is provided between the holes so as to be fixed to the surface of the second electrode, and the second electrode and the semiconductor substrate are electrically insulated by the insulating film. A plurality of ultrasonic transducers each having a second electrode provided in an area including at least a side surface are arranged in an array, and each ultrasonic transducer has an electrode on at least one side of the first and second electrodes. An ultrasonic transducer characterized by being capable of inputting and outputting mutually independent electrical signals.