JPH05672B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an ultrasonic transducer, and in particular to a high-performance, compact and lightweight electrostatic aerial transducer that can be used for detecting proximity sense in industrial robots. The present invention relates to the structure of a sonic 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 reduce the size and weight of 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, and a plurality of holes 101 having a depth of several to several tens of μm are formed on the surface by machining. On the upper surface of this hole 101, a polyester film 48 having a thickness of 6 to 20-odd micrometers is sandwiched and fixed between the metal case 41 and the aluminum alloy plate 47. An electrode 49 made of gold foil or the like is 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 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 fixed to the plastic case 42. 44 and 45 are electrode terminals, 44 is constructed integrally with the leaf spring 46, and 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,
On the other hand, the potential of the electrode terminal 45 is equal to that of the electrode 49 via the metal case 41.

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, the polarity of the voltage of the oscillation circuit 55 is set to the bias voltage 5.
In the case opposite to 3, a potential difference equal to the difference between these voltages is applied to the diaphragm 51a and the fixed plate 51b, so that the flexure of the diaphragm 51a becomes small. Therefore,
When the oscillation circuit 55 periodically changes the voltage across the oscillation circuit, the diaphragm 51a vibrates and ultrasonic waves are 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. The case of transmitting ultrasonic waves has been described above, but in the case of receiving waves, the fifth
55 in the figure may be a receiving circuit that performs amplification compensation and the like. At this time, the diaphragm 51a vibrates due to the ultrasonic waves entering from the outside, and the capacitance between the diaphragm 51a and the fixed plate 51ab 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
This corresponds to the gap between the diaphragm 51a and the fixed plate 51b shown in the figure, and when the dimensions and outer shape vary, the force driving the diaphragm 51a varies,
In the end, there was a drawback that the transmission and reception characteristics of ultrasonic waves were not constant. Furthermore, as mentioned earlier, in ultrasonic transducers, the combination of mechanical and electrical elements is inevitable.
When attempting to realize a device with even higher performance using a conventional structure, the area occupied by the electrical elements tends to become larger and the device becomes 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 airborne ultrasonic transducer with uniform characteristics, high performance, small size and light weight.

(Means for Solving Problems) According to the present invention, a minute hole is provided in a semiconductor substrate, a lower electrode is provided on the surface of the hole, and an upper electrode is provided on one side covering the area where the hole is provided and the area around it. An ultrasonic transducer is provided with an organic thin film on which a conductive thin film is formed, and a microscopic cavity is formed between the organic thin film and the hole, wherein the surrounding area and the hole are formed. An ultrasonic transducer characterized in that a step is provided between regions so that the former is lower than the latter, and a plurality of such ultrasonic transducers are arranged in an array, and the upper part of each transducer is arranged in an array. Alternatively, there can be obtained an ultrasonic transducer characterized in that mutually independent electrical signals can be input and output to at least one of the lower electrodes.

(Function) The ultrasonic transducer of the present invention is an electrostatic ultrasonic transducer that has a manufacturing method compatible with silicon IC process technology and enables integration of peripheral circuits, as shown in Fig. 2. Ultrasonic waves are transmitted by a polyester film, which is an elastic vibrating body, moving up and down according to changes in the potential difference applied to electrodes above and below the polyester film. On the other hand, when this device is used to receive ultrasonic waves, the polyester membrane vibrates due to the pressure of external ultrasonic waves, and as a result, the potential difference between the upper and lower electrodes of the polyester membrane changes. It is possible to detect the pressure of external ultrasound waves as a change in the value of current flowing through an electrical 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 necessary to bring the polyester film into close contact with the lower electrode provided on the silicon substrate. In the present invention, as shown in FIG. 2 as an example, by making the surface of the lower electrode higher than the outer peripheral surface of this electrode,
We have achieved close contact between the polyester film and the lower electrode. In addition, since the ultrasonic transducer of the present invention uses a silicon substrate, (1) holes can be made with high accuracy on the silicon substrate using silicon micro-etching technology, and device characteristics resulting from the manufacturing process can be (2) The oscillator circuit and receiver circuit can be integrated using silicon IC process technology, making it possible to manufacture high-performance ultrasonic transducers in a compact and lightweight manner. Ta.

(Example) Hereinafter, an example of the present invention 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, or the like is deposited on the upper surface of the polyester film 48, which is an organic thin film that transmits and receives ultrasonic waves in this embodiment. This polyester film 48 covers the silicon substrate 1
The ultrasonic wave is transmitted and received by vibrating up and down above the etched hole 12 that is not penetrated. An upper electrode 49 and a lower electrode 6 are arranged on both sides of the main surface of the polyester film 48, and when transmitting waves, an AC voltage is applied to vibrate the polyester film 48. When receiving waves, the polyester film 48 vibrates to generate voltage. One main surface of the silicon substrate 1 is processed so that the surface of the lower electrode 6 is higher than the surface height of the outer periphery 29 of the lower electrode, as shown in FIG. this is,
It serves to bring the lower electrode 6 and the polyester film 48 into close contact with each other, and reduces the minute gap (not shown) that actually exists between the surface of the lower electrode 6 other than the etched hole 12 and the polyester film 48. can do. The capacitance between the upper electrode 49 and the lower electrode 6 caused by this minute gap reduces the sensitivity of the wave transmission/reception characteristics of the transducer, so it is desirable to reduce this capacitance. With the configuration according to the present invention, the distance between the upper electrode 49 and the lower electrode 6 can be reduced, and as a result, the sensitivity of the wave transmission and reception characteristics of the device can be increased. Note that 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 fabricated on the silicon substrate 1 via an aluminum wiring (not shown) also placed on the oxide film 3. . In addition, the etching hole 12
In order to finish the dimensions and shape with high precision,
For example, it is manufactured by applying silicon anisotropic etching technology. This means, for example, that a plurality of squares with one side aligned in the <110> direction are placed on one side of a silicon substrate 1 whose main surface is in the (100) direction.
After forming a pattern on the SiO ₂ film using photolithography, the sample is immersed in an anisotropic etching solution such as hydrazine. In this case, the etching hole 1 is in the shape of a pyramid-shaped square pyramid.
One of the features of this method is that the silicon etching automatically stops when 2 is completed. In addition, 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, it is possible to immerse the sample in a liquid and perform etching. Because we do
It has the advantage of being able to process a large amount of samples at once. On the other hand, the outer periphery 29 of the lower electrode is
When the etching hole 12 is produced, it can be produced simultaneously using an anisotropic etching technique.

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 an opening 30 having the same shape as the etching hole 12 in Figure 1 and a lower electrode formed by using photolithography on a silicon substrate 1 having a (100) plane with an oxide film 3 on both sides. An opening 31 for the outer periphery 29 is formed. When forming the openings 30 and 31, it is necessary to arrange them so that the sides of the etched holes 12 in FIG. 1 face in the <110> direction. This sample is immersed in an aqueous solution of EDP (ethylenediamine pyrocatechol) or hydrazine to perform silicon anisotropic etching (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 12 and grooves 3 shown in Figure b can be formed
2 can be produced. Next, the sample is placed in the oxidation furnace again in order to form an oxide film 3 in the etching holes 12 and grooves 13, and then a normal silicon
Using IC process technology, an integrated circuit 8 for transmission and reception is formed (c in the same figure). Next, aluminum wiring (not shown) is connected to the lower electrode 6 and the integrated circuit 8.
is formed by vapor deposition or the like (d in the same figure). The lower electrode is
Cr base layer to improve bonding with oxide film 3.
Although it is desirable to have Au on top, it is not necessarily limited to this, and metals such as aluminum may be used instead. Thereafter, the polyester film 48 with the upper electrode 49 deposited thereon is adhered to the silicon substrate 1, and then the device is mounted in a package.

FIGS. 6 and 7 are plan views showing an embodiment of the second invention of the present application. In the figures, the same numbers as in FIGS. 1 and 2 indicate the same components.
In these examples, the rectangle 7 indicated by the dashed line
0 indicates a vibrating body element included on the same lower electrode shown in FIGS. 1 and 2. However, the integrated circuit 8 is not included. In addition, the vibrating body element 70
Electrodes formed on the upper and lower surfaces of are connected to a part of the integrated 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. It has the advantage of being less distracting from 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 embodiment shown here, the central vibrator element 70
There is also an embodiment (not shown) in which the area of the vibrating body element 70 is increased and the area of the vibrating body element 70 is decreased toward the periphery. 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.

FIGS. 8 and 9 also show other embodiments of the second invention of the present application, and correspond to a plan view and a sectional view, respectively. In the figure, the same numbers as in FIG. 6 indicate the same components. In the embodiment of the present invention, the lower electrodes 6 formed on the vibrating body element 70 are arranged separated from each other via the outer periphery 29 of the lower electrodes, and are each connected to the integrated circuit 8 via aluminum wiring. There is something special about being there. 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 lower surface of the vibrating body element 70 are separated for each vibrating body element 70, but
Conversely, even if the electrodes on the bottom surface of each vibrating body element 70 are made common and the electrodes 49 on the top surface of each vibrating body element 70 are separated for each vibrating body element 70, a device having the same effect as described above can be realized. be able to. 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 integrated circuit 8, electrical power is generated in two-dimensional directions. A two-dimensional ultrasound transducer capable of scanning can be realized. In addition, in the ultrasonic transducer array described in this embodiment, the lower surface electrode of each vibrator element 70 is
Another major advantage over conventional techniques is that they can be formed simultaneously and easily using IC process technology.

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.

Note that in the above embodiments, the sensitivity of ultrasonic wave transmission and reception can be increased by increasing the area of the vibrating body or decreasing its thickness. 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 vibrator must be determined so that

(Effects of the Invention) As explained above, according to the present invention, it has become possible to provide a high-performance, small-sized, lightweight aerial integrated ultrasonic transducer 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. Also,
The ultrasonic transducer of the present invention can be manufactured in large quantities using a manufacturing method that is compatible with conventional silicon IC process technology, so that manufacturing costs can be reduced. These effects are significant;
The present invention is effective.

[Brief explanation of the drawing]

1 and 2 are a plan view and a sectional view, respectively, of an embodiment of the first invention of the present application, and FIGS. 3 a to d
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 an embodiment of the second invention of the present application, and FIGS. 8 and 9 show an embodiment of the ultrasonic transducer array according to the second invention of the present application. Plan and sectional views. DESCRIPTION OF SYMBOLS 1...Silicon substrate, 3...Oxide film, 6...Lower electrode, 8...Integrated circuit, 12...Etching hole, 29...
outer periphery of the lower electrode, 30, 31...opening, 32...groove,
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 element, 51a... Vibration plate, 51b... Fixed plate, 52...
Electrical element, 53...bias voltage, 54...resistance,
55... Transmitting and receiving circuit, 70... Vibrating body element.

Claims (1)

[Scope of Claims] 1. A device in which a minute hole is provided in a semiconductor substrate, a lower electrode is provided on the surface of the hole, and a conductive thin film is formed on one side of the semiconductor substrate to cover the area where the hole is provided and the area around it. The ultrasonic transducer is provided with a body thin film and a microscopic cavity is formed between the organic thin film and the hole, and a step is provided between the surrounding area and the area where the hole is provided so that the former is An ultrasonic transducer characterized by being lower than the latter. 2 A microscopic hole is formed in a semiconductor substrate, a lower electrode is provided on the surface of the hole, and an organic thin film is provided covering the area where the hole is provided and the area around it with a conductive thin film formed on one side to serve as the upper electrode. An ultrasonic transducer in which a microscopic cavity is formed between an organic thin film and a hole, and a step is provided between the surrounding area and the area where the hole is provided so that the former is lower than the latter. An ultrasonic transducer characterized in that a plurality of ultrasonic transducers are arranged in an array, and mutually independent electric signals can be input and output to at least one of the upper or lower electrode of each transducer. Yusa.