JPH067719B2 - Ultrasonic transducer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an ultrasonic transducer, and more particularly to a structure of a high-performance, small-sized and lightweight ultrasonic transducer that can be used for detecting a sense of proximity of an industrial robot. Is.

(Prior Art and its Problems) Conventionally, in the field of industrial robots, solid-state imaging sensors using visible light such as CCD have been widely used for recognizing the distance, size, shape, etc. of a target object. However, a sensor using visible light has a drawback that it 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 technique has appeared that attempts to use ultrasonic waves for recognizing a target object instead of visible light. In an ultrasonic transducer, ultrasonic waves are transmitted and received by one or a plurality of devices. Therefore, mechanical elements for oscillating and receiving ultrasonic waves and electrical circuits such as an oscillation circuit and a receiving circuit for assisting this are provided. The elements need to be well combined and constructed. Especially, when trying to radiate ultrasonic waves into the air by vibrating a certain surface, the response (acoustic impedance) of the air to this surface is much smaller than that of liquids and solids, so the emission of ultrasonic waves with high intensity Is difficult. Therefore, it is necessary not only to design the mechanical element so that the ultrasonic wave is efficiently radiated, but also to devise the electrical element so that the small signal is compensated and received by the amplification compensation circuit. . However, in the ultrasonic transducers that are commonly used at present, the mechanical element and the electrical element are not integrated but separated. Hereinafter, a conventional example will be described with reference to the drawings, and at the same time, its drawbacks will be described.

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, in which a groove 101 having a depth of several tens to several hundreds of μm is formed in the center. On the upper surface of this groove 101, a polyester film 48 having a thickness of 6 to 20 μm is inserted and fixed by a metal case 41 and an aluminum alloy plate 47. On the surface of the polyester film 48, an electrode 49 of gold foil or the like is vapor-deposited on the surface opposite to the surface in contact with the aluminum alloy plate 47. Reference numeral 43 in the figure is a protective screen and a metal case 41.
It prevents the polyester film 48 from being damaged from the outside. On the other hand, a leaf 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. The leaf spring 46 is fixed to the plastic case 42. 44 and 45 are electrode terminals, 44 is integrally formed with the leaf spring 46, while 45 is integrally formed 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 leaf spring 46, while the potential of the electrode terminal 45 is equal to that of the electrode 49 via the metal case 41. From this, the electrode terminals 44, 45
When a voltage is applied to the plate, 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 the electrostatic force. Therefore, when the voltage applied to the electrode terminals 44 and 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. To be done. FIG. 5 is a diagram showing the principle of the electrostatic ultrasonic transducer described in FIG. 4, in which a mechanical element 51 that vibrates and an electrical element 52 other than this.
It consists of The mechanical element 51 is composed of a vibrating plate 51a and a fixed plate 51b, and has, for example, the structure shown in FIG. On the other hand, the electric element 52 includes a bias voltage 53, a resistor 54, and an oscillation circuit 55 in the case of transmitting ultrasonic waves. Now, when no signal is generated from the oscillation circuit 55, the diaphragm 51a is fixed by the bias voltage 53.
It is pulled and bent by 1b. Then, when an AC voltage smaller than the bias voltage 53 is generated in the oscillation circuit 55, it changes as follows depending on the polarity of the voltage generated across the oscillation circuit 55. That is, when the polarity of the voltage generated across 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 vibrating plate 51a and the fixed plate 51b, so that the bending of the vibrating plate 51a becomes large. On the other hand, when the polarity of the voltage of the oscillation circuit 55 is opposite to that of the bias voltage 53, a potential difference equal to the difference between these voltages is applied to the vibrating plate 51a and the fixed plate 51b, so that the bending of the vibrating plate 51a becomes small. Therefore, when the voltage across the oscillating circuit is periodically changed by the oscillating circuit 55, the diaphragm 51a vibrates and ultrasonic waves are radiated to the surface. The resistor 54 is the diaphragm 51a.
It 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 fixing plate 51b and the fixing plate 51b. Although the case of transmitting ultrasonic waves has been described above, in the case of receiving waves, 55 in FIG. 5 may be used as a receiving circuit for performing amplification compensation and the like. At this time, the ultrasonic wave entering from the outside vibrates the vibrating plate 51a and changes the capacitance between the vibrating plate 51a and the fixed plate 51b. Therefore, an alternating current flows in the receiving circuit 55, and the ultrasonic wave can be received by amplifying and compensating the alternating current. The conventional electrostatic ultrasonic transducer has been described above with reference to examples. As shown here, in the ultrasonic transducer, it is inevitable to combine the mechanical element and the electric element, and the ultrasonic transducer shown in FIG. 4 as a conventional example also has the mechanical element of FIG. The whole was configured with an external electric circuit. Therefore, when it is attempted to realize a high-performance device with the conventional structure, the area occupied by the electrical elements is further increased, and the device tends to be large. This trend has become increasingly problematic when trying to realize ultrasonic transducer arrays. It is known that the wiring connecting the electrodes of the arrayed transducers can actually be quite large. On the other hand, as mentioned above, a high-performance and small-sized ultrasonic transducer is required in the field of industrial robots. Therefore, there has been a strong demand for a device in which the electrical elements of the ultrasonic transducer are integrated by utilizing the silicon IC process technology and the mechanical elements for vibrating the elements are integrally formed to realize a small size and light weight. However, in the ultrasonic transducer having the conventional structure, it is impossible to manufacture the mechanical element in conformity with the IC process technology of silicon, so that there is a drawback that the device cannot be made smaller and lighter. .

(Object of the Invention) An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and provide a high-performance, small-sized and lightweight ultrasonic transducer.

(Structure of the Invention) According to the present invention, in an electrostatic ultrasonic transducer including a diaphragm having a first electrode on one side of the surface and a second electrode facing the diaphragm via a spacer. An ultrasonic transducer in which the diaphragm is composed of a composite layer of an inorganic insulating film and a polymer film, and the spacer is composed of silicon; and a diaphragm having a first electrode on one side of the surface. In the electrostatic ultrasonic transducer composed of a second electrode facing the diaphragm via a spacer, the diaphragm is composed of a composite layer of an inorganic insulating film and a polymer film, and the spacer is composed of silicon. Ultrasonic transducer as one element, and multiple elements on the same silicon substrate As a result, an ultrasonic transducer is obtained in which at least one of the first and second electrodes is separated for each element, and different voltages are applied to the diaphragm of each element for each element.

(Principle of Operation of the Invention) An ultrasonic transducer according to the present invention is a monolithic ultrasonic transducer capable of integrating a manufacturing method and peripheral circuits conforming to silicon IC process technology.
As shown in the figure, the diaphragm, which is mainly composed of a polymer film having a small elastic constant, is deformed according to the change in the potential difference applied to the upper and lower electrodes, and is designed to transmit ultrasonic waves. When this device is used to receive ultrasonic waves, the change in the current flowing in the electric circuit is utilized by utilizing the fact that the capacitance between the upper and lower electrodes of the diaphragm changes when the diaphragm vibrates due to external ultrasonic waves. Can be read as. Further, since the spacer inserted between the diaphragm and the lower electrode is made of silicon, the oscillation circuit and the receiving circuit can be integrated in the region of this spacer by the IC process technology, and thus the high performance is achieved. Performance Ultrasonic transducer can be manufactured in a small size and light weight.

(Example) Hereinafter, the Example of this invention is described with reference to drawings. FIG. 1 is a sectional view showing an embodiment of the present invention,
FIG. 2 is a conceptual diagram showing the operating principle of the present invention. In the figure, the same reference numerals as those of FIGS. 4 and 5 shown as a conventional example indicate the same constituent elements. The diaphragm 22 for transmitting and receiving ultrasonic waves in this embodiment is composed of a thin inorganic insulating film 1 made of silicon dioxide (SiO ₂ ) and a polymer film 2 made of a polyimide resin having a thickness of several to 20 μm. Since it is constructed, it has a small elastic constant, which makes it easy to deform due to vibration. In addition to the present embodiment, the film 1 is a silicon nitride film (Si ₃ N ₄ ) or Si ₃ N ₄ / S.
A three-layer structure film of iO ₂ / Si ₃ N ₄ or the like may be used, and has a role of protecting the polymer film 2 when the groove 12 is formed by chemically etching the silicon substrate 9. Also, the polymer film 2
With the use of the spin coating method, the thickness can be precisely controlled, and a photoresist may be used as a material other than that of this embodiment. Gold or the like is attached to one surface of the diaphragm 22 having such a structure by vapor deposition or the like to form the first electrode 3. On the other hand, on the back surface of the diaphragm 22, a second electrode 4 is attached on the insulating case 5 such as Bakelite so as to face the first electrode 3.
The diaphragm 22 and the silicon substrate 9 are inserted by the first electrode 3 and the second electrode 4. The silicon substrate 9 functions as a spacer between the diaphragm 22 and the second electrode 4,
An oscillation and reception circuit denoted by 8 is integrated by IC process technology on the surface in contact with the diaphragm 22. On the surface of the silicon substrate 9 opposite to the surface on which the diaphragm 22 is formed, the gold-silicon eutectic alloy 13 is formed.
The silicon substrate 9 is adhered to the electrode 4 and the insulating case 5 by the above. In the figure, 10 and 11 are leads for inputting / outputting signals between the integrated circuit 8 and an external power supply and control device (not shown) via the bonding wire 6 and the aluminum wiring 7, respectively. The lead 11 is
It is connected to the second electrode 4 as shown in the figure, and the same potential as that of the electrode 4 is applied to the terminal of the integrated circuit 8. 2A shows a case where the polarity of the voltage generated across the oscillation circuit 55 is opposite to that of the bias voltage 53,
FIG. 6B shows a case where the polarities of the voltages are the same.
As shown in the figure, the diaphragm 22 is
The displacement is larger than that in the figure (a). Therefore, when the voltage of the oscillating circuit 55 changes in alternating current to change the polarity, the diaphragm 22 is deformed as shown in (a) → (b) → (a) → ... As a result, the diaphragm 22 is deformed. Ultrasonic waves are radiated on the front surface of the. The larger the bias voltage 53 is, the stronger the intensity of the ultrasonic waves is radiated. On the other hand, when the bias voltage 53 is too large, the device may be damaged due to discharge between the diaphragm 22 and the electrode 4. There is. Therefore, the bias voltage 53 should be designed to an appropriate value. As described above, when the device is used for receiving ultrasonic waves, 55 in FIG. 2 may be replaced with an appropriate receiving circuit. At this time, the first electrode 3
Since the capacitance between the second electrode 4 and the second electrode 4 changes in accordance with the deformation of the diaphragm 22, when the ultrasonic wave invading from the outside deforms the diaphragm 22 in the same manner as (a) → (b) → (a) → ... The value of the current flowing across the receiving circuit 55 changes. Ultrasonic waves can be received by appropriately performing signal processing on this current value by the receiving circuit 55. It is needless to say that the transmitting circuit and the receiving circuit described in this embodiment are not particularly limited, and all known circuit technologies are included in the present invention.

FIG. 3 shows an example of a procedure for manufacturing an ultrasonic transducer having an embodiment of the present invention. Figure (a)
The peripheral circuit 32 is formed on the surface of the silicon substrate 30 by using a normal silicon IC process technology.
At this stage, since the oxide film 31 is usually formed on the front and back surfaces of the silicon substrate 30, the oxide film 31 is completely removed by etching (FIG. 7B). Subsequently, an oxide film 31 is formed on the front side of the silicon substrate 30 by the CVD method (FIG. 3C), and thin oxide films are further formed on the front and back surfaces of the silicon substrate 30 by the thermal oxidation method (FIG.
(d)). The reason for performing the above procedure is that the silicon substrate 30
This is because the stress generated in the oxide film 31 on the front surface of the is suppressed to a low level, and it is necessary for the etching to stop at the oxide film 31 at the stage of FIG. Now, a polyimide resin or the like is spin-coated on the front side of the silicon substrate 30 of FIG. 3D, and the polymer film 33 is formed by baking and solidifying the polyimide resin, and then the electrodes of the peripheral circuit 32 are protected by a photoresist or the like. A contact hole 34 for taking it out is opened (FIG. 6 (e)). Then, after depositing aluminum or the like on the front side of the silicon substrate 30, unnecessary portions are removed to form electrodes 35 and aluminum wirings 38 (FIG. 7F). The oxide film 31 in the region of the groove pattern 36 is removed from the back side of the silicon substrate 30 (FIG. 9 (g)). After that, the silicon substrate 30 is etched using a jig in which only the back side of the silicon substrate 30 is brought into contact with the etching solution, and the groove 3 is formed.
Form 7. At this time, as an etching liquid for silicon,
When an anisotropic etching solution such as KOH or hydrazine is used, there is no unnecessary etching in the lateral direction.
7 can be formed with precise control. When a large stress is present in the oxide film 31 formed on the front side of the silicon substrate 30, a crack is generated in the oxide film 31 covering the groove 37 when the groove 37 shown in FIG. That is, the polymer film 33 is etched through the cracks. Therefore, care must be taken not to cause a large stress in the oxide film 31 on the front side of the silicon substrate 30.

6 and 7 are plan views showing another embodiment of the present invention. In the figure, the same numbers as in FIG. 1 indicate the same components. In these examples, a plurality of rectangles indicated by broken lines indicate the diaphragm 22. Also,
The electrode 3 formed on the upper surface of the diaphragm 22 is connected to the peripheral circuit 8 via the aluminum wiring 60 and the contact hole 61.
Connected with some of. In these figures,
The aluminum wiring connecting the peripheral circuits 8 is omitted in the drawing. When a plurality of the diaphragms 22 are arranged as shown in the embodiment of FIGS. 6 and 7, ultrasonic waves are strongly radiated to a small front angle, or ultrasonic waves of only a small front angle are strongly received. The feature is that it is less likely to be disturbed by ambient noise. Also,
Compared to a single large area diaphragm structure,
When divided into a plurality of small diaphragms as shown in this embodiment, there is an advantage that the signals of the harmonics other than the fundamental mode can be reduced, and this is also useful for reducing the noise of the signals. Furthermore, when the technique of anisotropic etching of silicon described in the description of FIG. 3 (h) is used, the diaphragms 22 having exactly the same shape can be simultaneously formed, so that the quality and the time required for manufacturing can be reduced. It has the feature that there is no problem at all. In addition to the embodiment shown here, there is also an embodiment in which the area of the central diaphragm 22 is increased and the area of the diaphragm 22 is decreased toward the periphery (not shown). In this case, there is an advantage that the above directivity is further improved and a high-quality device with less noise can be provided.

FIG. 8 also shows another embodiment of the present invention. In the figure, the sixth
The same reference numerals as those in the figure indicate the same components. In the embodiment of the present invention, the electrodes 3 formed on the upper surface of the diaphragm 22 are separately arranged for each diaphragm 22, and the aluminum wiring 60 and the contact hole 61 are respectively provided.
It is characterized in that it is connected to the peripheral circuit 8 via. Therefore, in the ultrasonic transducer having the configuration of this embodiment, it becomes possible to apply voltages having different intensities and phases to the respective diaphragms 22.
In particular, by applying voltages having different phases to the diaphragms 22, it is possible to change the directions of transmission and reception of ultrasonic waves. Therefore, a high-performance ultrasonic transducer for electrically scanning can be provided. It has the feature that it can be provided. In the embodiment shown in FIG. 8, the electrode 3 on the upper surface of the diaphragm 22 is separated for each diaphragm 22, but in addition to this, the electrode 3 on the upper surface of the diaphragm 22 is shared and the second electrode on the lower surface of the diaphragm 22 is shared. A device having the same effect as above can be realized by separating (not shown) for each diaphragm 22. Further, both the first electrode and the second electrode may be separated for each diaphragm 22. Although FIG. 8 shows an ultrasonic transducer array of 1 row and 5 columns, the number of diaphragms 22 need not be limited. For example, in the embodiment of FIG. 7, when the electrodes 3 on the upper surface of the diaphragm 22 are separately arranged for each diaphragm 22 and each electrode is connected to the peripheral circuit 8, the electrodes 3 are electrically scanned in a two-dimensional direction. It is possible to realize a two-dimensional ultrasonic transducer capable of performing. Further, in the ultrasonic transducer array described in this embodiment, the upper electrode of each diaphragm can be simultaneously and easily formed by using a normal IC process technique, which is a great advantage over the conventional technique. .

The present invention has been described in detail above with reference to examples.
The configuration of the present invention is established regardless of whether the ultrasonic wave used as a signal changes continuously or changes in a pulsed manner with only a few wavelengths.
Further, it is established regardless of whether the wavelength of ultrasonic waves is single or plural. Further, in the embodiment of the present invention, the air is confined in the groove below the diaphragm, but in addition to this structure, there is a structure in which a hole is opened at the bottom of the groove to allow the air to flow. Furthermore, the present invention also has a configuration in which the influence of the back side of the device is reduced by a method such as placing a substance that absorbs sound such as sponge outside the groove, and a configuration in which a horn is placed in front of the diaphragm to increase the sensitivity. include.

In the above embodiment, the sensitivity of ultrasonic wave transmission and reception is increased by increasing the area of the diaphragm, reducing the thickness, or reducing the thickness of the silicon substrate used as a spacer. Can be higher. However, in this case, the frequency characteristics of the device change at the same time, so when designing the ultrasonic sensor, considering the above effects, the diaphragm and the diaphragm should be optimized to optimize the sensitivity and frequency characteristics. Spacer dimensions must be determined.

(Effects of the Invention) As described above, according to the present invention, it is possible to supply a high-performance, small-sized and lightweight ultrasonic transducer. As a result, it has become possible to use high-performance ultrasonic transducers for detecting proximity sensation in the field of industrial robots and the like. Further, since the ultrasonic transducer of the present invention can be mass-produced by a manufacturing method that matches the conventional silicon IC process technology, the manufacturing cost can be reduced. These effects are remarkable, and the present invention is effective.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention, FIG. 2 is a conceptual diagram showing the operating principle of the present invention, and FIG. 3 is a conceptual diagram showing an embodiment of a method for manufacturing the embodiment of the present invention. 4 is a sectional view of a conventional ultrasonic transducer, FIG. 5 is a principle view of a conventional electrostatic transducer, FIGS. 6 and 7 are plan views showing another embodiment of the present invention, and FIG. FIG. 3 is a plan view showing an embodiment of an ultrasonic transducer array according to the present invention. 1, 31 ... Oxide film 2, 33 ... Polymer film 3, 4, 35, 49 ... Electrode 5 ... Insulating case 6 ... Bonding wire 7, 38, 60 ... Aluminum wiring 8, 32 ... Peripheral circuit 9, 30 ... Silicon substrate 10, 11 ... Lead 12, 37, 101 ... Groove 13 ... Gold-silicon eutectic alloy 22 ... Diaphragm 34, 61 ... Contact hole 36 ... Groove pattern 41 ... Metal case 42 ... Plastic case 43 ... Protective screen 44, 45 ... Electrode Terminal 46 ... Leaf spring 47 ... Aluminum alloy plate 48 ... Polyester film 51 ... Mechanical element 51a ... Vibration plate 51b ... Fixed plate 52 ... Electrical element 53 ... Bias voltage 54 ... Resistor 55 ... Transmitting and receiving circuit.

Claims (2)

[Claims] 1. An electrostatic ultrasonic transducer comprising a diaphragm having a first electrode on one side of a surface thereof and a second electrode facing the diaphragm via a spacer, wherein the diaphragm is made of an inorganic insulating material. An ultrasonic transducer comprising a composite layer of a film and a polymer film, and the spacer being made of silicon. 2. In an electrostatic ultrasonic transducer composed of a diaphragm having a first electrode on one side of a surface and a second electrode facing the diaphragm via a spacer, the diaphragm is made of an inorganic insulating material. An ultrasonic transducer composed of a composite layer of a film and a polymer film, and the spacer made of silicon is used as one element, and a plurality of the elements are arranged on the same silicon substrate to form the first or second electrode. An ultrasonic transducer, wherein at least one of the elements is separated for each element, and a different voltage is applied to the diaphragm of each element for each element.