JPH0547160B2 - - 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 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, 47 is a circular aluminum alloy plate, and a plurality of holes 101 having a depth of several to several + micrometers are formed on the surface 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 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. 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, the diaphragm 51a vibrates due to the ultrasonic waves that entered from the outside, and the diaphragm 51a and the fixed plate 51
The capacitance between b changes. Therefore, the receiving circuit 55
An alternating current flows through the device, and by amplifying and compensating this, 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 51b and the fixed plate 51 shown in the figure, and when the dimensions and external shape vary,
There was a drawback that the force for driving the diaphragm 51a varied, and as a result, the transmission and reception characteristics of the ultrasonic waves were 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 and provide an ultrasonic transducer with uniform characteristics, high sensitivity, small size, light weight, and good environmental resistance.

(Means for Solving the Problems) According to the present invention, an ultrasonic transformer includes a first electrode made of a metal thin film and a second electrode provided on the surface of a semiconductor substrate having a hole on the surface. In Jusa, an insulating thin film is provided between the semiconductor substrate and the second electrode to insulate them, and an insulating thin film is provided between the first electrode and the second electrode so as to be fixed to the surface of the second electrode. , an ultrasonic transducer characterized in that a signal input/output electrode is provided on the same side of the semiconductor substrate as the second electrode is obtained.

Further, according to the present invention, in an ultrasonic transducer including a first electrode made of a metal thin film and a second electrode provided on the surface of a semiconductor substrate having a hole on the surface, the semiconductor substrate and the second electrode are provided. An insulating thin film is provided between the two electrodes to insulate them, an insulating thin 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 second electrode is attached to the semiconductor substrate. A plurality of ultrasonic transducers each having a signal input/output electrode on the same side as the second electrode are arranged in an array, and independent electrical signals can be input/output to the second electrode of each ultrasonic transducer. An ultrasonic transducer characterized by the following features is obtained.

(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. A metal film 10, which is an elastic vibrating body, is provided on a silicon substrate 1.
Ultrasonic waves are transmitted by moving the CVDSiO ₂ film 3 up and down according to changes in the potential difference applied to the upper and lower electrodes. On the other hand, when this device is used for receiving ultrasonic waves, the metal film 10 vibrates due to the pressure of external ultrasonic waves, and as a result, the above-mentioned
By utilizing the change in capacitance between the upper and lower electrodes of the CVDSiO ₂ film 3, it is possible to detect the pressure of external ultrasound as a change in the value of the current flowing through the electric circuit (to which a bias voltage is applied). It is. At this time, in order to increase the sensitivity of the wave transmission and reception characteristics of the transducer, it is necessary to reduce the distance between the metal film 10 serving as the upper electrode and the lower electrode 6 provided on the silicon substrate 1. In the present invention, the second
As shown in the figure as an example, by fixing a thin insulating film on the surface of the lower electrode 6 by oxidation, CVD, sputtering, coating, etc., good insulation between the metal film 10, which will become the upper electrode, and the lower electrode 6 can be maintained. Tsutsu,
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 oscillation circuit and reception circuit can be integrated using semiconductor IC process technology, making it possible to manufacture high-performance ultrasonic transducers in a compact and lightweight manner. .

(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. The metal film 10 shown in this embodiment functions as a vibrating film for transmitting and receiving ultrasonic waves, and at the same time has the function of an upper electrode for electricity. Although a thin film of gold, amyl, or the like can be used as the material for the metal film 10, a thin film of titanium is particularly preferable because of its low specific gravity. Therefore, titanium is used in this embodiment. This titanium film 10' is
It vibrates up and down above a non-penetrating etched hole 12 made in the silicon substrate 1 to transmit and receive ultrasonic waves. provided on the lower surface of the titanium film 10'.
On both sides of the CVDSiO ₂ film 3, a titanium film 10' as an upper electrode and a lower electrode 6 are arranged.
When transmitting waves, an AC voltage is applied to the titanium film 10'.
vibrate. When receiving waves, a voltage is generated by the vibration of the titanium film 10'. On one main surface of the silicon substrate 1, as shown in FIG. 2, a CVDSiO ₂ film 3 is provided between the lower electrode 6 and the titanium film 10' serving as the upper electrode.
This helps maintain electrical insulation between the titanium film 10' and the lower electrode 6. Furthermore, the said
When the thickness of the CVDSiO ₂ film 3 is about 1 μm, the spatial distance between the metal film 10 serving as the upper electrode and the lower electrode 6 is also about 1 μm. Compared to the case where the distance between the electrodes was approximately the thickness of the polyester film 48 (approximately 12 μm), there is an advantage that the distance between the electrodes can be significantly reduced. Titanium film 1
Since the electrostatic force acting on the electrode 0' is approximately inversely proportional to the square of the distance between the metal film 10 serving as the upper electrode and the lower electrode 6, the distance between the electrodes can be reduced by the configuration according to the present invention. As a result, the sensitivity of the wave transmission and reception characteristics of the device can be increased. 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 an aluminum wiring for signal input/output (not shown), which is also provided on the CVDSiO ₂ film 3.
It is electrically connected to an integrated circuit 8 for driving and receiving fabricated on the silicon substrate 1 via. 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 precision in size and shape. For example, a pattern of multiple square SiO ₂ films with one side aligned in the <110> direction is formed using photolithography technology on one side of a silicon substrate 1 whose main surface is in the (100) direction. After forming using
The sample is immersed in an anisotropic etching solution such as hydrazine. In this case, at the stage when the etched hole 12 in the shape of a pyramid-shaped square pyramid is formed,
The feature is that silicon etching automatically stops. 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. 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 numerals as those in FIG. 1 and Group 2 shown earlier 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 its front and back surfaces are
A square opening 3 having the same shape as the etching hole 12 shown in _FIG .
0 is formed. When forming the opening 30, the side of the etched hole 12 in FIG.
It must be placed facing the direction. This sample is immersed in an aqueous solution of EDP (ethylenediamine pyrocatechol) or hydrazine to perform anisotropic etching of the silicon (Figure b). Aqueous solutions such as EDP and hydrazine have a property that the etching rate for the (100) plane of silicon is significantly higher than that for the (111) plane (anisotropy).
It has Therefore, by immersing the sample shown in FIG. 1A in the aqueous solution, the etching hole 12 shown in FIG. Subsequently, the sample is put into the oxidation furnace again in order to apply the SiO ₂ film 20 to the etching hole 12, and then the integrated circuit 8 for transmitting and receiving is formed using the usual silicon IC process technology (FIG. 3(c)). Next, a thin aluminum 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. form (d in the same figure).

The lower electrode 6 is desirably made of Au on a Cr base to improve bonding with the SiO ₂ film 20, but is not necessarily limited to this.
Metals such as aluminum may be used instead. Thereafter, a titanium film 10' having a thickness of several μm is adhered to the CVDSiO ₂ film 3, and then the device is mounted on a package (see e in the figure).

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 this feature. In addition to the embodiments shown here, there is also an embodiment (not shown) in which the area of the vibrating body element 70 at the center is increased and the area of the vibrating body element 70 is decreased toward the periphery. In this case, the directivity described above is further improved,
This has the advantage of being able to provide a high quality device with less noise.

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 wave reception can be changed, and therefore, high-performance ultrasonic wave that conducts electrical scanning can be achieved. It has the feature of being able to provide a transducer.

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, the electrodes on the upper and lower surfaces of the vibrating body elements 70 are arranged separately for each vibrating body element 70,
By connecting each electrode to the peripheral circuit 8, a two-dimensional ultrasonic transducer capable of electrically scanning in two-dimensional directions 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 the embodiment in which the lower electrode is separated, one vibrating body element 70 has been described as having a plurality of etched holes as shown in FIGS. 1 and 2, but the present invention is not limited to this. One etched hole in FIG. 2 may be considered to correspond 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 metal film that contributes to vibration. Furthermore, the sensitivity can also be increased by making the CVDSiO ₂ film 3 between the metal film and the lower electrode thinner. but,
In this case, changes in the frequency characteristics of the device occur at the same time, so when designing an ultrasonic sensor, consider the above effects 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.

Although the titanium film 10' was used as the metal film 10 in the above embodiment, the present invention is not limited to this. Furthermore, the CVDSiO ₂ film 3 shown in Fig. 2 is not limited to this, but any material that can be adhered to the surface of _the lower electrode 6 in a thin film form by CVD, sputtering, coating, etc., such as Si _{3 N 4} , SiO _x N _y , or polyimide, can be used. be able to.

(Effects of the Invention) As explained above, according to the present invention, it has become possible to provide an integrated ultrasonic transducer that has less variation in characteristics, is highly sensitive, is small and lightweight, and has good environmental resistance. In particular, by using a metal film as the vibrating membrane instead of the conventional polyester membrane, it has become possible to provide a device with good environmental resistance against temperature and the like. the result,
High-performance ultrasonic transducers can now be used to detect proximity sense in fields such as industrial robots. Further, since the ultrasonic transducer of the present invention can be manufactured in large quantities using a manufacturing method that is compatible with conventional semiconductor IC 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 ... metal film, 10' ... titanium film, 12 ... etching hole,
20... SiO ₂ film, 30... Opening, 41... Metal case, 42... Plastic case, 43...
Protective screen, 44, 45... Electrode terminal, 46
...Plate spring, 47...Aluminum alloy plate, 48...
Polyester film, 49... Upper electrode, 51...
Mechanical element, 51a...diaphragm, 51b...fixing plate, 52...electrical element, 53...bias voltage, 54...resistance, 55...transmission and reception circuit, 70...vibrating body element.

Claims (1)

[Claims] 1. An ultrasonic transducer comprising a first electrode made of a metal thin film and a second electrode provided on the surface of a semiconductor substrate having a hole in the surface, wherein the semiconductor substrate and the second An insulating thin film is provided between the first electrode and the second electrode to insulate them, an insulating thin 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 second electrode is attached to the semiconductor substrate. An ultrasonic transducer characterized by having a signal input/output electrode provided on the same side as the electrode. 2. In an ultrasonic transducer equipped with a first electrode made of a metal thin film and a second electrode provided on the surface of a semiconductor substrate having a hole on the surface, an insulating layer is provided between the semiconductor substrate and the second electrode. A thin film is provided to insulate them, an insulating thin film is provided between the first electrode and the second electrode so as to be fixed to the surface of the second electrode, and a signal is placed on the same side of the semiconductor substrate as the second electrode. A plurality of ultrasonic transducers provided with input/output electrodes are arranged in an array, and independent electrical signals can be input/output to the second electrodes of each ultrasonic transducer. Ultrasonic transducer.