JPH0476560B2 - - 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 a method of manufacturing 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 oscillate and receive ultrasonic waves, as well as oscillating circuits, receiving circuits, etc. that assist in this process. It is necessary to properly combine electrical elements. 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 this mechanical element 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 micrometers 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 a metal case 41 and an aluminum alloy plate 47. The surface of the polyester film 48 has an electrode 49 made of gold foil or the like on the surface opposite to the surface in contact with the aluminum alloy plate 47.
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.
is 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.
Equal to 9. As a result, when a voltage is applied to the electrode terminals 44 and 45, a voltage equal to the applied voltage is generated between the aluminum alloy plate 47 and the electrode 49, causing the polyester film 48 to bend due to 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 membrane 48 also changes with alternating current, causing the polyester membrane 48 to vibrate, and as a result, ultrasonic waves are directed to the front surface. radiated. FIG. 5 is a diagram showing the principle of the electrostatic ultrasonic transducer described in FIG. The mechanical element 51 is composed of a diaphragm 51a and a fixed plate 51b, and has the structure shown in FIG. 4, for example. On the other hand, the electric element 52 has a bias voltage of 5 when transmitting ultrasonic waves.
3, 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 bypass voltage 53 and is bent. Subsequently, when an AC voltage smaller than the bias voltage 53 is generated in the oscillation circuit 55, the polarity of the voltage generated across the oscillation circuit 55 changes as follows. 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 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, so that the deflection of the diaphragm 51a is reduced. 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. In addition, 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 vibrates.
The capacitance between a 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 corresponds to the gap between the diaphragm 51a and the fixing plate 51b shown in FIG. The drawback was that the transmission and reception characteristics were not constant. Also, as mentioned earlier,
In ultrasonic transducers, the combination of mechanical and electrical elements is unavoidable, and as we try to realize even higher performance devices using conventional structures, the proportion of this electrical element will increase. As the area became larger, there was a trend toward larger devices. In fact, it is known that the wiring connecting the electrodes of arrayed transducers can become quite large just by twisting.
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 a method for manufacturing an airborne ultrasonic transducer that has uniform characteristics, high performance, small size, and light weight.

(Means for solving the problem) A plurality of holes are formed on one main surface of a semiconductor substrate by anisotropic etching, an insulating film is formed on the surface of the holes, and a first electrode film is formed on the insulating film. A method for manufacturing an ultrasonic transducer is obtained, which comprises forming an organic thin film having a second electrode on one surface and pasting it on the surface of the substrate on the side with the hole.

(Function) The ultrasonic transducer of the present invention is a semiconductor
This is an electrostatic ultrasonic transducer that has a manufacturing method compatible with IC process technology and the integration of peripheral circuits.As shown in Figure 2, a polyester film, which is an elastic vibrator, It is designed to move up and down according to changes in the potential difference applied to the electrodes, and to transmit ultrasonic waves. In addition, when this device is used to receive ultrasonic waves, when the polyester membrane is vibrated by external ultrasonic waves, the potential difference between the upper and lower electrodes of the polyester membrane changes. It can now be read out as changes in In addition, since the manufacturing method of the present invention uses a silicon substrate, (1) holes can be made with high accuracy on the silicon substrate using silicon micro-etching processing technology, and ultrasonic transmission and reception of the device resulting from the manufacturing process can be performed. Variations in various characteristics can be suppressed. (2) The oscillation circuit and reception circuit are made of silicon.
Can be integrated using IC process technology,
Therefore, it has become possible to manufacture a high-performance ultrasonic transducer that is small and lightweight.

(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, etc. 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 vibrates up and down above the unpierced etched holes 12 made in the silicon substrate 1 to transmit and receive ultrasonic waves. Upper electrodes 4 are provided on both sides of the main surface of the polyester film 48.
9 and a lower electrode 6 are arranged, and different potential differences are applied or generated when the polyester film 48 vibrates. 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 21 also placed on the oxide film 3 . The etching holes 12 are made by applying silicon anisotropic etching technology, for example, in order to finish the etching holes 12 with high precision in size and shape. For example, a plurality of squares with one side aligned in the <110> direction are printed on one surface of a silicon substrate 1 whose main surface is in the (100) direction using photoresist technology, and then the sample is This is done by immersing it in an anisotropic etching solution such as hydrazine. This case has the advantage that silicon etching is automatically stopped when the pyramid-shaped etched hole 12 is formed. Furthermore, as mentioned above, in order to create the shape of the etching hole 12 using photoresist technology,
This method has the advantage that minute shapes can be formed with high precision, and since the sample is immersed in a liquid for etching, a large amount of sample can be processed at one time.

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 a silicon substrate 1 having a (100) plane with an oxide film 3 on both sides, and an opening 30 having the same shape as the etching hole 12 shown in Figure 1, using photo-etching technology. be. When forming the opening 30, it is necessary to arrange it so that the sides of the etched hole 12 in FIG. 1 face in the <110> direction. This sample is immersed in an aqueous solution of EDP (ethylene diamine pyrocatechol) or hydrazine to perform anisotropic etching of the silicon (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 FIG. 1A in the aqueous solution, the etching hole 12 shown in FIG. Next, the sample is placed in the oxidation furnace again to form an oxide film 3 in the etching hole 12, and then, using normal silicon IC process technology,
An integrated circuit 8 for transmission and reception is formed (c in the same figure). Subsequently, aluminum wiring 21 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 preferably has Au on top of a Cr base to improve bonding with the oxide film 3.
The material is not necessarily limited to this, and metals such as aluminum may be used instead. After this, the upper electrode 49
A polyester film 48 deposited on a silicon substrate 1
After bonding the device to the package, the device is mounted on the package.

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 dashed rectangles 70 indicate 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). As shown in the embodiments of FIGS. 6 and 7, when a plurality of the vibrating body elements 70 are arranged, it is possible to strongly radiate ultrasonic waves at a small angle on the front surface, or strongly radiate ultrasonic waves only at a small angle on the front surface. It has the advantage of being able to receive signals, and 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, 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, 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 also shows another embodiment of the present invention. In the figure, the same numbers as in FIG. 6 indicate the same components. In the embodiment of the present invention, the vibrating body element 70
The structure is characterized in that lower electrodes formed in the structure are arranged separately for each vibrating body element 70, and each is 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 disassembled for each vibrating body element 70, but in addition to this, the electrodes on the bottom surface of each vibrating body element 70 are made common, and Even if the electrodes (not shown) are separated for each vibrating body 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.
A two-dimensional ultrasonic transducer that can electrically scan in two-dimensional directions by separately arranging electrodes on the upper and lower surfaces of 0 for each vibrating body element 70 and connecting each electrode to a peripheral circuit 8. can be realized. In addition, in the ultrasonic transducer array described in this embodiment, each vibrator element 7
Another great advantage over the prior art is that the 0 bottom electrode can be formed simultaneously and easily using normal 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. In addition, in the embodiment of the present invention, air was trapped in the hole under the vibrating body, but 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. be. 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. .

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. 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 process technology, manufacturing costs can be reduced. These effects are remarkable and the present invention is effective.

[Brief explanation of drawings]

1 and 2 are a plan view and a sectional view of an embodiment of the present invention, respectively, FIGS. 3 a to d are conceptual diagrams showing an embodiment of a method for manufacturing the embodiment of the present invention, and FIG. 4 is a sectional view of a conventional ultrasonic transducer, FIG. 5 is a principle diagram of a conventional electrostatic transducer, FIGS. 6 and 7 are plan views showing other embodiments of the present invention, and FIG. The figure is a plan view showing one embodiment of an ultrasonic transducer array according to the present invention. 1... Silicon substrate, 3... Oxide film, 6... Lower electrode, 8... Integrated circuit, 21... Aluminum wiring,
12...Etching hole, 30...Opening, 41...
Metal case, 42...Plastic case, 43
...protective screen, 44, 45...electrode terminal,
46...Plate 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... Transmission and reception circuit, 70... Vibrating body element.

Claims (1)

[Claims] 1. A plurality of holes are formed in one main surface of a semiconductor substrate by anisotropic etching, an insulating film is formed on the surface of the holes, and a first electrode film is formed on the insulating film,
1. A method of manufacturing an ultrasonic transducer, comprising: attaching an organic thin film having a second electrode on one surface to the surface of the substrate on the side with the hole.