JPH07121160B2 - Ultrasonic transducer - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic transducer, and more particularly, to a structure of a high-performance, small-sized and lightweight aerial ultrasonic transducer that can be used for detecting a sense of proximity of an industrial robot. It is a thing.

(Prior Art and Its Problems) Conventionally, in the field of industrial robots, a solid-state image sensor using a visible light such as a CCD has 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 that uses ultrasonic waves instead of visible light to recognize a target object has appeared. 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.
In particular, when trying to radiate ultrasonic waves into the air by vibrating a certain surface, the response (acoustic impedance) of the air to that surface is much smaller than that of liquid or solid,
Emission of ultrasonic waves with high intensity is difficult. Therefore,
It is necessary not only to design the mechanical element so that the ultrasonic waves are efficiently radiated, but also to devise the electrical element so that a 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 defects will be described.

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,
A groove 101 having a depth of several tens to several hundreds μm is formed in the center. On the upper surface of the 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. The surface of the polyester film 48 is on the surface opposite to the surface in contact with the aluminum alloy plate 47,
An electrode 49 made of gold foil or the like is vapor-deposited. Reference numeral 43 in the figure is fixed to the protective screen metal case 41, and 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 attached to the metal case 41.
Is pressed against. The leaf spring 46 is fixed to the plastic case 42. 44 and 45 are electrode terminals, 44 is formed integrally with the leaf spring 46, while 45 is a metal case 41.
It is configured integrally with. 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.
Is equal to Therefore, when a voltage is applied to the front electrode terminals 44 and 45, a voltage equal to this applied voltage is applied to the aluminum alloy plate 47.
Between the electrode 49 and the electrode 49
Bend 48. Therefore, when the voltage applied to the electrode terminals 44, 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 radiate to the front surface. To be done. FIG. 5 is a diagram showing the principle of the electrostatic ultrasonic transducer described in FIG. 4, and is composed of a mechanical element 51 that vibrates and an electrical element 52 other than this. The mechanical element 51 is composed of a vibrating plate 51a and a fixed plate 51b.
It has the structure shown in the figure. On the other hand, the electric element 52 is composed of 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 to the fixed plate 51b.
It is pulled by and is bent. Then, when an AC voltage smaller than the bias voltage 53 is generated in the oscillation circuit 55, the oscillation circuit
It changes as follows depending on the polarity of the voltage generated across 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 vibration plate 51a and the fixed plate 51b, so that the vibration plate 51a is largely bent. On the other hand, when the polarity of the voltage of the oscillator 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 diaphragm 51a bends less. Therefore, the oscillator circuit 5
When the voltage across the contacting circuit is periodically changed by 5, the diaphragm 51a vibrates, and ultrasonic waves are radiated to the front surface.
The resistor 54 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 vibrating plate 51a and the fixed 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 diaphragm 51a is vibrated by the ultrasonic waves entering from the outside, and the capacity between the diaphragm 51a and the fixed plate 51b is changed. Therefore, a traffic current flows in the receiving circuit 55, and the ultrasonic wave can be received by amplifying and compensating the traffic 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. In fact, it is known that the wiring connecting the electrodes of the arrayed transducers will 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 electrical elements of an ultrasonic transducer are integrated by utilizing silicon IC process technology and mechanical elements for vibrating the elements are integrally formed to realize a small size and light weight. However, the ultrasonic transducer with the conventional structure has a drawback that it is impossible to reduce the size and weight of the device because it is impossible to manufacture the mechanical element in conformity with the silicon IC process technology. .

(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 aerial ultrasonic transducer.

(Structure of the Invention) In order to achieve the above object, the present invention provides an oxide film on the upper surface of a rectangular silicon thin plate containing a high concentration of boron impurities, and an upper electrode on the upper surface of a rectangular piezoelectric thin film and a lower surface on the lower surface. An electrode is provided on the upper surface of the oxide film to form a vibrating body, a peripheral circuit is provided in the peripheral portion on the silicon substrate, and two vibrating bodies are formed by connecting two opposite sides of the lower surface of the vibrating body to the silicon substrate. A plurality of dimensions are provided, a polyimide resin is provided on a part of the upper electrode of the vibrating body and the peripheral circuit, and the upper electrode of the vibrating body and the peripheral circuit are connected through a through hole formed in the polyimide resin. , A voltage having different intensity and phase is applied to each vibrator.

(Principle of Operation of the Invention) The ultrasonic transducer of the present invention is a monolithic ultrasonic transducer capable of integrating a peripheral circuit with a manufacturing method conforming to the IC process technology of silicon, and has a small rigidity as shown in FIG. A vibrating body mainly composed of a silicon thin plate and a piezoelectric thin film, which has a bridge shape, moves up and down according to the change in the potential difference applied to the upper and lower electrodes of the piezoelectric thin film, and transmits ultrasonic waves. Has been done. When this device is used to receive ultrasonic waves, it flows into an electric circuit by utilizing the fact that the potential difference between the upper and lower electrodes of the piezoelectric thin film changes when the vibrator vibrates by external ultrasonic waves. It can be read as a change in current. In addition, since the vibrating body can be manufactured on the silicon substrate, the oscillation circuit and the receiving circuit can be integrated at the same time by using the silicon IC process technology, and therefore, a high-performance ultrasonic transducer can be manufactured in a small size and a light weight. It became possible to do. Further, by coating the upper and lower electrodes of the piezoelectric thin film of the vibrating body and the integrated circuit with polyimide resin and placing the aluminum wiring on this, it is possible to prevent the aluminum wiring from being cut, and the yield of device fabrication is improved. Significantly improved.

(Example) Hereinafter, the Example of this invention is described with reference to drawings.

1 and 2 show an embodiment of the present invention and correspond to a plan view and a sectional view, respectively. The vibrating body 20 that transmits and receives ultrasonic waves of the present embodiment is
It is mainly composed of a silicon thin plate 2 containing a high concentration of boron impurities (≧ 1 × 10 ²⁰ cm ⁻³ ) and a piezoelectric thin film 4 such as ZnO or AlN. Are integrally connected to the silicon substrate 1 to form a bridge shape. This vibrating body 20 is a groove carved in the silicon substrate 1.
It vibrates up and down in 12 to transmit and receive ultrasonic waves. An upper electrode 5 and a lower electrode 6 are provided on both sides of the main surface of the piezoelectric thin film 4.
Are arranged, and different potential differences are applied or generated when the vibrating body 20 vibrates. An oxide film 3 is inserted between the lower electrode 6 and the silicon thin plate 2 to prevent a current from leaking between the electrode 6 and the thin plate 2. Lower electrode 6
Is also electrically connected to an integrated circuit 8 for driving and receiving formed on the silicon substrate 1 through an aluminum wiring 21 also placed on the oxide film 3. On the other hand, the upper electrode 5
When the integrated circuit 8 and the integrated circuit 8 are connected to each other, the aluminum wiring is often cut due to the presence of a step due to the thickness of the piezoelectric thin film in the conventional wiring path. In order to solve this drawback, a polyimide resin 7 is applied on a part of the upper electrode 5 and the integrated circuit 8, and the polyimide resin 7 has a through hole 11 connected to the upper electrode 5 and a through hole connected to the integrated circuit. A structure was used in which 10 openings were provided and aluminum wiring 9 for conducting the through holes 10 and 11 was formed on the polyimide resin 7. As a result, it has become possible to completely prevent disconnection of the aluminum wiring 9. 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. Further, the ultrasonic transducer of the bridge structure of the present invention has superior durability and can withstand long-term use as compared with the cantilever dyeing structure in which only one side is fixed. On the other hand, compared with a diaphragm structure in which the four sides are fixed, it has a merit that it can take a larger amplitude and is excellent in efficiency.

FIG. 3 shows an example of a procedure for manufacturing an ultrasonic transducer having an embodiment of the present invention. In the drawings, the same reference numerals as those shown in FIGS. 1 and 2 which have been described above as an embodiment of the present invention indicate the same components. The same figure (a)
Is an oxide film 3 on the front and back of the silicon substrate 1 having a (110) plane.
The first part of the
An opening hole 30 having the same shape as the vibrating body 20 in the figure is formed. When forming the opening hole 30, it is necessary to arrange so that the fixed side of the vibrating body 20 of FIG. 1 and the side wall (111) surface of the groove 12 supporting the vibrating body 20 are oriented in the vertical direction. High-concentration boron is diffused through this opening 30 to form a region which will later become the silicon thin plate 2 (FIG. 2B). The entire upper surface is again covered with the oxide film 3, and an opening hole (not shown) having the same shape as the groove 12 of FIG. 1 is formed by the photoetching technique (FIG. 2C). This sample is immersed in an aqueous solution of EDP (ethylenediaminepyrocatechol) or hydrazine to anisotropically etch silicon (FIG. 2 (d)). ED
An aqueous solution of P, hydrazine, etc. has a property that the etching rate on the (100) plane is significantly higher than the etching rate on the (111) plane of silicon (anisotropy), and 1 ×
It has the selectivity that the etching rate of silicon containing high-concentration boron impurities of 10 ²⁰ cm ^-3 or more is extremely small.
Therefore, the silicon thin plate 2 and the groove 12 shown in FIG. 9D can be manufactured by immersing the sample shown in FIG. Then, using a normal silicon IC process technology, an integrated circuit 8 for transmission / reception is formed, and a contact hole 32 for the first wiring is opened in this integrated circuit 8 (FIG. 8E). Then, the lower electrode 6 is formed by vapor deposition or the like ((f) in the figure). It is desirable that the lower electrode has Au as an underlayer of Cr in order to improve the bonding with the oxide film 3, but the lower electrode is not necessarily limited to this, and a metal such as aluminum may be used instead. Moreover, it is necessary to have ohmic conduction with the integrated circuit 8 through the contact hole 32. After that, a piezoelectric material such as ZnO or AlN is deposited on the silicon thin plate 2 by sputtering or the like to form a piezoelectric thin film 4, and an upper electrode 5 is formed on the piezoelectric thin film 4 (FIG. 9 (g)). The piezoelectric thin film 4 is subjected to ordinary dielectric polarization treatment, and the integrated circuit 8
After the second wiring contact hole 33 is opened in the same, a coating process using a polyimide resin, a baking process, and an etching process are sequentially performed, and the process shown in FIG. And the second contact hole 33
A through hole 10 that leads to the. Finally, the aluminum wiring 9 for electrically connecting the upper electrode 5 and the integrated circuit 8 through the through holes 10 and 11 is formed on the polyimide resin 7 ((i) in the figure).

FIG. 6 is a sectional view showing another embodiment of the present invention. In the figure, the same numbers as those in FIGS. 1 and 2 indicate the same components. The embodiment of the present invention is characterized in that the structure shown in FIGS. 1 and 2 is realized by using a silicon substrate having a (110) plane orientation in which high-concentration boron is formed on the surface by epitaxial growth. If this epi-substrate is used, a new step of removing the surface boron layer in the region where the integrated circuit 8 and the groove 12 are formed is required. This is nitric acid
It can be easily realized by using a mixed solution of hydrofluoric acid, acetic acid and the like. Reference numerals 61 and 62 in the same figure show the boron layer remaining after this step. After this, FIG. 3 (c)-
The ultrasonic transducer shown in FIG. 6 can be manufactured by performing the same step as (i). The present invention has the advantages that the step of FIG. 3 (b) is unnecessary and the thickness of the silicon thin plate can be controlled with high accuracy, as compared with the inventions shown in FIGS. 1 and 2 above. There is. Further, in the present invention, a step also exists between the lower electrode 6 and the integrated circuit 8, but similarly to the above, the wiring of the lower electrode 6 and the integrated circuit 8 is made of polyimide resin through a through hole. By connecting via 7, the problem of disconnection could be overcome (not shown).

7 and 8 are plan views showing another embodiment of the present invention. In the figure, the same numbers as those in FIGS. 1 and 2 indicate the same components. In these examples,
A plurality of rectangles 70 indicated by broken lines indicate vibrator elements except the integrated circuit 8 shown in FIGS. 1 and 2. Also,
The 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 embodiment of FIGS. 7 and 8, ultrasonic waves are strongly radiated to a small front angle, or ultrasonic waves of only a small front angle are strongly received. It has the feature that it is less likely to be confused by ambient noise. Further, compared to a single bridge structure having a large area, when divided into a plurality of small bridges as shown in the present embodiment, there is an advantage that harmonic signals other than the fundamental mode can be reduced. Yes, this also helps reduce signal noise. Furthermore, by using the technique of anisotropic etching of silicon described in the explanation of FIG. 3 (d), the vibrator element 70 having the same shape can be accurately formed at the same time. From the point of view, there is no problem at all. In addition to the embodiment shown here, there is also an embodiment in which the area of the vibrator element 70 at the center is increased and the area of the vibrator element 70 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. 9 also shows another embodiment of the present invention. In the figure, the 7th
The same reference numerals as those in the figure indicate the same components. In the embodiment of the present invention, the electrodes formed on the upper surface of the vibrating body element 70 are separately arranged for each vibrating body element 70, and are connected to the peripheral circuit 8 via aluminum wiring. Is characterized by. 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 vibrating body elements 70. In particular, by applying voltages having different phases to the respective vibrating body elements 70, it is possible to change the directions of transmission and reception of ultrasonic waves, and therefore high-performance ultrasonic waves for electrically scanning. The feature is that a transducer can be provided. In this embodiment, the electrodes on the upper surface of the vibrating body element 70 are disassembled for the respective vibrating body elements 70. A device having the same effect as above can be realized by separating the second electrode (not shown) for each vibrator element 70. In FIG. 9, an ultrasonic transducer array of 1 row and 5 columns is shown.
There is no need to limit the number of 70's. For example,
In the embodiment of FIG. 8, the electrodes on the upper surface of the vibrating body element 70 are separately arranged for each vibrating body element 70, and when the respective electrodes are connected to the peripheral circuit 8, the electrodes are electrically scanned in a two-dimensional direction. It is possible to realize a two-dimensional ultrasonic transducer that can be used. Further, in the ultrasonic transducer array described in the present embodiment, the upper electrode of each vibrating element 70 can be simultaneously and easily formed by using a normal IC process technique, which is also large compared with the conventional technique. It is an advantage.

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 vibrating body, but in addition to this structure, there is also a structure in which a hole is opened in the bottom of the groove to allow the air to flow. . In addition, a structure that reduces the influence on the back side of the device by placing a substance such as a sponge on the outside of the groove to absorb sound, and a structure that increases the sensitivity by placing a horn on the front surface of the vibrating body are also available. Included in the invention.

In the above embodiment, the sensitivity of ultrasonic wave transmission and reception can be increased by increasing the area of the vibrating body or decreasing the thickness. However, in this case, the frequency characteristics of the device will change at the same time. Therefore, when designing the ultrasonic sensor, considering the above effects, the vibration body should be optimized to optimize the sensitivity and frequency characteristics. Must determine the dimensions of.

(Effects of the Invention) As described above, according to the present invention, it is possible to supply a high-performance, small-sized and lightweight airborne integrated 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 is consistent with 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]

1 and 2 are a plan view and a sectional view, respectively, of an embodiment of the present invention, FIG. 3 is a conceptual diagram showing an embodiment of a method for manufacturing the embodiment of the present invention, and FIG. FIG. 5 is a sectional view of an ultrasonic transducer, FIG. 5 is a principle view of a conventional electrostatic transducer, FIG. 6 is a sectional view of another embodiment of the present invention, and FIGS. 7 and 8 are other embodiments of the present invention. FIG. 9 is a plan view showing an example, and FIG. 9 is a plan view showing an embodiment of an ultrasonic transducer array according to the present invention. 1 ... Silicon substrate, 2 ... Silicon thin plate, 3 ... Oxide film, 4 ... Piezoelectric thin film, 5 ... Upper electrode, 6 ... Lower electrode, 7 ... Polyimide resin, 8 ... Integrated circuit, 9 , 21 …… Aluminum wiring, 10,11 …… Through hole, 12 …… Groove, 20 …… Vibrator, 30 …… Opening hole, 32,33 …… Contact hole, 41 …… Metal case, 42 …… Plastic Case, 43 …… Protective screen, 44,45 …… Electrode terminal, 46 …… Leaf spring, 47 …… Aluminum alloy plate, 48 …… Polyester film, 49 …… Electrode, 51 …… Mechanical element, 51a ...... Vibration plate, 51b ...... Fixed plate, 52 ...... Electrical element, 53 ...... Bias voltage, 54 ...... Resistance, 55 ...... Transmission and reception circuit, 61,62 ...... High concentration boron layer, 70 ...... Vibratory element.

Claims (1)

[Claims] 1. A rectangular silicon thin plate containing a high concentration of boron impurities is provided with an oxide film on the upper surface, and a rectangular piezoelectric thin film having an upper electrode on the upper surface and a lower electrode on the lower surface is provided on the upper surface of the oxide film. A vibrating body, a peripheral circuit is provided around the silicon substrate, and two or more vibrating bodies in which two opposite sides of the lower surface of the vibrating body are connected to the silicon substrate are two-dimensionally provided. A polyimide resin is provided on part of the peripheral circuit and the peripheral circuit, and the upper electrode of the vibrating body is connected to the peripheral circuit through a through hole formed in the polyimide resin. Furthermore, different strength and phase are set for each vibrating body. An ultrasonic transducer, wherein an applied voltage is applied.