JPH07121159B2 - 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 acoustic 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 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 elements such as an oscillation circuit and a receiving circuit for assisting this are provided. It is necessary to make a good combination of physical elements. 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, so the emission of ultrasonic waves with high intensity Is difficult. Therefore, it is necessary to design the mechanical element so that the ultrasonic waves are efficiently radiated, and also to improve 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 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. On the surface of the polyester film 48, an electrode 49 made 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 denotes a protective screen which is fixed to the 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.
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, and 44 is formed integrally with the leaf spring 46, while
45 is formed 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 leaf spring 46, while the potential of the electrode terminal 45 is equal to that of the electrode 49 through the metal case 41. Thus, when a voltage is applied to the electrode terminals 44 and 45, 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, 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. Fifth
The figure is a diagram showing the principle of the electrostatic ultrasonic transducer described in FIG. 4, and is composed of an opportunistic element 51 for vibrating and an electrical element 52 other than this. 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 electrical element 52 is a bias voltage 53, a resistor 54, an oscillator circuit 55 in the case of ultrasonic wave transmission.
Composed of. 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 alternating 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.
The deflection of 51a becomes large. 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 vibrating plate 51a and the fixed plate 51b.
The deflection of the diaphragm 51a becomes small. Therefore, when the voltage across the oscillation circuit is periodically changed by the oscillation circuit 55,
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 vibration plate 51a is vibrated by the ultrasonic waves entering from the outside, and the vibration width 51a
And the capacity between the fixed plate 51b changes. Therefore, the receiving circuit 5
An alternating current flows in 5, and ultrasonic waves can be received by amplifying and compensating this. 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, in order to realize a high-performance device with the conventional structure, the area occupied by these electrical elements becomes larger and larger, 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 a 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, compact and lightweight air conditioning 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 on the periphery of the silicon substrate, and at least one side of the lower surface of the vibrating body is connected to the silicon substrate. A plurality of vibrators are provided two-dimensionally so that each area increases or decreases as the distance from the center of the silicon substrate increases, and a polyimide resin is provided on a part of the upper electrode of the vibrator and the peripheral circuit. The upper electrode of the vibrating body and the peripheral circuit are connected through a through hole formed in the polyimide resin.

(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 and having a shape such as a cantilever dye moves up and down according to the change in the potential difference applied to the upper and lower electrodes of the piezoelectric thin film to transmit ultrasonic waves. Has been devised. 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. Also, 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 wiring on this, it is possible to prevent disconnection of the wiring and significantly improve the device manufacturing yield. did.

(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
A silicon thin plate 2 containing a high concentration of boron impurities (≧ 1 × 10 ²⁰ cm ⁻³ ) and a piezoelectric thin film 4 of ZnO, AlN or the like is mainly used. One side of the rectangular silicon thin plate 2 is a silicon substrate 1. And cantilevered dyeing to form a cantilever dye. The vibrating body 20 vibrates vertically in the groove 12 engraved in the silicon substrate 1 to transmit and receive ultrasonic waves. An upper electrode 5 and a lower electrode 6 are arranged on both sides of the main surface of the piezoelectric thin film 4, 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. The lower electrode 6 is also electrically connected to an integrated circuit 8 for driving and receiving formed on the silicon substrate 1 via an aluminum wiring 21 also placed on the oxide film 3. On the other hand, the upper electrode 5 and the integrated circuit 8
At the time of connecting, the aluminum wiring was often cut due to the presence of a step due to the thickness of the piezoelectric thin film in the path of the conventional wiring. To solve this drawback,
A part of the upper electrode 5 and the integrated circuit 8 are coated with a polyimide resin 7, and the polyimide resin 7 is provided with through holes 11 connected to the upper electrode 5 and through holes 10 connected to the integrated circuit. The aluminum wiring 9 for connecting the through holes 10 and 11 to each other is formed on the polyimide resin 7 to be used. 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.

FIG. 3 shows an example of a procedure for manufacturing a frequency 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 shown as an embodiment of the present invention indicate the same components. In the figure, (a) shows an opening hole 30 having the same shape as the vibrating body 20 shown in FIG. It was done. When forming the opening hole 30, the vibrating body of FIG.
Care must be taken that the four sides of 20 are oriented in the (110) 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). Again, the entire upper surface of the drawing is covered with the oxide film 3, and the opening hole 31 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)). Aqueous solutions of EDP, hydrazine, etc. are (100) less than the etching rate for the (111) surface of silicon.
It has the property that the etching rate with respect to the surface is extremely large (anisotropic), and the etching rate of silicon containing a high concentration boron impurity of 1 × 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, the peripheral circuit 8 for transmission / reception is formed by using a normal silicon IC process technology, and the contact hole 32 for the first wiring is formed in the peripheral circuit 8 (FIG. 8E). Then, the lower electrode 6 is formed by vapor deposition or the like ((f) in the figure). In order to improve the bonding with the oxide film 3, it is preferable that the lower electrode has Au as an underlayer of Cr, but the lower electrode is not necessarily limited to this, and a metal such as aluminum may be used instead. However, it is necessary that the peripheral circuit 8 is electrically connected to the peripheral circuit 8 through the contact hole 32. Then, a piezoelectric material such as ZnO or AlN is deposited on the silicon autumn 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 a normal dielectric polarization treatment, the second wiring contact hole 33 is opened in the integrated circuit 8, and then the steps of coating, baking, and etching are sequentially performed using a polyimide resin. 7A and 7B, a through hole 11 communicating with the upper electrode 5 and a through hole 10 communicating with the second contact hole 33 are prepared.

Finally, the through hole 10 and the polyimide resin 7
An aluminum wiring 9 is formed to electrically connect the upper electrode 5 and the peripheral circuit 8 via 11 (FIG. 9 (i)).

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 uses a silicon substrate having a (100) plane orientation in which high-concentration boron is formed on the surface by epitaxial growth, and FIGS.
The feature is that the structure of the figure is realized. If this epitaxial substrate is used, a new step of removing the surface boron layer in the region where the peripheral circuit 8 and the groove 12 are formed is required. This can be easily realized by using a mixed solution of nitric acid, 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 that, the same steps as those in FIGS. 3C to 3I were performed, and the ultrasonic transducer shown in FIG. 6 could be manufactured. 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, there is a step between the lower electrode 6 and the peripheral circuit 8 as well. However, similarly to the above, the wiring of the lower electrode 6 and the peripheral circuit 8 is polyimide resin via the 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 embodiments, a plurality of rectangles 70 indicated by broken lines indicate the vibrator elements except the peripheral circuit 8 shown in FIGS. 1 and 2. The electrodes formed on the upper and lower surfaces of the vibrating body element 70 are connected to part of the peripheral circuit 8 via aluminum wiring (not shown). As shown in the embodiment of FIG. 7 and FIG.
When multiple 70s are lined up, ultrasonic waves can be emitted strongly at a small front angle, or ultrasonic waves at only a small front angle can be strongly received, and the noise in the figure can be confusing. There is a feature that it decreases. Further, compared with a single cantilevered structure having a large area, when dividing into a plurality of small cantilevered dyes as shown in this embodiment, it is possible to reduce harmonic signals other than the fundamental mode. The advantage is that it also helps reduce signal noise. Further, when the silicon anisotropic etching technique described in the explanation of FIG. 3 (d) is used, it is possible to form the vibrating body elements 70 having exactly the same shape at the same time.
There is no problem in terms of quality and manufacturing time. In addition to the embodiment shown here, there is also an embodiment in which the area of the vibrator element 70 in 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 same numbers as in FIG. 7 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.
It has the feature that it can provide a high-performance ultrasonic transducer that electrically scans. In this embodiment, the electrodes on the upper surface of the vibrating body element 70 are separated for each vibrating body element 70, but in addition to this, the electrode on the upper surface of each vibrating body element 70 is shared, Even if the second electrode (not shown) is separated for each vibrator element 70, the dehydration having the same effect as above can be realized. Although FIG. 9 shows an ultrasonic transducer array of 1 row and 5 columns, the number of the vibrator elements 70 need not be limited. For example, in the embodiment shown in FIG. 8, when the electrodes on the upper surface of the vibrating body element 70 are separately arranged for each vibrating body element 70 and each electrode is connected to the peripheral circuit 8, the electrodes are electrically connected in a two-dimensional direction. A two-dimensional ultrasonic transducer capable of scanning can be realized. 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 invention has been described in detail above with reference to examples.

The above-mentioned vibrating body has a so-called cantilever structure in which only one side is connected to the substrate, but the present invention is not applicable to a diaphragm structure in which all the peripheral sides are fixed in addition to this. Needless to say.

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 one or several 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. . Further, 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 hole, and a configuration in which a horn is placed on the front surface of the vibrating body to increase the sensitivity include.

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. In particular, by wiring the vibrating body and the integrated circuit via the polyimide resin, the disconnection of the wiring, which often occurs in the past, is significantly reduced, and the product reliability is increased. 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 shows an example of the ultrasonic transducer array according to the present invention as seen from above. 1 ... Silicon substrate, 2 ... Silicon thin plate, 3 ... Oxide film, 4 ... Piezoelectric thin film, 5 ... Upper electrode, 6 ... Lower electrode, 7 ... Polyimide resin, 8 ... Peripheral circuit, 9 , 21… Aluminum wiring, 10,11 …… Through hole, 12 …… Groove, 20 ……
Vibrating body, 30,31 …… Opening hole, 32,33 …… Contact hole, 41
…… Metal case, 42 …… Plastic case, 43 …… Protective screen, 44,45 …… Electrode terminals, 46 …… Leaf springs, 47
…… Aluminum alloy plate, 48 …… Polyester film, 49 ……
Electrode, 51 ... Mechanical element, 51a ... Vibrator, 51b ... Fixed plate, 52 ... Electrical element, 53 ... Bias voltage, 54 ... Resistance, 55 ... Transmission and reception circuit, 61,62 …… High-concentration boron layer, 70 …… Vibrator 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. To form a vibrating body, provide a peripheral circuit on the periphery of the silicon substrate, connect at least one side of the lower surface of the vibrating body to the silicon substrate, and as the individual area of the vibrating body moves away from the center of the silicon substrate. A plurality of vibrators are provided in a two-dimensional manner to increase or decrease, a polyimide resin is provided on a part of the upper electrode of the vibrator and the peripheral circuit, and vibration is performed through a through hole formed in the polyimide resin. An ultrasonic transducer comprising an upper electrode of the body and a peripheral circuit connected to each other.