JPH01269079A - Ultrasonic transducer and its manufacture - Google Patents

Abstract

PURPOSE:To improve the sensitivity of the title transducer by forming grooves at the sections which becomes the peripheral section of each device when a semiconductor base plate is divided into individual devices in the same process as that forming holes when the holes are formed on the surface of the base plate and forming an insulating film on the surface of the base plate thereafter. CONSTITUTION:Openings 31 which become the peripheral margin of each device and opening 30 having the same shape as etching hole have are formed on a silicone base plate 1 provided with SiO2 films 20 on both surfaces. After forming etching holes and peripheral margin grooves in the openings 30 and 31, the sample is thermally oxidized and integrated circuits 8 for transmission and reception are formed. After forming the circuits 8, patterning of lower electrodes 6 and wiring connected with the circuits 8 is performed and an SiO2 film 3 is formed. Then the base plate is separated into individual chips along the groves and a thin film 10 of an organic substance 10 on which an upper electrode 49 is vapor-deposited is directly stuck to the foundation 22 of a package. Because of the SiO2 film 3, the thin film 10 can be reduced in thickness and sensitivity of the transducer can be improved.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an ultrasonic transducer,
The present invention relates to the structure and manufacturing method of a high-performance, compact and lightweight electrostatic ultrasonic transducer that can be used, for example, for detecting adjacent rooms in industrial robots or as back sensors in automobiles.

(Prior Art) This technique has the disadvantage that it cannot be used when the body 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, and electrical elements such as oscillation circuits and reception circuits that support this. It is necessary to combine the elements properly. 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. .

However, because of the currently commonly used ultrasound transformer,
Another drawback is that it is difficult to reduce the size and weight of the device. Hereinafter, a conventional example will be explained with reference to figures.

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 pm are formed on the surface by machining. On the upper surface of this hole 101, a polyester film 48 having a thickness of about 1211 m is fixed between a metal case 41 and an aluminum alloy plate 47. On the surface of the polyester film 48, an upper electrode 49 made of gold or the like is deposited on the surface opposite to the surface in contact with the aluminum alloy plate 47. 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, on the back side of the aluminum alloy plate 47 is a plate spring 46 made of metal.
is attached, and an aluminum alloy plate 47 is pressed against the metal case 41. Further, the leaf spring 46 is fixed to the plastic case 42. Reference numeral 45 is an electrode terminal, and reference numeral 45 is an electrode terminal that is integrated with a leaf spring 46.
5 is constructed integrally with a metal case 41. Therefore,
The potential of the electrode terminal 45 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 upper electrode 49 via the metal case 41.

FIG. 5 is a diagram for explaining the operating principle of the electrostatic ultrasonic transducer described in FIG. The mechanical element 51 includes a diaphragm 51a and a fixed plate 51
b, and has the structure shown in FIG. 4, for example. On the other hand, the electric element 52 includes a bias power supply 53, a resistor 54, and an oscillation circuit 55 when transmitting ultrasonic waves. Now, when no signal is generated from the oscillation circuit 55, the diaphragm 51a is bent by the fixed plate 51b due to the bias voltage applied by the bias power supply 53.

Subsequently, when an AC voltage having a smaller amplitude than the bias voltage 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, a potential difference equal to the sum of these voltages is applied to the diaphragm 51a and the fixed plate 51b.
The deflection of will increase. On the other hand, when the electric polarity of the oscillation circuit 55 is opposite to the bias voltage, 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 becomes small. 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 includes a diaphragm 51a and a fixed plate 51b.
It has the function of protecting the circuit so that a large current does not flow in the circuit if a discharge occurs between the two. Although the case of ultrasonic wave transmission has been described above, in the case of transmission, 55 in FIG. 5 may be a receiving circuit that performs amplification compensation and the like. At this time, the vibration plate 5 is
1a vibrates, and the capacitance between the diaphragm 51a 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 transmit and 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 variations in the size and shape of the hole. this hole 1
01 corresponds to the gap between the diaphragm 51a and the fixed plate 51b shown in FIG. 5, and when the dimensions and outer shape vary, the force driving the diaphragm 51a varies, and eventually,
There was a drawback that the transmission and reception characteristics of the ultrasonic waves were not constant.

Further, the thinner the polyester film 48 (FIG. 4) is, the higher the sensitivity is. This is because the distance between the upper electrode 49 and the aluminum alloy plate 47, which is the lower electrode, becomes smaller. However, as the polyester film 48 is made thinner, minute holes are generated in the film during manufacturing, and a high bias voltage causes a discharge between the electrode 49 and the aluminum alloy plate 47, destroying the device. This often happened. This discharge often occurs where the peripheral edge of the aluminum alloy plate 47 and the polyester film 48 come into contact. This is leaf spring 46
This is because the distance between the electrode 49 and the aluminum alloy plate 47 is shortened because the polyester film 48 is pressed against the metal case 41. Therefore, discharge is likely to occur at the peripheral edge, causing the polyester film 48 to tear or the electrode 49 to evaporate. Therefore, there was a difficulty in that the thickness of the polyester film 48 could not be reduced and the sensitivity could not be increased.

As combinations are inevitable, and attempts are made to create even higher-performance devices using conventional structures, the area occupied by these electrical elements becomes larger and larger, resulting in larger devices. was there. 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 drawback 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 provide an ultrasonic transducer that eliminates the drawbacks of the prior art described above, reduces discharge, has uniform characteristics, is highly sensitive, small and lightweight, and a method for manufacturing the same.

(Means for Solving the Problems) According to the present invention, a thin film having a first electrode on one surface and a second electrode provided on the surface of a semiconductor substrate having a hole on the surface, In an ultrasonic transducer in which an insulating film is provided between a first electrode and the second electrode so as to be fixed to the second electrode, the surface of the peripheral edge of the semiconductor substrate when separated into individual devices is also An ultrasonic transducer characterized by being provided with an insulating film is obtained.

Further, according to the present invention, the thin film has a first electrode on one surface, and a second electrode provided on the surface of the semiconductor substrate having a hole on the surface, and the first electrode and the second electrode are provided on the surface of the semiconductor substrate. In a method of manufacturing an ultrasonic transducer in which an insulating film is fixedly attached to a second electrode between two electrodes, when holes are formed in the surface of the semiconductor substrate using an anisotropic etching technique, individual A method for manufacturing an ultrasonic transducer is obtained, which includes the steps of forming a groove in a portion that will become a peripheral edge when separating into devices in the same step, and then forming an insulating film on the surface of the substrate.

Further, according to the present invention, a thin film having a first electrode on one surface and a second electrode provided on the surface of the semiconductor substrate having a hole on the surface, the first electrode and the second electrode are provided. A plurality of ultrasonic transducers each having an insulating film fixed to the second electrode are arranged in an array, and each ultrasonic transducer is connected to at least one of the first and second electrode sides. A characteristic ultrasonic transducer is obtained.

(Function) The ultrasonic transducer of the present invention uses an IC made of silicon or the like.
This is an electrostatic ultrasonic transducer that has a manufacturing method that matches process technology and the integration of peripheral circuits.For example, as shown in FIG. 1, an organic thin film 10 that is an elastic vibrator is
Ultrasonic waves are transmitted by moving up and down according to changes in the potential difference applied to the upper and lower electrodes 49.6 of the SiO2 film 3 provided on the silicon substrate 1. On the other hand, when this device is used for transmitting ultrasonic waves, the organic thin film 10 vibrates due to the pressure of external ultrasonic waves, and as a result, the capacitance between the upper and lower electrodes of the SiO2 film 3 changes. Using this, it is possible to detect the pressure of external ultrasound as a change in the current value flowing through an electric circuit (to which a bias voltage is applied). At this time, in order to increase the sensitivity of the wave transmitting and receiving characteristics of the transducer, it is possible to maintain good silicon insulation with the upper electrode 49 deposited on the organic thin film 10 and reduce the distance between them to increase the sensitivity. And so.

Furthermore, by providing the SiO□ film 3 on the surface of the peripheral portion of the silicon substrate 1, a certain distance is provided between the upper electrode 49 and the surface of the substrate 1, and electric field concentration is prevented from occurring at the peripheral portion to prevent discharge. Preventing. In addition, since the ultrasonic transducer of the present invention uses a semiconductor substrate, (1) holes and peripheral grooves can be formed on the semiconductor substrate with high accuracy and simultaneously using semiconductor micro-etching technology, and the manufacturing process It is possible to suppress variations in device characteristics that affect the manufacturing process without increasing
(2) The oscillator circuit and the receiver circuit can be integrated using semiconductor IC process technology, making it possible to manufacture a high-performance ultrasonic transducer in a small size and light weight.

(Example) Hereinafter, an electrostatic ultrasonic transducer that is 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 are a sectional view and a plan view, respectively. FIG. 1 shows a cross section taken along line AN in FIG. 2.

In this embodiment, an upper electrode 49 made of gold, aluminum, etc. is deposited on the lower surface of an organic thin film 10 made of polyester or the like that transmits and receives ultrasonic waves. As shown in FIG. 2, this organic thin film 10 vibrates up and down above unpierced etched holes 12 regularly drilled in the silicon substrate 1 to transmit and receive ultrasonic waves. SiO provided below the organic thin film 10
An upper electrode 49 and a lower electrode 6 are arranged on both sides of the two membranes 3, and when transmitting waves, an alternating current voltage is applied to vibrate the organic thin film 10. During delivery, the organic thin film 10 vibrates and a voltage is generated. The 8102 film 3 helps maintain good electrical insulation between the upper electrode 49 and the lower electrode 6. Furthermore, the thickness of the 5102 film 3 is set to lp
m, the spatial distance between the upper electrode 49 and the lower electrode 6 is also about lpm, and conventionally, as shown in FIG. (12pm), compared to
This has the advantage that the distance between the electrodes can be significantly reduced. Since the electrostatic force acting on the upper electrode 49 is approximately inversely proportional to the square of the distance between the two electrodes 49 and 6, the sensitivity of the wave transmission and reception characteristics of the device can be increased. As shown in FIG. 1, a taper 15 is provided on the peripheral edge of the silicon substrate 1, and an 81 oz film 3 is provided on the taper 15 so as to substantially cover the silicon substrate 1.

As a result, the upper electrode 49 does not come into direct contact with the silicon substrate 1 and can be bonded to the stem 22 of the package while maintaining a distance from the surface of the substrate 1 by at least the thickness of the 8102 film 3. The trouble of electric discharge between the upper electrode 49 and the lower electrode 6 via the electrode 6 has been almost eliminated.

Note that there is also a SiO2 film 2 between the lower electrode 6 and the silicon substrate 1.
0 and 20 to prevent current from leaking between the lower electrode 6 and the silicon substrate 1. The lower electrode 6 is an aluminum wiring (not shown) also formed on the SiO□ film 3.
It is electrically connected to an integrated circuit 8 for driving and receiving fabricated on the silicon substrate 1 via. In addition, the etching hole 12 and the taper 15 at the peripheral edge of the device
is manufactured by applying silicon anisotropic etching technology in order to finish the dimensions and shape with high precision. For example, a silicon substrate 1 having a main surface in the (100) direction
After using photolithography to form a pattern of multiple square 8102 films with - sides aligned in the <110> direction, the sample was placed in an anisotropic etching solution such as hydrazine. Do it by soaking it. This case has the advantage that silicon etching is automatically stopped when the pyramid-shaped etching hole 12 is formed. In addition, as mentioned earlier, since the shape of the etched hole 12 is created using photolithography technology, it is possible to form a minute shape with high precision, and furthermore, the etching is performed by immersing the sample in a liquid. This method has the advantage that a large amount of samples can be processed at one time.

FIGS. 3(a) to 3(e) are cross-sectional views showing an example of a procedure for manufacturing an ultrasonic transducer according to 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 with a (100) plane.
An 8102 film 3 is attached on the front and back surfaces of the etched film using a thermal oxidation method, and one side of the same shape as the opening 31 that will become the periphery of the device shown in FIG. 1 and the etching hole 12 in FIG. A square opening 30 with a length of several tens of pm is formed. When forming the opening 30, the required sample, which is arranged so that the sides of the etching hole 12 in FIG. Perform directional etching (Figure 3(b)
)). Aqueous solutions of FDP, hydrazine, etc.
It has a property (anisotropy) that the etching rate for the (100) plane is significantly higher than the etching rate for the (111) plane. Therefore, by immersing the sample shown in FIG. 3(a) in the aqueous solution, the etching holes 12 and peripheral grooves 32 shown in FIG. 2(b) can be produced. With this method, the etching hole 12 and the peripheral groove 32 can be made in the same process, so the process does not become long. Since the silicon substrate 1 is divided into individual devices at the peripheral groove 32, it is desirable that the depth of the groove 32 is at least half the thickness of the substrate 1 to facilitate the division. Subsequently, the sample is thermally oxidized again in order to fill the entire SiO2 film 20 in the etching hole 12 and the peripheral groove 32, and then an integrated circuit 8 for transmitting and receiving is formed using normal silicon IC process technology. Figure (C)). Subsequently, 81 on the integrated circuit 8 is formed to form the lower electrode 6 and wiring (not shown) connected to the integrated circuit 8.
02 film 20 is partially removed and aluminum is deposited, so Si
Only the O2 film 3 is shown. The lower electrode 6 is preferably made of Au on a Cr base to improve adhesion with the SiO□ film 3, but it is not necessarily limited to this, and metals such as aluminum may be used instead. . Peripheral groove 32
After separating the chips into individual chips along
22 (see figure (e)).

In one embodiment of the invention shown in FIGS. 1 and 2, a configuration is shown in which the upper electrode 49 is directly bonded to the 5102 membrane 3. On the other hand, the present invention also includes a structure in which the positional relationship between the upper electrode 49 and the organic thin film 10 is reversed, and the structure is similar to that of the conventional example shown in FIG. In this case, the distance between the upper electrode 49 and the lower electrode 6 is larger than in the previous embodiment, so there is a drawback that the sensitivity is lowered.
Since there is an opening between the two membranes 3 and the organic thin film 10, electrical insulation between the two electrodes is sufficiently compensated. Therefore, short-circuit accidents between both electrodes are reduced, and device reliability is improved. Also, SiO2
Since the film 3 is present, it is also possible to use a metal thin film such as gold or titanium instead of the tangible thin film 10. This has the advantage that the melting point of the metal is higher than that of the organic material, making it possible to operate the transducer at higher temperatures.

Further, instead of adhering the organic thin film 10 to the pedestal 22 as in this embodiment, they may be sandwiched between the two using a holding jig.

FIGS. 6 and 7 are plan views showing other embodiments of the present invention. In the figures, the same numbers as in FIGS. 1 and 2 indicate the same components. In these examples,
A rectangle 70 indicated by a broken line indicates a vibrating body element included on the same lower electrode 6 shown in FIGS. 1 and 2.

However, the integrated circuit 8 is not included. In addition, the vibrating body element 70
The electrodes formed on the upper and lower surfaces of the integrated peripheral circuit 89
(not shown). When a plurality of vibrating body elements 70 are arranged in a row as shown in the embodiments of FIGS. 6 and 7, it is possible to simultaneously form vibrating body elements 70 of the same shape by strongly applying ultrasonic waves to a small angle in the front surface. Therefore, the quality is stable and the time required for manufacturing is short. In addition to the embodiment 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 shows a plan view of an embodiment of the third invention of the present application. In the figure, the same numbers as in FIG. 6 indicate the same components. In the embodiment of the present invention, 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, the electrodes on the bottom surface of each vibrating body element 70 having different phases are separated for each vibrating body element 70, but conversely, the electrodes on the bottom surface of each vibrating body element 70 are made common and each vibrating body element 70 has a different phase. Even if the electrode 49 on the upper surface of the element 70 is separated for each vibrator element 70, a device having the same effect as above can be realized. Although FIG. 8 shows an array of ultrasonic transducers arranged in 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, if the electrodes on the upper and lower surfaces of the vibrating body element 70 are arranged separately for each vibrating body element 70 and each electrode is connected to the peripheral circuit 8', electric power is generated in a two-dimensional direction. A two-dimensional ultrasonic transducer capable of scanning can be realized. Another great advantage of the ultrasonic transducer described in this embodiment over the conventional technology is that the lower electrodes of each vibrating body element 70 can be formed simultaneously and easily using normal IC process technology. It is.

In the embodiment in which the lower electrode or the upper electrode is separated, one vibrating element 7o 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. It may be considered that each rounded hole in the figures and FIG. 2 corresponds to one vibrator element.

The present invention has been described above in detail using 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 - to several 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 serve as a through hole, and the device is mounted on a perforated pedestal to allow air to flow with the outside. 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 organic thin film that contributes to vibration. Furthermore, the sensitivity can also be increased by making the SiO□ film between the organic thin film and the lower electrode thinner. 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. vibrating body and 5
102 The dimensions of the membrane must be determined.

Although the Sio2 film 3 was used in the above embodiments, the present invention is not limited to this, and any material such as Si3N, 5iOxNy1 polyimide, etc., which can be adhered to the surface of the lower electrode in a thin film form by CVD, sputtering, coating, etc., can be used.

(Effects of the Invention) As explained above, according to the present invention, it has become possible to provide an integrated ultrasonic transducer that is small in size, lightweight, and highly sensitive with little variation in characteristics. Furthermore, the problem of electrical discharge that destroys devices has been almost eliminated. As a result, it has become possible to use high-performance ultrasonic transducers to detect adjacent rooms in the field of industrial robots and the like. 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]

1 and 2 are a cross-sectional view and a plan view, respectively, of an embodiment of the first invention of the present application, and FIGS. 3(a) to 3(e) are conceptual diagrams showing an embodiment of the second invention of the present application. 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 first invention of the present application, and FIG. Figure 8 is the third part of the present application.
1 is a plan view showing an embodiment of an ultrasonic transducer array according to the invention; FIG. 1...Silicon substrate, 3,20."5t02 film, 6.
...Lower electrode, 8, ...Integrated circuit, 8'-...Peripheral circuit, 10...Organic thin film, 12-0. Etched hole, 2
2... Pedestal, 30.31... Opening, 32... Peripheral groove, 41... Metal case, 42... Plastic case, 43... Protective screen, 44.45-...
Electrode terminal, 46... Leaf spring, 47... Aluminum alloy plate, 48... Polyester film, 49... Upper electrode, 51... Mechanical element, 51a... Vibration plate, 51b
. . . Fixed plate, 5 . Patent applicant: Director of the Agency of Industrial Science and Technology Kozo Iizuka Figure 1 Figure 2 Figure 3 Figure 4 Figure 6 Figure 8

Claims (3)

[Claims] (1) A thin film having a first electrode on one surface and a second electrode provided on the surface of a semiconductor substrate having a hole on the surface, and a thin film having a first electrode on one surface and a second electrode provided on the surface of a semiconductor substrate with a hole on the surface, An ultrasonic transducer in which an insulating film is fixed to the second electrode between the two electrodes, characterized in that the insulating film is also provided on the peripheral surface of the semiconductor substrate when separated into individual devices. Ultrasonic transducer. (2) A thin film having a first electrode on one surface and a second electrode provided on the surface of a semiconductor substrate having a hole on the surface, and a thin film having a first electrode and a second electrode. A method for manufacturing an ultrasonic transducer in which an insulating film is fixedly attached to a second electrode in between, wherein a hole is formed in the surface of the semiconductor substrate using an anisotropic etching technique, and the semiconductor substrate is later separated into individual devices. 1. A method for manufacturing an ultrasonic transducer, comprising the steps of forming a groove in a portion that will become a peripheral edge in the same process, and then forming an insulating film on the surface of the substrate. (3) A thin film having a first electrode on one surface, and a second electrode provided on the surface of a semiconductor substrate having a hole on the surface, and the first electrode and the second electrode are connected to each other. A plurality of ultrasonic transducers each having an insulating film fixed to a second electrode are arranged in an array, and each ultrasonic transducer has an electrode on at least one side of the first and second electrodes. An ultrasonic transducer capable of inputting and outputting electrical signals independent of each other, characterized in that an insulating film is also provided on the peripheral surface of a semiconductor substrate when separated into individual devices. .