JP6752727B2 - Ultrasound Transducer and Ultrasound Imaging Device - Google Patents

Description

The present invention relates to an ultrasonic transducer and an ultrasonic imaging device using the same.

The ultrasonic transducer element is incorporated in an ultrasonic imaging device and is used for various purposes such as diagnosis of a tumor in a human body and inspection of a crack generated in a building by transmitting and receiving ultrasonic waves.

Conventionally, piezoelectric ceramics represented by PZT (lead zirconate titanate) and the like have been used as ultrasonic transducer elements of ultrasonic imaging devices, but in recent years, capacitance detection type having wider band characteristics than piezoelectric ceramics has been used. Ultrasonic transducers (Capacitive Micromachined Ultrasonic Transducer; hereinafter abbreviated as CMUT) are attracting attention and research and development are underway.

The basic structure of the CMUT is that a cavity is provided in the insulating layer between the lower electrode and the upper electrode arranged above the lower electrode, and the insulating layer above the cavity and the upper electrode are a membrane (also called a diaphragm). It functions as. When transmitting ultrasonic waves, a DC voltage and an AC voltage are superimposed and applied between the upper electrode and the lower electrode, and the electrostatic force generated between the two electrodes causes the membrane to vibrate at the frequency of the AC voltage. .. On the other hand, at the time of reception, the membrane is vibrated by the pressure of ultrasonic waves reaching the surface of the membrane, and the change in the distance between both electrodes generated at that time is electrically detected as a capacitance change.

As an example of this type of CMUT, Patent Document 1 provides a concentric convex corrugated region whose center is the same as the center of the membrane on the membrane outside 70% of the radius of the cavity, and substantially the outer periphery of the membrane. A technique is disclosed in which the specific rigidity is made smaller than the rigidity of a region other than the outer peripheral portion.

According to CMUT of Patent Document 1, when a voltage is applied between the upper electrode and the lower electrode, a relatively wide area other than the outer peripheral portion of the membrane is attracted to the substrate side while maintaining parallelism. A CMUT having excellent sensitivity and reception sensitivity can be obtained.

Japanese Unexamined Patent Publication No. 2007-0746228

The ultrasonic imaging device incorporating the above-mentioned CMUT inserts the CMUT built in the tip of the catheter into the body of the subject (patient) to transmit and receive ultrasonic waves, so that it has high sensitivity in the high frequency band. Therefore, low voltage drive is required from the aspect of safety.

In order to increase the sensitivity of CMUT in the high frequency band, it is necessary to vibrate the membrane at a high frequency, but in order to increase the vibration frequency of the membrane, it is necessary to increase the driving voltage of the membrane.

However, since the resonance frequency (f) of the membrane is proportional to the square root of the spring constant (k) of the membrane, it is necessary to increase the spring constant (k) of the membrane in order to increase the vibration frequency of the membrane. Since there is a proportional relationship between the spring constant (k) of the membrane and the drive voltage, if the spring constant (k) of the membrane is to be increased, the drive voltage will also increase.

As described above, it is difficult for the conventional CMUT to achieve both high-frequency vibration and low-voltage drive of the membrane, but the CMUT described in Patent Document 1 described above achieves both high-frequency vibration and low-voltage drive of the membrane. No consideration is given to that.

The above and other objects and novel features of the present invention will become apparent from the description and accompanying drawings herein.

A brief overview of typical embodiments disclosed in the present application is as follows.

The CMUT according to a typical embodiment has a lower electrode formed on a substrate via a first insulating film, a second insulating film formed on the lower electrode, and a second insulating film formed on the second insulating film. The three insulating film, the cavity formed between the second insulating film and the third insulating film, and the upper electrode formed on the third insulating film and arranged so as to overlap the cavity in a plan view. The upper electrode is located between the outer edge portion and the central portion having the first film thickness and the outer edge portion and the central portion, and is thinner than the first film thickness. It is provided with a groove having a film thickness of.

According to a typical embodiment, it is possible to realize a CMUT that achieves both high-frequency vibration of the membrane and low-voltage drive.

FIG. 5 is a plan view of a main part of the CMUT according to the first embodiment. FIG. 1A is a sectional view taken along line AA of FIG. 1, and FIG. 1B is a sectional view taken along line BB of FIG. It is a top view which shows the whole structure of CMUT which concerns on Embodiment 1. FIG. It is a perspective view of the upper electrode of CMUT which concerns on Embodiment 1. FIG. (A) and (b) are cross-sectional views of a main part showing an example of the manufacturing method of CMUT according to the first embodiment. (A) and (b) are cross-sectional views of a main part showing a method of manufacturing a CMUT following FIG. (A) and (b) are cross-sectional views of a main part showing a method of manufacturing a CMUT following FIG. (A) and (b) are cross-sectional views of a main part showing a method of manufacturing a CMUT following FIG. 7. It is a top view of the upper electrode in the manufacturing process. (A) and (b) are cross-sectional views of a main part showing a method of manufacturing a CMUT following FIG. It is a top view of the upper electrode in the manufacturing process. (A) and (b) are cross-sectional views of a main part showing a method of manufacturing a CMUT following FIG. (A) and (b) are cross-sectional views of a main part showing a method of manufacturing a CMUT following FIG. (A) and (b) are cross-sectional views of a main part showing a method of manufacturing a CMUT following FIG. (A) to (h) are plan views showing another example of the upper electrode of the CMUT according to the first embodiment. It is a graph which shows the simulation result of the correlation between the area ratio of the groove part occupying the upper electrode, the resonance frequency of the membrane, and the drive voltage. It is a graph which shows the simulation result of the correlation between the distance from the central part of the upper electrode to the outer edge part, the resonance frequency of the membrane, and the drive voltage. (A) to (d) are plan views showing another example of the upper electrode of the CMUT according to the first embodiment. It is a perspective view which shows the appearance of the ultrasonic image pickup apparatus provided with CMUT of Embodiment 1. FIG. It is a block diagram which shows the function of the ultrasonic image pickup apparatus shown in FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all the drawings for explaining the embodiment, members having the same function are designated by the same reference numerals, and the repeated description thereof will be omitted. In addition, in the embodiments, the description of the same or similar portions will not be repeated in principle unless particularly necessary. Further, in the drawings for explaining the embodiments, hatching may be added even in the plan view in order to make the configuration easy to understand.

(Embodiment 1)
1 is a plan view of a main part showing a unit cell of CMUT according to the present embodiment, FIG. 2A is a sectional view taken along line AA of FIG. 1, and FIG. 2B is B- of FIG. It is a cross-sectional view of line B. Note that FIG. 1 mainly shows the planar layout of the upper and lower electrodes and the cavity formed between them, and the illustration of the insulating film is omitted.

The CMUT cell has an insulating film 11 formed on a substrate 10 made of single crystal silicon or the like, a lower electrode 12 formed on the insulating film 11, and two layers of insulating films 13 and 15 formed on the lower electrode 12. , A cavity 20 formed between the insulating film 13 and the insulating film 15, an upper electrode 16 formed on the upper portion of the insulating film 15, and a two-layer insulating film 17 formed on the upper portion of the upper electrode 16. , 19. Further, a protective film (not shown) for preventing foreign matter from adhering to a polyimide resin or the like is provided above the insulating film 19 on the uppermost layer, if necessary.

Here, of the insulating film 15, the upper electrode 16, and the insulating films 17 and 19, the region overlapping the cavity 20 in a plan view functions as a membrane M that vibrates when transmitting and receiving ultrasonic waves, and functions as a membrane M. The area surrounding the membrane M functions as a fixing portion for supporting the membrane M.

A pad 21 for external connection in which the insulating films 19 and 17 are etched to expose a part of the upper electrode 16 and the insulating films 19, 17, 15 and 13 are etched in a part of the region surrounding the cavity 20. A pad 22 for external connection is formed in which a part of the lower electrode 12 is exposed. A DC voltage and an AC voltage are applied to the CMUT from an external power source through these pads 21 and 22. Reference numeral 18 in the drawing indicates an opening formed in the insulating films 15 and 17 in the step of forming the cavity 20 on the substrate 10 (described later).

As shown in FIG. 3, the actual CMUT has a configuration in which a large number of unit cells as described above are arranged on the substrate 10.

The CMUT of the present embodiment is characterized by the shape of the upper electrode 16. That is, as shown in FIG. 2B, the upper electrode 16 of the CMUT has a relatively thick outer edge portion and a central portion of a region overlapping the cavity 20 in a plan view (in other words, a region functioning as a membrane M). A groove portion 23 having a first film thickness and having a second film thickness thinner than the first film thickness is provided in the region between the outer edge portion and the central portion.

Further, as shown in FIG. 4 (perspective view of the upper electrode 16), one end of the groove portion 23 having the second film thickness is connected to the outer edge portion of the upper electrode 16 and intersects with each other at the central portion of the upper electrode 16. It is supported by a plurality of support portions 24. These support portions 24 have the same first film thickness as the outer edge portion of the upper electrode 16.

FIG. 4 shows an example in which three support portions 24 intersect with each other at the central portion of the upper electrode 16, but the number of support portions 24 is not limited to three. However, from the viewpoint of ensuring the uniformity of vibration of the membrane M, it is preferable that the adjacent support portions 24 are arranged at equal intervals from each other. That is, it is preferable that the groove portion 23 is evenly supported by the support portion 24. In other words, it is preferable that the plurality of groove portions 23 separated by the plurality of support portions 24 have the same area as each other in a plan view.

Next, an example of the method for manufacturing the CMUT of the present embodiment will be described with reference to FIGS. 5 to 14. 5 to 8, 10 and 12 to 14, FIG. 5A is a cross-sectional view corresponding to line AA of FIG. 1A, and FIG. It is sectional drawing corresponding to line B. 9 and 11 are plan views of the upper electrodes during the manufacturing process, respectively.

First, as shown in FIG. 5, the insulating film 11 is formed on the substrate 10, and then the lower electrode 12 is formed on the insulating film 11. The insulating film 11 is made of, for example, a silicon oxide film having a film thickness of about 500 nm deposited by a CVD (Chemical Vapor Deposiotion) method or a thermal oxidation method. Further, the lower electrode 12 is made of, for example, an aluminum alloy film having a film thickness of about 100 nm deposited by a sputtering method.

Next, as shown in FIG. 6, an insulating film 13 is formed on the upper portion of the lower electrode 12, and then a sacrificial layer (dummy layer) 14 is formed on the insulating film 13. The insulating film 13 is made of, for example, a silicon oxide film having a film thickness of about 200 nm deposited by a plasma CVD method. In the sacrificial layer 14, for example, a polycrystalline silicon film is deposited on the insulating film 13 by a CVD method, and then the polycrystalline silicon film is patterned by using a photolithography technique and a dry etching technique to form a cavity 20 in a later step. It is formed by leaving a polycrystalline silicon film in the region.

Next, as shown in FIG. 7, the insulating film 15 is formed on the insulating film 13 and the sacrificial layer 14, and then two metal films 16a and 16b are formed on the insulating film 15. The lower metal film 16a is made of, for example, a W (tungsten) film having a film thickness of about 50 nm deposited by a sputtering method, and the upper metal film 16b is, for example, a TiN (titanium nitride) film having a film thickness of about 50 nm deposited by a sputtering method. Consists of. The metal films 16a and 16b may be composed of two or more kinds of metal films having different etching rates, and are not limited to the combination of the W film and the TiN film.

Next, as shown in FIGS. 8 and 9, two layers of metal films 16b and 16a are sequentially patterned using photolithography technology and dry etching technology, and 2 in the region where the upper electrode 16 is formed in a later step. The metal films 16a and 16b of the layer are left. When patterning the two-layer metal films 16a and 16b, the upper metal film 16b is selectively patterned using a predetermined etching gas, and then the etching gas is changed to pattern the lower metal film 16a.

Next, as shown in FIGS. 10 and 11, the metal film 16b is patterned using photolithography technology and dry etching technology to expose a part of the metal film 16a in the region overlapping the cavity 20 in a plan view. The groove portion 23 is formed. The groove portion 23 is formed by selectively removing only the upper metal film 16b using a predetermined etching gas by utilizing the difference in etching rates between the two layers of metal films 16a and 16b. Further, at this time, in the region inside the outer edge portion of the region overlapping the cavity 20, the region where the upper metal film 16b is left becomes the support portion 24 that supports the groove portion 23 having a thin film thickness.

Next, as shown in FIG. 12, an insulating film 17 made of a silicon oxide film having a thickness of about 200 nm is deposited on the insulating film 15 and the upper electrode 16 by a plasma CVD method, and then a photolithography technique and a dry etching technique are applied. By removing each part of the insulating film 17 and the insulating film 15 under the insulating film 17 using the insulating film 17, an opening 18 reaching the sacrificial layer 14 is formed.

Next, as shown in FIG. 13, a wet etching solution such as an aqueous potassium hydroxide solution is brought into contact with the surface of the sacrificial layer 14 through the opening 18. Specifically, the substrate 10 having the openings 18 formed in the insulating films 17 and 15 is immersed in the wet etching solution. As a result, the sacrificial layer 14 is dissolved and disappears by the wet etching solution, and the cavity 20 is formed in the region where the sacrificial layer 14 is arranged.

Next, as shown in FIG. 14, an insulating film 19 made of a silicon oxide film having a film thickness of about 500 nm is deposited on the insulating film 17 by a plasma CVD method. As a result, the insulating film 19 is embedded in the opening 18, and the cavity 20 sealed by the insulating films 13, 15 and 19 is completed.

After that, a part of each of the insulating films 19 and 17 is removed by using a photolithography technique and a dry etching technique, and a part of the upper electrode 16 is exposed to form the pad 21. Further, the pad 22 is formed by removing each part of the insulating films 19, 17, 15, and 13 and exposing a part of the lower electrode 12. By the steps up to this point, the CMUT shown in FIGS. 1 and 2 is completed.

The CMUT electrode material and insulating film material described above are preferable examples, and are not limited thereto. As the material of the lower electrode 12, a metal material other than the aluminum alloy, for example, W, Ti, TiN, Al, Cr, Pt, Au, polycrystalline silicon or amorphous silicon doped with impurities at a high concentration can also be used. .. Further, instead of the insulating film made of a silicon oxide film, a silicon nitride film, a hafnium oxide film, a silicon-doped hafnium oxide film, or the like can be used. The sacrificial layer 14 is not limited to the polycrystalline silicon film as long as it is a material having a high etching selectivity with respect to these insulating films, and may be, for example, a metal film or an SOG (Spin-on-Glass) film.

Next, the effect of the CMUT of the present embodiment in which the groove portion 23 is provided in a part of the upper electrode 16 will be described.

As shown in FIG. 15, in the upper electrode 16 of the region overlapping the cavity 20 (the region functioning as the membrane M), the position where the groove 23 is arranged and the area ratio occupied by the groove 23 can be variously changed, but the groove 23 There is a difference between the magnitude of the drive voltage and the vibration frequency of the membrane M depending on the position and area ratio of.

FIG. 16 is a graph showing a simulation result of the correlation between the area ratio of the groove 23 in the upper electrode 16 and the resonance frequency and drive voltage of the membrane M. The horizontal axis of the graph shown in FIG. 16 shows the ratio of the area of the groove 23 to the total area of the upper electrode 16 in the region overlapping the cavity 20, and the vertical axis shows the resonance frequency and the driving voltage of the membrane M.

As is clear from FIG. 16, as the area ratio of the groove 23 to the upper electrode 16 increases, the resonance frequency of the membrane M increases and the drive voltage decreases. This effect becomes remarkable when the area ratio of the groove portion 23 to the upper electrode 16 is 20% or more, particularly 50% or more.

On the other hand, FIG. 17 is a graph showing the simulation result of the correlation between the distance from the central portion to the outer edge portion of the upper electrode 16 and the resonance frequency and the driving voltage of the membrane M. The horizontal axis of the graph shown in FIG. 17 shows the distance from the outer edge of the upper electrode 16 to the groove 23 when the distance from the outer edge to the center of the upper electrode 16 is 1, and the vertical axis represents the resonance of the membrane M. It shows the frequency and drive voltage.

As is clear from FIG. 17, the driving voltage of the membrane M is such that the distance from the outer edge portion of the upper electrode 16 to the groove portion 23 is around 0.75 (= 75%) of the distance from the outer edge portion to the central portion of the upper electrode 16. It becomes maximum at, and gradually decreases at more and less. On the other hand, the distance from the outer edge portion of the upper electrode 16 to the groove portion 23 is within the range of about 0.66 to 0.81 (= about 66% to 81%) of the distance from the outer edge portion to the central portion of the upper electrode 16. Then, the resonance frequency of the membrane M becomes lower as the distance from the central portion of the upper electrode 16 to the groove portion 23 becomes shorter.

From the simulation results of FIG. 16 and the simulation results of FIG. 17, it is said that the membrane M can be driven at a low voltage and a high frequency by providing the groove portion 23 having a relatively thin film thickness in a part of the upper electrode 16. The effect is obtained. Further, it can be seen that the above effect can be remarkably obtained by maximizing the area ratio of the groove portion 23 to the upper electrode 16 at a position of 75% or more of the distance from the central portion to the outer edge portion of the upper electrode 16.

By providing the groove portion 23 in a part of the upper electrode 16 in this way, it is possible to realize a CMUT capable of driving at a low voltage and a high frequency.

The groove 23 of the upper electrode 16 can be provided on the lower surface (bottom surface) of the upper electrode 16 or on both the upper surface and the lower surface (bottom surface) of the upper electrode 16, but as in the present embodiment, the upper surface of the upper electrode 16 is provided. It is desirable to provide it on the side. In other words, it is desirable that the lower surface of the upper electrode 16 is flat as shown in FIG.

When the lower surface of the upper electrode 16 is flat, the distance between the upper electrode 16 and the lower electrode 12 is equal in the entire region of the cavity 20, whereas the groove 23 is provided on the lower surface side of the upper electrode 16. If this is the case, a region where the distance between the upper electrode 16 and the lower electrode 12 becomes large is locally generated. Therefore, when the lower surface of the upper electrode 16 is flat, the electrostatic force between the two electrodes generated at a constant driving voltage can be increased as compared with the case where the lower surface of the upper electrode 16 has a step.

Further, the material of the support portion 24 that supports the groove portion 23 is not limited to the conductive material, and may be an insulating material. However, when the support portion 24 is made of an insulating material, the electrical resistance of the upper electrode 16 is increased as compared with the case where the support portion 24 is made of a conductive material, and the manufacturing process of the upper electrode 16 becomes complicated.

Further, in the present embodiment, the planar shape of the cavity 20 and the planar shape of the upper electrode 16 in the region overlapping the cavity 20 are hexagonal, but the planar shapes of the cavity 20 and the upper electrode 16 are limited to hexagons. It may be, for example, a circle, an ellipse, a quadrangle, an octagon, or the like. Even in these cases, from the viewpoint of ensuring the uniformity of vibration of the membrane M, it is preferable that the adjacent support portions 24 are arranged at equal intervals with each other as shown in FIG. That is, it is preferable that the groove portion 23 is divided into an even area by the support portion 24.

(Embodiment 2)
FIG. 19 is a perspective view showing the appearance of the ultrasonic imaging device provided with the CMUT of the first embodiment, and FIG. 20 is a block diagram showing the function of the ultrasonic imaging device shown in FIG.

The ultrasonic image pickup device 301 has a main body 305 that houses an ultrasonic transmission / reception circuit that transmits / receives ultrasonic waves, a signal processing circuit that processes an echo signal received by the ultrasonic transmission / reception circuit, and generates an ultrasonic image to be inspected. , Connected to the main body 305 via a display unit 303 connected to the main body 305 and displaying an ultrasonic image and a GUI for interface with an operator, an input unit 304 operated by the operator, and a catheter connecting part 306. The catheter 302 is provided. The catheter 302 is a device that is inserted into the body of a subject (patient) and transmits / receives ultrasonic waves to / from the subject, and a CMUT 307 connected to an ultrasonic transmission / reception circuit in the main body 305 is built in at the tip thereof. Has been done. The CMUT 307 is configured by arranging the unit CMUT of the first embodiment in a range of several hundred to 10,000 in a one-dimensional or two-dimensional array.

Note that FIG. 19 shows, as an example, a movable ultrasonic image pickup device provided with a caster 308 at the bottom of the main body 305, but the ultrasonic wave image pickup device 301 of the present embodiment is an ultrasonic image pickup device fixed to an examination room. It can be applied to a sound wave imaging device, a portable ultrasonic imaging device such as a notebook type or a box type, and other known ultrasonic imaging devices.

As shown in FIG. 20, the main body 305 of the ultrasonic imaging device 301 includes an ultrasonic transmission / reception unit 411, a signal processing unit 412, a control unit 413, a memory unit 414, a power supply device 415, and an auxiliary device 416.

The ultrasonic transmission / reception unit 411 generates a drive voltage for transmitting ultrasonic waves from the CMUT 307 and receives an echo signal from the CMUT 307, and includes a delay circuit, a filter, a gain adjustment circuit, and the like.

The signal processing unit 412 performs processing necessary for correction such as LOG compression and depth correction and image creation on the received echo signal, such as a DSC (digital scan converter), a color Doppler circuit, and an FFT analysis unit. May include. The signal processing by the signal processing unit 412 can be either analog signal processing or digital signal processing, some of which can be realized by software, and ASIC (application specific integrated circuit) or FPGA (field-programmable gate array). It is also possible to realize it.

The control unit 413 controls each circuit of the main body 305 and the equipment connected to the main body 305. Information and parameters required for signal processing and control and processing results are stored in the memory unit 414. The power supply device 415 supplies necessary power to each part of the ultrasonic imaging device. The auxiliary device 416 is for realizing a function associated with the ultrasonic image pickup device 301, for example, sound generation, in addition to the above-mentioned parts, and is appropriately added as needed.

Since the ultrasonic imaging device 301 of the present embodiment uses the CMUT of the first embodiment as the CMUT 307 of the catheter 302, the ultrasonic wave is performed at a low voltage that is safe even if it is inserted into the body of the subject (patient). Can be transmitted and received with high sensitivity.

Although the invention made by the present inventor has been specifically described above based on the embodiment thereof, the present invention is not limited to the embodiment and can be variously modified without departing from the gist thereof. ..

The CMUT of the present invention can be applied not only to an ultrasonic imaging device but also to various applications such as crack inspection of LSI packages and crack inspection of buildings.

10 Substrate 11 Insulation film 12 Lower electrode 13 Insulation film 14 Sacrificial layer 15 Insulation film 16 Upper electrode 16a Metal film 16b Metal film 17 Insulation film 18 Opening 19 Insulation film 20 Cavity 21 Pad 22 Pad 23 Groove 24 Support part M Membrane 301 Ultrasonic Imaging device 302 Catheter 303 Display unit 304 Input unit 305 Main body 306 Catalyst connection unit 307 CMUT
308 Caster 411 Ultrasonic transmitter / receiver 412 Signal processing unit 413 Control unit 414 Memory unit 415 Power supply device 416 Auxiliary device

Claims (7)

With the board
A lower electrode formed on the substrate via a first insulating film,
A second insulating film formed on the lower electrode and a third insulating film formed on the second insulating film,
A cavity formed between the second insulating film and the third insulating film,
An upper electrode formed on the third insulating film and arranged so as to overlap the cavity in a plan view,
Have,
The upper electrode is located between the outer edge portion and the central portion having the first film thickness and the outer edge portion and the central portion, and has a groove portion having a second film thickness thinner than the first film thickness. equipped with a door,
An ultrasonic transducer having the first film thickness and supported by a support portion connecting the outer edge portion and the central portion . With the board
A lower electrode formed on the substrate via a first insulating film,
A second insulating film formed on the lower electrode and a third insulating film formed on the second insulating film,
A cavity formed between the second insulating film and the third insulating film,
An upper electrode formed on the third insulating film and arranged so as to overlap the cavity in a plan view,
Have,
The upper electrode is located between the outer edge portion and the central portion having the first film thickness and the outer edge portion and the central portion, and has a groove portion having a second film thickness thinner than the first film thickness. With and
An ultrasonic transducer in which the lower surface of the upper electrode is flat. In the ultrasonic transducer according to claim 1 or 2 .
An ultrasonic transducer in which the ratio of the area of the groove to the total area of the upper electrode is 20% or more. In the ultrasonic transducer according to claim 1 or 2 .
An ultrasonic transducer in which the distance from the central portion of the upper electrode to the groove portion is 75% or more of the distance from the central portion of the upper electrode to the outer edge portion. In the ultrasonic transducer according to claim 1 ,
An ultrasonic transducer in which each of the grooves separated into a plurality of regions by the support has an area equal to each other. In the ultrasonic transducer according to claim 1 or 2 .
The outer edge portion and the central portion of the upper electrode are composed of a laminated film of two types of conductive films having different etching rates, and the groove portion is composed of a conductive film of a lower layer of the two types of conductive films. Ultrasonic transducer. An ultrasonic imaging apparatus comprising the ultrasonic transducer according to claim 1 or 2 .

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