HK1112659A - Multilayer ultrasonic transducer and method for manufacturing same - Google Patents

Description

Multilayer ultrasonic transducer and method of manufacturing the same

Technical Field

The present invention relates to a multilayer ultrasonic transducer and a method of manufacturing the same, and particularly to a multilayer ultrasonic transducer having improved vibration characteristics and a method of manufacturing the same.

Background

Ultrasound transducers used for medical imaging have many elements and the distances between the elements become smaller. As the size of elements in an ultrasound transducer decreases, the mismatch of electrical impedance between the ultrasound transducer and the ultrasound imaging diagnostic system is becoming a serious problem to be solved.

Generally, the impedance of the elements in an ultrasound transducer is in the range of 100 to 500 ohms, while the impedance of a typical cable used for communication between the ultrasound transducer and an ultrasound imaging diagnostic system is in the range of 50 to 85 ohms, which exhibits a large difference therebetween. This mismatch results in a reduction in energy conversion efficiency, which in turn leads to a reduction in sensor sensitivity and an increase in signal-to-noise ratio, thereby preventing processing of the signals representing the ultrasound images. The most important factors in ultrasound imaging diagnosis are brightness and image resolution. However, impedance mismatch between the ultrasound transducer and the ultrasound imaging diagnostic system prevents the presentation of bright images.

If piezoelectric substrates of the same thickness are acoustically connected in series with each other and elastically connected in parallel with each other, the relationship between the voltage, the impedance, and the number of piezoelectric substrates can be expressed as follows (refer to Michael Greenstein and Umesh Kumar, "multilayered piezoelectric resonators for a physical ultrasonic transducer," IEEETRANSACTIONS Ultrasonics, Ferroelectrics and Frequency Control, vol.43, pp.622-624, 1966):

V(N)＝V(1)/N

Z(N)＝Z(1)/N²

where N, V and Z represent wafer number, voltage, and impedance, respectively.

That is, as the number of piezoelectric substrates increases, the impedance decreases in proportion to the square of N. Thus, by lowering the high impedance of the sensor element based on this principle, it is possible to solve the above-mentioned mismatch problem.

In this regard, there have been many attempts to apply a Multi-layer piezoelectric transducer to a medical ultrasonic transducer (see, David m.mill et al, "Multi-layered PZT-Polymer composition information to noise ratio and resolution for a medical ultrasonic transducer," IEEE transactions on ultrasound, ferroelectrics, and frequency control, vol.46, No.4, July 1999).

However, such a multi-layer piezoelectric ultrasonic transducer mentioned above has a disadvantage of poor vibration characteristics due to an additional layer beside the matching layer coupled to the front surface of the sensor. For example, U.S. Pat. nos. 6121718 and 6437487 disclose ultrasonic transducers using piezoelectric materials, in which FPCBs (flexible printed circuit boards) are formed on both front and rear surfaces of a laminated assembly for electrical connection. Therefore, the laminated assembly structure is: a polyimide/copper layer of several tens of micrometers or a copper layer of several tens of micrometers is deposited on the front surface of the multilayer sensor. Therefore, the vibration characteristics of the laminated assembly are deteriorated.

DISCLOSURE OF THE INVENTION

Technical problem

It is therefore an object of the present invention to provide a multilayer piezoelectric substrate assembly for an ultrasonic transducer and a method of manufacture.

Another object of the present invention is to provide a multilayer ultrasonic transducer with improved oscillation characteristics using a multilayer piezoelectric substrate assembly and a method of manufacturing the same.

Technical scheme

According to a first aspect of the present invention, there is provided a multilayer piezoelectric substrate assembly comprising: a first piezoelectric substrate having first electrode layers formed on first and second main surfaces and first and second side surfaces thereof, the first piezoelectric substrate having first and second discontinuities on the first and second main surfaces for dividing the first electrode layer into a first electrode and a second electrode isolated from each other; and a second piezoelectric substrate having a second electrode layer formed on the first and second main surfaces and the first and second side surfaces of the second piezoelectric substrate, the second piezoelectric substrate having third and fourth fractures dividing the second electrode layer into third and fourth electrodes isolated from each other, the first fracture being formed on the first main surface, wherein the first and second piezoelectric substrates are coupled to each other such that the second and third fractures face each other, thereby forming a first electrode node and a second electrode node, the first electrode node having the first and third electrodes and the second electrode node having the second and fourth electrodes.

According to a second aspect of the present invention, there is provided a multilayer ultrasonic transducer including the multilayer piezoelectric substrate assembly as described above.

According to a third aspect of the present invention, there is provided a method of manufacturing a multilayer piezoelectric substrate assembly, comprising the steps of: preparing first and second piezoelectric substrates on which electrode layers of a conductive material are deposited, respectively; forming first and second discontinuities and third and fourth discontinuities on top and bottom surfaces of the first and second piezoelectric substrates, respectively, to divide the electrode layer into first and second electrodes and third and fourth electrodes isolated from each other; and laminating the first and second piezoelectric substrates on top of each other by allowing the second discontinuity of the first piezoelectric substrate to face the third discontinuity of the second piezoelectric substrate to thereby form a first electrode node having the first and third electrodes coupled to each other and a second electrode node having the second and fourth electrodes coupled to each other.

According to a fourth aspect of the present invention, there is provided a method of manufacturing a multilayer ultrasonic transducer comprising a multilayer piezoelectric substrate assembly manufactured in accordance with the steps described above.

Advantageous effects

As described, the present invention is technically characterized in that electrodes can be isolated by forming fractures and grinding off edge portions in manufacturing a multilayer piezoelectric substrate assembly for manufacturing a multilayer ultrasonic transducer according to the present invention. By forming the multilayer substrate assembly having such a structure, the grounded flexible printed circuit board is coupled to the multilayer piezoelectric substrate assembly by using only the edge portions and the side surfaces of the electrodes, which can eliminate the need for an additional layer deposited between the multilayer piezoelectric substrate assembly and the matching layer. Accordingly, a multilayer ultrasonic transducer having improved oscillation characteristics, a wide bandwidth, and high sensitivity can be provided.

The method of manufacturing the multilayer piezoelectric substrate assembly according to the present invention can be used in the case of using piezoelectric single crystals and using piezoelectric ceramics. Conventionally, an ultrasonic transducer using a piezoelectric single crystal has a bandwidth 40% to 50% higher than that of a conventional transducer using a piezoelectric ceramic such as PZT, and is capable of achieving high resolution in ultrasonic image diagnosis. However, the ultrasonic transducer using the piezoelectric single crystal substrate also has the same problem as that in the ultrasonic transducer using the piezoelectric ceramic substrate, that is, it is difficult to improve the sensitivity and the signal-to-noise (S/N) ratio of the transducer because the mismatch between the transducer element and the system is large. In addition, since the piezoelectric single crystal substrate is mechanically and thermally fragile, it is easily damaged in a machining process including lapping, polishing, slicing steps, and a transducer manufacturing process including a bonding step and the like. However, according to the present invention, there is no layer on the front surface of the transducer, so the conventional problem that the sensitivity is lowered can be solved, and the problem that the piezoelectric single crystal substrate may be damaged in the manufacturing process is also solved because the electrodes are separated using a simple method such as grinding off the edges.

The piezoelectric element formed of the piezoelectric single crystal according to the present invention provides a higher dielectric constant than the piezoelectric element formed of the PZT type ceramic commonly used in the art. Therefore, by using the piezoelectric element formed of the piezoelectric single crystal according to the present invention, cable or device loss caused by parasitic capacitance therein can be reduced, which makes it possible to obtain a signal of higher sensitivity.

Drawings

The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments thereof, taken in conjunction with the accompanying drawings, in which:

FIGS. 1-7 illustrate a sequential process for fabricating a multi-layer piezoelectric substrate assembly in accordance with the present invention;

FIGS. 8-10 illustrate a sequential process for fabricating a multi-layer ultrasonic transducer using the multi-layer piezoelectric substrate assembly shown in FIGS. 1-7;

FIG. 11 shows a schematic view of the multi-layer ultrasound transducer shown in FIG. 10;

FIGS. 12 and 13 depict waveforms and spectra, respectively, that represent the oscillation characteristics of a PZT single layer transducer;

FIGS. 14 and 15 depict waveforms and spectra, respectively, that represent the oscillation characteristics of a PMN-PT single layer transducer; and

fig. 16 and 17 demonstrate waveforms and spectra representing oscillation characteristics of a multi-layered ultrasonic transducer according to the present invention.

Best mode for carrying out the invention

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

The multi-layer ultrasonic transducer according to the present invention is manufactured through a process sequentially illustrated in fig. 1 to 10.

As shown in fig. 1, first, two piezoelectric substrates, only one of which is shown in the drawing for simplicity, are prepared. Although the use of two piezoelectric substrates is shown and described in this embodiment, it is also possible to use more than two piezoelectric substrates to thereby manufacture a multilayer ultrasonic transducer having three or more substrate layers, if necessary. These piezoelectric substrates are used to oscillate upon application of Alternating Current (AC) to generate an ultrasonic signal in an ultrasonic transducer. The first piezoelectric substrate 10 has a first major (or top) surface 12, a second major (or bottom) surface 14, a first (or left) side surface 16 and a second (or right) side surface 18.

Then, as shown in fig. 2, an electrode layer 21 of a conductive material is uniformly deposited on each of the four surfaces 12 to 18 of the first piezoelectric substrate 10 using a sputtering, electron beam, thermal evaporation, or plating method. Subsequently, first and second discontinuities 32 and 34 are formed on the first and second main surfaces 12 and 14 of the first piezoelectric substrate 10, respectively, so that the two sections extend in the length direction of the first and second side surfaces 16 and 18. By forming the first and second discontinuities 32 and 34, the electrode layer 12 is divided into the first and second electrodes 22 and 24 isolated from each other, thus obtaining the piezoelectric substrate 10 on which the two isolated electrodes 22 and 24 are formed. The first and second electrodes 22 and 24 will function as a primary (negative) electrode and a secondary (positive) electrode, respectively.

The piezoelectric substrate 10 used in the present invention may be a piezoelectric ceramic substrate or a single crystal piezoelectric substrate, and its thickness is in the range of about 22 □ to 500 □, and preferably in the range of 50 □ to 220 □.

The electrodes 22 and 24 may be formed of a conductive film made of chromium, copper, nickel, gold, etc., and the thickness of the electrodes 22 and 24 may be in the range of about 100 □ to 1000 □.

Such an isolated electrode layer 21 can be obtained by forming a break of a certain thickness using, for example, a dicing saw. Specifically, the first and second discontinuities 32 and 34 are formed at predetermined distances from the opposite sides of the first and second surfaces 12 and 14 of the first piezoelectric substrate 10, respectively, to thereby divide the electrode layer 12 into (a) the first electrode layer 22 covering a small portion of the second main surface, the first side surface 16, and a large portion of the first main surface 12; and (b) a second electrode 24 covering a minor portion of the first major surface 12, the second side surface 18, and a major portion of the second major surface 14.

A first discontinuity 32 is formed at a location spaced apart from the right edge of the first main surface 12 of the first piezoelectric substrate 10, wherein the spaced-apart area is for receiving an adhesive to couple the electrode layer 21 and a ground electrode plate (not shown). For example, the first discontinuity 32 is preferably formed to have a width of about 0.03mm to 0.1mm and is formed at a distance of about 1mm to 1.5mm inward from the right edge of the first main surface 12. Meanwhile, the second discontinuity 34 is preferably formed to have a width of about 0.2mm to 0.5mm and is formed at a distance of about 1mm to 1.5mm inward from the left edge of the first main surface 14.

According to the present invention, it is preferable that the second discontinuity 34 is formed to be wider than the first discontinuity 32. Further, the depths of the first and second discontinuities 32 and 34 are preferably equal to about 70% to 80% of the thickness of the first piezoelectric substrate 10 to suppress the generation of oscillation. The adhesive for coupling the electrode layer 21 and the ground electrode plate may be an epoxy paste and preferably a silver epoxy paste.

Then, another piezoelectric substrate is prepared and manufactured as follows. As shown in fig. 4, by using the same method as described in fig. 2, an electrode layer of a conductive material is deposited on four surfaces of the other of the two substrates, i.e., the second piezoelectric substrate 20, and then the third discontinuity 36 is formed in the electrode layer 21 on the first main surface 12. In addition, the edge portion of the electrode layer 21 between the second main surface 14 and the second side surface 18 is ground away in the second side surface length direction, thereby forming an edge discontinuity 38. Therefore, similarly to the above, the electrode layer is divided into the third and fourth electrodes 26 and 28 isolated from each other to thereby obtain the second piezoelectric substrate 20 on which the isolated electrodes 26 and 28 are formed. The third and fourth electrodes 26 and 28 will function as secondary (positive) and primary (negative) electrodes, respectively.

More specifically, the third discontinuity 36 is formed on the first main surface of the second piezoelectric substrate 20 so as to make the discontinuity 36 away from the left edge of the first main surface 12 of the second piezoelectric substrate 20, wherein the distance to the left edge is equal to the interval maintained between the first side surface of the first piezoelectric substrate 10 and the second discontinuity 34 in fig. 2. In addition, the third discontinuity 36 has the same shape as the second discontinuity 34, while the edge discontinuity 38 is formed by abrasion.

Subsequently, the first and second piezoelectric substrates 10 and 20 on which the electrodes are formed as described above are polarized as shown in fig. 3 and 5, respectively, so that the first and fourth electrodes 22 and 28 are polarized as primary (negative) electrodes, and the second and third electrodes 24 and 26 are polarized as secondary (positive) electrodes. Then, the first piezoelectric substrate 10 is connected to the second piezoelectric substrate 20, or vice versa, so that the primary electrodes are connected to each other (i.e., the second discontinuity 34 and the third discontinuity 36 are adjacent to each other) and the secondary electrodes are connected to each other as shown in fig. 6 and 7. Thus, the first electrode node 42 and the second electrode node 44 are formed to thereby obtain the multilayer piezoelectric substrate assembly 100.

The two piezoelectric substrates can be joined using a silver epoxy adhesive as is well known in the art. Since the second and third discontinuities 34 and 36 isolate the electrodes with relatively wide channels, it is possible to prevent a short circuit from occurring between the primary electrode and the secondary electrode even in the case where the two piezoelectric substrates are misaligned with each other when connected.

After the multi-layer piezoelectric substrate assembly 100 is obtained, a stapler-shaped thin FPCB (flexible printed circuit board) 400 for signaling is coupled to the first electrode node 42 on the second main surface of the second piezoelectric substrate 20, and then a backing block 300 is disposed under the FPCB 400 so that the top surface and opposite side surfaces of the backing block 300 are surrounded by the FPCB 400. The FPCB 400 transmits and receives an electrical signal to and an ultrasonic signal from the multilayer piezoelectric substrate assembly 100. The backing plate 300 serves to absorb ultrasonic signals to prevent the oscillations caused by the ultrasonic signals generated by the multi-layer piezoelectric substrate assembly 100 from generating undesirable signals. In this regard, the FPCB 400 and the backing plate 300 may be coupled to each other in advance such that the FPCB 400 surrounds three surfaces of the backing plate 300, and then, the FPCB 400 thus surrounding the backing plate 300 may be coupled to the first electrode node 42.

Thereafter, as shown in fig. 9, a flexible electrode plate 500 connected to ground is disposed on one of the side surfaces in the vicinity of the first discontinuity 32, and connected to the second electrode node 44 with silver epoxy paste 600.

Subsequently, as shown in fig. 10, the acoustic matching layer 700 is coupled on the first electrode node 42 on the multilayer piezoelectric substrate assembly 100. The acoustic matching layer 700 has a smaller area than that of the multilayer piezoelectric substrate assembly 100, and the acoustic matching layer 700 is disposed on the multilayer piezoelectric substrate 100 so as to slightly extend through the second discontinuity 32. The acoustic matching layer 700 serves to match the piezoelectric substrate assembly 100 and a medium, for example, a human body, so that an ultrasonic signal from the piezoelectric substrate assembly 100 can smoothly propagate toward the medium in a desired direction. Then, the acoustic matching layer 700 is covered with an acoustic lens (not shown) to thereby obtain a multilayer ultrasonic transducer. Here, it is possible to stack two or more acoustic matching layers on the top surface of the multilayer laminated piezoelectric substrate assembly 100.

Fig. 8 shows a schematic cross-sectional view of the multi-layer ultrasound transducer shown in fig. 10. The thus obtained multilayer ultrasonic transducer according to the present invention has excellent oscillation characteristics, so that it can be used for various devices such as medical ultrasonic diagnostic systems and military/industrial ultrasonic transducers.

Hereinafter, preferred embodiments of the present invention will be described in detail. Here, it should be noted that the present invention is not limited thereto.

Examples of the invention

The multilayer ultrasonic transducer according to the preferred embodiment of the present invention is manufactured as follows.

A <001> single crystal piezoelectric substrate (PMN- (0.3 to 0.35)) PT having a thickness of about 0.4mm to 0.5mm and a size of about 25mm to 22mm × about 15mm to 22mm was prepared (see FIG. 1). Then, an electron beam deposition method is used to deposit the electrode layer 12 of conductive material having a thickness in the range of about 1000 □ to 2200 □ on the first main surface 12, the second main surface 14, the first side surface 16, and the second side surface 18 of the first piezoelectric substrate 10.

Then, another single-crystal piezoelectric substrate on which electrodes are formed is manufactured using the same method as above to thereby obtain a second piezoelectric substrate 20.

Subsequently, using a dicing saw, fractures 32 and 34 are formed in the electrode layers on the first and second main surfaces 12 and 14 of the first piezoelectric substrate 10, respectively, so as to divide the electrode layers into two electrodes 22 and 24 isolated from each other (refer to fig. 2). The discontinuities 32 and 34 are formed at a distance of about 1mm to 1.5mm inward from the second side surface 18 and the first side surface 16 of the first single piezoelectric substrate 10, respectively, and each have a depth of about 0.25mm to 0.35 mm.

As for the second single piezoelectric substrate 20, a break 36 is formed in the electrode layer on the first main surface of the second piezoelectric substrate 20 using a dicing saw, and the electrode layer at the edge portion between the second main surface and the second side surface of the second piezoelectric substrate 20 is removed to form an edge break 38 and divide the electrode layer into two electrodes 26 and 28 (refer to fig. 4). At this time, the discontinuity 36 is formed to have the same shape as the discontinuity 34 of the first piezoelectric substrate 10, and an edge discontinuity 38 is formed by grinding off the electrode layer of the edge portion between the second main surface and the second side surface of the second piezoelectric substrate 20.

Then, the first and second piezoelectric substrates 10 and 20 are polarized as shown in fig. 3 and 5 to set the electrodes 22 and 26 as primary (negative) electrodes, and the electrodes 24 and 28 as secondary (positive) electrodes. Then, as shown in fig. 6 and 7, the two substrates 10 and 20 are bonded to each other using a silver epoxy resin to make the fractures 34 and 36 abut each other, so that the primary electrodes are connected to each other and the secondary electrodes are connected to each other, thereby forming first and second electrode nodes 42 and 44. Thus, a layered piezoelectric single-crystal substrate assembly 100 according to the present invention was obtained.

Thereafter, as shown in fig. 8, the top surface of the FPCB 400, which is coupled to the first main surface and the two opposite side surfaces of the backing 300 in advance, is abutted to the first electrode node 42 located on the second main surface of the second piezoelectric substrate 20 of the multilayer laminated piezoelectric substrate assembly 100.

Then, as shown in fig. 9, the flexible ground electrode plate 500 is coupled to the second electrode node 44 of the layered piezoelectric substrate assembly 100 at the front side of the first discontinuity 32 using silver epoxy paste 600. Subsequently, as shown in fig. 10, an acoustic matching layer 700 is formed on the first electrode layer located on the first main surface of the first piezoelectric substrate 10, and then, by covering the acoustic matching layer 700 with an acoustic lens, a multilayer ultrasonic transducer according to the present invention is finally obtained.

Experimental examples

The pulse echo characteristics of each multilayer ultrasonic transducer according to the present invention were examined; PZT (Acuson P2-3AC available from Madison co.ltd, korea) similar to that disclosed in U.S. patent No. 6437487 (comparative example 1); and PMN- (0.3-0.35) PT system (comparative example 2) single layer transducer, and the results are provided in table 1 below and fig. 9-11.

Table 1

Properties of		Comparative example 1 (Single layer PZT)	Comparative example 2 (Single layer PMN-PT)	Preferred embodiment (multilayer PMN-PT)
					Relative sensitivity	DB	0	+4.1	+7.8
Center frequency	MHz	2.85	3.66	4.01
					-6dB bandwidth	％	60.2	107.9	101.0
-22dB bandwidth	％	98.7	134.7	137.4

From table 1, it can be found that the multilayer sensor according to the present invention has highly improved sensitivity and a larger bandwidth compared to a single layer PZT or a single layer crystal piezoelectric transducer.

Furthermore, by comparing fig. 9-11, it was found that the sensitivity of the multi-layer piezoelectric transducer according to the present invention is higher than that of the single-layer transducer by more than 4 dB.

As described above, the multilayer ultrasonic transducer according to the present invention is manufactured by forming electrodes in a novel structure by laminating a plurality of layers of piezoelectric materials. Thus, the multilayer ultrasonic transducer has improved oscillation characteristics, a wide bandwidth, and high sensitivity.

While the invention has been illustrated and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.

Claims (16)

1. A multi-layer piezoelectric substrate assembly comprising:

a first piezoelectric substrate having first electrode layers formed on first and second main surfaces and first and second side surfaces thereof, the first piezoelectric substrate having first and second discontinuities on the first and second main surfaces for dividing the first electrode layer into a first electrode and a second electrode isolated from each other; and

a second piezoelectric substrate having a second electrode layer formed on first and second main surfaces and on first and second side surfaces thereof, the second piezoelectric substrate having third and fourth discontinuities dividing the second electrode layer into a third electrode and a fourth electrode isolated from each other, the first discontinuities being formed on the first main surface,

wherein the first and second piezoelectric substrates are coupled to each other such that the second and third discontinuities are opposed to each other, thereby forming a first electrode node having the first and third electrodes and a second electrode node having the second and fourth electrodes.

2. The multi-layer piezoelectric substrate assembly of claim 1, wherein each of the first and second piezoelectric substrates comprises a single crystal piezoelectric substrate.

3. The multi-layer piezoelectric substrate assembly of claim 1, wherein each of the first and second piezoelectric substrates comprises a piezoelectric ceramic substrate.

4. The multi-layer piezoelectric substrate assembly of claim 1, wherein each of the first through third discontinuities are formed having a depth equal to about 70% to 80% of a thickness of a substrate on which the each of the first through third discontinuities are formed.

5. The multi-layer piezoelectric substrate assembly of claim 1, wherein the fourth discontinuity is formed between the second major surface and the second lateral surface of the second piezoelectric substrate.

6. The multi-layer piezoelectric substrate assembly of claim 1, wherein the second discontinuity has a width greater than the width of the first discontinuity and substantially the same as the width of the third discontinuity.

7. The multi-layer piezoelectric substrate assembly of claim 6, wherein the width of the second and third discontinuities are set in the range from about 0.2mm to 0.5mm, and the width of the first discontinuity is set in the range from about 0.03mm to 0.1 mm.

8. The multi-layer piezoelectric substrate assembly of claim 1, wherein the first and second discontinuities are each formed about 1mm to 1.5mm inward from the first and second side surfaces of the first piezoelectric substrate, respectively, and the third discontinuity is formed about 1mm to 1.5mm inward from the first side surface of the second piezoelectric substrate.

9. A multilayer ultrasonic transducer comprising the multilayer piezoelectric substrate assembly of claim 1.

10. The multi-layer ultrasound transducer of claim 9, further comprising:

a flexible printed circuit board coupled to the first electrode node;

a backing plate surrounded by the flexible printed circuit board;

a grounded flexible printed circuit board coupled to the second electrode node; and

an acoustic matching layer deposited on the multi-layer piezoelectric substrate assembly.

11. A method for manufacturing a multilayer piezoelectric substrate assembly, comprising the steps of:

preparing first and second piezoelectric substrates on which electrode layers of a conductive material are deposited, respectively;

forming first and second discontinuities and third and fourth discontinuities on top and bottom surfaces of the first and second piezoelectric substrates, respectively, to divide the electrode layer into first and second electrodes and third and fourth electrodes isolated from each other; and

stacking the first and the second piezoelectric substrates on top of each other by making the second discontinuity of the first piezoelectric substrate face the third discontinuity of the second piezoelectric substrate to thereby form a first electrode node having the first and the third electrodes coupled to each other and a second electrode node having the second and the fourth electrodes coupled to each other.

12. The method of claim 11, further comprising the step of:

polarizing the first and second substrates to produce the first and second electrode nodes having different polarities from each other.

13. The method of claim 11, wherein each of the first, second, and third interruptions is formed using a dicing saw.

14. The method of claim 11, wherein the fourth discontinuity is formed between the second major surface and the second lateral surface of the second piezoelectric substrate by abrasion.

15. A method for manufacturing a multilayer ultrasonic transducer comprising the multilayer piezoelectric substrate assembly manufactured by the method of claim 11.

16. The method of claim 15, further comprising:

coupling a flexible printed circuit board to the first electrode node;

coupling a grounded flexible printed circuit board to the second electrode node; and

an acoustic matching layer is formed on the multilayer piezoelectric substrate assembly.