JP3906126B2 - Ultrasonic transducer and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic transducer mainly used in a medical ultrasonic diagnostic apparatus and a nondestructive inspection apparatus, and more particularly to an ultrasonic transducer using a laminated piezoelectric material and a manufacturing method thereof.
[0002]
[Prior art]
In the field of medical ultrasonic diagnostic equipment and non-destructive testing equipment, PZT (zircon-lead titanate) -based piezoelectric ceramics and relaxors / lead titanate-based piezoelectric single crystals are used as ultrasonic transducers for transmitting and receiving ultrasound. ing.
[0003]
Conventionally, a one-dimensional array probe in which a plurality of PZT piezoelectric ceramic vibrators processed in a strip shape is arranged is mainly used as an ultrasonic transducer of a medical ultrasonic diagnostic apparatus. Recently, in order to increase the sensitivity of this one-dimensional array probe or to enable low voltage driving, an ultrasonic transducer using a laminated piezoelectric material has been developed.
[0004]
In addition, research on a two-dimensional array probe in which minute rod-shaped vibrators are two-dimensionally arranged has been performed in response to a demand from a conventional two-dimensional (tomographic) image to a three-dimensional image. In a two-dimensional array probe, since one element is very small, when conventional piezoelectric ceramics are used, impedance increases and transmission / reception sensitivity decreases. For this reason, a two-dimensional array probe using a laminated piezoelectric material has been studied.
[0005]
The laminated piezoelectric material has a structure in which a plurality of piezoelectric materials and internal electrodes are alternately laminated, and PZT ceramics is used as the piezoelectric material, and Pt and Ag / Pd are used as the internal electrodes by simultaneous firing (1100 to 1250 ° C.). Can be configured. These techniques are described in USP 5,163,436 and R.I. L. Goldberg, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, vol. 41, no. 5 September 1994, pp. 5-7. 761 to 771 and the like. The internal electrodes in such a laminated piezoelectric material are, for example, covered every other layer with an insulating material such as glass, and the internal electrode ends exposed every other layer are commonly connected with a conductive material. By doing so, conduction is achieved. Although it is necessary to perform the polarization treatment of the piezoelectric body after connecting the wiring of the internal electrode, it becomes structurally difficult to apply an ideal electric field as the vibrator becomes finer. As a result, sufficient polarization processing cannot be performed. Furthermore, the mechanical load generated by the material connecting the wirings of the internal electrodes on the side surface of the vibrator also increases, making it difficult to fully draw out the characteristics inherent to the piezoelectric body. Actually, the vibrator manufactured by the co-firing has a tendency to decrease the electromechanical coupling coefficient although the effective capacity increases.
[0006]
On the other hand, since the co-fired laminated piezoelectric material is expensive and difficult to manufacture, a piezoelectric plate having a plurality of gap grooves is laminated with an adhesive in advance, and then divided by dicing and ultrasonic probe is performed. A method for manufacturing a child has been proposed (Japanese Patent Laid-Open No. 2001-29346). However, in this method, the upper and lower gap grooves cannot be easily aligned. In addition, since it is an adhesive laminate, there is a problem that mechanical strength is insufficient and division by dicing is difficult.
[0007]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a fine high-performance ultrasonic transducer having a sufficient mechanical strength with little deterioration in piezoelectric and dielectric characteristics such as an electromechanical coupling coefficient.
[0008]
In addition, the present invention makes it easy to manufacture fine high-performance ultrasonic transducers with sufficient mechanical strength, with less degradation of piezoelectric and dielectric properties such as electromechanical coupling coefficient, using a co-fired laminated piezoelectric material. It aims to provide a way to do.
[0009]
[Means for Solving the Problems]
According to one aspect of the present invention, a backing material, a plurality of laminated piezoelectric bodies arranged in an array on the backing material, and a plurality of acoustic matching layers arranged on each of the laminated piezoelectric bodies, Have
The laminated piezoelectric body is
A laminate comprising first and second piezoelectric bodies alternately laminated and fully polarized ;
First and second external electrodes respectively disposed on opposing first and second side surfaces of the laminate;
The first piezoelectric body is disposed in direct contact with the upper surface of the first piezoelectric body and the lower surface of the second piezoelectric body stacked on the first piezoelectric body, and is electrically connected to the first external electrode. A first internal electrode in contact with the second external electrode through a U-shaped insulating portion including an insulating material having an acoustic impedance value of 3 Mrayls or less ;
The upper surface of the second piezoelectric body and the lower surface of the first piezoelectric body laminated on the second piezoelectric body are arranged in direct contact with each other and electrically connected to the second external electrode. There is provided an ultrasonic transducer comprising a second internal electrode in contact with the first external electrode through a U-shaped insulating portion containing an insulating material having an acoustic impedance value of 3 Mrayls or less. The
[0010]
According to another aspect of the present invention, a plurality of piezoelectric bodies and internal electrodes are alternately stacked and fired simultaneously, and each piezoelectric body is subjected to polarization treatment and cut into a predetermined shape, and then the Curie temperature of the piezoelectric body The U-shaped insulating portion containing an insulating material having an acoustic impedance value of 3 Mrayls or less is formed on every other end of the internal electrode while keeping the temperature below, and the exposed end of the internal electrode is formed. Forming a laminated piezoelectric body by forming an external electrode connected to the portion;
An ultrasonic wave comprising: a step of arranging a plurality of the laminated piezoelectric bodies in an array on a backing material; and a step of arranging an acoustic matching layer on the laminated piezoelectric bodies arranged in the array. A method of manufacturing a transducer is provided.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing an example of the structure of a laminated piezoelectric material used in an ultrasonic transducer according to an embodiment of the present invention.
[0012]
The laminated piezoelectric material shown in FIG. 1 covers a plurality of piezoelectric materials 1a and 1b laminated only via internal electrodes 2a and 2b, and ends of each of the internal electrodes 2a and 2b on every other side. And insulating electrodes 4 and external electrodes 3a and 3b electrically connected to the ends of the internal electrodes 2a and 2b exposed on the other side surface, respectively. As the piezoelectric bodies 1a and 1b, piezoelectric ceramics such as PZT and barium titanate, PZNT (Pb (Zn _1/3 Nb _2/3 ) O ₃ -PbTiO ₃ ) and PMNT (Pb (Mg _1/3 Nb _{2/3) are used.} ) A piezoelectric single crystal such as O ₃ —PbTiO ₃ ) is used, and each is completely polarized in the direction indicated by the arrow in the figure. The two types of piezoelectric bodies that are alternately stacked and polarized in opposite directions can be referred to as first and second piezoelectric bodies. Specifically, the first piezoelectric body 1a and the second piezoelectric body 1b disposed on the first piezoelectric body 1a are joined only through the first internal electrode 2a. The first internal electrode 2 a is electrically connected to the first external electrode 3 a and is in contact with the second external electrode 3 b through the insulating material 4. Further, the second piezoelectric body 1b and the first piezoelectric body 1a disposed thereon are joined only through the second internal electrode 2b. The second internal electrode 2 b is electrically connected to the second external electrode 3 b and is in contact with the first external electrode 3 a through the insulating material 4.
[0013]
Pt, Ag / Pd or the like can be used as the internal electrodes 2a and 2b, and an Au / Cr sputtered film or the like is used as the external electrodes 3a and 3b. Further, as the insulating material 4, a material that cures at a temperature lower than the Curie temperature of the piezoelectric body 1, for example, an epoxy resin is used.
[0014]
The laminated piezoelectric material used in the embodiment of the present invention can be manufactured, for example, by the following method. First, the piezoelectric bodies 1 and the internal electrodes 2 are alternately laminated, and a laminated piezoelectric body is manufactured by simultaneous firing. The thickness of the piezoelectric body 1 per layer is about 10 to 300 μm, the thickness of the internal electrode 2 is about 0.5 to 10 μm, and about 2 to 10 layers are laminated. At this time, in order to remove unpolarized portions or non-uniformly polarized portions by processing after polarization, it is desirable that the width and length of the laminated piezoelectric material be sufficiently large. For example, when obtaining a plate-like vibrator having an area of 12 mm × 24 mm, the width and length are about 22 mm and 34 mm, respectively. After lamination, the internal electrodes 2 are temporarily connected every other layer, and an electric field of 1 to 3 kV / mm is applied for several minutes to subject the piezoelectric body 1 to polarization treatment. Thereafter, it is cut into a shape used as an ultrasonic transducer, for example, a plate having an area of about 12 × 24 mm. Since it is cut into a predetermined shape after performing the polarization treatment, a state in which all the piezoelectric layers are completely polarized to the end after cutting, that is, a state in which the directions of polarization are aligned in the entire plane is obtained. .
[0015]
Next, a concave groove is formed on the side surface of the multilayer dielectric using a dicing saw or the like every other layer so as to remove the end portion of the internal electrode 2 exposed on one side surface of the multilayer piezoelectric body. . The groove depth (lateral direction in FIG. 1) is preferably about 10 to 100 μm. When the thickness is less than 10 μm, it is difficult to sufficiently insulate. On the other hand, when the thickness exceeds 100 μm, a portion where voltage cannot be applied becomes a non-negligible size and the piezoelectric characteristics may be deteriorated. In particular, it is preferable that the groove depth is determined so as to satisfy the condition expressed by the following mathematical formula (1), since the piezoelectric characteristics are hardly deteriorated and the characteristics of the ultrasonic transducer are improved.
[0016]
w ₂ / w ₁ ≦ 0.15 (1)
(W ₁ is the width of the piezoelectric body, and w ₂ is the depth of the groove.)
The width of the groove (vertical direction in FIG. 1) is preferably about 10 to 30 μm. If the thickness is less than 10 μm, it is difficult to sufficiently insulate, while if it exceeds 30 μm, the influence of a mechanical load due to the insulating material to be filled appears and the piezoelectric characteristics may be deteriorated. In particular, when the groove width is determined so as to satisfy the condition expressed by the following mathematical formula (1), it is preferable because the performance of the ultrasonic transducer is improved with almost no deterioration of the piezoelectric characteristics.
[0017]
t ₂ / t ₁ ≦ 0.5 (2)
(Here, t ₁ is the thickness of the piezoelectric body, and t ₂ is (groove width) / 2.)
The side surface after the groove processing is immersed in an etching solution such as ammonium fluoride or nitric acid. By this etching process, the concave groove is isotropically etched, so that a corner is removed and a U-shaped shape is obtained. The most preferred shape is a semicircle because the cross-sectional area is small and stress is not concentrated. As shown in the figure, U-shaped grooves are similarly formed on the opposite side surfaces so that the grooves on both side surfaces are staggered. Since the groove formed on the side surface of the laminated piezoelectric material is U-shaped and does not have a corner portion, there is no risk of crack breakage from the corner portion, which is advantageous in terms of mechanical strength. In addition, since the cross-sectional area of the groove is smaller than in the case of the concave square groove, the mechanical load is small and the piezoelectric characteristics are improved.
[0018]
The U-shaped groove formed in this way is filled with an insulating material 4 such as an epoxy resin, which is applied and cured, or deposited and deposited by sputtering. A normal epoxy resin has an acoustic impedance value of about 3.2 Mrayls, but the smaller the value, the better the characteristics such as the electrical coupling coefficient. For example, the acoustic impedance of some special epoxy resins such as EPO-TEK301 (manufactured by epoxy technology) is about 3Mrays, and the acoustic impedance of liquid or air is about 2Mrays. Therefore, it is most preferable that the U-shaped insulating portion is constituted by a groove and an insulating material such as liquid or air filled therein.
[0019]
Since the piezoelectric layer is subjected to polarization treatment in the preceding process, the subsequent processes such as application and curing of the insulating material must be performed at a temperature equal to or lower than the Curie temperature of the piezoelectric body. The Curie temperature is determined according to the type of the piezoelectric body, and is, for example, about 200 to 300 ° C. for PZT piezoelectric ceramics and about 175 ° C. for PZNT piezoelectric single crystals.
[0020]
After the U-shaped insulating portion is formed, electrode films to be the external electrodes 3a and 3b are formed on both side surfaces by sputtering. The external electrodes 3a and 3b are also formed at a temperature lower than the Curie temperature of the piezoelectric body as described above.
[0021]
10 layers of the piezoelectric body 1 having an area of 12 × 24 mm and a thickness of 60 μm were laminated through the internal electrode 2 by the above method, and processed into a strip-shaped vibrator having a width of 0.200 mm, as shown in FIG. Such a laminated piezoelectric material was obtained. When the electromechanical coupling coefficient of the laminated piezoelectric material was measured, an electromechanical coupling coefficient k ′ ₃₃ of about 66% was obtained. This value is almost the same as the 69% value of the bulk piezoelectric material that is not laminated. Therefore, it was confirmed that the use of the embodiment of the present invention hardly caused the characteristic deterioration due to the lamination. The impedance characteristics of the laminated piezoelectric vibrator obtained here are shown in the graph of FIG. In the graph of FIG. 2, the size of the arrow corresponds to the size of the coupling coefficient.
[0022]
For comparison, FIG. 3 shows the impedance characteristics of a multilayered piezoelectric material that was prototyped using the prior art. Specifically, a multilayer piezoelectric body was manufactured by adopting a method described in Japanese Patent Application Laid-Open No. 2001-102647. In the laminated piezoelectric material thus manufactured, the insulating material portion is concave, and the cross section is larger than that of the U-shape. In addition, since an adhesive curing process of 200 ° C. or higher is included, the polarization treatment is performed after laminating a plurality of piezoelectric layers. For this reason, an ineffective portion is generated at the end of the piezoelectric layer, and unnecessary vibration may occur as shown in the graph of FIG. 3, and the electromechanical coupling coefficient may be reduced.
[0023]
As shown in the graph of FIG. 2, the laminated piezoelectric vibrator manufactured by the above-described method has no unnecessary vibration, and the electromechanical coupling coefficient maintains the characteristics of the bulk piezoelectric substance that is not laminated. In such a laminated piezoelectric material, since the piezoelectric material layer is laminated only through the internal electrodes and is produced by simultaneous firing, there is no adhesive. For this reason, a decrease in mechanical strength due to the adhesive is avoided. In addition, since the laminated body is cut into a desired shape, the laminated body can be manufactured without a complicated process such as positioning by a groove provided in the piezoelectric body. In addition, since the apparent dielectric constant increases several times as many as the number of layers, the ultrasonic transducer according to the embodiment of the present invention using this layered piezoelectric body can be expected to improve characteristics such as a significant improvement in sensitivity.
[0024]
FIG. 4 is a schematic diagram showing the configuration of an ultrasonic transducer according to an embodiment of the present invention. The illustrated ultrasonic transducer is a one-dimensional array probe in which a plurality of laminated piezoelectric bodies 11 in which a first acoustic matching layer 12 and a second acoustic matching layer 13 are sequentially laminated are arranged one-dimensionally on a backing material 14. It is. Although not clearly shown in FIG. 4, the laminated piezoelectric material 11 has a structure in which the laminated piezoelectric material 11 is laminated in the same direction as in FIG. 1, and is manufactured by the method described above. Such a one-dimensional array probe can be manufactured by the following method, for example. First, the laminated piezoelectric material 11 is bonded to the backing material 14, and then the acoustic matching layers 12 and 13 are formed. Finally, array processing is performed in a direction perpendicular to the side surface on which the external electrode (not shown) is formed, and signal lines (not shown) are wired to the external electrode on one side surface of each array, and the other side surface These external electrodes are commonly connected to a GND line (not shown).
[0025]
In the ultrasonic transducer of this embodiment, the apparent dielectric constant of each transducer is improved, and the electromechanical coupling coefficient can maintain the characteristics of the bulk piezoelectric material that is not stacked. Therefore, the sensitivity can be greatly improved and the driving voltage can be reduced.
[0026]
FIG. 5 is a schematic diagram showing the configuration of an ultrasonic transducer according to another embodiment of the present invention. The illustrated ultrasonic transducer includes a two-dimensional array probe in which a plurality of laminated piezoelectric bodies 11 in which a first acoustic matching layer 12 and a second acoustic matching layer 13 are sequentially laminated are two-dimensionally arranged on a backing material 14. It is. Such a two-dimensional array probe is basically the above-described primary except that one column is prepared and array processing is performed, and a signal line and a GND line are connected, and then a plurality of transducer groups for one column are joined. It can be manufactured by the same method as the original array probe.
[0027]
An example of a method for manufacturing the two-dimensional array probe shown in FIG. 5 is shown in FIG.
[0028]
First, as shown in FIG. 6A, one row of laminated piezoelectric elements 11 is bonded to a flexible printed circuit board (FPC) 15 having a predetermined wiring pattern. The laminated piezoelectric body 11 can have a structure shown in FIG. 1, for example. Next, the ground side electrode 16 and the signal side electrode 17 of the FPC 15 and the electrode of the laminated piezoelectric body 11 are connected as shown in FIG. 6B using a thin film electrode 18 such as an Au sputtered film. Further, the acoustic matching layers 12 and 13 are formed in the ultrasonic transmission / reception direction as shown in FIG. 6 (c), and the array division processing is performed as shown in FIG. 6 (d). Finally, as shown in FIG. 6E, a filling resin is filled between the divided elements, and the backing material 14 is bonded.
[0029]
Through the above process, one row of the two-dimensional array probe is produced. A two-dimensional array probe can be obtained by stacking and joining a plurality of transducers for one row as shown in FIG.
[0030]
FIG. 7 is a cross-sectional view showing the structure of another example of the laminated piezoelectric material used in the ultrasonic transducer according to the embodiment of the present invention.
[0031]
The laminated piezoelectric material shown in the figure has basically the same configuration as that shown in FIG. 1 and can be manufactured by the same process as described above. However, as the insulating material 4, a resin having a low adhesive strength with the piezoelectric body 1 such as an epoxy resin is used. By using such a resin, a gap as illustrated is formed between the concave groove on the side surface of the piezoelectric body 1 and the insulating material 4. Even when no gap is formed, a state in which the piezoelectric body 1 and the insulating material 4 are mechanically loosely bonded can be obtained. By adopting such a structure, the mechanical load applied to the side surface of the piezoelectric body 1 is reduced, so that a decrease in piezoelectric / dielectric characteristics such as an electromechanical coupling coefficient can be reduced.
[0032]
A laminated piezoelectric material as shown in FIG. 7 was fabricated by forming an epoxy resin as the insulating material 4 by sputtering and having a partial gap between the concave groove and the insulating material (epoxy resin). As a result of evaluating the obtained laminated piezoelectric material, the value of the electromechanical coupling coefficient k ′ ₃₃ is about 67%, which is a better characteristic than when an epoxy adhesive having high adhesive strength with the piezoelectric material is used. was gotten.
[0033]
Furthermore, the laminated piezoelectric material used in the ultrasonic transducer according to the embodiment of the present invention may have a cross-sectional structure as shown in FIG.
[0034]
In the laminated piezoelectric material shown in FIG. 8, the U-shaped concave grooves 5 are all voids. This void can be formed by the following method after the U-shaped groove is formed by the same process as described with reference to FIG. The U-shaped groove is filled with a material that can be removed by etching, such as a resist material, and cured. The material filled here is dissolved and removed using an etching solution after external electrodes are formed on both side surfaces. Alternatively, even if the U-shaped groove is filled with a material that is melted by heat such as wax, the void can be formed by the same process.
[0035]
As described above, since the acoustic impedance of air is 2 Mrayls or less, the piezoelectric characteristics such as the mechanical coupling coefficient can be remarkably improved by making the inside of the U-shaped groove hollow. This is because the inner surface of the groove is not subjected to any mechanical load because it is hollow.
[0036]
As a result of trial manufacture and evaluation of a laminated piezoelectric material having such a structure, an electromechanical coupling coefficient almost equal to that of a bulk piezoelectric material was obtained.
[0037]
【The invention's effect】
As described above in detail, according to one aspect of the present invention, there is provided a fine high-performance ultrasonic transducer having a sufficient mechanical strength with little decrease in piezoelectric / dielectric characteristics such as an electromechanical coupling coefficient. In addition, according to another aspect of the present invention, a fine high-performance ultrasonic transducer having a sufficient mechanical strength and having a sufficient decrease in piezoelectric / dielectric properties such as an electromechanical coupling coefficient, and a co-fired laminated piezoelectric A method of easily manufacturing using a body is provided.
[0038]
The present invention can be suitably used for a medical ultrasonic diagnostic apparatus, a nondestructive inspection apparatus, and the like, and its industrial value is tremendous.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing the structure of a laminated piezoelectric body in an ultrasonic transducer according to an embodiment of the present invention.
FIG. 2 is an impedance characteristic diagram of a laminated piezoelectric body in the ultrasonic transducer according to the embodiment of the invention.
FIG. 3 is an impedance characteristic diagram of a conventional laminated piezoelectric material.
FIG. 4 is a schematic diagram showing the configuration of a one-dimensional array ultrasonic transducer according to an embodiment of the present invention.
FIG. 5 is a schematic diagram showing a configuration of a two-dimensional array ultrasonic transducer according to another embodiment of the present invention.
FIG. 6 is a process diagram illustrating a manufacturing process of the two-dimensional array ultrasonic transducer according to the embodiment of the invention.
FIG. 7 is a cross-sectional view showing the structure of a laminated piezoelectric body in the ultrasonic transducer according to the embodiment of the invention.
FIG. 8 is a cross-sectional view showing the structure of a laminated piezoelectric body in the ultrasonic transducer according to the embodiment of the invention.
[Explanation of symbols]
1a, 1b ... piezoelectric bodies 2a, 2b ... internal electrodes 3a, 3b ... conductive films (external electrodes)
DESCRIPTION OF SYMBOLS 4 ... Insulator 5 ... U-shaped groove 11 ... Laminated piezoelectric material 12 ... 1st acoustic matching layer 13 ... 2nd acoustic matching layer 14 ... Backing material 15 ... Flexible printed circuit board 16 ... Ground side electrode 17 ... Signal line side electrode 18 ... Thin film electrode

Claims (4)

A backing material, a plurality of laminated piezoelectric bodies arranged in an array on the backing material, and a plurality of acoustic matching layers arranged on each of the laminated piezoelectric materials,
The laminated piezoelectric material is
A laminate comprising first and second piezoelectric bodies alternately laminated and fully polarized ;
First and second external electrodes respectively disposed on opposing first and second side surfaces of the laminate;
The first piezoelectric body is disposed in direct contact with the upper surface of the first piezoelectric body and the lower surface of the second piezoelectric body stacked on the first piezoelectric body, and is electrically connected to the first external electrode. A first internal electrode in contact with the second external electrode through a U-shaped insulating portion including an insulating material having an acoustic impedance value of 3 Mrayls or less ;
The upper surface of the second piezoelectric body and the lower surface of the first piezoelectric body laminated on the second piezoelectric body are arranged in direct contact with each other and electrically connected to the second external electrode. An ultrasonic transducer comprising: a second internal electrode in contact with the first external electrode through a U-shaped insulating portion containing an insulating material having an acoustic impedance value of 3 Mrayls or less . 2. The ultrasonic transducer according to claim 1, wherein the U-shaped insulating portion includes a concave groove that is provided over the first and second piezoelectric bodies adjacent to each other and is filled with air as an insulating material. . The U-shaped insulating portion includes a concave groove provided over the adjacent first and second piezoelectric bodies, and an insulating material disposed in the concave groove without being mechanically coupled to these piezoelectric bodies. The ultrasonic transducer according to claim 1, further comprising: A plurality of piezoelectric bodies and internal electrodes are alternately laminated and fired at the same time, and each piezoelectric body is subjected to polarization treatment and cut into a predetermined shape, and then the internal temperature is kept below the Curie temperature of the piezoelectric body. A U-shaped insulating portion including an insulating material having an acoustic impedance value of 3 Mrayls or less is formed on one end of the electrode, and an external electrode connected to the exposed end of the internal electrode is formed. Obtaining a laminated piezoelectric material;
A step of arranging a plurality of the laminated piezoelectric bodies in an array on a backing material; and
Steps of arranging acoustic matching layers on the laminated piezoelectric elements arranged in the array
A method of manufacturing an ultrasonic transducer, comprising:

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