JPH01174199A - Manufacture of multi-layer ultrasonic probe - Google Patents

Abstract

PURPOSE:To improve the reliability and resolution by applying a paste including ceramic powder to a green sheet of a piezoelectric ceramics, making a laminator, incorporating the internal electrode layer and forming an outer electrode layer. CONSTITUTION:A paste material 2 having a composition of arranging 16-25wt.% of piezoelectric ceramic powder to internal electrode metallic powder is applied to a green sheet 1 making the piezoelectric ceramics as the major component in the thickness of 10-15mum. The green sheet 1 is used to form a laminator where at least one layer of the coating film of the paste material 2 is interposed in its inside. The laminator is calcined to incorporate the internal electrode layer in the piezoelectric ceramics layer. Moreover, after the outer electrode layer is formed, the resulting layer is cut off as arrays.

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention (Field of Industrial Application) The present invention relates to a method of manufacturing a multilayer ultrasound probe used in an ultrasound diagnostic device or the like.

(Prior art) An ultrasonic probe is an ultrasonic transducer using a piezoelectric element, and is used in medical ultrasonic diagnostic equipment and ultrasonic metal flaw detection equipment that inspects the internal state of objects by reflecting ultrasonic waves. It is used in Among various types of ultrasound probes, so-called array-type ultrasound probes, in which a plurality of elongated transducers are arranged in an array for the purpose of increasing resolution, are often used. Also, in recent years,
Ultrasonic diagnostic devices capable of obtaining Doppler information on blood flow have been developed and manufactured. The ultrasonic probe used in such a device is called an electronic sector ultrasonic probe, and has a similar structure to the array type ultrasonic probe, but is smaller in shape. . These array-type ultrasound probes and electronic sector ultrasound probes are used, for example, in research to obtain Doppler signals from the coronary arteries of the heart, so the demand for them is expected to increase further in the future. .

On the other hand, when considering signal transmission between the ultrasonic probe and the transmitting/receiving system, it is desirable to reduce the impedance from the viewpoint of improving S/N. For this reason, efforts are being made to develop piezoelectric ceramic materials and to laminate piezoelectric ceramic layers and internal electrode layers. For example, a method of manufacturing an array-type ultrasonic probe having the following laminated structure is known. First, a paste containing metal powder for internal electrodes is applied onto a green sheet whose main component is lead zirconate titanate (PZT)-based piezoelectric ceramics, and then the green sheet is used to apply the paste. A laminate having at least one layer interposed therein is produced. Subsequently, this laminate is fired to integrate an internal electrode layer between the piezoelectric ceramic layers, and after processing the outer diameter, an external electrode layer is formed. Next, this laminated structural material is fixed to the backing material, and the leads are connected to the external 'K1 layer. After forming a matching layer on the upper surface, the matching layer and the laminated structural material are shaped into an array using a diamond blade or the like. An array-type ultrasonic probe is manufactured by cutting into pieces. The ultrasonic probe manufactured in this way has at least one internal electrode layer formed between a plurality of piezoelectric ceramics, and the laminated structure material that formed the external electrode is cut into an array shape with a blade. It is composed of vibrators, a backing material for fixing these vibrators, lead wires connected to external electrodes of the vibrators, and a matching layer provided on the surface of each vibrator. In a probe having such a structure, it is necessary to cut the laminated structure material on which the external electrode layer is formed into a narrow width with a blade in order to improve the resolution mentioned above.

Further, after cutting with the blade, it is necessary that the internal electrode layer integrated with the piezoelectric ceramic layer by firing is connected along the cutting direction so that an open failure of the internal electrode does not occur.

Furthermore, since high frequencies will be applied to the external and internal electrodes through the leads in the future for the purpose of improving the resolution, it is necessary to maintain the internal electrodes in a good conductive state.

However, in the ultrasonic probe manufactured by the method described above, the internal electrode layer containing metal powder does not adhere well to the piezoelectric ceramic layer after firing, so when cutting with a diamond blade, the internal electrode layer does not adhere well to the piezoelectric ceramic layer. There was a problem with peeling. In particular, as the cutting pitch by the blade becomes narrower, peeling tends to occur more easily. A vibrator whose internal electrode is partially peeled off excites unwanted mode vibrations,
Cannot withstand use as an ultrasound probe.

For this reason, a paste-like material containing 2 to 15% piezoelectric ceramic powder mixed with metal powder for internal electrodes is printed and applied onto a green sheet whose main component is piezoelectric ceramic. JP-A No. 57-36880 discloses that a piezoelectric vibrator is manufactured by producing a laminate using the above method and sintering it in the same manner as described above. However, in this method, in order to ensure good adhesion of the internal electrode layer to the piezoelectric ceramic layer after firing, it is necessary to apply the paste to the green sheet with a relatively thin thickness of 5 to 9 μm. be. the result,
The thickness of the internal electrodes after cutting is not made sufficiently thick, and the conductivity deteriorates, making it difficult to drive at high frequencies. Also,
Even when the thickness of the internal electrode layer is made thinner, the piezoelectric ceramics are roughly dispersed in the mesh-like internal electrode metal that makes up the electrode layer, and after cutting with a blade, the wires do not connect along the cutting direction and break in the middle. There is a risk that it will be done.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned conventional problems, and it is possible to reduce the impedance.
A multilayer superstructure that allows for the formation of internal electrode layers that adhere well to the piezoelectric ceramic layer, have a network structure in which the electrode metal is well connected along the cutting direction of the blade, and have sufficient conductivity. The present invention aims to provide a method for manufacturing a sonic probe.

[Objective of the Invention] (Means for Solving the Problems) The present invention provides a paste-like material having a composition in which 16 to 25 weight 96 of piezoelectric ceramic powder is blended with metal powder for internal electrodes.
10 on a green sheet whose main component is piezoelectric ceramics
After coating to a thickness of ~15 μm, the green sheet is used to create a laminate in which at least one layer of the paste-like material is interposed, and the laminate is fired to form a layer between the piezoelectric ceramic layers. The method is characterized by comprising a step of integrating an internal electrode layer with the electrode layer, further forming an external electrode layer, and then cutting the electrode layer into an array shape.

Examples of the piezoelectric ceramics mentioned above include lead zirconate titanate (PZT), three-component ceramics in which magnesium and lead niobate are dissolved in PZT as a base, and those in which this three-component lead is combined with barium, strontium, etc. Examples include those substituted with alkaline earth elements.

The piezoelectric ceramic powder mixed in the paste-like material plays the role of firmly adhering the internal electrode layer to the upper and lower piezoelectric ceramic layers after firing.
It is desirable to increase the degree of contact between the piezoelectric ceramic powder in the internal electrode layer and the upper and lower piezoelectric ceramic layers by making the piezoelectric ceramic powder approximate the thickness of the internal electrode layer after sintering.

Examples of the metal for the internal electrodes include Pt, Pd, and A.
Examples include g-Pd and the like. In addition, examples of the metal for the external electrode include Ag and the like.

The reason for limiting the blending amount of the piezoelectric ceramic powder constituting the paste is that if the amount is less than 16% by weight relative to the internal electrode metal powder, the paste can be applied thickly within the above range. After firing, the adhesion between the upper and lower piezoelectric ceramic layers cannot be sufficiently improved, and on the other hand, if the amount exceeds 25% by weight, the amount of insulating piezoelectric ceramics in the internal electrode layer increases and its conductivity deteriorates. This is because sex is damaged.

The reason for limiting the coating thickness of the paste to the above range is that if the thickness is less than 10 μm, the conductivity of the internal electrode layer formed by firing will be impaired; This is because the piezoelectric ceramic powder is buried in the internal electrode layer and the degree of contact with the upper and lower piezoelectric ceramics is reduced, making it impossible to make good contact between the internal electrode layer and the piezoelectric ceramic. Note that if the size of the piezoelectric ceramic powder is approximated to the thickness of the internal electrode layer after firing as described above, it is possible to apply a paste to a thickness exceeding 15 μm, but in such a case In this case, the particle size of the piezoelectric ceramic powder itself added to the paste becomes large, and the mutual sinterability of the powders decreases, so the upper limit of the thickness of the paste is limited to 15 μm or less.

The firing temperature of the laminate is preferably 1100 to 1300°C. The firing may be performed in an oxidizing atmosphere such as the air. Note that the piezoelectric ceramic may be fired in a lead vapor atmosphere in order to suppress volatilization of lead, which is a component of the piezoelectric ceramic.

(Function) According to the present invention, a paste having a composition in which a predetermined amount of piezoelectric ceramic powder is mixed with metal powder for internal electrodes is applied to a green sheet whose main component is piezoelectric ceramic to a predetermined thickness, and then By preparing a laminate in which at least one coating film of the paste-like material is interposed inside using a green sheet and firing it, the piezoelectric ceramic layers have good adhesion to the ceramic layer, and the internal electrode It is possible to obtain a laminated structure material having a network structure in which the cutting metal is connected along the direction of cutting by the blade, and in which an internal electrode layer having sufficient conductivity is integrally formed. As a result, by forming external electrodes on the laminated structure material, fixing it to a predetermined backing material, etc., and cutting it with a diamond blade, etc., it has good conductivity without partial peeling or oven failure in the cutting direction. A multilayer ultrasonic probe with low impedance and high resolution that can be driven at high frequency can be manufactured, which includes a vibrator in which internal electrodes are interposed between piezoelectric ceramic layers.

(Examples of the invention) Examples and comparative examples of the invention will be described in detail below with reference to the drawings.

Example First, platinum powder with an average particle size of 0.5 μm was mixed with an average particle size of 1.3 μm.
Piezoelectric ceramic powder whose main component is PZT with a diameter of 2 μm
An organic binder, a dispersant, and a solvent were added to the mixture to prepare a paste for internal electrodes.

Note that the PZT-based ceramic has an ε5. T/ε. −＋
=2000, k33se 0.75, QM-80, Nt
It has various characteristics of 72000 (Hz m ) and a cure temperature of about 290°C.

Next, the same calcined PZT piezoelectric ceramic powder and acrylic binder as described above were mixed at a weight ratio of 6:4, and this mixture was stirred in the presence of a solvent for 20 hours to form a slurry. Thickness is reduced to 0 using the doctor blade method.
．． A 25M green sheet was molded. Next, the previously prepared internal electrode paste was printed on the green sheet using a 325 mesh screen to form two coating patterns 2.2 on the green sheet 1 as shown in FIG. Formed. In addition, these coating film patterns 2
．． When the film thickness of No. 2 was measured at 5 points with a micrometer, the average value was 12 to 13 μm.

Next, the green sheet with a thickness of 0.25 mm formed in the above step was placed on the surface of the green sheet on the coating pattern side, and then heated in a mold at 70°C and 300/(g/-) for 30 minutes. A laminate with a total thickness of 0.48B was produced by heat-pressing.Subsequently, this laminate was heated in the atmosphere at 1200°C.
The temperature was raised to 100.degree. C., held for 2 hours to perform firing, and then slowly cooled to produce a laminated structure material having a thickness of approximately 0.39 mm and having two internal electrode layers sandwiched between piezoelectric ceramic layers. Subsequently, as shown in FIG. 2, the laminated structure material 3 was cut along the dashed line with a diamond blade to give it an external shape. Through this process, two piezoelectric vibrator materials are produced.

Next, silver paste was screen printed on the piezoelectric vibrator material and baked at 800°C for 10 minutes to form an external electrode layer.
Polarization treatment was performed by applying a voltage of V for 30 minutes, and then a voltage of 50 V was applied for 30 minutes.
Figure 3 (
15X 15X O, 39IIIj shown in A) to (C)
l! A two-layer piezoelectric vibrator 4 was manufactured. In addition, Figure 3 (
A) is a top view of the piezoelectric vibrator, (B) is a rear view of the piezoelectric vibrator, and a sectional view taken along the line X-X in (C) and (A) of the same figure. Such a two-layer piezoelectric vibrator 4 includes a piezoelectric ceramic layer 5 polarized in the direction of the arrow, an internal electrode layer 6 covered by the piezoelectric ceramic layer 5 and having a - side exposed to the outside, and a piezoelectric ceramic layer 5 that is polarized in the direction of the arrow. one external electrode 7a formed over the surface of the internal electrode layer 6 excluding one side and the peripheral edge orthogonal thereto, the side surface and back surface opposite to one side of the internal electrode 6; and the piezoelectric ceramic layer 5. The external electrode layer 7b is provided on one side of the internal electrode layer 6 and is connected to the internal electrode layer 6.

Comparative Example The above PZT piezoelectric ceramic powder with an average particle size of 1.3 μm was added to platinum powder with an average particle size of 0.5 μm.
An organic binder, a dispersant, and a solvent were added to the mixture to prepare a paste for internal electrodes. Next, apply this paste to a thickness of 0.25 mm similar to the example.
After printing on a green sheet using a 325 mesh screen to form two coating patterns with an average thickness of 7 to 8 μm, print on the surface of the green sheet on the coating pattern side the same thickness as above. Green sheets of 0.25 mm were stacked and heat-pressed in a mold at 70° C. and 300° C. for 30 minutes to produce a laminate with a total thickness of about 0.48 mm. Thereafter, a two-layer piezoelectric vibrator was manufactured using the same process as in the example.

The capacitance and tan δ at 1 kHz were measured for the two-layer piezoelectric vibrators of the present example and comparative example described above. As a result, the piezoelectric vibrators of this example and comparative example have a capacitance, tan
Both δ agree within the measurement error range, C=35 nF,
The tan δ was -0,018. As a result, it was found that there was no difference in the electrical characteristics of the plate-shaped piezoelectric vibrator between the example and the comparative example before cutting into narrow widths.

In addition, the two-layer piezoelectric vibrator of the example and comparative example was
Test pieces were prepared by cutting them into dimensions of , and the peel strength of the internal electrode layer was measured when tensile force was applied from both sides of these test pieces. As a result, the peel strength of the internal electrode layer and the piezoelectric ceramic layer of the piezoelectric vibrators of the present example and the comparative example both matched within the measurement error range, and was 80 to 150/(g/d).

This revealed that there was no difference in the peel strength of the plate-shaped piezoelectric vibrator before cutting it into narrow widths between the example and the comparative example.

Furthermore, the surfaces of the internal electrode layers of Examples and Comparative Examples after peeling were observed using a scanning electron microscope. Those micrographs are shown in the schematic diagrams of FIGS. 4 and 5. From the schematic diagrams in FIGS. 4 and 5, it can be seen that in the internal electrode layers of the example and comparative example, platinum 21, which is the metal for internal electrodes, and piezoelectric ceramic gold 21 are connected in a two-dimensional network inside the piezoelectric ceramic 22. I can see that it is being done. A typical width of the platinum 21 is 3 to 8 μm, but there were some places where the platinum 21 was connected with a width of 1 μm or less.

In addition, evidence that the piezoelectric ceramic 22 was in close contact with the upper and lower piezoelectric ceramic layers was observed everywhere.

This is because piezoelectric ceramic particles can be seen protruding from between the platinum 21 to the surface of the internal electrode layer, and the platinum 21
It was also determined that the piezoelectric ceramic particles visible in between had an outer shape formed by straight lines. However, in the internal electrode layer (shown in FIG. 4) of this embodiment, the piezoelectric ceramics 22 are finely dispersed in the platinum mesh 21, and even after cutting with a blade, the piezoelectric ceramics 22 can be well connected along the cutting direction. On the other hand, in the internal electrode layer of the comparative example (shown in FIG. 5), the piezoelectric ceramics 22 are roughly dispersed in the mesh-like platinum 21 and are not connected along the cutting direction after cutting with a blade, so there is a risk of disconnection in the middle. There is.

Next, manufacturing of an array type ultrasonic probe for medical diagnostic equipment from the two-layer piezoelectric vibrators of the above-mentioned Examples and Comparative Examples will be explained.

First, one external electrode layer 7 in the two-layer piezoelectric vibrator 4
A plurality of signal-side lead wires 8 of a flexible printed circuit board were connected to a by soldering, and a grounding electrode 9 made of a copper plate having a thickness of 0.05 mm was connected to the other external electrode layer 7b by soldering. Subsequently, an adhesive is applied to the surface of the ferrite rubber backing material 1o, and the signal side lead wire 8 and the ground electrode 9, to which the two-layer piezoelectric vibrator 4 has been bonded in advance, are placed on the adhesive layer. They were placed so that they were in contact and glued. Subsequently, an acoustic matching layer 11 made of epoxy resin and having a thickness of λ/4 (λ: wavelength) was formed on the piezoelectric vibrator 4. After that, a diamond blade with a thickness of 0.05zx attached to a scriber dicer is used to cut arrows from the acoustic matching layer 11 side to the backing material 10 surface at a pitch of 0.25 am in line with each signal side lead wire of the flexible printed circuit board. Resonance frequency 3.7 with 48 strip-shaped vibrators (elements) cut in the direction
A 5MHz two-layer array type ultrasonic probe was manufactured (6th
Figures (A) and (B) shown).

6(A) is a perspective view of a two-layer array type ultrasonic probe, and FIG. 6(B) is a sectional view taken along line Y--Y in FIG. 6(A).

Regarding the manufactured array type ultrasonic probes of Examples and Comparative Examples, the resonance characteristics (k33-) of each strip-shaped vibrator were measured, and the operating status of the vibrator was investigated.

As a result, abnormal resonance was observed in 7 of the 48 strip-shaped vibrators in the probe of the comparative example. All of these seven failure modes are caused by the internal electrodes; three of the vibrators have an internal electrode that is disconnected midway, the impedance is high, and the resistivity of the internal electrodes is high midway. There were four vibrators that generated spurious waves at their resonance points due to the The occurrence of these seven failure modes is because the piezoelectric ceramics 22 are roughly dispersed in the mesh-like platinum 21 in the internal electrode layer as shown in FIG. This is thought to be due to the fact that the shaped vibrators were not connected along the cutting direction and were broken midway, and that the internal electrodes were thin and had low conductivity. On the other hand, in the ultrasonic probe of this example, it was confirmed that all 48 strip-shaped vibrators had normal resonance characteristics.

In addition, the two-layer array type ultrasonic probe of this example and the piezoelectric vibrator were made into a single layer, but the structure was the same as that of the example, the same method was used,
The pulse echo characteristics of a single-layer array type ultrasonic probe (conventional example) having the same resonant frequency (3.75 MHz) were investigated. As a result, in the conventional single-layer array type ultrasound probe, the pulse echo characteristic diagram shown in FIG.
With the layer array type ultrasonic probe, a diagram of pulse echo characteristics shown in FIG. 8 was obtained. As is clear from these FIGS. 7 and 8, the ultrasonic probe of this example can obtain almost the same waveform as the conventional single-layer ultrasonic probe, and the sensitivity has improved by 7 dB. It has been shown that multi-layering is useful.

Furthermore, the two-layer array type ultrasound probe of this example was incorporated into an actual medical ultrasound diagnostic apparatus, and an evaluation test was conducted. As a result, the sensitivity and S/N of the actual device are improved compared to the single-layer array type ultrasound probe, and the images are also remarkable, such as being able to observe areas that could not be seen with conventional probes. A significant performance improvement was observed. Furthermore, durability against continuous driving was also confirmed, and it was confirmed that the ultrasonic probe of the example had mechanical strength that could withstand practical use.

In the above embodiment, two coating patterns of paste-like material for internal electrodes were formed on the green sheet, but the present invention is not limited thereto. For example, four, six, eight, etc. coating patterns may be formed on the green sheet.

In the above embodiment, the manufacturing of a two-layer array type ultrasound probe has been described, but the present invention can be similarly applied to the manufacturing of a multilayer array type ultrasound probe having three or more layers.

[Effects of the Invention] As detailed above, according to the present invention, it is possible not only to reduce impedance, but also to achieve good adhesion to the piezoelectric ceramic layer, and to ensure that the electrode metal is well aligned along the cutting direction by the blade. It is possible to form an internal electrode layer with a connected network structure and sufficient conductivity, and even after cutting into narrow widths to form an array, it is possible to form a vibrator with uniform characteristics, which prevents defects. It is possible to provide a method for manufacturing a highly reliable and high-resolution multilayer ultrasonic probe useful for medical ultrasonic diagnostic equipment, ultrasonic metal flaw detection equipment, etc., in which mechanical strength is significantly reduced and a predetermined mechanical strength is maintained.

[Brief explanation of the drawing]

1 to 3 are diagrams showing the manufacturing process of a two-layer piezoelectric vibrator in an embodiment of the present invention, in which FIGS. 1 and 2 are plan views, FIG. 3 (A) is a top view, The same figure (B) is the same figure (A)
The rear view of the same figure (C) is a sectional view taken along the line XX of the same figure (A). FIG. 4 is a schematic diagram of an electron micrograph of the internal electrode layer according to the present example, FIG. 5 is a schematic diagram of an electron micrograph of the internal electrode layer according to the comparative example, and FIG. 6 (A) is a schematic diagram of the internal electrode layer according to the present example. FIG. 8 is a diagram showing the pulse echo characteristics of the manufactured two-layer array type ultrasound probe.
FIG. 3 is a diagram showing pulse echo characteristics of a layer array type ultrasound probe. DESCRIPTION OF SYMBOLS 1... Green sheet, 2... Coating film pattern of paste-like material, 4... Two-layer piezoelectric vibrator, 5... Piezoelectric ceramic layer, 6... Internal electrode layer, 7a, 7b.・
- External electrode layer, 10... Backing material, 11... Acoustic matching layer, 21... Platinum (metal for internal electrode), 22.
...Piezoelectric ceramics. Applicant's agent Patent attorney Takehiko Suzue Figure 2 (A) (B) Figure 3 Figure 4 Figure 5 (A) (B) Figure 6 Figure 8

Claims (1)

[Claims] 16 to 2 pieces of piezoelectric ceramic powder is added to the metal powder for internal electrodes.
After applying a paste with a composition of 5% by weight to a thickness of 10 to 15 μm on a green sheet mainly composed of piezoelectric ceramics, use this green sheet to coat the inside with at least a coating film of the paste. The method included a step of producing a laminate with one layer interposed therebetween, a step of firing the laminate to integrate an internal electrode layer between the piezoelectric ceramic layers, further forming an external electrode layer, and then cutting it into an array shape. A method for manufacturing a multilayer ultrasonic probe characterized by the following.