JPH01460A - Array type ultrasound probe - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application #) The present invention relates to an array ultrasonic probe used for ultrasonic diagnosis ff11i and the like.

(Prior art) An ultrasonic probe generates ultrasonic waves using a piezoelectric element and uses the reflected waves to inspect the condition of an object.It is useful for one-person internal diagnosis, flaw detection inside metal welds, etc. It is used for various purposes. As ultrasonic probes, so-called array-type ultrasonic probes in which a plurality of rectangular concentrators are arranged in an array are often used. In recent years, eyebrow ultrasound diagnostic devices that can obtain Doppler information on blood flow have been developed and manufactured. The ultrasonic probe manufactured by MH et al. for such a device is called an ultrasonic probe for the electronic sector.

It has a beak structure similar to the conventional array sonic probe, but
The TFE shape is even smaller. Research and development are currently underway to obtain Doppler signals from, for example, the coronary arteries of the heart, and it is expected that the demand for the above-mentioned ultrasound probes will further increase.

On the other hand, when considering signal transmission between the ultrasound probe and the transmission/reception system, it is desirable that the impedance of the ultrasound probe be small in order to improve the S/N ratio. The impedance of the ultrasonic probe is determined by the gt component of the fIIL element. In other words, given the shape of the vibrator and the driving frequency,
The magnitude of impedance is determined by the dielectric constant of the vibrator, and when the dielectric constant is large, the impedance is small.

Lead zirconate titanate (PZT)-based 0EEfi ceramics are partially used as piezoelectric vibrators for ultrasonic probes. Other piezoelectric materials include PbTi0. There are piezoelectric ceramics, polymer piezoelectric materials, double pressure bodies, etc.
At the practical level, some fields or some diagnostic lfr
The current situation is that it has only reached Surai. The disadvantage of these materials is that they have a lower electrical contact rate than PZT-based piezoelectric ceramics, and on the other hand, PZT-based piezoelectric ceramics have a large pneumatic-mechanical coupling coefficient (kt" knee 0).
．． 5), and the specific casting rate is large (K = 2000
~3000) is a feature. However, 7
′? .

For example, even when used on a material with a relative dielectric strength of IE'l:2000.

- In an ultrasonic probe for the electronic sector with an element length of 11.2 mm and a width of 2.5 MHz, the impedance near the resonance point is approximately 1k.
It becomes O. The Q% impedance of the cable connecting the transducer and the transmitting/receiving system is usually 50Ω or 75Ω, and the input impedance of the receiving system is from several tens of Ω to several tens of Ω.
Considering that it is 00, the input impedance of the ultrasonic probe is about 5000 at most, even if a few sacrifices are made, and the input impedance of the AT wave probe in the above example should be reduced to only 5000 degrees. I can't. Therefore, studies are being conducted to reduce the impedance by using the product riJ ratio of piezoelectric ceramics. If n is the product number, the specific vane impedance is 1/nt in the case of a single layer. This is a piezoelectric ceramic with a uniform layer ratio.
The area is 1 times larger and the thickness is 1/n, so the answer is n!
This is because it becomes one sound. For example, if a material r of 5lJ2ooo is used, the impedance is IKΩ in the case of simple and simple, and the friend's impedance is reduced to 250 (,1).On the other hand, the interwave number is lost in the overall thickness, so compared to the eruption layer. Methods for determining the lamination ratio that do not change any time include lamination by adhesion of pressure-sensitive ceramic veneers, and the final firing method.However, if the points such as placement and homogeneity are zero, the method falls short to single firing. The simultaneous firing method is a method of simultaneously forming the piezoelectric ceramic and the metal for the internal electrode to make the product 1. Metal powder for the internal battery is coated on the piezoelectric ceramic green sheet, A laminated structure of piezoelectric ceramic and metal can be obtained by heating and pressing several such green sheets to form a single piece.

The firing temperature of PZT-based pressure-core ceramics is usually 1100'C.
The temperature is ~1300℃, but the partial pressure of electrons during firing in air can withstand this temperature, and does it have a negative effect on the properties of piezoelectric ceramics? It doesn't affect the ninth place.

As the internal metal 4, precious metals such as platinum are used.

(Problem to be Solved by the Invention) When the piezoelectric ceramic and metal lambda layer plate made by the method described above is cut into array elements,
Since the cutting pitch is narrow, for example 0.25mm or less,
There is a 1-d area in which 6 places inside are easy to peel off. When cutting or renewing this with a diamond cutter etc.,
product! # This is because the piezoelectric plate is subject to sliding stress, and it is thought that it is particularly likely to peel off when the area of each element of the vibrator is small.

9. When an array type vibrator made by the method described above is driven continuously at the resonant frequency, the internal l! There is a problem that the hermitage part is easy to peel off. this is.

When a piezoelectric vibrator is in a resonant state, there is a distribution of stress inside the vibrator, and there are places where large stress is locally applied. 1 Normal sonic probes are often used to excite the fundamental mode, but in this case, the center of the vibrator is The stress becomes extremely large in the vicinity, and in the case of the 211.41... structure, it almost coincides with the position of the internal VL pole.

Furthermore, it is made by the method described above. Multi-T-shaped piezoelectric ceramic internal snowball contains platinum r and other high PA points vI4'kO! Must be the cost of raw materials and °C inside! Is most of it metal for koshiki? There is a problem of occupation.

The purpose of the present invention is to solve the problem of at least one internal IE electrode, which not only has high mechanical strength near the internal IE pole, but also reduces the amount of fecal mold on the metal in the pot, and has a cheap laminated structure array type A sound wave. The purpose is to provide a probe.

[Animei O composition]

(Means for solving the problem) The present invention provides an ultrasonic sensor made of multi-layered piezoelectric ceramic, in which the metal for the internal electrode is configured in a two-dimensional net shape, thereby preventing stains. - It is an array type R&I sonic probe characterized by mechanical close reading. The interval or period of the internal electric oven metal is made into a nine-mesh pattern.
The above-mentioned array-type ultrasonic probe is characterized by having a diameter of 0 μm or less.

Piezoelectric ceramic consisting of multilayers is made of 4 ceramic materials and 1
! It has a structure 1 in which metal for the kettle is layered.

The piezoelectric ceramic has at least two layers. Q, which is sandwiched and embedded inside the piezoelectric ceramic as an electrode, is an internal electrode, and by firing it at the same time as the piezoelectric ceramic, the integrated ratio 1. Metal is formed into a two-dimensional net within the plane of the internal electrode. The mesh O pattern may be irregular as shown in Figure 1 (t4).

It is essential to have two-dimensional concubinage within the plane.

This electrically connects the metal parts of the inner part.

In this case, the average dry thickness of the internal It pot is preferably 3 μm or more. In the meshes of gold 4 (the non-metal spaces between the meshes), the upper and lower piezoelectric ceramics sandwiching the internal electrodes t are partially mechanically interconnected by sintering. Furthermore, the fineness of the mesh is 1. The mesh period (in the case of irregular meshes, the average mesh spacing) is configured to be less than ilOμm.

Furthermore, as a ninth method for configuring internal electrodes in rows, a mixed powder of piezoelectric ceramic powder and internal powder was applied on the Wang'ya ceramic O green sheet, and the piezoelectric ceramic and internal electrodes were combined. This manufacturing method is characterized by using a method in which both are fired at the same time.

(Function) Although the piezoelectric ceramic and the internal electrode are formed and integrated at the same time, their adhesion strength is not strong.This is because a high melting point O metal such as platinum is used as the metal for the internal electrode. This is because it hardly reacts with the piezoelectric ceramic and is not chemically bonded with it, and even if it does bond, residual strain will occur from the interface with the piezoelectric ceramic during cooling due to the difference in thermal expansion coefficient. Conceivable. For this reason, piezoelectric vibrators with a laminated structure are prone to breakage at the interface between the internal dL pot and the piezoelectric ceramic.Compared to this, it is relatively rare for the inside of the piezoelectric ceramic to break apart, and the particles of the piezoelectric ceramic are sintered together. It is well known that the strength of the piezoelectric ceramic is at least stronger than the strength of the interface between the internal electrode and the piezoelectric ceramic.

The electrical role of the internal electrode is to generate a uniform electric field in the piezoelectric ceramic as well as uniform strain and stress due to the piezoelectric effect. Therefore, it is necessary that the electrical resistance is low. For this purpose, the electrically most ideal electrode is a low-resistance 4O metal formed over one surface without any gaps. However, even if the inside of the mesh is made into poles as in the present invention, it functions satisfactorily as IE1j for an ultrasonic probe for the following reasons. First of all, if the period of the mesh is sufficiently small compared to the thickness of the piezoelectric ceramic, a substantially uniform electric field can be applied to most of the piezoelectric ceramic. For example, 3.
The thickness of one layer of the piezoelectric ceramic of the T211 groove-shaped vibrator for 75 MHz is about 9.2 mm (in the case of PZT-based piezoelectric ceramic). In comparison, it has been shown by calculations or experiments that if the interval between the meshes is sufficiently small (jL) with a period (1/20) of 10 μm or less, a substantially uniform electric field will be applied to most of the piezoelectric ceramics.

(9) When platinum is used as the metal for the kettle inside.

The resistivity of platinum is 10.6X10-・Ω・cl′-1: At a certain Q, 1 width Q, 2 mm, length 11.2 mm, thickness 5 μm
The electrical resistance in the longitudinal direction of the internal electrode is about 10. Normally, the area near the resonance point of an array type ultrasonic probe, i.e. 2.5
Considering that the impedance near MHz is several hundred ohms to IK ohms, there is a margin for the IE electrical resistance of the internal electrodes.

Even if you make it into a rope shape, there is no peace.

By making the internal electrodes mesh-like as described above.

Electrically, the entire surface is shaped like 51F, and it can perform the same function as the Kyuden kettle, but from a mechanical point of view, the strength is significantly improved for the following reasons.

Assuming that the strength at the interface between the internal electrode and the piezoelectric ceramic is tσ1 and the strength within the piezoelectric ceramic is rσ, the average strength σ of the internal electrode layer obtained by forming the mesh is σ=A, σ1+A, σ, (1) It is expected that it will be given by Here A, and A,
are each one internal pole; - the area allocation of the internal electromagnetic metal and piezoelectric ceramic to the total area; (0≦A,
A, ≦1, A, 10A, ≦1) Since σ has a strength at least 10 times stronger than σ1, the inside is made into a very reticulated structure A,? By increasing it, you can improve your strength even more.

The thickness of the internal electrode is preferably 3 μm or more, which is about the same as a piezoelectric ceramic sintered compact with 0 grains, to maintain two-dimensional contact dt even if it is made into a net shape, and from the viewpoint of 1-air resistance Q, there is a margin for making it into a net shape. ? It is necessary to maintain a thickness of 3 μm or more.

Furthermore, the present invention can reduce raw material cost by 1-1 for the following reasons. For example, if the internal ti is used,
Platinum accounts for at least 90L4 of the raw material cost of the bond layer piezoelectric material for the ultrasonic wave probe. This reduction in the amount of platinum used is the most effective method for lowering raw material costs. By making the internal vL pole t-reticular and lowering the area fraction of the P'3 portion, it is possible to reduce the amount of platinum used, which is effective in reducing costs.

is reduced, and a nine-super wave probe is obtained.

(Example) This will be explained below using an example of real power.

A piezoelectric ceramic whose main component is pb(Zr Tl) Osk'x 1-x 21-thickness type piezoelectric vibrator for 3.75MHz? Created.

We prototyped an array-type probe for medical ultrafracture diagnostic equipment.

The nine PZT-based piezoelectric ceramics used are a'rs
/ε022000-Kms≧0.75,QMζ80
It has the following characteristics and has a Curie temperature of approximately 290°C.

First, we fabricated a piezoelectric ceramic green sheet gold. The calcined powder of piezoelectric ceramic and the acrylic binder T were mixed at a ratio of 6 to 4 and mixed for 20 hours, resulting in a muddy odor.
The green sheet was formed using the doctor blade method, and the average thickness of the green sheet was 255 μm.

Next, apply platinum paste to the screen print on this green sheet. Piezoelectric ceramic powder was mixed into the platinum paste. The mixed 9-pressure 'α ceramic Q 1,000-uniform grain size was 1.3 μm, and the intermittent ratio of platinum to piezoelectric ceramic was 8:2. 300 screens were used for printing
The thickness of the film is 5 μm. Print slam? Shown in Figure 2.

- In order to compare with the strength wood invention, a simple platinum paste 2 was warped and 4 lines of similar printing were performed.This sample was treated as a conventional example, and all other processes were performed in the same manner as in the embodiment.

The platinum paste was printed in a predetermined pattern on the green sheet.Then, the green sheet was printed with nothing, and the platinum paste was printed on the green sheet. 1g of 92 crimped green sheets
, the thickness is 255 μm, and the thickness of the crimped layer is 480 μm, t, and the crimped temperature is 70'C, 30
The temperature was then raised to 1200° C. and held for 2 hours under the condition of 0 kp/cm”, and the thickness of the sintered stage was about 390 μm.

It was cut as shown in FIG. 3 using a sintered piezoelectric ceramic diamond cutter. In this diagram, the broken line cuts the nine-faced place? 6 Next, as external electrodes, silver paste was screen printed and baked, and the printed pattern yx (shown in Figures 4 and 5, Figure 44 corresponds to the machine, Figure 45 corresponds to the back side, 1 front side, 4 sound waves) The release and detection were performed, the lead and edge were removed 8 times on the back side, and silver paste was applied at 800° C. for 10 minutes.

FIG. 6 shows a cross-sectional view of the two-layer pressure vibrator manufactured as described above. Dimensions are 15 x 25 x O, 39m
It is m. In Figure 6 of the bundle, the arrow indicates the direction of separation r.The zero polarization treatment was carried out in silicone oil at 100'C by applying 480V for 30 minutes, and then the aging treatment was carried out at 50C for 8 days.

At this point, each bite was measured using tanavi at IKHz.

What are working examples and comparative examples? Both li and tana matched within the measurement error range, and C=35 nF and tan δ=0.018. It can be seen from this that when a voltage r of the same magnitude is applied, an electric field of the same magnitude as that of the comparative example is applied to the piezoelectric ceramic of the example.

Next, this pressure is determined by the peel strength of the vibrator [Taku 1 and 9].

The peel strength of the inner ′ ff1ld and the pressure 1 ceramic layer is
In the comparative example, it was 7-19 kg/c+n%, whereas in the example of Ippon Yumei, it was 79-147 kg.
p/cm'. In this way, Akira Motonuma's example shows a stronger and denser layer between the piezoelectric ceramic and the internal electrode than in the comparative example, and the variation in strength is also small. After observing it with an electron microscope, the following findings were obtained. In the comparative example, the entire surface is covered with platinum except for some holes R, and the holes 1 are 3 to 4 μm thick.
The short ends of the adjacent holes υ are approximately 20 to 30 μm in length. i9, 1 hole inside? There was no evidence that the upper and lower piezoelectric ceramics were connected through the wire. On the other hand, in the example, the internal electrodes were connected in an irregular network.

Typical electrode widths are 3-8 .mu.m and are spread out in a two-dimensional network with spacing t of 69.3-5 .mu.m.

In addition, evidence of connection between the upper and lower piezoelectric ceramics between '1110' was observed everywhere. This is because there are grains of piezoelectric ceramic protruding from between the electrodes to above the pole surfaces, and grains of piezoelectric ceramic visible from between the electrodes have an acute-angled shape. It was judged. From these O, the inside of the multilayer piezoelectric ceramic of this example! It was confirmed that the extremely sharp edges were formed into a two-dimensional net shape, and the distance between them was 10 μm or less. Figures 7 and 8 show the impact of the electronic charge on the electrode surface of the example and comparative example.

Next, we will create an array type ultrasound probe for medical diagnostic equipment using this 2rtI type piezoelectric transducer! k i'l: External view of the manufactured t-array type probe kfi9 (Figure fa), l! !
It is shown in the fr view t(b).

First of all, a 0.05 tnm thick copper plate as a lead extraction plate for the earth * pole on a two-layer piezoelectric ceramic. A unique pattern was formed as a lead extraction plate for the signal electrode, and nine flexible printed circuit boards were joined by soldering. Subsequently, Cemedine 15651 was applied to the ferrite rubber backing material, and the above product 1fj piezoelectric ceramic? Glue nine. Then, it was formed on an acoustic matching layer having a thickness of λ/4 (λ: wavelength) using Stycast 2651 (manufactured by Brace Japan).

Next, use a scriber dicer (Disco W).

Q, 0.25 with Q5+nm thick diamond blade
Forty-eight elements were cut along the pattern of the flexible printed circuit board at a pitch of mm.

The resonance characteristic tI1%lI of the manufactured Kutani element was determined, and the QvJ production status tv@beno was used as a vibrator. As a result, in the comparative example, 8 out of 48 elements did not resonate at all or exhibited abnormal resonance. The failure modes are all caused by one internal element, the open type, @■ type has 3 elements, and the T type has 5 elements, where the resonance level is highest at a frequency approximately twice the desired resonance frequency. And nine. In both cases, part or all of the internal aX peeled off from the piezoelectric ceramic.

The internal 1E box is 1. ! FR line and t, either one'
There is a gap between the can and the ceramic. On the other hand, in the example of the present invention, all 48 elements were confirmed to operate normally as transducers. Next, we observed the pulse echo characteristics of the 21i ultrasonic probe according to this example. , 4-line comparison with conventional drug R-type probe, No. 10
Figure ta) shows the pulse echo characteristics of the medicine type 1 ultrasound probe of the comparative example, and (b) shows the pulse echo characteristics of the present example measured using the same test method and the same scale. The same materials are used for the piezoelectric ceramic, silver paste, backing material, regular 111J-wire, and adhesive, and both have the same resonant frequency of 3.75 MHz. From this figure, it can be seen that the pulse echo characteristics of the 2J-type probe of this fourth example have a waveform that is almost the same as the pulse echo characteristics of the conventional Ko1mei probe, and the rlA degree is improved by 7 dB. It became clear that the multi-type R11 sound probe Q was useful.

Furthermore, the two-layer type @Kobami probe of this example was installed in an actual medical ultrasound diagnostic device, and an evaluation test was conducted. As a result, even in the desert, the sensitivity was improved compared to a single layer probe, and the same level of sensitivity was obtained for a single painter. Furthermore, durability against continuous driving was also confirmed.

The probe according to this IFIJ K is suitable for practical use. It was confirmed that it has a certain strength.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to achieve comparable strength.
The L9 multi-layered Mi Hakamami probe can provide a probe that is sufficiently durable for processing and actual use. In addition, internal ILf [Kuta 4
Type 4#a has the effect of reducing the cost of raw materials for the probe.

[BRIEF DESCRIPTION OF THE DRAWINGS] J Figure 1 is a diagram showing an example of a representative metal pattern for internal tti according to the present invention. The figure shown in Fig. 3 is a figure showing one place where the heat-pressed and fired ceramic is cut. Figure 4J shows the pattern of silver paste applied to the outer side of the fired and cut 92J complex type FE electroceramic, and Figure @5 shows the pattern of silver paste applied to the back side of the fired and cut t2 Akebono type piezoelectric ceramic. A diagram showing the pattern of
FIG. 6 is a cross-sectional view of a two-layer piezoelectric ceramic for an ultrasonic probe. 8g7 Figure 1 is an internal electrode formation pattern according to an embodiment of the present invention? 8 is a diagram showing the internal electrode formation pattern of a comparative example, and FIG. 9 is a diagram showing the configuration of an ffl sonic probe 0 for a medical bell IIv device using a two-layer piezoelectric ceramic.
(a) is an external view, (b) is a cross-sectional view, and Figure 1O shows the details of one-type and multilayer piezoelectric ceramics. Figure 1 shows the pulse echo characteristics of the ultrasonic probe used. (a) is the prefectural layer type. tb) is a two-layer type, the horizontal axis is time, the vertical axis is voltage t, and the figures are on the same scale. 1...Piezoelectric ceramic green sheet, 2...Inner part where gold Y4 is sprinkled, 3...Dotted line indicating the cutting location. 4... Piezoelectric ceramic, 5... External silver paste mold part, 6... External! Others, 7... Internal electrode, 8...
...An arrow indicating the direction to minutes, 9...Backing material, 10
...Setting 11.11... Earth is the pole, 12... Signal side is the pole. l 2 2nd r! A Fig. 3 Fig. 5 Fig. 6 Fig. 7 Fig. 1OPFrL L-m-" Fig. 8 10p" Fig. 9

Claims (2)

[Claims] (1) In an ultrasonic transducer made of multilayer piezoelectric ceramics, an array type ultrasonic transducer is characterized in that the metal for the internal electrodes is configured in a two-dimensional net shape and is electrically and mechanically connected. Sonic probe. (2) Array-type ultrasound according to claim 1, characterized in that the period or interval of the metal for internal electrodes configured in a net shape is 10 μm or less, and the average thickness is 3 μm or more. probe.