JP4118115B2 - Ultrasonic probe - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic probe.
[0002]
[Prior art]
In the field of medical ultrasonic diagnostic equipment and non-destructive inspection equipment, in order to image the internal state of an object, ultrasonic waves are irradiated toward the object, and reflection from the interface with different acoustic impedance of the object is performed. An ultrasonic probe that receives an echo is used.
[0003]
In general, a piezoelectric vibrator (piezoelectric body) that generates vibration when a voltage is applied is used as an ultrasonic probe. Conventionally, as a piezoelectric material, an electromechanical coupling coefficient k₃₃Since 'is as high as about 70%, a lead zirconate titanate (PZT) -based piezoelectric ceramic having high conversion efficiency from an electric signal to mechanical vibration has been used.
[0004]
In contrast, in recent years, for example, Pb ((Zn) made of a solid solution of lead zinc niobate and lead titanate._1/3Nb_2/3)_0.91Ti_0.09) O_ThreeElectromechanical coupling constant k, such as a piezoelectric single crystal₃₃A highly efficient piezoelectric single crystal having a high 'is about 80% or more has been developed (for example, see Patent Document 1). In addition, a piezoelectric single crystal has a mechanical strength smaller than that of a piezoelectric ceramic, and chipping and the like frequently occur, leading to a decrease in reliability and sensitivity. reference).
[0005]
However, when an ultrasonic probe is manufactured using the piezoelectric single crystal described above, although the generation of chipping and cracks has been improved, there is still a problem that the sensitivity variation of the probe is still large.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 06-38963 (page 3-13, FIG. 1)
[0007]
[Patent Document 2]
JP 2000-14672 A (page 3-6, FIG. 1)
[0008]
[Problems to be solved by the invention]
An object of the present invention is to provide an ultrasonic probe with small sensitivity variations.
[0009]
[Means for Solving the Problems]
  Therefore, an ultrasonic probe according to an embodiment of the present invention includes an acoustic backing material, a piezoelectric body provided on the acoustic backing material, formed of a piezoelectric single crystal, and a first surface where the piezoelectric body faces the acoustic backing material. And a piezoelectric element having a pair of electrodes provided on the second surface opposite to the first surface, and a piezoelectric element provided on the second surface of the piezoelectric element, the acoustic impedance of the piezoelectric body A first acoustic matching layer made of a solid inorganic material having an acoustic impedance of 40% or more and 85% or less, and a second acoustic wave provided on the first acoustic matching layer and having an acoustic impedance smaller than that of the first acoustic matching layer A plurality of laminates including a piezoelectric element, a first acoustic matching layer, and a second acoustic matching layer are arranged in a one-dimensional or two-dimensional array on the acoustic backing material.The space between the laminates arranged in an array has a filling rate of 5% by volume or less.It is characterized by that.
[0010]
In the ultrasonic probe according to the embodiment of the present invention, a flexible printed wiring board may be provided between the acoustic backing material and the piezoelectric element.
[0011]
In the ultrasonic probe according to the embodiment of the present invention, the piezoelectric single crystal is Pb (B1, B2)._1-xTi_xO_Three(However, the value of x is 0.04 ≦ x ≦ 0.55, B1 is at least one selected from the group consisting of Zn, Mg, Ni, Sc, In and Yb, and B2 is composed of Nb and Ta. Or at least one selected from the group).
[0012]
In the ultrasonic probe according to the embodiment of the present invention, the first acoustic matching layer is made of SiO.₂MgO and Al₂O_ThreeCeramics containing Si and Si_ThreeN_Four, AlN, Al₂O_ThreeAnd ZrO₂And at least one ceramic selected from the group consisting of ceramics including calcium silicate and lithium aluminosilicate, fluorine phlogopite mica ceramics, and hexagonal boron nitride ceramics.
[0014]
In the ultrasonic probe according to the embodiment of the present invention, the piezoelectric element may have a configuration in which a plurality of piezoelectric bodies are provided and electrodes are provided between the piezoelectric bodies and these are alternately stacked.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an ultrasonic probe according to an embodiment of the present invention will be described with reference to the drawings.
[0016]
FIG. 1 is a cross-sectional view illustrating an ultrasonic probe according to an embodiment of the present invention. As shown in FIG. 1, the ultrasonic probe according to the embodiment of the present invention includes an acoustic backing material 2, a piezoelectric body 1 formed on the acoustic backing material 2 and formed of a piezoelectric single crystal, and the piezoelectric body 1 is acoustic. A second electrode 4 provided on a first surface facing the backing material 2, a first electrode 5 provided on a second surface opposite to the first surface of the piezoelectric body 1, It has the 1st acoustic matching layer 3a provided on the 1st electrode 5, and the 2nd acoustic matching layer 3b provided on the 1st acoustic matching layer 3a. Here, in the ultrasonic probe according to the embodiment of the present invention, the first acoustic matching layer 3 a is made of a solid inorganic material, and the acoustic impedance of the first acoustic matching layer 3 a is 40% of the acoustic impedance of the piezoelectric body 1. It is 85% or less. The acoustic impedance of the second acoustic matching layer 3b is smaller than the acoustic impedance of the first acoustic matching layer 3a. Also, a laminate in which a piezoelectric element composed of the first electrode 5 and the second electrode 4 and the piezoelectric body 1 sandwiched between them, a first acoustic matching layer 3a, and a second acoustic matching layer 3b are laminated. Since the body is divided into a plurality of bodies, a plurality of bodies are arranged in an array. In FIG. 1, the acoustic lens 8 is provided on the second acoustic matching layer 3b. However, the configuration is not limited to this. For example, in the case where a laminate in which a piezoelectric element, a first acoustic matching layer 3a, and a second acoustic matching layer 3b are laminated is arranged in a two-dimensional array, the acoustic lens 8 is not provided. The resolution and sensitivity can be significantly improved.
[0017]
In the ultrasonic probe according to the embodiment of the present invention, a plurality of acoustic matching layers are provided, and the first acoustic matching layer 3a on the side in contact with the piezoelectric element is made of a solid inorganic material and is 40% or more of the acoustic impedance of the piezoelectric body 1. It has an acoustic impedance of 85% or less. By providing a plurality of acoustic matching layers, the acoustic impedance can be matched. By adopting the above configuration as the first acoustic matching layer 3a, unnecessary vibration of the piezoelectric body can be suppressed, and variation in dielectric constant is reduced. Therefore, it is possible to reduce the sensitivity variation among the laminates composed of piezoelectric elements and acoustic matching layers in the ultrasonic probe, that is, the sensitivity variation between channels. Hereinafter, a mechanism capable of reducing variations in sensitivity between channels by the configuration according to the embodiment of the present invention will be described.
[0018]
FIG. 2 is a perspective view of one piezoelectric body 1 shown in FIG. K in FIG.₃₃It is assumed that the first electrode 5 and the second electrode 4 are formed on the upper and lower surfaces of the piezoelectric body 1 when the arrow direction 'is the vertical direction (thickness direction). When the piezoelectric body 1 transmits and receives an ultrasonic wave, the piezoelectric body 1 has a thickness direction (k₃₃'Mode) and k₃₁Arrow direction (length direction, k₃₁Mode). Further, the electromechanical coupling coefficient k is determined by the magnitude of vibration in the thickness direction of the piezoelectric body 1.₃₃′ Is determined, and the electromechanical coupling coefficient k is determined by the magnitude of vibration in the length direction.₃₁Is decided.
[0019]
On the other hand, the sensitivity of an ultrasonic probe in which piezoelectric elements are arranged in an array has a dielectric constant ε at a high frequency._S1S3Depending on this ε_S1S3Is the electromechanical coupling coefficient (k₃₁, K₃₃′) And dielectric constant ε at low frequencies (usually 1 kHz)_TAnd is expressed by the following equation (1).
[0020]
ε_S1S3= (1-k₃₃′) × (1-k₃₁ ²) × ε_T      (1)
As a result of attempts to improve sensitivity by various methods, the present inventors have determined the magnitude of vibration in the length direction, that is, k₃₁As the value varies, the dielectric constant ε at high frequencies_S1S3It has been found that the sensitivity between the channels of the ultrasonic probe varies. The first acoustic matching layer on the side close to the piezoelectric body is made of a solid inorganic material and has an acoustic impedance of 40% to 85% of the acoustic impedance of the piezoelectric body. This suppresses the variation in sensitivity of the piezoelectric body. Solid inorganic material means a material that does not contain carbon, and by using the solid inorganic material as the first acoustic matching layer, it is possible to obtain the effect of suppressing vibration in the length direction by mechanically fixing the piezoelectric body. I can do it. In addition, since the acoustic impedance of the first acoustic matching layer is 40% or more and 85% or less of the acoustic impedance of the piezoelectric body, the acoustic impedance is obtained while achieving acoustic matching between the piezoelectric body and an object such as a human body. Since it is large, an effect of suppressing vibration in the longitudinal direction of the piezoelectric body can be obtained. If it is less than 40%, the effect of suppressing the vibration in the longitudinal direction of the piezoelectric body cannot be obtained sufficiently, and it becomes difficult to suppress the variation between the channels. On the other hand, if it exceeds 85%, for example, acoustic matching with an object such as a human body cannot be achieved, and ultrasonic transmission / reception efficiency may be significantly reduced. Examples of solid inorganic substances having such acoustic impedance characteristics include SiO.₂MgO and Al₂O_ThreeCeramics containing Si, Si_ThreeN_Four, AlN, Al₂O_ThreeAnd ZrO₂Ceramics containing calcium, ceramics containing calcium silicate and lithium aluminosilicate, fluorine phlogopite mica ceramics, hexagonal boron nitride ceramics, etc., or at least one selected from these may be used, good. Moreover, you may add an additive element to these. Of these, especially SiO₂MgO and Al₂O_ThreeCeramics containing, have good workability, little damage to the single crystal during dicing, and high strength, so that the mechanical strength of the ultrasonic probe can be improved.
[0021]
In the ultrasonic probe of FIG. 1, a piezoelectric element comprising a first electrode 5 and a second electrode 4 and a piezoelectric body 1 sandwiched between them, a first acoustic matching layer 3a, and a second acoustic matching layer The laminated body in which 3b is laminated is divided into a plurality of parts, and there is a gap between the laminated bodies for simplicity. Conventionally, this void portion (groove) has been filled with an organic resin or the like in order to prevent the piezoelectric body from cracking and maintain mechanical strength. In the ultrasonic probe according to the embodiment of the present invention, the filling rate (E / D) is 5% by volume or less, where D is the volume of the groove between the laminates and E is the volume of the filling material in the groove. It is preferable that In the ultrasonic probe according to the embodiment of the present invention, since the first acoustic matching layer that is a solid inorganic substance and has a predetermined acoustic impedance is present on the side close to the piezoelectric element as described above, The strength is strong enough. In addition, since the electromechanical coupling coefficient and the dielectric constant can be prevented from being reduced by reducing the filling material, the characteristics of the piezoelectric body can be sufficiently extracted. By setting the filling rate to 5% by volume or less, the adjacent piezoelectric body is not in close contact, and the sensitivity of the ultrasonic probe can be kept high without suppressing vibration in the thickness direction related to transmission / reception of ultrasonic waves. As the filler, a silicon-based resin or an epoxy-based resin can be used, but a silicon-based resin is more preferable because it is difficult to suppress vibration in the thickness direction because it is soft. The filling rate is more preferably 3% by volume or less.
[0022]
Further, in the ultrasonic probe according to the embodiment of the present invention, as shown in FIG. 3, a piezoelectric element and an acoustic backing material comprising the first electrode 5 and the second electrode 4 and the piezoelectric body 1 sandwiched between them. 2 is preferably provided with a flexible printed wiring board (FPC) 6. By providing the FPC 6 between the piezoelectric element and the acoustic backing material 2, the piezoelectric element is sandwiched between the first acoustic matching layer 5 and the FPC 6, so that vibration in the length direction is suppressed and the sensitivity of the piezoelectric body 1 is improved. The effect of reducing variation increases.
[0023]
FIG. 4 shows the structure of the FPC 6 as viewed from the side in contact with the piezoelectric element. As shown in FIG. 4, the FPC 6 includes an insulating layer 6b and a conductive layer 6a printed thereon, and each conductive layer 6a is electrically connected to each piezoelectric element. The insulating layer 6b is made of polyimide or the like. The conductive layer 6a portion in contact with the piezoelectric element is made of a metal such as copper or gold and has an acoustic impedance value of about 30 to 40 Mrays. Therefore, the length of the piezoelectric body 1 is the same as that of the first acoustic matching layer 5. Since the vibration in the direction is suppressed, the effect of reducing the variation in sensitivity between channels can be enhanced. It is preferable that 50% or more of the contact area between the FPC 6 and the piezoelectric element is the contact between the conductive layer 6a and the piezoelectric element. In such a range, the vibration of the piezoelectric body 1 in the longitudinal direction is caused. It can be effectively suppressed. At that time, the acoustic impedance of the conductive layer 6 a is preferably 100% or more of the acoustic impedance of the piezoelectric body 1. As shown in FIG. 3, a ground plate 7 provided for transmitting and receiving ultrasonic waves and made of a conductive layer 7a and an insulating layer 7b is electrically connected to the second acoustic matching layer 3b. FPC may not be used. In FIG. 3, a third acoustic matching layer 3 c is provided between the ground plate 7 and the acoustic lens 8. The acoustic impedance of the third acoustic matching layer 3c is assumed to be smaller than the acoustic impedance of the second acoustic matching layer 3b. Thus, by making the acoustic matching layer three or more layers, acoustic matching between the piezoelectric body (acoustic impedance: about 20 to 30) and an object such as a human body (acoustic impedance of the human body: 1.5) can be achieved. Easy to take.
[0024]
The piezoelectric single crystal is preferably a solid solution piezoelectric single crystal containing at least lead titanate. By using a piezoelectric body made of such a solid solution single crystal, the speed of sound can be made slower than that of a piezoelectric body made of piezoelectric ceramic, so that a highly sensitive ultrasonic probe can be obtained. In particular, as the solid solution type piezoelectric single crystal of lead zinc niobate-lead titanate, it is desirable to use a lead titanate having a mole fraction of 20% or less. Further, the piezoelectric single crystal is Pb (B1, B2)._1-xTi_xO_Three(However, the value of x is 0.04 ≦ x ≦ 0.55, B1 is at least one selected from the group consisting of Zn, Mg, Ni, Sc, In and Yb, and B2 is composed of Nb and Ta. It is desirable to have a composition represented by the general formula (at least one selected from the group). In this general formula, if x is less than 0.04, the Curie temperature of the piezoelectric single crystal is lowered, and there is a risk of depolarization when the piezoelectric single crystal is cut. On the other hand, if x exceeds 0.55, a large electromechanical coupling coefficient cannot be obtained, and there is a possibility that matching of electrical impedance becomes difficult to perform when transmitting and receiving due to a decrease in dielectric constant.
[0025]
The piezoelectric element may have a structure in which a plurality of piezoelectric bodies are provided, electrodes are provided between the piezoelectric bodies, and the piezoelectric bodies and the electrodes are alternately stacked. Usually, in a piezoelectric body in which n layers are stacked, the thickness of the piezoelectric body per layer is 1 / n in order to obtain the same resonance frequency as that of a single-layer piezoelectric body. For example, when two layers of piezoelectric materials are stacked, the thickness of one layer of piezoelectric material is ½, and when three layers of piezoelectric materials are used, the thickness of one layer of piezoelectric material is １ ／. Furthermore, (n-1) layers of electrode (internal electrode) layers made of metal or the like exist between the laminated piezoelectric bodies. For example, when the piezoelectric material has two layers, the internal electrode is one layer, and when the piezoelectric material has three layers, the internal electrode is two layers. Since these internal electrodes are made of metal or the like, the acoustic impedance is as high as 30 to 40 Mrayls, and it is difficult to expand and contract. is there. Therefore, by providing a plurality of piezoelectric bodies as piezoelectric elements, vibrations in the length direction of the piezoelectric bodies can be more effectively reduced, and variations in sensitivity of the ultrasonic probe can be suppressed.
[0026]
The ultrasonic probe according to the embodiment of the present invention can be used as follows. As shown in FIG. 3, the first electrode 5 is connected to an ultrasonic diagnostic apparatus (not shown) through the ground plate 7 and the second electrode 4 through the FPC 6. By applying a drive signal voltage from the ultrasonic diagnostic apparatus to the piezoelectric body 1, the piezoelectric body 1 is vibrated to transmit ultrasonic waves from the acoustic lens 8 side. Further, at the time of reception, the ultrasound received from the acoustic lens 8 side is converted into an electrical signal by the piezoelectric body 1, and the received signal of each channel is delayed by a beam former in the ultrasound diagnostic apparatus, and then the ultrasound diagnostic apparatus Phased and added by the adder inside. Thereafter, when the fundamental wave is measured, the fundamental wave passing filter in the ultrasonic diagnostic apparatus is passed, and when the second harmonic is measured, the fundamental wave component in the ultrasonic diagnostic apparatus is removed. The image is displayed on a monitor (not shown) through a band-pass filter.
[0027]
Next, a method for producing an ultrasonic probe according to an embodiment of the present invention will be described.
[0028]
First, a method for producing a piezoelectric single crystal used as a piezoelectric body will be described. Here, a method for producing a solid solution single crystal of lead zinc niobate-lead titanate will be described.
[0029]
Chemically high purity PbO, ZnO, Nb as starting materials₂O_FiveTiO₂Then, these are weighed so that zinc niobate (PZN) and lead titanate (PT) have a desired molar ratio, and PbO is added as a flux. Pure water is added to this powder, for example, ZrO.₂Mix for a desired time in a ball mill containing the balls. After removing the water from the obtained mixture, the mixture is sufficiently pulverized by a pulverizer such as a reiki machine, and further put into a rubber-type container, and a rubber press is performed at a desired pressure. The solid matter taken out from the rubber mold is placed in a container of a desired volume made of platinum, for example, and dissolved at a desired temperature. After cooling, the solid material is further put into the container and sealed with a lid made of, for example, platinum, and the container is placed in the center of the electric furnace. The temperature is raised to a temperature higher than the melting temperature, gradually cooled to the vicinity of the melting temperature at a desired temperature lowering rate, and then cooled to room temperature. Thereafter, a desired concentration of nitric acid is added to the container, and the solution is boiled to take out a solid solution single crystal to obtain a piezoelectric single crystal.
[0030]
The solid solution single crystal of zinc niobate-lead titanate can be similarly manufactured by, for example, the Bridgman method, the Kilo-Puros method, the hydrothermal growth method, etc. in addition to the flux method described above. Here, zinc zinc niobate-lead titanate was given as an example, but the starting materials ZnO and Nb₂O_FiveIt is also possible to produce a solid solution type piezoelectric single crystal containing lead titanate obtained by substituting other elements.
[0031]
Next, a method for manufacturing an ultrasonic probe using such a piezoelectric single crystal will be described.
[0032]
First, as shown in FIG. 3, a block-shaped piezoelectric single crystal is used as the piezoelectric body 1, and a conductive film is deposited on the piezoelectric body 1 by a sputtering method. The first electrode 5 and the second electrode 4 are respectively formed on the side surfaces to obtain a piezoelectric element. Subsequently, a first acoustic matching layer 3a having a conductive layer (not shown) formed on the entire surface is bonded to the first electrode 5 side of the piezoelectric element with, for example, an epoxy adhesive. The first acoustic matching layer 3 a is made of a solid inorganic material and has an acoustic impedance of 40% or more and 85% or less of the acoustic impedance of the piezoelectric body 1. Similarly, a second acoustic matching layer in which a conductive layer (not shown) made of metal or the like is formed on the entire surface of the first acoustic matching layer 3a by plating or the like is bonded. The acoustic impedance of the second acoustic matching layer 3b is made smaller than the acoustic impedance of the first acoustic matching layer 3a in order to achieve acoustic impedance matching with the object. Next, the FPC 6 having a plurality of conductor layers (cables) 6a on the insulating layer 6b is bonded to the second electrode 4 side of the piezoelectric element by, for example, an epoxy adhesive. Thereafter, these are bonded on the acoustic backing material 2 so that the FPC 6 contacts the acoustic backing material 2. By cutting a plurality of times from the acoustic matching layer to the FPC 6 using a blade, the laminate of the piezoelectric elements and the acoustic matching layer is arranged in an array on the acoustic backing material 2 and separated from each other. Next, the ground plate 7 in which the conductive layer 7a is plated on the insulating layer 7b is bonded onto the second acoustic matching layer 3b with, for example, an epoxy adhesive. Further, an ultrasonic probe is obtained by bonding the third acoustic matching layer 3c on the ground plate 7 with an epoxy adhesive and forming the acoustic lens 8 thereon.
[0033]
In order to obtain a structure in which a plurality of piezoelectric bodies and electrodes are alternately laminated as a piezoelectric element, the piezoelectric element may be formed by the following process. For example, in the case of a piezoelectric element having three layers of piezoelectric bodies, as shown in FIG. 5, the piezoelectric bodies and the electrodes are laminated so that all the piezoelectric bodies are sandwiched between the electrodes. At that time, the electrodes are alternately extended to two opposite side surfaces. Then, by forming electrodes on the two side surfaces and connecting them to the stacked electrodes, the third electrode 11 or the fourth electrode 12 can be formed by every other layer of electrodes stacked with the electrodes formed on the side surfaces. In order to selectively connect each electrode to the third electrode or the fourth electrode, it is preferable to insulate by forming a resin or the like between the stacked electrode and the electrode on the side surface not connected thereto. . Then, by applying a predetermined voltage between the third electrode 11 and the fourth electrode 12, a piezoelectric element in which adjacent piezoelectric bodies are polarized in the opposite direction as shown by arrows in the figure is formed. It becomes possible to do. Even when three layers are stacked, the total thickness t is the same as that of a single-layer piezoelectric element. In the laminated piezoelectric material, for example, the lowermost electrode of the third electrode in FIG. 5 becomes the first electrode, and the uppermost electrode of the fourth electrode becomes the second electrode.
[0034]
When the piezoelectric single crystal used as the piezoelectric body 1 is rhombohedral or pseudo-cubic, it is desirable that the ultrasonic transmission / reception surface on the first electrode 5 side is a (001) plane. Such a piezoelectric body 1 is produced by cutting perpendicularly to the [001] axis (C axis) of the piezoelectric single crystal. The piezoelectric body 1 preferably has a thickness in the thickness direction of about 200 to 400 μm.
[0035]
The first electrode 5 and the second electrode 4 are formed by, for example, Ti / Au, Ni / Au or Cr / Au two-layer conductive film, or silver baking including glass frit.
[0036]
Further, although the two-layer structure and the three-layer structure are shown as the acoustic matching layer, a multilayer structure having more than that may be used. Note that the second or more acoustic matching layers do not need to be a solid inorganic material, and it is sufficient that the acoustic impedance decreases in order from the piezoelectric body toward the object.
[0037]
The ground plate 7 is bonded to the second acoustic matching layer 3b obtained by sputtering the conductive layer, but it is not necessary to bond to the entire second acoustic matching layer 3b, and may be bonded only to both ends. The ground plate 7 may be bonded to the first acoustic matching layer 3a.
[0038]
Hereinafter, the present invention will be described in more detail with reference to specific examples, but the present invention is not limited thereto.
[0039]
【Example】
Example 1
First, lead zinc niobate Pb (Zn_1/3Nb_2/3) O_Three(PZN) and lead titanate PbTiO_Three(PT) was weighed to a molar ratio of 91: 9, placed in a 200 cc platinum container together with a Pb flux composed of PbO, heated to 1200 ° C. and dissolved, and then cooled to room temperature to form a solid solution piezoelectric single crystal. I grew up. Thereafter, this piezoelectric single crystal was oriented with the <001> axis using a Laue camera and cut with a cutter perpendicularly to this axis to obtain a wafer having a thickness of 500 μm. The cut piezoelectric single crystal is polished to a thickness of 300 μm to obtain a piezoelectric body having a size of 30 mm × 20 mm × 0.3 mm, and then a first electrode and a second electrode made of Cr / Au are formed by sputtering. And it was set as the piezoelectric element. The piezoelectric element was subjected to polarization treatment by applying an electric field of 1 kV / mm. The acoustic impedance of this piezoelectric element was 22 Mrayls.
[0040]
On the first electrode side of the piezoelectric element, a Cr / Au electrode was formed on the entire surface by a sputtering method, and a first acoustic matching layer made of silicate glass having an acoustic impedance of 9 Mrays was adhered with an epoxy adhesive. On the first acoustic matching layer, a second acoustic matching layer made of a mixture of alumina powder and epoxy resin to which conductivity is added by applying an electrode made of sputtered Cr / Au is used as an epoxy adhesive. And glued. The acoustic impedance of the second acoustic matching layer was 5 Mrayls. Thereafter, an FPC having a conductive layer made of copper with an acoustic impedance of 35 Mrays on the second electrode side of the piezoelectric element and an acoustic backing material were bonded in order with an epoxy adhesive. Of the area where the FPC and the piezoelectric element contact, 50% is the contact between the conductive layer and the piezoelectric element. Next, the laminate composed of the piezoelectric element and the acoustic matching layer was cut into an array at a pitch of 200 μm with a dicing saw having a blade having a thickness of 50 μm. Thereafter, a ground plate made of gold was bonded to the entire second acoustic matching layer with an epoxy adhesive, and an acoustic lens made of silicon rubber was bonded to the ground plate. Since the ground plate was bonded with an epoxy adhesive, 5% by volume of the grooves between the laminates was filled with the epoxy adhesive. The capacitance of the piezoelectric body of the completed ultrasonic probe is measured from the end of the FPC at 10 MHz (twice the anti-resonance frequency), and the dielectric constant ε_S1S3As a result, the average value of the piezoelectric bodies of 100 channels arranged in one ultrasonic probe was 370, and the variation was a good value of 10% or less. After that, when an electrostatic probe characteristic was evaluated by connecting a coaxial cable having a capacitance of 110 pF / m and a length of 2 m to an FPC and connecting it to a diagnostic device, it had a high sensitivity, a wide bandwidth and a channel. The sensitivity variation between them was as small as 7% or less.
[0041]
(Example 2)
As the first acoustic matching layer, SiO having an acoustic impedance of 13 Mrays₂MgO and Al₂O_ThreeAn ultrasonic probe is manufactured in the same manner as in Example 1 except that a third acoustic matching layer made of a polyethylene sheet and having an acoustic impedance of 2 Mrays is formed on a ground plate, and an acoustic lens is formed. did. Dielectric constant ε in the same manner as in Example 1._S1S3As a result, the average value of the piezoelectric material of 100 channels included in one ultrasonic probe was 350, and the variation was a good value of 8% or less. In addition, when the ultrasonic probe characteristics were evaluated in the same manner as in Example 1, the sensitivity variation between channels was very small, 6% or less, with high sensitivity and wide bandwidth.
[0042]
(Example 3)
First, lead indium niobate Pb (In_1/2Nb_1/2) O_Three(PIN) and lead magnesium niobate Pb (Mg_1/3Nb_2/3) O_Three(PMN) and lead titanate PbTiO_Three(PT) mixed powder 0.16Pb (In) weighed to a molar ratio of 16:51:33_1/2Nb_1/2) O_Three-0.51Pb (Mg_1/3Nb_2/3) O_Three-0.33PbTiO_Three(PIMNT 16/51/33), PbO used as flux, B₂O_ThreeAnd PIMNT16 / 51/33: PbO: B₂O_ThreeIn a 200 cc platinum container so as to have a molar ratio of 50:40:10, the solution was heated to 1250 ° C. and dissolved, and then cooled to room temperature to grow a solid solution piezoelectric single crystal. Thereafter, this piezoelectric single crystal was oriented with the <001> axis using a Laue camera and cut with a cutter perpendicularly to this axis to obtain a wafer having a thickness of 600 μm. The cut piezoelectric single crystal is polished to a thickness of 400 μm to obtain a piezoelectric body having a size of 30 mm × 20 mm × 0.4 mm, and then a first electrode and a second electrode made of Cr / Au are formed by sputtering. And it was set as the piezoelectric element. The piezoelectric element was subjected to polarization treatment by applying an electric field of 1 kV / mm. The acoustic impedance of this piezoelectric element was 25 Mrayls.
[0043]
Thereafter, an ultrasonic probe was produced in the same manner as in Example 2. Dielectric constant ε in the same manner as in Example 1._S1S3As a result, the average value of 100 piezoelectric bodies of one ultrasonic probe was 340 pF, and the variation was a good value of 8% or less. In addition, when the ultrasonic probe characteristics were evaluated in the same manner as in Example 1, the sensitivity variation between channels was very small as 7% or less with high sensitivity and wide bandwidth.
[0044]
Example 4
Fluorophlogopite ceramic with an acoustic impedance of 16 Mrayls is used as the first acoustic matching layer, and an alumina and epoxy resin coated with an electrode made of Cr / Au with an acoustic impedance of 7 Mrayls and sputtered as the second acoustic matching layer An ultrasonic probe was manufactured in the same manner as in Example 2 except that an epoxy resin having an acoustic impedance of 3 Mrayls was used as the third acoustic matching layer. Dielectric constant ε in the same manner as in Example 1._S1S3As a result, the average value of the 100-channel piezoelectric bodies of one ultrasonic probe was 300, and the variation was a good value of 6% or less. Further, when the ultrasonic probe characteristics were evaluated in the same manner as in Example 1, the sensitivity variation between the channels was very small as 5% or less with high sensitivity and wide bandwidth.
[0045]
(Example 5)
An ultrasonic probe was produced in the same manner as in Example 2 except that a ground plate was adhered to the second acoustic matching layer using a film adhesive. Since a film adhesive was used, 3% by volume of the groove between the laminates was filled with the adhesive. Dielectric constant ε in the same manner as in Example 1._S1S3As a result, the average value of 100-channel piezoelectric bodies of one ultrasonic probe was 390, and the variation was a good value of 6% or less. Further, when the ultrasonic probe characteristics were evaluated in the same manner as in Example 1, the sensitivity variation between the channels was very small as 5% or less with high sensitivity and wide bandwidth.
[0046]
(Examples 6 and 7)
When the laminated body composed of the piezoelectric element and the acoustic matching layer is cut into an array shape with a dicing saw, the filling rate of the organic resin composed of the silicone-based resin adhesive in the grooves between the laminated bodies is 50 volume% and 95 volume, respectively. Example 6 and 7 are ultrasonic probes manufactured by the same process as in Examples 1 and 2 except that the composition is filled to be%.
[0047]
Evaluation is performed in the same manner as in Example 1. First, dielectric constant ε for Example 6_S1S3As a result, the average value of 100-channel piezoelectric bodies of one ultrasonic probe was 330, and the variation was a good value of 8% or less. Further, when the ultrasonic probe characteristics of Example 6 were evaluated in the same manner as in Example 1, the sensitivity variation between channels was very small as 7% or less with high sensitivity and wide bandwidth.
[0048]
Further, in Example 7, the dielectric constant ε_S1S3As a result, the average value of the piezoelectric material of 100 channels included in one ultrasonic probe was 310, and the variation was a favorable value of 7% or less. Further, when ultrasonic probe characteristics were evaluated in the same manner as in Example 1 for Example 7, the sensitivity variation between channels was very small, with a high sensitivity and a wide bandwidth of 6% or less.
[0049]
(Example 8)
A piezoelectric single crystal was formed in the same manner as in Example 1, and this wafer was polished to a thickness of 150 μm to form two piezoelectric bodies having a size of 30 mm × 20 mm × 0.15 mm, and then Cr / Au was formed by sputtering. The electrode which consists of was formed in both surfaces. At this time, an electrode is not formed at the end of one side on one side, and an electrode is not formed at the end of a side that is point-symmetric with this side on the side opposite to this side. In such electrode patterning, the electrode may be formed after masking the piezoelectric body, or the electrode may be formed on both surfaces of the piezoelectric body and then part of the electrode may be removed by dicing. The two piezoelectric bodies were bonded with an epoxy adhesive so that the electrodes overlapped in the same shape. By bonding with an epoxy adhesive, the electrodes are electrically connected, and the end of the side that does not form the electrode is filled with an epoxy adhesive, and the electrodes alternately appear on opposite sides. became. Then, by forming electrodes also on the two side surfaces where the electrodes are alternately projected, a third electrode composed of an electrode sandwiched between the piezoelectric bodies and a side electrode connected thereto, and two sandwiching the piezoelectric bodies The electrode and the 4th electrode which consists of an electrode of the side surface connected to these were made. And when the electric field of 1 kV / mm was applied between the 3rd electrode and the 4th electrode and the polarization process was performed, the acoustic impedance of this piezoelectric element was 22Mrayls.
[0050]
Thereafter, an ultrasonic probe was produced in the same manner as in Example 2. Dielectric constant ε in the same manner as in Example 1._S1S3As a result, the average value of the 100-channel piezoelectric bodies included in one ultrasonic probe was 1000, and the variation was a good value of 6% or less. Further, when the ultrasonic probe characteristics were evaluated in the same manner as in Example 1, the sensitivity variation between the channels was very small as 5% or less with high sensitivity and wide bandwidth.
[0051]
(Comparative Example 1)
An ultrasonic probe was produced in the same manner as in Example 1 except that the acoustic matching layer was produced by the following method.
[0052]
On the first electrode side of the piezoelectric element, a Cr / Au electrode is formed on the entire surface by sputtering, the acoustic impedance is 7 Mrays, and the first acoustic matching layer made of a mixture of an epoxy resin and alumina is used as an epoxy adhesive. Glue with. Next, on the first acoustic matching layer, a second acoustic matching layer made of an epoxy resin having an acoustic impedance of 3 Mrays and added with conductivity by forming a Cr / Au electrode on the entire surface by sputtering. Are bonded with an epoxy adhesive.
[0053]
Dielectric constant ε in the same manner as in Example 1._S1S3As a result, the average value of 100-channel piezoelectric bodies was 360, and the variation was as large as 25% or more. This is because the acoustic impedance value of the first acoustic matching layer is less than 40% of the acoustic impedance value of the piezoelectric body, and the first acoustic matching layer made of an organic material is used. It is considered that the vibration cannot be suppressed and the variation of the dielectric constant of the piezoelectric body is increased. Further, when the ultrasonic probe characteristics were evaluated in the same manner as in Example 1, although there were some channels having high sensitivity and wide bandwidth, the sensitivity variation between the channels was as large as 20% or more. Such sensitivity variations between channels adversely affected the image quality of tomographic images displayed on the diagnostic apparatus.
[0054]
(Comparative Example 2)
An ultrasonic probe was manufactured in the same manner as in Example 1 except that a mixture of epoxy resin and tungsten powder having an acoustic impedance of 9 Mrays was used as the first acoustic matching layer. Dielectric constant ε in the same manner as in Example 1._S1S3As a result, the average value of the piezoelectric material of 100 channels included in one ultrasonic probe was 340, and the variation was as large as 20% or more. Although the acoustic impedance value is 40% or more of the acoustic impedance value of the piezoelectric body as the first acoustic matching layer, since the organic material is used, the organic material has stretchability. It is considered that the variation of the dielectric constant of the piezoelectric material is increased. Further, when the probe characteristics were evaluated in the same manner as in Example 1, although channels showing relatively good sensitivity and bandwidth were found in various places, the sensitivity variation between channels was as large as 15% or more. Such sensitivity variations between channels adversely affected the image quality of tomographic images displayed on the diagnostic apparatus.
[0055]
(Comparative Example 3)
As the first acoustic matching layer, lead metaniobate PbNb having an acoustic impedance of 20 Mrays₂O₆And using a mixture of alumina and an epoxy resin with an acoustic impedance of 7 Mrayls and applying an electrode made of Cr / Au by sputtering as the second acoustic matching layer, ultrasonic waves are obtained in the same manner as in Example 2. A probe was made. Dielectric constant ε in the same manner as in Example 1._S1S3As a result, the average value of the piezoelectric material of 100 channels included in one ultrasonic probe was 300, and the variation was a good value of 5% or less. However, when the ultrasonic probe characteristics were evaluated in the same manner as in Example 1, since the acoustic impedance was too large and the acoustic matching between the object such as the human body and the piezoelectric body was insufficient, the obtained super The frequency spectrum of the sonic probe was not uniform and low sensitivity and narrow band characteristics were shown. The tomographic image displayed on the diagnostic apparatus was significantly inferior.
[0056]
As described above, in each of the comparative examples, the sensitivity variation is large or the acoustic matching is insufficient in each comparative example, compared to the case where an ultrasonic probe having high sensitivity and wide bandwidth and small sensitivity variation is obtained. It has become a new ultrasonic probe.
[0057]
In particular, among the examples, it can be seen that an ultrasonic probe with less variation in sensitivity can be obtained by using three or more acoustic matching layers. In addition, when the acoustic impedance value of the first acoustic matching layer is set to 40% to 85% of the acoustic impedance value of the piezoelectric body, the lower the acoustic impedance of the first acoustic matching layer, the lower the dielectric impedance of the piezoelectric body. The rate can be increased, and the higher the sensitivity, the less the variation in sensitivity between channels. Furthermore, the dielectric constant of the piezoelectric body can be increased by setting the filling rate of the resin between the laminated bodies to 5% by volume or less, and the effect is further enhanced by setting the filling rate to 3% by volume or less. In addition, by including a plurality of piezoelectric bodies as piezoelectric elements and a structure in which a plurality of piezoelectric bodies and electrodes are stacked, variation in sensitivity between channels can be reduced, and the dielectric constant of the piezoelectric body can be significantly increased. It becomes possible.
[0058]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to provide an ultrasonic probe with small variations in sensitivity.
[Brief description of the drawings]
FIG. 1 is a perspective view illustrating an ultrasonic probe according to an embodiment of the present invention.
FIG. 2 is a perspective view illustrating a vibration direction of a piezoelectric body.
FIG. 3 is a cross-sectional view illustrating an ultrasonic probe according to an embodiment of the present invention.
FIG. 4 is an explanatory view showing a structure of a flexible printed wiring board.
FIG. 5 is a perspective view for explaining a piezoelectric element formed by alternately laminating a plurality of piezoelectric bodies and electrodes.
[Explanation of symbols]
1 ... Piezoelectric body
2 ... Acoustic backing material
3a ... first acoustic matching layer
3b ... second acoustic matching layer
3c ... third acoustic matching layer
3 ... Acoustic matching layer
4 ... Second electrode
5 ... 1st electrode
6a ... conductive layer
6b ... Insulating layer
6 ... Flexible printed circuit board
7a ... conductive layer
7b ... Insulating layer
7 ... Earth plate
8 ... Acoustic lens
11 ... Third electrode
12 ... Fourth electrode

Claims (5)

An acoustic backing material, a piezoelectric body provided on the acoustic backing material and formed of a piezoelectric single crystal, a first surface where the piezoelectric body faces the acoustic backing material, and a side opposite to the first surface A piezoelectric element having a pair of electrodes respectively provided on the second surface, and an acoustic impedance of 40% or more of the acoustic impedance of the piezoelectric body, provided on the second surface of the piezoelectric element. % Of the first acoustic matching layer made of a solid inorganic material and a second acoustic matching layer provided on the first acoustic matching layer and having an acoustic impedance smaller than that of the first acoustic matching layer. and, wherein the piezoelectric element and the first acoustic matching layer and the second plurality of laminates including an acoustic matching layer is arranged on the acoustic backing material in a one-dimensional or two-dimensional array, in an array Array Void portion between the laminate, ultrasonic probe, wherein the filling rate is less than 5 vol%. The ultrasonic probe according to claim 1, further comprising a flexible printed wiring board between the acoustic backing material and the piezoelectric element. The piezoelectric single crystal is Pb (B1, B2) _1-x Ti _x O ₃ (where x is 0.04 ≦ x ≦ 0.55, B1 is Zn, Mg, Ni, Sc, In and 3. The ultrasonic probe according to claim 1, wherein the ultrasonic probe has a composition represented by: at least one selected from the group consisting of Yb, and B2 is at least one selected from the group consisting of Nb and Ta. . Ceramics containing a ceramic first acoustic matching layer comprises SiO _2, MgO and _{Al 2 O 3, Si 3 N} 4, AlN, and ceramics containing Al ₂ O ₃ and ZrO _2, calcium silicate and lithium aluminosilicate The ultrasonic probe according to claim 1, further comprising at least one ceramic selected from the group consisting of: fluorinated phlogopite ceramics and hexagonal boron nitride ceramics. The ultrasonic probe according to claim 1, wherein the piezoelectric element includes a plurality of layers of the piezoelectric bodies, and has an electrode between the piezoelectric bodies and is alternately stacked.

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