JP2008048276A - Ultrasonic transducer and ultrasonic transducer array - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a practical broadband ultrasonic transducer by actualizing the broadband frequency characteristics without reducing output of transmitted ultrasonic waves. <P>SOLUTION: The ultrasonic transducer comprises a plurality of piezoelectric body layers 12 and 13 stacked alternately with a plurality of electrode layers and the total thickness of the piezoelectric body layers changes with inclination so that it becomes thicker from a first side toward a second side. It has an acoustic-matching layer 14 formed on the plurality of piezoelectric body layers via the electrode layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ultrasonic transducer and an ultrasonic transducer array used in an ultrasonic imaging apparatus for medical use or nondestructive inspection.

  Conventionally, as an element used for transmission / reception of ultrasonic waves in an ultrasonic imaging apparatus (also called an ultrasonic diagnostic apparatus, an ultrasonic inspection apparatus, etc.), a piezoelectric ceramic represented by PZT (lead zirconate titanate), PVDF ( 2. Description of the Related Art An ultrasonic transducer in which an electrode is formed on a piezoelectric material such as a polymer piezoelectric material represented by (polyvinylidene fluoride) is known. When a voltage is applied to the electrodes of such an ultrasonic transducer, the piezoelectric body expands and contracts due to the piezoelectric effect, and ultrasonic waves are generated. Therefore, an ultrasonic beam transmitted in a desired direction can be formed by arranging such a plurality of ultrasonic transducers in one or two dimensions and sequentially driving the ultrasonic transducers. Further, the ultrasonic transducer expands and contracts by the ultrasonic wave propagated from the subject and generates an electric signal. This electric signal is used as an ultrasonic reception signal.

  By the way, in ultrasonic diagnosis, it is known that the width of the ultrasonic frequency band affects the quality of the ultrasonic image. In general, an ultrasonic wave having a relatively high frequency is easily attenuated, but has a high depth resolution. On the other hand, an ultrasonic wave having a relatively low frequency easily reaches a deep part, but the depth resolution is likely to be lowered. It has the property of Therefore, by using ultrasonic waves having a wide frequency band, it is possible to identify fine structures and tissues in the subject and obtain high-quality ultrasonic images.

  Here, the frequency band in the vibrator depends on the composition of the piezoelectric material, the structure such as the grain size and density, and is determined by the thickness of the vibrator when the materials are the same. For this reason, the band of the vibrator can be changed by changing the composition of the piezoelectric material, but it is not easy to widen the band.

  Patent Document 1 discloses a plurality of ultrasonic transducers each including a piezoelectric material layer in which a first electrode and a second electrode are respectively formed on a first surface and a second surface facing each other. An ultrasonic transducer array including a plurality of ultrasonic transducers having a second surface inclined with respect to one surface and a filler disposed between the plurality of ultrasonic transducers is disclosed. That is, in Patent Document 1, the frequency band is expanded by changing the thickness of the vibrator depending on the location.

  Incidentally, FIG. 12A shows a structure of a general ultrasonic transducer, and FIG. 12B shows frequency characteristics of ultrasonic waves transmitted and received therefrom. As shown in FIG. 12A, in a general ultrasonic transducer, electrodes 92 and 93 are formed on both surfaces of a piezoelectric layer 91 having a substantially uniform thickness, and an acoustic matching layer 94 is further formed. Has been placed. FIG. 13 (a) shows the structure of the broadband ultrasonic transducer disclosed in Patent Document 1, and FIG. 13 (b) shows the frequency characteristics of the ultrasonic waves transmitted and received therefrom. Yes. As shown in FIG. 13A, in this wide-band ultrasonic transducer, electrodes 96 and 97 are formed on both surfaces of an inclined piezoelectric layer 95, and an acoustic matching layer 98 is further disposed. . In (b) of FIG. 12 and (b) of FIG. 13, the horizontal axis indicates the frequency (MHz), and the vertical axis transmits ultrasonic waves by applying a predetermined voltage to the ultrasonic transducer. The voltage (reception voltage, arbitrary unit) output from the ultrasonic transducer by receiving the reflected wave is shown.

Here, as described in Patent Document 1, the vibration frequency of the ultrasonic transducer is inversely proportional to the thickness of the piezoelectric material. Therefore, as shown in FIG. 13A, the frequency characteristics with a wide band can be obtained by synthesizing the frequency characteristics corresponding to the portions where the thickness of the piezoelectric material is Z _{1 to} Z ₃ . (B) of FIG. 13 is obtained by synthesizing the frequency characteristics at three locations of thicknesses Z ₁ and Z ₃ and intermediate Z ₂ for the sake of simplicity.

As is clear from comparison between FIG. 12B and FIG. 13B, the frequency bandwidth of a general ultrasonic transducer is about 50%, whereas broadband ultrasonic waves are used. In the transducer, the frequency bandwidth is about 63%, which indicates that the bandwidth is widened. Here, the frequency bandwidth (%) means a width Δf = f _H −f _L between two frequencies f _H and f _{L at} which the sound pressure is attenuated by 6 dB from the peak value, and a center value (center frequency) f thereof. It is obtained by dividing by _C = (f _H + f _L ) / 2 (Δf / f _C ).

However, on the other hand, the reception voltage of the broadband ultrasonic transducer is generally lowered, and is about 46% when a general ultrasonic transducer is used as a reference. This is presumably because the emitted energy is dispersed due to the wide band.
In addition, when the ultrasonic transducer array is applied to an ultrasonic endoscope, it is necessary to downsize the entire array. In such a case, a transmission system circuit (drive system) to which the ultrasonic transducer is connected. In addition, it becomes difficult to obtain electrical matching with the wiring cable.
JP 2005-110116 A

  Therefore, in view of the above points, an object of the present invention is to provide a practical broadband ultrasonic transducer by widening the frequency characteristics without causing a decrease in the output of ultrasonic waves.

  In order to solve the above-described problem, an ultrasonic transducer according to one aspect of the present invention includes a plurality of piezoelectric layers alternately stacked with a plurality of electrode layers, and the total thickness of the plurality of piezoelectric layers. Are a plurality of piezoelectric layers that change in an inclined manner so as to increase in thickness from the first side toward the second side, and an acoustic wave formed on the plurality of piezoelectric layers via an electrode layer. And a matching layer.

  According to the present invention, the ultrasonic transducer is broadened by changing the thickness of the piezoelectric layer in an inclined manner, and the decrease in output is compensated for by laminating a plurality of piezoelectric layers, which is suitable for practical use. A broadband ultrasonic transducer can be realized.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, the same reference number is attached | subjected to the same component and description is abbreviate | omitted.
FIG. 1 is a perspective view showing an ultrasonic transducer according to the first embodiment of the present invention. As shown in FIG. 1 (a), the ultrasonic transducer according to this embodiment has, for example, a minute columnar shape with a bottom width of about 0.1 mm to 15 mm and a height of about 0.2 mm to 1.0 mm. The structure is a lower electrode layer 11, a piezoelectric layer 12 whose thickness changes in an inclined manner, two piezoelectric layers 13 having a substantially uniform thickness, an acoustic matching layer 14, and an arrangement between them. A plurality of internal electrode layers 15a to 15c. In addition, the ultrasonic transducer according to the present embodiment includes insulating films 16 that are alternately formed on the left and right end surfaces of the internal electrode layers 15a to 15c (portions exposed on the left and right side surfaces of the ultrasonic transducer in FIG. 1). Alternatively, as shown in FIG. 1B, side electrodes 17a and 17b may be included. In FIG. 1A, two piezoelectric layers 13 are shown. However, at least one piezoelectric layer 13 is sufficient, and three or more piezoelectric layers 13 may be provided.

  The piezoelectric layers 12 and 13 are made of, for example, a piezoelectric ceramic represented by PZT (lead zirconate titanate), a polymer piezoelectric material represented by PVDF (polyvinylidene fluoride), or the like. These piezoelectric layers 12 and 13 expand and contract when an electric field is applied through the lower electrode layer 11 and the internal electrode layers 15a to 15c formed on both surfaces thereof.

In the piezoelectric layer 12, the upper surface (the internal electrode 15a side) is inclined with respect to the lower surface (the lower electrode layer 11 side). The piezoelectric layer 13 is disposed on the slope of the piezoelectric layer 12. As a result, the total thickness of the stacked piezoelectric layers 12 and 13 changes from Z ₁ to Z ₃ in an inclined manner. Here, since the resonance frequency f ₀ of the ultrasonic transducer is inversely proportional to the thickness of the piezoelectric layer, the resonance of the ultrasonic transducer is provided by providing an inclination in at least one piezoelectric layer in this way. The frequency can be widened.

  The acoustic matching layer 14 is formed of, for example, Pyrex (registered trademark) glass that easily transmits ultrasonic waves, epoxy resin containing metal powder, or the like, and mismatching of acoustic impedance between the subject that is a living body and the ultrasonic transducer. By eliminating the above, the propagation efficiency of ultrasonic waves is increased. As shown in FIG. 1A, the acoustic matching layer 14 has a lower surface (internal electrode 15 c side) along the inclination of the piezoelectric layers 12 and 13, and the upper surface is the lower surface of the piezoelectric layer 12. It is designed to be parallel to. Thereby, the ultrasonic transducer 10 has a rectangular parallelepiped shape as a whole.

  The insulating film 16 is formed so as to alternately cover the end surfaces of the lower electrode layer 11 and the internal electrodes 15a to 15c exposed on the two opposing surfaces (the left side and the right side in FIG. 1) of the ultrasonic transducer 10. Has been.

  When driving such an ultrasonic transducer, a side electrode 17a is formed on one side of the ultrasonic transducer 10 so as to pass outside the insulating film 16, as shown in FIG. The side electrode 17b is formed on the other side so as to pass outside the insulating film 16. Thereby, the internal electrode layer 15a and the internal electrode layer 15c are electrically connected, and the lower electrode layer 11 and the internal electrode layer 15b are electrically connected. Then, a drive signal having a predetermined waveform (for example, a pulse wave) is supplied to the ultrasonic transducer 10 via the side electrodes 17a and 17b.

  The surface on which the insulating film 16 and the side electrodes 17a and 17b are formed is not limited to the two surfaces shown in FIG. 1. If the lower electrode layer 11 and the internal electrodes 15a to 15c can be wired in common every other layer, the ultrasonic transducer Any area is acceptable. For example, the insulating film 16 and the side electrodes 17a and 17b may be formed on the front and back surfaces (that is, the surface on which the electrode layer is inclined) in FIG. Or you may connect a lead wire to the lower electrode layer 11 and the internal electrode layers 15a-15c instead of forming a side electrode.

FIG. 2 shows a simulation result of frequency characteristics of ultrasonic waves transmitted and received from the ultrasonic transducer 10 shown in FIG.
In this simulation, the acoustic impedance of the piezoelectric layers 12 and 13 is set to 34 Mrayl, and the thickness of each part (the left end, the center, and the right end in the figure) is set to Z ₁ = 342 μm, Z ₂ = 273.6 μm, and Z ₃ , respectively. = 228 μm. And what synthesize | combined the frequency characteristic in those three places was made into the frequency characteristic of the ultrasonic transducer | vibrator which concerns on this embodiment. The center frequency corresponding to the thickness of each portion, _{respectively, Z 1: 6.0MHz, Z 2} : 7.5MHz, Z 3: a 9.0MHz.

In addition, the acoustic matching layer 14 was designed in the following manner with an acoustic impedance of 6 Mrayl. That is, the entire ultrasonic transducer has a rectangular parallelepiped shape by aligning the lower surface with the inclination of the piezoelectric layers 12 and 13 and the upper surface parallel to the lower surface of the piezoelectric layer 12. At that time, the thickness of the central portion (the upper portion of the thickness of the piezoelectric layer is Z ₂ parts), ultrasound (center frequency: 7.5 MHz) generated from the piezoelectric layer having a thickness Z ₂ of the acoustic matching It was set to be 1/4 of the propagation wavelength in the layer 14. This is because the highest propagation efficiency can be obtained at this time. As a result, the thickness of each portion of the acoustic matching layer 14 was 14.93 μm at the left end, 83.3 μm at the center portion, and 128.93 μm at the right end.
Furthermore, the simulation was performed under the condition that a backing material having an acoustic impedance of 5.5 Mrayl is disposed on the back surface of the ultrasonic transducer.

(A) in FIG. 2 shows (i) the frequency characteristics (broadband, three layers) of the ultrasonic transducer according to the present embodiment (see FIG. 1), and (ii) a superstructure with two layers of piezoelectric layers. For comparison with the frequency characteristics (broadband, two layers) of the acoustic transducer (one piezoelectric layer 13 in FIG. 1), (iii) the frequency of a broadband ultrasonic transducer with a single piezoelectric layer It shows the characteristics (broadband / single layer) and (iv) the frequency characteristics (normal) of a general ultrasonic transducer having a uniform piezoelectric layer thickness and a single layer. _Further, three curves are described as Z _1, Z 2, _{Z 3} represents the frequency characteristic of the ultrasonic transducer (single layer) the thickness of the piezoelectric layer is _{Z 1,} Z 2, _{Z 3} respectively It is used when obtaining the frequency characteristics of a broadband / single-layer ultrasonic transducer. In FIG. 2A, the horizontal axis indicates the frequency (MHz), and the vertical axis indicates the voltage output from the ultrasonic transducer by transmitting the ultrasonic transducer ultrasonic wave and receiving the reflected wave ( Received voltage, arbitrary unit). That is, the vertical axis means transmission efficiency × reception efficiency. Also, (b) in FIG. 2 standardizes (i) wideband and three-layer frequency characteristics and (iv) normal frequency characteristics among the frequency characteristics shown in FIG. 2 (a). Is.

  As shown in FIG. 2A, in the ultrasonic transducer in which the thickness of the piezoelectric layer is changed in an inclined manner, the bandwidth is wider than that of a normal ultrasonic transducer. For example, as shown in FIG. 2B, the frequency bandwidth of a general ultrasonic transducer is about 50%, whereas the frequency bandwidth of a wide-band ultrasonic transducer is expanded to about 63%. Further, when three broadband ultrasonic transducers are compared, it is confirmed that the reception voltage increases as the number of layers increases. This is because if the number of piezoelectric layers is increased without changing the overall thickness (that is, each piezoelectric layer becomes thinner), the electric field strength applied to each piezoelectric layer increases.

When the frequency characteristics of Z ₁ , Z ₂ , and Z ₃ are compared, the received voltages of Z ₁ and Z ₃ are generally decreased as compared to the received voltage of Z ₂ . This is because the acoustic matching layer, the thickness of the piezoelectric layer is designed as appropriate propagation efficiency is obtained when the Z _2.

As described above, according to the present embodiment, the vibration frequency of the ultrasonic transducer can be widened by changing the thickness of the piezoelectric layer in an inclined manner. At that time, by laminating a plurality of piezoelectric layers, it is possible to suppress a decrease in output of ultrasonic waves. Therefore, since the transmission sensitivity can be maintained even if the ultrasonic transducer is downsized, the ultrasonic probe and the entire ultrasonic endoscope to which such an ultrasonic transducer is applied can be used in a wide band while maintaining the performance. And miniaturization. Further, by laminating the piezoelectric layers, it is easy to achieve electrical matching with a transmission system circuit (drive system) and a wiring cable, so that it is possible to improve transmission sensitivity and reception sensitivity.
In this embodiment, since the entire ultrasonic transducer has a rectangular parallelepiped shape, when another acoustic matching layer or acoustic lens is disposed on the acoustic matching layer 14, design and operability are facilitated.

Next, an ultrasonic transducer according to a second embodiment of the present invention will be described with reference to FIG.
In the ultrasonic transducer according to the present embodiment, an acoustic matching layer 21 shown in FIG. 3 is arranged instead of the acoustic matching layer 14 shown in FIG. Other configurations are the same as those shown in FIG.

Here, as shown in FIG. 2A, when the acoustic matching layer is designed in accordance with the thickness (for example, Z ₂ ) of a specific portion of the piezoelectric layer, the thickness of the other portions is designed. The propagation efficiency of frequency components corresponding to (for example, Z ₁ and Z ₃ ) is reduced. Therefore, in the present embodiment, the acoustic matching layer is designed so that appropriate propagation efficiency is obtained for the frequency component corresponding to the thickness of each part of the piezoelectric layer.

That is, when the ultrasonic wave passes through the acoustic matching layer, the propagation efficiency is most improved when the thickness of the acoustic matching layer is 1/4 times the wavelength λ of the ultrasonic wave propagating therethrough (hereinafter referred to as the following). In λ / 4 matching). Therefore, the thickness of each portion of the acoustic matching layer 21 is defined so that λ / 4 matching is satisfied with respect to the frequency component corresponding to the thickness of the piezoelectric layers 12 and 13 below the acoustic matching layer 21. Here, the speed of sound in the acoustic matching layer 21 is c, and the frequency of the ultrasound and _{f i,} the wavelength lambda _i is represented by λ _i = c / _{f i.} Accordingly, the thickness d ₁ at the left end of the acoustic matching layer 21 is d ₁ = (c / f ₁ ) / 4, where f ₁ is the center frequency of the ultrasonic wave generated from the piezoelectric layer having the thickness Z _1. Become. Further, the thickness d ₃ at the right end of the acoustic matching layer 21 is d ₃ = (c / f ₃ ) / 4, where f ₃ is the center frequency of the ultrasonic wave generated from the piezoelectric layer having the thickness Z _3. Become.

  By designing the acoustic matching layer 21 in this way, it is possible to reduce acoustic energy loss for each band of ultrasonic waves generated from the piezoelectric layers 12 and 13 whose thickness changes in an inclined manner. As a result, the transmission / reception efficiency of ultrasonic waves can be improved regardless of the band.

  FIG. 4 shows a simulation result of frequency characteristics of ultrasonic waves transmitted and received from the ultrasonic transducer shown in FIG. In FIG. 4A, the horizontal axis indicates the frequency (MHz), and the vertical axis indicates the voltage (reception voltage, output from the ultrasonic transducer that transmits the ultrasonic transducer ultrasonic wave and receives the reflected wave). Arbitrary unit). 4B is a standardized version of FIG. 4A.

In this simulation, the acoustic impedance of the piezoelectric layers 12 and 13 is set to 34 Mrayl, and the thickness of each part (the left end, the center, and the right end in the figure) is set to Z ₁ = 342 μm, Z ₂ = 273.6 μm, and Z ₃ , respectively. = 228 μm. The center frequency of the frequency characteristics in portions thereof, _{respectively, Z 1: 6.0MHz, Z 2} : 7.5MHz, Z 3: a 9.0MHz. The acoustic impedance of the acoustic matching layer 21 is 8 Mrayl, and the thickness of each part (left end, center, right end) is 106.64 μm, 83.33 μm, and 69.32 μm, respectively, so that λ / 4 matching can be achieved. did. Further, the calculation was performed under the condition that a backing material having an acoustic impedance of 5.5 Mrayl is disposed on the back surface of the ultrasonic transducer.

As shown in FIG. 4 (b), broadband ultrasonic transducer thickness of the piezoelectric layer and the frequency characteristic of the ultrasonic transducer of Z _2, the thickness of the piezoelectric layer varies from Z ₁ to Z ₃ Comparing with the frequency characteristics, the bandwidth of the former is about 56%, while the bandwidth of the latter is expanded to about 62%, confirming that the bandwidth is widened. In addition, the level of the reception voltage rises not only in the vicinity of the center but also on the whole including the low frequency side and the high frequency side.

  As described above, according to the present embodiment, the shape of the acoustic matching layer is determined according to the thickness of each part of the piezoelectric layer. Therefore, the propagation efficiency of the ultrasonic wave is improved over a wide band from low to high. It becomes possible to improve.

Next, an ultrasonic transducer according to a third embodiment of the present invention will be described with reference to FIG.
The ultrasonic transducer according to the present embodiment includes two piezoelectric layers 31 and 32 and an acoustic matching layer 33 shown in FIG. 5 instead of the two piezoelectric layers 13 and the acoustic matching layer 21 shown in FIG. It is. Other configurations are the same as those shown in FIG.

  In the present embodiment, not only the piezoelectric layer 12 but also the piezoelectric layers 31 and 32 disposed thereon are changed in an inclined manner. The acoustic matching layer 33 is designed so that λ / 4 matching is satisfied for each of the piezoelectric layers 12, 31, and 32 that change in an inclined manner.

  In this way, by changing the thickness of each of the piezoelectric layers 12, 31, and 32 in an inclined manner, ultrasonic waves in a plane including a low range to a high range (in a plane parallel to the paper surface in FIG. 3) The radiation characteristics can be made uniform. As a result, the transmission power, transmission sensitivity, and reception sensitivity can be made uniform regardless of the frequency band. Therefore, the signal processing for the reception signal output by receiving the drive signal and the ultrasonic wave for generating the ultrasonic wave is performed. Can be simple.

Next, an ultrasonic transducer according to a fourth embodiment of the present invention will be described with reference to FIG.
The ultrasonic transducer according to the present embodiment is obtained by further providing a dummy layer 41 with respect to the ultrasonic transducer shown in FIG. Here, in the ultrasonic transducer shown in FIG. 5, in each of the piezoelectric layers 12, 31 and 32 and the acoustic matching layer 33, the low frequency side (left side in the figure) is thickened. As a whole, the difference in thickness between the low frequency side and the high frequency side becomes large. However, considering the arrangement of an acoustic lens on the acoustic matching layer 33 and operability, it is more practical and preferable to make the upper surface (ultrasonic wave transmitting / receiving surface) of the ultrasonic transducer parallel to the lower surface. Therefore, in the present embodiment, the dummy layer 41 is provided on the acoustic matching layer 33, thereby eliminating the thickness gap between the low frequency side and the high frequency side.

As a material for the dummy layer 41, it is desirable to use a material having an acoustic impedance relatively close to that of a living body such as silicone rubber so as not to hinder the propagation efficiency of ultrasonic waves.
Such a dummy layer may be provided in the ultrasonic transducer shown in FIG.

Next, an ultrasonic transducer according to a fifth embodiment of the present invention will be described with reference to FIG.
The ultrasonic transducer according to this embodiment is obtained by further providing a backing layer 42 having an inclination with respect to the ultrasonic transducer 10 shown in FIG. Here, as described above, it is desirable that the ultrasonic transmission surface of the ultrasonic transducer be parallel to the back surface of the ultrasonic transducer. Therefore, in the present embodiment, the inclined backing layer 42 is disposed on the back surface of the piezoelectric layer 12.

Next, an ultrasonic transducer array according to an embodiment of the present invention will be described with reference to FIG.
As shown in FIG. 8, the ultrasonic transducer array includes a backing layer 51 in which wirings 52 and 53 are formed, and a plurality of ultrasonic transducers 10 arranged on the backing layer 51. Although not shown, a filler that fixes and protects the arrangement of the ultrasonic transducers 10 is disposed between and around these ultrasonic transducers 10.

  The plurality of ultrasonic transducers 10 are arranged in, for example, 128 rows in the azimuth direction (scanning direction) and 7 columns in the elevation direction (direction orthogonal to the azimuth direction). Each ultrasonic transducer 10 is arranged such that the piezoelectric layer 12 (FIG. 1) is inclined in the azimuth direction. The seven ultrasonic transducers 10 included in one row are connected to common wires 52 and 53 via side electrodes 17a and 17b, respectively. Further, an acoustic lens for converging the ultrasonic waves to a predetermined depth is disposed above the ultrasonic transducers 10.

In such an ultrasonic transducer array, an ultrasonic beam having a focal point at a predetermined depth is transmitted by driving the ultrasonic transducers 10 wired in common in units of one row or in units of several rows. By sequentially performing such an operation in the azimuth direction, the subject is scanned with the ultrasonic beam.
In the present embodiment, the array is formed by the ultrasonic transducer according to the first embodiment, but the ultrasonic transducer according to the second to fifth embodiments may be applied instead. .

  FIG. 9 shows a modification of the ultrasonic transducer array according to this embodiment. As shown in FIG. 9, each ultrasonic transducer 10 may be arranged such that the piezoelectric layer 12 (FIG. 1) is inclined in the elevation direction.

Next, a method for manufacturing an ultrasonic transducer array according to an embodiment of the present invention will be described with reference to FIGS.
First, as shown in FIG. 10A, a sheet-like laminate including a piezoelectric layer 61 whose thickness changes in an inclined manner, an electrode layer 62, and a piezoelectric layer 63 is formed. Here, at least one piezoelectric layer 63 may be formed. Alternatively, three or more electrode layers 62 and piezoelectric layers 63 may be alternately formed. Further, the thickness of the piezoelectric layer 63 may be uniform, or may be changed in an inclined manner like the piezoelectric layer 61. Such a sheet-like laminate is produced by alternately laminating piezoelectric layers and electrode layers having a uniform thickness, and then polishing the lowermost piezoelectric layer obliquely. Alternatively, the thickness may be changed by tilting the squeegee when the piezoelectric material layer is formed using the green sheet method. The latter can also be applied when an inclination is provided in the second or more piezoelectric layers.

  Next, by cutting the sheet-like laminate at the broken line shown in FIG. 10A, bar-like laminates are sequentially produced as shown in FIG. 10B. Then, by polishing the bottom surface of the piezoelectric layer 61, the heights of the plurality of bar-shaped stacked bodies are made uniform.

  Next, as shown in FIG. 10C, the electrode layer 64 is formed on the lower surface of the piezoelectric layer 61 and the electrode layer 65 is formed on the upper surface of the piezoelectric layer 63. Further, the acoustic matching layer 66 is disposed on the electrode layer 65. 10 (c) shows an acoustic matching layer 66 whose upper surface is horizontal (parallel to the lower surface of the piezoelectric layer 61), but as shown in FIG. An acoustic matching layer whose upper surface is inclined according to the thickness of 63 may be formed.

  Next, as illustrated in FIG. 10D, insulating films 67 are formed on the two side surfaces parallel to the longitudinal direction of the bar-shaped stacked body so as to alternately cover the electrode layers 64, 62, and 65. The insulating film 67 may be formed by applying and curing a resin material using a dispenser, or may be formed by depositing an insulating material such as glass by an electrodeposition method or a sputtering method.

  Next, as shown in FIG. 11A, side electrodes 68 are formed outside the insulating film 67. The side electrode 68 may be formed on the entire two side surfaces, or a pattern may be formed (see FIG. 1) in accordance with the cutting pitch in a later step. Thereby, a bar-shaped ultrasonic transducer 69 is produced.

  Next, as shown in FIG. 11B, bar-shaped ultrasonic transducers 69 are arranged on the substrate 71 according to the pitch in the azimuth direction. Then, as shown in FIG. 11C, the bar-shaped ultrasonic transducer 69 is cut in accordance with the pitch in the elevation direction. Thereby, an array of ultrasonic transducers 10 is formed. Further, the array is fixed by pouring a filler between these ultrasonic transducers 10 and solidifying them. And the board | substrate 71 is removed and the backing material in which wiring was formed instead is arrange | positioned instead. Thereby, the ultrasonic transducer array shown in FIG. 8 is completed.

(Example)
An ultrasonic transducer array according to an embodiment of the present invention was fabricated and its characteristics were tested. Experimental conditions and results are as follows. The sound speed in the 33 mode was 3100 m / s, and the sound speed in the sliver mode was 4100 m / s. Here, the 33 mode is an ultrasonic transducer having a bottom surface of a substantially square with a side length of w, where w / t is about 0.6 or less when the thickness (height) is t. The vibration mode in the case of. The sliver mode is a bar-shaped ultrasonic transducer whose bottom is a rectangle whose one side is W ₀ (fixed value) and whose other side is w (w <w ₀ ). This refers to the vibration mode when w / t is in the vicinity of 0.6 when the thickness (height) is t.
(1) Ultrasonic transducer A
Size: Bottom 0.3mm x 0.3mm, height 0.478mm
Number of stacked piezoelectric layers: 3 layers
Piezoelectric material: PZT
Dielectric constant 4000 (effective value near resonance frequency)
５ 5800 (around 1kHz)
Resonance frequency: 3.00MHz
Capacitance: 6.67pF
Impedance: 7949Ω
Vibration mode: 33 modes

When this ultrasonic transducer A was driven at a drive frequency of 3.00 MHz, the sensitivity (reception voltage / transmission voltage) was improved by about 38.1 dB over the single-layer ultrasonic transducer. This value can be said to be much higher than the sensitivity of a normal ultrasonic transducer (broadband / single layer).
Such an ultrasonic transducer A can be applied, for example, to an ultrasonic transducer array for a fetal observation two-dimensional electronic scan probe by arranging in 32 rows and 32 columns.
(2) Ultrasonic transducer B
Size: Bottom 5mm x 0.11mm, Height 0.25mm
Number of stacked piezoelectric layers: 3 layers
Piezoelectric material: Same as (1) above
Resonance frequency: 7.59 MHz
Capacitance: 77.92pF
Impedance: 269Ω
Vibration mode: Sliver mode

When this ultrasonic transducer B was driven at a drive frequency of 7.59 MHz, the sensitivity (reception voltage / transmission voltage) was improved by about 10.1 dB over the single-layer ultrasonic transducer. This value can be said to be much higher than the sensitivity of a normal ultrasonic transducer (broadband / single layer).
Such ultrasonic transducers B can be applied to a one-dimensional array for gastrointestinal endoscopes, for example, by arranging them in 128 rows.
(3) Ultrasonic transducer C
Size: Bottom 0.5mm x 0.11mm, Height 0.2mm
Number of stacked piezoelectric layers: 3 layers
Piezoelectric material: Same as (1) above
Resonance frequency: 9.49 MHz
Capacitance: 9.74 pF
Impedance: 1722Ω
Vibration mode: Sliver mode

When this ultrasonic transducer C was driven at a driving frequency of 10.25 MHz, the sensitivity (reception voltage / transmission voltage) was improved by about 25.0 dB over the single-layer ultrasonic transducer. This value can be said to be much higher than the sensitivity of a normal ultrasonic transducer (broadband / single layer).
Such an ultrasonic transducer C can be applied to a 1.5-dimensional array for gastrointestinal endoscopes, for example, by arranging in 10 rows and 128 columns. Here, the 1.5-dimensional array is an array in which a plurality of ultrasonic transducers are arrayed on a two-dimensional surface, and the number of arrays in the column direction is larger than the number of arrays in the row direction and the array pitch. An array with a small array pitch.

  The present invention can be used in an ultrasonic transducer and an ultrasonic transducer array used in an ultrasonic imaging apparatus for medical use or nondestructive inspection.

1 is a perspective view showing a structure of an ultrasonic transducer according to a first embodiment of the present invention. It is a figure which shows the frequency characteristic of the ultrasonic wave transmitted / received from the ultrasonic transducer shown in FIG. It is a perspective view which shows the structure of the ultrasonic transducer based on the 2nd Embodiment of this invention. It is a figure which shows the frequency characteristic of the ultrasonic wave transmitted / received from the ultrasonic transducer shown in FIG. It is a perspective view showing the structure of the ultrasonic transducer concerning a 3rd embodiment of the present invention. It is a perspective view showing the structure of an ultrasonic transducer concerning a 4th embodiment of the present invention. It is a perspective view which shows the structure of the ultrasonic transducer | vibrator which concerns on the 5th Embodiment of this invention. 1 is a perspective view showing an ultrasonic transducer array according to an embodiment of the present invention. It is a perspective view which shows the modification of the ultrasonic transducer array which concerns on one Embodiment of this invention. It is a figure for demonstrating the manufacturing method of the ultrasonic transducer array which concerns on one Embodiment of this invention. It is a figure for demonstrating the manufacturing method of the ultrasonic transducer array which concerns on one Embodiment of this invention. It is a figure which shows the structure of a general ultrasonic transducer, and its frequency characteristic. It is a figure which shows the structure of the conventional broadband ultrasonic transducer, and its frequency characteristic.

Explanation of symbols

10, 69 Ultrasonic transducer 11 Lower electrode layers 12, 13, 31, 32, 61, 63 Piezoelectric layers 14, 21, 66 Acoustic matching layers 15a-15c Internal electrode layers 16, 67 Insulating films 17a, 17b, 68 Side electrodes 41 Dummy layers 42, 51 Backing layer (backing material)
52, 53 Common wiring 62, 64, 65 Electrode layer 71 Substrate

Claims (9)

In a plurality of piezoelectric layers alternately stacked with a plurality of electrode layers, the total thickness of the plurality of piezoelectric layers changes in an inclined manner so that the total thickness increases from the first side toward the second side. A plurality of piezoelectric layers,
An acoustic matching layer formed on the plurality of piezoelectric layers via an electrode layer;
An ultrasonic transducer comprising: The thickness of the first layer of the plurality of piezoelectric layers is changing in an inclined manner,
The thickness of the second and subsequent layers of the plurality of piezoelectric layers is substantially uniform.
The ultrasonic transducer according to claim 1.   2. The ultrasonic transducer according to claim 1, wherein the thickness of each of the plurality of piezoelectric layers changes in an inclined manner so as to increase from the first side toward the second side.   The ultrasonic transducer according to claim 1, wherein the thickness of the acoustic matching layer changes in an inclined manner so as to increase from the first side toward the second side.   The ultrasonic transducer according to claim 4, wherein a thickness of each portion of the acoustic matching layer is determined based on a thickness of a corresponding portion of the plurality of piezoelectric layers.   The ultrasonic transducer according to claim 1, wherein an upper surface of the acoustic matching layer is parallel to lower surfaces of the plurality of piezoelectric layers.   The ultrasonic transducer according to claim 1, further comprising a dummy layer formed on the acoustic matching layer and having an upper surface parallel to the lower surfaces of the plurality of piezoelectric layers.   The ultrasonic transducer according to claim 1, further comprising a backing layer formed on a lower surface of the plurality of piezoelectric layers, the lower surface being parallel to an upper surface of the acoustic matching layer. A plurality of ultrasonic transducers according to any one of claims 1 to 8,
A filler disposed between the plurality of ultrasonic transducers;
An ultrasonic transducer array comprising:

Images