JP2006101204A - Acoustic matching layer and its manufacturing method, and ultrasonic transducer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To further increase the propagation efficiency of a transmitted ultrasonic wave to an object under test, in an ultrasonic transducer comprising an acoustic matching layer, and to reduce noise resulting from multiple reflection in the ultrasonic transducer. <P>SOLUTION: This acoustic matching layer 14 matches an acoustic impedance between the object under test and a piezoelectric material layer 10 forming a piezoelectric vibrator for transmitting and receiving an ultrasonic wave in the ultrasonic transducer, and is formed by performing film forming by using a plurality of materials having acoustic impedances different from one another, and changing the ratios of mixing of the plurality of materials according to the thickness of deposited films. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an acoustic matching layer used for matching an acoustic impedance between a transducer that transmits and receives ultrasonic waves and a subject in an ultrasonic probe, a method for manufacturing the acoustic matching layer, and the transducer and acoustics. The present invention relates to an ultrasonic transducer including a matching layer.

  FIG. 13 shows the structure of an ultrasonic probe used in a general ultrasonic diagnostic apparatus. The ultrasonic probe 100 includes a plurality of transducers 101 that transmit and receive ultrasonic waves. As the vibrator 101, an electrode 103 is provided on a piezoelectric body 102 including a piezoelectric ceramic represented by PZT (lead zirconate titanate) or a polymer piezoelectric material represented by PVDF (polyvinyl difluoride). An attached piezoelectric element is used. Each electrode 103 is connected to an electronic circuit included in the ultrasonic diagnostic apparatus main body via a lead wire 104.

  A backing layer 105 is provided behind the transducer 101 (on the side opposite to the ultrasonic transmission direction). The backing layer 105 suppresses noise caused by multiple reflections of ultrasonic waves in the probe by absorbing and quickly attenuating the ultrasonic waves. For the backing layer 105, a material that easily absorbs ultrasonic waves, such as epoxy resin or rubber, is used.

  In addition, an acoustic matching layer 106 is disposed in front of the transducer 101 (on the ultrasonic wave transmission direction side). Further, an acoustic lens material 107 such as silicon rubber is disposed in front of the acoustic matching layer 106 in order to form a focal point at a desired depth by focusing ultrasonic waves.

  Here, when a ceramic body such as PZT is used as the material of the vibrator, the acoustic propagation properties between the living body as the subject and the vibrator are greatly different. Ratios will be reflected at their boundaries. As a result, the ultrasonic waves cannot be efficiently propagated inside the subject, or the reflected ultrasonic waves are reflected multiple times inside the vibrator, thereby generating noise. Therefore, a general ultrasonic probe has an acoustic impedance (acoustic impedance = substance density × ultrasonic velocity) between the ultrasonic transducer and the living body as an acoustic matching layer. By arranging the members, ultrasonic propagation loss and noise are reduced. Note that the acoustic impedance of a general PZT as a material of the vibrator is about 35 MRayl, and the acoustic impedance of a living body is about 1.5 MRayl.

  In general, when an ultrasonic transducer including an acoustic matching layer is manufactured, the vibrator and the acoustic matching layer are bonded to each other using an adhesive or the adhesiveness of the material of the acoustic matching layer itself. As this adhesive, an epoxy, urethane, silicon or the like having a relatively small acoustic impedance (for example, about 2 MRayl to 5 MRayl) is generally used. Therefore, there is a problem that the presence of the adhesive itself or adhesion unevenness that occurs when the adhesive is applied affects the transmission of ultrasonic waves between the vibrator and the acoustic matching layer.

  Conventionally, as the acoustic matching layer, a member having an acoustic impedance of about 4 MRayl to 5 MRayl or a member in which a material having an acoustic impedance of about 10 MRayl and a material having an acoustic impedance of about 2 MRayl to 3 MRayl are sequentially stacked may be used. Many. Since the reflectance of ultrasonic waves increases as the difference between the acoustic impedances of two substances in contact with each other increases, it is better to change the acoustic impedance stepwise between the transducer and the subject as in the latter case. Sound wave propagation loss and noise can be effectively reduced.

  On the other hand, since the ultrasonic wave generated from the transducer is attenuated to some extent while propagating through the acoustic matching layer, it is desirable to reduce the thickness of the acoustic matching layer as much as possible in order to shorten the propagation distance. However, in order to increase the number of layers constituting the acoustic matching layer without increasing the thickness of the entire acoustic matching layer, it is necessary to reduce the thickness of each layer. In addition, the low manufacturing yield is a problem. In addition, when a plurality of layers are bonded together, an adhesive is often used, so that ultrasonic waves are also reflected between the acoustic matching layers. Furthermore, it is difficult to select a material that has a desired acoustic impedance, hardly absorbs ultrasonic waves, and can withstand the manufacturing process as described above. Under such circumstances, at present, the limit of the number of layers constituting the acoustic matching layer is 2-3.

  Incidentally, in recent years, research on a film forming method called an aerosol deposition method (hereinafter also referred to as an AD method) has been advanced. The AD method is a method of forming a film by generating an aerosol containing raw material powder (film-forming powder), spraying it from a nozzle and spraying it onto a substrate. Here, the aerosol refers to solid or liquid fine particles suspended in a gas. The AD method is also called a jet deposition method or a gas deposition method. In the AD method, film formation is performed by a mechanism in which a raw material powder sprayed at a high speed collides with a lower layer, bites and breaks, and a crushing surface generated at that time adheres to the lower layer. This film formation mechanism is called a mechanochemical reaction, and this reaction makes it possible to form a dense and strong film that does not contain impurities. Therefore, new material development utilizing such a special film formation mechanism and application to various applications are expected.

  In Patent Document 1, in order to manufacture piezoelectric ceramics without using an organic binder, to use an adhesive, and to produce a high-performance transducer with a high yield without using a cutting process, AD The use of the law is disclosed. That is, in an ultrasonic transducer having a piezoelectric element layer, an acoustic matching layer, and a damping layer as basic components, the piezoelectric element layer is a laminated piezoelectric element in which a plurality of piezoelectric elements and electrodes are stacked by spraying and depositing ultrafine particles. Element (first page).

Further, Patent Document 1 has a multilayer acoustic matching layer by producing an acoustic matching layer using the AD method (page 3), or by using a plurality of nozzles and material ultrafine particles for the acoustic matching layer. It has also been suggested to form an ultrasonic transducer (page 4).
However, in order to form a high-quality film by the AD method, it is important to adjust film forming conditions such as aerosol spray pressure, substrate hardness, film forming temperature, etc. according to the type of film forming powder. If the nozzle is replaced each time a layer constituting the acoustic matching layer is formed, it takes time until the above film forming conditions are satisfied, and the efficiency is poor. Further, if nozzles are prepared according to the number of layers constituting the acoustic matching layer (that is, the type of material), the apparatus becomes complicated and large.
Japanese Patent No. 3356820 (first page, third page, fourth page)

  In view of the above points, the present invention can further improve the propagation efficiency of ultrasonic waves to an object in an ultrasonic transducer including an acoustic matching layer, and reduce noise caused by multiple reflections in the ultrasonic transducer. It is an object of the present invention to provide an acoustic matching layer that can be produced, a manufacturing method thereof, and an ultrasonic transducer including such an acoustic matching layer.

  In order to solve the above-described problems, an acoustic matching layer according to the present invention is an acoustic matching layer that matches acoustic impedance between a piezoelectric layer forming a transducer for transmitting and receiving ultrasonic waves and a subject in an ultrasonic transducer. In this case, a plurality of materials having different acoustic impedances are used, and film formation is performed while changing the mixing ratio of the plurality of materials in accordance with the thickness of the deposited film.

  The acoustic matching layer manufacturing method according to the present invention is a method for manufacturing an acoustic matching layer in an ultrasonic transducer, in which acoustic impedance is matched between a piezoelectric layer forming a transducer for transmitting and receiving ultrasonic waves and a subject. A step (a) of storing the first powder, which is the first raw material of the acoustic matching layer, in the first container, and generating an aerosol containing the first powder; The second powder, which is the second raw material of the acoustic matching layer having a different acoustic impedance, is stored in a container, and an aerosol containing the second powder is generated (b) and generated in the step (a). A step of controlling the injection pressure of the first aerosol beam by injecting the aerosol from the injection nozzle to generate a first aerosol beam, and injecting or sucking the gas to the first aerosol beam (c) ) The aerosol generated in the step (b) is ejected from the ejection nozzle to generate a second aerosol beam, and a gas is ejected or sucked into the second aerosol beam, whereby the second aerosol beam The step (d) of controlling the injection pressure, and the first and second aerosol beams are injected toward the same region on the piezoelectric layer or the electrode layer formed on the piezoelectric layer, thereby And a step (e) of depositing a second raw material on the piezoelectric layer or the electrode layer at a predetermined ratio.

  According to the present invention, since the acoustic impedance in the acoustic matching layer is changed while being inclined in the thickness direction, unnecessary reflections caused by acoustic impedance mismatch can be efficiently reduced. Therefore, since the propagation efficiency of ultrasonic waves can be improved and noise can be reduced, the generation efficiency and image quality of ultrasonic images can be improved. In addition, according to the present invention, such an acoustic matching layer is formed by changing the mixing ratio of a plurality of raw materials using an aerosol deposition method, so that a plurality of layers whose acoustic impedance changes stepwise are formed. The included acoustic matching layer and the acoustic matching layer whose acoustic impedance changes continuously can be easily and efficiently produced without using an adhesive.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. The same constituent elements are denoted by the same reference numerals, and the description thereof is omitted.
FIG. 1 is a cross-sectional view showing an ultrasonic transducer including an acoustic matching layer according to the first embodiment of the present invention. The ultrasonic transducer 1 shown in FIG. 1 includes a vibrator 13 having electrodes 11 and 12 formed on both ends of a piezoelectric body 10 and an acoustic matching layer 14 laminated on the vibrator 13 via the electrode 11. . Further, the ultrasonic transducer 1 may include a backing layer 15 disposed on the surface of the vibrator 13 opposite to the acoustic matching layer 14.

As the piezoelectric body 10, a piezoelectric ceramic represented by PZT (lead zirconate titanate) or a polymer piezoelectric element represented by PVDF (polyvinylidene difluoride) is used. In the present embodiment, PZT (acoustic impedance: about 35 MRayl) is used. When a voltage is applied to the electrodes 11 and 12 formed at both ends of the piezoelectric body 10 by applying a pulsed electric signal or a continuous wave electric signal, the piezoelectric body 10 expands and contracts to generate ultrasonic waves. The piezoelectric body 10 expands and contracts by receiving propagating ultrasonic waves and generates an electrical signal. This electrical signal is output as an ultrasonic reception signal via the electrodes 11 and 12 and the wiring connected to these electrodes.
As a material for the electrodes 11 and 12, a metal such as platinum (Pt), gold (Au), silver (Ag), nickel (Ni), or an alloy containing these metals can be used. Platinum is used.

  The acoustic matching layer 14 according to the present embodiment includes a plurality of layers 14a, 14b,... Having different compositions. These layers 14a, 14b,... Are formed directly on the vibrator 13 and the lower layer without using an adhesive or the like by the AD method described later, so that the acoustic impedance changes stepwise in the thickness direction. Has been placed. Although FIG. 1 shows the acoustic matching layer 14 having a five-layer structure, any number of layers may be used as long as the number of layers is two or more. In the present embodiment, the layer 14a is made of PZT, and the layer 14e is made of porous alumina whose acoustic impedance is relatively close to that of a living body. The layers 14b to 14d contain PZT and porous alumina, and the mixing ratio thereof is determined so that PZT gradually decreases and the porous alumina gradually increases in the order of the layers 14b, 14c, and 14d. .

  The backing layer 15 is provided to quickly attenuate the ultrasonic waves generated from the back surface (surface opposite to the ultrasonic transmission direction) of the ultrasonic transducer 13 and reduce noise in the ultrasonic probe. Yes. The backing layer 15 is formed of a material that easily absorbs ultrasonic waves, such as polyimide resin, epoxy resin containing metal powder, and rubber containing ferrite powder.

Next, a method for manufacturing the acoustic matching layer according to the present embodiment will be described with reference to FIGS. The acoustic matching layer manufactured in the present embodiment is formed on the vibrator 13 shown in FIG.
FIG. 2 is a schematic diagram showing a configuration of a film forming apparatus used when manufacturing the acoustic matching layer according to this embodiment. This film forming apparatus uses an aerosol deposition (AD) method in which a raw material powder (film forming powder) is sprayed and deposited on a lower layer.

  The film formation apparatus shown in FIG. 2 includes a film formation chamber 20 where film formation is performed, an exhaust pump 21 that maintains a predetermined degree of vacuum by exhausting the film formation chamber 20, and a substrate 22 on which a film is formed. The substrate stage 23 to hold | maintain is included. The substrate stage 23 is a movable stage that moves three-dimensionally, and changes the film formation target region by moving under the control of the control unit 31 described later.

  In addition, the film forming apparatus includes a first aerosol generation chamber 24a and a second aerosol generation chamber 24b, a first aerosol transfer line 25a and a second aerosol transfer line 25b, a first injection nozzle 26a and a first aerosol generation chamber 24b. Two injection nozzles 26b, a first compressor (compression pump) 27a and a second compressor 27b, a first air supply line 28a and a second air supply line 28b, a first control valve 29a and a second The control valve 29b, the first side nozzle 30a and the second side nozzle 30b, and the control unit 31 are included.

The aerosol generation chambers 24a and 24b are containers in which minute powders (film forming powders) of raw materials are placed. Compressed gas supply lines such as gas cylinders are connected to the aerosol generation chambers 24a and 24b, respectively, from which nitrogen (N ₂ ), oxygen (O ₂ ), helium (He), argon (Ar), or drying A carrier gas such as air is introduced. Thereby, in the aerosol generation chambers 24a and 24b, the film-forming powder is blown up to generate aerosol. The aerosols generated in the aerosol generation chambers 24a and 24b are introduced into the film forming chamber 20 through the aerosol transport pipes 25a and 25b, and are sprayed toward the substrate 27 from the spray nozzles 26a and 26b, respectively. The directions of the openings of the injection nozzles 12 a and 12 b are adjusted so that the aerosol injected from the respective nozzles overlaps on the film formation surface of the substrate 27.

  The compressor 27a pumps air to the side nozzle 30a through the air supply line 28a. The air supply line 28a is provided with a control valve 29a that operates under the control of the control unit 31, thereby adjusting the supply of air to the side nozzle 30a. Similarly, the compressor 27b pressure-feeds air to the side nozzle 30b via an air supply line 28b provided with a control valve 29b.

  FIG. 3 is a diagram for explaining the positional relationship between the injection nozzle and the side nozzle shown in FIG. 2. Here, since FIG. 3 shows a state where the region including the injection nozzle and the side nozzle of FIG. 2 is viewed from the left side of the drawing, the injection nozzle 26b and the side nozzle 30b are shown. However, the injection nozzle 26a and the side nozzle 30a are also arranged so as to have the same positional relationship as in FIG.

  As shown in FIG. 3, the injection nozzle 26 b and the side nozzle 30 b are supported by a nozzle guide 32. The side nozzle 30b is disposed in the vicinity of the opening of the injection nozzle 26b, and blows gas, for example, air toward the aerosol injected from the injection nozzle 26b.

  Here, in order to perform film formation by the AD method, the substrate conditions such as the kind of film forming powder, the pressure of aerosol (aerosol beam) sprayed onto the substrate, etc. (film forming powder injection pressure), the hardness of the substrate, It is necessary that the four conditions of the film formation temperature be satisfied with a good balance. If even one of these conditions is missing, the performance of the formed film will change, the film forming speed will decrease, or the film itself will not be formed. Therefore, by spraying air on the aerosol to disturb the aerosol air flow, the spray pressure is controlled by changing the conditions related to the spray pressure of the film-forming powder among the above four conditions. Thereby, it is possible to prevent the deposition powder from being deposited on the substrate or the like, or to reduce the proportion of deposition powder that can be deposited. On the contrary, deposition of film deposition powder is resumed by stopping the air blowing, reducing the amount or speed of air ejection, and quickly recovering the original film deposition powder injection pressure that meets the film deposition conditions. The ratio of film-forming powder that can be deposited or deposited can be increased.

As shown in FIG. 3, the direction of the air injected from the side nozzle 30b is preferably a direction having a direction cosine with respect to the traveling direction of the aerosol. That is, as shown in FIG. 3A, when the air has a negative velocity component with respect to the traveling direction of the aerosol beam, or as shown in FIG. When the air has a positive velocity component with respect to the direction, the velocity component toward the substrate direction that the aerosol has can be changed, so the above-mentioned conditions regarding the film-forming powder injection pressure are effectively Can be changed.
Referring to FIG. 2 again, the control unit 31 controls the relative position between the substrate stage 23 and the injection nozzles 26a and 26b according to the film pattern to be formed, and also controls the opening and closing of the control valves 29a and 29b. .

4 and 5 are diagrams for explaining a method of manufacturing the acoustic matching layer according to the present embodiment.
First, a PZT member 10 on which an electrode layer 11 is formed is prepared, and as shown in FIG. 4A, the electrode layer 11 side is set as a film formation surface and set on the substrate stage 23 shown in FIG. As the PZT member 10, a PZT plate material may be used, or a PZT thick film formed by an AD method and heat-treated as necessary may be used. The electrode layer 11 is formed by depositing a conductive film such as platinum on the PZT member 10 by using, for example, sputtering or vacuum evaporation. The thickness of the electrode layer 11 is desirably 200 nm to 300 nm or more. The reason is that when the film is formed on the electrode layer 11 by the AD method, a phenomenon called anchoring occurs in which the powder bites into the lower layer when the raw material powder is sprayed on the lower layer. This is because, in consideration of the depth of about 10 nm to 300 nm, the above-described thickness is necessary for the electrode layer to function well. Further, the inside of the film forming chamber 20 is kept at a predetermined temperature, and the exhaust pump 21 is used to evacuate to a predetermined vacuum level.

Next, in the film forming apparatus shown in FIG. 2, one of the two types of film forming powders for producing the acoustic matching layer (material A) is placed in the aerosol generation chamber 24a, and the other (material B) is used. It arrange | positions in the aerosol production | generation chamber 24b. Examples of the material A include magnesium (about 10.0 MRayl), silica (SiO ₂ , about 12 MRayl to about 15 MRayl), quartz, glass (about 13 MRayl to about 15 MRayl), marble (about 16 MRayl), PZT (about 35 MRayl), A material such as alumina (Al ₂ O ₃ , approximately 40 MRayl) or the like whose acoustic impedance is relatively close to that of the vibrator (PZT) is used. Further, as the material B, a material having an acoustic impedance relatively close to that of a living body such as porous silica or porous alumina is used. The acoustic impedance of these porous bodies varies depending on the degree of pores contained therein, but is usually in the range of about 0.1 to 1.0 times the acoustic impedance of silica or alumina. In the present embodiment, PZT is used as the material A, and porous alumina is used as the material B. Further, aerosol generation is started in the aerosol generation chambers 24a and 24b, respectively.

  Next, the control valves 29a and 29b are opened to eject air from the side nozzles 30a and 30b, and the aerosol generated in the aerosol generation chambers 24a and 24b is introduced into the injection nozzles 26a and 26b, respectively, and injected. Thereby, as shown to (a) of FIG. 4, the aerosol injected from the injection nozzle 26a and the aerosol injected from the injection nozzle 26b are each disturbed by the air injected from the side nozzles 30a and 30b.

  Next, by closing the control valve 29a shown in FIG. 2, the injection pressure of the aerosol injected from the injection nozzle 26a is recovered as shown in FIG. 4B. Then, while moving the substrate stage 23, an aerosol beam 33a is sprayed onto the electrode layer 11, thereby forming a PZT layer 14a having a predetermined thickness.

  Next, by opening the control valve 29a shown in FIG. 2 by a predetermined amount and closing the control valve 29b by a predetermined amount, the injection pressures of the aerosol beams 33a and 33b are changed as shown in FIG. Adjust to a predetermined ratio. Thereby, PZT and porous alumina are mixed and deposited on the film formation surface. Further, by moving the substrate stage 23, the layer 14b having a predetermined thickness and containing PZT and porous alumina mixed at a predetermined ratio M: N (for example, M> N) is formed on the layer 14a. Form.

  Subsequently, while gradually opening the control valve 29a shown in FIG. 2 and gradually closing the control valve 29b, as shown in FIGS. 5A and 5B, the injection pressure of the aerosol beam 33a is gradually suppressed. On the contrary, the spray pressure of the aerosol beam 33 is gradually recovered. Thereby, layers 14c (for example, M = N) and 14d (for example, M <N) in which PZT and porous alumina are mixed at a predetermined ratio M: N are sequentially formed. In the layers 14b to 14d, the mixing ratio of PZT gradually decreases, and the mixing ratio of porous alumina gradually increases accordingly. In FIGS. 4C to 5B, for the purpose of explanation, the ratio of the injection pressures of the aerosol beams 33a and 33b is changed in three stages. By making the degree small, it is possible to form a larger number of layers.

  Next, the control valve 29a shown in FIG. 2 is fully opened and the control valve 29b is completely closed, thereby blocking the aerosol injected from the injection nozzle 26a as shown in FIG. The injection pressure of the beam 33b is recovered. Thereby, a layer 14e of porous alumina having a predetermined thickness is formed on the layer 14d. In the case of producing an acoustic matching layer having a two-layer structure, as shown in FIG. 4B, after the first layer is formed using one kind of material, the two kinds of materials are mixed. Thus, the second layer may be formed using the other material as shown in FIG.

  After forming the acoustic matching layer 14 including the layers 14a to 14e in this manner, the PZT member 10 is removed from the substrate stage 23, and sputtering or vacuum deposition is used on the opposite side of the electrode layer 11 of the PZT member 10. An electrode layer 12 (FIG. 1) is formed, and a backing layer 15 is further disposed. Thereby, the ultrasonic transducer 1 including the acoustic matching layer 14 and the backing layer 15 is manufactured. When the backing layer 15 is disposed, a sound absorbing material such as an epoxy resin may be attached to the electrode layer 12 using an adhesive, or a thick film of the sound absorbing material is formed on the electrode layer 12 using the AD method. May be formed. In the latter case, since the reflection of ultrasonic waves caused by the adhesive can be suppressed, the ultrasonic attenuation effect by the backing layer 15 can be enhanced.

  FIG. 6 shows a result obtained by calculating the relationship between the number of layers constituting the acoustic matching layer 14 shown in FIG. 1 and the transmittance of ultrasonic waves between the transducer and the living body. As shown in FIG. 6, when the acoustic matching layer is not disposed (the number of layers = 0), the transmittance is about 8%, but by providing the acoustic matching layer without using an adhesive, The rate is increasing. For example, in the case of a single-layer acoustic matching layer (number of layers = 1), the transmittance is about 12%, which is about 1.5 times larger. Further, in the case of an acoustic matching layer having a two-layer structure, which has hitherto been limited due to technical problems, the transmittance is about 14%, but by increasing the number of layers to 10, the transmittance is about By increasing the number of layers to 30 by increasing the number to 18.5% (about 2.3 times in the case of 0 layers, about 1.3 times in the case of 2 layers), the transmittance is about 20% (0 layers) About 2.5 times that of the case of 2 and about 1.4 times that of the case of two layers). Here, since the transmittance affects both the transmission and reception of the ultrasonic wave, for example, when the transmittance is increased by a factor of 2, the transmission efficiency of the ultrasonic wave is quadrupled (2 × 2) in the forward path and the return path. Times). That is, when converted to transmission / reception sensitivity, it increases by about 12 dB, so that the image quality of the ultrasonic image can be improved in each stage. Such an acoustic matching layer including a large number of layers can be easily produced by using the acoustic matching layer manufacturing method according to the present embodiment.

  FIG. 7 is a diagram illustrating a result of obtaining an ideal distribution of acoustic impedance in an acoustic matching layer composed of a plurality of layers by four-terminal calculation. It is most efficient and desirable that the acoustic impedances of the plurality of layers constituting the acoustic matching layer are distributed as shown in FIG. 7 rather than linearly changing in the layer thickness direction. For example, when the acoustic matching layer is composed of 35 layers, the acoustic impedance is about 25 MRayl in the fourth layer from the side closer to the transducer (PZT), about 15 MRayl in the 10th layer, about 5 MRayl in the 22nd layer, 35 The thickness is changed to about 2 MRayl in the layer. Conventionally, it has been difficult to select a material having a desired acoustic impedance, but by changing the mixing ratio of a plurality of different materials as in the method of manufacturing an acoustic matching layer according to the present embodiment, FIG. The distribution of acoustic impedance as shown in FIG.

  As described above, according to the present embodiment, the aerosol sprayed from the two spray nozzles is respectively disturbed, thereby adjusting the spray pressure of the aerosol beam, and spraying those aerosol beams on the same region, A film in which two kinds of materials are mixed at a desired ratio M: N (M ≧ 0, N ≧ 0) can be efficiently formed. Here, the case of M = 0 or N = 0 means that the aerosol sprayed from one of the spray nozzles 26a and 26b (FIG. 2) is blocked so that the film-forming powder is applied only from the other spray nozzle. Represents spraying on. Therefore, a desired number of layers each having a desired acoustic impedance can be easily stacked without using an adhesive. Therefore, by applying the acoustic matching layer thus manufactured to the ultrasonic transducer, reflection due to acoustic impedance mismatch between the transducer and the subject can be reduced as much as possible. Therefore, the sensitivity at the time of ultrasonic transmission / reception can be dramatically improved. Moreover, since unnecessary scattering and reflection within the acoustic matching layer are reduced, the ultrasonic band can be improved. Therefore, by using the ultrasonic transducer including the acoustic matching layer according to the present embodiment, it is possible to improve the generation efficiency and image quality of ultrasonic images in the ultrasonic diagnostic apparatus. As a result, it is possible to improve diagnostic accuracy in medical diagnosis such as early detection of lesions.

  Here, in the present embodiment, the aerosol is disturbed by blowing air to the aerosol ejected from the ejection nozzle, but on the contrary, the same effect can be obtained by sucking the aerosol from the side nozzle. . In that case, an exhaust pump may be provided in place of the compressors 29a and 29b shown in FIG. As shown in FIG. 2, the side nozzles do not necessarily have to be arranged in the immediate vicinity of the opening of the injection nozzle. For example, the side nozzles may be arranged just before the substrate or in the middle of the aerosol transport line.

  In this embodiment, the acoustic matching layer is produced using two kinds of raw material powders, but three or more kinds of raw material powders may be used. In that case, the film formation apparatus illustrated in FIG. 2 may be provided with an aerosol generation chamber, an injection nozzle, a compressor, a control valve, and a side nozzle in accordance with the number of types of powder.

Furthermore, in the present embodiment, all the layers constituting the acoustic matching layer 14 are formed by the AD method. However, in some cases, adjacent layers may be bonded using an adhesive. For example, in the acoustic matching layer 14, the acoustic impedance of the region close to the side in contact with the subject is often relatively close to the acoustic impedance of the adhesive (for example, about 2 MRayl to 5 MRayl). This is because in such a region, there are few adverse effects such as unnecessary reflection by the adhesive.
In this embodiment, the platinum electrode layer 11 is formed between the piezoelectric layer 10 and the acoustic matching layer 14. However, the material disposed on the piezoelectric matching layer 10 side (layer 14 a) of the acoustic matching layer 14. When a metal such as magnesium is used, it is not necessary to provide the electrode layer 11.

FIG. 8 is a cross-sectional view showing an ultrasonic transducer including an acoustic matching layer according to the second embodiment of the present invention.
The ultrasonic transducer 2 shown in FIG. 8 includes an acoustic matching layer 40 formed on the vibrator 13. Acoustic matching layer 40 according to this embodiment, the transducer 13 side (lower side in the drawing) has an acoustic impedance Z ₁ close relatively to the piezoelectric layer 10, the side (diagram is brought into contact with the living body in the upper side), and has an acoustic impedance Z ₂ relatively close to the living body. In addition, between them, the acoustic impedance continuously changes while tilting in the thickness direction from Z ₁ to Z ₂ . Thus, by changing the acoustic impedance in the acoustic matching layer, the reflection of ultrasonic waves inside the acoustic matching layer is almost eliminated, and the transmission / reception sensitivity and bandwidth of the ultrasonic waves can be further improved.

  Such an acoustic matching layer uses the film forming apparatus shown in FIG. 2 as in the method of manufacturing the acoustic matching layer according to the first embodiment of the present invention, and adjusts the ratio of the jet pressures of the two aerosol beams. In this case, the control valves 29a and 29b can be produced by continuously changing the opening and closing of the control valves 29a and 29b according to the film thickness.

Next, a method for manufacturing an ultrasonic transducer array in which a plurality of ultrasonic transducers including the acoustic matching layer according to the first or second embodiment of the present invention are arranged will be described with reference to FIGS.
First, as shown in FIG. 9A, a laminate 53 including an PZT layer 50, an electrode layer 51, and an acoustic matching layer 52 and having an area corresponding to an array is manufactured. The laminate 53 can be manufactured in the same manner as the method for manufacturing an ultrasonic transducer described with reference to FIGS.

Next, as shown in FIG. 9B, grooves 54 are formed in the laminate 53 from the acoustic matching layer 52 side. At that time, a part of the plurality of ultrasonic transducers 55 divided by the groove 54 is kept connected by being put in the groove 54 halfway through the PZT layer 50.
Next, as shown in FIG. 9C, a filler 56 such as an epoxy resin is injected into the groove 54 and cured. Further, by polishing the PZT layer 50 to the broken line shown in FIG. 9C, the plurality of ultrasonic transducers 55 are separated from each other. Thereby, as shown in FIG. 9D, an ultrasonic transducer array 57 in which a plurality of ultrasonic transducers 55 are arranged one-dimensionally is produced.

Further, as shown in FIG. 10A, in the ultrasonic transducer array 57, the surface of the piezoelectric layer 50 where the acoustic matching layer 52 is not formed (upper side in the drawing) is formed by sputtering, vacuum deposition, or the like. An electrode layer (common electrode) 58 is formed, and a backing layer 59 is disposed thereon as shown in FIG. Instead of forming the electrode layer 58, a substrate on which wiring is formed may be disposed.
Furthermore, by pulling out the wiring from the electrode layer 51 and the common electrode 58 of each ultrasonic transducer 55 and housing the ultrasonic transducer array 57 in the housing, the ultrasonic probe is completed.

Next, another method for manufacturing an ultrasonic transducer array in which a plurality of ultrasonic transducers including the acoustic matching layer according to the first or second embodiment of the present invention are arranged will be described with reference to FIGS. To do.
First, as shown in FIG. 11A, a laminate 65 including an PZT layer 60, an electrode layer 61, an acoustic matching layer 62, an electrode layer 63, and a backing layer 64 and having an area corresponding to an array. Is made. The laminate 65 can be manufactured in the same manner as the method for manufacturing an ultrasonic transducer described with reference to FIGS.

  Next, as shown in FIG. 11B, a groove 66 is formed in the laminate 65 from the backing layer 64 side. At that time, by inserting into the groove 66 halfway through the acoustic matching layer 62, a part of the plurality of ultrasonic transducers 67 divided by the groove 66 is kept connected.

Next, as shown in FIG. 12A, a filler 68 such as an epoxy resin is injected into the groove 66 and cured. Further, the acoustic matching layer 62 is polished to the broken line shown in FIG. 12A to separate the plurality of ultrasonic transducers 67 from each other. Thereby, as shown in FIG. 12B, an ultrasonic transducer array 69 in which a plurality of ultrasonic transducers 67 are arranged one-dimensionally is produced.
Furthermore, by pulling out the wiring from the electrode layers 62 and 63 of each ultrasonic transducer 67 and housing the ultrasonic transducer array in the housing, the ultrasonic probe is completed.

  Here, as shown in FIGS. 9 and 11, in the above-described ultrasonic transducer manufacturing method, a one-dimensional ultrasonic transducer array is formed by forming grooves 54 or 66 in one direction in the laminate 53 or 65. However, a two-dimensional ultrasonic transducer array may be manufactured by forming grooves in two different directions.

  The present invention can be used in an ultrasonic transducer that transmits and receives ultrasonic waves in an ultrasonic probe.

It is sectional drawing which shows the structure of the ultrasonic transducer containing the acoustic matching layer which concerns on the 1st Embodiment of this invention. It is a schematic diagram which shows the structure of the film-forming apparatus used when manufacturing the acoustic matching layer which concerns on the 1st Embodiment of this invention. It is a schematic diagram for demonstrating the positional relationship of the injection nozzle and side nozzle which are shown in FIG. It is a figure for demonstrating the manufacturing method of the acoustic matching layer which concerns on the 1st Embodiment of this invention. It is a figure for demonstrating the manufacturing method of the acoustic matching layer which concerns on the 1st Embodiment of this invention. It is a figure which shows the relationship between the number of the layers which comprise an acoustic matching layer, and the transmittance | permeability of an ultrasonic wave. It is a figure which shows the ideal distribution of the acoustic impedance in the acoustic matching layer comprised by several layers. It is sectional drawing which shows the structure of the ultrasonic transducer containing the acoustic matching layer which concerns on the 2nd Embodiment of this invention. It is a figure for demonstrating the manufacturing method of the ultrasonic transducer array containing the acoustic matching layer which concerns on the 1st or 2nd embodiment of this invention. It is a figure for demonstrating the manufacturing method of the ultrasonic transducer array containing the acoustic matching layer which concerns on the 1st or 2nd embodiment of this invention. It is a figure for demonstrating another manufacturing method of the ultrasonic transducer array containing the acoustic matching layer which concerns on the 1st or 2nd embodiment of this invention. It is a figure for demonstrating another manufacturing method of the ultrasonic transducer array containing the acoustic matching layer which concerns on the 1st or 2nd embodiment of this invention. It is a schematic diagram which shows the structure of the conventional probe for ultrasonic waves.

Explanation of symbols

1, 2, 55, 67 Ultrasonic transducers 10, 102 Piezoelectric bodies 11, 12, 103 Electrodes 13, 101 Vibrators 14, 40, 52, 62, 106 Acoustic matching layers 14a, 14b, ... Layers 15, 59, 64, 105 Backing layer 20 Deposition chamber 21 Exhaust pump 22 Substrate 23 Substrate stages 24a and 24b Aerosol generation chambers 25a and 25b Aerosol transfer lines 26a and 26b Injection nozzles 27a and 27b Compressors (compression pumps)
28a, 28b Air supply line 29a, 29b Control valve 30a, 30b Side nozzle 31 Control unit 32 Nozzle guide 33a, 33b Aerosol beam 50, 60 Piezoelectric layers 51, 58, 61, 63 Electrode layers 53, 65 Laminates 54, 66 Grooves 56 and 68 Fillers 57 and 69 Ultrasonic transducer array 100 Ultrasonic probe 104 Lead wire 107 Acoustic lens material

Claims (9)

In the ultrasonic transducer, an acoustic matching layer that matches an acoustic impedance between a subject and a piezoelectric layer that forms a vibrator that transmits and receives ultrasonic waves,
The acoustic matching layer formed by forming a film using a plurality of materials having different acoustic impedances and changing a mixing ratio of the plurality of materials according to a thickness of the deposited film.   The acoustic matching layer according to claim 1, wherein the acoustic matching layer is formed by performing deposition using an aerosol deposition method in which powder of a raw material is sprayed and deposited on the piezoelectric layer or an electrode layer disposed on the piezoelectric layer. .   The acoustic matching layer according to claim 1 or 2, wherein a mixing ratio of the plurality of materials changes stepwise according to a distance from a lower layer.   The acoustic matching layer according to claim 1, wherein a mixing ratio of the plurality of materials continuously changes according to a distance from a lower layer. An ultrasonic transducer that transmits and receives ultrasonic waves to and from a subject,
A piezoelectric layer;
An acoustic matching layer formed on the piezoelectric layer or an electrode layer disposed on the piezoelectric layer, and the acoustic matching layer according to any one of claims 1 to 4,
An ultrasonic transducer comprising: In the ultrasonic transducer, a method for producing an acoustic matching layer for matching an acoustic impedance between a piezoelectric layer forming a vibrator for transmitting and receiving ultrasonic waves and a subject,
Storing the first powder, which is the first raw material of the acoustic matching layer, in a first container, and generating an aerosol containing the first powder;
Storing a second powder, which is a second raw material of the acoustic matching layer, having an acoustic impedance different from that of the first raw material in a container, and generating an aerosol containing the second powder;
The aerosol generated in the step (a) is ejected from the ejection nozzle to generate a first aerosol beam, and the first aerosol beam is ejected by ejecting or sucking a gas to the first aerosol beam. A step (c) of controlling the pressure;
The aerosol generated in the step (b) is ejected from the ejection nozzle to generate a second aerosol beam, and the second aerosol beam is ejected by ejecting or sucking a gas to the second aerosol beam. Step (d) of controlling the pressure;
By injecting the first and second aerosol beams toward the same region on the piezoelectric layer or the electrode layer formed on the piezoelectric layer, the first and second raw materials are injected at a predetermined ratio. Depositing on the piezoelectric layer or the electrode layer (e);
A method for producing an acoustic matching layer comprising:   In each of the steps (c) and (d), the ratio M: N of the first raw material and the second raw material deposited on the piezoelectric layer or the electrode layer is set such that M ≧ 0 and N ≧ 0. The method for producing an acoustic matching layer according to claim 6, further comprising changing the injection pressures of the first and second aerosol beams so as to change within a range of.   Injecting the first and second aerosol beams so that each of steps (c) and (d) changes the ratio stepwise depending on the thickness of the deposited first and second materials. The method for producing an acoustic matching layer according to claim 7, comprising changing each of the pressures.   Each of steps (c) and (d) injects the first and second aerosol beams such that the ratio is continuously changed according to the thickness of the deposited first and second raw materials. The method for producing an acoustic matching layer according to claim 7, comprising changing each of the pressures.

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