Porous piezoelectric material including pour path (hole path) and method for manufacturing the same

Abstract

To provide a manufacturing method capable of manufacturing a microstructure molding of a piezoelectric material and a resin layer constituting a composite piezoelectric material.SOLUTION: A method for manufacturing a composite piezoelectric material using a porous piezoelectric material 81 includes: preparing a vacuum impregnation device, beaker, a resin for vacuum impregnation (e.g., an epoxy resin) and a produced porous piezoelectric material specimen 81; putting a required low-viscosity epoxy resin into the beaker; immersing the porous piezoelectric material specimen therein; setting the beaker into the vacuum impregnation device; driving the vacuum impregnation device to bring the inside of the vacuum impregnation device into vacuum; sucking air in a pore path of the composite piezoelectric material and simultaneously filling a space part with an epoxy resin 142; cutting and polishing unwanted epoxy resin layers 16 and 17 using a polisher; defining the result as a composite piezoelectric material 83; providing electrodes 18 and 19 on upper and lower surfaces of the composite piezoelectric material of which the dimensioning is finished; and obtaining a composite piezoelectric product 84.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to piezoelectric materials, and more particularly to piezoelectric materials that constitute electromechanical conversion parts of various transducers, and to methods for manufacturing the same. That is, the present invention relates to a porous piezoelectric material in which pores exist, which is obtained by adding a pore-forming material to a powder raw material of a piezoelectric material having a composition that exhibits piezoelectric properties, and then firing the material, and to a method for producing the same. As already introduced in Patent Documents 1 and 2, the physical properties of this porous piezoelectric material can be theoretically and artificially changed due to the presence of pores. As shown in Figure 1, when a pore-forming material 1 is mixed into a piezoelectric material 2 and sintered, the pore-forming material 1 becomes independent pores, resulting in a porous piezoelectric material 111. This is a piezoelectric material with unprecedented functionality. Porous piezoelectric materials use the properties of the base piezoelectric material as a base, and by changing the porosity, it is possible to set the functions (physical properties) to the intended values. By utilizing this functional design, porous piezoelectric materials can be significantly improved in various properties, making it possible to provide various transducers that are optimal for the intended use. This has also been introduced in Patent Documents 1 and 2. [Background technology]

[0002] The field of transducers that requires the most advanced and precise design and manufacturing techniques is medical applications. Therefore, narrowing the application of porous piezoelectric materials to medical applications will undoubtedly provide a guide to solving problems related to the transducer as a whole. Unlike other diagnostic devices, ultrasound diagnostic devices for medical applications do not involve exposure to radiation, and are non-invasive, so they have been widely used for diagnosis in medical institutions, both in internal medicine and surgery. An ultrasound diagnostic device is a diagnostic device that transmits ultrasound signals to the subject using a probe (vibrator) that converts electrical signals into ultrasound signals. The probe then receives the reflected ultrasound waves generated by changes in density in the subject's area, converts them into electrical signals, and visualizes the information as visible images that are used to diagnose the subject. The typical basic element that makes up the probe normally uses a longitudinal vibration mode to improve the efficiency of the electromechanical conversion coefficient. As a typical example, in a 5 MHz probe, the element has a height of 200 to 250 μm, a width of 40 to 50 μm, and a length of 8 to 15 mm. Usually, a group of four to five basic elements is used as one unit element, and a probe is made up of an array of 64 to 256 of these elements. Similarly, the ultrasonic sensors used in intravascular ultrasound (IVUS) diagnostic devices are extremely small, with a typical sensor measuring approximately 0.5 mm wide x 0.7 mm long x 100 μm thick. In either application, uniformity of the mechanical and electrical properties of a single element is highly required.

[0003] Probes, which are key devices in ultrasound diagnostic equipment, and many of the sensor materials used in IVUS have been made from lead zirconate titanate (hereinafter abbreviated as PZT) piezoelectric material. PZT piezoelectric materials have been widely used due to their high efficiency in converting electrical signals into ultrasonic waves (electromechanical coupling coefficient). Another characteristic of piezoelectric materials that has a significant effect on the characteristics of the probe is the equivalent piezoelectric constant d, which indicates the amount of displacement that occurs per unit voltage. 33 and sound waves are received and converted into voltage according to their strength. 33 And the value of the relative dielectric constant ε has been considered important. The mechanical quality factor Qm and acoustic impedance (AI), which have a significant impact on the electrical characteristics, i.e., bandwidth characteristics and pulse width, are also important indicators. In particular, it is important and indispensable for the transducer to have the ability to efficiently transmit ultrasound waves to the subject after conversion.

[0004] Typically, piezoelectric materials for medical applications are used in longitudinal vibration mode, as mentioned above, taking into consideration the efficiency of mechanical-electrical conversion. When a piezoelectric material is used in longitudinal vibration mode, the specified electromechanical coupling coefficient k 33 , starting with the equivalent piezoelectric constant d 33 and voltage output coefficient g 33The value shown in has been considered important and has been used as a measure for evaluating the characteristics of piezoelectric materials. 33 ×g 33 The value is also an important measure for evaluating sensor function.

[0005] In order to meet the required characteristics described in paragraphs 0003 and 0004, there has been a recent trend in the design of probes for medical ultrasound diagnostic equipment, with a shift to those using single-crystal piezoelectric materials that have extremely excellent piezoelectric properties. (1) Single crystallization has confirmed the significantly improved properties of piezoelectric materials that have never been seen before. That is, the value of the relative dielectric constant ε is very large, and the mechanoelectric coupling coefficient k 33 High piezoelectric constant d 33 is large, therefore, g 33 also becomes a large value. (2) In addition, the frequency bandwidth is significantly wider than that of conventional polycrystalline PZT. (3) In conjunction with (2), the sensitivity has been improved by 4 to 8 dB. (4) On the other hand, these single crystal piezoelectric materials are very brittle and have extremely poor processability. (5) Furthermore, single-crystal piezoelectric materials have slow crystal growth, which means that commercialization takes a long time and there are limitations on the shape they can be made into. As a result, the raw materials are very expensive. In addition, it is mechanically very fragile, making it difficult to process, further increasing the price, which is 8 to 10 times more expensive (electrodes with a plated finish and a substrate of the same shape) than the polycrystalline PZT that has traditionally been used for probes. (6) In addition to (5), for the same reason, the yield of the manufacturing process up to the point of making the probe is extremely low. The reason why the trend in probes is toward single crystal piezoelectric materials, despite the above-mentioned seemingly fatal drawbacks, is as follows. First, not only have the piezoelectric properties been significantly improved, but the frequency bandwidth has also become much wider than that of conventional PZT ceramic piezoelectric materials, so whereas previously two probes, one for 2.5 MHz and one for 5 MHz, were required, it is now possible to cover both frequencies with just one 3.5 MHz probe. Considering that the price of a single probe can range from tens of thousands to hundreds of thousands of yen, this is an outstanding economical solution. The improved sensitivity has made it possible to obtain high-quality images deep inside the human body, which is another major reason why the monopoly of single-crystal PZT probes is acceptable. Incidentally, the frequency of ultrasound pulses used in biological diagnosis is determined by taking into account the depth from the body surface to the organ and the attenuation of ultrasound. The central frequency is 2 to 5 MHz for the circulatory system and abdomen, 5 to 7.5 MHz for children, breast tissue, and peripheral areas, and 10 to 30 MHz for blood vessels.

[0006] In addition to the probes using single-crystal piezoelectric materials described above, there is a major trend in probes that attempt to improve characteristics by using porous piezoelectric materials, as shown in Figure 1, and composite materials that combine piezoelectric materials and resins, as shown in Figure 2.

[0007] As introduced in Patent Documents 1 and 2, porous piezoelectric materials are noteworthy in that they can be designed to function and have properties that surpass those of single-crystal piezoelectric materials.

[0008] The piezoelectric material shown in Figure 2 is named a 1-3 type composite piezoelectric material, and has attracted much attention due to the characteristics described below. Many studies have been carried out, including those in Patent Document 3 and Non-Patent Document 3, and the material has been commercialized. 1) The electromechanical coupling coefficient is equivalent to that of PZT piezoelectric ceramics. 2) Depending on the ratio of PZT to resin, the acoustic impedance can be made infinitely smaller than that of PZT piezoelectric ceramics. 3) The structure is mechanically flexible. 4) The piezoelectric material is surrounded by resin, so it is mechanically isolated in the lateral direction. 5) Wider bandwidth. 6) Pulse characteristics are significantly improved. These properties cannot be obtained by single crystal PZT or PZT ceramics alone, and are It is possible to achieve an acoustic impedance as close as possible to the The advantage of this method is that it has a very high degree of freedom and can be adapted to various types of probes. Thus, the 1-3 type piezoelectric composite is highly useful as a piezoelectric material for ultrasonic probes. Since then, various manufacturing processes have been investigated. The combined piezoelectric material is collectively called a composite piezoelectric material.

[0009] Representative composite materials are as shown in Figure 2, but we will now discuss detailed explanations and issues. (1) A method in which PZT square columns or cylinders 3 are arranged, and resin 4 is injected into the gaps between them to embed the PZT material and form a predetermined composite material 21. As a specific example of this technique, a cylindrical fiber Φ300μm was produced by electrodepositing PZT onto a carbon fiber and scattering the carbon by firing, as shown in Non-Patent Document 2, but this has not yet been put to practical use. □ There have also been attempts to commercialize products using cylinders or rectangular pillars of this size. (2) A manufacturing method called the dicing method (Non-Patent Document 3, Patent Document 3) will be explained with reference to Figure 3. This method involves fixing a PZT plate 7 to a support 5 and dicing it with a diamond cutter, and then filling the grooves 6 left by the cut with resin 8 to form a composite piezoelectric element 31. This is a manufacturing method that is widely used as a means of commercialization. Element size: 75 μm □ 1-3 type composite piezoelectric elements with an element spacing of 25 μm have already been commercialized. However, the manufacturing process is long because it requires machining, and there are natural limitations to the processing methods used to create fine structures. Therefore, the performance is limited, and at the same time, the product has the serious drawback of being expensive. In other words, there are currently no suitable composite materials required for probes. The present invention aims to solve this problem by placing emphasis on this point. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. WO2020 / 017478A1 [Patent Document 2] Patent No. 6741931 [Patent Document 3] Patent No. 4222467 [Non-patent literature]

[0011] [Non-Patent Document 1] Fuji Ceramic Co., Ltd. Technical Information [Non-patent document 2] Ultrasonic Techno Vol.14 No.4(2002) pp23~26 [Non-patent document 3] Japan Radio Technical Journal No.71 (2020) pp62-66 Toshihiko Miyashita Summary of the Invention [Problem to be solved by the invention]

[0012] As mentioned in paragraph 0005, currently, single crystal PZT is superior in overall evaluation to the single piezoelectric material PZT. However, if the elements that make up the probe can be miniaturized, the porous piezoelectric material mentioned in paragraph 0007 and the composite piezoelectric material mentioned in paragraph 0008 will surpass single crystal PZT in all respects, and are, overall, extremely excellent materials for use as piezoelectric elements in probes. Therefore, the biggest challenge can be summarized as whether it is possible to manufacture a microstructure molded body of the piezoelectric material and resin layer that make up the composite piezoelectric material. [Means for solving the problem]

[0013] The present inventors have discovered that a composite piezoelectric material can be produced by adding an organic resin material or the like that acts as a pore-forming material to the raw materials that make up the piezoelectric material and then firing it, resulting in a porous piezoelectric material that has at least one or more red coral reef-structured pores (hereinafter referred to as a pore path to distinguish them from independent pores). The pore paths (void passages) vary slightly in diameter depending on the particle size of the pore-forming material, but are characterized by being uniform and with little variation. Furthermore, this composite piezoelectric material, in which resin is filled inside the pore paths, is a groundbreaking invention that eliminates the mechanical processing that was a previous drawback described in paragraph 0009, while at the same time solving all problems.

[0014] There are two methods for manufacturing piezoelectric ceramics: (1) dry pressing and (2) wet method (doctor blade method). If you want to create independent spherical particle pores in a piezoelectric material, it was thought that both of the above manufacturing methods could basically be applied. The manufacturing of porous piezoelectric materials by dry methods has already been demonstrated in examples that have been patented (Patent Document 3). The present invention is a novel porous piezoelectric material that was discovered in the process of producing a porous piezoelectric material with independent, spherical particulate pores present in the piezoelectric material by a manufacturing method known as a wet process.

[0015] The pores present in the porous piezoelectric material produced by the dry pressing method are uniformly dispersed, independent spherical particle pores.The porous piezoelectric material produced by the wet method was newly discovered to have a pore structure that resembles a red coral reef, and this was the pore path structure named in paragraph 0013. The pore paths (void paths) exist in some cases that are open on the surface of the piezoelectric material, and in others that are not. The details of how the pore paths (void paths) were discovered will be described in the following paragraphs.

[0016] When manufacturing porous piezoelectric materials using a wet method, first, fine powder of the piezoelectric material is put into a solution of a resin-based solvent, a binder made of a solvent that dissolves the resin, and a plasticizer to form a slurry of the fine powder of the piezoelectric material.

[0017] A pore-forming material, for example, minute spherical PMMA, is added to this slurry, and the constituent materials are homogenized and dispersed using a planetary mixer or the like.

[0018] In Figure 4, the above-mentioned slurry 10 containing the pore-forming material is stored in a slurry storage tank 9, and then coated onto a carrier resin sheet 13. A slit called a doctor blade 11 is provided midway to ensure spacing. Slurry 12, with the desired thickness controlled, is coated onto the carrier resin sheet 13 to produce a so-called green sheet (a raw piezoelectric material sheet before firing) 41.

[0019] The thickness of this green sheet can be manufactured in the range of several mm to 50 μm depending on the required thickness. The thickness is determined in advance according to the required sample shape, taking into consideration shrinkage and warping due to firing.

[0020] The sample cut to a predetermined size is placed in a jig made of alumina ceramic (99.99%) before firing.

[0021] The binder and pore-forming material PMMA are heated according to a specified temperature profile to be dispersed by thermal decomposition, after which the main firing process begins.

[0022] A micrograph of one surface of the porous piezoelectric material sintered under the above manufacturing conditions is shown in FIG. 5 (5-1). This SEM photograph shows a porous piezoelectric material (PZT) with a porosity of 45%, and it was found that the white parts 15 are PZT crystals, and the parts indicated by ● (black circles) are part of the pores, which are the openings of the pore paths 14, which will be mentioned later. Incidentally, the openings indicated by ● (black circles) indicate approximately 100 per mm, which suggests that there are approximately 10,000 pore openings per square centimeter.

[0023] By chance, we encountered a problem in the next process, which was to create electrodes. That is, in Figure 7 (7-2), electrodes 18 and 19 were provided on the upper and lower surfaces of a sample of porous piezoelectric material 71, and a high voltage was applied between the two electrodes, and cases were found in which the upper and lower electrodes 18 and 19 were short-circuited during the polarization process. Since the pores in the porous piezoelectric material produced by the dry pressing method were completely independent, we initially assumed that the pores in the porous piezoelectric material produced by the wet method would also be independent. We once again conducted a comprehensive review of the above-mentioned 45% porous piezoelectric material (PZT) sample, approximately 250 μm thick, fabricated by a wet method. Observation under a microscope confirmed that the openings of the pores were connected from the front to the back of the sample. An example of this result is shown in the micrograph in Figure 6. A very low viscosity red flaw detection fluid for penetrant testing, which is used to detect microcracks, was used. When this fluid was dropped onto the surface of the sample, red flaw detection fluid was confirmed on the opposite side of the sample within a few minutes. After drying the sample, it was cut and an enlarged photograph of the cross section was taken. It was then possible to confirm that the pore paths had been filled with red flaw detection fluid and that the pore paths had been stained 141 across the entire cross section of the sample.

[0024] The cross-sectional structure of the porous piezoelectric material obtained based on paragraphs 0022 and 0023 is shown in Figure 7 (7-1). As mentioned above, the porous piezoelectric material 71 after firing did not have independent pores but pore paths with a red coral reef structure, and the piezoelectric material exhibited a relatively regular pumice structure (Figure 5 (5-2)). The results of these considerations are shown in 711 as an enlarged view of part A in Figure (7-1).

[0025] In order to prevent short circuits between the electrodes, the viscosity of the silver paste for the electrodes was increased (reduced fluidity), and electrodes 18 and 19 were provided on both sides of this porous piezoelectric material 71 by printing, producing porous piezoelectric material 72 whose characteristics could be confirmed, which was used as a sample for collecting characteristics. Although it exhibits slightly different properties from porous piezoelectric materials with independent pores, it basically falls within the category of porous piezoelectric materials.

[0026] As mentioned in paragraphs 0008 and 0009, 1-3 type composite piezoelectric materials have also attracted a great deal of attention. On the other hand, the porous piezoelectric material 71 mentioned in paragraph 0023 is considered to be a material that is of great interest in relation to the above paragraph. In other words, the pore paths are not produced by mechanical processing but are formed by a chemical reaction, and have a very fine structure that retains a relatively regular shape. Therefore, impregnating these pore paths with resin leads to the provision of a completely new 1-3 type composite piezoelectric material that has never existed before, and also to the production method for such a material.

[0027] We will now discuss the composite piezoelectric material using the porous piezoelectric material 81 (71) shown in Figure 8 (8-1) and its manufacturing method. A vacuum impregnation device, a beaker, a vacuum impregnation resin (for example, epoxy resin), and the fabricated porous piezoelectric material sample 81 are prepared. (1) The required low-viscosity epoxy resin is placed in a beaker, and the porous piezoelectric material sample 81 is immersed in the resin. (2) The beaker is placed in a vacuum impregnation device, which is then driven to create a vacuum inside the device. (3) The air in the pore paths of the composite piezoelectric material is sucked out, and at the same time, the formed spaces are filled with epoxy resin 142.

[0028] By returning the vacuum impregnation device to atmospheric pressure, the remaining pore paths in the composite piezoelectric material The space is completely replaced with epoxy resin 142. The surface of the composite piezoelectric material is covered with epoxy layers 16 and 17 to form composite piezoelectric material 82 .

[0029] At this stage, the unnecessary epoxy resin layers 16 and 17 shown in FIG. 8 (8-2) are covering the outside of the composite piezoelectric material that is actually required.

[0030] In order to remove unnecessary resin layers 16 and 17 and ensure the required dimensions of the sample for commercialization, the sample is cut and polished with a polishing machine to produce a composite piezoelectric material 83 as shown in FIG. 8 (8-3).

[0031] After the dimensions have been determined, electrodes 18 and 19 are provided on the surface of the composite piezoelectric material 83, as shown in Figure 8 (8-4). The electrodes are generally formed by screen printing a silver-based paste and fixing it to the piezoelectric material by heating, or by sequentially evaporating chromium, nickel, copper, and gold onto the desired surface of the piezoelectric material.

[0032] Through the steps from paragraph 0024 to paragraph 0031, completely new composite piezoelectric materials 72 and 84 that have never been seen before can be obtained. Next, a test sample was produced to examine the characteristics of this new composite piezoelectric material. In the probe for ultrasonic diagnostic equipment, the constants k of the longitudinal vibration mode are basically 33 ,d 33 For IVUS sensors, the thickness vibration mode kt is the main focus, and the hydrostatic performance index is also important. 31 The values of are also required. Test pieces were fabricated and measured according to the respective specifications.

[0033] The longitudinal mode sample is 3 mm □ × 9 mmL (L ≥ length of one side × 2.5), and the specimen for extension mode is width a: 3 mm × length l: 12 mm × thickness t: 1.0 mm (l / a ≥ 4, a / t ≥ 3, l ≥ 12). These test samples have dimensions determined in accordance with prescribed test standards.

[0034] In Non-Patent Document 1 and Patent Document 2, d is a very important index for evaluating the properties of piezoelectric materials. 33 The values of d and relative dielectric constant are shown. 33 The improvement measures have resulted in a decrease in the relative permittivity. Because of these contradictory relationships, experimental implementation measures have only shown qualitative results. But d 33 is the electromechanical conversion coefficient k 33 , dielectric constant ε r and Young's modulus Y 33 There is a relationship between them as shown in equation (1). d33 =k 33 ×(ε r ×1 / Y 33 )^(1 / 2) (1) Also, k 33 can be determined by analyzing the piezoelectric material as an electrical equivalent circuit using an impedance analyzer. k 33 2 =π / 2×fs / fp×cot(π / 2×fs / fp) (2) Also, fp=1 / 2l×1 / √ρ×S 33 D There is a relationship between... (3) Here, l (the English letter el) is the length of the test sample. These relationships can be used to derive the properties of piezoelectric materials. Porous piezoelectric materials were fabricated by changing the porosity in the piezoelectric material, and their characteristics were calculated using an impedance analyzer. First, the resonant frequency fs and anti-resonant frequency fp obtained by the impedance analyzer, and the electromechanical conversion efficiency k obtained from these were calculated. 33 The values for the change in porosity are shown in Table 1. [Table 1]

[0035] The various properties of the piezoelectric material can be determined using the values obtained by the impedance measurement method of the sample prepared in paragraph 0034. Table 2 is a graph showing the main properties of the porous piezoelectric material 72 produced by the method of the present invention in relation to the porosity. [Table 2] [Effects of the Invention]

[0036] As mentioned at the beginning, the probability of a groundbreaking invention of a piezoelectric material is so low that it occurs once every few decades, if at all. Naturally, the properties of the invented piezoelectric material are uniquely determined, and it is impossible to fundamentally change the properties unless the composition of the piezoelectric material is changed. One of the advantages of the present invention is that it has become possible to freely change the various properties of a specific piezoelectric material by varying the porosity of the piezoelectric material, something that was previously impossible. In particular, it has become possible to intentionally and significantly improve the properties, which is a groundbreaking effect that has not been seen before.

[0037] The 1-3 type composite piezoelectric material, one of the conventional composite piezoelectric materials, was made by first processing the piezoelectric material and then impregnating it with a resin layer. This meant that a step of machining the piezoelectric material was required. Therefore, this had the fatal drawback of being restricted by the machining limits. The method of the present invention does not require a process equivalent to conventional machining, and pore paths are formed by a controlled reaction between organic resin particles added as a pore-forming material and an organic resin added as a binder to the piezoelectric material, making it possible to manufacture a composite piezoelectric material with a microscopic red coral reef structure that has not been seen before.This completely new manufacturing method for composite piezoelectric materials has brought about immeasurable effects both directly and indirectly on various transducers when used.

[0038] It was known that the best probe transducer would be a piezoelectric material with an acoustic impedance as close as possible to that of the human body, but this value was uniquely determined by the piezoelectric material, and at the same time, it was very high. In other words, this was the biggest factor in the necessity of a matching layer. However, with the composite piezoelectric material of the present invention, it is now possible to design an acoustic impedance value that does not require a matching layer by adjusting the porosity it contains. The solution to one problem automatically led to the solution of other problems. This also applies to cases where the medium is a gas such as air. However, in the case of airborne sensors, even if efforts are made to reduce the acoustic impedance as much as possible on the porous piezoelectric material side, there is still a large difference between the acoustic impedance of the porous piezoelectric material and that of air, and in many cases a matching layer is required due to the mechanical strength of the porous piezoelectric material.

[0039] While we have been talking about probes, it goes without saying that this patent has also been shown to be extremely effective in intravascular ultrasound diagnosis, or IVUS, for the exact same reasons.

[0040] Furthermore, although this application has been limited to medical probes and IVUS, it can be easily assumed from what has been described that the present invention can be widely applied to piezoelectric materials for industrial transducers in general, and the effects thereof also extend to these.

[0041] In summary, (1) we have established a method for functional design (characteristics) by controlling the porosity based on existing piezoelectric materials (characteristics). (2) The effect of being able to adapt the various transducers used to the equipment while optimizing their characteristics is extremely significant and beneficial.

[0042] Moreover, from a broader perspective, the effects of the present invention are not limited to piezoelectric materials, and pores (void paths) can be produced regardless of the raw material.

[0043] The raw materials that form the base of porous materials include metals, metal oxides (single elements), composite metal oxides (glass, clay, various ceramics, etc.), etc. It is possible to produce porous materials with a pore (vacant passage) structure regardless of the raw material.

[0044] The porous materials with pore structures made from the above-mentioned various materials can be used as various filters, lightweight materials, gas reservoirs, etc., and will have a tremendous impact on industry. [Brief explanation of the drawings]

[0045] Figure 1 shows an electron microscope image of a cross section of a porous piezoelectric material manufactured by powder molding. Figure 2 shows the structure of a composite piezoelectric material called type 1-3. Figure 3 shows a typical manufacturing method for composite materials. Figure 4 shows the manufacturing process for a piezoelectric material sheet using a wet method (doctor blade method). Figure 5 shows a micrograph of a composite piezoelectric material produced by the wet method. Figure 6 shows the penetration continuity of the pore path. Figure 7 shows the structure of the porous piezoelectric material produced by the wet method (doctor blade method). Figure 8 shows the manufacturing process of a composite material made of porous piezoelectric material using a wet method. Figure (8-1) is a cross-sectional view of a composite piezoelectric material that has been sintered with the addition of a pore-forming material. Figure (8-2) is a diagram showing the state of a composite piezoelectric element 81 impregnated with low-viscosity epoxy resin. Figure (8-3) shows the composite piezoelectric material 83 after fitting, lapping and polishing. Figure (8-4) A diagram showing electrodes attached to both surfaces of a composite piezoelectric material 83. [Example]

[0046] In order to manufacture the desired porous piezoelectric material using the wet method, we will first discuss the wet method, then the characteristics of the base raw material, the selection of the pore-forming material, and the manufacturing method of the slurry. As an example, we will provide details on a porous piezoelectric material with a porosity of 45%.

[0047] The wet method is a manufacturing method in which slurry 10 of piezoelectric raw material shown in FIG. 4 is uniformly applied 12 onto carrier tape 13 through the gap of a control plate (doctor blade) 11 provided to control the thickness from a container 9 storing the slurry 10, thereby producing a green sheet 41. By adjusting the gap of the control plate 11, a green sheet having a desired thickness can be produced.

[0048] Among the various properties of piezoelectric materials for medical applications, d 33 and g 33 Therefore, the NP-7 piezoelectric material shown in Table 4 below was used as the raw material.

[0049] Next, pore-forming materials are generally granular particles made from organic resin. There are many such products on the market from various chemical product manufacturers, but in the examples of this invention, Soken Chemical's PMMD:MD-1000 was used. This is because it has an average particle size of 10 μm and a narrow particle size distribution, in other words, very little variation in the particles. As already explained in paragraphs 0016 to 0018, when producing ceramics by a wet method, it is necessary to prepare a slurry of the piezoelectric material in advance. Table 3 shows an example of the composition of the slurry used to manufacture a porous piezoelectric material with a porosity of 45%. (Table 3) PZT (NP-7) fine powder: particle size 2μm or less 3,300g Nikko Pore forming material: MD-1000, Particle size (10μm) 2,700g Soken Chemical PVA binder: PVA-117 500g Kuraray Binder AS-1100 200g Toagosei Plasticizer P-0292 25g Tokyo Chemical Industry Antifoaming agent CC-130B 6g NOF Solvent (pure water) 8,249g

[0050] First, the procedure for producing the slurry will be outlined. Weigh out the binders PVA-117 and AS-1100 into a 1.2L plastic bottle and dissolve them in the required amount of purified water. 2. Weigh the PZT and add it to the plastic bottle in step 1. 3. Weigh out the PMMA and pour it into the plastic bottle from step 1. Place it on the ball mill stand and leave it overnight to disperse. 4. Place the plastic bottle in an ultrasonic cleaner to disperse the mixture. 5. Weigh out the PVA aqueous solution and add it to step 4, then stir gently. 6. Close the plastic bottle lid and place it on the ball mill to mix. The rotation speed is about 200 rpm. Mix for about 5 hours. 7. After step 6 above, add the specified amount of antifoaming agent CC-130B dropwise and mix.

[0051] Next, the manufacturing process of the green sheet will be described. A green sheet is produced by the method described in paragraph 0018 using the slurry of piezoelectric material produced in paragraph 0050. This process is carried out in a clean room.

[0052] When using this green sheet to fabricate the sample 71 shown in FIG. 7, it is necessary to pay attention to the correlation with the shape of the target sample. When the shape 71 of the target porous piezoelectric material is, for example, 10 mm wide x 100 mm long x 0.25 mm thick, it is not preferable to set the gap of the doctor blade to a thickness of 0.25 mm from the beginning. That is, problems related to uneven shrinkage and warpage due to subtle unevenness of the slurry are encountered. Therefore, the thickness of the sheet that can obtain a relatively stable green sheet is determined in advance from the manufacturing technology perspective for the slurry composition. It is necessary to secure the cutting allowance and grinding allowance by scraping in advance. In this example, the optimum thickness of the sheet was 50 μm. Therefore, a 150 mm diameter sample was used to obtain a sample with a thickness of 250 μm. □ Eight green sheets of 50 μm each were stacked and pressed together in a press to form a 150 mm □ A green sheet of 400 μm was prepared. The pressure bonding conditions were 50°C and 200 kg / cm. 2 was optimal.

[0053] Next, the slurry is subjected to a preliminary sintering process called binder removal, in which organic resin components such as binders present in the slurry are burned and sublimated. What is important in the preliminary sintering process is to select a temperature profile that is suited to the organic resin material, which requires the highest temperature for the process leading to thermal decomposition and sublimation among the organic resin materials other than the piezoelectric material (PZT) that make up the slurry.

[0054] In order to sublimate the binder in the green sheet, the workpiece green sheet is first placed on an alumina substrate with zirconia powder or the like interposed therebetween. This is then placed in a jig consisting of an alumina box. This jig is then set in a pre-sintering furnace and sintered at a rate of approximately 200 g / cm. 2 The binder is removed by applying a load of 0.05g and following the temperature profile below. It takes 4 hours to heat from 20°C to 150°C, then 24 hours to heat from 150°C to 350°C. Then it takes 36 hours to heat from 350°C to 550°C, hold at 550°C for 12 hours, and then cool from 550°C to 20°C over 12 hours.

[0055] Next, the actual firing begins. In this example, an aluminum tray containing fine lead oxide (PbO) powder is placed inside an alumina box removed from the pre-sintering furnace. An alumina lid is then placed over the opening of the alumina box, sealing the workpiece. This is a protective measure to prevent the PbO that makes up the piezoelectric material from evaporating and disappearing from lead titanate-zirconate, a component of the piezoelectric material, due to the high vapor pressure of PbO as the temperature rises during firing. Therefore, dummy PbO powder was placed in an alumina box and sealed. This is a measure to saturate the PbO vapor pressure inside the box as the temperature rises, and to suppress the evaporation of the PbO that makes up the piezoelectric material. After taking these precautions into consideration, the alumina box, sealed with a lid, is placed in the main firing furnace and fired and sintered using the following temperature profile. The temperature is raised from 20°C (room temperature) to 1,150°C over 6 hours, held at 1,150°C for 2 hours, and then cooled from 1,150°C to 20°C (room temperature) over 6 hours.

[0056] The dimensions of the product after firing shrink according to the amount of binder, and the dimensions of the porous piezoelectric material 71 (Fig. 7) after firing are 110 mm on average. □ ×300 μm. Next, the manufacturing process for carrying out the present invention will be described in detail with reference to FIG.

[0057] The porous piezoelectric material 81 is placed in a container that can store it, and this is filled with low-viscosity epoxy resin "Bond E205: Konishi Co., Ltd." This container is placed in a vacuum impregnation device PHIL:1MH-S type, and the device is operated for 30 minutes to perform vacuum degassing and vacuum impregnation with the resin, thereby producing a composite piezoelectric element 82. For commercialization, it is necessary to remove the low viscosity epoxy resin layers 14 and 15 covering the composite piezoelectric element 82 and to adjust the dimensions.

[0058] The composite piezoelectric element 82 is polished with a lapping machine in order to remove the low-viscosity epoxy resin layers 14 and 15 covering the composite piezoelectric element 82 and to secure the desired dimensions. Multiple openings 120mm □ A 0.5 mm thick stainless steel jig plate is prepared, and the thickness of this stainless steel jig plate is adjusted to 250 μm by lapping. Next, this stainless steel jig plate is set in a lapping machine, and the composite piezoelectric element 82 is set in the opening. The composite piezoelectric element 82 is carefully polished to the desired dimensions using silicon carbide (SiC) with a grain size of 2 to 3 μm.

[0059] Once the desired thickness is achieved, the composite piezoelectric element 83 is cut to the required dimensions of a product: width 10 mm, length 100 mm, and thickness 0.25 mm. Next, electrodes 16 and 17 are provided on the top and bottom surfaces in the thickness direction to produce composite piezoelectric element product 84.

[0060] As for the electrode material, there is a method of applying a paste made by mixing ultrafine powders of silver and copper with a resin binder by screen printing and sintering it to form an electrode, and a method of forming an electrode by vapor deposition of metal in a vacuum chamber. In the examples, electrodes were fabricated by vapor deposition, assuming soldering. Specifically, metallic chromium (Cr) was deposited on which metallic nickel (Ni) and metallic gold (Au) were deposited. The electrode deposited with a ratio of Cr / Ni / Au: 200nm / 600nm / 200nm passed the thermal shock test of 400~500 without any problems. The thermal shock test conditions are as follows: A small environmental test chamber (constant temperature and humidity test chamber) manufactured by Espec Corporation: ARSF-250-10 was used. Test conditions: One cycle consisted of 30 minutes at -40°C, 5 minutes at room temperature, and 30 minutes at 80°C.

[0061] The piezoelectric material to which electrodes have been attached is polarized by applying a voltage in the thickness direction. In this example, a voltage equivalent to 1 Kv / mm was applied between the two electrodes in silicone oil at 40° C. and maintained for 15 minutes for polarization, and a + sign was placed on the surface of the positive side.

[0062] The properties of the samples obtained in the examples were measured using the methods described in paragraphs 0034 and 0035, and are shown in Table 4. We believe that the electrical characteristics, i.e., frequency bandwidth, pulse characteristics, sensitivity, etc., are undoubtedly excellent, but as measurements are currently being conducted, we plan to add additional information to the patent text through a separate amendment procedure. [Table 4] Explanation of symbols

[0063] 1: Isolated voids in piezoelectric materials 2: Piezoelectric materials 111: Porous piezoelectric material 3: Piezoelectric material rectangular or cylindrical 4: Embedding resin 21:1-3 type composite piezoelectric material (commonly known as) 5: Support stand 6: Groove cut with a diamond cutter 7: Plate-shaped piezoelectric material 8: Resin layer impregnated in the notch 31:1-3 type composite piezoelectric material 9: Slurry storage tank 10: Slurry 11: Control plate (doctor blade) 12: Controlled slurry layer 13: Carrier - resin sheet 41: Green Sheet 14: Pore path 15: Piezoelectric materials 141: Traces of colored flaw detection fluid passing through the pore path 71: Porous piezoelectric material with pore paths 711: Enlarged view of part A in Figure 7(7-1) 72: Piezoelectric material with electrodes attached to porous piezoelectric material 71 142: Resin-filled pore path 16: Resin layer 17: Resin layer 81: Porous piezoelectric material with pore paths Composite piezoelectric material made by impregnating 82:81 piezoelectric material with resin 18: Electrode 19: Electrode 83: Composite piezoelectric material 82: Composite piezoelectric material with the resin layer on the surface removed by polishing 84: Composite piezoelectric material 83 coated with electrodes

Claims

1. A porous piezoelectric material and its manufacturing method are characterized in that a pore-forming material made of an organic resin or the like is added to a piezoelectric material, and during the process of firing the piezoelectric material, the pore-forming material forms pore paths (void paths) in the piezoelectric material, and the piezoelectric material artificially forms a fine pumice structure.

2. A composite piezoelectric material and a manufacturing method thereof, which includes claim 1 and is characterized in that an organic resin is impregnated into pore paths (void paths) formed by a pore-forming material.

3. A process for preparing a piezoelectric material by the manufacturing method described in any one of claims 1 and 2; a process for providing electrodes on the surface of the piezoelectric material; a process for forming a transducer by configuring piezoelectric vibrators made of the piezoelectric material individually or in an array; a process for providing a backing material on the back surface of the transducer; and a process for attaching an acoustic matching layer to the front surface of the transducer as needed, and attaching an acoustic lens to the surface of the acoustic matching layer as needed. A transducer and a manufacturing method thereof characterized by being assembled and configured by each of the above processes.

4. A porous material comprising the base material of claims 1 to 3, characterized in that it is made of a metal, a metal oxide, or a composite oxide of a metal (glass, clay, various ceramics), and a method for producing the same.

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