Piezoelectric single crystal transducer element and its manufacturing method

Abstract

The present invention relates to a piezoelectric single crystal transducer element and a method for manufacturing the same. The piezoelectric single crystal transducer element comprises a PZN-PT single crystal and at least one metallized layer on the crystal. The transducer element is adapted for use in high-frequency underwater acoustic transducers as a core component of underwater SONAR, ultrasound medical transducers, low-field-driven actuators, electroacoustic transducers, and piezoelectric MEMS devices. The method of the present invention is a conventional method for obtaining piezoelectric single crystal transducer element arrays for use in high-frequency underwater acoustic transducers.

Description

[Technical Field]

[0001] The present invention relates to a piezoelectric device. In particular, the present invention relates to a piezoelectric single crystal transducer element and a method for manufacturing the same.

[0002] Definition of Terms As used herein, the following terms are generally intended to have the following defined meanings, unless the context dictates otherwise.

[0003] Piezoelectric Material: “The term piezoelectric material refers to a material that is capable of generating electrical energy when subjected to mechanical stress.

[0004] Relaxor material: The term "relaxor material" hereinafter refers to a ferroelectric material that exhibits high electrostrictive properties.

[0005] PZN-PT: The term "PZN-PT" refers to a lead zinc niobate:lead titanate material.

[0006] Piezoelectric single crystal transducer element array: "Piezoelectric single crystal transducer element array" refers to a 0001-oriented (1-x) PZN-xPT single crystal with a morphotropic phase boundary composition (x = 9%) having a domain-engineered structure that has been processed into a transducer element array.

[0007] Relaxor: The term "relaxor" refers to a ferroelectric material that exhibits high electrostrictive properties, which refers to the property of any insulator or dielectric material to change shape when an electric field is applied.

[0008] Crystallographic orientation: Crystallographic orientation refers to the orientation of a surface or crystal plane depending on how the plane (or any plane parallel to it) intersects with the major crystallographic axis of the solid. This orientation is defined by Miller indices (hkl), which are a set of numbers that quantify the intercept of a crystal plane and are used to uniquely identify a particular crystal plane or surface.

[0009] Remanent polarization: The term remanent polarization refers to the amount of polarization.

[0010] Coercive Field: The term coercive field refers to the field strength required to achieve a polarization value of zero.

[0011] Unipolar Distortion: The term unipolar distortion refers to distortion that occurs in response to a single polarity of electric field (unipolar drive mode).

[0012] Longitudinal piezoelectric strain coefficient: Refers to the ratio of the strain occurring in the same direction (longitudinal direction) as the longitudinal piezoelectric strain coefficient.

[0013] Electromechanical Coupling Coefficient: The term "electromechanical coupling coefficient" of a piezoelectric material refers to the efficiency of conversion between electrical energy and mechanical energy in the piezoelectric material.

[0014] Longitudinal Piezoelectric Voltage Coefficient: The term longitudinal piezoelectric voltage coefficient refers to the ratio of the resulting (longitudinal) electric field to the mechanical stress applied in the longitudinal direction.

[0015] Type 1-3 piezoelectric composite: The term type 1-3 piezoelectric composite refers to a structure that combines a piezoelectrically active material (such as a ferroelectric ceramic) with a non-piezoelectric material such as a polymer or epoxy resin.

[0016] Connectivity: Connectivity is defined as the number of dimensions along which the material remains continuous. The connectivity of piezoelectric composites is represented by a combination of two numbers, such as 1-3, 2-2, or 0-3, where the first number indicates the piezoelectrically active material and the second number indicates the non-piezoelectric material. In 1-3 type piezoelectric composites, the piezoelectric material is continuous in one direction.

[0017] Back-reflection Laue Diffraction: The term back-reflection Laue diffraction refers to a technique primarily used to determine the orientation of large single crystals. In this method, white X-rays are irradiated onto a fixed crystal and the diffraction pattern reflected or transmitted by the crystal is recorded on photographic film. There are two types of Laue diffraction: (i) back-reflection Laue and (ii) transmission Laue. In the back-reflection method, a photographic film is placed between the X-ray source and the crystal. The back-diffracted X-rays are recorded.

[0018] DC Magnetron Sputtering: The term DC magnetron sputtering or direct current (DC) sputtering refers to a technique that uses ionized gas molecules to sputter-evaporate molecules from a target material into a plasma state, depositing a thin film. Sputtering is a physical vapor deposition process in which atoms are ejected from a source (target) by bombardment with high-energy ions. A DC sputtering system consists of a pair of planar electrodes. The target material acts as the cathode, and the substrate is placed at the anode. An inert gas is introduced into the sputtering chamber, and a DC voltage of several thousand volts is applied between the electrodes, triggering a glow discharge. The inert gas ions in the glow discharge are accelerated by the cathode and sputter off the target material, depositing a thin film on the substrate.

[0019] Field cooling: The term field cooling refers to a technique in which the temperature of a sample, such as a crystal, is reduced to room temperature under the application of a polarizing electric field. [Background technology]

[0020] The following background information is relevant to the present invention but is not necessarily prior art.

[0021] High-performance piezoelectric materials are crucial to meeting the ever-increasing demand for advanced piezoelectric devices, such as underwater sonar, medical ultrasound transducers, low-field-driven actuators, electro-acoustic transducers, etc. The global piezoelectric device market is experiencing continuous growth, which clearly demonstrates the importance of piezoelectric materials and the expanding applications of advanced piezoelectric devices.

[0022] Relaxor PbTiO3 single crystals adopt specific crystal orientations and domain-engineered structures at the morphotropic phase boundary (MPB) composition and exhibit extremely large piezoelectric responses when subjected to an external electric field. However, growing relaxor PbTiO3 single crystals is an extremely challenging process because it consists of several components with complex thermodynamic behaviors and the kinetic parameters are prone to error.

[0023] The main challenge for growing large relaxor PbTiO3 single crystals is the formation of a defect pyrochlore phase, which causes instability during the crystallization process and leads to the formation of point defects such as inclusions / voids and polycrystals. Other challenges for growing relaxor PbTiO3 single crystals include the volatilization of PbO at high temperatures, which causes the parasitic pyrochlore phase to segregate during the crystal growth process, resulting in structural variations throughout the grown crystal and inhomogeneous properties. High-temperature crystal growth faces technical barriers, including the breakage of platinum crucibles and the volatilization of PbO. The low thermal conductivity (0.01 W / mK) hinders the transport of latent heat released during the crystallization process, resulting in issues such as interfacial instability, defects, inclusions, and phase segregation. Summary of the Invention [Problem to be solved by the invention]

[0024] Traditionally, relaxor PbTiO3 single crystals have been grown by various crystal growth techniques. High-temperature solution growth (also known as flux crystal growth) has been widely adopted for the growth of binary relaxor-PbTiO3 single crystals because this technique is inherently suitable for growing non-congruent melting materials and materials that are highly volatile before reaching their melting point. Conventional flux crystal growth is based on the principle of spontaneous nucleation. Nucleation is achieved by a supersaturated solution, which is achieved by a slow cooling process. Disadvantages of flux crystal growth include the difficulty of controlling spontaneous nucleation, the difficulty of growing large single crystals, slow growth rates, flux inclusions, and crystal orientation problems.

[0025] Furthermore, the main factor hindering widespread use of relaxor PbTiO3 single crystals in advanced piezoelectric devices is the unavailability of large-size and high-quality single crystals.

[0026] Therefore, there exists a need for a piezoelectric single crystal transducer element and method of manufacturing the same that overcomes the above-mentioned disadvantages or at least provides an alternative solution.

[0027] Object of the invention Some of the objects of the present invention, of which at least one embodiment is sufficient to be mentioned herein, are as follows.

[0028] It is an object of the present invention to ameliorate one or more of the problems of the prior art, or at least to provide a useful alternative.

[0029] Some of the objects of the present invention, of which at least one embodiment is sufficient to be mentioned herein, are as follows.

[0030] It is an object of the present invention to ameliorate one or more of the problems of the prior art, or at least to provide a useful alternative.

[0031] Another object of the present invention is to provide a piezoelectric single crystal element.

[0032] It is yet another object of the present invention to provide a piezoelectric single crystal transducer element that is relatively large in size.

[0033] It is yet another object of the present invention to provide a piezoelectric single crystal transducer element having a high longitudinal piezoelectric strain coefficient.

[0034] It is yet another object of the present invention to provide a method for manufacturing a piezoelectric single crystal transducer element.

[0035] Another object of the present invention is to provide a method for fabricating a piezoelectric single crystal transducer element that controls spontaneous nucleation.

[0036] It is yet another object of the present invention to provide a method for manufacturing piezoelectric single crystal transducer elements with a relatively high yield.

[0037] Other objects and advantages of the present invention will become more apparent from the following description, which is not intended to limit the scope of the invention thereto. [Means for solving the problem]

[0038] The present invention relates to a piezoelectric single crystal transducer element. The piezoelectric single crystal transducer element comprises a PZN-PT single crystal having predetermined dimensions, an upper active surface and a lower active surface, and at least one metallized layer having a predetermined thickness on the upper and lower active surfaces. The crystal is polarized in the

[0001] direction.

[0039] The present invention also provides a method for fabricating a piezoelectric single crystal transducer element. By this method, a PZN-PT single crystal is prepared. The PZN-PT single crystal is oriented along a predetermined direction, resulting in a unidirectionally oriented PZN-PT single crystal. The oriented PZN-PT single crystal is then sequentially diced, lapped, and polished to obtain a PZN-PT single crystal having predetermined dimensions and upper and lower active surfaces. A metallized layer is deposited on the upper and lower active surfaces of the PZN-PT single crystal of predetermined dimensions to obtain a metallized crystal. This metallized crystal is then poled along a predetermined direction to obtain a piezoelectric single crystal transducer element.

[0040] The invention will now be explained with the aid of the accompanying drawings, in which: [Brief explanation of the drawings]

[0041] [Figure 1] Figure 1(a and b) illustrates a PZN-PT single crystal grown by the method according to the present invention. [Figure 2] FIG. 2 illustrates an optical microscope image of the surface morphology of a PZN-PT single crystal grown according to the present invention. [Figure 3] FIG. 3 illustrates (a) a diced PZN-PT single crystal element, (b) a polished PZN-PT single crystal element, and (c) a metallized PZN-PT single crystal element in accordance with the present invention. [Figure 4] FIG. 4 illustrates optical microscope images of (a) a diced PZN-PT single crystal element, (b) a lapped PZN-PT single crystal element, and (c) a polished PZN-PT single crystal element according to the present invention. [Figure 5] Figure 5 illustrates a conceptual chart of the optimal method sequence for fabricating a PZN-PT single crystal transducer element according to the present invention, showing the steps of (a) grown crystal, (b) dicing, (c) lapping, (d) polishing, (e) Au / Cr electrode formation, and (f) polarization treatment. [Figure 6] FIG. 6 illustrates the Laue diffraction pattern of a <0001> oriented single crystal element according to the present invention. [Figure 7] FIG. 7 illustrates the X-ray powder diffraction pattern of the PZN-PT single crystal according to the present invention. [Figure 8] FIG. 8 illustrates a high-resolution X-ray diffraction rocking curve of a <0001> oriented PZN-PT single crystal element according to the present invention. [Figure 9] FIG. 9 illustrates the domain structure of a <0001> oriented PZN-PT single crystal element according to the present invention. [Figure 10] FIG. 10 illustrates the hysteresis loop of the ferroelectric of a PZN-PT single crystal element according to the present invention. [Figure 11]FIG. 11 illustrates the unipolar strain response of a PZN-PT single crystal element according to the present invention. [Figure 12] FIG. 12 illustrates the relationship between the impedance spectrum and the phase angle of the PZN-PT single crystal element according to the present invention. [Figure 13] FIG. 13 illustrates (a) an assembled PZN-PT single crystal transducer array, and (b) a transducer array of shaped PZN-PT single crystals according to the present invention. [Figure 14] FIG. 14 is a graph of receiver sensitivity versus frequency to compare the receiver sensitivity of a conventional 1-3 piezo composite material and a PZN-PT single crystal transducer element manufactured according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0042] Embodiments of the present invention will now be described with reference to the accompanying drawings.

[0043] The embodiments described herein will enable those skilled in the art to fully and completely grasp the scope of the present invention. Numerous details relating to individual components and methods may be set forth to fully grasp the embodiments of the present invention. It will be apparent to those skilled in the art that the details of the embodiments should not be construed as limiting the scope of the present invention. In some embodiments, well-known processes, well-known device structures, and well-known techniques are not described in detail.

[0044] In the present invention, the terms used are used only to describe particular embodiments and should not be construed as limiting the scope of the present invention. As used herein, nouns are intended to include plural references unless the context dictates otherwise. Terms such as "comprises" and "having" are inclusive transitional terms and thus specify the presence of a function, feature, integer, step, operation, element, or component described herein, but do not preclude the presence or addition of other functions, integers, steps, operations, elements, components, or groups of components. The particular order of steps disclosed in the methods and processes of the present invention should not be construed as indicating that the performance described or illustrated is necessarily essential. It should also be understood that additional or alternative steps may be used.

[0045] When an element is described as being "engaged," "connected," or "coupled" with another element, this includes being directly engaged, connected, or coupled with the other element. As used herein, the term "or" includes any combination of one or more of the associated listed elements.

[0046] The terms first, second, third, etc. may be used only to distinguish one element or component, region, layer, or section from another component, region, layer, or section, and therefore should not be construed as limiting the scope of the present invention. The terms first, second, third, etc. do not imply a particular permutation or order unless expressly stated herein.

[0047] High-performance piezoelectric materials are crucial to meeting the ever-increasing demand for advanced piezoelectric devices, such as underwater sonar, medical ultrasound transducers, low-field actuators, and electroacoustic transducers. The global piezoelectric device market is experiencing continuous growth, which clearly demonstrates the importance of piezoelectric materials and their expanding applications in advanced piezoelectric devices. Traditionally, relaxor PbTiO3 single crystals have been grown by various crystal growth techniques.

[0048] High-temperature solution growth (also known as flux crystal growth) has been widely adopted for the growth of binary relaxor PbTiO3 single crystals because this method is inherently suitable for growing non-congruent melting materials or materials that are highly volatile before reaching their melting point. Traditional flux crystal growth is based on the principle of spontaneous nucleation. Nucleation occurs in a supersaturated solution, which is achieved by a slow cooling process. Disadvantages of flux crystal growth include the difficulty of controlling spontaneous nucleation, the difficulty of growing large single crystals, slow growth rates, flux inclusions, and crystal orientation issues. Furthermore, the main factor hindering the widespread use of relaxor PbTiO3 single crystals in advanced piezoelectric devices is the lack of availability of large, high-quality single crystals.

[0049] The present invention provides a piezoelectric single crystal transducer element and a method for manufacturing the same.

[0050] In one aspect, the present invention relates to a piezoelectric single crystal transducer element comprising a PZN-PT single crystal having predetermined dimensions, an upper active surface, an lower active surface, and at least one metallized layer having a predetermined thickness, the PZN-PT single crystal having at least one metallized layer of the predetermined thickness on the upper and lower active surfaces, the crystal being polarized in the 0001 direction.

[0051] According to an embodiment of the present invention, the dimensions of the piezoelectric single crystal are 35 x 30 x 20 mm. 3 From 40 x 40 x 30 mm 3 In one embodiment, the dimensions of the piezoelectric single crystal are in the range of 35 x 30 x 20 mm.3 is.

[0052] According to an embodiment of the present invention, the metallization layer is composed of at least one metal selected from gold and chromium, hi one embodiment, the metallization layer is a gold layer.

[0053] According to an embodiment of the present invention, the thickness of the metallization layer is in the range of 250 nm to 350 nm, hi one embodiment, the thickness of the metallization layer is 300 nm.

[0054] According to an embodiment of the present invention, the transducer element has a capacitance of 24 μC / cm at a frequency of 1 Hz. 2 to 27.5 μC / cm 2 In one embodiment, the remanent polarization is 26 μC / cm at a frequency of 1 Hz. 2 is.

[0055] According to an embodiment of the present invention, the transducer element is characterized by a coercive field of 3.5 kV / cm to 4.0 kV / cm at a frequency of 1 Hz. In one embodiment, the coercive field is 3.8 kV / cm at a frequency of 1 Hz.

[0056] According to an embodiment of the present invention, the transducer element has a longitudinal piezoelectric strain coefficient d in the range of 2000 pm / V to 2100 pm / V at a frequency of 1 Hz. 33 In one embodiment, the longitudinal piezoelectric strain coefficient d 33 is 2100 pm / V at a frequency of 1 Hz.

[0057] According to an embodiment of the present invention, the transducer element has an electromechanical coupling coefficient k in the range of 73% to 75% in the Silver mode of vibration. 33 In one embodiment, the electromechanical coupling coefficient k 33 ' is 75%.

[0058] According to an embodiment of the present invention, the transducer element has a longitudinal voltage coefficient g in the range of 42 mV.m / N to 50 mV.m / N.33 It has the characteristic of having: In one embodiment, the longitudinal voltage coefficient g 33 is 48 mV.m / N.

[0059] In accordance with embodiments of the present invention, the transducer element is adapted for use as a key component in underwater high frequency acoustic transducers in the frequency range of 100 kHz to 200 kHz, for underwater SONAR, ultrasonic medical transducers, low field driven actuators, electroacoustic transducers, and piezoelectric MEMS devices.

[0060] According to an embodiment of the present invention, when this transducer element is used as a high-frequency underwater transducer of 100 kHz to 200 kHz, the receiving sensitivity is improved by 10 dB or more compared to the 1-3 type piezoelectric composite material.

[0061] The PZN-PT single crystal of the present invention has a longitudinal piezoelectric strain coefficient d 33 exceeds 2000 pC / N, and the electromechanical coupling coefficient k 33 These PZN-PT single crystals are characterized by a high dielectric constant (ε>5000) at the morphotropic phase boundary (MPB) composition with a low hysteretic strain of over 1%, inherent orientation, and domain-engineered structures. The outstanding properties of these PZN-PT single crystals make them promising candidates for replacing conventional PZT ceramics in strategic military applications.

[0062] In another aspect, the present invention provides a method for manufacturing a piezoelectric single crystal transducer element. This method involves preparing a PZN-PT single crystal. The PZN-PT single crystal is then oriented in a predetermined direction to obtain an oriented PZN-PT single crystal. The oriented PZN-PT single crystal thus obtained is then sequentially diced, lapped, and polished to obtain a PZN-PT single crystal of predetermined dimensions with an upper and lower active surface. A metallized layer of predetermined dimensions is deposited on the upper and lower active surfaces of the PZN-PT single crystal to obtain a metallized crystal. The metallized crystal is then poled in a predetermined direction to obtain an array of piezoelectric single crystal transducer elements.

[0063] This method is described in detail below.

[0064] In the first step, a piezoelectric single crystal, a PZN-PT single crystal, is prepared.

[0065] To prepare PZN-PT single crystals, predetermined amounts of lead precursor, zinc precursor, niobium precursor, and titanium precursor are mixed to obtain a mixture. This mixture is then placed in a sealed precious metal container, which is then placed in an alumina outer container with a gas purge function. The alumina outer container is then heated to a first predetermined temperature at a predetermined heating rate while simultaneously introducing a type of gas at a predetermined flow rate through the alumina outer container. The first predetermined temperature is then maintained for a first predetermined time to obtain a preform. The preform is then cooled to a second predetermined temperature at a predetermined cooling rate to obtain the PZN-PT single crystal.

[0066] According to an embodiment of the present invention, the lead precursor is lead oxide. In one embodiment, the lead precursor is lead dioxide.

[0067] According to an embodiment of the invention, the predetermined amount of lead precursor is in the range of 81.0% to 82.0% by weight based on the total weight of the mixture. In one embodiment, the predetermined amount of lead precursor is 81.7% by weight based on the total weight of the mixture, i.e., up to 245 g out of 300 g.

[0068] According to an embodiment of the present invention, the zinc precursor is zinc oxide.

[0069] According to an embodiment of the present invention, the amount of zinc precursor ranges from 4.0% to 4.5% by weight based on the total weight of the mixture. In one embodiment, the amount of zinc precursor is 4.2% by weight based on the total weight of the mixture, i.e., 12.6 g out of 300 g.

[0070] According to an embodiment of the present invention, the niobium precursor is niobium oxide. In one embodiment, the niobium precursor is niobium(V) oxide.

[0071] According to an embodiment of the invention, the amount of niobium precursor ranges from 13 wt% to 14 wt% of the total weight of the mixture. In one embodiment, the amount of niobium precursor is 13.8 wt% of the total weight of the mixture, i.e., 41.4 g in 300 g.

[0072] According to an embodiment of the present invention, the titanium precursor is titanium oxide. In one embodiment, the titanium precursor is titanium(IV) oxide.

[0073] According to an embodiment of the present invention, the amount of titanium precursor ranges from 0.5 wt % to 1.2 wt % based on the total weight of the mixture. In one embodiment, the amount of titanium precursor is 0.6 wt % based on the total weight of the mixture, i.e., 1.8 g in 300 g.

[0074] According to an embodiment of the present invention, the input gas is oxygen.

[0075] According to an embodiment of the present invention, the sealed vessel made of a precious metal is a precious metal crucible with a precious metal lid, and the precious metal is at least one precious metal selected from platinum and iridium.

[0076] According to an embodiment of the present invention, the alumina outer vessel is an alumina crucible with an alumina lid.

[0077] According to an embodiment of the present invention, the first predetermined temperature is in the range of 1240° C. to 1260° C. In one embodiment, the first predetermined temperature is 1250° C.

[0078] According to an embodiment of the present invention, the predetermined heating rate ranges from 60° C. / hour to 80° C. / hour. In one embodiment, the predetermined heating rate is 70° C. / hour.

[0079] According to an embodiment of the present invention, the second predetermined temperature is in the range of 880° C. to 920° C. In one embodiment, the second predetermined temperature is 900° C.

[0080] According to an embodiment of the present invention, the first predetermined period of time is between 4 and 6 hours. In one embodiment, the first predetermined period of time is 5 hours.

[0081] According to an embodiment of the present invention, the predetermined cooling rate ranges from 0.9° C. / hour to 1.0° C. / hour. In one embodiment, the predetermined cooling rate is 1.0° C. / hour.

[0082] According to an embodiment of the present invention, the predetermined gas flow ranges from 0.7 l / min to 2 l / min. In one embodiment, the predetermined gas flow is 1 l / min.

[0083] According to an embodiment of the present invention, spontaneous nucleation was controlled during the growth of large PZN-PT single crystals, where large single crystals (over 35 mm edge length) were grown in a stress-free manner in the center of the lower crucible. The grown PZN-PT single crystals had dimensions of 35 × 30 × 20 mm. 3 The weight of the grown crystal was 103 g, which corresponds to 71% of the total charge amount used as raw material. The grown PZN-PT single crystal exhibited a pure perovskite phase by maintaining specific chemical parameters, such as charge-to-flux ratio and flux composition, and thermal parameters, such as soaking temperature and heating rate. The perovskite phase was revealed by powder X-ray diffraction patterns, which confirmed that the PZN-PT single crystal belonged to the tetragonal crystal system.

[0084] Next, the obtained PZN-PT single crystal is oriented in a predetermined direction in the second step to obtain an oriented PZN-PT single crystal.

[0085] According to an embodiment of the present invention, the predetermined direction of orientation is

[0001] .

[0086] According to an embodiment of the present invention, orientation was performed using back-reflection Laue diffraction.

[0087] Backscattered Laue diffraction is a method typically used to determine the orientation of large single crystals in which white radiation is allowed to impinge on a fixed crystal and the white radiation reflected from or through the crystal is recorded on photographic film. There are two types of Laue techniques: (i) back-reflection Laue and (ii) transmission Laue. In the back-reflection technique, a photographic film is placed between the X-ray source and the crystal. The back-diffracted X-rays are recorded.

[0088] The single crystals prepared according to the present invention are inherently anisotropic in nature, exhibiting unique physical properties depending on the crystallographic direction, and these properties can be exploited by orienting them along a specific crystallographic direction.

[0089] In the third step, the obtained oriented PZN-PT single crystal is sequentially diced, lapped, and polished to obtain a PZN-PT single crystal of predetermined dimensions having an upper and lower working surface.

[0090] According to an embodiment of the present invention, an oriented PZN-PT single crystal is diced using a diamond wire saw to cut it into appropriate dimensions to fit the transducer design. The diced crystal is then lapped using a series of silicon carbide (SiC) sheets to eliminate surface irregularities caused by the dicing process. The single crystal is then polished to remove structural damage induced by the previous dicing and lapping processes, extending from the surface to a depth of 500 nm to 50 μm.

[0091] According to the embodiment of the present invention, the oriented PZN-PT single crystal was diced and lapped to a size of 35 × 30 × 20 mm. 3 From 40 x 40 x 30 mm 3 In one embodiment, the predetermined dimensions are 35 x 30 x 20 mm. 3 is.

[0092] In the fourth step, a metallized layer is deposited on the upper and lower working surfaces of the PZN-PT single crystal of predetermined dimensions to obtain a metallized crystal.

[0093] According to an embodiment of the present invention, this metallization layer is deposited using a DC magnetron sputtering process at room temperature for 3 to 5 minutes at a power range of 80 W to 100 W.

[0094] The DC magnetron sputtering process is a physical vapor deposition process in which atoms are ejected from a source material (target) by the bombardment of high-energy ions. A DC sputtering system consists of a pair of planar electrodes. The target material serves as the cathode, and the substrate is placed on the anode. An inert gas is introduced into the sputtering chamber, and a DC voltage of several thousand volts is applied between the electrodes, triggering a glow discharge. The inert gas ions in the glow discharge are accelerated by the cathode and sputter the target material, depositing a thin film on the substrate.

[0095] In accordance with an embodiment of the present invention, a gold / chromium (Au / Cr) metal layer is deposited on the top and bottom surfaces of a PZN-PT single crystal. Here, a 300 / 30 nm thick Au / Cr layer is deposited on both sides of the single crystal parallel to the <0001> orientation by DC magnetron sputtering. The metal layer's properties and thickness are selected in such a way that the metal layer can withstand the strong electric field applied during poling without altering the natural electrical properties of the single crystal. A chromium interlayer is employed to ensure adhesion of the gold on the PZN-PT single crystal, and the metal-to-interlayer thickness ratio is optimized to prevent delamination of the metal layer.

[0096] Next, in the fifth step, the metallized crystal is polarized in a predetermined direction to obtain a piezoelectric single crystal transducer element.

[0097] According to an embodiment of the present invention, poling of the metallized crystal is performed by applying an electric contact poling to the metallized crystal using a field cooling method, where a poling field in the range of 5.25 kV / cm to 6.0 kV / cm, which is 1.5 times the coercive field, is applied at room temperature.

[0098] The field cooling method is a technique in which the temperature of a sample (which is a crystal in this specification) is gradually decreased in a polarization electric field at room temperature.

[0099] According to an embodiment of the present invention, the metallized crystal was poled along the <0001> orientation, where a <0001>-oriented PZN-PT single crystal in the tetragonal phase was poled in the <0001> direction by electrical contact polarization. The poling conditions were optimized to improve the piezoelectric and electromechanical properties of the PZN-PT single crystal. The PZN-PT single crystal was poled in a DC electric field of 5.25 kV / cm to 6.0 kV / cm for 30 minutes at room temperature.

[0100] Poling is the process of orienting electric dipoles in the direction of an external electric field, i.e., a "poling reversal" process. PZN-PT single crystals are inherently anisotropic, i.e., directionally dependent, and exhibit different electromechanical properties when polarized in different directions. Poling PZN-PT single crystals along their polarization direction results in a "single-domain state," whereas poling them in other directions results in the coexistence of multiple domain configurations. However, PZN-PT single crystals with multiple domain configurations exhibit exaggerated piezoelectric coefficients for the longitudinal vibration mode, while single-domain crystals exhibit very low longitudinal vibration properties and ultrahigh shear properties. The electric field, temperature, and duration of poling are the three main factors that affect the poling process. Therefore, optimizing the poling conditions is essential to obtain optimal piezoelectric properties.

[0101] Figure 3 shows the sequence of processes used to fabricate transducer elements from as-grown crystals. The as-grown crystals are oriented in the 0001 direction before dicing (see Figure 3a). The diced crystals are then lapped (Figure 3b) and polished (Figure 3c) to correct surface imperfections introduced during the dicing process.

[0102] Figure 4 illustrates optical microscope images of (a) a diced PZN-PT single crystal element, (b) a lapped PZN-PT single crystal element, and (c) a polished PZN-PT single crystal element according to the present invention. Figure 4 shows optical microscope images of a PZN-PT single crystal after each of the processes used to convert the grown crystal into a transducer element, including dicing, lapping, and polishing. The images show how the surface roughness of the PZN-PT crystal changes after each process.

[0103] Figure 8 shows a high-resolution X-ray diffraction (HRXRD) image of a <0001>-oriented PZN-PT single crystal. This image shows that the PZN-PT crystal is linear in nature and oriented in the <0001> direction. The full width at half maximum (FWHM) of the HRXRD curve indicates that the PZN-PT single crystal is of high quality in terms of crystallinity.

[0104] Figure 9 illustrates the domain structure of a <0001>-oriented PZN-PT single crystal element according to the present invention. That is, Figure 9 shows the domain pattern of the polished PZN-PT crystal, which confirms that the PZN-PT single crystal is oriented in the <0001> direction.

[0105] FIG. 10 illustrates the ferroelectric hysteresis loop of a PZN-PT single crystal, which can confirm that the PZN-PT single crystal has ferroelectric properties.

[0106] Figure 12 shows the characteristic curves of impedance and phase angle of the PZN-PT single crystal after polarization. The impedance spectrum confirms that the PZN-PT single crystal is polarized along the

[0001] direction.

[0107] The characteristics of the obtained piezoelectric single crystal transducer element according to the embodiment of the present invention were evaluated in accordance with the IEEE standard, where the ferroelectric properties were measured using a modified Sawyer-Tower circuit method. When an electric field was applied stepwise to the PZN-PT single crystal, the ferroelectric properties were confirmed by a well-saturated hysteresis behavior. The PZN-PT single crystal exhibited a ferroelectricity of 24 μC / cm at 1 Hz.2 ~27.5 μC / cm 2 and coercive electric field (Ec): in the range of 3.5 to 4.0 kV / cm.

[0108] According to an embodiment of the present invention, the characteristics of the piezoelectric single crystal transducer element obtained above were evaluated in accordance with the IEEE standard. At this time, the piezoelectric characteristics were measured using a unipolar strain measurement method using a single beam laser interferometer (SBLI). The unipolar strain of PZN-PT single crystals is measured after poling. The non-hysteretic linear behavior confirms the 4R domain-engineered structure of the PZN-PT single crystals. The unipolar strain and longitudinal piezoelectric strain coefficient d33 of the PZN-PT single crystals range from 0.125% to 0.128% and 2000 pm / V to 2100 pm / V at 1 Hz.

[0109] The characteristics of the piezoelectric single crystal transducer element obtained according to the embodiment of the present invention were evaluated in accordance with the IEEE standard, and the characteristics of the PZN-PT single crystal were measured using the virtual current method. The capacitance-voltage characteristics showed an inverted butterfly loop, which verified the validity of the ferroelectric properties of the PZN-PT single crystal. The dielectric constant and dielectric loss of the PZN-PT single crystal were 4500 to 5000 and 0.10% to 0.12%, respectively, at a frequency of 1 Hz.

[0110] According to the embodiment of the present invention, the characteristics of the obtained piezoelectric single crystal transducer element were evaluated in accordance with the standard, and the electromechanical characteristics of the PZN-PT single crystal were measured using an impedance analyzer. 33 ' is measured in vibration silver mode and ranges from 73% to 75%.

[0111] According to the embodiment of the present invention, the characteristics of the obtained piezoelectric single crystal transducer element were evaluated in accordance with the IEEE standard. At this time, the longitudinal voltage coefficient g 33 ranged from 42 mV·m / N to 50 mV·m / N.

[0112] The characteristics of the obtained piezoelectric single crystal transducer element according to the embodiment of the present invention were evaluated in accordance with the IEEE standard, and the surface behavior of the grown PZN-PT single crystal was observed using an optical microscope. The optical microscope observation of the grown PZN-PT single crystal revealed that it was growing as a layer.

[0113] The characteristics of the obtained piezoelectric single crystal transducer element according to the embodiment of the present invention were evaluated in accordance with the IEEE standard. At this time, it was confirmed from the powder X-ray diffraction (XRD) pattern that the PZN-PT single crystal was in a tetragonal phase and had a pure perovskite structure that did not contain a pyrochlore phase.

[0114] The characteristics of the obtained piezoelectric single crystal transducer element according to the embodiment of the present invention were evaluated in accordance with the IEEE standard. In this case, the PZN-PT single crystal was confirmed to be oriented in the

[0001] direction by back-reflection Laue diffraction, and the crystallinity and

[0001] orientation were confirmed by the four-fold symmetry.

[0115] According to an embodiment of the present invention, the characteristics of the obtained piezoelectric single crystal transducer element were evaluated in accordance with the IEEE standard, and the structural quality of the PZN-PT single crystal was measured by high-resolution X-ray diffraction, and the full width at half maximum (FWHM) of (001) was in the range of 0.54° to 0.57°.

[0116] The characteristics of the obtained piezoelectric single crystal transducer element according to the embodiment of the present invention were evaluated in accordance with the IEEE standard, and the domain structure of the <0001>-oriented PZN-PT single crystal was examined using an optical microscope. The domain structure of the grown PZN-PT single crystal confirmed that the domains were aligned parallel to the thickness direction. This confirmed that the single crystal was oriented along the <0001> crystallographic direction.

[0117] According to an embodiment of the present invention, the characteristics of the obtained piezoelectric single crystal transducer elements were evaluated in accordance with the IEEE standard, and the standard deviations between different single crystal elements in the ferroelectric, piezoelectric, and electromechanical properties were less than 5%, which confirmed high homogeneity.

[0118] The characteristics of the piezoelectric single crystal transducer element obtained according to the embodiment of the present invention were evaluated in accordance with the IEEE standard. The weight of the grown PZN-PT single crystal was approximately 103 g, which corresponds to 71% of the total charge amount of the raw material. It was confirmed that the PZN-PT single crystal grown by the innovative bottom cooling method has a higher yield, which reduces the cost of the single crystal element.

[0119] According to an embodiment of the present invention, the characteristics of the obtained piezoelectric single crystal transducer elements were evaluated in accordance with IEEE standards, and a high-frequency (100 kHz - 200 kHz) underwater acoustic transducer was fabricated from them. The high-frequency underwater acoustic transducer here consists of PZN-PT single crystal elements. A linear array of PZN-PT single crystal elements was assembled in a Teflon housing, and the entire array was molded using acoustically transparent polyurethane. The transducer elements were reinforced with a pressure-relief material, which was then reinforced with a rigid backing material. The single crystal elements were connected with a low-noise, two-core, shielded, twisted-pair cable (shown in Figures 13a and 13b).

[0120] According to an embodiment of the present invention, the characteristics of the obtained piezoelectric single crystal transducer element were evaluated in accordance with the IEEE standard, and this was then processed into a high-frequency (100 kHz - 200 kHz) underwater acoustic transducer, and its underwater performance was further evaluated. Here, in the frequency range from 100 kHz to 200 kHz, the receiving sensitivity of the high-frequency underwater acoustic transducer based on PZN-PT single crystal was 10 dB better than that of the 1-3 type piezoelectric composite material based on PZT.

[0121] Furthermore, the present invention provides a piezoelectric single crystal transducer element array composed of morphotropic phase boundary composition, oriented PZN-PT single crystals. The PZN-PT single crystals were grown by a high-temperature flux crystal growth method. A specific bottom cooling structure controls spontaneous nucleation, thereby significantly reducing polynucleation, enabling large-size (over 35 mm side length) crystal growth in the center of the crucible bottom. This innovative method significantly improves yield and therefore reduces single crystal growth costs. Furthermore, the crystal growth system was designed and developed in-house, providing optimal conditions for growing large-size single crystals that are more economically feasible than commercially available flux crystal growth systems.

[0122] According to an embodiment of the present invention, the grown single crystals exhibit a yellowish-brown color. The PZN-PT single crystals are oriented along the 0001 crystallographic direction using Laue diffraction patterns to exploit their anisotropic properties. Powder X-ray diffraction patterns indicate that the grown single crystals have a tetragonal structure of the pure perovskite phase.

[0001] Oriented single crystals were processed through a series of successive steps to realize a transducer element array. The oriented crystals were diced and lapped to a consistent thickness. A mechanical polishing process resulted in a surface roughness of 1 to 2 nm. After polishing, the single crystals were annealed at 200 °C to reduce residual stresses introduced during the above steps.

[0123] According to an embodiment of the present invention, single crystals were treated by a polarization process of electrical contacts in a silicone oil bath at room temperature. The polarization electric field was applied at a strength 1.5 times stronger than the coherent electric field (5.25-6.0 kV / cm), and a field cooling method was applied. The PZN-PT single crystals exhibited longitudinal piezoelectric strain coefficients of 2000 pC / N to 2100 pC / N with strains of 0.10% to 0.12%, which were close to those of 91PZN-9PT single crystals. This value was higher than that of conventional piezoceramics. The electromechanical coupling coefficients of the PZN-PT single crystals in the vibration silver mode were k, respectively. 33 The value obtained was ' = 0.73 - 0.75.

[0124] Its ultra-high piezoelectric coefficient, strain characteristics with minimal hysteresis, and large electromechanical coupling coefficient make it an inevitable next-generation material for underwater devices using piezoelectric MEMS. It has been used to fabricate PZN-PT single-crystal high-frequency (100 kHz to 200 kHz) underwater acoustic transducers, and the receiver sensitivity of the manufactured acoustic transducers has been enhanced by up to 10 dB compared to conventional PZT-based 1-3 type piezoelectric composites.

[0125] The present invention is further described below with the aid of the following examples. The experiments used herein are solely intended to facilitate understanding of how the embodiments of the present invention can be put into practice and to enable those skilled in the art to practice the embodiments of the present invention. Therefore, the following examples should not be construed as limiting the scope of the embodiments of the present invention. [Example]

[0126] Example 1 Example 1 illustrates the production of PZN-PT single crystals in accordance with the present invention. High purity (99.95%) PbO, ZnO, Nb2O5, and TiO2 were weighed and mixed. The flux ratio to charge was 55 mol% PbO:45 mol% PZN-PT to obtain the mixture. 91PbZn grown at the morphotropic phase boundary (MPB) composition 1 / 3 Nb 2 / 3 -9PbTiO3 single crystal. The quantities of the precursors are: lead dioxide (II) up to 245 g, zinc oxide up to 12.6 g, niobium oxide (V) up to 41.4 g, and titanium oxide up to 1.8 g. The mass percentages of each precursor are: 84.9204% PbO: 3.3842% ZnO: 11.0531% niobium oxide (V): 0.6423% titanium oxide. 300 g of this mixture was packed into a platinum crucible (120 cc, 1 mm wall thickness, mass 250 g) and fitted with a platinum lid to prevent PbO evaporation. The crucible containing the above mixture was placed in an Al2O3 crucible, which was then placed in an Al2O3 crucible and fitted with an Al2O3 lid to prevent PbO vapor from damaging the heating module due to breakage of the platinum crucible. With this configuration, PbO mass loss was reduced to less than 2% within a total growth time of 700 hours. The alumina crucible was placed within the required temperature gradient range of the developed flux crystal growth system. It was heated from 1240 °C to 1260 °C at a heating rate of 70 °C / h and maintained at this temperature for an additional 5 h. A gas flow of 1 l / min was maintained throughout the crystal growth period, and gas supply at the bottom of the crucible reduced the number of multinuclei. This process induced the growth of a single crystal in the center of the platinum crucible. Because this configuration created a large inverse temperature gradient (up to 50 °C) between the bottom and top of the crucible, growth was initiated from the bottom of the crucible. After the high-temperature soak, the crystal growth system was cooled to 900 °C at a cooling rate of 1 °C / h. The crucible was dried at 900 °C and then cooled to room temperature at an increased cooling rate (60 °C / h). The total growth time was approximately 30 days. The crystals were separated from the flux remaining in the platinum crucible by leaching using boiling 30% nitric acid. Observation and Inference

[0127] Large-scale device-grade PZN-PT crystal growth was observed. Large PZN-PT single crystals (over 35 mm in edge length) have been grown using the above method with a translucent, pale yellow color and prominent <0001> planes, as shown in Figure 1. The grown crystals exhibited natural surface appearance, and the dimensions of the grown crystals were up to 35 mm x 30 mm x 20 mm, with a weight of 103 g (Figure 1). The grown crystals showed that atomically flat surfaces only occurred when the grown crystals were in a stable mode from high-temperature solution, and furthermore, the crystals grew by layer expansion, as shown in Figure 2.

[0128] Example 2 In Example 2, the orientation, dicing, and polishing of PZN-PT single crystal elements obtained in Example 1 according to the present invention were compared with conventionally prepared PZN-PT single crystal elements. Appropriately sized PZN-PT single crystals were used in various devices and for the development of these devices, and the single crystal elements underwent various sample preparation steps. Conventionally prepared PZN-PT single crystals were oriented along <0001> and cut to the target dimensions. It was observed that PZN-PT single crystals prepared by conventional methods contained undesirable defects such as scratches, cracks, and other damage. These defects occurred at a depth of approximately 200 nm from the surface of the PZN-PT single crystals. Furthermore, the cutting process of these PZN-PT single crystals reduced the crystals' mechanical strength, limiting their expected lifespan in practical applications. The PZN-PT single crystal prepared according to Example 1 was cut and further polished. The grown PZN-PT single crystal was attached to a graphite plate using crystal mounting wax, and Laue diffraction measurements were performed to confirm its orientation along the <0001> direction. The oriented crystal was diced at a speed of 0.3 mm / min using a 0.1 mm diamond wire saw cutting system (STX-203, MTI Corporation, California, USA). Deionized water was sprayed on the crystal during the dicing process to prevent heat generation. The diced crystal was placed in the center of an alumina polishing disk, and dummy crystals were attached to the corners of this disk with crystal mounting wax. The surface of the single crystal was flattened using a series of silicon carbide (SiC) polishing sheets with grit sizes of SiC 800 and SiC 2000. To polish the crystal side and reduce the number of dummy samples, the diced PZN-PT crystals were encapsulated in resin using the cold mounting method. A mold was created using cold mounting resin (Technovit 5071), a mixture of equal parts liquid and powder. Cold mounting resin has the advantage of forming a mold, and after polishing, the PZN-PT crystals were removed from the mold by immersing them in acetone for approximately 12 hours. The polishing process was crucial in removing the damaged surface layer. The strain layer was generated by the treatment of the crystal during the cutting and lapping process. A mechanical polishing process was used to fine-tune the surface layer to a so-called "mirror-finish surface." During the polishing process, a "surface strain layer" can actually occur when using SiC polishing lapping sheets with grain sizes exceeding (1-3) μm. The formation of this damaged surface layer was due to concentrated compression during the polishing process, and this damaged layer is thought to consist of an overstressed structure with tetragonal symmetry. The surface-strained layer exhibited different mechanical properties from the inner layer beneath the "surface strain layer." Concentrated compression during the cutting, lapping, and polishing processes also resulted in the formation of a "strained surface layer" in the piezoelectric material and the associated modification of the surface domain structure. To avoid these consequences, a controlled polishing process using a grain size of 0.03 μm was used to prevent unwanted defects in the surface layer. The polishing process was performed using diamond paste with a particle size of 1 μm, and the surface was finished using 0.03 μm Al2O3 powder suspended in water. Both the diamond paste and Al2O3 slurry were used with a soft polishing cloth to obtain single crystal surfaces with good visual quality. The main purpose of using Al2O3 slurry in the polishing process was to remove distortions in the crystalline structure below the crystal surface caused by intensive compression that may have occurred during the sample preparation stage. The polished crystals were then annealed at 200 °C to reduce any residual stresses introduced in the previous step.

[0129] Example 3 Example 3 is an example of a method for making electrical contacts for a PZN-PT single crystal element prepared according to the present invention. To form electrical contacts, Au / Cr films with thicknesses of 300 / 30 nm were deposited perpendicular to the thickness direction on both working surfaces of the PZN-PT single crystal element by DC magnetron sputtering. The PZN-PT single crystal was washed with conventional organic solvents to ensure the surface was sufficiently clean for electrical contact formation. The other side was protected from electrode deposition to prevent short-circuiting between the upper and lower electrodes. A transition metal layer (Cr) and a metal layer (Au) were deposited on the PZN-PT single crystal using a DC magnetron sputtering system (Mini Lab 060, Moorfield, Manchester, UK). Cr was used as the intermediate layer between the PZN-PT single crystal and Au as the top layer. The deposition process is defined below: The PZN-PT single crystal element was mounted on a 4-inch substrate holder installed inside the sputtering chamber. A circular Au / Cr target (purity 99.99%) with a diameter of 50.8 mm and a thickness of 1.6 mm was placed facing two cylindrical magnetrons at an off-axis angle of 15°. The main chamber had a 5 × 10 -6 The samples were evacuated using a turbomolecular pump to a vacuum of 1000 mbar. The Au and Cr targets were cleaned with isopropanol to prevent contamination. The distance from the source (Au / Cr) to the substrate (PZN-PT crystal) was kept constant at approximately 15 cm, and sputter growth was carried out in a high-purity argon (Ar) gas atmosphere. Ar acts as a carrier gas, and the Ar is ionized by secondary electrons that eject target atoms toward the substrate. + To ignite the plasma, high-pressure Ar gas was introduced at a pressure of 40 μbar and a DC power of 85 W to form a self-sustaining plasma. Plasma power (100 W) was used for the deposition of Au / Cr, and a substrate rotation speed of 5 rpm was maintained throughout the deposition process to maintain a constant thickness across the single-crystal element. Au and Cr were deposited at room temperature. Base pressure was 5 × 10 -6 After reaching a pressure of approximately 2.5 × 10 mbar, Ar gas was introduced into the plasma chamber. -2 mbar. 10 × 10 -3 The pressure was reduced again to mbar. Cr was evaporated onto the PZN-PT single crystal element, and then Au was evaporated while maintaining the vacuum. A 30 nm thick Cr layer and a 300 nm thick Au layer were evaporated onto the PZN-PT single crystal element.

[0130] Example 4 Example 4 is an example of a method for poling a PZN-PT single crystal element in accordance with the present invention. The PZN-PT single crystals were subjected to a poling process in which different electric field strengths were applied for 30 min at room temperature. The DC voltage was applied using a high-voltage power supply configuration (aixACCT Systems GmbH, Aachen, Germany). Poling is the process of orienting electric dipoles in the direction of an external electric field, i.e., a "poling reversal" process. PZN-PT single crystals are inherently anisotropic, i.e., directionally dependent, and exhibit different electromechanical properties when polarized in different directions. Poling PZN-PT single crystals along their polarization direction results in a "single-domain state," whereas poling them in other directions results in the coexistence of multiple domain configurations. However, PZN-PT single crystals with multiple domain configurations exhibit exaggerated piezoelectric coefficients for the longitudinal vibration mode, while single-domain crystals exhibit very low longitudinal vibration characteristics and ultrahigh shear properties. Electric field, temperature, and poling duration are the three main factors affecting the poling process. Therefore, optimizing the poling conditions is essential to obtain optimal piezoelectric properties. To polarize the PZN-PT single crystal, we used the electric contact polarization method, in which Au metal electrodes were in direct contact with an electric probe. A direct current (DC) electric field was applied between the electrodes and increased stepwise from 25 V to several kV in 100 V steps over 5 minutes. The current flowing between the electrodes was kept below 1 μA as a prerequisite. After immersing the sample in the polarization voltage for 30 minutes, the voltage was decreased in 100 V steps over 5 minutes. c / T R-T is relatively low, and the poling temperature in all poling steps was fixed at room temperature. The poling field was varied with respect to the coercive field, and the optimum poling field was obtained when it was 1.5 times the coercive field.

[0131] Example 5 Example 5 is a qualitative analysis of the piezoelectric single crystal transducer element array fabricated according to Examples 1-4. The structural properties of the piezoelectric single crystal element arrays were investigated using a Rigaku grazing incidence X-ray diffractometer (GIXRD) using CuKα radiation (λ = 0.15418 nm) at an operating voltage of 40 kV / current of 30 mA, and Laue diffraction patterns were recorded at room temperature. The ferroelectric properties of the metallized single crystal were measured using a TF Analyzer 2000 ferroelectric tester (aixACCT Systems GmbH, Aachen, Germany). An electric field was applied between the upper and lower Au electrodes, and the crystal was immersed in a silicone oil bath to prevent discharge. A sinusoidal bipolar electric field of 6 kV / cm at a frequency of 1 Hz was applied using a high-voltage amplifier (10 / 10B-HS, Trek, Inc., New York, USA). Longitudinal piezoelectric strain coefficient (d 33 ) was measured from the indirect piezoelectric effect based on a unipolar strain loop. The unipolar strain response was measured as a function of electric field in the frequency range of 1 Hz using a single-beam laser interferometer system (aixACCT Systems GmbH, Aachen, Germany). The impedance characteristics as a function of frequency were measured using a high-precision impedance analyzer (Agilent 4294A, California, USA). structural analysis

[0132] The structural characteristics of the piezoelectric single-crystal transducer element array were analyzed by X-ray diffraction analysis. Based on the X-ray diffraction patterns, structural characteristics such as phase purity and crystallinity were analyzed throughout the single-crystal element. Powder X-ray diffraction analysis of the PZN-PT single-crystal element was performed using a Rigaku X-ray diffractometer equipped with graphite-monochromated CuKα radiation (wavelength 0.15418 nm) at 40 kV and 30 mA. All powder XRD patterns were recorded in the θ-2θ mode from 10 to 70°. The scan rate and step size were 2° / min and 0.01°, respectively. The XRD patterns were analyzed using X'Perthigh score plus software, and the results were compared with JCPDS data. Based on the powder XRD pattern (Fig. 7), it can be inferred that the PZN-PT single crystal forms a perovskite structure without any defect pyrochlore phase. The X-ray diffraction (200) peak appears at 2θ = 43.9.° This suggests that the PZN-PT single crystals are in the tetragonal phase. The calculated full width at half maximum (FWHM) based on the XRD patterns ranges from 0.54° to 0.56°, demonstrating that good quality PZN-PT single crystals were obtained. Based on the Laue diffraction pattern, the grown crystals are oriented in three mutually perpendicular directions [ <100> , <010> ,

[0001] ], i.e., along the a, b, and c directions (Figure 6). The backscattering Laue diffraction patterns for the three orientations were simulated using ORIENTEXPRESS software and compared with the Laue diffraction patterns described above. Electrical characteristics

[0133] The field dependence of the polarization of PZN-PT single crystals is shown in Figure 11. At 1 Hz and room temperature, the field is varied from 0 to 6.0 kV / cm. The hysteresis loops are well saturated and the remanent polarization values ​​are large, suggesting ferroelectricity in nature. The hysteresis loops are symmetric on both sides of the zero field. The polarization response to the external field remains constant for both field polarities. The resulting remanent polarization values ​​are 24–27.5 μC / cm. 2 , the coercive field is 3.5 to 4.0 kV / cm. The unipolar strain versus electric field operation was measured based on the inverse piezoelectric effect and is shown in Figure 11. The inverse strain experiment was carried out after poling at room temperature with a frequency of 1 Hz. Comparing the distortion curve with the electric field curve, the distortion value is zero after the electric field is removed, i.e., ΔS E=0 = 0, indicating that no depolarization effect occurred in the PZN-PT crystals after poling. Unipolar strain-field curves show approximately hysteretic behavior and a rapid increase in strain value, occurring linearly at an electric field of 6.0 kV / cm. The maximum strain observed ranges from 0.10% to 0.12%. The longitudinal piezoelectric strain coefficients range from 2000 pm / V to 2100 pm / V, and the values ​​were evaluated based on the slopes of the strain-field response curves. The area under the strain-field response curves identifies the PZN-PT single crystals as being near the morphotropic phase boundary (MPB) composition. The measured impedance and phase angle of the PZN-PT single crystal are shown in Figure 13. The impedance and phase angle were measured in the frequency range from 40 Hz to 1 MHz. The fundamental resonance frequency of the thickness mode vibration at the minimum impedance was 240 kHz to 242 kHz, and the anti-resonance frequency at the maximum impedance was 335 kHz to 340 kHz. When the impedance magnitude was 10 3 Omega to 10 6 The Ω indicates that the crystal element maintained its resistive properties after poling and no depolarization effect occurred.

[0134] Example 6 Example 6 is the fabrication and evaluation of a high frequency underwater acoustic transducer utilizing a PZN-PT single crystal according to the present invention. Methods: A linear array of eight elements was fabricated using PZN-PT single crystals measuring 4.5 mm × 2.5 mm × 4.2 mm. The dimensions of the PZN-PT single crystals were chosen to achieve a resonant frequency greater than 200 kHz and a difference between the resonant and antiresonant frequencies greater than approximately 80 kHz. All elements were assembled in a Teflon housing, and the entire assembly was molded from acoustically transparent polyurethane to a thickness of 15 mm. The backs of the transducer elements were supported by a sound pressure release material, which in turn reinforced the backs with a rigid material and connected with a low-noise two-core shielded twisted-pair cable. It was confirmed that the resonant frequency of the PZN-PT single crystal decreased by 70 kHz after molding due to the charging effect caused by molding. Furthermore, molding also reduced the sharpness of the resonance. The same phenomenon was observed in the case of type 1-3 piezoelectric composites. The transducer array was calibrated over a frequency range of 50 kHz to 350 kHz using the second calibration method. As shown in Figure 14, the receiver sensitivity (RS) of the PZN-PT single crystal element array was plotted on a plotter using a frequency reference and compared with that of the 1-3 type piezoelectric composite. In the frequency range of 100 kHz to 200 kHz, the receiving sensitivity of the PZN-PT single crystal (-210 to -215 dB, measured at 1 V / μPa without a preamplifier) ​​was up to 10 dB higher than that of the 1-3 type piezoelectric composite.

[0135] Technological advances The present invention as described above has several technical advantages, including but not limited to the incorporation of piezoelectric single crystal transducer elements. exceptionally high Longitudinal piezoelectric strain coefficient d 33 > 2000 pC / N, Electromechanical coupling coefficient k33 > 90 %, low hysteresis distortion > 1 % and It exhibits an excellent dielectric constant ε > 5000 under the morphotropic phase boundary (MPB) condition in the inherent orientation and domain engineered configuration. Its superior properties make it capable of replacing PZT ceramics in strategic military applications. moreover, A method for manufacturing a piezoelectric single crystal transducer element. This method comprises: Simple and cutting edge, Economically competitive, It is possible to scale it up for practical use, Spontaneous nucleation can be controlled, It exhibits a relatively high growth rate.

[0136] PZN-PT single crystal elements have good uniform composition, resulting in electrical properties with a variation of less than 3% from element to element. Consistent electrical properties between each single crystal element are highly desirable in strategic military and commercial applications to obtain precise and consistent device response.

[0137] This piezoelectric single crystal transducer element array is a key component in underwater SONAR, ultrasound medical transducers, low-field driven actuators, electroacoustic transducers, and other next-generation piezoelectric MEMS devices.

[0138] Throughout this specification, the terms "comprise" and "constitute" and their variants "composed" or "comprising" are intended to imply the inclusion of a stated element, integer or step or group of elements, integers or steps, but not the exclusion of other elements, integers or steps or other groups of elements, integers or steps.

[0139] The use of the phrase "at least" or "at least one" suggests the use of one or more elements or ingredients or quantities, as may be used in the practice of the invention to achieve one or more desired substances or results. While several embodiments of the invention have been described, these embodiments are set forth by way of example only and are not intended to limit the scope of the invention. Formulations or modifications of the preparations of the invention may be made by one skilled in the art upon consideration of the present invention, provided they fall within the scope of the invention. Such variations and modifications are within the intended scope of the invention.

[0140] Numerical values ​​representing different physical parameters, dimensions, and quantities are approximate, and any higher value substituted for the physical parameter, dimension, or quantity is intended to be within the scope of the present invention, unless expressly stated to the contrary in the specification.

[0141] While considerable emphasis has been placed on certain features of the present invention, various modifications can be made, and many additions can be made to the preferred embodiment without departing from the principles of the invention. Modifications to the characteristics of the present invention or the preferred embodiment will be apparent to those skilled in the art, and it should be clearly understood that the foregoing description is merely illustrative of the present invention and should not be construed as limiting.

Claims

1. 1. A piezoelectric single crystal transducer element, said piezoelectric single crystal transducer element comprising: a. A PZN-PT single crystal of predetermined dimensions having an upper and lower active surface; and β. having at least one metallized layer of a predetermined thickness on said upper and lower active surfaces; Here, the crystal is polarized along the [001] direction.

2. 10. A transducer element as claimed in claim 1, wherein said dimensions of said transducer element piezoelectric single crystal are 35 x 30 x 20 mm. 3 From 40 x 40 x 30 mm 3 The range is.

3. 10. A transducer element as claimed in claim 1, wherein said metallization layer is made of at least one metal selected from gold and chromium, and wherein the thickness of said metallization layer is in the range of 250 nm to 350 nm.

4. A transducer element as claimed in claim 1, α. Residual polarization is 24 μC / cm at a frequency of 1 Hz 2 to 27.5 μC / cm 2 is in the range of β. The coercive field is in the range of 3.5 kV / cm to 4.0 kV / cm at a frequency of 1 Hz; χ. Unipolar distortion at a frequency of 1 Hz is in the range of 0.125% to 0.128%; δ. Longitudinal piezoelectric strain coefficient d 33 ranges from 2000 pm / V to 2100 pm / V at a frequency of 1 Hz, ε. Electromechanical coupling coefficient k in the vibration Silver mode 33 ' ranges from 73% to 75%; φ. Longitudinal voltage coefficient g 33 It is characterized by a range of 42 mV.m / N to 50 mV.m / N.

5. The transducer element claimed in claim 1 is adapted for application in high frequency underwater acoustic transducers with frequencies in the range of 100 kHz to 200 kHz as a core component of underwater SONAR, ultrasonic medical transducers, low electric field driven actuators, electroacoustic transducers, and piezoelectric MEMS devices.

6. A transducer element as claimed in claim 1, wherein said transducer element, when applied to a high frequency underwater acoustic transducer having a frequency in the range of 100 kHz to 200 kHz, has a receiving sensitivity that is 10 dB or more higher than that of a 1-3 type piezoelectric composite material.

7. A method for manufacturing a piezoelectric single crystal transducer element comprising: α. PZN-PT single crystals were prepared. β. The PZN-PT single crystal is oriented in a predetermined direction to obtain an oriented PZN-PT single crystal; χ. The oriented PZN-PT single crystal is diced, lapped, and polished in this order to obtain a PZN-PT single crystal having predetermined dimensions and an operating upper surface and an operating lower surface; δ. depositing a metallized layer on the upper and lower working surfaces of the PZN-PT single crystal having predetermined dimensions to obtain a metallized crystal; ε. The metallized crystal is poled in the predetermined direction to obtain a piezoelectric single crystal transducer element.

8. The method as claimed in claim 7, wherein the PZN-PT single crystal obtained in step (a) is prepared by the following steps: mixing a lead precursor, a zinc precursor, a niobium precursor, and a titanium precursor in predetermined amounts to obtain a mixture; placing the mixture in a sealed noble metal vessel having a gas inlet and a gas outlet, and then placing the sealed noble metal vessel within an outer alumina vessel; introducing a predetermined flow of gas through the sealed precious metal vessel while heating the alumina outer vessel at a predetermined heating rate to a first predetermined temperature, and then maintaining the first predetermined temperature for a first predetermined time to obtain a preform; The preform is cooled to a second predetermined temperature at a predetermined cooling rate to obtain the PZN-PT single crystal.

9. 10. A method as claimed in claim 8, wherein said lead precursor is lead oxide.

10. 10. The method as claimed in claim 8, wherein said zinc precursor is zinc oxide.

11. 10. The method as claimed in claim 8, wherein said niobium precursor is niobium oxide.

12. 10. The method as claimed in claim 8, wherein said titanium precursor is titanium oxide.

13. 10. The method as claimed in claim 8, wherein said gas is oxygen.

14. 10. The method as claimed in claim 8, wherein said predetermined amount of said lead precursor ranges from 81% to 82% by weight based on the total weight of said mixture.

15. 10. The method as claimed in claim 8, wherein the predetermined amount of zinc precursor ranges from 4.0% to 4.5% by weight based on the total weight of the mixture.

16. A method as claimed in claim 8, wherein the predetermined amount of niobium precursor ranges from 13% to 14% by weight based on the total weight of the mixture.

17. A method as claimed in claim 8, wherein the predetermined amount of titanium precursor ranges from 0.5% to 1.2% by weight based on the total weight of the mixture.

18. 10. The method as claimed in claim 8, wherein said sealed vessel made of precious metal is a precious metal crucible with a precious metal lid, and wherein said precious metal is at least one precious metal selected from platinum and iridium.

19. A method as claimed in claim 8, wherein said alumina outer vessel is an alumina crucible with an alumina lid.

20. A method as claimed in claim 8, wherein the first predetermined temperature is in the range of 1240°C to 1260°C.

21. A method as claimed in claim 8, wherein said predetermined heating rate is in the range of 60° C. / hour to 80° C. / hour.

22. A method as claimed in claim 8, wherein the second predetermined temperature is in the range of 880°C to 920°C.

23. A method as claimed in claim 8, wherein said first predetermined time period is between 4 and 6 hours.

24. A method as claimed in claim 8, wherein said predetermined cooling rate is in the range of 0.9°C / hour to 1°C / hour.

25. A method as claimed in claim 8, wherein said predetermined gas flow is in the range of 0.7 l / min to 2 l / min.

26. The method as claimed in claim 7, wherein said orientation in the predetermined direction [001] and said orientation in step (b) is performed using backscattered Laue diffraction.

27. 8. The method as claimed in claim 7, wherein said oriented PZN-PT single crystal has predetermined dimensions of 35 x 30 x 20 mm after said dicing, lapping and polishing. 3 From 40 x 40 x 30 mm 3 The range is.

28. The method as claimed in claim 7, wherein the deposition of said metallization layer in step (d) is carried out using a DC magnetron sputtering process.

29. 29. The method as claimed in claim 28, wherein said DC magnetron sputtering is carried out at room temperature for 3 to 5 minutes at a power of 80 W to 100 W.

30. A method as claimed in claim 8, wherein the poling of the metallized crystal involves subjecting the metallized crystal to an electrical contact poling process and applying an electric field cooling method to reach a multi-domain 4R engineered state, wherein a poling field in the range of 5.25 kV / cm to 6.0 kV / cm is applied at room temperature, which is 1.5 times the coercive field.

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