Piezoelectric film and method for manufacturing the same

Abstract

The present invention generally relates to compounds having the empirical formula (K 1‑x Na x ) y A piezoelectric film of NbO3, wherein 0≤x≤1 and 0.64≤y≤0.95. Specifically, the piezoelectric film comprises at least two adjacent NbO2 planes located in an antiphase domain boundary, and the at least two adjacent NbO2 planes are shifted from each other by about half a lattice length in a (100), (010) or (100) crystal plane. The present invention also relates to a method for manufacturing the piezoelectric film.

Description

Technical Field

[0001] The present invention generally relates to piezoelectric thin films. The present invention also relates to a method of manufacturing piezoelectric thin films.

[0002] Background

[0003] Piezoelectric materials are materials that can convert mechanical energy into electrical energy and vice versa. Piezoelectric materials can be used to perform various desired functions. They are widely used as actuators, where a piezoelectric element deforms with the application of an electric field, and as sensors, where any physical quantity can be indirectly detected by utilizing the voltage generated in the piezoelectric element due to deformation.

[0004] Piezoelectric thin films are very thin sheets of piezoelectric materials. Piezoelectric thin films are connected to a substrate and have many practical applications. Some conventional applications of piezoelectric thin films include ultrasonic transducers, micropumps, microcantilever-based mass sensors, inkjet print heads, gyroscopes, and accelerometers. Piezoelectric thin films can be easily integrated into microelectromechanical systems (MEMS). For specific applications, such as fuel injectors, micro Langevin transducers, and nano control systems for optical cavities, etc., a high effective longitudinal piezoelectric coefficient (d 33 *) is required to obtain a large piezoelectric piston-like deformation in piezoelectric thin film actuators.

[0005] The most widely used piezoelectric materials are lead-based perovskite ferroelectrics and are commonly referred to as PZT with the chemical formula PbZr 1-x Ti x O3, 0 < x < 1. PZT has excellent piezoelectric properties at x = 0.48 because two different crystal structures, namely the rhombohedral phase and the tetragonal phase, also known as the morphotropic phase boundary (MPB), coexist simultaneously.

[0006] However, the use of lead-based piezoelectric materials has elevated environmental concerns, and thus, there is a strong demand for lead-free piezoelectric materials due to concerns about lead pollution. Several lead-free piezoelectric materials are being studied, among which ceramic systems based on alkali metal niobates, generally represented by the general formula K 1-x Na x NbO3, 0 < x < 1, have relatively good piezoelectric properties among the tested systems. However, the piezoelectric properties still cannot be compared with those of lead-based piezoelectric materials. In this regard, there is great concern about enhancing the d 33 * of alkali metal niobate-based piezoelectric ceramics. Recent achievements in this direction include obtaining a d 33 * of up to 250 pm / V in a 2.7-μm-thick piezoelectric thin film with phase coexistence, and manufacturing 0.95(K 0.48 Na 0.52 )(Nb 0.95 Sb0.05 )O 3-0.05 Bi 0.5 (Na 0.82 K 0.18 ) 0.5 Complex compositions of ZrO3. However, for practical applications, such complex compositions are challenging in large-scale manufacturing that requires precise control, and there is still a need to improve the piezoelectric properties to compete with lead-based piezoelectric materials.

[0007] With the advancement of technology, there is a need for miniaturization and higher performance for functional components including piezoelectric materials used in electronic devices. Research efforts and industrial developments have been made to reduce the thickness of piezoelectric materials in the form of piezoelectric thin films for various applications. On the other hand, sputtering has been used to fabricate thin film actuators based on alkali metal niobates on Si substrates. However, generally, the piezoelectric properties of thin films based on alkali metal niobates lag far behind those of PZT. For example, by adding a crystal structure to a film composed of particles with a columnar structure, the piezoelectric coefficient can be improved in a piezoelectric thin film having the general formula (Na x K y Li z )NbO3, (0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 0.2, x + y + z = 1), provided that the angle between the columnar crystal axis and the substrate surface normal is in the range of 0° to 10°.

[0008] However, after such great efforts, the piezoelectric properties of thin films based on lead-free alkali metal niobates still cannot be comparable to those of lead-based piezoelectric thin films. Another strategy is to obtain piezoelectric thin films with complex compositions, such as having the chemical formula (K x Na 1-x ) 1-y A y Nb 1-z B z O3, where A = Li, Bi, Ba and B = Sb, Ta, Zr, Hf, 0 < x < 1, 0 < y ≤ 0.06, 0 < z ≤ 0.1, which shows significantly improved piezoelectric properties. Such piezoelectric thin films can be produced by the chemical solution method, where an amorphous thin film is deposited on a substrate. This process is repeated in many cycles until the desired film thickness is obtained. In the large-scale production of such piezoelectric thin films derived from chemical solutions with complex compositions, it is challenging to control the processing, composition, and thus the performance consistency.

[0009] Piezoelectric films are typically prepared on Si or MgO substrates buffered with a thin layer of Pt. A (111) oriented Pt layer with a thickness of no more than 200 nm is prepared on an oxidized Si substrate to obtain a piezoelectric polycrystalline film based on alkali metal niobates, which has grains preferentially oriented in the

[001] crystal direction. Alternatively, a perovskite oxide layer such as LaNiO3 can also be prepared on top of the Pt layer to obtain similar or better results. However, such piezoelectric films are not absolutely oriented in the (001) direction and may have only 80-90% orientation in the (001) direction. In addition, during the heat treatment of the piezoelectric layer, it is very difficult to avoid the pyrochlore phase in piezoelectric films based on alkali metal niobates due to evaporation of the alkali metal.

[0010] It would be desirable to overcome or ameliorate at least one of the above problems, or at least provide a useful alternative.

[0011] Overview

[0012] The present invention is based on the following discovery: a large longitudinal piezoelectric coefficient can be obtained in an alkali metal niobate-based piezoelectric epitaxial film having the formula (K,Na)NbO3 grown on a (001) oriented single crystal substrate, such that the (K+Na) / Nb ratio is about 0.64 to about 0.95. And because the film is composed of columnar crystals perpendicular to the film surface and separated by antiphase domain boundaries, its density can be controlled by controlling the (K+Na) / Nb ratio in the film.

[0013] The present invention provides a piezoelectric film element, comprising:

[0014] a) a piezoelectric film having an empirical formula (K 1-x Na x ) y NbO3, wherein 0≤x≤1 and 0.64≤y≤0.95; and

[0015] b) a single crystal substrate having a (001), (010) or (100) crystal plane perpendicular to the surface;

[0016] wherein the piezoelectric film is adjacent to the surface of the single crystal substrate, and the piezoelectric film is oriented so that its (001) crystal plane is substantially parallel to a (001), (010) or (100) crystal plane of the single crystal substrate; and

[0017] The piezoelectric film includes at least two adjacent NbO2 planes located in an antiphase domain boundary, and the at least two adjacent NbO2 planes are shifted from each other by about half a lattice length in a (100), (010) or (100) crystal plane.

[0018] Advantageously, having a (K+Na) / Nb ratio greater than or equal to 0.64 and less than or equal to 0.95 in a piezoelectric film grown on, for example, a (001) oriented single crystal substrate results in the formation of imperfect grain boundaries in which NaO / KO planes are missing and two adjacent NbO2 planes are arranged in anti-phase with respect to each other (anti-phase domain boundaries). Advantageously, this allows the effective longitudinal piezoelectric coefficient (d 33 *) Increase by at least 1000pm / V.

[0019] In certain embodiments, the piezoelectric film has columnar crystals oriented in the corresponding

[001] ,

[010] , or

[100] directions.

[0020] In certain embodiments, at least two adjacent NbO2 planes located in an antiphase boundary are shifted from each other by about 0.220 nm to about 0.260 nm in the (100), (010), or (100) crystal planes.

[0021] In some embodiments, the density of the antiphase domain boundaries of the piezoelectric film is about 0.05 nm -1 to about 0.30nm -1 .

[0022] In certain embodiments, the piezoelectric film has an effective longitudinal piezoelectric coefficient (d ) of about 1200 pm / V to about 1700 pm / V at an applied voltage of about 60 kV / cm and a frequency of about 1 kHz. 33 *).

[0023] In certain embodiments, the piezoelectric film has a columnar structure, and the columnar crystals have a width of about 3 nm to about 6 nm.

[0024] In certain embodiments, the piezoelectric film has a thickness of about 100 nm to about 500 nm.

[0025] In certain embodiments, the substrate is an optionally doped perovskite single crystal.

[0026] In certain embodiments, the substrate is selected from SrTiO3, LaAlO3, DyScO3, (La, Sr)(Al, Ti)O3, Si, NdGaO3, LiTaO3, YAlO3, La x Sr 1-x FeO3、La x Ca 1-x FeO3、La x Sr 1-x CoO3、La x Sr 1-x Perovskite single crystals of MnO3, LaNiO3 and SrRuO3.

[0027] In certain embodiments, the piezoelectric film further includes a perovskite oxide layer sandwiched between the piezoelectric film and the substrate.

[0028] In certain embodiments, the perovskite oxide layer is selected from La x Sr 1-x FeO3、La x Ca 1-x FeO3、La x Sr 1-x CoO3、La x Sr 1-x MnO3, LaNiO3 and SrRuO3.

[0029] In certain embodiments, the perovskite oxide layer has a thickness of about 1 nm to about 300 nm.

[0030] In certain embodiments, the piezoelectric film element further includes an electrode stacked on top of the piezoelectric film.

[0031] In certain embodiments, the electrode is selected from Pt, Au, Ag, Cu, Cr, Al, La x Sr 1-x FeO3、La x Ca 1-x FeO3、La x Sr 1-x CoO3、La x Sr 1-x MnO3, LaNiO3 and SrRuO3.

[0032] The present invention also provides a piezoelectric device, comprising:

[0033] a) a piezoelectric thin film element as disclosed herein; and

[0034] b) at least two electrodes in contact with the piezoelectric film.

[0035] In certain embodiments, a single crystal substrate is one of at least two electrodes in a piezoelectric device.

[0036] The present invention also provides a method for manufacturing a piezoelectric thin film element, comprising:

[0037] A single crystal substrate is formed with the empirical formula (K 1-x Na x ) y Piezoelectric film of NbO3, wherein 0≤x≤1 and 0.64≤y≤0.95;

[0038] wherein the single crystal substrate has a (001), (010) or (100) crystal plane perpendicular to the surface;

[0039] wherein the piezoelectric film is adjacent to the surface of the single crystal substrate, and the piezoelectric film is oriented so that its (001), (010) or (100) crystal plane is substantially parallel to the (001), (010) or (100) crystal plane of the single crystal substrate; and

[0040] The piezoelectric film includes at least two adjacent NbO2 planes located in an antiphase domain boundary, and the at least two adjacent NbO2 planes are shifted from each other by about half a lattice length in a (100), (010) or (100) crystal plane.

[0041] In certain embodiments, the step of forming the piezoelectric film includes depositing the piezoelectric film using sputtering.

[0042] In certain embodiments, the step of forming the piezoelectric film comprises sputtering at a substrate temperature of about 680° C. and a discharge power of about 120W.

[0043] In certain embodiments, sputtering is performed for at least 2 hours.

[0044] In certain embodiments, sputtering is performed at an argon-to-oxygen ratio (Ar / O) of about 50 / 15.

[0045] In certain embodiments, at about 3.5×10 -3 Sputtering was performed at a total pressure of mtorr.

[0046] In certain embodiments, the sputtering angle, substrate-target distance, argon-oxygen ratio, and / or deposition temperature are controlled such that the (K+Na) / Nb ratio is from about 0.64 to about 0.95.

[0047] In certain embodiments, the vertical distance between the target and the substrate is between about 5 cm and 15 cm.

[0048] In certain embodiments, the angle between the target normal and the substrate normal is an obtuse angle.

[0049] In certain embodiments, the method further comprises the step of cutting and polishing the surface of the single crystal substrate having (001), (010) or (100) crystal planes perpendicular to the surface before the sputtering.

[0050] BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Embodiments of the invention will now be described by way of non-limiting examples with reference to the accompanying drawings, in which:

[0052] Figure 1 A schematic diagram showing a perovskite unit cell of (K,Na)NbO3 is shown;

[0053] Figure 2 shows a regular perfect boundary 1 and has a shift of 1 / 2a <100> Schematic diagram of the antiphase domain boundary 2 of the NbO2 plane at a distance;

[0054] Figure 3 A structural diagram showing a piezoelectric thin film element (a piezoelectric thin film 4 manufactured on a conductive single crystal substrate 3) is shown;

[0055] Figure 4 A structural diagram of a conductive perovskite layer 6 between a piezoelectric film 4 and an insulating single crystal substrate 5 is shown;

[0056] Figure 5 The structure diagram of the top electrode 7 on the piezoelectric film 4 made on the conductive single crystal substrate 3 is shown;

[0057] Figure 6 A structural diagram showing a top electrode 7 on a piezoelectric film 4 with an underlying conductive perovskite layer 6 and an insulating single crystal substrate 5;

[0058] Figure 7 A bright field scanning transmission electron micrograph of an exemplary piezoelectric film cross section is shown, showing a 300 nm thick piezoelectric film 9 on a conductive 0.5% Nb-doped SrTiO 3 single crystal substrate 8 according to Example 1;

[0059] Figure 8 shows a high-angle annular dark-field scanning transmission electron micrograph of the surface of a piezoelectric film, showing fine grains separated by niobium-rich antiphase domain boundaries according to Example 1 (only Nb atoms are visible in the micrograph);

[0060] Fig. 9 An enlarged high-angle annular dark-field scanning transmission electron micrograph of the antiphase domain boundary enclosed in the rectangle is shown (only Nb atoms are visible in the micrograph);

[0061] Fig.10 An exemplary piezoelectric response of a piezoelectric film to which a sinusoidal wave electrical signal with a frequency of 1 kHz is applied according to Example 1 is shown;

[0062] Fig.11 An exemplary bright field scanning transmission electron micrograph of a cross section of a piezoelectric film is shown, showing a 300 nm thick piezoelectric film on a conductive 0.5% Nb-doped SrTiO3 single crystal substrate according to Example 2; and

[0063] Fig.12 An exemplary piezoelectric response of the piezoelectric film according to Example 2 to which a sinusoidal wave electrical signal having a frequency of 1 kHz is applied is shown.

[0064] Details

[0065] The present invention is based on the general formula K 1-xNa x Sodium potassium niobate of NbO3, where 0 < x < 1 (also known as KNN). KNN is a lead-free piezoelectric ceramic system with a perovskite structure. In the form of a piezoelectric thin film, it exists in an orthorhombic or tetragonal structure, with potassium (K) or sodium (Na) at the A position (the vertex position of the lattice), niobium (Nb) at the B position (the body-centered position of the lattice), and oxygen (O) around Nb forming an octahedron (see Figure 1 ).

[0066] The inventors have reviewed past work and found that by specifically adjusting the ratio of alkali metal to Nb and controlling its crystal growth, the piezoelectric properties of alkali metal niobate thin films can be improved.

[0067] In this regard, existing piezoelectric thin films with the general formula (K 1-x Na x ) y NbO3 show that when 0.4 ≤ x ≤ 0.7 and y is close to 1, the typical piezoelectric property of d 33 is lower than 180 pm / V (considering that d 31 is usually approximately -d 33 / 2). In another example, polycrystalline alkali metal niobate thin films with the general formula (K 1-x Na x ) y NbO3 grown on a Pt-buffered Si substrate can improve the piezoelectric coefficient, i.e., up to d 33 = 218 pm / V, where 0.4 ≤ x ≤ 0.7 and 0.75 ≤ y ≤ 0.90. In another example, when the (001) crystal peak occupies 80% or more of the diffraction pattern, piezoelectric thin films with the general formula (K 1-x Na x ) y NbO3 (0 < x < 1) show piezoelectric properties.

[0068] Therefore, the present invention is based on the opposite understanding to that of polycrystalline films. Single crystal films grow due to the perfect atomic arrangement determined by the terminating substance on the substrate surface. For example, in the island growth mode of KNN films with a (K + Na) / Nb ratio close to 1, different grains nucleate from the surface of the substrate and combine with continuous grain boundaries [see 1 in Figure 2 . It has been found that when the (K + Na) / Nb ratio is less than 1 in a KNN piezoelectric thin film grown on a single crystal substrate with, for example, a 001 orientation, some particles show atypical nucleation and result in the formation of imperfect grain boundaries when grown on a single crystal substrate lacking the NaO / KO plane. In particular, two adjacent NbO2 planes can be arranged in antiphase with each other [see Figure 2The arrangement of the antiphase boundaries causes one of the adjacent NbO2 layers to shift horizontally by half the lattice length (1 / 2 <100> a or 1 / 2 <010> a) and the distance between NbO2 planes is in the range of 0.225 to 0.252 nm.

[0069] Based on this understanding, the inventors have found that, in general, a compound having the general formula (K 1-x Na x ) y NbO3 based piezoelectric thin films, in (K 1-x Na x ) y The (K+Na) / Nb ratio in the NbO3 film is less than 1, and the above-mentioned antiphase boundaries can be formed when grown on a single crystal substrate. Specifically, the (K+Na) / Nb ratio can be about 0.64 to about 0.95. In addition, such films with antiphase boundaries can have large d 33 *, up to 1621.9 pm / V was measured at an applied voltage and frequency of 58.3 kV / cm and 1 kHz, respectively. The density of antiphase boundaries (the number of antiphase boundaries per unit length of the lattice) increases with decreasing (K+Na) / Nb ratio, such that when the (K+Na) / Nb ratio is between 0.95 and 0.64, the density of antiphase boundaries is between 0.08 and 0.23 nm -1 In addition, the d of 1621.9pm / V 33 *Can be used with 0.23nm -1 The density of antiphase boundaries and a (K+Na) / Nb ratio equal to 0.64 are achieved in thin films. Therefore, when grown on a single crystal substrate, the d of alkali niobate thin films can be controlled by adjusting the content of Nb in the film relative to the alkali metals K and Na. 33 *. In addition, the thickness of the film of the present invention (about 300 nm) can be much thinner than the films disclosed in the previous inventions.

[0070] For the avoidance of doubt, as used herein, "piezoelectric film element" refers to a piezoelectric film combined with a substrate. "Piezoelectric film" refers to the membrane portion only; that is, without the substrate.

[0071] A substrate is usually required to grow piezoelectric thin films. Although the substrate is a support for the thin film during the growth process, the substrate can also be an essential component that gives the thin film the desired structure during the growth process. The inventors have discovered and as presented in certain embodiments, a

[001] oriented substrate can be used to obtain a thin film with high d 33In other embodiments, a substrate with a

[010] or

[100] orientation can also be used. It should be noted that in the form of a final product, the piezoelectric film can be used without a substrate; that is, the substrate can be removed after the piezoelectric film is formed. For example, a water-soluble single crystal substrate and / or an organic single crystal substrate can be used.

[0072] In certain embodiments, the piezoelectric film element is composed of a piezoelectric film and a substrate. The substrate can be a conductive single crystal having a perovskite structure, such as 0.5% Nb-doped SrTiO3. The substrate is cut and polished perpendicular to one of the main crystal axes, such as (001). A piezoelectric film is manufactured on top of the substrate. The piezoelectric film has the general formula (K, Na) NbO3 and has a (K + Na) / Nb ratio of about 0.64 to about 0.95, and has a preferred orientation in, for example, the

[001] crystal direction, with columnar crystals oriented parallel to the normal to the film surface. These columnar crystals are separated from each other by antiphase boundaries (APBs), so that when the (K + Na) / Nb ratio is between 0.95 and 0.64, respectively, the density of the antiphase boundaries is between 0.080.23nm -1 APBs make the KO or NaO layer missing in the conventional perovskite structure, and two NbO2 layers are adjacent to each other at the antiphase boundary. In addition, one of these adjacent NbO2 layers is moved 1 / 2a from its normal position. <100> or 1 / 2a <010> , where “a” is the lattice parameter of the perovskite unit cell in the horizontal direction.

[0073] Other crystal axes can also be used. For example, the (001), (010) and (100) crystal axes of the substrate can be used, which results in the corresponding piezoelectric film having a (001), (010) or (100) crystal orientation with columnar crystals oriented parallel to the normal to the film surface.

[0074] As used herein, round brackets, such as (001), are used to indicate crystal planes, while square brackets, such as

[001] , are used to indicate crystal directions.

[0075] The empirical formula of a chemical is a simple expression of the relative number of each type of atom or the ratio of elements in a compound. The empirical formula is standard for ionic compounds such as CaCl2 and macromolecules such as SiO2. The empirical formula makes no reference to the isomerism, structure, or absolute number of atoms. The term empirical refers to the method of elemental analysis, an analytical chemistry technique used to determine the relative percentage composition of a pure chemical substance by elements. For example, hexane has C6H 14The molecular formula or structure of hexane is CH3CH2CH2CH2CH2CH3, which means it has a chain structure of 6 carbon atoms and 14 hydrogen atoms. However, the empirical formula of hexane is C3H7. Likewise, the empirical formula of hydrogen peroxide, H2O2, is simply HO, which expresses a 1:1 ratio of the component elements. Formaldehyde and acetic acid have the same empirical formula of CH2O. This is the actual chemical formula of formaldehyde, but acetic acid has twice the number of atoms.

[0076] The present invention is based on a piezoelectric film grown on a single crystal substrate having a (001), (010) or (100) direction parallel to the film growth direction. By using a single crystal substrate, 100% orientation, such as the

[001] crystal direction, is achieved in the alkali metal-based piezoelectric film. In this regard, the piezoelectric film is completely or at least substantially oriented in the

[001] direction and / or the (001) plane. In addition, the piezoelectric film can be free of a secondary pyrochlore phase. To achieve this, the lattice parameter in the horizontal plane of the substrate is preferably close to (or matches) the lattice parameter in the horizontal plane of the piezoelectric film.

[0077] In certain embodiments, the piezoelectric film has an effective longitudinal piezoelectric coefficient d of 1621.9 pm / V when the applied voltage and frequency are 58.3 kV / cm and 1 kHz, respectively. 33 *. This exceeds commercially available lead-based piezoelectric films. In addition, the piezoelectric film is free of other foreign elements, which are necessary to increase the piezoelectric performance to such an extent. In addition, the piezoelectric film is manufactured using a sputtering process.

[0078] As described above, the piezoelectric film of the present invention can obtain an effective longitudinal piezoelectric coefficient d of 1621.9 pm / V at a driving voltage of 58.3 kV / cm and a frequency of 1 kHz. 33 *. Advantageously, this is a higher longitudinal piezoelectric response than existing lead-based and lead-free piezoelectric films. This also opens up the possibility of developing more sensitive and energy-efficient lead-free electromechanical devices.

[0079] In addition, by growing thin films on single-crystalline substrates, the high density of antiphase boundaries can lead to large d 33 *. Antiphase boundaries can be generated, and the density of antiphase boundaries can be controlled by adjusting the niobium content relative to the alkali metal in the film. In this case, the Nb content in the sputtering target directly affects the amount of Nb in the film. Advantageously, the d of the piezoelectric film can be significantly increased simply by adjusting the stoichiometry of the target composition during sputtering, compared to conventional methods of generating phase boundaries by adding expensive dopants. 33 *. This simple method offers the advantage of improved reproducibility and thus the opportunity for large-scale production.

[0080] Advantageously, the piezoelectric film, piezoelectric film element and / or device complies with the Restriction of Hazardous Substances (RoHS), which currently restricts the use of lead in consumer products. Due to the unavailability of suitable substitutes, the current workaround is the use of PZT in electronic products that have now been exempted from RoHS. The present invention may potentially lead to lead-free piezoelectric materials replacing PZT in many devices and applications.

[0081] Advantageously, a higher d 33 * Enables piezoelectric film actuators to be driven at very low voltage, thus facilitating further miniaturization and broadening their applications. High d of 1621.9 pm / V 33 * Significantly higher than lead-based counterparts used commercially for practical applications. In addition, such high piezoelectric constants are achieved without the addition of complex dopants, and the piezoelectric films are prepared by a simple sputtering process.

[0082] A typical sensor or actuator device based on a piezoelectric film has at least two electrodes to connect to a voltmeter to measure the deviation or to a voltage source to drive the actuation. In some embodiments, the substrate can be conductive and can serve as one of the electrodes (see Figure 3 3). For example, one of these electrodes can be a conductive substrate used in the growth process, i.e., the piezoelectric thin film element. In some embodiments, a Nb-doped SrTiO3 conductive substrate is used. In the Nb-doped substrate, the Nb can make the SrTiO3 conductive (SrTiO3 is an insulator). In other embodiments, an intrinsic conductive substrate can also be used.

[0083] Insulating perovskite single crystals including but not limited to SrTiO3, LaAlO3, DyScO3, (La, Sr)(Al, Ti)O3, Si, NdGaO3, LiTaO3, YAlO3 can also be used (see Figure 4 ). The inventors have found that the piezoelectric film of the present invention can be manufactured using an insulating substrate. However, it has been found that its applicability as a device is limited. Therefore, to address this, the inventors have found that a conductive perovskite layer can be located between the piezoelectric film and the substrate. Therefore, the conductive layer can act as a bottom electrode for the device. In this case, the conductive layer of the conductive perovskite 6, preferably including but not limited to La x Sr 1-x FeO3、La x Ca 1-x FeO3、La x Sr 1-x CoO3、La x Sr 1-x Metal oxides of MnO3, LaNiO3, and SrRuO3 are formed on top of the above insulating substrate (see Figure 4). Typically, the thickness of the conductive electrode is between 1 and 250 nm.

[0084] The electrode 7 can be deposited on the top surface of the piezoelectric film (see Figure 5 and 6 ). The top electrode is preferably a metal, such as, but not limited to, Pt, Au, Ag, Cu, Cr, Al or a conductive perovskite as previously listed. The top layer is preferably deposited by using a sputtering or vapor deposition method, or an electroplating method or a slurry coating method.

[0085] Also disclosed herein is a method for making a piezoelectric film having the general formula (K,Na)NbO3 and a (K+Na) / Nb ratio of about 0.64 to about 0.95. For the embodiments of the invention discussed below, the substrate is a 5 mm×5 mm×0.5 mm, 0.5% Nb-doped SrTiO3 conductive perovskite single crystal cut and polished perpendicular to the (001) crystal plane. The piezoelectric film is directly formed thereon by radio frequency magnetron sputtering at a substrate temperature of 680°C, and the discharge power used is 120 W. Other conditions are: at 3.5×10 - 3 At a total pressure of 100 mtorr, the chamber gas was Ar / O=50 / 15 and the sputtering duration was 2 hours. In addition, a 200 μm diameter Pt electrode with a thickness of 100 nm can be deposited at room temperature using a mask with a sputtering power of 80 W and a duration of 10 minutes. For (K,Na)NbO3 films, the (K+Na) / Nb ratio can be controlled by adjusting the Nb content in the sputtering target. For a (K+Na) / Nb ratio less than 1, when the (K+Na) / Nb ratio is 1, excess Nb can be added to the sputtering target compared to the stoichiometric target. Similarly, (K+Na) / Nb can also be controlled by adjusting the sputtering angle, substrate-target distance, argon-oxygen ratio and / or deposition temperature.

[0086] Therefore, the present invention provides a piezoelectric thin film element, comprising:

[0087] a) a piezoelectric thin film having the formula (K,Na)NbO3 and the film having a (K+Na) / Nb ratio of about 0.64 to about 0.95; and

[0088] b) a single crystal substrate having a (001), (010) or (100) crystal plane perpendicular to the surface;

[0089] The piezoelectric film is adjacent to a surface of the single crystal substrate, and is oriented such that its (001), (010) or (100) crystal plane is parallel to the (001), (010) or (100) crystal plane of the single crystal substrate.

[0090] In this regard, the piezoelectric film is oriented so that its (001) crystal plane is parallel to the (001), (010) or (100) crystal plane of the single crystal substrate. The piezoelectric film can also be oriented so that its (010) crystal plane is parallel to the (001), (010) or (100) crystal plane of the single crystal substrate. The piezoelectric film can also be oriented so that its (100) crystal plane is parallel to the (001), (010) or (100) crystal plane of the single crystal substrate.

[0091] It should be understood that as long as the "atomic spacing information" from the crystal plane can be imparted from the substrate to the formed piezoelectric film, the piezoelectric film does not have to be in physical and / or chemical contact with the substrate. In this regard, the piezoelectric film adjacent to the surface of the single crystal substrate is in close proximity to the surface of the single crystal substrate. This means that the piezoelectric film can be physically and / or chemically contacted / connected to the surface of the single crystal substrate (without an intermediate structure in between), or spaced / separated from the surface of the single crystal substrate by a small distance / space (through an intermediate structure in between). Therefore, the "information" is directly relayed from the substrate, allowing the formation of a piezoelectric film in physical and / or chemical contact with the substrate. This means that when the piezoelectric film is grown on the substrate, the single crystal substrate has perfect atomic alignment with the piezoelectric film, and these atoms are chemically bonded to each other. When the "information" is relayed indirectly through the intermediate structure, the "information" from the substrate is transmitted and contained in the intermediate structure, which is then transmitted to the formed piezoelectric film. For example, the intermediate structure can be a conductive film grown on the substrate, which has the same (or substantially the same) crystal plane orientation as the substrate. To this end, the intermediate structure can be crystallographically similar to the substrate (single crystal with the same orientation), such that the intermediate structure is chemically bonded to the thin film and the substrate, but may have different physical properties (eg, electrical conductivity).

[0092] In certain embodiments, the present invention provides a piezoelectric film element comprising:

[0093] a) a piezoelectric thin film having the formula (K,Na)NbO3 and the film having a (K+Na) / Nb ratio of about 0.64 to about 0.95; and

[0094] b) a single crystal substrate having a (001), (010) or (100) crystal plane perpendicular to the surface;

[0095] The piezoelectric film is adjacent to the surface of the single crystal substrate, and is oriented so that its (001), (010) or (100) crystal plane is parallel to the corresponding (001), (010) or (100) crystal plane of the single crystal substrate.

[0096] In certain embodiments, if the single crystal substrate has a (001) crystal plane perpendicular to the surface, the piezoelectric film is oriented so that its (001) crystal plane is parallel to the (001) crystal plane of the single crystal substrate. In other embodiments, if the single crystal substrate has a (010) crystal plane perpendicular to the surface, the piezoelectric film is oriented so that its (010) crystal plane is parallel to the (010) crystal plane of the single crystal substrate. In other embodiments, if the single crystal substrate has a (100) crystal plane perpendicular to the surface, the piezoelectric film is oriented so that its (100) crystal plane is parallel to the (100) crystal plane of the single crystal substrate.

[0097] In certain preferred embodiments, a SrTiO3 (STO) single crystal substrate is used. The STO substrate is cubic, so (001), (010) and (100) are equivalent planes. In this sense, no matter which substrate orientation of STO is used, the piezoelectric film plane parallel to the substrate plane (perpendicular to the surface) will be (001).

[0098] Therefore, in certain embodiments, the present invention provides a piezoelectric film element comprising:

[0099] a) a piezoelectric thin film having the formula (K,Na)NbO3 and the film having a (K+Na) / Nb ratio of about 0.64 to about 0.95; and

[0100] b) a single crystal substrate having a (001), (010) or (100) crystal plane perpendicular to the surface;

[0101] The piezoelectric film is adjacent to a surface of the single crystal substrate, and the piezoelectric film is oriented such that a (001) crystal plane thereof is parallel to a (001), (010) or (100) crystal plane of the single crystal substrate.

[0102] In certain embodiments, y is less than 0.95. In other embodiments, y is less than or equal to 0.95. In other embodiments, 0.60≤y≤0.95 or 0.60≤y≤0.90 or 0.60≤y≤0.85 or 0.60≤y≤0.80 or 0.60≤y≤0.75.

[0103] In certain embodiments, the piezoelectric film element comprises:

[0104] a) a piezoelectric film having an empirical formula (K 1-x Na x ) y NbO3, wherein 0≤x≤1 and y≤0.95; and

[0105] b) a single crystal substrate having a (001), (010) or (100) crystal plane perpendicular to the surface;

[0106] wherein the piezoelectric thin film is adjacent to the surface of the single crystal substrate, and the piezoelectric thin film is oriented such that its (001), (010), or (100) crystal plane is substantially parallel to the (001), (010), or (100) crystal plane of the single crystal substrate.

[0107] In certain embodiments, the piezoelectric thin film has the empirical formula (K 1-x Na x ) y NbO3, where 0 ≤ x ≤ 1 and 0.64 < y ≤ 0.95. In other embodiments, the piezoelectric thin film has the empirical formula (K 1-x Na x ) y NbO3, where 0 ≤ x ≤ 1 and 0.64 ≤ y ≤ 0.95.

[0108] In certain embodiments, the piezoelectric thin film element comprises:

[0109] a) a piezoelectric thin film having the empirical formula (K 1-x Na x ) y NbO3, where 0 ≤ x ≤ 1 and 0.64 ≤ y ≤ 0.95; and

[0110] b) a single crystal substrate having a (001), (010), or (100) crystal plane perpendicular to the surface;

[0111] wherein the piezoelectric thin film is adjacent to the surface of the single crystal substrate, and the piezoelectric thin film is oriented such that its (001), (010), or (100) crystal plane is substantially parallel to the (001), (010), or (100) crystal plane of the single crystal substrate.

[0112] In certain embodiments, the piezoelectric thin film element comprises:

[0113] a) a piezoelectric thin film having the empirical formula (K 1-x Na x ) y NbO3, where 0 ≤ x ≤ 1 and 0.64 ≤ y ≤ 0.95; and

[0114] b) a single crystal substrate having a (001), (010), or (100) crystal plane perpendicular to the surface;

[0115] wherein the piezoelectric thin film is adjacent to the surface of the single crystal substrate, and the piezoelectric thin film is oriented such that its (001), (010), or (100) crystal plane is substantially parallel to the corresponding (001), (010), or (100) crystal plane of the single crystal substrate, or the (001) crystal plane of the single crystal substrate.

[0116] In certain embodiments, the piezoelectric film element comprises:

[0117] a) With empirical formula (K 1-x Na x ) y A piezoelectric film of NbO3, wherein 0≤x≤1 and 0.64≤y≤0.95; and

[0118] b) a single crystal substrate having a (001), (010) or (100) crystal plane perpendicular to the surface;

[0119] The piezoelectric film is adjacent to a surface of the single crystal substrate and is oriented such that its (001), (010) or (100) crystal plane is substantially parallel to the corresponding (001), (010) or (100) crystal plane of the single crystal substrate.

[0120] In certain embodiments, the piezoelectric film element comprises:

[0121] a) With empirical formula (K 1-x Na x ) y A piezoelectric film of NbO3, wherein 0≤x≤1 and 0.64≤y≤0.95; and

[0122] b) a cubic single crystal substrate having (001), (010) or (100) crystal planes perpendicular to the surface;

[0123] The piezoelectric film is adjacent to a surface of the single crystal substrate, and the piezoelectric film is oriented such that a (001) crystal plane thereof is substantially parallel to a (001), (010) or (100) crystal plane of the single crystal substrate.

[0124] In certain embodiments, the piezoelectric film element comprises:

[0125] a) With empirical formula (K 1-x Na x ) y A piezoelectric film of NbO3, wherein 0≤x≤1 and 0.64≤y≤0.95; and

[0126] b) a single crystal substrate having a (001), (010) or (100) crystal plane perpendicular to the surface;

[0127] wherein the piezoelectric film is adjacent to a surface of the single crystal substrate, and the piezoelectric film is oriented such that a (001), (010) or (100) crystal plane thereof is substantially parallel to a (001), (010) or (100) crystal plane of the single crystal substrate;

[0128] wherein the piezoelectric film has columnar crystals oriented in the corresponding

[001] ,

[010] or

[100] directions; and

[0129] The piezoelectric film includes at least two adjacent NbO2 planes located in the anti-phase domain boundary.

[0130] In one aspect, the present invention provides a piezoelectric thin film element, comprising:

[0131] a) a piezoelectric film having an empirical formula (K 1-x Na x ) y NbO3, wherein 0≤x≤1 and 0.64≤y≤0.95; and

[0132] b) a single crystal substrate having a (001), (010) or (100) crystal plane perpendicular to the surface;

[0133] wherein the piezoelectric film is adjacent to a surface of the single crystal substrate, and the piezoelectric film is oriented such that a (001), (010) or (100) crystal plane thereof is substantially parallel to a (001), (010) or (100) crystal plane of the single crystal substrate; and

[0134] The piezoelectric film includes at least two adjacent NbO2 planes located in an antiphase domain boundary, and the at least two adjacent NbO2 planes are shifted from each other by about half a lattice length in a (100), (010) or (100) crystal plane.

[0135] In certain embodiments, the piezoelectric film element comprises:

[0136] a) a piezoelectric film having an empirical formula (K 1-x Na x ) y NbO3, wherein 0≤x≤1 and 0.64≤y≤0.95; and

[0137] b) a single crystal substrate having a (001) crystal plane perpendicular to the surface;

[0138] wherein the piezoelectric film is adjacent to a surface of the single crystal substrate, and the piezoelectric film is oriented such that a (001) crystal plane thereof is substantially parallel to a (001) crystal plane of the single crystal substrate; and

[0139] The piezoelectric film includes at least two adjacent NbO2 planes located in an antiphase domain boundary, and the at least two adjacent NbO2 planes are shifted from each other by about half a lattice length in a (100), (010) or (100) crystal plane.

[0140] In certain embodiments, the piezoelectric film is oriented so that its (001) crystal plane is completely parallel to the (001) crystal plane of the single crystal substrate. In other embodiments, the piezoelectric film is oriented so that its (010) crystal plane is completely parallel to the (010) crystal plane of the single crystal substrate. In other embodiments, the piezoelectric film is oriented so that its (100) crystal plane is completely parallel to the (100) crystal plane of the single crystal substrate. At this point, 100% of the piezoelectric film is oriented parallel to the single crystal substrate. In certain embodiments, the piezoelectric film is oriented so that its (001) crystal plane is substantially parallel to the (001) crystal plane of the single crystal substrate. In certain embodiments, the piezoelectric film is oriented so that its (010) crystal plane is substantially parallel to the (010) crystal plane of the single crystal substrate. In certain embodiments, the piezoelectric film is oriented so that its (100) crystal plane is substantially parallel to the (100) crystal plane of the single crystal substrate. As used herein, the piezoelectric film is oriented substantially parallel to the single crystal substrate means that at least 90%, at least 92%, at least 94%, at least 96%, at least 98%, or at least 99% of the piezoelectric film is oriented parallel to the single crystal substrate. Preferably, the piezoelectric film is oriented 100% parallel to the single crystal substrate.

[0141] In some embodiments, the piezoelectric film has columnar crystals oriented in the

[001] direction. In some embodiments, the piezoelectric film has columnar crystals oriented in the

[010] direction. In some embodiments, the piezoelectric film has columnar crystals oriented in the

[100] direction.

[0142] In certain embodiments, the piezoelectric film includes at least two adjacent NbO2 planes located in an antiphase boundary. In certain embodiments, the piezoelectric film includes at least two adjacent NbO2 planes located in an antiphase boundary, and the at least two adjacent NbO2 planes are shifted from each other by about half a lattice length in a (001), (100) or (010) crystal plane. In this regard, at least two NbO2 planes are in contact with each other and shifted from each other by about half a lattice length.

[0143] In certain embodiments, at least two adjacent NbO2 planes located in the antiphase boundary are shifted from each other by about 0.220 nm to about 0.260 nm in the (100) crystal plane. In this regard, at least two NbO2 planes are in contact with each other and shifted from each other by about 0.220 nm to about 0.260 nm.

[0144] In certain embodiments, at least two adjacent NbO2 planes located in the antiphase boundary are shifted from each other by about 0.220 nm to about 0.260 nm in the (010) crystal plane. In this regard, at least two NbO2 planes are in contact with each other and shifted from each other by about 0.220 nm to about 0.260 nm.

[0145] In certain embodiments, at least two adjacent NbO2 planes located in the antiphase boundary are shifted from each other by about 0.220 nm to about 0.260 nm in the (001) crystal plane. In this regard, at least two NbO2 planes are in contact with each other and shifted from each other by about 0.220 nm to about 0.260 nm.

[0146] In some embodiments, the density of the antiphase domains of the piezoelectric film is about 0.05 nm. -1 to about 0.30nm -1 In other embodiments, the density of the antiphase boundaries of the piezoelectric film is about 0.10 nm -1 to about 0.30nm -1 , about 0.15nm -1 to about 0.30nm -1 or about 0.20nm -1 to about 0.30nm -1 .

[0147] In certain embodiments, the piezoelectric film element comprises:

[0148] a) With empirical formula (K 1-x Na x ) y A piezoelectric film of NbO3, wherein 0≤x≤1 and 0.64≤y≤0.95; and

[0149] b) a single crystal substrate having a (001) crystal plane perpendicular to the surface;

[0150] wherein the piezoelectric film is adjacent to a surface of the single crystal substrate, and the piezoelectric film is oriented such that a (001) crystal plane thereof is substantially parallel to a (001) crystal plane of the single crystal substrate;

[0151] wherein the piezoelectric film has columnar crystals oriented in the

[001] direction; and

[0152] The piezoelectric film includes at least two adjacent NbO2 planes located in the anti-phase domain boundary.

[0153] In certain embodiments, the piezoelectric film has an effective longitudinal piezoelectric coefficient (d 33 *). In other embodiments, d 33 *From about 1000 pm / V to about 2000 pm / V or from about 1200 pm / V to about 1700 pm / V at an applied voltage of about 60 kV / cm and a frequency of about 1 kHz.

[0154] In certain embodiments, the piezoelectric film element comprises:

[0155] a) With empirical formula (K1-x Na x ) y A piezoelectric film of NbO3, wherein 0≤x≤1 and 0.64≤y≤0.95; and

[0156] b) a single crystal substrate having a (001) crystal plane perpendicular to the surface;

[0157] wherein the piezoelectric film is adjacent to a surface of the single crystal substrate, and the piezoelectric film is oriented such that a (001) crystal plane thereof is substantially parallel to a (001) crystal plane of the single crystal substrate;

[0158] wherein the piezoelectric film has columnar crystals oriented in the

[001] direction;

[0159] wherein the piezoelectric film comprises at least two adjacent NbO2 planes located in an antiphase domain boundary; and

[0160] The piezoelectric film has an effective longitudinal piezoelectric coefficient (d ) of about 1200 pm / V to about 1700 pm / V at an applied voltage of 60 kV / cm and a frequency of about 1 kHz. 33 *).

[0161] In certain embodiments, the piezoelectric film has a columnar structure having a width of about 3 nm to about 6 nm.

[0162] In certain embodiments, the piezoelectric film has a thickness of about 100 nm to about 500 nm.

[0163] In certain embodiments, the substrate is an optionally doped perovskite single crystal. For example, the perovskite can be doped with Nb. The doping can be about 0.01% to 1%, or preferably 0.5%.

[0164] The single crystal substrate can be a perovskite single crystal substrate. In this regard, the single crystal substrate can have a cubic structure. Alternatively, the cubic structure can evolve into a tetragonal, orthorhombic or rhombic structure with lower symmetry, which originates from lattice distortion caused by heat or stress.

[0165] In certain embodiments, the substrate is selected from SrTiO3, LaAlO3, DyScO3, (La, Sr)(Al, Ti)O3, Si, NdGaO3, LiTaO3, YAlO3, La x Sr 1-x FeO3、La x Ca 1-x FeO3、La x Sr 1-x CoO3、La x Sr 1-xPerovskite single crystals of MnO3, LaNiO3 and SrRuO3.

[0166] Advantageously, the crystal planes of the piezoelectric film perpendicular to the film surface can be aligned with the substrate plane perpendicular to its surface during its formation. The crystal planes of the piezoelectric film parallel to the film surface are free to form their own lattice spacing or interplanar spacing.

[0167] In certain embodiments, the piezoelectric film element further includes a perovskite oxide layer sandwiched between the piezoelectric film and the substrate. The perovskite oxide layer can be an intermediate structure described herein.

[0168] In certain embodiments, the perovskite oxide layer is selected from La x Sr 1-x FeO3、La x Ca 1-x FeO3、La x Sr 1-x CoO3、La x Sr 1-x MnO3, LaNiO3 and SrRuO3.

[0169] In certain embodiments, the perovskite oxide layer has a thickness of about 1 nm to about 300 nm.

[0170] In certain embodiments, the piezoelectric film element further includes an electrode stacked on top of the piezoelectric film.

[0171] In certain embodiments, the electrode is selected from Pt, Au, Ag, Cu, Cr, Al, La x Sr 1-x FeO3、La x Ca 1-x FeO3、La x Sr 1-x CoO3、La x Sr 1-x MnO3, LaNiO3 and SrRuO3.

[0172] The present invention also provides a piezoelectric device, comprising:

[0173] c) a piezoelectric thin film element as disclosed herein; and

[0174] d) at least two electrodes in contact with the piezoelectric thin film element.

[0175] In certain embodiments, the single crystal substrate in the piezoelectric thin film element is one of the at least two electrodes.

[0176] The present invention also provides a method for manufacturing a piezoelectric thin film element, comprising:

[0177] forming a piezoelectric thin film on a single crystal substrate, the piezoelectric thin film having a (K+Na) / Nb ratio of about 0.64 to about 0.95;

[0178] wherein the single crystal substrate has a (001), (010) or (100) crystal plane perpendicular to the surface; and

[0179] The piezoelectric film is adjacent to a surface of the single crystal substrate, and is oriented such that its (001), (010) or (100) crystal plane is substantially parallel to the (001), (010) or (100) crystal plane of the single crystal substrate.

[0180] The present invention also provides a method for manufacturing a piezoelectric thin film element, which comprises:

[0181] forming a piezoelectric thin film on a single crystal substrate, the piezoelectric thin film having a (K+Na) / Nb ratio of about 0.64 to about 0.95;

[0182] wherein the single crystal substrate has a (001), (010) or (100) crystal plane perpendicular to the surface; and

[0183] wherein the piezoelectric film is adjacent to a surface of the single crystal substrate, and the piezoelectric film is oriented so that its (001), (010) or (100) crystal plane is substantially parallel to the (001), (010) or (100) crystal plane of the single crystal substrate; and

[0184] The piezoelectric film includes at least two adjacent NbO2 planes located in an antiphase domain boundary, and the at least two adjacent NbO2 planes are shifted from each other by about half a lattice length in a (100), (010) or (100) crystal plane.

[0185] In certain embodiments, a method of making a piezoelectric film element includes:

[0186] A single crystal substrate is formed with the empirical formula (K 1-x Na x ) y Piezoelectric film of NbO3, wherein 0≤x≤1 and y≤0.95;

[0187] wherein the single crystal substrate has a (001), (010) or (100) crystal plane perpendicular to the surface; and

[0188] wherein the piezoelectric film is adjacent to a surface of the single crystal substrate, and the piezoelectric film is oriented such that a (001), (010) or (100) crystal plane thereof is substantially parallel to a (001), (010) or (100) crystal plane of the single crystal substrate; and

[0189] The piezoelectric film includes at least two adjacent NbO2 planes located in an antiphase domain boundary, and the at least two adjacent NbO2 planes are shifted from each other by about half a lattice length in a (100), (010) or (100) crystal plane.

[0190] In certain embodiments, a method of making a piezoelectric film element includes:

[0191] On a single crystal substrate, a 1-x Na x ) y Piezoelectric film of NbO3, wherein 0≤x≤1 and 0.64≤y≤0.95;

[0192] wherein the single crystal substrate has a (001), (010) or (100) crystal plane perpendicular to the surface; and

[0193] wherein the piezoelectric film is adjacent to a surface of the single crystal substrate, and the piezoelectric film is oriented such that a (001), (010) or (100) crystal plane thereof is substantially parallel to a (001), (010) or (100) crystal plane of the single crystal substrate; and

[0194] The piezoelectric film includes at least two adjacent NbO2 planes located in an antiphase domain boundary, and the at least two adjacent NbO2 planes are shifted from each other by about half a lattice length in a (100), (010) or (100) crystal plane.

[0195] In certain embodiments, a method of making a piezoelectric film element includes:

[0196] On a single crystal substrate, a 1-x Na x ) y Piezoelectric film of NbO3, wherein 0≤x≤1 and 0.64≤y≤0.95;

[0197] wherein the single crystal substrate has a (001), (010) or (100) crystal plane perpendicular to the surface; and

[0198] wherein the piezoelectric film is adjacent to a surface of the single crystal substrate, and the piezoelectric film is oriented such that a (001), (010) or (100) crystallographic plane thereof is substantially parallel to a (001), (010) or (100) crystallographic plane of the single crystal substrate;

[0199] wherein the piezoelectric film has columnar crystals oriented in the corresponding

[001] ,

[010] or

[100] directions; and

[0200] The piezoelectric film includes at least two adjacent NbO2 planes located in the anti-phase domain boundary.

[0201] In certain embodiments, a method of making a piezoelectric film element includes:

[0202] A single crystal substrate is formed with the empirical formula (K 1-x Na x ) y Piezoelectric film of NbO3, wherein 0≤x≤1 and 0.64≤y≤0.95;

[0203] wherein the single crystal substrate has a (001) crystal plane perpendicular to the surface; and

[0204] The piezoelectric film is adjacent to a surface of the single crystal substrate, and the piezoelectric film is oriented such that a (001) crystal plane thereof is substantially parallel to a (001) crystal plane of the single crystal substrate.

[0205] In certain embodiments, a method of making a piezoelectric film element includes:

[0206] A single crystal substrate is formed with the empirical formula (K 1-x Na x ) y Piezoelectric film of NbO3, wherein 0≤x≤1 and 0.64≤y≤0.95;

[0207] wherein the single crystal substrate has a (001) crystal plane perpendicular to the surface; and

[0208] wherein the piezoelectric film is adjacent to a surface of the single crystal substrate, and the piezoelectric film is oriented such that a (001) crystal plane thereof is substantially parallel to a (001) crystal plane of the single crystal substrate; and

[0209] The piezoelectric film includes at least two adjacent NbO2 planes located in an antiphase domain boundary, and the at least two adjacent NbO2 planes are shifted from each other by about half a lattice length in a (100), (010) or (100) crystal plane.

[0210] In certain embodiments, a method of making a piezoelectric film element includes:

[0211] A single crystal substrate is formed with the empirical formula (K 1-x Na x ) y Piezoelectric film of NbO3, wherein 0≤x≤1 and 0.64≤y≤0.95;

[0212] wherein the single crystal substrate has a (001) crystal plane perpendicular to the surface; and

[0213] wherein the piezoelectric film is adjacent to a surface of the single crystal substrate, and the piezoelectric film is oriented such that a (001) crystal plane thereof is substantially parallel to a (001) crystal plane of the single crystal substrate;

[0214] wherein the piezoelectric film has columnar crystals oriented in the

[001] direction; and

[0215] The piezoelectric film includes at least two adjacent NbO2 planes located in the anti-phase domain boundary.

[0216] In certain embodiments, the step of forming the piezoelectric thin film includes depositing the piezoelectric thin film using sputtering.

[0217] In certain embodiments, the step of forming the piezoelectric thin film includes sputtering at a substrate temperature of about 680° C. and a discharge power of about 120W.

[0218] In certain embodiments, sputtering is performed for at least 2 hours. Sputtering can be performed for at least 1.5 hours, at least 3 hours, or at least 4 hours.

[0219] In certain embodiments, sputtering is performed at an argon-to-oxygen ratio (Ar / O) of about 50 / 15.

[0220] In certain embodiments, at about 3.5×10 -3 Sputtering was performed at a total pressure of mtorr.

[0221] In certain embodiments, the sputtering angle, substrate-target distance, argon-oxygen ratio, and / or deposition temperature are controlled such that the (K+Na) / Nb ratio is from about 0.64 to about 0.95.

[0222] In certain embodiments, the method further comprises the step of cutting and polishing the surface of the single crystal substrate having (001), (010) or (100) crystal planes perpendicular to the surface prior to sputtering.

[0223] In certain embodiments, the piezoelectric film can be grown on a water-soluble single crystal substrate. In certain embodiments, the piezoelectric film can be grown on an organic single crystal substrate. Therefore, and in such cases, the piezoelectric film can be obtained by removing the substrate via a post-deposition step. Example

[0224] Embodiments of the present invention will be discussed below, however the scope of the present invention is not limited to these embodiments.

[0225] Example 1

[0226] A piezoelectric film having the formula (K, Na) NbO3, wherein the total content of K and Na is assumed to be 100%, wherein the content ratio of K is 30%, wherein the (K+Na) / Nb ratio is 0.64, and which is grown on a (001)-oriented 0.5% Nb-doped SrTiO3 single crystal substrate, and has a columnar structure having columnar crystals extending from a substrate surface perpendicular to a horizontal plane of the film (see Figure 7 The average width of the columnar crystals was no more than 5 to 6 nm, and the total thickness of the film was 300 nm (see Figure 8 ) These particles are separated from each other by antiphase domain boundaries or antiphase grain boundaries, and their density is measured to be 0.23nm -1 , the specific antiphase domain boundary is formed by two adjacent NbO2 planes, one of which moves 1 / 2 <100> a or 1 / 2 <010> a, where a is the horizontal lattice parameter, and <100> and <010> is a family of two horizontal crystal directions (see Fig. 9 ). When a voltage of 58.3 kV / cm is applied at 1 kHz, the film shows an effective longitudinal piezoelectric coefficient d 33 *1621.9pm / V (see Fig.10 ). This piezo film is well suited for stroke-based applications such as micro-blowers, micro-pumps, micro-syringes, switches.

[0227] Example 2

[0228] A piezoelectric film having the formula (K, Na) NbO3, wherein assuming the total content of K and Na is 100%, the content ratio of K is 30%, wherein the (K+Na) / Nb ratio is 0.92, and which is grown on a (001) oriented 0.5% Nb-doped SrTiO3 single crystal substrate, has a columnar structure similar to that of Example 1, wherein the columnar crystals have an average width of 10 nm (see Fig.11 ). The (K+Na) / Nb ratio in the film was 0.92, compared to 0.64 in the film mentioned in Example 1. The piezoelectric film showed a d of 1293.7 pm / V at a driving voltage of 75 kV / cm measured at 1 kHz. 33 *( Fig.12 ).

[0229] The scanning transmission electron micrographs shown here were taken using a JEOL ARM 200F atomic resolution electron microscope equipped with a cold field emission gun and an ASCOR fifth-order aberration corrector. The chemical composition of the film was measured using a Zeiss Supra 40VP scanning electron microscope equipped with an Oxford Instruments energy dispersive spectrometer running at 20.0 kV. The voltage-dependent displacement of the piezoelectric film was measured using an OFV-3001-SF6 PolyTech GmbH (Germany) scanning laser vibrometer. An Au electrode with a diameter of 200 μm was sputtered on the film and then baked at 200 ° C for 15 minutes. The bottom electrode was exposed by depositing an Au film on a small patch at one corner of the substrate before scratching the film with a diamond knife. The laser was scanned on the electrode using a circular profile while the electrode was excited with an AC voltage. The density of the antiphase domain boundary was estimated by measuring the number of boundaries per unit length of the lattice. Five line scans were taken from random locations on a 25 nm × 25 nm STEM micrograph and the number of boundaries crossing the 25 nm long scan was counted. The average number of APBs intersecting the line was then divided by the length of the line scan, i.e., 25 nm.

[0230] It will be appreciated that numerous other modifications and permutations of various aspects of the described embodiments are possible, such as varying the substrate and A-site element doping. Accordingly, the described aspects are intended to embrace all such changes, modifications and variations that fall within the spirit and scope of the appended claims.

[0231] In this specification and the following claims, unless the context requires otherwise, the word "comprise" and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0232] Reference in this specification to any prior publication (or information derived therefrom), or any known matter, is not and should not be taken as an acknowledgement or acknowledgment or any form of teaching that the prior publication (or information derived therefrom) or known matter forms part of the common general knowledge in the field to which this specification relates.

Claims

1. A piezoelectric thin film element, comprising: a) With empirical formula (K 1-x Na x ) y A piezoelectric film of NbO3, wherein 0≤x≤1 and 0.64≤y≤0.95; and b) a cubic single crystal substrate having (001), (010) or (100) crystal planes perpendicular to the surface; wherein the piezoelectric film is adjacent to the surface of the single crystal substrate, and the piezoelectric film is oriented so that its (001) crystal plane is parallel to the (001), (010) or (100) crystal plane of the single crystal substrate; and The piezoelectric film includes at least two adjacent NbO2 planes located in an antiphase domain boundary, and the at least two adjacent NbO2 planes are shifted from each other by half a lattice length in a (100), (010) or (100) crystal plane.

2. The piezoelectric thin film element according to claim 1, which has columnar crystals oriented in the corresponding [001], [010] or [100] direction.

3. The piezoelectric thin film element of claim 1 or 2, wherein the at least two adjacent NbO2 planes located in the antiphase boundary are shifted from each other by 0.220 nm to 0.260 nm in the (001), (010) or (100) crystal plane.

4. The piezoelectric thin film element according to claim 1, wherein the density of the antiphase domain boundary of the piezoelectric thin film is 0.05 nm -1 To 0.30nm -1 .

5. The piezoelectric film element according to claim 1, wherein the piezoelectric film has an effective longitudinal piezoelectric coefficient (dP) of 1200 pm / V to 1700 pm / V at an applied voltage of 60 kV / cm and a frequency of 1 kHz. 33 *). 6 . The piezoelectric film element according to claim 2 , wherein the piezoelectric film has a columnar structure, and the columnar crystals have a width of 3 nm to 6 nm. 7 . The piezoelectric thin film element according to claim 1 , wherein the piezoelectric thin film has a thickness of 100 nm to 500 nm.

8. The piezoelectric thin film element according to claim 1, wherein the substrate is an optionally doped perovskite single crystal.

9. The piezoelectric thin film element according to claim 1, wherein the substrate is selected from SrTiO3, LaAlO3, DyScO3, (La, Sr)(Al, Ti)O3, Si, NdGaO3, LiTaO3, YAlO3, La x Sr 1-x FeO3、La x Ca 1-x FeO3、La x Sr 1-x CoO3、La x Sr 1-x Perovskite single crystals of MnO3, LaNiO3 and SrRuO3.

10. The piezoelectric film element according to claim 1, wherein the piezoelectric film further comprises a perovskite oxide layer sandwiched between the piezoelectric film and the substrate.

11. The piezoelectric thin film element according to claim 10, wherein the perovskite oxide layer is selected from La x Sr 1-x FeO3、La x Ca 1-x FeO3、La x Sr 1-x CoO3、La x Sr 1-x MnO3, LaNiO3 and SrRuO3. 12 . The piezoelectric thin film element according to claim 10 , wherein the perovskite oxide layer has a thickness of 1 nm to 300 nm.

13. The piezoelectric film element according to claim 1, further comprising an electrode stacked on top of the piezoelectric film.

14. The piezoelectric thin film element according to claim 13, wherein the electrode is selected from Pt, Au, Ag, Cu, Cr, Al, La x Sr 1-x FeO3、La x Ca 1-x FeO3、La x Sr 1-x CoO3、La x Sr 1-x MnO3, LaNiO3 and SrRuO3.

15. A piezoelectric device comprising: a) The piezoelectric thin film element according to any one of claims 1 to 14; as well as b) at least two electrodes in contact with the piezoelectric film.

16. The piezoelectric device of claim 15, wherein the single crystal substrate in the piezoelectric thin film is one of the at least two electrodes.

17. A method for manufacturing a piezoelectric thin film element, comprising: A cubic single crystal substrate with the empirical formula (K 1-x Na x ) y Piezoelectric film of NbO3, wherein 0≤x≤1 and 0.64≤y≤0.95; wherein the cubic single crystal substrate has a (001), (010) or (100) crystal plane perpendicular to the surface; wherein the piezoelectric film is adjacent to the surface of the single crystal substrate, and the piezoelectric film is oriented so that its (001), (010) or (100) crystal plane is parallel to the (001), (010) or (100) crystal plane of the single crystal substrate; and wherein the piezoelectric film comprises at least two adjacent NbO2 planes located in an antiphase domain boundary, wherein the at least two adjacent NbO2 planes are shifted from each other by half a lattice length in a (100), (010) or (100) crystal plane; The step of forming the piezoelectric film includes sputtering at a substrate temperature of 680° C. and a discharge power of 120W.

18. The method of claim 17, wherein the sputtering is performed for at least 2 hours.

19. The method of any one of claims 17, wherein the sputtering is performed at an argon-oxygen ratio (Ar / O) of 50 / 15.

20. The method of claim 17, wherein at 3.5×10 -3 The sputtering was performed at a total pressure of mtorr.

21. The method of claim 17, wherein the sputtering angle, substrate-target distance, argon-oxygen ratio and / or deposition temperature are controlled so that the (K+Na) / Nb ratio is 0.64 to 0.

95.

22. The method of claim 17, further comprising the step of cutting and polishing a surface of the single crystal substrate having a (001), (010) or (100) crystal plane perpendicular to the surface before the sputtering.

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