Piezoelectric thin film and method for producing same

Abstract

The present invention generally uses the empirical formula (K 1-x Na x ) y The present invention relates to a piezoelectric thin film comprising NbO3, where 0≦x≦1 and 0.64≦y≦0.95. In particular, the piezoelectric thin film includes at least two adjacent NbO2 planes at antiphase boundaries, the at least two adjacent NbO2 planes being offset from each other by approximately half a lattice length in either the (100), (010), or (100) crystallographic plane. The present invention also relates to a method for fabricating the piezoelectric thin film.

Description

Technical Field

[0001] The present invention generally relates to piezoelectric thin films. The present invention also relates to a method for fabricating a piezoelectric thin film.

Background Art

[0002] 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 in which a piezoelectric element deforms due to the application of an electric field, and as sensors in which any physical quantity can be indirectly detected by utilizing the voltage generated in the piezoelectric element due to deformation.

[0003] A piezoelectric thin film is a very fine lamella of a piezoelectric material. Piezoelectric thin films are attached to a substrate and have many practical applications. Some conventional applications of piezoelectric thin films include ultrasonic transducers, micropumps, mass sensors based on microcantilevers, inkjet printer heads, gyroscopes, and accelerometers. Piezoelectric thin films can be easily incorporated into microelectromechanical systems (MEMS). In certain applications such as fuel injectors, microlangmuir transducers, and nanocontrol systems for optical cavities, a high-efficiency longitudinal piezoelectric coefficient (d 33 * ) is required to obtain large piezoelectric piston-like deformations in piezoelectric thin film actuators.

[0004] The most widely used piezoelectric materials are lead-based perovskite ferroelectrics, generally having the chemical formula PbZr 1-x Ti x O 3 , called PZT with 0 < x < 1. PZT has excellent piezoelectric properties at x = 0.48 because two different crystal structures, namely rhombohedral and tetragonal crystal phases, coexist, which is also known as the morphotropic phase boundary (MPB).

[0005] However, the use of lead-based piezoelectric materials raises 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 under investigation, among which the alkali niobate-based ceramic system generally represented by the general formula K 1-x Na x NbO 3 , 0 < x < 1 shows relatively good piezoelectric properties among the systems being tested. However, the piezoelectric properties are still not equivalent to those of lead-based piezoelectric materials. In this regard, much attention has been paid to enhancing the d 33 * of alkali niobate-based piezoelectric ceramics. As recent achievements in this area, a piezoelectric film with a complex composition of coexistence and 0.95(K 0.48 Na 0.52 )(Nb 0.95 Sb 0.05 )O 3-0.05 Bi 0.5 (Na 0.82 K 0.18 ) 0.5 ZrO 3 and made by the improved sol-gel method has obtained a maximum d 33 * of 250 pm / V. However, in practical applications, such complex compositions require precise control and may be difficult to manufacture in large quantities, and the piezoelectric properties need to be further improved to compete with lead-based piezoelectric materials.

[0006] With the progress of technology, functional components including piezoelectric materials used in electronic devices are required to be miniaturized and have higher performance. Research efforts and industrial development have been made to reduce the thickness of piezoelectric materials in the form of piezoelectric thin films used in various applications. On the other hand, sputtering has been used to fabricate alkali niobate-based thin film actuators on Si substrates. However, generally, the piezoelectric properties of alkali niobate-based thin films still lag far behind those of PZT. For example, if the angle between the axis of columnar particles and the normal of the substrate surface is in the range of 0° to 10°, by adding a crystal texture to the film composed of particles having a columnar structure, the general formula (Na x K yLi z )NbO 3 The piezoelectric coefficient can be improved in a piezoelectric thin film having (0≦x≦1, 0≦y≦1, 0≦z≦0.2, x + y + z = 1).

[0007] However, even after such great efforts, the piezoelectric properties of lead - free alkaline niobate - based thin films still do not match those of lead - based piezoelectric thin films. Another method is to obtain a piezoelectric thin film having a complex composition such as the chemical formula (K x Na 1-x ) 1-y A y Nb 1-z B z O 3 where A = Li, Bi, Ba, B = Sb, Ta, Zr, Hf, 0 < x < 1, 0 < y ≦ 0.06, 0 < z ≦ 0.1, etc. Such a piezoelectric thin film shows significantly improved piezoelectric properties. Such a piezoelectric thin film can be manufactured by a chemical solution method in which an amorphous thin film is formed on a substrate and then this structure including the substrate is exposed to a high temperature to promote crystallographic growth. This process is repeated in a number of cycles until the desired thickness of the thin film is obtained. In the mass production of such piezoelectric thin films obtained from chemical solutions having complex compositions, it is difficult to control the consistency of processing, composition, and thus performance.

[0008] Piezoelectric thin films are generally made on Si or MgO substrates buffered by a thin layer of Pt. A (111) - oriented Pt layer having a thickness of 200 nm or less is made on an oxidized Si substrate so as to obtain an alkaline niobate - based piezoelectric polycrystalline thin film having crystal grains preferentially oriented in the

[0001] crystal orientation. Alternatively, a perovskite - type oxide layer such as LaNiO 3 etc. may be made on the Pt layer to obtain the same or better results. However, such piezoelectric thin films are not completely oriented in the (001) orientation and may have only 80 - 90% orientation in the (001) orientation. Furthermore, since alkali metals evaporate during the heat treatment of the piezoelectric layer, it is very difficult to avoid the pyrochlore phase in alkaline niobate - based piezoelectric thin films. Summary of the Invention [Problem to be solved by the invention]

[0009] It would be desirable to overcome or ameliorate at least one of the above problems, or at least provide a useful alternative. [Means for solving the problem]

[0010] The present invention relates to a crystalline crystalline material of the formula (K,Na)NbO grown on a (001) oriented single crystal substrate with a (K+Na) / Nb ratio of about 0.64 to about 0.95. 3 It is based on the discovery that a large longitudinal piezoelectric coefficient can be obtained in an alkali niobate-based piezoelectric epitaxial thin film having the following properties: the thin film is composed of columnar grains perpendicular to the film surface and separated by antiphase boundaries, and the density of the antiphase boundaries can be controlled by controlling the (K+Na) / Nb ratio in the thin film.

[0011] The present invention relates to a) The empirical formula (K 1-x Na x ) y NbO 3 (wherein 0≦x≦1 and 0.64≦y≦0.95); b) a single crystal substrate having a (001), (010), or (100) crystal face perpendicular to the surface; A piezoelectric thin film element comprising: a piezoelectric thin film adjacent to a surface of the single crystal substrate, the piezoelectric thin film being oriented such that a (001), (010), or (100) crystallographic plane of the piezoelectric thin film is substantially parallel to either a (001), (010), or (100) crystallographic plane of the single crystal substrate; The piezoelectric thin film has at least two adjacent NbO 2 NbO 2 The faces are offset from each other by approximately half a lattice length in either the (100), (010), or (100) crystal planes. A piezoelectric thin film element is provided.

[0012] Advantageously, for example, in a piezoelectric thin film grown on a (001) oriented single crystal substrate, having a (K+Na) / Nb ratio of 0.64 or more and 0.95 or less results in the loss of the NaO / KO plane and the formation of two adjacent NbO 2 This leads to the formation of imperfect grain boundaries where the planes are arranged in antiphase with respect to one another (antiphase boundaries). Advantageously, this leads to an effective longitudinal piezoelectric coefficient (d 33 * ) to allow for an increase in

[0013] In some embodiments, the piezoelectric thin film has columnar grains oriented in respective

[0001] ,

[0010] , or

[0100] orientations. In some embodiments, at least two adjacent NbO 2 The planes are offset from one another by about 0.220 nm to about 0.260 nm in the (100), (010), or (100) crystal planes.

[0014] In some embodiments, the density of antiphase boundaries in the piezoelectric thin film is about 0.05 nm -1 ~about 0.30nm -1 It is. In some embodiments, the piezoelectric thin film has an effective longitudinal piezoelectric coefficient (d 33 * ).

[0015] In some embodiments, the piezoelectric thin film has a columnar structure, and the columnar structure has a width of about 3 nm to about 6 nm. In some embodiments, the piezoelectric thin film has a thickness of about 100 nm to about 500 nm.

[0016] In some embodiments, the substrate is a perovskite single crystal, which is optionally doped. In some embodiments, the substrate is SrTiO 3 , LaAlO 3 , DyScO 3 , (La,Sr)(Al,Ti)O 3 ,Si,NdGaO3 , LiTaO 3 , YAlO 3 , La x Sr 1-x FeO 3 , La x Ca 1-x FeO 3 , La x Sr 1-x Chief of Staff 3 , La x Sr 1-x MnO 3 , LaNiO 3 , and SrRuO 3 The perovskite single crystal is selected from the following:

[0017] In some embodiments, the piezoelectric thin film element further includes a perovskite oxide layer sandwiched between the piezoelectric thin film and the substrate. In some embodiments, the perovskite oxide layer comprises La x Sr 1-x FeO 3 , La x Ca 1-x FeO 3 , La x Sr 1-x Chief of Staff 3 , La x Sr 1-x MnO 3 , LaNiO 3 , and SrRuO 3 is selected from.

[0018] In some embodiments, the perovskite oxide layer has a thickness of about 1 nm to about 300 nm. In some embodiments, the piezoelectric film element further includes an electrode overlying the piezoelectric film.

[0019] In some embodiments, the electrodes are made of Pt, Au, Ag, Cu, Cr, Al, La. x Sr 1-x FeO 3 , La x Ca 1-x FeO 3 , La x Sr 1-x Chief of Staff3 , La x Sr 1-x MnO 3 , LaNiO 3 , and SrRuO 3 is selected from.

[0020] The present invention also provides a) a piezoelectric thin film element as disclosed herein; b) at least two electrodes in contact with the piezoelectric thin film; A piezoelectric device is also provided, including:

[0021] In some embodiments, the single crystal substrate is one of at least two electrodes in a piezoelectric device. The present invention also provides a method for fabricating a piezoelectric thin film element, comprising the steps of: Empirical formula (K 1-x Na x ) y NbO 3 forming a piezoelectric thin film having the formula: (wherein 0≦x≦1 and 0.64≦y≦0.95) on a single crystal substrate; Including, The single crystal substrate has a (001), (010), or (100) crystal face perpendicular to the surface; a piezoelectric thin film adjacent to a surface of a single crystal substrate, the piezoelectric thin film being oriented such that a (001), (010), or (100) crystallographic plane of the piezoelectric thin film is substantially parallel to any of the (001), (010), or (100) crystallographic planes of the single crystal substrate; The piezoelectric thin film has at least two adjacent NbO 2 NbO 2 the faces are offset from one another by approximately half a lattice length in either the (100), (010), or (100) crystal planes; A method is also provided.

[0022] In some embodiments, forming the piezoelectric thin film includes depositing the piezoelectric thin film using sputtering. In some embodiments, forming the piezoelectric thin film includes sputtering at a substrate temperature of about 680° C. and a discharge power of about 120 W.

[0023] In some embodiments, the sputtering is carried out for at least 2 hours. In some embodiments, sputtering is performed at an argon-oxygen ratio (Ar / O) of about 50 / 15.

[0024] In some embodiments, sputtering is about 3.5×10 -3 This is done under a total pressure of mtorr. In some embodiments, the sputtering angle, substrate-target distance, argon-oxygen ratio, and / or deposition temperature are controlled such that y is 0.64≦y≦0.95.

[0025] In some embodiments, the vertical distance between the target and the substrate is about 5 cm to 15 cm. In some embodiments, the angle between the target normal and the substrate normal is an obtuse angle.

[0026] In some embodiments, the method further comprises cutting and polishing the surface of the single crystal substrate prior to sputtering, the surface having a (001), (010), or (100) crystallographic plane perpendicular to the surface.

[0027] Embodiments of the invention will now be described by way of non-limiting examples with reference to the figures. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 is a schematic diagram showing a perovskite unit cell of (K,Na)NbO3. [Diagram 2] Regular perfect boundary 1 and (1 / 2)a <100> FIG. 2 is a schematic diagram showing an antiphase boundary 2 with NbO2 planes shifted by a distance of 1. [Diagram 3] FIG. 1 is a structural diagram showing a piezoelectric thin film element (a piezoelectric thin film 4 formed on a conductive single crystal substrate 3). [Figure 4] 1 is a structural diagram showing a conductive perovskite layer 6 between a piezoelectric thin film 4 and an insulating single crystal substrate 5. FIG. [Diagram 5] FIG. 2 is a structural diagram showing an upper electrode 7 on a piezoelectric thin film 4 formed on a conductive single crystal substrate 3. [Figure 6] FIG. 2 is a structural diagram showing a top electrode 7 on a piezoelectric thin film 4 with a conductive perovskite layer 6 and an insulating single crystal substrate 5 immediately below. [Figure 7] FIG. 2 is a bright-field scanning transmission electron microscope image of an exemplary piezoelectric thin film cross section showing a 300 nm thick piezoelectric thin film 9 on a conductive 0.5% Nb-doped SrTiO3 single crystal substrate 8 according to Example 1. [Figure 8] FIG. 2 shows a high-angle annular dark-field scanning transmission electron microscope image of a piezoelectric thin film surface showing fine grains separated by niobium-rich anti-phase boundaries according to Example 1 (only Nb atoms are visible in the microscope image). [Figure 9] FIG. 1 shows a magnified, high-angle, annular, dark-field scanning transmission electron microscope image of an antiphase boundary enclosed within a rectangle (only Nb atoms are visible in the microscope image). [Figure 10] 4 is a graph illustrating an exemplary piezoelectric response of a piezoelectric thin film when subjected to a sinusoidal electrical signal at a frequency of 1 kHz according to Example 1. [Figure 11] FIG. 13 is an exemplary bright-field scanning transmission electron microscope image of a piezoelectric thin film cross section showing a 300 nm thick piezoelectric thin film on a conductive 0.5% Nb-doped SrTiO3 single crystal substrate according to Example 2. [Figure 12] 4 is a graph illustrating an exemplary piezoelectric response of a piezoelectric thin film when subjected to a sinusoidal electrical signal at a frequency of 1 kHz according to Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] The present invention relates to a compound of the general formula K 1-x Na x NbO 3、Based on potassium sodium niobate with 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, KNN exists in an orthorhombic or tetragonal structure, where potassium (K) or sodium (Na) is at the A-site (the vertex of the crystal lattice), niobium (Nb) is at the B-site (the body-centered of the crystal lattice), and oxygen (O) forms an octahedron around Nb (see Figure 1).

[0030] The inventors reexamined past research and found that the piezoelectric properties of alkali niobate thin films can be specifically improved by adjusting the ratio of alkali metal to Nb and controlling its crystallographic growth.

[0031] Regarding this, prior art piezoelectric thin films having the general formula (K 1-x Na x ) y NbO 3 show piezoelectric properties with a typical d 33 less than 180 pm / V when 0.4 ≤ x ≤ 0.7 and y is close to 1 (considering that d 31 is typically approximately -d 33 / 2). In another example, polycrystalline alkali niobate-based thin films having the general formula (K 1-x Na x ) y NbO 3 grown on a Pt-buffered Si substrate with 0.4 ≤ x ≤ 0.7 and 0.75 ≤ y ≤ 0.90 can improve the piezoelectric coefficient, i.e., d 33 can be improved up to 218 pm / V. In another example, a piezoelectric film having the general formula (K 1-x Na x )NbO 3 , (0 < x < 1) shows piezoelectric properties if the crystallographic peak of (001) occupies more than 80% of the diffraction pattern.

[0032] Therefore, the present invention is envisaged based on the understanding that, in contrast to polycrystalline thin films, single crystal films grow based on a perfect atomic arrangement determined by the end species on the substrate surface. For example, in the island-like growth mode of KNN thin films with a (K+Na) / Nb ratio close to 1, various grains nucleate from the surface of the substrate and merge with continuous grain boundaries [see FIG. 2, 1]. For example, it has been found that in KNN piezoelectric thin films grown on 001-oriented single crystal substrates, when the (K+Na) / Nb ratio is less than 1, some grains show irregular nucleation when grown on the single crystal substrate, leading to the formation of incomplete grain boundaries and the loss of NaO / KO planes. In particular, two adjacent NbO 2 The planes can be arranged in antiphase with each other [see 2 in Figure 2]. This arrangement of antiphase boundaries occurs when adjacent NbO 2 One of the layers is horizontally shifted by a distance of half the lattice length (1 / 2 <100> a or 1 / 2 <010> a) NbO 2 The arrangement is such that the distance between the faces is within the range of 0.225 to 0.252 nm.

[0033] Based on this understanding, the inventors generally 1-x Na x )NbO 3 The general formula (K+Na) / Nb ratio in the thin film (0≦x≦1) is less than 1. 1-x Na x )NbO 3 It has been found that KNN-based piezoelectric thin films can result in the formation of the above antiphase boundaries when grown on single crystal substrates. In particular, the (K+Na) / Nb ratio may be from about 0.64 to about 0.95. Furthermore, such thin films with antiphase boundaries exhibit very large d values ​​of up to 1621.9 pm / V measured at an applied voltage and frequency of 58.3 kV / cm and 1 kHz, respectively. 33 * It is possible to show that the density of antiphase boundaries (the number of antiphase boundaries per unit length of the crystal lattice) increases with decreasing (K+Na) / Nb ratio, so that the density of antiphase boundaries is 0.08-0.23 nm when the (K+Na) / Nb ratio is between 0.95 and 0.64, respectively. -1 Furthermore, the range is 0.23 nm. -1and a d of 1621.9 pm / V for a thin film with a (K+Na) / Nb ratio equal to 0.64. 33 * Therefore, when grown on a single crystal substrate, the d 33 * can be controlled by adjusting the Nb content in the film relative to the alkali metals K and Na. Furthermore, the thickness of the film of the present invention (about 300 nm) can be much thinner than the films disclosed in previous inventions.

[0034] For the avoidance of doubt, "piezoelectric thin film element" as used herein refers to a piezoelectric thin film in combination with a substrate. "Piezoelectric thin film" refers to the film portion only, i.e. does not include the substrate. A substrate is generally required on which to grow the piezoelectric thin film. While the substrate is a support for the thin film during the growth process, the substrate may also be essential to impart the desired structure to the thin film during growth. As shown in some embodiments, the inventors have demonstrated that high d 33 It has been found that a substrate with a

[0001] orientation may be used to obtain a piezoelectric thin film having a

[0010] or

[0100] orientation. In other embodiments, a substrate with a

[0010] or

[0100] orientation may be used. It should be noted that in the form of a final product, the piezoelectric thin film may be utilized without a substrate, i.e., the substrate may be removed after formation of the piezoelectric thin film. For example, a water-soluble single crystal substrate and / or an organic single crystal substrate may be used.

[0035] In some embodiments, the piezoelectric thin film element comprises a piezoelectric thin film and a substrate. The substrate is made of 0.5% Nb-doped SrTiO 3 The substrate may be a conductive single crystal having a perovskite-type structure such as . The substrate is cut and polished perpendicular to one of the main crystallographic axes, e.g. (001). A piezoelectric thin film is fabricated on the substrate. The piezoelectric thin film has the general formula (K,Na)NbO 3and a (K+Na) / Nb ratio of about 0.64 to about 0.95, e.g., a preferred orientation in the crystallographic direction of

[0001] , with the columnar grains oriented parallel to the normal to the film surface. These columnar grains are separated from each other by antiphase boundaries (APBs), so that the density of the antiphase boundaries is 0.08 to 0.23 nm when the (K+Na) / Nb ratio is between 0.95 and 0.64, respectively. -1 APB is a structure in which a layer of KO or NaO is lost in the ordered perovskite structure, and two NbO 2 The layers are adjacent to each other at antiphase boundaries. 2 One of the layers is (1 / 2)a from its normal position. <100> or (1 / 2)a <010> where “a” is the lattice parameter of the perovskite cell in the horizontal direction.

[0036] Other crystallographic axes may also be used, for example the (001), (010), and (100) crystallographic axes of the substrate may be used, which would result in a corresponding piezoelectric thin film having either a (001), (010), or (100) crystallographic orientation, with the columnar grains oriented parallel to the normal to the film surface.

[0037] As used herein, parentheses such as "(001)" are used to denote crystallographic planes, while square brackets such as "

[0001] " are used to denote crystallographic orientations. The empirical formula of a chemical substance is a simple expression of the relative numbers of each type of atom or ratio of elements in the compound. The empirical formula is CaCl 2 For ionic compounds such as SiO 2 Empirical formulas are standards for macromolecules such as C, C10, C20, C30, C40, C50, C60, C70, C80, C90, C100, C120, C140, C160, C180, C20, C30, C40, C50, C60, C70, C80, C90, C120, C140, C160, C180, C2 ...60, C180, C16 6 H 14 The molecular formula is CH 3 CH 2 CH 2 CH 2 CH 2 CH3 This suggests a chain structure of 6 carbon atoms and 14 hydrogen atoms. However, the empirical formula of hexane is C 3 H 7 Similarly, hydrogen peroxide H 2 O 2 Its empirical formula is simply HO, which represents a 1:1 ratio of the constituent elements. Formaldehyde and acetic acid have the same empirical formula CH 2 O. This is the actual chemical formula for formaldehyde, but acetic acid has twice the number of atoms.

[0038] The present invention foresees a piezoelectric thin film grown on a single crystal substrate with (001), (010), or (100) orientation parallel to the growth direction of the thin film. By using a single crystal substrate, for example, 100% orientation to the

[0001] crystallographic direction is achieved in an alkali-based piezoelectric thin film. In this regard, the piezoelectric thin film is completely or at least substantially oriented in the

[0001] direction and / or in the (001) plane. Furthermore, the piezoelectric thin film can be free of secondary pyrochlore phases. To achieve this, the lattice parameters of the horizontal planes of the substrate are preferably close to (or match) the lattice parameters of the horizontal planes of the piezoelectric thin film.

[0039] In some embodiments, the piezoelectric thin film has an effective longitudinal piezoelectric coefficient d of 1621.9 pm / V at an applied voltage and frequency of 58.3 kV / cm and 1 kHz, respectively. 33 * This exceeds the piezoelectric coefficient of commercially available lead-based piezoelectric thin films. Furthermore, the piezoelectric thin films do not contain other foreign elements that would otherwise be required to enhance the piezoelectric properties to such an extent. Furthermore, the piezoelectric thin films are made using a sputtering process.

[0040] As already mentioned, the piezoelectric thin film of the present invention has 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 thin films. This also opens up the possibility of developing more sensitive and energy-saving lead-free electrochemical devices.

[0041] Furthermore, by growing the thin film on a single crystal substrate, a high density of antiphase boundaries is observed, which leads to the gigantic d 33 * It is possible to create anti-phase boundaries, the density of which can be controlled by adjusting the niobium content in the film relative to the alkali metal. In such cases, the Nb content in the sputtering target directly affects the amount of Nb in the film. Advantageously, the d of the piezoelectric thin film can be controlled by simply adjusting the stoichiometry of the sputtering target composition, compared to the conventional method of creating phase boundaries by adding expensive dopants. 33 * This simple method offers the advantage of improved reproducibility, thereby opening up the opportunity for mass production.

[0042] Advantageously, the piezoelectric thin film, piezoelectric thin film element, and / or device are compliant with the Restriction of Hazardous Substances (RoHS), which currently restricts the use of lead in consumer products. Due to the unavailability of suitable alternatives, the current workaround has been to exclude PZT from RoHS consideration for the time being for use in electronic products. The present invention could potentially result in a lead-free piezoelectric material to replace PZT in many devices and applications.

[0043] Advantageously, a higher d 33 * This allows piezoelectric thin film actuators to be driven at very low voltages, thus facilitating further miniaturization and broadening their applications. 33 *is significantly higher than that of the lead-based counterparts commercially used in practical applications. Moreover, such high piezoelectric constants are achieved without the addition of complex dopants, and the piezoelectric thin films are prepared by a simple sputtering process.

[0044] A typical sensor or actuator device based on a piezoelectric thin film has at least two electrodes for attaching a voltmeter to measure the bias or a power supply to drive the motion, respectively. In some embodiments, the substrate may be conductive and may function as one of the electrodes (see 3 in FIG. 3). For example, one of these electrodes may be a conductive substrate used in the growth process, i.e., in the growth process of the piezoelectric thin film element. In some embodiments, Nb-doped SrTiO 3 A conductive substrate was used. In this Nb-doped substrate, Nb is SrTiO 3 can be made conductive (SrTiO 3 is an insulator). In other embodiments, inherently conductive substrates may also be used.

[0045] Including, but not limited to, SrTiO 3 , LaAlO 3 , DyScO 3 , (La,Sr)(Al,Ti)O 3 ,Si,NdGaO 3 , LiTaO 3 , YAlO 3 Insulating perovskite single crystals 5 from the group including may also be used (see FIG. 4). The inventors have found that an insulating substrate can be used to make the piezoelectric thin film of the present invention. However, it has been found that its applicability as a device may be limited. Therefore, to solve this, the inventors have found that a conductive perovskite layer can be placed between the piezoelectric thin film and the substrate. This conductive layer can then function as a bottom electrode for use as a device. In such a case, preferably, but not limited to, La x Sr 1-x FeO 3 , La xCa 1-x FeO 3 , La x Sr 1-x Chief of Staff 3 , La x Sr 1-x MnO 3 , LaNiO 3 , SrRuO 3 A conductive layer of a conductive perovskite 6, a metal oxide from the group including, is fabricated on top of the insulating substrate (see FIG. 4) described above. Typically, the conductive electrode has a thickness of 1-250 nm.

[0046] An electrode 7 may be deposited on top of the piezoelectric thin film (see Figures 5 and 6). This top electrode is preferably a metal such as, but not limited to, Pt, Au, Ag, Cu, Cr, Al, or a conductive perovskite as listed above. The top layer is preferably deposited using a sputtering or evaporation method, or a plating method, or a pasting method.

[0047] General formula (K,Na)NbO 3 Also disclosed herein is a method for fabricating a piezoelectric thin film having a (K+Na) / Nb ratio of about 0.64 to about 0.95. In an embodiment of the invention discussed below, the substrate is a 5 mm×5 mm×0.5 mm 0.5% Nb-doped SrTiO 3 wafer cut and polished perpendicular to the (001) crystal plane. 3 The conductive perovskite single crystal is used. A piezoelectric thin film is formed on it by direct RF magnetron sputtering at a substrate temperature of 680 °C, and the discharge power used is 120 W. Other conditions are that the chamber gas is 3.5 × 10 -3 The total pressure of mtorr is Ar / O=50 / 15, and the sputtering time is 2 hours. Furthermore, a Pt electrode with a diameter of 200 μm and a thickness of 100 nm may be deposited using a mask at room temperature at a sputtering power of 80 W and a duration of 10 minutes. (K,Na)NbO 3For thin films, the (K+Na) / Nb ratio can be controlled by adjusting the Nb content in the sputtering target. At (K+Na) / Nb ratios less than 1, excess Nb may be added to the sputtering target compared to a stoichiometric target where the (K+Na) / Nb ratio is 1. Similarly, (K+Na) / Nb can also be controlled by adjusting the sputtering angle, substrate-target distance, argon-oxygen ratio, and / or deposition temperature.

[0048] Therefore, the present invention a) Formula (K,Na)NbO 3 a piezoelectric thin film having a (K+Na) / Nb ratio of about 0.64 to about 0.95; b) a single crystal substrate having a (001), (010), or (100) crystal face perpendicular to the surface; A piezoelectric thin film element comprising: the piezoelectric thin film is adjacent to a surface of the single crystal substrate, the piezoelectric thin film being oriented such that its (001), (010), or (100) crystallographic plane is parallel to either the (001), (010), or (100) crystallographic plane of the single crystal substrate; A piezoelectric thin film element is provided.

[0049] In this regard, the piezoelectric thin film is oriented such that its (001) crystal plane is parallel to either the (001), (010), or (100) crystal plane of the single crystal substrate. The piezoelectric thin film may also be oriented such that its (010) crystal plane is parallel to either the (001), (010), or (100) crystal plane of the single crystal substrate. The piezoelectric thin film may also be oriented such that its (100) crystal plane is parallel to either the (001), (010), or (100) crystal plane of the single crystal substrate.

[0050] It should be appreciated that the piezoelectric thin film does not need to be in physical and / or chemical contact with the substrate, so long as the "atomic spacing information" from the crystal planes can be imparted from the substrate to the formed piezoelectric thin film. In this regard, a piezoelectric thin film adjacent to the surface of a single crystal substrate is in close proximity to the surface of the single crystal substrate. This means that the piezoelectric thin film may either be in physical and / or chemical contact / bond with the surface of the single crystal substrate (with no intervening structure between them) or be separated / separated by a small distance / spacing from the surface of the single crystal substrate (by an intervening structure between them). Thus, the "information" is relayed directly from the substrate, allowing the formation of a piezoelectric thin film in physical and / or chemical contact with the substrate. This means that when the piezoelectric thin film is grown on the substrate, the single crystal substrate has a perfect atomic match with the piezoelectric thin film, and these atoms are chemically bonded to each other. When the "information" is relayed indirectly by an intervening structure, the "information" from the substrate is conveyed and embodied in the intervening structure, which is then conveyed to the formed piezoelectric thin film. For example, the intervening structure may be a conductive thin film grown on a substrate, with the same (or substantially the same) crystallographic plane orientation as the substrate. To this end, the intervening structure may be crystallographically similar to the substrate (single crystal with the same orientation), such that the intervening structure is chemically bonded to both the thin film and the substrate, but may have different physical properties (such as electrical conductivity).

[0051] In some embodiments, the present invention provides a) Formula (K,Na)NbO 3 a piezoelectric thin film having a (K+Na) / Nb ratio of about 0.64 to about 0.95; b) a single crystal substrate having a (001), (010), or (100) crystal face perpendicular to the surface; A piezoelectric thin film element comprising: the piezoelectric thin film is adjacent to a surface of the single crystal substrate, the piezoelectric thin film being oriented such that its (001), (010), or (100) crystallographic plane is parallel to the respective (001), (010), or (100) crystallographic plane of the single crystal substrate; A piezoelectric thin film element is provided.

[0052] In some embodiments, when the single crystal substrate has a (001) crystal plane perpendicular to the surface, the piezoelectric thin film is oriented such that its (001) crystal plane is parallel to the (001) crystal plane of the single crystal substrate. In other embodiments, when the single crystal substrate has a (010) crystal plane perpendicular to the surface, the piezoelectric thin film is oriented such that its (010) crystal plane is parallel to the (010) crystal plane of the single crystal substrate. In other embodiments, when the single crystal substrate has a (100) crystal plane perpendicular to the surface, the piezoelectric thin film is oriented such that its (100) crystal plane is parallel to the (100) crystal plane of the single crystal substrate.

[0053] In some preferred embodiments, SrTiO 3 A (STO) single crystal substrate is used. The STO substrate is cubic, so (001), (010), and (100) are equivalent planes. In this regard, no matter what substrate orientation of STO is used, the plane of the piezoelectric thin film parallel to the substrate plane (perpendicular to the surface) will be (001).

[0054] Thus, in some embodiments, the present invention provides a method for treating a cancer cell comprising: a) Formula (K,Na)NbO 3 a piezoelectric thin film having a (K+Na) / Nb ratio of about 0.64 to about 0.95; b) a cubic single crystal substrate having a (001), (010), or (100) crystal face perpendicular to the surface; A piezoelectric thin film element comprising: the piezoelectric thin film is adjacent to a surface of the single crystal substrate, the piezoelectric thin film being oriented such that its (001) crystallographic plane is parallel to the (001), (010), or (100) crystallographic plane of the single crystal substrate; A piezoelectric thin film element is provided.

[0055] In some embodiments, y is less than 0.95. In other embodiments, y is equal to or less than 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.

[0056] In some embodiments, the piezoelectric thin film element comprises: a) a piezoelectric thin film having the empirical formula (K 1-x Na x ) y NbO 3 (where 0 ≦ x ≦ 1 and y ≦ 0.95), and b) a single crystal substrate having a (001), (010), or (100) crystal plane perpendicular to the surface, 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 one of the (001), (010), or (100) crystal planes of the single crystal substrate.

[0057] In some embodiments, the piezoelectric thin film has the empirical formula (K 1-x Na x ) y NbO 3 (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 NbO 3 (where 0 ≦ x ≦ 1 and 0.64 ≦ y ≦ 0.95).

[0058] In some embodiments, the piezoelectric thin film element comprises: a) a piezoelectric thin film having the empirical formula (K 1-x Na x ) y NbO 3 (where 0 ≦ x ≦ 1 and 0.64 ≦ y ≦ 0.95), and b) a single crystal substrate having a (001), (010), or (100) crystal plane perpendicular to the surface, 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 one of the (001), (010), or (100) crystal planes of the single crystal substrate. In some embodiments, the piezoelectric thin film element comprises: a) a piezoelectric thin film having the empirical formula (K 1-x Na x ) yNbO 3 (wherein 0≦x≦1 and 0.64≦y≦0.95); b) a single crystal substrate having a (001), (010), or (100) crystal face perpendicular to the surface; wherein the piezoelectric thin film is adjacent to a surface of the single crystal substrate, and the piezoelectric thin film is oriented such that a (001), (010), or (100) crystallographic plane thereof is substantially parallel to the respective (001), (010), or (100) crystallographic plane of the single crystal substrate, or to a (001) crystallographic plane of the single crystal substrate.

[0059] In some embodiments, the piezoelectric thin film element comprises: a) Empirical formula (K 1-x Na x ) y NbO 3 (wherein 0≦x≦1 and 0.64≦y≦0.95); b) a single crystal substrate having a (001), (010), or (100) crystal face perpendicular to the surface; the piezoelectric thin film is adjacent to a surface of the single crystal substrate, the piezoelectric thin film being oriented such that a (001), (010), or (100) crystallographic plane thereof is substantially parallel to the respective (001), (010), or (100) crystallographic plane of the single crystal substrate.

[0060] In some embodiments, the piezoelectric thin film element comprises: a) Empirical formula (K 1-x Na x ) y NbO 3 (wherein 0≦x≦1 and 0.64≦y≦0.95); b) a cubic single crystal substrate having a (001), (010), or (100) crystal face perpendicular to the surface; the piezoelectric thin film is adjacent to a surface of the single crystal substrate, the piezoelectric thin film being oriented such that a (001) crystallographic plane of the piezoelectric thin film is substantially parallel to a (001), (010), or (100) crystallographic plane of the single crystal substrate.

[0061] In some embodiments, the piezoelectric thin film element comprises: a) Empirical formula (K 1-xNa x ) y NbO 3 (wherein 0≦x≦1 and 0.64≦y≦0.95); b) a single crystal substrate having a (001), (010), or (100) crystal face perpendicular to the surface; Including, the piezoelectric thin film is adjacent to a surface of the single crystal substrate, the piezoelectric thin film being oriented such that a (001), (010), or (100) crystallographic plane of the piezoelectric thin film is substantially parallel to either a (001), (010), or (100) crystallographic plane of the single crystal substrate; The piezoelectric thin film has columnar grains oriented in the respective

[0001] ,

[0010] , or

[0100] orientations, The piezoelectric thin film is composed of at least two adjacent NbO 2 Includes faces.

[0062] In one aspect, the present invention provides a method for producing a) Empirical formula (K 1-x Na x ) y NbO 3 (wherein 0≦x≦1 and 0.64≦y≦0.95); b) a single crystal substrate having a (001), (010), or (100) crystal face perpendicular to the surface; A piezoelectric thin film element comprising: a piezoelectric thin film adjacent to a surface of the single crystal substrate, the piezoelectric thin film being oriented such that a (001), (010), or (100) crystallographic plane of the piezoelectric thin film is substantially parallel to either a (001), (010), or (100) crystallographic plane of the single crystal substrate; The piezoelectric thin film has at least two adjacent NbO 2 NbO 2 the faces are offset from one another by approximately half a lattice length in either the (100), (010), or (100) crystal planes; A piezoelectric thin film element is provided.

[0063] In some embodiments, the piezoelectric thin film element comprises: a) Empirical formula (K 1-x Nax ) y NbO 3 (wherein 0≦x≦1 and 0.64≦y≦0.95); b) A single crystal substrate having a (001) crystal face perpendicular to the surface. Including, the piezoelectric thin film is adjacent to a surface of the single crystal substrate, the piezoelectric thin film being oriented such that its (001) crystallographic plane is substantially parallel to the (001) crystallographic plane of the single crystal substrate; The piezoelectric thin film is composed of at least two adjacent NbO 2 NbO 2 The faces are offset from one another by approximately half a lattice length in either the (100), (010), or (100) crystal planes.

[0064] In some embodiments, the piezoelectric thin film is oriented such that its (001) crystal plane is perfectly parallel to the (001) crystal plane of the single crystal substrate. In other embodiments, the piezoelectric thin film is oriented such that its (010) crystal plane is perfectly parallel to the (010) crystal plane of the single crystal substrate. In other embodiments, the piezoelectric thin film is oriented such that its (100) crystal plane is perfectly parallel to the (100) crystal plane of the single crystal substrate. In this regard, 100% of the piezoelectric thin film is oriented parallel to the single crystal substrate. In some embodiments, the piezoelectric thin film is oriented such that its (001) crystal plane is substantially parallel to the (001) crystal plane of the single crystal substrate. In some embodiments, the piezoelectric thin film is oriented such that its (010) crystal plane is substantially parallel to the (010) crystal plane of the single crystal substrate. In some embodiments, the piezoelectric thin film is oriented such that its (100) crystal plane is substantially parallel to the (100) crystal plane of the single crystal substrate. As used herein, a piezoelectric film oriented substantially parallel to the single crystal substrate refers to one in which 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 100% oriented parallel to the single crystal substrate.

[0065] In some embodiments, the piezoelectric thin film has columnar grains oriented in a

[0001] direction. In some embodiments, the piezoelectric thin film has columnar grains oriented in a

[0010] direction. In some embodiments, the piezoelectric thin film has columnar grains oriented in a

[0100] direction.

[0066] In some embodiments, the piezoelectric thin film is made of at least two adjacent NbO 2 In some embodiments, the piezoelectric thin film includes at least two adjacent NbO 3 crystals aligned in the (001), (100), or (010) crystal planes, offset from each other by about half a lattice length. 2 In this regard, at least two NbO 2 The faces are in contact with each other and are offset from each other by approximately half a grating length.

[0067] In some embodiments, at least two adjacent NbO 2 The planes are offset from each other by about 0.220 nm to about 0.260 nm in the (100) crystal plane. 2 The faces are in contact with each other and are offset from each other by about 0.220 nm to about 0.260 nm.

[0068] In some embodiments, at least two adjacent NbO 2 The planes are offset from each other by about 0.220 nm to about 0.260 nm in the (010) crystal plane. 2 The faces are in contact with each other and are offset from each other by about 0.220 nm to about 0.260 nm.

[0069] In some embodiments, at least two adjacent NbO 2 The planes are offset from each other by about 0.220 nm to about 0.260 nm in the (001) crystal plane. 2 The faces are in contact with each other and are offset from each other by about 0.220 nm to about 0.260 nm.

[0070] In some embodiments, the density of antiphase boundaries in the piezoelectric thin film is about 0.05 nm -1 ~about 0.30nm -1 In another embodiment, the density of antiphase boundaries in the piezoelectric thin film is about 0.10 nm -1 ~about 0.30nm -1 , about 0.15nm -1 ~about 0.30nm -1 , or about 0.20 nm -1 ~about 0.30nm -1 It is.

[0071] In some embodiments, the piezoelectric thin film element is a) Empirical formula (K 1-x Na x ) y NbO 3 (wherein 0≦x≦1 and 0.64≦y≦0.95); b) A single crystal substrate having a (001) crystal face perpendicular to the surface. Including, the piezoelectric thin film is adjacent to a surface of the single crystal substrate, the piezoelectric thin film being oriented such that its (001) crystallographic plane is substantially parallel to the (001) crystallographic plane of the single crystal substrate; The piezoelectric thin film has columnar grains oriented in the

[0001] direction. The piezoelectric thin film is composed of at least two adjacent NbO 2 Includes faces.

[0072] In some embodiments, the piezoelectric thin film has an effective longitudinal piezoelectric coefficient (d 33 * In another embodiment, d 33 * is about 1000 pm / V to about 2000 pm / V, or 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.

[0073] In some embodiments, the piezoelectric thin film element comprises: a) Empirical formula (K 1-x Na x ) y NbO 3(wherein 0≦x≦1 and 0.64≦y≦0.95); b) A single crystal substrate having a (001) crystal face perpendicular to the surface. Including, the piezoelectric thin film is adjacent to a surface of the single crystal substrate, the piezoelectric thin film being oriented such that its (001) crystallographic plane is substantially parallel to the (001) crystallographic plane of the single crystal substrate; The piezoelectric thin film has columnar grains oriented in the

[0001] direction. The piezoelectric thin film is composed of at least two adjacent NbO 2 Including the face, The piezoelectric thin film has an effective longitudinal piezoelectric coefficient (d 33 * ).

[0074] In some embodiments, the piezoelectric thin film has a columnar structure, and the columnar structure has a width of about 3 nm to about 6 nm. In some embodiments, the piezoelectric film has a thickness of about 100 nm to about 500 nm.

[0075] In some embodiments, the substrate is a perovskite single crystal that is optionally doped. For example, the perovskite may be doped with Nb. The doping may be about 0.01% to 1%, or preferably 0.5%.

[0076] The single crystal substrate may be a perovskite single crystal substrate. In this regard, the single crystal substrate may have a cubic crystal structure. Alternatively, the cubic crystal structure may change due to thermally or stress-induced lattice distortion to tetragonal, orthorhombic, or the less symmetrical rhombohedral.

[0077] In some embodiments, the substrate is SrTiO 3 , LaAlO 3 , DyScO 3 , (La,Sr)(Al,Ti)O 3 ,Si,NdGaO 3 , LiTaO 3 , YAlO3 , La x Sr 1-x FeO 3 , La x Ca 1-x FeO 3 , La x Sr 1-x Chief of Staff 3 , La x Sr 1-x MnO 3 , LaNiO 3 , and SrRuO 3 The perovskite single crystal is selected from the group consisting of:

[0078] Advantageously, the crystal planes of the piezoelectric thin film perpendicular to the surface of the film can be aligned with the planes of the substrate perpendicular to the surface of the substrate during formation, while the crystal planes of the piezoelectric thin film parallel to the surface of the film are free to form their own lattice spacing or interplanar spacing.

[0079] In some embodiments, the piezoelectric thin film element further comprises a perovskite oxide layer sandwiched between the piezoelectric thin film and the substrate. The perovskite oxide layer may be of an interposed structure as described herein.

[0080] In some embodiments, the perovskite oxide layer comprises La x Sr 1-x FeO 3 , La x Ca 1-x FeO 3 , La x Sr 1-x Chief of Staff 3 , La x Sr 1-x MnO 3 , LaNiO 3 , and SrRuO 3 is selected from.

[0081] In some embodiments, the perovskite oxide layer has a thickness of about 1 nm to about 300 nm. In some embodiments, the piezoelectric film element further includes an electrode overlying the piezoelectric film.

[0082] In some embodiments, the electrodes are made of Pt, Au, Ag, Cu, Cr, Al, La x Sr 1-x FeO 3 , La x Ca 1-x FeO 3 , La x Sr 1-x Chief of Staff 3 , La x Sr 1-x MnO 3 , LaNiO 3 , and SrRuO 3 is selected from.

[0083] The present invention relates to c) a piezoelectric thin film element as disclosed herein; d) at least two electrodes in contact with the piezoelectric thin film element; A piezoelectric device is also provided, including:

[0084] In some embodiments, the single crystal substrate in the piezoelectric thin film element is one of the at least two electrodes. The present invention also provides a method for producing a piezoelectric thin film element, comprising the steps of: 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; Including, The single crystal substrate has a (001), (010), or (100) crystal face perpendicular to the surface; a piezoelectric thin film adjacent to a surface of a single crystal substrate, the piezoelectric thin film being oriented such that its (001), (010), or (100) crystallographic plane is substantially parallel to either the (001), (010), or (100) crystallographic plane of the single crystal substrate; A method is also provided.

[0085] The present invention also provides a method for producing a piezoelectric thin film element, comprising the steps of: 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; Including, The single crystal substrate has a (001), (010), or (100) crystal face perpendicular to the surface; the piezoelectric thin film is adjacent to a surface of the single crystal substrate, the piezoelectric thin film being oriented such that a (001), (010), or (100) crystallographic plane of the piezoelectric thin film is substantially parallel to either a (001), (010), or (100) crystallographic plane of the single crystal substrate; The piezoelectric thin film has at least two adjacent NbO 2 NbO 2 the faces are offset from one another by approximately half a lattice length in either the (100), (010), or (100) crystal planes; A method is provided.

[0086] In some embodiments, a method for fabricating a piezoelectric thin film element includes: Empirical formula (K 1-x Na x ) y NbO 3 forming a piezoelectric thin film having the formula: Including, The single crystal substrate has a (001), (010), or (100) crystal face perpendicular to the surface; the piezoelectric thin film is adjacent to a surface of the single crystal substrate, the piezoelectric thin film being oriented such that a (001), (010), or (100) crystallographic plane of the piezoelectric thin film is substantially parallel to either a (001), (010), or (100) crystallographic plane of the single crystal substrate; The piezoelectric thin film is composed of at least two adjacent NbO 2 NbO 2 The faces are offset from one another by approximately half a lattice length in either the (100), (010), or (100) crystal planes.

[0087] In some embodiments, a method for fabricating a piezoelectric thin film element includes: Empirical formula (K 1-x Na x ) y NbO 3 forming a piezoelectric thin film having the formula: (wherein 0≦x≦1 and 0.64≦y≦0.95) on a single crystal substrate; Including, The single crystal substrate has a (001), (010), or (100) crystal face perpendicular to the surface; the piezoelectric thin film is adjacent to a surface of the single crystal substrate, the piezoelectric thin film being oriented such that a (001), (010), or (100) crystallographic plane of the piezoelectric thin film is substantially parallel to either a (001), (010), or (100) crystallographic plane of the single crystal substrate; The piezoelectric thin film is composed of at least two adjacent NbO 2 NbO 2 The faces are offset from one another by approximately half a lattice length in either the (100), (010), or (100) crystal planes.

[0088] In some embodiments, a method for fabricating a piezoelectric thin film element includes: Empirical formula (K 1-x Na x ) y NbO 3 forming a piezoelectric thin film having the formula: (wherein 0≦x≦1 and 0.64≦y≦0.95) on a single crystal substrate; Including, The single crystal substrate has a (001), (010), or (100) crystal face perpendicular to the surface; the piezoelectric thin film is adjacent to a surface of the single crystal substrate, the piezoelectric thin film being oriented such that a (001), (010), or (100) crystallographic plane of the piezoelectric thin film is substantially parallel to either a (001), (010), or (100) crystallographic plane of the single crystal substrate; The piezoelectric thin film has columnar grains oriented in the respective

[0001] ,

[0010] , or

[0100] orientations, The piezoelectric thin film is composed of at least two adjacent NbO 2 Includes faces.

[0089] In some embodiments, a method for fabricating a piezoelectric thin film element includes: Empirical formula (K 1-x Na x ) y NbO 3 forming a piezoelectric thin film having the formula: (wherein 0≦x≦1 and 0.64≦y≦0.95) on a single crystal substrate; Including, The single crystal substrate has a (001) crystal face perpendicular to the surface. 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) crystallographic plane is substantially parallel to the (001) crystallographic plane of the single crystal substrate.

[0090] In some embodiments, a method for fabricating a piezoelectric thin film element includes: Empirical formula (K 1-x Na x ) y NbO 3 forming a piezoelectric thin film having the formula: (wherein 0≦x≦1 and 0.64≦y≦0.95) on a single crystal substrate; Including, The single crystal substrate has a (001) crystal face perpendicular to the surface. the piezoelectric thin film is adjacent to a surface of the single crystal substrate, the piezoelectric thin film being oriented such that its (001) crystallographic plane is substantially parallel to the (001) crystallographic plane of the single crystal substrate; The piezoelectric thin film is composed of at least two adjacent NbO 2 NbO 2 The faces are offset from one another by approximately half a lattice length in either the (100), (010), or (100) crystal planes.

[0091] In some embodiments, a method for fabricating a piezoelectric thin film element includes: Empirical formula (K 1-x Na x ) y NbO 3 forming a piezoelectric thin film having the formula: (wherein 0≦x≦1 and 0.64≦y≦0.95) on a single crystal substrate; Including, The single crystal substrate has a (001) crystal face perpendicular to the surface. the piezoelectric thin film is adjacent to a surface of the single crystal substrate, the piezoelectric thin film being oriented such that a (001) crystallographic plane of the piezoelectric thin film is substantially parallel to a (001) crystallographic plane of the single crystal substrate; The piezoelectric thin film has columnar grains oriented in the

[0001] direction. The piezoelectric thin film is composed of at least two adjacent NbO2 Includes faces.

[0092] In some embodiments, forming the piezoelectric thin film includes depositing the piezoelectric thin film using sputtering. In some embodiments, forming the piezoelectric thin film includes sputtering at a substrate temperature of about 680° C. and a discharge power of about 120 W.

[0093] In some embodiments, sputtering is performed for at least 2 hours. Sputtering may be performed for at least 1.5 hours, at least 3 hours, or at least 4 hours. In some embodiments, sputtering is performed at an argon-oxygen ratio (Ar / O) of about 50 / 15.

[0094] In some embodiments, sputtering is about 3.5×10 -3 This is done under a total pressure of mtorr. In some embodiments, the sputtering angle, substrate-target distance, argon-oxygen ratio, and / or deposition temperature are controlled to provide a (K+Na) / Nb ratio of about 0.64 to about 0.95.

[0095] In some embodiments, the method further comprises cutting and polishing the surface of the single crystal substrate prior to sputtering, the surface having a (001), (010), or (100) crystallographic plane perpendicular to the surface.

[0096] In some embodiments, the piezoelectric thin film may be grown on a water-soluble single crystal substrate. In some embodiments, the piezoelectric thin film may be grown on an organic single crystal substrate. In such cases, the piezoelectric thin film can then be obtained by removing the substrate in a post-deposition step. EXAMPLES

[0097] Examples of the present invention will now be discussed below, however, the scope of the present invention is not limited to only these examples. Example 1 Assuming that the total content of K and Na is 100%, the K content ratio is 30%, the (K+Na) / Nb ratio is 0.64, and the (001)-oriented 0.5% Nb-doped SrTiO 3 Grown on a single crystal substrate, of formula (K,Na)NbO 3 The piezoelectric thin film having a columnar structure with columnar grains extending from the substrate surface perpendicular to the horizontal plane of the film (see FIG. 7). Such columnar grains have an average width of 5-6 nm or less, and the total thickness of the film is 300 nm (see FIG. 8). These grains are separated from each other by antiphase boundaries or antiphase grain boundaries, the density of which is 0.23 nm. -1 This clear antiphase boundary is formed between two adjacent NbO 2 The two NbO 2 One of the faces is 1 / 2 <100> a or 1 / 2 <010> They are offset by a distance a, where a is the horizontal lattice parameter, <100> and <010> are the set of two horizontal crystallographic orientations (see Figure 9). When a voltage of 58.3 kV / cm is applied at 1 kHz, the film has an effective longitudinal piezoelectric coefficient d 33 * Such piezoelectric thin films are highly suitable for stroke-based applications such as microblowers, micropumps, microinjectors, and switches (see FIG. 10).

[0098] Example 2 Assuming that the total content of K and Na is 100%, the K content ratio is 30%, the (K+Na) / Nb ratio is 0.92, and the (001)-oriented 0.5% Nb-doped SrTiO 3 Grown on a single crystal substrate, of formula (K,Na)NbO 3 The piezoelectric thin film has a columnar structure similar to that of Example 1, with the columnar grains having an average width of 10 nm (see FIG. 11). The (K+Na) / Nb ratio of this film is 0.92, compared to 0.64 for the film described in Example 1. This piezoelectric thin film has a d of 1293.7 pm / V measured at 1 kHz at a driving voltage of 75 kV / cm. 33 * is shown (Figure 12).

[0099] The scanning transmission electron microscope images shown here were taken using a JEOL ARM200F atomic resolution electron microscope equipped with a cold field emission gun and an ASCOR fifth-order aberration corrector. The chemical composition of the thin films was measured using a Zeiss Supra 40VP scanning electron microscope equipped with an Oxford Instruments energy dispersive spectrometer operating at 20.0 kV. The voltage-dependent displacement of the piezoelectric thin films was measured using an OFV-3001-SF6 PolyTech GmbH (Germany) scanning laser vibrometer. Au electrodes with a diameter of 200 μm were sputtered onto the thin films, followed by baking at 200 °C for 15 min. The bottom electrode was exposed by previously peeling the film using a diamond knife and depositing a Au film on a small patch at one corner of the substrate. The laser was scanned over the electrodes using a circular profile while exciting the electrodes with an AC voltage. The antiphase boundary density is estimated by measuring the number of boundaries per unit length of the crystal 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 scans was counted, then the average number of APBs crossing a line was divided by the length of the line scan, i.e., 25 nm.

[0100] It will be appreciated that many further modifications and permutations of various aspects of the described embodiments are possible, such as substrate variations and A-site elemental doping, etc. Accordingly, the described aspects are intended to embrace all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims.

[0101] Throughout this specification and the claims which follow, unless the context otherwise requires, 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 integer or step, or group of integers or steps.

[0102] Reference in this specification to any prior publication (or information derived therefrom) or to any known matter is not to be considered, and should not be regarded, as an admission or acknowledgment, or any form of suggestion, 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 pertains.

Claims

1. a) Empirical formula (K １－ｘ Na ｘ ) ｙ NbO ３ wherein 0≦x≦1 and 0.64≦y≦0.95; b) a cubic single crystal substrate having a (001), (010), or (100) crystal face perpendicular to the surface; A piezoelectric thin film element comprising: a piezoelectric thin film adjacent to a surface of the single crystal substrate, the piezoelectric thin film being oriented such that its (001) crystallographic plane is substantially parallel to either a (001), (010), or (100) crystallographic plane of the single crystal substrate; The piezoelectric thin film is formed by at least two adjacent NbO ２ At least two adjacent NbO ２ the faces are offset from one another by approximately half a lattice length in either the (001), (010), or (100) crystal planes; Piezoelectric thin film element.

2. A piezoelectric thin film element as described in claim 1, wherein the piezoelectric thin film has columnar grains oriented in the respective [001], [010], or [100] orientations.

3. At least two adjacent NbO ２ 3. The piezoelectric thin film element of claim 1, wherein the planes are misaligned from one another by about 0.220 nm to about 0.260 nm in either the (001), (010), or (100) crystal planes.

4. The density of antiphase boundaries in the piezoelectric thin film is about 0.05 nm －１ ~about 0.30nm －１ 4. The piezoelectric thin film element according to claim 1, wherein

5. The piezoelectric thin film has an effective longitudinal piezoelectric coefficient (d ３３ ＊ 5. The piezoelectric thin film element according to claim 1, further comprising:

6. 6. The piezoelectric thin film element according to claim 1, wherein the piezoelectric thin film has a columnar structure, and the columnar grains have a width of about 3 nm to about 6 nm.

7. 7. The piezoelectric thin film element according to claim 1, wherein the piezoelectric thin film has a thickness of about 100 nm to about 500 nm.

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

9. The substrate is SrTiO ３ , LaAlO ３ , DyScO ３ , (La,Sr)(Al,Ti)O ３ , Si, NdGaO ３ , LiTaO ３ , YAlO ３ , La ｘ Sr １－ｘ FeO ３ , La ｘ Ca １－ｘ FeO ３ , La ｘ Sr １－ｘ CoO ３ , La ｘ Sr １－ｘ MnO ３ , LaNiO ３ , and SrRuO ３ 9. The piezoelectric thin film element according to claim 1, which is a perovskite single crystal selected from the group consisting of:

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

11. The perovskite oxide layer is La ｘ Sr １－ｘ FeO ３ , La ｘ Ca １－ｘ FeO ３ , La ｘ Sr １－ｘ CoO ３ , La ｘ Sr １－ｘ MnO ３ , LaNiO ３ , and SrRuO ３ The piezoelectric thin film element according to claim 10, wherein the piezoelectric thin film element is selected from the group consisting of

12. 12. The piezoelectric thin film element according to claim 10, wherein the perovskite oxide layer has a thickness of about 1 nm to about 300 nm.

13. 13. The piezoelectric thin film element according to claim 1, further comprising an electrode overlaid on the piezoelectric thin film.

14. The electrode is Pt, Au, Ag, Cu, Cr, Al, La ｘ Sr １－ｘ FeO ３ , La ｘ Ca １－ｘ FeO ３ , La ｘ Sr １－ｘ CoO ３ , La ｘ Sr １－ｘ MnO ３ , LaNiO ３ , and SrRuO ３ The piezoelectric thin film element according to claim 13, wherein the piezoelectric thin film element is selected from the group consisting of

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

16. 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 fabricating a piezoelectric thin film element, comprising the steps of: Empirical formula (K １－ｘ Na ｘ ) ｙ NbO ３ forming a piezoelectric thin film having the formula: (wherein 0≦x≦1 and 0.64≦y≦0.95) on a cubic single crystal substrate; Including, The cubic single crystal substrate has a (001), (010), or (100) crystal face perpendicular to the surface; a piezoelectric thin film adjacent to a surface of a single crystal substrate, the piezoelectric thin film being oriented such that a (001), (010), or (100) crystallographic plane of the piezoelectric thin film is substantially parallel to either a (001), (010), or (100) crystallographic plane of the single crystal substrate; The piezoelectric thin film is formed by at least two adjacent NbO ２ At least two adjacent NbO ２ the faces are offset from one another by approximately half a lattice length in either the (001), (010), or (100) crystal planes; method.

18. 20. The method of claim 17, wherein forming the piezoelectric thin film comprises depositing the piezoelectric thin film using sputtering.

19. 19. The method of claim 17 or 18, wherein the step of forming the piezoelectric thin film comprises sputtering at a substrate temperature of about 680° C. and a discharge power of about 120 W.

20. 20. The method of claim 18 or 19, wherein sputtering is carried out for at least 2 hours.

21. 21. The method according to any one of claims 18 to 20, wherein the sputtering is carried out with an argon-oxygen ratio (Ar / O) of about 50 / 15.

22. Sputtering is about 3.5 x 10 －３ 22. The process of any one of claims 18 to 21, carried out at a total pressure of mtorr.

23. 23. The method of any one of claims 18 to 22, wherein the sputtering angle, substrate-target distance, argon-oxygen ratio, and / or deposition temperature are controlled to provide a (K+Na) / Nb ratio of about 0.64 to about 0.

95.

24. 21. The method of any one of claims 17 to 20, further comprising the step of cutting and polishing the surface of the single crystal substrate prior to sputtering, the surface having a (001), (010), or (100) crystallographic plane perpendicular to the surface.

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