Thin-film device, electroceramic thin film, use of BFO-BTO, piezoelectric material, precursor solution, process of forming a thin film

Abstract

The present application addresses a thin-film device having a thin film comprising a BiFeO3-BaTiO3-based material.

Description

[0001] P2024,1131 WO N April 16, 2025 - 1 - Description Thin-film device, electroceramic thin film, use of BFO-BTO, piezoelectric material, precursor solution, process of forming a thin film The present application relates to a thin-film device, an electroceramic thin film, a use of BFO-BTO, a piezoelectric material, a precursor solution and a process of forming a thin film. Electroceramic thin films find application in many applications such as high-energy capacitors, ferroelectric memories, pyroelectric elements, piezoelectric energy harvesters, piezoelectric actuators, such as micro mirrors, inkjet printing heads or haptic devices, or piezoelectric sensors, such as pressure sensors or accelerometers. So far, to the best of the knowledge of the inventors, only lead-based materials have been used in such thin-film devices. For example lead-based perovskites such as Pb[ZrxTi1−x]O3(PZT) or (1-x)Pb(Mg1 / 3Nb2 / 3)O3-xPbTiO3(PMN-PT) were applied. The terms “perovskite” and “perovskite lattice” are to be understood as perceived by the person ordinarily skilled in the art. In particular, “perovskite lattice” may be understood as the structure of a material that follows the formula ABO3which has a crystal structure similar to that of the mineral perovskite (CaTiO3). This is not to be understood as limitation to cubic perovskites, but includes any distorted perovskite, such as orthorhombic, tetragonal or P2024,1131 WO N April 16, 2025 - 2 - trigonal structures. As indicated by ABO3, in a perovskite A- sites and B-sites may be distinguished. These sites may be occupied by different cations. For example, in the case of PZT, the A-site is at least formally occupied by Pb-ions and the B-site is at least formally occupied by Zr-ions and Ti- ions. The above-mentioned lead-based materials have good electromechanical or piezoelectric properties, but severe environmental and health issues are associated with these materials. Accordingly, it is a task of the present application to provide a material that is non-lead based. Furthermore, it may also be a task that it has good electromechanical properties, which makes it advantageous for a thin film. According to claim 1 and according to other independent claims, the above-mentioned task is fulfilled at least partially. According to dependent claims, embodiments are claimed and disclosed which provide other properties. Other embodiments are also disclosed in the following which may have additional advantages. In the following embodiments are explained which may share the properties of each of the disclosed embodiments as far as applicable. According to a first embodiment, a thin-film device is disclosed. The thin-film device has a thin film that comprises a BiFeO3-BaTiO3-based material. The BiFeO3-BaTiO3- based material may be abbreviated as “BFO-BT”, or “BFO-BTO”, with “BFO” standing for BiFeO3or a BiFeO3-based component P2024,1131 WO N April 16, 2025 - 3 - and “BT” or “BTO” standing for BaTiO3or a BaTiO3-based component. According to another embodiment, a thin film is also disclosed. The features disclosed for the thin film may apply to the thin film and to the thin-film device having the thin film and vice versa. According to an embodiment, the thin film is a ceramic thin film. The BiFeO3-BaTiO3-based material may be a ceramic material. According to an embodiment that may be preferred, the thin film is purely based on or made from a BiFeO3-BaTiO3-based material. This may mean in particular that other materials such as, for example, strontium titanate (SrTiO3), do not form a basis for the material of the thin film or preferably are not present in the thin film. In this case, only doping materials or materials as explained below may be present in the material in addition to the components BiFeO3and BaTiO3. This may also apply, for example, to cases in which strontium (Sr) is used as a dopant. In such cases according to stoichiometry, strontium titanate (SrTiO3) could at least be formally calculated from the resulting composition but is no main component and has not been basis for the material of the thin film. Also, unavoidable impurities of Sr or SrTiO3may be present in small quantities as a distinct compound within the thin film, but also in this case this does not render strontium titanate (SrTiO3) as a basis of or for the thin film. Furthermore, according to an embodiment, a BiFeO3-BaTiO3- based material can be understood as a material, preferably a P2024,1131 WO N April 16, 2025 - 4 - ceramic material, that has a composition formula which can be derived from the two components BiFeO3and BaTiO3. As explained below in embodiments, the material may contain dopants or additives. Generally, the ratio between a BiFeO3-based component (here short BFO) and a BaTiO3-based component (here short BTO) is not limited. According to an embodiment, the BFO to BTO ratio can be between 99.999 mol% of BFO to 0.001 mol% of BFO. By changing the BFO to BTO ratio, the temperature of the Curie Point may be adapted. For example, the compositions rich in BFO will have a higher Curie point. This may be useful for high-temperature applications. In contrast, solutions rich in BTO content can have reduced leakage current of the resulting material. Changing the BFO to BTO ratio may also influence the obtained phase of the thin film and influence material properties. According to a preferred embodiment the composition is close to the morphotropic phase boundary (short: MPB), i.e. the composition where the material exhibits the highest piezoelectric coefficients. This is particularly advantageous for piezoelectric applications. The location of the MPB with respect to BFO to BTO ratios can be different for doped BFO- BT material. According to preferred embodiments, the MPB may be at compositions that contain between 20 and 40 mol% of BTO. According to a preferred embodiment, the BiFeO3-BaTiO3-based material is a solid solution of the compounds BiFeO3and BaTiO3. A solid solution may be understood according to the IUPAC definition, according to which a solid solution is a solid in which components are compatible and form a unique P2024,1131 WO N April 16, 2025 - 5 - phase. All compounds preferably are present in the same crystal structure. In case of dopants these preferably also are part of the solid solution. Thus, for an example of BiFeO3-BaTiO3which has 30 mol% BTO, and with the formula ABO3in mind, the 30% of A-sites are occupied by Ba-ions and 70% by Bi-ions. The same is true for B-site ions, where in the example 30% of B-sites are occupied by Ti-ions and 70% by Fe- ions. Thus, for any single A-site the probability of finding a Ba-ion in it, is 30% in the example. The same applies to the other ions. Such a solid solution, for example, is in contrast to composite materials, in which components are not present in a common unique phase and / or differences in crystal structure between different grains or phases are present. It is noted that the BiFeO3-BaTiO3-based material in a ceramic form in a thin film, of course may have grains. For example, grain boundaries or similar secondary phases may be present in such a ceramic material. The above said regarding the solid solution according to a preferred embodiment applies to the individual grains or the main material of the grains. The term “thin film” as well as the term “thin-film device” may be understood as the term is understood in the field. According to an embodiment, for example, a thin film may be a film that has a thickness of 50 µm or below and preferably of 20 µm or below. The thin film may be an “electroceramic thin film”. In particular, the electroceramic properties may be provided by the BiFeO3-BaTiO3-based material. According to a most preferred embodiment, the thin film has piezoelectric properties and may be a piezoelectric thin film. P2024,1131 WO N April 16, 2025 - 6 - The inventors of the present invention have found that BiFeO3-BaTiO3-based materials can be used for thin-film devices and in particular for electroceramic thin-film devices. They allow lead-based materials to be replaced. At least they may help to strongly reduce the content of lead in these applications, even if small quantities of lead may be present as dopant. According to a preferred embodiment, the thin film is free from lead completely, except for unavoidable impurities, which may mean that no intentional doping by lead is present. According to an embodiment, unavoidable impurities may be present in concentrations that are lower than the concentration of intentionally added dopants. More preferred such impurity-concentrations are at least one order of magnitude smaller than the concentrations of dopants. For example, unavoidable impurities may be present at a concentration of below 0.1 mol% or preferably below 0.01 mol% relative to BFO-BT. Furthermore, the inventors of the present invention have found that so far, the above-named BiFeO3-BaTiO3-based material was only employed as bulk, but not as thin film material. An example of such bulk material used can be found in Chen Y, Mei K, Wong C-M, Lin D, Chan HLW, Dai J. Ultrasonic Transducer Fabricated Using Lead-Free BFO-BTO+Mn Piezoelectric 1-3 Composite. Actuators. 2015; 4(2):127-134. The inventors of the present invention found that employing the BiFeO3-BaTiO3-based material in a thin film may lead to unexpected advantageous properties, as is also shown below. From the properties as a bulk-material it is not apparent why the BFO-BT-based material should be suitable as a thin film material. As bulk-material BFO-BT tends to be polycrystalline P2024,1131 WO N April 16, 2025 - 7 - with grains, a considerable portion of grain boundaries or also voids. The composition of such grain boundaries in BFO- BT bulk is likely to deviate from the composition of the cores of the grains. Also, secondary phases may sometimes form which have a different phase to the main grains. Such secondary phases can form in the voids, for example. Also, as a bulk material the BFO-BT-based material does not show any tendency to crystallize with a preferred orientation. In contrast to this, surprisingly, when employed in a thin film and in particular one that has been prepared using chemical solution deposition, the BFO-BT-based material may, according to embodiments, be more monocrystalline with large island-like grains or even form columns. Also, the portion of grain-boundaries and / or secondary phases may be reduced. In particular, the inventors found that in a thin film the material is more likely to adopt a preferential orientation. This may help to provide good piezoelectric properties, for example. For the bulk material also often only a limited selection of starting materials or raw materials, such as typically oxides or carbonates, are available. In contrast, as is shown below, the inventors found that for forming a thin film, a wide variety of starting materials is available. The bulk material is typically formed from a mixture of solid components, which are for example in powder form, with grain sizes in the order of magnitude of about 100 nm to 10 µm. Such materials often are difficult to dope homogeneously, in particular when aiming at small quantities of doping or implementing several dopants. In such cases unintended or uncontrolled uneven distributions of dopants may occur in the P2024,1131 WO N April 16, 2025 - 8 - bulk material. In contrast, the approaches discussed below for the thin film may help to achieve more uniform or homogenous material properties. Regarding the background of producing a bulk material, classic bulk ceramics are typically prepared from a starting material (powder) via solid-state synthesis approach. The inventors found that this reaction is diffusion-driven and occurs during the calcination and sintering. Further the inventors observed that due to the diffusion process, especially materials with high complexity (more than three elements, such as Bi, Fe, Ba, Ti, O) often tend to have a non-homogeneous element distribution after sintering. The temperatures at which the solid-state reaction occurs typically range from about 10% below the melting point of the starting materials. The sintering is, for example, performed above 1000°C, as can be seen in the citation above or even above 1300°C. In contrast, the inventors found that when preparing a thin film by a chemical solution deposition process, the pre- synthesized precursor solutions are chemically homogeneous on an atomic level. Therefore, the chemical homogeneity is preserved in the fabricated thin films. This may help to achieve outstanding performance. The chemical-solution- deposition-derived thin films, according to an embodiment, are therefore not prepared like bulk ceramics, by solid-state synthesis (diffusion-driven process), but by decomposition of organic compounds and crystallization process. In the bulk material the inventors also found drawbacks regarding limited individual optimizability of the individual components or expensive or complex production. In contrast, P2024,1131 WO N April 16, 2025 - 9 - the thin films can be highly tunable, even allowing for realization of intentional gradients over the thickness of a film. Also, bulk BFO-BT may in some cases require high sintering temperatures, that for example lie close to the melting point of the material, which in the bulk material may be required so that the different ions (e.g. Bi, Ba, Fe, Ti) can diffuse into each other to form a “solid solution”. In contrast in thin films the inventors found that it may be possible to have lower crystallization temperatures, for example due to the initial homogeneity of the to be crystallized material. Thus, high temperatures can be avoided, which otherwise may lead to evaporation of some components, which can make the stoichiometry difficult to adjust in bulk materials. According to a further embodiment, the thin film may have a thickness of 10 nm to 20 µm. According to preferred embodiments, a lower range for the thickness can be 20 nm, 50 nm or 100 nm According to preferred embodiments, an upper thickness range can be 1 µm, 2 µm or 5 µm. According to a preferred embodiment of the thin-film device, the thin film can be arranged above a substrate. According to variations of this embodiment, the thin film can be arranged directly on a substrate surface. Alternatively, layers such as those explained below may be arranged between the substrate and the thin film. Generally, the substrate is not limited. For example, the following substrates may be used. P2024,1131 WO N April 16, 2025 - 10 - For example, silicon wafers may be used as a substrate. An example of these can be silicon-on-insulator (SOI) substrates. Such a substrate may be used for any of the named applications. In particular, micromechanical devices such as MEMS devices are preferably built with such a substrate. Alternatively, ceramic substrates such as alumina or zirconia or other ceramic substrates may be used. Also, glass substrates may be used. Examples of glass substrates may be fused silica or borosilicate glass substrates. Such substrates may be particularly preferable for transparent and flexible electronics such as displays. Alternatively, substrates may be single crystalline materials such as sapphire or other single crystals. Also, these can be used for high performance transparent electronics. Also, according to embodiments, transparent and conductive materials such as indium tin oxide (ITO), fluorine tin oxide (FTO), aluminum zinc oxide (AZO) or antimony tin oxide (ATO) may be used as substrate material. Another preferred type of substrate may be metal foils. In particular copper, silver or base metal (e.g. titanium, nickel, or aluminum), alloys (e.g. brass, Invar, Kovar, stainless steel) foils can provide cost-efficient substrates. Such materials may also provide flexible substrates for flexible electronics. Also, such substrates may allow for biocompatible electronics. Also, polymers such as polyimide (PI) or polyethylene terephthalate (PET) can be used as substrate materials. For example, they can be used to produce cost-efficient or flexible electronic substrates. P2024,1131 WO N April 16, 2025 - 11 - According to an embodiment of the thin-film device, a layer that has a buffer function and / or a seed function may be arranged between the substrate and the thin film. In the case that it has a buffer function, such a layer may be called a “buffer layer”. A buffer layer can be configured to suppress or reduce diffusion between the thin film and layers below. Such underlying layers may be, for example, an electrode material or the substrate directly. Regarding the electrode material, it is referred to other embodiments. Examples of materials that have a buffer function are layers comprising or consisting of LaNiO3, HfO2or Al2O3. In the case that such a layer has a seed function, it can be called a “seed layer”. Seed layers may support the grain growth and crystal orientation of the thin film. The seed layer may help to define the surface orientation of the above-lying layer. Such layers may comprise or consist of LaNiO3, PbTiO3or TiO2. As one can see from the listing of examples above, some materials may have both the property of a buffer layer and of a seed layer, such as for example LaNiO3. According to preferred embodiments, the layer that has a buffer and / or a seed function is preferably in direct contact with the thin film arranged above. In particular in the case of a buffer function, diffusion into the thin film or out of the thin film can be better suppressed. Similarly, in the case of a seed layer function, due to direct contact the seed layer can directly influence the crystal orientation of the above-arranged thin film. According to an embodiment, the thin film in the thin film device can be electrically contacted. Any material in such a P2024,1131 WO N April 16, 2025 - 12 - device with which voltage can be applied or that can transfer charge from or to the thin film and accordingly contact, can be called an electrical contact. According to a preferred embodiment, a separate electrode may be realized for electrically contacting the thin film. An electrode can be a separate layer for contacting the thin film electrically. The arrangement of electrodes on or in the thin film is not limited and can be chosen depending on the application. For example, the electrodes can be applied such that voltage can be applied to produce a piezoelectric effect such as contraction or elongation. Alternatively, it can be used as a readout, for example to detect mechanical force or mechanical input on the piezoelectric film. In the following embodiments of electrode configurations are discussed. These can be summarized under two concepts, named metal-insulator-metal (MIM) design and interdigital electrodes (IDE) design. For example, in the metal-insulator-metal (MIM) design the following stacking may be used in this order from bottom to top: substrate, bottom electrode, electroceramic thin film, top electrode. According to a variation or preferred embodiment, an adhesion layer may be arranged between substrate and electrode. Other layers as explained elsewhere in this description may also be part of such a stack. According to an embodiment, external electrodes can be applied to contact the bottom electrode and / or the top electrode. In this case the bottom electrode and the top electrodes are internal electrodes. P2024,1131 WO N April 16, 2025 - 13 - According to an embodiment, for example in a MIM design, etching may be used to externally contact the thin film. For example, parts of the electrodes, such as a top electrode, may be etched. In addition, parts of the ceramic thin film may be etched. This etching can, for example, be performed via the direction of the substrate. Subsequently, external electrodes can be applied with or without etching. According to embodiments, multiple layers can be applied to one substrate in an MIM design. For example, the above- explained design may be applied to two opposite sides of one substrate. Also, several alternating layers of electrode and thin film can be arranged one upon the other on one or more than one side of the substrate. These embodiments may also be combined. According to an embodiment of an interdigital electrodes (IDE) design, no bottom electrode may be realized. For example, the thin film may be arranged on or above a substrate or optionally on or above an adhesion layer, a buffer layer and / or a seed layer. In this embodiment, only a top electrode layer is realized. In this top electrode layer, there are electrically separate portions which are separate in a horizontal plane parallel to the substrate. By this, voltage can be applied between two electrodes in this horizontal plane, which may lead to bending. Also alternatively, bending may be detected for example. Forming the electrodes is generally not limited. According to embodiments which may preferably be used in the above- described setups and in particular with the described thin films, magnetron sputtering, chemical or physical vapor deposition, evaporation, screen printing, electroplating or P2024,1131 WO N April 16, 2025 - 14 - chemical solution deposition may be used. As chemical solution deposition methods, for example spin coating, dip coating, spray coating, or inkjet printing may be used, for example. Also, the electrode materials are not limited. For example, transition metals or noble metals may be used. For example, platinum, gold, chromium, silver or copper may be used. Alternatively, alloys such as, for example, brass, may also be used. Alternatively, conductive oxides may also be used as electrode materials. Examples of conductive oxides are RuO2, ZnO, LaNiO3, SrVO3, SrRuO3, SrMoO3, (La0.7Sr0.3)MnO3, (La0.7Ca0.3)MnO3, IrO2, (Sr0.5Ba0.5)RuO3, BiFeO3, SrTiO3:Nb, indium tin oxide (ITO) In2O3:Sn, antimony doped tin oxide (ATO) SnO2:Sb, aluminum doped zinc oxide (AZO) ZnO:Al, gallium doped zinc oxide ZnO:Ga, fluor doped tin oxide (FTO) SnO2:F, hydrogen doped zinc oxide ZnO:H, hydrogenated indium oxides IO:H, tungsten doped hydrogenated indium oxide IWO:H, and cerium doped hydrogenated indium oxide ICO:H, for example. According to an embodiment, the thickness of the electrode can be between 50 nm and 500 nm. Thinner electrodes with a lower thickness, such as 100 nm to 300 nm or such as between 150 nm to 250 nm may also be preferred. In particular, thinner electrodes may be preferred in the case of the more expensive materials such as noble metals. Also, for electrodes below 500 nm, the inventors found that such a thickness may help to reduce internal stress or risk of delamination. This effect may be even more pronounced for the thinner electrode thicknesses. P2024,1131 WO N April 16, 2025 - 15 - According to an embodiment, an adhesion layer may be realized above the substrate surface. For example, it may be arranged between the substrate and an electrode or between the substrate and the thin film. Embodiments of this are explained above with respect to the MIM design and IDE design. According to an embodiment, the adhesion layer may comprise a transition metal and / or a transition metal oxide. A transition metal, for example, may be any transition metal from the fourth, fifth or sixth period of the periodic table. For example, the adhesion layer may comprise Ti, Ta or W as the transition metal. Accordingly, Ti, Ta or W may be comprised in metallic form or oxides of these may be comprised. For example, for Ti and Ta the metallic form may be advantageous. For Ti, the oxide, such as TiO2may also be advantageous. Alternatively, the adhesion layer can have more than one layer. For example, it may have a transition metal oxide layer and a transition metal layer. It may also have a sandwich structure in which a transition metal layer is sandwiched between two oxide layers or, vice versa, a transition metal oxide layer is sandwiched between two transition metal layers. According to an embodiment, the thickness of the adhesion layer can be between 1 nm and 100 nm. More preferably it can be between 10 nm and 50 nm. For example, and relevant in many practical scenarios, the thickness of the adhesion layer can be between 15 nm and 30 nm. Even more preferably it can be between 15 nm and 100 nm, such as between 15 nm and 50 nm or between 15 nm and 30 nm. The inventors of the present invention have found that if the adhesion layer is too thin, delamination can still take place and the diffusion-inhibiting properties are also reduced. In particular for thicknesses above 15 nm, the above-described P2024,1131 WO N April 16, 2025 - 16 - adhesion and diffusion reduction properties are particularly preferable. Generally, the method by which the thin film is formed is not limited. According to a preferred embodiment, the thin film may be a film that is obtained or obtainable by chemical solution deposition. The inventors found that chemical solution deposition is highly advantageous and highly versatile for forming the thin films having a BiFeO3-BaTiO3- based material. Films produced with this method have shown advantageous material properties, advantageous structures or otherwise advantageous properties. Accordingly, even though this feature is primarily a process feature, it also may characterize a film. Further details may also be found in relation to the process below. In principle, physical vapor deposition (PVD) (such as (magnetron-) sputtering, or pulsed laser deposition, for example) from a target may also be used, but this has been found to be less advantageous as it has higher risk of affecting the thin film composition. Generally, the inventors found several unexpected advantages for forming a BiFeO3-BaTiO3-based thin film by chemical solution deposition. For example, the inventors found that chemical solution deposition may allow for large flexibility in selection of raw materials and / or process routes for the precursor solutions, as is also shown below. Also, it may allow for fine tuning of each individual component of the composition. Also, chemical solution deposition may use homogeneous and molecularly dispersed solutions. The inventors assume that this helps to produce homogeneous layers (solid solutions). Besides, the chemical solution deposition method may be carried out using mild conditions, such as comparatively low crystallization temperatures. P2024,1131 WO N April 16, 2025 - 17 - In contrast, PVD processes, for example, often only allow for very few raw materials to be used. Also, PVD-methods, such as sputtering, often lead to a deviation in the material composition between the sputtering target or source and the thin film that is formed. In particular using PVD it may be sometimes difficult to predict or modify the composition, which means that some material combinations simply cannot be realized by PVD, even if a suitable target were available. Chemical solution deposition may also be a comparatively inexpensive process and quickly customizable, in contrast to some PVD processes which require expensive and complex machinery. Also, chemical solution deposition is more easily scalable, which is expensive for PVD. Chemical solution deposition also can be applied to large substrates, whereas PVD has substrate size limitations. Also, gradients of components in the thin film may be easily set or adjusted by varying the concentration in the precursor solutions for chemical solution deposition. In contrast, in PVD adjustment of the process may be considerably more difficult. Also, setting of gradients in PVD often is de facto impossible, as a separate target would be required for each gradation. Besides this, in PVD, if a change in film composition is to be implemented, a new target or source has to be produced, which is expensive and time-consuming. Therefore, tests and adaptations, such as variation of amounts of dopants, can be very time-consuming and there may be batch-dependent deviations in sample composition. Also, chemical solution deposition allows for depositing on a variety of substrates, including temperature sensitive P2024,1131 WO N April 16, 2025 - 18 - substrates, due to the mild temperature treatment conditions available. In contrast in PVD there may be limitations to substrates. A main advantage of chemical solution deposition is also that the layer thicknesses can be easily varied over a wide range, while via PVD often only low thickness thin films are available. Thin films, prepared by other methods, such as physical vapor deposition or in particular sputtering or pulsed laser deposition, where the films are deposited by a bombardment or energizing the target, the thin films also tend to be less chemically homogeneous than is achievable in films prepared by chemical solution deposition. The homogeneity achievable by chemical solution deposition may be particularly advantageous when compared to physical vapor deposition methods. For some of the latter, such as in particular pulsed laser deposition, there may be considerable changes in thin film composition within the lateral dimensions. For example in particular for pulsed laser deposition on wafer substrates there may be considerable differences in composition between the center of the substrate and the periphery, for example. According to an embodiment the film may undergo a crystallization treatment, i.e. it may be obtainable by a process including such crystallization treatment. According to an embodiment that is particularly relevant in the case of chemical solution deposition, the thin film is crystallized at a temperature that lies between 500 °C to 1300 °C such as preferably 600 °C to 1000 °C. An upper limit may, according to embodiments, also be 900°C or 800°C which P2024,1131 WO N April 16, 2025 - 19 - may each be combined with the above lower limit of 500 °C or 600 °C. According to another specific embodiment, a sintering temperature may be 700 ± 50 °C. As discussed in the embodiment above, the inventors found that the crystallization can be carried out at comparatively low temperatures. In particular, the crystallization may take place at considerably lower temperatures than the temperatures at which the bulk ceramics is sintered, as they are sintered at least at temperatures of above 1000°C or even of above 1300°C. Furthermore, according to a further embodiment, it may be preferred in some cases that more than one partial layer of the thin film is formed before crystallization. In chemical solution deposition the material to be deposited is present in a dissolved state. It is preferable to crystallize the material after deposition. In order to form a thin film of a certain thickness, several depositions may be accumulated. One deposition may form one partial layer. The present embodiment may be understood such that it is advantageous that a crystallization step is not performed after each single chemical solution deposition step but that several depositions are stacked one above the other. For example, as also explained below for the process, a drying step and / or a pyrolysis step may be applied preferably before crystallization. Thus, it may be preferable in this case that chemical solution deposition, drying, and pyrolysis in this order are performed more than once before crystallization. The inventors of the present invention have found that for the BiFeO3-BaTiO3-based material, advantageous properties may be achieved when more than one such partial layer is P2024,1131 WO N April 16, 2025 - 20 - deposited before crystallization. In particular, according to a preferred embodiment, three depositions are performed before crystallization. Furthermore, according to another preferred embodiment, six depositions are performed before crystallization. According to a variation of this embodiment, the substrate is a titanium foil. The inventors found that with six depositions above titanium foils preferable film properties may be achieved. According to an embodiment, the BiFeO3-BaTiO3-based material can be based on the following formula 1: [Bix+aBa1−x+b][Fex+cTi1−x+d]O3Formula 1 Formula 1 represents the composition of bismuth, barium, iron and titanium in a precursor solution without the addition of any dopants. The indices of the material are explained in more detail for formula 2. According to an embodiment, the BiFeO3-BaTiO3-based material can be obtainable by chemical solution deposition of a dissolved precursor of the following formula 2: ^O^, Formula 2 Furthermore, the following applies: Formula 3. As can be seen, formula 2 is in principle based on formula 1 but in addition has dopants µ and β. The listing of μ^^^μ^^^ … μ^^^and ^^^^ ^^^^ … ^^^^ indicates that none, one, or more P2024,1131 WO N April 16, 2025 - 21 - than one dopant may be present. Furthermore, the following applies: 0 < x < 1, -0.1 ≤ a ≤ 0.3, -0.1 ≤ b ≤ 0.3, -0.1 ≤ c ≤ 0.3, -0.1 ≤ d ≤ 0.3, 0 ≤ y ≤ 0.3, 0 ≤ z ≤ 0.3, x+a > 0, 1-x+b > 0, x+c > 0, and 1-x+d > 0. Formula 2 represents a composition in solution that may be deposited by a chemical solution deposition technique. This composition may be regarded as an initial composition. During certain steps, such as drying, pyrolysis or crystallization, compositions may change in principle. Accordingly, the application covers all thin films obtainable by chemical solution deposition of the material of formula 2. However, according to a preferred embodiment, at least a part of the material in the thin film or, more preferably, the entire material of the thin film after formation can be defined by the above formula 2. Accordingly, according to a preferred embodiment, the BiFeO3-BaTiO3-based material is represented by the above formula together with the above- named features. Formulas 1 and 2 are to be treated as sum formulas covering every material that falls into the component ratio covered by the formulas. As can be seen from the writing of formula 1 and formula 2, the assumption may be made that certain substances, such as bismuth and barium and dopants represented by the sign µ, occupy certain crystal positions. Iron, titanium and the dopants represented by β occupy other crystal positions. Here it is assumed that a perovskite crystal structure applies. However, the material defined by formulas 1 and 2 are not limited to this assumption and such materials only constitute a preferred embodiment. P2024,1131 WO N April 16, 2025 - 22 - In this context and according to an embodiment, the inventors found that during film formation and after the film is readily formed, the dielectric tends to be charge neutral. To achieve this, A-site (e.g. Bi vacancies), B-site (e.g. Fe vacancies), or oxygen vacancies may be formed, or elements could be present in different charge states. For example, iron may partially adopt the Fe3+and / or the Fe4+state. Accordingly, the above formulas 1 and 2 also cover such compositions or structures. As can be seen from the more general formula 1, but also applying to formula 2, according to embodiments the Bi to Fe ratio can vary and Bi can be added in excess. Moreover, the Ba to Ti ratio can vary and deficiency of Ba is possible. As can be seen in the above formula, by the defined sum of x+a bismuth must always be present. However, a allows for a bismuth deficit (for example if a < 0) or bismuth excess (for example if a > 0). The same holds true in a similar manner for the other components as provided by the above formulas or in equations, according to the limits defined in the context of formula 2. According to a preferred embodiment x+a ≥ 0.01 applies. According to another preferred embodiment 1-x+b ≥ 0.01 applies. According to another preferred embodiment x+c ≥ 0.01 applies. According to a further preferred embodiment 1-x+d ≥ 0.01 applies. The inventors found that within the above range, and in particular within the preferred ranges, preferable material properties can be achieved. In particular, in these ranges advantageous material properties may be achieved, at least P2024,1131 WO N April 16, 2025 - 23 - for some cases, that allow for high performance thin-film devices that may rival lead-based thin-film devices. According to a preferred embodiment, x may be larger or equal to 0.3, be larger or equal to 0.4, be larger or equal to 0.5, larger or equal to 0.6 or larger or equal to 0.65. Also, according to an embodiment, x may be smaller or equal to 0.99, such as smaller or equal to 0.95, such as smaller or equal to 0.94, such as smaller or equal to 0.9, or such as smaller or equal to 0.8, or smaller or equal to 0.75. For example, the following may apply 0.5 ≤ x ≤ 0.95, such as for example 0.5 ≤ x ≤ 0.9 such as for example 0.6 ≤ x ≤ 0.8 or such as 0.65 ≤ x ≤ 075. The value x may be regarded as the mole fraction of the BFO-derived component. These mole fractions of the BFO-derived component may apply in a generalized manner also to the other BFO-BT-materials that are not limited to the composition. For example, according to an embodiment, x can be smaller or equal to 0.85 and larger or equal to 0.6 (0.6 ≤ x ≤ 0.85). This corresponds to a mole fraction of the BTO-derived component of 15 to 40 mol%. For example, for x the following may apply, 0.65 ≤ x ≤ 0.85, or 0.67 ≤ x ≤ 0.85, or 0.65 ≤ x ≤ 0.8, or 0.65 ≤ x ≤ 0.75, or 0.67 ≤ x ≤ 0.75, or in particular 0.69 ≤ x ≤ 0.75, which corresponds to a mole fraction of the BTO-derived component of 15 to 35 mol%, 15 to 33 mol%, 20 to 35 mol%, 25 to 35 mol%, 25 ton 33 mol%, and 25 to 31 mol%, respectively. For the previous ranges high values for e31,fmay be achieved. These values are particularly advantageous when used in a thin film. Also, these values are particularly advantageous in connection with doping, such as Mn-doping, which is explained below. P2024,1131 WO N April 16, 2025 - 24 - The inventors found that surprisingly there might be some shift of highest e31,fas a function of BFO to BT ratio between bulk-materials and thin films. The morphotropic phase boundary (MPB) of bulk-material BFO-BT was reported in Lee, M.H., Kim, D.J., Park, J.S., Kim, S.W., Song, T.K., Kim, M.- H., Kim, W.-J., Do, D. and Jeong, I.-K. (2015), High- Performance Lead-Free Piezoceramics with High Curie Temperatures. Adv. Mater., 27: 6976-6982. For the thin films of the present application the inventors found a region of highest e31,fand thus also presumably of the morphotropic phase boundary (MPB) that lay considerably lower. In particular in the thin films highest e31,fwas found for values of x ≥ 0.67 such as x ≥ 0.68 and in particular x ≥ 0.69. According to a further preferred embodiment, the sum of all doping can be smaller or equal to 0.3. For example, it may lie between 0.001 ≤ y+z ≤ 0.3. More preferably it may be 0.0025 ≤ y+z ≤ 0.3, 0.0026 ≤ y+z ≤ 0.3, such as 0.005 ≤ y+z ≤ 0.3, or also 0.005 ≤ y+z ≤ 0.2. Even more preferably it may be 0.01 ≤ y+z ≤ 0.3. Also, preferably it may be 0.01 ≤ y+z ≤ 0.1 or even more preferably 0.01 ≤ y+z ≤ 0.05. In certain cases, a lower limit may also be 0.02. In particular, the inventors have found advantageous properties for the above values and in particular for values of above 0.01. The above values disclosed for y+z may also apply individually to y or z and to individual components, i.e., the above ranges may be defined for either y or z. This means in particular that y may be 0.001 ≤ y ≤ 0.3 or 0.005 ≤ y ≤ 0.2 or any of the ranges discussed for y+z. Alternatively, this means in particular that z may be 0.001 ≤ y ≤ 0.3 or 0.005 ≤ y ≤ 0.2 or any of the ranges discussed for y+z. P2024,1131 WO N April 16, 2025 - 25 - According to another preferred embodiment, the inventors found that preferably 0.0 ≤ a ≤ 0.20 applies. Even more preferably, 0.01 ≤ a ≤ 0.15 may apply. Or even more preferably 0.04 ≤ a ≤ 0.12 may apply. According to specific embodiments, 0.0 ≤ a ≤ 0.09 may apply. In this case preferably, 0.0 ≤ a ≤ 0.085 may apply. Or even more preferably 0.0 ≤ a ≤ 0.084 may apply. According to a preferred embodiment, the BiFeO3-BaTiO3-based material comprises one or more dopants selected from Li, Na, K, Rb, Cs, Mg, Ca, Sr, Be, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, Al, Ga, In, Ge, Sn, Pb, As, Sb, Se, Te, Si, Tl. This may mean that the material based on the formula 1 ([Bix+aBa1−x+b][Fex+cTi1−x+d]O3) in addition may contain one or more of these dopants. In the case of the materials represented by formula 2, in principle all of these dopants might take or occupy places marked by µ or β. This may mean that there is no restriction to whether any of the above dopants occupy A-sites or B-sites in ABO3. The above defined ranges for y and z, may apply individually to any dopant. This may mean that if more than one dopant is realized, with y or z being between 0 and 0.3, the sum of all dopants may be higher than 0.3. However, according to a preferred embodiment, the sum of all dopants does not exceed 0.6 and more preferably does not exceed 0.3. The inventors of the present invention assume that the following dopants as shown for µ and β in the following Table 1 tend to either occupy bismuth or barium places (A-sites) in the case of µ, or iron and titanium places (B-sites) in the P2024,1131 WO N April 16, 2025 - 26 - case of β. The above preferred ranges for y and z particularly apply to these dopants. Table 1 Dopants µ Li, Na, K, Rb, Cs, Ca, Sr, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Cu, Ag, Au, Cd, In, Tl, Pb, Si β Li, Na, K, Mg, Ca, Sr, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, Al, Ga, In, Ge, Sn, Pb, Sb, Te, Si According to an embodiment, the following may apply for each of the dopants below, 0.001 ≤ yi≤ 0.15 and / or 0.001 ≤ zi≤ 0.15. Preferably the following may apply, 0.005 ≤ yi≤ 0.10 and / or 0.005 ≤ zi≤ 0.10. Also, a preferred list of dopants can be found in Table 2. The preferred ranges for yiand zimay particularly apply to the preferred dopants. The preferred dopants tend to provide advantageous electromechanical or dielectric properties to the thin film. This is particularly relevant for Mn. Also, Pb may provide said properties. Nonetheless it may be advantageous according to embodiments not to use Pb in order to not only reduce but to fully avoid Pb. P2024,1131 WO N April 16, 2025 - 27 - Table 2 Periodic table group Preferred dopants 1 Na 2 Mg, Ca, Sr 3 Y 4 Zr, Hf 5 Nb 6 Cr 7 Mn 9 Co 10 Ni 11 Cu 12 Zn 13 Al, Ga, In, Tl 14 Sn, Pb, Si 16 Se, Te Lanthanides La According to embodiments, the thin-film device is employed in or is a high-energy capacitor, a ferroelectric memory, a pyroelectric element, a piezoelectric energy harvester, a piezoelectric actuator, such as for example a micro mirror, an inkjet printing head or a haptic device, or a piezoelectric sensor, such as for example a pressure sensor or an accelerometer. According to an embodiment, the properties of the material of the thin film may fulfill one or more and preferably all of the properties disclosed in Table 3. P2024,1131 WO N April 16, 2025 - 28 - Table 3 Property Unit Preferred More preferred range for range certain applications Capacitors Actuators Relative / 10 - 2000 300 - 2000 10 - 1200 permittivity - εrLoss tangent - % < 20 < 10 < 15 tan δ Maximum µC / cm210 - 60 30 - 60 10 - 40 polarization - ^^^^Remanent µC / cm20 - 40 0 - 30 0 - 30 polarization - ^^Coercive field - kV / cm 0 - 250 0 - 150 0 - 150 ^^Breakdown field kV / cm > 100 > 300 > 500 - ^^Leakage current µA / cm2< 50 < 5 < 20 density - ^ Longitudinal pm / V 10 - 300 < 50 > 30 piezoelectric coeff. – d33Furthermore, the inventors found that the above-mentioned electroceramic material can also be advantageous for other applications besides thin films. Accordingly, all properties of the material may also be considered advantageous individually without limitation to features of the thin film. The properties discussed in the following may also apply to the material applied to the thin film but are not limited to this. P2024,1131 WO N April 16, 2025 - 29 - According to an embodiment, an electroceramic material that is BiFeO3-BaTiO3-based is disclosed. It may be doped by at least one dopant selected from Li, Na, K, Rb, Cs, Mg, Ca, Sr, Be, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, Al, Ga, In, Ge, Sn, Pb, As, Sb, Se, Te, Si, Tl. The inventors found it particularly advantageous that the concentration of the dopant or of all dopants is above 1 mol%, this may alternatively be written as 0.01 < y+z, when alternatively referencing to formulas 2 and 3. For example, the maximum concentration of each individual dopant may be below or equal to 5 mol%. When alternatively reference is made to formulas 2 and 3, according to a preferred embodiment, 0.01 < y+z ≤ 0.05 may apply. According to an even more preferred embodiment, a lower range may be 2 mol% or above, which may be written as 0.02 ≤ y+z. In particular, according to an embodiment, the concentration of all dopants that are not Mn, individually may be between 0 and 30 mol%, or other above-described ranges may apply. According to a preferred embodiment of the electroceramic material, at least one dopant contained in the electroceramic material is Mn. In this embodiment, a Mn-concentration equal or above 1 mol%, or preferably of 2 mol% or above, or 3 mol% or above has been found to be advantageous. An upper limit may be 5 mol% or below. For example, the inventors found that for Mn concentrations in this range the PE-loop can be improved and a leakage current may be reduced. In the case that, according to an embodiment, Mn is the only dopant, formula 2 can be rewritten as formula 4: P2024,1131 WO N April 16, 2025 - 30 - [(Bix+aBa1-x+b)][(Fex+cTi1-x+d)1-zMnz]O3formula 4 For this composition the above-described preferred ranges for x, b, c, d and z may particularly apply. In the following, embodiments of a process of forming a thin film and in this context also a precursor solution are discussed. According to embodiments, the features and advantages disclosed with respect to the process and precursor solution may tie into the properties of the thin film and the thin-film device discussed above, and vice versa. According to an embodiment, a process of forming a thin film may comprise the following steps: First a precursor solution comprising a precursor compound for a BiFeO3-BaTiO3-based material dissolved in a solvent is provided. This precursor solution is deposited above or on a substrate via chemical solution deposition. Then a crystallization step that is configured to crystallize the BiFeO3-BaTiO3-based material is performed. According to an embodiment, the precursor solution is formed by dissolving metal precursors in the solvent. The precursors are precursors for a BiFeO3-BaTiO3-based material. The solution may be called a BFO-BT precursor solution. According to an embodiment, the metal precursors may comprise a Bi-precursor, an Fe-precursor, a Ba-precursor and a Ti- precursor in which the metal is present in atomic or ionic form. P2024,1131 WO N April 16, 2025 - 31 - According to embodiments, a metal precursor may be a covalent or ionic chemical compound containing at least a metal atom or ion in its chemical formula. Ligands or counterions can be of organic or inorganic nature. The metal precursor may be chosen to provide solubility in a certain solvent. According to embodiments, ligands and / or counter ions in the precursors may be selected from nitrate, acetate, citrate, tert-pentoxide, 2,3-dimethyl-2-butoxide, hydroxide, tert- butoxide, acetylacetonate, ethoxide, glyoxylate, methoxide, ethoxide, propoxide, iso-propoxide, butoxide, oxyacetylacetonate, dimethylamino, ethylhexyloxide, di-iso- propoxide, peroxocitrate, and water. Such ligands or counter ions are advantageous to provide good solubility in many precursor solutions. Below an exemplary list of metal precursors is provided in Table 4.

[0002] P2024,1131 WO N April 16, 2025 - 32 - Table 4 Bi precursors Fe precursors Ba precursors Ti precursors Bismuth(III) Iron(III) Barium nitrate Titanium(IV) nitrate nitrate methoxide Bismuth(III) Iron(III) Barium acetate Titanium(IV) nitrate nitrate ethoxide pentahydrate nonahydrate Bismuth(III) Iron(III) Barium acetate Titanium(IV) acetate acetate hydrate propoxide Bismuth(III) Iron(III) Barium Titanium(IV) citrate citrate hydroxide iso-propoxide Bismuth(III) Iron(III) Barium Titanium(IV) tert- acetylacetonate hydroxide butoxide pentoxide monohydrate Bismuth(III) Iron(II) Barium Titanium(IV) 2,3-dimethyl- acetate hydroxide oxyacetyl- 2-butoxide octahydrate acetonate Iron(III) Barium iso- Tetrakis(dimet ethoxide propoxide hylamido) titanium(IV) Barium tert- Titanium(IV) butoxide tert-butoxide Barium acetyl- Titanium(IV) acetonate 2-ethyl- hexyloxide Barium acetyl- Titanium(IV) acetonate bis(acetyl- hydrate acetonate) di- iso-propoxide Barium Titanium(IV) glyoxylate peroxocitrate Barium tert- pentoxide P2024,1131 WO N April 16, 2025 - 33 - According to an embodiment, the precursor solution can be prepared in concentrations up to 1.0 M (1 M = 1 mole per liter). This can mean that the concentration of the precursor(s) for a BiFeO3-BaTiO3-based material can be 1.0 M or below. For example, a Bi-precursor, a Fe-precursor, a Ba- precursor and Ti-precursor may be present in this concentration, and in particular this may apply to the examples of table 4. In principle there is no bottom concentration limit. If the concentration of the precursor solution is low, such as 0.1 M or below, film thickness per deposition is lower and more layers have to be deposited to achieve a certain final thickness. Thus, according to an embodiment, it may be preferred to have a concentration of 0.1 M or higher. The use of more highly concentrated precursor solutions, such as above 1 M or in some cases above 0.8 M, may increase the chance of formation of a porous microstructure or a cracked film. Thus, if such a structure is targeted, the higher concentrations may be applied. For more homogeneous films, concentrations of 0.1 to 0.8 M or even more preferably concentrations of 0.2 M to 0.6 M may be used. For forming the precursor solution, the solvent and other components in it are not limited. It is highly preferred that the solvent is capable of dissolving one or more, or more preferably all, precursor compounds. According to a preferred embodiment, the solvent and / or other components of the solution are chosen such that properties, P2024,1131 WO N April 16, 2025 - 34 - such as viscosity, surface tension or density are advantageous for the chemical solution deposition. According to an embodiment, a mixture of two or more solvents can be used. Having more than one solvent in the solvent mixture may help to adjust the properties to be advantageous for chemical solution deposition. Also, it may help to improve the solubility of two or all metal precursors in one mixture. According to an embodiment, one or more than one additive may also be added to the solution. The term “additive” may be understood as the word is recognized in the field. For example, and preferably, it may be understood as a chemical compound that may play a particular role in the solution, such as stabilization of metal precursors, suppression of the hydrolysis reactions or condensation reactions, tuning of physicochemical properties or similar, but the concentration of which is comparatively low when compared to the solvent. For example, an additive may have a concentration of below 20 wt% of the total solution. Chemically some compounds may be used as additives or solvents. According to an embodiment, the solvent can be of inorganic nature. For example, an inorganic solvent can be water or aqueous ammonia. According to a preferred embodiment, the solvent can be an organic solvent. For example, it can be aliphatic or aromatic. Examples for this may be pentane, hexane, cyclohexane, heptane, toluene, benzene, any xylene (i.e. o-, p- or m-xylene), ethylbenzene, 1,3,5-trimethylbenzene. P2024,1131 WO N April 16, 2025 - 35 - According to an embodiment, a solvent may be an organic compound comprising heteroatoms. For example, heteroatoms such as oxygen, nitrogen, sulfur or phosphorus may be preferred. According to a preferred embodiment, the solvent may be selected from alcohols, ethers, carboxylic acids, esters, ketones, aldehydes, carbonate esters, acid anhydrides, amines, imines, amidines, amides, carbamates, carbamides and imides. Examples of heteroatom-containing solvent molecules can be formic acid, 2-ethylhexanoic acid, iso-butyl acetate, acetic anhydride, acetic acid, ethyl acetate, pentyl acetate, succinic acid, propionic acid, propyl acetate, iso-pentyl acetate, succinic anhydride, butyric acid, iso-propyl acetate, oxalic acid, butyl acetate, methanol, 1-butanol, ethylene glycol, glycerol, ethanol, 2-butanol, propylene glycol, 1-propanol, 2-methyl-1-propanol, propane-1,3-diol, 2- propanol, 2-methyl-2-propanol, butane-1,4-diol, diethyl ether, 1,3-dioxane, bis(2-ethoxyethyl) ether, 15-crown-5 ether, tetrahydrofuran, 1,4-dioxane, 12-crown-4 ether,18- crown-6 ether, tetrahydropyran, anisole, diethylene glycol, 2-methoxyethanol, 1-methoxy-2-propanol, 2-ethoxyethanol, 2- propoxyethanol, 2-iso-propoxyethanol, 2-butoxyethanol, acetone, butanone, acetylacetone, acetophenone, propylene carbonate, 1,2-butylene carbonate, dimethyl carbonate, diethyl carbonate, tartaric acid, lactic acid, citric acid, pyruvic acid, acetoacetic acid, methylamine, ethylamine, propylamine, butylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, formamide, N,N- dimethylformamide, ethylene diaminetetraacetic acid, tris(hydroxymethyl)-aminomethane, ethanolamine, N- methylformamide. P2024,1131 WO N April 16, 2025 - 36 - As discussed above, the above compounds may serve as solvents or additives. According to embodiments, the following compounds are particularly preferred to be usable as solvents and additives. Such compounds may be polymers such as poly(vinyl pyrrolidone), poly(methyl methacrylate), poly(vinyl alcohol) or polyethylene glycol. According to a further embodiment, certain chemical compounds may act as a solvent and additionally as a stabilization agent. Such compounds may be added to other solvents or used as solvents. Examples for this are 2-methoxyethanol and acetic acid. Acetic acid, for example, can dissolve metal precursors, but it also can be a chelating agent and may stabilize the precursor solutions by decreasing the reactivity of the alkoxide. The 2-methoxyethanol can dissolve metal precursors, but it may also react with alkoxide (transalcoholysis), which results in decreased hydrolysis sensitivity of a starting reagent. According to further embodiments, the solvent may fall into one, more than one, or preferably all preferred ranges as shown in table 5. Even more preferably it falls into the even more preferred range. P2024,1131 WO N April 16, 2025 - 37 - Table 5 Property Preferred range More preferred range Boiling point (°C) 50 to 300 100 to 200 Viscosity (mPa s) 0.5 to 5000 1 to 10 Surface tension (mN / m) 10 to 100 20 to 50 Density (g / mL) 0.5 to 1.5 0.75 to 1.25 Dielectric constant 1.5 to 200 2 to 100 According to an embodiment, the composition of the precursor compounds may be selected such that they follow formulas 2 and 3. According to an embodiment in chemical solution deposition, more than one partial layer can be deposited, i.e. at least a first and a second partial layer is deposited. The first partial layer is deposited from a first precursor solution and the second partial layer is deposited from a second precursor solution. The first and the second precursor solution have a different composition. Also, according to embodiments more than two partial layers may be deposited, such as three, four, five or more. For example, according to an embodiment a process with at least three deposition steps can be described. Therein at least one partial layer or several partial layers are produced by using a first solution having a stochiometric A- site (e.g. Bi) to B-site (e.g. Fe) ratio. Subsequently one or several second partial layers are formed from a second solution comprising a medium excess of A-site (e.g. Bi) to B- site (e.g. Fe) ratio, which is a higher A-site (e.g. Bi) to B-site (e.g. Fe) ratio than that of the first solution. Subsequent to that one or several third partial layers are produced from a third solution, comprising a high excess of P2024,1131 WO N April 16, 2025 - 38 - A-site (e.g. Bi) to B-site (e.g. Fe) ratio, which means that the amount of A-site (e.g. Bi) in relation to the B-site (e.g. Fe) is highest in comparison to the other solutions. For example, after this crystallization may be performed. This approach may also be performed with two partial layers of different A-site (e.g. Bi) to B-site (e.g. Fe) ratios or with higher numbers of partial layers, such as for example four or five or even more solutions. For higher numbers for example a continuing variation in concentration may be used. Alternatively, one or several lower partial layers can have stoichiometric composition and some of the last partial layers can have a difference in concentration. A similar approach can be performed for introducing wanted gradients. Also, such an approach may be implemented for any ion in the precursor solution including dopants. According to another embodiment it is also possible to use solutions that can differ in viscosity, solvents, concentration. This may help to fine tune the processing parameters and thin film properties and / or quality. According to embodiments, the chemical solution deposition step can be a spin-coating step, a dip-coating step, a spray- coating step or an inkjet printing step. In particular, spin coating has shown to provide high quality thin films. According to an embodiment, the spin-coating can be carried out such that the solution is dispensed on the substrate. Subsequently it may be rotated at a speed of 1000 to 5000 rpm. A rotation time for which the rotation speed may be maintained can be 10 s to 60 s. According to a preferred P2024,1131 WO N April 16, 2025 - 39 - embodiment, a spin-coating speed may be 2000 to 3500 rpm. A preferred time may be 20 s to 40 s. According to an embodiment, the solution may be filtered before deposition, for example via a syringe filter. For example, a 0.2 µm syringe filter can be used. According to an embodiment, the substrate may be cleaned before deposition. For example, a UV / ozone cleaning can be applied. This may help to remove organic residues. The UV / ozone cleaning may be applied for 5 to 20 min, for example. According to a preferred embodiment, the UV / ozone cleaning may be applied for 5 to 15 min. According to an embodiment, after a chemical solution deposition step a drying and / or a pyrolysis step may be performed before crystallization. By drying, solvents can be evaporated and a dry preliminary thin film layer or partial layer can be formed. The pyrolysis step may also dry and drive off the solvent. More preferably the pyrolysis is capable of pyrolyzing organic residues in the forming thin film layer. According to embodiments, the drying and the pyrolysis can be performed in separate steps or in combined single step. According to a preferred embodiment, and as also indicated above, before crystallization more than one combined step of chemical solution deposition, subsequent drying and subsequent pyrolysis may be performed. Thus, more than one partial layer that may be amorphous may be formed before crystallization. This can have the advantage of improved film quality. P2024,1131 WO N April 16, 2025 - 40 - According to an embodiment, drying can be a heating step that includes heating at 50 °C to 250 °C. A drying time for which the temperature is held may be 1 to 10 min. These ranges can be preferable for evaporating the above-mentioned solvents. Even more preferably, according to an embodiment, the drying temperature can be between 110 to 200 °C. A preferred drying time may be 1 to 5 min, according to an embodiment. According to an embodiment, pyrolysis can be a heating step that includes heating at 150 °C to 550 °C. A pyrolysis time for which the temperature is held can be 1 to 30 min. These ranges have been shown to be efficient in burning organic residues with the inventive compositions. Even more preferably, according to an embodiment, the pyrolysis temperature can be between 300 to 450 °C. A preferred pyrolysis time may be 1 to 5 min, according to an embodiment. According to embodiments, the drying and / or the pyrolysis may be performed on a hot plate. The drying and pyrolysis can be performed on separate plates or performed in a single step on one plate. The inventors found these embodiments to be efficient for a chemical solution deposition process. According to an embodiment, crystallization can be a heating step that includes heating at 500 °C to 1200 °C. A crystallization time for which the temperature is held can be 1 to 30 min. Depending on the exact material composition, high quality films can be formed within these ranges. According to a preferred embodiment, the crystallization temperature may lie between 600 to 1000 °C. According to a further preferred embodiment, the time for which the temperature is held can be 1 to 20 min. P2024,1131 WO N April 16, 2025 - 41 - According to an embodiment, the crystallization can be performed in a furnace. According to an embodiment, one combined step of chemical solution deposition, drying, pyrolysis and crystallization may be performed. In other words, several crystalized sublayers may be accumulated one upon the other to form a thin film of a certain thickness. In the following, exemplary embodiments and experiments are discussed with respect to figures. From these exemplary embodiments further features or advantages of the present invention can be seen. However, the invention is not limited to these exemplary embodiments. All figures that are not images or graphs are not true to scale and no lengths or length ratios can be taken from them. On the contrary, in such figures length or length ratios may be distorted to allow for better visibility of certain features. In the figures, elements that are identical or have similar or identical function are labeled by the same reference number. Figure 1 shows a schematic cross-section of a first exemplary embodiment of a thin-film device. Figure 2 shows a schematic cross-section of a second exemplary embodiment of a thin-film device. Figure 3 shows a schematic cross-section of a third exemplary embodiment of a thin-film device. Figure 4 shows a schematic cross-section of a fourth exemplary embodiment of a thin-film device. P2024,1131 WO N April 16, 2025 - 42 - Figure 5 shows a schematic cross-section of a fifth exemplary embodiment of a thin-film device. Figure 6 shows a schematic cross-section of a sixth exemplary embodiment of a thin-film device. Figure 7 shows a schematic cross-section of a seventh exemplary embodiment of a thin-film device. Figure 8 shows a schematic representation of a mode of electrical contacting for the seventh exemplary embodiment. Figure 9 shows a schematic cross-section of an eighth exemplary embodiment of a thin-film device. Figure 10 shows a schematic representation of a mode of electrical contacting for the eighth exemplary embodiment. Figure 11 shows a photograph of a nineth exemplary embodiment of a thin-film device. Figure 12 shows a photograph of a tenth exemplary embodiment of a thin-film device. Figure 13 shows a photograph of an eleventh exemplary embodiment of a thin-film device. Figure 14 shows a first photograph of a twelfth exemplary embodiment of a thin-film device. Figure 15 shows a second photograph of the twelfth exemplary embodiment of a thin-film device. P2024,1131 WO N April 16, 2025 - 43 - Figure 16 shows a flowchart representation of an exemplary embodiment of a manufacturing process of a thin film. Figure 17 shows a first set of X-ray diffraction patterns of exemplary embodiments of thin films. Figure 18 shows a second set of X-ray diffraction patterns of exemplary embodiments of thin films. Figure 19 shows an on-top scanning electron microscopy image of an exemplary embodiment of a thin film. Figure 20 shows a cross-section scanning electron microscopy image of the exemplary embodiment of Figure 19. Figure 21 shows a cross-section scanning electron microscopy image of another exemplary embodiment of a thin film. Figures 22 to 29 show cross-section EDX-measurements on the sample of Figure 21. Figures 30 to 38 show various hysteresis loops and polarization curves for various samples. In Figure 39 leakage current versus Mn-content in BFO-BT thin films is shown. Figure 40 shows current versus electric field curves for different manganese doping levels. Figure 41 shows displacement curves for a PZT material and for a BFO-BT material. P2024,1131 WO N April 16, 2025 - 44 - Figure 42 shows a false color representation of crystal orientations of an exemplary embodiment of a BFO-BT film. Figure 43 shows the curve of |e31,f| versus the content of BT- derived component in BFO-BT films. Figure 44 shows polarization curves of samples with bismuth excess. Figure 45 shows current versus electric field curves of samples with bismuth excess. Figures 46 shows polarization curves of samples with bismuth excess and manganese doping. Figures 47 shows current versus electric field curves of samples with bismuth excess and manganese doping. In Figure 1 a first exemplary embodiment of a thin-film- device 1 is shown in schematic cross-section. The thin-film device is constructed in metal-insulator-metal (short: MIM) electrode configuration. In this exemplary embodiment an adhesion layer 3 is positioned on the surface of a substrate 2. The substrate may be any suitable substrate as described in the introduction. The adhesion layer 3 comprises a transition metal or transition metal oxide. The transition metal preferably is Ta, Ti or W. Accordingly a transition metal oxide preferably has these elements. A first electrode 4 is positioned on top of the adhesion layer 3. The electrode 4 can comprise or consist of the materials discussed for electrodes in the introduction. In this stack the electrode layer 4 can be called “bottom electrode”. An electroceramic P2024,1131 WO N April 16, 2025 - 45 - thin film 5 is positioned above the bottom electrode layer 4. The electroceramic thin film 5 comprises or is made of a BiFeO3-BaTiO3-based material following the general formula 2, as introduced in the introduction above. A top electrode 6 is arranged on top of the electroceramic layer 5. The top electrode 6 can be any conducting electrode. For example, the top electrode 6 can be of the same material as the bottom electrode 4. Not depicted explicitly, but in many cases preferred, a seed layer or a buffer layer can be positioned between the electroceramic layer and the electrode. For example, such a layer can comprise or consist of LaNiO3, which can fulfill both the seed function and the buffer function. The thickness ranges for the layers may be those of the introduction. Figure 2 shows a schematic cross-section of a second exemplary embodiment of a thin-film device 1, which is also configured in the MIM electrode configuration. The thin-film device 1 of Figure 2 is identical to the thin-film device of Figure 1 in the upper portion, i.e. the layers with the reference numbers 2, 3, 4, 5, and 6 are identical to those described for the first exemplary embodiment. However, also on the other surface of the substrate 2, a second adhesion layer 3’, a second bottom electrode 4’, a second thin film 5’ and a second top electrode 6’ are arranged. The materials of these layers can correspond to those of the first adhesion layer 3, the first bottom electrode 4, the first thin film 5 and the first top electrode 6. Accordingly, this results in a mainly symmetrical layer arrangement with respect to the layers with reference numbers 2 to 6. This can have the P2024,1131 WO N April 16, 2025 - 46 - advantage that stress inflicted by the piezoelectric films during operation acts symmetrically on the substrate. This may lead to reduced deformation. This is particularly advantageous in case of flexible substrates. In Figure 3 a schematic cross-section of a third exemplary embodiment of a thin-film device 1, which is also configured in the MIM electrode configuration, is shown. This thin-film device 1 is a modification of the first exemplary embodiment shown in Figure 1. On the substrate 2, it has the first adhesion layer 3, the first bottom electrode 4, the first thin film 5 and the first top electrode 6. A thin film 5’’ is arranged above the first top electrode 6. A second top electrode 6’’ is arranged on top of the second thin film 5’’. For this setup, the first top electrode 6 acts as a bottom electrode for the second thin film 5’’. Also, the second thin film 5’’ has a BiFeO3-BaTiO3-based material following the general formula 2, which preferably has the same composition as the first thin film 5. Also, the materials of the second top electrode 6’’ can be selected from the same materials from which the material of the first top electrode 6 is selected. In a similar manner as shown in Figure 3, multiple further electroceramic layers and top electrodes can be stacked alternatingly. It is preferred that such a stack is terminated by a top electrode. The third exemplary embodiment can of course be combined with the second exemplary embodiment, i.e. the two-sided arrangement as shown in Figure 2. Thus, either symmetrical or asymmetrical stacks can be formed i.e. multilayer arrangements with the same number of layers on both sides of P2024,1131 WO N April 16, 2025 - 47 - the substrate or with different numbers of layers on both sides, respectively. The exemplary embodiments explained for Figures 2 and 3 have the advantage that the piezoelectric properties of several thin films are accumulated. In Figure 4 a fourth exemplary embodiment of a thin-film device 1 with MIM electrode configuration is depicted. It has the same layer stacking as the first exemplary embodiment. It differs from the first exemplary embodiment in that it has a partial removal region 7 that facilitates electrically contacting the bottom electrode 4. For example, if a thin film 5 is deposited on a metallized oxidized silicon wafer as substrate 2, a conductive path to the bottom electrode 4 can be provided via the partial removal region 7. The partial removal region 7 may be achieved by partial removal of the ceramic thin film 5. The thin film 5 can be removed, for example, by dry or wet etching. Etching can be done through the thin film 5 or alternatively through the substrate 2. The top electrode 6 can be externally contacted, as it is externally accessible anyway. This contact technique can also be applied to the other exemplary embodiments addressing a MIM electrode configuration. In Figure 5 a fifth exemplary embodiment of a thin-film device 1 with MIM electrode configuration is depicted. It is also mainly identical to the first exemplary embodiment but shows an alternative means for contacting the bottom electrode 4. The bottom electrode 4 is connected to a side portion 8, that can act as external electrode or external contact. The side portion 8 is a metallization. This contact P2024,1131 WO N April 16, 2025 - 48 - technique can also be applied to the other exemplary embodiments addressing a MIM electrode configuration. In Figure 6 a sixth exemplary embodiment of a thin-film device 1 with MIM electrode configuration is depicted. It is based on the stacking according to the second exemplary embodiment, and shows a further alternative means for externally contacting the bottom electrodes 4 and 4’ and the top electrodes 6 and 6’. As can be seen, both bottom electrodes 4 and 4’ are connected to a side portion 8 that is a metallization. Both top electrodes 6 and 6’ are connected to a further side portion 9, that also is fabricated as a metallization. The side portions 8 and 9 can act as external electrodes and allow to apply the identical external voltage to the electrodes. Contacting more than one thin film in parallel may allow to reduce the operation voltage as compared to a device with one electrode stack with the sum of layer thickness of thin film 5 and thin film 5’. Also, the third exemplary embodiment depicted in Figure 3 can be modified by such a contacting. In Figure 7 a seventh exemplary embodiment of a thin-film device 1 is depicted. It is a thin-film device 1 with an interdigital electrode (short: IDE) configuration. It can be seen that the stacking is mainly identical to the first exemplary embodiment, except that no bottom electrode is realized. In an interdigital electrode design separate areas of the upper electrode layer 6 which are electrically isolated from each other are realized. Via these, a voltage can be applied that can produce a piezoelectric effect, for example. Also, a voltage may be detected originating from bending, for example. P2024,1131 WO N April 16, 2025 - 49 - In Figure 8 a mode of contacting for the seventh exemplary embodiment is shown. The top electrode layer here has two separate partial top electrode layers 6a and 6b that are electrically separated from each other. Here the separation is realized via a gap between the partial top electrode layers 6a and 6b. Alternatively an insulating material may be present between the partial top electrode layers 6a and 6b. Via partial top electrode layers 6a and 6b a voltage can be applied that can produce a piezoelectric effect, for example. Also, a voltage may be detected originating from bending, for example. In Figure 9 an eighth exemplary embodiment of a thin-film device 1 is depicted, again representing an IDE configuration. Its stacking is mainly identical to the second exemplary embodiment, except that no bottom electrodes are realized. The contacting is in principle similar to that described for the seventh exemplary embodiment. In particular, a mode of contacting is shown in Figure 10. For top electrode layers, partial top electrode layers 6a and 6b and 6a’ and 6 b’ are realized. The two-sided configuration shown for the eighth exemplary embodiment has the advantage that an IDE configuration can be realized and in addition the piezoelectric response of the device be increased by doubling the number of thin films compared to the seventh exemplary embodiment. Figure 11 depicts a ninth exemplary embodiment of a thin film device 1 in a top view. It has an electroceramic BiFeO3- BaTiO3-based thin film 5 deposited on a platinized Ti-foil with sputtered top electrodes 6, two of which are indicated explicitly in the figure. Silver paste is used to contact the bottom electrode. The setup can have a configuration such as P2024,1131 WO N April 16, 2025 - 50 - according to the first exemplary embodiment, for example. The device 1 is flexible and can be easily bent without any evidence of irreversible mechanical damage. Therefore, it can be used in sensor applications, such as vibrometers, or in event detection, such as detection of impact events. As a modification of this design (not depicted), it is possible to achieve a bender configuration with a symmetric configuration as shown for the second exemplary embodiment, for example. This modified setup may allow for independent electrical contacting of the thin films on both sides of the substrate, which allows controlled bending. Figure 12 depicts a tenth exemplary embodiment of a thin-film device 1 in a top view. It has an electroceramic BiFeO3- BaTiO3-based thin film 5 deposited on a Si-wafer substrate with sputtered top electrodes. The internal structure may be that of the first exemplary embodiment. Silver paste is used to contact the bottom electrode. Figure 13 depicts an eleventh exemplary embodiment of a thin- film device 1 in a top view. It shows a thin-film device that has an interdigital electrode design and may have the internal structure as depicted in the seventh exemplary embodiment of Figures 7 and 8. In particular, the partial top electrodes 6a and 6b that are arranged on the thin film, which is BiFeO3-BaTiO3-based, can be identified. Several pairs of such electrodes are realized. Two pairs are indicated exemplarily. All partial top electrodes 6a are connected to a common contact track 8a. All partial top electrodes 6b are connected to a common contact track 9b. P2024,1131 WO N April 16, 2025 - 51 - In Figures 14 and 15 a twelfth exemplary embodiment of a thin-film device 1 is shown. The twelfth exemplary embodiment is a high-frequency 2D bi-resonant MEMS micromirror. Figure 14 shows a photograph of the device. Figure 15 shows a microscopic image of the micromirror. The micromirror 10 has a mirror platelet or mirror surface 13 with a diameter of 1.5 mm. The mirror can be tilted or brought into vibration along the so-called fast axis 12 and the slow axis 11. Under operation, the actuator ring 14 is put under voltage. The actuator ring 14 comprises a structure according to the invention. Its construction is mainly identical to the stacking shown in Figure 1. In particular, on a SOI substrate with the properties as described for Figure 1, a tantalum layer of 20 nm thickness is deposited as an adhesion layer. The bottom electrode is formed from a 200 nm platinum electrode. The electroceramic layer is an approximately 2 µm thick BiFeO3-BaTiO3-based layer which, for example, can be formed according to the process described below. The top electrode is formed from a 20 nm thick chromium layer and a 200 nm thick gold layer. Figure 16 shows a flowchart representation of an exemplary embodiment of a manufacturing process of a thin film. This process can be used in producing the above-described embodiments. Prior to the start of the process flow, a substrate is provided and prepared with layers, such as a bottom electrode, an adhesion layer or similar. A seed layer may also be formed on the substrate. As substrates, the following may be used: P2024,1131 WO N April 16, 2025 - 52 - • Si-wafers (e.g. silicon-on-insulator; SOI); for example for MEMS fabrication • Ceramics (e.g. alumina, zirconia) • Glass (e.g. fused silica, borosilicate glass); e.g. for transparent and flexible electronics (e.g. displays) • Single crystals (e.g. sapphire); for example for high- performance transparent electronics • Metal foils (e.g. Cu, Ti, Ni and stainless steel); for example for cost-efficient flexible electronics; in some cases, biocompatible electronics • Polymers (e.g. PI, PET); for example for cost-efficient flexible electronics • Conductive oxides (e.g. ITO, FTO, AZO or ATO); for example for conductive and transparent material for photovoltaic applications, displays The bottom electrodes are applied to the substrate by magnetron sputtering, evaporation, screen printing, electroplating or a chemical solution deposition (short: CSD) process. Different deposition techniques can be used for the CSD-derived electrodes, such as spin coating, dip coating, spray coating, and inkjet printing. The material of the bottom or top electrodes can vary from transition to noble metals (e.g. Pt, Au, Cr, Ag, Cu, Ni) to alloys (e.g. brass) and further to conductive oxides (e.g. RuO2, ZnO, LaNiO3, SrVO3, SrRuO3, SrMoO3, (La0.7Sr0.3)MnO3, (La0.7Ca0.3)MnO3, IrO2, (Sr0.5Ba0.5)RuO3, BiFeO3, SrTiO3:Nb, indium tin oxide (ITO) In2O3:Sn, antimony doped tin oxide (ATO) SnO2:Sb, aluminum doped zinc oxide (AZO) ZnO:Al, gallium doped zinc oxide ZnO:Ga, fluor doped tin oxide (FTO) SnO2:F, hydrogen doped zinc oxide ZnO:H, hydrogenated indium oxides IO:H, tungsten doped hydrogenated indium oxide IWO:H, cerium doped hydrogenated indium oxide ICO:H). The thickness of the P2024,1131 WO N April 16, 2025 - 53 - electrode can be between 50 nm and 500 nm. In particular, in the case of more expensive noble metals, a lower thickness may be preferred, such as between 100 nm and 300 nm or such as between 150 to 250 nm. In addition, electrode layers that are too thick tend to delaminate due to internal stresses. Buffer layers can be applied to suppress the diffusion between the electroceramic thin film and electrode material and / or electroceramic thin film and substrate. For example, buffer layers comprise or consist of LaNiO3, HfO2and Al2O3. Seed layers are used to control the grain growth and crystal orientation of the electroceramic thin film as the growth is defined by the surface orientation of the layer below. (e.g., LaNiO3, PbTiO3and TiO2between the bottom electrode and the electroceramic thin film.) Note that selected materials (e.g., LaNiO3) can serve as a buffer layer and seed layer. The buffer layer or the seed layer can, for example, be formed by a CSD process. A precursor solution is also prepared. The precursor solution may be prepared according to the embodiments as described in the introduction which may be called “general synthesis route 1”. Exemplary embodiments for the synthesis of the precursor solution can be found in tables 6 and 7.

[0003] P2024,1131 WO N April 16, 2025 - 54 - Table 6 Route Precursors Solvents Bi(III) nitrate, Fe(III) acetic acid, 2- 2 nitrate, Ba acetate, Ti(IV) methoxyethanol butoxide Bi(III) tert-pentoxide, Ba 2-methoxyethanol, 3 acetate, Ti(IV) butoxide, acetic acid Fe(III) acetylacetonate Bi(III) nitrate pentahydrate, acetic acid, 2- 4 Fe(III) nitrate nonahydrate, Ba methoxyethanol, acetate, Ti(IV) propoxide acetic anhydride Bi(III) tert-pentoxide, Ba butanoic acid, 2- 5 acetate, Ti(IV) butoxide, methoxyethanol Fe(III) ethoxide Bi(III) tert-pentoxide, Ba 2-methoxyethanol, 6 acetate, Ti(IV) butoxide, acetic acid Fe(III) acetylacetonate Bi(III) nitrate pentahydrate, citric acid, 7 Fe(III) nitrate nonahydrate, ethylene glycol, Ti(IV) iso-propoxide, Ba acetate water acetic acid, 2- Ba acetate, Bi(III) nitrate, methoxyethanol, 8 Fe(III) nitrate, Ti(IV) butoxide acetylacetone, ethanolamine Ba acetate, Ti(IV) butoxide, 2-methoxyethanol, 9 Bi(III) tert-pentoxide, Fe(III) acetylacetone acetylacetonate water, Bi(III) citrate, Fe(III) ethanolamine, 10 citrate, Ti(IV) iso-propoxide, ammonia, citric Ba tert-butoxide acid, hydrogen peroxide P2024,1131 WO N April 16, 2025 - 55 - Table 7 Route Precursors Solvents Bi(III) tert-pentoxide, Fe(III) 11 ethoxide, Ti(IV) iso-propoxide, 2-methoxyethanol Ba iso-propoxide Bi(III) acetate, Fe(III) propanoic acid, 2- 12 acetylacetonate, Ba acetate, methoxyethanol Ti(IV) butoxide Fe(III) acetylacetonate, Ba acetylacetonate, Ti(IV) tert- benzene, 2- 13 butoxide, Bi(III) 2,3-dimethyl- methoxyethanol 2-butoxide Bi(III) nitrate pentahydrate, acetic acid, 2- Fe(III) nitrate nonahydrate, Ba 14 methoxyethanol, nitrate, Ti(IV) acetic anhydride oxyacetylacetonate Bi(III) acetate, Fe(III) propanoic acid, 15 acetate, Ba tert-pentoxide, ethylene glycol Ti(IV) 2-ethylexyloxide Bi(III) citrate, Fe(III) water, citric 16 citrate, Ba hydroxide, Ti(IV) acid, ethanolamine peroxocitrate Bi(III) tert-pentoxide, Fe(III) ethylene glycol, 17 acetate, Ba acetate, Ti(IV) ethanol butoxide Bi(III) acetate, Fe(III) 18 acetylacetonate, Ba acetate, propanoic acid Ti(IV) propoxide The following further conditions apply for these exemplary embodiments. P2024,1131 WO N April 16, 2025 - 56 - Route 2: Mix listed precursors in listed solvents at room temperature (for example 25 ± 2 °C) to dissolve all precursors. Synthesis is performed in a water-free atmosphere. After all compounds are dissolved, the precursor solution can be stored at 6 °C or below. Route 3: Mix listed precursors in listed solvents and heat the solution to a temperature 10 to 20 °C below the boiling temperature of the solvent-mixture to dissolve all precursors. Synthesis is performed in a water-free atmosphere. After cooling to room temperature (for example 25 ± 2 °C), the solution can be stored at 6 °C or below. Route 4: Dissolve nitrates in acetic acid and add acetic anhydride to convert crystal water to more acetic acid. Add 2-methoxyethanol and the precursor that was missing up to this point. Heating the solution between 60 and 80 °C helps to dissolve all precursors. After cooling to room temperature (for example 25 ± 2 °C), the solution can be stored at 6 °C or below. After acetic anhydride is added, the synthesis is carried out in a water-free atmosphere. Route 5: Mix listed precursors in listed solvents and heat the solution between 100 and 120 °C to dissolve all precursors. Synthesis is performed in a water-free atmosphere. After cooling to room temperature (for example 25 ± 2 °C), the solution can be stored at 6 °C or below. Route 6: Mix listed precursors in listed solvents and heat the solution between 100 and 120 °C to dissolve all precursors. Synthesis is performed in a water-free atmosphere. After cooling to room temperature (for example 25 ± 2 °C), the solution can be stored at 6 °C or below. P2024,1131 WO N April 16, 2025 - 57 - Route 7: First citric acid is dissolved in water, then the precursors are added and the mixture is heated to 70 °C to 90 °C to dissolve all precursors. After cooling to room temperature (for example 25 ± 2 °C), the solution can be stored at 6 °C or below. Routes 8, 9 and 17: Mix listed precursors in listed solvents at room temperature (for example 25 ± 2 °C) to dissolve all precursors. Synthesis may be easily carried out without the necessity of a water free atmosphere. After all compounds are dissolved, the solution can be stored at room temperature and no cooling is required. Route 10: Mix Bi(III) citrate with water, ethanolamine and ammonia. Dissolve Fe(III) citrate in water at 80 °C. Mix Bi- solution with Fe-solution, add water and adjust pH to 7. Hydrolyze Ti(IV) isopropoxide in water. Mix the obtained Ti(IV) hydroxide with citric acid and hydrogen peroxide and heat the solution to 60 °C. Mix Bi(III) citrate with water, ethanolamine and ammonia. Mix the Ti-solution with the Bi- solution. Finally, mix the Bi-Fe-solution with the Ti-Bi- solution. This solution is preferably stored at 6 °C or below. Route 11: This synthesis is best performed in a water-free atmosphere. All precursors can be dissolved in 2- methoxyethanol at 90 °C and stirred for 18 h. Storing the solution in a dry atmosphere is recommended. Route 12: Mix listed precursors in listed solvents and heat the solution to a temperature 10 to 20 °C below the boiling temperature of the solvent mixture to dissolve all P2024,1131 WO N April 16, 2025 - 58 - precursors. Synthesis is performed in a water-free atmosphere. After cooling to room temperature (for example 25 ± 2 °C), the solution can also be stored at room temperature. Route 13: Mix listed precursors in listed solvents and heat the solution between 60 and 80 °C to dissolve all precursors. Synthesis is performed in a water-free atmosphere. After cooling to room temperature (for example 25 ± 2 °C), the solution may be stored at 6 °C or below. Route 14: Dissolve nitrates in acetic acid and add acetic anhydride to convert crystal water to more acetic acid. Add 2-methoxyethanol and the missing precursor. Heating the solution to between 60 and 80 °C helps to dissolve all precursors. After cooling to room temperature (for example 25 ± 2 °C) the solution may be stored at 6 °C or below. The whole synthesis is carried out in a water-free atmosphere after acetic anhydride was added. Route 15: Mix listed precursors in listed solvents and heat the solution under reflux for 2 h to dissolve all precursors. The synthesis is carried out in a water-free atmosphere. After cooling to room temperature (for example 25 ± 2 °C), the solution may be stored at 6 °C or below. Route 16: Dissolve citric acid in water and add ethanolamine. Afterwards add listed precursors and heat to 40 °C to dissolve the precursors. After cooling to room temperature (for example 25 ± 2 °C), the solution may be stored at 6 °C or below. P2024,1131 WO N April 16, 2025 - 59 - Route 18: Mix listed precursors in a listed solvent and heat the solution to a temperature 10 to 20 °C below the boiling temperature of the solvent to dissolve all precursors. The synthesis carried out in a water-free atmosphere. After cooling to room temperature (for example 25 ± 2 °C), the solution may also be stored at room temperature. The amounts of the precursors are chosen to fit formulas 2 and 3 Formula 2 Furthermore, the following applies: Formula 3. In addition, the dopants µ and β are chosen from table 8. These can be introduced into the precursor solution from compounds with similar counter ions or ligands as discussed for the metal precursors. Table 8 Dopants µ Li, Na, K, Rb, Cs, Ca, Sr, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Cu, Ag, Au, Cd, In, Tl, Pb, Si β Li, Na, K, Mg, Ca, Sr, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, Al, Ga, In, Ge, Sn, Pb, Sb, Te, Si Furthermore, the ranges of table 9 apply. P2024,1131 WO N April 16, 2025 - 60 - Table 9 0.01 ≤ x ≤ 0.99 -0.10 ≤ a ≤ 0.30 -0.10 ≤ b ≤ 0.30 -0.10 ≤ c ≤ 0.30 -0.10 ≤ d ≤ 0.30 0 ≤ y ≤ 0.30 0 ≤ z ≤ 0.30 x+a > 0.01 1-x+b > 0.01 x+c > 0.01 1-x+d > 0.01 These compositions address initial compositions in the precursor solution. The thin film preparation method may influence the composition of the final thin film. This may, for example, be the case if elements such as Bi and Ba would be present in their metallic form during thermal treatment due to their high vapor pressure. In the case that the starting elements are kept in their oxidized state, evaporation losses are expected to be minimal. Furthermore, during film formation the dielectric tends to be charge neutral. To achieve this, A-site vacancies (e.g. Bi vacancies), B-site vacancies (e.g. Fe vacancies), or oxygen vacancies may form, or elements could be present in different charge states (e.g. iron partially adopting the Fe3+and Fe4+state). The occurrence of such defects is considered during the synthesis of the precursor solution and further depends on the thermal treatment (e.g. crystallization temperature, number of crystallization steps, or holding time during crystallization) during the deposition process. P2024,1131 WO N April 16, 2025 - 61 - The as-prepared substrate, with optional additional layers depending on the design, is pretreated in a UV / ozone cleaner for 5 to 20 min or preferably 5 to 15 min, as indicated by the first step in the flowchart named “Substrate pre- treatment”. Subsequently, the prepared solution is dispensed onto the substrates and spin-coated at 1000 to 5000 rpm for 10 to 60 s, as indicated by “Spin coating layeri”. Preferably, a spin-coating speed may be 2000 to 3500 rpm. A preferred time may be 20 s to 40 s. The spin coated layer is then dried and pyrolyzed on hot plates. Alternatively, drying and pyrolysis can be performed in a single step (i.e. on the same hot plate). Drying of the wet spin coated layer is done at a temperature between 50 to 250 °C for 1 to 10 minutes. More preferably the drying temperature can be between 110 to 200 °C. A preferred drying time may be 1 to 5 min. Pyrolysis is done at temperatures between 150 and 550 °C for 1 to 30 minutes. More preferably the pyrolysis temperature can be between 300 to 450 °C. A preferred pyrolysis time may be 1 to 5 min. By these steps a first amorphous partial layer is formed as is also indicated by the index “i” in “Spin coating layeri”. As indicated by “ai=0 ?” this step of deposition, drying and pyrolysis may be repeated n-times (i=1, 2, 3, …, n), i.e. several amorphous partial layers may be formed one upon the other. When ai≠0, the process starts over again at spin coating, i.e. the spin coating-drying-pyrolysis subsequence is repeated. In principle, a different precursor solution can be used for every formation of a partial layer. Solutions may differ by concentration, solvents, stoichiometry and / or presence of dopants. This approach can be used to induce or counteract chemical gradients in the thin film or introduce a P2024,1131 WO N April 16, 2025 - 62 - graded doping within the thin film or at the interfaces. An example of this is provided below. The stack of partial layers accumulated may be called an amorphous sublayer. The number of layers that are deposited before the film is crystallized may be adapted for the specific precursor system being used. As shown below, the number of partial layers formed like this may influence the thin film properties. Subsequently, crystallization in a furnace at 500 to 1200 °C for 1 to 30 minutes is carried out. The inventors found that a preferred range of temperature for crystallization may be between 600 to 1000 °C. A preferred time for which the temperature is held can be 1 to 20 min. By crystallization the amorphous sublayer becomes a crystalline sublayer. As explained for “ai”, the field “bi=0 ?” also indicates that the whole process after the spin coating may be carried outonce or may be repeated, i.e. when ^^ ≠ 0 aftercrystallization, the process starts over at spin coating. The number of these repetitions depends on the targeted thin film thickness. The number of repetitions, for example depends on the concentration of the precursor solution. The overall process ends after the nthpartial layer and the resulting last sublayer are processed, i.e. when an=bn=0. The number of layers that are deposited before the film is crystallized may be adapted for the specific precursor system used. As shown below, the number of partial layers formed like this may influence the thin film properties. P2024,1131 WO N April 16, 2025 - 63 - It is advantageous to carry out the above-described process in a temperature and partial pressure regime favoring the oxidized state. This can be the case under the above conditions. Accordingly, the above discussed composition (formulas 2 and 3) may also represent the composition of the final BFO-BT thin film. As can be seen for various exemplary embodiments and different compositions in the X-ray diffraction patterns of Figures 17 and 18, the electron microscopy images of Figures 19, 20 and 21 and the results of the EDX-Measurements of Figures 22 to 29, high-quality films of good crystallinity and defined elemental distribution can be obtained by the described process. For example, the X-ray diffraction patterns show pure BFO-BT phase without indicating the formation of secondary phases. Further details of the measurements are discussed in the following when discussing examples regarding the composition. An exemplary embodiment of the process for forming a thin film of n=12 partial layers can be found in table 10. Table 10 ^1 2 3 4 5 6 7 8 9 10 11 12^^0 1 1 0 1 1 0 1 1 0 1 0^^1 0 0 1 0 0 1 0 0 1 0 0In this case (see table 10) for i=1, first a single partial layer is deposited, dried, pyrolyzed and, as a1=0, crystallized. The thus formed layer may be called a sublayer. As b1=1 (i.e. b1≠0) the next cycle 2 is started. In this cycle one partial layer is deposited, dried and pyrolyzed. As a2=1 (i.e. a2≠0) the next cycle 3 is started and so forth. P2024,1131 WO N April 16, 2025 - 64 - Thereby, except for the first and the last cycle, three partial layers are always stacked before a crystallization step is carried out. A further exemplary embodiment of the process for forming a thin film of n=12 layers can be found in table 11. This table is to be read like table 10. It shows a case of crystallization after each deposition. Table 11 ^1 2 3 4 5 6 7 8 9 10 11 12^^0 0 0 0 0 0 0 0 0 0 0 0^^1 1 1 1 1 1 1 1 1 1 1 0As discussed above, compositions in the precursor solutions may be varied, according to embodiments. The variation may be between partial layers or sublayers. Preferably the variation is between partial layers. It is possible to change the precursor solution in between the deposition steps. For example, for any partial layer, a first precursor solution may be applied and for another partial layer a different precursor solution may be applied. Changing the precursor solution may help to get a homogeneous distribution of ions throughout the whole deposited thin film or help to implement intentional component concentration gradients. For example, the first partial layer can have a stoichiometric Bi-amount, a second partial layer that is deposited on the first partial layer can have little Bi-excess, whereas a last deposited partial layer has even more Bi-excess. Subsequent to deposition such layer stack of three partial layers is then crystallized. The inventors think that this may help reducing unwanted gradients. For example, it is assumed that evaporation of volatile metallic Bi is strongest close to the P2024,1131 WO N April 16, 2025 - 65 - surface of the partial layers. To counteract this, in amorphous state the topmost partial layer has the highest Bi concentration. After crystallization, the Bi content in the formed sublayer may be more homogenous throughout the thickness of the sublayer. According to a generalized embodiment of this approach a process with at least three deposition steps can be described. Wherein at least one partial layer or several partial layers are produced by using a first solution having a stochiometric A-site (e.g. Bi) to B-site (e.g. Fe) ratio. Subsequently one or several second partial layers are formed from a second solution comprising a medium excess of A-site (e.g. Bi) to B-site (e.g. Fe) ratio, which is a higher A-site (e.g. Bi) to B-site (e.g. Fe) ratio than that of the first solution. Subsequent to that one or several third partial layers are produced from a third solution, comprising a high excess of A-site (e.g. Bi) to B-site (e.g. Fe) ratio, which means that the amount of A-site (e.g. Bi) in relation to the B-site (e.g. Fe) is highest in comparison to the other solutions. This approach may also be performed with two partial layers of different A-site (e.g. Bi) to B-site (e.g. Fe) ratios or with higher numbers of partial layers, such as for example four or five or even more solutions. For higher numbers for example a continuing variation in concentration may be used. Alternatively, one or several lower partial layers can have stoichiometric composition and some of the last partial layers can have a difference in concentration. P2024,1131 WO N April 16, 2025 - 66 - A similar approach can be performed for introducing wanted gradients. Also, such an approach may be implemented for any ion in the precursor solution including dopants. According to another embodiment it is also possible to use solutions that can differ in viscosity, solvents, concentration to fine tune the processing parameters and thin film properties and / or quality. In Figures 30 and 31 results for thin film properties are shown in which the number of partial layers was varied. All samples are based on the following composition formula [(Bi0.7Ba0.3)][(Fe0.7Ti0.3)]O3 of the precursor solution and the film thickness in all of these examples was 320 nm. The substrate was a platinized silicon wafer. Sample CTF_1337 (curve represented by dots) was formed according to the protocol of table 11, which means that crystallization was carried out after each partial layer was deposited. Sample CTF_1338 (curve represented by dashes) was formed according to the protocol of table 10, which means that crystallization, except for the outer portions of the thin film, was carried out after three amorphous partial layers were formed. Sample CTF_1339 (lines represented by the continuously drawn line) was formed similar to sample CTF_1338, except that crystallization, except for the outer portions of the thin film, was carried out after six amorphous partial layers were formed. As can be seen from the hysteresis plots in Figures 30 and 31, samples CTF_1338 and CTF_1339 have considerably better properties than sample CTF_1337. Sample CTF_1338 showed even better results than sample CTF_1339. Accordingly, 3 depositions before crystallization seem advantageous. The P2024,1131 WO N April 16, 2025 - 67 - inventors think that more than one deposition before crystallization may already bring considerable advantages. Also, 6 or more depositions before crystallization may be advantageous, for example in case of temperature-sensitive substrates. For example, in the case a Ti-substrate is used, 6 or more depositions were found to be advantageous. In the following exemplary embodiments regarding the influence of doping and the composition of the thin films are discussed. In Figures 19 and 20, a thin film 5 of 320 nm thickness is depicted in top view and in cross-section in a scanning electron microscopy image. The stacking of the layers is equivalent to the one shown for the first exemplary embodiment, but no top electrode is realized. A Ti-adhesion layer 3 is realized on a silicon substrate 2 of which only the uppermost silicon oxide layer is visible. A Pt-bottom electrode 4 is arranged on the adhesion layer 3. The thin film has a BiFeO3-BaTiO3-based composition and has 3 mol% doping with Mn. Clear grain boundaries on the surface can be identified in the top view of Figure 19. A well-defined columnar grain growth is visible in the cross-section of Figure 20. The cross-section scanning electron microscopy image shown in Figure 21 shows the same stacking as the experimental embodiment in Figure 20. However here the thin film has a thickness of 1150 nm. A highly dense structure was also obtained for this film. P2024,1131 WO N April 16, 2025 - 68 - In Figures 22 to 29, EDX-measurements for the sample of Figure 21 are shown. The EDX measurements were carried out at 15 kV and a working distance of 8.4 mm. Oxygen was found in the BFO-BT thin film as well as in the SiO2layer (see Figure 22). At the Si-image in Figure 23, the pure Si and the SiO2layer that terminate the substrate towards the thin film are visible. Mn (see Figure 24), Fe (see Figure 25), Ba (see Figure 26) and Bi (see Figure 27) were found in the thin film and are evenly distributed. Ti is found in the thin film as well as in the adhesion layer below the Pt (see Figure 28). Pt was found as the bottom electrode between the thin film and the adhesion layer (see Figure 29). As can be seen, in summary, clearly defined elemental distributions are achieved for a BFO-BT thin film deposited via chemical solution deposition. Also, from the Figures 32 to 35 it can be seen that a BiFeO3- BaTiO3-based composition with 3 mol% doping of Mn has good properties as a piezoelectric material in a thin film. The thin film of sample CTF_1371 for which the graphs of Figures 32 and 33 were measured had the composition [(Bi0.7Ba0.3)][(Fe0.7Ti0.3)0.97Mn0.03]O3. This film was employed in the exemplary embodiment depicted in Figure 12. In Figures 34 and 35 comparisons of the sample named CTF_1552 (different sample than the one of Figures 32 and 33) to a PZT material are shown. The measurements were carried out at 100 Hz measured frequency on a sample of 430 nm thin film thickness on a platinized Si-wafer and an electrode size of 0.92 mm2. P2024,1131 WO N April 16, 2025 - 69 - Furthermore, the following results shown in table 12 were obtained. The following applied in the measurements: - d: film thickness - Pr+: remanent polarization after an electric field of 600 kV / cm was applied (frequency of 100 Hz and electrode area of 0.92 mm²) - j+: leakage current at DC-field of 120 kV / cm and electrode area of 0.92 mm² - e31,f+: effective transverse piezoelectric coefficient; measurement frequency of 10 Hz; electrode size: 20.65 mm² - εr: relative permittivity at 225 Hz, 0 V DC bias voltage and electrode area of 0.92 mm² - tan(δ): losses at 225 Hz, 0 V DC bias voltage and electrode area of 0.92 mm² - d33,f: longitudinal piezoelectric coefficient; measurement frequency of 1 kHz Table 12 d Pr+j+e31,f+εrtan(δ) d33,fSample (nm) (µC / cm²) (µA / cm²) (C / m²) ( ) ( ) (pm / V) BFO-BT thin 430 13.3 18.5 -7 463 0.12 40 film PZT thin 430 17.6 0.2 -13 1115 0.06 75 film Figure 41 shows displacement measurements of the PZT material and the BFO-BT-material of Table 12. Using such curves, it is possible to calculate the e31,f+values that are shown in table 12. P2024,1131 WO N April 16, 2025 - 70 - From the figures 34 and 35 as well as table 12 it can be concluded that BFO-BT thin films may even compete with PZT thin films. The inventors assumed that doping may strongly help to improve the thin film properties. Accordingly, this and features of the composition are analyzed in the following. This assumption is strengthened when regarding the graphs of Figures 36 and 37. In Figure 36, a current density versus electric field hysteresis loops is shown, whereas in Figure 37, polarization versus electric field is shown. Both samples are based on [(Bi0.7Ba0.3)][(Fe0.7Ti0.3)1−zMnz]O3 and the film thickness was 320 nm. For the sample “CTF_1338; 0 % Mn- doped”, represented by the dashed line, z was 0.00. For the sample “CTF_1371; 3 % Mn-doped” that is represented by the solid line, z was 0.03. As can be seen, doping with Mn can considerably reduce the leakage current, which influences the shape of the hysteresis loops. Without doping, the PE-loop of sample “CTF_1338; 0 % Mn-doped” has some features even of a ferroelectric material, whereas Mn can change the shape of the PE-loop. The leakage current is reduced significantly with small amounts of Mn. Additional experiments have been conducted to further investigate this effect, the results of which are depicted in Figure 17, Figure 38, Figure 39 and Figure 40. In Figure 17 X-ray diffraction (XRD) patterns of Mn-doped BFO-BT thin films are shown. All samples show pure BFO-BT phases without secondary phases formation. Additional signals, which are not from the substrate, correspond to the P2024,1131 WO N April 16, 2025 - 71 - BFO-BT perovskite phase. No secondary phases were detected. The lowest pattern assigned “S” shows the reflexes of the substrate itself. All other XRD patterns are associated with samples based on the formula [(Bi0.7Ba0.3)][(Fe0.7Ti0.3)1−zMnz]O3, wherein the following applies for the samples: C1: z = 0.00; C2: z = 0.01; C3: z = 0.02; C4: z = 0.03; C5: z = 0.04; C6: z = 0.05. For the same samples, the PE-loop is shown in Figure 38. As can be seen, when compared for example to the sample of Figures 36 and 37, doping with z = 0.01 (1 mol%) can already significantly improve the material. Already small amounts of Mn can change the shape of the PE-loop. From Figure 36 it can be seen that, in particular for z ≥ 0.03, further considerable improvements are observed. From this the inventors conclude that values of z ≥ 0.02 may be particularly advantageous. This trend is confirmed in Figure 39, which shows DC-leakage currents measured at 120 kV / cm for z = 0.00 to 0.05. Already the small amounts of doping investigated here can strongly reduce the leakage current. In Figure 40 the current versus electric field curves for the same samples are shown. It confirms the same trends as Figure 38. In particular it can be seen in Figure 40 that the current is not increasing by increasing the electric field up to a value of nearly 1 MV which means that the leakage current remains low for the manganese-doped samples. In Figure 18, a further experiment of varying the Bi-excess and the Mn-doping has been carried out and X-ray diffraction patterns are recorded. Similarly to Figure 17, sample “S” P2024,1131 WO N April 16, 2025 - 72 - also shows the reflexes of the substrate. All samples show pure a BFO-BT phase without formation of a secondary phase. The samples are based on the following formula of [(Bi0.7+aBa0.3)][(Fe0.7Ti0.3)1−zMnz]O3. The following applies for the samples: C7: a = 0.028, z = 0; C8: a = 0.056, z = 0; C9: a = 0.084, z = 0; C10: a = 0.084, z = 0.02; C11: a = 0.084, z = 0.03; C12: a = 0.028, z = 0.03 The above measurements are summarized and complemented by the results shown in tables 13 and 14. Table 13 shows a comparison of tested samples based on the formula [(Bi0.7+aBa0.3)][(Fe0.7Ti0.3)1−zMnz]O3. Table 14 shows corresponding properties. The following applies in Table 14: - d: film thickness - Pr+: remanent polarization after an electric field of 1 MV / cm was applied (frequency of 1 kHz and electrode area of 0.077 mm²) - j+: leakage current at DC-field of 120 kV / cm and electrode area of 0.077 mm² - e31,f+: effective transverse piezoelectric coefficient; measurement frequency of 10 Hz; electrode size: 20.65 mm² - εr: relative permittivity at 1 kHz, 0 V DC bias voltage and electrode area of 0.077 mm² - tan(δ): losses at 1 kHz, 0 V DC bias voltage and electrode area of 0.077 mm² - d33,f: longitudinal piezoelectric coefficient; measurement frequency of 1 kHz P2024,1131 WO N April 16, 2025 - 73 - - *) overestimation of the polarization due to high leakage current - n.m.: not measured For the measurements of the effective transverse piezoelectric coefficient |e31,f| the samples were not hot poled prior to the measurements. Note that hot poling of the piezoelectric thin film might further increase the performance of the electroceramic thin film. Table 13 Sample x a b c d β1z11338 0.70 0 0 0 0 - - 1343 0.70 0 0 0 0 Mn 0.01 1345 0.70 0 0 0 0 Mn 0.02 1371 0.70 0 0 0 0 Mn 0.03 1395 0.70 0 0 0 0 Mn 0.04 1397 0.70 0 0 0 0 Mn 0.05 1286 0.70 0.028 0 0 0 - - 1287 0.70 0.056 0 0 0 - - 1288 0.70 0.084 0 0 0 - - 1375 0.70 0.084 0 0 0 Mn 0.02 1433 0.70 0.084 0 0 0 Mn 0.03 1456 0.70 0.028 0 0 0 Mn 0.03 1392 0.70 0 0 0 0 Mn 0.03 1552 0.70 0 0 0 0 Mn 0.03 As can be seen from Table 14 below, preferential properties were observed for the index a lying roughly between 0 and 0.084. The inventors think that this may also apply to slightly larger ranges for a of 0 to 0.09 or even to 0 to 0.10. Also, the results of the table prove that Mn doping considerably improves the material properties. P2024,1131 WO N April 16, 2025 - 74 - Table 14 Sample d Pr+j+e31,f+εrtan(δ) d33,f(nm) (µC / cm²) (µA / cm²) (C / m²) ( ) ( ) (pm / V) 1338 320 115.6* 430 -2.8 422 0.08 n.m. 1343 320 9.31 0.11 n.m. 328 0.06 n.m. 1345 320 10.3 1.2 -3.7 305 0.07 n.m. 1371 320 18.5 19 -0.1 406 0.09 n.m. 1395 320 17.2 72 -7.2 336 0.11 n.m. 1397 320 17.1 206 -5.4 327 0.14 n.m. 1286 320 223.1* 1967 -4.8 522 0.07 n.m. 1287 320 232.6* 1298 -4.9 518 0.08 n.m. 1288 320 269.3* 1052 -6.0 503 0.08 n.m. 1375 320 9.3 5.4 -2.8 266 0.07 n.m. 1433 320 18.3 16 n.m. 345 0.07 n.m. 1456 320 11.8 8.1 n.m. 320 0.07 n.m. 1392 1150 16.8 18 n.m. 436 0.09 n.m. 1552 430 17.2 17 -7.1 432 0.08 40 Figure 42 shows a false color representation of the orientation of an exemplary embodiment of a BFO-BT thin film. As can be seen in the false color plot, the film mostly exhibits the same orientation as indicated by the green color. Only a small portion has a different orientation as indicated by the violet color. This indicates a thin film with a highly oriented and homogeneous structure. In the context of Figure 43 and Tables 15 and 16, aspects regarding the morphotropic phase boundary (MPB) and high e31,f+are discussed. In Table 15, compositions of samples having a varied ratio of BFO to BT are shown. All of the P2024,1131 WO N April 16, 2025 - 75 - samples are doped with 3 mol% of Mn. Table 16 shows corresponding measured data for these samples. Table 15 Sample x a b c d β1z11681 0.62 0 0 0 0 Mn 0.03 1678 0.66 0 0 0 0 Mn 0.03 1748 0.69 0 0 0 0 Mn 0.03 1552 0.70 0 0 0 0 Mn 0.03 1750 0.71 0 0 0 0 Mn 0.03 1753 0.72 0 0 0 0 Mn 0.03 1675 0.74 0 0 0 0 Mn 0.03 1684 0.78 0 0 0 0 Mn 0.03 In Table 16 the following applies: - d: film thickness - Pr+: remanent polarization after an electric field of 1 MV / cm was applied (frequency of 100 Hz and electrode area of 0.92 mm²) - j+: leakage current at DC-field of 120 kV / cm and electrode area of 0.92 mm² - e31,f+: effective transverse piezoelectric coefficient; measurement frequency of 10 Hz; electrode size: 20.65 mm² - εr: relative permittivity at 225 Hz, 0 V DC bias voltage and electrode area of 0.92 mm² - tan(δ): losses at 225 Hz, 0 V DC bias voltage and electrode area of 0.92 mm² P2024,1131 WO N April 16, 2025 - 76 - Table 16 Sample d Pr+J+e31,f+εrtan(δ) (nm) (µC / cm²) (µA / cm²) (C / m²) ( ) ( ) 1681 480 7.5 2.7 2.5 257 0.06 1678 480 11.4 5.8 4.0 324 0.10 1748 480 15.7 8.9 4.5 418 0.11 1737 480 17.8 10.7 5.1 444 0.12 1750 480 18.0 10.4 4.6 397 0.12 1753 480 19.5 10.7 4.5 385 0.12 1675 480 23.0 14.2 5.1 464 0.12 1684 480 24.9 26.1 4.6 283 0.07 In Figure 43 the average value of e31,f+is plotted against the content of BT in BFO-BT. It is noted that in Formula 2 the BT-derived content is 1-x. The BFO-derived content can be calculated from this as 1 – BT-content. It is noted also that the BT-derived content is provided in mol%. In the context of Formula 2 this mol% value would have to be devided by 100 to get the value for 1-x. As can be seen in Figure 43, all plotted samples show sufficiently high e31,f+,from which the inventors conclude that between 20 mol% and 40 mol% of BT content good material properties can be achieved. However, it is apparent that in particular between 22 and 34 mol% of BT high values for e31,f+are achieved. In particular, the highest values are achieved below 33 mol %, such as between 26 and 31 mol%. This observation was surprising, as the morphotropic phase boundary (MPB) of bulk-material BFO-BT was reported for higher BT contents for example in Lee, M.H., Kim, D.J., Park, J.S., Kim, S.W., Song, T.K., Kim, M.-H., Kim, W.-J., Do, D. and Jeong, I.-K. (2015), High-Performance Lead-Free P2024,1131 WO N April 16, 2025 - 77 - Piezoceramics with High Curie Temperatures. Adv. Mater., 27: 6976-6982. Furthermore, in Figures 44 and 45 data provided in Tables 13 and 14 are evaluated regarding the effect of bismuth excess. The data for Figures 44 and 45 was measured at a frequency of 1 kHz and with an electrode size of 0.077 mm3. In particular, in Figures 44 and 45 the results for the samples 1286, 1287 and 1288 of Tables 13 and 14 are compared. As can be seen, both the polarization curve and the current versus field curve show some influence of leakage. Nonetheless, it can be seen that for higher bismuth excess, higher switching currents can be achieved. The same can be observed for Figures 46 and 47 which show data on the influence of bismuth excess in manganese-doped samples. In particular, samples 1375, 1433 and 1456 of the Tables 13 and 14 are compared. The data for Figures 46 and 47 was measured ad a frequency of 1 kHz and with an electrode size of 0.077 mm3. From these results the inventors concluded that a bismuth excess can help to increase the switching currents. In particular good material properties can be achieved in the combination with manganese-doped samples.

[0004] P2024,1131 WO N April 16, 2025 - 78 - Reference sign list 1 thin-film device 2 substrate 3 adhesion layer 3’ second adhesion layer 4 bottom electrode 4’ second bottom electrode 5 thin film 5’, 5’’ second thin film 6a, 6a’, 6b, 6b’ partial top electrode 6 top electrode 6’, 6’’ second top electrode 7 partial removal region 8 side portion 9 side portion 9b common contact track 11 slow axis 12 fast axis 13 mirror surface 14 actuator ring

Claims

1. P2024,1131 WO N April 16, 2025 - 79 - Claims 1. Thin-film device having a thin film comprising a BiFeO3- BaTiO3-based material.

2. Thin-film device according to claim 1, wherein the thin film has a thickness of 50 µm or below, preferably of 20 µm or below.

3. Thin-film device according to any of the preceding claims, wherein the thin film is arranged above a substrate.

4. Thin-film device according to the preceding claim, wherein a layer that has a buffer-function and / or a seed-function is arranged between the substrate and the thin film.

5. Thin-film device according to any of the preceding claims further comprising an electrode for electrically contacting the thin film.

6. Thin-film-device according to any of the preceding claims, wherein the substrate is a metal substrate, a lower electrode is arranged between the thin film and the substrate, and an adhesion layer is arranged between the substrate and the electrode.

7. Thin-film-device according to any of claims 1 to 5, wherein, the substrate is a semiconductor substrate or an insulator substrate,P2024,1131 WO N April 16, 2025 - 80 - a lower electrode is arranged between the thin film and the substrate, and an adhesion layer is arranged between the substrate and the electrode.

8. Thin-film device according to any of the preceding claims, wherein the thin film is obtainable by chemical solution deposition.

9. Thin-film device according to the preceding claim, wherein more than one partial layer is deposited before crystallizing.

10. Thin-film device according to any of the preceding claims, wherein the BiFeO3-BaTiO3-based material is obtainable by chemical solution deposition of a dissolved precursor of the formula ^O^,wherein μ^^^μ^^^ …and ^^^^ ^^^^ … ^^^^ are dopants, and wherein 0 < x < 1, -0.1 ≤ a ≤ 0.3, -0.1 ≤ b ≤ 0.3, -0.1 ≤ c ≤ 0.3, -0.1 ≤ d ≤ 0.3, 0 ≤ y ≤ 0.3, 0 ≤ z ≤ 0.3, x+a > 0, 1-x+b > 0, x+c > 0, and 1-x+d > 0 applies.P2024,1131 WO N April 16, 2025 - 81 - 11. Thin-film device according to any of the preceding claims, wherein the BiFeO3-BaTiO3-based material is represented by the formula ^O^,whereinand ^^^^ ^^^^ … ^^^^ are dopants, and wherein 0 < x < 1, -0.1 ≤ a ≤ 0.3, -0.1 ≤ b ≤ 0.3, -0.1 ≤ c ≤ 0.3, -0.1 ≤ d ≤ 0.3, 0 ≤ y ≤ 0.3, 0 ≤ z ≤ 0.3, x+a > 0, 1-x+b > 0, x+c > 0, and 1-x+d > 0 applies.

12. Thin-film device according to claim 10 or 11, wherein 0,3 ≤ x ≤ 0,9, such as in particular 0,5 ≤ x ≤ 0,9, or preferably 0.65 ≤ x ≤ 0.85, or 0.67 ≤ x ≤ 0.85, or in particular 0.69 ≤ x ≤ 0.75 applies.

13. Thin-film device according to any of claims 10 to 12, wherein 0.001 ≤ y+z ≤ 0.3, or preferably 0.005 ≤ y+z ≤ 0.2, applies.

14. Thin-film device according to any of claims 10 to 13, wherein 0.0025 ≤ y+z ≤ 0.3, such as 0.0026 ≤ y+z ≤ 0.3, or such as 0.01 ≤ y+z ≤ 0.3, or 0.01 ≤ y+z ≤ 0.1, or preferably 0.01 ≤ y+z ≤ 0.05, such as for example 0.02 ≤ y+z ≤ 0.05, applies.P2024,1131 WO N April 16, 2025 - 82 - 15. Thin-film device according to any of claims 10 to 14, wherein 0 ≤ a ≤ 0.09, or preferably 0.025 ≤ a ≤ 0.085, applies.

16. Thin-film device according to any of the preceding claims, wherein the portion of the BiFeO3-derived component in the BiFeO3-BaTiO3-based material is between 99.999 mol% to 0.001 mol%.

17. Thin-film device according to any of the preceding claims, wherein the film is crystalized at a temperature of 500 °C to 1200 °C.

18. Thin-film device according to any of the preceding claims, wherein the BiFeO3-BaTiO3-based material comprises one or more dopants selected from Li, Na, K, Rb, Cs, Mg, Ca, Sr, Be, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, Al, Ga, In, Ge, Sn, Pb, As, Sb, Se, Te, Si, Tl.

19. Thin-film device according to any of the preceding claims, wherein said thin-film device is a high-energy capacitor, a ferroelectric memory, a pyroelectric element, a piezoelectric energy harvester, a piezoelectric actuator, such as for example a micro mirror, an inkjet printing head or a haptic device, or a piezoelectric sensor, such as for example a pressure sensor or an accelerometer.

20. Electroceramic thin film comprising a BiFeO3-BaTiO3-based material.P2024,1131 WO N April 16, 2025 - 83 - 21. Use of a BiFeO3-BaTiO3-based material in a thin film or for forming a thin film.

22. Piezoelectric material comprising a BiFeO3-BaTiO3-based material which is doped by at least one dopant selected from Li, Na, K, Rb, Cs, Mg, Ca, Sr, Be, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, Al, Ga, In, Ge, Sn, Pb, As, Sb, Se, Te, Si, Tl, wherein the concentration of each applied dopant is above 1 mol%.

23. Piezoelectric material according to claim 22, wherein at least one dopant contained is Mn and its concentration is 2 mol% or above and / or 5 mol% or below.

24. Precursor solution for chemical solution deposition comprising a precursor compound for a BiFeO3-BaTiO3-based material and having a boiling point of 50 to 300 °C, a viscosity of 0.5 to 5000 mPa·s, a surface tension of 10 to 100 mN / m, a density of 0.5 to 1.5 g / ml and a dielectric constant of 1.5 to 200.

25. Precursor solution according to the preceding claim comprising a solvent comprising one or more of water, ammonia, aromatic hydrocarbons, alcohols, ethers, carboxylic acids, esters, ketones, aldehydes, carbonate esters, acid anhydrides, amines, imines, amidines, amides, carbamates, carbamides and imides.

26. Precursor solution according to claim 24 or 25, wherein the concentration of the precursor compound is 1 M or below, such as preferably 0.1 M to 1.0 M.P2024,1131 WO N April 16, 2025 - 84 - 27. Process of forming a thin film, wherein a precursor solution comprising a precursor compound for a BiFeO3-BaTiO3-based material dissolved in a solvent is provided, the precursor solution is deposited above a substrate via chemical solution deposition, a crystallization step that is configured to crystallize the BiFeO3-BaTiO3-based material is performed.

28. Process according to the preceding claim, wherein the precursor solution is formed by dissolving metal precursors in the solvent.

29. Process according to the preceding claim, wherein the metal precursors comprise a Bi-precursor, an Fe-precursor, a Ba-precursor and Ti-precursor in which the metal is present in atomic or ionic form.

30. Process according to claim 28 or 29, wherein ligands and / or counter ions in the precursors are selected from nitrate, acetate, citrate, tert-pentoxide, 2,3-dimethyl-2-butoxide, hydroxide, iso-propoxide, tert-butoxide, acetylacetonate, ethoxide, glyoxylate, methoxide, ethoxide, propoxide, iso- propoxide, butoxide, oxyacetylacetonate, dimethylamino, ethylhexyloxide, di-iso-propoxide, peroxocitrate, and water.

31. Process according to any of claims 27 to 30, wherein the composition of the precursor compound is represented by the following sum formula ^O^,P2024,1131 WO N April 16, 2025 - 85 - whereinand ^^^^ ^^^^ … ^^^^ are dopants, and wherein 0 < x < 1, -0.1 ≤ a ≤ 0.3, -0.1 ≤ b ≤ 0.3, -0.1 ≤ c ≤ 0.3, -0.1 ≤ d ≤ 0.3, 0 ≤ y ≤ 0.3, 0 ≤ z ≤ 0.3, x+a > 0, 1-x+b > 0, x+c > 0, and 1-x+d > 0 applies.

32. Process according to any of claims 27 to 31, wherein the chemical solution deposition step is a spin-coating step, a dip-coating step, a spray-coating step or an inkjet printing step.

33. Process according to any of claims 27 to 32, wherein, after a chemical solution deposition step, a drying and a pyrolysis step is performed before crystallization.

34. Process according to claim 33, wherein, before crystallization, more than one combined step of chemical solution deposition and subsequent drying and subsequent pyrolysis is performed.

35. Process according to claim 33 or 34, wherein drying is performed at 50 °C to 250 °C for 1 to 10 min, pyrolysis is performed at 150 °C to 550 °C for 1 to 10 min and crystallization is performed at 500 °C to 1200 °C for 1 to 30 min.P2024,1131 WO N April 16, 2025 - 86 - 36. Process according to any of claims 33 to 35, wherein more than one combined step of chemical solution deposition, drying, pyrolysis and crystallization is performed.

37. Process according to any of claims 33 to 36, wherein a first partial layer and a second partial layer are deposited from a first precursor solution and a second precursor solution, respectively, the first precursor solution having a different composition of precursor compounds than the second precursor solution.

38. Process according to claim 37, wherein the second partial layer is deposited on or above the first partial layer and the second precursor solution has a higher relative concentration of bismuth relative to the other precursor compounds than the first precursor solution.

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