Multilayer structure and process of forming a multilayer structure

Abstract

A multilayer structure is provided that comprises a metal substrate and an electrode above the metal substrate. An adhesion layer is arranged between a main surface of said metal substrate and said electrode.

Description

[0001] P2024,0572 WO N April 16, 2025 - 1 - Description Multilayer structure and process of forming a multilayer structure The present application relates to a multilayer structure and a process of forming such a multilayer structure. Multilayer structures in general, and electroceramic thin films in particular, are widely applied in several technical fields. In particular, this includes high-energy capacitors, ferroelectric memories, piezoelectric actuators such as micromirrors or inkjet printing heads, microfluidic pumps, piezoelectric sensors such as pressure sensors or accelerometers, piezoelectric energy harvesters, electrocaloric solid-state cooling devices, thermistors or applications where a material with high dielectric permittivity is needed. Such devices often have an electroceramic thin film as a functional unit. According to the state of the art, such films are typically deposited on or above silicon wafers. Such wafers may have an oxide layer. Such setups can have a classical metal- insulator-metal (short: MIM) electrode configuration. The forming of PZT films above silicon-based substrates is known from Schwartz et al. (C. R. Chimie 7, 433–461, 2004). The deposition of PZT films above stainless steel foils is known from Won et al. (Nano Energy 55, 182–192, 2019). The deposition of an oriented PZT film above a nickel substrate is known from Yeo et al. (J. Appl. Phys. 116, 014105, 2014). Furthermore, in the patent application WO 2017 / 045700 A1 it P2024,0572 WO N April 16, 2025 - 2 - is published that a piezoelectric transducer can be formed based above a titanium foil as a substrate. However, these or similar approaches for depositing the films on substrates other than silicon wafers often resulted in unsatisfying properties of the piezoelectric thin film, such as degradation of the dielectric or piezoelectric properties, compared to other state-of-the-art thin films, in particular those deposited above silicon wafers. Accordingly, it is an object of the present application to provide an improved electroceramic thin film in a multilayer structure and devices having such a structure. For example, at least in some cases electroceramic thin films with significantly improved dielectric and piezoelectric properties can be achieved by the invention. Some of the disadvantages described above are at least partially overcome by the subject-matter of claims 1 and 2 or other advantages are associated with the subject-matter of claims 1 and 2. Furthermore, other preferred embodiments or alternative embodiments are described in the further claims. According to a first embodiment, a multilayer structure is provided. This multilayer structure comprises a metal substrate and an electrode above the metal substrate. An adhesion layer is arranged between a main surface of said metal substrate and said electrode. The inventors have found that providing an adhesion layer between the electrode and the metal substrate improves the adhesion of said electrode. Furthermore, the adhesion layer, unexpectedly, may also improve the properties of an electroceramic layer arranged above the electrode. P2024,0572 WO N April 16, 2025 - 3 - The use of a metal substrate instead of a silicon wafer has the advantage that the formed multilayer structure can be flexible or bendable. These bendable or flexible substrates may enable the preparation of bendable devices. "Bendability" or "flexibility" may be understood in the general sense of the technical understanding in the field. It may be understood as an elastic deformation. For example it may mean that such multilayer structures may sustain bending of up to 90° on a length of 20 mm, for example. It may be preferred that such a bending can be performed without degradation of the individual layers or plastic deformation of the overall structure. According to an embodiment, the material of the adhesion layer can comprise a transition metal and / or a transition metal oxide. The above wording includes that more than one transition metal or transition metal oxide can be applied. Also, an alloy of said metals can be used to form the adhesion layer or a transition metal oxide can be formed from said alloys. "Transition metal" here and in the following can be understood in the general sense of the technical understanding in the field. In particular it can at least include any transition metal belonging to period 4, 5 and 6 of the periodic table. Preferably here and in the following the transition metal can be titanium, tantalum, or tungsten. Of these in particular, tantalum has been found to be advantageous in several cases. P2024,0572 WO N April 16, 2025 - 4 - The inventors have found that transition metals or their oxides are preferable for promoting adhesion between an electrode and a metal substrate and may help the formation of high-quality electroceramic films. The inventors have further found that an adhesion layer comprising a transition metal or transition metal oxide helps to suppress migration or diffusion of atoms or substances between the metal substrate and the electrode or layers above the electrode. In particular this can help to suppress diffusion of atoms or substances into the electroceramic layer arranged above the electrode, as their composition is less likely to change during preparation of the multilayer structures or over time. The properties of many electroceramic layers such as piezoelectric layers may suffer from substances diffusing into said electroceramic layers. According to an embodiment, the adhesion layer can comprise a first adhesion sublayer and a second adhesion sublayer. The stacking order of these sublayers is generally not limited. According to an embodiment, the first adhesion sublayer can comprise a transition metal and the second adhesion sublayer can comprise a transition metal oxide. The transition metal of the transition metal oxide of the second adhesion sublayer can be the same transition metal as that comprised in the first adhesion sublayer. It also may be a different transition metal, i.e. in this case the transition metal of the transition-metal-oxide-based second adhesion sublayer may be a different transition metal to that comprised in the first adhesion sublayer. Alternatively, according to an embodiment, both the first adhesion sublayer and the second adhesion sublayer can be P2024,0572 WO N April 16, 2025 - 5 - metallic. In this case, the transition metal of the first adhesion sublayer is different to the one of the second adhesion sublayer. Also alternatively, according to an embodiment, both the first adhesion sublayer and the second adhesion sublayer can comprise a transition metal oxide. In this case, the transition metal of the first adhesion sublayer is different to the one of the second adhesion sublayer. According to an even more generalized embodiment, the adhesion layer may have n sublayers with n ≥ 2. Each of the sublayers comprises a transition metal. Each layer may be either metallic or comprise the transition metal as a transition metal oxide. The above features discussed for a first and a second sublayer also apply to an adhesion layer with more than two sublayers. As stated above, an adhesion layer comprising a transition metal or a transition metal oxide may help to suppress migration and diffusion. This effect can be improved for an adhesion layer comprising a first adhesion sublayer comprising a transition metal and a second adhesion sublayer comprising a transition metal oxide. According to an embodiment, the first adhesion sublayer comprising the transition metal in metallic form can be in direct contact with the metal substrate. Above or on top of it the second adhesion sublayer comprising the transition metal oxide can be arranged. According to another embodiment, a reverse stacking, in which the second adhesion sublayer having the transition metal oxide is arranged directly on the substrate and the first sublayer having the transition metal P2024,0572 WO N April 16, 2025 - 6 - is arranged above it, is also possible. Also embodiments with similar construction that have more than one metallic sublayer with different transition metals instead of the first sublayer can be formed. Also, embodiments with similar construction that have more than one transition-metal-oxide- based sublayer with different transition metals instead of the second sublayer can be formed. According to another embodiment, the first adhesion sublayer comprising the transition metal is arranged directly on the substrate. Above it, the second adhesion sublayer comprising the transition metal oxide is arranged. A third adhesion sublayer, again comprising a transition metal, can be arranged above the second adhesion sublayer. Thereby a three- layered structure can be formed, in which the oxide- containing second adhesion sublayer is sandwiched by the first and third sublayer comprising the transition metal. In some cases a structure having these three adhesion sublayers can be particularly advantageous. The inventors think that the first and third adhesion sublayer may be particularly helpful in providing improved adhesion and the second adhesion sublayer comprising the oxide helps to provide improved suppression of diffusion. According to another embodiment, the reverse structure can also be formed, in which a transition-metal-based metallic adhesion sublayer is sandwiched by two transition metal-oxide based-adhesion sublayers. Again, embodiments with similar construction that have more than one metallic sublayer with different transition metals instead of the first sublayer can be formed. Also, embodiments with similar construction that have more than one transition-metal-oxide-based sublayer with different transition metals instead of the second sublayer can be formed. Also, embodiments with similar construction that have more than one metallic sublayer with different P2024,0572 WO N April 16, 2025 - 7 - transition metals instead of the third sublayer can be formed. According to an embodiment, the thickness of the adhesion layer can be between 1 and 100 nm. More preferably it can be between 10 and 50 nm. Alternatively, the thickness can be between 15 and 100 nm, such as between 15 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. The inventors of the present invention have found that in the case that the adhesion layer is too thin, peeling can still take place and the diffusion-inhibiting properties are also reduced. In particular for thicknesses above 10 or particularly above 15 nm, the above-described adhesion properties and the diffusion reduction properties are particularly preferable. In case that sublayers are realized, each sublayer may have a thickness of 1 to 50 nm or preferably of 1 to 25 nm. According to an embodiment the electrode comprises or consists of a noble metal, an alloy of noble metals or a conductive oxide. The above transition metal adhesion layers have been found to be particularly advantageous in terms of improving the adhesion towards a metal substrate for metallic electrodes comprising a noble metal. Also, the adhesion could be greatly improved for said conductive oxides. Here and in the following "noble metals" are understood in the general sense of the technical understanding in the field. These may at least be understood as ruthenium, rhodium, palladium, silver, osmium, iridium, platinum and gold. P2024,0572 WO N April 16, 2025 - 8 - According to an embodiment, the electrode comprises or consists of platinum or iridium. For these two noble metals, in particular for platinum, particularly good results for adhesion with the above adhesion layers have been observed. As a conductive oxide iridium oxide, rhodium oxide, rhenium oxide, ruthenium oxide, strontium ruthenium oxide or lanthanum nickel oxide have been found to provide good conductive electrodes that can be adhered by the above- described adhesion layer. Chemical formulas for these oxides may be IrO2, RhO2, ReO2, RuO2, SrRuO3, LaNiO3. According to an embodiment, the thickness of the electrode can be between 50 nm to 500 nm. In particular, a lower thickness is preferred in the case of more expensive noble metals, such as between 100 nm and 300 nm, for example between 150 to 250 nm. In addition, electrode layers that are too thick tend to cause internal stress in the device which can be disadvantageous for the adhesion between layers. According to an embodiment, an electroceramic layer can be positioned above the electrode in the multilayer structure. In this case the electrode can serve as a bottom electrode for said electroceramic layer. In the setup it is not necessary for the electrode to be directly in contact with the electroceramic layer. As described below, intermediate layers can be arranged between the electrode and the electroceramic layer, for example to facilitate certain crystal orientations. As has been stated above, unexpectedly, having an adhesion layer may help to improve the quality or the properties of the electroceramic layer. This effect is particularly pronounced for the above-described adhesion layers having a transition metal or transition metal oxide. P2024,0572 WO N April 16, 2025 - 9 - Also, the structures having a sublayer are preferred. Furthermore, in combination with the adhesion layer the above-described electrodes, in particular a platinum- containing electrode, may help to form an electroceramic layer with improved properties. An electroceramic layer can be understood in the general technical meaning. It is preferred that the electroceramic provides a functionality to the multilayer structure. Such a functionality may be: ^ High dielectric permittivity, which may be used in capacitors for example; ^ Pyroelectricity, which may be used in infrared sensors for example; ^ Ferroelectricity which may be used in memories for example; ^ Piezoelectricity, which may, for example, be used in the devices described at other points in the application; ^ Temperature-dependent resistance; this may be provided via thermistor ceramic materials, such as materials with positive temperature coefficient (PTC) or materials with negative temperature coefficient (NTC). The inventors have found the above-described advantages in particular for piezoelectric films. However, the inventors also unexpectedly found that these advantages also apply to other types of electroceramic films. In the previous embodiment it may be preferred that a top electrode is arranged above the electroceramic layer. The top electrode can be of the same or of a different material as the other electrode, which in this case can be addressed as a bottom electrode. P2024,0572 WO N April 16, 2025 - 10 - According to an embodiment, the following electroceramic materials can be used for forming an electroceramic layer: Pb[ZrxTi1−x]O3(abbreviated PZT), (1−x) Pb[Mg1 / 3Nb2 / 3O3] – x PbTiO3(abbreviated PMN-PT), [KxNa1−x]NbO3(abbreviated KNN), (1−x) BiFeO3– x BaTiO3(abbreviated BFO-BT), Ba[ZrxTi1−x]O3(abbreviated BZT), (1-x)[Bi1 / 2Na1 / 2]TiO3- x [Bi1 / 2K1 / 2]TiO3(abbreviated BNT-BKT), (1-x) BiFeO3– x Ba[TiyZr1-y]O3(abbreviated BFO-BZT), AlMgZrN, or [AlxSc1-x]N. In all of these examples, x and y are a number between zero and one, i.e. 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1. The above listed electroceramic materials can modified by doping. Doping is understood as intentional addition of impurities to tune the electric and / or piezoelectric properties of the electroceramic layer. The inventors have found that having an adhesion layer can improve the quality of the electroceramic layer. In particular, according to an embodiment, the electroceramic layer can have crystal grains in the size range of 10 to 1000 nm. Also, according to a further embodiment, due to the adhesion layer the electroceramic layer may comprise crystalline columns that extend over the entire thickness of the electroceramic layer In particular said properties may be realized in PZT films According to another embodiment the electroceramic layer can have a granular structure. For example, grains of 10 nm to 1 µm can be present. Such granular structure may for example be realized by electroceramic layers formed with barium titanate. According to an embodiment, the electroceramic layer may comprise or consist of two or more electroceramic sublayers. P2024,0572 WO N April 16, 2025 - 11 - The electroceramic sublayers may correspond with the sublayers or the partial layers described with respect to the deposition process and may be the direct result of such deposition, however the electroceramic sublayers here are not limited to that. One electroceramic sublayer is structurally or chemically different from a neighboring sublayer. For example, two sublayers may have a different functionality, for example by comprising a different electroceramic material. However, more preferably two sublayers are based on or comprise the same electroceramic material, but have a different structure or different chemical composition. For example, both materials can be a PZT-based material, but have different composition. For example, components such as dopants or main ions such as La, Pb, Zr or Ti may have different concentrations in both sublayers. The same holds true for any of the above-described materials. According to an embodiment the electroceramic layer can be applied directly on the electrode. According to an alternative embodiment, a support layer can be applied between the electrode and the electroceramic layer. The support layer can provide a supporting functionality. For example, it may be layer of or that comprises a conductive material. It may thus facilitate charge transport or application of voltage from the electrode to the electroceramic layer. Alternatively or additionally it may provide a buffer-function, which may reduce chemical exchange between the electrode and the electroceramic layer. Also, the support layer may have a functionality that aids in crystal growth or aids in oriented crystal growth of the electroceramic layer. In particular in this case the support layer can be addressed as a seed layer that is applied P2024,0572 WO N April 16, 2025 - 12 - between the electroceramic layer and the electrode. The seed layer may help to improve crystal orientation of an electroceramic film grown on it. Support layer materials in general and seed layer materials in particular can, for example, be selected from lead titanate (PbTiO3), lanthanum nickel oxide (LaNiO3), lead oxide (PbO) or titanium oxide (TiO2). The thickness of the electroceramic layer is generally not limited. According to an embodiment, the electroceramic layer can have a thickness of 10 nm to 20 µm. Preferably, a lower range for the thickness can be 20 nm, 50 nm or 100 nm. Preferably, an upper range of the thickness can be 10 µm, 5 µm, 2 µm or 1 µm. For example, a thickness may be 100 nm to 5 µm, such as 1 µm to 3 µm or 1.7 to 2.5 µm. The above- mentioned values for the lower and the higher range can substitute the lower and the higher value in all these given examples. According to an embodiment, the thickness of the support layer is considerably thinner than that of the electroceramic layer. According to an embodiment the substrate may be provided in the form of a flexible platelet or foil. According to an embodiment the substrate can comprise or consist of a base metal or an alloy comprising a base metal. The term "base metal" can be understood in the general technical sense. Base metals or base metal alloys are often comparatively cheap and easy to work with and possibly flexible in comparison to rigid silicon wafers. Preferred examples of base metals or base metal alloys are titanium, P2024,0572 WO N April 16, 2025 - 13 - aluminum, nickel, copper, brass or stainless steel. For example, titanium or certain types of stainless steel can be biocompatible. In particular, also substrates made with the above-listed base metals can be flexible. The inventors have found that the above-described advantages are particularly pronounced for base metal substrates in general and for the listed examples in particular. Of these substrate materials, titanium is particularly preferred. It has the above-described benefits, but additionally has a thermal expansion coefficient that is relatively close to many of the electroceramic materials used, in particular close to PZT, for which multilayer structures can easily be manufactured. Furthermore, warpage can be reduced. Also, titanium is chemically well compatible with, for example, PZT, BZT, BT, PMN-PT and BFO-BT in the sense that titanium does not contain foreign elements which tend to diffuse into the PZT and thereby affect the ceramic material’s properties. Due to cost-efficient metal or in particular base metal substrates, the invention helps to cost-efficiently fabricate of electroceramic thin film devices with excellent performance. When the substrates are provided in platelet or as a foil, the fabrication can be carried out by a batch process or by a continuous process, such as for example roll-to-roll fabrication. In contrast Si-wafer-based substrates are typically not only more expensive but also can only be processed in a batch process. P2024,0572 WO N April 16, 2025 - 14 - According to another embodiment, the thickness of the metal substrate can be in the range of 1 µm to 500 µm. More preferably, and in particular because of bendability, a thickness of between 10 µm and 200 µm is preferred. Even more preferable for such an application is a thickness between 20 µm and 100 µm. According to a further embodiment, the inventors have found that unpolished substrates can be used when using an adhesion layer. In particular, the metal substrate can have a surface roughness (Ra) of up to 2 µm. In contrast, mirror polished substrate surfaces are typically used for silicon substrate based approaches so far. More preferably a surface roughness can be 1 µm or smaller. Of course, the invention also works for mirror-polished substrate surfaces, but these are not required. However also for the inventive multilayer structure, lower surface roughness may be advantageous as it may increase the yield of the functional devices. Accordingly, the invention easily allows for the use of substrates having a surface roughness of above 10 nm. More preferably they can also have a surface roughness of above 20 nm, above 50 nm or above 100 nm, as thus a less thorough polishing can be used or unpolished substrates may also be used. In general, polishing is a complicated and expensive process. In addition, it can also introduce impurities that may deteriorate the performance as well as yield of the devices. Accordingly, this aspect may help to overcome such issues. According to another embodiment, a multilayer structure is described which has the above-described arrangement and which has a second electrode that is arranged on a second main surface of the metal substrate. In this case a second P2024,0572 WO N April 16, 2025 - 15 - adhesion layer is arranged between the second main surface and the second electrode. Accordingly, a symmetrical multilayer structure can be formed which has electrodes on two sides of the metal substrate and adhesion layers mediating the adhesion on both sides. The second electrode and the second adhesion layer can have the above-described properties. Preferably the first and second adhesion layer have the same material, simplifying the manufacturing. The materials may also differ. Similarly the electrodes can comprise the same material on both sides, which can be preferred to simplify manufacturing. But the material of the electrodes can also differ. In a case with two symmetrically arranged adhesion layers on two opposite main surfaces of the substrate, warpage can be reduced. In particular for Ti-substrates this advantage is particularly pronounced, as it already has reduced warpage, as described above. According to a preferred example of the last embodiment, a second electroceramic layer can be positioned above or on the second bottom electrode. The second electroceramic layer may have the above-described properties or advantages of the first electroceramic layer. Also, here both electroceramic layers can comprise the same material, which can be preferred to simplify manufacturing. But the material of the electroceramic layers can also differ. The present invention is particularly suited for forming such symmetrical structures, as the above-described adhesion- layer-based technique allows for the use of rough substrates. Accordingly, both surfaces of the substrate can be used without polishing, which would have to be performed on each surface individually. In some cases, polishing can be a P2024,0572 WO N April 16, 2025 - 16 - problem as, if both surfaces need to be polished, it can be difficult to avoid damaging the polish. Accordingly, the present application has a synergetic effect for these symmetrical setups. According to another embodiment, the multilayer structure can have a further electrode arranged on the electroceramic layer. In addition, a further electroceramic layer can be arranged on or above the further electrode. The above- described properties can apply here for the further electrode and the further electroceramic layer. The material of the further electroceramic layer can be the same as that of the lower electroceramic layer. It may also be different. The further electrode may have the same material as the other electrode, yet it may also differ. In a similar manner several layers of electrodes and electroceramic layers can be stacked upon another. It is preferred that such stacks are terminated by a top electrode, which can have the above- described properties. According to an embodiment, the present application can be used in high-energy capacitors, ferroelectric memories, piezoelectric actuators, such as micro mirrors or inkjet printing heads, in piezoelectric sensors, such as pressure sensors, tire sensors, or accelerometers, microfluidic pumps, piezoelectric energy harvesters, or electrocaloric solid stage cooling devices. For example, the piezoelectric sensor can be integrated into the tire for gathering and processing data from the wheel or tire, in a road interface or in a car bumper to evaluate the location and magnitude of the impact with another vehicle or obstacle. Accordingly, the above- described multilayer structures can be comprised in these applications. P2024,0572 WO N April 16, 2025 - 17 - According to a further embodiment, a process of forming a multilayer structure is described. For the process, the above-described advantages and properties apply mutatis mutandis as far as applicable. In an embodiment of the process of forming a multilayer structure, first an adhesion layer is arranged on a main surface of a base metal substrate. The adhesion layer can be deposited or arranged on the metal substrate. Preferably it is formed via physical vapor deposition, such as for example magnetron sputtering or evaporation. A bottom electrode containing a noble metal or conductive oxide is arranged on the adhesion layer. The bottom electrode can be arranged or deposited by any means. Preferably chemical vapor deposition or physical vapor deposition, such as, for example, magnetron sputtering or evaporation can be used. An electroceramic material is subsequently deposited on top of the bottom electrode. For example, the electroceramic materials can be the above-defined electroceramic materials. In order to deposit the electroceramic material, chemical solution deposition, magnetron sputtering, atomic layer deposition or pulsed laser deposition may be applied, for example. The electroceramic layer may be formed via subsequent deposition of thin layers of electroceramic material. For example, layers with a thickness of 50 to 200 nm per deposition step may be stacked one upon another. For example, in the case of chemical solution deposition, first a precursor solution comprising an electroceramic material precursor can be deposited. The deposition method can be, for example, spin coating. Subsequently, the solvents from the precursor solution can be removed by drying. Subsequently, P2024,0572 WO N April 16, 2025 - 18 - any organic residues may be removed by a pyrolysis step. Subsequently, an annealing step, which leads to crystallization of the previously amorphous metal oxide, is performed. The deposition can be repeated in order to achieve an electroceramic layer in the orders of several micrometers. According to an embodiment, a high quality PZT film can be formed by depositing and spin coating a solution of PZT on the substrate. The PZT film can be formed from one solution creating one partial layer of the PZT film. It can be created also from two or more solutions of different PZT-component concentrations, from which sublayers of a partial layer are formed. One solution can be Zr-rich and a second solution can be Ti-rich. The principles of the embodiment explained next may apply to the cases of two or more solutions. According to an embodiment a process with at least three deposition steps can be applied. Wherein at least one layer or several layers are produced by using a first solution, a second sublayer is produced by having one or several layers produced from a second solution and a third sublayer is produced by forming one or more layers from a third solution. In this case the electroceramic material is PZT or comprises PZT. The first solution comprises a high zirconium to titanium ratio. The first solution is deposited above the bottom electrode forming the first sublayer. This also may include subsequent deposition and annealing in order to make the first sublayer thicker than that achieved by one deposition. Likewise, a second sublayer is formed from a second solution comprising a medium zirconium to titanium ratio, which is a lower zirconium to titanium ratio than that of the first solution. Again, here subsequent depositions and annealings can be used. Above this, a third sublayer is P2024,0572 WO N April 16, 2025 - 19 - formed, again via one or several depositions and annealings. This third sublayer is formed using a third solution comprising a small zirconium to titanium ratio, which means that the amount of zirconium in relation to the titanium is lowest in comparison to the other solutions. This solution, or this layer, is deposited on the second sublayer. The first solution can be noted as zirconium-rich. The second solution can be noted as a morphotropic phase boundary solution. And the last solution can be called a titanium-rich solution. This principle can be adopted to more than three solutions. For example, four or five or even more differently concentrated solutions can be applied with varying concentrations of Zr and Ti, wherein the concentration is gradually changed from Zr-rich to Ti-rich. As discussed above- also a two-solution based approach can be used in which also there is a switch from Zr-rich to Ti-rich. In the following the invention is described with respect to exemplary embodiments and figures. The figures also comprise schematic drawings. Such schematic drawings are not true to scale and dimensions and dimension ratios may be distorted. Accordingly, no lengths or ratios can be taken directly from the schematic figures except when indicated otherwise. Figure 1 shows a schematic cross-section of a first exemplary embodiment of a multilayer structure. Figure 2 shows a schematic cross-section of a second exemplary embodiment of a multilayer structure. Figure 3 shows a schematic cross-section of a third exemplary embodiment of a multilayer structure. P2024,0572 WO N April 16, 2025 - 20 - Figure 4 shows a schematic cross-section of a portion of a fourth exemplary embodiment of a multilayer structure. Figure 5 shows a schematic cross-section of a portion of a fifth exemplary embodiment of a multilayer structure. Figure 6 shows a schematic cross-section of a portion of a sixth exemplary embodiment of a multilayer structure. Figure 7 shows a schematic cross-section of a portion of a seventh exemplary embodiment of a multilayer structure. Figure 8 shows a schematic view of a tire having a tire pressure sensor. Figure 9 shows a schematic cross-section of a portion of the embodiment of the tire having the tire pressure sensor. Figure 10 shows a schematic representation of a vibration energy harvester. Figure 11 shows an exemplary embodiment of a flexible cantilever. Figure 12 shows a chart flow representation of a manufacturing process of an embodiment of a multilayer structure. Figure 13 shows an X-ray diffraction pattern of a PZT thin film of an exemplary embodiment of a multilayer structure. P2024,0572 WO N April 16, 2025 - 21 - Figure 14 shows a top view scanning electron microscopy image of a PZT film of an exemplary embodiment of a multilayer structure. Figure 15 shows a cross-section scanning electron microscopy image of an exemplary embodiment of a multilayer structure. Figure 16 shows a transmission electron microscopy image of a PZT thin film of an exemplary embodiment of a multilayer structure. Figure 17 shows a polarization-electric field loop of an exemplary embodiment of a PZT thin film within a multilayer structure. Figure 18 shows a relative permittivity-electric field loop of an exemplary embodiment of a PZT thin film within a multilayer structure. Figure 19 shows a bipolar displacement curve of an exemplary embodiment of a PZT thin film within a multilayer structure. Figure 20 shows a unipolar displacement curve of an exemplary embodiment of a PZT thin film within a multilayer structure. Figure 21 shows a photograph of an exemplary embodiment of a clamped cantilever device. Figure 22 shows the first resonant mode of the exemplary embodiment of the clamped cantilever device. Figure 23 shows a schematic cross-section of an eighth exemplary embodiment of a multilayer structure. P2024,0572 WO N April 16, 2025 - 22 - Figure 24 shows a schematic cross-section of a portion of a ninth exemplary embodiment of a multilayer structure. Figure 25 shows a schematic cross-section of a portion of a tenth exemplary embodiment of a multilayer structure. Figure 26 shows a schematic cross-section of a portion of an eleventh exemplary embodiment of a multilayer structure. Figure 27 shows a schematic cross-section of a portion of a twelfth exemplary embodiment of a multilayer structure. Figure 28 shows a schematic cross-section of a portion of a thirteenth exemplary embodiment of a multilayer structure. Figure 29 shows a schematic cross-section of a fourteenth exemplary embodiment of a multilayer structure. In Figure 1 a first exemplary embodiment of a multilayer structure 1 is shown in schematic cross-section. In this exemplary embodiment an adhesion layer 3 is positioned on a base metal substrate 2. The adhesion layer 3 comprises a transition metal or transition metal oxide. A transition metal can be any transition metal from the fourth, fifth or sixth period of the periodic table. An electrode layer 4 is positioned on top of the adhesion layer 3. The electrode 4 can comprise or consist of a noble metal or a conducting oxide. In this stack the electrode layer 4 can be addressed as a bottom electrode. An electroceramic layer 5 is positioned above the bottom electrode layer 4. The electroceramic layer 5 can be a piezoelectric layer. A top electrode 6 is arranged on top of the electroceramic layer 5. The top electrode 6 can be any conducting electrode. For P2024,0572 WO N April 16, 2025 - 23 - example the top electrode 6 can be a noble metal or conducting oxide electrode, similarly to the bottom electrode 4. The materials described for the different layers can be those named in the introduction. A particularly preferred example is a titanium substrate 2, a tantalum containing adhesion layer 3, a platinum electrode layer 4, an electroceramic layer comprising a PZT material, and a gold top electrode 6. In this particular case the titanium foil can have a thickness of 50 µm, the tantalum adhesion layer 3 can have a thickness of 20 nm, the platinum electrode 4 can have a thickness of 200 nm. The PZT electroceramic layer 5 can have a thickness of 1.7 to 2.5 µm. The top electrode 6 can have a thickness of 200 nm. Not depicted explicitly, but in many cases preferred, a support layer, such as a seed layer can be positioned between the electroceramic layer and the electrode. The seed layer can additionally facilitate crystalline and / or oriented growth of the electroceramic layer 5. The present setup has the advantage of forming an electroceramic film 5, such as said PZT electroceramic film 5, with a high degree of orientation on a cost-efficient titanium substrate 2 or another cost-efficient substrate 2. Furthermore, the films can be prepared without having to polish the substrate 2 or otherwise control the surface roughness. As is shown below, outstanding performances can be achieved for such multilayer structures 1. Moreover, the use of titanium as a substrate 2 has multiple benefits. Since the coefficient of thermal expansion (CTE) has a value close to that of PZT, warpage of the substrate 2 is reduced. P2024,0572 WO N April 16, 2025 - 24 - Furthermore, the adhesion layer not only facilitates adhesion between the different layers, but also acts as a chemical barrier. In addition, titanium has been found to be chemically compatible with PZT in the sense that it does not contain any foreign elements that tend to diffuse into PZT and cause undesired doping effects on the material’s properties. Figure 2 shows a schematic cross-section of a second exemplary embodiment of a multilayer structure 1. The multilayer structure 1 of Figure 2 is identical to the multilayer structure 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, here also on the other surface of the substrate 2, a second adhesion layer 3’, a second bottom electrode 4’, a second electroceramic layer 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 electroceramic layer 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. In Figure 3 a schematic cross-section of a third exemplary embodiment of a multilayer structure 1 is shown. This third exemplary embodiment of a multilayer structure 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 electroceramic layer 5 and the first top electrode 6. A second electroceramic layer 5’’ is arranged above the first top electrode 6. A second top electrode 6’’ is arranged on top of P2024,0572 WO N April 16, 2025 - 25 - the second electroceramic layer 5’’. For this setup, the first top electrode 6 acts as a bottom electrode for the second electroceramic layer 5’’. The materials of the second electroceramic layer 5’’ can be selected from the same materials from which the material of the first electroceramic layer 5 is selected. 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 arrangements as shown in Figure 2. Thus either symmetrical or asymmetrical stacks can be i.e. multilayer arrangements with the same number of layers on both sides of the substrate or with different numbers of layers on both sides, respectively. Figure 4 shows a schematic cross-section of a portion of a fourth exemplary embodiment of a multilayer structure 1. Figure 4 can represent an arrangement of an adhesion layer 3 on a substrate 2 in the first, second and third exemplary embodiment of a multilayer structure 1 depicted in Figures 1, 2, and 3, respectively. In this fourth exemplary embodiment the adhesion layer 3 is arranged on the substrate 2. The adhesion layer 3 comprises or consists of one type of material and has no internal material layer boundaries. In the present case the adhesion layer consists only of a transition metal or an alloy of transition metals. However, P2024,0572 WO N April 16, 2025 - 26 - alternatively, it could completely consist of an oxide of a transition metal or a mixed oxide of transition metals. Figure 5 shows a schematic cross-section of a portion of a fifth exemplary embodiment of a multilayer structure 1. Figure 5 can represent an arrangement of an adhesion layer 3 on a substrate 2 in the first, second and third exemplary embodiment of a multilayer structure 1 depicted in Figures 1, 2, and 3, respectively. In this case the adhesion layer 3 comprises a first adhesion sublayer 3a which consists of a transition metal or an alloy of transition metals. On top of this, a second adhesion sublayer 3b that comprises or consists of a transition metal oxide is arranged. The transition metal of the transition metal oxide may be the same or may differ from the transition metal of the first adhesion sublayer 3a. Figure 6 shows a very similar setup as that of Figure 5, as a sixth exemplary embodiment of a multilayer structure 1, but with a reverse stacking of the first adhesion sublayer 3a and the second adhesion sublayer 3b. Here the second adhesion sublayer 3b, comprising or consisting of a transition metal oxide, is arranged directly on the substrate 2 and the first adhesion sublayer 3a, consisting of the transition metal, is arranged on top of it. Also, the stacking in Figure 6 can represent an arrangement of an adhesion layer 3 on a substrate 2 in the first, second and third exemplary embodiment of a multilayer structure 1 depicted in Figures 1, 2, and 3, respectively. Figure 7 shows a schematic cross-section of a portion of a seventh exemplary embodiment of a multilayer structure 1, which is a modification of the stacking as shown in Figure 5, P2024,0572 WO N April 16, 2025 - 27 - i.e. of the fifth exemplary embodiment. On top of the first adhesion sublayer 3a, the second adhesion sublayer 3b is positioned in the same way as in Figure 5. On the second adhesion sublayer 3b a third adhesion sublayer 3a’ is arranged that comprises or consists of a transition metal. The transition metal in the first and third adhesion sublayer 3a and 3a’ can be identical but may also be different. Otherwise, the above-described properties may apply. Not depicted, but also possible is a reverse arrangement of layers here. For example, a transition metal containing adhesion sublayer can be sandwiched by two transition metal oxide containing adhesion sublayers. For the adhesion layers 3 in Figures 4 to 7 the inventors have found out that by using a transition metal, adhesion can be improved between a base metal substrate, such as a titanium foil, and an electrode, such as a platinum electrode or other noble metal electrode. Furthermore, the transition metal can prevent migration of substances between the other layers. In particular, if an oxide layer is present the diffusion or migration of ions or atoms seems to be even better suppressed. In the context of the previous exemplary embodiments, the inventors developed some further exemplary embodiments which relate to properties of the previous exemplary embodiments or which are more generalized versions of these exemplary embodiments. In Figure 23, an eighth exemplary embodiment of a multilayer structure is shown. Principally, it has the same layer stacking as the first exemplary embodiment of a multilayer P2024,0572 WO N April 16, 2025 - 28 - structure which is depicted in Figure 1. However, instead of the electroceramic layer 5 being directly positioned on the electrode 4, a support layer SL is arranged between the electrode 4 and the electroceramic layer 5. In the present case, the support layer SL is a lanthanum nickel oxide support layer (LNO; LaNiO3) that acts as a conducting layer and also has a seed-layer-functionality that helps to facilitate crystal growth and oriented crystal growth. Alternatively, the support layer SL can also be lead titanate (PbTiO3), lead oxide (PbO) or titanium oxide (TiO2). Despite the impression given by the figure, the support layer SL is preferably considerably thinner than the electroceramic layer. In in the present exemplary embodiment, also the adhesion layer 3 is modified in comparison to the adhesion layer described for the first exemplary embodiment shown in Figure 1. Instead of a single layer, the adhesion layer 3 comprises more than one adhesion sublayer. The adhesion layer 3 comprises the adhesion sublayer 3a and in addition further adhesion sublayers which are indicated to count up to n layers, with n representing an arbitrary counting variable. The layers are numbered 3a to 3n. Each of the adhesion sublayers is either a metallic layer comprising or consisting of a transition metal or an oxidic layer comprising or consisting of a transition metal oxide. Each of the adhesion sublayers in Figure 23 is either structurally or chemically different to at least a neighbouring sublayer. This may mean for an arbitrary sublayer 3i (one of the sublayers in 3a to 3n) a neighbouring sublayer 3i+1 is chemically or structurally different. For example, the arbitrary sublayer 3i could be metallic and the neighbouring sublayer 3i+1 is P2024,0572 WO N April 16, 2025 - 29 - also metallic, but both comprise a different transition metal. Also, in another example, the arbitrary sublayer 3i could comprise transition metal oxide and the neighbouring sublayer 3i+1 comprises a different transition metal oxide. Also, in another example, the arbitrary sublayer 3i could comprise transition metal oxide and the neighbouring sublayer 3i+1 is metallic, and either comprises the same or a different transition metal than the transition metal of the oxide of the arbitrary sublayer 3i. Of course, the same relation could also be present the other way round. Of course, independent from the relation of the sublayers 3i and 3i+1, the same relations may apply for the neighbouring sublayers 3i and 3i-1. A specific example that may be represented by the eighth exemplary embodiment of Figure 23 has a titanium substrate 2, with a titanium oxide layer which may be considered as first adhesion sublayer 3a and a second adhesion sublayer 3b comprising or consisting of metallic Ta is arranged on the titanium oxide (first adhesion sublayer). The electrode 4 is made of Pt. On the electrode 4 a lanthanum nickel oxide supporting layer SL is arranged. Above an electroceramic layer 5 comprising or consisting of PZT is arranged. In particular for this arrangement a high film quality was found. Further examples of adhesion which would fall under the general description of the adhesion layer 3 described for Figure 23 are given in the following. Furthermore, it is noted that the sublayer arrangement of Figure 23 and also of the other adhesion layers could be P2024,0572 WO N April 16, 2025 - 30 - applied to any of the other examples and is not limited to an example having a support layer SL. In Figure 24 a schematic cross-section of a portion of a ninth exemplary embodiment of a multilayer structure 1 is shown. In its general setup this exemplary embodiment is similar to the exemplary embodiments shown for Figure 5 and Figure 6, i.e. it has an adhesion layer that comprises a first sublayer and a second sublayer. The first sublayer 3a comprises a first transition metal and is metallic. The second adhesion sublayer 3b in this case comprises a second transition metal and is also metallic, but the second transition metal is different from the first transition metal. For example, the first transition metal may be tantalum and the second transition metal may be titanium. Alternatively, the first adhesion sublayer may be chromium and the second adhesion sublayer 3b may be nickel. In a similar manner also a third adhesion sublayer might be realized (not depicted) that is metallic having a third transition metal, different to the second transition metal. For example, the third transition metal could be silver. A similar setup (not shown) may also be formed for adhesion sublayers that all comprise an oxide. For example, a first adhesion sublayer may comprise a first transition metal oxide, while a second transition metal sublayer comprises a second transition metal oxide. The first transition metal oxide could be, for example, titanium oxide and the second transition metal oxide could be tantalum oxide. Similarly, also a third adhesion sublayer (not depicted) comprising a third transition metal oxide top. The third transition metal oxide is different than the second transition metal oxide. For example, it may be aluminum oxide. P2024,0572 WO N April 16, 2025 - 31 - Figure 25 shows a schematic cross-section of a portion of a tenth exemplary embodiment of a multilayer structure 1. This tenth exemplary embodiment is structurally based on the fifth exemplary embodiment. However, instead of the first adhesion sublayer 3a, a first adhesion sublayer 3a1 and a second adhesion sublayer 3a2 are realized. Both the first adhesion sublayer 3a1 and the second adhesion sublayer 3a2 are metallic. The transition metal comprised in the first adhesion sublayer 3a1 is different to the transition metal comprised in the second adhesion sublayer 3a2. In a similar manner, instead of the second adhesion sublayer 3b shown in the exemplary embodiment of Figure 5, a third adhesion sublayer 3b1 and a fourth adhesion sublayer 3b2 are realized. The third adhesion sublayer 3b1 comprises a first transition metal oxide. The transition metal of the first transition metal oxide of the third adhesion sublayer 3b1 can be the same or different to the transition metal that is comprised in the first adhesion sublayer 3a1 or the second adhesion sublayer 3a2. Also, the fourth adhesion sublayer 3b2 comprises a transition metal oxide (second transition metal oxide). The transition metal of the second transition metal oxide is different to the transition metal of the first transition metal oxide. Otherwise, there is no limitation to the transition metal of the transition metal oxide of the fourth adhesion sublayer 3b2. It can be the same or different to any of the transition metal of the first and the second adhesion sublayers 3a1 and 3a2. Figure 26 shows a schematic cross-section of a portion of an eleventh exemplary embodiment of multilayer structure 1. This eleventh exemplary embodiment is a modification of the sixth exemplary embodiment in the same manner as the tenth P2024,0572 WO N April 16, 2025 - 32 - exemplary embodiment is a modification of the fifth exemplary embodiment. The stacking order shown for the eleventh exemplary embodiment is different to the stacking order shown in the tenth exemplary embodiment. However, otherwise the explanations regarding the individual adhesion sublayers explained for the tenth exemplary embodiment apply. Figure 27 shows a schematic cross-section of a portion of a twelfth exemplary embodiment of a multilayer structure 1. The twelfth exemplary embodiment is a modification of the stacking shown for the eleventh exemplary embodiment shown in in Figure 26. This means that regarding the third adhesion sublayer 3b1, the fourth adhesion sublayer 3b2, the first adhesion sublayer 3a1 and the second adhesion sublayer 3a2, the features explained for the eleventh exemplary embodiment depicted in Figure 26 apply. In addition, a fifth adhesion sublayer 3c1 and a sixth adhesion sublayer 3c2 are arranged above the second adhesion sublayer 3a2. The fifth adhesion sublayer 3c1 comprises a transition metal oxide. Similarly, the sixth adhesion sublayer 3c2 also comprises a transition metal oxide which, however, has a different transition metal than the transition metal of the fifth adhesion sublayer 3c1. Otherwise, there is no limitation regarding the transition metal of the fifth and sixth adhesion sublayer 3c1 and 3c2. For example, the transition metal oxide of the fifth adhesion sublayer 3c1 may be the same as either of the third or the fourth adhesion sublayer 3b1 and 3b2. The same holds true for the sixth adhesion sublayer 3c2. Figure 28 shows a more generalized exemplary embodiment based on the fifth exemplary embodiment. It shows that there may be several adhesion metal sublayers 3a1, which are all metallic and each of which has a different transition metal oxide to P2024,0572 WO N April 16, 2025 - 33 - the neighbouring metallic adhesion sublayers. The principles explained for the eighth exemplary embodiment shown in Figure 23 apply here. Transition metal oxide-based sublayers 3b1 to 3bm are arranged above the metallic adhesion sublayers. Their number may be the same or may be different than the number of metallic adhesion sublayers. For each of the transition metal oxide-based adhesion sublayers in principle the same applies as was discussed for the metallic adhesion sublayers, i.e. the transition metal in each of them is different to the neighbouring oxidic sublayers. The last metallic adhesion sublayer 3an and the first transition metal oxide-based adhesion sublayer 3b1, which neighbour each other, may share the same transition metal oxide, but this is not required. The principles explained for the eighth exemplary embodiment shown in Figure 23 apply here. In Figure 29 a fourteenth exemplary embodiment of a multilayer structure is shown in schematic cross section. It is based on the first exemplary embodiment shown in Figure 1. However, instead of one mainly uniform electroceramic layer 5, here the electroceramic layer 5 has a first electroceramic sublayer 5a and a second electroceramic sublayer 5b. The first electroceramic sublayer 5a and the second electroceramic sublayer 5b are based on the same electroceramic material, as for example PZT. However, the composition of the two sublayers is different. For example, components such as dopants or main ions such as La, Pb, Zr or Ti may have different concentrations in both sublayers. In the Figures 8 to 10 some exemplary applications using an above-described multilayer structure are depicted. P2024,0572 WO N April 16, 2025 - 34 - In Figure 8 a tire 11 is depicted which has a piezoelectric sensor, which is an example of a piezoelectric device 10. The piezoelectric device 10 in this case can be applied to the inside of the tire. Figure 9 shows a portion of the tire 11 on a rim 12. As is depicted in Figure 9, upon contact during rolling of the tire, the piezoelectric sensor (piezoelectric device 10) can detect the repeated contact with the ground 13, as the tire becomes distorted in the region which is in contact with the ground. This distortion transfers to the piezoelectric device 10 and a voltage indicating the distortion can be recorded. The number of such distortion events can give the rotational speed from which the speed of the car can be deduced. Also, the degree of distortion may contain information on the air pressure in the tire, as the degree of distortion may depend on the pressure. Also, it may enable stress or bumps of the tire to be recorded, as this affects the degree of bending or distortion. The inventive concept is particularly suited for building such piezoelectric sensors, as the invention enables flexible multilayer structures with a sensitive piezoelectric response to be manufactured. A vibration energy harvester is shown in Figure 10. It comprises a piezoelectric device 10 which comprises a multilayer structure 1 as shown previously. A cantilever 14 is made to vibrate. Thereby the piezoelectric device 10 creates voltage and current which can be stored in an energy storage device 15. Other examples of applications, in particular piezoelectric applications, include micromirrors, microfluidic pumps, inkjet print heads, haptic elements, strain and pressure P2024,0572 WO N April 16, 2025 - 35 - sensors, tire sensors, shock sensors, energy harvesters, speakers, acceleration sensors and hearing aids. In Figure 11 an exemplary embodiment of a flexible cantilever is shown. This flexible cantilever-shaped device comprises a multilayer structure according to the present invention which includes a PZT thin film deposited above a titanium foil. For example, this cantilever device might be employed in an energy harvester according to Figure 10. Figure 12 shows a flowchart of a process of forming a PZT thin film on a titanium foil as a metal substrate. In the flowchart in Figure 12 the herewith explained steps are briefly depicted. First a titanium foil is provided as a metal substrate. The titanium foil has a thickness of 50 µm. The titanium foil is cleaned by rinsing with acetone, isopropanol and deionized water. Furthermore, it is treated in a UV / ozone cleaner for 15 min. After the cleaning, an adhesion layer of Ta with a thickness of 20 nm is deposited via room temperature DC magnetron sputtering at 500 W. No polishing is required in the preparation of the substrate. The adhesion layer can promote adhesion for quite rough surfaces up to 1 µm or even up to 2 µm. On top of said tantalum layer, a platinum layer of 200 nm is deposited again with room temperature DC magnetron sputtering at 500 W. Thus, a layering with a Ti-foil substrate, a Ta adhesion layer and a Pt bottom electrode layer is formed. After that a lead titanate (PbTiO3) seed layer is deposited on the platinum electrode. For this, first a seed layer P2024,0572 WO N April 16, 2025 - 36 - solution comprising PbTiO3was formed. The solution had a concentration of 0.0625 mol / l of PbTiO3and a 10% molar excess of lead in order to compensate for evaporation during crystallization. Before deposition, the seed layer solution was filtered through an 0.2 µm PTFE syringe filter. Subsequently, the seed layer solution was dispensed on the bare platinum surface and spin-coated at a rotation speed of 3000 rotations per minute for 30 seconds deposition. The thus deposited amorphous seed layer was dried at a temperature of 150 °C on a hot plate and subsequently crystallized in a rapid thermal annealing furnace at 520 °C. Thereby a seed layer of approximately 10 nm was formed. Thus, a stack of a titanium foil, an adhesion layer, a platinum electrode layer and a seed layer was formed. Subsequently, the PZT electroceramic film is formed by depositing several partial layers which each comprise three sublayers. To form a first zirconium-enriched sublayer, first a zirconium-enriched first precursor solution is prepared by dissolving lead(II) acetate in a solution of zirconium(IV) propoxide and titanium(IV) isopropoxide in acetic acid and 2- methoxyethanol. Upon dissolution of the lead precursor at 60 °C, the resulting solution was refluxed for 2 h under nitrogen atmosphere. After distillation of the by-products, the mixture was diluted to achieve a concentration of 0.5 mol / l. The composition of the thus prepared solution corresponds to a composition of Pb(Zr0.63Ti0.37)O3for the sublayer to be formed. The solution is prepared such that it also has a 15% molar excess of lead. Before deposition, the zirconium-enriched first precursor solution was filtered P2024,0572 WO N April 16, 2025 - 37 - through an 0.2 µm PTFE syringe filter. Subsequently, the zirconium-enriched first precursor solution was dispensed on the seed layer and spin-coated at a rotation speed of 3000 rotations per minute for 30 seconds. The as deposited zirconium-enriched sublayer was dried and pyrolyzed at a temperature of 150 °C and 350 °C, respectively. Subsequently, to form a medium concentrated second sublayer, first a medium concentrated second precursor solution is prepared by dissolving lead(II) acetate in a solution of zirconium(IV) propoxide and titanium(IV) isopropoxide in acetic acid and 2-methoxyethanol. Upon dissolution of the lead precursor at 60 °C, the resulting solution was refluxed for 2 h under a nitrogen atmosphere. After distillation of the by-products, the mixture was diluted to achieve a concentration of 0.5 mol / l. The composition of the thus prepared solution corresponds to a composition of Pb(Zr0.53Ti0.47)O3 for the sublayer to be formed. The solution is prepared such that it also has a 15% molar excess of lead. Before deposition, the medium concentrated second precursor solution was filtered through an 0.2 µm PTFE syringe filter. Subsequently, the medium concentrated second precursor solution was dispensed on the dried and pyrolyzed zirconium- enriched sublayer and spin-coated at a rotation speed of 3000 rotations per minute for 30 seconds. The thus deposited medium concentrated second sublayer was dried and pyrolyzed at a temperature of 150 °C and 350 °C, respectively. Subsequently to form a titanium-enriched third sublayer, first a titanium-enriched third precursor solution is prepared by dissolving lead(II) acetate in a solution of zirconium(IV) propoxide and titanium(IV) isopropoxide in acetic acid and 2-methoxyethanol. Upon dissolution of the P2024,0572 WO N April 16, 2025 - 38 - lead precursor at 60 °C, the resulting solution was refluxed for 2 h under nitrogen atmosphere. After distillation of the by-products, the mixture was diluted to achieve a concentration of 0.5 mol / l. The composition of the as prepared solution corresponds to a composition of Pb(Zr0.43Ti0.57)O3for the sublayer to be formed. The solution is prepared such that it also has a 15% molar excess of lead. Before deposition, the titanium-enriched third precursor solution was filtered through an 0.2 µm PTFE syringe filter. Subsequently, the titanium-enriched third precursor solution was dispensed on the dried and pyrolyzed medium concentrated second sublayer and spin-coated at a rotation speed of 3000 rotations per minute for 30 seconds. The thus deposited titanium-enriched third sublayer was dried and pyrolyzed at a temperature of 150 °C and 350 °C, respectively. The partial layer formed from the three sublayers so far is amorphous. It has a thickness of between 50 to 200 nm. After forming of this amorphous partial layer, it is subjected to a crystallization step in a rapid thermal annealing furnace at 650 °C. In order to form a PZT electroceramic layer of a thickness of between 1.7 to 2.5 µm the above described formation of partial layers was repeated 24 to 36 times. In the present example, a thickness of 1.7 or 2.5 µm corresponds to 24 or 36 partial layers, respectively. Thus, stacking of a titanium foil substrate, a tantalum adhesion layer, a platinum electrode layer, a seed layer and a PZT electroceramic functional layer can be achieved. Finally, not depicted in Figure 12, a top electrode can be deposited, for example by DC magnetron sputtering. The top electrode may be, for example, gold or platinum in the present case. P2024,0572 WO N April 16, 2025 - 39 - The above process can be adapted for other materials or other thicknesses of layers. Figure 13 shows an X-ray diffraction pattern of a PZT thin film of an exemplary embodiment of a multilayer structure. The film was formed according to the above-described process. The diffraction pattern clearly shows that the PZT film is crystallized in the perovskite phase with {100} preferred orientation. The degree of crystallinity and orientation is high in the present case. High degree of crystallization was achieved in the presence of the adhesion layer and additionally facilitated by the PbTiO3 seed layer. In Figure 14 a scanning electrode microscopy image in top view is shown. It shows that PZT grains are formed in the thin film with a size range of 100 to 500 nm. Furthermore, there is no evidence of secondary phases such as pyrochlore. Figure 15 shows a scanning electron microscopy cross-section image of a multilayer structure. The multilayer structure has basically the same arrangement of layers as described in Figure 1. As is described below, it has highly advantageous properties. Figure 16 shows a transmission electron microscopy image of a PZT thin film deposited above a titanium foil. As can be seen in the picture, the electroceramic film 5 consisting of PZT is arranged above the platinum bottom electrode 4. In this cross-sectional image, crystalline columns 7 (as indicated in the Figure) can be identified which extend across the entire thickness of the electroceramic film 5. The width of said columns 7 matches the size of the grains observed from the P2024,0572 WO N April 16, 2025 - 40 - top view with scanning electron microscopy as shown in Figure 14. This very good columnar grain growth is preferred as it leads to high electromechanical response. The TEM confirmed the absence of secondary phases, such as pyrochlore, which is known to decrease the performance of the electroceramic element significantly. In Figures 17 to 20, the results of various electrical and piezoelectric characterizations of films are shown. For these measurements PZT films above a titanium foil substrate were formed according to the above-described process. For the top electrodes, a 25 nm chromium adhesion layer and 200 nm gold electrode were deposited via magnetron sputtering. The graphs for Figures 17 to 19 were recorded for the same sample. They were recorded for a sample with an area of 20.65 mm2. The thickness of the substrate was 50 µm. The thickness of the PZT-film was 1.7 µm. In Figure 17, a graph of polarization versus electric field recorded at a frequency of 10 Hz is depicted. The curve drawn with a continuous line, which is the curve that appears larger with respect to the y-axis, belongs to the polarization depicted on the left side of the graph, as also indicated by the associated arrow pointing left. The other, curve represented by a dashed line belongs to the right y- axis of the graph (current density), as also indicated by the associated arrow pointing right. As can be seen, a ferroelectric switching is observed with a remanent polarization Prof 35 µC cm−2. Furthermore, a coercive field of Ecof 40 kV cm−1is observed. Also, the observed polarization electric field loop is highly symmetric. P2024,0572 WO N April 16, 2025 - 41 - In Figure 18, the relative permittivity and the loss tangent are plotted versus the DC bias electric field. The applied frequency here was 1 kHz. The measurement was carried out at 1 kHz frequency and with a small signal amplitude of 5 kV / cm. No leakage at high DC fields was observed in this case. The continuously drawn curve that is visible further up in the graph is the relative permittivity shown on the left side of the image indicated by the associated arrow pointing left. The curve that is represented by a dashed line and that is shown below belongs to the loss tangent on the right side, also indicated by the associated arrow pointing right. As can be seen, the relative permittivity at zero DC bias approaches a value of 700, while the loss remains below 10%. Figure 19 shows a bipolar displacement curve. This was recorded at a frequency of 0.5 Hz. The bipolar displacement curve is symmetrical and exhibits the typical butterfly shape of high quality PZT layers. The stress curve of Figure 20 was recorded on a similarly formed but not identical electroceramic thin film element which has the same values as the other substrate. In Figure 20, a high linearity is observed for the curve. In Table 1 results for the piezoelectric coefficient for the graph of Figure 20 are summarized Table 1: -e31,f+-e31,f- Average of Δe31,f|e31,f| Sample of 10.83 C m−210.41 C m−210.62 C m−20.42 C m−2Figure 20 P2024,0572 WO N April 16, 2025 - 42 - The highly effective transverse piezoelectric coefficient |e31,f| of 10.6 C m−2and the low difference between -e31,f+and -e31,f+, without any preliminary hot poling of the thin film under DC electric field, shows the high quality of the film formed. Note that hot poling or doping by intentional addition of impurities in the piezoelectric thin film may further increase the performance of the electroceramic thin film. In Figure 21 the experimental setup of a clamped cantilever device actuated at its resonant frequency is depicted. The maximum displacement at the tip of the cantilever is in the order of several millimeters. Figure 22 shows the relative amplitude of the cantilever displacement. Bending can be observed in the active part of the cantilever, which corresponds to the region covered by a top electrode.

[0002] P2024,0572 WO N April 16, 2025 - 43 - Reference sign list 1 multilayer structure 2 metal substrate 3 adhesion layer 3a first adhesion sublayer 3b second adhesion sublayer 3a’ third adhesion sublayer 3a1 first adhesion sublayer 3a2 second adhesion sublayer 3b1 third adhesion sublayer 3b2 fourth adhesion sublayer 3c1 fifth adhesion sublayer 3c2 sixth adhesion sublayer 3’ second adhesion layer 4 electrode 4’ second bottom electrode 5 electroceramic layer 5a first electroceramic sublayer 5b second electroceramic sublayer 5’, 5’’ second electroceramic layer 6 top electrode 6’, 6’’ second top electrode 7 column 10 piezoelectric device 11 tire 12 rim 13 ground 14 cantilever 15 energy storage device SL support layer

Claims

P2024,0572 WO N April 16, 2025 - 44 - Claims 1. A multilayer structure comprising a base metal substrate, for example comprising titanium, aluminum, nickel, copper, brass or stainless steel, an electrode containing a noble metal or a conductive oxide arranged above the base metal substrate, and a piezoelectric layer arranged above or on the electrode, wherein an adhesion layer comprising a transition metal or transition metal oxide is arranged between and in direct contact with a main surface of said metal substrate and the electrode.

2. A multilayer structure comprising a metal substrate and an electrode, wherein an adhesion layer is arranged between a main surface of said metal substrate and the electrode.

3. The multilayer structure according to claim 2, wherein the material of the adhesion layer comprises a transition metal and / or a transition metal oxide.

4. The multilayer structure according to any of claims 1 to 3, wherein the adhesion layer comprises a first adhesion sublayer comprising a transition metal and a second adhesion sublayer comprising a transition metal oxide.

5. The multilayer structure according to any of the preceding claims, wherein the adhesion layer comprises n adhesion sublayers each comprising a transition metal in metallic form or a transition metal oxide with n ≥ 2, wherein an individual adhesion sublayer is chemically or structurally different from a directly neighboring adhesion sublayer.P2024,0572 WO N April 16, 2025 - 45 - 6. The multilayer structure according to claim 5, wherein the one of the adhesion sublayers and is directly neighboring adhesion sublayer are chemically different in that both are metallic and comprise a different transition metal, or both comprise differing transition metal oxides, or one is metallic and one has a transition metal oxide.

7. The multilayer structure according to any of claims 1, or 3 to 6, wherein the transition metal is selected from Ti, Ta or W or alloys of these.

8. The multilayer structure according to any of claims 1 to 7, wherein the electrode comprises or consists of a noble metal or an alloy of noble metals or a conductive oxide.

9. The multilayer structure according to any of claims 1 to 8, wherein the electrode comprises or consists of Pt or Ir.

10. The multilayer structure according to any of claims 1 to 8, wherein the electrode comprises or consists of an iridium oxide, a rhodium oxide, a rhenium oxide, a ruthenium oxide, a strontium ruthenium oxide or a lanthanum nickel oxide.

11. The multilayer structure according to any of claims 1 to 10, wherein an electroceramic layer is positioned above the electrode or on the electrode.

12. The multilayer structure according to claim 11, wherein the electroceramic layer comprises or consists of a dielectric, pyroelectric, ferroelectric, piezoelectric or thermistor material.P2024,0572 WO N April 16, 2025 - 46 - 13. The multilayer structure according to claim 11 or 12, wherein the electroceramic layer comprises a first and a second electroceramic sublayer.

14. The multilayer structure according to any of claims 11 to 13, wherein a supporting layer is arranged between the electrode and the electroceramic layer.

15. The multilayer structure according to claim 14, the supporting layer having an electrically conducting property and / or facilitates crystal growth of the electroceramic layer and / or facilitates uniform crystal orientation of the electroceramic layer.

16. The multilayer structure according to claim 14 or 15, wherein the support layer comprises or consists of lead titanate, lanthanum nickel oxide, lead oxide, or titanium oxide.

17. The multilayer structure according to any of claims 1 to 16, wherein the substrate comprises or consists of a base metal or an alloy comprising a base metal.

18. The multilayer structure according to any of claims 1 to 17, wherein the substrate comprises or consists of titanium, aluminum, nickel, copper, brass or stainless steel.

19. The multilayer structure according to any of claims 1 to 18, wherein on its main surface the metal substrate has a surface roughness (Ra) of 10 nm to 2 µm.

20. The multilayer structure according to any of claims 1 to 19, wherein a second electrode is arranged above a secondP2024,0572 WO N April 16, 2025 - 47 - main surface of said metal substrate, wherein a second adhesion layer is arranged between said second main surface and the second electrode, and wherein a second electroceramic layer is positioned above or on the second electrode.

21. The multilayer structure according to any of claims 1, or 11 to 16, wherein a further electrode is arranged above the electroceramic layer and a further electroceramic layer is arranged on or above the further electrode.

22. High-energy capacitor comprising a multilayer structure according to any of claims 1 to 21.

23. Ferroelectric memory device comprising a multilayer structure according to any of claims 1 to 21.

24. Piezoelectric device comprising a multilayer structure according to any of claims 1 to 21.

25. Electrocaloric solid-state cooling device comprising a multilayer structure according to any of claims 1 to 21.

26. Energy harvester comprising a multilayer structure according to any of claims 1 to 21.

27. Pyroelectric device comprising a multilayer structure according to any of claims 1 to 21.

28. Thermistor device comprising a multilayer structure according to any of claims 1 to 21.

29. Process of forming a multilayer structure, whereinP2024,0572 WO N April 16, 2025 - 48 - an adhesion layer is arranged on a main surface of a base metal substrate, an electrode containing a noble metal or a conductive oxide is arranged above the adhesion layer, an electroceramic material is deposited above the electrode.

30. Process according to claim 29, wherein the electroceramic layer is a PZT ceramic layer that is formed including at least two steps, wherein a first solution comprising a first Zr / Ti ratio is deposited above the electrode and a first sublayer of the electroceramic layer is formed by drying and / or annealing, a second solution comprising a second Zr / Ti ratio is deposited above the first sublayer of the electroceramic layer, whereby a second sublayer is formed, wherein the second Zr / Ti ratio is smaller than the first Zr / Ti ratio.

31. Process according to claim 30, wherein a third solution comprising a third Zr / Ti ratio is deposited above the second sublayer of the electroceramic layer, whereby a third sublayer is formed, wherein the third Zr / Ti ratio is smaller than the first and the second Zr / Ti ratio.

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