Multilayer structure and methods for producing a multilayer structure

Abstract

A multilayer structure is provided, comprising a metal substrate and an electrode above the metal substrate. An adhesion layer is positioned between a main surface of the metal substrate and the electrode.

Description

[0001] The present application relates to a multilayer structure and a method for producing such a multilayer structure.

[0002] Multilayer structures in general, and electroceramic thin films in particular, find widespread application in various technical fields. These include, in particular, high-energy capacitors, ferroelectric storage devices, piezoelectric actuators such as micromirrors or inkjet printheads, microfluidic pumps, piezoelectric sensors such as pressure sensors or accelerometers, piezoelectric energy harvesters, electrocaloric solid-state cooling devices, thermistors, and applications requiring a material with a high dielectric constant. Such devices often incorporate an electroceramic thin film as a functional unit.

[0003] According to current technology, such layers are typically deposited on or over silicon wafers. These wafers may have an oxide layer. Such structures may feature a classic metal-insulator-metal (MIM) electrode configuration.

[0004] The formation of PZT layers on silicon-based substrates is known from Schwartz et al. (CR Chimie 7, 433-461, 2004). The deposition of PZT layers on stainless steel foils is known from Won et al. (Nano Energy 55, 182-192, 2019). The deposition of an oriented PZT layer on a nickel substrate is known from Yeo et al. (J. Appl. Phys. 116, 014105, 2014). Furthermore, patent application WO 2017 / 045700 A1 discloses that a piezoelectric transducer can be formed using a titanium foil as a substrate.

[0005] However, these or similar approaches to depositing the layers on substrates other than silicon wafers often led to unsatisfactory properties of the piezoelectric thin film, such as a deterioration of the dielectric or piezoelectric properties, compared to other state-of-the-art thin films, especially those deposited on silicon wafers.

[0006] Accordingly, an objective of the present application is to provide an improved electroceramic thin film in a multilayer structure and devices with 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.

[0007] 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, additional preferred embodiments or alternative embodiments are described in the further claims.

[0008] According to a first embodiment, a multilayer structure is provided. This multilayer structure comprises a metal substrate and an electrode above the metal substrate.

[0009] An adhesive layer is positioned between a major surface of the metal substrate and the electrode. The inventors have discovered that providing an adhesive layer between the electrode and the metal substrate improves the electrode's adhesion. Furthermore, the adhesive layer unexpectedly also enhances the properties of an electroceramic layer positioned over the electrode.

[0010] Using a metal substrate instead of a silicon wafer has the advantage that the resulting multilayer structure can be flexible or bendable. These bendable or flexible substrates can enable the fabrication of flexible devices.

[0011] "Flexibility" or "flexibility" can be understood in the sense of the general technical understanding in this field. It can be understood as elastic deformation. For example, it can mean that such multilayer structures can withstand a bending of up to 90° over a length of, for example, 20 mm. It may be preferable that such bending can be carried out without deterioration of the individual layers or plastic deformation of the overall structure.

[0012] According to one embodiment, the material of the adhesion layer can comprise a transition metal and / or a transition metal oxide. The above formulation includes the possibility of using more than one transition metal or transition metal oxide. Furthermore, an alloy of the aforementioned metals can be used to form the adhesion layer, or a transition metal oxide can be formed from the aforementioned alloys.

[0013] The term "transition metal" can be understood here and in the following in the sense of the general technical understanding in this field. In particular, it can include at least any transition metal of periods 4, 5, and 6 of the periodic table. Preferably, the transition metal can be titanium, tantalum, or tungsten. Of these, tantalum has proven particularly advantageous in several cases.

[0014] The inventors have discovered that transition metals or their oxides can be advantageous for promoting adhesion between an electrode and a metal substrate and contributing to the formation of high-quality electroceramic layers. The inventors have further discovered that an adhesion layer containing a transition metal or a transition metal oxide helps to suppress the migration or diffusion of atoms or substances between the metal substrate and the electrode or the layers above the electrode. This can particularly help to suppress the diffusion of atoms or substances into the electroceramic layer above the electrode, as its composition is less likely to change during the fabrication of the multilayer structures or over time. The properties of many electroceramic layers, e.g.,The performance of piezoelectric layers can be impaired by the diffusion of substances into these electroceramic layers.

[0015] According to one 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.

[0016] According to one embodiment, the first adhesion sublayer can comprise a transition metal and the second adhesion sublayer a transition metal oxide. The transition metal of the transition metal oxide in the second adhesion sublayer can be the same transition metal that is also contained in the first adhesion sublayer. It can also be a different transition metal; that is, in this case, the transition metal of the transition metal oxide-based second adhesion sublayer can be a different transition metal than the one contained in the first adhesion sublayer.

[0017] Alternatively, according to another embodiment, both the first and second adhesive layers can be metallic. In this case, the transition metal of the first adhesion sublayer is different from that of the second adhesion sublayer.

[0018] Alternatively, according to one embodiment, both the first adhesion sublayer and the second adhesion sublayer can contain a transition metal oxide. In this case, the transition metal of the first adhesion sublayer is different from that of the second adhesion sublayer.

[0019] In a further generalized embodiment, the adhesion layer can have n sublayers with n ≥ 2. Each of the sublayers contains a transition metal. Each layer can be either metallic or contain the transition metal in a transition metal oxide. The features discussed above for a first and a second sublayer also apply to an adhesion layer with more than two sublayers.

[0020] As mentioned above, an adhesion layer containing a transition metal or a transition metal oxide can help suppress migration and diffusion. This effect can be enhanced in an adhesion layer that has a first adhesion sublayer with a transition metal and a second adhesion sublayer with a transition metal oxide.

[0021] According to one embodiment, the first adhesion sublayer, which contains the transition metal in metallic form, can be in direct contact with the metal substrate. The second adhesion sublayer, which comprises the transition metal oxide, can be arranged above or on top of this. According to another embodiment, a reverse stacking arrangement is also possible, in which the second adhesion sublayer with the transition metal oxide is arranged directly on the substrate and the first sublayer with the transition metal is arranged above it. Embodiments with a similar structure can also be formed that, instead of the first sublayer, have more than one metallic sublayer with different transition metals. Likewise, embodiments with a similar structure can be formed that, instead of the second sublayer, have more than one transition metal oxide-based sublayer with different transition metals.

[0022] According to another embodiment, the first adhesion sublayer, which contains the transition metal, is arranged directly on the substrate. Above this, the second adhesion sublayer, which contains the transition metal oxide, is arranged. A third adhesion sublayer, also containing a transition metal, can be arranged above the second adhesion sublayer. This allows a three-layer structure to be formed, in which the oxide-containing second adhesion sublayer is positioned between the first and third sublayers containing the transition metal. In some cases, a structure with these three adhesion sublayers can be particularly advantageous. The inventors assume that the first and third adhesion sublayers can be particularly helpful in achieving improved adhesion, and that the second adhesion sublayer, containing the oxide, contributes to improved diffusion suppression.According to another embodiment, the reverse structure can also be formed, in which a transition-metal-based metallic adhesion sublayer is embedded between two transition-metal oxide-based adhesion sublayers. Here too, embodiments with a similar structure can be formed, which have more than one metallic sublayer with different transition metals instead of the first sublayer. Again, embodiments with a similar structure can be formed, which have more than one transition-metal oxide-based sublayer with different transition metals instead of the second sublayer. Embodiments with a similar structure can also be formed, which have more than one metallic sublayer with different transition metals instead of the third sublayer.

[0023] According to one embodiment, the thickness of the adhesive layer can be between 1 and 100 nm. Preferably, it can be between 10 and 50 nm. Alternatively, the thickness can also be between 15 and 100 nm, such as between 15 and 50 nm. For example, the thickness of the adhesive layer can be between 15 nm and 30 nm, which is relevant in many practical scenarios. The inventors of the present invention have found that if the adhesive layer is too thin, delamination can still occur, and the diffusion-inhibiting properties are also reduced. The adhesion properties and diffusion-inhibiting properties described above are particularly advantageous for layer thicknesses above 10 nm, and especially above 15 nm. If sublayers are implemented, each sublayer can have a thickness of 1 to 50 nm, or preferably 1 to 25 nm.

[0024] According to one embodiment, the electrode contains or consists of a noble metal, an alloy of noble metals, or a conductive oxide. The transition metal adhesion layers mentioned above have proven particularly advantageous for improving the adhesion of a noble metal-containing metal electrode to a metal substrate. Adhesion could also be significantly improved for the conductive oxides mentioned.

[0025] Here and in the following, "precious metals" are understood in the sense of the general technical understanding in this field. This can include at least ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold.

[0026] According to one embodiment, the electrode contains or consists of platinum or iridium. Particularly good results in adhesion with the aforementioned adhesion layers were observed for these two precious metals, especially platinum.

[0027] As conductive oxides, iridium oxide, rhodium oxide, rhenium oxide, ruthenium oxide, strontium ruthenium oxide, and lanthanum nickel oxide have proven to be highly conductive electrodes that can be bonded by the adhesion layer described above. Chemical formulas for these oxides include IrO₂, RhO₂, ReO₂, RuO₂, SrRuO₃, and LaNiO₃.

[0028] According to one embodiment, the electrode thickness can range from 50 nm to 500 nm. Particularly with more expensive precious metals, a smaller thickness is preferred, for example, between 100 nm and 300 nm, or between 150 nm and 250 nm. Furthermore, excessively thick electrode layers tend to induce internal stresses in the device, which can adversely affect the adhesion between the layers.

[0029] According to one embodiment, an electroceramic layer can be arranged above the electrode in the multilayer structure. In this case, the electrode can serve as the lower electrode for this electroceramic layer. It is not necessary for the electrode to be in direct contact with the electroceramic layer. As described below, intermediate layers can be arranged between the electrode and the electroceramic layer to, for example, enable specific crystal orientations. As already mentioned, the presence of an adhesion layer can surprisingly contribute to an improvement in the quality or properties of the electroceramic layer. This effect is particularly pronounced with the adhesion layers described above that contain a transition metal or transition metal oxide. Structures with a partial layer are also preferred.Furthermore, the electrodes described above, in particular a platinum-containing electrode, can contribute to the formation of an electroceramic layer with improved properties in combination with the adhesion layer.

[0030] An electroceramic layer can be understood in a general technical sense. It is preferred that the electroceramic imparts functionality to the multilayer structure. Such functionality can be: • High dielectric constant, which can be used, for example, in capacitors; • Pyroelectricity, which can be used, for example, in infrared sensors; • Ferroelectricity, which can be used, for example, in storage devices; • Piezoelectricity, which can be used, for example, in devices described elsewhere in the application; • Temperature-dependent resistance; this can be provided via ceramic thermistor materials, such as materials with a positive temperature coefficient (PTC) or materials with a negative temperature coefficient (NTC).

[0031] The inventors discovered the advantages described above specifically for piezoelectric films. However, they also unexpectedly found that these advantages apply to other types of electroceramic films as well.

[0032] In the previous embodiment, it may be preferred that an upper electrode is arranged above the electroceramic layer. The upper electrode may be made of the same or a different material as the other electrode, which in this case can be referred to as the lower electrode.

[0033] According to one embodiment, the following electroceramic materials can be used to form an electroceramic layer: Pb[Zr]x Ti 1-x ]O3 (abbreviated PZT), (1-x) Pb[Mg2 1 / 3 Note 2 / 3 O3] - x PbTiO3 (abbreviated PMN-PT), [K x N / a 1-x ]NbO3 (abbreviated KNN), (1-x) BiFeO3 - x BaTiO3 (abbreviated BFO-BT), Ba[Zr x Ti 1-x ]O3 (abbreviated BZT), (1-x) [Bi 1 / 2 N / a 1 / 2 ]TiO3 - x [B 1 / 2 K 1 / 2 ]TiO3 (abbreviated BNT-BKT), (1-x) BiFeO3 - x Ba[Ti y Zr 1-y ]O3 (abbreviated BFO-BZT), AlMgZrN, or [Al x Sc 1-x In all these examples, x and y are numbers between zero and one, i.e., 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1. The electroceramic materials listed above can be modified by doping. Doping refers to the intentional addition of impurities to adjust the electrical and / or piezoelectric properties of the electroceramic layer.

[0034] The inventors have found that an adhesion layer can improve the quality of the electroceramic layer. In particular, according to one embodiment, the electroceramic layer can have crystal grains in the size range of 10 to 1000 nm. Furthermore, according to another embodiment, the electroceramic layer can exhibit crystalline columns extending over its entire thickness due to the adhesion layer. These properties can be realized, in particular, in PZT films.

[0035] According to another embodiment, the electroceramic layer can have a granular structure. For example, grains ranging in size from 10 nm to 1 µm can be present.

[0036] Such a granular structure can be achieved, for example, by producing electroceramic layers with barium titanate.

[0037] According to one embodiment, the electroceramic layer can have or consist of two or more electroceramic sublayers. The electroceramic sublayers can correspond to the sublayers or partial layers described in connection with the deposition process and can be the direct result of such deposition; however, the electroceramic sublayers are not limited to this. An electroceramic sublayer is structurally or chemically different from an adjacent sublayer. Thus, two sublayers can have different functionalities, for example, by containing different electroceramic materials. Preferably, however, two sublayers are based on or consist of the same electroceramic material but have a different structure or chemical composition.For example, both materials can be PZT-based but have different compositions. Components such as dopants or major ions like La, Pb, Zr, or Ti can have different concentrations in the two sublayers. The same applies to each of the materials described above.

[0038] According to one embodiment, the electroceramic layer can be applied directly to the electrode.

[0039] According to an alternative embodiment, a support layer can be placed between the electrode and the electroceramic layer. The support layer can provide a supporting function. For example, it can be a layer of a conductive material or contain one. It can thus facilitate charge transport or the application of voltage between the electrode and the electroceramic layer. Alternatively or additionally, it can have a buffering function that can reduce the chemical exchange between the electrode and the electroceramic layer. The support layer can also have a functionality that supports crystal growth or oriented crystal growth of the electroceramic layer. In particular, in this case, the support layer can be referred to as a nucleation layer placed between the electroceramic layer and the electrode.The nucleation layer can help improve the crystal orientation of an electroceramic layer grown on it. Support layer materials in general, and nucleation layer materials in particular, can be selected from, for example, lead titanate (PbTiO3), lanthanum nickel oxide (LaNiO3), lead oxide (PbO), or titanium oxide (TiO2).

[0040] The thickness of the electroceramic layer is generally not limited. According to one 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 for the thickness can be 10 µm, 5 µm, 2 µm, or 1 µm. For example, a thickness of 100 nm to 5 µm can be 1 µm to 3 µm or 1.7 to 2.5 µm. The aforementioned values ​​for the lower and upper ranges can substitute for the lower and upper values ​​in all these examples.

[0041] According to one embodiment, the thickness of the support layer is significantly less than that of the electroceramic layer.

[0042] According to one embodiment, the substrate can be provided in the form of a flexible plate or a film.

[0043] According to one embodiment, the substrate may comprise or consist of a base metal or a base metal alloy. The term "base metal" is to be understood in a general technical sense. Base metals or base metal alloys are often relatively inexpensive and easy to machine, and may be flexible compared to rigid silicon wafers. Preferred examples of base metals or base metal alloys are titanium, aluminum, nickel, copper, brass, or stainless steel. For example, titanium or certain types of stainless steel can be biocompatible. In particular, substrates made of the aforementioned base metals can also be flexible.

[0044] The inventors have found that the advantages described above are particularly pronounced in non-precious metal substrates in general, and in the examples listed in particular.

[0045] Of these substrate materials, titanium is particularly preferred. It exhibits the advantages described above, but additionally has a coefficient of thermal expansion that is relatively close to that of many of the electroceramic materials used, especially PZT, which is why multilayer structures can be easily fabricated. Furthermore, distortion can be reduced. Titanium is also chemically compatible with PZT, BZT, BT, PMN-PT, and BFO-BT, as it contains no foreign elements that could diffuse into the PZT and thereby impair the properties of the ceramic material.

[0046] Thanks to cost-effective metal or, in particular, non-precious metal substrates, the invention helps to manufacture electroceramic thin-film components with excellent performance in a cost-efficient manner.

[0047] If the substrates are in the form of plates or films, production can be carried out in a stacking process or in a continuous process, such as roll-to-roll manufacturing. In contrast, silicon wafer-based substrates are generally not only more expensive but can also only be processed in a batch process.

[0048] According to another embodiment, the thickness of the metal substrate can range from 1 µm to 500 µm. Preferably, and particularly because of its flexibility, the thickness is between 10 µm and 200 µm. Even more preferred for such use is a thickness between 20 µm and 100 µm.

[0049] According to a further embodiment, the inventors have found that unpolished substrates can also be used when employing an adhesion layer. In particular, the metal substrate can have a surface roughness (R aThe surface roughness of the substrates can be as low as 2 µm. In contrast, mirror-polished substrate surfaces are typically used for silicon substrates. Preferably, the surface roughness can be 1 µm or less. Of course, the invention also works with mirror-polished substrate surfaces, but these are not required. However, even for the multilayer structure according to the invention, a lower surface roughness can be advantageous, as it can increase the yield of the functional components. Accordingly, substrates with a surface roughness of over 10 nm can easily be used within the scope of the invention. Preferably, they can also have a surface roughness of over 20 nm, over 50 nm, or over 100 nm, since then a less thorough polishing can be used, or even unpolished substrates can be employed. In general, polishing is a complicated and expensive process.Furthermore, impurities can be introduced that may impair the performance and yield of the components. Accordingly, this aspect can help to overcome such problems.

[0050] According to a further embodiment, a multilayer structure is described which has the arrangement described above and which includes a second electrode positioned over a second main surface of the metal substrate. In this case, a second 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 on both sides that mediate the adhesion. The second electrode and the second adhesion layer can have the properties described above. Preferably, the first and second adhesion layers have the same material, which simplifies manufacturing. However, the materials can also be different. Similarly, the electrodes can have the same material on both sides, which may be preferred for simplifying manufacturing.But the material of the electrodes can also vary.

[0051] With two symmetrically arranged adhesion layers on two opposing main surfaces of the substrate, distortion can be reduced. This advantage is particularly pronounced with titanium substrates, as they already exhibit reduced distortion, as described above.

[0052] According to a preferred example of the last embodiment, a second electroceramic layer can be arranged above or on top of the second lower electrode. The second electroceramic layer can have the properties or advantages of the first electroceramic layer described above. Again, both electroceramic layers can be made of the same material, which may be preferred for manufacturing simplification. However, the material of the electroceramic layers can also be different.

[0053] The present invention is particularly well suited for the fabrication of such symmetrical structures because the adhesion-layer-based approach described above allows the use of rough substrates. Accordingly, both surfaces of the substrate can be used without polishing, which would otherwise have to be performed on each surface individually. In some cases, polishing can be problematic because, if both surfaces need to be polished, it can be difficult to avoid damaging the polished area. Therefore, the present application offers a synergistic advantage for such symmetrical arrangements.

[0054] According to a further embodiment, the multilayer structure can include an additional electrode arranged on the electroceramic layer. Furthermore, another electroceramic layer can be arranged on or above this additional electrode. The properties described above can apply to both the additional electrode and the additional electroceramic layer. The material of the additional electroceramic layer can be the same as that of the lower electroceramic layer, or it can be different. The additional electrode can be made of the same material as the other electrode, or it can be made of a different material. Similarly, several layers of electrodes and electroceramic layers can be stacked on top of each other. It is preferred that such stacks be capped by an upper electrode, which can have the properties described above.

[0055] According to one embodiment, the present application can be used in high-energy capacitors, ferroelectric storage devices, piezoelectric actuators such as micromirrors or inkjet printheads, piezoelectric sensors such as pressure sensors, tire pressure sensors, or accelerometers, microfluidic pumps, piezoelectric energy harvesters, or electrocaloric solid-state cooling devices. For example, the piezoelectric sensor can be integrated into the tire to collect and process data from the wheel or tire, or into a road interface or a vehicle bumper to evaluate the location and extent of an impact with another vehicle or obstacle. Accordingly, the multilayer structures described above can be incorporated in these applications.

[0056] According to a further embodiment, a method for producing a multilayer structure is described. The advantages and properties described above apply accordingly to this method, insofar as they are applicable.

[0057] In one embodiment of the method for forming a multilayer structure, an adhesion layer is first arranged on a main surface of a non-precious metal substrate. The adhesion layer can be deposited or arranged on the metal substrate. Preferably, it is formed by physical deposition from the gas phase, such as magnetron sputtering or evaporation. A lower electrode containing a noble metal or a conductive oxide is arranged on the adhesion layer. The lower electrode can be arranged or deposited in any desired manner. Preferably, chemical or physical deposition from the gas phase, such as magnetron sputtering or evaporation, can be used. Subsequently, an electroceramic material is deposited on the lower electrode. The electroceramic materials can be, for example, those defined above.For the deposition of the electroceramic material, methods such as chemical solution deposition, magnetron sputtering, atomic layer deposition or pulsed laser deposition can be used.

[0058] The electroceramic layer can be formed by successive deposition of thin layers of electroceramic material. For example, layers with a thickness of 50 to 200 nm can be stacked on top of each other in each deposition step. In chemical deposition from solution, a precursor solution containing an electroceramic starting material can first be deposited. The deposition method can be, for example, spin coating. Subsequently, the solvents can be removed from the precursor solution by drying. Then, any organic residues can be removed by a pyrolysis step. Following this, an annealing step is performed, which leads to the crystallization of the previously amorphous metal oxide. The deposition process can be repeated to obtain an electroceramic layer on the order of several micrometers.

[0059] According to one embodiment, a high-quality PZT layer can be formed by deposition and spin coating of a PZT solution onto the substrate. The PZT film can be formed from a single solution that creates a sublayer of the PZT film. It can also be produced from two or more solutions with different concentrations of PZT components, forming sublayers of a sublayer. One solution can be Zr-rich and a second solution can be Ti-rich. The principles of the embodiment described below can be applied to the cases involving two or more solutions.

[0060] According to one embodiment, a method with at least three deposition steps can be used. In this method, at least one layer or multiple layers are produced using a first solution, a second sublayer is produced by producing one or more layers using a second solution, and a third sublayer is produced by forming one or more layers using a third solution. In this case, the electroceramic material is or has a high zirconium-to-titanium ratio. The first solution has a high zirconium-to-titanium ratio. The first solution is deposited above the bottom electrode, forming the first sublayer. This can also include further deposition and annealing to make the first sublayer thicker than would be achieved by a single deposition.Similarly, a second sublayer is formed from a second solution with a medium zirconium-to-titanium ratio, i.e., a lower zirconium-to-titanium ratio than the first solution. Further deposition and heating steps can be used here as well. A third sublayer is then formed on top of this, again through one or more deposition and heating steps. This third sublayer is formed with a third solution that has a low zirconium-to-titanium ratio, meaning that the proportion of zirconium relative to titanium is the lowest compared to the other solutions. This solution, or layer, is deposited on top of the second sublayer. The first solution can be described as zirconium-rich. The second solution can be described as a morphotropic phase boundary solution. And the last solution can be described as a titanium-rich solution.

[0061] This principle can be applied to more than three solutions. For example, four, five, or even more solutions with different concentrations of Zr and Ti can be used, with the concentration gradually changing from Zr-rich to Ti-rich. As discussed above, a two-solution approach can also be used, likewise changing from Zr-rich to Ti-rich.

[0062] The invention is described below with reference to exemplary embodiments and figures. The figures also include schematic drawings. Such schematic drawings are not to scale, and dimensions and proportions may be distorted. Accordingly, lengths or ratios cannot be directly determined from the schematic figures unless otherwise stated. Fig. Figure 1 shows a schematic cross-section of a first embodiment of a multilayer structure. Fig. Figure 2 shows a schematic cross-section of a second embodiment of a multilayer structure. Fig. Figure 3 shows a schematic cross-section of a third embodiment of a multilayer structure. Fig. Figure 4 shows a schematic cross-section of part of a fourth embodiment of a multilayer structure. Fig. Figure 5 shows a schematic cross-section of part of a fifth embodiment of a multilayer structure. Fig. Figure 6 shows a schematic cross-section of part of a sixth embodiment of a multilayer structure. Fig. Figure 7 shows a schematic cross-section of part of a seventh embodiment of a multilayer structure. Fig. Figure 8 shows a schematic view of a tire with a tire pressure sensor. Fig. Figure 9 shows a schematic cross-section of a part of the tire with the tire pressure sensor. Fig. Figure 10 shows a schematic representation of a vibration energy collector. Fig. Figure 11 shows an embodiment of a flexible cantilever. Fig. Figure 12 shows a flowchart of a manufacturing process for an embodiment of a multilayer structure. Fig. Figure 13 shows an X-ray diffraction pattern of a PZT thin film of an embodiment of a multilayer structure. Fig. Figure 14 shows a scanning electron microscope image of a PZT film of an embodiment of a multilayer structure in top view. Fig. Figure 15 shows a scanning electron microscope cross-sectional image of an embodiment of a multilayer structure. Fig. Figure 16 shows a transmission electron microscopy image of a PZT thin film of an embodiment of a multilayer structure. Fig. Figure 17 shows a polarization-electric field loop of an embodiment of a PZT thin film within a multilayer structure. Fig. Figure 18 shows a relative permittivity electric field loop of an embodiment of a PZT thin film within a multilayer structure. Fig. Figure 19 shows a bipolar displacement curve of an embodiment of a PZT thin film in a multilayer structure. Fig. Figure 20 shows a unipolar displacement curve of an embodiment of a PZT thin film in a multilayer structure. Fig. Figure 21 shows a photograph of an exemplary embodiment of a clamped cantilever device. Fig. Figure 22 shows the first resonant mode of the exemplary embodiment of the clamped cantilever device. Fig. Figure 23 shows a schematic cross-section of an eighth embodiment of a multilayer structure. Fig. Figure 24 shows a schematic cross-section of part of a ninth embodiment of a multilayer structure. Fig. Figure 25 shows a schematic cross-section of part of a tenth embodiment of a multilayer structure. Fig. Figure 26 shows a schematic cross-section of part of an eleventh embodiment of a multilayer structure. Fig. Figure 27 shows a schematic cross-section of part of a twelfth embodiment of a multilayer structure. Fig. Figure 28 shows a schematic cross-section of part of a thirteenth embodiment of a multilayer structure. Fig. Figure 29 shows a schematic cross-section of a fourteenth embodiment of a multilayer structure.

[0063] In Fig. Figure 1 shows a first embodiment of a multilayer structure 1 in schematic cross-section. In this embodiment, an adhesion layer 3 is arranged on a non-precious metal substrate 2. The adhesion layer 3 comprises a transition metal or a 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 located on the adhesion layer 3. The electrode 4 can contain or consist of a precious metal or a conductive oxide. In this stack, the electrode layer 4 can be referred to as the lower electrode. Above the lower electrode 4 is an electroceramic layer 5. The electroceramic layer 5 can be a piezoelectric layer. An upper electrode 6 is arranged above the electroceramic layer 5.The upper electrode 6 can be any conductive electrode. For example, the upper electrode 6 can be a noble metal or a conductive oxide electrode, similar to the lower electrode 4.

[0064] The materials mentioned in the introduction can be used for the various layers. 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 top gold electrode 6. In this specific case, the titanium foil can have a thickness of 50 µm, the tantalum-containing adhesion layer 3 a thickness of 20 nm, and the platinum electrode 4 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.

[0065] Although not explicitly shown, a support layer, such as a nucleation layer, can be arranged between the electroceramic layer and the electrode in many cases, which is preferred. The nucleation layer can further facilitate the crystalline and / or oriented growth of the electroceramic layer 5.

[0066] The present structure has the advantage that an electroceramic layer 5, such as the aforementioned PZT electroceramic layer 5, can be formed with a high degree of orientation on a cost-effective titanium substrate 2 or another cost-effective substrate 2. Furthermore, the layers can be produced without the need to polish the substrate 2 or otherwise control the surface roughness. As will be shown below, excellent performance can be achieved with such multilayer structures 1. In addition, the use of titanium as a substrate 2 has several advantages. Since its coefficient of thermal expansion (CTE) is close to that of PZT, the distortion of the substrate 2 is reduced. Moreover, the adhesive layer not only facilitates adhesion between the different layers but also acts as a chemical barrier.Furthermore, titanium has proven to be chemically compatible with PZT, as it does not contain any foreign elements that could diffuse into PZT and cause undesirable doping effects on the material properties.

[0067] Fig. Figure 2 shows a schematic cross-section of a second embodiment of a multilayer structure 1. The multilayer structure 1 of the Fig. 2 is identical in its upper part to the multilayer structure of the Fig. 1, i.e., the layers with reference numerals 2, 3, 4, 5, and 6 are identical to those described for the first embodiment. However, here a second adhesion layer 3', a second lower electrode 4', a second electroceramic layer 5', and a second upper electrode 6' are also arranged on the other surface of the substrate 2. The materials of these layers can correspond to those of the first adhesion layer 3, the first lower electrode 4, the first electroceramic layer 5, and the first upper electrode 6. Accordingly, a largely symmetrical layer arrangement results with respect to the layers with reference numerals 2 to 6.

[0068] In Fig. Figure 3 shows a schematic cross-section of a third embodiment of a multilayer structure 1. This third embodiment of a multilayer structure 1 is a modification of the one described in Figure 3. Fig. The first embodiment shown in Figure 1 comprises the first adhesion layer 3, the first lower electrode 4, the first electroceramic layer 5, and the first upper electrode 6 on the substrate 2. A second electroceramic layer 5'' is arranged above the first upper electrode 6. A second upper electrode 6'' is arranged above the second electroceramic layer 5''. In this arrangement, the first upper electrode 6 acts as the lower electrode for the second electroceramic layer 5''. The materials of the second electroceramic layer 5'' can be selected from the same materials as the material of the first electroceramic layer 5. Similarly, the materials of the second upper electrode 6'' can be selected from the same materials as the material of the first upper electrode 6.

[0069] In a similar way to in Fig. As shown in Figure 3, several further electroceramic layers and top electrodes can be stacked alternately. Preferably, such a stack is terminated by a top electrode.

[0070] The third exemplary embodiment can of course be combined with the second exemplary embodiment, i.e., the two-sided arrangements as in Fig. 2. can be combined. This allows for the creation of either symmetrical or asymmetrical stacks, i.e., multilayer arrangements with the same number of layers on both sides of the substrate or with a different number of layers on both sides.

[0071] Fig. Figure 4 shows a schematic cross-section through part of a fourth embodiment of a multilayer structure 1. Fig. Figure 4 can represent an arrangement of an adhesion layer 3 on a substrate 2 in the first, second and third embodiments of a multilayer structure 1, which in the Fig. 1, Fig. Figures 2 and 3 are shown. In this fourth embodiment, the adhesion layer 3 is arranged on the substrate 2. The adhesion layer 3 comprises or consists of a single type of material and has no internal material layer boundaries. In this case, the adhesion layer consists only of a transition metal or an alloy of transition metals. Alternatively, it can also consist entirely of an oxide of a transition metal or a mixed oxide of transition metals.

[0072] Fig. Figure 5 shows a schematic cross-section through part of a fifth embodiment of a multilayer structure 1. Fig. Figure 5 can represent an arrangement of an adhesion layer 3 on a substrate 2 in the first, second and third embodiments of a multilayer structure 1, as described in the Fig. 1, Fig. Figures 2 and 3 are shown. In this case, the adhesion layer 3 has a first adhesion sublayer 3a, which consists of a transition metal or an alloy of transition metals. A second adhesion sublayer 3b, which comprises or consists of a transition metal oxide, is arranged on top of this. The transition metal of the transition metal oxide can be the same as, or different from, the transition metal of the first adhesion sublayer 3a.

[0073] Fig. 6 shows a very similar structure to that in Fig. 5, as a sixth embodiment of a multilayer structure 1, but with a reversed stacking of the first adhesion sublayer 3a and the second adhesion sublayer 3b. Here, the second adhesion sublayer 3b, which comprises or consists of a transition metal oxide, is arranged directly on the substrate 2, and the first adhesion sublayer 3a, which consists of the transition metal, is arranged above it. The stacking in Fig. 6 can be an arrangement of an adhesion layer 3 on a substrate 2 in the first, second and third embodiments of a in the Fig. 1, Fig. 2 or 3 represent the multilayer structure 1 shown.

[0074] Fig. Figure 7 shows a schematic cross-section of part of a seventh embodiment of a multilayer structure 1, which is a modification of the one described in Fig. The stacking shown in Figure 5 represents the fifth embodiment. The second adhesion sublayer 3b is stacked on the first adhesion sublayer 3a in the same manner as in Figure 5. Fig. 5. On the second adhesion sublayer 3b, a third adhesion sublayer 3a' is arranged, which contains or consists of a transition metal. The transition metal in the first and third adhesion sublayers 3a and 3a' can be identical or different. Otherwise, the properties described above can apply.

[0075] Not shown, but also possible, is a reversed arrangement of the layers. For example, a transition metal-containing adhesion sublayer can be positioned between two transition metal oxide-containing adhesion sublayers.

[0076] For the adhesion layers 3 in the Fig. In figures 4 to 7, the inventors discovered that the use of a transition metal improves the adhesion between a non-precious metal substrate, such as a titanium foil, and an electrode, such as a platinum electrode or another precious metal electrode. Furthermore, the transition metal can prevent the migration of substances between the other layers. In particular, when an oxide layer is present, the diffusion or migration of ions or atoms appears to be suppressed even more effectively.

[0077] In connection with the preceding embodiments, the inventors have developed some further embodiments which relate to properties of the preceding embodiments or which are generalized versions of these embodiments.

[0078] In Fig. Figure 23 shows an eighth embodiment of a multilayer structure. This has essentially the same layer structure as the first embodiment of a multilayer structure, which is shown in Fig. Figure 1 shows the process. However, instead of the electroceramic layer 5 being positioned directly on the electrode 4, a support layer SL is arranged between the electrode 4 and the electroceramic layer 5. In this case, the support layer SL is a lanthanum-nickel oxide support layer (LNO; LaNiO3), which acts as a conductive layer and also has a nucleation layer function that promotes crystal growth and oriented crystal growth. Alternatively, the support layer SL can be lead titanate (PbTiO3), lead oxide (PbO), or titanium oxide (TiO2).

[0079] Contrary to the impression given by the figure, the support layer SL is preferably significantly thinner than the electroceramic layer.

[0080] In the present embodiment, the adhesion layer 3 is also different compared to the adhesion layer used in the first embodiment in Fig. The adhesion layer 3, as described in section 1, has been modified. Instead of a single layer, the adhesion layer 3 comprises more than one adhesion sublayer. The adhesion layer 3 includes the adhesion sublayer 3a and, in addition, further adhesion sublayers, which are specified as having up to n layers, where n is an arbitrary counting variable. The layers are numbered 3a to 3n. Each of the adhesion layers is either a metallic layer containing or consisting of a transition metal, or an oxide layer containing or consisting of a transition metal oxide. Each of the adhesion sublayers in Fig. Sublayer 23 differs either structurally or chemically from at least one neighboring sublayer. This can mean that for any sublayer 3i (one of the sublayers in 3a to 3n), a neighboring sublayer 3i+1 is chemically or structurally different. For example, any sublayer 3i could be metallic, and the neighboring sublayer 3i+1 could also be metallic, but they could each contain a different transition metal. In another example, any sublayer 3i could contain a transition metal oxide, and the neighboring sublayer 3i+1 could contain a different transition metal oxide. In yet another example, any sublayer 3i could contain a transition metal oxide, and the neighboring sublayer 3i+1 could be metallic and contain either the same or a different transition metal than the transition metal of the oxide in any sublayer 3i. The same relationship could, of course, also exist in reverse.Regardless of the relationship between sublayers 3i and 3i+1, the same relationships can of course apply to the neighboring sublayers 3i and 3i-1.

[0081] A specific example, illustrated by the eighth embodiment of the Fig. As can be seen in Figure 23, the system has a titanium substrate 2 with a titanium oxide layer, which can be considered the first adhesion sublayer 3a, and a second adhesion sublayer 3b, which contains or consists of metallic Ta, arranged on the titanium oxide (first adhesion sublayer). The electrode 4 consists of Pt. A lanthanum-nickel oxide support layer SL is arranged on the electrode 4. Above this is an electroceramic layer 5, which contains or consists of PZT. A high layer quality was found, particularly for this arrangement.

[0082] Further examples of adhesion layers that fall under the general description of in Fig. The adhesion layer 3 described in section 23 would fall are listed below.

[0083] Furthermore, it should be noted that the sublayer arrangement of Fig. 23 and could also be applied to any of the other adhesion layers and is not limited to an example with a support layer SL.

[0084] In Fig. Figure 24 shows a schematic cross-section of part of a ninth embodiment of a multilayer structure 1. This embodiment is similar in its general structure to the embodiments of Fig. 5 and Fig. 6, i.e., it has an adhesion layer comprising a first sublayer and a second sublayer. The first sublayer 3a contains a first transition metal and is metallic. The second adhesion layer 3b, in this case, contains a second transition metal and is also metallic; however, the second transition metal is different from the first transition metal. The first transition metal could be, for example, tantalum and the second transition metal titanium. Alternatively, the first adhesion sublayer could be chromium and the second adhesion sublayer 3b nickel. Similarly, a third adhesion sublayer (not shown) could also be realized, which is metallic and contains a third transition metal different from the second transition metal. The third transition metal could be, for example, silver.

[0085] A similar structure (not shown) can also be formed for adhesion sublayers, each containing an oxide. For example, a first adhesion sublayer might contain a first transition metal oxide, while a second adhesion sublayer might contain 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, a third adhesion sublayer (not shown) also contains a third transition metal oxide. This third transition metal oxide differs from the second transition metal oxide. It could, for example, be aluminum oxide.

[0086] Fig. Figure 25 shows a schematic cross-section of part of a tenth embodiment of a multilayer structure 1. This tenth embodiment is structurally based on the fifth 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 contained in the first adhesion sublayer 3a1 differs from the transition metal contained in the second adhesion sublayer 3a2. Similarly, instead of the second adhesion sublayer 3b, which is present in the embodiment of Fig. As shown in Figure 5, a third adhesion sublayer 3b1 and a fourth adhesion sublayer 3b2 are realized. The third adhesion sublayer 3b1 contains a first transition metal oxide. The transition metal of the first transition metal oxide of the third adhesion sublayer 3b1 can be the same as or different from the transition metal contained in the first adhesion sublayer 3a1 or the second adhesion sublayer 3a2. The fourth adhesion sublayer 3b2 also contains a transition metal oxide (second transition metal oxide). The transition metal of the second transition metal oxide differs from the transition metal of the first transition metal oxide. Otherwise, there is no restriction on the transition metal of the transition metal oxide of the fourth adhesion sublayer 3b2. It can be identical to or different from the transition metal of the first and second adhesion sublayers 3a1 and 3a2.

[0087] Fig. Figure 26 shows a schematic cross-section of part of an eleventh embodiment of a multilayer structure 1. This eleventh embodiment is a modification of the sixth embodiment in the same way that the tenth embodiment is a modification of the fifth embodiment. The stacking sequence shown for the eleventh embodiment differs from the stacking sequence shown for the tenth embodiment. Otherwise, however, the explanations given for the individual adhesion sublayers for the tenth embodiment apply.

[0088] Fig. Figure 27 shows a schematic cross-section of part of a twelfth embodiment of a multilayer structure 1. The twelfth embodiment is a modification of the one described in Figure 27. Fig. 26 Stacking of the eleventh embodiment shown.

[0089] This means that the features applicable to the third adhesion sublayer 3b1, the fourth adhesion sublayer 3b2, the first adhesion sublayer 3a1 and the second adhesion sublayer 3a2 are the same as those described in Fig. The eleventh exemplary embodiment shown in Figure 26 has been explained. In addition, a fifth adhesion layer 3c1 and a sixth adhesion layer 3c2 are arranged above the second adhesion layer 3a2. The fifth adhesion layer 3c1 comprises a transition metal oxide. The sixth adhesion layer 3c2 also comprises a transition metal oxide, but it is a different transition metal than the transition metal of the fifth adhesion layer 3c1. Otherwise, there are no restrictions regarding the transition metal of the fifth and sixth adhesion layers 3c1 and 3c2. For example, the transition metal oxide of the fifth adhesion layer 3c1 can be the same as that of the third or fourth adhesion layers 3b1 and 3b2. The same applies to the sixth adhesion layer 3c2.

[0090] Fig. Figure 28 shows a generalized embodiment based on the fifth embodiment. It shows that there can be several metallic adhesion sublayers 3a1, all of which are metallic and each of which has a different transition metal oxide than the adjacent metallic adhesion sublayers. The principles that apply to the eighth embodiment, which is shown in Fig. The points shown in section 23, which have been explained, also apply here.

[0091] The transition metal oxide-based sublayers 3b1 to 3bm are arranged above the metallic adhesion sublayers. Their number can be the same or different from the number of metallic adhesion sublayers. In principle, the same applies to each of the transition metal oxide-based adhesion sublayers as to the metallic adhesion sublayers; that is, the transition metal in each of them is different from that in the adjacent oxide sublayers. The last metallic adhesion sublayer 3an and the first transition metal oxide-based adhesion sublayer 3b1 that are adjacent to each other may, but need not, contain the same transition metal oxide. The principles described for the eighth embodiment in Fig. The points explained in section 23 also apply here.

[0092] In Fig. Figure 29 shows a fourteenth embodiment of a multilayer structure in schematic cross-section. It is based on the first, in Fig. In the embodiment shown in Figure 1, instead of a substantially uniform electroceramic layer 5, the electroceramic layer 5 here comprises 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, such as PZT. However, the composition of the two sublayers differs. For example, components such as dopants or main ions such as La, Pb, Zr, or Ti can have different concentrations in the two sublayers.

[0093] In the Fig. Figures 8 to 10 show some exemplary embodiments in which a multilayer structure as described above is used.

[0094] In Fig. Figure 8 shows a tire 11 equipped with a piezoelectric sensor, which is an example of a piezoelectric device 10. The piezoelectric device 10 can be attached to the inside of the tire in this case. Fig. Figure 9 shows part of the tire 11 on a rim 12. As in Fig. As shown in Figure 9, the piezoelectric sensor (piezoelectric device 10) can detect repeated contact with the ground 13 as the tire rolls, because the tire deforms in the area of ​​contact with the ground. This deformation is transmitted to the piezoelectric device 10, and a voltage indicating the deformation can be recorded. The rotational speed can be derived from the number of such deformation events, from which the vehicle's speed can be deduced. The degree of deformation can also provide information about the tire pressure, as the degree of deformation can depend on the pressure. Stresses or irregularities in the tire can also be detected, as these influence the degree of deformation.The concept according to the invention is particularly suitable for the construction of such piezoelectric sensors, since the invention enables the production of flexible multilayer structures with sensitive piezoelectric response.

[0095] In Fig. Figure 10 shows a vibration energy harvester. This consists of a piezoelectric device 10 comprising a multilayer structure 1, as previously shown. A cantilever 14 is set into vibration. This causes the piezoelectric device 10 to generate voltage and current, which can be stored in an energy storage device 15.

[0096] Other examples of applications, especially piezoelectric applications, include micromirrors, microfluidic pumps, inkjet printheads, haptic elements, strain and pressure sensors, tire sensors, shock sensors, energy harvesters, loudspeakers, accelerometers and hearing aids.

[0097] In Fig. Figure 11 shows an embodiment of a flexible cantilever. This flexible cantilever-shaped device comprises a multilayer structure according to the present invention, which includes a PZT thin film applied over a titanium foil. This cantilever device could, for example, be used in an energy harvesting device according to Fig. 10 can be used.

[0098] Fig. Figure 12 shows a flowchart of a process for producing a PZT thin film on a titanium foil as a metal substrate. The flowchart in Fig. The steps described herein are briefly outlined in 12.

[0099] First, a titanium foil is provided as the metal substrate. The titanium foil has a thickness of 50 µm. The titanium foil is cleaned by rinsing with acetone, isopropanol, and deionized water. It is then treated for 15 minutes in a UV / ozone cleaner. After cleaning, an adhesion layer of titanium (Ta) with a thickness of 20 nm is deposited by direct current magnetron sputtering at room temperature using 500 W. Polishing is not required during substrate preparation. The adhesion layer can promote adhesion to relatively rough surfaces down to 1 µm or even 2 µm.

[0100] A 200 nm thick platinum layer is then deposited onto this tantalum layer by direct current magnetron sputtering at room temperature with 500 W. This results in a layered structure consisting of a titanium foil substrate, an adhesion layer of titanium, and a lower electrode layer of platinum.

[0101] A lead titanate (PbTiO3) nucleation layer is then deposited on the platinum electrode. For this purpose, a PbTiO3 nucleation solution was first prepared. The solution had a concentration of 0.0625 mol / L PbTiO3 and a 10% molar excess of lead to compensate for evaporation during crystallization. Before deposition, the nucleation solution was filtered through a 0.2 µm PTFE syringe filter. The nucleation solution was then applied to the bare platinum surface and spin-coated at a rotation speed of 3000 revolutions per minute for 30 seconds. The resulting amorphous nucleation layer was dried on a hot plate at 150 °C and subsequently crystallized in a rapid thermal oven at 520 °C. This process formed a nucleation layer approximately 10 nm thick.

[0102] This resulted in a stack consisting of a titanium foil, an adhesion layer, a platinum electrode layer, and a nucleation layer.

[0103] The PZT electroceramic layer is then formed by depositing several sublayers, each consisting of three sublayers.

[0104] To form a first zirconium-rich sublayer, a zirconium-rich 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. After dissolving the lead precursor substance at 60 °C, the resulting solution was refluxed for 2 hours under a nitrogen atmosphere. After distillation off the byproducts, the mixture was diluted to a concentration of 0.5 mol / L. The composition of the solution thus prepared corresponds to a composition of Pb(Zr)₂. 0,63 Ti 0,37)O3 for the sublayer to be formed. The solution is prepared to also contain a 15% molar excess of lead. Before deposition, the zirconium-rich first precursor solution was filtered through a 0.2 µm PTFE syringe filter. Subsequently, the zirconium-rich first precursor solution was applied to the seed layer and spin-coated for 30 seconds at a rotation speed of 3000 revolutions per minute. The resulting zirconium-rich sublayer was dried at 150 °C and 350 °C and then pyrolyzed.

[0105] Subsequently, to form a medium-concentrated second sublayer, a medium-concentrated second precursor solution was first prepared by dissolving lead(II) acetate in a solution of zirconium(IV) propoxide and titanium(IV) isopropoxide in acetic acid and 2-methoxyethanol. After dissolving the lead precursor substance at 60 °C, the resulting solution was refluxed for 2 hours under a nitrogen atmosphere. After distillation off the byproducts, the mixture was diluted to a concentration of 0.5 mol / L. The composition of the solution thus prepared corresponds to that of Pb(Zr). 0,53 Ti 0,47)O3 for the sublayer to be formed. The solution is prepared to also contain a 15% molar excess of lead. Before deposition, the medium-concentrated second precursor solution was filtered through a 0.2 µm PTFE syringe filter. Subsequently, the medium-concentrated second precursor solution was applied to the dried and pyrolyzed, zirconia-rich sublayer and spin-coated for 30 seconds at a rotational speed of 3000 revolutions per minute. The resulting medium-concentrated second sublayer was dried and pyrolyzed at temperatures of 150 °C and 350 °C, respectively.

[0106] To form a titanium-rich third sublayer, a titanium-rich third precursor solution is first prepared by dissolving lead(II) acetate in a solution of zirconium(IV) propoxide and titanium(IV) isopropoxide in acetic acid and 2-methoxyethanol. After dissolving the lead precursor substance at 60 °C, the resulting solution was refluxed under a nitrogen atmosphere for 2 hours. After distillation off the byproducts, the mixture was diluted to a concentration of 0.5 mol / L. The composition of the solution thus prepared corresponds to that of Pb(Zr). 0,43 Ti 0,57)O3 for the sublayer to be formed. The solution is prepared to also contain a 15% molar excess of lead. Before deposition, the titanium-enriched third precursor solution was filtered through a 0.2 µm PTFE syringe filter. Subsequently, the titanium-rich third precursor solution was applied to the dried and pyrolyzed, medium-concentration second sublayer and spin-coated for 30 seconds at a rotational speed of 3000 revolutions per minute. The resulting titanium-rich third sublayer was dried and pyrolyzed at temperatures of 150 °C and 350 °C, respectively.

[0107] The partial layer formed from the three sublayers is amorphous. It has a thickness of 50 to 200 nm. After the formation of this amorphous partial layer, it undergoes a crystallization step in a rapid thermal heating oven at 650 °C.

[0108] To obtain a PZT electroceramic layer with a thickness between 1.7 and 2.5 µm, the sublayer formation described above was repeated 24 to 36 times. In the present example, a thickness of 1.7 or 2.5 µm corresponds to 24 or 36 sublayers, respectively. In this way, a stack consisting of a titanium foil substrate, a tantalum adhesion layer, a platinum electrode layer, a nucleation layer, and a PZT electroceramic functional layer can be formed. Finally, what is described in Fig. Figure 12 (not shown) shows that an upper electrode can be deposited, for example by direct current magnetron sputtering. In this case, the upper electrode could be, for example, gold or platinum.

[0109] The above procedure can be adapted for other materials or other layer thicknesses.

[0110] Fig. Figure 13 shows an X-ray diffraction pattern of a PZT thin film from an exemplary embodiment of a multilayer structure. The film was fabricated according to the method described above. The diffraction pattern clearly shows that the PZT film crystallizes in the perovskite phase with a {100} preferred orientation. The degree of crystallinity and orientation is high in this case. The high degree of crystallinity was achieved in the presence of the adhesion layer and further enhanced by the PbTiO3 nucleation layer.

[0111] In Fig. Figure 14 shows a top-down scanning electrode microscopy image. It reveals that PZT grains with a size of 100 to 500 nm have formed in the thin film. Furthermore, there is no evidence of secondary phases such as pyrochlore.

[0112] Fig. Figure 15 shows a scanning electron microscope cross-sectional image of a multilayer structure. The multilayer structure has essentially the same layer arrangement as in Fig. 1 described. As described below, it has very advantageous properties.

[0113] Fig. Figure 16 shows a transmission electron micrograph of a PZT thin film deposited over a titanium foil. As can be seen in the figure, the electroceramic film 5, consisting of PZT, is located above the lower platinum electrode 4. In this cross-sectional image, crystalline columns 7 are visible (as shown in the figure) extending over the entire thickness of the electroceramic layer 5. The width of these columns 7 corresponds to the size of the grains observed in the top view with the scanning electron microscope, as shown in Fig. Figure 14 illustrates this excellent columnar grain growth, which is preferred because it leads to a high electromechanical response. TEM analysis confirmed the absence of secondary phases such as pyrochlore, which are known to significantly reduce the performance of the electroceramic element.

[0114] In the Fig. Figures 17 to 20 present the results of various electrical and piezoelectric characterizations of the layers. For these measurements, PZT layers were fabricated over a titanium foil substrate using the method described above. A 25 nm thick chromium adhesion layer and a 200 nm thick gold electrode were deposited for the upper electrodes by magnetron sputtering.

[0115] The diagrams in the Fig. Images 17 to 19 were taken for the same sample. They were taken for a sample with an area of ​​20.65 mm². 2Recorded. The substrate thickness was 50 µm. The PZT film thickness was 1.7 µm.

[0116] In Fig. Figure 17 shows a plot of the polarization against the electric field, recorded at a frequency of 10 Hz. The curve drawn with a solid line, which appears larger with respect to the y-axis, corresponds to the polarization shown on the left side of the diagram, as indicated by the associated left-pointing arrow. The other curve, represented by a dashed line, corresponds to the right y-axis of the diagram (current density), as indicated by the associated right-pointing arrow. As can be seen, a ferroelectric circuit with a remanent polarization P r of 35 µC cm -2 observed. Furthermore, a coercive field of E is observed. c of 40 kV cm -1observed. The observed polarization-electric loop is also highly symmetrical.

[0117] In Fig. Figure 18 shows the relative permittivity and the loss factor as a function of the DC bias field. The applied frequency was 1 kHz. The measurement was performed at a frequency of 1 kHz and with a small signal amplitude of 5 kV / cm. In this case, no leakage currents were observed at high DC fields. The solid curve, shown higher up in the diagram, is the relative permittivity, indicated on the left side of the image by the corresponding left-pointing arrow. The curve represented by a dashed line, shown below, corresponds to the loss factor on the right side, also indicated by the corresponding right-pointing arrow. As can be seen, the relative permittivity approaches a value of 700 at zero DC bias, while the loss remains below 10%.

[0118] Fig. 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.

[0119] The stress curve in Fig. 20 was recorded on a similarly shaped, but not identical, electroceramic thin-film element that exhibits the same values ​​as the other substrate. In Fig. A high degree of linearity of the curve can be observed in 20.

[0120] Table 1 shows the results for the piezoelectric coefficient for the graph in Fig. 20 summarized Table 1: -e 31, f + -e 31, f - Average of |e 31,f | Δe 31,f example of Fig. 20 10,83 C m -2 10,41 C m -2 10,62 C m -2 0,42 C m -2

[0121] The highly effective transverse piezoelectric coefficient |e 31 , f | from 10.6 C m -2 and the small difference between -e 31 , f + and -e 31 , f+ The fact that the thin film can be produced without prior hot-polishing under a constant electric field demonstrates the high quality of the formed layer. It should be noted that hot-polishing or doping by intentionally adding impurities to the piezoelectric thin film can further enhance the performance of the electroceramic thin film.

[0122] In Fig. Figure 21 shows the experimental setup of a clamped cantilever device excited to its resonant frequency. The maximum deflection at the tip of the cantilever is on the order of a few millimeters. Fig. Figure 22 shows the relative amplitude of the cantilever deflection. The bending is observed in the active part of the cantilever, which corresponds to the area covered by an upper electrode. Reference symbol list 1 Multi-layer structure 2 Metal substrate 3. Adhesive layer 3a first adhesion layer 3b second adhesion layer 3a' third adhesion sublayer 3a1 first adhesion layer 3a2 second adhesion layer 3b1 third adhesion sublayer 3b2 fourth adhesion sublayer 3c1 fifth adhesion sublayer 3c2 sixth adhesion sublayer 3' second adhesion layer 4 electrode 4' second lower electrode 5 electroceramic layer 5a first electroceramic sublayer 5b second electroceramic sublayer 5', 5'' second electroceramic layer 6 upper electrode 6', 6'' second upper electrode 7th pillar 10 piezoelectric device 11 tires 12 rim 13 Floor 14 Cantilever 15 Energy storage device SL support layer QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2017 / 045700 A1

[0004] Cited non-patent literature

[0000] Schwartz et al. (CR Chimie 7, 433-461, 2004

[0004] Won et al. (Nano Energy 55, 182-192, 2019

[0004] Yeo et al. (J. Appl. Phys. 116, 014105, 2014

[0004]

Claims

[1] having a multilayer structure a non-precious metal substrate, which contains, for example, titanium, aluminum, nickel, copper, brass or stainless steel, an electrode arranged above the non-precious metal substrate, containing a precious metal or a conductive oxide, and a piezoelectric layer arranged above or on the electrode, wherein an adhesion layer comprising a transition metal or a transition metal oxide, arranged between and in direct contact with a main surface of the metal substrate and the electrode. [2] Multilayer structure with a metal substrate and an electrode, wherein an adhesion layer is arranged between a main surface of the metal substrate and the electrode. [3] Multilayer structure according to claim 2, wherein the material of the adhesion layer comprises a transition metal and / or a transition metal oxide. [4] Multilayer structure according to one of claims 1 to 3, wherein the adhesion layer comprises a first adhesion sublayer with a transition metal and a second adhesion sublayer with a transition metal oxide. [5] Multilayer structure according to one 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 a single adhesion sublayer differs chemically or structurally from a directly adjacent adhesion sublayer. [6] Multilayer structure according to claim 5, wherein one of the adhesion sublayers and the directly adjacent adhesion sublayer are chemically different, in that both are metallic and contain a different transition metal, or Both have different transition metal oxides, or one is metallic and the other has a transition metal oxide. [7] Multilayer structure according to one of claims 1 or 3 to 6, wherein the transition metal is selected from Ti, Ta or W or their alloys. [8] Multilayer structure according to any one of claims 1 to 7, wherein the electrode comprises or consists of a precious metal or an alloy of precious metals or a conductive oxide. [9] Multilayer structure according to any one of claims 1 to 8, wherein the electrode comprises or consists of Pt or Ir. [10] Multilayer structure according to any one 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] Multilayer structure according to one of claims 1 to 10, wherein an electroceramic layer is arranged above or on the electrode. [12] Multilayer structure according to claim 11, wherein the electroceramic layer comprises or consists of a dielectric, pyroelectric, ferroelectric, piezoelectric material or a thermistor material. [13] Multilayer structure according to claim 11 or 12, wherein the electroceramic layer comprises a first and a second electroceramic sublayer. [14] Multilayer structure according to one of claims 11 to 13, wherein a support layer is arranged between the electrode and the electroceramic layer. [15] Multilayer structure according to claim 14, wherein the support layer has an electrically conductive property and / or promotes the crystal growth of the electroceramic layer and / or promotes a uniform crystal orientation of the electroceramic layer. [16] 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] Multilayer structure according to any one of claims 1 to 16, wherein the substrate comprises or consists of a non-precious metal or an alloy comprising a non-precious metal. [18] Multilayer structure according to any one of claims 1 to 17, wherein the substrate comprises or consists of titanium, aluminium, nickel, copper, brass or stainless steel. [19] Multilayer structure according to any one of claims 1 to 18, wherein the metal substrate has a surface roughness (R) on its main surface a ) from 10 nm to 2 µm. [20] Multilayer structure according to any one of claims 1 to 19, wherein a second electrode is arranged over a second main surface of the metal substrate, wherein a second adhesion layer is arranged between the second main surface and the second electrode, and wherein a second electroceramic layer is arranged over or on the second electrode. [21] Multilayer structure according to one 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 one of claims 1 to 21. [23] Ferroelectric storage device comprising a multilayer structure according to any one of claims 1 to 21. [24] Piezoelectric device comprising a multilayer structure according to any one of claims 1 to 21. [25] Electrocaloric solid-state cooling device comprising a multilayer structure according to any one of claims 1 to 21. [26] Energy harvester comprising a multi-layer structure according to any one of claims 1 to 21. [27] Pyroelectric device comprising a multilayer structure according to any one of claims 1 to 21. [28] Thermistor device comprising a multilayer structure according to any one of claims 1 to 21. [29] Method for producing a multilayer structure, wherein an adhesion layer is arranged on a main surface of a non-precious metal substrate, An electrode containing a precious metal or a conductive oxide is placed above the adhesion layer. An electroceramic material is deposited over the electrode. [30] Method according to claim 23, wherein the electroceramic layer is a PZT ceramic layer formed in at least two steps, wherein a first solution with a first Zr / Ti ratio is deposited over the electrode and a first sublayer of the electroceramic layer is formed by drying and / or heating, a second solution with a second Zr / Ti ratio is deposited over the first sublayer of the electroceramic layer, thereby forming a second sublayer, where the second Zr / Ti ratio is smaller than the first Zr / Ti ratio. [31] Method according to claim 24, wherein a third solution with a third Zr / Ti ratio is deposited over the second sublayer of the electroceramic layer, thereby forming a third sublayer, wherein the third Zr / Ti ratio is smaller than the first and the second Zr / Ti ratio.

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