Substrate for a ceramic thin film and thin-film device

Abstract

Substrate (2) comprising a base layer (3) comprising titanium and an intermediate layer (4) comprising titanium oxide, wherein the intermediate layer can be produced by a two-stage thermal treatment of the base layer (3), wherein during the thermal treatment the base layer (3) is heated in a first step to a first holding temperature and in a second step to a second holding temperature which is higher than the first holding temperature.

Description

The present invention relates to a substrate for depositing a ceramic thin film and a thin film device containing the substrate and the ceramic thin film, and to manufacturing methods for the substrate and the thin film device.Ceramic thin film elements consisting of a metallic substrate and a dielectric ceramic thin film are usually produced by chemical solution deposition (CSD).Substitution of the ceramic material by impurities is usually used to alter and adapt the properties of the ceramic material, such as the dielectric constant or the piezoelectric coefficient, to the particular application.The ceramic thin films can be formed on a metal substrate, but conventional processing involves many application steps to achieve the final layer thickness. This processing promotes atomic and ionic inter-diffusion between the substrate and the thin film and increases the residual stress.Moreover, the numerous coating steps increase costs and the total processing time, which also damage the finished stack.In general, stainless steel is chosen as the metallic substrate for such devices because it is inexpensive and readily available. An example of the prior art is described in WO 2021 / 249 844 A1. Other metals suitable as metallic substrates are described, for example, in US 2004 / 0 175 585 A1 and in the non-patent document J. F. Ihlefeld et al.: Journal of Materials Research, Volume 20, Edition 10, October 2005, pp. 2838-2844. Suitable ceramic material compositions are described, for example, in WO 2021 / 064036 A1 and WO 2019 / 174 719 A1. WO 2022 / 122 445 A2 describes ceramic thick layers which contain such suitable ceramic material compositions and are deposited on ceramic substrates.In order to avoid inter-diffusion between the stainless steel substrate and the ceramic thin film, an intermediate layer such as lanthanum nickelate (LNO) is generally applied.However, the LNO layer does not contribute to the reduction of the defects which arise on crystallization of the thin film on the stainless steel at high temperatures, such as atomic and ionic inter-diffusion and the formation of an undesirable mixed oxide layer on the substrate surface.Furthermore, a dielectric thin-film structure, in particular of lead zirconium titanate, appears to be known from DE 601 24 529 T2. A titanium foil can function as the support. However, an inter-diffusion preventing layer is not separately formed beforehand.A titanium foil as a carrier material also appears to be known from JP H10-270 766 A.The scientific publications of Chen et al. (CHEN, C.C.; CHEN, S.Y.; LIU, D.M: Structural evolution and optical properties of thin films prepared by thermal oxidation of sputtered Ti films. In: Journal of Applied Physics, 88, 2000, 8, 4628-4633) and Narushima et al. (NARUSHIMA, T. et al.: Evaluation of Photocatalytic Activity of the TiO2layer formed on Ti by Thermal Oxidation. In: Interface Oral Health Science - Innovative Research on Biosis-Abiosis Intelligent Interface. 2014, pp. 68-68) additionally show structural and optical properties of a thermally oxidized titanium film.In view of the deficiencies of the prior art products and methods, it is the object of the present invention to disclose an improved substrate, thin film device and fabrication method.The invention is defined by the claims.The invention relates in particular to a substrate which is produced according to a method according to the invention.The substrate comprises at least a base layer and an intermediate layer. The substrate is such that a ceramic thin film layer can be deposited on the intermediate layer.The base layer is a metal layer comprising titanium. Titanium is the major constituent of the base layer. The base layer may be made of a composition containing 100 at% of titanium (Ti). Preferably, the base layer is made of titanium.Other possible but not inventive materials for the metal layer may comprise or consist of copper, nickel or steel.The base layer of titanium has several advantages.Since titanium is electrically conductive, the base layer can serve as a base electrode with which the thin film can be electrically contacted.In addition, the base layer exhibits a flexible or elastic mechanical behavior.In addition, titanium can be handled and processed in an air atmosphere. Exclusion of atmospheric oxygen is not necessary.The intermediate layer comprises titanium oxide. The titanium oxide is preferably thermally grown titanium oxide. Alternatively, the titanium oxide may be an anodically grown titanium oxide.Other possible but not inventive materials for the intermediate layer may comprise or consist of copper oxide, nickel oxide or oxidized steel surfaces.Titanium oxide (TiO 2) is the main component of the intermediate layer. The intermediate layer may be made of a composition containing 100 atomic % of titanium oxide. Preferably, the intermediate layer is titanium oxide.The described intermediate layer has a high homogeneity, in particular a homogeneous structure and composition, and thus homogeneous electrical and mechanical properties. The electrical and mechanical properties can be adjusted accurately.An oxidation layer formed by natural oxidation would contain various impurities and not consist of pure titanium oxide.In one embodiment, the substrate is configured for deposition of a ceramic thin film.In particular, the intermediate layer can be designed such that a ceramic thin-film layer can be applied to the intermediate layer.The intermediate layer has a suitable structure, density and thickness to prevent inter-diffusion between the base layer and the thin film.In addition, the intermediate layer enables stable and permanent deposition of the thin film on the substrate.The intermediate layer preferably has a suitable structure and minimum layer thickness to exhibit self-healing oxidation properties.In particular, the intermediate layer can be cured itself by applying an electric field to the substrate which stimulates the formation of new titanium oxide.In one embodiment, the intermediate layer and the base layer are directly adjacent layers. No layer is applied between these two layers.Furthermore, no other structures are arranged between the intermediate layer and the base layer.The intermediate layer prevents the formation of a mixed oxide layer between the base layer and the ceramic thin film layer.In one embodiment, the substrate is comprised of the base layer and the intermediate layer.No further functional layers are required. The base layer may serve as a base electrode.In other embodiments, the substrate may include a separate electrode layer or additional pattern or protective layers.The electrode layer or multiple electrode layers may be made of a conductive metal such as gold, chromium, silver, platinum, copper, titanium or a combination thereof or a metal oxide having a thickness of up to 1 μm.Examples of metal oxides are lanthanum nickel oxide (LNO), indium tin oxide (ITO) and aluminum zinc oxide (AZO).Moreover, the electrode may be composed of a stack of a plurality of metal layers stacked one above the other, for example, a Cr / Ni / Ag stack or a Cr / Ni / Au stack.The electrode layer may be deposited by chemical solution deposition, sputtering, lithography, screen printing, inkjet printing, or other suitable technique.In an embodiment, the base layer has a thickness between 5 μm and 1000 μm. Preferably, the base layer has a thickness between 5 μm and 200 μm, more preferably between 5 μm and 100 μm. The base layer is thus highly flexible. The material consumption for the production of the substrate can be reduced.In one embodiment, the base layer has a surface roughness Ra of less than 0.5 μm, preferably less than 0.3 μm. Thus, the surface of the base layer is suitable for forming a smooth intermediate layer thereon. Thus, the geometric and structural properties of the intermediate layer can be adjusted exactly.In one embodiment, the intermediate layer has a thickness between 0.1 μm and 2 μm, preferably between 0.8 μm and 1 μm.The thickness of the intermediate layer is preferably significantly greater than the thickness of a natural oxidation layer on the titanium base layer. The intermediate layer having the described thickness has the desired mechanical and electrical properties. In particular, the intermediate layer has self-healing properties.Due to the selected thickness, the intermediate layer is very flexible. The material consumption for the production of the substrate can be reduced. On the other hand, the intermediate layer has a sufficient thickness to prevent inter-diffusion between the base layer and the ceramic thin film layer.Further, the invention relates to a thin film device comprising the above-described substrate and the ceramic thin film layer.By combining the described substrate with a base layer of titanium and an intermediate layer of titanium oxide and the ceramic thin film, the inter-diffusion, in particular the atomic and ionic inter-diffusion, between the base layer and the thin film can be suppressed during a production process or a deposition process of the ceramic thin film on the substrate. Thus, the substrate and the thin film consist of homogeneous material phases with only few or preferably no impurities. As a result, the mechanical and electrical properties of the substrate can be adjusted accurately.The ceramic thin film layer is deposited or deposited on the intermediate layer.In one embodiment, the intermediate layer and the ceramic thin film layer are directly adjacent layers. The intermediate layer is capable of accommodating the ceramic thin film layer.In other embodiments, further functional or structural layers may be arranged between the intermediate layer and the ceramic thin-film layer, e.g. an inner electrode layer.In one embodiment, the thin film device is comprised of the substrate and the ceramic thin film layer. Further layers are not required.In one embodiment, the ceramic thin film may have a polycrystalline, oligocrystalline or monocrystalline structure.In this embodiment, the device may be used as a dielectric electrode structure to apply an electric field to a selected object.In one embodiment, the thin film device includes an inner electrode layer for electrical connection.In one embodiment, the thin film device includes a plurality of inner electrode layers. In this embodiment, the device can be used as a multilayer electrode capacitor or as a multilayer ceramic capacitor. An electric field may be applied to the thin film layer between two or more inner electrode layers.In one embodiment, the device may comprise a plurality, e.g. two or more, of thin film ceramic layers. The ceramic thin film layers may be disposed between the individual electrode layers. The ceramic thin film layers and the electrode layers may form a stack.The thin film device may be supplemented by an upper electrode. No further ceramic thin film layer is applied to the upper electrode. The upper electrode completes the thin film device on a side of the thin film device opposite to the side completed by the substrate.The upper electrode may, but need not, cover the entire surface of the ceramic thin film layer and may have various shapes.The electric field may be applied in a stacking direction of the layers. Thus, the stack may form a multilayer electrode capacitor structure in which a plurality of capacitor elements are connected in series.The electric field may also be applied in a direction perpendicular to the stacking direction. The inner electrodes may contact the outer electrodes on two sides of the stack perpendicular to the stacking direction. In this way, a multilayer ceramic capacitor (MLCC) can be formed.In one embodiment, the ceramic thin film comprises a ceramic material that is a perovskite ceramic having the general structure ABO 3.In one embodiment, the ceramic thin film comprises a ceramic material having a ceramic composition Ba(Zr x Ti 1-x) O 3, wherein preferably 0.05≤x≤0.6 is satisfied.In one embodiment, the ceramic thin film layer may be made of the ceramic material.In addition, the ceramic material may contain dopants to alter the properties of the ceramic.In one embodiment, the ceramic material comprises y wt % of a rare earth metal dopant, in particular yttrium, wherein preferably 0.2≤y≤2 is fulfilled. The ratio y refers to 100 wt % of Ba(Zr x Ti 1-x) O 3.In one embodiment, the ceramic material comprises z wt % of a transition metal dopant, in particular manganese, wherein preferably 0.11≤z≤1 is fulfilled. The ratio z refers to 100 wt % of Ba(Zr x Ti 1-x) O 3.The ceramic material has favorable electrical and mechanical properties, especially when used in a thin film. In addition, the material is environmentally compatible since it is lead-free.In alternative embodiments, a lead-containing ceramic material is selected such as (Pb x Zr 1-x) TiO 3 with preferred x values between 0.4 and 0.6 (0.4 ≤ x ≤ 0.6), or Pb(MnNb 1-x) O 3+ PbTiO 3 with preferred x values between 0.2 and 0.4 (0.2 ≤ x ≤ 0.4), which also have favorable electrical and mechanical properties when used in a thin film.In one embodiment, the thin film device is configured as a circular plate.A round shape has advantages in production, handling and use, for example in terms of mechanical stability.In one embodiment, the thin film device is configured as a three-dimensionally folded film.The folded film can be adapted in a flexible manner to the shape of various application objects.In particular, the film can be elastic and can be folded into various shapes and subsequently be folded back into its original shape.In particular, the film may have several cuts or recesses according to the Japanese Kirigami technique in order to achieve the desired flexible properties for the folding.In one embodiment, the ceramic thin film has a thickness between 0.3 μm and 5 μm, preferably between 0.3 μm and 1.5 μm.Since these dimensions are sufficient to achieve the desired mechanical properties, the consumption of ceramic material can be reduced. The thin film layer preferably has homogeneous mechanical and electrical properties.In the present invention, the above-described thin film device may be used as a dielectric electrode structure or a capacitor structure or a multilayer capacitor structure as described in detail above.The invention further relates to a dielectric electrode structure, a capacitor structure, a multilayer capacitor structure, in particular a multilayer electrode capacitor structure or a multilayer ceramic capacitor structure (MLCC), which comprises the thin-film device described in detail above.Further, the invention relates to a medical device for medical, diagnostic or therapeutic treatment, e.g. electrical cancer treatment, comprising the thin film device or in particular the dielectric electrode structure.The invention further relates to a method for producing a substrate for the deposition of a thin film, which comprises a plurality of steps.The substrate and the ceramic thin film may be configured as described above. In particular, the above-described substrate and the ceramic thin film can be produced by the following method.In a first step, a titanium foil is provided as a base layer.In a further step, the base layer is thermally treated to form an intermediate layer directly adjoining the base layer. The intermediate layer comprises titanium oxide or consists of titanium oxide.By forming the titanium oxide layer directly on the base layer, formation of a natural misch metal oxidation layer is prevented.According to the invention, during the thermal treatment, the base layer is heated in a first step to a first holding temperature, preferably between 550° C. and 620° C., and in a second step to a second holding temperature, preferably between 640° C. and 700° C.By the above-described stepwise thermal processing, a dense base layer having no open porosity can be produced.By the thermal treatment described, the intermediate layer having the desired properties is formed.The invention further relates to a method of manufacturing a thin film device comprising the substrate for the deposition of a thin film. The method may comprise the aforementioned steps. Further, the method may include a plurality of additional steps.In one step, a ceramic material for a ceramic thin film layer is provided in a viscous state. The ceramic material in the viscous state may be a viscous paste containing organic substances and / or solvents.In a further step, the ceramic material is arranged in the viscous state on a surface of the intermediate layer facing away from the base layer in order to form a ceramic thin-film layer.After deposition, the deposited ceramic thin film layer is dried, preferably on a hot plate. Preferably, the drying of the ceramic thin film is carried out at a temperature between 150° C. and 250° C. In this step, residual solvents can be removed.After drying, the dried ceramic thin film layer is calcined or pyrolyzed. Preferably, the calcination of the thin film is carried out in two steps at temperatures between 300°C and 600°C, preferably in an oven. A first calcination step may be performed between 300° C. and 400° C. A second calcination step may be carried out between 500°C and 600°C. In this step, residual organic substances can be removed.In a further step, the calcined ceramic thin-film layer is crystallized, preferably in a furnace. The crystallization of the thin film is preferably carried out at a temperature between 600° C. and 700° C.In one embodiment, the ceramic material is deposited by slot die coating (slot coating).By coating with slot nozzles, the ceramic thin film layer can be deposited to a desired thickness and structure.Alternative methods for the deposition of the thin film layer are spin coating or dip coating, spray pyrolysis and inkjet printing. Alternatively, the thin film layer may also be deposited by physical methods such as sputtering, physical vapor deposition (PLD), or aerosol deposition. In this case, a solid ceramic target and / or ceramic powder having the desired composition is used.In an embodiment, the ceramic material is deposited by stacking a plurality of sub-layers, each sub-layer having a thickness between 0.1 μm and 0.5 μm.Preferably, each sub-layer has a thickness between 0.2 μm and 0.3 μm. The required thickness of the sub-layers is achieved by the selection of a suitable viscous ceramic material, e.g. a suitable ceramic paste having a suitable composition. Preferably, the ceramic paste is made of an organic polymer material.By applying the sub-layers with the described thickness, the entire ceramic thin-film layer can be formed by applying only a few sub-layers, preferably one to five sub-layers.The entire process of deposition, drying, calcination / pyrolysis and crystallization can be carried out one to five times until the final thickness of the ceramic thin films is reached.By reducing the number of sub-layers, a homogeneous structure of the ceramic thin-film layer can be achieved. The susceptibility to defects or damage during production is reduced.In one embodiment, the provision of the ceramic material in the viscous state comprises a plurality of steps. Preferably, the steps comprise a method of depositing a chemical solution.In one step, a first solution is prepared by dissolving a barium salt, e.g., barium acetate. The barium salt can be dissolved in glacial acetic acid, water and ethanolamine.Optionally, an yttrium salt, e.g. yttrium acetate, and a manganese salt, e.g. manganese acetate, may be dissolved in the first solution to obtain a doped ceramic material.In a further step, a second solution is prepared by dissolving an organic polymer in a suitable solvent, e.g. ethanol and acetic acid. The organic polymer may be polyvinylpyrrolidone (PVP).In a further step, titanium tetraethoxide and zirconium propoxide are dissolved in the second solution. At the same time, the solution can be stirred.Then, the first and second solutions are mixed and preferably stirred to form a sol-gel.In a preferred embodiment, the first solution is prepared by dissolving a stoichiometric amount of barium acetate and optionally yttrium acetate and manganese acetate in 5 to 15 moles of glacial acetic acid and 2 to 8 moles of water and ethanolamine. Further, 0.1 to 0.8 mol of polyvinyl pyrrolidone is dissolved in 3 to 10 mol of ethanol and 15 to 30 mol of acetic acid to prepare the second solution. Titanium tetraethoxide and zirconium propoxide are added stoichiometrically to the second solution with stirring. Then, the first solution is added to the second solution. The two solutions are mixed with one another while stirring.Preferably, the resulting solution forms a ceramic paste having a viscosity between 10 and 100 cP (1 cP=10 -3 kg / ms).In one embodiment, the geometric shape of the thin film device is shaped by cutting, e.g., by mechanical cutting or laser cutting, or by punching.In one embodiment, the thin film device is three-dimensionally formed by cutting or punching and folding the thin film device. In particular, the thin film device can be formed three-dimensionally by the Kirigami technique, a combination of cutting and origami folding. Cut or punched out portions can make the thin film device more flexible. The thin film device can be adapted to the external shape of various items on which the device is mounted.The application of the Kirigami technique makes it possible to convert flat device structures into three-dimensional structures when a force is applied and return to the original flat structure when the force is removed without deforming the device.Kirigami cutters are superior to other thin film ceramic devices because they can adapt to moving or expanding elements and optimize contact with these elements, particularly for larger contact areas. Exemplary elements are movable machine elements or a human or animal body.Differently shaped motifs can be cut or punched into the devices.The invention is explained in more detail below with reference to the attached drawings. The drawings show: FIG. 1 shows a first embodiment of a thin film device in a cross-sectional view. FIG. 2 is a SEM (scanning electron microscopy) image of a cross section of the first embodiment of the thin film device. FIG. 3 shows a second embodiment of a thin film device in a cross-sectional view. FIG. 4 shows a third embodiment of a thin film device in a cross-sectional view. FIG. 5 shows a fourth embodiment of a thin film device in a cross-sectional view. FIG. 6 shows a process diagram with the most important production steps. Fig. 7 shows a possible circular shape of the finished thin film device. Fig. 8 shows a possible three-dimensional folded shape of the finished thin film device. FIG. 9 shows two SEM images. On the right, the cross section of the first embodiment of the thin film device is seen. On the left is depicted a cross section through a differently fabricated thin film device for comparison. Fig. 10 shows the electric power dissipation vs. electric frequency dependence for the two thin film devices shown in Fig. 9. Fig. 11 shows the dependence of the capacitance density and the electric power loss on the electric frequency for the first embodiment of the thin film device. Fig. 12 shows the dependence of capacitance and electric power loss on temperature for the first embodiment of the thin film device. A temperature range around the body temperature (37° C.) was chosen. FIG. 13 shows the dependence of capacitance and electrical power dissipation on temperature for differently manufactured ceramic devices shown on the left for comparison in FIG. 9. Here too, a temperature range around the body temperature (37° C.) is selected. Fig. 14 shows the dielectric breakdown strength of the first embodiment of the thin film device. The dependence of the electric current on the electric field is measured. The breakdown point is about 33 kV / mm.Similar or apparently identical elements in the figures are denoted by the same reference numerals. The figures and the proportions in the figures are not scalable.FIG. 1 shows an embodiment of the thin film device 1. the thin film device 1 comprises a substrate 2 comprising the base layer 3 and an intermediate layer 4 and a ceramic thin film layer 5.The layers mentioned are arranged in a stack and form a multilayer device 1.The base layer 3 is made of titanium metal. Preferably, the layer 3 is made of titanium (Ti).The base layer 3 may be made of a Ti film. The thickness of the Ti film may be between 5 μm and 1000 μm, preferably between 5 μm and 100 μm.The intermediate layer 4 is arranged directly on a surface of the base layer 3. No further layer or structure is arranged between the base layer 3 and the intermediate layer 4.The intermediate layer 4 comprises titanium oxide TiO 2 or preferably consists of titanium oxide. The titanium oxide preferably has a rutile structure.The thickness of the intermediate layer may be between 0.1 μm and 2 μm, preferably between 0.8 μm and 1 μm.The substrate 2 can function as an electrode for contact with the ceramic thin film. Alternatively, in another embodiment, a separate electrode layer may be provided configured as a lower electrode between the substrate 2 and the ceramic thin film layer 5 or as an upper electrode, the ceramic thin film layer 5 being interposed between the substrate and the upper electrode.On the surface of the intermediate layer 4 opposite to the contact surface with the base layer 3, the ceramic thin film layer 5 is deposited.The ceramic thin film may have a thickness between 0.3 μm and 5 μm, preferably between 1.5 μm and 5 μm.In the embodiment shown, the ceramic thin-film layer 5 directly adjoins the intermediate layer 4. no further layers or structures are arranged therebetween.The ceramic thin film 5 can comprise or consist of a ceramic material with the composition Ba(Zr x Ti 1-x) O 3 wherein preferably 0.05≤x≤0.6 is fulfilled.Table 1 shows the results of an EDX (energy-dispersive X-ray spectroscopy) measurement of the composition of the base layer, the intermediate layer and the ceramic thin film of an exemplary ceramic thin film device. The ratios of the various elements are given in atomic %. Table 1: Table 1:Ceramic Thin Film6714218Intermediate layer: intermediate layer6535--Base layer-100--Furthermore, the ceramic material preferably contains dopants in order to change the properties of the ceramic.In particular, the ceramic material comprises, for example, y wt % of a rare earth metal dopant, in particular yttrium, wherein 0.2≤y≤2 is satisfied. The ratio y refers to 100 wt % of Ba(Zr x Ti 1-x) O 3. Furthermore, the ceramic materials contain, for example, wt % of a transition metal dopant, in particular manganese, wherein 0.11≤z≤1 is satisfied. The ratio z refers to 100 wt % of Ba(Zr x Ti 1-x) O 3.FIG. 2 is an SEM image of a cross section through the thin film device 1 according to the first embodiment. The base layer 3, the intermediate layer 4 and the ceramic thin-film layer 5 are shown. The surface of the base layer 3 shown has an advantageously low surface roughness Ra of less than 0.3 μm.FIG. 3 shows a further embodiment of the device 1.Unlike the first embodiment, the second embodiment of the device 1 comprises some additional layers.Between the intermediate layer 4 and the thin-film layer 5, a metallic inner electrode layer 6 for electrical contact is arranged.On the opposite surface of the thin film layer 5, a second electrode 7 is deposited.The second embodiment of the thin film device 1 can be used as an electric capacitor, while the first embodiment can be used as a dielectric electrode structure for applying an electric field to a selected object, in particular to a human body, e.g. for medical, diagnostic or therapeutic applications.Because of its electrical properties, the thin film device 1 can be used generally at body temperature.FIG. 4 shows a device 1 in the form of a multilayer electrode capacitor. The capacitor device 1 is constructed by stacking a plurality of ceramic thin film layers 5 and electrode layers 7. In this manner, a series of individual capacitor elements are formed.FIG. 5 shows a device 1 in the form of a ceramic multilayer capacitor (MLCC). The capacitor device 1 comprises a plurality of ceramic thin film layers 5 and electrode layers 7, the electrode layers being contacted alternately by two different external electrodes on opposite side surfaces of the device 1.In FIG. 6, selected steps of the manufacturing process of the first embodiment of the thin film device 1 are summarized graphically.A first solution is prepared by dissolving, for example, barium acetate, yttrium acetate and manganese acetate in glacial acetic acid, water and ethanolamine. In a second solution, polyvinylpyrrolidone is dissolved in ethanol and acetic acid. Titanium tetraethoxide and zirconium propoxide are added to the second solution with stirring. The first and second solutions are mixed to form a sol-gel.In step S 1, which is depicted graphically, the titanium foil is provided for the substrate 2 and is thermally treated in an oven in an air atmosphere by heating it in a first step to a temperature between 550° C. and 620° C. and in a second step to a temperature between 640° C. and 700° C. By the above-described thermal treatment method, the intermediate layer 4 is formed on the surface of the titanium base layer 3.In step S 2, the prepared sol gel is applied to the substrate 2 by spin coating, dip coating or slot die coating, for example, to a thickness of up to 0.05 mm. In step S 3, the thin film 5 is then dried, for example, on a heating plate at a temperature between 150° C. and 250° C. Subsequently, in step S 4, the ceramic thin film is pyrolyzed twice by heating the device 1 in a furnace under an air atmosphere at temperatures between 300° C. and 400° C. and subsequently at 500° C. and 600° C.In addition, the ceramic thin film 5 is crystallized in an oven between 600° C. and 700° C. under an air atmosphere.The process of deposition, drying, calcination / pyrolysis and crystallization is performed three to five times until the final thickness of the ceramic thin film 5 is reached in step S 5.Subsequently, a preferred geometric shape can be punched or cut out of the provided layer structure in order to obtain a desired shape of the device 1.FIG. 7 shows an exemplary circular stamped shape of a finished thin film device having a through hole in the center.The circular element may have a diameter between 10 mm and 25 mm and may have a concentric through bore with a diameter between 3 mm and 4 mm.Generally, the ceramic thin film 5 may cover an entire surface of the substrate 2 or only a certain area. For example, a portion of the substrate near the edge of the substrate may remain uncovered, as shown, for example, in Figure 7.FIG. 8 shows a further embodiment of the device 1, alternatively to FIG. 7, The device 1 is produced using the Kirigami technique.The illustration in FIG. 8 is only an example of a Kirigami pattern. By cutting or punching different motifs into the provided multilayer structure, further different patterns can be produced.Fig. 9 again shows, on the right side, the SEM image of a cross section through the first embodiment of the thin film device 1 according to the present invention. Further, Fig. 9 shows, for comparison, on the left side, an SEM image of another thin film device prepared by a method other than the above-described method.The device on the left, which does not form part of the invention, consists of a stainless steel substrate 8 on which an undesirable mixed metal oxide layer 9 is formed. No smooth surfaces are provided between the individual layers. An intermediate layer 10 between the metal oxide layer and a ceramic thin film 11 is made of lanthanum nickelate (lanthanum nickel oxide, LNO). The ceramic thin film is composed of a barium zirconium titanate ceramic and undesirable metal impurities formed by inter-diffusion between the metal and metal oxide layers and the ceramic thin film.The contaminants significantly impair the mechanical and in particular the electrical properties of the ceramic thin-film layer 5.Table 2 shows the results of EDX measurement of the composition of the base layer, the intermediate layer and the ceramic thin film of the non-inventive device. The above-described impurities due to inter-diffusion effects can be seen. The ratios of the various elements are given in atomic %. Table 2: Table 2:Ceramisc her thin film64.7-11.8-1.12-1.919.31.1Intermediate layer49.30.31.42.43.821.40.42.618.3The metal oxide layer is a layer of metal oxide41.91.6-27.414.14.6--6.4Base layer-1.6-17.173.86.1---FIG. 10 shows the losses of electrical power at different applied electrical frequencies in comparison between the first embodiment of the device 1 according to the invention (solid line) and the embodiment of a thin-film device not according to the invention (dashed line).The electrical losses are indicated as tan (delta). The frequency is given in hertz (Hz). The measurements were carried out at room temperature.It can clearly be seen in FIG. 10 that in the embodiment according to the invention the electrical losses are lower and are less dependent on the frequency. In particular, as the frequency rises, the losses can be significantly reduced.Fig. 11 shows the capacitance density in nF / cm 2( solid line) and again the electrical losses (dotted line) for the same embodiment of the thin film device 1 according to the invention.The measurements were carried out again at room temperature.FIG. 12 shows the dependence of the electrical capacitance and the electrical losses on temperature for the first embodiment of the thin film device 1 according to the invention. Thus, the thin film device 1 is suitable for body temperature applications, e.g., human body.In particular, the thin film device 1 can be used as a dielectric electrode structure for applying an electric field to the human body for cancer treatment by tumor-treating electric fields.For comparison, FIG. 13 shows the dependence of the electrical capacitance and the electrical losses on the temperature for the embodiment of the device which is not according to the invention. In a temperature range between 19.5° C. and 42° C., both values experience a large variation.As a result, the device 1 according to the invention has a lower temperature dependence of the electrical capacitance and of the electrical losses.Moreover, the thin film device has high dielectric breakdown strength.Fig. 14 shows the dielectric breakdown strength of the first embodiment of the thin film device. The dependence of the electric current on the electric field is measured. The breakdown point is about 33 kV / mm.Reference numerals denote reference numerals1 Thin film device 2 Substrate 3 Base layer 4 Intermediate layer 5 Ceramic thin film layer 6,7 Electrode layers 8 Stainless steel substrate 9 Mixed metal oxide layer 10 LNO layer 11 Ceramic thin film layer with impurities

Claims

Substrate (2) comprising a base layer (3) comprising titanium and an intermediate layer (4) comprising titanium oxide, wherein the intermediate layer can be produced by a two-stage thermal treatment of the base layer (3), wherein during the thermal treatment the base layer (3) is heated in a first step to a first holding temperature and in a second step to a second holding temperature which is higher than the first holding temperature.The substrate (2) according to claim 1, wherein the titanium oxide is titanium dioxide TiO 2.Substrate (2) according to claim 1 or 2, wherein the intermediate layer (4) is adapted for the deposition of a ceramic thin film (5).Substrate (2) according to any one of claims 1 to 3, wherein the intermediate layer (4) and the base layer (3) are directly adjacent to each other.The substrate (2) according to any one of claims 1 to 4, wherein the substrate (2) is composed of the base layer (3) and the intermediate layer (4).The substrate (2) according to any one of claims 1 to 5, wherein the base layer (3) has a thickness between 5 μm and 1000 μm.The substrate (2) according to any one of claims 1 to 6, wherein the base layer (3) has a surface roughness Ra of less than 0.3 μm.The substrate (2) according to any one of claims 1 to 7, wherein the intermediate layer has a thickness higher than the thickness of a natural oxidation layer on the base layer.Substrate (2) according to any one of claims 1 to 8, wherein the intermediate layer (4) has a thickness comprised between 0.1 μm and 2 μm.Substrate (2) according to claim 9, wherein the intermediate layer (4) has a thickness between 0.8 μm and 1 μm.The substrate (2) according to any one of claims 1 to 10, wherein the base layer (3) is made of titanium and the intermediate layer (4) is made of titanium oxide.Substrate (2) according to any one of claims 1 to 11, wherein the intermediate layer (4) has self-healing oxidation properties.Substrate (2) according to any one of claims 6 to 12, wherein the base layer (3) has a thickness between 5 μm and 100 μm.The substrate of any one of claims 1 to 13, wherein the intermediate layer has a suitable structure, density and thickness to prevent atomic or ionic inter-diffusion between the base layer and the thin film.The substrate (2) according to any one of claims 1 to 14, wherein the substrate comprises a separate electrode layer and / or additional structure layers and / or protective layers.The substrate (2) according to the preceding claim, wherein the separate electrode layer consists of a conductive metal or a metal oxide, wherein the electrode layer has a maximum thickness of up to 1 μm.The substrate (2) according to the preceding claim, wherein the conductive metal is gold, chromium, silver, platinum, copper, titanium or a combination thereof.The substrate (2) according to claim 16, wherein the metal oxide is lanthanum nickel oxide, indium tin oxide or aluminum zinc oxide.Substrate (2) according to claim 15, wherein the separate electrode layer consists of a stack of several metal layers lying one above the other, preferably a chromium-nickel-silver stack or a chromium-nickel-gold stack.The substrate (2) according to any one of claims 15 to 19, wherein the separate electrode layer is deposited by chemical solution deposition, sputtering, lithography, screen printing or ink jet printing.A thin film device (1) comprising the substrate (2) according to any one of claims 1 to 20 and the ceramic thin film layer (5) disposed on the intermediate layer.The thin film device (1) according to claim 21, wherein the intermediate layer (4) and the ceramic thin film layer (5) are directly adjacent to each other.The thin film device (1) according to claim 21 or 22, wherein the thin film device (1) comprises further functional layers or structural layers between the intermediate layer and the ceramic thin film layer (5).The thin film device (1) according to any one of claims 21 to 23, wherein the thin film device (1) is composed of the substrate (2) and the ceramic thin film layer (5).The thin film device (1) according to any one of claims 21 to 23, wherein the thin film device (1) comprises exactly one inner electrode layer (6, 7) or a plurality of inner electrode layers (6, 7).The thin film device (1) according to claim 25, wherein the thin film device (1) comprises a plurality of ceramic thin film layers (5).The thin film device (1) according to claim 26, wherein the ceramic thin film layers and the inner electrode layers (6, 7) form a stack, each individual ceramic thin film layer (5) being respectively arranged between two inner (6, 7) electrode layers.The thin film device (1) according to any one of claims 25 to 27, wherein the thin film device (1) comprises an upper electrode to which no further ceramic thin film layer is applied, the upper electrode completing the thin film device on a side opposite to the side completed by the substrate.The thin film device of any of claims 21 to 28, wherein the ceramic thin film comprises a ceramic material that is a perovskite ceramic having the general structure ABO 3.The thin film device (1) according to claim 29, wherein the ceramic thin film layer (5) comprises a ceramic material having a composition of Ba(Zr x Ti 1-x) O 3 where 0.05 ≤ x ≤ 0.6 is satisfied, or comprises a ceramic material (Pb x Zr 1-x) TiO 3 where 0.4 ≤ x ≤ 0.6 is satisfied, or comprises a ceramic material Pb(Mn x Nb 1-x) O 3+ PbTiO 3 where 0.2 ≤ x ≤ 0.4 is satisfied.Thin film device (1) according to claim 30, wherein the ceramic materials further comprise y wt.% of a rare earth metal dopant, in particular yttrium, and z wt.% of a transition metal dopant, in particular manganese, wherein 0.2 ≤ y ≤ 2 and 0.1 ≤ z ≤ 1 are fulfilled.The thin film device (1) according to any one of claims 21 to 31, wherein the thin film device (1) is formed as a circular plate.The thin film device (1) according to any one of claims 21 to 31, wherein the thin film device (1) is formed as a three-dimensionally folded sheet.The thin film device (1) according to any one of claims 21 to 33, wherein the ceramic thin film layer (5) has a thickness between 0.3 μm and 5 μm, preferably between 0.3 μm and 1.5 μm.A dielectric electrode structure comprising a thin film device (1) according to any one of claims 21 to 34.A capacitor structure comprising a thin film device (1) according to any one of claims 21 to 34.A multilayer ceramic capacitor structure comprising a thin film device (1) according to any one of claims 21 to 34.A medical device for medical, diagnostic or therapeutic treatment comprising a thin film device (1) according to any one of claims 21 to 34 or a dielectric electrode structure according to claim 35.Method for producing a substrate (2) for the deposition of a ceramic thin film (5), comprising the following steps: - providing a titanium foil for forming a base layer (3), - thermally treating the base layer (3) to form an intermediate layer (4) comprising titanium oxide directly adjoining the base layer (3), wherein during the thermal treatment the base layer (3) is heated in a first step to a first holding temperature and in a second step to a second holding temperature which is higher than the first holding temperature.The method according to claim 39, wherein during the thermal treatment of the base layer (3), the first holding temperature is between 550°C and 620°C and the second holding temperature is between 640°C and 700°C.A method for manufacturing a thin film device (1) comprising the steps of manufacturing the substrate (2) according to any one of claims 39 to 40 and further comprising the steps of: - providing a ceramic material for a ceramic thin film layer (5) in a viscous state, - depositing the ceramic material in the viscous state on a surface of the intermediate layer (4) facing away from the base layer (3) to form a ceramic thin film layer (5), - drying the deposited ceramic thin film layer (5), - calcining the dried ceramic thin film layer (5), - crystallizing the calcined ceramic thin film layer (5).The method of claim 41, wherein providing the ceramic material in the viscous state comprises the steps of: - dissolving a barium salt in a first solution, - dissolving an organic polymer in a second solution, - dissolving titanium tetraethoxide and zirconium propoxide in the second solution, - mixing the first and second solutions to form a sol-gel.The method of claim 42 wherein the organic polymer of the second solution is polyvinylpyrrolidone.A method according to any one of claims 41 to 43, wherein the deposition of the ceramic material is by slot die coating.Method according to claim 44, wherein the ceramic material is deposited by stacking a plurality of sub-layers, each sub-layer having a thickness between 0.1 μm and 0.5 μm, preferably between 0.2 μm and 0.3 μm.The method according to any one of claims 41 to 45, wherein the drying of the ceramic thin film layer (5) is performed at a temperature between 150°C and 250°C, the calcining of the thin film layer (5) is performed in two steps at temperatures between 300°C and 600°C, and the crystallizing of the thin film layer (5) is performed at a temperature between 600°C and 700°C.The method according to any one of claims 41 to 46, wherein a geometric shape of the thin film device (1) is formed by cutting or punching.Method according to any of claims 41 to 47, wherein the thin film device (1) is three-dimensionally shaped by cutting and folding the thin film device, in particular by using the Kirigami technique.

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