EP1938417A1

EP1938417A1 - Thin film and composite element produced from the same

Info

Publication number: EP1938417A1
Application number: EP06804808A
Authority: EP
Inventors: Ludwig J. Gauckler; Daniel Beckel; Ulrich Muecke; Patrik MÜLLER; Jennifer Rupp
Original assignee: Eidgenoessische Technische Hochschule Zurich ETHZ
Current assignee: Eidgenoessische Technische Hochschule Zurich ETHZ
Priority date: 2005-10-19
Filing date: 2006-10-16
Publication date: 2008-07-02
Also published as: WO2007045111A1; US20090029195A1; CN101326669A; JP2009512166A; KR20080080083A

Abstract

The invention relates to a thin film (10) consisting of at least two layers (S1, S2, S3 ) of a ceramic material, a ceramic and metallic material, or in the case of several layers (S1, S2, S3 ) a metallic material. All layers (S1, S2, S3 ) of the thin film (10) have a maximum average particle size (K) of approximately 500 nm and at least two layers consist of different material. In at least one of said layers, an essentially stable average particle size (K) remains after a relaxation time (t), even in an increased temperature range (T). The mechanical stability is preferably reinforced by a supporting, essentially flat substrate (12). In the composite element (13), the thickness (ds) of the substrate (12) is at least five times and in particular between ten and a hundred times the thickness dD of the thin film (10). The composite element (13) can be successfully used in a miniaturised electrochemical device, in particular in a solid oxide fuel cell SOFC (18), a sensor (36) or as a gas separation membrane (17).

Description

Thin film and composite element produced therewith

Technical area

The invention relates to a thin film of at least two layers of a ceramic, ceramic and metallic or metallic material in several layers and a composite element with the substrate supporting it. Furthermore, the invention relates to uses of the composite element with the thin film. State of the art

Thin films, in particular electrically conductive, of ceramic and / or metallic materials are currently gaining in importance. The thin films usually consist of several layers, in particular three to five, wherein the material and / or the morphology of the individual layers are usually different. The thin film is typically deposited in layers on the substrate using conventional thin film techniques, for example, chemical vapor deposition, pulsed laser evaporation, sol-gel, especially spin coating, or spray pyrolysis. Further, the thin film may be applied to the substrate as a whole or in layers as such. After or during application, the layers or thin film as a whole are annealed in a single or multi-stage process to obtain a partially or fully crystalline microstructure. Multilayer thin films are also called laminates.

The US 6896989 B2 also describes applied to a substrate, consisting of several layers of thin films, which can be used as electrodes and solid electrolyte in fuel cells. Between these functional layers, further layers, also of the material of the electrodes, are arranged. Optionally, additional can

Layers of different materials are added. The individual layers of the

According to this patent specification, thin films are known per se using methods known per se, such as RF (radio frequency) sputtering, PVD (physical vapor deposition), CVD

(chemical vapor deposition) and electrophoresis.

Presentation of the invention

The present invention has for its object to increase the resistance of thin films of the type mentioned above, in particular connected to a substrate, against aging, so that produced with the thin films miniaturized electrochemical devices suffer for a long time no, or only a small, loss of performance , The object is achieved with respect to the thin films according to the invention that the thin film in all layers has an average grain size of at most about 500 nm wherein at least two layers of different material, and in at least one of these layers after a relaxation time in an elevated temperature range in the substantially stable average grain size is maintained. Specific and further developing embodiments of the thin film are the subject of dependent claims.

A major advantage of these thin films is that the grains of at least one layer only show a time-limited grain growth, they no longer grow after reaching an averaged grain size dependent on the material and the production method. The relaxation time is usually between 5 and 20 hours, especially about 10 hours. A substantially stable average particle size can be maintained at temperatures of preferably up to about 1 100 ^0C. This advantageous property results from an unusually high proportion of amorphous material in the thin film before the annealing process, which greatly inhibits grain growth by building up microscopic stress between the amorphous matrix and the relatively small grains. Most materials show, if the average grain size is not in the range according to the invention, for very long times an unlimited grain growth at a constant and elevated temperature and thus an increased aging / degradation.

In the present case, an approximately stable average particle size is understood to mean that the deviation after the expansion time is at most about ± 10%, preferably at most about ± 5%. With an average particle size of, for example, 500 nm, the subsequent grain growth is expediently in the range of at most approximately 25 nm, in particular of at most approximately 10 nm.

In practice, the individual layers of the thin film have a thickness of 5 to 10,000 nm, preferably 10 to 1000 nm, with an average grain size K of at most about 200 nm, preferably from 5 to 100 nm. Based on the layer thickness of a single layer of Thin film, the average grain size K is preferably at most about 50%, in particular at most about 20%. Here and below, an amorphous or partially amorphous layer structure is not specifically mentioned, it is assigned analogously to the fine-grained thin films. According to a particularly advantageous embodiment of the invention, the thin film always has at least two layers which are ionic or ionic and electronically conductive, in particular for O ^{2 "} ions At least one of these layers is always predominantly ionic, if necessary even slightly electronically conductive.

The electrical conductivity is usually in the range of 0.02 to 10 ⁵ S / m (Siemens / meter). An electrical conductivity may be required for the application, for example in electrochemically active electrodes and electrolytes, which are used as miniaturized sensors or fuel cells.

The thin films may consist of different, lamellar, inherently homogeneous layers with layerwise continuously slightly modified chemical composition,

Morphology and / or porosity, with a gradient with respect to the chemical

Composition, morphology and / or porosity is produced. If z. For example, when one or more layers of the thin film are porous, the porosity occurs in a range of> 0 to

70% by volume. From layer to layer, the porosity can vary with continuous increase or decrease to form a porosity gradient.

The most commonly used thin film in practice comprises an anode, a solid state electrolyte, and a cathode layer, with all layers being electrically conductive. These layers may comprise further intermediate layers or layers formed as cover layers as required.

The layers of the thin film consist of at least one ceramic or at least one metal, but also of a mixture of at least one ceramic and at least one metal, the latter composition is also called cermet. A thin film can not be purely metallic, at least one layer must be predominantly ionic. The individual layers (including the ceramic-containing layers) of the thin film may be amorphous, biphasic amorphous-crystalline or completely crystalline.

Sufficient mechanical stability is imparted to the thin film, since according to a further embodiment of the invention, the thickness of a substrate supporting it corresponds to at least about five times, preferably at least about ten times the total layer thickness of the thin film. The layer thickness of the substrate can also reach 100 times the layer thickness of the substrate or more. That from one any suitable material existing substrate can be flexible, z. B. as a film, or rigid, z. B. as a plate may be formed. Both embodiments of the substrate may be dense, porous over the entire area or parts thereof, and / or have arbitrarily configurable holes or channels, which is referred to as a structured substrate. At least parts of the porous area and the holes or channels are covered with the thin film, which in this function is called a membrane. The channels also serve the fluid distribution, they can also be formed as the substrate only partially thorough grooves.

The holes or channels penetrating the substrate are expediently at least 100 μm ^{2 in} size and of any desired, but expedient geometric shape. At the top, the area of these holes or channels is limited by the mechanical stability of the thin-film membrane.

The individual layers of the thin film covering the openings in the substrate need not be of equal size with respect to the area. At least one layer of the thin film must cover at least one of the substrate openings. Each of the other layers of the thin film may completely or partially cover this first layer or protrude beyond the first layer. The layers of the membrane-acting thin film may be patterned by selective deposition or etching, by lift-off or masking techniques, or by any combination of these depositions, and in any form.

For miniaturized devices with electrochemically active electrodes and a solid electrolyte, a thin film with at least three of these fine-grained layers is applied one above the other as a membrane to a substrate. The working techniques are, as mentioned above, known per se.

According to a first material-related variant of the invention, one or more layers of the thin film of a metal or a metal oxide, for example of Cu, Co, Mn, Ag, Ru or NiO _x , FeO _x , MnO _x , CuO _x , CoO _x , MnO _x , AgO _x , RuO _x or mixtures of metals and / or metal oxides. Further, a ceramic component with ionic or mixed ionic and electronic conductivity, such as doped ceria A _x Ce _1-x 0 _2-δ , wherein A = Gd, Sm, Y, Ca, 0.05 <x <0.3, or doped zirconia ln _y Zr1- _y O _2-δ, wherein ln = Y, Sc, Yb, Er, 0:08 <y <12:12 is, the metal, metal oxide or the mixture of metal and metal oxide are added. The volume fraction of metal and ceramic component is between 20 and 80% by volume. The volume fraction of metallic phase of the solid part of the cermet is between> 0 and 70 vol .-%. The ratio of metal to ceramic can be uniformly distributed, as well as singly or multiply graduated over the film thickness, with a ratio between 0 (no metal in the layer) and 100% (pure metal layer) metal at each point of the thin film. The porosity of the thin film ranges from 0 to 50% in the oxidized state, all metal components are present as metal oxide, and 0 to 70% for the reduced state, all metal components are present as metal, with a homogeneous or non-homogeneous distribution in the thin film. The porosity may be present as a gradient of close to 70% porosity of the thin film. The average particle size K of the materials can be determined by thermal annealing at different temperatures, it has average particle sizes K of 5 to 500 nm. The ceramic phase of the layers of the thin film exhibit stable microstructures as a function of time under reducing conditions at temperatures up to 700 ° C on. If the metal content is above a certain limit volume from which wahmehm- the metallic line bar, the overall electrical conductivity between room temperature and 700 ⁰ C is greater than 10 S / m, the metal is in a reduced, thus metallic state. All of these materials may be coated, impregnated, or doped with the following metals, or may form composites with these metals, eg, Ag, Au, Cu, Pd, Pt, Rh, and Ru.

According to a second material-related variant of the invention, one or more of the layers of the thin film of doped ceria A _x Ce _1-x O _2- s, where A = Gd, Sm, Y, Ca, 0.05 <x <0.3, or of doped Zirconia Ln _y Zr _{1 -y} O _2-5 , where Ln = Y, Sc, Yb, Er, 0.08 <y <0.12, or La ₁ Sr _x Ga _1-y Mg _y O _{3 ± δ} with 0 <x <1 and 0 <y <1. The layers of this thin film are of dense nanostructure and have a film thickness between 10 and 5000 nm. A thin film with layers of average particle size K between 5 and 500 nm can be produced. This thin film has the following electrical properties:

a) Total electrical conductivity between 0.02 and 5 S / m at 500 ⁰ C and 0.25 and 10 S / m at 700 ° C, both measured in air. b) An activation energy of electrical conductivity in air between 0.5 and 1.5 eV within the temperature range 100 to 1000 ⁰ C.

c) The electrolytic domain boundary at 500 ⁰ C at oxygen partial pressures less than 10 ^"19 atm and at 700 ⁰ C at oxygen partial pressures less than 10 ^{~ M} atm.

According to a material-related third variant of the invention, one or more layers of the thin film consist of a perovskite of the type A _× AV _× B _y BV _y O ₃₁₅ , where A, A ', B and B' are one of the following elements: Al, Ba, Ca, Ce, Co, Cu, Dy, Fe, Gd, La, Mn, Nd, Pr, Sm, Sr, Y and 0 <x <1, 0 <y <1. According to a sub-variant, pyrochlorobuthenates of composition A ₂ Ru ₂ O ₇ ± _δ , where A = Bi, Y, Pb or A ₂ ^ A ' _α M0 _{4 ± δ} with (A = Pr, Sm; A' = Sr; M = Mn, Ni; 0 <α <1) or a material of the following composition: A ₂ NiO ₄₁₅ (A = Nd, La); A _x B _y NiO ₄₁₅ with A, B = Al, Ba, Ca, Ce, Co, Cu, Dy, Fe, Gd, La, Mn, Nd, Pr, Sm, Sr, Y and 0 <x <1.0 <y <1, or La ₄ Ni ₃ ^ Co _x O ₁₀₁₅ , or YBa (Co ₁ Fe) ₄ O ₇₁₅ or Baln _1-x Co _x 0 _3l5 or Bi ₂ _-x Y _x O ₃ (0 <x <1 ) or La ₂ Ni _1-x Cu _x 0 _{4 ± δ} (0 <x <1), or Y ₁ Ba ₂ Cu ₃ O ₇ . All of these materials can be coated, impregnated or doped with the following metals or composites formed with these metals: Ag, Au, Cu, Pd, Pt, Rh and Ru. Furthermore, the thin films of a mixture of these materials with doped ceria A _x Ce ₁ ^ O _2-5 , where A = Gd, Sm, Y, Ca, 0.05 <x <0.3 or doped zirconia UI _y Zr _Ly O _2-5 , where Ln = Y, Sc, Yb, Er, 0.08 <y <0.12 or La _1-x Sr _x Ga _1-y Mg _y 0 _{3l5 where} 0 <x <1 and 0 <y <1. The thin films have a layer thickness between 50 and 10,000 nm and an average grain size between 5 and 500 K nm. The total electrical conductivity at 550 ⁰ C is in the range 10 to 100,000 S / m in air. The thin films are stable in air and may be dense or porous with a porosity between> 0 to 70% by volume.

Finally, in addition to at least one ceramic or cermet layer, there may be one or more layers of the thin film of a metal or metal mixture, eg, Pt, Au, Ag, Ni and others, which may be sputtered, such as RF (radio frequency) or direct current Sputtering, vapor deposition or any other vacuum technique, electrochemical deposition or paste of metal oxide powder and any organic or non-organic component. From the following detailed description and the totality of the claims, further advantageous embodiments and feature combinations of the invention result.

Brief description of the drawings

The invention will be explained in more detail with reference to embodiments shown in the drawing, which are also the subject of dependent claims. The cross sections show schematically:

Fig. 1 shows a thin film with three layers

2 shows a composite element with a thin film according to FIG. 1

Fig. 3 shows a thin film of two layers as gas separation membrane

Fig. 4 shows a porous substrate with thin film

Fig. 5 is a dense substrate with a through hole or channel with thin film

6 a dense membrane with different hole shapes (top view)

7 shows a miniaturized fuel cell with a composite element

8 shows a variant of FIG. 7

9 shows another fuel cell (view from below)

10 shows a single-chamber fuel cell with electrodes of a thin-film membrane next to one another

Fig. 1 1 a single-chamber fuel cell with a porous solid electrolyte of the thin-film membrane FIG. 12 shows a fuel cell according to FIG. 7 with a protective layer on the substrate. FIG

13 shows a fuel cell according to FIG. 7 with a heating element

Fig. 14 shows a thin film with a gradient

15 shows a gas sensor with a thin-film membrane and

16 is a graph showing the average grain size growth.

Basically, the same parts are provided with the same reference numerals in the figures.

Ways to carry out the invention

1 shows a thin film 10 with a laminate structure comprising three layers, a first layer S ₁ , a second layer S ₂ and a third layer S ₃ . In the present case, the first layer S _{1 is} a cermet layer with a metal content of 40% and a ceramic content of 60%, it has the specification Ni-Ce ₀₈ Gd _0-2 O ₁₉ . The second layer S ₂ , which _conducts oxygen ions O ^{2 "} , has the specification Ce _0-8 Gd ₀₂ O _1-9 The third layer S _{3 here} has the specification La _0-6 Sr ₀₄ Co _0-2 Fe _0-8 O ₃ , where d _L is the thickness of a layer S ₁ , S ₂ , S ₃ .

FIG. 2 shows a thin film 10 according to FIG. 1 consisting of a laminate-like film composite, which is applied to a substrate 12 and forms a composite element 13, which serves as a functional element. This substrate 12 gives the thin film 10 the necessary mechanical strength. According to a preferred variant, the layers S ₁ , S ₂ and S _{3 are} deposited in series with a method known per se, wherein the surface area of the individual layers may also be different. A thin film 10 applied to a substrate 12 is also referred to as a thin film membrane. For reasons of clarity, the thickness of the substrate d _s here and in the rest is undersized, it amounts to a multiple of the layer thickness d _{D of} the thin film 10th In Fig. 3, a gas separation membrane 10 is shown, which consists only of two different, selectively gas-permeable layers S ₂ and S ₃ . A hole 14 or channel 15 that completely penetrates the substrate 12 exposes the underside of the thin-film membrane 10 and forms a window. The indicated with a straight arrow gas inlet 16, an air flow, is divided at the thin-film membrane 10. The oxygen can pass through the ion-conducting layers S ₂ and S ₃ and is separated from the deflected main flow of predominantly nitrogen N ₂ and carbon dioxide CO ₂ . The thin layer 10 of the layers S ₂ and S ₃ is therefore also referred to as gas separation membrane 17.

4 shows a porous substrate 12. A fraction of the gas inflow passing through a thin-film membrane 10 can flow off through the porous substrate 12 without holes 14 or channels 15 having to be provided ,

A fraction of a gas inflow impinging on a gas-tight substrate 12 according to FIG. 5 after passing through the thin film must be able to flow off, as shown in FIG. 3, for which reason at least one hole 14 or a corresponding channel 15 penetrating the substrate 12 must be provided.

Fig. 6 shows a selection of possible embodiments of holes 12 penetrating the substrate 12, which are circular, oval, polygonal or arbitrarily shaped. These holes 14 are always covered by a thin film 10, not shown. In the case of a multilayer thin-film membrane, the holes must be covered by at least one layer, and the remaining layers can only partially cover the hole, as indicated in the octagonal hole 14. The layer S ₂ , a solid electrolyte, covers the octagonal hole 14 completely, the layer S _3, for example, a cathodic layer, only partially.

7 and 8 show an essential field of application of the thin film 10 or composite element 13 according to the invention, a miniaturized solid oxide fuel cell (SOFC) 18, of which the essential functional elements are shown in two variants. 7 additionally shows the gas flows, namely the gas inflow 16 surrounding the cathodic third layer S ₃ and the anodic first Layer S ₁ flushing H ₂ and / or hydrocarbon-containing gas stream. The atmosphere is oxidizing or reducing according to the electrode. Fig. 8 also shows the electrochemical reaction sequence.

The thin-film membrane 10 with the electrochemically active layers of the miniaturized fuel cell 18 essentially comprises

an anode first layer S ₁ made of a cermet lying on a rigid substrate plate 12 with holes 14 or channels 15, a second layer S ₂ also forming the anode laterally, designed as a solid electrolyte, and a cathodic third layer resting on the solid electrolyte S ₃ .

The anodic layer S ₁ and the cathodic layer S ₃ are each connected to a metallic current conductor 20, 22 and carry the generated direct electrical current via a load 24. The electrodes S ₁ , S ₃ may contain catalytically active metal particles.

The electrode layers S ₁ and S ₃ are gas-permeable, the electrolyte layer S ₂ is gas-tight, but permeable to oxygen ions, which is indicated in Fig. 8. As already shown in FIG. 3, when gas 16, in the present case air, flows in, the nitrogen N ₂ and the carbon dioxide CO _{2 are} deflected, the oxygen ions O ^{2 "} pass through the solid electrolyte layer S ₂ to the anodic first layer S ₁ and react at the Oxidation interface with the hydrogen supplied as fuel to water, which is removed as exhaust gas.

As shown in FIG. 8, the electrons e ^' released during the oxidation of the oxygen ions O ^{2 are conducted} via a consumer 24 to the cathodic layer S ₃ , where the reaction is restarted and oxygen is reduced.

9 is a schematic diagram of the functional parts of a fuel cell SOFC 18 shown below. Through four holes 14 in a substrate 12, the anodic first layer S _{1 of} a thin-film membrane 10 applied to the substrate 12 is visible. Connected to this layer S ₁ is a metallic anodic current conductor 20, which is connected via a Consumer 24 and a metallic cathodic conductor 22 is electrically connected to the non-visible cathodic layer of the thin-film membrane.

FIG. 10 shows the functional principle of a miniaturized single-chamber fuel cell 18, in which the anodic first layer S ₁ and the cathodic third layer S _{3 are arranged} on the same side of the second layer S ₂ , a solid-state electrolyte. The thin film 10 is in turn applied to a substrate 12 to form a composite element and forms a composite element 13. The electrical current generated by the miniaturized fuel cell SOFC 18 during operation is conducted via the metallic current conductors 20, 22 to a load 44.

1 1 shows a further miniaturized fuel cell SOFC 18 with a second layer S ₂ formed as a porous solid-state electrolyte. This layer, together with the anodic first layer S ₁ and the cathodic layer S _{3, forms} the thin-film membrane 10, which is supported by a substrate 12 with a hole 14 or channel 15. As usual in a single-chamber SOFC, both the anodic layer S ₁ and the cathodic layer S _{3 are surrounded} by a mixture of air, fuel and exhaust gas, which is indicated by arrows 26. A hydrocarbon introduced as fuel in addition to or instead of H ₂ may be liquid or gaseous.

A miniaturized SOFC 18 shown in FIG. 12 essentially corresponds to that of FIG. 7. The only essential difference is that between the anodic layer S ₁ and the part of the solid-state electrolyte layer S ₂ enclosing this anode and the substrate 12 on the other hand, a protective layer 28 is arranged. In the present case, this consists of silicon nitride Si ₃ N ₄ .

Another variant according to FIG. 7 is shown in FIG. 13. Between a central web 34 of the substrate 12, which separates the two channels 15 for fluid distribution, and the anodic first layer S ₁ , a heating element 30 is arranged, which is fed by a DC power source 32. The heating element 30 may extend over other areas.

In FIG. 14, a thin film 10 having a total of 13 layers is formed, in addition to the layers S _b S ₂ and S ₃ designated in the preceding figures, the layers S ₄ to S ₁₃ . The porosity is constant within the individual layers S ₁ to S ₁₃ , the individual layers however, show a gradually decreasing porosity. As a result, a gradient is formed. Also parameters other than porosity may form a gradient, for example the chemical composition and / or the morphology.

FIG. 15 shows the structure principle of a sensor 36 with a thin film 10 on a substrate 12. The second layer S ₂ forming the solid electrolyte is connected over its entire area to the dense substrate 12. On the other side of the second layer S ₂ , two electrodes are arranged separately from one another, a noble metal electrode forming the first layer S ₁ , in the present case of platinum, and a metal oxide electrode forming the third layer S ₃ , in this case La _{0 6} Sr _0-4 CrO ₃ ,

The oxygen ion permeable solid electrolyte, the layer S ₂ , in the present case consists of 8% Y ₂ O ₃ doped ZrO ₂ . The resistance measured via current conductors 20, 22 is supplied to a measuring instrument 38 with a display panel.

The graph according to FIG. 16 shows the average mean particle size K of electrolyte layers in nanometers (nm), which is plotted against time t in hours (h) for different temperatures (T). The values are based on measurements of electrolyte layers of Ce Gd _{0 8} _{0 2} _{1 9} O which were prepared by spray pyrolysis and have layer thicknesses in the submicron range. Such layers are in a dense but partially amorphous state after deposition and are completely free of cracks. In a further process step, the layers are heated at a rate of 3 ° C / min to the temperatures (T) indicated in Fig. 16 between 600 and 1200 ⁰ C and isothermally annealed for 35 h at the corresponding temperature. Electrolyte layers of Ce _{0 8} Gd ₀₂ O _{1 9} , which are annealed, for example, at 600 ⁰ C, have at the time t = 0 h an average grain size of 10 ± 3 nm and an amorphous phase content of 31 ± 9 vol%. Within the first 12 ± 3 h, the grains grow to a stable particle size of 16 ± 3 nm, after which no further grain growth can be observed with progressing annealing.

The diagram (Fig. 16) can be seen further that, in general, at temperatures up to 1 100 ⁰ C at the latest after about 12 hours no measurable Komgrössenwachstum longer occurs. At a temperature of 1200 ⁰ C, however, the curve continues to increase after 15 hours. The oxide ceramic investigated here for the solid electrolyte layer is therefore no longer usable because of the grain growth above a temperature of 1 100 ⁰ C.

Claims

claims

1. thin film (10) of at least two layers (S ₁ , S ₂ , S ₃ ) of a ceramic, ceramic and metallic or in the case of several layers (S ₁ , S ₂ , S ₃ ) also metallic material,

characterized in that

the thin film (10) in all layers (S ₁ , S ₂ , S ₃ ) has an average grain size (K) of at most about 500 nm, wherein at least two layers consist of different material, and in at least one of these layers after a relaxation time ( t) a substantially stable average grain size (K) is maintained even in an elevated temperature range (T).

2. thin film (10) according to claim 1, characterized in that the individual layers (S ₁ , S ₂ , S ₃ ) a thickness (DJ from 5 to 10,000 nm, preferably from 10 to 1000 nm, an average grain size (K) of at most about 200 nm, preferably 5 to 100 nm, wherein the average grain size (K) is at most about 50%, in particular up to about 20%, of the respective layer thickness (d _L ).

3. thin film (10) according to claim 1 or 2, characterized in that it after a relaxation time (t) of 5 to 20 h, preferably about 10 h, and a temperature (T) to 1 100 ⁰ C, a substantially stable averaged Grain size (K) has.

4. Thin film (10) according to any one of claims 1 to 3, characterized in that the average Komgrössen (K) after the relaxation time (t) at a maximum

Deviation of about ± 10%, preferably about + 5%, are stable.

5. thin film (10) according to any one of claims 1 to 4, characterized in that at least one layer (S ₂ ) is ionic or ionic and electronically conductive, in particular for O ^{2 "} ions.

6. thin film (10) according to one of claims 1 to 5, characterized in that electrically conductive layers (S ₁ , S ₂ , S ₃ ) have a material and temperature-dependent conductivity of 0.02 to 10 ⁵ S / m.

7. Thin film (10 according to any one of claims 1 to 6, characterized in that the chemical composition, the morphology and / or the porosity of adjacent layers (S ₁ , S ₂ , S ₃ ), which are homogeneous within a single layer , continuously increasing or decreasing to form a corresponding gradient.

8. thin film (10) according to one of claims 1 to 7, characterized in that at least one layer (S ₁ , S ₂ , S ₃ ) has a porosity of> 0 to 70 vol .-%.

9. thin film (10) according to any one of claims 1 to 8, characterized in that it comprises an anodic (S ₁ ), a solid electrolyte (S ₂ ) and a cathodic layer (S ₃ ), wherein all layers are preferably electrically conductive ,

10. Thin film (10) according to one of claims 1 to 9, characterized in that at least one layer (S ₁ , S ₂ , S ₃ ) consists of at least one ceramic or of at least one ceramic and at least one metal.

1. A composite element (13) with a thin film (10) according to one of claims 1 to 10, characterized in that it comprises a thin film (10) supporting, substantially flat substrate (12), wherein the thickness (d _s ) of the supporting and connected to him substrate (12) at least about five times, preferably about ten to a hundred times the total layer thickness (d _D ) of the thin film (10).

12. composite element (13) according to claim 1 1, characterized in that the thin-film membrane (10) porous zones and / or at least one through hole (14) or spans a continuous channel (15) of the supporting substrate (12).

13. Composite element (13) according to claim 12, characterized in that the holes (14) or channels (15) in the supporting substrate (12) are at least 100 μm ² large and of any geometric shape.

14 composite element (13) according to any one of claims 1 1 to 13, characterized in that the supporting substrate (12) is designed as a flexible film or as a rigid plate.

15 composite element (13) according to any one of claims 1 1 to 14, characterized in that between the thin film (10) and the substrate (12) a protective layer (28) is arranged, preferably made of silicon nitride.

16, composite element (13) according to any one of claims 1 1 to 15, characterized in that at least on a part of the composite region between the thin film (10) and the substrate (12) a heating element (30) is arranged.

17. Use of a composite element (13) according to any one of claims 1 1 to 16 with a thin film according to one of claims 1 to 10 in a miniaturized electrochemical device, in particular a solid fuel cell SOFC (18), a sensor (36) or as a gas separation membrane (17).