Electromechanical actuator with ceramic insulation and method for its manufacture

Description

[0001] The present invention relates to an electromechanical actuator according to the preamble of claim 1, comprising a stacked arrangement of ceramic base material with electromechanical properties and electrodes, as well as ceramic insulation for use of the actuator in humid environments. Such an actuator is also referred to as a multilayer actuator or linear actuator. A further aspect of the invention relates to a method for manufacturing an actuator with ceramic insulation.

[0002] The service life of electromechanical actuators is limited, among other things, by the degradation mechanism via humidity when used in static or quasi-static applications. In particular, the diffusion or penetration of water vapor molecules into the stacked assembly causes a partial or total loss of function of the actuator, as this leads to a deterioration of its electrical and elastic behavior. An increased service life can be achieved by insulating the actuator, especially with or made of a ceramic material. Such an electromechanical or piezoelectric actuator with ceramic insulation is known from DE 100 21 919 C2. Compared to actuators with polymer insulation, ceramic-insulated actuators can exhibit a mean time to failure (MTTF) that is two to three orders of magnitude higher when driven with direct current (DC).

[0003] EP 2 530 756 A1 also discloses a piezoelectric actuator which is provided with an inorganic layer, for example of lead zirconate titanate (PZT), on its side surfaces. US 7,065,846 B2 also discloses a piezoceramic actuator with ceramic insulation.

[0004] However, such ceramic insulation has physical limitations. Currently, ceramic-coated actuators typically exhibit an electrically induced piezoelectric strain of approximately 1.0‰ to 1.1‰ of the actuator's active length when driven with an electric field strength of 2 kV DC / mm. Increasing the electrically induced piezoelectric strain to, for example, > 1.25‰ of the active length, as is possible, for instance, through optimization of the electromechanical material system lead zirconate titanate (PZT), leads to the uncontrolled formation and growth of cracks in the ceramic insulation, which adversely affects the actuator's service life. Due to the design of linear actuators, the electrodes do not extend into the insulation, as the electrodes must be protected from moisture. Consequently, the ceramic insulation may be compromised.Only electrical stray fields excite the ceramic insulation, resulting in a lower, or even no, piezoelectrically induced strain. Consequently, mechanical tensile stress arises during actuator activation or strain, which, under continuous or alternating load, can lead to cracking and may result in actuator failure or loss of function, or reduce its service life in humid environments. JP 2006-303349 A discloses a multilayer actuator made of piezoelectric ceramic and internal electrodes with ceramic insulation applied to opposite side surfaces in the form of strips on alternately exposed ends of the internal electrodes. The ceramic insulation may have a smaller average grain size and a different material composition than the ceramic base material.

[0005] WO 2017 / 032868 A1 discloses a piezoelectric multilayer actuator with a protective layer on the actuator surface produced by airflow deposition (see p. 4, lines 14-16) consisting of fractured ceramic particles bonded together, for example, by annealing (see p. 4, line 28 - p. 5, line 2). This protective layer is said to be very dense and pore-free and to contain no "grain boundaries" such as those formed by sintering processes, so that the protective layer allegedly remains crack-free even at low thicknesses during actuator operation (see p. 5, lines 5-10). DE 102011 081279 A1 discloses a similar piezoelectric multilayer actuator with a ceramic insulating layer extending over the entire stack height on approximately three sides, produced by aerosol deposition of, for example, PZT. The insulation is made of the same material as the piezoceramic layers.

[0006] EP 2 667 425 B1 discloses a piezoelectric element with an inorganic coating in which metal particles are dispersed. Due to the metal particles, there is a risk of conductive paths forming in the coating, particularly at defects, which can accelerate failure mechanisms. JP 2015-142027 A describes stacked actuators made of a piezoceramic base material with ceramic insulation on at least two opposite faces, where the ceramic insulation has a smaller average grain size than the piezoceramic base material. Here too, the insulation and base material are identical (e.g., PZT), but the insulation does not extend to the end faces of the stack.

[0007] The present invention is based on the objective of providing an electromechanical actuator that has an extended service life even when the electromechanical strain increases, by preventing the formation of cracks in a sintered ceramic insulation.

[0008] The object of the invention is achieved by the electromechanical actuator according to claim 1 and a method for manufacturing an electromechanical actuator according to claim 9. Advantageous further developments of the invention are claimed in the dependent claims.

[0009] The electromechanical actuator according to the invention comprises a stacked arrangement of a ceramic base material with electromechanical properties and electrodes, as well as ceramic insulation for use of the actuator in humid environments, wherein the microstructure of the ceramic insulation has a smaller average grain size than the microstructure of the ceramic base material. By specifically selecting a ceramic insulation with a smaller average grain size than the microstructure of the ceramic base material, the strength (yield strength, see Hall-Petch relationship) of the ceramic insulation and its resistance to cracking are increased.By increasing this resistance, an extended actuator lifespan can be achieved even at higher electromechanical strains. This is made possible by the larger average grain size in the microstructure of the ceramic base material, as the usable electrically induced strain of the material increases with increasing grain size. Preferably, the ceramic base material is a piezoceramic base material. The electromechanical properties of the actuator are preferably modified or adjusted after shaping the ceramic base material, e.g., by polarization.

[0010] It can be advantageous if the ratio of the mean grain size of the insulation to the ceramic base material is 3 / 4 or less, preferably 1 / 2 or less, and particularly preferably 1 / 3 or less. The smaller the mean grain size of the insulation, the higher its strength and resistance to crack growth. The aforementioned ratios yield advantageous results, taking into account the mechanical interactions between the base material and the insulation.

[0011] Furthermore, it may be advantageous if the mean particle size of the insulation is 20 µm or less, preferably 5 µm or less, particularly preferably 1 µm or less.

[0012] Furthermore, it can prove advantageous if the mean grain size of the ceramic base material decreases towards the insulation, preferably across the insulation, and preferably continuously. A continuous decrease in the mean grain size in the area where the insulation borders the ceramic base material can prevent a sudden increase in strain or stress in this area.

[0013] It can prove useful if the insulation consists of an electromechanical, preferably piezoelectric and especially preferably piezoceramic material.

[0014] Furthermore, it can be advantageous if the insulation is impermeable to water vapor / moisture. This prevents water vapor molecules from diffusing or penetrating the stacked arrangement.

[0015] It can be advantageous if the insulation consists of at least one layer, preferably two or three layers, with a total insulation thickness of 500 µm or less, preferably 100 µm or less, and particularly preferably 60 µm or less. By providing multiple layers, manufacturing defects, such as holes or pores, in a single layer can be covered by the subsequent layers, thus improving the insulation. The probability of defects passing through the entire thickness of the insulation is therefore reduced by each additional layer.

[0016] According to the invention, the insulation has a different material composition than the ceramic base material.

[0017] Furthermore, it can be advantageous to provide two external electrodes for contacting the electrodes in the stacked arrangement. These electrodes can be located on the same outer surface or on two different outer surfaces of the actuator, with at least one electrode-free outer surface of the actuator featuring ceramic insulation. By attaching the external electrodes and providing ceramic insulation to the electrode-free outer surfaces, the actuator can be reliably insulated.

[0018] According to the invention, the ceramic base material and the electrodes are arranged along a stacking axis, the stacking arrangement having two end faces oriented perpendicular to the stacking axis and at least one side surface extending between the end faces, and the ceramic insulation extending from one end face to the other on the at least one side surface. The provision of ceramic insulation on these side surfaces prevents the diffusion or penetration of water vapor molecules between the electrodes and the ceramic base material.

[0019] Another aspect of the invention relates to a method for manufacturing an electromechanical actuator, in particular an actuator according to one of the preceding embodiments, comprising the steps of: A: Forming a stack arrangement of electrodes and of ceramic base material with electromechanical properties along a stack axis, such that the stack arrangement has two end faces oriented perpendicular to the stack axis and at least one side surface extending between the end faces; B: Providing the stack arrangement with ceramic insulation, such that this extends on the at least one side surface from one end face to the other end face, the microstructure of the insulation has a smaller mean grain size than the microstructure of the ceramic base material, and the insulation has a different material composition than the ceramic base material.

[0020] Furthermore, it can be useful if the procedure includes at least one of the following sub-steps: A1: Forming the stack arrangement from the electrodes and from green foils made of the ceramic base material, A2: Sintering the stack arrangement so that the ceramic base material is transformed into a solid ceramic structure.

[0021] However, it can also be advantageous if the procedure includes at least one of the following sub-steps: B1: Applying at least one, several or all layers of the insulation to the stacked arrangement by coating, preferably with a green film, injection molding, plasma spraying, dip coating, preferably in ceramic slurry, spraying and / or using the sol-gel process; B2: Sintering the ceramic insulation and optionally the ceramic base material, such that the ceramic insulation and optionally the ceramic base material is / are transformed into a solid ceramic structure; B3: Adjusting the mean grain size of the insulation and optionally the mean grain size of the ceramic base material by selecting different materials for the ceramic base material and the ceramic insulation and / or by selecting the process parameters during sintering.

[0022] Furthermore, it can be advantageous if the method includes the following step: C: Polarizing the ceramic base material, and preferably the ceramic insulation, to adjust the electromechanical properties of the actuator. As mentioned above, providing ceramic insulation on these side surfaces prevents water vapor molecules from diffusing or penetrating between the electrodes and the ceramic base material.

[0023] A method for controlling an electromechanical actuator, in particular an actuator according to one of the preceding embodiments, with an electric field strength of at least 2 kV DC / mm, at room temperature and preferably at at least 80%, preferably at least 85%, preferably at least 90% and particularly preferably at least 92% relative humidity, is also disclosed, such that a quasi-static strain of 1.25‰ or more of the active length of the actuator and a mean time to failure (MTTF) of the actuator of 10,000 hours or more is achieved.

[0024] Additionally, a method for controlling an electromechanical actuator, in particular an actuator according to one of the preceding embodiments, with an electric field strength of at least 2 kV DC / mm, at 90 °C and preferably at at least 80%, preferably at least 85%, preferably at least 90% and particularly preferably at least 92% relative humidity is disclosed, such that a quasi-static strain of 1.25 ‰ or more of the active length of the actuator and a mean time to failure (MTTF) of the actuator of 500 hours or more is achieved. Terms and definitions Green foil made of ceramic material

[0025] Green film made of ceramic material refers to a flexible film which is produced from ceramic slip through a film casting process. insulation

[0026] Insulation refers to a protective layer that prevents moisture from penetrating the stack actuator. actuator

[0027] The term actuator is used synonymously for a stack actuator, multi-layer actuator, multi-layer actuator or linear actuator. Ceramic base material with electromechanical properties

[0028] A ceramic base material with electromechanical properties is defined as a material that, when an electrical voltage is applied, produces a mechanical (elastic) deformation. This material can start from a ceramic powder, which is sintered to achieve its shape. The sintered ceramic is a polycrystalline material in its microstructure, whose crystallites exhibit domains with dipoles whose orientation is statistically distributed throughout the material. To adjust the electromechanical properties of the actuator, the dipoles are aligned, preferably by polarization. polarization

[0029] For the production of most electromechanical actuators, the material is polarized after sintering by applying an external DC field; that is, the dipoles are aligned in the same direction. This polarization allows for the adjustment of the desired electromechanical properties of the actuator. Brief description of the characters

[0030] Figure 1 shows a top view of the actuator according to the invention as well as sections along lines AA and BB. Detailed description of preferred embodiments

[0031] Figure 1Figure 1 shows an electromechanical actuator consisting of a rod-shaped stacked arrangement 1 made of a ceramic base material with electromechanical properties and electrodes 2, which are alternately positioned on opposite sides of the actuator. An outer electrode 3 is applied to each of these two sides for contacting the electrodes 2. The outer electrodes 3 are each connected to a conductor 4. The sides of the actuator not covered by the outer electrodes are provided with ceramic insulation 5.

[0032] The basic structure of this stacking arrangement is known from DE 100 21 919 C2 and will not be explained in detail here. Instead, the focus will be primarily on the differences according to the invention compared to the known stacking arrangement, which are explained below.

[0033] According to the invention, the microstructure of the ceramic insulation 5 has a smaller average grain size than the microstructure of the ceramic base material. Due to the small average grain size, the microstructure of the ceramic insulation 5 exhibits a small pore size or porosity, which reduces the defect size in the microstructure and counteracts the formation or growth of cracks.

[0034] According to the invention, the ceramic base material and the electrodes are arranged along a stacking axis, wherein the stacking arrangement of ceramic base material and electrodes has two end faces oriented perpendicular to the stacking axis and at least one side surface extending between the end faces, and the ceramic insulation extends from one end face to the other end face on the at least one side surface. Without the ceramic insulation, the electrodes would be exposed at the circumferential side surfaces. The provision of the ceramic insulation on these side surfaces therefore prevents the diffusion or penetration of water vapor molecules between the electrodes and the ceramic base material.

[0035] In a preferred embodiment, the ratio of the mean particle size of the insulation to the ceramic base material is 3 / 4 or less, preferably 1 / 2 or less, and particularly preferably 1 / 3 or less. The mean particle size of the insulation can be 20 µm or less, preferably 5 µm or less, and particularly preferably 1 µm or less.

[0036] The ceramic base material is preferably a piezoceramic material, such as lead zirconate titanate (PZT). However, it can also be an electrostrictive or magnetostrictive material. The ceramic insulation 5 consists of a different material than the ceramic base material, in particular an oxide ceramic, and preferably also exhibits piezoelectric properties.

[0037] The ceramic insulation 5 can consist of a single layer. In a preferred embodiment, however, the ceramic insulation 5 has several layers, in particular two or three, in order to cover manufacturing defects in a single layer with another layer. This prevents crack growth at the interface between two insulation layers. Consequently, the ceramic insulation 5 can be reliably made impermeable to the penetration or diffusion of water vapor molecules into the stacked arrangement. The individual layers can differ from one another in their composition or in their mean grain size. The thickness of an individual layer is a multiple, preferably five to twenty times, of the mean grain size in that layer.In general, a thin overall thickness of the ceramic insulation is desirable, as the elongation of the ceramic base material is less restricted by a thinner insulation. In a preferred embodiment, the overall thickness of the insulation is 500 µm or less, preferably 100 µm or less, and particularly preferably 60 µm or less.

[0038] The following describes a method according to the invention for manufacturing an actuator, preferably an actuator according to the above embodiments.

[0039] The production of a stacking arrangement made of ceramic base material with electromechanical properties and electrodes is basically known from DE 100 21 919 C2, but is briefly outlined again to improve the understanding of the method according to the invention.

[0040] The starting point for the production of the stacking arrangement 1 is a ceramic powder material, preferably a PZT powder material, which is mixed with a binder solution and a solvent. In the further course of the process, the ceramic slurry consisting of the powder material and binder solution is cast into so-called green films made of ceramic base material, and the solvent evaporates. The flexible green films are then cut to size and stacked, with an electrode 2 being inserted between each pair of a predefined number of green films. For this purpose, a metal paste is screen-printed onto the corresponding green film. The stacking arrangement 1 thus produced is then isostatically pressed.

[0041] The method according to the invention provides for providing such a stacking arrangement 1 with a ceramic insulation 5 such that the microstructure of the ceramic insulation 5 has a smaller average grain size than the microstructure of the ceramic base material. In a preferred embodiment, one or more green films with a different material composition or with different material properties than the green films of the ceramic base material are applied to at least one side surface of the stacking arrangement 1. Subsequently, the stacking arrangement 1 and the ceramic insulation 5 are sintered together, whereby the green films of the ceramic base material and the ceramic insulation 5 are transformed into a solid ceramic microstructure.By selectively adjusting the composition and / or properties of the starting materials of the ceramic base material and the ceramic insulation 5, a smaller average grain size can be achieved in the solid microstructure of the ceramic insulation 5 than in the microstructure of the ceramic base material. After sintering, external electrodes 3 are applied to the side surfaces of the actuator. These surfaces are designed for electrical contact with the electrodes 2 in the stack arrangement 1 and do not have any ceramic insulation 5. After the external electrodes are applied, a constant electric field is applied to generate polarization of the ceramic base material, and preferably the ceramic insulation 5. The process described above is a single-stage process, since the stack arrangement 1 and the ceramic insulation 5 are sintered together.Alternatively, a two-stage process can be carried out in which the stack arrangement 1 is first sintered, then one or more layers of the ceramic insulation 5 are applied to the sintered stack arrangement 1, and finally the stack arrangement with the ceramic insulation 5 is sintered again. The adjustment of the different average grain sizes in the microstructure of the ceramic insulation 5 and the ceramic base material can be achieved in particular by the targeted selection of the process parameters in the individual sintering stages.

[0042] According to the embodiments described above, the adjustment of the mean grain sizes in the corresponding microstructures in the single-stage process is achieved essentially by the different compositions or properties of the starting materials of the ceramic base material and the ceramic insulation 5, whereas in the two-stage process it is achieved essentially by the selection of the process parameters in the individual sintering processes. However, the process according to the invention is not limited to such a single- or multi-stage process.

[0043] In addition, the desired average grain size in the corresponding microstructures can also be achieved in a single-stage process by appropriately selecting the process parameters. In microwave sintering, which is described in more detail below, an uneven heat distribution occurs in the stacked arrangement. Due to the energy radiated from the surface of the stacked arrangement, lower temperatures are present in the outer regions of the insulation, resulting in greater grain growth in the center than in the insulation.

[0044] Uneven temperature distribution within the stack during the sintering process can also be achieved by applying a suitable electrical voltage to the actuators. This is because the resulting current flow causes heating, and due to energy radiation at the surface of the stack, the surface temperature is lower than its core. The electric field generated within the stack by the voltage can also have a positive influence on grain growth and grain size distribution within the stack and the insulation.

[0045] Furthermore, grain growth can also be influenced by an external electric field, without a conductive contact to the actuators, in the sense mentioned above (gradual change in grain size in ceramic insulation).

[0046] Furthermore, in the two-stage process, different material compositions or material properties can be used in addition to different process parameters in the individual sintering processes.

[0047] The following are some examples of how to achieve different compositions or properties of the starting materials, which can contribute to the adjustment of different average grain sizes in the corresponding microstructures.

[0048] Firstly, it is recommended to use a ceramic base material whose average grain size is sufficiently large during typical sintering to achieve strains > 1.1‰. For the ceramic insulation 5, this material can be doped with a grain growth inhibitor to inhibit grain growth in the microstructure of the ceramic insulation 5 compared to grain growth in the microstructure of the ceramic base material during a subsequent sintering process.

[0049] On the other hand, a starting material can be used for the ceramic insulation 5 whose average grain size is sufficiently small during typical sintering to meet the strength requirements of the insulation. This material can be doped with a grain growth accelerator to accelerate grain growth in the microstructure of the ceramic base material compared to grain growth in the microstructure of the ceramic insulation 5 during a subsequent sintering process.

[0050] Furthermore, the starting materials of the ceramic base material and the ceramic insulation 5 can differ in their initial grain size. This means that a particularly finely ground powder can be used for the ceramic insulation 5 compared to the ceramic base material, which also leads to a smaller average grain size in the microstructure of the ceramic insulation 5 after sintering.

[0051] In addition, particularly in the case of PZT materials, it is possible to select different starting materials for the ceramic base material and the ceramic insulation 5, as these differ in their affinity for lead. If a starting material with a higher affinity for lead is chosen for the ceramic base material than the starting material for the ceramic insulation 5, the ceramic base material will extract some of the lead contained in the ceramic insulation. This extraction slows down the grain growth dynamics in the ceramic insulation 5.

[0052] To adjust the desired difference in mean grain sizes in the corresponding microstructures, the above-mentioned possibilities for realizing different material compositions or material properties can be applied alone or in combination.

[0053] For the respective sintering processes, the temperature or temperature profile over time, the holding time, electric fields in the environment and the ambient atmosphere, in particular the oxygen content and atmospheric pressure, essentially describe the adjustable process parameters, which alone or in combination can contribute to realizing different average grain sizes in the corresponding microstructures.

[0054] Furthermore, the difference in mean grain size in the respective microstructures can also be achieved through the use of microwave sintering. Due to the dipole structure of piezoceramics, heat during microwave sintering is generated within the volume of the component. Since heat is transferred from the surface of the component to the colder environment, i.e., the atmosphere and walls of the sintering system, the sintering temperature of the surface, and thus of the ceramic insulation 5, is lower than the core temperature of the ceramic base material. As a consequence of this temperature difference, grain growth in the ceramic insulation 5 proceeds more slowly.

[0055] The present process is not limited to the layer application of the ceramic insulation 5 in the form of a green film. In addition, the starting material for the ceramic insulation 5 can be applied by injection molding, plasma spraying, dip coating in ceramic slurry, spraying, or using the sol-gel process. With the exception of plasma spraying, all of the aforementioned layer application methods can be used for both a one-stage and a two-stage sintering process, as described above. Plasma-sprayed layers do not require re-sintering; they can already exhibit their desired properties after layer application. However, subsequent heat treatment can be advantageous.

[0056] Each of the above-mentioned layer deposition methods can be combined with the previously mentioned possibilities of different material compositions or material properties and process parameters during sintering. Furthermore, one or more layers of ceramic insulation 5 can be realized with all of the mentioned methods.

[0057] By selecting different material compositions or material properties in each layer of the ceramic insulation 5, or by sintering each of these layers individually, a grain size gradient can be established across the ceramic insulation 5. Furthermore, interaction, particularly diffusion, also results in a grain size gradient at the layer boundaries of layers with different material compositions or material properties. Such a grain size gradient helps to avoid abrupt changes in strain or stress.

[0058] Inventively polarized actuators were subjected to a static lifetime test at constant voltage (DC). Simultaneously, actuators with ceramic insulation were tested according to the prior art. The drive voltage was selected such that the actuators exhibited an active region strain of 1.47‰. Based on the failure times of the actuators in each test group, the mean time to failure (MTTF) of the actuators was determined. The determined values ​​and the test conditions are shown in Table 1.

[0059] The MTTF for polymer-coated actuators was calculated using the lifetime formula of the respective manufacturer.

[0060] The MTTF of the actuators according to the invention at 25°C and 30% relative humidity was determined by extrapolation based on a series of tests. Table 1 Actuator type Test conditions Average service life (MTTF) Polymer-coated multilayer actuators 1.47‰ elongation, 80°C, 80% relative humidity, DC 44 h Ceramic-insulated multilayer actuators with the same average grain size in the insulation as in the base material 1.47‰ elongation, 80°C, 80% relative humidity, DC 1360 h Ceramic-insulated multilayer actuators with a smaller average grain size in the insulation than in the base material (according to the invention) 1.47‰ elongation, 80°C, 80% relative humidity, DC 2460 h Ceramic-insulated multilayer actuators with a smaller average grain size in the insulation than in the base material (according to the invention) 1.47‰ elongation, 25°C, 30% relative humidity, DC > 500000 h Reference symbol list

[0061] 1 Stacking arrangement 2 Electrodes 3 External electrodes 4 Connecting conductors 5 Ceramic insulation

Claims

1. Electromechanical actuator comprising a stack arrangement (1) made of ceramic basis material having electromechanical properties and electrodes (2) that are arranged along a stack axis, as well as a ceramic insulation (5) for use of said actuator in a humid environment, said stack arrangement (1) comprises two end faces aligned perpendicular to said stack axis and at least one side surface extending between said end faces, where said ceramic insulation (5) on said at least one side surface extends from one end face to the other end face, wherein the structure of said ceramic insulation (5) has a smaller average grain size than the structure of said ceramic basis material and wherein said insulation (5) has a different material composition than said ceramic basis material.

2. Actuator according to claim 1, wherein the ratio of the average grain sizes of insulation (5) to ceramic basis material is 3 / 4 or less, preferably 1 / 2 or less, particularly preferably 1 / 3 or less.

3. Actuator according to one of the preceding claims, wherein the average grain size of said insulation is 20 µm or less, preferably 5 µm or less, particularly preferably 1 µm or less.

4. Actuator according to one of the preceding claims, wherein the average grain size of the ceramic basis material decreases preferably continuously towards said insulation (5), preferably beyond said insulation (5).

5. Actuator according to one of the preceding claims, wherein said insulation (5) is made of electromechanical, preferably piezoelectric, particularly preferably piezoceramic, material.

6. Actuator according to one of the preceding claims, wherein said insulation (5) is impermeable to water vapor / moisture.

7. Actuator according to one of the preceding claims, wherein said insulation (5) is made of at least one layer, preferably of two or three layers, where the total thickness of said insulation (5) is 500 µm or less, preferably 100 µm or less, particularly preferably 60 µm or less.

8. Actuator according to one of the preceding claims, wherein two exterior electrodes (3) are provided for contacting said electrodes (2) in said stack arrangement (1) and are arranged on the same outer surface or on two different outer surfaces of said actuator, where at least one electrode-free outer surface of said actuator comprises said ceramic insulation (5).

9. Method for the production of an electromechanical actuator, preferably said actuator according to one of the preceding claims, comprising the steps of: A: forming a stack arrangement (1) from electrodes (2) and from a ceramic basis material having electromechanical properties along a stack axis so that said stack arrangement comprises two end faces oriented perpendicular to said stack axis and at least one side surface extending between said end faces, B: providing said stack arrangement (1) with a ceramic insulation (5) such that the latter extends on said at least one side surface from one end face to the other end face, the structure of said insulation (5) has a smaller average grain size than the structure of said ceramic basis material and said insulation (5) has a different material composition than said ceramic basis material.

10. Method according to claim 9 comprising at least one of the following partial steps of: A1: forming said stack arrangement (1) from said electrodes (2) and from green tapes made of said ceramic basis material, A2: sintering said stack arrangement (1) so that said ceramic basis material is transformed into a solid ceramic structure.

11. Method according to claim 9 or 10 comprising at least one of the following partial steps of: B1: applying at least one, several, or all layers of said insulation (5) onto said stack arrangement (1) by coating, preferably with a green tape, injection molding, plasma spraying, immersion coating, preferably in ceramic slurry, spraying, and / or by way of a sol-gel method, B2: sintering said ceramic insulation (5) and possibly said ceramic basis material so that said ceramic insulation (5) and possibly said ceramic basis material is / are transformed into a solid ceramic structure, B3: setting the average grain size of said insulation (5) and possibly the average grain size of said ceramic basis material by selecting different materials for said ceramic basis material and said ceramic insulation (5) and / or by selecting the process parameters during sintering.

12. Method according to one of the claims 9 to 11 comprising the step of: C: polarizing said ceramic basis material and preferably said ceramic insulation (5) to set the electromechanical properties of said actuator.