Multilayer structure and methods for producing a multilayer structure

Abstract

This application provides a multilayer structure. This multilayer structure comprises a semiconductor or insulator substrate. The substrate has a main surface. An electrode containing a noble metal or a conductive oxide is arranged above this main surface. An electroceramic layer is arranged above the electrode. In the multilayer structure, an adhesion layer is arranged between the main surface of the substrate and the electrode.

Description

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

[0002] Multilayer or thin-film structures, in general, are used in many technical fields. These often feature electroceramic thin films. Such multilayer structures are used, for example, in high-energy capacitors, ferroelectric storage devices, piezoelectric actuators such as micromirrors or inkjet printheads, microfluidic pumps, and piezoelectric sensors such as pressure sensors, accelerometers, piezoelectric energy harvesters, or electrocaloric solid-state cooling devices, thermistors, or in applications where a material with a high dielectric constant is required. In such devices, the electroceramic thin film within the multilayer structure can form the functional unit.

[0003] According to current technology, such multilayer structures are typically formed on or over silicon wafer-based substrates. These wafers may contain an oxide layer.

[0004] The formation of PZT layers over silicon-based substrates is known, for example, from Schwartz et al. (CR Chimie 7, 433-461, 2004). Furthermore, the following documents address the formation of adhesion layers over silicon wafer-based substrates, which reduce the adhesion between an electrode and the silicon wafer-based substrate: Shelton et al., Adv. Funct. Mater. 22, 2295-2302, 2012 Maeder et al, Jpn. J. Appl. Phys. 37 (4A), 2007-2012, 1998 Halder et al., Appl. Phys. A 87, 705-708, 2007

[0005] However, these or similar approaches have the disadvantage that the adhesion of electrodes in functional multilayer devices with ceramic layers may still be insufficient. For example, delamination is likely in some cases under certain conditions.

[0006] Accordingly, one objective of the present invention is to provide an improved multilayer structure.

[0007] Accordingly, at least some of the disadvantages described above are at least partially overcome or compensated for by the subject matter of claim 1. Furthermore, further preferred embodiments or alternative embodiments are described in the dependent claims.

[0008] According to a first embodiment, a multilayer structure is provided. This multilayer structure comprises a semiconductor or insulator substrate. The substrate has a main surface. An electrode containing a noble metal or a conductive oxide is arranged above this main surface. An electroceramic layer, which imparts function to the multilayer structure, is arranged above the electrode. An adhesion layer is arranged between the main surface of the substrate and the electrode in the multilayer structure.

[0009] The adhesion layer can be in direct contact with both the main surface of the substrate and the electrode. The adhesion layer contains a transition metal or a transition metal oxide. The term "transition metal" also includes alloys of transition metals. The term "transition metal oxide" also includes mixed transition metal oxides.

[0010] Within the scope of this application, the term "transition metal" can be understood to mean anything generally understood by that term in the technical field. In particular, it can include at least any transition metal of periods 4, 5, and 6 of the periodic table. Preferably, the transition metal here and in the following may be titanium, tantalum, or tungsten, or alloys of these metals. Of these, tantalum has proven particularly advantageous in several cases. In particular, tantalum in combination with a platinum electrode, as described below, has proven to be especially preferred.

[0011] The inventors of the present invention have discovered that adhesion layers based on transition metals or transition metal oxides are able to ensure good adhesion between a semiconductor or insulator substrate and an electrode containing a precious metal or a conductive oxide.

[0012] Furthermore, the inventors have discovered that the use of such adhesive layers can reduce or even completely eliminate delamination. Thermal stability can also be improved. This can be important, for example, during the manufacturing process, as the adhesive layer can help prevent the electrode from dewetting from the substrate surface during the production of the electroceramic layer. Surprisingly, the quality of the electroceramic layer can also be improved.

[0013] Any type of substrate that exhibits semiconductor behavior can be understood as a semiconductor substrate. Likewise, any type of substrate that would be considered an electrical insulator in practice can be considered an insulator substrate.

[0014] According to one embodiment, a further electrode, which can be referred to as the upper electrode, can be arranged on or above the electroceramic layer. Similarly, the electroceramic layer can be arranged between the previously described electrode, which can be a lower electrode, and the upper electrode.

[0015] According to one embodiment, the substrate can be a silicon wafer-based substrate. A silicon wafer-based substrate is defined as any substrate that can be formed from or contains a silicon wafer. The silicon in the silicon wafer-based substrate can be in crystalline or amorphous form. It can also be doped or undoped. The silicon wafer-based substrate can consist of or be made from a single-crystal or polycrystalline silicon wafer. The silicon wafer-based substrate can consist of or be formed from a bare silicon wafer. The silicon wafer-based substrate can also have a portion consisting mainly of elemental silicon and a portion consisting of or containing silicon oxide. The term "silicon wafer-based substrate" also includes silicon-on-insulator (SOI) wafers. Such SOI wafers can have multiple layers.For example, they can have a so-called silicon handle layer and a silicon device layer, separated by an embedded silicon oxide layer.

[0016] According to one embodiment, the semiconductor or insulator substrate can be a sapphire substrate. "Sapphire substrate" is understood to mean what a person skilled in the art would normally understand by that term. A sapphire substrate can be an aluminum oxide-based material crystallized in a hexagonal crystal structure.

[0017] According to another embodiment, a semiconductor or insulator substrate can be a glass substrate. Here, any type of silicon oxide-based glass can be understood as a glass substrate.

[0018] The semiconductor or insulator substrates described above allow for the easy production of multilayer structures in industrially accessible high volumes. However, the adhesion of electrodes selected from precious metals or conductive oxides to such substrates can be poor. Therefore, an adhesion layer made of a transition metal or transition metal oxide can improve adhesion in these cases.

[0019] In particular, the inventors found that electrode materials often cannot be deposited on pure silicon because chemical exchange, such as diffusion, can occur and impair the properties of the substrate or the electrode. If the electrode material is deposited on an oxidized wafer, i.e., on silicon oxide, adhesion is often very poor and delamination is likely. The adhesion layer according to the invention can help to improve adhesion and reduce the diffusion of substances or atoms, as explained in more detail below.

[0020] According to one embodiment, the adhesion layer can comprise a first adhesion sublayer and a second adhesion sublayer. The stacking order of these sublayers is generally not limited.

[0021] According to one embodiment, the first adhesion sublayer comprises a transition metal and the second adhesion sublayer comprises a transition metal oxide. The inventors assume that the presence of both a transition metal and a transition metal oxide can not only improve adhesion or contribute to reducing delamination, but also reduce the diffusion or migration of chemical elements between the layers. Furthermore, the inventors assume that the thermal stability of the noble metal electrode can be improved. Accordingly, the electroceramic layer can be protected from elements that diffuse from the substrate into the electroceramic layer. Likewise, the reverse properties of the substrate, particularly in the case of a semiconductor substrate, remain largely unaffected, since no material diffuses from the electroceramic layer into the substrate.

[0022] In the embodiment described above, in which there is a first adhesion sublayer and a second adhesion sublayer, the transition metal of the first adhesion sublayer can be the same as or different from the transition metal that forms the transition metal oxide of the second adhesion sublayer, i.e., in this case, the transition metal of the transition metal oxide-based second adhesion sublayer can be a different transition metal than the one contained in the first adhesion sublayer.

[0023] Alternatively, according to one embodiment, both the first and second adhesion sublayers can be metallic. In this case, the transition metal of the first adhesion sublayer is different from that of the second adhesion sublayer.

[0024] Alternatively, and according to one embodiment, both the first adhesion sublayer and the second adhesion sublayer can comprise or consist of a transition metal oxide. In this case, the transition metal of the first adhesion sublayer is different from that of the second adhesion sublayer.

[0025] According to a further generalized embodiment, the adhesion layer can have n sublayers with n ≥ 2. Each of the sublayers contains a transition metal. The layer can either be metallic or contain the transition metal as a transition metal oxide. The features discussed above for a first and a second sublayer also apply to an adhesion layer with more than two sublayers.

[0026] According to one embodiment, the first adhesion sublayer, which contains the transition metal in metallic form, can be in direct contact with the substrate. The second adhesion sublayer, which contains the transition metal oxide, can be arranged above or on top of this. According to another embodiment, a reverse stacking arrangement can be implemented, in which the second adhesion sublayer, containing the transition metal oxide, is arranged directly on the substrate and the first adhesion sublayer, containing a transition metal, is arranged above it. Embodiments with a similar structure can also be formed that, instead of the first sublayer, have more than one metallic sublayer with different transition metals. Similarly, embodiments with a similar structure that, instead of the second sublayer, have more than one transition metal oxide-based sublayer with different transition metals can also be formed.

[0027] According to another embodiment, the first adhesion sublayer, containing the transition metal, is arranged directly on the substrate as described above. A second adhesion sublayer, containing the transition metal oxide, is arranged above this. Additionally, a third adhesion sublayer, again containing a transition metal, can be arranged above the second adhesion sublayer. This results in a three-layer structure in which the oxide-containing second adhesion sublayer is sandwiched between the first and third sublayers containing the transition metal. In some cases, a structure with these three adhesion sublayers can be particularly advantageous. The inventors found that the first and third adhesion sublayers may provide improved adhesion and / or improved thermal stability.The second adhesion sublayer, containing the oxide, can contribute to improved suppression of element diffusion between the layers. According to another embodiment, the reverse structure can also be formed, in which a transition-metal-based metallic adhesion sublayer is sandwiched between two transition-metal oxide-based adhesion sublayers. Here, too, embodiments with a similar structure can be formed that have more than one metallic sublayer with different transition metals instead of the first sublayer. Similarly, embodiments with a similar structure can be formed that have more than one transition-metal oxide-based sublayer with different transition metals instead of the second sublayer.It is also possible to form embodiments with a similar structure that have more than one metallic sublayer with different transition metals instead of the third sublayer.

[0028] According to one embodiment, the thickness of the adhesion layer can be between 1 and 100 nm. Preferably, it can be between 10 and 50 nm. Even more preferably, it can be between 15 and 100 nm, for example, between 15 and 50 nm or between 15 and 30 nm. The inventors of the present invention have found that if the adhesion layer is too thin, delamination is more likely and the diffusion-inhibiting properties may also be reduced. The adhesion and diffusion-inhibiting properties described above are particularly preferred for thicknesses above 10 nm. If sublayers are implemented, each sublayer can have a thickness of 1 to 50 nm or, preferably, 1 to 25 nm.

[0029] As described above, the electrode contains or consists of a precious metal or a conductive oxide. The term "precious metal" can be understood in its technical sense. Within the context of this application, the term precious metal also includes alloys of precious metals. At a minimum, ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold can be considered precious metals. Of these, iridium and platinum have proven particularly advantageous as electrodes. The combination with tantalum-containing adhesion layers has proven especially effective. The above statements regarding mass transfer on bare silicon surfaces and very poor adhesion to silicon oxide surfaces apply particularly to iridium and even more so to platinum as electrode materials. Therefore, an adhesion layer, and especially one containing tantalum, is preferred.

[0030] According to another embodiment, the electrode can have a conductive oxide. In principle, any conductive oxide can be used. It can be an oxide of a metal. Examples of preferred conductive oxides are iridium oxide, rhodium oxide, rhenium oxide, ruthenium oxide, lanthanum nickel oxide, or strontium ruthenium oxide. The chemical formulas for these oxides can be IrO₂, RhO₂, ReO₂, RuO₂, or SrRuO₃, but the elemental ratios are generally not limited to those given in the formulas. It has been found that the adhesion layer described above can provide particularly good adhesion to insulating or semiconductor substrates.

[0031] According to one embodiment, the electrode thickness can range from 50 nm to 500 nm. Particularly with more expensive precious metals, a smaller thickness may be preferred, such as between 100 nm and 300 nm or between 150 nm and 250 nm. Furthermore, excessively thick electrode layers tend to delaminate due to internal stresses.

[0032] In this application, an electroceramic layer can be understood in the general technical sense. It is preferred that the electroceramic imparts functionality to the multilayer structure. Such functionality can be: • High dielectric constant, which can be used, for example, in capacitors; • Pyroelectricity, which can be used, for example, in infrared sensors; • Ferroelectricity, which can be used, for example, in storage devices; • Piezoelectricity, which can be used, for example, in the devices described elsewhere in the application; • Temperature-dependent resistance; this can be provided by ceramic thermistor materials, such as positive temperature coefficient (PTC) or negative temperature coefficient (NTC) materials.

[0033] According to one embodiment, the electroceramic material in the multilayer structure can comprise or consist of a piezoelectric ceramic material. The inventors of the present invention have found that the structure described above, with a precious metal-based electrode or an electrode based on a conductive oxide, which adheres to a semiconductor- or insulator-based substrate by means of an adhesion layer, can be used to produce high-quality piezoelectric thin films in such multilayer structures.

[0034] The following piezoelectric ceramic materials have proven to be preferred: Pb [Zr x Ti 1-x ]O3 (abbreviated PZT) , (1-x) Pb[Mg 1 / 3 Note 2 / 3 O3] - x PbTiO3 (abbreviated PMN-PT), [K x N / a 1-x ]NbO3 (abbreviated KNN), (1-x) BiFeO3 - x BaTiO3 (abbreviated BFO-BT), Ba[Zr x Ti 1-x ]O3 (abbreviated BZT) (1-x) [Bi 1 / 2 N / a 1 / 2 ]TiO3 - x [Bi 1 / 2 K 1 / 2 ]TiO3 (abbreviated BNT-BKT), (1-x) BiFeO3 - x Ba[Ti y Zr 1-y ]O3 (abbreviated BFO-BZT), AlMgZrN, or [Al x Sc 1-x In all these examples, x and y are numbers between zero and one, i.e., 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1. The electroceramic materials mentioned above can be modified by doping. Doping is the deliberate addition of impurities to alter the electrical and / or piezoelectric properties of the electroceramic layer.

[0035] According to one embodiment, the electroceramic layer can have or consist of two or more electroceramic sublayers. The electroceramic sublayers can correspond to the sublayers or partial layers described in connection with the deposition process and can be the direct result of such deposition; however, the electroceramic sublayers are not limited to this. An electroceramic sublayer is structurally or chemically different from an adjacent sublayer. Thus, two sublayers can have different functionalities, for example, by containing different electroceramic materials. Preferably, however, two sublayers are based on or consist of the same electroceramic material but have a different structure or chemical composition.For example, both materials can be based on PZT but have different compositions. Components such as dopants or major ions like La, Pb, Zr, or Ti can have different concentrations in the two sublayers. The same applies to each of the materials described above.

[0036] According to one embodiment, the piezoelectric ceramic material can be in direct contact with the electrode.

[0037] According to an alternative embodiment, a support layer can be placed between the electrode and the electroceramic layer. The support layer can provide a supporting function. For example, it can consist of or contain a conductive material. It can thus facilitate charge transport or the application of voltage between the electrode and the electroceramic layer. Alternatively or additionally, it can provide a buffer function that can reduce the chemical exchange between the electrode and the electroceramic layer. The support layer can also have a function that supports crystal growth or oriented crystal growth of the electroceramic layer. In this case, the support layer can be referred to, in particular, as a nucleation layer located between the electroceramic layer and the electrode.Support layer materials in general, and nucleation layer materials in particular, can be selected from, for example, lead titanate (PbTiO3), lanthanum nickel oxide (LaNiO3), lead oxide (PbO) or titanium oxide (TiO2).

[0038] According to one embodiment, an electroceramic layer can comprise a ceramic material to realize one of the functionalities mentioned above. The inventors of the present invention initially observed the advantages of the inventive design using an adhesive layer for piezoelectric materials as described above. To their surprise, the inventors found that, in general, any electroceramic layer can benefit from such a design. In particular, the inventors found that thermistor materials also exhibit improved properties when the design described above, with an adhesive layer between a lower electrode and the underlying substrate, is used.

[0039] Accordingly, the electroceramic layer can, according to one embodiment, consist of or incorporate a thermistor material. Of the materials with temperature-dependent resistance, the following have proven particularly advantageous: Ni-Mn-Cu oxides, Ni-Mn-Co oxides, Co-Fe oxides, Cr-Co-Ba-Fe-Bi oxides, and barium titanate (BaTiO3). According to one embodiment, the thermistor materials can have a spinel-based or perovskite structure.

[0040] In general, the thickness of the electroceramic layer is not limited and can be selected according to the application. According to one embodiment, the electroceramic layer can have a thickness of 10 nm to 20 µm. Preferably, a lower range for the thickness can be 20 nm, 50 nm, or 100 nm. Preferably, an upper range for the thickness can be 10 µm, 5 µm, 2 µm, or 1 µm. For example, a thickness of 100 nm to 5 µm can be 1 µm to 3 µm or 1.7 to 2.5 µm. The aforementioned values ​​for the lower and upper ranges can each replace the lower and upper values ​​in all these examples.

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

[0042] The inventors have found that the quality of the electroceramic layer can be improved by the structure described above, in particular by an adhesion layer. Specifically, according to one embodiment, the electroceramic layer can have crystal grains in the size range of 10 to 1000 nm.

[0043] According to another embodiment, the adhesion layer can contribute to the formation of high-quality electroceramic layers, in particular with crystalline columns extending over the entire thickness of the electroceramic layer.

[0044] According to another embodiment, the electroceramic layer can have a granular structure. For example, grains ranging in size from 10 nm to 1 µm can be present. Such a granular structure can be achieved, for example, by electroceramic layers produced with barium titanate or Mn-Co-Ni oxide.

[0045] According to one embodiment, a multilayer structure is described which can have the arrangement described above. Furthermore, it can have a second electrode arranged on a second main surface of the substrate. The second main surface can be a surface opposite the first main surface described above. A second adhesion layer is arranged between the second main surface and the second electrode. The second adhesion layer can have the properties described above for the first adhesion layer. Accordingly, a symmetrical multilayer structure can be formed in its layering.

[0046] Preferably, the first and second adhesion layers can be made of the same material, as this can simplify manufacturing. However, the materials can also be different. Similarly, the electrodes on both sides can be made of the same material, which may be preferred due to simplified manufacturing. Again, the electrode materials can differ.

[0047] According to one embodiment, a second electroceramic layer can also be arranged above the second electrode in this case. The electroceramic layer can have the properties described above. It can be the same as, or different from, the first electroceramic layer.

[0048] The present invention is particularly suitable for the production of such symmetrical structures, as this can contribute to further increasing the yield. Even with rougher surfaces, several advantages can be achieved through simplified handling, which are described below.

[0049] According to another embodiment, which can be combined with any of the embodiments described above, the multilayer structure can include a further electrode arranged on the electroceramic layer. This electroceramic layer can be referred to here as the first electroceramic layer. The further electrode described here can be referred to as the first upper electrode.

[0050] According to a modification of the previous embodiment, a further electroceramic layer, which may be referred to or addressed here as the second electroceramic layer, can be arranged on or above the first upper electrode. The properties described above can apply to the further electrode and the further electroceramic layer. The material of the further electroceramic layer can be the same as that of the lower or first electroceramic layer. Depending on the application, however, it can also be different. Similarly, the electrode can also have the same material as the other electrode, but it can also be different. Another upper electrode can be arranged on the stack.Accordingly, a structure is provided comprising the substrate, the adhesion layer, the lower electrode, the first electroceramic layer, the first upper electrode, the second electroceramic layer, and the second upper electrode. Similarly, multiple layers of electrodes and electroceramic layers can be stacked on top of each other. Preferably, such stacks are capped by a top electrode.

[0051] According to one embodiment, the multilayer structure according to the present invention can be used in micromirrors. In this case, it is advantageous for the electroceramic layer to comprise a piezoelectric material. The deflection of the mirror can then be driven by the piezoelectric multilayer structures. Alternatively, the invention can be used in high-energy capacitors, ferroelectric storage devices, piezoelectric actuators such as micromirrors, microfluidic pumps, or inkjet printheads. It can be used in piezoelectric sensors such as pressure sensors or accelerometers. Furthermore, it can be used in piezoelectric energy harvesters or electrocaloric solid-state cooling devices. In principle, it can also be used in any other type of piezoelectric device.

[0052] According to one embodiment, the main surface of the substrate can be polished or even mirror-polished. A mirror-polished surface can have a surface roughness (R). a ) of less than 20 nm. A mirror-polished surface can increase the yield of functional devices fabricated with the multilayer substrate. These mirror-polished substrates are preferably silicon substrates with a mirror-polished surface.

[0053] However, the inventors found that mirror-polished surfaces are not always necessary due to the adhesion layer. The inventors discovered that substrates with a roughness (R) aSurface roughness of up to 2 µm can be used. The inventors have found that the use of an adhesive layer eliminates the need for time-consuming polishing. Preferably, the surface roughness is a maximum of 1 µm. Any roughness below 2 µm, and even more preferably below 1 µm, is technically feasible with the invention. Unpolished or only partially smoothed surfaces can have a surface roughness of over 10 nm, over 20 nm, or even over 50 nm or 100 nm. Accordingly, a surface roughness between 10 nm and 2 µm, such as 20 nm and 1 µm, is well suited to the invention. The other values ​​mentioned above can replace the upper or lower values. Even with rough surfaces, the inventors have found that the quality of the electroceramic film can be exceptionally high by using an adhesive layer. In general, polishing is a complicated and expensive process.Furthermore, impurities can be introduced that may impair the performance and yield of the components. Therefore, this aspect can help to overcome these problems.

[0054] According to a further embodiment, a method for producing a multilayer structure is described. The advantages described above apply accordingly to this method, insofar as they are applicable.

[0055] According to one embodiment of the method for forming a multilayer structure, an adhesion layer is first arranged on a major surface of a semiconductor-based or insulator-based substrate. The adhesion layer can be deposited on the substrate. Preferably, the adhesion layer is produced by physical deposition from the gas phase, e.g., by magnetron sputtering or evaporation. A lower electrode containing a noble metal or a conductive oxide is arranged on the adhesion layer. The lower electrode can be arranged or deposited in any desired manner. Preferably, chemical or physical deposition from the gas phase, e.g., by magnetron sputtering or evaporation, can be used. Subsequently, an electroceramic material is deposited on the lower electrode. The electroceramic materials can be, for example, those defined above.Methods such as chemical solution deposition, magnetron sputtering, atomic layer deposition or pulsed laser deposition can be used for the deposition of the electroceramic material.

[0056] The electroceramic layer can be deposited successively in thin layers. For example, layers with a thickness of 10 to 200 nm can be stacked on top of each other in each deposition step. In chemical solution deposition, a precursor solution containing an electroceramic starting material can first be deposited. The deposition method can be, for example, spin coating. Subsequently, the solvents can be removed from the precursor solution by drying at elevated temperature. Any organic residues can then be removed by a pyrolysis step. The drying and pyrolysis can be carried out sequentially at different temperatures or during a single heating process. A heating step (annealing step) can then be performed, leading to the crystallization of the previously amorphous metal oxide.To achieve an electroceramic layer on the order of several micrometers, such a deposition can be repeated.

[0057] According to one embodiment, a high-quality PZT layer can be formed by deposition and spin coating of a PZT solution onto the substrate. The PZT film can be formed from a single solution that creates a sublayer of the PZT film. It can also be produced from two or more solutions with different concentrations of PZT components, each forming sublayers of a sublayer. One solution can be Zr-rich and a second solution can be Ti-rich. The principles of the embodiment described below can be applied to the cases involving two or more solutions.

[0058] According to one embodiment, a method with at least three deposition steps can be used. In this method, at least one first sublayer is produced using a first solution. A second sublayer is deposited or arranged over the first sublayer using a second solution, and a third sublayer is produced using a third solution deposited over the second sublayer. The electroceramic material for this approach is preferably PZT or contains PZT. In this case, the first solution has a high zirconium-to-titanium ratio. The first solution is deposited over the lower electrode, forming the first sublayer. The formation of the first sublayer can be achieved through one or more deposition steps. Subsequently, the first sublayer is annealed. If more than one deposition step is performed, intermediate heating can be carried out.Similarly, a second sublayer is formed from the second solution, which has a medium zirconium-to-titanium ratio. This medium zirconium-to-titanium ratio is lower than that of the first solution. After deposition, heating can be performed. A third sublayer is formed over the second sublayer, which in turn can consist of one or more layers. The third sublayer is formed with a third solution that has a low zirconium-to-titanium ratio, meaning that the proportion of zirconium relative to titanium is the lowest compared to the other solutions. In other words, the first solution can be described as zirconium-rich. The second solution can be described as a morphotropic phase boundary solution, and the last solution as a titanium-rich solution.The formed sublayers can be described as a zirconium-rich sublayer, a morphotropic phase boundary sublayer, and a titanium-rich sublayer.

[0059] This approach has the advantage that chemical gradients during annealing or crystallization can be reduced or avoided.

[0060] This principle can be applied to more than three solutions. For example, four, five, or even more solutions with different concentrations of Zr and Ti can be used, with the concentration gradually changing from Zr-rich to Ti-rich. As described above, a two-solution approach can also be used, likewise changing from Zr-rich to Ti-rich.

[0061] The invention is described below with reference to exemplary embodiments and figures. The figures also include schematic drawings. Such schematic drawings are not to scale, and dimensions or dimensional ratios may be distorted. Accordingly, lengths or ratios cannot be directly determined from the schematic figures unless otherwise indicated. Fig. Figure 1 shows a schematic cross-section of a first embodiment of a multilayer structure. Fig. Figure 2 shows a schematic cross-section of a second embodiment of a multilayer structure. Fig. Figure 3 shows a schematic cross-section of a third embodiment of a multilayer structure. Fig. Figure 4 shows a schematic cross-section of part of a fourth embodiment of a multilayer structure. Fig. Figure 5 shows a schematic cross-section of part of a fifth embodiment of a multilayer structure. Fig. Figure 6 shows a schematic cross-section of part of a sixth embodiment of a multilayer structure. Fig. Figure 7 shows a schematic cross-section of part of a seventh embodiment of a multilayer structure. Fig. Figure 8 shows a polarization-electric field loop of an embodiment of a PZT thin film within a multilayer structure. Fig. Figure 9 shows a relative permittivity-electric field loop of an embodiment of a PZT thin film within a multilayer structure. Fig. Figure 10 shows a bipolar displacement curve of an embodiment of a PZT thin film in a multilayer structure. Fig. Figure 11 shows a unipolar displacement curve of an embodiment of a PZT thin film in a multilayer structure. Fig. Figure 12 shows a photograph of a first embodiment of a MEMS mirror device. Fig. Figure 13 shows a light microscope image of an exemplary embodiment of a MEMS mirror device. Fig. Figure 14 shows an optical field of view measurement as a function of the drive frequency for the fast axis of the MEMS mirror device. Fig. Figure 15 shows an optical field of view measurement as a function of the drive frequency for the slow axis of the MEMS mirror device. Fig. Figure 16 shows a false color plot graph as a function of the axis drive frequency for both axes during the horizontal movement of the mirror. Fig. Figure 17 shows a false color graph as a function of the axis drive frequency for both axes during the vertical movement of the mirror. Fig. Figure 18 shows a light microscopic image of a device with a delaminated lower electrode. Fig. Figure 19 shows a light microscopic image of the device. Fig. 18. Fig. Figure 20 shows a light microscope image of an embodiment of a MEMS device according to the invention. Fig. 21 shows an enlarged light microscopic image of the in Fig. 20 shown embodiment without delamination. Fig. Figure 22 shows a scanning electron microscope cross-sectional image of an embodiment of an NTC thin-film multilayer component. Fig. Figure 23 shows a flowchart of a manufacturing process for an embodiment of a multilayer structure. Fig. Figure 24 shows a schematic cross-section through an eighth embodiment of a multilayer structure. Fig. Figure 25 shows a schematic cross-section through part of a ninth embodiment of a multilayer structure. Fig. Figure 26 shows a schematic cross-section through part of a tenth embodiment of a multilayer structure. Fig. Figure 27 shows a schematic cross-section through part of an eleventh embodiment of a multilayer structure. Fig. Figure 28 shows a schematic cross-section through part of an embodiment of a multilayer structure. Fig. Figure 29 shows a schematic cross-section through part of a thirteenth embodiment of a multilayer structure. Fig. Figure 30 shows a schematic cross-section through a fourteenth embodiment of a multilayer structure. Fig. Figure 31 shows a scanning transmission electron micrograph of a PZT thin film of an embodiment of a multilayer structure.

[0062] In Fig. Figure 1 shows a first embodiment of a multilayer structure 1 in schematic cross-section. In this exemplary embodiment, an adhesion layer 3 is arranged on a silicon wafer-based substrate 2. The adhesion layer 3 comprises a transition metal or a transition metal oxide. A transition metal can be any transition metal from the fourth, fifth, or sixth period of the periodic table. An electrode layer 4 is located on the adhesion layer 3. The electrode 4 can contain or consist of a noble metal or a conductive oxide. In this stack, the electrode layer 4 can be referred to as the bottom electrode. Above the bottom electrode 4 is an electroceramic layer 5. The electroceramic layer 5 can be a dielectric, pyroelectric, ferroelectric, piezoelectric layer, or a layer with a thermistor ceramic.An upper electrode 6 is arranged on the electroceramic layer 5. The upper electrode 6 can be any type of conductive electrode. For example, the upper electrode 6 can be a noble metal electrode or a conductive oxide electrode. It can be made of the same or a different material than the lower electrode 4.

[0063] The materials described for these various layers can be those mentioned in the introduction. A particularly preferred example for substrate 2 is a silicon-on-insulator wafer (SOI wafer). A tantalum-containing adhesion layer 3 is particularly preferred. It can comprise metallic tantalum and / or tantalum oxide. A platinum electrode 4 is preferably arranged on this layer. The electroceramic layer 5 can preferably comprise a PZT material or a thermistor material such as an NTC material. A chromium / gold electrode is preferred as the top electrode 6.

[0064] The SOI wafer substrate can have the following internal layer structure from bottom to top: A 450 µm thick silicon handle layer is located on a 1.5 µm thick silicon oxide layer. A 1 µm thick silicon oxide buried layer is positioned above the silicon handle layer. A 150 µm thick silicon device layer is positioned on top of the embedded oxide layer. A 1 µm thick silicon oxide layer is positioned on top of the silicon device layer.

[0065] In a preferred embodiment with an SOI layer, the tantalum adhesion layer has a thickness of 20 nm. The lower platinum electrode 4 can have a thickness of 200 nm. The PZT electroceramic layer 5 can have a thickness of 1.7 µm. The upper electrode can be formed with a chromium and a gold electrode. These can be implemented as successively applied layers. A chromium layer can be 20 nm thick and can be positioned between the PZT layer and the gold layer. The gold layer can have a thickness of 200 nm.

[0066] Although not explicitly shown, a nucleation layer can be positioned between the electroceramic layer and the electrode in many cases. This nucleation layer can further facilitate the crystalline and / or oriented growth of the electroceramic layer.

[0067] The present structure has the advantage that an electroceramic layer 5, such as the aforementioned electroceramic PZT layer or the aforementioned electroceramic NTC layer, is formed with a high degree of orientation and good adhesion to the substrate. Furthermore, the multilayer structure can be produced without the need to polish the substrate 2 or otherwise control the surface roughness. As will be shown below, excellent performance can be achieved with such multilayer structures.

[0068] Fig. Figure 2 shows a schematic cross-section of a second embodiment of a multilayer structure 1. The multilayer structure 1 of the Fig. 2 is identical in its upper part to the multilayer structure of the Fig. 1, i.e., with respect to the layers with reference numerals 2, 3, 4, 5, and 6, which are identical to those described for the first embodiment. However, a second adhesion layer 3', a second electrode 4', a second electroceramic layer 5', and a second upper electrode 6' are also arranged on the other main surface of the substrate 2. The materials of these layers can correspond to those of the first adhesion layer 3, the first lower electrode 4, the first electroceramic layer 5, and the first upper electrode 6. Accordingly, a largely symmetrical layer arrangement results with respect to the layers with reference numerals 2 to 6.

[0069] In Fig. Figure 3 shows a schematic cross-section of a third embodiment of a multilayer structure 1. This third embodiment of a multilayer structure 1 is a modification of the one described in Figure 3. Fig. Figure 1 shows the first embodiment. Here, the first adhesion layer 3, the first lower electrode 4, the first electroceramic layer 5, and the first upper electrode 6 are arranged on the substrate 2. A second electroceramic layer 5'' is arranged above the first upper electrode 6. The second upper electrode 6'' is arranged above the second electroceramic layer 5''. In this arrangement, the first upper electrode 6 acts as the lower electrode for the second electroceramic layer 5''. The materials of the second electroceramic layer 5'' can be selected from the same materials as the material of the first electroceramic layer 5. Similarly, the materials of the second upper electrode 6'' can be selected from the same materials as the material of the first electrode 6.

[0070] In a similar way to in Fig. As shown in Figure 3, several further electroceramic layers and top electrodes can be stacked alternately. Preferably, such a stack is terminated by a top electrode.

[0071] The third embodiment can of course be combined with the second embodiment, i.e., with the two-sided arrangement as described in Fig. Figure 2 illustrates this. This can result in a symmetrical stacking where both sides have the same number of stacks. Alternatively, a stack can be formed where both sides have a different number of electroceramic layers and top electrodes.

[0072] Fig. Figure 4 shows a schematic cross-section through part of a fourth embodiment of a multilayer structure 1. Fig. 4 can be an arrangement of an adhesion layer 3 on a substrate 2 in the first, second or third embodiment of a multilayer structure, as described in the Fig. 1, Fig. Figures 2 and 3 represent the embodiment. In this fourth embodiment, the adhesion layer is arranged on the substrate 2. The adhesion layer 3 comprises or consists of a single material and has no internal material layer boundaries. In this case, the adhesion layer consists only of a transition metal or an alloy of transition metals.

[0073] Fig. Figure 5 shows a schematic cross-section of part of a fifth embodiment of a multilayer structure 1. Fig. 5 can be an arrangement of an adhesion layer 3 on a substrate 2 in the first, second and third embodiments of a multilayer structure 1, as in the Fig. 1, Fig. Figures 2 and 3 represent the adhesion layer. In this case, the adhesion layer comprises a first adhesion sublayer 3a, which contains or consists of a transition metal or an alloy of transition metals. A second adhesion sublayer 3b, which contains or consists of a transition metal oxide, is arranged on top of this. This means that the transition metal oxide layer can also be a mixed oxide containing a transition metal oxide. The transition metal of the transition metal oxide can be the same as or different from the transition metal of the first adhesion sublayer 3a.

[0074] Fig. Figure 6 shows, as the sixth embodiment of a multilayer structure 1, a structure that is in principle similar to that of the Fig. 5 but with a reversed stacking of the first adhesion sublayer 3a and the second adhesion sublayer 3b. Here in the sixth embodiment, the second adhesion sublayer 3b, which comprises or consists of a transition metal oxide, is arranged directly on the substrate 2. The first adhesion sublayer 3a, which comprises or consists of the transition metal, is arranged above it. The stacking in this exemplary embodiment of Fig. 6 can be an arrangement of an adhesion layer 3 on a substrate 2 in the first, second or third embodiment of a multilayer structure 1, as described in the Fig. 1, Fig. 2 or 3 are shown to represent.

[0075] Fig. Figure 7 shows a schematic cross-section of part of a seventh embodiment of a multilayer structure 1, which is a modification of the one described in Fig. The stacking shown in Figure 5 represents the fifth embodiment. The second adhesion sublayer 3b is stacked on the first adhesion sublayer 3a in the same manner as in Figure 5. Fig. 5. On the second adhesion sublayer 3b, a third adhesion sublayer 3a' is arranged, which contains or consists of a transition metal. The transition metal in the first and third adhesion sublayers 3a and 3a' can be identical or different. Otherwise, the properties described above can apply.

[0076] Not shown, but also possible, is a reversed arrangement of the adhesion sublayers. For example, a transition metal-containing adhesion sublayer can be sandwiched between two transition metal oxide-containing adhesion sublayers.

[0077] For those in the Fig. In the adhesion layers shown in Figures 4 to 7, the inventors have discovered that the use of a transition metal improves the adhesion between a silicon wafer-based substrate, and more generally between a semiconductor or insulator substrate, and an electrode such as a platinum or other noble metal electrode. Furthermore, the inventors have found that the transition metal can at least partially prevent the migration of elements or substances between the layers. In particular, when an oxide layer is present, the diffusion or migration of ions appears to be suppressed even more effectively.

[0078] In connection with the preceding embodiments, the inventors have developed some further embodiments which relate to properties of the preceding embodiments or which are generalized versions of these embodiments.

[0079] In Fig. Figure 24 shows an eighth embodiment of a multilayer structure. This has essentially the same layer structure as the first embodiment of a multilayer structure, which is shown in Fig. Figure 1 illustrates this. However, instead of placing the electroceramic layer 5 directly onto the electrode 4, a support layer SL is arranged between the electrode 4 and the electroceramic layer 5. In this case, the support layer SL is a lanthanum-nickel oxide support layer (LNO; LaNiO3), which acts as a conductive layer and also has a nucleation layer function, promoting crystal growth and oriented crystal growth. Alternatively, the support layer SL can also be made of lead titanate (PbTiO3), lead oxide (PbO), or titanium oxide (TiO2).

[0080] Contrary to the impression given by the figure, the support layer SL is preferably significantly thinner than the electroceramic layer.

[0081] In the present embodiment, the adhesion layer 3 is also different compared to that of the first embodiment. Fig. The adhesion layer described in section 1 has been modified. Instead of a single layer, adhesion layer 3 has more than one adhesion sublayer. Adhesion layer 3 comprises adhesion sublayer 3a and, in addition, further adhesion sublayers, which are indicated to be numbered up to n layers, where n is an arbitrary counting variable. The layers are numbered 3a to 3n. Each of the adhesion layers is either a metallic layer containing or consisting of a transition metal, or an oxide layer containing or consisting of a transition metal oxide. Each of the adhesion sublayers in Fig. Sublayer 24 differs either structurally or chemically from at least one neighboring sublayer. This can mean that for any sublayer 3i (one of the sublayers in 3a to 3n), a neighboring sublayer 3i+1 is chemically or structurally different. For example, any sublayer 3i could be metallic, and the neighboring sublayer 3i+1 could also be metallic, but they could both contain a different transition metal. In another example, any sublayer 3i could contain a transition metal oxide, and the neighboring sublayer 3i+1 could contain a different transition metal oxide. In yet another example, any sublayer 3i could contain a transition metal oxide, and the neighboring sublayer 3i+1 could be metallic and contain either the same or a different transition metal than the transition metal of the oxide in any sublayer 3i. The same relationship could, of course, also hold in reverse.Regardless of the relationship between sublayers 3i and 3i+1, the same relationships can of course apply to the neighboring sublayers 3i and 3i-1.

[0082] A specific example, illustrated by the eighth embodiment of the Fig. The component shown in Figure 24, which only has a partial layer, has a silicon oxide-terminated silicon substrate 2. An adhesion layer 3, comprising or consisting of metallic titanium (Ta), is arranged on the titanium oxide (first adhesion sublayer). The electrode 4 is made of platinum (Pt). A lanthanum-nickel oxide support layer SL is arranged on the electrode 4. An electroceramic layer 5, comprising or consisting of platinum (PZT), is arranged above this. A high layer quality was found, particularly for this arrangement.

[0083] Further examples of adhesion layers that fall under the general description of the Fig. The adhesion layer 3 described in section 24 would fall are listed below.

[0084] Furthermore, it is pointed out that the sub-layer arrangement of Fig. 24 and the other adhesion layers can be applied to each of the other examples and is not limited to an example with a support layer SL.

[0085] In Fig. Figure 25 shows a schematic cross-section of part of a ninth embodiment of a multilayer structure 1. This embodiment is similar in its general structure to the embodiments of the Fig. 5 and Fig. 6, i.e., it has an adhesion layer comprising a first sublayer and a second sublayer. The first sublayer 3a contains a first transition metal and is metallic. The second sublayer 3b, in this case, contains a second transition metal and is also metallic, but the second transition metal is different from the first transition metal. The first transition metal could be, for example, tantalum and the second transition metal titanium. Alternatively, the first adhesion sublayer could be chromium and the second adhesion sublayer 3b nickel. Similarly, a third adhesion sublayer could also be realized (not shown), which is metallic and contains a third transition metal different from the second transition metal. The third transition metal could be, for example, silver.

[0086] A similar structure (not shown) can also be formed for adhesion sublayers, each containing an oxide. For example, a first adhesion sublayer might contain a first transition metal oxide, while a second transition metal sublayer might contain a second transition metal oxide. The first transition metal oxide could be, for example, titanium oxide, and the second transition metal oxide could be tantalum oxide. Similarly, a third adhesion sublayer (not shown) also contains a third transition metal oxide. This third transition metal oxide differs from the second transition metal oxide; it could, for example, be aluminum oxide.

[0087] Fig. Figure 26 shows a schematic cross-section of part of a tenth embodiment of a multilayer structure 1. This tenth embodiment is structurally based on the fifth embodiment. However, instead of the first adhesion sublayer 3a, a first adhesion sublayer 3a1 and a second adhesion sublayer 3a2 are realized. Both the first adhesion sublayer 3a1 and the second adhesion sublayer 3a2 are metallic. The transition metal in the first adhesion sublayer 3a1 differs from the transition metal contained in the second adhesion sublayer 3a2. Similarly, instead of the second adhesion sublayer 3b, which is shown in the embodiment of Fig. As shown in Figure 5, a third adhesion sublayer 3b1 and a fourth adhesion sublayer 3b2 are realized. The third adhesion sublayer 3b1 contains a first transition metal oxide. The transition metal of the first transition metal oxide of the third adhesion sublayer 3b1 can be the same as or different from the transition metal contained in the first adhesion sublayer 3a1 or the second adhesion sublayer 3a2. The fourth adhesion sublayer 3b2 also contains a transition metal oxide (second transition metal oxide). The transition metal of the second transition metal oxide differs from the transition metal of the first transition metal oxide. Otherwise, there is no restriction on the transition metal of the transition metal oxide of the fourth adhesion sublayer 3b2. It can be identical to or different from the transition metal of the first and second adhesion sublayers 3a1 and 3a2.

[0088] Fig. Figure 27 shows a schematic cross-section of part of an eleventh embodiment of a multilayer structure 1. This eleventh embodiment is a modification of the sixth embodiment in the same way that the tenth embodiment is a modification of the fifth embodiment. The stacking sequence shown for the eleventh embodiment differs from the stacking sequence shown in the tenth embodiment. Otherwise, however, the descriptions of the individual adhesion sublayers explained for the tenth embodiment apply.

[0089] Fig. Figure 28 shows a schematic cross-section through part of a twelfth embodiment of a multilayer structure 1. The twelfth embodiment is a modification of the one described in the eleventh embodiment. Fig. 27 stacking shown. This means that the features applicable to the eleventh embodiment in Figure 27 apply to the third adhesion sublayer 3b1, the fourth adhesion sublayer 3b2, the first adhesion sublayer 3a1 and the second adhesion sublayer 3a2. Fig. 27. In addition, a fifth adhesion sublayer 3c1 and a sixth adhesion sublayer 3c2 are arranged above the second adhesion sublayer 3a2. The fifth adhesion sublayer 3c1 contains a transition metal oxide. The sixth adhesion sublayer 3c2 also contains a transition metal oxide, but it contains a different transition metal than the transition metal of the fifth adhesion sublayer 3c1. Otherwise, there is no restriction regarding the transition metal of the fifth and sixth adhesion sublayers 3c1 and 3c2. For example, the transition metal oxide of the fifth adhesion sublayer 3c1 can be the same as that of the third or fourth adhesion sublayers 3b1 and 3b2. The same applies to the sixth adhesion sublayer 3c2.

[0090] Fig. Figure 29 shows a generalized embodiment based on the fifth embodiment. This shows that there can be several metallic adhesion sublayers 3a1, all of which are metallic and each of which has a different transition metal oxide than the adjacent metallic adhesion sublayers. The principles that apply to the eighth embodiment in Fig. The points explained in section 24 also apply here.

[0091] Transition metal oxide-based sublayers 3b1 to 3bm are arranged above the metallic adhesion sublayers. Their number can be the same or different from the number of metallic adhesion sublayers. In principle, the same applies to each of the transition metal oxide-based adhesion sublayers as to the metallic adhesion sublayers, i.e., the transition metal in each of them differs from the neighboring oxide sublayers. The last metallic adhesion sublayer 3an and the first transition metal oxide-based adhesion sublayer 3b1, which are adjacent to each other, can have the same transition metal oxide, but they do not have to. The principles that apply to the eighth embodiment, which is described in Fig. The information shown in section 24, which has been explained, also applies here.

[0092] In Fig. Figure 30 shows a fourteenth embodiment of a multilayer structure in schematic cross-section. This is based on the one described in Fig. In the first embodiment shown in Figure 1, instead of a substantially uniform electroceramic layer 5, the electroceramic layer 5 here has a first electroceramic sublayer 5a and a second electroceramic sublayer 5b. The first electroceramic sublayer 5a and the second electroceramic sublayer 5b are based on the same electroceramic material, such as PZT. However, the composition of the two sublayers differs. For example, components such as dopants or main ions such as La, Pb, Zr, or Ti can have different concentrations in the two sublayers.

[0093] In the Fig. Figures 8 to 11 present the results of electrical and piezoelectric characterization measurements. The measurements were performed on a multilayer structure as described in Fig. Figure 1 shows the process, which was carried out on an SOI wafer with the properties described above, where the piezoelectric layer had a thickness of 1.7 µm. The layer thicknesses were as described above. A 25 nm thick chromium layer and a 200 nm thick gold layer were sputtered over the electroceramic PZT layer to form the top electrode. Cantilever components with a large-area top electrode of 19.45 mm² were then produced from these components. 2 The sample was cut and used for characterization. All measurements were performed on the same sample.

[0094] Fig. Figure 8 shows a diagram of the polarization with respect to the electric field, recorded at 10 Hz. The curve represented by the dashed line, which has the greater y-axis deflection and is indicated by a left-pointing arrow, corresponds to the left y-axis, labeled "Polarization." The curve represented by the solid line, which also has a smaller y-axis deflection, corresponds to the measured current density, as indicated by the right-pointing arrow. The polarization-electric field loop clearly shows ferroelectric switching with a remanent polarization P. r of approximately 20 µC cm -2 and a coercive field E c of approximately 30 kV cm -1 .

[0095] Fig. Figure 9 shows the relative permittivity and the loss factor as a function of the DC electric field, measured at a small signal frequency of 225 Hz and a small signal amplitude of 5 kV cm. -1The curve shown above in the figure, represented by a dashed line and dashed circular data points, is the measurement of the relative permittivity associated with the left y-axis, as indicated by the left-pointing arrow. The curve shown below in the figure, represented by the solid line and solid circular data points, corresponds to the loss factor on the right y-axis, as also indicated by the small right-pointing arrow. The measurements clearly show that the relative permittivity is approximately 1700 at a bias field of zero, while the loss remains below 10%. The high quality of the film is further demonstrated by the fact that no leakage was observed at high DC fields.

[0096] Fig. Figure 10 shows a bipolar displacement curve recorded at 10 Hz. The bipolar displacement curve is symmetrical and exhibits the typical butterfly shape of high-quality PZT films.

[0097] Fig. Figure 11 shows a unipolar displacement curve. The values ​​summarized in Table 1 were derived from this curve. Table 1: -e 31,f + -e 31,f - Average of |e 31,f | Δe 31,f example of Fig. 11 22.43 C m -2 17.60 C m -2 20.02 C m -2 4.84 C m -2

[0098] As can be seen from Table 1, the effective transverse piezoelectric coefficient |e 31 , f | at 20°C m -2 determined. In this measurement, no hot galvanizing of this thin film under a DC electric field was performed. Within the scope of the invention, it would be possible to further improve the piezoelectric thin film by additional hot galvanizing. Doping can also further improve the piezoelectric thin film.

[0099] In the Fig. 12 and Fig. Figure 13 shows an embodiment of a bi-resonant 2D-MEMS high-frequency micromirror 10. Fig. Figure 12 shows a photograph of the device. Fig. Figure 13 shows a microscopic image of the micromirror. The micromirror 10 has a mirror plate or mirror surface 13 with a diameter of 1.5 mm. The mirror can be tilted or set into oscillation along the so-called fast axis 12 and the slow axis 11. During operation, the actuator ring 14 is subjected to voltage.

[0100] The actuator ring 14 comprises a multilayer structure according to the invention. Its structure is essentially identical to that described in Fig. Stacking shown in 1. In particular, on an SOI substrate with the properties as shown in Fig. Figure 1 describes a 20 nm thick tantalum layer deposited as an adhesion layer. The lower electrode is formed from a 200 nm thick platinum electrode. The electroceramic layer is a 1700 nm thick PZT layer, which can be produced, for example, using the method described below. The upper electrode is formed from a 20 nm thick chromium layer and a 200 nm thick gold layer.

[0101] In the Fig. Figures 14 to 17 show the measurements of the optical field of view (FoV). Fig. Figure 14 shows measurements of the optical field of view for the drive frequency of the fast axis at different voltages. The data points are always shown together with a fit curve. Similarly, in Fig. Figure 15 shows the optical field of view measurement for the slow axis at different voltages. These diagrams in Fig. 14 and Fig. Figure 15 represents 1D operations at different drive voltages.

[0102] As can be seen, the achieved values ​​for the maximum optical field of view demonstrate the stability and adhesion strength achieved with an adhesive layer. The adhesion is so good that the limiting factor for the achievable maximum optical field of view is not the layer stack, but the mechanical strength of the underlying silicon-based substrate. Furthermore, the measurements in the Fig. 14 and Fig. 15, that the layer stack even generates enough force and energy to excite a high-frequency mechanical mode close to 40 kHz without cracking.

[0103] The Fig. 16 and Fig. Figure 17 shows false-color representations depicting a 2D measurement in which both torsion bars are actuated simultaneously. Fig. 16 and Fig. Figure 17 shows measurements of the optical field of view as a function of the drive frequencies of both axes for the horizontal ( Fig. 16) and the vertical ( Fig. 17) Optical field of view of the implemented MEMS mirror device in the case of such 2D operation. These results confirm that the layer stack is even able to simultaneously drive both axes of the mirror with a relatively high optical field of view of 31° × 42° without damage occurring. The representations of the Fig. 16 and Fig. 17 thus demonstrate the high quality of the multilayer structure according to the invention.

[0104] In the Fig. 18 and Fig. 19 shows a case in which a micromirror is subjected to similar stresses as in the Fig. 14 to 17 exhibits a failure and, in particular, a delamination. Fig. Figure 18 shows a light microscopic image in which the lower electrode was damaged during the wire bonding process. Fig. Figure 19 shows delamination between the SiO2 and the adhesion layer. These effects are frequently observed when titanium oxide is used as the adhesion layer. As described above, tantalum exhibits significantly better adhesion.

[0105] The observation that tantalum exhibits far better adhesion than titanium oxide can also be found in the Fig. 20 and Fig. 21 can be seen. Fig. Figure 20 shows a light microscope image of a device in which tantalum was used as the material for the adhesion layer. Wire bonding can be easily performed here without damaging the lower electrode stack. As in Fig. As can be seen in Figure 21, there are no signs of delamination at any interface, even over large areas.

[0106] In Fig. Figure 22 shows a scanning electron microscope cross-sectional image of a multilayer structure with an NTC layer. A silicon wafer was used as the silicon substrate, featuring a 1 µm thick silicon oxide layer on one side, followed by a 675 µm thick silicon layer and a second 1 µm thick silicon oxide layer. As can be seen in the cross-sectional image, only the upper part of the substrate is visible, namely the silicon layer 2a and the upper silicon oxide layer 2b. A 20 nm thick adhesion layer 3 is deposited onto the silicon oxide layer 2b. Its position is roughly indicated by the lighter line in the image. A platinum electrode 4 with a thickness of 200 nm is positioned above this. An electroceramic layer 5 is positioned above the platinum electrode 4. The electroceramic layer 5 consists of an NTC film made of Mn-Co-Ni oxide. The NTC layer has a thickness of 125 nm.

[0107] The setup was prepared such that the silicon wafer was first treated with UV light and ozone for 10 minutes. Subsequently, the tantalum and platinum were sequentially deposited onto the silicon wafer by DC magnetron sputtering at room temperature using 200 W. For this, an NTC precursor solution was first prepared. This solution was filtered before deposition. The NTC precursor solution was applied to the substrate and coated by spin coating. A first partial layer of the NTC precursor solution was deposited onto the appropriately prepared bare substrate and then dried and pyrolyzed on a hot plate at 350–450 °C. To achieve the desired thickness, the coating, drying, and pyrolysis processes were repeated five times. The amorphous film was then crystallized in an RTA furnace at 650–770 °C.

[0108] As in Fig. As can be seen in image 22, the NTC layer was free of cracks and defects. Furthermore, the scanning electron micrograph confirmed a dense NTC thin film and showed no signs of delamination of the NTC layer or the lower electrode.

[0109] Fig. Figure 31 shows a scanning transmission electron microscopy (STEM) image of a PZT thin film deposited on a silicon wafer-based substrate 2. Only the terminal silicon oxide layer of the silicon wafer-based substrate 2 is visible. As can be seen in the image, the PZT electroceramic layer 5 is located above the lower platinum electrode 4. In this cross-sectional image, crystalline columns 7 (as shown in the figure) are visible, extending over the entire thickness of the electroceramic layer 5. This excellent columnar grain growth is desirable because it leads to a high electromechanical response. The STEM confirmed the absence of secondary phases, such as pyrochlore, which is known to significantly impair the performance of the electroceramic element.The adhesion layer 3, which in this case is a Ta layer located between substrate 2 and electrode 4, is so thin that it is barely visible at the interface between substrate 2 and electrode 4. Despite its small thickness, at least part of the high-quality columnar growth of the electroceramic layer 5 is attributable to the presence of an adhesion layer.

[0110] Fig. Figure 23 shows a flowchart of a process for producing a PZT thin film on an SOI substrate. The layer produced accordingly can, for example, be used in Fig. 1 shown or the one in the Fig. 12 and Fig. The micromirrors shown in the 13 images were used.

[0111] The substrate used was an SOI wafer, consisting of, from bottom to top, an approximately 1.5 µm thick silicon oxide layer, a 450 µm thick silicon handle layer, a 1 µm thick silicon oxide buried layer, a 150 µm thick silicon device layer, and a 1 µm thick top silicon oxide layer. This top silicon oxide layer was first treated with a UV-ozone cleaner for 10 minutes. After this cleaning, a 20 nm thick tantalum adhesion layer was deposited at room temperature by 500 W DC magnetron sputtering.

[0112] A 200 nm thick platinum layer is deposited on the tantalum layer, again at room temperature and by DC magnetron sputtering at 500 W. The sputtering took place in an argon working gas atmosphere with an argon pressure between 1 × 10 -3 mbar and 8×10 -2mbar. The distance between the target and the substrate was 12 to 18 cm. This creates a stack comprising the silicon wafer with the tantalum layer and the platinum layer.

[0113] A lead titanate (PbTiO3) seed layer is then deposited on the platinum electrode. For this purpose, a seed layer solution of PbTiO3 was first prepared. The solution had a concentration of 0.0625 mol / l PbTiO3 and a 10% molar excess of lead to compensate for evaporation during crystallization. Before deposition, the seed layer was filtered through a 0.2 µm PTFE syringe filter.

[0114] The nucleation solution was then applied to the bare platinum surface and deposited by spin coating at a rotational speed of 2000 revolutions per minute for 30 seconds. The resulting amorphous nucleation layer was dried and pyrolyzed on a hot plate at 150 °C and subsequently crystallized in a rapid thermal oven at 520 °C. This process formed a nucleation layer of approximately 10 nm. The resulting stack consists of an SOI substrate, a tantalum bonding layer, a platinum electrode layer, and a nucleation layer.

[0115] The PZT electroceramic layer is then formed by depositing several sublayers, each consisting of three sublayers.

[0116] First, a zirconium-rich sublayer is formed. For this purpose, a first zirconium-rich precursor solution is prepared by dissolving lead(II) acetate in a solution of zirconium(IV) propoxide and titanium(IV) isopropoxide in acetic acid and 2-methoxyethanol. After dissolving the lead precursor at 60 °C, the resulting solution was refluxed under a nitrogen atmosphere for 2 hours. After distillation off the byproducts, the mixture was diluted to a concentration of 0.5 mol / L. The composition of the first prepared solution corresponds to the composition of Pb(Zr). 0.63 Ti 0.37O3 for the sublayer to be formed. The solution is prepared to also contain a 15% molar excess of lead. Before deposition, the zirconium-rich first precursor solution was filtered through a 0.2 µm PTFE syringe filter. Subsequently, the zirconium-rich first precursor solution was applied to the seed layer and coated by spin coating at 2000 revolutions per minute for 30 seconds. The resulting zirconium-rich sublayer was dried at 150 °C and 350 °C, respectively, and pyrolyzed.

[0117] Subsequently, to form a medium-concentrated second sublayer, a medium-concentrated second precursor solution was first prepared by dissolving lead(II) acetate in a solution of zirconium(IV) propoxide and titanium(IV) isopropoxide in acetic acid and 2-methoxyethanol. After dissolving the lead precursor at 60 °C, the resulting solution was refluxed for 2 hours under a nitrogen atmosphere. After distillation off the byproducts, the mixture was diluted to a concentration of 0.5 mol / L. The composition of the solution thus prepared corresponds to the composition of Pb(Zr). 0.53 Ti 0.47O3 for the sublayer to be formed. The solution is prepared to also contain a 15% molar excess of lead. Before deposition, the medium-concentrated second precursor solution was filtered through a 0.2 µm PTFE syringe filter. Subsequently, the medium-concentrated second precursor solution was applied to the dried and pyrolyzed, zirconium-rich sublayer and spin-coated for 30 seconds at a rotational speed of 2000 revolutions per minute. The resulting medium-concentrated second sublayer was dried and pyrolyzed at temperatures of 150 °C and 350 °C, respectively.

[0118] To form a titanium-rich third sublayer, a titanium-rich third precursor solution is first prepared by dissolving lead(II) acetate in a solution of zirconium(IV) propoxide and titanium(IV) isopropoxide in acetic acid and 2-methoxyethanol. After dissolving the lead precursor at 60 °C, the resulting solution was refluxed under a nitrogen atmosphere for 2 hours. After distilling off the byproducts, the mixture was diluted to a concentration of 0.5 mol / L. The composition of the solution thus prepared corresponds to that of Pb(Zr). 0.43 Ti 0.57O3 for the sublayer to be formed. The solution is prepared to also contain a 15% molar excess of lead. Before deposition, the titanium-rich third precursor solution was filtered through a 0.2 µm PTFE syringe filter. Subsequently, the titanium-rich third precursor solution was applied to the dried and pyrolyzed second sublayer and spin-coated for 30 seconds at a rotational speed of 2000 revolutions per minute. The resulting titanium-rich third sublayer was dried and pyrolyzed at temperatures of 150 °C and 350 °C, respectively.

[0119] The partial layer formed so far from the three sublayers is amorphous. It has a thickness of 50 to 200 nm. After the formation of this amorphous partial layer, it undergoes a crystallization step in a rapid thermal heating oven at 650°C.

[0120] To obtain a PZT electroceramic layer with a thickness of 1.7 to 2.5 µm, the sublayer formation described above was repeated 24 times. In this example, a thickness of 1.7 µm corresponds to 24 sublayers. This allows for the stacking of an SOI substrate, a tantalum adhesion layer, a platinum electrode layer, a seed layer, and a PZT electroceramic layer. Finally, an upper electrode, which is in Fig. 23 is not shown, e.g. deposited by DC magnetron sputtering.

[0121] The upper electrode can, for example, contain gold or platinum and / or, in the present case, a partial layer of chromium.

[0122] The above procedure can be adapted for other materials or other layer thicknesses. List of reference symbols 1 Multi-layer structure 2 Metal substrate 3. Adhesive layer 3a first adhesion layer 3b second partial adhesion layer 3a' third partial liability layer 3a1 first adhesion layer 3a2 second adhesion layer 3b1 third adhesion sublayer 3b2 fourth adhesion sublayer 3c1 fifth adhesion sublayer 3c2 sixth adhesion sublayer 3' second adhesion layer 4 electrode 4' second lower electrode 5 electroceramic layer 5', 5'' second electroceramic layer 6 upper electrode 6', 6'' second upper electrode 7th pillar 10 micromirrors 11 slow axis 12 fast axis 13 Mirror surface 14 Drive ring QUOTES INCLUDED IN THE DESCRIPTION

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

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

[0004] Shelton et al., Adv. Funct. Mater. 22, 2295-2302, 2012

[0004] Maeder et al, Jpn. J. Appl. Phys. 37 (4A), 2007-2012, 1998 Halder et al., Appl. Phys. A 87, 705-708, 2007

[0004]

Claims

[1] Multilayer structure which has a semiconductor or insulator substrate, an electrode comprising a precious metal or a conductive oxide and positioned above the semiconductor or insulator substrate, and an electroceramic layer that is arranged above or on the electrode, wherein an adhesion layer comprising a transition metal or transition metal oxide, arranged between and in direct contact with a main surface of the substrate and the electrode. [2] Multilayer structure according to claim 1, wherein the substrate is a silicon wafer-based substrate, a sapphire-based substrate or a glass substrate. [3] Multilayer structure according to claim 1 or 2, wherein the substrate has a surface roughness Ra of 10 nm to 2 µm, preferably of 20 nm to 1 µm, on its main surface. [4] Multilayer structure according to one of claims 1 to 3, wherein the adhesion layer comprises a first adhesion sublayer comprising a transition metal and a second adhesion sublayer comprising a transition metal oxide. [5] Multilayer structure according to one of the preceding claims, wherein the adhesion layer comprises n adhesion sublayers, each comprising a transition metal in metallic form or a transition metal oxide, with n ≥ 2, wherein a single adhesion sublayer differs chemically or structurally from a directly adjacent adhesion sublayer. [6] Multilayer structure according to claim 5, wherein one of the adhesion sublayers and the directly adjacent adhesion sublayer are chemically different, in that both are metallic and contain another transition metal, or Both contain different transition metal oxides, or one is metallic and the other contains a transition metal oxide. [7] Multilayer structure according to any one of claims 1 to 6, wherein the transition metal is selected from Ti, Ta or W or alloys thereof. [8] Multilayer structure according to any one of claims 1 to 7, wherein the adhesion layer has a thickness of 1 nm to 100 nm, preferably 10 to 50 nm. [9] Multilayer structure according to any one of claims 1 to 8, wherein the electrode comprises or consists of Pt or Ir. [10] Multilayer structure according to any one of claims 1 to 9, wherein the electrode comprises or consists of an iridium oxide, a rhodium oxide, a rhenium oxide, a ruthenium oxide or a strontium ruthenium oxide. [11] Multilayer structure according to any one of claims 1 to 8, wherein the electroceramic layer comprises or consists of a dielectric, piezoelectric, pyroelectric, ferroelectric ceramic material or a thermistor ceramic material. [12] Multilayer structure according to any one of claims 1 to 9, wherein a second electrode is arranged on a second main surface of the substrate, wherein a second adhesion layer is arranged between the second main surface and the second electrode, and wherein a second electroceramic layer is arranged above or on the second electrode. [13] Multilayer structure according to one of claims 1 to 12, wherein a further electrode is arranged on the adhesion layer and a further electroceramic layer is arranged on or above the further electrode. [14] Multilayer structure according to one of the preceding claims, wherein the electroceramic layer comprises a first and a second electroceramic sublayer. [15] Multilayer structure according to one of the preceding claims, wherein a support layer is arranged between the electrode and the electroceramic layer. [16] Multilayer structure according to claim 15, wherein the support layer has an electrically conductive property and / or promotes the crystal growth of the electroceramic layer and / or promotes a uniform crystal orientation of the electroceramic layer. [17] Multilayer structure according to claim 15 or 16, wherein the support layer comprises or consists of lead titanate, lanthanum nickel oxide, lead oxide or titanium oxide. [18] Micromirror having the multilayer structure according to any one of claims 1 to 17. [19] High-energy capacitor comprising the multilayer structure according to any one of claims 1 to 17. [20] Piezoelectric device comprising the multilayer structure according to any one of claims 1 to 17. [21] Electrocaloric solid-state cooling device comprising the multilayer structure according to any one of claims 1 to 17. [22] Ferroelectric storage device comprising the multilayer structure according to any one of claims 1 to 17. [23] Thermistor device comprising the multilayer structure according to any one of claims 1 to 17. [24] Pyroelectric device comprising the multilayer structure according to any one of claims 1 to 17. [25] Microfluidic pump having the multilayer structure according to any one of claims 1 to 17. [26] Method for producing a multilayer structure, wherein an adhesion layer is arranged on a main surface of a semiconductor or insulator substrate, an electrode containing a precious metal or a conductive oxide is arranged above the adhesion layer, and an electroceramic material is deposited above the electrode. [27] Method according to claim 26, wherein the electroceramic layer is a PZT ceramic layer formed including at least two steps, wherein a first solution with a first Zr / Ti ratio is deposited over the electrode and a first partial layer of the electroceramic layer is formed by drying and / or heating, a second solution with a second Zr / Ti ratio is deposited over the first sublayer of the electroceramic layer, thereby forming a second sublayer, where the second Zr / Ti ratio is smaller than the first Zr / Ti ratio. [28] Method according to claim 27, wherein a third solution with a third Zr / Ti ratio is deposited over the second sublayer of the electroceramic layer, forming a third sublayer, wherein the third Zr / Ti ratio is smaller than the first and the second Zr / Ti ratio.

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