Electrodes for microacoustic components

Abstract

Electrodes for microacoustic components, in which each individual electrode consists of at least one stack of layers of at least two layers, one of which is at least predominantly a structure of a material of the formula Ru ((100At.-%)-x) Al x with x = 5-80 atm% and / or made of a material of the formula (Ru y M ((100At.-%)-y) ) 100-x Al x , with M = Cu, Ti, Ta, Ni, Pt, Ir, Rh and / or Pd, and with y ≥ 50 to < 100 At.-% and with x = 5 - 80 At.-% and the second layer consists at least predominantly of semiconducting RuAl2.

Description

[0001] The invention relates to the field of electrical engineering and acoustoelectronics and concerns electrodes for microacoustic components, which can be used, for example, as filter components in mobile phones, as sensors or actuators, or in resonators or delay lines, or in integrated circuits, microprocessors, or in optoelectronics.

[0002] SAW (surface acoustic wave) components are frequently used as microacoustic components.

[0003] A SAW component generally consists of a piezoelectric single crystal on which at least one interdigital transducer (IDT) consisting of a pair of comb-shaped interlocking electrodes (whose prongs are also called fingers) is applied, which is manufactured using structuring processes in planar technology (e.g. wet or dry etching or lift-off technique) (Wikipedia, keyword Acoustic surface wave filter).

[0004] Depending on the type and function of the SAW component, further electrode structures, such as additional IDTs and / or reflectors formed from individual or groups of electrode strips, may also be applied to the piezoelectric substrate.

[0005] Such SAW components, especially as sensors, have been increasingly used for high-temperature applications in recent years.

[0006] However, this requires the use of material systems, especially for the electrodes, that exhibit high thermomechanical stability, low electrical resistance, and high oxidation and corrosion resistance.

[0007] In recent years, various metallization systems for electrodes on piezoelectric substrates have been investigated for their high-temperature stability, e.g. Pt- or Ir-based materials (Thiele, JA et al.: IEEE Trans. Ultrason. Ferroelect. Freq. Contr. 2005, 52, 545-549), other high-melting-point metals (Rane, GK et al.: Materials 2016, 9, 101) or oxide dispersion-cured materials (Menzel, SB et al.: Materials 2019, 12, 2651).

[0008] One material suitable for high-temperature stable interdigital converters is the RuAl alloy with its high melting temperature of 2050 °C (Okamoto, HJ Phase Equilib, 1997, 18, 105) and high resistance to oxidation and corrosion.

[0009] Therefore, in recent years the high-temperature stability of RuAl thin films has been investigated on high-temperature stable piezoelectric Ca3TaGa3Si2O 14 -(CTGS) and La3Ga5SiO 14 -(LGS)substrates examined.

[0010] The experiments showed that an oxidation barrier between the substrates and the RuAl layer was required to prevent a chemical reaction between the Al and the CTGS or LGS when the samples were annealed at 800 °C in high vacuum (HV) (Seifert, M. et al: J. Alloys Compd. 2016, 664, 510-517). However, this reaction could be suppressed by applying a 10 nm thick sputtered SiO2 layer to the substrate (Seifert, M. et al: J. Alloys Compd. 2016, 688, 228-240).

[0011] Based on these investigations, the oxidation resistance of RuAl thin films was also examined, and it was found that a combined barrier layer of 20 nm AIN and 20 nm SiO2 is able to prevent the oxidation of the RuAl layer on CTGS up to 800 °C in air and 900 °C in HV. Stable layers are achieved on LGS up to 600 °C in air and 900 °C in HV. These results represent a significant advance in the realization of material systems for electrodes in SAW devices for high-temperature applications (Seifert, M.: Materials 2020, 13, 1605).

[0012] Furthermore, semiconductors are known that are solids whose electrical conductivity lies between that of electrical conductors (> 10 4 S / cm) and that of non-conductors (< 10 8The temperature coefficient of conductivity (S / cm) is approximately 10⁻⁶. An important characteristic of semiconductors is that their electrical conductivity increases with rising temperature. Near absolute zero, semiconductors are insulators. Furthermore, the conductivity and conduction characteristics (electron and hole conduction) can be selectively influenced within wide limits by introducing foreign atoms from a different chemical group (doping) (Wikipedia, keyword semiconductor).

[0013] If transparency is important for the use and application of electrodes, the use of tin-doped indium oxide (ITO) is known.

[0014] Von Devkota, J. et al: Sensors & Actuators, B. Chemical 354 (2022) 131229 investigated a SAW sensor for the detection of hydrogen in gases at medium temperatures. Indium oxide (IO) and ITO were used as electrode materials.

[0015] For high-temperature applications, bond-stable ITO / Pt films were investigated as electrodes of the SAW device according to Li, H. et al: J. of Nanomat. Vol. 2022, Art. ID 2599390.

[0016] Von Idhaiam, KSV et al: Sensors 2022, 22,2165 investigated ceramic wireless temperature sensors with ITO electrodes that can be used at temperatures from 200 to 1200 °C.

[0017] According to Pan, Y. et al: J. of Electronic Mat., Vot. 46, No. 11, 2017, RuAl₂ is known as an intermetallic semiconducting compound. However, the influence of vacancies on the electronic and mechanical properties of RuAl₂ is unknown. Understanding the vacancy patterns provides information about the electronic properties of RuAl₂ and how these properties can be improved.

[0018] Similarly, Mandrus, D. et al. (Phys. Rev. B, Vol. 58, No. 7, August 15, 1998) reported measurements of the resistivity, thermal power, thermal conductivity, Hall coefficient, and magnetic susceptibility of RuAl2 over a wide temperature range. They found that at low temperatures, RuAl2 behaves like a semimetal with low charge carrier density. As the temperature increases, RuAl2 behaves like a semiconductor. They also found that the electrical properties of RuAl2 are not good enough to make it an attractive thermoelectric material.

[0019] Furthermore, from DE 10 2022 117 507 A1, a material system for the production of electrodes in microacoustic components and / or antennas is known, which contains at least two layers, one layer of which is made of Ru (100 At.-%)-x Al xwith x = 5 - 80 atm% and the second layer contains Al, Ru, Cu, Ti, Ta, Ni, Pt, Ir, Rh and / or Pd, or contains at least one layer containing Ru y M (100At-%)-y Al x containing M = Cu, Ti, Ta, Ni, Pt, Ir, Rh and / or Pd, and with y > 50 to < 100 at.-% and with x = 5 - 80 at.-%, and from which electrodes in microacoustic components and / or antennas are produced by thermal conditioning.

[0020] A disadvantage of the known solutions of the prior art is that such electrodes cannot be used for a wide temperature range and, in particular, not for high temperatures with good microacoustic properties.

[0021] The object of the present invention is therefore to provide electrodes for microacoustic components that can be used in a wide temperature range and in particular for high temperatures and that have good microacoustic properties.

[0022] The problem is solved by the invention specified in the claims. Advantageous embodiments are the subject of the dependent claims, and the invention also includes combinations of the individual dependent claims in the sense of an AND conjunction, provided they are not mutually exclusive.

[0023] In the electrodes for microacoustic components according to the invention, each individual electrode consists of at least one stack of layers comprising at least two layers, one of which is at least predominantly a structure of a material of the formula Ru ((100At.-%)-x) Al x with x = 5-80 atm% and / or made of a material of the formula (Ru y M ((100At.-%)-y) ) 100-x Al x , with M = Cu, Ti, Ta, Ni, Pt, Ir, Rh and / or Pd, and with y ≥ 50 to < 100 At.-% and with x = 5 - 80 At.-% and the second layer consists at least predominantly of semiconducting RuAl2.

[0024] Advantageously, the layer stack for the at least one electrode is arranged on a piezoelectric substrate and / or on a piezoelectric layer on a non-piezoelectric substrate and / or on a non-piezoelectric substrate on a piezoelectric layer.

[0025] Further advantageously, the layer stack for the at least one electrode is arranged on a substrate which is in the form of a wafer, a plate or a film or a microchip, and the substrate - made of glass / glasses / ceramics, such as SiO2, Al2O3, Si3N4, TiN, SiN, borosilicate glass, or - made from piezoelectric materials such as quartz, LiNbO3, black-LiNbO3, yellow-black LiNbO3, LiTaO3, AIN, Sc-AIN, ZnO, CTGS, langasite, gallium orthophosphate, or - made of metals / metal alloys, such as Cu, Ti, Ta, TiAl, CuTi, or - from semiconductors such as Si, GaAs, InAs, GaN, or - consists of combinations of these materials and / or is present as a layer of the aforementioned materials on another substrate, wherein Ca3TaGa3Si2O is advantageously present as a substrate or as a layer on a substrate 14 (CTGS) or La3Ga5SiO 14 (LGS) is present.

[0026] It is also advantageous that one or more additional layers are present in the layer stack as barrier layers, cover layers, adhesive layers or protective layers, each made of oxides, nitrides, carbides, advantageously made of SiO2, Al2O3, Si3N4, SiAlON, TiN, AIN and / or SiC.

[0027] And, advantageously, one or more AIN layers and / or SiO2 layers are still present in the layer stack. It is also advantageous if the second layer contains one or more elemental semiconductor materials, compound semiconductor materials and / or doped semiconductor materials in addition to RuAl2, wherein the elemental semiconductor materials are further advantageously Si, Ge, Se, B, Te, C and / or the compound semiconductor materials are GaP, GaAs, InP, InSb, InAs, GaSb, GaN, AIN, InN, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, BeSe, BeTe, HgS, GaS, GaSe, GaTe, InS, InSe, InTe, SiC, SiGe and / or SnTe.

[0028] Furthermore, it is advantageous if the material of at least the second layer is present in the form of binary and / or ternary phases.

[0029] It is also advantageous if the thickness of the layer stack is between 40 and 900 nm.

[0030] It is also advantageous if the layer thickness of the layer containing at least predominantly RuAl2 is greater than the layer thickness of all other layers in the layer stack according to the invention combined.

[0031] It is also advantageous if the electrodes in microacoustic components are applicable within a temperature range of 4 to 1400 K for the operating temperature.

[0032] It is also advantageous if the electrodes have been subjected to thermal conditioning, wherein the electrodes are advantageously subjected to thermal conditioning at a temperature between 800 and 1400 K for a period of 10 to 50 h, preferably 10 to 20 h, and / or wherein the thermal conditioning is carried out, at least in a shortened time, directly during the production of the layer stack or subsequently.

[0033] With the present invention, it is possible for the first time to specify electrodes for microacoustic components that can be used in a wide temperature range and in particular for high temperatures and have good microacoustic properties.

[0034] According to the invention, this is achieved by electrodes for microacoustic components, in which each individual electrode consists of at least one stack of layers of at least two layers.

[0035] Advantageously, more than two layers can be present in the layer stack, wherein further functional layers and / or one or more additional layers as barrier layers, cover layers, adhesive layers or protective layers, each made of oxides, nitrides, carbides, or more advantageously of SiO2, Al2O3, Si3N4, SiAlON, TiN, AIN and / or SiC, are present above or below the layers or the layer stack.

[0036] In the context of the present invention, functional layers are understood to be layers made of a material that realize the electrode function as an electrically conductive material.

[0037] It is also advantageous to have one or more AIN layers and / or SiO2 layers present as an additional layer in the layer stack.

[0038] The use of barrier and cover layers for the electrodes according to the invention is advantageous because it protects the functional materials of the layer stack and / or the substrate or layers that are exposed to environmental conditions during use, and in particular to temperature increases or decreases, and prevents undesirable chemical reactions of the layer materials that could disrupt the functionality of the microacoustic component or lead to its complete failure.

[0039] Furthermore, the electrodes according to the invention are advantageously arranged on a piezoelectric substrate and / or on a piezoelectric layer on a non-piezoelectric substrate and / or on a non-piezoelectric substrate under a piezoelectric layer.

[0040] It is also advantageous that the layer stack for the electrodes according to the invention can be arranged on a substrate which is in the form of a wafer, a plate or a film or a microchip, and the substrate - made of glass / glasses / ceramics, such as SiO2, Al2O3, Si3N4, TiN, SiN, borosilicate glass, or - made from piezoelectric materials such as quartz, LiNbO3, black-LiNbO3, yellow-black LiNbO3, LiTaO3, AIN, Sc-AIN, ZnO, CTGS, langasite, gallium orthophosphate, or - made of metals / metal alloys, such as Cu, Ti, Ta, TiAl, CuTi, or - from semiconductors such as Si, GaAs, InAs, GaN, or - consists of combinations of these materials.

[0041] The materials mentioned as substrates can also be present as a layer on another substrate.

[0042] Even more advantageously, Ca3TaGa3Si2O can be used as a substrate or as a layer on a substrate. 14 (CTGS) or La3Ga5SiO 14 (LGS) available.

[0043] According to the invention, the layer stack for the electrodes for the microacoustic components consists of at least one layer which at least predominantly has a structure made of a material of the formula Ru ((100At.-%)-x) Al x with x = 5-80 atm% and / or made of a material of the formula (Ru y M ((100At.-%)-y) ) 100-x Al x , with M = Cu, Ti, Ta, Ni, Pt, Ir, Rh and / or Pd, and with y ≥ 50 to < 100 at.-% and with x = 5 - 80 at.-%.

[0044] Advantageously, a material is used for the one layer where x = 40 - 60 at.-% and / or y > 70 to ≤ 90 at.-% and / or M = Ti, Ni and / or Pt.

[0045] Furthermore according to the invention, the layer stack for the electrodes for the microacoustic components consists, in addition to the aforementioned at least one layer, of at least one further layer, which consists at least predominantly of RuAl2.

[0046] The use of RuAl2 as the predominant second layer material is of particular importance according to the invention, since RuAl2 has semiconducting properties.

[0047] In addition to RuAl2, this second layer may contain one or more elemental semiconductor materials, compound semiconductor materials and / or doped semiconductor materials.

[0048] Advantageously, the material of at least the second layer can be present in the form of binary and / or ternary phases.

[0049] Advantageously, elemental semiconductor materials such as Si, Ge, Se, B, Te, C and / or compound semiconductor materials such as GaP, GaAs, InP, InSb, InAs, GaSb, GaN, AIN, InN, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, BeSe, BeTe, HgS, GaS, GaSe, GaTe, InS, InSe, InTe, SiC, SiGe and / or SnTe may also be present.

[0050] Advantageously, the thickness of the layer stack of the electrodes according to the invention is 40 to 900 nm.

[0051] Advantageously, the layer thickness of the layer containing predominantly RuAl2 is greater than the layer thickness of all other layers in the layer stack according to the invention combined, which makes the semiconducting properties of this layer particularly advantageous.

[0052] The electrodes for the microacoustic components are also advantageously applicable in a temperature range of 4 to 1400 K for the operating temperature.

[0053] The electrodes can be manufactured using known deposition methods such as sputtering, ALD, CVC or PVD.

[0054] The electrodes according to the invention can be subjected to thermal conditioning during or after their manufacture.

[0055] If RuAl2 is directly deposited during the production of the electrodes, no thermal conditioning is required, or a shorter thermal conditioning period is possible to further optimize the functionality of the electrodes.

[0056] In the case that only precursors for RuAl2 are deposited during the production of the electrodes, thermal conditioning is required, which can be carried out directly during the production of the electrodes or afterwards, for example before or after structuring.

[0057] Thermal conditioning can be carried out at a temperature between 800 and 1400 K for a duration of 10 to 50 hours, advantageously from 10 to 20 hours. If the thermal conditioning is carried out for a shorter time during the production of the layer stack, it can be performed at a lower temperature, between 600 and 1000 K, for the duration of the production process.

[0058] The electrodes according to the invention have the special feature that at least one layer consists of a metallic material and the at least second layer consists of an electrically semiconducting material.

[0059] This means that when the electrodes according to the invention are used in temperature ranges where the metals exhibit good electrical conductivity and good electrical properties, but also in temperature ranges where the metals lose their electrical conductivity more or less rapidly, the electrical conductivity of the electrodes according to the invention is taken over by the electrically semiconducting materials. As a result, the electrodes according to the invention can be used over a very wide temperature range, such as between 4 and 1400 K, and especially at high temperatures, without their electrical conductivity decreasing or being lost.

[0060] In the context of the present invention, high temperatures are understood to mean temperatures relating to the operating temperatures of the electrodes according to the invention and which are limited only by the melting temperatures of the respective materials used.

[0061] The electrically semiconducting materials of the second layer can be, in particular, those that exhibit the low electrical resistance required for the application of the semiconductor material and the most pronounced negative temperature coefficient possible. These properties can be adjusted, for example, through appropriate bulk properties and / or doping.

[0062] The use of predominantly RuAl2 in the second layer is also advantageous for the electrodes according to the invention because RuAl2 has high thermomechanical stability and high resistance to oxidation and corrosion.

[0063] The use of predominantly RuAl2 in at least the second layer is particularly advantageous because no additional materials are introduced into the layer stack, and thus all layers in the layer stack can be directly deposited or generated by the interdiffusion of Ru and Al in the layers during a heat treatment of the layer stack in the boundary layers.

[0064] Due to the negative temperature coefficients of the at least second layer made predominantly of RuAl2, achieved when using electrically semiconducting material layers in the layer stack, variable layer thicknesses of the layer stack for the electrodes from 40 to 900 nm are possible.

[0065] Further advantages of the solution according to the invention are: a) Depending on the operating temperature and depending on the electrical resistances of the at least one metallic and one semiconducting layer, their thickness ratio can be chosen so that an approximately constant total resistance is obtained for the specific operating temperature range, so that the electrodes of the microacoustic component become insensitive to temperature fluctuations and thus stable in their electrically conductive function. b) If the proportion of the semiconducting layer predominates in the total resistance, the much greater change in resistance with temperature can result in a higher sensitivity of the microacoustic component to temperature changes and thus an increase in sensitivity. c) A microacoustic component can be designed by combining electrodes made of metallic and semiconducting layers in such a way that its function, e.g., the filtering of specific frequencies or the sensitivity to a measured quantity, can be specifically adjusted by actively changing its temperature. Thus, a single microacoustic component can perform different functions or have varying sensitivities to a measured quantity by actively changing its temperature, for example, using a heating source such as a resistance heater. In this way, a single microacoustic component can perform the function of several differently designed components.

[0066] The electrically semiconducting layer(s) can be isolated from the metallic layers by one or more barrier layers in such a way that no interdiffusion can occur between the layers during further heat treatments. Likewise, cover layers can be present to protect the layers or layer stack from oxidation or other degradation at high temperatures.

[0067] It is well known that the properties, and especially the readout frequency, of interdigital converters change with different thicknesses and widths of the finger electrodes. However, the thicknesses and widths of the finger electrodes of SAW devices are also crucial for their functionality, as their dimensions influence the readout frequency.

[0068] The layer stack of electrodes according to the invention can be deposited technically simply and quickly using known technologies such as sputtering, PVD, or CVD. Likewise, the necessary materials are significantly cheaper compared to platinum or other precious metal layers, thus making industrial mass production more cost-effective.

[0069] The microacoustic components with the electrodes according to the invention also exhibit improved acoustic properties, based on the advantageously significantly higher reflection factors compared to known high-temperature electrode metallizations of the same thickness made of platinum, which means that fewer reflectors are needed, allowing components with smaller dimensions to be manufactured.

[0070] The electrodes according to the invention, made from combined metallic and semiconducting layers, can open up new fields of application and possibilities for microacoustic components, especially with regard to operating and service temperatures.

[0071] The invention will now be explained in more detail using several exemplary embodiments. Example 1

[0072] On a single-crystal substrate containing a Y-section of catangasite (Ca3TaGa3Si2O) 14The microacoustic component (CTGS) consists of an interdigital transducer between two reflectors in the form of a resonant cavity. The substrate, interdigital transducer, and the two reflectors together form a one-port resonator device for surface acoustic waves. The one-port resonator comprises an interdigital transducer with 20 transducer cells and reflectors, each consisting of 50 reflector cells with collecting electrodes, where the cell length ratio of the interdigital transducer to the reflectors is 1.003.

[0073] On the substrate, a 20 nm thick SiO2 layer and a 20 nm thick AINO layer positioned on top of it are first deposited as barrier layers. SiO2 is sputtered from a SiO2 target at a temperature of 180 °C using a sputtering gas of O2 and Ar in a ratio of 1:6. AINO is sputtered from an AINO target using a sputtering gas of N2 and Ar in a ratio of 1:11.

[0074] Subsequently, 80 nm RuAl is produced from Ru and Al element targets by co-sputtering according to the formula Ru ((100At.-%)-x) Al x A 50 atm alloy is deposited. A 7 nm thick AINO layer is then deposited as a diffusion barrier. Finally, 100 nm of RuAl₂ alloy is deposited over this layer by co-sputtering from Ru and Al element targets. These layers are deposited at room temperature (20 °C).

[0075] All electrodes consist of a layer stack of 40 nm SiO2 / AlNO as a barrier to the substrate, 80 nm RuAl as a metallic conductive layer, 7 nm AINO as a diffusion barrier, and 100 nm semiconducting RuAl2 layer. The total thickness of the layer stack is 227 nm.

[0076] After the entire layer stack is deposited on the substrate, structuring is performed by ion beam etching. The finger width and spacing of the interdigital converter electrodes are 2.09 µm, resulting in an operating frequency of 330 MHz.

[0077] Subsequently, the entire layer stack is covered with a 20 nm thick layer of SiO2 and a 20 nm thick layer of AINO by sputtering under the above-mentioned conditions.

[0078] Afterwards, thermal conditioning is carried out at 700 °C for 10 hours in ultra-high vacuum.

[0079] The microacoustic component produced in this way, with the electrodes according to the invention, operates as a resonator without malfunction for at least 1000 hours at varying operating temperatures between room temperature and 900 °C. Example 2

[0080] On a single-crystal substrate containing a Y-section of catangasite (Ca3TaGa3Si2O)14 The microacoustic component (CTGS) consists of an interdigital transducer between two reflectors in the form of a resonant cavity. The substrate, interdigital transducer, and the two reflectors together form a one-port resonator device for surface acoustic waves. The one-port resonator comprises an interdigital transducer with 40 transducer cells and reflectors, which together consist of 60 reflector cells with collecting electrodes, where the cell length ratio of the interdigital transducer to the reflectors is 1.003.

[0081] On the substrate, a 20 nm thick SiO2 layer and a 20 nm thick AINO layer positioned on top of it are first deposited as barrier layers. SiO2 is sputtered from a SiO2 target at a temperature of 180 °C using a sputtering gas of O2 and Ar in a ratio of 1:6. AINO is sputtered from an AINO target using a sputtering gas of N2 and Ar in a ratio of 1:11.

[0082] After deposition of the barrier layers, the substrate is heated to 600 °C. A 150 nm thick RuAl₂ layer is deposited from Ru and Al element targets by co-sputtering. Subsequently, 7 nm of AINO is deposited. In the next step, 20 nm of Pt is deposited by sputtering from a Pt element target. Another 7 nm thick AINO barrier layer is then deposited. Finally, a 110 nm thick RuAl layer is deposited according to the formula Ru ((100At.-%)-x) Al x with x = 50 at.-% as an alloy of Ru and Al element targets by means of co-sputtering.

[0083] After the entire layer stack has been deposited on the substrate, structuring is carried out by ion beam etching. The finger width and spacing of the interdigital converter electrodes are 3.05 µm, resulting in an operating frequency of approximately 226 MHz.

[0084] Subsequently, the entire layer stack is covered with a 20 nm thick layer of SiO2 and a 20 nm thick layer of AINO by sputtering under the above-mentioned conditions.

[0085] The microacoustic component produced in this way, with the electrodes according to the invention, operates as a resonator without malfunction for at least 1000 hours at varying operating temperatures between room temperature and 900 °C.

Claims

[1] Electrodes for microacoustic components, wherein each individual electrode consists of at least one stack of at least two layers, one of which is at least predominantly a structure of a material of the formula Ru ((100At.-%)-x) Al x with x = 5-80 atm% and / or made of a material of the formula (Ru y M ((100At.-%)-y) ) 100-x Al x , with M = Cu, Ti, Ta, Ni, Pt, Ir, Rh and / or Pd, and with y ≥ 50 to < 100 At.-% and with x = 5 - 80 At.-% and the second layer consists at least predominantly of semiconducting RuAl2. [2] Electrodes according to claim 1, wherein the layer stack for the at least one electrode is arranged on a piezoelectric substrate and / or on a piezoelectric layer on a non-piezoelectric substrate and / or on a non-piezoelectric substrate on a piezoelectric layer. [3] Electrodes according to claim 1, wherein the layer stack for the at least one electrode is arranged on a substrate which is in the form of a wafer, a plate or a film or a microchip, and the substrate - made of glass / glasses / ceramics, such as SiO2, Al2O3, Si3N4, TiN, SiN, borosilicate glass, or - made from piezoelectric materials such as quartz, LiNbO3, black-LiNbO3, yellow-black LiNbO3, LiTaO3, AIN, Sc-AIN, ZnO, CTGS, langasite, gallium orthophosphate, or - made of metals / metal alloys, such as Cu, Ti, Ta, TiAl, CuTi, or - from semiconductors such as Si, GaAs, InAs, GaN, or - consists of combinations of these materials and / or is present as a layer of the aforementioned materials on another substrate. [4] Electrodes according to claim 3, wherein Ca3TaGa3Si2O is used as a substrate or as a layer on a substrate 14 (CTGS) or La3Ga5SiO 14 (LGS) is present. [5] Electrodes according to claim 1, wherein one or more additional layers are present in the layer stack as barrier layers, cover layers, adhesive layers or protective layers, each made of oxides, nitrides, carbides, advantageously made of SiO2, Al2O3, Si3N4, SiAlON, TiN, AIN and / or SiC. [6] Electrodes according to claim 1, wherein one or more AIN layers and / or SiO2 layers are further present in the layer stack. [7] Electrodes according to claim 1, wherein the second layer contains, in addition to RuAl2, one or more elemental semiconductor materials, compound semiconductor materials and / or doped semiconductor materials. [8] Electrodes according to claim 7, wherein the elemental semiconductor materials are Si, Ge, Se, B, Te, C and / or the compound semiconductor materials are GaP, GaAs, InP, InSb, InAs, GaSb, GaN, AIN, InN, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, BeSe, BeTe, HgS, GaS, GaSe, GaTe, InS, InSe, InTe, SiC, SiGe and / or SnTe. [9] Electrodes according to claim 1, wherein the material of the at least second layer is present in the form of binary and / or ternary phases. [10] Electrodes according to claim 1, wherein the thickness of the layer stack is 40 to 900 nm. [11] Electrodes according to claim 1, wherein the layer thickness of the layer containing at least predominantly RuAl2 is greater than the layer thickness of all other layers in the layer stack according to the invention combined. [12] Electrodes according to claim 1, wherein the electrodes are applicable in microacoustic components in a temperature range of the operating temperature from 4 to 1400 K. [13] Electrodes according to claim 1, wherein the electrodes have been subjected to thermal conditioning. [14] Electrodes according to claim 13, wherein the electrodes have been subjected to thermal conditioning at a temperature between 800 and 1400 K for a period of 10 to 50 h, advantageously 10 to 20 h. [15] Electrodes according to claim 13, wherein the thermal conditioning is carried out at least in a shortened time directly during the production of the layer stack or subsequently.