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DE-102024119648-B4 - Electrodes for microacoustic components

DE102024119648B4DE 102024119648 B4DE102024119648 B4DE 102024119648B4DE-102024119648-B4

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 has at least a predominantly microstructure of a material of the formula Ru ((100At.-%)-x) Al x with x = 5-80 At.-% and/or 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 RuAl 2 .

Inventors

  • Marietta Seifert
  • Thomas Gemming
  • Hagen Schmidt

Assignees

  • LEIBNIZ-INSTITUT FÜR FESTKÖRPER- UND WERKSTOFFFORSCHUNG DRESDEN E.V.

Dates

Publication Date
20260513
Application Date
20240710

Claims (15)

  1. 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 has at least a predominantly microstructure of a material of the formula Ru ((100At.-%)-x) Al x with x = 5-80 At.-% and/or 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 RuAl 2 .
  2. Electrodes after Claim 1 , in which 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 after Claim 1 , in which 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 consists of glass/glasses/ceramics/ceramics, such as SiO2 , Al2O3 , Si3N4 , TiN , SiN, borosilicate glass, or of piezoelectrics, such as quartz, LiNbO3 , black- LiNbO3 , yellow-black LiNbO3 , LiTaO3 , AIN, Sc-AIN, ZnO, CTGS, langasite, gallium orthophosphate, or of metals/metal alloys, such as Cu, Ti, Ta, TiAl, CuTi, or of semiconductors, such as Si, GaAs, InAs, GaN, or of combinations of these materials and/or is present as a layer of the aforementioned materials on another substrate.
  4. Electrodes after Claim 3 , in which Ca 3 TaGa 3 Si 2 O 14 (CTGS) or La 3 Ga 5 SiO 14 (LGS) is present as a substrate or as a layer on a substrate.
  5. Electrodes after Claim 1 , in which 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 SiO 2 , Al 2 O 3 , Si 3 N 4 , SiAlON, TiN, AIN and/or SiC.
  6. Electrodes after Claim 1 , in which one or more AIN layers and/or SiO2 layers are still present in the layer stack.
  7. Electrodes after Claim 1 , in which the second layer contains one or more elemental semiconductor materials, compound semiconductor materials and/or doped semiconductor materials in addition to RuAl 2 .
  8. Electrodes after Claim 7 , in which the elemental semiconductor materials Si, Ge, Se, B, Te, C and/or the compound semiconductor materials 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 are present.
  9. Electrodes after Claim 1 , in which the material of at least the second layer is present in the form of binary and/or ternary phases.
  10. Electrodes after Claim 1 , where the thickness of the layer stack is 40 to 900 nm.
  11. Electrodes after Claim 1 , in which the layer thickness of the layer containing at least predominantly RuAl 2 is greater than the layer thickness of all other layers in the layer stack according to the invention combined.
  12. Electrodes after Claim 1 , where the electrodes in microacoustic components are applicable in a temperature range of 4 to 1400 K.
  13. Electrodes after Claim 1 , in which the electrodes have been subjected to thermal conditioning.
  14. Electrodes after Claim 13 , in which 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 after Claim 13 , in which the thermal conditioning is carried out at least in a shortened time directly during the production of the layer stack or subsequently.

Description

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. SAW (surface acoustic wave) components are frequently used as microacoustic components. A SAW device generally consists of a piezoelectric single crystal on which at least one interdigital transducer (IDT) is applied, consisting of a pair of comb-shaped interlocking electrodes (whose prongs are also called fingers), which is manufactured using structuring methods in planar technology (e.g. wet or dry etching or lift-off technique) (Wikipedia, keyword Acoustic surface wave filter). 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. Such SAW components, especially as sensors, have been increasingly used for high-temperature applications in recent years. 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. 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 ). One material suitable for high-temperature stable interdigital converters is the RuAl alloy with its high melting point of 2050 °C ( Okamoto, HJ Phase Equilib, 1997, 18, 105 ) and high resistance to oxidation and corrosion. Therefore, in recent years the high-temperature stability of RuAl thin films on high-temperature stable piezoelectric Ca 3 TaGa 3 Si 2 O 14 -(CTGS) and La 3 Ga 5 SiO 14 -(LGS) substrates has been investigated. 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 a 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 ). 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 for SAW devices in high-temperature applications (Seifert, M.: Materials 2020, 13, 1605). Semiconductors are also known; these are solids whose electrical conductivity lies between that of electrical conductors (> 10⁴ S/cm) and that of insulators (< 10⁸ S/cm). An important characteristic of semiconductors is that their electrical conductivity increases with rising temperature. Near absolute zero, semiconductors are insulators. Furthermore, by introducing foreign atoms from a different chemical group (doping), the conductivity and conduction characteristics (electron and hole conduction) can be selectively influenced within wide limits (Wikipedia, entry: Semiconductor). If transparency is important for the use and application of electrodes, the use of tin-doped indium oxide (ITO) is known. From Devkota, J. et al: Sensors & Actuators, B. Chemical 354 (2022) 131229 A SAW sensor for detecting hydrogen in gases at medium temperatures has been investigated. Indium oxide (IO) and ITO were used as electrode materials for this purpose. For high-temperature applications, according to Li, H. et al: J. of Nanomat. Vol. 2022, Art. ID 2599390 Connection-stable ITO/Pt films were investigated as electrodes for the SAW device. From Idhaiam, KSV et al: Sensors 2022, 22,2165 Ceramic wireless temperature sensors with ITO electrodes were investigated, which can be used at temperatures from 200 to 1200 °C. According to Pan, Y. et al: J. of Electronic Mat., Vot. 46, No.11, 2017RuAl₂ is known as an intermetallic semiconducting compound. However, the influence of vacancies on the electronic and mechanical properties of RuAl₂ is unknown. Knowledge of the vacancies provides information about the electronic properties of RuAl₂ and how these can be improved. Likewise, have Mandrus, D. et al: Phys. Rev. B, Vol. 58, No. 7, August 15, 1998 -I reported on meas