Tungsten/molybdenum thin films for application as interdigital transducers on high temperature stable piezoelectric substrates La3Ga5SiO14 and Ca3TaGa3Si2O14

• Refractory metals as IDT material for surface acoustic wave based high temperature sensors.
• Multilayer stacking in order to obtain low electrical resistivity and for tuning residual stress.
• New piezoelectric substrate for high temperature applications.
• High thermal stability with improved interfacial structure of multilayer films.

Sputter-deposited single, bi- and multilayers of W and Mo on Si substrate and high temperature stable piezoelectric substrates La3Ga5SiO14 (LGS) and Ca3TaGa3Si2O14 (CTGS) have been studied as electrode material for high temperature applications of surface acoustic wave (SAW) devices up to 800 °C. We show for the first time that the film resistivity lowers with decreasing the individual layer thickness of W in the W/Mo multilayer stack. This has been attributed to the low electron mean free path of W of about ∼4 nm as well as low electron scattering of the electrons at the W–Mo interface as a result of the formation of coherent interfaces. The stability of the films on Si and CTGS has been demonstrated up to 800 °C while the films on the LGS substrate fail already at 600 °C due to the inherent instability of the LGS substrate under vacuum annealing.