Lithium niobate acoustic resonators operating beyond 900 $^\circ$C

In this paper, fundamental shear-horizontal SH0 mode Leaky Surface Acoustic Wave (LSAW) resonators on X-cut lithium niobate leveraging dense and robust electrodes such as gold and tungsten are demonstrated for extreme temperature operation in harsh environments. A novel post-processing approach based on in-band spurious mode tracking is introduced to enable reliable characterization under extreme parasitic loading during testing. Devices exhibit stable performance throughout multiple thermal cycles up to 1000 $^\circ$C, with an extrapolated electromechanical coupling coefficient kt2 = 25% and loaded quality factor Qp = 12 at 1000 $^\circ$C for tungsten devices, and kt2 = 17%, Qp = 100 at 900 $^\circ$C for gold devices.