Y-36 Lithium Niobate Films Support f-Q of $5.5\cdot 10^{13}$ Hz in the 1-10 GHz Range

In this work we examine frequency-quality factor product $\boldsymbol{(f Q)}$ in the 1–10 GHz range in Y-36 Lithium Niobate (LN) through the use of High-overtone Bulk Acoustic Resonators (HBARs). HBAR structures allow for excitation and measurement of 100s of resonant frequencies from a single device, but typically have limits on upper frequency set by substrate thickness. We surpass this by fabricating HBARs with AIN transducers on top of suspended 20 $\boldsymbol{\mu} \mathbf{m}$ thick LN films. We probe the lower frequency spectrum using 500 $\boldsymbol{\mu}\mathbf{m}$ thick LN substrates. We then separate transducer and LN loss by modeling relative energy distribution using finite element analysis. We ultimately extract Y-36 LN $\boldsymbol{fQ}\mathbf{s}$ of $\boldsymbol{5.5\cdot 10^{13}}$ Hz for 20 $\boldsymbol{\mu}\mathbf{m}$ and 500 $\boldsymbol{\mu}\mathbf{m}$ thick LN films.