A Fin-Mounted A5-Mode Lithium Niobate Resonator at 27.58 GHz with $k^{2}$ of 4.4%, $Q_{\mathrm{p}}$ of 448, and FoM of 19.7

This work presents a fin-mounted A5-mode Lamb wave acoustic resonator based on Y128°-cut lithium niobite thin film for millimeter wave (mmWave) frequencies. By using a new fin-mounted structure and optimized electrode geometry, we designed and fabricated a spurious-free A5-mode resonator at 27.58 GHz with
$k^{2}$
of 4.4% and
$Q_{\mathrm{p}}$
of 448 to achieve a Figure of Merit (FoM) of 19.7, which is the highest in the frequency band around 30 GHz. In addition, a ladder-type filter for 3GPP Band n261 with a center frequency of 27.92 GHz was simulated based on the fin-mounted resonators. This demonstration provides a viable solution for high-frequency lithium niobate (LiNbO
3
or LN) acoustic resonators to be applied in the 5G Frequency Range 2 (FR2) frequency band.