5 GHz laterally‐excited bulk‐wave resonators (XBARs) based on thin platelets of lithium niobate

Abstract

In a free-standing 400-nm-thick platelet of crystalline ZY-LiNbO 3 , narrow electrodes (500 nm) placed periodically with a pitch of a few microns can eXcite standing shear-wave bulk acoustic resonances (XBARs), by utilising lateral electric fields oriented parallel to the crystalline Y-axis and parallel to the plane of the platelet. The resonance frequency of ∼4800 MHz is determined mainly by the platelet thickness and only weakly depends on the electrode width and the pitch. Simulations show quality-factors (Q) at resonance and anti-resonance higher than 1000. Measurements of the first fabricated devices show a resonance Q-factor ∼300, strong piezoelectric coupling ∼25%, (indicated by the large Resonance-antiResonance frequency spacing, ∼11%) and an impedance at resonance of a few ohms. The static capacitance of the devices, corresponds to the imaginary part of the impedance ∼100 Ω. This device opens the possibility for the development of low-loss, wide band, RF filters in the 3-6 GHz range for 4th and 5th generation (4G/5G) mobile phones. XBARs can be produced using standard optical photolithography and MEMS processes. The 3rd, 5th, 7th, and 9th harmonics were observed, up to 38 GHz, and are also promising for high frequency filter design.

Enabling Higher Order Lamb Wave Acoustic Devices With Complementarily Oriented Piezoelectric Thin Films

“…Similarly, the degradation from the perceived k 2 is due to the existence of the in-band spurious modes (Modes 2-9 in Table V). Compared to prior A1 mode resonators in conventional Z-cut LiNbO 3 above 3 GHz [38]- [40], the S2 mode resonator in the COP platform shows an improved Q (above 600) with a similar k 2 (above 20%). The S6 resonance at 9.045 GHz shows a perceived k 2 of 3.80% and a 3-dB Q of 660 [ Fig.…”

“…For more information, see https://creativecommons.org/licenses/by/4.0/ LiNbO 3 for operation beyond 3 GHz. The thinner film leads to more severe surface losses [16], thus limiting the quality factor (Q) of the demonstrated A1 resonators (below 400 [38]- [40]), and the propagation loss (PL) of A1 ADLs (above 0.02 dB/μm [47]). Moreover, lateral field excited A1 devices with spurious mode suppression have a small capacitance per unit area [48].…”

5-GHz Antisymmetric Mode Acoustic Delay Lines in Lithium Niobate Thin Film

“…Recently, acoustic devices using the first-order antisymmetric (A1) mode in Z-cut LiNbO3 have been reported with high k 2 and low loss above 4 GHz [57]- [59]. Different from SH0 and S0, A1 is higher-order in the thickness direction, thus significantly enhancing vp in in-plane dimensions [60] and improving frequency scalability.…”

Dissipation Analysis Methods and Q-Enhancement Strategies in Piezoelectric MEMS Laterally Vibrating Resonators: A Review

“…Recently, sc-LN LVRs utilizing the first-order asymmetric modes (A 1 ) have gained considerable attention due to its high acoustic velocity (>10,000 m/s) and large electromechanical coupling (>10%) [ 125 , 126 ]. It has been demonstrated that sc-LN LVRs operating in A 1 mode can achieve resonant frequency as high as 5 GHz with k eff 2 of 25% [ 127 , 128 ]. However, the reported Qs of sc-LN LVRs remain comparatively low relative to AlN LVRs.…”