Intrinsically switchable dual-band scandium-aluminum nitride Lamb-wave filter

A dual-band scandium-aluminum nitride (Sc${}_{0.28}$Al${}_{0.72}$N) Lamb-wave bandpass filter is implemented with intrinsically configurable center frequencies at 628 MHz and 1.07 GHz. The filter is created from electrical coupling of dual-mode resonators with complementary-switchable operation states defined by spatial polarization tuning in ferroelectric Sc${}_{0.28}$Al${}_{0.72}$N film. The resonators are created with patterning interdigitated transducers (IDT) on the top surface and exploit the floating bottom electrode for application of low-frequency polarization switching pulses. Switching polarization direction under consecutive electrode fingers in unified and alternating directions results in excitation of Lamb modes with different wavelengths equal and twice the IDT pitch size, with a frequency ratio of ≈1.70. The intrinsically configurable dual-band filter shows bandwidths of 11.9 MHz and 10.8 MHz, insertion losses of 2.6 and 2.8 dB, and on-off switching isolations of 12 and 9 dB, when operating at 628 MHz and 1.07 GHz, respectively. The intrinsic configuration of center frequency, enabled by ferroelectric polarization switching, highlights the potential of dual-band scandium-aluminum nitride Lamb-wave filters for creation of compact multifrequency spectral processors. (© 2022 Wiley‐VCH GmbH)