Periodically Poled Aluminum Scandium Nitride Lamb-Wave Resonators Excited by Fully Covered Electrodes

Ferroelectric characteristics of aluminum scandium nitride (Al1−xScxN) enable area-selective poling for excitation of in-plane acoustic resonance modes without the need for patterned interdigital transducer (IDT) electrodes. This work presents Lamb-wave resonators created by periodic poling of a 195-nm-thick Al0.7Sc0.3N film and excited using fully covered electrodes. The polarization is switched every half wavelength using sacrificial mode-mediating electrodes, and the resulting poling pattern is verified using polarization-selective wet etching. The performance is compared with uniformly poled counterparts employing IDTs to excite the same Lamb modes. At a wavelength of 4.8 µm, a periodically poled resonator operating at 1.45 GHz exhibits a quality factor (Q) of 912, approximately 15% higher than that of the IDT-based counterpart, and an electromechanical coupling coefficient (kt2) of 5.8%, representing a 0.3% absolute reduction compared to the IDT device. The larger transduction area of the unpatterned electrodes also yields an approximately 8 dB higher admittance. Across wavelengths from 4.8 to 16 µm, the periodically poled resonators exhibit 14–50% higher Q (3–33% higher f·Q product), while IDT-based resonators show fewer spurious modes. These results indicate the potential of periodically poled Lamb-wave resonators for compact multi-frequency filter arrays, provided that their spurious modes can be suppressed.