*Article* **Dual-Mode Scandium-Aluminum Nitride Lamb-Wave Resonators Using Reconfigurable Periodic Poling**

**Sushant Rassay , Dicheng Mo and Roozbeh Tabrizian \***

Electrical and Computer Engineering Department, University of Florida, Gainesville, FL 32603, USA; sushantrassay@ufl.edu (S.R.); dicheng.mo@ufl.edu (D.M.)

**\*** Correspondence: rtabrizian@ece.ufl.edu

**Abstract:** This paper presents the use of ferroelectric behavior in scandium–aluminum nitride (ScxAl1−xN) to create dual-mode Lamb-wave resonators for the realization of intrinsically configurable radio-frequency front-end systems. An integrated array of intrinsically switchable dual-mode Lamb-wave resonators with frequencies covering the 0.45–3 GHz spectrum. The resonators are created in ferroelectric scandium–aluminum nitride (Sc0.28Al0.72N) film and rely on period poling for intrinsic configuration between Lamb modes with highly different wavelengths and frequencies. A comprehensive analytical model is presented, formulating intrinsically switchable dual-mode operation and providing closed-form derivation of electromechanical coupling (*k* 2 *t* ) in the two resonance modes as a function of electrode dimensions and scandium content. Fabricated resonator prototypes show *k* 2 *t* s as high as 4.95%, when operating in the first modes over 0.45–1.6 GHz, 2.23% when operating in the second mode of operation over 0.8–3 GHz, and series quality factors (*Qs*) over 300–800. Benefiting from lithographical frequency tailorability and intrinsic switchability that alleviate the need for external multiplexers, and large *k* 2 *t* and *Q*, dual-mode Sc0.28Al0.72N Lamb-wave resonators are promising candidates to realize single-chip multi-band reconfigurable spectral processors for radio-frequency front-ends of modern wireless systems.

**Keywords:** ferroelectric; scandium–aluminum nitride; Lamb-wave resonators; complementary switchable
