A Multimodal Piezoelectric Vertical Sidewall Architecture for Scalable In‐Plane NEMS Resonators

ABSTRACT The continued scaling of wireless communication systems toward higher operating frequencies and increased data traffic places growing demands on radio‐frequency (RF) resonators in terms of footprint, multiband capability, and power efficiency. While piezoelectric microelectromechanical systems (MEMS) resonators based on aluminum nitride (AlN) represent mature technology, their conventional planar designs rely on thickness‐defined frequency, which limits their chip‐level integration. We report a unified vertical in‐plane piezoelectric platform capable of multimodal lithography‐defined resonant operation using a fully released, symmetric sidewall transducer design. The resonator is first validated at the microscale, demonstrating a clear length‐extensional resonance response. This foundation is used for a further transition into the nanoscale high‐frequency regime via a cavities‐first process flow, with conformal atomic layer deposition (ALD) of AlN to realize piezo‐transducer stacks on high‐aspect‐ratio vertical surfaces. The impact of fabrication‐induced deviations, including silicon sidewall taper, process‐specific patterning approach, and AlN crystal quality, is studied using finite‐element reverse modeling. The resulting structures preserve first‐order width‐extensional operation at X‐band (∼10 GHz), while the current properties of ALD‐AlN primarily limit electromechanical performance. These results establish a scalable nanoscale fabrication and design platform for a new generation of in‐plane piezoelectric NEMS resonators and adaptive RF components.