Super High Frequency Simple Process Flow Cross-Sectional Lamé Mode Resonators in 20% Scandium-Doped Aluminum Nitride

Abstract

This paper presents a promising device design for Super High Frequency (SHF) Lateral Field Excitation Cross-sectional Lame Mode Resonators (LFE CLMRs). Advancements over the state-of-the-art are made possible by harnessing the full capabilities of 20% Scandium doped Aluminum Nitride (ScAlN) through a very simple fabrication process that relies only on 2 masks (Fig. 2). The impact of top metal selection is explored, and metal reflector-based cavity definition is used to ease etching tolerance in fabrication. These design considerations result in SHF devices in which ScAlN can be deposited on bare Si, ScAlN sidewall definition is not critical, and piezoelectric film thickness of $1.0-0.5 \mu \mathrm{m}$ can be used to define resonators operating between 3 and 6 GHz. Design is experimentally validated through fabrication of 20% ScAlN resonators operating around 3 GHz with static capacitance of 0.7 pF—for use in $50 \Omega$ matched filters—with electromechanical coupling coefficient ( $k_{t}{}^{2}$ ) of 5.0-6.5%, and quality factor at series resonance $(Q_{s}) > 500$ .