Room Temperature Nanophononics from 1 GHz – 110 GHz with Composite Piezoelectric Transducer HBARs

This paper presents epitaxially grown high overtone bulk acoustic resonators (epi-HBARs) demonstrating a dense spectrum of acoustic/phononic cavity overtone modes in an unprecedented range from 1 GHz to 110 GHz in a single device at room temperature. A critical element is the use of the composite structure of the ScAlN/AlN piezoelectric transducer to enable preferential transduction of higher order envelope modes. The strongest modes presented in this work lie in the 35 GHz – 50 GHz envelope, with Bode quality factor (Q Bode ) as high as 1000 (f × Q > 4×10 ¹³ Hz). This extreme embodiment of a multi-mode MEMS resonator can be developed into a platform for phonon spectroscopy and coupled-physics experiments.