Laterally-excited silicon bulk acoustic resonators with sidewall AlN

This paper presents lateral silicon bulk acoustic resonators that are piezoelectrically excited using a thin layer of AlN on their vertical sidewalls. Sputtered AlN coats the sidewalls of a 20 um thick resonator conformally and uniformly, enabling the excitation of width-extensional modes in a suspended silicon microstructure using the longitudinal piezoelectric stress coefficient e₃₃. A motional resistance of ~35 Ω was measured in air for a 100 MHz silicon resonator, showing at least ten times smaller motional resistance compared to its capacitive counterpart.