1 GHZ phononic band gap structure in air/aluminum nitride for symmetric lamb waves

This paper presents the first demonstration of a new class of phononic band gap (PBG) structures in air/aluminum nitride (AlN) at 1 GHz for symmetric lamb waves. The unit cell of this design utilizes an X-shaped air inclusion, instead of the conventional circular ones, in a solid host material. This novel design extends the operating frequency of the AlN PBG to the GHz range by using a structure minimum feature size of 750 nm, instead of 300 nm required by the conventional circular design, which therefore lessens the requirements during the photolithography process. The experimental results confirm the existence of a frequency band gap from 860 MHz to 1.2 GHz with maximum attenuation of 40 dB in the Γ-X direction. The amplitude of rejection and the frequency stop band is verified by COMSOL^® finite element method (FEM) simulation, proving, for the first time, that COMSOL^® can be employed for the full characterization of these structures. Low-loss acoustic delay lines in AlN were employed to form the reference response to which the PBG is compared. The integration of PBGs with these acoustic elements is a clear evidence of the possibility to synthesize miniaturized RF MEMS platforms in the ultra high frequency (UHF) range.