Evidence of acoustic wave focusing in a microscale 630 MHz Aluminum Nitride phononic crystal waveguide

This paper reports on the evidence of acoustic wave focusing in an Aluminum Nitride (AlN) phononic crystal (PC) waveguide by means of a PC-tapered lens at 630 MHz. The PC array exhibits a complete stop band ranging from 560 to 680 MHz. The phononic band gap (PBG) waveguide, which is obtained by opening a pathway having a width equal to one lattice constant of the PC array, forms a pass-band centered around 630 MHz inside the PBG. Experimental results also indicate an enhancement in the pass-band transmission (centered at 630 MHz) when the PC waveguide is cascaded with a PC tapered lens with respect to a PBG waveguide located two lattice constants away from the acoustic source. Acoustic waves were launched in the phononic crystals by means of wideband AlN piezoelectric lamb wave transducers, which were integrated in the same plane of the PC. All the devices were micro-fabricated in a three-mask post-CMOS compatible process.