Ultra high frequency resonant cavity in Aluminum Nitride phononic crystals

This paper presents the first experimental demonstration of the ultra high frequency (UHF) phononic crystal (PnC) resonant cavities in Aluminum Nitride (AlN) sputtered films. Two types of square lattice designs were investigated: the conventional PnC with air circular scatterer and the inverse acoustic band gap (IABG) structure. By removing 3 periods of PnC columns in the array, a cavity is formed to trap acoustic energy within, which results in a resonance in the frequency domain. The designed PnC cavities exhibited resonant frequencies about 660 MHz with quality factors of 675 and 220 for the conventional circular air scatterer PnCs and IABG, respectively. The IABG cavity also showed another resonance at a higher frequency of 916 MHz with Q of 525. More intriguingly, the cavities displayed low intrinsic acoustic loss (as low as 4 dB in the normalized response). These preliminary results are an important stepping stone in showing potential use of PnC for signal processing and frequency referencing.