Realization of a phononic crystal operating at gigahertz frequencies

Abstract

We report on the experimental realization of a phononic crystal, designed to operate at gigahertz frequencies. Detailed studies of the structure have been performed using finite difference time domain method to determine effects of slab modes in finite-thickness slabs, thus enabling precise guidance of experimental efforts. In particular, we find the slab mode effects mitigated in ultrathin ͑thickness less than lattice periodicity͒ and ultrathick ͑thickness more than ten times lattice periodicity͒ slabs. Gigahertz-frequency phononic crystals are well poised to find usage as high-Q resonators, waveguides, and coupling elements in a variety of application areas including RF communications.

Thermal transport in phononic crystals and the observation of coherent phonon scattering at room temperature

“…8). It is particularly interesting that the hybrid model agrees well with the experimental data when the TMFP is large enough to cover 3-5 lattice periods, as this is similar to the literature-accepted bounds 10,[33][34][35][36][37][38][39] for the fewest and largest number of periods needed to observe PnC behaviour.…”

Realization of a 33 GHz phononic crystal fabricated in a freestanding membrane

“…Studies show that thin membranes produce a band gap that is unaltered by slab modes. 7 More specifically, the membrane must be thinner than the lattice spacing. For a 33 GHz PnC, the device layer must be less than or equal to 100 nm.…”

“…For 2D lattices, frequencies up to approximately 1 GHz have been demonstrated. 3,7 The lattice constants for the 2D PnCs were between 1.36 μm and 2.5 μm. Manipulation of THz frequency phonons requires a further reduction of the lattice constant of the inclusions and their radii.…”

“…1 The inclusions are typically cylindrical in shape and are filled with a fluid [2][3][4] or a solid. [5][6][7] Recent work shows that solid inclusions open wider band gaps than fluid inclusions in PnCs for a large range of frequencies. 1 Choosing the proper matrix and inclusion materials is also based on acoustic impedance, Z (Z = √ Eρ), where E is the elastic modulus of the material and ρ is the density; larger differences in Z lead to wider band gaps.…”

“…1 The highest operating frequencies reported for PnCs are in the 1-12 GHz range. 3,7,12,13 For PnCs with 1D lattices, measurements have been made up to 12 GHz. 13 Though appealing due to their simplicity, 1D lattices are not capable of opening band gaps nearly as wide as 2D lattices due to their decreased symmetry.…”