Designing a hypersonic filter on a nanophononic crystal platform

We are reporting the design of a new hypersonic filter with the operating frequency of ~ 2-7 GHz, by means of a 2D nanophononic crystal (NPnC) platform. The 2D NPnC is composed of a periodic array of infinitely long nanorods of silicon, arranged in a square lattice of constant a₀=96 nm, in air background. The radii of the CMOS compatible Silicon nanorods are r₀=40 nm. Mechanical waves propagating through this particular NPnC are of hypersonic type. For a given crystal structure, there may exists a phononic bandgap (PnBG) over a frequency range in which normally incident hypersonic waves cannot propagate. Existence and the size of this phononic bandgap depend on the density contrast, sound velocity contrast, lattice fill factor and topology. The calculated band structure has two complete PnBGs over two frequency ranges of 1.75 GHz ≤ f ≤ 2.25 GHz and 6.87 GHz ≤ f ≤ 7 GHz. Simulations are done by employing plane wave expansion (PWE) and finite element (FE) methods.