Reducing extrinsic damping of surface acoustic waves at gigahertz frequencies
Author(s)
Gelda, Dhruv
Sadhu, Jyothi
Ghossoub, Marc G.
Ertekin, Elif
Sinha, Sanjiv
Issue Date
2016-04-22
Keyword(s)
Surface Acoustic Waves
Gigahertz Frequencies
Extrinsic Damping
Bulk Radiation
Bragg Reflectors
Intrinsic Damping
Thermoelastic Damping
Quality Factor
Phonon Lifetime
Abstract
High-frequency surface acoustic waves (SAWs) in the GHz range can be generated using absorption from an ultrafast laser in a patterned metallic grating on a substrate. Reducing the attenuation at these frequencies can yield better sensors as well as enable them to better probe phonon and
electron-phonon interactions near surfaces. It is not clear from existing experiments which mechanisms dominate damping at high frequencies. We calculate damping times of SAWs due to various mechanism in the 1-100 GHz range to find that mechanical loading of the grating on the substrate dominates dissipation by radiating energy from the surface into the bulk. To overcome this and enable future measurements to probe intrinsic damping, we propose incorporating distributed acoustic
Bragg reflectors (DABRs) in the experimental structure. Layers of alternating materials with contrasting acoustic impedances embedded a wavelength away from the surface serve to reflect energy
back to the surface. Using numerical simulations, we show that a single Bragg reflector is sufficient to increase the energy density at the surface by more than ve times. We quantify the resulting damping time to find that it is longer than the intrinsic damping time. The proposed structure can
enable future measurements of intrinsic damping in SAWs at ~ 100 GHz.
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