Buckling-Mediated Phase Transitions in Nano-Electromechanical Phononic Waveguides

Abstract

Waveguides for mechanical signal transmission in the megahertz to gigahertz regimes enable on-chip phononic circuitry, which brings new capabilities complementing photonics and electronics. Lattices of coupled nano-electromechanical drumhead resonators are suitable for these waveguides due to their high Q-factor and precisely engineered band structure. Here, we show that thermally induced elastic buckling of such resonators causes a phase transition in the waveguide leading to reversible control of signal transmission. Specifically, when cooled, the lowest-frequency transmission band associated with the primary acoustic mode vanishes. Experiments show the merging of the lower and upper band gaps, such that signals remain localized at the excitation boundary. Numerical simulations show that the temperature-induced destruction of the pass band is a result of inhomogeneous elastic buckling, which disturbs the waveguide’s periodicity and suppresses the wave propagation. Mechanical phase transitions in waveguides open opportunities for drastic phononic band reconfiguration in on-chip circuitry and computing.

Phonon Engineering of Micro‐ and Nanophononic Crystals and Acoustic Metamaterials: A Review

“…[ 206 ] Midtvedt et al [ 207 ] achieved GHz frequency tuning and coupling by distorting the periodicity of pinned and atomically thin membranes due to geometric nonlinearity. Kim et al [ 208 ] used thermally induced buckling due to nonlinearity in nanoelectromechanical phononic waveguides to modulate phonon dispersion relation. Although the membrane itself (made of silicon nitride) is not hyperelastic material in this study, the dispersion‐tuning capability is also a result of a similar mechanical instability mechanism due to material and geometric nonlinearity.…”

“…Once in the postbuckled state, the second‐pass frequency rises due to an increase in the total bending with an additional in‐plane compression. [ 208 ] Kurosu et al [ 190 ] and Hatanaka et al [ 209 ] have experimentally demonstrated four‐wave mixing due to mechanical Kerr nonlinearity [ 210 ] at the microscale, which promises the possibility of generating and fully manipulating a range of nonlinear phenomena using on‐chip mechanical platforms. Specifically, the spectral response of a continuous wave (signal, ) and the intense pulse (pump, ) excited from the IDT generate a new signal (idler, ) due to the four‐wave mixing process, which satisfies the energy‐conservation requirement , Figure 7e–i.…”

“…a–d) Reproduced with permission. [ 208 ] Copyright 2021, American Chemical Society. e) A schematic showing the device and the measurement setup for an on‐chip nanoelectromechanical waveguide structure with an IDT.…”

“…where f λ 0 is the equilibrium Bose-Einstein distribution and v λ is the particle velocity in the state λ. Here the usual assumption of the local equilibrium is made on the left-hand side of the [208] Copyright 2021, American Chemical Society. e) A schematic showing the device and the measurement setup for an on-chip nanoelectromechanical waveguide structure with an IDT.…”

Relaxation and dynamics of high-stress pre-displaced string resonators

“…In engineering, buckling may result in catastrophic failure of structures, but in micromechanics buckling can also be harnessed to implement a variety of functions in micromechanical devices, e.g. for information storage [27,28] or to control propagation of waves [29]. As explained above, when pre-displaced strings relax towards the line connecting the clamping points, their curve length shortens and the tensile stress decreases.…”