As electronic devices shrink, there’s an increasing need for on-chip high-performance functions such as unidirectional waveguides (isolators), filters, and delay lines, especially those with key parameters that can be controlled on chip. A team of researchers from ZTH Zurich and Caltech is using silicon-nitride (SiN) nanomembranes that operate at high frequencies (10-20 MHz) as conduits for phonons, the acoustic-like waves passing through a solid or liquid material to build such devices (a situation very roughly analogous to surface-acoustic-wave, or SAW, devices). The nanoelectromechanical metamaterials (NEMM) include the voltage-controlled frequency tuning of the individual resonators.
They fabricated and tested high-frequency “topological” insulators with six lattice sites in a unit cell. The nanoelectromechanical lattice (NEML) design has periodically etched holes of 500 nm diameter in an extended honeycomb lattice, and insulating Si-rich silicon-nitride (SiNx) membranes (average thickness of ~79 nm) that form a phononic crystal with periodic, curved boundaries (see figure 1).