Phononic microdevices are critical components of today’s technology ecosystem, serving as sensors, transducers, frequency synthesizers, and radio-frequency (RF) signal processing systems. This talk will present recent advances in high-frequency phononic technology, encompassing a combination of novel material systems, device physics, designs, nanofabrication, and high-precision metrology. Such advances at the device level enable continuous innovation at higher levels of abstraction, leading to novel technologies that are more efficient, functionally agile, smarter, and better connected.
Phononic devices and integrated systems involving phononics, electronics and photonics have recently been implemented using piezoelectric semiconductors such as GaN, GaAs, n-AlN, and 4H-SiC. To illustrate the capabilities of these systems, I will present my work on GaN micromechanical resonators (with integrated CNT or Plasmonic absorbers) as low-noise infrared sensor arrays. I will discuss phonon-electron interactions in piezoelectric semiconductors, and the conditions for achieving directional attenuation/amplification of phonons. My talk will present the first measurements of acoustoelectric amplification in GaN resonant cavities, leading to the design of mechanically amplified RF oscillators. I will discuss energy dissipation mechanisms that impose fundamental limits on the performance of phononic devices, and strategies to mitigate or eliminate them. I will present our recently developed Scanning Dynamic Strain Microscopy technique that has enabled the first direct measurements of high-frequency strain, making it possible to meaningfully quantify tether loss. I will highlight the successful use of phononic crystal (PnC) tethers for mitigating this tether loss, resulting in resonators operating at the intrinsic loss limit.
I will briefly discuss future directions for phononic microsystems, including multifunctional sensors, travelling-wave acoustic amplifiers, non-reciprocal RF communication systems, and electrically-pumped coherent acoustic phonon (CAP) sources. CAP sources can enable compact phonon spectroscopy and on-chip phononics, key technologies for a new generation of MEMS and microsystems operating in the underutilized GHz-THz spectrum.