arXiv subjects

Stefano Valle

Publications and source records attributed to Stefano Valle.

4 recordsLinked to original sources

arXiv2021

Gallium nitride phononic integrated circuits for future RF front-ends

Achieving monolithic integration of passive acoustic wave devices, in particular RF filters, with active devices such as RF amplifiers and switches, is the optimal solution to meet the challenging communication requirements of mobile devices, especially as we move towards the 6G era. This requires a significant ($\approx$100x) reduction in the size of the RF passives, from mm$^2$ footprints in current devices to tens of $μm^2$ in future systems. Applying ideas from integrated photonics, we demonstrate that high frequency (>3 GHz) sound can be efficiently guided in $μ$m-scale gallium nitride(GaN) waveguides by exploiting the strong velocity contrast available in the GaN on silicon carbide (SiC) platform. Given the established use of GaN devices in RF amplifiers, our work opens up the possibility of building monolithically integrated RF front-ends in GaN-on-SiC.

physics.app-ph↗

arXiv2021

Cryogenic operation of MEMS-based suspended high overtone bulk acoustic wave resonators for microwave to optical signal transduction

Suspended high-overtone bulk acoustic wave resonators (HBARs) can serve as a viable optomechanical platform for efficient transduction of signals from the microwave to the optical frequency domain. In contrast to 1D nanobeam optomechanical crystals, HBARs benefit from very high RF to phonon injection efficiency ($η_{PIE}\approx$1) and low optical pump induced heating at cryogenic temperatures. By building small mode volume optical cavities around these devices, one can in principle achieve optomechanical cooperativities comparable to 1D nanobeam optomechanical crystals. In this work, we demonstrate cryogenic operation ($\approx$10 K) of such suspended HBAR devices and show classical signal modulation upto 3.5 GHz and response times $\approx$ 524 ns (for the fundamental mode at 340 MHz). While the transduction efficiency is currently limited by the material and device fabrication processes used in this work, we show that with reasonable modifications, efficient quantum transduction is within reach using this approach.

physics.optics↗

arXiv2019

High frequency guided mode resonances in mass-loaded, thin film gallium nitride surface acoustic wave devices

We demonstrate high-frequency (> 3 GHz), high quality factor radio frequency (RF) resonators in unreleased thin film gallium nitride (GaN) on sapphire and silicon carbide substrates by exploiting acoustic guided mode (Lamb wave) resonances. The associated energy trapping, due to mass loading from the gold electrodes, allows us to efficiently excite these resonances from a 50 $Ω$ input. The higher phase velocity, combined with lower electrode damping, enables high quality factors with moderate electrode pitch, and provides a viable route towards high-frequency piezoelectric devices. The GaN platform, with its ability to guide and localize high-frequency sound on the surface of a chip with access to high-performance active devices, will serve as a key building block for monolithically integrated RF front-ends.

physics.app-ph↗

arXiv2019

High-frequency, resonant acousto-optic modulators fabricated in a MEMS foundry platform

We report the design and characterization of high frequency, resonant acousto-optic modulators (AOM) in a MEMS foundry process. The doubly-resonant cavity design, with short ($L{\sim}10.5\, μm$) acoustic and optical cavity lengths, allows us to measure acousto-optic modulation at GHz frequencies with high modulation efficiency. In contrast to traditional AOMs, these devices rely on the perturbation induced by the displacement of cavity boundaries, which can be significantly enhanced in a suspended geometry. This platform can serve as the building block for fast 2D spatial light modulators (SLM), low-cost integrated free space optical links and optically enhanced low-noise RF receivers.

physics.app-ph↗