arXiv subjects

Marco Liffredo

Publications and source records attributed to Marco Liffredo.

3 recordsLinked to original sources

arXiv2026

Loss Mechanisms in High-coherence Multimode Mechanical Resonators Coupled to Superconducting Circuits

Circuit quantum acoustodynamics (cQAD) devices have a wide range of applications in quantum science, all of which depend crucially on the quantum coherence of the mechanical subsystem. In this context, high-overtone bulk acoustic-wave resonators (HBARs) are particularly promising, since they have shown very high quality factors with negligible dephasing. However, the introduction of piezoelectric films, which are necessary for coupling to a superconducting circuit, can lead to additional loss channels, such as surface scattering and two-level systems (TLS). Here, we study the acoustic dissipation of HBAR resonators in cQAD systems and find that the defect density of the piezoelectric material and its interface with the bulk are limiting factors for the coherence. We measure acoustic modes with phonon lifetimes up to 400 $\mu$s and lifetime-limited coherence times approaching one millisecond in the quantum regime. When coupled to a superconducting qubit, this leads to a hybrid system with a large quantum coherence cooperativity of $C_{T_2}=1.1\times10^5$. These results represent a new milestone for the performance of cQAD devices and offer concrete paths forward for further improvements.

quant-ph↗

arXiv2024

Rayleigh Wave Suppression in Al0.6Sc0.4N-on-SiC Resonators

We report on the fabrication of a Hybrid SAW/BAW resonator made of a thin layer of Sc-doped AlN (AlScN) with a Sc concentration of 40 at% on a 4H-SiC substrate. A Sezawa mode, excited by a vertical electric field, exploits the d31 piezoelectric coefficient to propagate a longitudinal acoustic wave in the AlScN. The resonant frequency is determined via the pitch in the interdigitated transducer (IDT) defined by Deep Ultraviolet (DUV) lithography. The resonant mode travels in the piezoelectric layer without leaking in the substrate thanks to the mismatch in acoustic phase velocities between the piezoelectric and substrate materials. We show the impact of the piezoelectric and IDT layers' thickness on the two found modes. Importantly, we show how thin piezoelectric and electrode layers effectively suppress the Rayleigh mode. While some challenges in the deposition of AlScN remain towards a large coupling coefficient k_eff^2, We show how wave confinement in the IDT obtains a good quality factor. We also show how modifying the IDT reflectivity allows us to engineer a stopband to prevent unwanted modes from being excited between resonance and antiresonance frequencies. Finally, we validate the simulation with fabricated and measured devices and present possible improvements to this resonator architecture.

cond-mat.mtrl-sci↗

arXiv2024

More-than-Moore Microacoustics: A Scalable Fabrication Process for Suspended Lamb Wave Resonators

Deep Ultraviolet (DUV) Photolithography is currently used to fabricate mass-scale integrated circuits (ICs). Its high throughput and resolution could benefit large-scale RF MEMS production for the telecommunication market. We present a process flow to fabricate suspended acoustic resonators using DUV Photolithography. This method allows for scalable production of resonators with critical dimensions of 250 nm and alignment accuracy of less than 100 nm. We show how photoresists and anti-reflective coatings integrate with the process, help with deposition quality and resolution, and how Ion Beam Etching allows for vertical sidewalls of the resonators. We measure resonance frequencies (fr) up to 7.5 GHz and electromechanical couplings up to 8%, and we investigate the uniformity of this process by analyzing the deviation of fs over the wafer surface for four main resonance modes. We show that the deviation of the S0 mode can be kept below 1%. These results indicate the suitability of this process for quick scale-up of Lamb wave resonator technology, bridging the gap from research to industry.

eess.SY↗