Membrane phononic crystals for high-Qm mechanical defect modes in piezoelectric aluminum nitride

TL;DR

This paper demonstrates a high-Qm localized phononic defect mode in a strained aluminum nitride membrane phononic crystal, advancing the development of low-loss nanomechanical resonators for quantum and sensing applications.

Contribution

It introduces a novel membrane phononic crystal in crystalline AlN with a high-Qm defect mode at room temperature, leveraging piezoelectric properties for future quantum device integration.

Findings

Achieved a Qxf-product of 1.5x10^13 Hz at 1.8 MHz

Demonstrated localized phononic defect mode in AlN membrane

Potential for integrated piezoelectric quantum devices

Abstract

Nanomechanical resonators with exceptionally low dissipation are advancing mechanics-based sensors and quantum technologies. The key for these advances is the engineering of localized phononic modes that are well-isolated from the environment, i.e., that exhibit a high mechanical quality factor, Qm. Membrane phononic crystals fabricated from strained thin films can realize high-Qm single or multiple localized phononic defect modes at MHz frequencies. These defect modes can be efficiently interfaced with out-of-plane light or coupled to a microwave quantum circuit, enabling readout and control of their motion. When membrane phononic crystals are fabricated from a crystalline film, they could offer built-in functionality. We demonstrate a membrane phononic crystal realized in a strained 90 nm-thin film of aluminum nitride (AlN), which is a crystalline piezoelectric material. We engineer a high-Qm localized phononic defect mode at 1.8 MHz with a Qxf-product of 1.5x10^13 Hz at room temperature. In future devices, the built-in piezoelectricity of AlN can be utilized for direct coupling to qubits or in-situ tuning of mechanical mode frequencies, defect mode couplings, or acoustic bandgaps, which can be used as building blocks of tunable phononic circuits or low-noise sensors.