Highest-quality-factor nanomechanics: a monolithic approach

• Applicants: Professor Dr. Heiko B. Weber; Professorin Dr. Eva M. Weig
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 565790649

In recent years, nanomechanical resonators have attained an impressive level of quality and control, and their application potential reaches into both classical and quantum technologies. In particular silicon carbide (SiC) is expected to become a leading technology platform in this field. This is a consequence of its superb material properties promising the best mechanical quality factors attainable, the availability of wafer-scale material and processing techniques, and the possibility to form hybrid integrated quantum systems via SiC’s color centers for spin-mechanical or spin-cavity optomechanical applications. The proposed project sets out to realize this potential. We will focus on nanomechanical resonators made of high-quality 4H-SiC. We seek to reach the highest mechanical quality factors, addressing both the intrinsic quality factor and its dissipation dilution by means of the incorporation of tensile prestress. We plan to integrate electronic functionality and control monolithically. To reach these goals, a number of technological and scientific questions have to be addressed and resolved. They define the main objectives of the project: (1) Understand the prevalent dissipation mechanisms. This is an essential prerequisite for their successive mitigation. A particular focus lies on the exploration of fundamental dissipation mediated by phonon scattering. (2) Develop process routines to create the purest resonators and develop novel design concepts to improve their performance. This includes the suppression of all extrinsic as well as bulk and surface-limited losses to approach the limit of phonon-scattering mediated losses, and, specifically, the quantum limit of dissipation set by Akhiezer damping. The combination of (1) and (2) will yield ultimate values of the intrinsic quality factor. (3) Incorporate tensile prestress to exploit dissipation dilution. This will enhance the underlying intrinsic quality factor, potentially by several orders of magnitude. However, the tensile prestress may compromise the crystal quality and thus reduce the intrinsic quality factor. Main challenges will be to keep its value close to its fundamental limit, and to understand the impact of tensile stress on its value. This will allow to reach the highest quality factors available. (4) Establish means of integrated controls based on epitaxial graphene grown on the SiC surface, study their functionality as well as their impact on the quality factor. Our monolithic approach is targeted to reach unprecedented quality and control for the field of nanomechanics, and simultaneously to enhance the mechanical functionality of the SiC platform, preparing integration with both classical and quantum applications.

• DFG Programme: Research Grants