Damping of metallized bilayer nanomechanical resonators at room temperature

TL;DR

This study examines how gold thin-films affect the damping and quality factors of silicon nitride nanomechanical resonators at room temperature, revealing metal losses dominate damping.

Contribution

We derive analytical models for bilayer resonators and experimentally show how gold film thickness influences damping and quality factors.

Findings

Inverse quality factor scales linearly with gold thickness

Damping increases over tenfold with gold deposition

Quality factors of gold films can be improved by single-step deposition

Abstract

We investigate the influence of gold thin-films subsequently deposited on a set of initially bare, doubly clamped, high-stress silicon nitride string resonators at room temperature. Analytical expressions for resonance frequency, quality factor and damping for both in- and out-of-plane flexural modes of the bilayer system are derived, which allows for the determination of effective elastic parameters of the composite structure from our experimental data. We find the inverse quality factor to scale linearly with the gold film thickness, indicating that the overall damping is governed by losses in the metal. Correspondingly, the mechanical linewidth increases by more than one order of magnitude compared to the bare silicon nitride string resonator. Furthermore, we extract mechanical quality factors of the gold film for both flexural modes and show that they can be enhanced by complete deposition of the metal in a single step, suggesting that surface and interface losses play a vital role in metal thin-films.