# Influence of clamp-widening on the quality factor of nanomechanical silicon nitride resonators

## TL;DR

This study investigates how clamp-widening affects the quality factors of silicon nitride nanomechanical string resonators, revealing that the impact varies with orientation and is likely due to intrinsic surface and radiation losses.

## Contribution

It provides experimental and simulation analysis of clamp-widening effects on resonator Qs, challenging previous assumptions and highlighting orientation-dependent behaviors.

## Key findings

- Clamp-widening slightly increases Q for diagonal strings at small radii.
- Perpendicular strings' Qs deteriorate with increased clamp width.
- Measured Qs align with finite element simulations, suggesting intrinsic loss mechanisms.

## Abstract

Nanomechanical resonators based on strained silicon nitride (Si$_3$N$_4$) have received a large amount of attention in fields such as sensing and quantum optomechanics due to their exceptionally high quality factors ($Q$s). Room-temperature $Q$s approaching 1 billion are now in reach by means of phononic crystals (soft-clamping) and strain engineering. Despite great progress in enhancing $Q$s, difficulties in fabrication of soft-clamped samples limits their implementation into actual devices. An alternative means of achieving ultra-high $Q$s was shown using trampoline resonators with engineered clamps, which serves to localize the stress to the center of the resonator, while minimizing stress at the clamping. The effectiveness of this approach has since come into question from recent studies employing string resonators with clamp-tapering. Here, we investigate this idea using nanomechanical string resonators with engineered clampings similar to those presented for trampolines. Importantly, the effect of orienting the strings diagonally or perpendicularly with respect to the silicon frame is investigated. It is found that increasing the clamp width for diagonal strings slightly increases the $Q$s of the fundamental out-of-plane mode at small radii, while perpendicular strings only deteriorate with increasing clamp width. Measured $Q$s agree well with finite element method simulations even for higher-order resonances. The small increase cannot account for previously reported $Q$s of trampoline resonators. Instead, we propose the effect to be intrinsic and related to surface and radiation losses.