Investigation of mechanical losses of thin silicon flexures at low temperatures

TL;DR

This study measures the mechanical loss of silicon flexures at low temperatures, revealing surface loss as a limiting factor for silicon-based oscillators and providing a surface loss parameter relevant for gravitational wave detectors.

Contribution

It provides new measurements of silicon flexure losses at low temperatures and introduces a surface loss parameter, highlighting differences from fused silica.

Findings

Lowest mechanical loss observed was 3×10⁻⁸ at 10 K

Surface loss parameter α_s = 0.5 pm for silicon

Surface loss is lower than that of fused silica

Abstract

The investigation of the mechanical loss of different silicon flexures in a temperature region from 5 to 300 K is presented. The flexures have been prepared by different fabrication techniques. A lowest mechanical loss of $3\times10^{-8}$ was observed for a 130 $\mu$m thick flexure at around 10 K. While the mechanical loss follows the thermoelastic predictions down to 50 K a difference can be observed at lower temperatures for different surface treatments. This surface loss will be limiting for all applications using silicon based oscillators at low temperatures. The extraction of a surface loss parameter using different results from our measurements and other references is presented. We focused on structures that are relevant for gravitational wave detectors. The surface loss parameter $\alpha_s$ = 0.5 pm was obtained. This reveals that the surface loss of silicon is significantly lower than the surface loss of fused silica.