We study the mechanical quality factors of bilayer aluminum/silicon-nitride membranes. By coating ultrahigh-Q Si3N4 membranes with a more lossy metal, we can precisely measure the effect of material loss on Q's of tensioned resonator modes over a large range of frequencies. We develop a theoretical model that interprets our results and predicts the damping can be reduced significantly by patterning the metal film. Using such patterning, we fabricate Al-Si3N4 membranes with ultrahigh Q at room temperature. Our work elucidates the role of material loss in the Q of membrane resonators and informs the design of hybrid mechanical oscillators for optical-electrical-mechanical quantum interfaces.
@article{arxiv.1111.1703,
title = {Control of Material Damping in High-Q Membrane Microresonators},
author = {P. -L. Yu and T. P. Purdy and C. A. Regal},
journal= {arXiv preprint arXiv:1111.1703},
year = {2012}
}