Stressed nanomechanical resonators are known to have exceptionally high
quality factors (Q) due to the dilution of intrinsic dissipation by stress.
Typically, the amount of dissipation dilution and thus the resonator Q is
limited by the high mode curvature region near the clamps. Here we study the
effect of clamp geometry on the Q of nanobeams made of high-stress
Si3​N4​. We find that tapering the beam near the clamp - and locally
increasing the stress - leads to increased Q of MHz-frequency low order modes
due to enhanced dissipation dilution. Contrary to recent studies of
tethered-membrane resonators, we find that widening the clamps leads to
decreased Q despite increased stress in the beam bulk. The tapered-clamping
approach has practical advantages compared to the recently developed
"soft-clamping" technique. Tapered-clamping enhances the Q of the fundamental
mode and can be implemented without increasing the device size