  Nanomechanical resonators with increasingly high quality factors are enabled
following recent insights into energy storage and loss mechanisms in
nanoelectromechanical systems (NEMS). Consequently, efficient, non-dissipative
transduction schemes are required to avoid the dominating influence of coupling
losses. We present an integrated NEMS transducer based on a microwave cavity
dielectrically coupled to an array of doubly-clamped pre-stressed silicon
nitride beam resonators. This cavity-enhanced detection scheme allows resolving
the resonators' Brownian motion at room temperature while preserving their high
mechanical quality factor of 290,000 at 6.6 MHz. Furthermore, our approach
constitutes an "opto"mechanical system in which backaction effects of the
microwave field are employed to alter the effective damping of the resonators.
In particular, cavity-pumped self-oscillation yields a linewidth of only 5 Hz.
Thereby, an adjustement-free, all-integrated and self-driven
nanoelectromechanical resonator array interfaced by just two microwave
connectors is realised, potentially useful for applications in sensing and
signal processing.
