  Since the discovery of electrons, an accurate detection of electrical charges
has been the dream of scientific community. Due to some remarkable advantages,
micro/nano-electromechanical systems (M/NEMS) based resonators have been used
to design electrometers with exquisite sensitivity and resolution. Inevitably,
some limits including requisite ultra-low environmental temperature,
complicated resonator structure and measurement circuit, required linear
dynamic response, will cause a gap with respect to practical application. Here,
we demonstrate a novel ultra-sensitive charge detection based on the linear
dependence of peak frequency drift on the coupling voltage variation of two
coupled nonlinear micromechanical resonators. We achieved ultra-high resolution
of 2.051E-3 fC (about 13 electrons) of charge detection at the room
temperature. We also show an extra application of this device for weak and
ultra-low-frequency (ULF) signal detection. Our findings provide a simple
strategy for measuring electron charges in an extreme accuracy and developing
electrometers in smaller sizes.
