Charge noise is critical in the performance of gate-controlled quantum dots
(QDs). Here we show the 1/f noise for a microscopic graphene QD is
substantially larger than that for a macroscopic graphene field-effect
transistor (FET), increasing linearly with temperature. To understand its
origin, we suspended the graphene QD above the substrate. In contrast to large
area graphene FETs, we find that a suspended graphene QD has an
almost-identical noise level as an unsuspended one. Tracking noise levels
around the Coulomb blockade peak as a function of gate voltage yields potential
fluctuations of order 1 "{\mu}eV", almost one order larger than in GaAs/GaAlAs
QDs. Edge states rather than substrate-induced disorders, appear to dominate
the 1/f noise, thus affecting the coherency of graphene nano-devices.Comment: 14pages,5figur
