  Nonlinear electrical properties of graphene-based three-terminal
nanojunctions are presented. Intrinsic rectification of voltage is observed up
to room temperature. The sign and the efficiency of the rectification can be
tuned by a gate. Changing the charge carrier type from holes to electrons
results in a change of the rectification sign. At a bias < 20mV and at a
temperature below 4.2K the sign and the efficiency of the rectification are
governed by universal conductance fluctuations.
