  We demonstrate top-gated field effect transistor made of reduced graphene
oxide (RGO) monolayer (graphene) by dielectrophoresis. Raman spectrum of RGO
flakes of typical size of 5{\mu}m x 5{\mu}m show a single 2D band at 2687 cm-1,
characteristic of a single layer graphene. The two probe current - voltage
measurements of RGO flakes, deposited in between the patterned electrodes with
a gap of 2.5 {\mu}m using a.c. dielectrophoresis show ohmic behavior with a
resistance of ~ 37k{\Omega}. The temperature dependence of the resistance (R)
of RGO measured between temperatures 305 K to 393 K yields temperature
coefficient of resistance [dR/dT]/R ~ -9.5x10-4 K-1, same as mechanically
exfoliated single layer graphene. The field effect transistor action was
obtained by electrochemical top-gating using solid polymer electrolyte (PEO +
LiClO4) and Pt wire. Ambipolar nature of graphene flakes is observed upto a
doping level of ~ 6x1012/cm2 and carrier mobility of ~ 50 cm2V-1sec-1. The
source - drain current characteristics shows a tendency of current saturation
at high source - drain voltage which is analyzed quantitatively by a diffusive
transport model.
