  We demonstrate tunable solid state and flexible graphene field effect devices
(FEDs) fabricated using a poly(methylmethacrylate) (PMMA) and lithium fluoride
(LiF) composite dielectric. Increasing the concentration of LiF in the
composite dielectric reduces the operating gate voltages significantly from 10
V to 1 V required leading to a decrease in resistance. Electron and hole
mobility of 350 and 310 cm2/Vs at VD = -5 V are obtained for graphene FEDs with
10 % LiF concentration in the composite. Using composite dielectric also
enabled excellent performance on flexible substrates without any significant
change in mobility and resistance. Flexible FEDs with only 5 % and 12 %
variation in mobility for 300 and 750 bending are obtained.
