From the point of view of electronic devices, the thinness, two-dimensional geometry, and high mobility of graphene have suggested its application as the conduction channel of scaled transistors. However, the absence of an energy gap in two-dimensional monolayer graphene has hampered the fabrication of graphene-based MOS (metal-oxide-semiconductor) transistors with a ION/IOFF ratio sufficiently high to allow their use for digital circuits  (the ION/IOFF ratio is the ratio between the current flowing through the device in its ON state and in its OFF state). The ambipolar behavior characteristic of pristine graphene represents a further drawback, since the possibility of using complementary devices would be desirable. To date, these limitations have limited the possible application of graphene transistors to analog electronics, particularly in the radiofrequency field . Meanwhile, for the realization of graphene-based digital devices, alternative operating principles such as that of the tunnel-field-effect-transistor  have been proposed. However, many efforts have been focused on the improvement of the switching properties of graphene-based transistors. Even though the possibility of surpassing or even approaching the commutation properties of traditional transistors currently seems out of reach, the availability of well-operating digital graphene field-effect-transistors (FETs) would allow us to benefit from the excellent properties of this material. For example, it would make it possible to fabricate flexible, transparent, and low-cost all-graphene electronic circuits, high-speed devices, or devices in which also the mechanical, thermal, or optical properties of graphene could be exploited. Several methods have been proposed to induce an energy gap in graphene , such as transversal confinement , doping , strain , the introduction of an antidot lattice , functionalization , or the application of an electric field orthogonally to bilayer graphene .