**4.1. Short channel effects**

mentally. [19, 53] Graphene with a size in either x or y under 10 nm is known as a graphene nanoribbon and it suffers, like many other graphene synthesis techniques, from a lack of a reliable production technique. [53] Traditional semiconductor line definition techniques cannot reliably get a line definition below 20 nm, with large problems creating lines with acceptable line edge roughness. For graphene nanoribbons, the resistance induced through scattering from the line edge roughness is coupled with a lack of graphene conformality, not knowing whether the line definition will create "zig-zag" or "arm-chair" end terminations that provide different conductivity values. [19, 53] The difference between "zig-zag" and "armchair" end terminations is shown in Figure 16 and the difference in conductivities between the two create a discrepancy when designing a device utilizing multiple nanoribbons or multiple

**Figure 15.** Different defined graphene sheet edge states and the associated band diagrams showing opening according

The induced line edge roughness produces many scattering defect reducing the lattice periodicity, obliterating the induced band gap, and decreasing the mobility ultimately limiting the usefulness of graphene nanoribbon formation. [16, 19] Thus, to achieve useful devices from geometry restricted graphene, a reliable method of patterning graphene with low line edge

**4. Graphene Field Effect Transistors (GFETs) and Radio Frequency (RF)**

There has been an interest in looking at graphene for nanoelectronics applications due to its high intrinsic mobility allowing for greater switching speed. [18] The main problem with the

**Figure 16.** A picture showing the difference between zig-zag and armchair graphene end terminations [54].

devices utilizing a graphene nanoribbon. [54]

72 Graphene - New Trends and Developments

roughness and uniform width must be developed.

to edge definitions [52].

**electronics**

Graphene normally has a grain size of several to tens of microns with the desire to use a single grain as the channel material to avoid scattering at grain edges (also a factor in current MOSFET structures that is why single crystalline Si is used as a substrate). [16] This creates many of the short channel effects commonly seen in MOSFETS such as drain induced barrier lowering, surface scattering, velocity saturation, impact ionization, and hot-electron effects. [16] Specif‐ ically for graphene, drain-induced barrier lowering, surface scattering, and hot electron effects are all in play. Surface scattering is due to the intrinsic susceptibility of graphene to surface contamination and scattering sites, while the hot electron and barrier lowering effects affect graphene due to the pinchoff formation needed to have the large Ion/Ioff ratio required for typical electronics applications and to create large enough voltage and power gains for RF applications.
