SymFET: A proposed symmetric graphene tunneling field effect transistor

The expressions given in previous section, is for T = 0K. The room temperature results need to consider the Fermi distribution with integral over energy. The corresponding device parameters are labeled in the figures. A graphene length L = 100 nm is assumed. When the tunnel barrier is thicker, the resonant peak current decreases as expected (Figure 2 (a)). Thinner t_gate offers better gate control and higher gate induced doping (and more resonant current). The corresponding resonance peaks increase and shift to higher bias (Figure 2 (b)). Figure 3 explores the entire bias phase space of the I-V characteristics. Though the on/off ratio of the SymFET is not a true performance metric, from equation (1) and (3) we find it is given by I_on/I_off ≈ LΔE/ħv_F, (~100 for L ~ 100nm, ~1000 for L ~ 1 μm). It is independent of temperature and increases with size. The I_D-V_DS characteristics at fixed VG are shown in Figure 4(a). In Figure 4(b), the ID-VG curve shows strong non-linear behavior. The transconductance can be large in the bias range where the resonant current peak exists. The I_D-V_DS curve (e.g. resonant width) is insensitive to the temperature (Figure 5), because of tunneling mechanism, except for Fermi function smearing. The slight difference at low V_DS, is due to the Fermi function varying with temperature. The increase of resonant peak current is because Fermi tail extends to high energy with larger density of states. The nonlinear symmetric I_D-V_DS behavior can also be used for purposes of frequency multiplication; if a dc voltage bias at the current peak V_DSp is superposed with an ac signal, the frequency of the output current will be doubled (Figure 6 schematic). The SymFET is expected to be intrinsically fast since it relies entirely on tunneling; high frequency digital operation and a host of analog appl- cations such as frequency multiplication are thus possible by exploiting the symmetry of the bandstructure of 2D graphene.