Fig. 1: SET process for graphene memristors.
From: Graphene memristive synapses for high precision neuromorphic computing
a Schematic and (b) false-colored scanning electron microscope (SEM) image of a graphene memristor. c Raman spectrum of the graphene channel, taken at a wavelength of 532 nm. Output characteristics (i.e., the source-to-drain current (IDS) versus the drain-to-source voltage (VDS)) of an as-fabricated graphene field effect transistor (GFET) at VBG = 0 V for different VDS sweep ranges (denoted by VDSmax), from (d) 1 V to 6.5 V and (e) −1 V to −6.5 V in steps of 0.5 V. The arrows denote the sweep direction (blue for the forward sweep and black for the reverse sweep). In either case, the hysteresis window initially increases with increasing VDSmax before reversing direction and starting to decrease past VDSmax = 5 V for (d) and VDSmax = −5.5 V for (e). These results indicate switching between states of lower and higher conductance in GFETs. Transfer characteristics at VDS = 10 mV following the sweeps of (f) VDSmax = 1 V and VDSmax = 6.5 V and (g) VDSmax = −1 V and VDSmax = −6.5 V. Sweeping the GFET to a higher positive VDSmax results in a large shift of the Dirac voltage from VDirac = 6.4 V to VDirac = −5.8 V, making the GFET more n-type, whereas sweeping the GFET to a higher negative VDSmax results in a smaller shift from VDirac = 6.5 V to VDirac = −0.2 V, making the GFET more ambipolar. h Difference between the conductance of two states as a function of VBG after the sequential application of positive and negative VDS pulses of magnitude 5 V for different pulse durations (t) at VDS = 10 mV. i Switching endurance. Histogram of conductance distributions following 200 cycles of SET (red) and RESET (blue) pulses of different magnitudes. Conductance states obtained using VDS pulses of magnitude 5 V display both a relatively large difference in conductance and a switching endurance >200 cycles. These experiments demonstrate the ability to SET and RESET conductance states in graphene by applying VDS pulses of opposite polarity, making it attractive for non-volatile memory (NVM) applications.
