Field-Controlled Ion Doping of Graphene
The dry transfer process is illustrated in Fig. 1. To create the top portion of the device, source and drain contacts are patterned onto wide area graphene formed by chemical vapor deposition. Polyisobutylene (PIB) and a PDMS stamp are then applied as handling layers (Fig. 1b). The Cu substrate is then etched in ammonium persulfate (APS) and the top portion is joined to the bottom (Fig. 1e). We have fabricated devices with both Au and graphene backgates, and initial tests were performed with an Au backgate, patterned into stripes to minimize leakage current through the electrolyte (Fig. 2).
Doping in the graphene channel is controlled by the backgate voltage (Vbg). The conductivity, monitored by the drain current, (Id), is varied by a factor of four by sweeping Vbgat 0.5 V/s from −10 to 10 V (Fig. 3). The shift of the current minima (Dirac points) from zero are a direct measure of the ion doping of the graphene channel.
To characterize the retention of electrostatic doping, a 5 V backgate pulse is applied for 1 second and removed for 10 seconds while monitoring the drain current (Fig. 4). The current decreases by ~10% as the ions are polarized and then released.
Acknowledgements: This work was supported in part by the Center for Low Energy Systems Technology (LEAST), one of the six SRC STARnet Centers, sponsored by MARCO and DARPA.
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