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(Color online) (a) Layout of a graphene SGFET showing the Ag/AgCl reference electrode used to control the graphene/electrolyte interfacial potential. (b) Modulation of the charge carrier density by the electrolyte gate: the applied gate voltage shifts the Fermi level in graphene below (shown) or above the Dirac point (ED ), defining the density and type of charge carriers. (c) Optical micrograph of an SGFET array with large access regions (scale bar corresponds to 100 μm).
(Color online) (a) Drain-source current vs. gate voltage for SiC (red circles) and CVD (black squares) graphene SGFETs (Channel length 20 μm). The solid lines correspond to the expected currents with the contribution of the access resistance taken into account. The small insets indicate the positions of the Fermi levels for ungated SiC (left) and CVD (right) graphene. (b) Transconductance of a CVD graphene SGFET. The symbols represent the experimental results, whereas the line shows the internal transconductance calculated by considering the access resistance. (c) Normalized transconductance of SGFETs based on graphene and other materials shifted by the transistor threshold voltage UT (UD for graphene devices). Open symbols represent p-type and closed symbols n-type devices. All transistors have the same channel length-to-width ratio.
(Color online) (a) Capacitance of the graphene-water interface (CePB ) calculated using an extended Poisson-Boltzmann model and its two in-series contributions: the electrolyte double-layer capacitance (Cdl ) and the quantum capacitance of graphene (CQ ). (b) Field effect mobility extracted from the transistor measurements using the calculated interfacial capacitance. Open and solid symbols represent p-type and n-type carriers, respectively.
Comparison of the materials’ properties and the measured maximum transconductance for silicon, diamond, AlGaN/GaN, and graphene SGFETs. The values for mobility and capacitance correspond to the gate voltage where gm is maximum.
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