Frequency response of electrolyte-gated graphene electrodes and transistors

Abstract

The interface between graphene and aqueous electrolytes is of high importance for applications of graphene in the field of biosensors and bioelectronics. The graphene/electrolyte interface is governed by the low density of states of graphene that limits the capacitance near the Dirac point in graphene and the sheet resistance. While several reports have focused on studying the capacitance of graphene as a function of the gate voltage, the frequency response of graphene electrodes and electrolytegated transistors has not been discussed so far. Here, we report on the impedance characterization of single layer graphene electrodes and transistors showing that due to the relatively high sheet resistance of graphene, the frequency response is governed by a distribution of resistive and capacitive circuit elements along the graphene/electrolyte interface. Based on an analytical solution for the impedance of the distributed circuit elements, we model the graphene/electrolyte interface both for the electrode and the transistor configurations. Using this model, we can extract relevant material and device parameters such as the voltage-dependent intrinsic sheet and series resistances as well as the interfacial capacitance. The model also provides information about the frequency threshold of electrolyte-gated graphene transistors above which the device exhibits a non-resistive response, offering important insight into the suitable frequency range of operation of electrolyte-gated graphene devices.

Development of a Synthetic Pathway Toward a Bowl-Shaped C 27H12 Polycyclic Aromatic Hydrocarbon

“…which suggests that the electrolyte-graphene interface behaves as a CPE rather than an ideal capacitor. A similar result was reported by [209] in which a capacitive regime with a phase shift of around -85° was observed. Using the Randles circuit model, we analyzed the impedance of the graphene electrode at different gate voltages.…”

“…The total capacitance of the electrolyte-graphene interface is governed by two factors: the capacitance of the electrical double layer (EDL) ( EDL ) and the quantum capacitance ( Q ) of the graphene channel [208]. Considering the series arrangement of these two capacitors, the total capacitance ( total ) of the electrolyte-graphene interface can be calculated as [208,209]…”

“…At low gate potentials, the total capacitance ( total ) of the electrolytegraphene interface is dominated by the quantum capacitance ( Q ) of graphene, which is smaller than the capacitance of EDL ( EDL ) [208,210]. Therefore, to better understand the capacitance behavior of the electrolyte-graphene interface, the contribution of the quantum capacitance has to be taken into account [209].…”

Distortion‐Free Sensing of Neural Activity Using Graphene Transistors

“…The V gs axis can be rescaled by the ratio between the gate capacitance of any sensor and the graphene–electrolyte interface capacitance of the devices reported here. [ 20 ] The A sig axis can also be rescaled in the same manner for any GFET‐based device in which a small voltage signal applied at the gate is detected.…”

“…The electrochemical potential in the electrolyte can therefore be regarded as the gate‐to‐source voltage ( V gs ), which couples with the channel through the graphene–electrolyte interface capacitance ( C int ). [ 20,21 ] The electric field at the interface produces a change in the number of charge carriers in the graphene channel and therefore a variation in the drain‐to‐source current ( I ds–sig ) for a constant drain‐to‐source bias ( V ds ). These current changes are proportional to the signal at the gate ( V gs–sig ) and to the transconductance ( G m ) (see Figure 1b), which represents the input‐output relation of the g‐SGFET, also referred to as its transfer function.…”