Origins of leakage currents on electrolyte-gated graphene field-effect transistors

TL;DR

This study investigates the origins of leakage currents in electrolyte-gated graphene FETs, revealing their electrochemical nature and how oxygen reduction induces defects, affecting device performance.

Contribution

It provides new insights into the electrochemical mechanisms behind gate leakage currents and defect formation in CVD-grown graphene FETs.

Findings

Gate currents are capacitive or Faradaic depending on doping type.

Oxygen reduction causes defect formation on graphene surface.

Leakage currents increase with repeated measurements.

Abstract

Graphene field-effect transistors are widely used for development of biosensors. However, certain fundamental questions about details of their functioning are not fully understood yet. One of these questions is the presence of gate (leakage) currents in the electrolyte-gated configuration. Here, we report our observations considering causes of this phenomena on chemical vapor deposition (CVD) grown graphene. We observed that gate currents reflect currents that occur on the transistor surface similarly to a working electrode - counter electrode pair currents in an electrochemical cell. Gate currents are capacitive when the graphene channel is doped by holes and Faradaic when it is doped by electrons in field-effect measurements. The Faradaic current is attributed to a reduction of oxygen dissolved in the aqueous solution and its magnitude increases with each measurement. We employed cyclic voltammetry with a redox probe Fc(MeOH)2 to characterize changes of the graphene structure that are responsible for this activation. Collectively, our results reveal that through the course of catalytic oxygen reduction on the transistor's surface more defects appear.