(562f) Electric Double Layer Gating of Transition Metal Dichalcogenide Field-Effect Transistors Using a Monolayer Solid-State Electrolyte

Electrical double layer (EDL) gating using a monolayer electrolyte developed by our group has been demonstrated on transition metal dichalcogenide (TMD) field-effect transistors (FETs). An EDL is formed by the accumulation of ions near the two dimensional (2D) semiconducting channel surface, which induces image charges in the channel. In 2D crystals with a polymer electrolyte gate, this approach yields large capacitance densities corresponding to sheet carrier densities on the order of 10¹³ -10¹⁴ cm^-2. In this study, a monolayer electrolyte consisting of cobalt crown ether phthalocyanine (CoCrPc) and lithium perchlorate (LiClO₄) is used, which can be deposited on the surface of 2D crystals including graphene and TMDs simply by drop-casting and annealing. The CoCrPc is a single molecule thick, can lie flat on a 2D surface and is electrically insulating (measured band gap ~1.34 eV). Each of the four crown ethers in a CoCrPc molecule can solvate one Li⁺. To demonstrate the EDL gating, back-gated MoS₂ and WSe₂ FETs were fabricated by electron beam lithography (EBL), followed by the deposition of the monolayer electrolyte. FET transfer characteristics of the monolayer electrolyte-gated MoS₂ FETs show a non-volatile and reversible shift in the threshold voltage, where the direction and magnitude of the shift depend on the polarity and magnitude of the applied field. The magnitude of threshold voltage shift is ~10 V after the programming test, corresponding to a sheet carrier density change of 3.2 × 10¹² cm^-2. Two distinct states of channel conductivity are maintained (i.e., bistability) after the bias is removed, indicating non-volatility on the timescale of the measurement. Electrical measurements of monolayer electrolyte-gated WSe₂ FETs will also be presented. Graphene/h-BN layers have also been added to top-gate the devices, creating an all-2D EDL FET.

Acknowledgements: This work was supported in part by the NSF (ECCS-GOALI #1408425) and the Center for Low Energy Systems Technology (LEAST), one of six SRC STARnet Centers, sponsored by MARCO and DARPA.