Low-Voltage 2D Material Field-Effect Transistors Enabled by Ion Gel Capacitive Coupling

Capacitive coupling between an overlying ion gel electrolyte and an underlying oxide thin film is utilized to substantially suppress the operating voltage of field-effect transistors (FETs) based on two-dimensional (2D) transition metal dichalcogenides and black phosphorus. The coupling of the layers is achieved following device fabrication by laminating an ion gel layer over an oxide-gated 2D FET through solution-casting methods. While the original pristine 2D FET requires tens of volts for gating through the oxide layer, the laminated ion gel layer reduces the operating voltage to below 4 V even when the same underlying substrate is used as the back gate electrode. Moreover, this capacitive coupling approach allows low-voltage operation without compromising the off-current level, which often occurs when ion gel electrolytes are directly employed as the gate dielectric material. This approach can likely be generalized to a wide variety of thin-film FETs as a postfabrication method for reducing operating voltages and power consumption.