Electrostatic and Electrochemical Nature of Liquid-Gated Electric-Double-Layer Transistors Based on Oxide Semiconductors

Abstract

The electric-double-layer (EDL) formed at liquid/solid interfaces provides a broad and interdisciplinary attraction in terms of electrochemistry, photochemistry, catalysts, energy storage, and electronics because of the large interfacial capacitance coupling and its ability for high-density charge accumulation. Much effort has recently been devoted to the fundamental understanding and practical applications of such highly charged EDL interfaces. However, the intrinsic nature of the EDL charging, whether it is electrostatics or electrochemistry, and how to distinguish them are far from clear. Here, by combining electrical transport measurements with electrochemical impedance spectroscopy (EIS), we studied the charging mechanisms of highly charged EDL interfaces between an ionic liquid and oxide semiconductor, ZnO. The direct measure for mobile carriers from the Hall effect agreed well with that from the capacitance-voltage integration at 1 Hz, implying that the pseudocapacitance does not contribute to carrier transport at EDL interfaces. The temperature-frequency mapping of EIS was further demonstrated as a "phase diagram" to distinguish the electrostatic or electrochemical nature of such highly charged EDL interfaces with densities of up to 8 × 10(14) cm(-2), providing a guideline for electric-field-induced electronic phenomena and a simple method for distinguishing electrostatic and electrochemical charging in EDLTs not only based on a specific oxide semiconductor, ZnO, but also commonly applicable to all types of EDL interfaces with extremely high-density carrier accumulation.

Nanoionics-Based Three-Terminal Synaptic Device Using Zinc Oxide

“…35 However, dissolution of the IGZO films in water and irreversible electrochemical reactions at interface are a major concern in these types of devices. 36 TCO devices employing a ferroelectric gate insulator have also been reported to show EPSC behaviour. 28,37 The (fig 1i).…”

Large Conductance Modulation of Gold Thin Films by Huge Charge Injection via Electrochemical Gating

“…Note that, after the first voltage step, a non-vanishing gate current continues to flow indefinitely. This current is due to the flow of charges necessary to maintain the gradient of ion concentration when tunneling effect through the EDL [17] or diffusion of electroreactants [18] take place. The shape of Q(t) shows indeed that two phenomena occur on very different length scales: a rather fast EDL charging/discharging (that gives Q an exponential time dependence) and other effects of electrochemical nature that give a t 1 2 dependence.…”

Large modulation of zero-dimensional electronic states in quantum dots by electric-double-layer gating

“…1a. In order to avoid any possible interfacial electrochemistry between the ionic liquid and the InAs channel, transport measurements were mainly performed at 215 K and below, where it has been proved that the interfacial chemistry is suppressed by cooling 34 . The lever-arm factor is defined as the conversion ratio of the gate voltage to the shift in the energy levels.…”