Gate-tunable Thermoelectric Effect in Oxide Thin Films at Room Temperature

Over the past several decades, major efforts have been directed toward the optimization of carrier concentrations to maximize thermoelectric performance. Chemical doping is an effective way to control carriers, but electrostatic gating provides a continuous tuning knob that enables effective and dynamic changes to the carrier density. Here, a method is reported that uses an electric-double-layer (EDL) transistor-based ionic liquids gating to adjust the thermoelectric properties of thin films made from Nb-doped SrTiO₃ (Nb-STO). This technique allows us to effectively change these properties at room temperature by varying the concentration of charge carriers within a broad range. A combination of lower film thickness and intrinsic carrier concentration leads to an enhanced ionic liquid-gated response, resulting in an 18-fold enhancement in power factor at room temperature for a 14 nm thin 4% Nb-STO film at gate voltages within ±3.0 V. The present study offers new insights and strategies toward enhanced gate tunable thermoelectric properties in thin films.