Gate-Tunable Transport in Hybrid-MBE-Grown RuO₂ Thin Films Using Ionic Gel

RuO₂ films are of great interest due to their exceptional conductivity, surface activity and emerging potential for spintronic applications. In this talk, we present the effect of ion-gel gating on the electrical properties of epitaxial RuO₂ films grown on TiO₂ (110) substrates using hybrid MBE. The 3-unit-cell-thick RuO₂ films, capped with ultrathin insulating layer, exhibited excellent conductivity (376 µΩ·cm at 2 K) and linear Hall behavior with electron majority carriers. We applied a bias ranging from +3 V to −3 V using a polymer-based ion-gel electrolyte consisting of poly vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) polymer and 1-ethyl-3-methyl-imidazaolium bis-trifluoromethylsulfonyl imide (EMI/TFSI) ionic liquid. This resulted in non-reversible changes in electronic transport, indicating an electrochemical effect. The accompanied Hall resistance became non-linear across all applied biases. Oxygen annealing restored the linear Hall behavior suggesting the important role of oxygen vacancies on electrical transport. Thickness-dependent transport and the effect of external bias on crystal structure and electronic properties will be discussed.