Metallic transport properties and electrostatic resistance modulations in LaNiO3 ultrathin channels electrochemically etched in electric-double-layer transistors

Abstract

We fabricated electric double-layer transistors with perovskite nickelate LaNiO3 epitaxial films as a channel and an ionic liquid as a gate insulator and investigated the channel's transport behavior at negative gate bias voltages. We found that when the negative VG is low enough, the channel resistance undergoes reversible changes due to electrostatic carrier accumulation. On the other hand, with increasing VG, electrochemical decomposition of the channels due to the VG-induced instability of the unusually high Ni valence state [Ni(3+δ)+] occurs and the channels are etched, which is seen as an irreversible increase in the channel resistance. We also show that channel layers electrochemically etched to a few nanometers thick exhibit metallic transport behavior and the electrostatic carrier accumulation in the etched metallic channels results in 30% reductions in the channel resistance at 220 K, which are about twice as large as those seen for the ultra-thin insulating film channels. These observations indicate that surface defects and dangling bonds in the electrochemically etched channel layers differ from those in ultrathin films. Our results highlight that the electrochemical decomposition and etching in electric double-layer transistors is a unique approach for fabricating ultrathin oxide films and exploring electric field-induced effects on their functional properties.