Ion-dependent gate dielectric characteristics of ion-conducting SiO2 solid-electrolytes in oxide field-effect transistors

Abstract

The effect of ions on the gate dielectric behavior of oxide field-effect transistors (FETs) was studied using lithium ion-incorporated porous SiO₂. The frequency dependence of the impedance was observed to vary with the ion concentrations in the ion-conducting SiO₂ solid-electrolyte. The microstructure of the porous SiO₂ was tailored by changing the depositions and porous SiO₂ with an ordered columnar microstructure was realized, which provides an unobstructed pathway for the transportation of electrolyte ions. An enhanced electric-double-layer (EDL) capacitance of 11.9 μF cm⁻² and an improved EDL formation upper-limit-frequency of ∼10⁵ Hz were obtained. Due to the enhanced EDL capacitance, oxide FETs gated by these solid-electrolytes showed a very low operating voltage of 0.6 V. A current on/off ratio of ∼10⁶, a subthreshold swing of ∼82 mV per decade, a near-zero threshold voltage of ∼−0.01 V, and an electron field-effect mobility of ∼27.1 cm² V⁻¹ s⁻¹ were obtained. These ultra low-voltage FETs have potential applications in portable devices and biochemical sensors.