Threshold switching into conductance quantized states in vanadium/amorphous-vanadium pentoxide/vanadium thin film structures.

摘要

The objective of this research was to investigate a new type of low voltage threshold switch (LVTS). As distinguished from the many other types of electronic threshold switches, the LVTS is; voltage controlled, occurs at low voltages, involves no memory, and has long term dynamical stability under bias. Most importantly, it switches from an initially low conductance state into a succession of quantized states of higher conductance. Previously, the LVTS had been observed only in electroformed Cr{dollar}vert{dollar}amorphous-Si:H{dollar}vert{dollar}V thin film devices. Because switching in these devices was associated with unknown structural rearrangements, they could not be used to study the structure-property relationships involved in the switching mechanism.; V{dollar}vert{dollar}amorphous-{dollar}rm Vsb2Osb5vert{dollar}V thin film structures were selected for the dissertation experiments because they were expected to exhibit LVTS switching without electroforming. Indeed, the LVTS was observed in more than 100 as-deposited V{dollar}vert{dollar}amorphous-{dollar}rm Vsb2Osb5vert{dollar}V devices. The average threshold voltage {dollar}{dollar} = 218 mV ({dollar}sigma{dollar} = 24mV {dollar}sim{dollar} kT/q), and was independent of the device area ({dollar}times{dollar}100) and amorphous oxide thickness ({dollar}times{dollar}10). Extensive studies of the electronic transport conclusively showed that switching occurred in an {dollar}sim{dollar}22A thick interphase of the V{dollar}vert{dollar}amorphous-{dollar}rm Vsb2Osb5{dollar} contacts. At V{dollar}sb{lcub}rm LVT{rcub}{dollar} there was a transition from an initially low conductance (OFF) state into a succession of quantized states of higher conductance (ON). The OFF state was spatially homogeneous and dominated by tunneling into the interphase. The ON state conductances were consistent with the quantized conductances of ballistic transport through a one dimensional, quantum point contact.; The temperature dependence of V{dollar}sb{lcub}rm LVT{rcub},{dollar} and fit of the material parameters (dielectric function, barrier energy, conductivity) to the data, showed that transport in the OFF and ON states occurred in an interphase with the characteristics of, respectively, semiconducting and metallic VO{dollar}sb2.{dollar} The data suggests that the transition was reversible, but were inconclusive to determine if the interphase transition occurred at a critical energy, critical electric field, or critical input power density.; The dissertation results suggest that the LVTS is likely to be observed in interphases produced by contact reactions and metastabilized in close proximity to a metal-nonmetal phase transition.