Bistable switching and conduction mechanisms in Nb-Nb2O5-Bi junctions

Bistable switching and conduction in niobium-niobium oxide-bismuth devices has been investigated. A number of these devices were found to be stable for more than 10⁶switching cycles and a limited number for more than 10⁹cycles. Upper bounds of 1 and 20 µs for switching from high to low and low to high resistance states, respectively, were observed. Three distinct types of conduction mechanisms are observed in an unformed device. These are the following: 1) the space-charge-limited current flow at high temperatures and low voltages; 2) Poole-Frenkel process at low temperatures and high voltages; and 3) field-assisted tunneling from traps at very low temperatures and high voltages. Conduction in the switching states is found to occur in a singular spot of approximately 2 µ²in area, created while forming. In the high-resistance state an activated process similar to Schottky mechanism seems to be responsible for electrical conduction. The low-resistance state increases very slightly in value on cooling from 300 to 1.6 K, has a small negative resistance "kink" in the curves at about 0.3 V, and exhibits near ohomic behavior and "power law" behavior below and above the kink, respectively.