TEM of Conducting Filament in Nb-Nb2O5-Bi Switching Glass Structure

Abstract

There has been considerable interest in the electronic component industry concerning the switching phenomena exhibited by certain glasses. Switching is observed in thin Nb2O5 glass sandwiched between Niobium and Bismuth conductors. A typical device vertical structure is shown in Fig. 1. Transmission electron microscopic techniques were used to consider structural aspects of the Nb-Nb2O5-Bi devices. First, the microstructure of the conducting filament was unknown and secondly, optical and scanning electron microscopy showed the top of the one micron wide filament to be shaped like a volcano and situated in the center of a large six to ten micron wide crater in the Bi top conductor with no apparent metallic contact to the Bi. This last point is illustrated in the optical micrograph, Fig. 2a, and the SEM photo, Fig. 2b.The Bi metallurgy to filament conducting scheme was immediately obvious in TEM. The floor of the six to ten micron wide large crater was covered with ∼500Å thick Bi up to the lip of a minor crater, within which thinner, ∼200Å thick, Bi was continuous up to the filament.