On state of amorphous threshold switches

Abstract

A detailed study of the on state of amorphous threshold switches has been performed. Transient and steady-state I-V characteristics have been investigated as functions of film thickness, pore size, and electrode material. Velocity saturation effects in amorphous/crystalline Si heterojunctions and threshold recovery curves were also studied. It is found that the on-state resistivity is approximately 0.08 Ω cm, independent of electrode material. The on state is that of a semiconductor whose electronic band structure and carrier mobility are essentially unchanged from the off state, but in which a concentration of about 7×1018 free electron/cm3 produces the high conductivity observed. The decay of the on state is due to a combination of diffusion of the free carriers out of the filament, together with direct carrier recombination. A major result of this work is the determination of the size of the conducting filament as a function of operating current. As expected, the current density in the filament is essentially independent of on-state current, provided the filament does not saturate the device pore. However, the filament turns out to be much larger than previous speculations, leading to the result that heating effects are negligible at currents below those for which the pore saturates.