  Resistive switching devices based on transition metal oxides require
formation of a conductive filament in order for the device to be able to
switch. Such filaments have been proposed to form by the reduction of the oxide
due to application of the electric field, but this report seeks to rebut that
interpretation. Frequently reported physical changes during electro-formation
include delamination of electrodes, crystallization of functional oxide,
intermixing of electrode and oxide materials, and extensive loss of oxygen
presumably to the ambient. Here we show that most of these effects are not
inherent to the formation and switching processes and instead are due to an
experimental artifact: the discharge of parasitic capacitances in the forming
circuit. Discharge of typical BNC cables can raise the temperature of the
filament to between 2,000 and 5,000 K resulting in extensive physical changes.
Discharge and associated effects mentioned above can be eliminated using an
on-chip load element without affecting the ability to switch.
