Electro-Thermal Model of Threshold Switching in TaOx-Based Devices

Pulsed and quasi-static current–voltage (I–V) characteristics of threshold switching in TiN/TaOx/TiN crossbar devices were measured as a function of stage temperature (200–495 K) and oxygen flow during the deposition of TaOx. A comparison of the pulsed and quasi-static characteristics in the high resistance part of the I–V revealed that Joule self-heating significantly affected the current and was a likely source of negative differential resistance (NDR) and thermal runaway. The experimental quasi-static I–V’s were simulated using a finite element electro-thermal model that coupled current and heat flow and incorporated an external circuit with an appropriate load resistor. The simulation reproduced the experimental I–V including the OFF-state at low currents and the volatile NDR region. In the NDR region, the simulation predicted spontaneous current constriction forming a small-diameter hot conducting filament with a radius of 250 nm in a 6 μm diameter device.