Formation of Filament in TaOx RRAM Devices
The widely accepted model of the formation of non-volatile conducting filament in oxide switching devices assumes that applied electric field induces a transfer of oxygen ions from the functional layer to the metal electrode. The process creates local deficiency of oxygen in the functional oxide with the vacancies acting as shallow donors. This process converts highly resistive oxide into an n-type semiconductor. The model has surprisingly little direct experimental support in form of electron microscopy or elemental maps of the filament. What is available was typically obtained on structures formed with high current compliance. We propose a different model for filament formation and present the supporting evidence. The typical I-V of metal/oxide/metal structures exhibits a negative differential resistance region in which the uniform current flow spontaneously constricts to a small portion of the device area. This locally increases the temperature of the device and sets up high lateral temperature gradient. The gradient, in turn, drives the thermo-diffusion (also known as Soret effect) with tantalum atoms moving toward the high temperature region and oxygen moving in direction opposite to the gradient. The process results in accumulation of tantalum at the location of the high current density domain and depletion of oxygen. The elemental distribution was evaluated by High Angle Annular Dark Field, Electron Energy Loss Spectroscopy and Energy Dispersive X-ray Spectroscopy imaging and clearly show the lateral separation within TaOx layer.
|Formation of Non-volatile Filament in TaOx Resistive Switching Devices|
Wednesday, May 17, 2017, 11 a.m.–noon PT
Los Angeles, CA, United States