Threshold Switching and Conductance Quantization in Al/HfO

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Volatile threshold switching and non-volatile memory switching modes of resistive switching are reported in Al/HfO<inf>2</inf>/Si(p) metal--oxide--semiconductor structures with different values of current compliance limit during electroforming. When the current is limited to below 100 μA, a reproducible threshold switching loop is reported under injection from the p-type silicon substrate. The conduction in the low resistance state is linear above a voltage threshold called holding voltage and the conductance is a non-integer multiple of the quantum of conductance. Depending on the size of the conducting filament created during the electroforming process, one or several quasi-one dimensional quantum subbands are found to contribute to the current. Abrupt transitions between different discrete conductance values are reported during increasing and decreasing voltage sweeps. These results provide strong experimental evidence suggesting that the conduction filament behaves as a quantum wire (QW). No structural instability of the filament has to be invoked to explain either the highly structured conduction properties or the set and reset switching transitions. It is claimed that the whole phenomenology can be understood by electron injection from the valence band into a narrow conducting path which behaves as a QW.
2013-04-25