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Low-frequency noise measurements were performed on HfO2-based bipolar resistive switching memory devices. A 1/fα DC noise power spectral density was observed with α ∼ 1 for a low resistance state and α ∼ 2 for a high resistance state. We developed an electron tunneling model to elucidate the conduction process, which showed that the 1/fα behavior was due to the distribution of relaxation times of electron tunneling between the electrodes and the traps in the conducting filaments. The transition of the slope index α from 1 to 2 at a certain cutoff frequency indicates that there is a tunneling gap formed between electrodes and the residual of the conductive filaments in the high resistance state. [ABSTRACT FROM AUTHOR]

Many chalcogenide glasses undergo a breakdown in electronic resistance above a critical field strength. Known as threshold switching, this mechanism enables field-induced crystallization in emerging phase-change memory. Purely electronic as well as crystal nucleation assisted models have been employed to explain the electronic breakdown. Here, picosecond electric pulses are used to excite amorphous Ag4In3Sb67Te26. Field-dependent reversible changes in conductivity and pulse-driven crystallization are observed. The present results show that threshold switching can take place within the electric pulse on subpicosecond time scales--faster than crystals can nucleate. This supports purely electronic models of threshold switching and reveals potential applications as an ultrafast electronic switch. [ABSTRACT FROM AUTHOR]