Evidence for thermally assisted threshold switching behavior in nanoscale phase-change memory cells

Abstract

In spite of decades of research, the details of electrical transport in phase-change materials are still debated. In particular, the so-called threshold switching phenomenon that allows the current density to increase steeply when a sufficiently high voltage is applied is still not well understood, even though there is wide consensus that threshold switching is solely of electronic origin. However, the high thermal efficiency and fast thermal dynamics associated with nanoscale phase-change memory (PCM) devices motivate us to reassess a thermally assisted threshold switching mechanism, at least in these devices. The time/temperature dependence of the threshold switching voltage and current in doped Ge2Sb2Te5 nanoscale PCM cells was measured over 6 decades in time at temperatures ranging from 40 °C to 160 °C. We observe a nearly constant threshold switching power across this wide range of operating conditions. We also measured the transient dynamics associated with threshold switching as a function of the applied voltage. By using a field- and temperature-dependent description of the electrical transport combined with a thermal feedback, quantitative agreement with experimental data of the threshold switching dynamics was obtained using realistic physical parameters.

Redefining the Speed Limit of Phase Change Memory Revealed by Time-resolved Steep Threshold-Switching Dynamics of AgInSbTe Devices

“…For instance, a steep leading edge (rise time, t r ) enables determining the delay time precisely1127, the pulse width (t w ) controls the crystallization of the PC material5 and the trailing edge (fall time, t f ) shows the status of device resistance. Therefore, for the present investigation to validate the dependency of transient parameters on applied voltage, pulses of various amplitudes such as 1.8 V, 2.1 V and 2.6 V having the pulse parameters of leading edge of 1 ns and pulse width/trailing edge of 100 ns were used.…”

Te-based chalcogenide materials for selector applications

“…In recent years, various models attempting to explain the switching phenomenon have been developed, such as Poole-Frenkel ionization, field-induced delocalization of tail states, space-charge limited currents, optimum channel hopping in thin films, optimum channel field emission, percolation band conduction, transport through crystalline inclusions 30 or thermally-assisted threshold switching 31 .…”

Temperature Evolution in Nanoscale Carbon-Based Memory Devices Due to Local Joule Heating

“…This allows us to examine the time response of the current on the applied voltage and, as a consequence, enables us to select a pulse long enough to exclude any 'undesirable' transient effects prior to memory switching (e.g., due to thermal capacitances [24]). This, in turn, allows us to obtain a realistic temperature profile of the memory device at the onset of memory switching.…”