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Crystallization (set) time is a key bottleneck to achieve high-speed programming in phase change memory (PCM). Overcoming this limitation requires a deeper understanding of the solidification processes within nanoscale device configuration. This study explores crystallization dynamics in Ge2Sb2Te5 by measuring the transient resistance and power during the set process in confined PCM cells with nanosecond resolution. The transient resistance probes the phase, while the power can be used to evaluate temperature, thus uncovering details of the phase change dynamics. Our findings reveal a notable trend indicating that solidification from the melt results in faster crystallization compared with annealing the glassy state. Moreover, we observed notable differences in the solidification dynamics during set (crystallization) and reset (amorphization) pulses. Our nanosecond transient measurement methodology proves valuable in revealing crucial aspects of PCM crystallization dynamics, holding the potential to enable higher-speed programming. [ABSTRACT FROM AUTHOR]

Despite their great synaptic potential, the trade-off between programming speed and energy consumption of electrochemical random-access memory (ECRAM) devices are major hindrance to their incorporation into practical applications. In this work, we experimentally study the main limiting factor for high-speed programming of ECRAMs, the ionic current in the gate stack. We use two-terminal structures composed of LiCoO2/Li3PO4/amorphous-Si to represent the ECRAM gate stack (reservoir/electrolyte/channel). We perform electrical characterization including impedance spectroscopy (small-signal) and large-signal transient measurements across nine orders of magnitude in the time domain. We find that at the sub-microseconds range, the current is governed by the energy barrier for Li+ ions at the electrolyte interfaces. After a period of ∼1 μs, ionic migration through the ∼80 nm electrolyte layer dictates the current. At ∼50 μs, the ionic double layer at the interface is fully charged and the gate current drops by several orders of magnitude, indicating that the Li3PO4/Si interface is saturated, and the measured current is dominated by the electronic leakage component. Furthermore, we evaluate ECRAM performance under various pulse parameters. Our predictions show that an aggressively scaled (atomically thin) channel having a low carrier density of ∼1011 cm−2 can be programmed at ∼nanosecond using a gate current of ∼100 A/cm2. [ABSTRACT FROM AUTHOR]

One of the key challenges of phase change memory (PCM) is its high power consumption during the reset operation, when the phase change material (typically Ge2Sb2Te5, i.e., GST) heats up to ∼900 K or more in order to melt. Here, we study the temperature-dependent behavior of PCM devices by probing the reset power at ambient temperatures from 80 to 400 K. We find that different device structures exhibit contrasting temperature-dependent behavior. The reset power in our confined-type PCM is nearly unchanged with ambient temperature, corresponding to a temperature-dependent thermal resistance, whereas results for mushroom-type PCM from the literature show a linear relation between power and temperature, suggesting a more constant thermal resistance. This discrepancy is ascribed to different temperature distributions and thermal properties of the dominant components of the PCM cell thermal resistance, as shown by electro-thermal modeling. In the confined cell, the thermal boundary resistance of the GST and the thermal conductivity of the bottom electrode dominate the thermal resistance, while for the mushroom cell, the GST thermal conductivity plays a greater role. These findings can help to design more power- and energy-efficient PCM devices by better focusing thermal management efforts on the key components of the device. [ABSTRACT FROM AUTHOR]