This report discusses the electrical characteristics of two-terminal synaptic memory devices capable of demonstrating an analog change in conductance in response to the varying amplitude and pulse-width of the applied signal. The devices are based on Mn doped HfO2 material. The mechanism behind reconfiguration was studied and a unified model is presented to explain the underlying device physics. The model was then utilized to show the application of these devices in speech recognition. A comparison between a 20 nm × 20 nm sized synaptic memory device with that of a state-of-the-art VLSI SRAM synapse showed ~10× reduction in area and >106 times reduction in the power consumption per learning cycle.
In this paper, we report multi-level cell (MLC) switching characteristics of resistive random access memory devices with a W/Zr/HfO 2 /TiN stack. A multi-step forming technique was implemented in this work which efficiently suppressed the forming current overshoot and allowed device switching at a low set/reset voltage and current. Four distinct resistance states, achieved by controlling the reset stop voltages, showed excellent endurance. Write/read/erase energy values for different states were also calculated. Amongst four MLC states, it was found that the lowest resistance state of three distinct high-resistance states was prone to failing over time under constant voltage stress.
We report the switching dynamics and charge transport studies on Ru/HfO2/TiOx/Ru resistive random access memory devices in low resistance state (LRS), high resistance state (HRS), and virgin resistance state (VRS). The charge transport in LRS is governed by Ohmic conduction of electrons through local filamentary paths while it is governed by a combination of Frenkel-Poole emission and trap assisted tunneling process in HRS and VRS. The area of the filament in LRS is extracted and related to the compliance current. The thickness of the re-oxidized filament is extracted and related to the reset voltage in HRS. The energy consumed during the reset process was analyzed on the time-scale to experimentally demonstrate joule-heating mediated oxidation dynamics of filament during device reset.
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