Towards Synaptic Behavior of Nanoscale ReRAM Devices for Neuromorphic Computing Applications

AbstractResistive Random Access Memory (ReRAM), a form of non-volatile memory, has been proposed as a Flash memory replacement. In addition, novel circuit architectures have been proposed that rely on newly discovered or predicted behavior of ReRAM. One such architecture is the memristive Dynamic Adaptive Neural Network Array, developed to emulate the functionality of a biological neuron system. We demonstrated ReRAM devices that show a synaptic tendency by changing their resistance in an analog fashion. The CMOS compatible nanoscale ReRAM devices shown are based on an HfO2 switching layer that sits on a tungsten electrode and is covered by a titanium oxygen scavenger layer and a titanium nitride top electrode. In this work, we showed devices exceeding endurance values of 10B cycles with a discrete Roff/Ron ratio of 15. Multi-level states were achieved by using consecutive ultra-short 5/1.5 ns pulses during the reset operation. A neural network simulation was performed in which the synaptic weights were perturbed with the ReRAM variability, which was extracted from two different characterization methods: (1) via direct write, and (2) via a write/read verification approach during the reset operation. A substantial improvement of the neural network fitness was demonstrated when using the write/read verification approach.