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Dynamics of Amorphous Semiconductors: Intrinsic Nature and Application in Neuromorphic Hardware

Periodic Reporting for period 5 - NEURAMORPH (Dynamics of Amorphous Semiconductors: Intrinsic Nature and Application in Neuromorphic Hardware)

Reporting period: 2021-10-01 to 2022-09-30

After decades of perfecting the established way of computing, it is now evident that the fundamental logic of today’s computers will prevent them from ever reaching the efficiency of neural networks as found in nature. Neuromorphic hardware promises a leap forward by following the inherent working principles of biological neural networks. In very-large-scale integrated neuromorphic circuits incorporating an immense number of artificial neurons, the even much larger number of synapses poses the challenge of imitating especially the synaptic functionality in a most compact way. Over the last years, various memristive devices, i.e. devices with tunable resistance, have been proposed to represent the weight of a synapse, determining how well electrical spikes are transmitted from one neuron to another.

The NEURAMORPH project aimed to develop a simple and compact circuit element to modify the strength of synaptic connections between artificial neurons. The dynamics of electrical excitability intrinsic to the employed amorphous semiconductors should naturally be able to mimic features known from biological neural networks. For full control over the properties of these synaptic access elements, a fundamental understanding of the relaxation processes in such amorphous materials was imperative. To this end, in this project we performed physical experiments and computer simulations to elucidate the relationship between chemical composition, structural dynamics and changing electrical excitability.
We established a novel experimental method for characterizing the switching and relaxation dynamics in threshold-switching materials. We were able to derive relevant insights about the impact of defect occupation on conduction in the threshold-switching material Ge2Sb2Te5, the prototypical phase change material. Also, we worked on a model of collective structural relaxation in amorphous phase-change materials. Moreover, we broke out of the common ranges of known threshold-switching materials by demonstrating the essential properties of a threshold-switching device for pure Sb.
A deeper understanding of the switching and relaxation processes in amorphous materials showing threshold switching, which is required for the realization of novel neuromorphic circuit elements based on such materials.
Pure Antimony cutting through the maze of compositional complexity