Memory retention in substrate environment and its role in feedback mechanism in neuromorphic devices*

Substrates used for thin film growth are often seen as fixed and unaffected by the processes occurring in the films they support. Using a novel full-field diffraction-contrast x-ray microscope, we investigate the effects a thin-film device has on its substrate during a voltage-driven phase transition. We studied VO2/Sapphire and showed there is significant strain originating from the film at the activation site of the filament formation in VO2. These strain effects propagate perpendicular to the filament causing displacement and reorientation of the local structure of the substrate which have remnants after voltage is removed. These results are further reinforced by effects seen in LSMO/STO systems which show strain, reorientation, and hysteretic effects. This presents one of the first investigations, to our knowledge, of the effects of the film on the substrate which may be further used for network tuning and information propagation in neuromorphic systems.