A nanoscale investigation of the electrical response of plasma deposited AgNPs-based nanocomposites for in-memory computing
Résumé
The main challenge for efficient neuromorphic computing with non-volatile memory cells is to control the electrical properties at the device scale, in terms of charges trapping, and transport or relative dielectric permittivity. To improve device performance, inorganic nanocomposites, and particularly materials based on silver nanoparticles (AgNPs) embedded in a silica (SiO2) matrix appear attractive. Besides, electrical modes derived from Atomic Force Microscopy are appropriate to address their electrical response at local (nano-)scale: Conductive AFM (C-AFM) for current measurements, Kelvin Probe Force Microscopy (KPFM) for charge injection and transport or Electrostatic Force Microscopy (EFM) for relative dielectric permittivity.
This work investigates the electrical properties of dielectric nanocomposites comprising a 2-dimensional (2D) network of AgNPs inserted in SiO2 at a well-controlled distance from the surface. The structures were synthesized in a hybrid plasma process, successfully combining sputtering of a silver target for the AgNPs and plasma polymerization for the SiO2 matrix. After a structural characterization of the samples, the impact of AgNPs size, shape and inter-particle distance on charge transport and relative dielectric permittivity is investigated by KPFM and EFM. The results demonstrate that the electrical response of the nanostructures can finely be controlled by a proper inclusion of the AgNPs [3]. Indeed, the 2Dnetwork of AgNPs induces a modulation of the relative dielectric permittivity at nanoscale (lowering it above and increasing it in-between the AgNPs) which entails a modification of the macroscale apparent dielectric permittivity. Modifications of the designed electric field distribution in the nanocomposite due to the presence of a 2D-network of AgNPs is discussed as well. Such issues strongly impact the device performance and shall be accounted for when taking electrical contacts to connect the device with external circuity.
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