Speaker
Description
Over the past decade, additive direct-write nanomanufacturing has emerged as a powerful approach for the localized synthesis of functional materials with minimal constraints on substrate choice or geometry. Among the available nanoscale techniques, Focused Electron Beam Induced Deposition (FEBID) has gained increasing attention due to its capability to directly synthesize nanostructures from precursor molecules with nanometer-scale precision. While FEBID is now widely recognized for the fabrication of complex 3D architectures, its potential for the direct synthesis of functional electronic materials in planar device geometries remains relatively unexplored. In particular, beam-written materials for memristive devices represent a promising route toward highly localized neuromorphic hardware elements and may ultimately enable adaptive networks extending even into three dimensions.
Here, we investigate the feasibility of synthesizing Nb-based memristive materials using FEBID from a Nb(NMe$_2$)$_3$(N-t-Bu) precursor. First, we confirm that the precursor enables reliable deposition of Nb-containing structures. A systematic parameter study is then performed to identify process windows allowing the fabrication of sub-nanometer-flat, homogeneous deposits, which are essential for integration in memristive devices. The intrinsic electrical properties of the resulting Nb–N–O material are subsequently evaluated using multi-electrode test structures. In this context, the influence of post-growth treatments, including electron beam curing, H₂O-assisted purification, and ambient exposure, is examined. It is found that the electrical behavior remains largely stable across these processing conditions, indicating robust conduction pathways within the material.
Based on these findings, stacked Au–(Nb–N–O)–Co₃Fe devices are fabricated with progressively reduced active layer thicknesses. While intermediate thicknesses (≈ 50–15 nm) exhibit stable conduction behavior with only minor processing dependencies, clear memristive characteristics emerge when the active layer thickness is reduced to the sub-5 nm regime. In such geometries, the devices show reproducible hysteretic I–V behavior following a short conditioning phase during the first measurement cycles. In contrast to purely ohmic conduction, a non-linear transport characteristic is observed. This suggests field-assisted conduction through defect states within the ultrathin Nb–N–O layer, consistent with trap-mediated transport mechanisms. Within this picture, charge transport is governed by the filling and emptying of localized defect states, giving rise to non-linear current–voltage behavior and the formation of dynamically evolving conductive pathways across the ultrathin layer, as commonly observed in amorphous nanogranular materials.
These results demonstrate that FEBID enables the direct synthesis of Nb-based memristive materials and provides a promising starting point for further research towards nanoscale memristive devices and beam-written neuromorphic architectures, both in planar and future 3D device designs.