Effect of molecular-filament orientation on conductance in tyrosine-based amino acid synaptic devices

Neuromorphic computing via memristive devices has expanded across diverse materials, with interest shifting toward bio-compatible, amino-acid-based active layers. Such devices aim to replicate the buildup of ion concentration gradients that precede neurotransmitter release in biological synapses. Among implementations that use amino-acid-rich solutions as the active layer, tyrosine-based devices have recently attracted attention. While tyrosine-based memristors show promise for replicating biological synaptic behavior, the role of molecular orientation with respect to the conductive filament (CF) remains underexplored. This work presents a density functional theory study of the interaction between different spatial orientations of tyrosine molecules and a silver filament in an Ag/tyrosine/Ag two-terminal nanodevice. The proposed model comprises a sequential chain of five tyrosine molecules arranged in parallel with silver conductive filaments and positioned between source and drain terminals. The source-to-drain current was calculated for three different orientations under a similar biasing scheme. The results indicate that conductance was maximized when the CF was perfectly oriented with the molecular main backbone, from the N-terminus (amino end) to the C-terminus (carboxyl end).