Experimental Robust Spontaneous Synchronizations in Coupled NbO$_{\textit{x}}$ Oscillation Neurons for Unconventional Computing

In this brief, we demonstrate experimentally achieved oscillation dynamics in coupled NbO $_{\textit{x}}$ threshold switch (TS)-based oscillation neurons (ONs). We first show the challenges in observing oscillation caused by device variability, which is further validated through HSPICE simulations. To obtain robust oscillation response, a reliable TS developed via atomic layer deposition for conformal NbO $_{\textit{x}}$ is introduced. By developing coupled NbO $_{\textit{x}}$ ONs using a coupling resistor ( $\textit{R}_{\textit{C}}$ ), the out-of-phase synchronization is demonstrated owing to the weak connection. Moreover, we achieve a transition to in-phase synchronization as the coupling strength increases, showing an inverse relationship with the magnitude of $\textit{R}_{\textit{C}}$ . Based on these results, oscillatory neural networks, where multiple NbO $_{\textit{x}}$ ONs are fully connected, are examined to execute pattern recognition via MATALB simulations.