Area and Thickness Scaling of NbOₓ-Based Threshold Switches for Oscillation Neurons

Abstract

The reversible transition between the on and off states of threshold switches under a constant pulse generates voltage oscillation, which can be exploited for compact neuron element in neuromorphic systems. Because the transition voltages play an important role in the oscillation behavior, area and thickness scaling analysis of NbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> -based devices is performed to identify the underlying mechanism. The threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{th}$ </tex-math></inline-formula> ) is sensitive to the device area, indicating that the on state of the device is achieved by the local formation of a conductive phase. On the other hand, the area-independent hold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm{ hold}}$ </tex-math></inline-formula> ) becomes smaller due to the higher compliance current and increased temperature ambient, which implies that spontaneous dissolution of the phase is retarded. Through HSPICE simulation, we reveal that the greater difference between <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\mathrm{ hold}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\mathrm{ th}}$ </tex-math></inline-formula> enables a high degree of freedom of oscillation frequency modulation.