Measurement of the Crystallization and Phase Transition of Niobium Dioxide Thin-Films for Neuromorphic Computing Applications Using a Tube Furnace Optical Transmission System

TL;DR

This study develops an optical measurement system to monitor the phase transition of niobium dioxide thin films during annealing, providing insights for neuromorphic computing applications by tracking spectral transmissivity and phase changes.

Contribution

A novel in situ optical system for real-time spectral measurement of niobium dioxide thin films during crystallization and phase transition processes.

Findings

Transition temperature from metallic to non-metallic phase occurs about 100°C lower on sapphire.

Crystalline Nb2O5 was successfully produced and characterized.

Spectral transmissivity changes correlate with phase transitions during annealing.

Abstract

Significant research has focused on low-power stochastic devices built from memristive materials. These devices foster neuromorphic approaches to computational efficiency enhancement in merged biomimetic and CMOS architectures due to their ability to phase transition from a dielectric to a metal at an increased temperature. Niobium dioxide has a volatile memristive phase change that occurs $\sim$800$^\circ$C~that makes it an ideal candidate for future neuromorphic electronics. A straightforward optical system has been developed on a horizontal tube furnace for \emph{in situ} spectral measurements as an as-grown \NbtOf\ film is annealed and ultimately crystallizes as \NbOt. The system measures the changing spectral transmissivity of \NbtOf\ as it undergoes both reduction and crystallization processes. We were also able to measure the transition from metallic-to-non-metallic \NbOt\ during the cooldown phase, which is shown to occur about 100$^\circ$C~ lower on a sapphire substrate than fused silica. After annealing, the material properties of the \NbtOf\ and \NbOt\ were assessed via X-ray photoelectron spectroscopy, X-ray diffraction, and 4-point resistivity, confirming that we have made crystalline \NbOt.