Thermally induced crystallization in NbO₂ thin films.

Area of Science:

• Materials Science
• Solid State Physics
• Device Physics

Background:

• Niobium dioxide (NbO2) exhibits negative differential resistance (NDR) in metal-insulator-metal (MIM) devices.
• NDR in NbO2 is promising for nonvolatile memory (NVM) selectors and neuromorphic computing elements.

Purpose of the Study:

• Investigate the impact of thermal annealing on NbO2 thin films within MIM devices.
• Compare structural and compositional changes in nanoscale NbO2 films versus thicker reference films.

Main Methods:

• Fabrication of 15 nm NbO2-based MIM devices.
• Thermal annealing of MIM devices and blanket NbOx films (x=2, 2.5).
• Transmission electron microscopy (TEM) for structural analysis.
• Electron energy loss spectroscopy (EELS) for quantitative composition analysis.

Main Results:

• Amorphous NbO2 transitions to a distorted rutile structure upon annealing.
• Transition temperature observed at 700°C for MIM devices and 750°C for reference films.
• EELS revealed non-stoichiometry in the as-fabricated NbO2 layer due to electrode interaction, exacerbated by annealing.

Conclusions:

• Thermal annealing induces a crucial structural transformation in NbO2 for potential device applications.
• Electrode material interactions significantly influence NbO2 stoichiometry during processing.
• Understanding these effects is vital for optimizing NbO2-based NVM and neuromorphic devices.