Enhancement in neuromorphic NbO2 threshold switching at cryogenic temperatures

The electrical properties and performance characteristics of niobium dioxide (NbO2)-based threshold switching devices are examined at cryogenic temperatures. Substoichiometric Nb2O5 was deposited via magnetron sputtering and patterned in microscale (2×2−15×15 μm2) crossbar Au/Ru/NbOx/Pt devices and electroformed at 3–5 V to make NbO2 filaments. At cryogenic temperatures, the threshold voltage (Vth) increased by more than a factor of 3. The hold voltage (Vh) was significantly lower than the threshold voltage for fast voltage sweeps (200 ms per measurement). If the sample is allowed to cool between voltage measurements, the hold voltage increases, but never reaches the threshold voltage, indicating the presence of nonvolatile Nb2O5 in the filament. The devices have an activation energy of Ea≈1.4 eV, lower than other NbO2 devices reported. Our work shows that even nominally "bad" selector devices can be improved by reducing the leakage current and increasing the sample resistance at cryogenic temperatures.