Impact of vacuum on the resistive switching in HfO₂-based conductive-bridge RAM with highly-doped silicon bottom electrode

Moisture can modulate the resistive switching dynamics in oxide-based electrochemical metallization devices. Unconventional testing environments such as vacuum, could possibly shift the device characteristics, requiring therefore a careful investigation. This work investigates the write/erase behavior of Cu/HfO₂(~80-nm-thick)/p⁺-Si devices in ambient atmosphere and vacuum, under similar electrical bias applied to the top Cu electrode. In vacuum (~5.3 × 10⁻³ Pa), a parasitic negative SET (N-SET) readily arises during the “erase” operation, unlike in ambient air. The electrical studies and physicochemical analyses of electrically-biased and pristine devices reveal that the “erase” process is sensitive to the environment. Vacuum facilitates the electric-field-controlled generation of an oxygen-vacancy-based path that likely induces a parasitic N-SET at the negative voltage. This path is aided by the presence of partially-ruptured copper filaments at the HfO₂/p⁺-Si interface. The vacuum effects leading to the N-SET are eliminated by introducing a passivating gas environment (zero-air or nitrogen), or device encapsulation.