Repeatable unipolar/bipolar resistive memory characteristics and switching mechanism using a Cu nanofilament in a GeO _x film

This paper investigates the repeatable unipolar/bipolar resistive switching memory characteristics in a copper/germanium-oxide/tungsten (Cu/GeO _x/W) structure. The switching mechanism occurs because of the lower barrier height for hole injection rather than electron injection. Therefore, Cu ions, as a positive charge, migrate before initiating growth at the GeO _x/W interface and dissolving at the GeO _x/Cu interface. The diameter of the Cu nanofilament increases linearly from 0.13 Å to 25 nm as current compliances increase from 1 nA to 10 mA, as calculated using the other approach. The crystalline Cu nanofilament was also confirmed by high-resolution transmission electron microscopy analysis under SET. Good data retention with high resistance ratios of 10 ²-10 ⁵ (and >10 ⁴ at 85 °C) and ∼10 ⁹ was obtained under the bipolar and unipolar modes, respectively. Therefore, a maximum memory size of 5000 Pbit/in ² can be designed in the future.