Thickness effect of ultra-thin Ta 2 O 5 resistance switching layer in 28 nm-diameter memory cell

Resistance switching (RS) devices with ultra-thin Ta 2 O 5 switching layer (0.5-2.0 nm) with a cell diameter of 28 nm were fabricated. The performance of the devices was tested by voltage-driven current - voltage (I-V) sweep and closed-loop pulse switching (CLPS) tests. A Ta layer was placed beneath the Ta 2 O 5 switching layer to act as an oxygen vacancy reservoir. The device with the smallest Ta 2 O 5 thickness (0.5 nm) showed normal switching properties with gradual change in resistance in I-V sweep or CLPS and high reliability. By contrast, other devices with higher Ta 2 O 5 thickness (1.0-2.0 nm) showed abrupt switching with several abnormal behaviours, degraded resistance distribution, especially in high resistance state, and much lower reliability performance. A single conical or hour-glass shaped double conical conducting filament shape was conceived to explain these behavioural differences that depended on the Ta 2 O 5 switching layer thickness. Loss of oxygen via lateral diffusion to the encapsulating Si 3 N 4 /SiO 2 layer was suggested as the main degradation mechanism for reliability, and a method to improve reliability was also proposed.