Pulse Dependent Threshold Voltage Variation of the Ovonic Threshold Switch in Cross-Point Memory

Abstract

We report the pulse dependent threshold voltage ( ${V} _{t}$ ) variation of the Ovonic Threshold Switch (OTS) and its effect on the read window margin (RWM) in Cross-Point Memory (XPM). We found that OTS ${V} _{t}$ varies by the height and width of the write-current pulse. The varied ${V} _{t}$ is persistently maintained even after 2E4 cycling of the write pulse, which means that the phenomenon is not a temporary one, but a type of memory effect in OTS itself. Therefore, it would affect the overall ${V} _{t}$ window ( $\Delta {V}_{t}$ ) of XPM by changing the Set ${V} _{t}$ ( ${V} _{t\_{}{\text {Set}}}$ ) and Reset ${V} _{t}$ ( ${V} _{t\_{}{\text {Reset}}}$ ) when combined with either phase-change memory (PCM) or resistive memory (RM). High-resolution transmission electron microscopy (HRTEM) and fast Fourier transform (FFT) images have proved that this phenomenon is not caused by the phase change of the OTS. Instead, a sub-threshold analysis extracted from the Poole-Frenkel model suggests that the phenomenon is associated with the variation of the amorphous network either by changes in the atomic bonding configuration or trap density.