A Study on Improved Read Operation to Enhance Reliability for Cross-Point Phase Change Memory

Abstract

As the total amount of data increased explosively, it caused the shift from compute-centric to memory-centric servers leading to bottleneck in data processing. The bottleneck between the main memory and storage memory occurs due to the performance gap. Storage class memory has emerged as a breakthrough for fulfilling the performance gap. Phase change random access memory with ovonic threshold switching selector (OTS) cross-point memory is one of the suitable candidates for storage class memory. However, snapback phenomenon exists in the threshold switching of OTS selector that induces a rapid current called snapback current, resulting in read interference.

In this study, a sensing scheme with current discharge path is introduced as a solution to reduce the effect of snapback current. Also, two improved sensing schemes with current discharge path are investigated that shows sensitive operation of initial state when OTS is turned on. The sensing scheme is verified using HSPICE. Pre-charge sensing scheme with current discharge path circuit shows 75% shorter sensing time, and energy dissipation improvement of 62%. Adding feedforward path reduces the energy dissipation from 16.05uW to 12.07uW, sensing time from 3.26ns to 3.11ns, and peak power level from 37.2fJ to 27.5fJ as compared to the original discharging path. Adding snapback current controller shows the similar effect with that of feedforward path exhibiting energy dissipation of 33.4fJ, peak power of 12.60uW, and sensing time of 3.8ns.