Active Width Modulation (AWM) for cost-effective and highly reliable PRAM

This paper presents, for the first time, the Active Width Modulation (AWM) technology which compensates a string resistance with the active widths of local Y selectors for the purpose of increasing the number of cells-per-string (CPS). The AWM is demonstrated using 58 nm 512 Mb PRAM with 32 CPS instead of 8 CPS [1], which can reduce the chip size by 4.3%. Also, the systematic variability of a program current, ΔI_PGM, is reduced from 17.8% to 0.82%, and that of a write energy, ΔE_PGM, from 47.9% to 2.0%. Both write endurance and disturbance of >1M cycles are achieved for 512 Mb PRAM. The AWM can be further applied to increase CPS to 64 or 128, together with the reduction of a reset current, I_RESET, for sub-40 nm PRAM technology and so on.