A Highly Punchthrough-Immune Array Architecture and Program Method for Floating-Gate NOR-Type Nonvolatile Memory

A novel array architecture is proposed for floating-gate nor-type nonvolatile memory cells. By embedding a floating n+ region between two cells in each memory pair, punchthrough (PT) immunity is greatly improved. Since the operating cell and the cascade cell belong to two independent word-lines, bit-pattern effect on read and program characteristics is mitigated, and multilevel-cell storage can be easily realized. No additional program disturb has been found. Erase, endurance, and retention characteristics are comparable with its conventional counterpart. According to simulations, L_g as short as 56 nm, which is projected to serve for 28 nm technology node, is feasible without suffering a serious PT effect.