On resistive open defect detection in DRAMs: The charge accumulation effect

The test complexity of high density DRAMs increases with technology evolution, due to a larger impact of process variation and weak defects. In particular, resistive open defects turn to be a major concern in DRAMs. Our analysis and simulation results show that an important phenomenon exists, charge accumulation, which is currently not considered in DRAM testing. Charge accumulation occurs in DRAM cells that suffer from internal resistive opens; a weak value stored at a cell is strengthened when a sequence of read operations is applied to it. Typical DRAM testing procedures (like March tests) fail to provide enhanced coverage of resistive open defects, since they do not consider charge accumulation. This paper provides an effective test algorithm that targets resistive open defects, while considering the bit-line imbalance and the charge accumulation mechanisms.