DRAM Static Refresh Weak Cell Characterization and Structure Analysis

Data retention characteristic is one of the most critical issues in low power DRAMs because it determines idle currents of self-refresh operation. Compared to normal healthy cells, a few ppm orders of cells in a tail distribution have much higher leakage currents. The origin of the leaky cells (so called weak cells or tail cells) has been quite arguable for the past decades [1, 2], but it should be scrutinized in order to achieve long data retention time. In this paper, we have thoroughly investigated the behavior of the retention weak cells using a newly generated combination program and TEM analysis so as to discover and explain their origins