SRAM cell reliability degradations due to cell crosstalk

Abstract

The capacitance between adjacent SRAM cells due to defectivity can increase in smaller geometry technologies. However, the abnormal behaviors due to such defective capacitance in SRAM are often neglected and can cause NTF (No Trouble Found) failures. The effective testing or calibration methods for such capacitance due to defects are not easily available in today's manufacturing. In this paper, a 3-D field solver was used to see the potential ranges of the defective capacitance. The crosstalk AC current through the coupling capacitance, which is referred to as cell coupling capacitor (CCCP) is newly modeled as a current source to build modified SNM (Static Noise Margin). The two metrics, SNM and VDDMIN show that the reliability under the CCCP can be significantly degraded during memory operations. Even with a marginal CCCP, SNM variation is 40mV at a read operation and VDDMIN shift is 110mV at a write operation in a 65nm SRAM cell.