Influence of Bit-Line Coupling and Twisting on the Faulty Behavior of DRAMs

With the continued advances in miniaturization, bit-line (BL) coupling is becoming ever more influential on the memory behavior. This paper discusses the effects of BL coupling on the faulty behavior of defective dynamic RAMs. It starts with an analytical evaluation of coupling effects, followed by a simulation-based fault analysis using a Spice simulation model. Two BL coupling mechanisms are identified (pre-sense and post-sense coupling), which are found to have a partly opposing effect on the faulty behavior. It is shown that BL coupling causes a special kind of coupling fault between adjacent memory cells. In addition, the influence of BL twisting on the faulty behavior of the memory is analyzed and simulated. The results indicate strong correspondence between theory and simulation and show the importance of Spice simulation as a vital tool for fault analysis