New 4T-based DRAM cell designs

Abstract

Dynamic Random Access Memories (DRAM) are widely used in processor design. Different cells have been proposed in the past to overcome concerns associated with low retention time, degradation in performance due to process variations and susceptibility to soft errors. This paper proposes two novel DRAM cells (referred to as 4TI and 4T1D) that utilize the techniques of gated diode and forward body-biasing to overcome the above issues. The designs of these cells are evaluated by HSPICE simulation; different figures of merits (such as Read delay, Write delay, retention time, power dissipation, critical charge and layout area) are assessed and a comparative analysis of the proposed cells with existing cells is pursued. The 4TI cell achieves the best power dissipation, while the 4T1D achieves the best retention time, the highest critical charge and the least average Read delay. An extensive simulation based evaluation of process variations is also presented to confirm that using static and Monte Carlo based analysis, the proposed cells are likely to be less affected by process variations (in threshold voltage and effective channel length) than the other cells found in the technical literature.