Design of a Nonvolatile 7T1R SRAM Cell for Instant-on Operation

Energy consumption is a major concern in nanoscale CMOS ICs; the power-Off operational mode and low-voltage circuits have been proposed to alleviate energy dissipation. Static random access memories (SRAMs) are widely used in today's chips; nonvolatile SRAMs (NVSRAMs) have been proposed to preserve data, while providing fast power- On/Off speeds. Nonvolatile operation is usually accomplished by the use of a resistive RAM circuit (hence referred to as RRAM); the utilization of a RRAM with an SRAMs not only enables chips to achieve low energy consumption for nonvolatile operation, but it also permits to restore data when a restore on power-up is performed (this operation is also commonly referred to as “Instant-on”). This paper presents a novel NVSRAM circuit for “Instant-on” operation and evaluates its performance at nanometric feature sizes. The proposed memory cell consists of a SRAM core (in this case, a 6T cell) and an oxide resistive RRAM circuit (1T1R), thus making a 7T1R scheme. The proposed cell offers better nonvolatile performance (in terms of operations such as “Store,” “Power-down,” and “Restore”) when compared with existing nonvolatile cells. The scenario of multiple-context configuration is also analyzed. Figures of merit such as energy, operational delay, and area are also substantially improved, making the proposed design a better scheme for “Instant-on” operation.