Aliens

Abstract

Passive crossbar arrays of resistive random-access memory (RRAM) have shown great potential to meet the demands of future memory. By eliminating transistor per cell, the crossbar array possesses a higher memory density but introduces sneak currents which incur extra energy waste and reliability issues. The complementary resistive switch (CRS), consisting of two anti-serially stacked memristors, is considered as a promising solution to the sneak current problem. However, the destructive read of the CRS results in an additional recovery write operation which strongly restricts its further promotion. Exploiting the dual CRS/memristor mode of CRS devices, we propose Aliens, a novel hybrid architecture for resistive random-access memory which introduces one alien cell (memristor mode) for each wordline in the crossbar to provide a practical hybrid memory without operating system's intervention. Aliens draws advantages from both modes: restrained sneak current of CRS mode and non-destructive read of memristor mode. The simple and regular cell mode organization of Aliens enables an energy-saving read method and an effective mode switching strategy called Lazy-Switch. By exploiting memory access locality, Lazy-Switch delays and merges the recovery write operations of the CRS mode. Due to fewer recovery write operations and negligible sneak currents, Aliens achieves improvement in energy, overall endurance, and access performance. The experiment results show that our design offers average energy savings of 13.9× compared with memristor-only memory, a memory lifetime 5.3× longer than CRS-only memory, and a competitive performance compared with memristor-only memory.