An Energy-Efficient Computing-in-Memory (CiM) Scheme Using Field-Free Spin-Orbit Torque (SOT) Magnetic RAMs

The separation of memory and computing units in the von Neumann architecture leads to undesirable energy consumption due to data movement and insufficient memory bandwidth. Energy-efficient in-memory computing platforms have the potential to address such issues. Due to its non-volatility and advantageous features over CMOS (such as low power, near-zero leakage current and high integration density), spin-based devices have been advocated for in-memory computing. This paper proposes a field-free Spin Orbit Torque (FF-SOT) MRAM based computing-in-memory (CiM) scheme that realizes XNOR/XOR logic and a cascading adder. This novel FF-SOT-CiM design does not require expensive peripheral circuits for computation while using the same memory cell design as a SOT-MRAM. Furthermore, FF-SOT-CiM does not require additional write cycles to save the result of its computations in the memory. The design offers higher write speed and; lower operating energy compared to CiM schemes based on other technologies; it also alleviates the source degeneration effect by leveraging an advanced switching mechanism. Extensive simulation results show that the proposed FF-SOT-CiM achieves up to 3.1x (2.6x) latency (energy) reduction compared to SRAM-based CiM, with negligible hardware overhead when performing in-memory XOR. ADD operations; the proposed FF-SOT-CiM can be to 5.0X and 1.5X faster and 3.4X and 1.1X more energy efficient than existing STT-based and FeFET-based schemes, respectively.