Interplay Bitwise Operation in Emerging MRAM for Efficient In-memory Computing

In order to realize high efficient magnetization switching in magnetic tunnel junction (MTJ), several potential mechanisms have been realized as the interplay effect to MTJ device, such as the interaction between spin orbit torque-spin transfer torque (STT) and voltage-controlled magnetic anisotropy (VCMA)-STT. The interplay mechanisms have been experimentally explored with improved switching energy efficiency comparing with traditional STT method. Considering the requirement of mixed-precision memory, we propose a novel write-only in-memory computing paradigm based on interplay bitwise operation in two terminal or three terminal MRAM bit-cell, which aims to reduce the layout overhead of peripheral computing circuits, as well as to eliminate read decision failure in the procedure of in-memory computing. Specifically, the proposed write-only bitwise in-memory computing is demonstrated with OR, AND, XOR, full adder operations. Four nonvolatile approximate full adders (AxFAs) are proposed and implemented in different MRAM bit-cells. The AxFAs can be easily reconfigured into memory units with simple connections. Image processing applications are used to demonstrate the in-memory computing, include FA, XOR operation. Comparing with traditional sensing based approach, more than 80% energy reduction is obtained using the proposed interplay writing-only in memory computing with approximation setup. A 61.4% energy reduction is achieved using VCMA mechanism interaction based XOR functions.