Interplay Bitwise Operation in Emerging MRAM for Efficient In-memory Computing
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Interplay Bitwise Operation in Emerging MRAM for Efficient In‑memory Computing Hao Cai1 · Honglan Jiang2 · Yongliang Zhou1 · Menglin Han1 · Bo Liu1 Received: 17 February 2020 / Accepted: 22 July 2020 © China Computer Federation (CCF) 2020
Abstract 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 inmemory 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. Keywords MTJ interplay writing · Mixed-precision memory · In-memory computing · Image processing
1 Introduction As a promising candidate to replace traditional memories, the wide range application of spin transfer torque magnetic random access memory (STT-MRAM) is delayed due to its intrinsic limitations (Kanai et al. 2012; Wang et al. 2012; Maruyama et al. 2009; Wang et al. 2018a). Alternatively, magnetic tunnel junction (MTJ) with voltage-controlled magnetic anisotropy (VCMA) effect provides flipping of the magnetization upon a voltage pulse, irrespective of This work is funded with National Key R&D Program of China under Grant 2018YFB2202800 and National Natural Science Foundation of China under Grant 61904028. * Hao Cai [email protected] 1
National ASIC System Engineering Center, School of Electronic Science and Engineering, Southeast University, Nanjing 210096, China
Institute of Microelectronics, Tsinghua University, Beijing 100084, China
2
the initial state. Thus, this magnetoelectric random access memory achieves less energy consumption and higher density, as well as the improved switching latency thanks to the very little charge flow required to operate (Wang et al. 2012; Maruyama et al. 2009). Another switching method referred to as the spin orbit torque (S
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