The field of spintronics has attracted tremendous attention recently owing to its ability to offer a solution for the present-day problem of increased power dissipation in electronic circuits while scaling down the technology. Spintronic-based structures utilize electron’s spin degree of freedom, which makes it unique with zero standby leakage, low power consumption, infinite endurance, a good read and write performance, nonvolatile nature, and easy 3D integration capability with the present-day electronic circuits based on CMOS technology. All these advantages have catapulted the aggressive research activities to employ spintronic devices in memory units and also revamped the concept of processing-in-memory architecture for the future. This review article explores the essential milestones in the evolutionary field of spintronics. It includes various physical phenomena such as the giant magnetoresistance effect, tunnel magnetoresistance effect, spin-transfer torque, spin Hall effect, voltage-controlled magnetic anisotropy effect, and current-induced domain wall/skyrmions motion. Further, various spintronic devices such as spin valves, magnetic tunnel junctions, domain wall-based race track memory, all spin logic devices, and recently buzzing skyrmions and hybrid magnetic/silicon-based devices are discussed. A detailed description of various switching mechanisms to write the information in these spintronic devices is also reviewed. An overview of hybrid magnetic /silicon-based devices that have the capability to be used for processing-in-memory (logic-in-memory) architecture in the immediate future is described in the end. In this article, we have attempted to introduce a brief history, current status, and future prospectus of the spintronics field for a novice.

Spintronics is one of the growing research areas which has the capability to overcome the issues of static power dissipation and volatility suffered by the complementary metal-oxide-semiconductor (CMOS) industry. Magnetic tunnel junction (MTJ), one of the prominent spintronic devices, is not only used to develop the fully non-volatile-logic (NV-L) but combines magnetism and electronics to develop next-generation NV-memory (NV-M) and hybrid CMOS/MTJ circuits. To be specific towards hybrid CMOS/MTJ circuits, the fabrication of first hybrid full-adder in 2009, fabrication of MTJ based 240-tile NV-field programmable gate array (NV-FPGA) chip in 2013, fabrication of a 3000-6-input-LUTs based NV-FPGA chip in 2015, fabrication of MTJ based NV-logic-in-memory-large scale integration (NV-LIM-LSI) in 2017 and recently the fabrication of a full hybrid magnetic/CMOS System on Chip (SoC) under EU GREAT Project in 2019 has strengthened the belief and motivated the researcher to be continued in this domain. This review article aims to provide the complete design flow of hybrid CMOS/MTJ circuits developed using one of the fab compatible MTJ spintronic devices and its integration with conventional CMOS logic. The broad coverage of the article is MTJ construction, its switching mechanisms, a brief history of various compact models, reliability issues, and the concept of logic-in-memory (LIM) architecture. Finally, the article concludes with the challenges and future prospects of hybrid CMOS/MTJ circuits, which will motivate people in academia to cultivate research in this domain and industry to realize the prototype for a wide range of potential applications.

Surge in the power dissipation due to increased leakage current has become one of the major concern in conventional CMOS VLSI design because of reduced transistor size, lower threshold voltage and lower supply voltage. To alleviate this, we have designed hybrid magnetic tunnel junction (MTJ)/CMOS circuits based on logic-in-memory (LIM) structure for various logic gates such as NAND/AND, NOR/OR and XNOR/XOR. This paper investigates the performance of hybrid gates and the results are compared with the conventional CMOS based gates in-terms of power, delay and device count. Hybrid gates designed in this paper are not only non-volatile in nature due to the use of MTJs but also they are found superior than the conventional CMOS circuits by dissipating less power and occupying smaller die area.

Emerging hybrid spin-Hall-effect-assisted+spin transfer torque-magnetic tunnel junction (SHE+STT-MTJ)/CMOS logic-in-memory (LIM) architecture is considered as the promising next-generation candidate for the future digital integrated circuits. It overcomes the limitations of von Neumann architecture such as memory wall and also rises in the standby mode energy consumption. There are several full adder (FA) circuits based on the LIM architecture, which are either fully nonvolatile (NV) or partially NV. As the main disadvantage, these circuits suffer from wastage of write energy during the MTJ writing process. Furthermore, the existing fully NVFA can be used only for approximate computing. Hence, in this article, we have proposed fully NVFA for exact computation with self-write-termination read-write (SWTRW) circuitry. In SWTRW circuitry, wastage of write energy is eliminated due to a continuous monitoring (CM) and self-write-termination (SWT) process which saves a significant amount of energy of 95.88%. With the adaption of an improved sense amplifier, the NVFA developed in this article saves energy of 88.1% during computation/reading compared with its conventional counterpart. To add on, writing and reading the energy delay product (EDP) are also reduced by 90.56% and 78.76%, respectively.