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Demands for spin-based nonvolatility in emerging digital logic and memory devices for low power computing

Sverdlov Viktor (Christian Doppler Laboratory for Nonvolatile Magnetoresistive Memory and Logic at the Institute for Microelectronics, Wien, Austria + Institute for Microelectronics, Wien, Austria)
Selberherr Siegfried (Institute for Microelectronics, Wien, Austria)

Miniaturization of semiconductor devices is the main driving force to achieve an outstanding performance of modern integrated circuits. As the industry is focusing on the development of the 3nm technology node, it is apparent that transistor scaling shows signs of saturation. At the same time, the critically high power consumption becomes incompatible with the global demands of sustaining and accelerating the vital industrial growth, prompting an introduction of new solutions for energy efficient computations. Probably the only radically new option to reduce power consumption in novel integrated circuits is to introduce nonvolatility. The data retention without power sources eliminates the leakages and refresh cycles. As the necessity to waste time on initializing the data in temporarily unused parts of the circuit is not needed, nonvolatility also supports an instanton computing paradigm. The electron spin adds additional functionality to digital switches based on field effect transistors. SpinFETs and SpinMOSFETs are promising devices, with the nonvolatility introduced through relative magnetization orientation between the ferromagnetic source and drain. A successful demonstration of such devices requires resolving several fundamental problems including spin injection from metal ferromagnets to a semiconductor, spin propagation and relaxation, as well as spin manipulation by the gate voltage. However, increasing the spin injection efficiency to boost the magnetoresistance ratio as well as an efficient spin control represent the challenges to be resolved before these devices appear on the market. Magnetic tunnel junctions with large magnetoresistance ratio are perfectly suited as key elements of nonvolatile CMOS-compatible magnetoresistive embedded memory. Purely electrically manipulated spin-transfer torque and spin-orbit torque magnetoresistive memories are superior compared to flash and will potentially compete with DRAM and SRAM. All major foundries announced a near-future production of such memories. Two-terminal magnetic tunnel junctions possess a simple structure, long retention time, high endurance, fast operation speed, and they yield a high integration density. Combining nonvolatile elements with CMOS devices allows for efficient power gating. Shifting data processing capabilities into the nonvolatile segment paves the way for a new low power and high-performance computing paradigm based on an in-memory computing architecture, where the same nonvolatile elements are used to store and to process the information.

Keywords: digital spintronics, SpinFET, SpinMOSFET, spin-transfer torque, STT, spin-orbit torque, SOT, MRAM, in-memory computing