Introduction to spin wave computing

Abstract

This paper provides a tutorial overview over recent vigorous efforts to develop computing systems based on spin waves instead of charges and voltages. Spin-wave computing can be considered a subfield of spintronics, which uses magnetic excitations for computation and memory applications. The Tutorial combines backgrounds in spin-wave and device physics as well as circuit engineering to create synergies between the physics and electrical engineering communities to advance the field toward practical spin-wave circuits. After an introduction to magnetic interactions and spin-wave physics, the basic aspects of spin-wave computing and individual spin-wave devices are reviewed. The focus is on spin-wave majority gates as they are the most prominently pursued device concept. Subsequently, we discuss the current status and the challenges to combine spin-wave gates and obtain circuits and ultimately computing systems, considering essential aspects such as gate interconnection, logic level restoration, input-output consistency, and fan-out achievement. We argue that spin-wave circuits need to be embedded in conventional complementary metal-oxide-semiconductor (CMOS) circuits to obtain complete functional hybrid computing systems. The state of the art of benchmarking such hybrid spin-wave-CMOS systems is reviewed, and the current challenges to realize such systems are discussed. The benchmark indicates that hybrid spin-wave-CMOS systems promise ultralow-power operation and may ultimately outperform conventional CMOS circuits in terms of the power-delay-area product. Current challenges to achieve this goal include low-power signal restoration in spin-wave circuits as well as efficient spin-wave transducers.

Spin Wave Based Approximate Computing

“…The SW amplitude and phase can be used to encode information at different frequencies, which enables parallelism 14,17 . The interaction between multiple SWs present in the same waveguide is based on the interference principle.…”

“…Logic 0 refers to a SW with φ = 0, and a logic 1 refers to a SW with φ = π. B is the medium for SW propagation and can be made of different magnetic materials, e.g., Permalloy, Yttrium iron garnet, CoFeB 14 . The waveguide material is an important parameter as it fundamentally determines the SW properties.…”

Spin Wave Based Approximate Computing

“…While in the last decades CMOS downscaling has been able to enable high performance computing platforms required to process the information technology revolution induced huge data amount 1 , it becomes very difficult to keep the same downscaling pace due to 2 : (i) leakage wall, (ii) reliability wall, and (iii) cost wall. This predicts that Moore's law will come to the end soon and, as a result, researchers have started to explore different technologies (e.g., memristors [3][4][5][6] , graphene devices [7][8][9] , and spintronics [10][11][12][13] ) among which Spin Wave (SW) stands apart as one of the most promising due to its [14][15][16][17][18][19][20] : (i) Ultra-low energy consumption -SW computing depends on wave interference instead of charge movements. (ii) Acceptable delay.…”

Inverse-design magnonic devices

“…Spin waves are propagating disturbances in the spin system of a solid body that can be used for a low-loss information transfer without any motion of real particles [5][6][7] . They have wavelengths ranging from micrometers down to atomic scales [7][8][9] and show a variety of pronounced nonlinear phenomena [10][11][12] that makes spin waves to be promising for Boolean computing [13][14][15] , radio frequency applications 16,17 and neuromorphic computing 18,19 at the nanoscale. Many magnonic devices have been demonstrated recently: frequency (de-) multiplexers 16,17 , nonlinear units 12,19 , nonreciprocal diodes/ circulators [20][21][22] , and an integrated magnonic half-adder 23 .…”

“…However, nonlinear phenomena, e.g., the dependence of the wavelength on the amplitude, are strongly needed for a computing system, which is still a challenge due to the rather low intrinsic photonic nonlinearity 29 . Besides, (1) the pronounced natural nonlinearity, the field of magnonics offers (2) a scalability of the devices down to the scale of a few nanometers 6,30 and, thus the integrability with CMOS devices 13 and (3) pronounced nonreciprocal properties associated with the gyrotropic magnetization precession motion and breaking of time symmetry [20][21][22]31 .…”