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 as 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 towards practical spin-wave circuits. After an introduction to magnetic interactions and spin-wave physics, all relevant 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 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.

Achieving Wave Pipelining in Spin Wave Technology

“…When the magnetic material magnetization is out of equilibrium, its dynamics caused by the magnetic torque can be described using Equation (1), which is called the Landau-Lifshitz-Gilbert (LLG) equation [14].…”

“…The information can be encoded in the amplitude, and phase at multiple frequencies in the SW technology [10], [14]. The interaction between SWs is governed by the interference principle.…”

“…The interaction between SWs is governed by the interference principle. For instance, if SWs with the same amplitude, frequency, and wavelength meet at an intersection point, they interfere constructively if they have the same phase Δϕ = 0, whereas if they are out of phase, i.e., Δϕ=π, they interfere destructively [10], [14]. In addition, SW interference provides natural support for Majority function evaluation.…”

“…For example, if 3 SWs with the same amplitude, frequency, and wavelength propagate through waveguides, the interference result is based on a Majority decision, i.e., the resulting SW has phase Δϕ=0 if no more than one input SW has a phase Δϕ=π, and a phase Δϕ=π if at most one input SW has a phase Δϕ=0. Thus, one single SW device evaluates 3-input Majority [10], [14], while a CMOS counterpart needs 18 transistors. Note that logic 1 represents Δϕ=π, and Δϕ=0 reflects logic 0 in this paper [10], [14].…”

Local non-linear excitation of sub-100 nm bulk-type spin waves by edge-localized spin waves in magnetic films

“…However, the usefulness of the higher harmonic generation of SWs for magnonics, has not yet been demonstrated. One of the vital challenges in miniaturization of magnonic circuits, expected for the next generation of the information and communications technology 18 limiting their practical application 19 , is the excitation of sub-100 nm wavelength SWs. A transducer directly converting microwave currents into short-wavelength SWs would be especially effective, but due to the limitations related to the downsizing of microwave antennas 20,21 , alternative techniques are used.…”