Patterning Spin-Wave reconfIgurable Nanodevices for loGics and computing.

Periodic Reporting for period 2 - SWING (Patterning Spin-Wave reconfIgurable Nanodevices for loGics and computing.)

Periodo di rendicontazione: 2018-11-01 al 2019-10-31

The global need for ever-increasing computational power has driven the development and downscaling of CMOS technology close to its physical limits, so that the search for novel concepts beyond conventional CMOS electronics has become crucial. The control of spin-waves (also called magnons) in magnetic materials offers a great potential in this view.
Spin-waves are propagating perturbations in the alignment of spins in ferromagnetic materials. From the technological point of view, spin-waves hold great promise because they have the potential to merge in one single platform the advantages of electromagnetic waves (typically exploited in photonics), with the versatility and nanoscale dimensions of electronics. Recently, we demonstrated a new technique called thermally assisted magnetic scanning probe lithography (tam-SPL), to realize magnonic building blocks for controlling spin-waves.
The main objective of project SWING is to enable major advances in the field of magnonics, by using tam-SPL for stabilizing nanoscale structures in the spin-texture of ferromagnets (such as magnetic domain walls or magnetic vortices), and to use these structures for generating and manipulating spin-waves with unprecedented precision and capabilities.
The research objectives of SWING project have been fully reached. We started from the optimization of the t-SPL technique, to the extension of its applicability to new materials and systems, such as synthetic antiferromagnets, out-of-plane magnetized materials, 2D semiconductors. We then moved towards the demonstration of novel spin-wave circuits for confining and steering spin-waves, the stabilization of topological spin textures, up to the final demonstration of a novel optically inspired platform for analog computing. Overall, SWING project had a remarkably high impact on the scientific community, and in particular in the communities of magnetism and nanolithography. Its ground-breaking results pave the way towards a range of applications especially for beyond-CMOS computing, with clear potential for both further scientific investigation and commercial application.

The work was carried out mainly at the CUNY Advanced Science Research Center (New York, USA), and Politecnico di Milano (Milan, Italy). The activity ranged from the optimization of the tam-SPL patterning technique, to the demonstration of the building blocks of magnonic devices, to the realization of optically-inspired spin-wave platforms for analog computing. These results, reported below, set a strong basis for the realization of computing devices using spin-waves, and demonstrated the versatility and potential of thermal nanolithography for the realization of innovative nanodevice architectures.

Realization of reconfigurable spin-wave nanocircuits.
The realization of a nanoscale spin-wave circuitry for guiding and manipulating the interaction of magnons, is still an open challenge. In this work (Figure 2), we demonstrated the fundamental building blocks of spin-waves circuitry, i.e. magnonic nanowaveguides and a spin-wave circuit allowing for the tunable superposition of signals propagating in two converging waveguides. This work demonstrates that engineered spin-textures (Figure 1) represent a powerful tool for realizing such a circuitry, marking a fundamental step towards the development of nanomagnonic computing devices.
The results have been published in the papers E. Albisetti et al, Communications Physics, 1, 56 (2018), E. Albisetti et al, AIP Advances, 7(5), 55601 (2017), E. Albisetti et al, Applied Physics Letters 113, 162401 (2018).

Realization of an optically-inspired nanomagnonic platform for analog computing.
Optically-inspired wave-based processing is envisioned to outperform digital architectures in specific tasks, such as image processing and speech recognition. In this work (Figure 3), an optically-inspired platform using spin waves is realized for the first time, demonstrating the wavefront engineering and interference of spin waves with nanoscale wavelength. In particular, magnonic nanoantennas based on spin textures are used for launching spatially shaped wavefronts, diffraction-limited spin-wave beams, and generating robust multi-beam interference patterns, which spatially extend for several times the spin-wave wavelength. The unique combination of these features gives rise to a versatile playground for studying the physics of nonreciprocal spin-wave propagation, and represents a fundamental step towards optically-inspired spin-wave processing. The results of this work have been accepted for publication in Advanced Materials (preprint arXiv:1902.09420).

Realization of field-effect transistors on 2D semiconductors via thermal nanolithography
One of the critical aspects in the fabrication of high-performance field-effect transistors on 2D semiconductors is the realization of high-quality metal/semiconductor contacts. The low quality of such contacts is in fact often the limiting factor in the performance of the FETs. In this work (Figure 4), a novel methodology based on thermally assisted scanning probe lithography is presented for nanofabricating low resistivity contacts on 2D materials. Compared to Electron Beam Lithography, this approach offers advantages in terms of device performance and capabilities, and could lead to low-cost, one-step industrial metal nanomanufacturing for the fabrication of integrated nanoelectronic computing platforms.
The results of this work have been published in the paper: X. Zheng, A. Calò, E. Albisetti et al, Nature Electronics 2, 17–25 (2019).

In the first part of SWING project, we pushed magnonics and nanomagnetism substantially beyond the state of the art. First, by demonstrating a new way for stabilizing magnetic quasiparticles with highly controlled properties in magnetic systems and second, by realizing the first demonstration of a fully reconfigurable spin-wave circuit for confining and controlling the interaction of propagating spin waves. The experimental realization of a reconfigurable nanoscale spin-wave circuitry paves the way to the development of integrated nanomagnonic computing devices.
In the second part of the project, we focused on the study and realization of novel platforms for beyond-CMOS computing. We realized a versatile optically-inspired platform for nanomagnonics based on the combination of tam-SPL and synthetic antiferromagnets. This platform represents a substantial step towards the realization of spin wave nanodevices for analog computing and a versatile platform for studying the physics of non-reciprocal spin-wave propagation.
Finally, we demonstrated for the first time the fabrication of high-quality field effect transistors based on monolayer 2D semiconductors (i.e. MoS2 and WSe2) via thermal nanolithography. In particular, the extreme cleanliness of the t-SPL process, in combination with in-situ thermal nanoscopy, allowed the nanofabrication of metal contacts with extremely low contact resistance, resulting in record-performance FETs.
Overall, the research objectives of SWING project have been fully reached. SWING project had a remarkably high impact on the scientific community, and in particular in the communities of magnetism and nanolithography. Its ground-breaking results pave the way towards a range of applications especially for beyond-CMOS computing, with clear potential for both further scientific investigation and commercial application.

Patterning of 0-dimensional topological magnetic spin-textures.

Demonstration of optically-inspired spin-wave platform.

Patterning of metal contacts on 2D semiconductors via t-SPL.

Demonstration of reconfigurable magnonic circuits.

Periodic Reporting for period 2 - SWING (Patterning Spin-Wave reconfIgurable Nanodevices for loGics and computing.)

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