Unleashing the Magic of Nanomagnet Assemblies - Direct-Write Deposition of Nanomagnet Logic Circuitry
Authors: Wanzenboeck Heinz , Gavagnin Marco , Bertagnolli Emmerich 
Published: February 2020

Magnetic nanomaterials play important roles in information storage, sensors, and microelectromechanical systems (MEMS). Many of these applications require the magnetic material to be in a specific shape and at specific positions, so that stochastically distributed magnetic nanostructures (e.g. nanodots) cannot fulfill the requirements for an application. The classical patterning approach is based on the top-down patterning of magnetic layers using a lithographic photoresist to generate the pattern. In this work we will present a direct-write deposition that is capable to fabricate individual nanomagnets or designed nanomagnet assemblies without a photomask or without a photoresist. Also deposition of nanomagnets on non-planar structures and even deposition of 3-dimensional nanomagnets is feasible. This work reports on this new fabrication approach and its application for logic computer devices.

Direct writing of iron and cobalt structures has been developed. This new process was performed by locally confined chemical vapor deposition initiated by a focused electron beam of a scanning electron microscope. Iron carbonyl or cobalt carbonyl were injected via a nozzle to the sample surface and where then decomposed by the energy of a 5 keV electron beam. By deliberately scanning the electron beam with a pattern generator also complex patterns could be deposited as lateral – but also as 3-diemnsional structures. This work addresses the chemistry of the deposition reaction and analysis of the resultingmaterial purity, the physics of magnetic shape anisotropy of nanomagnets, and the engineering of magnetic coupling between nanomagnets. These fundamental insights provide an understanding of the correlations between deposition parameters, film composition, and structure.

Nanomagnets of various geometries, including circular, ellipsoidal, triangular, square and hexagonal have been fabricated and allowed to design a shape-controlled domain distribution. Finally we will present and device based on nanomagnets that cannot only store, but also perform logical operations. Investigation of these structures was performed by magnetic force microscopy.

Moving towards an , complex assemblies of magnetic nanowires with 100 nm length, 50 nm width and a custom designed height (that could be adapted by a longer electron exposure) have been fabricated. The coupling between these nanomagnets within an array was investigated and as an application nanomagnet logic (NML) devices were fabricated. Using nanomagnerts as building blocks nanomagnet-logic gates were fabricated that can perform logic operations without electronic charges but just by magnetic coupling between neighboring nanomagnets. We also address specific issues of NML such as fan outs, majority gates. Our ultimate progress was to include perpendicular magnetic nanopillars and thus to create for the first time 3-dimensional NML gates.

Direct writing has several advances over the conventional lithography base approaches. It has been shown that this novel direct-write approach is capable of fabricating functional nanomagnet logic as shown in the schematic illustration in Fig 1.

Figure 1