3DMAGNANOW · Fabrication of three dimensional magnetic nanowires for information storage

Fabrication of three dimensional magnetic nanowires for information storage

Project context The tremendous impact of information technology (IT) has become possible because of the progressive down-scaling of integrated circuits and storage devices. However, this spectacular down-scaling is reaching its technological limits, and the continuation of the IT revolution must be supported by new ideas for information storage or processing, leading to greater integration, high operation speeds and low power consumption. The possibility of creating 3D-memories is an objective being actively pursued by researchers working in nanoelectronics. These devices might bring great benefits to society, such as much lower power consumption, higher computational efficiency, minimisation of data losses, etc. Recently, researchers worldwide have focused their investigation on the use of magnetic nanowires (NWs) for the transmission and storage of information. A NW is a structure of nanometre scale in two dimensions (thickness and width), and macroscopic in one (length). To fabricate NWs, lithography techniques are used which pattern the selected material in the correct shape. Due to this geometrical confinement, the magnetisation of a magnetic NW can only point along the direction of the wire axis, becoming a simple way to encode binary information: 0 (left) or 1 (right). A NW can store multiple bits along its length, with sections of left- and right-pointing magnetisation, which can be moved for subsequent information reading or writing. Due to its simplicity, non-volatility (information is stored when electricity is off) and low power consumption, this technology has been proposed as an alternative to currently existing ones, based on semiconductors (RAM, FLASH) or granular materials (hard-disk drives). However, the limited storage density of these devices, of a few Gbits/in2, prevents this technology from becoming a reality. So far, for patterning of NWs, conventional lithography techniques from the microelectronics industry have been used, which involve multiple complex steps. A fundamental problem using standard techniques is that, whereas they are capable of fabricating complex structures lying on a substrate, i.e. in two dimensions, they are not able to make structures in the out-of-plane direction. Project objectives The main objective of the 3DMAGNANOW project was to investigate 3D magnetic nanostructures for the controlled motion of domain walls in the third dimension. To achieve that, two routes have been explored simultaneously. The first one focused on the 3D-stacking of 2D ferromagnetic (FM) layers separated by a nonmagnetic spacer (NM), forming (FM/NM)x heterostructures. The second strategy consisted in directly fabricating out-of-plane FM nanowires, using an advanced nanolithography technique, focused electron beam induced deposition (FEBID). The project has covered many challenging aspects not studied so far, regarding growth and fabrication processes, three-dimensional characterisation or domain-wall physics. During these two years, the Marie Curie fellow, together with the scientist in charge and the rest of the group in Cambridge (UK) made important efforts to produce two deliverables corresponding to two work packages on fabrication and magnetics of 3D nanostructures, as well as four related milestones. The objectives of the 3DMAGNANOW project have been fully reached. The main results of the project can be summarised in five points: - Domain-wall motion operating margins can be tuned in 2D cobalt nanowires by focused ion beam global irradiation; -Controllable conduction of 3D-domain walls has been achieved in (FM/NM)x, multilayers, for x < 9, using the anti-ferromagnetic coupling between neighbouring layers; -3D high-aspect-ratio nanowires have been fabricated using FEBID;-The first magnetometry measurements on 3D nanostructures have been performed; -The functionality of 3D-FEBID magnetic nanostructures for future spintronic devices has been investigated. Project impacts The need for a technological breakthrough in data storage technology is real. The future of spintronics will be part of this revolution if it can help move storage architectures into the third dimension. The development of new flexible nanolithography tools is key to achieving this objective. The results we obtained during this project prove that functional high-aspect-ratio 3D nanostructures can be fabricated using FEBID. These results pave the way for the fabrication of 3D magnetic nanodevices for the storage and logic operation of information in the third dimension. Moreover, the controllable mechanisms found for the injection of 3D domain walls in multilayers is a very interesting route to propagate magnetic information in the out-of-plane direction, which could be exploited in pseudo-3D architectures.

Data: CORDIS, © European Union