Dec 11, 2008
3D nanolithography route to reliable spintronics
As reported by Wolf et al. (Science 294 1488), until recently, the spin of the electron has been ignored in mainstream charge-based electronics. The review article - Spintronics: a spin-based electronics vision for the future - goes on to explain that spintronics has emerged as an alternative technology in which it is not an electron's charge but its spin that carries information. And adds that this offers opportunities for a new generation of devices combining standard microelectronics with spin-dependent effects that arise from the interaction between the spin of the carrier and the magnetic properties of the material.
There are two distinct paths that can be taken towards fabrication of nanometer-scale structures for the study of spin-electronic properties: the usual top-down approach uses lithographic patterning techniques to define device structures by the removal of unwanted material and to mask the subsequent growth of different layers; the alternative bottom-up route requires directed additive assembly of subunits.
In a recent spintronics study, which was published in Nanotechnology, the authors used a top-down approach for the fabrication of nanopillar spin-electronic devices from metal heterostructures utilizing a novel three-dimensional focused ion beam (FIB) lithography process. In the FIB system high-energy (30 keV) gallium ions can be focused to a very small region of about 10 nm diameter.
Such a fine high-energy beam can be used for nanometer-scale milling of almost any material. Conventionally FIB is used for creating 2D structures; however, researchers at Cambridge and Leeds extended its functionality for fabricating 3D nanostructures for spintronics. In addition, the 3D-FIB process does not require any resist, which makes it more versatile than conventional lithography processes.
The researchers also used finite element simulation to optimize the geometry of the nanopillar device and demonstrate that current can be forced to flow perpendicular to the magnetic layers within the active region of the device. These technological advancements make it possible to observe clear zero-field current-induced magnetization switching, which is a direct effect of transferring spin angular momentum from current to the magnetic layer, at room temperature.
3D-FIB nanolithography provides an efficient method for fabricating reliable magnetic devices for developing spin transfer torque random access memory (STT-RAM) and nanoscale microwave emitters. STT-RAM has a great potential for becoming universal non-volatile memory and nano-microwave oscillators can revolutionize communication technologies.
• This article was updated on 10 March 2010 to include a reference to the work of Wolf et al. (Science 294 1488)
About the author
The work was performed at the University of Cambridge and the University of Leeds and supported by the UK Engineering and Physical Sciences Research Council under the Spin@RT consortium, which comprises eight UK institutions including Cambridge, Leeds, City, Durham, Exeter, Glasgow, Imperial College and Rutherford Appleton Laboratory. Ming-Che Wu is a PhD student studying Materials Science at the University of Cambridge. He was financially supported by the Ministry of Education of Taiwan. Dr Atif Aziz is a postdoctoral researcher in the Device Materials Group. James Witt is a PhD student in the Device Materials Group. Prof. Mark Blamire is the head of the Device Materials Group at the University of Cambridge and he is also the vice-president of Hughes Hall. Dr Mark Hickey used to work in the Condensed Matter Group of the University of Leeds and now works at MIT. Dr Mannan Ali is a research fellow in the Condensed Matter Group of the University of Leeds. Dr Christopher Marrows is a reader in Condensed Matter Physics at the University of Leeds. Prof. Bryan Hickey is the head of the Condensed Matter Group at the University of Leeds.