INSTITUTE OF PHYSICS PUBLISHING NANOTECHNOLOGY Nanotechnology 17 (2006) 2722–2729 doi:10.1088/0957-4484/17/11/002 Interdigitated 50 nm Ti electrode arrays fabricated using XeF 2 enhanced focused ion beam etching Ch Santschi 1,2 , M Jenke 2 , P Hoffmann 2 and J Brugger 1 1 Laboratoire de Microsyst` emes (LMIS), Station 17, CH1015 Lausanne, Switzerland 2 Laboratoire d’Optique Appliqu´ ee (LOA), ´ Ecole Polytechnique F´ ed´ erale de Lausanne, Station 17, CH1015 Lausanne, Switzerland E-mail: Juergen.Brugger@epfl.ch Received 1 November 2005, in final form 5 April 2006 Published 16 May 2006 Online at stacks.iop.org/Nano/17/2722 Abstract The fabrication of interdigitated titanium nanoelectrode arrays of 50 nm in width and spacing is described in this work. The nanoarrays have been realized using a Ga + focused ion beam (FIB). FIB milling is typically accompanied by redeposition of removed material, which represents an important hindrance for milling closely spaced nanostructures. Redeposition effects have been reduced by means of XeF 2 gas assistance, which increases the etch yield by a factor of seven compared with pure ion milling. Furthermore, we used a simple adsorption model, which led to the conclusion that dwell time and refresh time should be <500 ns and >30 ms, respectively, for optimized XeF 2 assisted Ti milling. The measured resistance R of the electrodes is higher than 1 G. 1. Introduction The progress in fabrication methods for nanostructures made in the last few years opens the door for new applications in fields such as biotechnology [1] and microelectrochemistry [2–4], as well as microelectronics [5]. Interdigitated electrode arrays (IEAs) of micrometric dimensions and nanometric gaps and widths offer various advantages compared to micrometric IEAs. Applications for nano-IEAs are, for instance, impedance spectroscopy of biomolecules [6], DNA biosensors [7, 8], and gas sensors [9]. In the domain of sensors, handling of small amounts of the substances under test and on-chip solutions including various functions such as mixing, heating, and in situ detection is desirable and becomes feasible using nanoscale IEAs. The generation of strong and localized electrical fields is very useful, for example, to change the dipole orientation of molecules or diffusion of ions in a solution in the sphere of very small volumes. Such strong electrical fields constrict, for instance, the rotational motion of dipoles in solution, which manifest itself by a gradual decrease of the electric permittivity, which is proportional to the square of the field strength [10]. Such high electrical field strength may be achieved using interdigitated nanoelectrodes. Thus, there is a considerable interest in fabrication methods for nanoscale IEAs. Despite the overall recent progress in nanofabrication technology, the realization of arrayed nanoscale electrode is still challenging, especially in the sub-100 nm range. Pairs of nanometric electrodes were recently fabricated by Nagase et al [11]. Two electrodes were engraved in a 10–30 nm thick gold layer covering an oxidized Si substrate employing focused ion beam (FIB) techniques. Electrode pairs of similar size have also been produced by Zandbergen [12]. They modified a free-standing gold layer using a highly focused electron beam obtained in a transmission electron microscope (TEM). This permits in situ observation of the fabrication process and therefore a very precise control of the feature size. Arrays of vertically aligned electrodes with a few tens of nanometres width have been realized with a bottom- up approach using carbon nanotubes [3, 4]. Furthermore, nanoscale IEAs have been fabricated by Montelius [6] using electron beam lithography (EBL) and the lift-off technique. These structures were realized in 20 nm Au and eutectic Au/Ge layers that are evaporated onto a wet oxidized SiO 2 . They achieved arrays with electrode spacing down to 150 nm. Nanoimprint (NIL) and UV lithography (UVL) are further potential nanostructuring methods. Applying these techniques IEAs with down to 100 nm separation between electrodes 0957-4484/06/112722+08$30.00 © 2006 IOP Publishing Ltd Printed in the UK 2722