Reduction of current instabilities in silicon nanogaps Jonas Berg * , Per Lundgren, Peter Enoksson Solid State Electronics Laboratory, Department of Microtechnology and Nanoscience (MC2), Chalmers University of Technology, SE-41296 Go ¨ teborg, Sweden Received 14 February 2006; accepted 9 May 2006 Available online 21 June 2006 Abstract Silicon nanogaps are electrodes for connecting nanoscale elements to silicon technology. Two silicon electrodes are separated by a thin silicon dioxide layer, which is removed by selective etching to create a nanometer sized accessible gap. Parasitic gap currents with large instabilities occur after the etching. These are compared to the instabilities in ordinary MOS (metal oxide silicon) devices after soft break- down. Clear similarities are seen when subjecting the devices to constant voltage stress, storing them and annealing them. We discuss a percolation-based model for the instable current, in which the percolation clusters are defects in the oxide surface created during the etching, or possibly contaminating residuals from the same process. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Silicon nanogaps; Soft breakdown; Percolation; Selective etching; Parasitic currents; Native oxide 1. Introduction With a merge of organic electronics and silicon-based technology the performance improvement of electronics can continue [1]. Attaching organic molecules to silicon surfaces has seen a large interest lately [2–6], and one pos- sible continuation is to attach organic molecules between pairs of silicon electrodes. An overview on the attachment of organic molecules onto silicon wafers have been com- piled by Buriak [7]. Liu and coworkers have demonstrated silicon-based molecular memories that survive silicon device processing and 10 12 read-write cycles [8]. Richter et al. have used Si–O bonds to attach insulating molecules onto silicon wafers, and deposited a top metal electrode [9]. Unfortunately, in their approach pinholes in the organic film short-circuit the molecular layer. Our scheme is to first make a pair of silicon electrodes (spaced a few nanometers apart) and then deposit organic molecules in order to avoid pinhole creation. Using silicon electrodes can eliminate the problems with filament formation and electromigration that has been shown to occur when using metal electrodes [10]. Our nanogap structure consists of two silicon electrodes separated by a thin (a few nm) layer of silicon dioxide. By selective etching the thin oxide is partly removed, and a gap is created between the electrodes. Silicon nanogaps have applications in memory technology [11], for sensor applica- tions [12], and can also be used for studying the electrical properties of organic molecules. In this paper, we make a detailed study of the current instabilities that appear after the activation (etching) of the nanogaps, and compare with the current instabilities that can appear for devices with thin oxides having soft breakdown (SBD). We discuss a model based on percola- tion theory previously employed to describe SBD, for current instabilities in the nanogap. We have earlier stud- ied the low-frequency noise properties of the current instabilities for these silicon nanogaps [13]. Also the sur- face leakage currents that can be present on chips sub- jected to chemical treatments have been studied [12,14]. Howell and coworkers have used silicon nanogaps to study the electrical properties of multi-layer nanoparticle films [15]. 0167-9317/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2006.05.001 * Corresponding author. Tel.: + 46 31 772 1859; fax: + 46 31 772 3622. E-mail address: jonas.s.berg@home.se (J. Berg). www.elsevier.com/locate/mee Microelectronic Engineering 83 (2006) 2469–2474