Thermally-treated Pt-coated silicon AFM tips for wear resistance in ferroelectric data storage Bharat Bhushan * , Manuel Palacio, Kwang Joo Kwak Nanotribology Laboratory for Information Storage and MEMS/NEMS (NLIM), The Ohio State University, 201 West 19th Avenue, Columbus, OH 43210, USA Received 25 February 2008; received in revised form 21 April 2008; accepted 22 April 2008 Available online 2 June 2008 Abstract In ferroelectric data storage, a conductive atomic force microscopy (AFM) probe with a noble metal coating is placed in contact with a lead zirconate titanate (PZT) film. The understanding and improvement of probe tip wear, particularly at high velocities, is needed for high data rate recording. A commercial Pt-coated silicon AFM probe was thermally treated in order to form platinum silicide at the near- surface. Nanoindentation, nanoscratch and wear experiments were performed to evaluate the mechanical properties and wear perfor- mance at high velocities. The thermally treated tip exhibited lower wear than the untreated tip. The tip wear mechanism is adhesive and abrasive wear with some evidence of impact wear. The enhancement in mechanical properties and wear resistance in the thermally treated film is attributed to silicide formation in the near-surface. Auger electron spectroscopy and electrical resistivity measurements confirm the formation of platinum silicide. This study advances the understanding of thin film nanoscale surface interactions. Ó 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Thin films; Mechanical properties; Nanoindentation; Atomic force microscopy; Wear 1. Introduction With the advent of scanning probe microscopes (SPM), probe-based recording technologies are being developed for ultrahigh areal density. Many approaches using probe-based techniques have been proposed. Various recording techniques using thermomechanical, phase change, magnetic, thermomagnetic, optical, electrical and ferroelectric methods have been demonstrated [1,2]. One of the new alternative ferroelectric data storage methods is a mechanically addressed storage system using probe- based recording. A schematic for domain writing and read- ing in ferroelectric films is shown in Fig. 1. A conductive AFM tip is placed in contact with a PbZr 0.52 Ti 0.48 O 3 / SrRuO 3 (PZT/SRO) double layer [3–6]. The SRO serves as the bottom electrode, and PZT represents the ferroelec- tric film. Ferroelectric domains can be polarized by apply- ing short voltage pulses (10 V, 100 ls) between the AFM tip and the SRO electrode that exceed the coercive field of the PZT layer, resulting in local, nonvolatile changes in the electronic properties of the underlying film. The PZT surface is in contact with the probe tip during writing, and the scanning is performed at high velocities for high data rate recording. These conditions can lead to stiction, friction and wear issues after prolonged device operation. A crucial mechanical reliability concern in probe-based data storage is wear of the tip after repeated tip-surface contact [7–9]. PZT has a high hardness and elastic modu- lus, 13 and 200 GPa, respectively [10]. During contact, the tip is subjected to high stresses on the order of 1 GPa, making it easily susceptible to deformation [11]. Therefore, a high surface hardness of the metal-coated tip is essential 1359-6454/$34.00 Ó 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.actamat.2008.04.052 * Corresponding author. Tel.: +1 614 292 0651. E-mail address: Bhushan.2@osu.edu (B. Bhushan). www.elsevier.com/locate/actamat Available online at www.sciencedirect.com Acta Materialia 56 (2008) 4233–4241