SmCo micromolding in an aqueous electrolyte
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TECHNICAL PAPER
SmCo micromolding in an aqueous electrolyte K. Chouarbi • M. Woytasik • E. Lefeuvre J. Moulin
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Received: 13 July 2012 / Accepted: 16 April 2013 / Published online: 25 April 2013 Ó Springer-Verlag Berlin Heidelberg 2013
Abstract The micromolding technique has been successfully applied to samarium–cobalt (SmCo) films electrodeposited in an aqueous solution. After optimization of the deposition conditions in a Hull cell, taking into account the supplying mode, the pulse time and the addition of supporting electrolyte, films with thickness between 1 and 1.5 lm have been patterned in 1 mm 9 1 mm squares. Is has been found that high Sm/(Sm ? Co) ratio can be obtained in direct current mode, with or without supporting electrolyte. In addition, the micromolding process reduces the contamination in oxygen due to oxidation and/or incorporation of precipitates, from 20 to 30 % in the Hull cell to 10–15 % in the pattern.
1 Introduction Despite the advantages of magnetic actuation, only few MEMS including magnetic forces have been published. Most of the applications involve microspeakers (Je et al. 2009a, b; Shahosseini et al. 2013), magnetically actuated micro switch (Ruan et al. 2001), magnetic nanoparticle assemblers (Yellen et al. 2005) or MOEMS (Reyne 2002). At this time, the development of magnetic microdevices is
This work has been originally presented at DTIP Conference, Cannes, France, 25–27 April 2012. K. Chouarbi M. Woytasik (&) E. Lefeuvre J. Moulin Institut d’Electronique Fondamentale, Universite´ Paris Sud CNRS UMR 8622, 15 rue G. Cle´menceau, 91405 Orsay, France e-mail: [email protected] K. Chouarbi STMicroelectronics, 12 Rue Jules Horowitz, 38000 Grenoble, France
limited by the integration of micromagnets (Cugat et al. 2003). Indeed, none of the existing film deposition and patterning techniques allows integration of micromagnet with hard magnetic properties comparable to the one of bulk materials. In the domain of hard magnetic materials, rare earth– transition metal (RE–TM) alloys are the most efficient. In this family, samarium–cobalt (SmCo) magnets have the advantages to operate at high temperature and to show a high electrical resistivity (85 lX cm) which limits Eddy currents. Sputtering has been applied for depositing SmCo thin films (Cadieu et al. 1983). Classical deposition/etching or lift-off techniques can be applied for patterning these films but realization of micromagnets need large volume of material. More recently, thick films are produced with properties comparable to bulk alloys, i.e. a coercivity of 400 kA/m (Walther et al. 2009). However, the elaboration process requires special equipment for obtaining high deposition rate and, most important, the deposition must be made at high temperature in order to induce crystallization. This excludes the standard processes used in microelectronics for micropatterning. An alternative way to deposition/etching or lift-off process is electrodeposition through a mold, i.e. micromolding. This low-cost process is compatible
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