Magnets for MEMS

Magnetic MEMS is an emerging domain of applications for hard magnetic materials [1]. However, its development has been hindered by the non-availability of high performance magnets of the appropriate dimensions (5-100 µm) which can be prepared using techniques compatible with MEMS fabrication. Since a few years we have been working on addressing this need, in close collaboration with researchers from the micro-system team at G2ELab (ex-LEG). To this end, we developed a dedicated high rate sputtering machine (deposition rate = 20 µm / hr) which was designed to accommodate 100mm wafers so as to be compatible with existing micro-fabrication platforms (e.g. CEA/Léti, PTA). We concern ourselves with high performance hard magnetic materials based on rare earth – transition metal compounds (e.g. NdFeB and SmCo) and L10 alloys (e.g. FePt). Our aim is to prepare and study them at the scale adapted to MEMS applications. To date, most work has been carried out on the NdFeB system (F. May (Masters 2003-2004) and A. Walther (PhD 2004-2007)). We have demonstrated the feasibility of preparing high energy product films (BHmax = 400 kJ/m3 – to our knowledge the largest reported value for film magnets) on Si substrates. We clearly established the influence of deposition temperature on the inducement of out-of-plane texture for films prepared using a two-step procedure (collaboration: O. Gutfleisch, IFW Dresden). Details of this work can be found in two recent papers [2,3].

Influence of deposition temperature on the texture of NdFeB films
NdFeB film deposited on a pre-patterned substrate
The integration of these films into a proto-type RF micro-switch is being studied within the framework of an ANR (French research funding agency) pre-industrial project Nanomag2, in collaboration with G2Elab, CEA/LETI and Alcatel Space. The influence of micro-structuration on the magnetic properties of such materials is now being examined. We are also studying the SmCo (A. Walther (PhD 2004-2007)) and FePt systems (C. N’dao (PhD 2006-2009)).

Related publications

[1] O. Cugat, J. Delamare and G. Reyne, IEEE Trans. Mag. 39-6 (2003) 3608

[2] High performance hard magnetic NdFeB thick films for integration into Micro-Electro-Mechanical-Systems , N.M. Dempsey, A. Walther, F. May and D. Givord, K. Khlopkov and O. Gutfleisch, Appl. Phys. Lett. 90 092509 (2007)

[3] Evolution of magnetic and microstructural properties of thick sputtered NdFeB films with processing temperature, A. Walther, K. Khlopkov, O. Gutfleisch, D. Givord and N.M. Dempsey, J. Magn. Magn. Mat. 316, 174 (2007).

Contributors: N.M. Dempsey, A. Walther, C. N’dao, S. Diaz and D. Givord

Technical support: D. Barral, R. Haettel, J.S. Pelle, L. Ortega and A. Lienard

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