Eur. Phys. J. B (2012) 85: 377
https://doi.org/10.1140/epjb/e2012-30794-5

Regular Article

Casimir attractive-repulsive transition in MEMS

¹ Department of Energy and Process Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway
² Department of Materials Science and Engineering, Royal Institute of Technology, 10044 Stockholm, Sweden
³ Department of Physics, University of Oslo, P.O. Box 1048 Blindern, 0316 Oslo, Norway
⁴ Division of Theory and Modeling, Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden

^a e-mail: bos@ifm.liu.se

Received: 24 May 2012
Received in final form: 25 September 2012
Published online: 19 November 2012

Abstract

Unwanted stiction in micro- and nanomechanical (NEMS/MEMS) systems due to dispersion (van der Waals, or Casimir) forces is a significant hurdle in the fabrication of systems with moving parts on these length scales. Introducing a suitably dielectric liquid in the interspace between bodies has previously been demonstrated to render dispersion forces repulsive, or even to switch sign as a function of separation. Making use of recently available permittivity data calculated by us we show that such a remarkable non-monotonic Casimir force, changing from attractive to repulsive as separation increases, can in fact be observed in systems where constituent materials are in standard NEMS/MEMS use requiring no special or exotic materials. No such nonmonotonic behaviour has been measured to date. We calculate the force between a silica sphere and a flat surface of either zinc oxide or hafnia, two materials which are among the most prominent for practical microelectrical and microoptical devices. Our results explicate the need for highly accurate permittivity functions of the materials involved for frequencies from optical to far-infrared frequencies. A careful analysis of the Casimir interaction is presented, and we show how the change in the sign of the interaction can be understood as a result of multiple crossings of the dielectric functions of the three media involved in a given set-up.