Casimir attractive-repulsive transition in MEMS

TL;DR

This paper demonstrates that non-monotonic Casimir forces, transitioning from attractive to repulsive with increasing separation, can occur in standard MEMS/NEMS materials with dielectric liquids, without exotic materials, based on precise permittivity data.

Contribution

The study shows non-monotonic Casimir force behavior in typical MEMS/NEMS systems using accurate permittivity data, highlighting the importance of material properties for force sign reversal.

Findings

Non-monotonic Casimir force observed in silica-zinc oxide/hafnia systems.

Force sign change explained by dielectric function crossings.

Emphasizes need for precise permittivity data across frequencies.

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.