Electrical relaxation induced by magnetostriction in a MEMS device

Electrical resistance relaxation measurements were performed on a regular array of Co magnetic antidots submitted to a magnetic field, using a thin Cu film with bone-like shape positioned across the pattern; the introduction of a thin resist layer spin-coated on the Cu bridge before the deposition of the external leads introduced a hopping-dominated path for injected currents, controlled by the barrier thickness. The in-plane magnetic field generated by an electromagnet was switched between 0 and 3.5 kOe (fully saturated Co) and kept constant while the resistance was continuously monitored under steady current injection. A strong, unsaturating resistance variation with time after field switching was measured, corresponding to a resistance decrease greater than 20% after tents of ks. When the field was switched from 3.5 kOe back to zero the measured resistance displayed a corresponding positive variation. The two effects were repeatedly observed by subsequently cycling the magnetic field. Electron microscopy analysis showed that a peculiar dendritic structure had developed in the polymeric resist, consisting of mass density oscillations whose principal arms were oriented roughly at 45° with respect to the current density vector, possibly because of the mechanical stress induced by magnetostriction of Co antidots. A detailed analysis showed that mass density fluctuations within dendritic structures may be correlated with specific perturbation events observed in the electrical resistance relaxation during the measurements. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2010