Migration of Chromium on the Silicon Oxide Surface under a Strong Electric Field

Migration of chromium, which acts as an adhesive material for planar electrodes of a MEMS switch, over the surface of a thermally oxidized silicon wafer is demonstrated. Voltage pulses lead to the formation of chromium and carbon nanostructures on the driving electrode and their growth towards the signal electrode. Over time, the structures reach micron sizes and cover the interelectrode gap. Migration is activated by an electric field of about 108 V/m. The first structures appear after applying 102–105 pulses, but the process accelerates as they grow. For platinum electrodes, migration is faster and requires a lower voltage compared to gold electrodes. Material transfer occurs not only in the gap between the electrodes but also on the SiO2 surface around the positive electrode. The material also moves under the Pt and Au films, peeling them off from the substrate. The described phenomena can damage electrostatically actuated MEMS switches and other devices that use high electric fields.