Discharge characteristics of the planar microscale gap electrodes with various geometry structures in the atmosphere environment

Abstract

The discharge of microscale gaps for MEMS systems is a serious issue. To reveal the dark discharge characteristics of the microscale gap, electrodes with various gap feature sizes were prepared, and the DC current–voltage characteristics for the electrodes were implemented in atmospheric air. The results showed minor differences in dark discharge current on a nanoampere scale among electrodes with varying gap sizes of micro-protrusions. The current formation mechanism was consistent with the electron avalanche theory. Morphological characterization identified the presence of non-ideal thin-layer trailings at the electrode edges. To evaluate the effect of trailings on the dark discharge characteristics of the microscale gap structures, the electrodes with varying trailing lengths were fabricated. It showed that the current increased exponentially in the presence of long thin-layer trailing. In this case, the breakdown is most pronounced with an effective gap distance of 30 μm and a trailing length of 14.34 μm for the electrodes. For this structure, the dark discharge current was 198 nA at 36 V bias voltage, while the discharge current increased to 50 µA when the bias was increased to 37 V, and stabilized at 100 µA when the bias voltage was higher than 39 V. The rapid increase in current caused by trailing originates from the field emission as judged by the Fowler-Nordheim theory. Simulation results showed that the field strength can reach up to 3.76 × 109 V/m at a thin layer trailing length of 3.5 μm and a bias voltage of 200 V, which matches the conditions for the field emission. By calculating the effective secondary electron emission coefficient, it was found that thin-layer trailing significantly intensifies the ion-enhanced effect, further lowering the threshold for field emission and resulting in a rapid increase in microscale gap current at lower voltages.