Experimental study of electrical breakdown in MEMS devices with micrometer scale gaps
We present an experimental study of the DC breakdown voltage of MEMS interdigitated aluminum electrodes with gaps ranging from 10 to 500 μm. Unlike most research on MEMS electrodes that was done at atmospheric pressure, our work has focused on the effect of gas pressure and gas type on the breakdown voltage. A main goal was to identify geometries that favor the creation of low-voltage discharges. Helium, argon and nitrogen pressure was varied from 10^2 to 8.104 Pa (1 to 800 mbar). The breakdown voltage was plotted as a function of the Paschen reduced variable Pred = p·d. For higher values of pressure, p or gap, d (high Pred), classical Paschen scaling was observed. For lower values of Pred however, significant deviations were seen, particularly at low pressures. We attribute these differences not to field emission, but to the scale of the mean free path (which explains the higher than predicted voltages), and principally to the many length scales effectively present in our planar geometry (on-chip and even off-chip, that lead to the superposition of several Paschen curves). Guidelines are proposed for low-pressure operation of MEMS to avoid or to encourage breakdown.