The Coupling of Ion-Enhanced Field Emission and the Discharge During Microscale Breakdown at Moderately High Pressures

Recent studies have shown that, in microscale electrode gaps, the traditional Paschen´s curve fails as the left branch sharply decreases with electrode spacing, thus resulting in the modified Paschen´s curve. This deviation from Paschen´s curve is attributed to ion-enhanced field emission and notably breaks pressure times distance (pd) scaling. Here, 1-D particle-in-cell/Monte Carlo collision simulations at moderately high pressures are used to predict breakdown and reproduce the modified Paschen´s curve, which is in good agreement with existing theory. These simulations reveal that the net positive space charge that accumulates in the electrode gap enhances the electric field, subsequently enhancing field emission from the cathode. Because the emitted electrons generate additional ions in the discharge, a positive feedback mechanism occurs, where the field-emitted electrons produce the ions that enhance the electric field. It is revealed that this coupling between field emission and the discharge is necessary in order for breakdown to occur.