Experimental study of gas breakdown and electron emission in nanoscale gaps at atmospheric pressure

Abstract

While experiment, simulation, and theory all show that the gas breakdown voltage decreases linearly with gap distance for microscale gaps at atmospheric pressure due to the contribution of field emitted electrons, the continuing reduction in device size motivates a more fundamental understanding of gas breakdown scaling for nanoscale gaps. In this study, we measure current–voltage curves for electrodes with different emitter widths for 20–800 nm gaps at atmospheric pressure to measure breakdown voltage and assess electron emission behavior. The breakdown voltage [Formula: see text] depends more strongly on effective gap distance [Formula: see text] than the ratio of the emitter width to the gap distance. For 20 and 800 nm gaps, we measure [Formula: see text] V and [Formula: see text] V. Independent of emitter width, [Formula: see text] decreases linearly with decreasing [Formula: see text] for [Formula: see text] nm; for [Formula: see text] nm, [Formula: see text] decreases less rapidly with decreasing [Formula: see text] which may correspond to a change in the field enhancement factor for smaller gaps. While gas breakdown usually proceeds directly from field emission, as for microscale gaps, some cases exhibit space-charge contribution prior to the transition to breakdown, as demonstrated by orthodoxy tests. Applying nexus theory, we determine that the range of [Formula: see text] studied is close to the transitions between field emission and space-charge-limited current in vacuum and with collisions, necessitating a coupled theoretical solution to more precisely model the electron emission behavior. Implications on device design and an overall assessment of the dependence of emission and breakdown on gap distance are also discussed.