Electrical breakdown from macro to micro/nano scales: a tutorial and a review of the state of the art

Fundamental processes for electric breakdown, i.e., electrode emission and bulk ionization, as well as the resultant Paschen’s law, are reviewed under various conditions. The effect of the ramping rate of applied voltage on breakdown is first introduced for macroscopic gaps, followed by showing the significant impact of the electric field nonuniformity due to gap geometry. The classical Paschen’s law assumes uniform electric field; a more general breakdown scaling law is illustrated for both DC and RF fields in geometrically similar gaps, based on the Townsend similarity theory. For a submillimeter gap, effects of electrode surface morphology with local field enhancement and electric shielding on the breakdown curve are discussed, including the most recent efforts. Breakdown characteristics and scaling laws in microgaps with both metallic and non-metallic (e.g., semiconductor) materials are detailed. For gap distance down to micro/nano scales, the breakdown characteristics and the breakdown mode transition from the secondary electron emission to the electric field emission or thermionic emission dominant regime. Additionally, the combined thermo-field emission regime is also reviewed. Previous efforts, including key simulations and experiments, have been devoted to diagnosing breakdown path evolution, measuring breakdown fields, and quantifying breakdown dependence on frequencies for gaps down to micro/nano scales. By summarizing and analyzing fundamental theories, recent progress, and on-going challenges, this tutorial review seeks to provide basic understanding and the state of the art of electric breakdown, which aids in advancing discoveries and promoting application prospects for discharge devices engineered in a wide range of regimes.