The importance of microwave device reliability and performance for microscale devices motivates a more fundamental understanding of breakdown mechanisms in this regime. Microwave breakdown theories predict breakdown when electron production balances electron loss. Electron production depends strongly on the ionization rate ; however, previous studies either used the measured in macroscale gaps or the empirical formula for DC voltage, inaccurately predicting in microscale gaps. Alternatively, this work characterizes in microwave microplasmas by using particle-in-cell simulations. We calculated in argon gas at atmospheric pressure for 2–10 μm gaps under AC fields ranging from 1 to 1000 GHz. The behavior of may be separated into two regimes by defining a critical frequency that depends on the amplitude of the applied voltage, gap distance, and pressure. For frequency , the electrodes collect the electrons during each cycle and the electron number oscillates with the electric field, causing to roughly scale with the reduced effective field . For , the phase-space plots indicate that the electrons are confined inside the gap, causing the electron number to grow exponentially and to become a function of . These results elucidate the ionization mechanism for AC fields at microscale gap distances and may be incorporated into field emission-driven microwave breakdown theories to improve their predictive capability.
Particle-in-cell simulations of the ionization process in microwave argon microplasmas
Haoxuan Wang, Ayyaswamy Venkattraman, Amanda M. Loveless, Allen L. Garner; Particle-in-cell simulations of the ionization process in microwave argon microplasmas. J. Appl. Phys. 14 September 2023; 134 (10): 103303. https://doi.org/10.1063/5.0161880
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