Calculation of Ionization Coefficient in Microscale and Nanoscale Gaps Using PIC/MCC Simulations*

Applications requiring microplasmas, such as combustion and medicine, and those that require the avoidance of gas breakdown such as field emission devices and MEMS, require improved prediction of gas breakdown for microscale and smaller gaps 1 . Traditionally, gas breakdown is driven by Townsend avalanche and predicted mathematically using Paschen’s law 1 . The ionization coefficient α is an essential parameter for calculating breakdown voltage; however, the standard semi-empirical model for α is only valid for 100 < E / p < 1000 V cm -1 Torr -1 , where E is the applied electric field and p is the gas pressure. The strong electric fields required for microscale gaps cause E / p to exceed this range 1 , necessitating a correction factor for α 2 , 3 . However, a comprehensive assessment of this correction for various gap distances, pressures, and electric fields that may be incorporated into analytic theories 3 has not been developed.