Micro-discharge is the process that gas breakdown occurs on a small spatial scale to generate plasma. With the decrease of the discharge scale, the high electric field makes the field emission (FE) play a leading role in the breakdown process of the micro-discharge, which is one of the reasons that the breakdown voltage deviates from the Paschen curve in a small gap. A one-dimensional implicit particle-in-cell Monte Carlo collision (PIC/MCC) model is used to simulate the whole breakdown process of direct current (DC) micro-discharge sustained by FE in argon. The results show that the discharge after breakdown is in arc mode, the breakdown process can be divided into three stages: the pre-breakdown stage, the breakdown stage, and the post-breakdown stage. In the pre-breakdown stage, the sheath and plasma are not formed, the external electric field can penetrate the entire gap. In the breakdown stage, gas breakdown occurs. As the sheath is formed, the rate of change of plasma parameters increases rapidly and the discharge gap changes from capacitive to resistive. In the post-breakdown stage, the anode sheath gradually becomes thinner, but the region where the field is reversed still exists. The particle and energy balance gradually reach equilibrium, and the entire discharge evolves to a quasi-steady-state.

Gas breakdown driven by thermionic emission(TE) in a microgap to produce low
temperature plasma was studied by one-dimensional implicit Particle-in-cell/Monte
Carlo collision(PIC/MCC) model. The influence of background gas pressure, external
driving voltage, cathode temperature and discharge gap on argon glow micro-discharge
in the parallel plate was simulated. Different parameters and conditions have different
effects on the gas breakdown at small size. The discharge gap of 100’s μm has little
influence on gas breakdown and only changes the plasma distribution. As the applied
voltage increases, the gas changes from non-breakdown mode to breakdown mode, and
gas breakdown is more sensitive to the applied voltage than the gas pressure at low
voltages. In all breakdown modes, the gas pressure hardly changes the plasma evolution
characteristics. At appropriate cathode temperatures, the density of electrons and ions
increases rapidly, forming a stable sheath and the equivalent resistance of the discharge
gap becomes smaller as the temperature rises, the plasma is in abnormal glow discharge.

Micro-discharges have many excellent characteristics, such as generation of high-density and non-equilibrium plasmas at atmospheric pressure. In this paper, we used an implicit particle-in-cell/Monte Carlo collision method for three-dimensional velocities in a one-dimensional space combined with the secondary electron emission model to study the characteristics of micro-discharges driven by dual radio frequency (RF) power. The effect on plasma parameters was observed by varying the voltage of the RF power, the frequency, and the gas pressure of the discharge. Since the electrode spacing is very small in micro-discharges, the voltage change will affect the characteristics of micro-discharges. In addition, the plasma density increases with the frequency and the discharge mode changes at different frequencies. Finally, the influence of gas pressure on the characteristics of micro-discharges cannot be ignored. When the air pressure decreases, the ion flux reaching the electrodes is significantly increased, and the energy distribution of ions increases in the high-energy portion.