Diagnostic study of micro-discharges of inert gas under atmospheric pressure

Summary form only given. The characterization of microplasmas driven by DC and AC (50~1000 Hz) power supplies with a voltage up to 1000 V at atmospheric pressure is performed. Parallel planar aluminum electrodes with an inter-electrode gap 20~200 mm are patterned on a glass substrate by semiconductor fabrication processes. Pure argon and helium are used as the feedstock. Filamentary-like discharges are mostly observed in argon discharges and highly-nonuniform discharges result in locally high current densities, which lead to a severe damage of the electrode. In helium discharges, a corona-like discharge is observed when the plasma is ignited with the applied voltage slightly higher than the breakdown voltage. Under certain conditions, such discharges occupy the entire inter-electrode space. With the increase in the applied voltage, the transition to filamentary-like discharges is occurred. It is shown that the breakdown voltage increases with the gap, and the voltage is 100-200 V higher than that shown in the right branch of the Paschen curve. Oscillations of current and voltage waveforms at different frequencies are observed after the plasma is ignited. Preliminary studies show that the MHz-high frequency oscillation is associated with the external circuits due to the sudden voltage drop after the breakdown. The low frequency oscillation, few tens of kHz, is a result of the repetitive ignition and extinguishment of the discharge. No stable discharge is obtained. Such a behavior is seen in both DC-and AC-driven discharges. P-spice circuit simulation is performed to study the effects of the external circuitry on the discharge behavior. The I-V characteristics are simulated, and results qualitatively agree with the experimental measurements. The optical emission emanating from the plasma is monitored and the broadening of hydrogen emission lines is used to estimate the plasma characteristics, namely the electron density and neutral gas temperature. Finally, the potential using such a discharge in materials processing will be demonstrated.