An inductively coupled miniature plasma jet source at microwave frequencies

A miniature double plasma jet source driven at microwave frequencies (∼2.45 GHz) was developed and analyzed. The source consists of a copper resonator (screened within an aluminum housing) that excites plasma simultaneously in two alumina tubes of 5 mm internal diameter. Field and plasma simulations were performed using the software Comsol. Assuming a homogeneous electron distribution we calculate the plasma impedance as a function of its conductivity. The electron density and the plasma conductivity are estimated as a function of the absorbed power in plasma for argon and oxygen. Experimentally it was shown that the microwave energy is coupled into oxygen plasma with an efficiency of >85% and into argon plasma with ∼30%. The source efficiently produces atomic oxygen and nitrogen as is demonstrated by plasma-enhanced atomic layer deposition. Finally, the time evolution during ignition, the transition from low efficient capacitive to highly efficient inductive coupling, the free electron distribution as a function of time and other parameters are analyzed. (paper)