Study Of Low Power Microwave Plasma Excitation Based On Microstrip Split-ring Resonator

The applications of microelectromechanical systerms (MEMS) have broadened in recent years. Great efforts to fabricate microplasma sources based on microstip strcture that can be integrated with other MEMS devices have been made. Such microplsma sources can be integrated into small scale portable devices and offer the advantages of small size, low power, long-time operation under normal atmospheric pressure. Plasma-based Microsystems can find applications in microbial analysis system, bio-MEMS sterilization, microchemical analysis systems, small-scale materials processing and micropropulsion .A microwave-induced microplasma source based on a microstrip slit-ring resonator (MSRR-MIP) has been designed, and its working principles and characteristics of microplasma discharge are analyzed extensively and validated by experiments.Firstly, the low-temperature plasma and microstrip resonator theory are introduced as the design basis. Then the MSRR-MIP source device is modeled and analyzed as a microwave transmission line circuit. The model identifies the electrical parameters of the device, including input impedance, voltage across the gap and plasma impedance in the formulation of closed-form expression. The discharge traits and affection to the resonator are analyzed in theory, especially the affection of plasma impedance and energy efficiency. It can be found that matching of the microstrip characteristic impedance with the microplasma impedance is the key factor for the performance of the device, and even more critical than the quality factor of the ring resonator.Based on the theory analysis above, the structure of microstrip line and resonator simulated and optimized using HFSS software and three split-width resonators,200μm, 100μm and 25μm, are fabricated. The microplasma discharges in the low-pressure air are obtaind successfully. The resonance frequency and voltage reflection coefficient S₁₁ are measured with the plasma as the terminal load, and the equivalent plasma impedance is computed. Experiment results indicate the validity and reliability of the analysis and simulation of the paper.In addition, an improved MSRR-MIP source fed directly without the impedance matching network is developed. It features smaller size and more efficiency to obtain the gas discharge under the normal air pressure.