Low-power microwave plasma source based on a microstrip split-ring resonator

Microplasma sources can be integrated into portable devices for applications such as bio-microelectromechanical system sterilization, small-scale materials processing, and microchemical analysis systems. Portable operation, however, limits the amount of power and vacuum levels that can be employed in the plasma source. This paper describes the design and initial characterization of a low-power microwave plasma source based on a microstrip split-ring resonator that is capable of operating at pressures from 0.05 torr (6.7 Pa) up to one atmosphere. The plasma source's microstrip resonator operates at 900 MHz and presents a quality factor of Q=335. Argon and air discharges can be self-started with less than 3 W in a relatively wide pressure range. An ion density of 1.3/spl times/10/sup 11/ cm/sup -3/ in argon at 400 mtorr (53.3 Pa) can be created using only 0.5 W. Atmospheric discharges can be sustained with 0.5 W in argon. This low power allows for portable air-cooled operation. Continuous operation at atmospheric pressure for 24 h in argon at 1 W shows no measurable damage to the source.