Scaling of Microwave Plasma Sources to Small
Dimensions for Microsystem Applications
Scaling of plasma sources down to small sizes for use
in microsystems is a current project of Timothy Grotjohn and Jes Asmussen.
This project is funded by the National Science Foundation and it is investigating
and establishing the scientific basis and engineering principles for the
design and operation of small microwave plasma sources with discharge dimensions
ranging from 0.2-10 millimeters. Past investigations on microwave discharges
by researchers have primarily focused on discharges that were a few centimeters
to almost a meter in size. However, careful investigations of microwave
discharges with dimensions of 10 mm down to 0.2 mm have not been done,
especially in the GHz frequency range. The emphasis in this project is
on developing electrodeless plasma sources that will operate without the
electrode erosion and contamination problems of small plasma electrode-based
(dc and ac) systems. Small microwave discharges operate with low input
power, while having very high power densities (i.e. highly reactive species
outputs). The low input power feature allows the sources to operate with
coherent and controllable power supplies currently available for mobile
communication systems with power levels of one to a few watts. The availability
of very small, coherent, physically compact microwave power sources combined
with small microwave plasma sources opens the possibility of many here-to-for
unthought of microwave plasma applications.
The research is experimentally evaluating and theoretically
modeling the behavior of microwave discharges as the discharge size is
decreased. One of the microwave plasma systems being developed uses microstripline
technology to power the plasma discharge. An example of such a microstripline
based plasma source is shown in the photograph below. The microwave power
couples from the microstripline into the discharge and the discharge fills
the two millimeter diameter tube, which has a loop shape in the photograph.
Microstripline based plasma sources have been constructed with discharge
diameters as small as 200 microns.
