Biomedical Engineering Reference
In-Depth Information
Fig. 23
Plasma chamber (
a
) before ignition; (
b
) at ignition pressure after arc discharge; (
c
) at
operation pressure
the plasma is sustained and the gas pressure can be reduced. Figure
23
demonstrates
the ignition of plasma in a PIMMS-chip:
As known from plasma physics the potential of the electrode with smaller area,
which is the powered electrode in PIMMS, will turn negative. This DC-bias voltage
is used for the detection that the plasma is on.
Thus, to ignite, sustain, and control the microplasma the following electronic
components are necessary:
pressure and valve controller, as described in Sect.
6.2
,
high voltage pulse generator to generate the arc discharges,
RF-Generator,
DC-Bias-Voltage measurement of the powered electrode.
The high voltage pulses are generated by discharging of a capacitor via the sec-
ondary winding of a transformer. As a consequence the primary winding delivers a
high voltage pulse. Since the igniting electrodes in the plasma chamber are very
closely spaced, an arc discharge is easily generated, when the local gas pressure is
high (Fig.
3
). The arc current has to be limited to avoid evaporation of the elec-
trodes. With the present solution >50,000 ignition cycles were performed on one
chip without observing any structural change of the electrodes.
