Electrical probe calibration and power calculation for a miniature 13.56 MHz plasma source

The paper highlights and provides solutions to the difficulties encountered with electrical probe measurements performed on a miniature, high capacitive impedance plasma device excited at 13.56 MHz. It is shown that a proper calibration of the phase angle between the circuit current and load voltage signals is required when commercial capacitive voltage probes (Tektronix P6139A and P5100 models) are used. A method to calculate the electrical characteristics of the plasma source and accounting for this calibration is described. The P6139A probe, which has the largest input capacitance and shortest cable length, introduced the smallest phase angle (+2 +/- 1 degrees), while the P5100 probe, which is used for higher input voltages and has a longer cable length, introduced a considerably larger phase angle (-34 +/- 1 degrees) for typical resistive loads. Simple circuit models are developed in an attempt to isolate the phase induced by the probe capacitance and cable length. The application of the proposed calibration to a miniature atmospheric pressure glow discharge source considerably reduced the error in the calculation of the power dissipated in the plasma device, though it remained relatively high ( 1 W +/- 42%) due to the highly capacitive nature of the device.