Measurement of a plasma in the AC plasma display panel using RF capacitance and microwave techniques

The existence of a long-lived plasma in the gas volume is demonstrated by two techniques. By using a suitable RF frequency, the capacitance of plasma cells is shown to vary due to the production and decay of the plasma. In a special large-area cell constructed to minimize stray-capacitance problems, the plasma caused the capacitance to increase by a factor of 7 over the neutral value. This means that at the peak, the plasma filled about 6/7 of the discharge gap. By constructing a special-geometry plasma cell in the shape of a strip-transmission line, the microwave transmission properties were determined at 10 GHz. When the plasma is in the volume, the transmission is cut off. There is strong correlation between the capacitance variation and the microwave transmission variation. Depending on various conditions, the two techniques show the plasma to exist between 10 and 100 µs after the discharge-current peak. The plasma can be swept out of the volume by either positive- or negative-going applied voltage pulses. Thus the plasma is usually swept out upon the fall of the sustain voltage, especially when the sustain duty factor is less than 100 percent.