Resistive arc protection for field-emitter-array cold cathodes used in X-band inductive output amplifiers

Abstract

Field emitter arrays (FEAs) can provide advantages over gridded thermionic emitters when used as cold cathodes in inductive output amplifier (IOA) tubes. However, they are prone to destructive arcing currents that reduce their lifetime. Display developers have alleviated this problem by means of integral resistors formed in series with the emitting tips, but the resistive layers as currently used preclude gate modulation at X-band frequencies. By using a vertical instead of a lateral resistor, the layer can act as its own bypass capacitor under high frequency operation. An analysis of the effect of the resistive layer on rf performance is given. It is shown that reducing the thickness of the layer results in an acceptable bypass capacitor value, while still maintaining sufficient arc current protection. This is confirmed by means of an analytical model and SPICE simulation of a resistively protected FEA in an IOA configuration. FEAs fabricated with such resistive layers showed improvements in lifetime under dc test conditions.