Review of field emitter array cathodes

The need for cathodes that operate at 10 A/cm²or greater with long life, instant turn on, ambient temperature operation, and capable of being modulated with small voltages has led to the development of Field Emitter Array Cathodes (FEA's). FEA's are arrays of micron-sized pointed emitter cones positioned approximately one micron from a micron-sized aperture in an electrically isolated extractor grid. With a small positive voltage (100-200 volts) applied to the extractor, the high field gradient produced by the close spacing and the enhancement from the pointed tips results in field emission. Through the application of thin film microfabrication and crystal growth technology, arrays of 10⁶-10⁷electron guns/cm²are currently being developed by different fabrication techniques at three laboratories. Experiments at two of the laboratories have demonstrated current densities of 10-20 A/cm²and with reasonable advances, increases in current density of an order of magnitude are projected.