Role of space charge in field emission cathodes

Space charge plays an extremely important role in thermionic vacuum tubes. Normally it can be neglected in the operation of field emitter cathodes because the very high electric fields at the cathode negates the formation of space charge. However at very high current densities, it may be evident in field emission cathodes. This article explores the region where space charge affects the potential distribution in field emission cathodes of the type proposed for use in vacuum microelectronics applications. Rectangular, cylindrical, and spherical geometries are considered.