Energy coupling in a diode with a die

Among the various electron emission mechanisms the emission using ferroelectric ceramics is the ‘‘junior’’ process. It was observed at very low current density levels ~10 pA/cm! in 1984 by Rosenman. Five years later, Riege and his co-workers at CERN demonstrated current densities that are 13 orders of magnitude higher. In 1990 Airapetov reported the highest current density so far when measuring order of 400 A/cm. From the early nineties a significant effort was devoted to the investigation of the emission from ferroelectric ceramics: Nation and his group at Cornell University has pioneered this activity in the US followed by Integrated Applied Physics ~IAP! in collaboration with MIT, LLNL, and University of New Mexico. In parallel the topic has been investigated in Japan. In all the experiments performed so far the cathode consists of a ferroelectric ‘‘capacitor’’ with a uniform back electrode and a thin gridded one, facing the diode gap. Electrons emission is triggered by applying to the back electrode a fast electric field that is larger than the coercive field ;1 310 V/m. Anode current occurs independent of the initial polarization state of the ceramic and irrespective if the ferroelectric undergoes phase-transition or not, however, its intensity is dependent on these characteristics. The electron emission was shown to be accompanied, in case of phase transition, by a burst of energetic electrons ~25 keV! and of microwave radiation in the GHz range. In this context it is important to distinguish between two cases: pure ferroelectric emission and assisted ferroelectric emission. As Riege et al. emphasize in Ref. 11, in the case of ‘‘pure’’ ferroelectric emission, electrons are emitted from the surface without the need of an anode voltage and this is a result of internal polarization reversal that releases the screening electrons from the surface. In what we call the ‘‘assisted’’ ferroelectric emission, the cathode takes advantage of the high dielectric coefficient of the ceramic, its nonlinear character as well as part of the screening charge to facilitate emission. It is the last regime that will be the focus of our investigation here.