Abstract
We develop a model of the non-uniform thermionic emission from spatially heterogeneous cathode surfaces in a parallel diode, including both 3-D space charge and patch field effects. This model is able to predict both the temperature-limited (TL) emission and the full-space-charge-limited (FSCL) emission, as well as the TL-FSCL transition, i.e. the so-called “knee” in the Miram (current density vs. temperature) curve. The modeling results indicate that a thermionic cathode with a spatial distribution of work functions will have a smooth TL-FSCL transition as a result of both the 3-D space charge and patch field effects, even if the work function values are discrete-valued. Such behavior of a smooth Miram curve knee is in agreement with experimental results. This model provides a more physical method to modeling thermionic emission from heterogeneous surfaces. This model helps to understand the insight of emission physics, cathode development, and the design of vacuum electronic devices.
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