The spatial dispersion of the electric field for field emission microtriodes

The spatial dispersion of the electric field on the emitter is studied for field emission microtriodes (FEMTs). An analytical two-dimensional FEMT model is developed. It is shown that the electric field on the emitter as a function of the angular position E(/spl phi/) is obtained as a sum of an "anode" field term E/sub a/(/spl phi/) and a "gate" field term E/sub g/(/spl phi/). The anode term has a maximal value located on the emitter apex. For the gate placed far away from the emitter, the gate term E/sub g/(/spl phi/) has a maximum on the emitter apex, like E/sub a/(/spl phi/). For small emitter-gate distances, E/sub g/(/spl phi/) has a lateral maximum. The resulting field distribution E(/spl phi/) depends on the relative magnitude of the anode gate voltages and the geometry of the system. These features are further studied considering a three-dimensional FEMT numerical model. The emitter has a conical body with spherical tip and a plane gate. The emission current is obtained using the standard Fowler-Nordheim relationship and integrating the current density over the emitter surface. The anode I/sub a/ and gate I/sub g/ currents are computed assuming a simple model for the trajectories of the emitted electrons. The spatial field dispersion E(/spl phi/) and the current ratio I/sub a/ I/sub g/ are outlined as a function of model parameters.