DC IV CHARACTERISTICS OF FIELD EMITTER TRIODES

Gate currents and collector currents as a function of collector voltage, and Fowler-Nordheim emission have been measured for a Spindt-type field emitter triode at pressures ranging from 3-5 x 10(-9) torr. Experimentally, it has been observed that the gate current at zero collector voltage follows the same Fowler-Nordheim law as the collector current at high collector voltage, and that for low emission current densities, the sum of gate and collector currents is constant for any collector voltage and is given by the Fowler-Nordheim current I(FN). The gate current I(g) at a given gate voltage V(g), as a function of collector voltage V(c) is modeled by the empirical relationship I(g) = I(FN)[V(g)/(V(g) - V(th) + V(c))]m with m ranging from 2.0 to 2.7. V(th) is a threshold voltage varying from 0 to approximately V(g), depending on the dynamic state of the emission sites. Based on these observations, a simple model has been developed to calculate the I-V characteristics of a triode. By measuring the Fowler-Nordheim emission, emission area and field enhancement can be obtained assuming a value for the barrier height. Incorporating the gate current, the collector current can then be calculated from I(c) = I(FN) - I(g) as a function of collector voltage. The model's accuracy is best at low current density. At higher emission currents, deviations occur at low collector voltages due to the fact that the constancy of gate and collector currents is violated.