Space charge effects on the current-voltage characteristics of gated field emitter arrays

Abstract

Interplay of current crowding and current self-quenching effects in planar cold cathodes Space-charge effects and current self-quenching in a metal/CdS/LaS cold cathode Effects of space charge on the current-voltage characteristics of field emitter arrays AIP Conf.Microfabricated field emitter arrays ͑FEAs͒ can provide the very high electron current densities required for rf amplifier applications, typically on the order of 100 A/cm 2 . Determining the dependence of emission current on gate voltage is important for the prediction of emitter performance for device applications. Field emitters use high applied fields to extract current, and therefore, unlike thermionic emitters, the current densities can exceed 10 3 A/cm 2 when averaged over an array. At such high current densities, space charge effects ͑i.e., the influence of charge between cathode and collector on emission͒ affect the emission process or initiate conditions which can lead to failure mechanisms for field emitters. A simple model of a field emitter will be used to calculate the one-dimensional space charge effects on the emission characteristics by examining two components: charge between the gate and anode, which leads to Child's law, and charge within the FEA unit cell, which gives rise to a field suppression effect which can exist for a single field emitter. The predictions of the analytical model are compared with recent experimental measurements designed to assess space charge effects and predict the onset of gate current. It is shown that negative convexity on a Fowler-Nordheim plot of I anode (V gate ) data can be explained in terms of field depression at the emitter tip in addition to reflection of electrons by a virtual cathode created when the anode field is insufficient to extract all of the current; in particular, the effects present within the unit cell constitute a newly described effect. ͓S0021-8979͑97͒03214-3͔

(AASERT-97) Development of a Field Emitter Cathode for Low-Power Hall Thrusters

“…The work function typically used for Mo is 4.3-4.4 eV. 79 Performance degradation rates were predicted assuming three different work function values and the same E^ value of 39 eV. The results showed that performance degradation rates predicted using each <| > w value were consistent with experimental results when an E^ value of 39 eV was used.…”

Theory of Field Emission

“…In experiments, the gate is not a ring of charge, and a sheet of charge representing the remainder of the gate [113] must be added. The potential on axis becomes…”

“…If higher terms were retained, A FN and B FN would no longer be constant but would depend on x = 1/V and therefore, become local intercept and slope parameters (see discussion in Ref. [113]). In terms of data, x 0 represents the midpoint of 1/V , and δ governs the range over which 1/V varies.…”

Space charge effects in field emission: One dimensional theory

“…Nevertheless, there have been several theoretical efforts [11][12][13][14][15][16]: in particular, the treatment of the 1D field emission / space charge problem (Ref. [17] and references therein), the usage of Particle-in-Cell codes to treat field emission (Ref.…”