Simulations of emission characteristics of a multigated single carbon nanotube field emitter

Abstract

In this study, a two-dimensional, particle-in-cell computer simulation code MAGIC was used to investigate the field emission characteristics from a single closed-capped multiwalled carbon nanotube (MWCNT) in a particular quadruple-gated focusing configuration. Simulations have been done on a single MWCNT assuming it is a cylinder with an ellipsoidal cap of 40nm major radius and 10nm minor radius, 20nm in base diameter, and 0.2 or 0.3μm in height. Other simulation parameters in the base case are 0.1μm thickness for each gate, uniform gate hole radius of 0.45μm, and an anode-cathode distance of 20μm. A particular quadruple-gated focusing configuration has been investigated with individual gate bottom to cathode top distances of 1.1, 1.8, 2.9, and 3.9μm, respectively. For this particular quadruple-gated structure with a cathode voltage of 0V, 85V in voltage of the first gate, 224V in voltage of the second gate, 1320V in voltage of the third gate, 1331V in voltage of the fourth gate, and an anode voltage of 1331V, simulation result showed that a current-weighted beam spot radius on the anode plane can be reduced to 17.4nm for a MWCNT height of 200nm. The emission current, however, varies only slightly from 0.311to0.375pA, as the voltage on the third gate is changed from 200to1500V. The region in the vicinity of the second gate acts to focus the emitted electron beam, while that of the third gate acts to diverge the beam. It was also found that using a higher MWCNT would reduce the applied voltages, but the emitted electrons could not be as well focused as the case with shorter MWCNT. For a MWCNT height of 300nm at about 0.3pA emission current, the weighted beam radius is increased slightly to 28.8nm at the optimum focusing condition. For the MWCNT height of 300nm at a higher emission current about 3nA, the weighted beam radius was found to increase to 46.4nm at the optimum focusing condition. This study shows that it is possible to design a quadruple-gated MWCNT field emitter having few tens of nanometer focused beam size at picoampere to nanoampere emission current range and the designed field emitter is suitable for parallel electron-beam lithography applications.