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

摘要

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 40 nm major radius and 10 nm minor radius, 20 nm in base diameter, and 0.2 or 0.3 μm in height. Other simulation parameters in the base case are 0.1 μm thickness for each gate, uniform gate hole radius of 0.45 μm, and an anode-cathode distance of 20 μm. 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 3.9 μm, respectively. For this particular quadruple-gated structure with a cathode voltage of 0 V, 85 V in voltage of the first gate, 224 V in voltage of the second gate, 1320 V in voltage of the third gate, 1331 V in voltage of the fourth gate, and an anode voltage of 1331 V, simulation result showed that a current-weighted beam spot radius on the anode plane can be reduced to 17.4 nm for a MWCNT height of 200 nm. The emission current, however, varies only slightly from 0.311 to 0.375 pA, as the voltage on the third gate is changed from 200 to 1500 V. 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 300 nm at about 0.3 pA emission current, the weighted beam radius is increased slightly to 28.8 nm at the optimum focusing condition. For the MWCNT height of 300 nm at a higher emission current about 3 nA, the weighted beam radius was found to increase to 46.4 nm 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.