Reducing electron energy dispersion of nonformed metal--insulator--metal electron emitters using the near-threshold drive method

The energy distribution of electrons emitted from an Al/Al2O3/Au metal--insulator--metal (MIM) electron emitter is measured. The thickness of the insulator is 5.5 nm. The energy distribution becomes narrower as the operating voltage Vd decreases since the low energy tail of the distribution is cut off by the potential barrier of the surface work function φ of the emitter. When the emitter is operated in the nonformed state, ΔE, the full width at half-maximum of the distribution, is 0.32 eV for Vd=5.0 V, which is slightly above φ of Au (4.7 eV). As Vd increases, the high-energy tail of the distribution broadens whereas the shape of the low-energy tail remains unchanged. For a formed MIM emitter, ΔE becomes broader by 0.15--0.2 eV more than ΔE of a nonformed emitter at each Vd; thus, operation in the nonformed state is essential to obtain good monochromaticity. The spatial distribution of the work function in the emitter surface is also measured by the retarding potential method. The variation of φ, which limits the ultimately attainable monochromaticity with the near-threshold drive method, is measured as 0.05 eV. It is estimated that ΔE less than 0.2 eV could be attained by the near-threshold drive if the insulator thickness and Vd are further reduced. copyright 1995 American Vacuum Society