Emission characteristics of NbC/Nb field emitters

摘要

For several years we have searched for emitter materials that are capable of high currents and are environmentally tolerant. Our studies have focused on the refractory carbides of transitions metals. We have reported promising results with, HfC and ZrC at several International Vacuum Microelectronics Conference (IVMC) conferences. Then we reported at the two previous IVMCs, on studies of gated arrays with individually addressable emitters made of niobium carbide, other transition metal carbides, and, platinum. Here we report on an extensive study of the emission characteristics (noise and stability) of individual NbC/Nb field emitters at currents of about 1 muA and at residual pressures ranging from 2 x 10(-9) to 2 x 10(-5) Torr, for five different residual gases (H-2, CO, CH4, Ar, and Xe). We conclude that flicker noise amplitude at similar to10 Hz increases slowly with residual pressure, according to an empirical formula: mu(p) = mu(0)(p/p(0))(n) with n congruent to 0.2-0.3. For our studies of medium term stability, for given residual gas and pressure, we record about 30 consecutive I(V) characteristics and plot the corresponding points on a Fowler-Nordheim slope-intercept chart. We have developed different analytical expressions for slope and intercept for smooth emitters and for emitters with sharp protrusions. Analysis of slope-intercept charts leads to several conclusions, particularly that emission is dominated by small, sharp nano protrusions that are relatively unstable. Future plans include testing various tip conditioning techniques to improve stability. (C) 2004 American Vacuum Society.