  Carbon nanotube (CNT) based electronic devices are promising for
beyond-silicon solid-state electronics and vacuum micro-nano-electronics.
Despite rapid progress in CNT field-effect transistor related solid-state
electronics, the development of CNT-based vacuum nanoelectronic devices is
substantially blocked by the longstanding challenges in demanding high-current
field-emission (FE) electron sources at low operating voltage. In addition to
CNTs' properties, FE characteristics are also affected by substrate morphology
and interface state. This work demonstrates high-current FE characteristics at
relatively low operating voltage by using CNT films grown directly on
commercially available 2.5D substrates with matched feature size and improved
interface contact. Simulation results indicate that the commercially available
2.5D substrate including nickel foam (NiF) and carbon cloth (CC) with
appropriate feature size would dramatically help to enhance emission current at
a relatively lower voltage. Modified fabrication process results in improved
contact between CNTs and the underlying 2.5D substrates. Twenty times higher
emission current density with halved lower turn-on electric field achieved by
CNTs grown directly on randomly picked NiF shows the potential of 2.5D
substrate with good contact in improving FE characteristics. Finally, a high
emission current (6 mA) with approximately 75 percent decrease in turn-on
electric field was realized by matching the feature size of 2.5D substrate with
that of CNTs, bringing us significantly closer to reliable high-current and
low-voltage FE electron sources for practical applications.
