High-current CNT films grown directly on commercially available 2.5D substrates for low-voltage field-emission electron sources

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.