Impact of Anode Configuration on Performance of Field Emitter Arrays

We demonstrate the first steps in engineering the anode of field emitter arrays (FEAs) for optimal vacuum packaging by studying a parallel anode-cathode configuration. As part of our study, we report an unexpected gate-controlled negative differential resistance (NDR) region in the output characteristics of FEA-based triodes. The FEA triode consists of an FEA cathode and a silicon MEMS anode that are separated by insulated standoffs to form a vacuum channel. The FEA cathode is an array of high-aspect nanowires connected in series with gated emitter tips. Electrons extracted by the gate-emitter voltage undergo ballistic transport to the anode. It is generally assumed that a parallel anode-cathode triode structure would be ideal due to its geometrical compactness and symmetry. In this work, an on-chip integrated flat silicon anode was fabricated to characterize the parallel configuration for well-defined anode-to-emitter distances of $\leq 100~\mu $ m. The observation of NDR in the “triode” operation regime, which is space-charge limited, suggests that the parallel anode-cathode structure will not be ideal for the integration of triodes for some circuit applications because of unfavorable electrostatics in the vacuum channel between the cathode and the anode. In addition, we demonstrated that the performance of the triodes could be engineered to reduce the on-resistance ( ${R}_{\text {ON}}$ ) and increase the output current by varying the geometry and position of the anode.