Field emitter array
A field emitter array (FEA) is a particular form of large-area field electron source. FEAs are prepared on a silicon substrate by lithographic techniques similar to those used in the fabrication of integrated circuits. Their structure consists of a very large number of individual, similar, small field electron emitters, usually organized in a regular two-dimensional pattern. FEAs need to be distinguished from "film" or "mat" type large-area sources, where a thin film-like layer of material is deposited onto a substrate, using a uniform deposition process, in the hope or expectation that (as a result of statistical irregularities in the process) this film will contain a sufficiently large number of individual emission sites.
The original form of FEA was the Spindt array, in which the individual field emitters are small sharp molybdenum cones. Each is deposited inside a cylindrical void in an oxide film, with a counterelectrode deposited on the top of the film. The counterelectrode (called the "gate") contains a separate circular aperture for each conical emitter. The individual cones are sometimes called Spindt tips. The device is named after Charles A. Spindt, who developed this technology at SRI International.
Because it has a relatively sharp apex, a Spindt tip can create a high electric field at a relatively low voltage, and thus emits significant amounts of current at relatively low gate voltages (less than 100 V). Because of the use of lithographic techniques, the individual emitters can be packed close together. The average (or "macroscopic") current density that can be obtained from a Spindt array can be as much as 2×107 A/m2.
One of the earliest article describing a single emitter tip microfabricated on a wafer dates back to 1968. Spindt, Shoulders and Heynick filed a U.S. Patent  in 1970 for a vacuum device comprising an array of emitter tips.
An alternative form of FEA is fabricated by creating voids in an oxide film (as for a Spindt array) and then using standard methods to grow one or more carbon nanotubes (CNTs) in each void.
It is also possible to grow "free-standing" CNT arrays.
The main use of a FEA is in connection with a form of electronic information display (a "flat panel display") known as a field emission display (or, more recently as a "nano-emissive display".)
However, possible uses as microwave generators and as space-vehicle neutralisers have also been explored.
- C. A. Spindt, "A thin-film field-emission cathode", Journal of Applied Physics, vol. 39, no. 7, pages 3504-3505, 1968
- U.S. Patent 3,755,704 granted on August 28, 1973