Applying microfabrication to helical vacuum electron devices for THz applications

A new class of helical THz vacuum electron devices is under development using unconventional applications of microfabrication technology, modern computer modeling, and novel materials. The resulting slow wave circuits consist of a coil of gold wire, smaller in outside diameter than a human hair, supported by a thin diamond sheet and suspended within a diamond box. This configuration will extend the operating range of the helical slow wave circuit into the THz frequency band. Previously, the advantages of the wide bandwidth and high efficiency of the helical slow wave circuit have been available only for operation at frequencies below 50 or 60 GHz because of the difficulty of winding small coils of wire and because it is impossible to transmit a significant beam current through the small aperture offered by the center of the helix. These obstacles are overcome by fabricating the helices lithographically and by passing the electron beam around the outside of the helix. The design and fabrication of a 650 GHz backward wave oscillator (BWO) will be described as well as proposed applications of this technology to traveling wave tubes (TWTs) operating at frequencies as high as 1.0 THz. A THz amplifier, possibly with multioctave bandwidth, would have a wide range of important applications.