Microfabrication of diamond-based slow-wave circuits for mm-wave and THz vacuum electronic sources

Abstract

Planar and helical slow-wave circuits for THz radiation sources have been made using novel microfabrication and assembly methods. A biplanar slow-wave circuit for a 650 GHz backward wave oscillator (BWO) was fabricated through the growth of diamond into high aspect ratio silicon molds and the selective metallization of the tops and sidewalls of 90 µm tall diamond features using lithographically created shadow masks. Helical slow-wave circuits for a 650 GHz BWO and a 95 GHz traveling wave tube were created through the patterning of trenches in thin film diamond, electroplating of gold half-helices, and high accuracy bonding of helix halves. The development of new techniques for the microfabrication of vacuum electronic components will help to facilitate compact and high-power sources for terahertz range radiation.

Vane-Loaded Planar Helix Slow-Wave Structure for Application in Broadband Traveling-Wave Tubes

“…Moreover, dielectric substrates can be chosen to have a high value of thermal conductivity to facilitate dissipation of heat from the SWS in a TWT. In this context, a promising choice for dielectric substrates would be CVD diamond, which has been proposed in the recent years [13]; it has a relatively low dielectric constant (ε r = 5.7), can be made in very thin self-supporting membranes that have a very good mechanical strength, and possesses a high thermal conductivity.…”

“…For instance, structures called square helix and planar helix, compatible with microfabrication technology, have been proposed and computationally investigated in [12] for Ka-band applications, but no results for fabrication and measurements have been provided. Design and fabrication of 95-GHz TWT and 650-GHz backward-wave oscillator based on microfabricated helix has also been reported extensively [13], [14]. However, these papers do not discuss dispersion control or dispersion shaping.…”

Studies on planar helical slow-wave structures for traveling-wave tube applications

“…With regard to high frequency VEDs, microfabrication of several SWSs has been reported in the literature. [36], double corrugated waveguide [94], raised meander-line [37], biplanar interdigital [38], and circular helix [38] and [95] Unlike the all metal structures, the structures that involve dielectric loading normally require more fabrication steps since the metallization is on top of a patterned dielectric substrate. For instance, the raised meander-line structure [37] involves selectively metalizing the high-aspect-ratio serpentine dielectric ridge.…”

“…Many efforts have been made to reduce the dielectric surrounding the structure. The fabrication of circular helix [38] and [95] involves a thin sheet of diamond for supporting the structure; such a configuration enjoys excellent thermal dissipation, moderate dielectric loading, high dielectric strength and low loss. However, the circular shape is difficult to realize faithfully in microfabrication and may need to be approximated as octagonal or square [95].…”

“…However, the circular shape is difficult to realize faithfully in microfabrication and may need to be approximated as octagonal or square [95]. Among the various SWSs, in general the helix structure holds a unique position since the fabrication has less stringent alignment issues due to their broadband nature [38]. Studio (MWS) [102], and Ansoft High Frequency Structure Simulator (HFSS) [103].…”