Prototyping of electromagnetic components of sub-terahertz vacuum electron devices

Trends concerning the acceleration of the development of novel millimeter and terahertz-band vacuum microelectronic devices highly demand rapid and cost-effective techniques that allow microfabrication of the proof-of-concept physical models. The additive manufacturing can meet the abovementioned requirements. Nowadays, vat photopolymerization is one of the most flexible and precise additive technologies that allows fabrication of microsized elements with tolerance down to tens of microns. We proposed an approach based on the liquid crystal display vat photopolymerization and vacuum magnetron sputtering for rapid and low-cost microfabrication of the key sub-terahertz-band electromagnetic components. To validate the proposed approach, several samples of single grating slow-wave structure for a W-band (75–110 GHz) vacuum-tube device were successfully microfabricated for the first time. The structure with total length of 60 mm consisted of a 20-pitch uniform section and two 11-pitch tapered sections at both ends in order to reduce the reflections. Magnetron sputtering was used to deposit the thin copper film onto the inner surface of the fabricated samples. The surface roughness was measured before and after metallization using profilometry. Morphological and profilometric analyses have shown a decrease in the surface roughness up to 30% after 1-µm-thick metallization and up to 50% after 3-µm-thick metallization. Results indicate that a 3-µm-thick metallization layer sufficiently meets requirements for suitable reflection and transmission losses in the W-band. Reflection and transmission losses in the W-band of the fabricated slow-wave structure were measured using a vector network analyzer and compared with the results of numerical simulation using 3D finite-difference time-domain code. Comparison with the numerical simulation results shows good qualitative and quantitative agreement. The measured reflections were below – 20 dB in the 88–105 GHz frequency range. The specific transmission attenuation was measured to be 0.08 dB per pitch. This study underscores the promise of the proposed method for swiftly prototyping complex electromagnetic structures, leading to significant time savings in proof-of-concept research endeavors.