340-GHz Folded Waveguide Fabricated by Two- Step UV-LIGA for Backward-Wave Oscillators

This article focuses on fabricating a 340-GHz folded waveguide (FWG) at frequencies ranging from 335 to 345 GHz using two-step UV-Lithographie Galvonoformung Abformung (LIGA) technology. The accuracy of the height and width of the 340-GHz FWG is ±5 and
$\pm 1 \mu \text{m}$
, respectively, and the alignment precision between the longitudinal beam tunnel and the serpentine waveguide is
$\pm 2 \mu \text{m}$
, which are primarily determined by the process parameters. This article explains—in detail—the effects of processing parameters on patterns such as soft bake, exposure dose, post-bake, and electroforming current. The transmission properties of the microfabricated 340-GHz FWG are measured using an Agilent vector network, and the results verify its performance. The capability of making two-layer structures demonstrates that a two-step UV-LIGA technology has great promise for microfabricating FWGs on the order of micrometers for THz vacuum electronic devices.