Multi-layer metal micromachining for THz waveguide fabrication

Thick multi-layer metal stacking offers the potential for fabrication of rectangular waveguide components, including horn antennas, couplers, and bends, for operation at terahertz frequencies, which are too small to machine traditionally. Air-filled, TE10, rectangular waveguides for 3 THz operation were fabricated using two stacked electroplated gold layers on both planar and non-planar substrates. The initial layer of lithography and electroplating defined 37 micrometer tall waveguide walls in both straight and meandering geometries. The second layer, processed on top of the first, defined 33 micrometer thick waveguide lids. Release holes periodically spaced along the center of the lids improved resist clearing from inside of the electroformed rectangular channels. Processing tests of hollow structures on optically clear, lithium disilicate substrates allowed confirmation of resist removal by backside inspection.