  Compact and robust waveguide chips are crucial for new integrated terahertz
applications, such as high-speed interconnections between processors and
broadband short-range wireless communications. Progress on topological photonic
crystals shows potential to improve integrated terahertz systems that suffer
from high losses around sharp bends. Robust terahertz topological transport
through sharp bends on a silicon chip has been recently reported over a
relatively narrow bandwidth. Here, we report the experimental demonstration of
topological terahertz planar air-channel metallic waveguides which can be
integrated into an on-chip interconnect. Our platform can be fabricated by a
simple, cost-effective technique combining 3D-printing and gold-sputtering. The
relative size of the measured topological bandgap is ~12.5%, which entails
significant improvement over all-silicon terahertz topological waveguides
(~7.8%). We further demonstrate robust THz propagation around defects and delay
lines. Our work provides a promising path towards compact integrated terahertz
devices as a next frontier for terahertz wireless communications.
