Freeform terahertz structures fabricated by multi-photon lithography and metal coating

Abstract

Direct-write multi-photon laser lithography (MPL) combines highest resolution on the nanoscale with essentially unlimited 3D design freedom. The groundbreaking potential of this technique has been demonstrated in various application fields, including micromechanics, material sciences, microfluidics, life sciences, as well as photonics, where in-situ printed optical coupling elements offer new perspectives for package-level system integration. However, millimeter-wave (mmW) and terahertz (THz) devices did not yet leverage the unique strengths of MPL, even though the underlying devices and structures could also greatly benefit from 3D freeform microfabrication. A key challenge is that functional mmW and THz structures require materials with high electrical conductivity and low dielectric losses, which are not amenable to structuring by multi-photon polymerization. In this work, we introduce and experimentally demonstrate a novel approach that leverages MPL for fabricating high-performance mmW and THz structures with hitherto unachieved functionalities. Our concept exploits in-situ printed polymer templates that are selectively coated through highly directive metal deposition techniques in combination with precisely aligned 3D-printed shadowing structures. The resulting metal-coated freeform structures (MCFS) offer high surface quality, low dielectric losses, and conductivities comparable to bulk material values, while lending themselves to in-situ fabrication on planar mmW and THz circuits. We experimentally show the viability of our concept by demonstrating functional THz structures such as ultra-broadband chip-chip interconnects, THz probe tips, and suspended THz antennas. We believe that our approach offers disruptive potential in the field of mmW and THz technology and may unlock an entirely new application field for laser-based 3D manufacturing.