On-Chip THz-TDS Platform for High-Sensitivity Analysis of Graphene and Thin-Film Conductors.

Terahertz (THz) technology enables nondestructive characterization of conductive thin films but faces challenges in analyzing ultrathin, weakly conductive two-dimensional materials because of their weak light-matter interactions. On-chip spectroscopy (OCS) using planar waveguides addresses this limitation by confining THz fields, thereby enhancing electromagnetic coupling to samples. However, most OCS devices are firmly integrated with samples, limiting their reusability. Here, we developed a compact, high-sensitivity on-chip THz sensor featuring a symmetric coplanar stripline embedded in low-permittivity polymer films. Its modular design, comprising a rigid motherboard and a detachable daughterboard for sample mounting, enabled multisample testing with a single device. Air-gap-dependent measurements confirmed effective field coupling. Our THz OCS platform demonstrated absorption enhancements exceeding 8.8 dB for graphene and 21.6 dB for chromium with distinct phase shifts and pulse broadening compared to conventional free-space systems. The exchangeable daughterboard allows tunable and reproducible sample interactions for highly sensitive characterization of ultrathin films.