Design and optimization of a quasi-optical system for characterizing the terahertz dielectric properties of millimeter-scale integrated circuit materials

Abstract To enable high-precision, non-destructive measurement of dielectric properties in millimeter-scale integrated circuit (IC) materials at terahertz frequencies, this paper proposes dual-lens pair based beam spot optimization model. Addressing limitations of traditional setups, the model allows precise alignment and beam control, significantly reducing spot size and enhancing measurement accuracy. The optimized configuration parameters satisfy the plane-wave assumption, ensuring the applicability of the inversion algorithm. Measurements were performed in the 325–500 GHz range on four IC materials, namely fused silica, GaAs, InP, and silicon. The extracted complex permittivity values showed less than 1% relative error compared to reference data, confirming the system’s capability for accurate characterization across millimeter-scale sample sizes. This study demonstrates a practical solution for terahertz dielectric analysis and provides both simulation and experimental insight into the co-optimization of beam focusing and inversion modeling.