Application of Terahertz Time-Domain Spectroscopy in Characterizing Thin Metal Film–Substrate Structures

Simultaneous measurement of the substrate/film thickness and film conductivity in a thin metal film/substrate structure is still challenging. In this article, we propose a method for the measurement based on a terahertz time-domain spectroscopy system by combining time-domain and frequency-domain analysis, in which an error function is established, whereas quasi-Newton algorithm is employed. The advantage of the proposed method is that neither the substrate thickness nor the terahertz transmission of the bare substrate is prerequisite before the measurement. The feasibility of the method is validated by our experimental conclusion that agrees well with the theoretical model.