Guidelines for the Design of Thin Film Microstrip Lines for Signal Integrity Analysis

This article investigates the performance of thin-film microstrip lines (TFMSLs), characterized by low-resistivity substrates, and proposed as interconnects in high-speed links for applications such as the fifth generation of communication systems (5G). The main contribution of this work is the study of the impact of the geometry of such lines and the data rate and load conditions of the overall signaling system. To this end, several test structures based on coupled TFMSLs with different geometric configurations are here designed, fabricated, and experimentally characterized. These structures introduce mismatching, bends, and unwanted coupling with adjacent traces. An electromagnetic model and a circuital one are here adopted to analyze these TFMSLs, which are validated against each other and against the measurements. Frequency analysis allows highlighting the different behaviors of the considered structure in terms of mixed-mode S-parameters and insertion loss (IL). A time-domain analysis is also carried out to assess the signal integrity (SI) performance of high-speed data link systems based on these TFMSLs. Another contribution of this work is given by the derivation of design maps based on eye-diagram metrics, which can be useful to find the optimized trade-offs for the operating conditions to be imposed on these links, such as data-rate values or load impedance.