Modeling and Analysis of T-coils with Improved Quality Factor by Patterned Floating/Ground Shields in Millimeter-Wave Regime

T-coil, a special inductor which has symmetric coils with center tap, receives widespread adoption in differential circuits and broadband high-order matching networks. In this paper, to investigate and improve its electrical performance, T-coils with three traditional shields and the proposed reduced ladder shield are analyzed and compared by the double-π equivalent circuit model up to 110 GHz. Two-step model parameters extraction flow is established, i.e., linear regression based low frequency extraction and differential evolution based global refinement extraction from DC to 110GHz. Modeling results reveal that the root mean square error between simulated and modeled electrical performance are all below 10%. The T-coil with proposed reduced ladder shield achieves a 3.4% improvement in quality factor in 110 GHz compared with the T-coil with no metal fill. The layout of the optimal shield design is achieved by minimizing the capacitive coupling to the substrate and reducing the resistive loss.