Resistive Coupling Efficiency Criterion for Evaluating Substrate Shielding Structures of Transformers

This letter presents a new way to evaluate the transformer substrate effect by computing its resistive coupling efficiency coefficient eta Kr . To assess eta Kr , a set of transformers with and without shielding structures was fabricated using standard 0.18-mum CMOS process. The resistive coupling factor eta Kr and efficiency eta Kr were extracted. It was found that substrate and shielding effects are better quantified with eta Kr than with G max and S parameters. The larger the relative shielding dimensions, the higher the eta Kr is. With eta Kr as a figure of merit, we see clearly that a large 3-D patterned floating shield improves transformer performance more than a 2-D one. It was also found that shielding efficiency is correlated with shielding structure dimensions and that the performance of shielded transformers is less sensitive to temperature variations.