RF characteristics of a high-performance, 10-fF/μm2 capacitor in a deep trench

We report the properties of a novel polysilicon-insulator-polysilicon trench capacitor with a 380-Angstrom Si3N4 dielectric that is designed and fabricated for high-frequency bypass and decoupling applications. The capacitor has a specific capacitance as high as 10 fF/mum(2) normalized to its footprint area, and a breakdown voltage greater than 15 V at room temperature. The measured S-parameters are in excellent agreement with simulations of an equivalent circuit model that includes a shunt substrate resistance to ground (R-sub). A geometric factor mu is defined as the ratio of the imaginary parts of Y-11 and -Y-21 at low frequency. The values of mu and, consequently, R-sub are extracted from fitting the measured S-parameter data, and the layout dependence of mu and R-sub is also explained by the model.