Design and modeling of Faraday cages for substrate noise isolation

• Faraday cages constructed of through-substrate vias suppress substrate noise.
• We developed lumped-element, equivalent circuit models of the Faraday cage.
• An optimal Faraday cage design requires low substrate via impedance.
• The design of the Faraday cage can be optimized for the frequency of operation.

A Faraday cage structure using through-substrate vias is an effective strategy to suppress substrate crosstalk, particularly at high frequencies. Faraday cages can reduce substrate noise by 32 dB at 10 GHz, and 26 dB at 50 GHz. We have developed lumped-element, equivalent circuit models of the Faraday cages and test structures to better understand the performance of the Faraday cages. These models compare well to measured results and show that the vias of the Faraday cage act as an RLC shunt to ground that draws substrate current. Designing a Faraday cage to achieve optimum isolation requires low via impedance and mitigation of via sidewall capacitance. The Faraday cage inductance is correlated to the number of vias and via spacing of the cage and can be optimized for the frequency of operation.