IPD capacitor with pseudo-symmetry for isolated differential signal transfer applications

Abstract

In this paper, capacitors fabricated by an integrated passive device technology for isolated signal transfer applications are presented. The shapes of the capacitor plates are designed to achieve a symmetrical capacitive coupling matrix. Without using any highly doped shielding layer, the interference through the substrate can be eliminated in both forward and reverse directions for differential isolated signal transfer, regardless of the waveforms of the transmitter circuit. An isolation capacitor array with 3 channels and 700 ​fF capacitance values is experimentally demonstrated using a multilayer Cu/polyimide process. The capacitors show accurate capacitance values, 5kVrms isolation voltage and low leakage current of tens of pA at working voltage. Measurement results also show that the capacitor array with pseudo-symmetry reduces the mismatched interference signal by 5 times.