Quality Factor Model for Integrated Inductors in CMOS Technology

Abstract

Inductors quality factor is limited by resistive losses in metal traces and by induced currents in both, metal strips and lossy Si substrate. Skin and eddy losses are carefully studied and a new physically based fitting model is presented. The behaviour of spiral inductors fabricated in a standard CMOS 0.6 urn process is modeled. A closed formula that depends on the geometrical parameters and the fabrication process has been obtained. The inductance value has only a ± 10 % error against measured values for a set of six CMOS inductors. Our model is capable to predict the frequency at which maximum Q is obtained. This has been validated against measured data. These equations are coded in a program that requests the desired inductance value at a determined frequency and gives back the geometrical parameters for the inductors with high Q. This methodology can be extended to other technologies varying only the technological process parameters.