Empirical model of the metal losses in integrated inductors

Abstract

Integrated inductors are key components in Radio Frequency Integrated Circuits (RFICs) because they are needed in several building blocks, such as voltage-controlled oscillators, low-noise amplifiers, mixers, or filters. The cost reduction, achieved in the circuit assemblage, makes them preferable to Surface Mounted Devices in spite of the different sources of losses that limits the use of integrated inductors; the substrate losses, and the metal losses. We report, in this work, our research in modeling integrated inductors, particularly the losses in the metals. The model is derived from measurements taken from integrated spiral inductors designed and fabricated in a standard silicon process. The measurements reveal that the widely accepted lumped equivalent model does not properly predict the integrated inductor behavior at frequencies above 3 GHz for our technology. We propose a simple modification in the lumped equivalent circuit model: the introduction of an empirical resistor in the port 1-to-port 2 branch of the equivalent circuit. As a result, it will be demonstrated that the integrated inductor behavior is adequately predicted in a wider frequency range than does the conventional model. In addition, the new model is used to build-up an integrated inductor library containing optimized integrated inductors.