High Q MMIC spiral inductor study using production silicon process

Abstract

This paper documents the results of a study based on measurements of 240 microwave monolithic spiral inductors fabricated using an industry standard silicon process. Measurements at frequencies between 1GHz and 40GHz are presented which demonstrate inductance values of 0.4nH are achievable at 15GHz with quality factors of 20. To the authors' knowledge this is one of the highest reported Qs of a monolithic inductor created in a standard RF silicon process. Four square and four octagonal inductors were design with target inductances of 0.4nH, 0.5nH, 1.0nH, and 1.5nH. Each inductor was fabricated three ways: in top metal only, in top and second from top metal layers with the layers joined by vias along the length of the inductor, and in top metal with a 1µm wide trench in the silicon substrate between the inductor windings. Ten of each inductor version were measured to increase the statistical significance of the results. Three de-embedding techniques for removing pad and feed line parasitics from the inductor measurements are discussed. As well, the efficacy of HP EEsof Series IV Momentum in predicting the performance of one of the square inductors is presented.