Microwave passive components in thin film technology

Abstract

This chapter is dedicated to a theoretical investigation of the electrical behaviour of inductors and transmission lines integrated on thin silicon wafers. Using electromagnetic simulations, it is shown that thinning a standard silicon substrate to ∼20-70 μm yields a ∼20-30% increase in the maximum quality factor and resonance frequency of typical integrated spiral inductors. This improvement is due to a higher spreading substrate resistance between the inductor and the physical ground. However, further improvement of the quality factor requires substrates thinned to several microns in order to reduce the effect of stray electric fields induced between different points on the conductor, e.g., between adjacent windings. In the case of coplanar waveguide and microstrip transmission lines, significant improvement in device quality is only observed when silicon thickness reaches values below 10 μm. On highly conductive silicon, the behaviour of inductors and transmission lines as a function of substrate thickness becomes strongly dependent on silicon resistivity. In particular, thinning substrates with a resistivity in the 0.01-2 Ω-cm range may even have an adverse effect on device performance. © 2011 Springer Science+Business Media, LLC.