1. Statement of the Technical Field
The invention is directed to integrated circuit (IC) devices, and more particularly IC devices including inductor structures formed therein.
2. Description of the Related Art
Reactive components, such as capacitors and inductor, are important components for implementing various types of signal processing devices, including low-noise amplifiers (LNAs), voltage controlled oscillators (VCOs), filters, and impedance matching networks, to name a few. As a result, a significant number of components are typically needed to implement such devices. However, the number of components for such devices can be reduced by using an IC including inductors and capacitors formed therein. As a result, signal processing devices can be formed in a compact package, reducing overall device size.
The performance of inductors, including inductors formed within an IC (monolithic inductor), is typically evaluated based on the quality (Q) factor. An ideal inductor will generally be lossless irrespective of the amount of current through the winding. However, inductors, including monolithic inductors, typically have winding resistance from the electrically conductive materials used for forming the coils. Since the winding resistance appears as a resistance in series with the inductor, it is often called the series resistance. The inductor's series resistance converts electrical current through the coils into heat, thus causing a loss of inductive quality. The Q factor measures this loss (i.e., the inductor's efficiency), as Q factor for an inductor is the ratio of its inductive reactance to its resistance at a given frequency. In general, the higher the Q factor of the inductor, the closer it approaches the behavior of an ideal, lossless, inductor. In general, the Q factor of an inductor can be computed from Q=(ωL)/R, where R is its internal electrical resistance of the inductor and ωL is capacitive or inductive reactance at resonance.
In the case of monolithic inductors, the Q factor is primarily limited by conductor losses arising from conductor resistances, the conductive silicon substrate, and parasitic substrate capacitances (which lower the inductor self-resonant frequency). Additionally, time-varying magnetic fields can penetrate the silicon substrate and cause eddy currents as per Lenz's law, thus resulting in power loss. Furthermore, eddy currents create their own magnetic fields that oppose those of the monolithic inductor and effectively decrease the inductance of the inductor.