Radio Frequency Integrated Circuit Design - Webs

5
The Use and Design of Passive Circuit
Elements in IC Technologies
5.1 Introduction
In this chapter, passive circuit elements will be discussed. First, metallization
and back-end processing (away from the silicon) in integrated circuits will be
described. This is the starting point for many of the passive components. Then
design, modeling, and use of passive components will be discussed. These
components are interconnect lines, inductors, capacitors, transmission lines, and
transformers. Finally, there will be a discussion of the impact of packaging.
Passive circuit elements such as inductors and capacitors are necessary
components in RF circuits, but these components often limit performance, so
it is worthwhile to study their design and use. For example, inductors have
many applications in RF circuits, as summarized in Table 5.1. An important
property of the inductor is that it can simultaneously provide low impedance
to dc while providing finite ac impedance. In matching circuits or tuned loads,
this allows active circuits to be biased at the supply voltage for maximum
linearity. However, inductors are lossy, resulting in increased noise when used
in an LNA or oscillator. When used in a power amplifier, losses in inductors
can result in decreased efficiency. Also, substrate coupling is a serious concern
because of the typically large physical dimensions of the inductor.
5.2 The Technology Back End and Metallization in IC
Technologies
After all the front-end processing is complete, the active devices are connected
using metal (the back end), which is deposited above the transistors as shown
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