Si CMOS technologies have become the de facto choice for digital
and low-frequency analog circuit manufacturing. However, the requirements for RF
circuits include more than just high-speed devices. A technology suitable for RFICs
must also offer low noise transistors capable of gain, high linearity, and output power;
high-quality RF passives (inductors and capacitors); and accurate device models.
Until recently, these demands received little attention in the development of advanced
CMOS technologies. Motivated by the emerging wireless market though, the 2003
ITRS updated its list of economic drivers for technological development and now
include these new market forces. System drivers for technology advancement are
presently divided into four main categories: microprocessors, embedded memory,
SoC, and RF and analog/mixed-signal (AMS). The last two drivers are directly
targeted by this work.
Established silicon fabrication facilities can produce integrated circuits at relatively
low costs in massive quan ities. From an economic standpoint, extending a siliconbased
process to facilitate high frequency circuits is very attractive. Furthermore,
directly integrating high frequency analog circuits alongside high-speed digital components
offers exciting possibilities, as discussed in Section 1.1. Therefore, methods
to extend the capabilities of Si to the high frequency regime, in direct competition
with III-V materials, have been sought.
Figure 1.3 shows the RF/microwave/millimeter-wave frequency spectrum divided by
application with an approximate breakdown of the relevant semiconductor technologies.
Recent advances in CMOS technology, specifically so-called ?RF CMOS,? have
pushed the applicable region of Si of Figure 1.3 further to the right. Today, Si CMOS
technology dominates at frequencies below 10 GHz and active research is focused on
circuit applications in the 28 and 60GHz bands; similarly, advances in SiGe have
pushed its application to frequencies further to the right, encroaching on the range
once dominated solely by III-V technologies such as GaAs.