SiGe HBT Technology
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I. BANDGAP ENGINEERING IN SILICON
WE LIVE in a silicon world. Greater than 95% of
today’s $200 billion global semiconductor market
uses the semiconductor silicon (Si) to realize a host of integrated
circuits (IC’s) ranging from 233-MHz microprocessors
to 64-Mb dynamic random-access memory (DRAM) chips.
Indeed, it is the very existence of Si microelectronics which
has enabled the emergence of the Information Age which
is so profoundly reshaping the way we live and work and
play. Why Si? This profound market dominance of Si rests
on a number of surprisingly practical advantages Si has
over the other numerous semiconductors, including


II. SiGe HBT TECHNOLOGY
In order to provide a logical framework for this paper, the
experimental results presented will be largely from IBM’s
SiGe HBT technology [25]. This technology is representative
of the state-of-the-art in 1998, is currently qualified and in
commercial production on 200-mm wafers in an advanced
CMOS fabrication facility, and is thus arguably the most
“real” SiGe HBT technology worldwide. The basic tenets
which dictate the final implementation of IBM’s SiGe HBT
technology are: 1) maintain strict processing compatibility
with existing CMOS tool sets and metallization schemes;
2) use only thermodynamically stable SiGe films that can
be deposited using a batch process in manufacturing mode
on large (200-mm) wafers; 3) choose an SiGe HBT device
structure which naturally preserves a path to SiGe BiCMOS
integration without compromising the SiGe HBT performance;

III. THE SiGe HBT
This section gives an overview of the performance
capabilities of state-of-the-art SiGe HBT’s. Basic device
physics, dc and ac performance advantages over Si BJT’s,
low-frequency and broad-band noise characteristics, radiation
tolerance, temperature effects, and reliability issues are
addressed. For brevity, only the final results of the basic
device physics derivations are included. The interested reader
is referred to [58] for more complete derivations.

A. DC Characteristics
The dc consequences of introducing Ge into the base region
of an SiGe HBT can best be understood by considering an
energy-band diagram of the resultant device and comparing
it to Si. As shown in Fig. 5 by the dashed line, the Ge is
compositionally graded from low concentration at the EB
junction to high concentration at the collector–base (CB)
junction.