IEEE Spectrum October, 2011 - 54

Evolution of a radar
Bosch's latest long-range system greatly simplifies the radar's printed circuit board. Instead of a handful of gallium arsenide chips to
generate, amplify, and detect the 77-gigahertz microwaves, the system uses just one or two (as shown) of Infineon's silicon germanium chips.

Second-generation
long-range radar

Third-generation
long-range radar

Radar dome

Printed circuit
board for
processing and
power supply

Body with
separate
connector

Body

Radar
printed
circuit board

Plastic backplane
with connector

Infineon's prototype could operate up
to only about 80 GHz, good enough for
use in an oscillator but not in the amplifier. That's because for a transistor to
deliver reasonable gain at a given frequency, it needs to top out at about three
times that value. In 2007, by improving the quality of the boron-doped silicon germanium in the base, Infi neon's
engineers increased the transistor's
maximum operating frequency to the
requisite level and soon went on to produce the first commercial silicon germanium automotive radar chips, which ran
at 77 GHz. Four years later, Infineon continues to churn out the chips at its huge
fab in Regensburg, Germany.
Inserting the silicon germanium layer
into the device requires no exotic techniques or extraordinary tools: Infi neon
simply uses 200- millimeter silicon
wafers and grows thin silicon fi lms on
top using conventional chemical-vapor
54

NA * Ieee Spectrum * october 2011

deposition. At the appropriate point
during the process, a valve opens,
germanium-based gases flow into the
growth chamber, and a silicon germanium film forms.
One such wafer can yield thousands of
chips. "This gives us enough headroom
to produce as many automotive radar
systems as we would like," explains
Lachner. In fact, most of the fab's output
of 10 000 wafers goes to other purposes.
If Infineon somehow captured the entire
automotive market overnight, it could
easily satisfy the demand.
So why do other companies, such
a s T r i Q u i n t S e m i c o n d u c t o r, i n
Hillsboro, Ore., and United Monolithic
Semiconductors, in Orsay, France, still
produce automotive radar chips based
on pricey gallium arsenide? For one
thing, gallium arsenide is still the biggest
player in the radar market at the moment,
and these firms can sell a lot of chips, at

Printed circuit
board for
processing and
power supply
Die-cast
backplane

least for a few years. Also, these companies don't necessarily have silicon production lines to switch to, nor would it
make sense to build a full-blown silicon
fab for car radar alone.

Cost isn't the only thing driving
change. It's not only cheaper to use
one Infineon chip (or two, in the fancier system); it's also more effective
than the handful of gallium arsenide
chips it replaces. When Bosch upgraded
Infineon's product during the development of its third-generation long-range
radar (dubbed, unimaginatively, the
LRR3), both the minimum and maximum
ranges of its system got better: The minimum range dropped from 2 meters to half
SPECTRUM.IEEE.ORG

BOSCH (2)

Radar printed circuit board

http://SPECTRUM.IEEE.ORG

Table of Contents for the Digital Edition of IEEE Spectrum October, 2011