INTEGRATED MISSION SOLUTIONS DD(X ... - Raytheon

take to transit the channel region must be
limited sharply. This leads to the conclusion
that short channel gates are required for
microwave and millimeter wave devices.
Gate lengths on the order of 0.5 microns
are used for devices at X-band, and gate
lengths of as little as 80 nanometers are
used for millimeter-wave devices useful at
W-band. Scanning electron microscope
photos of microwave gate sections are
shown in Figures 2a and b. Figure 2a shows
a typical tee-gate structure. Figure 2b
shows a close up of the channel structure
and the bottom of the tee-gate. The necessity
to fabricate features on this scale places
severe stress on the equipment that must
be used to fabricate such devices. Present
processing equipment relies heavily on
e-beam lithography in order to provide
quarter-micron and shorter gate structures.
300 nm
Figure 2a. Tee-gate pHEMT Section
Figure 2b. Tee-gate pHEMT Close-up TEM
Microwave and millimeter-wave chip
technology is very definitely a niche market.
Large-scale semiconductor fabrication facilities
to make advanced CMOS devices typi-
Figure 3. Roadmap of Process Development at RRFC
cally cost in the region of five billion to
build and bring on-line. This is obviously
not an investment that a company like
Raytheon would make just to support the
relatively modest quantities involved in
government phased array systems.
Therefore, companies like Raytheon walk a
fine line between being able to provide
state of the art capability while trying to
keep costs in line with making affordable
T/R modules.
Equipment such as the e-beam lithography
tool is very expensive to procure as well as
expensive to operate and maintain. This,
however, is almost an entry-level for making
state of the art millimeter and
microwave devices at the present time.
Raytheon RF Components (RRFC), part
of the Integrated Defense Systems (IDS)
business, is presently the Raytheon facility
for providing state-of-the-art microwave
and millimeter-wave components for use in
Raytheon systems. This facility, located in
Andover, Massachusetts is capable of producing
as many as 7,500 four-inch gallium
arsenide wafers annually. At full capacity,
this facility is capable of providing T/R
module chip sets to programs for approximately
$100 per channel, depending on
functionality quantities, and particular specifications.
At this price point, the T/R module
GaAs MMICs are considered relatively
affordable in view of the functionality they
provide to the system.
Due to the nature of Raytheon's primary
defense business, a facility such as RRFC
must continually be reinventing its technology
to remain state-of-the-art and stay
ahead of the competition. Program wins are
heavily dependent on the ability to provide
advanced capabilities in the semiconductor
electronics going into phased arrays. When
Raytheon won the GBR program in 1991,
gallium arsenide metal semiconductor field
effect transistor (MESFET) devices were considered
the current state of the art. During
that time, Raytheon was developing PHEMT
technology. The use of PHEMT technology
allowed Raytheon to offer the Army customer
substantial improvement in system
sensitivity at no increase in cost. Figure 3
shows a roadmap of the technologies that
have been developed and that are under
development at RRFC.
summer 2003 17