InP electronics industry
rhombus4
program - building an amplifier that on to the chip, or off of it, then it can improvements in contact resistances
produced a couple of milliWatts at consult with Gabriel Rebeiz from the that are commensurate with
340 GHz. In addition, it has been a University of California, San Diego. reductions in area. Realizing this gets
key participant in the Technology for The Jet Propulsion Laboratory is tougher and tougher as the devices
Frequency Agile Digitally Synthesized another important team member in get smaller, because the periphery
Transmitters (TFAST) program, which Teledyne’s effort, and its role is to dimensions increase relative to those
has helped it to hone its expertise in measure the device and circuit of the bulk as the transistor is scaled.
high-frequency electronics. The performance. Brar says that the team “If you have good junctions that are
TFAST project demanded the at the Jet Propulsion Laboratory is a well-passivated at 0.5 µm emitter
development of transistors with cut- world leader for this type of dimensions, at 125 nm the problem
off frequencies of up to 500 GHz, measurement, which is essential for becomes at least four times worse,”
and fabrication of complex circuits meeting the program goals. The final says Brar. “The area has shrunk, but
based on these devices. 100 member of the team is Raytheon. Its the perimeter-to-area ratio has
transistors are needed in very fast expertise lies with systems, rather increased.”
dividers, and 5000 are used to make than components, and it is well
digital synthesizers. “They had yield positioned to advise on how to apply Another challenge facing the
goals as well,” explains Bobby Brar, the technology. engineers involved in the terahertz
executive director of the electronics electronics program relates to circuit
division at Teledyne. “End-of-program To increase the operating frequencies design. Care is needed to avoid
goals were 50-60 percent yield.” of its HBTs, Teledyne is shrinking issues cropping up at higher
device dimensions. “Making smaller frequencies that have no impact at
Teledyne produced these circuits dimensions is a piece of cake these tens of gigahertz. “Having done the
with InP HBTs, a technology that it days,” claims Brar. “But you have got work at 340 GHz, we are confident
will use throughout the terahertz to make sure that you scale your that we can handle those kinds of
electronics program. According to transistors in such a way that you get problems,” says Brar. Potential
Brar, one of the advantages of using good contact resistances, low pitfalls include losses in the
the HBT, rather than the HEMT, is parasitic capacitances, and low semiconductors, and issues that
that it can be used to build all the leakage currents.” Teledyne is able to arise because the dimensions of the
circuits needed by the program. “If draw on the work of others regarding substrate are comparable to the
successful, we would have one approaches to scale InP bipolar wavelength of the radiation. The latter
circuit that would be monolithic. And transistors. “Mark Rodwell has can lead to the excitation of modes DARPA has set
that’s a big deal, because getting on essentially published a roadmap for that hamper coupling of radiation go, no go
and off a chip at those kinds of scaling InP bipolar, so we know what between the chip and the outside (GNG) targets
frequencies is non-trivial.” Another the challenges are,” says Brar. environment. for each of the
advantage of the HBT is that it can three phases of
be manufactured with much tighter Reducing parasitic resistances is one Teledyne is still to publish its best its terahertz
threshold voltages than a HEMT, of the bigger challenges. Preventing results, but Brar says that they are electronics
which simplifies the design of digital any increase in overall resistance “pretty close” to the goals at 670 program
blocks, dividers and mixers. In during the scaling process requires GHz. He believes that it will not be
addition, the problems associated
with parasitics are less of a challenge
when scaling HBTs.
Teledyne’s partners
Teledyne carries out everything from
the fabrication of devices to chip
packaging, and many of its partners
in the terahertz electronics project
are there to provide guidance when
needed. If the company runs into
problems related to transistors or
circuits, then it can turn to Mark
Rosker at the University of California,
Santa Barbara. And if it is
experiencing difficulties related to the
coupling of electromagnetic radiation
October 2009 www.compoundsemiconductor.net 35
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