[Discuss-gnuradio] Radio-Ready Chips (Intel)

[flexradio]

/* N.B.: I tried to d/l this pdf and got 'internal' acrobat errors
   displaying them (in case anyone from Intel is listening).
  <ftp://download.intel.com/labs/eml/download/EML_mems.pdf>   */

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<http://www.techreview.com/articles/innovation10602.asp>

Radio-Ready Chips

Innovation  By Wade Roush   June 2002

All-silicon radios could make everything wireless.

Intel makes microchips, not radios. But if the company's newest
manufacturing plans pan out, the distinction between the two products may
disappear. According to chief technology officer Patrick Gelsinger, Intel
is quickly learning how to build tiny radio transceivers from the same
material it uses in microchips: silicon. Research progress inspired
Gelsinger to announce in February an audacious plan to put a silicon-based
radio on the corner of every microchip the company sells, within as little
as five years, at no extra cost to customers.

The announcement puts Intel at the forefront of industry efforts to build
all-in-one chips that could replace the jumble of costly parts in cell
phones and other wireless gadgets. Silicon integrated circuits already
dominate when it comes to the digital "back end" of cell phones and other
wireless communications devices, where signals are decoded for conversion
into sound. But the analog "front-end" components, which capture and
amplify radio signals and convert them to digital bits, are typically found
on a separate, radio frequency section of the wireless circuit board. This
section houses both large, three-dimensional parts such as capacitors and
oscillators and transistorized components like amplifiers, which run at
such high speeds that they have traditionally been made only using faster,
more expensive "compound semiconductors" like gallium arsenide.

But Intel and other chip makers would prefer to stick all these functions
onto a single silicon chip, which could be patterned using well-established
photolithographic techniques and would cost about one-tenth as much as
chips using compound semiconductors. For engineers and computer scientists
looking to a future where computing power is ubiquitous and wireless, the
potential cost and space savings of putting all of a radio's parts onto the
same chip that holds the computing components has a powerful appeal. "We
can safely say that any intelligent device needs both a processor and some
form of wireless connectivity," says Turner Whitted, manager of the
Hardware Devices Research group at Microsoft Research in Redmond, WA. "It
makes sense to combine these functions to the greatest extent possible."

There are still big technical barriers to mass-producing silicon radios,
such as reducing three-dimensional parts to the micrometer scale with the
needed precision and uniformity. But Gelsinger made his announcement on the
strength of recent work in the labs of Steve Pawlowski, director of Intel
Labs' Communications and Interconnect Technology Group in Portland, OR, and
Valluri Rao, who heads the company's Analytical and Microsystems
Technologies division. Rao's staff is using silicon to build tiny
structures that duplicate the functions of traditional capacitors,
oscillators and other components. Pawlowski and his colleagues, meanwhile,
are testing silicon circuitry that performs the amplifying, mixing and
filtering functions typically handled by separate, more expensive front-end
chips. By working out these core technologies, "We're going to be able to
dramatically reduce the size and cost of the components required in radio
circuits," Gelsinger says.

This is an ambitious agenda, considering that many of these components only
work because of their macroscopic size and their three-dimensionality.
Oscillators, which help to tune in and amplify radio signals, are one
example. These crucial components are often made from quartz crystals that
resonate electrically when a voltage is applied, with a resonant frequency
partly determined by their dimensions-typically up to a centimeter square.
Variable capacitors, used to filter out all frequencies except that of the
signal, are another example; they usually consist of interleaved metal
plates that hold a varying charge depending on the amount of space between
them. Putting space between the plates requires depth, but a typical
integrated circuit consists only of thin layers of semiconducting silicon
and conducting substrates.

That's why Rao and his fellow researchers have started thinking out of the
plane, turning to microelectromechanical (MEMS) manufacturing techniques
developed over the last decade in numerous labs at universities and startup
firms. These labs have created a wide assortment of tiny structures like
beams, bridges and springs from strips of silicon only a micrometer wide.
But no one has yet fashioned such structures into a fully functional radio,
or built them on a piece of silicon that contains all of the
signal-processing circuitry needed to handle today's digital cell phone
transmissions.

Rao and his group believe this can be done without any revolutionary
changes in manufacturing techniques. "You can actually build a mechanical
device like a variable capacitor using the lithography we have available,"
he says. Conventional lithography uses light to carve tiny features on
silicon chips; MEMS builders go a step further, excavating around these
features to make such suspended three-dimensional structures as
cantilevers.

Rao's group is using these lithography-based MEMS techniques to build
prototype silicon capacitors in which the upper plates are suspended by
tiny silicon springs. Applying a voltage makes the plates move up or down,
changing the capacitance. It turns out that such structures leak far less
charge to surrounding materials than conventional capacitors, Rao says. His
researchers are also experimenting with oscillators made from free-hanging
cantilevers. "Imagine a tuning fork with one prong, but so small that its
resonant frequency is measured in gigahertz," Rao explains. "That lets you
start doing things at radio frequencies."

While researchers at Intel and elsewhere have managed to build small
clusters of tiny capacitors and resonators, building hundreds or thousands
of identical MEMS structures using lithography is still a problem. "We're
looking at our lithographic process from the point of view of getting very
uniform behavior over a wafer, so that we can build these things at high
volume," Rao says.

Pawlowski's group, meanwhile, is demonstrating digital circuitry on silicon
for components such as mixers and analog-to-digital converters, achieving
what he calls "pretty good signal gain" even at the high frequencies
usually handled by gallium arsenide chips. And while they're at it,
researchers in his group are designing signal-processing circuitry with the
brains to switch between competing wireless-communications protocols. "If
somebody is in a Starbucks and they have a connection on their laptop to a
wireless local-area network, and they walk out, they need a second radio to
keep the connection open," notes Pawlowski. "The promise of this
architecture is that it could run multiple protocols without having to have
multiple, separate radios."

Laptops, cell phones and other devices that let you roam seamlessly between
wireless networks are only one of the industry niches where silicon radios
could eventually dominate. Armies of small, low-power, constantly connected
devices could eventually infiltrate the appliances and structures all
around us. "For example, tiny sensors that communicate through different
methods could go inside every window and every ventilation duct to monitor
environmental conditions and improve energy efficiency," says computer
scientist Gaetano Borriello, who leads an Intel-sponsored
ubiquitous-computing laboratory at the University of Washington in Seattle.
"Eventually, they could even go inside of people. What we're doing is
expanding the range of possibilities."

Wade Roush is a Senior Editor at Technology Review.