Designed for use in an implantable eye-pressure monitor, Univ. of Michigan researchers developed what is believed to be the first complete millimeter-scale computing system. Credit: Greg Chen |
A prototype implantable eye pressure monitor for glaucoma
patients is believed to contain the first complete millimeter-scale computing
system.
And a compact radio that needs no tuning to find the right frequency
could be a key enabler to organizing millimeter-scale systems into wireless
sensor networks. These networks could one day track pollution, monitor
structural integrity, perform surveillance, or make virtually any object smart
and trackable.
Both developments at the Univ. of Michigan
are significant milestones in the march toward millimeter-scale computing,
believed to be the next electronics frontier.
The work is being led by three faculty members in the U-M
Department of Electrical Engineering and Computer Science: professors Dennis
Sylvester and David Blaauw, and assistant professor David Wentzloff.
Bell’s Law and the promise of pervasive computing
Nearly invisible millimeter-scale systems could enable ubiquitous computing,
and the researchers say that’s the future of the industry. They point to Bell’s
Law, a corollary to Moore’s
Law.
Bell’s Law says there’s a new class of smaller, cheaper
computers about every decade. With each new class, the volume shrinks by two
orders of magnitude and the number of systems per person increases. The law has
held from 1960s’ mainframes through the ’80s’ personal computers, the ’90s’
notebooks and the new millennium’s smart phones.
“When you get smaller than hand-held devices, you turn
to these monitoring devices,” Blaauw said. “The next big challenge is
to achieve millimeter-scale systems, which have a host of new applications for
monitoring our bodies, our environment and our buildings. Because they’re so
small, you could manufacture hundreds of thousands on one wafer. There could be
10s to 100s of them per person and it’s this per capita increase that fuels the
semiconductor industry’s growth.”
The first complete millimeter-scale system
Blaauw and Sylvester’s new system is targeted toward medical applications. The
work they present at ISSCC focuses on a pressure monitor designed to be
implanted in the eye to conveniently and continuously track the progress of
glaucoma, a potentially blinding disease.
In a package that’s just over 1 cubic mm, the system fits an
ultra low-power microprocessor, a pressure sensor, memory, a thin-film battery,
a solar cell and a wireless radio with an antenna that can transmit data to an
external reader device that would be held near the eye.
“This is the first true millimeter-scale complete computing
system,” Sylvester said.
“Our work is unique in the sense that we’re thinking
about complete systems in which all the components are low-power and fit on the
chip. We can collect data, store it and transmit it. The applications for
systems of this size are endless.”
The processor in the eye pressure monitor is the third
generation of the researchers’ Phoenix
chip, which uses a unique power gating architecture and an extreme sleep mode
to achieve ultra-low power consumption. The newest system wakes every 15
minutes to take measurements and consumes an average of 5.3 nanowatts. To keep
the battery charged, it requires exposure to 10 hours of indoor light each day
or 1.5 hours of sunlight. It can store up to a week’s worth of information.
While this system is miniscule and complete, its radio
doesn’t equip it to talk to other devices like it. That’s an important feature
for any system targeted toward wireless sensor networks.
A unique compact radio to enable wireless sensor networks
Wentzloff and doctoral student Kuo-Ken Huang have taken a step toward enabling
such node-to-node communication. They’ve developed a consolidated radio with an
on-chip antenna that doesn’t need the bulky external crystal that engineers
rely on today when two isolated devices need to talk to each other. The crystal
reference keeps time and selects a radio frequency band. Integrating the
antenna and eliminating this crystal significantly shrinks the radio system.
Wentzloff’s is less than 1 cubic mm in size.
He and Huang’s key innovation is to engineer the new antenna
to keep time on its own and serve as its own reference. By integrating the
antenna through an advanced CMOS process, they can precisely control its shape
and size and therefore how it oscillates in response to electrical signals.
“Antennas have a natural resonant frequency for
electrical signals that is defined by their geometry, much like a pure audio
tone on a tuning fork,” Wentzloff said. “By designing a circuit to
monitor the signal on the antenna and measure how close it is to the antenna’s
natural resonance, we can lock the transmitted signal to the antenna’s resonant
frequency.”
“This is the first integrated antenna that also serves
as its own reference. The radio on our chip doesn’t need external tuning. Once
you deploy a network of these, they’ll automatically align at the same
frequency.”
The researchers are now working on lowering the radio’s power
consumption so that it’s compatible with millimeter-scale batteries.