|
A Sub-200mV 6-Transistor SRAM for Ultra-Low-Power Data Storage
 A
deep-subthreshold 6-transistor-cell static random access memory (SRAM)
has been successfully developed for the first time. The 2k-bit test
chip was fabricated in an industrial 0.13µm CMOS technology and uses
a single-ended structure to ensure reliable read and write operation.
Measurements show that a typical die functions from 193mV to 1.2V. Adjustable
footers and headers with an on-chip bias generator are introduced to
allow extremely low-voltage operation. Assuming 2% bit redundancy, the
design can operate below 170mV. The minimum retention voltage is 134mV,
at which level the array consumes 26nW in standby power. Compared to
a previous mux-based subthreshold design, it provides an improvement
in energy efficiency of 1.6 times with similar speed and only half the
area.
Contact: D. Sylvester
Miniaturized On-Chip Antennas in Standard CMOS for Fully-Integrated
Single-Chip Transceivers
 Integration
of an antenna with the rest of a transceiver on a single IC is perhaps
the last barrier to achieving a totally integrated single-chip wireless
system. In the past, on-chip antennas fabricated in standard CMOS processes
have demonstrated very low efficiencies, primarily due to the close
proximity of the antenna to the lossy silicon substrate underneath it.
This loss significantly deteriorates the gain and radiation efficiency
of these antennas. In this work, both the efficiency and gain of an
on-chip antenna have been increased by order of magnitude through the
use of a slot-type antenna (as opposed to a dipole antenna) and the
effective shielding of the antenna from the lowresistivity silicon substrate.
A prototype on-chip slot antenna operating in the 9-10GHz frequency
band was demonstrated. The prototype antenna was implemented in a standard
0.13µm RF CMOS process. The antenna occupies a die area of only 0.3mm2,
has a measured active gain of -4.4dBi at 9.3GHz, and measured efficiency
of 9%. The antenna alone, without the integrated LNA, achieves a measured
gain of -10.0dBi.
Contact: K. Sarabandi
A Digital Frac-N Modulator With Improved Energy Efficiency and
Data Rate
 The
fractional-N frequency synthesizer is a key building block of wireless
systems since it can both generate a high-frequency signal with a well-defined
frequency and modulate that signal, allowing an entire wireless transmitter
to be implemented with only a fractional-N synthesizer and a power amplifier.
Two limitations of this architecture have been addressed here: the reliance
on complex analog circuitry in deep sub-micron technology, and the trade-off
between low loop bandwidth for good ΣΔ noise rejection and
high loop bandwidth for fast modulation rates. New techniques make design
more straightforward by eliminating analog circuitry and improve energy
efficiency by allowing signal processing to be done digitally in nanometer
CMOS technology. The new architecture uses a novel all-digital phase
detector in place of the conventional analogintensive phase detector,
charge pump and loop filter blocks. In addition, a digital dual-modulation
scheme is used to alleviate the tradeoff between loop bandwidth and
switching speed. A 14mW 2.2GHz MSK transmitter with a transmission rate
of 927.5kbit/s has been demonstrated. Energy efficiency is improved
by a factor of 3 compared to the state-of-the-art.
Contact: M. P. Flynn
A Wireless Micromachined Geiger Counter Utilizing Inherent Pulse
Discharges
 We
have developed a new wireless sensing scheme for discharge-based sensors
such as micromachined Geiger counters. The microGeiger device uses a
glass-Si-glass sandwich with a gas-discharge cavity and externally-located
permanent magnets. As beta particles pass through the glass window,
they ionize the gas atoms, resulting in a micro-discharge. This current
pulse results in a wide-band RF transmission at frequencies up to 2.8GHz,
within the FCC approved ultra-wideband (UWB) window of communication.
Networked radiation sensors are envisioned for monitoring public buildings
with high pedestrian traffic such as train stations, football stadiums
and shopping malls.
Contact: Y. Gianchandani
Chronic Wireless Recording with a 64-channel Integrated Cortical
Microsystem
 The
past year saw an important milestone reached with the realization of
wireless neural recordings from motor cortex for periods of more than
a month. The integrated microsystem consists of two 32-site high-density
silicon recording arrays driving four 16-channel amplifier chips over
integrated silicon and parylene ribbon cables. The amplifiers provide
a per-channel gain of 1000. The system operates in two modes. In Monitor
mode, the signal from a selected site is amplified and digitized at
8-bit resolution. The bits are assembled into data packets, Manchester
encoded, and transmitted wirelessly to an external user interface, where
the data are decoded, displayed, and written to file for further analysis.
In Scan mode (shown at right), the signals from all 64 channels are
amplified and scanned, and a neural processing chip detects neural spike
discharges above a threshold that can be programmed by the user over
a broad range (positive, negative, or biphasic). The site addresses
where spikes are detected are assembled in data packets, Manchester
encoded, and transmitted to the external world for additional processing
and display. The microsystem can be powered over an inductively-coupled
RF link, which is also used for bidirectional data transfer. For a 2MHz
clock, the channel scan rate for spike detection is 62.5kS/Sec and the
total system power dissipation at 1.8V is 14.4mW. The implantable version
of the microsystem weighs 275mg and measures 1.4cm x 1.55cm, fitting
in the space of a U.S. penny.
Contact: K. D. Wise
Complex Mixture Analysis with a Wireless Microsystem
 Determining
the composition of complex mixtures of gases and vapors in situ
is critically important to effective security screening, human and ecological
exposure assessments, industrial emission monitoring, and biomedical
surveillance and diagnosis. The WIMS micro-GC (µGC) is a low-power
integrated microsystem designed to meet the needs of all such applications.
Representing the culmination of several years of work, the µGC
combines the following components, all made using MEMS technologies:
a sample inlet with particulate filter, passive calibration-vapor source,
multi-stage preconcentrator/focuser (µPCF), dual-column separation
module with pressure- and temperature-programmed separation tuning,
an array of microsensors for analyte recognition and quantification,
and system pressure and temperature sensors. Flow is provided by a miniature
off-substrate pump. This year we have succeeded in integrating fluidic,
electronic, and rf-wireless subsystems in a hybrid prototype and to
perform rapid, high-quality analyses of multi-vapor mixtures. The prototype
system (upper right) was used to analyze a mixture of 19 indoor air
contaminants of anthropogenic and microbial origin in just under four
minutes (see single-detector chromatogram at lower right). Drawing on
the collective expertise of students and faculty from numerous disciplines
across several departments and universities, this effort epitomizes
the type of multi-disciplinary research made possible by ERC funding.
This integrated microsystem has garnered active interest from numerous
governmental and private-sector organizations seeking to license the
technology and/or engage in collaborative, application-specific development
projects.
Contact: E. T. Zellers
First Micro-Pump Driven Micro-GC Separations
 The
capability of gas chromatographic (GC) analyzers to separate and quantify
the components of complex vapor mixtures renders them invaluable tools
for chemical analysis. The WIMS µGC development program exemplifies
efforts by several groups around the world to realize a high-performance
gas analyzer small enough to fit in a shirt pocket or to be deployed
unobtrusively in the environment as part of a wireless sensing network.
Among several unique features of the WIMS µGC that sets it apart
from others is the incorporation of a MEMS vacuum pump to provide gas
transport through the microsystem. Since prior efforts to develop low-power
micropumps with a combination of high volumetric gas flow rate and high
differential pressure generation have been unsuccessful, gas analyzers
have had to rely on large off-chip pumps, which preclude full miniaturization
and limit field applications. Last year, we reported on the development
of such a micropump. This year, we have succeeded in integrating it
with a microcolumn and a microsensor array to achieve the first micropump-driven
multi-vapor chromatographic analyses ever reported. The separation and
detection of 11 volatile organic compounds with this all-MEMS microsystem
was achieved in <80sec while consuming just 15mW of power. With temperature
programming this analysis can be completed in 24sec with only a slight
loss in resolution.
Contact: E. T. Zellers
|
In
an effort to expand the options available for continuing and professional
education in WIMS, a 15-credit Certificate Program in integrated microsystems
was developed in 2006. This complements the 30-credit Master of Engineering
(M.Eng.) program that was established in 2002. Tailored for the industry
professional, these programs offer cross-disciplinary flexibility and
distance-learning options, with specializations ranging from ultra-low-power
integrated circuits and wireless interfaces to microfluidics. The courses
offer in-depth knowledge of integrated microsystems (including design/analysis
and applications), product development, and microfabrication. The interdisciplinary
programs also incorporate courses in business and management along with
training in technical communication. The Certificate of Advanced Studies
in Engineering (CASE) in Integrated Microsystems can be completed in
one year.
During
the past year, a company specializing in educational modules for use
by elementary, middle school and high school students has been spun
out from WIMS ERC activities. Nanobrick, LLC, launched by Michigan State
University Professor Dean Aslam, seeks to commercialize Technology-Assisted
Science, Engineering, and Math (TASEM) modules and toys. Included are
C-programmable robots that are the smartest such devices in their class,
RFID tags that can be used on toy robots and in table-top factories,
sensors and other devices that allow students to explore uses of static
charge, and blue-tooth-equipped robots also with GPS.
As
part of the College of Engineering’s 150th Anniversary campaign,
the University of Michigan is expanding and upgrading its micro/nanofabrication
facilities. The $48M project will add 5,000sq.ft. of cleanroom, upgrade
silicon processing to 6 inch wafers, improve all cleanroom safety systems,
and add new cleanroom space and equipment for nanotechnology and organic
devices. It will also consolidate all major micro- and nano-fabrication
capabilities in one facility. The privately-funded expansion will support
research and development in all aspects of micro- and nano-technologies
for the next two decades, and was launched by a $15M gift from the Robert
and Anne Laurie Foundation in 2002. A drawing of the exterior of the
facility is shown here. The new addition is key in improving the research
infrastructure for wireless integrated microsystems and is expected
to be operational by early 2008.