research activities in 2007 - CSEM

MICROELECTRONICS
Christian Enz
The research activities conducted in the field of Integrated
Systems for Information Technology (ISIT) are focused on the
design of highly integrated systems targeting low-power and
low-voltage applications. The latter systems typically include
complex microelectronics Systems-on-Chip (SoCs),
embedding many functionalities on a single chip, together with
other heterogeneous devices such as RF passives,
resonators and filters, silicon time basis and sensors into
advanced Systems-in-Package (SiPs). The research is
organized around four different generic technology platforms:
• Digital SoC platform
• Sensory Information Processing platform
• Integrated RF Circuits and Systems platform
• RF and Piezoelectric Components platform.
The achievements made during 2007 in these different
platforms are discussed in more detail below.
The Digital SoC platform aims at developing all the key digital
components required in a SoC, including low-leakage
memories and highly energy-efficient processors. The latter
include the Macgic, a 4 MAC digital signal processor (DSP)
developed for intensive digital signal processing and the
icyflex, a 32-bit microcontroller core with additional DSP
capabilities, for simple signal processing. These processors
have now reached a certain degree of maturity and have
started to be integrated in several industrial SoCs. As an
example, four Macgic DSPs have successfully been used in a
programmable multi-processor engine for an ultra low-power
mobile digital TV. The icyflex has now become the heart of all
CSEM SoCs replacing the long-time used 8-bits CoolRISC
microcontroller. It is also used in the new generation of digital
vision sensors SoC called icycam.
The Sensory Information Processing platform implements
powerful vision systems that are able to extract essential
image features in real-time and at low-power. These features
include the three most important information categories that
are used by the basic operation of the human vision, namely,
the contrast (intensity variation), the direction of contrast
(feature orientation) and the motion (spatio-temporal contrast
variation). The new vision sensor platform has been migrated
from the former 0.5 µm CMOS process towards a 0.18 µm
process. In the former version, the contrast extraction and
calculation was fully done in the analog domain, making it
difficult to migrate. In order to take full advantage of
technology scaling, the core of the vision sensor architecture
has been profoundly modified and is now essentially digital.
This also allows taking advantage of the icyflex processor in
the newly designed icycam vision sensor SoC. The ability of
vision sensors to process the image feature locally enables it
to be used together with other vision sensors connected
together with a rather low data rate wireless channel. Such a
network allows performing data fusion of signals provided by
several vision sensors and 3D cameras in order to track
persons in buildings. Another SoC including the icyflex is used
for nanometric absolute position encoding. Such miniaturized
optical encoders have a great potential for applications in
robotics, automation and machine tools.
The Integrated RF Circuits and Systems platform mainly
targets ultra low-power short-range and low data rate
applications. A new development platform has been
engineered for the design of narrow-band RF transceivers
operating in the 868 MHz and 915 MHz ISM bands. It includes
an integrated front-end IC with a low-IF super-heterodyne
receiver architecture and a newly designed direct modulation
RF transmitter. The on-chip analog baseband uses a phaseto-digital
converter and is followed by a digital baseband
implemented in a FPGA in order to keep a maximum of
flexibility. This platform allows experimenting on different
modulation schemes. The efficient combination of MEMS such
as BAW resonators and ICs has always been a strong
research topic in the field of ultra low-power radio design.
After having realized a BAW RF front-end, the BAW is also
used in the frequency synthesizer. A new architecture is
proposed to take advantage of the low-phase noise but
circumvent the limited frequency tuning range of the BAW
VCO. It uses a quasi-harmonic relaxation oscillator featuring a
large tuning range compensating the limited one of the RF
VCO. This architecture is similar to the one used in the radio
that will be used within the PackTime MIP.
The new radio and synthesizer architectures mentioned above
rely heavily on the BAW and silicon resonators developed in
the RF and Piezoelectric Components platform. These
devices take advantage of the AℓN thin film piezo-electric
technology available at CSEM. Silicon MEMS resonators can
potentially achieve similar performance to crystal quartz with a
smaller size. However, they suffer from the high temperature
coefficient of silicon and imperatively have to be compensated
in temperature. This can be done electronically by using an
on-chip temperature sensor or by depositing an additional
layer of proper thickness made of SiO2 having a positive
temperature coefficient. Two families of Si-resonators have
been developed: temperature compensated 20 to 140 KHz
flexural resonators and high-Q 1 MHz extensional resonators.
These MEMS are activated thanks to an AℓN piezoelectric
layer, making them compatible with the voltages used in
SoCs.
The four technology platforms are evolving towards ever more
complex systems combining the different technologies. In this
sense there is clearly a convergence of the overall research
activity in this field. This concentration should help to solve the
important challenges that lie ahead. Among those we can
mention the migration towards ultra deep sub-micron CMOS
process, with its inherent leakage and parameter variability
issues. Also, the packaging remains the main issue for
combining MEMS and SoC together for new low-power and
ultra miniaturized systems. It is the believe of CSEM that the
Integrated Systems for Information Technology platform is
well armed to face and solve these important challenges!
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