Semiconductor
Research Corporation (SRC), a university-research
consortium for semiconductors and related technologies, and Cornell
University researchers are working to advance on-chip silicon
development to enable new generations of smaller and more sophisticated
mobile electronic devices.
The
research—conducted via funding from SRC’s Global Research Collaboration
and Focus Center Research Program Center for Materials, Structures and
Devices—ntroduces a novel micromechanical resonator design that
simultaneously achieves low loss and high quality factor at RF
frequencies. The combination of the new resonators with surrounding
circuitry will one day allow the realization of on-chip channel-select
filters and oscillators, two system components that have traditionally
proven difficult to integrate on-chip.
The
design highlighted in this research is a single-crystal silicon
micromechanical resonator acoustically coupled to junction field effect
transistor (JFET) built on a SOI substrate. The high quality factor and
low loss can be attributed to the use of single-crystal silicon and an
efficient high frequency transduction technique, also developed at
Cornell, which circumvents the need for a separate transducer material.
This transduction method also results in significantly improved
temperature stability for silicon resonators, one of the main challenges
to using such devices as frequency references for communication
systems. The use of a JFET as the amplifying element will prove
beneficial for use in low phase noise oscillators due to its low flicker
noise.
While
Moore’s Law has enabled exponential increases in the number of
transistors and functionality on a single chip with every technology
generation, there are still a few critical functions that cannot be
realized by using transistors alone. Narrowband RF filtering and the
generation of stable clocks are important examples.
“Currently,
such functions are implemented using off-chip quartz or acoustic-wave
devices, and they limit the system size,” said Sunil Bhave, professor of
Electrical and Computer Engineering at Cornell, who led the research
team. “The most straightforward and feasible solution to this problem is
to implement these functions using integrated silicon devices, which
would allow us to make use of conventional semiconductor fabrication
methods to reduce the size with minimal tradeoff in performance.”
This
research builds upon previous developments in resonant transistors (at
Cornell, MIT, EPFL and CNRS) to demonstrate a transconductance-to-bias
current ratio—a meaningful efficiency metric – greater than 1 Volt-1,
which is important for low-power RF design.
“Companies
designing RF solutions in CMOS-related technologies could certainly
benefit from this research, but this work is ultimately about driving
the development of next-generation revolutionary mobile technologies
that significantly contribute to the day-to-day lives of consumers,”
said Kwok Ng, Senior Director of Device Sciences at SRC. “Successful
research in this area can also lead to the development of a RF frequency
source fully integrated into a foundry CMOS process along with other
surrounding circuitry.”
More
information about the research is published in the paper titled,
“Platform for JFET-based Sensing of RF MEMS Resonators in CMOS
Technology,” presented this week at IEEE’s 2011 International Electron
Devices Meeting in Washington D.C. The paper is co-authored by Eugene
Hwang, Andrew Driscoll and Sunil Bhave of Cornell.