Microelectronics/MEMS
Research
Sensors and actuators constitute the front-end devices of intelligent
systems for information acquisition and action, namely, to perform the
transduction function. Advances in Microsystems Technology (or
MEMS: MicroElectroMechanical Systems) have brought about further integration
of machine intelligence into microsensors and microactuators. Signals
from the natural world are intrinsically analog and so are the signals
for controlling actuators. In between the microsensors and microactuators
is a whole range of microelectronic circuitry for signal conditioning
and processing, in both analog and digital form. Accelerometers, inkjet
print heads, projection displays, read/write data storage heads, biosensor
chips, optical switches are just some of the many new products, based
on this technology, that have come onto the market in recent years.
Market projection for MEMS products is about US$40B by 2002.
Academic staff in the Microelectronics discipline have focused their
research on three major areas: MEMS devices, Quantum computing,
Analog integrated circuit design and microwave circuits, Very Large
Scale Integration (VLSI) devices, Ferrielectrics . The academics
are Assoc. Prof. C Y Kwok, Dr. S Nooshabadi, Dr. A Dzurak and Dr. R
Ramer, Prof. G A Rigby.
Research Activities
The Microelectronics Group is active in research activities in the areas of Micro Electro Mechanical Systems (MEMS), Quantum Computing, Analog IC Design, Very Large Scale Integration (VLSI) devices and Ferrielectrics.The main projects of the group are:
Analog applications
of multi-input floating-gate CMOS (neu-MOS) circuits
(Kwok, Michael, Huang, Wong, Rigby)
Floating-gate technology has been employed in non-volatile memory (EEPROM)
devices for many years. The storage of charge in the floating
is used to distinguish between a logic 1 and logic 0. We have
exploited the floating-gate CMOS devices for its analog applications
by making use of a very important property of the floating-gate potential.
A floating-gate MOS transistor may have several inputs, each of which
is capacitively coupled to the floating-gate. The potential at
the floating-gate is determined by the weighted sum of the input signals
where the weights are derived from the capacitances associated with
the floating-gate. This allows some degree of ?computation? to
be done at the floating-gate level. Over the years we have
successfully design and fabricated at MOSIS four quadrant analog
square-law multiplier and pseudologarithmic rectifier using floating-gate
CMOS. We were the first to report on a 1 volt 8 bit D-A
converter which uniquely makes use of the two input floating-gate MOS
transistor as a combined switch and current mirror. The figure
below is a photomicrograph of the chip. Further research
is in progress in the development of 8 bit resolution analog memory
cell and eventually an analog memory array.
Differential
opto-mechanical microaccelerometer
(Choawicharat, Kwok, Rigby)
Acceleration is measured by the force exerted on the proof mass (seismic
mass). Micro accelerometers find wide applications in automotive
and motion control areas. In this ARC funded microaccelerometer
design, the seismic mass consist of an optical grid suspended by four
folded tethers over a photodiode area under a LED light source.
The force of acceleration causes the seismic mass to move and modulates
the amount of incident light on to the photodiode to produce a differential
photocurrent. Silicon surface micromachining is the key technology employed
in the fabrication of the photodiode and seismic mass structure and
is conducted in the SNF. The seismic mass is designed with electrostatic
comb drive actuators to facilitate self-test and force balanced feedback
control. An ASIC chip is designed to close the feedback loop. The microaccelerometer
is designed for 10mg -50g operation.
Integrated
electromagnetic micropump
(Rojapornpun, Kwok, Rahman)
Precision drug delivery systems require very low flow rates.
The project involves the design and fabrication of an integrated electromagnetic
reciprocating micropump operating at relatively low voltage of about
1-2 volts and flow rate range of 0.1 - 3 ul/min. The actuation
mechanism is electromagnetic. There are three parts to the pump which
is individually silicon micromachined. The parts are as follows:
body housing for surface micromachined multi-layered Cu coil, body for
diaphragm and integrated permanent magnet, body for surface micromachined
passive valves and inlet/outlet connections. Key technologies
for the fabrication of the electromagnetic micropump are silicon bulk
and surface micromaching, electro-deposition and magnetic material deposition.
Microelectrodes
for intra-ocular implant
(Wibowo, Kwok, Lovell)
The work is part of a larger project in the development of intra-ocular
implant for the profoundly blind. It is done in collaboration
the Dr. Lovell of the Graduate School of Biomedical Engineering who
will be developing the electronics, RF signal transfer, and encapsulation
issues. Blind patients suffering from retinitis pigmentosa fortunately
continue to have functional ganglion cells in the retina. Conceptually,
the system is designed for delivery of images to the neural tissue of
the retina and utilising the well defined topographic mapping of visual
space in the retina. Our part of the work, which is funded by
a small ARC grant, involves the development of a special array of electrodes
that can conform to the near semi-hemispherical shape of the retina
without developing excessive pressure on the retina. The idea
being to bring the stimulation electrodes in closest proximity to the
retina. The electrode arrays are fabricated by surface micromachining
for mounting onto a specially designed ceramic body. Development
of technology for the shaping the electrodes is in progress.
MEMs based
optical waveguide switch array
(Mackenzie, Kwok)
Free space optical switches are proving to be a viable option for reconfigurable
optical network. This work involves the development of switching
micro-mirror arrays for optical switching with provision for active
control. Unlike other approaches using polysilicon micromirrors,
we make use of the <111> silicon surface to form the micromirror.
Two actuation options are being studied: piezoelectric and bimorph.
Key technologies include wet anisotropic wet etching, deep RIE etching
and lithography and patterning over large step heights. Specially
etched trenches in the silicon facilitate precise location of the optical
fibre. Work at a latter date will extend to integration of the
switches with optical waveguides where integration with Array Wave Guides
for dense wavelength division multiplexing (DWDM) would be desirable.
Optical angular
rate sensor
(Shin, Kwok)
Most micromachined angular rate sensors rely on the detection of the
Coriolis force which is directly related to the angular rate.
In this work, the suspended seismic mass is electrostatically actuated
along the X axis and with rotation about the Z axis, and Coriolis force
along the Y axis is created. The double framed seismic mass is
surface micromachined such that X-axis motion is driven by a set of
electrostatic comb-drives and the Y axis motion arising from the Coriolis
force due to rotation about the Z axis moves the shutters, which is
part of the seismic mass, across optical paths consisting of a gap between
two optical waveguides. The moving shutter differentially modulates
the optical transmission which is a measure of the angular rate.
The system is designed to achieve 0.1 deg/s resolution over a range
of 90 deg/s. Angular rate sensors are widely used in the automotive
and motion control applications.
Mobile communication
systems
(Banciu, Ramer)
In this work, four major issues in mobile communications are addressed.
(1) RF electronics: receivers (up/down link) for smart antenna
in GSM900 standard and receiver/transmitter in DCS1800 standard.
Transmission channel testing for bit error rate. (2) Application of
Finite Difference Time Domain software for RF/microwave device design
for mobile communications where conventional software like Touchstone
is inadequate. PML (Perfect Matched Layer) implementation to improve
FDTD accuracy. (3) Low insertion loss filters for receiver front-end
and microstrip dual-mode filters, narrow band Cheyshev and elliptic
filters. (4) Studies of high temperature superconducting thin
film properties for base station front-end applications. Overall
objective of this work is to improve signal strength, increase call
duration and quality of mobile communication.