Recent projects (1997-2001)
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A Study and Fabrication of Field Emitter Arrays for Application in Field Emission Display
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Micromachined Gas Chromatography System for Detection of Pollutant Gases
An Intelligent Sensor System for Environmental Monitoring
PhD Candidate: Salam Maria Srie Rezeki
The system is to be equipped with self-diagnosis and
self-calibration capabilities. It advises the central computer through the
communication interface whenever a faulty sensor is located and needs to be
replaced. Thus the system can be operated with minimum maintenance. The
figure next page shows a simplified block diagram of the distributed
intelligent sensor system.
The shaded area is the intelligence section that controls the self-diagnosis and self-calibration. The self-diagnosis is to ascertain whether the sensor is functioning correctly. It uses the majority voting scheme to detect hard errors while the parameters extracted from the sensor output are used as the additional indicators for the soft-error check.
The implementation is intended to use a combination of conventional signal processing circuits and artificial (fuzzy) neural network. The calibration is needed to ensure that the sensor conforms to a known performance. It is performed at two stages, the primary and the pro-measurement calibrations. The former is mainly for the initial calibration. It consists of the calibration of signal processing circuits (such as offset and gain drift calibration) and the calibration of sensor output (for example, multi-point, temperature, and humidity calibrations) against the standard or reference sample. With the standard or reference sample provided on-site, the primary calibration is intended to be a self-operated procedure.
The pro-measurement calibration is performed when
the drift condition is detected provided that the drift is within an
acceptable range and can be corrected. This technique will be developed to
suit the sampling methodology used by the sensors, in this particular
project there are two possibilities, ie. chromatographic system (for gas
sample) and flow-injection (for ion detection). The communication to the
host computer can be made through I2C interface and sent via one of several
mediums such as a two wire bus, telephone line or RF transmission.
A Study and Fabrication of Field Emitter Arrays for Application in Field
Emission Display
PhD Candidate: In-Jae Chung
The aim of this project is to develop an X-Y
addressable, 2" in diagonal silicon based field emitter array having
improved electrical performances for application in Field Emission Displays
(FED). There have been increasing interest about FED (Field Emission
Display) because of its capabilities of producing high quality colour image,
thin profile, low power consumption, low manufacturing cost and etc.
Though FED is regarded as one of the flat panel
displays which can replace CRT in the near future, there still remains some
problems which have not been fully solved nor analysed yet, and have to be
overcome. Namely, how to increase the fabrication uniformity of field
emitters and improve stability in operation, how to reduce the driving
voltages of the field emitters etc. The above mentioned problems are closely
correlated with material design, field emitter design, manufacturing process
and so on.
This second year's experimental work has been focused
on the two subjects: First to investigate the electrical stability of a
metal silicided silicon field emitter. Several silicide materials such as
Cr, Ta, Ti, etc. have been examined in this study. Among the results, Cr
silicided silicon field emitters showed more stabilised current emission
characteristics and work at a lesser vacuum than a pure silicon field
emitter. These results will be used for the building of a FED with longer
life, stable operation and lower manufacturing cost.
The second subject was the optimisation of FED design. The electro-optical characteristics of a FED are mainly determined by the field emitter construction. However, because of a large number of field emitters in each pixel, through micron-size and process turbulence effects, it is very hard to fabricate a uniform field emitter array throughout the panel. For dealing with such a problem, a robust design concept was introduced. The Taguchi statistical method was used for it is simple to apply and very accurate. With the help of the field emission simulation program (SCALA), optimisation analysis have been executed under the multiple effects of various conditions.
The results of this work is represented in the figure
as a signal to noise ratio of the proposed field emitter. It shows that the
highest point in each graph represents the robust design point which have
reduced insensitivity against outer variance caused by process, misalignment
and so on.
These results were used to design a 1.8" diagonal,
120 x 64 pixels, X-Y matrix driven, silicon based field emitter array.
Silicon Micromachined Diaphragm Micropump
PhD Candidate: In-Byeong Kang
Supervisors: M R Haskard
The work done over the 1st year of this project has
involved literature search, the outcome being a new pump structure following
the micromachining processes such as silicon bulk etching, wafer bonding
using positive photo-resist and an electroplating process.
Literature search is being applied for the project
proposal and new micropump structure. The cross-sectional view of the
proposed silicon micromachined micropump is shown in the figure below. The
micropump employs two floating passive valves (input valve & output
valve), and a variable pressure chamber with a pneumatic actuator. The
micropump will be expected to have a good pumping characteristics especially
on low leakage and high pressure head.
Electroplated nickel has been used to fabricate the
floating passive valves, due to its low adhesion characteristics to the
silicon and easier fabrication process for a thick layer. An electroplating
process through the etched silicon mould provides good reproducibility of
floating microvalve, always having well defined shape. The floating
microvalve structure has been successfully made by using silicon bulk
etching with an EPW etchant and a nickel electroplating process through the
etched silicon shape. The figure below shows fabricated microvalve
structure.
In the next two years, an assembly technique using
wafer bonding and a packaging process will be developed for the micropump.
To evaluate the performance of the micropump, test procedures will be
advised and implemented for all phases. Based on the characteristics of
initial prototype, design parameters will be optimised to improve the
overall performance.
A Micromachined Reaction Column for a Portable Modular Flow Injection
Analysis System
PhD Candidate: M Son
Supervisors: F Peddie and D Davey
With the recent advance of electroanalytic chemistry,
various sensors for metal ion and biochemical molecules have been developed.
Those sensors are small enough to require very small volume of sample,
promising the reduction of overall instrument size if they are combined with
appropriate sample handling technique.
Flow injection analysis (FIA) is a field of analytical
chemistry researching into the efficient methods to deliver a sample
solution to a sensor surface. The FIA was developed in mid-70s and has grown
rapidly to yield commercial automatic FIA system.
The fact that FIA enables the biochemical sensor to be
used for automatic and reproducible monitoring, it has stimulated a lot of
engineering research to produce the system cheaply because typical FIA
system are currently very expensive.
One approach is to use micromachining since it allows
mass production of small reproducible devices. In the late '80s, many
prototypes of micromachined FIA system were reported which have a
micromachined injector, pump, column or detector. However, to fabricated a
practical FIA system using only micromachining technique is very difficult
at this stage.
Individual micromachined module may still have problems
such as a weak outlet pressure for the pump module, a complicated structure
for the micromachined injector and a non-circular cross-section for the
reaction column.
To compromise the demand for a cheap FIA system and the
difficulty in micromachining of FIA modules, a modular approach is tried in
this research. The resulting system is sufficiently small enough to enable
portable use and easy maintenance.
This research to make a portable-modular FIA (PMFIA)
system uses conventional fabrication techniques (namely, plastic machining)
plus micromachining to make a reaction column module whose plastic
counterpart is usually large in size.
Micromachining gives a reduction in the column module
from a 2m x 1.6 mm tube to a 20mm x 20 mm plate. Bulk etching techniques
were used to generate V-groove on silicon wafer followed by anodic bonding
(electrostatic bonding under 1000V, 500oC for 14 minutes), the etched wafer
to pyrex #7740 glass bond was tight without any noticeable defect. The inlet
and outlet holes were created and trimmed after the bonding.
The micromachined column is currently being tested. The
specifications of it are as follows:
Total length of channel : 80 cm
Number of fold: 62
Channel width: 250 micrometre
Thick film Multi-Ion Microsensor System for Waste-Water Analysis
PhD Candidate: Hiskia Sirait
Supervisors: Prof Malcolm Haskard, A/Prof D Mulcahy, Dr D Davey, and Dr
S Soegidjoko
The aim of this project is to develop a sensitive,
selective, robust and low cost thick film multi-ion microsensor system. It
will be applied initially to the determination of a single solution species,
H2S, and later to multiple parameters, for example inorganic sulphur
speciation: H2S, pH, Redox, H2SO4/SO2. The detection of heavy metal such as
copper (Cu2+), cadmium (Cd2+), lead (Pb2+) may also be considered. In the
future the sensor system will be develop as part of a portable instrument
for the detection of multiple species in aqueous streams above and below
ground.
Initial work will concentrate on the design of sensors,
flow cells and the sensor interface electronics which is use to amplify the
signal, reduce the noise, and transmit the signal for data processing.
Sensor design specifications include type of membrane, electrode material,
surface area, geometry, surface condition factors and interactions among
electrode elements.
The purpose was to develop Thick Film microsensor array
to detect pH and H2S. The sensor is based on Thick Film metal-metal oxide
electrodes.
The multi-layer sensor structures consist of conductor, interfacial layer and membrane deposited sequentially on an alumna ceramic substrate by screen printing process.
The chemically sensitive layer consists of a pressed
pellet prepared by mixing sensitive powders such as Antimony (Sb) and Ag2S
with organic binders. The pressed pellet size was about 2 mm and 1.5 mm. The
pH effect was measured by Orion model 720A digital pH meter. Reference
electrode is an Ag/AgCl electrode. Test device is shown in Figure 2. The
sensitivity of the pH electrodes is good, +/- 50 mV/pH.
R : the reference Electrode, C : the carrier or reagent
solution, S : the samples solution, P1, P2 : peristaltic pumps, V : a rotary
valve, L : the sample Loop, M : the mixing coil, MTR : the ISE Meter, FC :
the flow cell with the Detector, PC : the Personal Computer, W : the outlet
to waste.
The flow cell was designed to achieve the following objectives : minimum dispersion, minimum dead volume, and efficient use of the sample plug by making the membranes in series in the cell. The cell, which is about 7.0 cm x 4.5 cm, consists of two perspex halves separated by a Teflon gasket, which controls the cell volume at 180 mm3.
Micromachined Gas Chromatography System for Detection of Pollutant Gases
PhD Candidate: Goib Wiranto
Supervisors: Prof M R Haskard, A/Prof D E Mulcahy and
Dr D E Davey
The aim of this research is to develop a micromachined
gas chromatography (GC) system for detection of pollutant gases, such as CO,
CO2, CH4, NO2, etc. The system is expected to be capable of sensing parts
per million (ppm) levels of pollutant gases and performing fast separation
of gas mixtures (in the order of a few seconds). The micromachined system
will also be small in size (portable) for on-site monitoring.
Just as their conventional counterparts, the proposed
miniaturised GC system (except the carrier gas) will consists of five major
components: carrier gas, sample injection system, micromachined column, gas
detector, and electronic circuitry. The prototype system will be constructed
in three separate modules to allow flexibility in component failure
analysis.
The heart of the GC system is the micromachined
capillary (open tubular) column where separation of sample mixtures takes
place. It is designed as an interlocking spiral shape with 100 micron wide
and at least 1 meter long. The column will be fabricated on borosilicate
glass (Pyrex) by chemical etching and anodic bonding method in a sandwich
structure.
Column operation is determined by the coating of a
stationary phase over the column walls. It will serve as a media of
adsorption and chemisorption with the injected gas sample to produce
propagation delay for each of the gas sample component. Candidates for
stationary phase are many including carbon and metal-based phthalocyanine.
Novel deposition technique will be used to deposit the stationary phase into
the GC column.
Sample injector is used to introduce a finite and
precise amount of gas sample into the stream of carrier gas that flows
continuously into the column. In addition, as a requirement of the GC
operation, the volume of the injected gas sample has to be much smaller than
that of the GC column. Therefor the injection system will be designed and
constructed on silicon as a three-way microvalve to satisfy the above
requirements. The valve will then allow instantaneous injection of the
sample pulse.
The gas detector(s) will be constructed along with the
electronic circuitry in a single module. It is a multiple detector structure
with individual sensor being sensitive to a specific gas, therefor
compensating for lack of selectivity. However, the use of a multi purpose
detector such as acoustic wave sensor has not been ruled out.
This research is part of a multi project work in developing a smart sensor system for detection of pollutant species below and above ground. It is a collaborative work with Institute Teknologi Bandung (ITB) under Targeted Institutional Links (TIL) project.